JP2980918B2 - Magnetic recording media - Google Patents

Description

The present invention relates to a magnetic recording medium used for, for example, a video tape, an audio tape, and the like.
Good dispersibility of ferromagnetic powder and excellent production stability,
Moreover, the present invention relates to a magnetic recording medium having excellent running durability and electromagnetic conversion characteristics.

[Prior Art and Problems to be Solved by the Invention] In recent years, for example, in the audio field, DAT (Digital Audio Tape Recorder) has appeared, and in the VTR field, the width is smaller than the conventional 1/2 inch width standard. Narrow 8
Due to the fact that the mm width standard has appeared and is becoming widespread,
With respect to magnetic recording media, demands for high-density recording are increasing, and higher-performance magnetic recording media, that is, magnetic recording media excellent in electromagnetic conversion characteristics and running durability, are desired.

In response to this request, fine-grained ferromagnetic powders have been used for the purpose of improving the electromagnetic conversion characteristics of magnetic recording media. Poor dispersibility in the interior.

As a result, in a magnetic recording medium using finely divided ferromagnetic powder, the electromagnetic conversion characteristics may not be sufficiently improved. Some of the particles that are detached during running may adhere to the magnetic head instantaneously, and at this moment, the reproduction output is reduced. Various problems such as impaired smoothness, head clogging and edge breakage are likely to occur, and the running durability is reduced.

Therefore, the fact is that a magnetic recording medium which has improved dispersibility of the ferromagnetic powder and has excellent running durability and electromagnetic conversion characteristics without lowering the production stability is expected.

The present invention has been made based on the above circumstances.

An object of the present invention is to provide a magnetic recording medium which has good dispersibility of ferromagnetic powder, excellent production stability, excellent running durability, and high electromagnetic conversion characteristics suitable for high density recording. Is to do.

[Means for Solving the Problems] In order to solve the problems, the inventors of the present invention have conducted intensive studies, and as a result, have determined that the silicon content within a specific range, a specific average long axis length, and a specific A magnetic recording medium having a magnetic layer formed of a ferromagnetic powder having an axial ratio within a range and a binder containing a specific resin has a good dispersibility of the ferromagnetic powder and a high production stability. The present invention was found to be excellent in running durability and electromagnetic conversion characteristics, and suitable for high-density recording.

That is, the constitution of the present invention comprises a ferromagnetic powder containing silicon at a ratio of 0.1 to 0.35% by weight, having an average major axis length of 0.35 μm or less and an axial ratio of 7 to 11, and -SO ₃ M (M
Represents hydrogen or an alkali metal. A) a magnetic layer having a binder containing a polyvinyl chloride-based resin having a) and a polyurethane resin containing a negative functional group at a ratio of 1 to 6 / molecule on a non-magnetic support. Magnetic recording medium.

The nonmagnetic support and the magnetic layer constituting the magnetic recording medium of the present invention will be described below.

(Non-magnetic support) Materials for forming the non-magnetic support include, for example, polyethylene terephthalate and polyethylene-2,6.
-Polyesters such as naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polycarbonate. Further, metals such as Cu, Al, Zn, etc., glass, and various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.) can also be used.

There is no particular limitation on the form of the non-magnetic support,
Any of a tape shape, a sheet shape, a card shape, a disk shape, a drum shape and the like may be used, and various materials can be selected and used according to the form and as needed.

The thickness of these supports is usually 3 to 100 μm, preferably 3 to 50 μm in the case of a tape or sheet.
It is. In the case of a disk or card, the thickness is usually 30 to 100 μm. Further, in the case of a drum shape, a shape corresponding to a recorder to be used, such as a cylindrical shape, can be adopted.

A back coat layer may be provided on the surface (back surface) of the non-magnetic support on which the magnetic layer is not provided, for the purpose of improving the runnability of the magnetic recording medium, preventing charging and preventing transfer, and the like.

Further, on the surface of the non-magnetic support on which the magnetic layer is provided, for the purpose of improving the adhesion between the magnetic layer and the non-magnetic support, and the like,
An intermediate layer (for example, an adhesive layer) may be provided.

(Magnetic Layer) A magnetic layer is provided on the non-magnetic support.

The magnetic layer is a layer formed by dispersing ferromagnetic powder in a binder.

Examples of the ferromagnetic powder include γ-Fe ₂ O ₃ , Fe
₃ O ₄ , Co-adsorbed iron oxide, iron oxide magnetic powder such as Co solid-solution iron oxide, Fe, Ni, Co, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, Fe
-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co-Ni alloy, Fe, Ni, metal magnetic powder whose main component is Co or the like, CrC _2, Fe ₄ N, like other magnetic powders such as BaO-6Fe ₂ O _3.

Among them, γ-Fe ₂ O ₃ , Co-containing iron oxide and Cr ₂ O ₃ are preferable.

In the magnetic recording medium of the present invention, the silicon content of the ferromagnetic powder is 0.1% with respect to 100% by weight of the ferromagnetic powder.
0.30.35% by weight, preferably 0.15-0.30% by weight. Further, the ferromagnetic powder has an average major axis length of 0.35 μm or less, preferably 0.25 to 0.33 μm, and an axial ratio of 7 to 11, preferably 9 to 10.

The ferromagnetic powder contains 0.1 to 0.35% by weight of silicon in the ferromagnetic powder, has an average major axis length of 0.35 μm, and has an axial ratio in the range of 7 to 11. While improving the dispersibility of the magnetic coating material, it is possible to improve the production stability by suppressing an increase in viscosity when the magnetic coating material is used, and to improve the adhesion between the ferromagnetic powder and a binder described below in a magnetic layer. Thus, the running durability of the magnetic recording medium can be improved.

In other words, the silicon content in the ferromagnetic powder is
If it is less than 0.1% by weight, the stagnant viscosity of the magnetic paint increases, while if it exceeds 0.35% by weight, the magnetic properties deteriorate. When the average major axis length of the ferromagnetic powder is 0.35 μm or more, the surface properties of the medium are reduced, and the S / N ratio is deteriorated. Also,
When the axis ratio of the ferromagnetic powder is 7 or less, the orientation of the magnetic field decreases, and the output deteriorates. On the other hand, if it exceeds 11, dispersion is difficult and the filter pressure increases.

The shape of the ferromagnetic powder is not particularly limited as long as the average major axis length and the axial ratio are within the above specified range,
For example, a needle-like, column-like, or ellipsoid-like shape can be used.

In the magnetic recording medium of the present invention, the binder is-
Polyvinyl chloride resin having SO ₃ M (where M represents a hydrogen atom or an alkali metal) [hereinafter referred to as “resin A”. ] And a polyurethane resin having a negative functional group [hereinafter referred to as resin B]. And 1 to 6 negative functional groups are present in one molecule of the polyurethane resin.

The resin A and the resin B have the average major axis length, and together with silicon and a ferromagnetic powder having an axial ratio within the above range, improve the dispersibility of the ferromagnetic powder in the magnetic layer. It has the effect of achieving high electromagnetic conversion characteristics.

—SO ₃ M (where M represents the same meaning as described above) contained in the resin A is the vinyl alcoholic OH group contained in the polyvinyl chloride-based resin, and Cl—CH ₂ CH. _Two
And chlorine sulfonic acid metal salt containing chlorine SO ₃ M and the like, dimethyl formamide, in a polar solvent such as dimethyl sulfoxide, for example pyridine, picoline, amine salts such as triethylamine, ethylene oxide, propylene oxide, etc It can be suitably produced by a method of performing a dehydrochlorination reaction in the presence of a dehydrochlorination agent such as an epoxy compound.

The metal M of the resin A is an alkali metal such as lithium, potassium, and sodium, and potassium is particularly preferable in terms of solubility, reactivity, yield, and the like.

Examples of the polyvinyl chloride resin include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl maleate-vinyl alcohol copolymer , Vinyl chloride-vinyl propionate-vinyl maleate-acryl glycidyl ether-
(2-acrylamide-2-methylpropane potassium)
A vinyl chloride copolymer such as-(allyl-2-hydroxypropyl ether) copolymer can be used.

The vinyl chloride copolymer can be obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing a salt of sulfonic acid, and if necessary, another copolymerizable monomer. Since this copolymer is obtained by vinyl synthesis, it can be easily synthesized, and various copolymer components can be selected, so that the properties of the copolymer can be adjusted optimally.

As the copolymerizable monomer containing sulfonate, for _{example, CH 2 = CHCH 2 SO 3} M 0 CH 2 = C (CH 3) CH 2 SO 3 M 0 CH 2 = CHCH 2 OCOCH (CH 2 COOR) ^{_{SO 3 M 0 CH 2 = CHCH}} 2 OCH 2 CH (OH) CH 2 SO 3 M 0 CH 2 = C (CH 3) COOC 2 H 4 SO 3 M 0 CH 2 = CHCOOC 4 H 8 SO 3 M 0 CH 2 = CHCONHC (CH ₃₎ such as ₂ CH ₂ SO ₃ M ⁰ and the like.

[However, in the above, M ⁰ represents an alkali metal,
R represents an alkyl group having 1 to 20 carbon atoms. Examples of the copolymerizable monomer to be copolymerized as necessary include various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, various acrylic esters, methacrylic esters, Ethylene, propylene,
Examples thereof include isobutene, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, and maleic ester.

The resin B has -SO ₃ M ¹ and -OSO as negative functional groups.
₃ M ¹ , (Where M ¹ is a hydrogen atom or an alkali metal,
M ² and M ³ are each a hydrogen atom, an alkali metal or an alkyl group. Also the M ² and M ^3, may be different from each other, it may be the same. And a polyurethane resin having at least one of the above.

The polyurethane resin containing a negative functional group is composed of a dicarboxylic acid containing a negative functional group, which is a starting material of the polyester containing a negative functional group, a dicarboxylic acid containing no negative functional group, and a diol. It can be obtained by a condensation reaction and an addition reaction using various kinds of compounds and diisocyanate.

Further, a method of modifying the polyurethane resin to introduce a negative functional group is also conceivable.

That is, with these polyurethane resins, for example, (Wherein, M ¹ , M ² and M ³ have the same meanings as described above.) The compound containing the above-mentioned negative functional group and chlorine is condensed by a dehydrochlorination reaction and introduced into the molecule. Is the way.

The carboxylic acid component used to obtain the polyurethane resin, terephthalic acid, isophthalic acid,
Aromatic dicarboxylic acids such as orthophthalic acid and 1,5-naphthalic acid; p-oxybenzoic acid, p- (hydroxyethoxy)
Aromatic oxycarboxylic acids such as benzoic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid; tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid and pyromellitic acid; Is mentioned.

Among these, terephthalic acid, isophthalic acid, adipic acid and sebacic acid are preferred.

Examples of the dicarboxylic acid component containing a negative functional group include 5-sodium sulfoisophthalic acid,
-Potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 2-potassium sulfoterephthalic acid, and the like.

Examples of the diol component include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,
6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-
Examples include trimethyl-1,3-opentanediol, 1,4-cyclohexanedimethanol, an ethylene oxide adduct of bisphenol A, an ethylene oxide adduct of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. In addition, tri and / or tetraol such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol can be used in combination.

Examples of the isocyanate component used for obtaining the polyurethane resin include 4,4-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, and m-phenylene. Diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate,
3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,3-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanate methylcyclohexane , 1,4
-Diisocyanatomethylcyclohexane, 4,4'-diisocyanatodicyclohexane, 4,4'-diisocyanatodicyclohexylmethane, isophorone diisocyanate and the like.

The binder in the present invention is emulsion polymerization, solution polymerization,
It is polymerized by a polymerization method such as suspension polymerization or bulk polymerization. In any of the methods, a known technique such as divisional addition or continuous addition of a molecular weight regulator, a polymerization initiator, and a monomer can be applied as necessary.

The molecular weight of the resin B is usually 2,000 to 70,000, preferably 4,000 to 50,000. If the molecular weight exceeds 70,000, the viscosity of the magnetic coating material becomes too high to exceed the allowable range, and the object of the present invention may not be achieved. On the other hand, if the molecular weight is less than 2,000, an unreacted portion occurs at the stage where the magnetic paint is applied on the non-magnetic support and then cured using a curing agent, and a low molecular weight component remains. As a result, the physical properties of the coating film may be degraded.

The resin B has 1 to 6 negative functional groups in one molecule, and has a molecular weight of 200 to 7 per negative functional group.
It is desirable to be within the range of 0,000. If the number of the negative functional groups exceeds 6 per molecule, the hydrophilicity is too strong, causing a decrease in solubility in a solvent, compatibility with other resins in a binder, and moisture resistance of a magnetic layer. In addition, the rigidity of the obtained treated film is reduced, and the edge damage after long running is increased. On the other hand, if there is no negative functional group, the dispersibility may not be sufficiently improved.

The mixing ratio of the binder containing the resin A and the resin B is usually 5 to 40 parts by weight based on 100 parts by weight of the ferromagnetic powder.
Parts by weight, preferably 10 to 30 parts by weight.

By setting the compounding ratio within the above range, the dispersion state of the ferromagnetic powder in the magnetic layer can be improved, and the dispersion speed can be improved.

In the present invention, the durability of the magnetic layer can be improved by adding a polyisocyanate-based curing agent together with the resin B to the bonding agent.

Examples of the polyisocyanate-based curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.), Desmodur L (trade name, manufactured by Bayer AG) ) Or a polyisocyanate that can be used as a curing agent, such as a trifunctional isocyanate or a urethane prepolymer containing an isocyanate group at both terminals. can do.

The amount of the curing agent used is usually 5 to 80 parts by weight of the total binder amount.

The mixing ratio of the ferromagnetic powder and the binder in the magnetic layer is usually 1 to 200 parts by weight, preferably 1 to 50 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder.

If the amount of the binder is too large, the amount of the ferromagnetic powder may be reduced as a result and the recording density of the magnetic recording medium may decrease. Running durability may decrease.

In the magnetic recording medium of the present invention, the magnetic layer may further contain a lubricant, an abrasive, an antistatic agent and the like.

Examples of the lubricant include solid lubricants such as carbon black, graphite, carbon black graft polymer, molybdenum disulfide, and tungsten disulfide, silicon oil, modified silicon compounds, and carbon atoms.
A fatty acid ester (a so-called wax) composed of a monobasic fatty acid of 12 to 16 and a monohydric alcohol having a carbon number of 21 to 23 in total with the number of carbon atoms of the fatty acid; Fatty acids and the like.

Among them, preferred are carbon black, modified silicon compounds, fatty acids and fatty acid esters.

These may be used alone or in combination of two or more.

The amount of the lubricant to be used is generally 0.05 to 10 parts by weight based on 100 parts by weight of the ferromagnetic powder. Examples of the abrasive include aluminum oxide, titanium oxide (TiO, TiO
₂ ), inorganic powders of silicon oxide (SiO, SiO ₂ ), silicon nitride, chromium oxide and boron carbide, and organic powders such as benzoguanamine resin powder, melamine resin powder and phthalocyanine compound powder.

The average particle size of the abrasive is usually in the range of 0.1 to 1.0 μm.

Further, the amount of the abrasive is usually in the range of 0.5 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder.

Examples of the antistatic agent include carbon black, graphite, tin oxide-antimony oxide compounds,
Conductive powders such as tin oxide-titanium oxide-antimony oxide compounds and carbon black graft polymers; natural surfactants such as saponins; nonionic surfactants such as alkylene oxide, glycerin and glycidol; higher alkylamines; Cationic surfactants such as quaternary pyridine, other heterocycles, phosphonium and sulfoniums: Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, and phosphate group: amino acids And amphoteric surfactants such as aminosulfonic acid, sulfuric acid and phosphoric acid ester of amino alcohol.

These may be used alone or in combination of two or more.

The compounding amount of the antistatic agent is usually 0.5 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder.

The lubricant, the antistatic agent and the like do not have only a single action. For example, one compound may function as a lubricant and an antistatic agent.

Therefore, the above-mentioned classification in the present invention shows the main action, and the action of the classified compound is not limited to the action shown in the classification.

Next, a method for manufacturing the magnetic recording medium of the present invention will be described.

(Manufacturing method) The magnetic recording medium of the present invention is characterized in that the magnetic layer forming components such as the ferromagnetic powder and the binder are kneaded and dispersed in a solvent to prepare a magnetic coating material. It can be produced by coating and drying on the body.

Examples of the solvent used for kneading and dispersing the components for forming the magnetic layer include acetone, methyl ethyl ketone (MEK),
Ketones such as methyl isobutyl ketone (MIBK) and cyclohexanone: alcohols such as methanol, ethanol, propanol and butanol; S-types such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol monoacetate;
Ethers such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran and dioxane; aromatic hydrocarbons such as benzene, toluene and xylene; methylene chloride, ethylene chloride,
Halogenated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene can be used.

In kneading the magnetic paint components, the ferromagnetic powder and other magnetic paint components are simultaneously or individually charged into a kneader. For example, first, the magnetic powder is added to a solution containing a dispersant, kneaded for a predetermined time, then the remaining components are added, and further kneading is continued to obtain a magnetic paint.

For kneading and dispersion, various kneading machines can be used. Examples of the kneading machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a side grinder, a Sqegvagi attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disper kneader, a high-speed mixer, a homogenizer, and an ultrasonic wave. Dispersing machines and the like are mentioned.

A dispersant can be used for kneading and dispersing the ferromagnetic powder.

Examples of the dispersant include lecithin, phosphate, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinate, known surfactants and the like, salts thereof, and negative organic groups ( For example, -COOH,-
PO ₃ H) salts of polymer dispersants and the like.

These may be used alone or in combination of two or more.

The amount of the dispersant added is usually 1 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder.

The coating solution of the magnetic layer forming component thus prepared is
It is coated on a non-magnetic support by a known method.

Coating methods that can be used in the present invention include, for example, gravure roll coating, knife coating, wire bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, skies coating, kiss coating and And phantin coating.

The thickness of the magnetic layer applied in this manner is usually 1 to 10 μm in dry thickness.

The magnetic layer is usually formed as a single layer on the support, but may be formed as two or more layers for higher density.

Further, the back surface of the support may be back-coated to protect the support, prevent static charge, and improve running properties.

After the components for forming the magnetic layer are applied in this manner, if necessary, a magnetic field orientation treatment is performed in an undried state, and a surface smoothing treatment is usually performed using a super calender roll or the like.

Next, by cutting into a desired shape, a magnetic recording medium can be obtained.

The magnetic recording medium of the present invention can be used as a magnetic tape such as a video tape or an audio tape by cutting into a long shape, or as a floppy disk or the like by cutting into a disk shape. In addition, like a normal magnetic recording medium,
A form such as a cylindrical shape can also be used.

[Examples] Next, examples of the present invention and comparative examples will be shown, and the present invention will be described more specifically. In Examples and Comparative Examples described below, “parts” means “parts by weight”.
Shall be expressed.

(Example 1) A magnetic layer composition having the composition shown below was mixed and dispersed using a ball mill for 48 hours to obtain a dispersion, and then a polyisocyanate compound [trade name "Coronate L"; 5 parts) were added and mixed to prepare a magnetic paint.

Co-containing iron oxide-based ferromagnetic powder 100 parts [Silicon content 0.25% by weight, average major axis length 0.27μ
m, axis ratio 10] α-Al ₂ O ₃ [0.2 μm] 5 parts Carbon black [Average particle diameter 40 μm] 0.3 parts Potassium sulfonate group-containing polyvinyl chloride resin 9 parts Polyurethane resin (with negative functional group) 6 parts [Toyobo Co., Ltd .; UR-8700] Myristic acid 1 part Stearic acid 1 part Butyl stearate 0.5 part Cyclohexane 100 parts Methyl ethyl ketone 100 parts Also, a mixture having the following composition was prepared in the same manner as the above magnetic paint. To this mixture, methyl ethyl ketone and toluene were added as solvents, and the mixture was dispersed with a sand grinder to a viscosity of 10 cps.
Parts were added.

Polyurethane resin 50 parts Carbon black [Average particle diameter; 20 µm, oil absorption; 115 ml / 100 g] 100 parts Nitrocellulose 40 parts First, the obtained magnetic paint is applied on a 10 µm thick polyethylene terephthalate film so that the dry thickness becomes 3 µm. Was applied.

Next, a back coat layer was applied to the back surface of the film so that the dry thickness became 1.0 μm.

Then, after removing the solvent under heating, the surface was smoothed with a super calender and cut to a width of 12.65 mm to produce a 12.65 mm video tape.

Various characteristics of this 12.65 mm video tape were measured.

 The results are shown in Table 2.

 In addition, each characteristic was measured as follows.

Magnetic layer surface roughness (Ra); 3D roughness measuring instrument SE-3FK
The sample surface (or the surface of the back coat layer) was measured at a cutoff of 0.25 and a stylus pressure of 30 mg with a 2.5 mm cutoff (manufactured by Kosaka Laboratories).

Electromagnetic conversion characteristics; RF output; output during playback with 100% white signal
The tape of Example 1 was used as a reference tape and determined by comparison.

Lumi S / N; Use a noise meter (manufactured by Shibasoku)
With the tape of Example 1 as a reference, the difference in S / N of the sample at 100% white signal was determined in comparison with the tape of Example 1.

Young's modulus: Tensilon HTM-100 is used. The crosshead speed is 100 mm / min, and the sample length is 400 mm. The load at 1% elongation is measured (unit: kg / mm ² ). Running test; using HR-S7000 manufactured by JVC,
The produced video tape was run for 100 hours and evaluated by observing the presence or absence of edge breakage.

(Examples 2, 3 and Comparative Examples 1 to 4) In Example 1, the silicon content and the axial ratio of the ferromagnetic powder in the magnetic paint prepared in Example 1 and / or
Alternatively, a magnetic paint was prepared using the ferromagnetic powder and / or resin B shown in Table 1 in place of the number of polar groups and the weight average molecular weight per molecule of resin B, in the same manner as in Example 1 above. Then, a video tape was produced, and various characteristics of the obtained video tape were measured.

In addition, only in Example 3, the magnetic layer on the polyethylene terephthalate film was a multilayer.

In the magnetic layer of this multilayer, the upper layer uses a magnetic paint having the same composition as that of the above-mentioned Example 1, and the lower layer contains the magnetic paint of Example 1 with an average silicon content of 0.1% by weight of Co-containing iron oxide. The major axis length is reduced to 0.30μm, and carbon black [20mμ]
The same composition was used except that 10 parts was used.

Table 1 shows the composition of each magnetic paint. Table 2 shows the obtained results.

(Evaluation) As is clear from Table 1, the magnetic recording medium of the present invention is excellent in surface roughness and electromagnetic conversion characteristics of the magnetic layer of the completed recording medium, and not inferior in Young's modulus and running test. Was observed.

In addition, in the case of Example 3 in which the back layer was provided, it was recognized that the Young's modulus at room temperature and at 40 ° C., 80%, and 100 hours after was increased.

According to the present invention, (1) a ferromagnetic powder having a specific silicon content and a specific average major axis length and / or a specific axial ratio, and a resin having a specific polar group are contained. (2) Excellent running durability and no edge damage, (3) Small surface roughness of the obtained magnetic layer, (4) In addition, it is possible to provide a magnetic recording medium having such advantages that it has good electromagnetic conversion characteristics and can be suitably used for high-density recording.

Continuation of the front page (56) References JP-A-59-213626 (JP, A) JP-A-63-13121 (JP, A) JP-A-1-89019 (JP, A) (58) Fields investigated (Int .Cl. ⁶ , DB name) G11B 5/702 G11B 5/842 C09D 5/23 C09D 127/06 C09D 175/04

Claims (1)

(57) [Claims] 1. A ferromagnetic powder containing 0.1 to 0.35% by weight of silicon, having an average major axis length of 0.35 μm or less and an axial ratio of 7 to 11, and -SO ₃ M (M is hydrogen). A magnetic layer comprising a polyvinyl chloride resin having an atomic or alkali metal) and a binder containing a polyurethane resin containing 1 to 6 negative functional groups per molecule.
A magnetic recording medium comprising at least one layer provided on a nonmagnetic support.