JPH1173641A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium having a multilayer structure and ensuring improved output of reproduction of a high density record and a reduced error rate. SOLUTION: The magnetic recording medium has a lower magnetic layer 3 and an upper magnetic layer 4. The total thickness of the magnetic layers 3, 4 is 1.0-2.0 μm and the ratio of the thickness of the upper magnetic layer 4 to that of the lower magnetic layer 3 is 0.1-0.3. The average particle diameter of each of all powders contained in the lower magnetic layer 3 is 0.01-0.5 μm and the peak value (Rp) of the surface roughness of the upper magnetic layer 4 is <=70 nm.

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 tape and a magnetic disk.
The present invention relates to a magnetic recording medium having a multilayer structure in which reproduction output from a magnetic recording medium on which high-density recording is performed is increased and an error rate is reduced.

[0002]

2. Description of the Related Art In recent years,
The magnetic recording medium has a multi-layer structure by providing a relatively thick non-magnetic intermediate layer on a non-magnetic support, and a relatively thin magnetic layer on the intermediate layer in response to the increase in recording density. The output has been improved, and the effect of the roughness of the surface of the non-magnetic support has been eliminated to maintain the electromagnetic conversion characteristics.

For example, JP-A-5-73883 discloses a magnetic recording medium in which a lower nonmagnetic layer and an upper magnetic layer having an average dry thickness of 1 μm or less are provided on a nonmagnetic support by a wet-on-wet method. Is disclosed. However, the above publication describes a very wide range in which the thickness of the lower non-magnetic layer is 1 to 30 times the thickness of the upper magnetic layer with respect to the thickness of the multilayer. It was found from experiments that the error rate characteristics and the output characteristics were not necessarily obtained at satisfactory levels in all cases.

Accordingly, it is an object of the present invention to provide a magnetic recording medium having a multilayer structure in which reproduction output from high-density recording is improved and an error rate is reduced.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that in the case of a magnetic recording medium having a lower magnetic layer and an upper magnetic layer provided on a non-magnetic support, the total thickness of these magnetic layers With a specific range, the ratio of the thickness of the upper magnetic layer to the thickness of the lower magnetic layer (upper layer / lower layer) is reduced to a specific range to reduce the thickness of the upper magnetic layer. It has been found that the object of the present invention can be achieved by reducing the surface roughness of the upper magnetic layer by setting the powder in a fine particle size range.

Accordingly, the present invention is based on the above-mentioned findings, and in a magnetic recording medium having a lower magnetic layer and an upper magnetic layer in this order on a non-magnetic support, the magnetic recording medium comprises the lower magnetic layer and the upper magnetic layer. The total thickness of the magnetic layer is 1.0 to 2.0 μm
Wherein the ratio of the thickness of the upper magnetic layer to the thickness of the lower magnetic layer (upper layer / lower layer) is 0.1 to 0.3, and all the powders contained in the lower magnetic layer have an average particle size of 0.1 to 0.3, respectively. A magnetic recording medium having a diameter of 0.01 to 0.5 μm and a peak value (Rp) of the surface roughness of the upper magnetic layer of 70 nm or less.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention will be described below in detail. FIG. 1 schematically illustrates a preferred configuration of a magnetic recording medium according to the present invention. The magnetic recording medium 1 shown in FIG. 1 includes a nonmagnetic support 2, a lower magnetic layer 3 provided on the surface side of the nonmagnetic support 2, and an uppermost layer provided adjacent to the lower magnetic layer 3. And a back coat layer 5 provided on the back surface of the nonmagnetic support 2.

Incidentally, the magnetic recording medium of the present invention may be provided with another layer. Specifically, an adhesive layer is provided between the non-magnetic support 2 and the lower magnetic layer 3 or the non-magnetic support 2
An adhesive layer is provided between the non-magnetic support 2 and the lower magnetic layer 3 for recording a servo signal or the like corresponding to a hard system using a long-wavelength signal. Another magnetic layer or non-magnetic layer may be provided.

An important feature of the magnetic recording medium of the present invention is that the upper magnetic layer 4 and the lower magnetic layer 3 satisfy the following condition (a).
To satisfy (d). (A) Total thickness of magnetic layer, ie, thickness (d ₁ ) of upper magnetic layer 4
And the thickness (d ₂ ) of the lower magnetic layer 3 is 1.0
To 2.0 μm, preferably 1.5 to 1.9 μm. (B) d ₁ / d ₂ is 0.1 to 0.3, preferably 0.
1 to 0.25. (C) All the powders contained in the lower magnetic layer have an average particle size of 0.01 to 0.5 μm, preferably 0.1 to 0.5 μm.
01 to 0.3 μm. (D) The peak value (Rp) of the surface roughness of the upper magnetic layer is 7
0 nm or less, preferably 60 nm or less, more preferably 55 nm or less.

The total thickness of the magnetic layer and the ratio of the upper magnetic layer 3 to the lower magnetic layer 4 are in the above ranges [conditions (a) and (b)].
Is satisfied, the thickness of the upper magnetic layer 3 is reduced, so that high-density recording can be reproduced with high output. On the other hand, when the thickness of the lower magnetic layer 4 is small, the lower magnetic layer 4 is easily affected by agglomerates present in the paint for forming the lower magnetic layer 4 and the surface roughness of the nonmagnetic support. On the other hand, if the thickness of the lower magnetic layer 4 is too large, good surface properties cannot be obtained after the application of the paint. However, the above condition (a)
By satisfying (b) and (b), the lower magnetic layer 4 has an appropriate thickness. Further, a method in which a thin adhesive layer is provided between the non-magnetic support 2 and the lower magnetic layer 4 to provide an adhesive function and make the surface roughness of the non-magnetic support 2 smoother can be adopted. By using a fine powder that satisfies the above range [condition (c)] as the powder contained in the lower magnetic layer, (a) and (b) are satisfied and the thickness of the upper magnetic layer 3 is reduced. In a thin medium, the influence on the surface roughness of the upper magnetic layer 4 can be significantly reduced. Therefore, the peak value (Rp) of the surface roughness of the upper magnetic layer 4 should be 70 nm or less, that is, the condition (D) can be satisfied. By satisfying the above condition (d), the smoothness of the surface is maintained, and as a result, the occurrence of an error rate is reduced.

On the other hand, if the above condition (a) is not satisfied and the total thickness of the magnetic layer exceeds 2.0 μm, the surface properties after applying the coating material for forming the magnetic layer will deteriorate, and a good reproduction output will be obtained. If the total thickness is less than 1.0 μm, the error rate increases. In addition, the reproduction output is reduced in any case regardless of whether d ₁ / d ₂ is more than 0.3 or less than 0.1 without satisfying the above condition (b).

If the above condition (c) is not satisfied and the lower magnetic layer 3 contains powder having an average particle size of more than 0.5 μm, the peak value of the surface roughness of the upper magnetic layer 4 is reduced to 70 nm.
It becomes difficult to do the following and the error rate increases,
When a powder having an average particle size of less than 0.01 μm is present, it becomes difficult to disperse the powder during preparation of a coating material for forming the lower magnetic layer 3, and undispersed agglomerates are present, or re-agglomeration of the powder occurs. This is likely to occur, and protrusions will be present on the medium surface after application of the paint, causing an error.
In the present specification, the “average particle size” means the average particle size of the primary particles, which is determined by measuring the length of the portion having the largest dimension in the powder, and the specific measurement The method will be described in detail in Examples described later. Therefore, for example, when the powder is acicular, the average particle size is determined by the major axis length, and when the powder is plate-shaped, the average particle size is determined by the plate diameter. Further, the condition (d) was not satisfied, and the peak value (Rp) of the surface roughness of the upper magnetic layer 4 was 70%.
If it exceeds nm, the error rate increases, which is not preferable.

In this specification, the term "total thickness of the magnetic layer" means the sum of the thickness of the upper magnetic layer 3 as the uppermost layer and the thickness of the lower magnetic layer 4 adjacent to the upper layer. Even if another magnetic layer exists between the lower magnetic layer 4 and the lower magnetic layer 4, the thickness of the other magnetic layer is not included.

The details of the support and each layer constituting the magnetic recording medium of the present invention will be described below. First, the nonmagnetic support 2 used in the present invention will be described. As the nonmagnetic support 2, a generally known nonmagnetic support can be used without any particular limitation. Specifically, a flexible film or disk made of a polymer resin, a nonmagnetic metal such as Cu, Al, or Zn, a film made of glass, ceramics such as porcelain, ceramics, and the like, a disk, and a card can be used.

Examples of the polymer resin forming the flexible film and the disk include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, and polyethylene bisphenoxycarboxylate; , Polypropylene and other polyolefins; cellulose derivatives such as cellulose acetate and cellulose acetate propionate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; polyamides; polyimides;
Polysulfone; polyether / ether ketone; polyurethane and the like. Upon use, a film singly or as a mixture of two or more kinds can be used.

Further, in the magnetic recording medium of the present invention, the back coat layer 5 provided on the back surface of the non-magnetic support as necessary can be formed using a known back coat paint without any particular limitation.

Next, the upper magnetic layer 4 will be described. The upper magnetic layer 4 is usually the uppermost layer of the magnetic recording medium 1, that is, a layer existing on the surface of the magnetic recording medium 1, and contains a magnetic powder, a binder resin and, if desired, a nonmagnetic powder.

As the above magnetic powder, for example, γ-Fe
Examples include iron oxide-based magnetic powder such as ₂ O ₃ and Co-attached γ-Fe ₂ O ₃ , ferromagnetic metal powder mainly composed of iron, and hexagonal ferrite powder.

The ferromagnetic metal powder has a metal content of 5%.
0% by weight or more, and a ferromagnetic metal powder in which 60% by weight or more of the metal component is iron. Specific examples of the ferromagnetic metal powder include Fe-Co, Fe-Ni, Fe
-Al, Fe-Ni-Al, Fe-Co-Ni, Fe-
Powders of alloys such as Ni-Al-Zn and Fe-Al-Si are given. The ferromagnetic metal powder mainly composed of iron oxide and iron preferably has a needle-like or spindle-like shape. And the major axis length is preferably 0.05 to
It is 0.25 μm, more preferably 0.05 to 0.2 μm. Further, a preferable needle ratio is 3 to 20, a preferable particle size is 130 to 250 ° as a value measured by an X-ray method, and a preferable specific surface area (BET method) is 30 to 60 m ² /.
g.

Further, as the above hexagonal ferrite,
Barium ferrite and strontium ferrite in the form of microplates and part of their Fe atoms are Ti, Co,
Examples include magnetic powders substituted with atoms such as Ni, Zn, and V. The hexagonal ferrite powder has a preferable plate diameter of 0.02 to 0.09 μm, a preferable plate ratio of 2 to 7, and a preferable specific surface area of 30 to 60 m ² / m.
g.

The coercive force of the magnetic powder is 120 to 210
kA / m, preferably 130 to 200 k
A / m is preferable. Within the above range, the RF output in all wavelength regions can be obtained without excess and deficiency, and the overwrite characteristics are also good.

The iron oxide-based magnetic powder and the ferromagnetic metal powder preferably have a saturation magnetization of 100 to 180 Am ² / kg, more preferably 110 to 160 Am ² / kg. The saturation magnetization of the hexagonal ferrite powder is preferably 30~70Am ² / kg, it is preferable that particularly 45~70Am ² / kg. Within the above range, a sufficient reproduction output can be obtained.

The magnetic powder contained in the upper magnetic layer 4 may contain a rare earth element or a transition metal element as required.

In the present invention, the magnetic powder may be subjected to a surface treatment in order to improve the dispersibility of the magnetic powder. The above surface treatment is described in the section
of Poder Surfaces "(Academic Press), and the like. For example, a method of coating the surface of the magnetic powder with an inorganic oxide is described, and it is preferable to employ the method. it can. The inorganic oxide that can be used at this time is Al ₂ O
₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂
O ₃ , ZnO and the like can be mentioned, and these may be used alone or in combination of two or more. In addition, the surface treatment is a silane coupling treatment other than the above method,
Organic treatment such as titanium coupling treatment and aluminum coupling treatment can also be performed.

Examples of the binder resin contained in the upper magnetic layer 4 include a thermoplastic resin, a thermosetting resin, and a reactive resin. When used, they can be used alone or in combination. Specific examples of the binder resin include vinyl chloride resins, polyesters, polyurethanes, nitrocellulose, epoxy resins and the like. In addition, JP-A-57-162128, page 2, upper right column, line 19 to Resins and the like described on page 19, lower right column, line 19, and the like are included. Further, the binder resin may contain a polar group for improving dispersibility and the like. The mixing ratio of the binder resin is preferably from 5 to 200 parts by weight, more preferably from 5 to 70 parts by weight, based on 100 parts by weight of the magnetic powder.

The upper magnetic layer may contain a non-magnetic powder. Examples of the nonmagnetic powder include graphite, carbon black, titanium oxide, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, zinc oxide, calcium oxide, magnesium oxide, magnesium dioxide, alumina, tungsten disulfide, and molybdenum disulfide. , Boron nitride, tin dioxide, silicon dioxide, non-magnetic chromium oxide, silicon carbide, cerium oxide, corundum,
Artificial diamond, non-magnetic iron oxide, non-magnetic iron oxide containing manganese, garnet, silica, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite, resinous powder, etc. Is mentioned. Among them, carbon black, alumina (abrasive) nonmagnetic iron oxide, manganese-containing nonmagnetic iron oxide, titanium oxide, silicon oxide, silicon nitride, boron nitride and the like are preferably used. These non-magnetic powders may be used alone or in combination of two or more.

The shape of the non-magnetic powder may be spherical, plate-like, needle-like, or amorphous. The size of the non-magnetic powder is 5 to 200 nm in the case of spherical, plate-like or amorphous. Preferably, the needle-shaped one has a major axis length of 20.
It is preferable that the needle ratio is 3 to 20 at ~ 300 nm.

In order to improve the dispersibility of the non-magnetic powder, the surface treatment can be applied to the non-magnetic powder in the same manner as the magnetic powder.

The upper magnetic layer 4 is coated with a magnetic coating material for forming an upper magnetic layer (hereinafter referred to as an upper magnetic coating material) mainly composed of a magnetic powder, a binder resin, a solvent and, if desired, a nonmagnetic powder. Can be formed.

Solvents contained in the upper magnetic coating material used for forming the upper magnetic layer 4 include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents and chlorinated solvents. Hydrocarbon solvents and the like, specifically, the solvents described in JP-A-57-162128, page 3, lower right column, line 17 to page 4, lower left column, line 10 are used. Can be. The amount of the solvent used is 80 to 500 parts per 100 parts by weight of the magnetic powder.
The weight is preferably set to 100 parts by weight, and more preferably 100 to 350 parts by weight.

The upper magnetic coating material may contain additives, such as a dispersant, a lubricant, an antistatic agent, a rust inhibitor, an antifungal agent and an antifungal agent, which are used in ordinary magnetic recording media, if necessary. Can be added. Specific examples of the above-mentioned additives include the above-mentioned JP-A-57-162128, page 2, lower left column, line 6 to page 2, lower right column, line 10 and page 3, lower left column, line 6 to page 3, upper right column 18 Various additives described in the column and the like can be mentioned.

The thickness of the upper magnetic layer 4 satisfies the above conditions (a) and (b) and is 0.05 to 0.4.
5 μm, preferably 0.10 to 0.35
μm is preferred. When the thickness is within the above range, a better reproduction output can be obtained.

As described above, the peak value (Rp) of the surface roughness of the upper magnetic layer 4 is 70 nm or less, preferably 60 nm or less, more preferably 55 nm or less. When the peak value of the surface roughness exceeds 70 nm, the error rate increases as described above. In order to make the peak value of the surface roughness 70 nm or less, the above conditions (a) and (b)
If (c) is satisfied, this can be easily achieved by offline calendar processing described in the embodiment described later. The peak value (Rp) of the surface roughness is also called an average line (center line) depth, and as shown in FIG. 2, the average line (center line) of the roughness curve at the reference length L.
And the distance between the highest peak. The specific measuring method will be described in detail in Examples described later. The lower limit of the peak value (Rp) of the surface roughness is not particularly limited and is preferably as small as possible. However, in order to prevent an increase in friction coefficient and adsorption to a magnetic head and realize stable running, the lower limit is set. The value is 5 nm
It is about.

Next, the lower magnetic layer 3 provided adjacent to the upper magnetic layer 4 will be described. The lower magnetic layer 3 is a layer having magnetism and contains magnetic powder.

As the magnetic powder contained in the lower magnetic layer, a ferromagnetic powder is preferably used, and as the ferromagnetic powder, both a soft magnetic powder and a hard magnetic powder are preferably used. The kind of the soft magnetic powder is not particularly limited, but is preferably used for a so-called weak electric device such as a magnetic head or an electronic circuit. (Shokabo, 1
Soft magnetic materials (soft magnetic materials) described on pages 368 to 376 of 1984 can be used, and specifically, oxide soft magnetic powders can be used.

As the oxide soft magnetic powder, a spinel type ferrite powder is preferably used. As the spinel type ferrite powder, MnFe ₂ O ₄ , Fe ₃ O ₄ ,
CoFe ₂ O ₄ , NiFe ₂ O ₄ , MgFe ₂ O ₄ , L
i _0.5 Fe _2.5 O ₄ , Mn-Zn ferrite, Ni
-Zn ferrite, Ni-Cu ferrite, Cu-
Zn-based ferrite, Mg-Zm-based ferrite, Li-Z
Examples thereof include n-based ferrite, Zn-based ferrite, and Mn-based ferrite. These oxide soft magnetic powders may be used alone or in combination of two or more.

As the soft magnetic powder, a metal soft magnetic powder can be used. Examples of the metal soft magnetic powder include Fe-Si alloys and Fe-Al alloys (Alperm,
Alfenol, Alfer), permalloy (Ni-Fe-based binary alloy and multi-component alloy added with Mo, Cu, Cr, etc.), sendust (Fe-9.6 wt% Si-5.4)
wt% Al), an Fe-Co alloy, and the like. These metal soft magnetic powders may be used alone or in combination of two or more.

The coercive force of the above oxide soft magnetic powder is usually 8
A / m to 12 kA / m, and the saturation magnetization is usually 30 to
90Am is a ² / kg. The coercive force of the metal soft magnetic powder is usually 1.6 A / m to 8 kA / m, and the saturation magnetization is usually 50 to 500 Am ² / kg.

The shape of the soft magnetic powder is not particularly limited, but may be spherical, plate-like, needle-like or the like, and the average particle size is in the range of 0.01 to 0.5 μm as described above.

Examples of the hard magnetic powder include iron oxide-based magnetic powder, ferromagnetic metal powder mainly composed of iron, and hexagonal ferrite powder contained in the lower magnetic layer 4. Physical properties such as coercive force, saturation magnetization, shape, and specific surface area of the hard magnetic powder are the same as those of the iron oxide magnetic powder, ferromagnetic metal powder, and hexagonal ferrite powder used for forming the magnetic layer 4. is there. However, the average particle size of these powders is in the range of 0.01 to 0.5 μm as described above. Particularly preferred hard magnetic powders have an average particle size of 10 to 10.
An 80 nm hexagonal ferromagnetic powder can be mentioned.
As the hexagonal ferromagnetic powder, the same one as the hexagonal ferrite contained in the upper magnetic layer 4 can be used. As the magnetic powder of the lower magnetic layer, the above average particle diameter of 10
Use of a hexagonal ferromagnetic powder having a thickness of from 80 to 80 nm facilitates dispersion of the lower magnetic coating material and reduces occurrence of errors due to agglomerates in the final coating film, which is preferable.

The magnetic powder contained in the lower magnetic layer may contain a rare earth element or a transition element, if necessary. The same surface treatment as that of the magnetic layer 4 may be performed on the magnetic powder.

The lower magnetic layer 3 usually contains, in addition to the magnetic powder, a binder resin and, if desired, a non-magnetic powder. As for the type of the binder resin and the type of the nonmagnetic powder, the description regarding the binder resin and the nonmagnetic powder contained in the upper magnetic layer 4 can be applied. However, the average particle size of the non-magnetic powder is 0.1 as described above.
01 to 0.5 μm.

In the lower magnetic layer 3, the binder resin is preferably used in an amount of 5 to 70 parts by weight based on 100 parts by weight of the total amount of the magnetic and non-magnetic powders.

The thickness of the lower magnetic layer 3 satisfies the above conditions (a) and (b) and is 0.5 to 2.5 μm.
m, more preferably 0.5 to 2.0 μm, and particularly preferably 0.8 to 1.7 μm. When the thickness of the lower magnetic layer 3 is within the above range, the dropout is good and the reproduction output is good, so that a preferable result is obtained.

As described above, all powders contained in the lower magnetic layer include magnetic powders and non-magnetic powders, and have an average particle size of 0.01 to 0.5 μm, preferably 0.1 to 0.5 μm. 01 to 0.3 μm.

The lower magnetic layer 3 can be formed by applying a lower magnetic layer forming paint (hereinafter referred to as a lower magnetic paint). The lower magnetic coating material is mainly composed of a magnetic powder, a binder resin, a solvent, and a non-magnetic powder used as desired. If necessary, a dispersant, a lubricant such as a fatty acid or a fatty acid ester, and carbon black. And other additives used in ordinary magnetic recording media, such as antistatic agents, rust preventives, fungicides and antifungal agents. Among these additives, those having a powder have an average particle size of 0.01 to 0.5 μm.

As the solvent, the same solvent as that contained in the upper magnetic paint used for forming the upper magnetic layer 4 is used. The amount of the solvent used is 80 with respect to 100 parts by weight of the total amount of the magnetic powder and the non-magnetic powder.
The amount is preferably from 500 to 500 parts by weight, more preferably from 100 to 350 parts by weight.

An example of a method for manufacturing the magnetic recording medium illustrated in FIG. 1 will be briefly described. First, the lower magnetic paint for forming the lower magnetic layer 3 on the support 2 and the upper magnetic paint for forming the upper magnetic layer are mixed so that the dry thickness of the lower magnetic layer and the upper magnetic layer becomes a desired thickness. Then, a coating film of each layer can be formed by a simultaneous multilayer coating method. The simultaneous multilayer coating method can be carried out according to the method described in JP-A-5-73883, column 42, line 31 to page 43, line 31. Next, the coating film is subjected to a magnetic field orientation treatment, dried, and subjected to a calendar treatment. Thereafter, the back coat paint is applied to the back surface of the support to form a back coat layer, and a drying treatment is performed. Furthermore, after performing an aging process, it is cut into a desired width.

The magnetic field orientation treatment is performed before the lower magnetic coating material and the upper magnetic coating material are dried. For example, when the magnetic recording medium of the present invention is a magnetic tape, the magnetic recording medium is oriented in a direction parallel to the surface to which the lower magnetic coating material is applied. About 40 kA / m or more, preferably 8
A method of applying a magnetic field of 0 to 800 kA / m, or an upper magnetic paint and an upper magnetic paint in a wet state of 80 to 800 kA / m.
It can be performed by a method of passing through a kA / m solenoid or the like.

The above-mentioned calendering can be performed by a super-calendering which passes between two rolls such as a metal roll and a cotton roll or a synthetic resin roll, a metal roll and a metal roll.

The drying treatment is carried out, for example, at 30 to 120 ° C.
In this case, the degree of drying of the coating film can be adjusted by controlling the temperature of the gas and the amount of the supplied gas.

[0052]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited by the examples. In the following, "parts" means parts by weight unless otherwise specified.

Example 1 Upper magnetic paint A, lower magnetic paint B and back coat paint C of the following composition
A magnetic tape is manufactured according to the following [Method of manufacturing a magnetic recording medium], and a lower magnetic layer as an intermediate layer is formed by a lower magnetic paint B, and a magnetic layer as an uppermost layer is formed by an upper magnetic paint A. Was obtained as a magnetic recording medium on which was formed. When the coercive force and the saturation magnetic flux density of the upper magnetic layer were measured according to the [measurement method] described later, the coercive force was 150 kA / m and the saturation magnetic flux density was 0.37.
8T. The average particle size of each powder was measured according to the measurement method described later.

<Blending of upper magnetic paint A> 100 parts of acicular ferromagnetic metal powder mainly composed of iron Fe: Al: Y: Co: Ca (weight ratio) = 85: 4: 2: 8: 1 Magnetic force: 145 kA / m Saturation magnetization: 136 Am ² / kg Long axis length: 0.11 μm, BET specific surface area: 58 m ² / g X-ray particle size: 15 nm ・ Alumina powder (average particle size: 0.3 μm) 10 parts ・ Carbon black (Average particle size: 30 nm) 1 part ・ Sulfonate group / epoxy group-containing vinyl chloride copolymer 10 parts (Sulfonate group content: 1.5 × 10 ⁻⁴ eq / g, epoxy group content: 3.5) %, GPC number average molecular weight: 17000) 5 parts of sulfonic acid group-containing polyurethane resin (sulfonic acid group content: 1.8 × 10 ^-4 eq / g, GPC number average molecular weight: 36,000) ・ 3 parts of butyl stearate・ Stearie 2 parts of acid "Coronate L" 3 parts [trade name, Nippon Polyurethane Industry Co., Ltd., a polyisocyanate compound] Methyl ethyl ketone 120 parts Toluene 120 parts Cyclohexane 50 parts

<Blending of Lower Layer Magnetic Coating B> ・ Hexagonal ferromagnetic powder 50 parts Plate diameter: 0.03 μm, BET specific surface area: 39 m ² / g ・ Acicular α-Fe ₂ O ₃ powder 50 parts Long axis Length: 0.15 μm, needle ratio: 8, BET specific surface area: 52 m ² / g 5 parts carbon black (average particle size 18 nm) 10 parts vinyl chloride copolymer containing sulfonic acid / epoxy groups (sulfonic acid (Group content: 1.5 × 10 ⁻⁴ eq / g, epoxy group content: 3.5%, GPC number average molecular weight: 17000) 5 parts of sulfonic acid group-containing polyurethane resin (sulfonic acid group content: 1. ^{8 × 10 -4 eq / g,} GPC number-average molecular weight: 36 000), 2-ethylhexyl Pal 2 parts palmitate 2 parts stearic acid "Coronate HX" 3 [trade name, manufactured by Nippon polyurethane industry Co., Poriisoshi Sulfonate] Methyl ethyl ketone 80 parts 80 parts Cyclohexane 40 parts of toluene

<Blending of backcoat paint C> 38.5 parts of “carbon black” (average particle size 18 nm) 1.5 parts of “carbon black” (average particle size 75 nm) 50 parts of “Nipporan 2301” Name, Nippon Polyurethane Industry Co., Ltd., polyurethane] ・ "Celnova BTH 1/2" 28.6 parts [trade name, Asahi Kasei Kogyo Co., Ltd., nitrocellulose] ・ "D-250N" 4 parts [trade name, • Polyisocyanate manufactured by Takeda Pharmaceutical Co., Ltd.]-Copper phthalocyanine 5 parts-Stearic acid 1 part-Methyl ethyl ketone 140 parts-Toluene 140 parts-Cyclohexane 140 parts

[Production of Magnetic Recording Medium] On the surface of a 4.5 μm-thick polyethylene terephthalate film, the dry thickness of the upper magnetic paint A was 0.24 μm, and the dry thickness of the lower magnetic paint B was 1.0 μm. The upper magnetic coating material A and the lower magnetic coating material B were applied by a simultaneous multilayer coating method at a line speed of 250 m / min to form a magnetic layer composed of an upper magnetic layer and a lower magnetic layer. Next, the coating film is passed through a solenoid of 400 kA / m while the coating film is wet to perform a magnetic field orientation treatment, and hot air at a temperature of 90 ° C. is blown at a wind speed of 15 ° C.
Drying was performed for 30 seconds in a drying furnace supplied at m / sec. Next, the roll surface temperature was 80 ° C., and the roll linear pressure was 2
After performing a calendering process under the condition of 50 kg / cm to form a magnetic layer and an intermediate layer, the film was wound up. Next, a back coat paint was applied on the back surface of the non-magnetic support so that the dry thickness became 0.5 μm, dried at 90 ° C., and wound up. Thereafter, it was cut into a width of 12.7 mm (１ ／ inch), and the surface layer and the back layer were subjected to a cleaning treatment with a nonwoven fabric to obtain a magnetic tape, thereby forming a pancake. The coating and calendering were performed on separate lines (off-line method). With respect to the obtained magnetic tape as a magnetic recording medium, a reproduction output, an error rate, and a peak value (Rp) of the surface roughness of the magnetic layer were evaluated as described below. In addition, the center line average roughness Ra of the surface after application of the paint and after calendering was also measured as described below. The results are shown in [Table 1].

[Measurement Method] 平均 Average Particle Size For each powder, the length of the portion having the largest dimension in the powder was measured from a scanning electron micrograph, converted to weight, and determined from the cumulative frequency distribution.

The thickness of each magnetic layer The thickness of the upper magnetic layer is previously measured by observation with a transmission electron microscope, and the correlation between the thickness and Ms (saturation magnetization) is determined in advance. Then, the thickness of the upper magnetic layer was determined from the difference between the Ms of the coated sample in which only the lower magnetic layer was formed and the Ms of the sample in which the upper and lower magnetic layers were formed. The thickness of the lower magnetic layer is determined by peeling a part of the upper magnetic layer in the multilayer coating film after the calendering treatment with a solvent, and measuring the thickness of the sample after peeling by a contact-type film thickness meter (0.01 μm display). ) And the difference from the thickness of the upper magnetic layer.

ピ ー ク Peak value of surface roughness (Rp) Five points in a sample of 12.6 mm × 40 mm were measured under the following measurement conditions, and the average value of each peak value was obtained. The obtained magnetic tape was cut into an appropriate size to prepare a measurement sample piece, and the sample piece was fixed on a microscope slide glass with an adhesive tape so as not to generate wrinkles. Next, the fixed sample piece was manufactured by ZYGO and trade name “Laser interferometric Microscope Maxim 3D Model
5700, using the Maxim Advanced Application,
Make the zeau lens 40x, no cut-off, and
The peak value of the surface roughness (Rp), where moved is the cylinder
Was measured.

The center line average roughness Ra was measured under the same conditions using the same apparatus as the peak value (Rp) of the surface roughness.

Reproduction output The recording was performed at a tape speed of 1.2 m / s and a writing frequency of 2.5 MHz using a pancake evaluator using a fixed head.

エ ラ ー Error rate (dropout) A value smaller than 35% of the average signal output was defined as dropout, and the number per 100 m was compared.

Examples 2 to 5 and Comparative Examples 1 and 2 A magnetic tape was prepared in the same manner as in Example 1 except that the thicknesses of the upper magnetic layer and the lower magnetic layer were as shown in Table 1, respectively. , Was evaluated. Table 1 shows the results.

[0065]

[Table 1]

From the results of Table 1 above, the following is clear. That is, the total thickness of the upper magnetic layer and the lower magnetic layer, the ratio of the thicknesses of these layers, the average particle size of the powder blended in the lower magnetic layer, and the surface roughness of the upper magnetic layer specified in the present invention. The magnetic tape satisfying the peak value (Rp) of Example (Examples 1 to 5) has a high reproduction output and a small dropout. On the other hand, the magnetic tape in which the ratio of the thickness of the upper magnetic layer to the lower magnetic layer exceeds 0.3 and Rp exceeds 70 nm (Comparative Example 1) has a low reproduction output and a remarkably large dropout. The magnetic tape (Comparative Example 2) in which the thickness of the lower magnetic layer is large and the total thickness of the magnetic layer is 2.0 μm or more has a low reproduction output.

[0067]

The magnetic recording medium of the present invention has a high reproduction output for high-density recording and a low error rate such as dropout.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a magnetic recording medium according to the present invention.

FIG. 2 is a schematic diagram showing a method for measuring a peak value (Rp) of surface roughness.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Non-magnetic support 3 Lower magnetic layer 4 Upper magnetic layer 5 Back coat layer

Claims (2)

[Claims] In a magnetic recording medium having a lower magnetic layer and an upper magnetic layer on a non-magnetic support in this order, the total thickness of the lower magnetic layer and the upper magnetic layer is 1.0 to 2.2.
0 μm, the ratio of the thickness of the upper magnetic layer to the thickness of the lower magnetic layer (upper layer / lower layer) is 0.1 to 0.3, and all powders contained in the lower magnetic layer are average A magnetic recording medium having a particle size of 0.01 to 0.5 μm and a peak value (Rp) of surface roughness of the upper magnetic layer of 70 nm or less. 2. The magnetic recording medium according to claim 1, wherein said lower magnetic layer contains, as magnetic powder, hexagonal ferromagnetic powder having an average particle size of 10 to 80 nm.