JPH0520811B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium having a back coat layer, and mainly relates to a magnetic recording medium with improved surface lubricity of the back coat layer. BACKGROUND OF THE INVENTION Magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks are widely used in the audio field for recording sound, the video field for recording images, and the computer field. Magnetic recording media used in these various fields include coatings in which a magnetic coating consisting mainly of magnetic powder, binder resin, and solvent is applied onto a support and dried to form a magnetic layer on the support. type is widely used. In addition, as the demand for high-density recording has recently increased, we have developed an alternative to this coated type, which has a lower recording density due to the amount of binder.It has a high saturation magnetization and does not require a binder, and can be supported by direct vapor deposition, sputtering, ion plating, etc. Thin-film magnetic recording media, in which a ferromagnetic metal thin film can be formed on the body, have come into widespread use. In such magnetic recording media, electromagnetic conversion is performed when the magnetic layer is rubbed and scanned by a magnetic head during recording and reproduction, so it is necessary that the magnetic layer has good magnetic properties or electromagnetic conversion properties. be. For this purpose, the sliding condition between the magnetic head and the magnetic layer must be constant, and when a magnetic tape is used, for example, the edges of the tape must be aligned in one plane, and the tape can be rewound and used repeatedly. Stable running performance is sometimes required so that the sliding condition with the head does not fluctuate. When such a magnetic tape is actually used, it is stored in a cassette, for example, and the cassette is attached to a video deck, and the tape is guided by guide poles or guide rollers and run while being rubbed and scanned by a magnetic head. Ru. In order to record images on magnetic tape or reproduce them in this way, in order to improve the sensitivity, especially the output in the high frequency range, the magnetic layer is The surface is finished smooth. Since this smooth surface tends to stick to magnetic heads, etc., efforts have been made to improve its running properties. However, if the part of the back side of the magnetic tape that is rubbed by the guide poles and guide rollers has poor running performance, excessive tension is applied to the running magnetic tape, causing the magnetic layer to move against the magnetic head. Excessive abrasion not only causes damage to the magnetic layer and flaking of magnetic powder in the magnetic layer, but also changes in strength and strength of the tension at which the magnetic tape is wound, resulting in fluctuations in the winding pressure, making it difficult to reuse the tape. When the vehicle runs unevenly. When these things occur, various characteristics such as skew, jitter, tracking deviation, and S/N deteriorate. For this reason, a back coat layer is provided on the back side of the magnetic tape to stabilize its running properties. In particular, trends in magnetic recording technology in recent years include, for example, the use of compact cassettes in the audio tape field is transitioning to the use of microcassettes, and in the field of video, the current VHS and β formats have been replaced by 8mm video, With the transition to electronic cameras, they are becoming smaller, more densely packed, and more easily portable. As video recording is becoming more and more common in certain situations, it is hoped that magnetic tape will also be suitable for these situations. In other words, the miniaturization and higher density of video equipment requires higher recording density for magnetic tape, but it is necessary to increase the number of tape turns as much as possible for a given tape winding diameter. A thin support was used, and efforts were made to smooth the magnetic layer.
For this reason, supports with smoother surfaces have come to be used more and more. However, the smoother the surface of the magnetic layer and the support on the opposite side, the worse the running properties and durability of the magnetic tape become. As the tape becomes more complicated and has more opportunities to come into contact with guide poles, guide rollers, etc., and is rubbed more frequently, it not only worsens the situation but also makes the tape more likely to be deformed and damaged. Therefore, efforts have been made to improve the surface lubricity of the back coat layer provided on the back surface of the magnetic tape. Among these ideas, there is one in which an inorganic powder is contained in the resin layer. This includes carbon black, titanium dioxide, calcium carbonate,
The surface of the back coat layer is roughened by coating the amount of a solution in which inorganic powder such as alumina, graphite, silicon dioxide, etc. is dissolved or dispersed in a polymer or dispersant, reducing the contact area with guide poles, etc., and reducing the friction. By reducing the coefficient, the edges of the tape are prevented from folding. For example, JP-A-57
-130234, JP-A-58-161135, JP-A-57-53825, and JP-A-58-2415 all show examples using inorganic powder, and many of these also include is shown with a limited particle size. However, even when these inorganic powders are used, not only do they not provide sufficient slipperiness, but when the back coat layer containing them is rubbed, the binding force of the particles to the binder to resist this is insufficient, resulting in powder falling off. In addition, when the magnetic tape is wound and the magnetic layer comes into contact with the back coat layer, the protrusions of the back coat layer may fall off the magnetic layer. Chroma S/N indicates the degree of color noise in the image when the magnetic layer is scanned and the image is reproduced.
It may damage electromagnetic conversion characteristics such as Further, the back coat layer may peel off, staining the deck, and metal members such as guide poles that come into contact with the back coat layer of the tape may wear out. For this reason, examples are known in which not only the above-mentioned surface roughening agents but also fatty acids or fatty acid esters are used as lubricants for the back coat layer. For example, JP-A-57-28637 discloses an example in which lauric acid, butyl stearate, etc. are used together with polyurethane, nitrocellulose, vinyl chloride-vinyl acetate copolymer, and isocyanate. Further, JP-A-58-37840 discloses an example in which a fatty acid having 12 or more carbon atoms such as stearic acid or an ester thereof is used together with a cellulose resin, polyurethane, or polyisocyanate. However, such a lubricant tends to ooze out onto the surface of the back coat layer, and if it oozes out excessively onto the back coat layer surface, it will adhere in the form of particles or oil, increasing the friction between the tape and the guide pole, etc. This results in an increase in running tension, sticking to guide poles, etc., and furthermore, when the tape is wound, the edges of the tape become uneven, resulting in poor winding appearance and poor running performance during reuse. In addition, as a result of poor compatibility with the binder, there is a drawback that uneven coating occurs when applying the coating liquid, and when this uneven coating occurs, it is not possible to obtain running stability and it also causes uneven wear resistance. It turns out. In this way, if the lubricity of the back coat layer is poor and the running stability of the magnetic tape is deteriorated, electromagnetic conversion characteristics such as brightness S/N, jitter, and squareness ratio may be impaired, and output fluctuations and dropouts may become worse. I will do it. Therefore, attempts have been made to use fatty acids or fatty acid esters that have a relatively low melting point, or to use fatty acid esters that have good compatibility with resins, but these are still insufficient and improvements have been desired. OBJECTS OF THE INVENTION A first object of the present invention is to provide a magnetic recording medium having a back coat layer that does not cause blooming of additives and is coated uniformly. A second object of the present invention is to provide a magnetic recording medium having a back coat layer containing additives that can provide high lubricity with a small amount. A third object of the present invention is to provide a magnetic recording medium that improves the squareness ratio, S/N, etc., and reduces output drop, output fluctuation, dropout, etc. by achieving each of the above objects. . Structure of the Invention As a result of intensive research to achieve the above object, the present inventor discovered that when a dibasic carboxylic acid monoester is used as an additive in the back coat layer, a specified lubricating effect can be achieved with a small amount of addition. This led to the present invention. Therefore, the magnetic recording medium of the present invention has a magnetic layer on one side of a support and a back coat layer on the other side of the support, in which the back coat layer is dibasic. It is characterized by containing carboxylic acid monoester. The present invention will be explained in more detail below. The dibasic carboxylic acid monoester used in the present invention is represented by the general formula HOOC-Y-COOR. Here, Y is an organic residue other than the carboxyl group of a compound collectively called dibasic carboxylic acid, and is a saturated aliphatic hydrocarbon group such as an alkylene group, for example, introducing an unsaturated bond into an alkylene group. unsaturated aliphatic hydrocarbon groups, groups with aryl groups, ether bonds, or thioether bonds introduced into some of these saturated or unsaturated aliphatic hydrocarbon groups, groups of saturated or unsaturated alicyclic compounds, hetero groups of cyclic compounds, groups of aromatic compounds such as aryl groups,
Further examples include groups in which each of these groups is substituted with a saturated or unsaturated linear or branched alkyl group, alkenyl group, aryl group, or various other functional groups. Examples of R include an alkyl group, an aryl group, and an arylalkyl group. Specifically, the following can be mentioned. (1) HOOC−CH＝CH−COOC ₁₇ H ₃₅ (3) HOOC(CH ₂ ) ₉ COOC ₅ H ₁₁ (4) HOOC(CH ₂ ) ₈ COOC ₅ H ₁₁ (5) HOOC(CH ₂ ) ₁₂ COOC ₂ H ₅ (6) HOOC(CH ₂ ) ₅ COOC _{10 H21} The dibasic carboxylic acid monoester used in the present invention can be used alone, but other lubricants can also be used in combination. Lubricants that can be used in combination include aliphatic dibasic carboxylic acids, aromatic carboxylic acids, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids with 12 to 16 carbon atoms, and 3 carbon atoms. ~Fatty acid esters consisting of 12 monohydric alcohols, 21-23 carbon atoms consisting of monobasic fatty acids with 17 or more carbon atoms and monohydric alcohols
fatty acid esters, etc. These are described in Japanese Patent Publication No. 43-23889.
In particular, when used in combination with a fatty acid ester having 17 or more carbon atoms, the lubricity increases. The dibasic carboxylic acid monoester used in the present invention is used in combination with a resin. Examples of resins that can be used in combination include thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, and mixtures thereof. As a thermoplastic resin, the softening temperature is 150℃ or less,
Average molecular weight is 10000~200000, degree of polymerization is about 200~
For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer,
Acrylic acid ester-vinylidene chloride copolymer,
Acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-vinylidene chloride copolymer,
Methacrylic acid ester-styrene copolymer, urethane elastomer, 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-acrylic acid ester copolymer, amino resin, various synthetic rubber-based thermoplastic resins, and mixtures thereof, etc. is used. These resins are disclosed in Japanese Patent Publications No. 37-6877 and No. 39-
No. 12528, No. 39-19282, No. 40-5349, No. 40-
No. 20907, No. 41-9643, No. 41-14059, No. 41-
No. 16985 No. 42-6428, No. 42-11621, No. 43-
No. 4623, No. 43-15206, No. 44-2889, No. 44-
No. 17947, No. 44-18232, No. 45-14020, No. 45
-14500, 47-18573, 47-22063, 47-22063, 47-18573, 47-22063,
No. 47-22064, No. 47-22068, No. 47-22069,
Publications No. 47-22070 and No. 48-27886, U.S. Patent No. 3144352, U.S. Patent No. 3419420, U.S. Patent No. 3499789,
It is described in the specification of the same No. 3713887. As the thermosetting resin or reactive resin, one is used that has a molecular weight of 200,000 or less in the state of a coating solution and becomes insolubilized by a reaction such as condensation or addition after coating and drying. Among these resins, those that do not soften or dissolve before the resin is thermally decomposed are preferred. Specifically, for example, phenolic resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, vinyl chloride-vinyl acetate resin, methacrylate copolymer. and diisocyanate prepolymers, mixtures of high molecular weight polyester resins and isocyanate prepolymers, urea formaldehyde resins, mixtures of polyester polyols and isocyanates,
Polycarbonate-type polyurethane, polyamide resin, mixture of low molecular weight glycol, high molecular weight diol, triphenylmethane triisocyanate,
These include polyamine resins and mixtures thereof. These resins are listed in Special Publication No. 39-8103 and No. 40-9779.
No. 41-7192, No. 41-8016, No. 41-14275,
No. 42-18179, No. 43-12081, No. 44-28023,
No. 45-14501, No. 45-24902, No. 46-13103,
No. 47-22067, No. 47-22072, No. 47-22073,
No. 47-28045, No. 47-28048, No. 47-28922,
58-4051, Japanese Patent Publications No. 57-31919, 58-60430, Japanese Patent Application No. 58-151964, 58-120697
No. 58-120698, U.S. Patent No. 3144353
No. 3320090, No. 3437510, No. 3437510, No.
It is described in the specifications of No. 3597273, No. 3731210, and No. 3731211. Examples of electron beam irradiation-curable resins include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, polyester acrylic type,
Polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., and polyfunctional monomers include ether acrylic type, urethane acrylic type, phosphate ester acrylic type, aryl type, hydrocarbon type, etc. In order to improve the durability of the back coat layer of the magnetic recording medium according to the present invention, the back coat layer can contain various hardening agents, for example, isocyanate. Aromatic isocyanates that can be used include, for example, tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI), and combinations of these isocyanates with active hydrogen compounds. There are adducts of
The average molecular weight is preferably in the range of 100 to 3000. On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, trimethylhexamethylene diisocyanate (TMDI), and adducts of these isocyanates with active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred. In addition, examples of alicyclic isocyanates among the aliphatic isocyanates include methylcyclohexane-2,4-diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate) Examples include isophorone diisocyanate and adducts of its active hydrogen compounds. Examples of the adduct of the above-mentioned isocyanate and an active hydrogen compound include an adduct of a diisocyanate and a trivalent polyol. Polyisocyanates can also be used as curing agents, including, for example, a pentamer of diisocyanate, a decarboxylation compound of 3 moles of diisocyanate and water, and the like. Examples of these include 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, a pentamer of tolylene diisocyanate, and 3 moles of tolylene diisocyanate. and 2 moles of hexamethylene diisocyanate, and these can be easily obtained industrially. In order to form the back coat layer of the magnetic recording medium of the present invention using these isocyanates, a coating material is prepared by mixing and dispersing the above-exemplified resin and various additives described below as necessary in an organic solvent. The above-mentioned isocyanate (preferably aromatic isocyanate and aliphatic isocyanate) added thereto is applied onto a support such as a polyester film, and dried if necessary. In this case, the amount of isocyanate added is preferably 5 to 15% by weight based on the resin. If it is less than 5% by weight, the coating film tends to be insufficiently cured, and if it is more than 15% by weight, the coating film becomes too hard, which is not preferable. When the dibasic carboxylic acid monoester used in the present invention is used together with a resin, the amount used is preferably 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the resin. When the amount of this dibasic carboxylic acid monoester added is less than 0.5 parts by weight, the lubricity effect on the surface of the back coat layer and the effect on the wear resistance of the magnetic layer are not significant, and when it exceeds 20 parts by weight, the effect on the surface of the magnetic layer is It can cause a blooming phenomenon, excessively plasticize the coating film and reduce its strength, and even cause so-called interlayer adhesion, in which the tapes stick together when the magnetic tape is wound. The thickness of the layer containing the dibasic carboxylic acid monoester used in the present invention or a mixture thereof with another lubricant and the above resin is suitably 0.3 to 1.5 μm. When the dibasic carboxylic acid monoester used in the present invention is used together with a resin, additives such as a roughening agent and an antistatic agent may be further included. Examples of surface roughening agents include carbon black,
Silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide,
Examples include inorganic powders made of α-Fe ₂ O ₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., or benzoguanamine resin powders, preferably carbon black or titanium oxide. It is. In addition, carbon black is used as an antistatic agent.
Conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, carbon black graft polymers; natural surfactants such as saponin; alkylene oxide-based, glycerin-based, glycidol-based, etc. Nonionic surfactants; cationic surfactants such as pyridine and other heterocycles, phosphoniums or sulfoniums; carboxylic acids, sulfonic acids,
Examples include, but are not limited to, anionic surfactants containing acidic groups such as phosphoric acid, sulfuric ester groups, and phosphoric ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric esters of amino alcohols. These surfactants that can be used as antistatic agents are US Pat.
No. 2288226, No. 2676122, No. 2676924, No. 2676924, No.
No. 2676975, No. 2691566, No. 2727860, No. 2730498, No. 2742379, No. 2739891, No. 3068101, No. 3158484, No. 3201253,
Same No. 3210191, Same No. 3294540, Same No. 3415649,
3441413, 3442654, West German Patent Publication (OLS) 1942665, British Patent No. 1077317,
1198450, etc., Ryohei Oda et al., ``Synthesis of Surfactants and Their Applications'' (Maki Shoten 1964 edition); AW Peiri, ``Surf S Active Agents'' (Interscience Publications Inc. 1958) 2008 edition): "Encyclopedia of Surf S Active Agents Volume 2" by TR Sisley (Chemical Publishing Company 1964 edition): "Surfactant Handbook" 6th edition (Sangyo Tosho Co., Ltd. December 20, 1964)
It is written in books such as Japan). These surfactants may be added alone or in combination. These are used as antistatic agents, but may also be used for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids. The following method can be used to prepare the coating liquid for forming the back coat layer of the magnetic recording medium according to the present invention. A solution prepared by dissolving a lubricant such as a dibasic carboxylic acid monoester in an organic solvent such as toluene, methyl ethyl ketone, ethyl cellosolve, acetone, cyclohexanone, tetrahydrofuran, or methanol is added to the resin solution and mixed with stirring to form a solution. Alternatively, a resin and a lubricant such as a dibasic carboxylic acid monoester are stirred and mixed in these solvents to form a solution. Note that lubricants with poor solubility are milled and dispersed. Application methods for forming the back coat layer according to the present invention include dipping method, reverse roll method, extrusion method, knife blade method, doctor blade method, gravure printing method,
A spray method or the like is used, and the coating film applied by these methods is dried by an appropriate means. The back coat layer formed in this way is
Excellent lubricity can be achieved by adding a small amount of dibasic carboxylic acid monoester. In the present invention, a ferromagnetic metal thin film and a coated type are used for the magnetic layer, and the ferromagnetic metal thin film is
Metals such as Fe, Co, Ni, or Fe-Co, Fe-Ni,
Co−Ni Fe−Co−Ni, Fe−Rh, Fe−Cu, Co−
Cu, Co-Au Co-Y, Co-La, Co-Pr, Co-
Gd, Co−Sm, Co−Pt Ni−Cu, Mn−Bi, Mn
-Sb, Mn-Al, Fe-Cr, Co-Cr, Ni-Cr,
A ferromagnetic alloy such as Fe-Co-Cr, Fe-Co-Ni-Cr, etc. formed into a thin film by vacuum deposition, ion plating, sputtering, etc. is used. The thickness of this metal thin film is preferably about 0.02μ to 5.0μ. Examples of magnetic materials used in the coated magnetic layer of the present invention include γ-Fe ₂ O ₃ and Co-containing γ-
Fe ₂ O ₃ , Co adhesion γ- Fe ₂ O ₃ , Fe ₃ O ₄ , Co containing
Oxide magnetic materials such as Fe ₃ O ₄ , Co-coated Fe ₃ O ₄ , CrO ₂ ,
For example, Fe, Ni, Co, Fe-Ni alloy, Fe-Co alloy,
Fe-Ni-P alloy, Fe-Ni-Co alloy, Fe-Mn-
Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co-Ni alloy, Co-
Examples include various ferromagnetic materials such as P alloy, Co-Cr alloy, and metal magnetic powder containing Fe, Ni, and Co as main components.
Additives to these metal magnetic materials include Si,
Elements such as Cu, Zn, Al, P, Mn, and Cr, or compounds thereof may be included. Hexagonal ferrites such as barium ferrite and iron nitride are also used. The resin used in the back coat layer is used as a binder in the coated magnetic layer.
A dispersant is also used in this magnetic layer. Examples of the dispersant include lecithin; caprylic acid,
Capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, olefiic acid, elaidic acid, linoleic acid, linolenic acid, etc. with 8 carbon atoms
~18 fatty acids (R-COOH, where R is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms); alkali metals (Li, Na, K
etc.) or alkaline earth metals (Mg, Ca, Ba, etc.)
Examples include metal soaps made of. In addition, higher alcohols having 12 or more carbon atoms, sulfuric esters, and the like can also be used. Moreover, commercially available general surfactants can be used. These dispersants may be used alone or in combination of two or more. These dispersants are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the magnetic material. These dispersants are disclosed in Japanese Patent Publication No. 39-28369,
It is described in US Pat. No. 44-17945, US Pat. No. 48-15001, US Pat. No. 3,587,993, and US Pat. No. 347,021. Examples of the support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Metals such as Cu, Al, Zn, glass,
Ceramics such as BN, Si carbide, porcelain, and ceramics can also be used. The thickness of these supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm.
30 μm to 10 in the case of disks and cards.
mm, and in the case of a drum, it is used in a cylindrical shape, and its shape is determined depending on the recorder used. Further, the support may be in any form such as a tape, sheet, card, disk, or drum, and various materials may be selected as necessary depending on the form. Note that the back coat layer containing dibasic carboxylic acid monoester includes not only the case where the dibasic carboxylic acid monoester is contained in the polymer film but also the case where it is attached to the surface of the polymer film. Effects of the Invention According to the present invention, since the dibasic carboxylic acid monoester is contained in the back coat layer, the lubricating effect is improved with a small amount added compared to the conventional additive of a mixture of fatty acid and fatty acid ester. do. If the amount of such additives is small, it is difficult to cause blooming when used together with resin to form a back coat layer, so excessive exudation of the additives on the surface may cause damage to porcelain recording media, such as porcelain tapes. The magnetic layer is less likely to be damaged or powder falls off due to excessive tension. Also, uneven coating of the back coat layer is eliminated. As a result, it is possible to reduce output fluctuations, dropouts, etc. of the magnetic tape, and maintain good electromagnetic conversion characteristics such as various S/N.
Furthermore, since the shape of the roll is improved, the output characteristics and electromagnetic conversion characteristics can be maintained even when reused. In this way, recent demands for high-density recording and further improvement in durability can be met. EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited thereto. Example 1 The following composition is charged into a ball mill and dispersed to prepare a dispersion liquid. This dispersion is filtered through a 1 μm filter, and 5 parts by weight of a polyfunctional isocyanate is added to the filtrate and mixed to prepare a magnetic paint. This magnetic paint was applied to a thickness of 5 μm on a support using a reverse roll coater, dried, and then supercalendered. A solution having the composition shown in the column was prepared by stirring and mixing and coated using a reverse roll coater to form a back coat layer. The thickness of this back coat layer was 0.8 μm. The magnetic tape of Example 1 was then slit into 1/2 inch pieces. Co-containing γ-Fe ₂ O ₃ 400 parts by weight Polyurethane (Estan 5701 manufactured by Gutsudoritsuchi)
60 parts by weight Nitrocellulose (Daicel RS1/2) 20 parts by weight Lecithin 7 parts by weight Cyclohexanone 500 parts by weight Methyl ethyl ketone 250 parts by weight Toluene 250 parts by weight Examples 2 to 4 In Example 1, the composition in the Example 1 column of Table 1 Instead of using the solutions of Examples 2-
Example 2 was carried out in the same manner, except that a solution prepared in the same manner as above and having the composition shown in column 4 was used.
~4 magnetic tapes were created. Comparative Examples 1 to 4 In Example 1, instead of using the solution having the composition in the Example 1 column of Table 1, each of Comparative Examples 1 to 4 in Table 1 was used.
Magnetic tapes of Comparative Examples 1 to 4 were prepared in the same manner, except that solutions prepared in the same manner as above and having the compositions shown in columns 1 to 4 were used. The magnetic tapes of Examples 1 to 4 and Comparative Examples 1 to 4 were tested for each item shown in Table 2, and the results are shown in the corresponding columns. The measurement method is as follows. (a) Jitter value (μsec): Measured with a jitter meter by inputting a black and white step signal. (b) Bleed-out: The magnetic tape was held at -10℃ for 12 hours, then at 40℃ and 80% relative humidity for 12 hours. This was repeated 10 times, and the surface of the back coat layer was observed under a microscope. Those with granular or oily exudates were marked as x, and those without were marked as ○. (c) Volume: Video deck (equipment name: VICTOR
HR-7100) and repeatedly run it 400 times, and if the edges of the tape are aligned on one plane, mark it as ○.
Items that are not aligned are marked as ×. (d) Abrasion resistance: Using a simulated head, slide the loop-shaped 5 m long magnetic tape of each of the above examples and comparative examples at a speed of 7 m/sec, and then observe the surface of the tape with the naked eye. The determination was made by observation using a microscope. From the results in Table 2, it can be seen that the magnetic tapes using dibasic carboxylic acid monoester of Examples 1 and 2 have a lower amount of dibasic carboxylic acid monoester than the magnetic tape using capric acid of Comparative Example 1. It can be seen that a better jitter value is obtained even when the amount of capric acid added is less than half, and that bleed-out is difficult to occur because the amount added is small. As described above, the magnetic tape of the example has a good winding appearance because the amount of exudation of the additive is small, whereas the magnetic tape of Comparative Example 1 has an excessive amount of exudation of the additive, so the winding appearance is not good as a result. I understand that. In addition, the magnetic tape of Comparative Example 2 has no bleed-out, but has an inferior jitter value.
The appearance of the roll is also poor. This seems to be due to insufficient lubricity as a result of the small amount of capric acid added. In addition, the magnetic tapes of Examples 3 and 4, in which butyl stearate was used in combination with Examples 1 and 2, had good properties, whereas the magnetic tapes in Comparative Examples 3 and 4, in which butyl stearate was used in combination with Comparative Examples 1 and 2, had good properties. The properties of magnetic tape are not good. Examples 5 to 9 In Example 1, exemplified compound (4) of the above general formula
Magnetic tapes were prepared in the same manner as in Example 1, except that two copies each of (1), (2), (7), (8), and (9) were used instead of , and the results were measured in the same manner as in Example 1. Shown in 3.

【table】

【table】

【table】

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer on one side of a support and a back coat layer on the other side of the support, characterized in that the back coat layer contains a dibasic carboxylic acid monoester. magnetic recording media.