JPH0679373B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium capable of high density recording having a magnetic layer containing hexagonal ferrite fine powder.

[Technical Background of the Invention and Problems Thereof] A magnetic recording medium is generally composed of a base made of a resin material such as polyethylene terephthalate, and a magnetic layer formed by coating on the surface of the base. The substrate is a non-magnetic material. The magnetic layer contains fine particles of magnetic material and various binder resins as main components.

Conventionally, as magnetic powder, γFe ₂ O ₃ , CrO ₂ , Co-γFe ₂
Needle-like fine powders such as O ₃ and metallic iron have been used. However, these acicular magnetic powders have not been able to meet the ever-increasing demand for high-density recording.

Generally, in a magnetic recording medium capable of high density recording, the particle size of the magnetic powder contained in the magnetic layer is small, the magnetic powder is uniformly dispersed in the magnetic layer, and the surface of the magnetic layer is smooth. And that the magnetic layer is as thin as possible.

Although much research has been done on magnetic recording media that satisfy such conditions, magnetic powders of hexagonal ferrite have been recently developed, and magnetic recording media containing the magnetic powders in magnetic layers have high density recording. It has become clear that it is suitable for.

By the way, this hexagonal ferrite fine powder has an extremely fine average particle size of 0.02 to 0.2 μm. When manufacturing a magnetic recording medium using this fine powder, first, the fine powder is thoroughly kneaded with a binder resin and a solvent to prepare a viscous magnetic coating material. Then, this paint is applied to the surface of the substrate and then dried. Finally, the surface of this coating layer is smoothed to obtain the desired magnetic recording medium.

The magnetic recording medium manufactured as described above has the above-mentioned 4
It is found that the above condition is useful, but it causes a big problem in practical use. That is, this magnetic recording medium has a high translucency. For example, the light transmittance at a wavelength 900nm in the case of forming the magnetic layer of 3μm thick with cobalt substitution of hexagonal barium ferrite of Example 1 of the present invention, the same using a conventional γFe ₂ O _{3 3}
It becomes 2 to 8 times as large as when a magnetic layer having a thickness of μm is formed. This is not only based on the fact that hexagonal ferrite such as barium ferrite and strontium ferrite is a material having a relatively high light-transmitting property, and the particle size of this fine powder is sufficiently large compared to the wavelength of visible light. This phenomenon is based on the reasons that it is small, that it is well dispersed in the magnetic layer, that the surface of the magnetic layer is very smooth, and that the coating layer is thin.

In the magnetic recording devices currently on the market, the light-shielding property of a magnetic recording medium is used to detect the starting point or the ending point of a mounted magnetic tape or magnetic disk. For example, in the case of a magnetic tape, both the first part (leader tape part) and the end part of the tape are transparent, and the intermediate part between them is composed of an opaque magnetic recording medium. When this tape is mounted on a device and operated, the presence / absence of a magnetic recording medium can be confirmed by detecting transparent-opaque.

As described above, the conventional magnetic recording device is designed on the premise of the light shielding property of the magnetic recording medium. Therefore, when the above-mentioned magnetic recording medium using the fine powder of hexagonal ferrite is applied to a conventional device, the device does not function smoothly.

Therefore, for the purpose of lowering the light-transmitting property of the magnetic layer containing the hexagonal ferrite fine powder, a pigment that further reduces the light transmittance is added to the magnetic layer.

However, when the magnetic recording medium manufactured by this method is applied to high-density recording, the reproduction output thereof is lowered, and at the same time, noise is increased, and the deterioration of the characteristics as a whole cannot be avoided.

Therefore, in a magnetic recording medium containing hexagonal ferrite fine powder in the magnetic layer, it is an important issue to improve the light-shielding property without deteriorating the characteristics related to high-density recording.

[Object of the Invention] An object of the present invention is to provide a magnetic recording medium having a novel structure that solves the above-mentioned problems.

[Summary of the Invention] As a result of intensive studies to achieve the above object, the present inventors have found that if a magnetic recording medium is formed by forming an independent light blocking layer separately from the magnetic layer, the Based on the idea that the light-shielding property is imparted without impairing the reproducing characteristic, the magnetic recording medium of the present invention has been developed.

That is, the magnetic recording medium of the present invention is characterized in that the magnetic layer containing the hexagonal ferrite and the light blocking layer are separately formed on the surface of the substrate. The magnetic recording medium of the present invention has a composite structure of a substrate, a magnetic layer and a light blocking layer.

First, the base is not particularly limited as long as it is a non-magnetic material that has been conventionally used. For example,
Examples thereof include polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, polycarbonates, polyimides and polyamides.

The magnetic layer is various cobalt substitution products of barium ferrite,
It is composed of various cobalt substitution products of strontium ferrite, various W-type barium ferrites, various fine particles of hexagonal ferrite such as various W-type strontium ferrites, and a binder resin for binding them. As the binder resin, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, acrylic ester-
Acrylic nitrile copolymer, polyamide resin, polyvinyl butyral resin, cellulose derivative, polyester resin, polyurethane resin, urea resin, melamine resin, silicone resin, acrylic resin, phenol resin, epoxy resin, magnetic layer The content of the hexagonal ferrite fine powder in the magnetic layer is appropriately selected depending on factors such as the recording / reproducing characteristics required for the magnetic layer and the quality of the coating operation when forming the magnetic layer.

The greatest feature of the present invention is that the below-described light blocking layer is formed separately from the substrate and the magnetic layer.

The light blocking layer in the present invention is formed in the following three locations. The first is the case where it is formed between the base and the magnetic layer. In this case, the light blocking layer is an undercoat layer of the magnetic layer, and the magnetic recording medium has a three-layer structure in which a substrate, a light blocking layer, and a magnetic layer are laminated in this order. At this time, the light blocking layer provided as an undercoat layer functions as an anchor coat for improving the adhesiveness between the body and the magnetic layer, or functions as a conductive layer that imparts conductivity and prevents the medium from being charged. You can also Secondly, when it is formed on the surface of the substrate opposite to the surface having the magnetic layer. In this case, the magnetic recording medium has a three-layer structure in which the light blocking layer-the body-the magnetic layer are laminated in this order. At this time, the light blocking layer can be made to function as a lubricating layer for improving the running property of the medium, or can be made to function as the above-mentioned conductive layer for antistatic. Third is the first and second
This is the case when is done at the same time.

Such a light blocking layer is preferably a layer having a small light transmittance and shielding light efficiently, and a layer having a large light transmittance per unit thickness as compared with the magnetic layer.

The light blocking layer is composed of powders of various pigments described below and a binder resin that binds these powders. The binder resin used for this is the same resin as that for the magnetic layer.

Examples of the pigment include the following.
That is, MgO, BaO, VO, FeO, αFe ₂ O ₃ , αAl ₂ O ₃ , Cr ₂ O ₃ , Mn _{2
O 3, La 2 O 3,} Ce 2 O 3, SiO 2, GeO 2, SnO 2, In 2 O 3, TiO 2, MnO 2, Ce
O ₂ ,, V ₂ O ₅ ,, WO ₃ , SnO, Bi ₂ O ₃ ,, MnAl ₂ O ₄ ,, CoAl ₂ O ₄ ,, NiAl ₂ O ₄ ,, CuAl
₂ O ₄ ,, MgCr ₂ O ₄ ,, MnCr ₂ O ₄ ,, FeCr ₂ O ₄ ,, NiCr ₂ O ₄ ,, ZnCr ₂ O ₄ ,, NiCr ₂ O
₄ , CaIn ₂ O ₄ , SrIn ₂ O ₄ , SnCo ₂ O ₄ , Ni ₁₂ Fe ₈ Ti ₄ O ₃₂ , NiMn ₂ O ₄ , Co
_{Mn 2 O 4 Ti 3 O 5} , FeTiO 3, MgTiO 3, MnTiO 3, FeTiO 3, CoTiO 3, NiTi
O ₃ , ZnTiO ₃ , LiNbO ₃ , LiTaO ₃ , SrTiO ₃ , SrZnO ₃ , SrSnO ₃ , SrFeO
_{3, BaZrO 3, BaSnO 3,} BaThO 3, BaTiO 3, PbTiO 3, LaCoO 3, LaFe
_{O 3, CaTiO 3, PbZrO 3} , Sr 2 TiO 4, Ca 2 MnO 4, Sr 2 MoO 4, BaSnO 4, La
_{2 NiO 4, NiWO 4, MgCO} 3, CaCO 3, SrSO 4, BaSO 4, FeSiO 4, ZrSiO 4
Pigments of metal oxides such as ZnS, SnS, SnS ₂ , FeS _{1 + δ} , CuS,
NiS, CoS, MoS ₂ , WS ₂ , FeS ₂ , CoS ₂ , MnS ₂ , NiS ₂ , Al ₂ S ₃ , Ni ₃ S ₂ , F
eCr ₂ S ₄ ,, Co ₃ S ₄ ,, Ni ₃ S ₄ ,, CuV ₂ S ₄ ,, CuFeS ₂ ,, CuAlS ₂ ,, CuInS ₂ ,, CuF
Metal sulfide pigments such as eS ₂ ; BN, AlN, Si ₃ N ₄ , TiN, ZrN, V
Pigments of metal nitrides such as N, CrN, NbN; aluminum,
Pigments of fine metal powders such as copper, silver, titanium, chromium, nickel, cobalt and iron; organic pigments such as aniline black, polychlorophthalocyanine and nickel complex salts.

Each of these pigments is in the form of fine powder dispersedly contained in the light shielding layer, and the particle size at that time is preferably 1 μm or less, and more preferably 0.5 μm or less in order to make the entire magnetic recording medium thinner.

The content of the pigment in the light blocking layer is determined in relation to the thickness of the light blocking layer. In the present invention, the product of the pigment content (expressed in wt%) and the thickness of the light blocking layer (expressed in μm) in the coating material for the light blocking layer is 0.05 or more, preferably 0.1 or more. It is preferable to control the content of the pigment so that For example, when the thickness of the light-shielding layer is 1 μm, the paint used may contain 5% by weight or more of the pigment (and thus less than 95% by weight of the binder resin). This value is 0.05
If it is less than the above range, the light blocking property of the light blocking layer is insufficient. The thickness of the light blocking layer should be inversely defined from the intended thickness of the entire magnetic recording medium, and therefore cannot be uniquely determined, but it is preferable that it be as thin as possible.

The magnetic recording medium of the present invention can be manufactured as follows. First, a base made of a predetermined material is prepared. Further, a paint forming the magnetic layer and a paint forming the light blocking layer are prepared. A predetermined amount of each of these paints may be applied in the order of forming the composite structure described above, and then the curing / smoothing process may be performed.

[Examples of the Invention] Example 1 A magnetic paint having the following composition was prepared.

Cobalt substitution of hexagonal barium ferrite (average particle size
0.08 μm, coercive force 800 Oe) 100 parts by weight Carbon black 5 parts by weight Aluminum oxide 2 parts by weight Vinyl chloride-vinyl acetate copolymer 10 parts by weight Urethane resin 10 parts by weight Lubricant (mixed fatty acid) 1.5 parts by weight Methyl ethyl ketone 60 parts by weight Toluene 60 parts by weight Cyclohexanone 60 parts by weight Curing agent (tolylene diisocyanate) 6 parts by weight Next, a light-shielding paint having the following composition was prepared.

αFe ₂ O ₃ (average particle size 0.2 μm) 100 parts by weight carbon black 6 parts by weight Vinyl chloride-vinyl acetate copolymer 10 parts by weight Urethane resin 10 parts by weight Curing agent (tolylene diisocyanate) 6 parts by weight Methyl ethyl ketone 600 parts by weight Cyclohexanone 100 Parts by Weight First, the former magnetic coating material was applied to one surface of a polyethylene terephthalate base sheet having a thickness of 14 μm and calendered to form a magnetic layer having a thickness of 3 μm, and this layer was cured.

The latter light-shielding coating material was applied to the opposite substrate surface to form a back coat layer having a thickness of 0.5 μm after drying. This is the light blocking layer. After the back coat layer was cured, it was slit to obtain a magnetic tape having a width of 1/2 inch.

The light transmittance (wavelength 900 nm) of this tape was 1.2%.
On the contrary, the light transmittance (wavelength: 900 nm) when the back coat layer was not formed was 12%.

In addition, the influence of the back coat layer formation on the magnetic property of the tape was investigated. Recording frequency of 1 MH under the conditions of relative speed between tape and ferrite ring head of 3.75 m / sec, track width of 35 μm, head gap of 0.2 μm, and winding number of 18 turns.
When recorded at z, 2MHz, 3MHz, 5MHz, and measured the playback output in each case, 300μV, 2 for each of the two tapes.
It was 50 μV, 200 μV and 160 μV, and no difference was observed between the two. Also, there was no increase in noise.

Example 2 A light-shielding paint having the following composition was prepared.

Carbon black 50 parts by weight Copper oxide (CuO, average particle size 0.15 μm) 50 parts by weight Urethane resin 200 parts by weight Methyl ethyl ketone 1000 parts by weight Cyclohexanone 100 parts by weight Curing agent (tolylene diisocyanate) 60 parts by weight This paint is used in Example 1 An undercoat layer having a thickness of 0.6 μm after drying by coating on one side of the base sheet was formed. Then, the magnetic coating material of Example 1 was applied onto this layer, and the same treatment as in Example 1 was performed to form a magnetic layer, and a similar magnetic tape was manufactured.

The light transmittance of this tape (wavelength: 900 nm) was 3.0%, and no change in magnetic characteristics was observed.

Reference Example Aluminum was applied on one side of the base sheet used in Example 1
0.05 μm was deposited. The magnetic paint of Example 1 was applied to the other surface to form a magnetic layer.

The light transmittance (wavelength 900 nm) of this magnetic tape was less than 1%. No change in magnetic properties was observed.

[Effects of the Invention] As is clear from the above description, in the magnetic recording medium of the present invention, since the magnetic layer contains hexagonal ferrite, high density recording is possible. Since the light-shielding light-shielding layer is formed separately from the magnetic layer, high-density recording can be performed without changing the design of conventional equipment. Further, the light blocking layer is provided with a function of improving the adhesiveness between the base and the magnetic layer, preventing charging of the recording medium, or enhancing the lubricity of the magnetic recording medium to improve the running property. The industrial value is great because it has the effect of enabling

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Claims (4)

[Claims] 1. An average particle diameter of magnetic powder on the surface of a substrate
Magnetic layer mainly composed of hexagonal ferrite of 0.02 to 0.2 μm, and at least one selected from pigments of metal oxides, pigments of metal sulfides, pigments of metal nitrides, and fine metal powders having a particle diameter of 1 μm or less. 2. A magnetic recording medium characterized in that a light-shielding layer mainly composed of the above pigment is individually formed. 2. The magnetic recording medium according to claim 1, wherein the light shielding layer is an undercoat layer formed between the substrate and the magnetic layer. 3. The magnetic recording medium according to claim 1, wherein the light-shielding layer is formed on the surface of the substrate opposite to the surface having the magnetic layer. 4. The light shielding layer according to claim 1, wherein the light shielding layer is formed between the substrate and the magnetic layer, and is also formed on the surface of the substrate opposite to the surface having the magnetic layer. Magnetic recording medium.