JPH02199619A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To increase dispersion stability of magnetic powder and adsorption to a binder and to obtain excellent electromagnetic conversion characteristics and traveling durability by incorporating iron nitride magnetic powder and polyurethane having negative functional groups as inner salt into the magnetic layer. CONSTITUTION:Iron nitride powder is used for the magnetic powder of the magnetic layer, by which the intrinsic properties of nitride such as good Hc distribution, high Br, high sigmas and high hardness can sufficiently be utilized. As for the binder of the magnetic layer, polyurethane resin having negative functional groups as inner salt is used. Even when the iron nitride is made into fine particles, the dispersibility thereof is enough to give the advantages of nitride to the medium. Since the polyurethane has high adsorption strength to iron nitride or iron alloy nitride and superior holding effect, the dispersion stability of the magnetic layer is improved, wherein the magnetic powder is homogeneously incorporated at a high density.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

BACKGROUND OF THE INVENTION Generally, magnetic recording media such as magnetic tapes are manufactured by applying a magnetic paint made of magnetic powder, binder resin, etc. onto a support and drying it.

In these magnetic recording media, especially video tapes,
Conventionally, I Fe2O2, CorFe20. etc. have been commonly used as magnetic powders. And recently, higher S
/N, their particle diameters have become even smaller. In addition, metal magnetic powder has also come to be used in pursuit of higher density recording.

In addition, magnetic powder made of iron nitride (iron nitride) is described in "Technical Report of the Institute of Electronics and Communication Engineers J Vol.
For example, FeaN magnetic powder has a large audio output and is superior in stability, hardness, and Hc distribution compared to metal magnetic powder. Co-coated TFe has a larger σS (larger output) than O.

As described above, iron nitride is worthy of attention as a magnetic powder for magnetic recording media, but it has difficulty dispersing in the magnetic layer and has not always been able to demonstrate its features. Dispersion using a vinyl chloride resin or polyurethane having a polar group such as a sulfonic acid group may be considered, but it has been difficult to achieve both high electrical properties, dispersibility, and running durability associated with highly fine magnetic powder particles.

The object of the present invention is to provide iron nitride or iron alloy nitride with high adsorption power and dispersion stability to a binder, excellent electromagnetic conversion characteristics, running durability, and good light shielding properties. To provide magnetic recording media.

20 Structure of the invention and its effects The present invention is characterized in that a magnetic layer contains iron nitride magnetic powder and/or iron alloy nitride magnetic powder and polyurethane in which a negative functional group forms an inner salt in the molecule. This relates to magnetic recording media.

First, "polyurethane in which the negative group forms an inner salt" will be described.

First, the manufacturing method will be described.

Similar to the usual polyurethane synthesis method, it is synthesized by reacting a high molecular weight polyol (molecular weight 500 to 3000) such as a polycarbonate polyol, polyester polyol, polylactone polyol, or polyether polyol with a polyfunctional aromatic or aliphatic isocyanate. As a result, polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate are synthesized.

These polyurethanes are primarily produced by the reaction of polyisocyanates with polyols and optionally other copolymers, and may also be in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups; The isocyanate component may be of various diisocyanate compounds, such as hexamethylene diisocyanate (HMDI), diphenylmethane diisocyanate (
MDI), hydrogenated MDI (H, □MD toluene diisocyanate (TDI), 1,5 naphthalene diisocyanate (NDI), tolidine diisocyanate) (TOD
I), lysine diisocyanate methyl ester (LD), isophorone diisocyanate (IPDI), etc. can be used.

Also, if necessary, 1,4-butanediol, ■.

Using low-molecular polyfunctional alcohols such as 6-hexanediol and 1,3-butanediol, the molecular weight (2) and resin physical properties can be adjusted.

The functional group forming the inner salt may be introduced into the isocyanate component, but it can also be introduced into the polyol component, and further into the above-mentioned low-molecular polyfunctional alcohol.

Polyester polyols in which the negative functional groups form an inner salt contain various dicarboxylic acid components, polyhydric alcohol components, and dicarboxylic acid components and/or negative functional groups in which the negative functional groups form an inner salt. It can be synthesized by polycondensing polyhydric alcohol components forming an inner salt.

Examples of dicarboxylic acid components include terephthalic acid, isophthalic acid, sebacic acid, adipic acid, trimerized lyluic acid, and maleic acid. As a polyhydric alcohol component,
Glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or polyhydric alcohols such as trimethylolpropane, hexanetriol, glycerin, trimethylolpropane, trimethylolethane, and pentaerythritol, or these glycols and polyhydric alcohols Two or more arbitrary types selected from these can be exemplified.

Polycarbonate polyols in which the negative functional group forms an inner salt are generally synthesized by a transesterification method between a polyhydric alcohol and a dialkyl carbonate or diallyl carbonate, or can be obtained by condensation of a polyhydric alcohol and phosgene. can.

When producing the above polyester polyol and polycarbonate polyol (including polycarbonate polyester polyol), the following aromatic polyhydric alcohols can be used. Moreover, when reacting the above-mentioned polyester polyol or polycarbonate polyol with polyisocyanate, the following aromatic polyhydric alcohol can be used.

Aromatic polyhydric alcohol: (n-12) [R is -(CI z-1-CH(CHi)-CFl
Indicates z-CHz-.

X is -so, -, -co-1-C(CH3)z-1-
C(CHs)z−CJ<−C(C)lzb−. ]
Ho-(cL), %+CHz) -OR [n represents 1 or 2. ] HO (CHz) -0+0 (CHg) 11OH [n represents 1 or 2. ] HO (CHz) - ◎ Σ (CH,), OH [n indicates 1 or 2. ] Ha<cHt>fiO<positive eo (CHz) fiO
H [n represents 1 or 2. ] [R represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R' represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, or an aryl group. ] [n represents an integer of 1-10. ] In the polyurethane having these aromatic polyhydric alcohol components in the main chain, the content of these components is preferably 5a+of% or more of the entire polyhydric alcohol component.

In order to produce a lactone polyester polyol in which the negative functional group forms an inner salt, S-caprolactam, α-methyl-1-caprolactam, S-methyl-8
- The above functional group may be introduced into lactams such as caprolactam and γ-butyrolactam.

In order to produce a polyether polyol in which a negative functional group forms an inner salt, the above functional group may be introduced into ethylene oxide, propylene oxide, butylene oxide, or the like.

As the functional group forming the inner salt, a betaine group mentioned below can be exemplified.

A polyester polyol in which the negative functional group forms an inner salt will be further described.

- A simple method for synthesizing polyester is carried out by a condensation reaction between an acid component having an aliphatic or aromatic polyfunctional acid or a derivative thereof and an aliphatic or aromatic polyfunctional alcohol component. Intramolecular amphoteric base of the present invention (betaine group, etc.)
may be contained in either the acid component or the alcohol component, or a method of introducing a betaine group or the like into the polymer as a polymer reaction may be used. However, in consideration of unreacted components and the introduction rate, it is easier to control if the polymer monomer has the functional group.

Examples of the betaine group include a sulfobetaine group, a phosphobetaine group, and a carboxybetaine group. The general formula of these betaine type functional groups is expressed as follows.

Na 1+: Contained in the urethane chain.

x knee so, e-o-so, e)-coo○OP O3
HOP Oxe -〇PO□H2 A: Hydrogen or an alkyl group having 1 to 60 carbon atoms (eg, methyl group, ethyl group, etc.).

m: an integer from 1 to 10.

vinegar B: -Coo or C0NH.

R: an alkyl group, alkenyl group, or aryl group having 1 to 12 carbon atoms.

n, m: integer from l to IO.

Examples of usable betaine group-containing monomers include the compounds listed below, but it goes without saying that the polyurethane resin used in the present invention is not limited to those using these monomers.

The monomer in which the negative functional group forms an inner salt is available as a commercially available drug, but it can be easily obtained by the method described below.

1) Synthesis method using monochloroacetic acid RN (CHz C00H)z +CI CHt
C0OHR = alkyl group such as methyl, ethyl, etc. 2) Synthesis method using monochlorosuccinic acid CH, -CO
OH 3) Synthesis method using propane sultone CHt -CO
A compound having an OH group, etc. is synthesized, and this is reacted in equimolar amounts with a polyfunctional isocyanate such as diisocyanate to obtain a reaction product of NCO5, one of the diisocyanates, and the hydroxyl group in the above compound. Then, by reacting the OH groups of the polyurethane with unreacted NCO5, a polyurethane into which betaine groups and the like have been introduced can be obtained.

Examples of the above-mentioned compounds having a hydroxyl group and a betaine group include, but are not limited to, the following compounds.

Furthermore, as a polymer reaction, a reaction for introducing betaine groups and the like into a polymer will be described. In this method, a compound having a betaine group or the like is reacted with an OH group present at the end or side chain of a polyurethane whose chain has been extended to a predetermined molecular weight by a polymerization reaction. In this case, first, hydroxyl groups and betaine The amount of betaine groups etc. introduced into the polyurethane resin of the present invention is 0.01 to 1. It is preferably Ommol/g, more preferably 0.1-0.5ra
It is in the range of tsa l/g. If the amount of the polar group introduced is less than 0.01 ++ vol/g, it will be difficult to see a sufficient effect on the dispersibility of the ferromagnetic powder. Also, if the amount of the polar group introduced is 1, Ommo jl! If it exceeds /g, intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility, but also causes selectivity to the solvent, which may make it impossible to use ordinary general-purpose solvents.

Further, the number average molecular weight of the polyurethane resin according to the present invention is 5
000-100000, more preferably 10000-5
Preferably, it is in the range of 0000. If the number average molecular weight is less than 5,000, the coating film-forming ability of the resin is likely to be insufficient, and if the number average molecular weight exceeds 100,000, problems may occur in paint manufacturing processes such as mixing, transport, and coating. There is.

Synthesis Example (a) 1 mole of N-methyljetanolamine and 1 mole of propanesultone were reacted at a temperature of 120''C for 3 hours to obtain a sulfobetaine type polyfunctional monomer.

Next, 1.5 moles of adipic acid, 1.7 moles of 1,4-butanediol, and 0.06 moles of the above sulfobetaine type acid-base polyfunctional monomer were charged, and the mixture was heated at 150 to 200°C for about 30 minutes.
The temperature was raised over time, and the reaction was further carried out at 200°C for 4 hours.
Unreacted raw materials were removed at ~5 mmHg, and the reaction continued until the acid value reached 2 or less. The molecular weight of the obtained copolymerized polyester is Mw
It was 2500. 165 g of copolymerized polyester was dissolved in 300 parts of methyl ethyl ketone, 80 parts of diphenylmethane diisocyanate was added, and the mixture was reacted for 2 hours at 80°C. 20 parts of 1.4-butanediol was added and the mixture was further reacted for 2 hours. -4 parts of butanediol were added and reacted for 1 hour. The molecular weight of the obtained polyurethane is Mw=3
．． 50,000, and M n =22,000.

Next, "iron nitride magnetic powder J" and "iron alloy nitride magnetic powder" will be described.

This is synthesized by a nitriding reaction of powder of iron or an iron alloy (iron-based alloy diferon-nickel, iron-cobalt, etc.).

Specifically, for example, iron or iron alloy powder is converted into NH.

+Nitriding in a H2 stream at temperatures around 300°C to 500'C. Iron nitride mainly composed of 1-Fe and N can be produced from iron powder.

Iron nitride or iron alloy nitride can also be surface oxidized in the air or in an oxygen atmosphere at room temperature to about 50°C for several hours to more than ten hours. This gradual oxidation causes iron oxide Fe0x (4/3≦X≦3/2
) is formed.

Nitride contains 1-Fe, N, and ε- as stable phases at room temperature.
Fe, ~, N, Fe, N exist. Among these, Fe,
N has a large magnetic moment and is suitable as a ferromagnetic material. Therefore, the iron nitride magnetic powder can be made entirely or mostly of Fe and N.

Metallic iron can be manufactured as follows.

(1) Reducing iron oxyoxide (α-FeOOH) or iron oxide in a gas phase.

(2) The organic acid salt of a ferromagnetic metal is thermally decomposed and reduced in a reducing gas.

(3) Thermal decomposition of metal (iron) carbonyl compounds.

(4) Evaporate the ferromagnetic metal in a low pressure inert gas.

(5) Reduction using a reducing substance (eg, hydrogenated boronate, hypophosphite, or hydrazine) in an aqueous solution of a salt of a metal (iron) capable of producing a ferromagnetic material.

Among these methods, method (1) is preferred in consideration of the properties and cost of the metal iron obtained.

When making metallic iron powder, Ni, Co, A1. , S
iSP,,S,Ti5Cu,Mn,Zn.

Iron alloy powder can be obtained by coexisting metal salts such as.

Crystallite size of iron nitride magnetic powder, iron alloy nitride magnetic powder (
The X-ray crystal size) is preferably 150 to 250 people.

The coercive force of iron nitride or iron alloy nitride is 800-1000
The specific surface area is preferably in the range of 10 to 80 rrf/g in terms of BET value, more preferably 35 nf/g or more, and more preferably 40 rrf/g or more. Saturation magnetization (σS) is 75-10100
e/g, and the residual magnetic flux density (Br) in the in-plane direction of the magnetic layer is preferably 1500 to 2500 Gauss.

The above specific surface area is expressed as a BET value, which refers to the surface area per unit weight, and is a physical quantity that is completely different from the average particle diameter.For example, even if the average particle diameter is the same, there are Some have a small surface area. To measure the specific surface area, for example, first heat the powder at around 250°C for 30°C.
The powder was degassed during heat treatment for ~60 minutes to remove what was adsorbed to the powder, and then introduced into a measuring device, the initial pressure of nitrogen was set to 0.5 kg/rrf, and the powder was degassed with nitrogen. Perform adsorption measurements at liquid nitrogen temperature (-195 °C) (
Generally B.

A method for measuring specific surface area called the E, T method. For details, see J, Ame, Chem, Soc, 60309 (1
938)).

This specific surface area (BET value) measuring device uses a digestion battery.
It is also possible to use the "powder measuring device (Cantersorb)" jointly manufactured by Digestion Ionics ①. A general explanation of the specific surface area and its measurement method is given in "Measurement of Granules" (J. M. DALLAVALLE,
Co-authored by CIJ Kuchi EORR Jr., translated by Benguchi and others; published by Sangyo Toshosha), and also in ``Chemistry Handbook''.
(Applied Edition, pp. 1170-1171, published by Nippon Kagaku Gosen, Maruzen, April 30, 1966).
f/gr), which is the same as the specific surface area in this specification. ).

The amount of the polyurethane in which the negative group forms an inner salt according to the present invention is preferably 100 to 1 part by weight, more preferably 50 to 2 parts by weight, per 100 parts by weight of the magnetic powder.

The magnetic recording medium of the present invention has the following remarkable features.

That is, since iron nitride and/or iron alloy nitride is used as the magnetic powder of the magnetic layer, the original features of these nitrides such as HC distribution, high Br, high σS1, and high hardness can be utilized.

What is important here is that "polyurethane in which negative functional groups form an inner salt" is used as the binder for the magnetic layer, which allows iron nitride etc. to be made into fine particles. As will be described later, the dispersibility becomes sufficient and all of the above-mentioned features of the nitride can be exhibited.

That is, according to the studies of the present inventors, the above polyurethane has extremely high adsorption power and holding power to iron nitrides and iron alloy nitrides, shortens the time required for dispersing magnetic powder, and improves dispersion stability. , the magnetic powder was more densely and uniformly filled into the magnetic layer, and the output, SZN ratio, etc. were improved.

The reason why the above-mentioned remarkable effects can be achieved by the magnetic recording medium of the present invention is considered to be as follows.

The surface of magnetic powder such as iron nitride is complex, and the surface is charged with positive and negative charges due to hydration (surface hydroxyl groups, structural defects, ion substitution, etc.). When selecting, important factors include the acidity, basicity, acidity, and basic strength of the magnetic powder surface, and the number of acidic and basic sites.For example, in order to uniformly disperse magnetic powder in a short time, various Ideally, a binder having strong acidic and basic (polar) groups is used to adsorb these acidic and basic sites to the surface active sites of the magnetic powder.

However, simply introducing functional groups of the same polarity into the binder was far from this ideal.

It is also conceivable to use a binder having a polar functional group and to simultaneously use binders having functional groups of the same polarity and different strengths. However, in this case, the magnetic powder is competitively adsorbed preferentially to the side of the binder having a stronger functional group, making it difficult to achieve sufficient adsorption as a whole, resulting in poor dispersion stability of the magnetic paint. Furthermore, it is also conceivable to use a binder having a polar functional group and to simultaneously use a binder having a different type of functional group. However, in this case, the interaction between the polar groups is strong, and adsorption of the binder to the surface of the magnetic powder is difficult to occur, and the viscosity of the magnetic paint increases, making it impossible to prepare a magnetic paint.

The present invention solves these problems by converting the acid sites and basic sites in the inner salt in the binder to the surface active sites (basic sites and acid sites) of the iron nitride and iron alloy nitride magnetic powder. It is thought that the adsorption force to the magnetic powder is high and the dispersibility is significantly improved. Moreover, since the negative functional groups of the same binder form an inner salt, the above-mentioned problem does not occur.

Further, iron nitrides and iron alloy nitrides have high light-shielding properties, and even if the magnetic layer is formed into a thin film, the light transmittance can be sufficiently reduced.

Also, because of its high hardness, it is also possible to reduce the amount of abrasive.

Next, the overall structure of the magnetic recording medium of the present invention will be further described.

Other known binders can also be used.

Binders that can be used in combination include those with an average molecular weight of about too
~200,000, such as urethane resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer,
Butadiene-acrylonyl-IJ copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, Polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea resin, melamine resin,
Phenoxy resin, silicone resin, acrylic reactive resin,
Examples include mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof.

These binders are -3o, M, -COOM, P O
(OM) A resin containing a hydrophilic polar group such as t (where M is hydrogen or an alkali metal such as lithium, potassium, or sodium, and M is an alkali metal such as hydrogen, lithium, potassium, or sodium, or a hydrocarbon residue). It's good to have one. In other words, the polar groups in the molecules of these resins improve their compatibility with the magnetic powder, which further improves the dispersibility of the magnetic powder and prevents agglomeration of the magnetic powder, further improving the stability of the coating liquid. This can also improve the durability of the medium.

[Polyurethane in which a negative functional group forms an inner salt] of the present invention is a vinyl chloride resin, a vinyl chloride copolymer (
It is preferable to use it in combination with vinyl chloride-vinyl acetate copolymer, etc.). In this case, the weight ratio of the polyurethane of the present invention to the vinyl chloride resin and vinyl chloride copolymer is (
The ratio is preferably from 2:8) to (8:2), and more preferably from (3-near) to (7:3). As the vinyl chloride copolymer, those containing the above-mentioned hydrophilic polar groups are particularly preferred.

The binder used in combination, especially the vinyl chloride copolymer, can be obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and other copolymerizable monomers as necessary. Can be done.

Since this copolymer is based on vinyl synthesis, it is easy to synthesize, and various copolymer components can be selected, so that the properties of the copolymer can be optimally adjusted.

The metal of the above-mentioned sulfonic acid or phosphoric acid salt is an alkali metal (especially sodium, potassium, lithium), and potassium is particularly preferable in terms of solubility, reactivity, yield, etc.

The above copolymerizable monomer containing a sulfonate salt is CHt = CHS Os MCHz = Cf (CHz S Os MCHz = C
(CH3) CH2303MCHz = CHCHz
OCOCH(CHz COOR)SO,M CHt =CHCHt 0CHz CH(OH)CH,
So, M CH,=C(CH3)coocz H4303MCH,
=CHC00C,H,So,M CHz =CHC0NHC(CHi)z CHz S
Examples include Ox.

In addition, as a phosphate, CHz = CHCH, OCH, CH(OH)CH.

0-PO3MY' CH,=CHC0NHC(CH,)z CHzO-PO
3MY” PO2MX' CHt =CHCH,O(CH,CH,O)mPO□
MX” In the above, M is an alkali metal, R is a carbon atom number of 1 to 2
0 alkyl groups, Y' is H, M or CHz =CHC
Hz 0CHi CH(OH)CHt-Y2 is H, M or CH2=CHC0NHC(CH3)! CH! X' is OH or OM;
is a positive number.

Copolymerizable polymers to be copolymerized as necessary include known polymerizable monomers, such as various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, and various acrylic monomers. Examples include acid ester, methacrylic ester, ethylene, propylene, isobutyne, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, and maleic ester.

The binder is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization. In either method, known techniques such as divisional addition or continuous addition of molecular weight regulators, polymerization initiators, and monomers can be applied as necessary.

The amount of salt containing the acidic group in the binder is 0.0
It is preferably 1 to 30 mol%. If the amount of the salt-containing monomer is too large, the solubility in solvents will be poor and gelation will likely occur. Moreover, if the amount of salt-containing upper salt is too small, desired properties cannot be obtained.

The vinyl chloride copolymer described above may further contain an epoxy group or a hydroxyl group. By the way, conventional vinyl chloride copolymers (for example, VAGH manufactured by U, C, C, Inc.) are composed of the following copolymer components.

6CH, -CH-)7 0H: indicates a copolymerization unit.

However, it is thought that the CH and Co-0- groups here do not easily contribute to the crosslinking reaction with the curing agent and the like. Therefore,
It is preferable to contain an epoxy group such as the following instead of CH or Co. For example, a copolymer having the following units may be mentioned.

OH (X: monomer unit portion containing an alkali metal salt of a sulfo group or a phospho group) Note that it is also possible to incorporate the above betaine type functional group into the vinyl chloride resin.

"Polyurethane in which negative functional groups form an inner salt"
may be used in combination with an epoxy resin (particularly a phenoxy resin), a polyester resin, or a nitrocellulose resin (hereinafter referred to as other resin). In this case, the blending ratio of the urethane resin and other resin is such that the other resin is 90%
It is desirable that the amount is 10 parts by weight, more preferably 80 to 20 parts by weight.

If the above blending ratio exceeds 90 parts by weight, the coating film becomes brittle (too much), and the durability of the coating film deteriorates significantly, and the adhesion to the support also deteriorates.If the above blending ratio is less than 90 parts by weight, , magnetic powder is more likely to fall off.

Incorporating carbon black in the magnetic layer is further advantageous in terms of improving runnability and electromagnetic conversion characteristics, and also slightly improves dispersibility and reduces the amount of residual solvent in the magnetic layer.

If a light shielding carbon black is used as such carbon black, the degree of light shielding can be further increased. As the light-shielding carbon black, for example, Raben 2000 manufactured by Columbia Carbon Co., Ltd. (specific surface area: 190
m/g, particle size 18 m u ), 2100.1170.
1000, #lOO, #75, #40 manufactured by Mitsubishi Kasei ■
#35, #30, etc. can be used.

Further, as the conductive carbon black, for example, Conductex (Columbia Carbon Co., Ltd.) is used.
x) 975 (BET value (hereinafter abbreviated as BET)
250 i/g, DBP oil absorption (hereinafter abbreviated as DBP) 170
ml/100 gr, particle size 24 mμ), Conductex 900 (BET125 nf/g, particle size 27
mμ), Conductex 40-220 (particle size 20
mam), D Dactex S C (B E T22
0 rrf/gr, DB P115 ml/1
00gr, particle size 20mμ), Cabot Vulcan X C-72 (specific surface area 254rrT/g, particle size 30mμ), Pulcan PC
BET143n(/gr, D B P 118 m
l/100gr, particle size 20rnμ), Raven 10
40.420, Black Pearls 2000 (particle size 15
mμ), #44 manufactured by Mitsubishi Kasei ■, etc.

Other carbon blacks that can be used in the present invention include Conductex (manufactured by Columbia Carbon) (
Conductex ) -3C, (BET220rr
r/g, DBP115 mf/loo g, particle size 20
mμ), Vulcan manufactured by Cabot
9 (BE T140 nl/g, D B P1
14 mf/100 g, particle size 19 mμ), #80 manufactured by Asahi Carbon Co., Ltd. (B ET117 rrf/ g, DB
P113 ml/100 g, particle size 23 mμL H3100 manufactured by Denki Kagaku Co., Ltd. (BET32rIf/g SDBP18
0mf/100g, particle size 53mμ), # manufactured by Mitsubishi Chemical Corporation
22B (BET55rrf/g,, DBP131 m
l/100g.

Particle size 40mμ), #2OB (BET56n (7g, D
BP115 mf/100 g, particle size 40 m u >
, #3500 (B ET47rrf/g, DB P
2H4ml/100g, particle size 40mμ), as well as CF9, #4000, and MA-6 manufactured by Mitsubishi Chemical Corporation.
00, Cabot's Black Burls
k Pearls) L, Monarch
) 800, Black Burls 700, Black Pearls 1000, Black Burls 880, Black Burls 900, Black Burls 1300,
Black Pearls 2000, Sterling
ling) V1 Columbian Carbon's Raven 410, Raven 3200, Raven 430, Raven 450, Raven 825, Raven 1
255, Raben 1035, Raben 1000, Kuben 5000. Examples include Ketschen Black FC.

Furthermore, in the present invention, durability can be improved by further adding a polyisocyanate curing agent to the magnetic paint containing a binder.

Examples of such polyisocyanate curing agents include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, as well as coronate and Nippon Polyurethane Industries.
Trifunctional isocyanates such as Desmodul (manufactured by Bayer AG), desmodulite (manufactured by Bayer AG), or urethane prepolymers containing isocyanate groups at both ends, which are conventionally used as curing agents, can also be used as curing agents. Any polyisocyanate can be used. The polyisocyanate curing agent is used in an amount of 5 to 80 parts by weight based on the total amount of binder.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
It has a magnetic layer 2 on a non-magnetic support 1 such as polyethylene terephthalate, and if necessary, an 80 layer 3 is provided on the opposite side of the magnetic layer 2. Also,
As shown in FIG. 2, an overcoat layer (QC layer) 4 may be provided on the magnetic layer 2 of the magnetic recording medium shown in FIG.

Further, the magnetic recording media shown in FIGS. 1 and 2 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may be provided with no undercoat layer. It's okay. The support may also be subjected to corona discharge treatment.

In addition to the above-described magnetic powder and binder, the magnetic layer 2 may contain a fatty acid and/or a fatty acid ester as a lubricant. As a result, while demonstrating the respective features of both, it offsets the defects that occur when used alone, improves the lubrication effect, improves still image durability, running stability, and S/N.
It is possible to increase the ratio etc. In this case, the amount of fatty acid added is preferably 0.2 to 10 parts by weight, more preferably 0.85 to 8.0 parts by weight, per 100 parts by weight of the magnetic powder. If the fatty acid content falls outside of this range, the dispersibility of the magnetic powder decreases and the runnability of the medium tends to decrease, and if the fatty acid content exceeds this range, the fatty acid tends to seep out and the output decreases. The amount of fatty acid ester added is o, i to 100 parts by weight of magnetic powder.
10 parts by weight is better, and 0.2 to 8.5 parts by weight is even better.

If the amount of ester decreases outside of this range, the effect of improving still durability will be poor, and if it increases, the ester will easily seep out and the output will decrease.

In addition, in order to better achieve the above effects, the weight ratio of fatty acids and fatty acid esters should be set as fatty acid/fatty acid ester =
IO/90 to 90/10 is preferred. Note that fatty acids also have a dispersing effect, and it is thought that by using fatty acids, the amount of other low molecular weight dispersants used can be reduced, and the Young's modulus of the magnetic recording medium can be improved by that amount.

Fatty acids may be monobasic or dibasic.

Fatty acids having 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms, are preferred. Examples of fatty acids are as follows.

(1) Caproic acid (2) Caprylic acid (3) Capric acid (4) Lauric acid (5) Myristic acid (6) Palmitic acid (7) Stearic acid (8) Isostearic acid (9) Rilunic acid (10) Linoleic acid (11) Oleic acid (12) Elaidic acid (13) Behenic acid (14) Malonic acid (15) Succinic acid (16) Maleic acid (17) Glutaric acid (18) Adipic acid (9) Pimelic acid (20) Azelain Acid (21) Sebacic acid (22) 1.12-Dodecanedicarboxylic acid (23) Octanedicarboxylic acid Examples of the above fatty acid esters are as follows.

(1) Oleyl oleate (2) Oleyl stearate (3) Isocetyl stearate (4) Dioleyl maleate (5) Butyl stearate (6) Butyl palmitate (7) Butyl myristate (8) Octyl myristate ( 9) Octyl palmitate (10) Amyl stearate (11) Amyl palmitate (12) Isobutyl oleate (13) Stearyl stearate (14) Lauryl oleate (15) Octyl oleate (16) Inbutyl oleate (17) Ethyl oleate (18) Isotridecyl oleate (19) 2-ethylhexyl stearate (20)
2-ethylhexyl myristate (21) ethyl stearate (22) 2-ethylhexyl palmitate (23) isopropyl palmitate (24) isopropyl myristate (25) butyl laurate (26) cetyl-2-ethyl hexalate ( 27) Dioleyl adipate (28) Diethyl adipate (29) Diisobutyl adipate (30) Diisodecyl adipate In addition to the above-mentioned fatty acids and fatty acid esters, other lubricants (such as silicone oil, carboxylic acid-modified, ester-modified Graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide, etc.) may be added to the magnetic layer.

Non-magnetic abrasive particles can also be added to the magnetic layer. For example, α-alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, silicon carbide, zirconium oxide, zinc oxide, cerium oxide, magnesium oxide, boron nitride, etc. are used. The average particle diameter of this abrasive is preferably 0.6 μm or less. Moreover, it is preferable that the Mohs hardness is 5 or more.

In addition, the magnetic layer further contains an antistatic agent such as graphite.
A dispersing agent such as powdered lecithin or phosphate ester can be added. Furthermore, carbon black can also be used in combination.

In addition, the non-magnetic particles contained in the back coat layer are
It is more preferable that the average particle size is within the range of 10 mμ to 1000 mμ. This is because within the above range, the non-magnetic particles will not become too fine and the addition effect will be good.

Non-magnetic particles include silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide,
Examples include zinc oxide, α-Fe, O, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbide, barium sulfate, and the like. In addition, organic powders such as benzoguanamine resins, melamine resins, phthalocyanine pigments, etc. can also be used, and organic powders and the above-mentioned inorganic powders can also be used in combination.

Furthermore, it is more preferable to use carbon black together with the above-mentioned non-magnetic particles. This further stabilizes the running properties of the medium, and in combination with the effect of the non-magnetic particles described above, it is possible to further improve the durability of the medium.

The thickness of the magnetic layer is preferably thin in order to achieve a high S/N ratio, and thicker in terms of running performance and still durability. Therefore, 6.0 to 1.0 μm is preferable,
It is more preferable to set it to 5.0 to 2.0 am.

Examples of the material forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene 2,6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; plastics such as polycarbonate, etc. can be mentioned. Furthermore, Cu
, Al, Zn, glass, and various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.) can also be used.

The form of the non-magnetic support is not particularly limited, and may include tape,
It may be a sheet, card, disk, drum, etc. (various materials can be selected and used depending on the form and as necessary.

When the non-magnetic support is in the form of a tape or sheet, the thickness is usually within the range of 3 to 1100 μm, preferably within the range of 5 to 50 μm. Furthermore, in the case of a disk or card shape, the thickness can usually be within the range of 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.

E, Example The present invention will be explained in detail below.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, in the following examples, "parts J" are all parts by weight.

<Preparation of Videotape> First, a magnetic layer was formed on a 14 μm thick polyethylene terephthalate base film as a support in the following manner.

That is, using the specified magnetic powder shown in Table 1 below, Table 1
A magnetic paint is prepared by dispersing each resin and various additives shown in the following, this magnetic paint is filtered through a 1 μm filter, 6 parts of trifunctional isocyanate is added, and a 4.0 μm thick film is applied onto a support.
It was coated thickly and supercalendered to produce magnetic layers having various compositions shown in Table 1.

Thereafter, a paint for the BC layer having the following composition was applied to the opposite surface of the magnetic layer to a dry thickness of 0.4 μm.

Carbon black (Condextex-9F5 manufactured by Columbian Carboff) 40 parts Barium sulfate (average particle size 0.1 μm) 10 parts Nitrocellulose 25 parts N-
2301 (made by Nippon Polyurethane) 25 parts Coronate L (
) 10 parts cyclohexanone
400 parts methyl ethyl ketone
250 parts toluene
250 parts A wide magnetic film having a magnetic layer and a BC layer of a predetermined thickness was obtained in this way, and this was wound up.

This film was cut to a width of 3 inches to produce each videotape shown in Table 1. However, the numerical values shown in Table 1 represent parts by weight.

(Margin below) The magnetic powders shown in Table 1 are both acicular iron powders and NH.

and H, (3:1) by heating at 400°C for 14 hours.

BC 7-FeaN 7-Fe, N 7-Fe, N The polyurethane resins (a) to (c) according to the present invention are as follows.

Polyurethane (a) according to the present invention was synthesized as shown in Synthesis Example (a) above, and (b) and (c) were synthesized in the same manner.

(a) Sulfobetaine type modified group content Number average molecular weight 2,20,000 Tg-20'C polar group concentration 0.
04 mmo 1/g The vinyl chloride resins shown in Table 1 are as follows.

A: Sulfo group-containing vinyl chloride resin polar group concentration 0.03 lIIago 1 / g
Degree of polymerization 300 B: Vinyl chloride resin containing sulfo group and epoxy group Vinyl chloride component 77 wt% Sulfate group 0.8 iyt% Epoxy group 3.9 wt% Hydroxyl group 0.5 wt% C: rVAGHJ (U, manufactured by C0C) (CHri:
l Polyurethane chain 0 = S = O ρ (b) Carboxybetaine type modification group content number average molecular weight 1
．． 50,000 Tg -10°C Polar group concentration 0.1 mmol
/g CH.

CH.

l\θ Polyurethane chain (c) Phosphobetaine type modified group content Number average molecular weight 30,000 Tg O°C polar group concentration 0
．． 07 n+mol/gCH.

CH.

Polyurethane chain HO-P=0 e Polyurethane: Nistan 5701 (manufactured by Gutdrich) Sulfo group-containing polyurethane: r U R-8300J (Toyobo Co., Ltd.) carboxyl group-containing polyurethane: Sanyo Chemical Co., Ltd. r TIM-3005J (videotape) Performance Evaluation> The characteristics shown in Table 2 below were evaluated for each videotape shown in Table 1.

The measurement method for each evaluation data is as follows.

<Electromagnetic conversion characteristics> Video S/N, RF output crab Measurement was performed using HR-37000 manufactured by Victor Company of Japan.

<100 pass tape> Pack the sample tape into a VHS cassette and heat at 20°C 160%
The ctoo pass tape was repeatedly run for 100 passes in RH using an NV-6200 (manufactured by Matsushita Electric) deck. Regarding this, the following measurements were carried out, and RF output fluctuations and the presence or absence of tape damage were also investigated.

Dynamic friction coefficient: Tape runability tester TBT3 at 25°C
00 D (Yokohama System Research Institute) Wrap tape at 180 @ on a chrome plated stainless steel 4φ bottle, tape speed l cn+/
sec Measured with 20g of % rotion, and calculated μ using the following formula.
K was calculated.

Dropout: Using a dropout counter VD-5M manufactured by Victor Japan Co., Ltd., the output that is longer than 15 μsec and is 20 dB or more lower than the output of the RF envelope is regarded as one dropout, and the total length is measured, and the average value per minute is calculated. I asked for it.

Tape damage O...No stretching on one side, bending on edges, etc.

Δ・・・・・・・・・　〃〃　　　　A little.

×・・・・・・・・・　　〃〃　　　　　　A lot.

(The following is a blank space) As shown in Table 2, the sample dispersed using the polyurethane according to the present invention has excellent electromagnetic conversion characteristics compared to the sample of the comparative example (Example 6 and Comparative Example (4) The same vinyl chloride resin is used and the two are compatible.) Also, 1
Even after the 00 pass running test, there was no tape damage such as edge bending or one-sided stretching, and the coefficient of dynamic friction was small. In addition, the output fluctuation range is small. Dropouts have also remained at a low level.

In addition, when the light transmittance of the video tapes of Examples 1 to 4 was measured using light with a wavelength of 900 nm, it was found to be 0.02
% (Example 1.4), 0.03% (Example 2.3)
An extremely good value was obtained.

[Brief explanation of the drawing]

FIGS. 1 and 2 are partially enlarged sectional views showing examples of magnetic recording media. In addition, in the symbols shown in the drawings, 1...Nonmagnetic support 2...Magnetic layer 3...Back coat Ji (BC layer )
4... Overcoat layer (QC layer).

Claims (1)

[Claims] 1. Iron nitride magnetic powder and/or iron alloy nitride magnetic powder,
A magnetic recording medium in which a magnetic layer contains polyurethane in which negative functional groups form an inner salt.