JPS6228927A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the durability, surface property and electromagnetic transducing characteristic of the titled medium by forming a magnetic layer consisting of ferromagnetic powder with a polyurethane resin contg. the tertiary amine salt of a sulfonic acid in the molecule as a polar group as the binder. CONSTITUTION:A magnetic layer consisting essentially of ferromagnetic powder and a binder is formed on a nonmagnetic carrier to obtain the magnetic recording medium. A polyurethane resin contg. the tertiary amine salt of a sulfonic acid in the molecule as a polar group is used as the binder of the magnetic layer. The polyurethane resin is formed by the reaction of a long-chain diol having about 500-5,000mol.wt. and a short-chain diol having about 50-500mol. wt. as the polyhydroxy compds. and an org. diisocyanate as the polyisocyanate. The durability, surface property and electromagnetic transducing characteristic of the magnetic recording medium can be improved in this way.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks, and more specifically, the present invention relates to magnetic recording media such as magnetic tapes and magnetic disks, and more specifically, the present invention relates to magnetic recording media such as magnetic tapes and magnetic disks. This invention relates to improvements in binders.

[Summary of the invention]

The present invention provides a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support. A polyurethane resin containing a sulfonic acid 8th class amine salt is used as the dispersibility of the magnetic powder and the surface Il;t of the magnetic layer.
The aim is to improve the durability, magnetic properties, electromagnetic conversion properties, etc. of the resulting magnetic recording medium.

[Conventional technology]

In recent years, improvements have been made in magnetic properties and electromagnetic conversion properties of magnetic recording media, especially those for VTRs (hypertape recorders), in order to obtain high playback output even when recording at short wavelengths. It is requested.

As a measure to this end, efforts have been made to make the magnetic powder particles finer and to increase its magnetic force, but there is a strong tendency to increase the packing density of the magnetic powder in the magnetic layer, the so-called panokine density.

On the other hand, conventionally used bond cutting materials for magnetic recording media include Nitrocell [j-su, polyester resin, polyurethane resin, hinyl chloride-hinyl acetate copolymer,
Examples include binders such as hinyl chloride-hinyl acetate-vinyl alcohol copolymers.

Due to the increase in the specific surface area due to the finer particles of the magnetic powder and the increase in cohesive force due to the increase in magnetic force, satisfactory dispersibility and surface properties cannot be obtained with the binder described above.
It is also difficult to increase the panokine density of magnetic powder.

Therefore, durability, magnetic properties (%), and electromagnetic conversion characteristics were also insufficient.Alternatively, methods such as using a surfactant as a dispersant have been considered, but in this case, the surfactant is Since it is a low molecule, the presence of this surfactant in the magnetic layer causes problems such as powder shedding and mechanical strength and durability such as bloom mink due to changes over time.

Under these circumstances, there is a need for binders that can further improve these properties. Special Publication No. 58-41.565) etc. have been proposed.

However, the above-mentioned binders have some effect on dispersion improvement (441) compared to conventional binders in which no rod groups are introduced (although they do not show ultrafine magnetic powder or high magnetization). Performance against magnetic 14g powder (sufficient is 41゛).

[Problem that the invention seeks to solve]

In this way, it does not show sufficient dispersibility even for ultrafine magnetic particles, and is not used as a h''44 mixture. Therefore, in a magnetic recording medium using this ultrafine particles, It was difficult to ensure durability, magnetic properties, and electromagnetic conversion characteristics.

Therefore, the present invention was proposed in order to eliminate the above-mentioned drawbacks in the technical field, and it has been proposed to significantly improve the dispersibility of magnetic powder and the surface properties of the magnetic layer, and to achieve excellent durability and Another object of the present invention is to provide a magnetic recording medium with good electromagnetic conversion characteristics.

=3- [Means for solving the problem] As a result of intensive research to achieve the above-mentioned objective, the present inventors have found that a polyurethane resin having a sulfonic acid 8th class amine salt as a polar group has a high resistance to magnetic powder. The present invention has been completed by discovering that it exhibits high affinity for
In a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, the magnetic layer is a polyurethane resin containing a sulfonic acid 8th class amine salt as a polar group in the molecule. It is characterized by containing as a binder.

The polyurethane resin according to the present invention is obtained by reacting a polyhydroxy compound with a polyisocyanate, and the polyhydroxy compound has a molecular weight of about 500 to about 5000.
It is preferable to use long chain diols having a molecular weight of about 50 to about 500;
- It is preferable to use organic diisocyanate for binding.

The above-mentioned long-chain diols are roughly classified into, for example, polyester diols, polyether diols, polyether ester glycols, and the like. As for polyester diol,
Specifically, examples include succinic acid, adipic acid, sebacic acid,
Aliphatic dicarboxylic acids such as acelaic acid, terephthalic acid,
Aromatic dicarboxylic acids such as isophthalic acid or lower alcohol esters, ethylene glycol, ],
, ] 8-propylene glycol] ] I4-Butylene glycol 1 , 6-H-t-san glycol, diethylene glycol, neopentyl glycol, or an ethylene oxide additive of bisphenol A, etc., or a mixture thereof. and lactone-based polyester diols obtained by ring-opening polymerization of rough I·n such as ε-caprolactone. Examples of the polyether diol include polyalkylene ether glycols such as polyethylene glycol, polypropylene ether glycol, Horite I/lanonalene ether glycol, and copolymerized polyether glycols thereof.

Examples of polyether ester glycols include polyester glycols obtained by reacting with aliphatic or aromatic carphonic acid as a polyalkylene ether glycol component. If the molecular weight of the polyurethane resin is too small, the concentration of methane groups in the resulting polyurethane resin will be too high, resulting in poor resin flexibility and poor solubility in solvents, making it difficult to use as a binder for magnetic recording media. It is not very preferable for use.Also, if the long chain diol molecule "i" is too thick, the long chain diol content in the resin will be too large and the urethane group concentration will be relatively very small. ,
The abrasion resistance and surface 1 heat resistance of the resin decrease.

” - Short chain diols include, for example, ethylene glycol,
Ethylene oxide adducts or propylene oxide adducts to aliphatic glycols or bisphenols such as 1, small-bunalendalicol, ■,6-hexahexylicol, and neopentyl glycol, ethylene oxide adducts of hydroquinone, etc. There are aromatic diols such as 4-hydrocarbons, and these can be used individually or mixed in various ratios depending on the desired properties of the polyurethane resin.

In addition, chrycerin, ethylene oxy-4-hydro-addition of chrycerin, 2-methylpropane-1-2.

8-triol, 4(-[bis(2-hydroxyethyl), II-2-hydrothousypentane, 8-methylpenkune-1., 8, 5-l-liol,]-
, 2, 6-hexane I-liol, 1-bis(2
It is also possible to use a triol such as a propylene oxide additive of (hydroxyethyl)amino-2-propasol and jetanolamine in combination.

Examples of the above-mentioned organic diisocyanates include aliphatic diisocyanates such as tetramethylene diisocyanate-1-, hexamena diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 2.
4-tolylene diisocyanate, 2,6-l-lylene diisocyanate, diphenylmethane diisocyanate, 3,8-dinotogycin 4-,4-biphenylene diisocyanate, cyachi 1-,4. , 4-diisocyanate phenyl ether, ■, 5-naphthalene diisocyanate 1-, 2.4+-naphthalene diisocyaner]・
Aromatic diisocyanates such as 1,3-diisocyanatomethylcyclohexane, ■,4(-diisocyanatomethylcyclohexyl→)-one, 4,4-diisocyanatodicyclohexylmethane, inophorone diisocyanate 1- Examples include alicyclic diisocyanates such as -1.

The reaction methods employed in the production of the polyurethane resin according to the present invention include melt polymerization in which the reaction is carried out in a molten state, and addition of the above-mentioned raw materials in an inert solvent such as ethyl acetate, methyl ethyl ketone, acetone, toluene, etc. alone or in combination. There is solution polymerization, which is carried out by dissolving
Solution polymerization is an effective method for producing polyurethane resins, which are often dissolved in solvents and used as binders for magnetic recording media. It is more preferable to carry out solution polymerization by adding the above-mentioned inert solvent to the solution.

In the reaction, an organometallic compound such as an organotin compound such as stannous ofnalate or dibutyltin dilaurate, or a tertiary amine such as N-methylmorpholine or l-lienalamine may be added as a catalyst. In order to increase the stability of the product, antioxidants, ultraviolet absorbers, hydrolysis inhibitors, etc. may be added in an amount of up to about 5% based on the solid content.

Furthermore, a sulfonic acid tertiary amine salt is introduced as a polar group into the above polyurethane resin, and the method for introducing it is as follows: (1) Sulfonic acid 3
A method in which a compound containing a class amine salt is mixed.

(11) A method of modifying the hydroxyl groups remaining at the ends or side chains of a polyurethane resin with a compound containing a tertiary amine sulfonic acid salt.

etc.

In the method (I), the sulfonic acid 8th class amine salt-containing compound is polymerized with other raw materials to form part of the polymer molecular chain of the polyurethane resin, and as a result, the sulfonic acid 8th class amine salt is added to the polyurethane resin described in -. An amine salt is introduced through the polar group.

Here, as the sulfonic acid 8th class amine salt-containing compound,
Examples include diols containing sulfonic acid 8th class amine salts, carboxylic acid components that do not have sulfonic acid tertiary amine salts,
It is obtained by reacting a glycol component and a dicarboxylic acid component having a sulfonic acid tertiary amine salt.

Examples of the carbonic acid component not having the above-mentioned sulfonic acid tertiary amine salt include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid,
- Aromatic oxycarboxylic acids such as oxybenzoic acid and p-(hydroxyethoxy)benzoic acid, aliphatic dicarboxylic acids such as succinic acid, adipic acid, acelaic acid, sebacic acid, and dodecanedicarboxylic acid, trinolisotonic acid, pyronolitic acid, etc. and tetracarboxylic acids.

The glycol components include ethylene glycol, phlopylene glycol, 1,3-propanediol,
4(-butanediol, 1,5-pencunediol, 1
．． G-hexanediol, neopentyl glycol, ethylene glycol, dipropylene glycol, 2,
2, 4-l-umenal-1,3-pencundiol,
]-]24-Cyclohexane dimethanol Examples of adducts of ethylene oxide and propylene oxide to bisphenol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol are listed. In addition, trinotyrolethane, l-IJ methylolpropane, chrycerin, penquelisol I-L, etc.
- and diol may be used in combination.

Examples of the dicarboxylic acid component having a tertiary amine salt of sulfonic acid include those shown below. On the other hand, in method (II), the terminal or side chain t of a polyurethane resin whose chain has been extended to a predetermined molecular weight by a polymerization reaction is used.
In contrast to the existing OH groups, a tertiary amine is reacted with a compound containing a sulfonic acid group. The reaction formula is as follows.

(iii-a (in the formula, RPU represents polyurethane resin, R4゜R5
, R6 each represent a hydrocarbon group having 1 to 6 carbon atoms. ) (::l I) (In the formula, Rpu represents a polyurethane resin.) In this case, as the sulfonic acid tertiary amine salt to be introduced, the following can be specifically mentioned.

-8doi-INo(Ca H7) 8■0 The amount of polar groups introduced into the polyurethane resin according to the present invention is 0
．． O1~1.0Im101/g
More preferably, it is in the range of 0.1 to 0.5 mmol/g. The amount of introduced polar group is 0.01 mmo I
If it is less than /i, a sufficient effect on the dispersibility of the ferromagnetic powder will not be recognized. Further, the amount of the polar group introduced is 1. Om
When the molZg is exceeded, intermolecular or intramolecular aggregation tends to occur, which adversely affects dispersibility, or selectivity to the solvent occurs, and there is a possibility that ordinary general-purpose solvents cannot be used.

Further, the number average molecular weight of the polyurethane resin according to the present invention is 1
0000~]-〇〇〇〇〇, more preferably 10000
The range is preferably from 60,000 to 60,000. If the number average molecular weight is less than -0000, the coating film forming ability of the resin will be insufficient, and if the number average molecular weight exceeds 60,000, problems will occur in paint manufacturing processes such as mixing, transport, and coating. There is a risk.

The polyurethane resins according to the invention can be used in combination with other thermoplastics, thermosets or reactive resins.

The plasticizable resin mentioned above has a softening temperature of 150°C or less, an average molecular weight of 10,000 to 200,000, and a polymerization degree of about 200 to 2,000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-chloride, etc. Vinyritine copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, thermoplastic polyurethane elastomer, polyvinyl fluoride, vinyl chloride,
= IJ Synthetic rubber-based thermoplastic resins such as den-acryloni I.Ryl copolymer, butadiene-acryloni I.Ryl copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives, polyester resin, polybutadiene, etc. can be mentioned. Examples of thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, melamine resins, alkyd resins, silicone resins, acrylic reactive resins, epoxy-polyamide resins, nitrocellulose-melamine resins, Mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycols/polymeric liver diols/tripolymers Examples include mixtures of phenylmethane triisocyanate, polyamine resins, and mixtures thereof. Among these, it is desirable to use in combination those with good dispersibility in ferromagnetic powder.

A magnetic layer is formed by dissolving the above-mentioned binder in an organic solvent in which ferromagnetic powder is dispersed and applying the solution to a non-magnetic support.

Examples of the ferromagnetic powder used in the present invention include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite particles, iron nitride, and the like.

The above-mentioned ferromagnetic iron oxide particles have a value of X in the range of 183≦X≦1.50 when expressed by the general formula FeOx, that is, Machemai l゛ (γ-Fez03).

X=]. 50), magnetite l- (Fe804,X=
]-, 88) and their solid solutions (FeOx, 1
．． 8 8 (X(1.5 0 ).Furthermore, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force.Cobalt-containing iron oxides can be roughly divided into doped type and uncoated type. There are two types of clothing.

Regarding the above-mentioned ferromagnetic chromium dioxide, Cr 0 2 or Ru is added to these for the purpose of improving coercive force.

Sn, Te, Sb, Fe, Ti
, V, Mn, etc. can be used.

Examples of the ferromagnetic alloy powder include Fc, Co, and Ni.

Fe-Co, Fe-Ni, Fe--Co
-Ni,C.

-Ni, Ii"e-Co -B, Ii"e-
Co-Cr-13゜Mn-Bi, Mn-A
I, Fe-Co-V, etc. can be used, and Ai, 81,
Metal components such as Ti, Cr, Mll, Cu, Z+] may also be added.

Furthermore, in addition to the binder and ferromagnetic fine powder, additives such as a dispersant, an f4 WR agent, a II agent, an antistatic agent, and a rust preventive agent may be added to the magnetic layer.

The above dispersants (pigment wetting agents) include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid,
Fatty acids with 12 to 18 carbon atoms (R?C00I-I) such as lyrinnic acid and stearolic acid.

R7 has 11 to 17 carbon atoms. alkyl or alkenyl groups), alkali metals (Ll) of the fatty acids mentioned above.

(Na, etc.) or alkaline earth metals (Mg, Ca, etc.).

A metal soap consisting of Ba), a fluorine-containing compound of the aforementioned fatty acid ester, an amide of the aforementioned fatty acid, a polyalkylene oxalkyl nitride phosphate, 1
-realkylpolyolefin' xy quaternary ammonium salt (al; tolu has 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), etc. are used. In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters can also be used. In addition to these, sulfuric acid and the like can also be used. These dispersants are added in an amount of 05 to 20 parts by weight per 100 parts by weight of the binder.

The above lubricants include dialkylpolysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxypolysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkylmonoalkoxypolysiloxane (alkyl has 1 to 4 carbon atoms), conductive fine powder such as graphite, Inorganic fine powder such as molybdenum disulfide and tungsten disulfide, polyethylene, polypropylene (cobylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene, etc.), α-olefin polymer, unsaturated liquid at room temperature Aliphatic hydrocarbons (n
- Compounds in which an olefinic double bond is bonded to the terminal carbon,
(approximately 20 carbon atoms), fatty acid esters consisting of a monobasic fatty acid having 12 to 20 carbon atoms and a monohydric alcohol having 8 to 12 carbon atoms, fluorocarbons, and the like can be used. These lubricants are used in an amount of 0.2 to 2 parts by weight per 100 parts by weight of binder.
It is added in an amount of 0 parts by weight.

The above-mentioned abrasives include commonly used materials such as fused alumina, silicon carbide, chromium oxide (Cr2(h), corundum, artificial corundum, diamond, artificial diamond, sacrostone, emery (main components: colander lx, 5 magnetite), etc. These abrasives have a Mohs hardness of 5 or more and an average particle size of 0.05 to 5 μm, particularly preferably 0.1 to 2 μm.

These abrasives are used in an amount of 0.5 to 100 parts by weight of the binder.
It is added in an amount of 20 parts by weight.

The antistatic agents mentioned above include conductive fine powders such as Tsunobon black and carbon black kraft poly, natural surfactants such as Zabonin, alkylene oxynide, glycerin, and cricidol. 7-ionic surfactants, higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, cationic surfactants such as phosphoniums, carboxylic acids, sulfonic acids, phosphoric acids, sulfuric ester groups, phosphoric ester groups 7,-1-ton surfactants containing acidic groups, such as amino acids, aminosulfonic acids, amphoteric surfactants such as sulfuric acid or phosphoric acid esters of amino alcohols, and the like are used. 2 to 20 parts by weight of the conductive fine powder and 0.1 to 10 parts by weight of the surfactant are added to 100 parts by weight of the binder. These surfactants may be added alone or in combination. Although these are used as antistatic agents, they are sometimes used for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids. Acid, sulfamide, quayucine, birinone, amine, urea, zinc chrome-l-1:
h Lucium Kurome ~]・,su)・Ronnaum Chrono
However, special
1., cyinobrobylamine litholite, jetanolamine phosphate 1., cyclohexylammonium carbonate 1., hexylene diamine carbonate I., propylene diamine stearate 1., guanidine carbonate. The rust prevention effect is improved by using a volatile rust inhibitor (an inorganic acid salt or an organic acid salt of an amine, amide or imide) such as 1., I. amine nitrite, and morpholine stearate. These rust inhibitors are used in an amount of 0.0'1 to 20 parts per 100 parts of ferromagnetic fine powder.
Used in parts by weight range.

In addition, the constituent materials of the magnetic layer are dissolved in an organic solvent to prepare a magnetic smear and smear, and this is applied to a non-magnetic support.
Solvents for the magnetic paint include acetic acid, methyl ethyl ketone, methyl isobunal ketone, carbon threads such as cyclohexylone, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, acetic acid monoethyl ether. esters such as glycolone methyl ether, glycol monoethyl ether, glycol ethers such as diokylene, aromatic hydrocarbons such as benzene,], luene, xylene, aliphatic such as hexane, \butane, etc. Hydrocarbons, notylene chloride, enalenc[colyte, carbon tetrachloride, chlorof-coform, egg chloride,
Examples include chlorinated hydrocarbons such as Nuku [] Lehenzen.

In addition, materials for the non-magnetic support include polyesters such as polyethylene telecrate, polyethylene-2,6-naphclay [. In addition to plastic snacks such as cellulose derivatives such as cellulose acetate bunarate P1 Cobione-1, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyimide, polyamideimide, etc., aluminum 23 = ram depending on the application. Non-magnetic metals, such as copper, tin, zinc or non-magnetic alloys, such as glass, ceramics, porcelain, etc.; Papers coated or laminated with α-polyolefins having 2 to 1.0 carbon atoms such as co-butene co-V can also be used.The non-magnetic support can also be in the form of film, tape, sheet, tape, card, etc. Any drums etc. are fine.

[For production]

As mentioned above, the polyurethane resin containing sulfonic acid 8th class amine salt in its molecule is a binder. By doing so, the affinity for magnetic powder is greatly improved, and even ultrafine magnetic powder or magnetic powder with a large amount of magnetization can be well dispersed.

〔Example〕

Hereinafter, specific example 1 of the present invention will be explained,
The present invention is not limited to these examples.

Polyurethane resins according to the invention are synthesized by the methods described herein. Table 1 shows the composition of the synthesized resin.

Table 1 Example I Co-coated r-Fe 208 ], 00
Part by weight hinyl chloride-vinyl acetate copolymer 1-(]〃(
V4GH manufactured by U, C, C) Polyurethane resin (resin A) 15 Dispersant (lecithin) 05 Lubricant (silicone oil) Abrasive (Cr20a) 2 ``Methyl ethyl ketone 0011 notyl isobunal ketone 50/l toluene
50 The above composition was mixed in a ball mill for 48 hours, filtered through a 3μ filter, 2.5 parts by weight of a curing agent (Tesmogyel L manufactured by Bayer AG) was added, and further mixed for 30 minutes. Polyenalene terephthalate film with a dry thickness of 6
It was coated so as to have a diameter of μ, subjected to magnetic field orientation treatment, dried and rolled up. After calendaring this, ]722
A sample tape was created by cutting it into inch pieces.

Example 2 In the composition of Example 1, a polyurethane resin (resin B) was used instead of the polyurethane resin (resin A), and Example]-
A sample tape was prepared in the same manner as above.

Example 8 A non-pull tape was prepared in the same manner as in Example 1, using a polyurethane resin (resin C) in place of the polyurethane resin (resin N) in the composition of Example.

Example 4 - Using a polyurethane resin (resin D) instead of the polyurethane resin (resin N) in the composition of example]
A no-pull tape was prepared using the same ls method.

Example 5 A sample tape was prepared in the same manner as in Example 1, using a polyurethane resin (resin E) instead of the polyurethane resin (resin N) in the composition of example (1).

Example 6 In the composition of Example 1, a polyurethane resin (resin F) was used for the polyurethane resin (resin N), and Example 1
A sample tape was prepared in the same manner as -.

Comparative Example 1 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin O) was used instead of polyurethane resin (Resin N) in the composition of Example 1.

Comparative Example 2 A sample tape was prepared in the same manner as in Example 1, using a polyurethane resin (Resin H) instead of the polyurethane resin (Resin A) in the composition of Example 1.

Table 2 shows the measurement results of the surface gloss, amount of dust, amount of abrasion, and still characteristics of the → no-pull tape described above.

In addition, the surface gloss is measured using a glossy needle with an incident angle of 75 and a reflection angle of 7.
The reflectance at No. 5 was measured.

To determine the amount of powder falling, visually observe the amount of powder falling on the head drum, guide, etc. after running the shuttle 100 times for 60 minutes, and set the maximum to 0.
The score was evaluated with the lowest score being 15 points.

Abrasion t is 50g of Zand paper and sample tape.
The sample tape was run 20 times under a load of 1, and the amount of weight loss of the sample tape was measured.

Still characteristics were determined by recording a 4.2 MHz video signal on a sample tape and measuring the time until the playback output attenuated to 50%.

Table 2 As is clear from the results in Table 2, by using a polyurethane resin containing SuJ'l/phonic acid tertiary amine salt as a binder for the magnetic layer, the durability and strength of the magnetic recording medium can be improved. The dispersibility of the magnetic powder is greatly improved.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
Since the binder of the magnetic layer is a polyurethane resin having a sulfonic acid 8th class amine salt as a molecular group,
Magnetic 14 (exhibits high affinity for powder, and has good dispersibility even if it is an ultrafine magnetic powder or a magnetic powder with a large amount of magnetization. Therefore, the durability of the resulting magnetic recording medium is The properties and outer surface area are improved, and the electromagnetic conversion properties are also extremely excellent.

Claims (1)

[Claims] A magnetic recording medium comprising a magnetic layer mainly composed of ferromagnetic powder and a binder formed on a non-magnetic support, wherein the magnetic layer is a polyurethane resin containing a sulfonic acid tertiary amine salt as a polar group in the molecule. A magnetic recording medium characterized by containing as a binder.