JP2538296B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium used in, for example, video tapes, audio tapes, and the like. More specifically, the increase in viscosity of a magnetic coating material used for forming a magnetic layer is described. The present invention relates to a magnetic recording medium which is small, has excellent stability in stagnation, has a good dispersion state of a ferromagnetic alloy powder, has excellent electromagnetic conversion characteristics, running properties, and durability, and is suitable for high-density recording.

[Prior Art and Problems Thereof] A magnetic recording medium basically comprises a non-magnetic support and a magnetic layer containing a ferromagnetic powder, and is formed by providing a magnetic layer on the non-magnetic body. .

The magnetic layer is generally composed of a ferromagnetic powder dispersed in a binder.

In the magnetic recording medium having such a structure, particularly in the magnetic recording medium for VTR, in recent years, for example, an 8 mm width standard, which is narrower than the conventional 1/2 inch width standard, has appeared and is becoming widespread. Due to such circumstances, there is a strong demand for high density recording.

Therefore, in order to realize this high-density recording, a metal oxide-based ferromagnetic powder such as γ-Fe ₂ O ₃ which has been conventionally used as a ferromagnetic powder and an oxide containing other components such as cobalt are used. In place of the iron-based ferromagnetic powder, a ferromagnetic alloy powder that can be used for higher density recording by pulverizing it has been used.

However, for example, if the ferromagnetic alloy powder is used in a fine powder to improve the S / N, the dispersibility of the ferromagnetic alloy powder in the binder is deteriorated and the viscosity of the magnetic coating material is greatly increased, resulting in a magnetic This causes a problem that the stagnation stability of the paint is reduced.

These problems adversely affect the electromagnetic conversion characteristics, surface properties, durability, etc. of the magnetic layer, and also cause deterioration of workability during manufacture of the magnetic recording medium.

Therefore, for the purpose of improving the dispersion state of the ferromagnetic alloy powder in the binder, for example, -SO in the binder is used.
₃ M, -OSO ₂ M, -COOM and (Wherein, M represents a hydrogen atom, one of lithium and sodium, M ¹ and M ² are each a hydrogen atom, is either lithium, potassium, sodium and the alkyl group. The M ¹ and M ² may be the same as or different from each other.) A magnetic recording medium has been proposed in which the binder contains a resin having at least one kind of polar group selected from the group consisting of (JP-A-59-5423, JP-A-59-5424, JP-A-59-5424)
See Japanese Patent No. 59-8127. ).

However, in these magnetic recording media, the dispersion state immediately after dispersion of the ferromagnetic alloy powder is certainly good, but the dispersion state deteriorates due to an increase in viscosity and the like when the stagnation time becomes long, so good running property is obtained. However, there is a new problem in that the edge of the magnetic recording medium and the head clogging occur.

That is, in the magnetic recording medium containing the binder into which the above polar group is introduced, there is still room for improvement in the mechanical properties of the magnetic layer, and it cannot be said that the running property and durability are sufficient. .

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

The object of the present invention is that the increase in viscosity of the magnetic coating material forming the magnetic layer is small and the stagnation stability is good, and the dispersion state of the ferromagnetic alloy powder is good, and the electromagnetic conversion characteristics are excellent, and the running property and An object of the present invention is to provide a magnetic recording medium having excellent durability and suitable for high density recording.

[Means for Solving the Problems] In order to solve the problems, the inventors of the present invention have conducted extensive studies, and as a result, have a specific polar group other than -COOM among the above polar groups. With a binder containing a resin in a specific ratio and an Fe-Al alloy powder having a specific surface area, having the above polar group in the magnetic layer, and having a molecular weight within a specific range. In the magnetic recording medium containing the compound, the increase in viscosity of the magnetic coating is small, and
The inventors have reached the present invention by discovering that the Fe-Al alloy powder has a good dispersion state, excellent electromagnetic conversion characteristics, excellent durability and running properties, and is suitable for high-density recording.

That is, the constitution of the present invention is such that Fe-on a non-magnetic support.
In a magnetic recording medium provided with a magnetic layer containing an Al-based alloy powder and a binder, the specific surface area of the Fe-Al-based alloy powder by the BET method is 45 m ² / g or more, and the binder is polar. a resin having a group in a proportion of more than 90 wt%, more polar groups of the resin having a polar group, -SO ₃ M, -OS
O ₃ M and (In the formula, M is any one of hydrogen ion, alkali metal ion, alkaline earth metal ion, ammonium ion and alkylammonium ion, and M ¹ and M ² are hydrogen ion, alkali metal ion and alkyl group, respectively. M ¹ and M ² may be the same as or different from each other.) And the magnetic layer is —SO ₃ M, —OSO. ₃ M and (However, in the formula, M is a hydrogen ion, an alkali metal ion, an alkaline earth metal ion, an ammonium ion or an alkali ammonium ion, and M ¹ and M ² are either a hydrogen ion or an alkali metal ion, respectively. M ¹ and M ² may be the same as or different from each other.) Of these, a compound having at least one kind of polar group and having a molecular weight of 300 to 4000 is contained. It is a characteristic magnetic recording medium.

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

(Non-magnetic support) Examples of materials for forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate. A plastic such as polycarbonate may be used. Further, metals such as Cu, Al, and Zn, glass, various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.), and the like can be used.

The form of the non-magnetic support is not particularly limited and may be a tape, a sheet, a card, a disc, a drum or the like, and various materials may be selected depending on the form and as necessary. Can be used.

The thickness of the non-magnetic support is usually in the range of 3 to 100 μm, preferably 5 in the case of tape or sheet.
Within the range of 50 μm. In the case of a disc or a card, it is usually in the range of 30 to 100 μm. Further, in the case of a drum shape, it can be formed into a shape corresponding to the recorder to be used, such as a cylindrical shape.

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 running property of the magnetic recording medium, preventing charging, and preventing transfer.

Further, on the surface of the non-magnetic support on which the magnetic layer is provided, for the purpose of improving the adhesiveness between the magnetic layer and the non-magnetic support,
It is also possible to provide an intermediate layer (for example, an adhesive layer).

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

The magnetic layer is a layer formed by dispersing the Fe-Al alloy powder in a binder.

Examples of the Fe-Al alloy powder include Fe-Al alloy powder and Fe-Al-Ni alloy powder. The Fe-Al alloy powder has excellent weather resistance.

The specific surface area of the Fe-Al alloy powder by the BET method is 45 m ² /
It is g or more, preferably 45 to 80 m ² / g. This specific surface area is 4
If it is less than 5 m ² / g, the S / N ratio of the magnetic recording medium may decrease, and it may become unsuitable for high density recording.

The shape of the Fe-Al-based alloy powder is not particularly limited, and for example, a needle-shaped, spherical, or ellipsoidal shape can be used.

One of the important points in the present invention is that the binder has a polar group [hereinafter, referred to simply as resin (A)]. ] 90% by weight or more.

The resin having a polar group [resin (A)] improves the dispersed state of the Fe-Al alloy powder in the binder of the magnetic recording medium of the present invention, and prevents powder falling and head clogging. Have.

Resin having a polar group [Resin (A)] is, -SO ₃ M, -OSO ₃ M and a polar group (However, in the formula, M is any one of a hydrogen atom, an alkali metal ion (lithium ion, sodium ion, etc.), an alkaline earth metal ion, an ammonium ion and an alkylammonium ion, and M ¹ and M ² are each hydrogen. Atom, alkali metal ion (lithium ion,
Potassium ion, sodium ion, etc.) and an alkyl group. Further, M ¹ and M ² may be different from each other or may be the same. ) At least one of the above.

Examples of the resin that constitutes the resin (A) include vinyl chloride resin, polyurethane resin, polyester resin, polyethylene resin and the like.

These resins can be obtained by various methods.
For example, a metal sulfonate-containing polyester resin is obtained by using a dicarboxylic acid containing a metal sulfonate as a part of the dicarboxylic acid component and condensing this with a dicarboxylic acid having no metal sulfonate together with a diol. be able to.

Polyurethane resin containing sulfonate metal base,
Condensation using three types of compounds, a dicarboxylic acid containing a metal sulfonate base, which is a starting material for a polyester containing a metal sulfonate base, a dicarboxylic acid not containing a metal sulfonate base, and a diol, and diisocyanate. It can be obtained by a reaction and an addition reaction.

Furthermore, a method of modifying a polyester resin, a polyurethane resin, or a vinyl chloride resin to introduce a polar group can be considered.

In other words, with these resins, for example, _{Cl-CH 2 CH 2 SO 3} M, Cl-CH 2 CH 2 OSO 3 M (However, in the formula, M, M ¹ and M ² have the same meanings as described above.) In a method of introducing the above polar group and a compound containing chlorine into the molecule by condensation by dehydrochlorination reaction. is there.

Examples of the carboxylic acid component used to obtain the polyester resin and the polyurethane resin include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid; p-oxybenzoic acid, p- ( Aromatic oxycarboxylic acids such as (hydroxyethoxy) benzoic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, trimellitic acid, trimesic acid, pyromellitic acid and tri- and tetra- Examples thereof include carboxylic acid.

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

Examples of the dicarboxylic acid component containing the metal sulfonate group include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid.

Examples of the diol component include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,
6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-
Trimethyl-1,3-opentanediol, 1,4-cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like can be mentioned. Further, tri and / or tetraol such as trimethylol ethane, trimethylol propane, glycerin and pentaerythritol can be used together.

Examples of the above-mentioned isocyanate component used for obtaining the polyurethane resin include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate and tetra. Methylene 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-diisocyanate methylcyclohexane, 4,4'-
Diisocyanate dicyclohexane, 4,4'-diisocyanate dicyclohexylmethane, isophorone diisocyanate and the like can be mentioned.

When the vinyl chloride resin is modified to introduce a metal sulfonate group, examples of the vinyl chloride resin include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, A vinyl chloride-vinyl acetate-vinyl maleate-vinyl alcohol copolymer, a vinyl chloride-vinyl propionate-vinyl maleate-vinyl alcohol copolymer and the like can be used.

Vinyl alcohol OH contained in these copolymers
A base, said _{Cl-CH 2 CH 2 SO 3} M, and chlorine sulfonic acid metal salt containing Cl-CH ₂ CH ₂ OSO ₃ chlorine M such as dimethylformamide, in a polar solvent such as dimethyl sulfoxide, For example, a method of carrying out a dehydrochlorination reaction in the presence of a dehydrochlorination agent such as an amine salt such as pyridine, picoline or triethylamine, an epoxy compound such as ethylene oxide or propylene oxide can be preferably used.

Among the resins (A), vinyl chloride copolymers are preferable.

The vinyl chloride-based copolymer is a vinyl chloride monomer,
It can be obtained by copolymerizing a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid and, if necessary, another copolymerizable monomer. Since this copolymer is produced by vinyl synthesis, it is easy to synthesize, various copolymerization components can be selected, and the properties of the copolymer can be optimally adjusted.

The metal of the salt of sulfonic acid or phosphoric acid is an alkali metal (particularly sodium, potassium, lithium), and potassium is particularly preferable in terms of solubility, reactivity, yield and the like.

Examples of the copolymerizable monomer containing a sulfonate include CH ₂ ═CHSO ₃ M CH ₂ ═CHCH ₂ SO ₃ M CH ₂ ═C (CH ₃ ) CH ₂ SO ₃ M CH ₂ ═CHCH ₂ OCOCH ( CH ₂ COOR) SO ₃ M CH ₂ = CHCH ₂ OCH ₂ CH (OH) CH ₂ SO ₃ M CH ₂ = C (CH ₃ ) COOC ₂ H ₄ SO ₃ M CH ₂ = CHCOOC ₄ H ₈ SO ₃ M CH ₂ = CHCONHC (CH ₃₎ such as ₂ CH ₂ SO ₃ M and the like.

As the _{phosphate, CH 2 = CHCH 2 OCH 2} CH (OH) CH 2 -O-PO 3 M 3 Y 1 CH 2 = CHCONHC (CH 3) 2 CH 2 -O-PO 3 M 3 Y 2 CH ₂ ═CHCH ₂ O (CH ₂ CH ₂ O) _m POMX ² [wherein M represents an alkali metal,
R represents an alkyl group having 1 to 20 carbon atoms, Y ¹ represents a hydrogen atom, M, or CH ₂ ═CHCH ₂ OCH ₂ CH (OH) CH ₂ —, Y ² represents a hydrogen atom, M and CH ₂ CH = CONHC (CH ₃ ) ₂ CH ₂ −, and X ¹ is X ² represents CH ₂ CHCHCH ₂ O (CH ₂
CH ₂ O) represents one of _m −, OH and OM. Also, m
And n are positive numbers from 1 to 100. 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 acid esters, methacrylic acid esters, ethylene. ,propylene,
Examples thereof include isobutene, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid and maleic acid ester.

The binder in this invention is emulsion polymerization, solution polymerization,
Polymerization is carried out by a polymerization method such as suspension polymerization or bulk polymerization. In any of the methods, known techniques such as molecular weight regulator, polymerization initiator, and monomer addition or continuous addition can be applied as necessary.

The amount of the acid group salt-containing monomer in the binder is 0.01 to 30.
It is preferably mol%. If the amount of the salt-containing monomer is too large, the solubility in a solvent may be poor and gelation may easily occur. On the other hand, if the amount of the salt-containing monomer is too small, desired properties may not be obtained.

The vinyl chloride-based copolymer preferably further contains an epoxy group or a hydroxyl group.

By the way, the conventional vinyl chloride-based copolymer has been, for example, a copolymer of the following monomer units.

[However, j, k and 1 represent an integer. However, here, it is considered that the CH ₃ CO—O— group hardly contributes to a crosslinking reaction with a curing agent or the like.

Therefore, in the present invention, instead of CH ₃ CO, It is preferable to contain an epoxy group such as

Specifically, the resin of the combination of the following units can be illustrated.

[However, q, r and s have the same meanings as described above, and t
Is an integer. Z is a monomer unit part containing an alkali metal salt of a sulfo group or a phospho group. The molecular weight of the resin (A) is usually 2,000 to 70,000, preferably 4,000 to 50,000. If this molecular weight exceeds 70,000, the viscosity of the magnetic coating will increase beyond the permissible range,
The object of the present invention may not be achieved. on the other hand,
When the molecular weight is less than 2000, in the step of applying a magnetic coating on the non-magnetic support and then curing with a curing agent,
Unreacted parts may be generated, and low molecular weight components may remain, which may deteriorate the physical properties of the coating film.

The resin (A) has a molecular weight per polar group of
It is desirable to be in the range of 200 to 70,000. If the molecular weight per polar group is less than 200, the hydrophilicity is too strong,
The solubility in a solvent, the compatibility with other resins in the binder, and the moisture resistance of the magnetic layer may be deteriorated. On the other hand, if the molecular weight per polar group exceeds 70,000, the dispersibility may not be sufficiently improved.

The content of the resin (A) in the binder is 90% by weight.
Or more, preferably 95% by weight or more. This content is 90
If it is less than wt%, the dispersion state of the Fe-Al alloy powder may be deteriorated, and the electromagnetic conversion characteristics and the running property of the magnetic recording medium may be deteriorated. In addition, the content of the resin (A)
When it is 90% by weight or more, still durability can be particularly improved.

In the magnetic recording medium of the present invention, a resin which does not have a polar group in the binder together with the resin (A) [hereinafter, may be simply referred to as a resin (B). ] May be contained.

Here, having no polar group means that it has no polar group that is particularly easily adsorbed on the surface of the Fe-Al alloy powder, such as the polar group in the resin having the polar group, and Even if it has such a polar group,
It means that the amount is a very small amount that does not substantially adsorb to the magnetic powder.

The resin (B) functions to improve the mechanical strength and durability of the magnetic layer in the magnetic recording medium of the present invention and to increase the friction coefficient of the smooth magnetic layer surface realized by the resin (A). Has the effect of preventing

The glass transition temperature (Tg) of the resin (B) is usually 25
C. or higher, preferably 45.degree. C. or higher. If the glass transition temperature (Tg) is less than 25 ° C., the rigidity of the magnetic layer itself is lowered, and the tape may be broken at the edges of the tape or the head may be clogged during repeated running.

The resin (B) has an average molecular weight of about 10,000 to 200.
Resins within the range of 000 can be used.

Specifically, for example, urethane resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative. (Example: cellulose acetate butyrate, cellulose diacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubber binders, phenol resin, epoxy resin,
Urea resin, melamine resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol and high molecular weight diol compound And mixtures thereof.

 Among these, urethane resin is preferable.

When a urethane resin is used, the compounding ratio of the resin (A) to the urethane resin is usually 90 to 10
It is in the range of parts by weight, preferably in the range of 80 to 20 parts by weight.

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

Examples of the polyisocyanate 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 Co., Ltd.). ), Etc., or urethane prepolymers containing isocyanate groups at both ends, such as those conventionally used as curing agents, and those that are polyisocyanates that can be used as curing agents. can do.

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

The mixing ratio of the Fe-Al alloy powder and the binder (including the curing agent when the curing agent is used) in the magnetic layer is 100 parts by weight of the Fe-Al alloy powder. Usually, the binder is 1 to 200 parts by weight, preferably 1 to 50 parts by weight. Too much binder will result in Fe.
If the amount of the —Al alloy powder is reduced, the recording density of the magnetic recording medium may be reduced. If it is too small, the strength of the magnetic layer may be reduced and the running durability of the magnetic recording medium may be reduced.

One of the important points in the present invention is that the magnetic layer
-SO ₃ M, -OSO ₃ M and (However, in the formula, M, M ¹ and M ² , M is a hydrogen ion,
Alkali metal ion, alkaline earth metal ion, ammonium ion and alkylammonium ion, M ¹ and M ² are each hydrogen ion and alkali metal ion, and M ¹ and M ² are each other. It may be the same or different. A compound having at least one kind of polar group among the above) and having a molecular weight in the range of 300 to 4000 [hereinafter, may be simply referred to as compound (C). ] Is contained.

The compound (C) has a function of preventing edge breakage of the magnetic recording medium of the present invention, realizing a good running property, and a function of improving stagnation stability of the magnetic coating material.

The molecular weight of the compound (C) is in the range of 300 to 4000. If the molecular weight is less than 300, the strength of the magnetic layer may be lowered, and the running durability of the magnetic recording medium of the present invention may be deteriorated. On the other hand, when it exceeds 4000, the dispersion state of the Fe-Al alloy powder in the magnetic layer may be deteriorated.

The compound (C) is in the form of a salt,
Those which satisfy the conditions such as being an azo compound and having a red color are preferable.

Specifically, the following formula (a); (In the formula, X represents any one of chlorine atom, nitro group, methyl, ethyl, methoxy and ethoxy, Y represents chlorine atom, Z represents sulfo group or its ammonium salt, alkali metal salt, alkali Represents an earth metal salt or an organic amine salt, n ₁ and n ₂ each represent an integer of 0 to 5, and m ₁ and m ₂ each represent an integer of 0 to 2). Organic dye compounds can be mentioned as preferred ones.

Specific examples of the compound represented by the formula (a) include: And the like.

The organic dye compound represented by the formula (a) is
It is not limited to the above, but various substitutions for modification are possible.

Further, as the preferable compound (C), the following formula (b); {However, in the formula (b), A is a hydroxyl group [R is a hydrogen atom or an aliphatic residue having 1 to 30 carbon atoms. ] Is shown and n is an integer greater than or equal to 6. } The phosphoric acid ester represented by these can be mentioned.

Examples of the phosphoric acid ester represented by the formula (b) include, for example, And / or this diphosphate ester, and the like.

The compound (C) may be used alone, or 2
You may use it in combination of 2 or more types.

The molecular weight of the compound (C) is in the range of 300 to 4000. If the molecular weight is less than 300, the strength of the magnetic layer may be lowered, and the running durability of the magnetic recording medium of the present invention may be deteriorated. On the other hand, when it exceeds 4000, the dispersion state of the Fe-Al alloy powder in the magnetic layer may be deteriorated.

The addition amount of the compound (C) is the Fe-Al alloy powder.
Usually, 0.1 to 20 parts by weight, preferably 100 parts by weight,
It is 0.1 to 10 parts by weight. If the amount added is less than 0.1 parts by weight, the running properties of the magnetic recording medium of the present invention may not be sufficiently improved. On the other hand, if it exceeds 20 parts by weight, the strength of the coating film may be lowered, and powder falling or edge breakage may occur.

In the present invention, other lubricant may be used together with the compound (C).

Examples of the lubricant include solid lubricants such as carbon black, graphite, carbon black graft polymer, molybdenum disulfide, and tungsten disulfide; silicone oils, modified silicone compounds, fatty acids and fatty acid esters, and the like.

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

The amount of the lubricant used is usually 0.05 to 10 parts by weight with respect to 100 parts by weight of the Fe-Al alloy powder.

In the magnetic recording medium of the present invention, the magnetic layer may contain the resin (A), the resin (B), the compound (C) and the above-mentioned lubricant, as well as an abrasive and an antistatic agent.

Examples of the abrasive include inorganic powders such as aluminum oxide, titanium oxide (TiO, TiO ₂ ), silicon oxide (SiO, SiO ₂ ), silicon nitride, chromium oxide and boron carbide, and besozoguanamine resin powder, melamine resin powder and phthalocyanine. Organic powders such as compound powders may be mentioned.

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 compounded is the Fe-Al alloy powder.
It is usually in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight.

Examples of the antistatic agent include conductive powders such as graphite, carbon black, tin oxide-antimony oxide compounds, tin oxide-titanium oxide-antimony oxide compounds, and carbon black graft polymers; natural surfactants such as saponin; Nonionic surfactants such as alkylene oxides, glycerins, and glycidols; cationic surfactants such as higher alkylamines, quaternary pyridines, other heterocycles, phosphoniums and sulfoniums: carboxylic acids, sulfonic acids, and phosphoric acids Anionic surfactants containing an acidic group such as a sulfuric acid ester group, a phosphoric acid ester group and the like: amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid and phosphoric acid esters of amino alcohol;

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

The blending amount of the antistatic agent is usually 0.5 to 20 parts by weight with respect to 100 parts by weight of the Fe-Al alloy 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 classification in the present invention shows the main effects, and the effects of the classified compounds are not limited by the effects 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 comprises the Fe-Al alloy powder,
A magnetic coating composition can be produced by kneading and dispersing a magnetic layer forming component such as a binder in a solvent to prepare a magnetic coating, and then coating the resulting magnetic coating on the non-magnetic support and drying.

Examples of the solvent used for kneading / dispersing the magnetic layer forming components include acetone, methyl ethyl ketone (MEK),
Ketones such as methyl isobutyl ketone (MIBK) and cyclohexanone: alcohols such as methanol, ethanol, propanol and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol monoacetate;
Ether systems such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, 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 composition of the magnetic paint components, the Fe-Al alloy powder and the other magnetic paint components are simultaneously or individually added to the kneader. For example, first add the magnetic powder in a solution containing a dispersant, after kneading for a predetermined time,
The rest of the components are added, and kneading is continued to obtain a magnetic paint.

For kneading and dispersing, various kneaders can be used. Examples of this kneader include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a side grinder, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disperkneader, a high-speed mixer, a homogenizer, and an ultrasonic wave. Examples include a disperser.

The coating solution of the magnetic layer-forming component prepared in this way is
The non-magnetic support is coated by a known method.

Examples of coating methods that can be used in the present invention include gravure roll coating, wire bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, squeeze coating, kiss coating and fantin coating. And so on.

The thickness of the magnetic layer thus coated is usually 0.5 to 20 μm as a dry thickness.

In this way, after applying the magnetic layer-forming component, magnetic field orientation treatment is carried out if necessary in the final dried state, and further surface smoothing treatment is usually conducted using a super calender roll or the like.

Then, 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 by cutting into a disk shape. Furthermore, like a normal magnetic recording medium, a card shape,
It can also be used in the form of a cylinder or the like.

EXAMPLES Next, examples and comparative examples of the present invention will be shown to more specifically describe the present invention. In the examples and comparative examples described below, "part" means "part by weight".

(Example 1) A magnetic layer composition having the following composition was mixed and dispersed in a ball mill for 48 hours to prepare a dispersion liquid, and the polyisocyanate compound [trade name "Coronate L"; Nippon Polyurethane Co., Ltd.] was added to the dispersion liquid. Co., Ltd.] 5 parts were added and mixed to prepare a magnetic paint.

Fe-Al-based ferromagnetic alloy powder (specific surface area 50 m ² / g) 100 parts Sodium sulfonate group-containing vinyl chloride-vinyl acetate copolymer 15 parts Sodium sulfonate group-containing polyurethane 10 parts Sulfonic acid group-containing salt Azo compound 2 Parts α-Al ₂ O ₃ 7 parts Stearic acid 2 parts Butyl stearate 2 parts Methyl ethyl ketone 300 parts Toluene 100 parts [wherein the sulfonic acid group-containing salt azo compound has the following formula; Is a compound represented by. The obtained magnetic paint was applied onto a polyethylene terephthalate film having a thickness of 10 μm so that the dry thickness would be 3 μm.

Then, after removing the solvent under heating, a surface was smoothed by applying a super calendar, and slit into an 8 mm width to produce an 8 mm video tape.

 Various properties of this 8 mm video tape were measured.

 The results are shown in Table 1.

 In addition, each characteristic was measured as follows.

Paint viscosity; B type rotary viscometer is used, 30 by No. 4 rotor
Measured by rotation.

Squareness ratio: Using VSM (measurement magnetic field 10 kOe), the ratio (Bm / Br) between the residual magnetic flux density (Br) and the saturation magnetic flux density (Bm) was obtained.

Y-S / N; noise meter (made by Shibasoku) is used, HP
The measurement was performed under the conditions of F (high-pass filter) 10 KHz and LPF (low-pass filter) 4.2 KHz.

Dust removal: Dirt on the tape running portion in the deck after repeated running (100 times) was wiped off, and the degree of dirt was visually determined.

Head clogging: Recording / playback was performed over the entire length of the tape, and it was examined whether RF-DOT was reduced due to head clogging.

Still durability: The time from the initial output in the still mode until the output decreased by 2db was measured.

Example 2 In Example 1, 7.5 parts of polyurethane containing sodium sulfonate group and 2.5 parts of polyurethane (without polar group) were used instead of 10 parts of polyurethane containing sodium sulfonate group.
Example 1 was repeated except that a mixture with parts was used.

 The results are shown in Table 1.

(Example 3) In Example 1, instead of the sulfonic acid group-containing azo compound, the following formula: Example 1 was repeated except that the phosphoric acid ester represented by

 The results are shown in Table 1.

(Comparative Example 1) In Example 1, except that a mixture of 5 parts of a sodium sulfonate group-containing polyurethane and 5 parts of polyurethane (without a polar group) was used in place of the sodium sulfonate group-containing polyurethane of 10 parts, An 8 mm video tape was produced in the same manner as in Example 1.

Various characteristics of this 8 mm video tape were measured in the same manner as in Example 1.

 The results are shown in Table 1.

As is clear from Table 1, the magnetic recording medium of this comparative example has a large increase in the viscosity of the magnetic paint and is poor in stagnation stability as compared with the magnetic recording medium of the present invention, and has a squareness ratio and a Y-S ratio. Inferior electromagnetic conversion characteristics from the / N measurement result,
Since running powder and clogging of the head were observed, the running performance and durability were also poor.

Comparative Example 2 An 8 mm video tape was produced in the same manner as in Example 1 except that lecithin was used instead of the azo group-containing azo compound in Example 1.

Various characteristics of this 8 mm video tape were measured in the same manner as in Example 1.

 The results are shown in Table 1.

As is clear from Table 1, the magnetic recording medium of this comparative example has a large increase in the viscosity of the magnetic paint and is poor in stagnation stability as compared with the magnetic recording medium of the present invention, and has a squareness ratio and a Y-S ratio. Inferior electromagnetic conversion characteristics from the / N measurement result,
Since the powder had fallen off and the head was clogged, and the still durability was extremely poor, the running performance and durability were also poor.

(Comparative Example 3) In Example 1, the following formula was used instead of the azo group-containing azo compound; Other than using the compound represented by (molecular weight 4700),
An 8 mm video tape was produced in the same manner as in Example 1.

Various characteristics of this 8 mm video tape were measured in the same manner as in Example 1.

 The results are shown in Table 1.

As is clear from Table 1, the magnetic recording medium of this comparative example has a large increase in the viscosity of the magnetic paint and is poor in stagnation stability as compared with the magnetic recording medium of the present invention, and has a squareness ratio and a Y-S ratio. Inferior electromagnetic conversion characteristics from the / N measurement result,
Since running powder and clogging of the head were observed, the running performance and durability were also poor.

(Comparative Example 4) In the same manner as in Example 1 except that the sulfonic acid group-containing azo compound was not used in Example 1 above.
8mm video tape was made.

Various characteristics of this 8 mm video tape were measured in the same manner as in Example 1.

 The results are shown in Table 1.

As is clear from Table 1, the magnetic recording medium of this comparative example has a large increase in the viscosity of the magnetic paint and is poor in stagnation stability as compared with the magnetic recording medium of the present invention, and has a squareness ratio and a Y-S ratio. Inferior electromagnetic conversion characteristics from the / N measurement result,
Since the powder had fallen off and the head was clogged, and the still durability was extremely poor, the running performance and durability were also poor.

Used in Comparative Example 5 Example 1, in place of the Fe-Al-based ferromagnetic alloy powder (specific surface area ^{50m 2 / g), Fe-} Zn-Ni ferromagnetic alloy powder (specific surface area 50 m ² / g) An 8 mm video tape was manufactured in the same manner as in Example 1 except for the above.

Various characteristics of this 8 mm video tape were measured in the same manner as in Example 1.

 The results are shown in Table 1.

As is clear from Table 1, the magnetic recording medium of this comparative example had powder falling and head clogging and the still durability was extremely poor as compared with the magnetic recording medium of the present invention. And was inferior in durability.

[Advantages of the Invention] According to the present invention, (1) since a binder containing a resin having a specific polar group in a proportion of 90% by weight or more is used, the increase in viscosity of the magnetic coating is small and the stagnation stability is improved. Excellent and good dispersion state of the ferromagnetic alloy powder, (2) therefore excellent in electromagnetic conversion characteristics, (3) In addition, still durability can be improved especially when used as a video tape, (4) ) Furthermore, since a compound having a specific polar group and a specific molecular weight is contained in the magnetic layer, good running property and durability can be realized without deteriorating mechanical properties, and particularly high It is possible to provide a magnetic recording medium which has various advantages such as being suitable for use as a magnetic recording medium for density recording.

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer containing Fe--Al alloy powder and a binder, wherein the Fe--Al alloy powder has a specific surface area of 45 m ² by the BET method. /
g or more, and the binder is a resin having a polar group 9
0 in a proportion by weight% or more, more polar groups of the resin having a polar group, -SO ₃ M, -OSO ₃ M and (In the formula, M is any one of hydrogen ion, alkali metal ion, alkaline earth metal ion, ammonium ion and alkylammonium ion, and M ¹ and M ² are hydrogen ion, alkali metal ion and alkyl group, respectively. M ¹ and M ² may be the same as or different from each other.) And the magnetic layer is —SO ₃ M, —OSO. ₃ M and (However, in the formula, M is any one of a hydrogen ion, an alkali metal ion, an alkaline earth metal ion, an ammonium ion and an alkylammonium ion, and M ¹ and M ² are each a hydrogen ion and an alkali metal ion. M ¹ and M ² may be the same as or different from each other.) Of these, a compound having at least one polar group and having a molecular weight of 300 to 4000 is contained. Characteristic magnetic recording medium.