JP2897032B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic recording medium.
The present invention relates to a magnetic recording medium in which the dispersibility of a ferromagnetic powder is improved, the electromagnetic conversion characteristics are excellent, and the balance of characteristics such as slipperiness and running durability is excellent.

[Problems to be Solved by the Related Art and the Invention] A magnetic recording medium useful as a recording / reproducing element in an information processing device has high and precise electromagnetic conversion characteristics, good running properties, durability and durability. It is required that the composition has such properties as to guarantee the properties, and it is particularly required to maintain these properties in a well-balanced manner.

In order to improve the electromagnetic conversion characteristics of the magnetic recording medium, a fatty acid may be added to the magnetic layer to improve the dispersibility of the ferromagnetic powder. The presence of the fatty acid on the surface of the magnetic layer is also useful for improving the slipperiness of the magnetic recording medium.

Incidentally, fatty acids useful for improving the dispersibility of the ferromagnetic powder in the magnetic layer and the slipperiness of the magnetic recording medium have polarity, and it is known that a large amount of the fatty acid plasticizes the coating film.

Therefore, if a large amount of fatty acid is added to the magnetic layer coating solution so that a large amount of fatty acid is present on the surface of the magnetic layer, the coating film becomes softer than necessary, improving the dispersibility of the ferromagnetic powder and the slipperiness of the magnetic recording medium. At the same time, there is a problem that the running durability, particularly the running durability under high temperature and high humidity, becomes remarkable.

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

An object of the present invention is to provide a magnetic recording medium in which the dispersibility of the ferromagnetic powder is improved, the electromagnetic conversion characteristics are excellent, and the characteristics balance such as slipperiness and running durability is excellent.

[Means for Solving the Problems] As a result of intensive studies by the present inventors to solve the above problems, the present inventors have a plurality of magnetic layers and the fatty acids contained in each magnetic layer satisfy a specific quantitative relationship. The present inventors have found that the magnetic recording medium has improved dispersibility of the ferromagnetic powder and has excellent electromagnetic conversion characteristics, and also has an excellent balance of characteristics such as slipperiness and running durability.

According to the structure of the first aspect of the present invention, an n-layer (where n is an integer of 2 or more) containing a ferromagnetic powder and a binder is provided on the non-magnetic support. , A first magnetic layer, a second magnetic layer,..., An n-th magnetic layer (where n represents an integer of 2 or more), and the amount of fatty acid present on the surface of the n-th magnetic layer ( F _s ) is not more than 0.2 g / m ² , and the amount of fatty acid (F _s ) present on the surface of the n-th magnetic layer and the total amount of free fatty acid (F _f ) in each magnetic layer are: following formula _{[I]; F s ≦ F} f ...... satisfy the relationship represented by [I], the adsorption amount of fatty acids present on the surface of the n-th magnetic layer (F _s) on the ferromagnetic powder in the magnetic layer and to have the total amount of fatty acid (F _a) is the following formula [II]; a F _s ≦ F _a ...... magnetic recording medium and satisfies the relationship represented by [II],請The structure of the invention in claim 2, wherein the total amount (F _a) is 1.0 g / m of the fatty acid adsorbed on the ferromagnetic powder in the magnetic layer
^2. The magnetic recording medium according to claim 1, wherein the number of fatty acids (F _p ) released in the n-th magnetic layer is less than or equal to (n−1). ) The amount ( _Fq ) of the free fatty acid in each magnetic layer from the magnetic layer to the first magnetic layer in each layer is represented by the following formula [II]
I]; _Fp ≧ _Fq ... [III] The magnetic recording medium according to claim 1 or 2, which satisfies a relationship represented by the following expression.

Hereinafter, the magnetic recording medium of the present invention will be described in detail for a magnetic layer, a non-magnetic support, and the like.

(Magnetic Layer) The magnetic recording medium of the present invention has an n-layer (where n represents an integer of 2 or more) magnetic layer each containing a ferromagnetic powder and a binder on a non-magnetic support. .

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

Examples of the ferromagnetic powder include Co-coated γ-Fe ₂ O ₃
Powder, Co-coated Fe ₃ O ₄ powder, Co-coated FeO _x (4/3 <x <3/2)
Powder, or Fe-Al metal powder, Fe-Ni metal powder, Fe-
Al-Ni metal powder, Fe-Al-P metal powder, Fe-Ni-Si-Al
Metal powder, Fe-Ni-Si-Al-Mn metal powder, Ni-Co metal powder, Fe-Mn-Zn metal powder, Fe-Ni-Zn metal powder, Fe-Co
Ferromagnetic metal powders such as -Ni-Cr metal powder, Fe-Co-Ni-P metal powder, Co-Ni metal powder and Co-P metal powder.

Among them, preferred is Co-coated γ-Fe ₂ O ₃ powder.

The coercive force (Hc) of the ferromagnetic powder is generally 500 Oe or more, preferably 600 Oe or more.

The specific surface area of the ferromagnetic powder by the BET method is usually 35 m
² / g or more, preferably 40 to 80 m ² / g.

The shape of the ferromagnetic powder is not particularly limited, and for example, any of acicular, spherical, and elliptical shapes can be used.

In the present invention, the binder preferably contains a urethane resin.

The urethane-based resin can be usually synthesized by a reaction between a polyisocyanate and a polyol.

Examples of the polyisocyanate that can be used for the synthesis of the urethane resin include tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), and 3,3. '-Dimethyl-4,4'-biphenylene diisocyanate (TODI), xylylene diisocyanate (XDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), crude TDI, polymethylene polyphenyl isocyanate (crude MDI ), Isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), hydrogenated xylylene diisocyanate (HXD
In addition to I) and the like, modified isocyanurates of these isocyanates, modified carbodiimides, buret modified products, and the like can be given.

These may be used alone or as a mixture of two or more.

Examples of the polyol include phthalic acid, isophthalic acid, terephthalic acid, maleic acid, succinic acid, adipic acid, organic dibasic acids such as sebacic acid, and ethylene glycol, propylene glycol, diethylene glycol,
Glycols such as polyethylene glycol; polyhydric alcohols such as trimethylolethane, trimethylolpropane, hexanetriol, glycerin and pentaerythritol; polyhydric phenols such as hydroquinone and bisphenol A; Polyester polyols synthesized by the reaction of two or more polyols selected from polyhydric phenols; lactams such as s-caprolactam, α-methyl-1-caprolactam, s-methyl-s-caprolactam, and γ-butyrolactam Lactam-based polyester polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, and the like.

These may be used alone or as a mixture of two or more.

The urethane resin may be a urethane resin or a urethane polymer whose terminal is at least one of an isocyanate group, a hydroxyl group and a carboxyl group, or may be a urethane elastomer containing no reactive terminal group. .

The compounding ratio of the urethane-based resin is the ferromagnetic powder 10
Usually, 1 to 200 parts by weight, preferably 1 to 0 parts by weight is used.
5050 parts by weight. If the compounding ratio is less than 1 part by weight, the dispersibility of the ferromagnetic powder may not be sufficiently improved, and the electromagnetic conversion characteristics of the magnetic recording medium may be reduced. Meanwhile, 20
If the amount is more than 0 parts by weight, the effect corresponding to the increase in the used amount may not be exhibited.

The binder, together with the urethane-based resin, for example, other resins such as thermoplastic resins, thermosetting resins, reactive resins, electron beam irradiation-curable resins or mixtures thereof conventionally used in magnetic recording media Ingredients can be used.

Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, and acrylate-vinylidene chloride copolymer. Polymer, methacrylate-vinylidene chloride copolymer, methacrylate-
Ethylene copolymer, polyvinyl fluoride, vinylidene chloride
Acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate), cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer, Examples include polyester resins, chlorovinyl ether acrylate copolymers, amino resins, and synthetic rubber-based thermoplastic resins.

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

As the thermosetting resin or the reactive resin, for example, a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, an acrylic reaction resin, a high molecular weight polyester resin and an isocyanate prepolymer. , A mixture of a methacrylate copolymer and a diisocyanate prepolymer, a urea formaldehyde resin, and a polyamine resin.

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

Examples of the electron beam irradiation-curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type; ether acrylic type And polyfunctional monomers such as urethane acrylic type, epoxy acrylic type, phosphoric acid ester acrylic type, aryl type and hydrocarbon type.

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

When the urethane resin and the other resin component are used in combination, the mixing ratio is usually 9: 1 by weight ratio of (urethane resin) :( other resin component).
1: 1: 9, preferably 8: 2 to 2: 8. If the mixing ratio is out of the above range, the electromagnetic conversion characteristics of the magnetic layer in the magnetic recording medium of the present invention may be reduced, or the dispersibility of the ferromagnetic powder may be reduced.

In the present invention, the urethane-based resin or the mixture of the urethane-based resin and the other resin component may be used as a binder as it is, and further, the urethane-based resin or the urethane-based resin may be used as a binder. A binder may be used by using a curing agent together with a mixture with other resin components.

Examples of the curing agent include polyisocyanate compounds (eg, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, and adducts of these polyisocyanate compounds with trivalent polyols, A pentamer of diisocyanate, an adduct of 3 mol of tolylene diisocyanate and 1 mol of trimethylolpropane, an adduct of 3 mol of metaxylylene diisocyanate and 1 mol of trimethylolpropane, and a pentamer of tolylene diisocyanate.

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

In the magnetic layer, the mixing ratio of the ferromagnetic powder and the binder (including the curing agent when the curing agent is used) is usually 5 parts by weight per 100 parts by weight of the ferromagnetic powder. -400 parts by weight, preferably 10-200 parts by weight.
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.

The magnetic layer in the magnetic recording medium of the present invention contains a fatty acid.

The fatty acid may be monobasic or dibasic, but the fatty acid preferably has 6 to 30, particularly 12 to 22, carbon atoms in the present invention.

Preferred fatty acids include, for example, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, linoleic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid , Maleic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,
Examples include 12-dodecanedicarboxylic acid, octanedicarboxylic acid and the like.

Among these, myristic acid, oleic acid and stearic acid are particularly preferred.

In the present invention, the fatty acids may be used alone or in combination of two or more.

In the present invention, the amount of fatty acids (F _s ) present on the surface of the uppermost magnetic layer (the n-th magnetic layer) among the n magnetic layers and the total amount of fatty acids released in each magnetic layer (F _f ) must satisfy the relationship represented by the formula [I]; F _s ≦ F _f ... [I].

At the same time, the amount of fatty acids (F _s ) present on the surface of the n-th magnetic layer and the total amount of fatty acids (F _a ) adsorbed on the ferromagnetic powder in each magnetic layer are represented by the following formula [II]; F _s ≦ F _a ... The relationship represented by [II] must be satisfied.

That is, in the present invention, the uppermost magnetic layer (the n-th magnetic layer) of the n
The presence of the fatty acid on the surface of the magnetic layer) [abundance (F _s)]. However, if the amount of the fatty acid present on the surface of the n-th magnetic layer is too large, a so-called blooming phenomenon occurs in which the fatty acid precipitates on the surface of the magnetic layer. (F _s ) needs to be less than or equal to the total amount of free fatty acids (F _f ) in each magnetic layer coating. The amount of fatty acids (Fs) present on the surface of the n-th magnetic layer refers to the amount of fatty acids extracted by immersing the sample in cyclohexane at room temperature for 2 minutes, and is released in each of the magnetic layers. The total amount of the fatty acids (Ff) refers to the total amount of the fatty acids extracted by holding each peeled magnetic layer in boiling cyclohexane for 1 hour.

In the present invention, the so-called blooming is achieved by setting the amount of fatty acid (F _s ) present on the surface of the n-th magnetic layer to the total amount of free fatty acid (F _f ) in each magnetic layer coating film or less. It is possible to supplement the fatty acid present on the surface of the n-th magnetic layer, which disappears gradually as the running time of the magnetic recording medium is increased, from the coating of each magnetic layer while preventing the phenomenon from occurring.

Further, the fatty acid adsorbed on the ferromagnetic powder in each magnetic layer is in an amount sufficient to satisfy the dispersibility and stagnant stability of the magnetic layer coating solution, and the presence of the fatty acid in an amount not exceeding the required amount of the coating film allows the Since it is necessary to control the hardness and not to deteriorate the running durability, the amount of the fatty acid (F _s ) present on the surface of the n-th magnetic layer and the amount of the ferromagnetic powder in each magnetic layer are reduced. The total amount (F _a ) of the adsorbed fatty acids must satisfy the relationship represented by the above formula [II]; F _s ≦ F _a ... [II]. The amount of fatty acid adsorbed on the ferromagnetic powder in each magnetic layer refers to the boiling methyl isobutyl ketone (MIB
K) for 3 hours, the extract obtained by concentrating the extract was added with cyclohexane, and the extract was extracted for 1 hour. The quantitative value of the fatty acid and the 6N hydrochloric acid / ethanol (1: 1) solution The total amount of fatty acids adsorbed on the ferromagnetic powder in each of the magnetic layers means the total amount (Fa) of the fatty acids obtained by similarly performing extraction after MIBK after immersion in the magnetic layer. And the total amount of the fatty acids for each magnetic layer thus obtained.

In order to reduce the amount of the fatty acid (F _s ) present on the surface of the n-th magnetic layer, for example, the amount of the fatty acid added to the upper layer is made smaller than that of the other layers, the temperature is increased under the heat retaining conditions, or the heat retaining time is increased. May be lengthened. In order to increase the total amount (F _a ) of the fatty acid adsorbed on the ferromagnetic powder in each magnetic layer, for example, the amount of the dispersant added may be reduced or the 4,4′- A polyurethane resin using diphenylmethane diisocyanate (MDI) or a polyurethane resin having a high molecular weight may be used.

Further, in the present invention, the amount of fatty acid (F _p ) released in the n-th magnetic layer and the amount of fatty acid released in each of the magnetic layers from the (n-1) -th magnetic layer to the first magnetic layer. It is preferable that the amount (F _q ) of the fatty acid in each layer satisfies the relationship represented by the above formula [III]; F _p ≧ F _q ... [III]. (N-
1) When the total amount ( _Fq ) of the fatty acids released in each magnetic layer from the magnetic layer to the first magnetic layer satisfies the relationship represented by the above formula [III], the deterioration of the magnetic layer coating film It is possible to replenish the consumed fatty acid on the surface of the n-th magnetic layer while minimizing the amount of the fatty acid.

Specifically, for example, by increasing the drying temperature to cause convection or prolonging the drying time, more fatty acids can be liberated in the upper layer than in the lower layer.

In order to suppress a decrease in the strength of the magnetic layer coating film, it is necessary to reduce the total amount of fatty acids (F _a ) adsorbed on the ferromagnetic powder in each magnetic layer coating film as much as possible. In order to reduce the total amount (F _a ) of the fatty acid adsorbed on the ferromagnetic powder in each magnetic layer coating film, for example, a dispersant that is more easily adsorbed on the ferromagnetic powder than the fatty acid may be used.

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 (eg, -COOH, -PO
₃ H) and salts of the polymeric dispersants.

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

In the present invention, among the dispersants, lecithin can be suitably used.

The amount of the dispersant added is usually 7 parts by weight or less, preferably 5 parts by weight or less, based on 100 parts by weight of the ferromagnetic powder.

In the present invention, the amount of the fatty acid (F _s ) present on the surface of the n-th magnetic layer is 0.2 g / m ² or less, particularly 0.15 g / m ² or less. When this (F _s ) exceeds 0.2 g / m ² , the so-called blooming phenomenon may occur.

The amount of the fatty acid (F _s ) present on the surface of the n-th magnetic layer
Is usually 10 parts by weight or less, preferably 7 parts by weight or less with respect to 100 parts by weight of the ferromagnetic powder.

In the present invention, the total amount (F _a ) of the fatty acid adsorbed on the ferromagnetic powder in each magnetic layer is 1.0 g / m ² or less, particularly 0.8 g / m ² or less.
It is preferably at most g / m ² . When the total amount (F _a ) of the fatty acid adsorbed on the ferromagnetic powder in each magnetic layer exceeds 1.0 g / m ² , the coating of the magnetic layer becomes softer than necessary and the running durability is deteriorated. There is.

The mixing ratio of the fatty acid in each magnetic layer to make the total amount (F _a ) of the fatty acid adsorbed on the ferromagnetic powder in each magnetic layer not more than 1.0 g / m ² is 100 parts by weight of the ferromagnetic powder. On the other hand, it is usually at most 8 parts by weight, preferably at most 6 parts by weight.

The magnetic layer preferably contains a fatty acid ester together with the fatty acid. When the magnetic layer contains a fatty acid ester together with the fatty acid, the friction coefficient of the magnetic layer is reduced, and the running properties and durability of the magnetic recording medium of the present invention are further improved.

Examples of the fatty acid ester include oleyl oleate, oleyl stearate, isocetyl stearate, dioleyl maleate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, amyl stearate,
Amyl palmitate, stearyl stearate, lauryl oleate, octyl oleate, isobutyl oleate,
Ethyl oleate, isotridecyl oleate, 2-ethylhexyl stearate, 2-ethylhexyl myristate, ethyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, cetyl-2-ethyl hexalate, Dioleyl adipate, diescyl adipate,
Examples include diisobutyl adipate and diisodecyl adipate.

Among these, butyl stearate and butyl palmitate are particularly preferred.

The above-mentioned various fatty acid esters may be used alone or in a combination of two or more.

When the fatty acid ester is used, the mixing ratio of the fatty acid ester is based on 100 parts by weight of the ferromagnetic powder.
Usually, it is 0.1 to 100 parts by weight, preferably 0.1 to 10 parts by weight.

The magnetic layer of the magnetic recording medium of the present invention may contain another lubricant together with the fatty acid or the fatty acid ester.

Other lubricants include, for example, silicone-based lubricants,
Fatty acid-modified silicone-based lubricants, fluorine-based lubricants, liquid paraffin, squalane, carbon black, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, and the like.

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

When the other lubricant is used, the mixing ratio of the other lubricant is based on 100 parts by weight of the ferromagnetic powder.
Usually, it is at most 20 parts by weight, preferably at most 10 parts by weight.
If the compounding ratio is more than 20 parts by weight, the amount of the lubricant may be excessive and the surface of the magnetic layer may be easily stained.

The magnetic layer may further contain an abrasive and an antistatic agent in addition to the various components described above.

Note that the antistatic agent or the dispersant described below does not have only a single action. For example, one compound sometimes acts 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 by the action shown in the classification.

(Non-magnetic support) Materials for forming the non-magnetic support in which the plurality of magnetic layers are laminated include, for example, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; cellulose triacetate; Examples include cellulose derivatives such as cellulose diacetate; and plastics such as polycarbonate. Further, metals such as Cu, Al, and Zn, and various ceramics such as glass, so-called new ceramics (for example, boron nitride, boron carbide, and the like) can also be used.

The form of the non-magnetic support is not particularly limited, and may be any of a tape form, a sheet form, a card form, a disk form, a drum form, and the like. Depending on the form, and if necessary, various materials may be used. Can be selected and used.

The thickness of the support is usually 3 to 100 μm, preferably 5 to 50 μm when it is in the form of a tape or a sheet. In the case of a disc or a card, 30
100100 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 running properties of the magnetic recording medium, preventing charging and preventing transfer, and the like.

An intermediate layer (for example, an adhesive layer) may be provided 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.

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 prepared by kneading and dispersing the magnetic layer forming components such as the ferromagnetic powder, urethane-based resin, and fatty acid in a solvent to prepare a magnetic coating material. It can be produced by coating and drying on a magnetic support.

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

In kneading and dispersing, various kneaders 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 Sqegvari 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 can be mentioned.

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, Meyer bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, skies coating, kiss coating, and phantin coating. And the like.

The thickness of the magnetic layer applied in this manner is such that the dry thickness of the n-th magnetic layer (the uppermost magnetic layer among the n-layers) is 0.1 to 5 μm, particularly 0.2 to 4 μm. The total dry thickness of the layers is usually from 0 to 6 μm.

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, for example, by cutting into a long shape, as a magnetic tape such as video tape, audio tape, or by cutting into a disk shape,
It can be used as a floppy disk or the like. Further, similarly to a normal magnetic recording medium, it can be used in the form of a card, a cylinder, or the like.

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

(Example 1) Preparation of magnetic paint Each of the first magnetic layer (lower layer) composition and the second magnetic layer (upper layer) composition having the following compositions was sufficiently stirred and mixed using a ball mill to form a dispersion. After that, 5 parts of a polyfunctional isocyanate compound [trade name “Coronate L”; manufactured by Nippon Polyurethane Co., Ltd.] is added to the dispersion and mixed, and the obtained mixture is filtered through a filter having an average pore diameter of 1 μm. A magnetic paint was prepared.

First magnetic layer (lower layer) composition Co-coated γ-Fe ₂ O ₃ powder [specific surface area 38 m ² / g (BET value, coercive force H _c 650e) 100 parts Urethane elastomer 10 parts [4,4′-diphenylmethane diisocyanate , 1,4-
Consisting of butanediol and adipic acid, -SO ₃ Na0.0
5 mmol / g content, molecular weight 30,000] vinyl chloride-vinyl acetate copolymer 5 parts myristic acid 2 parts palmitic acid butyl ester 2 parts methyl ethyl ketone 150 parts cyclohexanone 150 parts lecithin 3 parts 2nd magnetic layer (upper layer) composition Co-coated γ -fe ₂ O ₃ powder [specific surface area of 48m ² / g (BET value, coercive force H _c 850e] 100 parts of alumina powder 5 parts urethane elastomer 10 parts [4,4'-diphenylmethane diisocyanate, 1,4
Synthesized from butanediol and adipic acid, molecular weight 30,0
00] Vinyl chloride-vinyl acetate copolymer 5 parts Myristic acid 4 parts Palmitic acid butyl ester 2 parts Methyl ethyl ketone 150 parts Cyclohexanone 150 parts Carbon black [Conductex 975, manufactured by Columbian Carbon Co., Ltd.] 5 parts Lecithin 3 parts Video tape After the first magnetic paint obtained above was applied on a 14 μm-thick polyethylene terephthalate film to a dry thickness of 2.7 μm, the second magnetic paint obtained above was applied on the coating film of the first magnetic paint. The magnetic paint was applied to a dry thickness of 0.5 μm.

Next, after removing the solvent under heating, a surface smoothing treatment was performed at 70 ° C. and 200 kg / cm ² using a super calender roll to obtain a wide magnetic film having a magnetic layer of a predetermined thickness. .

About this magnetic film, the fatty acid amount in each magnetic layer was measured.

 The results are shown in Table 1.

 The measurement of the fatty acid amount was performed as follows.

(1) Fatty acid amount on the surface of the uppermost magnetic layer a) A sample corresponding to 253 cm ² of the uppermost magnetic layer, specifically
Approximately 50m of cyclohexane for 2m of 1/2 inch width tape
l was added and left for 2 minutes. It was then filtered and the sample was washed with a small amount of cyclohexane and combined with the extract.

B) To this extract, 5 ml of a methyl palmitate / cyclohexane solution adjusted to a concentration of 40 ppm was added.

Next, cyclohexane was evaporated from this solution using a rotary evaporator.

0.2 ml of cyclohexane was newly added to the concentrated extract, and 1 μ of the extract was subjected to gas chromatography.

From the relationship between the concentration of methyl palmitate and the fatty acid and the peak area, the amount of the fatty acid extracted from the calibration curve prepared in advance was determined.

(2) Amount of Free Fatty Acid in Each Magnetic Layer Each magnetic layer was peeled in advance, and about 50 ml of cyclohexane was added to each sample corresponding to 253 cm ² of each magnetic layer.

These were boiled under reflux for 1 hour, returned to room temperature, and the sample was washed with a small amount of cyclohexane and combined with the extract.

Thereafter, the same treatment as in (b) of the above (1) was performed to determine the amount of fatty acid.

(3) Amount of fatty acid adsorbed on ferromagnetic powder in each magnetic layer Each magnetic layer was peeled off in advance, and about 253 cm ² of each magnetic layer was added to a sample corresponding to methyl isobutyl ketone (MIBK).
50 ml was added.

These were boiled under reflux for 3 hours, returned to room temperature, and the samples were washed with a small amount of MIBK and then combined with the extract.

Next, MIBK was evaporated from these solutions using a rotary evaporator.

Approximately 50 ml of cyclohexane was newly added to the concentrated extract, and the mixture was boiled under reflux for 1 hour. After returning to room temperature, the cyclohexane extract was fractionated.

Thereafter, the same treatment as in (b) of the above (1) was performed to determine the amount of fatty acid.

Those strongly adsorbed are immersed in a 6N hydrochloric acid / ethanol (1: 1) solution, extracted from MIBK and thereafter, treated in the same manner as in (1) b), and treated with Was determined, and this quantitative value was added to the above quantitative value to obtain the amount of fatty acid adsorbed on the ferromagnetic powder.

In the gas chromatography, "HP5890A" manufactured by Yokogawa Electric Corporation was used as a column, and "Ultra 1" manufactured by Hewlett-Packard Company was used as a filler.

Next, the magnetic film was left in an environment of 60 ° C. for 24 hours, cut into a 1/2 inch width to produce a video tape, and various characteristics of the video tape were measured.

 The results are shown in Table 2.

 In addition, each characteristic was measured as follows.

Dynamic friction coefficient; tape running tester (of Yokohama System Laboratory, Ltd., "TBT-300D") using the tension in the load 20g as T, Euler equation: from _{μ k = 1 / π · ln} (T / 20) The dynamic friction coefficient μ _k was calculated.

Blooming: The tape surface was visually observed, and the surface where precipitation was observed was evaluated as x, and the surface where no precipitation was observed was evaluated as ○.

Squareness ratio; using Toei Kogyo Co. vibrating sample magnetometer, H _m 5k
Remanence (B _r) and the saturation magnetic flux density (B _m) and the ratio of (B _r / B _m) obtained in oe.

Powder drop: After running the tape for 100 hours using a VCR (manufactured by JVC, "HR-S7000") at a temperature of 40 ° C and a humidity of 80%, observe the dirt attached to the head. Of 4
It was rated on a scale.

 A: No dirt is observed.

 B: Almost no dirt is observed.

 C: Stain is observed.

 D: Remarkable dirt is observed.

RF output decrease; The difference between the initial output and the output after running the tape for 100 hours at a temperature of 40 ° C and a humidity of 80% using a VCR (JVC, “HR-S7000”) I asked.

Edge damage; VCR (JVC, "HR-700
0 "), recording the first 5 minutes under the conditions of temperature 20 ° C and humidity 65%, observing the state of the tape edge when the reproduction was repeated 400 times, and evaluated the following three levels .

 ：: No edge damage was observed.

 Δ: The edge part is broken.

 ×: Edge breakage is observed.

Increased dropout; VCR (JVC, "HR-700
0 ”), recording the first 5 minutes under the conditions of temperature 20 ° C and humidity 65%, repeat the playback 400 times and dropout at the first playback and dropout at the 400th playback The case where the dropout at the 400th reproduction was increased was increased, and the case where no increase was seen was not increased.

(Example 2, Comparative Examples 1 to 5, 7, 8, 11) In Example 1, the amounts of urethane elastomer, fatty acid and lecithin in the first magnetic layer (lower layer) composition and the second magnetic layer (upper layer) composition A magnetic film and a video tape were prepared in the same manner as in Example 1 except that the heat retention conditions until cutting were changed as shown in Table 3, and the amount of fatty acid in each magnetic layer in the magnetic film, Various properties of the tape were measured.

 The results are shown in Tables 1 and 2.

(Example 3) Preparation of magnetic paint In Example 1, the first magnetic layer (lower layer) having the following composition was used instead of the first magnetic layer (lower layer) composition and the second magnetic layer (upper layer) composition. ) A magnetic paint was prepared in the same manner as in Example 1 except that the composition, the second magnetic layer (intermediate layer) composition, and the third magnetic layer (upper layer) composition were used.

First magnetic layer (lower layer) composition Co-coated γ-Fe ₂ O ₃ powder [specific surface area 35 m ² / g (BET value, coercive force H _c 650e) 100 parts Urethane elastomer 10 parts [4,4′-diphenylmethane diisocyanate , 1,4-
Butanediol and adipic acid, -SO ₃ Na0.05mmol / g
Content, molecular weight 30,000] vinyl chloride-vinyl acetate copolymer 5 parts myristic acid 2 parts stearic acid 1 part butyl palmitate 2 parts lecithin 2 parts cyclohexanone 150 parts methyl ethyl ketone 150 parts second magnetic layer (intermediate layer) composition Co coating wearing γ-Fe ₂ O ₃ powder [specific surface area of 38m ² / g (BET value, coercive force H _c 750e] 100 parts of urethane elastomer 10 parts [4,4'-diphenylmethane diisocyanate, 1,4
Butanediol and adipic acid, -SO ₃ Na0.05mmol / g
Containing, molecular weight 30,000] vinyl chloride-vinyl acetate copolymer 5 parts myristic acid 2 parts stearic acid 2 parts palmitic acid butyl ester 2 parts lecithin 2 parts cyclohexanone 150 parts methyl ethyl ketone 150 parts third magnetic layer (upper layer) composition Co adhered γ-Fe ₂ O ₃ powder [specific surface area 48 m ² / g (BET value, coercive force H _c 850 e) 100 parts Alumina powder 5 parts Urethane elastomer 10 parts [synthesized from toluene diisocyanate, neopentyl glycol and adipic acid, molecular weight 40,000] Vinyl chloride-vinyl acetate copolymer 5 parts Oleic acid 2 parts Myristic acid 2 parts Stearic acid 2 parts Palmitic acid butyl ester 2 parts Lecithin 2 parts Cyclohexanone 150 parts Methyl ethyl ketone 150 parts Production of video tape A 14 μm-thick polyethylene Coating on phthalate film, first magnetic layer (dry thickness) on non-magnetic support
2.5 μm), a second magnetic layer (dry thickness 0.5 μm) and a third magnetic layer (dry thickness 0.3 μm) were applied in this order from the nonmagnetic support side to produce a magnetic film.

For this magnetic film, the amount of fatty acid in each magnetic layer was measured in the same manner as in Example 1.

 The results are shown in Table 1.

Next, this magnetic film was cut into 1/2 inch width to produce a video tape, and various characteristics of this video tape were measured in the same manner as in Example 1.

 The results are shown in Table 2.

(Comparative Examples 6, 9, and 10) In Example 3, the urethane elastomer, fatty acid and fatty acid in the first magnetic layer (lower layer) composition, the second magnetic layer (intermediate layer) composition, and the third magnetic layer (upper layer) composition were used. A magnetic film and a video tape were prepared in the same manner as in Example 3 except that the amount of lecithin and the heat retention conditions until cutting were changed as shown in Table 3, and the fatty acid in each magnetic layer in the magnetic film was changed. The amount and characteristics of the video tape were measured.

 The results are shown in Tables 1 and 2.

[Effects of the Invention] According to the present invention, (1) a plurality of magnetic layers are provided, and the fatty acid contained in each magnetic layer satisfies a specific quantitative relationship, so that the dispersibility of the ferromagnetic powder is improved. And (2) to provide an industrially useful magnetic recording medium having the advantages of improved slipperiness and excellent balance between the improved slipperiness and running durability. can do.

Claims (3)

(57) [Claims] An n-layer containing a ferromagnetic powder and a binder on a nonmagnetic support (where n represents an integer of 2 or more).
., An n-th magnetic layer (where n represents an integer of 2 or more) from the non-magnetic support side, and the n-th magnetic layer The amount of fatty acid (F _s ) present on the surface of the layer is 0.2 g / m ² or less, the amount of fatty acid (F _s ) present on the surface of the n-th magnetic layer and the amount of fatty acid released in each magnetic layer and the total amount of (F _f), but the formula [I]; met F _s ≦ F _f ...... relationship represented by [I], the amount fatty acid present on the surface of the n-th magnetic layer (F _s) each The total amount (F _a ) of the fatty acid adsorbed on the ferromagnetic powder in the magnetic layer satisfies the relationship represented by the following formula [II]; F _s ≦ F _a ... [II] Magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the total amount (F _a ) of the fatty acid adsorbed on the ferromagnetic powder in each magnetic layer is 1.0 g / m ² or less. 3. The amount of fatty acid (F _p ) released in the n-th magnetic layer and the amount of fatty acid released in each magnetic layer from the (n-1) -th magnetic layer to the first magnetic layer. the amount in each layer of the fatty acid and (F _q), but the formula _{[III]; F p ≧ F} q ...... [III] the magnetic recording medium according to claim 1 or claim 2, wherein satisfies the relationship represented by.