JPH08329448A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To attain high output in a short wavelength region by forming a coating film contg. a binder and nonmagnetic particles on a flexible substrate, stretching the film, together with the substrate, so that a prescribed thickness is attained and then forming a magnetic layer on the stretched film. CONSTITUTION: A coating film 20 contg. a binder and nonmagnetic particles is formed on a flexible substrate 10 by coating and drying, and the film 20, together with the substrate 10, is stretched at least once so that the thickness of the film 20 is regulated to 0.05-0.7μm, preferably 0.1-0.5μm. The prescribed nonmagnetic particles are contained in the coating film 20, the prescribed stretching is carried out to impart workability to the film 20 and surface properties of a thin magnetic layer 30 formed on the film 20 are improved by calendering the surface of 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 coating type magnetic recording medium suitable for high density recording.

[0002]

2. Description of the Related Art In recent years, due to the demand for high-density recording, ferromagnetic powders have been made finer, alloy magnetic powders have been used, or the amount of magnetization of a recording medium has been increased, the coercive force has been increased, and the surface of a magnetic layer has been smoothed. Various methods such as vertical (oblique) orientation of the magnetic layer and thinning of the magnetic layer have been studied. In addition to these demands for high-density recording, further miniaturization of magnetic recording media is required, and thinning of media, especially thinning of magnetic layers has become a major issue.

However, when the magnetic layer is simply thinned, even if the surface property is finally improved by calendering, the effect of calendering does not remarkably appear. Therefore, the surface property of the magnetic layer is not improved, and the deterioration of electromagnetic conversion characteristics as medium characteristics has been a serious problem.

In order to solve such problems, a method of providing an undercoat layer between the magnetic layer and the flexible support has been studied in order to make the surface of the medium (in particular, the magnetic layer) smooth.

Regarding the method of providing the undercoat layer, for example, as proposed in JP-A-57-198536, after forming the flexible support, an undercoat layer is formed on the flexible support. A method of forming a magnetic layer after coating and drying the undercoat layer, and JP-B-5-5949.
As proposed in Japanese Unexamined Patent Publication (Kokai) No. 0, a subbing layer is coated on a flexible support, and while the subbing layer is in a wet state,
There is a method of forming a magnetic layer. Further, it is not necessarily used exclusively for a magnetic recording medium,
JP-A-8-29626 discloses a coating film (adhesive layer) containing polyester as a main component on a polyester film substrate as a polyester film for improving adhesiveness.
A method for producing a film has been proposed, in which the film is applied and then subjected to a stretching heat treatment to complete the oriented crystallization.

[0006]

However, in the method proposed in Japanese Patent Laid-Open No. 57-198536, the functions of the undercoat layer and the magnetic layer can be optimized, but the fineness at the time when the undercoat layer is provided. Film thickness fluctuations tend to occur, and process control tends to be complicated. Further, in order to prevent this minute fluctuation of the film thickness, it is possible to perform calendering after forming the undercoat layer and drying it, but the production process becomes more complicated and the yield is likely to decrease. Further, it has a drawback that the orientation is likely to be deteriorated because the undercoat layer is dried as the magnetic layer becomes thinner.

Further, in the method proposed in Japanese Patent Publication No. 5-59490, it is possible to apply the undercoat layer and the magnetic layer by one-time application. Can be simplified. However, there is a possibility that the interface between the undercoat layer and the magnetic layer is disturbed and the paints are mixed with each other, so that the finished medium may have an output fluctuation, which is a characteristic of the medium. In addition, there is a regulation that the coating itself cannot be performed without considering the matching of the paint between the undercoat layer and the magnetic layer, the selection range of the paint is limited, and the composition itself of the undercoat layer and the magnetic layer cannot be optimized. There are drawbacks.

On the other hand, JP-A-58-29626
The method disclosed in Japanese Patent Laid-Open Publication No. 2003-187242 has a main purpose only of adhesion to a film to be adhered, and in particular, a base film as an undercoat layer for a magnetic recording medium having a thin magnetic layer suitable for high density recording. The specification setting of is not proposed.

As a technique similar to the above, in Japanese Patent Laid-Open No. 4-248116, a polyester film is coated with a coating liquid containing carbon black and a water-soluble polyurethane resin as a main component, stretched, and then magnetically treated. There has been proposed a magnetic recording medium characterized by providing a layer.
However, the main purpose of this proposal is to reduce the electric resistance, the thickness of the magnetic layer is as thick as 4 μm, and the average particle size of carbon black is 0.1 to 0.
Particles as large as 5 μm are used, and it is not intended to improve the surface roughness when a thin magnetic layer is applied.

Furthermore, since carbon black has poor dispersibility, the surface of the base film is apt to be rough due to aggregation. Therefore, it is not suitable for a magnetic recording medium intended for high density recording. Further, the inclusion of carbon black is not preferable from the viewpoint of effective utilization of resources, which is a social demand, because it interferes as an impurity when the base film is recycled.

The present invention was devised under such circumstances, and an object thereof is to provide a magnetic recording medium which has both high output and running durability in a short wavelength region and which is excellent in productivity. To provide.

[0012]

In order to solve such an object, the inventors of the present application have established a relationship between a thin magnetic layer and a coating layer formed on a support. As a result of diligent research, the coating film not only excels in productivity but also achieves high output in the short wavelength region by improving the surface property of the thin magnetic layer, and also has excellent running durability. The present invention has been accomplished by finding optimum conditions for layers and magnetic layers.

That is, the present invention provides a magnetic recording medium comprising a flexible support, a coating layer formed on the support, and a magnetic layer formed on the coating layer. The coating layer has a binder and non-magnetic particles, is applied on the flexible support, and is stretched at least once. The coating layer has a thickness of 0.05 to 0. 7μ
The magnetic layer contains magnetic powder, a binder, and an abrasive and has a thickness of 0.05 to 1.0.
μm, and the non-magnetic particles contained in the coating layer are
The average particle diameter is 0.01 to 0.08 μm, and the abrasive contained in the magnetic layer has an average particle diameter of 0.05.
.About.0.8 .mu.m and satisfy the conditions of the following formulas (1) and (2).

Maximum particle size (d _mx ) ≦ (average particle size (d _av ) × 2.0) +0.5 Formula (1) Maximum particle size (d _mx ) ≦ (thickness of coating layer (t _c ) + the thickness of the magnetic layer (t _m)) + 0.5 ... magnetic recording medium of formula (2) the present invention, on a flexible support, at least once and having a binder and nonmagnetic particles Since it is provided with a coating layer having a predetermined thickness that has been subjected to a stretching treatment and a predetermined magnetic layer formed on this coating layer, it has excellent productivity as well as a thin magnetic layer. The surface property can be improved and high output in the short wavelength region can be achieved. Furthermore, it has excellent running durability.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of a magnetic recording medium of the present invention will be described below with reference to FIG. FIG. 1 is a sectional view of a magnetic recording medium of the present invention. According to this figure, the magnetic recording medium 1 of the present invention comprises a flexible support 10, a coating layer 20 coated and stretched thereon, and a magnetic layer formed on this coating layer. Equipped with 30.

As the flexible support 10 used in the present invention, polyesters such as polyethylene terephthalate and polyethylene 2,6 naphthalate, and various plastics such as polyamide and polyimide can be used. However, since polyamide and polyimide have a small stretching ratio, the level of uniformity of film thickness due to stretching tends to be low.

The thickness of the flexible support 10 is not particularly limited, but is 2 to 14 μm, preferably 3 to 10 μm in order to meet the demand for miniaturization of the magnetic recording medium. Is good.

The coating layer 20 formed on the flexible support 10 has a binder and non-magnetic particles and is coated on the flexible support 10. Installation
After being dried, it is stretched at least once while being integrated with the flexible support 10. The final thickness of the coating film layer 20 after stretching is 0.05 to 0.7 μm.
m, more preferably 0.1 to 0.5 μm.

When the thickness of the coating film layer 20 is less than 0.05 μm, particles are more likely to fall off during the coating process, resulting in an inconvenience of increasing dropout as a tape quality. When it exceeds the
The coating film is prone to cracks and the like, which makes it difficult to obtain a smooth coating film.

The stretching treatment of the coating layer 20 is performed integrally with the flexible support 10 as described above, and the stretching ratio is 3 to.
It is 10 times, preferably 4 to 8 times. If such a coating layer 20 is not stretched, the surface of the magnetic layer formed thereon cannot be smoothed by final calendering or the like. That is, in the present invention, the coating layer 2
0 contains predetermined non-magnetic particles and is subjected to a predetermined stretching treatment to obtain a film thickness range of a predetermined thickness so that the coating layer 20 itself has processability (flexible deformability). hand,
The surface property of the thin magnetic layer 30 is improved by calendering the surface of the magnetic layer.

The coating layer 20 is applied to the flexible support 1
From the viewpoint of improving productivity, it is preferable to perform in-line extrusion of 0 and further perform at least one stretching treatment of the coating layer 20 in-line.

The average particle size of the non-magnetic particles contained in the coating layer 20 is 0.01 to 0.08 μm, more preferably,
It is 0.02 to 0.06 μm. If the average particle size of the non-magnetic particles is less than 0.01 μm, there is a disadvantage that the particles cannot be sufficiently dispersed in the paint. On the other hand, if the average particle size exceeds 0.08 μm, the coating surface roughness of the coating layer 20 becomes large, and the output, which is the medium characteristic of the magnetic recording medium that is the final product, is reduced. Occurs.

The average particle size of the non-magnetic particles contained in the coating layer 20 is defined as follows in the present invention. That is, the maximum length of each particle is measured for each particle, and it is determined as the arithmetic mean of them. As a specific measuring method, a magnetic recording medium is embedded with a thermosetting epoxy resin, and a sample sliced with a diamond cutter is observed with a transmission electron microscope (TEM) (JEM100CX manufactured by JEOL Ltd.). However, the total number of particles is 100 or more, and the average value is obtained. Coating layer 20
The thickness of the sample is a transmission electron microscope (TEM) (JE manufactured by JEOL Co., Ltd.)
(M100CX, etc.), the observation location is changed, the thickness at 10 locations is measured, and the average value is obtained.

Specific non-magnetic particles used include:
For example, silica, silica sol, alumina, alumina sol, zirconium sol, calcium carbonate, titanium oxide,
Polystyrene resin, styrene-ethylene glycol dimethacrylate, styrene-divinylbenzene, methylmethacrylate-divinylbenzene, silicone resin,
Examples include melamine resin and formaldehyde resin. Of course, a combination of these may be used. Of these, colorless or from the viewpoint of recycling the flexible support,
It is preferable to use particles that are white.

Such non-magnetic particles are usually contained in the coating layer 20 in an amount of 3 to 60% by weight, preferably 20 to 50%.
Wt% is contained. If this value is less than 3 wt%,
There is a manufacturing inconvenience that the running stability of the support during coating of the magnetic layer is significantly deteriorated, and the value is 60.
If the content exceeds wt%, the number of non-magnetic particles dropped from the coating layer 20 increases, which causes an inconvenience that dropouts and the like increase.

The binder (resin component) used for forming the coating layer 20 is selected from thermoplastic resins and thermosetting resins. Above all, it is preferable to use a water-soluble or water-dispersible resin from the viewpoint that the production process does not need to have an explosion-proof structure and does not adversely affect the environment. Specifically, water-soluble or water-dispersible polyester resin, urethane resin, (meth) acrylic resin, polypropylene resin, polyamide, vinyl resin, butadiene resin, epoxy resin, silicon resin, carbonate Examples thereof include resins, melamine resins, vinylidene chloride resins, vinyl alcohol resins, gelatins and the like.
Further, the binder may be a copolymer of these or a mixture thereof.

As the water-soluble or water-dispersible polyester resin, one containing a sulfonate, carboxylate, polyoxyalkylene glycol, etc. in the molecule of the polyester resin is used. To introduce the sulfonate group into the molecule, for example, 5-Nasulfoisophthalic acid, 5-ammoniumsulfoisophthalic acid, 4-methylammoniumsulfoisophthalic acid, 2-Nasulfoterephthalic acid, 5-Ksulfoisophthalic acid. Acids, 4-K sulfoisophthalic acid, 2-K sulfoterephthalic acid, Na sulfosuccinic acid, and other sulfonic acid alkali metal salt-based compounds or sulfonic acid amine salt-based compounds can be used. The polyvalent carboxylic acid or polyhydric alcohol having a sulfonate group is usually 2 to 60 mol%, preferably 8 to 2 in the total polyvalent carboxylic acid component or polyhydric alcohol component.
It is preferable to occupy 5 mol%. If this value is less than 2 mol%, the hydrophilicity is poor, and 60 mol%
If it exceeds, the water resistance will be poor and it will be disadvantageous in the production of the polymer.

The other components used as the polycarboxylic acid are
Terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimetic acid, pyromellitic acid, dimer acid, itaconic acid,
Etc. can be illustrated. As the polyhydric alcohol component, ethylene glycol, dipropylene glycol,
Examples thereof include 1,6-hexanediol, 1,4-cyclohexanedimethanol, xylene glycol, dimethylolpropane, poly (ethylene oxide) glycol and poly (tetramethylene oxide) glycol. Further, hydroxycarboxylic acids such as p-hydroxybenzoic acid and p- (β-hydroxyethoxy) benzoic acid can be used together with these components. This polyester resin is synthesized from the above-mentioned polyvalent carboxylic acid or its ester-forming derivative and the above-mentioned polyhydric alcohol or its ester-forming derivative by a known method.

Further, in order to enhance solvent resistance, it is preferable to add a crosslinking binder to the coating layer 20 to increase the crosslinking density of the coating layer 20. As the cross-linking agent, for example, a melamine-based cross-linking agent, a urea-based cross-linking agent, an epoxy-based cross-linking agent, an isocyanate-based cross-linking agent, etc. may be used alone or in combination. The amount of the cross-linking agent added is usually 100
It is about 1 to 20 parts by weight with respect to parts by weight. Too much cross-linking agent is not preferable from the viewpoint of recycling.

Further, the coating layer 20 may contain a lubricant. Examples of lubricants used include monobasic fatty acids; silicone oils represented by dimethylsiloxane; fluorine-based lubricants; mineral oils; hydrocarbons represented by α-olefin oligomers and n-paraffins; animal oils;
Vegetable oil and the like can be mentioned.

Specific examples of these include monobasic fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid and elaidic acid, and butyl myristate. , Butyl palmitate, butyl stearate, neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl stearate, isotridecyl stearate, octyl stearate, Examples thereof include fatty acid ethers such as isooctyl stearate, amyl stearate, butoxyethyl stearate, 2-ethylhexyl stearate, and trimethylolpropane trioleate. These are generally widely used as lubricants. Usually, the amount of such a lubricant added is preferably in the range of 0.1 to 30 wt% with respect to 100 wt% of the resin. Of course, two or more kinds of lubricants may be combined. The magnetic layer 30 is formed on the coating layer 20.
The magnetic layer 30 contains magnetic powder, a binder (binder), and an abrasive as main components. further,
The thickness of the magnetic layer is 0.05 to 1.0 μm, preferably 0.08 to 0.7 μm, more preferably 0.1 to 1.0 μm.
It is set to 0.5 μm. If this value is less than 0.05 μm, uniform coating cannot be performed with the current coating technology, resulting in a disadvantage of large fluctuation in film thickness. If this value exceeds 1.0 μm, short wavelength Durability deteriorates due to lower output in the area and burial of the abrasive due to calendering. In order to prevent this, it is necessary to increase the amount of the abrasive added, and this causes the disadvantage that the electromagnetic conversion characteristics deteriorate.

The abrasive contained in such a magnetic layer has an average particle diameter of 0.05 to 0.8 μm, preferably 0.1.
08-0.5 μm, more preferably 0.1-0.3 μm
An abrasive having a particle size in the range of m and satisfying the conditions of the following formulas (1) and (2) is used.

Maximum particle size (d _mx ) ≦ (average particle size (d _av ) × 2.0) +0.5 Formula (1) Maximum particle size (d _mx ) ≦ (thickness of coating layer (t _c ) + the thickness of the magnetic layer (t _m)) + 0.5 ... formula (2) in the above formula (1) and (2), (d _mx), (d
The units of _av ), (t _c ), and (t _m ) are μm. Also
In the above formulas (1) and (2), the average particle size (d _av ) and the maximum particle size (d _mx ) of the abrasive are defined as follows in the present invention. That is, the average particle size (d _av ) is
The maximum length of each particle is measured for each particle, and the maximum average length of these particles is calculated. In addition, the maximum particle size (d _mx ) is obtained by measuring the maximum length of each particle with respect to each particle and obtaining the particle size distribution thereof, and determining the particle size distribution from the larger particle size side by 5%. It is defined by the value of the particle size when the number is cut. As a specific measuring method, a cross-sectional photograph of the recording medium is taken, and 10 of them are arbitrarily selected.
Sampling 0 or more abrasive particles, measuring the maximum length of these particles, and _dav , d according to the above-mentioned calculation method.
_mx , each value is calculated.

If the average particle diameter of the above-mentioned abrasive is less than 0.05 μm, the disadvantage that the paint cannot be sufficiently dispersed occurs, and this value exceeds 0.8 μm, or
If the above expressions (1) and (2) are not satisfied, the gap between the magnetic layer and the head becomes large due to the influence of the abrasive, which causes a disadvantage that the output is significantly reduced in the short wavelength region.

Examples of the abrasive that can be used include inorganic powders such as metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides and metal sulfides.

Specifically, α-alumina, β-alumina, γ-alumina, θ-alumina, δ-alumina, dichromium trioxide, α-iron oxide, γ-iron oxide, goethite, S
iO ₂ , ZnO, TiO ₂ , ZrO ₂ , SnO ₂ , silicon nitride, boron nitride, silicon carbide, titanium carbide, molybdenum carbide, boron carbide, tungsten carbide, calcium carbonate,
Barium carbonate, strontium carbonate, magnesium carbonate, barium sulfate, zinc sulfide, molybdenum disulfide, tungsten disulfide, artificial diamond and the like are used alone or in combination.

The weight ratio of these abrasives to the magnetic powder is usually 0.1 to 20 wt%, preferably 0.5.
It is used in the range of -15 wt%, more preferably 1-10 wt%.

These abrasives may be used alone or in combination of two or more in accordance with the required characteristics of the magnetic layer, and may be used in an appropriate combination. When two or more kinds are mixed and used, each of the mixed ones needs to satisfy the above range.

The above-mentioned abrasive does not necessarily have to be 100% pure, and the effect does not decrease if the main component is 70% or more.

Further, these abrasives need to contain a small amount of water-soluble alkali metal, alkaline earth metal, chlorine, sulfuric acid, nitric acid, etc. ions, and a large amount thereof will result in storage when used as a medium. It adversely affects the characteristics.

Further, the magnetic layer 30 contains magnetic powder. Examples of the magnetic powder used include iron oxide magnetic powder, ferromagnetic metal powder, plate-shaped hexagonal ferrite, and chromium dioxide. Among these, it is particularly preferable to use ferromagnetic metal powder and plate-shaped hexagonal ferrite.

As the ferromagnetic metal powder, Fe, Ni, C
o and these alloys are illustrated, α-Fe, Fe-C
o, Fe-Ni, Fe-Co-Ni, Co, Co-Ni
When using a ferromagnetic metal element such as
It is preferable to contain metal (Fe, Co, Ni, etc.) or alloy in an amount of 70 wt% or more, and further preferable to include 75 wt% or more. In a ferromagnetic metal magnetic powder containing Fe as a main component and further containing at least Co, the amount of Co atoms to Fe atoms is usually 5 to 40 w.
t%, preferably 6 to 35 wt%. Further, the ferromagnetic metal powder containing Fe and / or Co as a main component preferably further contains a rare earth element containing Y. Further, the ferromagnetic metal powder may be an oxide film on the surface of the particle, a partially carbonized or nitrided ferromagnetic metal powder, or a ferromagnetic metal powder having a carbonaceous film on the surface. The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. As these ferromagnetic metal powders, those obtained by a known manufacturing method can be used, and the following methods can be mentioned. Examples of the production method include a method of reducing an organic acid salt (mainly an oxalate) of a ferromagnetic metal with a reducing gas such as hydrogen, an iron oxide hydroxide or an iron oxide obtained by heating an iron oxide hydroxide to hydrogen etc. , A method of thermally decomposing a metal carbonyl compound, a method of reducing an aqueous solution of a ferromagnetic metal with a reducing agent such as sodium borohydride, hypophosphite or hydrazine, and a low pressure metal. And a method of obtaining a fine powder by evaporating in an inert gas. The ferromagnetic metal powder thus obtained is subjected to a known gradual oxidation treatment, that is, a method of immersing it in an organic solvent and then drying it, and immersing it in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and then drying it. Any of the method of forming the oxide film on the surface by adjusting the partial pressure of oxygen gas and the inert gas without using an organic solvent can be used.

The plate-like hexagonal ferrite is a hexagonal plate-like ferromagnetic powder having an axis of easy magnetization in the direction perpendicular to the flat plate, and examples thereof include Ba-ferrite, Sr-ferrite, Pb-ferrite, Ca-ferrite and these. Examples thereof include metal atom-substituted ferrite in which the valences of Fe atoms are matched, hexagonal Co powder, and the like. More specifically, magnetoplumbite-type Ba-ferrite and Sr-ferrite, and magnetoplumbite-type Ba partially containing a spinel phase.
-Ferrite, Sr-ferrite, and the like are mentioned, and particularly preferable are metal atom-substituted ferrites in which the valences of Fe atoms are adjusted to control the coercive force of Ba-ferrite and Sr-ferrite. As the metal atom used by substitution for controlling the coercive force,
Co-Ti, Co-Ti-Sn, Co-Ti-Zr, C
It is preferable to use u-Zn, Cu-Ti-Zn, Ni-Ti-Zn, or the like. When using Ba-ferrite,
The plate diameter means the plate width of hexagonal plate-like particles, and is measured using an electron microscope. The plate diameter is about 0.01 to 0.1 μm, and the plate thickness is about 1/2 to 1/20 of the diameter.

All of the above magnetic powders include Al, Si, Cr, Mn, Co, Ni, Zn and C.
u, Zr, Ti, Bi, Ag, Pt, B, C, P, N,
Y, S, Sc, V, Mo, Rh, Pd, Ag, Sn, S
b, Te, Ba, Ca, Ta, W, Re, Au, Hg,
A small amount of an element such as Pb, La, Sr, or a rare earth element may be added. Among these elements, Al,
Addition of Si, P, Y, and a rare earth element has the effects of improving the particle size distribution and preventing sintering.

These magnetic powders include Al, Si, P
Or even if it is covered with these oxide films, Si, A
It may be surface-treated with a coupling agent such as 1 or Ti or various surface active agents.

In the case of ferromagnetic metal powder, water-soluble N
It may contain inorganic ions such as a, K, Ca, Fe and Ni, but the amount thereof is usually preferably 500 ppm or less.

These magnetic powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before the dispersion.

The water content of the magnetic powder is usually 0.1 to 2%.
However, it is preferable to optimize it depending on the type of binder.

The pH of the magnetic powder is preferably optimized depending on the combination with the binder used, and the range is usually 4 to 12, but preferably 6 to 10.

[0050] Expressed these magnetic powders in specific surface area by the BET method, generally from 25~100m ² / g, preferably 40~85m ² / g, noise increases less than 25 m ² / g, If it exceeds 100 m ² / g, the smoothness of the tape cannot be obtained because it is difficult to disperse, which is not preferable.

Such magnetic powder is usually used in the binder 1.
The content of the magnetic powder in the magnetic layer is 50-95% of the total.
If the content of the magnetic powder is too large, the amount of additives such as resin in the magnetic layer decreases relatively, so that the durability of the magnetic layer decreases. However, if the number is too small, high playback output cannot be obtained.

These magnetic powders may be used alone or in combination of two or more kinds (for example, Ba-ferrite and metal magnetic powder).

As the binder contained in the magnetic layer 30,
A thermoplastic resin, a thermosetting or reactive resin, an electron beam sensitive modified resin, or the like is used, and the combination thereof is appropriately selected and used according to the characteristics of the medium and the process conditions.

The thermoplastic resin generally has a softening temperature of 150 ° C. or lower and an average molecular weight of 5,000 to 200,00.
0, the degree of polymerization is about 50 to 2,000, and the thermosetting resin, the reaction type resin or the electron beam functional type modified resin has the same average molecular weight and degree of polymerization as the thermoplastic resin, and the coating, drying, By heating and / or irradiating with an electron beam after calendering, the molecular weight becomes infinite due to reactions such as condensation and addition.

Of these, a combination of a vinyl chloride copolymer and a polyurethane resin as shown below is preferably used.

The vinyl chloride copolymer preferably has a vinyl chloride content of 60 to 95 wt%, particularly 60 to 90 wt%, and its average degree of polymerization is preferably about 100 to 500.

As such a vinyl chloride-based copolymer, one containing a sulfuric acid group and / or a sulfo group as a polar group (hereinafter referred to as S-containing polar group) is preferable, and an S-containing polar group (-SO ₄ Y,- In SO ₃ Y), Y may be either H or an alkali metal, but Y = K and —SO
₄ K and —SO ₃ K are particularly preferable, and these S-containing polar groups may be either one or both, and when both are contained, the ratio is arbitrary. .

Further, these S-containing polar groups are 0.01 to 10 wt%, particularly 0.1 to 5 w as S atoms in the molecule.
It is preferable that t% is included.

As the polar group, if necessary, in addition to the S-containing polar group, —OPO ₂ Y group, —PO ₃ Y group, —COO.
Y group (Y is H, alkali metal), amino group (-NR
_{2), - NR 3 Cl (} R may also be contained H, methyl, ethyl) and the like.

Of these, the amino group may not be used in combination with S and may be various ones, but a dialkylamino group (preferably alkyl having 1 to 10 carbon atoms) is particularly preferable.

Such an amino group is usually obtained by amine modification, and a copolymer of vinyl chloride / alkylcarboxylic acid vinyl ester is dispersed or dissolved in an organic solvent such as alcohol, and an amine compound (aliphatic amine) is contained therein. , A cycloaliphatic amine, alkanolamine, alkoxyalkylamine, etc.) and an epoxy group-containing compound for facilitating the saponification reaction. The vinyl unit having an amino group is obtained by
At t%, ammonium base may still be included as a result.

The resin skeleton to which these S-containing polar groups are bonded is a vinyl chloride resin, and vinyl chloride, a monomer having an epoxy group, and, if necessary, another monomer copolymerizable therewith. Can be obtained by polymerizing in the presence of a radical generator having a strong acid radical containing S such as potassium persulfate and ammonium persulfate, and the amount of these radical generators is usually 0.3-9.0 wt
%, Preferably 1.0 to 5.0 wt%, and since many of them are water-soluble in polymerization, emulsion polymerization or suspension polymerization using alcohol such as methanol as a polymerization medium,
Solution polymerization using a ketone as a solvent is preferable.

The polyurethane resin used in combination with such a vinyl chloride resin is particularly effective in that it has good abrasion resistance and adhesiveness to a support.
It may have a hydroxyl group or the like, and particularly preferably has a polar group containing sulfur or phosphorus.

These polyurethane resins are a general term for resins obtained by reacting a hydroxy group-containing resin such as polyester polyol and / or polyether polyol with a polyisocyanate-containing compound.
The synthetic raw materials detailed below have a number average molecular weight of 500 to 20.
It was polymerized to about 0000, and its Q value (weight average molecular weight / number average molecular weight) was about 1.5 to 4.

Further, these urethane resins have a glass transition temperature Tg of −20 ° C. ≦ Tg ≦ in the binder used.
At least two or more different substances in the range of 80 ° C., and the total amount thereof is 10 to 90 wt% of the total binder,
It is preferable to contain a plurality of these polyurethane resins from the viewpoint that the running stability in a high temperature environment, the calendar processability, and the electromagnetic conversion characteristics can be balanced.

Further, these vinyl chloride copolymers and S
And / or the P-containing polar group-containing urethane resin is preferably mixed and used so that the weight mixing ratio is 10:90 to 90:10.

In addition to these resins, a total of 20
Various known resins may be contained in the range of not more than wt%.

As the polar group contained in the urethane resin,
As examples of _{-SO 3 M, -SO 4 M,} P -containing polar groups are S-containing _{group, = PO 3 M, = PO} 3 M, = POM, -P
= O (OM1) (OM2), -OP = O (OM1) (O
_{M2), - COOM, -NR 4} X ( wherein, M, M1,
M2 is, H, Li, Na, K , -NR 4, shows a -NHR _3, R represents an alkyl group or H, X is a halogen ^{_{atom) -OH, -NR 2, -N +}} R 3, (R is a hydrocarbon group), it is preferable to use at least one polar group selected from an epoxy group, —SH, —CN or the like introduced by copolymerization or an addition reaction. Among them, M is particularly Na. Is preferable, and these polar groups are 0.01 to 10 wt% in the molecule as atoms, and particularly 0.02 to 3 w.
It is preferable that these polar groups are contained in the main chain or the branches of the skeletal resin.

Such a urethane resin is reacted by a known method with a specific polar group-containing compound and / or a raw material containing a raw material resin reacted with the specific polar group-containing compound in a solvent or in the absence of a solvent. Can be obtained.

Examples of thermoplastic resins other than these include (meth) acrylic resins, polyester resins, acrylonitrile-butadiene copolymers, polyamide resins, polyvinyl butyral, nitrocellulose, styrene-butadiene copolymers, polyvinyl alcohol resins. , Polyfunctional polyethers such as acetal resin, epoxy resin, phenoxy resin, polyether resin, polycaprolactone, polyamide resin, polyimide resin, phenol resin, polybutadiene elastomer, chlorinated rubber, acrylic rubber, isoprene rubber, epoxy modified Examples thereof include rubber.

Further, as the thermosetting resin, polycondensation phenol resin, epoxy resin, polyurethane curable resin, urea resin, butyral resin, formal resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, polyamide resin , Epoxy-polyamide resin, saturated polyester resin, urea formaldehyde resin and the like.

Among the above-mentioned copolymers, those having a hydroxyl group at the terminal and / or side chain are preferable as the reactive resin because crosslinking using an isocyanate and electron beam crosslinking modification can be easily utilized. -COOH to or side chain as a polar _{group, -SO 3 M, -OSO 3 M} , -OPO
_{3 X, -PO 3 X, -PO} 2 X, -N + R 3 Cl -, -
It may contain an acidic polar group such as NR _{2 and the} like, a basic polar group and the like, and the inclusion of these is suitable for improving dispersibility. These may be used alone or in combination of two or more.

As the cross-linking agent for curing the binder resin, various polyisocyanates can be used. One or more of tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, etc. can be used as trimethylol propane, etc. It is preferable to use a cross-linking agent modified to have a plurality of hydroxyl groups, or an isocyanurate-type cross-linking agent in which 3 molecules of a diisocyanate compound are bonded, and the content of the cross-linking agent is 1 to 5 with respect to 100 wt% of the resin.
It is preferably 0 wt%, and the cross-linking agent can three-dimensionally bond with a hydroxyl group or the like contained in the binder resin to improve the durability of the coating layer.

Specifically, Coronate L, Coronate HL, Coronate 3041, manufactured by Nippon Polyurethane Co., Ltd.
Coronate 2030, Asahi Kasei Corporation 24A-10
0, TPI-100, and Death Modules L and N manufactured by BF Goodrich.

Generally, to cure such a reactive or thermosetting resin, heating in a heating oven at 50 to 80 ° C. for 6 to 100 hours or at a low speed of 8
It is run in an oven at 0 to 120 ° C.

Further, according to the method known to the above copolymer,
It is also possible to use an electron beam-sensitive modification by introducing a (meth) acrylic double bond. To carry out this electron beam-sensitive modification, tolylene diisocyanate (TDI) and 2-hydroxyethyl ( A urethane-modified, ethylenically unsaturated double bond that reacts with a reaction product (adduct) with (meth) acrylate (2-HEMA) is 1
More than one and one isocyanate group in one molecule,
Further, improved urethane modification using a monomer having no urethane bond in the molecule (2-isocyanate ethyl (meth) acrylate) and a resin having a hydroxyl group or a carboxylic acid group, a (meth) acrylic group and a carboxylic acid anhydride or a dicarboxylic acid. It is well known that ester modification is carried out by reacting a compound having an acid. Among these, the modified urethane modification does not become brittle even if the content ratio of vinyl chloride resin is increased, and the dispersibility and surface properties are also improved. It is preferable because an excellent coating film can be obtained.

The electron beam functional group content is 1 to 40 mol%, preferably 10 to 30 mol% in the hydroxyl group component in view of stability during production, electron beam curability and the like. In the case of combination, an electron beam curable resin having excellent dispersibility and curability can be obtained by reacting the monomers so that the number of functional groups per molecule is 1 to 20, preferably 2 to 10.

The term "acrylic double bond" as used herein means a (meth) acryloyl group which is a residue of (meth) acrylic acid, (meth) acrylic acid ester or (meth) acrylic acid amide.

When using these electron beam sensitive modified resins,
In order to improve the crosslinking rate, conventionally known polyfunctional acrylates may be mixed and used in an amount of 1 to 50 wt%.

When the electron beam sensitive modified resin is used as a binder, an electron beam is used as a radiation source at the time of curing from the viewpoint of controlling the absorbed dose, introducing it into the manufacturing process line, and shielding ionizing radiation. The method and / or the method using ultraviolet rays are advantageous, in the case of electron beams an accelerating voltage of 100 KV to 750 KV, preferably 150 to 30.
Absorbed dose is 20 ~ 200 using 0KV electron beam accelerator
It is convenient to irradiate so that it is a kilogray.

At the time of electron beam crosslinking, the oxygen concentration is 1
It is important to irradiate the electron beam in an atmosphere of an inert gas such as N ₂ or less, such as N ₂ , He, or CO _{2 in} order to prevent O _{3 and the} like generated by irradiation from trapping radicals.

On the other hand, when ultraviolet rays are used, a conventionally known photopolymerization sensitizer is added to the binder containing the electron beam curable resin, and the irradiation thereof is performed with a xenon discharge tube or a hydrogen discharge tube. An ultraviolet light bulb or the like may be used.

The solvent contained in the magnetic coating material for forming the magnetic layer 30 is not particularly limited, but is appropriately selected in consideration of the solubility of the binder, the compatibility, the drying efficiency, and the like. For example, methyl ethyl ketone, Methyl isobutyl ketone, ketones such as cyclohexanone, toluene,
Aromatic hydrocarbons such as xylene, ethyl acetate, esters such as butyl acetate, alcohols such as isopropanol and butanol, dioxane, tethydrofuran, dimethylformamide, hexane, diluents or solvents such as chlorine-substituted hydrocarbons Used as a single solvent or a mixed solvent of these in arbitrary ratios.

These organic solvents are not necessarily 100% pure and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides and water in addition to the main components. 5% by weight or less is preferable, and more preferably 3% by weight or less, and if there are many impurities, the dispersibility of the magnetic powder, the storage stability of the paint, the curing characteristics of the magnetic layer, the storage characteristics in the medium, etc. Adversely affect.

These solvents are used in an amount of 10 to 10000 wt% with respect to the total amount of the binder so that the viscosity of the paint is 5 to 100 cp at a shear rate of 3000 sec ^-1 by a cone plate type or double cylinder type viscometer at the application stage. %,
In particular, it is used in a proportion of 100 to 5000 wt%, and the solvent proportion of the entire paint is 5% solid (nonvolatile) concentration.
It may be used in an amount of about 40 to 40 wt%, preferably about 10 to 35 wt%, but to determine the solvent type, mixing ratio, and amount used, the type of pigment used in the paint, specific surface area, particle size, magnetic properties In the case of powder, the amount of magnetization, the volume or weight filling degree of the pigment, the dilution stability of the coating material, and the like may be taken into consideration so as to be adjusted to the above viscosity range before use.

The solvent addition operation is preferably carried out stepwise in each step of the paint production. For example, the solvent may be added sequentially while stirring in the tank with the flow rate regulated, or gradually mixed with the paint in a pipe. It is preferable to carry out the operation, and it is more preferable to carry out filtration and / or dispersion treatment at the time of solvent addition or dilution, if possible. By carrying out these operations, the stability of the paint and the generation of aggregates and foreign substances can be prevented. It is possible to suppress.

A lubricant is usually contained in the magnetic coating material for forming the magnetic layer. As the lubricant to be used, it is preferable to use a fatty acid and / or a fatty acid ester, among various known lubricants, which has 12 to 24 carbon atoms.
A monobasic fatty acid (which may contain an unsaturated bond or may be branched), a monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) Fatty acid and C2-C22 (whether or not unsaturated bond is contained or branched) monovalent, divalent, trivalent, tetravalent,
Mono-fatty acid ester, di-fatty acid ester, tri-fatty acid ester, a mixture thereof, or a combination of two or more thereof, which is composed of any one of cyclic or polysaccharide reducing alcohols such as pentahydric, hexahydric alcohol, sorbitan and sorbitol Good.

Specific examples of the monobasic fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid and elaidic acid. , For fatty acid esters, butyl myristate,
Butyl palmitate, butyl stearate, neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl stearate, isotridecyl stearate, octyl stearate, iso Octyl stearate, amyl stearate,
Butoxyethyl stearate and the like can be mentioned.

The effect of these fatty acids and / or fatty acid esters as a lubricant or dispersant appears when the ferromagnetic fine powder is added in an amount of 0.1 wt% or more, thereby increasing the content rate. By letting
The effect becomes remarkable, but if the total content exceeds 20 wt% with respect to the ferromagnetic fine powder, it will not be retained in the magnetic layer and will be discharged onto the surface of the coating film to stain the magnetic head. , And adversely affect the output.

Therefore, the content of fatty acid and / or fatty acid ester in the magnetic layer is preferably 0.1 to 20 wt% as the total amount with respect to the ferromagnetic fine powder.
15 wt% is preferable, and 1 to 12 wt% is more preferable.

Further, when there is a back coat layer, a large amount of lubricant may be contained on the back coat layer side to improve the surface lubricity by transfer to the surface of the magnetic layer.

These fatty acids and / or fatty acid esters are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposition products and oxides in addition to the main component. . These impurities are preferably 40% or less, more preferably 20% or less.

Further, all or part of the fatty acids, fatty acid esters, additives and the like used may be added in any step of the production of the coating material for forming the magnetic recording medium. For example, when mixed with the pigment powder before the kneading step, when added in the kneading step with the pigment powder, the binder and the solvent, when added in the dispersion step, when added after the dispersion, when added immediately before coating, in the solvent There is a method such as applying a diluted or dispersed solution onto a previously applied layer.

In the magnetic coating material for forming the magnetic layer 30,
Usually, additives are added for exhibiting a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like. For example, silicone oils, fluorine oils, alcohols containing fluorine-substituted hydrocarbon groups, fatty acids, esters, ethers, paraffins, and metals of the above-mentioned monobasic fatty acids (Li, N
a, K, Ca, Ba, Cu, Pb, etc.) salts, alcohols for producing the above fatty acid ester, alkoxy alcohols, fatty acid esters of polyethylene oxide-added monoalkyl ether, aliphatic or cyclic amines, fatty acid amides, Quaternary ammonium salts, polyolefins, polyglycols, polyphenyl ethers, fluorine-containing alkyl sulfates and their alkali metal salts, alkylene oxides, glycerins, glycidols, nonionic surfactants such as alkylphenol ethylene oxide adducts, phosphonium or Cationic surfactants such as sulfonium and alkali metal salts thereof,
Anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid ester group and the like, and alkali metal salts thereof, amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of aminoalcohol, alkyl betaine type Amphoteric surfactants such as and the like can also be used.

These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.).

The total amount of these additives is 10 wt% or less based on the magnetic powder, particularly 0.01 to 5 wt%, and when the magnetic powder is not present, 0.005% based on the binder.
It may be used in the range of ˜50 wt%.

Further, these inorganic compounds may be added simultaneously at the time of kneading or dispersing with the magnetic powder, or may be previously dispersed with a binder and added at the time of dispersing the magnetic coating material.

Further, the magnetic paint may contain carbon black. Furnace carbon black, thermal carbon black,
Acetylene black or the like can be used. The particle size and the like of these carbon blacks may be set arbitrarily, but may be appropriately selected from the electrical resistance and friction characteristics required for the medium and the output balance (surface roughness) at the shortest recording wavelength. However, a mixed system may be used, and the particle size distribution and the like can be selected independently. The average particle size of these carbon blacks is 10 nm to 400 nm, preferably 2
0 to 350 nm, and more specifically, 20 to 40 nm is preferable when the electromagnetic conversion characteristics are preferentially considered, and when importance is attached to the friction characteristics, the electromagnetic conversion characteristics are as large as possible in the range of 40 to 350 nm. It is preferred to use particle size. Further, in selecting carbon black, it is necessary to consider not only the particle size but also the BET value and the DBP value, but since the particle size, the BET value and the DBP value of carbon black are closely related, they are separated from each other. Since it is impossible to realize numerical values, it is necessary to experimentally select these three elements depending on the required characteristics of the medium and the dispersion characteristics and flow characteristics of the paint.

These carbon blacks are used in a weight ratio of 10 to 500 wt% with respect to the binder, or 0.1 to 20 wt% with respect to the magnetic powder. It is necessary to select experimentally according to the dispersion characteristics and flow characteristics. These carbon blacks may be appropriately combined and used according to the required characteristics of the magnetic layer, the back coat layer, the underlayer and the like.
Further, these carbon blacks may be added simultaneously at the time of kneading or dispersing with the magnetic powder, or may be previously dispersed with a binder and added at the time of dispersing the magnetic coating material.

Further, these carbon blacks may be surface-treated with a lubricant, a dispersant, or the like, or a part of the surface thereof may be graphitized.

The carbon black that can be used in the present invention is
For example, "Carbon Black Handbook", edited by Carbon Black Association can be referred to.

Further, the magnetic paint may contain a non-ferromagnetic organic powder. As the non-ferromagnetic organic powder used, acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, phthalocyanine pigment, azo pigment, polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide system Resin powder, fluorohydrocarbon resin powder, divinylbenzene resin powder and the like can be mentioned. The non-ferromagnetic organic powder has a weight ratio of 0.1 to 20 w with respect to the binder.
Used in the range of t%.

The magnetic coating material may be applied to the support by extrusion nozzle coating method, reverse roll coating method, gravure roll coating method, knife coater coating method, doctor blade coating method, kiss coat coating method, color coat coating method, A slide bead coating method or the like can be used. Among these, the gravure roll coating method is particularly excellent in productivity, and the reverse roll coating method is preferable because it has a wide range of coating materials that can be used for coating. Further, the extrusion nozzle coating method is excellent in that simultaneous multilayer coating is possible. Among these three preferable methods, the extrusion nozzle coating method is particularly preferable in terms of easy control of the coating film thickness.

Magnetic coating material coated on a support by such a method (this forms a so-called magnetic layer)
Are subjected to magnetic field orientation treatment, drying treatment, smoothing treatment, and the like. As the smoothing treatment of the magnetic layer, calendering is performed. As the calendering roll, epoxy, polyester, nylon, polyimide, polyamide, polyimideamide or other heat-resistant plastic roll (carbon,
A metal or other inorganic compound may be kneaded therein) and a combination of metal rolls (combination of 3 to 7 stages) or metal rolls may be treated together, and the treatment temperature is preferably 70 ℃ or more, more preferably 80 ℃ or more, the linear pressure is preferably 200kg / c
m, more preferably 300 kg / cm, the speed is 2
It is in the range of 0 m / min to 700 m / min. Then, for example, the magnetic recording medium is formed by cutting into a desired shape.

In the present invention, if necessary,
Between the flexible support 10 and the coating layer 20, an intermediate layer in which the particle size and addition amount of the nonmagnetic particles are controlled or a resin layer having a low glass transition temperature (Tg) may be appropriately provided.
By doing so, it may be expected that the uniformity of the surface roughness and the workability of the calendar can be further improved.

Further, in the magnetic recording medium 1 of the present invention, a so-called various known back coat layer may be provided on the back surface side (the surface on which the magnetic layer is not formed) of the flexible support 10.

[0107]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

Example 1 Preparation of Flexible Support 10 An ethylene glycol slurry containing SiO ₂ particles was prepared and transesterified with dimethyl terephthalate for polycondensation to give a predetermined amount of SiO ₂ particles. The contained polyethylene terephthalate (PET) chips were made.
The chips are dried under reduced pressure at 180 ° C. for 3 hours, supplied to an extruder and melted at 300 ° C. The extruded polymer is wound around a casting drum having a surface temperature of 30 ° C. by an electrostatically applied casting method and cooled. It solidified and the unstretched film of the thermoplastic polymer was produced. Then, this unstretched film was stretched 3.5 times in the longitudinal direction at a temperature of 80 ° C. by utilizing the peripheral speed difference of the rolls.

Formation of Coating Layer 20 On the PET flexible support 10 thus prepared, the coating layer 20 was provided and stretched in the following manner. That is, an aqueous solution prepared by containing 40 wt% of organic particles (styrene-ethylene glycol dimethacrylate) having an average particle diameter of 40 nm (0.04 μm) in a water-soluble polyester resin and dispersing the organic particles was used for the above-mentioned flexibility with a bar coater. After being coated on the support 10, this uniaxially stretched film was used in a width direction at 4.0 ° C. by a tenter method at 4.0 ° C.
It was stretched twice. The coating layer 20 was dried at the same time as the transverse stretching. Further, it was stretched again 1.6 times in the longitudinal direction by utilizing the peripheral speed difference of the roll under the condition of 110 ° C. afterwards,
The film was heat-treated at 220 ° C. for 5 seconds under a fixed length to obtain a biaxially oriented polyester film having a total thickness of 5.5 μm and a coating film dry thickness of 0.05 μm.

Formation of Magnetic Layer 30 The following magnetic layer 30 was provided on the coating layer 20 side of this polyester film.

Hc = 2000 Oe, σ _s = 140 emu
/ G, average major axis length 0.08 μm, average axis ratio 5 ferromagnetic metal magnetic powder (Fe / Co / Al / Y = 100/2
The following composition containing 0 / 4.2 / 5.3 (weight ratio) was used to prepare a magnetic coating material for forming a magnetic layer.

Magnetic coating composition for forming magnetic layer Ferromagnetic metal magnetic powder: 100 parts by weight Vinyl chloride copolymer (Zeon Corporation, MR-110): 8.3 parts by weight Polyester polyurethane resin (Toyobo Co., Ltd.) Co., Ltd., UR-8300) 8.3 parts by weight α-alumina 5 parts by weight stearic acid 1 part by weight butyl stearate 1 part by weight methyl ethyl ketone 111 parts by weight toluene 111 parts by weight cyclohexanone 74 parts by weight This composition After a part or all of the product was sufficiently kneaded with a kneader, it was dispersed and mixed and diluted with a sand grinder mill. A magnetic layer-forming coating material obtained by adding 3.3 parts by weight of a curing agent (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) to the magnetic coating material obtained in this way was prepared by the nozzle coating method in the above-described manner. Thickness 5.
It was applied on a 5 μm PET film support (on the side of the coating layer 20) so that the dry thickness of the magnetic layer was 0.2 μm, and then subjected to orientation treatment, drying and calendar treatment.

On the other hand, on the opposite surface of the PET film support (the surface on which the magnetic layer is not provided), a back coat composition having the following composition was added with a curing agent (manufactured by Nippon Polyurethane Industry Co., Ltd.,
A coating material for forming a back coat layer, in which 2 parts by weight of Coronate L) was added and mixed, was applied, calendered, and then heat-cured. Thereafter, this was cut into a width of 8 mm to prepare a tape-shaped magnetic recording medium sample (Example sample 1).

Composition for back coat layer Carbon black-1 (manufactured by Colombian Carbon Co., Ltd., Conductex SC Ultra: average particle diameter 21 nm, BET value 220 m ² / g) ... 80 parts by weight carbon black-2 (columbian) Carbon Co., Sevacurve MT: Average particle size 350 nm, BET value 8 m ² / g) 1 part by weight α-iron oxide (Toda Kogyo Co., Ltd., TF-100: average particle size 0.1 μm) 1 Parts by weight Vinyl chloride-based copolymer A (manufactured by Nisshin Chemical Industry Co., Ltd., MPR-TA (vinyl chloride-vinyl acetate-vinyl alcohol copolymer): average degree of polymerization 420) ... 40 parts by weight Vinyl chloride-based copolymer B (manufactured by Nisshin Chemical Industry Co., Ltd., MRR-ANO (L) (vinyl chloride-vinyl acetate-vinyl alcohol copolymer): nitrogen atom 390 ppm content, average degree of polymerization 340) ... 25 parts by weight polyester Polyurethane resin (Toyobo Co., TS9555: -SO ₃ Na content, a number average molecular weight 40000) ... 35 parts by weight Methylethyl ketone 700 parts by weight Toluene 400 parts by weight Cyclohexanone 300 parts by weight (Example 2-4) above In Example 1, the thickness of the coating layer 20 was variously changed as shown in Table 1 below. Other than that, the sample of Examples 2-4 was produced like Example 1 above.

(Examples 5 to 9) In the above Example 3,
The thickness of the magnetic layer 30 was variously changed as shown in Table 1 below. Except for this, the fifth embodiment is similar to the third embodiment.
9 samples were prepared.

(Examples 10 to 12) In Example 3 described above, the particle diameter of the non-magnetic particles contained in the coating layer 20 was changed as shown in Table 1 below. Other than that, the sample of Examples 10-12 was produced like Example 3 above.

(Examples 13 and 14) In Example 3 above, the addition amount of the non-magnetic particles contained in the coating layer 20 was changed as shown in Table 1 below. Except for this, the samples of Examples 13 and 14 were prepared in the same manner as in Example 3 above.

Example 15 In Example 3, the material of the substrate composed of the flexible support 10 and the coating layer 20 was changed as follows. A sample of Example 15 was made in the same manner as Example 3 except for the above.

That is, a substrate film consisting of a flexible support and a coating layer was prepared in the following manner.

Preparation of Flexible Support An ethylene glycol slurry containing SiO ₂ particles was prepared and transesterified with dimethyl naphthalene-2,6-dicarboxylate to cause polycondensation to give a predetermined amount of SiO ₂ particles. Containing polyethylene naphthalate (PEN)
I made a chip. A thermoplastic polymer was prepared using this chip. This polymer was dried under reduced pressure at 280 ° C. for 4 hours, fed to an extruder and melted at 295 ° C. This polymer was wound around a casting drum using an electrostatically applied casting method to be cooled and solidified to obtain a thermoplastic polymer. A stretched film was produced. Then, this unstretched film was stretched 2.5 times in the longitudinal direction at a temperature of 145 ° C. by utilizing the difference in peripheral speed of rolls.

A coating layer was formed on the thus prepared flexible support in the following manner and stretched and dried. That is, an aqueous solution prepared by containing 40 wt% of organic particles (styrene-ethylene glycol dimethacrylate) having an average particle diameter of 40 nm (0.04 μm) in a water-soluble polyester resin and dispersing the organic particles was used for the above-mentioned flexibility with a bar coater. After coating on the support, it was dried at the same time as the transverse stretching. The dry thickness was 0.2 μm.

This uniaxially stretched film was stretched 4.2 times in the width direction at 135 ° C. by a tenter method, and then heat set at 210 ° C. This heat-fixed film was re-stretched about 1.9 times in the longitudinal direction by utilizing the peripheral speed difference of the roll under the condition of 160 ° C. Then, it was heat-set for 5 seconds at 220 ° C. under a fixed length to obtain a biaxially oriented polyester film having a total thickness of 5.5 μm.

(Examples 16 to 19) In Example 3 above, as shown in Table 2 below, the thickness of the magnetic layer 30 and the average particle size and maximum particle size of the abrasive contained in the magnetic layer were varied. changed. Except for this, the samples of Examples 16 to 19 were produced in the same manner as in Example 3 above.

Example 20 In Example 3, the kind of the non-magnetic particles contained in the coating layer 20 was changed to silica (symbol B in the table) as shown in Table 2 below. A sample of Example 20 was made in the same manner as Example 3 except for the above.

Example 21 In Example 3, the average particle size and the maximum particle size of the abrasive contained in the magnetic layer 30 were changed as shown in Table 2 below. A sample of Example 21 was made in the same manner as Example 3 except for the above.

Example 22 In the above Example 21,
The thickness of the magnetic layer 30 was changed as shown in Table 2 below. Other than that, Example 22 is performed in the same manner as Example 21 above.
The sample of was produced.

(Example 23) In the above Example 19,
As shown in Table 2 below, the average particle diameter and the maximum particle diameter of the abrasive contained in the magnetic layer 30 were changed. A sample of Example 23 was made in the same manner as Example 19 except for the above.

Examples 24 to 26 In Example 4, the average particle size and the maximum particle size of the abrasive contained in the magnetic layer 30 were changed as shown in Table 2 below. Further, the thickness of the magnetic layer 30 was changed. Except for this, the samples of Examples 24 to 26 were manufactured in the same manner as in Example 4 above.

(Examples 27 and 28) In Example 3 described above, the average particle size and the maximum particle size of the abrasive contained in the magnetic layer 30 were changed as shown in Table 2 below. Further, the thickness of the magnetic layer 30 was changed. Otherwise, Example 3 above
Samples of Examples 27 and 28 were prepared in the same manner as in.

Example 29 In Example 3, the thickness of the magnetic layer 30 was changed as shown in Table 2 below. A sample of Example 29 was made in the same manner as Example 3 except for the above.

Example 30 In the above Example 26,
As shown in Table 2 below, the average particle diameter and the maximum particle diameter of the abrasive contained in the magnetic layer 30 were changed. A sample of Example 30 was made in the same manner as Example 26 except for the above.

(Examples 31 to 35) In Example 2 described above, the particle size and the addition amount of the non-magnetic particles contained in the coating layer 20 were changed as shown in Table 3 below. Other than that,
Samples of Examples 31 to 35 were prepared in the same manner as in Example 2 above.

(Example 36) In Example 3 above, the addition amount of the non-magnetic particles contained in the coating layer 20 was changed as shown in Table 3 below. A sample of Example 36 was made in the same manner as Example 3 except for the above.

Examples 37 and 38 Example 12 above
In Table 3, the addition amount of the non-magnetic particles contained in the coating layer 20 was changed as shown in Table 3 below. Except for this, the samples of Examples 37 and 38 were produced in the same manner as in Example 12 above.

(Examples 39 and 40) In Example 3 above, the type of the non-magnetic particles contained in the coating layer 20 was changed as shown in Table 3 below. Except for this, the samples of Examples 39 and 40 were produced in the same manner as in Example 3 above.

In the table, particle C represents a styrene-divinylbenzene-based organic particle, and particle D represents a methylmethacrylate-divinylbenzene-based organic particle.

(Example 41) Further, a tape-shaped magnetic recording medium sample of the present invention was prepared in the following manner.

Preparation of Flexible Support 10 and Coating Layer 20
Of 100 parts by weight of dimethyl terephthalate, 65 parts by weight of ethylene glycol and 0.09 parts by weight of magnesium acetate were placed in a reactor, and transesterification was performed while heating and heating and distilling off methanol. It took about 4 hours after the start of the reaction, and the temperature was raised to 230 ° C. to substantially complete the transesterification. Here, 0.3 part by weight of SiO ₂ particles having an average particle size of 0.1 μm was added as an ethylene glycol slurry, and then 0.4 part by weight of ethyl acid phosphate and 0.04 part by weight of antimony oxide were added to carry out the reaction. At the same time that the system pressure was reduced from room temperature, the temperature was raised by heating, and finally the conditions were 1 mmHg and 285 ° C. After 4 hours, the system was returned to normal pressure to obtain polyethylene terephthalate (hereinafter referred to as PET) having an intrinsic viscosity of 0.66.

The PET thus obtained was
After drying at ℃ for 4 hours, it is fed to an extruder and melted at 290 ℃, and the extruded polymer is wound around a casting drum with a surface temperature of 40 ℃ using an electrostatic cast method to cool and solidify, and unstretched. Got the sheet.

The unstretched sheet was stretched in the machine direction at 89 ° C. to 2.
The film was stretched 6 times and further 1.73 times at 80 ° C. by a roll stretching method. Then, in order to form the coating layer 20, a coating solution having the same composition as in Example 1 described above is applied with a bar coater, and the film after application is guided to a tenter, and the film is applied in the lateral direction 12
Stretching 3.2 times at 0 to 145 ° C., then 22
Heat setting was carried out at 0 ° C. for 10 seconds to obtain a biaxially oriented polyester film having a total thickness of 5.5 μm and a coating layer having a dry thickness of 0.2 μm.

Formation of Magnetic Layer 30 On the side of the coating layer 20 of the polyester film, the same coating material for forming the magnetic layer as in Example 1 was applied by the nozzle coating method to give a dry thickness of the magnetic layer of 0.2 μm. As described above, the alignment treatment, the drying treatment and the calendar treatment were performed.

On the other hand, a coating material for forming a back coat layer similar to that in Example 1 was applied to the opposite surface of the polyester film (the surface on which the magnetic layer was not provided), calendered, and then thermoset. I went. Thereafter, this was cut into a width of 8 mm to prepare a tape-shaped magnetic recording sample 41.

(Comparative Example 1) In Example 1 above, the thickness of the coating layer 20 was 0.03 μm as shown in Table 3 below.
Changed to. A sample of Comparative Example 1 was prepared in the same manner as in Example 1 except above.

(Comparative Example 2) In Example 3 above, the thickness of the magnetic layer 30 was changed to 1.5 μm as shown in Table 3 below. A sample of Comparative Example 2 was prepared in the same manner as in Example 3 except the above.

Comparative Examples 3 to 6 In the above Example 1,
The coating layer 20 was not provided. Further, the thickness of the magnetic layer is 1.
Various changes were made to 5 μm, 0.2 μm, 0.7 μm and 1.0 μm. Other than that, the sample of Comparative Examples 3-6 was produced like Example 1 above.

Comparative Example 7 In Example 3, the average particle diameter and the maximum particle diameter of the abrasive contained in the magnetic layer 30 were changed. A sample of Comparative Example 7 was prepared in the same manner as in Example 3 except the above. Incidentally, this sample does not satisfy the conditions of the above formulas (1) and (2).

Comparative Example 8 In Example 3, the thickness of the magnetic layer 30 and the maximum particle size of the abrasive contained in the magnetic layer 30 were changed. A sample of Comparative Example 8 was prepared in the same manner as in Example 3 except above. Incidentally, this sample does not satisfy the conditions of the above formulas (1) and (2).

(Comparative Example 9) In the above-mentioned Example 3, the coating layer 20 was changed to a base layer made of the following coating composition.
Of course, this underlayer is simply applied on the flexible support and then dried, and is not stretched.
A sample of Comparative Example 9 was prepared in the same manner as in Example 3 except above.

Coating composition for forming the underlying layer Needle-like α-iron oxide (average major axis length 0.15 μm, BET 53 m ² / g) ... 100 parts by weight carbon black (Colombex Carbon SC, Conductectex SC) ) ... 25 parts by weight Vinyl chloride copolymer (manufactured by Nippon Zeon Co., Ltd., MR-110) ... 10 parts by weight Polyurethane resin A (manufactured by Toyobo Co., Ltd., UR8200) ... 5 parts by weight Polyurethane resin B (Toyobo Co., Ltd.) Co., Ltd., UR8700) ... 5 parts by weight α-alumina (Sumitomo Chemical Co., Ltd., HIT60A) ... 10 parts by weight stearic acid ... 2 parts by weight butyl stearate ... 1 part by weight methyl ethyl ketone ... 80 parts by weight toluene ... 80 Parts by weight Cyclohexanone ... 80 parts by weight After kneading a part or all of the above materials with a kneader, put them in a sand grinder mill. Dispersed and mixed, was diluted. Further, just before coating the coating material, 3.6 parts by weight of a curing agent (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added and mixed, and coating was performed.

(Comparative Example 10) In Example 3 above, as shown in Table 4 below, the thickness of the coating layer 20, the coating layer 20
The particle size and addition amount of the non-magnetic particles contained in were changed. Other than that, it carried out similarly to the said Example 3, and the comparative example 10
The sample of was produced.

(Comparative Example 11) In the above-mentioned Example 21,
The thickness of the coating layer 20 was changed as shown in Table 4 below.
A sample of Comparative Example 11 was made in the same manner as Example 21 except for the above. By the way, this sample does not satisfy the condition of the above formula (2).

Comparative Example 12 In Example 4, the average particle size and the maximum particle size of the abrasive contained in the magnetic layer 30 were changed as shown in Table 4 below. A sample of Comparative Example 12 was produced in the same manner as in Example 4 except the above. By the way, this sample does not satisfy the condition of the above formula (1).

Comparative Example 13 In Comparative Example 7, the thickness of the magnetic layer 30 was changed as shown in Table 4 below. A sample of Comparative Example 13 was prepared in the same manner as in Example 7 except above. Incidentally, this sample does not satisfy the conditions of the above formulas (1) and (2).

(Comparative Example 14) In the above-mentioned Example 23,
The thickness of the magnetic layer 30 was changed as shown in Table 4 below.
A sample of Comparative Example 14 was made in the same manner as Example 23 except for the above. By the way, this sample does not satisfy the condition of the above formula (2).

(Comparative Example 15) In the above-mentioned Example 30,
The thickness of the magnetic layer 30 was changed as shown in Table 4 below.
A sample of Comparative Example 15 was made in the same manner as Example 30 except for the above. By the way, this sample does not satisfy the condition of the above formula (2).

Thus, as shown in Tables 1 to 4 below, various samples (Examples 1 to 41, Comparative Examples 1 to 1)
5) was prepared, and the magnetic properties, electromagnetic conversion properties, and tape surface properties of these were evaluated.

Surface Roughness SRa Kosaka Laboratory "Surforder ET-30HK"
Magnification 20000 times, CUT-OFF 80μ
m, X pitch 1 μm, Y pitch 20 μm, X Le
ngth was measured at 500 μm × 30 pieces. In addition, one sample was measured three times, and an average value thereof was used as measurement data.

Electromagnetic conversion characteristics (output) With a Hi8 deck (EV-S900 manufactured by Sony Corporation),
The reproduction output of the recording signal having a wavelength of 7.0 MHz was measured.
The sample of Comparative Example 1 was used as a standard (0 dB) for relative evaluation.

Still characteristics The tape was loaded on a Hi8 deck (EV-S900 manufactured by Sony Corp.), and the state where the tape was temporarily stopped was continued.
The time until the output reaches −16 dB was measured.

Dropout (DO) number Hi8 deck (EV-S900 manufactured by Sony Corp.) to R
The F output was input to a DO counter to measure the number of DOs in 1 minute (however, the counting conditions were a width (time) of 5 μsec or more and a depth (output drop) of -16 dB or less).

The results are shown in Tables 1 to 4 below.

[0162]

[Table 1]

[0163]

[Table 2]

[0164]

[Table 3]

[0165]

[Table 4] In the above Tables 1 to 4, the particle type A of the coating layer is that the non-magnetic particles used are organic particles of styrene-ethylene glycol dimethacrylate, and the particle type B is that the non-magnetic particles used are silica. That the particle type C is a styrene-divinylbenzene-based organic particle, and the particle type D is
It is shown that they are organic particles of methylmethacrylate-divinylbenzene type. In the display of the comprehensive evaluation, ◎ is the best, followed by ◯, ×, XX.

By the way, the criterion of ◎ is output +5 dB
As described above, the number of stills is 30 minutes or more and the number of DOs is 20 or less. Further, the judgment criteria of ◯ are: output +2 dB or more, still 30 minutes or more, and 20 DOs or less. Those that did not satisfy these criteria were judged as x or xx depending on their degree. In addition, in the case of Comparative Example 10, in particular, many particles were dropped out in the coating layer.

(Example 42) A floppy disk sample of the present invention was prepared in the following manner.

Preparation of Flexible Support 10 and Coating Layer 20
Of 100 parts by weight of dimethyl terephthalate, 65 parts by weight of ethylene glycol and 0.09 parts by weight of magnesium acetate were placed in a reactor, and transesterification was performed while heating and heating and distilling off methanol. It took about 4 hours after the start of the reaction, and the temperature was raised to 230 ° C. to substantially complete the transesterification. Here, 0.3 part by weight of SiO ₂ particles having an average particle size of 0.1 μm was added as an ethylene glycol slurry, and then 0.4 part by weight of ethyl acid phosphate and 0.04 part by weight of antimony oxide were added to carry out the reaction. At the same time that the system pressure was reduced from room temperature, the temperature was raised by heating, and finally the conditions were 1 mmHg and 285 ° C. After 4 hours, the system was returned to normal pressure to obtain polyethylene terephthalate (hereinafter referred to as PET) having an intrinsic viscosity of 0.66.

The PET thus obtained was
After drying at ℃ for 4 hours, it is fed to an extruder and melted at 290 ℃, and the extruded polymer is wound around a casting drum with a surface temperature of 40 ℃ using an electrostatic cast method to cool and solidify, and unstretched. A film (sheet) was obtained.

This unstretched film (sheet) was stretched in the machine direction at 85 ° C. by a stretch ratio of 3.6 times by a roll stretching method. Next, in order to form the coating layer 20, a coating solution having the same composition as in Example 1 above is applied to both sides of the above film by a bar coater, and the film after application is introduced into a tenter, The film was stretched in the transverse direction at a temperature of 120 to 145 ° C by a factor of 4.0 and then heat set at 220 ° C for 10 seconds to give a total thickness of 62 µm and a dry thickness of the coating layer of 0.2 µm (value on one side). A biaxially oriented polyester film having a total coating layer thickness of 0.4 μm on both sides was obtained.

Formation of Magnetic Layer 30 The following magnetic layers 30 were provided on both sides of the polyester film.

Hc = 1680 Oe, σ _s = 140 emu
A magnetic coating material for forming a magnetic layer was prepared using the following composition containing a ferromagnetic metal magnetic powder having an average major axis length of 0.15 μm / g.

Magnetic coating composition for forming a magnetic layer Ferromagnetic metal magnetic powder: 100 parts by weight Thermosetting vinyl chloride copolymer (MR-110, manufactured by Nippon Zeon Co., Ltd.): 15 parts by weight Thermosetting Polyurethane resin (UR-8200, manufactured by Toyobo Co., Ltd.) 16 parts by weight α-alumina 12 parts by weight carbon black 4 parts by weight Methyl ethyl ketone 70 parts by weight toluene 30 parts by weight Cyclohexanone 100 parts by weight or more Was dispersed with a sand grinder mill, the following composition was added, and further dispersed to prepare a magnetic coating material.

Butyl stearate 1 part by weight sorbitan monostearate 3 parts by weight neopentyl glycol dioleate 5 parts by weight methyl ethyl ketone 46 parts by weight toluene 20 parts by weight cyclohexanone 66 parts by weight Obtained in this way Hardening agent (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to magnetic paint 100
12 parts by weight was added to 0 parts by weight and mixed, and the magnetic coating material was prepared by the nozzle coating method in a thickness of 6 as described above.
Coating on both surfaces of a 2 μm PET film support so that the dry thickness of the magnetic layer is 0.3 μm, and then orientation treatment,
It was dried and calendered. After that, this is punched out into a donut shape with a diameter of 3.5 inches at 60 ° C for 2
A floppy disk was produced by leaving it for 4 hours or longer (sample of Example 42).

(Comparative Example 16) In the above-mentioned Example 42,
The coating layer 20 was not provided. Other than that, Example 4 above
A sample of Comparative Example 16 of floppy disk was prepared in the same manner as in 2.

(Comparative Example 17) In the above-mentioned Example 42,
The thickness of the magnetic layer 30 was changed to 1.5 μm. Other than that,
A sample of Comparative Example 17 of floppy disk was prepared in the same manner as in Example 42 above.

Three such samples (Example 42,
For Comparative Example 16 and Comparative Example 17), the output, resolution, overwrite characteristics (O / W characteristics) and durability were evaluated based on the evaluation methods shown below.

Evaluation method Floppy disk drive FD133 manufactured by NEC Corporation
5, the output, the resolution and the overwrite characteristic were examined as follows. The above-mentioned floppy disk drive is of the MFM (modified frequency modulation) recording system, and the number of recording wavelengths was changed as follows for the measurement with the (2,7) code system.

Standard specifications 1F: 321.5 KHz, 2F: 625 KHz (F is an abbreviation for Frequency) Modified specifications RL7: 234 KHz, RL2: 625 KHz (RL is an abbreviation for Run Length) The above-mentioned floppy disk drive is Rotational speed 360R.
P. M. , The track radius is 23.01 on the innermost side 1
4 mm, the outermost peripheral side 0 is 39.500 mm, and the wavelength and recording density when recording the above frequency are as follows.

When RL7 is recorded on the outermost peripheral side 0: wavelength 6.35 μm recording density 8.0 KFCI When RL2 is recorded on the outermost peripheral side 0: wavelength 2.38 μm recording density 21.3 KFCI RL7 on the innermost peripheral side 1 Recording: wavelength 3.70 μm recording density 13.7 KFCI recording RL2 on innermost side 1: wavelength 1.39 μm recording density 36.6 KFCI (above FCI stands for Flux Change per Inch) output RL2 was recorded on the innermost side 1 and the average signal amplitude was measured with an oscilloscope.

Resolution RL7 and RL2 were recorded on the innermost side 1 and the average signal amplitude was measured with an oscilloscope, and the resolution was calculated by the following formula.

Resolution = (RL2 average signal amplitude / RL7 average signal amplitude) × 100 Overwrite characteristic (O / W characteristic) RL7 is recorded at the outermost peripheral side 0 and the average signal amplitude is measured. Next, RL2 was overwritten without erasing, the residual average signal amplitude of RL7 was measured, and the overwrite value (O / W value) was calculated by the following formula. A spectrum analyzer was used to measure these average signal amplitudes.

O / W value = 20 log (RL7 residual average signal amplitude / RL7 average signal amplitude) Durability Continuous under low temperature (0 ° C.) and high temperature and low humidity (60 ° C., 10% RH) measurement environment conditions, respectively. Recording / reproducing was performed, and the time required to reach 80% of the initial output was measured to examine the durability of the disk.

The results of these measurements are shown in Table 5 below.

[0185]

[Table 5] From the results shown in Table 5, the sample of Example 42 of the present invention has extremely good results in all the measurement items. The sample of Comparative Example 16 has good overwrite characteristics, but has poor calendering workability.
The output is low and the durability is not good. The sample of Comparative Example 17 is particularly poor in overwrite characteristics because the magnetic layer is thick.

(Example 43) Hc = 2000 Oe, σ _s
= 140 emu / g, average major axis length 0.08 μm, average axis ratio 5 ferromagnetic metal magnetic powder (Fe / Co / Al /
A magnetic coating material for forming a magnetic layer was prepared using the following composition containing Y = 100/20 / 4.2 / 5.3 (weight ratio)).

Magnetic coating composition for forming magnetic layer Ferromagnetic metal magnetic powder: 100 parts by weight Vinyl chloride copolymer (MR-110, manufactured by Nippon Zeon Co., Ltd.) 8.3 parts by weight Polyester polyurethane resin (Toyobo Co., Ltd.) Co., Ltd., UR-8300) ... 8.3 parts by weight α-alumina ... 1 part by weight stearic acid ... 1 part by weight butyl stearate ... 1 part by weight methyl ethyl ketone ... 111 parts by weight toluene ... 111 parts by weight cyclohexanone ... 74 parts by weight This composition The product was sufficiently kneaded with a kneader and then dispersed with a sand grinder mill. 3.3 parts by weight of a curing agent (Nippon Polyurethane Industry Co., Ltd., Coronate L) was added to and mixed with the magnetic coating material thus obtained,
A coating material for forming the magnetic layer was prepared.

Then, a coating material for forming a base layer was prepared in the following manner.

Coating composition α-Fe ₂ O ₃ (DPN250BX manufactured by Toda Kogyo Co., Ltd.) for forming an underlayer : 100 parts by weight Vinyl chloride copolymer (MR-110 manufactured by Nippon Zeon Co., Ltd.) 10 parts by weight polyester polyurethane resin (manufactured by Toyobo Co., Ltd., UR8700) 10 parts by weight α-Al ₂ O ₃ 3 parts by weight stearic acid 1 part by weight butyl stearate 1 part by weight methyl ethyl ketone 80 parts by weight toluene 80 parts by weight Cyclohexanone ... 80 parts by weight This composition was sufficiently kneaded in a kneader and then dispersed in a sand grinder mill. 4 parts by weight of a curing agent (Nippon Polyurethane Industry Co., Ltd., Coronate L) was added to and mixed with the magnetic coating material thus obtained to prepare a coating material for forming an underlayer.

The undercoat layer-forming coating composition was applied onto the support (coating layer 20) used in Example 3 so that the undercoat layer had a thickness of 0.5 μm, and dried. Then, calendering was performed, and further heat curing was performed to form an underlayer. Next, the above magnetic coating material was applied onto the underlayer so that the dry thickness of the magnetic layer was 0.2 μm, and thereafter, orientation treatment, drying and calendar treatment were performed.

Next, the coating for forming the back coat layer used in Example 1 was applied to the opposite surface of the support (the surface on which the magnetic layer was not provided), and calendering was performed, followed by thermosetting treatment. I went. Thereafter, this was cut into a width of 8 mm to prepare a tape-shaped magnetic recording medium sample (Example sample 43).

(Comparative Example 18) A support having no coating layer 20 was used in the above-mentioned Example Sample 43. A sample of Comparative Example 18 was made in the same manner as Example 43 except for the above.

With respect to such two kinds of samples (Example 43 and Comparative Example 18), the measurement items on the above-mentioned magnetic tape, that is, surface roughness SRa, electromagnetic conversion characteristics (output), still characteristics and dropout were measured. , (DO)
The number was measured.

The results are shown in Table 6 below.

[0195]

[Table 6] From the results shown in Table 6, since the sample of Comparative Example 18 has no coating layer, the effect of calendering is small even if the underlayer is provided, and the surface roughness SRa as a medium is large. Therefore, the electromagnetic conversion characteristics (output) are low.

[0196]

The effects of the present invention are clear from the above results. That is, the magnetic recording medium of the present invention comprises a coating layer having a predetermined thickness, which has a binder and non-magnetic particles and is stretched at least once on a flexible support. Since it has a predetermined magnetic layer formed on it, not only the productivity is excellent, but also the surface property of the thin magnetic layer can be improved. As a result, there is an effect that high output can be achieved in the short wavelength region. Furthermore, it has the effect of being excellent in running durability.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a magnetic recording medium of the present invention.

[Explanation of symbols]

 1 ... Magnetic recording medium 10 ... Flexible support 20 ... Coating layer 30 ... Magnetic layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Harada 347 Inoguchi, Yamato-cho, Sakata-gun, Shiga Daia Foil Hoechst Central Research Institute

Claims (4)

[Claims] 1. A magnetic recording medium comprising a flexible support, a coating layer formed on the support, and a magnetic layer formed on the coating layer. Has at least one after having a binder and non-magnetic particles and coated on said flexible support.
It has been stretched once and its thickness is 0.05 ~
0.7 μm, the magnetic layer contains magnetic powder, a binder, and an abrasive and has a thickness of 0.05 to 1.0 μm, and the non-magnetic layer contained in the coating layer. The particles have an average particle diameter of 0.01 to 0.08 μm, the abrasive contained in the magnetic layer has an average particle diameter of 0.05 to 0.8 μm, and the following formula ( A magnetic recording medium which satisfies the conditions 1) and (2). Maximum particle size (d _mx ) ≦ (average particle size (d _av ) × 2.0) +0.5 Equation (1) Maximum particle size (d _mx ) ≦ (coating layer thickness (t _c ) + magnetism Layer thickness (t _m )) + 0.5 Equation (2) 2. The magnetic recording medium according to claim 1, wherein the content of the non-magnetic particles contained in the coating layer is 3 to 60 wt%. 3. The magnetic recording medium according to claim 1, wherein the content of the abrasive contained in the magnetic layer is 0.1 to 20 wt%. 4. The magnetic recording medium according to claim 1, wherein the binder of the coating layer is a water-soluble or water-dispersible resin.