JPH02139713A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To shorten the time required for dispersion of magnetic powder and to improve dispersion stability by incorporating a Co-contg. iron oxide magnetic powder as the magnetic powder and polyurethane having negative functional groups as inner salt as a binder into the magnetic layer. CONSTITUTION:The magnetic layer 2 in the magnetic recording medium contains the Co-contg. iron oxide magnetic powder as magnetic powder and polyurethane having negative functional groups as inner salt as a binder. For example, the magnetic layer 2 is provided on a nonmagnetic supporting body 1 such as polyethylene terephthalate and if required, a back coating layer 3 is provided on the opposite side of the substrate to the magnetic layer 2. Fatty acids and/or fatty acid esters can be also incorporated as a lubricant into the magnetic layer 2. Thereby, the binder is smoothly adsorbed on the surfaces of the magnetic powder, and consequently, the time of dispersion of the magnetic powder is decreased and dispersion stability is enhanced. The obtained recording medium has superior electromagnetic conversion characteristics.

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.

Prior Art Recently, magnetic recording media such as magnetic tapes have become denser and have higher S/S.
With the shift to nitrogen, magnetic powders with smaller particle diameters are being used.

In addition, for the purpose of improving the electromagnetic conversion characteristics of magnetic recording media, acicular cobalt-containing iron oxide powder is used as a ferromagnetic powder, with a cobalt-containing iron oxide layer formed on the surface of γ-Fet03. It has reached this point.

Generally, it is said that the S/N ratio of a magnetic recording medium is proportional to the square root of the number of particles of magnetic powder in the recording material involved in recording and reproduction. Therefore, when applying the same weight of magnetic powder,
The use of magnetic powder with a smaller particle size is more advantageous in improving the S/N. Further, by making the magnetic powder into fine particles and increasing its BET value, the surface of the magnetic layer becomes smoother and spacing loss is reduced, which is advantageous in obtaining high electromagnetic conversion characteristics.

However, since the surface area of particles increases in inverse proportion to the square of the particle diameter, dispersion of particles becomes rapidly difficult as the particle diameter decreases, and dispersion stability also deteriorates. In this case, the orientation of the ferromagnetic material in the magnetic layer, the smoothness of the surface of the magnetic layer, etc. deteriorate, and as a result, an excellent squareness ratio and S/N ratio cannot be obtained, which is disadvantageous.

Conventionally, polyester-type polyurethanes and vinyl chloride-vinyl acetate copolymers have been mainly used as binders for magnetic tapes. However, this does not provide sufficient dispersibility, so the degree distribution of the magnetic powder is adjusted to improve the dispersibility of the magnetic powder in the binder.
Surfactants have been used as dispersants.

Furthermore, the binder is modified by introducing a hydrophilic group, such as a hydroxyl group, a phosphor group, a sulfur group, or a carboxy group,
Methods have been proposed to improve the characteristics.

However, even with such a binder, sufficient dispersibility may not be obtained in some cases. Therefore, increasing the density of magnetic powder,
With the adoption of cobalt-containing iron oxide magnetic powder, it is expected that a binder having a higher adsorption power to the surface of such magnetic powder will appear.

C.3 Purpose of the Invention The purpose of the present invention is to provide magnetic recording with smooth adsorption of a binder to the magnetic powder surface, short time required for dispersing the magnetic powder, high dispersion stability, and excellent electromagnetic conversion characteristics. It is to provide a medium.

D0 Structure of the invention and its effects The present invention provides a magnetic recording medium having a magnetic layer containing magnetic powder and a binder, in which cobalt-containing iron oxide magnetic powder is contained as the magnetic powder, and a negative functional group is present. The present invention relates to a magnetic recording medium characterized in that polyurethane forming an inner salt is contained as the binder.

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

First, the manufacturing method will be described.

Like ordinary polyurethane synthetic spheres, they are synthesized by reacting high molecular weight polyols (molecular weight 500 to 3000) such as polycarbonate polyols, polyester polyols, polylactone polyols, and polyether polyols with polyfunctional aromatic or aliphatic isocyanates. 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 are in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups. , or may be one that does not contain these reactive end groups (for example, in the form of a urethane elastomer).

Isocyanate components include various diisocyanate compounds, such as hexamethylene diisocyanate (HMD).
I), diphenylmethane diisocyanate-1-(MDI
), hydrogenated MDI (H+zMD I), toluene diisocyanate (TDI), 1,5-naphthalene diisocyanate (MDI),) lysine diisocyanate (
TODI), lysine diisocyanate methyl ester (
LDI), isophorone diisocyanate (IPDI), etc. can be used.

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

A low-molecular polyfunctional alcohol such as 6-hexanediol or 1,3-butanediol is used to adjust the molecular weight, resin properties, etc.

The functional groups forming the inner salt may be introduced into the isocyanate component, but they can also be introduced into the polyol component, and may further be introduced into the 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, diethylene glycol, trimethylolpropane, hexanetriol,
Examples include polyhydric alcohols such as glycerin, trimethylolpropane, trimethylolethane, and pentaerythritol, or any two or more types selected from these glycols and polyhydric alcohols.

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.

In producing the above-mentioned polyester polyols and polycarbonate polyols (including polycarbonate polyester polyols), 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: [R is -(C11□)2-1-C1f(CH3)-CI
ip-CHI- is shown.

X is -5o2- -co-1-C(CH3)z-C(C
)13)Z-C&L-C(C)13)2- is shown. ] [
R represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms,
Ro represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, or an alkyl group having 1 to 7 carbon atoms. ] [n represents an integer of 1 to 10.

] (n-L 2) [n indicates 1 or 2] +10 (CHz), O+0 (CHz), Ol
l [n represents 1 or 2. ] [n represents 1 or 2. ] [n represents 1 or 2. ] [n represents 1 or 2. ] In the polyurethane having these aromatic polyhydric alcohol components in the main chain, the content of these components is 10a+o I! of the entire polyhydric alcohol component. % or more.

To produce a lactone-based polyester polyol in which the negative functional group forms an inner salt, 3-caprolactam,
The above functional group may be introduced into lactams such as α-methyl-1-caprolactam, S-methyl-S-caprolactam, and T-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 general 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 inclusion rate, it is easier to control if the functional group exists in the polymer monomer.

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

Examples of betaine group-containing monomers that can be used are the following compounds, and the polyurethane resin used in the present invention is one in which these monomers are used. Needless to say, it is not limited to.

OPOsH0P()+〇-〇PO□H20 A: Hydrogen or an alkyl group having 1 to 60 carbon atoms (e.g. methyl group, ethyl group, etc.) m: An integer of 1 to 10 B Coo or C0NF (R: 1 to 60 carbon atoms 12 alkyl group, alkenyl group or aryl group 3) Synthesis method using propane sultone The polymer in which the negative functional group forms an inner salt is available as a commercially available drug, but it can be obtained by the following method. easily obtained.

1) Synthesis method using monochloroacetic acid RN (CHt CC00H) + cJ CHt C
00HR = Alkyl group such as methyl or ethyl 2) Synthesis method using monochlorosuccinic acid CH, -COOH Also, as a polymer reaction, a reaction to introduce a betaine group or 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 polyurethane whose chain has been extended to a predetermined molecular weight by a polymerization reaction. In this case, first, a compound having a hydroxyl group and a betaine group is synthesized, and this is reacted with an equimolar amount of a polyfunctional isocyanate such as a diisocyanate.
A reaction product of one of the NGO groups of the diisocyanate and the hydroxyl group in the above compound is obtained. Then, by reacting the OH groups of the polyurethane with the unreacted NGO groups, a polyurethane into which betaine groups and the like are 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.

The amount of betaine groups etc. introduced into the polyurethane resin of the present invention is preferably 0.01 to 1.0 mmol/g, and the preferred amount is 0.1 to 0.5 a+moA.
/g range. The amount of introduced polar group is 0.01
mmo (If it is less than 1/8, sufficient effect on the dispersibility of the ferromagnetic powder will not be recognized. If the amount of the polar group introduced exceeds 1.Q mmol/g, intermolecular or intramolecular aggregation will occur. This 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 to 100,000, more preferably 10,00
It is preferably in the range of 0 to 40.000. If the number average molecular weight is less than 5,000, the coating film-forming ability of the resin will be insufficient, and if the number average molecular weight exceeds 100,000, problems may occur during paint manufacturing processes such as mixing and coating. be.

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 mol of adipic acid, 1.7 mol of
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 mHg, and the reaction was carried out until the acid value reached 2 or less. The molecular weight of the obtained copolymerized polyester is Mw250
It was 0. 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 at 80°C for 2 hours.
-Add 20 parts of butanediol and react for an additional 2 hours.
, 3-butanediol were added thereto, and the mixture was reacted for 1 hour. The molecular weight of the obtained polyurethane is MW=35,000, Mn=
It was 22,000.

The amount of "polyurethane whose 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.

Next, the "cobalt-containing iron oxide magnetic powder" will be described.

As ferromagnetic iron oxide particles, when expressed by FeOx for -C, the value of X is in the range of 1.33≦X≦1.50, that is, magnetite (γ-Fg203x-1.50).
, magnetite (Fe+ 04
1.50).

γ-Fe2O3 and Fe50. is usually obtained by the following manufacturing method.

Ferrous hydroxide is generated by adding an alkali to a ferrous salt solution, and oxidized by blowing air at a predetermined temperature and pH to obtain acicular hydrated iron oxide, which is heated in air at 250-400℃. It is heated and dehydrated, and then heated and reduced at 300 to 450°C in a reducing atmosphere to obtain acicular magnetite particles. Furthermore, if necessary, the magnetite is reoxidized at 200 to 350°C to form acicular magnetite (γ-Fe, O,).

Among these ferromagnetic iron oxides, the cobalt-containing iron oxide magnetic powder according to the present invention can be broadly classified into two types: doped type and coated type.

Co-doped iron oxide particles can be produced by (1) hydrothermally treating ferric hydroxide containing cobalt hydroxide in an alkaline atmosphere and reducing and oxidizing the resulting powder; and (2) synthesizing goethite. In this method, a solution of cobalt salt is added in advance, and goethite containing cobalt is synthesized while adjusting p), and this is reduced and oxidized. A method in which a reaction similar to the reaction in (2) is carried out to grow goethite containing CO, and then reduced and oxidized (4) On the surface of acicular goethite or maghemite,
There is a method in which Co compounds are adsorbed by treatment in an alkaline aqueous solution containing a Co salt, followed by reduction/oxidation or heat treatment at a relatively high temperature.

Co-coated iron oxide magnetic particles are produced by mixing acicular magnetic iron oxide and cobalt salt in an alkaline aqueous solution and heating the mixture to make the iron oxide particles adsorb cobalt compounds such as cobalt hydroxide, which are washed with water and then heated. Dry and collect, then in air, N,
Obtained by heat treatment in a non-reducing atmosphere such as gas.

Co-coated particles are superior to Co-doped particles in terms of heating and/or pressure fIim of the magnetic layer of the medium, and it is preferable to use Co-coated particles except in special fields.

Cobalt content is 1.0 to 5.0% by weight of the entire magnetic powder
It is preferable that The coercive force (Hc) of magnetic powder is 60
It is preferable to set it as 0-1100 oersted.

The specific surface area of the fox/h powder is preferably within the range of 10 to 70 m/g in terms of BET value, and is 35n? /g or more, more preferably 45rrf/g or more. The average particle diameter is 0.8 to 0.2 μm on the long axis and 0.2 to 0.01 on the short axis.
It is preferable to set it to about μm.

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 to 6
The powder is degassed while being heated for 0 minutes to remove the substances adsorbed on the powder, and then introduced into the measuring device, the initial pressure of nitrogen is set to Q, 5 kg/rrr, and liquid nitrogen is removed by nitrogen. Adsorption measurements are carried out at temperatures (-195°C) (generally B
, a method for measuring specific surface area called the E,T method. For details, J, Aa+e, Che*, Soc, 60 30
9 (193B)).

This specific surface area (BET value) measuring device uses Yuasa battery ■
It is also possible to use the "powder measuring device (Cantersoap)" jointly manufactured by Yuasa Ionics ■. A general explanation of the specific surface area and its measurement method can be found in ``Measurement of Granules'' (J, M., DALLAVALL
Co-authored by E. and CLYDEORRJ, translated by Benta et al.; published by Sangyo Toshosha), and also in ``Chemistry Handbook''.
(Applied edition, pp. 1170-1171, edited by the Chemical Society of Japan, published by Maruzen on April 30, 1966).
In addition, in the above-mentioned "Chemical Handbook", specific surface area is simply defined as surface area (m
/gr), which is the same as the specific surface area in this specification. ).

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

That is, since the functional groups contained in the polyurethane of the present invention form an inner salt, it is smoothly adsorbed onto the surface of the cobalt-containing iron oxide magnetic powder, and the time required for dispersing the magnetic powder is shortened. Dispersion stability is improved. This results in
Cobalt-containing iron oxide magnetic powder (particularly highly finely divided powder) is uniformly and densely filled in the magnetic layer, improving output, S/N ratio, etc.

The reason for this can be considered as follows.

The surface of metal oxides is complex, and the surface is charged with positive and negative charges due to surface hydroxylation due to hydration, structural defects, ion substitution, etc. Therefore, when selecting a binder for magnetic powder, important factors include the acid and basic properties of the surface of the magnetic powder, the acid and basic strength, and the number of acid and basic sites. For example, to uniformly disperse cobalt-containing iron oxide magnetic powder in a short time,
Ideally, binders having acidic and basic (polar) groups of various strengths are used to adsorb these acidic and basic sites to the surface active sites of the cobalt-containing iron oxide 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, this strengthens the interaction between the polar groups, making it difficult for the binder to adsorb to the surface of the magnetic powder, and also increases the viscosity of the magnetic paint, making it impossible to prepare a magnetic paint.

The present invention solves these problems because the acid sites and basic sites in the inner salt in the binder are adsorbed to the surface active sites (base sites and acid sites) of the cobalt-containing iron oxide magnetic powder. The adsorption power to magnetic powder is high (dispersibility is thought to be significantly improved).Moreover, the negative functional groups of the same binder form an inner salt, so the above problems do not occur. .

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

"Polyurethane in which negative functional groups form an inner salt"
Other known binders can also be used.

The binder that can be used in combination has an average molecular weight of about 10,000.
~200,000, such as urethane resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer,
Butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose SXH4 (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubber, 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.

The resins mentioned above are SO3M and C00M.

-PO(OM')z (where M is hydrogen or lithium,
It is preferable that the resin contains a hydrophilic polar group such as an alkali metal such as potassium or sodium; M is an alkali metal such as hydrogen, lithium, potassium, or sodium, or a hydrocarbon residue). 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.

The "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 (
2: 8) to (8: 2), preferably (3
:7) to (7:3) is more preferable. As the vinyl chloride copolymer, those containing the above-mentioned hydrophilic polar groups are particularly preferred.

The binder used, 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 preferred in terms of solubility, reactivity, yield, etc.

The above copolymerizable monomer containing a sulfonate salt is as follows: CHz=CHS ChM CHz= CHCH,S OhM CHt= C(CH3) CT(zS OzMCHt±
CHCHt OCOCH (CHt COOR) S O
x MCH2=CHCH*0CH2CH(OH)CH2
SO3MCH1=C(CH2)COOC! H4SChM
CHt=CHCOOCa Hs SO3MCHt=
Examples include CHCON HC(CHs')zCHtS OsM.

Also, as a phosphate, CHz = CHCHz OCHt CH(OH) C
Hz OP 03 M Y 'CH2=CHC0NH
C(CH3)ICHI-0-PO3MY"CHz=CH
CHzO(CH2CH2O)mPchMX" In the above, M is an alkali metal, R is an alkyl group having 1 to 20 carbon atoms, and Yl is H, M or CH!=CHCH20CH2
CH(OH)CH2-Y2 is H, M or CHz = CHCON HC(CH3) t CHz
XI is 0H or ○M;
is a positive number.

Copolymerizable monomers 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 esters. , methacrylic ester, ethylene, propylene, isobutyne, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, maleic ester and the like.

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.

Preferably, the vinyl chloride copolymer further contains an epoxy group or a hydroxyl group.

By the way, conventional vinyl chloride copolymers (for example, U.

VAC manufactured by C, C, H) consisted of the following copolymerized components.

: Indicates a copolymerization unit.

However, it is thought that the CHlGo-0- group here does not easily contribute to the crosslinking reaction with the curing agent and the like. So C
It is preferable to contain an epoxy group such as in place of H3Co. For example, a copolymer having the following units may be mentioned.

(X: Monomer unit portion containing an alkali metal salt of a sulfo group or a phospho group) "Polyurethane in which a negative functional group forms an inner salt"
It is also preferable to use epoxy resins (particularly phenoxy resins), polyester resins, and nitrocellulose resins (hereinafter referred to as other resins) in combination. In this case, the blending ratio of the urethane resin and other resins is preferably 90 to 10 parts by weight, more preferably 80 to 20 parts by weight.

If the above-mentioned blending ratio exceeds 90 parts by weight, the coating film becomes too bulky and the durability of the coating film is significantly deteriorated, and the adhesion to the support also deteriorates. Further, when the above blending ratio is less than 10 parts by weight,
Magnetic powder is more likely to fall off.

When a carbon blank is included in the magnetic layer, it is further advantageous in terms of improving runnability and electromagnetic conversion characteristics, the dispersibility is also improved to some extent, and the amount of residual solvent in the magnetic layer is further reduced.

If a light shielding carbon blank is used as such a carbon blank, the degree of light shielding can be increased.

As a light-shielding carbon blank, for example, Raben 2000 manufactured by Columbia Carbon Co., Ltd. (specific surface area 190nf/g) is used.
, particle size 18m, c+), 2100.1170.100
0, Mitsubishi Chemical #100, #75, #40, #35
, #30, etc. can be used.

Further, as a conductive carbon blank, for example, Conductex 975 manufactured by Columbia Carbon Co., Ltd. (BET value (hereinafter abbreviated as BET) 250 m/g, DBP oil absorption (hereinafter abbreviated as DBP) 170 m I2/100 gr, grain Diameter 24 mμ), Conductesox 900 (B E T
125m/g, particle size 27m, cr), Conductenox 40-220 (particle size 20mμm), Conductenox SC (BET 220m/gr, D B P
115ml/100gr, particle size 20mu),
Cabot Vulcan
)
f/gr, D B P 118m 1. /100gr
, particle size 20 mμ), Raven 1040.420, Prasokvars 2000 (particle size 15 mμ), and #44 manufactured by Mitsubishi Kasei ■.

In addition, other carbon blacks that can be used in the present invention include Conductenx (manufactured by Columbia Carbon Co., Ltd.).
Conductex) -S C, (B E T 22
0rd/g, DBP 115m1/100g, particle size 2
0mμ), Vulcan manufactured by Cabot
9 (BET140rrr/g, DBP 11
4mj! / 100g, particle size 19mμ) #80 manufactured by Asahi Carbon Co., Ltd. (B ET 117m/g).

DBP 113m! ! / 100g, particle size 23
mμ), HS manufactured by Denki Kagaku Co., Ltd., 100 (B ET3
2i/g, DBP 180ml/100g,
Particle size: 53 mμ), #22B manufactured by Mitsubishi Chemical Corporation (B ET
55n? / g, DB P 131m6/ 100g
-Particle size 40mμ), #20B (BET56n?/g
SDBP115ml/100g - particle size 40mμ
), #3500 (BET47rd/g, D
B P 187m A / 100g, particle size 40mμ
), and there are also C1-9 and #4 manufactured by Mitsubishi Chemical Corporation.
000, MA-600, Blank Pearls (Black Pearls) L% Monarch (manufactured by Cabo Soto)
Monarck) 800, Black Burls 700.
Black Burls 1000, Blank Pearls 88
0, Black Burls 900, Black Burls 1
300, Blank Burls 2000, Sterling (
Sterling) V, Raven 410, Raven 3200 manufactured by Columbia Carbon Co., Ltd.
Raben 430, Raben 450, Raben 825, Raben 1255, Raben 1035, Raben 1000
, Raven 5000, Ketchen Black FC, etc. The amount of carbon black added is preferably 0.1 to 10.0 parts by weight per 100 parts by weight of the magnetic powder.

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

Examples of such polyisocyanate curing agents include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate; trifunctional isocyanates such as Coronat (manufactured by Nippon Polyurethane Industries) and Desmod (manufactured by Bayer); Any conventionally used curing agent, such as a urethane prepolymer containing isocyanate groups at both ends, or polyisocyanate that can be used as a curing agent 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.
A magnetic layer 2 is provided on a non-magnetic support 1 such as polyethylene terephthalate, and if necessary, a BCC 20 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, and even more preferably 0.5 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 output decreases. The amount of fatty acid ester added was 10% of the magnetic powder (0.1% per 1 part by weight).
-10 parts by weight is good, and 0.2-8.5 parts by weight is even better. If the amount of ester is outside this range and the amount of ester decreases, the effect of improving running performance will be poor, and if the amount 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 =
10/90 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) Valmitic 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 (19) Pimelic acid (20) Azelaic acid (21) Sebacic acid (22) 1,12-dodecanedicarboxylic acid (23)
Octane dicarboxylic 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 Octyl Palmitate Amyl stearate Amyl palmitate Isobutyl oleate Stearyl stearate Lauryl oleate Octyl oleate Isobutyl oleate Ethyl oleate Isotridecyl oleate 2-Ethylhexyl stearate 2-Ethylhexyl myristate Ethyl stearate 2-Ethylhexyl palmitate Isopropyl palmi tate isopropyl myristate butyl laurate cetyl-2-ethylhexalate dioleyl adipate diethyl adipate (29) diisobutyl adipate (30) diisodecyl adipate In addition to the fatty acids and fatty acid esters mentioned above, 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. These include, 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, a carbon blank can also be used in combination.

Further, it is more preferable that the average particle size of the non-magnetic particles contained in the B-7 coating layer 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 203 , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbide, barium sulfate, and the like. In addition, organic powders such as penduguanamine 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 a carbon blank 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 still durability. Therefore, 6.0 to 1.0 μm is preferable, and 5.9 to 1.0 μm is preferable.
It is more preferable to set it to 2.0 μm.

The surface roughness of the magnetic layer is an average surface roughness Ra of 0.005 to
It is preferable to set it as 0.02oIim. This does not reduce running performance and improves the S/N ratio.

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. Further C
Metals such as u % Al and Zn, glass, and various ceramics such as so-called new ceramics (eg, 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., and 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 100 μm, preferably 5 μm.
It can be made within the range of ~50 μm. Further, in the case of a disk shape 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.

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

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, all "parts" are parts by weight.

<Preparation of Videotape> First, a magnetic layer was formed on a polyethylene terephthalate base film having a thickness of 10 μm as a support in the following manner.

That is, using the specified cobalt-containing iron oxide magnetic powder shown in Table 1 below, a magnetic paint was prepared by dispersing each resin and various additives shown in Table 1, and this magnetic paint was filtered with a 1 μm filter. , 7 parts of trifunctional isocyanate were added, and the mixture was coated onto a support to a thickness of 2.5 μm and supercalendered to obtain 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 (Sieben 255; manufactured by Columbia Carboff) (Average particle size 20 mμ) 40 parts Barium sulfate (Average particle size 0.1 μm) 10 parts Nitrocellulose 25 parts N-230
1 (made by Nippon Polyurethane) 25 parts Coronet) L (〃
) 10 parts cyclohexanone
400 parts methyl ethyl ketone 2
50 parts toluene 250
In this manner, a wide magnetic film having a magnetic layer and a BC layer of a predetermined thickness was obtained, and this was wound up.

This film was cut into 1/2 inch width to produce the video tapes shown in Table 1. However, the numerical values shown in Table 1 represent parts by weight.

(Margin below, continued on next page) Cor-Fez O3 (adhered) shown in Table-1, A-
E has the following properties.

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

(b) Contains sulfobetaine type modified group Number average molecular weight 22,000 Tg Polar group concentration 0.04 mmol/g-20℃ The vinyl chloride resin B shown in Table 1 is as follows.

B: Vinyl chloride resin containing sulfo group and epoxy group Vinyl chloride component 77 wt% Sulfate group 0.8 wt% Epoxy group 3.9 wt% Hydroxyl group 0.5 wt% The polyurethane resins (a) to (d) according to the present invention are Number average molecular weight containing carboxybetaine-type modifying group that is:
15,000 Tg -10℃0℃Polar group concentration 0.1
mo+ol/g (c) Number average molecular weight containing phosphobetaine type modified group 20,000 Tg Polar group concentration 0.07 mmol/gO℃ (d) Weight average molecular weight containing sulfobetaine type modified group 55,000 Tg -5℃ polar group concentration 0.0511010 (1/g composition:
(Mole ratio) Diphenylmethane diisocyanate 3.2 Bisphenol A-propylene oxide (divalent) adduct 1.1-3.6 Isophthalic acid 1.6 1.4-Butadiene 10.0 Adipic acid
7.5 ○ Sulfonic acid-modified polyurethane resin: UR-8300: Carboxylic acid-modified polyurethane resin manufactured by Toyobo Co., Ltd.: TIM-3005: Characteristics evaluated as shown in Sanyo Chemical Co., Ltd.

The measurement method for each evaluation data is as follows.

Power is a conversion characteristic> The output during playback of a 100% white signal from an RF output was determined using the tape of Comparative Example (3) as a reference and in comparison with the tape of Comparative Example (3).

Lumi-3/N: Using a noise meter (manufactured by Shibaku Corporation), the difference in S/N of the sample at 100% white signal was determined in comparison between the tape and a reference tape (manufactured by Konica ■).

Chroma-3/N: Using a noise meter (manufactured by Shibatsu Co., Ltd.), the difference in S/N of the sample in the chroma signal was determined by comparing the tape with a reference tape (manufactured by J Nika ■).

Fast running, durability〉 Jitter? VTR jitter maker MK-612A
Measured at (Meguro Radio).

Still life: The time until the RF specific output decreases by 1 dB in still mode using NV-6200 (manufactured by Matsushita Electric).

<100 Tape> and <Virgin Tape> Rf output fluctuation, dynamic friction coefficient, and dropout were measured for unused tape (virgin tape). In addition, the sample tape was
Packed in S case, NV- in 20℃, 60%RH.
6200 (Matsushita Electric!!!) was used to repeatedly run 100 buses (100 bus tapes).The above measurements were performed and the presence or absence of damage to the tape was examined.

Dynamic friction coefficient: Tape runability tester TBT30 at 25°C
At 0 D (Yokohama System Research Institute), 1806 tapes were wrapped around a chrome-plated stainless steel 4Φ bottle, and the tape speed was 10/5ec.
The measurement was performed using 20 g of s person's rotation, and μ was calculated using the following formula.

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.

(The following is a blank space, continued on the next page) Conclusion> Sample 1 dispersed using the polyurethane resin according to the present invention
-8 are different from (1) to (4) using polyurethane resin, which have been used so far, have improved electromagnetic conversion characteristics (Lumi S/N).
, chroma S/N5Rf conversion power), jitter, and still life. Further, even after 100 bus running tests, 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.

[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 layer (BC layer) 4...Overcoat layer (00 layer) be. Agent: Patent Attorney Hiroshi Aisaka (Volunteer) Proceedings, Seishohei Jj! Date of March 1st, 1988 Patent Application No. 266440 Name of the invention Relationship to the person who corrects magnetic recording media case Patent applicant address Nishi, Shinjuku-ku, Tokyo Shinjuku 1-26-2 Name
(127) Konica Corporation

Claims (1)

[Claims] 1. In a magnetic recording medium having a magnetic layer containing magnetic powder and a binder, the polyurethane containing cobalt-containing iron oxide magnetic powder as the magnetic powder and in which the negative functional group forms an inner salt is used. A magnetic recording medium characterized in that it is contained as a binder.