JPH03203015A - Discoid magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and durability and to reduce dropout by incorporating polyurethane resin, chromium oxide particles and magnetic powder into a magnetic layer and dispersing the chromium particles into a binder. CONSTITUTION:The medium has a magnetic layer 24 composed of metal mag netic powder dispersed in the binder. The magnetic layer 24 incorporates a first binder composed of polyurethane resin having at least one polar group selected from a group of -SO3M, -OSO3M, -COOM, -PO(OM')2, and -OPO(OM')2 (wherein M and M' are hydrogen atom or alkali metal atom), chromium oxide particles having 0.3-0.5 mum mean particle size, and metal powder composed essentially of iron and incorporating aluminum. The chromium oxide particles are preliminarily dispersed in a second binder.

Description

[Detailed description of the invention] It is.

BACKGROUND ART Conventionally, as a disk-shaped magnetic recording medium for still videos, computers, etc., there has been a magnetic recording medium in which a magnetic layer in which ferromagnetic alloy powder is dispersed in a binder is coated on a non-magnetic support. It is used. Recently, as the density and S/N of such magnetic recording media have increased, magnetic materials have been made into finer particles. Rising drop ala l- (Dlo),
Problems such as head clogging and decreased durability occur.

Furthermore, since the ferromagnetic alloy powder originally does not have very good dispersibility in the binder, it is actually difficult to obtain the expected electromagnetic conversion characteristics.

As a measure to prevent the above-mentioned decrease in durability, head clogging, etc., conventional AI-to3. S i C1
It has been proposed to add abrasives such as Cr, O, etc. to the magnetic layer, but adding a large amount of such abrasives may cause deterioration in the filling degree and dispersibility of the magnetic powder in the magnetic recording medium. Accordingly, deterioration of electromagnetic conversion characteristics due to deterioration of surface properties becomes a problem.

Also, if you reduce the amount of abrasive added to improve the surface quality,
Although the electromagnetic conversion characteristics are improved, sufficient abrasiveness cannot be obtained, resulting in decreased durability and insufficient prevention of head clogging.

On the other hand, Cr, O, and particles inherently require time to disperse, and if magnetic paint is prepared with this dispersion in mind, not only is the efficiency poor, but the magnetic powder may break and its magnetic properties deteriorate. There is a risk of Moreover, if CrzO3 particles are added as they are, the surface of the magnetic layer will become rough due to poor dispersion, and CrzO3 particles may become rough.
The z particles themselves are missing, causing dropouts and the like.

Objectives of the invention The objectives of the invention are to improve durability, reduce head clogging,
An object of the present invention is to provide a disk-shaped magnetic recording medium that achieves a reduction in Dlo and has high electromagnetic conversion characteristics, and a method for manufacturing the same.

20 Structure of the Invention That is, the present invention provides a disk-shaped magnetic recording medium having a magnetic layer in which metal magnetic powder is dispersed in a binder.
505M, -030,M, -COOM, PO(OM')
, and -○PO(oM')z (provided that M and M' are hydrogen atoms or alkali metal atoms). of binder and an average particle size of 0.3 to 0.
．． The magnetic layer contains chromium oxide particles having a diameter of 5 μm and metal magnetic powder mainly composed of iron and containing aluminum, and the chromium oxide particles are dispersed in a second binder in advance. This relates to a disk-shaped magnetic recording medium contained in.

The present invention also provides metal magnetic powder and -3O,M.

It has at least one polar group selected from the group consisting of 0303M, C00M, PO(OM')z and -0PO(OM"h (where M and M' are hydrogen atoms or alkali metal atoms). A first binder made of polyurethane resin and an average particle size of 0.3 to 0.5 μm
When producing a disk-shaped magnetic recording medium in which the magnetic layer contains chromium oxide particles falling within the range of The present invention also provides a method for manufacturing a disk-shaped magnetic recording medium, in which the magnetic coating composition is added to the magnetic coating material for the magnetic layer in a state in which it is dispersed in a binder.

According to the disk-shaped magnetic recording medium of the present invention, metal magnetic powder (ferromagnetic alloy powder) such as Fe-Af type is used as the magnetic powder of the magnetic layer.
e-Al system, Fe-Al-Ni system, Fe-Al-Zn system, Fe-Al-C.

system, Fe-Ni-Al system, FeFe-Ni-3i-Af
- system, Fe-Ni -S i -AX-Zn system, Fe-
Aj! Examples include -3i series, Fe-Af-Ca series, and the like.

These have excellent corrosion resistance and dispersibility. Furthermore, due to the aluminum content, the coercive force is high and the hardness itself is relatively large, and the running durability of the electromagnetic conversion characteristics is improved.

The content ratio of Fe atoms and Al atoms contained in the ferromagnetic metal powder is in the atomic ratio of Fe:Al=100:1 to 100:20, and the surface area is 100λ or less in analysis depth by ESCA of the ferromagnetic metal powder. The content ratio of Fe atoms and Al atoms present in the atomic number ratio is Fe:Ai, = 30 near 0 to 7
It has a structure of 0:30.

The ferromagnetic alloy powder used in the present invention is 40rd/g.
It is preferable to use a material having a specific surface area (BET value) of the above value.

Furthermore, by using the above-mentioned ferromagnetic alloy powder having a specific surface area (BET value) of 42rd/g or more, the electromagnetic conversion characteristics are greatly improved. In addition, the coercive force (coercive force) of the ferromagnetic metal powder is usually 10,000e or more (preferably 12,000e or more).
e or more).

Further, there is no particular restriction on the shape of the magnetic powder that can be used in the present invention, and for example, acicular, spherical, etc. can be used.

The reduction in polishing power due to the finer particles of the ferromagnetic alloy powder as described above can be effectively prevented by adding chromium oxide (Crz03) particles with an average particle size of 0.3 to 0.5 μm.
The durability of the magnetic layer can be greatly improved.

These chromium oxide particles have superior abrasive power compared to alumina, etc., and can prevent magnetic powder dropouts and head clogging. It should be .3 μm or more, and it should be 0.5 μm or less in terms of head wear prevention and electromagnetic conversion characteristics.

Only with such an average particle size range can a disk-shaped magnetic recording medium for magnetic disks withstand much harsher usage conditions than magnetic tape or the like.

The average particle size of this chromium oxide is further 0.32 to 0.45μ
It is more preferable that m is less than 0.35 to 0.40 μm.

In addition, as a method for measuring the average particle size, the cross section of the magnetic layer is observed with an electron microscope and the diameter of each particle is measured.
The average value of the major diameters of individual chromium oxide particles is defined as the "average particle diameter."

The amount of chromium oxide added is 2 parts per 100 parts by weight of magnetic powder.
It is preferably 0 parts by weight or less, and even more preferably 10 to 13 parts by weight.

Since the magnetic powder used in the present invention is the above-mentioned alloy magnetic powder,
Although it is difficult to perform sufficient dispersion, this can be sufficiently prevented by the above-mentioned polyurethane resin, and the dispersibility can be improved.

That is, the polyurethane resin used is the above-mentioned 15o, M
, -osoi M, -COOM.

-PO(OM"h, OPO(OM')! (where M is hydrogen or an alkali metal such as lithium, potassium, or sodium; M' is an alkali metal such as hydrogen, lithium, potassium, or sodium); a negative functional group consisting of Contains one or more types of (hydrophilic polar groups).These polar groups in the molecule improve the compatibility between the resin and the magnetic powder, which improves the dispersibility of the magnetic powder and improves the magnetic properties. Powder aggregation can also be prevented, thereby further improving the stability of the coating liquid and, in turn, improving the durability of the medium.

Regarding the base of such a polyurethane resin, a reaction between a polyol and a polyisocyanate, which is a commonly used method, can be used. As the polyol component, generally used is a polyester polyol obtained by the reaction of a polyol and a polybasic acid. Therefore, if the above-mentioned polyester polyol having a polar group is used as a raw material, a polyurethane having a polar group can be produced.

Polyols that can be used include organic dibasic acids such as phthalic acid, adipic acid, trimerized lyluic acid, and maleic acid;
Glycols such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, trimethylolpropane, hexanetriol,
A polyester polyol obtained by reaction with polyhydric alcohols such as glycerin, trimethylolethane, and pentaerythritol, or any two or more polyols selected from these glycols and polyhydric alcohols; or, Lactone polyester polyols derived from lactams such as S-caprolactam, a-methyl-1-caprolactam, S-methyl-3-caprolactam, and T-butyrolactam; These polyols include tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMD), methylene diisocyanate, metaxylylene diisocyanate,
Diphenylmethane-4,4'-diisocyanate (MD
I), 1,5-naphthalene diisocyanate (NDI)
, tolisine diisocyanate (TODI), lysine isocyanate methyl ester (LDI), etc., resulting in urethanized polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate. be synthesized. These polyurethanes are usually produced primarily by the reaction of polyisocyanates and polyols and are also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups, or containing reactive end groups of these. (for example, in the form of a urethane elastomer).

Since the methods for producing polyurethane, urethane prepolymers, urethane elastomers, curing and crosslinking methods, etc. are well known, detailed explanation thereof will be omitted.

Alternatively, for example, a polyurethane resin into which polyfunctional -OH has been introduced is produced, and this polyurethane resin is reacted with a compound containing a polar group and chlorine described below (dehydrochloric acid reaction) to impart a polar group to the polyurethane resin. You can use the method of introduction.

C/:CH2CHz 303M.

cxcHz　CHz　0303　M.

C1, CHl C00M.

cpcHz po (aM”)z The weight average molecular weight of this polyurethane resin is generally 1
It is preferable to set the reaction conditions so as to fall within the range of 150,000 to 150,000 (preferably 20,000 to 60,000).

In addition, the above polyurethane resin usually has a content of repeating units having polar groups in the copolymer from 0.01 to
The content is preferably within the range of 5 mol% (preferably 0.1 to 2.0 mol%).

Regarding the introduction of polar groups into polyurethane, please refer to Japanese Patent Publication No. 5B-41565, Japanese Patent Publication No. 57-92422, Japanese Patent Publication No. 57-92423, Japanese Patent Publication No. 59-8127, Japanese Patent Publication No. 59-5.
No. 423, No. 59-5424, No. 62-121923
There are descriptions in publications such as No., and these can also be used in the present invention.

The above-mentioned polyurethane resin improves the abrasion resistance of the magnetic layer and can also impart appropriate flexibility.

When a vinyl chloride resin is used in combination with this polyurethane resin, the magnetic powder can be well dispersed, and
The mechanical strength of the magnetic layer can be improved. In this case, the weight ratio of vinyl chloride resin and polyurethane resin is usually 80:20 to 20:80 (preferably 70:20 to 20:80).
: 30 to 40 : 60).

Usable vinyl chloride resins can be synthesized by adding to a copolymer containing an OH group, such as a vinyl chloride-vinyl alcohol copolymer, by reaction with a compound containing a polar group and a chlorine atom, as shown below. can do.

CI　CHz　CHz　S　Os　M.

CI　CHt　CHz　OS　Os　M.

(IcH, PO(OM”).

Cl2CH, C00M.

Taking CICHt CHt SOz Na as an example, (CHzCH) + C1(CHz)z 5OJ
aH → −(CL-CI) + HCAO(CH
z) z 5OJa.

Alternatively, there is a method of copolymerizing all of them as copolymerizable monomers. That is, a predetermined amount of a reactive polymer having an unsaturated bond into which a repeating unit containing a polar group is introduced is poured into a reaction vessel such as an autoclave, and a polymerization initiator such as BPO (benzoyl peroxide), etc. AIBN(
Polymerization can be performed using a polymerization initiator such as a radical polymerization initiator such as azobisisobutyronitrile), a redox polymerization initiator, an anionic polymerization initiator, or a cationic polymerization initiator. For example, specific examples of reactive monomers for introducing sulfonic acid or its salts include unsaturated hydrocarbon sulfonic acids such as vinylsulfonic acid, allylsulfonic acid, methacrylsulfonic acid, p-styrenesulfonic acid, and salts thereof. can be mentioned.

Furthermore, sulfoalkyl esters of acrylic acid or methacrylic acid such as 2-acrylamido-2-methylpropanesulfonic acid, (meth)acrylic acid sulfoethyl ester, (meth)acrylic acid sulfopropyl ester, salts thereof, or acrylic acid. -2-ethyl sulfonate, etc. can be mentioned.

When introducing carboxylic acid or its salt (introduction of COOM), (meth)acrylic acid, maleic acid, etc. are used, and when phosphoric acid or its salt is introduced, (meth)acrylic acid-2-phosphate ester is used. good.

Further, it is preferable that an epoxy group is introduced into the vinyl chloride copolymer. Introduction of epoxy groups improves the thermal stability of vinyl chloride copolymers. When introducing an epoxy group, the content of repeating units having epoxy groups in the copolymer is preferably 1 to 30 mol% (more preferably 1 to 20 mol%). Glycidyl acrylate is preferably used as the monomer for introduction.

Regarding the introduction of polar groups into vinyl chloride copolymers, please refer to JP-A Nos. 57-44227, 58-108052, 59-8127, 60-101161, 6
No. 0-235814, No. 60-238306, No. 60
-238371, 62-121923, 62-
There are descriptions in publications such as No. 146432 and No. 62-146433, and these can also be used in the present invention.

In the present invention, in addition to the binder described above, conventionally used unmodified vinyl chloride resins, polyurethane resins, or polyester resins may be used in combination, and cellulose resins, phenoxy resins, or specific Thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, and the like may be used in combination.

In the present invention, the above-mentioned modified polyurethane resin is
As a binder, the above-mentioned alloy magnetic powder is dispersed in a binder whose main component is this first binder, and the above-mentioned chromium oxide particles are previously dispersed in a separately prepared second binder. It is important to mix and add this dispersion with the magnetic powder dispersion.

That is, while the alloy magnetic powder can be sufficiently dispersed with the above-mentioned modified polyurethane resin, in order to pre-disperse the chromium oxide particles, which originally require time to disperse, the chromium oxide particles are already dispersed in the binder. This means that it can be added in a sufficiently dispersed state. Therefore, the magnetic paint can be prepared in a short time and more than adequately.

CrtO used in the present invention is inherently difficult to disperse, and the time and conditions required for dispersion are different from those of ferromagnetic metal alloy powder. For sufficient dispersion, Crt
Os requires about 3 to 5 times as long as ferromagnetic metal powder. However, conventionally, in order to disperse together with the ferromagnetic metal alloy powder, the dispersion time and conditions of the ferromagnetic metal powder are adjusted. If we adjust this to the dispersion conditions of CrzOz, we get
Poor dispersion of the ferromagnetic metal alloy powder may occur, or if the dispersion times are adjusted, the ferromagnetic metal alloy powder may break, resulting in a significant deterioration of electromagnetic conversion characteristics. For this reason, conventionally, Cr and O exist in magnetic paints in a state where they are not sufficiently dispersed.

In this case, if the CrzOs is aggregated, it will protrude to the surface of the magnetic layer, impairing the smoothness of the magnetic layer and worsening the electromagnetic conversion characteristics. This results in a decrease in the yield of the magnetic disk.

Therefore, in the present invention, CrzO= is sufficiently dispersed in advance as a separate dispersion under optimal conditions, and then added to the dispersion of ferromagnetic metal alloy powder (coating liquid composition for forming a magnetic layer). .

The method of dispersion treatment is not particularly limited, and the order of addition of various components such as dispersions of Cr, O, etc. can be determined as appropriate. However, to mix completely, Crt
It is more preferable to further disperse after adding the dispersion of O. Equipment used for dispersion processing includes, for example, two-roll mills, three-roll mills, ball mills, thoron mills, sand grinders, high-speed impellers, high-speed stone mills, dispersion gourds, high-speed mixers, ribbon blenders, co-kneaders, and intensive mixers. -, tumblers, blenders, dispersers, homogenizers, ultrasonic dispersers, etc., which can be appropriately selected and used for carrying out the present invention.

The second binder used for this pre-dispersion of chromium oxide is preferably a binder having a polar group, such as a modified polyurethane resin similar to the first binder. The number may be less than the first binder. Note that this second binder may be made of an unmodified polyurethane resin or other resins mentioned above.

In addition to the magnetic powder and binder described above, the magnetic layer contains a lubricant (
For example, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, basic fatty acids (such as stearic acid), fatty acid esters, etc. may be added.

In addition, alumina (α-AI!
t O+ (corundum), etc.), artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond,
α-Fe, O.

(hematite), artificial diamond, garnet, emery (main components: corundum and magnetite), etc. may also be used in small amounts. An antistatic agent such as carbon black may be added to the magnetic layer.

Solvents that can be used in magnetic paints (and paints for back coat layers, etc. described later) include ketones (e.g. methyl ethyl ketone), ethers (e.g. diethyl ether), esters (e.g. ethyl acetate), aromatic solvents ( Examples include toluene), alcohols (eg methanol), and these can be used alone or in combination.

For example, the disk-shaped magnetic recording medium of the present invention is shown in FIG.
As shown, magnetic layers 24 are provided on both sides of a non-magnetic support 21 via an intermediate layer 22 if necessary. If necessary, an overcoat layer (not shown) may be further provided on the magnetic layer.

The dry film thickness of the magnetic layer 24 is preferably from 0.5 to 4.5 μm, and even more preferably from 3.0 to 4.0 am.

When providing the intermediate layer 22 under the magnetic layer, an undercoat layer may be formed by coating the various binders described above. This intermediate layer is provided as an adhesive layer or an undercoat layer for the purpose of improving adhesiveness between the magnetic layer and the support, improving conductivity, and the like.

Examples of materials for the support 21 include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polycarbonate. be able to. Furthermore, Cu,
Non-magnetic metals such as Al and Zn, glass, so-called new ceramics, etc. can also be used.

The thickness of the support formed using these materials is usually 1
It is within the range of 0 to 80 μm.

A magnetic layer is provided on at least one surface of the support, but usually the other surface also has a magnetic layer as described above. By providing magnetic layers on both sides in this manner, deformation (curling) of the magnetic disk can be effectively prevented. However, it is also possible to prevent curling by providing a back coat layer on the back surface.

Note that the present invention may be applied to magnetic disks such as video floppies and data floppies for electronic still cameras, for example.

E, Example The present invention will be explained in detail below.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention.

(Example 1) The components of the paint (1) shown below were thoroughly kneaded and dispersed using a disperser and a ball mill, and chromium oxide (C
Paint (1), which is a homogeneous dispersion of Rtes) powder, was prepared.

10 parts by weight of chromium oxide (CrzOs)
Average particle size: 0.4 μm) Polyurethane 2 parts by weight (UR8200 manufactured by Toyobo Co., Ltd., containing -SOg Na group) Cyclohexanone 6 parts by weight Methyl ethyl ketone 3 parts by weight Toluene
3 parts by weight On the other hand, the following paint (II
) are sufficiently kneaded and dispersed using a disperser kneader and a ball mill, and during the process, the coating material (1) obtained as above is added, and the dispersion treatment is continued to obtain a uniform dispersion as a whole. was prepared. Then, immediately before coating, 5 parts by weight of a polyisocyanate compound (Coronate, manufactured by Nippon Polyurethane) was added and mixed to prepare a magnetic paint.

Ichikuri Beni 11 iron-aluminum ferromagnetic alloy powder (aluminum content: 4% by weight, specific surface area: 47 bo/g, coercive force (Hc): 12500e) 100 parts by weight Polyurethane 6 parts by weight (Toyobo Co., Ltd.) 10 parts by weight of vinyl chloride copolymer (UR8300, manufactured by Nippon Zeon Co., Ltd., containing -5O3Na group) 0.5 parts by weight of carbon black (MRIIO, manufactured by Nippon Zeon, containing -5O, Na group) (average particle size: 55 nm)
, BET specific surface area: 32r+f/g, DBP oil absorption: 180. wffi/100g)
Oleic acid 1 part by weight Butyl stearate 1 part by weight Cyclohexanone 100 parts by weight Methyl ethyl ketone 100 parts by weight Toluene
100 parts by weight of the obtained magnetic paint was filtered to remove poorly dispersed components, and coated on both sides of a polyethylene terephthalate film (thickness: 32 μm) using a reverse roll coater so that the dry thickness of each layer was 3.5 μm. After the solvent was removed under heating, a calendering process was carried out, followed by heat curing for the polyisocyanate compound.

After heating and curing, it was punched out into a disk shape of 2 inches in diameter and placed in a cassette to produce an electronic still video floppy.

(Example 2) In the paint [11] of Example 1, except that polyurethane containing -COOH groups (TIM-6001 manufactured by Sanyo Kaoru Co., Ltd.) was used instead of polyurethane containing -3o and Na groups. produced an electronic still video floppy in the same manner.

(Example 3) In the paint (1) of Example 1, polyurethane UR82
An electronic still video floppy was produced in the same manner except that polyurethane containing a -5Os Na group (UR8300 manufactured by Toyobo Co., Ltd.) was used instead of 00.

(Example 4) In the paint [I] of Example 1, the average particle size was 0.38 μm.
Cr with an average particle size of 0.30 um instead of Cr, O,
,0. An electronic still video floppy was manufactured in the same manner except that .

(Example 5) In the paint (1) of Example 1, the average particle size was 0.38 μm.
Cr, O, with an average particle size of 0.50tIm
An electronic still video floppy was manufactured in the same manner except that r, O, was used.

(Example 6) In the paint [I] of Example 1, the same 30. An electronic still video floppy was produced in the same manner except that polyurethane containing no Na group was used.

(Example 7) An electronic still video floppy was manufactured in the same manner as in Example except that polyurethane containing -3O groups was used instead of polyurethane containing -5Ox Na groups.

(Example 8) An electronic still video floppy was produced in the same manner as in Example 1 except that polyurethane containing OS Os Na groups was used instead of polyurethane containing -801Na groups in the paint [■]. .

(Example 9) In the paint (11) of Example 1, P O (ON a ) was used instead of the polyurethane containing -3o and Na groups.
An electronic still video 7o tube was produced in the same manner except that polyurethane containing a z group was used.

(Example 10) An electronic still video was produced in the same manner as in Example 1 except that polyurethane containing -0PO(ONa)z groups was used instead of polyurethane containing -3O,Na groups. Manufactured Fronby.

(Comparative Example 1) An electronic still video floppy was produced in the same manner as in Example 1 except that N2301 (manufactured by Nippon Polyurethane ■) was used instead of the -303Na group-containing polyurethane in paint [II].

(Comparative Example 2) In the paint [■] of Example 1, the average particle size was 0.38 μm.
Cr with an average particle size of 0.25 μm instead of Cr, O,
An electronic still video floppy was manufactured in the same manner except that z○ was used.

(Comparative Example 3) In the paint (1) of Example 1, the average particle size o was 38 μm.
Cr, 0. Cr with an average particle size o of 55 μm instead of
,0. An electronic still video floppy was manufactured in the same manner except that .

(Comparative Example 4) An electronic still video was produced in the same manner as in Example 1 except that the following iron-nickel ferromagnetic alloy powder was used instead of the iron-aluminum ferromagnetic alloy powder in the paint (n). Manufactured floppies.

Iron-nickel based ferromagnetic alloy powder (100 parts by weight, nickel content: 4% by weight, specific surface area = 47bo/g, coercive force (Hc): 12500e) (Comparative Example 5) Paint [1] of Example 1 Not used, Cr in paint (If)
An electronic still video floppy was manufactured in the same manner except that z03 was added in powder form to prepare a magnetic coating.

(Comparative Example 6) In Example 1, CrzO3 with an average particle size of 0.38 μm
An electronic still video floppy was produced in the same manner except that AltO3 having an average particle size of 0.38 μm was used instead.

The following performance evaluations were performed on each of the above video floppies, and the results are shown in Table 2 below.

Seek commercially available electronic still video floppy recorder (AG8
00, manufactured by Matsushita Electric Industrial ■), the image signal is
In the still mode of the electronic still video floppy recorded on all 0 tracks, playback of 4 seconds of each trunk is continuously repeated from 1 to 50 tracks, and the playback output increases from the initial value to 3.
The time until the image quality decreased by dB or until image quality deterioration such as dropout occurred in the reproduced image was measured. The results are shown in Table 2 below. In addition, in the same table, 100 hours or more means that the playback output decreases by 3dB even after 100 hours of playback.
This means that the image quality did not deteriorate and the image quality did not deteriorate.

A 7 MHz sine wave signal was recorded using a Sony MVR-5500, and the reproduced RF output was measured. The measured reproduced RF outputs are listed in Table 2 as relative values to the gold reference values. The larger the RF output value, the better the electronic still video floppy.

KR-400 (still video player) manufactured by Konica ■
was measured under the following conditions.

Temperature: Normal temperature and humidity Discs are replaced every 100 hours.

Stills are performed for 3 minutes each from the l track, and when the still is completed up to the 501-rack, the process returns to the l track. This is considered as 1 bus, and 40 buses are repeated for 100 hours.

This was carried out for 1000 hours, and the amount of wear on the head was measured.

Judgment will be as shown in Table 1 below.

Table = 1 Embryo rate Using a dropout measuring machine manufactured by Konica ■, length 15μ
sec or more, dropout of 12dB or more in depth is 1
When electronic still video floppy disks with three or more floppy disks are treated as dropout No. 0 products (defective products), the pass rate (C%) when 100 disks are measured is shown as the yield.

Table (top and bottom margins) Note: The durability of the disc is less than 100 hours, so it cannot be measured.

From this result, by configuring a disk-shaped medium based on the present invention, it is possible to improve durability, reduce gutter clogging, reduce Dlo, and provide a magnetic disk with high electromagnetic conversion characteristics. can.

9. Functions and Effects of the Invention As mentioned above, the present invention has the above-mentioned -30. A polyurethane resin having a polar group such as M and an average particle size of 0.3 to
Chromium oxide particles within the range of 0.5 μm and Fe-A
1 magnetic powder is contained in the magnetic layer, and the chromium oxide particles are dispersed and contained in the second binder in advance.
Improved dispersibility of metal magnetic powder and high electromagnetic conversion characteristics due to the Fe-Al alloy are obtained, and further improvements in electromagnetic conversion characteristics due to pre-dispersion of chromium oxide particles and reduction in dropouts due to improved durability are also achieved. It can be realized by

[Brief explanation of drawings]

The drawing is a cross-sectional view of an example of a disk-shaped medium according to the present invention. In addition, in the reference numerals shown in the drawings, 21...Nonmagnetic support 22...Intermediate layer 24...Magnetic layer.

Claims (1)

[Claims] 1. In a disk-shaped magnetic recording medium having a magnetic layer in which metal magnetic powder is dispersed in a binder, -SO_3M,
-OSO_3M, -COOM, -PO(OM')_2 and -OPO(OM')_2 {However, M and M' are hydrogen atoms or alkali metal atoms. } A first binder made of a polyurethane resin having at least one polar group selected from the group consisting of; and an average particle size of 0.3 to 0.5.
The magnetic layer contains chromium oxide particles within the μm range and metal magnetic powder containing iron as a main component and aluminum, and the chromium oxide particles are previously dispersed in a second binder. A disk-shaped magnetic recording medium contained in. 2. Metal magnetic powder and -SO_3M, -OSO_3M, -
COOM, -PO(OM')_2 and -OPO(OM'
)_2 {However, M and M' are hydrogen atoms or alkali metal atoms. } A first binder made of a polyurethane resin having at least one polar group selected from the group consisting of; chromium oxide particles having an average particle size within the range of 0.3 to 0.5 μm; When producing a disk-shaped magnetic recording medium in which the magnetic layer contains a metal magnetic powder containing aluminum as a main component, the chromium oxide particles are dispersed in a second binder in advance, and the magnetic powder is dispersed in a second binder. A method for manufacturing a disk-shaped magnetic recording medium by adding it to a magnetic coating for a layer.