JPH0546615B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention is widely applied to magnetic recording media, magneto-optical recording media, magnetic heads, magneto-optical elements, microwave elements, magnetostrictive elements, magnetoacoustic elements, etc.
This method relates to a method for producing a spinel-type ferrite film containing Fe ³⁺ , in which crystallinity of a spinel-type structure is applied to the surface of a solid such as a metal or a non-metal at a low temperature of 100°C or lower using an aqueous solution containing at least ferrous ions. The present invention relates to a method for efficiently depositing and creating ferrite, and a reaction cell used therein. [Background of the Invention] Conventionally, methods for forming a ferrite film on a solid surface include a coating method using a binder, a sheet method,
There are two known methods that do not use a binder, but the former method has problems such as low magnetic recording density due to the presence of a non-magnetic binder between ferrite particles, while the latter method Methods for producing ferrite films that do not use ferrite film require heat treatment at a high temperature of several hundred degrees Celsius or higher, which has limitations such as the inability to use materials with low melting points and low decomposition temperatures as the substrate that provides the solid surface. In addition to the conventional method described above, a so-called "wet plating" method was proposed in which a layer of ferrite film was deposited on the surface of a solid in an aqueous solution at a temperature of 100°C or less (Japanese Patent Laid-Open No. 59/1999).
In this method, an aqueous solution containing at least ferrous ions as metal ions is brought into contact with the solid surface, and FeOH ^{+ or FeOH +} and other hydroxide metals are applied to the solid surface. This method involves adsorbing ions and oxidizing the adsorbed FeOH ⁺ to cause a ferrite crystallization reaction. By the way, when forming a ferrite film on a solid surface according to the above-mentioned "wet plating" method, it is still difficult to produce a product in which the entire film is homogenized and uniform with good productivity on an industrial scale. It is pointed out that there are points that need improvement. For example, a raw material aqueous solution whose composition is controlled to be suitable for the ferrite film formation reaction is appropriately supplied to the solid surface on which the ferrite film is deposited, while a ferrite film is formed from the liquid near the solid surface. It is desirable to reduce as much as possible the influence of inhibiting uniformity and homogenization of the film by removing extra components (such as ferrite particles generated in the liquid) that interfere with the process. . [Object of the Invention] The present invention has been made in view of the above points, and its object is to cause a ferrite crystallization reaction for forming a ferrite film to occur continuously over time on a solid surface, thereby The goal is to realize a highly productive method for forming ferrite films. Another object of the present invention is to prepare and store a raw material aqueous solution used for forming a ferrite film in a deoxidized state, and to supply this raw material aqueous solution to a solid surface when forming a ferrite film. This prevents the formation of ferrite fine particles in the stored raw material aqueous solution, thereby improving the efficiency of the use of the raw material aqueous solution. The aim is to improve the prevention of contamination by inhibitory substances (ferrite fine particles). Still another object of the present invention is to further reduce the possibility that ferrite fine particles generated in an aqueous solution near a solid surface will be mixed into a ferrite film deposited on the solid surface. In order to improve the uniformity and homogenization of the solid material, it is an object of the present invention to provide a method in which fine ferrite particles near the solid surface are conveniently removed from the system of the ferrite film forming reaction. Another object of the present invention is to control the oxygen concentration in the raw material aqueous solution supplied to the solid surface, which is one of the important factors for forming a high-quality ferrite film.
It provides a method suitable for strict control. Another object of the present invention is to provide a reaction cell suitably applied to the above method. [Summary of the Invention] The method for forming a ferrite film according to the present invention, which has been made to achieve these various objects, is characterized by the fact that a flat space in the thin film is substantially separated from the outside air. In the reaction cell to be formed, an aqueous solution containing at least ferrous ions as metal ions and an oxidizing solution containing oxygen are filled in the space and allowed to flow together in one direction within the flat surface of the reaction cell. A solid having an adsorption active surface is immersed in a reaction cell to form a ferrite film on the adsorption active surface. The reason why the above configuration is adopted in the present invention is as follows. The outline of the reaction on the solid surface in the so-called "wet plating" method to which the present invention is applied is summarized as follows.
It consists of processes (1), (2), and (3). (1) Adsorption of ferrous hydroxide ions (2) Oxidation of ferrous hydroxide ions (3) Ferrite crystallization reaction Of these, processes (1) and (2) are usually extremely rapid; The rate of ferrite film formation is as described above.
The rate is determined by the reaction rate of (3). When the oxidation reaction in (2) above is carried out using oxygen, the oxidation rate is determined by the dissolved oxygen concentration (equilibrium oxygen concentration partial pressure) based on the movement rate and diffusion rate of oxygen molecules in the solution.
Depends on. Therefore, when oxygen is used as an oxidizing agent, the rate of formation of the ferrite plating film is determined by the oxidation reaction described in (2) above, so accurately controlling the oxidation reaction will form a uniform film. becomes important. This fact indicates that controlling the oxygen partial pressure is an important factor in forming a uniform film. By the way, when carrying out the "wet plating" method on an industrial scale, it is desirable to isolate the prepared raw material aqueous solution from the reaction system and store it under non-oxidizing conditions, as mentioned above. . Therefore, when using such a raw material aqueous solution, it is important to efficiently supply oxygen together with the raw material aqueous solution to the solid surface on which the ferrite film is to be formed and deposited, and how to effectively utilize the raw material aqueous solution. It's okay. From this point of view, for example, there is a method of keeping the solid surface continuously wetted with a liquid film of the raw material aqueous solution as thin as possible to favor oxygen diffusion, and simultaneously supplying oxygen from the surface of this liquid film. is possible. This operation to keep the solid surface always wet with a thin liquid film is carried out, for example, by flowing or spraying an aqueous solution at a small flow rate, and also by keeping the solid surface evenly wet. In order to make the thickness of the liquid film as thin as possible, fluidity is further imparted by gravity and centrifugal force. However, when using the above-mentioned spray method, it is difficult to control the relationship between the spray flow rate and the oxygen partial pressure in the atmosphere, making it difficult to precisely control the oxygen partial pressure, making it difficult to manufacture high-quality products. However, when using the rotating disk method, which gives fluidity to the liquid film by rotating the solid surface, it is necessary to extremely strictly control the amount of oxygen that dissolves from the liquid film surface. Generally, it is difficult to strictly control the oxygen-containing gas in the reaction cell, especially near the surface of the liquid film, due to uneven oxygen concentration distribution, and the apparatus becomes complicated. Furthermore, in any of these methods,
A considerable amount of ferrous ions in the raw material aqueous solution supplied to the solid surface is wasted because it is consumed in producing ferrite fine particles in the liquid, and there is also the problem that reaction temperature control is not easy. Therefore, in the present invention, the structure of the present invention is adopted, which is suitable for forming a thin liquid film on a solid surface and for strictly controlling the amount of oxygen in this film liquid. According to such a configuration, since the reaction cell that provides a thin film flat cavity filled with an aqueous solution substantially separates this cavity from the outside air, it is necessary to consider the dissolution of oxygen from the liquid film surface. The oxygen required for the reaction of forming the ferrite film is supplied by mixing an oxidizing liquid or an oxygen-containing gas (hereinafter this mixed liquid is referred to as the reaction liquid) before introducing the raw material aqueous solution into the reaction cell. Therefore, it is possible to precisely control the amount of oxygen in the liquid near the solid surface by controlling the composition of the oxidizing liquid and the flow rate of the oxidizing liquid introduced. In addition, the reaction solution consisting of the raw material aqueous solution and the oxidizing solution, which are flowed together, is continuously introduced into the reaction cell in one direction within the flat surface of the hollow space of the thin film.
Therefore, the reaction liquid near the solid surface is constantly renewed, and it becomes easy to maintain the conditions for the ferrite film forming reaction approximately constant over time. According to the method for forming a ferrite film of the present invention, the flow rates of the raw material aqueous solution and the oxidizing liquid, the amount of oxygen contained in the oxidizing liquid, the temperature in the reaction cell, the metal ion concentration in the raw material aqueous solution, the pH, etc. are mainly controlled. By appropriately setting and controlling these parameters, unstable factors in the microscopic range can be sufficiently suppressed, and high-quality products can be obtained. In the present invention, the raw material aqueous solution used for forming the ferrite film contains ferrous hydroxide ions.
An aqueous solution in which FeOH ⁺ and optionally other hydroxide metal ions MOH ^{+ (n-1)} are present, typically consisting of a given metal salt in water (usually degassed distilled water). Obtained by melting. In addition to these metal ions, various acid groups are used as anions to be present in the raw material aqueous solution. From the above, in order to make ferrous ions (Fe ²⁺ ) and other necessary metal ions (M ⁿ⁺ ) exist in the raw material aqueous solution, it is common to use ferrous or cobalt, nickel, or copper together with ferrous iron. ,zinc,
Metal salts such as manganese (hydrochloride, acetate, sulfate,
Carbonates, etc.) are dissolved in water, and an alkali is added to the solution to adjust the pH. In this case, the alkali added is NaOH,
Amines such as ammonia, alkylamines, alkanolamines, and pyridine can be used. Since ferrous ions are susceptible to oxidation, the operation is usually carried out under a non-oxidizing atmosphere. When other metal ions are co-existed in the raw material aqueous solution containing ferrous ions described above, they may be prepared simultaneously in the same tank, or prepared in separate tanks and introduced into the reaction cell. It may be mixed immediately beforehand, and it is sufficient that the raw material aqueous solution contains the necessary metal ions when being supplied to the solid surface. The pH of an aqueous solution is determined by the anions present in the solution,
It is appropriately selected and controlled depending on the type of metal ion, but preferably 6 to 11, more preferably 6.5 to 11.
It is recommended that the numerical value range is 8.5. When the raw material aqueous solution suitably prepared by the various methods described above contains only Fe ²⁺ ions as metal ions, it is spinel ferrite, that is, magnetite Fe ₃ O ₄ or maghemite γ-Fe ₂ containing only iron as a metal element. obtained as a film of O ₃ and an aqueous solution containing Fe ²⁺ ions and other transition metal ions M ⁿ⁺
(M=Zn ²⁺ , Co ^2,3+ , Ni ²⁺ , Mn ^2,3+ , Fe ³⁺ , Cu ²⁺ ,
V ^3,4,5+ , Sb ⁵⁺ , Li ⁺ , Mo ^4,5+ , Ti ⁴⁺ , Rd ³⁺ ,
Mg ²⁺ , Al ³⁺ , Si ⁴⁺ , Cr ³⁺ , Sn ^2,4+ , Ca ²⁺ , Cd ²⁺ ,
In ³⁺ , etc.), a ferrite film containing a metal element other than iron, such as cobalt ferrite (CoxFe _3-x O ₄ ), nickel ferrite (NixFe _3-x O ₄ ), if M is one type. When there are several types of M, Mn−Zn ferrite (Mn _x Zn _y
Although a film of mixed crystal ferrite such as Fe _3-xy O ₄ ) is obtained, the present invention can be applied to the production of any of these films. The oxidizing solution used in the present invention supplies the oxygen necessary for oxidizing ferrous iron (or other metal ions) adsorbed on the solid surface in the reaction cell, and generally contains dissolved oxygen. An aqueous solution is used. Specifically, an oxidizing liquid with a constant amount of dissolved oxygen may be prepared by bubbling a mixed gas having a predetermined partial pressure ratio (oxygen/nitrogen) into degassed distilled water. Furthermore, nitric acid and/or nitrates, hydrogen peroxide solution, etc. can also be used as the oxidizing liquid. Furthermore, as described above, the oxidizing liquid may be replaced by blowing an oxygen-containing gas directly into the raw material aqueous solution. The reaction cell used in the present invention is formed to have a wall structure as a case portion of the main body structure, which substantially separates the thin film flat space from the outside air. The flat space of the thin film makes it possible to supply a sufficient amount of reaction liquid for reaction to the solid surface, so the space is several tens of μm to several mm, excluding the solid (tape, etc.) to be immersed.
However, if the gap becomes larger than necessary,
There are problems such as leakage of the reaction liquid from the reaction cell, increased difficulty in controlling the ferrite film forming reaction, presence of liquid flow sections that are hardly involved in the reaction, and a decrease in economic efficiency due to the floating of ferrite particles. Therefore, it is generally desirable that the thickness be several mm or less. The width of the void in the flat direction is determined depending on the material form of the target base material on which the ferrite film is to be formed.
When a long tape is continuously processed, the reaction time is sufficient to form a ferrite film of a predetermined thickness while moving the long tape into the reaction cell cavity from one end and moving it out to the other end. Due to the need to ensure this, the tape is constructed to have a sufficient length along the tape moving direction, although it depends on the moving speed of the tape. Generally, this length is often provided over several tens of centimeters to several tens of meters. An inlet for the reaction liquid is opened at one end in the flat direction of the cavity of the reaction cell, and an outlet for the reaction liquid is opened at the other end. In addition, in the case of the continuous processing of the long tape described above, an opening for the introduction and removal of the tape is formed from the outside of the wall structure to the internal space; For the purpose of ensuring desirable isolation between the outside air and the outside air, it is preferable that air-tight seals be provided at the outlet and inlet openings. A heater is usually attached to the reaction cell for the purpose of smoothly carrying out the reaction at a relatively high temperature of 100°C or less. Therefore, the wall structure that limits the void space in the reaction cell must have dimensional stability, water resistance, resistance to raw material aqueous solutions, and the ability to limit the void space in a range including high temperature conditions up to about 100°C. From the viewpoint of usage, since it is undesirable for a ferrite film to be deposited on the surface of the wall, stainless steel is preferably used, but other metals, glass, plastics, etc. can also meet the above conditions. There is no problem if it is. The solid material to be used as the target substrate for the formation of the ferrite film according to the present invention is particularly suitable as long as it can be immersed into the reaction cell as described above and can provide an adsorption active surface for the formation of the ferrite film. There are no restrictions on the material. Examples of substances that can be used as such solids include iron oxides, such as iron oxides.
Fe ₃ O ₄ , γ-Fe ₂ O ₃ , α-Fe ₂ O ₃ ferrite, etc.
Exemplary examples include noble metals such as gold, platinum, and palladium, saccharides having OH groups such as sucrose and cellulose, and plastics such as PET, Teflon, acrylic, and polycarbonate. The surface of the solid is desired to have a desired surface smoothness in addition to exhibiting adsorption activity. In addition to cases in which the adsorption activity is inherent in the solid itself, it is also possible to form an adsorption active layer as a surface layer on a material that does not inherently have such properties. You can also do this. When forming such a surface layer with adsorption activity, most substances that inherently have the above-mentioned properties can be used as the surface layer coating, and as a means of forming the coating layer, solid As long as it can withstand high temperatures, iron oxide, etc. may be coated on the solid surface using vacuum deposition methods such as sputtering, vacuum evaporation, arc discharge, and welding. The surface layer may be formed using a chemical plating method. In addition to these methods, a pretreatment method in which the solid surface is subjected to plasma treatment to obtain adsorption activity is also particularly effective. The plasma treatment here refers to surface activation by plasma generated by glow discharge, corona discharge, or microwave discharge, and may be performed at normal pressure or reduced pressure. The material form of the solid immersed in the reaction cell may be a short flat plate, a disk, etc. in the case of a method in which the solid is fixed in the reaction cell and processed in batches. Further, in the case of a method in which a long tape or the like is continuously transferred into and removed from the reaction cell, a long tape can be used. A typical example of such a long tape is the case where a magnetic tape for audio is produced using a plastic tape such as PET (polyethylene terephthalate). The heating conditions for carrying out the reaction are below the boiling point of the aqueous solution, usually 40°C to 95°C, preferably 60°C.
It is preferable to carry out the reaction at a temperature in the range of ℃ to 90℃. The reaction liquid flowing through the cavity of the reaction cell causes the reactions (1), (2), and (3) described above while flowing over the surface of the immersed target substrate (solid), and ferrite is formed on the solid surface. The flow rate relative to the solid surface is determined by the reaction conditions (metal ion concentration,
It is determined as appropriate depending on the amount of oxygen, temperature, pH, etc.). When carrying out the continuous treatment using a moving long tape or the like as a target substrate, the direction of flow of the reaction liquid and the direction of movement of the target substrate are not particularly limited to the same direction, opposite direction, or right angle direction, etc. However, it is often preferable to make the moving direction of the tape and the flow direction the same because the contact time can be extended. In addition, the moving speed of this long tape in the reaction cell depends on the reaction temperature, the thickness of the ferrite film to be formed, the metal ion concentration of the reaction solution, the size of the reaction cell, etc. to ensure the necessary immersion time. It may be determined as appropriate. The reaction liquid drawn out from inside the reaction cell can be reused after removing impurities such as ferrite particles in the liquid. (Examples of the Invention) The present invention will be described below with reference to Examples. FIG. 1 is for explaining an example of a general configuration of a batch processing apparatus for forming a ferrite film on one side of a rectangular flat plate as a target substrate by the method of the present invention. The wall structure forming the section is constructed by placing a silicone rubber packing 2 as a surrounding wall on the top surface of a stainless steel base 1 forming a pedestal, and stacking a glass flat plate 3 and a stainless steel press plate 4 from above. The illustrated fastening support frame forms a reaction cell cavity 5 which is sealed from the outside in a liquid-tight manner. The thickness of the space may be changed by replacing the gasket. Further, in the base, an inlet pipe 7 for the reaction liquid is connected to an opening 6 provided at one end of the space, and an outlet pipe 9 for the reaction solution is connected to an opening 8 provided at the other end of the space 5. is connected. Note that the introduction tube 7 for the reaction liquid is an outer tube 7.
The oxidizing liquid is supplied from the inner pipe 7b, and the raw material aqueous solution is supplied from the outer pipe 7a, and these are brought together and mixed at the opening 6. There is. Reference numeral 10 indicates a flat plate as a target substrate placed in the reaction cell cavity, and the reaction liquid flows from the opening 6 of the inlet pipe to the surface of the flat plate and reaches the opening 8 to the outlet pipe. Ru. Note that a current plate, a weir, etc. may be provided in the reaction cell space 5 if necessary. Figure 2 is for explaining an example of the general configuration of a continuous processing apparatus using a long tape as the target substrate. The tube 7 and the outlet tube 9 are generally similar to those shown in FIG. However, in this example, in order to continuously process the long tape, the long tape 11, which is the target substrate, is transferred into and out of the reaction cell space 5, and the space 5 is substantially protected from the outside air. A pair of roll seal parts 12, 1 are provided at the inlet and outlet parts of the long tape for the purpose of partitioning the long tape into sections.
It has a characteristic structure with 3. If such a reaction cell is used, continuous processing of long tapes can be preferably realized. Note that 14 is a presser roll for stably supporting the moving trajectory of the tape within the reaction cell. However, it goes without saying that the implementation of the present invention is not limited to the above devices and embodiments. Examples of preparing an aqueous solution and examples of forming a ferrite film will be shown below. Example of creating aqueous solution (1) Raw material aqueous solution Dissolve 4 g of ferrous chloride and cobalt chloride (1.6 g, 4 g) in 1000 ml of distilled water degassed with nitrogen gas, and adjust this solution to pH 8.0 with 0.1N NaOH solution. I adjusted it as follows. (2) Oxidizing liquid An oxidizing liquid with a pH of 9.2 maintained in an equilibrium state was obtained by bubbling a mixed gas with an oxygen partial pressure of (oxygen/nitrogen) = 1/100 into degassed distilled water. Example Using the raw material aqueous solution (1) and oxidizing liquid (2) described above,
The device shown in Figure 1 uses PET and glass whose surfaces have been given adsorption activity by plasma treatment in advance as target substrates (dimensions of reaction cell cavity: length x width x height =
60 cm x 16 cm x 100 μm) to form a ferrite film. The treatment conditions are shown in Table 1 below. The obtained ferrite film was a thin film with an even, glossy appearance, and was confirmed to be Fe ₃ O ₄ or cobalt ferrite (see Table 1 for composition) by the results of X-ray diffraction. Film thickness, coercive force, uniformity,
The results of peelability etc. are shown in Table 1. According to the electron micrograph attached as FIG. 3, it was confirmed that the thin film was a uniform ferrite film without unevenness.

【table】

[Table] (Effects of the Invention) According to the present invention, the following excellent effects can be obtained, and its usefulness is extremely great. (1) High productivity is achieved because the process for forming the ferrite film can be performed continuously over time. (2) Since the raw material aqueous solution is stored in a deoxidized state, the raw material aqueous solution can be used extremely efficiently;
Effective use of resources and cost reduction are realized. (3) Ferrite fine particles generated in the liquid near the solid surface that forms the ferrite film are continuously discharged to the outside of the reaction cell by the flow of the reaction liquid, so they are easily mixed into the ferrite film. is prevented. (4) It is easy to extremely strictly control the oxygen concentration in the reaction solution, which is an important factor in the formation of a ferrite film on a solid surface, and a high-quality ferrite film can be obtained. (5) The apparatus including the reaction cell can be constructed as a relatively small device, and industrial-scale equipment can be obtained at low cost.

[Brief explanation of the drawing]

FIGS. 1A and 1B show an example of a general configuration of an apparatus that performs batch processing according to the method of the present invention.
FIG. 2 shows an example of a general configuration of an apparatus that performs the same continuous processing. FIG. 3 is an electron micrograph showing the crystal structure of the ferrite film obtained in Example 1.

Claims (1)

[Scope of Claims] 1. A raw material aqueous solution containing at least ferrous ions as metal ions and an oxidized oxide containing oxygen are added to a reaction cell formed in a state where a thin film flat space is substantially separated from the outside air. The liquid is filled in the cavity and allowed to flow together in one direction within the flat surface, and a solid having an adsorption active surface is immersed in this reaction cell to form a ferrite film on the adsorption active surface. A method for forming a ferrite film characterized by the following. 2. The method of forming a ferrite film according to claim 1, wherein the raw material aqueous solution and the oxidizing solution are mixed immediately before introduction into the reaction cell. 3. A method for forming a ferrite film according to claim 1 or 2, characterized in that a solid having an adsorption-active surface is fixed in a reaction cell. 4. A patent claim characterized in that a long tape having an adsorption active surface is continuously moved into and out of the reaction cell cavity from one end in the flat direction to the other end along the length of the tape. A method for forming a ferrite film according to item 1 or 2. 5. A wall structure formed in a state in which a thin film flat space is substantially separated from the outside air, and an opening into the space located at one end side in the flat direction of the thin film flat space of this wall structure. 1. A reaction cell used for forming a ferrite film, comprising a liquid inlet and a liquid outlet located at the other end in the flat direction and opening into the space.