JP2001331921A - Magnetic recording medium, magnetic powder used for magnetic recording medium, its manufacturing method and surface treatment method of powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a magnetic recording medium having a coating film of a magnetic layer, being excellent in durability, and to provide magnetic powder used for the magnetic layer and a method capable of uniformly and efficiently reforming the surface of the powder of this kind, when the magnetic recording medium of this kind is realized. SOLUTION: A surface finishing agent is uniformly adhered to the surface of a magnetic powder base material by mechanically loosening the magnetic powder base material beforehand and successively spraying or dropping the surface finishing agent on the base material while stirring the base material uniformly and slowly so that excess heat generation is not locally generated. Thus obtained magnetic powder is used to obtain the magnetic recording medium provided with the magnetic layer having prescribed physical properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating type magnetic recording medium obtained by forming a magnetic layer coating film on a non-magnetic support, a magnetic powder used for this type of magnetic recording medium, The present invention relates to a powder surface treatment technique suitable for obtaining various types of magnetic powder.

[0002]

2. Description of the Related Art A coating type magnetic tape is conventionally produced, for example, as follows. First, the magnetic powder is mixed with a binder resin solution, and kneaded with a kneader or the like so that the binder resin is adapted to the magnetic powder as much as possible. Furthermore, a solvent is gradually added with stirring to obtain a fluid paint, and
After stirring, the magnetic powder is further strongly mixed and stirred with a disperser such as a sand mill to disperse the magnetic powder. Also, fillers and lubricants are added at a predetermined time during such a process,
These are stirred so that they are uniformly mixed. As the lubricant in this case, a fatty acid or a fatty acid ester (hereinafter, referred to as a fatty acid or the like) is generally used. Next, after adding a crosslinking agent to the magnetic paint thus obtained, the magnetic paint is quickly applied to form a magnetic layer coating film on a base (non-magnetic support) such as polyester. Thereafter, for example, a magnetic field orientation treatment for orienting the magnetic powder in the magnetic layer in a predetermined direction by an external magnetic field, a surface treatment for smoothing the surface of the magnetic layer, and a cutting process for cutting the tape to a predetermined width are performed. Then, a magnetic tape as a finished product is obtained.

Meanwhile, in magnetic recording media such as coating-type magnetic tapes and magnetic disks, metal powders having better magnetic properties have recently been used as magnetic powders instead of conventional γ-iron oxide powders. To do more. Therefore, if the conventional method as described above is applied as it is,
The following problems occur.

That is, γ used in the prior art
-In the case of magnetic powders made of iron oxide, etc., although the active sites on the surface have no catalytic activity to modify other substances by acting on them, the reaction activity was not so high. In recent magnetic powders, which are the center, the fineness of the particles has been advanced and the composition of the surface has been changed as compared with the conventional magnetic powder, so that the activity on the surface of the powdery fine particles has been relatively high. For this reason, when the magnetic recording medium is manufactured according to the conventional method as described above, in the manufacturing process, the solvent is deteriorated due to the catalytic action or reaction activity of the surface of the magnetic powder. Fatty acids and the like used as an agent are adsorbed on the particle surface of the magnetic powder, so that the fatty acids and the like cannot move toward the surface of the magnetic layer coating film after the formation of the magnetic layer coating film. Loses the original lubricating function (inhibits the lubricating function) and denatures the cross-linking agent added just before the coating step, so that the binder resin and other constituent materials (magnetic powder and non-magnetic support) Problems such as a decrease in the bonding force between them and the strength of the binder resin itself occur. All of these causes a decrease in the durability of the magnetic layer coating film and, consequently, a decrease in the durability of the magnetic recording medium.

In order to avoid such a problem and improve the durability of the coating film of the magnetic layer, it is necessary to suppress the surface activity of the magnetic powder to prevent the adsorption of fatty acids and the like. As means for that purpose, for example, a magnetic powder whose surface is modified with a polyfunctional low-molecular compound such as citric acid or the like is used (Japanese Patent Laid-Open No. 1-11 / 1999).
Japanese Patent Application Laid-Open No. 6-105214), and use of magnetic powder whose surface has been modified with an organic acid having an acid dissociation constant (pKa) higher than that of a fatty acid (see JP-A-4-105214). .

[0006]

However, although it has been proposed to use a magnetic powder having been subjected to the above-mentioned surface treatment, as far as the inventor of the present application knows, it has been proposed to use such a magnetic powder. There is no concrete proposal of the surface treatment method. In other words, the surface treatment agent can be uniformly and efficiently modified on the surface of the magnetic powder without any adverse effects by applying the surface treatment agent to the surface of the magnetic powder in any state and to what extent. It was completely unknown whether it could be done. For this reason, in practice, the effect of applying the surface treatment agent to the surface of the magnetic powder and the state of application were not appropriate, so that the expected effect could not be obtained. Problems may arise.

For example, when the surface treating agent is not strongly bonded to the surface of the magnetic powder, the magnetic powder is easily peeled off from the surface of the magnetic powder due to the approach of another material or the like, and the magnetic powder regains its surface activity. As a result, a decrease in the durability of the magnetic layer coating film (and, consequently, the magnetic recording medium) cannot be avoided. In addition, when the magnetic powder or the like is agglomerated due to the action of the surface treating agent (so-called stepped state), not only the desired surface coating effect cannot be obtained but also the magnetic layer coating film. It also has an adverse effect on the durability and magnetic properties. Further, because the amount of the surface treatment agent acting on the magnetic powder was excessive, if the surplus surface treatment agent not adhered to the surface of the magnetic powder remained in the magnetic paint or the magnetic layer, A situation occurs in which they adversely affect other constituent materials (for example, change physical properties).

The present invention mainly addresses the above-mentioned problems in magnetic recording media, and an object of the present invention is to firstly realize a magnetic recording medium having a magnetic layer coating film having excellent durability. A second object is to provide a magnetic powder suitable for realizing such a magnetic recording medium and a method for easily obtaining the magnetic powder. In the present invention, a surface treatment technique generally applicable not only when the surface of the magnetic powder is coated, but also when the surface of the fine particle powder having active sites on the surface needs to be uniformly and efficiently coated. Is also provided.

[0009]

Means for Solving the Problems (Invention according to claim 1)
The invention according to claim 1 of the present application employs the following configuration as means for achieving the first object. That is, a magnetic layer formed by applying a magnetic paint containing a magnetic powder, a binder resin, a fatty acid, and an organic solvent on a nonmagnetic support or on a layer formed on the nonmagnetic support. In the magnetic recording medium having a thickness of the coating layer including the magnetic layer formed on the non-magnetic support is 1.5 to 5.0 μm
The thickness of the magnetic layer alone is 1.5 to 4.0 μm, and the crosslinkability is 50 times or more. However, the crosslinkability in this case is defined as follows.

<Definition of crosslinkability>: A cotton swab is impregnated with cyclohexanone, and the surface of the magnetic layer of the magnetic recording medium is repeatedly rubbed in one direction at a rate of about once per second with the cotton swab. The number of times of rubbing until the (nonmagnetic support) is exposed is defined as crosslinkability. In this case, the angle between the swab and the surface of the magnetic recording medium is about 30 °, and the load strength is about 50 g.

The crosslinkability varies depending on the porosity in the magnetic layer, the type of solvent, and the like, but generally increases as the crosslinking of the binder resin in the magnetic layer progresses. The more effectively the cross-linking agent is used, the more this cross-linkability increases. On the other hand, magnetic powder (for example, metal powder) has a catalytic action to modify the cross-linking agent, and the surface modification efficiency of the magnetic powder by a surface treating agent (in the present invention, an organic acid is used as described later, the same applies hereinafter). The higher the value, the more the denaturing catalytic action on the surface of the magnetic powder can be suppressed. Therefore, the crosslinking property is an index of the surface modification efficiency of the magnetic powder.

(Invention according to claim 2) In the invention according to claim 2 of the present application, the following configuration is employed as means for achieving the first object. That is, on a non-magnetic support,
Or a magnetic recording medium having a magnetic layer formed by applying a magnetic paint containing a magnetic powder, a binder resin, a fatty acid and an organic solvent on a layer formed on a non-magnetic support, The thickness of the coating layer including the magnetic layer formed on the support is 1.5 to 5.0 μm, the thickness of the magnetic layer alone is 1.5 to 4.0 μm, and the fatty acid extraction rate is 1% or more. And 50% or less. However, the fatty acid extraction rate in this case is defined as follows.

<Definition of Fatty Acid Extraction Rate>: A magnetic recording medium having a unit volume of a magnetic layer is cut out to obtain a sample, which is then subjected to hexane → tetrahydrofuran → acetic acid using hexane, tetrahydrofuran and acetic acid. The fatty acid is extracted from the sample in three stages in the order of the above, and the ratio of the amount of the fatty acid extracted by the acetic acid to the obtained amount of the total fatty acid (the total amount of the fatty acid present in the magnetic layer) is determined by the fatty acid extraction. Defined as rate.

The surface modification efficiency of the magnetic powder in the magnetic layer of the magnetic recording medium can be determined by the above-described fatty acid extraction pattern. In this case, the fatty acid extracted by the third acetic acid is mainly the fatty acid adsorbed on the surface of the magnetic powder. Therefore, the higher the surface modification efficiency of the magnetic powder with the surface treatment agent, the lower the above-mentioned fatty acid extraction rate.

(Invention of claim 3) In the invention of claim 3 of the present application, the following configuration is adopted as means for achieving the above-mentioned second object. That is, on a non-magnetic support, or on a layer formed on the non-magnetic support,
In the magnetic powder used for the magnetic recording medium having a magnetic layer formed by applying a magnetic paint containing a magnetic powder, a binder resin, a fatty acid, and an organic solvent, the fatty acid adsorption amount measured under the following conditions is: 5mg / g or more and 50
mg / g or less.

<Measurement Conditions of Fatty Acid Adsorption Amount>: Magnetic Powder 1
g fatty acid solution containing 0.5% by weight of fatty acid
ml (the fatty acid content is 835 mg),
After standing for a day, the supernatant is collected, the amount of residual fatty acid therein is measured, and the amount of fatty acid adsorbed is calculated from the measured value.

When a fatty acid solution is added to the magnetic powder and left for a certain period of time, if a basic active site exists on the surface of the magnetic powder, the fatty acid adheres thereto. Therefore, the surface modification efficiency of the magnetic powder (the magnetic powder material after the surface modification) can be determined by measuring the amount of the fatty acid adsorbed. That is, the smaller the amount of the fatty acid adsorbed is, the more efficiently the surface of the magnetic powder is modified. The magnetic powder according to the present invention is characterized by having a fatty acid adsorption amount having such a meaning of 5 mg / g or more and 50 mg / g or less.

(Invention of Claim 4) In the invention of Claim 4 of the present application, the following configuration is adopted as means for achieving the above-mentioned second object. That is, on a non-magnetic support, or on a layer formed on the non-magnetic support,
In the magnetic powder used for a magnetic recording medium having a magnetic layer formed by applying a magnetic paint containing a magnetic powder, a binder resin, a fatty acid, and an organic solvent, a modified organic solvent measured under the following conditions: Production amount is 600mg / g
Or less (preferably 500 mg / g or less).

<Measurement conditions for the amount of modified organic solvent produced>
1 g of magnetic powder is mixed with an organic solvent 2 used for preparing a magnetic paint.
After 0 ml was added and the mixture was allowed to stand at 30 ° C. for 3 days, the supernatant was collected, and the amount of the resulting organic solvent-modified product was measured.

The active sites present on the surface of the magnetic powder have a catalytic activity to modify the organic solvent used when preparing the magnetic paint. For this reason, the more the coating of the magnetic powder surface is incomplete, the larger the amount of the organic solvent-modified product produced. When the magnetic powder surface is uniformly coated by increasing the coating efficiency, the amount of the organic solvent denatured product is reduced. Therefore, the amount of the modified organic solvent is an index for determining the surface modification efficiency of the magnetic powder of the surface treating agent. The magnetic powder according to the present invention is characterized in that the amount of the modified organic solvent having such a meaning is not more than 600 mg / g.

(Embodiments of Claims 5, 6, 7, and 8) The magnetic powder as described above is a magnetic powder material,
That is, it can be obtained by applying the following powder surface treatment method to the magnetic powder (specifically, for example, metal powder) before the surface treatment. In other words, when the surface of a powder composed of fine particles having a site having a high reaction activity (a basic active site in the case of the above-mentioned magnetic powder) is coated on the surface with a surface treating agent, the powder is previously treated with a chopper or the like. The surface treatment agent is mechanically loosened using a crusher and then sprayed or dropped onto the surface of the magnetic powder material while uniformly and gently mixing without excessive heat generation locally. Is applied uniformly.

As the surface treating agent to be used, a phosphoric acid-based organic acid (specifically, for example, phenylphosphonic acid) is preferable. This type of surface treatment agent has a strong acidity and a relatively high acid dissociation constant compared to fatty acids, so it is suitable for magnetic powders, such as metal powders, which have many basic active sites on the surface. And strongly binds to the active site on the surface. Therefore, even if fatty acids and other materials attack this portion, the surface treatment agent is not peeled off from the surface of the metal powder.

However, in the case where the surface of the magnetic powder is coated with such a surface treating agent having a strong adhesive force, the surface treating agent must be applied to the surface of the magnetic powder in an initial stage in an appropriate state. It cannot be denied that the surface treatment agent is applied to a portion of the magnetic powder surface which is completely unrelated to the predetermined active site and is not separated therefrom, and as a result, there is a possibility that a problem such as the formation of a step may occur.

In order to prevent this kind of problem from occurring,
In the present invention, the method described above, that is, the magnetic powder material (magnetic powder before surface treatment) is mechanically loosened in advance, and then uniformly and gently mixed without locally generating excessive heat. The mechanical element added to the magnetic powder is appropriately controlled by, for example, spraying or dropping the surface treatment agent. As a result, the surface treatment agent can be uniformly applied only to the active sites on the surface of the magnetic powder, and even to the surface of the magnetic powder, so that a problem such as generation of a step in the surface treatment step for the magnetic powder is prevented. It becomes possible.

(Others) The present invention is not limited to a magnetic recording medium in which a magnetic layer is directly provided on a nonmagnetic support, but another layer (nonmagnetic layer) is provided as a lower layer on the nonmagnetic support. The present invention is also applicable to a magnetic recording medium having a magnetic layer provided thereon or a magnetic recording medium having a backcoat layer provided on the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is formed. Further, the surface treatment method of the powder according to the present invention, in the various types of magnetic recording media as described above, a layer other than the magnetic layer, powder fine particles having a highly reactive active site on the surface is contained. When it is present, it can be similarly applied to these fine powder particles. Next, examples of more specific configurations, materials, means, and the like that can be employed in the present invention will be listed.

<Magnetic Layer> In the present invention, the thickness of the magnetic layer is
1.5 μm or more and 4.0 μm or less, preferably 2 μm or more and 4.0 μm or less
μm or less is more preferable. This range is preferred because 1.
If the thickness is less than 5 μm, the head output becomes small due to a small leakage magnetic field from the magnetic layer, and if it exceeds 4.0 μm, the head output becomes small due to thickness loss. The coercive force in the longitudinal direction of the tape is 135-280 kA / m (1700-3
500 Oe), the residual magnetic flux density in the longitudinal direction of the tape is 0.18
T (1800 G) or more is preferable. This range is preferable because, when the coercive force is less than 135 kA / m, the output decreases due to the demagnetizing field, and when it exceeds 280 kA / m, writing by the head becomes difficult. The reason why the residual magnetic flux density is preferably equal to or greater than 0.18 T is that if the residual magnetic flux density is less than 0.18 T, the output decreases. Coercive force is 160-2
Those with 40 kA / m (2000 to 3000 Oe) and residual magnetic flux density of 0.2 to 0.4 T (2000 to 4000 G) are more preferable.

<Layer formed between nonmagnetic support and magnetic layer> An undercoat layer is provided between the nonmagnetic support and the magnetic layer for the purpose of improving the durability of the tape and the like. Is preferred. The thickness of the undercoat layer is preferably 0.01 to 1.0 μm, and 0.1 to 0.1 μm.
7 μm is more preferred. This range is preferably 0.0
If it is less than 1 μm, the durability of the magnetic tape may be deteriorated. If it exceeds 1.0 μm, not only the effect of improving the durability of the magnetic tape is saturated, but also the total thickness of the tape becomes thicker, and the length of the tape per roll is reduced. This is because the storage capacity becomes shorter and the storage capacity becomes smaller.

In the undercoat layer, carbon black is added for the purpose of improving the conductivity, and non-magnetic particles are added for the purpose of controlling the viscosity of the paint and the rigidity of the tape. Non-magnetic particles used for the undercoat layer include titanium oxide, iron oxide, and alumina, and iron oxide alone or a mixed system of iron oxide and alumina is used. In the undercoat layer, 15 to 35% by weight of carbon black having a particle size of 10 to 100 nm, based on the weight of the entire inorganic powder in the undercoat layer, 0.05 to 0.20 μm in major axis length, and minor axis length 5-200n
m of non-magnetic iron oxide in an amount of 35 to 83% by weight and, if necessary, 0 to 20% by weight of alumina having a particle size of 10 to 100 nm. This is preferable because the surface roughness is reduced. The non-magnetic iron oxide is usually acicular, but when granular or amorphous non-magnetic iron oxide is used, the particle size is 5 to 200 n.
m of iron oxide is preferred. Note that addition of a large-diameter CB having a particle size of 100 nm or more is not excluded as long as the surface smoothness is not impaired. In that case, the CB amount is preferably such that the sum of the small particle size CB and the large particle size CB is within the above range.

The carbon black (C) to be added to the undercoat layer
As B), acetylene black, furnace black, thermal black and the like can be used. Usually, particles having a particle size of 5 nm to 200 nm are used.
100 nm is preferred. This range is preferable because the carbon black has a structure, so that when the particle size is 10 nm or less, CB is difficult to disperse.
If the thickness is 100 nm or more, the smoothness becomes poor. CB
The addition amount varies depending on the particle diameter of CB, but is 15 to 35.
% By weight is preferred. This range is preferable because the effect of improving conductivity is poor when the content is less than 15% by weight, and the effect is saturated when the content exceeds 35% by weight. Particle size 15nm-80n
More preferably, CB having a particle size of 20 nm to 50 nm is used in an amount of 20 to 30% by weight.
More preferably, it is used. By adding carbon black having such a particle size and amount, electric resistance is reduced and running unevenness is reduced.

The non-magnetic iron oxide to be added to the undercoat layer is preferably in the form of a needle having a major axis length of 0.05 to 0.20 μm and a minor axis length (particle size) of 5 to 200 nm. In the case of an amorphous material, the particle size is preferably 5 to 200 nm. The particle size is more preferably 0.05 to 150 nm, and the particle size is 0.05 to 1 nm.
00 nm is more preferred. Needle-like ones are more preferable because the orientation of the magnetic layer is improved. The addition amount is 35-
83% by weight is preferred, and 40-80% by weight is more preferred. A particle size in this range (short axis length in the case of a needle shape) is preferable because if the particle size is less than 5 nm, uniform dispersion is difficult.
If m exceeds m, unevenness at the interface between the undercoat layer and the magnetic layer increases. The addition amount in this range is preferable because the effect of improving the strength of the coating film is small when the amount is less than 35% by weight, and the strength of the coating film decreases when the amount exceeds 83% by weight.

The undercoat layer may contain alumina in addition to iron oxide. The particle size of alumina is preferably 10 to 100 nm, more preferably 20 to 100 nm, and 30 to 10 nm.
0 nm is more preferred. A particle size in this range is preferable because if the particle size is less than 10 nm, uniform dispersion is difficult and 100 n
If m exceeds m, unevenness at the interface between the undercoat layer and the magnetic layer increases. The addition amount of alumina is usually 0 to 20% by weight, but 2 to 10% by weight is more preferable.

<Backcoat Layer> In the magnetic recording medium of the present invention, it is preferable to provide a backcoat layer as described above. For this type of back coat layer, a conventionally known back coat layer having a thickness of 0.2 to 0.8 μm can be used for the purpose of improving running properties. The reason why this range is good is that when the thickness is less than 0.2 μm, the effect of improving the running property is insufficient, and when the thickness exceeds 0.8 μm, the total thickness of the tape becomes thick and the storage capacity per one roll becomes small. For example, carbon black (CB) is added to the back coat layer in order to further improve the running property. As the carbon black in this case, acetylene black, furnace black, thermal black, or the like can be used. Usually, a small particle size carbon black and a large particle size carbon black are used. As the small particle size carbon black, those having a particle size of 5 nm to 200 nm are used, and those having a particle size of 10 nm to 100 nm are more preferable. If the particle size is less than 10 nm, it is difficult to disperse CB. If the particle size is more than 100 nm, it is necessary to add a large amount of CB, and in any case, the surface becomes rough, and the set-off (emboss) to the magnetic layer is caused. Because it becomes. As the large particle size carbon black, 5 of the small particle size carbon black
When a large particle size carbon black having a particle size of 300 to 400 nm is used, the surface is not roughened, and the effect of improving the running property is increased. The total amount of the small particle size carbon black and the large particle size carbon black is 60 to 98% by weight based on the total weight of the inorganic powder contained in the back coat layer.
Is preferable, and 70 to 95% by weight is more preferable. The center line average surface roughness Ra of the back coat layer is preferably from 3 to 8 nm, more preferably from 4 to 7 nm.

Further, iron oxide having a particle diameter of 0.1 μm to 0.6 μm is preferably added to the back coat layer for the purpose of improving strength, more preferably 0.2 μm to 0.5 μm. The addition amount of iron oxide is preferably 2 to 40% by weight based on the total weight of the inorganic powder contained in the back coat layer, and 5 to 3% by weight.
0% by weight is more preferred.

<Fatty Acid> It is preferable to use a fatty acid having 10 or more carbon atoms. The fatty acid having 10 or more carbon atoms may be any of linear, branched and cis / trans isomers, but a linear type having excellent lubricating performance is preferred. Examples of such fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid and the like. Among these, myristic acid, stearic acid, palmitic acid and the like are preferable.

The fatty acid is usually used in an amount of 0.5 to 5 with respect to the magnetic powder.
% By weight. When the amount is less than 0.5% by weight, the amount required as a lubricant does not reach the required amount, and the running durability at the time of sliding of the tape / head due to the lubricating action on the tape surface is not preferable. On the other hand, if it exceeds 5% by weight, although it depends on the molecular weight, the excess fatty acid seeps onto the tape surface and causes blooming, and the excess fatty acid is adsorbed on the magnetic powder or becomes compatible with the binder resin and becomes plastic. Cause the tape to lose its durability.

<Magnetic Powder> Ferromagnetic iron-based metal powder is preferably used as the magnetic powder. In this case, the average major axis length of the ferromagnetic iron-based metal powder is preferably 0.03 to 0.2 μm, and 0.03 to 0.2 μm.
0.18 μm is more preferable, and 0.04 to 0.15 μm is further preferable. Average long axis length of ferromagnetic iron-based metal powder is 0.03
When it is less than μm, the surface energy increases and the catalytic activity also increases. On the other hand, if it is larger than 0.2 μm, the coercive force decreases and the particle noise based on the particle size increases. The average major axis length is obtained by actually measuring the particle size of a photograph taken with a scanning electron microscope (SEM),
It is obtained from the average value of 100 pieces. The BET specific surface area of the ferromagnetic iron-based metal powder is preferably 35 m ² / g or more, more preferably 40 m ² / g or more, and 50 m ² / g or more.
Most preferably, it is at least m ² / g.

<Organic Solvent> As the solvent for the undercoat layer and the coating for the magnetic layer, any of those conventionally used for magnetic recording media can be used. For example, ketone solvents such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone are used. solvent,
Ether solvents such as tetrahydrofuran and dioxane, and acetate solvents such as ethyl acetate and butyl acetate are used alone or as a mixture, and further used in a mixture with toluene.

<Binder Resin> Examples of the binder resin usable for the undercoat layer and the magnetic layer include vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl resin. Examples thereof include a combination of at least one selected from an alcohol copolymer resin, a vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, and nitrocellulose with a polyurethane resin. Can be Among them, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination. Polyurethane resins include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and the like.

Further, as a functional group, -COOH, -SO _{3
M, -OSO 2 2M, -P =} O (OM) 3, -O-P =
O (OM) _2, [M represents a hydrogen atom, an alkali metal base or an amine salt], - OH, -NR 'R '', - N + + R'''
R ″ ″ R ′ ″ ″ [R ′, R ″, R ′ ″, R ″ ″,
R ′ ″ ″ is a hydrogen or hydrocarbon group], and a binder resin such as a urethane resin made of a polymer having an epoxy group is preferably used. Such a binder resin is preferable because the dispersibility of the magnetic powder and the like is improved as described above. When two or more resins are used in combination, it is preferable that the polarities of the functional groups are the same, and a combination of -SO3M groups is particularly preferable.

These binder resins are used in the magnetic layer in an amount of 7 to 5 parts by weight based on 100 parts by weight of the ferromagnetic iron-based metal powder.
0 parts by weight, preferably 10 to 35 parts by weight. Particularly, as the binder resin, vinyl chloride resin 5
It is most preferred to use a composite of 〜30 parts by weight and 2-20 parts by weight of a polyurethane resin.

It is desirable to use together with these binder resins, a thermosetting cross-linking agent that bonds to a functional group contained in the binder resin and cross-links them. Examples of such cross-linking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and the reaction products of these isocyanates with those having a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates such as are preferred. These crosslinking agents are generally used in a proportion of 10 to 50 parts by weight based on 100 parts by weight of the binder resin. More preferably, it is 15 to 35 parts by weight.

<Other Additives> Conventionally known abrasives can be added to the magnetic layer. Examples of these abrasives include α-alumina, β-alumina, silicon carbide, chromium oxide, oxide Cerium, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, boron nitride, mainly those having a Mohs hardness of 6 or more are used alone or in combination, Among these, alumina is particularly preferable because of its high hardness and excellent head cleaning effect with a small amount of addition. The particle size of the abrasive depends on the thickness of the magnetic layer, but is usually preferably from 0.02 to 0.4 μm, more preferably from 0.03 to 0.3 μm, as the average particle size. The amount of the abrasive added is 5 to 20% by weight based on the ferromagnetic iron-based metal powder.
Is preferred. More preferably, it is 8 to 18% by weight.

Further, the magnetic layer of the present invention may contain conventionally known carbon black (CB) for the purpose of improving conductivity and surface lubricity. Examples of such CB include acetylene black and furnace black. And thermal black. In that case, the particle size is 5n
m to 200 nm, but a particle size of 10 nm to
100 nm is preferred. This range is preferable because the dispersion of CB is difficult when the particle size is 10 nm or less,
If it is 100 nm or more, it is necessary to add a large amount of CB, and in any case, the surface becomes rough, which causes a decrease in output. The addition amount is 0.
2-5% by weight is preferred. More preferably, it is 0.5 to 4% by weight.

<Nonmagnetic Support (Base)> Examples of the nonmagnetic support that can be used in the magnetic recording medium of the present invention include polyethylene terephthalate, polyethylene naphthalate, aromatic polyamide, aromatic polyimide and the like. The thickness of the nonmagnetic support varies depending on the application, but is usually 2 to 5 μm.
Is used. More preferably, it is 2.5 to 4.5 μm. When a non-magnetic support having a thickness in this range is used, it is difficult to form a film if the thickness is less than 2 μm, the strength of the tape is small, and if it exceeds 5 μm, the total thickness of the tape is large, and the storage capacity per tape roll is large. Is smaller.

<Mixing / Stirring Means> In the powder surface treatment method according to the present invention, as a means for mixing or stirring the powder, for example, a rolling method such as Aggromaster (AGM-25) manufactured by Hosokawa Micron Corporation is used. A gas blow-up stirrer utilizing a flow effect, a rotary mixer such as an axial mixer manufactured by Matsuyama Heavy Industries, a Henschel mixer manufactured by Mitsui Mining, and the like can be used.

<Crushing Means> As means for mechanically unraveling (crushing) the powder, for example, a Henschel mixer (Model FM-20B) manufactured by Mitsui Mining Co., Ltd., an agromaster (AGM-25) manufactured by Hosokawa Micron Co., Ltd. A pulse jet type crusher or the like attached to the device can be used.

<Spray / Drip Means> As a means for spraying or dropping the surface treating agent, for example, a spray gun mounted on an agromaster (AGM-25) manufactured by Hosokawa Micron Corp. or an axial mixer manufactured by Matsuyama Heavy Industries, Ltd. is used. be able to. Although not particularly limited, it is preferable that the mist can be sprayed as wide as possible and the mist is easily diffused uniformly in the reaction system.

[0048]

The magnetic recording medium according to claim 1 has a crosslinkability of 50.
More than once. This is because, since the surface modification efficiency of the magnetic powder contained in the magnetic layer coating film is high, the catalytic action of the magnetic powder surface on the modification of the crosslinking agent is suppressed. The crosslinking of the binder resin contained in the layer was not hindered, meaning that the molecular chains of the binder resin were to be sufficiently bonded by the crosslinking. Since the binding strength of the binder resin is thus increased, the durability of the magnetic layer coating film can be improved.

The magnetic recording medium according to claim 2 has a fatty acid extraction ratio of 1% or more and 50% or less. This directly means that the amount of the fatty acid adsorbed on the surface of the magnetic powder is not more than 50% of the total amount of fatty acids present in the magnetic layer coating film, but indirectly, This means that the surface modification efficiency of the magnetic powder by the treating agent was high, so that the adsorption of the fatty acid to the surface of the magnetic powder was suppressed to a relatively low level. In other words, the fact that the adsorption of the fatty acid on the surface of the magnetic powder is suppressed to a relatively low level proves that the surface of the magnetic powder has been efficiently and uniformly modified by the surface treating agent. Therefore, according to this magnetic recording medium, not only the lubricating action of the fatty acid is not hindered, but also the denaturing catalytic action of the surface of the magnetic powder on other materials is suppressed.

The magnetic powder according to the third aspect has a fatty acid adsorption amount of 50 mg / g or less measured under the above-mentioned predetermined conditions. In the case of a magnetic powder (metal powder) used in a conventional magnetic recording medium (magnetic tape), the fatty acid adsorption amount measured in the same manner as described above is, for example, 57 to 60 mg / g (see Examples described later). Comparative Examples 1 to 3 described above). In other words, the magnetic powder according to the present invention has a smaller amount of fatty acid adsorption than the conventional magnetic powder, which means that the surface of the magnetic powder according to the present invention is efficiently modified. Therefore, when the magnetic powder of the present invention is used for the magnetic recording medium, not only can the lubricating action of the fatty acid be exerted well, but also as in the case of the above-described magnetic recording medium of the present invention, when forming the magnetic layer coating film. In this case, the crosslinking of the binder resin is not hindered, so that a magnetic layer coating film having excellent durability can be formed.

According to a fourth aspect of the present invention, the amount of the modified product of the organic solvent measured under the above-mentioned predetermined conditions is 600 mg.
/ G or less. In the case of a magnetic powder (metal powder) used in a conventional magnetic recording medium (magnetic tape), the amount of the modified product of the organic solvent measured in the same manner as described above is, for example, 85.
The amount is 0 to 1500 mg / g (see Comparative Examples 1 to 3 described in [Examples] described later). In other words, the magnetic powder according to the present invention has a smaller amount of a modified product of the organic solvent than the conventional magnetic powder, but this means that the surface of the magnetic powder according to the present invention is efficiently modified. . If the surface of the magnetic powder is not sufficiently modified or if the surface modification is not uniform, the ratio of modifying the organic solvent by the surface activity of the magnetic powder at the time of preparing the magnetic paint increases.
Therefore, if the magnetic powder of the present invention is used for a magnetic recording medium, the mixing / dispersion processing in the preparation step of the magnetic paint can be performed smoothly. Moreover, similarly to the case of the magnetic powder according to claim 3, since the cross-linking of the binder resin is not inhibited at the time of forming the magnetic layer coating film, a magnetic layer coating film having excellent durability can be formed, Further, after the magnetic layer coating film is formed, the lubricating action of the fatty acid can be favorably exhibited.

The invention according to claim 5 or 6 applies the method for surface treatment of powder according to claim 7 in obtaining the magnetic powder as described above. In this method of surface treatment of powder, the powder (magnetic powder before surface treatment, metal powder in the above example) is mechanically loosened in advance using a crusher such as a chopper, and then excessively locally. By spraying or dropping the surface treatment agent while mixing uniformly and gently without generating heat, the surface treatment agent is uniformly applied to the surface of the powder. By mechanically loosening the powder in advance as described above, the powder can be uniformly mixed during the subsequent powder surface modification, and the surface of the powder can be uniformly coated with the surface treatment agent. It becomes possible to wear. Then, in the subsequent step of applying the surface treatment agent, the surface treatment agent is sprayed or dropped while being uniformly mixed under the mild conditions as described above without giving excessive mechanical energy, so that the powder Damage due to heat generation can be reduced or avoided, and the reaction itself can be performed uniformly. Thereby, not only a defect such as the generation of a step during surface treatment can be prevented, but also the surface treatment agent can be uniformly and efficiently applied to the surface of the powder.

In the invention according to claim 8, in treating the surface of the magnetic powder as described above, a phosphoric acid-based organic acid (specifically, for example, phenylphosphonic acid) is used as the surface treating agent. Phosphoric acid-based organic acids are more acidic than fatty acids and have a relatively high acid dissociation constant, and thus strongly bind to basic active sites present on the surface of magnetic powder (metal powder). Therefore, even when the fatty acid or other material attacks, the surface treatment agent does not peel off from the surface of the magnetic powder, so that a stable surface treatment (modification) effect can be maintained.

[0054]

Embodiments of the present invention will be described below. However, the present invention is not limited to the following examples.

<Example 1> A magnetic metal powder (hereinafter, metal powder) was used as a magnetic powder material (magnetic powder before the surface modification treatment), and the surface modification treatment was performed as follows. First, argon gas (Ar gas) was fed into a crusher having a capacity of 30 liters (pulse jet system equipped on an agromaster manufactured by Hosokawa Micron Corporation) to perform gas purging. In this state, 3.5 kg of granular metal powder was charged into the crusher, and the magnetic metal powder was crushed by a chopper provided in the crusher. At this time, the chopper rotation speed of the crusher was 3000 rotations per minute. Next, the crushed metal powder was put into a mixer (here, an axial mixer manufactured by Sugiyama Heavy Industries), and the metal powder was gently mixed while continuing the Ar gas purge. At this time, the rotation speed of the mixer was set to 300 rotations per minute, and the conditions were such that the magnetic metal powder was uniformly mixed inside the mixing vessel. While mixing the metal powder, a surface treatment agent solution (540 g) was dropped at a low speed (required time: 20 minutes) using a microtube pump. In this case, phenylphosphonic acid was used as the surface treatment agent, and a solution obtained by dissolving 140 g of this phenylphosphonic acid in 400 g of ethanol was used as the surface treatment agent solution. After the dropping of the surface treatment agent solution, the mixing operation was further continued for 2 minutes, and then the metal powder (treated powder) was taken out of the mixer.

<Example 2> Instead of the operation of dropping the surface treatment agent solution in Example 1, the surface treatment agent solution (same as in Example 1) was sprayed using a spraying device installed inside the mixer. It was the same as Example 1 except that the required time was 20 minutes.

Comparative Example 1 The same metal powder as in Examples 1 and 2 was used as a magnetic powder material (magnetic powder before the surface modification treatment), and the surface modification treatment was performed as follows. 3.5 kg of granular metal powder having an average particle diameter of 0.5 mm was directly charged into the mixer without going through a crushing step, and uniformly mixed at a rotation speed of 300 rotations per minute under an Ar gas purge. . Since the mixing of the metal powder was continued in this manner, a surface treating agent solution (the same one as in Example 1 was used) was added thereto. The time required for the compounding operation was 2 minutes. Subsequently, after mixing was continued for 2 minutes, metal powder (processed powder) was taken out of the mixer.

<Comparative Example 2>
Comparative Example 1 was the same as Comparative Example 1 except that the same crushing step as in the case of was added.

Comparative Example 3 Comparative Example 1 was the same as Comparative Example 1 except that the surface treatment agent was added by the spraying method and the spraying time was set to 20 minutes. The spraying was performed by a spray gun device installed in an axial mixer.

<Evaluation of the treated powder> The treated powder (metal powder after the surface modification treatment) obtained in each of Example 1.2 and Comparative Examples 1, 2, and 3 was obtained by the following method using a fatty acid. (Here, myristic acid is used) and organic solvent (here, anone, ie, cyclohexanone)
Of the modified product (here, anone condensate) was measured. Anone was used as a solvent in producing a magnetic paint described later.

Measurement of Fatty Acid Adsorption Amount of 0.5 wt% myristic acid solution (20 ml) was added to 1 g of the treated powder.
(Myristic acid content: 83.5 mg) and added at 30 ° C.
After standing for one day, the supernatant was collected and the amount of myristic acid adsorbed, that is, the amount of adsorbed fatty acid, was calculated by quantifying the residual myristic acid.

Measurement of Anone Condensate Formation Amount 20 ml of anone was added to 1 g of the treated powder, left at 30 ° C. for 3 days, the supernatant was collected, and the amount of the generated anone condensate was measured.

Table 1 shows the above results.

[0064]

[Table 1]

As shown in Table 1, the treated powder obtained in Examples 1 and 2 had a fatty acid adsorption amount of 42 mg /
g and 31 mg / g in Example 2, whereas Comparative Example 1
・ The treated powder obtained in 2.3 has fatty acid adsorption of 57 to 6
It was in the range of 0 mg / g. The amount of anone condensate produced was 540 mg / g for the treated powder of Example 1 and that of Example 2
440 mg / g for the treated powder of Comparative Example 1
850mg at least in processed powder in 2.3
/ G (Comparative Example 2). From these points, Example 1
In each of the treated powders according to 2, the amount of adsorbed fatty acid was smaller than that in each of the comparative examples, and it can be seen that the surface of the treated powder was uniformly coated with the surface treating agent and the surface treatment agent was efficiently modified. Therefore, if each of the treated powders according to Examples 1 and 2 is used as the magnetic powder to be contained in the magnetic layer of the magnetic tape, not only can the lubricating action of the fatty acid be exerted well, but also the step can be performed during the preparation of the magnetic paint. Since it does not occur or does not hinder the crosslinking of the binder resin when forming the magnetic layer coating film, it is possible to form a magnetic layer coating film having excellent durability in a good state. These points are also demonstrated from the evaluation of the characteristics of the magnetic tape described later.

<Evaluation of Magnetic Tapes Produced Using Treated Powder> Next, using the metal powders of the respective Examples and Comparative Examples produced (that is, surface-modified) by the above method,
Magnetic tapes were produced by the following methods. Note that the following method is a method that is usually adopted when producing a magnetic tape. The produced magnetic tape is a so-called single-layer tape in which the coating layer formed on the nonmagnetic support is a magnetic layer only, and the thickness of the magnetic layer is all 3 μm.

First, a predetermined amount of surface-modified metal powder, a solid additive such as carbon black, and a solvent (cyclohexanone) are mixed, and a resin solution is added thereto, followed by sufficient kneading. Next, a binder resin is added while diluting with a solvent, and the slurry is loosened. Subsequently, the mixture is sufficiently dispersed by a sand mill, and finally, additives, a crosslinking agent, and the like are mixed to obtain a magnetic paint. This is applied on a PET base film (non-magnetic support), and a magnetic tape is obtained through a magnetic field orientation, drying, and slitting steps.

In order to examine the characteristics of each of the obtained magnetic tapes, crosslinkability and fatty acid extraction rate were measured by the following methods.

A magnetic tape is placed on a glass substrate with its magnetic layer facing up, and the surface of the magnetic layer is repeatedly rubbed in one direction with a cotton swab impregnated with cyclohexanone at a rate of about once / second. The number of times of rubbing until the magnetic layer peels and the underlying base layer is exposed is defined as crosslinkability. The crosslinkability varies depending on the porosity in the magnetic layer, the type of solvent, and the like, but generally increases as the crosslinking of the binder in the magnetic layer proceeds.
The more effectively the cross-linking agent is used, the more this cross-linkability increases. On the other hand, metal powder has a cross-linking agent-modifying catalytic action, and the higher the surface-modifying efficiency of the metal powder with a surface treating agent (organic acid, phenylphosphonic acid in this case), the more this denaturing catalytic action can be suppressed. Become. Therefore, this crosslinkability is an index of the surface modification efficiency of the metal powder.

Fatty Acid Extraction Rate The fatty acid extraction rate is for determining the surface modification efficiency of metal powder based on the extraction pattern of fatty acids extracted from the magnetic layer in a unit volume. Fatty acids are measured as follows. First, a magnetic tape having a unit volume of a magnetic layer is cut, and fatty acids are extracted from the cut magnetic tape in three stages in the order of hexane → tetrahydrofuran → acetic acid. Fatty acids extracted by acetic acid are mainly fatty acids adsorbed on the metal powder surface. The ratio of the amount of fatty acid extracted by acetic acid to the total amount of extracted fatty acids present in the magnetic layer is defined as “fatty acid extraction amount”. The higher the surface modification efficiency of the metal powder with the organic acid, the lower the fatty acid extraction rate.

Table 2 shows the measurement results for the above-mentioned crosslinkability and fatty acid extraction rate.

[0072]

[Table 2]

As shown in Table 2, the tape 1 using the treated powder of Example 1 had 70 crosslinkability, and the tape 2 using the treated powder of Example 2 had 100 crosslinkability. On the other hand, tape 3 using the treated powder of Comparative Examples 1, 2, and 3
-In 4.5, the number of crosslinkability was 30 times even in the one having the largest crosslinkability (Comparative Example 3). This is tape 3 for tapes 1 and 2.
-Compared with 4.5, the crosslinking of the binder resin in the magnetic layer is directly promoted, and as a result, the binder resin is more strongly bonded to each other. Therefore, it is understood that a magnetic tape having a magnetic layer coating film having excellent durability can be obtained by using the treated powders of Examples 1 and 2.

The extraction rate of fatty acids was determined in Example 1.
The tapes 3 and 4 using the treated powders of Comparative Examples 1, 2, and 3 were 45% in the tape 1 using the treated powder of Example 2, and 48% in the tape 2 using the treated powder of Example 2. In 5, the lowest value (Comparative Example 2) was 75%. For this reason, in the tapes 1 and 2, as the magnetic powder constituting the magnetic layer, the treated powders of Examples 1 and 2 whose surfaces were uniformly coated with a surface treating agent (phenylphosphonic acid) and efficiently modified were used. Tapes 3 and 4 because they are used
It can be seen that the fatty acid present in the magnetic layer is less likely to adhere to the surface of the magnetic powder as compared with No. 5. Thus,
It can be confirmed that the use of the treated powders of Examples 1 and 2 provides a magnetic tape capable of effectively exerting the lubricating action of fatty acids.

All of these results indicate that the surface of the magnetic powder was efficiently and uniformly modified by the surface treatment agent, in other words, the basic active sites on the surface of the magnetic powder were appropriately coated with the surface treatment agent. It is shown that it is done. Therefore, the various problems caused by the active sites on the surface of the magnetic powder include the problems described above, including the problems that occur in the manufacturing process of the magnetic tape and the problems such as the inhibition of the lubricating action that occurs in the magnetic tape after the product is manufactured. This can be all solved by modifying the surface of the magnetic powder by the method of the present invention described above or by using the magnetic powder whose surface has been modified by the method of the present invention.

[0076]

As described above, according to each of the magnetic recording media according to the first and second aspects of the present invention, not only can the durability of the coating film of the magnetic layer be improved, but also the lubricating action of the fatty acid can be effectively reduced. It is possible to exert the effect, and it is also possible to suppress the modification catalytic action on other materials by the surface of the magnetic powder. Such a magnetic recording medium can be easily realized by using the magnetic powder according to claims 3 and 4 of the present invention. Further, such a magnetic powder can be easily obtained by modifying the surface of the magnetic powder by the method according to claim 5 or 6 or 7 of the present invention at the time of manufacturing the magnetic powder. In particular, by using the powder surface treatment method according to claim 5 of the present invention, it is possible to uniformly and efficiently coat the surface of not only magnetic powder but also, in general, fine powder having active sites on the surface. It becomes possible.

Claims (8)

[Claims] 1. A magnetic coating material comprising a magnetic powder, a binder resin, a fatty acid and an organic solvent, which is formed on a non-magnetic support or on a layer formed on the non-magnetic support. A magnetic recording medium having a magnetic layer, wherein the thickness of the coating layer including the magnetic layer formed on the non-magnetic support is
1.5 to 5.0 μm, and the thickness of the magnetic layer alone is 1.5 to 4.0
μm, and a magnetic recording medium specified by having a crosslinkability defined below of 50 times or more. <Cross-linking property>: A cotton swab is impregnated with a cyclohexanone, and the surface of the magnetic layer of the magnetic recording medium is repeatedly rubbed in one direction at a rate of about once / second with the cotton swab. The number of times of rubbing until () is exposed. The angle between the swab and the surface of the magnetic recording medium is about 30 °,
The load strength is about 50 g. 2. A magnetic coating material comprising a magnetic powder, a binder resin, a fatty acid and an organic solvent, which is formed on a non-magnetic support or on a layer formed on the non-magnetic support. A magnetic recording medium having a magnetic layer, wherein the thickness of the coating layer including the magnetic layer formed on the non-magnetic support is
1.5 to 5.0 μm, and the thickness of the magnetic layer alone is 1.5 to 4.0
A magnetic recording medium which is specified by a fatty acid extraction rate of 1% or more and 50% or less as defined below. <Fatty acid extraction ratio>: A magnetic recording medium having a unit volume of a magnetic layer was cut out to obtain a sample, and this sample was subjected to three stages of hexane → tetrahydrofuran → acetic acid using hexane, tetrahydrofuran and acetic acid. Fatty acid is extracted from the sample, and the ratio of the fatty acid amount extracted by the acetic acid to the obtained total fatty acid extraction amount (total fatty acid amount present in the magnetic layer). 3. A magnetic paint containing a magnetic powder, a binder resin, a fatty acid and an organic solvent is applied on a non-magnetic support or on a layer formed on the non-magnetic support. The magnetic powder for use in a magnetic recording medium having a magnetic layer, wherein the magnetic powder is identified by having a fatty acid adsorption amount of 5 mg / g or more and 50 mg / g or less measured under the following conditions. <Measurement conditions of fatty acid adsorption amount>: To 1 g of magnetic powder, 20 ml of a fatty acid solution containing 0.5% by weight of the above fatty acid (the content of the fatty acid is 835 mg) was added, and the mixture was allowed to stand at 30 ° C. for 3 days. The supernatant is collected, and the amount of fatty acid adsorbed is calculated by quantifying the remaining fatty acid therein. 4. A magnetic coating material comprising a magnetic powder, a binder resin, a fatty acid, and an organic solvent, which is formed on a non-magnetic support or on a layer formed on the non-magnetic support. The magnetic powder for use in a magnetic recording medium having a magnetic layer, wherein the magnetic powder is identified by a modified product amount of an organic solvent of 600 mg / g or less measured under the following conditions. <Measurement conditions of the amount of modified organic solvent produced>: 20 ml of the above organic solvent was added to 1 g of magnetic powder, left at 30 ° C. for 3 days, the supernatant was collected, and the amount of the produced modified organic solvent was measured. . 5. A method for coating a surface of a powder having a site having a high reaction activity on the surface with a surface treatment agent, wherein the powder is mechanically loosened in advance, and then locally excessive heat generation is prevented. A powder surface treatment method, characterized in that the surface treatment agent is uniformly applied to the surface of the powder by spraying or dripping the surface treatment agent while uniformly and gently mixing. 6. A method for producing a magnetic powder, wherein the magnetic powder according to claim 3 is obtained by treating the surface of a magnetic powder material with the method according to claim 5. 7. A method for producing a magnetic powder, wherein the magnetic powder according to claim 4 is obtained by treating the surface of the magnetic powder material with the method according to claim 5. 8. The method for producing a magnetic powder according to claim 6, wherein a phosphoric acid-based organic acid is used as the surface treatment agent.