JPH09255899A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium suitable for high-density magnetic recording, capable of suppressing induction of deterioration of magnetic characteristics caused by a back coated layer and securing stable traveling properties and prescription characteristics by forming a metal magnetic thin film on one side of a nonmagnetic substrate and making a specific back coated layer on another side. SOLUTION: This magnetic recording medium is obtained by forming a metal magnetic thin film 2 on one side of (A) a nonmagnetic substrate 12 and making a back coated layer 3 comprising (B1 ) a chlorine ion (B2 ) a sulfate ion and (B3 ) a fatty acid amide in another side of the component A. The back coated layer 3 of the recording medium is formed, for example, by coating the surface of the back coated layer composed of the components B1 and B2 with the component B3 or by adding 0.01-10 pts.wt. of the component B3 based on 100 pts.wt. of a binder to a coating material containing 0.1-20wt.ppm of the component B1 and 0.1-20wt.ppm of the component B2 to give a coating agent and applying the agent to the other side of the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called metal thin film type magnetic recording medium in which a metal magnetic thin film is formed as a magnetic layer on a non-magnetic support by a vacuum thin film forming technique such as vacuum deposition or sputtering. For example, the present invention relates to a magnetic tape and a magnetic disk suitable for recording and reproducing a short wavelength magnetic recording signal (high density magnetic recording) such as a high band 8 mm video tape and a digital VTR (video tape recorder), and a manufacturing method thereof.

[0002]

Conventionally, as a magnetic recording medium, containing γ-Fe ₂ O _3, Co on a nonmagnetic support gamma-Fe ₂ O
_{3, Fe 3 O 4, Fe} 3 O 4 containing Co, γ-Fe
Bertride compound of ₂ O ₃ and Fe ₃ O ₄ , Bertride compound containing Co, oxide ferromagnetic powder such as CrO ₂ or alloy magnetic powder containing Fe, Co, Ni or the like as a main component A so-called coating type magnetic recording medium in which a magnetic layer is formed by coating and drying a magnetic coating material in which a magnetic material is dispersed in an organic binder such as a vinyl chloride-vinyl acetate copolymer, polyester resin, or polyurethane resin is dried. Widely used.

On the other hand, with the increasing demand for high-density magnetic recording, ferromagnetic metal materials such as Co--Ni alloys have been used.
A so-called ferromagnetic metal thin film type magnetic recording medium directly deposited on a non-magnetic support such as a polyester film or a polyimide film by plating or vacuum thin film forming technology (vacuum deposition method, sputtering method, ion plating method, etc.) Proposed and attracting attention.

This ferromagnetic metal thin film type magnetic recording medium is
Not only has excellent coercive force and squareness ratio, excellent electromagnetic conversion characteristics at short wavelengths, but also because the magnetic layer can be made extremely thin, recording demagnetization and thickness loss during reproduction are extremely small. In addition, since it is not necessary to mix an organic binder that is a non-magnetic material in the magnetic layer, there are various advantages such as the packing density of the magnetic material can be increased.

Thus, for example, a so-called vapor-deposited tape using a ferromagnetic metal thin film as a magnetic layer has characteristics superior to other magnetic recording media such as a coating type in terms of recording density,
It has already been put to practical use as a magnetic recording medium for a video recorder. Also, considering future developments in the field of magnetic recording, it is expected that the application fields will be wide, such as support for higher-quality video recorders such as digital video recorders and support for digital tape recorders.

In the vapor-deposited tape, the surface of the magnetic layer is close to a mirror surface state, and the substantial wear coefficient tends to increase. Therefore, the surface roughness of the non-magnetic support on the side where the magnetic layer is not provided is increased. It is practiced to form a back coat layer set to an appropriate value.

The back coat layer suppresses electrification and
It is indispensable for the purpose of eliminating the influence of dust and stabilizing the running.Usually, a non-magnetic pigment such as carbon having an appropriate particle size is dispersed and mixed with a binder, an organic solvent, etc. to form a paint. It is formed by preparing and applying this.

By the way, the present inventor has conducted various studies on the practical use of the vapor-deposited tape. As a result, the formation of the above-mentioned back coat layer has a great merit in that the running property is improved, but the back coat to be used is used. It has been found that it is necessary to pay attention to this point when developing the backcoat layer, because some ferromagnetic coating materials may induce deterioration of magnetic properties in the ferromagnetic metal thin film.

That is, in the conventional vapor-deposited tape having a back coat layer formed thereon, the metal magnetic thin film is kept in a wound state (that is, a state where the metal magnetic thin film and the back coat layer are in contact with each other) under high temperature and high humidity for a long time. Some of the magnetic properties are deteriorated and the tape properties are significantly deteriorated, and the improvement is required. It is presumed that this is because the back coat layer has some adverse effect.

In a home digital VTR or the like for recording digital image signals, the recording track pitch is extremely narrow at 10 μm due to the necessity of high-density magnetic recording, and even a small one that has been overlooked is more than ever. The impact is likely to appear and thorough improvement is necessary.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and an object thereof is to suppress the induction of the deterioration of the magnetic characteristics of the metal magnetic thin film by the back coat layer as much as possible and to ensure stable running. It is possible to provide excellent magnetic recording medium which is capable of ensuring the storage property and the storage characteristic and is most suitable for high-density magnetic recording, and a manufacturing method thereof.

[0012]

Means for Solving the Problems As a result of intensive studies to eliminate the above-mentioned adverse effects of the back coat layer, the present inventor has found that chlorine ions and sulfate ions remain in the back coat layer. We have come to the knowledge that there is.

The present invention has been completed based on these findings, and a metal magnetic thin film is formed on one surface of a non-magnetic support, and the non-magnetic support on the side opposite to the metal magnetic thin film is formed. A magnetic recording medium having a back coat layer containing chloride ions and sulfate ions formed on the other surface of the body, wherein a fatty acid amide is added to the back coat layer. Is.

In the present invention, a metal magnetic thin film is formed on one surface of the non-magnetic support, and chlorine ions and sulfuric acid are formed on the other surface of the non-magnetic support opposite to the metal magnetic thin film. Also provided is a method for producing a magnetic recording medium, which comprises adding a fatty acid amide to a coating material for forming the back coat layer when producing a magnetic recording medium having a back coat layer containing ions. Is.

When the amount of chlorine ions and the amount of sulfate ions contained (or remaining) in the back coat layer are large, for example, when the magnetic surface and the back coat surface are in contact with each other and stored in a high temperature and high humidity environment, metal The magnetic characteristics of the magnetic thin film deteriorate, the dropout characteristics deteriorate, and the durability also deteriorates. In the present invention, a fatty acid amide is added to the back coat layer from the viewpoint of reducing dropout increase deterioration due to magnetic property deterioration to a practical level and ensuring durability.

Fatty acid amide is generally known as a release agent, but when it is stored in a high temperature and high humidity environment with the magnetic surface and the back coat surface in contact with each other, magnetic characteristics deteriorate and dropout characteristics deteriorate. In contrast to the problem of deterioration in durability, the fatty acid amide added to the back coat layer covers the outermost surface of the back coat layer. Therefore, the effect of reducing the area where the back coat layer directly contacts the magnetic surface (that is, chlorine ions and sulfate ions remaining in the back coat layer act on the magnetic surface) is exerted, and the magnetic characteristics of the magnetic surface are deteriorated. It is possible to suppress it.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In the magnetic recording medium and the method for producing the same of the present invention, it is desirable that the fatty acid amide covers the surface of the back coat layer.

Also for this purpose, when the back coat layer is formed by applying the coating material in which the non-magnetic pigment is dispersed in the binder, the chlorine ion and the sulfate ion are each 0.1 to 20 ppm by weight, and further 1 In the case of the above-mentioned coating material containing 20 ppm by weight, the above-mentioned effect by adding the fatty acid amide is great.

In order to exert the effect of the fatty acid amide, the amount of the fatty acid amide added to the above coating composition is preferably 0.01 to 10 parts by weight (PHR) per 100 parts by weight of the binder.

This fatty acid amide can be used in any commercially available type such as stearic acid amide, palmitic acid amide, myristic acid amide, lauric acid amide, oleic acid amide, etc., and is not particularly limited by material and trade name. Absent.

Here, the concentration of the fatty acid amide in the paint is
It is preferably 0.01 PHR to 10 PHR, but 0.1 PHR
More preferably, it is R to 5 PHR. If this concentration is too low, the effect of improving mold release does not appear, and
If the amount is too large, a sticking phenomenon occurs between the guide roll of the tape path of the manufacturing equipment and the metal thin film, and the tape is likely to be cut.

From the viewpoint of sufficiently preventing the deterioration of magnetic properties, it is preferable that the content of chlorine ion and the content of sulfate ion in the coating material be 5 wtppm or less, and further 3 wtppm or less.

In the present invention, in order to measure the content of chloride ions and sulfate ions in the back coat layer or the coating material thereof, ion chromatography (anion chromatography) using a sampling sample according to a predetermined extraction method, for example, the following extraction method: (Ion) inspection method can be adopted.

That is, the coating material for the back coat layer was evaporated to dryness at 60 ° C., the solvent was removed, and the obtained solid was ground and weighed 5 g. To this powder sample, 100 ml of pure water was added, and heat extraction was performed at 100 ° C for 3 hours. Then, 50 ml was added to make a sample solution for extraction measurement, and chloride ion amount and sulfate ion amount were measured by ion chromatography. taking measurement. here,
The heat extraction time is set to 3 hours, but the time is not limited as long as the extraction is performed at a saturated temperature.

However, if the amount of chlorine ions and the amount of sulfate ions contained in the back coat layer exceed 0.1 wt% to 20 wt ppm, and particularly exceed 5 wt ppm, for example, the magnetic surface and the back coat surface are in contact with each other in a high temperature and high humidity environment. When stored below, the magnetic characteristics are deteriorated, the dropout characteristics are easily deteriorated, and the durability is also easily deteriorated. From the viewpoint of reducing the deterioration of the characteristics due to the increase of the dropout due to the deterioration of the magnetic characteristics to a practical level and ensuring durability, the chlorine ion content and the sulfate ion content in the back coat layer are 0.1 to 20 ppm by weight. It is particularly desirable that the content is not more than ppm by weight, more preferably not more than 3 ppm by weight.

The coating material for the back coat layer generally contains a non-magnetic pigment as a main component kneaded in a binder, and a small amount of an additive such as a dispersant is added thereto. From the point of view of source control,
Although it is preferable to regulate each material composition at the raw material stage, it can be judged as a paint as in the present invention in the meaning of making a final selection as a paint for the back coat layer and from the point of selecting a commercially available back coat paint. The point is very convenient.

That is, the amount of chlorine ions and the amount of sulfate ions contained in the back coat layer are influenced by the method of synthesizing the coating material for the back coat layer, the material, etc., and therefore, those which satisfy the above conditions are selected from the commercially available products. You can use it.

As the non-magnetic pigment dispersed in the coating material for the back coat layer, in addition to carbon, if necessary, hematite, mica, silica gel, magnesium oxide, zinc sulfide, tungsten carbide, boron nitride, starch, oxidation Zinc, kaolin, talc, clay, lead sulfate, barium carbonate, calcium carbonate, magnesium carbonate, boehmite (γ
_{-Al 2 O 3 · H 2 O} ), alumina, tungsten sulfide, titanium oxide, polytetrafluoroethylene powder, may be used in combination of polyethylene powder, polyvinyl chloride powder, metal powder or the like. Needless to say, it is desirable that the content of chlorine ions and the content of sulfate ions are small in these non-magnetic materials as well.

The back coat layer is prepared by kneading the above-mentioned non-magnetic pigment with a binder and an organic solvent to prepare a back coat layer coating material, and applying this to the surface of the non-magnetic support opposite to the magnetic layer. The binder and the organic solvent used at this time can be selected from conventionally known ones and are not limited at all.

For example, as the binder, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer Polymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride , Vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, butadiene-acrylonitrile-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin Resins, thermosetting polyurethane resins,
Examples include urea resins, melamine resins, alkyd resins, urea-formaldehyde resins, and mixtures thereof.

These may be those in which an isocyanate compound is used as a cross-linking agent to further improve durability or a suitable polar group is introduced. Needless to say, it is desirable that the content of chlorine ions and the content of sulfate ions are small at the material stage of these binders.

As the solvent, acetone, methyl ethyl ketone, methyl isobutyl ketone, ketone solvents such as cyclohexanone, methyl acetate, ethyl acetate, butyl acetate,
Ethyl lactate, ester solvents such as glycol acetate glycol monoethyl ester, glycol dimethyl ether, glycol monoethyl ether, glycol ether solvents such as dioxane, aromatic hydrocarbon solvents such as benzene, toluene, xylene, methylene chloride, ethylene chloride, Organic chlorinated compound solvents such as carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene are exemplified.

The thickness of the back coat layer is usually 0.4 to 1.2.
μm.

On the other hand, the magnetic layer is made of Co, Co-Ni, Co-
A ferromagnetic metal thin film such as Fe-Ni is deposited by a vacuum thin film forming technique such as vapor deposition (oblique vapor deposition, vapor deposition in an atmosphere containing oxygen, and further a combination thereof) and sputtering. The metal magnetic thin film is formed as a magnetic layer by directly depositing a ferromagnetic metal material, but any metal magnetic material can be used as long as it is used for a usual vapor deposition tape.

For example, ferromagnetic metals such as Fe, Co and Ni, Fe-Co, Co-Ni, Co-Fe-Ni and F
e-Cu, Co-Cu, Co-Au, Co-Pt, Mn
-Bi, Mn-Al, Fe-Cr, Co-Cr, Ni-
Cr, Fe-Co-Cr, Co-Ni-Cr, Fe-C
Examples include ferromagnetic alloys such as o-Cr-Ni. These may be a single-layer film or a multilayer film.

Furthermore, between the non-magnetic support and the metal magnetic thin film,
Alternatively, in the case of a multilayer film, an underlayer or an intermediate layer may be provided in order to improve the adhesive force between the layers and control the coercive force. Further, for example, the vicinity of the surface of the magnetic layer may be made of an oxide for improving corrosion resistance and the like.

As a means for forming the metal magnetic thin film, a vacuum evaporation method of heating and evaporating a ferromagnetic material under vacuum and depositing it on a non-magnetic support, or an ion plating method of evaporating a ferromagnetic metal material during discharge. A so-called PVD technique such as a sputtering method or a sputtering method in which atoms on the target surface are knocked out by argon ions generated by glow discharge in an atmosphere containing argon as a main component may be used.

The thickness of the metal magnetic thin film is usually 0.02 to 1 μm.
It is.

Further, a protective film layer may be formed on the ferromagnetic metal thin film formed on the non-magnetic support, and this material is used as a protective film for ordinary metal magnetic thin films. Any commonly used one may be used.

By way of example, carbon, CrO ₂ , Al ₂
O ₃ , BN, Co oxide, MgO, SiO ₂ , Si ₃ O
_{4, SiN X, SiC, SiN} X -SiO 2, Zr
O ₂ , TiO ₂ , TiC and the like can be mentioned. These may be a single layer film, a multilayer film or a composite film.

As the material for the non-magnetic support, any of the conventionally known materials used in this type of medium can also be used.

For example, as the material of the non-magnetic support, polyesters such as polyethylene terephthalate, polyethylene such as polypropylene, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate and cellulose acetate butyrate, polyvinyl chloride, polychlorination. Vinyl-based resin such as vinylidene, plastic such as polycarbonate, polyimide, polyamide, polyamide-imide, metal such as paper, aluminum and copper, light alloy such as aluminum alloy and titanium alloy, and ceramic single crystal silicon. The form of the nonmagnetic support may be any of a film, a tape, a sheet, a disk, a card, a drum, and the like.

FIG. 1 shows an example (V of the magnetic recording medium of the present invention.
(Magnetic tape for TR). That is, the above-mentioned metal magnetic thin film 2 is formed on the non-magnetic support 12 via an underlayer if necessary, and the above-mentioned back coat layer 3 is provided on the other surface.

FIG. 2 shows the structure of a vacuum vapor deposition apparatus that can be used to manufacture the magnetic recording medium of the present invention.

In this apparatus, exhaust ports provided at the top and bottom of the upper and lower chambers partitioned by the partition plate 21 respectively.
The inside of the vacuum chamber 10, which has been evacuated from 25 and has a vacuum inside, has a feed roll 13 that rotates at a constant speed in the counterclockwise direction in the figure.
And a take-up roll that rotates at a constant speed in the counterclockwise direction in the figure.
14 and are provided, and these feed rolls 13 to take-up rolls are provided.
The tape-shaped non-magnetic support 12 is sequentially run on the tape 14.

The rolls 13 and 14 described above are provided in the middle of the non-magnetic support 12 running from the feed roll 13 to the take-up roll 14 side.
A cooling can 15 having a diameter larger than the diameter is provided. The cooling can 15 is provided so as to pull out the non-magnetic support 12 downward in the drawing, and is configured to rotate at a constant speed in the clockwise direction in the drawing. The feed roll 13, the winding roll 14, and the cooling can 15 are each a non-magnetic support.
It has a cylindrical shape of approximately the same length as the width of 12,
Further, the cooling can 15 is provided with a cooling device (not shown) inside so as to suppress deformation and the like of the non-magnetic support 12 due to temperature rise.

Therefore, the non-magnetic support 12 is formed by the feed roll 13
Are sequentially sent out from the cooling can 15, pass through the peripheral surface of the cooling can 15, and are wound up by the winding roll 14. In addition, between the feed roll 13 and the cooling can 15,
Guide rolls 16 and 17 are provided between the cooling can 15 and the winding roll 14, respectively. The feeding roll 13 to the cooling can 15 and the cooling can 15 to the winding roll are provided.
A predetermined tension is applied to the non-magnetic support 12 that runs over 14 so that the non-magnetic support 12 runs smoothly. Further, in the vacuum chamber 10, a crucible 18 is provided below the cooling can 15, and the crucible 18 is filled with a metal magnetic material 19. The crucible 18 has a width substantially the same as the width of the cooling can 15 in the longitudinal direction.

On the other hand, an electron gun 20 for heating and evaporating the metallic magnetic material 19 filled in the crucible 18 is attached to the side wall of the vacuum chamber 10. The electron gun 20 is arranged at a position such that the emitted electron beam X irradiates the metallic magnetic material 19 in the crucible 18. The metal magnetic material 19 evaporated by the electron gun 20 is deposited and formed as a magnetic layer on the non-magnetic support 12 that runs at a constant speed on the peripheral surface of the cooling can 15.

A shutter 23 is provided between the cooling can 15 and the crucible 18 and near the cooling can 15. The shutter 23 is formed so as to cover a predetermined region of the non-magnetic support 12 that runs at a constant speed on the peripheral surface of the cooling can 15.
The metallic magnetic material evaporated by the shutter 23
19 is obliquely deposited on the non-magnetic support 12 within a predetermined angle range (the deposition angle is Φ at maximum). Further, in such vapor deposition, the non-magnetic support 12 is passed through the oxygen gas introduction port 24 provided to penetrate the side wall of the vacuum chamber 10.
Oxygen gas is supplied to the surface of the to improve magnetic properties, durability and weather resistance.

FIG. 3 shows an example of a coating device for forming the back coat layer 3.

The non-magnetic support 12 is unrolled from the supply roll 43, passes through the guide roller 44, and passes through the backup roll.
It is sandwiched between 34 and the gravure roll 32, and a fatty acid amide-containing back coat layer coating material 46 is applied. At the time of applying this paint, the non-magnetic support 12 is rotated by a gravure roll 32 that is rotated while partially dipping it in the paint 46 contained in the solution tank 35 and scraped off the excess paint with a doctor blade 33.
Is coated on the surface opposite to the metal magnetic thin film.

The non-magnetic support 12 coated with the coating material 46 passes through the guide rollers 37, 37 and the dryer 36, where the coating liquid is fed by hot air to form a back coat layer.
It is wound around the winding roll 42 via the guide roller 37.

[0053]

EXAMPLES Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to the following examples.

First, backcoat layer coating materials having different amounts of chlorine ions and sulfate ions contained in the backcoat layer were used, and each coating material was applied to a polyethylene terephthalate film by the coating device shown in FIG. Layers were formed. The backcoat layer coating is solid
15%, PB ratio (mixing ratio of non-magnetic pigment and binder) is 1.2
As the above, 10 PHR (10 parts by weight to 100 parts by weight of the binder) of Coronate L-50 (curing agent: manufactured by Nippon Polyurethane Co., Ltd.) was added. In this case, fatty acid amide was added to the back coat layer coating material in various amounts.

The conditions for forming this back coat layer are summarized below. Coating material: Carbon 100 parts by weight Binder: Polycarbonate / Polyurethane 100 parts by weight Fatty acid amide: Stearic acid amide 0.5 parts by weight Curing agent: Coronate L-50 10 parts by weight Solvent: Methyl ethyl ketone 450 parts by weight Toluene 250 parts by weight Backcoat layer Application: Application of a mixture of carbon and polycarbonate binder to a thickness of 0.5 μm

On the other hand, on the surface opposite to the back coat layer,
Using the vacuum deposition apparatus shown in FIG. 2, Co80% -Ni20
A ferromagnetic metal having a composition of 100% was obliquely vapor-deposited in an oxygen atmosphere to form a ferromagnetic metal thin film having a thickness of 200 nm as a magnetic layer.

The respective conditions for forming this metal magnetic thin film are summarized below. Base: polyethylene terephthalate (6 μm thick, 150
mm width) Deposition degree of vacuum: 7 × 10 ^-2 Pa Deposition thickness of metal magnetic thin film: 200 nm

On the metal magnetic thin film, perfluoropolyether was applied as a top coat layer (lubricant layer).

Then, the nonmagnetic support having the metal magnetic and backcoat layers prepared as described above was slit into a width of 8 mm to prepare a magnetic tape.

The amount of chlorine ions and the amount of sulfate ions contained in the back coat layer were measured by the ion chromatography (anion) inspection method using a sampling sample by the following extraction method.

That is, the coating material for the back coat layer was evaporated to dryness at 60 ° C. to remove the solvent, and the obtained solid was ground and weighed 5 g. Add 100 ml of pure water to this powder sample, and
After heat-extracting for an hour, 50 ml of the sample was added to make an extraction measurement sample liquid, and the amount of chloride ion and the amount of sulfate ion were measured by ion chromatography.

According to the above-mentioned method, several kinds of sample tapes were prepared by using the coating materials for the back coat layer having different amounts of chloride ion and sulfate ion. The chlorine ion content and the sulfate ion content of the back coat layer coating material used in each sample tape are as shown in Table 1 below.

Next, 0.5 PHR of fatty acid amide was added to the coating material for the back coat layer of each of these samples, and sample trial production was carried out. Although stearic acid amide was used as this fatty acid amide, any commercially available type such as palmitic acid amide, myristic acid amide, lauric acid amide, and oleic acid amide can be used.
It is not limited by product name.

The concentration of the fatty acid amide in the paint is 0.01 PH.
R to 10 PHR is preferred, 0.1 PHR to 5 PH
More preferably, it is R. Here, it is set to 0.5 PHR.

For each of the above tapes, the rate of decrease in magnetic flux (Δφ), which is an index for the occurrence of magnetic property deterioration of the metal magnetic thin film (in high temperature and high humidity environment: 60 ° C., 95% RH, after storage for 10 days), and The still characteristics and the dropout increase rate after storage at high humidity (45 ° C., 80% RH, after storage for 4 days) were examined. For the measurement of dropout, a modified EVS-900 machine manufactured by Sony Corporation was used. The recording signal was 50% white. The results are shown in Table 1 below.

[0066]

From these results, the addition of fatty acid amide to the coating material for the back coat layer has a great influence on the deterioration of the magnetic properties and the durability, and the deterioration of the magnetic properties of the metal magnetic thin film is reduced or prevented, whereby the durability, It is clear that tape characteristics such as dropout can be greatly improved, and stable running property and storability can be obtained.

Such an effect is obtained especially when the amount of chlorine ions and the amount of sulfate ions in the coating material for the back coat layer are each 0.1 to
20 weight ppm, and further 1 to 20 weight ppm, of which 5 weight
It becomes noticeable by setting it to be ppm or less (particularly 3 ppm by weight or less).

Next, in Example 6, when the addition amount of the fatty acid amide in the coating material for the back coat layer was changed, the results shown in Table 2 below were obtained.

[0070] * Because of the high density, it could not be measured because it did not run on the rotating drum.

This result shows that the addition amount of fatty acid amide was 0.01
A dropout and durability of 10 to 10 PHR, especially 0.5 to 10 PHR are shown to be good.

[0072]

As described above, according to the present invention, a metal magnetic thin film is formed, and chlorine ions and sulfate ions are contained in 0.1
In a magnetic recording medium with a backcoat layer containing up to 20 ppm by weight, a fatty acid amide with an excellent releasing effect is added to the backcoat layer, so this fatty acid amide should cover the outermost surface of the backcoat layer. Therefore, the effect of reducing the area in which the backcoat layer directly contacts the magnetic surface (that is, chlorine ions and sulfate ions remaining in the backcoat layer act on the magnetic surface),
It is possible to suppress deterioration due to occurrence of deterioration of magnetic characteristics of the magnetic surface.

As a result, the dropout increase is small,
It is possible to ensure stable running properties and storage characteristics, and it is possible to provide an excellent high-density magnetic recording medium.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one structural example of a magnetic recording medium to which the present invention is applied.

FIG. 2 is a schematic cross-sectional view of a vacuum vapor deposition apparatus that can be used for forming a metal magnetic thin film of the magnetic recording medium.

FIG. 3 is a schematic view of a coating apparatus that can be used for forming a back coat layer of the magnetic recording medium.

[Explanation of symbols]

2 ... Ferromagnetic metal thin film, 3 ... Back coat layer, 10 ... Vacuum tank, 12 ... Non-magnetic support, 15 ... Cooling can, 18 ... Crucible, 19
... Metal magnetic material, 20 ... Electron gun, 21 ... Partition plate, 22 ... Mask, 23 ... Shutter, 24 ... Gas introduction pipe, 25 ... Exhaust port, 32 ...
Gravure roll, 33… Doctor blade, 34… Backup roll, 36… Dryer, 46… Paint for back coat layer

Claims (10)

[Claims] 1. A metal magnetic thin film is formed on one surface of a non-magnetic support, and a back containing chloride ions and sulfate ions is formed on the other surface of the non-magnetic support opposite to the metal magnetic thin film. A magnetic recording medium having a coat layer, wherein a fatty acid amide is added to the back coat layer. 2. The magnetic recording medium according to claim 1, wherein the fatty acid amide covers the surface of the back coat layer. 3. A back coat layer is formed by applying a coating material in which a non-magnetic pigment is dispersed in a binder, and a fatty acid is added to the coating material containing 0.1 to 20 ppm by weight of chlorine ion and sulfate ion, respectively. An amide is added,
The magnetic recording medium according to claim 1. 4. The amount of the fatty acid amide added to the paint is 0.01 to 10 parts by weight per 100 parts by weight of the binder.
2. The magnetic recording medium described in 1. above. 5. The magnetic recording medium according to claim 1, wherein the content of chlorine ion and the content of sulfate ion in the coating material are each 5 ppm by weight or less. 6. A metal magnetic thin film is formed on one surface of a non-magnetic support, and a back containing chlorine ions and sulfate ions is formed on the other surface of the non-magnetic support opposite to the metal magnetic thin film. A method for producing a magnetic recording medium, which comprises adding a fatty acid amide to a coating material for forming the back coat layer when producing a magnetic recording medium having a coat layer formed thereon. 7. The production method according to claim 6, wherein the surface of the back coat layer is covered with a fatty acid amide. 8. A fatty acid amide is added to the above coating containing 0.1 to 20 ppm by weight of chlorine ion and sulfate ion, respectively, when a back coat layer is formed by applying a coating composition in which a non-magnetic pigment is dispersed in a binder. The manufacturing method of Claim 6 which adds. 9. The amount of the fatty acid amide added to the paint is 0.01 to 10 parts by weight per 100 parts by weight of the binder.
Production method described in 1. 10. The production method according to claim 6, wherein the content of chlorine ion and the content of sulfate ion in the coating material are each 5 ppm by weight or less.