JPH1040537A - High-density magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which can realize shortening of a recording wavelength and a high recording density. SOLUTION: A magnetic layer having magnetic bodies dispersed in a resin binder is provided on the surface of an application layer of a biaxially oriented polyester film. The application layer is formed in a film formation process. The relation between the Young's modulus YT (kg/mm<2> ) in a lateral direction of the biaxial polyester film, the thickness t (μm) of the application layer and the thickness tM (μm) of the magnetic layer satisfies formulae 800<=YT, 0.05<=t<=-0.95×10<-3> YT+1.76 and 0.05<=tM<=1.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium capable of high-quality recording for a long time and suitable for high-density recording.

[0002]

2. Description of the Related Art In recent years, magnetic recording media (magnetic recording tapes) such as VTR tapes, audio tapes, and computer tapes have achieved high performance, long-time recording, and small size and light weight. Therefore, the necessity of thinning and high-density recording of a magnetic recording tape is increasing. To reduce the thickness of the magnetic recording tape, it is effective to reduce the thickness of the base film. However, when the thickness of the base film is reduced, the stiffness of the magnetic recording tape decreases, and recording, reproduction, and fast-forwarding are performed. However, there is a problem in that the edge of the magnetic recording tape is deformed during tape running such as rewinding, the contact with the magnetic head is deteriorated, the electromagnetic output is reduced or fluctuated, and the characteristics of the magnetic recording tape are deteriorated.

Conventionally, a so-called supertensilized film having a high Young's modulus in the longitudinal direction (hereinafter referred to as the longitudinal direction) of a magnetic recording tape has been used as a base film of a magnetic recording tape for long-time recording. However, the conventional supertensilized film has a high Young's modulus in the vertical direction, but a Young's modulus in a direction perpendicular to the vertical direction (hereinafter, referred to as a horizontal direction) is at most about 450 kg / mm ^2. Is not sufficient to satisfy the required characteristics.

[0004] On the other hand, in order to achieve high-density recording of a magnetic recording tape, it is essential to shorten the recording wavelength. However, when the thickness of the magnetic layer exceeds a certain value for a certain recording wavelength, there is a problem in that the magnetic flux of the magnetic substance in the deep layer is lost because it forms a closed loop without passing through the reproducing head. Therefore, in principle, thinning of the magnetic layer is more advantageous as the recording wavelength is shorter. Therefore, a so-called ME (metal evapolated) type magnetic recording medium in which a recording layer is formed extremely thin by a method such as evaporation or sputtering of a ferromagnetic metal and thickness loss is reduced due to shortening of the recording wavelength. Has been put to practical use.

[0005] However, the ME type magnetic recording medium has a disadvantage that a ferromagnetic metal such as cobalt constituting the magnetic layer is easily rusted. Various improvements have been made, but at present the reliability of storage of recorded information for a long time is poor.

On the other hand, a so-called M obtained by applying a magnetic paint composed of a ferromagnetic metal and a resin binder on a base film.
The P (metal powder) type magnetic recording medium is relatively easy to prevent rust. For example, a method of forming an antioxidant film on the surface of metal particles can be adopted.

However, the thinning of the magnetic layer of the MP type magnetic recording medium has a production problem that coating defects such as pinholes and streaks tend to occur. In addition, the low filling factor of the magnetic material due to the resin binder containing various additives is also a factor that hinders the thinning of the magnetic layer.

In order to solve the above-mentioned drawbacks of the coating type magnetic recording medium, Japanese Patent Application Laid-Open No. Hei 4-271016 discloses a method in which a magnetic layer to be coated on a base film is divided into a lower layer and an upper layer and simultaneously coated. Japanese Patent Application Laid-Open No. 5-28464 proposes a method in which a nonmagnetic layer is interposed between a base film and a magnetic layer, and the magnetic layer is coated while the nonmagnetic layer is in a wet state. Japanese Patent Publication No. 5-59490 proposes a method in which a non-magnetic undercoat layer and a magnetic layer are simultaneously coated on a base film, and a magnetic field is applied while both layers are not dried.

However, in the method described in Japanese Patent Application Laid-Open No. Hei 4-271016, in which the magnetic layer is divided into two layers and coated simultaneously, the interface between the lower magnetic layer and the upper magnetic layer is likely to be disturbed. The obtained magnetic recording tape has a problem that the tape modulation noise is easily generated. Also, the method described in JP-A-5-28464 in which the magnetic layer is coated while the non-magnetic layer is in a wet state cannot completely prevent the disturbance of the interface, and the method described in JP-B-5-59490. The same applies to.

Japanese Patent Application Laid-Open No. 57-198653 discloses that in order to eliminate spacing loss and dropout of an MP type magnetic recording medium, a magnetic layer is formed after a non-magnetic undercoat layer is coated on a base film. Coating methods have been proposed. However, simply interposing a non-magnetic undercoat layer between the base film and the magnetic layer cannot sufficiently realize a reduction in the recording wavelength and an increase in the recording density.

Furthermore, Japanese Patent Application Laid-Open No. 5-250559 discloses a magnetic recording medium in which a base film having a high Young's modulus is used and the ratio of the thickness of the base film to the total thickness of the magnetic recording medium is specified within a specific range. Proposed. However,
Since such a magnetic recording medium has a large magnetic layer thickness, it is difficult to perform high-density recording with an extremely short recording wavelength.

[0012]

Means for Solving the Problems In view of the above problems, the present inventors have conducted intensive studies, and as a result, according to a magnetic recording medium having a specific configuration, a shorter recording wavelength and a higher recording density have been realized. They have found that they can do this, and have completed the present invention.

That is, the gist of the present invention is to provide a biaxially oriented polyester film having a coating layer provided in a film forming step, in which a magnetic layer having a magnetic material dispersed in a resin binder is provided on the surface of the coating layer. And the transverse Young's modulus YT of the biaxial polyester film (kg / m
m ² ), thickness of coating layer t (μm) and thickness of magnetic layer t M
(μm) simultaneously satisfies the following expressions (1) to (3).

[0014]

(2) 800 ≦ YT (1) 0.05 ≦ t ≦ −0.95 × 10 ⁻³ YT + 1.76 (2) 0.05 ≦ tM ≦ 1.0 (2) 3)

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the magnetic recording medium of the present invention, it is necessary to use a biaxially oriented polyester film as a base film, and the biaxially oriented polyester film has a coating layer provided on one surface in a film forming step of the film. Need to be. Hereinafter, the biaxially oriented polyester film provided with the coating layer may be simply referred to as a support film.

The polyester in the present invention is obtained by using an aromatic dicarboxylic acid such as terephthalic acid or 2,6-naphthalenedicarboxylic acid or an ester thereof and ethylene glycol as main starting materials.
% Or more is ethylene terephthalate unit or ethylene-
A polyester having 2,6-naphthalate units. Among the above polyesters, ethylene-2,6- is preferred from the viewpoint of film formability and quality stability of the film.
Polyesters having naphthalate units are preferred.

The above-mentioned polyester may contain a third component other than the above-mentioned polymerization component as a copolymerization component.
Examples of the third component dicarboxylic acid component include, for example, isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and the like.Examples of the third component glycol component include diethylene glycol, propylene glycol, Butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like.

Fine particles can be contained in the above polyester, if necessary. Examples of the fine particles for imparting light-shielding properties to the film include, for example, titanium oxide, carbon black, calcium carbonate, barium sulfate, and the like.Examples of the fine particles for imparting slipperiness to the film include, for example, calcium carbonate and calcium phosphate. , Barium sulfate, titanium oxide, kaolin, talc, clay,
Examples include crosslinked organic particles such as alumina, silica, carbon black, crosslinked polystyrene resin and crosslinked acrylic resin. These fine particles may be used alone or in combination of two or more. The average particle diameter of the fine particles is usually 0.1.
001 to 5.0 μm, preferably 0.01 to 1.0 μm
m, the amount added is usually 10% by weight or less, preferably 5% by weight or less, based on the polyester resin.

The support film in the present invention needs to be biaxially oriented by biaxial stretching, and the Young's modulus YT (kg / mm ² ) in the transverse direction satisfies the following formula (1). is important.

[0020]

[Equation 3] 800 ≦ YT (1)

The upper limit of the above Young's modulus is usually 1800K
g / mm ² or less, but the preferred range of Young's modulus is 850 to 1600 kg / mm ² , and the more preferred range of Young's modulus is 900 to 1500 kg / mm ² .

The transverse Young's modulus YT is 800 kg / mm
If it is less than ^2, the magnetic recording tape thinned for long-time recording will have low stiffness, and the contact between the magnetic head and the magnetic layer surface will be poor, resulting in the electromagnetic output of the magnetic recording tape. Decrease. Furthermore, when running repeatedly under severe conditions, the edge of the magnetic recording tape stretches and deforms into a wakame shape, or the tape end bends when it comes into contact with the lateral regulation guide, and the characteristics of the magnetic recording tape Be impaired. The transverse Young's modulus YT is 1800 kg / mm
If it exceeds ² , productivity during film stretching tends to decrease, which is not preferable for practical use.

On the other hand, the Young's modulus of the support film in the longitudinal direction is not particularly limited, but usually becomes longer as the magnetic recording tape because the long axes of the magnetic substances in the magnetic layer are arranged in the longitudinal direction. Therefore, the Young's modulus in the vertical direction of the supporting film may be lower than the Young's modulus in the horizontal direction.
/ Mm ² or more.

The above support film is usually obtained by heat setting after biaxial stretching. The shrinkage in the longitudinal and transverse directions of the film after heat treatment at 100 ° C. for 30 minutes is 2.
It is preferably 0% or less. In addition, the polyester film may be a laminated film formed by coextrusion or the like, if necessary.

The resin constituting the coating layer of the support film is as follows:
Excellent adhesion with the magnetic layer formed on the coating layer surface,
It is preferable that the magnetic layer has a property of being plastically deformed and flattened during calendering of the surface of the magnetic layer. As such a resin, for example, it can be selected from polyester, polyamide, polystyrene, polyacrylate, polycarbonate, polyarylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, polyvinyl alcohol, polyurethane, and copolymers and mixtures thereof. I can do it. The preferred resin among these is a polyester resin.

The coating layer of the supporting film is formed in a polyester film forming step. Therefore, the above resin is
From the viewpoint of safety and hygiene in the film forming process, a water-soluble or water-dispersible resin that can serve as an aqueous medium coating agent is preferable. The aqueous medium coating agent may contain an organic solvent as an auxiliary within a range that does not impair the above purpose.

The aqueous medium coating agent may be a coating agent forcibly dispersed with a surfactant or the like, but is preferably
It is a self-dispersing coating agent having a cationic group such as a hydrophilic nonionic component such as polyethers or a quaternary ammonium salt, and more preferably a water-soluble or water-dispersing coating agent having an anionic group. is there. The water-soluble or water-dispersible coating agent having an anionic group can be obtained by using a resin to which a compound having an anionic group is bonded by copolymerization, graft polymerization or the like. As the anionic group,
Sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, and salts thereof are exemplified.

The counter ion of the anionic group is preferably an alkali metal ion, but may be an amine onium ion containing an ammonium ion. The content of the anionic group in the resin is preferably 0.05 to 8% by weight.
When the content of the anionic group is less than 0.05% by weight,
Water-soluble or water-dispersible resin is not enough, 8% by weight
When it exceeds, the water resistance of the coating layer is inferior.

Examples of the polycarboxylic acid constituting the polyester resin include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4′-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, and the like.
2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid,
5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, trimellitic Monopotassic acid salts and their ester-forming derivatives.

On the other hand, polyhydric hydroxy compounds include ethylene glycol, 1,2-propylene glycol,
1,3-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetraethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, dimethyl And potassium methylolpropionate.

The polyester resin is obtained by a conventional polycondensation reaction between a polyvalent carboxylic acid selected from the above compounds and a polyvalent hydroxy compound. In the present invention, in addition to the polyester resin, JP-A-1-1656-1
No. 33, a composite polymer having a polyester component such as a polyester polyurethane obtained by chain-extending a polyester polyol with an isocyanate or a so-called acrylic graft polyester can also be used. As an example of a suitable commercially available polyester resin, there is a product “RZ-105” manufactured by Ryo Kagaku Co., Ltd.

Incidentally, the calendar processing is usually performed by 60
This is performed at a temperature of about 150 ° C. and a linear pressure of about 100 to 500 kg / cm. Therefore, in order to plastically deform the coating layer, the composition of the resin constituting the coating layer has a glass transition temperature of 60%.
℃ or less, more preferably 50 ℃ or less, Vicat softening temperature is 60 ℃
Hereinafter, it is preferable to select the temperature so as to be 50 ° C. or less.

In the present invention, one example of a particularly suitable polyester resin is terephthalic acid or polycarboxylic acid.
It is a water-dispersible polyester obtained using isophthalic acid and 5-sodium sulfoisophthalic acid, and ethylene glycol, diethylene glycol and 1,4-butanediol as polyhydric hydroxy compounds.

It is preferable that the coating liquid contains inorganic particles or organic particles. Examples of the inorganic particles include silica, alumina, zirconium, kaolin, talc, calcium carbonate, calcium phosphate, titanium oxide, barium sulfate, molybdenum sulfide, and antimony oxide. Fine particles which may contain, as organic particles, a cross-linking agent composed of a homopolymer or a copolymer of carbon black, polystyrene, polyethylene, polyamide, polyester, polyacrylate, epoxy resin, polyvinyl acetate or polyvinyl chloride, or the like. , Silicone resin, fluorine resin and the like. Among these, crosslinked polymer particles having little thermal deformation are preferable. The above fine particles may be used alone or in combination of two or more.

The fine particles improve the running property of the film in the film forming process. In addition, the above-mentioned fine particles act as a medium for transmitting calender pressure during the later-described calendering process, and have an effect of forming a flattened coating layer by effectively plastically deforming the coating layer. In particular, the crosslinked polymer particles have an appropriate hardness and can easily impart a shape with no corners, so that the coating layer can be flattened without any roughening during the calendering process. , Better than inorganic particles.

As the above-mentioned crosslinked polymer particles, for example,
Copolymers of a monovinyl compound having one aliphatic unsaturated bond in the molecule and a compound having two or more aliphatic unsaturated bonds in the molecule (crosslinking agent) are exemplified. Specifically, thermosetting phenolic resin, thermosetting epoxy resin,
Thermosetting urea resin, benzoguanamine resin and the like can be mentioned.

The average particle diameter of the above fine particles is preferably smaller than the thickness of the coating layer, and specifically, usually 0.005.
The thickness is 1 to 1.0 μm, preferably 0.01 to 0.5 μm. Particles larger than the thickness of the coating layer may form protrusions when the coating layer is plastically deformed by the calendering treatment, and may hinder the flattening of the surface of the magnetic layer.

The content of the particles in the coating layer is usually 10 to 60% by weight, preferably 20 to 5% by weight, as a solid concentration.
0% by weight, more preferably 30 to 50% by weight.
If the content of the particles exceeds 60% by weight, the adhesion between the coating layer and the polyester film may be deteriorated, or the strength of the coating layer may be reduced and peeling may occur in each step after the coating step. If the content is less than 10% by weight, the plastic deformation of the coating layer is inferior.

In order to improve the adhesion (blocking property), water resistance, solvent resistance, and mechanical strength of the coating layer,
As a crosslinking agent, methylolated or alkylolated urea-based, melamine-based, guanamine-based, acrylamide-based, polyamide-based compounds, epoxy compounds, aziridine compounds, block polyisocyanates, silane coupling agents, titanium coupling agents, zircon -An aluminate coupling agent, a peroxide, a heat or photoreactive vinyl compound or a photosensitive resin may be contained.
Further, if necessary, a lubricant, an antifoaming agent, a coating improver,
It may contain a thickener, an antistatic agent, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

The support film of the present invention is formed by forming a coating layer on one surface. When the coating layer is formed on both sides, when performing the calendering process after providing the magnetic layer on one side, the coating layer without the magnetic layer is adhered to the calender roll, and when winding the film. However, there is a possibility that inconveniences such as adhesion between the magnetic layer and the coating layer on which the magnetic layer is not provided may occur. Therefore, the coating layer is preferably provided only on one side of the polyester film.

The magnetic layer in the present invention is obtained by applying a magnetic paint composed of a magnetic substance and a resin binder. As the magnetic material, a known ferromagnetic powder for high-density magnetic recording can be used. That is, examples of the metal oxide-based or different metal-added metal oxide-based magnetic material include needle-like powders such as γ-iron oxide, Co-added γ-iron oxide, and chromium oxide. nickel,
Examples thereof include iron, alloys thereof, and alloys thereof with chromium, tungsten, and the like. Examples of the hexagonal ferrite magnetic material include plate-like powders such as Ba ferrite and Sr ferrite. These ferromagnetic powders preferably have an Hc of 1000 (Oe) or more, more preferably 1200 (Oe) or more. In particular, as the ferromagnetic metal powder, a powder whose surface has been subjected to a known antioxidant film processing is preferable.

The resin binder for dispersing the ferromagnetic powder and additives such as a crosslinking agent, a lubricant, an antistatic agent, an abrasive, an antioxidant, and a fungicide are added to the resin binder.
In each case, known materials can be used. Further, a known method can be used for applying the magnetic paint to the surface of the coating layer of the support film.

After the magnetic material is oriented in a magnetic field, the solvent is evaporated and dried, and the surface is flattened by calendering. For the calendering process, for example, a known method using a super calender roll can be used. The calendering temperature is usually 60
° C or higher, preferably 70 ° C or higher, more preferably 80 ° C
As described above, the pressure is usually at least 100 kg / cm, preferably at least 200 kg / cm, more preferably at least 300 kg / cm as a linear pressure. By the calender treatment under such conditions, the coating layer can be effectively plastically deformed. If the coating layer is not plastically deformed by the calendering treatment, the surface of the magnetic layer provided on this surface may show the unevenness of the support film itself and become rough, and the electromagnetic conversion characteristics of the magnetic recording tape may be reduced.

In the high-density magnetic recording medium of the present invention,
Lateral Young's modulus of support film YT (kg / mm ² )
Satisfy the above expression (1), and the relationship between the thickness t (μm) of the coating layer and the thickness tM (μm) of the magnetic layer must simultaneously satisfy the following expressions (2) and (3).

[0045]

(4) 0.05 ≦ t ≦ −0.95 × 10 ⁻³ YT +1.76 (2) 0.05 ≦ tM ≦ 1.0 (3)

When the thickness t of the coating layer is less than the above range, the flattening by the calendering treatment becomes insufficient, and the flatness of the surface of the magnetic layer cannot be obtained, so that good output characteristics cannot be obtained. When the thickness t of the coating layer exceeds the above range,
The stretchability when the support film is horizontally stretched is deteriorated, causing frequent film breakage, and the drying speed of the coating layer is reduced, resulting in poor productivity. On the other hand, when the thickness tM of the magnetic layer is less than the above range, when the magnetic paint is applied, the dispersion state of the magnetic material in the magnetic paint becomes non-uniform, and the film thickness varies,
Output characteristics are extremely deteriorated. If the thickness tM of the magnetic layer exceeds the above range, a large number of magnetic layers in a deep layer form a closed loop during short-wavelength recording. The thickness tM of the magnetic layer is preferably 0.05 to 0.8 μm,
More preferably, it is 0.1 to 0.5 μm.

The center line average roughness (sRa) of the magnetic layer surface of the magnetic recording medium of the present invention is preferably 12 nm or less, more preferably 10 nm or less, particularly preferably 8 nm or less. The center line average roughness (sRa) of the magnetic layer surface is 12
If it is larger than nm, the gap between the magnetic head and the surface of the magnetic layer, that is, the so-called spacing loss increases, and the electromagnetic conversion characteristics tend to deteriorate.

In the magnetic recording medium of the present invention, a known back coat layer can be provided on the surface opposite to the surface on which the magnetic layer has been applied. The back coat layer is provided for the purpose of improving the runnability as a magnetic recording tape, and a composition obtained by adding carbon black, fine particles such as alumina, an antistatic agent, a lubricant, etc. to a resin binder is applied on a film. It is formed.

Next, a method for forming a support film according to the present invention will be described. The support film of the present invention is composed of a base polyester film and a coating layer provided on the surface thereof. A known method can be adopted as a method for forming a polyester film.

For example, polyester is heated at 270-320 ° C.
After melt-extruding into a sheet in the following manner, the mixture is cooled and solidified at 40 to 80 ° C. to obtain an amorphous sheet (unstretched film).
Biaxial stretching or simultaneous biaxial stretching is performed at 80 to 150 ° C. so that the area ratio becomes 10 to 30 times in the vertical and horizontal directions.
By performing the heat treatment at ~ 250 ° C, a polyester film having a transverse Young's modulus of 800 kg / mm ² or more can be obtained. Further, if necessary, the biaxially stretched polyester film is heated at 120 to 160 ° C for 1.1 to 1.5.
After re-stretching twice as long, at 180-250 ° C, 1.2-2.
It is also possible to adopt a method in which the film is stretched 0 times again and then heat-treated at the highest transverse stretching temperature.

In the present invention, the coating layer is provided by a method of applying the polyester film in the film forming step, that is, a so-called in-line coating method. In the method of coating after film formation, the so-called off-line coating method, the adhesion between the film and the coating layer is not sufficiently obtained, and the coating layer is peeled off in each step after the coating step, or the thickness of the coating layer is reduced. Problems such as non-uniformity occur. Further, in the in-line coating method, the application is completed at the same time as the film formation, so that the production cost is lower than the off-line coating method which requires a separate coating step after the film formation.

As a method of coating in the film forming process, a coating solution is applied to an unstretched film and then sequentially or simultaneously biaxially stretched, or a uniaxially stretched film is then stretched in a direction perpendicular to the uniaxial stretching direction. And a method in which the film is applied to a biaxial film and then redrawn in the horizontal and / or vertical directions.

As a coating method of the in-line coating method, a reverse roll coater, a gravure coater, an air doctor coater, or any other coating apparatus described in “Coating Method”, published by Yuji Harasaki, Maki Shoten, 1979, may be used. Can be done.

[0054]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. The methods for measuring the physical properties of the support film and the characteristics of the magnetic recording medium in Examples and Comparative Examples are as follows. Further, “parts” of the component ratios described in the examples indicate “parts by weight”.

(1) Thickness configuration of each layer: In order to observe a cross section in the thickness direction, a magnetic recording medium or a supporting film is embedded in a resin and fixed, and a 100 nm thick section is cut out with a microtome. The cross section was observed with a transmission electron microscope (“H-9000” manufactured by Hitachi, Ltd.) to measure the thickness configuration of each laminated portion (photograph magnification: 10,000 to 2).
0000 times, acceleration voltage 100 kV).

(2) Young's modulus: Using a tensile tester (“Intesco Model 2001” manufactured by Intesco Corporation)
In a room adjusted to a temperature of 23 ° C. and a humidity of 50% RH, a sample having a length of 300 mm was pulled at a strain rate of 10% / min, and the first straight line portion of the obtained tensile stress-strain curve was used. Calculated by formula. The width of the sample was 20 mm.

[0057]

E = Δσ / Δε In the above equation, E is Young's modulus (kg / mm ² ), Δσ is a stress difference due to the original average cross-sectional area between two points on a straight line, and Δε is strain between the same two points. Indicates the difference.

(3) Productivity of support film: The film formation speed of the support film, the yield due to breakage during stretching, and the like were used as indices, and the results were evaluated according to the ranks shown in Table 1 below. It was determined.

[0059]

[Table 1]

(4) Center line average roughness (sRa) of the support film surface: The center line average roughness (sRa) of the support film coating layer surface was measured using a non-contact roughness meter. The measurement was performed using a three-dimensional roughness meter (“MAXIMIID58” manufactured by ZYGO).
00 ").

(5) Output measurement: A signal of 20.96 MHz was recorded and reproduced using a drum tester (rotation speed: 9000 rpm, cylinder diameter: 21.7 mm) and measured.
Comparative Example 1 was relatively evaluated as 0 dB.

(6) Dropout (D / O): Hi8
An RF output was input from a deck ("EV-S900" manufactured by Sony Corporation) to a dropout counter, and the number of dropouts per minute was measured. However, the count condition was set to 5 μsec in width (time) and -16 dB or less in depth (output decrease).

(7) Still: The tape was loaded on the Hi8 deck, and the tape was paused during reproduction, and the time required for the RF output to decrease from the initial value to 16 dB was measured.

(8) Durability: A Hi8 deck (“EV-S55” manufactured by Sony Corporation) is used, and the temperature is 40 ° C. and 80% R.
After recording the full length of the sample in the environment of H, the full length reproduction was performed 49 times. And let the output at that time be recorded on a chart,
Clogging, output fluctuation, and edge damage were examined, and durability was determined based on the evaluation criteria shown in Table 2 below.

[0065]

[Table 2]

Example 1 <Production of polyester> 100 parts of 2,6-naphthalenedicarboxylic acid dimethyl ester, ethylene glycol 55
Parts and 0.09 parts of magnesium acetate are taken in a reactor,
The reaction start temperature was set to 180 ° C., and the reaction temperature was gradually increased while distilling off methanol to carry out a transesterification reaction.

After the start of the reaction, the temperature was raised to 230 ° C. in about 4 hours, and the transesterification was substantially completed. Here, 0.1 part of silica particles having an average particle size of 0.12 μm was added as an ethylene glycol slurry, and then 0.4 parts of ethyl acid phosphate and 0.4 part of antimony trioxide were added.
After adding 04 parts, a polymerization reaction was carried out by a conventional method to obtain polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.51. The obtained polymer was 0.3 mmHg at 235 ° C.
Polyethylene with intrinsic viscosity of 0.65
2,6-Naphthalate was obtained.

<Production of Polyester Film> The above-mentioned polyethylene-2,6-naphthalate was dried at 180 ° C. for 4 hours, melted at an extrusion temperature of 295 ° C., filtered through a filter equivalent to # 3000 mesh, and formed into a sheet form from a die. And cooled and solidified on a casting roll at 60 ° C. by applying an electrostatic adhesion method to obtain an amorphous sheet. And
The amorphous sheet was stretched 4.0 times in the length direction at 136 ° C. to obtain a uniaxially stretched film. For this stretching, a roll stretching method was used.

Next, an aqueous medium comprising 60 parts (solid weight, the same applies hereinafter) of a polyester aqueous dispersion and 40 parts of styrene-divinylbenzene organic particles having an average particle diameter of 0.05 μm was applied to one side of the above film. The liquid was applied by a bar coating method. The component composition of the polyester in the coating solution is as follows: terephthalic acid 56 mol%, isophthalic acid 40 mol%, 5-sodium sulfoisophthalic acid 4 mol%, ethylene glycol 70 mol%, diethylene glycol 13
Mol%, and 17 mol% of 1,4-butanediol.

Next, the above film was guided to a tenter and stretched 5.4 times in the width direction at 140 ° C.
For 5 seconds to obtain a support film having a coating layer thickness of 0.2 μm and a base film thickness of 5.5 μm. The Young's modulus of the obtained support film is 900 kg /
mm ² , and 600 kg / mm ² in the longitudinal direction.

<Manufacture of magnetic recording tape> A part or all of the compositions shown in Table 3 below were thoroughly kneaded with a kneader, dispersed and mixed with a sand grinder mill, diluted, and further cured. (Nippon Polyurethane Industry Co., Ltd.
3.3 parts of Coronate L) were added and mixed to prepare a magnetic paint.

[0072]

[Table 3]

The above magnetic paint was applied to the surface of the polyester coating layer of the support film so that the thickness after drying became the value shown in Table 7, and the magnetic field orientation, drying treatment, and calender treatment were sequentially performed. . In this calendering process, a facing roll made of polyester and a metal roll subjected to hard chrome treatment were used. Metal roll temperature 100 ℃, linear pressure 3
At a pressure of 00 kg / cm, plastic deformation and flattening of the polyester coating layer and mirror finishing of the magnetic layer were simultaneously performed so that the magnetic layer surface was in contact with the metal roll to obtain a magnetic recording tape.

Next, a backcoat material having the composition shown in Tables 4 and 5 below, which had been prepared by dispersing and mixing with a ball mill for 48 hours in advance, on the diamagnetic surface side of the above magnetic recording tape, was adjusted to a thickness after drying. Apply and dry to 0.5 μm,
A back coat layer was formed.

[0075]

[Table 4]

[0076]

[Table 5]

Next, the magnetic recording tape on which the above-mentioned back coat layer was formed was slit into a width of 8 mm, and was assembled into a cassette of 8 mm to prepare a tape for VTR. Table 7 shows the properties of the obtained VTR tape. In the magnetic recording tape obtained in this example, even if the thickness of the magnetic layer is 1 μm or less, the coating layer is plastically deformed and flattened by calendering, so that the surface of the magnetic layer is flat. As a result, it is excellent in RF output.

Examples 2 and 3 VTR tapes were prepared in the same manner as in Example 1 except that the thickness of the dried magnetic layer was changed as shown in Table 7. Table 7 shows the properties of the obtained VTR tape.

Examples 4 to 6 In Example 1, the thickness of the coating layer of the support film was determined as shown in Table 6.
Except that the VT was changed as shown in FIG.
An R tape was made. Table 7 shows the properties of the obtained VTR tape.

Examples 7 to 12 VTR tapes were prepared in the same manner as in Example 1 except that the amount of the organic particles in the coating layer of the support film was changed as shown in Table 6. VT obtained
Table 7 shows the characteristics of the R tape.

Examples 13 to 15 VTR tapes were prepared in the same manner as in Example 1 except that the same polyester and coating solution as in Example 1 were used and the film forming conditions were changed as follows. That is, the film is stretched 4.1 times in the longitudinal direction at 136 ° C., and then a coating solution is applied by a bar coating method.
, And then heat-treated at 140 ° C. Thereafter, the film was stretched in the transverse direction again at a predetermined temperature in the temperature range of 170 to 210 ° C. and heat-fixed at 210 ° C. for 5 seconds to obtain a biaxially oriented support film having a total thickness of 5.5 μm. In Example 13, the magnification of the above-mentioned transverse stretching is 1.
5 times, 1.7 times in Example 14, 2.0 times in Example 15
Doubled. Table 7 shows the properties of the obtained VTR tape.
The magnetic recording tape obtained in this example has a Young's modulus in the lateral direction of the supporting film of 1000 kg / mm ² (Example 1).
3) 1200 kg / mm ² (Example 14) 1500
Since it is as high as kg / mm ² (Example 15), it has excellent electromagnetic characteristics after running in durability and deformation resistance of the tape edge.

Examples 16 and 17 VTR tapes were prepared in the same manner as in Example 1, except that the types of particles to be mixed in the coating layer of the support film were changed as shown in Table 6. Table 7 shows the properties of the obtained VTR tape.

Example 18 100 parts of dimethyl terephthalate, 65 parts of ethylene glycol and 0.09 part of magnesium acetate were placed in a reactor and subjected to transesterification while heating and evaporating methanol. About 4 hours after the start of the reaction, 23
The temperature was raised to 0 ° C. to substantially complete the transesterification reaction. Here, silica particles having an average particle size of 0.12 μm 0.1
Was added as an ethylene glycol slurry, and then 0.4 parts of ethyl acid phosphate and 0.04 part of antimony trioxide were added. The pressure in the reaction system was gradually reduced from normal pressure, and the temperature was raised while heating. 1mmHg,
285 ° C. After 4 hours, the pressure in the system was returned to normal pressure, and polyethylene terephthalate having an intrinsic viscosity of 0.66 was obtained.

The obtained polyethylene terephthalate was
After drying at 80 ° C. for 4 hours, melt extrusion was performed at an extrusion temperature of 290 ° C. At this time, the mixture was filtered with a filter equivalent to # 3000 mesh, melt-extruded into a sheet form from a die, and cooled and solidified on a casting roll at 40 ° C. by applying an electrostatic adhesion method to obtain an unstretched sheet. Next, the unstretched sheet was stretched by a multi-stage roll stretching method. That is, the film was stretched 1.8 times at 128 ° C as the first step in the longitudinal direction and continuously 2.4 times at 114 ° C as the second step in the longitudinal direction. In addition, a non-adhesive roll made of Teflon was used for the multi-stage roll stretching method.

Next, a coating solution having the same composition as in Example 1 was applied by a bar coating method, and the obtained coating film was guided to a tenter and stretched 2.8 times at 105 ° C. in the horizontal direction. The obtained stretched film was guided to a simultaneous biaxial stretching tenter, stretched 2.0 times in the longitudinal and transverse directions at 160 ° C., and heat-set at 210 ° C. for 5 seconds to obtain a supporting film having a total thickness of 5.5 μm. The Young's modulus of this support film is 850K in the transverse direction.
g / mm ^2, the vertical direction was 570 kg / mm ^2. Thereafter, a VTR tape for 8 mm was prepared in the same manner as in Example 1. Table 7 shows the properties of the obtained VTR tape.

Example 19 A VTR tape was prepared in the same manner as in Example 13, except that the thickness of the coating layer of the support film was changed as shown in Table 6. Table 7 shows the properties of the obtained VTR tape.

Comparative Example 1 In Example 1, the thickness of the coating film of the support film was determined as shown in Table 8.
Except that the VT was changed as shown in FIG.
An R tape was made. The properties of this tape are shown in Table 9. The thickness of the coating layer is less than the lower limit specified in the present invention, and the plastic deformation during the calendering of the magnetic layer surface is insufficient. Inferior.

Comparative Example 2 In Example 1, the thickness of the coating film of the support film was determined as shown in Table 8.
Except that the VT was changed as shown in FIG.
An R tape was made. The properties of this tape are shown in Table 9, where the thickness t of the coating layer exceeds the upper limit specified in the present invention, and it takes a long time to dry the film, and the film-forming speed has to be lowered. Is inferior.

Comparative Examples 3 and 4 A VTR tape was prepared in the same manner as in Example 13, except that the thickness of the coating layer of the support film was changed as shown in Table 8. The properties of this tape are shown in Table 9, but the relationship between the Young's modulus in the transverse direction and the thickness of the coating layer in the supporting film does not satisfy the requirements specified in the present invention, and the stretching yield at the time of film formation decreases. And productivity is poor.

Comparative Examples 5 and 6 VTR tapes were prepared in the same manner as in Example 1, except that the thickness of the magnetic layer was changed as shown in Table 9. The properties of this tape are shown in Table 9. Since the thickness of the magnetic layer exceeds the upper limit specified in the present invention, the loss of magnetic flux due to the closed loop becomes large, and the VT is reduced in terms of RF output.
The properties of the R tape are inferior.

Comparative Examples 7 and 8 In Example 1, the blending amount of the organic particles in the coating layer of the support film was changed as shown in Table 8, and the film forming conditions of the support film were changed as follows. The film was stretched 2.9 times in the longitudinal direction at 83 ° C, and continuously stretched 1.3 times in the longitudinal direction at 76 ° C. Next, the coating solution of Example 1 was applied by a bar coating method, and this film was guided to a tenter and set to 4.0 at 100 ° C.
Alternatively, the film was stretched 5.0 times in the transverse direction, and subsequently heat-set at 210 ° C. for 5 seconds to obtain a biaxially oriented polyester film having a total thickness of 5.5 μm. On this film, a magnetic layer having exactly the same composition as in Example 1 was provided in a thickness shown in Table 9 by the same method, and a back coat layer having the same composition was provided by the exactly same method, and slitting was performed. , 8 mm VTR tape.

Table 9 shows the characteristics of the tapes. The coating layer was plastically deformed and flattened by calendering to flatten the surface of the magnetic layer. The tape ends are deformed during this,
Poor contact with the magnetic head results in poor RF output, dropout and durability.

In the following tables, the meanings of the symbols indicating the types of non-magnetic particles are as follows. That is, “A” is a styrene-divinylbenzene-based crosslinked polymer particle (d ₅₀ :
0.05 μm), “B” is silica sol (d ₅₀ : 0.06
μm) and “C” represent methyl methacrylate-divinylbenzene crosslinked polymer particles (d ₅₀ : 0.05 μm).

[0094]

[Table 6]

[0095]

[Table 7]

[0096]

[Table 8]

[0097]

[Table 9]

[0098]

The magnetic recording tape of the present invention described above has a high strength in the lateral direction of the supporting film, so that it has excellent edge deformation resistance during running, good contact with the magnetic head, and good electromagnetic output characteristics. Also excellent. Therefore, the magnetic recording tape of the present invention is, of course, not only a VHS type VTR tape,
S-VHS, W-VHS, 8mm, high band 8mm,
It is useful as a magnetic recording medium such as a digital VTR for HDTV, a digital VTR for consumer use, a digital VTR for business use, and a computer tape.

Further, the magnetic recording tape of the present invention has a feature that the coating layer and the magnetic layer are simultaneously flattened by the calendering process during the manufacturing process. Short wavelength recording can be performed.
Further, since the coating layer which can be plastically deformed by the calendering process is applied on the film by the in-line coating method, the adhesion to the film is good and the control is not difficult unlike the multi-layer magnetic layer. Thus, according to the present invention,
A high-density recording medium can be efficiently produced by the same process as in the past.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoichi Yoshimura 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Shigeharu Watase 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Inside the corporation

Claims (1)

[Claims] 1. A biaxially oriented polyester film having a coating layer provided in a film forming step, wherein a magnetic layer in which a magnetic material is dispersed in a resin binder is provided on the surface of the coating layer. Lateral Young's modulus YT (kg / mm ² ) of polyester film, thickness t (μm) of coating layer
And the thickness tM (μm) of the magnetic layer is expressed by the following equation (1).
A high-density magnetic recording medium satisfying (3). (1) 0.05 ≦ t ≦ −0.95 × 10 ⁻³ YT + 1.76 (2) 0.05 ≦ tM ≦ 1.0 (1) 3)