JPH043323A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To form a three-layered magnetic layer which has the electromagnetic conversion characteristic improved and has functions separated without increasing the thickness by laminating a first magnetic layer containing a prescribed amount of an iron oxide red, which has specific surface roughness and BET value, and second and third magnetic layers whose sum of thickness is a specific value. CONSTITUTION:First to third magnetic layers are laminated in order on a nonmagnetic supporting body, and the first magnetic layer contains an iron oxide red having <=0.02mum Ra and 15 to 100m<2>/g BET value by 1 to 60wt.% of magnetic powder, and the sum of thickness of second and third magnetic layers is set to <=2mum. Then, a magnetic recording medium is obtained where the three-layered magnetic layer which has the electromagnetic conversion characteristic improved and has functions separated is formed.

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, to minimize the influence of unevenness on the surface of a non-magnetic support on a magnetic layer, and to improve light-shielding properties. The present invention relates to a magnetic recording medium having a magnetic layer with excellent electromagnetic conversion characteristics.

[Section I# that attempts to solve conventional techniques and inventions! ] Conventionally, magnetic recording media such as magnetic tapes are manufactured by applying a magnetic paint made of magnetic powder, binder resin, etc. onto a non-magnetic support and drying it. 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 used to improve high-frequency recording characteristics and require low noise.

However, although high-frequency characteristics are improved by using magnetic powder with high He 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 in both the high frequency region and the low frequency region of the magnetic recording medium are improved. In order to balance the high-frequency characteristics, a magnetic recording medium having multiple magnetic layers has been proposed (Japanese Patent Application Laid-Open No. 1983-1989-1).
9880:1, JP-A-59-172142, JP-A-32-2218, JP-A-51-56228, JP-A-63-146211, etc.).

According to these known techniques, the upper and lower layers of the magnetic layer are designed to 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 such functionally separated magnetic layers, the surface roughness of the non-magnetic support has a large effect on the magnetic layer, and the electromagnetic conversion characteristics of the functionally separated magnetic layer deteriorate. There are new problems.

Furthermore, since it is necessary for magnetic recording media to 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 be overcome by increasing the thickness of the magnetic layer. If this happens, the overall thickness of the magnetic layer will increase and the head contact will deteriorate, resulting in deterioration of the electromagnetic conversion characteristics.

The purpose of the present invention is to consist of a magnetic layer having a three-layer structure with separate functions, and to avoid increasing the thickness of the magnetic layer itself even in such a magnetic layer, and to reduce electromagnetic conversion due to the surface roughness of the non-magnetic support. It is an object of the present invention to provide a magnetic recording medium having a magnetic layer having electromagnetic conversion characteristics superior to those of conventional magnetic recording media without deteriorating the characteristics or reducing the light shielding properties of conventional magnetic recording media.

[Means for Solving the Problems] The magnetic recording medium of the present invention for solving the problems described above comprises laminating a 1111st layer, a second J11th layer, and a third magnetic layer in this order on the surface of a nonmagnetic support. At the same time, the first
The magnetic layer has a surface roughness Ra of 0.02 μm or less, contains red iron oxide having a BET value of 15 to 100 m2/g in an amount of 1 to 60% by weight based on the magnetic powder, and the thickness of the second magnetic layer is and the thickness of the third magnetic layer is 2 μLm or less.

The present invention will be explained in detail below.

One magnetic layer 1 The magnetic layer in the magnetic recording medium of the present invention is a first layer laminated on the surface of a non-magnetic support in order from the side of the non-magnetic support.
It consists of a magnetic layer, a second magnetic layer, and a third magnetic layer.

One of the important things in the present invention is that the surface roughness Ra of the first magnetic layer is 0.02 pm or less, preferably 0.016 μm or less, and more preferably 0.01 μm or less.
It should be 2 μm or less.

If the surface roughness Ra of the first magnetic layer exceeds the above 0.02ILm, even if the specific red iron oxide is used, the adverse effect on the surface of the third magnetic layer caused by the surface roughness of the non-magnetic support can be effectively prevented. I can't think of anything to do. If you change your perspective,
When the surface roughness Ra of the first magnetic layer exceeds 0.02 uLm, the surface roughness of the third magnetic layer becomes large due to the influence on the surface roughness of the non-magnetic support or the surface roughness of the third magnetic layer. As a result, powder falling off from the third magnetic layer becomes severe, or if the surface roughness of the third magnetic layer is forcibly adjusted to a suitable value during the manufacturing process of the magnetic recording medium. However, due to the surface roughness of the non-magnetic support, the thickness of the entire magnetic layer becomes non-uniform, resulting in deterioration of the electromagnetic conversion characteristics.

In order to adjust the surface roughness Ra of the first m magnetic layer to below the above value, it can be achieved, for example, by appropriately selecting Venkara, magnetic powder, Hinter resin, etc., which will be described later. This can be achieved by smoothing the surface using a heat roller after forming the layer.

What is also important in the present invention is that this first magnetic layer has a BETl of 5 to 100 m2/g, preferably 20 to 80 m2/g.
m2/g, more preferably 35 to 70 m2/g, of red iron to the magnetic powder in the first magnetic layer.
The content is preferably 5 to 50% by weight.

When the first magnetic layer contains red iron, it has better dispersibility than carbon black, so the surface roughness Ra of the first magnetic layer can be easily adjusted. It is possible to form a magnetic recording medium whose running control is easier than when a magnetic recording medium is mixed with a magnetic recording medium.

Furthermore, if the BET value of red iron incorporated in the first magnetic layer is adjusted within the above range, and the amount thereof is also adjusted within the above range, even if the surface of the non-magnetic support is rough, the roughness will be reduced. can be easily adjusted to the value of the surface roughness Ra of the first magnetic layer. In other words, if the BET value of red iron is less than the above 15 m''/g, the surface roughness Ra of the first magnetic layer becomes larger than the above 0.02 pm, making it impossible to achieve the object of the present invention. Also,
If it exceeds 100 m2/g, the dispersibility of iron oxide deteriorates, and the surface roughness Ra of the first magnetic layer cannot be adjusted within the range defined by the present invention due to agglomeration of iron oxide.

The red iron oxide that can be contained in the first magnetic layer includes, for example, red iron oxide manufactured by a dry method, red iron oxide manufactured by a wet method, and crude iron oxide manufactured from iron plate pickling waste. Dowa Kogyo (
I would like to mention examples such as Red Garla developed by Kaihatsu Co., Ltd.

As long as the first magnetic layer in this magnetic layer has the specific surface roughness Ra and contains red iron having the BET value in a proportion within the specific range, is there no particular restriction on its properties? Since the first magnetic layer is adjacent to the nonmagnetic support, it is preferable that it has properties as an underlayer.

That is, it is preferable that this first magnetic layer has excellent adhesion to the non-magnetic support and elasticity.

The adhesive force of the first magnetic layer to the non-magnetic support may be, for example, peel strength of 0.5 Kg/cm2 or more, preferably 0.7 to 10 Kg/cm2, and elasticity of 0.5 Kg/cm2 or more, preferably 0.7 to 10 Kg/cm2. 150-850Kg/cm2. Preferably it is 200 to 500 kg/cm2.

Such adhesive strength 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 from a binder resin, red iron oxide, magnetic powder, and other additives blended as necessary, as long as the above conditions are satisfied.

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 use .

Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-donylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, and acrylic ester-vinylidene chloride copolymer. copolymer, methacrylic acid ester-donylidene 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 tstylate), cellulose diacetate,
Examples include cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amino resins, and synthetic rubber-based thermoplastic resins.

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

Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin, high molecular weight polyester resin, and isocyanate prepolymer. Mixtures, mixtures of methacrylate copolymers and shiisocyanate prebolimers, mixtures of polyester polyols and polyisocyanates, mixtures of polycarbonate polyols and polyisocyanates, urea-based luminaldehyde resins, low molecular weight glycols/high molecular weight diols/triphenylmethane Mixtures of triisocyanates, polyamine resins, and the like.

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; , urethane acrylic type, epoxy acrylic type, phosphoric acid ester acrylic type, aryl type, and pytrocarbon type.

These may be used singly 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 (eg, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate).

Naphthylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate and adducts of these polyisocyanate compounds with trivalent polyols, diisocyanate pentamers, adducts of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, metaxylylene diisocyanate Examples include an adduct of 3 moles of isocyanate and 1 mole of trimethylolpropane, and a pentamer of tolylene diisocyanate.

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

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

The functional groups include -3o, M', OS O*M'
, -COOM'OM" / is a metal, M"J and M3 are hydrogen atoms,
Either an alkali metal or an alkyl group. Furthermore, M2 and M3 may be different from each other or may be the same.

Among the various binder resins mentioned above, the first one in the present invention is
Binder resins suitable for forming the magnetic layer include:
MRIIO (manufactured by Nippon Zeon).

UR8300 (manufactured by Toyobo Co., Ltd.), UR8700 (manufactured by Toyobo Co., Ltd.), N-3032, N-3132 (manufactured by Nippon Polyurethane Co., Ltd.), N-3141-7 (manufactured by Nippon Polyurethane Co., Ltd.),
S-LEC E (manufactured by M Suikagaku Co., Ltd.), E620. E551.
E701 (manufactured by Sokoen Yakuhin Co., Ltd.), VAGH, VMCH (
Examples include resins having an average molecular weight of 10.000 to 200.000, such as Nistan 5701 (manufactured by Kuttriuchi), and Ti2067 (manufactured by Sanyo Kasei).

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 Usually 8 to 60% by weight based on the entire magnetic layer,
Preferably it is 12 to 30% by weight.

Examples of the magnetic powder that can be contained in the first magnetic layer include Co-containing -Fe20:+ powder, Co-containing F
e3O4 powder, Co-containing Fed, (4/3 < x
< 3/2) powder or Fe-An metal powder, F
e-Ni metal powder, Fe-Al-Ni metal powder, F
e -A11-P metal powder, Fe-Ni-3i-All
Metal powder, Fe-Ni-5i-A 41-Mn metal powder, Ni-Co metal powder, Fe-Mn-)! n metal powder,
FeNi-Zn metal powder, Fe-Co-Ni-Cr metal powder, Fe-C.

N1-P metal powder, Go-Ni metal powder and Go-P
Examples include fine ferromagnetic metal powder such as metal powder. Among these, preferred is fine CO-containing -F
eJ: + powder.

When the first magnetic layer contains magnetic powder, the first magnetic layer is capable of recording low-frequency signals, and it is desirable that the magnetic powder has the following properties.

In other words, the BET value of magnetic powder is usually 20m 27g
Above, preferably 25 to 46 m2/g.

Further, the shape of the magnetic powder is not particularly limited as long as it is fine, and for example, any shape such as acicular, spherical, or ellipsoidal shape may be used. However, acicular magnetic powder is preferable for recording low frequency signals, and moreover, it is preferable because its particle size is more uniform than the magnetic powder contained in the second and third magnetic layers described later.

The blending amount of the magnetic powder is usually 20 to 85% by weight, preferably 40 to 85% by weight, based on the Hinter resin in the first magnetic layer.
It is 80% by weight.

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

As the dispersant, for example, an azo pigment dispersant (AZP
D), fatty acids, amine compounds, alkyl sulfates,
Fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid esters, known surfactants, salts thereof, negative organic groups (e.g. -
COOHl-PO,H) A salt of a polymer dispersant or the like can be added to the magnetic layer.

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

Among the above dispersants, azo pigment dispersants are preferred.

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.

Furthermore, 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, lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecy oleate, 2-ethylhexyl stearate, 2-ethylhexyl myristate, ethyl stearate, 2-ethylhexyl palmitate, isopropyl Palmitate, isopropyl myristate, butyl laurate, cetyl-2-
Examples include ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, and diisodecyl acylate. Among these, butyl stearate and butyl palmitate are particularly preferred. The aforementioned various fatty acid esters may be used alone or in combination of two or more.

The amount of the fatty acid ester added is usually 0.5 to 10 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the magnetic powder.
The amount may be 1 to 5 parts by weight.

By reducing the amount of a dispersant such as a fatty acid or a plasticizer such as a fatty acid ester as described above, it is possible to improve the running durability of a magnetic recording medium particularly under high temperature and high humidity conditions.

Examples of the antistatic agent include conductive powders such as graphite, carbon black, tin oxide-antimony oxide compounds, tin oxide-titanium oxide-antimony oxide compounds, and carbon black graft polymers; natural surfactants such as saponin; Nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, quaternary trisine, and other heterocycles;
Cationic surfactants such as phosphonium and sulfoniums: Anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfate ester groups, phosphoric ester groups, amino acids, aminosulfonic acids, sulfuric and phosphoric acids of amino alcohols Examples include amphoteric surfactants such as ester gR.

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

The amount of the antistatic agent blended is usually 0.5 to 20 parts by weight per 100 parts by weight of the magnetic powder.

Note that the above-mentioned lubricant and antistatic agent or the dispersant described below do not have a sole function; for example, a - compound may act as a lubricant and an antistatic agent.

Therefore, the above-mentioned classifications in this invention indicate the main actions, and are not limited by the actions of the classified compounds or the actions shown in the classification.

The thickness of the 11a layer is usually 1 to 5 μm.

Preferably it is 1.2 to 3.5 Bm. If the thickness of the first magnetic layer is less than 1 μm, it may not be possible to effectively prevent the influence of surface irregularities of the non-magnetic support, and if the thickness of the first magnetic layer exceeds 5 μm, the relative In some cases, the thicknesses of the second magnetic layer and the third magnetic layer become so small that it becomes impossible to effectively record high-frequency signals.

Next, in addition to the specific requirements for the first magnetic layer, what is important in the present invention is whether the total thickness of the second magnetic layer and the thickness of the third magnetic layer is 2.0. μm or less, preferably 0.3 to 1
．． 5 kLm, more preferably 0.4 to 1.3 m. The total thickness of the second magnetic layer and the third magnetic layer is
．． When it becomes thicker than 0μm, the thickness of the magnetic layer is usually 3~
Since the thickness is 5 μm, the thickness of the first magnetic layer must be reduced, and the influence of surface irregularities of the non-magnetic support on the magnetic layer may become large, resulting in deterioration of electromagnetic conversion characteristics.

As long as such conditions are satisfied, the second magnetic layer and the third magnetic layer can be formed from magnetic powder, a binder resin, and other additives mixed as necessary.

The magnetic powder contained in the second m layer and the third ai layer includes magnetic powders that can be used to form the first magnetic layer. However, the second magnetic layer is located in the middle of the magnetic layers and receives high-frequency signals among low-frequency signals, while the third magnetic layer receives high-frequency signals and does not transmit signals to the second magnetic layer. The magnetic powder contained is preferably needle-shaped, rod-shaped, or similar magnetic powder, and specifically includes magnetic powder having an aspect ratio of 2 to 2o, preferably 5 to 18. The magnetic powder contained in the third magnetic layer is preferably a magnetic powder smaller than the second magnetic powder, specifically, the particle size is 0.2 to 0.01 μm, preferably 0.1 to 0.0 μm. Examples include magnetic powder having a diameter of .02 μm. Hexagonal ferrite is also preferred.

The content of the magnetic powder in the second magnetic layer is usually 65 to 87% by weight, preferably 70 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 have excellent binding force with the binder and to reduce noise due to high filling.

The content ratio of magnetic powder in the third magnetic layer is Ft3
It is usually 70 to 90% by weight, preferably 72 to 85% by weight, based on the entire layer. By the content ratio of the magnetic powder in the third magnetic layer being within the above range,
It has excellent wear resistance and enables improved electromagnetic conversion characteristics, especially high-frequency output.

Examples of the binder resin used to form the second magnetic layer and the third AI layer include the binder resins exemplified for forming the first magnetic layer. Note that, since the third magnetic layer is the outermost magnetic layer among the magnetic layers, it is desirable that the third magnetic layer is a magnetic layer with a high # property, which has excellent wear resistance and does not shed magnetic powder or the like. Due to such demands,
Examples of binder resins that can be used in the third magnetic layer include vinyl chloride copolymers containing epoxy groups and maleic anhydride groups, vinyl chloride copolymers containing epoxy groups and sulfonic acid groups, aromatic polyester polyurethanes, and fatty acids. Examples include polyester polyurethane, polycarbonate polyurethane, and the like.

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

The amount is usually 10 to 40% by weight, preferably 15 to 35% by weight, based on the entire second magnetic layer. If the content of the binder resin is less than 10% by weight, the mechanical strength of the second magnetic layer may decrease, and if the content of the binder resin exceeds 40% by weight, the magnetic powder will be relatively weak. The content may decrease, leading to a decline in magnetic properties.

The content of the binder resin in the third magnetic layer is usually 10 to 30% by weight, preferably 1% by weight, based on the entire third magnetic layer.
It is 5 to 28% by weight. Binder resin content or 1 above
If it is less than 0% by weight, the mechanical strength of the third magnetic layer may be reduced, and the content of the binder resin may be less than 30% by weight.
If it exceeds % by weight, the content of magnetic powder becomes relatively small, which may lead to deterioration of magnetic properties and abrasion resistance.

The second magnetic layer and the third magnetic layer may contain a dispersant, a plasticizer, an antistatic agent, etc., which may be used in forming the first magnetic layer.

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 fatty acids, fatty acid esters, silicone lubricants, fatty acid-modified silicone lubricants, fluorine-based lubricants, liquid paraffin, squalane 2 carbon black, graphite, carbon flak craft polymers, molyfden disulfide, Examples include tungsten sulfide.

Among these, preferred lubricants include melting points of -10 to
Examples include fatty acids with a melting point of 50°C, fatty acid esters with a melting point of 15 to 35°C, 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 10 Ojll of the magnetic powder. If the blending ratio exceeds 20 parts by weight, the amount of lubricant may become excessive and dirt may easily adhere to the surface of the magnetic layer.

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

The thickness of this second magnetic layer is usually 0.05 to 1.1 μm,
The thickness of the third magnetic layer is preferably 0.1 to 0.3 μm, and the thickness of the third magnetic layer is usually 0.1 to 1.1 μm, preferably 0.1 to 0.3 μm.
It is 15-0.8 μm.

(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, and polyolefins such as polypropylene. ; cellulose derivatives such as cellulose triacetate and cellulose tiacetate; and plastics such as polycarbonate. Further C
Metals such as U, An, and In, glass, and various ceramics such as so-called new ceramics (eg, boron nitride, silicon carbide, etc.) may 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 shapes may be used depending on the form and as necessary. You can choose and use materials.

The thickness of the support is 1 if it is in the form of a tape or sheet.
Usually, it is 3 to 100 μm, preferably 5 to 50 μm. In addition, in the case of disk-shaped or cart-shaped, usually 30
~100 μm. Furthermore, in the case of a drum shape, the shape can be made to correspond to the recorder used, such as a cylindrical shape.

On the surface (back surface) of the nonmagnetic support on which the magnetic layer is not provided, an 8-ink coat may be 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, a method for manufacturing the magnetic recording medium of the present invention will be described.

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

Examples of solvents used for crosstalk and dispersion of the compositions for the first to third magnetic layers include acetone, methyl ethyl ketone (M
EK), ketones such as methyl isobutyl ketone (JIBK) and cyclohexanone; alcohols such as methanol, ethanol, propatool and butanol;
Ester systems such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol 1,000 acetate, ether systems such as diethylene glycol dimethyl ether 2-ethoxyethanol, tetrahydrofuran, dioxane, etc., Hensen, toluene, xylene, etc. Aromatic hydrocarbons; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene can be used.

When mixing the first to third magnetic layer sets, the magnetic powder and other magnetic paint components (hereinafter sometimes referred to as raw materials) are fed into the mixing machine simultaneously or sequentially. . For example, first, the magnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined period of time, the remaining components are added and mixing is continued to obtain a magnetic paint.

To disperse crosstalk, various types of crosstalk devices can be used. Examples of this mixer include a two-roll mill, a three-roll mill, a ball mill, a befur mill, a cytoclinter, a Sqegvari attritor, a high-speed impeller splitter, a high-speed stone mill, a high-speed impact mill, a dispersion mill, a high-speed mixer, and a homogenizer. , ultrasonic molecules & machines, etc.

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

Coating methods that can be used in the present invention include, for example, gravure roll coating, wire bar coach ink, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coach ink, squeeze coating, and kiss coach ink. Inc. and Fantin Coach Inc.

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

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 disk by cutting it into a disk shape. Ru. Furthermore, similar to ordinary magnetic recording media, it can also be used in cart-like, cylindrical, or other forms.

[Examples] Next, the present invention will be described in more detail based on Examples and Comparative Examples. In the following, "part" means "part by weight".

Note that the methods for measuring physical properties adopted in Examples and Comparative Examples are as described below.

(a) RF specific output Lumi-5N, Chroma output Kashihak noise meter 925C, JVC HR-S 700
Measured using 0 deck.

(b) Dropout (Do) Run the sample in the HR-S 7000 deck, l
5g5, signal loss with a magnitude of -15 dB or more was measured every minute for 20 minutes, and the average value per minute was calculated.

(c) Still durability HR-S 7000 deck T-120 type video cassette center part (near the beginning of the tape or 6120m)
The time required for the signal to drop by 6 dB was measured by outputting the image signal recorded in the video or by playing back the still mode.

(d) Running Durability The entire length was repeatedly run at 40'C and 180% RH to check for abnormalities in running performance. Further, the tape was removed from the video cassette after the test, and the degree of damage to the edges and the presence or absence of scratches on the back surface were checked.

When the backcoat layer was scraped, those with obvious changes in gloss were judged as NG, and those with no change in gloss and powder falling off or sticking to hands were judged OK. In addition, the amount of wear was measured from the change in the amount of protrusion of the head of the video deck before and after the tape was run.

(Example 1.2 and Comparative Examples 1 to 4) First magnetic layer composition magnetic powder (Go-containing-Fe20i, specific surface area BET
Straight 35m2/g) ・ ・ ・ ・ ・ ・
・ ・ 100 parts alumina (average particle size 0.1 μ
m, spherical)・3 parts hinyl chloride-vinyl acetate copolymer (contains 0.3% maleic anhydride copolymer)・17 parts polyurethane with Tubonone N: +022)・・13 parts stearic acid・・・・・・・... 1 part of the above composition, 12 parts of methyl ethyl ketone, and 12 parts of toluene were kneaded in advance, and then 88 parts of methyl ethyl ketone, 88 parts of toluene, and 100 parts of cyclohexanone were added to prepare paint A'. After adding the following red iron dispersion to this paint A' in the proportions shown in Table 1, the mixture was thoroughly mixed and dispersed, and the magnetic paint A (A-1, A-2, A-3, A
-4) was obtained.

Red red dispersion (x -Fe2O:+ (spherical BET value 37m2/g
) -100 parts Nyl chloride-vinyl acetate copolymer (maleic anhydride #0.3% copolymer) 17 parts Bourethane and Tubonone N 3022) 13 parts stearic acid ...1 part methyl ethyl ketone ...43 parts toluene ...
・・・・・・・・・43 parts cyclohexanone・・・・
43 parts Next, the following composition for the second magnetic layer, 12 parts of methyl ethyl ketone and 12 parts of toluene were kneaded in advance, and then 88 parts of methyl ethyl ketone and 8 parts of toluene were kneaded.
8 parts and 100 parts of cyclohexanone were added, thoroughly mixed and dispersed, and passed through a filter to obtain magnetic paint B.

Composition magnetic powder for second magnetic layer (Co-γ-Fe20.,...lOD
Part BET value 40 nt2/g) Alumina (average particle size 0.1 pm, spherical)...5 parts Vinyl chloride-vinyl acetate copolymer <E Kizeon MRIIO)...17 parts Polyurethane ( Carbonate-containing type, sulfonic acid metal base containing)...13 parts stearic acid...
・・・・・・・・・1 part phtyl stearate・・・・
...... 1 part Next, the following composition for the third magnetic layer, 14 parts of methyl ethyl ketone, and 14 parts of toluene were kneaded in advance, and then the following alumina component Ill was added, and further 40 parts of methyl ethyl ketone and 40 parts of toluene were kneaded. 1 part and 60 parts of cyclohexanone were added and dispersed by Santomil.

To the resulting dispersion were further added 8 parts of trifunctional incyanate (Coronate L), 45 parts of methyl ethyl ketone, and 4 parts of toluene.
After adding 5 parts and 40 parts of cyclohexanone and thoroughly mixing the mixture, the mixture was passed through a filter to obtain magnetic paint C.

Composition for third magnetic layer Magnetic powder (Go -y -Fe2O: + BET value 55m27g) Loo part salt part vinyl-based copolymer poxy group.

(contains gold sulfonate group)...13 parts polyurethane (aromatic polyester), 8 parts stearic acid...
・・・・・・・・・・・・Two parts phthyl stearate・・・
...... 2 parts Alumina dispersion Alumina (0.2 m spherical) 6 parts Polyurethane (aromatic polyester) 1 part Methyl ethyl ketone-toluene-cyclohexanone 1:1 : Compound 18...7 parts Next, magnetic paints A, B, and C produced as described above were coated on a polyester base with a thickness of 13.0 μm using a precision extrusion coater (FEC) as shown in Table 2. Simultaneous multilayer coating was performed with the coating thickness shown in .

Then, while the coating film was still wet, it was heated in a solenoid for 2000 min.
After magnetic field orientation at 0e, calender treatment was performed, and then a coating consisting of the following backcoat composition was applied to the back side of the polyester base so that the thickness of the dried coating film was 0.6 μm. The coating was applied to obtain a raw fabric.

Then, this original fabric was slit into 1/2 inch width to obtain samples.

On the other hand, magnetic paint A alone was applied to a different polyester base having a thickness of 13.0 μm to the same thickness, and the same treatment as above was performed, and the roughness of the paint film was measured.

Back coat composition D Carphone black 0 particle size 22 mμ) ・・・DO part Carbon flux (particle size 75 μL) ・・10 parts Calcium carbonate powder (particle size 130 mg) ・・10 parts Nitrocellulose (Asahi Kasei Co., Ltd. (manufactured by Seltsuba BTHI/2)...40 parts polyurethane resin (N 3141 low molecular weight type manufactured by Nippon Polyurethane Co., Ltd., MW 50,000.

OH group, urethane main chain contains secondary amine/tertiary amine) 50 parts Polyisocyanate (Coronate 3041) 15 parts Cyclohexanone 275 parts Methyl ethyl ketone...500 parts Toluene...
Table 2 shows the thickness of each magnetic layer of the 50074 samples and the roughness of the coating film of paint A. Further, the results of measuring the physical properties of the samples are shown in Table 3.

(Comparative Example 5) In Example 2, benzoguanamine resin powder with an average particle size of 0.4μ was added to paint A-2 as surface control particles by magnetic powder 1.
A sample was obtained by performing the same treatment as in Example 2 except that 1 part per 00 parts was added. Table 3 shows the physical properties of the sample.

(Comparative Example 6) A sample was obtained by performing the same treatment as in Example 2 except that only paint A-2 was obtained without passing it through the filter.

The physical properties of this sample are shown in Table 3.

(Comparative Example 7) A sample was obtained by carrying out the same treatment as in Example 2, except that in Example 2, a red iron dispersion having a BET value of 8 m27H was used as α-Fe20U.

The physical properties of this sample are shown in Table 3.

(Comparative Examples 8 to 16) For back coats having the same composition as in Example 1.2 and Comparative Examples 1 to 7, except that only the polyurethane resin was replaced with N3127 manufactured by Nippon Polyurethane Co., Ltd. instead of the composition eJD for the hard coat. Paints were prepared using the compositions, and samples were obtained in the same manner as in Example 1.2 and Comparative Examples 1 to 7, respectively.

The physical properties of this sample are shown in Table 4.

[Effects of the Invention] According to the present invention, the surface unevenness of the non-magnetic support is effectively prevented, and the non-uniform thickness of the magnetic layer caused by the surface unevenness 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.

Furthermore, this magnetic recording medium has excellent running durability and can easily run stably for a long time.

Further, according to the present invention, it is possible to provide a magnetic recording medium that does not wear out the head and exhibits little deterioration in image quality even after long-term use.

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 surface roughness Ra of 0.02 μm or less and contains red iron oxide having a BET value of 15 to 100 m^2/g in an amount of 1 to 60% by weight based on the magnetic powder. A magnetic recording medium characterized in that the sum of the thickness of the third magnetic layer and the thickness of the third magnetic layer is 2 μm or less.