JPS61120338A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a medium having excellent running durability and good electromagnetic conversion characteristic by incorporating the polycarbonate polyurethane having the repeating unit derived from arom. polyhydric alcohol into a binder. CONSTITUTION:A non-magnetic substrate which is ordinarily used is used and there is no particular limitation for ferromagnetic powder but the binder contains the polycarbonate polyurethane having the repeating unit derived from the atom. polyhydric alcohol. The content of the total binder in the magnetic layer of the magnetic recording medium is usually 10-60pts.wt. in the case of using a metallic oxide and more preferably 20-40pts.wt. by 100pts.wt. the ferromagnetic powder. Said content is usually 10-100pts.wt., more preferably 20-50pts.wt. in the case of using the ferromagnetic metallic powder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to improvements in magnetic recording media comprising a nonmagnetic support and a magnetic layer.

[Background of the invention and description of prior art]

Generally, magnetic recording media consist of a non-magnetic support made of a high-strength resin film such as polyethylene terephthalate resin, and a magnetic material made of ferromagnetic powder dispersed in a binder provided on the non-magnetic support. It has a basic structure consisting of layers.

As a binder for the magnetic layer of a magnetic recording medium having the basic structure as shown in item h, a binder containing an expanded vinyl/vinyl acetate copolymer as a main component is generally used. Usually, ferromagnetic powder such as metal oxide is dispersed in this binder.

γ-Fe2O, a conventionally used ferromagnetic powder
3. Metal oxides such as Fe3O4, Co-modified iron oxide, modified barium ferrite, and modified strontium ferrite have relatively high hardness; The running durability of a magnetic recording medium made of a magnetic layer by dispersing it in a general binder such as a binder was relatively good.

However, ferromagnetic metal fine powder, which is increasingly being used as magnetically ferromagnetic powder in response to the high recording density of magnetic recording media, has a coercive force (
Hc) and residual magnetic flux density (B r) are high, essentially it is possible to increase the recording density of the magnetic recording medium. However, since ferromagnetic metal fine powder inherently has low hardness, a magnetic layer formed by dispersing ferromagnetic metal fine powder in a common binder such as vinyl chloride/vinyl acetate copolymer, There is a problem that it may peel off during running or be damaged by friction with a magnetic head or the like. Such peeling or damage to the magnetic layer causes dropouts in the case of video tapes, for example, and is a major defect in the magnetic recording medium.

Therefore, in order to use fine ferromagnetic metal powder to achieve higher density in magnetic recording media, it is necessary to take a considerable amount of effort to compensate for the weakening of the magnetic layer caused by the use of fine ferromagnetic metal powder. It is necessary to use a strong bonding agent.

On the other hand, various improvements regarding the binder have been attempted with the aim of improving the running durability of a 1-meter recording medium. For example, JP-A-58-80430 discloses an invention of a magnetic recording medium whose main feature is the use of carbonate polyester polyurethane as a binder. In the publication in which this invention is described, a carbonate polyester polyurethane prepared using a metal oxide as a ferromagnetic powder and an aliphatic polyhydric alcohol as a polyhydric alcohol is used as a binder. A magnetic recording medium with improved abrasion resistance, that is, running durability is exemplified.

In other words, it has been shown that magnetic recording media using this carbonate polyester polyurethane as a binder have superior running durability when compared to conventional magnetic recording media when the ferromagnetic powder is a metal oxide. ing.

[Object of the Invention] The first object of the present invention is to provide a novel magnetic recording medium.

A second object of the present invention is to provide a magnetic recording medium with excellent running durability.

A third object of the present invention is to provide a magnetic recording medium that has excellent running durability and good electromagnetic conversion characteristics.

A fourth object of the present invention is to provide a magnetic recording medium that has excellent running durability and is capable of high-density recording with good electromagnetic conversion characteristics.

[Summary of the Invention] The present invention provides a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder dispersed in a binder on the support, wherein the binder is an aromatic polyvalent A magnetic recording medium comprising polycarbonate polyurethane having repeating units derived from alcohol.

The binder containing the polycarbonate polyurethane having a repeating unit derived from an aromatic polyhydric alcohol of the present invention can be used in a magnetic layer using a ferromagnetic metal fine powder, for example, when a ferromagnetic metal fine powder is used as the ferromagnetic powder. Various properties such as running durability, which is a particular problem in the field, are particularly desirable.

However, the binder containing polycarbonate polyurethane having a repeating unit derived from an aromatic polyhydric alcohol of the present invention can also be used as a binder for a magnetic layer containing a metal oxide, which has been conventionally used as a ferromagnetic powder. It works more effectively than previously known binders.

The binder for the magnetic recording medium of the present invention is preferably a polycarbonate polyurethane derived using bisphenol A as the aromatic polyhydric alcohol.

〔Effect of the invention〕

The magnetic recording medium of the present invention not only has excellent running durability but also has good electromagnetic conversion characteristics.

Furthermore, the magnetic paint used to prepare the magnetic layer of the magnetic recording medium of the present invention is unlikely to cause undesirable changes over time, such as agglomeration of magnetic particles or deterioration of the binder, which makes it difficult to manufacture the magnetic recording medium. The surface of the magnetic layer formed exhibits high smoothness.

[Detailed Description of the Invention] The magnetic recording medium of the present invention has a basic structure in which a nonmagnetic support and a magnetic layer made of a magnetic material dispersed in a binder are provided on the nonmagnetic support. It is.

In the present invention, any commonly used nonmagnetic support can be used for the magnetic recording medium. Examples of materials forming the non-magnetic support are polyethylene terephthalate, polypropylene, polycarbonate, and polyethylene naphthalate.

Examples include various synthetic resin films such as polyamide, polyamideimide, and polyimide, and metal foils such as aluminum foil and stainless steel foil.

Further, the nonmagnetic support used generally has a thickness of 3 to 50 pm, preferably 5 to 30 pm.

The nonmagnetic support may be provided with a backing layer on the side on which the 1m layer is not provided.

The magnetic recording medium of the present invention is one in which a magnetic layer in which ferromagnetic powder is dispersed in a binder is provided on a nonmagnetic support as described above.

The ferromagnetic powder used in the present invention is not particularly limited. Examples of the ferromagnetic powder include fine ferromagnetic metal powder containing iron as a main component and 20 g of γ-Fe.

Examples include gold hazes such as Fe1O4, Co-modified iron oxide, modified barium ferrite, and modified strontium ferrite.

The purpose of the present invention is to provide a magnetic recording medium with excellent characteristics even when metal oxides conventionally used as ferromagnetic powders are used.

The effect becomes remarkable when using a ferromagnetic metal fine powder containing iron, cobalt, or nickel and having a specific surface area of 40 rn'/g or more.

Examples of this ferromagnetic metal fine powder include 1 Ferromagnetic gold f1: The metal content in the fine powder is 75% by weight or more, and 80% by weight or more of the metal content is at least one type of ferromagnetic metal or alloy (e.g. , Fe, Co, Ni, Fe-Co, Fe-
Ni, Co-Ni.

Co-N1-Fe), and other components (e.g. A, Si, S, Sc) within a range of 20% by weight or less of the metal content + 7)
, Ti, V, Cr, Mn, Cu, Zn, Y, Mo, R
h, Pd, Ag, Sn, Sb, Te,
Ba, Ta, W, Re, Au,
Hg, Pb.

Mention may be made of alloys which may contain Bi, La, Ce, Pr, Nd, B, P). Furthermore, the ferromagnetic metal component may contain a small amount of water, hydroxide, or oxide, and methods for producing these ferromagnetic metal fine powders are already known, and the ferromagnetic metal used in the present invention Ferromagnetic metal fine powder, which is an example of the powder, can also be manufactured according to these known methods.

In other words, as an example of the method for producing 1 ferromagnetic metal fine powder,
The following methods can be mentioned.

(a) Method of reducing complex organic acid salts (mainly oxalates) with a reducing gas such as hydrogen: (b) Obtaining Fe or Fe-Co particles by reducing iron oxide with a reducing gas such as hydrogen Method; (e) Method of thermally decomposing a metal carbonyl compound: (d) Adding sodium borohydride to an aqueous solution of a ferromagnetic metal;
A method in which the metal is reduced by adding a reducing agent such as hypophosphite or hydrazine; (e) A method in which ferromagnetic metal powder is electrolytically deposited using a mercury cathode and then separated from mercury; (f) A method in which the metal is subjected to low pressure A method of obtaining a fine powder by evaporation in an inert gas.

When using ferromagnetic metal fine powder, there are no particular restrictions on its shape; however, needle-shaped, granular, dice-shaped, rice-grain-shaped, plate-shaped ones are usually used.

The content of the total binder in the magnetic layer of the magnetic recording medium of the present invention is usually 10 to 60 parts by weight per 100 parts by weight of ferromagnetic powder when a metal oxide is used. is 20 to 40 parts by weight. In addition, when using 1 ferromagnetic metal fine powder, 1 is usually 10-too parts by weight,
Preferably 2.>-5Q4 turtle'! 4 and 1 S.

The main feature of the magnetic recording medium of the present invention is that the binder contains polycarbonate polyurethane having repeating units derived from an aromatic polyhydric alcohol.

Generally, polycarbonate polyurethane is produced by the reaction between polycarbonate polyol and polyisocyanate.
Alternatively, it is synthesized by reacting a polycarbonate polyester polyol synthesized from a polycarbonate polyol and a dicarboxylic acid with a polyinsyanate. The above-mentioned polycarbonate polyol is generally synthesized by a transesterification method between a polyhydric alcohol and a dialkyl carbonate, or can be obtained by condensation of a polyhydric alcohol and phosgene.

However, the polyhydric alcohol used in the present invention.

It needs to be an aromatic polyhydric alcohol.

In the present invention, an aromatic polyhydric alcohol refers to one in which a hydroxyl group is directly bonded to an aromatic ring, or one in which a hydroxyl group is not directly bonded to an aromatic ring, but a relatively short chain bonded to an aromatic ring. Refers to substances in which hydroxyl groups are bonded via hydrocarbons, etc.

Examples of aromatic polyhydric alcohols that can be used in the present invention include the following compounds.

(However, R1 represents -H or an alkyl group having 1 to 3 carbon atoms, and t represents -H or a furkyl group having 1 to 7 carbon atoms or an aryl group.) (However, n is 1 to 10 ) (however,
n indicates 1 or 2. ) (However, n indicates 1 or 2.) (However, n indicates 1 or 2.) (
However, n indicates l or 2. ) (where n is l
Or indicate 2. ) (where R is -(CH2)2-
,or.

-(:H(CH x ) -CCHz ) z-, X is -SO2-, -CD-, -C(CHz) z
−.

-(:(CHz) z CaHa-(:(GHz)
In the present invention, it is particularly preferable to use bisphenol A as the aromatic polyhydric alcohol.

The aromatic polyhydric alcohol used in preparing the polycarbonate polyurethane, which is the binder of the magnetic recording medium of the present invention, does not need to be entirely aromatic polyhydric alcohol, but may include, for example, 1. Aliphatic polyhydric alcohols such as 6-hexanediol and 1°4-butanediol can also be used. In this case, at least 1 oil L% of the polyhydric alcohol used is
If the amount of the aromatic polyhydric alcohol (preferably an aromatic polyhydric alcohol) used is less than 10% by weight, the running durability of the resulting magnetic recording medium may not be sufficiently improved.

Polycarbonate polyurethane, which is the binder for the magnetic recording medium of the present invention, can be prepared using the above-mentioned aromatic polyhydric alcohol according to a conventional method.

There are no particular limitations on the polyisocyanate that reacts with polycarbonate polyol or polycarbonate polyester polyol synthesized from polycarbonate polyol and dicarboxylic acid.

Examples of polyisocyanates that can be used include tolylene diisocyanate, a reaction product of 3 moles of a diisocyanate such as xylylene diisocyanate and 1 mole of trimethylolpropane, a biuret adduct compound of 3 moles of hexamethylene diisocyanate, triresine isocyanate 5 Mention may be made of 7 mol incyanurate duct compounds, 3 mol tolylene diisocyanate and 2 mol hexamethylene diisocyanate isocyanurate adduct compounds, and polymers of diphenylmethane diincyanate.

Polycarbonate polyurethane has an average molecular weight (tll
Polycarbonate polyurethanes with average molecular weights ranging from 500,000 to 200,000 are generally used.6 If polycarbonate polyurethanes with molecular weights smaller than 5,000 are used, running durability may not be sufficiently improved; If a certain amount is used, the dispersibility may be poor.

Although the polycarbonate polyurethane described above can be used alone as a binder, it is usually used in combination with other binders. The amount of polycarbonate polyurethane used in combination with other binders is preferably 10% by weight or more of the total binder, and particularly preferably 30% by weight or more of the polycarbonate polyurethane.

There are no particular restrictions on other binders used in combination with the polycarbonate polyurethane described in F. Examples of other binders include vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl acetate and vinyl alcohol, maleic acid. and/
Or copolymers with acrylic acid, vinyl chloride/vinylidene chloride copolymers, vinyl chloride/acrylonitrile copolymers, ethylene-vinyl acetate copolymers, cellulose derivatives such as nitrocellulose resins, acrylic resins, polyvinyl acetal resins, polyvinyl Mention may be made of butyral resins, epoxy resins and phenoxy resins.Other binders for the magnetic recording medium of the present invention are copolymers of vinyl chloride/vinyl acetate with vinyl alcohol, maleic acid and/or acrylic acid. is preferable, and a vinyl chloride/vinyl acetate/maleic acid copolymer is particularly preferable.

The magnetic recording medium of the present invention has a magnetic layer with a Mohs hardness of 6 or more -H.
It is also possible to add an abrasive. There is no particular restriction on the abrasive to be used, and commonly used abrasives can be used. Examples of abrasives include a-Al2O2,S
Mention may be made of iC, CrtO2 and α-Fe201, which can be used alone or in mixtures.

The content of the abrasive is usually 0.2 to 10 parts by weight per 100 parts by weight of the ferromagnetic powder.

Further, in addition to the above-mentioned abrasives, it is preferable to contain carbon black (particularly one having an average particle size of 10 to 300 mp).6 Next, the method for manufacturing the magnetic recording medium of the present invention will be described.

First, a magnetic paint is prepared by kneading ferromagnetic powder such as ferromagnetic metal fine powder, a binder, and, if necessary, an abrasive or a filler with a solvent. As the solvent used during kneading, solvents commonly used in the preparation of magnetic paints can be used.

There is no particular restriction on the method of cross-talk, and the order of addition of each component can be set as appropriate.

An ordinary kneading machine can be used to make rIi magnetic paint. Examples of kneading machines are Miki roll mill, Miki roll mill, ball mill, and pebble mill.

Thoron mill, sand glider, 'zB mari attritor, high speed impete disperser, high speed stone mill,
Mention may be made of high-speed impact mills, dispersers, negoos, high-speed mixers, homogenizers and ultrasonic dispersers.

For details on the technology for crosstalk dispersion, please refer to TJ, PA↑↑ON
Author “Pa1nt Flow and Pigme”
nt Dispersion' (19B4Ja
published by H.N. Wiler & 5ons).

Also, U.S. Patent No. 2,581,414 and U.S. Pat.
In the present invention, which is also described in specifications such as No. 855,156, a magnetic paint can be prepared by carrying out crosstalk dispersion according to the method described in the above-mentioned documents.

When preparing a magnetic paint, known additives such as a dispersant, an antistatic agent, and a lubricant may also be used.

Examples of dispersants include fatty acids having 12 to 22 carbon atoms (e.g.
caprylic acid, capric acid, lauric acid, myristic acid,
Valmitic acid, stearic acid.

behenic acid, oleic acid, elaidic acid, linoleic acid, lyluic acid, stearolic acid), the above fatty acids and alkali metals (e.g. lithium, sodium).

metal soaps consisting of potassium) or alkaline earth metals (e.g. magnesium, calcium, barium), esters of the above fatty acids and compounds in which some or all of the hydrogen atoms in these compounds have been replaced with fluorine atoms, amides of the above fatty acids , aliphatic amines, higher alcohols, polyfulkylene oxide furkyl phosphates, furkyl phosphates, alkyl borates, sarcosinates, alkyl ether esters, trifurkylboriolefin, quaternary ammonium salts, and lecithin. When a dispersant is used, it is usually used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the ferromagnetic powder used.

Examples of antistatic agents include conductive fine powders such as carbon black and carbon black graft polymers; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; and higher furkylamines. , quaternary ammonium salts, salts of pyridine and other complex compounds, cationic surfactants such as phosphoniums or sulfoniums;
Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, and ester phosphate group; Examples include amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of amino alcohols. be able to. When using the above-mentioned conductive fine powder as an antistatic agent, it is usually used in the range of 0.1-10 parts by weight per 100 parts by weight of ferromagnetic powder, and when using a surfactant, Similarly, it is used in a range of 0.1 to 10 parts.

Examples of lubricants include the above-mentioned fatty acids, higher alcohols, butyl stearate, monobasic fatty acids with 12 to 20 carbon atoms such as neat sorbitan, and fatty acids consisting of monohydric or polyhydric alcohols with 3 to 20 carbon atoms. esters,
In addition to mineral oils, animal and vegetable oils, olefin low polymers, α-olefin low polymers, known lubricants such as fine graphite powder, fine molybdenum disulfide powder, fine Teflon powder, and lubricants for plastics can be mentioned. The amount of the lll lubricant added can be arbitrarily determined according to known techniques.

Note that the additives such as dispersants, antistatic agents, and lubricants mentioned above are not strictly limited to having only the above-mentioned effects; for example, one dispersant may be used as a lubricant. Alternatively, it may act as an antistatic II agent. Therefore, the effects of the compounds exemplified by the above classification are as follows.

Of course, it is not limited to the items listed in the above classification, and when using a substance that has multiple effects, the amount added is determined by taking into account the effects of that substance. It is necessary to.

The magnetic paint thus prepared is applied onto the aforementioned non-magnetic support. Coating can be done directly onto the non-magnetic support, but it can also be applied onto the non-magnetic support via an adhesive layer or the like.

Examples of coating methods on non-magnetic supports include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, impregnation coating, and reverse roll coating.

Transfer roll coat, gravure coat.

Methods such as kiss coating, cast coating, spray coating, and spin cording can be mentioned, and methods other than these can also be used. Specific explanations of these coating methods are described in detail in "Coating Engineering" published by Shokusen Shoten, pages 253 to 277 (published in 1972).

Further, details of the method of dispersing the above-mentioned fine ferromagnetic metal powder and binder and the method of applying it to the support are disclosed in Japanese Patent Application Laid-Open No. 54-46
It is described in various publications such as No. 011 and No. 54-21805.

The magnetic layer applied in this way generally has a dry thickness in the range of about 0.5 to 10 μm, preferably 1.5 to 7 μm.
．． It is applied to a range of 0 pm.

A magnetic layer is usually coated on a non-magnetic support.

After performing a process to orient the ferromagnetic powder in the first magnetic layer, that is, a magnetic field orientation process, it is dried. The magnetic recording medium that has been subjected to surface smoothing treatment, etc., is then cut into a desired shape.

The magnetic recording medium of the present invention is a medium that exhibits excellent running durability, and when used as a videotape, for example,
It has the advantage that almost no head clogging occurs, and it has a long still life and good running durability.Furthermore, as a videotape, it has a high video output and exhibits good electromagnetic conversion characteristics. At the same time, since the magnetic paint prepared to form the magnetic layer of the magnetic recording medium of the present invention changes little over time, the magnetic paint remains stable even if the time from the preparation of the magnetic paint to the manufacture of the tape is prolonged or fluctuates. Almost no change in layer properties occurs.

The above-mentioned tendency appears even when a metal oxide is used as the ferromagnetic material, but it becomes particularly noticeable when a ferromagnetic metal fine powder is used. Namely.

Head clogging, which is a disadvantage when using ferromagnetic metal fine particles, hardly occurs, and therefore there is almost no decrease in output due to head clogging.Furthermore, it has a long still life and exhibits excellent running durability. It has high output and excellent electromagnetic conversion characteristics.

Next, Examples and Comparative Examples of the present invention will be shown. In the Examples and Comparative Examples, the expression ``part r'' is as follows.

It indicates "parts by weight."

[Example 1] The composition shown below was mixed and dispersed using a ball mill.
A magnetic paint was prepared by filtration using a filter having an average pore size of m. The obtained magnetic paint was coated on a polyethylene terephthalate nonmagnetic support having a thickness of 10 tm using a reverse roll so that the thickness of the magnetic layer after drying was 4.04 m.

I-H: 5? White 砿jし１上”E虞 Ferromagnetic metal fine powder (composition: 94% Fe.

Zn4%, NL2%, Hc: 15000e.

Specific surface 111 [38E? ]:50rn'/g) t
oo part+! Engineered vinyl/vinyl acetate/woodless maleic acid copolymer (Nippon Zeon GA: 400X11QA, concentration: 400) 12 parts polycarbonate polyurethane 8 parts α-alumina (average particle size:
500m4゜Mohs hardness: 9) 2 parts carbon black (average particle size: 40m #L) 2 parts stearin 1%j 2 parts butyl stearate 2 parts methyl ethyl ketone 300 parts However, the above polycarbonate polyurethane (1) urethane can be prepared by the following method. It was manufactured by.

100 parts of bisphenol A, 100 parts of l,6-hexanediol, and 100 parts of diethyl polycarbonate were mixed into 15
A polycarbonate polyol was prepared by melting at 0°C and transesterifying the resulting ethyl alcohol while removing it under reduced pressure.Next, 1,10-decanedicarboxylic acid 2ooaK was added to 100 parts of the obtained polycarbonate polyol at 200°C. A polycarbonate polyester polyol was obtained by the reaction. To 100 parts of the obtained polycarbonate polyester polyol, 1.6-
10 parts of hexanediol, inphorondiamine toa1
1 and 100 parts of water-added MDI (4,4-diphenylmethane diisocyanate) were reacted to obtain a polycarbonate polyurethane. The 151 average molecular weight of the obtained polycarbonate polyurethane was 30,000.

The non-magnetic support coated with the magnetic paint is subjected to a magnetic field orientation treatment using a 3000 Gauss magnet while the magnetic paint is still wet.After drying, the non-magnetic support is subjected to a supercalender treatment, and then each portion is slit into 2-inch widths. A VH3 type videotape was manufactured.

The video tape obtained as described above was recorded at 4 MHz using a video recorder (Model NV-6600 manufactured by Matsushita Electric).
The signal was recorded and played back. The 4MHz output of the reference tape (Fuji Photo Film VHS videotape) is OdB.
The relative video output was 12.8 dB.

Using the above videotape, one recording was performed in still mode, and the time until significant defects appeared on the screen (still life) was investigated. The still life of the above videotape was 240 minutes.

Glossiness of the surface of the magnetic layer of a videotape obtained by applying the magnetic paint to the support immediately after preparation, and surface gloss of the magnetic layer of the videotape obtained by applying the magnetic paint to the support 10 hours after preparation. The total reflectance at an incident angle of 45 degrees and a reflection angle of 45 degrees was measured using a standard gloss meter (manufactured by Suga Test Instruments, Digital Gloss Meter GK).
45D model) to examine the influence of changes in the magnetic paint over time on the magnetic layer of the tape. As a result, the decrease in gloss of the tape magnetic layer due to changes in the magnetic paint over time was 1.

Signals were recorded for 120 minutes on a videotape obtained using a video recorder (Model NV-660Q manufactured by Matsushita Electric),
When this was reproduced, the reproduction output due to head clogging was measured, and no decrease was observed in the reproduction output after 120 minutes of reproduction time had elapsed.

Further, when the head was observed, no head clogging was observed.

In addition, video output, still life, temporal change of magnetic paint, and head clogging in the Examples and Comparative Examples shown below were measured by the method described below.

[Comparative Example 1] In Example 1, bisphenol A used in the preparation of polycarbonate polyurethane was replaced.

A videotape was produced in the same manner except that polycarbonate polyurethane was prepared using only 1,6-hexanediol.

The relative video output of the resulting videotape was 9,6
dB, still life was 125 minutes.

Note that no decrease in the reproduction output was observed after the reproduction time of 120 minutes had elapsed, and when the magnetic head was observed, no head clogging was observed. Further, the decrease in the glossiness of the tape magnetic layer due to aging of 6ii coating #1 was 5.

[Comparative Example 2] In Example 1, a polyester polyurethane was prepared using 1,6-hexanediol, adipic acid, and tolylene diisocyanate (TDI) instead of polycarbonate polyurethane, and video was produced in the same manner as in Example 1 except that this was used. manufactured the tape.

The relative video output of the resulting videotape was 8.1d
B. Still life was 60 minutes. Further, after a reproduction time of 120 minutes, a decrease in reproduction output was observed, and when the magnetic head was observed, it was found that the head was clogged. Also,
The decrease in gloss of the tape magnetic layer due to changes in the magnetic paint over time was 16.

[Example 2] The same procedure as in Example 1 was performed except that a metal oxide (group dt: y-Fez03.He: 3800e, specific surface area [S BETI: 25rrf/g) was used instead of the ferromagnetic metal fine powder. and produced a videotape.

The relative video output of the resulting videotape is 3.0d
It had a high rating of B, and the still life was 300 minutes. Also, I
a No deterioration in the glossiness of the tape magnetic layer due to aging of the magnetic paint was observed.

[Comparative Example 3] Same operation as in Comparative Example 1 except that a metal oxide (composition: y-Fe201.Hc: 3800e, specific surface area [S BETI: 25 m'/+r) was used instead of 1 ferromagnetic metal fine powder. and produced a videotape.

The relative video output of the resulting videotape is 1.2d
B. Still life was 150 minutes.

Furthermore, the decrease in gloss of the tape magnetic layer due to changes in the magnetic paint over time was 4.

[Comparative Example 4] In Comparative Example 2, gold i oxide (composition: y-Fe202, HC: 3800e, specific surface 1
A videotape was produced in the same manner except that i[s8E〒]: 25rre/g) was used.

The relative video output of the resulting videotape is 0.0d
B. Still life was 110 minutes.

Further, the decrease in gloss of the tape magnetic layer due to changes in the magnetic paint over time was 12.

As described above, the magnetic recording medium of the present invention has excellent running durability and electromagnetic conversion characteristics.

Claims (1)

[Claims] 1. A magnetic recording medium having a nonmagnetic support and a magnetic layer containing ferromagnetic powder dispersed in a binder on the support, wherein the binder is an aromatic polyhydric alcohol. 1. A magnetic recording medium comprising polycarbonate polyurethane having repeating units derived from polyurethane. 2. The magnetic recording medium according to claim 1, wherein the polycarbonate polyurethane is contained in an amount of 10% by weight or more based on the total amount of the binder. 3. The magnetic recording medium according to claim 1, wherein the aromatic polyhydric alcohol is bisphenol A. 4. The magnetic recording medium according to claim 1, wherein the binder contains a vinyl chloride/vinyl acetate/maleic anhydride copolymer. 5. The magnetic recording medium according to claim 1, wherein the magnetic layer contains an abrasive having a Mohs hardness of 6 or more. 6. The abrasive material is α-Al_2O_3, SiC, α-F
6. The magnetic recording medium according to claim 5, wherein the abrasive is one type of abrasive selected from the group consisting of e_2O_3 and Cr_2O_3. 7. The magnetic recording medium according to any one of claims 1 to 6, wherein the ferromagnetic powder is a fine ferromagnetic metal powder having a specific surface area of 40 m^2/g or more.