JPH0328732B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks. Structures of conventional examples and their problems A thin film of iron, cobalt, nickel, or an alloy containing these as main components, or a thin film of their oxides is formed into a polyester film using vacuum film forming methods such as vacuum evaporation, sputtering, and ion plating. , polymer films such as polyimide films,
Ferromagnetic thin-film magnetic recording media formed on substrates made of non-magnetic thin metal plates can dramatically improve recording density compared to conventional coating-type magnetic recording media. To achieve this, it is necessary to reduce the gap of the magnetic head and to smooth the surface of the magnetic recording medium to reduce spacing loss as much as possible. However, if the surface is made too flat, it will cause problems in head touch and runnability, so it is necessary to solve this problem by controlling the fine shape of the surface. The surface properties of ferromagnetic thin film magnetic recording media are such that the magnetic layer thickness is 0.01 to 0.5μ.
Since it is very small, about m, it is highly dependent on the surface shape of the plastic film that is the substrate. Therefore, many proposals have been made regarding the surface properties of films. An example is JP-A-52
-18770 Publication, JP-A-52-84264, JP-A-Sho
54-40883, JP 53-116115, JP 53-128685, JP 54-94574,
It is described in JP-A-56-10455, JP-A-56-16937, etc. In all of these examples, the surface shape is roughened relatively finely and uniformly, for example, by forming wrinkle-like protrusions, earthworm-like protrusions, or granular protrusions, thereby improving head touch and running properties at once. This is an attempt to improve. The surface condition seen in the above example can be obtained by touching the head at normal temperature and humidity.
It is very effective in terms of head running properties. However, it has the disadvantage that the cylinder part of the rotating head tends to generate noise in high humidity conditions such as 30°C and 80-90% R.H. One way to solve this problem is to use a polyester film as a substrate, and when forming a ferromagnetic layer in vacuum, the polyester oligomer contained therein is precipitated as fine crystals on the substrate surface, and then the ferromagnetic layer is deposited on the substrate surface. The present inventors have already made a proposal to form a metal thin film layer, but in this case, the frequency of precipitation of oligomer crystals is highly dependent on location, and it is difficult to evenly distribute and precipitate oligomer crystals over the entire surface. It is difficult to control the population, and distribution tends to be uneven depending on location. Therefore, there was a drawback that the envelope characteristics of the resulting magnetic recording medium were likely to be disturbed. In addition, a film in which a ferromagnetic thin film is formed on a polyester film with protruding thermoplastic particles on the surface as described in JP-A No. 53-107314 has good running properties and good image quality at room temperature and humidity. It has been known. 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 will occur and the running performance will deteriorate. OBJECTS OF THE INVENTION It is an object of the present invention to provide a metal thin film magnetic recording medium that improves noise in high humidity environments, improves reproduced image quality, and is suitable for high-density recording. Structure of the Invention The magnetic recording medium of the present invention has a particulate projection formed on a plastic film substrate surface with a height of 30 to 500 Å with silica fine particles as a core and a resin as a binder, and the spread of the particulate projection is 1 to 20 times the height. 1000 granular protrusions
The present invention is characterized in that an undercoat layer having a magnetic flux per square meter/mm ² or more is provided, a ferromagnetic metal thin film is formed on the undercoat layer, and a lubricant is further present in an amount of 0.5 to 500 mg/m ² on the metal thin film. DESCRIPTION OF EMBODIMENTS Figures 1 and 2 show cross sections of embodiments of the magnetic recording medium of the present invention, in which 1 and 11 are plastic film substrates, 2 and 12 are fine particle cores made of silica, and 3 and 13 are plastic film substrates. 4, 14 are ferromagnetic metal thin films;
5 is a lubricant. In these figures, the combination of fine particle core 2 and binding resin 3 and the combination of fine particle core 12 and binding resin 13 are the undercoat layer. In FIG. 1, the lubricant 5 is present on the entire surface of the ferromagnetic metal thin film 4, but in FIG. The height of the particulate protrusions was measured using a high-precision stylus-type surface roughness measuring device (TALYSTEP-1, TAYLOR-
(manufactured by HOBSON), and is measured by JIS
Maximum surface roughness specified in BO601, Rmax
If the distance is expressed as the distance from the top of the uneven mountain to the bottom of the valley according to
Å, more preferably 50 to 300 Å. If it is less than 30 Å, it is difficult to obtain the effect of preventing squealing in high humidity, and if it is more than 500 Å, the envelope is likely to be disturbed. The planar spread of the particulate projections is suitably 1 to 20 times, more preferably 2 to 10 times, their height. If it is 20 times or more, the anti-squeal effect in high humidity will be reduced. The density of particulate protrusions is 1000 per ^mm2 of surface.
A value of 1,000 or more, more preferably 2,500 or more is appropriate, and a number of 1,000 or less reduces the squeal prevention effect in high humidity. This density can be determined by observing a minimum of 10 fields of view using a differential interference light microscope with a magnification of 400 or by observing a minimum of 10 fields of view with a scanning electron microscope at a magnification of 3000. It is calculated and converted to ^1mm2 . Examples of plastic films include polyester films made of polyethylene terephthalate or its copolymers or mixtures, polyethylene naphthalate or its copolymers or mixtures, etc., polyimide films such as polyesterimide or polyimide, aromatic polyamide films, etc. For example, a polyester film with particularly excellent surface smoothness contains almost no microprotrusions made of polymerization catalyst residue, or has a smooth surface with a microprotrusion size of several hundred angstroms or less. Suitable materials include those having good quality, those having uniform fine protrusions such as the aforementioned wrinkles, earthworms, and grains formed on the surface and having a surface roughness of several hundred angstroms or less. As a method for forming an undercoat layer having particle-like protrusions on these films, for example,
20~10~10000 ppm of silica fine particles dispersed in a silica colloid solution containing 20~10~10000 ppm of resin as a binder.
There is a method of dissolving 10,000 ppm and then coating it on a plastic film and drying it. The fine silica particles used in the present invention include, for example, fine powder silica obtained by a dry method from silicon tetrachloride (e.g. Aerosil: Nippon Aerosil Co., Ltd.), fine powder obtained by decomposing sodium silicate with acid or alkali. There are silica (e.g. Syloid: Fuji Davison Chemical Co., Ltd.), silica sol obtained by ion exchange of sodium silicate (e.g. Snowtex: Nissan Chemical Co., Ltd.), etc., and these can be mixed with water, alcohol, ketone, It is used by dispersing it in a solution mainly consisting 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, nylon 610,
Polyamides such as nylon 11 and nylon 12, polystyrene, polycarbonate, polyarylate,
Various resins such as polysulfone, polyethersulfone, polyacrylate, polyvinyl chloride, polyvinyl butyral, polyphenylene oxide, and phenoxy resin, copolymers, or mixtures thereof can be used, and epoxy resins and urethane resins can be used. Crosslinkable resins such as resins, silicone resins, phenolic resins, melamine resins, or modified resins thereof can also be used. Examples of ferromagnetic metal thin films include Co, Ni, and
Metal thin films mainly composed of Fe, etc., metal thin films mainly composed of alloys thereof (e.g. Co-Cr perpendicular magnetization film)
However, for the purpose of improving the adhesion strength with the plastic film or 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. It is desirable to use a ferromagnetic metal thin film containing. 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. In addition, if necessary, prior to forming a ferromagnetic metal thin film, a thin film with a mechanical reinforcing effect,
For example, oxygen-containing metal thin films such as Ti, Cr, Ni, etc.
It is also possible to form a thin film of oxides such as Al ₂ O ₃ and SiO ₂ . The combination of the above-mentioned ferromagnetic metal thin film containing oxygen, or the above-mentioned non-magnetic metal layer formed thereunder as required, and the underlayer having particle-like protrusions allows for a long still life. It is possible to improve the width. 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 it is Å or more. By allowing a lubricant to exist on the surface of the ferromagnetic metal thin film layer, 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. The lubricant on the ferromagnetic metal thin film may be present on the entire surface as shown in FIG. 1, or may be present locally as shown in FIG. As a means of doing so,
In addition to coating or vapor-depositing directly on the surface of a ferromagnetic metal thin film, there is also a method of coating or vapor-depositing on the back side of a magnetic recording medium and stacking (winding) the magnetic recording medium.
Sometimes, a method of transferring it to the surface of a ferromagnetic metal thin film is also possible. It is also possible to use a resin binder or the like to firmly fix the lubricant. As the lubricant, fatty acids, fatty acid esters, fatty acid amides, metal soaps, aliphatic alcohols, paraffins, silicones, fluorine surfactants, inorganic lubricants, etc. can be used. The amount of lubricant present is 0.5 to 500 mg ^per square meter of surface, more preferably 5 to 500 mg.
200mg is appropriate. Fatty acids include lauric acid, myristic acid,
Those having 12 or more carbon atoms such as palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, and linolenic acid can be used. Fatty acid esters include ethyl stearate, butyl stearate, amyl stearate,
Stearic acid monoglyceride, palmitic acid monoglyceride, oleic acid monoglyceride, pentaerythritortetrastearate, 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 bis stearic acid amide, etc. Can be used. Metal soaps include zinc, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, etc.
Salts with lead, nickel, cobalt, iron, aluminum, magnesium, strontium, copper, etc., salts with sulfonic acids such as lauryl, palmityl, myristyl, stearylbehenyl, oleyl, linole, linolenic, etc. and the various metals listed above can be used. . As the aliphatic alcohol, cetyl alcohol, stearyl alcohol, etc. can be used. As paraffin, n-octadecane, n-
nonadecane, n-tridecane, n-docosane, n
- Saturated hydrocarbons such as dotriacontane can be used. As the silicone, polysilotesanes 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 salts of perfluoroalkyl carboxylic acids and perfluoroalkyl sulfonic acids with sodium, potassium, magnesium, zinc, aluminum, iron, cobalt, nickel, etc., perfluoroalkyl phosphate esters, and perfluoroalkyl phosphates. Alkyl betaine, perfluoroalkyltrimethylammonium salt, perfluoroethylene oxide, perfluoroalkyl fatty acid ester, etc. can be used. Examples of the inorganic lubricant include graphite powder, molybdenum disulfide powder, tungsten dioxide powder, molybdenum selenide powder, tungsten selenide powder, calcium fluoride powder, and the like. Rust is prevented by known means on the front surface, the back surface, or the vicinity thereof of the magnetic recording medium of the present invention, the air gap in the ferromagnetic metal thin film, the interface between the ferromagnetic metal thin film and the plastic film substrate, the inside of the plastic film substrate, etc. Various additives such as antistatic agents, antistatic agents, and antifungal agents can be added as necessary. Example 1 On a smooth polyethylene terephthalate biaxially stretched film that has significantly suppressed protrusions caused by polymerization catalyst residue and has a surface roughness of 30 Å or less, the following composition solution was continuously coated and dried to a thickness of about 10 μm. A long film sample was obtained on the surface of which was formed an undercoat layer having about 5 million particulate protrusions with a height of about 100 Å ^each consisting of silica particles as cores. This sample is designated as A. Liquid composition Snowtex-O...2 phr (Nissan Chemical Industries, Ltd.) Methanol...200 phr Ethyl acetate...800 phr Polyester...0.3 phr (Vylon #200 Toyobo Co., Ltd.) Example 2 The liquid in Example 1 By changing the composition to the following, a height of approximately 80 mm with silica fine particles as the core.
A long film sample was obtained on which an undercoat layer was formed having about 1,000,000 particulate protrusions/ ^mm2 . This sample is designated as B. Liquid composition Syloid#255...0.05 phr (manufactured by Fuji Davison Chemical Co., Ltd.) Methylene chloride...600 phr Toluene...100 phr Methyl ethyl ketone...300 phr Polyether sulfone...0.2 phr (PES200p made by ICI Japan Co., Ltd.) Example 3 By changing the liquid composition in Example 1 to the following, the height of the silica fine particles as a core was approximately
A long film sample was obtained on which an undercoat layer was formed having approximately 200,000 particulate protrusions/mm ² with a diameter of 200 Å. This sample is designated as C. Liquid composition Methanol silica sol...0.1phr (manufactured by Nissan Chemical Industries, Ltd.) Methanol...200phr Ethyl acetate...1000phr Toluene...100phr Polyester...0.5phr (Byron #200 manufactured by Toyobo Co., Ltd.) Example 4 Implementation By changing the liquid composition in Example 1 to the following, the height of the silica fine particles as a core is approximately
A long film sample was obtained in which an undercoat layer was formed having approximately 500,000 particulate projections/mm ² of 250 Å. This sample is designated as D. Liquid composition Aerosil #972...0.1phr Acetone...500phr Ethyl acetate...400phr Toluene...100phr Phenoxy resin...0.3phr (manufactured by Tomoe Kogyo Co., Ltd.) Example 5 Contains almost no particulates due to polymerization catalyst residue A thin layer of different polymers consisting of fine wavy irregularities with a surface roughness of 100 Å is formed by applying and curing a liquid mainly consisting of a modified silicone emulsion containing a thickener to the surface during film formation and stretching. Samples K, L, M, and N were obtained by applying the same coating treatment as in Examples 1 to 4 to form an underlayer on the biaxially stretched polyester film. The particulate protrusions formed on the surfaces of these samples were in almost the same state as those of the corresponding samples A to D, respectively. Comparative Example 1 The plastic films used in Examples 1 to 4 and Example 5 were used as samples S, T, and
shall be. A CoNi ferromagnetic metal thin film (Ni = 20 wt%, film thickness 1000 Å) was formed on each surface in the presence of a trace amount of oxygen by continuous vacuum oblique evaporation method in which each of the above samples A to T was sequentially connected. The oxygen content of the magnetic layer was 5% in terms of atomic ratio to the metal. After that, apply various lubricant solutions to the surface of each sample and slit them into a predetermined width to make magnetic tape.
Using a prototype video recorder under these conditions, we measured the squealing state of the rotating head cylinder, the envelope, and the still life. As a comparative example, Sample T was heat-treated before vapor deposition to precipitate polyester oligomer crystals on the surface, and then vapor-deposited in the same manner as described above. 100,000 pieces/mm ² ) was coated with a lubricant solution and made into a magnetic tape, and a specific sample from A to T above was made into a magnetic tape without applying a lubricant solution after vapor deposition. The above measurements were also carried out on the sample. These results are shown in the table below.

[Table] In the previous table, Nos. 1 to 4 refer to Examples 1 to 4 described above.
This is a case using a smooth polyester film having various particulate resin protrusions shown in Nos. 5 to 8.
Similarly, the various particulate protrusions shown in Examples 1 to 4 described above are formed on a polyester film having fine wavy irregularities as shown in Example 5. Although they are composite types with steep grain-like protrusions, all of them achieve the effects of the present invention, namely, no squealing at high temperatures, a good envelope, and a still life of 30 minutes or more. On the other hand, when using a film that does not have granular protrusions and is smooth or has only wavy irregularities, noise occurs as shown in Comparative Examples (9) and (10), the envelope is poor, and the still life is 10%. Short, less than a minute. When oligomers were precipitated on the surface of wavy irregularities and used as granular protrusions, squealing occurred as in Comparative Example (11), and the envelope was also poor. This is due to the fact that the oligomer precipitation frequency is highly dependent; that is, depending on the location, the density may vary depending on the location.
This is due to the fact that it is less than mm ² . Furthermore, in the case where no lubricant is present, squealing occurs as in Comparative Examples (12) and (13), the envelope tends to be poor, and the still life is short. Effects of the Invention As is clear from the above examples, the magnetic recording medium of the present invention does not generate squealing even in high humidity, has a good envelope, and exhibits stable running performance. Furthermore, the still life in high humidity conditions is good, and its practical value is extremely high.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a magnetic recording medium in one embodiment of the present invention, and FIG. 2 is a cross-sectional view of a magnetic recording medium in another embodiment of the present invention. 1, 11...Plastic film substrate, 2,
12... Nucleus of fine particles, 3,13... Resin, 4,1
4...Ferromagnetic thin film, 5,15...Lubricant.

Claims (1)

[Claims] 1. Particulate projections with a height of 80 to 250 Å and a spread of 1 to 20 times the height, with silica fine particles as the core and resin as the binder, are spread over the entire surface that is to become the magnetic surface.
1. A magnetic recording medium characterized in that a ferromagnetic metal thin film with a thickness of 400 Å or more is formed on a plastic film substrate provided with an undercoat layer having a density of 10,000 particles/mm ² or more, and a lubricant is present on the ferromagnetic metal thin film.