JPH0612651A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium excellent in electromagnetic conversion characteristic, traveling property, and durability. CONSTITUTION:This magnetic recording medium has a magnetic layer containing at least a ferromagnetic iron oxide powder and a binder resin on a nonmagnetic supporting body. The magnetic layer has <=0.015mum surface roughness Ra and 125000-250000 projections of >=0.03mum height per one mm<2> on its surface. Thereby, the obtd. magnetic recording medium has excellent electromagnetic conversion characteristic, traveling property, and durability in good balance.

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 excellent in electromagnetic conversion characteristics and durability.

[0002]

2. Description of the Related Art Obtained by forming a magnetic layer by coating a magnetic coating material prepared by mixing and dispersing ferromagnetic powder, binder resin, organic solvent and other necessary components on a substrate such as polyester film. The so-called coated magnetic recording medium is widely used as a recording tape, a video tape, a computer data cassette, a floppy disk, or the like.

In recent years, the density of magnetic recording has been increasing, and in high density recording with a recording wavelength of 1 μm or less, for example, when the recording density is smaller than this, there is no problem in practical use of the magnetic layer surface. Even fine irregularities and non-uniformities cause a decrease in output due to spacing loss, an increase in noise, and the occurrence of dropouts.Therefore, as the density of magnetic recording media increases, the smoothness of the magnetic layer surface is improved. Efforts are being made to raise it.

[0004]

However, although the electromagnetic conversion characteristics are improved when the surface of the magnetic layer is smoothed, it directly contacts and slides with the magnetic layer such as a guide pin that constitutes a running system of the magnetic head or tape. Since the substantial contact area between the moving member and the magnetic layer is increased, friction is increased and sticking is caused.As a result, running performance and running stability in the recording / reproducing apparatus are deteriorated. Or, damage due to abrasion of the magnetic layer or peeling is more likely to occur, resulting in an increase in dropout and a decrease in durability.

Therefore, as a method for achieving both surface smoothness, running property, and durability, a method of adding a lubricant to the magnetic paint,
Alternatively, a method of applying a lubricant to the surface of the magnetic layer is known. As such a lubricant, mineral oil, silicone oil, higher alcohol, higher fatty acid, fatty acid ester,
Animal oil, vegetable oil, etc. have been used. However, these lubricants, when used in a small amount, have a low effect of reducing friction and an effect of improving durability. Also, if the amount used is increased to obtain a sufficient effect, the mechanical strength of the magnetic coating decreases due to plasticization, and the wear of the magnetic layer easily occurs, or the surface of the magnetic layer is likely to be stored during storage. A phenomenon called blooming occurs in which a large amount of lubricant oozes out, which may rather deteriorate the running performance.

In addition, the environment in which magnetic recording media are used is becoming more and more diverse, and magnetic recording media that can guarantee stable running and high durability even under severe operating conditions such as low temperature and low humidity or high temperature and high humidity are available. Is sought after,
The above-mentioned known lubricants have not always been sufficient. On the other hand, as another means for improving the running property and durability, a method of adding hard fine particles called an abrasive to the magnetic layer is also known. However, although the running durability is certainly improved by adding a considerable amount of the polishing agent, the surface property of the magnetic layer may be deteriorated to impair the electromagnetic conversion characteristics. As described above, it is difficult to obtain a magnetic recording medium having a good balance between electromagnetic conversion characteristics and running durability and excellent characteristics.

[0007]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied to obtain a well-balanced magnetic recording medium excellent in electromagnetic conversion characteristics, runnability, and durability. As a result, the surface roughness of the magnetic layer and It has been found that the protrusion density on the surface of the magnetic layer is related to these characteristics, and the above problems are solved in the case of a specific combination thereof, and the present invention has been completed.

That is, the gist of the present invention is, in a magnetic recording medium having a magnetic layer containing at least a ferromagnetic iron oxide powder and a binder resin on a non-magnetic support, the surface roughness Ra of the magnetic layer is 0.015 μm or less. And the number of protrusions having a height of 0.03 μm or more on the surface of the magnetic layer is 12 per square mm.
The magnetic recording medium is characterized by the presence of 5,000 to 250,000.

When the surface roughness Ra of the magnetic layer is 0.015 μm or less, a sufficient reproducing output can be obtained because the spacing loss between the magnetic head and the magnetic recording medium is reduced, and this value should be small. The smaller the value, the more the electromagnetic conversion characteristics can be improved. However, the surface roughness Ra of the magnetic layer is 0.005 to 0.015 μm, because sufficient runnability and durability may not always be obtained in an ultra-smooth magnetic layer whose surface roughness Ra is too small. Is preferred.

In the present invention, when the protrusion density of the protrusions having a height of 0.03 μm or more is less than 125,000 per square mm, the effect of reducing the friction between the magnetic layer and the magnetic head or the traveling system member is small, The running performance and durability cannot be sufficiently enhanced. When the projection density of the projections having a height of 0.03 μm or more is more than 250,000 per square mm, the electromagnetic conversion characteristics are adversely affected.

It is preferable that the protrusions are evenly distributed over the entire surface of the magnetic recording layer, for example, locally.
Even if the protrusion density is uneven, the effect of the present invention may be impaired. Such protrusions are formed by using Al ₂ O ₃ , TiO ₂ , SiO which are conventionally used abrasives.
It can be obtained by adding hard fine particles such as ₂ , SnO ₂ , Cr ₂ O ₃ , and α-Fe ₂ O ₃ to the magnetic coating material. In addition, fine particles having excellent wear resistance and lubricity, for example, inorganic fine powder such as graphite, MoS ₂ and TiS ₂ ,
It can be obtained by adding resin fine powder such as silicone resin, polyethylene, polytetrafluoroethylene, urea resin and the like.

In the case of projections formed by these fine particles, when the projection height is larger than the radius of the particles, they easily fall off by sliding with the magnetic head or the traveling system member, and so-called powder drop easily occurs. It is desired that the projections are smaller than the radius of the particles because they may stain the system or damage the magnetic layer. Further, the protrusions having a height smaller than 0.03 μm are buried in the magnetic coating film when they come into contact with the magnetic head or the traveling system member, so that the magnetic head or the traveling system member and the magnetic coating film make a real contact. There is no need to limit the protrusion density because it does not work to reduce the area.

In the present invention, the height of the protrusions is determined by the scanning toluene microscope (STM), atomic force microscope (AFM),
It can be measured using Elionix. As a simpler method, as shown in FIG. 1, in the case of the protrusion 2'formed by the spherical particles 2 in the magnetic layer 1, the radius a (μm) of the exposed portion on the surface of the magnetic layer and the spherical particles Radius b (μ
The height d (μm) of the protrusion can be determined from m) as d = b− (b ² −a ² ) ^1/2 .

The ferromagnetic iron oxide powder used in the present invention is not limited to the ferromagnetic γ-iron oxide powder, but if it is the ferromagnetic iron oxide powder, the ratio of divalent iron / trivalent iron is particularly limited. Other examples include Co-doped ferromagnetic γ-iron oxide powder, barium ferrite powder, and strontium ferrite powder. The shape and size of the ferromagnetic iron oxide powder are not particularly limited, but from the viewpoint of electromagnetic conversion characteristics, those having a needle shape or a plate shape are preferable, and as the size, in order to achieve a high recording density, Those having a primary particle diameter of 0.05 μm or less and a BET specific surface area of 30 m ² / g or more are particularly preferable, but larger particles may be used. The ferromagnetic powder can be used without particular limitation as to pH and whether or not surface treatment is performed.

Examples of the binder resin used in the present invention include thermoplastic resins, thermosetting resins, radiation curable resins, and mixtures thereof which have been used in magnetic recording media. Among them, vinyl chloride resin,
Cellulose resins are preferable because they have high dispersibility of ferromagnetic powder and urethane resins are excellent in wear resistance of the magnetic coating film.

In particular, at least one of the binder resins is --COOM, --SO ₃ M, --OSO ₃ M,
At least one polar group of —PO ₃ M ₂ , —OPO ₃ M ₂ , and —NR ¹ R ² R ³ X (where M is a hydrogen ion, an alkali metal ion, or an optionally substituted ammonium ion). And R ¹ , R ² and R ³ represent hydrogen or an aliphatic hydrocarbon group and may be the same or different from each other. X represents a halogen ion) 10 ⁻⁶ to 10 ⁻ per 1 gram of the resin. A resin having ⁴ mol is preferable. Further, in —NR ¹ R ² R ³ X, R ¹ ,
R ² and R ³ are preferably an aliphatic hydrocarbon group having a small number of carbon atoms, and particularly preferably an aliphatic hydrocarbon group having a carbon number of 1 to 6 in order to bond more strongly to the surface of the ferromagnetic powder or other powder. .

Examples of the polar group-containing resin include the above-mentioned polar group-containing polyurethane resin, polyester resin, vinyl chloride resin, vinyl chloride-acrylic copolymer,
Examples include nitrocellulose resin. These polar group-containing resins are strongly adsorbed on the surface of ferromagnetic powders and other powders, and their steric repulsion weakens the cohesive force between powders, resulting in excellent dispersibility and smoothing of the magnetic layer surface. It is considered effective. Further, since the powder and the resin are strongly bonded to each other, it is considered that the powder is prevented from falling off and the magnetic layer is peeled off, which is also effective in improving the durability.

The binder resin may be hardened by adding a hardener such as isocyanate. In the present invention, the content of the total binder resin (including the curing agent) in the magnetic layer is usually 10 per 100 parts by weight of the ferromagnetic powder.
-40 parts by weight, more preferably 15-30 parts by weight. When the content of the total binder resin is higher than the above range, the filling degree of the ferromagnetic powder is low and it is difficult to obtain sufficient electromagnetic conversion characteristics. On the contrary, when the content is low, the durability may be deteriorated.

Examples of the material for the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polyethylene, cellulose derivatives such as cellulose triacetate, resins such as polycarbonate, polyimide and polyamide-imide. Furthermore, metal foil such as aluminum foil can be used.

The form of the support may be any of tape, disk, film, sheet, card, drum and the like. In the present invention, a lubricant may be mixed in the magnetic layer. Lubricants that can be used include saturated or unsaturated fatty acids and salts thereof, fatty acid amides, fatty acid esters, higher fatty acid alcohols, higher fatty acid amines, paraffins, modified or unmodified silicone oils, animal and vegetable oils, mineral oils, perfluoro. Examples thereof include polyether and fluorocarbon.

When used internally in the magnetic layer, the amount used is usually 3 to 10 parts by weight per 100 parts by weight of the ferromagnetic powder. When the surface of the magnetic layer is top-coated, 20-100 mg / m ² is suitable. Furthermore, in the present invention, in addition to the lubricant in the magnetic layer, a dispersant,
Additives such as antistatic agents can be mixed if necessary.

As the dispersant, fatty acids, fatty acid metal salts,
Examples thereof include fatty acid amides, fatty acid esters, higher alcohols, aliphatic amines, polyalkylene oxides, alkyl phosphates, sugars, lecithin and the like. The dispersant is usually used in an amount of 0.
1 to 5 parts by weight.

As the antistatic agent, carbon black,
SnO ₂ , indium tin oxide (ITO), conductive fine powder such as metal powder, nonionic surfactant such as alkylene oxide, cationic surfactant such as phosphonium or sulfonium, carboxylic acid, Examples thereof include anionic surfactants such as phosphoric acid type, sulfuric acid ester type or phosphoric acid ester type, and amphoteric surfactants such as amino acid type or aminosulfonic acid type.

The amount of the antistatic agent used is usually in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the ferromagnetic powder. It should be noted that additives such as lubricants, dispersants, antistatic agents, etc. are not limited to those having only the above-described effects, and actually, for example, lubricants act as dispersants. It is possible to do it. Therefore, it goes without saying that the action of the compounds exemplified by the above classification is not limited to the above classification, and when an additive having a plurality of effects is used, it is preferable to determine the amount to be used in consideration of the effects. .

Next, a method for manufacturing the magnetic recording medium of the present invention will be described. First, ferromagnetic powder and binder resin,
If necessary, other additives and the like are mixed with a solvent, kneaded and dispersed to prepare a magnetic coating material. As the solvent, those conventionally used for magnetic paints can be used without particular limitation. The method of mixing, kneading, and dispersing, the apparatus used therefor, etc. are not particularly limited. Moreover, the order of addition of each component can be set arbitrarily.

The magnetic coating material thus prepared is filtered through a suitable filter and then coated on a non-magnetic support. The coating can be carried out directly on the support, but it can also be carried out via an intermediate layer such as an adhesive layer or a conductive layer. When used as a tape-shaped magnetic recording medium, the magnetic layer coated on the non-magnetic support is subjected to a magnetic field orientation treatment for orienting the ferromagnetic powder in the magnetic layer, and then dried. On the other hand, when used as a disk-shaped magnetic recording medium, in order to remove the direction dependence of magnetic characteristics,
It is dried after being subjected to a non-oriented treatment by a magnetic field. After that, if necessary, a surface smoothing treatment with a calendar is performed, and if necessary, a heat curing treatment and a radiation curing treatment are performed, followed by cutting into a desired shape such as a tape shape or a disk shape for magnetic recording. A medium can be manufactured.

The magnetic layer according to the present invention having a specific surface roughness and a specific number of projections having a specific height distributed in the magnetic layer has a kind, a size, an amount of the abrasive, a kind of the binder resin and a solvent. It can be formed by appropriately selecting the type. Further, it can be formed by appropriately selecting the kneading / dispersing conditions of the magnetic paint, the calendering conditions and the like.

[0028]

EXAMPLES Next, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. Example 1 Co-doped γ-iron oxide powder was blended in the following composition,
It was well mixed and dispersed for 72 hours using a ball mill.

[0029]

[Table 1]

Thereafter, 5 parts by weight of polyisocyanate (“Coronate L” manufactured by Nippon Polyurethane Co., Ltd.) was added, and the mixture was uniformly mixed and dispersed for 1 hour to prepare a magnetic coating material. This magnetic paint was passed through a filter having an average pore size of 2 μm, and then applied onto a polyester film having a thickness of 75 μm so that the thickness after drying would be 1 μm, and after mirror finishing, it was cured. This magnetic sheet was punched into a disk shape to prepare a floppy disk, and the surface roughness Ra, surface protrusion density, electromagnetic conversion characteristics (2f output), rotation torque and durability were evaluated.

The surface roughness Ra was obtained by measuring the test length of 1 mm 5 times using a stylus type surface roughness meter (Taristep) and taking the average value thereof. The surface projection density was determined by observing the surface of the magnetic layer with a scanning electron microscope (SEM) in the range of 1000 μm ² , and among the particles exposed on the surface within the field of view, the radius of the exposed portion was d = 0. It was determined by counting the number of particles having a size larger than a, which was obtained as 1/2 of the particle diameter added with 03 μm and b.

For the 2f output, a 500 Hz digital signal is recorded on a disk rotated at 300 rpm using a ferrite head having a head gap of 0.9 μm, and the reproduction output is 100 times that of the disk of Comparative Example 1 described later.
Was calculated as a relative value. The rotation torque was evaluated by the value of the current flowing through the motor of the drive after rotating the head position on the track 39 in the drive.

The durability was evaluated by rotating the head position on the track 79 in a drive, and under a condition of a temperature of 60 ° C. and a humidity of 30%, the life was evaluated at the point when a clear head sliding mark was generated. The results are shown in Table-1.

Example 2 In Example 1, 3 parts by weight of alumina fine particles (average particle size 0.5 μm) and silicone resin fine particles (average particle size 0.3 μm, manufactured by Toshiba Silicone Co., Ltd., were used instead of 5 parts by weight of alumina fine particles. Tospearl 103 ")) A floppy disk was prepared in the same manner as in Example 1 except that 2 parts by weight were used, and the same evaluation was performed. The results are shown in Table-1.

Comparative Example 1 In Example 1, the alumina fine particles had an average particle size of 0.
A floppy disk was prepared and evaluated in the same manner as in Example 1 except that the disk having a thickness of 3 μm was used. The results are shown in Table-1.

Comparative Example 2 A floppy disk was prepared and evaluated in the same manner as in Example 1 except that the amount of alumina fine particles added was 3 parts by weight. The results are shown in Table-1.

Comparative Example 3 In Example 1, instead of the vinyl chloride-acrylic copolymer containing -SO ₃ M group ("MR110" manufactured by Zeon Corporation), a vinyl chloride-vinyl acetate copolymer ("V110 manufactured by UCC") was used.
A floppy disk was prepared and evaluated in the same manner as in Example 1 except that AGH ") was used. The results are shown in Table-1.

[0038]

[Table 2]

[0039]

INDUSTRIAL APPLICABILITY The magnetic recording medium of the present invention has a well-balanced magnetic conversion surface, running property and durability because the surface of the magnetic layer is highly smooth and has appropriate protrusions. And is industrially useful.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a state of protrusions in a magnetic layer.

[Explanation of symbols]

 1 magnetic layer 2 spherical particles 2'projections

Claims (2)

[Claims] 1. In a magnetic recording medium having a magnetic layer containing at least a ferromagnetic iron oxide powder and a binder resin on a non-magnetic support, the surface roughness Ra of the magnetic layer is 0.015.
projections having a height of 0.03 μm or more on the surface of the magnetic layer are 125,000 to 250,
A magnetic recording medium characterized by the presence of 000 magnetic recording media. 2. At least one kind of binder resin
Resin is -COOM, -SO₃M, -OSO₃M, -P
O₃M₂, -OPO₃M₂And -NR¹R ²R³X's
At least one polar group (where M is hydrogen
Ion, an alkali metal ion or an optionally substituted
Represents an ammonium ion. R¹, R²And R³Is hydrogen
Or represents an aliphatic hydrocarbon group, the same or different from each other
May be. X represents a halogen ion. ) Resin 1
10 per gram^-6-10^-FourThat it is a resin that has moles
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a magnetic recording medium.