JP5081130B2 - Surface modifier for powder, magnetic paint and non-magnetic paint containing the same, and magnetic recording medium - 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.
The present invention further relates to a magnetic recording medium, and more particularly to a magnetic recording medium having excellent surface smoothness.

  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. The introduction of polar groups into the binder is an effective means for improving the dispersibility by efficiently adsorbing the binder (polymer) to the surface of the powder such as magnetic powder. If the amount is excessive, the dispersibility may be reduced. Therefore, it is conceivable to use an additive (dispersant) for imparting a dispersion effect. As the dispersant, phosphoric acid compounds such as phosphonic acids and phosphoric acids are widely used. Patent Document 2 proposes the use of a hydroxamic acid derivative to enhance the dispersibility of the ferromagnetic powder.
Japanese Patent Laid-Open No. 2003-132931 JP-A-1-236425

  In order to increase the dispersibility of the powder in the magnetic recording medium, it is highly adsorbed on the powder surface and has a good affinity for the binder, and is interposed between the powder surface and the binder. It is effective to use a compound that can increase the adsorption rate of the binder on the surface as an additive. That is, in order to improve dispersibility, it is preferable to use a compound that exhibits good affinity for both the powder and the binder. However, currently phosphonic acids and phosphoric acids widely used as dispersants in magnetic recording media have relatively good affinity with magnetic powders, but have poor affinity with binders. Therefore, the effect of improving the dispersibility by these general-purpose dispersants is not always sufficient.

  On the other hand, as a property required for the additive of the magnetic recording medium, there is little deterioration of the medium performance due to the addition. However, as a result of the study by the present inventors, the hydroxamic acid derivative described in Patent Document 2 has a problem that precipitates are generated on the medium surface when the derivative is used as a magnetic layer component. It became clear.

Accordingly, a first object of the present invention is to provide a means for modifying the surface of the powder in order to improve the dispersibility of the powder such as magnetic powder in the magnetic coating material. More specifically, the powder is obtained by modifying the surface of the powder. An object of the present invention is to provide a surface modifier for powder capable of increasing the amount of binder adsorbed on and a magnetic paint and a non-magnetic paint containing the surface modifier for powder.
A second object of the present invention is to provide a magnetic recording medium having excellent surface smoothness without causing deterioration of medium performance such as generation of precipitates.

  As a result of intensive studies to achieve the above object, the present inventors have shown that the urethane bond-containing compound represented by the following general formula (I) has a good affinity for both the powder and the binder. In addition, the present inventors have found that by using it in a magnetic recording medium, it is possible to provide a magnetic recording medium having excellent surface smoothness and suppressing or reducing the generation of precipitates, and the present invention has been completed. .

［一般式（Ｉ）中、Ｒ¹はアルキル基またはアリール基を表し、Ｒ²は水酸基を表す。］
［２］磁性塗料用分散剤または非磁性塗料用分散剤として使用される［１］に記載の粉末用表面改質剤。
［３］非磁性支持体上に強磁性粉末および結合剤を含む磁性層を有する磁気記録媒体であって、
前記磁性層は、下記一般式（Ｉ）で表される化合物を更に含むことを特徴とする磁気記録媒体。

［一般式（Ｉ）中、Ｒ¹はアルキル基またはアリール基を表し、Ｒ²は水酸基を表す。］
［４］前記磁性層は、ステアリルアミンを更に含む［３］に記載の磁気記録媒体。
［５］非磁性支持体と磁性層との間に、非磁性粉末および結合剤を含む非磁性層を有する［３］または［４］に記載の磁気記録媒体。
［６］前記非磁性層は、前記一般式（Ｉ）で表される化合物を更に含む［５］に記載の磁気記録媒体。
［７］前記非磁性層は、ステアリルアミンを更に含む［５］または［６］に記載の磁気記録媒体。
［８］前記結合剤はポリウレタン樹脂を含む［３］〜［７］のいずれかに記載の磁気記録媒体。
［９］［１］または［２］に記載の粉末用表面改質剤と、磁性粉末と、結合剤とを含む磁性塗料。
［１０］前記磁性粉末は強磁性六方晶フェライト粉末または強磁性金属粉末である［９］に記載の磁性塗料。
［１１］前記結合剤はポリウレタン樹脂を含む［９］または［１０］に記載の磁性塗料。
［１２］磁気記録媒体の磁性層形成用塗布液として使用される［９］〜［１１］のいずれかに記載の磁性塗料。
［１３］［１］または［２］に記載の粉末用表面改質剤と、非磁性粉末と、結合剤とを含む非磁性塗料。
［１４］前記非磁性粉末は、非磁性金属粉末である［１３］に記載の非磁性塗料。
［１５］前記結合剤はポリウレタン樹脂を含む[１３]または[１４]に記載の非磁性塗料。
［１６］磁気記録媒体の非磁性層形成用塗布液として使用される［１３］〜［１５］のいずれかに記載の非磁性塗料。 That is, the above object has been achieved by the following means.
[1] A powder surface modifier containing a compound represented by the following general formula (I) , wherein the powder is selected from the group consisting of a magnetic powder and a nonmagnetic powder .

[In the general formula (I), R ¹ represents an alkyl group or an aryl group, R ² represents a hydroxyl group. ]
[2 ] The powder surface modifier according to [ 1 ], which is used as a dispersant for magnetic paint or a dispersant for nonmagnetic paint.
[ 3 ] A magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
The magnetic recording medium, wherein the magnetic layer further contains a compound represented by the following general formula (I):

[In the general formula (I), R ¹ represents an alkyl group or an aryl group, R ² represents a hydroxyl group. ]
[4 ] The magnetic recording medium according to [ 3], wherein the magnetic layer further includes stearylamine.
[ 5 ] The magnetic recording medium according to [ 3 ] or [4] , which has a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer.
[ 6 ] The magnetic recording medium according to [ 5 ], wherein the nonmagnetic layer further includes a compound represented by the general formula (I).
[ 7 ] The magnetic recording medium according to [ 5 ] or [ 6 ], wherein the nonmagnetic layer further contains stearylamine.
[ 8 ] The magnetic recording medium according to any one of [ 3 ] to [ 7 ], wherein the binder includes a polyurethane resin.
[ 9 ] A magnetic coating material comprising the powdery surface modifying agent according to [1] or [2], a magnetic powder, and a binder.
[ 10 ] The magnetic paint according to [ 9 ], wherein the magnetic powder is a ferromagnetic hexagonal ferrite powder or a ferromagnetic metal powder.
[ 11 ] The magnetic paint according to [ 9 ] or [ 10 ], wherein the binder includes a polyurethane resin.
[ 12 ] The magnetic paint according to any one of [ 9 ] to [ 11 ], which is used as a coating liquid for forming a magnetic layer of a magnetic recording medium.
[ 13 ] A nonmagnetic paint comprising the powdery surface modifying agent according to [1] or [2], a nonmagnetic powder, and a binder.
[ 14 ] The nonmagnetic paint according to [ 13 ], wherein the nonmagnetic powder is a nonmagnetic metal powder.
[ 15 ] The nonmagnetic paint according to [ 13 ] or [ 14 ], wherein the binder contains a polyurethane resin.
[ 16 ] The nonmagnetic paint according to any one of [ 13 ] to [ 15 ], which is used as a coating liquid for forming a nonmagnetic 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.
Furthermore, according to the present invention, it is possible to provide a magnetic recording medium having excellent surface smoothness and reduced or suppressed generation of precipitates.

[Surface modifier for powder]
The surface modifier for powder of the present invention contains a compound represented by the following general formula (I).

［一般式（Ｉ）中、Ｒ¹はアルキル基またはアリール基を表し、Ｒ²は水酸基またはアリール基を表す。］

[In General Formula (I), R ¹ represents an alkyl group or an aryl group, and R ² represents a hydroxyl group or an aryl group. ]

  The surface modifier for powder of the present invention (hereinafter, also simply referred to as “surface modifier”) may contain a compound having another surface modification effect together with the compound represented by the general formula (I). It is preferably composed of one or more compounds represented by the general formula (I).

  As shown in the Example mentioned later, it can confirm that the adsorption amount of the binder to powder increases by adding the compound represented with general formula (I) to the coating material containing a powder and a binder. The reason why the amount of the binder adsorbed on the powder is increased by the addition of the compound represented by the general formula (I) as described above is that the compound represented by the general formula (I) is good for both the powder and the binder. In order to show high affinity, the powder surface is first adsorbed to a high level so that the powder surface is covered with the compound, and the binding agent is adsorbed to the compound existing on the powder surface with a high adsorption rate. As a result, it is considered that the adsorption rate of the binder to the powder surface can be improved. Furthermore, since the compound represented by the general formula (I) can be highly adsorbed on the powder surface, the proportion of the component that cannot be adsorbed on the powder surface and released is small, and it is considered that the addition does not affect the system. .

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 The compound represented by the general formula (I) adheres to the powder surface because the concentration of the compound observed from the supernatant liquid is smaller than the added concentration when the powder and the compound are mixed. Can be confirmed.
Hereinafter, the compound represented by formula (I) will be described in more detail.

Compound represented by general formula (I)

In general formula (I), R ¹ represents an alkyl group or an aryl group. The alkyl group represented by R ¹ 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. The alkyl group represented by R ¹ is preferably an alkyl group having 1 to 3 carbon atoms, such as a methyl group, an ethyl group, or a propyl group, from the viewpoint of the surface modification effect.

The aryl group represented by R ¹ is a substituted or unsubstituted aryl group, and preferably a substituted or unsubstituted aryl group having 6 to 30 carbon atoms such as a phenyl group, p- A tolyl group, a naphthyl group, an m-chlorophenyl group, and an o-hexadecanoylaminophenyl group.

In general formula (I), R ² represents a hydroxyl group or an aryl group. Details of the aryl group represented by R ² are the same as those of the aryl group represented by R ¹ . From the viewpoint of the surface modification effect, the compound represented by the general formula (I) is preferably a compound in which R ² is a hydroxyl group, that is, a hydroxyurethane compound.

  The type, number, and substitution position of the substituent that the alkyl group and aryl group may have are not particularly limited. Specific examples of the substituent include a halogen atom (for example, fluorine atom, chlorine atom, bromine). Atom, iodine atom, preferably bromine atom), aryl group (preferably a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, such as phenyl group, tolyl group, xylyl group, mesityl group, biphenylyl group, naphthyl group, anthryl group) Group, phenanthryl group, fluorenyl group, pyrenyl group), alkyl group (preferably a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, such as methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec -Butyl group, tert-butyl group, n-pentyl group, neopentyl group, hexyl group, heptyl group, Butyl group, nonyl group, decyl group, undecyl group, dodecyl group, cyclopentyl group, cyclohexyl group, benzyl group, phenethyl group, diphenylmethyl group and a trityl group). Moreover, carbon number with respect to a certain group shall mean the carbon number of the part except a substituent, when this group has a substituent.

  Specific examples of the compound represented by the general formula (I) include compounds described in Examples described later.

  The compound represented by the general formula (I) can be easily synthesized by a known method, and some compounds are commercially available.

  The amount of the compound represented by the general formula (I) relative to the powder can be appropriately set. The compound represented by the general formula (I) is added to the magnetic layer forming coating solution or nonmagnetic layer coating solution of the magnetic recording medium. If excessively added, the film may be plasticized and peeling of the film may occur, so an excessive amount is not preferable. From this viewpoint, the amount of the compound represented by the general formula (I) 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 improve the dispersibility of the powder in the paint containing the powder and the binder by modifying the powder surface such as magnetic powder and non-magnetic powder. Therefore, the surface modifier of the present invention is preferably used as a dispersant in various paints containing powder and binder, more preferably used as a dispersant in magnetic paints and non-magnetic paints, and for magnetic layer formation. It is particularly preferable to use it as a dispersant in paints or nonmagnetic layer-forming paints. 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 recording medium]
The present invention further relates to a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support. The magnetic recording medium of the present invention contains the compound represented by the general formula (I) in the magnetic layer together with the ferromagnetic powder and the binder.

  As described above, the compound represented by the general formula (I) can improve the dispersibility of the magnetic layer by modifying the surface of the ferromagnetic powder to increase the amount of binder adsorbed on the surface of the ferromagnetic powder. Thus, a magnetic recording medium excellent in surface smoothness can be obtained.

  As described above, the compound represented by the general formula (I) is excellent in adsorptivity with the ferromagnetic powder. If the component added to improve the dispersibility is poorly adsorbed to the ferromagnetic powder, a large amount of free component may migrate from the surface of the medium during storage or running of the medium, leading to increased head dirt or reduced running durability. is there. On the other hand, according to the compound having excellent adsorptivity with the ferromagnetic powder, the dispersibility of the magnetic layer can be enhanced without causing such a problem.

  On the other hand, when the hydroxamic acid derivative described in Patent Document 2 (Japanese Patent Application Laid-Open No. 1-223625) is used as a magnetic layer component, precipitates may be generated on the surface of the magnetic layer. As a result of the examination, it was newly discovered. Although details of the generation mechanism of the precipitates are not clear, according to the study by the present inventors, the generation of precipitates was remarkable on the surface of the magnetic layer containing stearylamine as a lubricant. It is considered that stearylamine is precipitated on the surface of the magnetic layer by adding the hydroxamic acid derivative. However, since stearylamine exhibits an excellent effect as a lubricant for magnetic recording media, it is not preferable to exclude it as a magnetic layer component. On the other hand, even when the compound represented by the general formula (I) was added as a magnetic layer component together with stearylamine, no precipitate was observed on the surface of the magnetic layer as shown in Examples described later. Therefore, the compound represented by the general formula (I) is suitable for combined use with stearylamine. From the above points, the magnetic recording medium of the present invention containing the compound represented by the general formula (I) as the magnetic layer component and / or the nonmagnetic layer component contains stearylamine in the magnetic layer and / or the nonmagnetic layer. Is preferred. Note that the lubricant component in the nonmagnetic layer can exhibit an effect of maintaining a good lubricating effect over a long period of time by shifting to the magnetic layer over time. The stearylamine content in the magnetic recording medium of the present invention is preferably 0.05 to 1.0 parts by mass per 100 parts by mass of magnetic powder in the magnetic layer from the viewpoint of lubricating effect, and in the nonmagnetic layer. The amount is preferably 0.05 to 1.0 part by mass per 100 parts by mass of the nonmagnetic powder.

  The magnetic recording medium of the present invention can also have a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. In this case, the compound represented by the general formula (I) can also be included in the nonmagnetic layer. By including the compound represented by the general formula (I) in the nonmagnetic layer, the adsorptivity between the nonmagnetic powder and the binder can be increased and the dispersibility of the nonmagnetic layer can be increased.

  Details of the compound represented by the general formula (I) and the amount of the compound used with respect to the powder are as described above.

The magnetic recording medium of the present invention can be formed using the magnetic paint and / or nonmagnetic paint of the present invention. The details of the magnetic layer and the nonmagnetic layer in the magnetic recording medium of the present invention are the same as those described below regarding the magnetic coating material and the nonmagnetic coating material of the present invention.
Details of the magnetic recording medium of the present invention will be further described below.

Non-magnetic support Examples of the non-magnetic support include known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable. These supports may be subjected in advance to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like. The surface roughness of these non-magnetic supports is such that the center surface average roughness Ra measured with an optical interference type surface roughness meter HD-2000 manufactured by WYKO is 6.0 nm or less, more preferably 4.0 nm or less. It is preferable to use one.

Layer Configuration The magnetic recording medium of the present invention may be a disk-shaped medium in which a nonmagnetic layer and a magnetic layer are provided on both surfaces of a nonmagnetic support, or a tape-shaped medium or a disk-shaped medium provided on only one side. The thickness of the nonmagnetic support is, for example, 2 to 100 μm, preferably 2 to 80 μm. In the case of computer tape, the non-magnetic support has a thickness in the range of 3.0 to 6.5 μm (preferably 3.0 to 6.0 μm, more preferably 4.0 to 5.5 μm). Can be used.

  An undercoat layer may be provided between the nonmagnetic support and the nonmagnetic layer or magnetic layer to improve adhesion. The thickness of the undercoat layer is, for example, 0.01 to 0.5 μm, preferably 0.02 to 0.5 μm. A known undercoat layer can be used.

  The thickness of the magnetic layer is optimized according to the saturation magnetization amount, head gap length, and recording signal band of the magnetic head to be used, but is generally 10 to 150 nm, preferably 20 to 120 nm, and more preferably. Is 30 to 100 nm, particularly preferably 30 to 80 nm. Further, the thickness variation rate of the magnetic layer is preferably within ± 50%, more preferably within ± 30%. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.

  The thickness of the nonmagnetic layer is, for example, 0.1 to 3.0 μm, preferably 0.3 to 2.0 μm, and more preferably 0.5 to 1.5 μm. The non-magnetic layer of the magnetic recording medium of the present invention exhibits its effect if it is substantially non-magnetic. For example, even if it contains a small amount of magnetic material as an impurity or intentionally, This shows the effect of the invention and can be regarded as substantially the same configuration as the magnetic recording medium of the invention. Note that “substantially the same” means that the residual magnetic flux density of the nonmagnetic layer is 10 mT or less or the coercive force is 7.96 kA / m (100 Oe) or less, and preferably has no residual magnetic flux density and coercive force. Means.

Backcoat layer A backcoat layer may be provided on the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is provided in order to provide effects such as antistatic and curl correction. The coating material for the back coat layer disperses a particle component such as an abrasive and an antistatic agent and a binder in an organic solvent. Various inorganic pigments and carbon black can be used as the particulate component. Moreover, as a binder, resin, such as a nitrocellulose, a phenoxy resin, a vinyl chloride resin, a polyurethane, can be used individually or in mixture, for example. This thickness is, for example, 0.1 to 4 μm, preferably 0.3 to 2.0 μm. A well-known backcoat layer can be used.

Method for Producing Magnetic Recording Medium The magnetic recording medium of the present invention uses the magnetic coating composition of the present invention as a coating solution for forming a magnetic layer and / or the nonmagnetic coating composition of the present invention as a coating solution for forming a nonmagnetic layer. Can be manufactured using. For example, the magnetic coating and / or nonmagnetic coating of the present invention is applied to the surface of a nonmagnetic support under running so as to have a predetermined thickness, and the magnetic layer and / or the nonmagnetic layer is applied. . Here, a plurality of magnetic paints may be applied successively or simultaneously, and a nonmagnetic paint and a magnetic paint may be applied successively or simultaneously. As an application machine for applying the magnetic paint and / or non-magnetic paint, air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, Kiss coat, cast coat, spray coat, spin coat, etc. can be used. As for these, for example, “Latest Coating Technology” (May 31, 1983) issued by General Technology Center Co., Ltd. can be referred to.

  In the case of a magnetic tape, the magnetic paint coating layer may be subjected to a magnetic field orientation treatment using a cobalt magnet or a solenoid on the ferromagnetic powder contained in the magnetic paint coating layer. In the case of a disk, a sufficiently isotropic orientation may be obtained even without non-orientation without using an orientation device, but known random methods such as alternately arranging cobalt magnets obliquely and applying an alternating magnetic field with a solenoid. It is preferable to use an alignment device. In the case of a ferromagnetic metal powder, the isotropic orientation is generally preferably in-plane two-dimensional random, but can also be three-dimensional random with a vertical component. Further, isotropic magnetic characteristics can be imparted in the circumferential direction by using a well-known method such as a counter-polarized magnet and making it vertically oriented. In particular, when performing high density recording, vertical alignment is preferable. Moreover, circumferential orientation can also be achieved using spin coating.

  It is preferable that the drying position of the coating film can be controlled by controlling the temperature, air volume, and coating speed of the drying air, the coating speed is preferably 20 m / min to 1000 m / min, and the temperature of the drying air is preferably 60 ° C. or higher. Also, moderate pre-drying can be performed before entering the magnet zone.

  The coating raw material thus obtained is usually wound up once by a winding roll, and then unwound from the winding roll and subjected to a calendar process. For the calendar process, for example, a super calendar roll or the like is used. The calendering improves the surface smoothness and eliminates the voids generated by the removal of the solvent during drying and improves the filling rate of the ferromagnetic powder in the magnetic layer. Can be obtained. The step of calendering is preferably performed while changing the calendering conditions according to the smoothness of the surface of the coating raw material. As the calender roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, polyamideimide or the like can be used. Moreover, it can also process with a metal roll. As suitable calendering conditions, the temperature of the calender roll is, for example, in the range of 60 to 100 ° C., preferably in the range of 70 to 100 ° C., particularly preferably in the range of 80 to 100 ° C., and the pressure is, for example, 100 to 500 kg. / Cm (98 to 490 kN / m), preferably 200 to 450 kg / cm (196 to 441 kN / m), particularly preferably 300 to 400 kg / cm (294 to 392 kN / m). It is.

  The magnetic recording medium obtained after the calendering process can also be thermo-cured by a thermo treatment. Such thermo-treatment conditions may be appropriately determined depending on the formulation of the magnetic paint, and are, for example, 35 to 100 ° C., and preferably 50 to 80 ° C. The thermo treatment time is, for example, 12 to 72 hours, preferably 24 to 48 hours.

  The obtained magnetic recording medium can be cut into a desired size using a cutting machine or the like. The cutting machine is not particularly limited, but is preferably provided with a plurality of pairs of rotating upper blades (male blades) and lower blades (female blades). The slitting speed, the engagement depth, and the upper blade (male blade) are appropriately selected. The peripheral speed ratio (upper blade peripheral speed / lower blade peripheral speed) between the blade and the lower blade (female blade), the continuous use time of the slit blade, and the like are selected.

Physical Properties The magnetic recording medium of the present invention can have extremely excellent surface smoothness by the compound represented by formula (I) exhibiting an excellent effect of improving dispersibility. The surface smoothness of the magnetic recording medium of the present invention is preferably in the range of 0.1 to 4 nm, more preferably 1 to 3 nm, in terms of the center plane average roughness of the surface. The 10-point average roughness Rz on the surface of the magnetic layer is preferably 30 nm or less. The surface property of the magnetic layer can also be controlled by controlling the surface property with a filler of the support or the surface of a calendered roll. The curl is preferably within ± 3 mm.

  The saturation magnetic flux density of the magnetic layer is preferably 100 to 400 mT. The coercive force (Hc) of the magnetic layer is preferably 143.2 to 318.3 kA / m (1800 to 4000 Oe), more preferably 159.2 to 278.5 kA / m (2000 to 3500 Oe). The coercive force distribution is preferably narrow, and SFD and SFDr are preferably 0.6 or less, more preferably 0.3 or less.

The friction coefficient with respect to the head of the magnetic recording medium of the present invention is, for example, 0.70 or less, preferably 0.5 or less, in the temperature range of −10 to 40 ° C. and humidity of 0 to 95%. The surface resistivity is preferably a magnetic surface of 10 ⁴ to 10 ⁸ Ω / sq, and the charged position is preferably within −500 V to +500 V. The elastic modulus at 0.5% elongation of the magnetic layer is preferably 0.98 to 19.6 GPa (100 to 2000 kg / mm ² ) in each in-plane direction, and the breaking strength is preferably 98 to 686 MPa (10 to 70 kg). / Mm2), the elastic modulus of the magnetic recording medium is preferably 0.98 to 14.7 GPa (100 to 1500 kg / mm ² ) in each in-plane direction, and the residual spread is preferably 0.5% or less and 100 ° C. or less. The thermal contraction rate at any temperature is preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less.

The glass transition temperature of the magnetic layer (maximum point of loss elastic modulus measured by dynamic viscoelasticity measured at 110 Hz) is preferably 50 to 180 ° C, and that of the nonmagnetic layer is preferably 0 to 180 ° C. The loss elastic modulus is preferably in the range of 1 × 10 ⁷ to 8 × 10 ⁸ Pa (1 × 10 ⁸ to 8 × 10 ⁹ dyne / cm ² ), and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. These thermal characteristics and mechanical characteristics are preferably almost equal within 10% in each in-plane direction of the medium.

The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less. The porosity of the coating layer is preferably 30% by volume or less, more preferably 20% by volume or less for both the nonmagnetic layer and the magnetic layer. The porosity is preferably small in order to achieve high output, but it may be better to ensure a certain value depending on the purpose. For example, in the case of a disk medium in which repeated use is important, a larger void ratio is often preferable for running durability.

  When the magnetic recording medium of the present invention has a nonmagnetic layer and a magnetic layer, these physical characteristics can be changed between the nonmagnetic layer and the magnetic layer according to the purpose. For example, the elastic modulus of the magnetic layer can be increased to improve running durability, and at the same time, the elastic modulus of the nonmagnetic layer can be made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

[Magnetic paint]
The magnetic paint of the present invention contains the surface modifier for powder of the present invention, magnetic powder, and a binder. In the magnetic coating material of the present invention, the adsorptivity between the magnetic powder and the binder is improved by the action of the surface modifier, whereby the magnetic powder can be highly dispersed. The details of the surface modifier are as described above.
Below, each component contained in the magnetic coating material of this invention is demonstrated. These components can also be used as magnetic layer components of the magnetic recording medium of the present invention.

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.

(Ii) Ferromagnetic metal powder 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, 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.

Since the surface modifier of this invention has a urethane bond, it can show high affinity with respect to a polyurethane resin. Therefore, the surface modifier of the present invention is preferably used in combination with a polyurethane resin. 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 is a hydrogen atom or an alkali metal base), —OH, —NR ₂ , —N ⁺ R ₃ (R is a hydrocarbon group), epoxy group, —SH, — It is preferable to use one in which at least one polar group selected from CN and the like 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. In particular, the surface modifier of the present invention is preferably used in combination with a sulfonic acid (salt) group-containing binder from the viewpoint of affinity with the binder. In the present invention, the sulfonic acid (salt) group includes a sulfonic acid group (—SO ₃ H) and a sulfonic acid group (SO ₃ M: M is an alkali metal atom such as lithium, sodium, or potassium).

  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.

  As an abrasive, α-alumina, β-alumina, α-alumina of 90% or more, fine particle diamond, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, titanium dioxide Known materials having a Mohs hardness of 6 or more, such as silicon and boron nitride, can be used alone or in combination. Moreover, you may use the composite_body | complex (what surface-treated the abrasive | polishing agent with the other abrasive | polishing agent) of these abrasive | polishing agents. These abrasives may contain compounds or elements other than the main component, but the effect remains the same as long as the main component is 90% by mass or more.

When the magnetic paint of the present invention is used as a coating solution for forming a magnetic layer of a magnetic recording medium, the powder size of these abrasives is preferably 0.01 to 1 μm. A narrower particle size distribution is preferred. Further, in order to improve the durability, it is possible to combine abrasives having different powder sizes as necessary, or to obtain the same effect by widening the particle size distribution even with a single abrasive. It is preferable that the tap density is 0.3 to 1.5 g / cc, the water content is 0.1 to 5% by mass, the pH is 2 to 11, and the specific surface area is 1 to 40 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but those having a corner in a part of the shape are preferable because of high polishing properties. Specifically, AKP-10, AKP-15, AKP-20, AKP-30, AKP-50, HIT-20, HIT-30, HIT-50, HIT-60A, HIT-50G, HIT manufactured by Sumitomo Chemical Co., Ltd. -70, HIT-80, HIT-82, HIT-100, Reynolds ERC-DBM, HP-DBM, HPS-DBM, Fujimi Abrasives WA10000, Uemura Kogyo UB20, Nippon Kagaku Kogyo G -5, Chromex U2, Chromex U1, TF100, TF140 manufactured by Toda Kogyo, Beta Random Ultra Fine manufactured by Ibiden, B-3 manufactured by Showa Mining Co., etc. These abrasives can be added to the nonmagnetic paint of the present invention as required. By adding the abrasive to the nonmagnetic layer, the surface shape of the magnetic recording medium can be controlled, and the protruding state of the abrasive can be controlled. Of course, the powder size and amount of the abrasive added to the magnetic layer and the nonmagnetic layer should be set to optimum values. The amount of abrasive used is, for example, 2 to 20 parts by mass with respect to 100 parts by mass of ferromagnetic powder as the amount of abrasive in the magnetic layer, and 100 parts by mass of nonmagnetic powder as the amount of abrasive in the nonmagnetic layer. On the other hand, it can be 2-20 mass parts.

Examples of lubricants, antifungal agents, antistatic agents, and antioxidants include tungsten disulfide, graphite, fluorinated graphite, silicone oil, silicone having a polar group, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, Fluorine-containing ester, polyolefin, polyglycol, polyphenyl ether, phenylphosphonic acid, benzylphosphonic acid group, phenethylphosphonic acid, α-methylbenzylphosphonic acid, 1-methyl-1-phenethylphosphonic acid, diphenylmethylphosphonic acid, biphenylphosphonic acid Benzylphenylphosphonic acid, α-cumylphosphonic acid, toluylphosphonic acid, xylylphosphonic acid, ethylphenylphosphonic acid, cumenylphosphonic acid, propylphenylphosphonic acid, butylphenylphosphonic acid, heptylphenol Aromatic ring-containing organic phosphonic acids such as nylphosphonic acid, octylphenylphosphonic acid, nonylphenylphosphonic acid and alkali metal salts thereof, octylphosphonic acid, 2-ethylhexylphosphonic acid, isooctylphosphonic acid, isononylphosphonic acid, isodecylphosphonic acid Acids, isoundecyl phosphonic acid, isododecyl phosphonic acid, isohexadecyl phosphonic acid, isooctadecyl phosphonic acid, isoeicosyl phosphonic acid, alkylphosphonic acids and alkali metal salts thereof, phenyl phosphate, benzyl phosphate, phosphoric acid Phenethyl, α-methylbenzyl phosphate, 1-methyl-1-phenethyl phosphate, diphenylmethyl phosphate, biphenyl phosphate, benzylphenyl phosphate, α-cumyl phosphate, toluyl phosphate, xylyl phosphate, ethyl phosphate Phenyl, Aromatic phosphates such as cumenyl phosphate, propylphenyl phosphate, butylphenyl phosphate, heptylphenyl phosphate, octylphenyl phosphate, nonylphenyl phosphate, and alkali metal salts thereof, octyl phosphate, 2-ethylhexyl phosphate , Alkyl phosphates such as isooctyl phosphate, isononyl phosphate, isodecyl phosphate, isoundecyl phosphate, isododecyl phosphate, isohexadecyl phosphate, isooctadecyl phosphate, isoeicosyl phosphate, and alkali metal salts thereof, alkylsulfonic acid Esters and alkali metal salts thereof, fluorine-containing alkyl sulfates and alkali metal salts thereof, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, L Monobasic fatty acids which may contain or be branched from C10-24 unsaturated bonds such as acids and their metal salts, or butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, myristic Even if it contains an unsaturated bond having 10 to 24 carbon atoms such as octyl acid, butyl laurate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, etc. A monobasic fatty acid and a C1-C22 unsaturated bond which may be branched or contained, or an alkoxy which may be branched or contained a C12-22 unsaturated bond Any one of alcohol or alkylene oxide polymer monoalkyl ether Mono-fatty acid esters consisting of, di-fatty acid esters or polyvalent fatty acid esters, fatty acid amides having 2 to 22 carbon atoms, and aliphatic amines having 8 to 22 carbon atoms can be used. In addition to the above hydrocarbon groups, alkyl groups, aryl groups, and aralkyl groups substituted with nitro groups and groups other than hydrocarbon groups such as halogen-containing hydrocarbons such as F, Cl, Br, CF ₃ , CCl ₃ , and CBr ₃ You may have something. As the lubricant, stearylamine is preferably used for the reasons described above. The amount of addition is as described above.

  In addition, nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or sulfoniums, etc. Amphoteric interfaces such as cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, and sulfate ester groups, amino acids, aminosulfonic acids, sulfuric or phosphate esters of aminoalcohols, and alkylbetaines An activator or the like can also be used. These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.). These additives are not necessarily pure and may contain impurities such as isomers, unreacted products, side reaction products, decomposition products, oxides, etc. in addition to the main components. These impurities are preferably 30% by mass or less, more preferably 10% by mass or less.

Examples of the carbon black include a furnace for rubber, a thermal for rubber, a black for color, conductive carbon black, and acetylene black. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, average particle size is 5 nm to 300 nm, pH is 2 to 10, moisture content is 0.1 to 10% by mass, tap density is 0. It is preferably 1 to 1 g / cc. Specific examples of carbon black that can be used include BLACKPEARLS 2000, 1300, 1000, 900, 905, 800, 700, VULCAN XC-72, manufactured by Cabot, # 80, # 60, # 55, # 50, manufactured by Asahi Carbon. # 35, Mitsubishi Chemical # 2400B, # 2300, # 900, # 1000 # 30, # 40, # 10B, Colombian Carbon CONDUCTEX SC, RAVEN 150, 50, 40, 15, RAVEN-MT-P, Ketjen Ketjen Black EC manufactured by Black International, etc. Carbon black may be surface-treated with a dispersant or the like, or may be used after being grafted with a resin, or may be obtained by graphitizing a part of the surface. Further, carbon black may be dispersed in a binder in advance before being added to the magnetic paint or nonmagnetic paint. These carbon blacks can be used alone or in combination. Carbon black functions in the magnetic layer and nonmagnetic layer of the magnetic recording medium to prevent electrification, reduce the coefficient of friction, impart light-shielding properties, improve film strength, and the like, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the magnetic layer and the non-magnetic layer, and are based on the above-mentioned characteristics such as particle size, oil absorption, conductivity, pH, etc. Of course, it is possible to use them properly according to the purpose, but rather they should be optimized in each layer. The carbon black that can be used in the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

  As the organic solvent for preparing the magnetic paint, known ones 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 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. As dispersion media other than glass beads, zirconia beads, titania beads, and steel beads, which are high specific gravity dispersion media, are suitable. 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, a binder is added.
(4) A magnetic powder, a surface modifier and a binder are simultaneously added and dispersed in an organic solvent.

  The magnetic coating material of the present invention is suitable as a coating solution for forming a magnetic layer of a magnetic recording medium requiring high dispersibility because the magnetic powder is highly dispersed, and forms the magnetic layer of the magnetic recording medium of the present invention. Can be used to

[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. These components can also be used as a nonmagnetic layer component of the magnetic recording medium of the present invention.

  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, Sakai Chemical's FINEX-25, BF-1, BF-10, BF-20, ST-M, Sum Mining Ltd. DEFIC-Y, DEFIC-R, manufactured by Japan Aerosil AS2BM, TiO2P25, manufactured by Ube Industries, Ltd. 100A, 500A, include those fired Titan Kogyo Ltd. Y-LOP and it. 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. The details of each component of the non-magnetic paint, the mixing method, the addition amount, etc. are the same as those described for the magnetic paint of the present invention.

  The non-magnetic coating material of the present invention is suitable as a coating liquid for forming a non-magnetic layer of a magnetic recording medium that requires high dispersibility since the non-magnetic powder is highly dispersed. It can be used to form a magnetic layer.

  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. “Part” described below indicates “part by mass”.

1. Confirmation of compatibility with binder (1) 1.0 part of a polyurethane binder containing 3.3 × 10 ⁻⁴ mol / g of —SO ₃ Na group, 3.1 parts of 2-butanone, and cyclihexanone 2 Dissolved in 1 part. To this solution, 0.045 part of N-hydroxyurethane was added and stirred for 1 hour to completely dissolve. This liquid was measured in a 1 ml glass petri dish and dried under conditions of normal pressure, 70 ° C., and 48 hours. It was transparent when solid content was judged visually. The compatibility was confirmed in the same manner by changing the amount of N-hydroxyurethane added.
(2) In the above (1), a similar experiment was conducted by replacing 0.045 part of N-hydroxyurethane with 0.045 part of phenylphosphonic acid. When the solid content was judged visually, a light yellow turbidity was confirmed. Compatibility was confirmed in the same manner by changing the amount of phenylphosphonic acid added.
The results are shown in Table 1.

  From the results shown in Table 1, N-hydroxyurethane has good compatibility with the binder, whereas phenylphosphonic acid has a light yellow turbidity when the amount of the binder added is increased and is inferior in compatibility. I understand.

2. Confirmation of adsorptivity to magnetic powder (1) 5.0 parts of the following ferromagnetic metal powder and 0.26 part of N-hydroxyurethane were suspended in 47.4 parts of cyclohexanone and stirred for 20 hours using a magnetic stirrer. . The liquid was allowed to stand, and N-hydroxyurethane in the supernatant was measured by titration according to the following method, and N-hydroxyurethane was not observed. From this result, it was confirmed that N-hydroxyurethane was excellent in the adsorptivity to the magnetic powder surface.
Ferromagnetic metal powder composition Co / Fe: 23.7 atomic%, Y / Fe: 15.3 atomic%, Al / Fe: 9.3 atomic%
Hc: 194 kA / m (2400 Oe), average major axis length: 45 nm, average needle ratio: 4.2
BET specific surface area: 67 m ² / g
σs: 110 A · m ² / kg (110 emu / g)
pH: 9

[Measuring method]
The suspension was allowed to stand and 3 ml of the supernatant was weighed and the mass was measured. The supernatant was dissolved in N, N-dimethylformamide and the pH was adjusted with 0.1N hydrochloric acid. Titration was performed using an automatic titrator GT-100 / WIN made by Mitsubishi Chemical, and the mass of N-hydroxyurethane contained in the supernatant was measured.

(2) The same ferromagnetic metal powder (5.0 parts) as in (1) above and 0.26 parts of 5-tert-butylisophthalic acid are suspended in 47.4 parts of cyclohexanone and stirred for 20 hours using a magnetic stirrer. did. The solution was allowed to stand, and 5-tert-butylisophthalic acid in the supernatant was measured by the above titration. As a result, 0.003 part of 5-tert-butylisophthalic acid was observed. This result shows that 5-tert-butylisophthalic acid is inferior in the adsorptivity to the magnetic powder surface.

3. Examples and comparative examples using ferromagnetic hexagonal ferrite powder

[Example 1]
The following ferromagnetic hexagonal ferrite powder 7.3 parts, sulfonic acid group-containing polyurethane (sulfonic acid group content: 3.3 × 10 ⁻⁴ mol / g) 1 part, N-hydroxyurethane 0.27 part was added to cyclohexanone 11. It was suspended in a solution consisting of 9 parts and 17.1 parts of 2-butanone. 27 parts of zirconia beads (Nikkato) were added to the suspension and dispersed for 6 hours. The abundance ratio of the dispersed liquid polyurethane in the magnetic powder surface / solution was measured by the following method and found to be 5.7 / 1.
The dispersion was applied onto a support made of polyethylene terephthalate having a thickness of 9.5 μm so that the thickness after drying was 0.4 μm, and was naturally dried at room temperature. When the center line average surface roughness Ra of the coated surface was measured by the following method, it was 9.5 nm.
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

[Measurement method of binder abundance ratio]
The magnetic powder and the solution were centrifuged under conditions of 100,000 rpm and 80 minutes using a Hitachi separation microcentrifuge 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 binder non-adsorbed solid content, and the ratio of the binder present in the magnetic powder surface / solution was calculated.

[Measurement method of centerline average surface roughness]
Scan Length was measured at 5 μm by scanning white light interferometry using a general-purpose three-dimensional surface structure analyzer NewView 5000 manufactured by ZYGO. The measurement visual field was 350 μm × 260 μm, and the center line average surface roughness Ra was determined.

[Example 2]
Surface / solution of polyurethane magnetic powder of dispersion obtained by performing the same treatment as in Example 1 except that 0.43 part of N-carbobenzoxyhydroxyamine was used instead of 0.27 part of N-hydroxyurethane It was 7.1 / 1 when the abundance ratio was measured by the said method.
The dispersion was applied onto a support made of polyethylene terephthalate having a thickness of 9.5 μm so that the thickness after drying was 0.4 μm, and was naturally dried at room temperature. The centerline average surface roughness Ra of the coated surface was measured by the above method and found to be 7.2 nm.

[Example 3]
Surface / solution of polyurethane magnetic powder of dispersion obtained by performing the same treatment as in Example 1 except that 0.37 part of tert-butyl N-hydroxycarbamate was used instead of 0.27 part of N-hydroxyurethane It was 6.7 / 1 when the abundance ratio was measured by the said method.
The dispersion was applied onto a support made of polyethylene terephthalate having a thickness of 9.5 μm so that the thickness after drying was 0.4 μm, and was naturally dried at room temperature. The centerline average surface roughness Ra of the coated surface was measured by the above method and found to be 8.0 nm.

[Comparative Example 1]
Except that 0.27 parts of N-hydroxyurethane was not used, the ratio of polyurethane in the magnetic powder surface / solution of the dispersion obtained by performing the same treatment as in Example 1 was measured by the above method. It was 2.6 / 1.
The dispersion was applied onto a support made of polyethylene terephthalate having a thickness of 9.5 μm so that the thickness after drying was 0.4 μm, and was naturally dried at room temperature. When the center line average surface roughness Ra of the coated surface was measured by the above method, it was 14.7 nm.

4). Examples and comparative examples using ferromagnetic metal powder

[Example 4]
The following ferromagnetic metal powder 4.5 parts, sulfonic acid-containing polyurethane (sulfonic acid group content: 3.3 × 10 ⁻⁴ mol / g) 0.68 parts, vinyl chloride copolymer (sulfonic acid group content: 1 0.22 × 10 ⁻⁴ mol / g) and 0.15 part of N-hydroxyurethane were suspended in a solution consisting of 6.8 parts of cyclohexanone and 6.3 parts of 2-butanone. 27 parts of zirconia beads (Nikkato) were added to the suspension and dispersed for 6 hours. The ratio of the dispersed liquid polyurethane + vinyl chloride copolymer in the magnetic powder surface / solution was measured by the above method and found to be 0.76 / 1.
The dispersion was applied onto a support made of polyethylene terephthalate having a thickness of 9.5 μm so that the thickness after drying was 0.4 μm, and was naturally dried at room temperature. When the center line average surface roughness Ra of the coated surface was measured by the above method, it was 7.7 nm.
Ferromagnetic 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

[Example 5]
A polyurethane + vinyl chloride copolymer of a dispersion obtained by performing the same treatment as in Example 4 except that 0.23 part of N-carbobenzoxyhydroxyamine was used instead of 0.15 part of N-hydroxyurethane. When the abundance ratio of the magnetic powder surface / in the solution was measured by the above method, it was 0.50 / 1.
The dispersion was applied onto a support made of polyethylene terephthalate having a thickness of 9.5 μm so that the thickness after drying was 0.4 μm, and was naturally dried at room temperature. When the center line average surface roughness Ra of the coated surface was measured by the above method, it was 12.6 nm.

[Example 6]
A polyurethane + vinyl chloride copolymer of a dispersion obtained by carrying out the same treatment as in Example 4 except that 0.19 part of tert-butyl N-hydroxycarbamate was used instead of 0.15 part of N-hydroxyurethane. The abundance ratio of the magnetic powder surface / in the solution was measured by the above method and found to be 0.59 / 1.
The dispersion was applied onto a support made of polyethylene terephthalate having a thickness of 9.5 μm so that the thickness after drying was 0.4 μm, and was naturally dried at room temperature. The centerline average surface roughness Ra of the coated surface was measured and found to be 11.1 nm.

[Comparative Example 2]
Except that 0.15 parts of N-hydroxyurethane was not used, the dispersion ratio obtained by performing the same treatment as in Example 4 was the ratio of the polyurethane + vinyl chloride copolymer in the surface / magnetic powder of polyurethane + vinyl chloride copolymer. It was 0.40 / 1 when measured by the method.
The dispersion was applied onto a support made of polyethylene terephthalate having a thickness of 9.5 μm so that the thickness after drying was 0.4 μm, and was naturally dried at room temperature. The centerline average surface roughness Ra of the coated surface was measured by the above method and found to be 14.4 nm.

Evaluation Results In comparison between Examples 1 to 3 and Comparative Example 1 and Examples 4 to 6 and Comparative Example 2, the abundance ratio of the magnetic powder surface of the binder in the Example was higher than the abundance ratio in the Comparative Example. It can be seen that the compound represented by the general formula (I) used in the examples showed the action of modifying the surface of the magnetic powder and increasing the binder adsorption amount. Increasing the amount of binder adsorbed to the magnetic powder in the magnetic coating leads to an improvement in the dispersibility of the magnetic powder. Therefore, it was confirmed that the compounds used in the examples can function as a dispersant in the magnetic coating. Since the coated surface applied with the magnetic coating material prepared in the example showed higher surface smoothness than the coated surface coated with the magnetic coating material prepared in the comparative example, the compound used in the example was magnetic in the magnetic coating material. It turns out that the effect | action which improves the dispersibility of powder was shown.

5). Examples and comparative examples using stearylamine

[Example 7]
When a magnetic recording medium was prepared by the following method and the magnetic layer surface was observed with an optical microscope, no precipitate was observed.
Nonmagnetic layer coating solution component (1)
Iron oxide powder (particle size: 0.15 × 0.02 μm): 70 parts Alumina (α conversion: 50%, particle size: 0.05 μm): 8 parts Carbon black (particle size: 15 nm): 20 parts Stearic acid : 1.5 parts Butyl stearate: 1.5 parts Stearylamine: 0.3 parts Vinyl chloride copolymer (containing -SO ₃ Na group: 1.2 × 10 ⁻⁴ equivalent / g): 10 parts Polyester polyurethane resin (Tg: 40 ° C., contained —SO ³ Na group: 1 × 10 ⁻⁴ equivalent / g): 6.6 parts Cyclohexanone: 130 parts Methyl ethyl ketone: 60 parts
Nonmagnetic layer coating solution component (2)
Stearic acid: 1.5 parts Stearate butyl: 1.5 parts Stearylamine: 0.3 parts Cyclohexanone: 40 parts Methyl ethyl ketone: 60 parts
Nonmagnetic layer coating solution component (3)
Polyisocyanate: 5.5 parts Cyclohexanone: 8 parts Methyl ethyl ketone: 18 parts

Magnetic layer coating solution component (1)
Ferromagnetic metal powder: 100 parts 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
Vinyl chloride-hydroxypropyl acrylate copolymer (containing —SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalent / g): 8.0 parts Polyester polyurethane resin (containing —SO ₃ Na group: 1.0 × 10 ^{− 4} equivalents / g): 15.5 parts α-alumina (average particle size: 0.15 μm): 12 parts α-alumina (average particle size: 0.05 μm): 4 parts 0.4 parts of carbon black (average particle size) : 50 nm, DBP oil absorption: 72 cc / 100 g)
N-hydroxyurethane: 3.3 parts stearic acid: 0.5 parts butyl stearate: 1.5 parts stearylamine: 0.3 parts cyclohexanone: 250 parts methyl ethyl ketone: 70 parts
Magnetic layer coating solution component (2)
Polyisocyanate: 3.0 parts Methyl ethyl ketone: 167 parts

  After kneading the non-magnetic layer coating solution component (1) with a kneader, adding (2) and stirring, the mixture is then dispersed in a sand mill with a residence time of 90 minutes, and then added with (3) and stirred and filtered. A nonmagnetic layer coating solution was obtained. Separately, after kneading the magnetic layer coating liquid component (1) with a kneader, the dispersion time was dispersed in a sand mill with a residence time of 60 minutes, and the magnetic layer coating liquid component (2) was added to this and stirred and filtered. A magnetic layer coating solution was obtained.

Backcoat layer coating solution component (1)
Carbon black 1 (average particle diameter: 20 nm): 80 parts Carbon black 2 (average particle diameter: 100 nm): 8 parts α-Fe ₂ O ₃ (average major axis length: 0.1 μm): 1 part Nitrocellulose resin: 65 Part Polyester polyurethane resin (Toyobo Co., Ltd .: UR-8300): 35 parts Methyl ethyl ketone: 260 parts Toluene: 260 parts Cyclohexanone: 260 parts
Backcoat layer coating solution component (2)
Stearic acid: 1 part Butyl stearate: 2 parts Methyl ethyl ketone: 210 parts Toluene: 210 parts Cyclohexanone: 210 parts

  The backcoat layer coating solution component (1) was put into a ball mill and dispersed for 24 hours. The backcoat layer coating solution component (2) was mixed and stirred in the dispersed slurry, and then dispersed again for 3 hours in a ball mill. One part of an isocyanate compound (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added to 100 parts of the paint after filtration, and the mixture was stirred and mixed to obtain a backcoat layer coating solution.

  The nonmagnetic layer coating solution is applied on a support made of a polyethylene terephthalate film having a thickness of 5 μm so that the thickness after drying and calendering becomes 1.1 μm. On the nonmagnetic layer, a magnetic layer is coated. The coating for coating is applied by dry-on-wet so that the thickness of the magnetic layer after orientation treatment, drying and calendering treatment is 0.05 μm, and after orientation treatment, it is dried using a dryer and far infrared rays, and then non-coated On the support opposite to the magnetic layer / magnetic layer, the backcoat layer coating solution is dried, coated to a thickness of 0.5 μm after calendering, and dried using a dryer and far infrared rays to form a web. Obtained. The web thus obtained was mirror-treated on a 5-stage calendar made of a metal roll under the conditions of a temperature of 80 ° C. and a linear pressure of 200 kg / cm and wound up. The raw roll was aged (heat treated) at 68 ° C. for 36 hours, and then cut into ½ mm width to obtain a magnetic tape.

[Comparative Example 3]
A magnetic tape was produced in the same manner as in Example 7 except that 3.3 parts of N-hydroxyurethane in the magnetic layer coating solution component of Example 7 was changed to 5.0 parts of octanohydroxamic acid. When the surface of the magnetic layer was observed with an optical microscope, precipitates were observed. The precipitate on the surface of the magnetic layer was collected with a manipulator and analyzed by FT-IR. As a result, it was confirmed that the precipitate was stearylamine.

  In Example 7, no precipitate was observed on the surface of the magnetic layer, whereas in Comparative Example 3, stearylamine was precipitated on the surface of the magnetic layer. Therefore, the surface modifier of the present invention is suitable for combined use with stearylamine. I understand that.

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

Claims (16)

A powdery surface modifier comprising a compound represented by the following general formula (I) , wherein the powder is selected from the group consisting of a magnetic powder and a nonmagnetic powder .

[In the general formula (I), R ¹ represents an alkyl group or an aryl group, R ² represents a hydroxyl group. ] The surface modifier for powder according to claim 1 , which is used as a dispersant for magnetic paint or a dispersant for nonmagnetic paint. A magnetic recording medium having a magnetic layer comprising a ferromagnetic powder and a binder on a nonmagnetic support,
The magnetic recording medium, wherein the magnetic layer further contains a compound represented by the following general formula (I):

[In the general formula (I), R ¹ represents an alkyl group or an aryl group, R ² represents a hydroxyl group. ] The magnetic recording medium according to claim 3 , wherein the magnetic layer further includes stearylamine. The magnetic recording medium according to claim 3 or 4 , wherein a nonmagnetic layer containing a nonmagnetic powder and a binder is provided between the nonmagnetic support and the magnetic layer. The magnetic recording medium according to claim 5 , wherein the nonmagnetic layer further includes a compound represented by the general formula (I). The non-magnetic layer, a magnetic recording medium according to claim 5 or 6 further including stearylamine. Wherein the binder magnetic recording medium according to any one of claims 3-7 comprising a polyurethane resin. A magnetic paint comprising the surface modifier for powder according to claim 1, magnetic powder, and a binder. The magnetic paint according to claim 9 , wherein the magnetic powder is a ferromagnetic hexagonal ferrite powder or a ferromagnetic metal powder. The magnetic paint according to claim 9 or 10 , wherein the binder contains a polyurethane resin. The magnetic paint according to any one of claims 9 to 11 , which is used as a coating liquid for forming a magnetic layer of a magnetic recording medium. A nonmagnetic paint comprising the surface modifier for powder according to claim 1, a nonmagnetic powder, and a binder. The nonmagnetic paint according to claim 13 , wherein the nonmagnetic powder is a nonmagnetic metal powder. The nonmagnetic paint according to claim 13 or 14 , wherein the binder contains a polyurethane resin. The nonmagnetic paint according to any one of claims 13 to 15 , which is used as a coating liquid for forming a nonmagnetic layer of a magnetic recording medium.