JPH10340445A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which has high durability and is suitable for high-density recording. SOLUTION: The magnetic powder of the magnetic recording medium having a laminated structure composed of a nonmagnetic ground surface layer and a magnetic layer having a thickness of <=0.5 μm is ferromagnetic acicular metallic powder having an average major axis length (L)<=0.2 μm and an aspect ratio(K)<=15 or hexagonal ferromagnetic powder having an average grain size (L')<=0.07 μm and a planar ratio (K')<=10. The fluctuation (D) at the boundary between a ground surface layer and the magnetic layer is D<=2L/K or 2L'/K'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a non-magnetic underlayer containing a binder and non-magnetic particles on a flexible non-magnetic support, and a magnetic layer containing a ferromagnetic needle-like metal powder and a binder thereon. The present invention relates to a magnetic recording medium having a layer, particularly a magnetic recording medium having high durability and suitable for high-density recording.

[0002]

2. Description of the Related Art In recent years,
Magnetic recording media are strongly required to be adapted to high-density recording at high frequencies. To meet this demand, magnetic recording media using a metal thin film for the magnetic layer are also being studied.
Since the coating type magnetic recording medium is superior in terms of durability, corrosion resistance, and the like, improvement studies of the coating type magnetic recording medium from many directions are being conducted. In high-frequency recording, the problems of self-demagnetization loss and overwrite characteristics at the time of recording are large. Therefore, it is necessary to make the magnetic layer thin to avoid these problems. However, when the magnetic layer is simply made thin, durability and surface properties are deteriorated. For this reason, a magnetic recording medium having a multilayer structure in which a non-magnetic layer mainly composed of a non-magnetic powder and a binder is provided below a magnetic layer has been proposed (Japanese Patent Application Laid-Open Nos. 62-154225 and 62-154225). 62-159338
issue). However, it has been difficult to obtain a magnetic recording medium suitable for high-density recording, which is rich in durability and excellent in electromagnetic conversion characteristics, simply by adopting a multilayer structure.

JP-A-7-287833 discloses a coating for a non-magnetic underlayer containing a non-magnetic powder coated with antimony or tin, and contains a magnetic powder while the coating is still wet. It has been proposed to improve the surface properties of a magnetic layer by applying a coating material for the magnetic layer. However, if the upper layer is applied while the lower layer is in a wet state, if the applied thickness of the upper layer is small, the interface becomes rough and the electromagnetic conversion characteristics deteriorate. Also, the roughness of the interface affects the surface, and satisfactory surface properties cannot be obtained. The present invention
In order to solve these problems, in a magnetic recording medium formed by laminating a magnetic layer and a non-magnetic layer, interface roughness between both layers is small,
It is an object of the present invention to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and a method of manufacturing the same.

[0004]

According to the present invention, there is provided a non-magnetic underlayer containing a binder and non-magnetic particles on a flexible non-magnetic support, and further thereon a binder and a ferromagnetic needle. In a magnetic recording medium having a magnetic layer containing a ferromagnetic metal powder or a hexagonal ferromagnetic powder (hereinafter sometimes collectively referred to as a ferromagnetic metal powder), the ferromagnetic needle-shaped metal powder has an average major axis length (L) Is 0.20 μm or less and the aspect ratio (K) is 15
The following materials are used, and as the hexagonal ferromagnetic powder, the plate diameter (L ′) is 0.07 μm or less, and the plate ratio (K ′) is 10
The following are used, the thickness of the magnetic layer is set to 0.5 μm or less, and the fluctuation of the interface between the magnetic layer and the nonmagnetic underlayer (D)
Is set to D ≦ 2L / K or D ≦ 2L ′ / K ′, it is possible to obtain a magnetic recording medium which is rich in durability and excellent in electromagnetic conversion characteristics, particularly excellent in output and overwrite characteristics and suitable for high-density recording. .

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail. The magnetic recording medium according to the present invention has a non-magnetic underlayer provided on a flexible non-magnetic support and a magnetic layer laminated thereon. Things. If desired, another layer may be provided between the support and the nonmagnetic underlayer or on the magnetic layer.

[0006] As the flexible non-magnetic support, any one which has been conventionally proposed for use in this application can be used. Typical 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. be able to. The form of the flexible non-magnetic support is usually in the form of a film or tape. In order to improve the adhesiveness between the flexible non-magnetic support and the non-magnetic underlayer, the flexible non-magnetic support is subjected to a corona discharge treatment, an aqueous amine solution, trichloroacetic acid, phenols or the like. Surface treatment with a modifier may be performed.

The non-magnetic underlayer mainly comprises non-magnetic particles and a binder. It is preferable to use carbon black as the non-magnetic particles, but in addition, titanium oxide, α-
Iron oxide, α-alumina, silicon carbide, chromium oxide, cerium oxide, goethite, corundum, silicon nitride, silicon dioxide, tin oxide, magnesium oxide, zirconium dioxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, etc. are used. Can be

When carbon black is used as the non-magnetic particles, its volatile content is usually 3% or more, and 3 to 10%.
It is preferred that According to the findings of the present inventors, the content of volatile matter is related to the dispersibility of carbon black, and the dispersibility of carbon black generally improves when the volatile matter content is high up to about 10% of volatile matter. Carbon black having a volatile content of less than 3% has poor dispersibility and tends to deteriorate the durability of the magnetic recording medium. In addition, volatile matter is JIS
According to K-6221-1982, put carbon black in a magnetic or platinum crucible with a dropping lid,
It means the loss of volatilization when heated for one minute. Carbon black accounts for 30 to 98% by weight of the nonmagnetic underlayer, especially 35 to 85%.
It preferably occupies weight%.

The specific surface area of carbon black is 10
0 m ² / g or more, preferably 100 to 150 m ² / g.
m ² / g is more preferred. An organic lubricant such as an aliphatic carboxylic acid or an ester thereof is often contained in the nonmagnetic underlayer and the magnetic layer thereon, but if carbon black having a very small specific surface area is used, the nonmagnetic underlayer becomes The effect of holding these organic lubricants is weak, and the durability of the magnetic recording medium may be deteriorated.

The average particle size of the primary particles of carbon black is preferably from 20 to 100 nm. The binder is excellent in adhesion and abrasion resistance to a support, has a glass transition point of -100 to 150 ° C, and a number average molecular weight of 1,000 to 150.
It is preferable to use those having a molecular weight of about 000. Examples of commonly used binders include, for example, polyurethane resins, polyester resins, cellulose derivatives such as cellulose acetate butyrate, cellulose diacetate and nitrocellulose, vinyl chloride-vinyl acetate copolymers, and vinyl chloride-vinylidene chloride copolymers. Coalesce, vinyl chloride resins such as vinyl chloride-acrylic copolymers, various synthetic rubbers such as styrene-butadiene copolymers, epoxy resins, phenoxy resins, and the like. These may be used alone or in combination of two or more. Can be used. The binder is preferably used such that the content in the nonmagnetic underlayer is 2 to 50% by weight, particularly 5 to 35% by weight.

The binder reacts with a low molecular weight polyisocyanate compound having a plurality of isocyanate groups, for example, a crosslinking agent such as trimethylolpropane adduct of trizine diisocyanate to form a three-dimensional network structure in the nonmagnetic underlayer. It is preferably formed. In addition to the binder, carbon black and other non-magnetic particles, the non-magnetic underlayer may contain other components as desired.
For example, an organic lubricant such as a fatty acid or a fatty acid ester may be contained and diffused little by little on the surface of the magnetic layer. In this case, the ratio of the non-magnetic particles to the binder of the non-magnetic under layer is adjusted so that the organic lubricant is stably adsorbed on the non-magnetic particles in the non-magnetic under layer and can be diffused for a long time. Preferably, it is higher. Normally, setting this ratio to 3.6 or more by weight contributes to improvement in durability. In calculating the ratio, when a crosslinking agent is used, the crosslinking agent is also included in the binder.

The magnetic layer must contain a ferromagnetic acicular metal powder or a hexagonal ferromagnetic powder and a binder.
The thickness of the magnetic layer is 0.5 μm or less. 0.5 magnetic layer
If the thickness is larger than μm, it is not suitable for high-density recording in terms of self-demagnetization loss, overwrite characteristics, and the like. The thickness of the magnetic layer is 0.
It is preferably from 0.01 to 0.5 μm, particularly preferably from 0.05 to 0.3 μm.

The ferromagnetic acicular metal powder has an average major axis length (L) of 0.20 μm or less, preferably 0.12 μm or less, and an aspect ratio (K) of 15 or less, preferably 12 or less.
Use the following. The lower limit of the aspect ratio is preferably about 5. As other characteristics, the specific surface area by the BET method is preferably 40 m ² / g or more, particularly preferably 45 m ² / g or more. If a material having a small specific surface area is used, it is difficult to increase the filling amount of the magnetic powder in the magnetic layer. As for the magnetic characteristics, it is preferable that σs is 140 emu / g or more and coercive force (Hc) is 1500 Oe or more.

The hexagonal ferromagnetic powder has a plate diameter (L ') of not more than 0.07 μm, preferably 0.05 μm.
Hereinafter, those having a plate ratio (K ') of 10 or less are used. The most common hexagonal ferromagnetic powder is barium ferrite, but strontium, lead, calcium,
Those substituted with a metal such as cobalt are also used. The specific surface area of the hexagonal ferromagnetic powder by the BET method is 40 to 70.
m ₂ / g, coercive force is 1000 Oe or more, σs is 50 em
u / g or more is preferable.

The ferromagnetic acicular metal powder or the hexagonal ferromagnetic powder is used in the magnetic layer in an amount of 50 to 90% by weight, particularly 65 to 80% by weight.
It is preferable to include them so that If the ratio of the magnetic powder is small, it is difficult to increase the recording density. Conversely, if this ratio is too large, the durability of the magnetic recording medium tends to decrease. The ferromagnetic acicular metal powder or hexagonal ferromagnetic powder preferably has a specific surface area of 35 m ² / g or more, more preferably 40 m ² / g or more, as measured by the BET method.

The binder is excellent in adhesion and abrasion resistance to the nonmagnetic underlayer, and has a glass transition point of -100 to 150.
It is preferable to use one having a number average molecular weight of about 1,000 to 150,000 at a temperature of about ℃. Commonly used binders include, for example, polyurethane resins, polyester resins, 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 is preferably used such that the content in the magnetic layer is 2 to 45% by weight, particularly 5 to 25% by weight.

The binder reacts with a low molecular weight polyisocyanate compound having a plurality of isocyanate groups, for example, a crosslinking agent such as trimethylolpropane adduct of trizine diisocyanate to form a three-dimensional network structure in the magnetic layer. Is preferred. Thereby, the mechanical strength of the magnetic layer can be improved. Such a low molecular weight polyisocyanate compound is used in an amount of 10 to 50 based on the binder.
It is preferred to use it in a percentage by weight.

It is preferable that at least a part of the binder of the nonmagnetic underlayer and the binder of the magnetic layer be common, because the adhesion at the interface between both layers is improved. Further, as the common binder, it is preferable to use polyurethane, particularly polyurethane having substantially no magnetic group. The magnetic layer may further contain various conventional additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent. For example, it is preferable to use a dispersant having a phosphate group such as polyether phosphate, polyoxyethylene alkylphenyl phosphate, and the like. Examples of such a dispersant having a phosphate group include phosphatidylcholine (lecithin), RE-610 (manufactured by Toho Chemical), and PW-36 (manufactured by Kusumoto Kasei). Further, in addition to those containing a phosphate group, fatty acids having 12 to 18 carbon atoms such as capric acid, lauric acid, myristic acid, oleic acid, and linoleic acid, and alkali metals or alkaline earth metals of the fatty acids Salts, that is, metal soaps and 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, particularly 1 to 5% by weight in the magnetic layer.

As the lubricant, various lubricants such as aliphatic, fluorine, silicone and hydrocarbon can be used. As the aliphatic lubricant, for example, fatty acids, fatty acid metal salts, fatty acid esters, fatty acid amides, fatty alcohols and the like are used. As fatty acids, for example, oleic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, and the like are used. As the fatty acid metal salt, for example, magnesium salt, aluminum salt, sodium salt, calcium salt and the like of these fatty acids are used.
As the fatty acid ester, for example, butyl ester, octyl ester or glyceride of these fatty acids is used. As the fatty acid amide, for example, amides of these fatty acids, linoleic acid amide, caproic acid amide, and the like are used. As the aliphatic alcohol, for example, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, oleyl alcohol and the like are used. As the fluorine-based lubricant, for example, perfluoroalkyl polyether, perfluoroalkyl carboxylic acid, or the like is used. As the silicone-based lubricant, for example, silicone oil, modified silicone oil and the like are used. In addition, solid lubricants such as molybdenum disulfide and tungsten disulfide, and phosphoric acid esters can also be used. As the hydrocarbon lubricant, for example, paraffin, squalane, or the like is used.

[0020] The content of the lubricant in the magnetic layer is set to 0.1.
1 to 15% by weight is preferable, 3 to 10% by weight is more preferable, and 5 to 10% is particularly preferable. In the case of a magnetic recording medium having a magnetic layer having a multilayer structure, the lubricant content may be changed in each layer. For example, at the time of coating, the amount may be larger on the lower magnetic layer side and smaller on the upper magnetic layer side.
This is because if the lubricant in the upper magnetic layer is insufficient, it can be supplemented from the lower magnetic layer. In the case of a magnetic layer having a multilayer structure, the content of the lubricant is preferably from 1 to 15% by weight in the magnetic layer in total of all the layers, and from 3 to 10% by weight.
% Is more preferred.

Further, since the lubricant in the magnetic layer can be supplemented from the non-magnetic underlayer, it is sufficient that at least one of the magnetic layer and the non-magnetic underlayer contains the lubricant. And
The content of the lubricant is preferably from 0.1 to 15% by weight, more preferably from 3 to 10%, still more preferably from 3 to 10% by weight, and more preferably from 5 to 10%, based on the total weight of the magnetic layer and the non-magnetic underlayer. Particularly preferred.

As the abrasive, 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 commercially available product, AKP- manufactured by Sumitomo Chemical Co., Ltd.
20, AKP-30, AKP-50, HIT-50, H
IT-100, TF-100, TF-1 manufactured by Toda Kogyo
20, TF-140, Ishihara Sangyo FT-1000,
FT-2000, STT-4D, ST manufactured by Titanium Industry Co., Ltd.
T-30, STT-65C, N-Chemical S-
1, G5, G7, etc. Among them, those having relatively high hardness are preferably used. The average particle size of the abrasive is preferably 0.5 μm or less. The amount of abrasive used is
It is preferable that the content in the magnetic layer is in the range of 1 to 10% by weight.

As the antistatic agent, carbon black,
Metals and conductive compounds thereof, natural surfactants such as saponins, nonionic surfactants such as alkylene oxides and glycerins, higher alkylamines, quaternary ammonium salts, pyridinium salts and salts of other nitrogen-containing heterocyclic compounds Anionic surfactants containing acidic groups such as carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, sulfuric acid ester groups, and phosphoric acid ester groups, amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of amino alcohols Amphoteric surfactants and the like are used. In addition,
These surfactants can be used alone or as a mixture.

As carbon black, any of acetylene black, furnace black and thermal black can be used. Commercially available products include BLACKPEARLS 2000, 1000, 9 manufactured by Cabot Corporation.
00, 800, VULCANXC-72, RAVEN 8800, 8000, 70 manufactured by Columbian Carbon Co., Ltd.
00, # 3750B, # 3750, # 3 manufactured by Mitsubishi Chemical Corporation
250B, # 3250, # 950, # 850B, # 65
OB, # 45, # 40, # 5, MA-77, MA-7 and the like. These carbon blacks, alone,
Alternatively, a plurality of them can be used in combination. Further, the surface of the carbon black may be treated with a dispersant or the like, or a part of the surface may be graphitized.

Examples of the metal conductive compound include tin oxide,
Indium tin oxide or the like can be used. Usually, the content of the antistatic agent is 0.1 to 1 in the magnetic layer.
The range is 0% by weight. As is clear from the above description, some additives have several effects at the same time.

In the present invention, the magnetic layer may be a single layer or a plurality of layers composed of two or more magnetic layers. For example, in the case of two magnetic layers, a high-density magnetic recording medium can be obtained by recording data at a short wavelength on an upper magnetic layer and recording a servo signal at a longer wavelength on a lower magnetic layer. In this case, for example, the upper magnetic layer has a thickness of 0.5 μm or less containing the above-described ferromagnetic powder and binder and a surface roughness of 0.02 μm or less, and the lower magnetic layer has a specific surface area of 30 m ^2. / G
As described above, a magnetic powder having a lower coercive force than the ferromagnetic powder used for the upper magnetic layer, for example, γ-Fe ₂ O ₃ , barium ferrite, α-Fe, or the like may be used. The binder may be the same as that of the upper magnetic layer.

The lower magnetic layer and the upper magnetic layer may be manufactured by either a sequential coating method or a simultaneous coating method, but the sequential coating method is preferable in that the interface between the two layers can be made uniform. The magnetic layer is applied and dried to reduce the residual solvent amount to 1 ×
It is preferable to apply the upper magnetic layer after the ^{concentration is adjusted} to 10 ^-15 to 1 × 10 ^-11 mg / μm ³ . In the magnetic recording medium according to the present invention, the components constituting the nonmagnetic layer underlayer and the magnetic layer are kneaded and dispersed together with an appropriate solvent to form a uniform coating, which is then coated on a flexible nonmagnetic support. It is manufactured by applying to

Examples of the solvent include ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; alcohols such as methanol, ethanol, propanol and isopropanol; esters such as methyl acetate, ethyl acetate and butyl acetate; diethyl ether and tetrahydrofuran. Ethers, aromatic hydrocarbons such as benzene, toluene, and xylene, and aliphatic hydrocarbons such as hexane are used.

The preparation of the coating material for forming the nonmagnetic underlayer and the magnetic coating material for forming the magnetic layer can be carried out by a conventional method using a conventional kneading and dispersing apparatus. The application of the non-magnetic underlayer and the magnetic layer can be performed by a conventional method using a conventional coating device such as gravure coating, roll coating, blade coating, or extrusion coating. Normally, a non-magnetic underlayer is applied, dried, and then a magnetic layer is applied thereon. According to such a sequential coating method, the fluctuation (D) of the interface between the non-magnetic underlayer and the magnetic layer falls within the range defined by the present invention of D ≦ 2L / K or D ≦ 2L ′ / K ′. Easy to put down. Note that D ≦ 2L / K or D ≦ 2L ′ / K ′ conceptually means that the fluctuation of the interface is within two magnetic powders. In a preferred embodiment of the present invention, after the non-magnetic underlayer is applied, the residual solvent amount of the non-magnetic underlayer is 1
× dried 10 ^-15 to be ^{~1 × 10 -11 mg / μm 3} , and then applying a coating of the magnetic layer thereon. In this way, disturbance at the interface between the two layers can be suppressed to a minimum, and a magnetic recording medium with low electromagnetic conversion characteristics, especially noise, can be obtained. Further, the amount of residual solvent in the entire magnetic recording medium can be reduced, and a magnetic recording medium having excellent durability can be obtained.

The magnetic layer is usually applied with a magnetic field before drying. After drying, the surface is smoothed by calendering. Normally, a roll of a calendering treatment is used in combination of a metal roll and a heat-resistant synthetic resin roll, but it is also possible to use a combination of a metal roll alone. The processing temperature is preferably from 70 to 120C, and the linear pressure is preferably from 200 to 500 kg / cm. When a crosslinking agent such as a trimethylolpropane adduct of tolylene diisocyanate is used in combination, a temperature of 50 to 70 ° C.
Curing for 160 hours is performed to cause a crosslinking reaction between the binder and the crosslinking agent.

The surface roughness of the magnetic recording medium according to the present invention is:
To minimize the distance between the head and the magnetic layer, 0.02
It is preferably not more than μm. In order to achieve this surface roughness, it is necessary to use fine magnetic powder having a large specific surface area and to sufficiently disperse the magnetic powder when preparing a coating material for the magnetic layer. In addition, it is preferable that the calendering after the application of the magnetic layer is also performed at a relatively high temperature. In consideration of the adsorption to the head, the surface roughness is 0.001 to 0.02.
μm is preferred.

Further, in the magnetic recording medium according to the present invention, the non-magnetic underlayer and the magnetic layer together have a residual solvent amount of 2 × 10
It is preferably dried so as to be ^-12 mg / μm ³ or less. When the amount of the residual solvent is larger than this, not only does the durability decrease, but also the interface between the nonmagnetic underlayer and the magnetic layer changes with time, the electromagnetic conversion characteristics deteriorate, and noise tends to increase. More preferably, the residual solvent content of the combined nonmagnetic underlayer and magnetic layer is 5 × 10 ⁻¹³ mg / μm ³ or less. The amount of the residual solvent can be reduced by adjusting the conditions of the drying, calendering, and curing steps after the application of the magnetic layer.

In the magnetic recording medium of the present invention, the preferred ranges for each component are as described above.
Next, two preferred embodiments of the present invention will be described below as combinations thereof. The first embodiment has a non-magnetic underlayer containing a binder and carbon black on a flexible non-magnetic support, and further has a binder and a BET specific surface area of at least 40 m ² / g. This is a magnetic recording medium having a magnetic layer containing magnetic metal powder. In this case, the non-magnetic underlayer and the magnetic layer contain a common binder, and this binder is adsorbed more on the carbon black of the non-magnetic underlayer than on the ferromagnetic metal powder of the magnetic layer. More preferably, The carbon black has a specific surface area of 120 m ² / g or more, an average particle diameter of 30 nm or less, and a DBP oil absorption of 70 ml / 100.
g or less and a pH of 4 or less are particularly preferred.

The second embodiment has a non-magnetic underlayer made of carbon black and a polyurethane resin on a flexible non-magnetic support, and further has a binder and a specific surface area of 35 m ² / g as determined by the BET method. In the magnetic recording medium having a magnetic layer containing the above ferromagnetic metal powder, the carbon black of the non-magnetic underlayer has a specific surface area of 100 m ² / g or more and a volatile content of 3%.
The magnetic recording medium is as described above. When the above two embodiments are used, the fluctuation (D) of the interface between the nonmagnetic underlayer and the magnetic layer is within the range defined by the present invention, which is D ≦ 2L / K or D ≦ 2L ′ / K ′. It is easy to settle down.

[0035]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples. "Parts" and "%" indicate "parts by weight" and "% by weight", respectively. Examples 1 to 7, Comparative Examples 1 and 2 , Preparation of paint for non-magnetic underlayer: Each component shown in Table 1 below was mixed to prepare a paint for a non-magnetic underlayer. The preparation method is carbon black, polyester polyurethane and solvent 120.
Parts were mixed and kneaded.
% And dispersed by a sand mill. To this, butyl stearate, oleic acid, a crosslinking agent, and the remaining solvent were added, and the mixture was filtered through a filter having an average pore diameter of 1 μm to obtain a paint.

[0036]

Table 1 Table 1 Paint for non-magnetic underlayer Carbon black 100 parts (Specific surface area by BET method: 138 m ² / g, DBP oil absorption: 60 ml / 100 g, average primary particle diameter: 24 nm) Polyester polyurethane resin 20 parts Crosslinking Agent 7 parts Butyl stearate 4 parts Oleic acid 1 part Solvent 400 parts (Mixture of methyl ethyl ketone 62.5%, cyclohexanone 37.5%)

Preparation of paint for magnetic layer: A paint for magnetic layer was prepared by mixing each component shown in Table 2 below. The preparation method is as follows: magnetic powder, vinyl chloride-based copolymer, polyester polyurethane resin, α-alumina, carbon black and some components of the solvent are mixed and kneaded at a solids concentration of 50%.
A solvent was added and the mixture was dispersed with a sand mill at a solid content of 30%.
To this, butyl stearate, oleic acid, a crosslinking agent, and the remaining solvent were added, and the mixture was filtered through a filter having an average pore diameter of 1 μm to obtain a paint.

[0038]

Table 2 Paint for magnetic layer Magnetic powder 100 parts Vinyl chloride copolymer 10 parts Polyester polyurethane resin 4 parts Crosslinking agent 5 parts α-alumina 8 parts (average particle diameter 0.2 μm, ratio by BET method) Surface area 9 m ² / g) Carbon black 3 parts Butyl stearate 6 parts Oleic acid 1 part Solvent 360 parts (mixture of 50% methyl ethyl ketone and 50% cyclohexanone)

Coating and post-treatment: A coating for a nonmagnetic underlayer was applied to a 75 μm-thick polyethylene terephthalate film by an extrusion method so that the dry thickness was 1.0 μm. After drying, a coating material for a magnetic layer was applied thereon by an extrusion method so as to have a dry film thickness of 0.3 μm, and dried at 80 ° C. for several seconds. Subsequently, after calendering at 100 ° C. and 200 kg / cm, curing was performed at 60 ° C. for 72 hours. This is 3.
A magnetic disk was punched out into a 5-inch disk, and its characteristics were evaluated. The results are shown in Table-3. In addition, the measurement was performed as follows.

Residual solvent amount: Measured with a gas chromatograph (GC-5A, Shimadzu Corporation). Column length 1m, packing material "Ch
romsorb 101 "(Johns Manvi
, helium as a carrier gas, and flowed at a speed of 50 m / min. In the measurement, the sample was heated at 150 ° C. to evaporate the residual solvent.

Surface roughness (Ra): Measured using a non-contact surface roughness meter (New View 100) manufactured by ZYKO, USA, using a 40 × lens. Durability: NEC floppy disk drive FD11
Measured at 37 ° C and 50% RH using 37C

Output: Using a MIG head with a gap length of 44 μm using a self-made spin stand, and a writing frequency of 50
360 rpm at 0 kHz, measurement position R30 mm
Measured at The output of Example 1 was set to 100. Overwrite: 250k after writing at 500kHz
Measured by overwriting at Hz.

C / N: spectrum analyzer Adva
The output and noise at 500 kHz were measured and calculated using ntest TR4171. Interfacial variation (D): A magnetic recording medium is cut perpendicular to the surface using a diamond cutter on a microtome. The cut surface is photographed at a magnification of 150,000 using a transmission electron microscope. The length 2.0μm portion of the cross-section 200 equally divided on photographs, the sum of the squares of the distances from the center line (a) to the interface (y _n)

[0044]

(Equation 1)

The center line (a) at which is minimized is determined. Interfacial fluctuation (D) is calculated by the following from the center line (a) as the arithmetic average of the absolute value of the distance to the interface (k _n).

[0046]

(Equation 2)

[0047]

[Table 3]

Examples 8 to 10 and Comparative Examples 3 to 5 Preparation of coating solutions: From the components shown in Tables 4 and 5 below,
Using a sand mill, a coating solution for the non-magnetic underlayer and a coating solution for the magnetic layer were prepared. However, the preparation of the coating solution for the magnetic layer was performed as follows. First, 30% by weight of a vinyl chloride copolymer was added to the alumina particles, and a solvent was further added to adjust the solid content concentration to 35%, followed by dispersion with a sand mill. Further, the remaining vinyl chloride copolymer and polyester polyurethane were added to the ferromagnetic metal powder, and a solvent was further added to knead to a solid content concentration of 75%, and then carbon black and a solvent were added thereto to obtain a solid content concentration of 35%. And dispersed with a sand mill. Next, the two mixtures were combined, tridecyl stearate, oleic acid and the remaining solvent were added, and the mixture was further subjected to a dispersion treatment to obtain a coating solution. In addition,
The carbon black of the nonmagnetic underlayer is as shown in Table 6 below, and as the polyester polyurethane of the binder,
The following Table 7 was used.

[0049]

Table 4 Coating solution for non-magnetic underlayer 100 parts Carbon black 100 parts Polyester polyurethane 20 parts Methyl ethyl ketone 200 parts Cyclohexanone 200 parts

[0050]

Table 5 Coating solution for magnetic layer 100 parts of ferromagnetic metal powder (Fe / Co = 87/13 (atomic ratio), σs = 150 emu / g, Hc = 1700 Oe, specific surface area by BET method = 42 m ²⁾ / G) Vinyl chloride copolymer 12 parts Polyester polyurethane (same as that of the non-magnetic underlayer) 6 parts α-alumina (particle size 0.2 to 0.4 μm) 10 parts Carbon black 3 parts (furnace black; average) Particle diameter = 25 nm, specific surface area by BET method = 130 m ² / g, DBP oil absorption = 65 ml / 100 g) 3 parts of carbon black (thermal black MT-CI; particle diameter = 200 to 500 nm, average particle diameter = 350 nm, BET method) specific by surface area = 8m ² / g, DBP oil absorption = 7 ml / 100 g) tridecyl stearate 7 parts oleic acid 1 part methyl Ethyl ketone 170 parts Cyclohexanone 170 parts

[0051]

[Table 6]

[0052]

[Table 7]

The amount of adsorption was measured using tetrahydrofuran 30
20 parts by weight of the binder is added to 0 parts by weight and dissolved. 100 parts by weight of powder is added to this solution, and the mixture is dispersed for 10 hours using a paint shaker. Then, the mixture is separated into a precipitate and a supernatant by an ultracentrifuge, and the concentration of the binder in the supernatant is measured.

Coating and post-treatment: A trimethylolpropane adduct of tolylene diisocyanate (manufactured by Mitsubishi Chemical Corporation, AD
30) was added, and the mixture was filtered through a filter having an average pore diameter of 1 μm to prepare a coating material. The coating material for the underlayer prepared above was applied to a polyethylene terephthalate film having a thickness of 32 μm by an extrusion method so as to have a dry thickness of 0.7 μm, and was sufficiently dried. Next, a coating material for a magnetic layer was applied thereon by the extrusion method and dried at 80 ° C. No alignment treatment was performed.
Then, after calendering at 80 ° C. and 300 kg / cm, it was punched into a disk. 60 this disk
Curing was carried out at 72 ° C. for 72 hours.

Evaluation of physical properties: For the magnetic disk obtained above, 60 ° gloss as an index of surface gloss and Haz
e, surface roughness, 35 Kft as an index of electromagnetic conversion characteristics
The output at pi, overwriting, and output fluctuation were measured as follows. The results are shown in Table-8. 60 ° gloss; BYK before calendering
Measured with a Gardner surface gloss meter. Haze: BYK G before calendar processing
Measure the intensity of the reflected light that deviates from the 20 ° glossy reflected light receiving unit with an ardner surface gloss meter.

Surface roughness: Non-contact surface roughness meter (Z
YGO). Playback output and overwrite; playback output is 35Kftp
The waveform of the signal recorded at the recording density of i was captured and read by an oscilloscope. Overwrite is 17.5Kf
After recording at a recording density of tpi, the output at that time was measured, then recording was performed at a recording density of 35 Kftpi, and reproduction was performed, overwriting the ratio of the output of 17.5 Kftpi before and after weight recording. The rotation speed of the disk is 500r
At pm, the head is a ferrite MIG head.

Output fluctuation value: 500 while contacting the head
The evaluation was based on the fluctuation of the output value before and after the rotation of 10,000 times. ○ Fluctuation is less than 5% △ Fluctuation is 5-10% × Fluctuation exceeds 10%

[0058]

[Table 8]

Example 11 and Comparative Examples 6 to 9 The output was obtained by using a MIG head in a spin stand, setting the rotation frequency to 2945 rpm, the measurement position to a point 20 mm from the center, and changing the recording frequency to change the recording frequency. The measurement was performed, and the values were displayed as relative values with the output of Example 1 taken as 100 (Table-3 shows the values at 40 K FTPI). The durability is 25 ° C and humidity 50% RH with the above spin stand.
After running for 120 hours with the rotation speed of 2945 rpm and the measurement position at a point 20 mm from the center in the atmosphere of
The output at 0KFTPI was measured and the output before traveling was 100
Was evaluated.

Preparation of paint for non-magnetic underlayer; Table 9 below
After blending and kneading each of the above components, the mixture was dispersed with a sand mill. A crosslinking agent (trimethylolpropane adduct of tolylene diisocyanate; AD manufactured by Mitsubishi Chemical Corporation)
30) was added in an amount of 6 parts by weight, and the mixture was filtered using a filter having an average pore diameter of 3 μm to obtain a paint for a nonmagnetic underlayer.

[0061]

Table 9 Non-magnetic base layer coating composition Lower layer coating composition Carbon black 100 parts Polyester polyurethane resin 20 parts Tridecyl stearate 3 parts Oleic acid 2 parts Methyl ethyl ketone 300 parts Cyclohexanone 100 parts

Preparation of paint for magnetic layer: The components shown in Table 10 below were blended and kneaded, and then dispersed by a sand mill.
A cross-linking agent (AD30 manufactured by Mitsubishi Chemical Corporation) is added to the dispersion liquid for 5 minutes.
In addition, the mixture was filtered with a filter having an average pore diameter of 1 μm to obtain a coating material for a magnetic layer.

[0063]

Table 10 Paint for magnetic layer Metal magnetic powder 100 parts (Fe—Co—Al alloy magnetic powder, average major axis length (L) = 0.11 μm, aspect ratio (K) = 10, coercive force = 1620 Oe Σs = 140 emu / g) Vinyl chloride copolymer 15 parts Polyester polyurethane resin having a sulfonic acid group 4 parts α-alumina 10 parts Carbon black 8 parts Tredecyl stearate 9 parts Oleic acid 1 part Methyl ethyl ketone 280 parts Cyclohexanone 120 parts

Manufacturing and Characteristic Evaluation of Magnetic Recording Medium; Thickness 6
The above-mentioned nonmagnetic underlayer coating material was applied to a 2 μm polyethylene terephthalate film so as to have a specified dry thickness, and dried at 80 ° C. for several minutes. Next, the above-mentioned coating material for a magnetic layer was dried thereon to a dry thickness of 0.3 μm.
And dried. 80 ° C, 30
After subjecting to a calendar treatment of 0 kg / cm, the diameter is 3.
Punched into a 5 inch disk. This was allowed to stand still at 50 ° C. for 48 hours and cured to obtain a magnetic recording medium. For this magnetic recording medium, the output and durability at 40 K FTPI, and D50 were measured. Table-Results
11 is shown.

[0065]

[Table 11]

The carbon black of the underlayer used was as follows. Underlayer carbon black A; specific surface area 120 m ² /
g, volatile content 3.5%, DBP absorption 65ml / 100
g, average particle size of primary particles 24 nm, carbon black B of the underlayer; specific surface area 240 m ² /
g, volatile content 1.0%, DBP absorption 165 ml / 100
g, average particle size of primary particles 28 nm

[0067]

According to the present invention, it is possible to provide a magnetic recording medium that is rich in durability and excellent in electromagnetic conversion characteristics, particularly excellent in output and overwrite characteristics, and suitable for high-density recording.

Claims (8)

[Claims] A non-magnetic underlayer containing a binder and non-magnetic particles is provided on a flexible non-magnetic support, on which an average major axis length (L) is 0.20 μm or less and an aspect ratio ( K) The ferromagnetic needle-shaped metal powder having a thickness of 15 or less and a binder containing a binder having a thickness of 0.1 mm.
A magnetic recording medium having a magnetic layer of 5 μm or less, wherein the variation (D) at the interface between the magnetic layer and the nonmagnetic underlayer is D ≦ 2L / K
A magnetic recording medium characterized by the following. 2. A non-magnetic underlayer containing a binder and non-magnetic particles is provided on a flexible non-magnetic support, and further, a plate diameter (L ') is 0.07 μm or less, and a plate ratio ( K ′) containing a hexagonal ferromagnetic powder of 10 or less and a binder, and having a thickness of 0.5 μm
A magnetic recording medium having the following magnetic layer, wherein the variation (D) at the interface between the magnetic layer and the nonmagnetic underlayer is D ≦ 2L ′ / K ′. 3. The magnetic recording medium according to claim 1, wherein the surface roughness of the magnetic layer is 0.02 μm or less. 4. The magnetic recording medium according to claim 3, wherein the ferromagnetic needle-like metal powder or the hexagonal ferromagnetic powder has a specific surface area by BET method of 35 m ² / g or more. 5. The non-magnetic underlayer and the magnetic layer include a common binder, and the binder is greater for the carbon black of the non-magnetic layer than for the ferromagnetic metal powder of the magnetic layer. The magnetic recording medium according to claim 3, wherein the magnetic recording medium is adsorbed. 6. The nonmagnetic underlayer contains carbon black and a polyurethane resin, and the carbon black has a specific surface area of 100 m ² / g or more and a volatile content of 3% or more. 6. The magnetic recording medium according to 5. 7. A coating for a non-magnetic underlayer containing a binder and non-magnetic particles on a flexible non-magnetic support, followed by drying to form a non-magnetic underlayer. 7. The method for manufacturing a magnetic recording medium according to claim 1, wherein a coating material for a magnetic layer containing a binder and a binder is applied. 8. A coating for a non-magnetic underlayer containing a binder and non-magnetic particles on a flexible non-magnetic support, followed by drying to reduce the residual solvent amount to 1 × 10 ^-15 to 1 × 10 ^-11. mg / μm ³
7. A method for manufacturing a magnetic recording medium according to claim 1, wherein a non-magnetic underlayer is formed, and a magnetic layer paint containing a ferromagnetic powder and a binder is applied thereon.