JP3481680B2 - 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 suitable for digital use, which is excellent in electromagnetic conversion characteristics and running durability.

[0002]

2. Description of the Related Art Conventionally, it has been known that the magnetic layer has a multi-layer structure instead of a single layer and has a layer structure suitable for each recording wavelength. Further, in order to improve electromagnetic conversion characteristics, an example of a multilayer structure in which a lower layer is a non-magnetic layer is disclosed in JP-A-63-18741.
8 and JP-A-63-191315. In the digital VTR proposed in the future, improvement of high frequency characteristics,
That is, it is important to improve the output in the short wavelength region and to secure the overwrite characteristic. In order to achieve this, it is essential that the medium has a multi-layered structure.
It is necessary to thin the upper magnetic layer and smooth the medium. However, it is not possible to sufficiently reduce the surface roughness of the medium surface only by the method shown in the above-mentioned patent publication,
As a result, improvement of high frequency characteristics cannot be achieved. As a result of analyzing the cause, the following was found. That is, it was found that as the upper layer is made thinner, the abrasive contained in the upper layer deteriorates the characteristics in the high frequency range, that is, the output in the high frequency range is lowered, and further the C / N ratio is remarkably lowered.
Further, if the amount of the abrasive added to the upper layer is reduced in order to solve the above problems, the output in a high frequency range and the C / N ratio are improved, but there are major problems in running durability and other items such as still characteristics. Caused

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a magnetic recording medium which is suitable as a magnetic recording medium for digital use and is excellent in electromagnetic conversion characteristics such as good reproduction output, head clog suppression and still characteristics, and running durability. The purpose is to do.

[0004]

The present invention for solving the above problems has the following constitution. (1) At least one lower layer obtained by dispersing nonmagnetic powder in a binder is provided on a nonmagnetic support, and an upper layer formed of a magnetic layer obtained by dispersing ferromagnetic powder in the binder. In the magnetic recording medium provided with, the average particle diameter of the abrasive in the upper layer is 5 to 70% of the upper layer film thickness, and the upper layer film thickness is 0.05 to 0.3 μm. A magnetic recording medium in which the average major axis length of the magnetic (metal) powder is 5 to 50% of the upper layer film thickness, and the coercive force of the medium is 1900 to 3000 Oe. (2) The nonmagnetic powder is placed on the nonmagnetic support. A magnetic recording medium comprising at least one lower layer dispersed in a binder, and an upper layer comprising a magnetic layer comprising ferromagnetic powder dispersed in the binder, the abrasive being contained in the upper layer. Has an average particle size of 5 to 70% of the upper layer film thickness, and the upper layer film in the abrasive The number of particles having a particle size exceeding 80% of the thickness is 3 to 40% of the total abrasive, and the upper layer film thickness is 0.05 to 0.3 μm.
(3) The ferromagnetic powder is a ferromagnetic (metal) powder containing Fe, Al and at least one rare earth element in the constituent elements, (1) or (2) The magnetic recording medium according to 1.

[0005]

According to the present invention, by improving the smoothness of the upper layer, it is possible to achieve high output and a high C / N ratio in a high frequency range and further secure running reliability.

In the region where the upper layer thickness is 0.3 μm or less, if the conventionally used abrasive is used as it is, the particle diameter of the abrasive with respect to the upper layer thickness becomes very large. For example, when the upper layer film thickness is 0.2 μm, the average particle size is 0.2 μm.
When m abrasive is added, magnetic powder cannot be present in the upper layer where the abrasive is present. Therefore, the continuity of magnetic recording is interrupted. This reduces the smoothness of the medium and the filling degree of the magnetic powder, and causes the output to drop in the high frequency range. In particular, the degree of influence is great for the C / N ratio.
The reason for this is not well understood. Therefore, the present inventors
In order to solve this problem, the particle diameter of the abrasive contained in the upper layer has a constant relationship with the upper layer film thickness, and the average major axis length of the ferromagnetic (metal) powder also has a constant relationship with the upper layer film thickness. We have found that having a relationship is a way to solve the above problem. On the other hand, it has been found that the same effect can be obtained by suppressing the particle diameter component, which has a constant relationship with the upper layer film thickness, of the particles contained in the abrasive to a constant value.
By the above method, the output is improved in the high frequency range, C
It was possible to achieve a significant improvement in the / N ratio and also to achieve running durability such as still characteristics.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention is described in detail below.

—Structure of Magnetic Recording Medium— The magnetic recording medium of the present invention comprises a nonmagnetic support (A), a lower layer (B), a ferromagnetic layer composed mainly of nonmagnetic powder in order from the nonmagnetic support. It has a magnetic layer provided with a layer containing the powder as an upper layer (C). Further, the magnetic recording medium of the present invention further comprises a magnetic layer and / or a non-magnetic powder between the lower layer (B) and the upper layer (C) or between the non-magnetic support (A) and the lower layer (B). You may provide the nonmagnetic layer containing. For example, the layer provided between the lower layer (B) and the upper layer (C) or between the non-magnetic support (A) and the lower layer (B) may be composed of a plurality of non-magnetic layers or may not be separated from the magnetic layer. It may be composed of a plurality of layers having a magnetic layer.

In the present invention, the dry film thickness of the lower layer is preferably 0.1 to 3.0 μm, preferably 0.2 to
The thickness is 2.0 μm, more preferably 0.5 to 2.0 μm. (A) Non-magnetic support Examples of materials for forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, and cellulose such as cellulose triacetate and cellulose diacetate. Examples thereof include derivatives and 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.

There are no particular restrictions on the thickness of the non-magnetic support, but in the case of a film or sheet, for example, the thickness is usually 2
The thickness is 100 μm, preferably 4 to 50 μm. In the case of a disc or a card, it is about 30 μm to 10 mm, and in the case of a drum, it is appropriately selected according to the recorder or the like.

The non-magnetic support may have a single-layer structure or a multi-layer structure. Further, this 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. However, an undercoat layer may be provided between the magnetic layer and the non-magnetic support. (B) Lower Layer The lower layer is not particularly limited except that it is a layer containing a non-magnetic powder, and can be formed by various methods. In particular, α-Fe ₂ O ₃ (referred to as α-iron oxide) powder is preferable as the non-magnetic powder.

The lower layer contains a non-magnetic powder and may further contain a binder and other components. In particular, α-iron oxide powder is preferable as the non-magnetic powder.

In the present invention, various known non-magnetic powders can be appropriately selected and used together with the α iron oxide powder shown above.

Examples of non-magnetic powders that can be used include carbon black, graphite and TiO.
₂ , barium sulfate, ZnS, MgCO ₃ , CaCO ₃ ,
ZnO, CaO, tungsten disulfide, molybdenum disulfide, boron nitride, MgO, SnO ₂ , Cr ₂ O ₃ , α-
Al ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, Si
C, 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, triboli, diatomaceous earth, dolomite and the like can be mentioned.

Of these, preferred are carbon black, CaCO ₃ , TiO ₂ , barium sulfate and α-Al.
Inorganic powders such as ₂ O ₃ , α-FeOOH and Cr ₂ O ₃ and polymer powders such as polyethylene.

In the present invention, it is preferable to use α-iron oxide powder having a needle-like powder shape. The use of the acicular α-iron oxide powder is preferable in that the surface smoothness of the lower layer can be improved and the surface smoothness of the upper layer laminated thereon can be improved at the same time. Furthermore, 0.01 to 5 wt% of γ-Fe is added to the α iron oxide powder.
₂ O _3, or at least one of Fe ₃ O _4, or α-iron oxide as a host, preferably contains at least one component of the _γ-Fe 2 _{O 3} or _Fe 3 _{O 4} in the powder structure. The coercive force of this powder is 200 to 600.
Oe is preferred.

The major axis diameter of the powder containing α-iron oxide as the main or base material is usually less than 0.30 μm, preferably 0.20 μm or less, and particularly preferably,
It is 0.15 μm or less.

The short axis diameter of the powder containing α-iron oxide as a main component or a matrix is usually 0.10 μm or less, preferably 0.08 μm or less, and particularly preferably,
It is 0.06 μm or less.

The axial ratio of the powder containing α-iron oxide as the main component or the matrix is usually 2 to 20, preferably 5
-15, particularly preferably 5-10. The axial ratio referred to here is the ratio of the major axis diameter to the minor axis diameter (major axis diameter /
Minor axis diameter).

[0022] As the specific surface area of the powder mainly or maternal the α-iron oxide is usually 10~250m ² / g, preferably 20~150m ² / g, particularly preferably, 30 to 100 m ² / It is g.

When a powder containing α-iron oxide as the main or base material having the major axis diameter, the minor axis diameter, the axial ratio and the specific surface area within the above ranges is used, the surface property of the lower layer can be improved and the upper layer can be obtained. The surface property of is also preferable in that it can be in a good state.

The content in the lower layer of the powder containing α-iron oxide as a main component or a matrix is 50 to 99% by weight, preferably 6% by weight, based on the total of all components constituting the lower layer.
0 to 95% by weight, particularly preferably 70 to 95% by weight. It is preferable that the content of the powder containing α-iron oxide as the main component or the base component is within the above range because the state of the coating film surfaces of the lower layer and the upper layer can be improved.

Regarding the magnetic properties of the lower layer using the α-iron oxide, the coercive force Hc is preferably 1000 (Oe) or less and the saturation magnetic flux density is less than 30 (G).

In the present invention, the average abundance ratio of the elements forming the surface of the powder containing α-iron oxide as the main component or the base substance present in the dried lower coating film is measured by an XPS surface analyzer. .

Next, the method will be described. The XPS surface analyzer is set under the following conditions.

X-ray anode; Mg resolution; 1.5 to 1.7 eV (resolution is clean A
g3d5 / 2 peak full width at half maximum) The XPS surface analyzer is not particularly limited, and any model can be used. In the present invention,
VG ESCALAB-200 was used.

Narrow scan is performed in the following measurement range,
The spectrum of each element was measured. At this time, the data acquisition interval is set to 0.2 eV, and it is necessary to integrate until the target peak has a count of the minimum count number or more shown below.

Peak measurement range Minimum detection intensity (binding energy eV) (count) Cls 305 to 280 arbitrary Fe2p3 / 2 730 to 700 600,000 Na (KL ₂₃ L ₂₃ ) 280 to 250 600,000 Auger peaks for the obtained spectrum And the peak position of Cls is 2
The energy position is corrected to be 84.6 eV.

Next, COMMON DATA PROCESSING S manufactured by VAMAS-SCA-JAPAN.
YSTEM Ver. In order to perform processing on 2.3 (hereinafter referred to as VAMAS software), the above-mentioned spectrum is used by the software provided by each device manufacturer to perform VAMAS.
Transfer to a computer that can use the software. Then, the transferred spectrum is converted into VAMAS format using VAMAS software, and then data processing is performed.

Before starting the quantitative treatment, Co
The unt Scale is calibrated and the 5-point smoothing process is performed. With the peak position of each element as the center, the peak area intensity (cps * eV) is determined in the quantitative range shown in the following table. The number of atoms of each element is calculated using the sensitivity coefficient shown below. The number of atoms is 1 Fe atom
It is converted into the number of atoms with respect to 00 and used as a quantitative value.

[0033]   Element Peak position (BE: ev) Quantitative range (BE: ev) Sensitivity coefficient   Around Fe 719.8 High B. E. Side 5eV 10.54                                     Low B. E. Side 7 eV   Na around 264.0 High B. E. Side 2 eV 7.99                                     Local minima in the vicinity,                                     Low B. E. Side 6 eV The elements other than the above elements were measured under the following conditions.

[0034]

[Table 2]

<Sample Preparation Method> Prior to the above measurement, the medium (magnetic tape) is pretreated.

The binder resin is removed from the magnetic tape by the plasma low temperature ashing method to expose the magnetic particles and non-magnetic particles. The treatment method is selected such that the binder resin is incinerated but the magnetic particles and the non-magnetic particles are not damaged.
For example, after treating with the equipment and treatment conditions described below, the average abundance ratio of elements forming the surface of the powder in the lower coating film was measured.

Equipment: Reiwa Shoji PL-850X Treatment conditions: FORWARD POWER 100W REFLECTED POWER 5W Vacuum degree 10Pa Introduced gas species Air Discharge time 1 min On the surface of the powder mainly composed of α iron oxide by the above-mentioned measurement method, The average abundance ratio of the elements forming S is 1 to 100 Al atoms and 100 S Fe atoms,
The number of i atoms is preferably 1 to 100.

Typical examples of the binder used in the lower layer of the present invention include polyurethane, polyethylene, vinyl chloride resins such as vinyl chloride copolymers, and the like. These resins are --SO ₃ M, --SO ₃ M, OSO ₃ M, -CO
It is preferable to include a repeating unit having at least one polar group selected from OM and —PO (OM ¹ ) ₂ and a sulfobetaine group.

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

In the present invention, a binder (binder)
The following resins can be used together in an amount of 20 to 80% by weight based on the total weight of the binder.

The resin has a weight average molecular weight of 10,
000 to 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), 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.

In the present invention, in order to improve the quality of the lower layer, an additive such as an abrasive, a lubricant, a curing agent, a dispersant, an antistatic agent and a conductive fine powder is contained as another component. You can

Examples of the polishing agent include Japanese Patent Application No. 4-241.
Known substances described in paragraph No. 0105 of No. 218 can be used. The average particle size of this abrasive is usually 0.05 to 0.6 μm, preferably 0.05 to 0.6 μm.
0.5 μm, particularly preferably 0.05 to 0.3 μm
m.

The content of this abrasive in the magnetic layer or the lower layer is usually 3 to 20 parts by weight, preferably 5 parts by weight.
~ 15 parts by weight.

Fatty acids and / or fatty acid esters can be used as the lubricant. In this case, the amount of fatty acid added is 0.2 to 10 with respect to the magnetic powder or the non-magnetic powder.
Weight% is preferable, and 0.5 to 5 weight% is particularly preferable. Fatty acid and fatty acid ester are 10:90 by weight ratio.
90:10 is preferable. The fatty acid may be a monobasic acid or a dibasic acid, and preferably has 6 to 30 carbon atoms, and more preferably 12 to 24 carbon atoms.

Specific examples of the fatty acid are described in JP-A-4-21.
The fatty acid described in paragraph No. 0102 of No. 4218 is a specific example of the fatty acid ester.
The fatty acid ester of 3 is mentioned.

As the lubricant other than the above-mentioned fatty acids and fatty acid esters, substances known per se can be used, and for example, silicone oil, fluorinated carbon, fatty acid amide, α-olefin oxide and the like can be used.

Examples of the curing agent include polyisocyanates. Examples of the polyisocyanates include aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and hexamethylene diisocyanate ( There are aliphatic polyisocyanates such as adducts of HMDI) with active hydrogen compounds. The weight average molecular weight of the polyisocyanate is
It is preferably in the range of 100 to 3,000.

As the dispersant, paragraph No. 009 of the same publication is used.
The compounds described in 3 can be mentioned. These dispersants are usually added to the magnetic powder or non-magnetic powder in an amount of 0.5 to
Used in the range of 5% by weight.

As the antistatic agent, paragraph 0 of the same publication is used.
The surfactant described in 107 can be mentioned. This antistatic agent is usually used in an amount of 0.01-40 with respect to the binder.
It is added in the range of weight%. Further, in the present invention, conductive fine powder can be preferably used as the antistatic agent. Examples of the antistatic agent include carbon black, graphite, tin oxide, silver powder, silver oxide, silver nitrate, organic compounds of silver, metal particles such as copper powder, and metal oxides such as zinc oxide, barium sulfate and titanium oxide. Examples include pigments coated with a conductive substance such as a tin oxide film or an antimony solid solution tin oxide film.

The average particle size of the conductive fine powder is
5 to 700 nm, more preferably 5 to 200 nm
Is. The content of the conductive fine powder is 1 to 20 parts by weight, preferably 2 to 7 parts by weight, based on 100 parts by weight of the α-iron oxide powder. (C) Upper Layer The upper layer is not particularly limited except that it is a layer containing a ferromagnetic powder, and can be formed by various methods,
It may contain a binder and other components.

As the ferromagnetic powder used in the present invention,
Examples thereof include ferromagnetic iron oxide powder, ferromagnetic metal powder, and hexagonal plate-shaped powder.

Among these, the ferromagnetic metal powder described later can be preferably used.

As the ferromagnetic oxide powder, γ-Fe ₂
O ₃ , Fe ₃ O ₄ , or an intermediate iron oxide of these Fe
Those represented by Ox (1.33 <x <1.5), Co
(Cobalt modified) Co-FeOx
Examples include those represented by (1.33 <x <1.5).

The ferromagnetic powder used in the present invention has a major axis diameter of less than 0.30 μm, preferably 0.04 to 0.2.
It is preferably 0 μm, and more preferably 0.04 to 0.12 μm. When the major axis diameter of the ferromagnetic powder is within the above range, the surface property of the magnetic recording medium can be improved and the electromagnetic conversion characteristics can be improved.

The crystallite size is 100 to 200Å and the axial ratio is 4 to 15.

The ferromagnetic powder used in the present invention is
The coercive force (Hc) is usually preferably in the range of 1200 to 5000 Oe. This coercive force is 1200 O
If it is less than e, the electromagnetic conversion characteristics may deteriorate,
Further, if the coercive force exceeds 5000 Oe, recording may not be possible with a normal head, which is not preferable.

The ferromagnetic powder preferably has a saturation magnetization amount (σs), which is a magnetic characteristic, usually 110 emu / g or more. This saturation magnetization is 110 emu / g
If it is less than the above range, the electromagnetic conversion characteristics may deteriorate. Further, it is desirable that this saturation magnetization amount is 125 emu / g or more.

Further, in the present invention, a ferromagnetic metal powder having a specific surface area by 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.

For the specific surface area and the measuring method thereof, see "Measurement of Powder" (JM.
e, Clyeorr Jr. Co-authored by Muta and other translations; published by Sangyo Tosho Co., Ltd.), and also described in "Chemical Handbook" Application, P1170-1171 (Chemical Society of Japan; Maruzen Co., Ltd., published April 30, 1966). Has been done.

The specific surface area can be measured, for example, by using a powder of 105
The mixture was deaerated while heat-treated at about 13 ° C for 13 minutes to remove what was adsorbed on the powder, and then this powder was introduced into a measuring device to set the initial pressure of nitrogen to 0.5 kg / m ² . The measurement is performed with nitrogen at a liquid nitrogen temperature (-105 ° C) for 10 minutes.

As the measuring device, for example, a counter soap (made by Yuasa Ionics Co., Ltd.) is used.

More preferable ferromagnetic metal powder is
These include: That is, Fe atoms, Al atoms, and rare earth element atoms are contained as elements forming the ferromagnetic metal powder, and the weight ratio of the elements in the entire ferromagnetic metal powder is 100 atomic parts by weight of Fe atoms to 2 atomic atoms.
-10 parts by weight, 1 to 8 parts by weight of atoms of rare earth elements,
In addition, the average abundance ratio of elements forming the surface of the ferromagnetic metal powder is such that the number of Al atoms is 70 to 2 with respect to 100 Fe atoms
00 and the number of atoms of the rare earth element are 0.5 to 30.

The ferromagnetic metal powder further contains Na atoms and Ca atoms as elements forming the ferromagnetic metal powder, and the weight ratio of the elements in the whole ferromagnetic metal powder is Fe.
Less than 0.1 part by weight of Na atom to 100 parts by weight of atom,
0.1 to 2 parts by weight of Ca atom, 2 to 10 parts by weight of Al atom,
The number of atoms of the rare earth element is 1 to 8 parts by weight, and the average abundance ratio of elements forming the surface of the ferromagnetic metal powder is 2 to 30 Na atoms and 5 Ca atoms with respect to 100 Fe atoms.
˜30, the number of Al atoms is 70 to 200, and the number of atoms of rare earth elements is 0.5 to 30.

The ferromagnetic metal powder further contains Co atoms, Ni atoms and Si as elements forming the ferromagnetic metal powder.
An atomic weight ratio of the elements in the whole ferromagnetic metal powder is 2 to 2 Co atoms with respect to 100 parts by weight of Fe atoms.
0 parts by weight, Ni atoms 2 to 20 parts by weight, Si atoms 0.3 to
5 parts by weight, less than 0.1 parts by weight of Na atom, 0.1 atom of Ca
˜2 parts by weight, Al atoms 2 to 10 parts by weight, rare earth element atoms 1 to 8 parts by weight, and the average abundance ratio of the elements forming the surface of the ferromagnetic metal powder is 100 Fe atoms. Co atom number less than 0.1, Ni atom number less than 0.1, S
The number of i atoms is 20 to 130, the number of Na atoms is 2 to 30, the number of Ca atoms is 5 to 30, the number of Al atoms is 70 to 200, and the number of rare earth element atoms is 0.5 to 30.

Further, in a magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a non-magnetic support, the average presence of elements forming the surface of the ferromagnetic metal powder oriented in the magnetic layer. Ratio is 10 Fe atoms
The number of Al atoms is 70 to 300, and the number of rare earth elements is 0.5 to 60.

It is characterized in that the atom of the rare earth element is at least one selected from the group consisting of Sm, Nd, Y and Pr.

In the present invention, the binder contained in the upper layer containing the ferromagnetic powder may be the same as the binder used in the lower layer.

The content of the binder in the upper layer is usually 10 to 40 with respect to 100 parts by weight of the ferromagnetic powder.
Parts by weight, preferably 10 to 30 parts by weight.

As the other components that can be contained in the upper layer, the same components as those contained in the lower layer can be used.

The content of the lubricant is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight based on the ferromagnetic powder.

The content of the dispersant is 0.5 to 5% by weight based on the ferromagnetic powder.

The content of the conductive fine powder is usually 1 to 20 parts by weight, and more preferably 3 to 15 parts by weight, based on 100 parts by weight of the magnetic powder.

The magnetic recording medium according to the present invention is preferably coated by a so-called wet-on-wet coating method in which the upper layer (magnetic layer) is coated when the lower layer is in a wet state. As the wet-on-wet coating method, a known method used for manufacturing a magnetic recording medium having a multilayer structure can be appropriately adopted.

For example, generally, a magnetic powder, a binder, a dispersant, a lubricant, an abrasive, an antistatic agent and a solvent are kneaded to prepare a high-concentration magnetic paint, and then the high-concentration magnetic paint is diluted. After adjusting the magnetic paint, the magnetic paint is applied to the surface of the non-magnetic support. As the solvent,
For example, the solvent described in paragraph No. 0119 of JP-A-4-214418 can be used. These various solvents may be used alone, or two or more of them may be used in combination.

In kneading the components for forming the magnetic layer, various kneading dispersers can be used. Examples of this kneading disperser include those described in paragraph 0112 of the above publication.

Among the kneading dispersers, 0.05 to 0.5 kW
The kneading disperser capable of providing a power consumption load (per 1 kg of magnetic powder) is a pressure kneader, an open kneader, a continuous kneader, a two roll mill, or a three roll mill.

In applying the coating material, in the wet-on-wet coating method, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, and the like can be used.
Furthermore, an air doctor coater, a blade coater, an air knife coater, a squeeze coater, an impregnation coater, a transfer roll coater, a kiss coater, a cast coater, a spray coater and the like can be combined.

In multi-layer coating in the wet-on-wet coating system, the upper layer is coated while the lower layer remains wet, so that the surface of the lower layer (that is, the boundary surface with the upper layer).
And the surface property of the upper coating film is improved, and the adhesion between the upper and lower layers is also improved.

As a result, the performance particularly required for the digital recording medium is satisfied. Further, the wet-on-wet coating method improves the coating film strength, the durability is sufficient, and the dropout is reduced, so that the reliability is also improved.

Next, surface smoothing treatment may be performed by calendering. After that, a burnishing treatment or a blade treatment is performed as necessary to perform slitting.

In the surface smoothing treatment, the calender conditions may include temperature, linear pressure, coating speed (C / S) and the like. In the present invention, the temperature is 50.
~ 140 ° C, the linear pressure is 50-1200 kg / cm,
It is preferable to keep the C / S at 20 to 600 m / min. Outside of these ranges, it becomes difficult to maintain the surface properties of the magnetic recording medium in good condition.

[0083]

EXAMPLES The constitution and effects of the present invention will be specifically described with reference to the following examples, but the components, ratios, and operation sequences shown below can be variously changed without departing from the scope of the present invention. It goes without saying that the present invention is not limited to the examples.

In the following examples, all "parts" are parts by weight.

The respective components of the upper layer magnetic coating material and the lower layer coating material having the following compositions were kneaded and dispersed using a kneader and a sand mill to prepare an upper layer magnetic coating material and a lower layer coating material. {Magnetic coating for upper layer} Ferromagnetic metal powder 100 parts A Fe Co Ni Ni Al Total composition (parts by weight) 100 20 1 8 5 Surface composition (atomic ratio) 100 5 0 10 100 (σs 145 emu / g, BET specific surface area 55 m ² / g) Crystallite size 150Å Axial ratio 6 B Fe Fe Co Al Si Overall composition (parts by weight) 100 10 3 3 Surface composition (atomic ratio) 100 1 90 35 (σs 130 emu / g, BET specific surface area 50 m ² / g) Crystallite size 165Å Axial ratio 8 Potassium sulfonate group-containing vinyl chloride resin 10 parts (Nippon Zeon Co., Ltd. MR-105) Sodium sulfonate group-containing polyurethane resin 10 parts (Toyobo Co., Ltd. UR-8700) Polishing Material (listed in the table) Stearic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ether Luketone 100 parts Toluene 100 parts {Coating for lower layer} Powder consisting mainly of α-iron oxide (described in the table, major axis diameter 0.12 μm) 100 parts Vinyl chloride resin containing potassium sulfonate group 12 parts (Nippon ZEON CORPORATION ) MR-105) Sodium sulfonate group-containing polyurethane resin 8 parts (Toyobo Co., Ltd. UR-8700) α-alumina (average particle size 0.17 μm) 5 parts Stearic acid 1 part Butyl stearate 1 part Carbon black (Average particle size 15 nm) 5 parts Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts For each of the obtained upper layer magnetic coating material and lower layer coating material,
5 parts of polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added. (Example A-1
-B-9 and Comparative Examples A-1 to B-5) Using the above-mentioned upper layer magnetic coating material and lower layer coating material containing the ferromagnetic metal powders shown in the respective tables, the thickness is determined by a wet-on-wet method. After coating on a 10 μm polyethylene terephthalate film, magnetic field orientation treatment was performed while the coating film was undried, followed by drying, and then surface smoothing treatment with a calendar to obtain the thickness shown in each table. A lower layer and an upper layer having a thickness were formed.

Further, the surface (rear surface) of the polyethylene terephthalate opposite to the side where the lower layer and the upper layer are provided.
A coating material having the following composition is applied to the above, the coating film is dried, and calendering is performed according to the above-mentioned calendering conditions to form a back coat layer having a thickness of 0.8 μm, and a wide raw anti-magnetic tape. Got {Paint for back coat layer} Carbon black (Raven 1035) (Average particle size 25 nm) 40 parts Barium sulfate (Average particle size 300 nm) 10 parts Nitrocellulose 25 parts Polyurethane resin 25 parts (Nippon Polyurethane Co., N- 2301) Polyisocyanate compound 10 parts (Nippon Polyurethane Co., Ltd., Coronate L) Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts The original antimagnetic tape thus obtained is slit to 8 m.
An m-wide magnetic recording medium for video was prepared. The following evaluations were performed on this magnetic recording medium. The results are shown in Tables 3-4.
It was shown to. << Evaluation >><Surface composition of powder mainly composed of α-iron oxide present in lower layer coating film> Measured by the method described in the text. <Playback output> Sony 8mm video camera CCD
The RF output (dB) at 8 MHz was measured by V-900. <Head Clog> The number of head clogs (head clogging) that occurred during 100 times of repeated running at 40 ° C. and 80% (average for each 1 pass) was shown. <Still characteristics> 50% white with environment set to -15 ° C
Output the signal (dB) immediately after playback, starting playback after recording the signal
It shows the time from when to 2 dB decrease. As the deck, BS-3000 manufactured by Sony was used.

[0087]

[Table 3]

[0088]

[Table 4]

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akira Saito Akira Nihonbashi 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Akihiko Seki 1-13-1 Nihonbashi Nihonbashi, Chuo-ku, Tokyo TDK Within the corporation (56) Reference JP-A-3-219421 (JP, A) JP-A-1-106331 (JP, A) JP-A-1-102730 (JP, A) JP-A-4-315812 (JP, A) A) JP-A-6-36265 (JP, A) JP-A-2-71428 (JP, A) JP-A-6-60362 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) ) G11B 5/68-5/718

Claims (3)

(57) [Claims] 1. A magnetic layer comprising a non-magnetic support and at least one lower layer having a non-magnetic powder dispersed in a binder, on which a ferromagnetic powder is dispersed. In the magnetic recording medium provided with the upper layer, the average particle diameter of the abrasive in the upper layer is 5 to 70% of the upper layer film thickness, and the upper layer film thickness is 0.05 to 0.3 μm. The average major axis length of the ferromagnetic (metal) powder is 5 to 50 of the upper layer thickness.
%, And the coercive force of the medium is 1900 to 3000 Oe. 2. A magnetic layer comprising a non-magnetic support and at least one lower layer having a non-magnetic powder dispersed in a binder, and a ferromagnetic powder dispersed on the non-magnetic support. In the magnetic recording medium having an upper layer of Is 3-40% of the total abrasive, and the upper layer film thickness is 0.05-0.
A magnetic recording medium having a thickness of 3 μm. 3. The ferromagnetic powder comprises Fe and A as constituent elements.
The magnetic recording medium according to claim 1 or 2, which is a ferromagnetic (metal) powder containing 1 and one or more rare earth elements.