JPH0565927B2 - - Google Patents

Description

[Detailed description of the invention]

(1) Industrial Application Field The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks. (2) Prior art In general, magnetic recording media are made by forming a support made of polyethylene terephthalate or the like into a tape or sheet shape, and coating this support with a magnetic paint containing magnetic powder and a binder as main components. formed by layers. Conventionally, in these magnetic recording media, various dispersants and surfactants have been used to disperse fine particulate magnetic powder in an organic solvent together with a binder resin when preparing a coating solution for manufacturing the media. . Examples of dispersants include oily lecithin or powdered lecithin, saturated or unsaturated fatty acids and their salts, hydrocarbons having polyoxyethylene chains, and sulfuric acid esters and phosphoric acid esters of higher alcohols. These dispersants are magnetic powder 100
It is added in an amount of 0.01 to 20 parts by weight. In recent years, in order to manufacture high-performance magnetic tapes, it is essential to make magnetic particles ultrafine and highly fine, but it is difficult to obtain a magnetic recording layer with desired characteristics using conventional additives. Therefore, even if a prototype in a laboratory has excellent characteristics, it may not be put into practical use due to mass production or production technology considerations.
In particular, it has been difficult to produce a uniform magnetic tape coating with low viscosity and excellent coating properties from ultrafine magnetic powder particles. In addition, in the conventional technology, the primary consideration is to disperse the magnetic powder into the binder solution by surface modification.
Little consideration was given to the stability and applicability of the produced paints. On the other hand, with the recent development of magnetic recording materials, magnetic tapes for videos, computers, audio, etc.
Magnetic disks are now required to have a high level of performance in terms of durability, and for video magnetic tapes where the relative speed between the head and the tape is high, it is necessary to combine magnetic powders to form a magnetic layer. A particularly wear-resistant binder is used. For example, polyurethane has strong adhesion to other materials, is mechanically strong to withstand repeated stress or bending, and has abrasion resistance.
It is said to have good weather resistance. Therefore, it is conceivable to use polyurethane as a binder for the magnetic layer, but as a result of the inventor's studies,
It has been found that simply using known polyurethane as a binder for the metal magnetic powder described above has the following fatal defects. That is, since polyurethane has a high coefficient of friction and poor surface lubricity, the frictional force increases during tape running, resulting in poor running. In order to prevent this, attempts have been made to blend other resins with polyurethane or blend low-molecular-weight lubricating agents. However, the compatibility between polyurethane and other resins is not so good, and when low-molecular-weight compounds are blended, "blooming" tends to occur, causing stains and clogging of the magnetic head, resulting in electromagnetic conversion. The characteristics become poor. Furthermore, since the film strength of the magnetic layer using polyurethane as a binder is insufficient, powder falling from the magnetic layer increases, causing an increase in trop-outs. Moreover, known polyurethanes have the disadvantage of insufficient heat resistance. As a modified form of polyurethane,
Polyester polyurethane disclosed in JP-A No. 56-137522 is known, but when this is used as a binder, the ester component improves heat resistance, but solvent solubility decreases and urethane The concentration cannot be made too high, resulting in a decrease in film strength. For this reason, when a lubricant is used in combination, the amount of lubricant must be increased in order to control the lubricity of the entire binder and maintain film strength, but it is necessary to use a large amount of low-molecular-weight lubricant. This is inappropriate because blooming will occur. As described above, no binder composition that has sufficient properties such as durability, heat resistance, moisture resistance, and mechanical strength has been proposed to date. The reality is that fatal defects such as defects and aging cannot be avoided. (3) Object of the Invention The object of the invention is to provide a magnetic recording medium in which magnetic powder or other filler is well dispersed, has excellent electromagnetic conversion characteristics, and has good stability over time and still durability. (4) Structure of the invention and its effects That is, the present invention comprises a magnetic substance, an organic dye compound represented by the general formula [X] having a carboxyl group or a sulfonic acid group, and a polycarbonate polyurethane having no ester bond. and a phenoxy resin. According to the present invention, since the organic dye compound represented by the general formula [X] having a carboxyl group or a sulfonic acid group is contained in the magnetic layer, the magnetic material is stably dispersed, and the S/N ratio is It is possible to provide a magnetic recording medium with significantly improved RF output, etc. It is preferable that the organic dye compound used in the present invention has one of the following conditions. a) The compound is represented by the following general formula [X]; b) It has a salt form; c) It is an azo compound; d) It is red. General formula [X] n ₁ and n ₂ are integers of 0 to 5, m ₁ and m ₂ are integers of 0 to 2, X is -Cl, Y is -Cl, -NO ₂ , -CH ₃ , -C ₂ H ₅ , −OCH ₃ ,−
OC ₂ H ₅ , Z ₁ is a carboxyl group, a sulfonic acid group or

[Formula] -CONH(CH ₂ ) ₁₀ COOH or each salt of an alkali metal or alkaline earth metal thereof, Z ₂ is a carboxyl group or a sulfonic acid group or their

[Formula] (R ₁ is H or lower alkyl (1 to 4 carbon atoms),
_R2 is H or long-chain alkyl (carbon number 10-30), alkali metal, alkaline earth metal salt, or (A is a carboxyl group or a sulfonic acid group, B is _-NO2 , -Cl; _-CH3 , _l1 is an integer from 0 to 1, _l2 is 0
Represents an integer between ~2. ) Exemplary compounds of the organic dye compound having a carboxyl group or sulfonic acid group represented by the general formula [X] are as follows, but are not limited to these, and various substitutions for modification are possible. be. In order to incorporate the organic dye compound used in the present invention into the magnetic layer of a magnetic recording medium, at least one organic dye compound according to the present invention is dissolved in water or an organic solvent such as toluene, methyl ethyl ketone, or cyclohexanone. Magnetic powder is immersed in the solution at a predetermined ratio, stirred and mixed, filtered and dried, and the resulting treated magnetic powder and binder are kneaded, or at least one of the organic dye compounds according to the present invention is mixed. The seeds may be added directly or dissolved in a suitable solvent during dispersion of the magnetic powder.
Furthermore, it is also possible to add the magnetic coating material before applying it to the support. The organic dye compound of the present invention is usually 0.1% to 20% by weight, preferably 0.1% by weight based on the magnetic powder.
It is desirable to use it in a range of ~10% by weight. The magnetic paint obtained by kneading and dispersing the magnetic powder and binder using the organic dye compound of the present invention using an organic solvent etc. has excellent dispersion stability and low viscosity, and also has little blooming over time.
Again, the dispersibility is easy, and the workability of coating is also excellent. In the present invention, it is also desirable to add another surfactant (for example, a nonionic surfactant, compound A or B described below) in combination with this organic dye compound. Furthermore, according to the present invention, a magnetic recording medium with excellent durability can be obtained by using polycarbonate-based polyurethane and phenoxy resin as the binder of the magnetic layer. At least polyurethane can be used as the binder resin for the magnetic layer in the magnetic recording medium of the present invention, and this can be synthesized by reacting polyol and polyisocyanate. Usable polyols include organic dibasic acids such as phthalic acid, adipic acid, dimerized linoleic acid, and maleic acid, and glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or trimethylolpropane, hexanetriol, For reaction with polyhydric alcohols such as glycerin, trimethylolpropane, hexanetriol, glycerin, trimethylolethane, pentaerythritol, or any two or more polyols selected from these glycols and polyhydric alcohols. polyester polyol synthesized by
s-caprolactam, α-methyl-1-caprolactam, s-methyl-s-caprolactam, γ-
Examples include lactone-based polyester polyols synthesized from lactams such as butyrolactam; and polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, and the like. These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, metaxylylene diisocyanate, etc.
As a result, urethanized polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate are synthesized. These polyurethanes are usually produced primarily by the reaction of polyisocyanates with polyols and are also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups, or containing reactive end groups of these. However, among these polyurethanes, in the present invention, polycarbonate polyurethane is particularly used as a binder for the magnetic layer. Demonstrated. Furthermore, the presence of the carbonate component improves heat resistance (Tg), provides running stability by reducing the coefficient of friction, and improves solubility in solvents, making it possible to increase the urethane concentration and increase the film strength. . In this case, since there are no ester bonds in the polyurethane molecules, no change over time due to hydrolysis of the ester bonds occurs even when used for a long time under high temperature and high humidity conditions. Therefore, the layer is not scratched or peeled off, and smooth running properties can be maintained. Here, the above-mentioned "ester bond" specifically refers to a bond formed by the reaction between a normal carboxylic acid and an alcohol, and is attached to a carbon atom forming a carbonyl bond (usually ) refers to those in which adjacent carbon atoms are directly bonded. -NHCOO- (urethane bond)

[Formula] (carbonate bond) is not included in the ester bond referred to here. Next, the structure of the polycarbonate polyurethane used as the binder for the magnetic layer of the magnetic recording medium of the present invention will be explained. This polyurethane is, for example, a polycarbonate polyol based on the following formula:

It is synthesized by a urethanization reaction between [Formula] and a polyvalent isocyanate (for example, OCN-R'-NCO). (However, R and R' are aliphatic or aromatic hydrocarbon groups. l is preferably 50 or less, preferably 1 to 30, to lower Tg and prevent stickiness. m is a group that maintains film-forming ability. And in order to improve solvent solubility, it is preferably 5 to 500, preferably 10 to 300.l and m are
The average molecular weight of this polycarbonate polyol polyurethane is desirably selected to be 50,000 to 200,000. ) The polycarbonate polyol that can be used here is formed by linking polyols with carbonate bonds, and is made by, for example, condensing a conventionally known polyhydric alcohol with phosgene, chloroformic acid ester, dialkyl carbonate, diallyl carbonate, etc. can get. The polyhydric alcohols include 1,10-decanediol, 1,6-hexanediol, 1,4-
Examples include butanediol, 1,3-butanediol, neopentyl glycol, 1,5-pentanediol, and the like. The number of carbon atoms in this polyhydric alcohol, such as a diol, is important, and is preferably set to 4 to 12, but as shown in Figure 1, if the number of carbon atoms is less than 4 and greater than 12, This is because powder fall-off (after 100 runs) is likely to occur. Correspondingly, the molecular weight of polycarbonate polyol is approximately 700 from the results shown in Figure 2 (powder falling off after 100 runs: 60℃, after storage for 1 week).
It is better to set it to ~3000. In the above-mentioned urethanization reaction, it is important that active hydrogen (due to -OH) exists in the polycarbonate, but in addition to the polyhydric alcohols listed above, there are other compounds that supply similar active hydrogen. , ethylene glycol, diethylene glycol, propylene glycol, 1,4-butylene glycol, bisphenol A, glycerin, 1,3,6-hexanetriol, trimethylolpropane, pentaerythritol, sorbitol, sucrose, dipropylene glycol,
Methyldiethanolamine, ethylbiisopropanolamine, triethanolamine, ethylenediamine, hexamethylenediamine, bis(p-
compounds such as aminocyclohexane), tolylene diamine, diphenylmethanediamine, methylenebis(2-chloroaniline), and/or these compounds, ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide, etc. (hereinafter simply referred to as alkylene Examples include polyether polyols obtained by adding one or more types of oxides (abbreviated as oxides). Next, although the active hydrogen-containing polycarbonate such as the above-mentioned polycarbonate polyol can be used alone, other polyhydric alcohols may be used in combination with the above-mentioned urethanization, and other known chain extenders may be used in combination. For example, when other low-molecular-weight polyhydric alcohols such as hexanediol and butanediol are used together, it can be expected that they will react with an excess amount of the polyisocyanate and promote gelation, but as shown in Figure 3, polycarbonate It is desirable to maintain the proportion of polyol at 80% or more in order to obtain sufficient wear resistance. Next, the above polyvalent isocyanate is preferably an aromatic isocyanate, such as tolylene diisocyanate (TDI) (2,4-
TDI, 2,6-TDI), dimer of 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI), naphthylene -1,5-diisocyanate (NDI), o-tolylene diisocyanate (TODI), and adducts of these isocyanates with active hydrogen compounds, etc., and those with an average molecular weight in the range of 100 to 3000 are suitable. . Specifically, the product names Sumidyur T80, Sumidyur 44S, Sumidyur PF, Sumidyur L, manufactured by Sumitomo Bayer Urethane Co., Ltd.
Desmodille T65, 15, R, RF, IL,
Same SL; Takenate 300S manufactured by Takeda Pharmaceutical Company,
500: Mitsui Nisso Urethane Co., Ltd. product “NDI”,
"TODI": Products manufactured by Nippon Polyurethane Co., Ltd. Desmodyur T100, Millioneroto MR, MT, Coronate L; Products manufactured by Kasei Upjiyon Co., Ltd. PAP1-135,
TD165, 80, 100, Isocyanate 125M,
One example is the 143L. On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, trimethylhexamethylene diisocyanate (THDI), 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. Specifically, for example, Sumidyur N and Desmodyur Z4273 manufactured by Sumitomo Bayer Urethane Co., Ltd., Dulanate 50M and Dulanate 24A-100 manufactured by Asahi Kasei Co., Ltd.
24A-90CX, Coronate HL manufactured by Nippon Polyurethane Co., Ltd., and TMDI manufactured by Hyurus Co., Ltd. Examples of alicyclic isocyanates among the aliphatic isocyanates include methylcyclohexane-2,4-diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), isophorone diisocyanate, and adducts of active hydrogen compounds thereof. I can do it. Specifically, the products “IPDI” and “IPDI-TI890” manufactured by Hyurus Chemical Co., Ltd.
There are the same-H2921, the same-B1065, etc. Examples of other polyvalent isocyanates include adducts of diisocyanates and trivalent polyols, and pentamers of diisocyanates. 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, and a pentamer consisting of 2 moles of tolylene diisocyanate. These can be easily obtained engineeringly. Among the polyvalent isocyanates mentioned above, aromatic ones act as hard components (hard segments), so polycarbonate (polyol)
It is desirable because it can sufficiently exhibit the rigidity of polyurethane. Figure 4 shows the change in adhesiveness depending on the average molecular weight of the same polyurethane.
If it is set in the range of 10,000, the tackiness can be kept low, but in this case, if an aromatic system is used as the isocyanate component of the polyurethane, the curve a
As shown in curve b, the still durability can be sufficiently increased, whereas when an aliphatic isocyanate is used, the still durability becomes low as shown in curve b. Among the aromatic isocyanates mentioned above, naphthylene-1,5-diisocyanate and diphenylmethane diisocyanate are particularly desirable. The amount of the above-mentioned isocyanate used is such that the NCO group (isocyanate group) contained in the polyisocyanate is in an equivalent ratio of 0.8 to 1.2 with respect to the total amount of active hydrogen contained in the active hydrogen-containing compound (for example, polycarbonate polyol), and more preferably 0.85
It is desirable that the equivalent ratio be ~1.1. When producing the polyurethane according to the present invention, the following solvents may be used as necessary.
Amides such as dimethylformamide and dimethylacetamide, sulfoxides such as dimethyl sulfoxide, cyclic ethers such as dioxane and tetrahydrofuran, cyclic ketones such as cyclohexanone, acyclic ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, Glycol ether type known as "cellosolve", "butyl cellosolve", "carbitol", "butyl carbitol" etc., product name "cellosolve acetate", "butyl cellosolve acetate", "carbitol acetate", "butyl carbitol acetate" One or more types of acetic acid glycol ether type solvents known as ``Diglyme'' and dibasic acid ester type solvents known as ``Diglyme'', and furthermore, combinations of the above solvents with ethyl acetate, butyl acetate, etc. Ester type,
These include aromatic hydrocarbon solvents such as benzene, toluene, and xylene, chlorine solvents such as methylene chloride, trichloroethylene, trichloroethane, and perchlorethylene, and mixed solvents with alcohol solvents such as methanol, ethanol, isopropanol, and butanol. Furthermore, 2,2,4-trimethyl 1,3-pentanediol monoisobutyrate (Kyowanol M: manufactured by Kyowa Hakko Co., Ltd.) can also be used as a solvent. To produce the polyurethane according to the present invention,
First, in a nitrogen atmosphere, for example, a polymer polyol and an isocyanate are reacted by heating at 60° C. to 100° C. for several hours in the presence of a catalyst and/or a solvent as necessary to produce a prepolymer. The reaction is further heated at the same temperature for several hours to obtain a polyurethane resin according to the present invention. If necessary, a reaction terminator can be added and the reaction can be carried out by heating. Further, a solvent is appropriately added to reduce the viscosity at each stage of the reaction. The obtained polyurethane resin solution according to the present invention has a solid content of 15 to 60%,
The viscosity is 200-70000cps/25℃. As explained in Figure 4, it is desirable to select the average molecular weight of the polycarbonate polyurethane synthesized as described above from 50,000 to 200,000. It has been confirmed that the surface properties of the magnetic layer also improve. The phenoxy resin according to the present invention is obtained by polymerizing bisphenol A and epichlorohydrin and has the following structure. Based on the above structure, various substituents such as halogen atoms and alkyl groups may be introduced, or ester bonding or silane modification may be performed focusing on the OH group. Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness. These advantages complement and complement the above-mentioned polycarbonate-based polyurethane, and can significantly improve the stability over time of the physical properties of the tape. As the phenoxy resin, PKHC, PKHH, PKHT, etc. manufactured by Union Carbide Co., Ltd. are available as commercial products. The physical properties of the film can be improved by using other binder resins (for example, polyurethanes other than the polycarbonate, vinyl chloride-vinyl acetate copolymer, nitrocellulose, etc.) in combination with the combination of the polycarbonate polyurethane and phenoxy resin according to the present invention. The dispersibility of magnetic powder, etc. can be further improved. When used in combination with other binder resins, polycarbonate-based polyurethane has good compatibility and stable film properties over time, improving the running properties of the magnetic tape. When a phenoxy resin and a vinyl chloride copolymer are combined, the film becomes too hard, but by incorporating the polyurethane of the present invention into the film, flexibility can be increased and the good adhesiveness of the phenoxy resin can be achieved. The vinyl chloride copolymer mentioned above has the following general formula [General formula] The molar ratio of the two repeating units given by l and m of each repeating unit is 95 to 50 mol% for the former repeating unit and 5 to 50 mol% for the latter. . Further, X represents a repeating unit copolymerizable with vinyl chloride, and represents at least one type selected from the group consisting of vinyl acetate, vinyl alcohol, maleic anhydride, and the like. The degree of polymerization expressed as (l+m) is preferably 100 to 600, and the degree of polymerization is 100 to 600.
If it is less than 600, the magnetic layer etc. tends to become sticky.
If it exceeds this, the dispersibility will deteriorate. The vinyl chloride copolymer described above may be partially hydrolyzed. The vinyl chloride copolymer is preferably a vinyl chloride-vinyl acetate copolymer (hereinafter referred to as
It is called "vinyl chloride-vinyl acetate copolymer." )
can be mentioned. Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride copolymers, and vinyl chloride-vinyl acetate-maleic anhydride copolymers.
Among the vinyl acetate copolymers, partially hydrolyzed copolymers are preferred. Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include “VAGH” and “VYHH” manufactured by Union Carbide;
"VMCH", "Esletsu A" manufactured by Sekisui Chemical Co., Ltd.,
“Eslec A-5”, “Eslec C”, “Eslec M”, “Denkabinil” manufactured by Denki Kagaku Kogyo Co., Ltd.
1000G", "Denkabinir 1000W", etc. can be used. In addition to the above, cellulose resins can be used as binder resins, such as cellulose ethers, cellulose inorganic acid esters, cellulose organic acid esters, and the like. As the cellulose ether, methyl cellulose, ethyl cellulose, etc. can be used. As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used. Further, as the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, butyryl cellulose, etc. can be used. Among these cellulose resins, nitrocellulose is preferred. In addition, regarding the entire binder composition, the ratio of the above-mentioned urethane resin to other resins (total amount of phenoxy resin, vinyl chloride copolymer, etc.) is 90/10 to 50/50 by weight. It has been confirmed that 85/15 to 60/40 is more desirable. Outside this range, if the amount of urethane resin is large, dispersion tends to be poor, and if the amount of other resins is large, surface properties tend to be poor. In the case of vinyl chloride-vinyl acetate, it can be mixed with the urethane resin with considerable flexibility, preferably 15 to 75% by weight of the urethane resin. Magnetic powders, particularly ferromagnetic powders according to the present invention include γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ ,
Co-containing iron oxide such as Fe ₃ O ₄ , Ba ferrite magnetic powder; Fe, Ni, Co, Fe-Ni, Fe-Al, Fe-Ni-
Co alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy,
Fe-Co-Ni-Cr alloy, Fe-Co-Ni-p alloy,
Examples include various ferromagnetic powders such as metal magnetic powders containing Fe, Ni, Co, etc. as main components such as Co-Ni alloys. FIG. 6 shows a cross section of the magnetic tape of the present invention.
1 is a support, 2 is a magnetic layer, and 3 is a back coat layer. As the binder for the magnetic layer 2, in addition to the binder according to the present invention described above, a mixture of this binder and a thermoplastic resin, a thermosetting resin, a reactive resin, or an electron beam curable resin may be used. As a thermoplastic resin, the softening temperature is 150℃ or less, the average molecular weight is 10,000 to 200,000, and the degree of polymerization is about 200.
~2000, such as acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic ester-
Acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, Styrene-butadiene copolymers, polyester resins, chlorovinyl ether-acrylic acid ester copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used. The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Moreover, among these resins, those which do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenolic resin, epoxy resin, urea resin, melamine resin,
These include alkyd resins, silicone resins, acrylic reactive resins, mixtures of methacrylate copolymers and diisocyanate prepolymers, urea formaldehyde resins, polyamine resins, and mixtures thereof. 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. The mixing ratio of the ferromagnetic powder and the binder according to the present invention is 5 to 400 parts by weight, preferably 10 to 200 parts by weight, per 100 parts by weight of the ferromagnetic powder. If the amount of binder is too large, the recording density of the magnetic recording medium will be reduced, and if it is too small, the strength of the magnetic layer will be poor, resulting in undesirable situations such as decreased durability and powder falling off. Furthermore, in order to improve the durability of the magnetic recording medium according to the present invention, in addition to the above-mentioned isocyanates, triphenylmethane triisocyanate, tris-(p-isocyanate phenyl) thiophosphite, and polymethylene polyphenyl isocyanate are used as crosslinking agents. may be included. The paint used to form the magnetic layer paint may contain additives such as a dispersant, a lubricant, an abrasive, an antistatic agent, and the like, if necessary. Examples of dispersants used in combination with the organic coloring compound according to the present invention include lecithin, phosphoric acid ester, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid ester, and the like. There are surfactants, etc. and their salts,
It is also possible to use salts of polymeric dispersants having negative organic groups (eg -COOH, _-PO3H ). 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 powder. These dispersants may be used to pre-treat the magnetic powder in advance. In addition, as lubricants, silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, monobasic fatty acids with 12 to 16 carbon atoms, and the number of carbon atoms in the fatty acids are used. Fatty acid esters (so-called waxes) consisting of monohydric alcohols having a total of 21 to 23 carbon atoms can also be used. These lubricants are added in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder. Abrasives that may be used include commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, and emery (main components: corundum and magnetite). be done. These abrasives have an average particle diameter of 0.05 to 5 μm, particularly preferably 0.1 to 2 μm. These abrasives are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the binder. Antistatic agents that may be used include carbon black, graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide, etc.
Conductive powders such as antimony oxide compounds; Natural surfactants such as saponins; Nonionic surfactants such as alkylene oxides, glycerin, and guillicidol; higher alkylamines, quaternary ammonium salts, pyridine, and other complexes Cationic surfactants such as rings, phosphoniums or sulfoniums; anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfuric acid ester groups, and phosphoric ester groups; amino acids, aminosulfonic acids, and amino alcohols; Examples include amphoteric activators such as sulfuric acid or phosphoric acid esters. The carbon black used preferably includes carbon black (hereinafter referred to as CB ₁ ) that imparts conductivity and carbon black (hereinafter referred to as CB ₂ ) that imparts light-shielding properties to the magnetic layer. . Generally, when static electricity is accumulated during use of a magnetic recording medium, discharge occurs between the medium and the magnetic head, which tends to generate noise, and dust and the like may be attracted, causing dropouts. Furthermore, for video, a method is known in which the running of the tape is adjusted by detecting the difference in light transmittance between a tape portion having a magnetic layer and a leader tape portion. For these reasons, it is generally required that the surface electrical resistance of the magnetic layer be 10 ⁹ Ω-cm or less, and that the light transmittance of the tape portion where the magnetic layer is located be 0.05% or less. For this purpose, carbon black particles are usually added to the magnetic layer. In this case, the above-mentioned carbon black CB ₁ ,
When using CB ₂ , the specific surface area of both carbon blacks should be 200 to 500 m ² /g (and
200-300m ² /g), and 40-200m ² /g for the latter.
It is desirable to do so. That is, as shown in FIG.
If the specific surface area of CB ₁ is less than 200 m ² /g, the particle size will be too large and conductivity will be insufficient even with the addition of carbon black, and if it exceeds 500 m ² /g, the particle size will be too small The dispersibility of carbon black tends to deteriorate. This carbon black CB ₁ is preferably one in which the particles are connected like a bunch of grapes, and is preferably porous and has a large specific area, that is, a high structure level.
Such carbon blacks include, for example, Conductex manufactured by Columbia Carbon.
-ctex) 975 (specific surface area 270 m ² /g, particle size 46 mμ),
Conductex 950 (specific surface area 245 m ² /g, particle size 46 mμ), Cabot Vulcan
XC-72 (specific surface area 257 m ² /g, particle size 18 mμ) etc. can be used. Regarding CB ₂ , as shown in Figure 9, if the specific surface area is less than 40 m ² /g, the particle size is too large and the light shielding properties tend to deteriorate, so it is necessary to increase the amount added more than necessary. Yes, also 200
m ² /g or more, the particle size is too small and dispersibility in the layer tends to be poor. Such light-shielding carbon black CB ₂ has a small particle size, a relatively low structure level, and a relatively low specific surface area, such as Raven 2000 manufactured by Columbia Carbon Co., Ltd. (specific surface area 180 m ^{2 )} . /g, particle size 19mμ), 2100, 1170, 1000, #100, #75,
#44, #40, #35, #30, etc. can be used. There is a certain preferable range for the mixing ratio (weight ratio) of each of the above carbon blacks, and CB ₁ / CB ₂
=90/10 to 50/50 is good, and 80/20 to 60/40 is even better. If this mixing ratio is larger than 90/10, the proportion of conductive carbon black CB ₁ will be large, resulting in insufficient light shielding properties, and if it is smaller than 50/50, the surface resistivity will be low due to the small amount of conductive carbon black CB ₁ . It will increase. In addition, in the above, "specific surface area" refers to the surface area per unit weight, and is a physical quantity completely different from the average particle diameter. For example, even if the average particle diameter is the same, the specific surface area is large, Some have small specific surface areas. To measure the specific surface area, first heat carbon black powder at around 250°C for 30~60°C.
Deaeration is performed during heat treatment for 30 minutes to remove substances adsorbed on the powder, and then the powder is introduced into a measuring device, the initial pressure of nitrogen is set to 0.5Kgγ/ ^m2 , and the liquid nitrogen temperature is Adsorption measurement is carried out at (-195℃) (Specific surface area measurement method generally referred to as BET method. For details, J.Ame.Chem.Soc, 60 309
(1938)). This specific surface area (BET value) measuring device is manufactured by Yuasa Battery Co., Ltd. and Yuasa Ionics.
You can use the "Powder and Granule Measurement Device (Cantersoap)" co-manufactured by Co., Ltd. A general explanation of the specific surface area and its measurement method can be found in “Powder Measurement” (JMD ALLAVALLE,
Co-authored by CLYDEORR Jr., translated by Benta et al.; published by Sangyo Toshosha). It is also described in detail in "Chemistry Handbook" (Application Edition, Sections 1170-1171, edited by the Chemical Society of Japan, published by Maruzen Co., Ltd., April 30, 1966). (Published on the same day). (In the above-mentioned "Chemical Handbook," the specific surface area is simply described as surface area (m ² /gr), but it is the same as the specific surface area in the present invention.) Solvent for magnetic paint or magnetic paint coating Solvents used include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, and butanol; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol monoacetate. Esters such as:
Ethylene glycol dimethyl ether, diethylene glycol monoethyl ether, dioxane,
Ethers such as tetrahydrofuran; benzene,
Aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used. Further, as the material of the support 1 mentioned above, polyethylene terephthalate, polyethylene-2,6
- Polyesters such as naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, plastics such as polycarbonate, metals such as Al and Zn, ceramics such as glass, silicon nitride, silicon carbide, porcelain, and earthenware. etc. are used. The thickness of these supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 100 μm.
50μm, and in the case of disk or card shape,
It is approximately 30 μm to 10 mm, and if it is drum-shaped, it is cylindrical, and its shape is determined depending on the recorder used. Coating methods for forming a magnetic layer by coating the magnetic paint on the support include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, and gravure coating. , kiss coat, cast coat, spray coat, etc., and other methods are also possible. The magnetic layer coated on the support by such a method is optionally treated to orient the ferromagnetic powder in the layer, and then the formed magnetic layer is dried. Further, if necessary, the magnetic recording body of the present invention is manufactured by subjecting it to surface smoothing processing or cutting it into a desired shape. Further, the magnetic recording medium shown in FIG. 6 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may not be provided with an undercoat layer (not shown). Same below). The non-magnetic powder contained in the back coat layer (BC layer) 3 in FIG. 6 includes carbon black, silicon oxide, titanium oxide, aluminum oxide,
Chromium oxide, silicon carbide, calcium carbide, zinc oxide, α-Fe ₂ O ₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably carbon black or titanium oxide Examples include those consisting of. Including these non-magnetic powders in the BC layer can improve the surface properties by appropriately roughening the surface of the BC layer (making it matte), and in the case of carbon black, it can also impart conductivity to the BC layer. Provides antistatic effect. It is advantageous to use carbon black and other non-magnetic powders in combination, since both the effects of improving surface properties (stabilizing runnability) and improving conductivity can be obtained. However, the surface roughness of the BC layer is such that the average roughness or height (Ra) of the center line of the surface irregularities is 0.01 to 0.1 μm, preferably 0.025 μm or less, and the maximum roughness (Rmax) is 0.20 to 0.80 μm. It is better to Regarding Ra, in order to improve chroma S/N, Ra≦
It is desirable to set it to 0.025μ. If the value of Ra or Rmax is too small, running stability and the winding appearance during tape winding will be insufficient, and if it is too large, transfer from the BC layer to the magnetic layer (during tape winding) will occur, making the surface even rougher. Put it away. In addition, the filler in BC layer 3 (including non-magnetic powder)
The particle size is preferably 0.5 μm or less, preferably 0.2 μm or less in order to obtain the above surface roughness. Also,
The BC layer 3 can be formed by coating in the same manner as described above, but the film thickness after coating and drying is 0.1~
The thickness is preferably 3.0 μm, preferably 1 μm or less, and more preferably 0.6 μm or less. The amount of non-magnetic powder added to the BC layer is generally
The amount is 100 to 400 mg/m ² , preferably 200 to 300 mg/m ² . Also, as a binder for the BC layer 3, the magnetic layer 2
By using the same binder resin according to the present invention (and in combination with the other resins mentioned above), the BC layer can also have the above-mentioned remarkable properties, which is advantageous in terms of reducing jitter, etc. It is. When the BC layer contains the resin according to the present invention as a binder, data having the same tendency as shown in FIGS. 1, 2, 3, 4, and 5 can be obtained. However,
In this case, the vertical axis in Figures 1 and 2 is the amount of jitter (μm), the vertical axis in Figure 3 is the wear resistance (the higher it goes, the better the wear resistance), and the vertical axis in Figure 4 is the adhesiveness. If the vertical axis in FIG. 5 is the amount of wear (the higher the top, the lower the tackiness), then data with almost the same tendency as the data shown in FIGS. 1 to 5 regarding the amount of magnetism can be obtained. Also,
The data in FIGS. 7 to 9 can be applied to the BC layer in almost the same way. Note that although the BC layer 3 is necessary for a high-quality tape, it does not necessarily need to be provided. FIG. 10 shows another magnetic recording medium in which an overcoat layer (OC layer) 4 is provided on the magnetic layer 2 of the medium in FIG. This OC layer 4 is provided to protect the magnetic layer 2 from damage, etc., and for this purpose, it needs to have sufficient slipperiness. Therefore, as the binder for the OC layer 4, it is preferable to use the binder used for the above-mentioned magnetic layer 2 (preferably in combination with a cellulose resin and a vinyl chloride copolymer). FIG. 11 shows a magnetic recording medium configured as a magnetic disk, in which magnetic layers 2 similar to those described above are provided on both sides of a support 1, respectively. OC layers similar to those shown in FIG. 10 may be provided on these magnetic layers, but these OC layers preferably contain a binder containing the above-mentioned polycarbonate polyurethane as a main component. (5) Examples The present invention will be described below with reference to specific examples. The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, all "parts" in the following examples represent "parts by weight."<Polycarbonate polyol synthesis example> 590 parts of diethyl carbonate and 650 parts of 1,6-hexanediol are reacted at 120°C to 200°C for 15 hours, then cooled to 150°C, and heated under reduced pressure for 20 to 50 mm.
The remaining ethanol and unreacted diol were sufficiently distilled off using Hg to obtain 770 parts of polycarbonate polyol. The hydroxyl value of this polyol was about 66 (molecular weight was about 1700). <Synthesis of polycarbonate polyol polyurethane> (Synthesis example 1) Polycarbonate polyol synthesized above
170 parts of diphenylmethane diisocyanate (MDI) and 25 parts of diphenylmethane diisocyanate (MDI) were dissolved in 580 parts of methyl ethyl ketone, 0.03 parts of dibutyltin dilaurylate was added as a urethanation catalyst, and the mixture was reacted at 80°C for 6 hours to form a solution of 770 parts of polycarbonate polyol polyurethane in methyl ethyl ketone. (solid content concentration 25.0
%, Mw of polyurethane 140,000). (Synthesis Example 2) Polycarbonate polyol synthesized above
162 parts of MDI and 25 parts of MDI were dissolved in 560 parts of methyl ethyl ketone, 0.03 parts of dibutyltin dilaurylate was added as a urethanization catalyst, and the reaction was carried out at 80°C for 4 hours. Furthermore, 0.45 parts of 1,3-butanediol was added and the mixture was reacted for 2 hours. Methyl ethyl ketone solution of polycarbonate polyol polyurethane reacted at 80℃
740 parts were obtained (solid content concentration 25.4%, Mw of polyurethane 130,000). (Synthesis Example 3) Polycarbonate polyol synthesized above
153 parts of MDI, 25 parts of MDI, and 1.1 parts of neopentyl glycol were dissolved in 540 parts of methyl ethyl ketone, 0.03 parts of dibutyltin dilaurylate was added as a urethanization catalyst, the mixture was reacted at 80°C for 6 hours, and 715 parts of a solution of polycarbonate polyol polyurethane in methyl ethyl ketone was dissolved. (solid content concentration 24.8%, Mw of polyurethane 95,000). (Synthesis Example 4) Polycarbonate polyol synthesized above
153 parts of MDI, 25 parts of MDI, and 1.2 parts of trimethanol propane were dissolved in 540 parts of methyl ethyl ketone, 0.03 parts of dibutyltin dilaurate was added as a urethanization catalyst, and the mixture was reacted at 80°C for 6 hours. (solid content concentration 25.0%, Mw of polyurethane 100,000). (Synthesis Example 5) 236 parts of diethyl carbonate and 520 parts of 1,6-hexanediol were reacted at 120°C to 200°C for 15 hours, then cooled to 150°C, and heated for 20 to 50 mm under reduced pressure.
The remaining ethanol and unreacted diol were sufficiently distilled off using Hg to obtain 520 parts of polycarbonate polyol. The hydroxyl value of this polyol is approximately. 426 (molecular weight approximately 263). In this polyol, 155 parts of 1,6-hexanediol and 1,10 parts of
- Add 600 parts of decanedicarboxylic acid, about 200 to 220
The reaction was carried out for 8 hours at a temperature of 30 to 50 mmHg, and 1150 parts of polycarbonate polyol was finally obtained. The molecular weight of this polycarbonate polyol is approximately 1700, and its hydroxyl value is approximately
It was 68. 150 parts of this polyol, 25 parts of hydrogenated MDI, and 0.5 parts of neopentyl glycule were added to medelthyl ketone.
The reaction was carried out in 520 parts at 80°C for about 6 hours to obtain a solution of polycarbonate polyurethane in methyl ethyl ketone (solid content concentration 28%). The polystyrene equivalent molecular weight Mw of the same polyurethane was determined by GPC to be 110,000. Example 1 A magnetic paint having the following composition was prepared. 100 parts of Co-containing γ-Fe ₂ O ₃ 6 parts of polyurethane (polyurethane of Synthesis Example 1) Nitrocellulose (Cellnova manufactured by Asahi Kasei Industries, Ltd.)
BTH1/2) 5 parts Phenoxy resin (PKHH manufactured by UCC) 1 part Exemplary compounds of organic dye compounds (1) 5 parts Myristic acid 2 parts Palmitic acid butyl ester 1 part Alumina 4 parts Methyl ethyl ketone 50 parts Cyclohexanone 100 parts Carbon black (Conductors) 975)
2 parts This composition was thoroughly stirred and mixed in a ball mill,
Furthermore, after adding 5 parts of polyfunctional isocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.), the average pore diameter
Passed through a 1 μm filter. The obtained magnetic paint was applied to the surface of a 14 μm thick polyethylene terephthalate base to a dry thickness of 4 μm. Thereafter, the surface of the magnetic layer was treated using a super calender roll to obtain a wide magnetic film having a magnetic layer of a predetermined thickness. This film was cut into 1/2-inch pieces to create magnetic video tape. Comparative Example 1 A magnetic tape was prepared under the same conditions as in Example 1, except that lecithin was used in place of Exemplified Compound (1) in Example 1. Comparative Example 2 236 parts of diethyl carbonate and 520 parts of 1,6-hexanediol were reacted at 120°C to 200°C for 15 hours, then cooled to 150°C, and heated 20 to 50 mm under reduced pressure.
The remaining ethanol and unreacted diol were sufficiently distilled off using Hg to obtain 520 parts of polycarbonate polyol. The hydroxyl value of this polyol is approximately
It was 426. (Molecular weight approximately 263). 155 parts of 1,6-hexanediol and 600 parts of 1,10-decanedicarboxylic acid were added to this polyol, and reacted at about 200 to 220°C for 8 hours, followed by a reduced pressure reaction at 30 to 50 mmHg, and finally 1150 parts of A polycarbonate polyester polyol was obtained. The molecular weight of this polyol was approximately 1,650, and its hydroxyl value was approximately 68. 150 parts of this polyol, 25 parts of hydrogenated MDI, and 0.5 parts of neopentyl glycol were reacted in 520 parts of methyl ethyl ketone at 80°C for about 6 hours to obtain a methyl ethyl ketone solution of polycarbonate polyester polyurethane (solid content concentration 28%). The polystyrene equivalent molecular weight Mw of the same polyurethane was determined by GPC to be 110,000. The thus obtained polycarbonate polyester polyurethane was used in place of the polycarbonate polyol polyurethane in the magnetic paint of Example 1, and the same amount of lecithin was used in place of exemplified compound (1) to prepare a magnetic paint. A magnetic layer was formed by coating the surface of the support in the same manner. (Magnetic paint composition) Fe-based magnetic powder (BET surface area 48m ² /g) 100 parts Polyester polyurethane 10 parts Phenoxy resin "PKHH" (manufactured by Union Carbide) 4 parts Lecithin 5 parts Myristic acid 0.5 parts Palmitic acid butyl ester 0.5 parts Alumina 4 Parts Methyl ethyl ketone 300 parts Cyclohexanone 100 parts Comparative Example 3 A magnetic tape was prepared under the same conditions as in Example 1 except that the same amount of vinyl chloride-vinyl acetate copolymer was used in place of the phenoxy resin. Next, tape sample 1 and comparative samples (1) to (3) obtained in Example 1 and Comparative Examples 1 to 3 were prepared.
Lumi S/N, chroma S/N, squareness ratio, adhesion,
Stability over time and still durability were measured. The measurement method is as follows. (a) Lumi S/N Color Video Noise Meter “Shibasoku
925D/1", and the output level after 700 times is shown as a relative value. (b) Chroma S/N Same as above (c) Adhesiveness A 1 m long sample tape was wound around a 36 mm diameter glass tube as a core, with a load of 15 kg applied, and the tape was heated at 60°C and 80% (relative humidity). Leave the tape for 24 hours in an atmosphere of 23℃ and 55% (relative humidity).
The tape was left for 24 hours in an atmosphere of In the table below,
The ○ mark indicates that the two do not stick together, the △ mark indicates that the two do not stick together, and the × mark indicates that the two do not stick together. (d) Stability over time The tape was stored at 90% RH and 80°C for one week, and the still durability was observed. (e) Still Endurance Indicates the time, in minutes, for a still image to degrade by 2 dB. The larger the value, the higher the durability and wear resistance of the magnetic recording medium. The above measurement results were as shown in Table 1 below.

[Table] Examples 2 to 6 First, the following compositions were prepared. Fe-based magnetic powder (BET surface area 48 m ² /g) 100 parts Synthesis examples (1 to 5) Polyurethane 10 parts Phenoxy resin "PKHH" (manufactured by Union Carbide) 4 parts Exemplary compound (1) 5 parts Myristic acid 0.5 parts Butyl palmitate Ester 0.5 parts Alumina 4 parts Methyl ethyl ketone 300 parts Cyclohexanone 100 parts Using this composition as a magnetic paint, magnetic tapes were prepared in the same manner as in Example 1, and Samples 2 to 6 of the present invention were prepared in the order of Synthesis Examples 1 to 5. Comparative Examples 4 to 6 In place of the non-ester polyurethane used in the magnetic paint formulations of Examples 2 to 6, the same amount of ester polyurethane used in Comparative Example 2, polyester polyurethane manufactured by Nippon Polyurethane Co., Ltd., and Magnetic tapes were prepared in the same manner as Examples 2 to 6 using a vinyl chloride-vinyl acetate copolymer and the same amount of lecithin instead of Exemplary Compound (1), and compared in the order of description of the resins above. Samples (4), (5) and
(6). Table 2 lists the characteristics of Samples 2 to 6 of the present invention and Comparative Samples (4) to (6).

【table】

[Table] From Tables 1 and 2, Comparative Samples 1 and 2 also show considerable dispersibility and durability. It can be seen that the present invention has further improved dispersibility and durability. These results demonstrate that the magnetic recording medium according to the present invention has superior performance in terms of dispersibility, abrasion resistance (still durability), adhesion, and stability over time compared to conventionally known magnetic recording media. I was able to confirm that there was. Examples 7 to 11 Magnetic tape samples were prepared in exactly the same manner as in Example 2, except that exemplified compounds (2) to (6) were used in place of exemplified compound (1), and exemplified compounds (2) to Samples 7 to 11 were made in the order of (6). Comparative Examples 7 to 9 Magnetic tape samples were prepared using the same amount of phosphoric acid ester, Compound A and Compound B shown below in place of Exemplified Compound (1) in Example 2, and in the same manner as above, and compared in the above order. Samples (7) to (9) were used. Compound A: Compound B: _C18H37O ( _CH2CH2O ) _6H The _measurement results of Samples 7 to 11 and Comparative Samples (7) to (9) are listed in Table _- 3.

[Table] Examples 12 to 32 Samples 12 to 23 using exemplified compounds (7) to (18) in place of exemplified compound (1) in Example 2 and the following compounds (19) to (27) corresponding sample 24
Got ~32. Table 4 shows the results of measuring the characteristics of the obtained samples.

【table】

[Table] The above RF output was measured at 4MHz using an RF output measurement VTR deck, and showed a value that was lower than the initial output after 100 playbacks (unit:
dB). From Tables 3 and 4, it can be seen that the exemplified organic dye compounds of the present invention also exhibit a better dispersion effect than conventionally known dispersants. (6) Effects of the invention In this way, by using the organic dye compound of the present invention as a dispersant and further using polycarbonate polyurethane and phenoxy resin as a binder, it is possible to achieve better dispersibility, abrasion resistance, and better wear resistance than conventionally known ones. A magnetic recording medium with excellent performance in both adhesiveness and stability over time was obtained.

[Brief explanation of the drawing]

The drawings are for explaining the present invention, and
Figure 1 is a graph showing the change in the amount of powder falling off depending on the number of carbon atoms in the diol, Figure 2 is a graph showing the change in the amount of falling powder depending on the average molecular weight of polycarbonate polyol, and Figure 3 is a graph showing the change in the amount of falling powder depending on the proportion of polycarbonate polyol. Figure 4 is a graph showing the still durability according to the average molecular weight of polycarbonate polyol polyurethane.
The figure is a graph showing the dispersibility according to the average molecular weight of polycarbonate polyol polyurethane, Figure 6,
Figures 10 and 11 are enlarged cross-sectional views of a portion of the magnetic tape according to each example, Figure 7 is a graph showing changes in tape characteristics depending on the blending ratio of resins other than polyurethane, and Figure 8 is a graph showing changes in tape properties depending on the blending ratio of resins other than polyurethane. FIG. 9 is a graph showing changes in still durability depending on the blending ratio with other resins, and FIG. 9 is a graph showing changes in tape characteristics depending on the specific surface area of carbon black. In addition, in the symbols used in the drawings, 2
...Magnetic layer, 3...Back coat layer (BC layer), 4
...Overcoat layer (OC layer).

Claims (1)

[Scope of Claims] 1. A magnetic recording medium in which a magnetic layer is provided on a support, the magnetic layer comprising an organic dye compound represented by the following general formula [X] having a carboxyl group or a sulfonic acid group; A magnetic recording medium comprising a polycarbonate polyurethane having no ester bond and a phenoxy resin. General formula [X] [However, in the general formula [X], n ₁ and n ₂ are 0 to 5
m ₁ and m ₂ represent integers of 0 to 2, X is -Cl, Y is -Cl, -NO ₂ , -CH ₃ , -C ₂ H ₅ , -OCH ₃ , -
OC ₂ H ₅ , Z ₁ is a carboxyl group, a sulfonic acid group or [Formula] -CONH (CH ₂ ) ₁₀ COOH or each salt of an alkali metal or alkaline earth metal thereof, Z ₂ is a carboxyl group or a sulfonic acid group or their [formula] (R ₁ is H or lower alkyl (1 to 4 carbon atoms),
_R2 is H or long-chain alkyl (carbon number 10-30), alkali metal, alkaline earth metal salt, or (A is a carboxyl group or a sulfonic acid group, B is _-NO2 , -Cl; _-CH3 , _l1 is an integer from 0 to 1, _l2 is 0
Represents an integer between ~2. ). ]