JPS61198426A - Magnetic recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and more specifically, a magnetic recording medium with excellent surface smoothness, magnetic powder dispersibility, durability, and output characteristics. It's about the medium.

[Conventional technology]

In recent years, with the rapid development of fields related to magnetic recording such as audio equipment, videos, and computers, there has been a growing demand for improved performance of magnetic recording media such as magnetic tape and magnetic flexible disks. Flexible disks are required to have high reproduction output and high durability for short wavelength recording. Conventionally, for this purpose, various improvements have been made to the binder in order to improve the dispersibility of the magnetic powder in the binder.

For example, 80. M group, 000M group (however, M is H, Li
, Na or K), etc. (JP-A-55-38695, JP-A-57-92425, JP-A-59-30255), tertiary ○H group and SO3M group, or 80. M group and (
! Polyurethane resins each having two OOM groups (JP-A-59-108025, JP-A-57-92422)
Attempts have been made to use materials such as (No. 1, Publication No. 1, No. 1, Publication No. 2003-2010) etc. as a binder.

In addition, for the purpose of achieving a higher N ratio of 87 and higher durability than before,
Magnetic powder is made into fine particles to increase the specific surface area of the magnetic powder. However, in this case, there are disadvantages associated with making the magnetic powder into fine particles. That is, finely divided magnetic particles have the disadvantage that they are very difficult to disperse in a binder. In order to improve this point, in JP-A-59-5425, the general formula % formula % (1) (where M is a hydrogen atom, lithium, sodium or potassium, and Ml and M2 are each hydrogen atom, lithium, sodium, potassium or alkyl group)
A method of solving the problem using a resin having at least one type of polar group selected from the group consisting of ``1'' and having a molecular weight of 5000 or less is shown.

[Problem that the invention seeks to solve]

However, although the polyurethane resins that have been developed so far have improved affinity and dispersibility for magnetic powder, the effects cannot necessarily be said to be sufficient. It has been observed that the mechanical properties of the resin deteriorate due to the polar groups, and therefore, when a magnetic recording medium is manufactured using the resin, the magnetic recording medium cannot exhibit sufficient durability.

Further, the operation of making magnetic powder into fine particles is an economically disadvantageous method. Furthermore, even when using micronized magnetic powder particles and further using a polyurethane resin having a polar group, it is currently difficult to sufficiently disperse the micronized magnetic powder particles in a binder.

[Means for solving problems]

Recently, among magnetic recording media, especially magnetic flexible disks, it has been found that higher durability can be obtained by using magnetic powder with a large particle size and smooth particle surface rather than fine particles. It has become clear through research by the present inventors that it has performance equivalent to or better than conventional finely divided magnetic powder in terms of reproduction output.

The high playback output and high durability of a magnetic recording medium are influenced by various factors, such as ■ the properties of the magnetic powder particles ■ the state of dispersion of the magnetic powder particles in the binder, etc. Ru.

The inventors of the present invention have conducted intensive studies to obtain a magnetic recording medium with high playback output and high durability by using magnetic particles with a large particle size, a smooth particle surface, and a small specific surface area. The inventors have discovered that the object can be achieved by using a polyurethane resin having a polar group as a binder, leading to the present invention.

That is, the present invention provides a magnetic recording medium in which a magnetic layer in which ferromagnetic iron oxide fine powder is dispersed in a binder is provided on a non-magnetic support, in which the ferromagnetic iron oxide fine powder has a ratio of 3 on2/r or less. To provide a magnetic recording medium, which has a surface area, and the binder is a polyurethane resin having one or more SO3M groups (M is HlLi, Na, or K) per molecule. It is.

The ferromagnetic iron oxide fine powder that can be used in the present invention includes γ-Fe205 + 7-Fe20s and Fe20s.
Examples include mixed crystals with sOn, or those obtained by coating or doping CO on these magnetic materials. The ferromagnetic iron oxide fine powder used in the present invention has a smooth surface and B
Any shape may be used as long as it has a specific surface area of 3 om2/V or less according to the IIiT method, and any shapes such as needle, plate, and spherical shapes can be used. The specific surface area of the ferromagnetic iron oxide fine powder particles is 30 m2/
If the magnetic particle is larger than F, the surface of the magnetic particle is relatively uneven and easily damaged by friction with the magnetic head, resulting in a problem in terms of durability. Moreover, dispersion into the lanthanum resin does not go well, and as a result, high reproduction output and high durability cannot be obtained. Magnetic particles with a specific surface area of less than S Om2/f have smooth surfaces, so they are not damaged by friction with the magnetic head and have excellent durability.

In the present invention, So and M groups (M
is a polyurethane resin containing H, Li, Na or K). The polyurethane resin that can be used in the present invention may be any resin as long as it has an SO3M group inside its molecular chain, one in which both ends of the molecule are incyanate groups, and one in which both ends are hydroxyl groups. It may be one in which one end is an incyanate group and the other end is a hydroxyl group. Further, the number average molecular weight of the polyurethane resin is 1000 to 100000,
Preferably 5000-5ooo.

If the number average molecular weight of the polyurethane resin is less than 1000, the mechanical properties, abrasion resistance, and moist heat resistance of the resin may be insufficient; If the polyurethane resin is dissolved in a solvent and made into a paint, although these properties are improved, the dispersibility of the magnetic powder is extremely poor, making it difficult to make a paint by dissolving the polyurethane resin in a solvent. I often get into situations. Number average molecular weight is 50
00 to so and ooo are especially advantageous in exhibiting the mechanical properties, abrasion resistance, and moist heat resistance required of the polyurethane of the present invention.゛Molecular chain internal 1'c that can be preferably used in the present invention 130. Examples of methods for producing polyurethane resins having M groups include the following methods.

(1)(a) Organic polyisocyanate, (1))
It is produced by reacting a high molecular weight polyol having So and M groups in the molecular chain, and if necessary, a chain extender (C). In this case, the chain extender may be one that does not have the above-mentioned polar group, or one that has it.

(2) (a) Organic polyisocyanate, (1))
High molecular weight polyol, and (C)' molecular chain internal K
80. It is produced by reacting a chain extender having an M group.

In this case, the high molecular weight polyol may be one that does not have the above-mentioned polar group or may have one.

In terms of ease of production and mechanical strength of the produced polyurethane resin, method (1) is preferred as the production method.

In the method (1), the organic polyisocyanate (a) includes hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, xylene diisocyanate, cyclohexane diisocyanate, toluidine diisocyanate F, 2=4-F lylene diisocyanate, 2.6 −) rerange incyane)
, 4.4'-diphenylmethane diisocyanate, p-
722 diisocyanate), m-naphthylene diisocyanate F, 1.5-naphthylene diisocyanate), 4.
4'-biphenyl diisocyanate, 3.3'-dimethylbiphenyl-4,4'-diincyanate, 3,3'
Examples include -dimethoxybiphenyl-4,'4'-diisocyanate, and hydrogenated products and mixtures of these aromatic incyanates. Among these, 4,4'-diphenylmethane diisocyanate, 2,4- and 2,6-dolylene diisocyanate, and these are particularly preferably used in the present invention from the viewpoint of the strength of the produced polyurethane resin. It is a mixture of These organic polyinsyanates are also used in method (2).

In method (1), SO3 inside the molecular chain of (b)
As a high molecular weight polyol having an M group, SO3M
A compound with a molecular weight of 500 synthesized according to a known method from a dibasic acid and/or low molecular weight glycol having a molecular weight of about 50 to 500 and a dibasic acid and/or low molecular weight glycol commonly used in the synthesis of polyester polyols.
~6000 polyester polyols may be mentioned.

SO3M used in the synthesis of the polyester polyol
Examples of dibasic acids having groups include 5-sodium sulfoisophthalic acid, 5-sodium sulfoisophthalic acid, 2
-sodium sulfoterephthalic acid, 2-potassium sulfoterephthalic acid, sodium sulfosuccinic acid, potassium sulfosuccinic acid and their mono- and/or dialkyl esters. Examples of the above-mentioned low molecular weight glycols having an SO3M group include linear diols such as 2-radium sulfo-1,4-butanediol and 2-botanium sulfo-1,4-butanediol.
3M group, a compound having ethylene oxide and/or propylene oxide added to the compound represented by the following formula, each of the following groups (H.

A sulfonated compound obtained by adding ethylene oxide and/or propylene oxide to the compound represented by the above, and an alkali metal salt compound thereof (containing one or more 80.M groups in this case), 5-sodicum Examples include ethylene oxide or propylene oxide adducts of sulfobis-β-hydroxyethyl isophthalate, 5-sodicum sulfoisophthalic acid, and sodium sulfosuccinic acid.

Furthermore, 80. Polyether polyols having a molecular weight of 500 to 8,000 obtained by adding ethylene oxide and/or propylene oxide to these dibasic acids or glycols having an M group can also be used. From the viewpoint of mechanical strength of the produced polyurethane resin, polyester polyols are particularly preferred as the high molecular weight polyols used in the present invention.

In this method, in addition to high molecular weight polyols having EIO and M groups inside the molecule, high molecular weight polyols commonly used in polyurethane resin synthesis can also be used. For example, ethylene oxide, propylene oxide, etc. are added to low molecular polyols or amine compounds. Examples include polyether polyols and polytetramethylene ether glycols obtained by adding alkylene oxide, and furthermore, ethylene glycol, propylene glycol, 1. Polyester polyols and polycondensates of polyhydric alcohols such as a-butanediol and polybasic acids such as phthalic acid, maleic acid, malonic acid, succinic acid, adipic acid, and terephthalic acid, and which have hydroxyl groups at the terminals. caprolactone polyol, polycarbonate polyol,
Examples include acrylic polyol, mustard oil, and tall oil. Furthermore, liquid rubbers having active hydrogen groups such as hydroxyl groups, amino groups, imino groups, carboxyl groups, and mercapto groups at the molecular terminals and mixtures thereof can also be used. From the viewpoint of mechanical strength of the created polyurethane resin, polyester polyols are particularly preferred as the high molecular weight polyols used in the present invention.

As the chain extender (C) in the method (1),
Chain extenders commonly used in the synthesis of polyurethane resins can be used, such as ethylene glycol, 1.2-
Propylene glycol, 1.3-propylene glycol, 1.5-butanediol, 1.4-butanediol,
Neopentyl glycol, diethylene glycol, 1,
Low molecular weight glycols such as 5-pentamethylene glycol, 1,6-hexane glycol, cyclohexane-1,4-diol, cyclohexane-4-dimetatool, bis-β-hydroxyethylhydroquinone, ethylenediamine, 1,2-propylene Diamine, 1,3-
Globylene diamine, 1.4-butanediamine, 1.6
-hexanediamine, 4゜4'-methylenebis-2-chloroaniline, 4,4'-methylenebis-2-ditylaniline 177. 4.4'-methylenebisdiphenylamine, inphoronediamine, 2.4-diaminotoluene, 2
．． Examples include low molecular weight diamines such as 6-diaminotoluene and mixtures thereof.

The polyurethane resin that can be used in the present invention has an 80% polar group inside its molecular chain. K 000M group other than M group (where M is H, Li, Na, or X), PO (OM')
2 groups (however, M' is a monovalent hydrocarbon group with or without a hydroxyl group), PO (OM' ) group (however, M' is H,
Contains one or more polar groups such as Li, Na, or ammonium), OH groups (provided that the OH groups are located at positions other than both ends of the molecule, and are primary, secondary, or tertiary). 0 In order to introduce these polar groups into a polyurethane resin, (A) synthesize a polyurethane resin using a high molecular weight polyol having these polar groups (B) a chain extender having these polar groups Examples include methods such as synthesizing polyurethane resin using.

Among the above-mentioned high molecular weight polyols, those having a C00M group include glycols represented by the general formula % (1) (wherein R is an alkyl group having 1 to 3 carbon atoms), ethylene glycol, and trimethylene glycol. , polyester polyols obtained by a known dehydration condensation reaction from a glycol such as tetramethylene glycol and a carboxylic acid such as adipic acid, heptanocinic acid, phthalic acid, etc. Examples include polyether polyols having a 000M group obtained by adding ethylene oxide and/or propylene oxide to the glycol represented by the formula. As the glycol represented by the above general formula (r), 2.2-
Examples include dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, and the like.

In addition, as a chain extender having a 000M group, 2.2
-dimethylolpropionic acid, 2.2-dimethylolbutyric acid, 2.2-dimethylolvaleric acid, 1゜2-diaminotoluenoic acid, diaminobenzoic acids, s,s'-dicarboxybenzidine, s,s'-carboxy- 4,4'-
Examples include diaminodiphenylmethane and ethylene oxide or propylene oxide adducts of these aminocarboxylic acids.

Further, as a chain extender having a PO(OM') group, a monophosphoric acid ester of a polyhydric alcohol such as glycerin or trimethylolpropane, or a compound having the following general formula (I[
) and the like.

(In the formula, M' is a monovalent hydrocarbon group with or without a hydroxyl group, and these may be different.
1, R2 is a divalent alkylene group or oxyalkylene group with or without a substituent, and may be the same or different. Y represents a hydroxyl group or a hydrogen atom. ! is 0 to 10, n + n2 is an integer from 1 to 10) Formula (
Specific examples of what is represented by I[) include those shown below.

0H.

Oh.

n Furthermore, examples of the chain extender having a FO(OM") group include those represented by the following general formula @).

(In the formula, M# is H, Li, Na, jC, or ammonium salt. R1 and R2 have a substituent or have a divalent (7) alkylene group or an oxyalkylene group, and may be the same or different. It's okay. nl.

(n2 represents an integer of 1 to 10) Compounds used when forming the ammonium salt of the compound represented by formula (b) include the general formula % formula % () (in the formula R,, R,, R, are each independently selected from a saturated or unsaturated alkyl group, alkanol group, cycloalkyl group, alkylaryl group, aralkyl group, aryl group or hydrogen). Specific examples of compounds represented by the above formula (@) include the following, and these compounds and salts of these compounds can be used.

Among chain extenders having an OH group, examples of chain extenders having a primary OH group include N-hydroxyethylethylenediamine, 1,3-diamino-2-propanol, etc. Examples of the chain extender include glycerin, ethylene oxide adduct of glycerin 1
11216-hexanetriol 5a-C bis(2-hydroxyethyl)]-]2-hydroxypentane and jetanolamine propylene oxide adducts, etc., and examples of the chain extender having a tertiary OH group include,
1,2,3-hydroxy-2-ethylfuropane, 1,2
j-hydroxy-2-ethylfuropane, 1,2.4-hydroxy-2-methylbutane, 1,2.5-hydroxy-2-methylpentane, 1,3.5-hydroxy-
5-methylpentane, 1,3.6-hydroxy-5-methylhexane, 1,2,5.6-hydroxy-2,3-
dimethylhexane, 1,2,4.6-hydroxy-2,
Examples include 4-dimethylhexane alone or in mixtures.

In producing the polyurethane resin used as the binder in the magnetic recording medium of the present invention, conventionally known methods can be used. For example, after thoroughly mixing the reactants, the reaction mixture is poured onto a flat plate or a pan). A method of heating, then cooling and then crushing, or a single or mixed solvent such as dimethylformamide, toluene, xylene, benzene, dioxane, tetrahydrofuran, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, etc. A manufacturing method such as a solution reaction method in which the reaction is carried out in an organic solvent of the system can be adopted. On this occasion,
A reaction catalyst can also be added to reduce the reaction temperature or shorten the reaction time. Specific examples of reaction catalysts include amine compounds and salts thereof such as triethylenediamine, tetramethylethylenediamine/nato-2methylhexanecyaquine, dibutyltin dilacrate, tin octylate, and octylic acid. Examples include organometallic compounds such as lead and manganese octylate, and mixtures thereof. In addition, for the purpose of increasing the stability of polyurethane resin, antioxidants, ultraviolet absorbers,
Hydrolysis inhibitors and the like can be added alone or in combination.

Further, in the present invention, in order to improve the durability of the polyurethane resin, the polyurethane resin is used after being cured using a suitable curing agent.

Curing agents that can be used in the present invention include:
Examples include low molecular weight polyisocyanates having two or more incyanate groups, and compounds in which a polyisocyanate compound is reacted with a low molecular weight polyol to form an isocyanate group at the end of the molecule, and the molecular weight thereof ranges from 150 to 70.
Among these, low molecular weight polyisocyanates having two or more incyanate groups are particularly preferred.

As the low molecular weight polyinsyanate having two or more incyanate groups, (a) in the method (1) above is used.
In addition to those mentioned above, mention may be made of reaction products of 3 moles of diisocyanate such as tolylene diisocyanate and hexamethylene diisocyanate and 1 mole of trimethylolpropane, and polyfunctional incyanate compounds such as modified diphenylmethane diisocyanate and polyphenylmethane polyisocyanate. I can do it. These compounds are manufactured by Nippon Polyurethane Co., Ltd. under trade names such as "Coronate,""CoronateHLJ,""Coronate 2030 J,""MillionateMRJ," and "Millionate MTLJ. T,
J,rDesmodule N","Desmodule L",
With product names such as ``Desmodule HL'', ``Desmodule R'', and ``Desmodule RFJ'', Shikinichi Pharmaceutical Co., Ltd.
Takenate) D-102J, "Takenate D-11ONJ
, ``Takenate D-202J'' and other trade names.

In the present invention, polar group-containing polyurethane resin 100
The mechanical strength, abrasion resistance, and
Heat resistance, heat and humidity resistance, solvent resistance, and adhesion to substrates can be greatly improved.

The polyurethane resin having a polar group used in the present invention can be used in combination with a generally known polyurethane resin or other resins. For example, resins used in combination include nitrocellulose, cellulose acetate,
Cellulose derivatives such as cellulose acetate butyrate; salts such as vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl acetate/vinyl alcohol copolymer, vinyl chloride/vinyl acetate/maleic acid copolymer; vinyl acetate resin; vinylidene chloride / Vinylidene chloride resins such as vinyl chloride copolymers and vinylidene chloride/acrylonitrile copolymers; Polyester resins such as alkyd resins and linear polyesters; (meth)acrylic acid/acrylonitrile copolymers, (meth)
Acrylic resins such as methyl acrylate/acrylonitrile copolymer; acetal resins such as polyvinyl acetal and polyvinyl butyral; phenoxy resins, epoxy resins, polyamide resins, butadiene/acrylonitrile copolymers, styrene/butadiene copolymers, and the like.

These resins may be used alone or in combination.

The magnetic recording medium of the present invention uses a polyurethane resin produced by K as described above as a binder, and a magnetic paint in which the binder, ferromagnetic iron oxide fine powder, additives, etc. are dispersed together with an organic solvent is coated on a non-magnetic support. It is manufactured by coating it on the body and drying it. The ratio of the binder and the ferromagnetic iron oxide fine powder in this case is 10 to 10 parts by weight of the binder to 100 parts by weight of the ferromagnetic iron oxide fine powder.
The amount is 100 parts by weight, preferably 20 to 50 parts by weight. That is, if the amount of binder is less than 10 parts by weight with respect to 100 parts by weight of ferromagnetic iron oxide fine powder, the bonding force between the binder and the magnetic powder decreases, resulting in poor mechanical strength and wear resistance. In addition, if more than 100 parts by weight of the binder is used, the magnetic powder density in the magnetic layer decreases, and sufficient performance (playback output, etc.) as a magnetic recording medium may not be obtained. do not have.

In particular, when 20 to 50 parts by weight of a binder is added to 100 parts by weight of magnetic powder, not only the mechanical strength and abrasion resistance, which is the purpose of the present invention, are enhanced, but also the playback output of the magnetic recording medium is improved. It is also preferable from the point of view.

The magnetic layer consisting of a binder and fine ferromagnetic iron oxide powder is formed by adding aluminum oxide, chromium oxide, silicon oxide as reinforcing agents, plasticizers such as dibutyl phthalate, triphenyl phosphate, zinc stearate, Lubricants such as silicone oil, dispersants such as soybean oil lecithin,
Various antistatic agents such as carbon black can also be added.

These materials constituting the magnetic layer are dissolved in an organic solvent to prepare a magnetic coating, and a magnetic recording medium is manufactured by coating this on a support. Solvents for preparing magnetic paints include ketones such as acetone and methyl ethyl ketone, alcohols such as methanol and ethanol, esters such as ethyl acetate and butyl acetate, ethers such as dioxane and tetrahydrofuran, and benzene and toluene. Examples include aromatic hydrocarbon solvents and aliphatic hydrocarbon solvents such as hexane.0 The support to which the magnetic paint is applied may be non-magnetic, such as polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, etc. , cellulose derivatives such as cellulose triacetate, polycarbonate, polyvinyl chloride, polyimide, polyamide,
Alternatively, metals such as aluminum may be used. [Function] In the present invention, ferromagnetic iron oxide fine powder having a specific surface area of Som2/ or less and 80. When manufacturing a magnetic recording medium using an M group-containing polyurethane resin, the mechanism of action of these two materials to bring about the effects of the present invention will be described below.

Although the mechanism of this action is not necessarily clear, since the magnetic powder with a small specific surface area used in the present invention generally has a smooth surface, it is thought that it is extremely unlikely to be damaged by friction with the magnetic head. Therefore, it is excellent in terms of durability. On the other hand, magnetic powder particles with a large specific surface area have relatively uneven surfaces.
Easily damaged by friction with the magnetic head.

However, since the magnetic particles used in the present invention have a small specific surface area, the adhesive strength between the particles and the binder in one magnetic layer is low, and there is a slight tendency for the durability to decrease. Therefore, by using a polyurethane resin having So and M groups, which interact particularly strongly with magnetic powder particles, as a binder, the bonding force at the interface between the magnetic powder and the binder is improved, and as a result, the magnetic powder particles can be bonded to the magnetic layer. Because it can be strongly held in
It is thought that a high reproduction output can be obtained due to the high dispersion effect that the M group originally has.

〔Example〕

The present invention will be specifically explained below with reference to Examples.
The present invention is not limited to these examples. In addition, all "parts" in one example indicate "parts by weight."

(Example of synthesis of polyester polyol) Isophthalic acid, adipic acid,
A polyester polyol (A) having a molecular weight of 2000 and having one SO and Na group per molecule was synthesized from dimethyl 5-sodium sulfoisophthalate, ethylene glycol, and neopentyl glycol.

(Production example of polyurethane resin) Production example 1 In a reaction vessel equipped with a thermometer, a stirrer, and a reflux type condenser, methyl ethyl ketone sbzm, 90 parts of cyclohexanone, 60 parts of polyester polyol cA), and polybutylene adipate (molecular weight 2000) were placed. 124 parts, butanediol 17 parts, neopentyl glycol 10 parts s 4,
Add 90 parts of 4'-diphenylmethane diisocyanate and 0.5 part of dibutyltin silacrate as a catalyst,
The reaction was carried out at ℃ for 10 hours.

The obtained polyurethane resin has So and Na groups as polymer 1.
It has 3 molecules and its molecular weight is 30.000
Production Example 2 In a container similar to Production Example 1, 302 parts of methyl ethyl ketone,
40 parts of polyester polyol (A), 3 parts of polybutylene adipate (molecular weight 2000) ICl, 13 parts of butanediol, 48 parts of 4,4'-diphenylmethane diisocyanate, 0.5 parts of dibutyltin dilaurate as a catalyst
of the mixture was added, and the mixture was reacted at 80°C for 10 hours.

The obtained polyurethane resin had one So or Na group per polymer molecule, and its molecular weight was 10,000.Production Example 3 Polyester polyol (A) used in Production Example 1
Polybutylene adipate (molecular weight 2000)
) A polyurethane resin was produced in the same manner as in Production Example 1 except that

Production Example 4 Polyester polyol (A) used in Production Example 2
Instead of polycaprolactone polyol (molecular weight 20
A polyurethane resin was produced in the same manner as in Production Example 2, except that 0) was used.Example 1 -co-adhered y-Fe20. (Specific surface area 25 rn2/
l)・1・・100 parts・Vinyl lye) VAGI Union Carbide Co., USA, vinyl chloride-vinyl acetate-vinyl alcohol copolymer)
20 parts Polyurethane of Production Example 1 (non-volatile content 40%) -75 parts Carbon plaque 3 parts Lubricant 2 parts Methyl ethyl ketone 200 parts・Cyclohexanone...100 parts After dispersing and mixing the above composition in a ball mill for 488 hours to prepare a magnetic paint, 100 parts
After adding a curing agent (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) and dispersing and mixing for an hour, a dry film thickness of 1.2 μm was coated on a polyethylene terephthalate base film with a thickness of 75 μm.
After coating to a thickness of μm, it was calendered, cured and aged, and then cut into a predetermined size to produce a magnetic disk.

For Examples 2 to 6 and Comparative Examples 1 to 5 below, magnetic disks were produced in the same manner as in Example 1. In addition, in each composition, '7AG11. Since the types and amounts of carbon black, lubricant, and solvent were exactly the same as in Example 1, their descriptions were omitted.

Example 2 ・CO deposited r-Fe,,O,(specific surface area 20 m2/
f)...100 parts Polyurethane of Production Example 1 (40% non-volatile content)----
-75 parts Example 3 -Co deposited 7-Fe2O3 (specific surface area 10m22/g)
... e... 100 parts Polyurethane of Production Example 1 (non-volatile content 40%) - fist 0 75 parts Example 4 Co coated t"-Fe20. (Specific surface area 25 In2
/f) 1.. 9100 parts Polyurethane of Production Example 2 (40% non-volatile content) ---
- 75 parts Example 5 - co-adhered r-Fe2o, (specific surface area 20 m27
f)...100 parts Polyurethane of Production Example 2 (40% non-volatile content) 1-0
75 parts Example 6 - co-adhered 7-Fe 205 (specific surface area 10 m22
/g) φ---- 100 parts - Polyurethane of Production Example 2 (40% non-volatile content) -...
・ 75 parts Comparative Example 1 Bow 0 coating r-Pe, , O, (specific surface area 20 m2/l)■
- 100 parts - Thermoplastic polyurethane resin (N-23 (N, manufactured by Nippon Polyurethane Industry Co., Ltd.) (40% non-volatile content) - φψ
075 parts Comparative Example 2 CO adhesion r-ye,, o, (specific surface area 60 m2/
t)・-San〇Ken 100 parts・Polyurethane of Production Example 3 (40% non-volatile content)・1 fist・
75 parts Comparative Example 3 -co adhesion γ-ve2os (specific surface area 45 m22/
g)・1・100 parts・Polyurethane of Production Example 4 (non-volatile content 40%)・・・
- Table 1 shows the results of measuring various properties of the magnetic disks obtained in Examples 1 to 6 and Comparative Examples 1 to 3 containing 75 parts or more.

Table 1 (Note) Report 1: ◎Excellent O Excellent Δ Average × Poor × × Very poor This was done by observing the surface condition. Regarding the output, we installed the created magnetic disk in the drive and output 250K.
The evaluation was made by measuring the output in Hz. As for durability, attach the created magnetic disk to the drive,
Evaluation was made by measuring the time it took for the output to drop to 50%.

〔Effect of the invention〕

As specifically shown in the examples, the magnetic recording medium of the present invention has unprecedented effects in terms of magnetic particle dispersibility, reproduction output, and durability. This effect is due to the use of magnetic powder having a specific surface area of 50 m22/g or less and the use of polyurethane resin having SO3M groups as polar groups. This effect allows the performance of the magnetic recording medium to be maintained at an extremely high level compared to the performance of conventional ones. It is thought that it can meet the demand for durability.

Applicant's agent Kaoru Furuya Proceedings Proceedings Proceedings 1
Issued on April 3, 1985 1, Indication of the case Patent Application No. 60-38506 2, Name of the invention Magnetic recording medium 3, Person making the amendment Relationship to the case Patent applicant (091) Kao Soap Co., Ltd. 4 , Agent: Nakai Building 6, 1-3 Nihonbashi Yokoyama-cho, Chuo-ku, Tokyo Contents of amendment (1) Specification page 15, lines 12-13 "Hydroxyl group...
``Hydrocarbon group'' was corrected to ``■* Lt+ Nat K+ Thiaminen (1) ``or ammonium'' on page 15, line 14, was corrected to ``, amine, ammonia, or alkyl group.'' Next, insert "and/or tetrahydrofuran" (11. Corrected "polyether" at the end of page 16 to "polyalkylene ether" (1) Corrected "polyether" to "polyalkylene ether" on page 18, line 1-2 "Hydroxyl group...hydrocarbon group") ” was corrected to “rH, Li, Na, K, amine, ammonia or alkyl group” (1) Lines 4-3 from the bottom of 19, “or ammonium salt” was corrected to “, amine, ammonia or alkyl group”

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer in which ferromagnetic iron oxide fine powder is dispersed in a binder is provided on a non-magnetic support,
The ferromagnetic iron oxide fine powder has a specific surface area of 30 m^2/g or less, and the binder is SO_3M group (however,
1. A magnetic recording medium, wherein M is a polyurethane resin containing one or more H, Li, Na, or K per molecule.