JP5199788B2 - Surface modifier for ferromagnetic hexagonal ferrite powder and magnetic coating containing the same - Google Patents

Description

The present invention relates to a powder surface modifier, and more particularly to a powder surface modifier that can improve the dispersibility of powder in magnetic paints and non-magnetic paints.
Furthermore, this invention relates to the magnetic coating material and nonmagnetic coating material containing the said surface modifier for powders.

  In recent years, means for transmitting information at a high speed have remarkably developed, and it has become possible to transfer images and data having enormous information. Along with the improvement of this data transfer technique, recording and reproducing devices and recording media for recording, reproducing and storing information are required to have higher density recording.

  In order to obtain good electromagnetic conversion characteristics in a high-density recording region, it is known that it is effective to use fine magnetic particles and to disperse the fine magnetic materials to a high degree to improve the smoothness of the magnetic layer surface. ing. In addition, by increasing the dispersibility of the magnetic material, a magnetic recording medium having a high glossiness can be obtained. Furthermore, as a means for increasing the smoothness of the magnetic layer surface, it is also effective to increase the dispersibility of the nonmagnetic powder contained in the nonmagnetic layer located below the magnetic layer.

As a means for improving the dispersibility of the powder used in the magnetic recording medium such as magnetic powder, for example, as described in Patent Document 1, there is a method in which a polar group such as SO ₃ Na group is contained in the binder. Widely used. Moreover, phosphonic acid, phosphoric acids, etc. are known as an additive for imparting a dispersion effect.
Japanese Patent Laid-Open No. 2003-132931

  In order to improve dispersibility, it is important to efficiently adsorb the binder (polymer) on the surface of a powder such as a magnetic powder. Further, since the free binder causes head dirt during running on the magnetic recording medium, it is required to increase the adsorption rate of the binder to the powder surface in order to reduce head dirt and ensure running durability. . As described in Patent Document 1, introduction of a polar group into a binder is an effective means for efficiently adsorbing a binder to a powder surface such as a magnetic powder. If the amount is excessive, the dispersibility may be reduced. Therefore, it is conceivable to use a dispersant, but the effect of improving dispersibility by the above-described phosphonic acid, phosphoric acid, etc. is not sufficient.

  Accordingly, an object of the present invention is to provide a means for modifying the surface of the powder in order to enhance the dispersibility of the powder such as magnetic powder in the magnetic coating, and more specifically, to adsorb the binder to the powder by modifying the surface of the powder. An object of the present invention is to provide a powder surface modifier capable of increasing the amount, and a magnetic coating material and a nonmagnetic coating material containing the powder surface modifier.

In order to increase the dispersibility of the powder in a system including the powder and the binder, it is important to increase the adsorptivity between the powder and the binder. However, the binder used in the magnetic layer is generally highly hydrophobic, whereas the magnetic powder surface is highly hydrophilic and therefore difficult to adsorb on the magnetic powder surface. Therefore, as a result of intensive studies to find a means for hydrophobizing the surface of the magnetic powder, the present inventors have found that benzene and cyclohexane have a hydrophilic polar group (hydroxyl group and / or carboxyl group) and a hydrophobic substituent ( It was newly found that by introducing an alkyl group and / or an alkoxyl group), the amount of binder adsorbed on the magnetic powder can be increased and the dispersibility of the magnetic powder can be improved. The inventors presume this reason as follows.
The cyclic compound can be highly adsorbed on the surface of the magnetic powder by the hydrophilic-hydrophilic interaction between the hydrophilic polar group and the surface of the magnetic powder. Furthermore, good affinity for the binder can be exhibited by the hydrophobic-hydrophobic interaction between the hydrophobic substituent and the binder. The benzene ring and cyclohexane ring are themselves hydrophobic, but by introducing the above hydrophobic substituent into the ring part, it is possible to hydrophobize a wider space around the surface of the magnetic powder, resulting in magnetic properties. It is considered that the affinity between the powder and the binder can be remarkably improved. The reason why the amount of the binder adsorbed on the nonmagnetic powder can be increased by the cyclic compound is also presumed to be the same as or similar to the above. In other words, the above cyclic compound can act as a surfactant between the powder and the binder, and can increase the affinity between the powder and the binder, thereby allowing the powder to be highly dispersed. It is done.
The present invention has been completed based on the above findings.

That is, the above object was achieved by the following means.
[1] A surface modifier for ferromagnetic hexagonal ferrite powder containing at least one cyclic compound selected from the group consisting of the following compounds (a) and (b).
Compound (a): benzene compound substituted with the following substituent A and substituent B (b): cyclohexane substituent A substituted with the following substituent A and substituent B: hydroxyl group and / or carboxyl group substituent B: alkyl Group and / or alkoxyl group (in the compound (a), the alkoxyl group is substituted at the meta position with respect to the substituent A, and the alkyl group excluding the methyl group is a carbon atom adjacent to the carbon atom substituted by the substituent A) Will not be replaced.)
[2] The surface modifier for ferromagnetic hexagonal ferrite powder according to [1], wherein the compound (a) has a substituent A at a meta position or a para position with respect to the substituent B.
[3] The surface modifier for ferromagnetic hexagonal ferrite powder according to [1], wherein the compound (b) has a substituent A at the 4-position with respect to the substituent B.
[4] The surface modifier for a ferromagnetic hexagonal ferrite powder according to any one of [1] to [3], wherein the substituent B is a branched alkyl group.
[5] The surface modifier for ferromagnetic hexagonal ferrite powder according to any one of [1] to [4], wherein the powder is a magnetic powder .
[5 ] The surface modifier for a ferromagnetic hexagonal ferrite powder according to any one of [ 1 ] to [4], which is used as a dispersant for a magnetic coating .
[6 ] A magnetic paint comprising the surface modifier for a ferromagnetic hexagonal ferrite powder according to any one of [1] to [ 5 ], a ferromagnetic hexagonal ferrite powder, and a binder .
[7 ] The magnetic paint according to [ 6], wherein the binder is a sulfonic acid group-containing binder.
[ 8 ] The magnetic paint according to [ 6 ] or [7], which is used as a coating solution for forming a magnetic layer of a magnetic recording medium.

  According to the present invention, the surface of the powder can be modified to increase the amount of binder adsorbed on the powder, thereby improving the dispersibility of the magnetic powder in the magnetic paint and the nonmagnetic powder in the nonmagnetic paint. it can.

[Surface modifier for powder]
The surface modifier for powder of the present invention contains at least one cyclic compound selected from the group consisting of the following compounds (a) and (b).
Compound (a): benzene compound substituted with the following substituent A and substituent B (b): cyclohexane substituent A substituted with the following substituent A and substituent B: hydroxyl group and / or carboxyl group substituent B: alkyl Group and / or alkoxyl group (in the compound (a), the alkoxyl group is substituted at the meta position with respect to the substituent A, and the alkyl group excluding the methyl group is a carbon atom adjacent to the carbon atom substituted by the substituent A) Will not be replaced.)
The powder surface modifying agent of the present invention (hereinafter also simply referred to as “surface modifying agent”) may contain other compounds having a surface modifying effect together with the cyclic compound, but one or more kinds thereof may be included. It is preferable to consist of the said cyclic compound. For example, as shown in the examples described below, the surface modifier of the present invention modifies the powder surface by changing the amount of binder adsorbed to the powder in the paint depending on the presence or absence of the surface modifier of the present invention. You can confirm that
Hereinafter, the compounds (a) and (b) will be described in more detail.

Compound (a)
The substituent A is a hydroxyl group (—OH) and / or a carboxyl group (—COOH). The number of groups selected from a hydroxyl group and a carboxyl group per one molecule of benzene is at least one, preferably 1 to 3, more preferably 1 or 2, and most preferably 1.

  The substituent B is an alkyl group and / or an alkoxyl group. The number of groups selected from an alkyl group and an alkoxyl group in one molecule of benzene is at least one, preferably 1 to 3, and most preferably 1.

  The alkyl group may be linear, branched or cyclic, and may have a substituent or may be unsubstituted. As the alkyl group, an alkyl group having 1 to 30 carbon atoms, for example, methyl group, ethyl group, n-propyl group, isopropyl group, t-butyl group, n-octyl group, eicosyl group, 2-chloroethyl group, 2-cyanoethyl. Group and 2-ethylhexyl group. Furthermore, a cycloalkyl group (preferably a substituted or unsubstituted cycloalkyl group having 3 to 30 carbon atoms such as a cyclohexyl group, a cyclopentyl group, 4-n-dodecylcyclohexyl group), a bicycloalkyl group (preferably a carbon number) A substituted or unsubstituted bicycloalkyl group having 5 to 30, that is, a monovalent group obtained by removing one hydrogen atom from a bicycloalkane having 5 to 30 carbon atoms, for example, bicyclo [1,2,2] heptane-2 -Yl, bicyclo [2,2,2] octane-3-yl), and tricyclo structures having more ring structures.

  As the alkyl group, in order to improve the affinity between the binder and the powder, a branched alkyl group having a large steric hindrance and capable of hydrophobizing a wide space, specifically, an isopropyl group, t- A butyl group, a cyclohexyl group, a sec-butyl group and the like are preferable.

  The alkoxyl group is preferably a substituted or unsubstituted alkoxy group having 1 to 30 carbon atoms, such as a methoxy group, an ethoxy group, an isopropoxy group, a t-butoxy group, an n-octyloxy group, or a 2-methoxyethoxy group. Can be mentioned.

  However, in the compound A, when the substituent B is an alkyl group other than a methyl group, the substituent B is not substituted with a carbon atom adjacent to the carbon atom substituted by the substituent A. That is, in the above embodiment (when the substituent B is an alkyl group other than a methyl group), the substituent A is not substituted in the ortho position with respect to the substituent B. This is because, when substituted at the ortho position, the substituent A, which is a hydrophobic group, is oriented in the powder direction, resulting in steric repulsion between the powder and benzene, reducing the affinity with the binder. Because it ends up. However, since the methyl group has no great steric hindrance, it can be introduced at the ortho position with respect to the substituent A. From the viewpoint of hydrophobizing a wide space by steric hindrance, the alkyl group is preferably located in the para position with respect to the substituent B.

  However, when the substituent B is an alkoxyl group in the compound (a), the alkoxyl group is substituted at the meta position with respect to the substituent A. The alkoxyl group has a high electron donating ability. Therefore, when the alkoxyl group is located at the ortho position and the para position with respect to the substituent A on the benzene ring, the acidity of the substituent A is greatly reduced. Since the change in the electronic state of the substituent A affects the affinity with the powder surface, from the viewpoint of hydrophilic-hydrophilic interaction, the alkoxyl group is introduced at a meta position that does not significantly change the electronic state of the substituent A. . On the other hand, the alkyl group has a lower electron donating property than the alkoxyl group, and the affinity with the powder surface is not significantly changed by introducing it into the ortho or para position with respect to the substituent A. From the standpoint of maintaining acidity, it is preferably located at the meta position.

Compound (b)
The details of the substituent A and the substituent B that the compound (b) has are the same as the substituents A and B that the compound (a) has. In the compound (b), the substituent A may be substituted at any position with respect to the substituent B. In order to make the wider space hydrophobic and effectively increase the affinity between the powder and the binder, The substituent A is preferably located at the 4-position with respect to the substituent B.

  The compound (a) and the compound (b) may have a substituent other than the substituents A and B, but have a substituent other than the substituents A and B in consideration of the influence of steric repulsion. Preferably not.

  Preferable specific examples of the cyclic compound include compounds used in the examples described later.

  The cyclic compound can be easily synthesized by a known method, and some of the cyclic compounds are commercially available.

  The amount of the cyclic compound used relative to the powder can be set as appropriate. However, if the amount of the cyclic compound added to the powder in the powder-containing solution is excessive, it is difficult to ensure a concentration sufficient to exhibit the function of the powder. It may become. In addition, if an excessive amount of a cyclic compound is added to the coating solution for forming a magnetic layer of a magnetic recording medium, the film is plasticized and the film may be peeled off. From this viewpoint, the amount of the cyclic compound used is preferably 0.1 to 10 parts by mass, more preferably 2 to 8 parts by mass with respect to 100 parts by mass of the powder such as magnetic powder. The method for mixing the surface modifier and powder of the present invention will be described later.

  The surface modifier of the present invention can be used to improve the dispersibility of the powder in the paint by modifying the surface of the powder such as magnetic powder and non-magnetic powder, more specifically, by increasing the affinity between the powder and the binder. Can be increased. Accordingly, the surface modifier of the present invention is preferably used as a dispersant in a magnetic recording medium-forming paint, more preferably used as a dispersant in a magnetic paint and a non-magnetic paint, and a magnetic layer-forming paint or It is particularly preferable to use it as a coating for forming a nonmagnetic layer. A mode in which the surface modifier of the present invention is applied to magnetic paints and non-magnetic paints will be described later.

[Magnetic paint]
The magnetic paint of the present invention contains the surface modifier for powder of the present invention, magnetic powder, and a binder. The surface modifier can be highly adsorbed on the surface of the magnetic powder by the hydrophilic-hydrophilic interaction between the hydrophilic substituent and the surface of the magnetic powder. Furthermore, good affinity for the binder can be exhibited by the hydrophobic-hydrophobic interaction between the hydrophobic ring portion or the hydrophobic substituent B and the binder. Thus, the surface modifier of the present invention can act as a surfactant between the magnetic powder and the binder to increase the adsorption amount of the binder on the magnetic powder, thereby highly dispersing the magnetic powder. Can be made. The details of the surface modifier are as described above.
Below, each component contained in the magnetic coating material of this invention is demonstrated.

As the magnetic powder magnetic powder, a ferromagnetic powder that can be generally contained in a coating solution for forming a magnetic layer of a magnetic recording medium can be used. As such ferromagnetic powder, ferromagnetic hexagonal ferrite powder and ferromagnetic metal powder are preferable.

(I) Hexagonal ferrite powder The hexagonal ferrite powder includes, for example, barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and their substitutes such as Co. More specifically, magnetoplumbite type barium ferrite and strontium ferrite, magnetoplumbite type ferrite whose particle surface is coated with spinel, and magnetoplumbite type barium ferrite and strontium ferrite partially containing a spinel phase, etc. Is mentioned. In addition to predetermined atoms, Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg , Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B, Ge, and Nb may be included. In general, elements such as Co—Zn, Co—Ti, Co—Ti—Zr, Co—Ti—Zn, Ni—Ti—Zn, Nb—Zn—Co, Sb—Zn—Co, and Nb—Zn are added. Things can be used. Some raw materials and production methods contain specific impurities.

  It is preferable to use a hexagonal ferrite powder having an average plate diameter of 10 to 50 nm, more preferably 15 to 40 nm, and still more preferably 15 to 30 nm. The hexagonal ferrite powder having the above size is suitable as a magnetic material used in a magnetic recording medium for high density recording. According to the present invention, the dispersibility of the particulate hexagonal ferrite powder having the average plate diameter can be improved.

The average plate ratio [arithmetic average of (plate diameter / plate thickness)] of the hexagonal ferrite is preferably 1-15, and more preferably 1-7. When the average plate ratio is 1 to 15, sufficient orientation can be obtained while maintaining high filling properties in the magnetic layer, and noise increase due to stacking between particles can be suppressed. Further, the specific surface area (S _BET ) by the BET method within the above particle size range is preferably 40 m ² / g or more, more preferably 40 to 200 m ² / g, and 60 to 100 m ² / g. Is most preferred.

  The distribution of the particle plate diameter and plate thickness of the hexagonal ferrite powder is generally preferably as narrow as possible. The particle plate diameter and plate thickness can be measured, for example, by randomly measuring 500 particles from a particle TEM photograph. In many cases, the distribution of the particle plate diameter and plate thickness is not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average size = 0.1 to 1.0. In order to sharpen the particle size distribution, in general, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improving process. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known. Further, the pH of the hexagonal ferrite powder is usually about 4 to 12 and has an optimum value depending on the dispersion medium and the polymer, but generally about 6 to 11 is selected from the chemical stability and storage stability at the time of application of the medium. Moisture contained in the hexagonal ferrite powder also affects the dispersion. Although there is an optimum value depending on the dispersion medium and the polymer, 0.01 to 2.0% is usually selected.

The hexagonal ferrite powder is manufactured by mixing (1) barium oxide / iron oxide / metal oxide replacing iron and boron oxide as a glass forming substance so as to have a desired ferrite composition, and then melting and quenching. A glass crystallization method for obtaining barium ferrite crystal powder by washing and pulverizing after re-heating treatment, and (2) neutralizing barium ferrite composition metal salt solution with alkali to produce by-products Hydrothermal reaction method to obtain barium ferrite crystal powder by liquid phase heating at 100 ° C. or higher after removal of water, (3) neutralization of barium ferrite composition metal salt solution with alkali, by-product There is a coprecipitation method in which the product is removed, dried, treated at 1100 ° C. or lower, and pulverized to obtain a barium ferrite crystal powder, but the present invention does not select a production method. The hexagonal ferrite powder may be subjected to surface treatment with Al, Si, P, or an oxide thereof as required. The amount thereof is, for example, 0.1 to 10% by mass with respect to the ferromagnetic powder, and surface treatment is preferable because adsorption of a lubricant such as a fatty acid is 100 mg / m ² or less. The hexagonal ferrite powder may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr. Although it is preferable that these are essentially not present, if they are 200 ppm or less, they do not particularly affect the characteristics.

  The ferromagnetic metal powder is not particularly limited, but it is preferable to use a ferromagnetic metal powder containing α-Fe as a main component. These ferromagnetic metal powders include Al, Si, S, Sc, Ca, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, other than predetermined atoms. Atoms such as Ta, W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, and B may be included. In particular, at least one of Al, Si, Ca, Y, Ba, La, Nd, Co, Ni, and B is preferably included in addition to α-Fe, and it further includes at least one of Co, Y, and Al. preferable. The Co content is preferably 0 atom% or more and 40 atom% or less, more preferably 15 atom% or more and 35 atom% or less, more preferably 20 atom% or more and 35 atom% or less with respect to Fe. The Y content is preferably from 1.5 atomic percent to 12 atomic percent, more preferably from 3 atomic percent to 10 atomic percent, and particularly preferably from 4 atomic percent to 9 atomic percent. Al is preferably from 1.5 atomic percent to 12 atomic percent, more preferably from 3 atomic percent to 10 atomic percent, and even more preferably from 4 atomic percent to 9 atomic percent.

  The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. As the ferromagnetic metal powder, those obtained by a known production method can be used, and the following methods can be mentioned. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe-Co particles, a metal carbonyl compound A method of thermal decomposition, a method of reducing by adding a reducing agent such as sodium borohydride, hypophosphite, or hydrazine to an aqueous solution of a ferromagnetic metal, and evaporating the metal in a low-pressure inert gas to form a fine powder. How to get. The ferromagnetic metal powder obtained in this manner is a known gradual oxidation treatment, that is, a method of drying after immersing in an organic solvent, an oxygen-containing gas is sent after immersing in an organic solvent, and an oxide film is formed on the surface. Thereafter, either a drying method or a method of adjusting the partial pressures of oxygen gas and inert gas without using an organic solvent to form an oxide film on the surface can be applied.

The specific surface area by BET method of the ferromagnetic metal powder is preferably 45~100m ² / g, more preferably 50-80 m ² / g. If it is 45 m ² / g or more, the noise is low, and if it is 100 m ² / g or less, a magnetic layer having good surface properties can be formed. The crystallite size of the ferromagnetic metal powder is preferably 40 to 180 mm, more preferably 40 to 150 mm, and still more preferably 40 to 110 mm. The average major axis length (average particle size) of the ferromagnetic metal powder is preferably 10 to 50 nm, more preferably 10 to 40 nm, and further preferably 15 to 30 nm. According to the present invention, the dispersibility of the particulate ferromagnetic metal powder having the average major axis length can be enhanced. The acicular ratio of the ferromagnetic metal powder is preferably 3 or more and 15 or less, and more preferably 3 or more and 12 or less.

The moisture content of the ferromagnetic metal powder is preferably 0.01 to 2%. It is preferable to optimize the moisture content of the ferromagnetic metal powder depending on the type of the binder. The pH of the ferromagnetic metal powder is preferably optimized depending on the combination with the binder used. The range can be 4-12, preferably 6-10. The ferromagnetic metal powder may be surface-treated with Al, Si, P, or an oxide thereof as required. The amount thereof can be 0.1 to 10% with respect to the ferromagnetic metal powder, and the surface treatment is preferable because the adsorption amount of a lubricant such as a fatty acid is 100 mg / m ² or less. The ferromagnetic metal powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr. Although it is preferable that these are essentially not present, if they are 200 ppm or less, they hardly affect the characteristics. The ferromagnetic metal powder used in the present invention preferably has fewer vacancies, and its value is 20% by volume or less, more preferably 5% by volume or less. As for the shape, any of needle shape, rice grain shape, or spindle shape may be used as long as the above-mentioned characteristics regarding the particle size are satisfied.

As the binder, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof can be used. As the thermoplastic resin, those having a glass transition temperature of −100 to 150 ° C., a number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and a polymerization degree of about 50 to 1000 are used. can do.

  Examples of such include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether as a structural unit, polyurethane resins, and various rubber resins. Thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, acrylic reactive resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, polyester resins. And a mixture of an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, a mixture of a polyurethane and a polyisocyanate, and the like. These resins are described in detail in “Plastic Handbook” published by Asakura Shoten. It is also possible to use a known electron beam curable resin for each layer. These examples and their production methods are described in detail in JP-A No. 62-256219. The above resins can be used alone or in combination, but are preferably selected from vinyl chloride resin, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate vinyl maleic anhydride copolymer. A combination of at least one selected from the above and a polyurethane resin, or a combination of these with a polyisocyanate. The resin used as the binder can be synthesized by a known method or can be obtained as a commercial product.

As the structure of the polyurethane resin, known structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all binding agents indicated herein, if necessary in order to obtain more excellent dispersibility and _{durability, -COOM, -SO 3 M, -OSO} 3 M, -P = O (OM) 2, - O—P═O (OM) ₂ (wherein M represents a hydrogen atom, an alkali metal or ammonium), —OH, —NR ₂ , —N ⁺ R ₃ (R is a hydrocarbon group), an epoxy group, —SH It is preferable to use one in which at least one polar group selected from -CN, etc. is introduced by copolymerization or addition reaction. The amount of such a polar group is, for example, 10 ⁻¹ to 10 ⁻⁸ mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g. The alkyl group represented by M is preferably an alkyl group having 1 to 18 carbon atoms, and may have a linear structure or a branched structure.

Among the polar groups, a sulfonic acid group (—SO ₃ M) can exhibit a high effect of improving dispersibility, so that a sulfonic acid group-containing binder is widely used as a binder for magnetic recording media. Also in the present invention, a sulfonic acid group-containing binder can be used. The sulfonic acid group content in the sulfonic acid group-containing binder used in the present invention is preferably 0.01 to 0.7 meq / g, more preferably 0.04 to 0.6 meq / g, and still more preferably 0.8. 06-0.4 meq / g.

  In the magnetic coating material of the present invention, a binder can be used in the range of, for example, 5 to 50% by mass, preferably 10 to 30% by mass with respect to the magnetic powder. It is preferable to use a combination of 5 to 30% by mass when using a vinyl chloride resin, 2 to 20% by mass when using a polyurethane resin, and 2 to 20% by mass of polyisocyanate. However, for example, when head corrosion occurs due to a small amount of dechlorination, it is possible to use only polyurethane or only polyurethane and isocyanate.

  Examples of polyisocyanates include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate and the like. Moreover, the product of these isocyanates and polyalcohol, the polyisocyanate produced | generated by condensation of isocyanate, etc. can be used. These can be synthesized by known methods, and are also available as commercial products.

  In addition to the surface modifier, magnetic powder, and binder, an additive may be added to the magnetic paint of the present invention as necessary. Examples of the additive include an abrasive, a lubricant, an antifungal agent, an antistatic agent, an antioxidant, a solvent, carbon black and the like that are generally used in a coating solution for forming a magnetic layer of a magnetic recording medium.

  The magnetic coating material of the present invention can be obtained by mixing the surface modifier, magnetic powder, binder, and optionally used additives. Specifically, a general magnetic layer coating solution It can be obtained by a preparation method. A manufacturing process consists of a kneading | mixing process, a dispersion | distribution process, and the mixing process provided as needed before and behind these processes, for example. Each process may be divided into two or more stages. In the kneading step, it is preferable to use a kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, glass beads can be used to disperse the magnetic paint. Such glass beads are preferably zirconia beads, titania beads, and steel beads, which are high specific gravity dispersion media. The particle diameter and filling rate of these dispersion media are optimized. A well-known thing can be used for a disperser.

In order to effectively obtain the effect of adding the surface modifier of the present invention, it is preferable that the surface modifier is present when the magnetic powder and the binder are in contact with each other. This is to prevent the binder from coming into contact with the magnetic powder surface before the surface modifier of the present invention adheres to the magnetic powder surface. Therefore, the magnetic coating material of the present invention is obtained by mixing the magnetic powder, the binder, and the surface modifier of the present invention at the same time, or in the mixture obtained by mixing the magnetic powder and the surface modifier. It is preferable to prepare by mixing. Specifically, it is preferable to mix the components by the following method.
(1) A magnetic powder and a surface modifier are previously dispersed in a dry process for about 15 to 30 minutes, and then added to an organic solvent. The binder may be added simultaneously with the dispersion, or may be added after the dispersion is added.
(2) The magnetic powder and the surface modifier are dispersed in an organic solvent for about 15 to 30 minutes and then dried. The dried mixture is appropriately pulverized and added to an organic solvent. The binder may be added simultaneously with the mixture, or may be added after the mixture is added.
(3) After dispersing the magnetic powder and the surface modifier in an organic solvent for about 15 to 30 minutes. Add binder.
(4) A magnetic powder, a surface modifier and a binder are simultaneously added and dispersed in an organic solvent.

  Known organic solvents can be used. As the organic solvent, specifically, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc., methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, in any ratio Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, benzene, toluene, xylene , Aromatic hydrocarbons such as cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethyl Nkuroruhidorin, chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide, may be used hexane. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are preferably 30% by mass or less, more preferably 10% by mass or less. In order to improve the dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that 50% by mass or more of the solvent having a dielectric constant of 15 or more is included in the solvent composition. Moreover, it is preferable that a solubility parameter is 8-11.

  The magnetic coating material of the present invention is suitable as a coating solution for forming a magnetic layer of a magnetic recording medium that requires high dispersibility because the magnetic powder is highly dispersed.

[Non-magnetic paint]
The nonmagnetic coating material of the present invention includes the surface modifier for powder of the present invention, a nonmagnetic powder, and a binder. The nonmagnetic paint of the present invention has a good adsorptivity between the nonmagnetic powder and the binder due to the action of the surface modifier, whereby the nonmagnetic powder can be highly dispersed. Such a non-magnetic coating material is suitable as a coating liquid for forming a non-magnetic layer of a magnetic recording medium that requires high dispersibility. The details of the surface modifier are as described above.
Below, each component contained in the nonmagnetic coating material of this invention is demonstrated.

  The nonmagnetic powder may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. In terms of the surface modification effect, application to nonmagnetic metal powder is effective.

Specifically, titanium oxide such as titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , α-alumina, β-alumina having an α conversion of 90 to 100%, γ-alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide Titanium carbide or the like can be used alone or in combination of two or more. Preferred are α-iron oxide and titanium oxide.

  The shape of the nonmagnetic powder may be any of acicular, spherical, polyhedral and plate shapes. The crystallite size of the nonmagnetic powder is preferably 4 nm to 500 nm, more preferably 40 to 100 nm. These nonmagnetic powders preferably have an average particle size of 5 nm to 500 nm, more preferably 10 to 200 nm. The non-magnetic powder having the above size is suitable as a non-magnetic powder for use in a non-magnetic layer coating solution for a high-density recording magnetic recording medium that requires high surface smoothness. According to the surface modifier of the present invention, the nonmagnetic powder of the above size can be well dispersed in the nonmagnetic coating material.

The specific surface area of the nonmagnetic powder is, for example, 1 to 150 m ² / g, preferably 20 to 120 m ² / g, and more preferably 50 to 100 m ² / g. A specific surface area in the range of 1 to 150 m ² / g is preferable because a magnetic recording medium having a suitable surface roughness can be formed and can be dispersed in a desired amount of binder. The oil absorption using dibutyl phthalate (DBP) is, for example, 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. The specific gravity is, for example, 1 to 12, preferably 3 to 6. The tap density is, for example, 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. When the tap density is in the range of 0.05 to 2 g / ml, there are few particles to be scattered, the operation is easy, and there is a tendency that it is difficult to adhere to the apparatus. The pH of the non-magnetic powder is preferably 2 to 11, and particularly preferably 6 to 9. When the pH is in the range of 2 to 11, it is possible to prevent the friction coefficient from increasing due to high temperature, high humidity, or liberation of fatty acids. The water content of the nonmagnetic powder is, for example, 0.1 to 5% by mass, preferably 0.2 to 3% by mass, and more preferably 0.3 to 1.5% by mass. A water content in the range of 0.1 to 5% by mass is preferable because the dispersion is good and the viscosity of the paint after dispersion is stable. The ignition loss is preferably 20% by mass or less, and the ignition loss is preferably small.

When the nonmagnetic powder is an inorganic powder, the Mohs hardness is preferably 4-10. If the Mohs hardness is in the range of 4 to 10, the durability of the magnetic recording medium can be ensured. The stearic acid adsorption amount of the nonmagnetic powder is preferably 1 to 20 μmol / m ² , more preferably ² to 15 μmol / m ² . The heat of wetting of the nonmagnetic powder into water at 25 ° C. is preferably in the range of 200 to 600 erg / cm ² (200 to 600 mJ / m ² ). Moreover, the solvent which exists in the range of this heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C. is suitably 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 9. It is preferable that Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ and ZnO are present on the surface of these nonmagnetic powders by surface treatment. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , TiO ₂ , and ZrO ₂ , but more preferred are Al ₂ O ₃ , SiO ₂ , and ZrO ₂ . These may be used in combination or may be used alone. Further, a surface-treated layer co-precipitated according to the purpose may be used, or a method of treating the surface layer with silica after first treating with alumina, or vice versa may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.

  Specific examples of the non-magnetic powder include, for example, Showa Denko Nano Tight, Sumitomo Chemical HIT-100, ZA-G1, Toda Kogyo DPN-250, DPN-250BX, DPN-245, DPN-270BX, DPB-550BX, DPN-550RX, Ishihara Sangyo Titanium oxide TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO-55S, TTO-55D, SN-100, MJ-7, α-iron oxide E270 , E271, E300, STT-4D, STT-30D, STT-30, STT-65C made by Titanium Industry, MT-100S, MT-100T, MT-150T, MT-150W, MT-500B, T-600B, T-100F made by Taca, T-500HD etc. are mentioned. FINEX-25, BF-1, BF-10, BF-20, ST-M, Dowa Mining DEFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100A, 500A, Titanium Industry Y-LOP manufactured and the thing which baked it are mentioned. Particularly preferred nonmagnetic powders are titanium dioxide and α-iron oxide.

  The details of the binder added to the non-magnetic paint are the same as the binder contained in the magnetic paint of the present invention. The nonmagnetic paint may further contain various additives and solvents used for magnetic recording media. Details of each component of the non-magnetic coating material, a mixing method thereof, an addition amount, and the like are the same as those described later regarding the magnetic coating material of the present invention.

  The nonmagnetic coating material of the present invention is suitable as a coating liquid for forming a nonmagnetic layer of a magnetic recording medium that requires high dispersibility because the nonmagnetic powder is highly dispersed.

  Hereinafter, the present invention will be described more specifically with reference to examples. It should be noted that the components, ratios, operations, order, and the like shown here can be changed without departing from the spirit of the present invention, and should not be limited to the following examples.

1. Examples and comparative examples using ferromagnetic hexagonal ferrite powder (1)

[Example 1]
7.3 parts by mass of the following barium ferrite powder, 1 part by mass of sulfonic acid group-containing polyurethane (sulfonic acid group content: 3.3 × 10 ⁻⁴ mol / g), 0.47 parts by mass of 4-tertbutylcyclohexanecarboxylic acid It was suspended in a solution consisting of 11.9 parts by mass of cyclohexanone and 17.7 parts by mass of 2-butanone. 90 parts by mass of zirconia beads (manufactured by Nikkato) was added to the suspension and dispersed for 6 hours. When the ratio of the dispersed liquid polyurethane in the barium ferrite powder surface / solution was measured by the following method, it was 100/1 or more.
Ferromagnetic hexagonal barium ferrite powder Composition excluding oxygen (molar ratio): Ba / Fe / Co / Zn = 1/9 / 0.2 / 1
Hc: 176 kA / m (2200 Oe), average plate diameter: 25 nm, average plate ratio: 3
BET specific surface area: 65 m ² / g
σs: 49 A · m ² / kg (49 emu / g)
pH: 7

〔Measuring method〕
The magnetic substance and the solution were centrifuged under conditions of 100,000 rpm and 80 minutes using a Hitachi separation ultracentrifuge CS150GXL. 3 ml of the supernatant was weighed and the mass was measured. After drying at 40 ° C. for 18 hours, it was dried at 140 ° C. for 3 hours under vacuum. The mass of the dried product was defined as the non-adsorbing solid content of the binder, and the abundance ratio of the binder in the barium ferrite powder surface / solution was calculated.

[Example 2]
The strength of the polyurethane of the dispersion obtained by performing the same treatment as in Example 1 except that 0.47 parts by mass of 4-tertbutylbenzoic acid was used instead of 0.47 parts by mass of 4-tertbutylcyclohexanecarboxylic acid. The abundance ratio of the magnetic powder surface / solution was measured by the above method and found to be 55.6 / 1.

[Example 3]
The strength of the polyurethane of the dispersion obtained by performing the same treatment as in Example 1 except that 0.56 parts by mass of 5-tertbutylisophthalic acid was used instead of 0.47 parts by mass of 4-tertbutylcyclohexanecarboxylic acid. When the abundance ratio in the magnetic powder surface / solution was measured by the above method, it was 100/1 or more.

[Example 4]
Ferromagnetic properties of polyurethane in a dispersion obtained by performing the same treatment as in Example 1 except that 0.33 parts by mass of 4-isoisopropylphenol was used instead of 0.47 parts by mass of 4-tertbutylcyclohexanecarboxylic acid. When the abundance ratio in the body powder surface / solution was measured by the above method, it was 100/1 or more.

[Example 5]
A polyurethane ferromagnetic material in a dispersion obtained by performing the same treatment as in Example 1 except that 0.36 part by mass of 4-secbutylphenol was used instead of 0.47 part by mass of 4-tertbutylcyclohexanecarboxylic acid. When the abundance ratio in the powder surface / solution was measured by the above method, it was 100/1 or more.

[Example 6]
A polyurethane ferromagnetic material of a dispersion obtained by performing the same treatment as in Example 1 except that 0.43 part by mass of 4-cyclohexylphenol was used instead of 0.47 part by mass of 4-tertbutylcyclohexanecarboxylic acid. When the abundance ratio in the powder surface / solution was measured by the above method, it was 100/1 or more.

[Example 7]
The strength of the polyurethane of the dispersion obtained by performing the same treatment as in Example 1 except that 0.40 part by mass of 4-isopropylbenzoic acid was used instead of 0.47 part by mass of 4-tertbutylcyclohexanecarboxylic acid. When the abundance ratio in the magnetic powder surface / solution was measured by the above method, it was 100/1 or more.

[Example 8]
The ferromagnetism of the polyurethane of the dispersion obtained by performing the same treatment as in Example 1 except that 0.46 part by mass of 4-cyclohexylbenzoic acid was used instead of 0.47 part by mass of 4-tertbutylcyclohexanecarboxylic acid. When the abundance ratio in the body powder surface / solution was measured by the above method, it was 100/1 or more.

[Example 9]
The polyurethane of the dispersion obtained by performing the same treatment as in Example 1 except that 0.46 parts by mass of 4-trifluoromethylbenzoic acid was used instead of 0.47 parts by mass of 4-tertbutylcyclohexanecarboxylic acid. The abundance ratio in the ferromagnetic powder surface / solution was measured by the above method and found to be 11.9 / 1.

[Example 10]
Surface of ferromagnetic powder of polyurethane of dispersion obtained by performing the same treatment as in Example 1 except that 0.36 part of 3-tertbutylphenol was used instead of 0.47 part by weight of 4-tertbutylcyclohexanecarboxylic acid / The abundance ratio in the solution was measured by the above method and found to be 10.0 / 1.

[Example 11]
A polyurethane ferromagnetic material of a dispersion obtained by performing the same treatment as in Example 1 except that 0.33 part by mass of 4-tertbutylphenol was used instead of 0.47 part by mass of 4-tertbutylcyclohexanecarboxylic acid. The abundance ratio in the powder surface / solution was measured by the above method and found to be 10.0 / 1.

[Example 12]
The ferromagnetism of polyurethane in a dispersion obtained by performing the same treatment as in Example 1 except that 0.33 part by mass of 2-methylbenzoic acid was used instead of 0.47 part by mass of 4-tertbutylcyclohexanecarboxylic acid. It was 16.8 / 1 when the abundance ratio in the body powder surface / solution was measured by the above method.

[Example 13]
Ferromagnetic properties of polyurethane in a dispersion obtained by performing the same treatment as in Example 1 except that 0.33 parts by mass of 3-methylbenzoic acid was used instead of 0.47 parts by mass of 4-tertbutylcyclohexanecarboxylic acid. It was 19.0 / 1 when the abundance ratio in the body powder surface / solution was measured by the above method.

[Example 14]
Ferromagnetic properties of polyurethane in a dispersion obtained by performing the same treatment as in Example 1 except that 0.37 parts by mass of 3-methoxybenzoic acid was used instead of 0.47 parts by mass of 4-tertbutylcyclohexanecarboxylic acid. It was 16.8 / 1 when the abundance ratio in the body powder surface / solution was measured by the above method.

[Comparative Example 1]
A polyurethane ferromagnetic powder of a dispersion obtained by performing the same treatment as in Example 1 except that 0.40 part by mass of phenylphosphonic acid was used instead of 0.47 part by mass of 4-tertbutylcyclohexanecarboxylic acid. When the abundance ratio in the surface / solution was measured by the above method, it was 3.6 / 1.

[Comparative Example 2]
Except that no phenylphosphone was used, the dispersion ratio obtained by performing the same treatment as in Comparative Example 1 was measured by the above method to determine the abundance ratio of the polyurethane in the ferromagnetic powder surface / solution. there were.

[Comparative Example 3]
Surface of ferromagnetic powder of polyurethane in a dispersion obtained by performing the same treatment as in Comparative Example 1 except that 0.40 part by mass of 4-chlorobenzoic acid was used instead of 0.40 part by mass of phenylphosphonic acid When the abundance ratio in the solution was measured by the above method, it was 4.8 / 1.

[Comparative Example 4]
The surface of the polyurethane ferromagnetic powder in the dispersion obtained by performing the same treatment as in Comparative Example 1 except that 0.35 part by mass of 4-fluorobenzoic acid was used instead of 0.40 part by mass of phenylphosphonic acid / When the abundance ratio in the solution was measured by the above method, it was 4.9 / 1.

[Comparative Example 5]
The surface of the ferromagnetic powder / solution of polyurethane in a dispersion obtained by performing the same treatment as in Comparative Example 1 except that 0.36 parts by mass of 2-tertbutylphenol was used instead of 0.40 parts by mass of phenylphosphonic acid The abundance ratio was measured by the above method and found to be 4.0 / 1.

[Comparative Example 6]
The surface of the ferromagnetic powder of polyurethane in the dispersion obtained by performing the same treatment as in Comparative Example 1 except that 0.33 part by mass of 2-methoxybenzoic acid was used instead of 0.40 part by mass of phenylphosphonic acid / When the abundance ratio in the solution was measured by the above method, it was 3.8 / 1.

[Comparative Example 7]
The surface of the ferromagnetic powder of polyurethane in the dispersion obtained by performing the same treatment as in Comparative Example 1 except that 0.33 part by mass of 4-methoxybenzoic acid was used instead of 0.40 part by mass of phenylphosphonic acid / When the abundance ratio in the solution was measured by the above method, it was 3.8 / 1.

2. Examples and comparative examples using ferromagnetic hexagonal ferrite powder (2)

[Example 15]
7.3 parts by mass of the following barium ferrite powder, 1 part by mass of sulfonic acid group-containing polyurethane (sulfonic acid group content: 0.6 × 10 ⁻⁴ mol / g), and 0.33 part by mass of 3-tertbutylphenolic acid were added to cyclohexanone 11 It was suspended in a solution consisting of .9 parts by mass and 17.7 parts by mass of 2-butanone. 90 parts by mass of zirconia beads (manufactured by Nikkato) was added to the suspension and dispersed for 6 hours. The ratio of the dispersed liquid polyurethane in the barium ferrite powder surface / solution was measured by the following method and found to be 1.6 / 1.
Ferromagnetic hexagonal barium ferrite powder Composition excluding oxygen (molar ratio): Ba / Fe / Co / Zn = 1/9 / 0.2 / 1
Hc: 176 kA / m (2200 Oe), average plate diameter: 25 nm, average plate ratio: 3
BET specific surface area: 65 m ² / g
σs: 49 A · m ² / kg (49 emu / g)
pH: 7

[Example 16]
A polyurethane ferromagnetic powder of a dispersion obtained by performing the same treatment as in Example 15 except that 0.47 parts by mass of 4-tertbenzoic acid was used instead of 0.33 parts by mass of 3-tertbutylphenolic acid. When the abundance ratio in the surface / solution was measured by the above method, it was 1.7 / 1.

[Example 17]
A polyurethane ferromagnetic material of a dispersion obtained by performing the same treatment as in Example 15 except that 0.56 parts by mass of 5-tertbutylisophthalic acid was used instead of 0.33 parts by mass of 3-tertbutylphenolic acid. It was 1.6 / 1 when the abundance ratio in the powder surface / solution was measured by the above method.

[Example 18]
A polyurethane ferromagnetic powder of a dispersion obtained by performing the same treatment as in Example 15 except that 0.46 parts by mass of 4-cyclohexylbenzoic acid was used instead of 0.33 parts by mass of 3-tertbutylphenolic acid. The abundance ratio in the surface / solution was measured by the above method and found to be 2.0 / 1.

[Example 19]
A polyurethane ferromagnetic powder of a dispersion obtained by performing the same treatment as in Example 15 except that 0.33 part by mass of 2-methylbenzoic acid was used instead of 0.33 part by mass of 3-tertbutylphenolic acid. When the abundance ratio in the surface / solution was measured by the above method, it was 1.3 / 1.

[Example 20]
A polyurethane ferromagnetic powder of a dispersion obtained by performing the same treatment as in Example 15 except that 0.33 parts by mass of 3-methylbenzoic acid was used instead of 0.33 parts by mass of 3-tertbutylphenolic acid. When the abundance ratio in the surface / solution was measured by the above method, it was 1.3 / 1.

[Comparative Example 8]
Surface of the ferromagnetic powder of polyurethane in the dispersion / solution obtained by performing the same treatment as in Example 15 except that 0.21 part by mass of phenol was used instead of 0.33 part by mass of 3-tertbutylphenolic acid The abundance ratio was measured by the above method and found to be 1.0 / 1.

[Comparative Example 9]
The surface of the polyurethane ferromagnetic powder in the dispersion obtained by performing the same treatment as in Example 15 except that 0.40 part by mass of phenylphosphonic acid was used instead of 0.33 part by mass of 3-tertbutylphenolic acid / When the abundance ratio in the solution was measured by the above method, it was 0.6 / 1.

[Comparative Example 10]
Except that 3-tertbutylphenolic acid was not used, the ratio of polyurethane in the ferromagnetic powder surface / solution of the dispersion obtained by the same treatment as in Example 15 was measured by the above method. It was 5/1.

3. The ferromagnetic metal powder used in Reference Example, Comparative Reference Example

[ Reference Example 21]
7.3 parts by mass of the following metal powder, 1 part by mass of sulfonic acid group-containing polyurethane (sulfonic acid group content: 3.3 × 10 ⁻⁴ mol / g), and 0.40 part by mass of 4-t-pentylphenol were added to cyclohexanone 11 It was suspended in a solution consisting of .9 parts by mass and 17.7 parts by mass of 2-butanone. 90 parts by mass of zirconia beads (manufactured by Nikkato) was added to the suspension and dispersed for 6 hours. When the abundance ratio of the dispersed liquid polyurethane in the barium ferrite powder surface / solution was measured by the above method, it was 0.85 / 1 or more.
Metal powder Composition Co / Fe: 23.7 atomic%, Y / Fe: 15.3 atomic%, Al / Fe: 9.3 atomic%
Hc: 194 kA / m (2400 Oe), long axis length: 45 nm, needle ratio: 4.2
BET specific surface area: 67 m ² / g
σs: A · m ² / kg (110 emu / g)
pH: 9

[ Reference Example 22]
A polyurethane ferromagnetic material in a dispersion obtained by performing the same treatment as in Reference Example 21 except that 0.37 part by mass of 4-secBu-phenol was used instead of 0.40 part by mass of 4-t-pentylphenol. It was 0.83 / 1 when the abundance ratio in the powder surface / solution was measured by the above method.

[ Reference Example 23]
A polyurethane ferromagnetic material in a dispersion obtained by performing the same treatment as in Reference Example 21 except that 0.33 parts by mass of 4-Isopropylphenol was used instead of 0.40 parts by mass of 4-t-pentylphenol. It was 0.83 / 1 when the abundance ratio in the powder surface / solution was measured by the above method.

[ Reference Example 24]
Ferromagnetic properties of polyurethane in a dispersion obtained by performing the same treatment as in Reference Example 21, except that 0.40 part by mass of 4-Isopropylbenzoic acid was used instead of 0.40 part by mass of 4-t-pentylphenol. It was 0.57 / 1 when the abundance ratio in the body powder surface / solution was measured by the above method.

[ Reference Comparative Example 11]
Except that no 4-t-pentylphenol was used, the ratio of polyurethane in the ferromagnetic powder surface / solution of the dispersion obtained by the same treatment as in Reference Example 21 was measured by the above method. 52/1.

[ Reference Comparative Example 12]
The dispersion of polyurethane obtained in the same manner as in Reference Example 21 except that 0.21 part by mass of phenol was used instead of 0.33 part by mass of 3-tertbutylphenol. When the abundance ratio was measured by the above method, it was 0.49 / 1.

4). The nonmagnetic powder used in Reference Example, Comparative Reference Example

[ Reference Example 25]
3.7 parts by mass of the following nonmagnetic powder, 1 part by mass of sulfonic acid group-containing polyurethane (sulfonic acid group content: 3.3 × 10 ⁻⁴ mol / g), and 0.33 parts by mass of 3-tertbutylphenol were added to cyclohexanone. It was suspended in a solution consisting of 8 parts by mass and 10.3 parts by mass of 2-butanone. 90 parts by mass of zirconia beads (manufactured by Nikkato) was added to the suspension and dispersed for 6 hours. The ratio of the dispersed liquid polyurethane surface / non-magnetic powder surface / solution was measured by the above method and found to be 0.39 / 1.
Non-magnetic powder α-iron oxide Surface treatment layer: Al ₂ O ₃ , SiO ₂
Average long axis length: 0.15 μm
Average needle ratio: 7
Specific surface area by BET method: 52 m ² / g
PH: 8

[ Reference Example 26]
The surface of the polyurethane ferromagnetic powder in the dispersion obtained by performing the same treatment as in Reference Example 25 except that 0.33 parts by mass of 4-tertbutylphenol was used instead of 0.33 parts by mass of 3-tertbutylphenol. When the abundance ratio in the solution was measured by the above method, it was 0.51 / 1.

[ Reference Comparative Example 13]
Except that 3-tertbutylphenol was not added, the ratio of polyurethane in the nonmagnetic powder surface / solution of the dispersion obtained by performing the same treatment as in Reference Example 25 was measured by the above method. / 1.

Evaluation results Since the presence ratio of the polyurethane powder surface in the examples was higher than the existence ratio of the polyurethane powder surfaces in the comparative examples, the cyclic compounds used in the examples modified the powder surface and increased the amount of polyurethane adsorbed. It turns out that the effect was shown. Increasing the amount of binder adsorbed to the powder in the paint leads to an improvement in the dispersibility of the powder, so that it can be confirmed that the cyclic compound used in the examples can function as a dispersant in various paints.

  The surface modifier of the present invention is suitable as a dispersant for magnetic paint and a dispersant for nonmagnetic powder.

Claims (8)

A surface modifier for ferromagnetic hexagonal ferrite powder comprising at least one cyclic compound selected from the group consisting of the following compounds (a) and (b).
Compound (a): benzene compound substituted with the following substituent A and substituent B (b): cyclohexane substituent A substituted with the following substituent A and substituent B: hydroxyl group and / or carboxyl group substituent B: alkyl Group and / or alkoxyl group (in the compound (a), the alkoxyl group is substituted at the meta position with respect to the substituent A, and the alkyl group excluding the methyl group is a carbon atom adjacent to the carbon atom substituted by the substituent A) Will not be replaced.) 2. The surface modifier for a ferromagnetic hexagonal ferrite powder according to claim 1, wherein the compound (a) has a substituent A at a meta position or a para position with respect to the substituent B. 3. The surface modifier for a ferromagnetic hexagonal ferrite powder according to claim 1, wherein the compound (b) has a substituent A at the 4-position with respect to the substituent B. The surface modifier for a ferromagnetic hexagonal ferrite powder according to any one of claims 1 to 3, wherein the substituent B is a branched alkyl group. The surface modifier for ferromagnetic hexagonal ferrite powder according to any one of claims 1 to 4, which is used as a dispersant for magnetic paints. A magnetic paint comprising the surface modifier for a ferromagnetic hexagonal ferrite powder according to any one of claims 1 to 5 , a ferromagnetic hexagonal ferrite powder, and a binder. The magnetic paint according to claim 6, wherein the binder is a sulfonic acid group-containing binder. The magnetic paint according to claim 6 or 7, which is used as a coating liquid for forming a magnetic layer of a magnetic recording medium.