JPH01146122A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electromagnetic conversion characteristics as well as traveling property and durability of the title medium and to enable high- density recording by incorporating a binder contg. a specific urethane resin and specific fatty acid and fatty acid ester into a magnetic layer. CONSTITUTION:The magnetic layer contg. ferromagnetic alloy powder and the binder is provided on a nonmagnetic base. The binder contains the urethane resin satisfying the relation expressed by formula I and the magnetic layer contains the fatty acid and fatty acid ester. The fatty acid has <=250 neutralization value. In formula I, Mw denotes a weight average mol.wt. and Tg denotes a glass transition temp. The material forming the nonmagnetic base is exemplified by plastics such as polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, cellulose deriv. and polycarbonate. The electromagnetic conversion characteristic as well as the traveling property and durability are improved and the high-density recording is enabled.

Description

[Detailed description of the invention]

[Field of Industrial Application] This invention relates to magnetic recording media used for example in video tapes, audio tapes, etc. More specifically, the present invention relates to magnetic recording media used for video tapes, audio tapes, etc. The present invention relates to a magnetic recording medium suitable for. [Prior art and its problems] A magnetic recording medium basically consists of a nonmagnetic support and a magnetic layer containing ferromagnetic powder, and is constructed by providing a magnetic layer on the nonmagnetic material. . Generally, the magnetic layer is formed by dispersing ferromagnetic powder in a binder. A magnetic recording medium with such a configuration comes into violent sliding contact with the magnetic head during recording and playback, which can easily scratch or wear the magnetic layer, resulting in dropouts or head clogging. . Therefore, there is a need for a magnetic recording medium that has low surface abrasion resistance, excellent running properties, and has excellent durability with less magnetic powder falling off. In order to meet this demand, it is necessary to satisfy the following conditions: (1) the binder must have high strength and the ferromagnetic powder has excellent dispersibility; and (2) the magnetic layer must have lubricity. Conventional binders for magnetic recording media include vinyl chloride-vinyl acetate copolymers, cellulose derivatives, polyurethanes, nitrile-butadiene rubber, polyesters, acrylic resins, vinylidene chloride resins, epoxy resins, polyamides, and polyisocyanates. Are known. In addition, lubricants for magnetic recording media have conventionally been used, such as fatty acid esters such as butyl stearate and hexyl stearate, fatty acids such as valmitic acid, stearic acid, myristic acid, and oleic acid, stearylamide, oleylamide, and myristylamide. Fatty acid amides such as, fatty acid modified silicone, α-olefin oxide, etc. are used (see JP-A-59-8131, JP-A-61-178723, etc.). However, in recent years, as the demand for high-density recording has increased, γ-F, which has traditionally been used as a ferromagnetic powder, has increased.
In place of metal oxide-based ferromagnetic powders such as E, 03, and iron oxide-based ferromagnetic powders containing other components such as cobalt, ferromagnetic alloys that can be made into fine powders to enable even higher density recording. Powders are increasingly being used. However, this ferromagnetic alloy powder has the disadvantage that it is more prone to dusting than conventionally used metal oxide-based ferromagnetic powders, iron oxide-based ferromagnetic powders, and the like. Moreover, this ferromagnetic alloy powder, especially when it is made into a fine powder, does not have good dispersibility in the conventional binder, so a magnetic recording medium using a finely powdered ferromagnetic alloy powder should exhibit good dispersibility. However, there is a problem in that it may not be possible to obtain good Tt and magnetic conversion characteristics. Therefore, as a magnetic recording medium that aims to improve the dispersibility of ferromagnetic alloy powder, magnetic A recording medium has been proposed (Unexamined Japanese Patent Publication No. 1983
-5423 publication, 59-5424 publication, 59-
(See Publication No. 8127, etc.). However, although these binders can improve the dispersibility of the ferromagnetic alloy powder, they smooth the surface of the magnetic layer, leading to an increase in the coefficient of friction of the magnetic layer and reducing the running properties of the magnetic recording medium. A new problem arises. Is a lubricant used to solve this new problem?1If a conventional lubricant is to be used in a magnetic recording medium made of ferromagnetic alloy powder, the conventional lubricant is The amount of lubricant used must be increased compared to the amount of lubricant used in magnetic recording media using ferromagnetic powder, iron oxide-based ferromagnetic powder, and the like. On the other hand, if conventional lubricants are used in increased amounts, ■ Although running performance will improve, durability will decrease, and the still life under particularly harsh conditions will deteriorate. ■ Or, conversely, durability will decrease. Although it improves, there is a problem in that it causes a decrease in running performance. This invention has been made based on the above circumstances. An object of the present invention is to provide a magnetic recording medium that has good electromagnetic conversion characteristics, excellent runnability and durability, and is suitable for high-density recording. [Means for solving the above problems] In order to solve the above problems, the inventor has made extensive studies and has discovered that ferromagnetic alloy powder is dispersed in a binder containing a specific urethane resin. In addition, we discovered that a magnetic recording medium made by adding specific fatty acids and fatty acid esters to the magnetic layer has good electromagnetic conversion characteristics, has excellent durability and runnability, and is suitable for high-density recording. We have arrived at the invention of a lever. That is, the structure of the present invention is a magnetic recording medium in which a magnetic layer containing a ferromagnetic alloy powder and a binder is provided on a non-magnetic support, wherein the binder has the following formula [1]; % formula % [ 1] (In formula [1], Mw indicates the weight average molecular weight,
Tg indicates glass transition temperature. ) Contains a urethane resin that satisfies the relationship expressed by
The magnetic recording medium is characterized in that the magnetic layer contains a fatty acid and a fatty acid ester, and the fatty acid has a neutralization value of 250 or less. The nonmagnetic support and magnetic layer that constitute the magnetic recording medium of the present invention will be explained below. (Nonmagnetic Support) Materials for forming the nonmagnetic support include, for example, polyethylene terephthalate and polyethylene-2,6-
Examples include polyesters such as naphthalates, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polycarbonate. Furthermore, metals such as Cu, AM, and Zn, glass, and various ceramic roughs such as so-called new ceramics (eg, boron nitride, silicon carbide, etc.) can also be used. There is no particular restriction on the form of the non-magnetic support, and it may be tape-like, sheet-like, card-like, disc-like, drum-like, etc., and various materials may be used depending on the form and as necessary. can be selected and used. When the support is in the form of a tape or sheet, the thickness is usually 3 to 1]00IL, preferably 5 to 50IL.
It is pm. In addition, in the case of disk-shaped or card-shaped, 1
Usually 30-100 JLrn. Furthermore, in the case of a drum shape, it can be made into a cylindrical shape, etc., depending on the recorder used. A back coat layer may be provided on the surface (back surface) of the nonmagnetic support on which the magnetic layer is not provided for the purpose of improving the running properties of the magnetic recording medium, preventing electrification, preventing transfer, and the like. Furthermore, an intermediate layer (for example, an adhesive layer) may be provided on the surface of the nonmagnetic support on which the magnetic layer is provided, for the purpose of improving the adhesion between the magnetic layer and the nonmagnetic support. (Magnetic Layer) The magnetic layer is provided on the non-magnetic support. The magnetic layer is a layer formed by dispersing the ferromagnetic alloy powder in a binder. Examples of the ferromagnetic alloy powder include Fe-+1] alloy powder, Fe-A1]-P alloy powder, Fe-Ni-C
o Alloy powder, Fe-Mn-Zn alloy powder, Fe-Ni
-Zn alloy powder, Fe-Go-Ni-Cr alloy powder, F
Examples include e-Go-Ni-P alloy powder, (:o-Ni alloy powder, Co-P alloy powder, etc.), and ferromagnetic alloy powder mainly composed of ferromagnetic metals such as Fe, Ni, and CO. Among these, preferable are Fe-Al1 alloy powder,
It is an alloy powder containing aluminum such as Fe-AM-P alloy powder. This is because alloy powder containing aluminum has excellent weather resistance. The specific surface area of the ferromagnetic alloy powder measured by the BET method is usually 45 m''/g or more, preferably 45 to 80 m''/g. If this specific surface area is less than 45 m''71, the S/N ratio of the magnetic recording medium may be reduced. There is no particular restriction on the shape of the ferromagnetic alloy powder.
For example, a acicular, spherical or ellipsoidal shape may be used. One of the important points in this invention is that the binder has the formula

[1]: % formula % [1] (However, in formula [1], Mw indicates the weight average molecular weight,
Tg indicates glass transition temperature. In the urethane resin, the relationship between the weight average molecular weight Mw and the glass transition temperature Tg, that is, the formula [1]
The left side of (Mw +8.4 X 1]02T ) or 80
．． If it is less than 000, the coefficient of friction of the magnetic layer in the magnetic recording medium of the present invention increases, which may easily cause head clogging or sticking to the magnetic head (so-called JL loading). The urethane resin may be one in which the relationship between its weight average molecular weight Mw and glass transition temperature Tg satisfies the above formula [1].1 Usually, it is synthesized by a reaction between a polyisocyanate and a polyol. can. Examples of the polyisocyanate include tolylene diisocyanate (TDT), diphenylmethane-4,4
'-diisocyanate (MDI), naphthylene-t,
S-diisocyanate (MDI), 3.3=-dimethyl-4,4'-biphenylene diisodiisocyanate)
-(TODI), xylylene diisocyanate (XDI
), dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI), crude TDI, polymethylene
Polyphenyl isocyanate (crude MDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (+101), hydrogenated xylylene diisocyanate (HXDI), etc., as well as isocyanurate-modified products, carbodiimide-modified products of these isocyanates, Examples include burette modified products. These may be used alone or in combination of two or more. Examples of the polyols include organic dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, maleic acid, succinic acid, adipic acid, and sebacic acid; glycols such as ethylene glycol, propylene glycol, diethylene glycol, and polyethylene glycol; Polyhydric alcohols such as methylolethane, trimethylolpropane, hexanetriol, glycerin, and pentaerythritol; Polyhydric phenols such as hydroquinone and bisphenol A; Selected from the above glycols, polyhydric alcohols, and polyhydric phenols. Polyester polyols synthesized by the reaction of two or more types of polyols; lactam polyesters synthesized from lactams such as S-caprolactam, α-methyl-1-caprolactam, S-methyl-5-caprolactam, and γ-butyrolactam. Polyol: Examples include polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. These may be used alone or in combination of two or more. The urethane resin may be a urethane resin or a urethane polymer whose terminal end is at least one of an isocyanate group, a hydroxyl group, and a carboxyl group, or it may be a urethane elastomer containing no reactive end groups. . The blending ratio of the urethane resin is usually 3 to 50 parts by weight, preferably 5 to 30 parts by weight, based on 100 parts by weight of the ferromagnetic alloy powder. If the blending ratio is less than 3 parts, the dispersibility of the ferromagnetic alloy powder will not be sufficiently improved, and the electromagnetic conversion characteristics of the magnetic recording medium of the present invention may deteriorate. On the other hand, even if the amount is increased beyond 50 parts by weight, the effect commensurate with the increased amount may not be achieved. In addition to the urethane resin, the binder in the magnetic recording medium of the present invention includes, for example, thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, or Other resin components such as mixtures of these can be used. Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, and acrylic ester-vinylidene chloride copolymer. Polymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral,
Cellulose derivative (cellulose acetate butyrate)
, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.)
, styrene-butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, and synthetic rubber-based thermoplastic resin. These may be used alone or in combination of two or more. Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin, high molecular weight polyester resin, and isocyanate prepolymer. mixtures of methacrylate copolymers and shiisocyanate prebolimers, urea formaldehyde resins, and polyamine resins. These may be used alone or in combination of two or more. Examples of the electron beam curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type; ether acrylic type; , urethane acrylic type, epoxy acrylic type, phosphate ester acrylic type, aryl type, and hydrocarbon type. These may be used alone or in combination of two or more. When the urethane resin and the other resin components described above are used in combination, the weight ratio of (urethane resin):(other resin components) is usually 9:
The ratio is 1 to 1:9, preferably 8:2 to 2:8. If this blending ratio is out of the above range, the electromagnetic conversion characteristics of the magnetic layer in the magnetic recording medium of the present invention may deteriorate, or the dispersibility of the ferromagnetic alloy powder may deteriorate. In this invention, the urethane resin or a mixture of the urethane resin and the other resin components described above may be used as a binder as is, but the urethane resin or the mixture of the urethane resin and the other resin components described above may be used as the binder. A curing agent may be used as a binder together with a mixture with other resin components. Examples of the curing agent include polyisocyanate compounds (e.g., tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, and adducts of these polyisocyanate compounds with trivalent polyols, Examples include a pentamer of diisocyanate, an adduct of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, an adduct of 3 moles of metaxylylene diisocyanate and 1 mole of trimethylolpropane, and a pentamer of tolylene diisocyanate. These may be used alone or in combination of two or more. The ferromagnetic alloy powder and the binder (
When the above-mentioned hardening agent is used, the blending ratio with 100 parts by weight of the above-mentioned ferromagnetic alloy powder is as follows:
Usually 5 to 400 parts by weight of binder, preferably 10 to 20 parts by weight
It is 0 parts by weight. If the amount of binder blended is too large, the blended amount of ferromagnetic powder may be lowered and the recording density of the magnetic recording medium may be lowered. If it is too small, the strength of the magnetic layer may be reduced and the magnetic recording medium may be The running durability of the vehicle may be reduced. One of the important points in this invention is that the magnetic layer contains a fatty acid and a fatty acid ester having a neutralization value of 250 or less. The fatty acid and fatty acid ester have the effect of lowering the coefficient of friction of the smooth magnetic layer realized by the urethane resin to improve lubricity, and improving the runnability and durability of the magnetic recording medium of the present invention. have The neutralization value of the fatty acid is 250 or less. Neutralization value is 25
If it exceeds 0, the compatibility with the urethane resin used in the present invention may decrease and the improvement in lubricity may not be sufficient. Specific examples of fatty acids with a neutralization value of 250 or less include myristic acid (neutralization value 245.7), pentadecane a
(neutralization value 231.5), palmitic acid (neutralization value 218.
8), margaric acid (neutralization value 207.5), stearic acid (neutralization value 197.2), nonadecanoic acid (neutralization value 188.0), arachidic acid (neutralization value 179.5), behenugi ( Neutralization value: 164.7), ) Ricosanoic acid (Neutralization value: 158.2), Lignoceric acid (Neutralization value: 152.2)
, pentacosonic acid (neutralization value 145.6), cerotic acid (
neutralization value 141.4), heptacosanoic acid (neutralization value 13[i
, li), montanic acid (neutralization value 132.I), nonacosanoic acid (neutralization value 127.9), melisic acid (neutralization value 1
2:1.9), hentriacontanic acid (neutralization value 120.
2), Todoriacontanic acid (neutralization value 1] 6.7),
Straight chain fatty acids such as tetratriacontanoic acid (neutralization value 1] 0.2), hexatriacontanoic acid (neutralization value 104.5), octatriacontanoic acid (neutralization value 93.3): tuznic acid ( (neutralization value 247.9), physetoleic acid (neutralization value 247.9), myristoleic acid (neutralization value 247.9)
), 6-pentadecenoic acid (neutralization value 233.4), seamarinic acid (neutralization value 220.5), 2-palmitoleic acid (
(neutralization value 220.5), petroselic acid (neutralization value 198.
6), oleic acid (neutralization value 198.6), elaidic acid (neutralization value 198.6), trans-2-octadecenoic acid (neutralization value 198.5), gadolenic acid (neutralization value 180)
．． 7), bondoic acid (neutralization value 180.7), whale oil acid (neutralization value 165.7), erucic acid (neutralization value 165)
．． 7), linear monoenoic acids such as pracic acid (neutralization value 165.7) and ceracoleic acid (neutralization value 1510): linoleic acid (neutralization value 200.1), α-eleostearic acid (
neutralization value 201.5), α-parinaric acid (neutralization value 203
．． 0), arachidonic acid (neutralization value 184.3), and talpanodonic acid (neutralization value 170.8) and other di-, tri-, and tetraenoic acids. These may be used alone or in combination of two or more. The blending ratio of the fatty acid is usually 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the ferromagnetic alloy powder. This blending ratio is 0.1 i
If the amount is less than 1 part, the improvement in lubricity may not be sufficient. On the other hand, if the amount exceeds 10 parts by weight, the amount of lubricant becomes excessive and dirt may easily adhere to the surface of the magnetic layer. Examples of the fatty acid ester include vinyl myristate, propyl myristate, butyl myristate, heptyl myristate, myristyl myristate, vinyl palmitate, propyl palmitate, isopropyl palmitate, butyl palmitate, vinyl stearate, and propyl stearate. , butyl stearate, amyl stearate, propyl oleate, allyl oleate, butyl oleate 2-ethylhexyl palmitate,
2-ethylhexyl myristate. Examples include 2-ethylhexyl stearate. Among these, preferred are butyl stearate, butyl palmitate, 2-ethylhexyl palmitate,
2-ethylhexyl myristate and 2-ethylhexyl stearate. The blending ratio of the fatty acid ester is usually 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the ferromagnetic alloy powder. This blending ratio is 0
．． If the amount is less than 1 part by weight, the improvement in lubricity may not be sufficient. On the other hand, if the amount exceeds 10 parts by weight, the amount of lubricant becomes excessive and dirt may easily adhere to the surface of the magnetic layer. What is the usage ratio of the fatty acid and fatty acid ester? Weight ratio of (fatty acid):(fatty acid ester) is 95:5
~5: 95. Preferably it is 90:10 to 10:90. If this ratio is out of the above range, the compatibility between the fatty acid and the fatty acid ester will be poor, and phenomena such as blooming may occur. In this invention, other lubricants can be used in conjunction with the fatty acids and fatty acid esters. Examples of other lubricants include silicone lubricants, fatty acid-modified silicone lubricants, fluorine-based lubricants, liquid paraffin, squalane, carbon black, graphite, carbon black graft polymers, molybdenum disulfide, and tungsten disulfide. It will be done. These may be used alone or in combination of two or more. When the other lubricant is used, the blending ratio of the other lubricant is usually 10 parts by weight or less, preferably 5 parts by weight or less, based on 100 parts by weight of the ferromagnetic alloy powder. If this blending ratio exceeds 10 parts by weight, the amount of lubricant becomes excessive and dirt may easily adhere to the surface of the magnetic layer. In this invention, in addition to the ferromagnetic alloy powder, binder, fatty acid S, and fatty acid ester, an abrasive and an antistatic agent can be blended into the magnetic layer. Examples of the abrasives include inorganic powders such as aluminum oxide, titanium oxide (TiO1Tie2), silicon oxide (SiO□), silicon nitride, chromium oxide, and boron carbide, as well as benzoguanamine resin powder, melamine resin powder, and phthalocyanine compound powder. organic powders. These may be used alone or in combination of two or more. The average particle diameter of the abrasive is 1, usually 0.1 to 1. O.J.L.
It is m. Further, the blending amount of these abrasives is usually 0.5 to 20 parts by weight per 100 parts by weight of the ferromagnetic alloy powder. Examples of the antistatic agent include conductive powders such as graphite, carbon black, tin oxide-antimony oxide compounds, tin oxide-titanium oxide-antimony oxide compounds, and carbon black graft polymers; natural surfactants such as saponin; Nonionic surfactants such as alkylene oxide, glycerin, and glycidol: higher alkylamines, quaternary pyridine, and other heterocycles,
Cationic surfactants such as phosphoniums and sulfoniums: Anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfuric acid ester groups, and phosphoric ester groups Niamino acids, aminosulfonic acids, sulfuric acid and phosphoric acid esters of amino alcohols Examples include amphoteric surfactants such as . These may be used alone or in combination of two or more. The blending amount of the above antistatic agent is 100% of the above ferromagnetic alloy powder.
1 per part by weight, usually 0.5 to 20! It is i quantity part. Note that the above-mentioned antistatic agent or the dispersant described below does not have a sole function; for example, a - compound may act as a lubricant and an antistatic agent. Therefore, the above-mentioned classifications in this invention indicate the main actions, and are not limited by the actions of the classified compounds or the actions shown in the classification. Next, a method for manufacturing the magnetic recording medium of the present invention will be explained. (Manufacturing method) The magnetic recording medium of the present invention is produced by preparing a magnetic coating material by cross-dispersing magnetic layer forming components such as the ferromagnetic alloy powder, urethane resin, fatty acids, and fatty acid esters in a solvent.
It can be manufactured by applying the obtained magnetic paint onto the non-magnetic support and drying it. The solvent used for crosstalk and dispersion of the magnetic layer forming components is as follows:
Ketones such as acetone, methyl ethyl ketone (ME), methyl isobutyl ketone (MIBK) and cyclohexanone; alcohols such as methanol, ethanol, propatool and butanol; methyl acetate;
Ester systems such as ethyl acetate, butyl acetate, ethyl lactate, propyl acetate, and ethylene glycol monoacetate Ether systems such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane: Aromatic hydrocarbons such as benzene, toluene, and xylene: Methylene Chlorite, ethylene chloride, carbon tetrachloride, chloroform. Halogenated hydrocarbons such as ethylene chlorohydrin and dichlorobenzene can be used. When mixing the composition of the magnetic paint components, the ferromagnetic alloy powder and other magnetic paint components are fed into a mixer simultaneously or individually. For example, first, the magnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined time, the remaining components are added and kneading is continued to obtain a magnetic paint. Various types of crosstalk devices can be used to troubleshoot the crosstalk. Examples of this kneading machine include a Miki roll mill, a Miki roll mill, a ball mill, a pebble mill, a side grinder, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disper kneader-1 high-speed mixer, a homogenizer, and an ultrasonic mixer. Examples include a disperser. Note that a dispersant can be used for crosstalk dispersion of the ferromagnetic alloy powder. Examples of the dispersant include lecithin, phosphoric acid ester, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid ester, known surfactants and salts thereof, negative organic groups (e.g. -COOH,-
POJ) ii salts of coalescing dispersants, and the like. These may be used alone or in combination of two or more. The amount of the dispersant added is usually 1 to 20 parts by weight per 100 parts by weight of the ferromagnetic alloy powder. The coating solution of the magnetic layer forming component thus prepared is coated onto a non-magnetic support by a known method. Application methods that can be used in this invention include, for example, gravure roll coating, Meyer bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, squeeze coating, kiss coating, and fan tin coating. Examples include coating. The thickness of the magnetic layer coated in this way is usually 1 to 204 m in dry thickness. After the magnetic layer-forming components have been applied in this way, a magnetic field orientation treatment is carried out if necessary in a wet state, and a surface smoothing treatment is usually carried out using a super calender roll or the like. Next, a magnetic recording medium can be obtained by cutting into a desired shape. The magnetic recording medium of the present invention can be used, for example, by cutting it into a long shape, as a magnetic tape such as a video tape or audio tape, or by cutting it into a disk shape.
It can be used as a floppy disk, etc. Furthermore, like ordinary magnetic recording media, it can also be used in card-like, cylindrical, or other forms. [Example] Next, Examples and Comparative Examples of the present invention will be shown to further specifically explain the present invention. In addition, in the examples and comparative examples described below, "parts" shall represent "parts by weight." ■Tsuzumi-01] A magnetic layer composition having the composition shown below was prepared using a ball mill.
After mixing and dispersing for 48 hours to obtain a dispersion liquid, 5 parts of a polyisocyanate compound [trade name "Coronate L"; Japan Polyurethane-1] was added and mixed to prepare a magnetic paint. Fe-Al based ferromagnetic alloy powder 100 parts [specific surface! 145 servings/g (BET value) Polyurethane resin 13 parts Vinyl chloride-vinyl acetate copolymer 5 parts Fatty acid
1 part fatty acid ester
1 part α-A 203 5 parts (average particle size 0.2 ILm) Carbon black 3 parts (specific surface area 30 27 g, average particle size 50 ILm) Cyclohexanone 200 parts Methyl ethyl ketone 100 parts Toluene 100 parts Polyurethane resin Table 1 shows the glass transition temperature and average molecular weight, the type and neutralization value of fatty acids, and the type of fatty acid ester. (Essentials, below are blanks) ■81 ■ Bee-1 - Place the magnetic paint obtained in the above ■ into a sand mill.
After dispersion, a polyfunctional isocyanate triplex was added and applied onto a polyethylene terephthalate film having a thickness of 10 ILm to a dry thickness of 3 pm. Next, the solvent was removed under heating, the surface was smoothed using a super calender, and the tape was cut into a width of 8 mm to produce an 8 mm video tape. (Examples 1-12, Comparative Examples 1-8) Various properties were measured for the 8■ video tape obtained in the above (1). The results are shown in Table 2. In addition, each characteristic was measured as follows. Lumi S/N: Using a noise meter (manufactured by Shibatsu Corporation), the difference in S/N of each sample in a 10 weight 0% white signal was determined in comparison with a reference tape (manufactured by Konica ■). Note that an 8 AM type video deck [manufactured by Sony ■] was used as the video deck. Chroma S/N: Using a noise meter (manufactured by Shibaku Co., Ltd.), the difference in i/N of each sample in the chroma signal was determined in comparison with a reference tape (manufactured by Konica ■). Note that an am55j video deck [manufactured by Sony ■] was used as the video deck. The output at the time of reproduction in a 100% RF specific output white signal was determined by comparison with a reference tape [manufactured by Konica ■]. Still life: Adjust the output level before starting still mode
As B, the time required for the output to become 12 dB or less was measured. Head clogging: Under the conditions of temperature 40°C and humidity 80%,
The tape was run 100 times and the number of times clogging occurred was measured. Decrease in RF output: The difference between the initial output and the output after running the tape 100 times was determined under conditions of a temperature of 40° C. and a humidity of 80%. Powder removal: After the tape was run 100 times at a temperature of 40° C. and a humidity of 80%, stains were detected and evaluated on a scale of 1 to 5. 60: No stains observed at all. O: Almost no stains were observed. Δ: Stain is observed. ×: Considerable dirt is observed. XX = Significant stains are observed. In the measurement results of durability Nistil life, head clogging, RF output reduction, and powder falling, cases of deterioration were considered negative and the following raw scores were given. (Raiko, hereafter in the margin) Based on the total value of this raw score, it was evaluated in the following five stages. A: 6 points or more B; 3 to 5 points C knee 3 to 2 points Knee 5 to -2 points E Knee 5 points or less (essence, hereafter blank) (Evaluation) As is clear from Table 2, Example 1 The 81 video tapes in Comparative Examples 1 to 8 showed good results in terms of still life, head clogging, and powder removal, although there was almost no deterioration in electromagnetic conversion characteristics. It was confirmed that it has superior electromagnetic conversion characteristics and significantly improved durability compared to tape. Also, regarding each urethane resin used in Examples 1 to 12 and Comparative Examples 1 to 8. When the durability evaluation results were written in coordinates where the vertical axis represents the average molecular weight Mw and the horizontal axis represents the glass transition temperature Tg, the results shown in the first factor were obtained. From FIG. 1, it was confirmed that the urethane resin satisfying the average molecular weight Mw, glass transition temperature Tg, and the above formula [1]; % formula % has excellent durability. [Effects of the Invention] According to the present invention, (1) Since the magnetic layer contains a binder containing a specific urethane resin, a specific fatty acid, and a fatty acid ester, the dispersibility of the ferromagnetic alloy powder is good. At the same time, the coefficient of friction of the smooth magnetic layer can be reduced. (2) Therefore, the good electromagnetic conversion properties of ferromagnetic alloy powders do not deteriorate, and (3) phenomena such as so-called instantaneous head clogging and reed loading are less likely to occur, and the still life is good. It is possible to provide a magnetic recording medium that has various advantages such as excellent electromagnetic conversion characteristics, runnability, and durability, and can be suitably used for high-density recording.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the weight average molecular weight (Mw) and the glass transition temperature (Tg) of the urethane resins used in Examples and Comparative Examples of the present invention.

Claims (1)

[Claims] (1) In a magnetic recording medium in which a magnetic layer containing a ferromagnetic alloy powder and a binder is provided on a non-magnetic support, the binder has the following formula [1]; M_w+8.4×10^2Tg≧8 .0×10^4[1
] (However, in formula [1], M_w indicates the weight average molecular weight, and Tg indicates the glass transition temperature.) Contains a urethane resin that satisfies the relationship expressed by
A magnetic recording medium, wherein the magnetic layer contains a fatty acid and a fatty acid ester, and the fatty acid has a neutralization value of 250 or less.