JPH0855332A - Magnetic tape - Google Patents

Abstract

PURPOSE:To conduct high density recording by forming a second magnetic layer having specified coercive force and specified thickness on a first magnetic layer having high coercive force and not contributing to recording and reproducing. CONSTITUTION:On the one surface of a supporting body, a first magnetic layer 2 and a second magnetic layer 3 are formed in this order, and a back coating layer 4 is formed if necessary on the back surface of the supporting body 1 to obtain a magnetic tape. The thickness of the second magnetic layer 3 is specified to 0.05-1mum. The magnetic powder of the second magnetic layer 3 consists of ferromagnetic iron oxide comprising FeOx (1.33<=x<=1.5) added with Cr, Mn, Co, Ni ad the like and has 1700 to 2300Oe coercive force Hc. The first magnetic layer 2 is constituted of a hexagonal ferrite powder and the thickness thereof is specified to 0.5-4mum. The coercive force Hc of the first magnetic layer 2 is specified to such a level, for example to >=2500Oe, that the layer is not magnetized under operational conditions of the magnetic tape and does not contribute to recording and reproducing of video of audio signals.

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, a magnetic tape has been widely used as a magnetic recording medium. Such a magnetic tape 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 higher density recording on magnetic tapes, and in order to meet such demands, for example, an attempt to improve coercive force and saturation magnetization and a reduction in magnetic layer thickness are made. Proposals have been made. In addition to the above requirements, there is a strong demand for magnetic tapes having excellent output characteristics in order to meet the demands for high-quality magnetic tapes. Therefore, an object of the present invention is to provide a magnetic tape capable of high density recording and particularly excellent in output characteristics.

[0003]

As a result of various studies, the inventors of the present invention have a first magnetic layer and a second magnetic layer, and practically use it as a magnetic powder for the first magnetic layer. A magnetic powder having a high coercive force that cannot participate in recording and reproduction is used, a magnetic powder having a specific coercive force is used as the magnetic powder used in the second magnetic layer, and the thickness of the second magnetic layer is used. It was found that a magnetic tape having a specific thickness can achieve the above object.

The present invention has been made on the basis of the above findings, and includes a support, at least a first magnetic layer containing a first magnetic powder and provided on the support, and the first magnetic layer. In a magnetic tape having a second magnetic layer containing a second magnetic powder provided on one magnetic layer, the coercive force Hc of the second magnetic powder is 1700 to 2300 Oe. ,
The thickness of the second magnetic layer is 0.05 to 1 μm,
The above-mentioned first magnetic powder is to provide a magnetic tape characterized by having a high coercive force that does not substantially participate in recording and reproduction.

The magnetic tape of the present invention will be described in detail below. The magnetic tape of the present invention, as shown in FIG.
Support 1 and first magnetic layer 2 provided on the support 1
And a second magnetic layer 3 provided on the first magnetic layer 2, and a back coat layer 4 is provided on the back surface of the support 1 as necessary.

As the support 1, a magnetic support and a non-magnetic support are used. First, the magnetic support will be described.

As the above-mentioned magnetic support, a magnetic portion A comprising at least a matrix component made of a thermoplastic resin and a filler component made of magnetic powder (see FIGS. 2a to 2e).
A film-like material having:

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.

Ferromagnetic powders such as metal magnetic powders and oxide-based magnetic powders can be used as the magnetic powders. 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 above-mentioned magnetic powder, soft magnetic powder, iron oxide powder having a low remanent magnetization used in magnetic toner or the like (hereinafter referred to as "low remanent magnetization iron oxide powder") and the like are 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, the magnetic powder is surface-treated in order to improve the dispersibility of the magnetic powder such as the ferromagnetic powder, the soft magnetic powder, the low remanent magnetization iron oxide powder and the like. 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 of the magnetic tape which is located on the side of the second magnetic layer 3). 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.

The preferable thickness of the entire magnetic support having the structure shown in FIGS. 2a to 2e is 1 to 25 μm. Also,
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 structure shown in FIGS.
It is desirable that the ratio is 99 to 99: 1, preferably 2:98 to 98: 2, and more preferably 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. However, the thermoplastic resin used as the matrix component of the magnetic portion A can be preferably used, and the thermoplastic resin can be 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 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 later used for forming the first magnetic layer, and the particle size thereof is preferably 0.8 μm or less, more preferably 0.02 to 0. The content (blending amount) is preferably 5% by weight or less, more preferably 0.01 to 2% by weight in the non-magnetic portion.

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 body 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 with the solvent used when forming the first magnetic layer and the second magnetic layer provided on the film body 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 manufactured by the above-mentioned method or the like after producing the magnetic support having the structure shown in FIG. 2f, and then the magnetic support in the magnetic support having the structure shown in FIG. 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.

Next, the non-magnetic support will be described. Examples of the non-magnetic support include a film component having at least a matrix component or the matrix component and a filler component.

The matrix component is a component made of the thermoplastic resin or the like. Further, the filler component,
The non-magnetic support is used for controlling the surface properties and running properties of the outer surface of the non-magnetic support to a predetermined value, and specific examples thereof include the same non-magnetic powder as described below. The particle size is preferably 0.8 μm or less, more preferably 0.01 to 0.5 μm, and the content (blending amount) is preferably 5% by weight or less, more preferably 0.001 to It is 2% by weight. The filler component may be subjected to the above-mentioned surface treatment in order to improve the dispersibility and the like of the filler component.

Here, the preferable thickness of the entire non-magnetic support is 1 to 25 μm. Further, the non-magnetic support may have a layered structure of two or more layers of an upper layer and a lower layer, and the upper layer and the lower layer may have different surface roughnesses.

The first magnetic layer provided on the support is a layer formed by applying the first magnetic coating material on the support. The first magnetic paint used when forming the first magnetic layer is preferably a paint composed of the first magnetic powder, a binder, and a solvent.

As the above-mentioned first magnetic powder, hexagonal ferrite powder is preferable. As the above hexagonal ferrite powder, JP-A-4-313811, Nos. 5-6
Columns, JP-A-5-128497, columns 2-4, JP-A-5-135353, columns 7-8 and the like can be used without particular limitation, but specifically, for example, , Barium ferrite, strontium phyllite, lead ferrite, calcium phyllite, etc., and some of these solid solutions or iron elements are Ti, C
It is also possible to use those substituted with o, Zn, V, In, Mn, Ge, Hb or the like. The first magnetic powder may be subjected to the surface treatment described above in order to improve the dispersibility of the first magnetic powder.

The particle size of the first magnetic powder is preferably 0.001 to 3 μm, more preferably 0.005.
˜1 μm, most preferably 0.005 to 0.5 μm. The first magnetic powder is preferably contained in the first magnetic layer formed by applying the first magnetic coating material in an amount of preferably 5 to 99% by weight, more preferably 30 to 95% by weight,
It is desirable to mix it in the second magnetic paint so that it is most preferably contained in an amount of 50 to 95% 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.
As the binder, specifically, vinyl chloride resin, polyester, polyurethane, nitrocellulose,
Epoxy resin and the like can be mentioned.
Resins and the like described in JP-A No. 162128, page 2, 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, and particularly preferably 5 to 70 parts by weight, based on 100 parts by weight of the first magnetic powder.

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.

The first magnetic coating material contains a dispersant,
Lubricants, abrasives, antistatic agents, rust preventives, antifungal agents, hardeners and other additives usually used in magnetic recording media,
It can be added if necessary. Specific examples of the additive include page 2, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6 to page 3, upper right column 18 of JP-A-57-162128. There may be mentioned various additives described in the publications.

Further, a non-magnetic powder may be added to the above-mentioned first magnetic paint. 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, garnet , Garnet, silica stone, 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.

To prepare the first magnetic coating material, for example, the first magnetic powder and the binder are charged together with a part of the solvent into a Nauta mixer or the like and premixed to obtain a mixture. The obtained mixture is kneaded by a continuous pressure kneader or the like, and then it is diluted with a part of the solvent and subjected to a dispersion treatment using a sand mill or the like, and then an additive such as a lubricant is mixed and filtered. A method of mixing the remaining solvent, curing agent and the like can be mentioned.

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

The above-mentioned 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.

If desired, the second magnetic powder may contain a rare earth element or a transition metal element. In addition, as the second magnetic powder, fine tabular barium ferrite and some of its Fe atoms are T.
Magnetic powders substituted with atoms such as i, Co, Zn, and V can also be used. Further, in order to improve the dispersibility and the like of the first magnetic powder, the first magnetic powder is added to the first magnetic powder.
The above magnetic powder may be subjected to the above-mentioned surface treatment.

The particle size of the second magnetic powder is preferably 0.001 to 3 μm, more preferably 0.005.
˜1 μm, most preferably 0.005 to 0.5 μm. The second magnetic powder is preferably contained in the second magnetic layer formed by applying the second magnetic coating material in an amount of preferably 5 to 99% by weight, more preferably 30 to 95% by weight,
It is desirable to mix it in the second magnetic paint so that it is most preferably contained in an amount of 50 to 95% by weight.

As the binder and the solvent used in the second magnetic paint, the same binders and solvents as those used in the first magnetic paint can be used. The amount of the binder used is preferably about 5 to 100 parts by weight, more preferably 5 to 70 parts by weight, based on 100 parts by weight of the second magnetic powder. In addition, the above-mentioned additives and non-magnetic powder used in the above-mentioned first magnetic paint can be added to the above-mentioned second magnetic paint.

To prepare the second magnetic coating material, for example, the second magnetic powder and the binder are charged together with a part of the solvent into a Nauter mixer or the like and premixed to obtain a mixture. The resulting mixture is kneaded with a continuous pressure kneader or the like, then diluted with a part of the solvent and subjected to dispersion treatment using a sand mill or the like, and then additives such as a lubricant are mixed and filtered, and polyisocyanate is further added. And the like, and a method of mixing the remaining curing agent and the like.

Thus, in the magnetic tape of the present invention, the above-mentioned first magnetic powder has a high coercive force that does not substantially participate in recording and reproduction. The above "substantially high coercive force not involved in recording / reproduction" means a high coercive force that cannot be recorded / reproduced without being magnetized under the conditions required for a magnetic tape, Specifically, preferably 250
It is 0 Oe or more, and more preferably 2500 to 5500 Oe or more. Also, the coercive force Hc of the second magnetic powder described above.
Is 1700 to 2300 Oe, preferably 1750 to 2
It is 250 Oe. When the coercive force is less than 1700 Oe, it is disadvantageous in terms of high density recording, and when it exceeds 2300 Oe, the head magnetic field is insufficient and recording cannot be performed sufficiently. Further, the thickness (dry thickness) of the second magnetic layer is 0.05 to 1 μm, preferably 0.1 to 0.8 μm.
m. If the thickness is less than 0.05 μm, uniform coating is difficult, and if it exceeds 1 μm, the output is reduced in terms of thickness loss. The thickness (dry thickness) of the first magnetic layer is preferably 0.5 to 4 μm, more preferably 0.5 to 3.5 μm, and most preferably 0.5 to 3 μm.
Is.

Next, the outline of the method for producing the magnetic tape of the present invention will be described. First, the first magnetic coating material and the second magnetic coating material are wet-on on the magnetic support so that the dry thicknesses of the first magnetic layer and the second magnetic layer are the above-mentioned thicknesses. Simultaneous multilayer coating is performed by a wet method to form coating films for the first magnetic layer and the second 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, the temperature may be 6 to 72 at 40 to 70 ° C.
Time aging and slit to 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 publication, the second magnetic layer is formed before the first magnetic coating material forming the first magnetic layer is dried. The method of applying the second magnetic coating composition, wherein the boundary surface between the first magnetic layer and the second magnetic layer is smoothed and the surface property of the second magnetic layer is improved. , Low dropout, high density recording and coating film (second
A magnetic tape excellent in durability of the magnetic layer and the first magnetic layer) can be obtained.

The magnetic field orientation treatment is carried out before the second magnetic paint is dried, for example, about 500 Oe or more, preferably about 1000 Oe in a direction parallel to the application surface of the second magnetic paint. The method of applying a magnetic field of 10,000 to 10,000 Oe, and the second magnetic coating material in a wet state of 1,000 to
It can be performed by a method of passing through a solenoid of 10,000 Oe or the like.

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.

Further, 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 of the magnetic support (the surface on the side where the first magnetic layer and the second magnetic layer are not provided). It is obtained by applying a back coat coating composition, which is usually used for forming a back coat layer, on the magnetic support. The back coat paint is obtained by appropriately selecting and mixing the first magnetic powder, the binder, the dispersant, the lubricant, the curing agent, the solvent and the like described in detail in the first magnetic paint. is there. The back coat paint can be prepared by a generally known back coat paint manufacturing method.

In the production of the magnetic tape of the present invention, a finishing step such as polishing or cleaning of the surface of the second magnetic layer may be carried out if necessary. The application of the first magnetic coating material and the second magnetic coating material can also be performed by a generally known sequential multilayer coating method.

[0046]

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 support] (Production of non-magnetic support) Polyethylene terephthalate (intrinsic viscosity 0.60) was used for extrusion molding.
A film having a thickness of 7 μm was obtained and used as a support.

(Production of magnetic support b): Two layers (upper layer is a non-magnetic portion) Polyethylene terephthalate particles having an intrinsic viscosity of 0.60 and acicular γ-Fe ₂ O ₃ magnetic powder are prepared. 1 magnetic powder
The mixture was adjusted to be 5 wt% and melt-mixed using an extruder to obtain a mixture of particles. Then, the mixture and a polyethylene terephthalate granular material containing no magnetic material were coextruded to obtain a double-layer film. 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 give a total thickness of the magnetic support of 7 μm.
A magnetic support b having the structure shown in FIG. 2b (the thickness of the magnetic portion A being 1.5 μm) was obtained.

[Preparation of First Magnetic Paint, Second Magnetic Paint and Backcoat Paint] Each of the components of the following paints except polyisocyanate, fatty acid and fatty acid ester is now taken together with a part of the solvent. The resulting mixture was kneaded with a continuous pressure kneader. Then, respectively, diluted with a part of the solvent, after dispersion treatment with a sand mill, mixed with a fatty acid and a fatty acid ester, filtered, further mixed with the remaining solvent and polyisocyanate, the first magnetic coating, A second magnetic paint and back coat paint were obtained.

(Composition of Second Magnetic Paint) Needle-like metal magnetic powder mainly composed of iron (Fe: Al: Ba: Si: Ni: Co = 89: 2: 1: 1: 3: 4, coercive force 1620 Oe , Saturation magnetization 128 emu / g) 100 parts by weight Alumina (average particle size 0.3 μm, specific surface area 11 m ² / g) 9 parts by weight Carbon black (average primary particle size 20 nm) 3 parts by weight Sulfonic acid group- and epoxy group-containing vinyl chloride Resin (Average degree of polymerization 250) 9 parts by weight Sulfonate group-containing polyurethane (GPC number average molecular weight 25000) 7 parts by weight Stearic acid 1.5 parts 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 100 parts by weight Toluene 50 parts by weight Cyclohexanone 100 parts by weight

(Composition of Magnetic Paint A [First Magnetic Paint]) First magnetic powder; Co—Ti substituted barium ferrite powder (coercive force 3650 Oe, saturation magnetization 49 emu / g, average plate diameter 0.07 μm, plate State ratio 5) 100 parts by weight carbon black (average primary particle size 20 nm) 5 parts by weight Sulfonic acid group- and epoxy group-containing vinyl chloride resin (average polymerization degree 250) 6 parts by weight Sulfonic acid group-containing polyurethane (GPC number average molecular weight 25,000) ) 6 parts by weight myristic acid 0.5 parts by weight butyl oleate 2 parts by weight Polyisocyanate [Nippon Polyurethane Industry Co., Ltd., trade name "Coronate L"] 2 parts by weight Methyl ethyl ketone 70 parts by weight Toluene 35 parts by weight Cyclohexanone 70 parts by weight

(Composition of Magnetic Paint B) As the first magnetic powder, Co-γ-FeOx (1.33 <x <1.5, coercive force 890 Oe, saturation magnetization 82 emu / g, average plate diameter 0.
19 μm), except that the composition of magnetic paint B is the same.

(Composition of Magnetic Paint C) As the first magnetic powder, an acicular metal powder mainly composed of iron (Fe: Al: Si: N)
i: Co = 85: 3: 1: 1: 5, coercive force 1470O
e, saturation magnetization 142 emu / g, average major axis length 0.17 μ
m, specific surface area 51 m ² / g), except that the same composition as in magnetic paint B was used.

(Blending of back coat paint) Carbon black (average primary particle size 0.028 μm) 32 parts by weight Carbon black (average primary particle size 0.062 μm) 8 parts by weight “Nipporan 2301” [trade name, Nippon Polyurethane Industry ( Polyurethane manufactured by Co., Ltd.] 20 parts by weight nitrocellulose (viscosity display made by Hercules Powder Co. of 1/2 second) 20 parts by weight polyisocyanate (trade name “D-250N” manufactured by Takeda Pharmaceutical Co., Ltd.) 4 parts by weight Copper phthalocyanine 5 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 Tape] The above-mentioned magnetic coating material (first magnetic coating material) and the above-mentioned second magnetic coating material are dried on the surface of the above-mentioned support to have the dry thicknesses shown in [Table 1]. As described above, simultaneous multi-layer coating was performed by the wet-on-wet method to form coating films for the first magnetic layer and the second magnetic layer. Then, when the coating film is wet, 5000O
The magnetic field orientation processing is performed by passing through the solenoid of e.
After being dried at 0 ° C., it was wound up. Then 85
Calendered under the conditions of ℃ and 350kg / cm,
After forming the first magnetic layer and the second magnetic layer, a back coat paint is dried to a thickness of 0.5 on the back surface of the magnetic support.
It was coated to a thickness of μm, dried at 90 ° C., and then wound up. Then, it was aged at 50 ° C. for 16 hours and slit into 8 mm width to obtain an 8 mm width magnetic tape. The output (7 MHz) and the output fluctuation (%) of the obtained magnetic tape were measured according to the following measuring methods. The results are shown in [Table 1]. Further, a recording / reproducing test and a magnetic development test were conducted on the above-mentioned second magnetic paint and the above-mentioned magnetic paint B (first magnetic paint), B and C. The results are shown below.

[Measurement Method] Output (7 MHz) The obtained 8 mm wide magnetic tape was loaded in an 8 mm VTR cassette to obtain a test 8 mm VTR tape cassette. Obtained test 8mm VTR tape cassette and commercial Hi8V
Using a device modified from TR, 7M was added to the above magnetic tape.
A Hz signal was recorded and the output (reproduction output) when the signal was reproduced was measured. The recording wavelength of 7MHz is 0.54μ
It was m. Output fluctuation In measuring the recording / reproducing characteristics, the value of output fluctuation between tracks defined by the following equation was measured. Output fluctuation (%) = B / A × 100 A: maximum value of output between 1 tracks [V] B: minimum value of output between tracks [V] That is, the larger the value obtained by the above equation is the output It can be said that the envelope characteristics are good with little fluctuation. Recording / reproduction test The obtained magnetic paints a, b and c were coated on the above-mentioned support so that the dry thickness was 2 μm, calendered, and then a back coat layer was formed to form an 8 mm width. It was slit into a magnetic tape for testing. Recording was performed on the obtained magnetic tape in the same manner as in the measurement of the output, and then reproduction was further performed to determine whether or not a video signal was recorded. As a result, the magnetic paint B was not recorded, but the magnetic paints B and C were recorded. still,
The above second magnetic paint was recorded. ◎ Magnetic development test The obtained magnetic tape was cut out to prepare a tape section. After removing the first magnetic layer from the obtained slice, a magnetic fluid (trade name “Fericolloid HC
Magnetic development using 10 times diluted solution of 60 ", and further SE
M observation was performed to determine whether or not magnetized. As a result, the magnetic paint B was not magnetized, but the magnetic paints B and C were magnetized. The second magnetic layer was magnetized.

Example 2 A magnetic tape obtained in the same manner as in Example 1 was applied except that the thicknesses of the first magnetic layer and the second magnetic layer were changed to those shown in [Table 1]. Evaluation was carried out according to the method of Example 1. The results are shown in [Table 1].

Example 3 A magnetic tape obtained in the same manner as in Example 1 was applied except that the thicknesses of the first magnetic layer and the second magnetic layer were changed to those shown in [Table 1]. Evaluation was carried out according to the method of Example 1. The results are shown in [Table 1].

Example 4 As a support, a magnetic support b
The magnetic tape obtained in the same manner as in Example 2 except that was used was evaluated according to the method of Example 1. The results are shown in [Table 1].

<Comparative Examples 1 to 3> Magnetic tapes were prepared in the same manner as in Example 1 except that the thickness of the first magnetic layer was as shown in Table 1 and the second magnetic layer was not provided. Each magnetic tape produced and evaluated was evaluated according to the method of Example 1. The results are shown in [Table 1].

<Comparative Example 4> Implementation was carried out except that the thickness of the first magnetic layer was set to the thickness shown in [Table 1] and the second magnetic layer was formed by using the magnetic coating composition shown in [Table 1]. The magnetic tape obtained in the same manner as in Example 1 was evaluated according to the method of Example 1. The results are shown in [Table 1].

<Comparative Example 5> Implementation was carried out except that the thickness of the first magnetic layer was set to the thickness shown in [Table 1] and the second magnetic layer was formed using the magnetic coating material shown in [Table 1]. The magnetic tape obtained in the same manner as in Example 1 was evaluated according to the method of Example 1. The results are shown in [Table 1].

[0063]

[Table 1]

[0064]

INDUSTRIAL APPLICABILITY The magnetic tape of the present invention is capable of high density and is particularly excellent in output characteristics.

[Brief description of drawings]

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

FIG. 2 is a schematic view showing a structure of a magnetic support of the above-mentioned magnetic tape, (a) is a schematic view showing a structure in which only a magnetic portion is a single layer, and (b) is a magnetic portion. Schematic showing a structure in which a non-magnetic portion is provided on the surface of the two-layer structure, (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 (3)

[Claims] 1. A support, a first magnetic layer containing at least a first magnetic powder provided on the support, and a second magnetic layer provided on the first magnetic layer. A magnetic tape comprising a second magnetic layer containing magnetic powder, wherein the coercive force Hc of the second magnetic powder is 1700 to 23.
00 Oe, the thickness of the second magnetic layer is 0.05 to 1 μm, and the first magnetic powder has a high coercive force that does not substantially contribute to recording and reproduction. tape. 2. The coercive force Hc of the first magnetic powder is
The magnetic tape according to claim 1, which has a value of 2500 Oe or more. 3. The magnetic tape according to claim 2, wherein the first magnetic powder is hexagonal ferrite powder.