JPS63229610A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the travelling performance and durability by laminating a specified under coat layer and a thin ferromagnetic metallic film on a plastic film substrate and forming spherical projections on the surface of the metallic film. CONSTITUTION:An under coat layer contg. fine particles as nuclei and resin as a binder and having >=1,000 particle-shaped projections of 30-500Angstrom height per 1mm<2> layer and a thin ferromagnetic metallic film are laminated on a plastic film substrate and spherical projections of 1-100mum average height are formed on the surface of the metallic film at a density of 10<-4>-2X10<-2> projection per 1mm<2> film. Microscopic surface roughness is provided to the surface of the metallic film by the under coat layer and macroscopic surface roughness by the spherical projections. The resulting magnetic recording medium ensures smooth touch with a head, that is, high travelling performance and the durability, especially the still characteristics at low temp. and humidity can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium suitable for a magnetic tape for a rotary head type video tape recorder.

(Prior art) Iron, cobalt, nickel, alloys containing these as main components, or thin films of their oxides are used to form high-quality polyester films, polyimide films, etc. using vacuum film forming methods such as vacuum evaporation, sputtering, and ion blasting. Ferromagnetic metal thin film magnetic recording media formed on substrates made of molecular films, non-magnetic metal thin films, etc. can dramatically improve recording density compared to conventional coated magnetic recording media. In order to achieve this high density, it is necessary to reduce the gap of the magnetic head and to smooth the surface of the magnetic recording medium to reduce the spacing loss as much as possible. 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. Since the surface properties of ferromagnetic metal thin film magnetic recording media are very small, with a magnetic layer thickness of about 0.1 to 0.5 -, it is highly dependent on the surface shape of the plastic substrate. Many proposals have been made regarding the superficiality of . Examples are JP-A-53-116115 and JP-A-53-12868.
Publication No. 5.

JP-A-54-94574, JP-A-56-1045
No. 5, JP-A-56-16937, etc. In all of these examples, the surface shape is relatively finely and uniformly roughened. For example, attempts are being made to improve head touch, that is, running performance, all at once by forming wrinkle-like projections, earthworm-like or granular projections. Very effective.

(Problems to be solved by the invention) However, regarding durability, especially still characteristics,
Sufficient improvement was not seen. This is because the rotating head mechanically destroys the ferromagnetic metal thin film, that is, it causes transmission scratches throughout the thickness of the thin film in a short period of time. Japanese Patent Application Laid-open No. 59-4263 partially improved this problem.
No. 7, Japanese Patent Application Laid-Open No. 59-48826, etc., and it is described that particulate protrusions with fine particles as a core and a resin as a binder are used as a base layer, but under normal environment. In this case, a sufficient improvement effect on the above-mentioned durability can be seen. However, under low temperature and low humidity (e.g. 5℃).

20% RH), the above-mentioned durability problem occurs.

In view of the above problems, the present invention provides a magnetic recording medium with improved running performance and durability.

(Means for Solving the Problems) The above-mentioned problem part is: Herad touch in a rotating head type video tape recorder of a ferromagnetic metal thin film type magnetic recording medium;
In order to solve the problem of durability, the magnetic recording medium of the present invention includes a plastic film substrate, and particles with a particle height of 3.5 mm on the plastic film substrate with fine particles as a core and a resin as a binder.
an undercoat layer having 0 to 500 particle-like protrusions of 1000 pieces/mm or more; a ferromagnetic metal thin film layer formed on the undercoat layer; 1
00-, density to-'~2 x 10-2 pieces/rar
The undercoat layer forms a microscopic level of surface roughness on the surface of the ferromagnetic metal thin film, and the spherical protrusions form a macroscopic level of surface roughness.

(Function) With the above-described formation, the magnetic recording medium of the present invention can improve durability, particularly still characteristics under low temperature and low humidity conditions, while ensuring smooth head touch, that is, running performance.

(Embodiment) An embodiment of the magnetic recording medium of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a plan view of a magnetic recording medium according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA' in FIG. Note that FIGS. 1 and 2 are conceptual diagrams based on observation at a magnification of 3000 using a scanning electron microscope. FIG. 3 is a plan view of a magnetic recording medium in another embodiment of the invention.

FIG. 4 shows a sectional view taken along the line BB' in FIG. 3. Note that FIGS. 3 and 4 are conceptual diagrams based on observation with a differential interference optical microscope with a magnification of 100.

In the same figure, ■ is a plastic film, 2 is a core made of fine particles made of carbon fine particles, silica fine particles, a hydrolysis product of metal alkoxide, or a mixture of multiple types selected from these fine particles, and 3 is a nucleus consisting of fine particles selected from these fine particles. A binding resin for fixing the core 2 on the plastic film 1, 4 a ferromagnetic metal thin film layer, 5 a lubricant, and 6 spherical protrusions.

In FIGS. 2 and 4, the lubricant 5 is present on the entire surface of the ferromagnetic metal thin film layer 4;
The height of the particle-like protrusions, which may exist only in a specific part of the top, can be measured using a high-precision stylus-type surface roughness measuring device
STEP-1, 7AYLOR-14 (manufactured by OBSON), and is expressed as the distance from the top of the unevenness to the bottom of the valley according to the maximum surface roughness value Rrsax specified in JIS BO601. The height of the particulate protrusions suitable for the present invention is preferably in the range of 30 to 500 people. When forming particulate protrusions, it is generally difficult to obtain runnability if the nuclei are formed with a height of 30 Å or less.
If it is 0 Å or more, 81! As for the density of 0 particle protrusions that tend to cause a decrease in l force and disturbance of the envelope, the surface 1
A suitable number is 1,000 or more, more preferably 2,500 or more per m garden, and if it is less than 1,000, it is difficult to obtain good runnability.

Furthermore, this density is &1! with a minimum field of view of 10 at a magnification of 3000 using a scanning electron microscope! The number of particulate protrusions existing within the field of view was determined and converted to 1 m + a".The planar spread of particulate resin protrusions is 1 to 20 times their height. , more preferably 2 to 10
Double is appropriate. At 20 times or more, running performance is not obtained.

Next, the formation of spherical protrusions will be explained. The undercoat layer is provided on a plastic film substrate, and the ferromagnetic metal thin film layer is provided on the undercoat layer.

Subsequently, a lubricant is applied to the surface of the ferromagnetic metal thin film layer, and while the plastic film substrate including the ferromagnetic metal thin film layer is run, the metal exhibiting an appropriate surface roughness is
plastics, ceramics.

The spherical protrusions are formed by inserting between rollers made of rubber or the like (referred to as surface transfer rollers for short) and transferring the surface roughness of the surface transfer rollers to the surface of the ferromagnetic metal thin film layer. .

FIG. 5 and FIG. 6, which is an enlarged view of a portion of FIG. 5 (indicated by CC'), are conceptual diagrams showing a method for forming the spherical protrusions on the surface of the ferromagnetic metal thin film layer. A surface transfer roller 7 having an appropriate surface roughness and the magnetic recording medium 1 facing the surface transfer roller 7 together with the surface transfer roller 7.
By conveying the magnetic recording medium 10 including the ferromagnetic metal thin film layer between the pinch rollers 8 which push out the magnetic recording medium 10 (the pressing force is indicated by P) while applying a pressure of 0.0, the surface transfer is performed. The surface roughness of the roller 7 forms spherical protrusions 6 on the surface of the ferromagnetic metal thin film layer.

As shown in FIG.
It goes without saying that it should be placed on the side.

Note that spherical projections are formed on the surface of the ferromagnetic metal thin film layer 4, and on the surface of the plastic film (if a known back coat is provided on the magnetic recording medium, the surface of the back coat). , a concave-like spherical depression is formed.

The height and density of the spherical protrusions formed on the surface of the ferromagnetic metal thin layer 4 are determined by the surface shape on the surface of the surface transfer roller, the above-mentioned pressing force 29 and the surface transfer roller 7.
, the speed at which the magnetic recording medium 10 is conveyed between the surface transfer roller 7 and the pinch roller 8, the diameter of the surface transfer roller and the pinch roller 9, and the height of the spherical protrusion. is preferably in the range of 1 to 100 houses, preferably 1 to 10 houses. If it exceeds 1100p, the envelope will be disturbed. If it is less than 1, it is difficult to obtain sufficient durability, especially still characteristics.

The height of the spherical protrusion is determined by actual measurement using the aforementioned stylus type surface roughness measuring device. Alternatively, as a simple method, it may be determined using a differential interference optical microscope with a magnification of 400 based on the difference in depth of focus.

The density of spherical protrusions is 10− per surface L am”.
4 to 2 x 10-" pieces, more preferably 10-3 to 10-"
Two pieces is appropriate. If the number is less than 10-9, it is difficult to obtain sufficient still characteristics, and if the number is more than 2×10'', the envelope will be disturbed and noise will increase in the low frequency range.

The density of spherical protrusions was measured using a differential interference optical microscope with a magnification of 100 and a minimum of 10 fields of view. The number of spherical protrusions present within the field of view was calculated by holding a festival and converting it to 1 m2. The planar extent of the spherical protrusions is suitably 0.5 to 10 times, more preferably 1 to 5 times, their height. If it is 10 times or more, the envelope will be disturbed and noise will increase in the low frequency range. When it is 0.5 times or less, it is difficult to obtain sufficient still characteristics.

Note that the density of the particulate protrusions is determined from the number present at a magnification of 3000, and the density of the spherical protrusions is determined from the number present at a magnification of 100.For convenience, the former is determined from the surface at a microscopic level. The latter can be viewed as adding surface roughness on a macroscopic or level level.

Examples of plastic films include polyester films made of polyethylene terephthalate or copolymers and mixtures thereof, polyethylene naphthalate or copolymers and mixtures thereof, polyimide films such as polyesterimide and polyimide, and aromatic polyamide films. For example, a polyester film has good surface smoothness, containing almost no microprotrusions made of polymerization catalyst residues, or having microprotrusions with a size of several hundred Å or less, as mentioned above. Wrinkled, worm-like.

Suitable materials include those on which uniform fine protrusions such as granules are formed on the surface, and the surface roughness is several hundred angstroms or less.

Next, a method for forming particulate resin protrusions on these films will be explained. When fine particles of thermoplastic resin are used as the core, for example, a solution that does not easily dissolve the resin is added to a thermoplastic resin solution, applied on the film surface, and dried; There are methods such as applying a material to which other soluble resin is added onto the film surface and drying it.

Examples of thermoplastic resins include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and copolymers thereof, nylon 6, nylon 66, nylon 610, etc.
Nylon 11. Nylon 12. Or various polyamides, polycarbonates, polyarylates, and polysulfones made of copolymers thereof.

Polyether sulfone, polyphenylene oxide, phenoxy, etc. are most suitable, but other resins, e.g.
Polystyrene, polyacrylate, 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, the particle size is, for example, 10 to 5.
A resin serving as a binder is added to a carbon colloid solution in which 5 to 5,000 ppm of carbon fine particles are dispersed.
There is a method of dissolving 0 to 10,000 ppm and then coating it on a plastic film and drying it. In that case, the carbon fine particles are carbon black, acetylene black, etc. produced by an oil furnace method, a gas furnace method, a channel method, a thermal method, etc., in an organic solvent such as a ketone, ester, alcohol, aliphatic or aromatic hydrocarbon. The powder is dispersed in the form of fine particles, and if necessary, coarse particles are removed by filtration before use. Examples of resins that serve as binders include polyethylene terephthalate, polybutylene terephthalate,
Saturated polyesters such as polyethylene naphthalate, nylon 6, nylon 66, nylon 610. nylon 11
．． Polyamide such as nylon 12, polystyrene, polycarbonate, polyarylate, polysulfone, polyethersulfone, polyacrylate.

Various resins, such as polyvinyl chloride, polyvinyl butyral, polyphenylene oxide, phenoxy resin, etc. alone, copolymers, or mixtures thereof can be used, and epoxy resins, urethane resins, silicone resins, phenol resins, melamine resins, or any of these resins can be used. Crosslinked resins such as modified resins can also be used.

When using silica fine particles as the core, 1, for example, the particle size is 10 to 50.
A resin serving as a binder is added to a silica colloid solution in which 10 to 10,000 ppwi of silica fine particles are dispersed.
There is a method of dissolving 0 to 10,000 ppm, then coating it on a plastic film and drying it. Examples of fine silica particles include fine powder silica obtained by a dry method made of silicon tetrachloride (e.g., Aarosil; Nippon Aerosil ■), fine powder silica obtained by decomposition of sodium silicate with acid or alkali (e.g., 5yloid Ni-Fuji). Davison Chemical [), silica sol obtained by ion exchange of sodium silicate (e.g. Snowtex; Nissan Chemical Industries ■), etc., and these can be mixed with water, alcohol, ketones,
It is used by dispersing it in a solution mainly composed of esters, etc., and removing coarse particles by filtration if necessary. Examples of resins used as binders include saturated polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, nylon 6, nylon 66, and nylon 6.
10. Nylon 11. Polyamide polystyrene such as nylon 12, polycarbonate, polyarylate, polysulfone, polyether sulfone, polyacrylate.

Various resins such as polyvinyl chloride, polyvinyl butyral, polyphenylene oxide, phenoxy resin, etc. alone, copolymers, or mixtures thereof can be used, and also epoxy resins, urethane resins, silicone resins, phenol resins, melamine resins, Alternatively, crosslinkable resins such as modified resins thereof can also be used.

When fine particles consisting of a hydrolysis product of a metal alkoxide are used as cores, a dilute solution of the metal alkoxide (10 to 1
, 000ppn+) with water at 10-10. OOOpp
The metal alkoxide is hydrolyzed by adding 1 to 50% of an organic solvent containing m to form a solution in which fine particles with a particle size of 10 to 500 are precipitated and dispersed.
There is a method of dissolving 5,000 ppm, applying it on a substrate, and drying it.

Examples of metal alkoxides include tetraethoxysilane, aluminum S-butoxide, aluminum t-butoxide, aluminum isopropylborate, trimethylborate, tri-tert-butylborate, tetra-1-propoxytitanium, tetra-n-butoxytitanium, and tetrakis(2).・Ethylhexoxy) titanium, tri-n-butoxytitanium monostearate, tetramethyl titanate, tetraethyl titanate, zirconium tetra-t-butoxide, tetraisopropyl zirconate, indium isopropoxide, etc. As for the resin that serves as a binder, Saturated polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, nylon 6, nylon 66, nylon 610. Nylon 11. Polyamide such as nylon 12.

polystyrene, polycarbonate, polyarylate,
Single substances, mixtures, or copolymers of various resins such as polysulfone, polyethersulfone, polyacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, polyphenylene oxide, and phenoxy resin can be used, and epoxy resins and urethane resins can be used. Crosslinkable resins such as resins, silicone resins, and phenolic resins can also be used.

Next, the ferromagnetic metal thin film and the lubricant will be explained.

The ferromagnetic metal thin film includes, for example, a metal thin film mainly made of Co, Ni, Fe, etc. formed by oblique evaporation or perpendicular evaporation, and a metal thin film mainly made of an alloy thereof (for example, a Co-Cr perpendicular magnetization film). However, for the purpose of improving the adhesion strength with plastic films or improving the corrosion resistance and abrasion resistance of the ferromagnetic metal thin film itself, the oxygen obtained when the atmosphere during vapor deposition is made to be an atmosphere dominated by oxygen gas can be used. It is desirable to use a ferromagnetic metal thin film that contains oxygen.
% or more, preferably 5% or more. Also, if necessary, prior to the formation of the ferromagnetic metal thin film.

Thin film with mechanical reinforcing effect, for example, oxygen-containing metal thin film such as Ti, Cr, Ni, etc., AIIz03. It is also possible to form an oxide thin film such as SiO□.

The combination of the above-mentioned ferromagnetic metal thin film containing oxygen, or the above-mentioned non-magnetic metal layer formed thereunder as necessary, and a base layer having particle-like protrusions, can greatly extend the life of the still. Improvements are 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 400 Å, the still life decreases rapidly.
It is desirable that the thickness is 00 Å or more.

By providing a lubricant on the surface of the ferromagnetic metal thin film layer, it is possible to enhance the effect of improving bed touch, that is, running performance. As a means of achieving this, 1. In addition to coating directly on the surface of the ferromagnetic metal thin film or vapor-depositing it, the ferromagnetic metal thin film is coated or vapor-deposited on the back side of the magnetic recording medium, and when the magnetic recording medium is laminated (rolled), the ferromagnetic metal thin film is coated or vapor-deposited. 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 lubricants, fatty acids, fatty acid esters, fatty acid amides,
Metal soap, aliphatic alcohol, paraffin.

Silicones, fluorosurfactants, inorganic lubricants, etc. can be used. The amount of lubricant present is 0.5 to 1 lb per surface.
A suitable amount is 500 g, more preferably 5 to 200 mg.

Fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, and oleic acid.

Those having 12 or more carbon atoms such as linoleic acid and linoleic acid can be used.

Ethyl stearate is a fatty acid ester.

Butyl stearate, acyl stearate, stearic acid monoglyceride, valmitic acid monoglyceride, oleic acid monoglyceride, pentaerythritol tetrastearate, etc. can be used.

Fatty acid amides include caproic acid amide, capric acid amide, uraric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide,
linoleic acid amide, methylene bisstearic acid amide,
Ethylene bisstearamide, etc. can be used.

Metal soaps include zinc, lead, nickel, cobalt, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, lyuronic acid, etc.
Salts with iron, aluminum, magnesium, strontium, copper etc., lauryl, palmityl.

Salts of sulfonic acids such as myristyl, stearyl, behenyl, oleyl, linole, rinne and the above various metals can be used.

Cetyl alcohol is an aliphatic alcohol.

Stearyl alcohol etc. can be used.

As the paraffin, saturated hydrocarbons such as n-ocdadecane, n-nonadecane, n-tridecane, n-tocosan, and n-todoriacontane can be used.

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

Examples of fluorine-based surfactants include perfluoroalkyl carboxylic acid and perfluoroalkyl sulfinic acid, sodium, potassium, magnesium, zinc, aluminum, iron,
Salts with cobalt, nickel, etc., perfluoroalkyl phosphates, perfluoroalkyl betaines, perfluoroalkyltrimethylammonium salts, perfluoroethylene oxide, perfluoroalkyl fatty acid esters, 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.

An anti-mold agent is applied to the front surface, the back surface or the vicinity thereof of the magnetic recording medium of the present invention, the gap in a ferromagnetic metal thin film, the interface between a ferromagnetic metal thin film and a plastic film, the inside of a plastic film, etc. by known means.

Various additives such as rust preventive agents and antistatic agents may be present as necessary.

The magnetic recording medium of the present invention will be described below with reference to more specific examples.

Example-1 The following composition solution was applied continuously to a thickness of about 10 coats on a smooth polyethylene terephthalate biaxially stretched film that had significantly suppressed protrusions caused by polymerization catalyst residue and had a surface roughness of 30 Å or less. , dried, and on the surface there are about 10,000/ll+ particulate protrusions with a height of about 500 people with carbon fine particles at the core.
A long film sample on which an undercoat layer having 12 layers was formed was obtained. This sample is designated as A.

Composition liquid-1 Carbon ・・・・・・0.1p
hrEthyl acetate...50
0 phr toluene...
500phr polyester...song...
0.5 phr Example-2 By changing composition liquid-1 in Example-1 to the following, an undercoat layer having 200,000/mm2 of particulate protrusions with a height of about 100 particles using silica fine particles as cores was created. A long film sample was obtained. This sample is designated as B.

Composition liquid-2 Methanol silica gel... group 0.08Phr
(Made by Nissan Chemical Industries ■) Methanol ・・・・・・2.00p
hrEthyl acetate...100
0phrToluene・・・・・・1
00phr polyester ・・・・・・
0.5 phr Example-3 By changing composition liquid-1 in Example-1 to the following, an undercoat having particle-like protrusions made of nylon 66 with a particle height of about 500 and about 50,000/mm" was obtained. A long film sample with layers formed thereon was obtained.

This sample is designated as C.

Composition liquid-3 Nylon 66...04
5Phr phenol ・・・・・・3
00 phr Cellosolve acetate ・・・・・・
700 hpr The above samples A, B, and C were successively connected and a (o, Ni ferromagnetic metal thin film (NC 20 νt%, film thickness approximately 2000 mm) was deposited on each surface by continuous vacuum oblique evaporation method in the presence of a trace amount of oxygen. The oxygen content of the magnetic layer was 5% in atomic ratio to the metal.Thereafter, a fluorine-based lubricant perfluoroalkyl fatty acid ester was applied to the surface of the ferromagnetic metal thin film for each sample. did.

Next, each of A, B, and C was divided into equal parts in the longitudinal direction of each sample, and one part was transported between the surface transfer roller 7 and the pinch roller 8 shown in FIGS. 5 and 6. , and the other sample was not transported. The transported sample was transferred to A1. B
, ,C, and the untransferred sample is A2. B2. C2, and the sample was then slit into a predetermined width to form a magnetic tape.

Sample D as a comparative example is a film in which the ferromagnetic metal thin film layer is provided directly on the smooth polyethylene terephthalate biaxially stretched film, and a fluorine-based lubricant perfluoroalkyl fatty acid ester is applied to the surface of the ferromagnetic metal thin film layer. is coated and slit into a predetermined width without being conveyed between the surface transfer roller 7 and the pinch roller 8. These samples A, , B1. C1, A,, B2. Tests regarding runnability, that is, measurements of the coefficient of kinetic friction μ as shown below, were carried out in an environment of 30°C and 90% R (() for C2 and D. A post with a diameter of 4φ and a material of 5US420J2 was installed. The surface of the post was wrapped with the surface of the ferromagnetic metal thin film of the above-mentioned prototype magnetic tape in contact with it.
Moreover, the dynamic friction coefficient μ was measured using a dynamic friction coefficient measuring machine that applied a constant tension to the prototype magnetic tape and fed the prototype magnetic tape at a speed of 18 mm/see. The following table shows the results. This is what is shown.

The table contains data on the behavior of the kinetic friction coefficient μ when the prototype magnetic tape was reciprocated 100 times in the kinetic friction coefficient measuring machine, and in particular, the kinetic friction coefficient during the "first" and "100th" reciprocations. The absolute value of μ is shown. For "stability" in the table, the ratio of the dynamic friction coefficient at the "100th" reciprocation to the "initial" dynamic friction coefficient is 1. If it is less than L, there is little variation in the coefficient of dynamic friction, rOJ; if it is 1.1 to 1.5, it is "ΔJ," and if it is more than 1.5, it is marked with "X", which means that variation is large. In addition, "presence or absence of scratches" in the same table refers to the presence or absence of scratches on the surface of the ferromagnetic metal thin film of the above-mentioned prototype magnetic tape after 100 reciprocations in the same friction coefficient measuring machine. If there are scratches, it is said to be "present," and if there are no scratches, it is said to be "absent."

Next, the measurement of still life described in the last section of the same table will be explained. The still life of the above prototype tape was measured in a prototype deck having functions roughly equivalent to a commercially available 8 mm video tape recorder. The measured environment is 5
℃ and 20% RH.

In the above-mentioned prototype deck, the back tension applied to the above-mentioned prototype tape was 30 g, and under this tension, the prototype tape was brought into a still state, and scratches were created across the entire thickness of the ferromagnetic metal thin film of the prototype tape. The time until this occurs was defined as the "still life."

In the same table, the still life is "O" when it is 60 minutes or more.
"Δ" indicates a range of 30 to 60 minutes, and "x" indicates a period of 30 minutes or less.

The following can be seen from the table. An undercoat layer containing the above particulate projections is provided on a smooth biaxially stretched polyethylene terephthalate film, a ferromagnetic metal thin film layer is formed on the undercoat layer, and spherical projections are further formed on the surface of the ferromagnetic metal thin film layer. A magnetic tape Ai equipped with

Works B and C were found to have good running performance as determined by the measurement of the coefficient of dynamic friction μ, and improved still characteristics, that is, durability, as determined by still measurements at low temperature and low humidity.

(Effects of the Invention) The magnetic recording medium of the present invention comprises a plastic film substrate, on which fine particles are used as cores and resin is used as a binder. mm” or more, a ferromagnetic metal thin film layer formed on the undercoat layer, and an average height of 1 to 1100 J and a density of io on the surface of the ferromagnetic metal thin film layer.
-' to 2×10−”/l1l12 spherical protrusions, and can greatly improve running performance, that is, head touch, and durability, that is, still life.

[Brief explanation of the drawing]

FIG. 1 shows a magnetic recording medium according to an embodiment of the present invention at a magnification of 3.
2 is a cross-sectional view taken along line A-A' in FIG. 1, and FIG. 3 is a magnetic recording of another embodiment according to the present invention. Magnify the medium to 100
A plan view based on observation with a differential interference optical microscope.
Fig. 4 is a cross-sectional view taken along the line BB' in Fig. 3, Fig. 5 is a conceptual diagram showing a method for forming a spherical protrusion, and Fig. 6 is an enlarged view of the main part of Fig. 5. It is. DESCRIPTION OF SYMBOLS 1...Plastic film, 2...Carbon fine particles, 3...Binding resin, 4...Ferromagnetic metal thin film layer, 5...Lubricant, 6...Spherical protrusion. Patent Applicant Matsushita Electric Industrial Co., Ltd. Figure 1 A' Figure 2 1 2 people Keckfube L 2゛・Carbon 1 particle 3 3゛ Binding resin 4・Onikame Kin, & Bookmark 5 Condition 6 Spherical Toto Figure 3 Figure 5 Figure 6 Diamond surface transfer roller hina roller stone k) to record the image (

Claims (1)

[Claims] A plastic film substrate, and 1000 particulate protrusions/mm^2 with a particle height of 30 to 500 Å using fine particles as cores and resin as a binder on the plastic film substrate.
An undercoat layer having the above, a ferromagnetic metal thin film layer formed on the undercoat layer, and a ferromagnetic metal thin film layer having an average height of 1 to 100 μm and a density of 10^-^4 to 2x10 on the surface of the ferromagnetic metal thin film layer.
A magnetic recording medium characterized by having 2 spherical protrusions/mm^2.