JPH04181515A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electromagnetic conversion characteristic by forming a magnetic layer in three layers and plending non-magnetic powders of a first magnetic layer in a specific ratio. CONSTITUTION:A magnetic layer is formed of a first, a second and a third magnetic layers on the surface of a non-magnetic supporting body. The three layers are layered in this order from the side of the non-magnetic supporting body. The first layer handles low frequency signals, the second layer treating high frequency signals of the low frequency signals, and the third layer treating high frequency signals. The blending ratio of non-magnetic powders to magnetic powders in the first layer is 0.15-0.95 by weight %, favorably 0.3-0.9 by weight %. Accordingly, the magnetic layer is rid of rough parts resulting from the surface roughness of the non-magnetic supporting body, without generating a dropout. The electromagnetic conversion characteristic can be improved.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a magnetic recording medium, and more specifically, the present invention relates to a magnetic recording medium, and more specifically, it minimizes the influence of unevenness on the surface of a non-magnetic support on a magnetic layer, and improves electromagnetic conversion characteristics. The present invention relates to a magnetic recording medium having an excellent magnetic layer.

[Lesson II to solve the conventional technology and invention] Conventionally,
Magnetic recording media such as magnetic tapes are made by coating a magnetic paint made of magnetic powder, binder resin, etc. on a non-magnetic support.
It is produced by drying. In conventional magnetic recording media, since the magnetic layer is a single layer, it is necessary to cover a wide frequency band from low to high frequencies using one type of magnetic powder. In particular, with the recent trend toward higher recording densities, magnetic powders with high Hc and high BET values are being used because recording characteristics in the high frequency range are improved and low noise is required.

However, although high-frequency characteristics are improved by using magnetic powder with high Hc and high BET values in one type of magnetic layer, a problem arises in that the low-frequency characteristics become insufficient.

In order to solve this problem, in magnetic recording media such as video magnetic recording media, the magnetic recording capacity is increased, or the magnetic recording characteristics of the magnetic recording media are improved in both the high frequency region and the low frequency region. In order to balance the high frequency characteristics, a magnetic recording medium having multiple magnetic layers has been proposed (Japanese Patent Laid-Open No. 48-98
No. 803, JP-A-59-172142, JP-A No. 172142-
No. 2218, JP-A No. 51-56228, JP-A No. 63-
(Refer to each publication such as No. 146211).

According to these known techniques, the upper and lower layers of the magnetic layer are designed to have separate functions, with the upper layer receiving the video output and the lower layer receiving the chroma and audio outputs.

However, in conventional magnetic recording media having functionally separated magnetic layers, the surface roughness of the non-magnetic support has a large effect on the magnetic layer.

A new problem arises in that the electromagnetic conversion characteristics of the magnetic layer whose functions have been painstakingly separated are deteriorated.

Furthermore, since the magnetic recording medium must have light-shielding properties, carbon black is blended into the magnetic layer.

However, carbon black itself has a problem of poor dispersibility in the magnetic layer, causing unnecessary unevenness on the surface of the magnetic layer and deteriorating electromagnetic conversion characteristics.

However, when carbon black is dispersed in the magnetic layer, the surface unevenness of the magnetic layer caused by carbon black with poor dispersibility can also be eliminated by increasing the thickness of the magnetic layer to be laminated. If this happens, the thickness of the entire magnetic layer will increase, resulting in deterioration of electromagnetic conversion characteristics.

It is an object of the present invention to consist of a magnetic layer having a three-layer structure with separate functions, to prevent the thickness of the magnetic layer from increasing even in such a magnetic layer, and to prevent the surface of the non-magnetic support from being increased by the first Im magnetic layer. By smoothing out the roughness to an appropriate level and acting as the first magnetic layer or underlayer, the unevenness of the surface of the non-magnetic support can be prevented from having an adverse effect on the magnetic layer, making it more effective than conventional magnetic recording media. An object of the present invention is to provide a magnetic recording medium having a magnetic layer having excellent electromagnetic conversion characteristics.

[Means for Solving the Problems] A magnetic recording medium of the present invention for solving the problems described above includes a first magnetic layer, a second magnetic layer, and! on the surface of a nonmagnetic support. $
The three magnetic layers are laminated in this order, and the first magnetic layer has a weight ratio of non-magnetic powder to magnetic powder in the first magnetic layer of 0.15 to 0.95.
It is characterized by

The present invention will be explained in detail below.

One magnetic layer The magnetic layer in the magnetic recording medium of the present invention includes a first magnetic layer, a second magnetic layer, and a second magnetic layer laminated on the surface of a non-magnetic support in order from the non-magnetic support side. and a third magnetic layer.

By configuring the magnetic layer with three functionally separated layers, the thickness of the magnetic layer itself is not increased, and the electromagnetic conversion characteristics are prevented from deteriorating due to surface roughness of the non-magnetic support. You can reduce it.

Also, by having three layers, the first magnetic layer receives low frequency signals, the second magnetic layer receives high frequency signals among the low frequency signals, and the third magnetic layer receives high frequency signals among the low frequency signals.
Since the magnetic layer can functionly separate and receive high-frequency signals, the magnetic recording medium of the present invention has a magnetic layer that has electromagnetic conversion characteristics superior to conventional magnetic recording media.

What is important in the present invention is that in the first magnetic layer, the mixing ratio or weight ratio of the non-magnetic powder in the first magnetic layer to the magnetic powder in the first magnetic layer is 0.15 to 0.95, preferably 0.3. ~0,9.

By setting the blending ratio or weight ratio of the non-magnetic powder in the first magnetic layer to the magnetic powder in the first magnetic layer to 0.15 to 0.95, the unevenness of the surface of the non-magnetic support can be controlled to have an adverse effect on the magnetic layer. It can be effectively prevented.

That is, by configuring a first magnetic layer containing magnetic powder and non-magnetic powder in a specific ratio on a non-magnetic support,
While maintaining an appropriate roughness that does not make the surface of the non-magnetic support too smooth, it is possible to fill in large protrusions on the surface of the non-magnetic support to make the base uniform and even out the unevenness of the surface of the non-magnetic support. It is possible to minimize the negative effect that this has on the magnetic layer.

If the weight ratio of the non-magnetic powder to the magnetic powder in the first magnetic layer is less than 0.15, the first magnetic layer will become too smooth, and even if the second magnetic layer and the third magnetic layer are This is because it is only possible to impart appropriate undulations.

Further, if the weight ratio of the non-magnetic powder to the magnetic powder in the first magnetic layer exceeds 0.95, the signal recording characteristics of the first magnetic layer deteriorate.

Examples of the magnetic powder that can be contained in the first magnetic layer include Co-containing -Fe20° powder, Go-containing Fe=O powder, and Co-containing FeOx (4/3 <
x < 3/2) powder, or Fe-Al metal powder, Fe-Ni metal powder, Fe-An-Ni metal powder, Fe-AM-P metal powder, Fe-Ni-3i-Al
Metal powder, FeFe-Ni-3i-All-metal powder,
Ni-Co metal powder, Fe-Mn-Zn metal powder, Fe-N1-Zn metal powder, Fe-Co-Ni
-Cr metal powder, Fe-Co-N1-P metal powder, Co
Fine ferromagnetic metal powders such as -Ni metal powder and Co-P metal powder are included. Among these, preferred is fine Co-containing -Fe.

03 powder.

When the first magnetic layer contains magnetic powder, since the first magnetic layer has the ability to record low frequency signals, it is desirable that the preferred magnetic powder has the following properties.

That is, the BET value of magnetic powder is 1 normally, 23rrf/g
Above, preferably 30 to 45 rr+'/g.

Further, the shape of the magnetic powder is not particularly limited as long as it is fine; for example, any shape such as needle, spherical, or ellipsoid can be used. However, acicular magnetic powder is preferable for recording low frequency signals, and moreover, it is preferable that the particle size is more uniform than that of the magnetic powder contained in the second magnetic layer and the third magnetic layer, which will be described later.

However, in the present invention, the particle size of the magnetic powder contained in the first magnetic layer may be a fine magnetic powder, and it is preferable that the magnetic powder has a particle size of 1 particle or a fine magnetic powder.

The reason for this is that since non-magnetic powder is blended, the distance between the magnetic powders increases, or this reduces interaction between particles, making it possible to improve low-frequency output.

In this respect, the present invention is advantageous in that the present invention can be used when it is desired to contain extremely fine magnetic powder particles in the magnetic layer.

The blending amount of the magnetic powder is usually 20 to 850% by weight, preferably 10% by weight, based on the binder resin in the first magnetic layer.
It is 0 to 700% by weight.

The non-magnetic powder that can be contained in the first magnetic layer may be any solid powder that does not have magnetism, such as graphite carbon black, which is an antistatic agent, tin oxide-antimony oxide, etc. based compounds, tin oxide-
Examples include conductive powders such as titanium oxide-antimony oxide compounds and carbon black graft polymers.

These may be used alone or in combination of two or more.

Further, fillers such as red iron oxide, Cr, 03, and calcium carbonate powder can be mentioned.

Further, zinc oxide and the like can be mentioned.

Preferably, the first magnetic layer has excellent adhesion to the non-magnetic support and elasticity.

Such adhesive force and elasticity can be adjusted by selecting the type and amount of the binder resin or other optional components, which will be described later.

Here, the first magnetic layer may be formed of a binder resin, the magnetic powder, the non-magnetic powder, and other additives blended as necessary, as long as the above conditions are met.

Examples of the binder resin that can form the first magnetic layer include thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, or mixtures thereof, which are conventionally used in magnetic recording media. You can also use something like

Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, and acrylic ester-vinylidene chloride copolymer. Polymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-ethylene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin,
Polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate), cellulose diacetate,
Examples include cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amino resins Σ, and synthetic rubber-based thermoplastic resins.

These may be used alone or in combination of two or more.

As the above thermosetting resin or reactive resin.

For example, phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, silicone resins, acrylic reaction resins, mixtures of high molecular weight polyester resins and isocyanate brepolymers,
Mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, mixtures of polycarbonate polyols and polyisocyanates, urea formaldehyde resins,
Examples include mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanate and polyamine resins.

These may be used alone or in combination of two or more.

Examples of the electron beam curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type; ether acrylic type; Examples include polyfunctional monomers such as urethane acrylic type, epoxy acrylic type, phosphoric acid ester acrylic type, aryl type, and hydrocarbon type.

These may be used alone or in combination of two or more.

In this invention, the various resins mentioned above may be used as they are as a binder resin, or furthermore, a curing agent may be used together with the various resins mentioned above to form a binder resin.

Examples of the curing agent include polyisocyanate compounds (e.g., tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, and adducts of these polyisocyanate compounds with trivalent polyols, Pentamer of diisocyanate, adduct of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, metaxylylene diisocyanate 3 moJ and dorimethylo-λlegloba 21
adduct with molar, pentamer of tolylene diisocyanate)
Examples include.

These may be used alone or in combination of two or more.

Among the various binder resins, thermoplastic resins are preferred, and thermoplastic resins having functional groups are more preferred.

The functional groups include -3o, M', -0SO, M'
, -COOM', (In formula 1, Ml is a hydrogen atom or an alkali metal, and 1M2 and Ml are each a hydrogen atom, an alkali metal, or an alkyl group. Also, M2 and Ml are different from each other. ) can be mentioned. Also preferred are epoxy groups and amino groups.

Among the various binder resins mentioned above, two are the first in the present invention.
Binder resins suitable for forming the magnetic layer include:
Vinyl chloride-vinyl acetate-maleic anhydride copolymer, vinyl chloride copolymer containing epoxy group and sulfonic acid metal base, vinyl chloride-vinyl acetate copolymer containing hydroxyl group, polycarbonate polyurethane, polyester polyurethane, etc., with an average molecular weight of 10 ,000 to zoo, ooo can be mentioned.

The amount of the binder resin in the first magnetic layer is determined so that the first magnetic layer has appropriate adhesion and elasticity to the non-magnetic support, as described above, or It is usually 6 to 80% by weight based on the entire magnetic layer,
Preferably it is 8 to 45% by weight.

Examples of additives that can be included in the first magnetic layer include dispersants, plasticizers, and the like.

As the dispersant, for example, lecithin, carbon number 10-2
5 fatty acids, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic acid esters, known surfactants, salts thereof, negative organic groups (e.g. -C
OOHl-PO3H) polymer dispersant salts and the like can be added to the magnetic layer.

These may be used alone or in combination of two or more.

The amount of the dispersant added is generally 10 parts by weight or less, preferably 3 parts by weight or less, per 100 parts by weight of the magnetic powder.

Further, a fatty acid ester can be added to the magnetic layer as the plasticizer. Examples of the fatty acid ester include oleyl oleate, oleyl stearate, incetyl stearate, dioleyl maleate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, amyl stearate, and amyl palmitate. tate, stearyl stearate, amyl palmitate, stearyl stearate,
Lauryl oleate, octyl oleate.

Inbutyl oleate, ethyl oleate, intridecyl oleate, 2-ethylhexyl stearate, 2-ethylhexyl myristate, ethyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, Cetyl-2-ethyl hexalate, dioleyl adipate,
Examples include diethyl adipate, diisobutyl adipate, diisodecyl adipate, and the like. Among these,
Particularly preferred are butyl stearate and butyl palmitate. The various fatty acid esters mentioned above may be used alone or in combination of two or more.

The amount of the fatty acid ester added is usually 1 to 10 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of the magnetic powder.

By reducing the amount of dispersants such as fatty acids and plasticizers such as fatty acid esters added in this manner, the running durability of the magnetic recording medium can be improved, especially under high temperature and high humidity conditions.

The thickness of the first magnetic layer is usually 0.8 to 4.0 pm,
Preferably it is 1.0 to 3.5 μm.

Next, in one aspect of the present invention, a second magnetic layer is laminated on the first magnetic layer.

The second magnetic layer can be formed of magnetic powder, non-magnetic powder, binder resin, and other additives mixed as necessary. These magnetic powders, nonmagnetic powders, binder resins, and other additives may be appropriately selected from those used in forming the first magnetic layer.

Examples of the magnetic powder contained in the second magnetic layer include magnetic powders that can be used to form the first magnetic layer. However, since the second magnetic layer is located in the middle of the magnetic layers and receives signals on the high frequency side of the low frequency signals,
The magnetic powder contained in the magnetic layer is preferably needle-shaped, rod-shaped, or similar in shape, and specifically includes magnetic powder having an aspect ratio of 2 to 12, preferably 3 to 10.

The content of the magnetic powder in the second magnetic layer is usually 2 to 88% by weight, preferably 72 to 85% by weight, based on the entire second magnetic layer. By setting the content of the magnetic powder in the second magnetic layer within the above range, it is possible to balance still durability and powder falling off during repeated running.

What is important about the second magnetic layer in the present invention is that the second magnetic layer
Carbon black with a particle size of 25 to 150 nm is used in the magnetic layer.
0.1 to 10% by weight based on the magnetic powder in the second magnetic layer
It is to contain.

By containing carbon black in the second magnetic layer, that is, in the intermediate layer, it is possible to form a fine surface shape in the uppermost layer, and it is possible to balance durability and electromagnetic conversion characteristics.

Furthermore, by containing carbon black, it can play a role in preventing static electricity, and can play a role in preventing sticking of the magnetic tape head and dust adhesion.

Furthermore, by containing such carbon black, not only the durability at room temperature but also the durability under high temperature conditions are improved.

By using carbon black with a particle size of 25 to 150 nm, high output and high S/S can be achieved without adding carbon to the top layer.
N is obtained, and running properties can be maintained due to the appropriate roughness.

If the particle size of the carbon black is less than 2 SILm, the dispersibility will deteriorate and the surface properties cannot be controlled sufficiently, and 150. If it exceeds Bm, the surface of the coating becomes rough and the output decreases.

By containing a specific ratio of carbon black in the second magnetic layer, the optical density of the magnetic tape as a whole is adjusted, running control is made safe and secure, and charging problems are eliminated. It is possible to suppress unevenness and adjust surface roughness.

When the weight ratio of the carbon black content to the magnetic powder in the second magnetic layer is less than 0.1 wt%.

Light-shielding properties are poor, and dropouts due to static electricity tend to increase.

Furthermore, if the weight ratio of the carbon black content to the magnetic powder in the second magnetic layer exceeds 10 wt %, the surface of the second magnetic layer becomes too rough and the electromagnetic conversion characteristics deteriorate.

Examples of the nonmagnetic powder contained in the second magnetic layer include nonmagnetic powders that can be used to form the first magnetic layer.

Examples of the binder resin used to form the second magnetic layer include the binder resins exemplified for forming the first magnetic layer.

What is the binder resin content in the second magnetic layer?

The amount is usually 12 to 25% by weight, preferably 15 to 21% by weight, based on the entire second magnetic layer. If the content of the binder resin is less than 12% by weight, the mechanical strength of the second magnetic layer may decrease, and if the content of the binder resin exceeds 25% by weight, the magnetic powder will be relatively weak. If the content is reduced, it may cause magnetic properties.

In the second magnetic layer, a dispersant and a plasticizer that can be used in forming the first magnetic layer can be blended.

The thickness of the second magnetic layer is 1 usually 0.05 to 0.5 #Lm
and preferably 0.2 to 0.4 gm.

Next, in the present invention, #! A third magnetic layer is laminated on the second magnetic layer.

The third magnetic layer can be formed of magnetic powder, non-magnetic powder, binder resin, and other additives mixed as necessary. These can be used by appropriately selecting those that can be used to form the first magnetic layer and the second a magnetic layer.

Since the third magnetic layer receives high frequency signals, it is preferable that the magnetic powder contained in the third magnetic layer is smaller than the second magnetic powder, and specifically, the particle size is 0.01 to 0.01. 0.2
gm, preferably Q, QI ~ (1.1 μm). - The content of magnetic powder in the third a magnetic layer is usually 60 to 80% by weight based on the entire third magnetic layer. , preferably 70 to 78% by weight. By having the content of the magnetic powder in the third magnetic layer within the above range, the durability of the coating film can be maintained while the magnetic properties of the highly packed magnetic powder can be improved. A good magnetic layer can be obtained. As the binder resin used to form the third magnetic layer, the binder resins exemplified for forming the first magnetic layer can be mentioned. Since the third magnetic layer is the outermost magnetic layer among the magnetic layers, it is desirable to have a magnetic layer with high abrasion resistance, no falling off of magnetic powder, etc., and high rigidity. Examples of binder resins that can be used include epoxy group/sulfonic acid metal salt-containing vinyl chloride resins, vinyl chloride-vinyl acetate copolymers,
Maleic acid-containing vinyl chloride-vinyl acetate copolymer, thermoplastic polyurethane (polyester, polycarbonate,
(polyether type), etc.

What is the content of binder resin in the third magnetic layer?

! The amount is usually 12 to 25% by weight, preferably 15 to 21% by weight, based on the entire 3m layer. If the content of the binder resin is less than 12% by weight, the mechanical strength of the third magnetic layer may decrease.
If it exceeds % by weight, the content of magnetic powder becomes relatively small, which may lead to deterioration of magnetic properties.

In the third magnetic layer, a dispersant, a plasticizer, an antistatic agent, etc., which are sometimes used in forming the first magnetic layer, can be blended.

Further, since the third magnetic layer is required to have excellent wear resistance as described above, it is preferable that the third magnetic layer contains a lubricant as an additive.

Examples of such lubricants include silicone-based lubricants, fatty acid-modified silicone-based lubricants, fluorine-based lubricants,
Examples include liquid paraffin, squalane, carbon black, graphite, carbon black graft polymer, molyfden disulfide, and tungsten disulfide.

Among these, preferred lubricants include carbon black and the like.

These may be used alone or in combination of two or more.

The blending ratio of the lubricant is usually 20 parts by weight or less, preferably 10 parts by weight or less, based on 100 parts by weight of the magnetic powder. If this blending ratio exceeds 20 parts by weight, the amount of lubricant becomes excessive and dirt may easily adhere to the surface of the magnetic layer.

1i! The third magnetic layer may further contain an abrasive in addition to the various components described above.

The thickness of the third magnetic layer is usually 0.02 to 0.5 μm, preferably 0.05 to 0.4 μm.

Furthermore, the thickness of the second magnetic layer and #! The total thickness of the three magnetic layers is preferably 0.7 μm or less.

(1) Non-magnetic support (1) Materials for forming the non-magnetic support on which the three-layered magnetic layer is formed include, for example, polyesters such as polyethylene terephthalate and polyethylene-2゜6-naphthalate; polyolefins such as polypropylene. : cellulose derivatives such as cellulose triacetate and cellulose diacetate; and plastics such as polycarbonate. Zarani C
Metals such as u, AfL, and Zn, glass, and various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.) can also be used.

There is no particular restriction on the form of the non-magnetic support, and it may be tape-like, sheet-like, cart-like, disc-like, drum-like, etc., and various materials may be used depending on the form and as necessary. You can select and use it.

The thickness of the support is 1 if it is in the form of a tape or sheet.
Usually 3 to 1100 IL, preferably 5 to 50 gm. In addition, in the case of disk-shaped or cart-shaped, 4 usually,
It is 30-1100B. Furthermore, in the case of a drum shape, the shape can be made to correspond to the recorder used, such as a cylindrical shape.

A back coat layer may be provided on the surface (back surface) of the nonmagnetic support on which the magnetic layer is not provided for the purpose of improving the running properties of the magnetic recording medium, preventing charging, preventing transfer, and the like.

Furthermore, an intermediate layer (for example, an adhesive layer) may be provided on the surface of the non-magnetic support on which the magnetic layer is provided, for the purpose of improving the adhesion between the magnetic layer and the non-magnetic support.

Next, regarding the method of manufacturing the magnetic recording medium of the present invention,
Explain - do.

1. Manufacturing method-- The magnetic recording medium of the present invention is characterized in that the composition for the first magnetic layer, the composition for the second magnetic layer, and the composition for the third magnetic layer containing the magnetic powder, binder resin, etc. are dissolved in a solvent. After preparing a magnetic paint by cross-dispersing the three types of magnetic paints, the three types of magnetic paints are coated on the non-magnetic support and dried.

Examples of the solvent used for kneading and dispersing the compositions for the first to third magnetic layers include acetone, methyl ethyl ketone (1
11E), methyl isobutyl ketone (111111K
) and ketones such as cyclohexanone/methanol,
Alcohols such as ethanol, propatool and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol monoacetate: diethylene glycol dimethyl ether.

2-ethoxyethanol, tetrahydrofuran.

Ethers such as dioxane; aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene, etc. can be used. I'll come.

When mixing the compositions for the first to third magnetic layers, the magnetic powder and other magnetic paint components (hereinafter sometimes referred to as raw materials) are charged into the mixing machine simultaneously or sequentially. For example, the magnetic powder is first added to a solution containing a binder, kneaded for a predetermined period of time, and then the remaining components are added and kneaded further to form a magnetic paint.

Various types of crosstalk devices can be used to disperse crosstalk. Examples of this mixer include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a sight grinder, a Sqegvari attritor, a high-speed impeller splitter, a high-speed stone mill, a high-speed impact mill, a disper kneader-1 high-speed mixer, and a homogenizer. , ultrasonic disperser, etc.

The magnetic paint thus prepared is coated onto a non-magnetic support by a known method.

Application methods that may be utilized in the present invention include, for example, gravure roll coating, wire bar coating, doctor blade coating, Sohar roll coating, dip coating, air knife coating, calendar coating, squeegee coating, kiss coating and Examples include Fantin coating.

In this way, after sequentially applying the three types of magnetic paints, a magnetic field orientation treatment is performed if necessary in an undried state, and further,
Surface smoothing treatment is usually performed using a super calender roll or the like.

Next, a magnetic recording medium can be obtained by cutting it into a desired shape.

The magnetic recording medium of the present invention can be used, for example, as a magnetic tape such as a video tape or audio tape by cutting it into a long shape, or as a floppy disc or the like by cutting it into a disc shape. Furthermore, similar to ordinary magnetic recording media, cart-shaped, cylindrical, and other forms can also be used.

Example C Next, the present invention will be explained in more detail by giving Examples and Comparative Examples.

In addition, in the following, "1 part" means "part by weight".

(Example 1) Magnetic composition for upper layer (third layer) Co-γ-Fe*Os powder 100 parts (
Specific surface area: 55 m2/g) α-AI20z...4 parts (average particle size: 0.1 m) Epoxy group-containing vinyl chloride copolymer, 13 parts polycarbonate-containing polyester polyurethane ...9 parts (contains 0.03 m m o 17 g of sulfobetaine group) above magnetic composition for upper layer, 14 parts of methyl ethyl ketone, and 1 part of toluene
After kneading 4 parts, diluent solvent (methyl ethyl ketone/toluene/cyclohexanone mixing ratio 1/1/1) 15
0 parts were added and dispersed using a sand mill.

Trifunctional isocyanate (Takenate E
-31>7 parts, 150 parts of the above diluting solvent, and 1 part of stearic acid.
1 part and 1 part of butyl stearate were added, thoroughly mixed, and passed through a filter to obtain magnetic paint A.

Next, the following magnetic composition for an intermediate layer was thoroughly mixed and dispersed, and the above trifunctional incyanate was added.

After mixing well, the mixture was passed through a filter to obtain magnetic paint B.

Magnetic composition for intermediate layer (second layer) Co-γ-Fe*Oz powder 100 parts (
Specific surface area 45m''/g) Vinyl chloride-vinyl acetate-maleic anhydride copolymer...
・・・・・・・・・・・・10 parts (contains 0.4% maleic anhydride component) Polyurethane・・・・・・・・・・・・・
・12 parts [N 3022, manufactured by Nippon Polyurethane Co., Ltd.]
Carbon black dispersion [consisting of 2 parts of carbon black (particle size 40 mJL), 1 part of the above polyurethane, 2 parts of toluene and 2 parts of cyclohexanone. Costearic acid・・・・・・・・・・・・1 part Butyl stearate・・・・
・・・・・・1 part methyl ethyl ketone・・・・・・
...70 parts toluene...70
70 parts of cyclohexanone, followed by 1120 parts of the following Beret, 24 parts of Beret, 1 part of stearic acid, 2 parts of butyl stear, 80 parts of methyl ethyl ketone, 80 J of toluene, and cyclohexanone. After thoroughly mixing and dispersing 80 parts of hexanone to prepare a magnetic composition for the lower layer (first layer), 5 parts of the trifunctional isocyanate was added and the mixture was passed through a filter to obtain magnetic paint C.

Beret = C0-γ-Fezes powder...100 parts (
Specific surface area 35m”/g) Vinyl chloride-vinyl acetate-vinyl alcohol copolymer...7 parts (VAGH,
(Manufactured by UCC) Thermoplastic polyurethane 13 parts [N31
32.8 polyurethane manufactured by C Co.)] Beret ■: Carbon black 100 parts (average -
Particle size 62m IL) Vinyl chloride-vinyl acetate-vinyl alcohol copolymer...7 parts (VAGH, U
(manufactured by CC) Thermoplastic polyurethane 13 parts [N 3
132, manufactured by Nippon Polyurethane Co., Ltd.] Using magnetic paints A, B, and C prepared as described above, a film was coated with a precision extrusion coater (FEC) to a thickness of 13.07 parts m.
The thickness of the third layer after drying is 0.3 on the polyester base.
Simultaneous multilayer coating was carried out so that the thickness of the first layer was 4 m, the second layer was 3 gm, and the first layer was 2.8 m.

Subsequently, while the coating film was still undried, it was subjected to a magnetic field orientation treatment while drying at 20,000 e in a solenoid, and then subjected to a calender treatment.

Further, on the back side of the polyester base, a paint consisting of the following backcoat composition was applied to a film thickness of 0.0000.
A raw fabric was obtained by applying the coating to a length of 64 m.

Then, a sample of the magnetic recording medium was obtained by slitting one portion of this original fabric into a 2-inch width.

Back coat composition ゛Carbon black......85 parts (particle size 2
5m end) Carbon black 20 parts (particle size 7
0m end) Calcium carbonate・・・・・・・・・-20 parts (particle size 1
End of 10 parts) Nitrocellulose 40 parts [Seltsuba BTHI/2, manufactured by Asahi Kasei Corporation] Polyurethane...
......50 parts [N3141-7, manufactured by Nippon Polyurethane Co., Ltd., Mw 50,000, hydroxyl group, contains secondary amine and tertiary amine in the urethane main chain] Trifunctional incyanate... ......15 parts (Takenate E-31) Cyclohexanone...400 parts Methyl ethyl ketone...400 parts Toluene...
・・・・・・・・・40(l i Regarding the sample thus obtained, calculate the RF specific output Lumi S/N as follows.
The running durability was evaluated.

The results are shown in Table 2.

RF ratio output and Lumi S/N H made by JVC using noise meter 9250 made by Nijihack.
Relative values with respect to a reference tape [manufactured by Konica Corporation] are shown using an R-S 7000 deck.

Running durability: 4Ω℃ as VH3 cassette tape (T-120),
The entire length was repeatedly run 400 times on a video deck at 80% RH, and from the appearance of the monitor screen and tape,
Those with no problems at all were considered OK, and those with marked deterioration such as tape deformation, tape bending, or significant deterioration in image quality were judged NG.

(Examples 2 to 4, Comparative Examples 1 to 4) In Example 1, pellets I contained in the lower layer composition
Table 1 shows the blending amount of Tobe Sheet Toro, the blending amount of the magnetic powder in Beret-E and the carbon black in Beret ■, and the particle size of carbon black in the carbon black dispersion in the magnetic composition for the intermediate layer. A sample of a magnetic recording medium was prepared in the same manner as in Example 1 except for the following changes.

RF ratio output Lumi S/N performed in the same manner as in Example 1,
The results of running durability evaluation are shown in Table 2.

[Effects of the Invention] According to the present invention, surface irregularities of the non-magnetic support are effectively prevented, and non-uniformity in the thickness of the magnetic layer caused by the surface irregularities of the non-magnetic support is eliminated. The unevenness of the magnetic layer due to the unevenness of the surface of the magnetic body is eliminated, and it is therefore possible to provide a magnetic recording medium with excellent electromagnetic conversion characteristics without dropouts.

Claims (1)

[Claims] (1) Laminating a first magnetic layer, a second magnetic layer, and a third magnetic layer in this order on the surface of a nonmagnetic support, and
The magnetic layer has a blending ratio or weight ratio of non-magnetic powder in the first magnetic layer to magnetic powder in the first magnetic layer of 0.15 to 0.
．． 95. A magnetic recording medium characterized in that: 95.