JPH08329447A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a magnetic recording medium having a smooth surface and satisfactory electromagnetic transducing characteristics. CONSTITUTION: In this magnetic recording medium with a coating type magnetic layer contg. iron-base magnetic metal powder on the nonmagnetic substrate, the powder discharges the max. amt. of moisture at 300-500 deg.C when it is heated in inert gas. This magnetic recording medium has a smooth surface and is excellent in magnetic characteristics and electromagnetic transducing characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium,
In particular, it relates to a coating type magnetic recording medium having a smooth medium surface and good electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium having a coating type magnetic layer is required to have a high recording density, the thickness of the magnetic layer is reduced and the surface of the magnetic layer is smooth.
Various magnetic recording media have been developed in order to obtain magnetic recording media having good magnetic characteristics and electromagnetic conversion characteristics. That is, various researches and developments have been conducted on coating compositions such as various dispersants and binders, dispersion methods, and the like in order to improve the surface characteristics of magnetic recording media. A magnetic metal powder mainly composed of iron having a large amount of magnetization is also used as a magnetic powder for a coating type magnetic recording medium. Water existing on the surface of the metallic magnetic powder is roughly classified into physically adsorbed water released at a relatively low temperature and chemically adsorbed water released at a relatively high temperature. Conventionally, regarding the surface property of the metal magnetic powder itself, physical adsorption water released at a relatively low temperature has been emphasized. However, with respect to the chemically adsorbed water of the magnetic metal powder, there is no appropriate evaluation method for the chemically adsorbed water, and the relationship with the surface property of the recording medium has not been clarified. For this reason, the optimum material design of the surface of the magnetic metal powder is still insufficient, and at present the magnetic recording medium having a smooth surface has not been obtained.

[0003]

As described above, in the magnetic recording medium, it is necessary to dilute the paint with a solvent to reduce the viscosity in order to reduce the thickness of the magnetic layer, but the dilution causes a problem of agglomeration of the paint. Becomes Moreover, the cohesive force is generated by the magnetic attractive force between the magnetic powders, so that there is a problem that the magnetic powder with a large magnetization amount will further agglomerate. It is necessary to make a dispersed state that does not progress, but at present it is that a sufficient dispersed state has not been obtained with a coating composition such as a dispersant / binder, a dispersing method, good dispersibility, A magnetic powder having a good magnetic layer surface property and excellent magnetic properties is expected.

[0004]

DISCLOSURE OF THE INVENTION In order to obtain a magnetic recording medium having a smooth surface state by obtaining a dispersed state that does not agglomerate even when diluted, the present inventors have earnestly studied, and as a result, magnetic powder containing iron as a main component. Focusing on the surface state of the magnetic powder, it was found that the water state of the magnetic powder greatly affects the dispersion of the magnetic powder, and when the metal magnetic powder is heated, the water released at a relatively high temperature (chemical adsorption The present inventors have found that a magnetic powder having a maximum value of (water) can achieve the object, and arrived at the present invention. That is, the present invention provides (1) a magnetic recording medium having a coating type magnetic layer containing a metallic magnetic powder mainly composed of iron on a non-magnetic support, wherein the metallic magnetic powder mainly composed of iron is in an inert gas. A magnetic recording medium characterized in that when heated, the moisture released at 300 to 500 ° C. is a metal magnetic powder having a maximum value. (2) A metal magnetic powder mainly composed of iron in an inert gas When heated, 300-50
The amount of water released at 0 ° C is 0.8 to 1.8 × 10 ^-5 mol /
The magnetic recording medium according to (1) above, wherein the water content is m ² and the water released at 400 to 500 ° C. has a maximum value.

The present invention is a metallic magnetic powder containing iron as a main component, and when heated in an inert gas (eg, N ₂ , He, Ar, etc.), the released water has a maximum value at 300 to 500 ° C. Things are used. And preferably 300-
The amount of water released at 500 ° C is 0.8 to 1.8 × 10 ^-5
Those having a mol / m ² and having a maximum value of water released at 400 to 500 ° C. are used. 300-500
When the amount of water released at 0 ° C. is less than 1.0 × 10 ⁻⁵ mol / m ² , the yield value of the magnetic coating becomes high and the surface of the magnetic layer becomes rough. If the water content is larger than 1.8 × 10 ^-5 mol / m ² , the magnetic powder will be reduced in the magnetization amount and / or the free water content will be increased, so that the magnetic coating material will be aggregated and the surface property of the medium will be adversely affected. make worse. These iron-based metal magnetic powders have a needle-like shape and have an average axial length of 0.04 to 0.25.
μm, the axial ratio is 3 to 10 on average, and the crystallite diameter by X-ray is 1
It is preferably from 00 to 250Å. As magnetic properties, coercive force (Hc) is about 1800 to 2500 Oe, saturation magnetization (σs) is about 120 to 180 emu / g, and specific surface area by BET method is about 50 to 80 m ² / g. Further, the magnetic metal powder may have an oxide film on its surface. The magnetic recording medium using the metal magnetic powder having such an oxide film is advantageous for the deterioration of the magnetic flux density due to the external environment such as temperature and humidity and the deterioration of the characteristics due to the rusting of the magnetic layer. In the present invention, the magnetic layer is usually formed by using only such metal magnetic powder, but if necessary, other magnetic powder, for example, metal magnetic powder or oxide magnetic powder is used together in an amount of 50% by weight or less. May be.

The iron-based metal magnetic powder of the present invention is mixed with a suitable binder and additives and coated on a non-magnetic support to form a magnetic layer. As the binder of the present invention, any binder such as a thermoplastic resin, a thermosetting resin or a reactive resin, or an electron beam curing resin used for forming the magnetic layer of this kind of magnetic recording medium can be used. As a thermoplastic resin, the softening temperature is 150 ° C.
Hereinafter, those having an average molecular weight of about 5,000 to 200,000 are preferable, and for example, vinyl chloride copolymers, polyurethane resins, (meth) acrylic resins, polyester resins, acrylonitrile-butadiene copolymers, polyamide resins, polyvinyl butyral, nitrocellulose, Styrene-butadiene copolymer, polyvinyl alcohol resin, acetal resin, epoxy resin, phenoxy resin, polyether resin, polyfunctional polyethers such as polycaprolactone, polyamide resin, polyimide resin,
Examples thereof include phenol resin, polybutadiene elastomer, chlorinated rubber, acrylic rubber, isoprene rubber, and epoxy modified rubber. Among these resins, a combination of vinyl chloride copolymer and polyurethane resin is most preferably used. The above vinyl chloride-based copolymer,
Vinyl chloride content of 60 to 90 wt%, especially 60 to 95
wt% is preferable, and the average degree of polymerization is 100 to 5
It is preferably about 00. Particularly, a copolymer of vinyl chloride and an epoxy (glycidyl) group-containing monomer is preferable. As such a vinyl chloride-based copolymer, one containing a sulfuric acid group and / or a sulfo group (hereinafter, S-containing polar group) as a polar group is preferable. The S-containing polar group, for example -SO ₄ Y, -SO ₃ Y (provided that, Y
Represents H or an alkali metal), and among these, —SO ₄ K and SO ₃ K are particularly preferable. Such an S-containing polar group is obtained by polymerizing vinyl chloride and another copolymerizable monomer in the presence of a radical generator having a strong acid radical containing S such as potassium persulfate and ammonium persulfate. You can These S-containing polar groups are present as S atoms in the molecule in an amount of 0.001 to 10% by weight, particularly 0.1.
It is preferable that the content is 01 to 5 wt%. In addition to the S-containing polar groups, -OPO ₂ Y group, -PO ₃ Y group, -COO
Y group (Y is H, alkali metal), amino group (-N
R ₂ ), —NR ₃ Cl (R is H, methyl, ethyl) and the like can be contained. Among them, the amino group may not be used in combination with the S-containing polar group and may be various groups, but a dialkylamino group (preferably an alkyl group having 1 to 10 carbon atoms) is particularly preferable. Such an amino group is usually obtained by modifying the amine, and is obtained by carrying out a saponification reaction of vinyl chloride / alkylcarboxylic acid vinyl ester in the presence of an amine compound. The vinyl unit having the amino group is 0.05 to 5 wt%,
As a result, an um base or an amine base may be contained.
Other copolymer components contained in such a vinyl chloride-based copolymer include vinyl acetate, (meth) acrylic acid ester, and vinyl alcohol obtained by saponification of vinyl acetate.

The polyurethane resin used in combination with the above-mentioned vinyl chloride resin is particularly effective in that it has good abrasion resistance and adhesion to a support, and such polyurethane resin is a polyester polyol and / or poly It is a general term for resins obtained by the reaction of a hydroxy group-containing resin such as ether polyol and a polyisocyanate-containing compound, and a synthetic raw material having a number average molecular weight of 500 to
Polymerized to about 200,000, and its Q value (weight average molecular weight / number average molecular weight) is about 1.5 to 4. Such polyurethane resins, polar group in its resin skeleton may be one having a hydroxyl group, the polar group, for example -SO ₃ M (sulfonic acid groups), - SO ₄ M (sulfuric acid group), As the phosphoric acid-containing polar group, a phosphonic acid group = P
O ₃ M, phosphinic acid group = PO ₃ M, phosphinic acid group =
POM, -P = (OM1) (OM2), -OP = O (O
M1) (OM2), - COOM , -NR 3 X, -NR 2,
It is preferable to use at least one polar group selected from —OH, epoxy group, —SH, —CN and the like (here, M, M1 and M2 are H, LI, Na, K and —NR.
₃ , -NHR ₂ ; R represents an alkyl group or H; X represents a halogen atom). Na is particularly preferable as M. These polar groups may be present either in the main chain of the skeletal resin or in the branches, and 0.001 to 10 wt%, particularly 0.02 to 3 w, in the molecule as atoms.
It is preferable that t% is included. Further, in this polyurethane resin, at least two kinds of polyurethane resins having different glass transition temperatures Tg within the range of -20 ° C ≤ Tg ≤ 80 ° C in the binder to be used, and the total amount of the polyurethane resin is the total amount of the binder. 10 to 90 wt% of the above, and by containing these plural polyurethane resins,
It is preferable in that a balance between running stability in a high temperature environment, calendar processability, and electromagnetic conversion characteristics can be obtained. Furthermore, it is preferable that the vinyl chloride copolymer and the polyurethane resin are mixed and used so that the weight mixing ratio is 10:90 to 90:10. In addition to these resins,
Various known resins may be contained in the range of 20 wt% or less of the whole.

As the thermosetting resin, polycondensation phenol resin, epoxy resin, polyurethane curable resin, carbon resin, butyral resin, formal resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, polyamide resin, Epoxy-polyamide resin, saturated polyester resin, urea formaldehyde resin and the like can be mentioned. Various polyisocyanates can be used as a cross-linking agent for curing such a binder resin, and one or more of tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, etc. can be used as trimethylol propane, etc. Crosslinking agent modified to have a plurality of hydroxyl groups, or diisocyanate compound 3
It is preferable to use a molecule-bonded isocyanurate-type cross-linking agent, and the content of the cross-linking agent is preferably 10 to 30 wt% with respect to 100 wt% of the resin. And the durability of the coating layer can be improved by three-dimensionally bonding with each other, and in order to carry out these crosslinking reactions, heating is generally performed in a heating oven at 50 to 80 ° C. for 6 to 100 hours, or at a low speed, ~ 120
It may be run in an oven at ℃. Further, it is also possible to use a copolymer obtained by introducing a (meth) acrylic double bond and subjecting it to electron beam-sensitive modification. Here, the acrylic double bond means a (meth) acryloyl group which is a residue of (meth) acrylic acid, a (meth) acrylic acid ester, and a (meth) acrylic acid amide. To perform this electron beam sensitive modification, tolylene diisocyanate (TD
I) and 2-hydroxyethyl (meth) acrylate (2
-HEMA) monomer modified to react with a reaction product (adduct) with HEMA), having at least one ethylenically unsaturated double bond and one isocyanate group in the molecule, and having no urethane bond in the molecule Improved urethane modification using (2-isocyanatoethyl (meth) acrylate etc.) and ester modification by reacting a resin having a hydroxyl group or a carboxylic acid group with a compound having a (meth) acrylic group and a carboxylic acid anhydride or dicarboxylic acid It is well known that the improved urethane modification among them is not brittle even if the content ratio of the vinyl chloride resin is increased, and a coating film having excellent dispersibility and surface property can be obtained. Therefore, it is preferable. Further, the content of the electronic functional group is 1 to 4 in the hydroxyl group component in view of stability during production, electron beam curability and the like.
0 mol%, preferably 10 to 30 mol%, especially 1 to 20 per molecule in the case of a vinyl chloride copolymer,
It is possible to obtain an electron beam curable resin having excellent dispersibility and curability by reacting the monomer so that it preferably has 2 to 10 functional groups. When these electron beam sensitive modified resins are used, 1 to 50 wt% of a conventionally known polyfunctional acrylate may be mixed and used in order to improve the crosslinking rate.

An electron beam is used as a radiation source for curing when an electron beam sensitive modified resin is used as a binder, from the viewpoint of controlling absorbed dose, introducing it into a manufacturing process line, and shielding ionizing radiation. The method and / or the method using ultraviolet rays are advantageous, in the case of electron beams an accelerating voltage of 100 KV to 750 KV, preferably 150 to 30.
Absorbed dose is 20 ~ 200 using 0KV electron beam accelerator
It is convenient to irradiate so that it is a kilogray. When electron beam cross-linking is performed, N ₂ having an oxygen concentration of 1% or less,
It is important to irradiate with an electron beam in an atmosphere of an inert gas such as He or CO ₂ , and this is to prevent O ₃ or the like generated by the electron beam irradiation from trapping radicals. On the other hand, when ultraviolet rays are used, a conventionally known photopolymerization sensitizer is added to the binder containing the electron beam curable resin, and the irradiation is performed using ultraviolet rays such as xenon discharge tubes and hydrogen discharge tubes. A light bulb or the like may be used. The magnetic layer may appropriately contain known additives such as a dispersant, a lubricant, a surfactant, an antistatic agent, the inorganic fine particles as a surface improving agent, other additives and a solvent.

For the non-magnetic support of the present invention, known films of polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefins, polyamides, polyamide imides, polysulfone cellulose triacetate, polycarbonates and the like are used. Of these, PET,
PEN and aromatic polyamides are preferable, and composite films formed by multi-layer coextrusion of 2 to 3 kinds of PET or PEN are particularly preferable. When these films are used, electromagnetic conversion characteristics, durability, friction characteristics, film strength, Good balance of productivity. In addition, it is preferable to add inorganic compounds such as oxides and carbonates of Al, Ca, Si, Ti and the like, organic compounds such as fine particles of acrylic resin and the like to the non-magnetic support as fillers. It becomes possible to freely control the surface property by the size and size, and as a result, it becomes possible to control the electromagnetic conversion characteristics, durability, friction characteristics and the like. Furthermore, these non-magnetic supports have been previously treated with corona discharge treatment,
Plasma discharge and / or polymerization treatment, easy adhesive coating treatment, dust removal treatment, relaxation treatment by heat and / or humidity adjustment, etc. may be performed. The surface roughness of the non-magnetic support is a center line average roughness Ra of preferably 0.03 μm or less, more preferably 0.02 μm or less, and further preferably 0.01 μm.
m or less. Further, it is preferable that not only the surface roughness is small, but also there is no coarse protrusion of 0.5 μm or more.
Also, 100 ° C in the longitudinal and width directions of the non-magnetic support
The heat shrinkage at 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage at 80 ° C./30 minutes is preferably 1% or less, more preferably 0.5%. % Or less. The thickness of the non-magnetic support is 4.0 to 75.0 μm
It is preferred that If it is too thin, the mechanical strength of the magnetic recording medium cannot be maintained and the durability will decrease. If it is too thick, the total thickness of the magnetic recording medium becomes too thick, and the recording amount per unit volume decreases, which is not preferable. An undercoat layer may be provided on the magnetic layer of the present invention. Any known composition can be used for the undercoat layer, and the undercoat layer is composed of a known additive such as a non-magnetic inorganic substance, a lubricant, a surfactant, a conductive material and a dispersant, a binder and a solvent. The same binder as that of the magnetic layer may be used as the binder of the undercoat layer.

[0011]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Measurement method < Measurement method of moisture> Measurement of moisture desorption curve 50 mg of magnetic powder was placed in a sealed container, a sample with nitrogen as a carrier gas was heated at 1.5 ° C / min, and water contained in nitrogen was measured by TCD. (Thermal conductivity detector
Thermal conductivity detector). Next, the water content per unit weight of the magnetic powder up to 200 ° C. was determined by the Karl Fischer measurement method. The amount of magnetic powder is 100 mg, the measuring devices are Mitsubishi Chemical Corporation's trace moisture measuring device CA-05 and moisture vaporizing device VA-05, and the vaporizing temperature is 20 in a nitrogen gas stream.
It was measured at 0 ° C. Next, the amount of water released at 300 to 500 ° C was determined by the following procedure. The water content corresponding to the area from the room temperature to 200 ° C. of the water desorption curve is set equal to the water content determined by the Karl Fischer measurement method, and the water content per unit area (A) of the water desorption curve is determined.

[0012]

Embedded image

The area of the water desorption curve at 300 to 500 ° C. is obtained, and the amount of water (B) released at 300 to 500 ° C. is obtained from the value obtained at. B = area of moisture desorption curve from 300 to 500 ° C. × A <Magnetic characteristics> Using VSM manufactured by Toei Industry Co., Ltd., magnetic measurement was performed at an applied magnetic field of 10 kOe to measure the squareness ratio Br / Bm. <Electromagnetic conversion characteristics> Hi-8 deck (EV manufactured by Sony Corporation)
S-900) was used to measure the reproduction output of a recording signal having a wavelength of 7 MHz. <Surface roughness> Using a surface roughness meter (Rank Taylor Hobson Taristep), the surface roughness Ra (J
ISB06) was measured. (Stylus: 0.1 × 5 μm HPF: 167 μm LPF
3.3 μm) <Measurement of specific surface area> The specific surface area (surface area per unit weight) of the magnetic powder was measured by BET method using Multisorb 12 manufactured by Yuasa Ionics Co.
It was degassed with and measured by the adsorption amount of a mixed gas of N ₂ / He = 3: 7. The magnetic powders used in Examples and Comparative Examples of the present invention are shown in Table 1.

[0014]

[Table 1]

FIG. 1 shows the amount of water released from the magnetic powder used in Examples 1 to 3 and Comparative Example when heated, the maximum value and the temperature. FIG. 1 is a desorption curve of water in which 50 mg of magnetic powder was heated in a sealed container at 1.5 ° C./min in the presence of a nitrogen carrier gas, and the water contained in nitrogen was detected by TDC. << Preparation of Magnetic Recording Medium >> (1) Magnetic layer provided on support through non-magnetic layer A magnetic recording medium (magnetic tape) was prepared using the above magnetic powders A to D. A part or all of the following magnetic layer composition was kneaded with each of the metal magnetic powders by a kneader, and then dispersed, mixed and diluted with a sand mill to prepare each magnetic coating material. <Magnetic layer composition> Metal magnetic powder 100.0 parts by weight Vinyl chloride copolymer (containing potassium sulfate) 8.3 parts by weight (MR-110 manufactured by Nippon Zeon Co., Ltd.) Polyester polyurethane resin (containing sodium sulfonate) 8 .3 parts by weight (UR-8700 manufactured by Toyobo Co., Ltd.) α-alumina 5.0 parts by weight (HIT-60A manufactured by Sumitomo Chemical Co., Ltd.) 1.0 part by weight stearic acid 1.0 part by weight butyl stearate Methyl ethyl ketone 111.0 parts by weight Toluene 111.0 parts by weight Cyclohexanone 74.0 parts by weight 3.3 parts by weight of a curing agent (Coronate L; manufactured by Nippon Urethane Industry Co., Ltd.) was mixed and added to the obtained paint, and two more were added. Polyethylene terephthalate (thickness: 7.5 μm) with the non-magnetic lower layer paint shown below using an extrusion nozzle
On top, magnetic layer thickness 0.2 μm, non-magnetic lower layer thickness 2.0 μm
It was applied by a wet-on-wet method so as to have a (dry thickness), and thereafter, orientation, drying, calendering and curing were performed. <Nonmagnetic layer composition> 100.0 parts by weight of acicular α-iron oxide powder (DPN250BX manufactured by Toda Kogyo Co., Ltd. average major axis length 0.15 μm, axial ratio = 6.5) Vinyl chloride copolymer (containing potassium sulfate) ) 8.3 parts by weight (MR-110 manufactured by Nippon Zeon Co., Ltd.) Polyester polyurethane resin (containing sodium sulfonate) (UR-8700 manufactured by Toyobo Co., Ltd.) 4.7 parts by weight Polyester polyurethane resin (containing sodium sulfonate) ) (UR-8200 manufactured by Toyobo Co., Ltd.) 4.7 parts by weight α-alumina 5.0 parts by weight (HIT-60A manufactured by Sumitomo Chemical Co., Ltd.) Stearic acid 1.0 part by weight Butyl stearate 1.0 Parts by weight methyl ethyl ketone 88.0 parts by weight toluene 88.0 parts by weight cyclohexanone 60.0 parts by weight A curing agent (coronate; Japan 4.7 parts by weight of Polyurethane Co., Ltd. was mixed and added. The thus-prepared raw fabric was cut into a magnetic tape having a width of 8 mm, and the following characteristics were evaluated. Table 2 shows the results.

[0016]

[Table 2]

(2) Magnetic Layer Directly Provided on Support A single-layer magnetic recording medium (magnetic tape) was prepared using the magnetic powders of the above-mentioned magnetic powders A to D. After kneading a part or all of the following magnetic layer composition in each of the metal magnetic powders with a kneader, dispersing, mixing, and diluting with a sand mill,
Each magnetic paint was created. Metal magnetic powder 100.0 parts by weight Vinyl chloride copolymer (containing potassium sulfate) 8.3 parts by weight (MR-110 manufactured by Nippon Zeon Co., Ltd.) Polyester polyurethane resin (containing sodium sulfonate) 8.3 parts by weight ( UR-8700 Toyobo Co., Ltd. α-alumina 8.0 parts by weight (HIT-60A Sumitomo Chemical Co., Ltd.) Stearic acid 1.0 part by weight Butyl stearate 1.0 part by weight Methyl ethyl ketone 96.4 parts by weight Parts Toluene 96.4 parts by weight Cyclohexane 64.2 parts by weight 3.3 parts by weight of a curing agent (Coronate L; manufactured by Nippon Polyurethane Industry Co., Ltd.) is mixed and added to the obtained coating material to give a dry thickness of 2.0 μm. As shown above, it is applied on a polyethylene polyethylene terephthalate film having a thickness of 7.5 μm by an extrusion nozzle, and orientation, drying, calendering and curing are performed. Was Tsu. The thus-prepared original fabric was cut into a width of 8 mm to obtain a magnetic tape, and the magnetic tape was evaluated. The results are shown in Table 3.

[0018]

[Table 3]

As is clear from Tables 2 and 3, the water content released at 300 to 500 ° C. according to the present invention has a maximum value, particularly the water content released at 300 to 500 ° C. is 0.
In the case of using the magnetic powder having a maximum value of 8 to 1.8 × 10 ⁻⁵ mol / m ² and water released at 400 to 500 ° C., the squareness ratio Br / Bm, surface roughness (Ra), electromagnetic It also has excellent conversion characteristics.

[0020]

When heated according to the present invention, 300 to 500
A magnetic recording medium using a metal magnetic powder mainly composed of iron having a maximum value of water released at ° C has a smooth surface and is excellent in magnetic characteristics, electromagnetic conversion characteristics and the like.

[Brief description of drawings]

FIG. 1 is a moisture desorption curve showing the relationship between the temperature of a magnetic powder detected by TDC and the moisture release.

[Drawing reference number]

 a Magnetic powder of Examples 1 and 4 b Magnetic powder of Examples 2 and 5 c Magnetic powder of Examples 3 and 6 d Magnetic powder of Comparative Examples 1 and 2

Claims (2)

[Claims] 1. A magnetic recording medium having a coating type magnetic layer containing iron-based metallic magnetic powder on a non-magnetic support, wherein the iron-based metallic magnetic powder is heated in an inert gas. In this case, the magnetic recording medium is characterized in that the moisture released at 300 to 500 ° C. is a metal magnetic powder having a maximum value. 2. When the metallic magnetic powder mainly composed of iron is heated in an inert gas, the amount of water released at 300 to 500 ° C. is 0.8 to 1.8 × 10 ⁻⁵ mol / m ^2. And 400
The magnetic recording medium according to claim 1, wherein the moisture released at ˜500 ° C. has a maximum value.