JPH0729153A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To realize the balanced improvement of both durability and radio frequency characteristics and improve envelope characteristics. CONSTITUTION:An intermediate layer which contains soft-magnetic powder such as sendast, manganese-zinc system ferrite or nickel-zinc system ferrite whose average particle diameter is not larger than 0.1mum and a magnetic layer which contains magnetic powder such as metal powder, cobalt-coated iron oxide or hexagonal ferromagnetic powder are formed on a substrate.

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, and more particularly to a magnetic recording medium having excellent durability and high frequency characteristics and improved envelope characteristics.

[0002]

2. Description of the Related Art A coating type magnetic recording medium is obtained by coating a magnetic coating material obtained by dispersing magnetic powder in a binder and an organic solvent on a substrate such as polyester and drying it. There is an increasing demand for higher density recording such as high quality video tapes and large capacity floppy disks.

In order to achieve this object, it is required to make the magnetic layer as thin as possible by using magnetic powder having a high coercive force, a high saturation magnetization and a small particle size. Nowadays, cobalt-coated iron oxide, Ferromagnetic metal powder mainly composed of iron (hereinafter referred to as metal powder), hexagonal barium ferrite powder and the like are used. However, when fine particle powders are used with higher densities, it becomes difficult to disperse them, and the magnetic powders are not uniformly dispersed in the coating film, and it is often the case that the magnetic properties originally possessed by the magnetic powders cannot be sufficiently exhibited. there were.

In order to solve this problem, Japanese Patent Laid-Open No. 5-120668 discloses coexistence of a soft magnetic magnetic powder in a magnetic paint to promote dispersion of the magnetic powder and prevent reaggregation. A magnetic recording medium having an improved surface smoothness of the magnetic layer is obtained.

If the magnetic layer is thinned for high-density recording, the durability of the magnetic recording medium is lowered. For the purpose of reinforcing this, an intermediate layer made of non-magnetic particles is provided between the base material and the magnetic layer. A magnetic recording medium provided with is proposed. For example, JP-A-62-214514 discloses a magnetic recording medium having a non-magnetic layer having a specific surface roughness and a magnetic layer formed on the non-magnetic layer. In addition, Japanese Patent Laid-Open No. 62-2314
Japanese Patent No. 17 discloses a magnetic recording medium having a non-magnetic layer containing a lubricant and a magnetic layer containing a lubricant. JP-A-3-214422 and JP-A-3-214417 disclose that
Disclosed is a magnetic recording medium having a good surface state, which comprises a smooth nonmagnetic layer formed on a relatively inexpensive nonmagnetic support having a poor surface state and a magnetic layer formed on the nonmagnetic layer. There is. Further, in Japanese Patent Laid-Open No. 5-73883, the state of the interface between the non-magnetic layer and the magnetic layer is specified in detail.
It is disclosed that a magnetic recording medium having improved running performance and excellent output in a high frequency band can be obtained.

[0006]

However, a magnetic recording medium prepared by blending a soft magnetic magnetic powder in a magnetic coating as disclosed in Japanese Patent Laid-Open No. 5-120668 does not have sufficient durability.
Also, the high frequency output is insufficient.

Further, the magnetic recording medium having the intermediate layer is described in JP-A-62-214514, JP-A-62-231417, JP-A-3-214422, and JP-A-3-214417. The magnetic recording medium described has relatively good running properties and durability, but it is necessary to further improve the electromagnetic conversion characteristics in order to achieve the high-density recording required today.

As described above, as a magnetic recording medium intended for high density recording, a magnetic recording medium having improved durability and high frequency output in a well-balanced manner has not been obtained.

[0009]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a soft magnetic magnetic powder is used for an intermediate layer and a magnetic layer having a thickness of 1 μm or less is provided on the intermediate layer. As a result, it has been found that it is possible to obtain a magnetic recording medium in which both the durability and the high frequency output are improved in a well-balanced manner and the envelope characteristic is also improved, and the present invention has been completed.

That is, the present invention comprises a base material, an intermediate layer formed on the base material, the soft magnetic powder having an average particle size of 0.1 μm or less, and a binder, and the intermediate layer formed on the intermediate layer. A magnetic recording medium having a magnetic layer having a thickness of 1 μm or less.

In the present invention, by forming the intermediate layer containing the soft magnetic magnetic powder on the substrate and forming the magnetic layer on the intermediate layer, not only the durability of the magnetic recording medium but also the high frequency characteristics are improved. . Although the reason for this is not clear, the flow of the magnetic field in the intermediate layer is easy, which helps the head magnetic field to reach the deep portion of the magnetic layer. Therefore, even in the high frequency region, the magnetic layer is magnetized deeper,
Since there is a contribution from a portion deeper than this, it is considered that the high frequency characteristics during reproduction are improved.

The magnetic layer of the magnetic recording medium of the present invention will be described.

In the present invention, the magnetic powder forming the magnetic layer may be any of those usually used in this field. Particularly preferable magnetic powders include acicular metal powders containing iron as a main component (metal powders), acicular cobalt-coated iron oxides and hexagonal ferromagnetic powders.

As the metal powder, conventionally known ones mainly composed of iron can be used. Iron powder, iron and cobalt,
Examples thereof include alloy powders of nickel and the like, and alloy powders containing aluminum, chromium, manganese, silicon, zinc, transition metal elements, rare earth metal elements and the like. The metal powder has an average major axis length of 0.2 μm or less and a coercive force of 1700 Oe.
Above all, 1700 to 2000 Oe is particularly preferable. The magnetic characteristics other than the coercive force are not particularly limited. Further, the metal powder used is needle-shaped, and the needle-shaped ratio is preferably 3 or more. When the acicular ratio is less than 3, the magnetic field orientation tends to decrease.

As the acicular cobalt-deposited iron oxide, Co-deposited iron
Fe ₃ O ₄ , Co-deposited Fe ₂ O ₃ , Co-deposited FeO _x (1.34 ≦ x <1.50)
Is used, and Co-deposited FeO _x is particularly preferable. Further, the cobalt-adhered iron oxide used in the present invention is produced by a conventional cobalt-adhesion method using acicular iron oxide as a nucleus. The magnetic characteristics can be adjusted to predetermined values by controlling the amount of cobalt added and the amount of Fe ²⁺ in the manufacturing conditions. The amount of cobalt added is usually 1 to 20% by weight (based on iron oxide as a raw material), preferably 2 to 15% by weight, and the amount of Fe ²⁺ is usually 0.5 to 30% by weight (total cobalt-coated iron oxide). %), Preferably 1 to 25% by weight. Further, the cobalt-coated iron oxide used in the present invention is preferably acicular and has an axial ratio of 3-10.
Are preferred. The cobalt-coated iron oxide used in the present invention has an average major axis length of 0.2 μm or less and a coercive force of 1
It is preferably 600 Oe or more, particularly 1600 to 2000 Oe. The magnetic characteristics other than the coercive force are not particularly limited.

As the hexagonal ferromagnetic powder, barium ferrite, strontium ferrite, calcium ferrite, or a part of iron atoms constituting these ferrites is used.
Examples include those substituted with at least one element selected from the group consisting of Co, Ti, Zr, Ni, In, Cu, Ge, and Nb. Here, the hexagonal ferromagnetic powder means a powder of a magnetic metal compound having a hexagonal crystal structure. It is desirable that such a hexagonal ferromagnetic powder has as uniform particle shape and particle size distribution as possible. Specifically, in the case of a hexagonal plate-shaped crystal, assuming that the length of the diagonal line is d and the thickness of the plate is t, the length (d) is 0.03 to 0.2 μm, and the thickness of the plate relative to the length of the diagonal line ( Those having a d / t of 3 to 10 are usually available.
The hexagonal ferromagnetic powder used in the present invention has a coercive force
It is preferably 1400 Oe or more, particularly 1400 to 2000 Oe.
The magnetic characteristics other than the coercive force are not particularly limited.

The thickness of the magnetic layer containing the above-mentioned magnetic powder (the thickness of the dry coating film) is preferably 1 μm or less, more preferably 0.5 μm or less.

Next, the intermediate layer of the magnetic recording medium of the present invention will be described.

In the present invention, the intermediate layer on the substrate is formed of a soft magnetic magnetic powder having an average particle size of 0.1 μm or less and a binder. Average particle size of soft magnetic powder is 0.1μm
If it exceeds, the surface smoothness of the magnetic layer deteriorates. In general,
The soft magnetic magnetic powder is known as a powder having a high magnetic susceptibility and a low coercive force, which is made of metal, metal oxide, alloy, amorphous alloy or the like. Any of these may be used in the present invention, but those used in so-called weak electric devices such as magnetic heads and electronic circuits are particularly preferable. As the soft magnetic magnetic powder, for example, the soft magnetic materials described in "Physics of Ferromagnets (Lower) Magnetic Properties and Applications" by Satoshi Chikaku (Sokabo, 1984) pp. 368-376 can be used. Specifically, iron-silicon alloy, iron-aluminum alloy, iron-nickel alloy, iron-cobalt alloy, iron-cobalt-nickel alloy, nickel-cobalt alloy, sendust, manganese-zinc system ferrite, nickel-zinc system ferrite. , Magnesium-
Examples thereof include zinc-based ferrite and magnesium-manganese-based ferrite.

The intermediate layer contains the above-mentioned soft magnetic magnetic powder,
Other inorganic powders and organic powders may be used in combination. Examples of the inorganic powder include carbon black, graphite carbon, alumina, iron oxide, titanium oxide, barium sulfate and calcium carbonate. Further, as the organic powder, polystyrene beads, nylon powder, benzoguanamine resin beads, polyacrylic acid-based polymer beads, polyvinyl chloride resin beads, and other polymer beads can be used. Their average particle size is 0.1 μm
The following are preferred. The weight ratio of the soft magnetic magnetic powder to the other powder is as follows: soft magnetic magnetic powder: other powder = 100: 0
-10: 90 is preferable. If the content of other powders exceeds 90% by weight, the high frequency characteristics of the magnetic recording medium deteriorate.

In the present invention, in order to improve the dispersibility of the magnetic powder and the soft magnetic powder, they may be surface-treated. The surface treatment of such magnetic powder and soft magnetic powder is described in "Characterization of Powder Surfa
ces "; Academic Press can be referred to, and examples thereof include a method of coating the surface of the magnetic powder or the soft magnetic powder with an inorganic oxide. The inorganic oxides used here include Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , and Sb ₂ O.
₃ and ZnO. These may be used in combination or may be used alone.

In the present invention, the method of forming (coating) the magnetic layer and the intermediate layer includes a method of simultaneously forming the magnetic layer and the intermediate layer (multi-layer simultaneous forming method) or a method of sequentially forming one layer at a time (sequential forming method). Any of these may be used, and when forming one layer, calendering may be performed for each layer.

In the present invention, the compounded coating material for the intermediate layer and the magnetic coating material for the magnetic layer are composed of magnetic powder or soft magnetic magnetic powder, a binder, an organic solvent and the like. Also, a common binder or the like can be used.

As the binder used in the present invention, a polyurethane resin, particularly a sulfonic acid group, a sulfonic acid metal base, a sulfobetaine group, a carbobetaine group, an amino group,
Polyurethane resin containing polar groups such as hydroxyl group and epoxy group, vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Vinylidene chloride copolymers, vinyl chloride-based copolymers such as vinyl chloride-acrylonitrile copolymers, in particular sulfonic acid groups, metal sulfonate groups, vinyl chloride copolymers containing polar groups such as amino groups, Butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, Epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low Mixture of molecular weight glycol / high molecular weight diol / isocyanate, and mixtures thereof and the like can be exemplified. Normally, the binder is 3.0 to 10.0 in the magnetic paint.
It is blended in a weight percentage of about. Further, 10 to 400 parts by weight are used in the compounding paint for the intermediate layer, relative to 100 parts by weight in total of the above-mentioned soft magnetic magnetic powder and other powders optionally mixed.

As the organic solvent, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, benzene, toluene, xylene, dimethylsulfoxide, tetrahydrofuran, dioxane and the like are suitable solvents for dissolving the binder resin used. There is no particular limitation and they may be used alone or in combination of two or more. Usually, the organic solvent is compounded in the magnetic paint or the compounded paint for the intermediate layer in an amount of about 20 to 80% by weight.

In the magnetic coating composition, various commonly used additives such as a dispersant, an abrasive and a lubricant may be appropriately added and used. As the dispersant, lecithin,
Nonionic surfactants, anionic surfactants, cationic surfactants and the like can be used. As an abrasive, α-
A fine powder of alumina, fused alumina, chromium oxide (Cr ₂ O ₃ ), iron oxide, silicon carbide, corundum, diamond, etc. with an average particle size of 0.05 to 1 μm can be used, and usually 100 parts by weight of the binder as described above is used. 0.5 to 100 parts by weight is added. Examples of lubricants include silicone oils such as various polysiloxanes, graphite, inorganic powders such as molybdenum disulfide, fine plastic powders such as polyethylene and polytetrafluoroethylene, higher fatty acids, higher alcohols, higher fatty acid esters, and fluorocarbons. Etc. are added in a ratio of 0.1 to 50 parts by weight with respect to 100 parts by weight of the above-mentioned binder.

The base material used in the magnetic recording medium of the present invention includes synthetic resins (for example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyamides, polyolefins, cellulose derivatives), non-magnetic metals, glass, ceramics and papers. Etc., and the form thereof is used in films, tapes, sheets, cards, disks and the like.

Generally, when an intermediate layer is provided between the magnetic layer and the base material, the durability of the magnetic recording medium is improved, but in the present invention, the durability is further improved. Further, when the magnetic layer is made thin, the stiffness of the magnetic recording medium becomes weak and the envelope characteristics may deteriorate. However, in the present invention, the addition of the soft magnetic powder improves the envelope characteristics.

[0029]

According to the present invention, it is possible to obtain a magnetic recording medium in which both the durability and the high frequency characteristic are improved in a well-balanced manner and the envelope characteristic is improved.

[0030]

The present invention will be further described in the following examples, but the present invention is not limited to these examples.

Examples 1 to 4 and Comparative Examples 1 to 6 (1) Intermediate Layer Coating Material and Magnetic Coating Material Compound coating material for intermediate layer (hereinafter referred to as intermediate layer coating material) A and B and magnetic layer coating material shown below. 8 mm video cassettes were prepared using the magnetic paints I to III. The soft magnetic magnetic powders used in the intermediate layer coating were all surface-treated with an aqueous solution of aluminum nitrate containing aluminum corresponding to 2% by weight of the soft magnetic magnetic powder, washed, and dried.

<Intermediate Layer Paint A> 100 parts by weight of soft magnetic magnetic powder [Mn-Zn ferrite powder having an average particle size of 0.03 μm] 30 parts by weight of vinyl chloride / acrylic acid copolymer resin containing a sulfonic acid group Acid group-containing polyester-based polyurethane resin 30 parts by weight-Garfuck RE610 [Toho Chemical Co., Ltd.] 3 parts by weight-Polyisocyanate 3 parts by weight [Coronate HX, curing agent manufactured by Nippon Polyurethane Industry Co., Ltd.]-Solvent 200 parts by weight (Methyl ethyl ketone / toluene / cyclohexanone = 1/1/1).

<Intermediate Layer Coating Material B> In the formulation of the intermediate layer coating material A, soft magnetic magnetic powder having an average particle diameter of 0.04 μm is used.
A paint with the same composition as the paint A for the intermediate layer except that 100 parts by weight of Ni-Zn ferrite powder was used.

<Intermediate Layer Coating C> In the composition of the intermediate layer coating A, the soft magnetic magnetic powder and Garfac RE610 were not compounded, and the amount of the solvent was 150 parts by weight. Paint with the same formulation as.

<Magnetic Paint I> 100 parts by weight of acicular metal powder mainly composed of iron [Fe: Al: Ca: Si: Ni: Co = 92: 2: 1: 1: 2: 2, coercive force = 1730 Oe, average major axis length = 0.13 μm, saturation magnetization 132 emu / g] ・ Alumina (average particle size 0.3 μm) 7 parts by weight ・ Carbon black (average particle size 20 nm) 3 parts by weight ・ Sulfonic acid group-containing vinyl chloride-acrylic acid Copolymer resin 8 parts by weight Sulfonic acid group-containing polyurethane resin 6 parts by weight Stearic acid 1 part by weight 2-Ethylhexyl myristate 2 parts by weight Polyisocyanate 4 parts by weight [Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd. Curing agent] -Solvent 230 parts by weight (methyl ethyl ketone / toluene / cyclohexanone = 1/1/1).

<Magnetic Paint II> In the composition of Magnetic Paint I, in place of the acicular metal powder mainly composed of iron, cobalt-coated iron oxide [Co-γ-FeO _x (1.34 ≦ x <1.50), coercive force = 1650 Oe, average major axis length = 0.15 μm, saturation magnetization 81 emu /
g] is a magnetic paint.

<Magnetic Paint III> In the formulation of Magnetic Paint I, hexagonal plate-shaped barium ferrite powder [plate diameter = 0.05 μm, plate ratio = instead of needle-shaped metal powder mainly composed of iron]
5, magnetic coercive force = 1450 Oe, saturation magnetization = 55 emu / g]

(2) Preparation of 8 mm Video Cassette In the 8 mm video cassette of the example, a polyethylene terephthalate film having a thickness of 7 μm (so that the thickness after drying the above intermediate layer coating material by a gravure roll becomes 2 μm) ( PE
T) It is applied on a film and dried to form an intermediate layer, and then the above magnetic paint is applied on the intermediate layer by a gravure roll so that the thickness after drying becomes 0.4 μm,
After longitudinal orientation with a magnetic field strength of G, the magnetic layer was dried to form a magnetic layer, further calendered (80 ° C), and aged at 50 ° C for 24 hours. Further, in the 8 mm video cassette of the comparative example, since the intermediate layer was not formed, the magnetic paint was applied so that the thickness after drying was 2.9 μm.

Subsequently, the coating material for the back coat layer prepared by mixing the following components in a sand mill was applied to the surface of the film opposite to the surface provided with the magnetic layer so that the dry thickness would be 0.5 μm, and then Aged at 50 ° C for 24 hours. <Coating ingredients for back coat layer> ・ Carbon black (average particle size 0.02 μm) 32 parts by weight ・ Carbon black (average particle size 0.06 μm) 8 parts by weight ・ Polyurethane resin 20 parts by weight (Nipporan 2301 manufactured by Nippon Polyurethane Co., Ltd.) ) ・ Nitrocellulose 20 parts by weight (viscosity indication by Hercules Powder CO. Is 1/2 second) ・ Polyisocyanate 4 parts by weight [Coronate HX, a curing agent manufactured by Nippon Polyurethane Industry Co., Ltd.] ・ Stearic acid 1 part by weight -320 parts by weight of solvent.

As described above, the film on which the intermediate layer, the magnetic layer and the back coat layer are formed is cut into a tape shape having a width of 8 mm and loaded into an 8 mm cassette case to record for 120 hours.
8mm video cassette was made.

(3) Performance evaluation of 8 mm video cassette With respect to the 8 mm video cassette obtained as described above, durability, 7 MHz output and envelope characteristic were measured by the following methods. The results are shown in Table 1.

Durability 7mm with commercially available Hi8VTR device for 8mm video cassette
Signal was recorded, and a 50-pass running test was conducted using another Hi8 VTR device. The output of 7MHz before and after the running test was measured, and the value of 7MHz output after the running test was shown by the relative value (%) with respect to the value of 7MHz output before the running test.

Output of 7 MHz An 8 mm video cassette was attached to a commercially available Hi8VTR modified device, and recording / reproducing characteristics of 7 MHz were measured and the reproducing output was shown as a relative value with respect to a reference. The numerical values in Table 1 are relative values based on Comparative Example 2 as a reference (0 dB) in Example 1 and Comparative Example 1, and relative values based on Comparative Example 4 in Example 2 and Comparative Example 3. Yes, Example 3 and Comparative Example 5 are relative values with Comparative Example 6 as a reference (0 dB).

Envelope characteristics In the measurement of the recording / reproducing characteristics at 7 MHz described above, the value of the 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 exhibits good envelope characteristics with little fluctuation.

[0045]

[Table 1]

Claims (4)

[Claims] 1. A substrate, an intermediate layer formed on the substrate, comprising a soft magnetic powder having an average particle size of 0.1 μm or less and a binder, and a thickness of 1 μm formed on the intermediate layer. A magnetic recording medium having the following magnetic layer. 2. The magnetic recording medium according to claim 1, wherein the magnetic layer comprises an acicular metal powder mainly composed of iron having an average major axis length of 0.2 μm or less and a coercive force of 1700 Oe or more, and a binder. 3. The magnetic recording medium according to claim 1, wherein the magnetic layer comprises an acicular cobalt-coated iron oxide having an average major axis length of 0.2 μm or less and a coercive force of 1600 Oe or more, and a binder. 4. The magnetic recording medium according to claim 1, wherein the magnetic layer comprises a hexagonal ferromagnetic powder having a coercive force of 1400 Oe or more and a binder.