Titanium oxide film-covered powder and its production method

【0001】

[Technical field to which the invention belongs]

The present invention relates to a titanium oxide film-coated powder and a method for producing the same. This titanium oxide film-coated powder is colored blue or magenta due to the optical interference of the titanium oxide film coated on the surface, and is colored in blue or magenta, and is used for color inks, plastics, paper color fillers, color toners, and inkjets. It relates to colored powders used for various purposes such as color inks for printers and methods for producing them.

【0002】

[Conventional technology]

So far, the inventors have described a method for coating a titanium oxide film using a metal alkoxide (Patent Document 1 (Japanese Patent Laid-Open No. 06-228604), etc.) and a titanium oxide film using a titanyl sulfate solution. We have developed a coating method (Patent Document 2 (Japanese Unexamined Patent Publication No. 2000-345072), etc.). Furthermore, using these titanium oxide film coating methods, we have also developed and published a method of coating a black magnetic powder with an interference film made of silica and titanium oxide to color the black magnetic powder (Patent Document 3). (Japanese Patent Laid-Open No. 10-330644), etc.).

【0003】

On the other hand, as a method for coating a titanium oxide film, a method using a titanium (IV) chloride solution in addition to the above-mentioned titanium raw material is known, and these are described in Patent Document 4 (Japanese Patent Laid-Open No. 2000-86292). Many documents and patents such as Patent Document 5 (Japanese Patent Laid-Open No. 5-286738) have been published. Further, in Patent Document 6 (Japanese Unexamined Patent Publication No. 01-224220), a peroxotitanium solution is prepared from a titanium (IV) chloride solution, and the peroxotitanium solution is heated in the coexistence of a base material powder to obtain the base material. A method of coating a titanium oxide film on the powder surface has been disclosed. Further, in Patent Document 7 (Japanese Patent Laid-Open No. 09-71418), Patent Document 8 (Japanese Patent Laid-Open No. 10-67516), etc., a basic substance such as aqueous ammonia is added to a titanium-containing liquid such as a titanium (IV) chloride solution. The titanium hydroxide gel is added to precipitate, the precipitate is filtered and washed to prepare a dispersion liquid, and a hydrogen peroxide solution is added thereto to generate a peroxotitanium solution, and the surface treatment of the powder is performed with the peroxotitanium solution. The method is open to the public.

【0004】

[Patent Document 1]

Japanese Patent Application Laid-Open No. 06-228604 [Patent Document 2]

Japanese Unexamined Patent Publication No. 2000-345072 [Patent Document 3]

Japanese Unexamined Patent Publication No. 10-330644 [Patent Document 4]

Japanese Unexamined Patent Publication No. 2000-86292 [Patent Document 5]

Japanese Patent Application Laid-Open No. 5-286738 [Patent Document 6]

Japanese Unexamined Patent Publication No. 01-224220 [Patent Document 7]

Japanese Unexamined Patent Publication No. 09-71418 [Patent Document 8]

Japanese Unexamined Patent Publication No. 10-67516 [0005]

[Problems to be Solved by the Invention]

However, it has been found that there are various problems in the previously known coating methods for titanium oxide films as described above. First, when metal alkoxide is used as a raw material for coating a titanium oxide film, the metal alkoxide is unstable and its hydrolysis reaction is very fast, so the reaction system must be carried out under constant temperature and humidity, and the reaction Must be carried out in an organic solvent such as alcohol, which complicates the reaction apparatus.

【0006】

Further, when the titanyl sulfate solution is used as a titanium oxide film coating raw material, the problems are that the reaction of titanyl sulfate is slow and the film forming operation takes time, and the titanium oxide film that can be coated by one film forming operation. If there is a limit to the thickness and it is necessary to thicken the titanium oxide film, it is necessary to divide the titanium oxide film coating operation into a plurality of times. The titanium oxide film coating method using a titanium (IV) chloride solution can significantly shorten the reaction time compared to the case of using a titanyl sulfate solution, and a single titanium oxide film coating operation is sufficient. It has become possible to thickly coat the titanium oxide film. However, in the conventional titanium oxide film coating method using the above titanyl sulfate solution or titanium (IV) chloride solution, the pH of the reaction solution is acidic at 7 or less, so an iron powder or other material having weak acid resistance is used as the base powder. When it is made into a body, it is difficult to apply it due to the influence that the base powder is dissolved.

【0007】

Further, in the method for producing a titanium oxide film-coated powder published in Patent Document 6 (Japanese Unexamined Patent Publication No. 01-224220), the produced peroxotitanium solution is heated to 95 ° C. or higher in the presence of a base material powder. However, it is a method of coating the titanium oxide film on the surface of the base material powder by holding it for 8 hours or more, and cannot be said to be a method of easily coating the titanium oxide film on the powder surface in a short time. It was a thing. Further, the titanium oxide film coating method published in Patent Document 6 (Japanese Patent Laid-Open No. 01-224220), Patent Document 7 (Japanese Patent Laid-Open No. 09-71418), etc. describes the surface treatment of powder as an application. However, in order to obtain a peroxotitanium solution, which is a coating film raw material solution, the precipitate after adding a basic substance to the titanium-containing liquid must be filtered and washed, and then a hydrogen peroxide solution must be added. What is the thickness of the titanium oxide film that can be coated on the base material powder by a single titanium oxide film coating operation, that is, on the base material powder that is the object of this case. Since the method of coating the titanium oxide film has not been introduced, it is difficult to coat the titanium oxide film having a thickness that causes optical interference.

【0008】

In addition, the applicants have developed a method for coating a titanium oxide film on a base powder using a titanium (III) chloride solution (Japanese Patent Application No. 2001-308682). In this method, the titanium oxide film coating can be produced much more easily than before. However, in this method, foaming frequently occurs at the stage of adding the peroxide to the titanium (III) chloride solution in the process of peroxoizing the titanium (III) chloride solution, so that the peroxotitanium solution is prepared. Was not so easy. Therefore, a method for producing highly accurate titanium oxide-coated powder more easily and quickly has been required.

【0009】

[Means for solving problems]

As a result of diligent efforts, the authors were able to solve the above problems by using a titanium (IV) chloride solution and undergoing steps such as preparing a peroxotitanic acid solution, and the base metal powder was not dissolved. We have found a method that can coat a titanium oxide film on a metal powder. This method makes it possible to coat the titanium oxide film in a short time and at a low temperature.

【0010】

Such a method means that (1) an excess of a basic substance is added to a titanium (IV) chloride solution, and then a peroxide is added to generate a basic peroxotitanium solution, and the peroxotitanium solution is used as a base material. A method for producing a titanium oxide film-coated powder by coating a titanium oxide film on a base material powder, which comprises a step of dropping into a powder suspension. (2) The method for producing a titanium oxide film-coated powder according to (1), wherein the base material powder suspension is an alkaline buffer solution having a pH of 8 or more and a pH of 10 or less. (3) The method for producing a titanium oxide film-coated powder according to (1), wherein the titanium oxide film-coated reaction according to (1) is carried out at a reaction temperature of 15 ° C. or higher and 65 ° C. or lower. (4) The method for producing a titanium oxide film-coated powder according to (1), wherein the titanium oxide film-coated reaction according to (1) is carried out with a reaction time of 1 hour or more and 6 hours or less. (5) An excess of basic substance is added to the titanium (IV) chloride solution, and then a peroxide is added to generate a basic peroxotitanium solution, and the peroxotitanium solution is added dropwise to the base powder suspension. Powder coated with titanium oxide film by the titanium oxide film coating method, (6) (2) Titanium oxide film-coated powder by the titanium oxide film coating method described, (7) (3) Titanium oxide film-coated powder by the titanium oxide film coating method described in (3), (8) (4). It is a powder coated with a titanium oxide film by the titanium oxide film coating method of.

【0011】

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, an excess of a basic substance is added to a solution of (A) titanium chloride (IV), and (B) a peroxide is then added to generate a basic peroxotitanium solution, and (C) the peroxotitanium solution is prepared. The present invention relates to a method for producing a titanium oxide film-coated powder by coating a titanium oxide film on a base material powder, which comprises a step of dropping into the base material powder suspension. According to the present invention, a basic substance and a peroxide are sequentially added to a titanium (IV) chloride solution which is a titanium source, and the reaction solution is simply added dropwise to the base particle dispersion liquid on the base particles. A titanium oxide film can be formed on the surface. In the present invention, a titanium oxide film can be easily formed without going through complicated steps such as filtering and cleaning the precipitate, heating, and leaving it for a long time. The production method of the present invention will be described in detail below.

【0012】

(A) Step of adding excess basic substance to titanium (IV) chloride solution In the present invention, a commercially available titanium (IV) chloride solution can be used, but the Ti concentration is preferably 9% by mass. Use a titanium (IV) chloride solution having a content of 20% by mass or more and 20% by mass or less. More preferably, a titanium (IV) chloride solution having a Ti concentration of 14% by mass or more and 18% by mass or less is used. As such a titanium (IV) chloride solution, a commercially available reagent such as a reagent manufactured by Wako Pure Chemical Industries, Ltd. can be used.

【0013】

In the present invention, the basic substance added to the titanium (IV) chloride solution is not particularly limited as long as it forms a precipitate of titanium hydroxide gel by being added to the above-mentioned titanium (IV) chloride solution, but for example. Examples thereof include alkali metal hydroxide aqueous solutions such as ammonia water and sodium hydroxide aqueous solution. Preferably, ammonia water having an ammonia concentration of 9 to 35% by mass is used. As such ammonia water, a commercially available product such as a reagent special grade manufactured by Kanto Chemical Co., Inc. can be used. These basic substances can also be used in combination.

【0014】

The amount of the basic substance added to the titanium (IV) chloride solution is an excess amount with respect to the titanium (IV) chloride solution, and is not particularly limited as long as a precipitate of titanium hydroxide gel can be formed. The solution is added so that the pH is preferably 7.5 or more, more preferably pH 8 or more and pH 11 or less. Preferably, it is desirable to add an amount containing 4 times or more moles of the basic substance, and more preferably 8 times or more the number of moles of the basic substance with respect to titanium oxide in the titanium (IV) chloride solution. By adding an excess amount of the basic substance in this way, the pH of the produced titanium hydroxide gel solution is raised, the pH of the peroxotitanium solution obtained after adding the peroxide is raised, and the substrate which is vulnerable to low pH is raised. It is also possible to form a film on particles.

【0015】

The rate and temperature at which the basic substance is added are not particularly limited, but it is preferable not to heat or cool the substance in order to simplify the manufacturing process. More preferably, the reaction solution is added at 5 ° C to 50 ° C, more preferably between 10 ° C and 40 ° C.

【0016】

The peroxide added after adding the basic substance to the titanium (IV) chloride solution is not particularly limited as long as the precipitate of the titanium hydroxide gel can be dissolved to form a peroxo complex, but preferably hydrogen peroxide. Use a hydrogen peroxide solution having a hydrogen concentration of 25% by mass to 40% by mass. As such a peroxide, a commercially available product such as a reagent special grade manufactured by Kanto Chemical Co., Inc. can be used.

【0017】

(B) Step of adding peroxide to form a basic peroxotitanium solution The amount of peroxide added is not particularly limited as long as the precipitate of the titanium hydroxide gel can be dissolved to form a peroxotide complex, but titanium chloride. (IV) It is desirable to add a peroxide having a molar number of 3 times to 15 times, more preferably 5 times to 10 times the amount of titanium oxide in the solution. If the amount added is too small, the titanium hydroxide gel will not be sufficiently redissolved, resulting in a precipitate of the titanium hydroxide gel. In addition, if the amount of hydrogen peroxide solution added is too large, the excess amount of the added peroxide is decomposed and the generated foam foams the liquid, forming a precipitate of peroxotitanium hydrate. To do.

【0018】

The method of adding the peroxide is not particularly limited in the rate and temperature of addition, but it is preferable not to heat or cool the peroxide in order to simplify the manufacturing process. More preferably, the reaction solution is added at 5 ° C to 50 ° C, more preferably between 10 ° C and 40 ° C. After adding the peroxide to make a peroxo complex solution, further basic substances can be added to adjust the pH. The solvent for adjusting the pH is not particularly limited, but it is preferable to add a basic solvent such as aqueous ammonia. When a basic solvent is added here, the pH of the peroxotitanium solution after addition of the peroxide obtained by adjusting as described above is raised to 9 to 10, more preferably pH 9.2 to pH 9.5. It is preferable to add a sufficient amount.

【0019】

(C) Dropping of Peroxotitanium Solution into Substrate Powder Suspension A predetermined amount of peroxotitanium solution is preferable as the dropping rate when dropping the peroxotitanium solution into the base material powder suspension. Is preferably a speed that finishes in 20 to 60 minutes, more preferably a speed that finishes in about 20 to 40 minutes. If the dropping rate is shorter than 20 minutes, the precipitation of titanium oxide occurs rapidly, and it becomes difficult to coat the smooth titanium oxide film. At a dropping rate longer than 60 minutes, the properties of the titanium oxide film to be coated are almost the same as those at a dropping rate of 20 to 60 minutes, so the coating operation time is only unnecessarily lengthened.

【0020】

The base powder suspension into which the peroxotitanium solution is dropped is not particularly limited, but specifically, Tris-based, boric acid-based, borate-based, phosphoric acid-based, phosphate-based, glycine-based, Examples include carbonates. The pH of the suspension is preferably pH 8 to pH 10, and more preferably pH 9.0 to pH 9.2. Under pH conditions lower than this, titanium oxide particles are rapidly precipitated from the dropped peroxotitanium solution, making it difficult to smoothly coat the titanium oxide film on the base material powder. At the time of dropping, the reaction temperature of the reaction system is preferably between 15 ° C and 65 ° C, more preferably between 20 ° C and 55 ° C. If the reaction temperature of the reaction system is too low, the reaction rate of the peroxotitanium solution becomes slow, and it becomes difficult to coat the titanium oxide film having the desired thickness. This is because if the reaction temperature is too high, the reaction of the peroxotitanium solution becomes too fast, and it becomes difficult to coat the smooth titanium oxide film.

【0021】

The base material powder to be coated with the titanium film in the present invention is not particularly limited, but the base particles may be an inorganic substance containing a metal or an organic substance, and may be a magnetic material, a dielectric material, a conductor, an insulator, or the like. Good. When the substrate is a metal, any metal such as iron, nickel, chromium, titanium, and aluminum may be used, but those using the magnetism are preferably those having magnetism such as iron. These metals may be alloys, and when they have the above-mentioned magnetism, it is preferable to use a ferromagnetic alloy. When the substrate of the powder is a metal compound, the above-mentioned metal oxide can be mentioned as a typical example. For example, in addition to iron, nickel, chromium, titanium, aluminum, silicon and the like, calcium , Magnesium, barium and other oxides, or composite oxides thereof. Further, examples of the metal compound other than the metal oxide include metal nitrides, metal carbides, metal sulfides, metal fluorides, metal carbonates, metal phosphates and the like.

【0022】

Further, as the substrate particles, other than metal, metalloid and non-metal compounds, particularly oxides, carbides and nitrides, silica, glass beads and the like can be used. Other inorganic substances include inorganic hollow particles such as silas balloons (hollow silicic acid particles), microcarbon hollow spheres (crecus fair), fused alumina bubbles, Aerosil, white carbon, silica microhollow spheres, calcium carbonate microhollow spheres, etc. Calcium carbonate, pearlite, talc, bentonite, synthetic mica, muscovite and other mica, kaolin and the like can be used.

【0023】

As the organic substance, resin particles are preferable. Specific examples of the resin particles include cellulose powder, cellulose acetate powder, polyamide, epoxy resin, polyester, melamine resin, polyurethane, vinyl acetate resin, silicon resin, acrylic acid ester, methacrylic acid ester, styrene, ethylene, propylene and these. Examples thereof include spherical or crushed particles obtained by polymerization or copolymerization of the derivatives of the above. Particularly preferable resin particles are spherical acrylic resin particles obtained by polymerization of acrylic acid or methacrylic acid ester. As the film-forming method of the present invention, unlike the prior art, those weak to acid can also be used, so it is preferable to use the manufacturing method of the present invention for a substrate weak to acid. Examples of the acid-sensitive substrate include metal powder, particularly iron powder and iron-containing alloy powder.

【0024】

Further, the film-forming method of coating the substrate particles of the present invention with a titanium oxide film can further combine with a film-forming method for another substrate to form particles having a plurality of films. When the film-forming method of the present invention is used in combination with another film-forming method, for example, when a titanium oxide film is formed on a powder coated by another film-forming method using the film-forming method of the present invention, another The powder coated by the film forming method can be treated as the above-mentioned substrate particles. Similarly, the powder coated with the titanium oxide film by the method of the present invention can be used as the substrate particles to coat other films.

【0025】

The shape of the substrate is a sphere, a subsphere, an isotropic body such as a regular polyhedron, a rectangular parallelepiped, a rotating ellipsoid, a rhombohedron, a plate, a polyhedron such as a needle (cylinder, prism), and a crushed product. A completely amorphous powder can also be used. The particle size of these substrates is not particularly limited, but those in the range of 0.01 μm to several mm are preferable.

【0026】

(D) It is preferable to further provide a step of aging in which the reaction product is left to stand after dropping into the base powder suspension of the other step (C). The temperature at the time of aging is preferably between 15 ° C and 65 ° C, and more preferably between 20 ° C and 55 ° C. The aging time is preferably between 30 minutes and 6 hours, more preferably 1 hour and 3 hours. If the sum of the reaction time and the aging time is too short, the reaction of the dropped peroxotitanium solution may be insufficient and the titanium oxide film of the desired thickness may not be coated. If it is too long, the reaction of the dropped peroxotitanium solution has already been completed, and the coating operation time is only unnecessarily lengthened.

【0027】

In the film-forming method of the present invention, the thickness of the titanium oxide film formed on the substrate particles can be adjusted by optimizing the amount ratio of the materials.

【0028】

When the film-forming method of the present invention is used together with other film-forming methods to prepare a powder coated with a plurality of films, a special case is made by adjusting the thickness of each layer of the film layers involved in light interference. Can give a function. For example, an alternating coating film having different refractive indexes is applied to the surface of the substrate particles so that the refractive index n of the substance forming the film satisfies the following equation (1) and an integer of 1/4 of the wavelength of visible light. When an alternating film having a thickness d corresponding to m times is provided with an appropriate thickness and number of films, light of a specific wavelength λ (using the interference reflection of Fresnel) is reflected or absorbed.

【0029】

nd = mλ / 4 (1) [0030]

Utilizing this action, a film having a film thickness and a refractive index that satisfies Eq. (1) is formed on the surface of the substrate particles with respect to the target wavelength of visible light, and the refractive index is further formed on the film. A film having a reflection peak in the visible light region is formed by alternately coating different films once or more. At this time, the order of the substances to be formed is determined as follows. First, when the refractive index of the core substrate is high, it is preferable that the first layer is a film having a low refractive index, and in the opposite relationship, the first layer is preferably a film having a high refractive index.

【0031】

The film thickness is measured and controlled as a reflected waveform by a spectrophotometer or the like by measuring and controlling the change in the optical film thickness, which is the product of the refractive index of the film and the film thickness. Design the thickness. For example, if the peak position of the reflection waveform of each unit film constituting the multilayer film is precisely adjusted to a specific wavelength, a monochromatic colored powder such as blue, green, or yellow can be obtained without using a dye or pigment. it can. However, in the case of an actual substrate, it is necessary to consider the particle size and shape of the substrate, the phase shift at the mutual interface between the film substance and the substrate particulate matter, and the peak shift due to the wavelength dependence of the refractive index. For example, it is preferable to take into account the peak shift for the oxide layer on the surface of the substrate particles and the peak shift due to the wavelength dependence of the refractive index.

【0032】

Also, when metal or a nuclear particle or film with a large attenuation coefficient is used, phase shift occurs such that the reflected light on the surface of the substance with a large metal surface attenuation coefficient is elliptically polarized, and this interference occurs between the nuclear particle and the multilayer film, respectively. It is preferable to take this into consideration because it affects the mutual phase of the particles. Even if only the geometric film thickness is adjusted, the peak position shifts, so the color becomes pale, especially when coloring in a cyan color system. In order to prevent this, the influence of the phase shift on all the films is taken into consideration, and the combination of film thicknesses is designed to be optimal in advance by computer simulation.

【0033】

Further, there is a phase shift due to the oxide layer on the surface of the substrate and a peak shift due to the wavelength dependence of the refractive index. In order to correct these, it is necessary to find the optimum conditions so that the reflected peak becomes the target wavelength in the final target number of films with a spectrophotometer or the like.

【0034】

Interference of a film formed on a curved surface such as spherical powder occurs in the same manner as a flat plate, and basically follows Fresnel's interference principle. Therefore, the coloring method can also be designed for a specific color system. However, in the case of a curved surface, the light incident on the powder and reflected causes complex interference. These interference waveforms are almost the same as those of a flat plate when the number of films is small. However, as the number of films increases, the interference inside the multilayer film becomes more complicated. Even in the case of a multilayer film, the reflection spectroscopic curve can be designed in advance by computer simulation so that the combination of film thicknesses is optimized based on Fresnel interference. In particular, in the case of film formation on the surface of the substrate particles, the effect of phase shift on the surface of the substrate particles and all the films is taken into consideration, and the combination of film thicknesses is designed to be optimal in advance by computer simulation. Further, the peak shift for the oxide layer on the surface of the substrate particles and the peak shift due to the wavelength dependence of the refractive index are also taken into consideration. In actual sample production, the designed spectral curve is referred to, and in order to correct these in the actual film, the optimum conditions are changed while changing the film thickness so that the reflected peak reaches the target wavelength with the final target number of films using a spectrophotometer or the like. I have to find out.

【0035】

Also, when using metal or a nuclear particle or film with a large attenuation coefficient, phase shift occurs, such as elliptically polarized light reflected on the surface of a substance with a large metal surface attenuation coefficient, and this interference occurs between the nuclear particle and the multilayer film, respectively. It is very complicated to optimize each and obtain the target waveform because it affects the phase of each particle, and in order to obtain the optimum interference reflection waveform, the material of each of the nuclear particles and the multilayer film as described above. It is necessary to obtain the optical property value of the above, and to obtain the combination of the film thickness and the film from which the target waveform can be obtained in advance by computer simulation based on the value. Even when the powder of irregular shape is colored, interference due to the multilayer film occurs, and the basic film design is performed with reference to the conditions of the interference multilayer film of the spherical powder. The peak position of each unit film constituting the above-mentioned multilayer film can be adjusted by the film thickness of each layer, and the film thickness is a raw material under the coating forming conditions for forming a solid phase component such as a metal oxide on the surface of the substrate particles. By controlling the composition, the solid phase deposition rate, the amount of the substrate, and the like, the film thickness can be controlled with high accuracy, a film having a uniform thickness can be formed, and a desired color system can be colored.

【0036】

As described above, by finding the optimum conditions while changing the film forming conditions such as the film forming solution so that the peak of the reflection spectrum and the valley wavelength become the target wavelength in the final target number of films, a powder of a specific color system can be obtained. Obtainable. Further, the color development due to the interference of the multilayer film can be adjusted by controlling the combination of the substances constituting the multilayer film and the film thickness of each unit film. As a result, the powder can be vividly colored in a desired color system without using dyes or pigments. Further, in order to maximize the color shift, it is necessary to optimize the sharp reflection peak wavelength and the number of peaks, and optimize the film thickness control of each layer. Especially when the reflected peak appears in the visible range by changing the viewing angle from outside the visible range, or conversely, when the reflected peak in the visible range appears by changing the viewing angle, if it is a sharp reflection peak, it is slightly. By changing the viewing angle, the color can be changed at the same time, which is effective.

【0037】

Further, the color change due to the color shift can be predicted from the calculated value of the peak position when the incident angle is changed in the above formula 1 or the combination of the above formula 1 and the following formula 2. In producing the film-coated powder, it is necessary to select in advance the material of the substrate particles, the particle size of the substrate particles, the number of coating layers, the coating order of each coating layer, the material of each coating layer, and the desired reflected light wavelength. is there. In particular, selecting the material of the substrate particles and each coating layer naturally specifies their refractive indexes. The identification of the refractive index of the substrate particles and each coating layer is involved in the calculation of the Fresnel reflectance coefficient and the amplitude reflection intensity between the layers.

【0038】

By selecting the particle size of the substrate particles, the curvatures of the substrate particles and the multilayer film are specified. If the curvature is not specified, it becomes difficult to correct the spectrophotometric characteristics for film thickness monitoring, which will be described later. By selecting the number of coating layers, R described later_flatInvolved in value identification. Multilayer film reflection intensity R when the substrate particles are flat plates_flatFits the material (refractive index) of the substrate particles selected in advance, the number of coating layers, the coating order of each coating layer, the material of each coating layer (refractive index), and the desired reflected light wavelength to the following gradual equation 2. It is obtained by solving.

【0039】

[Formula 1]<img file="JP2004123801A_D0001.tif" /> 【0040】

(In the formula, R_{j + 1, j}: Amplitude reflection intensity between the jth layer from the bottom and the layer directly above it, an integer greater than or equal to j: 1 (J-1 = 0 indicates the base), i: Imaginary unit, r_{j + 1, j}: Fresnel reflectance coefficient of the interface between the jth layer from the bottom and the layer directly above it, R_{j, j-1}: Amplitude reflection intensity between the j-1st layer from the bottom and the layer directly above it, 2δ_j: Phase difference in the jth layer from the bottom, λ: Desired reflected light wavelength, n_j: Refractive index of the jth layer from the bottom, d_j: Film thickness of the jth layer from the bottom, φ_j: The angle of incidence of light on the jth layer from the bottom. ) Multilayer film reflection intensity R obtained as described above_flatIs not particularly limited as a method for correcting the above amount according to the shape of the substrate particles, but the R_flatThe value is further increased by the following equation 3 [0041]

[Equation 2]<img file="JP2004123801A_D0002.tif" /> 【0042】

(In the formula, θ: indicates the angle of incidence on the outermost layer), and the film thickness of each coating layer is determined so that the R (λ) value becomes the maximum or minimum value at the desired wavelength. Is preferable. R_flatApplying the value to the above equation 3 corrects the solution of the above equation 2 by approximating the angle distribution of the light incident angle to the multilayer film-coated powder to the light incident angle distribution to one coated hemisphere. Means that. When determining the film thickness of each coating film, it is efficient to perform a computer simulation.

【0043】

Next, each coating film is formed on the substrate particles so as to have the film thickness obtained as described above. However, as mentioned earlier, in the actual film-forming work of the multilayer film-coated powder, it is impossible to directly monitor the actual film thickness until the film thickness is as designed. To monitor the film thickness during film forming work, the wavelength at which the reflection intensity of the coated object coated with each coating layer becomes the maximum or minimum value is measured with a spectrophotometer, and the maximum or minimum reflection relative to the film thickness is measured. It is conceivable to end the film forming work when the wavelength value is reached. However, when the base material is powder, the relationship between the maximum or minimum reflected wavelength measurement value and the film thickness is out of order due to the curvature of each coating layer depending on the particle shape and particle size, and the spectrophotometer When the film is formed so that the maximum or minimum reflection wavelength to be measured becomes a desired value, there arises a problem that the finally obtained multilayer film-coated powder does not have a desired reflection intensity at a desired wavelength.

【0044】

Therefore, it is necessary to correct the curvature of each coating layer depending on the shape and particle size of the substrate particles. The correction method is not particularly limited, but each of the selected coating layers is coated on the selected substrate particles by gradually changing the film thickness to several types to obtain a film-coated powder for particle size correction, and the particle size correction is performed. Actual film thickness value of each coating layer of the film coating powder (d)_M), And each of the film-coated powders is measured with a spectrophotometer to obtain the optical film thickness (nd) of each coating layer of each particle size-correcting film-coated powder, and each particle size is corrected. The product (nd) of the actual film thickness value of each coating layer of the film coating powder for film and the refractive index (n)._M) To the ratio of the optical film thickness (nd) of each coating layer (nd / nd)_M), And 2δ of the above recurrence formula 2 to obtain the reflection intensity of the multilayer film._jTo the above ratio (nd / nd_M) Value is multiplied to correct the spectrophotometric characteristics of the powder having each coating layer, and each coating layer is preferably formed so as to have the corrected spectrophotometric characteristics.

【0045】

The actual film thickness value (d) of each coating layer of the above-mentioned film-coating powder for particle size correction._M) Is not particularly limited, but it is preferable to cut each of the particle size correction film-coated powders and measure from the cut surface. Further, when cutting the film coating powder for particle size correction, it is possible to perform the focused ion beam (FIB) processing to clarify the cut surface and the actual film thickness value (d) of each coating layer._M) Is suitable for measurement.

【0046】

The titanium oxide film-coated powder obtained by the method of the present invention exhibits blue or magenta due to the optical interference action of the titanium oxide film coated on the surface, and is a color ink, plastic, or color filler for paper. It can be used for various purposes such as color toner and color ink for inkjet printers.

【0047】

Among the cases of preparing a coating composition containing the titanium oxide film-coated powder obtained by the method of the present invention, (1) each specific color ink or paint-like composition (fluid) and (2) each specific color system. The toner and each specific color dry ink-like composition (powder) will be described in detail.

【0048】

(1) In the present invention, as the medium (vehicle) of the specific color ink or paint-like composition (fluid), a conventionally known varnish used for color printing, color magnetic printing, and color magnetic paint is used. For example, a liquid polymer, a polymer or a monomer dissolved in an organic solvent, or the like can be appropriately selected and used according to the type of powder, the method of applying the ink, and the intended use. Examples of the liquid polymer include dienes such as polypentadiene and polybutadiene, polyethylene glycols, polyamides, polypropylenes, waxes, and copolymers thereof.

【0049】

Polymers that dissolve in organic solvents include olefin polymers, acrylic resins such as oligoester acrylates, polyesters, polyamides, polyisocyanates, amino resins, xylene resins, ketone resins, and diene resins. , Rosin-modified phenolic resins, diene-based rubbers, chloroprene resins, waxes, modified products and copolymers thereof, and the like. Examples of the monomer that dissolves in the organic solvent include styrene, ethylene, butadiene, and propylene. Examples of the organic solvent include alcohols such as ethanol, isopropanol and normal propanol, ketones such as acetone, benzene, toluene, xylene, kerosine, benzine hydrocarbons, esters, ethers or modified products or copolymers thereof. Can be mentioned.

【0050】

(2) For the specific color toner, the specific color dry ink, and the specific color dry paint-like composition (powder), the above specific color multilayer film coating powder is used as a resin or, if necessary, as a toning material. Is directly kneaded with a screw type extruder, roll mill, kneader, etc., roughly crushed with a hammer mill, cutter mill, etc., then finely crushed with a jet mill, etc., and classified into the required particle size with an elbow jet, etc. to form powdery cyanide. Coloring material composition can be obtained. Further, a specific color-based multilayer film-coated powder can be used as a powder-like specific color-based coating composition by using a polymerization method such as an emulsion polymerization method or a suspension polymerization method. Further, the specific color-based multilayer film coating powder and the additive and solvent such as resin and toning agent can be liquefied with a colloid mill or three rolls to obtain a liquid specific color-based paint composition such as an ink paint.

【0051】

Examples of the toning material for increasing the brightness include white pigments (color-developing materials), for example, titanium oxide, zinc oxide, tin oxide, silicon oxide, antimony oxide, lead oxide and the like, or composite oxides thereof. Carbonates such as calcium carbonate, magnesium carbonate and barium carbonate, or sulfates such as barium sulfate and calcium sulfate, sulfides such as zinc sulfate or composite oxides obtained by sintering the oxides, carbonates and sulfates. Examples include composite hydroxides.

【0052】

In order to adjust the saturation and hue, the toning material used for color reproduction, especially in full-color color mixing, is a blue pigment (organic dye / pigment) such as alkaline blue rake, peacock rake, peacock rake blue, etc. Lake dyes and lake pigments, oil dyes such as oil blue, alcohol dyes such as alcohol blue, phthalocyanine pigments such as phthalocyanine and copper phthalocyanine, oxide sulfide composite pigments such as (inorganic pigment) ultramarine, iron blue, Copper-based ultramarine blue pigments such as millory blue, cobalt oxide-based composite oxides such as cobalt blue and cerulean blue Blue pigments, blue organic dyes and pigments, and blue inorganic pigments Lake dyes such as alkaline blue lake and peacock blue lake, lake Phthalocyanine dyes such as metal-free phthalocyanine and copper phthalocyanine And chrome-based oxides such as chrome green, zinc green, chromium oxide, hydrous chromium (viridian) and hydrous oxides, copper-based oxides such as emerald green, and cobalt-based oxides such as cobalt green, which are green pigments. Pigments or nitroso pigments such as pigment green and naphthol green, azo pigments such as green gold, phthalocyanine pigments such as phthalocyanine green and polychrome copper phthalocyanine, rakes such as malakite green lake and acid green lake, oils such as oil green, etc. Dye pigments Organic dye pigments such as alcohol dye pigments such as alcohol blue can be mentioned. However, the present invention is not limited to these.

【0053】

Further, when it is necessary to adjust the color using pigments or dyes such as blue, yellow, and magenta in delicate color tone control, it is preferable to add these pigments to obtain the optimum specific color. In the case of this powdery specific color paint composition, (a) the resin when produced by the above pulverization method is not particularly limited, but is not particularly limited, but is polyamide, epoxy resin, polyester, melamine resin, polyurethane, acetic acid. Examples thereof include vinyl resins, silicon resins, acrylic acid esters, methacrylic acid esters, polymers or copolymers of styrene, ethylene, butadiene, propylene and derivatives thereof. (b) In the case of the polymerization method, the polymerization is started from one or a mixture of one or more of esters, urethane, vinyl acetate, organic silicon, acrylic acid, methacrylic acid, styrene, ethylene, butadiene, propylene and the like, and the polymer or These copolymers and the like are formed.

【0054】

As described above, the coating composition containing the film coating powder of the present invention includes (1) each specific color ink or paint-like composition (fluid) and (2) each specific color toner and each specific color dry type. It can take the form of an ink-like composition (powder). In the case of a fluid, it is a specific color ink, paint, etc., and is a solidification accelerator for the toning material and a resin that dries slowly, a thickener for increasing the viscosity, and fluidization for decreasing the viscosity. Ingredients such as a dispersant can be included to disperse the agent and particles. On the other hand, in the case of powder, (a) when the powder is produced by the pulverization method, the toning material, the solidification accelerator for the slow-drying resin, and the flow to reduce the viscosity during kneading. Ingredients such as an agent, a dispersant for dispersing particles, a charge adjusting agent for fixing to paper, and a wax can be included. (b) When the polymerization method is used, the toning material, the polymerization initiator, the polymerization accelerator, the thickener for increasing the viscosity, the dispersant for dispersing the particles, and the fixing to paper, etc. Ingredients such as charge modifiers and waxes can be included. The multilayer film-coated powder of the present invention can be applied to wet and dry color printing, wet and dry color magnetic printing, and three primary color powders by combining a single powder or a plurality of powders having different spectral characteristics. Has a function to identify 6 types of combinations of visible light, invisible light (ultraviolet and cyan), fluorescent color development and magnetism, and electricity (change of electric field), and color magnetic ink for preventing counterfeiting of printed matter, etc. It can be applied to other applications that require security functions.

【0055】

The coating powder of the present invention is printed on a substrate as each specific color ink or paint-like composition or each specific color toner, each specific color dry ink-like composition, and each specific color dry paint composition. When it is melt-transferred or applied to an object to be coated, the relationship between the content of each specific color multilayer film coating powder and the resin in the coating composition is 1: 0.5 to 1:15 in terms of volume ratio. If the content of the medium is too small, the applied film will not adhere to the object to be coated. Further, if the amount is too large, the color of the pigment becomes too light and it cannot be said that the ink or paint is good. Further, the relationship between the total amount of each color-based color material and resin in each color-based ink or paint composition and the amount of solvent is 1: 0.5 to 1:10 in terms of volume ratio, and if the amount of solvent is too small, The viscosity of the paint is high and it cannot be applied evenly. Further, if the amount of the solvent is too large, it takes time to dry the coating film, and the efficiency of the coating work is extremely lowered.

【0056】

Further, the color density of the coating film when printing on the substrate, melt transfer, or applying the paint to the object to be coated is determined by the amount of the pigment placed per unit area of the object to be coated. The amount of the film-coated powder of the present invention on the object to be coated after the coating material has dried is 0.1 to 300 g per square meter in terms of area density when uniformly applied, preferably 0.1 to 100 g. A paint color can be obtained. If the area density is smaller than the above value, the background color of the object to be coated appears, and if it is larger than the above value, the color density of the coating color does not change, which is uneconomical. That is, even if the pigment is placed on the object to be coated with a certain thickness or more, the light does not reach the pigment under the coating film. It is uneconomical to make the coating film thicker than this thickness because the thickness exceeds the hiding power of the paint and the coating effect is not obtained. However, this does not apply to the case of thick coating because the thickness of the coating film is worn down in consideration of the wear of the coating film. Further, this does not apply to the case where a specific design or the like is partially formed.

【0057】

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited thereto.

【0058】

Example 1: Bluening of magnetite powder particles, water-based two-layer coating [first layer silica film coating operation]

(1) Adjustment of buffer solution 29.82 g (0.4 mol) of potassium chloride (Kanto Chemical Co., Ltd. reagent special grade) and 24.23 g (0.4 mol amount) of boric acid (Kanto Chemical Co., Ltd. reagent special grade) in 300 ml of ion-exchanged water. Was dissolved, and the solution was prepared by measuring up to 1000 ml with ion-exchanged water to prepare solution A. 16.0 g (0.4 mol) of sodium hydroxide (special grade reagent manufactured by Kanto Chemical Co., Inc.) was dissolved in 300 ml of ion-exchanged water, and the solution was prepared by measuring 1000 ml with ion-exchanged water. 250 ml of the above A solution and 115 ml of the B solution were mixed to prepare a buffer solution C. The pH of this buffer C was 9.1. (2) Preparation of sodium silicate aqueous solution (water glass solution) 100.0 g of sodium silicate solution (reagent manufactured by Kanto Chemical Co., Inc.) is diluted with ion-exchanged water so that the total amount becomes 1000.0 g, and 10 wt% silicate. Aqueous sodium solution was prepared.

【0059】

(3) 10 g of magnetite powder (average particle size 0.7 μm) was added to 540 ml of the buffer solution C prepared in advance as a silica film-coated base material powder, and this suspension was well dispersed. Immerse a container (1000 ml glass beaker) containing liquid in a 600 W, 28 kHz ultrasonic cleaning tank (Inuchi Seieidou US-6 type) and stir at 550 rpm. At the same time as the start of stirring, ultrasonic waves are irradiated. Next, 90 grams of a predetermined amount of 10 wt% sodium silicate aqueous solution is added dropwise to the previously agitated suspension at a dropping rate of 1.34 ml / min. After the dropping is completed, stirring is continued for another 1 hour, and the surface of the raw material magnetite is coated with a silica film. After a lapse of a predetermined time, the slurry containing the powder coated with the silica film was washed by repeating decantation with sufficient ion-exchanged water. After the washing operation, the slurry containing the silica film-coated powder is dried at 110 ° C. for 8 hours, and the silica film-coated magnetite powder D₁Got This silica film coated magnetite powder D₁As a result of measuring the spectral characteristics of the above with a spectrophotometer (Ubest550 manufactured by JASCO Corporation), the color was brown, and CIE (1976) L^*a^*b b^*L in the color system^*= 34.9, a^*= 0.4, b^*It was = -1.4.

【0060】

[Second layer titanium oxide film coating operation]

(1) Preparation of peroxotitanium solution Titanium chloride (IV) solution (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 2.2 ml (TiO₂Amount of 0.88 g (0.011 mol)) was diluted 10-fold with ion-exchanged water. Next, 5.34 grams of aqueous ammonia (special grade reagent manufactured by Kanto Chemical Co., Inc.) is added to this titanium (IV) chloride aqueous solution to prepare a titanium hydroxide slurry solution. Next, 10.0 g of hydrogen peroxide solution (special grade reagent manufactured by Kanto Chemical Co., Inc.) is slowly added to this titanium hydroxide slurry solution, and the mixture is sufficiently stirred to dissolve titanium hydroxide to obtain a yellow transparent peroxotitanium solution. .. The pH of this yellow transparent peroxotitanium solution was about 9.0. Finally, 0.50 g of aqueous ammonia (special grade reagent manufactured by Kanto Chemical Co., Inc.) was added to adjust the pH to make the pH alkaline at about 9.3. Peroxotitanium solution E₁To get.

【0061】

(2) Titanium oxide film coating Magnetite powder D coated with the above silica film₁6.0 grams was suspended in 560 grams of the same buffer C used in the first layer silica membrane coating operation. The container containing this suspension (1000 ml separable flask) is immersed in a constant temperature water tank kept at 50 ° C, and stirred at 700 rpm. When the temperature of the suspension reaches 50 ° C, the above-mentioned peroxotitanium solution E₁A predetermined amount of 39 grams (38 ml) of the above is added dropwise at a dropping rate of 1.8 ml / min. After the dropping is completed, stirring is continued for another 120 minutes, and the raw material, silica film-coated magnetite powder D₁Titanium oxide film coating is applied on top. After a lapse of a predetermined time, the slurry containing the powder coated with the titanium oxide film was washed by repeating decantation with sufficient ion-exchanged water. After the cleaning operation is completed, the slurry containing the titanium oxide film-coated powder is dried at 120 ° C. for 2 hours, and the titanium oxide film-coated magnetite powder F is dried.₁Got The obtained magnetite powder coated with a titanium oxide film F₁The results of measuring the spectral characteristics with a spectrophotometer (Ubest550 manufactured by JASCO Corporation) are shown in Table 1 and Fig. 1, which have a reflection peak (λ / 4 peak) near 350 nm and CIE (1976) L.^*a^*b b^*L in the color system^*= 35.9, a^*= -0.4, b^*It showed a blue color of = -5.9.

【0062】

Example 2: Reddish purple of magnetite powder particles, water-based two-layer coating [first layer silica film coating operation]

Magnetite powder D coated with silica film by the same operation as in Example 1.₁Got

【0063】

[Second layer titanium oxide film coating operation]

(1) Preparation of peroxotitanium solution Titanium chloride (IV) solution (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 4.4 ml (TiO₂Amount 1.76 grams (0.022 mol)) was diluted 10-fold with ion-exchanged water. Next, 10.69 grams of aqueous ammonia (special grade reagent manufactured by Kanto Chemical Co., Inc.) is added to this titanium chloride (lV) aqueous solution to prepare a titanium hydroxide slurry solution. Next, 20.0 grams of hydrogen peroxide solution (special grade reagent manufactured by Kanto Chemical Co., Inc.) is slowly added to this titanium hydroxide slurry solution, and the mixture is sufficiently stirred to dissolve titanium hydroxide to obtain a yellow transparent peroxotitanium solution. .. The pH of this yellow transparent peroxotitanium solution was about 9.0. Finally, as a pH adjustment, 1.00 g of aqueous ammonia (special grade reagent manufactured by Kanto Chemical Co., Inc.) was added to make the pH alkaline at about 9.3. Peroxotitanium solution E₂To get.

【0064】

(2) Titanium oxide film coating Magnetite powder D coated with the above silica film₁6.0 grams was suspended in 560 grams of the same buffer C used in the first layer silica membrane coating operation. The container containing this suspension (1000 ml separable flask) is immersed in a constant temperature water tank kept at 50 ° C, and stirred at 700 rpm. When the temperature of the suspension reaches 50 ° C, the above-mentioned peroxotitanium solution E₂A predetermined amount of 78 g (76 ml) of No. 1 is dropped at a dropping rate of 2.0 ml / min. After the dropping is completed, stirring is continued for another 120 minutes, and the raw material, silica film-coated magnetite powder D₁Titanium oxide film coating is applied on top. After a lapse of a predetermined time, the slurry containing the powder coated with the titanium oxide film was washed by repeating decantation with sufficient ion-exchanged water. After the cleaning operation is completed, the slurry containing the titanium oxide film-coated powder is dried at 120 ° C. for 2 hours, and the titanium oxide film-coated magnetite powder F is dried.₂Got The obtained magnetite powder coated with a titanium oxide film F₂The results of measuring the spectral characteristics with a spectrophotometer (Ubest550 manufactured by JASCO Corporation) are shown in the spectral reflectance curves in Table 1 and Fig. 1. ) Has two reflection peaks, CIE (1976) L^*a^*b b^*L in the color system^*= 37.1, a^*= 1.2, b^*It exhibited a reddish purple color of = -0.8.

【0065】

Example 3: Titanium oxide film coating on permalloy powder particles [Titanium oxide film coating operation]

(1) Preparation of peroxotitanium solution Peroxotitanium solution E by the same operation as in Example 1.₁To get. (2) Adjustment of buffer solution 29.82 g (0.4 mol) of potassium chloride (Kanto Chemical Co., Ltd. reagent special grade) and 24.23 g (0.4 mol amount) of boric acid (Kanto Chemical Co., Ltd. reagent special grade) in 300 ml of ion-exchanged water. Was dissolved, and the solution was prepared by measuring up to 1000 ml with ion-exchanged water. 16.0 g (0.4 mol) of sodium hydroxide (special grade reagent manufactured by Kanto Chemical Co., Inc.) was dissolved in 300 ml of ion-exchanged water, and the solution was prepared by measuring up to 1000 ml with ion-exchanged water. 250 ml of the above A solution and 115 ml of the B solution were mixed to prepare a buffer solution C. The pH of this buffer C was 9.1.

【0066】

(3) 29 g of permalloy powder (average particle size 16.7 μm) as a titanium oxide film-coated base material powder was put into 280 ml of the above-mentioned buffer solution C prepared in advance and dispersed well. The container containing this suspension was immersed in a constant temperature water tank kept at 23 ° C, and stirred at 700 rpm. Next, the above peroxotitanium solution E₁A predetermined amount of 39 grams (38 ml) of the above is added dropwise at a dropping rate of 1.8 ml / min. After the dropping is completed, stirring is continued for another 120 minutes to coat the raw material permalloy powder with a titanium oxide film. After a lapse of a predetermined time, the slurry containing the powder coated with the titanium oxide film was washed by repeating decantation with sufficient ion-exchanged water. After the cleaning operation is completed, the slurry containing the powder coated with the titanium oxide film is dried at 120 ° C. for 2 hours, and the permalloy powder G coated with the titanium oxide film is dried.₁Got The obtained titanium oxide film-coated permalloy powder G₁The results of measuring the spectral characteristics with a spectrophotometer (Ubest550 manufactured by JASCO Corporation) are shown in the spectral reflectance curves in Table 1 and Fig. 2. It has a reflection peak (2λ / 4 peak) near 330 nm and CIE ( 1976) L^*a^*b b^*L in the color system^*= 45.2, a^*= 5.4, b^*It showed a purple color of = -3.7.

【0067】

Example 4: Titanium oxide film coating on permalloy powder particles [Titanium oxide film coating operation]

(1) Preparation of peroxotitanium solution Titanium chloride (IV) solution (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 2.93 ml (TiO₂Amount of 1.17 grams (0.015 mol)) was diluted 10-fold with ion-exchanged water. Next, 7.12 grams of aqueous ammonia (special grade reagent manufactured by Kanto Chemical Co., Inc.) is added to this titanium (IV) chloride aqueous solution to prepare a titanium hydroxide slurry solution. Next, 20.0 grams of hydrogen peroxide solution (special grade reagent manufactured by Kanto Chemical Co., Inc.) is slowly added to this titanium hydroxide slurry solution, and the mixture is sufficiently stirred to dissolve titanium hydroxide to obtain a yellow transparent peroxotitanium solution. .. The pH of this yellow transparent peroxotitanium solution was about 9.0. Finally, as a pH adjustment, 1.00 g of aqueous ammonia (special grade reagent manufactured by Kanto Chemical Co., Inc.) was added to make the pH alkaline at about 9.3. Peroxotitanium solution E₃To get.

【0068】

(2) Adjustment of buffer solution 29.82 g (0.4 mol) of potassium chloride (Kanto Chemical Co., Ltd. reagent special grade) and 24.23 g (0.4 mol amount) of boric acid (Kanto Chemical Co., Ltd. reagent special grade) in 300 ml of ion-exchanged water. Was dissolved, and the solution was prepared by measuring up to 1000 ml with ion-exchanged water. 16.0 g (0.4 mol) of sodium hydroxide (special grade reagent manufactured by Kanto Chemical Co., Inc.) was dissolved in 300 ml of ion-exchanged water, and the solution was prepared by measuring up to 1000 ml with ion-exchanged water. 250 ml of the above A solution and 115 ml of the B solution were mixed to prepare a buffer solution C. The pH of this buffer C was 9.1.

【0069】

(3) 29 g of permalloy powder (average particle size 16.7 μm) as a titanium oxide film-coated base material powder was put into 280 ml of the above-mentioned buffer solution C prepared in advance and dispersed well. The container containing this suspension was immersed in a constant temperature water tank kept at 23 ° C, and stirred at 700 rpm. Next, the above peroxotitanium solution E₃A predetermined amount of 59 grams (58 ml) of the above is added dropwise at a dropping rate of 2.0 ml / min. After the dropping is completed, stirring is continued for another 120 minutes to coat the raw material permalloy powder with a titanium oxide film. After a lapse of a predetermined time, the slurry containing the powder coated with the titanium oxide film was washed by repeating decantation with sufficient ion-exchanged water. After the cleaning operation is completed, the slurry containing the powder coated with the titanium oxide film is dried at 120 ° C. for 2 hours, and the permalloy powder G coated with the titanium oxide film is dried.₂Got The obtained titanium oxide film-coated permalloy powder G₂The spectral characteristics were measured with a spectrophotometer (Ubest550 manufactured by JASCO Corporation). The results are shown in the spectral reflectance curves in Table 1 and Fig. 2, which have a reflection peak (2λ / 4 peak) near 400 nm and CIE (1976) L.^*a^*b b^*L in the color system^*= 52.5, a^*=-1.7, b^*It showed a blue color of = -11.0.

【0070】

Comparative Example 1 [Titanium oxide film coating]

(1) Preparation of peroxotitanium solution Titanium chloride (IV) solution (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 2.2 ml (TiO₂Amount of 0.88 g (0.011 mol)) was diluted 10-fold with ion-exchanged water. Next, slowly add 10.0 grams of hydrogen peroxide solution (special grade reagent manufactured by Kanto Chemical Co., Inc.), and add orange-red pertitanate solution E.₄Got The pH of this solution was about 1.3.

【0071】

(2) Titanium oxide film coating The dropping solution of Example 3 is an orange-red pertitanic acid solution E.₄The same operation was performed except that. As a result, the pH of the reaction solution after dropping the entire amount of the dropping solution dropped to around 2.2, fine particles of titanium oxide were formed, and the reaction solution became cloudy in pale yellow. In addition, the permalloy powder in the reaction solution was washed by repeating decantation with sufficient ion-exchanged water. After the washing operation was completed, the slurry containing the permalloy powder was dried at 120 ° C. for 2 hours, and the results were observed. The titanium oxide film was not coated at all by this method.

【0072】

[table 1]<img file="JP2004123801A_D0003.tif" /> 【0073】

[Effect of the invention]

According to the present invention, when the titanium oxide film is coated with the titanium (IV) chloride solution on the base metal powder, the pH of the reaction solution can be made alkaline at 7 or more. It has become possible to use many base metal powders without dissolving them. In addition, the film-forming reaction can be carried out in a short time, efficiently and at a low temperature.

【0074】

Further, the titanium oxide film can be coated with a titanium oxide film having a thickness sufficient to cause an optical interference by easily adjusting the film thickness by one coating operation of the titanium oxide film. It has become possible to cause a high optical interference effect on the overturned base material powder. Therefore, it has become possible to produce blue or magenta colored magnetic powder.

[Simple explanation of drawings]

FIG. 1 is a diagram showing spectral reflectance curves of the titanium oxide film-coated silica-coated magnetite powder obtained in Examples 1 and 2.

FIG. 2 is a diagram showing spectral reflectance curves of the titanium oxide film-coated permalloy powder obtained in Examples 3 and 4.