JP3538650B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium having excellent high-frequency characteristics, good signal overwriting (overwrite) characteristics, and good weather resistance (corrosion resistance). Magnetic recording media.

[0002]

2. Description of the Related Art In a conventional magnetic recording medium, a magnetic layer containing a ferromagnetic powder is formed on a nonmagnetic support. A magnetic recording medium having a magnetic layer containing a ferromagnetic powder and an upper layer containing a ferromagnetic alloy powder (Japanese Patent Application Laid-Open No. 64-19524).
No. JP-A-2-110823). Further, there is a proposal of a magnetic recording medium in which a layer containing a non-magnetic powder is provided in a lower layer and a ferromagnetic powder is contained in an upper layer (Japanese Patent Application Laid-Open No. Sho.
3-187418).

However, in the magnetic recording medium as described above, it is still difficult to sufficiently improve the characteristics in a high frequency band, particularly in a high density recording (digital recording). That is, when a magnetic layer is provided in the lower layer, the waveform of the reproduced signal is distorted during reproduction due to the residual magnetization of the lower layer (inter-waveform interference). As a result, the output peak value decreases and the peak position shifts, and the error rate and the like increase. Further, if there is residual magnetization in the lower layer, it becomes difficult to record a signal to be re-recorded, and so-called deterioration of overwrite characteristics occurs. On the other hand, when a layer containing nonmagnetic layer powder is provided as a lower layer, sufficient high-frequency characteristics cannot be obtained simply by using a layer containing nonmagnetic powder.

[0004] In addition, vapor-deposited tapes and the like are promising for high-density recording (digital recording), but may have problems in practical use due to poor characteristics such as corrosion resistance. Therefore, in view of the above circumstances, the present invention is excellent in high frequency characteristics,
It is an object of the present invention to provide a magnetic recording medium having good signal overwriting (overwrite) characteristics and also excellent weather resistance (corrosion resistance).

[0005]

Means for Solving the Problems To solve the above problems, the present inventors have studied the crystallite size of the ferromagnetic powder contained in the uppermost magnetic layer and the nonmagnetic layer contained in the lower magnetic layer. Focusing on the crystallite size of the non-magnetic powder, it has been achieved as a result of intensive studies, and the invention according to claim 1 has a composite layer on a non-magnetic support, layer is composed of a top layer made of a magnetic layer containing a ferromagnetic powder and a lower layer where in contact with the magnetic layer and having a nonmagnetic layer containing a nonmagnetic powder, the top layer
A is is 0.8μm or less the thickness of the layer, a metal magnetic powder the uppermost ferromagnetic powder contains Al as a main component Fe, and the average major axis length 0. With less than 25 [mu] m, the crystallite size by X-ray diffraction method of the ferromagnetic powder of the uppermost and L _1, and X of the non-magnetic powder of the magnetic layer
When the crystallite size due ray diffraction method was L _2, the crystallite size L ₁ and L _2, 100 ≦ L ₁ ≦ 250
(Å), and L ₂ <L ₁ and 5 <L ₂
What ≦ 200 (Å) Der, binder in the nonmagnetic layer
W ₂ parts by weight of the content for the non-magnetic powder 100 parts by weight of
When the content W _{2 of the} binder is 20 / ln
_{(L 2) ≦ W 2 ≦} 60 / ln (L 2) is a magnetic recording medium characterized der Rukoto, the invention described in claim 2, the ferromagnetic powder 100 of the binder in the uppermost layer weight
When the content relative to parts by weight is W ₁ parts by weight, the binder
The content W ₁ of a magnetic recording medium according to claim 1 which is _{65 / ln (L 1) ≦} W 1 ≦ 100 / ln (L 1), wherein
The invention according to claim 3 is the magnetic recording medium according to claim 1, wherein an uppermost layer is provided when the lower layer is in a wet state.

Hereinafter, the magnetic recording medium of the present invention will be described in detail. In the magnetic recording medium of the present invention, a composite layer is formed on a non-magnetic support, and the composite layer includes a top layer composed of a magnetic layer containing a ferromagnetic powder, and a non-magnetic layer containing a non-magnetic powder. And a lower layer in contact with the magnetic layer. The magnetic recording medium of the present invention is formed by laminating the lower layer and the uppermost layer in this order on a non-magnetic support.

[0007] - non-magnetic support - as a material for forming a non-magnetic support, for example, plus
Chick can be mentioned. As this plastic
For example, polyesters such as polyethylene terephthalate, and polyethylene-2,6-naphthalate , polyolefins such as polypropylene , cellulose
Over scan derivatives such as cellulose triacetate, and cell <br/> cellulose diacetate, polyamide, and the Porika <br/> Boneto.

[0008] As the shape of the non-magnetic support is not particularly limited, and specific examples thereof include a tape shape, film shape, sheet shape, card shape, disc shape, can be mentioned a drum-like shape. The thickness of the nonmagnetic support is not particularly limited. For example, in the case of a film or sheet, the thickness is usually 3 to 1
The thickness is about 30 μm to 10 mm in the case of a disk or card, and is appropriately selected according to, for example, a recorder in the case of a drum.

The nonmagnetic support may have a single-layer structure or a multilayer structure. The nonmagnetic support may have been subjected to a surface treatment, for example, a corona discharge treatment. It is preferable to provide a back coat layer on the surface of the non-magnetic support on which the magnetic layer is not provided (the back surface) for the purpose of improving the running property of the magnetic recording medium, for example, to prevent charge and transfer. An undercoat layer may be provided between the magnetic layer and the non-magnetic support.

-Uppermost magnetic layer-The uppermost magnetic layer contains ferromagnetic powder. Further, the uppermost magnetic layer may contain a binder described later and other components described later. Examples of the ferromagnetic powder, was
For example, a ferromagnetic iron oxide powder or a ferromagnetic metal powder described later can be suitably used. Examples of the ferromagnetic iron oxide powder include γ-Fe ₂ O ₃ , Fe ₃ O ₄ , or an intermediate iron oxide of FeO _x (1.33 <x <1.5).
And Co-added (cobalt-modified) Co-FeO _x (1.33 <x <1.5).

As the ferromagnetic metal powder, for example, F
e, Co, Fe-Al, Fe-Al-Ni
System, Fe-Al-Zn system, Fe-Al-Co system, Fe-
Al-Ca system, Fe-Ni system, Fe-Ni-Al system, F
e-Ni-Co system, Fe-Ni-Si-Al-Mn system,
Fe-Ni-Si-Al-Zn system, Fe-Al-Si
System, Fe-Al-Co system, Fe-Ni-Zn system, Fe-
Ni-Mn system, Fe-Ni-Si system, Fe-Mn-Zn
System, Fe-Co-Ni-P system, Ni-Co system, Fe, N
i, include ferromagnetic metal powders for example metal magnetic powder mainly composed of Co. Among them, Fe-based metal powder has excellent electrical characteristics.

On the other hand, from the viewpoint of corrosion resistance and dispersibility, Fe-Al, Fe-Al-Ca, Fe-Al-
Ni-based, Fe-Al-Zn-based, Fe-Al-Co-based, F
e-Ni system, Fe-Ni-Zn system, Fe-Ni-Si-
Al-Zn system, Fe-Ni-Si-Al-Mn system, Fe
-Ni-CO-based Fe-based ferromagnetic metal powder is preferred.

In particular, the ferromagnetic metal powder preferred for the purpose of the present invention is a metal magnetic powder containing iron as a main component, and Al and Ca are contained.
0: 0.5 to 100: 20, about Ca by weight ratio of F
e: Ca is desirably contained in the range of 100: 0.1 to 100: 10.

By setting the ratio of Fe: Al in such a range, corrosion resistance is remarkably improved, and by setting the ratio of Fe: Ca in such a range, electromagnetic conversion characteristics are improved and dropout is reduced. Can be done. The reason why the electromagnetic conversion characteristics are improved and the dropout is reduced is not clear, but it is considered that the coercive force is increased and the aggregates are reduced due to the improved dispersibility.

The ferromagnetic powder used in the present invention has an average major axis length of 0.25 as observed with a transmission electron microscope.
μm, preferably 0.10 to 0.22 μm, more preferably 0.10 to 0.18 μm, and a crystallite size of 250 ° or less by X-ray diffraction, particularly 100 to 18 μm.
It is preferably 0 °. When the average major axis length and the crystallite size of the ferromagnetic powder are within the above ranges, the electromagnetic conversion characteristics can be further improved.

Further, the ferromagnetic powder used in the present invention comprises:
It is preferable that the coercive force (Hc) is usually in the range of 600 to 5,000 Oe. This coercive force is 600 Oe
If it is less than 7, electromagnetic conversion characteristics may deteriorate, and if the coercive force exceeds 5,000 Oe, recording may not be possible with a normal head, which is not preferable.

The ferromagnetic powder preferably has a saturation magnetization (σ _s ), which is a magnetic characteristic, of usually 70 emu / g or more. If the saturation magnetization is less than 70 emu / g, the electromagnetic conversion characteristics may deteriorate. Further, in the present invention, a ferromagnetic powder having a specific surface area of 40 m ² / g or more by the BET method is preferably used according to the increase in recording density.

Preferred examples of the ferromagnetic powder used in the present invention include a Fe—Al ferromagnetic metal powder (Fe:
Al weight ratio = 100: 5, average major axis length 0.16 μm, holding force Hc: 1500 Oe, crystallite size 150 °),
Ferromagnetic iron oxide powder such as Co-γ-FeOx (average major axis length 0.21 μm, coercive force Hc: 1200 Oe, crystallite size 200 °) can be used.

In the present invention, the content of the ferromagnetic powder having a specific average major axis length and a specific crystallite size in the uppermost magnetic layer is usually 50 to 99% by weight, preferably 60 to 99% by weight. 99% by weight. When the ferromagnetic powder has an axis ratio (average long axis length / average single axis length) of 3 to 20, the reproduction output in a short wavelength region is further improved, which is preferable. The thickness of the uppermost magnetic layer is usually 1.0 μm or less, preferably 0.8 μm or less.

-Lower Layer- The lower layer is not particularly limited as long as it has a nonmagnetic layer containing a nonmagnetic powder, and may be formed of a single layer or a plurality of layers. -Non-magnetic layer-The non-magnetic layer contains a non-magnetic powder. Further, the non-magnetic layer may contain a binder described below and other components described later.

-Non-magnetic powder- As the non-magnetic powder, for example, titanium oxide, α-oxidized
Iron and the like.

[0022] - As the binder used in the binder over the present invention, for example, polyurethane, and a polyester, and vinyl resins such as vinyl chloride copolymer chloride typify, these resins are -SO ₃ M , -OSO ₃ M, -COOM and -PO
It is preferable to include a repeating unit having at least one polar group selected from (OM ¹ ) ₂ .

In the above polar group, M represents a hydrogen atom or an alkali metal such as Na, K, Li, etc.
M ¹ is a hydrogen atom or an alkali atom such as Na,
K, representing the Li.

The polar group has an effect of improving the dispersibility of the ferromagnetic powder in the magnetic layer and the non-magnetic powder in the lower layer, and the content in each resin is 0.1 to 8.0 mol%, preferably 0.5-6.0 mol%. When the content is less than 0.1 mol%, the dispersibility of the ferromagnetic powder in the magnetic layer and the non-magnetic powder in the lower layer decreases,
On the other hand, when the content exceeds 8.0 mol%, the magnetic coating material and the coating material for the lower layer tend to gel. The weight average molecular weight of each resin is preferably in the range of 15,000 to 50,000.

The amount contained in the uppermost magnetic layer of the binder, when the content based on 100 parts by weight of the ferromagnetic powder of the binder in the uppermost layer was set to W ₁ part by weight, the content W ₁ of the binder 65 / ln (L ₁ ) ≦ W ₁ ≦ 100 / ln (L ₁ ), and the content of the binder in the nonmagnetic layer is based on 100 parts by weight of the nonmagnetic powder of the binder in the nonmagnetic layer. When the content is W ₂ parts by weight, the content W _{2 of the} binder is 20 / ln (L ₂ ) ≦ W ₂ ≦ 60 / ln (L ₂ ).

The binder is not limited to one kind alone, and two or more kinds can be used in combination. In this case, the ratio of the polyurethane and / or polyester to the vinyl chloride resin is usually 90:10 by weight. The ratio is in the range of 70:30 to 30:70.

The polar group-containing vinyl chloride copolymer used as a binder in the present invention has, for example, a copolymer having a hydroxyl group, such as a vinyl chloride-vinyl alcohol copolymer, having the following polar group and chlorine atom. It can be synthesized by an addition reaction with a compound. _{Cl-CH 2 CH 2 SO 3} M, Cl-CH 2 CH 2 OSO 3 M, Cl-CH 2 COOM,
Cl—CH ₂ —P (= O) (OM ¹ ) ₂ (where M and M ¹ have the same meanings as described above.) From these compounds, Cl—CH ₂ CH ₂ SO ₃ Na is used as an example. to explain the reaction, as _{follows, -CH 2 C (OH) H} - + ClCH 2 CH 2 sO 3 Na → - CH 2 C (OCH 2 CH 2 sO 3
Na) H- .

In addition, a vinyl chloride copolymer containing a polar group is prepared by charging a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced into a reaction vessel such as an autoclave. Agents such as BPO
(Benzoyl peroxide), a radical polymerization initiator such as AIBN (azobisisobutyronitrile), a redox polymerization initiator, a cationic polymerization initiator, or the like, and can be obtained by performing a polymerization reaction.

Specific examples of the reactive monomer for introducing sulfonic acid or a salt thereof include unsaturated hydrocarbon sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, p-styrene sulfonic acid and the like. Salts may be mentioned. When introducing a carboxylic acid or a salt thereof, for example, (meth) acrylic acid or maleic acid is used, and when introducing a phosphoric acid or a salt thereof,
For example, (meth) acrylic acid-2-phosphate may be used.

It is preferable that an epoxy group is introduced into the vinyl chloride copolymer. This is because the heat stability of the polymer is improved. When an epoxy group is introduced, the content of the repeating unit having an epoxy group in the copolymer is preferably from 1 to 30 mol%,
20 mol% is more preferred. As a monomer for introducing an epoxy group, for example, glycidyl acrylate is preferable.

As to the technique for introducing a polar group into a vinyl chloride copolymer, Japanese Patent Application Laid-Open Nos.
8-108052, 59-8127, 60-1
No. 01161, No. 60-235814, No. 60-23
Nos. 8306, 60-238371, 62-121
No. 923, No. 62-146432, No. 62-1464
No. 33 and other publications, and these can be used in the present invention.

Next, the synthesis of the polyester and polyurethane used in the present invention will be described. Generally, polyesters are obtained by reacting a polyol with a polybasic acid. Using this known method, a polyester (polyol) having a polar group can be synthesized from a polyol and a polybasic acid partially having a polar group.

Examples of the polybasic acid having a polar group include 5
-Sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-
Examples include sulfoisophthalic acid, 3-sulfophthalic acid, dialkyl 5-sulfoisophthalate, dialkyl 2-sulfoisophthalate, dialkyl 4-sulfoisophthalate, dialkyl 3-sulfoisophthalate, and sodium and potassium salts thereof.

Examples of polyols include trimethylolpropane, hexanetriol, glycerin, trimethylolethane, neopentylglycol, pentaerythritol, ethyleneglycol and propyleneglycol.
1,3-butanediol, 1,4-butanediol
1,6-hexanediol, diethylene glycol
And cyclohexanedimethanol. In addition, a polyester having another polar group introduced therein can also be synthesized by a known method.

Next, polyurethane will be described. This results from the reaction of a polyol with a polyisocyanate. As the polyol, a polyester polyol obtained by reacting a polyol with a polybasic acid is generally used. Therefore, when a polyester polyol having a polar group is used as a raw material, a polyurethane having a polar group can be synthesized.

Examples of the polyisocyanate include diphenylmethane-4-4'-diisocyanate (MDI),
Hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI), tolidine diisocyanate (TODI), lysine isocyanate methyl ester (LDI) and the like.

As another method for synthesizing a polyurethane having a polar group, an addition reaction of a polyurethane having a hydroxyl group with the following compound having a polar group and a chlorine atom is also effective. _{Cl-CH 2 CH 2 SO 3} M, Cl-CH 2 CH 2 OSO 2 M, Cl-CH 2 COOM, Cl-
CH ₂ -P (= O) (OM ¹ ) _{2 As} a technique for introducing a polar group into polyurethane, JP-B-58-41565 and JP-A-57-9242 have been disclosed.
Nos. 2, 57-92423, 59-8127, 59-5423, 59-5424, 62-12
These are described in publications such as 1923, and these can be used in the present invention.

In the present invention, the following resins may be used together as a binder in an amount of 20% by weight or less of the total binder.

The resin has a weight average molecular weight of 1
For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, Cellulose derivatives (such as nitrocellulose), styrene-butadiene copolymer, phenolic resin, epoxy resin, urea resin, melamine resin,
Phenoxy resins, silicone resins, and acrylic resins, urea formamide resin, various synthetic rubber resins.

[0040] - Other components - to improve the quality of the magnetic layer and the lower layer in the present invention, the lubricant, durability improvers, dispersing agents, and other ingredients additives such as girdle antistatic agents and fillers Can be contained.

Fatty acids and / or fatty acid esters can be used as the lubricant. in this case,
The amount of the fatty acid to be added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the ferromagnetic powder in the uppermost layer or the nonmagnetic powder in the lower layer. 0.2 added
When the amount is less than 10% by weight, the runnability tends to decrease, and when the amount exceeds 10% by weight, the fatty acid easily exudes to the surface of the magnetic layer and the output tends to decrease.

The amount of the fatty acid ester to be added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the ferromagnetic powder in the uppermost layer or the nonmagnetic powder in the lower layer. When the addition amount is less than 0.2% by weight,
If the still durability is easily deteriorated, and if it exceeds 10% by weight, the fatty acid ester is likely to exude to the surface of the magnetic layer or the output is apt to be reduced.

When it is desired to further enhance the lubricating effect by using a fatty acid and a fatty acid ester in combination, the weight ratio of the fatty acid and the fatty acid ester is preferably from 10:90 to 90:10. The fatty acid may be a monobasic acid or a dibasic acid,
The carbon number is preferably from 6 to 30, and more preferably from 12 to 22.

Specific examples of fatty acids include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, oleic acid, elaidic acid, behenic acid, malonic acid, and succinic acid. Acid, maleic acid, glutaric acid, adipic acid,
Pimelic acid, azelaic acid, sebacic acid, 1,12-dodecane dicarboxylic acid, and octanoic acid.

Specific examples of fatty acid esters include oleyl oleate, isocetyl stearate, dioleyl malate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmate Tate, isobutyl oleate, stearyl stearate,
Lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate, 2-ethylhexyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, cetyl-2
-Ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate, 2-ethylhexyl myristate, isopentyl palmitate, isopentyl stearate, diethylene glycol mono-butyl ether palmitate, diethylene glycol mono- butyl ether palmitate, and the like.

[0046] In addition, the fatty acid, as a lubricant other than the fatty acid esters, such as silicone oil, graphite, fluorinated carbon, molybdenum disulfide, tungsten disulfide, fatty acid amides, alpha-olefin oxide may be used <br/> Can be.

Examples of the durability improver include polyisocyanates, and examples of the polyisocyanates include aliphatic polyisocyanates.
Can Ru. Examples of the aliphatic polyisocyanate include an aromatic polyisocyanate such as an adduct of tolylene diisocyanate (TDI) or the like and an active hydrogen compound;
Diisocyanates such as hexamethylene diisocyanate (HMDI) and adducts of active hydrogen compounds
Can be The weight average molecular weight of the polyisocyanate is preferably in the range of 100 to 3,000.

Specific examples of the dispersant include, for example,
C12-C18 fatty acids such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid; salts of these alkali metals or salts of alkaline earth metals or amides thereof; polyalkylene oxides it can be mentioned azo compounds having a carboxyl group and sulfonic acid group, alkyl phosphoric acid ester; lecithin; trialkyl polyolefin oxy quaternary ammonium salt. These dispersants are usually used in the range of 0.5 to 5% by weight based on the ferromagnetic powder in the uppermost layer or the nonmagnetic powder in the lower layer.

[0049]

Examples of the antistatic agent include a conductive powder.
For example, carbon black and graphite ; cationic field
Surfactants such as quaternary amines ; for example sulfonic acids,
Said sulfuric acid, phosphoric acid, phosphoric acid esters, and carboxylic acids
Anionic surfactants containing an acid group; Tato amphoteric surfactants
Amino acid if example; may be mentioned natural surfactants such Saponi <br/> down. The aforementioned antistatic agent is usually added in the range of 0.01 to 40% by weight based on the binder.

-Manufacture of Magnetic Recording Medium- In the magnetic recording medium of the present invention, the uppermost magnetic layer and the lower layer are applied by a wet-on-wet method. As the wet-on-wet method, a method used for manufacturing a known multilayer structure type magnetic recording medium can be appropriately adopted.

For example, in general, a coating is prepared by kneading a ferromagnetic powder, a binder, a dispersant, a lubricant, an abrasive, an antistatic agent and a solvent, and then diluting the coating to form a top layer. Is prepared. Also, generally, a non-magnetic powder, a binder, a dispersant, a lubricant, an abrasive, an antistatic agent and a solvent are kneaded with a lower layer to prepare a paint, and then the paint is diluted to form a lower layer. Prepare paint for use. Thereafter, the coating material for the uppermost layer and the coating material for the lower layer are applied to the nonmagnetic support.

Examples of the solvent include ketone solvents.
Acetone For example, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone <br/>emissions; alcohols such as methanol, ethanol, 及
Fine propanol, esters such as methyl acetate, ethyl acetate, and butyl acetate; cyclic ethers such as Tet <br/>Rahidorofuran; halogenated hydrocarbons such as methylene chloride, ethylene chloride, using carbon tetrachloride, chloroform, and dichlorobenzene be able to.

In kneading and dispersing the components for forming the uppermost magnetic layer and lower layer, various kneading / dispersing machines can be used. Examples of the kneading and dispersing machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a kobol mill, a tron mill, a sand mill, a sand grinder, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, and a disperser.
Examples include a high-speed mixer, a homogenizer, an ultrasonic disperser, an open kneader, a continuous kneader, and a pressure kneader. Among the kneading and dispersing machines, kneading and dispersing machines capable of providing a power consumption load of 0.05 to 0.5 KW (per 1 kg of magnetic powder) include a pressure kneader, an open kneader,
Continuous kneader, two-roll mill and three-roll mill.

In order to coat the uppermost magnetic layer and the lower layer on the non-magnetic support, specifically, as shown in FIG.
In addition, the extrusion type extrusion coater 10,
11, the uppermost magnetic layer coating material and the lower layer coating material are applied in a multi-layered manner by a wet-on-wet method, and then passed through an orientation magnet or a vertical orientation magnet 33, and dried.
And dried by blowing hot air from nozzles arranged above and below. Next, the dried nonmagnetic support 1 with each coating layer is guided to a super calender device 37 comprising a combination of calender rolls 38, where it is calendered, and then wound up on a take-up roll 39. The magnetic film thus obtained can be cut into a tape having a desired width to produce, for example, a magnetic recording tape for an 8 mm video camera.

In the above-mentioned method, each paint was extruded through an in-line mixer (not shown).
11 may be supplied. In the drawings, the arrows indicate the direction of transport of the non-magnetic support. Extrusion coaters 10 and 11 are provided with liquid reservoirs 13 and 14, respectively, and paints from each coater are overlaid in a wet-on-wet manner. That is, immediately after the lower layer coating material is applied (when it is in an undried state), the uppermost magnetic layer coating material is applied in multiple layers.

In the present invention, the extrusion coater 15 is preferably the extrusion coater 15 shown in FIG. The extruder coater 15 coextrudes the lower layer application material 2 and the uppermost magnetic layer coating material 3 and applies them in layers.

Examples of the solvent to be blended in the paint or a diluting solvent at the time of applying the paint include ketones.
For example, acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone ; alcohols
In methanol, ethanol, propanol, and butanol <br/> Lumpur, esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol Seno acetate, ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, Passing
And tetrahydrofuran ; aromatic hydrocarbons such as benzene, toluene, and xylene ;
Example, if methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used. These various solvents can be used alone, or two or more of them can be used in combination.

The magnetic field of the oriented magnet or the magnet for vertical orientation is about 20 to 5,000 Gauss, the drying temperature of the dryer is about 30 to 120 ° C., and the drying time is about 0.1 to 10 minutes. It is.

[0060] Incidentally, the wet - on - In the wet method, for example, may be a combination of a reverse roll and an extrusion coater, and also a combination of a gravure roll and an extrusion coater used. Furthermore , even if
If it can also be combined air doctor coater, a blade coater, air knife coater, Sukui's coater, impregnation coater, transfer roll coater, kiss coater, a cast coater, and spray coater.

In this multi-layer coating in the wet-on-wet method, the uppermost magnetic layer is coated while the upper layer of the lower layer is kept wet, so that the surface of the lower layer (ie, the uppermost layer) is coated. Interface between upper magnetic layer)
And the surface properties of the uppermost magnetic layer are improved, and the adhesion between the uppermost magnetic layer and the lower layer is also improved. As a result, it is possible to satisfy the performance required for a magnetic tape, for example, which requires high output and low noise for high-density recording, and also requires the layer to have high durability performance. Peeling is eliminated, the strength of the layer is improved, and the durability is sufficient. In addition, the wet-on-wet multi-layer coating method can reduce dropout and improve reliability.

-Smoothing of Surface- In the present invention, a surface smoothing process may be performed by calendering. Thereafter, a burnishing process or a blade process is performed as necessary to perform slitting. In the surface smoothing treatment, the calender conditions include , for example, temperature, linear pressure, C / S (coating speed).

In the present invention, the above temperature is usually set at 5
0 to 120 ° C, the above linear pressure is 50 to 400 kg / cm,
It is preferable to maintain the C / S at 20 to 600 m / min. The thickness of the uppermost layer as a result of the treatment as described above is 1.0 μm or less, preferably 0.8 μm or less. When the layer thickness exceeds 1.0 μm, the high-frequency characteristics and the overwriting (overwrite) characteristics of the signal are deteriorated, which is no different from a magnetic recording medium having a single-layer structure, thereby achieving the object of the present invention. Can not.

[0064]

Embodiments of the present invention will be described below. The components, ratios, and operation orders shown below can be variously changed without departing from the scope of the present invention. In the following examples, "parts" are all parts by weight.

A magnetic paint having the following composition was prepared. <Magnetic coating material A for magnetic layer on top layer> Co-γ-FeOx (1) (1.33 <x ≦ 1.5) 100 parts (average major axis length 0.21 μm, coercive force Hc = 1,200 Oe, Crystallite size 200 mm) Vinyl chloride resin (MR110 manufactured by Zeon Corporation) X part Polyurethane resin containing sulfonic acid metal salt Y part (UR8700 manufactured by Toyobo Co., Ltd.) α-alumina (particle diameter 0.1 μm) 5 Part Carbon black (average particle size 40 mμ) 0.5 part Myristinic acid 1 part Stearic acid 1 part Butyl stearate 1 part Methyl ethyl ketone 100 parts Toluene 100 parts Cyclohexanone After kneading and dispersing a composition of 100 parts or more, polyisocyanate Compound (Coronate L) was prepared by adding Z part.

<Magnetic Coating B for Uppermost Magnetic Layer> In the above magnetic coating A for the uppermost magnetic layer, Co-γ-
Instead of FeOx (1), Fe-Al-based ferromagnetic powder (average major axis length 0.16 μm, coercive force Hc = 1,500 O
e, except that the crystallite size was 150 °), except that the magnetic coating material A for the uppermost magnetic layer was prepared.

<Magnetic Coating C for Uppermost Magnetic Layer> In the magnetic coating A for the uppermost magnetic layer, Co-γ-
Instead of FeOx (1), Co-γ-FeOx (2)
(Average major axis length 0.28 μm, coercive force Hc = 1,200
Oe, crystallite size 300 °), except that the magnetic coating material A for the uppermost magnetic layer was prepared.

<Coating Material for Non-magnetic Layer a> Titanium oxide (1) (TiO ₂ , crystallite size 30 mm) 100 parts Vinyl chloride resin x part (MR110 manufactured by Zeon Corporation) Polyurethane resin containing sulfonic acid metal salt y Part (Toyobo Co., Ltd., UR8700) Methyl ethyl ketone 50 parts Toluene 50 parts Cyclohexanone A composition of 50 parts or more was kneaded and dispersed to prepare.

<Non-magnetic layer coating b> The non-magnetic layer coating except that titanium oxide (2) (crystallite size 10 °) was used instead of titanium oxide (1) in the non-magnetic layer coating a. Prepared in a similar manner to a.

<Non-magnetic layer coating c> The non-magnetic layer coating except that titanium oxide (3) (crystallite size: 100 °) was used instead of titanium oxide (1) in the non-magnetic layer coating a. Prepared in a similar manner to a.

<Non-magnetic layer coating material d> The non-magnetic layer coating material a except that titanium oxide (4) (crystallite size 300 mm) was used instead of titanium oxide (1) in the non-magnetic layer coating material a. Prepared in a similar manner to a.

<Coating Material for Nonmagnetic Layer e> Instead of titanium oxide (1) in the coating material a for nonmagnetic layer, α-Fe ₂ O ₃ (Bengara) (crystallite size 380) was used.
It was prepared in the same manner as in the non-magnetic layer coating material a except that 以外) was used.

<Magnetic paint D for lower layer> In the magnetic paint A for the uppermost magnetic layer, Co-γ-
Instead of FeOx (1), Co-γ-FeOx (3)
(Average major axis length 0.28 μm, coercive force Hc = 700 Oe,
It was prepared in the same manner as in the preparation of the magnetic coating material A for the uppermost magnetic layer except that the crystallite size was 330 °).

(Reference Example 1, Examples 2-6 and Comparative Examples 1
7) With a coating layer composition having the composition shown in Table 1, a magnetic recording medium having a width of 8 mm was prepared by a wet-on-wet method.
The following evaluation test was performed on this magnetic recording medium.

<C / N characteristics> 9 MHz using a commercially available 8 mm video tape recorder
Was recorded, and the output level when the signal was reproduced was represented by comparison with the reference sample (Comparative Example 1). <Overwrite characteristics> A 2 MHz signal was recorded at the saturation level, and then 9 MHZ was recorded.
The residual output level of the 2 MHz signal when the z signal was recorded (overwritten) was measured. It is assumed that the lower the residual output level, the better the overwrite characteristics.

<Weather Resistance> The output level at 9 MHZ was measured in advance, and the magnetic recording medium as a sample was allowed to stand at 60 ° C. and 80% (humidity) for 7 days. It was measured and the difference from the initial measured value was determined. Table 1 shows the above evaluation results. From the above evaluation results, a comprehensive evaluation of quality was performed.

[0077]

[Table 1]

[0078]

According to the present invention, a ferromagnetic powder of a predetermined size is provided in the ferromagnetic layer in the uppermost layer, and a nonmagnetic powder of a predetermined crystallite size is provided in the nonmagnetic layer in the lower layer.
By using this, it is possible to form a smooth layer, to have excellent high-frequency characteristics, and to overwrite signals (overwrite).
This has the technical effect of providing a magnetic recording medium having excellent characteristics and weather resistance (corrosion resistance).

[Brief description of the drawings]

FIG. 1 is a diagram for explaining multi-layer coating of a magnetic layer by a wet-on-wet coating method.

FIG. 2 is a diagram of an extrusion coater for applying a magnetic paint.

[Description of sign]

1 Non-magnetic support 2 Lower layer paint 3 Top magnetic layer paint 10 Extrusion coater 11 Extrusion coater 13 Liquid reservoir 14 Liquid reservoir 15 Extrusion coater 32 Supply roll 33 Magnet for orientation or magnet for vertical orientation 34 dryer 37 Super Calendar Device 38 Calendar Roll 39 Take-up roll

Claims (3)

(57) [Claims] A composite layer on a non-magnetic support,
The composite layer is composed of a top layer made of a magnetic layer containing a ferromagnetic powder and a lower layer where in contact with the magnetic layer and having a nonmagnetic layer containing a nonmagnetic powder, the most
A is is 0.8μm or less thickness of the upper layer, a metal magnetic powder the uppermost ferromagnetic powder contains Al as a main component Fe, and the average major axis length 0. With less than 25 [mu] m, the crystallite size by X-ray diffraction method of the uppermost ferromagnetic powder and L _1, and the crystallite size by X-ray diffraction method of the nonmagnetic powder of the non-magnetic layer L ₂ When the crystallite sizes L ₁ and L ₂ are 100 ≦ L ₁ ≦ 250
(Å), and L ₂ <L ₁ and 5 <L ₂
What ≦ 200 (Å) Der, binder in the nonmagnetic layer
W ₂ parts by weight of the content for the non-magnetic powder 100 parts by weight of
When the content W _{2 of the} binder is 20 / ln
_{(L 2) ≦ W 2 ≦} 60 / ln (L 2) magnetic recording medium characterized der Rukoto. 2. A ferromagnetic powder of a binder in the uppermost layer.
When the content relative to 100 parts by weight is W1 parts by weight,
The content W _{1 of the} binder is 65 / ln (L ₁ ) ≦ W ₁ ≦ 100 / ln (L ₁ ).
The magnetic recording medium according to claim 1. 3. When the lower layer is in a wet state,
2. The magnetic recording medium according to claim 1, wherein a layer is provided.
body.