JPH0576695B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium in which the surface properties of the back coat layer are improved in a magnetic tape having a magnetic layer on the surface of a support and a back coat layer on the back surface of the magnetic tape. BACKGROUND OF THE INVENTION Magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks are widely used in the audio, video, and computer fields. Among these, for example, in the case of magnetic tape in the video field, when recording and playing back images, the cassette is attached to a video deck, and the tape is guided to a guide pole or guide roller. While running, the magnetic head rubs and scans the magnetic head. 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, it is necessary to prevent the sliding condition of the magnetic tape against the magnetic head from changing. The surface of the magnetic layer is finished smooth. The magnetic layer is designed to have improved runnability and durability with respect to magnetic heads, guide rollers, and the like. However, when this magnetic tape is run on a video deck, not only the front surface of the magnetic tape but also the back surface is rubbed by the guide poles and guide rolls. Even if the magnetic tape has good durability, if the part of the back side of the magnetic tape that is rubbed does not have good running performance or durability, excessive tension will be applied to the running magnetic tape, and this will cause the magnetic layer to be excessively sensitive to the magnetic head. This not only causes damage to the magnetic layer and peeling off of the magnetic powder in the magnetic layer, but also causes the strength of the tension at which the magnetic tape is wound to fluctuate, resulting in fluctuations in the winding pressure and the appearance of the winding. This disarray causes the edges of the tape to become uneven, resulting in uneven running of the tape when it is reused. When these things occur, the image or electromagnetic characteristics such as skew, jitter, and chroma S/N deteriorate. Therefore, a back coat layer is provided on the back side of the magnetic tape. As mentioned above, this back coat layer is designed to improve running performance and durability against guide poles, guide rolls, guide pins, etc. One of these innovations is to incorporate inorganic powder into the resin layer. There is something. This is done by making the surface of the back coat layer rough to reduce the area of contact with guide poles and the like, thereby reducing the coefficient of friction. For example, Japanese Patent Application Laid-open No. 57-130234,
JP-A-58-161135, JP-A-57-53825, JP-A-58-2415, and JP-A-50-3927 all show examples using inorganic powder.
Furthermore, many of these have been shown to have limited particle sizes. However, even those using these inorganic powders not only do not provide sufficient slip properties, but also cause the back coat layer to come into contact with guide pins, etc., as in the case of the alumina particles described in Japanese Patent Publication No. 50-3927. Not only can the pins be scraped, damaging the function of the guide pins that guide and run the magnetic tape smoothly, but also the binder of particles that resist when the back coat layer containing them is rubbed. The bonding strength is insufficient and particles tend to fall off, and when the magnetic layer and back coat layer come into contact when the magnetic tape is wound, the protrusions of the back coat layer may damage the magnetic layer, and the unevenness may be transferred to the magnetic layer. This can impair electromagnetic properties such as chroma S/N, which indicates the degree of color noise in the image when the magnetic layer is scanned and the image is reproduced. In addition to being used alone as a surface roughening agent, such inorganic powders are also known to be used in combination with carbon black, which is not as hard as this, to give the back coat layer both a surface roughening effect and an antistatic effect. ing. For example, in JP-A-49-75102, JP-A-58-13975, JP-A-59-5248, and JP-A-59-14124, titanium oxide, calcium silicate, and calcium carbonate are added to carbon black, respectively. Examples are shown in which carbon black is mixed with barium sulfate, zinc oxide, etc., and also in which the particle size of these inorganic powders mixed with carbon black is limited. However, these
Inorganic powder titanium oxide described in Publication No. 49-75102 and Japanese Patent Publication No. 58-13975 and Japanese Patent Publication No. 58-13975
The calcium silicate described in Publication No. 13975 has a hardness of 6 to 7 and 4.5 on the Mohs scale, respectively, and even if carbon black, which is softer than these, is mixed, the back coat layer using only inorganic powder as described above cannot be used. It is not possible to improve the problems that have arisen. Since carbon black is necessary for the antistatic effect of the back coat layer, it has been desired to improve the above-mentioned properties in a system containing this carbon black. One of these causes is that inorganic powders are generally
This is because not only the particle shapes are diverse and not constant, but also the particle size distribution is wide. Generally, when the particle shape is spherical, the particles tend to be arranged regularly, and if these particles are arranged regularly on the surface of the back coat layer, when the back coat layer comes into contact with, for example, a guide pole, these particles come into contact with each other, so the coefficient of friction can be reduced. Furthermore, if the particle size distribution of the particles is narrow, even if the average particle size is the same, particularly large particles will not be mixed in, but this is difficult to expect in the case of inorganic powder. Therefore, when using inorganic particles, it is desirable to use particles with a relatively large size in order to make the surface of the back coat layer slippery. harm From this, for example, the surface roughness of the back coat layer can be
Center cm average roughness Ra of cut off 0.08mm from 0.010
At 0.026 μm, the coefficient of dynamic friction μ is set to 0.36 or less, so that unevenness is not transferred to the magnetic layer, and the runnability of the back coat layer is improved.
It is difficult to expect that only the durability will increase using only the inorganic powders described in the above publications. In addition, if the inorganic powders described in the above publications are used, they have a relatively good affinity with water, so magnetic recording media used in various atmospheres can be exposed to air during storage or use on video decks, etc. When a magnetic recording medium absorbs moisture in this way, its surface tends to stick to metal gadpoles, etc. When this adhesion occurs, the magnetic recording medium running in a steady state becomes It is temporarily stopped, and the next moment it suddenly starts to pull, which tends to cause so-called stake slip, which tends to make running unstable. Not only that, but
If the magnetic layer uses metal powder or a metal thin film formed by vapor deposition, moisture introduced into the back coat layer may corrode the magnetic layer, resulting in performance deterioration. Furthermore, in general, inorganic powders do not have very good dispersibility in binders, and not only do they require a lot of time to achieve sufficient dispersion, but even once they are dispersed, they tend to aggregate again. For example, when a dispersion of these inorganic powders is stored for a long period of time, the particles tend to settle because the specific gravity of the particles is large, and most of them, except for carbon black, have a specific gravity of 2 to 4. In particular, when the average particle size of the inorganic powder is 0.2 μm or less, poor dispersion tends to occur, and even after dispersion, the dispersion stability is lacking. If inorganic powders with poor dispersibility are used with poor dispersion, or if they agglomerate after dispersion, the surface roughness of the back coat layer will not be well controlled. For example, if too large particles are present, As a result of making the surface irregularities of the back coat layer too large, problems arise such as the irregularities being transferred to the magnetic layer and impairing the electromagnetic properties as described above. Conversely, the average particle size of inorganic powder is 0.2μ
In the above cases, the dispersion state in the paint is good, but since the raw material particles themselves are large, they tend to settle, resulting in poor dispersion stability and the surface roughness of the back coat layer being too large. If one dares to make it smaller, the filling rate of the inorganic powder in the binder must be lowered. If the filling rate of such inorganic powder is low, it may cause so-called interlayer adhesion in which the tapes stick to each other when the tape is wound, impair abrasion resistance and slipperiness, and make it more likely to cause stick slip. In addition, in general, inorganic powders do not mix well with binder resins, and may separate from the resin and cause powder to fall off, staining video decks, etc.
This may cause dropouts in the reproduction of images of the magnetic layer corresponding to the areas where the powder has fallen. In particular, carbon black is often used with an average particle size of 10 to 20 mμ, but carbon black with such a small particle size has extremely poor dispersibility in paints, and the back coat layer formed using this dispersion is Since the aggregated particles form unevenness on the surface, there is no uniformity, and since these aggregated particles do not have a strong binding force with the binder, they not only easily peel off, but also cause unevenness on the magnetic layer as described above. If the roughness of the back coat layer is not appropriate and powder falls off, and sufficient abrasion resistance and durability cannot be achieved, problems such as powder falling off of the magnetic layer may occur, resulting in reduced output. Not only the fluctuation but also the electromagnetic conversion characteristics such as the chroma S/N cannot be improved. In particular, recently, video equipment such as VHS video movies and β movies has become smaller and more dense, making it easier to carry. Since magnetic tapes are now being taken out and used to record video under various circumstances, it is hoped that magnetic tapes will also be compatible with these requirements. In other words, the miniaturization and high density of video equipment has made the path of the magnetic tape more complex, increasing the chances of the tape coming into contact with guide poles and guide rollers, increasing the frequency of friction, and improving running performance. There is a demand for improved abrasion resistance and durability to prevent powder falling, etc., and for this purpose, further improvement in the performance of the back coat layer is desired. As mentioned above, conventional back coat layers sometimes contain carbon black to provide an antistatic effect, but there are problems associated with the use of inorganic powders used together with carbon black, and improvements have been desired. OBJECTS OF THE INVENTION The first object of the present invention is to provide a magnetic recording medium having a back coat layer containing carbon black with good powder dispersibility and dispersion stability and easy control of surface roughness. . A second object of the present invention is to provide a magnetic recording medium having a back coat layer containing carbon black-containing particles that have high mechanical strength and are not too hard so that guide poles and the like are not excessively scraped. It's about doing. A third object of the present invention is to provide a magnetic recording medium containing carbon black and having a back coat layer that does not cause powder drop-off. A fourth object of the present invention is to provide a magnetic recording medium that achieves the above objects and has antistatic properties, runnability, and durability, and has less dropouts and the like. Structure of the Invention The above object is to provide 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, wherein the back coat layer is made of benzoguanamine resin powder, melamine resin powder, etc. The binder contains carbon black and any one organic powder selected from the group consisting of resin powder and phthalocyanine pigment powder, and the particle size of the organic powder is larger than the particle size of the carbon black. This is achieved by providing a magnetic recording medium characterized in that the mixing weight ratio of the powder and the carbon black is 19/1 to 1/100. When achieved as described above, the disadvantages mentioned above when using only inorganic powder can be overcome by the excellent properties of organic powder, and furthermore, since carbon black is included in the back coat layer, it can also have an antistatic effect. , the properties of organic powder and carbon black can be synergistically exhibited. That is, the organic powder is compatible with the same organic binder, and therefore has a large binding force due to the binder, so that the resistance against rubbing can be increased. Therefore, it not only improves abrasion resistance and durability, but also has good wettability with organic solvents and binders, and has a low specific gravity, making it difficult to settle, and improves the dispersion stability of the coating liquid for forming the back coat layer. can. In addition, as a result of experiments, it is easy to disperse using a ball mill, and the particles are also easy to form into spherical shapes, and the variation in particle size distribution can be reduced, so the coefficient of friction can be reduced without increasing the surface roughness much compared to the above-mentioned inorganic powder. By doing this, the hardness is smaller than that of the inorganic powder, and the wear of the guide pole etc. can be reduced. On the other hand, when carbon black is contained in the back coat layer, its antistatic effect appears, and the back coat layer does not impede its runnability against objects that come into contact with it. At this time, since the particle size of the organic powder is larger than that of the carbon black, the carbon black particles do not protrude from the softer organic powder on the surface of the back coat layer, and the organic powder is softer when it comes into contact with the magnetic layer. Therefore, not only are there no copies of the unevenness caused by the particles, but also there is no copying of the unevenness caused by the carbon black particles. Next, the present invention will be explained in detail. In the present invention, an organic powder and an inorganic powder are used together, and the true specific gravity of the organic powder is preferably 0.8 to 2.5. If it is too small than this range, it tends to float on the surface of the back coat layer and may become liberated. On the other hand, if it is too large than the above range, it becomes difficult to exist on the surface of the back coat layer and tends to cause sedimentation in the paint. Note that the true specific gravity is an expression for the bulk specific gravity, and means the true specific gravity that is not apparent.
Further, the average particle diameter is preferably 2μ or less, preferably 0.02 to 0.5μ. Particularly for magnetic tapes capable of high recording density, 0.1 μ to 0.5 μ is preferable. Examples of organic powders used in the present invention include benzoguanamine resin powders, melamine resin powders, and phthalocyanine pigments, which tend to have the above-mentioned properties, and relatively soft resin powders are used together with carbon black. By doing so, the hardness of the back coat layer can be made appropriate. The carbon black used in the present invention is preferably electrically conductive. Such carbon black is preferably one in which particles are connected together like a bunch of grapes, and preferably one that is porous and has a large specific surface, that is, a high structure level. In addition, its primary average particle size is 21 to 29 m.
μ is preferable, and among these, those with an oil absorption amount of 90 ml/100 g or more (using dibutyl phthalate as the oil) are preferable because they can easily form a structured structure and can be expected to have greater electrical conductivity. When a back coat layer is formed with carbon black having such a particle size and a binder described later, the average surface roughness thereof is smaller than 0.035 μm, preferably
Can be made smaller than 0.030μm. If the particle size of the carbon black is smaller than 21 μm, its dispersion in the paint will be poor and, as mentioned above, the surface of the back coat layer will become too rough, which is undesirable. Furthermore, if the particle size of the carbon black is larger than 29 mμ, there is a drawback that the irregularities on the surface of the back coat layer are too large and these irregularities are transferred to the magnetic layer when the tape is wound. From the above points, specifically preferred carbon blacks include Raven 1255, 1250, 1200, 1170, 1040 manufactured by Columbia Carbon Co., Ltd.
Examples include 1035, 1030, 1020, 1000, 890H, Conductex 975, 900, etc.
Carbon black, which is commonly used for magnetic layers other than these, can also be used. The mixing ratio of the carbon black and the organic powder is preferably 100/1 to 1/19, more preferably 100/1 to 100/10, by weight. If the ratio of organic powder is less than 1/100, even if a mixture of these is used in the back coat layer, carbon black properties will appear, the reinforcing effect of the organic powder on the back coat layer will be weakened, the layer strength will be reduced, and the average particle size will be reduced. In the case of particles having a diameter of 10 to 20 m.mu., the particles tend to aggregate due to poor dispersibility, resulting in a large amount of powder falling off, and if the amount of organic powder exceeds 19/1, the antistatic effect of the back coat layer decreases. For this reason, the mixing ratio of the organic powder and carbon black is preferably within the above range, whereby a synergistic effect between the above-described good properties of the organic powder and the properties of carbon black can be exhibited. The amount of the mixture of the above organic powder and carbon black is 1 to 200 parts by weight, particularly preferably 25 to 150 parts by weight, based on 100 parts by weight of the binder. If it is less than 1, running becomes unstable, and if it is more than 200, powder falls easily. . As mentioned above, there are preferable ranges for the ratio of organic powder to carbon black and the ratio of these powders to the binder, but if organic powder is used that has a larger particle size than carbon black, it will give the back coat layer the performance it should have. It can be expected that the characteristics of each powder will be better exhibited. For example, it is preferable because it eliminates the imprint of the above-mentioned unevenness on the magnetic layer due to carbon black particles, which are harder than organic powder, and effectively reduces, for example, dropout as a final performance of the magnetic recording medium. For example, for 100 parts by weight of 0.024μ fine particle carbon black,
A magnetic tape with a back coat layer containing 25 parts by weight of 0.3μ coarse-grained organic powder can effectively reduce its dropout. To explain the above organic powder in detail, an example of benzoguanamine-based resin is a resin whose basic structure is derived from a compound having the following structure and formaldehyde through a condensation reaction, etc., and includes methylolization, methylenation, and alkyl ether of benzoguanamine. It may be a resin obtained by a reaction such as chemical reaction, or it may be a resin powder obtained by copolymerizing benzoguanamine with urea, melamine, phenol, etc. In addition, the following compounds similar to the benzoguanamine resin may be used. Also included are benzoguanamine-based resins made from similar compounds having the same properties. This benzoguanamine resin is used in the form of powder, and the particles in the binder are preferably spherical. This is because when the spherical particles form the rough surface of the back coat layer, objects that come into contact with the rough surface come into point-like contact and the friction can be reduced.

[Chemical formula] However, the present invention is not limited to this, and any shape such as an ellipse or a rectangle may be used, and particles of different shapes may be mixed and used. The Mohs hardness of the benzoguanamine resin powder is preferably larger than that of polyfluoroethylene resin powder such as Teflon, and the Mohs hardness is preferably 5 or more, more preferably about 6 or more. . In addition, the true specific gravity of this benzoguanamine resin powder is 1.1 to 1.5.
is preferred. The most important properties of this benzoguanamine resin powder are its high mechanical strength and
This means that when dispersed with magnetic powder, binder resin, and other additives using a dispersion machine, it can withstand harsh dispersion conditions such as those used in ball mills, and these properties are superior to polyfluorinated ethylene resin powders. ing. Among benzoguanamine resin powders, those that are porous (for example, true specific gravity/bulk specific gravity 1.3 to 8) are particularly wettable with binder resins and solvents, and have excellent dispersion, so they can be dispersed without a dispersant, for example. The dispersion stability is also good, which is preferable. The maximum particle size of the above benzogamine resin powder is
The average particle diameter is preferably 2.0 μm or less, more preferably 0.02 to 0.5 μm. In this case, it is preferable that the particle size distribution has little variation. However, particles with a wide particle size distribution may also be used, or two or more types of particle groups with different particle size distributions may be mixed and used. A specific example of the benzoguanamine resin powder is Epostor (manufactured by Nippon Shokubai Kagaku Co., Ltd.). The phthalocyanine pigment used in the present invention is
It is represented by the general formula (C ₈ H ₄ N ₂ ) R′n, and R′ is H, D, Na, K, Cu, Ag, Be, Mg, Ca, Zn,
Cd, Ba, Hg, Al, Ga, Ir, La, Nd, Sm,
Eu, Gd, Dy, Ho, Er, Th, Tm, Yb, Lu,
Ti, Sn, Hf, Pb, V, Sb, Cr, Mo, U, Mn,
Fe, Co, Ni, Rh, Pd, Os, Pt are mentioned, and n
is 0-2. The crystal forms of this phthalocyanine pigment include α, β, γ, χ, π, and ε. Moreover, those having a substituent such as chlorine in the above general formula are also included. The maximum particle size of the above phthalocyanine pigment powder is
The average particle size is preferably 2.0 μm or less, more preferably 0.02 to 0.5 μm. In this case, it is preferable that the particle size distribution has little variation. However, particles with a wide particle size distribution may also be used, or two or more types of particle groups with different particle size distributions may be mixed and used. Inorganic powders other than those mentioned above can also be used in the present invention, and these include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, α
−Fe ₂ O ₃ , talc, kaolin, calcium sulfate,
Examples include those made of boron nitride, zinc fluoride, molybdenum dioxide, and the like. If an appropriate amount of these inorganic powders is used, the strength of the back coat layer will also be increased. The binder used in the present invention uses the resins described below, and among these, a mixed resin of urethane resin and vinyl chloride vinyl acetate copolymer resin, and a mixed resin of urethane resin and phenoxy resin have adhesive properties to the support described below. Vinyl chloride vinyl acetate copolymer resins are particularly preferred because they have better compatibility with urethane resins than other resins and their mixing ratio can be increased. The preferred mixing ratio of the vinyl chloride vinyl acetate copolymer resin to the urethane resin is 15% by weight to 75% by weight. Among the above-mentioned urethane resins, polyester type resins are preferable to polyether type resins in terms of dispersibility in carbon black. It is preferable to use a curing agent in combination with the above-mentioned binder, and the well-known isocyanates described below are used as such curing agents, and among these, methylene diisocyanate type or tolylene diisocyanate type is preferable. The proportion of each of the above components in the binder is 40% to 80% by weight of the total for urethane resin.
is preferable, and the curing agent is preferably 20% by weight of the total.
40% by weight is preferred. If the amount of curing agent is too little or too much, the magnetic tape will be susceptible to stick slip. Binder resins that can be used in the back coat layer include thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, and mixtures thereof. Thermoplastic resins used as binder resins have a softening temperature of 150℃ or less and an average molecular weight of 10,000~
200000, with a degree of polymerization of about 200 to 2000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid 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 derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, chlorovinyl ether
Acrylic ester copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used. 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 liquid and becomes insolubilized by a reaction such as condensation or addition after coating and drying. Among these resins, those that do not soften or melt 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. 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. 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. In addition to the above, it is preferable to use a lubricant in the back coat layer of the present invention, for example, a lubricant having a carbon number of 13
Esters of ~16 monohydric alcohols with stearic acid are preferred. In addition to these, fatty acid esters used in the magnetic layer, which will be described later, can be used. Further, the dispersant and antistatic agent described below can be used in the back coat layer of the present invention. The magnetic layer of the magnetic recording medium of the present invention may be a coated magnetic layer using magnetic powder, binder, dispersion, lubricant, etc., or may be formed by a vapor deposition method, a sputtering method, a vapor deposition method, etc. It may be a thin film type magnetic layer formed. The binder for the magnetic layer can be the same as the binder for the back coat layer, and
Examples of magnetic materials include γ-Fe ₂ O ₃ and Co-containing γ
- Fe ₂ O ₃ , Co deposited γ - Fe ₂ O ₃ , Fe ₃ O ₄ , Co included
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 paint forming the magnetic layer may contain additives such as a dispersant, a lubricant, an abrasive, an antistatic agent, and the like, if necessary. Examples of dispersants include lecithin; capric acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid,
Fatty acids having 8 to 18 carbon atoms such as elaidic acid, linoleic acid, and linolenic acid (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, etc.)
Examples include metal soaps made of Ba, etc.). 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 also be used.
These dispersants may be used alone or in combination of two or more. When these dispersants are used in the magnetic layer, they are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the magnetic material, and when used in the back coat layer, they are added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the binder.
It may be added in an amount of 2 to 20 parts by weight. In addition, as lubricants, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, fatty acid esters consisting of monobasic fatty acids with 12 to 16 carbon atoms and monohydric alcohols with 3 to 12 carbon atoms, carbon Fatty acid esters made of a monobasic fatty acid having 17 or more monobasic fatty acids and a monohydric alcohol having 21 to 23 carbon atoms in total are 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. An abrasive can also be used for this magnetic layer, and this abrasive includes commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond,
Garnet, emery (main ingredients are corundum and magnetite), titanium dioxide, etc. are used. These abrasives have an average particle diameter of 0.05 to 5μ, particularly preferably 0.1 to 2μ. These abrasives are used in amounts of 1 to 20 parts by weight per 100 parts by weight of magnetic powder.
It is added in a range of parts by weight. In addition to carbon black, antistatic agents include conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, carbon black graft polymers, and natural interfaces such as saponin. Active agent: Nonionic surfactant such as alkylene oxide type, glycerin type, glycidol type; Cationic surfactant such as pyridine and other heterocycles, phosphonium or sulfonium type; Carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid Examples include anionic surfactants containing acidic groups such as ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of amino alcohols. 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. Solvents to be added to the above paint or diluting solvents when applying this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; alcohols such as methanol, ethanol, propanol and butanol; methyl acetate and ethyl acetate. , esters such as butyl acetate, ethyl lactate, and ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, Halogenated hydrocarbons such as carbon tetrachloride, chloroform, and dichlorobenzene can be used. 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. An intermediate layer for improving adhesion may be provided between the support and the back coat layer. Application methods for forming the above-mentioned back coat layer on the support include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, and cast coating. , spray coat, etc. can be used, but are not limited to these. Effects of the Invention As described above, in the present invention, a specific organic powder and carbon black are contained in a back coat layer with the particle size of the former larger than that of the latter. It is possible to provide a magnetic recording medium equipped with a back coat layer that has a synergistic effect with the characteristics of black. In other words, organic powder has good dispersibility and dispersion stability in binder resins, etc., and its particle size and shape can be easily controlled, so it is possible to control the surface roughness of the back coat layer formed using the paint. Coupled with the fact that the particle size of the organic powder is larger than that of carbon black, it is possible to eliminate problems such as the unevenness of the back coat layer being transferred to the magnetic layer, and also to reduce the coefficient of friction. Can be made smaller. In addition, the organic powder is strong and not too hard, so there is less chance of powder falling off.Also, since the particle size of the organic powder is larger than that of carbon black, it can be used for guide poles and guides for video decks and cassettes. This prevents the need to scrape pins, etc. Furthermore, since the organic powder has good compatibility with the binder, its binding strength is large, and the powder falling off can be further reduced. On the other hand, carbon black provides an antistatic function to the back coat layer due to its conductivity, does not impede the movement of the magnetic recording medium against objects it comes into contact with, and has the effect of increasing layer strength due to its filling effect. Due to the excellent synergistic effect with the organic powder mentioned above, the runnability is improved.
Durability etc. can be improved, and performance as a magnetic recording medium can be significantly enhanced. In this way, it is possible to provide a magnetic recording medium having a back coat layer with excellent runnability and durability, and to suppress deterioration of the electromagnetic conversion characteristics of the magnetic recording medium, especially chroma S/N, and to reduce dropout. It is possible to improve the performance and meet the recent demands for high-density recording of magnetic recording media. EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited thereto. Note that parts indicate parts by weight. Example 1 The following composition was mixed and dispersed in a ball mill for 48 hours, and after adding 3 parts of isocyanate, the average particle size was 1μ.
It was filtered with a filter of m. Metal magnetic powder (average particle size 0.26μm x 0.03μm
×0.03μm) 100 parts vinyl chloride vinyl acetate copolymer (Vinyrite VAGH manufactured by Union Carbide Co., Ltd.) 4 parts polyurethane (Estan manufactured by Gutsudoritsu Co., Ltd.)
5701F1) 16 parts myristic acid 2 parts methyl ethyl ketone 200 parts toluene 170 parts This paint was applied to a 12 μm thick polyethylene terephthalate base film under an orienting magnetic field to a dry film thickness of 4 μm, and further dried. The dried product was calendered to form a magnetic layer on the base film. Next, the following composition was mixed and dispersed in a ball mill for 48 hours, and 20 parts of isocyanate as a curing agent was added to prepare a coating solution for a back coat layer. This coating solution was applied onto the base film on the opposite side of the magnetic layer using a reverse roll to a dry film thickness of 0.8 μm and dried to form a back coat layer. Created magnetic tape. Vinyl chloride vinyl acetate copolymer (Vinyrite VAGH manufactured by Union Carbide) 35 parts polyurethane (Estan manufactured by Gutudoritsu)
5701) 35 parts carbon black (Columbia Carbon Co., Ltd. Conductex 975, particle size 24μ) 15 parts benzoguanamine resin powder (average particle size 0.3μ)
75 parts Methyl ethyl ketone 500 parts Toluene 500 parts Example 2 In Example 1, Co-coated γ-Fe ₂ O ₃ (axial ratio 10, major axis length
A magnetic layer was formed in the same manner except that 0.25μ) was used. Furthermore, the following composition was dispersed in a ball mill in the coating solution for the back coat layer, and the isocyanate was added to the dispersion.
A magnetic tape of Example 2 was prepared in the same manner except that 20 parts of the magnetic tape was added. Phenoxy resin (manufactured by Union Carbide)
PKHH) 35 parts polyurethane (Estan manufactured by Gutsudoritsuchi)
5701) 35 parts carbon black (Columbia Carbon Co., Ltd. Conductex 975, particle size 24 mμ) 10 parts phthalocyanine blue (average particle size 0.3 μm) 25 parts methyl ethyl ketone 500 parts toluene 500 parts Example 3 Diagonally on the surface of a 10 μm thick polyethylene terephthalate film A Co-Ni (Ni 20% by weight) magnetic film (thickness: 0.1μ) was provided by vapor deposition, and after forming a lubricating oil film (thickness: 0.01μ) on the surface of this magnetic layer, the following composition was dispersed in a ball mill. A coating solution for a back coat layer was prepared by adding 20 parts of isocyanate to the solution, and this coating solution was coated on the polyethylene terephthalate film on the side opposite to the magnetic layer to form a back coat layer. A magnetic tape of Example 3 was prepared. Nitrocellulose (RS1/2) 35 parts polyurethane (Estan manufactured by Gutsudoritsuchi)
5701) 35 parts carbon black (Columbia Carbon Co., Ltd. Conductex 975, particle size 24 mμ) 25 parts melamine resin powder (average particle size 0.3 μm) 4 parts methyl ethyl ketone 500 parts toluene 500 parts Comparative Example 1 In Example 1, for the back coat layer A magnetic tape of Comparative Example 1 was prepared in the same manner except that calcium carbonate (average particle size: 0.3 μm) was used in place of the benzoguanamine resin powder in the coating solution. Comparative Example 2 A magnetic tape of Comparative Example 2 was prepared in the same manner as in Example 2, except that titanium oxide (average particle size: 0.3 μm) was used instead of the phthalocyanine blue pigment in the coating solution for the back coat layer. Comparative Example 3 A magnetic tape of Comparative Example 3 was prepared in the same manner as in Example 3, except that calcium silicate (average particle size: 0.3 μm) was used instead of the melamine resin powder in the coating solution for the back coat layer. Comparative Example 4 A magnetic tape of Comparative Example 4 was prepared in the same manner as in Example 1, except that the particle size of the carbon black paint for the back coat layer was changed to 24 mμ, and the average particle size of the benzoguanamine resin powder was changed to 0.02μ (20 mμ). did. Comparative Example 5 A magnetic tape of Comparative Example 5 was prepared in the same manner as in Example 2, except that the particle size of carbon black in the back coat layer paint was changed to 20 mμ, and the average particle size of phthalocyanine blue was changed to 0.02μ (20 mμ). . Comparative Example 6 A magnetic tape of Comparative Example 6 was prepared in the same manner as in Example 3, except that the particle size of the carbon black paint for the back coat layer was changed to 24 mμ, and the average particle size of the melamine resin powder was changed to 0.02μ (20 mμ). did. The magnetic tapes of Examples 1 to 3 and Comparative Examples 1 to 6 were tested as shown in the table below and in FIGS. 1 and 2 by the following method. Table 1 shows the measurement results of the abrasion of the cassette pin, Table 2 shows the measurement results of the average surface roughness, friction coefficient, and jitter (μsec). ) and the average surface roughness Ra (μm) of the back coat layer was formed by applying the coating solution after the storage time had elapsed. , Comparative Example 4 (×) is shown,
FIG. 2 shows the measured values of chroma S/N (dB) of magnetic tapes having each of these back coat layers. The above measurement method is as follows. Measuring cassette pin wear: using magnetic tape
The sample was packed in a VHS video cassette, operated on a Victor video deck HR-7100, and the degree of wear of the two non-rotating pins in the cassette was observed. ○ indicates no scratches, △ indicates slight scratches, and × indicates severe scratches. Surface roughness Ra (μm): Measured using a three-dimensional roughness measuring instrument 3E-3RK manufactured by Kosaka Institute. Measurement of coefficient of dynamic friction: After leaving the magnetic tape in an atmosphere at 25°C and 90% relative humidity (atmosphere during rainy weather) for 24 hours (humidity conditioning), measure the coefficient of friction of the back coat layer of each magnetic tape. The coefficient of dynamic friction was measured using a rotating drum type surface property measuring device manufactured by Shinto Kagaku Co., Ltd.
Measurement was carried out using a rod with a diameter of mm at a load of 30 g and a rotation speed of 159 rpm. Jitter (μsec): Measured with a VTR jitter meter manufactured by Meguro Electric Corporation Mori. The measurement conditions were 25°C and 90% relative humidity. Chroma S/N (dB): Chroma signal (3.58MHz)
is set to 0.714Vp-p and recorded on the luminance signal,
When this recording is played back and only the chroma signal is extracted, it represents the ratio between its effective value (S) and the noise level (N) when the chroma signal is removed.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a graph showing the storage period (stagnation time) of the coating solution for the back coat layer and the average surface roughness of the back coat layer formed with the coating solution after storage.
FIG. 2 is a graph showing the chroma S/N of the back coat layer.

Claims (1)

[Claims] 1. In 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, the back coat layer contains benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment. The binder contains any one organic powder selected from the group consisting of powder and carbon black, and the particle size of the organic powder is larger than the particle size of the carbon black, and the organic powder and the carbon black have a particle size larger than that of the carbon black. Mixed weight ratio
1. A magnetic recording medium characterized in that the magnetic recording medium is 1/19/1 to 1/100.