JPS6228926A - 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 on a nonmagnetic carrier with a polyurethane resin contg. a quaternary ammonium salt 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. a quaternary ammonium salt 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. isocyanate 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, in which the binder constituting the magnetic layer has polar groups in its molecules. Using a polyurethane resin containing quaternary ammonium salts, we aim to improve the dispersibility of magnetic powder and the surface properties of the magnetic layer, and aim to improve the durability, magnetic properties, electromagnetic conversion properties, etc. of the resulting magnetic recording medium. It is something to do.

[Conventional technology]

In recent years, there has been a demand for improved magnetic properties and electromagnetic conversion properties in magnetic recording media, especially magnetic recording media for VTJ video tape recorders, in order to obtain high playback output even when recording at short wavelengths. .

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

On the other hand, conventionally used binders for magnetic recording media include nitrocellulose, polyester resin, polyurethane resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate rubinyl alcohol copolymer, etc. Examples include agents.

However, as the specific surface area increases due to the finer particles of magnetic powder and the cohesive force increases due to higher magnetic force, the above-mentioned binders are unable to provide satisfactory dispersibility and surface properties, and the panoply of magnetic powder It is also difficult to increase the zinc density.
There are things and stones.

Therefore, the durability, magnetic properties, and electromagnetic conversion properties were also insufficient. Alternatively, methods such as using a surfactant as a dispersant have been considered, but in this case, since the surfactant is a low molecular weight, the presence of this surfactant in the magnetic layer Problems have arisen in terms of mechanical strength and durability, such as powder shedding and blooming due to changes over time.

Under these circumstances, there is a need for a binder that can further improve these properties. Kosho 58-41-565) etc. have been proposed.

However, although the above-mentioned binders show some effect in improving dispersibility compared to conventional binders in which no polar groups are introduced, The performance against this cannot be said to be sufficient.

[Problem that the invention seeks to solve]

As described above, there is no known binder that exhibits sufficient dispersibility even for ultrafine magnetic powder, and therefore magnetic recording media using ultrafine magnetic powder must have the required durability and magnetic properties. , it was difficult to ensure electromagnetic conversion characteristics.

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

-8= [Means for Solving the Problems] As a result of intensive research to achieve the above-mentioned purpose, the present inventors found that a polyurethane resin having a quaternary ammonium salt as a polar group is effective against magnetic powder. The present invention was completed after discovering that a magnetic recording medium exhibits high affinity, and in which a magnetic layer consisting mainly of ferromagnetic powder and a binder is formed on a non-magnetic support. The magnetic layer is characterized in that it contains a polyurethane/resin containing a quaternary ammonium salt as a polar group in the molecule 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 polyester diol,
Specifically, examples include succinic acid, adipic acid, sebacic acid,
Aliphatic dicarboxylic acids such as acelaic acid, aromatic dicarboxylic acids such as teI/fucuric acid, isophthalic acid, or their lower alcohol nysterates, ethylene crico/l/,
1 + 3-propylene glycol, 1,4j-butylene glycol, 1,6-hexane glycol, diethylene glycol, neopentyl glycol, or an ethyl oxide adduct to hisphenol, or a mixture thereof. and lactone-based polyester diols obtained by ring-opening polymerization of lactones such as ε-caprolactone. Examples of the polyether diol include polyalkylene ether glycols such as polyethylene glycol, polypropylene ether glycol, and polytetramethylene ether glycol, or copolymerized polyether glycols thereof.

Examples of polyether ester glycols include polyester glycols obtained by reacting the above polyalkylene ether glycol as a polyol component with aliphatic or aromatic dinonorponic acid. If the molecular weight of this long-chain diol is too small, the urethane group concentration of the resulting Boliu 1/Kun resin will become too large, resulting in poor flexibility of the resin and poor solubility in solvents, resulting in poor bonding of magnetic recording media. It is not very suitable for use as an agent. Furthermore, if the molecular weight of the long-chain diol is too large, the content of the long-chain diol in the resin will be too large, and the degree of urethane group breakage will be relatively small, resulting in poor wear resistance and heat resistance of the resin. descend.

The above-mentioned short chain diol is, for example, edil/glycol,
Propylene glycol, ], , ]4. -Aromatic diols such as aliphatic glycols such as butylene glycol, 6-hexahexylicol, and neopentyl glycol, ethylene oxide adducts or propylene oxide adducts to bisphenol, and ethylene oxide adducts of hydroquinone, etc. Depending on the desired properties of the polyurethane resin, these can be used alone or in combination in various ratios.

Furthermore, chrycerin, ethylene oxide adduct of chrycerin, 2-methylpropane-1,2゜3-triol, 4-[bis(2-hy[~loxethyl)]-2-hydroxypencune, 8-methylpentane-1 , 3,5-triol, 1,2,6-hexanetriol, ■-his(2-hydroxymediethyl)amine-2-propanol, propylene oxide adduct of jetanolamine, etc. are used in combination. It is also possible.

-Organic diinocyanars 1 and 1, including aliphatic diisocyanates such as tetraethylene diisocyanate and hexane diisocyanate, nl -phenylene diisocyanates 1 and 1) -phenylene diisocyanates 1 and 1, respectively , 2, 41-1-lylene diisocyanate, 2
, 6-1-lylene diisocyanate, diphenylmethane diisocyanate 1-18,8-dimethoxy-small, 4-
Biphenylene diisocyanate, 3,3-dinotyl-4
Aromatic isocyaners 1-, 1,3-, such as 4-biphenylene diisocyanate, 4,4 sage isocyanate diphenyl ether, 5-naphclean diisocyanate, 2,4+-naphthalene diisocyanate-1.
Diisocyanatomethylcyclohexane, ] , ]4-
Diisocyanate methylcyclohexane 4.4-Diisocyanate dicyclohexylmethane, alicyclic diisocyanate such as isophorone diisocyanate=1-, and the like.

In addition, the reaction method adopted in the production of the polyurethane resin according to the present invention includes melt polymerization in which the reaction is stirred in a molten state, a single method using ethyl acetate, methylmorpholine, acetone, toluene, etc., or a method using an inert solvent such as a mixed solvent. Solution polymerization is carried out by dissolving and blending the raw materials described above, but solution polymerization is preferable for producing polyurethane resins that are often used by dissolving them in solvents, such as binders for magnetic recording media. It is more preferable to carry out melt polymerization during preparation, and to carry out solution polymerization by adding the above-mentioned inert solvent before performing the chain extension reaction.

In the reaction, an organometallic compound such as a tin compound such as stannous ocdylate or dibutyltin dilaurate, or a tertiary amine such as N-methylmorpholine or triethylamine may be added as a catalyst. Antioxidants, ultraviolet absorbers, hydrolysis inhibitors, etc. may be added in an amount up to about 5% based on the solids content to increase the stability of the product.

Furthermore, a quaternary ammonium salt is introduced as a polar group into the polyurethane resin, and the method for introducing it is as follows: (1) A method of mixing a quaternary ammonium salt-containing compound as a raw material for the polyurethane resin.

(:*) A method of modifying the hydroxyl groups remaining at the ends or side chains of polyurethane resin with a quaternary ammonium salt-containing compound.

can be mentioned.

In method (1), the quaternary ammonium 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 quaternary ammonium salt-containing compound is added to the polyurethane resin. Salts are introduced as polar groups.

Here, examples of the quaternary ammonium salt-containing compound include a quaternary ammonium salt-containing seal.

This Φ-class ammonium salt-containing alcohol is, for example, a quaternary
It is synthesized by reacting a nonorponic acid component that does not have a quaternary ammonium salt, a glycol component, and a dicarboxylic acid component that has a quaternary ammonium salt.

Examples of the carbonic acid component not having a quaternary ammonium salt include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-naphthalic acid, p-
Aromatic oxycarboxylic acids such as oxybenzoic acid and p-(hydroxyethoxy)benzoic acid, aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and toticanedicarboxylic acid, trinolinodoic acid, pyromellitic acid, etc. and tri- and tetracarboxylic acids.

-1- glycol components include ethylene glycol, propylene glycol, l, 8-7"ropanediol, 2,2.Φ-1-1,J Nof-4,8
-pencunsool, 1,4-cyclohegizansimethanol, ethyleneoxy 1-adduct to hisphenol and propylene oxytoy-]adduct, polyethylene glycol, voliv [J-pyrene glycol, bolitetramedium] Examples include Len Rekol and the like. Further, triols and triols such as trinotylolethane, trimethylolpropane, chrycerin, and pentaerythritol may be used in combination.

Examples of the dicarboxylic acid component having the quaternary ammonium salt include those shown below.

-11~ (However, Rz, R2, and Rg each represent an alkyl group having 1 to 6 carbon atoms, and X represents Cl, 13r, or 1.) On the other hand, the method (11) uses a polymerization reaction to obtain a predetermined molecular weight. In this method, a compound having a primary ammonium salt is reacted with the OH group present at the end or side chain of a polyurethane resin whose chain has been extended.

In this case, first, a compound having a hydroxyl group and a quaternary ammonium salt is synthesized, and this is reacted with a diisocyanate compound in equimolar amounts to combine one NCO group of diisocyanate-1 and the Of-I group in the above molecule. By obtaining the reaction product and further reacting it with the OH group of a polyurethane resin, a polyurethane resin into which a quaternary ammonium salt has been introduced can be obtained. The reaction formula is as follows.

(ii-]) Substitution reaction Ca -11,A -C71+KOI-J--→Cg
-4%A -0f-ICa -R,A -0I-T +
N(Rn) 8n OHRA -N+-Rn -Ci- B (in the formula, RA represents a divalent hydrocarbon group, and R
n represents a monovalent hydrocarbon group such as an alkyl group. ) Specifically, i) f(OCH2CH(OH)CHzN”(CI(g
)a・C11-f:) f(OCJ-hcI-hN″
(C2I(5) 8・Cg-:il) f-IOCH
2CHzCI-T2CH2N+(CH3)a・CJ-i
V) l-10c(h cf-12C0N)-I(
CI-h)2N”(CI(a)s・C
6- etc. are mentioned.

(ii-2) B OCN-Rc-NCO-)OH-RA-N”-Rn −
CI-R,B-0CN-Rc-NHCOO-RA-N''-fLB-C
I -R, n 1i, n [mopu -0H-t-OCN-Rc -NHCOO-
One? , A --N"=I is also I3 ・C: 71-I
'(,n ■'LB -Rpu-OCON-R,c-NHCOO-R*,-N
4-Rn -C71-■ also represents B (in the formula, RA and Rc represent a divalent hydrocarbon group, R and B represent a monovalent hydrocarbon group such as an alkyl group, and RP
IJ represents polyurethane resin. ) The amount of polar groups introduced into the polyurethane resin according to the present invention is 0.01 to 1. Omm
ol/, ii'-C alcohol is better, more preferably in the range of 01 to 0.5 mmol/, y. If the amount of the polar group introduced is less than 0.01 mmol/g, a sufficient effect on the dispersibility of the ferromagnetic powder will not be observed.

Furthermore, if the amount of the polar group introduced exceeds 1.0 mmol/g, intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility, but also causes selectivity to the solvent, making it difficult for ordinary general-purpose solvents to There is also a risk that it may become unusable.

Further, the number average molecular weight of the polyurethane resin according to the present invention is 1
0000~100000. More preferably from 10,000
If the number average molecular weight is preferably in the range of 60,000, the coating film forming ability of the resin will be insufficient, and if the number average molecular weight exceeds 60,000, it will be difficult to manufacture paints. There is a risk that problems may occur in processes such as

The polyurethane resin according to the invention can be used in combination with other thermoplastic resins, thermosetting resins or reactive resins.

The above thermosetting resin has a softening temperature of 150°C or less,
The average molecular weight is 10,000 to 200,000 and the degree of polymerization is approximately 2.
00 to 20,000, such as vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyritine chloride copolymers, vinyl chloride-acrylonitrile copolymers, acrylic ester-acrylonitrile copolymers, thermoplastic polyurethane elastomers, Examples include synthetic rubber-based thermoplastic resins such as polyvinyl fluoride, hnyritene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyranope cellulose derivative, polyester resin, and polybutadiene. 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 incyanate prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycols/high molecular weight 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 dispersing ferromagnetic powder in the above-mentioned binder, dissolving it in an organic solvent, and coating it on a nonmagnetic 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, when expressed by the general formula FeOx, have a value of X in the range of 1.33≦X≦1.50, that is, maghemite (γ-Fe20a).

X=1.50), magneta 4 5 (FeaC) 4,
X=1.33) and Hikore et al.'s solid solution (FeOx
, 1.83 (X(L50)). 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.

The above-mentioned ferromagnetic chromium dioxide may include CrOz, or Ru and Sn for the purpose of improving coercive force thereof.

Te, Sb, F”e, Ti, V
, Mn, etc. can be used.

The ferromagnetic alloy powder includes i, +”c, Co,
Ni.

Fe-Co, Fe-Ni
, I'e-Go-Ni, C.

-Ni, Fe-Co-B, Fe-Co
-Cr-H.

Mn-Bi, Mn-A-71, Fe-Co-
V, etc. can be used, and metal components such as AA, Si 2 , Ti 2 , Cr, Mn, Cu, and Zn may be added to these for the purpose of improving various properties.

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

The above-mentioned dispersants (pigment wetting agents) include tunoprlic acid, capric acid, lauric acid, myristic acid, valmitic acid,
Fatty acids with 12 to 18 carbon atoms (R7C00f), such as stearic acid, oleic acid, elaidic acid, linoleic acid, lylunic acid, and stearic acid.

R7 is an argyl group or alkenyl group having 11 to 17 carbon atoms), an alkali metal of the above-mentioned fatty acid (L+).

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

Metal soaps consisting of Ba), fluorine-containing compounds of the fatty acid esters mentioned above, amino+- of the fatty acids mentioned above, polyalkylene Ogisai I alkyl phosphate esters, 1-herylkyl polyolefin oxy quaternary ammonium salts (
The alkyl has 1 to 5 carbon atoms, and the olefin includes ethylene, propylene, etc. In addition, carbon number 12
In addition to the following higher alcohols and these, sulfuric esters and the like can also be used. These dispersants are binders 100%
It is added in an amount of 0.5 to 20 parts by weight.

The above lubricants include dialkylpolysiloxane (argyl has 1 to 5 carbon atoms), dialkylpolysiloxane (alkoxy has 1 to 4 carbon atoms), monoargylmonoalkoxypolysiloxane (alkyl has 1 to 5 carbon atoms). ,
Alkoxy has 1 to 4 carbon atoms), phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbon atoms) f9i silicone oil, conductive fine powder such as graphite, molybdenum disulfide, tungsten disulfide Nato's inorganic fine powder, polyethylene, polypropylene,
Polyethylene-hinyl chloride copolymer, plastic fine powder such as polytetrafluoroethylene, α-olefin polymer, unsaturated aliphatic hydrocarbon that is liquid at room temperature (compound with n-olefin double bond bonded to the terminal carbon, carbon (approximately 20), monobasic fatty acids having 12 to 20 carbon atoms, fatty acid esters consisting of monohydric alcohols having 3 to 12 carbon atoms, fluorocarbons, and the like can be used. These lubricants are added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder.

The above-mentioned abrasives are commonly used materials such as fused alumina, silicon carbide, chromium oxide (Cr20a), corundum, artificial corundum, diamond, artificial diamond, garnet, and emery (main components are corundum and magnetite).
etc. are used. 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 added in an amount of 0.5 to 20 parts by weight based on 100 parts by weight of the binder.

The antistatic agents mentioned above include conductive fine powders such as carbon blank, carbon blank Guow I, and polymers, natural surfactants such as saponin, alkylene oxide type,
Nonionic surfactants such as glycerin and glycidol, higher argylamines, quaternary ammonium salts,
Pyridine and other heterocycles, cationic surfactants such as phosphoniums, anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfuric ester groups, phosphoric ester groups, amino acids, amine sulfonic acids , amphoteric activators such as sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. The above conductive fine powder is added in an amount of 0.2 to 20 parts by weight, and the surfactant is added in an amount of 0.1 to 0.0 parts by weight 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 applied for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids.

As the above-mentioned rust preventive agent, phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, zinc chloride, calcium chlornaute, stolone-1-ramfuronaute, etc. can be used, but in particular, zinc [lhexylaminenite] Rai I., cyclohexylamine tetramate, diinopropylamine nitrite, jetanolamine phosphate, cyclohexylammonium carbonate I.
, hegisamethylenediamine carbonate I, propylene diamine stearate 1, guanidine carbonate 1,
The antirust effect is improved by using a volatile rust inhibitor (inorganic or organic acid salt of amine, amide or imide) such as triethanolamine (triethanolamine)-lite and morpholine stearate. These rust inhibitors are made of ferromagnetic fine powder 100
It is used in a range of 0.001 to 20 parts by weight.

In addition, the constituent materials of the magnetic layer are dissolved in an organic solvent to prepare a magnetic paint, which is coated on a non-magnetic support.The solvent for the magnetic paint may be acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohegizanone, etc.・Esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether,
Glycol ethers such as glycol dimedyl ether, glycol monoethyl ether, and oxane; aromatic hydrocarbons such as benzene, toluene, and chlorine; aliphatic hydrocarbons such as ・＼kizan, -＼pukun, and methylene chloride. , ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, and other chlorinated hydrocarbons. In addition, the materials for the non-magnetic support are polyethylene telecrate, polyethylene-2
, 6-naphthalene=1, etc., polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate butylene acetate l/-1-, cellulose acetate probionate, polyvinyl chloride,
In addition to vinyl resins such as polyvinyritine chloride, plastics such as polycarbonate I, polyimide, and polyamideimide, non-magnetic metals such as aluminum, copper, tin, zinc, and non-magnetic alloys containing iron, etc., depending on the application. glass, pottery, porcelain, ceramics, paper, like or polyethylene,
Papers coated with or laminated with α-poly primary nophines having 2 to 10 carbon atoms such as polypropylene and ethylene-butene copolymers can also be used. The nonmagnetic support may be in any form such as a film, tape, sheet, disk, card, or drum.

[For production]

As mentioned above, by using polyurethane resin containing quaternary ammonium wheels in the molecule as a binder, the affinity for magnetic powder is greatly improved, making it possible to create ultra-fine magnetic powders and large amounts of magnetization. Even magnetic powders are well dispersed.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

Resin Synthesis Example A polyurethane resin according to the present invention was synthesized by the method described herein. Table 1 shows the properties of the synthesized resin.

Table 1 Examples] Co-adhered r-F”ezOa ]-007 amount HIH vinyl chloride-vinyl acetate copolymer 1o (U,
C, C, manufactured by VA, G f () polyurethane resin (
(contains resin) 15 Dispersant (lecithin)
o5 Lubricant (silicone oil)
1 Abrasive (Cr20g) 2
``Methyl ethyl ketone Joo 〃Methyl isobutyl ketone 5o〃1゛toluene
5o〃The above composition was mixed in a ball mill for 48 hours, filtered through an 8μ filter, and then mixed with a curing agent (Tess-E Series L manufactured by Bayer AG) of 2.5
Parts by weight were added and mixed for an additional 30 minutes. This was applied onto a polyethylene terephthalate film having a thickness of 16 μm so that the thickness after drying would be 6 μm. After performing a magnetic field orientation treatment, it was dried and wound up. This was subjected to force/under treatment and then cut to a width of 172 inches to produce a no-pull tape.

Example 2 A sample tape was prepared in the same manner as in Example 1, using Boliu I/Tan resin (Resin 13) instead of the polyurethane resin (Resin N) in the composition of Example 1.

Example 3 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin C) was used in place of the polyurethane resin (Resin A) in the composition of Example 1.

Example 4 In the composition of Example 1, polyurethane resin (Resin I) was used instead of polyurethane resin (Resin A), and Example 1
A sample tape was prepared in the same manner as in 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 A) in the composition of Example 1. It was created.

Example 6 A non-pull tape was prepared in the same manner as in Example 1 except that polyurethane resin (resin-containing) was used instead of polyurethane resin (resin-containing) in the composition of Example 1.

Comparative Example ■ A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (resin O) was used in place of the polyurethane resin (resin-containing) in the composition of Example 1.

Comparative Example 2 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin H) was used instead of polyurethane resin (Resin N) in the composition of Example 1.

Surface gloss, amount of powder falling off, amount of abrasion,
Table 2 shows the measurement results of still characteristics.

The surface gloss was measured using a gloss meter at 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.

The amount of abrasion is 50% between the sandpaper and the sample tape.
The sample tape was run 20 times under a load of 9, and the weight loss of the sample tape was measured.

The still characteristics are 4.2 MHz c on the sample tape.
r) A video signal was recorded, and the time until the playback output attenuated to 50% was measured.

Table 2 By using a polyurethane resin containing a monium salt as a binder for a magnetic layer, surface durability of a magnetic recording medium, dispersibility of ferromagnetic powder, etc. are significantly improved.

〔Effect of the invention〕

As is clear from the above explanation, in the present invention ζ, quaternary ammonium niuno, ji,
Since the polyurethane resin with i has a low binder in the magnetic layer, it has a high affinity for magnetic powder, and even if it is an ultra-fine magnetic powder or a magnetic powder with a large amount of magnetization, it has good dispersibility. It will be good. Therefore, the durability and surface properties of the obtained magnetic recording medium are improved, and the electromagnetic conversion characteristics are also extremely excellent.

Claims (1)

[Claims] 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 made of a polyurethane resin containing a quaternary ammonium salt as a polar group in the molecule. A magnetic recording medium comprising a binder as a binder.