JP2980919B2 - Magnetic recording media - Google Patents

Description

The present invention relates to a magnetic recording medium used for, for example, a video tape, an audio tape, and the like.
The present invention relates to a magnetic recording medium having good dispersibility of ferromagnetic powder, excellent production stability, and excellent running durability and electromagnetic conversion characteristics.

[Prior Art and Problems to be Solved by the Invention] In recent years, for example, in the audio field, DAT (Digital Audio Tape Recorder) has appeared, and in the VTR field, the width is smaller than the conventional 1/2 inch width standard. Narrow 8
Due to the fact that the mm width standard has appeared and is becoming widespread,
With respect to magnetic recording media, demands for high-density recording are increasing, and higher-performance magnetic recording media, that is, magnetic recording media excellent in electromagnetic conversion characteristics and running durability, are desired.

In response to this request, fine-grained ferromagnetic powders have been used for the purpose of improving the electromagnetic conversion characteristics of magnetic recording media. Poor dispersibility in the interior.

As a result, in a magnetic recording medium using finely divided ferromagnetic powder, the electromagnetic conversion characteristics may not be sufficiently improved. Some of the particles that are detached during running may adhere to the magnetic head instantaneously, and at this moment, the reproduction output is reduced. There are various problems that the smoothness is impaired, head clogging and edge breakage are liable to occur, and the running durability is reduced.

Therefore, while improving the dispersibility of the ferromagnetic powder, a magnetic recording medium having excellent running durability and electromagnetic conversion characteristics without deteriorating the production stability (stability of the magnetic paint, etc.) can be obtained. It is the fact that the appearance is awaited.

The present invention has been made based on the above circumstances.

An object of the present invention is to provide a magnetic recording medium having good dispersibility of ferromagnetic powder, excellent production stability, excellent running durability, and high electromagnetic conversion characteristics suitable for high-density recording. It is in.

[Means for Solving the Problems] In order to solve the problems, the inventors of the present invention have conducted intensive studies, and as a result, have determined that the silicon content within a specific range, a specific average long axis length, and a specific The magnetic recording medium having a magnetic layer formed of a ferromagnetic powder having an axial ratio within a range and a specific resin and a specific compound has good dispersibility of the ferromagnetic powder and production stability. The present invention has been found to be excellent in (e.g., stagnant stability of a magnetic paint), excellent in running durability and electromagnetic conversion characteristics, and suitable for high-density recording.

That is, the constitution of the present invention comprises a ferromagnetic powder containing silicon at a ratio of 0.1 to 0.35% by weight, having an average major axis length of 0.35 μm or less and an axial ratio of 7 to 11, and -SO ₃ M (M
Represents hydrogen or an alkali metal. The present invention relates to a magnetic recording medium comprising a magnetic layer having a polyvinyl chloride resin having the formula (1) and a phosphoric ester compound formed on a nonmagnetic support.

The nonmagnetic support and the magnetic layer constituting the magnetic recording medium of the present invention will be described below.

(Non-magnetic support) Materials for forming the non-magnetic support include, for example, polyethylene terephthalate and polyethylene-2,6.
-Polyesters such as naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polycarbonate. Further, metals such as Cu, Al, Zn, etc., glass, and various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.) can also be used.

There is no particular limitation on the form of the non-magnetic support,
Any of a tape shape, a sheet shape, a card shape, a disk shape, a drum shape and the like may be used, and various materials can be selected and used according to the form and as needed.

The thickness of these supports is usually 3 to 100 μm, preferably 3 to 50 μm in the case of a tape or sheet.
It is. In the case of a disk or card, the thickness is usually 30 to 100 μm. Further, in the case of a drum shape, a form corresponding to the recorder to be used, such as a cylindrical shape, can be adopted.

A back coat layer may be provided on the surface of the non-magnetic support on which the magnetic layer is not provided (the back surface) for the purpose of improving the runnability of the magnetic recording medium, preventing charging and preventing transfer, and the like.

Further, on the surface of the non-magnetic support on which the magnetic layer is provided, for the purpose of improving the adhesion between the magnetic layer and the non-magnetic support, and the like,
An intermediate layer (for example, an adhesive layer) may be provided.

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

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

Examples of the ferromagnetic powder include γ-Fe ₂ O ₃ , Fe
₃ O ₄ , Co-adsorbed iron oxide, iron oxide magnetic powder such as Co solid-solution iron oxide, Fe, Ni, Co, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, Fe
-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co-Ni alloy, Fe, Ni, metal magnetic powder whose main component is Co or the like, CrO _2, Fe ₄ N, like other magnetic powders such as BaO-6Fe ₂ O _3.

Among them, γ-Fe ₂ O ₃ , Co-containing iron oxide and Cr ₂ O ₃ are preferable.

In the magnetic recording medium of the present invention, the silicon content of the ferromagnetic powder is 0.1% with respect to 100% by weight of the ferromagnetic powder.
0.30.35% by weight, preferably 0.15-0.30% by weight. Further, the ferromagnetic powder has an average major axis length of 0.35 μm or less, preferably 0.25 to 0.33 μm, and an axial ratio of 7 to 11, preferably 9 to 10.

The ferromagnetic powder contains the silicon in the range of 0.1 to 0.35% by weight, the average major axis length is 0.35 μm, and the axial ratio is in the range of 7 to 11. While improving the dispersibility, it is possible to improve the production stability by suppressing the increase in viscosity when the magnetic paint is formed, and to improve the adhesion between the ferromagnetic powder and the binder described below in the magnetic layer. As a result, the running durability of the magnetic recording medium can be improved.

In other words, the silicon content in the ferromagnetic powder is
If it is less than 0.1% by weight, the stagnant viscosity of the magnetic paint increases, while if it exceeds 0.35% by weight, the magnetic properties deteriorate. When the average major axis length of the ferromagnetic powder is 0.35 μm or more, the surface properties of the medium are reduced, and the S / N ratio is deteriorated. Also,
When the axis ratio of the ferromagnetic metal powder is 7 or less, the magnetic field orientation decreases and the output deteriorates. On the other hand, if it exceeds 11, dispersion becomes difficult and the filter pressure increases.

The shape of the ferromagnetic powder is not particularly limited as long as the average major axis length and the axial ratio are within the above specified range,
For example, a needle-like, column-like, or ellipsoid-like shape can be used.

In the magnetic recording medium of the present invention, -SO ₃ M (however,
M represents a hydrogen atom or an alkali metal. ) (Hereinafter referred to as resin A). ] The ferromagnetic powder having the average major axis length, silicon and the axial ratio within the above range, and the phosphate compound further improve the dispersibility of the ferromagnetic powder in the magnetic layer. And acts as a binder to realize high electromagnetic conversion characteristics.

-SO ₃ M (however, M represents. A hydrogen atom or an alkali metal) contained in the resin A, a vinyl alcoholic OH groups contained in the polyvinyl chloride resin, Cl @ -
And chlorine sulfonic acid metal salt containing chlorine, such as CH ₂ CH ₂ SO ₃ M, dimethylformamide, in a polar solvent such as dimethyl sulfoxide, for example pyridine, picoline, amine salts such as triethylamine, ethylene oxide, It can be suitably produced by a method of performing a dehydrochlorination reaction in the presence of a dehydrochlorination agent such as an epoxy compound such as propylene oxide.

The metal M of the resin A is an alkali metal such as lithium, potassium and sodium, and potassium is particularly preferable in terms of solubility, reactivity, yield and the like.

Examples of the polyvinyl chloride resin include vinyl chloride-vinyl acetate copolymer and 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-acryl glycidyl ether -(2-acrylamido-2-methylpropane potassium)-(allyl-2-hydroxypropyl ether) copolymer or the like can be used.

The vinyl chloride copolymer can be obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing a salt of sulfonic acid, and if necessary, another copolymerizable monomer. Since this copolymer is obtained by vinyl synthesis, it is easy to synthesize, and various copolymer components can be selected, so that the characteristics of the copolymer can be adjusted optimally.

Examples of the copolymerizable monomer containing a sulfonate include CH ₂ CHCHCH ₂ SO ₃ M ¹ CH ₂ ＣC (CH ₃ ) CH ₂ SO ₃ M ¹ CH ₂ CHCHCH ₂ OCOCH (CH ₂ COOR) ^{_{SO 3 M 1 CH 2 = CHCH}} 2 OCH 2 CH (OH) CH 2 SO 3 M 1 CH 2 = C (CH 3) COOC 2 H 4 SO 3 M 1 CH 2 = CHCOOC 4 H 8 SO 3 M 1 CH 2 _{= CHCONHC (CH 3) 2 CH} 2 SO 3 , etc. M ¹ and the like.

[However, in the above, M ¹ represents an alkali metal,
R represents an alkyl group having 1 to 20 carbon atoms. Examples of the copolymerizable monomer to be copolymerized as necessary include various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, various acrylic esters, methacrylic esters, Ethylene, propylene,
Examples thereof include isobutene, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, and maleic ester.

The resin A in the present invention is emulsion polymerization, solution polymerization,
It is polymerized by a polymerization method such as suspension polymerization or bulk polymerization. In any of the methods, a known technique such as divisional addition or continuous addition of a molecular weight regulator, a polymerization initiator, and a monomer can be applied as necessary.

The mixing ratio of the binder is usually 5 to 40 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

By setting the compounding ratio within the above range, the dispersion state of the ferromagnetic powder in the magnetic layer can be improved and the dispersion speed can be improved.

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

Examples of the polyisocyanate-based curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.), Desmodur L (trade name, manufactured by Bayer AG) ) Or a polyisocyanate that can be used as a curing agent, such as a trifunctional isocyanate or a urethane prepolymer containing an isocyanate group at both terminals. can do.

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

The mixing ratio of the ferromagnetic powder and the binder in the magnetic layer is usually 1 to 200 parts by weight, preferably 1 to 50 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

If the amount of the binder is too large, the amount of the ferromagnetic powder may be reduced as a result and the recording density of the magnetic recording medium may decrease. Running durability may decrease.

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

This dispersant is used when magnetic powder is separated, magnetic powder is well dispersed in the binder resin and mixed. The dispersion of the magnetic powder has the greatest effect on the properties of the tape. Usually, for example, known surfactants such as lecithin, phosphate ester, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinate and the like, and salts thereof, negative polar groups (for example,- COOH,-
SO ₃ H, —PO ₃ H ₂ ) -containing polymers and salts thereof.

In the present invention, a phosphate compound having the following general formula is further employed.

The amount of the compound is usually 1 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder.

[However, A is -OH, -OM ² (where M ² is an alkali metal atom) or R represents a hydrogen atom or an aliphatic residue having 1 to 30 carbon atoms, n
Is an integer of n ≧ 6. Examples of the lubricant include solid lubricants such as carbon black, graphite, carbon black graft polymer, molybdenum disulfide, and tungsten disulfide; silicon oil, modified silicon compounds, and one base having 12 to 16 carbon atoms. Fatty acid esters (so-called waxes) composed of a fatty acid, a monohydric alcohol having 21 to 23 carbon atoms in total with the fatty acid, and fatty acids having 12 to 22 carbon atoms.

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

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

The amount of the lubricant to be used is generally 0.05 to 10 parts by weight based on 100 parts by weight of the ferromagnetic powder.

Examples of the abrasive include inorganic powders of aluminum oxide, titanium oxide (TiO, TiO ₂ ), silicon oxide (SiO, SiO ₂ ), silicon nitride, chromium oxide and boron carbide, benzoguanamine resin powder, melamine resin powder, and phthalocyanine compound. Organic powders such as powders.

The average particle size of the abrasive is usually in the range of 0.1 to 1.0 μm.

Further, the amount of the abrasive is usually in the range of 0.5 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder.

Examples of the antistatic agent include carbon black, graphite, tin oxide-antimony oxide compounds,
Conductive powders such as tin oxide-titanium oxide-antimony oxide compounds and carbon black graft polymers; natural surfactants such as saponins; nonionic surfactants such as alkylene oxide, glycerin and glycidol; higher alkylamines; Cationic surfactants such as quaternary pyridine, other heterocycles, phosphonium and sulfoniums: Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, and phosphate group: amino acids And amphoteric surfactants such as aminosulfonic acid, sulfuric acid and phosphoric acid ester of amino alcohol.

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

The compounding amount of the antistatic agent is usually 0.5 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder.

The lubricant, the antistatic agent and the like do not have only a single action. For example, one compound may function as a lubricant and an antistatic agent.

Therefore, the above-mentioned classification in the present invention shows the main action, and the action of the classified compound is not limited to the action shown in the classification.

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

(Manufacturing method) The magnetic recording medium of the present invention is prepared by kneading and dispersing the magnetic layer forming components such as the ferromagnetic powder and the binder in a solvent to prepare a magnetic paint, and then applying the obtained magnetic paint to the non-magnetic support. It can be manufactured by coating and drying.

Examples of the solvent used for kneading and dispersing the components for forming the magnetic layer include acetone, methyl ethyl ketone (MEK),
Ketones such as methyl isobutyl ketone (MIBK) and cyclohexanone: alcohols such as methanol, ethanol, propanol 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,
Halogenated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene can be used.

When kneading the magnetic paint components, the ferromagnetic powder and other magnetic paint components are simultaneously or individually charged into a kneader. For example, first, the magnetic powder is added to a solution containing a dispersant, kneaded for a predetermined time, then the remaining components are added, and further kneading is continued to obtain a magnetic paint.

In kneading and dispersing, various kneaders can be used. Examples of the kneading machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a side grinder, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disper kneader, a high-speed mixer, a homogenizer, and an ultrasonic wave. Dispersing machines and the like can be mentioned.

A dispersant can be used for kneading and dispersing the ferromagnetic powder.

In the case of the present invention, a phosphate compound having the general formula shown below is used.

[Where A is -OH, -OM ² (where M ² is an alkali metal atom), or R is a hydrogen atom or an aliphatic residue having 1 to 30 carbon atoms, and n is an integer of n ≧ 6. The coating liquid of the magnetic layer forming component thus prepared is
It is coated on a non-magnetic support by a known method.

Coating methods that can be used in the present invention include, for example, gravure roll coating, knife coating, wire bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, skies coating, kiss coating and And phantin coating.

The thickness of the magnetic layer applied in this manner is usually 1 to 10 μm in dry thickness.

The magnetic layer is usually formed as a single layer on the support, but may be formed as two or more layers for higher density.

Further, the back surface of the support may be back-coated to protect the support, prevent static charge, and improve running properties.

After the components for forming the magnetic layer are applied in this manner, if necessary, a magnetic field orientation treatment is performed in an undried state, and a surface smoothing treatment is usually performed using a super calender roll or the like.

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

The magnetic recording medium of the present invention can be used as a magnetic tape such as a video tape or an audio tape by cutting into a long shape, or as a floppy disk or the like by cutting into a disk shape. In addition, like a normal magnetic recording medium,
A form such as a cylindrical shape can also be used.

[Examples] Next, examples of the present invention and comparative examples will be shown, and the present invention will be described more specifically. In Examples and Comparative Examples described below, “parts” means “parts by weight”.
Shall be expressed.

(Example 1) A magnetic layer composition having the following composition was mixed and dispersed using a ball mill for 48 hours to obtain a dispersion (viscosity: 50 to 8).
0 poise), and a solvent was further added to the dispersion so that the viscosity became 10 to 20 poise. Then, 5 parts of a polyisocyanate compound (trade name "Coronate L"; manufactured by Nippon Polyurethane Co., Ltd.) was added. The mixture was added and mixed to prepare a magnetic paint.

Co-containing iron oxide-based ferromagnetic powder 100 parts [Silicon content 0.25% by weight, average major axis length 0.25 μm, axial ratio 8, coercivity 700Oe] Phosphate ester compound ^{* 1} 2 parts Polyvinyl chloride containing metal sulfonate Resin ^{* 2} 10 parts Polyurethane resin 5 parts (weight average molecular weight 60,000) Aluminum oxide (average particle size 0.2 μm) 5 parts Carbon black (average particle size 20 mμ) 8 parts Myristic acid 1 part Stearic acid 0.5 part Butyl stearate 0.5 part Part Toluene Appropriate amount Methyl ethyl ketone Appropriate amount [* 1 indicates GAFAC RP710 (hereinafter referred to as Type I) manufactured by Toho Chemical Co., Ltd. or GAFAC RE96 manufactured by Toho Chemical Co., Ltd.]
0 (hereinafter referred to as Type II)
Then Type I. * 2 indicates either one of MR110 (hereinafter, referred to as Resin I) or UCC VAGH (polyvinyl chloride-vinyl acetate copolymer; hereinafter, referred to as Resin II) manufactured by Zeon Corporation. I. Further, a mixture having the following composition was prepared in the same manner as in the magnetic coating, and methyl ethyl ketone and toluene were added as a solvent to the mixture, and the mixture was dispersed with a sand grinder to a viscosity of 10 cps. Before use, the polyisocyanate was used. 5
Parts were added.

First, the obtained magnetic paint was applied on a 10 μm-thick polyethylene terephthalate film so as to have a dry thickness of 3 μm.

Thereafter, after removing the solvent under heating, a surface smoothing treatment was performed by using a super calender, and cut into 8 mm width to obtain a surface.
mm video tape was prepared.

 Various characteristics of this 8 mm video tape were measured.

 The results are shown in Table 2.

 In addition, each characteristic was measured as follows.

Viscosity of paint (poise): The viscosity was measured immediately after the preparation of the paint and 48 hours after the preparation by a B-type rotational viscometer.

Increase in filter pressure: It was determined as a change in the filtration pressure before and after the passage of 6 hours when the paint was filtered through a filter having an average pore size of 1.0 μm. The flow rate of paint is 2kg / min.

Magnetic layer surface roughness (Ra): Determined by measuring the sample surface (backcoat layer surface) with a 3 mm roughness measuring instrument SE-3FK (manufactured by Kosaka Laboratories) at a cutoff of 0.25 and a stylus pressure of 30 mg on a 2.5 mm length. .

Electromagnetic conversion characteristics; RF output; output during reproduction of a 100% white signal was determined based on the reference tape of Example 1 in comparison with the reference tape.

Lumi S / N: Using a noise meter (manufactured by Shibasoku Co., Ltd.) and comparing the tape of Example 1 with the tape of Example 1, the S of the sample at 100% white signal was compared with the tape of Example 1.
/ N difference was determined.

(Example 2) Table 1 shows the silicon content, the axial ratio, and the average major axis length of the ferromagnetic powder, the type of the phosphate ester compound, the type of the polyvinyl chloride type, and the amount of each component. A magnetic paint was prepared according to the same procedure as in Example 1 and the above-mentioned magnetic paint was applied on the same polyethylene terephthalate film as in Example 1 to produce a video tape. .

Various characteristics of the obtained video tape were measured in the same manner as in Example 1. The results are shown in Table 2.

(Example 3) On the same polyethylene terephthalate film as in Example 1, a multilayer magnetic layer, in other words, a magnetic layer having an upper layer and a lower layer was formed.

In the magnetic layer, as shown in Table 1, a magnetic paint having the same composition as the magnetic paint of Example 1 was used for the lower layer. In the upper layer, as a ferromagnetic powder, Co having a coercivity of 900 Oe, a silicon content of 0.5% by weight, an axial ratio of 8, and an average major axis length of 0.20 μm is used.
Example 1 except that 2 parts of an iron oxide-based ferromagnetic powder was mixed, 0.3 parts of a product having an average particle size of 40 mμ was mixed as carbon black, and 2 parts of Type II was mixed as a phosphate compound. A magnetic paint having the same composition as that of the magnetic paint was used.

Various characteristics of the obtained video tape were measured in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Examples 1 to 8) Silicon content of ferromagnetic powder, axial ratio, average major axis length, type of phosphate ester compound, type of polyvinyl chloride resin, presence / absence of blending of each component and A magnetic paint was prepared according to the same procedure as in Example 1 while changing the compounding amount as shown in Table 1, and the magnetic paint was applied on the same polyethylene terephthalate film as in Example 1 according to the same procedure as in Example 1. To produce a videotape.

Various characteristics of the obtained video tape were measured in the same manner as in Example 1. The results are shown in Table 2.

(Evaluation) As is apparent from Table 1, the magnetic recording medium of the present invention is excellent in the viscosity increase and the filter pressure increase before and after the stagnation of the obtained magnetic paint, and the magnetic layer of the completed recording medium. Excellent surface roughness and electromagnetic conversion characteristics were observed.

In addition, in the case of Example 3 in which the magnetic layer was a multilayer, it was confirmed that the Lumi S / N was particularly excellent among the electromagnetic characteristics.

According to the present invention, (1) a ferromagnetic powder having a specific silicon content and a specific average major axis length and / or a specific axial ratio, a resin having a specific polar group, (2) The dispersion of the ferromagnetic powder is excellent, and the increase in the viscosity and the filter pressure before and after the stagnation of the coating material is small, and (3) the obtained magnetic layer (4) It is possible to provide a magnetic recording medium having the following advantages: (4) it has favorable electromagnetic conversion characteristics and can be suitably used for high-density recording.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-213626 (JP, A) JP-A-63-13121 (JP, A) JP-A-63-224025 (JP, A) JP-A-62 71024 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 5/706 G11B 5/716 G11B 5/842 C09D 127/06 C09D 5/23

Claims (1)

(57) [Claims] 1. A ferromagnetic powder containing silicon in a proportion of 0.1 to 0.35% by weight, having an average major axis length of 0.35 μm or less and an axial ratio of 7 to 11, and -SO ₃ M (M is hydrogen). A magnetic recording medium comprising a non-magnetic support and at least one magnetic layer containing a polyvinyl chloride resin having an atom or an alkali metal) and a phosphate compound.