JPS6332725A - Production of magnetic recording medium by execution of multi-stage dispersion - Google Patents

Abstract

PURPOSE:To produce a magnetic recording medium of a high dispersion equi. level by kneading and dispersing a magnetic material with a solvent soln. contg. a specific compd. such as sulfo group and without contg. a binder and suspending and dispersing the same with a binder contg. substantially no hydrophilic groups. CONSTITUTION:The magnetic coating liquid having excellent dispersibility is obtainable by milling 100pts. magnetic material Co-contg. gamma-Fe2O3, 5pts. dispersant including the compd. contg. the sulfo group, phospho group, carboxy group or boric acid residue, 150pts. cyclohexanone, 50pts. toluene without contg. the binder, and 5pts. additive gamma-Al2O3 for about 15hr in a ball mill, then adding the binder liquid prepd. by dissolving 10pts. vinyl chloride/acetate and 10pts. polyurethane with 100pts. cyclohexanone, 80pts. tetrahydrofuran and 10pts. toluene and contg. substantially no hydrophilic groups thereto, further milling the mixture for 3hr with the ball mill, and adding 5pts. multifunctional isocyanate thereto in order to improve the durability of the magnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention μ5 relates to a method for manufacturing a magnetic recording medium, and specifically relates to a method for preparing a magnetic coating material, and more particularly to a method for dispersing magnetic powder.

[Prior art]

The magnetic paint used to create magnetic recording media (hereinafter collectively referred to as magnetic tape) such as magnetic tapes, magnetic sheets, and magnetic disks consists of an organic solvent, a binder, magnetic powder, organic and/or V8! Contains fillers dispersed and suspended, and various additives dissolved therein.

Conventionally, the conventional method of dispersing magnetic powder, fillers, etc., involves several steps in which the dispersion of magnetic powder, fillers, etc. is uniformly dispersed in a binder solution using various kneading machines and dispersion rocks. The liquid is further added with a binder solution for concentration adjustment, various additives, and a binder curing agent, filtered, and finished as a magnetic paint.

The equilibrium dispersibility of the magnetic powder in this compounding process greatly affects the electromagnetic characteristics and durability of the magnetic tape, and the kinetic dispersion rate and dispersion stability are factors that greatly affect productivity. ing.

Regarding the dispersion of such powders in a dispersion medium, see “Paint Fluidization and Pigment Dispersion” by T. and C. Balaton.
om and Pig+oenL Disper9io
n) ”(2ndEdit, ;, iol+n Wili
If dispersion is difficult, a dispersant is generally added in addition to the powder, binder, and solvent to improve dispersibility.

However, magnetic powder has strong cohesiveness due to increased surface activity due to miniaturization and its own magnetism, and the finer the powder, the worse its dispersibility, dispersion speed, and dispersion stability.

On the other hand, however, the magnetic powder used in magnetic tapes is becoming increasingly finer, and an ET value of 50z2/gr or more is now considered to be an everyday standard.

In other words, the S/N ratio of a magnetic tape is said to be proportional to the square root of the number of magnetic particles in the recording material involved in recording and reproduction, so when the same weight of magnetic powder is applied, the particle diameter The smaller the magnetic material used, the more advantageous it is to improving the S/N. However, since the surface area of particles increases in inverse proportion to the square of the particle diameter, dispersion of particles becomes rapidly difficult as the particle diameter decreases, and dispersion stability deteriorates.

Normally, in order to disperse magnetic powder, it should be sufficient to use a dispersant sufficient to coat the surface of the magnetic powder particles, but in reality, this does not provide sufficient dispersibility and stability. Significant excess of dispersant is added. In this case, the dispersant that is not adsorbed to the magnetic powder mixes with the binder in the coating film, plasticizes the magnetic layer, and prevents the hardening of the binding, thereby significantly lowering the mechanical strength of the magnetic layer, especially the Young's modulus.

The magnetic powder is efficiently and stably dispersed, and the 8! Various techniques have been disclosed to prevent deterioration of mechanical properties. For example, JP-A-54-94308, JP-A-54-1
In No. 43894 and No. 50-921.03, magnetic powder is pretreated with a phosphate ester derivative.

Also, JP-A-50-108902, JP-A No. 49-97738
No. 51-33753, No. 53-116114,
In various publications such as No. 54-24000, the surface is treated with an anionic activator. However, the above technique cannot be said to be effective for small particle magnetic powder, especially for magnetic powder having an I)ET of 35 to 40z2/g or more.

Also, JP-A-51-103403, JP-A No. 47-3360
No. 2, No. 55-125169, No. 55-73929, No. 55-73930, No. 57-42888, No. 5
Publications such as No. 7-1026 disclose a technique for coating the surface of magnetic powder with an oligomer or polymer having a functional group that can be adsorbed to the magnetic powder.

In addition, for the dispersibility of magnetic powder, many technologies have been disclosed from the viewpoint of binders. were searched for and selected, and their mixed use was considered, as well as hydrophilic group modification to match the hydrophilicity of the magnetic powder surface by introducing a parent group such as a sulfo group, phospho group, or carboxy group into the molecule. There are many known binders in rice.

As for mechanical methods of dispersion treatment, the results of technical studies such as studies on dispersion devices, crosstalk, and dispersion means, and pretreatment with dispersants have been disclosed.

However, despite the above-mentioned technical efforts, there is a limit to the mechanical crushing of strong agglomerates made of fine primary particles of magnetic material, and the surface of the primary particles in the agglomerates that have been crushed to the maximum limit are It is difficult to reach dispersant molecules or binder molecules, and a satisfactory degree of dispersion has not been achieved.

[Problem that the invention seeks to solve]

In view of the above situation, 3.
As one method, pine breath kneading, which does not use a polymeric binder during the initial dispersion of magnetic powder, has attracted attention. For example, JP-A-60-263327
In this issue, as a pretreatment, magnetic powder is immersed in a solvent solution of an organic compound (surface treatment Pl! agent), and then the solvent is removed.The re-powdered pretreated magnetic powder is dispersed in a binder without hydrophilic groups. or a method of dispersing in a baking solution after the above-mentioned immersion treatment (JP-A-61-16023, JP-A-61-16023).
-17223 etc.) were disclosed.

However, the surface treatment agent preferentially adsorbs to the surface of the secondary particles and forms an adsorption film before penetrating into the interior of the secondary particles (=agglomerates of large particles), leaving the primary particles as secondary particles. It encapsulates and warps, causing dispersion into primary particles. This phenomenon tends to be stronger in metal magnetic powders with strong cohesive force.
This will slow down the dispersion speed and lower the dispersion equilibrium level.

Furthermore, due to factors such as reagglomeration and coarsening of the magnetic powder due to solvent removal and the unsuitability of surface treatment agents or dispersants for secondary particle dissociation, current magnetic recording media are required to dissociate secondary particles into primary particles. The dispersion level has not reached a level that is sufficient for the purpose of dispersion.

Therefore, an object of the present invention is to provide a method for producing a magnetic recording medium that provides a high dispersion balance level at a sufficient dispersion rate for magnetic powder, particularly ferromagnetic powder with strong cohesive force.

Another object of the present invention is to provide a method for producing a magnetic recording medium containing highly dispersed magnetic powder and having high electromagnetic characteristics and squareness.

[Means to solve the problem]

A cross-dispersion process that eliminates the dispersion obstruction caused by encapsulation of the magnetic powder and selects an appropriate surface treatment agent, and a suspension dispersion process that avoids the difficulty of reagglomeration and matches the binder's affinity with the magnetic powder. As a result of conducting studies based on the following points, we found that in the preparation process of magnetic paint, it is necessary to use compounds that contain at least Class 1a among compounds having sulfo groups, phospho groups, carboxyne groups, or boric acid residues, or derivatives of such compounds. By incorporating the step of cross-dispersing the raw powder of the magnetic material with a solvent solution containing no binder, and the step of dispersing at high temperature in the presence of a binder that does not substantially contain a hydrophilic group following this step, the above-mentioned The objectives of the invention have been achieved.

The above-mentioned "magnetic powder" is a magnetic powder used as a raw material for magnetic paint, and is used for surface treatment, as part of the preparation of magnetic paint.
This is a so-called magnetic powder that has not undergone any adjustment treatment such as pretreatment. Hereinafter, it will be referred to as magnetic cord powder.

Furthermore, "successively" does not include complete removal of the solvent between the crosstalk dispersion step and the suspension dispersion step.

Furthermore, "a binder that does not substantially contain hydrophilic groups" means that the content of hydrophilic groups in the binder is suppressed to such an extent that it does not interfere with the suspension and dispersion process of magnetic powder. ing. This binding will hereinafter be referred to as a non-polar binder.

In the present invention, in the cross-dispersion process of the solvent solution of the compound (dispersant) having a hydrophilic group selected as described above and the magnetic raw powder, the dispersant permeates from the surface of the secondary particles. It adsorbs onto the hydrophilic surface of the primary particles, orients the hydrophobic portion to the adsorbed surface, prepares the steps before dissociation of the secondary particles, and provides a favorable environment for mechanical dispersion.

The crosstalk dispersion step may be divided into small steps in which at least one type of dispersant is added in a determined order taking into consideration the permeability of the dispersant and the like.

After the crosstalk dispersion process is completed, the solvent is not removed, but the process proceeds to a suspension dispersion process in the non-polar binder solvent solution. At this time, as long as the solvent is not completely removed, viscosity adjustment and other steps may be performed in between.

In the suspension and dispersion process, the affinity between the primary particles, which have hydrophobic surfaces formed by the dispersant, and the non-polar binder is high and rapid.
This is advantageous for stable suspension dispersion.

The suspension and dispersion process is carried out in a non-polar manner, taking into consideration the dispersion situation of the large particles, the viscosity of the suspension dispersion, and the affinity between the hydrophobic surface formed on the surface of the large particle of the dispersant used and the non-polar binder. The mu and amount of the polar binder to be added may be divided into small steps in which the order is determined and the addition is done in parts.

After the above two dispersion steps, the curing agent effect, viscosity or properties of the magnetic layer: l! After going through a finishing step in which various binders and additives are added and adjusted for finishing, a hardening agent is added, and the material is subjected to a series of forming steps such as coating, drying, calendering, or cutting.

Next, the dispersant applied to the crosstalk dispersion process will be explained.

1. Dispersant having a phospho group The dispersant belonging to this group has the following general formula (1).
There is a compound represented by

General formula (1) The mouth is a positive number from 1 to 30.

Specific examples of the compound represented by the general formula (1) are as follows, but are not limited thereto.

Exemplary compound (Pl) and its monophosphoric acid ester (P2) i1 and its diester (P3) 0i+ and 1 its diester (P4) and its diester (P5) and its diester (P6) il and its diester ( Pl) H and its diester (P8) and 1 this diester 2, a dispersant having a carboxyl group or a sulfo group, an organic dye compound is selected as the dispersant, and (a
) salt form, (b) azo compound, (c) the following general formula (
It is preferable that either the compound shown in 2) or the red compound (d) is provided.

General formula (2) (wherein X C1, No2, CH3, C2H5, OCl
(y represents OC2115, Y represents C1, Z represents a carboxyl group or a sulfo group. It may also be in the form of a salt,
N H, alkali metals, alkaline earth metals, and organic amines are preferred in winter. Also, 111 and 1]2 is O ~ 5.1
and 糟□ represent an integer between θ and 2. Portrait and 1 cannot become 0 at the same time. ) Next, specific compounds of this group are illustrated.

(D 1 ) (D2) (D 3) (D 4) (D 5) (D 6) (D 7) (D 8) (D 9) (D 10) O (D 11) (D 12) (D 13) (D 14) I (D 15) g (D 16) (D 17) 3. Dispersant having boric acid residue Compounds included in the description according to the present invention are charge transfer complexes (c
Examples include boric acid esters that can form a 1+argc-transfer complex (hereinafter referred to as CTC) and are represented by the following general formula (3).

General formula (3) In the formula, R1 and R2 represent H, (CH2CH20)mH or COR3, (CH2CH20)IIIcOR'', and R3 is an i-prime P number of 4 to 30, preferably 6 to 22 hydrocarbon residues. group, [1 has 1 to 30 carbon atoms, preferably 2
~22 hydrocarbon residues. ω is a positive number from 1 to 30, and R1 and R2 may be the same or different.

Furthermore, R1 and R2 never become H at the same time.

Next, specific examples of the compound represented by the general formula (3) will be given.

(Ill) Glycerol borate/laurate (82
) // ・Palmitate (BS
) ・Stearate (134)
// ・Instearate (
BS) ・Hydroxystearate ([16) # ・Olate (
II7) ・Dilaurate (B
S) ・Tuvalmitate (8
9) # ・Distearate ([
1], O) l/ ・Diisostearate (811) // ・
Diolet ([112>Polyoxyethyleneglycerol borate/ratulate (1313) n ・Noglumitate ([114) // ・Stearate (815) ii ・Instearate (D16) h ・Olate (817) Polyoxyethylene glycerol Borate/dilaurate ((!18) II ・Dipalmitate (t) 19) tt ・Distearate (B 20 ) //
- Diisostearate ([121) polyoxyethylene glycerol borate/diolate 4, a dispersant having a carboxyl group This group includes saturated or unsaturated fatty acids as well as their alkali salts.

Specific examples include myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, sodium oleate, and the like.

The above-mentioned dispersants are used alone or in combination, and are used in an amount of 0.1 to 10%, preferably 0.5 to 7%, based on the magnetic cord powder.

Solvents used in the crosstalk dispersion process include ketonic acids such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propyl, and butanol; methyl acetate,
Esters such as ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol heptame acetate; ethers such as glycol methyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, xylene, etc. Can be used.

The above-mentioned solvents are also used in the suspension and dispersion process and the finishing process.

Next, the non-polar binder used in the suspension dispersion process does not have any hydrophilic groups in its molecules that are easily adsorbed to the surface of the magnetic particles, but even if it does, it is assumed that they are not substantially adsorbed to the magnetic particles. It is a non-polar polymer or oligomer having a trace amount of hydrophilic groups. When it has a hydrophilic group, its amount is preferably 0.03 wt% or less based on the total binder amount.

Examples of binders having hydrophilic groups include binders that have been modified with hydroxyl groups, carboxyl groups, sulfone groups, phosphoric acid groups, etc., and cellulose-based binders; thermosetting resin,
Thermoplastic a(jllF), reactive resin, or a mixture thereof can be used.

For example, vinyl chloride-vinyl acetate copolymer, acrylic resin, epoxy resin, polyamide resin, 19')ene resin, urethane elastomer, incyanate curable resin, cellulose ester that has lost a hydroxyl group, cellulose ether, etc. be used.

The degree of polymerization is preferably 100 to 10,000.

The above binders may be used alone or in combination.

Even in the case of a mixture, the total amount of functional groups based on the total amount of binder is preferably 0.03 wt% or less.

In the finishing step of the magnetic powder suspension solution which has undergone the two steps of cross-dispersion and suspension dispersion, restrictions on the binder or various additives are lifted.

In the present invention, conventional techniques can be used to form the magnetic layer, backfoot layer, or other constituent layers of the magnetic tape of the present invention.

The magnetic layer of the magnetic tape of the present invention is a coated magnetic layer using magnetic powder, binder, powder, lubricant, etc.

Examples of magnetic materials include γ-F e20 , CO-containing -F e20 , Co-coated γ-FezOi, Fe
:+04, Co containing Fe=04, Cot wearing Fe,
o,, CO-containing magnetic FcO+: (>x>-)Cr02
oxide magnetic materials such as Fe, Ni, Co, Fe
Ni alloy, Fe-C.

Alloy, Fe-Δ! alloy, FeAf-Ni alloy, Fe-N
1-P alloy, Fe-Ni Co alloy, Fe-Mn-Z
n alloy, Fe Ni Zn alloy, Fe-Co-Ni
Cr alloy, FeCo-N1-P alloy, Co-Ni alloy, Co-P alloy, CoCr alloy, etc.Fe%Ni1C
Examples include various ferromagnetic materials such as metal magnetic powder containing O and A1 as main components. Additives to these metal magnetic materials may include elements such as Sl, CuSZn, A1, P, Mn, and Cr, or compounds thereof. Also used are hexagonal hepterarite such as barium ferrite, iron nitride, and iron carbide.

The binder used in the final lifting magnetic paint, Barafco-1, layer paint, etc., includes abrasion-resistant polyurethane. It has strong adhesion to other substances, is mechanically strong against repeated stress or bending, and has good abrasion resistance and weather resistance.

In addition to polyurethane, if Wt, sli based resin and vinyl chloride based copolymer are also contained, the dispersibility of the magnetic powder in the magnetic layer is improved and its mechanical strength is increased. However, if only the iaz resin and the vinyl chloride copolymer are used, the layer becomes too hard, but this can be prevented by containing the above-mentioned polyurethane.

Usable #a, m base type (3) cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, etc. can be used.The above vinyl chloride copolymer is partially hydrolyzed Preferable examples of the vinyl chloride copolymer include copolymers containing vinyl chloride and vinyl acetate.

7e/kishi again! 4 fats can also be used.

Fair JIr resin has advantages such as high mechanical strength, excellent dimensional stability, and good heat resistance, water resistance, and chemical resistance.

These advantages are complementary to the above-mentioned polyurethane, and also help to significantly improve the stability over time in the physical properties of the tape.

In addition to the above-mentioned binders, resins generally used in magnetic recording media, various modified resins with hydrophilic groups such as sulfo groups, phospho groups, and carboxy groups, thermoplastic resins with characteristic behavior, and thermosetting resins can be used. Mixtures of resins, reactive resins, and electron beam curable resins may also be used.

In order to improve the durability of the magnetic layer of the magnetic tape of the present invention, the magnetic paint can contain various curing agents, such as incyanate.

Aromatic incyanates that can be used include, for example, tolylene diisocyanate (TDI) and adducts of these incyanates with active hydrogen compounds, and those having an average molecular weight in the range of 100 to 3,000 are preferable. It is.

Examples of aliphatic incyanates include hexamethylene diisocyanate (HMDI) and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these incyanates and active hydrogen compounds, those having a molecular weight range of OO to 3,000 are preferred. Among the aliphatic incyanates, non-TB cyclic incyanates and adducts of these compounds with active hydrogen compounds are preferred.

The magnetic paint used to form the magnetic layer may contain additives other than those mentioned above, such as a dispersant, a V-lubricant, an abrasive, other fillers, and an antistatic agent, if necessary. good.

Dispersants include lecithin, phosphate esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinates, known surfactants, and salts thereof. Salts of polymeric dispersants having negative acid groups (eg carboxy, sulfo, phospho groups) can also be used. These dispersants may be used alone or in combination of two or more. These dispersants are added in an amount of 0.1 to 20 parts by weight based on 1001 parts by weight of the binder.

Also usable as the lubricant are non-ferrous oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, fatty acids such as lauric acid and myristic acid, and fatty acid esters. These lubricants are added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder.

Commonly used abrasive materials include fused alumina (preferably α-alumina), silicon carbide, chromium oxide, α-iron oxide, titanium oxide, silicon nitride, aluminum nitride, boron nitride, furundum, and artificial corundum. , diamond, artificial diamond, garnet, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives have an average particle diameter of 0.05 to 5 μl, preferably 0.1 to 2 μl. These abrasives are added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the binder.

As other fisi, organic powders or inorganic powders may be used individually or in combination.

Examples of organic powders that may be used in the present invention include acrylic styrene resin, benzoguanamine resin powder, and melamine 1? , resin powder, and 7-thalocyanine pigments are preferred, but
Polyolefin resin powder, polyester resin powder,
Polyamide-based O (fat powder, polyimide-based U (powder), boria]ated ethylene 84 Ire powder, etc. can also be used, and inorganic powders include silicon oxide, titanium oxide, aluminum oxide, zinc oxide, tin oxide, molybdenum dioxide, calcium carbonate. , barium sulfate, calcium sulfate, zinc fluoride, calcium carbide 1, talc, and kaolin.

Antistatic agents include carbon black, graphite, conductive powders such as tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; fullkylene oxide, 7-ion surfactants such as glycerin and glycidol; cationic surfactants such as higher alkyl amines, quaternary ammonium salts, bilinone, other heterocycles, phosphonium or sulfonium; carboxylic acid, sulfonic acid, phosphoric acid , anionic surfactant containing acidic groups such as sulfate ester group, phosphate ester group; Ami7a
Examples include amphoteric activators such as m, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-su7ta1note, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose guiacetate, and plastics such as polyamide and polycarbonate. Metals such as n, glass, BN.

Ceramics such as Si carbide and porcelain can also be used.

The thickness of these supports is about 3 to 100 μl in the case of a film or sheet, preferably 5 to 50 μl,
In the case of a disk or card shape, the volume is about 30 μl to 10×m, and in the case of a drum shape, it is used in a cylindrical shape, and the type is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the magnetic layer.

Coating methods for forming the magnetic layer on the support include air knife coating, blade coating, air knife coating, squeeze coating, 2″ dip coating, reverse roll coating, trans7 roll coating, gravure coating, and kiss coating. , cast foot, spray coat, etc. can be used, but are not limited to these.

〔Example〕

The present invention will be specifically explained using examples.

Examples-1 to 4 The above-mentioned exemplified dispersant was used in the examples.

Example I Pi 〃 2 Dl 〃 3 B2 〃 4 Co-containing myristate-Fe20. 100 parts Exemplary dispersant 5 Microhexanone 150 Toluene 50 γ-A120. After milling the composition consisting of 5 or more in a ball mill for about 15 hours, 10 parts of salt vinyl acetate and 10 parts of polyurethane were mixed with cyclohexanone io.
A binder solution dissolved in 80 parts of OG, Tetrahydro 7 Run and 10 parts of toluene was added and milled for 3 hours in a ball mill to prepare a magnetic coating solution. Five parts of a polyfunctional isocyanate was added to this coating solution, and a sample was obtained through the steps of coating, drying, calendering, and slitting.

Examples-5 to 8 Comparative examples except that the magnetic powder was changed to ferromagnetic metal powder-
1. 5 parts of the dispersant Pi were dissolved in toluene with stirring, and 3100 parts of Co-γ-F coo was added thereto and stirred for 5 hours. Thereafter, the toluene was blown off in a vacuum dryer to obtain a pretreated magnetic powder.

Pretreated Co-γ-Fe, 03105 parts cyclohexanone 150 parts toluene
50 copies γ-Am! 20.
Part 5 The other parts are the same as in Example 1.

Comparative Example-2 Same as Comparative Example 1 except that the magnetic powder in Comparative Example 1 was replaced with ferromagnetic metal powder.

Comparative Example-3 Same as Example 1 except that the dispersant was a primary amine shown below.

CI+, (CI+2), -Nl2・2C)13(C11
□)5C11(011)CI12CI+=CII (C
11□), CI+.

is the same as in Example 1.

From the above results, the sample produced by the method of the present invention yields a tape with a high squareness ratio and high output.

〔Effect of the invention〕

1) A tape with a high squareness ratio and excellent dispersibility can be obtained.

2) Therefore, a tape with high output and high S/N ratio can be obtained.

Applicant: Konishiroku Photo Industry Co., Ltd. Margin below ＋　-L'　7'

Claims (1)

[Claims] In the process of preparing magnetic paint, a magnetic material is mixed with a solvent solution containing at least one of compounds having a sulfo group, phospho group, carboxy group, or boric acid residue, or derivatives of such compounds and containing no binder. 1. A method for manufacturing a magnetic recording medium, comprising the steps of cross-dispersing a raw powder, and subsequent to the step of suspending and dispersing it in the presence of a binder that does not substantially contain a hydrophilic group.