JP2002275504A - Surface treatment method for magnetic powder, production method for magnetic coating material and production method for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which the surface of magnetic powder can uniformly be to surface-treated, and therefore to realize a magnetic recording medium which has a magnetic layer coating film having excellent durability or the like. SOLUTION: The surface of magnetic powder is subjected to coating treatment with a surface treatment agent. In this case, as the surface treatment agent, a solid surface treatment agent is used, and this solid surface treatment agent and the magnetic powder have previously been mixed and crushed. After that, only an organic solvent is added to the mixture, and the surface treatment agent is dissolved. A binder and an addition agent are added to the surface- treated magnetic powder obtained in this way, and they are kneaded. Next, an organic solvent is added to the kneaded material, and they are diluted and dispersed to produce a magnetic coating material. The surface of a nonmagnetic supporting body is coated with the magnetic coating material, so that the magnetic recording medium is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating the surface of a magnetic powder, a method for producing a magnetic paint using the same, and a method for producing a coating type magnetic recording medium using the obtained magnetic paint. On how to do it.

[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 solution, and kneaded with a kneader or the like so that the binder fits into the magnetic powder as much as possible. Further, a solvent is gradually added with stirring to obtain a fluid coating. After mixing and stirring, the magnetic powder is further strongly mixed and stirred by a disperser such as a sand mill to disperse the magnetic powder. Further, at a predetermined time during such a process, a filler or a lubricant is added, and the mixture is stirred so as to be 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.

[0003] In recent years, with the increasing demand for higher capacity and higher density of recording media, there has been a strong demand for magnetic recording characteristics suitable for high density recording even in the above-mentioned coating type magnetic recording media. In order to realize a magnetic recording medium suitable for such high-density recording, magnetic powder must be present in a high-density and well-dispersed state in a magnetic paint used for forming a magnetic layer, that is, High filling and high dispersion of the magnetic powder is essential. In order to obtain this kind of magnetic paint having excellent filling and dispersibility, it is effective to knead the magnetic powder and the binder solution with a high shearing force using a kneader having a high shearing capacity such as a kneader. I know there is. In order to further increase the shearing force during this kneading,
There is also known a method of kneading a kneaded product with a higher viscosity by minimizing the amount of a solvent in the kneaded product.

On the other hand, in order to achieve higher recording density and higher capacity, recently, instead of γ-iron oxide powder or the like conventionally used as magnetic powder, metal powder or the like having more excellent magnetic recording characteristics has been used. In many cases, ferromagnetic metal powders have been used, and at the same time, their fine particles have been reduced. However, the use of such ferromagnetic metal powder with fine particles causes the following problems.

That is, in recent ferromagnetic metal powders, mainly metal powders, finer particles have been formed and the surface composition has changed as compared with conventionally used γ-iron oxide and the like. The activity on the surface of the fine particles is relatively high. Therefore, due to the catalytic action or reaction activity of the surface of the magnetic powder, the solvent and the cross-linking agent in the magnetic paint are denatured, and the magnetic layer is plasticized (that is, the coating film strength is reduced). Fatty acids and fatty acid esters) are adsorbed on the surface of the magnetic powder, causing problems such as losing the function as a lubricant. In addition, since the magnetic powder becomes fine particles, the interaction between the particles becomes stronger, so that the particles are liable to agglomerate and the dispersion becomes difficult.

To cope with such a problem, it is effective to uniformly treat the surface of the magnetic powder with a surface treating agent such as a fatty acid or an organic phosphoric acid. For example, Japanese Patent Application Laid-Open No. 3-26
No. 3615 proposes a method of uniformly treating the surface of a magnetic powder by mixing and pulverizing a magnetic powder (ferromagnetic powder) and a surface treating agent and then adding a binder.

[0007]

As described above, in order to highly fill and highly disperse the finely divided magnetic powder, the surface of the magnetic powder is uniformly treated to improve the dispersion stability. It is important to improve the filling and dispersibility of the magnetic powder in the magnetic paint by kneading under load. On the other hand, to uniformly treat the surface of the magnetic powder, it is necessary to make the inside of the system uniform.

However, if the concentration of the surface treatment agent solution to be added is reduced in order to make the inside of the system uniform in the surface treatment step, the solid concentration after the step is reduced. Therefore, when a binder is added to and kneaded with the magnetic powder after the surface treatment, kneading under a high load cannot be performed due to a decrease in the viscosity of the kneaded material, and high filling and dispersion of the magnetic powder in the magnetic paint can be prevented. The problem that it becomes difficult arises. In addition, since the amount of the solvent contained in the treated magnetic powder is large, there is a problem that it is necessary to pay attention to safety in handling, and a problem that the flowability of the powder is deteriorated and the workability is deteriorated. . Such a problem can be avoided by increasing the solid content concentration by drying the magnetic powder after the surface treatment. However, in such a case, there are problems such as a longer processing time and a higher cost for the treatment.

On the other hand, if the amount of the solvent added at the time of surface treatment is reduced for the purpose of kneading under a high load, the surface of the magnetic powder cannot be uniformly treated, so that active sites remain on the surface of the magnetic powder. As a result, the solvent may be denatured,
The magnetic powders are likely to agglomerate and difficult to disperse.

When a binder is added to a mixture of a magnetic powder and a surface treating agent, the surface treating agent and the binder react before the surface of the magnetic powder is treated with the surface treating agent. As a result, the magnetic powder cannot be sufficiently treated, the fluidity of the coating material deteriorates, and the modified product remains in the magnetic layer to cause plasticization of the magnetic layer. Furthermore, when the magnetic powder is mixed and pulverized using a kneading device or the like, the pulverizing ability and the mixing ability are insufficient, the magnetic powder cannot be sufficiently disintegrated, or the surface treatment agent and the magnetic powder are uniformly mixed. Or the magnetic powder cannot be uniformly surface-treated.

SUMMARY OF THE INVENTION The present invention addresses the above-mentioned problems, and has as its object to enable uniform surface treatment of magnetic powder and to enable proper kneading during preparation of magnetic paint. The object of the present invention is to provide a magnetic recording medium having excellent dispersibility and filling property.

[0012]

In the method for treating the surface of a magnetic powder according to the present invention, the surface of the magnetic powder is coated with a surface treating agent so that the surface of the magnetic powder can be uniformly treated. A solid surface treatment agent is used as a treatment agent. First, the solid surface treatment agent and the magnetic powder are preliminarily mixed and crushed by a mechanically crushable device.
Next, the surface treatment agent is uniformly coated on the surface of the magnetic powder by adding only the organic solvent to the mixture of the magnetic powder and the surface treatment agent thus mixed and crushed to dissolve the surface treatment agent. To wear. At this time, the amount or concentration of the solvent is adjusted so that the solid content concentration of the system immediately after the surface treatment is 80% by weight or more, and the solvent is dropped or sprayed on the mixture, so that the surface of the magnetic powder is Preferably, the surface treatment agent is adsorbed. If the solid content concentration of the system immediately after the surface treatment is adjusted to 80% by weight or more, when a magnetic paint described below is prepared and a binder and a solvent are added to the magnetic powder and kneaded, it is relatively hard to mix. This is because a kneaded material having a high viscosity is kneaded, and as a result, kneading can be performed with a high load, and high filling and dispersion of the magnetic powder can be performed. The term “solid” in the above “solid surface treatment agent” means that there is no liquid (solution) or gaseous state. Therefore, the “solid surface treatment agent” also includes a lump-like, relatively coarse powdery or granular surface treatment agent.

Further, the method for producing a magnetic paint according to the present invention is to prepare a magnetic paint using the magnetic powder subjected to the above-mentioned surface treatment. That is, in obtaining a coating material used for forming a magnetic layer on a non-magnetic support constituting a magnetic recording medium, a binder and an additive are added and kneaded to a magnetic powder surface-treated by the above method, and then kneaded. An organic solvent is added to the kneaded material, and the mixture is diluted and dispersed to produce a magnetic paint containing a magnetic powder, a binder, an additive, and an organic solvent.

Further, in the method for producing a magnetic recording medium according to the present invention, the magnetic paint and the additives are dispersed in the binder by applying the magnetic paint thus obtained on a non-magnetic support. A magnetic recording medium having a magnetic layer is manufactured. In this case, a predetermined undercoat paint is applied on the non-magnetic support, and a magnetic paint is applied thereon, thereby producing a magnetic recording medium having an undercoat layer and a magnetic layer on the non-magnetic support in this order. You can also. In this case, the undercoat layer is provided for the purpose of, for example, improving the durability of the entire coating film.

[0015]

According to the magnetic powder surface treatment method of the present invention,
After the surface treatment agent is uniformly mixed with the magnetic powder, the surface treatment agent dissolves and covers active sites on the surface of the magnetic powder, so that the surface of the magnetic powder can be uniformly treated. In addition, since the addition of the solvent and the adsorption of the surface treating agent occur simultaneously and in parallel, the surface can be treated without causing the solvent to undergo a denaturing reaction due to active sites on the surface of the magnetic powder. The magnetic powder obtained in this manner is hardly re-agglomerated because its surface is appropriately coated with the surface treating agent, and has excellent dispersibility as compared with the non-uniformly treated magnetic powder. .

Further, since it is not necessary to convert the surface treatment agent into a solution, the surface of the magnetic powder can be uniformly treated with a smaller amount of solvent than in a method in which a solution of the surface treatment agent is added. For this reason, the amount of the solvent can be adjusted as needed, and the mixture can be transferred to the kneading step with a high solid content without a special drying step.

As a result, according to the method for producing a magnetic paint according to the present invention, in which a magnetic paint is produced using the magnetic powder treated by such a method, kneading can be performed under a strong load. The fillability and dispersibility of the magnetic powder in it are improved. In particular, when the method of the present invention is performed using a continuous kneader capable of kneading a kneaded material with a high viscosity, a high effect is obtained.

Further, since the magnetic powder is pulverized before kneading, the bulk density of the magnetic powder becomes high, and in the subsequent kneading step, the magnetic powder requires a smaller amount of solvent than in the case where it has not been pulverized in advance. It becomes possible to begin kneading. For this reason,
The kneading under a high load can be performed, and the filling and dispersibility of the magnetic powder in the magnetic paint can be improved. Further, since the magnetic powder has been pulverized in advance, no untreated active sites appear in the kneading step.

Further, according to the method of manufacturing a magnetic recording medium of the present invention, the magnetic layer obtained by applying the magnetic paint obtained as described above is coated on a non-magnetic support. A magnetic recording medium having a magnetic layer in which magnetic powder is densely and satisfactorily dispersed, that is, a magnetic recording medium having excellent magnetic recording characteristics can be obtained. In the magnetic recording medium thus obtained, the modification of the cross-linking agent and the adsorption of the fatty acid due to the catalytic action on the surface of the magnetic powder are prevented or suppressed. If this occurs, plasticization of the magnetic layer (that is, a decrease in the strength of the coating film) and deterioration of the tape running property are less likely to occur.

[0020]

As described above, according to the present invention, it is possible to knead a magnetic powder having a uniformly treated surface under a high load, and to produce a magnetic paint having excellent dispersibility and filling properties. As a result, a magnetic recording medium having excellent magnetic recording characteristics can be obtained. In addition, since the catalytic action of the magnetic powder surface on the crosslinking agent and the fatty acid can be suppressed, problems such as a decrease in the coating film strength and a deterioration in the tape running property can be avoided. Furthermore, since the amount of solvent contained in the magnetic powder after the surface treatment is small and the surface of the magnetic powder is uniformly coated with the surface treating agent, the fluidity and safety of the powder are improved, and the workability is improved. There is an advantage of doing so.

[0021]

Next, more specific examples of the structure, material, means, and the like that can be adopted in the present invention will be listed. <Surface treatment agent> As the surface treatment 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.

<Fatty acids and the like> It is preferable to use fatty acids having 10 or more carbon atoms. As fatty acids having 10 or more carbon atoms,
Any of isomers such as linear, branched, and cis-trans may be used, but a linear type having excellent lubrication performance is preferable. 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 preferred.

The amount of the fatty acid is preferably 0.5 to 4% by weight based on the amount of the magnetic powder. If the amount is too large, the coating film will be weak. If the amount is too small, the required lubricating performance cannot be obtained, and the friction will increase.

<Magnetic Powder> The magnetic powder includes Fe powder, Fe-
Ferromagnetic iron-based metal powders such as Co powder and Fe-Nd-B powder, and hexagonal barium ferrite powder are used.
The coercive force of the ferromagnetic iron-based metal powder and hexagonal barium ferrite powder is preferably 120 to 320 kA / m, and the saturation magnetization is 120 to 200 A ·
m ² / kg (100 to 200 emu / g)
30 to 180 A · m ² / kg (130 to 180 emu /
g) is more preferred. For hexagonal barium ferrite powder, 50 to 70 A · m ² / kg (50 to 70 emu / g)
Is preferred. Both the magnetic properties of the magnetic layer and the magnetic properties of the ferromagnetic powder refer to values measured with an external magnetic field of 128 MA / m (16 kOe) using a sample vibrating magnetometer.

The Fe powder used in the present invention, Fe-
The average major axis length of the acicular ferromagnetic iron-based metal powder such as Co powder is preferably 0.03 to 0.2 μm, and 0.03 to 0.18.
μm is more preferred, and 0.04 to 0.15 μm is even more preferred. This range is preferable because the average major axis length is 0.03 μm.
If it is less than m, the cohesive force of the magnetic powder increases, making it difficult to disperse it in the coating. If it is more than 0.2 μm, the coercive force decreases and the particle noise based on the particle size increases. Further, in the case of granular ferromagnetic iron-based metal powder such as Fe-Co-B powder, the particle size is 5 to 20 for the same reason.
0 nm is preferred. Further, the hexagonal barium ferrite powder preferably has a plate diameter of 5 to 200 nm for the same reason. The average major axis length and the particle diameter are determined by measuring the particle size of a photograph taken with a scanning electron microscope (SEM) and averaging 100 particles. Also,
The BET specific surface area of this ferromagnetic iron-based metal powder is 35 m ²
/ G or more, more preferably at least 40 m ² / g, most preferably at least 50 m ² / g. The BET specific surface area of the hexagonal barium ferrite powder is 1 to 100 m ² /
g is preferred.

<Organic Solvent> The organic solvent to be added to the mixture of the magnetic powder and the surface treating agent may be the same as that used in the preparation of the magnetic paint (kneading / mixing).
The same type as that added during dispersion) is used.
As such a solvent, any of those conventionally used for magnetic recording media can be used, for example, methyl ethyl ketone, cyclohexanone, ketone solvents such as methyl isobutyl ketone, tetrahydrofuran, ether solvents such as dioxane, Ethyl acetate, acetate solvents such as butyl acetate and the like are used alone or in combination,
Furthermore, it is used by mixing with toluene or the like.

<Binder> As the binder, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, vinyl chloride Examples thereof include a combination of at least one selected from a vinyl acetate-maleic anhydride copolymer resin, a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, and nitrocellulose with a polyurethane resin. 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.

In the magnetic layer, these binder resins are used in an amount of 7 to 50 parts by weight based on 100 parts by weight of the ferromagnetic iron-based metal powder.
It is used in an amount of 10 parts by weight, preferably 10 to 35 parts by weight. In particular, as the binder resin, vinyl chloride resin 5-
30 parts by weight and 2 to 20 parts by weight of a polyurethane resin,
Most preferably, they are used in combination.

Along with these binder resins, a thermosetting crosslinking agent, for example, which bonds to a functional group contained in the binder resin and crosslinks them, is used. Examples of such a cross-linking agent 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 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, and 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 with respect to the ferromagnetic iron-based metal powder described above.
% By weight is preferred. More preferably, it is 8 to 18% by weight.

<Magnetic Layer> The thickness of the magnetic layer formed on the nonmagnetic support is preferably 0.02 μm or more and 1.0 μm or less.
0.02 μm or more and 0.5 μm or less, more preferably 0.02 μm
It is more preferably from m to 0.3 μm. The reason why this range is preferable is that when the thickness is less than 0.02 μm, the head output decreases due to a small leakage magnetic field from the magnetic layer, and when the thickness exceeds 1.0 μm, the head output decreases due to thickness loss. The coercive force (Hc) in the longitudinal direction of the tape is 135 to 280
kA / m (1700 to 3500 Oe), and the residual magnetic flux density in the longitudinal direction of the tape is preferably 0.18 T (1800 G) or more. This range is preferable because the coercive force is 135 kA / m.
Below, the output decreases due to the demagnetizing field, and 280 kA /
If it exceeds 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 160-240 kA / m (2000-3000O
e), the residual magnetic flux density is 0.2 to 0.4 T (2000 to 400 T)
0G) is more preferred.

The center line average surface roughness (Ra) of the magnetic layer formed on the nonmagnetic support is preferably from 1.0 to 8.5 nm.
1 to 7 nm is more preferable. If Ra is less than 1.0 nm, the magnetic layer becomes too smooth, the friction coefficient increases, and sticking to the head occurs. If Ra exceeds 8.5 nm, the output will be affected due to spacing with the head.

A conventionally known carbon black (CB) can be added to the magnetic layer for the purpose of improving conductivity and surface lubricity. As these CBs, acetylene black, furnace black, thermal black and the like can be used. In this case, particles having a particle diameter of 5 nm to 200 nm can be used, but particles having a particle diameter of 10 nm to 100 nm are preferable. This range is preferable because when the particle size is 10 nm or less, it is difficult to disperse CB, and when the particle size is 100 nm or more, it is necessary to add a large amount of CB, and in any case, the surface becomes rough and causes a decrease in output. That's why. The addition amount is preferably 0.2 to 5% by weight based on the ferromagnetic iron-based metal powder. More preferably, it is 0.5 to 4% by weight.

<Non-magnetic support> Non-magnetic support (base)
For example, polyethylene terephthalate, polyethylene naphthalate, aromatic polyamide, aromatic polyimide and the like can be used. The thickness of the nonmagnetic support varies depending on the application, but usually a thickness of 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, and the tape strength is low. Is smaller.

<Mixing / Stirring Means> As means for mixing or stirring magnetic powders and the like, for example, a gas blow-up stirrer utilizing a rolling flow effect such as Agromaster (AGM-25) manufactured by Hosokawa Micron Corporation, Matsuyama Heavy Industries A rotary mixer such as an axial mixer manufactured by Mitsui Mining and a Henschel mixer manufactured by Mitsui Mining Co., Ltd. can be used. For example, in the case of a Henschel mixer, the peripheral speed of the blade during mixing and stirring is preferably 10 to 30 m / sec. Below this, the mixing and crushing capacity is insufficient, and above this, the load may be too high and the heat generation may increase.

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

<Spraying / Dropping Means> As a means for spraying or dropping the organic solvent, for example, a spray gun mounted on an agromaster (AGM-25) manufactured by Hosokawa Micron Corporation, an axial mixer manufactured by Matsuyama Heavy Industries, etc. can be used. . 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.

[0039]

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

Example 1 A magnetic paint having the following composition was prepared. 100 parts by weight of magnetic powder (magnetic metal powder: average particle size: 0.1 μm, Hc: 147 kA / m, σs: 138 Am ² / kg) 4 parts by weight of surface treatment agent (phenylphosphonic acid) ・ vinyl chloride resin (Japan) Zeon MR110) 12 parts by weight-Polyurethane resin (UR8300 manufactured by Toyobo) 8 parts by weight-Crosslinking agent 5 parts by weight (polyisocyanate: Coronate L made by Nippon Polyurethane)-Carbon black (average particle diameter 45 nm) 5 parts by weight-Abrasive ( Al ₂ O ₃ : average particle size 0.2 μm) 5 parts by weight ・ fatty acid (myristic acid) 2 parts by weight ・ solvent tetrahydrofuran 20 parts by weight methylethyl ketone 50 parts by weight toluene 50 parts by weight cyclohexanone 120 parts by weight

In preparing this magnetic paint, first, a mixer (Henschel mixer manufactured by Mitsui Mining Co., Ltd .: FM-20B)
After the argon gas was fed into the mold and the gas was purged, the magnetic powder and the solid surface treatment agent were charged into the mixer, and the peripheral speed was 25%.
The mixture was stirred and mixed and pulverized at m / sec for 5 minutes. Next, 4 parts by weight of a solvent (tetrahydrofuran) was added dropwise thereto while stirring, and after stirring for further 10 minutes, carbon black was added and mixed to reduce the peripheral speed to 5 m / sec. After stirring for minutes, the magnetic powder (processed powder) was taken out of the mixer. These were charged into a twin-screw continuous kneader (KEX-40 manufactured by Kurimoto Iron Works), and kneaded, diluted, and dispersed to obtain the above magnetic paint. This magnetic paint was applied on a PET (polyethylene terephthalate) base film, and subjected to a magnetic field orientation, drying, and slitting steps to produce a magnetic tape. The dry thickness of the magnetic layer in the obtained magnetic tape is 3 μm.

Example 2 The procedure was the same as in Example 1 except that the amount of the solvent to the mixture of the magnetic powder and the surface treating agent in the mixer was 10 parts by weight.

Example 3 The procedure was the same as Example 2 except that the peripheral speed of the mixer was 5 m / sec.

<Comparative Example 1> After argon gas was fed into a mixer and gas purged, magnetic powder was charged, and a surface treatment agent solution having a solution concentration of 30% by weight was dropped while stirring at a peripheral speed of 5 m / sec. The mixture was further stirred for 10 minutes, and then the magnetic powder (processed powder) was taken out of the mixer. Thereafter, a magnetic paint was prepared in the same manner as in Example 1, and a magnetic tape was produced using the magnetic paint.

Comparative Example 2 The procedure of Comparative Example 1 was repeated except that the concentration of the surface treating agent solution in the magnetic powder surface treating step was changed to 12% by weight.

<Evaluation of Treated Powder> Each of the treated powders (magnetic powder after surface modification treatment) obtained in Examples 1 to 3 and Comparative Examples 1 and 2 was treated with fatty acid (myristine) in the following manner. Acid) (MA adsorption) and extraction rate (M
A extraction rate). In addition, the maximum magnetic flux density (Bm) and the center line average surface roughness (Ra) of the magnetic layer (coating film) were measured for each magnetic tape produced using these magnetic powders by the following method.

Measurement of fatty acid adsorption amount To 1 g of the treated powder, 20 ml of a 0.5% by weight myristic acid solution (myristic acid content: 83.5 mg) was added, left at 30 ° C. for 3 days, and the supernatant was collected. The residual myristic acid therein was quantified, and the amount of fatty acid adsorbed was 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 to the active site. Therefore, the surface modification efficiency of the magnetic powder (the magnetic powder 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, the more efficiently the surface of the magnetic powder is modified.

Measurement of Fatty Acid Extraction Rate A magnetic tape having a unit volume of a magnetic layer was cut out to obtain a sample, and hexane, tetrahydrofuran and acetic acid were used to prepare a sample of hexane → tetrahydrofuran → acetic acid in the order of hexane → tetrahydrofuran → acetic acid. In this step, a fatty acid (here, myristic 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) is calculated. Fatty acid extraction rate was used.

The surface modification efficiency of the magnetic powder in the magnetic layer of the magnetic tape 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.

Measurement of Maximum Magnetic Flux Density (Bm) of Magnetic Layer In each case, a sample vibration type magnetometer (VSM-5 manufactured by Toei Kogyo Co., Ltd.)
Bm of the magnetic layer was measured under an external magnetic field of 1.28 MA / m (16 kOe). Measurement of center line average surface roughness (Ra) Non-contact surface shape measurement device (NewView manufactured by ZYGO)
5000) using a sample (magnetic tape) 40 μm × 40
The center line surface roughness Ra per μm was measured at 60 points, and the average value was defined as Ra per the entire length of the magnetic tape.

[0052]

[Table 1]

As shown in Table 1, the treated powders obtained in Examples 1 to 3 had a fatty acid adsorption amount in the range of 32 to 42 mg / g, while Comparative Examples 1 and 2 The obtained treated powders had a fatty acid adsorption of 58 mg / g and 39 mg / g, respectively. The extraction ratio of fatty acid in the magnetic tape prepared using each of the treated powders was 45 to 59% for the treated powders of Examples 1 to 3, whereas the treated powders of Comparative Examples 1 and 2 were different. Were 78% and 52%, respectively. From these points, Example 1
In each of the treated powders of Nos. 1 to 3, the amount of adsorbed fatty acid is smaller than that of Comparative Example 1, and it can be seen that the surface of the treated powder is uniformly coated with the surface treating agent and is efficiently modified.

On the other hand, the treated powder according to Comparative Example 2
Since the amount of fatty acid adsorption is smaller than that of the treated powder according to the above, there is not much difference from Examples 1 to 3 in this point. The same applies to the fatty acid extraction rate in the magnetic tape produced using the treated powder obtained in Comparative Example 2. However, in the magnetic tape according to Comparative Example 2, Bm was as small as 0.308 T and Ra was 9.0 as compared with the magnetic tapes according to Examples 1 to 3.
It is as large as nm. That is, in the magnetic powder and the magnetic tape according to Comparative Example 2, the adsorption amount and the extraction rate of the fatty acid were as good as those in Examples 1 to 3, but the magnetic characteristics and surface roughness were as in Examples 1 to 3. Inferior to those of This indicates that the dispersibility and the filling property were inferior due to the low solid content at the time of kneading, and as a result, the magnetic properties and surface properties of the obtained magnetic tape were reduced. On the other hand, in Examples 1 to 3, the kneading was performed at a relatively high solid content, thereby enabling strong kneading and improving the dispersibility and the filling property. As a result, the magnetic properties and surface properties were improved. It is considered that a magnetic tape excellent in the above was obtained.

As described above, according to the methods according to Examples 1 to 3, not only can the lubricating action of the fatty acid be exerted well, but also a step occurs during the preparation of the magnetic paint or the formation of the magnetic layer coating film. It does not hinder the cross-linking of the binder resin, and further enhances the dispersibility and filling properties, so it has excellent lubrication performance and durability, as well as excellent magnetic properties and surface properties. A magnetic tape having a film can be obtained. These points are evident from the results of the fatty acid extraction rate and the evaluation results of the magnetic properties and surface properties of the obtained magnetic tape.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kazuhiko Nagiri 1-88 Ushitora, Ibaraki-shi, Osaka F-term in Hitachi Maxell Co., Ltd. 4K018 BA14 BA16 BA18 BB04 BC12 BC29 BD02 GA04 HA08 5D006 BA07 5D112 AA05 BB12 BB18

Claims (4)

[Claims] When coating the surface of a magnetic powder with a surface treatment agent, a solid surface treatment agent is used as the surface treatment agent, and the solid surface treatment agent and the magnetic powder are mixed and crushed in advance. A method for treating a surface of a magnetic powder, wherein the surface treatment agent is uniformly applied to the surface of the magnetic powder by adding only an organic solvent to the mixture and dissolving the surface treatment agent. 2. The surface treatment method for a magnetic powder according to claim 1, wherein the amount or concentration of the organic solvent is adjusted so that the solid content of the system immediately after the surface treatment is 80% by weight or more. Processing method. 3. A method for producing a magnetic paint containing a magnetic powder, a binder, an additive, and an organic solvent as a paint used for forming a magnetic layer on a non-magnetic support constituting a magnetic recording medium. The surface of the magnetic powder is coated in advance by the surface treatment method described in Item 1 or 2, a binder and an additive are added to the magnetic powder after the surface treatment, and the mixture is kneaded. Then, an organic solvent is added to the kneaded product. In addition, a method for producing a magnetic paint, characterized by being diluted and dispersed. 4. A method for producing a magnetic recording medium having a magnetic layer formed by applying a magnetic paint containing a magnetic powder, a binder, an additive and an organic solvent on a non-magnetic support. A method for manufacturing a magnetic recording medium, comprising using a magnetic paint obtained by the method according to claim 3 as the paint.