JPS6180525A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To reduce squeaking at high temp. and humidity by providing a substrate layer-1 having protrusions consisting of fine particles and a binder resin, a thin film layer-1, a substrate layer-2 having protrusions consisting of fine particles and a binder resin, and a ferromagnetic metallic thin film layer in said order on a nonmagnetic supporting body. CONSTITUTION:A coating liq. contg. a fine particle 3 of silica, carbon black, and a binder resin 4 is coated on a nonmagnetic supporting body 1, and dried to form the layer 2 of a substrate layer-1 having fine protrusions on the surface. A thin film layer 5 is formed on the layer 2 by the vapor deposition of SiO2, etc. A layer 6 to be used as a substrate layer-2 contg. fine particles 7 same as or different from those of the layer 2 and a binder resin 8 is provided on the layer 5. Then a ferromagnetic metallic thin film layer 9 is formed on the layer 6 by sputtering, etc. Consequently, the number of particles in the substrate layers 2 and 6 is regulated to >=1,000 particle/mm<2> and the height of the protrusion to 30-500Angstrom , and fine protrusions corresponding to said protrusions are provided to the surface of the magnetic layer 9. A lubricant 10 is delivered on the protrusion on the layer 9, or a lubricant film is provided on the whole surface of the layer 9. A magnetic recording medium without any squeaking at high temp. and humidity and having excellent durability, etc. is thus obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application) The present invention relates to a binder-free magnetic recording medium in which the magnetic layer is composed of a ferromagnetic thin film and does not contain binders, additives, or the like.

(Conventional column configuration and its problems) Conventionally, a magnetic layer has been deposited on a non-magnetic support such as a polymer film such as a polyester film or a polyimide film or a non-magnetic metal thin film by vacuum deposition, smearing, ion blating, etc. Binder-free magnetic recording media, which are composed only of ferromagnetic thin films and do not contain binder additives, have excellent electromagnetic conversion characteristics at short wavelengths, making use of the thin film forming method of It is said to be a medium.

In order to achieve this high density, it is necessary to reduce the spacing loss as much as possible by reducing the gap of the magnetic head and smoothing the surface of the magnetic recording medium. However, if the surface is made too flat, head touch and running performance will be affected, so it is necessary to solve this problem by controlling the fine shape of the surface.

The surface properties of non-binder type magnetic recording media largely depend on the surface shape of the substrate, such as the plastic film, because the magnetic layer thickness is as small as 6.01 to 0.5 μm. Therefore, many proposals have been made regarding the surface properties of films. The row is JP-A-52-187
No. 70, JP-A-52-84264, JP-A-53-11
No. 6115, JP-A-53-128685, JP-A-54
-40893, JP-A-54-9.4574, JP-A-56-10455, and JP-A-56-16937.

In all of these examples, the surface shape is roughened relatively finely and uniformly. For example, by forming wrinkle-like protrusions, it is attempted to improve head touch and running performance all at once.

The surface condition shown in the above-mentioned curve is very effective in terms of head touch and head running properties at room temperature and humidity.

However, it has the disadvantage that some parts of the cylinder tend to generate squeal when the cylinder rotates at 30° C. and 80 to 90XRI (at high temperature and high humidity).

To solve this problem, a polyester film is used as the substrate, and the polyester oligomer contained therein is deposited as fine crystals on the substrate surface when forming a magnetic layer in a vacuum, and then a ferromagnetic metal thin film layer is placed on top of the polyester oligomer. However, in this case, the frequency of precipitation of oligomer crystals is highly dependent on location, and it is difficult to precipitate oligomer crystals evenly distributed over the entire surface.
There was a drawback that the distribution was likely to be uneven depending on the location, and the enveloping characteristics of the obtained magnetic recording medium were likely to be disturbed.
It is known that by providing the layers disclosed in No. 26 and JP-A-59-42637, noise does not occur even in high humidity, and the envelope and still life in high humidity are improved. However, even in this case, as the recording wavelength is shortened, the envelope is not necessarily good.

Furthermore, as described in JP-A-53-107314, it is known that a magnetic thin film formed on a polyester film with protruding thermoplastic particles on the surface has good running properties and good image quality. There is. However, in this case, even if an attempt is made to improve the surface properties of the magnetic recording medium in order to increase the recording density, if the surface roughness becomes 0.03 μm or less, stick-slip occurs and running properties are deteriorated.

(Objective of the Invention) The object of the present invention is to eliminate the conventional drawbacks, reduce noise in high temperatures and high humidity, improve playback image quality at short wavelengths, and provide excellent running stability and durability. An object of the present invention is to provide a binder-free magnetic recording medium.

(Structure of the Invention) The magnetic recording medium of the present invention includes a non-magnetic support, and an underlayer-1 disposed on the non-magnetic support and having particulate protrusions with fine particles as cores and resin as a binder. And this base layer-
A thin film layer-1 disposed on the thin film layer-1, a base layer-2 disposed on the thin film layer-1 and having particulate protrusions with fine particles as cores and a resin as a binder, and this base layer. a ferromagnetic metal thin film layer disposed on top of the base layer-2, and the total number of particles present in the base layer-1 and base layer-2 is 1,000 particles/m
m2 or more, this particle has a particle height of 30 to 500^
It has a size of .

(Description of Embodiment) An embodiment of the present invention will be described based on FIGS. 1 to 3.

FIG. 1 is a plan view of the magnetic recording medium of the present invention, and FIGS. 2 and 3 are sectional views taken along the line AA' in FIG.

In the figure, 1 is a non-magnetic support, and a base layer 2 (abbreviated as base layer-1) is disposed on the non-magnetic support 1 and has particulate projections.
) is a resin used to bond a core 3 made of fine particles such as thermoplastic resin fine particles, carbon fine particles, silica fine particles, and metal alkoxide hydrolysis products, and the core 3 onto the non-magnetic support 1. The binder layer 4 is made of 5 arranged on the base layer-1 indicates a thin film layer, and the base layer 6 (abbreviated as base layer-2) arranged on the thin film layer 5 and having particulate protrusions is made of fine particles of thermoplastic resin. , a core 7 made of fine particles such as carbon fine particles, silica fine particles, or a hydrolysis product of a metal alkoxide, and a binder 8 made of a resin used to bond the core 7 onto the thin film layer 5. The reference numeral 9 disposed on the underlayer-2 indicates a ferromagnetic metal thin film layer, and the reference numeral 10 disposed on the metal thin film layer 9 is a lubricant.

Further, in FIG. 2, the lubricant 1o is the ferromagnetic metal thin film 9.
In FIG. 3, the lubricant 10' is present on the entire surface of the ferromagnetic metal thin film 9'. In addition, in FIG. 3, the core 3' and the core itself are connected to the non-magnetic support 1' and the thin film layer 5, respectively.
'It mainly shows cases where it is stuck.

The height of the particulate protrusions shown in FIGS. 2 and 3 is
High precision stylus surface roughness measuring device (TALYSTEP)
-1, manufactured by TAYLOR-HOBSON Co., Ltd., and the surface roughness is expressed as the distance from the top of the unevenness to the bottom of the valley according to the maximum value of surface roughness specified in JISBO601, Rmax. A suitable height is in the range of 30 to 500 x, more preferably 50 to 300 x. If it is less than 30X, it is difficult to obtain the effect of preventing squealing in high humidity, and if it is more than 500X, the envelope is likely to be noticeably disturbed.

The density of particulate protrusions is 1.00 per 1 mm2 of the surface.
The number is 0 or more, more preferably 2,500 or more. 1
If the number is less than 000, the squeal prevention effect under high humidity is reduced. This density can be determined by observing a minimum of 10 fields of view with a differential interference light microscope with a magnification of 400, or with a scanning electron microscope with a magnification of 30.
Observe a minimum of 10 fields of view with 00, and A protrusions that exist within those fields of view. Find the number, 1, -2, convert, 1
．． ). The planar extent 9 of the particulate resin protrusions is suitably 2 to 10 times their height.

If it is 20 times or more, the squeal prevention effect in high humidity will be reduced.

Examples of the non-magnetic support 1 include a polyester film made of polyethylene phthalate or a copolymer or mixture thereof, a polyimide film such as polyesterimide or polyimide, a plastic film made of an aromatic polyamide film, aluminum, alumina, stainless steel, etc.
Among glass, ceramic, non-magnetic thin metal sheets, etc., polyester films are considered to have particularly excellent surface smoothness, and they contain almost no microprotrusions made of polymerization catalyst residues, or they contain no microprotrusions. Appropriate materials include those with a size of several hundred times or less and good smoothness, and those with uniform fine protrusions such as the aforementioned wrinkles, worms, or granules formed on the surface and whose surface roughness is several hundred times or less. It is.

A method for forming particulate resin protrusions will be explained. When fine particles of thermoplastic resin are used as the core, for example, a method of adding a solvent that does not easily dissolve the resin to a thermoplastic resin solution and applying and drying it, or a method of adding a solvent that is soluble in the liquid to a dispersion of fine particles of thermoplastic resin, etc. There is a method of applying and drying a resin added with.

Thermoplastic resins include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, or copolymers thereof, nylon 6, nylon 66, nylon 610, nylon 11, nylon 12, or copolymers thereof. The most suitable resins are polyamides, polycargonates, polysulfones, polyethersulfones, polyphenylene oxides, phenoxy, etc., but other resins such as polystyrene, polyacrylates, polyvinyl chloride, etc. can also be used.

As the binding resin, in addition to various thermoplastic resins, crosslinkable resins such as epoxy, phenol, and silicone can also be used.

When carbon fine particles are used as the core, for example, 5 L 5000 carbon fine particles with a particle size of 10 to 500X are used.
20 to io, oo of a resin serving as a binder is added to a carbon colloid solution in which ppm is dispersed.

There is a method of applying and drying after dissolving ppm. In that case, carbon fine particles are produced in carbon black produced by oil furnace method, gas furnace method, channel method, thermal method, etc., diketones such as acetylene black, esters, alcohols, aliphatic or aromatic hydrocarbons, and other organic solvents. If necessary, coarse particles are removed by filtration and used in step 1-.

Examples of resins used as binders include saturated polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc. IJ ester, nylon 6, nylon 66, nylon 610, nylon 11, nylon 1
Single substances, copolymers of various resins such as polyamide, polystyrene, polycargonate, polyarylate, polysulfone, polyether sulfone, polyacrylate, polyvinyl chloride, polyvinyl butyral, polyphenylene oxide, phenoxy resin, or these Mixtures can be used, as well as crosslinked resins such as epoxy resins, urethane resins, silicone resins, phenolic resins, melamine resins or modified resins thereof.

When using silica fine particles as a core, for example, 10 to 10.000 silica fine particles with a particle size of 10 to 500X are used.
There is a method in which 20 to 10,000 pprn of a resin serving as a binder is dissolved in a silica colloid solution dispersed in ppm, and then applied and dried. Examples of fine silica particles include fine powder silica obtained by a dry method made of silicon tetrachloride (column: Aerosil: manufactured by Nippon Aerosil Co., Ltd.), fine powder silica obtained by decomposing sodium silicate with acid or alkali (e.g. 5yloid (manufactured by Fuji Davison Chemical Co., Ltd.), silica sol obtained by ion exchange of sodium silicate (column varnish nortex: manufactured by Nissan Chemical Industries, Ltd.), etc., and these are mainly composed of water, alnyl, ketone, ester, etc. dispersed in a solution of
If necessary, coarse particles are removed by filtration before use.

Examples of resins used as binders include saturated polyesters of polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, nylon 6, and nylon 66.
, polyamides such as nylon 610, nylon 11, and nylon 12, polystyrene, polycargonate, polyarylate, polysulfone, polyethersulfone, polyacrylate, polyvinyl chloride, polyvinyl butineal, polyphenylene oxide, and various resins such as phenoxy resin. Single substances, copolymers, or mixtures thereof can be used, and crosslinkable resins such as epoxy resins, urethane resins, silicone resins, phenol resins, melamine resins, or modified resins thereof can also be used.

When fine particles consisting of a hydrolysis product of a metal alkoxide are used as cores, water is added to a dilute solution (10 to 1.000 ppm) of the metal alkoxide at a concentration of 10 to 10.0 mm.
The metal alkoxide is hydrolyzed by adding 1 to 50% of an organic solvent containing 0.00 ppm to a particle size of 10 to 50 ppm.
There is a method in which 0X fine particles are precipitated and dispersed, a solution is prepared, and a resin serving as a binder is dissolved in the solution in an amount of 20 to 500 ppm, and then applied and dried. Examples of metal alkoxides include tetraethoxysilane, aluminum S- Butoxide, aluminum S-
Butoxide, aluminum isopropyl borate, trimethylpyrate, tri-tert-butylborate, tetra-1-7D titanium, tetra-n-butoxytitanium, tetrakis(2-ethylhexoxy)citane,
Examples include tri-n-butoxytitanium monostearate, tetramethyl titanate, tetraethyl titanate, zirconium tetra-t-butoxide, tetraisopropyl zirconate, and indium isogropoxy. Examples of resins used as binders include polyethylene terephthalate and polybutylene terephthalate. , saturated polyesters such as polyethylene naphthalate, polyamides such as nylon 6, nylon 66, nylon 6101, nylon 11, nylon 12, polystyrene, polycargonate, polyarylate, polysulfone, polyethersulfone, polyacrylate, polyvinyl chloride, Single substances, mixtures, or copolymers of various resins such as polyvinylidene chloride, polyvinyl butyral, polyphenylene oxide, and phenoxy resins can be used, and crosslinkable resins such as epoxy resins, urethane resins, silicone resins, and phenol resins can also be used. .

The ferromagnetic metal thin film may be, for example, a metal thin film mainly made of Co, Ni, Fe, etc. formed by an oblique evaporation method or a perpendicular evaporation method, or a metal thin film mainly made of an alloy thereof (for example, a Co-Cr perpendicularly magnetized film). ) can be used, but it can be obtained when the stirred atmosphere during deposition is made into an atmosphere dominated by oxygen gas for the purpose of improving the adhesion strength with the surface to be deposited, or improving the corrosion resistance and abrasion resistance of the ferromagnetic metal thin film itself. It is desirable to use a ferromagnetic metal thin film containing oxygen. The oxygen content is suitably at least 3% or more, preferably 5% or more in terms of atomic ratio to the ferromagnetic metal or nonmagnetic metal near the surface of the substrate film.

The ferromagnetic metal thin film containing oxygen as described above, or the combination of the above non-magnetic metal layer and an underlayer having particulate protrusions formed thereunder as required, can significantly improve the methyl lifespan. becomes possible. Note that the still life is also related to the thickness of the ferromagnetic metal thin film, and if the thickness becomes less than 400X, the still life will decrease rapidly.
It is desirable that it is 0X or more.

The thin film layers 5 and 5' shown in FIGS. 2 and 3 are
It may be a ferromagnetic metal thin film that is part of the ferromagnetic metal thin films 9 and 9'. In addition, if necessary, prior to shaping the ferromagnetic metal thin film, a thin film having a mechanical reinforcing effect, such as T.
Oxygen-containing metal thin film such as i, Cr, Ni, At2
03. S10. A thin film of oxide such as SiO2 or the like may be formed.

By providing a lubricant on the surface of the ferromagnetic metal thin film, it is possible to further enhance the running performance improvement effect based on the shape of the particulate protrusions. This further ensures complete prevention of squealing in high humidity environments.

As a means of making a lubricant exist on the surface of a ferromagnetic metal thin film,
In addition to applying directly to the surface of the ferromagnetic metal thin film, or applying vapor deposition and polymerization to the back surface of the magnetic recording medium, or applying vapor deposition and polymerization to the surface of the ferromagnetic metal thin film during stacking (winding) of the magnetic recording medium. It is also possible to transfer the image to It is also possible to use a resin binder or the like to firmly fix the lubricant. As the lubricant, fatty acids, fatty acid di-sters, fatty acid amides, metallurgical stones, aliphatic alcohols, tsukurafuin, silicones, fluorine-based surfactants, inorganic lubricants, etc. can be used. The appropriate amount of lubricant is 0.5 to 500 m9, more preferably 5 to 200 m9 per m2 of surface.

As the fatty acid, those having 12 or more carbon atoms can be used, such as lauric acid, myristic acid, p-lumic acid, stearic acid, behenic acid, oleic acid, linoleic acid, and linuric acid.

As the fatty acid ester, ethyl stearate, butyl stearate, amyl stearate, stearic acid monoglyceride, glumitic acid monoglyceride, oleic acid monoglyceride, RNtaeris IJ)-lutetrastearate, etc. can be used.

Examples of fatty acid amides include caproic acid amide, capric acid amide, lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide,
Linoleic acid amide, methylene bisstearic acid amide, ethylene bisstearic acid amide, etc. can be used.

Metal soaps include zinc, lead, nickel, cobalt, lauric acid, myristic acid, i4 lumitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, lylic acid, etc.
Salts with iron, aluminum, magnesium, strontium, copper, etc., and salts of nosulfonic acids such as lauryl, tukurumityl, myristyl, stearyl, behenyl, oleyl, linole, linole, and the above various metals can be used.

As the aliphatic fluorol, cetyl alcohol, stearyl alcohol, etc. can be used.

Saturated hydrocarbons such as n-octadecane, n-nonadecane, n-tridecane, n-tocosan, and n-todriacontane can be used as the 4-rafi/.

As silicon, polynoloxanes in which hydrogen is partially substituted with alkyl groups or phenyl groups, and those modified with fatty acids, aliphatic alcohols, acid amides, etc. can be used.

Examples of fluorine-based surfactants include nosofluoroalkylcarboxylic acid, nosofluoroalkylsulfinate, sodium, potassium, magnesium, zinc, aluminum,
Salts with iron, cobalt, nickel, etc., such as P-fluoroalkyl phosphate esters, fluoroalkyl betaines,
Perfluoroalkyltrimethylammonium salt, /%'
- Fluoroethylene oxide, pertomyloalkyl fatty acid ester, etc. can be used.

Examples of the inorganic lubricant include graphite powder, molybdenum disulfide powder, tungsten disulfide powder, molybdenum selenide powder, tungsten selenide powder, calcium fluoride powder, and the like.

Antifungal agents can be applied to the front surface, back surface, or the vicinity thereof of the magnetic recording medium of the present invention, the gap in the ferromagnetic metal thin film, the interface between the magnetic recording medium and the non-magnetic support, the inside of the non-magnetic support, etc. by known means. Various additives such as rust preventives, antistatic agents, etc. may be present as necessary.

Specific examples will be described below.

Example-1 The following composition liquid-1 was applied onto a smooth polyethylene terephthalate biaxially stretched film to significantly suppress protrusions caused by polymerization catalyst residue and reduce the surface roughness to 30X or less, resulting in a coating thickness of approximately 10 μm. After continuous coating and drying, approximately 50 particulate protrusions with a height of approximately 100X with silica fine particles as cores are formed on the surface.
A base layer-1 having 1,000,000 pieces/rrtn2 was formed, and a long film sample A was obtained.

Composition liquid-1 Methanol...200 phr
Ethyl acetate...800 phr
Subsequently, Si with a thickness of 1,000× is deposited on the base layer-1.
An O vapor deposited film was formed as a thin film layer-1 by a continuous vapor deposition method. Next, the above-mentioned composition liquid-1 is applied onto this thin film layer-1, and the coating is continuously coated and dried so that the coating thickness becomes about 12 μm. A base layer 2 having approximately 1 million protrusions/layer 2 was formed.

Example-2 By changing the liquid composition of Example VJIJ-1 to the following composition liquid-2, a height of approximately 100 mm with carpin fine particles as the core was obtained.
The base layer-1 has approximately 1,000,000/2 particulate protrusions with a height of X, and approximately 5 particulate protrusions with a height of 100X.
A base layer-2 having a density of 0,000 pieces/WIR2 was formed.

composition! -2 Methylene chloride...500 phr
Toluene...300 phr
Methyl ethyl ketone...200 phr
The film length sample thus obtained is designated as B.

Example 3 In Example Row 1, by changing the liquid composition to Composition Liquid 3 below, the height of particles made of polysulfone was increased to about 3
A base layer-1 having approximately 400,000 particulate protrusions/wn2 with a height of 50X and a base layer-2 having approximately 700,000 particulate protrusions/wn2 with a height of approximately 350X were formed.

Composition liquid-3 Methylene chloride...100 phr
Benzene...100 phr
Ethyl acetate...800 phr
The film length sample obtained in this manner is designated as C.

Comparative Example-1 The composition liquid-1 was applied to a smooth polyethylene terephthalate biaxially stretched film that had significantly suppressed protrusions caused by polymerization catalyst residue and had a surface roughness of 30^ or less to a coating thickness of about 15 μm. A long film sample was obtained by continuous coating and drying to form a base layer having about 1.5 million/M1n2 particulate protrusions with a height of about 100X with silica fine particles as cores on the surface. -2 In comparison row-1, by changing the liquid composition to the above-mentioned composition liquid-2, a height of approximately 100 mm with carpin fine particles as the core
A long film sample E was obtained in which a base layer having approximately 1.5 million particulate protrusions (X) per interval 2 was formed.

Comparative Release 3 In Comparative Series-1, by changing the liquid composition to the composition liquid-3, the height of the particles made of polysulfone was approximately 3.
A long film sample F was obtained, in which a base layer having approximately 1,000,000 50× particle-like projections/2 was formed.

Comparative Example 4 The sample of the smooth polyethylene terephthalate biaxially stretched film itself used in Examples 1 to 3 and Comparative Series 1 to Comparative Example 3 is designated as G.

The oxygen content of the magnetic layer is 5X in atomic ratio to the metal. Thereafter, various lubricant solutions were applied to the surface of each sample, and the tape was scraped and rolled to a predetermined width to form a magnetic tape.

These were applied to a prototype video tape encoder in an environment of 30° C. and 90% RH to measure the squealing state and output at a portion of the rotating head/cylinder. Magnetic tape has a wavelength of 0.8
The reproduction output at μm and 0.5 μm was observed using an oscilloscope to observe the absolute straightness of the output and the state of the envelope, and the results are shown in the table. The absolute value of the output in the table is a relative comparison, with the output at a wavelength of 0.8 μm of the magnetic tape using no lubricant for sample G taken as OdB. “○” and “Δ” written in the envelope section in the same table
, r It indicates the condition.

As can be seen from the table under an environment of 30°C and 90% RH, the magnetic recording medium with the structure of the present invention improves the squealing under high temperature and high humidity, and also has a good envelope at short wavelengths (0.5 μm), that is, reproduction A non-binder that improves image quality, has a small coefficient of dynamic friction, has little variation between the first and 100th reciprocation, and has no scratches on the magnetic tape, improving running stability and durability. type magnetic recording medium.

Although not specifically stated in the above examples and tables, polyethylene terephthalate, which contains almost no particulates due to polymerization catalyst residue, is used, and a modified silicone emulsion containing a thickener is applied to the surface during film formation and stretching. By applying and curing the main liquid, a polyester biaxially stretched film was formed to form a thin film layer of a different type of polymer consisting of fine wavy irregularities with a surface roughness of 100X. Similar base layer-1 and base layer-2
The above-mentioned ferromagnetic thin film layer was applied to the sample on which the ferromagnetic film had been formed, and then various lubricant solutions were applied to the surface of each sample, and the magnetic tape was made by scraping and tossing it to a predetermined width. The results obtained are almost the same as those obtained in the previous study.

(Effects of the Invention) The magnetic recording medium according to the present invention improves noise under high temperature and high humidity conditions, improves reproduced image quality under short wavelength conditions, and has excellent running stability and durability. Yes, and its practical effect is dogs.

[Brief explanation of the drawing]

FIG. 1 is a plan view of the magnetic recording medium of the present invention, and FIGS. 2 and 3 are cross-sectional views taken along line A-A' in FIG. 1.1'...Nonmagnetic support, 2...Underlayer-1, 3
゜3', 7, 7'... Core, 4, 8... Binder layer, 5, 5'... Thin film layer, 6... Base layer-2, 9,
9'...Ferromagnetic metal thin film layer, 10, 10'...Lubricant. Patent applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] a non-magnetic support; a base layer-1 disposed on the non-magnetic support and having particulate protrusions with fine particles as cores and a resin as a binder; and a thin film layer disposed on the base layer-1. -1 and
A base layer-2 disposed on the thin film layer-1 and having particulate projections having fine particles as cores and a resin as a binder, and a ferromagnetic metal thin film layer disposed on the base layer-2. The total number of particles present in the base layer-1 and base layer-2 is 1.0.
00 particles/mm^2 or more, and the size of the particles is 30 to 500 Å in terms of particle height.