JPH11259848A - Magnetic recording medium and manufacture therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium provided with sufficient durability and indicating excellent electromagnetic transducing characteristics. SOLUTION: This magnetic recording medium is provided with a non- magnetic under coating layer and a magnetic layer where ferromagnetic powder is dispersed in a binder on a flexible non-magnetic supporting body. The film thickness of the non-magnetic under coating layer is 0.2-4.0 μm, the film thickness of the magnetic layer is >=0.5 μm and <0.25 μm and the content of a non-magnetic conductive material in the magnetic layer is <=1 pts.wt. to the 100 pts.wt. of the ferromagnetic powder in the magnetic layer.

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 a high output at a high frequency, good overwrite characteristics, and excellent durability, particularly suitable for high-density recording.

[0002]

2. Description of the Related Art In recent years, portable personal computers such as notebook computers have become widespread, and accordingly, a small-sized recording device has been demanded. It has been demanded. In addition, as the capacity of magnetic recording media has been increased and the size of recording apparatuses has been further reduced, the recording density has been increased. In response to this demand for higher density, magnetic recording media using a metal thin film for the magnetic layer are also being studied. However, at present, coating type magnetic recording media are superior in terms of productivity, corrosion, etc. I have. For this reason, studies are being made to improve the electromagnetic conversion characteristics of the coating type magnetic recording medium. This means includes reducing the thickness of the magnetic layer, improving the surface properties, increasing the packing of the magnetic powder, increasing the coercive force of the magnetic powder, and increasing the squareness ratio of the magnetic hysteresis.

As the recording wavelength has been shortened along with the improvement in recording density, the surface of the magnetic layer has been required to be even smoother in order to minimize the loss of spacing between the head and the magnetic layer. Specifically, in order to smooth the surface of the magnetic layer, it is necessary to increase the degree of dispersion of the magnetic particles and to sufficiently perform calendering. This is also effective for reducing noise. Further, it is more effective and important to reduce the particle size of the magnetic particles. In addition, in order to promote the filling of magnetic powder, consider reducing the amount of fillers that contribute to conductivity and durability, such as carbon and abrasives, as much as possible, and using highly dispersible resin to reduce the amount of resin used. Has been made. It has also been considered to provide the undercoat layer with a conductive effect and to remove the conductive filler from the magnetic layer. As the magnetic powder in the magnetic layer, it is necessary to increase the coercive force to some extent with the shortening of the recording wavelength, and in recent years, ferromagnetic metal powder and barium ferrite magnetic powder have been used, and the particle size has also become smaller. Is coming. In addition, when recording at a short wavelength, the self-demagnetization loss during recording,
Since there is also a problem of thickness loss at the time of reproduction, a method of reducing the thickness of the magnetic layer has been proposed to solve this problem.

However, the magnetic recording media obtained by these methods have insufficient durability, are liable to cause clogging of the head, have a reduced output, and have a problem that the surface of the magnetic layer is scraped by the head. Had occurred. This is because the transfer of lubricant between the magnetic layer and the non-magnetic underlayer, the smoothness of the interface between the two layers, and the effect of the non-magnetic underlayer, which plays a role in supplying lubricant to the magnetic layer, have not been studied. This has not been done in detail yet, which has hindered the supply of magnetic recording media suitable for high density recording. The effect of carbon black in the magnetic layer is not limited to simply imparting conductivity, and the relationship with the supply of a lubricant to the surface of the magnetic layer has been studied, but there are still many unclear points.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium exhibiting excellent electromagnetic conversion characteristics and capable of coping with high-density recording and having sufficient durability, and a method of manufacturing the same.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have reached the present invention. That is, the present invention relates to a magnetic recording medium having a non-magnetic underlayer and a magnetic layer in which a ferromagnetic powder is dispersed in a binder, on a flexible non-magnetic support. Is 0.2 to 4.0 μm
And the thickness of the magnetic layer is 0.05 μm or more and 0.25 μm
A magnetic recording medium, wherein the content of the non-magnetic conductive material in the magnetic layer is 1 part by weight or less with respect to 100 parts by weight of the ferromagnetic powder in the magnetic layer; On a support, a non-magnetic undercoat layer and a magnetic layer are sequentially
It is intended to provide a method for manufacturing a magnetic recording medium, wherein the magnetic recording medium described above is obtained by performing surface finishing after laminating by a sequential coating method.

That is, the present invention provides a magnetic recording medium containing almost no conductive material in a magnetic layer in order to increase the filling amount of magnetic powder in a magnetic layer in consideration of electromagnetic conversion characteristics in order to cope with high-density recording. It was done. When the thickness of the magnetic layer is 0.
A magnetic recording medium exhibiting more excellent electromagnetic conversion characteristics and durability as a magnetic recording medium by providing an undercoat layer of carbon black containing a specific amount of a lubricant under severe conditions for durability, from 0.05 μm to less than 0.25 μm. Is obtained. That is, the magnetic layer thickness of the highly filled smooth magnetic layer is 0.25 μm.
By using a specific undercoating layer in the case where the amount is less than the above, the supply of the lubricant to the surface of the magnetic layer is excellent, and the durability can be greatly improved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a magnetic recording medium of the present invention, a non-magnetic undercoat layer and a magnetic layer are sequentially formed on a non-magnetic support.
As the material for forming the flexible non-magnetic support used in the present invention, a material having flexibility and durability can be widely used, but is excellent in heat resistance and dimensional stability. Are preferred. Examples thereof include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as aramid and polycarbonate. The form of the nonmagnetic support is not particularly limited, but may be a film, a tape, or the like. In order to improve the adhesiveness between the nonmagnetic support and the magnetic layer, for example, a corona discharge treatment or a surface treatment with a surface modifying agent such as an amine aqueous solution, trichloroacetic acid, or phenols is performed. You may.

The undercoat layer according to the present invention generally contains a nonmagnetic powder and a binder. Non-magnetic powders include carbon black, titanium oxide, α-iron oxide, α-alumina, silicon carbonate, chromium oxide, cerium oxide, goethite, corundum, silicon nitride, silicon dioxide, tin oxide, magnesium oxide, zirconium oxide, calcium carbonate, Examples thereof include calcium sulfate, barium sulfate, and molybdenum disulfide. The shape is needle-like, spherical, polyhedral,
Any of plate shapes may be used. Among these, carbon black, particularly those having an oil absorption of 50 to 300 ml / 100 g and a particle size of 20 to 100 nm, more preferably 20 to 50 nm are preferable because of supporting a lubricant, and carbon black and other nonmagnetic powder are used. When used in combination,
It is preferable that the carbon rack be 80% or more. The nonmagnetic powder is used in an amount of 100 parts by weight or more, preferably 140 to 400 parts by weight, based on 100 parts by weight of the binder.

As the binder, it is preferable to use a resin having excellent adhesion to a support and abrasion resistance, a glass transition point of -100 to 150 ° C. and a number average molecular weight of about 1,000 to 150,000. Examples of the resin used include polyurethane resins, polyester resins, cellulose acetate butyrate, cellulose derivatives such as cellulose diacetate and nitrocellulose, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, and chlorides. Vinyl chloride resins such as vinyl-acrylic copolymers, various synthetic rubbers such as styrene-butadiene copolymers, epoxy resins, phenoxy resins, and the like. These may be used alone or as a mixture of two or more. be able to. The content of the binder resin in the undercoat layer is 2 to 50% by weight, particularly 5 to 3% by weight.
Preferably, it is used so as to be 5% by weight.

[0011] In addition to the above, a crosslinking agent,
A lubricant, a dispersant, and the like can be contained, and the amount thereof is not particularly limited as long as the present invention is not hindered, and known techniques for the magnetic layer can be applied to the type and dispersion method. As the lubricant, various lubricants such as aliphatic, fluorine, silicone, and hydrocarbon can be used. Examples of the aliphatic lubricant include fatty acids,
Examples thereof include fatty acid metal salts, fatty acid esters, fatty acid amides, and aliphatic alcohols. In particular, fatty acid esters are desirable, and for example, butyl esters such as oleic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and behenic acid, octyl esters, and glycerides can be used. It is desirable that the lubricant containing a fatty acid ester as a main component be contained in an amount of 3 to 13% by weight based on the nonmagnetic powder in the nonmagnetic undercoat layer.

The thickness of the nonmagnetic undercoat layer is 0.2 to 4.0.
μm, preferably 0.4 to 3.0 μm. On the non-magnetic undercoat layer, a magnetic layer paint in which ferromagnetic powder is dispersed in a binder is applied to form a magnetic layer. The ferromagnetic powder used for the magnetic layer has a major axis length of 0.01 to 1.
0 μm, preferably 0.01 to 0.2 μm, with an axial ratio of 0.
05-20, preferably 5-15, specific surface area of 40 m ²
/ G or more, the coercive force is 1700 Oe or more, preferably 20
Strong metal magnetic powder of 00 Oe or more, preferably acicular metal magnetic powder, or having a specific surface area of 35
m ² / g or more, average particle size is 1 to 50 nm, coercive force is 18
A plate-like ferromagnetic powder of 00 Oe or more is preferable. The amount of the magnetic powder to be used in the magnetic layer is preferably 60 to 90% by weight, particularly preferably 65 to 80% by weight. If the content of the magnetic powder is small, the recording density is not sufficient and a high-density magnetic recording medium is unlikely to be obtained. Conversely, if the content is more than 90% by weight, the durability of the magnetic recording medium may be reduced.

In the present invention, the binder is excellent in adhesion to the undercoat layer and abrasion resistance, and has a glass transition point of -100.
It is preferable to use a resin having a number average molecular weight of about 1000 to 150,000 at about 150 ° C. As the resin used, for example, polyurethane resin, polyester resin, cellulose acetate butyrate, cellulose diacetate,
Cellulose derivatives such as nitrocellulose, vinyl chloride
Vinyl chloride resins such as vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylic copolymers, various synthetic rubbers such as styrene-butadiene copolymers, epoxy resins, phenoxy resins, etc. And
These can be used alone or in combination of two or more. The binder resin is preferably used such that the content in the magnetic layer is 2 to 50% by weight, particularly 5 to 25% by weight.

By further containing a low molecular weight polyisocyanate compound having a plurality of isocyanate groups in the magnetic coating solution, a three-dimensional network structure can be formed in the magnetic layer and the mechanical strength thereof can be improved. Examples of such a low molecular weight polyisocyanate compound include a trimethylolpropane adduct of tolylene diisocyanate. Such a low molecular weight polyisocyanate compound is preferably used at a ratio of 10 to 50% by weight based on the binder resin. The content of the nonmagnetic conductive material in the magnetic layer may be 1 part by weight or less based on 100 parts by weight of the ferromagnetic powder, and may not be contained at all.

It is preferable to use a dispersant having a phosphate group as the dispersant of the present invention. As the phosphate group, polyether phosphate,
Polyoxyethylene alkyl phenyl phosphate and the like. Examples of the phosphate group-containing dispersant include phosphatidylcholine (lecithin), RE-610
(Made by Toho Chemical), PW-36 (made by Kusumoto Kasei) and the like.
In addition to the above-mentioned one containing a phosphate ester group as a dispersant, a fatty acid having 12 to 18 carbon atoms such as capric acid, lauric acid, myristic acid, oleic acid, and linoleic acid, an alkali metal or alkaline earth of this fatty acid A metal soap made of a metal salt, lecithin or the like may be used in combination. It is preferable that the content of the dispersant is usually in the range of 0.1 to 10% by weight, preferably 1 to 5% by weight in the magnetic layer.

Further, in the magnetic coating solution for forming the magnetic layer, various additives such as a lubricant, an abrasive, an antistatic agent, and a dispersant can be used, if necessary. As the lubricant, various lubricants such as aliphatic, fluorine, silicone, and hydrocarbon can be used. Examples of the aliphatic lubricant include fatty acids, fatty acid metal salts, fatty acid esters, fatty acid amides, and aliphatic alcohols. Examples of the fatty acid include oleic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid and the like.

Examples of the fatty acid metal salts include magnesium salts, aluminum salts, sodium salts and calcium salts of these fatty acids. Examples of the fatty acid ester include butyl ester, octyl ester, and glyceride of the above-mentioned fatty acid, and examples of the fatty acid amide include amide of the above acid, linoleic acid amide, and caproic acid amide. Examples of the aliphatic alcohol include lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, oleyl alcohol and the like. Examples of the fluorine-based lubricant include perfluoroalkyl polyether, perfluoroalkyl carboxylic acid, and the like. Examples of the silicone-based lubricant include silicone oil and modified silicone oil. In addition, solid lubricants such as molybdenum disulfide and tungsten disulfide, and phosphate esters can also be used. Examples of the hydrocarbon-based lubricant include paraffin, squalane, and wax. The amount of the lubricant used is such that the content in the magnetic layer is usually in the range of 0.1 to 10% by weight, preferably 1 to 7% by weight. In the case of a medium having a multilayer structure, the content of the lubricant in each layer may be changed.

As abrasives, for example, α-alumina,
β-alumina, γ-alumina, α-iron oxide, silicon nitride, boron nitride, titanium oxide, silicon dioxide, tin oxide, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, tungsten oxide, silicon carbide, Chromium oxide or the like is used alone or in combination. As a specific example, AKP-
20, AKP-30, AKP-50, HIT-50, H
IT-100, TF-100, TF-12 manufactured by Toda Kogyo
0, TF-140, Ishihara Sangyo FT-1000, FT-
2000, STT-4D, STT-30 manufactured by Titanium Industry
STT-65C, Nihon Kagaku Kogyo S-1, G5, G7
Among them, those having relatively high hardness are preferably used. Further, the number average particle size is preferably 0.5 μm or less. The amount of the abrasive used is preferably in the range of 1 to 10% by weight in the magnetic layer.

In manufacturing the magnetic recording medium of the present invention,
According to the prior art, the constituent materials of each layer are kneaded and dispersed in a solvent or the like to form a coating material, which may be applied by appropriately selecting an application method, and any means may be used as long as the conditions of the present invention are satisfied. For example, as the solvent used in the present invention, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, methanol, ethanol, propanol, alcohols such as isopropyl alcohol, methyl acetate, ethyl acetate, esters such as butyl acetate, diethyl ether, Examples thereof include ethers such as tetrahydrofuran, aromatic hydrocarbons such as benzene, toluene, and xylene, and aliphatic hydrocarbons such as hexane. As a coating method, sequential coating is preferable in that the interface between the two layers can be made uniform. In this case, it is preferable to apply a subbing nonmagnetic layer, dry the coating, and then apply the upper magnetic layer. In this case, a magnetic layer (a single layer or a plurality of layers) may be formed on the undercoat layer without performing a calender treatment after the application of the undercoat layer, so that the upper magnetic layer is applied, dried, and then calendered. By performing the treatment, a magnetic recording medium having good electromagnetic conversion characteristics and durability can be obtained. In particular, in the case of an ultra-thin and smooth magnetic layer as in the present invention, there is an effect that a lubricant is carried on the undercoat layer and a small amount is supplied to the surface of the magnetic layer.

In the present invention, the thickness of the magnetic recording layer is 0.1.
When the thickness is from 0.05 μm to less than 0.25 μm, and is thicker than 0.25 μm, it is not always suitable for high-density recording due to problems such as self-demagnetization loss and thickness loss. You. The coercive force of the ferromagnetic metal powder and the barium ferrite magnetic powder used in the present invention is 20.
It is preferably at least 00 Oe from the viewpoint of short wavelength recording. The surface roughness Ra of the magnetic layer is preferably 0.015 μm or less.
０．００0.001 μm is preferable.

In the present invention, the magnetic layer may be a single layer or a plurality of layers composed of two or more magnetic layers with another magnetic layer interposed. For example, in the case of two magnetic layers, a high-density magnetic recording medium can be provided by recording data at a short wavelength in an upper magnetic layer and recording a servo signal at a longer wavelength in a lower magnetic layer. In this case, the upper magnetic layer contains the above-described ferromagnetic metal powder and a binder resin, the specific surface area of the ferromagnetic metal powder is 40 m ² / g or more, and the thickness of the magnetic layer is 0.1 mm or more.
20 μm or less, surface roughness 0.01 μm or less, the lower magnetic layer contains a magnetic powder having a specific surface area of 30 m ² / g or more and a binder resin, and the magnetic powder is lower than the magnetic component used in the upper magnetic layer. Coercive, such as γ-Fe ₂ O ₃ ,
Barium ferrite, α-Fe and the like can be mentioned. The same binder resin as that for the upper magnetic layer is used.
It is desirable that the surface resistance of the surface of the magnetic layer be 10 ⁶ Ω / □ or less.

[0022]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited to the following Examples without departing from the scope of the invention. In the examples, “parts” indicates “parts by weight”. Surface roughness (Ra) is US ZY
KO non-contact type surface roughness meter (New View 10)
0) was measured using a 40 × lens. The output in the electromagnetic conversion characteristics was obtained by using a MIG head with a self-made spin stand, writing frequency of 500 KHz, and rotating speed of 36.
Measured at 0 rpm and measurement position R30 mm. Similarly, the resolution was measured at frequencies of 500 KHz and 250 KHz. Durability, using NEC FD1137C, temperature 25 ℃,
The measurement was performed in an environment with a humidity of 50%.

Example 1 In order to produce a non-magnetic undercoat layer, the following material components were kneaded, and then dispersed by a sand mill to prepare a coating solution. After adding 7 parts by weight of polyisocyanate (AD30 manufactured by Mitsubishi Chemical Corporation) to the obtained undercoat layer dispersion, a 75 μm-thick polyethylene terephthalate film was added.
The undercoat layer was applied with a dry thickness of 1.0 μm. Undercoat layer coating composition Carbon black 100 parts (SSA = 138m ² / g, DBP = 60ml / 100g, average particle size 24nm) Polyester polyurethane resin 20 parts Butyl stearate 4 parts Myristinic acid 1 part Methyl ethyl ketone 200 parts Cyclohexanone 100 parts

Further, in order to form a magnetic layer, the following material compositions were kneaded, and then dispersed by a sand mill to prepare a coating solution. Paint composition for magnetic layer Metal magnetic powder 100 parts (Fe / Co = 90/10, σs = 142emu / g, Hc = 1800Oe, BET = 49m ²
/ g) vinyl chloride copolymer 10 parts polyester polyurethane resin 4 parts α-alumina 8 parts butyl stearate 6 parts myristic acid 1 part methyl ethyl ketone 180 parts cyclohexanone 180 parts

To this dispersion, 5 parts by weight of a polyisocyanate (AD30, manufactured by Mitsubishi Chemical Corporation) was added, and filtered using a filter having an average pore diameter of 1 μm. The magnetic layer was coated on the undercoated layer so that the dry thickness of the magnetic layer was 0.2 μm, and dried with a dryer at 80 ° C. for several minutes. Thereafter, a calender (100 ° C.) treatment was performed, followed by heat treatment, and punched out to 3.5 inches to produce a magnetic disk.

Example 2 A medium was produced in the same manner as in Example 1 except that the dry thickness of the magnetic layer was 0.12 μm. Example 3 A medium was produced in the same manner as in Example 1, except that the dry thickness of the undercoat layer was 0.5 μm.

Example 4 A medium was produced in the same manner as in Example 1 except that the amount of the lubricant in the undercoat layer was changed from 4 parts by weight to 12 parts by weight. Example 5 In Example 1, carbon black (manufactured by Cabot: XC72R) 0.8 in 100 parts of metal magnetic powder in the magnetic layer.
A medium was obtained in the same manner as in Example 1 except that a part of the medium was added.

Comparative Example 1 A medium was produced in the same manner as in Example 1 except that the dry thickness of the magnetic layer of Example 1 was applied to 0.3 μm. Example 6 A medium was produced in the same manner as in Example 2 except that the magnetic layer was calendered at 70 ° C. Example 7 A medium was obtained in the same manner as in Example 1 except that the carbon black content in the undercoat layer coating solution was changed to 80 parts.

Comparative Example 2 A medium was produced in the same manner as in Example 1, except that the dry thickness of the undercoat layer was 0.1 μm. Comparative Example 3 The same as Example 1 except that the dry thickness of the undercoat layer was applied to 4.5 μm in Example 1.

Example 8 A medium was obtained in the same manner as in Example 1 except that the amount of butyl stearate in the coating solution for the undercoat layer was changed to 2% by weight. Comparative Example 4 A medium was produced in the same manner as in Example 5, except that the content of carbon black was changed to 1.5 parts.

[0031]

[Table 1]

Claims (7)

[Claims] In a magnetic recording medium having a non-magnetic underlayer and a magnetic layer in which a ferromagnetic powder is dispersed in a binder on a flexible non-magnetic support, the thickness of the non-magnetic underlayer is 0.2
To 4.0 μm, the thickness of the magnetic layer is 0.05 μm or more and less than 0.25 μm, and the content of the nonmagnetic conductive material in the magnetic layer is 100 parts by weight of the ferromagnetic powder in the magnetic layer. The magnetic recording medium is not more than 1 part by weight. 2. The magnetic layer has a surface roughness Ra of 0.015 μm.
2. The magnetic recording medium according to claim 1, wherein: 3. The ferromagnetic powder in the magnetic layer has a major axis length of 0.0
1 to 0.2 μm, axial ratio 5 to 15, specific surface area 40 m ² / g
3. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a needle-shaped metal magnetic powder having a coercive force of Hc2000 Oe or more. 4. The magnetic recording medium according to claim 1, wherein the surface resistance of the surface of the magnetic layer is 10 ⁶ Ω / □ or less. 5. The non-magnetic undercoat layer has an oil absorption of 50 to 300.
The magnetic recording medium according to any one of claims 1 to 4, wherein the magnetic recording medium contains carbon black having an average particle size of 20 to 50 nm / ml. 6. The non-magnetic undercoat layer contains a lubricant containing a fatty acid ester as a main component in an amount of 3 to 13% by weight based on the amount of non-magnetic powder in the non-magnetic undercoat layer. 3. The magnetic recording medium according to claim 1. 7. The magnetic recording medium according to claim 1, wherein a non-magnetic undercoat layer and a magnetic layer are sequentially laminated on a non-magnetic support by a sequential coating method and then subjected to a surface finish. Of manufacturing a magnetic recording medium.