JPH076347A - Binder resin for magnetic recording medium and magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the binder resin having excellent affinity to magnetic powder by forming the binder resin of a copolymer consisting of vinyl monomers contg. functional groups, vinyl monomers contg. hydroxyl groups and vinyl chloride monomers. CONSTITUTION:The vinyl monomers contg. at least >=1 kinds of the functional groups selected from the vinyl monomers contg. epoxy groups, carboxyl groups, ternary amine, quaternary ammonium salt, So3M<1> group (M<1> is hydrogen, NH4, alkaline metal), PO2(OM<2>)2 group (M<2> is hydrogen, alkaline metal, hydrocarbon group) and sulfobetaine, etc., and the vinyl monomers contg. the hydroxyl groups are used alone or in combination of >=2 kinds. One or more kinds of any among surfactants having reactive double bonds expressed by formula I, formula II and formula III are used with these vinyl monomers and the mixture composed thereof is subjected to soln. polymn. in the presence of an oil-soluble radical initiator. The binder resin for the magnetic recording medium having the copolymer obtd. in such a manner is produced. In the formulas, R<1>, R<2>, R<3> are 1 to 22C alkyl groups, R<4>, R<5>, R<6> are H, Na, K, NH4,; w, x, y, z are an integer from 1 to 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder resin for a magnetic recording medium and a magnetic recording medium using the same.

[0002]

2. Description of the Related Art A coating type magnetic recording medium such as a magnetic tape or a magnetic card is generally manufactured by coating a polyester film with a magnetic coating material containing a magnetic powder and a binder resin to form a magnetic layer. The quality required for this magnetic recording medium includes electromagnetic conversion characteristics obtained by filling magnetic powder with high density and high orientation, and durability that can withstand friction with a magnetic head and the like. To be

Therefore, in the binder resin used in the magnetic recording medium, magnetic powder is highly dispersed in the magnetic paint to give the magnetic coating film excellent electromagnetic conversion characteristics, and at the same time, it is combined with a crosslinking agent such as an isocyanate compound. By doing so, strength is given to the magnetic coating film. Further, in order to maintain the quality of the magnetic recording medium and the magnetic characteristics for a long time, it is necessary that the magnetic powder in the magnetic coating film is not deteriorated.

In recent years, with the development of AV equipment and the like, high quality is required for magnetic recording media, and magnetic powder particles are more and more required for filling magnetic powder with higher density in a magnetic coating film. It tends to be atomized. Therefore, there has been a demand for a binder resin having more excellent dispersibility than ever.

Conventionally, as a vinyl chloride binder resin having excellent dispersibility, a vinyl chloride copolymer containing a functional group having high hydrophilicity and a hydroxyl group capable of undergoing a cross-linking reaction with an isocyanate compound or the like in order to obtain an affinity with the magnetic powder. Polymers are commonly used. Particularly, as the hydrophilic functional group having a strong affinity with the magnetic powder, for example, —COOH, —SO ₃
Na, -PO (OH) _2, etc. [Japan Adhesion Association Magazine 17, 1
55 (1981)] has been reported and Japanese Patent Publication No. 1-26.
JP-A-625 discloses, as a vinyl chloride-based binder resin having high dispersibility and excellent reactivity with a crosslinking agent, an unsaturated monomer having a strong acid group containing vinyl chloride, sulfur or phosphorus, and -X. A vinyl chloride-based copolymer comprising an -OH group (X is an organic residue) is disclosed.

[0006] Japanese Patent Publication No. 3-97764 discloses that
In order to obtain similar performance, a vinyl chloride-based binder resin containing a sulfonic acid group, a carboxyl group, and a phosphoric acid group is disclosed, and Japanese Patent Publication No. 1-26627 discloses that an epoxy group-containing monomer contains a strong acid. A resin for a magnetic coating in which an alkali metal salt is copolymerized with vinyl chloride is disclosed.

However, the dispersibility of the magnetic powder was still insufficient, and it was difficult to obtain a high-performance magnetic coating film.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and an object thereof is to have an excellent affinity with magnetic powder and to be able to fill the magnetic powder with high density and high orientation, A vinyl chloride-based binder resin for magnetic recording media, which can be easily manufactured to meet these required qualities, and a magnetic recording medium having a magnetic coating film excellent in electromagnetic characteristics, heat resistance, durability and abrasion resistance. To provide.

[0009]

The binder resin for a magnetic recording medium of the present invention is a vinyl monomer containing a functional group,
It is a copolymer composed of a vinyl monomer having a hydroxyl group and a vinyl chloride monomer.

Examples of the vinyl monomer containing a functional group include a vinyl monomer containing an epoxy group, a vinyl monomer containing a carboxyl group, a vinyl monomer containing a tertiary amine group, and a vinyl containing a quaternary ammonium salt group. Monomer, SO ₃ M ¹ group (M ¹ is hydrogen, NH
₄ ⁺ or an alkali metal), a vinyl monomer containing a PO ₂ (OM ² ) ₂ group (M ² represents hydrogen, an alkali metal or a hydrocarbon group) and sulfobetaine. May be used alone or in combination of two or more.

Examples of the vinyl monomer having an epoxy group include glycidyl methacrylate and allyl glycidyl ether.

Examples of the vinyl monomer containing a carboxyl group include (meth) acrylic acid, succinic acid mono (meth) acryloyloxyethyl ester, phthalic acid mono (meth) acryloyloxyethyl ester,
Examples thereof include one having one carboxyl group in a molecule such as succinic acid monomethacryloyloxyethyl ester, and one having a plurality of carboxyl groups in a molecule such as maleic acid and fumaric acid.

Examples of the vinyl monomer having a tertiary amine group include dimethylaminopropylmethacrylamide, N, N-dimethylaminopropylacrylamide and the like.

The vinyl monomer containing the quaternary ammonium salt group is, for example, 2-hydroxy-3-
Methacryloyloxypropyl trimethylammonium chloride, methacryloyloxyethyl trimethylammonium chloride, trimethyl-3-methacrylamido-propylammonium chloride and the like can be mentioned.

The SO ₃ M ¹ group-containing vinyl monomer is, for example, sodium ethylene sulfonate, potassium ethylene sulfonate, 2-acrylamido-2-methylpropane sulfonic acid soda, 2-acrylamido-
Examples thereof include ammonium 2-methyl propane sulfonate, sodium ethyl sulfonate methacrylate, allyl sulfonic acid, methacryl sulfonic acid, and styrene sulfonic acid.

Examples of the vinyl monomers containing PO ₂ (OM ² ) ₂ groups include acid phosphoxyethyl.
(Meth) acrylate, acid phosphoroxypropyl (meth) acrylate, 3-chloro-2-acid phosphoroxypropyl (meth) acrylate, methacryloyloxyethyl acid phosphate monoethanolamine half salt and the like can be mentioned.

Examples of the vinyl monomer containing sulfobetaine include N- (3-sulfopropyl)-
N-methacrylamidopropyl-N, N-dimethylammonium betaine, N- (3-sulfopropyl) -N-
Methacryloxyl-N, N-dimethylammonium betaine, 1- (3-sulfopropyl) -2-vinylpyridinium betaine and the like can be mentioned. It is also possible to use a reaction product of a vinyl monomer having a tertiary amine group such as N, N-dimethylaminoethyl acrylate and a sultone derivative such as 1,3-propane sultone.

When the content of the vinyl monomer having a functional group is small in the above copolymer, the affinity between the magnetic powder and the binder resin becomes insufficient, and it becomes difficult to highly disperse the magnetic powder. When the amount of the vinyl monomer increases, the viscosity of the magnetic coating material increases and the dispersibility of the magnetic powder decreases due to the interaction between the functional groups. Therefore, the content of the vinyl monomer is preferably 0.1 to 40% by weight, more preferably 0.4 ~ 9% by weight.

Examples of the vinyl monomer having a hydroxyl group include a reaction product of (meth) acrylic acid and a polyhydric alcohol, a (meth) acrylic acid amide, and the like.

Examples of the reaction product of the (meth) acrylic acid and the polyhydric alcohol include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and 3 - chloro-2-hydroxypropyl (meth) acrylate, CH ₂ = CR ⁷ -COO- [CH ₂
CH (CH ₃₎ - O] _p -H (R ⁷ is hydrogen or a methyl group,
p represents an integer of 2 to 6), polypropylene glycol mono (meth) acrylate represented by CH ₂ ═CR ⁸ —
_{COO- (CH 2 CH 2 O)} q -H (R 8 is hydrogen or a methyl group, q is an integer of 2-9) polyethylene glycol mono (meth) acrylate represented by 2-hydroxyethyl-2 ' -Acryloyloxyphthalate, C
^{_{H 2 = C (R 9)}} -COOCH 2 CH 2 -O- (CO-C
₅ H ₁₀ O) _r —H (R ⁹ is hydrogen or a methyl group, r is 1 to
A lactone (meth) acrylate represented by (denoting an integer of 5).

Examples of the (meth) acrylic acid amide include N-methylol (meth) acrylamide.

In the above copolymer, when the content of the vinyl monomer having a hydroxyl group is small, the reactivity with isocyanate is insufficient, so that the durability is deteriorated, and when the content is large, the solvent solubility is deteriorated and the interaction of hydroxyl groups is increased. As a result, the viscosity of the magnetic paint increases, so 1 to 50% by weight is preferable, and 2 to 20% by weight is more preferable.

The degree of polymerization of the above copolymer is preferably 100 to 900, more preferably 150 to 900, because the mechanical strength of the magnetic coating film decreases as the degree of polymerization decreases, and the viscosity increases and the solvent solubility decreases as the degree of polymerization increases. It is 600.

If desired, the above-mentioned copolymer may be copolymerized with a monomer having a copolymerizable unsaturated group.

Examples of such a monomer include α-olefins such as ethylene, propylene and 1-hexene; vinyl esters such as vinyl acetate and vinyl propionate; butyl vinyl ether, cetyl vinyl ether,
Vinyl ethers such as phenyl vinyl ether; aromatic vinyls such as styrene and α-methylstyrene; (meth)
Vinyl cyanides such as acrylonitrile; vinyl halides such as vinylidene chloride and vinyl fluoride; unsaturated dicarboxylic acid esters such as dimethyl maleate and dimethyl fumarate; unsaturated dicarboxylic acid anhydrides such as maleic anhydride; N -N-substituted maleimides such as phenylmaleimide and N-cyclohexylmaleimide; Formula CH ₂ typified by methyl methacrylate, n-butyl acrylate, etc.
_{^{= CR 4 -COO- (CH 2)}} s -CH 3 (R is a hydrogen or a methyl group, s is an integer of 0) alkyl (meth) acrylates represented by, 1,7,7-trimethyl Bicyclo [2.2.1] hept-2-yl acrylate etc. are mentioned.

In particular, in order to improve the solvent solubility of the copolymer and reduce the viscosity, n-butyl acrylate, 1,7,
7-Trimethylbicyclo [2.2.1] hept-2-yl acrylate is preferred.

In the copolymer, any one of the above-mentioned various monomers is selected from surfactants (reactive emulsifiers) having a reactive double bond represented by the general formulas (1), (2) and (3). It is obtained by solution polymerization using one or more kinds in the presence of an oil-soluble radical initiator.

The above-mentioned surfactants are represented by the general formulas (1) to (3).
It is represented by.

[0029]

[Chemical 4]

[0030]

[Chemical 5]

[0031]

[Chemical 6]

In the general formulas (1) to (3), R ¹ and R
² and R ³ are alkyl groups, and as the carbon number increases, the hydrophobicity increases, so the carbon number is limited to 1 to 22.
R ⁴ , R ⁵ and R ⁶ are H, Na, K or NH ₄
Is. w, x, y, and z are integers, and the emulsifying effect decreases with an increase in w, so the amount is limited to 1 to 30.

In the above solution polymerization, when the amount of the surfactant added is decreased, the amount of the monomer copolymerized in the polymer is decreased and the ability to disperse the magnetic powder is decreased. Therefore, the amount is preferably 0.1 to 10 parts by weight, and more preferably 0.2 to 3 parts by weight, based on 100 parts by weight of the vinyl chloride monomer used.

The oil-soluble radical initiator is not particularly limited, and those used in the conventional polymerization of vinyl chloride resin can be used. Examples thereof include azobisisobutyronitrile and dimethylazo. Azobis initiators such as bisvaleronitrile; lauroyl peroxide, benzoyl peroxide, di-t-butyl peroxide, di-t-butylperoxy-2-ethylhexanate, t-butylperoxyisobutyrate, di- −
Examples thereof include organic peroxides such as 2-ethylhexyl peroxydicarbonate.

Examples of the solvent used in the solution polymerization include n-hexane, lower alcohols such as methanol and ethanol, and other solvents generally used in solution polymerization.

Next, the second aspect of the present invention will be described. In the magnetic recording medium of the present invention 2, a magnetic layer is formed on one surface of a support and a non-magnetic layer is formed on the other surface, the magnetic layer is composed of magnetic powder and a binder resin, and the non-magnetic layer is composed of a binder resin. . At least one of the binder resins is the binder resin for a magnetic recording medium of the present invention.

Examples of the support include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, cellulosic derivatives such as polyolefin resins, cellulose triacetate and cellulose diacetate, films of vinyl resins, polyimide resins, polyamide resins or the like. Sheets; further, non-magnetic metal foils such as aluminum and copper; paper, ceramic sheets and the like.

The magnetic layer is formed by applying magnetic powder and a magnetic coating material obtained from the binder resin for a magnetic recording medium of the present invention, and drying, and the nonmagnetic layer is a binder for a magnetic recording medium of the present invention. It is formed by applying a non-magnetic paint obtained from a resin and drying.

The magnetic paint is produced from a binder resin resin composition for magnetic recording media, magnetic powder and a solvent.

Examples of the magnetic powder include γ-Fe ₂
O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , CrO ₂ , Co-Ni-P alloy, Fe
-Co-Ni alloy, Co ferrite, Ba ferrite,
Known ferromagnetic powders such as Sr ferrite, Fe alloy, Co alloy, and Ni alloy can be used.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl isobutyl ketone and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate and glycol monoethyl ether acetate; glycol. Glycol ethers such as dimethyl ether and dioxane; aromatic hydrocarbons such as benzene, toluene and xylene; methylene chloride, ethylene chloride, carbon tetrachloride,
Examples thereof include chlorinated hydrocarbons such as chloroform, ethylene chlorohydrin, and dichlorobenzene, which may be used alone or in combination of several kinds.

If desired, various additives such as a hardener, an abrasive, a lubricant, a dispersant, an antistatic agent and a stabilizer may be added to the magnetic paint.

As the above-mentioned curing agent, known ones such as polyisocyanate compounds are used, and as the lubricant, for example, dialkyl polysiloxane, phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl group having 1 to 5 carbon atoms) and the like. Inorganic powders such as silicone oil, molybdenum disulfide and tungsten disulfide, unsaturated aliphatic hydrocarbons and the like.

Examples of the dispersant include fatty acids having 12 to 18 carbon atoms such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid and linoleic acid.

Examples of the antistatic agent include conductive powders such as carbon black, alkylene oxide-based compounds,
Glycerin-based nonionic surfactants; cationic surfactants such as higher alkyl amines and quaternary ammonium salts; anionic surfactants containing acidic groups such as carboxyl groups, phosphate groups, sulfone groups; amino acids, amino sulfones Examples thereof include amphoteric surfactants such as acids.

Examples of the above-mentioned stabilizer include those represented by the general formula C ₁₇
H ₃₅ COOM ⁵ (wherein M ⁵ is Pb, Cd, Ba, Ca,
Zn, Mg or Al); organic tin compounds such as organic tin malate, organic tin laurate, organic tin mercapto, methyl tin, butyl tin and octyl tin.

In order to produce a magnetic coating material using the above binder resin, the magnetic powder is kneaded and dispersed with a binder resin solution (a binder resin and a polyurethane resin or a polycarbonate polyurethane resin dissolved in a solvent). Generally, a method of pre-dispersing with a two-roll mill, a three-roll mill, an open kneader, a pressure kneader, a continuous kneader or the like, and then post-dispersing with a sand grinder, a ball mill or the like is generally used.

In order to obtain a magnetic recording medium, it is preferable to form a magnetic layer on a support and then orient the magnetic layer through an electromagnet (solenoid).

The non-magnetic coating material is manufactured from a binder resin for magnetic recording medium and a solvent.

The magnetic coating material and the non-magnetic coating material can be applied to the support by air doctor coating, blade coating, rod coating, extrusion coating, air knife coating,
Squeeze coat, impregnation coat, reverse roll coat,
Examples include transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, spin coat and the like.

When a non-magnetic layer is laminated between the magnetic layer and the support, the binder resin for a magnetic recording medium of the present invention is also used to disperse the non-ferromagnetic powder in the non-magnetic layer. May be.

As the non-ferromagnetic powder, carbon black, graphite, titanium oxide, barium sulfate, Zn
S, MgCO ₃ , ZnO, CaO, γ-iron oxide, molybdenum disulfide, boron nitride, MgO, SnO ₂ , Si
O ₂ , CrO ₃ , Cr ₂ O ₃ , α-Al ₂ O ₃ , Si
C, cerium oxide, corundum, artificial diamond, α
-Iron oxide, garnet, garnet, silica, silicon nitride, silicon carbide, molybdenum carbide, tungsten carbide,
Examples include titanium carbide, tripoli, diatomaceous earth, dolomite, and the like.

The above magnetic recording medium is used, for example, as a magnetic tape such as an audio cassette tape, a VTR tape, a magnetic disk such as a floppy disk, and a magnetic card.

[0054]

EXAMPLES Examples of the present invention will be described below. The manufacturing [initial charge] internal volume 18 liters provided with stirrer stainless steel autoclave copolymer, methanol 6800
Parts by weight, 20 parts by weight of the reactive emulsifier represented by the general formula (Ia), and 28 parts by weight of t-butylperoxyneodecanoate as a polymerization initiator, and then exhausted with an aspirator for 5 minutes to leave residual air. After eliminating the above, 2800 parts by weight of vinyl chloride monomer was charged.

[Preparation of Post-Addition] After removing air from a 3 liter suspendable stainless steel container (hereinafter referred to as an addition container), 2-hydroxypropyl arylate 300 was added.
By weight, 55 parts by weight of 2-acryloyloxyethyl phthalic acid and 1095 parts by weight of methanol were suctioned, and 1400 parts by weight of vinyl chloride monomer were further press-fitted. Then, the addition container was shaken to sufficiently mix and dissolve the contents, and hung on a spring balance, and was connected from a valve at the bottom of the container to an addition nozzle provided in the polymerization reaction container using a flexible tube.

[Polymerization reaction operation] The rotation speed of the stirrer of the polymerization reactor was set to 250 rpm, 62 parts by weight of the mixed solution was added from the addition container to the polymerization reactor, and warm water was passed through the jacket to adjust the internal temperature of the reactor to 53 ° C. The temperature was raised to. Inner temperature is 5
When the temperature reached 3 ° C., 62 parts by weight of the mixed solution was added from the addition container to the polymerization reaction container, and then added in a total of 48 times every 5 minutes in accordance with the progress of the polymerization reaction. Further, the internal temperature of the polymerization reactor was raised and the temperature was adjusted from the time when it reached 53 ° C., so that it was kept constant at 53 ° C. during the reaction. Five minutes after the last addition was completed, the internal temperature was cooled to 25 ° C. to stop the polymerization reaction. After cooling, the vinyl chloride monomer remaining inside the polymerization reactor was discharged, and nitrogen gas was further aerated to sufficiently remove the vinyl chloride monomer. After that, the slurry was extracted from the lower part of the polymerization reactor, filtered, and then 5
Copolymer 170 of white powder after vacuum drying at 0 ° C. for 10 hours
0 parts by weight were obtained. The polymerization degree and composition of the resulting copolymer are shown in Table 1.

(Examples 2 to 8) Various components in the prescribed proportions shown in Tables 1 and 2 were polymerized in the same manner as in Example 1 to obtain copolymers. The polymerization degree and composition of the obtained polymer are shown in Table 1.
And 2 are shown.

[0058] (Comparative Example 1) in manufacturing [initial charge] internal volume 18 liters provided with stirrer stainless steel autoclave copolymer, methanol 7000
After charging 21 parts by weight of t-butylperoxyneodecanoate as a polymerization initiator, 5 parts by an aspirator were used.
It was evacuated for a minute to eliminate residual air and then charged with 3100 parts by weight of vinyl chloride monomer.

[Post-addition preparation] After removing air from a 3 liter addition container, 11 parts by weight of methacryloyloxyethyl trimethylammonium, 300 parts by weight of 2-hydroxypropyl acrylate and 1029 parts by weight of methanol were suctioned and further vinyl chloride monomer 1450 was added. Polymerization was carried out in the same manner as in Example 1 except that 1 part by weight of the copolymer was obtained by press-fitting. The polymerization degree and composition of the obtained copolymer are shown in Table 3.

(Comparative Examples 2 and 3) Various components shown in Table 3 in predetermined proportions were polymerized in the same manner as in Comparative Example 1 to obtain copolymers. The polymerization degree and composition of the obtained polymer are shown in Table 3.

Preparation of Magnetic Coating Solution A solution prepared by dissolving the copolymers obtained in the above Examples and Comparative Examples in a mixed solvent of toluene / methyl ethyl ketone (weight ratio 1: 1) so that the amount of the copolymer would be 15% by weight. In addition, a metal powder (BET value: 55 m ² /
g) and 6.5 parts by weight of an isocyanate compound (“Coronate L” manufactured by Nippon Polyurethane Industry Co., Ltd.) were added, and the mixture was shaken for 6 hours in a paint conditioner (manufactured by Red Devil Co.) to disperse the magnetic coating material.

Measurement of Physical Properties of Magnetic Paint The following physical properties of the above magnetic paint were measured and the results are shown in Tables 1 to 3. (1) Glossiness The above magnetic paint is applied on a polyester film, oriented,
A magnetic coating film was prepared by drying and allowing sufficient crosslinking reaction. For this magnetic coating film, the glossiness at an incident angle and a reflection angle of 60 degrees was measured using a digital variable angle gloss meter (“VG-1G” manufactured by Nippon Denshoku Industries Co., Ltd.). (2) Squareness Ratio The sample whose glossiness was measured was cut into a size of 4.5 × 7 cm, and a direct current magnetization characteristic recording device (“T /
3256-30 ").

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

The following surfactants were used.

[0067]

[Chemical 7]

[0068]

[Chemical 8]

[0069]

[Chemical 9]

[0070]

[Chemical 10] (However, m + n = 20)

[0071]

The binder resin for a magnetic recording medium of the present invention has the structure as described above, has an excellent affinity with the magnetic powder, and can be filled with the magnetic powder in a high density and a high orientation, and meets the required quality. Thus, various resin designs are easy, and it is possible to provide a wide variety of magnetic paints. The magnetic recording medium 2 of the present invention has a magnetic coating film having excellent electromagnetic characteristics, heat resistance, durability, and abrasion resistance, and thus is suitable for use in magnetic tapes, magnetic disks, magnetic cards and the like. .

Claims (2)

[Claims] 1. A vinyl monomer containing epoxy group,
Vinyl monomer containing ruboxyl group, tertiary amine
Group-containing vinyl monomer, quaternary ammonium salt group
Vinyl monomer containing SO₃M¹Group (M¹Is water
Elementary, NH_Four ⁺Or indicating an alkali metal)
Rumonomer, PO₂(OM²)₂ Group (M²Is hydrogen, alkali
Contains a metal or hydrocarbon group) and sulfobetaine
At least selected from the group consisting of vinyl monomers
Vinyl monomer containing at least one functional group, and hydroxyl group
Vinyl monomer containing, and vinyl chloride monomer
Is represented by the general formulas (1), (2) and (3)
Among surfactants (reactive emulsifiers) with double bonds
Use one or more kinds of oil-soluble radical initiator
From the copolymer obtained by solution polymerization in the presence of
A binder resin for a magnetic recording medium, wherein [Chemical 1][Chemical 2][Chemical 3][In the formula, R¹, R²And R³Is an alky having 1 to 22 carbon atoms
Lu group, R^Four, R^FiveAnd R ⁶Is H, Na, K, NH_FourShows
However, w, x, y, and z are integers of 1 to 30. ] 2. A magnetic recording medium having a magnetic layer composed of magnetic powder and a binder resin formed on one surface of a support and a non-magnetic layer composed of a binder resin formed on the other surface, wherein at least one of the binder resins comprises: A magnetic recording medium comprising the binder resin for a magnetic recording medium according to claim 1.