JPH03100918A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and durability of a medium by successively forming a first magnetic layer and a second magnetic layer on a nonmagnetic supporting body and incorporating amine-modified vinyl chloride copolymers as a binder into the second magnetic layer. CONSTITUTION:The first magnetic layer and second magnetic layer comprising ferromagnetic powder dispersed in binders are successively formed on the nonmagnetic supporting body to constitute the medium. Amine-modified vinyl chloride copolymers are incorporated as the binder into the second magnetic layer. The binder in the first layer is vinyl chloride copolymer containing at least one of polar groups such as -OH, epoxy group, -COOM, -SO3M, -OSO3M, -PO3M2, -OPO3M2 (wherein M is hydrogen, alkali metal or ammonium). By this method, the obtd. second magnetic layer has high packing property and smoothness, improves the electromagnetic conversion characteristics and gives a tough coating film. Thereby, deterioration of durability due to cracks or plastic change of a magnetic layer caused by sliding of a VTR head, etc., can be prevented.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magnetic recording medium comprising a non-magnetic support and a magnetic layer, and more specifically to a magnetic recording medium having at least two magnetic layers. It is related to.

[Conventional technology]

Magnetic recording media are widely used as recording tapes, video tapes, floppy disks, and the like. A magnetic recording medium basically consists of a magnetic layer in which ferromagnetic powder is dispersed in a binder, which is laminated on a non-magnetic support.

Magnetic recording media are required to have a high level of strength in mechanical properties such as electromagnetic conversion characteristics, running durability, and running performance. That is, audio tapes for music recording and playback are required to have higher original sound playback capabilities. Furthermore, video tapes are required to have excellent electromagnetic conversion characteristics, such as excellent original picture reproduction ability.

It is known that the electromagnetic characteristics of a magnetic recording medium using ferromagnetic powder vary considerably depending on the state of dispersion of the ferromagnetic powder in the magnetic layer. That is, even if a ferromagnetic powder with excellent magnetic properties tV is used for the purpose of improving electromagnetic conversion characteristics, if the dispersion state is poor, the excellent magnetic properties will not be reflected in the improvement of electromagnetic conversion characteristics.

Conventionally, as a method to improve the dispersion state of ferromagnetic powder in the magnetic layer, a method of long-time crosstalk dispersion was used during the production of magnetic paint for preparing the magnetic layer. Since there is a problem that the magnetic properties of ferromagnetic powder deteriorate due to dispersion, recently, polar groups have been added to the resin component forming the binder so that the binder of the magnetic layer has good affinity with the ferromagnetic powder. A method to introduce it has been proposed.

For example, Tokukai Akira! J. Hiroshi Tarr discloses an invention of a magnetic recording medium in which a resin having a specific polar group such as a sulfonic acid metal base is used as a binder for a magnetic layer in an amount of 17 weight or more.

By using a polar group-containing resin as the binder-forming resin component in this manner, a magnetic recording medium having a magnetic layer t in which ferromagnetic powder is well dispersed can be obtained, and the electromagnetic conversion characteristics are improved.

Furthermore, magnetic recording media containing resins having ammonium groups and ammonium bases among polar groups have been disclosed in Japanese Patent Application Laid-open No. 1983-1979 JJ.
/J, Japanese Patent Publication No. 6J-10744!4c.

JP-A Showa tco 2!71a/P-JP-A Showa 4J-73 Hiro 17
, JP-A-47-172710% JP-A-63-λ Kota 4/
It is disclosed in λ.

Resins containing amino groups and ammonium salts not only have good dispersibility of ferromagnetic powders like the sulfonic acid metal bases and other tombstones, but also have good dispersibility of ferromagnetic powder when used in combination with incyanate curing agents. It has the effect of accelerating the curing reaction. Although this improves the abrasion resistance of the surface of the magnetic layer by the VTR head, the entire magnetic layer tends to become hard and brittle. Problems caused by this include a decrease in smoothness due to a decrease in calender formability, resulting in a decrease in electromagnetic conversion properties, and a decrease in adhesive strength with the base, causing cracks in the magnetic layer at the tape edge part during slitting, and from that area. The magnetic layer may fall off and cause dropouts.

As a prior art of multi-layer structure, for example, Japanese Patent Application Laid-open No.
2/ can be given. This means that the Young's modulus in the thickness direction of the first magnetic layer attached on the non-magnetic support is lower than the Young's modulus in the thickness direction of the second magnetic layer attached on the second magnetic layer. Conventionally, in such a multilayer magnetic recording medium, as shown in Example 1, the first magnetic layer and the second magnetic layer use the same binder. Generally, vinyl chloride vinyl acetate/maleic anhydride copolymer is used.Tetravinyl chloride copolymer is a relatively hard binder and has traditionally been used as the main binder, and softer polyurethane resin. It was found that this property greatly affects the properties of the magnetic layer.Binders with carboxyl groups or sulfonic acid groups improve the dispersibility of ferromagnetic powder, but functional If a large number of crystals were present, the film would become hard after 10,000 yen.In other words, if binders containing the same amount of functional groups were used in the first and second magnetic layers, the first and second magnetic layers would become hard. Although the dispersibility of both the two magnetic layers is improved, the film becomes too hard and there is a problem of poor helad touch, especially in the second magnetic layer.

In the present invention, as a result of careful observation and intensive study of Nire et al.'s phenomenon, we have discovered that extremely good electromagnetic conversion characteristics can be obtained by using a binder containing a specific polar group in the second magnetic layer. This led to the present invention.

[Purpose of the invention]

An object of the present invention is to provide a magnetic recording medium, such as an audio tape or a video tape, which has excellent electromagnetic conversion characteristics and improved adhesion to a non-magnetic support.

[Structure of the invention]

That is, the above object of the present invention is to improve the bonding of the second magnetic layer in a magnetic recording medium comprising a first magnetic layer and a second magnetic layer in which ferromagnetic powder is dispersed in a binder on a non-magnetic support. This can be achieved by a magnetic recording medium characterized by containing an amine-modified vinyl chloride copolymer as an agent.

More preferably, the above object of the present invention is such that the binder of the first magnetic layer is -OH, epoxy group, -C00M%-SO5
M, -OSO5M, -PO3M2, OPOsM2 (
This can be achieved by a magnetic recording medium characterized by containing a vinyl chloride copolymer containing at least one polar group of M: hydrogen, alkaline metal, or ammonium.

In other words, the present invention is a magnetic recording medium having two magnetic layers, the second magnetic layer (upper layer) having high dispersibility and filling property (and hardening when used together with an incyanate curing agent). The magnetic recording medium uses a binder having high properties, and more preferably uses a binder in the first magnetic layer (lower layer) that has high adhesion to the support and has high calender formability.

Preferred embodiments of the present invention are as follows.

(2) A magnetic recording medium characterized in that the first magnetic layer and the second magnetic layer are coated simultaneously or sequentially by a multilayer coating method while the first magnetic layer is in a wet state.

(2) The ferromagnetic powder of the first magnetic layer has a specific surface area of ≠5 m 79 or less, a crystallite size λ OA or more, and the ferromagnetic powder of the second magnetic layer has a specific surface area of 30 m 1 jp or more by the BET method; The crystallite size is 4100 A or less, the specific surface area of the ferromagnetic powder of the first magnetic layer measured by the BET method is smaller than the specific surface area of the ferromagnetic powder of the second magnetic layer measured by the BET method, and the difference is greater than 1 m/i. Features of magnetic recording media.

(2) A magnetic recording medium characterized in that the second magnetic layer contains polyurethane and polyincyanate compounds in addition to the amine-modified vinyl chloride copolymer as a binder.

■ The content of amine or ammonium salt in the amine-modified vinyl chloride copolymer is from x10-6 to /X/
o Equivalent amount/,! A magnetic recording medium characterized in that i'(eq/, 9).

(2) A magnetic recording medium characterized in that the amine-modified vinyl chloride copolymer is copolymerized with an alkylcarboxylic acid vinyl ester and/or (methane acrylic ester) in an amount of 0.3 to 30% by weight (wt%). .

■ The amine-modified vinyl chloride copolymer has OH groups and/or epoxy groups f! x10-5eq/9~. 2×
A magnetic recording medium characterized by containing 097 g of lO.

(10H, epoxy group, -COOM, -SO3M, -OSO3M, PO3M2) as a binder for the first magnetic layer.
．． A magnetic recording medium comprising a vinyl chloride copolymer containing at least one polar group of OPO3M2 (M: hydrogen, alkali metal, or ammonium).

(2) The second magnetic layer is formed while the first magnetic layer is still wet, with the first magnetic layer coating liquid containing all the polyisocyanate compounds and the second magnetic layer coating liquid containing no polyisocyanate compound. A magnetic recording medium coated with tfF simultaneously or sequentially in multiple layers.

The magnetic recording medium of the present invention basically has a configuration in which at least two magnetic layers comprising ferromagnetic powder dispersed in a binder are provided on a non-magnetic support.

The amine-modified vinyl chloride copolymer used in the second magnetic layer of the present invention is a copolymer mainly composed of vinyl chloride units and further supported by amine-modified vinyl units, and may also contain other copolymerizable units. can.

Methods for introducing amine-modified vinyl units include a method in which a vinyl chloride copolymer is reacted with an amine compound, and a method in which an amine-modified vinyl monomer is copolymerized with vinyl chloride and other monomers.

Examples of the amine compounds include primary, -2B, and 7th-class amines such as aliphatic amines, alicyclic amines, alkanolamines, and alkoxy7-alkylamines.

In terms of appearance, methylamine, ethylamine, propylamine, butylamine, fluorohexylamine, ethanolamine, naphthylamine, aniline so I' luidine, dimethylamine, diethylamine, dioctylamine, diingthylamine, jetanolamine, methylethanolamine, Dimethylethanolamine, digtylethanolamine, methyljetanolamine, λ
-methoxyethylamine, dicomethoxyethylamine, N-methylaniline, trimethylamine, triethylamine, triinditylamine, tridecylamine,
N-methylethylamine, N-methylphenylamine,
Hexamethylenetetramine.

Examples include triethanolamine, dimethylpropylamine, pyridine, α-picoline, β-picoline, r-picoline, co-lutidine, quinoline, morpholine, diaminopropane, hexamethylenediamine, and the like.

In addition, when directly copolymerizing with vinyl chloride, primary, secondary
Monomers such as acrylic esters, methacrylic esters, or allyl ethers having a primary or tertiary aliphatic amino group, an alicyclic amino group, an alkanol amino group, or a primary ammoecium salt can be used.

The preferred amount of these amino groups or primary ammonium bases is 1xto-zxto-'eq/II (resin), and more preferably JXlo-'-/X10-
“It is eq/9.

If the amount is greater or less than this range, the dispersibility and filling properties will deteriorate.

Other monomers include carboxylic acid vinyl esters such as vinyl acetate, vinyl pionate, vinyl lafricate, vinyl stearate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-ethyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and other alkyl (meth)acrylates and alkyl allyl ethers are preferably copolymerized to improve solvent solubility.The preferred amount i; (7,jwt%~JO
wt*. Exceeding this range is undesirable because the mechanical strength of the entire resin decreases.

In addition, OHM-containing monomers include vinyl alcohol, human mixyalkyl (meth)acrylate, polyalkylene oxide (meth)acrylate, allyl ether of polyalkylene oxide, etc., and epoxy group-containing monomers such as glycidyl (meth)acrylate, allyl glycidyl ether, etc. When a polyisocyanate compound is used as a curing agent, copolymerization results in crosslinking, which improves mechanical strength and is preferable in terms of durability.

These OH groups, 2X10 per tg of epoxy baseline resin
eq-jXlo eq is preferred.

If it exceeds this range, the dispersibility will decrease.

In addition, vinylidene chloride, styrene, Zotadier, acrylonitrile, ethylene, vinyl butyral, vinyl acetal, acrylamide, etc. may be copolymerized.

Furthermore, if a (meth)acryloyl group or the like is added as a radiation-curable functional group, it can be applied to a radiation-curable magnetic layer.

The degree of polymerization of this resin is preferably 200 to 100, more preferably coto-azo. If it exceeds this range, the viscosity of the coating solution will increase and the dispersibility will decrease, and if it is too small, the mechanical strength will decrease, which is not preferable in terms of durability.

This amine-modified vinyl chloride copolymer is known as JP-A-47-/7λJ/J, JP-A-4J-107DAJ#,
JP-A-42-Jj74/ri, JP-A-6J-07j4i!
/7. JP-A-47-77J710, JP-A-47-7JJ
ri≦/J, JP-A-6l-J7jOJj, JP-A-47-2
76701. All the materials described in JP-A-47-J7 Tada λl can be used.

As the binder used in the first magnetic layer of the present invention, vinyl chloride resin is mainly preferred.

What is a vinyl chloride copolymer? It mainly contains vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid,
Acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral vinyl altar, vinyl ether, vinyl sulfonic acid, acrylamide, hydroxyethyl acrylate, glycudyl acrylate, etc. Polymers or polymers having polar groups introduced therein are used. The polar groups are -OR, epoxy group, -COOM, -SO3M.

-OSOaM, -PO3M2, -0P03M2 (M: hydrogen, alkali metal or ammonium).

It is preferable that the amount of these polar groups does not exceed an appropriate amount.

If the amount is too large, the physical properties of the coating film tend to become hard, the adhesion to the base decreases, and the calendar moldability tends to decrease.

This appropriate amount varies depending on the type of polar group. Relatively weak polar -OH&, epoxy group COX10-" 5 eq7g ~s-xio, strong polarity -COOH
For groups 7X10-'eq/p-/x10-'eq/I
, -SO3M, -0SOaM, which have even stronger polarity.

-p Q 3 M 2, -0P03M2 and X10-
'~zxto eq/I is preferred. These vinyl chloride copolymers include JP-A Showa Tough-Lu Cocoa,
JP-A-11-/77124I, JP-A-11-77124I;
Tokukai Akira! Tarzan ozJo, JP-A-Sho tO-231114c
, Japanese Patent Publication No. 4J-/31711? .

All of the materials listed in JP-A-Kokai Shobu Koko or Pico 3 can be used.

As the binder used in combination in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used for both the first magnetic layer and the second magnetic layer.

As a thermoplastic resin, the glass transition temperature is -lo o
−t zo 'C, number average molecular weight force t, o o
o -Joo, ooo, preferably 10.000 #1
0o, ooo, the degree of polymerization is about! It is about 0 to t, ooo.

Examples of such polymers or copolymers include acrylic acid, acrylic esters, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic esters, styrene, butadiene, ethylene, vinyl butyral, vinyl acetals, vinyl ethers, etc. There are polymers, polyurethane resins, and various rubber-based resins.

In addition, thermosetting resins or reactive resins include phenol resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin,
Examples include acrylic reactive resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, mixtures of polyester resins and incyanate prepolymers, mixtures of polyester polyols and polyincyanates, mixtures of polyurethane and polyincyanates, and the like.

These resins are described in detail in the "Plastic Handbook" published by Shokusen Shoten.

It is also possible to use a known electron beam curable resin for the first magnetic layer or the second magnetic layer.

Examples of these and their manufacturing methods are described in Japanese Patent Application Laid-open No.
It is described in detail in J 62 /.

The structure of polyurethane resin is polyester polyurethane,
Known materials such as polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycabrolactone polyurethane can be used.

For all the condensing agents shown in the table, use as necessary to obtain better dispersion and durability.

C00M% SO3M, OSO5M, P=O(OM)2
．． 0-P=0(OM)2, (M is a hydrogen atom,
alkali metal base or ammonium group), OH, NR%
N R (R is hydrocarbon) epoxy group, SH, CN,
At least one polar Xt selected from the following may be introduced by copolymerization or addition reaction. The amount of such polar groups is 10 −10 eq/
l/, and better < is 10 −10 eq/I
It is I.

The binder used in the present invention binds to the ferromagnetic powder in both the first magnetic layer and the second magnetic layer. ~10 weight range,
Preferably it is used in an amount of 10 to 300 to 30% by weight. PVC resin! - 30% by weight, 2 to 20% when using a binder such as a polyurethane resin.
It is preferable to use a combination of polyisocyanates in a range of 2 to 20% by weight.

In the present invention, when polyurethane is used, the glass transition temperature is -IO-100°C and the elongation at break is 1oo-2oo.
The os1 breaking stress is 0.0r-10Kp/cm2, and the yield point is 0,0! -/OKf/cm2 is preferred.

The magnetic recording medium of the present invention consists of two layers. Therefore, the amount of binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate, or other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of polar groups, or the resin mentioned above It is of course possible to change the physical properties of the first magnetic layer and the second magnetic layer as necessary.

Examples of the polyinsyanate used in the present invention include tolylene diisocyanate, $-1-diphenylmethane diincyanate, hexamethylene diincyanate, xylylene diincyanate, naphthylene-7,! - incyanates such as diincyanate, o-toluidine diincyanate, inphorone diincyanate, triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and products produced by condensation of incyanates Polyincyanate and the like can be used. Commercially available product names of these incyanates include Coronate L, =+a)HL, and Coronate λ03 manufactured by Nippon Polyurethane Co., Ltd.
0, Coronate Co031, Millionate MR, Millionate MTL.

Manufactured by Shikinichi Yakuhin Co., Ltd., Takenate D-10, Takenate) I)
-/10N, Takenate D-200, Takeneto) D-10-1 manufactured by Sumitomo Bayer, Desmodule L, Desmodule IL, 7' Sumodyur N.

There are desmodules HL1 and the like, and these can be used alone or in combination of two or more by taking advantage of the difference in curing reactivity as the first magnetic layer and the second magnetic layer.

When the first magnetic layer and the second magnetic layer are coated simultaneously or sequentially while the first magnetic layer is wet, a low-cutting amount polyincyanate compound is applied to either the first magnetic layer paint or the second magnetic layer paint. Even if it is added, a phenomenon of diffusion and mixing between the first magnetic layer and the second magnetic layer may occur immediately after coating.

As a method of actively utilizing C, there is a method in which the polyisocyanate compound is not added to the paint for the second magnetic layer containing the amine-modified vinyl chloride resin, but is added to the paint for the first magnetic layer. Since the amine-modified vinyl chloride resin does not accelerate the curing reaction of incyanate in the coating solution before application, it is possible to extend the pot life, which is preferable.

The ferromagnetic powder used for the first magnetic layer and the second magnetic layer of the present invention is Idr-FeOx (xmt·13~/, ri, Co-modified r-FeOx (xm/).

13-/, j), Fe or Ni or Co@main component (
Known ferromagnetic powders such as ferromagnetic alloy fine powder, barium ferrite, strontium ferrite, etc. can be used. In addition to the specified atoms, these ferromagnetic powders contain AI, 8i, 8°8c, Ti, v, Cr, Cu, Y.
,,Mo,Rh.

pct, Ag, , an%8b, Te, Ba, Ta, W
.

Re, Au, Hg, Pb, Bi, La, Ce, Pr, N
d, P, Co,, Mn%Zn%N ks 8r.

It may contain atoms such as B.

These ferromagnetic powders contain dispersants, lubricants,
It may be treated in advance with a surfactant, an antistatic agent, etc. before dispersion.

Among the above ferromagnetic powders, the ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. A ferromagnetic alloy fine powder obtained by a known manufacturing method can be used, and the following method can be used.

A method of reducing complex organic acid salts (mainly oxalates) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe-Co particles, and a method of reducing metal carbonyl compounds with a reducing gas such as hydrogen. A method of thermal decomposition, a method of reducing an aqueous solution of a ferromagnetic metal by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine,
This method involves evaporating a metal in an inert gas at low pressure to obtain a fine powder. The ferromagnetic alloy powder obtained in this way is subjected to a known gradual oxidation treatment, that is, immersed in an organic solvent and then dried. A method to reduce the partial pressure t of alkaline gas and inert gas without using organic solvents
Any method of forming a sensitized skin on the surface can be used.

In addition, the ferromagnetic powder used in the present invention has fewer pores -9
Preferably, the value is 20 or less, more preferably! Capacity - less than or equal to.

The ferromagnetic powder used in the present invention can be manufactured according to a known method. As for the shape, it may be acicular, granular, rice grain, or plate-like as long as it satisfies the characteristics regarding the particle size shown above. The ferromagnetic powder of the first magnetic layer has a specific surface area of arm2/9 or less, a crystallite size of 2yθA or more, and the BET of the ferromagnetic powder of the second magnetic layer is
It is preferable that the specific surface area JOm by the ET method be 279 or more and the crystallite size≠0sλ or less. Also, the difference in specific surface area is 7m279
It is preferable that there be more than one.

As the carbon black used in the present invention, furnace black for rubber, thermal black for rubber, black for color, acetylene black, etc. can be used.

Ratio ii1iMHt-j00m2/1. DBP oil absorption is 10-170081/100ji, particle size is t m #
``'3oomμ, pH is Col 10. Moisture content is Q, /~
70%, tap density is 0. /-/9/QC, is preferred.

A physical example of carbon black used in the present invention is BLACKPBARL8 20 manufactured by Cabot Corporation.
00,1300% / 000% 900, too, t
oo%VULCkNXC-74, manufactured by Asahi Carbon Co., Ltd., #t
o, #to, #t! , #! Q.

#3! , manufactured by Mitsubishi Chemical Industries, #2 HiroooB, +2300
, #ri00. #/ 000. #30, #Hiro01 #10
B, manufactured by Conlonbia Carboa, C0NDUCTEX
Examples include SC%RAVEN tro, to, 170, /j, etc. Carbon black may be surface-treated with a dispersant, grafted with a resin, or a portion of the surface may be graphitized. Further, carbon black may be dispersed in advance with a binder before being added to the magnetic paint.

Curl/Black prevents static electricity on the magnetic layer, reduces the coefficient of friction,
It has functions such as imparting light-shielding properties and improving film strength.These properties vary depending on the carbon black used. Therefore, the type, amount, and combination of these carbon blacks used in the present invention are changed in the first magnetic layer and the second magnetic layer, and the particle size,
Oil absorption, electrical conductivity.

Of course, it is possible to use them properly depending on the purpose based on the above-mentioned characteristics such as pn. For example, charging can be prevented by using carbon black with high conductivity in the first magnetic layer, and carbon black with a large particle size can be used in the second magnetic layer to lower the coefficient of friction.

For carbon black that can be used in the present invention, for example, "Carbon Black Handbook" edited by Carbon Black Association can be referred to.

The average particle diameter of the carbon black contained in the first magnetic layer is less than 20 mμ, and is /-20% per 100 parts by weight of ferromagnetic powder.
! It is preferable that the second magnetic layer contains carbon grains in an amount of 0.00 parts by weight based on 100 parts by weight of ferromagnetic powder when the average particle size of the carbon grains contained in the second magnetic layer is uO-rOmμ. It is preferable to include /-70 parts by weight.

The abrasives used in the present invention include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, and titanium silicon carbide. Carbide, titanium oxide, silicon dioxide, boron nitride, and other known materials having a Mohs hardness or higher are used singly or in combination. Further, a composite of these abrasives (an abrasive whose surface is treated with another abrasive) may be used. These abrasives Ilc may contain compounds or elements other than the main component, but as long as the main component is 20% or more, the effect remains the same. The particle size of these abrasives is 0.0/~λμ
However, if necessary, abrasives with different particle sizes may be combined, or a single abrasive may be used with a wide particle size distribution to provide the same effect. Tap density is 0
．． 3~λ1//cc, moisture content Bo, 1-re), pHa
J ~//.

The specific surface area is preferably 1 to zom, #.

The shape of the abrasive used in the present invention may be needle-like, spherical, or dice-like, but it is preferable to have a part of the shape with a corner because of its high abrasiveness.

Examples of the abrasive medium used in the present invention include AKP-20, AKP-io, AKP-to, manufactured by Sumitomo Chemical Co., Ltd.
, HIT-to, manufactured by Nihon Kagaku Kogyo Co., Ltd., G Yu, C7, S
-/% Toda Kogyosha! J4,100ED.

lμICED, etc.

Of course, the type, amount, and combination of the polishing agent used in the present invention can be changed between the first magnetic layer and the second magnetic layer, and can be used depending on the purpose. For example, to improve the durability of the magnetic layer surface, increase the amount of abrasive in the second magnetic layer, and to improve the durability of the end face of the magnetic layer, increase the amount of abrasive in the first magnetic layer. be able to. It is also preferable that the first magnetic layer contains an abrasive IKt with a Mohs hardness of less than 7, and the second magnetic layer contains an abrasive with a Mohs hardness of 7 or more.

These abrasives may be dispersed in advance with a binder and then added to the magnetic paint.

The number of abrasives present on the surface of the magnetic layer and the end face of the magnetic layer of the magnetic recording medium of the present invention is preferably t pieces/100 μm or more.

The additive used in the present invention has a lubricating effect.

Those having antistatic effect, dispersion effect, plasticizing effect, etc. are used. molybdenum dioxide, disulfide/gesten,
Graphite, boron nitride, graphite heptafluoride, silicone oil, silicone modified with polar group T-fatty acid, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyoleain, polyglycol,
Alkyl phosphates and alkali metal salts thereof, alkyl sulfate esters and alkali metal salts thereof, poly7enyl ether, fluorine-containing alkyl sulfate esters and alkali metal salts thereof, monobasic fatty acids with carbon numbers 1O to J4C, unsaturated bonds. may contain or be branched), and these metal salts (Li, Na,
Cu, etc.) or monovalent, divalent, trivalent, tetravalent, trivalent, hexavalent alcohol with a carbon number of 12 to 2λ (which may contain unsaturated bonds or be branched), carbon number l co~
Co2 alkoxy alcohol, carbon X number tO ~ 241 (D
- Monovalent fatty acid (which may contain unsaturated bonds or be branched) and monovalent, divalent, trivalent, tetravalent, trivalent, or hexavalent alcohol with a carbon number of ~lλ monofatty acid ester, difatty acid ester or trifatty acid ester consisting of one fatty acid ester (which may contain unsaturated bonds or be branched), fatty acid ester of monoalkyl ether of alkylene oxide polymer, carbon number t- J
A fatty acid amide having a carbon number of t-JJ, etc. can be used. Specific examples of these include lafric acid,
Myristic acid, /cermitic acid, stearic acid, behenic acid, zotyl stearate, oleic acid, linoleic acid, lylunic acid, elaidic acid, octyl stearate, amyl stearate, inoctyl stearate, octyl myristate, gutoxyethyl stearate, Examples include anhydrone rubitan monostearate, anhydrone rubitan distearate, anhydrone rubitan tristearate, oleyl alcohol, and alcohol.

In addition, nonionic surfactants such as alkylene oxide type, glycerin type, glycidol type, alkylphenol ethylene oxide adduct 1, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives,
Cationic surfactants such as heterocycles, phosphoniums or sulfoniums, anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfate ester crystals, phosphate groups, amino acids, amino sulfones Acids, amino alcohol sulfur #! Alternatively, amphoteric surfactants such as phosphoric acid esters, alkyl betaine type, etc. can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.).

These lubricants, antistatic agents, etc. are not necessarily i.

It is not 0% pure and may contain impurities such as isomers, unreacted products, side reaction products, decomposed products, and oxide 1 in addition to the main components. The content of these impurities is preferably 30% or less, more preferably 10% or less.

The types and amounts of these lubricants and surfactants used in the present invention can be selectively used in the first magnetic layer and the second magnetic layer as required. For example, fatty acids with different melting points are used in the first and second magnetic layers to control oozing to the surface, esters with different boiling points and polarities are used to control oozing to the surface, and the amount of surfactant is controlled. It is possible to improve the stability of the coating by adjusting the lubricant, or to improve the lubricating effect by increasing the amount of lubricant relative to the magnetic material in the first magnetic layer.Thermal theory is not limited to the examples shown here. .

Furthermore, all or part of the additives used in the present invention may be added at any step in the production of the magnetic coating material. For example, when it is mixed with ferromagnetic powder before the mixing process, when it is added during the kneading process of ferromagnetic powder, binder, and solvent, when it is added during the dispersion process, when it is added after dispersion, and when it is added just before coating. and so on.

Commercial examples of these lubricants used in the present invention include NAA-10, NAA-4t/j%NA manufactured by Nihon Yushi Co., Ltd.
A-j/2,NAA-/40%NAA-/If O,
NAA-/74A, NAA-/7j, NAA-
ko2λ, NAA-jj, NAA-31, NAA-/7
/, NAA-/Coco, NAA-/Hiroko, NAA-/ 4
01NAA-/77, castor hydrogenated fatty acid, NAA-
≠2, NAA-tap, cation SA, cation MA,
Cation AB, Cation BB, Naimeen L-207,
Naimeen L-JQJ, Naimeen 5-2o, Nonion E-2Or, /2A-7P-201, /Nio7B-2
07゜nonion 1λop, nonion NS-202, nonion NS-,2/(7, nonion yH8-2θg, nonion L-co, nonion S-2, nonion S-Hiroshi, nonion O-2, nonion LP-λQR , nonionic PP−≠O
R, nonion 5P-6OR, nonion yOP-raR, i
=OyOP-rzFt, Nonion 1. 'l'-22/
, Nonion 8T-2 col, Nonion 0T-2J/, Monoguri MB, Nonio yD8-to, Anon BF, Anon L
G, butyl stearate, butyl diurate, erucic acid, manufactured by Kanto Kagaku Co., Ltd., oleic acid, manufactured by Monomoto Yushi Co., Ltd., FAL-
KoQ! , FAL-/λ3, manufactured by Shin Nippon Rika Co., Ltd., NGL LO, NGL IPM, Sunnsizer E4to
io, manufactured by Shin-Etsu Chemical Co., Ltd., TA-3, KF-26, KF-tatL, KFri 4H% KF4t10. KF≠KO%KF
rijj, KFj≠, '0. KFj4, KFri07
, KFlr 11% X-JJ-rIP, X-22-
4JJ, KFYOI%KF700%KFIPI, KF-
rz7, KF-140%KF-t6! , X-ko J-tat
o%KF-10t%KF-10J, KF-10J, X-
Coco-J710゜X-JJ-J 7/, t, KF-
tto, KF-3PI3, Run-on Armor Co., Ltd., Armide P, Armide C1 Armoslip CP
, manufactured by Lion Oil Co., Ltd., Duo-on TDO 1 manufactured by Nisshin Oil Co., Ltd., BA-Sen IG, manufactured by Sanyo Chemical Co., Ltd., Pro 7 Anco 0/Co E
, Nieuport PE4/, Ione 7) MS-1700° Ionet MO-, zoo, Ionet DL-λQQ,
Ionetsu) DS-700, Ionetsu DB-1000,
Examples include Ionet DO-200.

Note that the amount of lubricant contained in the second magnetic layer is preferably greater than the amount of lubricant contained in the first magnetic layer.

The organic solvent used in the present invention is acetate/,
Methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone.

Ketones such as inphoron, tetrahytomifuran, alcohols such as methanol, ethanol, propatool, butanol, inbutyl alcohol, inpropyl alcohol, methylcyclohexanol, methyl acetate,
Aromas such as esters such as butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol dimethyl ether, glycol sonoethyl ether, dioxane, sodium glycol ethers, benzene, toluene, xylene, cresol, chlorobenzene, etc. group hydrocarbons, chlorinated hydrocarbons such as ethylene chloride, ethylene chloride, carbon tetrachloride, rhioform, ethylene chlorohydrin, bichlorobenzene, N
, N-dimethylformamide, hexane, etc. can be used.

These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, side reactants, decomposed products, oxides, and moisture in addition to the main components. The content of these impurities is preferably 30% or less, more preferably 10%.
It is as follows.

The type and amount of the organic solvent used in the present invention may be changed between the first magnetic layer and the second magnetic layer, if necessary. Improve the surface properties by using a highly volatile solvent in the first magnetic layer, improve coating stability by using a solvent with high surface tension (cyclohexanone, dioxane, etc.) in the first magnetic layer, and improve the solubility of the second magnetic layer. An example of this is increasing the degree of filling by using a solvent with a high oxidation meter, but it is a matter of opinion that it is not limited to these examples.

The thickness structure of the magnetic recording medium of the present invention is such that the non-magnetic support is /-
100μ, preferably t-coOμ, first magnetic layer force 1.0
-1011, preferably /, 0-j-μ, and the second magnetic layer has a thickness of 2.0 μ' or less, preferably 3 μ or less, more preferably /, J-μ or less.

The thickness of the magnetic layer used is in the range of 17,100 to 2 times the thickness of the nonmagnetic support. Additionally, an undercoat layer is provided between the non-magnetic support and the first magnetic layer to improve adhesion.

Alternatively, an intermediate layer such as a layer containing carbon black for antistatic purpose may be provided. The thickness of these is 0.0
/-Jμ, preferably o, or ~o.

! μ. Furthermore, a puncture coat layer may be provided on the side of the nonmagnetic support opposite to the magnetic layer side. This thickness is 0.
1-Jμ, preferably 0.3-1.

It is Oμ. Known intermediate layers and bank coat layers can be used.

The non-magnetic supports used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate,
Known films such as polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, etc. can be used. These supports may be subjected to corona discharge treatment, plasma treatment, adhesion treatment, heat treatment, dust removal treatment, etc. in advance. To achieve the objectives of the invention,
The center line average surface roughness (Ra) of the nonmagnetic support is o,
oittm or less, preferably o.

It is necessary to use a material of 0.0/μm or less, more preferably 0.0/μm or less. The cutoff value is O.

This is Kojmm. Furthermore, it is preferable that these nonmagnetic supports not only have a small center fiber average surface roughness, but also have no coarse protrusions of 1 μm or more. The roughness and shape of the surface can be freely controlled by adjusting the size and amount of filler added to the support, if necessary. Examples of these fillers include oxides and legates such as tICa and Si%Ti, as well as organic fine powders such as acrylic powders. The F-1 value of the nonmagnetic support used in the present invention in the tape running direction is preferably! ~jOKf)7mm
, the F-j value in the Arp width direction is preferably 3~j O
KP/mm”, and F- in the long direction of the tape
! Generally, the F-j value is higher than the Fj value in the tape width direction, but this is not a problem especially when it is necessary to increase the strength in the width direction.

Also, t in the tape running direction and width direction of the nonmagnetic support
The heat shrinkage rate in the oo'cio minute is preferably 3% or less, more preferably Bt, z% or less, and the heat shrinkage rate in the roocso minute is preferably 7% or less, and even more preferably 0.2s.
It is as follows. The breaking strength is j”/00 in both directions.
Kf/mm2, elastic modulus f110o Nko000Kg
7 mm" is preferable.

The process of manufacturing the magnetic paint for the magnetic recording medium of the present invention consists of at least a crosstalk process, a dispersion process, and a mixing process provided before and after these processes as necessary. Each individual process may be divided into one or more stages.

All raw materials used in the present invention, such as the ferromagnetic material, binder, carbon black, abrasive, antistatic agent, lubricant, and solvent, may be added at the beginning or during any step.

In addition, individual raw materials may be added in portions in λ or more steps. For example, polyurethane may be added in portions in the mixing step, the dispersion step, and the mixing step for adjusting the viscosity after dispersion.

In order to achieve the purpose of the present invention, it is of course possible to use conventional known manufacturing techniques for some of the processes, but in the mixing process, a device with strong kneading power such as a continuous kneader or a pressure kneader is used. It is preferable to use

When using a continuous kneader or pressure kneader, all or part of the ferromagnetic powder and binder (however, 3 of the total binder
(preferably 0% or more) and crosstalk treatment in a range of 75 to 200 parts by weight per 100 parts by weight of ferromagnetic powder. For details on these crosstalk processes, please refer to Japanese Patent Application Laid-Open No. 706331.
, JP-A No. 6≠-72 Core≠. The thickness of the second magnetic layer of the magnetic recording medium of the present invention is 2.0 μm or less, but in order to achieve such a full thickness, a conventional first magnetic layer is coated, and after drying, a second magnetic layer is applied. The sequential multilayer method in which layers are formed on top of each other causes coating defects and is difficult to produce in practice.In the present invention, simultaneous or sequential wetting (wet-on-wet) as shown in Japanese Patent Application Laid-open No. 1983-12-λl Kota 33 is used. ) Only by using a multilayer coating method can the thickness of the second magnetic layer of the present invention be 2.0 μm or less be obtained.

(Effects of the invention) As shown above, the water volume BA is small (both are magnetic recording media having two magnetic layers, and the second magnetic layer (upper layer) has high dispersibility, high filling properties, and When a cyanate curing agent is used in combination, a binder with high curability is arranged, and more preferably the first magnetic layer (lower layer) has a high adhesiveness with the support.
A binder with high calenderability is arranged.

For this reason, the second magnetic layer has high filling properties and smoothness, improves electromagnetic conversion characteristics, and provides a strong coating film, making it suitable for VTRs.
It is possible to prevent a decrease in durability due to changes in the magnetic layer due to abrasion of the magnetic layer due to the sliding of the head or the like. In addition, when all of the incyanate curing agents are used together in the second magnetic layer, the amine group and ammonium base of the binder of the present invention have the effect of accelerating the curing reaction of incyanate, so that the mechanical strength of the second magnetic layer is further improved. and durability can be further improved.

Unlike the second magnetic layer, the binder used for the first magnetic layer has high dispersibility, but the coating film is a relatively soft and acoustic binder, so it has high adhesion to the base and does not adhere to the tape edge during slitting. It is possible to prevent problems such as cracks occurring and the magnetic layer falling off in that area, causing dropouts. Furthermore, having soft physical properties of the coating film is also advantageous for calendar moldability. Even if it is calendered through the second magnetic Mit, this effect is achieved and the smoothness is improved.

The above-mentioned effects cannot be obtained by a single magnetic layer type magnetic recording medium, but are first realized by the arrangement of the binder in the first and second magnetic layers of the present invention.

(Examples) Next, the present invention will be explained in more detail by showing Examples and Comparative Examples. In each side, "parts" means "parts by weight" unless otherwise specified.

A magnetic coating liquid was prepared using the following recipe.

First magnetic layer coating liquid Cor-Fe203 100 parts (He:
6 r00e% Specific surface area by BET method: 30m2/p
, tap density o, r) vinyl chloride copolymer
Part ii (Details are as shown in Tables 1 and 2) Polyester polyurethane resin 6 parts (Lisbon 720 manufactured by Dainippon Ink & Chemicals) Coronate L 3 parts Carbon black Average particle size/rmμ 70 parts α-Fe20a Average particle size 0.1fi 10 parts butyl stearate 1 part stearic acid
7 parts glyph acetate
Koo part cyclohexanone
JO part second magnetic layer coating liquid Cor Fe2O3 100 parts (Hc: 7000e, specific surface area 2 m/, li' by BET method) Vinyl chloride copolymer 17 parts (Details are shown in Table 1 and 2 As shown in the table) Polyester polyurethane resin r part (carboxyl group-containing Sanyo Kasei Tl-3021) Coronae) L 3 parts Carbon black Average particle diameter r Omμ 5 parts α-Fe20a Average particle diameter 0.3μ Part Butyl stearate i, s Part stearic acid
Tripartite butyl acetate
JOO part methyl ethyl keto 7 40
For each of the above two paints, each component was kneaded using an open kneader manufactured by Kurade Seisakusho, and then dispersed using a sand glider. 4 parts of polyincyanate and 0 parts of butyl acetate were added to the obtained dispersion,
filtered using a filter with an average pore size of lμ, -
Coating liquids for forming the first magnetic layer and for forming the second magnetic layer were respectively prepared.

The obtained paint for the first magnetic layer was applied to the surface of the support while running at a speed of 7 minutes so that the thickness after drying was 3.0 parts m. It was applied using a reverse roll. Thereafter, the paint for the second magnetic layer is applied using a reverse roll so that the thickness after drying is /0 μm, and while the magnetic layer is still wet, it is oriented using the magnet, and after drying, it is -Calendered and slit to //J inch width to produce videotape.

[Videotape evaluation]

Regarding the videotapes obtained in the above examples.

Its properties were measured by the method described above. The result is the first
Shown in the table.

Measurement method 1) Magnetic layer Ra Optical interference three-dimensional roughness meter (UaA WYKO TOP
OJD) and the method described in Tokkenpei/-/216rit.

2) The 87N ratio of the luminance signal of the videotape was measured using a Y-8/N ratio noise meter (manufactured by Shiba Soku, FZJR).

The values listed in Table 1 are relative values when the 8/N ratio of the videotape luminance signal of sample t is set to t-0 dB. For the measurement, a high-speed filter/0kHz filter and a low-pass filter 10kHz were used. Note that the video tape recorder used for the measurements is a commercially available product.

3) C-87N ratio Using the same equipment as the Y-87N, the S/N ratio of the chroma signal of the videotape was measured.

The values are shown as relative values when taken as sample rfOdB.

4) Adhesion The adhesion between the magnetic layer and the support was investigated using an iT peel test.

Table 1 shows the force (weight) required for peeling.

Table 2 Vinyl chloride... Vinyl chloride Vinyl acetate... Vinyl acetate As is clear from the results in Table 1, the specific functionalities of the present invention x
It can be seen that when the vinyl chloride copolymer having i- is used for the second magnetic layer, the Y-S/N, C-S/N, and adhesive strength of the multilayer are significantly improved.

Even though the magnetic layers are multilayered, the samples using vinyl chloride, vinyl acetate, and maleic anhydride for the first and second magnetic layers do not have the characteristics of Y, 8/N, and C-8/N. However, the adhesion strength of sample 7, which used an amine-modified vinyl chloride copolymer and a vinyl chloride copolymer containing SO3 and Evoki groups in the single magnetic layer, was relatively high. There was a problem in that Y, 8/N, and C/S/N were significantly degraded.

Claims (2)

[Claims] (1) In a magnetic recording medium in which a first magnetic layer and a second magnetic layer in which ferromagnetic powder is dispersed in a binder are provided in this order on a nonmagnetic support, amine is used as the binder in the second magnetic layer. A magnetic recording medium characterized by containing a modified vinyl chloride copolymer. (2) As a binder for the first magnetic layer, -OH, epoxy group, -COOM, -SO_3M, -OSO_3M, -P
The magnetic recording medium according to claim 1, characterized in that it contains a vinyl chloride copolymer containing at least one polar group of O_3M_2, -OPO_3M_2 (M: hydrogen, alkali metal, or ammonium).