JP2007310941A - Magnetic powder and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which has superior electromagnetic transfer characteristics, as well as, superior running durability, and storage stability. <P>SOLUTION: Ferromagnetic powder has a first membrane and a second membrane, in this order, on the surface of a metal particle. The first membrane contains oxide of rare earth element and/or oxyhydroxide as primary components, and the second membrane contains oxide of silicon and/or oxyhdroxide as primary components. Furthermore, the metal particle includes Fe and/or Co as the main components. A magnetic recording medium has a magnetic layer which contains ferromagnetic powder and binder on a non-magnetic support. The ferromagnetic powder is aforementioned ferromagnetic powder. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a ferromagnetic powder suitable as a magnetic material contained in a magnetic layer in a magnetic recording medium for high density recording. Furthermore, the present invention relates to a magnetic recording medium containing the ferromagnetic powder in a magnetic layer.

  Magnetic recording technology enables other recordings such as the ability to repeatedly use media, the ease of digitizing signals, the construction of a system in combination with peripheral devices, and the simple modification of signals. Since it has excellent features not found in the system, it has been widely used in various fields including video, audio, and computer applications.

  In order to meet the demands for downsizing equipment, improving the quality of recording and playback signals, extending recording time, increasing recording capacity, etc., the recording density, reliability, and durability of magnetic recording media are improved. There has always been a desire for further improvement.

  In recent years, in order to achieve a high recording density of a magnetic recording medium, a shortening of the wavelength of a signal to be used has been strongly advanced. When the length of the signal recording area becomes comparable to the size of the magnetic material used, a clear magnetization transition state cannot be created, and recording becomes virtually impossible. For this reason, it is necessary to develop a magnetic material having a sufficiently small particle size with respect to the shortest wavelength to be used, and the finer magnetic material has been directed for many years.

  In the metal powder for magnetic recording, the particle shape is made acicular and shape anisotropy is imparted to obtain the desired coercive force. For high-density recording, the surface roughness of a medium obtained by refining ferromagnetic metal particle powder is reduced. However, the magnetic recording metal powder has a reduced acicular ratio as it is miniaturized, and a desired coercive force cannot be obtained. Recently, DVC systems for digitizing and recording video signals have been proposed, and high performance ME tapes and high performance MP tapes are used. Since the coercive force of the MP tape used for DVC is 2000 oersted or more, a ferromagnetic metal particle powder having a large coercive force and a fine particle size distribution is required. In addition, since the recording method overwrites a signal, it is desired that the overwrite characteristic is good.

Previously, the present applicant has proposed a ferromagnetic metal particle powder suitable for a DVC system and a magnetic recording medium using the same (Patent Document 1). Here, in order to obtain desired magnetic characteristics, high coercive force required for a DVC system of 2000 to 3000 Oe is realized by using Y and Al as sintering inhibitors.
JP 7-326035 A

  In recent years, for example, as in the ferromagnetic powder described in Patent Document 1, a sintering inhibitor such as yttrium or aluminum has been used to prevent sintering of a magnetic material and further to prevent oxidation. . In particular, in order to make the magnetic material fine particles for high density, it is required to effectively prevent the magnetic material from being sintered. However, as a result of repeated studies by the present inventors, in a magnetic recording medium including a magnetic material using such a sintering inhibitor, the head is stored by repeated storage or running under a severe environment such as high temperature and high humidity. It has been found that dirt may occur.

  Under such circumstances, an object of the present invention is to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent running durability and storage stability. In particular, the present invention has been made for the purpose of providing a novel ferromagnetic powder capable of realizing the above magnetic recording medium.

As a result of intensive studies to achieve the above object, the present inventors have obtained the following knowledge.
As described above, in a magnetic recording medium including a magnetic material using a sintering inhibitor, head contamination may occur due to storage at high temperature and high humidity. As a result of studying the cause of the head contamination by the present inventors, a salt of yttrium or aluminum used as a sintering inhibitor and a fatty acid or fatty acid ester salt added as a lubricant to the magnetic layer or the like adheres to the head. Was found to be the cause. In view of this, it is conceivable to reduce the amount of the sintering inhibitor in order to reduce head contamination, but it is difficult to reduce the amount of the sintering inhibitor in order to further reduce the size of the magnetic material. On the other hand, it is conceivable to reduce the amount of fatty acid or the like, but it is not preferable to reduce the amount of fatty acid or the like in order to ensure good running performance.
As a result of further investigation based on the above knowledge, the present inventors have used rare earth elements to prevent sintering and the like, and the surface layer of the ferromagnetic powder is made of silicon oxide and / or oxyhydroxide. It has been found that by coating with a film containing as a main component, it is possible to achieve both fine particles and high Hc of the magnetic material and good running properties and storage properties, and the present invention has been completed.

That is, the means for achieving the object of the present invention is as follows.
[1] A ferromagnetic powder having a first film and a second film in this order on the surface of a metal particle,
The first film contains a rare earth element oxide and / or oxyhydroxide as a main component,
2. The ferromagnetic powder according to claim 1, wherein the second film contains silicon oxide and / or oxyhydroxide as a main component, and the metal particles contain Fe and / or Co as a main component.
[2] The ferromagnetic powder according to [1], wherein the rare earth element is yttrium.
[3] A first layer containing, as a main component, an oxide and / or oxyhydroxide of one or more elements selected from the group consisting of Al, Si, Fe and Co between the metal particle surface and the first film. The ferromagnetic powder according to [1] or [2], further comprising three films.
[4] The ferromagnetic powder according to any one of [1] to [3], wherein the ferromagnetic powder has a coercive force Hc in the range of 1.35 × 10 ^{5 to} 3.18 × 10 ⁵ A / m.
[5] The ferromagnetic powder according to any one of [1] to [4], wherein a saturation magnetization σs of the ferromagnetic powder is in a range of 120 to 180 A · m ² / kg.
[6] The average major axis of the ferromagnetic powder is in the range of 10 to 120 nm, the average minor axis is in the range of 4 to 30 nm, and the average acicular ratio is in the range of 2 to 12. [1] to [ [5] The ferromagnetic powder according to any one of [5].
[7] The ferromagnetic powder according to any one of [1] to [6], wherein the ferromagnetic powder contains 10 to 40% by mass of Co with respect to Fe.
[8] A magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
The magnetic recording medium, wherein the ferromagnetic powder is the ferromagnetic powder according to any one of [1] to [7].
[9] The magnetic recording medium according to [8], wherein the magnetic layer has a thickness in the range of 0.01 to 0.5 μm.
[10] The magnetic recording medium according to [8] or [9], wherein the magnetic layer further contains a fatty acid and / or a fatty acid ester.
[11] The magnetic recording medium according to any one of [8] to [10], further including a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer.
[12] The magnetic recording medium according to [11], wherein the nonmagnetic layer further contains a fatty acid and / or a fatty acid ester.

  According to the present invention, high output and high C / N can be achieved with a fine particle, high coercive force, little demagnetization even in an environment such as high temperature and high humidity, and little production of fatty acid metal salt by reaction with fatty acid. Magnetic powder can be provided. Furthermore, according to the present invention, by using the above ferromagnetic powder, the noise is low, the C / N is high, the occurrence of demagnetization and head contamination in an environment such as high temperature and high humidity is reduced, and excellent. In addition, a magnetic recording medium having excellent running durability and storage stability can be provided.

Hereinafter, the present invention will be described in more detail.

[Ferromagnetic powder]
The ferromagnetic powder of the present invention is a ferromagnetic powder having a first film and a second film in this order on the surface of metal particles, wherein the first film comprises a rare earth element oxide and / or oxywater. The second coating film contains an oxide as a main component, the silicon oxide and / or oxyhydroxide as a main component, and the metal particles contain Fe and / or Co as a main component.

  In order to prevent sintering and oxidation of metal particles, the ferromagnetic powder of the present invention has a rare earth element oxide and / or oxyhydroxide (hereinafter also referred to as “rare earth oxide etc.”) in order to prevent sintering of metal particles. Cover with a first coating containing as a major component. Further, a second film containing a silicon oxide and / or oxyhydroxide (hereinafter also referred to as “silicon oxide or the like”) as a main component is provided thereon. Thus, by coating the surface of the metal particles with a rare earth oxide of a rare earth element having a large atomic radius, it is possible to obtain a sintering prevention effect and oxidation stability, and the fine particles, high coercive force, high temperature, high humidity, etc. Ferromagnetic powder with little demagnetization can be obtained even in an environment. Further, by coating the first film containing the rare earth oxide as a main component with silicon oxide or the like, the lubricant component (fatty acid, fatty acid ester) contained in the magnetic layer reacts with the rare earth element to attach a head. It can prevent that a kimono is produced | generated. Thus, according to the present invention, a ferromagnetic powder having fine particles and high coercive force, as well as excellent durability and storage stability can be obtained.

As the magnetic properties of the ferromagnetic powder of the present invention, the coercive force Hc is preferably in the range of 1.35 × 10 ^{5 to} 3.18 × 10 ⁵ A / m (1700 to 4000 Oersted), and 1.43 × More preferably, it is in the range of 10 ^{5 to} 2.79 × 10 ⁵ A / m (1800 to 3500 oersted), and the saturation magnetization σs is in the range of 120 to 180 A · m ² / kg (120 to 180 emu / g). It is more preferable that it is in the range of 135 to 170 A · m ² / kg (135 to 170 emu / g). The ferromagnetic powder having the above magnetic properties can provide a magnetic recording medium having a short wavelength output and a good S / N ratio and an excellent overwrite property, and a magnetoresistance requiring low noise and high Hc. This is suitable for a mold head (MR head) mounting system.

  Moreover, as a particle size of the ferromagnetic powder of this invention, it is preferable that an average major axis is the range of 10-120 nm. If the average major axis is 10 nm or more, the desired coercive force and saturation magnetization can be obtained, the dispersibility in the magnetic layer coating solution is good, and the effect of magnetic field orientation tends to appear. Further, when the average major axis is 120 nm or less, the reproduction loss with respect to the major axis is low, and medium noise can be reduced to obtain an excellent S / N. The average needle ratio of the ferromagnetic powder of the present invention is preferably in the range of 2 to 12, and more preferably in the range of 3 to 9. If the average needle ratio is within the above range, high Hc can be obtained by shape anisotropy, which is advantageous for high density recording. The average minor axis of the ferromagnetic powder of the present invention is preferably in the range of 4 to 30 nm, and more preferably in the range of 6 to 15 nm. As will be described later, the ferromagnetic powder of the present invention can also have a surface oxide film formed by a slow oxidation treatment, and in this case, the particle size relates to the ferromagnetic powder containing the surface oxide film.

  In the ferromagnetic powder of the present invention, it is preferable that the variation coefficient of the major axis and the needle ratio is small. If the variation coefficient of the major axis and the needle ratio is small, the Hc distribution is small, and in particular, r3000 / Hc = (ratio of the component that undergoes magnetization reversal at or above Hc3000 Oersted / Hc) is reduced, which is preferable in terms of overwrite characteristics. Also, the smaller the coefficient of variation of the major axis and the needle ratio, the higher the Hc and Hc distribution, the less the high coercive force component, and the smaller the SFD. The major axis variation coefficient is preferably 30% or less, and more preferably 25% or less. Further, the variation coefficient of the acicular ratio is preferably 30% or less, and more preferably 25% or less.

The average major axis of the ferromagnetic powder indicates the average of the major axis length of the metal powder particles, the average minor axis indicates the average of the minor axis length of the particles, and the average acicular ratio is The average value of needle ratio (major axis / minor axis). The coefficient of variation of the needle ratio refers to a value obtained by dividing the standard deviation of the needle ratio by the average needle ratio. The variation coefficient of the major axis refers to a value obtained by dividing the standard deviation of the major axis by the average major axis. In addition, each said average value is a value calculated by measuring about 500 particle | grains, for example. The ferromagnetic powder particles are usually composed of one to several metal crystallites. In the present invention, a portion containing (accumulating) all the crystallites is called a ferromagnetic powder particle. The average value can be obtained by observing the ferromagnetic powder with a high-resolution transmission electron microscope.
Below, the 1st membrane | film | coat, 2nd membrane | film | coat, metal particle, etc. in the ferromagnetic powder of this invention are demonstrated.

1st film | membrane The ferromagnetic powder of this invention has a 1st film | membrane and a 2nd film | membrane in this order on the said metal particle surface. The first film contains a rare earth element oxide and / or oxyhydroxide (such as a rare earth oxide) as a main component, and this film prevents the metal particles from being sintered and enables the formation of fine particles. In addition, the effect of preventing oxidation and preventing demagnetization can be obtained.

  The first film contains the rare earth oxide or the like as a main component. Here, “including as a main component” means that the rare earth oxide or the like occupies 50% by mass or more of the film.

  Examples of the rare earth element include yttrium (Y), cerium (Ce), neodymium (Nd), and samarium (Sm). Among them, yttrium is preferably used to obtain a high sintering preventing effect. . The content of the rare earth element in the first film may be, for example, 0.5 to 20% by mass, preferably 1 to 12% by mass with respect to the ferromagnetic powder. When the first coating contains the above-mentioned amount of rare earth element, a high sintering prevention effect and oxidation prevention effect can be obtained.

  The thickness of the first film is not particularly limited, but can be, for example, 0.3 to 10 nm, preferably 0.5 to 5 nm in order to effectively prevent sintering and oxidation. The thickness of the first film and the amount of the rare earth element contained in the film can be controlled by the concentration of the aqueous solution used for forming the film, the immersion time in the aqueous solution, and the like.

Second coating The second coating contains silicon oxide and / or oxyhydroxide (silicon oxide, etc.) as a main component, and is contained in the first coating located in the lower layer and the magnetic layer, etc. The agent component (fatty acid and / or fatty acid ester) functions to prevent head deposits from reacting with each other. In addition, about the 2nd membrane | film | coat, "it contains as a main component" means that the said silicon oxide etc. occupy 50 mass% or more in the said membrane | film | coat. The silicon content in the second coating can be, for example, 0.5 to 20% by mass, preferably 1 to 10% by mass with respect to the ferromagnetic powder. When the second coating contains the above amount of silicon, head contamination can be effectively prevented.

  The thickness of the second film is not particularly limited, but can be, for example, 0.3 to 10 nm, preferably 0.5 to 5 nm, in order to effectively prevent head contamination. The thickness of the second film and the amount of silicon contained in the film can be controlled by the concentration of the aqueous solution used for forming the film, the immersion time in the aqueous solution, and the like.

Metal particle The metal particle located in the core part of the ferromagnetic powder of the present invention contains Fe and / or Co as a main component. Here, “including as a main component” means that the atoms occupy 75 atomic% or more of the metal particles. The metal particles may contain Fe or Co as a main component, or may contain an Fe—Co alloy as a main component.

  In addition to the predetermined atoms, the metal particles include Al, Si, S, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Sr, W, Au. , Pb, Bi, La, Ce, Pr, Nd, P, Mn, Zn, Sr, B, and Ca. In addition to controlling the shape of the starting material, these elements are effective in preventing sintering between particles and promoting reduction, and controlling the shape of the reduced metal particles and the unevenness of the particle surface.

  In the present invention, in order to obtain a ferromagnetic powder having a desired particle size and magnetic properties, it is preferable to control the size and magnetic properties of the metal particle portion. The average major axis of the metal particles is preferably 25 to 90 nm, more preferably 35 to 90 nm. The average acicular ratio of the metal particles is preferably 3 to 12, and the average minor axis is preferably in the range of 4 to 14 nm. In addition, by observing the ferromagnetic powder of the present invention with a high-resolution transmission electron microscope, the core (metal particles) and the coating can be distinguished. Obtain the particle size of the core (metal particles) by observing the lattice image with a high-resolution transmission electron microscope, measuring the thickness of the coating, and subtracting the thickness of the coating from the particle shape of the ferromagnetic powder. Can do. In addition, the definition and calculation method of the average major axis, the average minor axis, and the average needle ratio for the metal particles are as described above for the ferromagnetic powder.

The coercive force Hc of the metal particles is 1.43 × 10 ^{5 to} 2.79 × 10 ⁵ A / m (1800 to 3500 Oe), and the saturation magnetization σs is 120 to 180 A · m ² / kg (120 to 180 emu / g). Each is preferred. By controlling the magnetic properties of the metal particles within the above range, a ferromagnetic powder having desired magnetic properties can be obtained.

  In the present invention, the composition of each film (first, second, and third film described later) contained in the ferromagnetic powder can be analyzed by, for example, ESCA depth profile analysis and X-ray diffraction. The content of various elements in the ferromagnetic powder can be determined by dissolving the ferromagnetic powder with hydrochloric acid and quantitatively analyzing it using an ICP (induction plasma) analyzer.

Next, the manufacturing method of the ferromagnetic powder of this invention is demonstrated.
The ferromagnetic powder of the present invention can be obtained by sequentially depositing a predetermined amount of a rare earth element compound and a silicon compound on a starting material such as iron oxyhydroxide or iron oxide and then reducing it. More specifically, a rare earth compound and an alkali are added to an aqueous solution containing a starting material, and then a silicon compound and an alkali are added to the aqueous solution to obtain a suspension. The suspension is washed with water and filtered. By subjecting the resulting particles to a reduction treatment, a ferromagnetic powder having a first film and a second film in this order on the surface of the metal particles can be obtained. In addition, it is preferable to perform the crushing process for making it the primary particle after drying the said filtered particle | grain.

  Examples of the rare earth compound used for forming the first film include chlorides such as Y, Ce, Nd, and Sm, nitrates, and the like. Examples of the silicon compound used for forming the second film include water glass and sodium silicate. As the alkali added together with the rare earth compound or silicon compound, ammonia water, NaOH, KOH or the like can be used, and among them, ammonia water from which metals such as Na and K are removed as trace elements by dry treatment. Is preferred. The concentration of the rare earth compound, silicon compound and alkali in the aqueous solution may be appropriately set so that a desired amount of rare earth element and silicon can be deposited.

In particular, in the present invention, a starting material having a long axis and a good needle ratio and a uniform particle size is subjected to a sintering prevention treatment with silica, phosphoric acid, aluminum-silica or the like, and a metal oxide (eg, FeOx: 1 ≦ x ≦ 1.5, for example, Fe ₂ O ₃ , Fe ₃ O ₄ ) to adjust the particle size of the metal particles in the ferromagnetic powder by controlling the needle ratio when reducing to metal (eg, Fe) It is preferable. As a starting material, for example, FeOOH, Fe ₂ O ₃ , Fe ₃ O _{4 and the} like, specifically, monodispersed goethite (α-FeOOH) or monodispersed hematite (α-Fe ₂ O ₃ ) can be used. The production method of the starting material is not particularly limited, and for example, the methods described in JP-A-7-109122 and JP-A-6-340426 can be applied.

The average major axis length of the starting material (goethite, hematite, etc.) is preferably 20 to 150 nm, and the acicular ratio is preferably 2 to 12. It is preferable that the starting materials have the same shape, major axis length, minor axis length, and needle ratio. By using a starting material having an average major axis length of 20 nm or more, a ferromagnetic powder having desired Hc and σ _s can be obtained. Further, if a starting material having an average major axis length of 150 nm or less is used, fine particulate ferromagnetic powder can be obtained.

  In order to control the shape, major axis, and minor axis size of the metal particles uniformly and in a desired range, the particle shape control of the ferromagnetic powder, the crystallinity control, and the reduction treatment and the gradual oxidation treatment are repeated stepwise. It is preferable to control the thickness and crystallinity of the surface oxide film formed by the slow oxidation treatment.

For example, after a predetermined amount of a rare earth compound and a silicon compound are sequentially deposited on monodispersed goethite (α-FeOOH) or monodispersed hematite (α-Fe ₂ O ₃ ), reduction treatment with pure hydrogen or the like is performed. The core goethite or hematite can be reduced to metal. In the middle of the process, annealing with α-Fe ₂ O ₃ is useful for increasing the crystal ratio. Moreover, when reducing from α-Fe ₂ O ₃ to Fe ₃ O ₄ and FeO, various reducing gases can be used instead of pure hydrogen. Since it is known that moisture is related to sintering during reduction, water generated by reduction can be removed from the system in a short period of time in order to suppress the formation of product nuclei as much as possible and increase the crystallinity. It is preferable to control the amount of water produced by removal or reduction. Such control of water can be performed by controlling the partial pressure of the reducing gas or by controlling the amount of reducing gas. The reduced ferromagnetic powder is preferably subjected to a gradual oxidation treatment to form an oxide film on the surface of the ferromagnetic powder particles in order to increase chemical stability. The core (metal particles) after reduction may contain a small amount of iron oxyhydroxide or iron oxide. If carbon dioxide gas is contained in the gas used during the gradual oxidation treatment, it is adsorbed at the basic point on the surface of the metal particles, and such carbon dioxide gas may be contained.

In addition, when producing magnetic metal powder using goethite (α-FeOOH) or hematite (α-Fe ₂ O ₃ ) as a starting material, it is deoxidized and reduced to metal, and at the same time, shrinkage of the outer shape of the particles is reduced. Wake up to obtain polycrystalline crystals with many voids. Therefore, by reducing the size and form of the starting material, especially the coefficient of variation of the major axis and the needle ratio, and controlling the major axis, minor axis and needle ratio of the metal particles, the coefficient of variation of the single crystal can be reduced by reducing the coefficient of variation. Metal particles containing a large number of structured particles can be obtained.

  Further, by selecting the pretreatment before reduction, for example, dehydration conditions such as goethite and hematite, annealing conditions, and the reduction conditions such as temperature, reducing gas, reduction time, etc., the magnetic properties of the ferromagnetic powder It is possible to control the physical properties of the metal particle portion that provides the characteristics. For example, preferable conditions when processing goethite are as follows. Examples of the dehydration condition include a rotary electric furnace in a nitrogen atmosphere at 250 to 400 ° C., preferably 300 to 400 ° C., for 0.5 to 2 hours, preferably 0.5 to 1 hour. Annealing conditions include a static reduction furnace in a nitrogen atmosphere at 500 to 800 ° C., preferably 550 to 700 ° C. for 1 to 5 hours, preferably 2 to 3 hours. After the dehydration treatment, a step of washing the hematite obtained by the dehydration treatment before the annealing treatment and removing the soluble alkali metal may be provided. Surfaces formed by metal particle shape control, crystallinity control and gradual oxidation treatment by performing dehydration and annealing treatment and gradual oxidation treatment stepwise and repeatedly, for example, gradually raising the temperature from low temperature to high temperature. It is effective to control the thickness and crystallinity of the oxide film.

  As the reducing conditions, 350 to 600 ° C., preferably 425 to 530 ° C., preferably 0.25 to 1 hour, preferably 0.25 to 0.5 hour in a hydrogen atmosphere in a stationary reducing furnace, After replacing the atmosphere with nitrogen, heat at 450 to 650 ° C., preferably 500 to 600 ° C., 0.5 to 3 hours, preferably 1 to 2 hours, and then switch to pure hydrogen for 3 to 5 hours at the above temperature. Reduction treatment can be mentioned. The shape of the metal particles can be controlled and the crystallinity can be increased by repeatedly performing the reduction treatment stepwise and repeatedly, for example, gradually raising the temperature from a low temperature to a high temperature. The end of the reduction can be determined by measuring the moisture in the drainage gas with a dew point meter.

  The ferromagnetic powder of the present invention is an oxide of one or more elements selected from the group consisting of Al, Si, Fe and Co between the surface of the metal particles and the first film in order to improve magnetic properties. It is preferable to further have a third film containing a product and / or oxyhydroxide as a main component. In particular, in order to increase the saturation magnetization σs and form a dense and thin film, the third film preferably contains a Co oxide as a main component. Here, “including as a main component” means that the component occupies 40% by mass or more in the film. Regardless of the presence or absence of the third film, the ferromagnetic powder of the present invention preferably contains 10 to 40% by mass (more preferably 15 to 35% by mass) of Co with respect to Fe. The third film can be formed by doping a part of the raw material at the time of preparation of the starting materials goethite and hematite, and then applying the above-described reduction treatment after depositing the required amount on the surface. The thickness of the third film is not particularly limited, but is, for example, 0.3 to 20 nm, preferably 0.5 to 10 nm.

  In addition, the ferromagnetic metal powder can be treated in advance with a dispersant, lubricant, surfactant, antistatic agent, etc., which will be described later, before dispersion. Specifically, Japanese Patent Publication No. 44-14090, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 47-22062, Japanese Patent Publication No. 47-22513, Japanese Patent Publication No. 46-28466, Japanese Patent Publication No. 46-38755. No. 47, No. 47-4286, No. 47-12422, No. 47-17284, No. 47-18509, No. 47-18573, No. 39-10307 No. 48-39639, U.S. Pat. Nos. 3,026,215, 3,031,341, 3,100,194, 3,342,005, and 3,389,014.

  The water content of the ferromagnetic powder of the present invention is preferably 0.01 to 2% by mass. It is desirable to optimize the moisture content according to the type of binder described below. The tap density of the ferromagnetic powder of the present invention is preferably 0.2 to 0.8 g / cc. If the powder is larger than 0.8 g / cc, it may not be uniformly oxidized when the powder is gradually oxidized, and it may be difficult to handle the powder safely or the magnetization of the obtained tape may decrease over time. is there. When the tap density is 0.2 g / cc or less, dispersion tends to be insufficient.

[Magnetic recording medium]
The magnetic recording medium of the present invention is a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support, wherein the ferromagnetic powder is the ferromagnetic powder of the present invention. . As described above, the ferromagnetic powder of the present invention has the first coating on the metal particles, so that it can obtain a sintering prevention effect and oxidation stability, and has fine particles, high coercive force, high temperature and high humidity, etc. Ferromagnetic powder with little demagnetization can be obtained even under the above environment. Furthermore, by covering this first film with a second film mainly composed of silicon oxide or the like, the lubricant component (fatty acid, fatty acid ester) contained in the magnetic layer and the like reacts with the rare earth element to attach a head. It can prevent that a kimono is produced | generated.

  In the magnetic recording medium of the present invention, the thickness of the magnetic layer is preferably in the range of 0.01 to 0.5 μm, more preferably in the range of 0.02 to 0.3 μm. It is preferable to set the optimum thickness according to the above. In general, if the magnetic layer thickness is 0.01 μm or more, high output and good C / N can be obtained. On the other hand, if the magnetic layer thickness is 0.5 μm or less, a good C / N can be obtained with less noise.

The coercive force Hc of the magnetic layer is preferably 1.35 × 10 ^{5 to} 3.18 × 10 ⁵ A / m (1700 to 4000 oersted), more preferably 1.43 × 10 ^{5 to} 3.02. × 10 ⁵ A / m (1800 to 3800 Oersted), more preferably 1.59 × 10 ^{5 to} 2.79 × 10 ⁵ A / m (2000 to 3500 Oersted), and Bm (maximum magnetic flux density) of the magnetic layer Is preferably 350 to 700 mT (3500 to 7000 Gauss (G)), more preferably 390 to 700 mT (3900 to 7000 G). If Hc and Bm are equal to or higher than the lower limit values, a sufficiently short wavelength output can be obtained, and if they are equal to or lower than the upper limit values, output can be ensured by preventing saturation of the head used for recording.

The magnetic recording medium of the present invention is most suitable for a DVC system proposed as a digital VTR system for vapor deposition tape, but is effective for a system having the following characteristics in addition to the DVC system.
1) Short wavelength recording with a recording wavelength of 0.6 μm or less.
2) The recording wavelength of the servo signal is 30 times or more the recording wavelength of the recording signal.
3) Record the recording signal and servo signal simultaneously.
4) Overwrite part of the record in 3).

  Here, the servo signal means a control signal and is usually used to indicate the position of the recording signal. The overwritten portion in 4) is usually a part in the width direction of the predetermined track already recorded in 3), and the recording signal to be overwritten preferably consists of only a short wavelength recording signal. The width of the writing portion is usually 10 to 80%, preferably 10 to 60% of the width of the magnetic head. Even if less than 10% or exceeding 80%, it is difficult to ensure tracking accuracy, which is not desirable.

  The track width is usually in the range of 5 to 20 μm, preferably 5 to 15 μm, the width of the magnetic head is 5 to 25 μm, preferably 10 to 20 μm, and the track width and the magnetic head width are almost equal. Although it may be different, it is desirable that the width of the magnetic head is slightly larger than the track width. Specifically, in the DVC system, the tape width is 1/4 inch width, the thickness is 7 μm, the track width is 10 μm, the magnetic head width is 15 μm, the overwriting width is 5 μm, the short wavelength recording signal is 0.5 μm, the servo. The signal is 22.5 μm.

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

  Such binder resins include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl. There are polymers or copolymers containing acetal, vinyl ether and the like as structural units, polyurethane resins, and various rubber resins.

  Thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, acrylic reactive resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, polyesters. Examples thereof include a mixture of resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like.

In order to obtain a superior dispersion effect of the ferromagnetic powder and durability of the magnetic layer in the binder resin, COOM, SO ₃ M, OSO ₃ M, P═O (OM) ₂ , O -P = O (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base), OH, NR ₂ , N ⁺ R ₃ (R is a hydrocarbon group), epoxy group, SH, CN, etc. It is preferable to introduce at least one polar group by copolymerization or addition reaction. The amount of such a polar group is, for example, 10 ⁻¹ to 10 ⁻⁸ mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g.

  The binder resin is used, for example, in the range of 5 to 50% by mass, preferably in the range of 10 to 30% by mass with respect to the ferromagnetic metal powder. It is preferable to use a combination of 5 to 100% by mass when using a vinyl chloride resin, 2 to 50% by mass when using a polyurethane resin, and 2 to 100% by mass of polyisocyanate.

The filling degree of the ferromagnetic powder in the magnetic layer can be calculated from the maximum saturation magnetization σs and the maximum magnetic flux density Bm of the used ferromagnetic powder (Bm / 4πσs), and the value is preferably 1.9 g / cc. Or more, more preferably 2.0 g / cc or more, and most preferably 2.2 g / cc or more. In the present invention, when polyurethane is used, the glass transition temperature is −50 to 100 ° C., the breaking elongation is 100 to 2000%, the breaking stress is 0.05 to 10 kg / mm ² (0.49 to 98 MPa), and the yield point is 0. It is preferable to use one having a thickness of 0.05 to 10 kg / mm ² (0.49 to 98 MPa).

  Polyisocyanates that can be used in the present invention include tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane. Examples thereof include isocyanates such as triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates. Commercially available product names of these isocyanates include Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical Taketake D-102, Takenate D-110N, Takenate D-200, Takenate D-202, Sumitomo Bayer's Death Module L, Death Module IL, Death Module N, Death Module HL, etc. It can be used in combination of the above.

  In the present invention, additives having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, and the like can be used for the magnetic layer. Specifically, molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, poly Glycol, alkyl phosphate ester and alkali metal salt thereof, alkyl sulfate ester and alkali metal salt thereof, polyphenyl ether, phenylphosphonic acid, α-naphthyl phosphoric acid, phenyl phosphoric acid, diphenyl phosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid, aminoquinones , Various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having 10 to 24 carbon atoms (including unsaturated bonds or branched And a metal salt thereof (Li, Na, K, Cu, etc.) or a monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol (unsaturated) having 12 to 22 carbon atoms. A bond may be included or branched), an alkoxy alcohol having 12 to 22 carbon atoms (which may include an unsaturated bond or branched), and a monobasic group having 10 to 24 carbon atoms Fatty acids (which may contain unsaturated bonds or may be branched) and any one of monovalent, divalent, trivalent, tetravalent, pentavalent and hexavalent alcohols having 2 to 12 carbon atoms (unsaturated) Mono-fatty acid ester or di-fatty acid ester or tri-fatty acid ester, fatty acid ester of monoalkyl ether of alkylene oxide polymer, fatty acid having 8 to 22 carbon atoms, which may contain a saturated bond or may be branched) Amides, aliphatic amines having 8 to 22 carbon atoms, and the like can be used.

  Specific examples of these fatty acids include capric acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, isostearic acid, and the like. . Esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate, 2-octyldodecyl palmitate 2-hexyldecyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, oleyl erucate, neopentyl glycol didecanoate, ethylene glycol dioleyl, oleyl alcohol, stearyl for alcohols Alcohol, lauryl alcohol, etc. are mentioned. Nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or sulfoniums, etc. Cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphate ester group, amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohol, Amphoteric surfactants such as alkylbedine type can also be used. These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides in addition to the main components. Absent. These impure amounts are preferably 30% by mass or less, more preferably 10% by mass or less.

  These lubricants and surfactants used in the present invention have different physical actions, and the type, amount, and combination ratio of lubricants that produce a synergistic effect are optimally determined according to the purpose. It should be done. Adjusting the amount of surfactant to control bleeding on the surface using fatty acids with different melting points in the nonmagnetic layer and magnetic layer, and controlling bleeding on the surface using esters with different boiling points, melting points and polarities. In this case, it is conceivable to improve the stability of coating and increase the lubricating effect by increasing the additive amount of the lubricant in the intermediate layer. Of course, it is not limited to the examples shown here. Generally, the total amount of the lubricant can be in the range of 0.1 to 50% by mass, preferably 2 to 25% by mass, with respect to the ferromagnetic powder or nonmagnetic powder. In particular, the magnetic recording medium of the present invention is a ferromagnetic powder having a coating (previously described second coating) for preventing a reaction between a rare earth element added to prevent sintering and the like and a fatty acid and / or a fatty acid ester. Therefore, even when fatty acids and / or fatty acid esters are contained in the magnetic layer and further in the nonmagnetic layer, it is possible to remarkably suppress the occurrence of head contamination. For example, the amount of fatty acid and / or fatty acid ester in the magnetic layer is 0.3 to 20% by mass relative to the ferromagnetic powder, and the amount of fatty acid ester and / or fatty acid ester in the non-magnetic layer is, for example, relative to the non-magnetic powder. 0.3 to 20% by mass

The magnetic layer of the magnetic recording medium of the present invention may contain conductive particles as an antistatic agent. However, in order to maximize the saturation magnetic flux density of the uppermost layer, it is preferable to add it to the uppermost layer as much as possible and add it to a coating layer other than the uppermost layer (for example, a nonmagnetic layer described later). In particular, carbon black is preferably added as an antistatic agent in order to reduce the surface electrical resistance of the entire medium. Examples of the carbon black that can be used in the present invention include furnace for rubber, thermal for rubber, black for color, conductive carbon black, acetylene black, and the like. Its specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 1500 ml / 100 g, particle diameter is 5 to 300 nm, pH is 2 to 10, water content is 0.1 to 10%, tap density is 0.1. ˜1 g / cc is preferred respectively. As specific examples of carbon black used in the present invention, BLACKPEARLS 2000, 1300, 1000, 900, 800, 700, VULCAN XC-72 manufactured by Cabot Corporation, # 80, # 60, # 55, # 50 manufactured by Asahi Carbon Co., Ltd. # 35, # 3950B, # 3250B, # 2400B, # 2300, # 900, # 1000, # 30, # 40, # 10B, manufactured by Mitsubishi Chemical Industries, Ltd., CONDUCTEX SC, Raven 150, 50, 40, manufactured by Columbia Carbon Co., Ltd. 15. Ketjen Black EC, Ketjen Black ECDJ-500, Ketjen Black ECDJ-600, etc. manufactured by Lion Aguzo. Carbon black may be surface-treated with a dispersant, carbon black may be oxidized, or may be grafted with a resin, or may be obtained by graphitizing a part of the surface. Carbon black may be dispersed with a binder in advance before being added to the magnetic layer coating solution. When carbon black is used for the magnetic layer, the amount based on the ferromagnetic powder is preferably 0.1 to 30% by mass. Furthermore, it is preferable to contain 3-20 mass% with respect to all nonmagnetic powders in the nonmagnetic layer mentioned later.

  In general, carbon black not only acts as an antistatic agent, but also acts to reduce the coefficient of friction, impart light shielding properties, improve film strength, etc., and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention Of course, it is possible to change the type, amount, and combination, depending on the purpose, based on the above-mentioned various properties such as particle size, oil absorption, electrical conductivity, and pH. The carbon black that can be used can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

  Forming two or more coating layers on a non-magnetic support is also effective in producing a magnetic recording medium having a high recording density, and the simultaneous coating method can produce an ultrathin magnetic layer. Are better. As a specific method of the wet-on-wet method as the simultaneous coating method, (1) a gravure coating, roll coating, blade coating, and extrusion coating apparatus generally used for coating a magnetic layer coating solution are first used to form a lower layer. While the layer is still wet, for example, non-magnetic supports disclosed in JP-B-1-46186, JP-A-60-238179 and JP-A-2-265672 A method of coating the upper layer with a pressure type extrusion coating apparatus; (2) a coating solution flow as disclosed in JP-A-63-88080, JP-A-2-17971 and JP-A-2-265672. A method of applying a lower layer coating solution and an upper layer coating solution almost simultaneously by a coating head having two liquid slits; (3) The backup roll with an extrusion coating apparatus disclosed in 174965 discloses a method of substantially simultaneously coating an upper layer and lower layer, and the like are exemplified.

  When applying a non-magnetic layer on a non-magnetic support by wet-on-wet method to provide a magnetic layer thereon, the flow characteristics of the magnetic layer coating liquid and the non-magnetic layer coating liquid should be as close as possible, It is possible to obtain a magnetic layer having a uniform thickness and a small thickness fluctuation, with no disturbance of the interface between the coated magnetic layer and the nonmagnetic layer. Since the flow characteristics of the coating liquid strongly depend on the combination of the powder particles and the binder resin in the coating liquid, attention should be paid particularly to the selection of the nonmagnetic powder used for the nonmagnetic layer.

[Nonmagnetic layer]
The magnetic recording medium of the present invention can further have a magnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. The nonmagnetic powder can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, having an α conversion rate of 90% or more, Acicular needles made by dehydrating and annealing titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, and magnetic iron oxide Alpha iron oxide and, if necessary, those surface-treated with aluminum and / or silica can be used alone or in combination. The particle size of these non-magnetic powders is usually in the range of 0.01 to 2 μm, preferably 0.015 to 1.00 μm, more preferably 0.015 to 0.50 μm. Different nonmagnetic powders can be combined, or even a single nonmagnetic powder can have the same effect by widening the particle size distribution. The tap density is usually 0.05 to 2 g / cc, preferably 0.2 to 1.5 g / cc. The water content is usually 0.1 to 5%, preferably 0.2 to 3%. The pH is usually 2-11. The specific surface area is usually 1 to 200 m ² / g, preferably 5 to 100 m ² / g, more preferably 7 to 80 m ² / g. The crystallite size is usually in the range of 0.010 to 2.00 μm, preferably 0.015 to 1.00 μm, and more preferably 0.015 to 0.50 μm. The oil absorption using DBP is usually 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. The specific gravity is usually 1 to 12, preferably 2 to 8. The shape may be any of a needle shape, a spherical shape, a dice shape, and a plate shape. The nonmagnetic powder is not necessarily 100% pure, and the surface may be treated with another compound depending on the purpose. At that time, if the purity is usually 70% or more, the effect is not reduced. For example, when titanium oxide is used, the surface is generally treated with alumina. The ignition loss is preferably 20% or less. The Mohs hardness of the inorganic powder used in the present invention is preferably 4 or more.

  Specific examples of the non-magnetic powder used in the present invention include UA5600, UA5605, Showa Denko AKP-20, AKP-30, AKP-50, HIT-50, HIT-100, ZA-G1, Nippon Chemical Industry Co., Ltd. G5, G7, S-1, Toda Kogyo TF-100, TF-120, TF-140, Ishihara Sangyo TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO- 55S, TTO-55D, FT-1000, FT-2000, FTL-100, FTL-200, M-1, S-1, SN-100, Titanium Industry ECT-52, STT-4D, STT-30D, STT -30, STT-65C, Mitsubishi Materials T-1, Nippon Shokubai NS-O, NS-3Y, NS-8Y, Teica MT-100S, MT-100T, M -150W, MT-500B, MT-600B, MT-100F, Sakai Chemical FINEX-25, BF-1, BF-10, BF-20, BF-1L, BF-10P, Dowa Mining DEFIC-Y, DEFIC -R, titanium industry-made Y-LOP is mentioned.

Moreover, it is preferable to use nonmagnetic powder and carbon black together in the nonmagnetic layer. Examples of the carbon black used in the nonmagnetic layer include a furnace for rubber, a thermal for rubber, a black for color, and acetylene black. The specific surface area is usually, 100~500m ² / g, preferably 150~400m ² / g, DBP oil absorption amount is usually, 20 to 400 ml / 100 g, preferably from 30 to 200 ml / 100 g. The particle diameter is usually 5 to 80 nm, preferably 10 to 50 nm, and more preferably 10 to 40 nm. Usually, the pH is preferably 2 to 10, the water content is preferably 0.1 to 10% by mass, and the tap density is preferably 0.1 to 1 g / cc. Specific examples of carbon black used for the nonmagnetic layer include Cabot's BLACKPEARLS 2000, 1300, 1000, 900, 800, 880, 700, VULCAN XC-72, Mitsubishi Kasei Kogyo Co., Ltd. # 3050B, 3150B, 3250B. # 3750B, # 3950B, # 950, # 650B, # 970B, # 850B, MA-600, Columbia Carbon Corporation CONDUCTEX SC, RAVEN 8800, 8000, 7000, 5750, 5250, 3500, 2100, 2000, 1800, 1500 1255, 1250, Ketjen Black EC manufactured by Akzo Corporation, and the like. Carbon black may be surface-treated with a dispersant or the like, or may be used after being grafted with a resin, or may be obtained by graphitizing a part of the surface. Further, carbon black may be dispersed in advance with a binder before being added to the nonmagnetic coating solution. These carbon blacks can be used in a range not exceeding 50% by mass with respect to the inorganic powder and in a range not exceeding 40% by mass of the total mass of the nonmagnetic layer. These carbon blacks can be used alone or in combination. For the carbon black that can be used in the nonmagnetic layer, for example, “Carbon Black Handbook (Edited by Carbon Black Association)” can be referred to.

  As the nonmagnetic powder of the nonmagnetic layer, it is also possible to use an organic powder, for example, acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, phthalocyanine pigment, polyolefin resin powder, Polyester resin powder, polyamide resin powder, polyimide resin powder, and polyfluorinated ethylene resin can be used. The manufacturing method is described in, for example, Japanese Patent Application Laid-Open Nos. 62-18564 and 60-255827.

  These nonmagnetic powders can be used in a mass ratio of 0.1 to 20 times and a volume ratio of 0.1 to 10 times the volume of the binder. There is no fundamental difference between the binder used in the magnetic layer of the magnetic recording medium of the present invention and the binder used in the nonmagnetic layer. Rather, it is desirable that the composition of the binder is close to the same because the flow characteristics of the non-magnetic layer coating solution and the magnetic layer coating solution are similar.

[Layer structure]
In this magnetic recording medium, the thickness of the nonmagnetic support is usually 1 to 100 μm, preferably 3 to 20 μm, and the thickness of the nonmagnetic layer is usually 0.5 to 10 μm, preferably 0.50. It is in the range of 5.0 μm, more preferably 0.50 to 3.0 μm. It is also possible to form other layers other than the magnetic layer and the nonmagnetic layer according to the purpose. For example, an intermediate layer such as an undercoat layer for improving adhesion may be provided between the nonmagnetic support and the nonmagnetic layer. This thickness is, for example, 0.01-2 μm, preferably 0.05-0.5 μm. Further, a backcoat layer may be provided on the side opposite to the nonmagnetic support-side magnetic layer side. This thickness is, for example: The thickness is 1 to 2 μm, preferably 0.3 to 1.0 μm. As these intermediate layer and back coat layer, known ones can be used. In the case of a disk-shaped magnetic recording medium, the above layer structure can be provided on both sides.

[Non-magnetic support]
There is no restriction | limiting in particular in the nonmagnetic support body used by this invention, The normally used thing can be used. Examples of the material forming the nonmagnetic support include polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, polyimide, polysulfone, polyethersulfone, and various synthetic resin films, and aluminum foil. And metal foil such as stainless steel foil.

The surface roughness of the nonmagnetic support is a centerline average surface roughness Ra (cutoff value 0.25 mm), for example, 0.03 μm or less, preferably 0.02 μm or less, more preferably 0.01 μm or less. . Further, it is preferable that these nonmagnetic supports not only have a small center line average surface roughness but also have no large protrusions of 1 μm or more. The roughness of the surface can be freely controlled by the size and amount of filler added to the nonmagnetic support as necessary. Examples of these fillers include oxides and carbonates such as Ca, Si, Ti, and organic resin fine powders such as acrylic. The F-5 value in the web running direction of the non-magnetic support used in the present invention is preferably 5 to 50 kg / mm ² (49 to 490 MPa), and the F-5 value in the web width direction is preferably 3 to 30 kg / mm. ² (29 to 294 MPa). In general, the F-5 value in the longitudinal direction of the web is higher than the F-5 value in the width direction of the web, but this is not necessarily the case when it is necessary to increase the strength in the width direction.

Further, the heat shrinkage rate at 100 ° C. for 30 minutes in the web running direction and the width direction of the support is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage rate at 80 ° C. for 30 minutes is preferred. Is 1% or less, more preferably 0.5% or less. The breaking strength in both directions 5~100kg / mm ² (49~980MPa), it is preferred that each elastic modulus is 100~2000kg / mm ² (0.98~19.6GPa).

  Examples of organic solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran, alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, and methylcyclohexanol. Esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, benzene, toluene, xylene, cresol, chlorobenzene, etc. Aromatic hydrocarbons, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin Dichlorobenzene, chlorinated hydrocarbons and the like, N, N- dimethylformamide, hexane, etc. can be used in any ratio. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. If necessary, the type and amount of the organic solvent used in the present invention may be changed between the magnetic layer and the nonmagnetic layer. Use a highly volatile solvent in the nonmagnetic layer to improve surface properties, use a solvent with high surface tension (cyclohexanone, dioxane, etc.) in the nonmagnetic layer to improve coating stability, and a solvent with a high solubility parameter in the magnetic layer For example, the degree of filling may be increased by using, but it is not limited to these examples.

  The magnetic recording medium of the present invention is obtained by applying a magnetic layer coating solution obtained by kneading and dispersing using an organic solvent together with the ferromagnetic powder, a binder resin, and other additives as required, onto a nonmagnetic support. And it can obtain by orienting and drying as needed. In this case, in the magnetic layer coating solution, basically, a nonmagnetic layer coating solution using a nonmagnetic powder instead of the ferromagnetic metal powder is applied to the nonmagnetic support before forming the magnetic layer coating solution. A magnetic layer may be formed. The coating method when the magnetic recording medium of the present invention has a multilayer structure is as described above.

  In the present invention, the step of producing the magnetic layer coating liquid comprises at least a kneading step, a dispersing step, and a mixing step provided as necessary before and after these steps. Each process may be divided into two or more stages. All raw materials such as ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or during any step. In addition, individual raw materials may be added in two or more steps. For example, polyurethane may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion.

  Various kneaders can be used for kneading and dispersing the magnetic layer coating liquid. For example, two roll mill, three roll mill, ball mill, pebble mill, tron mill, sand grinder, Segvari, attritor, high speed impeller disperser, high speed stone mill, high speed impact mill, disper, kneader, high speed mixer, homogenizer, ultra A sonic disperser or the like can be used.

  The nonmagnetic layer coating solution used in the present invention can be produced according to the above-described method for producing the magnetic layer coating solution. In order to achieve the object of the present invention, it is a matter of course that a conventional known manufacturing technique can be used as a part of the process, but in the kneading process, those having a strong kneading force such as a continuous kneader and a pressure kneader are used. By using it, a magnetic recording medium having a high Br can be obtained. When a continuous kneader or a pressure kneader is used, 15 to 500 parts by mass with respect to 100 parts by mass of all or part of the ferromagnetic powder and the binder (but preferably 30% by mass or more of the total binder) and the ferromagnetic powder. The kneading treatment can be carried out within the range described above. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-64-79274.

The residual solvent contained in the magnetic layer of the magnetic recording medium of the present invention is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less, and the residual solvent contained in the magnetic layer is contained in the nonmagnetic layer. Less than the solvent is preferred. The porosity of the magnetic layer and the nonmagnetic layer is preferably 30% by volume or less, more preferably 10% by volume or less. The porosity of the nonmagnetic layer is preferably larger than the porosity of the magnetic layer, but may be small as long as the porosity of the nonmagnetic layer is 5% by volume or more.

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

  By such a method, a magnetic layer can be formed by subjecting the magnetic layer coating solution applied on the support to a treatment for orienting the ferromagnetic powder in the layer, if necessary, and then drying. Further, the magnetic recording medium of the present invention can also be produced by performing a surface smoothing process if necessary or cutting it into a desired shape.

  Examples of the surface smoothing treatment include calender roll treatment, and preferably a combination of a metal roll / metal roll. The surface of the metal roll has a mirror finish, and since it has a very smooth surface and the surface is hard, the surface of the magnetic layer suitable for high-density recording can be molded with high performance. it can. As a material of the metal roll, for example, a material obtained by subjecting chromium molybdenum steel to hard chrome plating is suitable.

The elastic modulus at 0.5% elongation of the magnetic layer is preferably 100 to 2000 kg / mm ² (0.98 to 19.6 GPa) in both the web application direction and the width direction, and the breaking strength is preferably 1 to 30 kg / cm ^2. (0.0098 to 0.294 GPa), the elastic modulus of the magnetic recording medium is preferably 100 to 1500 kg / mm ² (0.98 to 14.7 GPa) in both the web coating direction and the width direction, and the residual spread is preferably 0.5. % At any temperature of 100 ° C. or less, preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less. Moreover, in order to ensure electromagnetic conversion characteristics and running durability, the center surface average surface roughness of the magnetic layer is preferably 0.5 to 5 nm, and more preferably 1 to 3 nm.

  The magnetic recording medium of the present invention may be a tape for video use, audio use, etc., or a flexible disk or magnetic disk for data recording use, but signal loss due to the occurrence of dropout becomes fatal. It is particularly suitable as a medium for digital recording applications. Furthermore, by providing a nonmagnetic layer and setting the thickness of the magnetic layer to 0.5 μm or less, it is possible to obtain a high-density and large-capacity magnetic recording medium having high electromagnetic conversion characteristics.

  Next, the present invention will be described specifically by way of examples. However, this invention is not limited to the aspect shown in the Example. Hereinafter, the display of “parts” represents “parts by mass”.

[Example 1]
(1) Preparation of ferromagnetic powder Hematite with a major axis length of 50 nm and a needle-like ratio of 6 and doped with Co and / or Al (Co / Fe = 15 mass%, Al / Fe = 2 mass in terms of Fe) %) In order to form a third film, 15% by mass of Co nitrate was added in terms of Co / Fe, and ammonia water was further added to deposit Co on the hematite (treatment (a)). ). Next, 8% by mass of Y nitrate was added to this solution in terms of Y / (Co + Fe), and ammonia water was further added to deposit Y on the hematite (treatment (b)). Next, 2% by mass of water glass was added to this solution in terms of SiO ₂ / (Co + Fe), and ammonia water was further added to deposit Si on the hematite (treatment (c)). The suspension thus obtained was washed with water and filtered. The filtered particles were dried and crushed to make primary particles.

The hematite subjected to the above treatment was heated and reduced in a hydrogen and nitrogen gas atmosphere, and then gradually oxidized with nitrogen gas. By the above treatment, the average major axis length including the surface oxide film (formed by the slow oxidation treatment) is 33 nm, the needle ratio is 5, the variation coefficient of the needle ratio is 28%, the variation coefficient of the major axis length is 24%, and Hc1.88. A ferromagnetic powder having the characteristics shown in Table 1 was obtained, which was × 10 ⁵ A / m (2360 oersted), σs 110 A · m ² / kg (110 emu / g), and the surface oxide film thickness was 1.8 nm. Further, as a result of ESCA depth profile analysis, the strength of Si Y and Co was higher in order from the surface of the ferromagnetic powder. Thereby, it was confirmed that the Si-containing film (second film), the Y-containing film (first film), and the Co-containing film (third film) were sequentially formed by the above treatment. From the X-ray diffraction results and the production method, it was confirmed that Si, Y, and Co existed in the state of an oxide and / or an oxyhydroxide (including an amorphous component).

(2) Production of Magnetic Tape Using the following magnetic layer coating liquid and nonmagnetic layer coating liquid, a magnetic tape having a multilayer structure was produced.
(Magnetic layer coating solution)
Ferromagnetic powder prepared in (1) 100 parts Binder resin Vinyl chloride polymer 13 parts (containing -SO ₃ Na group 1 × 10 ^-4 eq / g, degree of polymerization 300)
Polyester polyurethane resin 5 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 (molar ratio), containing —SO ₃ Na group 1 × 10 ⁻⁴ eq / g)
Alumina fine particle powder (average particle size 180 nm) 5 parts carbon black (average particle size 40 nm) 1 part butyl stearate 2 parts stearic acid 2 parts methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 200 parts

(Non-magnetic layer coating solution)
80 parts of acicular hematite (specific surface area 55 m ² / g by BET method, average major axis length 0.12 μm, acicular ratio 8, pH 8.8, aluminum treatment Al / Fe = 6.5 atomic%)
10 parts of carbon black
(Average primary particle diameter 17 nm, DBP oil absorption 80 ml / 100 g, specific surface area 240 m ² / g by BET method, pH 7.5)
Binder resin 12 parts of vinyl chloride polymer (containing 1 × 10 ⁻⁴ eq / g of —SO ₃ Na group, polymerization degree 300)
Polyester polyurethane resin 5 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 (molar ratio), containing —SO ₃ Na group 1 × 10 ⁻⁴ eq / g)
Butyl stearate 1 part Stearic acid 2.5 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 200 parts

  Each of the magnetic layer coating solution and the nonmagnetic layer coating solution was kneaded with a kneader and then dispersed using a sand grinder. To the obtained dispersion, 5 parts of polyisocyanate is added to the non-magnetic layer coating liquid, 6 parts to the magnetic layer coating liquid, and 20 parts of a 1: 1 mixed solvent of methyl ethyl ketone and cyclohexanone is added to have an average pore size of 1 μm. It filtered using the filter and the coating liquid for a nonmagnetic layer and a magnetic layer was prepared.

  The nonmagnetic layer coating solution obtained on a 7 μm thick polyethylene terephthalate support was applied so that the thickness after drying was 1.5 μm, and immediately thereafter, the coating solution for the nonmagnetic layer was still wet. In the meantime, wet simultaneous multilayer coating was performed so that the magnetic layer had a thickness of 0.15 μm thereon, and while both layers were still wet, they were passed through an orientation device and longitudinally oriented. At this time, the magnet is passed through a rare earth magnet (surface magnetic flux 500 mT (5000 gauss)) and then passed through a solenoid magnet (magnetic flux density 500 mT (5000 gauss)), and dried to such an extent that the orientation does not return in the solenoid. Further, the magnetic layer was dried and wound up. Thereafter, a 7-stage calendar composed of metal rolls was used to perform a calendar process at a roll temperature of 90 ° C. to obtain a web-like magnetic recording medium, which was slit to 8 mm width to prepare an 8 mm video tape sample.

[Example 2]
(1) Preparation of ferromagnetic powder Hematite with a major axis length of 57 nm and a needle ratio of 6 and doped with Co and / or Al (Co / Fe = 15 mass%, Al / Fe = 2 mass in terms of Fe) %) Was used in the same manner as in Example 1 except that a ferromagnetic powder having the physical properties shown in Table 1 was prepared. As a result of ESCA depth profile analysis of the obtained ferromagnetic powder, the strength of Si Y and Co was higher in order from the surface of the ferromagnetic powder. Thereby, it was confirmed that the Si-containing film (second film), the Y-containing film (first film), and the Co-containing film (third film) were sequentially formed by the above treatment. From the X-ray diffraction results and the production method, it was confirmed that Si, Y, and Co existed in the state of an oxide and / or an oxyhydroxide (including an amorphous component).
(2) Production of magnetic tape A magnetic tape was produced in the same manner as in Example 1 except that the ferromagnetic powder obtained above was used instead of the ferromagnetic powder obtained in Example 1.

[Example 3]
(1) Preparation of ferromagnetic powder Hematite with a major axis length of 66 nm and a needle ratio of 6.3 doped with Co and / or Al (Co / Fe = 15% by mass, Al / Fe = A ferromagnetic powder having the physical properties shown in Table 1 was prepared in the same manner as in Example 1 except that 2% by mass) was used as a starting material. As a result of ESCA depth profile analysis of the obtained ferromagnetic powder, the strength of Si Y and Co was higher in order from the surface of the ferromagnetic powder. Thereby, it was confirmed that the Si-containing film (second film), the Y-containing film (first film), and the Co-containing film (third film) were sequentially formed by the above treatment. From the X-ray diffraction results and the production method, it was confirmed that Si, Y, and Co existed in the state of an oxide and / or an oxyhydroxide (including an amorphous component).
(2) Production of magnetic tape A magnetic tape was produced in the same manner as in Example 1 except that the ferromagnetic powder obtained above was used instead of the ferromagnetic powder obtained in Example 1.

[Example 4]
(1) Preparation of ferromagnetic powder Hematite with a major axis length of 70 nm and a needle ratio of 6.2 and with addition of Co and Al by doping and / or deposition (Co / Fe = 15 mass% in terms of Fe, Al / Fe = A ferromagnetic powder having the physical properties shown in Table 1 was prepared in the same manner as in Example 1 except that 2% by mass) was used as a starting material. As a result of ESCA depth profile analysis of the obtained ferromagnetic powder, the strength of Si Y and Co was higher in order from the surface of the ferromagnetic powder. Thereby, it was confirmed that the Si-containing film (second film), the Y-containing film (first film), and the Co-containing film (third film) were sequentially formed by the above treatment. From the X-ray diffraction results and the production method, it was confirmed that Si, Y, and Co existed in the state of an oxide and / or an oxyhydroxide (including an amorphous component).
(2) Production of magnetic tape A magnetic tape was produced in the same manner as in Example 1 except that the ferromagnetic powder obtained above was used instead of the ferromagnetic powder obtained in Example 1.

[Comparative Example 1]
Production of Magnetic Tape A magnetic tape was produced in the same manner as in Example 1 except that a commercially available ferromagnetic powder having the physical properties shown in Table 1 was used instead of the ferromagnetic powder obtained in Example 1.

[Comparative Example 2]
(1) Preparation of ferromagnetic powder A ferromagnetic powder having the physical properties shown in Table 1 was prepared in the same manner as in Example 1 except that the treatment for forming the second film (treatment (c)) was not performed. did.
(2) Production of magnetic tape A magnetic tape was produced in the same manner as in Example 1 except that the ferromagnetic powder obtained above was used instead of the ferromagnetic powder obtained in Example 1.

[Comparative Example 3]
(1) Preparation of ferromagnetic powder A ferromagnetic powder having the physical properties shown in Table 1 was prepared in the same manner as in Example 4 except that the treatment for forming the second film (treatment (c)) was not performed. did.
(2) Production of magnetic tape A magnetic tape was produced in the same manner as in Example 1 except that the ferromagnetic powder obtained above was used instead of the ferromagnetic powder obtained in Example 1.

Evaluation Method (1) Magnetic Properties Magnetic properties of each ferromagnetic powder and tape sample were measured in parallel with the orientation direction with an external magnetic field of 400 kA / m using a vibrating sample magnetometer (manufactured by Toei Kogyo). The results are shown in Tables 1 and 2. SQ indicates a squareness ratio.
(2) Electromagnetic conversion characteristics (output, C / N)
The electromagnetic conversion characteristics were measured by the following method. 8mm deck for data recording, MIG head (head gap 0.2μm, track width 17μm, saturation magnetic flux density 1.5T, azimuth angle 20 °) and reproducing MR head (SAL bias, MR element is Fe-Ni, track width 6μm) , Gap length 0.2 μm, azimuth angle 20 °). Using the MIG head, the relative speed of the tape and the head is 10.2 m / sec, the optimum recording current is determined from the input / output characteristics of 1/2 Tb (λ = 0.5 μm), and the signal is recorded with this current. Played with. C / N is from the peak of the reproduced carrier to the demagnetizing noise, and the resolution bandwidth of the spectrum analyzer is 100 kHz. Table 2 shows the output and C / N of each sample as relative values to the sample of Comparative Example 1.
(3) Surface Roughness Using a light interference three-dimensional roughness meter “TOPO-3D” manufactured by WYKO (Arizona, US), a sample area of 250 μm square was measured. In calculating the measurement values, corrections such as tilt correction, spherical correction, and cylindrical correction were performed in accordance with JIS-B601, and the center plane average roughness Ra is shown in Table 2 as the surface roughness value.
(4) Surface Precipitated Particles The tape surface after 1 week storage at 60 ° C. and 90% RH was observed with an optical microscope and SEM, and the results evaluated in 4 stages according to the following criteria are shown in Table 2.
No precipitation on the surface of the tape (magnetic layer surface) 1
There is a little precipitation 2
There are 3 deposits.
Precipitation but many 4
(5) Head dirt The head surface after repeated (200 passes) running on an 8 mm deck for data recording was observed, and the results of evaluation in five stages according to the following criteria are shown in Table 2.
No head deposit 1
A little 2
Yes 3
Many 4
Excessive 5
(6) Demagnetization under high temperature and high humidity (Δσs, ΔBm)
Each ferromagnetic powder and tape sample were stored at 60 ° C. and 90% RH for 1 week, and σs and Bm before and after storage were measured by the same method as in (1) above to determine the rate of change (Δσs and ΔBm).
(7) Composition analysis of ferromagnetic powder Each ferromagnetic powder was dissolved in hydrochloric acid and quantitatively analyzed using an ICP analyzer to determine the contents of Co, Al, Y and Si with respect to Fe.

Evaluation Results As shown in Table 1, all the ferromagnetic powders produced in Examples 1 to 4 had small Δσs and good storage stability. As shown in Table 2, magnetic tapes produced using these ferromagnetic powders exhibit excellent electromagnetic conversion characteristics, have a small ΔBm, and have a Si film formed on the Y film. Also, the occurrence of head contamination was suppressed.
On the other hand, in the magnetic tapes of Comparative Examples 1 to 3 using the ferromagnetic powder containing the Y component but not having the Si film, the demagnetization was high under high temperature and high humidity, and further deposits and head contamination occurred. .
From the above results, it can be seen that according to the present invention, it is possible to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent storage stability and running durability.

  The ferromagnetic powder of the present invention is suitable as a magnetic substance contained in a magnetic layer in a magnetic recording medium for high density recording. By using the ferromagnetic powder of the present invention, a magnetic recording medium for high-density recording having excellent running durability and storage stability can be provided.

Claims (12)

A ferromagnetic powder having a first film and a second film in this order on the surface of metal particles,
The first film contains a rare earth element oxide and / or oxyhydroxide as a main component,
2. The ferromagnetic powder according to claim 1, wherein the second film contains silicon oxide and / or oxyhydroxide as a main component, and the metal particles contain Fe and / or Co as a main component. The ferromagnetic powder according to claim 1, wherein the rare earth element is yttrium. A third film containing as a main component an oxide and / or oxyhydroxide of one or more elements selected from the group consisting of Al, Si, Fe and Co between the surface of the metal particles and the first film The ferromagnetic powder according to claim 1, further comprising: The ferromagnetic powder according to claim 1, wherein the ferromagnetic powder has a coercive force Hc in the range of 1.35 × 10 ^{5 to} 3.18 × 10 ⁵ A / m. The ferromagnetic powder according to claim 1, wherein the ferromagnetic powder has a saturation magnetization σs in a range of 120 to 180 A · m ² / kg. The average major axis of the ferromagnetic powder is in the range of 10 to 120 nm, the average minor axis is in the range of 4 to 30 nm, and the average acicular ratio is in the range of 2 to 12. Item 1. The ferromagnetic powder according to item 1. The ferromagnetic powder according to claim 1, wherein the ferromagnetic powder contains 10 to 40% by mass of Co with respect to Fe. A magnetic recording medium having a magnetic layer comprising a ferromagnetic powder and a binder on a nonmagnetic support,
The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is the ferromagnetic powder according to claim 1. The magnetic recording medium according to claim 8, wherein a thickness of the magnetic layer is in a range of 0.01 to 0.5 μm. The magnetic recording medium according to claim 8, wherein the magnetic layer further contains a fatty acid and / or a fatty acid ester. The magnetic recording medium according to claim 8, further comprising a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. The magnetic recording medium according to claim 11, wherein the nonmagnetic layer further contains a fatty acid and / or a fatty acid ester.