JPH10188266A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the dispersibility of a powder material and to impart high electromagnetic conversion characteristics adequate for high-density recording to the medium by incorporating β-diketone into a magnetic coating material and nonmagnetic coating material to be used at the time of production. SOLUTION: A lower layer 2 contg. the ferromagnetic powder or nonmagnetic powder and binder is formed on one surface of a nonmagnetic base 1 and an upper layer 3 contg. the ferromagnetic powder and binder is formed thereon. The β-diketone is added to the upper layer 3 at 0.5 to 5 pts.wt. to 100 pts.wt. ferromagnetic powder. The β-diketone of the similar weight ratio is added to the lower layer 2 as well. The β-diketone forms strong bonds by interacting with the metal atoms on the surfaces of the ferromagnetic or nonmagnetic powder and forms adsorption layers by adsorbing to the powder surface but the β-diketone is not a high polymer and has a low mol.wt. and, therefore, the β-diketone has no repulsive force to counter the interpowder attraction. The stabilization of the powder dispersion may be consequently attained by the binder adsorption and the sufficient exhibition of the characteristics of the ferromagnetic powder is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium, and more particularly to a multilayer coating type magnetic recording medium having high electromagnetic conversion characteristics suitable for high density recording.

[0002]

2. Description of the Related Art Magnetic recording media include audio tapes,
Video tape, backup data cartridge,
Widely used as floppy disks and the like. In particular, recently, high-density recording such as a shorter recording wavelength or a digital recording method has been actively studied, and the development of a magnetic recording medium having excellent electromagnetic conversion characteristics has been demanded.

[0003] In the coating type magnetic recording medium, multilayering and thinning of the magnetic layer have been studied in order to improve the electromagnetic conversion characteristics. The latter is a method of improving the electromagnetic conversion characteristics by reducing the self-demagnetization loss at the time of recording.However, when a single thin magnetic layer of 0.5 μm or less is provided on a non-magnetic support, The influence of the surface shape is likely to appear, and it is difficult to obtain a smooth surface. For this reason, in practice, a method has been devised in which a nonmagnetic undercoat layer is provided between the magnetic layer and the nonmagnetic support to form a multilayer structure, thereby reducing the thickness of the magnetic layer and smoothing the surface of the magnetic layer. I have.

[0004] In the coating process of the multilayer coating type magnetic recording medium having such a multilayer structure, a uniform coating film free from coating defects and stripes is formed for the purpose of improving electromagnetic characteristics and reducing noise. Is required. As a coating method to meet the demand, an upper layer is formed by simultaneously applying a coating material in which a ferromagnetic powder or a non-magnetic powder and a binder are dispersed in an organic solvent on a non-magnetic support by an extrusion method (co-extrusion method). And a lower layer have been proposed. Further, this simultaneous multilayer coating method is also effective as a method for improving the adhesiveness of the interface between the upper layer and the lower layer, and has become a central coating method when manufacturing a multilayer coating type magnetic recording medium in recent years. It is getting.

In general, it is necessary to smooth the surface of a magnetic layer in order to minimize spacing loss during recording and reproduction. In particular, in high-density recording, the recording wavelength to be used is short, and it is easily affected by the surface roughness. Therefore, it is important to further smooth the surface, and therefore, control of the surface roughness is particularly important.

One of the important techniques for improving the electromagnetic conversion characteristics in relation to the control of the surface roughness is to improve the ferromagnetic powder contained in the magnetic layer. Improvements in such ferromagnetic powder include (1) using a ferromagnetic alloy powder as the ferromagnetic powder, (2) miniaturizing the ferromagnetic powder, and (3) increasing the holding power of the ferromagnetic powder. And making the holding force distribution uniform.

Improvements (1) and (2) of the above ferromagnetic powder
With respect to (1), ferromagnetic powders having a saturation magnetization exceeding 140 Am ² / kg and ferromagnetic powders having a major axis length of 0.1 μm or less have been developed.

As for the improvement (3) of the ferromagnetic powder, a ferromagnetic powder having a coercive force exceeding 160 KA / m has been developed, and the particle size distribution reflecting the coercive force distribution can be made extremely uniform. It has become.

Therefore, recently, it has been attempted to use such a ferromagnetic powder as a component of a magnetic paint when producing a multilayer coating type magnetic recording medium.

[0010]

However, in order for the magnetic recording medium to exhibit good electromagnetic conversion characteristics, the ferromagnetic powder must be uniformly dispersed in the binder in the magnetic layer. As the magnetic powder becomes finer, dispersion of the powder in the binder tends to be difficult. Especially,
In recent years, the use of ferromagnetic powder having a major axis length of 0.1 μm or less has been studied, and it is difficult to say that a dispersion technique corresponding to this has been established. This problem also occurs in the undercoat layer provided between the magnetic layer and the nonmagnetic support of the multilayer coating type magnetic recording medium.

For this reason, in the kneading step performed when preparing a magnetic paint or a non-magnetic paint, the shearing force applied to a mixture of a powder material such as a ferromagnetic powder or a non-magnetic powder and a binder or the like is increased. Alternatively, it is conceivable to lengthen the processing time by a sand mill or the like in the subsequent dispersing step, but this is not preferred because damage to the magnetic powder and a reduction in production efficiency occur.

[0012] Further, -SO ₃ M, -OSO ₃ M,
-COOM, -P = O (OM) 2, -NR 1 R 2, -NR 1 R
²⁺ R ³ X ⁻ ,> NR ¹ R ²⁺ X ⁻ etc. (M is a hydrogen atom or an alkali metal such as lithium, potassium, sodium, etc .; R ¹ , R ² , R ³ are a hydrogen atom or inorganic·
Organic ions. ) Has been attempted to enhance the interaction with the ferromagnetic powder and improve the dispersibility of the paint. However, although the binder having the functional group exhibits excellent performance as compared with the conventional binder, it is still difficult to sufficiently disperse the fine ferromagnetic powder developed for high-density recording. Is the current situation.

The present invention is intended to solve the above-mentioned problems of the prior art, and in particular, in a multilayer coating type magnetic recording medium, by imparting good dispersibility to a magnetic paint or a non-magnetic paint. An object is to provide a magnetic recording medium having high electromagnetic conversion characteristics suitable for high-density recording.

[0014]

SUMMARY OF THE INVENTION The object of the present invention is to provide a magnetic or non-magnetic paint used in the production of a magnetic recording medium containing β-diketone as a component for improving the dispersibility of the powder material. They have found that this can be achieved, and have completed the present invention.

That is, according to the present invention, a ferromagnetic powder or a non-magnetic powder is dispersed in a binder on a non-magnetic support, and the ferromagnetic powder is dispersed in the binder on the lower layer. A magnetic recording medium provided with an upper layer, wherein the upper layer contains 0.5 to 5 parts by weight of β-diketone with respect to 100 parts by weight of the ferromagnetic powder. In this case, the lower layer is also made of ferromagnetic powder or non-magnetic powder 100.
It is preferable to contain 0.5 to 5 parts by weight of β-diketone based on parts by weight.

Further, according to the present invention, a lower layer paint obtained by dispersing a ferromagnetic powder or a nonmagnetic powder and a binder in an organic solvent is applied on a nonmagnetic support to form a lower layer, and a lower layer is formed thereon. A method for producing an upper layer by applying an upper layer coating obtained by dispersing a ferromagnetic powder and a binder in an organic solvent while the lower layer is in an undried state; Provided is a production method characterized by containing 0.5 to 5 parts by weight of β-diketone per 100 parts by weight. Also in this case, the lower layer paint is made of a ferromagnetic powder or a non-magnetic powder 100.
It is preferable to contain 0.5 to 5 parts by weight of β-diketone based on parts by weight.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention will be described below in detail.

The basic aspect of the magnetic recording medium of the present invention is as follows.
As shown in FIG. 1, a lower layer 2 containing a ferromagnetic powder or a non-magnetic powder and a binder is formed on one surface of a non-magnetic support 1, and a ferromagnetic powder, a binder, and the like are formed thereon. It has a structure in which a contained upper layer (magnetic layer) 3 is formed. If necessary, a backcoat layer 4 mainly composed of a nonmagnetic powder and a binder may be formed on the back surface of the nonmagnetic support.

Here, at least the upper layer 3 (magnetic layer) has β
-Contains diketone. Preferably, in addition to upper layer 3, lower layer 2 also contains β-diketone. This β-diketone is
It interacts with metal atoms on the surface of the ferromagnetic powder or non-magnetic powder to form a strong bond and is adsorbed on the powder surface. Where β
-Although diketone forms an adsorption layer on the surface of the powder, it is not a polymer but has a relatively low molecular weight, so that a sufficient repulsive force against the attractive force between the powders cannot be obtained. Thus, in practice, the stabilization of the dispersion of the powder will be achieved by the adsorption of the binder, while the β-diketone plays its auxiliary role. Therefore, the properties of ferromagnetic powder are fully exhibited,
The electromagnetic conversion characteristics of the magnetic recording medium are improved. In addition, a coating material having good dispersibility can be prepared even when a fine powder material is used, so that the surface smoothness of the magnetic recording medium can be improved.

Specific examples of the β-diketone used in the present invention include acetylacetone, 3-methyl-2,4-pentanedione, 3-ethyl-2,4-pentanedione,
Examples thereof include n-butyl-2,4-pentanedione, trifluoroacetylacetone, dipivaloylmethane, and thenoyltrifluoroacetone. These can be used alone or in combination of two or more.

The amount of β-diketone contained in the upper layer or in both the upper layer and the lower layer depends on the amount of the ferromagnetic powder or non-magnetic powder.
It is 0.5 to 5 parts by weight with respect to 00 parts by weight. If the content of β-diketone exceeds the above range, metal atoms become metal chelates and elute in the coating material, and the adsorption of the binder is suppressed, so that the dispersibility is hindered. On the other hand, β
-When the content of the diketone is below the above range, it becomes insufficient to improve the dispersibility of the powder.

In the present invention, as the binder contained in the upper layer 3 and the lower layer 2, known thermoplastic resins, thermosetting resins, reactive resins and the like conventionally used as binders for magnetic recording media are used. Possible, with a number average molecular weight of 5
000 to 100,000 are preferred.

Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, and acrylate-acrylonitrile copolymer. Acrylate-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer Methacrylate-vinyl chloride copolymer, methacrylate-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose Derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene-butadiene copolymer, polyurethane resin, polyester resin, amino resin, synthetic rubber, and the like.

Examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curing resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, a polyamine resin, and a urea formaldehyde resin. .

All the above-mentioned binders include -SO ₃ M, -OSO ₃ M,-for the purpose of improving the dispersibility of the pigment.
A polar functional group such as COOM and P = O (OM) ₂ may be introduced. Here, M is a hydrogen atom or an alkali metal such as lithium, potassium, and sodium. Further, as the polar functional group, -NR ¹ R ² , -NR ¹ R
²⁺ R ³ X ^- that of side chain type having an end group of,> NR ¹ R ²⁺
X ^- there is one of the main chain type. Here, R ¹ , R ² , and R ³ are
X ^- is a halogen element ion such as fluorine, chlorine, bromine or iodine, or an inorganic or organic ion. Also, -OH, -SH, -CN,
There are also polar functional groups such as epoxy groups.

The amount of these polar functional groups is 10 ^-1 to 10 ^-8
mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g.
g. These binders can be used alone or in combination of two or more.

Regarding the amount of the binder described above, if the amount of the binder is too large, the ratio of the ferromagnetic powder in the upper layer 3 is relatively reduced, and the output is reduced. Plastic flow is likely to occur due to sliding or the like, leading to a decrease in the running durability of the medium. On the other hand, if the amount of the binder used is too small, both the upper layer 3 and the lower layer 2 become brittle, and the running durability of the medium decreases. Therefore, the amount of the binder used is preferably 1 to 200 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the ferromagnetic powder or nonmagnetic powder.

In the present invention, at least one of the upper layer 3 and the lower layer 2 may contain a crosslinking agent for crosslinking and curing the binder. As the crosslinking agent, a polyisocyanate, for example, toluene diisocyanate, an adduct thereof, an alkylene diisocyanate, an adduct thereof, and the like can be used.

The amount of the polyisocyanate to be used with respect to the binder is preferably 5 to 80 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the binder.

In the present invention, the ferromagnetic powder used in the upper layer 3 or the lower layer 2 includes metals such as Fe, Co and Ni,
Fe-Co, Fe-Ni, Fe-Al, Fe-Ni-A
1, Fe-Al-P, Fe-Ni-Si-Al, Fe-
Ni-Si-Al-Mn, Fe-Mn-Zn, Co-N
i, Co-P, Fe-Co-Ni, Fe-Co-Ni-
Cr, Fe-Co-Ni-P, Fe-Co-B, Fe-
Co-Cr-B, Mn-Bi, Mn-Al, Fe-Co
Alloys such as -V, iron nitride, iron carbide and the like. These may contain a light metal element such as Al, Si, P, or B added for the purpose of preventing sintering during reduction or maintaining the shape. Further, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe
Belt compound of ₂ O ₃ and Fe ₃ O ₄ , Co-containing γ-
Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , γ-Fe containing Co
Belt ride compound of ₂ O ₃ and Fe ₃ O ₄ , one for CrO ₂
One or more metal elements such as Te, Sb, Fe,
An oxide containing B or the like can be given. Further, hexagonal plate-like ferrite can also be used, and M type,
W-type, Y-type, Z-type barium ferrite, strontium ferrite, calcium ferrite, lead ferrite,
And Co-Ti, C
o-Ti-Zn, Co-Ti-Nb, Co-Ti-Zn
Those to which -Nb, Cu-Zr, Ni-Ti or the like is added can also be mentioned. These ferromagnetic powders can be used alone or in combination of two or more.

The specific surface area of the ferromagnetic powder used in the present invention is preferably 30 to 80 m ² / g, more preferably 40 to 70 m ² / g. When the specific surface area is in the above range, high-density recording can be performed with the formation of fine particles of the ferromagnetic powder, and a magnetic recording medium having excellent noise characteristics can be obtained.

Further, when the long axis length of the ferromagnetic powder used in the present invention is too short, dispersion in the magnetic paint becomes difficult, and when the long axis length is too long, the noise characteristics are deteriorated.
05 to 0.50 μm. Further, if the axial ratio is too small, the orientation of the ferromagnetic powder is reduced and the output is reduced.If the axial ratio is too large, the short-wavelength signal output may be reduced.
Preferably it is 2-15. Specifically, when the ferromagnetic powder is plate-like ferrite, the plate diameter is preferably about 0.01 to 0.5 μm, and the plate thickness is preferably about 0.001 to 0.2 μm.

The numerical ranges of the major axis length, the axial ratio, the plate diameter, and the plate thickness described above are based on an average value of 100 or more samples randomly selected from a transmission electron microscope photograph.

When the lower layer 2 is a nonmagnetic layer in the present invention, the nonmagnetic powder to be contained is, for example, α-F
Non-magnetic iron oxide such as e ₂ O ₃ , goethite, rutile type titanium oxide, anatase type titanium oxide, tin oxide, tungsten oxide, silicon oxide, zinc oxide, chromium oxide, cerium oxide, titanium carbide, BN, α-alumina , Β-alumina, γ-alumina, calcium sulfate, barium sulfate,
Molybdenum disulfide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, barium titanate and the like can be mentioned. These powders can be used alone or in combination of two or more.

The above non-magnetic powder can be doped with an appropriate amount of impurities according to the purpose. Further, for the purpose of improving dispersibility, imparting conductivity, improving color tone, etc., Al, S
Surface treatment with compounds such as i, Ti, Sn, Sb, and Zr is also possible.

The specific surface area of the nonmagnetic powder is preferably 30 to
80 m ² / g, more preferably 40~70m ² / g. If necessary, carbon black such as furnace furnace for rubber, pyrolytic carbon, black for color, and acetylene black may be contained. Here, the specific surface area of the carbon black is preferably 100 to 400 m ² /
g, and the DBP oil absorption is preferably 20 to 200 ml.
/ 100 g.

When the specific surface areas of the non-magnetic powder and carbon black are within the above range, the lower layer is smoothed as the shape becomes finer, and as a result, the upper layer can be smoothed. It is possible to obtain a magnetic recording medium less affected by spacing loss. Non-magnetic powders do not have magnetic cohesion, so they are easier to disperse than ferromagnetic powders.However, when the specific surface area is larger than the above range, powders can be obtained using the method of the present invention. Difficulty dispersing the body. If the specific surface area is too small, surface smoothness that can withstand high-density recording cannot be secured.

In the present invention, a lubricant can be contained in at least one of the upper layer 2 and the lower layer 3 as necessary. As the lubricant, graphite, molybdenum disulfide, tungsten disulfide, silicone oil, carbon number 10 to 2
And fatty acid esters, terpene-based compounds, and oligomers of these fatty acids and alcohols having 2 to 26 carbon atoms.

In the present invention, the upper layer 3 may contain abrasive particles. Examples of the abrasive include alumina (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, titanium carbide, titanium oxide (rutile, anatase) and the like. The amount of these particles used is
It is preferably at most 20 parts by weight, more preferably at most 10 parts by weight, based on 00 parts by weight. The Mohs hardness is
It is preferably 4 or more, more preferably 5 or more, the specific gravity is preferably 2 to 6, more preferably 3 to 5, and the average particle size is preferably 0.5 μm or less, more preferably 0.3 μm or less. .

The average particle size of the abrasive particles as described above is:
As in the case of the ferromagnetic powder, it is measured from a transmission electron micrograph and statistically processed.

As the non-magnetic support 1, the same one as used in known magnetic recording media can be used. For example, polyethylene terephthalate,
Polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, polymer materials such as vinyl resins, polyimides and polycarbonates, or metals And films or sheets of inorganic materials such as glass and ceramics.

On the surface (back surface) of the non-magnetic support 1 on which the upper layer 3 is not provided, the back coat layer 4 is provided for the purpose of improving the runnability of the magnetic recording medium, preventing charging and preventing transfer, and the like.
May be formed. In addition, an adhesive layer may be formed between the lower layer 2 and the non-magnetic support 1 for the purpose of enhancing their adhesiveness.

The magnetic recording medium of the present invention described above can be manufactured by sequentially laminating a lower layer 2 and an upper layer 3 on a non-magnetic support 1 by a known method. Here, when the lower layer 2 and the upper layer 3 are formed on the non-magnetic support 1, a method of applying and drying one layer at a time (so-called wet
An on-dry coating method) and a method of applying the upper layer 3 on the lower layer 2 in a wet state that has not been dried (so-called wet-on-wet coating method = wet multilayer coating method). In the present invention, among the latter wet multilayer coating methods, a simultaneous multilayer coating method in which a lower layer and an upper layer are simultaneously formed as shown in FIG. 2 is preferable as described below.

That is, when manufacturing the magnetic recording medium shown in FIG. 1, for example, the lower layer 2 and the upper layer 3 are extruded from the supply roll in the direction of arrow A while being extruded by the extrusion type extrusion coater 5. Paints 2 'and 3' are simultaneously applied in layers. That is, the lower layer paint 2 'and the upper layer paint 3' supplied from the liquid pools 6 and 7 provided in the extrusion coater 5 are simultaneously overlapped by a wet-on-wet method. Such wet
In the simultaneous wet application method of the on-wet method, since the upper layer (magnetic layer) forming paint 3 'is applied while the lower layer 2 is in a wet state, the surface of the lower layer 2 (that is, the boundary surface with the upper layer 3) is smooth. And the surface properties of the upper layer 3 are improved, and the adhesion between the upper layer 3 and the lower layer 2 is also improved.

As a result, the performance required for a magnetic recording medium which is required to have high output and low noise particularly for high-density recording is satisfied, film peeling is eliminated, and film strength is improved. In addition, dropout can be reduced, and reliability is improved.

On the other hand, for example, Japanese Unexamined Patent Application Publication No.
In the case of the wet-on-dry system described in JP-A-43-43, it is necessary to select the lower layer 2 having a sufficient solvent resistance to the paint of the upper layer 3. In addition, the smoothness of the surface is impaired, and as a result, the electromagnetic conversion characteristics are affected.

The upper layer 3 and the lower layer 2 formed by the wet-on-wet multi-layer coating method are mixed with components of a certain thickness except for a case where a clear boundary substantially exists. In some cases, there is a boundary region formed by the following method. The surface side excluding such a boundary region corresponds to the upper layer 3, and the nonmagnetic support 1 side corresponds to the lower layer 2.

After the above-mentioned multi-layer coating, it is introduced into a dryer, and further guided to a calender if necessary, and wound up on a winding roll. Further, the back coat layer 4 may be applied and formed on the back surface of the non-magnetic support 1.

When the upper layer 3 is formed by the wet-on-wet multilayer coating method, an upper layer paint in which a ferromagnetic powder, a binder and β-diketone are uniformly dispersed in an organic solvent is used. Similarly, when forming the lower layer 2,
Ferromagnetic powder or non-magnetic powder, binder and β-
An underlayer paint in which diketone is uniformly dispersed in an organic solvent is used. Here, the upper layer paint and the lower layer paint can be prepared by a method in which β-diketone is mixed with a ferromagnetic powder or a non-magnetic powder and a binder at the same time, followed by kneading and dispersion with a solvent. The timing of adding the β-diketone may be after kneading, that is, at the beginning of the dispersion step by a sand mill or the like, but the method of adding before kneading is more preferable.

Organic solvents usable for preparing the upper layer paint and the lower layer paint include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohol solvents such as methanol, ethanol and propanol, methyl acetate and acetic acid. Ester solvents such as ethyl, butyl acetate, propyl acetate, ethyl lactate and ethylene glycol acetate; ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran and dioxane; and aromatic hydrocarbon solvents such as benzene, toluene and xylene. , Methylene chloride, ethylene chloride, carbon tetrachloride,
Examples thereof include halogenated hydrocarbon solvents such as chloroform and chlorobenzene.

When preparing the upper layer paint or the lower layer paint, it can be carried out by a known kneading method, mixing method, dispersion method and the like. For dispersing and kneading, a roll mill, a ball mill, a sand mill, an agitator, a kneader, an extruder, a homogenizer, an ultrasonic disperser and the like can be used.

Further, when the upper layer paint and the lower layer paint prepared as described above are simultaneously coated on the non-magnetic support 1 in a multilayer manner,
It can be performed mainly using a die coater. Examples of the lip configuration of the die coater include a two-lip system, a three-lip system, and a four-lip system.

The magnetic recording medium thus obtained is
For example, a magnetic tape can be prepared by slitting it to a width of 8 mm, and this can be accommodated in a cassette and processed into a tape cassette.

[0054]

The present invention will be described below in more detail with reference to examples.

Examples 1 to 12 and Comparative Examples 1 to 5
Has a non-magnetic layer composed of non-magnetic powder in the lower layer,
Examples 13 to 21 and Comparative Examples 6 to 10 are examples in which a magnetic layer is provided in the upper layer and the lower layer.

Examples 1 to 11 and Comparative Examples 1 to 5 With the compositions shown in Tables 1 and 2, the upper layer and the lower layer were formed into paints, respectively. According to a conventional method, a magnetic powder or a non-magnetic powder, a binder, an additive, a predetermined amount of a solvent, and β-diketone are mixed, kneaded by an extruder, and dispersed by a sand mill for 6 hours. A paint and an undercoat were prepared.

[0057]

< Table 1 > Composition of upper layer coating composition Component (parts by weight) Fe-based metal ferromagnetic powder 100 (coercive force = 160 kA / m, saturation magnetization = 145 Am ² / kg, specific surface area = 51 m ² / g, major axis Length = 0.08 μm, needle ratio = 3) Polyvinyl chloride resin (manufactured by Zeon Corporation, MR-110) 14 Polyester polyurethane resin (manufactured by Toyobo) 3 Additive (Al ₂ O ₃ ) 5 β-diketone (Table _3- Table 4) Stearic acid 1 Heptyl stearate 1 Methyl ethyl ketone 150 Cyclohexanone 150

[0058]

[Table 2] <Lower layer coating composition> Component Compounding amount (parts by weight) Acicular α-Fe ₂ O ₃ 100 (specific surface area = 53 m ² / g, major axis length = 0.15 μm, acicular ratio = 5) Vinyl resin (manufactured by Zeon Corporation, MR-110) 13 Polyester polyurethane resin (manufactured by Toyobo) 4 β-diketone (described in Tables 3 and 4) Stearic acid 1 Heptyl stearate 1 Methyl ethyl ketone 105 Cyclohexanone 105

[0059]

[Table 3] β- diketone amount (parts by weight) Example 1 upper acetylacetone 2 lower No 0 2 upper 3-methyl-2,4-pentanedione 2 lower No 0 3 layer dipivaloylmethane 2 lower No 0 4 layer trifluoromethyl acetylacetone 2 Lower layer None 0 5 Upper layer Acetylacetone 5 Lower layer None 0 6 Upper layer Acetylacetone 0.5 Lower layer None 07 Upper layer Acetylacetone 2 Lower layer Acetylacetone 2 8 Upper layer Acetylacetone 1 Lower layer Dipivaloylmethane 2 9 Upper layer Dipivaloylmethane 1 Lower layer 3-methyl −2,4-pentanedione 1 10 upper layer 3-methyl-2,4-pentanedione 2 lower layer trifluoroacetylacetone 2 11 upper layer 3-methyl-2,4-pentanedione 3 lower layer acetylacetone 5

[0060]

[Table 4] Addition amount (parts by weight) of β-diketone Comparative Example 1 Upper layer None 0 Lower layer None 0 2 Upper layer acetylacetone 0.1 Lower layer None 0 3 Upper layer acetylacetone 8 Lower layer None 0 4 Upper layer acetylacetone 8 Lower layer 3-methyl-2,4-pentanedione 1 5 upper layer 3-methyl-2,4-pentanedione 10 lower layer dipivaloylmethane 10

To the obtained upper layer paint and lower layer paint, 3 parts by weight of each polyisocyanate was added, and simultaneously applied on a 7 μm thick PET (polyethylene terephthalate) film using a 4-lip die coater to form a solenoid coil. , And then dried, calendered, and cured. Here, the coating thickness of each layer is 0.
2 μm, lower layer 2.0 μm.

Further, a back coating having the composition shown in Table 5 was applied to the surface opposite to the above-mentioned coated surface, and slit to a width of 8 mm to produce an 8 mm video tape as a magnetic recording medium.

[0063]

[Table 5] <Back coating composition> Component Compounding amount (parts by weight) Carbon black Asahi # 80 100 Polyester polyurethane Nipporan N-2304 100 Methyl ethyl ketone 500 Toluene 500

With respect to the obtained video tapes (magnetic recording media) of Examples and Comparative Examples, the electromagnetic conversion characteristics were measured using a fixed-head type electronic measuring instrument. This measuring machine is composed of a rotating drum and a head that comes into contact with the rotating drum, and the tape is wound around the drum. The actual measurement is
First, a 10-MHz rectangular wave signal was recorded at the optimum recording current of each tape, and 10 MHz was recorded by a spectrum analyzer.
The output level is detected. The relative speed between the tape and the head was 3.33 m / s, and an 8 mm Hi8 tape manufactured by Sony was used as a reference (0 dB). Table 6 shows the obtained results.

The center line average roughness (Ra) of each tape was measured using a non-contact type surface roughness meter by a laser light interference method. Table 6 shows the obtained results.

[0066]

[Table 6]

Table 6 shows that the magnetic recording media of Examples 1 to 11 have a smooth surface and excellent electromagnetic conversion characteristics.

On the other hand, the magnetic recording media of Comparative Examples 1 and 2
It can be seen that the effect of β-diketone is not exhibited and the output is low. Also, the surface smoothness is not sufficient. In the case of Comparative Examples 3 to 5, since the amount of β-diketone contained in the upper layer or the lower layer was too large, the dispersion of the magnetic powder or the nonmagnetic powder was impaired, and the reproduction output and the surface roughness were unsatisfactory.

Example 12 An upper layer paint and a lower layer paint were prepared in the same manner as in Example 1 except that acetylacetone was added after kneading the paint, and a magnetic recording medium was obtained.

Table 7 shows the measurement results of the 10 MHz reproduction output and the surface roughness of the magnetic recording media produced in Examples 1 and 12.

[0071]

[Table 7]

As can be seen from Table 7, the magnetic recording medium obtained in Example 1 in which acetylacetone was added before kneading had a smoother surface and a higher reproduction output than the case in Example 12 in which acetylacetone was added after kneading. I understand. Therefore, it can be seen that the effect of β-diketone can be more efficiently obtained by adding β-diketone before kneading the paint.

Examples 13 to 21 and Comparative Examples 6 to 10 Instead of the needle-like α-Fe ₂ O ₃ of the lower layer paint used in Example 1, an Fe-based metal ferromagnetic powder (coercive force = 140 kA /
m, saturation magnetization = 130 Am ² / kg, specific surface area = 53
Examples 1-7 and 10-11 and Comparative Example 1 except that m ² / g, major axis length = 0.15 μm, needle ratio = 5) were used.
Magnetic recording media of Examples 13 to 21 and Comparative Examples 6 to 10 were produced in the same manner as in Examples 5 to 5.

With respect to the obtained video tapes (magnetic recording media) of Examples and Comparative Examples, the measurement of electromagnetic conversion characteristics and the center line average roughness (Ra) were measured in the same manner as in Example 1. Table 8 shows the obtained results.

[0075]

[Table 8]

From Table 8, it can be seen that the magnetic recording media of Examples 13 to 21 have smooth surfaces and excellent electromagnetic conversion characteristics. Further, it can be seen that the dispersibility of the lower layer paint is improved by blending β-diketone in the lower layer, the surface is smoothed, and the reproduction output is improved.

On the other hand, the magnetic recording media of Comparative Examples 6 and 7
It can be seen that the effect of β-diketone is not exhibited and the output is low. Also, the surface smoothness is not sufficient. Comparative Examples 8 to 10
In case (1), the amount of β-diketone contained in the upper layer or the lower layer was too large, so that the dispersion of the magnetic powder or the nonmagnetic powder was impaired, and the reproduction output and surface roughness were unsatisfactory.

[0078]

According to the present invention, a magnetic recording medium having high electromagnetic conversion characteristics suitable for high-density recording can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a magnetic recording medium of the present invention.

FIG. 2 is a preferred example of the production of the magnetic recording medium of the present invention.

[Explanation of symbols]

1 Non-magnetic support, 2 Lower layer, 3 Upper layer, 4 Back coat layer

Claims (4)

[Claims] 1. A ferromagnetic powder or a non-magnetic powder is dispersed on a non-magnetic support in a binder, and an upper layer on which a ferro-magnetic powder is dispersed in a binder is provided. The magnetic recording medium according to claim 1, wherein the upper layer contains 0.5 to 5 parts by weight of β-diketone with respect to 100 parts by weight of the ferromagnetic powder. 2. The method according to claim 1, wherein the lower layer comprises a ferromagnetic powder or a non-magnetic powder.
2. The magnetic recording medium according to claim 1, wherein the content of the β-diketone is 0.5 to 5 parts by weight with respect to parts by weight. 3. A lower layer coating comprising a ferromagnetic powder or a non-magnetic powder and a binder dispersed in an organic solvent is applied on a non-magnetic support to form a lower layer, on which a lower layer is formed. In a method for producing a magnetic recording medium in which an upper layer is formed by applying an upper layer paint obtained by dispersing a ferromagnetic powder and a binder in an organic solvent in a dry state, the upper layer paint is added to 100 parts by weight of the ferromagnetic powder. On the other hand, a production method comprising 0.5 to 5 parts by weight of β-diketone. 4. The lower layer is made of a ferromagnetic powder or a non-magnetic powder 100.
The method according to claim 3, wherein the β-diketone is contained in an amount of 0.5 to 5 parts by weight based on parts by weight.