JPH01154317A - Film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease noise generation when a magnetic recording medium is formed and to improve the electromagnetic conversion characteristics thereof by using a conductive coating material contg. fine metal oxide powder and forming conductive layers having specific pore voids on a polyester film. CONSTITUTION:The conductive layers consisting of a mixture composed of a conductor essentially consisting of the fine metal oxide powder and an org. high-polymer binder are provided on both faces of the polyester film and a magnetic recording layer is laminated on the surface of at least one conductive layer. The noise generation when the magnetic recording medium is formed is decreased by forming the conductive layers to <=15% pore voids.

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 a magnetic recording medium that generates less noise when used as a magnetic recording medium and has a high recording density.

[Prior Art] Biaxially stretched polyester films are widely used as a base for magnetic recording media because of their excellent mechanical properties and dimensional stability. However, in a binder-type magnetic recording medium in which a magnetic layer is coated on the film,
In general, since the surface electrical resistance is relatively high, static electricity generated during the running of the magnetic tape or rotation of the magnetic disk causes adhesion of dust, which increases the possibility of recording dropouts. It is known to have drawbacks such as generating noise and, in some cases, causing deformation of the magnetic recording medium and damage to the equipment used due to the transfer of attached dust. For this reason, it has become essential for magnetic recording media to maintain antistatic properties, and various studies have been made in the past.

For such magnetic recording media, we use a polyester film base material that has been given antistatic properties by coating it with a conductive paint consisting of a composition mainly composed of conductive metal oxide fine powder and an organic polymer binder. A magnetic recording medium made of the following is known. (Japanese Patent Application No. 60-229332) [Problems to be Solved by the Invention] However, the above-mentioned magnetic recording medium having antistatic properties has the following problems.

In other words, magnetic recording media can achieve high-density recording by obtaining the desired excellent antistatic performance that is not dependent on the environmental conditions during use, especially humidity. Because it is relatively small, extremely fine pores are likely to form on the surface of the conductive layer, and when a magnetic layer is formed on the conductive layer and used as a magnetic recording medium, noise generation becomes noticeable and electromagnetic conversion characteristics deteriorate. .

The present invention solves the drawbacks of the conventional technology, and when used as a magnetic recording medium, generates less noise and achieves high-density recording.
It is an object of the present invention to provide a base film for magnetic recording media that is free from dropouts and has excellent antistatic properties.

[Means for Solving the Problems] The present invention provides conductive layers made of a mixture of a conductor mainly composed of fine metal oxide powder and an organic polymer binder on both sides of a polyester film. A magnetic recording medium in which a magnetic recording layer is laminated on the surface of a conductive layer,
The conductive layer is intended to be a film for magnetic recording media having a pore porosity of 15% or less.

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 polycondensation with at least one glycol such as tetramethylene glycol, hexamethylene glycol, and decamethylene glycol. In addition, other types of polymers may be blended with the polyester within a range that does not impede the purpose of the present invention,
Antioxidants, heat stabilizers, lubricants, pigments, ultraviolet absorbers, etc. may be included. Intrinsic viscosity of polyester (25℃
(measured in orthochlorophenol) is from 0.4 to 2.0, preferably from 0.5 to 1.0.

In the present invention, particularly excellent effects can be obtained when polyethylene terephthalate or polyethylene 2,6-naphthalate is used as the polyester.

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 as used in the present invention has a composition consisting of at least one selected from tin oxide, antimony oxide, indium oxide, zinc oxide, and bismuth oxide, and has an average particle size of 0.5 μm or less, preferably is 0.3 μm or less,
More preferably, it is 0.2 μm or less.

If the average particle diameter is 0.5 μm or more, pores are likely to be generated on the surface of the conductive layer and the pore porosity becomes large, which is not preferable.

Moreover, 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 refers to a centrifugal sedimentation type particle size distribution measuring device (Model 5A-CP2 manufactured by Shimadzu Corporation) using fine metal powder as an ethylene glycol slurry.
Measured using . The term "main component" means that the component itself occupies 50% or more of the conductor.

The organic polymer binder in the present invention is selected from thermoplastic resins and thermosetting resins, and is water-soluble or water-dispersible.
Alternatively, resins soluble in well-known organic solvents may be used; specifically, acrylic, vinyl, urethane, epoxy, polyester, polypropylene, melamine, silicone, carbonate, and butyral resins. Copolymers and mixed systems of these can be used.

In the present invention, it is preferable to use a thermosetting resin in view of the solvent resistance, adhesiveness, abrasion resistance, mechanical strength, etc. of the conductive layer.
More preferably, as a crosslinking agent, for example, a melamine crosslinking agent, a urea crosslinking agent, an epoxy crosslinking agent, an isocyanate crosslinking agent, etc. are used in combination to increase the crosslinking density.

In addition, examples of the cloth solvent include alcohols, carboxylic acid esters, ketones, aliphatic hydrocarbons, alicyclic or aromatic hydrocarbons, and mixtures thereof, but in the present invention, A mixed system is preferable, and in addition, a low boiling point solvent (below 100°C), a medium boiling point solvent (above 100°C)
150°C or lower), high boiling point solvent (150°C or higher to 200°C
A mixture system selected from the following) with a low evaporation rate is preferred.

The mixing ratio can be adjusted as appropriate within a range that does not adversely affect the coating properties, pore porosity, surface roughness, etc. of the conductive layer.

Further, 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 intermetallic 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 W1% is more preferable. When the concentration of metal oxide fine powder is less than 55 wt%,
A conductive layer having the desired surface resistivity cannot be obtained.

If it exceeds 35 wt%, not only will the pore porosity of the conductive layer increase, but the surface of the conductive layer will become noticeably rough.
The wear resistance of the conductive layer decreases.

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

In addition, the surface roughness of polynisteri film is 0°015μ
m or less, preferably 0.010 μm or less, in order to prevent surface roughness 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 the conductive layer exceeds m, cracks may occur in the conductive layer due to bending during handling when used as a magnetic recording medium.

The surface roughness of the film of the present invention is preferably 0.015 μm or less, preferably 0.010 μm or less. If the surface roughness is 0.015 μm or more, it is not preferable because coercive force and dropout may be poor when used as a magnetic recording medium.

The surface resistivity of the film of the present invention is 105 to 109Ω,
Preferably, it is in the range of 10 6 to 10 8 Ω.

If the surface resistivity is less than 105 Ω, the surface resistivity of the magnetic recording medium will be too low, which will adversely affect the coercive force of the magnetic material, roughen the surface, and cause excessive current to flow in the equipment used, which is undesirable. . 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 film of the present invention has a conductive layer having a pore porosity of 15% or less,
The content should preferably be 10% or less, more preferably 8% or less. If the pore porosity is 15% or more, noise generation becomes noticeable when used as a magnetic recording medium, which is not preferable.

The magnetic layer in the present invention refers to oxide-based magnetic powder such as γ-Fe2O3, Co-doped 7-Fe2O3, Cro2, etc., or metal-based ferromagnetic powder such as Fe, Co, Ni, etc., together with auxiliary additives, as well as known 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 a 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 producing the film of the present invention will be explained.

(1) Polyester film! ! Manufacturing method A: First, polyester pellets polymerized by a conventional method are sufficiently dried, and then fed to a known extruder, preferably a melt extruder with a compression ratio of 3.8 or higher, and the polymer is heated to a temperature higher than the melting temperature of the pellets. Melt-extrude it into a sheet from a slit-shaped die at a temperature below the decomposition temperature, and apply an electrostatic charge to the
An unstretched film is prepared by cooling to 0°C. On this occasion,
The intrinsic viscosity of the unstretched film is desirably 0.5 or higher 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 usually the stretching temperature is 70 to 180°C in both the longitudinal and width directions of the film, preferably 90 to 150°C, and the stretching ratio is 2.0 to 7.5 times, respectively. Preferably it is 2.5 to 6.0 times.

Furthermore, a polyester film obtained by further stretching a biaxially oriented film in at least one direction not only further improves mechanical properties but also exhibits balanced properties in the plane, making it more preferable as a base film. In this case, the stretched strip 1-1 has a stretching temperature of 100 to 180°C.
The stretching ratio is 1.1 to 3.5 in both the longitudinal and width directions.
times, 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 a conductive layer In order to form a conductive layer on the polyester film, a coating material containing the conductive fine powder described above may be applied to both sides of the polyester film, and the coating film may be dried. At this time, the polyester film is subjected to known corona discharge treatment or plasma treatment (in air, nitrogen, carbon dioxide, etc.).
By applying this, the conductive layer can be formed more firmly on the film surface. The coating material can be applied by the known air doctor coating method, air knife coating method, dipping method, reverse roll coating method, gravure coating method, kiss coating method, cast coating method, etc.; A coating method is preferred.

Regarding the coating film drying conditions, it is particularly preferable that the drying temperature is set at a temperature gradient of low temperature, medium temperature, high temperature, and low temperature after coating, and that the drying rate is slow. Further, it is preferable to use far infrared rays and hot air together as the heat source. If the drying temperature is high, the film will be thermally deformed and its flatness will deteriorate, so it is desirable to carry out the drying within a range that does not have any adverse effects. The concentration of the coating material is not particularly limited, but it is preferably within a range that does not adversely affect the coating properties, pore porosity, surface roughness, etc. of the conductive layer.

[Evaluation method code] The characteristic values of the present invention are based on the following measurement method and evaluation criteria.

(1) Surface specific resistance Those with a surface specific resistance of 106 Ω or more were measured using a super megohmmeter VE-40 manufactured by Kawaguchi Electric Seisakusho (Tai).

For those with a surface resistivity value of less than 106 Ω, use the open insulation meter electrode "P-601 type" and Takeda Riken Kogyo's DI.
GITAL HULTIMETER"'TR-6855
''.

(2) Surface roughness Ra Measured using a stylus 2 surface roughness meter ET-10 manufactured by Kosaka Institute in accordance with 1.1 J15-8-0601. In addition,
The cut-on was 0.25 mm, and the measurement length was 4 mm.

(3) Blocking resistance The blocking property of the conductive layer is measured at a load of 500 g/l at 50°C and 80 to 90% RH according to JIS-Z-0219.
2cITf was applied and the blocking property was evaluated after 24 hours. The evaluation criteria were ◯: good, △: slightly poor, and X: poor.

(4> Adhesive force The adhesive force of the conductive layer/base film is determined by making cross cuts (100 pieces/af+) on the conductive layer and using cellophane tape at 45 degrees to the cross cut surface; ), apply a load of approximately 5 ka using a hand roller, press back and forth 10 times in the length direction (approximately 10 cm), peel off the sellotape by hand, and observe and evaluate the degree of peeling of the conductive layer. Judgment criteria were O; good (peeling area 5
% not 1), Δ: Slightly poor (peeled area of 5% or more and less than 20%), X: Poor (peeled area of 20% or more).

(5) Apply each of the organic solvents ethyl acetate, toluene, methyl ethyl ketone, acetone, and isopropanol twice to the surface of the solvent-resistant conductive layer using a cotton swab impregnated with the appropriate solvent.
The changes in surface condition after rubbing 5 times and 10 times (number of reciprocations) were observed visually and with a magnifying glass/or differential interference microscope, and the surface changes were compared relative to the untreated product and judged as follows.

○: The conductive layer does not dissolve.

Δ: The conductive layer is slightly dissolved.

X: The conductive layer is considerably dissolved.

(6) Antistatic properties Measured using 5HISHID (Static Honest Meter, Model S-4104 manufactured by Il).

The judgment criteria are O: Good (1 second or less), △: Fairly poor (2 seconds or less).
30 seconds), X: Defective (30 seconds or more).

(7) Pore porosity of conductive layer ``Porosimeter'' 2000 (manufactured by CARLOERBA)
The pore distribution characteristics (cumulative pore curve, histogram, etc.) were measured using the following formula.

Porosity (%) = Press-fitted volume L<1o of the conductive layer IQ.

Volume per 1 q of conductive layer The volume per 1 g of conductive layer is determined by the following equation.

Vm/Q=1/Faxφm However, Vmlo: Volume of conductive layer per IC1 φm
;Volume fraction Pa of the conductive layer ;Density of the sample Ta :Thickness of the sample Tf :Thickness of the base film (a) Coercive force of the recording medium A magnetic material having the following composition is applied to the sample film by 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-capturing magnetometer, and the coercive force was determined from the hysteresis curve.

The criteria for judgment is that a coercive force of 500 or more is good;
Less than 500 machining steps were considered defective.

(Composition of m-type material) - T-Fe203 powder 68 parts by weight - Carbon 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/Methyl isobutyl ketone 75 parts by weight/Toluene 75
Heavy World Section (9) Dropout of Magnetic Recording Medium ■Magnetic Tape The original magnetic tape fabricated in item (8) above was micro-slit into 1/2 inch pieces to obtain a magnetic tape.

This magnetic tape is run continuously for 100 hours on a household VTR (helical skittle). The tape was heated to 48℃ at 40℃.
Record and playback the tape that has been returned to room temperature after being held for a period of time, and use a dropout counter to increase the signal output to 50%.
I counted the following:

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 when there were 2 or more pieces, it was determined that dropout was poor.

■Magnetic disk The original magnetic tape prepared in the above (8) was rolled onto a disk to form a magnetic disk with a diameter of 8 inches.

This magnetic disk was used for recording and reproduction by a floppy disk drive, RF low signal envelope detection was performed, waveform shaping was performed 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.

θ0〉Noise (S/N ratio) A 50% white bell signal was recorded at the optimum current on the magnetic tape or magnetic disk made in the above (9) on a commercially available VHS system VIP, and the playback signal and noise ratio were Measuring device 9
Measured at 25D/1, using commercially available magnetic tapes and magnetic disks with base films of known technology as standards.
Comparison was made as db. The criterion is -'1. Less than Odb was considered poor, and -1°Odb or more was considered good.

[Operation of the invention] In the present invention, a conductive layer having a specific pore porosity is formed on a polyester film using a conductive coating material containing fine metal oxide powder. 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, it generates less noise and thus has excellent electromagnetic conversion characteristics (sensitivity, reproduction output).

(2) When used as a magnetic recording medium, since the magnetic recording medium has a high recording density, it is possible to make the magnetic recording medium more compact and to lengthen the magnetic recording time.

<3) When used as a la magnetic recording medium, it has excellent anti-static properties and can be stably obtained over a long period of time without being affected by external temperature or humidity, resulting in less dropouts due to attached dust.

(4) When manufacturing magnetic recording media, the magnetic layer is firmly formed on the conductive layer, and the surface of the magnetic layer is smooth, so when used as a magnetic recording medium, it has excellent electromagnetic conversion characteristics and fewer dropouts. Become something.

[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, embodiments of the present invention will be described based on Examples.

Example 1 A homopolymer pellet of polyethylene terephthalate (intrinsic viscosity 0.62, melting point 259) produced by a conventional method
°C) was dried under reduced pressure (3 mmHg) at 180 °C for 2 hours.

This chip was fed to an extruder equipped with a screw with a compression ratio of 3.8 at 280°C, and the T was melt-extruded from the die into a sheet, and wound around a cooling drum with a surface temperature of 20°C using an electrostatic application method. The mixture was cooled and solidified to obtain an unstretched film.

Next, the film was stretched 3.3 times in the longitudinal direction by a roll stretching method at 90°C, then 3.5 times in the width direction by a tenter stretching method, and heat treated at 220°C for 5 seconds to a thickness of 33 μm. A biaxially oriented film was obtained.

Next, toluene/methyl isobutyl ketone/cyclohexanone (mixing ratio: 3/3/4) was used as a solvent, and antimony was doped at 7% by weight to form particles with an average particle diameter of 0.18μ.
Fine metal oxide powder "ELCOM" (
(manufactured by Catalyst Kasei ■) and a binder made of acrylic urethane resin at a weight solids ratio of 60:40, and further added with 10 parts by weight of hexamethylene diisocyanate per solid content of the binder as a curing agent, and uniformly dispersed. A coating material with a concentration of 15% by weight was made. This coating material was applied to both sides of the biaxially oriented film using a reverse coating method to form a coating film of 5.
Dry at 0-120'C, conductive layer thickness on each side is 1.0
A µm conductive film was obtained.

The conductive layer thus obtained had a pore porosity of 6%, a surface roughness of 0.007 μm, and a surface resistivity of 6×10 6 Ω. Furthermore, the conductive layer had excellent adhesiveness, solvent resistance, blocking resistance, and antistatic property. The properties of this film when used as a magnetic tape are shown in Table 1, with little noise generation and good coercive force and dropout.

Example 2, Comparative Examples 1 to 2 Using the same biaxially oriented film as in Example 1, a conductive layer was formed on the film by slightly changing the coating material (particle size), coating conditions, etc. based on Example 1. We created films with different pore porosity.

Table 1 shows the properties of these films when used as magnetic recording media. When the film properties were within the range of the present invention (Example 2), a magnetic tape with little noise generation and good coercive force and dropout was obtained. However, in cases outside the invention (Comparative Examples 1 and 2), magnetic tapes with less noise generation could not be obtained.

Example 3 Using the same raw material polymer as in Example 1 but changing the film forming conditions, 1q of biaxially stretched film with a thickness of 75 μm with good orientation balance was produced. Next, the same conductive coating material as in Example 1 was applied to both sides of the film using the same method to form a conductive layer having a thickness of 0.9 μm. The pore porosity of this film was 7%, the surface roughness was o, oos μm, and the surface resistivity was 8×10 6 Ω. In general, the conductive layer had excellent adhesiveness, solvent resistance, blocking resistance, and antistatic properties. The properties of this film when used as a magnetic disk are shown in Table 1, with little noise generation and good coercive force and dropout.

Claims (4)

[Claims] (1) Conductive layers made of a mixture of a conductor mainly composed of fine metal oxide powder and an organic polymer binder were provided on both sides of the polyester film, and a magnetic recording layer was laminated on the surface of at least one of the conductive layers. 1. A film for a magnetic recording medium, wherein the conductive layer has a pore porosity of 15% or less. (2) Metal oxide fine powder is tin oxide, antimony oxide,
The film for magnetic recording media according to claim 1, characterized in that the film is at least one selected from indium oxide, zinc oxide, and bismuth oxide, and has an average particle size of 0.5 μm or less. (3) The film for magnetic recording media according to claim (1), wherein the conductive layer has a surface roughness (Ra) of 0.015 μm or less. (4) The film for magnetic recording media according to claim (1), wherein the conductive layer has a surface resistivity of 10^5 to 10^9 Ω.