JPH04222921A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To offer a magnetic recording medium excellent in traveling durability and electromagnetic conversion characteristics. CONSTITUTION:On the surface of a nonmagnetic supporting body, there are successively formed a first magnetic layer, second magnetic layer and third magnetic layer. The first magnetic layer contains 0.2-20wt.% carbon black having >=80cc/100g oil absorption to the amt. of the magnetic powder in the first magnetic layer. The third magnetic layer contains a binder resin having negative functional groups.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having a magnetic layer with excellent running durability and excellent electromagnetic conversion characteristics.

0002

[Prior Art and Problems to be Solved by the Invention] Conventionally, magnetic recording media such as magnetic tapes are produced by coating a magnetic paint made of magnetic powder, binder resin, etc. on a non-magnetic support and drying it. Manufactured.

In conventional magnetic recording media, since the magnetic layer is a single layer, it is not possible to sufficiently cover a wide frequency band from low to high frequencies with one type of magnetic powder.

However, with the recent trend toward higher recording densities, magnetic recording media with improved high-frequency recording characteristics and low noise are required.
Magnetic powder of high value is now used.

However, in a single-layer magnetic layer, high H
c. Although attempts have been made to improve high-frequency characteristics by using magnetic powder with a high BET value, the problem of insufficient low-frequency characteristics remains unsolved.

In order to solve this problem, it is necessary to increase the magnetic recording capacity of magnetic recording media, such as video magnetic recording media, or to improve both the magnetic recording characteristics in the high frequency region and the low frequency region of the magnetic recording medium. ,
In order to balance the low and high frequency characteristics,
Magnetic recording media with multiple magnetic layers have been proposed (
JP-A-48-988803, JP-A-59-17214
No. 2, Japanese Patent Publication No. 32-2218, Japanese Patent Publication No. 51-5622
8, Special Publication No. 63-146211, etc. )
.

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

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 are affected. A new problem has arisen: the situation is getting worse.

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

However, carbon black itself is
There is a problem in that the dispersibility in the magnetic layer is poor, causing unnecessary unevenness on the surface of the magnetic layer and deteriorating the 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 eliminated by further increasing the thickness of the magnetic layer to be laminated. Although it may be possible to do so, the thickness of the entire magnetic layer increases, resulting in deterioration of electromagnetic conversion characteristics, and in particular, poor head contact.

The object of the present invention is to have a functionally separated three-layer magnetic layer and have excellent electromagnetic conversion characteristics.
An object of the present invention is to provide a magnetic recording medium with improved running durability.

[0013]

[Means for Solving the Problems] The present invention for solving the problems described above includes laminating a first magnetic layer, a second magnetic layer and a third magnetic layer in this order on the surface of a non-magnetic support, and The first magnetic layer contains carbon black with an oil absorption of 80 cc/100 g or more in a content ratio of 0.2 to 20% by weight based on the magnetic powder in the first magnetic layer, and the third magnetic layer contains carbon black with an oil absorption of 80 cc/100 g or more, and the third magnetic layer contains carbon black with an oil absorption of 80 cc/100 g or more. A magnetic recording medium characterized in that is a resin having a negative functional group.

The present invention will be explained in detail below.

-Magnetic layer- The magnetic layer in the magnetic recording medium of the present invention comprises a first magnetic layer, a second magnetic layer and a third magnetic layer, which are laminated on the surface of a non-magnetic support in order from the side of the non-magnetic support. Consisting of

[0016] By configuring the magnetic layer with three functionally separated layers, the thickness of the magnetic layer itself does not increase even in such a magnetic layer, and the bottom layer and the intermediate layer provide an underlayer effect, making it possible to By forming the surface of the magnetic support with appropriate roughness, deterioration of electromagnetic conversion characteristics can be reduced.

Furthermore, by having three layers, the first magnetic layer functions to handle low frequency signals, the second magnetic layer functions to handle high frequency signals within the low frequency signals, and the third magnetic layer functions to separate high frequency signals. Therefore, the magnetic recording medium of the present invention has a magnetic layer that has better electromagnetic conversion characteristics than conventional magnetic recording media.

As the thickness of each layer, the thickness of the first magnetic layer is
Usually 4.0 to 1.0 μm, preferably 3.5 to 1
．． It is 5 μm. The thickness of the second magnetic layer is usually 0.5 to 0.
．． The thickness is 1 μm, preferably 0.4 to 0.2 μm. The thickness of the third magnetic layer is usually 0.6 to 0.1 μm,
Preferably, it is 0.5 to 0.1 μm. Further, the total thickness of the second magnetic layer and the third magnetic layer is preferably 0.7 μm or less.

[0019] The total thickness of the three layers is usually 4.5 to 1.5μ.
m, preferably 4.0 to 1.7 μm.

If this thickness is less than 1.5 μm, the electromagnetic conversion characteristics will deteriorate due to the base effect of the non-magnetic support, and if this thickness exceeds 4.0 μm, the coating film will be missing from the edge portion during cutting and drop. Out increases.

In the present invention, a first magnetic layer is laminated on a non-magnetic support as the lowest magnetic layer.

[0022] The first magnetic layer can be formed from magnetic powder, binder resin, carbon black, and additives blended as necessary.

What is important in the present invention is that the first magnetic layer contains carbon black with an oil absorption of 80 cc/100 g or more, preferably carbon black with an oil absorption of 85 to 180 cc/100 g.

[0024] By using carbon black with an oil absorption of 80 cc/100 g or more, the carbon black has good dispersibility and good compatibility with the binder resin of the first magnetic layer, which prevents powder from falling off when cutting the final product. There is no.

What is important in the present invention is that the carbon black content is 0.2 to 20% by weight, preferably 1.0 to 1.7% by weight, based on the magnetic powder in the first magnetic layer.
% by weight.

[0026] In the case of such a content, the running durability of the magnetic recording medium is improved due to excellent light-shielding properties.

[0027] Carbon black content is 0.2% by weight
If it is less than 20% by weight, the light shielding properties will be poor, and if it exceeds 20% by weight, the electromagnetic conversion characteristics will be poor.

[0028] Carbon black having an oil absorption of more than a specific oil absorption in the first magnetic layer, that is, an oil absorption of 80cc/100g.
By containing the above carbon black in a specific proportion, that is, 0.2 to 20% by weight, the dispersibility of carbon black in the binder resin is extremely improved, the light shielding property is also improved, and electromagnetic conversion is improved. It has excellent properties, improved running durability, and the final product is a good product that does not shed powder when cut.

The second magnetic layer in the present invention can be formed from a binder resin, magnetic powder, and other additives blended as necessary.

Examples of the binder resin that can form the first magnetic layer and the second magnetic layer include thermoplastic resins, thermosetting resins, reactive resins, and electron beam resins conventionally used in magnetic recording media. Radiation-curable resins or mixtures thereof can be used.

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-acrylonitrile copolymer. Vinylidene chloride copolymer, 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 derivative (cellulose acetate butyrate), cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc. ), styrene-butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, and synthetic rubber-based thermoplastic resin.

[0032] These may be used alone or in combination of two or more.

Examples of the thermosetting plastic 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. Mixtures of prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, mixtures of polycarbonate polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycols/high molecular weight diols/triphenyls Mixtures of methane triisocyanates, polyamine resins, and the like.

[0034] These may be used alone or in combination of two or more.

[0035] Examples of the electron beam curable resin include maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type,
Examples include unsaturated prepolymers such as polyether acrylic type, polyurethane acrylic type, and polyamide acrylic type; polyfunctional monomers such as ether acrylic type, urethane acrylic type, epoxy acrylic type, phosphate ester acrylic type, aryl type, and hydrocarbon type. It will be done.

[0036] These may be used alone or in combination of two or more.

In the present invention, the various resins mentioned above may be used as binder resins, but furthermore,
A curing agent may be used together with the above various resins to form a binder resin.

Examples of the curing agent include polyisocyanate compounds (eg, tolylene diisocyanate, 4,
4'-diphenylmethane diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate,
Cyclohexane diisocyanate and adducts of these polyisocyanate compounds and trivalent polyols, pentamers of diisocyanates, adducts of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, 3 moles of metaxylylene diisocyanate and 1 mole of trimethylolpropane Adduct with moles, 5 of tolylene diisocyanate
(quantity), etc.

[0039] These may be used alone 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.

[0041] The functional groups include -SO3 M1,
-OSO2 M1, -COOM1, and -P(=
O)(OM2)2 (wherein, M1 is a hydrogen atom,
or an alkali metal, and each of the two M2's is a hydrogen atom, an alkali metal, or an alkyl group. Further, the two M2's may be different from each other or may be the same. ) can be mentioned.

Among the various binder resins mentioned above, examples of binder resins suitable for forming the first magnetic layer in the present invention include thermoreversible resins, thermosetting resins, and reactive resins. Specifically, VYHH, VAGH, VMCH, and VMCC manufactured by Union Carbide
, Estan 5701 manufactured by Goodrich, MAG305 manufactured by Dainippon Ink Co., Ltd., N3127 and N3132 manufactured by Nippon Polyurethane Co., Ltd., etc., with an average molecular weight of 10,
000 to 200,000.

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.
Usually 30 to 85% by weight based on the entire first magnetic layer,
Preferably it is 40 to 80% by weight.

In addition to the above-mentioned resins, suitable binder resins for forming the second magnetic layer in the present invention include maleic acid-modified vinyl chloride-vinyl acetate copolymers, sulfonic acid metal bases and epoxy group-containing vinyl chloride copolymers. Examples include polymers, sulfonic acid metal base-containing polyurethanes, and polycarbonate polyurethanes.

The content of the binder resin in the second magnetic layer is 40 to 80% by weight, preferably 55 to 78% by weight, based on the entire second magnetic layer.

The magnetic powder that can be contained in the first magnetic layer and the second magnetic layer includes, for example, Co-containing γ-Fe2 O3 powder, Co-containing Fe3 O4 powder, Co-containing FeOX (4/3<x< 3/2) Powder, or Fe-Al metal powder, Fe-Ni metal powder, Fe
-Al-Ni metal powder, Fe-Al-P metal powder, Fe
-Ni-Si-Al metal powder, Fe-Ni-Si-Al
-Mn metal powder, Ni-Co metal powder, Fe-Mn-Z
n metal powder, Fe-Ni-Zn metal powder, Fe-Co-
Ni-Cr metal powder, Fe-Co-Ni-P metal powder,
Fine ferromagnetic metal powders such as Co-Ni metal powder and Co-P metal powder are included. Among these,
Preferred is fine Co-containing γ-Fe2O3 powder.

When the first magnetic layer contains magnetic powder, since the first magnetic layer is responsible for recording low frequency signals, it is desirable that the magnetic powder has the following properties.

That is, the BET value of magnetic powder is usually 2
It is 3 m2/g or more, preferably 25 to 45 m2/g.

[0049] 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 it is preferable that the particle size is more uniform than that of the magnetic powder contained in the second and third magnetic layers described later. .

The blending amount of the magnetic powder is usually 100 to 700% by weight based on the binder resin in the first magnetic layer.
Preferably it is 120 to 650% by weight.

Furthermore, when the second magnetic layer contains magnetic powder, the second magnetic layer is located in the middle of the magnetic layers and takes charge of signals on the high frequency side among low frequency signals, so the magnetic powder contained in the second magnetic layer The powder is preferably magnetic powder in the shape of needles, rods, or similar shapes, specifically those with an aspect ratio of 2 to 15.
, preferably 4 to 12 magnetic powders.

The content of the magnetic powder in the second magnetic layer is usually 68 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 maintain a balance between high residual magnetic flux density and elasticity of the magnetic layer.

[0053] Examples of additives that can be included in the first magnetic layer and the second magnetic layer include dispersants, plasticizers, antistatic agents, and the like.

Examples of the dispersant include lecithin, 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 ( For example -COOH
, -PO3H) and the like can be added to the magnetic layer.

[0055] These may be used alone or in combination of two or more.

The amount of the dispersant added is usually 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, isocetyl stearate, dioleyl maleate,
Butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, amyl stearate, amyl palmitate, 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,
Examples include cetyl-2-ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, and diisodecyl adipate. 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.

[0058] The amount of the fatty acid ester added is usually 0.5 to 10 parts by weight per 100 parts by weight of the magnetic powder.
Preferably, it can 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 added as described above, the running durability of the magnetic recording medium can be improved 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 saponins; nonionic surfactants such as alkylene oxides, glycerols, and glycidols; cationic surfactants such as higher alkylamines, quaternary pyridines, other heterocycles, phosphoniums, and sulfoniums. : Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric acid ester groups; Ampholytic surfactants such as amino acids, aminosulfonic acids, and sulfuric and phosphoric acid esters of amino alcohols. Can be mentioned.

[0061] These may be used alone or in combination of two or more.

[0062] The blending amount of the above antistatic agent is 10% of the magnetic powder.
It is usually 0.5 to 20 parts by weight relative to 0 parts by weight.

[0063] The above-mentioned lubricant, antistatic agent, dispersant, etc. do not have an independent effect;
For example, one compound may act as a lubricant and an antistatic agent.

[0064] Therefore, the above-mentioned classifications in this invention indicate the main actions, and the actions of the classified compounds are not limited by the actions shown in the classification. If the thickness of the first magnetic layer is less than 1.0 μm, it may not be possible to effectively prevent the influence of surface irregularities of the non-magnetic support;
If the thickness exceeds m, the thicknesses of the second magnetic layer and the third magnetic layer become relatively small, and effective recording of high frequency signals may not be possible.

In the present invention, the first magnetic layer and the second
A third magnetic layer is laminated on the magnetic layer.

[0066] The third magnetic layer can be formed of a binder resin, magnetic powder, and other additives blended as necessary.

[0067] Since the third magnetic layer is the outermost magnetic layer among the magnetic layers, it is desirable that the third magnetic layer is a highly rigid magnetic layer that has excellent abrasion resistance and does not cause particles such as magnetic powder to fall off.

What is important in the present invention is that the binder resin of the third magnetic layer is composed of a thermoplastic resin having a negative functional group.

By using a thermoplastic resin having a negative functional group as the binder resin of the third magnetic layer, it is possible to improve the dispersibility of the magnetic powder and improve the abrasion resistance.

As the binder resin in the present invention, a combination of the above-mentioned polyurethane having a negative functional group and a vinyl chloride resin is preferred.

Examples of the functional groups in the resins include -SO3 M, -OSO2 M, -COOM, and -P(=O)(OM3)2 (wherein M is a hydrogen atom, lithium, and sodium (The two M2's are each a hydrogen atom, an alkali metal, or an alkyl group.The two M2's may be different from each other or the same.) etc. can be mentioned.

These functional groups are compatible with resins such as vinyl chloride resins and polyurethane resins, for example, Cl-CH2C
H2 SO3 M, Cl-CH2 CH2 OSO2
M, Cl-CH2 COOM, Cl-CH2-P
(=O) (OM3)2 (However, M, M1 and M
2 has the same meaning as above. ) can be obtained by condensing a compound containing a negative functional group and chlorine in the molecule through a dehydrochloric acid reaction.

The polyurethane having the above-mentioned negative functional group can be the above-mentioned negative functional group.

The molecular weight of the polyurethane having negative functional groups is usually 2,000 to 70,000, preferably 4
,000 to 50,000.

If the molecular weight is less than 2,000, the uncrosslinked component becomes a plasticizer, resulting in decreased physical properties and poor durability under high temperature and high humidity conditions.

On the other hand, if the molecular weight exceeds 70,000, the dispersibility and dissolution of the magnetic powder will deteriorate.

Examples of the vinyl chloride resin include vinyl chloride-vinyl acetate-vinyl alcohol copolymer,
Examples include vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer, and vinyl chloride-vinyl propionate-maleic acid-vinyl alcohol copolymer.

[0078] The molecular weight of the vinyl chloride resin having the negative functional group is usually 5,000 to 35,000,
Preferably it is 10,000 to 30,000.

[0079] If the molecular weight is less than 5,000, the strength of the coating film decreases, particularly the durability under high temperature and high humidity conditions.

On the other hand, if the molecular weight exceeds 35,000, the dispersion of the magnetic powder will be poor and the expected performance will not be obtained.

As described above, the binder resin forming the third magnetic layer in the present invention is preferably a combination of polyurethane having a negative functional group and a vinyl chloride resin, and among these, MR110 (manufactured by Nippon Zeon Co., Ltd.) is preferable.
, sulfobetaine group-containing polycarbonate polyurethane is preferred.

Furthermore, when a resin having a negative functional group is used as the binder resin in the first magnetic layer and the second magnetic layer, the same binder resin can be used.

The blending amount of the binder resin in the third magnetic layer is usually 12 to 25% by weight, preferably 15 to 21% by weight, based on the entire third magnetic layer.

If the binder resin content is less than 12% by weight, the coating film will be brittle and powder will fall off during continuous running. Furthermore, if the content of the binder resin exceeds the above 25% by weight, the still durability will deteriorate and head clogging will occur.
Magnetic properties deteriorate.

[0085] Furthermore, polyfunctional isocyanate, Coronate L, AD31, etc. can be used as a curing agent for the binder resin.

The magnetic powder contained in the third magnetic layer can be appropriately selected from those that can be used to form the first magnetic layer and the second magnetic layer.

[0087] Since the third magnetic layer is in charge of high frequency signals,
Preferably, the magnetic powder is smaller than the first magnetic powder and the second magnetic powder, and specifically, the particle size is preferably 0.2 to 0.01 μm.

Other additives for forming the third magnetic layer can be appropriately selected from those that can be used to form the first and second magnetic layers.

Further, since the third magnetic layer is required to have excellent wear resistance as described above, it is preferable that a lubricant is contained 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, carbon black, graphite, carbon black graft polymers, Examples include molybdenum sulfide and tungsten disulfide.

Among these, preferred lubricants include:
Examples include carbon black, fatty acids with a melting point of -10°C to 50°C, and fatty acid esters with a melting point of 15 to 45°C.

[0092] These may be used alone or in combination of two or more.

The blending ratio of the lubricant is 10% of the magnetic powder.
The amount is usually 20 parts by weight or less, preferably 10 parts by weight or less. 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.

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

[0095] The thickness of the third magnetic layer is usually 0.5 to 0.0.
The thickness is 2 μm, preferably 0.4 to 0.05 μm.

-Nonmagnetic Support- Examples of materials for forming the non-magnetic support on which the three-layered magnetic layer is formed include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polypropylene, etc. polyolefins; cellulose derivatives such as cellulose triacetate and cellulose diacetate; and plastics such as polycarbonates. Further C
Metals such as u, Al, 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 in any form such as tape, sheet, card, disk, drum, etc.
Various materials can be selected and used as needed.

When the support is in the form of a tape or sheet, the thickness is usually 3 to 100 μm, preferably 5 to 5 μm.
It is 0 μm. Moreover, in the case of a disk shape or a card shape, it is usually 30 to 100 μm. Furthermore, in the case of a drum shape, it can be made into a cylindrical shape, etc., depending on the recorder used.

[0099] A back coat layer may be provided on the surface of the nonmagnetic support on which the magnetic layer is not provided (back surface) for the purpose of improving running properties of the magnetic recording medium, preventing electrification, preventing transfer, etc. .

[0100] 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. can.

Next, a method for manufacturing the magnetic recording medium of the present invention will be explained.

-Manufacturing method- The magnetic recording medium of the present invention comprises a first magnetic layer composition, a second magnetic layer composition, and a third magnetic layer composition each containing the magnetic powder, binder resin, etc. After preparing a magnetic coating material by kneading and dispersing it in a solvent, the three types of magnetic coating materials can be 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 (MEK), and methyl isobutyl ketone (MIB).
K) and ketone systems such as cyclohexanone; alcohol systems such as methanol, ethanol, propanol and butanol; Ethers such as ethoxyethanol, tetrahydrofuran, and dioxane; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform,
Halogenated hydrocarbons such as ethylene chlorohydrin and dichlorobenzene can be used.

[0104] When kneading the compositions for the first to third magnetic layers, the magnetic powder and other magnetic coating components (hereinafter referred to as
These are sometimes called raw materials. ) are charged into the kneading 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 obtain a magnetic paint.

[0105] Various kneaders can be used for kneading and dispersing. Examples of this kneading machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a side grinder, a SQEGVARI attritor, a high-speed impeller dispersion machine, a high-speed stone mill, a high-speed impact mill, a disperser kneader, a high-speed mixer, a homogenizer, and an ultrasonic mixer. Examples include a dispersing machine, a pressure kneader, and a continuous kneader.

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

Application methods that can be utilized in the present invention include, for example, gravure roll coating, Meyer bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, squeezing coating, kiss coating, and fan coating. Examples include tin coating.

[0108] After the three types of magnetic paints have been sequentially applied in this manner, a magnetic field orientation treatment is performed as necessary in an undried state, and a surface smoothing treatment is usually performed using a super calender roll or the like.

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

The magnetic recording medium of the present invention can be used 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 disc shape. . Furthermore, like ordinary magnetic recording media, it can also be used in card-like, cylindrical, or other forms.

[0111]

[Examples] The present invention will be explained below with reference to Examples.

[0112] In the examples, parts indicate parts by weight.

(Examples 1 to 6, Comparative Examples 1 to 12) Magnetic composition for upper layer (for third layer) Co-γFe2 O3 (Specific surface area: 55 m2
/g)...100 parts α-Al2O3 (average particle size: .0.1 μm)...4 parts Vinyl chloride-vinyl acetate-maleic anhydride copolymer (1.0% maleic anhydride copolymer) (polymerized)・・・・・・・・・
・・・・・・・・・・・・13 parts Polycarbonate polyurethane (containing sulfobetaine group)

・・・・・・9 parts.

The above composition, 10 parts of methyl ethyl ketone, and 14 parts of toluene were kneaded in advance, and then 44 parts of methyl ethyl ketone, 40 parts of toluene, and 60 parts of cyclohexanone were added and dispersed using a sand mill.

To the obtained dispersion were added 8 parts of trifunctional isocyanate (Coronate L), 45 parts of methyl ethyl ketone, 45 parts of toluene, 40 parts of cyclohexanone, 1 part of stearic acid, and 1 part of butyl stearate and mixed thoroughly. Then, magnetic paint C was obtained through a filter.

Next, the following magnetic coating composition for the intermediate layer (for the second layer), 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. ,
After thorough mixing and dispersion, 7 parts of trifunctional isocyanate (Coronate L) was added, mixed well, and passed through a filter to obtain magnetic paint B.

Magnetic coating composition for intermediate layer (for second layer) Co
-γFe2O3 (specific surface area; 55m2/g)...
...100 parts Vinyl chloride-vinyl acetate-maleic anhydride copolymer (anhydrous as a copolymerization component)
Contains 0.5% maleic acid)
...12 parts Polyurethane (N3022)
・・・・・・・・・・・・・・・11 parts Stearic acid・・・・・・・・・・・・・・・・・・・
...1 part Butyl stearate...
・・・・・・・・・・・・・Part 1.

Next, the following lower layer (first layer) magnetic coating composition, 10 parts of methyl ethyl ketone, and 14 parts of toluene were kneaded in advance, and then 90 parts of methyl ethyl ketone, 86 parts of toluene, and 100 parts of cyclohexanone were added. Add the carbon dispersion so that the ratio of carbon to magnetic powder is as shown in Table 1, mix and disperse thoroughly, add 8 parts of trifunctional isocyanate (Coronate L), and then filter Magnetic paint A (A-1 to A-
5) was obtained.

Magnetic coating composition for lower layer (for first layer) Co-
γFe2 O3 (specific surface area; 30m2/g)...
・100 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH manufactured by UCC)
)・・・・・・・・・・・・・・・8 parts Thermoplastic polyurethane・・・・・・・・・・・・・・・・
・12 parts (Japan Polyurethane N3132)
stearic acid···········
・・・・・・・・・・・・2 parts Butyl alate・
・・・・・・・・・・・・・・・・・・・・・・・・1 part
Carbon dispersion Carbon black・・・・・・・・・・・・・・・
...100 parts Vinyl chloride - Vinyl acetate -
vinyl alcohol copolymer
(VAG manufactured by UCC)
H) ・・・・・・・・・・・・8 parts
Thermoplastic polyurethane ・
・・・・・・・・・12 parts (Japan Polyurethane N3132) Methyl ethyl ketone ・・・・・・・・・
120 parts toluene
・・・・・・・・・120
part cyclohexane
・・・・・・・・・120 copies.

[0120]

[Table 1]

Next, magnetic paint A, magnetic paint B, and magnetic paint C manufactured as described above were coated on a polyester base with a thickness of 13.0 μm using a precision extrusion coater (FEC) after drying. First layer thickness: 0.1μm
, the third layer is 0.2 μm, and the third layer is 0.3 μm.
Simultaneous multilayer coating was performed.

[0122] Subsequently, while the coating film was still wet, it was dried in a solenoid at 2,000 Oe and oriented in a magnetic field.
After calendering, a back coat layer paint D consisting of the following back coat layer composition was applied to the back side of the polyester base film so that the thickness of the dried coating film was 0.6 μm. A sample for the example was obtained by slitting the original fabric into 1/2 inch width.

Composition D for back coat layer Carbon black (particle size, 22 μm)
...80 parts carbon black (
Particle size, 40 μm) ...30 parts Calcium carbonate (particle size, 110 μm) ...10 parts Nitrocellulose
...40 copies
(Cellnova BTH1/2 manufactured by Asahi Kasei Industries, Ltd.)
Polyurethane resin (Nippon Polyurethane Co., Ltd., N3
141 low molecular weight type, molecular weight 50,000, -OH group-containing, urethane main chain contains secondary amine and tertiary amine)
...50 parts Polyisocyanate (Coronate 3041)) 15 parts
cyclohexanone
...275 parts Methyl ethyl ketone ...500
Toluene
...500 copies.

Next, in the magnetic paint C for the upper layer (third layer), 13 parts of the vinyl chloride-vinyl acetate-maleic anhydride copolymer was mixed with a vinyl chloride copolymer (epoxy group, sulfonic acid metal base). A sample was produced in exactly the same manner except that 13 parts (containing) were substituted.

Further, 13 parts of vinyl chloride-vinyl acetate-maleic anhydride copolymer was replaced with 13 parts of vinyl chloride-vinyl acetate copolymer, 9 parts of polycarbonate polyurethane (containing sulfobetaine group) was replaced with polyester polyurethane (terminal O
A sample was prepared in exactly the same manner except that 9 parts (no functional groups other than H group) were used.

[0126]

[Table 2]

[0127]

[Table 3]

Based on this result, the amount of oil supplied to the first magnetic layer was 80
Contains carbon black of cc/100g or more,
It can be seen that the magnetic layer using a binder containing a negative functional group has an excellent balance between electromagnetic conversion characteristics and running durability.

The various characteristics of the magnetic recording medium were evaluated as follows.

(1) RF-output, Lumi-S/N, chroma-output; using a color video noise meter (manufactured by Shibasoku Co., Ltd., "925D/1"),
-S7000'' type deck was used to determine the value (dB) for the reference tape.

[0131] The frequencies of each signal are as follows.

[0132] RF-output: 6MHz Lumi-S/N: 6MHz Chroma S/N: 629KHz Chroma output: 629KHz.

(2) Running durability at room temperature (20°C, 80% RH) and at high temperature (40°C, 80% RH)
RH) A T120 videotape was run for 400 passes in a video deck, and if there was no change in the appearance or image quality of the tape, it was accepted; if the tape was worn out or the image quality clearly deteriorated, it was rejected. .

(3) Reproduction Demagnetization Measure the variation from the initial RF output for each sample after repeatedly running it 20 times in an atmosphere of 40°C and 80% RH on a tape deck HR-S6000 manufactured by Victor Corporation of Japan. did.

(4) Still durability The time required for the playback output of a still image to decrease by 2 dB in a tape deck HR-S6000 manufactured by Victor Company of Japan is expressed in minutes. In addition, in the still durability measurement display column, "120<" means that even after 120 minutes or more, 2
dB output did not occur.

[0136]

Effects of the Invention According to the present invention, by blending carbon black with a specific oil absorption amount in a specific ratio, the dispersibility of the carbon black is good, so surface irregularities of the non-magnetic support are effectively prevented, and the surface of the magnetic layer is improved. It is possible to provide a magnetic recording medium with an appropriate roughness and excellent electromagnetic conversion characteristics.

[0137] Furthermore, since this magnetic recording medium has excellent light-shielding properties, running control can be easily performed, and a magnetic recording medium with excellent running durability can be provided.

Furthermore, by improving the dispersibility of the magnetic powder, a magnetic recording medium with excellent wear resistance can be provided.

Claims (1)

[Claims] 1. A first magnetic layer, a second magnetic layer, and a third magnetic layer are laminated in this order on the surface of a non-magnetic support, and the first magnetic layer contains carbon black having an oil absorption of 80 cc/100 g or more. Magnetic recording characterized in that the content is 0.2 to 20% by weight relative to the magnetic powder in the first magnetic layer, and the binder resin of the third magnetic layer is a resin having a negative functional group. Medium.