JP2566134B2 - Magnetic recording media - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, particularly to a metal thin film type magnetic recording medium.

2. Description of the Related Art Prior Art and Problems There are active developments of magnetic recording media for video, audio, etc., which have a metal thin film type magnetic layer because of their compactness when formed into a tape and wound.

As a magnetic layer of such a metal thin film type medium, characteristically, vapor deposition is performed by a so-called oblique vapor deposition method in which vapor deposition is performed at a predetermined inclination angle with respect to the normal to the substrate, and vapor deposition of Co-based, Co-Ni-based, etc. Membranes are preferred.

However, such a magnetic layer has a large running friction, a low film strength, and a poor head touch. In particular, the running durability is low, and the output decreases due to repeated running.

On the other hand, a video medium has a short durability time in a still image mode called still.

 Furthermore, there are many so-called dropouts.

From such actual conditions, various top coat films for obliquely deposited magnetic film layers have been conventionally proposed.

A hydrocarbon-based plasma polymerized film is known as an example of the top coat film (Japanese Patent Laid-Open No. 59-72653).
59-154641, 59-160828, etc.).

However, the hydrocarbon-based plasma-polymerized film top coat obtained by the usual method is insufficient in terms of corrosion resistance,
Further, there are inconveniences such as poor running durability and reduced reproduction output, or insufficient strength.

Further, in order to improve durability and electromagnetic conversion characteristics, various proposals have been made that a ferromagnetic metal thin film layer has a multilayer structure of two or more layers (Japanese Patent Laid-Open Nos. 54-141608 and 56). −26
892, JP-A-57-130228, etc.).

However, at present, a technology that has good running properties, durability, and strength of a ferromagnetic thin film and does not cause any inconvenience in terms of electromagnetic conversion characteristics has not yet been realized.

II OBJECT OF THE INVENTION It is an object of the present invention to eliminate such inconveniences, to provide a metal thin film type magnetic recording medium having good corrosion resistance and durability and good electromagnetic conversion characteristics.

III Disclosure of the Invention Such an object is achieved by the present invention described below.

That is, the present invention is a plastic film substrate
It has a ferromagnetic metal thin film layer containing Co as a main component, and this ferromagnetic metal thin film layer has a multi-layer structure composed of two or more layers. The minimum incident angle of the adhering substance is 50 ° or less when the lowermost layer is formed on the substrate side,
20 ° to 90 ° when the uppermost layer is on the side opposite to the substrate, and is the value obtained by dividing the oxygen concentration C ₂ near the substrate-side interface of the lowermost layer by the oxygen concentration C ₁ near the surface on the opposite side of the uppermost substrate. Is 0.3 or less, the oxygen concentration C ₃ in the vicinity of the interface with the uppermost layer of the layer adjacent to the uppermost layer divided by the oxygen concentration C ₁ in the vicinity of the surface of the uppermost layer opposite to the substrate C ₃ / C ₁ Is 0.2 to 0.92, C ₁ is 0.2 to 0.7, and the average oxygen concentration of the top layer and all layers is 0.1 to 0.5, respectively.
The magnetic recording medium has a plasma polymerized film between the lowermost layer of the ferromagnetic metal thin film layer and the substrate, between the layers, or on the surface of the uppermost layer opposite to the substrate.

IV Specific Structure of the Invention Hereinafter, the specific structure of the present invention will be described in detail.
1 and 2 show an embodiment of the magnetic recording medium of the present invention.

The magnetic recording medium 1 of the present invention comprises a lower layer crystal grain 6 on a substrate 2.
A ferromagnetic metal thin film lower layer portion 3 and an upper layer crystal grain 7 having a ferromagnetic metal thin film upper layer portion 4 between the lower layer portion 3 and the upper layer portion 4 of the ferromagnetic metal thin film, and the lower layer portion 3 and the base body 2. Or a surface of the upper layer 4 opposite to the substrate 2 has a plasma polymerized film (in the illustrated example, the plasma polymerized film 5 is provided between the lower layer 3 and the upper layer 4 of the ferromagnetic metal thin film). Layered).

The ferromagnetic metal thin film layer as the magnetic layer in the present invention has a multi-layer structure including at least two layers. The ferromagnetic metal thin film layer used in the present invention has a composition containing Co as a main component, containing O, and optionally containing Ni and / or Cr.

That is, in a preferred embodiment, it may consist of Co alone or Co and Ni. When Ni is contained, the weight ratio Co / Ni is preferably 1.5 or more.

Further, Cr may be contained in the ferromagnetic metal thin film layer.

In such a case, the weight ratio of Cr / Co or Cr / (Co + Ni) is 0.1 or less, particularly 0.001 to 0.1, more preferably 0.005.
It is preferably ˜0.05.

Further, the ferromagnetic metal thin film of the present invention contains O.

The average oxygen content of the whole layer in the ferromagnetic metal thin film and the average oxygen content C ₁ ^* in the uppermost layer are atomic ratios, especially O / (Co or
The atomic ratio of Co + Ni is 0.1 to 0.5, preferably 0.
It is about 1 to 0.4.

If the average oxygen content C ₁ ^* is less than 0.1, it is insufficient in terms of corrosion resistance, running property, cracks in the magnetic layer, scratches, etc., and if it exceeds 0.5, the surface oxide layer increases and the spacing with the head causes This causes problems such as a decrease in output.

The oxygen concentration C _{2 in the} vicinity of the interface with the lowermost plastic film, in particular O / (Co or Co + Ni) atomic ratio, is the oxygen concentration C ₁ in the vicinity of the surface opposite to the uppermost plastic film, especially O / ( Co or Co + Ni) value divided by atomic ratio C ₂
/ C ₁ is 0.3 or less, more preferably 0.15 or less.

In this case, these oxygen concentrations can be measured by performing Auger spectroscopic analysis, SIMS (secondary ion mass spectrometry), etc. while the Ar layer ion-mills or ion-etches the ferromagnetic metal thin film.

That is, while performing ion etching, O, Co,
Ni, etc. are counted and the profiles in the film thickness direction are compared.

The O / (Co or Co + Ni) on the surface of the ferromagnetic metal thin film opposite to the plastic film is C ₁ . As for the bottom layer, the plastic film is etched and the O / (Co or Co
Let + Ni) be C ₂ .

Ion etching and Auger spectroscopy or SIMS
The measuring method of may be in accordance with a conventional method.

In this way, by increasing the oxygen concentration on the surface of the uppermost layer relatively, the coercive force Hc is increased, and by decreasing the oxygen concentration of the lowermost layer, the maximum residual magnetic flux φ _r and the squareness ratio S _Q are increased. Is high, and the magnetic layer has excellent electromagnetic conversion characteristics.

Further, in the ferromagnetic metal thin film layer as the magnetic layer of the present invention, the oxygen concentration C _{3 in the} vicinity of the interface between the uppermost layer and the adjacent uppermost layer, particularly the O / (Co or Co + Ni) atomic ratio, is the plastic of the uppermost layer. Oxygen concentration C ₁ near the surface opposite the film,
In particular, the value C ₃ / C ₁ divided by the O / (Co or Co + Ni) atomic ratio is 0.2
~ 0.92.

In this case, O / (Co or Co + Ni) C _{1 on the} surface of the ferromagnetic metal thin film opposite to the plastic film can be measured in the same manner as described above. Further, the oxygen concentration C ₃ in the vicinity of the interface between the uppermost layer and the layer adjacent to the uppermost layer is O / (Co or Co or
Calculate Co + Ni) and call this C ₃ . However, in each layer, the oxygen concentration becomes maximum on the surface opposite to the film substrate under normal film forming conditions. Therefore, normally, when O is counted while performing ion etching, the maximum value in the film may be set to C ₃ .

By relatively increasing the oxygen concentration C ₁ on the surface of the uppermost layer in this way, the coercive force H _C is increased, and in the portion below the surface of the uppermost layer to the vicinity of the layer adjacent to the uppermost layer. By setting the oxygen concentration to be relatively lower than the above C ₁ , the maximum residual magnetic flux φr and the squareness ratio S _Q are increased, and a magnetic layer having extremely good electromagnetic conversion characteristics is obtained. Therefore, a signal with a comparatively shallow magnetic field having a center frequency of about 5 MHz is effectively held in the uppermost layer.

Further, the oxygen concentration C ₃ in the vicinity of the interface between the uppermost layer adjacent to the uppermost layer, the relationship between the C ₁ is is C ₃ / C _1, as described above
By setting it to 0.2 to 0.92, the coercive force Hc in this portion becomes high, and the oxygen concentration in the portion below the interface with the uppermost layer of the layer adjacent to the uppermost layer is relatively lower than the above C _3. By doing so, the maximum residual magnetic flux φr and the squareness ratio S _Q are increased, and a magnetic layer having extremely good electromagnetic conversion characteristics is obtained.
Therefore, a signal with a comparatively deep magnetic field having a center frequency of about 0.7 MHz is effectively retained in the layers adjacent to the uppermost layer.

And, as described above, the relationship between C ₁ and C ₃ is C ₃ / C ₁ is
When it is 0.2 to 0.92, it becomes an excellent magnetic layer having the best balance of electromagnetic conversion characteristics and corrosion resistance of the magnetic layer.

The O / (Co or Co + Ni) C ₁ near the surface is 0.2-
It is 0.7, preferably 0.3 to 0.6.

Therefore, O / (Co or Co + near the film interface
Ni) C ₂ is preferably 0.06 to 0.21, more preferably 0.09 to 0.21.
It is 0.18.

Further, the O / (Co or Co + Ni) C _{3 in the} vicinity of the uppermost layer of the layer adjacent to the uppermost layer is preferably 0.07 to 0.6, more preferably
It is 0.1 to 0.5.

In addition, O / (Co or Co + Ni) C _{1 in the} entire top layer
^* Is 0.1 to 0.5, preferably 0.1 to 0.4. The O / (Co or Co + Ni) C ₂ ^* in the entire bottom layer is preferably 0.5 or less, more preferably 0.3 or less.

In addition, O / (Co or Co + in the entire layer adjacent to the uppermost layer
Ni) is preferably 0.5 or less, more preferably 0.3 or less.

At this time, electromagnetic conversion characteristics, corrosion resistance, running durability, magnetic film strength, etc. are extremely good.

In this case, in the case of a multi-layer structure of three or more layers, the O / (Co or Co + Ni) in each layer is generally 0.1 to
It is set to 0.5, preferably 0.1 to 0.3.

In this case, oxygen forms an oxide with the ferromagnetic metal (Co, Ni) on the surface of each layer of the ferromagnetic metal thin film layer.

That is, a peak showing an oxide is recognized by Auger spectroscopic analysis in the thickness range of 100Å to 2000Å, more preferably 500 to 1000Å from the surface of each layer.

In the present invention, the oxygen concentration between the ferromagnetic metal thin film layer surface and the film side interface is regulated, and the oxygen concentration between the ferromagnetic metal thin film layer surface and the uppermost layer adjacent to the uppermost layer is controlled. This is a restriction, and at that time, a predetermined effect of the present invention is realized.

Therefore, regarding the oxygen concentration profile in the film thickness direction of the ferromagnetic metal thin film, there is usually a peak of oxygen distribution at least at the interface between the uppermost layer and the layer adjacent to the lowermost layer.

In addition, normally, the ferromagnetic metal thin film may have two layers,
If necessary, the number of layers may be 3 or more, and particularly 3 to 5 layers.

Incidentally, in such a ferromagnetic metal thin film, further other trace components, especially transition elements such as Fe, Mn, V, Zr, Nb, Ta, Ti,
Zn, Mo, W, Cu, etc. may be contained.

In a preferred embodiment, such a ferromagnetic metal thin film layer is composed of an aggregate of columnar crystal grains containing Co as the main component.

In this case, the total thickness of the ferromagnetic metal thin film layer is 0.05 to
The thickness is 0.5 μm, preferably 0.07 to 0.3 μm.

The thickness ratio of each layer of the ferromagnetic metal thin film layer is not particularly limited, but in the case of a two-layer structure, for example, the thickness ratio of the upper layer and the lower layer is preferably about 0.1 to 10, more preferably 0.2 to 0.9, more preferably 0.4 to 0.9 is preferable.

And, the columnar crystal grains have a length extending over almost the entire area in various thickness directions, and in the longitudinal direction, the minimum angle with respect to the normal line of the main surface of the substrate is 20 to 90 ° in the uppermost layer, and more preferably. Is preferably in the range of 20 to 50 °, the lowermost layer is inclined at 50 ° or less, and more preferably in the range of 0 to 40 °.

In this case, in each of the intermediate layers in the structure of three or more layers, the tilt angle of the columnar crystal grains with respect to the normal to the main surface of the substrate is usually within the tilt angle range between the uppermost layer and the lowermost layer, and there is no particular limitation. .

In this case, the directions of inclination of the crystal grains of the magnetic layers adjacent to each other with respect to the normal to the main surface of the substrate may be the same in the longitudinal direction of the medium, but are preferably opposite to each other. preferable.

Such a crystal grain inclination direction is shown in FIG. 1 and FIG.
It will be schematically described with reference to the drawings.

In FIGS. 1 and 2, a magnetic recording medium 1 has a ferromagnetic metal thin film lower layer portion 3 and a ferromagnetic metal thin film upper layer portion 4 on a substrate 2. Then, the ferromagnetic metal thin film lower layer portion 3
The inclination direction of the lower crystal grains 6 in the inside and the inclination direction of the upper crystal grains 7 in the ferromagnetic metal thin film upper portion 4 are opposite to each other in the longitudinal direction a of the medium in FIG. In the figure, the length direction a of the medium is the same direction.

In the present invention, the crystal grain gradient shown in FIG. 1 or 2 may be used, but the crystal grain gradient shown in FIG. 1 is preferable.

It should be noted that oxygen is present in the form of a compound on the surface of the columnar crystal grains in the surface portion as described above.

There is no particular limitation on the oxygen concentration gradient of the ferromagnetic metal thin film layer.

Further, the minor axis of the crystal grains preferably has a length of about 50 to 500Å.

As described above, by forming the ferromagnetic metal thin film layer in a multi-layered structure, the length of the columnar crystal grains becomes small, so that the strong strength of the ferromagnetic metal thin film layer is improved.

In addition, the uppermost columnar crystal grains are 20 to 20
For example, the center frequency having a relatively shallow magnetic field because it has a slope of 90 °, and especially has a slope of 50 ° or more.
A signal of about 5 MHz can be effectively held in the uppermost layer.

Further, since the columnar crystal grains in the lowermost layer have an inclination of 50 ° or less with respect to the normal to the main surface of the substrate and stand upright with respect to the substrate, for example, a central frequency of a relatively deep magnetic field of 0.
A signal of about 75 MHz can be effectively held in the lower layer region of the lowermost grain.

Further, as described above, by increasing the oxygen concentration in the uppermost layer, oxides such as Co and Ni having excellent wear resistance are formed in the uppermost layer. The film strength of the magnetic metal thin film layer becomes higher.

The material of the substrate used in the magnetic recording medium of the present invention is not particularly limited as long as it is a non-magnetic plastic, but usually polyethylene terephthalate, polyethylene 2,6
-Polyester such as naphthalate, polyamide, polyimide, polyphenylene sulfide, polysulfone,
Wholly aromatic polyester, polyetheretherketone,
Polyether sulfone, polyether imide, etc. are used.

The thickness of the substrate is not particularly limited, but is preferably 8 μm or less, and particularly preferably about 5 to 7 μm.

If the thickness exceeds 8 μm, the objectives of downsizing the medium, recording for a long time, etc. cannot be achieved. On the other hand, if the thickness is too thin, the effect of the multilayer structure of the magnetic layer as described above to improve the film strength is offset, and problems such as runnability, output reduction, and head wear occur.

Then, the effect of improving the electromagnetic conversion characteristics by the multilayer structure of the ferromagnetic metal thin film layer of the present invention is more remarkable when the substrate is made thin.

For example, taking a two-layer structure as an example, when the thickness of the substrate is 10 μm, the improvement of electromagnetic conversion characteristics by changing the ferromagnetic metal thin film layer from the conventional single-layer structure to the two-layer structure of the present invention is as follows.
About +6 (dB) in the low frequency range of 0.75MHz, 5MHz
Although the signal in the high frequency region of is about +6 (dB), the improvement width when the thickness of the substrate is 7 μm is about +6 (dB) for the signal in the low frequency region of 0.75 MHz and when the substrate thickness is 10 μm. Equivalent, but +7.5 (dB) for signals in the high-frequency region of 5 MHz
Increase to a degree.

In this way, the improvement in the electromagnetic conversion characteristics of the 7 μm substrate is remarkable when compared with the 10 μm thick substrate.
When the thickness is changed from 7 μm to 7 μm, the head touch abruptly deteriorates due to the lack of rigidity of the substrate, and this effect is greater in a high frequency region such as 5 MHz, and in such a case, the effect of the present invention is exhibited.

In the present invention, the magnetic layer is preferably formed by a so-called oblique vapor deposition method.

In this case, the minimum incident angle of the vapor deposition material with respect to the normal to the substrate is 50 ° or less when the lowermost layer is formed, 20 ° to 90 ° when the uppermost layer is formed, and the intermediate angle in the case of a structure having three or more layers. It is preferable to set the angle to 20 ° to 50 ° when the layer positioned at is placed.

If the minimum incident angle deviates from the above-mentioned incident angle, the electromagnetic conversion characteristics deteriorate.

Further, the magnetic layer may be formed by continuously forming two or more layers in one step, but it is usually preferable that the magnetic layers are formed by flowing into the vapor deposition step for each stratum corneum.

In this way, by dividing the layers of the magnetic layer into layers, the directions of the inclinations of the magnetic columnar crystal grains with respect to the normal to the substrate are opposed to each other in the lengthwise direction of the medium as described above. It will be facing.

With such a magnetic layer structure, the electromagnetic conversion characteristics become extremely good.

The vapor deposition atmosphere is usually an atmosphere containing oxygen gas in an inert atmosphere such as argon, helium, or vacuum.
And ^-5 to 10 ⁰ Pa pressure of about, also deposition distance, the substrate transport direction, the structure of the can and the mask, arrangement and the like may be the same as known conditions.

Then, a metal oxide film is formed on the surface by vapor deposition in an oxygen atmosphere. The oxygen gas partial pressure at which the metal oxide is formed can be easily obtained from experiments.

Various oxidation treatments are possible to form a metal oxide film on the surface.

The following oxidation treatments can be applied.

1) Dry treatment a. Energetic particle treatment As described in Japanese Patent Application No. 58-76640, oxygen is energized to the magnetic layer as energetic particles by an ion gun or a neutral gun in the latter stage of vapor deposition.

b. Glow treatment O ₂ , H ₂ O, O ₂ + H ₂ O etc. and an inert gas such as Ar, N ₂ are used,
Glow discharge is performed to generate plasma, and the surface of the magnetic film is exposed to this plasma.

c. Oxidizing gas A gas that blows an oxidizing gas such as ozone or heated steam.

d. Heat treatment A substance that is oxidized by heating. Heating temperature is 60-150
℃ degree.

2) Wet treatment a. Anodizing b. Alkali treatment, c. Acid treatment Chromate treatment, permanganate treatment, phosphate treatment, etc. are used.

d. Oxidant treatment H ₂ O ₂ or the like is used.

In the present invention, the plasma is formed between the lowermost layer of the ferromagnetic metal thin film layer and the substrate, between the respective layers of the ferromagnetic metal thin film layer, or on the surface of the uppermost layer of the ferromagnetic metal thin film layer opposite to the substrate. The polymerized film 5 (in the illustrated example, provided between the lower layer portion 3 and the upper layer portion 4 of the ferromagnetic metal thin film layer having a two-layer structure) is a thin film containing carbon and hydrogen.

As the raw material gas, methane, ethane, propane, butane, pentane, ethylene, propylene, butene, butadiene, acetylene, methylacetylene, and other saturated or unsaturated hydrocarbons that are gaseous at room temperature are usually used because they have good operability. One or more of the above are used, but if necessary, they may be formed by plasma polymerization using a hydrocarbon that is liquid at room temperature as a raw material.

One or more of these hydrocarbons may be H ₂ , O ₂ , O ₃ , H
₂ O, N ₂ , NO, N ₂ O, NO ₂ and other NO _X , NH ₃ , CO, CO _{2 and} other 1
It is also suitable to use a material gas containing one or more species as the raw material gas.

Further, if necessary, sources such as Si, B, P and S can be added to the raw material as trace components.

Plasma polymerized film 5 formed using such a raw material
The film thickness of each is 3 to 80Å.

If this film thickness exceeds 80Å, spacing loss and the like increase, which is not preferable.

 Further, if it is less than 3Å, the present invention becomes ineffective.

An ellipsometer or the like may be used to measure the film thickness.

The film thickness can be controlled by controlling the reaction time at the time of forming the plasma polymerized film, the flow rate of the raw material gas, and the like.

The plasma polymerized film 5 forms a polymerized film by bringing the above-mentioned discharge plasma of the source gas into contact with the object to be processed.

To summarize the principle of plasma polymerization, when a gas is kept at a low pressure and an electric field is applied, the free electrons present in the gas in a small amount have a much larger intermolecular distance than normal pressure, so they are subjected to electric field acceleration and 5 to 10 eV Kinetic energy (electron temperature)
To win.

When the accelerated electrons collide with atoms or molecules, they break up the atomic orbitals and molecular orbitals and dissociate them into species that are unstable in normal conditions, such as electrons, ions, and neutral radicals.

The dissociated electrons are again accelerated by the electric field to dissociate another atom or molecule, and the chain action immediately turns the gas into a highly ionized state. And this is called plasma gas.

Since gas molecules have few opportunities to collide with electrons, they do not absorb much energy and are kept at a temperature close to room temperature.

Thus, the kinetic energy of electrons (electron temperature)
A system in which the thermal motion (gas temperature) of molecules is separated is called low-temperature plasma, and here we are creating a situation in which chemical species such as polymerization can proceed while the chemical species remain relatively intact.
The present invention utilizes this situation to form the plasma polymerized film 5 directly on the ferromagnetic metal thin film lower layer portion 3, for example. Note that since low-temperature plasma is used, there is no thermal influence on the object to be processed.

An example of an apparatus for forming a plasma polymerized film on the surface of an object to be processed is shown in FIG. FIG. 3 shows a plasma polymerization apparatus using a frequency variable power source.

In FIG. 3, in the reaction container R, the processing gas from the processing gas source 21 or 22 is supplied to the mass flow controller 23, respectively.
And via 24. When supplying different gases from the gas sources 21 or 22, they are mixed and supplied in the mixer 25.

The processing gases can each have a flow rate range of 1 to 250 ml / min.

In the reaction container R, a magnetic layer incorporating an organic substance is provided on the substrate. For example, the object to be processed on the film is unrolled from the unrolling roll 31 and wound by the winding roll 30. During this period, polymerization of the organic substance incorporated in the magnetic layer is performed.

Further explaining the polymerization processing device 20 in detail, electrodes 27 and 57 facing each other with the object to be processed interposed are provided, and one electrode 27 is connected to a frequency variable power source 26,
The other electrode 57 is grounded at 28.

Further, in the reaction vessel R, a vacuum system for exhausting the inside of the vessel is provided, and this is a liquid nitrogen trap 11
1, including an oil rotary pump 112 and a vacuum controller 113. These vacuum systems maintain the inside of the reaction vessel within a vacuum range of 0.01 to 10 Torr.

In operation, the inside of the reaction vessel R is first evacuated until the pressure in the reaction vessel R becomes 10 ^-3 Torr or less, and then the processing gas is supplied in a mixed state into the vessel at a predetermined flow rate.

At this time, the vacuum in the reaction vessel is controlled within the range of 0.01 to 10 Torr.

When the flow rate of the raw material gas becomes stable, the power is turned on.
Thus, the plasma polymerized film is formed on the surface of the object to be processed.

Note that Ar, N ₂ , He, H ₂ , or the like may be used as the carrier gas.

Further, the applied current, the processing time, etc. may be set under normal conditions.

As the plasma generation source, any of microwave discharge, direct current discharge, alternating current discharge and the like can be used in addition to high frequency discharge.

Here, the condition of plasma polymerization is that the value of W / (FM) is
It is preferable to carry out under the condition of larger than 10 ⁷ (Joule / kg). However, W: Plasma power (Joule / sec), F:
The raw material gas flow rate, the unit of FM is kg / sec, and M is the raw material gas molecular weight.

When W / (F · M) is less than 10 ⁷ , the denseness of the plasma polymerized film becomes insufficient, and the effect of the present invention is not sufficiently exhibited.

The upper limit of W / (FM) is generally about 10 ¹⁵ Joule / kg.

The plasma polymerized film thus formed has a carbon content of
It is 30 to 100 at%, and particularly preferably 30 to 80 at%.

The atomic ratio of carbon to hydrogen (C / H ratio) is preferably 1 to 6.

The plasma polymerized film having such a C / H ratio has a remarkable effect of improving corrosion resistance and durability.

On the other hand, if the C / N ratio is less than 1, practical use cannot be endured in terms of corrosion resistance, durability, and strength, and if it exceeds 6, the output reduction after endurance running becomes extremely large, and practical use cannot be endured.

In such a case, the plasma polymerized film may contain N, O, Si, B, P, S and the like in the range of 20 at% or less.

The C / H ratio may be in accordance with SIMS (secondary ion mass spectrometry) or the like. When SIMS is used, the plasma polymerized film 5 of the present invention has a thickness of 3 to 80 Å.
It may be calculated by counting C and H.

Alternatively, while performing ion etching with Ar or the like, C
Alternatively, the profile of H and H may be measured and calculated.

Regarding the measurement of SIMS, Volume 3, Basic course on surface science (1984) Basics and applications of surface analysis (P70) “SIMS and LAM
MA ".

Further, in the magnetic recording medium 1 of the present invention, before forming such a plasma polymerized film, the surface of the substrate 2 on the magnetic layer forming surface side, the surface of the lower layer portion 3 or the upper layer portion 4 of the ferromagnetic metal thin film is previously prepared. It is preferable to perform plasma treatment.

By performing such a treatment, the adhesive strength on the treated surface is increased, and the durability as a medium is also improved.

The principle, method, formation conditions, etc. of the plasma treatment method are basically the same as those of the plasma polymerization method described above.

However, as a general rule, the plasma treatment uses an inorganic gas as a treatment gas, and as a general rule, an organic gas (which may be mixed with an inorganic gas) is used as a source gas for the formation of the plasma-polymerized film by the above-mentioned plasma polymerization method. Used as.

 The plasma processing gas is not particularly limited.

That is, H ₂ , Ar, He, O ₂ , N ₂ , air, NH ₃ , O ₃ , H ₂ O,
Any one selected from NO _x such as NO, N ₂ O and NO ₂ and selected from these alone or mixed may be used.

Further, the frequency of the plasma processing power source is not particularly limited, and may be any of direct current, alternating current, microwave, and the like.

By providing such plasma-polymerized films 71 and 75, the durability, wear resistance, weather resistance, corrosion resistance, etc. of the medium are significantly improved.

It is preferable that a back coat layer is provided on the other surface of the plastic film on which the magnetic layer is not provided, via a backing layer or directly.

The backing layer is preferably a single metal thin film of Al, Cu, W, Mo, Cr, Ti or the like, or an alloy of these metals, or a thin film of an oxide of these.

The thickness of the backing layer formed as needed is 0.05
~ 1.5 μm.

Further, a back coat layer is provided on the backing layer provided as needed.

The back coat layer contains a pigment and a binder of a radiation curable compound.

The pigment includes 1) conductive carbon black and graphite, and 2) inorganic fillers such as SiO ₂ , TiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ and Si.
C, CaO, CaCO ₃ , zinc oxide, goethite, αFe ₂ O ₃ , talc, kaolin, CaSO ₄ , boron nitride, fluorinated graphite, molybdenum disulfate, ZnS, etc., among which CaCO ₃ , kaolin,
ZnO, goethite, ZnS and carbon are used.

The amount of such an inorganic pigment to be used is appropriately 20 to 200 parts by weight with respect to 100 parts by weight of the binder in 1) and 10 to 300 parts by weight with respect to 2). There is a drawback that the membrane becomes brittle and the dropouts increase.

The average particle diameter of the pigment is about 0.01 to 0.3 μm, more preferably 0.02 to 0.1 μm.

The binder of the radiation-curable resin used in the above back coat layer is a vinyl chloride-vinyl acetate-vinyl alcohol copolymer (including those containing a carboxylic acid), or an acrylic-modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer. A compound (including a compound introduced with a carboxylic acid) and a urethane acrylate are preferred.

Regarding the radiation-curable resin, in addition to the above preferable combinations, acrylic double bonds such as acrylic acid, methacrylic acid or their ester compounds showing an unsaturated double bond having radical polymerizability, such as diallyl phthalate. Such as allylic double bonds, unsaturated bonds such as maleic acid and maleic acid derivatives,
It is possible to use a resin in which a group that is crosslinked or polymerized by irradiation with radiation is contained or introduced in the molecule of the thermoplastic resin.

Other usable binder components include acrylic acid, methacrylic acid and acrylamide as monomers.

As the binder having a double bond, various polyesters, polyols, polyurethanes and the like can be modified with a compound having an acrylic double bond. Further, if necessary, a polyhydric alcohol may be mixed with a polycarboxylic acid to obtain various molecular weights.

The above are some of the radiation sensitive resins,
These can also be mixed and used.

More preferred is (A) a plastic compound having a molecular weight of 5,000 to 100,000 having two or more unsaturated double bonds curable by radiation, and (B) one unsaturated double bond curable by radiation. It has one or more or does not have radiation curability. Molecular weight
(A) 20 to 70% by weight, (B) 20 and (C) a rubber-like compound having a molecular weight of 300 to 100,000, and (C) a compound having one or more unsaturated double bonds curable by radiation. ˜80% by weight, and (C) 10 to 40% by weight.

This increases the breaking strength of the coating film, strengthening the coating film, less backcoat abrasion, less transfer of the inorganic filler powder from the backcoat layer to the magnetic layer, and less dropout, and roll-shaped. It is possible to obtain a magnetic recording medium having uniform properties in the length direction, which is free from winding tightness when cured in a wound form.

In the production of the magnetic recording medium of the present invention, if the organic binder is a thermosetting type, the lubricant of the back coat layer is transferred to the back side of the magnetic thin film in the production process, causing the output to drop due to unstable running as described above. However, the image does not appear, or the friction level is still large and insufficient,
The backside transfer causes a phenomenon that the ferromagnetic thin film is removed or destroyed, which is not preferable.

Therefore, for example, it is considered that the top coat formed on the magnetic layer is performed first, but it is often inconvenient and inconvenient in operation.

Further, in the case of the thermosetting type, since the backside surface of the backcoat surface is transferred due to the winding tightness at the time of curing, the difference in the electromagnetic conversion characteristics between the inside and the outside of the jumbo roll during the thermal curing becomes a problem.

On the other hand, in the case of radiation curable resin, continuous curing is possible in manufacturing, the curing time is short, and there is no back mold transfer as described above, so dropout can be prevented, and radiation curing and topcoat treatment Since it can be processed online, it can help save energy, reduce the number of personnel during manufacturing, and reduce costs.

In terms of characteristics, in addition to the dropout due to winding tightness during thermosetting, there is no difference in output due to the distance in the length direction of the magnetic tape due to the difference in pressure at the inner and outer diameters when wound in a roll shape. .

The unsaturated double bond in the compounds (A), (B) and (C) has 2 or more, preferably 5 or more (A) per molecule.
Above, (B) is 1 or more, preferably 5 or more, (C) is 1 or more.
Or more, preferably 3 or more.

The plastic-like compound (A) used in the present invention contains two or more unsaturated double bonds in the molecular chain so that a radical is generated by radiation and a cross-linked structure is produced. It can also be obtained by subjecting a resin to radiation-sensitive modification.

Specific examples of the radiation-curable resin include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds showing an unsaturated double bond having a radical polymerizable property, and an allyl series such as diacrylic phthalate. The double bond, maleic acid, unsaturated bond such as maleic acid derivative, etc. can be crosslinked by irradiation or polymerized and dried,
It is a resin contained or introduced in the molecule of the thermoplastic resin, and is a compound having an unsaturated double bond that is cross-linked and polymerized by irradiation with radiation, and has a molecular weight of 5,000 to 100,000, preferably 10,000 to 80,000. Can be used.

As a resin containing a group that is crosslinked or polymerized and dried by irradiation with radiation in the molecule of the thermoplastic resin, there is the following unsaturated polyester resin.

A polyester compound having a radiation-curable unsaturated double bond in the molecular chain, for example, a saturated polyester resin composed of the ester bond of polybasic acid and polyhydric alcohol of the following (2), in which a part of the polybasic acid is maleic acid And the unsaturated polyester resin containing a radiation-curable unsaturated double bond.

The radiation-curable unsaturated polyester resin is obtained by adding maleic acid, fumaric acid and the like to at least one polybasic acid component and at least one polyhydric alcohol component, and then in a conventional method, that is, in the presence of a catalyst, 180 to 200 ° C. After a dehydration or dealcoholization reaction in a nitrogen atmosphere, the temperature can be raised to 240 to 280 ° C. and the condensation reaction can be performed under a reduced pressure of 0.5 to 1 mmHg.

The content of maleic acid, fumaric acid, etc. is
1 to 40 mol% in the acid component, preferably from the viewpoint of radiation curability
It is 10 to 30 mol%.

Examples of the thermoplastic resin that can be modified into a radiation curable resin include the following.

(1) Vinyl chloride copolymer Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer,
Vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer, for example, UCC VROH, VYNC, VYBG
X, VERR, VYES, VMCA, VAGH, etc. are mentioned, and by this method, an acrylic double bond, a maleic acid double bond, an allyl double bond is introduced to perform radiation-sensitive modification. .

(2) Saturated polyester resin phthalic acid, isophthalic acid, terephthalic acid, succinic acid,
Saturated polybasic acids such as adipic acid, sebacic acid, and ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,2 propylene glycol, 1,3 butanediol, dipropylene glycol, 1,4
-Saturated polyester resin obtained by ester bond with polyhydric alcohol such as butanediol, 1,6 hexanediol, pentaerythritol, sorbitol, glycerin, neopentyl glycol, 1,4 cyclohexanedimethanol, or polyester resin thereof To SO ₃ N
An example is a resin modified with a or the like (for example, Vylon 53S), and these are similarly subjected to radiation-sensitive modification.

(3) Polyvinyl alcohol-based resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin and copolymers of these components are used, and the hydroxyl groups contained in these resins are subjected to radiation-sensitive modification by the method described below.

(4) Epoxy resin, phenoxy resin Epoxy resin obtained by the reaction of bisphenol A with Epchlorohydrin, Methylepichlorohydrin, for example, Shell Chemical (Epicoat 152,154,828,1001,1004,1007),
Dow Chemical's (DEN431, DER732, DER511, DER331), Dainippon Ink's (Epiclon 400, 800), and UPC's phenoxy resin (P
KHA, PKHC, PKHH), a copolymer of brominated bisphenol A and epichlorohydrin, manufactured by Dainippon Ink and Chemicals (Epiclone 145,152,153,1120), and the like.

Radiation-sensitive modification is carried out using the epoxy groups contained in these resins.

(5) Fibrin derivative Although various derivatives are used, particularly effective ones are preferably nitrified cotton, cellulose acetobutyrate, ethyl cellulose, butyl cellulose, acetyl cellulose and the like.

Radiation-sensitive modification is carried out by the method described below using the hydroxyl groups in the resin.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylporolidone resins and derivatives (PVP
An olefin copolymer), a polyamide resin, a polyimide resin, a phenol resin, a spiro acetal resin, an acrylic ester containing a hydroxyl group, and an acrylic resin containing at least one methacrylic ester as a polymerization component are also effective.

The polymer compound (B) used in the present invention is a thermoplastic elastomer or prepolymer, or a radiation-sensitive modification thereof, and the latter case is more effective.

Examples of the elastomer or prepolymer will be given below.

(1) Polyurethane Elastomer or Prepolymer Examples of the urethane compound include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-xylene diisocyanate and 1,4 as the isocyanate.
-Xylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, 3,3-
Dimethyl-4,4-diphenylmethane diisocyanate,
4,4-diphenylmethane diisocyanate, 3,3-dimethylbiphenylene diisocyanate, 4,4-biphenylene diisocyanate, hexamethylene diisocyanate,
Various polyvalent isocyanates such as isophorone diisocyanate, dicyclohexyl methane diisocyanate, desmodur L, desmodur N and linear saturated polyesters (ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,4-butanediol, 1,6- Polyhydric alcohols such as hexanediol, pentaerythritol, sorbitol, neopentyl glycol, 1,4-cyclohexanedimethynol and saturated polyhydric alcohols such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid. Polycondensation with basic acid), linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol), caprolactam, hydroxyl-containing acrylates, hydr Carboxymethyl containing various polyesters polyurethane elastomer consisting of condensates of methacrylic acid ester, the prepolymer is valid.

By reacting the terminal isocyanate group or hydroxyl group of these urethane elastomers with a monomer having an acrylic double bond or an allyl double bond,
Radiation-sensitive modification is very effective.

(2) Acrylonitrile-Butadiene Copolymer Elastomer Acrylonitrile butadiene copolymer prepolymer having a terminal hydroxyl group, which is commercially available as poly BD retied resin manufactured by Sinclair Petrochemical Co., Ltd., or elastomer such as Hiker 1432J manufactured by Nippon Zeon Co., Ltd. The double bond is suitable as an elastomer component which generates a radical by radiation and is crosslinked and polymerized.

(3) Polybutadiene Elastomer A prepolymer having a low molecular weight terminal hydroxyl group such as poly BD retied resin R-15 manufactured by Sinclair Petrochemical Co., Ltd. is particularly preferable in terms of compatibility with thermoplasticity.

Since the R-15 prepolymer has a hydroxyl group at the molecular end, it is possible to enhance the radiation sensitivity by adding an acrylic unsaturated double bond to the molecular end, which is more advantageous as a binder.

In addition, cyclized polybutadiene, CBR made by Japan Synthetic Rubber
-M901 also has excellent properties when combined with a thermoplastic resin.

Other suitable thermoplastic elastomers and prepolymers thereof include styrene-butadiene rubber, chlorinated rubber, acrylic rubber, isoprene rubber, and cyclized products thereof (CIR701 manufactured by Japan Synthetic Rubber), epoxy-modified rubber, Elastomers such as internally plasticized saturated linear polyester (Toyobo Byron # 300) can also be effectively used by the radiation sensitive modification treatment described below.

Examples of the compound (C) having a radiation-curable unsaturated double bond used in the present invention include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol acrylate, diethylene glycol dimethacrylate, 1,
6-hexanediglycol diacrylate, 1,6-hexaneglycol dimethacrylate, trimethylolpropane trimethacrylate, polyfunctional oligoester acrylate (Aronix M-7100, Toagosei), acrylic modified urethane elastomer (Nipporan 4040), or Examples thereof include those into which a functional group such as COOH has been introduced.

It is known that a polymer is one which is disintegrated by irradiation with radiation and one which causes intermolecular crosslinking.

Examples of those that cause cross-linking between molecules include pyriethylene, polypropylene, polystyrene, polyacrylic acid ester, polyacrylamide, polyvinyl chloride, polyester, polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolene.

With such a cross-linking polymer, a cross-linking reaction occurs even if the above-mentioned modification is not particularly performed. Therefore, in addition to the modified product, these resins can be used as they are as a back coating resin for radiation cross-linking. is there.

Furthermore, according to this method, even a solventless resin that does not use a solvent can be cured in a short time, and thus such a resin can be used for a back coat.

Particularly preferable combinations of the radiation curable resin composition used in the present invention are vinyl chloride-vinyl acetate copolymer partially saponified with the compound (A), vinyl chloride-vinyl acetate into which carboxylic acid is introduced. A compound obtained by reacting a copolymer, a compound having an isocyanate group obtained by reacting a polyisocyanate compound with a phenoxy resin, an acrylic compound having a functional group having reactivity with an isocyanate group, or a methacrylic compound. , (B) is a compound obtained by reacting an isocyanate compound or a polyol (polyurethane elastomer) obtained by reacting a polyol with an isocyanate compound, with an acrylic compound or methacrylic compound having a reactive functional group. , (C) is polyfunctional (meth) cryle Tomonoma, is that oligoester acrylate or low molecular weight compounds (B),.

The film thickness of such a back coat layer is 0.2 to 2.5 μm, and more preferably about 0.3 to 1.5 μm. Film thickness
When it is less than 0.2 μm, sufficient running stability cannot be obtained, and when it exceeds 2.5 μm, the back coat layer is distorted.

The back coat layer may contain various known additives such as a lubricant, if necessary, in addition to the above-described pigment and organic binder.

As the coating solvent, a ketone type solvent such as MEK, cyclohexanone and MIBK, an alcohol type solvent such as IPA, an aromatic type solvent such as toluene and a halogen type solvent such as dichloroethane are used.

When using, use one of these alone,
Two or more kinds may be mixed and used, or any of them may be used.

As the lubricant (including the dispersant), any of the types conventionally used for this type of backcoat layer can be used, but caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, Fatty acids having 12 or more carbon atoms such as stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearolic acid (RCOOH, R is 1 carbon atom)
1 or more alkyl groups); a metal soap consisting of the above-mentioned fatty acid alkali metal (Li, Na, K, etc.) or alkaline earth metal (Mg, Ca, Ba, etc.); lecithin, etc. are used.

In addition to these, higher alcohols having 12 or more carbon atoms, and their sulfates, surfactants, titanium coupling agents, silane coupling agents and the like can also be used.

These lubricants (dispersants) are added in the range of 1 to 20 parts by weight with respect to 100 parts by weight of the binder.

As the lubricant, in addition to the above, silicone oil, graphite, molybdenum difluoride, tungsten difluoride, fatty acid esters composed of monobasic fatty acids having 12 to 16 carbon atoms and monohydric alcohols having 3 to 12 carbon atoms A fatty acid ester comprising a monobasic fatty acid having 17 or more carbon atoms and a monohydric alcohol having 21 to 23 carbon atoms in total with the carbon number of the fatty acid is used.

These lubricants are 0.2 to 100 parts by weight of the binder.
It is added in the range of 20 parts by weight.

As the other additives, any of those used for this type of back coat can be used. For example, as an antistatic agent, a natural surfactant such as saponin; alkylene oxide type, glycerin type, glycidol Nonionic surfactants such as systems; higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, cation surfactants such as phosphonium or sulfoniums; carboxylic acid, sulfonic acid, phosphoric acid, sulfate group,
Anionic surfactants containing an acidic group such as a phosphate group; amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols, and the like are used.

Further, as the lubricant, antioxidant, etc. contained in the back coat layer or the top coat layer described later, a radiation curable type is preferable.

In such a case, the active energy ray used for the cross-linking is an electron beam having a radiation accelerator as a radiation source, γ-rays having Co60 as a radiation source, β-rays having Sr90 as a radiation source, and an X-ray generator. X-rays or ultraviolet rays having a radiation source of are used.

Particularly, as a radiation source, a method of using radiation by a radiation accelerator is advantageous from the viewpoints of controlling absorbed dose, introducing it into a manufacturing process line, and blocking ionizing radiation.

The radiation characteristics used when curing the above backcoat layer and the following topcoat layer are an acceleration voltage of 100 to 750 Kv, preferably a radiation accelerator of 150 to 300 Kv in terms of penetrating power, and an absorbed dose of 0.5. It is convenient to irradiate to ~ 20 megarads.

At the time of the above-mentioned radiation curing, a low-dose type radiation accelerator (electro curtain system) manufactured by US Energy Science Co., Ltd. is extremely used for introducing into the tape coating processing line and shutting off secondary X-rays inside the accelerator. It is advantageous.

Alternatively, a van de Graaff type accelerator, which has been widely used as a radiation accelerator, may be used.

Further, at the time of radiation crosslinking, it is important to irradiate the backcoat layer and the topcoat layer with radiation in a stream of an inert gas such as N ₂ gas and He gas. In crosslinking the components, radicals generated in the polymer under the influence of O _{3 and the} like generated by irradiation of radiation hinder the advantageous effect on the crosslinking reaction, which is extremely disadvantageous.

Therefore, it is important to maintain the atmosphere of the portion irradiated with the active energy ray as an atmosphere of an inert gas such as N ₂ , He or CO ₂ having an oxygen concentration of 5% at the maximum.

Further, the surface of the substrate or the lining layer on which the back coat layer is provided is preferably subjected to plasma treatment for the purpose of improving the adhesive strength. Such plasma treatment is usually performed using an inorganic gas as a treatment gas, and it is preferable to use a treatment gas containing O, N, and H among these treatment gases.

 There is no particular limitation on the frequency of the plasma treatment.

Such plasma treatment improves the adhesive strength between the backing layer and the back coat layer.

Fine protrusions may be provided at a predetermined density on the surface of the magnetic recording medium of the present invention.

Fine protrusions are 30-300Å, more preferably 50-250Å
It has the height of.

That is, the projections can be observed with an optical microscope and can be observed with a scanning electron microscope, not with a stylus type surface roughness meter.

If the projection height exceeds 300Å and can be observed with an optical microscope, electromagnetic conversion characteristics will deteriorate and running stability will decrease.

 Also, if it is less than 50Å, the improvement of physical properties is not effective.

And, the density is 10 ⁵ or more per 1 mm ^{2 on} average, more preferably 10 ⁵ to 10 ⁹ , and especially 10 ⁶ to 10 ⁸ .

When the protrusion density is less than 10 ⁵ pieces / mm ² , noise increases and the physical properties such as deterioration of still characteristics are deteriorated, and it is not practically usable.

On the other hand, if it exceeds 10 ⁹ pieces / mm ² , the effect on the physical properties will be reduced.

 The diameter of the protrusion is generally about 200 to 1000Å.

In order to provide such protrusions, it is usually sufficient to dispose fine particles on the substrate. The diameter of the fine particles may be 30 to 1000Å, whereby fine protrusions corresponding to the diameter of the fine particles are formed.

The fine particles used are those generally known as colloidal particles, for example, SiO ₂ (colloidal silica), Al ₂ O ₃ (alumina sol), MgO, TiO ₂ , ZnO, Fe.
₂ O ₃ , zirconia, CdO, NiO, CaWO ₄ , CaCO ₃ , BaCO ₃ , Co
CO ₃ , BaTiO ₃ , Ti (titanium black), Au, Ag, Cu, N
i, Fe, various hydrosols, resin particles and the like can be used. In this case, it is particularly preferable to use an inorganic substance.

Such fine particles are used as a coating liquid using various solvents,
This may be coated on a substrate and dried, or a coating solution to which a resin component such as various aqueous emulsions is added may be coated and dried.

In some cases, the coating liquid may be provided as a top coat layer on the magnetic thin film layer instead of being provided on the substrate.

Further, when a resin component is used, it is possible to provide a gentle protrusion by superposing on the fine protrusion based on these fine particles, but it is not usually necessary to do so.

If necessary, a non-magnetic metal thin film layer may be interposed between the uppermost layer and the lowermost layer of the ferromagnetic metal thin film layer.

In addition, when a plasma-polymerized film is formed on the magnetic thin film layer or the magnetic thin-film layer, a top coat layer may be formed on the plasma-polymerized film to further improve the running property.

As the top coat layer, various known ones can be applied. For example, a radiation curable compound, that is, one or more of a radiation curable polymer, a monomer or an oligomer, an antioxidant, and, if necessary, a lubricant or the like. And the like.

If necessary, various known underlayers may be interposed between the substrate and the ferromagnetic metal thin film layer.

V. Specific Actions and Effects of the Invention According to the present invention, the magnetic layer has a layered structure of two or more layers, so that the length of the magnetic columnar crystal grains is small, so that the film strength of the magnetic layer is improved. Therefore, running stability is extremely high, cracks in the magnetic layer and scratches on the magnetic surface due to running are extremely small, and the head wear amount,
The occurrence of dropouts is also extremely small.

In addition, the uppermost columnar crystal grain is 20
Some have a slope of ゜ to 90 ゜, especially more than 50 ゜, and at the same time, if the ratio C ₂ / C ₁ of the oxygen concentration C ₂ of the lowermost layer and the oxygen concentration C ₁ of the uppermost layer is 0.3 or less. If the ratio C ₃ / C ₁ of the oxygen concentration C ₃ near the uppermost layer interface of the layer adjacent to the uppermost layer and the oxygen concentration C ₁ of the uppermost layer is 0.2 to 0.92, the coercive force Hc of the uppermost layer is A signal having a relatively high magnetic field with a relatively shallow magnetic field and a center frequency of about 5 MHz is effectively held, and the resolution is good.

Furthermore, the columnar crystal grains in the lowermost layer are
When it has a tilt of 50 ° or less and stands upright with respect to the substrate, at the same time, the maximum residual magnetic flux φ _r ,
Since the squareness ratio is high and a peak of coercive force Hc exists near the uppermost layer interface of the layer adjacent to the uppermost layer, a signal with a center frequency of 0.75 MHz having a relatively deep magnetic field is effectively held. It is a thing.

Also, since the plasma-polymerized film is provided between the bottom layer of the ferromagnetic metal thin film layer and the substrate, between the layers, or on the surface of the top layer of the ferromagnetic metal thin film layer opposite to the substrate, the obtained medium is Excellent durability, abrasion resistance, weather resistance, corrosion resistance, etc.
There is little head adsorption, and it has extremely high reliability in practical use.

VI Specific Examples of the Invention Hereinafter, the present invention will be described in more detail by showing specific examples of the invention.

(Example 1) A polyester (PET) film having a thickness shown in Table 1 below was moved along a peripheral surface of a cylindrical cooling can, and O ₂ +
Ar (volume ratio 1: 1) is flown at a speed of 800 cc / min and the degree of vacuum is 1.0
The alloy of Co80 and Ni20 (weight ratio) was melted in the chamber of × 10 ^-4 Torr, and the incident angle was set to the incident angle shown in Table 1. By oblique deposition, the Co-Ni-O alloy shown in FIG. A two-layer thin film was formed.

For comparison, only a portion having an incident angle of 30 to 90 ° was obliquely vapor-deposited to form a 0.15 μm thick Co—Ni—O single-layer thin film.

A large amount of oxygen was unevenly distributed on the interface between the lower layer and the upper layer and on the surface opposite to the base. Also, the surface opposite to the base was almost entirely covered with oxide.

Hc-1000 Oe. The average oxygen content in the film is the atomic ratio to Co and Ni. Was 40%.

In Table 1, among the O / (Co or Co + Ni) atomic ratios obtained by performing Auger spectroscopic analysis while performing ion etching with Ar, C ₁ (surface), C ₁ ^* (upper layer average), and C ₂ ( The interface between the lower layer and the substrate), C ₂ ^* (average of the lower layer), and C ₃ (in the vicinity of the interface between the lower layer and the upper layer) are also described.

In addition, a plasma polymerized film was formed. The plasma-polymerized film was formed at any one of the position between the substrate and the magnetic layer, the surface of the magnetic layer on the side opposite to the substrate, and the magnetic layer which is a two-layer thin film.

The formation of the plasma-polymerized film was performed by placing the object to be formed in a vacuum chamber and temporarily drawing a vacuum of 10 ^-3 Torr, then introducing CH ₄ as a gaseous hydrocarbon and Ar as a carrier gas at a ratio of 1: 1.
While maintaining the gas pressure at 0.1 Torr, plasma was generated by applying a high-frequency voltage of 13.56 MHz of 500 W to form a plasma polymerized film.

 The film thickness was the value shown in Table 1.

The W / F · M was 5 × 10 ⁸ and the C / H ratio was 2.

After the back surface of this film was plasma-treated, a back coat layer as shown below was formed.

The plasma processing conditions were that the processing gas was O ₂ gas, the gas flow rate was 100 ml / min, the vacuum degree was 0.5 Torr, the power source was 50 KHz, 200 W, and the film traveling speed was 30 m / min.

Further, a back coat layer as shown below was formed on the side of the substrate opposite to the magnetic layer forming surface, and a top coat layer as shown below was formed on the magnetic layer.

(1) Formation of back coat layer Weight part of back coat layer Carbon black 7 SiO ₂ 2 Acrylic modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer 30 Acrylic modified polyurethane elastomer 10 Acrylic ester oligomer 4 Dispersion aid 0.4 The above mixture is ball milled. Disperse for 5 hours, apply on plasma treated backing layer, and irradiate electron beam in N ₂ gas with accelerating voltage 150 KeV, electrode current 10 mA, absorbed dose 5 Mrad using electro curtain type electron beam accelerator. Then
A back coat layer having a thickness of 0.5 μm was formed.

(2) Formation of Top Coat Layer The following composition was formed on the magnetic layer. Topcoat layer parts by weight Butyl myristate (fatty acid ester mp = 1.0 ℃) 0.5 (Radiation-sensitive unsaturated double bond-containing group) 0.3 MEK 30 Cyclohexanone 70 was stirred and mixed at room temperature for 1 hour, and the resulting mixture was gravure coated on the surface of the above magnetic layer to a uniform thickness. After drying at ℃ for 1 minute, 150 KeV in N ₂ gas, 6m
Electron beam irradiation was performed under the conditions of A and 3 Mrad to form a topcoat layer having a layer thickness of 25 Å.

The following measurement was performed on the sample thus produced. The medium running direction and the direction of inclination of the magnetic crystal grains with respect to the lower layer normal to the substrate were the same.

(1) Still durability The time required for the output to decrease by 5 dB under the condition of a temperature of 0 ° C was determined.

Deck used: SONY A-300 (I used it without the still-release mechanism) Head: Sputter Sendust (2) Electromagnetic conversion characteristics When the outputs of center frequencies 0.75MHz and 5MHz were measured and the output of sample No. 18 was set to 0dB The value of was calculated.

Deck used: SONY A-300 Head: Spatter Sendust mode: SP mode In addition, the level of these outputs affects the output after storage. Therefore, after storing at 60 ° C and 90% for 5 days,
The output of 5MHz was measured.

(3) Corrosion resistance Δ after initial storage and after storage for 7 days at 60 ° C and 90% relative humidity
φm / φm (%) was measured.

(4) Breaking strength The breaking strength of an 8 mm wide tape was measured. The measured value is shown as a relative value to the measured value of Sample No. 18 (base thickness 10 μm, magnetic layer constitution: single layer, no plasma polymerized film).

 The results are shown in Table 2.

(Example 2) A magnetic layer was formed by the same method as in Example 1 except that the ratio of the base thickness and the thickness of the upper and lower layers of the magnetic layer was as shown in Table 3, and the same back as in Example 1 was formed. Coat layer,
The samples shown in Table 3 were prepared using the top coat layer (Sample Nos. 21 to 27).

The same measurement as in Example 1 was performed on each of the samples thus formed.

Note that the electromagnetic conversion characteristics were obtained when the output of Sample No. 27 was 0 dB.

 The results are shown in Table 4.

In addition, the improvement range of the output of Sample Nos. 21 to 23 (base thickness 7 μm, magnetic layer configuration: 2 layers) with respect to the output of Sample No. 25 (base thickness 7 μm, magnetic layer configuration: single layer) is shown in Table 4 (). It is described inside.

From the results shown in Tables 1 to 4, the effect of the present invention is clear.

That is, it is clear that good values are obtained in all of the measurement items for the samples (No. 1,2,5,10 to 13,15) having the magnetic layer structure and the plasma polymerized film of the present invention. Is.

When the base thickness is 8 μm or less, the upper layer thickness / lower layer thickness is 0.
If it is 2 to 0.9, the output at 5 MHz and the durability are extremely improved (Sample No. 21), and even a thin base thickness that cannot withstand practical use at the output of 5 MHz is enough electromagnetic conversion to be practical. It can be seen that it exhibits characteristics and durability.

Example 3 Colloidal silica was applied to the surface of the substrate on which the magnetic layer was formed to obtain a substrate having fine protrusions.

In this case, the protrusion height was 250Å and the protrusion density was 5 × 10 ⁷ / mm ² .

Using this substrate, the same tests as in Example 1 and Example 2 were performed, and as a result, the amount of deposits on the head during high temperature running was reduced by 30 to 40%.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross section parallel to the medium direction of one embodiment of the magnetic recording medium of the present invention. FIG. 2 is a schematic view of a cross section parallel to the medium direction of another embodiment of the magnetic recording medium of the present invention. FIG. 3 is a schematic diagram of a plasma polymerization apparatus. DESCRIPTION OF SYMBOLS 1 ... Magnetic recording medium, 2 ... Substrate, 3 ... Ferromagnetic metal thin film lower layer part, 4 ... Ferromagnetic metal thin film upper layer part, 5 ... Plasma polymerized film, 6 ... Lower layer crystal grain, 7 ...... Upper crystal grains, 20 …… Polymerization processing equipment, 21, 22 …… Processing gas source, 23,24 …… Mass hollow controller, 25 …… Mixer, 26 …… DC, AC and variable frequency power supply, 27 , 57 ...... electrode, 30 ... direct winding roll, 31 ... unwinding roll, 111 ... liquid nitrogen trap, 112 ... oil rotary pump,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuru Takai 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Shigeo Kurose 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK (56) References JP 57-98133 (JP, A) JP 61-145722 (JP, A) JP 61-151837 (JP, A)

Claims (5)

(57) [Claims] 1. A ferromagnetic metal thin film layer containing Co as a main component on a plastic film substrate, and the ferromagnetic metal thin film layer has a multi-layer structure composed of two or more layers. The minimum incident angle of the substance to be deposited with respect to the normal to the substrate during layer deposition is 50 ° or less when the lowermost layer is formed on the substrate side and 20 ° to 90 ° when the uppermost layer is formed on the opposite side of the substrate. The value obtained by dividing the oxygen concentration C ₂ in the vicinity of the interface on the substrate side of the lower layer by the oxygen concentration C ₁ in the vicinity of the surface on the opposite side to the substrate of the uppermost layer is 0.3 or less, and in the vicinity of the interface with the uppermost layer of the layer adjacent to the uppermost layer. Oxygen concentration
The C ₃ is a value C ₃ / C ₁ obtained by dividing the oxygen concentration C ₁ at the opposite side surface near the top layer of the substrate .2 to .92, C ₁ is 0.2 to 0.7, the average of the top and all layers A magnetic recording medium having an oxygen concentration of 0.1 to 0.5, and having a plasma polymerized film either between the lowermost layer of the ferromagnetic metal thin film layer and the substrate, between various layers or on the surface opposite to the substrate of the uppermost layer. . 2. The magnetic recording medium according to claim 1, wherein the ferromagnetic metal thin film layer has a two-layer structure. 3. The plasma polymerized film is C, or C and H,
The magnetic recording medium according to claim 1 or 2, containing at least one of N and O. 4. The C content of the plasma polymerized film is 30 to 10
The magnetic recording medium according to claim 3, wherein the content is 0 at%. 5. The C / H atomic ratio in the plasma polymerized film is 1 to
6. The magnetic recording medium according to claim 4, which is 6.