JPH0612565B2 - Magnetic recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly, to a magnetic substance of a plate crystal having a flat plate shape having an easy axis of magnetization in a direction perpendicular to the plate surface and a carbonate bond. The present invention relates to a novel magnetic recording medium combined with a urethane resin.

BACKGROUND ART Conventionally, magnetic recording media such as magnetic tapes and magnetic disks are
It is widely used for recording various electrical signals such as video, audio and digital. As these magnetic recording media, those having a magnetic layer formed on a support are used, and there are two types depending on the magnetization direction of the magnetic layer. One of them is magnetized in the in-plane longitudinal direction of the magnetic layer, which is used, for example, when magnetizing a magnetic layer in which needle-like crystal magnetic bodies are arranged in the in-plane longitudinal direction.
The other is a perpendicular magnetization recording method in which magnetization is performed in the direction perpendicular to the magnetic layer, which is used, for example, when the plate-like crystal body is magnetized in a magnetic layer arranged parallel to the plane of the magnetic layer. This perpendicular magnetization recording method has characteristics suitable for high-density recording because the demagnetizing field acting on the residual magnetization in the magnetic layer decreases as the wavelength of the recording signal becomes shorter, and thus it is essentially suitable for high-density recording. This is a system, and recently, a proposal for this perpendicular magnetization recording system has been made. (For example, “Nikkei Electronics” No.192, August 7, 1978 issue). Since it is most suitable for a magnetic recording medium for digital recording, which requires a particularly large storage capacity, such as a digital VTR, a digital audio, a computer disk, etc., research for its practical use is being actively conducted.

The magnetic layer of the magnetic recording medium used for the perpendicular magnetization recording method is a method of forming a magnetic layer made of a Co-Cr alloy on a support having a high magnetic permeability layer by sputtering or vapor deposition, magnetic powder, and binder. A magnetic coating mainly composed of a resin and a solvent is applied on a support and dried to form a coating method. However, although a perpendicular magnetization type magnetic recording medium having a metal thin film type magnetic layer formed by sputtering or vapor deposition is optimal for high density recording, moisture in the air when exposed to the air , Not only lacking in chemical stability because it is corroded by oxygen, but it is easily scratched when rubbed by a magnetic head, easily worn, and has insufficient wear resistance and durability. Not in.

On the other hand, it has been conventionally practiced to form a magnetic layer on a support by a coating method and use this as a magnetic recording medium. Therefore, a perpendicular magnetization type magnetic layer should be formed by this coating method. Is easy. For a magnetic recording medium having a magnetic layer formed by this coating method,
A method for perpendicularly magnetizing a tabular magnetic material of hexagonal ferrite described in JP-A-58-85136, JP-A-58-56232, JP-A-58-12138, and JP-B-57-501053. A magnetic powder having a low axial ratio described in No. 1 is randomly arranged and recorded by utilizing a perpendicular magnetization component of the magnetic layer surface by a narrow gearup head, JP-B-49-15203, U.S. Pat. , US Pat. No. 3,052,567, etc., recording is carried out by using a needle-shaped magnetic powder and utilizing an oblique or perpendicular magnetization component which is not parallel to the magnetic layer. Among these methods, there is a problem in the stability of the magnetic recording medium itself, and the methods have the drawbacks of high noise level and low output. The method is the most excellent as a coating type perpendicular magnetization type recording medium with few of these defects.

By the way, since the magnetic layer formed by the above method has magnetic powder bound by a binder, it has the above-mentioned wear resistance and durability as compared with the magnetic layer of a metal thin film, and is flexible and excellent in head touch. There are advantages. Further, since it is an oxide, it is extremely stable and easy to handle without problems such as ignition and rusting unlike the magnetic metal powder. Especially in recent years, the trend of technology related to magnetic recording is shifting from the use of compact cassettes to the use of microcassettes in audio tapes, and VHS in the field of video.
The system is shifting from the β system to the 8 mm video system to the electronic camera, and both of them are aimed at further miniaturization and high density, so for example, in the case of magnetic tape, the tape passage becomes complicated. Further, since there are many occasions of contact with the guide pole, the guide roller, etc., they are frequently rubbed, and further improvement of the above mechanical properties has been desired.

From this viewpoint, a resin having abrasion resistance is used as the binder resin. Polyurethane resin, for example, is said to have strong adhesion to a support, resistance to repeated stress or bending, toughness, good abrasion resistance and weather resistance, and is widely used as a binder for magnetic layers. There is.

However, as a result of further detailed study by the present inventor,
The wear resistance and durability of the above magnetic recording media are insufficient if only the known polyurethane resin is used, and the storage stability such as hydrolysis of this resin is insufficient when exposed to high humidity. Is. This is because the polyurethane resin is a very soft resin, so that the coating film has a large friction coefficient with respect to the magnetic head, the guide pole, etc., and is easily scratched. In order to improve this, a hard resin or a low-molecular-weight lubricant is added, but the compatibility between the polyurethane resin and other resins is not so good, while the addition of a low-molecular-weight lubricant is not applied. It is difficult to achieve this delicate balance because the film is plasticized and the frictional force due to the lubricant is reduced and the frictional force is increased due to the plasticization of the coating film, which are in conflict with each other. Moreover, this balance is apt to change depending on the storage environment of the magnetic recording medium, for example, the magnetic tape, the operating conditions, etc., and when excessive lubricant oozes out on the surface, the surface is excessively plasticized to cause sticking, scratches, powder falling, running defects, etc. Causing troubles, lowering output,
This causes an increase in noise, an increase in dropouts in which pictures and sounds are partially omitted, and a decrease in still life, which is an endurance at the time of still image reproduction in the case of a video tape. If the lubricant does not ooze out too much, the coefficient of friction increases, causing problems such as sticking, slipping, powder falling, skewing, and winding disorder. Further, conventionally used polyurethane resin is generally polyester type polyurethane and has an ester bond in its molecule, so that when the magnetic layer containing this resin is exposed to the air, it is particularly high. Hydrolyzed under humidity relatively easily, the above wear resistance of the magnetic layer,
Not only does it significantly deteriorate mechanical properties such as durability,
The resulting low-molecular-weight decomposition product becomes a sticky gum-like substance, which causes sticking of the front surface and the back surface of the magnetic tape when wound, for example. This means that all recording on the tape is lost, which is a fatal defect for a recording medium.
In addition, the binding function of the binder in the magnetic layer deteriorates, which causes the magnetic powder to come off, which also causes dropout, which results in an error rate in the case of a high-density digital recording medium. In particular, when a back coat layer is provided to prevent curling of the magnetic tape, a polyurethane resin is also used for this back coat layer, and when the tape is wound, the front surface and the back surface are in contact with each other. This is an obstacle that is more likely to occur and must be solved in practice. Regarding the fact that the magnetic tape using polyester type polyurethane resin is relatively easily hydrolyzed in the environment of high humidity, see, for example, IEEE Trans Mag 12 No.2.
See pages 126, 16 No. 4 558 and 18 No. 5 993.

As described above, a hexagonal ferrite plate crystal is applied parallel to the magnetic layer, and the magnetic recording medium magnetized from the perpendicular direction has excellent characteristics that high density recording is possible. When it is composed of the magnetic layer of the mold, its binder is a conventional polyurethane resin, which is inherently soft and has insufficient wear resistance, durability, and storability. Improving this by adding a lubricant causes another problem. It did not become an essential solution due to the occurrence.

JP-A-58-60430 discloses that a magnetic recording medium having a magnetic layer using carbonate polyester polyurethane as a binder has abrasion resistance and the like.
Since this resin has an ester bond, it is essentially hydrolyzable in a high-humidity environment in the same manner as a magnetic tape using the above-mentioned polyester-type polyurethane resin as a binder, although there are differences in degree. There's a problem.

OBJECT OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having a coating type magnetic layer magnetized by a perpendicular magnetization method, in which the abrasion resistance, durability and storage stability of the magnetic layer are improved. To provide.

In particular, it is to provide a magnetic recording medium having a recording density several times higher than that of a conventional recording medium and having extremely excellent durability and storability.

Configuration of the Invention The above object is achieved by using a polycarbonate type polyurethane resin having no ester bond as a binder resin. The coating film of this polycarbonate polyurethane resin is harder than the coating film of the polyurethane resin because it is hard to be scratched, and the friction coefficient is also small, so that the addition amount of the lubricant can be reduced, so that not only the deterioration of the mechanical properties of the magnetic layer can be suppressed. Since it does not have an ester bond which is easily hydrolyzed, the storage stability is improved.

Therefore, the magnetic recording medium of the present invention is characterized by having a flat plate-shaped magnetic body whose easy axis of magnetization is perpendicular to this flat plate and a magnetic layer containing a polycarbonate-type polyurethane resin having no ester bond as a binder resin. It is what

Polycarbonate type polyurethane used in the present invention is disclosed in JP-A-57-31919, JP-A-58-60430, and JP-B-58-40.
Among those described in Japanese Patent Application No. 51-151964, Japanese Patent Application No. 58-151964, Japanese Patent Application No. 58-120697, and Japanese Patent Application No. 58-120698, there is no ester bond. The thing is illustrated. It does not contain an ester bond, which is good in terms of storability as described above. Furthermore, polycarbonate urethane containing a carboxyl group, a sulfo group, or a phospho group is also preferable from the viewpoint of improving dispersibility. The ester bond is usually a bond formed by the reaction of an alcohol and a carboxylic acid, and refers to a carbon atom forming a carbonyl bond to which an adjacent carbon atom is directly bonded (in the usual case).

Is not included in the ester bond here.

As described above, the polycarbonate polyurethane not containing an ester bond exhibits abrasion resistance peculiar to the urethane resin and is harder than the polyester polyurethane due to the presence of the carbonate component, so that the film thereof is not easily scratched and has a low friction coefficient. . Therefore, the amount of low-molecular lubricant used can be reduced. Further, since the solubility in the solvent is improved and the urethane concentration can be increased, the film strength can be increased. Moreover, since it does not contain ester bonds in the molecule, which is fundamentally different from conventional binders, it will not be hydrolyzed even after long-term use under high temperature and high humidity conditions, and therefore the magnetic layer will not be damaged or the film will be damaged. Smooth runnability can be maintained without peeling or adhesion between layers.

The structure of the polycarbonate polyurethane used in the present invention is, for example, based on the following formula: polycarbonate polyol And a polyisocyanate (OCN-R'-NCO).

(However, R and R'represent an aliphatic or aromatic hydrocarbon group. L is preferably 50 or less for decreasing Tg (secondary transition temperature) and preventing stickiness, and 1 to 30 is preferable. M is m In order to maintain the film-forming ability and to improve the solvent solubility, 5 to 500 is preferable, 10 to 300 is preferable, and l and m are such that the average molecular weight of this polycarbonate polyol polyurethane is desirably 50,000 to 200,000. Polycarbonate polyol that can be used here is a polyol obtained by chaining polyols with a carbonate bond, for example, by condensation of a conventionally known polyhydric alcohol with phosgene, chloroformic acid ester, dialkyl carbonate or diallyl carbonate. can get.

As the polyhydric alcohol, 1,10-decanediol,
1,6-hexanediol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, 1,5-pentanediol and the like can be mentioned. The number of carbon atoms in this polyhydric alcohol, such as a diol, is important and is preferably 4-12. As shown in FIG. 1, which shows the relationship between the jitter (μsec) showing the tape running stability and the number of carbon atoms of the diol compound, when the number of carbon atoms is less than 4 or greater than 12, Also, the above-mentioned magnetic powder is easily peeled off (after running the magnetic tape 100 times). Correspondingly, the molecular weight of the polycarbonate polyol is shown in Fig. 2 which shows the relationship between this molecular weight and the jitter (the magnetic powder peeled off after running the magnetic tape 100 times: 6
It is good to set it to about 700-3000 after storing at 0 ° C for 1 week). In the above-mentioned urethanization reaction, it is important that active hydrogen (H of —OH) is present in the polycarbonate. In addition to the polyhydric alcohol exemplified above as a compound capable of supplying active hydrogen similar to this. , Ethylene glycol, diethylene glycol, propylene glycol, 1,
4-butylene glycol, bisphenol A, glycerin, 1,3,6-hexaneditriol, trimethylolpropane, pentaerythritol, sorbitol, sucrose, dipropylene glycol, methyldiethanolamine, ethylbiisopropanolamine, triethanolamine, ethylenediamine, Hexamethylenediamine,
Compounds such as bis (p-aminocyclohexane), tolylenediamine, diphenylmethanediamine, methylenebis (2-chloroaniline) and / or these compounds may be added to ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide, etc. Polyether polyol obtained by adding one or two or more of (abbreviated as alkylene oxide). Although the active hydrogen-containing polycarbonates such as the above polycarbonate polyols can be used alone, other polyhydric alcohols may be used in combination in the urethanization, and other known chain extenders may be used in combination. For example, when other low molecular weight polyhydric alcohols such as hexanediol and butanediol are used in combination, it is expected that this reacts with an excess amount of the above polyisocyanate to promote gelation. As shown in FIG. 3 showing the relationship between the ratio (%) to the whole and the wear resistance, it is desirable that the ratio of the polycarbonate polyol is 80% or more so that the wear resistance can be sufficiently exhibited. The abrasion resistance was judged by the amount of abrasion loss when a sample of a fixed length was connected in a loop and was run for 10 minutes while slidingly contacting the magnetic head at high speed.

As the polyvalent isocyanate, aromatic isocyanate is desirable, for example, tolylene diisocyanate (TDI) (2,4-TDI, 2,6-TDI), a dimer of 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), meta-xylylene diisocyanate (MXDI),
There are naphthylene-1,5-diisocyanate (NDI), o-tolylene diisocyanate (TODI) and adducts of these isocyanates with active hydrogen compounds, and the average molecular weight thereof is preferably in the range of 100 to 3,000. .

Specifically, the product names of Sumitomo Bayer Urethane Co., Ltd., Sumidule T80, 44S, PF, L, Death Module
T65, 15, R, RF, IL, SL; Takeda Pharmaceutical Co., Ltd., trade name Takenate 300S, 500; Mitsui Nisso Urethane Co., Ltd. trade names "NDI", "TODI"; Nippon Polyurethane Co., Ltd. Product name Death Module T100, Millionate MR, MT, Coronate L, Kasei UPJUN product name PAPI-135: TD1
Products such as 65, 80, 100, 125 Mate, 143 L isonate are listed.

On the other hand, examples of the aliphatic isocyanate include hexamethylene diisocyanate (HMDI), lysine isocyanate, trimethylhexamethylene diisocyanate (TMDI) and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds,
Preferred are those with a molecular weight in the range 100-3,000. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds and active hydrogen compounds are preferable.

Specifically, for example, Sumitomo Bayer Urethane Co., Ltd. product name Sumidur N, Desmodur Z4273, Asahi Kasei product name Duranate 50M, 24A-100, 24A-90CX, Nippon Polyurethane product name Coronate HL, Huls There are products such as product name TMDI. Further, as the alicyclic isocyanate among aliphatic isocyanates, for example, methylcyclohexane-2,4-diisocyanate (structural formula) 4,4'-Methylenebis (cyclohexyl isocyanate) (Structural formula) Examples thereof include an adduct of isophorone diisocyanate and its active hydrogen compound.

Specifically, Huls Chemical Co., Ltd., trade name IPDI, IPDI-T189
There are products such as 0, H-2921, and B1065.

The other polyvalent isocyanate is an adduct of diisocyanate and trivalent polyol, or a pentamer of diisocyanate, and a decarbonizing compound of 3 mol of diisocyanate and water. Examples of these are an adduct of 3 moles of tolylene diisocyanate and 1 mole of trimethylol propane, an adduct of 3 moles of metaxylene diisocyanate and 1 mole of trimethylol peropan, and a pentamer of 2 moles of tolylene diisocyanate. Is easily obtained industrially.

Among the above-mentioned polyvalent isocyanates, the aromatic one acts as a hard component (hard segment),
It is desirable in that the rigidity of polycarbonate (polyol) polyurethane can be sufficiently exhibited. The tackiness of the aromatic polycarbonate (polyol) polyurethane depending on the average molecular weight can be kept low by setting the average molecular weight in the range of 50,000 to 200,000. Further, FIG. 4 shows the relationship between the molecular weight and the still durability. When the molecular weight is set to 50,000 to 200,000, the still durability is high, and when an aromatic type isocyanate component of the polyurethane is used, While the still durability can be made sufficiently large as shown by the curve a, when the aliphatic isocyanate is used, the still durability becomes low as shown by the curve b.
Of the above aromatic isocyanates, naphthylene-1,
5-diisocyanate and diphenylmethane diisocyanate are particularly desirable.

The amount of the above-mentioned isocyanate used is such that the NCO group (isocyanate group) contained in the polyisocyanate is 0.8 to 1.2 equivalent ratio, more preferably 0.85 equivalent to the total amount of active hydrogen contained in the active hydrogen-containing compound (polycarbonate polyol). It is desirable that the ratio is about 1.1 equivalent.

When producing the polyurethane according to the present invention, the following solvents can be used if necessary. Dimethylformamide, amide series such as dimethylacetamide, sulfoxide series such as dimethyl sulfoxide, dioxane, cyclic ether series such as tetrahydrofuran, cyclic ketone series such as cyclohexanone, acetone, non-cyclic ketone series such as methyl ethyl ketone methyl isobutyl ketone,
Cellosolve, butyl cellosolve, carbitol, glycol ether type known as butyl carbitol etc., acetic acid glycol ether type known as cellosolve acetate, butyl cellosol acetate, carbitol acetate etc. and for example trade name "Dygram"
One or more dibasic acid ester solvents known as the above, further, the above solvents and ester solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as benzene, toluene and xylene, methylene chloride, Examples thereof include mixed solvents with chlorine-based solvents such as trichlorethylene and perchlorethylene and alcohol-based solvents such as methanol, ethanol, isopropanol and butanol. Also, 2,2,4
-Trimethyl-1,3-pentanediol monoisobutyrate (Kyowanol M: manufactured by Kyowa Fermentation Co., Ltd.) and the like can also be used as a solvent.

To produce the polycarbonate-type polyurethane resin in the present invention, first, for example, a polymer polyol and an organic isocyanate are heated and reacted at 60 ° C. to 100 ° C. for several hours in the presence of a catalyst and / or a solvent, if necessary. Make a prepolymer. Further, it is heated and reacted at the same temperature for several hours to obtain a polycarbonate type polyurethane resin. A reaction terminator may be added if necessary. In addition, a solvent is appropriately added in order to reduce the viscosity at each reaction step. The obtained polycarbonate type polyurethane resin solution has a solid content of 15 to 60% and a viscosity of 200 to 70,000 cps / 25 ° C.

It has been explained with reference to FIG. 4 that it is desirable to make the average molecular weight of the polycarbonate (polyol) polyurethane synthesized as described above in the range of 50,000 to 200,000. It has been confirmed that the durability (that is, the surface property of the magnetic layer) is also improved as shown in FIG. 5 showing the relationship with the amount.

The polycarbonate (polyol) polyurethane resin described above is contained in the magnetic layer 2 formed on the support 1 of the magnetic recording tape to serve as a binder, as shown in FIG. 6, for example. A back coat layer (BC layer) 3 may be provided on the back surface of the support 1 for the winding appearance and running stability when the tape is wound.

The above polycarbonate (polyol) polyurethane resin is used alone as a binder for the magnetic layer. However, when a fibrin resin and a vinyl chloride resin or a phenoxy resin are used in combination, the dispersibility of the magnetic powder in the magnetic coating is improved and the magnetic properties are improved. The mechanical strength of the layer is increased. However, the layer becomes too hard only with these fibrous resin and vinyl chloride copolymer.

Cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester and the like can be used for the above fibrous resin. As the cellulose ether, methyl cellulose, ethyl cellulose, propyl cellulose, isopropyl cellulose, butyl cellulose, methyl ethyl cellulose, methyl hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl cellulose, carboxymethyl cellulose sodium salt, hydroxyethyl cellulose, benzyl cellulose, cyanoethyl cellulose, vinyl cellulose, Nitrocarboxymethyl cellulose, diethylaminoethyl cellulose, aminoethyl cellulose and the like can be used. As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate or the like can be used. Further, as the cellulose organic acid ester, acetyl cellulose,
Propionyl cellulose, butyryl cellulose, methacryloyl cellulose, chloroacetyl cellulose, β-
Oxypropionyl cellulose, benzoyl cellulose, p-toluenesulfonate cellulose, acetylpropiocellulose, acetylbutyryl cellulose and the like can be used. Of these fibrin-based resins, nitrocellulose is preferred. Specific examples of nitrocellulose include Cell Nova BTH1 / 2 and Nitrocellulose SL-1, manufactured by Asahi Kasei Corporation.
Nitrocellulose RS1 / 2 manufactured by Daicel Corporation can be used. The viscosity of nitrocellulose (specified in JIS, K-6703 (1975)) is preferably 2 to 1/64 seconds, and particularly preferably 1 to 1/4 seconds. If the amount is out of this range, the magnetic layer does not have sufficient film adhesion and film strength.

The vinyl chloride copolymer resin used in the present invention has a general formula: Some are represented by. In this case, the molar ratio derived from 1 and m is 95-50% for the former and 5-50 for the latter.
Mol%. X represents a monomer residue that can be copolymerized with vinyl chloride, and is vinyl acetate, vinyl alcohol, maleic anhydride, maleic anhydride ester, maleic acid, maleic acid ester, vinylidene chloride, acrylonitrile, acrylic acid, acrylic acid. Acid ester, methacrylic acid,
It represents at least one selected from the group consisting of methacrylic acid ester, vinyl propionate, glycidyl methacrylate and glycidyl acrylate. The degree of polymerization, expressed as (l + m), is preferably 100-600,
If it is less than 100, the magnetic layer tends to be tacky, and if it exceeds 600, the dispersibility becomes poor. The above vinyl chloride-based copolymer may be partially hydrolyzed. The vinyl chloride copolymer resin is preferably a copolymer containing vinyl chloride-vinyl acetate (hereinafter, referred to as "salt-vinyl acetate copolymer").
Is mentioned. Examples of salt-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-
Examples include vinyl acetate-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride-maleic acid copolymers, and the like, and vinyl chloride-vinyl acetate. Among the copolymers, a partially hydrolyzed copolymer is preferable. Specific examples of the above vinyl chloride-vinyl acetate-based copolymers include "VAGH" and "VYH" manufactured by Union Carbide Corporation.
"H", "VMCH", "S-REC A", "ES-REC A-5", "ES-REC C", "ES-REC M" manufactured by Sekisui Chemical Co., Ltd., "Denka Vinyl" manufactured by Denki Kagaku Kogyo Co., Ltd.
"1000G", "Denka vinyl 1000W", etc. can be used.

The above vinyl chloride-based copolymer and the fibrous resin may be used in any mixing ratio, but as shown in FIG. 7, the vinyl chloride-based resin: the fibrous resin is 90/10 to 5 / It is preferably 95, more preferably 80/20 to 10/90.

If the amount of the fibrous resin is out of this range, the calendering workability tends to deteriorate, and the surface smoothness of the magnetic layer containing this as a binder tends to deteriorate. For example, dropout tends to occur when a magnetic recording tape is used. Become. Further, when the amount of vinyl chloride polymer is large, the magnetic powder tends to be poorly dispersed, for example, the squareness ratio tends to be poor. C in FIG.
Indicates a tendency of calendering workability, and the calendering workability (calendering workability was judged by tape loss after calendering) is improved as the vertical axis goes up, and a good coating film is obtained. d shows the change in the squareness ratio.

The binder composition of the magnetic layer of the magnetic recording medium of the present invention comprises the above-mentioned polycarbonate (polyol) polyurethane and another resin (the total amount of the fibrin resin or the vinyl chloride copolymer or the phenoxy resin alone or in combination). It has been confirmed that the ratio is preferably 90/10 to 50/50 by weight, and more preferably 85/15 to 60/40, as shown in FIG. If the amount of the above polycarbonate-type polyurethane is out of this range, the film tends to be too soft and the still durability tends to deteriorate, and conversely, if the amount of other resins increases, the magnetic layer film becomes too hard and the calendar processability is poor, and therefore The surface smoothness deteriorates and the still characteristics also deteriorate. Especially when the content exceeds 60% by weight, the physical properties of the coating film are not so good as a whole.

In addition to the above, as the binder of the magnetic layer, a mixture of the above and other thermoplastic resin, thermosetting resin, or reactive resin may be used.

The thermoplastic resin that can be used in combination with the polycarbonate polyurethane resin used in the present invention has a softening temperature of 150 ° C.
Below, average molecular weight 10,000 ~ 200,000, degree of polymerization about 200 ~
About 2,000, for example, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-vinylidene chloride copolymer, acrylic acid ester-styrene copolymer, methacrylic acid ester, acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride Copolymer,
Methacrylic acid ester-styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer-acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, styrene-butadiene copolymer, polyester resin, chlorovinyl ether -Acrylic acid ester copolymers, amino resins, various synthetic rubber type thermoplastic resins, and mixtures thereof are used.

These resins are Japanese Examined Patent Publication Nos. 37-6877, 39-12528,
39-19282, 40-5349, 40-20907, 41-
9463, 41-14059, 41-16985, 42-6428
No. 42-11421, No. 43-4623, No. 43-15206, No.
44-2889, 44-17947, 44-18232, 45-14
020, 45-14500, 47-18573, 47-22063
No. 47, No. 47-22064, No. 47-22068, No. 47-22069,
No. 47-22070, No. 48-27886, U.S. Pat.
No. 144,352, No. 3,419,420, No. 3,499,789, No.
No. 3,713,887.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and is condensed after coating and drying,
Those which are insolubilized by a reaction such as addition are used. Among these resins, those that do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, vinyl chloride-
Vinyl acetate resin, methacrylate copolymer and diisocyanate prepolymer mixture, high molecular weight polyester resin and isocyanate prepolymer mixture, urea formaldehyde resin, polyester polyol and isocyanate mixture, polyamide resin, low molecular weight glycol
Examples thereof include a mixture of high molecular weight diol and triphenylmethane triisocyanate, a polyamine resin and a mixture thereof.

These resins are disclosed in Japanese Examined Patent Publication Nos. 39-8103 and 40-9779 41-
No. 7192, No. 41-8016, No. 41-14275, No. 42-18179
No. 43-12081, 44-28023, 45-14501,
45-24902, 46-13103, 47-22067, 47
-22072, 47-22073, 47-28045, 47-280
No. 48, No. 47-28922, U.S. Pat.
No. 3,320,090, No. 3,437,510, No. 3,597,27
No. 3, No. 3,781,210, and No. 3,731,211.

A crosslinking agent may be further mixed with the binder to improve the mechanical durability of the magnetic layer. Such a cross-linking agent may contain triphenylmethane triisocyanate, tris- (p-isocyanatephenyl) thiophosphite, and polymethylene polyphenyl isocyanate in addition to the above-mentioned isocyanate.

The magnetic substance in the present invention refers to, for example, a hexagonal ferrite, which is a flat plate crystal and has an easy axis of magnetization in the direction perpendicular to the plate surface. The tabular crystals are likely to be aligned parallel to the surface of the magnetic layer by a magnetic field or mechanical force, and thus are easily magnetized in the direction perpendicular to the magnetic layer. Hexagonal ferrite refers to barium ferrite, strontium ferrite, etc., where some of the iron elements are other elements, such as T
Those substituted with i, Ca, Zn, In, Mn, Ge, Hr, etc. are preferable. This magnetic material is described in detail in IEEE Trans Mag. MAG-18.

The mixing ratio of the magnetic powder and the binder in the magnetic layer of the present invention is 1 part by weight of the binder with respect to 100 parts by weight of the magnetic powder.
It is used in the range of 00 to 200 parts by weight, preferably 20 to 50 parts by weight. When the amount of the binder is more than the above range, the recording density when the magnetic recording medium is reduced is decreased, and when the amount is too small, the mechanical strength of the magnetic layer is deteriorated, durability is reduced, and undesirable phenomena such as peeling of magnetic powder occur. Occur.

The magnetic layer is formed by applying a magnetic paint, but the paint may contain additives such as a dispersant, a lubricant, an abrasive and an antistatic agent, if necessary. As a dispersant,
There are lecithin, phosphates, amine compounds, alkyl sulphates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinates, known surfactants and salts thereof, and salts thereof, and negative organic groups (for example, -COOH , —PO ₃ H) may also be used. These dispersants are 1
You may use it only by a kind. Binder with these dispersants
It is added in the range of 1 to 20 parts by weight with respect to 100 parts by weight.
The magnetic powder may be pretreated with these dispersants in advance. As the lubricant, silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, monobasic fatty acid having 12 to 16 carbon atoms and the number of carbon atoms of this fatty acid, A fatty acid ester composed of a monohydric alcohol having 21 to 23 carbon atoms in total can be used. These lubricants are added in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

As the abrasive, commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components are corundum and magnetite), and titanium dioxide are used. To be done. These abrasives have an average particle size of 0.
Those having a size of 05 to 5 μ are used, and particularly preferably 0.
1 to 2 μ. These abrasives are added in the range of 1 to 20 parts by weight with respect to 100 parts by weight of magnetic powder. These abrasives are disclosed in JP-A-49-115510 and U.S. Pat. No. 3,007,807.
No. 3,041,196, No. 3,687,725,
British Patent No. 1,145,349, West German Patent (DT-PS) 8
No. 53,211.

Further, as the antistatic agent, carbon black, graphite, tin oxide-antimony oxide type compounds, titanium oxide-tin oxide-antimony oxide type compounds, conductive powders such as carbon black graft polymer; natural surfactants such as saponin; alkylene. Nonionic surfactants such as oxide type, glycerin type and glycidol type; cationic surfactants such as pyridine and other heterocycles, phosphonium or sulfonium compounds; carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid ester group, etc. Anionic surfactants containing an acidic group; amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

As the carbon black, carbon black that imparts conductivity and carbon black that imparts light shielding properties to the magnetic layer are added. In the former case, static electricity is generally generated during use of the magnetic recording medium, and when the static electricity is accumulated, discharge is easily generated between the magnetic head and the magnetic head. The surface electric resistance of the magnetic layer is 10 ⁹
This is because it is less than Ω · cm. In the latter, the light transmittance of the magnetic part is set to 0.05% or less in order to adjust the running of the tape by detecting the difference in the light transmittance between the tape portion having the magnetic element of the video tape and the leader tape portion. This is because

As the solvent to be blended in the above paint or a diluent solvent at the time of applying this paint, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, butanol; methyl acetate, ethyl acetate , Esters such as butyl acetate, ethyl lactate, ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, xylene; methylene chloride, ethylene chloride, Halogenated hydrocarbons such as carbon tetrachloride, chloroform and dichlorobenzene can be used.

Further, as the support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Cu, Al, Zn and other metals, glass. , BN, Si carbide, porcelain, ceramics such as pottery can also be used.

The thickness of these supports is about 3 to 100 μm, preferably 5 to 50 μm in the case of film or sheet, 30 μm to 10 mm in the case of disc or card, and cylindrical in the case of drum. Used.

The support has a so-called back coat (Backcoa) on the surface opposite to the side on which the magnetic layer is provided for the purpose of preventing electrification and transfer.
t) may be done.

As a coating method for forming the magnetic layer by coating the magnetic coating on a support, air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat , Cast coat,
Spray coats can be used, but are not limited to these.

The orientation method of the flat magnetic powder is described in JP-A-58-80136, JP-A-58-12158, JP-A-53-12137, and JP-A-58-12136.
JP-A-58-12135, JP-A-55-142421, JP-A-5
There is a method of applying a magnetic field in the vertical direction to the undried coating film described in each publication of 5-163633, a method of orienting the tabular grains in a horizontal direction by rolling the highly adhesive coating between rolls,
Either method is also used.

After the orientation of the magnetic powder, the surface is further smoothed and cut into a desired shape to obtain a magnetic recording medium such as a tape, a sheet or a disk.

The magnetic recording medium thus prepared may have the structure shown in FIG. 6, but an undercoat layer (not shown) may be provided between the magnetic layer 2 and the support 1.

The back coat layer 3 shown in FIG. 6 contains a non-magnetic powdery substance for roughening the surface. Examples of the non-magnetic powder include carbon black, silicon oxide, titanium oxide, aluminum oxide and chromium oxide. , Silicon carbide, calcium carbide,
Examples thereof include those made of zinc oxide, α-Fe ₂ O ₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbonate and the like, preferably those made of carbon black or titanium oxide. By including these non-magnetic powders in the back coat layer, the surface of this layer can be appropriately roughened (matted) and the smoothness of the layer surface can be made uneven, for example, the frictional force against guide poles, guide pins, etc. Can be reduced. Further, carbon black imparts conductivity to prevent the back coat layer from being charged. It is preferable that the carbon black and another surface-roughening agent are used in combination to provide the running property and the antistatic effect. However, as for the surface roughness of the back coat layer, the average roughness or height (Ra) of the center line of the surface irregularities is 0.01 to 0.1 μm, preferably 0.025 μm.
The maximum roughness (Rmax) is preferably 0.20 to 0.80 μm. Regarding Ra, Ra ≦ 0.025 μm is desirable in order to improve the chroma S / N. Ra or Rmax
If the value is too small, the running stability and the winding appearance when the tape is wound will be insufficient, and if it is too large, the unevenness of the back coat layer will cause the magnetic layer to be transferred to the magnetic layer with an excessively rough surface. It may turn into.

The particle size of the particles contained in the back coat layer is 0.5 μm or less, preferably 0.2 μm or less in order to obtain the above surface roughness.
It is better to be less than m. The back coat layer can be formed by coating in the same manner as in the case of the above magnetic layer, but the thickness after coating and drying is 0.1 to 3.0 μm, preferably 1 μm or less, and more preferably 0.6 μm or less. The amount of nonmagnetic powder added to the backcoat layer is generally 100 to 400 mg / m ² , preferably
200 to 300 mg / m ² .

As the binder of the back coat layer, the same polycarbonate polyol polyurethane as that used in the magnetic layer or a mixture thereof with the other resin exemplified above is used, and the back coat layer has a friction coefficient similar to that of the magnetic layer. It has excellent effects such as reduction, increase in surface hardness, and prevention of interlayer adhesion between the front and back surfaces of the magnetic tape when it is wound, which results in reduction of running stability, skew and jitter of the magnetic tape. When a polycarbonate polyol polyurethane resin is contained in the back coat layer, the first
The same tendency as shown in FIGS. 5 to 7, 7 and 8 is shown.

Although the back coat layer is necessary for a high quality magnetic recording tape, it is not always necessary to provide the back coat layer for those which do not require a high quality.

FIG. 9 shows an overcoat layer 4 on the magnetic layer 2 shown in FIG.
Is provided. This overcoat layer is provided in order to protect the surface of the magnetic layer and prevent scratches, and for that purpose lubricity of the surface is required. For this purpose, the polycarbonate polyol polyurethane used for the magnetic layer is also used. This resin is advantageous as it has a low coefficient of friction. However, it is desirable to use a fibrous resin and a vinyl chloride copolymer together.

FIG. 10 shows a magnetic recording medium configured as a magnetic disk, in which the same magnetic layers 2 as described above are provided on both surfaces of the support 1. Although the same overcoat layer 4 as shown in FIG. 6 may be provided on each of these magnetic layers, a binder containing the above-mentioned polycarbonate polyol polyurethane resin as a main component is also used for these overcoat layers. Preferably.

As described above, according to the present invention, the plate-like magnetic powder having the easy axis of magnetization in the direction perpendicular to the plate surface is bound by the polycarbonate type polyurethane resin having no ester bond. Since it has an appropriate hardness compared to the polyurethane binder of No. 1, the friction coefficient is relatively small and the amount of lubricant added can be reduced accordingly, so problems such as sticking to the magnetic head and peeling of magnetic powder can be reduced, and magnetic properties can be reduced. The number of scratches on the layer surface can be reduced. This makes it possible to prevent the runnability and electromagnetic characteristics of the magnetic recording medium from being impaired. Moreover, not only the abrasion resistance peculiar to the urethane resin can be utilized, but the solubility of the solvent is better than that of the corresponding urethane resin by using the polycarbonate type polyurethane,
When the same solution viscosity is used for comparison, the urethane concentration can be increased, so the strength of the coating film can be increased and the advantages of urethane can be further utilized. By these, the running property and physical properties of the magnetic recording medium can be improved so that the electromagnetic characteristics are not impaired.

In addition, unlike the carbonate polyester polyurethane and other polyester polyurethanes, which are different in degree, the binder is not easily hydrolyzed under high humidity. In addition, the magnetic layer is not peeled off from the support, and the interlaminar adhesion does not occur when the tape is wound, so that the smooth running property can be maintained and the storability as a magnetic recording medium can be improved. This is because polycarbonate type polyurethane has excellent moisture resistance and low tackiness.

In this way, the wear resistance and durability of the magnetic recording medium are improved, and it is possible to meet the strict requirements associated with downsizing and high density of magnetic recording / reproducing equipment.

Examples The present invention will be described below based on examples, but the present invention is not limited thereto. Hereinafter, all "parts" represent "parts by weight".

<Example of synthesis of polycarbonate polyol> 590 parts of diethyl carbonate and 1,6-hexanediol
650 parts were reacted at 120 ° C. to 200 ° C. for 15 hours, then cooled to 150 ° C., and the remaining ethanol and unreacted diol were sufficiently distilled off under reduced pressure at 20 to 50 mmHg to obtain 770 parts of polycarbonate polyol. The hydroxyl value of this polyol was about 66. (Molecular weight is about 1700).

<Synthesis of Polycarbonate Polyol Polyurethane> (Synthesis Example 1) 170 parts of the polycarbonate polyol synthesized above and 25 parts of diphenylmethane diisocyanate (MDI) are dissolved in 580 parts of methyl ethyl ketone, and 0.03 part of dibutyltin dilaurate as a urethane-forming catalyst is added to this solution. , 80
The reaction was carried out at 6 ° C. for 6 hours to obtain 770 parts of a methyl ethyl ketone solution of polycarbonate polyol polyurethane. (Solid content concentration 25%, weight average molecular weight of polyurethane Mw 140,000) (Synthesis example 2) 162 parts of the polycarbonate polyol synthesized above and MDI
Dissolve 25 parts in 560 parts of methyl ethyl ketone, add 0.03 parts of dibutyltin dilaurate as a urethane-forming catalyst,
The reaction was carried out at 80 ° C. for 2 hours to obtain 740 parts of a methyl ethyl ketone solution of polycarbonate polyol polyurethane. (Solid content concentration 25.4%, polyurethane Mw 130,000) (Synthesis example 3) 153 parts of the polycarbonate polyol synthesized above and MDI
25 parts, neopentyl glycol 1.1 parts were dissolved in methyl ethyl ketone 540 parts, dibutyltin dilaurate 0.03 parts was added as a urethanization catalyst, and reacted at 60 ° C. for 6 hours,
715 parts of a methyl ethyl ketone solution of polycarbonate polyol polyurethane was obtained. (Solid content concentration 24.8%, polyurethane Mw 95,000) (Synthesis example 4) 153 parts of the polycarbonate polyol synthesized above and MDI
25 parts, 1.2 parts of triethanol propane are dissolved in 540 parts of methyl ethyl ketone, 0.03 parts of dibutyl tin dilaurate is added as a urethanization catalyst, and reacted at 80 ° C. for 6 hours,
714 parts of a methyl ethyl ketone solution of polycarbonate polyol polyurethane was obtained. (Solid content concentration 25.0%, polyurethane Mw 100,000) (Synthesis example 5) Diethyl carbonate 236 parts and 1,6-hexanediol
520 parts were reacted at 120 ° C to 200 ° C for 15 hours, then cooled to 150 ° C, and the remaining ethanol and unreacted diol were sufficiently distilled off under reduced pressure at 20 to 50 mmHg to obtain 520 parts of polycarbonate polyol. The hydroxyl value of this polyol is about 426.
Met. (Molecular weight is about 263). 1,6 in this polyol
155 parts of hexanediol and 1,10-decanedicarboxylic acid 6
00 parts was added and reacted at about 200 to 220 ° C. and 30 to 50 mmHg for 8 hours to finally obtain 1150 parts of polycarbonate polyester polyol. The molecular weight of this polycarbonate polyester polyol was about 1650, and its hydroxyl value was about 68.

150 parts of this polyol, 25 parts of hydrogenated MDI and 0.5 part of neopentyl glycol were reacted in 520 parts of methyl ethyl ketone at 80 ° C. for about 6 hours to obtain a solution of polycarbonate polyester polyurethane in methyl ethyl ketone. (Solid content concentration 28%) Example 1 A magnetic coating material having the following composition was prepared.

Hexagonal barium ferrite 100 parts (average particle size 0.1μ, plate thickness 0.03μ, Hc = 700Oe, σs = 57emu / g) Polyurethane of Synthesis Example 1 7 parts Nitrocellulose 4 parts (Asahi Kasei Co., Ltd. Cernova BTH1 / 2 ) Vinyl chloride-vinyl acetate copolymer 1 part (UCGH VAGH) Lecithin 2 parts Myristic acid 2 parts Palmitic acid butyl ester 1 part Alumina 4 parts Methyl ethyl ketone 50 parts Cyclohexanone 100 parts Carbon black 2 parts (Conductex 975) The above composition The product was sufficiently stirred and mixed in a sand mill, 5 parts of polyfunctional isocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added, and the mixture was filtered with a filter having an average pore size of 1 μm. The obtained magnetic paint was applied on the surface of a polyethylene terephthalate support having a thickness of 14 μm so that the dry film thickness was 4 μm. While the coating film on the support was still in a fluidized state, a magnetic field was applied perpendicularly to the coating film surface to orient the magnetic powder and dry it.

After this, surface treatment of the magnetic layer with a super calendar roll,
A wide magnetic film having a magnetic layer having a predetermined thickness was obtained.
This film was cut into 1/2 inch width to make a magnetic tape for video.

Examples 2 to 4 The procedure of Example 1 was repeated except that the polyurethanes of Synthesis Examples 2 to 4 were used instead of the polyurethanes of Synthesis Example 1, respectively. I made a tape.

Example 5 The same operation as in Example 1 was carried out except that a polyethylene terephthalate support having a thickness of 75 μ was used and a disk-shaped material was cut out from a wide magnetic film to obtain a magnetic dehexe of Example 5. did.

Comparative Example 1 In Example 1, polyester polyurethane (Nippolan) was used instead of the polycarbonate polyurethane of Synthesis Example 1.
N-2304) was used and the same operation as in Example 1 was carried out to prepare a magnetic tape of this comparative example.

Comparative Example 2 The magnetic property of Comparative Example 2 was the same as in Example 1 except that acicular metal ferromagnetic powder having a particle size of 0.3 μ, Hc = 1200 Oe, and σs = 130 emu / g was used in place of the hexagonal barium ferrite. I made a tape.

Comparative Example 3 In Comparative Example 1, the same operation as in Comparative Example 1 was performed except that the disk-shaped magnetic disk of this Comparative Example was cut out from the wide magnetic film as in Example 5.

Comparative Example 4 A magnetic tape of Comparative Example 4 was prepared in the same manner as in Example 1 except that the polyurethane of Synthetic Example 5 was used instead of the polyurethane of Synthetic Example 1.

Regarding the above examples and comparative examples, the magnetic tape was recorded on a video deck having a head with a narrow gap (0.2 μ), and the recorded matter was reproduced, and 4 M
The output in Hz was measured.

Next, each of the above tapes was run 400 times in an atmosphere of 23 ° C. and 80% relative humidity, and the decrease in output before and after this running was measured. The tape was stored for 10 weeks in an atmosphere of 23 ° C. and 80% relative humidity, and the acetone extraction rate of the tape before and after the storage was measured to examine the extent of hydrolysis of the binder. Since the decomposition product becomes soluble in acetone, the amount of extract increases as the decomposition of the binder occurs.

In addition, the disks of the above-mentioned examples and comparative examples were subjected to a normal floppy disk drive device and subjected to a path test 1 million times at 24 ° C. and a relative humidity of 60% to reduce the output of 125 kHz before and after the test. The surface roughness of the disks was measured and observed.

The above results are shown in Table 1 for tapes and Table 2 for disks. In Table 1, for the output test, the measured value of the tape before the test of Comparative Example 2 was used as a reference (0 dB).
It is shown in dB, and the acetone extraction rate is shown in%. In Table 2, the output test shows what percentage of the output after the test is the output before the test.

The magnetic tapes of polycarbonate polyurethane and barium ferrite of Examples 1 to 4 were used before and after the running test.
Less decrease in RF output, and less increase in acetone extraction rate before and after storage test. From this, it is understood that the magnetic tapes of Examples 1 to 4 have a high RF output and are excellent in durability and storability. On the other hand, the magnetic tape of Comparative Example 4 showed a large increase in the acetone extraction rate, and the magnetic tape of Comparative Example 1 showed a larger increase in the acetone extraction rate. This is because all of them have an ester bond, and the latter is because a normal type polyurethane is used. From this, it can be seen that the durability and storability of a magnetic tape using a normal type polyurethane as a binder are poor. Also, the magnetic tape of Comparative Example 2 has a low RF output,
The RF output drops significantly. This indicates that, since the magnetic metal powder is used, a higher output cannot be obtained and the stability is inferior to that of the barium ferrite of the above-mentioned embodiment.

[Brief description of drawings]

FIG. 1 is an example graph showing the relationship between the number of diol carbon atoms of the polycarbonate polyurethane resin used in the present invention and the jitter of the magnetic layer containing this resin, and FIG. 2 is the average molecular weight of the polycarbonate polyol of this resin component. A graph showing an example of the relationship with the jitter of the magnetic layer containing this resin, and FIG. 3 is a graph of an example showing the relationship between the proportion of polycarbonate polyol in this resin and the wear resistance of the magnetic layer containing this resin. FIG. 4 is an example graph showing the relationship between the average molecular weight of the polycarbonate polyol polyurethane used in the present invention and the still durability of the magnetic layer containing this resin, and FIG. 5 is the average molecular weight of this resin and this resin. 6 is a graph showing an example of the relationship of the wear amount of the magnetic layer, and FIG. 6 is a cross section showing the structure of an example of the magnetic recording medium of the present invention FIG. 7 is a graph showing the relationship between the ratio of the vinyl chloride copolymer used in combination with the polycarbonate polyurethane used in the present invention and the fibrin-based resin, and the calenderability of the magnetic layer containing them, and FIG. Is a graph showing the relationship between the ratio of the polycarbonate polyurethane used in the present invention to other resins used in combination with the still durability of the magnetic layer containing these resins, and FIG. Sectional view showing the configuration of the example of FIG.
The figure is a cross-sectional view showing the structure of a magnetic disk of another example.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic material having a flat plate shape and an axis of easy magnetization perpendicular to the flat plate, and a magnetic layer containing a polycarbonate type polyurethane resin having no ester bond as a binder resin. .