JPS6292230A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the characteristic of the titled magnetic recording medium by using a polyurethane resin having a siloxane coupling in the molecular chain and having a quaternary ammonium salt in the molecular side chain as a polar group in a binder constituting a magnetic layer on a nonmagnetic carrier. CONSTITUTION:A long-chain diol having 500-5,000mol.wt. and a short-chain diol having 50-500mol.wt. are used as a polyhydroxy compd., an org. diisocyanate is used as a polyisocyanate, further a quaternary ammonium salt- contg. compd. is incorporated, a stabilizer of the product such as an antioxidant is added and polymerization is carried out. A polyester diol, a polyether diol, etc., are used as the long-chain diol. When the mol.wt. of the diol is beyond the specified limits,the softness, solubility in solvents and resistance to wear and heat are deteriorated. An aliphatic glycol, an aromatic glycol or their mixture are used as the short-chain diol. The ultrafine particles of ferromagnetic powder are dispersed in the resin, the resin is dissolved in an org. solvent and the soln. is coated on the nonmagnetic carrier to form the magnetic layer. Consequently, the magnetic recording medium having excellent durability, traveling stability, magnetic characteristic and electromagnetic transducing characteristic can be obtained.

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. The present invention relates to improvements in binders used in the manufacturing process.

[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 a siloxane bond in its molecular chain. However, by using a polyurethane resin having a quaternary ammonium salt as a polar group in the molecular side chain, we can improve the dispersibility of the magnetic powder and the surface properties of the magnetic layer, and improve the durability of the resulting magnetic recording medium. The aim is to improve running stability, magnetic properties, electromagnetic conversion properties, etc.

[Conventional technology]

In recent years, magnetic recording media, especially magnetic recording media for VTRs (video tape recorders), are required to have improved magnetic properties and electromagnetic conversion properties 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, that is, the so-called banking 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-vinyl alcohol copolymer, etc. can be mentioned.

However, with the increase in the specific surface area due to the finer particles of magnetic powder and the increase in cohesive force due to higher magnetic force, the above-mentioned binders cannot provide satisfactory dispersibility and surface properties, and the backing of the magnetic powder becomes difficult. Increasing the density has also become difficult.

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 causes the powder to become powdery. Problems have arisen in terms of mechanical strength and durability, such as falling off and blooming due to changes over time.

Under these circumstances, there is a need for a binder that can further improve these properties, and attempts have been made to introduce hydrophilic polar groups into the side chains of various binder resins. Examples of the binder include polyester resin containing a sulfonic acid metal base (Japanese Patent Publication No. 57-3134), polyurethane resin containing a sulfonic acid metal base (Japanese Patent Publication No. 58-41565),
), -803M.

A binder resin (Japanese Unexamined Patent Application Publication No. 59-79427), etc., is known.

However, although the above-mentioned binders are effective to some extent in improving dispersibility compared to conventional binders in which polar groups are not introduced, the use of ultrafine magnetic powders and magnetic powders with high magnetization The performance for this cannot be said to be sufficient.

Furthermore, when the various binder resins mentioned above are used as binders for the magnetic layer, the resins themselves lack lubricity and have problems in running stability.

[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.

Furthermore, since the binder resin itself lacks lubricity, there is a problem in running stability of the magnetic recording medium.

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 provide excellent durability and running stability. The object of the present invention is to provide a magnetic recording medium with good characteristics and electromagnetic conversion characteristics.

[Means for solving problems]

As a result of intensive research to achieve the above-mentioned purpose, the present inventors have found that a polyurethane resin having a siloxane bond in its molecular chain and a quaternary ammonium salt as a polar group in its molecular side chain is suitable for magnetic powder. The present invention has been completed by discovering that the material has a high affinity for magnets, exhibits lubricity, and has excellent running stability. In a magnetic recording medium in which a magnetic layer is formed, the magnetic layer contains a polyurethane resin having a siloxane bond in its molecular chain and a quaternary ammonium salt as a polar group in its molecular side chain as a binder. This is a characteristic feature.

The polyurethane resin according to the present invention is obtained by the reaction of a polyhydroxy compound and a polyincyanate, and the polyhydroxy compound has a molecular weight of about 500 to about 5,000.
It is preferable to use long-chain diols having a molecular weight of about 50 to about 500, and it is preferable to use organic diisocyanates as the polyisocyanate.

The above-mentioned long-chain diols are roughly classified into, for example, polyester diols, polyether diols, polyether ester glycols, and the like. Specific examples of polyester diols include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and azelaic acid, aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid, or their lower alcohol nysterates, ethylene glycol, 1.3-propylene glycol, 1,4-butylene glycol, 1
, 6-hexane glycol, diethylene glycol, neopentyl glycol, or an ethylene oxide adduct of bisphenol A, or a mixture thereof, or a polyester diol obtained by ring-opening polymerization of a lactone such as ε-caprolactone. Examples include lactone-based polyester diols. 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 an aliphatic or aromatic dicarboxylic acid.

If the molecular weight of this long-chain diol is too small, the urethane group concentration of the resulting polyurethane resin will be too low, resulting in poor resin flexibility, poor solubility in solvents, and binding of magnetic recording media. It is not preferable to use it as an agent. When the molecular weight of the long-chain diol is too large, the long-chain diol content in the resin becomes too large and the urethane group concentration becomes relatively low, resulting in a decrease in the abrasion resistance and heat resistance of the resin.

The short chain diols mentioned above are, for example, ethylene glycol, propylene gelylcol, 1,4-butylene glycol,
Aliphatic glycols such as 6-hexane glycol and neohentyl glycol, or ethylene oxide adducts or propylene oxide adducts of bisphenol A;
There are aromatic diols such as ethylene oxide adducts of hydroquinone, and these can be used alone or in mixtures in various ratios depending on the desired properties of the polyurethane resin.

Furthermore, glycerin, glycerin ethylene oxide adduct, 2-methylpropane-1,2,3-triol,
4-[bis(2-hydroxyethyl))-2-hydroxypentane, 3-methylpentane-1,3,5-triol, 1,2.6-hexane glycol, 1-bis(2
It is also possible to use triols such as -hydroxyethyl)amino-2-gropanol and a propylene oxide adduct of jetanolamine.

Examples of the organic diisocyanate include aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2.6-1 lylene diisocyanate, diphenylmethane diisocyanate, 3,3'
-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-naphthalene diisocyanate, 2 ，
Aromatic diisonanates such as 4-naphthalene diisocyanate, 1,3-diincyanatomethylcyclohexane, 1,4-diincyanatomethylcyclohexane, 4,4'-diisocyanatodicyclohexylmethane, inphorone diisocyanate, etc. Examples include alicyclic diisocyanates.

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, solution polymerization in which ethyl acetate or methyl ethyl chloride is used, etc. Solution polymerization is preferred for the production of polyurethane resins, which are often used after being dissolved.In particular, when preparing a prepolymer, it is preferable to carry out melt polymerization, and then perform solution polymerization by adding the above-mentioned inert solvent before performing the chain extension reaction. More preferred.

In the reaction, an organometallic compound such as an organotin compound such as stannous octylate or dibutyltin dilaurate, or a tertiary amine such as N-methylmorpholine or triethylamine may be added as a catalyst. Also, to increase the stability of the product, antioxidants, ultraviolet absorbers,
A hydrolysis inhibitor or the like may be added in an amount of about 5% or less based on the solid content.

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

(11) A method of modifying a hydroxyl group remaining at the end or side chain of a polyurethane resin with a quaternary ammonium salt-containing compound.

can be mentioned.

In method 0), 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 forms a polar group in the polyurethane resin. It will be introduced as

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

This quaternary ammonium salt-containing diol is, for example, a quaternary ammonium salt-containing diol.
It is synthesized by reacting a carboxylic acid component not having a quaternary ammonium salt, a glycol component, and a dicarboxylic acid component having a quaternary ammonium salt.

Examples of the carboxylic 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, dodecanedicarboxylic acid, trimellitic acid, pyromellitic acid, etc. and tri- and tetracarboxylic acids.

The glycol components include ethylene glycol, phlopylene gellicol, 1,3-propanediol, 1.
4-butanediol, 1,5-bentanediol, l,
6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,
4-trimethyl-1,3-bentanediol, 114-
Examples include cyclohexane dimetatool, ethylene oxide adducts and propylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be used in combination. Examples of the dicarboxylic acid component having a quaternary ammonium salt include those shown below.

0OH (However, R,, R2, and R3 each represent an alkyl group having 1 to 6 carbon atoms, and X represents CA?, Br, or A compound having a quaternary ammonium salt is reacted with an OH group present at the end or side chain of a polyurethane resin whose chain has been extended to a molecular weight.

In this case, first, a compound having a hydroxyl group and a quaternary ammonium salt is synthesized, and this is reacted with a diincyanate compound in equimolar amounts to obtain a reaction product between one NCO group of the diisocyanate and the OH group in the above molecule. Then, by further reacting with the OH group of the polyurethane resin, a polyurethane resin into which a quaternary ammonium salt has been introduced can be obtained. The reaction formula is as follows.

C1-RA -OH+N(RB) 3B 0H-RA -N -Ra-C1 (However, in the formula, RA represents a divalent hydrocarbon group, and R
B represents a monovalent hydrocarbon group such as an alkyl group. ) Specifically i) HOCH2CH(0H)CH2N+(CH3)
s ・C1-ff) HOCH2CH2N”(C2H
5) s・C/-t! t) HOCHzCLCHzCH2
N+(CHs)s・C1-tV) HOCH2CH2C
ONH(CH2)2N+(CH3)!・C1- etc. are mentioned.

(ii-2) n RB ] RB (In the formula, RA + Rc represents a divalent hydrocarbon group, RB represents a monovalent hydrocarbon group such as an alkyl group, and RPU represents a polyurethane resin.) Furthermore, A siloxane bond is introduced into the molecular chain (main chain) of the polyurethane resin, and an example of an introduction method is to mix a compound having a siloxane bond into the starting material of the polyurethane resin. Specifically, a diol having a siloxane bond may be used as the compound having a siloxane bond, and the diol having a siloxane bond may be mixed into a part of the polyhydroxy compound.As the diol having a siloxane bond, the following general Examples include compounds represented by the formula.

(However, R represents a divalent hydrocarbon group.) The molecular weight of the above compound can be from 300 to 10,000.

It is also possible to use a polyhydroxy compound in which a siloxane group has been introduced in advance.

For example, when synthesizing polyhydroxy compounds such as polyester diols and polyether ester diols, the diols having the aforementioned siloxane bonds may be used.

The amount of polar groups introduced into the polyurethane resin according to the present invention is 0.
．． It is preferably in the range of 0.01 to 1,0 mmol/y, and more preferably in the range of 0.1 to 0.5 mmol/g. The amount of introduced polar group is 0.01rrLrrIO1/
If it is less than g, a sufficient effect on the dispersibility of the ferromagnetic powder will not be recognized. In addition, the amount of the polar group introduced is 1.0 mrn
If ol/y is exceeded, intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility, but also causes selectivity to the solvent, which may make it impossible to use ordinary general-purpose solvents.

Further, the siloxane group concentration of the polyurethane resin according to the present invention is preferably 0.03 mmol/g to 3 mmol/g, and 0.1 mmol/11 to 0.7 mmol/g.
More preferably, it is mmol/g. If the siloxane group concentration is less than 0.03 mmol/y, lubricity cannot be imparted;
If it exceeds mmol/Ii, the solubility with the solvent and the compatibility with other binders will deteriorate, and the physical properties such as the breaking strength and Young's modulus of the magnetic coating will deteriorate.

Further, the number average molecular weight of the polyurethane resin according to the present invention is 1
0000~100000, preferably 10000~
The range is preferably 60,000.

If the number average molecular weight is less than 10,000, the coating film forming ability of the resin will be insufficient, and if the number average molecular weight is less than 6,000.
If it exceeds 0, there is a risk that problems will occur in paint manufacturing processes such as mixing, transporting, and coating.

The polyurethane resins according to the invention can be used in combination with other thermoplastics, thermosets or reactive resins. The above-mentioned thermoplastic resin has a softening temperature of 150°C or less and an average molecular weight of 10,000 to 20,000.
0 and the degree of polymerization is about 200 to 2000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer. , thermoplastic polyurethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative, polyester resin, polybutadiene, and other synthetic rubber-based thermoplastic resins. It will be done.

Examples of thermosetting resins or reactive resins include:
Phenolic resin, epoxy resin, polyurethane curable resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin, epoxy-polyamide resin, nitrocellulose-melamine resin, mixture of high molecular weight polyester resin and incyanate prepolymer, methacrylic mixture of acid salt copolymer and diisocyanate prepolymer,
Examples include mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanates, 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 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 are those whose value of X is in the range of 1.33≦X≦1.50 when expressed by the general formula 1;
．． 50), magnetite (Fe3O4, X = 1.33
) and their solid solutions (FeOx, 1.33 <
x<1.50). Furthermore, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. There are two types of cobalt-containing iron oxide: doped type and deposited type.

The above-mentioned ferromagnetic chromium dioxide includes CrO2 or Ru and Sn for the purpose of improving coercive force.

A material to which at least one of Te, Sb, Fe, 'l'i, V, Mn, etc. is added can be used.

As the ferromagnetic alloy powder, Fe, Co, Ni
, Fe-Co, Fe-Ni, Fe-Co
-Ni, Co-Ni, Fe-Co-B,
Fe-Co-Cr-B, Mn-Bi,
Mn-AJI, FeCo-V, etc. can be used, and M, Si,
Ti, Cr.

Metal components such as Mn, Cu, and Zn may also be added.

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 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 (RCOOH) such as lyrinnic acid and stearolic acid.

R is an alkyl or alkenyl group having 11 to 17 carbon atoms), an alkali metal of the above fatty acid (LiINa, K
etc.) or alkaline earth metals (Mg, Ca.

Metal soaps consisting of Ba), fluorine-containing compounds of the above fatty acid esters, amides of the above fatty acids, polyalkylene oxide alkyl phosphate esters, trialkyl polyolefin oxy quaternary ammonium salts (alkyl has 1 to 5 carbon atoms, The olefins used include ethylene, propylene, etc. In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters can also be used. These dispersants are added in an amount of 0.5 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 5 carbon atoms) ,
Alkoxy has 1 to 4 carbon atoms), silicone oil such as phenylpolysiloxane, fluoroalkylpolysiloxane (alkyl has 1 to 5 carbon atoms), conductive powder such as graphite, and inorganic materials such as molybdenum disulfide and tungsten disulfide. Fine powder, polyethylene, polypropylene, polyethylene vinyl chloride copolymer, plastic fine powder such as polytetrafluoroethylene, α-olefin polymer, unsaturated aliphatic hydrocarbon that is liquid at room temperature (n-olefin double bond at the end) Compounds bonded to carbon, approximately 2 carbon atoms
0), monobasic fatty acids with 12 to 20 carbon atoms and 3 carbon atoms
Fatty acid esters consisting of ~12 monohydric alcohols, fluorocarbons, etc. 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 (Cr20), corundum, artificial corundum, diamond, artificial diamond, garnet, and emery (main ingredients: 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 0.65 to 20 parts by weight based on 100 parts by weight of the binder.

Examples of the antistatic agent include conductive fine powder such as carbon black and carbon black graft polymer, natural surfactants such as saponin, nonionic surfactants such as alkylene oxide, glycerin, and glycidol, higher alkyl amines, Cationic surfactants such as quaternary ammonium salts, pyridine and other heterocycles, phosphoniums, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric acid ester groups; Ampholytic active agents such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. The above conductive fine powder is binder 1
The surfactant is added in an amount of 0.2 to 20 parts by weight per 0.00 parts by weight, and a surfactant is added in an amount of 0.1 to 10 parts by weight. 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 chromate, calcium chromate, strontium chromate, etc. can be used, but in particular, dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, gel tanolamine phosphate,
Volatile rust inhibitors (inorganic or organic acid salts of amines, amides or imides) such as cyclohexylammonium carbonate, hexamethylene diamine carbonate, propylene diamine stearate, guanidine carbonate, triethanolamine nitrite, and morpholine stearate. When used, the rust prevention effect improves. These rust inhibitors are 0.01 parts by weight per 100 parts by weight of ferromagnetic fine powder.
It is used in a range of 20 parts by weight.

The constituent materials of the magnetic layer are dissolved in an organic solvent to prepare a magnetic paint, and this is coated on a non-magnetic support, but the solvent for the magnetic paint is a ketone-based solvent such as acetone, methyl ethyl ketone, methyl isobutyl ketone, or cyclohexanone. , methyl acetate, ethyl acetate, butyl acetate, ethyl lactate,
Ester types such as acetic acid glycol monoethyl ether, glycol ether types such as glycol dimethyl ether, glycol monoethyl ether, and dioxane, aromatic hydrocarbons such as Hensen, toluene, and xylene, hexane,
Examples include aliphatic hydrocarbons such as heptane, chlorine hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene. Materials for the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyoles such as polyethylene and polypropylene, fins, cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate, etc. In addition to cellulose derivatives such as Nate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, plastics such as polycarbonate, polyimide, and polyamideimide, aluminum, copper, tin, zinc, or non-magnetic alloys containing these, depending on the application. non-magnetic metals, glass, pottery, ceramics such as porcelain, paper, paper coated with or laminated with baryta or α-polyolefins having 2 to 10 carbon atoms such as polyethylene, polypropylene, and ethylene-butene copolymers. Paper can also be used. The nonmagnetic support may be in any form such as a film, tape, sheet, disk, card, or drum.

[For production]

By introducing a quaternary ammonium salt into the polyurethane resin, the affinity for magnetic powder is significantly improved. Therefore, by using this as a binder, even ultrafine magnetic powder or magnetic powder with a large amount of magnetization can be dispersed well.

At the same time, the siloxane bonds have a lubricating effect, which provides good running properties.

In addition, polyurethane resins are soluble in general-purpose solvent systems, are easy to handle, and exhibit excellent coating film properties.

〔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 containing a quaternary ammonium salt and a siloxane bond in the molecule was synthesized according to the synthesis method described above. Table 1 shows the properties of the synthesized resin.

(Otori et al.) Example I Co adhesion r Fe2O3 100 parts by weight Vinyl chloride-vinyl acetate copolymer 10〃(U, C, C, manufactured by V
AGH) Polyurethane resin 15 (Resin A) Dispersant (lecithin) 0.5 Lubricant (silicone oil) 1 Abrasive (C
rzos) 2 tt methyl ethyl ketone 100 tt methyl isobutyl ketone 50 toluene
50 The above composition was mixed in a ball mill for 48 hours, filtered through a 3 μm filter, 2.5 parts by weight of a curing agent (Desmodur L, manufactured by Bayer AG) was added, further mixed for 30 minutes, and the mixture was mixed to a thickness of 16 μm. It was coated onto a polyethylene terephthalate film so that the thickness after drying would be 6 μm, subjected to magnetic field orientation treatment, dried, and rolled up. This was calendered and then cut into 1/2 inch width to prepare sample tapes.

Example 2 A sample tape was prepared in the same manner as in Example 1 using a polyurethane resin (Resin B) as a substitute for the polyurethane resin (Resin A) in the composition of Example 1.

Example 3 A sample tape was prepared in the same manner as in Example 1 using a polyurethane resin (Resin C) as a substitute for the polyurethane resin (Resin A) in the composition of Example 1.

Example 4 A sample tape was prepared in the same manner as in Example 1 using a polyurethane resin (Resin D) as a substitute for the polyurethane resin (Resin A) in the composition of Example 1.

Example 5 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin E) was used in place of the polyurethane resin (Resin A) in the composition of Example 1.

Example 6 A sample tape was prepared in the same manner as in Example 1 except that a polyurethane resin (Resin F) was used instead of the polyurethane resin (Resin A) in the composition of Example 1.

Comparative Example 1 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin H) was substituted for the polyurethane resin (Resin A) 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 (Jinko) as the base of the polyurethane resin (Resin A) in the composition of Example 1.

Comparative Example 3 A sample tape was prepared in the same manner as in Example 1 using a polyurethane resin (Resin J) as a substitute for the polyurethane resin (Resin A) in the composition of Example 1.

Table 2 shows the measurement results of the coefficient of dynamic friction, surface gloss, amount of falling powder, adhesive properties, and still properties of the above sample tapes.

Note that the coefficient of dynamic friction is calculated at a low tape speed (0.4 mm/s
It was measured as the friction coefficient (load 50I) between the magnetic layer surface and IS stainless steel at ee ). The surface gloss was determined by measuring the reflectance at an incident angle of 75° and a reflection angle of 75° using a gloss meter. The amount of falling powder was evaluated by visually observing the amount of falling powder on the head drum, guide, etc. after running the shuttle 100@ for 60 minutes, and scoring the highest as 0 points and the lowest as 15 points. Adhesive properties were determined by winding the sample tape onto a reel and keeping it at a temperature of 40°C.
After being left under conditions of 80% humidity for 24 hours, the degree of peeling of the sample tape was visually evaluated and scored on a 10-point scale, with the better the adhesive properties, the lower the score. The methyl characteristics were measured by recording a 4.2 MHz video signal on a sample tape and measuring the time until the playback output attenuated to 50%.

As is clear from the results in Table 2, using a polyurethane resin containing a quaternary ammonium salt and a siloxane bond as a binder for the magnetic layer improves the coefficient of dynamic friction, surface gloss, and amount of powder falling off. is improved, and the adhesive properties and methyl properties are significantly improved. Therefore, the thermal properties, running properties, blocking resistance, durability, dispersibility of magnetic powder, etc. of the magnetic recording medium are significantly improved.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
Since the binder for the magnetic layer is a polyurethane resin that has a siloxane bond and a quaternary ammonium salt as a polar group in its molecule, it has a high affinity for magnetic powder, even if it is made into ultrafine particles or has a low magnetization amount. Even large magnetic powders have good dispersibility. Therefore, the durability and surface properties of the obtained magnetic recording medium are improved, and the electromagnetic conversion characteristics are also extremely excellent.

However, the addition of lubricity due to the inclusion of siloxane bonds reduces the coefficient of friction and improves running properties.

Furthermore, the polyurethane resin used in the present invention is soluble in general-purpose solvent systems, easy to handle, and has advantages in terms of productivity and workability, as well as excellent coating film properties.

Claims (1)

[Claims] A magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, wherein the magnetic layer has siloxane bonds in its molecular chains, and A magnetic recording medium comprising a polyurethane resin having a quaternary ammonium salt as a polar group in a side chain as a binder.