JPS6289219A - Film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent the drop-out and to improve an antistatic property by specifying the surface roughness of a conductive layer consisting of an electrical conductor essentially consisting of pulverized metallic oxide powder and and org. high-polymer binder to <=0.03mum and the specific surface resistivity thereof to 10<5>-10<9>OMEGA. CONSTITUTION:The conductive layer consists essentially of the pulverized metallic oxide powder and the org. high-polymer binder. The pulverized metallic oxide powder is a compsn. consisting of at least one kind selected from tin oxide, antimony oxide, indium oxide, and bismuth oxide. For example, acryl, vinyl, urethane, epoxy, polyester, PP, and copolymers and mixtures composed thereof are usable for the org. high-polymer binder. The surface roughness of the conductive layer is specified to <=0.03mum and the specific surface resistivity to a 10<5>-10<9>OMEGA range. The antistatic property is thereby stably obtd. for a long period of time and the drop-out is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a base film for magnetic recording media. Specifically, the present invention relates to a base film for magnetic recording media that has a high recording density when used as a magnetic recording medium and has excellent properties.

[Prior art]

Conventionally, biaxially oriented polyester films have been widely used as base films for magnetic recording media. but,
In binder-type magnetic recording media in which the film is coated with magnetic paint, static electricity generated during running of the magnetic tape or rotation of the magnetic disk causes adhesion of dust, which causes recording to drop out. Or,
In some cases, this method has the disadvantage of causing deformation of the magnetic recording medium and damage to the equipment used. For this reason, it is essential for magnetic recording media to have antistatic properties. As a magnetic recording medium that maintains antistatic properties,
For example, (1) A magnetic recording medium in which conductive particles such as carbon or metal powder are uniformly dispersed in a magnetic layer to provide antistatic properties.

(2) A magnetic recording medium that is provided with antistatic properties by using a polyethylene terephthalate film that has antistatic properties by coating or kneading a surfactant or the like.

(3) P with a thin metal film formed on its surface by vacuum evaporation, sputtering, ion blating, electroplating, etc.
A magnetic recording medium that uses ET film to provide antistatic properties.

(4) A magnetic recording medium in which the above (1) to (3) are combined as necessary.

etc. are known.

[Problem that the invention seeks to solve]

However, the above-mentioned magnetic recording medium having antistatic properties has the following problems.

In item (1) above, if conductive particles are mixed into the magnetic layer, it will have a negative effect on the magnetic material and reduce its holding power, making high-density recording impossible. becomes more likely to occur.

In item (2) above, since a durable antistatic effect cannot be obtained, the amount of charge increases during use, attracts dust, etc., and tends to cause dropouts. In general, for surfactants, etc., the environmental conditions when using them, especially the relative humidity of 5% f?
Antistatic properties are not exhibited in a dry atmosphere such as 11 or less.

In addition, in the above item (3), the adhesive force between the PET film and the formed metal thin film is weak, resulting in poor running durability and the magnetic layer peeling or falling off.

The present invention aims to eliminate these drawbacks of the conventional techniques and provide a base film for a magnetic recording medium that can achieve high-density recording, has no dropouts, and has excellent antistatic properties when used as a magnetic recording medium. It's something.

(Means for solving the problem) The present invention provides tin oxide on both sides of the polyester film.
At least one selected from antimony oxide, indium oxide, zinc oxide, and bismuth oxide with an average particle size of 1 μm
A magnetic recording medium comprising a conductive layer made of a conductor containing the following metal oxide fine powder as a main component and an organic polymer binder, and a magnetic recording layer laminated on at least one side of the conductive layer, the conductive layer The gist is a film for magnetic recording media having a surface roughness Ra of 0.03 μm or less and a surface resistivity in the range of 10 5 to 10 9 Ω.

The polyester referred to in the present invention is a known polyester, specifically, for example, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, bis-α,β(2-chlorophenoxy)ethane-4,4-dicarboxylic acid, adipine At least one difunctional carboxylic acid such as acid, sebacic acid, etc.
Seeds, ethylene glycol, triethylene glycol,
Examples include polyesters obtained by polycondensing 1q with at least one glycol such as tetramethylene glycol, hexamethylene glycol, and decamedylene glycol. Further, the polyester may be blended with other polymers within a range that does not impede the purpose of the present invention, and may contain antioxidants, heat stabilizers, lubricants, pigments, ultraviolet absorbers, etc. . Intrinsic viscosity of polyester (25
°C measured in orthochlorophenol) is 0.4 to 2.0
, preferably in the range of 0.5 to 1.0.

The present invention includes polyethylene terephthalate (hereinafter abbreviated as PET), polyethylene 2,
Particularly excellent effects are obtained when 6-naphthalate is used.

The conductive layer in the present invention is a layer mainly composed of metal oxide fine powder and an organic polymer binder.

The metal oxide fine powder has a composition consisting of at least one of tin oxide, antimony oxide, indium oxide, zinc oxide, and bismuth oxide, and has an average particle size of 1 μm.
Hereinafter, it is preferably 0.5 μm or less. If the average particle diameter is 1 μm or more, the surface roughness of the conductive layer becomes large and the abrasion resistance deteriorates, which is not preferable. Furthermore, aluminum oxide or magnesium oxide may be added to the metal oxide fine powder in an amount of 10 wt% or less of the total metal oxide amount, and antimony may be added in an amount of 20 wt% or less of the total metal oxide amount. Note that the average particle diameter here is
Centrifugal sedimentation type particle size distribution measurement equipment using fine metal powder as ethylene glycol slurry (Shimadzu Corporation ISA-CF)
2). The term "main component" means that the component itself occupies 50% or more of the conductor.

The organic polymer binder is a well-known solvent-soluble resin such as acrylic, vinyl, urethane, epoxy, etc.
Polyester-based, polypropylene-based, copolymers and mixed systems thereof, etc. can be used.

For the polyester film referred to in the present invention, it is desirable to use a polyester resin from the viewpoint of adhesion and abrasion resistance of the conductive layer. Examples of organic solvents that can be used include alcohols, carboxylic acid esters, ketones, aliphatic hydrocarbons, alicyclic or aromatic hydrocarbons, and mixtures thereof.

Furthermore, a dispersant such as a surfactant or a silane coupling agent may be used in the conductive coating material in order to uniformly disperse the metal oxide fine powder in the organic polymer binder.

The concentration of metal oxide fine powder in the conductive layer is 55 to 85
W1% is preferable, and a range of 65 to 75 wt% is more preferable. When the concentration of metal oxide fine powder is less than 55 wt%,
A 4H layer having the desired surface resistivity cannot be formed. If the content exceeds 85 wt%, the surface of the conductive layer becomes noticeably rough and the wear resistance of the conductive layer decreases.

The polyester film that also constitutes the film of the present invention is
It is at least biaxially oriented by a conventional method, and the thickness is preferably from 5 to 150 μm, more preferably from 6 to 100 μm, as it is excellent in practical handling as a base for magnetic recording media.

In addition, the surface roughness of the polyester film is 0°05μ
m or less, preferably 0.03 μm or less, in order to prevent surface roughening of the conductive layer formed on the film.

The laminated thickness of the conductive layer constituting the film of the present invention is preferably in the range of 0.05 to 2.0 μm, more preferably in the range of 0.1 to 1.0 μm on each side of the polyester film. If the laminated thickness is less than 0.05 μm, a magnetic recording medium having the desired surface resistivity cannot be obtained. 2.0μ
When used as a magnetic recording medium, some conductive layers may crack due to bending during handling.

The surface roughness of the film of the present invention is 0.03 μm or less, preferably 0.01 μm or less, and preferably 0.05 μm or less.
It is necessary that it is less than m.

If the surface roughness is 0.03 μm or more, it is not preferable because when used as a magnetic recording medium, coercive force and dropout will be poor.

The surface resistivity of the film of the present invention is 105 to 109Ω,
Preferably, it needs to be in the range of 10 6 to 10 8 Ω. If the surface resistivity is less than 10 5 Ω, the surface resistivity is too low when used as a magnetic recording medium, which is not preferable because it adversely affects the coercive force of the magnetic material or causes the surface to become rough. On the other hand, if it exceeds 10 9 Ω, the surface resistivity becomes high when used as a magnetic recording medium, the antistatic property decreases during use, and dropouts increase due to the adsorption of dust, which is undesirable.

The magnetic layer in the present invention refers to oxide-based magnetic powder such as γ-Fe2O3, Co-doped T-Fe203, CrO2, etc., or metal-based ferromagnetic powder such as Fe, Co, Ni, etc., together with auxiliary additives. This is a well-known magnetic layer formed by a so-called coating method in which the magnetic layer is uniformly dispersed in an organic polymer binder such as a thermoplastic resin or thermosetting resin. The thickness of the magnetic layer is desirably in the range of 0.5 to 10 μm, preferably 1 to 5 μm.

Next, a method for manufacturing the film of the present invention will be explained.

(1) Method for producing polyester film An example in which a PET film is used as the polyester film will be explained.

260-310 PET chips polymerized by conventional methods
The film is melt-extruded through a knot-shaped die at 20°C and cooled to 20 to 80°C while applying an electrostatic charge to form an unstretched film. At this time, it is desirable that the intrinsic viscosity of the unstretched film is 0.5 or more in view of film properties. Next, the unstretched film is biaxially stretched and oriented. As the stretching method, a sequential biaxial stretching method, a simultaneous biaxial stretching method, or a combination thereof can be used. The biaxial orientation conditions are not particularly limited, and are usually 70 to 1 in both the longitudinal and width directions of the film.
80'C1, preferably at a stretching temperature of 90-150'C,
The stretching ratio is 2.0 to 7.5 times, preferably 2
．． It is 5 to 6.0 times.

Further, a PET film obtained by further stretching a biaxially oriented film in at least one direction not only has further improved mechanical properties but also exhibits balanced properties in the plane, making it more preferable as a base film. In this case, the stretching conditions are such that the stretching temperature is 100 to 180°C, and the stretching ratio is 1.1 to 3.5 times in both the longitudinal direction and the width direction, preferably 1°4 times to 3.0 times.

Furthermore, the biaxially oriented film is heat treated if necessary. The heat treatment conditions were a temperature of 150 to 240'C and a time of 0.
A suitable time is 5 to 120 seconds, preferably 1.0 to 60 seconds.

(2) Method for Forming Conductive Layer To form a conductive layer on the polyester film described above, the coating material containing the conductive fine powder described above may be coated on both sides of the polyester film for 15 minutes, and the coating film may be dried. At this time, by subjecting the polyester film to a well-known corona discharge treatment or plasma treatment (in air, nitrogen, carbon dioxide, etc.) in advance, a conductive layer can be formed more firmly on the film surface. . The coating material can be applied using the known air doctor coating method, air knife coating method, dipping method,
Although a reverse roll coating method, a gravure coating method, a kiss coating method, a cast coating method, etc. can be applied, the gravure coating method is preferable from the viewpoint of accuracy of coating thickness. Although the coating material concentration and coating drying conditions are not particularly limited, it is desirable that the coating film drying conditions be within a range that does not adversely affect the polyester film.

The characteristic values of the present invention are measured by the following method. Depends on evaluation criteria.

(1> Surface specific resistance Items with a surface specific resistance value of 106Ω or more were measured using the “Chouzetsu Bin VE-40 model” manufactured by Kawaguchi Den!a Seisakusho Co., Ltd.. Items with a surface specific resistance value of less than 106Ω , 3.5cm
A copper electrode with a width of 5 mm and a thickness of 5 mm was prepared, a counter electrode was placed in parallel at a distance of 3.5 cm, and a load of 500 Q was applied to the electrode, which was determined using a tester.

(2) Surface roughness Ra Measured using a stylus surface roughness meter in accordance with J15-B-0601. By the way, the cutoff was 0°25 degrees and the measurement length was 4mm.

(3) Abrasion resistance The abrasion resistance of the conductive layer is made by Daiei Kagaku Seiki Co., Ltd.

A load of 500q was applied using the "Gakushin type abrasion fastness tester", and the friction surface was the evaluation sample and cloth (Kinkin No. 3).
The appearance of the coating film (scratches, amount of wear) after 00 times of rubbing was observed and evaluated. The evaluation criteria were: ◯: good, △: somewhat poor, and X: poor.

(4) Blocking resistance The blocking property of the conductive layer is measured at a load of 500q/in 50'C180~90%ru+ according to JIS-Z-0219.
12- was applied and the blocking property was evaluated after 24 hours.

The evaluation criteria were: ○: good, △: poor, X: poor.

(5) i! ii1''95 The chemical resistance of the conductive layer is determined by the appearance after the test (cloudiness, cracking, discoloration, swelling, etc.) according to J Is-7114.
The evaluation criteria were as follows: ◯: Good, △: Slightly poor, ×: Poor.

(6) Adhesive force The adhesive force of the conductive layer/base film is J l5 to the conductive layer.
- After pasting the adhesive tape with a width of 18n+ffl as specified in C-2338, apply a load of approximately 51 cm using a hand roller, press it back and forth twice in the length direction (approximately 10 cm), and then press the adhesive tape by hand. The conductive layer was peeled off and the degree of peeling of the conductive layer was observed and evaluated. Judgment criteria are: ○: Good, Δ: Slightly poor.
X: Defective.

(7) Coercive force of 1K recording medium Coat a magnetic material with the following composition on a sample film using a coating method,
It was dried to form a 2.5 μm thick magnetic layer, which was used as a magnetic recording medium. The magnetic properties of this magnetic recording medium were measured using a sample (combustion type magnetometer), and the holding force was determined from the hysteresis curve.The judgment percentage is that if the holding force is 500 or more steps, it is good, and if the holding force is less than 500 steps, it is bad. did.

(Composition of magnetic material) - γ-Fe203 powder 68 parts by weight - Carphone black 7 parts by weight - Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 26 parts by weight - Acrylonitrile-butadiene copolymer 5 parts by weight - Polyisocyanate 2 parts by weight / 75 parts by weight of methyl isobutyl ketone / Toluene 7
5 parts by weight (8) Dropout of magnetic recording medium ■Magnetic tape The original magnetic tape fabricated in item (7) above was microslit into 1/2 inch pieces to obtain a magnetic tape.

This magnetic tape is run continuously for 100 hours on a home VTR (helical scan). 4. Put the tape at 40'C.
After holding the tape for 8 hours and returning it to room temperature, the tape was recorded and played back, and a signal output of 50 was recorded using a dropout counter.
% or less were counted.

In addition, the measurement is 1/2 inch width and 780 m as one roll.
Measurement was performed for 0 rolls, and when the number of pieces per roll was less than 2, it was determined that dropout was good, and 2 (when the number of pieces per roll was less than 2), it was determined that dropout was poor.

■Magnetic disk The original magnetic tape prepared in the above item (7) was punched into a disk to obtain a magnetic disk with a diameter of 8 inches.

This magnetic disk was recorded and reproduced by a floppy disk drive, the envelope of the RF multiplied signal was detected, the waveform was shaped by a selection circuit, and the number of dropouts per unit time was measured. In addition, the measurement is based on 10 dropouts/
Minutes or less is good.

(9) Charging property evaluation method 5 Static honest meter manufactured by HISHID Co., Ltd.
It was measured using a model S-4104.

Judgment criteria are: ○: Good (1 second or less), △: Slightly poor (2
~3Q seconds), ×: Defective (30 seconds or more).

[Action of the invention]

In the present invention, a conductive layer having a specific surface roughness and surface resistivity is formed on a polyester film using a conductive coating material containing a specific metal oxide fine powder, so that the conductive layer and the magnetic layer are They demonstrated a unique interaction and were able to obtain the following excellent effects.

(Effects of the Invention) (1) When used as a magnetic recording medium, a high recording density can be obtained, so that the magnetic recording medium can be made compact and the magnetic recording time can be extended.

(2) When used as a magnetic recording medium, antistatic properties can be stably obtained over a long period of time without being affected by external temperature or humidity, so there are fewer dropouts due to deposits, etc.

(3) When manufacturing a magnetic recording medium, the magnetic layer is firmly formed on the conductive layer, and the surface of the magnetic layer is smooth, so when the magnetic recording medium is manufactured, there are fewer dropouts.

(Applications of the invention) The base film for magnetic recording media of the present invention can be applied to base films for magnetic recording media such as magnetic tapes, magnetic disks, and magnetic cards used for computers, audio, video, measurement, etc. However, it is particularly preferable to use it for magnetic disks.

(Example) Next, an actual IN aspect of the present invention will be described based on an example.

Example 1 PET homopolymer depth (
Intrinsic viscosity 0.62, melting point 259°C) at 180'C
Dry under reduced pressure (: 3 mmH (J)) for 2 hours.
It was fed into an extruder at 80'C, melt-extruded through a T-shaped nozzle into a sheet, and using an electrostatic application method, it was wound around a cooling drum with a surface temperature of 20'C to cool and solidify, to obtain an unstretched film. . Next, the film was stretched 3 degrees in the longitudinal direction at 90'C by a roll method, then stretched 3 degrees in the width direction by a tenter method, and then heat-treated at 220 degrees Celsius for 5 seconds to a thickness of 8 μm. A biaxially oriented film was obtained.

Next, methyl ethyl ketone/toluene (mixing ratio 1:1)
is used as a solvent, and to this is added metal oxide fine powder "ELCOM" (Catalyst Kasei Co., Ltd.) consisting of tin oxide with an average particle size of 0.5 μm.
A binder consisting of polyester resin PAVYLON 200 (Toyobo Co., Ltd.) was mixed with a weight solids ratio of 70.
: A coating material with a concentration of 15 wt% was made by uniformly dispersing the composition of 30. This coating material was applied to both sides of the biaxially oriented PET film by a gravure coating method, and the coating film was dried at 100'C to obtain a conductive film having a conductive layer thickness of 0.7 μm on each side.

The surface roughness of the conductive layer thus obtained was 0.018 μm.
The surface resistivity was 2×10 8 Ω.

Furthermore, the conductive layer had excellent adhesiveness, abrasion resistance, blocking resistance, and solvent resistance.

The properties of this film when used as a magnetic tape are shown in Table 1, and it had good holding power, dropout, and antistatic properties. However, when the metal oxide of the conductive layer and its particle size are outside the scope of the present invention (Comparative Examples 1 to
Regarding 4), a base film for a magnetic recording medium having good holding power, dropout, and antistatic properties could not be obtained.

Examples 2 to 5, Comparative Examples 5.6 Biaxially oriented films were made using the same polymer as in Example 1 but with slightly different film forming conditions. Example 1 to the film
A conductive layer was formed using the same method as described above, and a film of the present invention was produced in which the surface resistance and surface roughness of the conductive layer were changed. however,
The same solvents as in Example 1 were used in all cases.

Table 1 shows the properties when these films of the present invention were used as magnetic recording media. When the film properties of the present invention were within the range of the present invention (Examples 2 to 5), magnetic tapes with good holding power, dropout, and antistatic properties were obtained. However, in a case outside the present invention (Comparative Example 5.6)
However, a magnetic tape with good holding power, dropout, and antistatic properties could not be obtained.

Example 7 Using the same polymer as in Example 1 and changing the film forming conditions, a biaxially stretched film with a thickness of 75 μm and a well-balanced orientation was obtained. Next, conductive layers having a thickness of 0.8 μm were formed on both sides of the film using the same conductive material as in Example 1 using the same method. The surface roughness of this film is 0°015 μm, and the surface resistivity is 4.
It was X10Ω. The conductive layer had excellent adhesion, solvent resistance, and abrasion resistance. When this film is used as a magnetic disk, the holding force is 650 oersted,
The dropout rate was 1 dropout/min, and the antistatic properties were both good.

Claims (1)

[Claims] (1) On both sides of the polyester film, a conductor whose main component is at least one metal oxide fine powder selected from tin oxide, antimony oxide, indium oxide, zinc oxide, and bismuth oxide with an average particle size of 1 μm or less is coated. A magnetic recording medium comprising a conductive layer made of an organic polymer binder and a magnetic recording layer laminated on at least one side of the conductive layer, the conductive layer having a surface roughness Ra of 0.03 μm or less and a surface resistivity of A film for magnetic recording media, characterized in that the resistance is in the range of 10^5 to 10^9 Ω.