JPH05290359A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having satisfactory electromagnetic transducing characteristics and overwriting characteristics by forming a magnetic recording layer consisting of plural constituent layers on a nonmagnetic substrate and incorporating ferromagnetic metal powder having prescribed characteristics into the upper magnetic layer of the magnetic recording layer. CONSTITUTION:A magnetic recording layer consisting of plural constituent layers is formed on a nonmagnetic substrate. The upper layer of the magnetic recording layer is a magnetic layer contg. ferromagnetic metal powder having <=0.25mum average major axis size and <=200Angstrom particle diameter measured with X-rays. The coercive force of the magnetic layer is 1,700-2,200Oe and the saturation magnetic flux density is 3,000-4,500G. The magnetic recording layer has at least one layer contg. nonmagnetic powder or a high permeability material besides the magnetic layer. The objective magnetic recording medium having satisfactory electromagnetic transducing characteristics, digital recording properties and overwriting characteristics is obtd.

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 such as a magnetic disk, a magnetic tape or a magnetic sheet.

[0002]

2. Description of the Related Art In recent years, magnetic recording media have been increasingly oriented toward high performance, and the advent of magnetic disks, magnetic tapes and the like having high electromagnetic conversion characteristics capable of high density recording has been desired.

In order to improve the electromagnetic conversion characteristics of a magnetic recording medium, conventionally, use of magnetic powder having a large saturation magnetization amount, improvement of dispersibility of the magnetic powder, multilayer formation of the magnetic layer, squareness ratio, coercive force, Various attempts have been made to improve the saturation magnetic flux density and adjust the surface smoothness.

However, regarding the coercive force and the saturation magnetic flux density of the magnetic layer, for example, when a magnetic tape having a high coercive force is produced in order to improve the characteristics in the short wavelength region, the output in this region is improved, On the contrary, the output in the long wavelength region is greatly reduced. In this case, it is necessary to increase the saturation magnetic flux density to improve the output in the long wavelength region, but there is a contradiction that the output in the short wavelength region reciprocally decreases. Further, in the technique described in JP-A-63-187418, since the size of the magnetic powder in the magnetic layer, the coercive force, and the saturation magnetic flux density are insufficiently controlled, the CN ratio required for a tape for a digital VTR cannot be obtained.

Regarding the smoothness of the surface of the magnetic layer, for example, in JP-A-61-168124, the surface condition of the magnetic layer of the magnetic recording medium is defined by the center line average roughness _Ra and the maximum height of surface irregularities. R _max is defined and the electromagnetic conversion characteristics are improved together with the traveling performance. However, this technology improves the traveling performance to some extent, but the electromagnetic conversion characteristics such as RF output are not improved. ..

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium suitable for digital recording which exhibits high output in the short wavelength region.

[0007]

The above-mentioned object of the present invention is as follows:
Forming a plurality of magnetic recording layers on the non-magnetic support,
A magnetic layer occupies an upper layer of the magnetic recording layer, and the magnetic layer contains a ferromagnetic metal powder having an average major axis length of 0.25 μm or less and a particle size measured by X-ray of 200 Å or less, and the coercive force of the magnetic layer is 17
It is achieved by a magnetic recording medium having a magnetic flux density of 00 to 2200 Oe, a saturation magnetic flux density of 3000 to 4500 Gauss, and further having at least one layer other than the magnetic layer in the magnetic recording layer, the layer containing a non-magnetic powder or a high magnetic permeability material.

In the embodiment of the present invention, the surface roughness R _{z (10)} of the surface of the magnetic recording layer is 5 to 20 nm, and the thickness of the uppermost magnetic layer of the magnetic recording layer is 0.8 μm or less. Preferably.

Further, in coating a plurality of constituent layers on a non-magnetic support, a so-called wet-on-coating method of forming a magnetic recording layer by coating an upper constituent layer on a lower constituent layer in a wet state.
Wet (on wet) coating methods are preferred.

The magnetic recording medium of the present invention will be described in detail below.

-Non-magnetic support-As a material for forming the non-magnetic support, for example, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate, etc. Examples of the cellulose derivative include plastics such as polyamide and polycarbonate.

The form of the non-magnetic support is not particularly limited, and is mainly tape-like, film-like, sheet-like, card-like,
There are disc shape and drum shape.

The thickness of the non-magnetic support is not particularly limited, but in the case of a film or sheet, it is usually 3-10.
The thickness is 0 μm, preferably 5 to 50 μm, and is approximately 30 μm to 10 mm in the case of a disk or card, and is appropriately selected according to the recorder in the case of a drum.

The non-magnetic support may have a single-layer structure or a multi-layer structure. Further, the non-magnetic support may be subjected to surface treatment such as corona discharge treatment.

A back coat layer is 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. It is preferable that an undercoat layer be provided between the magnetic layer and the non-magnetic support.

-Magnetic Layer- The magnetic layer according to the present invention has a coercive force of 1700 to 2200 Oe and a saturation magnetic flux density of 3000 to 4500 gauss, but a preferable coercive force is 1700 to 2000 Oe and a saturation magnetic flux density is The coercive force is more preferably 1700 to 1900 Oe, and the saturation magnetic flux density is 3300 to 3900 gauss.

When the coercive force is less than 1700 Oe, demagnetization is likely to occur, so that RF output in the short wavelength region cannot be obtained, and 2200 Oe.
When the value exceeds, the writing capability of the head with respect to the medium is insufficient, and it becomes impossible to obtain RF output in the short wavelength region and the long wavelength region. Further, when the saturation magnetic flux density is less than 3000 gauss, the filling rate of the magnetic powder is lowered, so that the RF output in the entire band cannot be obtained at all, and when it exceeds 4500 gauss, the mutual attractive force between the magnetic powders is large during the production of the medium. As a result, an agglomerated state results and a large RF output cannot be obtained in the entire band. That is, when both the coercive force and the saturation magnetic flux density are out of the above ranges, the effect of the present invention is not exhibited.

In order to adjust the coercive force of the magnetic layer within the range of the present invention, there is a method of controlling the dispersibility of the magnetic paint, the magnetic field orientation conditions, the calendering conditions, the shape of the magnetic powder and the like. Further, as a method of adjusting the saturation magnetic flux density of the magnetic layer within the range of the present invention, control of dispersibility of the magnetic paint, magnetic field orientation conditions, calendar conditions and the like can be mentioned.

Ferromagnetic metal powders that can be used in the present invention include simple substances such as Fe, Ni, and Co, and Fe containing these as the main components.
Metal powders such as -Al-based, Fe-Ni-based, and Fe-Al-Ni-based powders, among which Fe-based powders are preferable.

Among the above-mentioned ferromagnetic metals, the crystallite size = particle size is obtained by the Scherrer method using Si powder as a reference, using the measured value of particle size by X-ray (the integrated width of the (110) diffraction line of Fe). ) Is 200 Å or less, further 100 to 180 Å, and the average major axis length is 0.25 μm or less, preferably 0.01 to 0.22 μm,
The thickness of 0.01 to 0.17 μm is preferable for adjusting the surface roughness and electromagnetic conversion characteristics of the magnetic layer.

Further, as a preferable structure of the ferromagnetic metal powder, Fe atoms and Al contained in the ferromagnetic metal powder are contained.
The content ratio with atoms is Fe: Al = 100: 1-100 in terms of the number ratio of atoms.
: 20, and the content ratio of Fe atoms and Al atoms existing in the surface region of 100 Å or less in the analysis depth by ESCA of the ferromagnetic metal powder is Fe: Al = 30: 70 to 70 in terms of atomic number ratio. It has a structure of: 30. Or Fe atom and Ni atom
Al atoms and Si atoms are contained in the ferromagnetic metal powder, and further Zn
At least one of atoms and Mn atoms is contained in the ferromagnetic metal powder, the content of Fe atom is 90 atomic% or more, the content of Ni atom is 1 atomic% or more, less than 10 atomic%, the content of Al atom. But
0.1 atomic% or more and less than 5 atomic%, the content of Si atoms is 0.1
Atomic% or more and less than 5 atomic%, Zn atom content and / or
The Mn atom content (however, the total amount when both Zn and Mn atoms are contained) is 0.1 atom% or more and less than 5 atom%, and the ferromagnetic metal powder has an analysis depth of 100 by ESCA. Å Fe atom, Ni atom, Al atom, Si atom, Zn atom and / or Mn atom existing in the surface area below is the atomic ratio of Fe: Ni: Al: Si (Zn and or Mn) = 100 : (4 or less): (10-60): (10-70): (20-80) Ferromagnetic metal powder having a structure.

In the present invention, a ferromagnetic metal powder having a specific surface area according to the BET method of 30 m ² / g or more, particularly 45 m ² / g or more is preferably used according to the higher recording density.

The specific surface area of the ferromagnetic metal powder in the present invention is a value measured by a specific surface area measuring method called BET method, and the surface area per unit gram is expressed in square meters. For the specific surface area and its measuring method, see "Measurement of powder" (JMDallav
Alle, Clydeorr Jr, co-authored, Benda et al .; published by Sangyo Tosho Publishing Co., Ltd.), "Chemical Handbook" Application, P1170-1171 (Chemical Society of Japan, Maruzen Co., Ltd., April 41, 1966) (Published on the day). The specific surface area is measured, for example, by degassing while heating the powder at about 105 ° C. for 13 minutes to remove what is adsorbed on the powder, and then introducing it into the measuring device to reduce the initial pressure of nitrogen to 0.5. Set to kg / m ² and perform adsorption measurement with nitrogen at liquid nitrogen temperature (-105 ° C) for 10 minutes. A counter soap (manufactured by Yuasa Ionics Co., Ltd.) was used as a measuring device.

In the present invention, the surface roughness R of the magnetic layer is
_{Z (10)} is preferably 5 to 20 nm, more preferably 12 to 15 nm.

The surface roughness R _{Z (10) according} to the present invention is as shown in FIG.
As shown in, the magnetic recording medium is moved within ± 2 from the midpoint P of the width direction W.
When cutting a reference length perpendicular to the longitudinal direction X in the range of mm (indicated by R in the figure), the straight line parallel to the average direction of the sectional curve on the cut surface passes through the 10th peak And two straight lines l ₁ and l passing through the bottom of the tenth depth
_It indicates the value of the altitude difference d between the _two .

To measure the above R _{Z (10)} , a Talystep roughness meter (Rank Taylor Hobson Co.) was used.
As the measurement conditions, the stylus was 2.5 × 0.1 μm, the needle pressure was 2 mg, the cut-off filter was 0.33 Hz, the measurement speed was 2.5 μm / sec, and the reference length was 0.5 mm. In the roughness curve, irregularities within 0.002 μm are cut.

In order to control the above R _{Z (10)} to 20 nm or less, for example, the calender conditions may be set in the above manufacturing process to control the surface smoothness of the magnetic layer. That is, in this surface smoothing treatment, the factors to be controlled as the calendar conditions are temperature, linear pressure, C / S.
(Coating speed) and the like can be mentioned. Other factors include the kneading conditions of the magnetic powder, the surface treatment, and the size and amount of the particles added to the magnetic layer.

To achieve the object of the present invention, the above temperature is usually 50 to 140 ° C., the above linear pressure is 50 to 400 kg / cm, and the above C
It is preferable to keep / S at 20 to 600 m / min. If the values are out of the range, it may be difficult or impossible to specify the surface roughness of the magnetic layer as described above.

Further, as a ferromagnetic metal powder used for the magnetic layer, Fe, Co, Fe-Al system, Fe-Al-Ni system, Fe-Al-Z are used.
n series, Fe-Al-Co series, Fe-Al-Ca series, Fe-Ni series, Fe-Ni-Al series,
Fe-Ni-Co system, Fe-Ni-Si-Al-Mn system, Fe-Ni-Si-Al-Zn system, Fe
-Al-Si system, Fe-Ni-Zn system, Fe-Ni-Mn system, Fe-Ni-Si system, Fe-M
Ferromagnetic powders such as n-Zn-based, Fe-Co-Ni-P-based, Ni-Co-based, and metal magnetic powders containing Fe, Ni, Co, etc. as main components can be mentioned. 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, Fe-Al-Zn, F
Fe-of e-Al-Co, Fe-Ni-Si-Al-Zn, Fe-Ni-Si-Al-Mn
Al-based metal powder is preferred.

Particularly preferred ferromagnetic metal powder for the purpose of the present invention is a magnetic metal powder containing iron as a main component, which is Al or Al.
And Ca and Al in a weight ratio of Fe: Al = 100: 0.5 to 10
0:20, Ca: Fe: Ca = 100: 0.1 to 100: by weight.
It is desirable to contain in the range of 10. By setting the ratio of Fe: Al in such a range, the corrosion resistance is remarkably improved, and
By setting the ratio of Fe: Ca in such a range, electromagnetic conversion characteristics can be improved and dropout can be reduced. 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 agglomerates are decreased due to the improved dispersibility.

In addition to the above-mentioned metal magnetic powder containing iron as a main component, a metal magnetic powder containing cobalt as a main component is also preferable.
Contains Ni in a weight ratio of Co: Ni = 99: 1 to 70:30
Co alloy can be mentioned.

The coercive force (Hc) of the ferromagnetic metal powder used in the present invention is usually preferably in the range of 600 to 5,000 Oe. If this coercive force is less than 600 Oe, the electromagnetic conversion characteristics may deteriorate, and the coercive force
If it exceeds 5,000 Oe, recording may not be possible with an ordinary head, which is not preferable.

The ferromagnetic metal powder preferably has a saturation magnetization (σ _s ) which is a magnetic property, usually 70 emu / g or more. If the saturation magnetization is less than 70 emu / g, electromagnetic conversion characteristics may deteriorate.

The thickness of the uppermost magnetic layer is usually preferably 0.8 μm or less, more preferably 0.5 μm or less. In particular
0.1 to 0.4 μm is preferable.

-A layer containing a non-magnetic powder (a non-magnetic layer) or a layer containing a high-permeability substance (a high-permeability layer) -In the magnetic recording layer of the embodiment of the present invention, it is provided on a non-magnetic support. A plurality of constituent layers are formed, and at least the constituent layer located under the magnetic layer is a non-magnetic layer or a high magnetic permeability layer. The layer functions as a base layer for maintaining surface smoothness and supplying a lubricant.

The high magnetic permeability material used in the present invention has a coercive force Hc of 0 <Hc ≦ 1.0 × 10 ⁴ (A / m), preferably 0 <Hc ≦ 5.0 × 10 ³ (A / m). .. When the coercive force is within the above range, the effect of stabilizing the magnetized region of the magnetic layer is exerted as a high magnetic permeability material. When the coercive force is within the above range, the characteristics as a magnetic material are exhibited, which is preferable.

As the high magnetic permeability material, a material within the range of the coercive force is appropriately selected. Examples of such a high magnetic permeability material include soft magnetic alloys and oxide soft magnetic materials.

As the soft magnetic alloy, Fe--Si alloy, F
e-Al alloys (Alperm, Alfenol, Alfer), Permalloy (Ni-F)
e-based binary alloys, multi-component alloys that include Mo, Cu, Cr, etc.), sendust (Fe-Si-Al: 9.6 wt% S)
i, 5.4% Al, the balance Fe)), Fe-Co alloy Fe-Si
-B-Cu-Nb alloy, Fe-Ru-Ga alloy, doped Si, doped Fe or amorphous Fe-Si-alloy, Co-Si-B alloy, Co-Nb-Zr alloy, doped Co, etc. be able to. Among these, permalloy is mentioned as a preferable soft magnetic alloy. The soft magnetic alloy as the high-permeability alloy is not limited to those exemplified above, and other soft magnetic alloys can be used. The high-permeability alloys may be used alone or in combination of two or more.

As the soft oxide magnetic material, spinel type ferrites such as MnFe ₂ O ₄ , Fe ₃ O ₄ , CoFe ₂ O ₄ and NiFe are used.
₂ O ₄ , MgFe ₂ O ₄ , MgFe ₂ O ₄ , Li _0.5 Fe _2.5 O ₄ , Mn-Zn ferrite, Ni-Zu ferrite, Ni-Cu ferrite, Cu-Z
Examples thereof include n-based ferrite, Mg-Zn-based ferrite, Li-Zn-based ferrite and the like. Among these, Mn-Zn ferrite and Ni-Zn ferrite are preferable. These soft oxide magnetic materials can be used alone or in combination of two or more.

This high-permeability substance is made into a fine powder using a ball mill or other crushing device, and its particle size is 1 to 300 n.
m, preferably 1 to 100 nm, more preferably 1 to 50 nm. In order to obtain such a fine powder, a soft magnetic alloy can be obtained by spraying a molten alloy in a vacuum atmosphere. Further, the soft oxide magnetic material can be made into a fine powder by a glass crystallization method, a coprecipitation firing method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method or the like.

As the non-magnetic powder used in the non-magnetic layer,
Organic powders or inorganic powders may be used individually or as a mixture.

As the organic powder used in the present invention,
Acrylic styrene-based resin, benzoguanamine-based resin powder, melamine-based resin powder, phthalocyanine-based pigment is preferred, but polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, polyfluorinated ethylene resin powder, etc. Can be used as inorganic powders such as carbon black, graphite, titanium oxide, barium sulfate, ZnS, MgCO ₃ , CaCO ₃ , ZnO, CaO, tungsten disulfide, molybdenum disulfide, boron nitride, Mg
O, SnO ₂ , SiO ₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , SiC, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, garnet, silica stone, silicon nitride, boron nitride, silicon carbide , Molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tribolite, diatomaceous earth, dolomide and the like.

Of these, preferred are carbon black, CaCO ₃ , titanium oxide, barium sulfate, α-Al ₂ O ₃ ,
Examples include inorganic powders such as α-iron oxide and polymer powders such as polyethylene.

The layer adjacent to the magnetic layer must be a layer containing a non-magnetic powder or a high magnetic permeability substance as a filler in order to achieve high density recording. Further, in order to keep the surface property of the uppermost layer good, the surface of the layer which is in contact therewith needs to be smooth, and for that reason, the filler used must be fine particles. The average particle size of the filler used is usually 1 to 100 nm, more preferably 1 to 50 nm.

In order to improve the calenderability, it is preferable to use two or more kinds of large and small fillers having different average particle diameters in combination. Difference in average particle size between large and small fillers is 10 nm
It is preferably not less than 50 nm, more preferably not less than 50 nm. The filler is preferably surface-treated with Si, Al or the like from the viewpoint of improving dispersibility.

By the way, in the layers other than the uppermost magnetic layer and containing the non-magnetic powder, the thickness of the magnetic layer is 0.8 μm or less, so that the uppermost magnetic layer is replenished with a lubricant. Functions as a layer. In order for the layer below the magnetic layer to function well as a lubricant replenishment layer, the nonmagnetic powder contained in the layer below the magnetic layer preferably has as little oil absorption as possible, usually 200 ml / 100 g or less. , Preferably 1
It is less than 00ml / 100g.

The content of the filler in the non-magnetic layer or the high magnetic permeability layer is 5 to 99 wt%, preferably 50 to 95 wt%, more preferably 60 to 90 wt%. When the content of the filler is within the above range, the effect of stabilizing the magnetization of the magnetic layer can be sufficiently obtained. On the other hand, if the content of the filler is less than 5 wt%, the effect as a non-magnetic layer or a high magnetic permeability layer may not be obtained, which is not preferable.

The film thickness of the non-magnetic layer or the highly permeable layer is 2.5 μm or less, preferably 0.5 to 2.0 μm.

Further, as a result of extensive studies on the method of coating the magnetic recording layer of the present invention, it is preferable to provide an intermediate layer between the magnetic layer and the non-magnetic layer or the high magnetic permeability layer, whereby the surface after coating is provided. Smoothness is further improved.

Although it is essential that the thickness of the intermediate layer after coating is sufficiently thin, it can be achieved by coating using a very dilute resin solution. Further, by coating the magnetic layer and the intermediate layer by simultaneous multi-layer coating by wet-on-wet extrusion coating, both coating layers can be further thinned and the surface smoothness becomes good. ..

-Binder Used in the Present Invention- As the binder used in the present invention, for example, polyurethane, polyester, vinyl chloride resin such as vinyl chloride copolymer and the like are typical, and these resins are used. Is -S
It is preferable to include a repeating unit having at least one polar group selected from O ₃ M, —OSO ₃ M, —COOM and —PO (OM ¹ ) ₂ , —OPO (OM ¹ ) ₂ .

However, in the above polar group, M represents a hydrogen atom or an alkali metal such as Na, K or Li, and M
¹ represents a hydrogen atom, an alkali atom such as Na, K and Li, or an alkyl group.

The above polar group has the function of improving the dispersibility of the ferromagnetic powder, and the content in each resin is 0.1 to 8.0 mol%,
It is preferably 0.5 to 6.0 mol%. When the content is less than 0.1 mol%, the dispersibility of the ferromagnetic powder is deteriorated, and when the content exceeds 8.0 mol%, the magnetic coating tends to gel. The weight average molecular weight of each resin is 15,000.
A range of up to 50,000 is preferred.

The content of the binder in the magnetic layer is usually 10 to 40 parts by weight, preferably 15 to 30 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

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

The polar group-containing vinyl chloride copolymer used as a binder is synthesized by an addition reaction between a copolymer having a hydroxyl group and a compound having a polar group and a chlorine atom, such as a vinyl chloride-vinyl alcohol copolymer. can do.

It is preferable that an epoxy group is introduced into the vinyl chloride copolymer. This is because the thermal stability of the polymer is improved by doing so.

When the epoxy group is introduced, the content of the repeating unit having an epoxy group in the copolymer is 1 to
30 mol% is preferable, and 1 to 20 mol% is more preferable.

As a monomer for introducing an epoxy group, for example, glycidyl acrylate is preferable.

Regarding the technique for introducing a polar group into a vinyl chloride-based copolymer, JP-A-57-44227 and JP-A-58-108052.
Issue 59-8127, Issue 60-101161, Issue 60-235814, Issue 6
0-238306, 60-238371, 62-121923, 62-146
No. 432, No. 62-146433, etc., and these can also be used in the present invention.

Next, the polyester is generally obtained by reacting a polyol with a polybasic acid.

By 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 polybasic acids having polar groups include 5-
Sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-sulfoisophthalic acid, 3-sulfophthalic acid, dialkyl 5-sulfoisophthalate, dialkyl 2-sulfoisophthalate, dialkyl 4-sulfoisophthalate, dialkyl 3-sulfoisophthalate and these And sodium salts thereof.

Examples of polyols include trimethylolpropane, hexanetriol, glycerin, trimethylolethane, neopentyl glycol, pentaerythritol, ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1 Examples thereof include 6,6-hexanediol, diethylene glycol, cyclohexanedimethanol and the like.

Incidentally, other polar group-introduced polyesters can also be synthesized by a known method.

Next, with respect to polyurethane, it is obtained from the reaction of a polyol and 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 polyisocyanates include diphenylmethane-4-4'-diisocyanate (MDI), hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI), tolidine diisocyanate (TOD).
I), lysine isocyanate methyl ester (LDI)
Etc.

As another method for synthesizing a polyurethane having a polar group, an addition reaction between a polyurethane having a hydroxyl group and a compound having a polar group and a chlorine atom is also effective.

As a technique for introducing a polar group into polyurethane, JP-B-58-41565 and JP-A-57-92422 are known.
Issue 57-92423, Issue 59-8127, Issue 59-5423, Issue 59-5
No. 424 and No. 62-121923, and these can be used in the present invention.

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

The resin has a weight average molecular weight of 10,0.
00-200,000 vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (nitrocellulose etc.) , Styrene-butadiene copolymer, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, urea formamide resin, various synthetic rubber resins and the like.

-Other Components- In the present invention, in order to improve the quality of the magnetic layer, additives such as a durability improver, a dispersant, a lubricant and an abrasive can be contained as other components.

Examples of the durability improver include polyisocyanate, and examples of the polyisocyanate include:
For example, there are aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and aliphatic polyisocyanates such as adducts of hexamethylene diisocyanate (HMDI) and active hydrogen compounds. The weight average molecular weight of the polyisocyanate is preferably in the range of 100 to 3,000.

Examples of the dispersant include fatty acids having 12 to 18 carbon atoms such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid; salts of these alkali metals or alkaline earth metals. Examples thereof include salts or amides thereof; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefinoxy quaternary ammonium salts; azo compounds having a carboxyl group and a sulfonic acid group. These dispersants are usually 0.
It is used in the range of 5 to 5 wt%.

Fatty acids and / or fatty acid esters can be used as the lubricant. In this case, the amount of fatty acid added is preferably 0.2 to 10 wt% with respect to the ferromagnetic powder,
0.5 to 5 wt% is more preferable. If the addition amount is less than 0.2 wt%, the running property is likely to deteriorate, and if it exceeds 10 wt%, the fatty acid is likely to seep out to the surface of the magnetic layer or the output is likely to decrease. The amount of fatty acid ester added is preferably 0.2 to 10 wt% and more preferably 0.5 to 5 wt% with respect to the ferromagnetic powder. If the addition amount is less than 0.2 wt%, the still durability is likely to deteriorate, and if it exceeds 10 wt%, the fatty acid ester is likely to seep out to the surface of the magnetic layer or the output is likely to decrease. When using a fatty acid and a fatty acid ester together to further enhance the lubricating effect, the weight ratio of the fatty acid and the fatty acid ester is preferably 10:90 to 90:10.

The fatty acid may be a monobasic acid or a dibasic acid, preferably having 6 to 30 carbon atoms, and 12 to 22 carbon atoms.
Is more preferable. 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, succinic acid, maleic acid. Acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,
12-dodecane dicarboxylic acid, octane dicarboxylic acid and the like can be mentioned.

Specific examples of the fatty acid ester include oleyl oleate, isocetyl stearate, dioleyl malate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmitate. 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.

As the lubricant other than the above fatty acids and fatty acid esters, for example, silicone oil, graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide and the like can be used.

Specific examples of the polishing agent include α-alumina, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, tungsten carbide, molybdenum carbide, boron carbide, corundum, and oxide. Examples thereof include zinc, cerium oxide, magnesium oxide and boron nitride.
The abrasive preferably has an average particle size of 0.05 to 0.6 μm, more preferably 0.1 to 0.3 μm.

Further, in the present invention, an antistatic agent can be supplementarily used. That is, the carbon black,
Besides conductive powders such as graphite, cationic surfactants such as quaternary amines; anionic surfactants containing acid groups such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester, carboxylic acid; amphoteric amphoteric acid such as aminosulfonic acid Surfactants; natural surfactants such as saponin and the like can be mentioned. The above-mentioned antistatic agent is usually added in the range of 0.01 to 40 wt% with respect to the binder.

-Manufacture of Magnetic Recording Medium- The magnetic recording medium of the present invention is preferably a so-called wet-on-wet system in which the magnetic layer is applied when the lower layer is in a wet state. This wet-on-wet method
A known method used for manufacturing a multilayer structure type magnetic recording medium can be appropriately adopted.

For example, in general, ferromagnetic powder, high-permeability substance, non-magnetic powder, binder, dispersant, lubricant, abrasive, antistatic agent and the like are kneaded with a solvent to prepare a high-concentration magnetic layer coating and Other constituent layer paints are prepared, and then these paints are diluted to prepare paints, which are then applied to the surface of the non-magnetic support.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) and cyclohexanone; alcohols such as methanol, ethanol and propanol; esters such as methyl acetate, ethyl acetate and butyl acetate. Cyclic ethers such as tetrahydrofuran and the like; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene can be used.

In kneading and dispersing the components for forming the magnetic layer,
Various kneading dispersers can be used.

Examples of the kneading / dispersing machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill,
Kobol Mill, Tron Mill, Sand Mill, Sand Grinder, Sqegvari Attritor, High Speed Impeller Disperser, High Speed Stone Mill, High Speed Impact Mill, Dispa, High Speed Mixer,
Examples thereof include a homogenizer, an ultrasonic disperser, an open kneader, a continuous kneader, and a pressure kneader. Among the above kneading dispersers, the kneading dispersers capable of providing a power consumption load of 0.05 to 0.5 KW (per 1 Kg of magnetic powder) are a pressure kneader, an open kneader, a continuous kneader, a two-roll mill and a three-roll mill. is there.

To coat the constituent layers on the non-magnetic support, specifically, as shown in FIG.
From the extrusion-type extrusion coaters 10 and 11 on the film-shaped support 1 fed from the above, each coating material is applied in multiple layers by the wet-on-wet method, and then passed through the orientation magnet or the vertical orientation magnet 33 and dried. It is introduced into the container 34, and hot air is blown from the nozzles arranged above and below to dry it. Next, the dried support 1 with each coating layer is guided to a super calender device 37 composed of a combination of calender rolls 38, where it is calendered and then wound on a winding roll 39. The magnetic film thus obtained can be cut into a tape having a desired width to produce a magnetic recording tape for an 8 mm video camera, for example.

In the above method, each paint may be supplied to the extrusion coaters 10 and 11 through an in-line mixer (not shown). In the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extrusion coaters 10 and 11 respectively,
Liquid reservoirs 13 and 14 are provided, and the paint from each coater is layered in a wet-on-wet system. That is, immediately after the coating of the lower-layer constituent layer coating material (when it is in a non-dried state), the uppermost magnetic layer coating material is finally applied in multiple layers.

The coater head shown in FIG. 3 (c) is preferable in the present invention.

As the solvent to be blended in the above paint or a diluent solvent when the paint is applied, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; alcohols such as methanol, ethanol, propanol, butanol; methyl acetate , Esters such as ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol senoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, xylene; methylene chloride, Ethylene chloride, carbon tetrachloride, chloroform,
A halogenated hydrocarbon such as dichlorobenzene can be used. These various solvents may be used alone or in combination of two or more.

The magnetic field in the oriented magnet or the magnet for vertical orientation is about 20 to 5,000 gauss, the drying temperature by the dryer is about 30 to 120 ° C., and the drying time is about 0.1 to 10 °.
It's about a minute.

In the wet-on-wet system, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, etc. can also be used. Furthermore, air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater,
It is also possible to combine a transfer roll coater, a kiss coater, a cast coater, a spray coater and the like.

In the multi-layer coating in the wet-on-wet system, since the upper magnetic layer is coated while the lower layer of the upper layer is in a wet state, the surface of the lower layer (that is, the boundary surface with the upper layer). ) Is smooth, the surface properties of the uppermost layer are good, and the adhesiveness between the upper and lower layers is also improved. As a result, especially for high-density recording, the performance required for high output and low noise such as a magnetic tape is satisfied, and film durability is also required for film peeling. Loss, the film strength is improved,
Durability is sufficient. In addition, the wet-on-wet multi-layer coating method can reduce dropout and improve reliability.

-Surface smoothing-In the present invention, it is also possible to carry out a surface smoothing process by calendering. After that, if necessary, burnishing or blade processing is performed for slitting.

In the surface smoothing treatment, the calender conditions are temperature, linear pressure, C / S (coating speed).
Etc. can be mentioned.

In the present invention, the above temperature is usually 50
〜120 ℃, the above linear pressure is 50 ~ 400kg / cm, the above C / S is 20
It is preferable to hold at ~ 600 m / min.

As a result of the above-mentioned treatment, the upper magnetic layer thickness should be 0.5 μm or less, preferably 0.3 μm or less.
It is preferable in terms of improving high frequency characteristics and overwrite characteristics.

[0100]

Embodiments of the present invention will be described below.

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

First, a magnetic layer coating material, a non-magnetic layer coating material or a high magnetic permeability coating material having the following compositional formulation is kneaded and dispersed by using a kneader and a sand mill, and each of the obtained coating materials is polyisocyanate (Coronate L). 5 parts by weight, manufactured by Nippon Polyurethane Industry Co., Ltd., and then added on a polyethylene terephthalate film having a thickness of 10 μm by the wet-on-wet method in the combinations shown in Table 1 to Examples 1 to 6 and Comparative Examples (1) to ( After applying the sample of 6), magnetic field orientation treatment is performed while the coating film is undried, followed by drying, and then surface smoothing treatment with a calendar to obtain a thickness of 1.0 μm.
Layer containing non-magnetic powder or layer containing high magnetic permeability material and thickness
A magnetic recording layer composed of a 0.4 μm magnetic layer was formed.

Magnetic layer paint prescription: (Paint A) Fe-Al based ferromagnetic metal powder 100 parts (Fe: Al weight ratio = 100: 8, average major axis length; 0.16 μm, axial ratio 8 Hc; 1720 Oe, σ _S ; 120 emu / g, crystallite size; 170 Å) Sulfonic acid metal salt-containing vinyl chloride resin 10 parts [Nippon Zeon Co., Ltd., MR-110] Sulfonic acid metal salt-containing polyester polyurethane resin [Toyobo Co., Ltd.] , UR-8700] 5 parts Alumina (α-Al ₂ O ₃ , average particle size: 0.2 μm) 6 parts Carbon black [average particle size 40 nm] 1 part Stearic acid 1 part Myristic acid 1 part Butyl stearate 1 part Cyclohexanone 100 Part Methyl ethyl ketone 100 parts Toluene 100 parts: Non-magnetic layer or highly permeable coating formulation: (Paint a; non-magnetic layer) Titanium oxide (particle size 30 nm) 90 parts Carbon black (particle size 20 nm) 10 parts Sulfonic acid metal salt Containing vinyl chloride resin 6 parts [NIPPON ZE Emissions Ltd., MR-110] sulfonic acid metal salt-containing polyester polyurethane resin [Toyobo Co., UR-8700] 3 parts of alpha-Al ₂ O ₃ [particle size 0.2μm] 6 parts Myristic acid 1 part Butyl Stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts (Paint b; high magnetic permeability layer) Fe-Si-Al sendust alloy powder [Hc = 40 (A / m), μ
i = 200 (H / m), particle size 50 nm] Same as the coating material a except that 100 parts were used.

Further, a coating material having the following composition is applied to the surface (rear surface) of the polyethylene phthalate film opposite to the magnetic recording layer, the coating film is dried, and calendering is performed according to the calendering conditions described later. By doing so, a back coat layer having a thickness of 0.8 μm was formed to obtain a wide original anti-magnetic tape.

Backcoat layer coating formulation: Carbon black 40 parts (Raven 1035) Barium sulfate 10 parts (Average particle size 300 mμ) Nitrocellulose 25 parts Polyurethane resin 25 parts (N-2301 manufactured by Nippon Polyurethane Co., Ltd.) Polyisocyanate compound 10 parts (Nippon Polyurethane Co., Ltd., Coronate L) Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts The raw material thus obtained was slit to prepare an 8 mm video tape.

The electromagnetic conversion characteristics and the like of this video tape were measured as follows. The results are shown in Table 1.

Comparative Example (5) is the same as Example 1 except that the lower constituent layer was applied and dried, and the upper constituent layer was wet-wet after calendering.

[0108]

[Table 1]

Characteristic measurement: (a) CN characteristic A single wave of 9 MHz was recorded and the output level when the signal was reproduced was expressed by comparison with a reference sample.

(B) Overwrite Characteristic The residual output level of the 2 MHz signal was recorded when a 2 MHz signal was recorded at the saturation level and then a 9 MHz signal was (overwritten) recorded. The lower the residual output level, the better the overwrite characteristics.

(C) Coatability The multilayer coatability was visually evaluated, and the occurrence of coating streaks was indicated as x, and the occurrence of coating streaks was indicated as o.

[0112]

According to the present invention, it is possible to provide a magnetic recording medium having excellent electromagnetic conversion characteristics, digital recording characteristics, and overwriting characteristics.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a magnetic layer surface roughness R _{z (10)} .

FIG. 2 is a diagram for explaining simultaneous multilayer coating of magnetic layers by wet-on-wet coating by an extrusion coating method.

FIG. 3 is a view of a coater head for applying paint.

[Explanation of symbols]

 1 Support 10 Coater 11 Coater 32 Supply Roll 33 Orientation Magnet 34 Dryer 37 Super Calendar Device 38 Calendar Roll 39 Winding Roll

Claims (4)

[Claims] 1. A magnetic recording layer having a plurality of constituent layers is formed on a non-magnetic support, and the magnetic layer occupies an upper layer of the magnetic recording layer.
The magnetic layer contains a ferromagnetic metal powder having an average major axis length of 0.25 μm or less and a particle size measured by X-ray of 200 Å or less, and the magnetic layer has a coercive force of 1700 to 2200 Oe and a saturation magnetic flux density of 3000 to 4
500 gauss, and at least 1 in the magnetic recording layer other than the magnetic layer
A magnetic recording medium having a layer containing a non-magnetic powder or a high magnetic permeability material. 2. The surface roughness R of the surface of the magnetic recording layer.
The magnetic recording medium according to claim 1, wherein _{z (10)} is 5 to 20 nm. 3. The thickness of the uppermost magnetic layer of the magnetic recording layer is
The magnetic recording medium according to claim 1, which has a thickness of 0.8 μm or less. 4. A magnetic recording layer according to any one of claims 1 to 3, wherein in coating a plurality of constituent layers on a non-magnetic support, an upper constituent layer is coated on a lower constituent layer in a wet state to form a magnetic recording layer. The magnetic recording medium according to 1.