JPH0229917A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain good dispersiveness of ferromagnetic powder, to improve production stability and traveling durability and to enable high density recording by incorporating a specific ferromagnetic metal powder and a binder having specific polar groups into the magnetic layer. CONSTITUTION:The magnetic recording medium has the magnetic layer containing the ferromagnetic metal powder and the binder formed on a nonmagnetic supporting body. The magnetic powder has adsorbed water content at 1.0-2.5wt.% with 9.0-11.5pH and a specific surface area of >=45m<2>/g measured by the BET method. Into the binder at least one kind of polar group among those shown in the formulae is incorporated. In the formulae, M represents an atom of H, Li, Na or K, and M<1> and M<2> represent atoms of H, Li, Na, K or alkyl groups. To control the proportion of adsorbed water of the metal powder, the powder is allowed to stand in an atmosphere of a specific water vapor concentration, for example. Shapes of the metal powder particles are not specified.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium used for example in video tapes, audio tapes, etc. The present invention relates to a magnetic recording medium that has excellent production stability, excellent running durability and electromagnetic conversion characteristics, and can be suitably used for high-density recording.

[Issues to be solved by conventional technology and the invention j11] In recent years, for example, DAT (digital audio tape recorder) has appeared in the audio field, and in the VTR field, the width is narrower than the conventional 172-inch width standard. Due to circumstances such as the appearance and widespread use of the 8mm width standard, there is an increasing demand for high-density recording in magnetic recording media. A magnetic recording medium with excellent properties is desired.

In response to this demand, finely divided ferromagnetic powder has come to be used for the purpose of improving the electromagnetic conversion characteristics of magnetic recording media. It has a problem of poor dispersibility inside.

That is, in a magnetic recording medium using finely divided ferromagnetic powder, (1) the electromagnetic conversion characteristics may not be sufficiently improved. ■Some of the particles of the ferromagnetic powder that were not sufficiently dispersed may be detached during running.■Some of the particles detached during running may momentarily adhere to the magnetic head.
There are problems such as so-called instantaneous head clogging, in which the reproduction output decreases at this instant.

Therefore, as a solution to this problem, a magnetic recording medium using ferromagnetic metal powder with an adsorbed moisture content of 1.2% or less has been proposed (Japanese Patent Laid-Open No. 111
(See Publication No.-8728).

However, this magnetic recording medium has a problem in that it is not possible to sufficiently suppress an increase in the viscosity of the magnetic paint.

In other words, the increase in the viscosity of the magnetic paint makes it difficult to smoothly transport the magnetic paint in, for example, the magnetic paint transfer process II during the manufacture of magnetic recording media, which tends to cause partial stagnation within the transport path. ■This will lead to a decrease in production stability, which will eventually lead to dropouts in the magnetic layer, which may reduce the electromagnetic conversion characteristics.■Also, in the coating process, magnetic paint should not be used. Since smoothing cannot be performed smoothly after coating on a non-magnetic support, the smoothness of the surface of the magnetic recording medium will be impaired, leading to head clogging, edge breakage, etc., resulting in poor running durability. This has various negative effects, such as a decrease in

Therefore, the emergence of a magnetic recording medium that has good dispersibility of ferromagnetic metal powder, does not cause a decrease in production stability, and exhibits excellent running durability and electromagnetic conversion characteristics is awaited. That is the reality.

This invention has been made based on the above circumstances.

The purpose of this invention is to provide a magnetic recording medium that has good dispersibility of ferromagnetic metal powder, excellent production stability, excellent running durability, and high electromagnetic conversion characteristics suitable for high-density recording. It is about providing.

[Means for solving the above-mentioned HN] In order to solve the above-mentioned problem, as a result of intensive studies by the present inventor, it was found that the HN has a specific specific surface area and adsorbed moisture and/or pH within a specific range. A magnetic recording medium that uses ferromagnetic metal powder and a binder containing a specific resin has good dispersibility of the ferromagnetic metal powder, excellent production stability, and excellent running durability and electromagnetic conversion characteristics. This invention was achieved by discovering that it is excellent in performance and suitable for high-density recording.

That is, the structure of the invention according to claim 1 is a magnetic recording medium in which a magnetic layer containing ferromagnetic metal powder and a binder is provided on a non-magnetic support, in which the adsorbed moisture of the ferromagnetic metal powder is 1. 0% by weight or more and 2.5% by weight or less, and the specific surface area of the ferromagnetic metal powder by the BET method is 45 m / g
The binder contains a resin having a polar group, and the polar group is -3O3M, -0503M.

(However, in the formula, 1M represents a hydrogen atom, lithium, sodium or potassium, Ml and Ml each represent a hydrogen atom, lithium, potassium, sodium or an alkyl group, and Ml and Ml may be the same) A magnetic recording medium is characterized in that it is at least one type of polar group selected from the group consisting of: In a magnetic recording medium provided with a magnetic layer containing a ferromagnetic metal powder and a binder, the PH of the ferromagnetic metal powder is 9.0 or more and 11.5 or less, and the ferromagnetic metal powder is measured by the BET method. The specific surface area is 45m271 or more, the binder contains a resin having a polar group, and the polar group is 13O3M, -05OsM, (wherein M is a hydrogen atom, lithium, sodium or potassium). Ml and Ml each represent a hydrogen atom, lithium, potassium, sodium, or an alkyl group, and Ml and Ml may be the same or different. A magnetic recording medium characterized by having at least one type of polar group.

The nonmagnetic support and magnetic layer that constitute the magnetic recording medium of the present invention will be explained below.

(Nonmagnetic Support) Materials for forming the nonmagnetic support include, for example, polyethylene terephthalate and polyethylene-2,6.
- Polyesters such as naphthalates, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polycarbonates. Furthermore, metals such as Cu, An, and Zn, glass, and various ceramics such as so-called new ceramics (eg, boron nitride, silicon carbide, etc.) can also be used.

There is no particular restriction on the form of the non-magnetic support, and it may be tape-like, sheet-like, card-like, disc-like, drum-like, etc., and various materials may be used depending on the form and as necessary. can be selected and used.

When the support is in the form of a tape or sheet, the thickness is usually 3 to 1100 JL, preferably 3 to 50 JL.
ILm. Moreover, in the case of a disk shape or a card shape, it is usually 30 to 100 #Lm. Furthermore, in the case of a drum shape, it can be made into a cylindrical shape, etc., depending on the recorder used.

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

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.

(magnetic layer) A magnetic layer is provided on the non-magnetic support.

The magnetic layer is a layer formed by dispersing ferromagnetic metal powder in a binder.

Examples of the ferromagnetic metal powder include Fe-Al1 metal powder, Fe-Ni metal powder, Fe-A1-Ni
Metal powder, Fe-A Emperor-P metal powder, Fs-Old-
stodoro metal powder, Fa-Ni-8i-All-Mu metal powder, old-Go metal powder, Fe-1n-Zn metal powder, Fe-Co-Ni metal powder%F@-Ni-Zn metal powder, Fe-Go-Xi-Cr metal powder, Fe-Go
-Ni-P metal powder, Go-Ni metal powder and Go
-P metal powder, etc., and ferromagnetic metal powder whose main component is a ferromagnetic metal such as F@, Ni, and Go.

Among these, preferred are Fe-An metal powder,
Fe-A-P metal powder, Fe-old metal powder, Fe-
AJl-Ni metal powder, Fe-Co-Ni metal powder,
Aluminum and/or Fe-Xl-Zn metal powder
Alternatively, it is a metal powder containing nickel, and particularly preferred is a metal powder having an aluminum content in the range of 1 to 18% by weight. This is because metal powder containing aluminum and/or nickel has excellent weather resistance. In the magnetic recording medium according to claim 1, the adsorbed moisture of the ferromagnetic metal powder is
The amount is in the range of 1.0% by weight or more and 2.5% by weight or less relative to 0% by weight. Furthermore, it is preferable that the adsorbed water content of the ferromagnetic metal powder is in the range of 1.0% by weight or more and 2.0% by weight or less.

By adsorbing moisture to the ferromagnetic metal powder at a rate in the range of 1.0% by weight or more and 2.5% by weight or less,
While improving the dispersibility of the ferromagnetic metal powder in the magnetic layer, it is possible to suppress the increase in viscosity when made into a magnetic paint, improving production stability, and to improve the dispersibility of the ferromagnetic metal powder in the magnetic layer and the ferromagnetic metal powder described below. The running durability of the magnetic recording medium can be improved by improving the adhesion with the binder.

In order to adjust the amount of moisture adsorbed by the ferromagnetic metal powder to a ratio within the above range, it is sufficient, for example, to leave it in an atmosphere with a predetermined water vapor concentration.

In this invention, the amount of adsorbed water is a value measured by the Karl Fischer method.

If the proportion of adsorbed water in the ferromagnetic metal powder is less than 1.0% by weight, the stagnation stability will decrease when used as a magnetic coating, and as a result, when used as a magnetic recording medium, for example, head clogging may occur. The running durability may be reduced due to the tendency of edge bending. On the other hand, if it exceeds 2.5% by weight, the dispersibility of the ferromagnetic metal powder in the magnetic layer may decrease.

In the magnetic recording medium according to claim 2, the ferromagnetic metal powder has a pn of 9.0 or more and 11.5 or less. Furthermore, the ferromagnetic metal powder has a pH of 9.0 or more and 11
．． It is preferably in the range of 5 or less.

By adjusting the pH of the ferromagnetic metal powder to the above range of 9.0 or more and 11.5 or less, the running durability and electromagnetic conversion characteristics of the magnetic recording medium can be improved.

In order to make the PH of the ferromagnetic metal powder within the above range, for example, the aluminum content in the ferromagnetic metal powder may be in the range of 2 to 10% by weight, preferably 2 to 8% by weight.

In the magnetic recording medium according to claims 1 and 2, the ferromagnetic metal powder has a specific surface area of 4 by the BET method.
It is 5m2/g or more. Furthermore, it is preferable that the specific surface area of the ferromagnetic metal powder measured by the BET method is 50 m27 g or more.

By using a ferromagnetic metal powder with a specific surface area of 45 m2/g or more, the packing density of the ferromagnetic metal powder can be increased and high electromagnetic conversion characteristics can be obtained. If it is less than 45 m2/g, the electromagnetic conversion characteristics of the magnetic recording medium may not be sufficient.

There is no particular restriction on the shape of the ferromagnetic metal powder,
For example, a needle-like, spherical or ellipsoidal shape can be used.

In the magnetic recording medium according to claims 1 and 2, the binder is a resin having a polar group [hereinafter referred to as resin (A
) may be said. ] Contains.

The resin (A), together with the ferromagnetic metal powder having the specific surface area and adsorbed water and/or pH within the above range, improves the dispersibility of the ferromagnetic metal powder in the magnetic layer. , has the effect of realizing high electromagnetic conversion characteristics.

The resin (A) has -303M and -050 as polar groups.
3M, (wherein M is a hydrogen atom, lithium, or sodium, and Ml and M2 are a hydrogen atom, lithium, potassium, sodium, or an alkyl group, respectively. Also, Ml and M2 are may be different from each other or may be the same.

Examples of the resin constituting the resin (A) include vinyl chloride resin, polyurethane resin, polyester resin, and polyethylene resin.

These resins can be obtained by various methods. For example, polyester resins containing sulfonic acid metal bases are
It can be obtained by using a dicarboxylic acid containing a sulfonic acid metal base as part of the dicarboxylic acid component and condensing this with a dicarboxylic acid not having a sulfonic acid metal base together with a diol.

The polyurethane resin containing a sulfonic acid metal base is a mixture of a dicarboxylic acid containing a sulfonate metal base, a dicarboxylic acid not containing a sulfonate metal base, and a diol, which are the starting materials for the above polyester containing a sulfonate metal base. It can be obtained by condensation reaction and addition reaction using various compounds and diisocyanate.

Furthermore, a method of modifying a polyester resin, polyurethane resin, or vinyl chloride resin to introduce a polar group is also considered.

That is, these resins and e.g. C1-CH2CH2SOs M.

C-CH2CH20S03 M.

(However, in the formula, M, Ml and M2 have the same meanings as above.) This is a method of condensing and introducing the above-mentioned polar group and a compound containing chlorine into the molecule by a dehydrochloric acid reaction.

The carboxylic acid components used to obtain polyester resins and polyurethane resins include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 1,5-naphthalic acid; p-oxybenzoic acid, p-(
Aromatic oxycarboxylic acids such as hydroxyethoxy)benzoic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid; tri- and tetrameric acids such as trimellitic acid, trimesic acid, and pyromellitic acid; Examples include carboxylic acids.

Among these, preferred are terephthalic acid, isophthalic acid, adipic acid, and sebacic acid.

Examples of the dicarboxylic acid component containing the sulfonic acid metal base include 5-sodium sulfoisophthalic acid,
Examples include 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid.

Examples of the diol component include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-bentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, and dipropylene glycol. ,2
, 2.4-trimethyl-1,3-opentanediol, 1.4-cyclohexane dimetatool, ethylene oxide adduct of bisphenol, ethylene oxide adduct of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetra Examples include methylene glycol. Further, tri- and/or tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol can also be used in combination.

The incyanate components used to obtain the polyurethane resin include, for example, 4.4-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2.8-)lylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate%m- Phenyl diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3.3'-dimethoxy-4,4'-biphenylene diisocyanate, 4.4'-diisocyanate-diphenyl ether% 1,3-naphthalene diisocyanate, p
-xylylene diisocyanate, m-xylylene diisocyanate), 1,3-diisocyanate methylcyclohexane, 1,4-diisocyanate methylcyclohexane, 4,4'-diisocyanate dicyclohexane, 4,4'-diisocyanate dicyclohexylmethane, inphoron Examples include diisocyanates.

When modifying a vinyl chloride resin to introduce a sulfonic acid metal base, examples of the vinyl chloride resin include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, Vinyl chloride-vinyl acetate-vinyl maleate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl maleate-vinyl alcohol copolymer, vinyl chloride-acrylic glycidyl ether-(2-acrylamide-2-methylpropanoic acid) potassium)-(allyl-
2-hydroxypropyl ether) copolymer, etc. can be used.

Vinyl alcohol OH contained in these copolymers
group and the aforementioned Cl-CI2CH2S03M.

The chlorine of a chlorine-containing sulfonic acid metal salt such as C1-CHzGHO8OsM is mixed with an amine salt such as pyridine, picoline, or triethylamine, or an epoxy compound such as ethylene oxide or propylene oxide in a polar solvent such as dimethylformamide or dimethyl sulfoxide. A method of carrying out a dehydrochlorination reaction in the presence of a dehydrochlorination agent can be suitably used.

Among the resins (A), vinyl chloride copolymers are preferred.

The vinyl chloride copolymer can be obtained by copolymerizing a vinyl chloride monomer, a copolymerizable polymer containing an alkali salt of sulfonic acid or phosphoric acid, and other copolymerizable monomers as necessary. . This copolymer is easy to synthesize because it is based on vinyl synthesis.
Moreover, various copolymerization components can be selected, and the properties of the copolymer can be optimally adjusted.

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

Examples of the copolymerizable monomer containing a sulfonate include: CH2CH303M CH2GHCH2SO3M CI2-C(CHz)CH3S(hN
SO3NCH2-CHClh 0CH20H(OH)
CH2S(h NCI2-C(CIls)COOCzH
4SOslCH2 MausoleumCHCOOCa Hs SOs N
(:Hz-CHCONHC(Glh)zcH2s(hN
Examples include.

In addition, as a phosphate, CI2~CHG1h 0CH2CH(OH)CH2-0
-PO3M3Y CI (2 CIGO 舊IC (CH3)
21J2-0-P03N3Y2CHr-CICI20(
CHzCHzO)sPONX2 [However, in the above, M represents an alkali metal, and R has 1 to 20 carbon atoms.
Yl represents a hydrogen atom of 1M, and CH2-ClCl20GHz CH(OH) C
H2-, I2 represents a hydrogen atom, M, or CH3CN-CONHC(CH3)2C1h-, XI represents either OH or OM, I2 represents CI2-CHCIhO(CH2CH2O)m -,
O)I represents either OJ: or OM, and m and n are positive numbers from 1 to 100. ] In addition, as copolymerizable monomers to be copolymerized as necessary, for example, various vinyl esters, vinylidene chloride,
Acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, various acrylic esters,
Examples include methacrylic acid ester, ethylene, propylene, isobutyne, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, and maleic ester.

The binder in this invention 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 a molecular weight regulator, a polymerization initiator, and a hexamer can be applied as necessary.

The amount of the acidic group salt-containing monomer in the binder is 0.01 to
If the amount of the salt-containing monolayer, which is preferably 30 mol %, is too large, the solubility in solvents may be poor and gelation may easily occur. On the other hand, if the amount of salt-containing monomer is too small, desired properties may not be obtained.

It is preferable that the vinyl chloride copolymer further contains an epoxy group or a hydroxyl group.

By the way, as a conventional vinyl chloride copolymer, there is, for example, a copolymer 't' of the following monomer unit 7).

-(CH2-CHteding: 厘l →CH-CI(teτ-- 0-C-CHz 澽-(CB-CHKe1-1■ H [However, j, and l represent integers.] but,
Here, the C1h Go-0- group is considered to be unlikely to contribute to the crosslinking reaction with a curing agent or the like.

Therefore, in this invention, CHs is replaced with CO.

It is preferable to contain an epoxy group such as.

Specifically, resins having the following unit combinations can be exemplified.

-(CH2-CHteT: l →CH2-CHte1-1-(CH-CHteτ-, →Zte1-H [however, 9% r and S have the same meanings as above,
t is an integer. Further, Z is a monomer unit portion containing an alkali metal salt of a sulfo group or a phospho group.

] The molecular weight of the resin (A) is usually 1, 2. Goo~TO,
Goo, preferably 4,000 to 50,000.

If the molecular weight exceeds 70,000, the viscosity of the magnetic coating material becomes unacceptably large, and the object of the present invention may not be achieved. On the other hand, if the molecular weight is less than 2000, unreacted portions will occur during the step of applying the magnetic paint onto the non-magnetic support and curing it using a curing agent.
Low molecular weight components may remain and deteriorate the physical properties of the coating film.

Further, the resin (A) has a molecular weight of 2 per polar group.
It is desirable that the molecular weight is within the range of 00 to To, 00G. If the molecular weight per polar group is less than 200, the affinity for wood will be too strong, resulting in poor solubility in solvents and poor interaction with other resins in the binder. This may lead to a decrease in the compatibility of the magnetic layer and the moisture resistance of the magnetic layer. On the other hand, if the molecular weight per polar group exceeds TO or Goo, the dispersibility may not be sufficiently improved.

In this invention, the binder contains at least one type of the resin (A), but it is preferable that the binder contains two or more types of the resin (A). When used together.

This is because the dispersibility of the ferromagnetic metal powder in the magnetic layer can be further improved.

The blending ratio of the resin (A) is usually 5 to 40 parts by weight, preferably 10 parts by weight, based on 100 parts by weight of the ferromagnetic powder.
~30 parts by weight.

By setting this blending ratio within the above range, it is possible to improve the dispersion rate while maintaining a good dispersion state of the ferromagnetic powder in the magnetic layer.

In the magnetic recording medium of the present invention, a resin (hereinafter sometimes simply referred to as resin (B)) which does not have a polar group together with the resin (A) in the binder is used. ] may be contained.

Here, "having no polar group" means that the ferromagnetic alloy powder does not have any polar groups that are particularly easily adsorbed to the surface of the ferromagnetic alloy powder, such as the polar groups in the resin having polar groups, and This means that even if the magnetic powder has a polar group, the amount is so small that it is not substantially adsorbed to the magnetic powder.

The resin (B) has the effect of improving the mechanical strength and durability of the magnetic layer in the magnetic recording medium of the present invention, and the increase in the friction coefficient of the smooth magnetic layer surface achieved by the resin (A). It has the effect of preventing

The glass transition temperature (Tg) of the resin (B) is:

The temperature is usually 25°C or higher, preferably 45°C or higher. If the glass transition temperature (Tg) is less than 25° C., the rigidity of the magnetic layer itself decreases, and the edges of the tape may break during repeated running or head clogging may occur.

The resin (B) has an average molecular weight of about 10. Goo
Resins within the range of .about.200,000 can be used.

Among these, urethane resins are preferred.

When using a urethane resin, the blending ratio of the resin (A) and the urethane resin is usually such that the resin (A) is 80 to 1 liters.
G, preferably within the range of 80 to 20 parts by weight.

In this invention, the durability of the magnetic layer can be improved by adding a polyisocyanate curing agent to the binder together with the resin.

Examples of the polyisocyanate curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (trade name: manufactured by Nippon Polyurethane Industries), Desmodur L (trade name: manufactured by Bayer), and the like. Trifunctional isocyanates, or urethane prepolymers containing isocyanate groups at both ends, which are conventionally used as curing agents, or polyisocyanates that can be used as curing agents, can all be used. I can do it.

The amount of the curing agent used is usually 5 to 80 parts by weight based on the total amount of binder.

The blending ratio of the ferromagnetic metal powder and the binder in the magnetic layer is as follows with respect to 100 parts by weight of the ferromagnetic metal powder:
Usually, the amount of binder is 1 to 200 parts by weight, preferably 1 to 50 parts by weight.

If the amount of the binder is too large, the amount of ferromagnetic metal powder mixed may become low, resulting in a decrease in the recording density of the magnetic recording medium. If it is too small, the strength of the magnetic layer will decrease, making magnetic recording difficult. The running durability of the media may be reduced.

In the magnetic recording medium of the present invention, the magnetic layer may further contain a lubricant, an abrasive, an antistatic agent, and the like.

Examples of the lubricant include solid lubricants such as carbon black, graphite, carbon black graft polymer, molybdenum disulfide, and tungsten disulfide; silicone oil, modified silicone compound, and carbon atom number 1;
2 to 1B monobasic fatty acids, fatty acid esters (so-called waxes) consisting of monohydric alcohols having a total number of carbon atoms of 21 to 23 carbon atoms, and fatty acids having 12 to 22 carbon atoms, etc. Can be mentioned.

Among these, carbon black, modified silicon compounds, fatty acids and fatty acid esters are preferred.

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

The amount of the lubricant used is usually 0.05 to 10 parts by weight per 100 parts by weight of the ferromagnetic metal powder.

Examples of the polishing agent include aluminum oxide, titanium oxide (Tie, Tf(h), silicon oxide (SiO
1Si02), inorganic powders of silicon nitride, chromium oxide and boron carbide, and benzoguanamine resin powder.

Examples include organic powders such as melamine resin powder and phthalocyanine compound powder.

The average particle diameter of the abrasive is usually 0.1 to 1.0 m.
is within the range of

Further, the blending amount of the abrasive is 10% of the ferromagnetic metal powder.
It is usually within the range of 0.5 to 20 parts by weight relative to 0 parts by weight.

Examples of the antistatic agent include carbon black,
Conductive powders such as graphite, tin oxide-antimony oxide compounds, tin oxide-titanium oxide-antimony oxide compounds, and carbon black graft polymers; natural surfactants such as saponin; alkylene oxide-based, glycerin-based, glycidol-based, etc. Nonionic surfactants; higher alkylamines, quaternary pyridines, other heterocycles,
Cationic surfactants such as phosphoniums and sulfoniums: Anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfuric acid ester groups, and phosphoric ester groups Niamino acids, aminosulfonic acids, sulfuric acid and phosphoric acid esters of amino alcohols Examples include amphoteric surfactants such as .

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

The blending amount of the antistatic agent is 100% of the ferromagnetic metal powder.
It is usually 0.5 to 20 parts by weight.

Note that the lubricant, antistatic agent, etc. do not have a sole function; for example, a - compound may act as a lubricant and an antistatic agent.

Therefore, the above classification in this invention.

The main effects are shown, and the effects of the classified compounds are not limited by the effects shown in the classification.

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

(Manufacturing method) The magnetic recording medium of the present invention is produced by preparing a magnetic paint by cross-dispersing magnetic layer forming components such as the ferromagnetic metal powder and binder in a solvent, and then applying the obtained magnetic paint to the magnetic support. On your body! mla and drying.

For example, acetone, methyl ethyl ketone (NEW) are used as solvents for crosstalk and separation of the magnetic layer type dL component.
, methyl isobutyl ketone (NIBK) and cyclohexanone; alcohols such as methanol, ethanol, propatool and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol monoacetate. Ethers such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane; Aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene, etc. halogenated hydrocarbons and the like can be used.

When kneading the composition of the magnetic paint components, the ferromagnetic metal powder and other magnetic paint components are charged simultaneously or individually into a mixer. For example, first, the magnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined time, the remaining components are added and kneading is continued to obtain a magnetic paint.

Various types of kneading machines can be used for cross-mixing and dispersion. Examples of this crosstalk machine include two-roll mills, three-roll mills, ball mills, pebble mills, side grinders, Sqegvar i attritors, and high-speed impellers! & machines, high-speed stone mills, high-speed impact mills, dispensing machines, high-speed mixers, homogenizers, ultrasonic dispersion machines, etc.

Note that a dispersant can be used for the crosstalk dispersion of the ferromagnetic metal powder.

Examples of the dispersant include lecithin, phosphate ester, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinate ester, known surfactants, salts thereof, negative organic groups ( For example -COOH,
-PO3H) salts of polymer dispersants, and the like.

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

The amount of the dispersant added is 100 f of the ferromagnetic metal powder.
It is usually 1 to 20 parts by weight per i part by weight.

The coating solution of the magnetic layer forming component thus prepared is coated onto our magnetic support by a known method.

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

The thickness of the magnetic layer thus applied is usually 1 to 10 JLm in dry thickness.

After the magnetic layer-forming components have been applied in this way, a magnetic field alignment treatment is carried out if necessary in an undried state, and a surface smoothing treatment is usually carried out using a super calender roll or the like.

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

The magnetic recording medium of the present invention can be used, for example, by cutting it into a long shape, as a magnetic tape such as a video tape or audio tape, or by cutting it into a disk shape.
It can be used as a floppy disk, etc. Furthermore, it can also be used in a card-like, cylindrical, or other form like a normal magnetic recording medium.

[Example] Next, Examples and Comparative Examples of the present invention will be shown to further specifically explain the present invention. In addition, in the Examples and Comparative Examples described below, "1 part" represents "part by weight".

(Example 1) A magnetic layer composition having the composition shown below was prepared using a ball mill.
After mixing and dispersing for 48 hours to obtain a dispersion liquid, 15 parts of a polyisocyanate compound [trade name "Coronate L" manufactured by Nippon Polyurethane ■] was added and mixed to the dispersion liquid to prepare a magnetic paint.

Fe-AJL-based ferromagnetic metal powder 100 parts [Ai
Content about 5%, adsorbed water content 1.0%] Sodium sulfonate group-containing vinyl resin 10 parts Polyurethane resin (no polar group) 15 parts Q-AJL20s
7 parts stearic acid
2 parts Butyl stearate 1 part Methyl ethyl ketone 200 parts Toluene 200 parts The obtained magnetic paint was applied onto a polyethylene terephthalate film having a thickness of 1 Gpm so that the dry thickness was 31 Lm.

Next, the solvent was removed under heating, the surface was smoothed using a super calender, and the tape was cut into 8 mm widths to produce an 8 mm video tape.

Various objects were measured for these 8■■ video tapes.

The results are shown in Table 1.

In addition, each characteristic was measured as follows.

Paint viscosity: 3 using a B-type rotational viscometer (No. 4 rotor)
The measurement was carried out under the condition of 0 rotation.

Squareness ratio: The ratio (Bm/Br) between the residual magnetic flux density (Br) and the saturation density (B■) was determined using VSM under the condition of a measurement magnetic field of 10 KOe.

Rumi-3/)I: Using a noise meter (manufactured by Shibaku), using the tape of Comparative Example 1 as a reference, measure the difference in S/N of the sample at 100% white signal in comparison with the tape of Comparative Example 1. I asked for it.

Head clogging: Recording and playback were performed over the entire length of the tape, and the presence or absence of a decrease in RF-DOτ due to head clogging was evaluated and evaluated on the following three levels.

0: Good (no clogging).

Δ: Clogging occurred momentarily.

×: Clogging occurs for a long time did.

Powder falling: under conditions of temperature 40°C and humidity 80%.

Dirt after running the tape 100 times was observed and evaluated in the following four stages.

O: No stains observed at all.

0: Almost no stains were observed.

Δ: Stain is observed.

×: Considerable dirt is observed.

(Examples 2 to 18 and Comparative Examples 1 to 2) In Example 1, instead of the ferromagnetic powder and/or resin (A) in the magnetic paint prepared in Example 1, the ferromagnetic powder shown in Table 2 was used. A videotape was prepared in the same manner as in Example 1, except that a magnetic paint was prepared using the powder and/or resin (A), and various physical properties of the obtained videotape were measured.

The results are shown in Table 1.

Note that the vinyl chloride resin containing polar groups (sodium sulfonate group, potassium sulfonate group) in Table 2 is vinyl chloride-acrylic glycidyl ether-(2-acrylamide-2-methylpropanoic acid potassium)-(allyl-2 -Hydroxypropyl ether) copolymer and each of them is a vinyl chloride resin obtained by introducing a polar group.

Further, the urethane resins containing polar groups (sodium phosphate group, sodium sulfonate group, potassium sulfonate group) in Table 2 are the carboxylic acid components (terephthalic acid) having the polar groups.

isophthalic acid, orthophthalic acid derivatives) and the above-mentioned carboxylic acid components (terephthalic acid, isophthalic acid, orthophthalic acid) and polyols (hexanediol, neopentyl glycol, diethylene glycol), polyisocyanate-based This is a urethane resin obtained by adding 4,4-diphenylmethane diisocyanate as a curing agent.

(Raiko, hereafter blank) Table (Evaluation) As is clear from Table 1, the magnetic recording medium of the present invention can sufficiently suppress the increase in the viscosity of the magnetic paint after stagnation, and has excellent stagnation stability. It was confirmed that the electromagnetic conversion characteristics and running durability were excellent compared to the magnetic recording medium of the comparative example.

[Effect of the invention] According to this invention.

(1) The ferromagnetic metal powder is made by using a ferromagnetic metal powder having a specific specific surface area, a specific adsorbed water content and/or a specific pH, and a binder containing a resin having a specific polar group. It has excellent dispersibility and can sufficiently suppress the increase in viscosity of magnetic paint.

(2) Therefore, the magnetic paint has excellent stagnation stability and good production stability as a medium.

(3) It is difficult to cause head clogging or powder falling, and has excellent running durability. (4) It also has good electromagnetic conversion characteristics, so it can be suitably used for high-density recording. A magnetic recording medium having advantages can be provided.

Claims (2)

[Claims] (1) In a magnetic recording medium in which a magnetic layer containing ferromagnetic metal powder and a binder is provided on a non-magnetic support, the adsorbed water content of the ferromagnetic metal powder is 1.0% by weight or more and 2.5% by weight. % or less, the specific surface area of the ferromagnetic metal powder by the BET method is 45 m^2/g or more, the binder contains a resin having a polar group, and the polar group is -SO_3M, -OSO_3M, and ▲ Numerical formulas, chemical formulas, tables, etc. M^1 and M^2 may be the same or different. recoding media. (2) In a magnetic recording medium comprising a magnetic layer containing ferromagnetic metal powder and a binder provided on a non-magnetic support, the pH of the ferromagnetic metal powder is 9.0 or more and 11.5 or less, The specific surface area of the ferromagnetic metal powder according to the BET method is 45
m^2/g or more, the binder contains a resin having a polar group, and the polar group is -SO_3M, -OSO_3M, and ▲Mathematical formula, chemical formula, table, etc.▼ (However, in the formula, M represents a hydrogen atom, lithium, sodium, or potassium; M^1 and M^2 each represent a hydrogen atom, lithium, potassium, sodium, or an alkyl group; M^1 and M^2 are the same. ) A magnetic recording medium characterized in that it is at least one type of polar group selected from the group consisting of: