JPH0266722A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To smooth the attraction of the binder to the surface of the magnetic powder incorporated into the magnetic layer of the magnetic recording medium and to stabilize the dispersion of the above-mentioned powder by incorporating at least either of silicon and aluminum into the above-mentioned magnetic powder and specifying the content of the silicon and the content of the aluminum. CONSTITUTION:The magnetic layer 2 is formed on a nonmagnetic base 1 of the magnetic recording medium and a back coating layer 4 is formed at need on the side opposite to the magnetic layer 2. At least either of the silicon and the aluminum are incorporated into the magnetic powder incorporated into the magnetic layer 2. The content of the silicon in the magnetic powder is specified to 0.01 to 0.60wt.% in case of incorporating the silicon into this magnetic powder and the content of the aluminum is specified to 0.001 to 0.30wt.% in case of incorporating the aluminum into the magnetic powder. The attraction of the binder to the magnetic powder surface is smoothed and the dispersion of the magnetic powder is executed stably in a short period of time.

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.

A conventional magnetic recording medium basically consists of a nonmagnetic support and a magnetic layer containing ferromagnetic powder, and is constructed by providing the magnetic layer on the nonmagnetic material.

Generally, the magnetic layer is formed by dispersing ferromagnetic powder in a binder.

In recent years, magnetic recording media with such a configuration, especially magnetic recording media for VTRs, have been developed to
The 8-inch width standard, which is narrower than the inch width standard, has appeared.
Due to its widespread use, there is a strong demand for high-density recording, and a magnetic recording medium with higher performance, that is, a magnetic recording medium with excellent electromagnetic conversion characteristics and running durability, is desired.

Therefore, with the aim of improving the electromagnetic conversion characteristics of magnetic recording media, acicular cobalt-containing iron oxide powder, which has a cobalt-containing iron oxide layer formed on the surface of γ-Fe20°, is used as a ferromagnetic powder. It has reached the point where

However, the surface characteristics of the acicular cobalt-containing iron oxide powder do not provide sufficient adsorption to binders, dispersants, etc. having functional groups. Therefore, in a magnetic recording medium using cobalt-containing iron oxide powder without surface treatment,
Due to poor dispersion of cobalt-containing iron oxide powder,
There is a problem that electromagnetic conversion +41t [and running durability deteriorates].

On the other hand, as binders for magnetic tapes, polyester-type polyurethanes and chlorinated fur-vinyl acetate copolymers have conventionally been mainly used.

However, since sufficient dispersibility cannot be obtained with conventional polyurethane resins, we have improved the dispersibility of magnetic powder in the binder by adjusting the particle size distribution of the magnetic powder, or used surfactants as a dispersant. There are things being done. Furthermore, the binder may be a hydrophilic group, such as a hydroxyl group, a phosphor group, a sulfo group,
Alternatively, a method has been proposed in which the properties are improved by modifying the material by introducing a carboxy group or the like.

However, even with such a binder, it may be difficult to obtain sufficient dispersibility, and the emergence of a binder that has even higher adsorption power to the surface of magnetic powder is expected.

C1 Purpose of the invention The purpose of the present invention is to provide magnetic recording with smooth adsorption of a binder to the surface of magnetic powder, short time required for dispersion of magnetic powder, high dispersion stability, and excellent electromagnetic conversion characteristics. It is to provide a medium.

21 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 at least one of silicon and aluminum is contained in the magnetic powder (provided that silicon is When contained in the magnetic powder, the content of silicon in this magnetic powder is i) 0.01 to 0.60% by weight, and when aluminum is contained in the magnetic powder, the content of silicon in this magnetic powder is 0.01 to 0.60% by weight. O&j
The content of aluminum is 0.001 to 0.30% by weight.
shall be. ), and a polyurethane in which the negative functional group forms an inner salt is contained as the binder.

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

The mass and manufacturing method will be described.

Similar to the usual polyurethane synthesis method, high molecular weight polyols (molecular weight 500 to 3000) such as polycarbonate polyols, polyester polyols, polylactone polyols, and polyether polyols are reacted with polyfunctional aromatic or aliphatic isocyanes 1. and synthesize. As a result, polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate I. are synthesized.

These polyurethanes are mainly produced by the reaction of polyisocyanates with polyols and optionally other copolymers, and also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups. Alternatively, it may be one that does not contain these reactive end groups (for example, in the form of a urethane elastomer). As the isocyanate component, various compounds such as hexamethylene diisocyanate (HMDI), diphenylmethane diisocyanate (MDI) hydrogenated MD T (HI2MD I ),
Toluene diisocyanate (IDI), 1.5 naphclean diisocyanate (NDJ), I-lysine diisonanate (TODI), lysine diisocyanate methyl ester (LDI), inphorone diisocyanate (IPDI), etc. can be used.

In addition, if necessary, 1,4-butanediol, 1゜6-
A low-molecular polyfunctional alcohol such as hexanediol or 1,3-butanediol is used to adjust the molecular weight, resin physical properties, etc.

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, sehasic acid, adipic acid, dimerizing luic 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.

To produce a lactone polyester polyol in which the negative functional group forms an inner salt: 1.1: s-caprolactam, α-methyl-1-caprolactam, S-methyl-
The above functional group may be introduced into lactams such as 5-caprolactam and γ-butyrolactam.

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

An example of the functional group forming the inner salt is the hetain group described below.

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 (hetaine 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 introduction rate, it is easier to control if the polymer monomer has the functional group.

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

e　　　　　○ OP　03　HOP　O3 0P 02H2.

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.

soil B: -Coo or C0NH.

R: [Number 1 to 12 alkyl group, alkenyl group, or aryl group.

n, m: integer from 1 to 10.

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 can be obtained manually as a commercially available chemical, but it can be easily obtained by the method described below.

■) Synthesis method using monochloroacetic acid R-N (CH□-COOH>x +Cβ-C■42-C
OOI (R-alkyl group such as methyl, ethyl etc. 2) Synthesis method using monochlorosuccinic acid CHzC)I
zOH Also, as a polymer reaction, a reaction for introducing a hetain group or the like into a polymer will be described. In this method, a compound having a -, tine group, etc. 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, a hetaine group, etc. is synthesized, and this is reacted in equimolar amounts with a polyfunctional isonoanate such as diisocyanate to obtain a reaction product of one NCOI of diisocyanate-1 and the hydroxyl group in the above compound. Then, if OH,l of polyurethane and unreacted NGO groups are reacted,
A polyurethane into which hetain groups and the like are introduced is obtained.

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

CII□-COO11 3) Synthesis method R-N using propanezalton ( , CII□CI+□014 +2) \. II. . II 2 So'? ＼ ○ CH□C82COO CIl. CI+□011 CII2CII□011 The amount of betaine groups etc. introduced into the polyurethane resin of the present invention is preferably 0.01 to 1, Ommo β/g, more preferably 0.1 to 9.5 mmof! /
g range. The amount of the above polar group introduced is 0.01 mmo
+! If it is less than /g, a sufficient effect on the dispersibility of the ferromagnetic powder will not be observed. Further, the amount of the polar group introduced is 1. If it exceeds Ommo 1 / g, intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility, but also causes selectivity to the solvent, which may make ordinary general-purpose solvents unusable.

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 will be insufficient, and if the number average molecular weight exceeds 100,000, problems may occur during paint manufacturing processes such as mixing, transport, and coating. be.

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

Next, 1.5 mol of adipic acid, 1.7 mol of 1,4-butanediol, and 0.06 mol of the above sulfobetaine type acid-base polyfunctional monomer were charged, and the mixture was heated at 150 to 200°C for about 3 hours. The temperature was raised at 200 °C for 4 hours, and 3
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, and 80 parts of (13) diphenylmethane diisocyanate was added.
React at 0°C for 2 hours, add 20 parts of 1,4-butanediol, further react for 2 hours, and add 20 parts of 1,4-butanediol.
1 part was added and reacted for 1 hour. The molecular weight of the obtained polyurethane was Mw=35,000 and Mn=22,000.

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

That is, since the C functional group contained in the polyurethane of the present invention forms an inner salt, the adsorption force to the magnetic powder surface,
Retention force is extremely high. Moreover, since the magnetic powder contains a predetermined amount of at least one of silicon and aluminum, the adhesion of the polyurethane to the magnetic powder is further increased by the action of silicon and aluminum deposited on the surface of the magnetic powder. The time required for dispersing the magnetic powder is shortened, and the dispersion stability is improved. As a result, the magnetic powder is more densely and uniformly filled into the magnetic layer, and the output, S/N ratio, etc. are improved.

Moreover, by limiting the content of aluminum and silicon in the magnetic powder, the effect of adding aluminum and silicon becomes very significant, and no adverse effects occur.

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 metal oxide is complex, and the surface is charged with positive and negative charges due to surface hydroxyl groups due to hydration, structural defects, ion substitution, etc. Therefore, when selecting a binder for magnetic powder, consider the acidity, basicity, and
Basic strength, acidity, number of basic sites, etc. are important factors. For example, in order to uniformly disperse magnetic powder in a short time, it is necessary to use binders with acidic and basic (polar) groups of various strengths, and to adsorb these acidic and basic sites to the surface active sites of the magnetic powder. is ideal.

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 almost the same polarity but different strengths. However, in this case, the magnetic powder competitively adsorbs preferentially to the binder having a stronger functional group, making it difficult to achieve sufficient adsorption as a whole (and the dispersion stability of the magnetic paint deteriorates. It is also possible to use a binder with a polar functional group and a binder with a sub-polar functional group at the same time.However, this would result in strong interactions between the polar groups, causing the binder to reach the surface of the magnetic powder. Adsorption is difficult to occur and the viscosity of the magnetic paint increases, making it impossible to prepare the magnetic paint.

The present invention solves these problems.

In other words, the acid sites and basic sites in the inner salt in the binder are efficiently adsorbed to the surface active sites (base sites and acid sites) of the magnetic powder. Since it is contained, base sites and acid sites can be appropriately provided to the surface of the magnetic powder by the action of silicon and aluminum on the surface of the magnetic powder, and the amount of adsorption to the binder can be further increased.

It is thought that this significantly improves dispersibility.

Next, the [magnetic powder] used in the magnetic recording medium of the present invention will be further described.

When silicon is contained in the magnetic powder, the silicon content in the magnetic powder is 0.01 to 0. QO weight% is 0.05
It is more preferable to set it to 0.30% by weight. If the silicon content in the magnetic powder is less than 0.01% by weight, the surface activity of the magnetic powder will not be increased, and the adsorption of the magnetic powder to the polyurethane of the present invention will be suppressed. Even if it exceeds 1% by weight, the effect commensurate with the increase in content may not be achieved, and it may instead be achieved by adding a soluble silicon compound to a dispersion prepared by dispersing magnetic powder with magnetic properties in an aqueous Flukali solution. can.

Examples of the silicon compound include orthosilicic acid (Iln
SiOa)-metasilicate ()I2Si(h), metatrisilicate (lt23i20), metatrisilicate (l(4S
iiOa), metatetrasilicic acid (HsSi40++); -silicon oxide, silicon dioxide; sodium orthosilicate (NaaSiOa), sodium metasilicate (N
aSiO+), pyrolithium metasilicate (KzSIOz)
, orthosilicate, calcium metasilicate (Ca2Si03), barium metasilicate (BazSiO+), cohar l-(
Examples include metal silicate salts such as Ca2Si03).

These silicon compounds may be used alone or in combination.
You may use a combination of more than one species.

When aluminum is contained in the magnetic powder, the content of aluminum in the magnetic Q powder is 0.001 to 0.4.
It is more preferably 0.01 to 0,425% by weight. If the content of aluminum oxide (LJ) in the magnetic powder is less than 0.001% by weight, the surface activity of the magnetic powder cannot be increased, and adsorption of the adhesive powder to the polyurethane of the present invention is suppressed. On the other hand, even if it exceeds 0.30% by weight,
The effect commensurate with the increase in content may not be achieved,
On the contrary, it may cause deterioration of magnetic properties.

In order to attach the aluminum to the magnetic powder, for example,
It can also be carried out by adding a soluble aluminum compound to a dispersion prepared by dispersing magnetic powder in an alkaline aqueous solution.

Examples of such aluminum compounds include aluminum oxide (8β203).

If the magnetic powder contains both silicon and aluminum, the surface activity of the magnetic powder cannot be increased, and adsorption of the magnetic powder to the polyurethane of the present invention tends to be suppressed. On the other hand, 0.90
Even if the content exceeds % by weight, the effect commensurate with the increase in content may not be achieved, and the magnetic properties may deteriorate on the contrary.

When the silicon (Si) and aluminum (A A ) are used together, the ratio of the silicon (Sl) and aluminum (A N ) is (Si): (A 1.)
The ratio is usually within the range of 30:I to 1.30, preferably within the range of 20:1 to 1:10.

Magnetic powder containing aluminum and/or silicon can also be produced by bringing the magnetic powder into contact with a gas containing aluminum and/or silicon. Furthermore, in the case of a metal magnetic powder obtained by thermal reduction of goethite, the above-mentioned treatment of Al (and/or) Si may be performed at the generation or treatment stage of the raw material goethite, and then this may be reduced.

It is preferable that aluminum and/or silicon exist in the form of an oxide or a hydrous oxide in the surface region of the magnetic powder.

In addition, when forming a heavy liquid film layer of a compound film containing aluminum and a film containing a silicon compound on the particle surface of the magnetic powder, the two films may be placed either on the top or bottom, but in particular, it is preferable to form a film layer of a compound containing aluminum. When provided on the upper layer side, durability is further improved. In this case, since the silicon-containing compound coating has excellent bonding strength to both the surface of the magnetic powder and the aluminum-containing compound coating, the double coating layer and the magnetic powder are bonded together. Since the particles are strongly bound and the compound containing aluminum has higher hardness, the surface hardness of the magnetic powder can be increased.

When magnetic powder contains both aluminum and silicon,
Each magnetic powder particle may contain both aluminum and silicon, or may be a mixture of magnetic particles containing only aluminum and magnetic particles containing only silicon.

In the former case where both aluminum and silicon are present on the surface of each magnetic powder, there is less local non-uniformity in durability on the surface of the magnetic layer. On the other hand, in the latter case, the process of depositing aluminum and silicon onto the magnetic powder only takes -.times.

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.

The content of magnetic powder in the magnetic layer is 15% by volume.
It is preferable to set it to ν01% or more.

Examples of "magnetic powder" include γ-F ez O3, F el
O4, intermediate oxides of these, cobalt-containing iron oxide magnetic powder obtained by doping or depositing cobalt atoms on these iron oxide magnetic powders, ferromagnetic chromium dioxide powder, iron nitride, iron carbide, alloy metal magnetic powder, halium Examples include ferrite or ferrite modified with metals such as titanium and cobalt.

As ferromagnetic iron oxide particles, when expressed as FeOx, the value of X is generally in the range of 1.33≦X≦1.50, that is, maghemite (r - Fe20s x = 1.
50), magnetite (pe304 x = 1.33)
, and their solid solutions (FeOx = 1.33 <
x < 1.50).

The method for producing Co-doped iron oxide particles includes (1) a method in which ferric hydroxide containing cobalt hydroxide is hydrothermally treated in an alkaline atmosphere, and the resulting powder is reduced and oxidized.

(2) When synthesizing goethite, a solution of cobalt and salt is added in advance, and while adjusting the pH, goethite containing cobalt is synthesized, and this is reduced and oxidized.

(3) A method in which Co-free goethite is used as a core, a reaction similar to that in (2) is performed on the core, Co-containing goethite is grown, and then reduced and oxidized.

(4) C on the surface of acicular goethite or maghemite
A method in which Co compounds are adsorbed by treatment in an alkaline aqueous solution containing salts, followed by reduction/oxidation or heat treatment at a relatively high temperature.

There is.

Co-coated iron oxide magnetic particles are prepared by mixing acicular magnetic iron oxide and cobalt salt in an alkaline aqueous solution and heating the mixture to adsorb cobalt compounds such as cobalt hydroxide to the iron oxide particles.
This is obtained by washing and drying with water, and then heat-treating in a non-reducing atmosphere such as air or N2 gas.

In the cobalt-containing iron oxide magnetic powder, the content of cobalt is preferably 1.0 to 5.0% by weight based on the total magnetic powder.

The magnetic powder preferably has a coercive force (Hc) of 600 to 1200 oersteds. The specific surface area of the magnetic powder is preferably within the range of 10 to 10rd/g in BET value,
It is more preferable to set the particle size to 35 m/g or more, more preferably 40 n (/g or more).The average particle diameter is 0.8 to 0.1 μm on the long axis,
It is preferable to set it as about 0.3-0.01 micrometer in a short axis.

The magnetic powder preferably has an oriented shape such as a needle shape or a plate shape.

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 30 minutes.
Deaeration is performed during heat treatment for 60 minutes to remove substances adsorbed on the powder, and then the powder is introduced into a measuring device to remove nitrogen. Adsorption measurements are carried out with nitrogen at liquid nitrogen temperature (-195'c) with the I11 pressure set at 0.5 kg/ffl (generally B, E).

A method for measuring specific surface area called the method. For details, please refer to J and A.
me, Chem, Soc, 60309 (193B)). As a device for measuring the specific surface area (BET value), it is possible to use "Powder/Grain Measuring Instrument W (Canterthorpe)" which is jointly manufactured by Digestion Battery (1) and Digestion Ionics (2). A general explanation of the method for measuring specific surface area and grain size can be found in [Measurement of Granules J (J, M.

It is described in detail in DALLAVALLE, CLYDEORR Jr. (translated by Benyo and others; published by Sangyo Toshosha).
Also, "Chemistry Handbook" (Application Edition, pp. 1170-1171,
It is also described in Maruzen (published on April 30, 1966), edited by the Chemical Society of Japan. (This is the same as the specific surface area in the specification.)

Next, the overall structure of the magnetic recording medium of the present invention will be further 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-9 polymer, vinyl chloride-hynylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer,
Butadiene-acrylonitrile 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 rubber, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polynisdel polyol and polyisocyanate, urea formaldehyde Examples include resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof.

The above resins are -8O:1M, -COOM, PO(0
M) A resin containing a hydrophilic polar group such as 2 (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. That is,
These resins have polar groups in their molecules that improve their compatibility with metal magnetic powder, thereby improving the dispersibility of magnetic powder.
It is possible to improve the interlayer stability of the coating liquid by preventing the agglomeration of the metal magnetic powder, and by extension, improving the durability of the medium.

The "polyurethane in which the negative functional group forms an inner salt" of the present invention is composed of 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) is preferable, and (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 in combination, especially the hinyl chloride copolymer, can be copolymerized with a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and other copolymerizable monomers as necessary. Therefore, it can be obtained. Since this copolymer is based on vinyl synthesis, it is easy to synthesize, and various copolymer components can be selected.
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 (particularly sodium, potassium, and sodium), and potassium is particularly preferred in terms of solubility, reactivity, yield, and the like.

The above copolymerizable monomer containing a sulfonate is CH2=CH3○3M CH2= CHCH2S O3M CHz -c (CH:1)CH□SO,MCHz -
CHCH20COCH(CH□C00R)OsM CH2=CHCH20CH2CH(OH)CH2SOf
fMCH2-C (CH:+) COOC2H45O7M
CHz = CHCOOC4H3S OzMCH□-C
HCON HC(CH3) 2 CH2S O:+M
can be mentioned.

Also, as a phosphate, CH2-CHCHz OCHz CH(OH) CH2
0-P03MY' CH2= CHCON HC(CH3)2CH20CH
2= CHCHzO(CHzCHtO)mP OtMX
2 In the above, M is an alkali metal and R is 1 carbon atom.
~20 alkyl groups, Yl is H, M or CHz =C
HC1(20CH2CH(OH)CH2Y2 is H, M or CH□=CHC0NHC(CH3)2CH20H or O
M and X2 are CH2=CHCHzO(CHzCHzO)m○H or OM. Further, n is a positive number of 1 to 100, and m is a positive number of 1 to 100.

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 nistyl, 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 monomer containing the salt of the acidic group in the binder is 0.0
If the amount of the salt-containing monomer is too large, it is preferably 1 to 30 mol %, the solubility in the solvent is poor and gelation tends to occur. Furthermore, if the amount of salt-containing monomer is too small, desired characteristics 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, C, C.

VAGH) manufactured by Co., Ltd. consisted of the following copolymerized components.

1+CH2CH’)’M OH: indicates a copolymerization unit.

However, it is thought that the CHjCO-0- group here does 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 CHffCO instead of CHffCO. For example, a copolymer having the following units may be mentioned.

-(-CHz -CH-'n, -fXn○H 01 Thousand unit part containing alkali metal salt of sulfo group or phospho group) "Polyurethane in which negative functional groups form an inner salt"
These are epoxy resins (particularly phenoxy resins), polyester resins, or nitrocellulose resins (hereinafter referred to as other resins). ) is also preferably used 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 will become too bulky and the durability of the coating film will be significantly deteriorated, and the adhesion to the support will also deteriorate. Further, when the above blending ratio is less than 10 parts by weight,
Magnetic powder easily falls off.

Incorporating a carbon blank in the magnetic layer is further advantageous in terms of improved runnability and electromagnetic conversion properties, as well as a slight improvement in dispersibility, and the use of residual solvent carbon black in the magnetic layer improves light shielding. The degree can be increased. As a light-shielding carbon blank, for example, Rahe 72000 manufactured by Columbia Carbon Co., Ltd. (specific surface area L90n (/g, particle size 18
mμ), 2100.1170.1000, #100, #75, #40, #35, #30 of Mitsubishi Kasei etc. can be used.

Further, as a conductive carbon blank, for example, Columbia Carbon Co., Ltd.'s Conduct
ex) 975 (abbreviated as BET below BET value C) 25
0 n(/g, DB P oil absorption (hereinafter abbreviated as DBP)
170m j! / 100gr, particle size 24mμ),
Conductesox 900 (BE T125 n(/
g, particle size 27rnu), Conductex 4O-22
0 (particle size 20 mμ), Conductesox SC (BET2
20rd/gr, DBP115ml! /100g
r.

Particle size: 20 mμ), Parcan (Cabo
tVulcan) X C-72 (specific surface area 254n (
/g, particle size 30mμ), Palcan P (BET143
g/gr, DBP118ml/100gr,
Examples include #2000 (particle size 20m), Raven 1040.420, Black Pearls 2000 (particle size 15mμ), and #44 manufactured by Mitsubishi Kasei ■.

In addition, other carbon blanks that can be used in the present invention include Conductesox (made by Columbia Carbon) (
Conductex) -S C, (B E T220
rr (/g, DBP113 νulcan 9 (B
ET140n (/g, D B P114 m I
t/long, particle size 19 mμ), # manufactured by Asahi Carbon Co., Ltd.
80 (BET117rd/g, DBP113m
R/100g, particle size 23mμ), manufactured by Denki Kagaku Co., Ltd.)
(5100(13ET32r+(/g, 1 T
3 P 1.80 rn (! / 1.00
g, particle size 53 mμ), #22B manufactured by Mitsubishi Chemical Corporation (B
T: T55m/g, DBP 131ml
/ 100g, particle size 40mtt), 920B
(BET56m/g, DB P115m ff/1
00g, particle size 4 (1mμ), #350Q (B P,
1″47m/g, D B 1)187mn/
100g, particle size 40mμ), and also CF-9, #4000 manufactured by Mitsubishi Chemical Corporation. MA-600, Black Pearls (Black P
earls) and Monarch (Monarck) 800
, Frank Perls 700 , Black Perls 1
000, Black Pearls 880, Black Pearls 900, Black Pearls 1300, Black Pearls
Pearls 2000, Staring (SLerl: nB)
V, , :] Lachen (1 aven) 4.10, Lachen 3200, Lachen 430, Lachen 450, Lachen 825, manufactured by 3in Co., Ltd.
Lachen 1255, Lachen 1035, Lachen 100
0, Lar\n5000, Ketschenblak FC, etc.

Furthermore, in the present invention, durability can be improved by further adding a polyisocyanate-based curing agent to the magnetic paint containing a binder. , for example, tolylene diisocyanate [, diphenylmethane diisocyanate-1,
Bifunctional isocyanates such as hexane diisocyanate,
Conventionally used as a curing agent for trifunctional isonanates such as Coronate Shikumekibo +) Urethane Kogyo), Desmodur l-7 (manufactured by Bayer), or urethane prepolymers containing incyanate groups at both ends. Any polyisocyanate or polyisocyanate that can be used as a curing agent can be used. In addition, the amount of the polyisocyanate curing agent is 5 to 50% of the total amount of binder.
80 parts by weight is used.

The magnetic recording medium of the present invention can be used, for example, as shown in FIG.
52. Non-magnetic support 1 such as polyethylene terephthalate
'': l'l It has a Kf magnetic layer, and if necessary, a BCC 84 is provided on the surface opposite to the magnetic layer 2. Further, as shown in FIG. 2, an overcoat layer (00 layer) 4 is provided on the magnetic layer 2 of the magnetic recording medium of FIG.
may be provided.

Further, the magnetic recording media shown in FIGS. 1 and 2 may have an undercoat layer (not shown) provided between the magnetic layer 2 and the support 1, or may have an undercoat layer provided between the magnetic layer 2 and the support 1. You don't have to. Further, the support may be subjected to corona discharge treatment.

In addition to the metal magnetic powder and binder described above, the magnetic layer 2 also contains:
Fatty acids and/or fatty acid esters can be contained as lubricants. As a result, while demonstrating each feature of both, it offsets the defects that would occur when used alone.
Improves lubrication effect, still image durability, running stability, S
/N ratio etc. can be increased. 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 is 0.00 parts by weight per 100 parts by weight of magnetic powder.
1 to 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 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 adjusted to -
10/90 to 90/lo 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 (19) Pimelic acid (20) Acelaic acid (21) Sebacic acid (22) 1, 12-1'decanedicarboxylic acid (2
3) Octane dicarboxylic acid Examples of the above fatty acid esters are as follows.

(1) Oleyl oleate 1 (2) Oleyl stearate 1 (3) Isocetyl stearate dioleyl maleate butyl stearate butyl palmitate butyl myristate octyl myristate octyl palmitate amyl stearate 1 to 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 palmitate (24) Isopropyl myristate (25 ) Butyl laurate (26) Cetyl-2-ethyl hexalate (27) Dioleyl adipate (28) Diethyl acylate (29) Diisobutyl adipate (30) Diisodecyl adipate In addition to the above-mentioned fatty acids and fatty acid esters, other Addition of lubricants (for example, silicone oil, carboxylic acid modified, ester modified), graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide, etc.) to the magnetic layer. You may do so.

Non-magnetic abrasive particles can also be added to the magnetic layer. For example, α-alumina, chromium oxide, titanium oxide, α-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.

In addition, the non-magnetic particles contained in the hack 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-Fetus, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbide, barium sulfate, and the like. In addition, organic powders such as henzoguanamine 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, carbon bra together with the above-mentioned non-magnetic particles.

It is more preferable to use both. 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.

Regarding the thickness of the magnetic layer, it is preferable that the magnetic layer be thin in order to achieve a high S/N ratio, and thicker in terms of still durability. Therefore, 6.0 to 1.0/Im is preferable.5.
More preferably, the thickness is 0 to 2.0 μm.

The surface roughness of the magnetic layer is an average surface roughness Ra of 0.005 to
The thickness is preferably 0.020 μm. This does not reduce running performance and improves the S/N ratio.

Elements forming the non-magnetic support (A includes, for example, polyesters such as polyethylene terephthalate and polyethylene 2,6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose d-iacetate-1; Examples include plastics such as polycarbonate 1-.Furthermore, metals such as Cu, Ar1, and 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, a cart, a disk, a 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 in the range of 3 to 100 μm, preferably in 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.

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, "1 part" is all parts by weight.

<Preparation of Videotape> First, a magnetic layer t was formed on a polyethylene terephthalate heath film having a thickness of 10 μm as a support in the same manner as described above.

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 with Atsuotsu cloth 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 40 parts Barium sulfate 10 parts Nitrocellulose 25 parts N-2301
(Japan Polyurethanes) 25 parts Coronate L ()
10 parts Cyclohexanone 400 parts Methyl ethyl getone 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.

One copy of this film was cut into a 2-inch width to make each videotape shown in Table 1. However, the numerical values shown in Table 1 represent parts by weight.

(Margin below) (4G) Table-1 Synthesized with.

(a) Sulfobetaine type modified group content Number average molecular weight 22,000 Tg -20℃ polar group concentration 0
．． 04 mmol/g CH.

■ +CHz N CHz+ Polyester type (CHz
) + polyurecne chain (b) Contains carboxybetaine type modification group Number average molecular weight 15,000 Tg - 10°C Polar group concentration 0.1 ml Ilol/g CH.

■ (-CH, -N-CH2+' Polyester type (c) Phosphobetaine type Modified group content Number average molecular weight 30,000 Tg 0℃ The Co-γ-Fetus magnetic powder shown in Table-1 has the following properties. It is something.

A BCD E F Silicon content 0
．． 030 0.100 0.550 0.01 0.0
05 0.650 (wt%) Aluminum 0.000 0.010 0.200 0
．． 250 0.000 0.330 Content (wt%) Coercive force 680 720 710 850
9/10 920 (Oersted) Specific surface area 30 41 38 47 4
9 62 (BET straight, m/g) Magnetization amount 76.5 78.0 76.8 75
．． 2 78.5 77.5 (emu/g) Particle diameter (long axis) 0.4 0.3 0.25
0.3 0.25 0.20 (μm) Axial ratio 10:1 9:1 8:L 9
:l 9:l 8:1 Wood The polyurethane resins (a) to (c) according to the invention are as follows.

Polyurethane (a) according to the present invention was synthesized by the method of Synthesis Example 1, and (b) and (c) were also synthesized by the same method with a polar group concentration of 0.
071 imol/g H2 HO-P = 0 Oθ <Evaluation of videotape performance> 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> RF ratio output The output during playback of a 100% white signal is based on the tape of Comparative Example (3), and the output of Comparative Example (3)
This was determined in comparison with the tape.

Lumi-3/N: Using a noise meter (manufactured by Shibaku Co., Ltd.), the difference in S/N of the sample falling at a 100% white signal was determined by comparing the tape with a reference tape (manufactured by Konica ■).

Chroma-3/N: Using a noise meter (manufactured by Shihasoku), the difference in S/N of the sample in the chroma signal was determined in comparison with a reference tape (manufactured by Konica ■).

<Running, durability> Ginocou: VTR Sissoku Manufacturer 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 pass tape> and <virgin tape> Unused tape (virgin tape) RF output fluctuation, dynamic friction coefficient, and dropout were measured. In addition, the sample tape was packed in a VHS case, 1, and placed at 20°C and 60% RH.
Using V-6200 (manufactured by Matsushita Electric) deck, 10
The tape was run repeatedly with 0 passes (100 pass tape). Regarding this, the above measurements were carried out and the presence or absence of tape damage was also investigated.

Dynamic friction coefficient: Tape runability tester TBT3 at 25"C
00 D (Yokohama System Research Institute) Wrap 1800 tapes around a chrome-plated stainless steel 4φ bottle, tape speed l c+n/sec, population tension 2
It was measured at 0 g, and μ was calculated using the following formula.

Dropout: 1.'rosopout counter VD manufactured by Japan Victor Co., Ltd.
-5M, longer than 15 u sec, and RF
Drop out the output that is 20dB or more below the envelope foot output -1
The total length was measured individually, and the average value per minute was determined.

Table 2) Samples of Examples 1 to 4 in which the polyurethane resin according to the present invention was used and magnetic powders A to D conforming to the structure of the present invention were dispersed were the same as those in Comparative Examples (]) to (4). Excellent electromagnetic conversion characteristics, jitter, and still life for samples. Also, 100
Even after bus running tests, there was no tape damage such as edge bending or one-sided stretching, and the coefficient of dynamic friction was low. In addition, the output fluctuation range is also small. Dropouts have also remained at a low level.

Next, in the videotape of Example 1, the silicon content in the magnetic powder was changed to various values, the other configurations and prescriptions were kept the same, and videotapes were produced for each, and the RF specific output was measured. This result is shown in the third centroid.

Further, in the videotape of Example 4, the aluminum content in the magnetic ↓l) was changed to various values, and videotapes were produced for each with the other configurations and prescriptions being the same, and the RF specific output was measured. The results are shown in FIG.

From the results shown in FIGS. 3 and 4, it can be seen that by limiting the contents of silicon and aluminum as shown in Ntr, the effects of the present invention are very noticeable.

[Brief explanation of the drawing]

FIGS. 1 and 2 are partially enlarged sectional views showing examples of magnetic recording media. FIGS. 3 and 4 are graphs showing changes in RF output with respect to changes in content of dissimilar metals in magnetic powder, respectively. 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). Agent Patent Attorney Hiroshi Aisaka 0.01 (J, l (J O, 400, 600, 80 Silicon Avalanche-i (It'/.)

Claims (1)

[Claims] 1. In a magnetic recording medium having a magnetic layer containing magnetic powder and a binder, at least one of silicon and aluminum is contained in the magnetic powder (however, if silicon is contained in the magnetic powder, this The silicon content in the magnetic powder is 0.01 to 0.60% by weight, and when aluminum is contained in the magnetic powder, the aluminum content in this magnetic powder is 0.001 to 0.30% by weight. do.)
, and a polyurethane in which a negative functional group forms an inner salt is contained as the binder.