JPH11203655A - Magnetic recording medium and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a magnetic recording medium excellent in dispersibility of ferromagnetic powder and non-magnetic powder and make it have a high electromagnetic transfer characteristic suitable for high-density recording. SOLUTION: This recording medium is composed of a lower layer 4 in which ferromagnetic powder or non-magnetic powder is dispersed in a bonding agent as a multi-layer applying type on non-magnetic supporting body 1, and an upper layer 2 in which ferromagnetism powder is dispersed in a bonding agent. As a bonding agent at least in the upper layer 2 of the upper layer 2 and the lower layer 4, a vinyl chloride series resin is used, which has a weight-average molecular weight from 8000 to 15000 and has an epoxy group, and a silane coupling agent is contained at least in the upper layer 2 of the upper layer 2 and the lower layer 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a lower layer obtained by dispersing ferromagnetic powder or nonmagnetic powder in a binder and an upper layer obtained by dispersing ferromagnetic powder in a binder on a nonmagnetic support. A multilayer coating type magnetic recording medium (magnetic tape,
And a manufacturing method thereof.

[0002]

2. Description of the Related Art Magnetic recording media are audio tapes,
Video tape, data cartridge for backup,
Widely used as floppy disks. Particularly in recent years, studies have been actively conducted on high-density recording such as a shorter recording wavelength or a digital recording method, and development of a magnetic recording medium excellent in electromagnetic conversion characteristics is required.

In a coating type magnetic recording medium in which a magnetic layer comprising a ferromagnetic powder and a binder is coated on a non-magnetic support, the magnetic layers are formed in multiple layers (multilayers) in order to improve electromagnetic conversion characteristics. And thinning is being studied.

The latter is a method of improving electromagnetic conversion characteristics by reducing self-demagnetization loss during recording. When a thin magnetic layer of 0.5 μm or less is provided as a single layer on a non-magnetic support, Since the surface shape of the non-magnetic support is likely to appear on the surface of the magnetic layer and it is difficult to obtain a smooth surface, for example, a non-magnetic undercoat layer is provided between the magnetic layer and the non-magnetic support. There has been proposed a method of providing a thin magnetic layer and realizing a smooth surface.

As described above, in coating a magnetic recording medium having a multi-layer structure on a non-magnetic support, for the purpose of improving electromagnetic conversion characteristics and reducing noise, a uniform coating without coating defects or coating streaks is provided. Although it is required to form a film, as a coating method, a so-called simultaneous multilayer coating method has been proposed in which an upper magnetic layer and a lower nonmagnetic layer are simultaneously coated on a nonmagnetic support by an extrusion method. Further, the coating method is also effective as a method for improving the adhesiveness of the interface between the upper and lower layers, and is becoming a central coating method for recent multilayer coating type magnetic recording media.

Further, in general, the surface of the magnetic layer is smoothed in order to minimize spacing loss during recording and reproduction. Particularly in high density recording, the recording wavelength used is short, and therefore, it is susceptible to the roughness of the surface of the magnetic layer, so that the control of the surface roughness is particularly important.

Further, improvement of the ferromagnetic powder is also an effective method. Specifically, (1) use of ferromagnetic alloy powder as ferromagnetic powder (2) miniaturization of ferromagnetic powder (3) increase of coercive force of ferromagnetic powder and uniformization of coercive force distribution.

With respect to (1) and (2), as a result of active improvement of magnetic materials (ferromagnetic powders), ferromagnetic powders having a saturation magnetization of more than 140 Am ² /kg and long axis lengths of 0 have been obtained. Ferromagnetic powders of less than 0.1 μm have been developed. Regarding (3), a ferromagnetic powder having a coercive force of more than 160 kA/m has appeared, and the particle size distribution that reflects the coercive force distribution is made extremely uniform, which is a remarkable development.

[0009]

In order for the magnetic recording medium to exhibit good electromagnetic conversion characteristics, the ferromagnetic powder must be uniformly dispersed in the binder. As a result, it tends to be difficult to disperse the powder in the binder. In particular, recently, the use of ferromagnetic powder having a major axis length of 0.1 μm or less has been considered,
It is hoped that a distributed technology will be established in response to this.

As a method for solving such a problem, in the kneading performed when preparing the coating material, the shearing force applied to the mixture of the powder and the binder is strengthened, or by a sand mill or the like in the subsequent dispersion step. Prolonging the processing time is conceivable, but it is not preferable because problems such as damage of the magnetic powder and a decrease in manufacturing efficiency occur.

On the other hand, as the binder, -SO ₃ M, -OSO ₃
M, -COOM, -P = O ( OM) 2, -NR 1 R 2,
^{-N (R 1 R 2 R 3} ) + X -,> N (R 1 R 2) + X -
Functional groups such as (wherein M is a hydrogen atom or an alkali metal such as lithium, potassium or sodium, R ¹ , R ² ,
R ³ is a hydrogen atom or a hydrocarbon group, and X ⁻ is a halogen element ion such as fluorine, chlorine, bromine or iodine, or an inorganic or organic ion. ) Is included,
Attempts have also been made to improve the dispersibility by strengthening the interaction between the ferromagnetic powder and the binder. Further, in order to obtain higher dispersibility, the molecular weight of the binder has been reduced.

However, although the above-mentioned binder having a functional group or a binder having a low molecular weight exhibits excellent dispersion performance as compared with the conventional binder, it has a fine strength developed for high density recording. At present, it is still difficult to sufficiently disperse the magnetic powder.

The present invention has been made in view of the above-mentioned conventional circumstances, and an object thereof is to achieve high density recording in a multilayer coating type magnetic recording medium in which ferromagnetic powder and non-magnetic powder are well dispersed. Another object of the present invention is to provide a magnetic recording medium having high electromagnetic conversion characteristics suitable for the above, and a manufacturing method thereof.

[0014]

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a vinyl chloride resin having an epoxy group and a relatively small weight average molecular weight and a silane coupling agent are used. It was found that by using the coating material, the ferromagnetic powder is well dispersed even in the thin magnetic layer.

That is, in the present invention, a lower layer obtained by dispersing ferromagnetic powder or nonmagnetic powder in a binder and an upper layer obtained by dispersing ferromagnetic powder in a binder are provided on a nonmagnetic support. In the multilayer coating type magnetic recording medium having the weight average molecular weight of 8000 or more and 1500 as the binder in at least the upper layer of the upper layer and the lower layer.
A magnetic recording, characterized in that a vinyl chloride resin having an epoxy group of 0 or less is used, and a silane coupling agent is contained in at least the upper layer of the upper layer and the lower layer. The present invention relates to a medium (hereinafter referred to as the magnetic recording medium of the present invention).

The present invention also provides a method for producing the magnetic recording medium of the present invention with good reproducibility by combining a ferromagnetic powder with a lower layer coating material prepared by dispersing a ferromagnetic powder or a non-magnetic powder in a binder. An upper layer coating material dispersed in a coating agent is applied on a non-magnetic support to produce a multilayer coating type magnetic recording medium, and at least the upper layer coating material is used for the upper layer coating material and the lower layer coating material. As the binder in the coating material, a vinyl chloride resin having a weight average molecular weight of 8,000 or more and 15,000 or less and having an epoxy group is used, and at least the upper layer coating material and the lower layer coating material in the upper layer coating material, A method for producing a magnetic recording medium containing a silane coupling agent (hereinafter referred to as the production method of the present invention) is provided.

In the magnetic recording medium and the manufacturing method of the present invention, the binder resin has a weight average molecular weight of 8000.
As described above, a vinyl chloride resin having an epoxy group of 15,000 or less is used. Thus, the weight average molecular weight is relatively small, and by using a vinyl chloride resin having an epoxy group in combination with the silane coupling agent, the dispersibility of the ferromagnetic powder in the magnetic layer is improved, and thus, high High electromagnetic conversion characteristics suitable for density recording can be obtained.

[0018]

[However, in the general formula (1), Y is one functional group selected from the group consisting of a methacryl group, an amino group, an epoxy group, a mercapto group, a vinyl group, and a ureido group (carbamide group), and X is an alkoxy group. A group (RO-: where R is a chain or alicyclic hydrocarbon group), and n is an integer of 2 or less (0, 1 or 2). ]

Generally, in the silane coupling agent represented by the general formula (1), the hydrophilic X (alkoxy group) is adsorbed to the ferromagnetic powder or the non-magnetic powder, and
Crosslinks with the binder resin at the above-mentioned Y (methacryl group, amino group, etc.) having an affinity for the binder resin, and therefore, good dispersibility and stability of the ferromagnetic powder and the non-magnetic powder in the binder resin are obtained. It is considered to be achieved.

Further, in the magnetic recording medium and the manufacturing method of the present invention, the bonding in at least the upper layer (or the upper layer coating material) of the upper layer (or the upper layer coating material) and the lower layer (or the lower layer coating material). As the agent, it is preferable that 40% by weight or more and 100% by weight or less of the vinyl chloride resin is mixed. This blending amount is a ratio that can make good use of the good dispersion characteristics of the vinyl chloride resin, and as the blending ratio of the vinyl chloride resin decreases, the amount of the coating material prepared by using only the binder to be blended at the same time becomes It goes without saying that it tends to be similar to the dispersion characteristics and the coating characteristics.

In the magnetic recording medium and the manufacturing method of the present invention, the silane coupling agent in at least the upper layer (or the upper layer coating) of the upper layer (or the upper layer coating) and the lower layer (or the lower layer coating) is 0.5 with respect to 100 parts by weight of the ferromagnetic powder or the non-magnetic powder
It is preferable that the content is not less than 5 parts by weight and not more than 5 parts by weight. The content is more preferably 1 part by weight or more and 3 parts by weight or less.

The action of the silane coupling agent in the magnetic recording medium of the present invention will be briefly described below.

Only the upper layer or the upper layer (magnetic layer)
The silane coupling agent used for both the lower layer and the lower layer interacts with the metal atom (hydrophilic) in the ferromagnetic powder or the non-magnetic powder in the alkoxy group portion (hydrophilic) to form a strong bond, Adsorbs on the surface of magnetic powder or non-magnetic powder.

Although the silane coupling agent forms an adsorption layer on the surface of the ferromagnetic powder or the non-magnetic powder,
Since its molecular weight is small, it is not possible to obtain a sufficient repulsive force against the attractive force between the ferromagnetic powder or the nonmagnetic powder.

Therefore, in practice, the dispersion of the ferromagnetic powder or the non-magnetic powder is stabilized by the weight average molecular weight of 8,000 or more,
It is 15,000 or less, which is achieved by adsorption of the vinyl chloride-based binder resin having an epoxy group, and the silane coupling agent plays a supplementary role.

That is, by setting the content of the silane coupling agent within the above range, the dispersing action of the silane coupling agent and the dispersing action of the vinyl chloride resin can be well balanced, and the ferromagnetic powder or The dispersibility and dispersion stability of the non-magnetic powder can be improved.

Hereinafter, the magnetic recording medium and the manufacturing method of the present invention will be described in more detail.

The binder according to the present invention is a vinyl chloride resin having an epoxy group and a weight average molecular weight of 8000 to 15000. As described above, the blending amount (blending ratio) in all the binders is 40% by weight or more, 1
The amount is preferably not more than 00% by weight, and therefore, depending on the purpose, a known thermoplastic resin, thermosetting resin, reactive resin or the like which has been conventionally used as a binder for a magnetic recording medium may be added in a mixing ratio of 0. % And 60% or less is possible.
However, when used in both the upper and lower layers, the compounding amounts can be added to the respective layers in the same amount, or can be changed at an arbitrary ratio.

As the vinyl chloride resin, for example,
Vinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-vinyl chloride-
Examples thereof include vinylidene chloride copolymers and vinyl chloride-acrylonitrile copolymers. Further, the epoxy group may be introduced in advance into the monomer during the polymerization of the vinyl chloride resin, but the amount introduced is 0.5 mmol/g or more,
It is preferably 1.5 mmol/g or less.

The effect of the epoxy group in the binder is to improve the stability of the vinyl chloride resin. This is because the epoxy group introduced into the side chain of the vinyl chloride resin is opened by hydrochloric acid and the hydrochloric acid is taken up. It is believed that this is because the dehydrochlorination from the vinyl chloride resin is suppressed and deterioration is prevented. Also, as other effects, the effect of increasing the strength of the paint by opening the epoxy group during curing of the paint and polymerizing with the epoxy group of other binder, and improving the dispersion in the paint due to the polarity of the epoxy group. Can be mentioned.

Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester- Acrylonitrile copolymer, acrylic ester-
Vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, methacrylic acid ester -Ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate , Nitrocellulose), styrene-butadiene copolymer, polyurethane resin, polyester resin,
Examples include amino resins and synthetic rubbers.

Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin,
Polyurethane curable resins, urea resins, melamine resins, alkyd resins, silicone resins, polyamine resins, urea formaldehyde resins and the like can be mentioned.

Further, all of the above-mentioned binders contain --SO ₃ M, --OSO ₃ M, and --SO ₃ M for the purpose of improving the dispersibility of the pigment.
A polar functional group such as —COOM or P═O(OM) ₂ may be introduced. Here, the M is a hydrogen atom or an alkali metal such as lithium, potassium or sodium. Further, as the polar functional group, -NR ¹ R ^2, -
Examples thereof include a side chain type having an N(R ¹ R ² R ³ ) ⁺ X ⁻ terminal group and a main chain type >N(R ₁ R ₂ ) ⁺ X ⁻ . Here, R ¹ , R ² and R ³ in the formula are each independently a hydrogen atom or a hydrocarbon group, and X ⁻ is a halogen element ion such as fluorine, chlorine, bromine or iodine, or an inorganic or organic ion. is there. Also, -OH, -SH,
There are also polar functional groups such as --CN and epoxy groups. The amount of these polar functional groups is preferably 10 ⁻¹ to 10 ⁻⁸ mol/g,
More preferably, it is 10 ^-2 to 10 ^-6 mol/g. These binders can be used alone or in combination of two or more.

The amount of the binder in the magnetic coating film or the non-magnetic coating film 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 the non-magnetic powder. If the amount of the binder used is more than the above range, in the upper magnetic layer, the ratio of the ferromagnetic powder in the magnetic layer tends to be relatively low, which tends to cause a decrease in output. The plastic flow is liable to occur due to repeated sliding, and the running durability of the medium may be deteriorated. On the other hand, if the amount of the binder is less than the above range, the coating film becomes brittle in both the upper and lower layers, and the running durability of the medium tends to decrease.

The silane coupling agent used in the magnetic recording medium and the manufacturing method of the present invention is represented by the following general formulas (1) and (1): YSi(CH ₃ ) _n X _3-n (where Y is methacryl) Group, amino group, epoxy group,
An organic functional group having a mercapto group, a vinyl group, a ureido group, or the like, X is preferably an alkoxy group, and n=0 to 2) is preferred to have a structural formula, and at least one of these is an upper layer only, or an upper layer and a lower layer. To be contained in. Needless to say, the types of silane coupling agents are not limited to the above.

The amount of the silane coupling agent contained in both the upper layer and the lower layer is 100 or less for the ferromagnetic powder or the non-magnetic powder.
It is preferably 0.5 to 5 parts by weight with respect to parts by weight. If the content is more than the above-mentioned amount, the dispersion of the binder may be impaired because the binding of the binder is suppressed. On the other hand, when the content of the silane coupling agent is less than the above amount, the function may not be sufficiently exhibited.

The magnetic coating material (upper or lower layer coating material) and the non-magnetic coating material (lower layer coating material) are prepared by mixing a silane coupling agent with a ferromagnetic powder or non-magnetic powder at the same time as a binder, and after kneading with a solvent, dispersion. Is adjusted by the method of doing. After kneading the addition timing of the silane coupling agent, that is, the dispersion of the powder is improved even if it is carried out at the beginning of the dispersion step using a sand mill, etc. The method of addition is superior.

A back coat layer is formed on the surface (back surface) of the non-magnetic support on which the magnetic layer is not provided for the purpose of improving the running property of the magnetic recording medium, the antistatic agent and the transfer prevention. It may be provided. Further, an undercoat layer may be provided between the lower layer and the non-magnetic support for the purpose of enhancing the adhesiveness between the coating film and the support. It goes without saying that this is different from the lower non-magnetic layer in the present invention.

In the present invention, polyisocyanate can be used in combination as a curing agent for crosslinking and curing the binder. Examples of the polyisocyanate include toluene diisocyanate and adducts thereof, alkylene diisocyanate and adducts thereof.
The amount of these polyisocyanates to be added to the binder is
The amount 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.

These polyisocyanates can be used in both upper and lower layers, or can be used by limiting to only one layer. When used in both upper and lower layers, the compounding amounts can be added in equal amounts to each layer, or can be changed in any ratio.

In the magnetic recording medium and the manufacturing method of the present invention, the ferromagnetic powder used in the magnetic layer (at least the upper layer of the upper layer and the lower layer) comprising the ferromagnetic powder and the binder is, for example, Fe, Co, Ni. Single metal such as Fe-C
o, Fe-Ni, Fe-Al, Fe-Ni-Al, Fe
-Al-P, Fe-Ni-Si-Al, Fe-Ni-S
i-Al-Mn, Fe-Mn-Zn, Fe-Ni-Z
n, Co-Ni, Co-P, Fe-Co-Ni, Fe-
Co-Ni-Cr, Fe-Co-Ni-P, Fe-Co
-B, Fe-Co-Cr-B, Mn-Bi, Mn-A
1, alloys such as Fe—Co—V, iron nitride, iron carbide and the like. Of course, even if a light metal element such as Al, Si, P, or B is contained in an appropriate amount for the purpose of preventing sintering during reduction or maintaining the shape, the effect of the present invention is not hindered.

Further, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ
-Beltolide compound of Fe ₂ O ₃ and Fe ₃ O ₄ , C
o-containing γ-Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , a beltride compound of γ-Fe ₂ O ₃ containing Co and Fe ₃ O ₄ , one or more metal elements in CrO ₂ , for example, Examples thereof include oxides containing Te, Sb, Fe, B and the like.

Further, hexagonal plate-shaped ferrite can be used, and M type, W type, Y type, Z type barium ferrite, strontium ferrite, calcium ferrite, lead ferrite, and these are used to control coercive force. For the purpose, Co-Ti, Co-Ti-Zn, Co-Ti-N
b, Co-Ti-Zn-Nb, Cu-Zr, Ni-Ti
It is also possible to use those to which etc. are added.

These ferromagnetic powders may 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 30~80m ² / g, more preferably 40~70m ² / g. When the specific surface area is within the above range, high density recording is possible due to the formation of fine particles in the shape of ferromagnetic powder, and it is possible to obtain a magnetic recording medium having excellent noise characteristics.

Further, this ferromagnetic powder has a major axis length of 0.0
It is preferably 5 to 0.50 μm and the axial ratio is 2 to 15. If the major axis length is less than 0.05 μm, it becomes difficult to disperse it in the magnetic paint, and if the major axis length exceeds 0.50 μm, the noise characteristics may deteriorate, which is not preferable. Further, when the axial ratio is less than 2, the orientation of the ferromagnetic powder is deteriorated, which causes a decrease in output, and when the axial ratio exceeds 15, the short wavelength signal output may be decreased. In the case of plate-shaped ferrite, the plate diameter is 0.01 to 0.5 μm and the plate thickness is 0.001 to 0.
About 2 μm is preferable. The major axis length, axial ratio, plate diameter, and plate thickness were randomly selected from transmission electron micrographs.
The average value of 00 samples or more is adopted.

In the magnetic recording medium and the manufacturing method of the present invention, when the lower layer is a non-magnetic layer, the non-magnetic powder contained is, for example, α-Fe ₂ O.
Non-magnetic iron oxide such as ₃ , goethite, rutile type titanium oxide, anatase type titanium oxide, tin oxide, tungsten oxide, silicon oxide, zinc oxide, chromium oxide, cerium oxide, titanium carbide, boron nitride (BN), α- Alumina, β-alumina, γ-alumina, calcium sulfate,
Barium sulfate, molybdenum disulfide, magnesium carbonate,
Calcium carbonate, barium carbonate, strontium carbonate,
There are barium titanate and the like, and these powders can be used alone or in combination of two or more.

The non-magnetic powder can be doped with an appropriate amount of impurities according to the purpose, and for the purpose of improving dispersibility, imparting conductivity, and improving color tone, Al, S, etc.
It is also possible to perform surface treatment with a single metal such as i, Ti, Sn, Sb, or Zr or a compound thereof. The specific surface area of the non-magnetic powder is preferably 30 to 80 m ² /g, 40 to 70 m ²
/G is more preferable. If necessary, a furnace for rubber, pyrolytic carbon, black for color, carbon black such as acetylene black may be contained. The specific surface area of these 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 with the formation of fine particles, and as a result, the upper layer can be smoothed, resulting in excellent modulation noise characteristics. It is possible to obtain a magnetic recording medium that is less affected by spacing loss. Since non-magnetic powder has no magnetic cohesive force, it is easier to disperse than ferromagnetic powder, but when the specific surface area is larger than the above range, it is difficult to disperse non-magnetic powder. Tends to be. On the other hand, if the specific surface area is too small, it tends to be impossible to secure the surface smoothness that can withstand high density recording.

In the magnetic recording medium and the manufacturing method of the present invention, a lubricant may be contained in the upper layer and/or the lower layer, if necessary. Examples of the lubricant include graphite, molybdenum disulfide, tungsten disulfide, silicone oil, fatty acids having 10 to 22 carbon atoms, and fatty acid esters consisting of this and alcohols having 2 to 26 carbon atoms, terpene compounds, and These include oligomers and the like. The lubricant can be added only to the upper layer, or can be added to both the upper and lower layers.

Further, the upper layer may contain abrasive particles. As the abrasive, for example,
Examples thereof include aluminum oxide (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, titanium carbide and titanium oxide (rutile, anatase). The amount of these particles is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, based on 100 parts by weight of the ferromagnetic powder. The Mohs hardness is preferably 4 or more, more preferably 5 or more, and the specific gravity is 2 to
6, further 3 to 5, and the average particle diameter is preferably 0.5 μm or less, more preferably 0.3 μm or less. The average particle size and the like of the non-magnetic reinforcing particles (abrasive particles) can also be obtained by measuring from a transmission electron micrograph and statistically processing as in the case of the ferromagnetic powder.

Examples of the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, vinyl resins and polyimides. Examples include polymer materials typified by polycarbonates, supports made of metal, glass, ceramics, and the like.

The coating film formed on the non-magnetic support is formed by coating the above-mentioned upper and lower layer forming materials with a coating material and drying it. The solvent used for this coating material is acetone, Ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohol solvents such as methanol, ethanol and propanol, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate and ethylene glycol acetate, diethylene glycol dimethyl ether. , Ether solvents such as 2-ethoxyethanol, tetrahydrofuran and dioxane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and chlorobenzene. Etc. are used.

The above-mentioned paint is prepared by the kneading step, the mixing step, and the dispersing step. For the dispersion and kneading, a roll mill, a ball mill, a sand mill, a kneader,
An extruder, homogenizer, ultrasonic disperser or the like is used.

Further, in the production method of the present invention, it is preferable that the coating material thus formed is applied on the non-magnetic support in multiple layers at the same time, but a die coater is mainly used for this. As the lip structure of the die coater, a 2-lip method, a 3-lip method, a 4-lip method, etc. are used.

FIG. 1 shows an example (8) of the magnetic recording medium of the present invention.
mm video tape). That is, the upper magnetic layer 2 containing the ferromagnetic powder and the binder is provided on one surface of the non-magnetic support 1 via the lower layer 4 containing the non-magnetic powder (or ferromagnetic powder) and the binder. is doing. Further, the other surface may have a back coat layer 3 mainly composed of a non-magnetic powder and a binder, as indicated by a chain line.

When the lower layer 4 and the magnetic layer (upper layer) 2 are formed on the non-magnetic support 1, a method of coating and drying one layer at a time (so-called wet-on-dry coating method) and a non-dry wet method. There is a method in which a magnetic layer is overlaid on a lower layer in a state (so-called wet-on-wet coating method: wet multi-layer coating method).

FIG. 2 shows an example of a manufacturing method based on the manufacturing method of the present invention. In this manufacturing method, in manufacturing the magnetic recording medium as shown in FIG. 1, for example, first, the film-shaped non-magnetic support 15 fed from a supply roll (not shown) is fed in the direction of arrow A in the drawing, while being extruded. The coating material 6 for the lower layer 4 and the coating material 7 for the magnetic layer 2 are simultaneously applied in multiple layers by an extrusion coater 18 of the method.

The extrusion coater 18 has a liquid reservoir 1
3 and 14 are provided, and the lower layer paint 6 and the upper layer paint 7 are
Through the slits 11 and 12, the non-magnetic support 15 is simultaneously coated by the wet-on-wet method.

In the simultaneous wet application method in such a wet-on-wet method, since the lower layer coating material 6 is coated with the magnetic coating material 7 which will be the upper magnetic layer 2 in a wet state, the surface of the lower layer (that is, the upper layer). The interface between the upper and lower layers is improved and the adhesiveness between the upper and lower layers is improved.

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

On the other hand, for example, Japanese Patent Laid-Open No. 6-2365
In the case of the wet-on-dry method disclosed in Japanese Patent Laid-Open No. 43-43, it is necessary to select, as the binder used for the lower layer 4, one having sufficient solvent resistance to the magnetic coating used for the upper magnetic layer 2. .. Even in such a case, the smoothness of the surface of the magnetic layer may be impaired, and as a result, electromagnetic conversion characteristics may be impaired.

There is a boundary region formed by the wet-on-wet multi-layer coating method, in which the components of both layers are mixed with a certain thickness except for the case where a clear boundary is substantially present. Although it may exist, the upper layer or the lower layer excluding the boundary region may be the upper magnetic layer or the lower layer. Either case is included in the scope of the present invention.

After the above-mentioned multi-layer coating, it is introduced into a drier, and if necessary, it is introduced into a calendar device and wound on a winding roll. Further, when the back coat layer is applied on the opposite surface of the multi-layer application, for example, a magnetic tape is prepared by slitting it into a width of 8 mm, and the magnetic tape is housed in a cassette to manufacture a tape cassette.

The magnetic recording medium of the present invention is not limited to a tape-shaped magnetic recording medium, but may be a disk-shaped, sheet-shaped, card-shaped magnetic recording medium or the like.

[0065]

EXAMPLES The present invention will be described below with reference to specific examples, but the present invention is not limited to the following examples.

Here, an example in which a non-magnetic layer composed of non-magnetic powder and a binder is arranged as the lower layer will be described, but the present invention is not limited to this, and the lower layer is the magnetic layer. It goes without saying that may be.

Preparation of Sample Tapes (Examples 1 to 24) The upper layer and the lower layer were made into paints with the following compositions. The mixing ratios of the vinyl chloride resin and urethane resin in the binder, the type and the amount of the silane coupling agent are shown in Table 1 below.

However, in Examples 21 to 23, instead of the vinyl chloride resin (polyvinyl chloride), a vinyl chloride resin having an epoxy group and a weight average molecular weight of 28,000 was used.
It is a mixture of 0% to 100%.

First, according to a conventional method, a ferromagnetic powder, a binder, an additive, a solvent, and a silane coupling agent are mixed in predetermined amounts according to a conventional method, and after kneading with an extruder, a sand mill is used. It was dispersed for 6 hours.

Polyvinyl chlorides other than those in Examples 21 to 23 had epoxy groups and had a weight average molecular weight of 900.
It is a vinyl chloride resin of 0.

[0071] <upper Coating Composition> Fe-based metal ferromagnetic powder 100 parts by weight of (coercive force = 160 kA / m, saturation magnetization = 145Am ² / kg, major axis = 0.18 .mu.m, acicular ratio = 3) Polyvinyl chloride Resin (excluding Examples 21 to 23 and Example 25) (described in Table 1) Polyester polyurethane resin (manufactured by Toyobo) (described in Table 1) Silane coupling agent (described in Table 1) Additive (Al ₂ O ₃ ) 5 Parts by weight stearic acid 1 part by weight heptyl stearate 1 part by weight methyl ethyl ketone 150 parts by weight cyclohexanone 150 parts by weight

Next, the coating of the non-magnetic layer coating material for the lower layer was performed in the same manner as the coating of the magnetic coating material for the upper layer. <Lower layer coating composition> 100 parts by weight of acicular α-Fe ₂ O ₃ (specific surface area=53 m ² /g, major axis length=0.15 μm, acicular ratio=5) polyvinyl chloride resin (excluding Examples 21 to 23) (Listed in Table 1) Polyester polyurethane resin (manufactured by Toyobo) (Listed in Table 1) Silane coupling agent (Listed in Table 1) Stearic acid 1 part by weight Heptyl stearate 1 part by weight Methyl ethyl ketone 105 parts by weight Cyclohexanone 105 parts by weight

Next, 3 parts by weight of polyisocyanate was added to each of the obtained upper layer coating material and lower layer coating material, and a thickness of 7 μm was obtained using the 4-lip type die coater shown in FIG.
Was simultaneously coated on the PET (polyethylene terephthalate) film, and subjected to orientation treatment with a solenoid coil, followed by drying, calendering and curing treatments to produce a magnetic recording medium having the structure shown in FIG. The coating thickness of each layer is 0.2 μm in the upper layer and 2.0 μm in the lower layer.

Further, a coating material for the back coat layer having the following composition was applied to the surface opposite to the above-mentioned coated surface and slit into a width of 8 mm to form a tape. <Backcoat layer coating composition> Carbon black (Asahi Carbon #80) 100 parts by weight Polyester polyurethane (Nipporan N-2304) 100 parts by weight Methyl ethyl ketone 500 parts by weight Toluene 500 parts by weight

The structure of the sample tape thus produced is shown in Table 1 below.

[0076]

[0077]

[0078]

[0079]

[0080]

However, in Table 1, all of the silane coupling agents are those in which X in the general formula (1) is “OCH ₃ ”, n is “0”, and the functional group Y is
Has the following structure.

[0082]

[Chemical 1]

In Table 1, "*1" is a vinyl chloride resin having an epoxy group and a weight average molecular weight of 28,000.

Evaluation The obtained magnetic tape was evaluated for electromagnetic conversion characteristics (reproduction output), surface roughness Ra of the magnetic layer, and dispersibility (squareness ratio).

The measurement of the electromagnetic conversion characteristics was carried out using a fixed head type electric characteristic measuring machine. This measuring machine consists of a rotating drum and a head that contacts the drum, and the tape is wound around the drum. In the actual measurement, first, a rectangular wave signal of 10 MHz is recorded at the optimum recording current of each tape, and the output level of 10 MHz is detected by a spectrum analyzer. The relative speed between the tape heads was 3.33 m/s, and the reference (0d
Hi8 tape manufactured by Sony Corporation was used for B).

The center line average surface roughness Ra of each tape was measured using a non-contact type surface roughness meter based on the laser light interference method. The measurement results of the electromagnetic conversion characteristics and the surface roughness are shown in Table 2 below.

[0087]

[0088]

Further, FIG. 3 is a graph showing the change in the 10 MHz reproduction output with the addition amount of the silane coupling agent, and FIG. 4 is a graph showing the change in the surface roughness Ra with the addition amount.
FIG. 6 shows a graph showing changes in the 10 MHz reproduction output depending on the blending ratio of the vinyl chloride resin, and FIG. 7 shows a graph showing changes in the surface roughness Ra depending on the blending ratio.

FIGS. 3 and 4 show Examples 1, 4, 7, and 8, Example 15, Example 16, Example 17, Example 18, and Example 24.
6 is a plot of the measurement results of FIG.
Is Example 4, Example 8, Example 9, Example 10, Example 11, Example 12, Example 1
9 is a plot of the measurement results of Example 9 and Example 20.

From Table 2, in particular, 100% of a vinyl chloride resin having an epoxy group and a weight average molecular weight of 9000 was used as a binder, and the addition amount of the silane coupling agent was 0.5 in both the upper layer and the lower layer. It can be seen that the sample tapes of Examples 1 to 8 containing 5 parts by weight or more and 5 parts by weight or less have a smooth surface and are excellent in electromagnetic conversion characteristics (10 MHz reproduction output).

On the other hand, even when the vinyl chloride resin is used, the sample tape of Example 13 having no silane coupling agent in both upper and lower layers, and Example 14 having the silane coupling agent only in the lower layer The sample tape of No. 2 did not have sufficient reproduction output and surface roughness.

From Table 2 and FIG. 3, even if 100% of the vinyl chloride resin was used as the binder resin, the addition amount of the silane coupling agent in the upper layer alone or in both upper and lower layers was 0.5 parts by weight. The sample tapes of 5 parts by weight or more and 5 parts by weight or less (Example 1, Example 4, Example 7 and Example 8) have very good reproduction output, but the addition amount is less than 0.5 parts by weight and 5 parts by weight. More than one sample tape (Example 15, Example 1)
6, Example 17, Example 18 and Example 24), it can be seen that sufficient reproduction output cannot be obtained.

Similarly, from Table 2 and FIG. 4, even if 100% of the vinyl chloride resin was used as the binder resin, the addition amount of the silane coupling agent in the upper layer alone or in both upper and lower layers was 0.5% by weight. Sample tapes of 1 part or more and 5 parts by weight or less (Example 1, Example 4, Example 7 and Example 8) have excellent surface properties, but the addition amount is less than 0.5 parts by weight or 5 parts by weight or more. Tape (Example 15, Example 16, Example 17, Example 1)
8 and Example 24), it is found that sufficient surface properties tend not to be obtained.

From Table 2 and FIG. 6, the addition amount of the silane coupling agent in the upper layer alone or in both the upper and lower layers was 3%.
Sample tape in which the content of the vinyl chloride resin is 40% by weight or more with respect to the total amount of the binder, which is an appropriate amount with parts by weight (Example 4, Example 8, Example 9, Example 10, Example 11 and Example 12).
Is excellent in reproduction output, but the blending ratio is 40
It can be seen that the sample tapes of less than wt% (Examples 19 and 20) tend not to obtain sufficient reproduction output.

Similarly, from Table 2 and FIG. 7, the addition amount of the silane coupling agent in the upper layer alone or in both the upper and lower layers was 3 parts by weight, which was an appropriate amount, and the vinyl chloride resin was added to the total amount of the binder. Sample tape with a ratio of 40% by weight or more (Example 4, Example 8, Example 9, Example 10, Example 11 and Example 1)
In the case of 2), although excellent surface properties were obtained, it can be seen that sufficient surface properties tend not to be obtained with the sample tapes (Example 19 and Example 20) in which the blending ratio is less than 40% by weight.

In particular, it is unthinkable with conventional vinyl chloride resins that the reproduction output and the surface property are improved as the blending ratio of the vinyl chloride resin is increased. this is,
This is because a vinyl chloride resin having an epoxy group and a weight average molecular weight of 9000 was used after using the silane coupling agent.

From the results of Examples 1 to 6, it can be seen that various coupling agents may be used as the silane coupling agent.

Further, even when the silane coupling agent was used as in Examples 21 to 23, the sample tapes using the vinyl chloride resin having the epoxy group and the weight average molecular weight of 28,000 were found to have good reproduction output and surface property. There is no sufficient improvement.

Next, for some sample tapes, the squareness ratio (R
s) was measured. The closer the squareness ratio is to 100%, the better the dispersibility of the magnetic powder in the upper magnetic layer is.

Examples 1 to 7, Example 9, Example 10, Example 13, Example 15 and Example 16 in which a silane coupling agent was added only to the upper layer.
The measurement results of the squareness ratio of the sample tape of Example 19 and Example 19 are shown in Table 3 below.

[0102]

From Table 3, all of the sample tapes of Examples 1 to 7 in which the vinyl chloride resin used in the upper layer had a compounding ratio of 100% had a large squareness ratio and the magnetic powder was dispersed in a small amount. It turns out that it is good.

On the other hand, even if the vinyl chloride resin is used, the sample tape of Example 13 having no silane coupling agent in both upper and lower layers does not sufficiently disperse the magnetic powder.

FIG. 5 is a graph showing changes in the squareness ratio Rs depending on the addition amount of the silane coupling agent, and FIG. 8 is a graph showing changes in the squareness ratio Rs depending on the blending ratio of the vinyl chloride resin. .. 5 is a graph plotting the measurement results of Example 1, Example 4, Example 7, Example 15 and Example 16, and FIG. 6 is a plot of the measurement results of Example 4, Example 9, Example 10 and Example 19. It is a graph.

From FIG. 5 and Table 3, even if 100% of the vinyl chloride resin is used as the binder resin, the addition amount of the silane coupling agent in the upper layer alone or in both the upper and lower layers is 0.5 parts by weight or more. The sample tapes of 5 parts by weight or less (Examples 1, 4 and 7) have very good dispersibility, but the sample tapes with the addition amount of less than 0.5 parts by weight or 5 parts by weight or more. In (Example 15 and Example 16), it can be seen that sufficient dispersibility tends not to be obtained.

From FIG. 8 and Table 3, the addition amount of the silane coupling agent in the upper layer alone or in both upper and lower layers was 3
Sample tapes (Example 4, Example 9 and Example 10) in which the mixing ratio of the vinyl chloride resin to the total amount of the binder is 40% by weight or more, which is an appropriate amount with parts by weight, are excellent in the dispersibility of the magnetic powder. However, it can be seen that the sample tape having the blending ratio of less than 40% by weight (Example 19) tends not to obtain sufficient dispersibility.

[0108]

According to the magnetic recording medium of the present invention, in the multilayer coating type magnetic recording medium, as the binder in at least the upper layer of the upper layer and the lower layer, the weight average molecular weight is 8,000 or more and 15,000 or less. A vinyl chloride resin having an epoxy group is used, and since at least the upper layer of the upper layer and the lower layer contains a silane coupling agent, the ferromagnetic powder in the magnetic layer is Excellent dispersibility, which in turn
A magnetic recording medium having high electromagnetic conversion characteristics suitable for high density recording can be obtained.

According to the manufacturing method of the present invention, the magnetic recording medium of the present invention can be manufactured with good reproducibility.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram showing a simultaneous multi-layer coating state by a 4-lip type die coater that can be used in the manufacturing method.

FIG. 3 10 MH depending on the amount of silane coupling agent added
It is a graph which shows change of z reproduction output.

FIG. 4 is a graph showing changes in surface roughness Ra depending on the amount of silane coupling agent added.

FIG. 5: Squareness ratio R depending on the amount of silane coupling agent added
It is a graph which shows the change of s.

FIG. 6 10 MHz depending on the blending ratio of vinyl chloride resin
It is a graph which shows change of reproduction output.

FIG. 7: Surface roughness R depending on the blending ratio of vinyl chloride resin
It is a graph which shows change of a.

FIG. 8: Squareness ratio Rs depending on the blending ratio of vinyl chloride resin
It is a graph which shows the change of.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Nonmagnetic support, 2... Upper magnetic layer, 3... Backcoat layer, 4... Lower layer, 6... Upper layer (magnetic layer) coating material, 7... Lower layer coating material, 11, 12... Slit, 13, 14... Liquid Reservoir, 15... Non-magnetic support, 18... Extrusion type extrusion coater (4 lip type die coater)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code FI G11B 5/842 G11B 5/842 Z

Claims (9)

[Claims] 1. A multilayer coating type having a lower layer formed by dispersing ferromagnetic powder or nonmagnetic powder in a binder and an upper layer formed by dispersing ferromagnetic powder in the binder on a nonmagnetic support. In the magnetic recording medium, the weight average molecular weight of 8000 or more is used as the binder in at least the upper layer of the upper layer and the lower layer.
5,000 or less, a vinyl chloride resin having an epoxy group is used, and a silane coupling agent is contained in at least the upper layer of the upper layer and the lower layer. Medium. 2. The magnetic recording medium according to claim 1, wherein a compound represented by the following general formula (1) is used as the silane coupling agent. Formula _{(1): YSi (CH 3} ) n X 3-n [However, the general formula (1), Y is a methacryl group, an amino group, an epoxy group, a mercapto group, a vinyl group,
One functional group selected from the group consisting of ureido groups, X is an alkoxy group, and n is an integer of 2 or less. ] 3. The magnetic recording medium according to claim 1, wherein the binder in at least the upper layer of the upper layer and the lower layer contains 40% by weight or more and 100% by weight or less of the vinyl chloride resin. .. 4. The silane coupling agent in at least the upper layer of the upper layer and the lower layer contains 0.5 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the ferromagnetic powder or the nonmagnetic powder. The magnetic recording medium according to claim 1, which is: 5. A non-magnetic support comprising a lower layer coating material obtained by dispersing ferromagnetic powder or non-magnetic powder in a binder, and an upper layer coating material obtained by dispersing ferromagnetic powder in the binder. When applied to produce a multilayer coating type magnetic recording medium, as the binder in at least the upper layer coating material among the upper layer coating material and the lower layer coating material, a weight average molecular weight of 8,000 or more and 15,000 or less, A method for producing a magnetic recording medium, which comprises using a vinyl chloride resin having an epoxy group, and wherein at least the upper layer coating material and the lower layer coating material contain a silane coupling agent. 6. The method for producing a magnetic recording medium according to claim 5, wherein the upper layer coating material is applied while the lower layer coating material is in an undried state. 7. The method for producing a magnetic recording medium according to claim 5, wherein a compound represented by the following general formula (1) is used as the silane coupling agent. Formula _{(1): YSi (CH 3} ) n X 3-n [However, the general formula (1), Y is a methacryl group, an amino group, an epoxy group, a mercapto group, a vinyl group,
One functional group selected from the group consisting of ureido groups, X is an alkoxy group, and n is an integer of 2 or less. ] 8. The vinyl chloride resin is blended in an amount of 40% by weight or more and 100% by weight or less as the binder in at least the upper layer coating material among the upper layer coating material and the lower layer coating material. Manufacturing method for magnetic recording medium. 9. The ferromagnetic powder or the non-magnetic powder 10 is used as the silane coupling agent in at least the upper layer coating material among the upper layer coating material and the lower layer coating material.
The method for producing a magnetic recording medium according to claim 5, wherein the content is 0.5 part by weight or more and 5 parts by weight or less with respect to 0 part by weight.