JPH0817039A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium capable of high density recording and excellent especially in output characteristics. CONSTITUTION:This magnetic recording medium consists essentially of a magnetic substrate 1, a nonmagnetic layer 2 formed on the substrate 1 and a magnetic layer 3 formed on the nonmagnetic layer 2. The nonmagnetic layer 2 has <=10% light transmissivity at 900nm.

Description

Detailed Description of the Invention

[0001]

The present invention enables high density recording,
In particular, it relates to a magnetic recording medium having excellent output characteristics.

[0002]

2. Description of the Related Art Conventionally, magnetic recording media have been widely used in the form of tapes, disks, drums or sheets. Such a magnetic recording medium is usually manufactured by coating a nonmagnetic support such as a polyester film with a magnetic coating material containing magnetic powder and a binder as main components. In recent years, in particular, there has been a demand for miniaturization of magnetic recording media and high density recording, and in order to meet such demands, for example, an attempt to improve coercive force or saturation magnetization or a magnetic layer Proposals have been made to reduce the thickness. In addition to the above requirements, there is a strong demand for a magnetic recording medium having particularly excellent output characteristics in order to meet the demand for a high-quality magnetic recording medium. Therefore, an object of the present invention is to provide a magnetic recording medium capable of high density recording and particularly excellent in output characteristics.

[0003]

As a result of various studies, the present inventors used a magnetic support instead of the non-magnetic support that has been conventionally used as a support, and specified the transmittance of the non-magnetic layer. It has been found that the magnetic recording medium having the above transmittance can achieve the above object.

The present invention has been made based on the above findings, and comprises a magnetic support, a non-magnetic layer provided on the magnetic support, and a magnetic layer provided on the non-magnetic layer. In the magnetic recording medium, the non-magnetic layer has 900 n
A magnetic recording medium having a light transmittance of 10% or less at m is provided.

The magnetic recording medium of the present invention will be described in detail below. As shown in FIG. 1, the magnetic recording medium according to the present invention includes a magnetic support 1, a non-magnetic layer 2 provided on the magnetic support 1, and a magnetic layer 3 provided on the non-magnetic layer 2. And a back coat layer 4 is provided on the back surface of the magnetic support 1 as required.

The magnetic support 1 comprises at least a magnetic portion A (see FIGS. 2a to 2e) consisting of a matrix component made of a thermoplastic resin and a filler component made of magnetic powder.

Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate and polyethylene bisphenoxycarboxylate, polyolefins such as polyethylene and polypropylene, and cellulose acetate butyrate. Cellulose derivatives such as cellulose acetate propionate, vinyl-based resins such as polyvinyl chloride and polyvinylidene chloride, or polyamides, polyimides, polycarbonates, polysulfones, polyether / etherketones, polyurethanes and the like are used. These resin components may be used alone or in combination.

As the magnetic powder, ferromagnetic powder such as metal magnetic powder or oxide-based magnetic powder can be used. Specific examples of the above oxide-based magnetic powder include the following. Iron oxide magnetic powder such as γ-iron oxide and magnetite; Cr, Mn,
Ferromagnetic powder containing a metal such as Co or Ni added thereto; chromium dioxide; a metal such as Na, K, Fe or Mn added to the chromium dioxide;
Ferromagnetic powder to which a non-metal element such as P or an oxide thereof is added; micro tabular barium ferrite; part of Fe atoms of the barium ferrite is Ti, Co, Zn, V
Ferromagnetic powder substituted with atoms such as. In addition, specific examples of the magnetic metal powder include Fe-Co, Fe-Ni, and Fe-A.
1, Fe-Ni-Al, Co-Ni, Fe-Co-N
i, Fe-Ni-Al-Zn, Fe-Al-Si, etc. are mentioned.

Further, in the present invention, as the magnetic powder, soft magnetic powder or iron oxide powder having a low remanent magnetization (hereinafter referred to as "low remanent magnetization iron oxide powder") used in magnetic toner is used. May be. The soft magnetic powder is a magnetic powder made of a metal, a metal oxide, an alloy, an amorphous alloy or the like and known as a powder having a high magnetic permeability and a low coercive force. In the present invention, any soft magnetic powder can be used, but those used for so-called weak electric devices such as magnetic heads and electronic circuits are particularly preferable. ) Magnetic Properties and Applications "(Shokabo, 1984), pages 368-376, soft magnetic materials can be used. Specific examples of the soft magnetic powder preferably used in the present invention include:
Iron-silicon alloy, iron-aluminum alloy, iron-nickel alloy, iron-cobalt alloy, iron-cobalt-nickel alloy,
Examples thereof include nickel-cobalt alloy, sendust, manganese-zinc ferrite, nickel-zinc ferrite, magnesium-zinc ferrite, magnesium-manganese ferrite, and the like. The low remanent magnetization iron oxide powder has a remanent magnetization of about 10 emu / g,
Examples thereof include magnetite powder having a coercive force of 150 Oe or less.

In the present invention, in order to improve the dispersibility of the magnetic powder such as the ferromagnetic powder, the soft magnetic powder and the low remanent magnetization iron oxide powder, the magnetic powder is surface-treated. May be given. The surface treatment is "Charac
terization of Powder Surfaces "; can be carried out by a method similar to the method described in Academic Press, and examples thereof include a method of coating the surface of the magnetic powder with an inorganic oxide. At this time, the inorganic oxides that can be used include Al ₂ O ₃ , SiO ₂ , and TiO ₂ .
₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO and the like can be mentioned, and when used, they can be used alone or in combination of two or more. The surface treatment may be performed by an organic treatment such as a silane coupling treatment, a titanium coupling treatment and an alumina coupling treatment other than the above method.

The magnetic support 1 may be composed of a single layer having only the magnetic portion A as shown in FIG. 2a, or as shown in FIGS. 2b to 2e, the magnetic portion A and the non-magnetic portion B may be multi-layered. It may be a structure. That is, the magnetic support 1 can have the following configurations a to e. a. As shown in FIG. 2 a, a structure consisting of a single layer of magnetic portion A only. b. As shown in FIG. 2B, the nonmagnetic portion B is provided on the surface of the magnetic portion A (the surface located on the magnetic layer 3 side in the magnetic recording medium). c. As shown in FIG. 2c, the magnetic part A is provided on the surface of the non-magnetic part B. d. As shown in FIG. 2D, a non-magnetic portion B is provided on each of the front surface and the back surface of the magnetic portion A. e. As shown in FIG. 2e, the nonmagnetic portion B is provided with magnetic portions A on the front surface and the back surface, respectively.

Here, the preferable thickness of the entire magnetic support having the structure shown in FIGS. 2A to 2E is 1 to 300 μm. Further, the ratio of the thickness of the magnetic portion A to the thickness of the non-magnetic portion B in the magnetic support having the configuration shown in FIGS.
1:99 to 99: 1, preferably 2:98 to 98: 2,
More preferably, the ratio is 5:95 to 95: 5.

The material for forming the non-magnetic portion B is not particularly limited as long as it is a non-magnetic material, but the thermoplastic resin used as the matrix component of the magnetic portion A can be preferably used. Although the non-magnetic portion B can be formed only by itself, in order to control the surface property and running property of the outer surface of the non-magnetic portion B to be a predetermined value, the material for forming the non-magnetic portion B is the formation material. It is preferable to use materials to which various fillers are added. Examples of the filler used in this case include the non-magnetic powder described below used for forming the non-magnetic layer, and the particle size thereof is preferably 0.8 μm or less, more preferably 0.0
2 to 0.2 μm, and its content (blending amount)
Is preferably 5% by weight or less in the non-magnetic portion, and more preferably 0.01 to 2% by weight.

The composition of the thermoplastic resin and the magnetic powder in the magnetic portion A can be appropriately changed according to the desired coercive force, saturation magnetization, etc., but in the magnetic support having the structure shown in FIGS. Is 0.1 to 1000 parts by weight of magnetic powder, preferably 0.1 to 100 parts by weight of the thermoplastic resin.
2 to 100 parts by weight, more preferably 0.3 to 80 parts by weight is desirable.

As another structure of the magnetic support, a non-magnetic film may be coated with a magnetic paint as shown in FIG. 2f. In this case, the non-magnetic portion is the non-magnetic film body B'and the magnetic portion is the magnetic film body A'formed by the magnetic paint containing the magnetic powder. Figure 2f
In the constitution of the film body A ′ shown in FIG.
10 to 1500 parts by weight of magnetic powder with respect to 00 parts by weight,
Preferably 200 to 1200 parts by weight, more preferably 5
It is desirable that the amount is from 0.00 to 1000 parts by weight.

Next, a preferred method for producing the above magnetic support will be described separately for the magnetic support having the structure shown in FIG. 2a and the magnetic support having the structure shown in FIGS. A preferred method for producing a magnetic support having the structure shown in FIG. 2a;
After the thermoplastic resin and the magnetic powder are sufficiently dried, they are mixed in the above composition range and melt-mixed using an extruder to obtain a mixture of particles (raw material mixture for magnetic part). A method of molding using a molding machine capable of melt extrusion. The magnetic powder may be mixed at the same time as the reaction monomer is added during the polymerization of the thermoplastic resin, or may be added and mixed during the polymerization of the thermoplastic resin. 2b-e is a preferred method for producing a magnetic support; the raw material mixture for the magnetic portion and the raw material for the non-magnetic portion mainly composed of the thermoplastic resin are coextruded using a molding machine capable of melt extrusion. A method of molding into a desired configuration.
In addition, as the above-mentioned "co-extrusion molding method", in addition to the method of simultaneously extrusion-molding the raw material mixture for the magnetic portion and the raw material for the non-magnetic portion to form a two-layer or multi-layer magnetic support, Either one of the raw material mixture for the magnetic portion and the raw material for the non-magnetic portion is extruded first to obtain a film-like material, and then the raw material mixture for the magnetic portion and / or the non-magnetic material is further formed on the film-like material. There is a method of forming a two-layer or multi-layer magnetic support by extrusion-molding a raw material for parts.

The magnetic support having the structure shown in FIG. 2f can be manufactured by the following method. In the process of extrusion molding using only the non-magnetic part raw material, the magnetic coating material is applied at any stage of the molding process to form the magnetic film body (magnetic part) A ′, A method for producing a magnetic support. However, in this case,
The above-mentioned magnetic film body A ′ in the configuration shown in FIG.
Is preferably one that does not swell or dissolve in the solvent used when forming the nonmagnetic layer and the magnetic layer provided on the film A ′.

When manufacturing the above magnetic support,
When forming the magnetic portion A or the magnetic film A ′, a magnetic field orientation treatment and a calender treatment can be performed, if necessary.

The magnetic support used in the present invention is obtained by manufacturing the magnetic support having the structure shown in FIG. 2f by the above-mentioned method and the like, and further, magnetic properties in the magnetic support having the structure shown in FIG. 2f. It may be manufactured by extruding the above-mentioned raw material for the non-magnetic portion or the like onto the film body A ′ or the like to form the non-magnetic portion B or the like.

The non-magnetic layer provided on the magnetic support is a layer formed by coating a non-magnetic paint on the magnetic support. The non-magnetic coating material used when forming the non-magnetic layer is preferably a coating material composed of non-magnetic powder, a binder and a solvent, or a coating material composed of the binder and the solvent. The non-magnetic powder is not particularly limited as long as it is non-magnetic, but carbon black, graphite, titanium oxide, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, zinc oxide, calcium oxide, magnesium oxide, tungsten disulfide. , Molybdenum disulfide, boron nitride, tin dioxide, silicon dioxide, non-magnetic chromium oxide, alumina, silicon carbide, cerium oxide, corundum, artificial diamond, non-magnetic iron oxide,
Pomegranate, garnet, silica, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite, resinous powder and the like, among them, carbon black, titanium oxide, barium sulfate,
Calcium carbonate, alumina, non-magnetic iron oxide and the like are preferably used. The non-magnetic powder may be subjected to the surface treatment described above in order to improve the dispersibility of the non-magnetic powder.

The particle size of the nonmagnetic powder is preferably 0.001 to 3 μm, more preferably 0.005 to 1 μm.
μm, most preferably 0.005-0.5 μm.
The amount of the non-magnetic powder used is preferably 30 to 30 in the non-magnetic layer formed by applying the non-magnetic coating material.
It is desirable to mix the above non-magnetic coating material so that the content is 92% by weight, more preferably 50 to 90% by weight.

The binder may be a thermoplastic resin, a thermosetting resin, a reactive resin or the like, which may be used alone or as a mixture.
Specific examples of the binder include vinyl chloride resins and the like, and in addition thereto, JP-A-57-16212.
Resins and the like described in page 8, upper right column, line 19 to page 2, lower right column, line 19 and the like can be mentioned. Further, the binder may contain a polar group for improving dispersibility and the like. The amount of the binder used is preferably about 5 to 100 parts by weight based on 100 parts by weight of the non-magnetic powder,
It is particularly preferable that the amount is 5 to 70 parts by weight.

Examples of the solvent include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, chlorinated hydrocarbon solvents, and the like. The solvents described in JP-A-57-162128, page 3, lower right column, line 17 to page 4, lower left column, line 10 and the like can be used.

In addition, the non-magnetic coating material contains additives usually used in magnetic recording media, such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive, a fungicide, and a curing agent. , Can be added if necessary. As the above additives,
Specifically, it is described in JP-A-57-162128, page 2, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6 to third page upper right column, line 18 and the like. Various additives may be mentioned.

To prepare the above non-magnetic paint, for example,
The non-magnetic powder and the binder are charged together with a part of the solvent into a Nauter mixer or the like to be premixed to obtain a mixture, and the obtained mixture is kneaded by a continuous pressure kneader or the like, and then it is mixed with the solvent. Examples include a method of diluting a part of the mixture, carrying out a dispersion treatment using a sand mill or the like, mixing an additive such as a lubricant, filtering, and further mixing the remaining solvent and a curing agent.

The magnetic layer provided on the non-magnetic layer is a layer formed by applying a magnetic paint on the non-magnetic layer. The magnetic paint used for forming the magnetic layer is preferably a paint containing magnetic powder, a binder, and a solvent as main components. Examples of the magnetic powder include ferromagnetic iron oxide, ferromagnetic chromium dioxide, and ferromagnetic metal powder.

The above ferromagnetic iron oxide is FeOx (1.33).
A metal such as Cr, Mn, Co, or Ni added to ≦ x ≦ 1.5) can be used. Further, the ferromagnetic chromium dioxide is CrO ₂ or Na, K, F in the CrO _2.
Metals such as e and Mn, oxides of the metals, and nonmetal elements such as P may be used. Examples of the ferromagnetic metal powder include ferromagnetic metal powders having a metal content of 70% by weight or more, and 80% by weight or more of at least one type of ferromagnetic metal (eg, Fe, Co, Ni). . Specific examples of the ferromagnetic metal powder include, for example,
Fe-Co, Fe-Ni, Fe-Al, Fe-Ni-A
1, Co-Ni, Fe-Co-Ni, Fe-Ni-Al
-Zn, Fe-Al-Si, etc. are mentioned.

Further, the magnetic powder may contain, if necessary,
A rare earth element or a transition metal element can be contained. In addition, as the magnetic powder, fine tabular barium ferrite and some of its Fe atoms are Ti, Co, Z.
Magnetic powders substituted with atoms such as n and V can also be used. The magnetic powder may be subjected to the above-mentioned surface treatment in order to improve the dispersibility of the magnetic powder.

As the binder and the solvent used in the magnetic paint, the same binders and solvents as those used in the non-magnetic paint can be used. Also,
The amount of the binder used is preferably about 5 to 100 parts by weight with respect to 100 parts by weight of the magnetic powder, and 5 to 7 parts by weight.
It is particularly preferable to use 0 part by weight. Further, the above-mentioned additives used in the above-mentioned non-magnetic paint can be added to the above-mentioned magnetic paint.

To prepare the above-mentioned magnetic coating material, for example, the above-mentioned magnetic powder and the above-mentioned binder are charged together with a part of the solvent into a Nauter mixer or the like and premixed to obtain a mixture, and the obtained mixture is continuously added. After kneading with a pressure kneader or the like, then diluting with a part of the solvent and dispersing treatment using a sand mill or the like, mixing additives such as a lubricant and filtering, and further curing agents such as polyisocyanate and the rest. And the like. In the magnetic recording medium according to the present invention, the dry thickness of the magnetic layer is preferably 0.
05-1.5 μm, more preferably 0.05-1.2 μm
m, most preferably 0.1 to 1 μm, and the dry thickness of the nonmagnetic layer is preferably 0.5 to 4 μm, more preferably 0.5 to 3.5 μm, and most preferably 0.5 to 3 μm.
μm.

In the magnetic recording medium of the present invention, the light transmittance of the nonmagnetic layer at 900 nm is 10% or less, preferably 0.01 to 9.5%, more preferably 0.01.
~ 9.0%. When the above light transmittance exceeds 10%,
Output fluctuations are relatively reduced, and durability is reduced. Here, the light transmittance is obtained by measuring with a near-infrared spectrophotometer in a state where only the nonmagnetic layer is applied to the measurement substrate.

Next, the outline of the method for producing the magnetic recording medium of the present invention will be described. First, wet-on the non-magnetic coating material and the magnetic coating material on the magnetic support so that the dry thicknesses of the non-magnetic layer and the magnetic layer are the above-mentioned thicknesses.
Simultaneous multi-layer coating is performed by a wet method to form coating films for the non-magnetic layer and the magnetic layer. Next, the coating film is subjected to a magnetic field orientation treatment, followed by a drying treatment and winding. After that, calendering is performed if necessary, and then a back coat layer is further formed if necessary. Then, if necessary, for example, in the case of obtaining a magnetic tape, 40 to 70
Aging treatment is performed at a temperature of 6 to 72 hours for slitting to a desired width.

The above-mentioned simultaneous multilayer coating method is disclosed in JP-A-5-73.
No. 42, line 31 to column 43, line 31, etc. of Japanese Patent No. 883, the above-mentioned magnetic coating material for forming the above-mentioned magnetic layer is applied before the above-mentioned non-magnetic coating material for forming the above-mentioned non-magnetic layer is dried. In this method, since the boundary surface between the non-magnetic layer and the magnetic layer is smooth and the surface property of the magnetic layer is good, dropout is small, high density recording is possible, and the coating film (magnetic layer Also, a magnetic recording medium having excellent durability of the (and non-magnetic layer) can be obtained.

The magnetic field orientation treatment is performed before the magnetic paint is dried. For example, when the magnetic recording medium of the present invention is a magnetic tape, the magnetic paint is applied in a direction parallel to the coated surface of the magnetic paint. About 500 Oe or more, preferably about 1000
It can be performed by a method of applying a magnetic field of 10,000 to 10,000 Oe, a method of passing a magnetic paint through a solenoid or the like of 1,000 to 10,000 Oe in a wet state.

The drying treatment is carried out, for example, at 30 to 120 ° C.
The heating can be performed by supplying the gas heated to the above temperature. At this time, the drying degree of the coating film can be controlled by controlling the temperature of the gas and the supply amount thereof.

The calendering treatment can be carried out by a super calendering method in which two rolls such as a metal roll and a cotton roll or a synthetic resin roll, a metal roll and a metal roll are passed. Also,
The conditions for the calendar treatment are 60 to 140 ° C. and 100
It can be up to 500 kg / cm.

The backcoat layer, which is provided if necessary, is provided on the back surface (the surface on which the nonmagnetic layer and the magnetic layer are not provided) of the magnetic support, and is usually a backcoat layer. It is obtained by applying the back coat paint used for forming the layer on the magnetic support. The back coat paint is obtained by appropriately selecting and mixing the non-magnetic powder, the binder, the dispersant, the lubricant, the curing agent, the solvent and the like described in detail in the non-magnetic paint. The back coat paint can be prepared by a generally known back coat paint manufacturing method.

When manufacturing the magnetic recording medium of the present invention, finishing steps such as polishing and cleaning of the surface of the magnetic layer may be carried out, if necessary. The non-magnetic coating material and the magnetic coating material can be applied by a generally known sequential multi-layer coating method.

[0039]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

<Example 1> (Production of magnetic support a): Single layer Granules of polyethylene terephthalate having an intrinsic viscosity of 0.60 and barium ferrite magnetic powder were thoroughly dried in advance, and then the magnetic powder was prepared. The body was adjusted to be 10 wt% and melt-mixed using an extruder to obtain a mixture of granular bodies. Then, the mixture was formed into a film by adjusting the discharge amount (thickness) using a biaxial stretching film forming machine equipped with a die capable of melt extrusion. The obtained film was stretched 3.3 times in the longitudinal direction and 3.3 times in the width direction, and then heat-treated to obtain a magnetic support a having a thickness of 10 μm and having a structure shown in FIG. 2a.
I got

[Production of Nonmagnetic Support] Intrinsic Viscosity 0.60
Except that only the polyethylene terephthalate particles were used in the same manner as in the production of the magnetic support a described above.
A film of m was obtained, and this was used as a non-magnetic support.

[Preparation of Magnetic Paint, Non-Magnetic Paint, and Backcoat Paint] In the respective formulations of the following paints, components except polyisocyanate, fatty acid, and fatty acid ester were put into a Nauta mixer together with a part of the solvent. The mixture was premixed to obtain a mixture, and the obtained mixture was pretreated by a continuous pressure kneader. Then, after diluting each with a part of the solvent and dispersing with a sand mill, the fatty acid and the fatty acid ester are mixed and filtered, and the remaining solvent and polyisocyanate are further mixed to obtain a magnetic paint and a non-magnetic paint. And a back coat paint was obtained.

[Blending of magnetic paint] -Acicular metal magnetic powder mainly composed of iron (coercive force = 1730 Oe, saturation magnetization = 132 emu / g, average major axis length = 0.13 μm); 100 parts by weight-alumina ( Average particle size 0.3 μm); 7 parts by weight Carbon black (average particle size 20 nm); 1 part by weight Sulfonic acid group-containing vinyl chloride resin (molecular weight 20000); 8 parts by weight Sulfonic acid group-containing polyurethane (molecular weight 25000) ); 6 parts by weight Stearic acid; 1 part by weight 2-Ethylhexyl oleate; 2 parts by weight Polyisocyanate [Nippon Polyurethane Industry Co., Ltd., trade name "Coronate L"]: 4 parts by weight Methyl ethyl ketone; 95 parts by weight -Toluene: 45 parts by weight-Cyclohexanone; 95 parts by weight

[Blending of Non-Magnetic Paint] Needle-like α-iron oxide (average particle size 0.07 μm); 100 parts by weight Carbon black (average particle size 17 nm); 8 parts by weight Alumina (average particle size 0. 2 μm); 3 parts by weight-Sulfonic acid group-containing vinyl chloride resin (molecular weight 20000); 8 parts by weight-Sulfonic acid group-containing polyurethane (molecular weight 25000); 6 parts by weight-oleyl oleate; 1 part by weight-Methyl ethyl ketone; 80 parts by weight -Toluene: 40 parts by weight-Cyclohexanone; 80 parts by weight-Polyisocyanate [Nippon Polyurethane Industry Co., Ltd., trade name "Coronate HX"] 3 parts by weight

[Blending of back coat paint] Carbon black (average particle size 0.02 μm); 32 parts by weight Carbon black (average particle size 0.06 μm); 8 parts by weight “Nipporan 2301” (trade name, Japan Polyurethane manufactured by Polyurethane Industry Co., Ltd .; 20 parts by weight-Nitrocellulose (viscosity display made by Hercules Powder Co. of 1/2 second); 20 parts by weight- "D-250N" (trade name, Takeda Yakuhin Kogyo) Polyisocyanate manufactured by the company); 4 parts by weight-stearic acid; 1 part by weight-methyl ethyl ketone; 120 parts by weight-toluene; 120 parts by weight-cyclohexanone; 120 parts by weight

[Production of Magnetic Recording Medium] The above magnetic support a
The non-magnetic coating material and the magnetic coating material on the surface of, so that the dry thicknesses are 2.0 μm and 0.3 μm, respectively.
Simultaneous multi-layer coating was carried out by the wet-on-wet method to form coating films for the non-magnetic layer and the magnetic layer. Then, while the coating film was in a wet state, the coating film was passed through a solenoid of 5000 Oe for magnetic field orientation treatment, dried at 80 ° C., and then wound. Next, 85 ℃, 350kg / cm
After forming the non-magnetic layer and the magnetic layer by calendering under the conditions described in 1. And then wound up. Then, it was aged at 50 ° C. for 16 hours and slit into a 3.81 mm width to obtain a 3.81 mm width magnetic tape. The output (4.7 MHz) and the still durability (min) of the obtained magnetic tape were measured according to the following measuring methods. The results are shown in [Table 1].

[Measurement Method] Output (4.7 MHz) The obtained 3.81 mm wide magnetic tape was loaded in a DAT cassette to obtain a DAT tape cassette for testing. Obtained DAT tape cassette for test and MediaLogic
Product name "Tape Evaluator Mode"
1 4500 "and 4.7M on the above magnetic tape.
A Hz signal was recorded and the output (reproduction output) when the signal was reproduced was measured. The recording wavelength at 4.7 MHz is 0.6
It was 7 μm.

◎ Still durability Commercially available D modified to enable continuous still mode
AT deck (brand name, "DTC-1000", Sony
Manufactured), the above-mentioned DAT tape cassette for testing was mounted, a signal of 4.7 MHz was recorded on the above-mentioned magnetic tape, the initial reproduction output was set to 100%, and the time until the reproduction output decreased to 70% was measured. Time was considered as still durability.

<Example 2> The thickness of the non-magnetic layer is 2.5 μm.
A magnetic tape was obtained in the same manner as in Example 1 except that the non-magnetic coating material was applied. The same test as in Example 1 was performed on the obtained magnetic tape. The results are shown in [Table 1].

<Example 3> The thickness of the non-magnetic layer is 3.0 μm.
A magnetic tape was obtained in the same manner as in Example 1 except that the non-magnetic coating material was applied. The same test as in Example 1 was performed on the obtained magnetic tape. The results are shown in [Table 1].

Comparative Example 1 Except that the non-magnetic layer is not provided,
A magnetic tape was obtained in the same manner as in Example 1. The same test as in Example 1 was performed on the obtained magnetic tape.
The results are shown in [Table 1].

<Comparative Example 2> As a non-magnetic coating material, the non-magnetic coating material prepared as described above with the following composition was used.
An attempt was made to manufacture a magnetic tape in the same manner as in Example 1,
The non-magnetic layer could not be formed sufficiently, a practical magnetic tape could not be obtained, and output and still durability could not be measured.

(Compounding) -Nitrocellulose (viscosity display made by Hercules Powder Co. of 1/2 second); 50 parts by weight-Polyester polyurethane ("Nipporan N2301" trade name, made by Nippon Polyurethane, molecular weight 30000); 50 parts by weight Toluene; 70 parts by weight Methyl ethyl ketone; 150 parts by weight Cyclohexanone; 180 parts by weight

Comparative Example 3 A magnetic tape was obtained in the same manner as in Example 1 except that a non-magnetic support was used instead of the magnetic support. The same test as in Example 1 was performed on the obtained magnetic tape. The results are shown in [Table 1].

[0055]

[Table 1]

[0056]

The magnetic recording medium of the present invention is particularly excellent in output characteristics and also excellent in durability.

[Brief description of drawings]

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

2A and 2B are schematic diagrams showing a structure of a magnetic support of the magnetic recording medium, FIG. 2A is a schematic view showing a structure in which only a magnetic portion is a single layer, and FIG. Schematic showing a structure in which a non-magnetic portion is provided on the surface of the portion to form two layers, (c)
Is a schematic diagram showing a configuration in which a magnetic portion is provided on the surface of a non-magnetic portion to form two layers, and (d) is a schematic diagram showing a configuration in which a non-magnetic portion is provided on each of the front surface and the back surface of the magnetic portion and forming three layers,
(E) is a schematic view showing a structure in which a magnetic portion is provided on each of the front surface and the back surface of the non-magnetic portion to form three layers, and (f) shows a configuration in which the magnetic portion is formed on the surface of the non-magnetic portion and formed into two layers. It is a schematic diagram.

Claims (4)

[Claims] 1. A magnetic recording medium comprising a magnetic support, at least a non-magnetic layer provided on the magnetic support, and a magnetic layer provided on the non-magnetic layer, wherein the non-magnetic layer is provided. Is a magnetic recording medium having a light transmittance at 900 nm of 10% or less. 2. The magnetic recording medium according to claim 1, wherein the thickness of the non-magnetic layer is 0.5 to 4 μm. 3. The magnetic recording medium according to claim 1, wherein the non-magnetic layer contains non-magnetic powder. 4. The magnetic recording medium according to claim 1, wherein the content of the nonmagnetic powder in the nonmagnetic layer is 30 to 92% by weight.