JPH0152814B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high density magnetic recording medium. More specifically, it has a low noise level and a good signal-to-noise ratio when reading data, especially when playing back high-density recording.
This relates to thin film magnetic recording media.

A common recording medium for current magnetic recording is a γ-Fe ₂ O ₃ , Co-doped treatment on the surface of a suitable base material, such as a flexible polymer film (polyester film, etc.) with a thickness of several μm to several tens of μm. γ−
A laminate in which a magnetic recording layer is formed by coating ferromagnetic powder such as Fe ₂ O ₃ , CrO ₂ or Fe dispersed in an organic binder to a thickness of several μm to about 10 μm. It is.

A required improvement in magnetic recording technology is to increase the recording density per given area. In magnetic memory devices used in disk, drum, or tape recording devices, the limit of recording density is determined by the ratio of the demagnetizing field to the coercive field. Further, the strength of the demagnetizing field is related to the saturation magnetization and thickness of the recording medium layer. In order to achieve an acceptable level of signal-to-noise ratio, it is necessary to obtain a thin recording medium layer capable of obtaining a sufficient output signal. This becomes easier to achieve as the saturation magnetic flux density and squareness ratio of the B-H curve of the recording medium become higher. In this sense, the purpose of the present invention is to
The objective is to provide a magnetic recording medium that has a high coercive force, a hysteresis loop with a good squareness ratio, a thin recording medium layer, and a high remanent magnetic moment, which has a particularly low noise level and is easy to read data. The object of the present invention is to provide a metal thin film magnetic recording medium that has a good signal-to-noise ratio during recording and has a low noise level, especially during high-density recording and reproduction.

In recent years, as high-density magnetic recording media, ferromagnetic metal has been developed by forming a thin metal film as a magnetic recording layer on a nonmagnetic support by a vacuum deposition method such as vacuum evaporation or sputtering, or a plating method without using a binder. A thin film magnetic recording material has been proposed. For example, Co vapor deposition tape (JP-A-54-147010
JP-A-52-134706) and a perpendicularly magnetized film made of a Co--Cr alloy (JP-A-52-134706). A metal thin film formed by such thin film forming means such as vapor deposition, sputtering, or ion plating has a thickness of 1.5 μm or less and is equivalent to a conventional coated recording medium in which the magnetic layer has a thickness of 3 μm or more. Performance can be obtained. Incidentally, it is considered that magnetic properties such as the coercive force Hc, which is a static property, or the squareness ratio of the hysteresis loop do not depend much on the surface condition of the nonmagnetic support used. An example of a structure based on this idea is a Co--Cr multilayer structure formed by vacuum deposition as disclosed in US Pat. No. 3,787,327. However, the formed metal thin film is thin, and the surface condition (surface irregularities) of the non-magnetic support directly manifests as irregularities on the magnetic film.
The drawback was that it caused noise.

From the viewpoint of noise, it is preferable that the surface condition of the nonmagnetic support is as smooth as possible. On the other hand, from the viewpoint of handling such as winding and unwinding of the film, if the film surface is smooth, the film-to-film slipperiness will be poor and a blocking phenomenon will occur, making it impossible to use as a product, and the base film surface will be rough. is required.

From the viewpoint of electromagnetic conversion characteristics, the surface of the nonmagnetic support is required to be smooth, and from the viewpoint of handling and running properties, it is required to be rough. The present invention was arrived at as a result of extensive research into a magnetic recording medium made of a nonmagnetic support that satisfies these two contradictory properties at the same time.

That is, the present invention is an oriented polyethylene terephthalate film, and the surface roughness of the film [CLA (unit/μm)], the protrusion height [h (unit/μm)], and the number of protrusions [unit: pieces/mm] ² ] is in the range shown by the following formula: CLA<0.005 −(1) 0.27<h ≦0.54…0.2 pieces/mm ² or less −(2), and the other side of the film is coated with water or a solvent-based lubricant. A non-magnetic film with different surfaces on both sides, which is coated with an easily slippery coating film by applying a solution containing dispersed ferromagnetic metal. This is a magnetic recording medium in which a magnetic thin film is supported on an oriented polyethylene terephthalate film support.

The polyethylene terephthalate referred to in the present invention includes not only a polyethylene terephthalate homopolymer but also a copolymerized polyethylene terephthalate in which 85% or more of the repeating units are composed of ethylene terephthalate units, and the remainder is other acid or glycol components.

All conventionally known methods can be used to form the magnetic thin film, but vacuum evaporation, ion plating, sputtering, and electroless plating are particularly preferred.

In the case of the vacuum evaporation method, the evaporated metal in a tungsten boat or alumina hearth is evaporated under a vacuum of 10 ^-4 to 10 ^-6 Torr by resistance heating, high-frequency heating, electron beam heating, etc., and deposited on the support. urge Fe, Ni, Co, and alloys thereof are usually used as the deposited metal. The present invention also includes O ₂
A reactive vapor deposition method in which Fe is vapor-deposited in an atmosphere to obtain an iron oxide thin film can also be applied. In the ion plating method, DC glow discharge or RF glow discharge is generated in an atmosphere containing an inert gas of 10 ^-4 to 10 ^-3 Torr as a main component, and metal is evaporated in the discharge. Ar is usually used as the inert gas. 10 ^-3 in the spatuta method
A glow discharge is generated in an atmosphere containing Ar as the main component at ~10 ^-1 Torr, and the generated Ar ions knock out atoms on the target surface. Methods for generating glow discharge include DC two-pole, three-pole sputtering methods, and high-frequency sputtering methods. There is also a magnetron sputtering method that uses magnetron discharge. In the electroless plating method, there are Co-P and Co-Ni-P plating films.

The thickness of the magnetic thin film according to the present invention must be such that it provides sufficient signal output as a high density magnetic recording medium. Therefore, the thickness of the magnetic thin film varies depending on the thin film formation method and application, but is generally 0.02 to 1.5 μm.
(200 to 15000 Å) is preferable.

Methods for forming magnetic thin films for longitudinal recording in audio, video, computers, etc. include methods such as vapor deposition (thermal vapor deposition, electron beam vapor deposition, etc.), sputtering (dipolar direct current sputtering, high frequency sputtering, etc.). In the case of vapor deposition, ferromagnetic metal such as Co is continuously obliquely vapor-deposited onto a non-magnetic oriented polyethylene terephthalate support so that the axis of easy magnetization appears in the horizontal direction of the tape, and by repeated lamination, crystal magnetic anisotropy is achieved. The tape exhibits anisotropy and shape anisotropy in the horizontal direction. Therefore, the total metal thin film thickness is 0.02 to 0.5μ.
It is preferable that the thickness is about m (200 to 5000 Å). Also,
In addition to the above-mentioned longitudinal recording for audio, video, computers, etc., high-density digital recording is possible by developing an easy axis of magnetization in the perpendicular direction of a non-magnetic oriented polyethylene terephthalate support for PCM and flexible disks. For example, in the perpendicular magnetic recording method, an appropriate amount of Cr (10 to 20%) is mixed into Co to suppress the generated demagnetizing field and to develop an axis of easy magnetization in the perpendicular direction, thereby recording in the perpendicular direction to the substrate surface. can also be applied.

Usually, a Co-Cr alloy with a thickness of 0.2 to 1.5μ is used by the sputtering method. At this time, peralloy (Fe-Ni) is placed between the non-magnetic oriented polyethylene terephthalate support and the magnetic recording layer having an axis of easy magnetization in the perpendicular direction.
A magnetic flux concentrator thin film made of a high magnetic permeability material such as a superalloy can be provided. The high permeability material as the magnetic flux concentrator is formed by sputtering, and the film thickness is 0.1 to 1 μm (1000 to 10000 Å) and is a thin film layer with a low coercive force (less than 500e). The film thickness is 0.2~1.5μm (2000~15000μm)
It is preferable to form it to a degree of Å).

The thickness of the metal thin film formed by means such as vapor deposition or sputtering is as thin as 1.5 μm at most, and the surface condition of the non-magnetic oriented polyethylene terephthalate support is directly expressed as unevenness of the magnetic film, causing noise. From the viewpoint of noise, it is preferable that the surface of the non-magnetic oriented polyethylene terephthalate support is smooth, and the average surface roughness CLA (unit: μm) of the oriented polyethylene terephthalate support is
If the number of protrusions (h (unit: μm)) 0.27<h≦0.54 is less than 0.005μm and the number of protrusions is less than 0.2/ ^mm2 , noise will be dramatically reduced when used as a metal thin film magnetic recording medium. However, the noise level is much better.
The average surface roughness CLA is preferably 0.004 μm or less, and the protrusion height of the protrusion is 0.27<h≦
It is preferable that the number of 0.54 pieces is substantially 0 pieces/mm ² . The lower limit of CLA is not particularly limited, but is usually 0.003μ
That's about it.

In order to impart such film surface characteristics,
For example, there are methods such as adding an inert inorganic compound to the polymer used as a film raw material, generating an insoluble catalyst residue, and performing mechanical or chemical surface roughening treatment. Polyethylene terephthalate alone is good because it forms a flat surface.

The inert inorganic compound includes a substance that is insoluble and does not react with the thermoplastic resin. For example, MgO, ZnO,
_MgCo3 , _CaCO3 , _CaSO4 , _BaSO4 , _{Al2O3 ,}
Examples of SiO ₂ and TiO ₂ include silica, kaolin, china clay, diatomaceous earth, calcium carbonate, aluminosilicate and its hydrate, calcium terephthalate, carbon black, calcium phosphate, and the like.

Desired surface properties can be obtained by appropriately combining the particle size, amount, and film forming conditions of the inert compound added. Particle size can be obtained in a variety of ways that can be performed by those skilled in the art, including additive milling and mixing operations.
For example, in the case of calcium carbonate, it can be obtained as a slurry of ethylene glycol by classifying it using a classifier (for example, P-660 Super Decanter manufactured by Tomoe Kogyo Co., Ltd.). In the case of calcium terephthalate, it can be obtained by applying loads such as shearing, compression, impact, etc. to obtain bulk particles of an appropriate size, and then classifying the particles. For calcium phosphate, prepare a commercially available phosphate dispersion and grind the dispersed phosphate in a sand mill. The dispersion can be obtained by repeating the milling operation one or more times to reduce the particle size of the additive in the slurry to the desired particle size.

The amount of inert inorganic compound added depends on the particle size distribution and cannot be determined unambiguously, but it is usually 0.01 to 1 wt%.
is good.

The preferred range of the particle size distribution of the inert inorganic compound is that the particle size [d (unit/μm)] ratio is expressed by the following formula: d>0.5...0% 1.5≧d>0.5...0~5% 0.5≧d> 0.2...20-50% 0.2≧d...45-80% Preferably.

The insoluble catalyst residue is formed by combining an appropriate amount of a transesterification catalyst and a stabilizer in polyester, for example, to form irregularities on the surface of the polyester film and control the surface characteristics.

Most preferably, a polyethylene terephthalate resin that forms an optically flat surface is obtained, for example, a lower alkyl ester of a difunctional carboxylic acid whose main component is terephthalic acid and a glycol whose main component is ethylene glycol. and, Mn, Zn,
A compound of one or more metals selected from Ca, Mg, and the following glycol solution [A] [A]: A solution obtained by heat-treating a tri-lower alkyl phosphate in ethylene glycol. , and a glycol solution of a phosphorus compound in which the amount of caustic potassium required for the solution to reach PH 9.5 when titrated with caustic potassium satisfies the following formula [] 0.53≦[P]/[KOH]≦0.71... [] (In the formula, [P] is the amount (mol) of phosphorus in the glycol solution subjected to titration,
[KOH] is the amount (mol) of caustic potassium required for titration. ) is used to carry out a transesterification reaction, and then the resulting transesterification reaction product is subjected to a polycondensation reaction. At this time, the reaction temperature when preparing the stabilizer is 130 to 180.
If the temperature is not within this range, a large number of protrusions due to catalyst residues tend to exist in the produced oriented polyethylene terephthalate film. The polyethylene terephthalate resin thus obtained is used alone, or an appropriate amount of an inert inorganic compound with a controlled particle size distribution is mixed into the above-mentioned polyethylene terephthalate resin, and the resin temperature is 260 to 320°C.
An unstretched film with an intrinsic viscosity [η] of 0.35 to 1.0 that is melt-extruded with a residence time of 2 to 20 minutes in an extruder,
Secondary transition point (Tg) of polyethylene terephthalate
Stretched in the longitudinal or transverse direction at a stretching ratio of 2.5 to 5.0 times at a temperature of 2.5 to 5.0 times (expressed as )Tg~(Tg
+70°C) at a stretching ratio of 2.5 to 5.0 times (the stretching may be such sequential biaxial stretching or simultaneous biaxial stretching, and the manufacturing method is not particularly limited). In some cases, it may be further stretched in the vertical or horizontal direction, resulting in a total stretching ratio of 2.5.
It may be stretched to about 6.0 times.

The biaxially oriented polyethylene terephthalate film thus obtained is usually heat-set for 1 to 100 seconds at a temperature of (Tg+70°C) to below the melting point.

The average surface roughness CLA (unit/μm) of the oriented polyethylene terephthalate support is 0.005 μm or less, and at the same time, the protrusion height [h (unit/μm)]
Depending on the type of inert substance, it may be difficult to carry out the slurry preparation method in which the number of particles with 0.27<h≦0.54 is completely 0/mm ² depending on the type of inert substance. The existence of a small number of h≦0.54 does not need to be excluded in practice.

The thus obtained oriented polyethylene terephthalate film has poor film-to-film slipping properties and causes a blocking phenomenon, and cannot be used as a product, so it is necessary to impart slipping properties. To impart slipperiness, a solution of a lubricant dispersed in water or a solvent is applied. Apply the solution and
All conventionally known methods can be used to impart slipperiness. For example, a method may be used in which an aqueous or solvent solution of (lubricant + polymeric binder + surfactant) is applied during film formation.

Examples of the lubricant include organic lubricants such as sorbitan, organic polymer lubricants such as Teflon and polyethylene, and inorganic lubricants such as alumina, kaolin, silica, and molybdenum sulfide.

Examples of the polymeric binder include copolymerized polyethylene terephthalate, polyurethane, nylon, and melamine.

A solution prepared by dispersing (lubricant + polymeric binder + surfactant) in water or a solvent can be applied during or after film formation and dried to impart slipperiness. At this time, it is of course possible to add ultraviolet absorbers, antistatic agents, etc.

The particle size composition ratio of the inert inorganic compound, its measurement method, and the measurement method of film surface properties are shown below.

1 Particle size composition ratio of inert substance Using Shimadzu centrifugal sedimentation type particle size distribution analyzer CP-50, Stokes' equation T=18ηh/G(ρ _p −ρ _p )×d ² However, in the formula, T: Sedimentation time (sec) η: Viscosity of medium (g/cm・sec=
h: Sedimentation distance (cm) G: Acceleration of gravity (980cm/sec ² ) ρ _p : Density of inert substance (g/cm ² ) ρ _p : Density of medium (g/cm ² ) d: Inert Calculate the settling time corresponding to each particle size using the particle size (diameter/cm) of the substance, find the settling time range corresponding to each particle size range, and calculate the settling time of the inert substance within that settling time range. Determine the weight of the inert substance, express the proportion to the total weight of the inert substance as a percentage, and use it as the composition ratio.

2 CLA [Center Line Average (Center Line Average)]
According to JIS B 0601, using a stylus type surface roughness meter (SURFCOM 3B) manufactured by Tokyo Seimitsu Co., Ltd.
Place the chart under the conditions of a needle radius of 2 μm and a load of 0.07 g, and extract a portion of measurement length L from the film surface roughness curve in the direction of its center line. When the roughness curve is expressed as Y=f(x), with the direction of Y being the Y axis, the value given by the following equation is expressed in μm.

R _CLA = 1/L∫ ^L _O |f(x)|dx In this measurement, 8 measurements were taken with the reference length as 0.25 mm, and the average value of 5 measurements excluding 3 from the largest value is expressed.

3 Number of surface projections: 400 to 500 on the surface of the film whose surface is to be observed.
Aluminum is uniformly vacuum-deposited to a thickness of 100 Å or less, and collodion is pasted on the opposite non-deposited surface (film side). After drying, a visible monochromatic light multiple interference reflection microscope (for example, manufactured by Carl Zeiss JENA) is used. ), take pictures of 100 or more locations at 100x magnification, find the number of protrusions corresponding to the protrusion height in each photo, and convert it to 1 mm ² . At this time, the field of view of one photo is
It is ^0.155mm2 .

Examples will be described below, but the method is not limited to these methods for any reason.

Examples 1 to 4; Comparative Examples 1 to 3 In Examples 1 to 4, 0.023 parts of zinc acetate (0.020 mol% to dimethyl terephthalate) was added as a catalyst to 100 parts of dimethyl terephthalate and 70 parts of ethylene glycol, and the mixture was heated at 150 to 240°C. Transesterification reaction was carried out while methanol was distilled off.

Next, a stabilizer (a glycol solution of a phosphorus compound) prepared by the method shown in Table 1 was once cooled to room temperature, and then 0.014 part in terms of trimethyl phosphate was added, and then 0.04 part of antimony trioxide was added as a polycondensation catalyst. Furthermore, a predetermined amount of a predetermined inert substance having the particle size and composition ratio listed in Table-1 (Table-1
(Reference, however, in Examples 1 to 3, no additives were used) and polycondensation reaction was carried out in a high vacuum of 1 mmHg or less for 4 hours. ) polyethylene terephthalate was obtained.

In Comparative Examples 1 to 3, 40 mmol % of zinc acetate, 20 mmol % of antimony trioxide, and 40 mmol % of phosphorous acid were added as catalysts to dimethyl terephthalate, and the transesterification reaction was carried out. A predetermined amount of a predetermined inert substance having a composition ratio (see Table 1, however, no additive was used in Comparative Example 1) was added to cause a polycondensation reaction, and polyethylene terephthalate with [η] 0.65 was obtained.

The polyethylene terephthalate obtained in Examples 1 to 4 and Comparative Examples 1 to 3 was dried at 160°C, melt-extruded at 290°C, rapidly solidified on a casting drum kept at 40°C, and then unstretched to a thickness of 130 μm. I got the film.

The unstretched film was sequentially biaxially stretched at a longitudinal stretching temperature of 90°C, a longitudinal stretching ratio of 3.5 times, a transverse stretching temperature of 129°C, and a transverse stretching ratio of 3.8 times, and a coating liquid having the following composition was applied.Composition of the coating liquid: Polysiloxane 45% by weight % aminosilane 40 〃 MoS ₂ 5 〃 surfactant 10 〃 A 1% aqueous solution of a composition.

After coating, heat set at 205℃ for 10 seconds to adjust the thickness.
A 10μ film was obtained.

The film thus obtained had good slipperiness and could be wound up smoothly without any blocking.

○ on the uncoated surface of the film obtained in this way.

Claims (1)

[Claims] 1. Surface roughness [CLA (unit/μm)] of one surface of oriented polyethylene terephthalate film and number of protrusions [h (unit/μm)] [unit: pieces/mm] ² ] is in the range shown by the following formula: CLA<0.005 −(1) 0.27<h ≦0.54…0.2 pieces/mm ² or less −(2), and the coating film has a lubricant dispersed on the other surface of the film. A magnetic thin film is supported on a non-magnetic oriented polyethylene terephthalate film support, which is a film with different surfaces on the front and back sides, in which a ferromagnetic metal is vacuum deposited or plated on the surface of the film without a coating film. magnetic recording media. 2. According to claim 1, the film surface roughness CLA and the number of protrusion heights h of the protrusions are within the range shown by the following formula: CLA≦0.004 0.27<h≦0.54...0 pieces/mm ² The magnetic recording medium described. 3. The magnetic recording medium according to claim 1 or 2, wherein the magnetic thin film has a thickness of 1.5 μm or less.