Pearl pigment, composition, and method for producing pearl pigment

Abstract

Provided are: a pearl pigment comprising lamellar particles of at least one type of vanadium phosphate selected from among VOPO4·2H2O and H0.6(VO)3(PO4)3(H2O)3·4H2O; a composition containing this pearl pigment; a method for producing a pearl pigment in which a vanadium compound, water, hydrogen peroxide and phosphoric acid are mixed at a temperature of 100°C or lower to produce VOPO4·2H2O; and a method for producing a pearl pigment in which a vanadium compound, water, hydrogen peroxide and phosphoric acid are subjected to a hydrothermal treatment at a temperature of 100°C or higher to produce H0.6(VO)3(PO4)3(H2O)3·4H2O.

Description

Pearl pigment, composition, and method for producing pearl pigment

[0001] The present invention relates to a pearl pigment, a composition containing the pearl pigment, and a method for producing the pearl pigment.

[0002] Various pigments have been developed and put to practical use and are used in a wide range of applications. Among them, pearlescent pigments that exhibit the luster (pearl luster) of pearls and the like are widely used in cosmetics, paints, printing inks, plastic products (molded articles), and the like. Such pearlescent pigments are generally synthetic pigments in which a titanium dioxide layer is formed by coating the surface of a mica substrate with titanium dioxide. In such pearlescent pigments, in order to control the pearl luster that exhibits the pearl luster and also the color (hue), it is necessary to strictly control the thickness of the titanium dioxide layer.

[0003] By the way, VOHPO ４ ・0.5H ２ Vanadium phosphates such as vanadium phosphates (VOHPO) have traditionally been used as catalysts for producing maleic anhydride and as battery materials, and various synthesis methods are known. For example, Patent Documents 1 and 2 and Non-Patent Document 1 are cited as documents describing vanadium phosphates and methods for producing them. Specifically, Patent Document 1 describes a vanadium-hydrogen-phosphorus-oxygen catalyst represented by a specific empirical formula or chemical formula as a catalyst for producing maleic anhydride. Furthermore, as a method for synthesizing this catalyst, for example, a method is described in which vanadium pentoxide and a reducing agent are heated and stirred to perform a reduction reaction, and then hydrogen peroxide is added to perform an oxidation reaction. Patent Document 2 and Non-Patent Document 1 describe vanadium phosphates (VOHPO) as a catalyst for producing maleic anhydride. ４ ・0.5H ２ O is described, and the method for producing this catalyst is VOPO. ４ ・2H ２ A method of reducing O by heating in alcohol is described.

[0004] Japanese Patent Publication No. 62-058777 Japanese Patent Application Laid-Open No. 2002-153756

[0005] Japan Petroleum Institute, Abstracts of Annual and Autumn Meetings, 57th Research Presentation, 2008, Session ID: C08

[0006] The above-mentioned pearlescent pigments composed of mica and a titanium dioxide layer are produced through two steps: preparing a mica substrate and coating it with titanium dioxide, and it is not easy to precisely control the thickness of the titanium dioxide layer. Therefore, conventional pearlescent pigments are generally expensive because it is difficult to control the pearlescent luster and hue of the pigments. However, in anticipation of the wide range of uses of pearlescent pigments, there is a need for the development of low-cost pearlescent pigments, particularly colored pearlescent pigments, that can be produced using a simple method while still maintaining controlled pearlescent luster. However, the vanadium phosphates described in Patent Documents 1 and 2 and Non-Patent Document 1 are synthesized as fine particles (porous particles) for catalytic applications, and no consideration is given to their pearlescent luster or hue. Furthermore, Patent Documents 1, 2, and Non-Patent Document 1 do not describe or suggest vanadium phosphates that can be used as pearlescent pigments.

[0007] The present invention provides a method for producing a pearlescent pigment that exhibits pearlescent luster using a low-cost and simple method.The present invention also provides a pearlescent pigment that is made of a specific vanadium phosphate and exhibits pearlescent luster even though it is in the form of self-supporting plate-like particles that do not require a substrate.

[0008] The present inventors have continued to study, based on conventional pearlescent pigments, particles of various compounds that can be used as pearlescent pigments and the expression of their pearlescent luster, and have come up with the idea that pearlescent luster may also be expressed in vanadium phosphate without using a mica substrate as in conventional pearlescent pigments. Based on this idea, further research has revealed that vanadium phosphate (seed crystals) can be generated and precipitated in a reaction system by a simple process in which hydrogen peroxide is coexisted in a solution process or hydrothermal synthesis process using vanadium and phosphoric acid, and the crystals can be grown to plate-like crystals (plate-like particles) large enough to express pearlescent luster. As a result, it has been discovered that free-standing plate-like crystals made of a specific vanadium phosphate component and not requiring a substrate function as a pearlescent pigment. Furthermore, it is possible to obtain VOPO by a simple reduction treatment or heat treatment while maintaining the properties. ４ ・2H ２ O (sometimes referred to as "VOP" in the present invention) and H ０.６(V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ The present invention was completed through further investigations based on these findings.

[0009] The object of the present invention has been achieved by the following means: <1> VOPO ４ ・2H ２ O and H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ <1> A pearl pigment comprising plate-like particles of at least one vanadium phosphate selected from the group consisting of vanadium phosphate ... ４ ・2H ２ <7> The method for producing a pearl pigment according to any one of <1> to <4>, wherein a vanadium compound, water, hydrogen peroxide, and phosphoric acid are mixed at a temperature of 100°C or less to produce VOPO. ４ ・2H ２ After generating O, an alcohol is further added and reduced at a temperature of 100°C or less to generate the H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ <8> The method for producing a pearl pigment according to any one of <1> to <4>, wherein a vanadium compound, water, hydrogen peroxide, and phosphoric acid are hydrothermally treated at a temperature of 100°C or higher to produce the H ０.６ (V.O.)３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ <9> The method for producing a pearl pigment according to any one of <1> to <4>, wherein a vanadium compound, water, hydrogen peroxide, and phosphoric acid are hydrothermally treated at a temperature of 100°C or higher to produce H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ After producing O, ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ O is heat-treated at a temperature of 350° C. or higher to obtain the VOPO ４ ・2H ２ <10> The method for producing a pearl pigment according to any one of <1> to <4>, wherein the heat treatment is carried out in an oxygen-containing gas atmosphere or an inert gas atmosphere.

[0010] The present invention can provide a method for producing a pearl pigment that exhibits pearl luster in a low-cost and simple manner. The present invention also provides a pearl pigment preferably produced by the above-mentioned production method, which is made of a specific vanadium phosphate and exhibits pearl luster despite being in the form of self-supporting plate-like particles that do not require a substrate. The above and other features and advantages of the present invention will become more apparent from the following description, taken in conjunction with the accompanying drawings where appropriate.

[0011] FIG. 1 is a diagram showing the evaluation results of the VOP produced in Example 1. FIG. 2 is a diagram showing the evaluation results of the HVP produced in Example 2. FIG. 3 is a diagram showing the evaluation results of the HVP produced in Example 3. FIG. 4 is a diagram showing the evaluation results of the VOP produced in Example 4. FIG. 5 is a diagram showing the evaluation results of the VOP produced in Example 5. FIG. 6 is an optical microscope image showing one image field when the HVP produced in Example 3 is observed with a scanning electron microscope, and the particle sizes of HVP particles present within the image field. FIG. 7 is a diagram showing the results of image-based particle size distribution measurement of the VOP produced in Example 1 and an SEM image indicating the particle sizes. FIG. 8 is a diagram showing the results of image-based particle size distribution measurement of the HVP produced in Example 2 and an SEM image indicating the particle sizes. FIG. 9 is a diagram showing the results of image-based particle size distribution measurement of the HVP produced in Example 3 and an SEM image indicating the particle sizes. FIG. 10 shows the results of image-based particle size distribution measurement of the VOP produced in Example 4 and an SEM image indicating the particle sizes. FIG. 11 shows the results of image-based particle size distribution measurement of the VOP produced in Example 5 and an SEM image indicating the particle sizes. FIG. 12A is a chart obtained by powder X-ray diffraction analysis of the SP-VOP (RT) produced in Example 6. FIG. 12B is a chart obtained by powder X-ray diffraction analysis of the SP-VOP (60°C) produced in Example 6. FIG. 12C is a chart obtained by powder X-ray diffraction analysis of the SP-VOP (90°C) produced in Example 6. FIG. 13A is an SEM image obtained by observing the SP-VOP (RT) produced in Example 6 with a scanning electron microscope, indicating the particle sizes. FIG. 13B is an SEM image of SP-VOP (60°C) produced in Example 6, indicating the particle size, obtained by observing it with a scanning electron microscope. FIG. 13C is an SEM image of SP-VOP (90°C) produced in Example 6, indicating the particle size, obtained by observing it with a scanning electron microscope. FIG. 14A is a chart obtained by powder X-ray diffraction analysis of HT-HVP (120°C) produced in Example 7. FIG. 14B is a chart obtained by powder X-ray diffraction analysis of HT-HVP (150°C) produced in Example 7. FIG. 14C is a chart obtained by powder X-ray diffraction analysis of HT-HVP (180°C) produced in Example 7.FIG. 14D is a chart obtained by powder X-ray diffraction analysis of the HT-HVP (210°C) produced in Example 7. FIG. 15A is an SEM image obtained by observing the HT-HVP (120°C) produced in Example 7 with a scanning electron microscope, indicating the particle size. FIG. 15B is an SEM image obtained by observing the HT-HVP (150°C) produced in Example 7 with a scanning electron microscope, indicating the particle size. FIG. 15C is an SEM image obtained by observing the HT-HVP (180°C) produced in Example 7 with a scanning electron microscope, indicating the particle size. FIG. 15D is an SEM image obtained by observing the HT-HVP (210°C) produced in Example 7 with a scanning electron microscope, indicating the particle size. FIG. 16 is a chart obtained by powder X-ray diffraction analysis of the VOPs produced in Examples 8 and 9. Fig. 17 is a chart obtained by powder X-ray diffraction analysis of the VOPs produced in Example 1 and Comparative Example 1. Fig. 18 is an SEM image showing the particle sizes of the VOPs produced in Example 1 and Comparative Example 1, obtained by observing them with a scanning electron microscope.

[0012] The abbreviations used in the drawings will be explained in the Examples section below.

[0013] In the present invention and this specification, "pearl luster" refers to the property of exhibiting a pearlescent luster, and refers to, for example, luster manifested by multiple reflections of light on the surface or inside, or by the interference phenomenon between light reflected on the surface and light reflected inside. In the present invention and this specification, "solution process" refers to a process carried out in a solvent at a temperature of 100°C or less, and the state of dissolution of the compound in the solvent is not particularly limited. For example, as long as a liquid mixture containing a compound and a solvent is treated at a temperature of 100°C or less, the compound may be dissolved in the solvent, or all or part of the compound may be dispersed (suspended) as unnecessary particles. Similarly, in the present invention and this specification, "hydrothermal synthesis process" refers to a process carried out in an aqueous solvent at a temperature of 100°C or more, preferably a temperature above 100°C, and the state of dissolution of the compound in the aqueous solvent is not particularly limited. For example, as long as a liquid mixture containing a compound and an aqueous solvent is treated at a temperature of 100°C or more, the compound may be dissolved in the aqueous solvent, or all or part of the compound may be dispersed (suspended) as particles insoluble in the aqueous solvent.

[0014] In the present invention and this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In this specification, when multiple numerical ranges are set in stages for the content of a component, physical properties, etc., the upper and lower limits that form the numerical range can be combined as appropriate.

[0015] [Pearl pigment] The pearl pigment of the present invention is a VOPO ４ ・2H ２ O and H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ The pearl pigment of the present invention is generally composed of plate-like particles of at least one vanadium phosphate selected from the group consisting of vanadium phosphate crystalline particles and vanadium phosphate ...

[0016] The plate-like particles preferably have a layered structure (multilayer structure) in order to exhibit excellent pearlescent luster, for example, a vivid pearlescent luster. The thickness of the plate-like particles is not particularly limited and can be determined as appropriate. From the viewpoint of exhibiting pearlescent luster, it is usually 10 to 800 nm, but can also be 5 to 1600 nm. In the present invention, plate-like particles having a layered structure usually form layered crystals in which multiple sheet-like crystals are stacked, and the thickness of the plate-like particles is synonymous with the total thickness of the layered crystals. Here, the layered crystals are crystals that are observed as integral plate-like crystals when visually inspecting an image obtained when measuring particle size by scanning electron microscopy. The number of stacked sheets in the layered crystals of the plate-like particles is not particularly limited and can usually be 1 to 100 layers, with 1 to 20 layers being preferred in terms of pearlescent luster. The distance between adjacent stacked layers is not particularly limited and can be determined as appropriate. The thickness of the plate-like particles and the presence or absence of a layered structure can be confirmed and identified using a scanning electron microscope.

[0017] The vanadium phosphate forming the plate-like particles is VOPO ４ ・2H ２ O and H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ O, and VOPO ４ ・2H ２ O and H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ One of O or VOPO ４ ・2H ２ O and H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２It should be noted that for vanadium phosphate, one type refers to a stoichiometric element ratio, i.e., VOPO ４ ・2H ２ O and H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ As long as the stoichiometric elemental ratio is satisfied, the term "vanadium phosphate" encompasses compounds in which the elemental ratio varies from the stoichiometric ratio due to the presence of defects or the like in the vanadium phosphate, for example, compounds in which the valence of the vanadium element varies. Note that it is common technical knowledge among those skilled in the art that the valence of vanadium varies in vanadium phosphate due to the presence of defects or the like.

[0018] VOPO ４ ・2H ２ O(VOP) is a monoclinic layered compound. This VOP is a compound in which the valence of vanadium is +5.0 of the stoichiometric ratio, but the present invention includes compounds in which the valence of vanadium varies from the stoichiometric ratio due to the presence of (surface) defects, etc. The valence of vanadium in VOP is preferably in a range that does not affect the crystal structure, and can be, for example, +4.5 to +5.0, and preferably +4.9 to +5.0. H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ O(HVP) is a monoclinic layered compound. This HVP is a compound in which the valence of vanadium is +4.8, which is the stoichiometric ratio, but like VOP, it also includes compounds in which the valence of vanadium varies from the stoichiometric ratio. The valence of vanadium in HVP is preferably within a range that does not affect the crystal structure, and can be, for example, +4.5 to +4.8, and preferably +4.7 to +4.8.

[0019] The plate-like particles constituting the pearl pigment preferably have a particle size of 5 μm or more. That is, the plate-like particles constituting the pearl pigment of the present invention preferably contain plate-like particles having a particle size of 5 μm or more (sometimes referred to as "large-diameter plate-like particles" for convenience in the present invention). When the pearl pigment of the present invention contains plate-like particles having a particle size of 5 μm or more, pearl luster is more likely to be exhibited. In the present invention, the "particle size of the plate-like particles" refers to the average value of the particle sizes of multiple plate-like particles measured by the measurement method described below, while the "particle size of a single plate-like particle" refers to the longest length of the plate-like particle. In the present invention, in order to exhibit significant pearl luster, the particle size of the plate-like particles is preferably 30 μm or more, and can be 30 to 400 μm, and can be further increased to 400 to 1000 μm as necessary. The particle size of the plate-like particles can be appropriately determined depending on the application of the pearl pigment, the pearl luster to be exhibited by the pearl pigment, and other factors. For example, when the pearl pigment is used in cosmetics as described below, the particle size of the (large diameter) plate-like particles can be 30 to 400 μm, preferably 30 to 50 μm, and when used in paints or plastic products, the particle size of the (large diameter) plate-like particles is preferably greater than 30 μm, can be 30 to 1000 μm, more preferably 30 to 400 μm. Note that, for one plate-like particle, the length in the width direction relative to the longest length, which is the particle size, is shorter than the longest length, but is preferably in the same range as the longest length, for example.

[0020] The particle size of the plate-like particles is calculated by observing the plate-like particles using a scanning electron microscope (SEM) or an optical microscope under the following observation conditions. Specifically, a plurality of plate-like particles (e.g., 18 particles) are arbitrarily selected in one visual field observed under the following conditions, and the longest length of each plate-like particle is measured. The arithmetic mean of the longest lengths of each plate-like particle is taken as the particle size of the plate-like particle. For example, FIG. 6 shows the state in which the longest lengths of all plate-like particles present in one visual field observed with an optical microscope for the HVP produced in Example 3 were measured. In FIG. 6, the particle size of each plate-like particle is indicated by a two-way arrow (the same applies to scanning electron microscope images such as FIG. 1). It should be noted that the maximum length in the direction perpendicular to the longest length of each plate-like particle can also be measured as the width. <Observation conditions> Scanning electron microscope: FESEM, SU6600 (manufactured by Hitachi Corporation) Magnification: Can be appropriately determined within a range of 300 to 10,000 times, for example, 500 times. Optical microscope: Digital microscope Microscope 3R-MSUSB390 (manufactured by Three R Solutions Corporation) Magnification: Can be appropriately determined within a range of 9 to 390 times, for example, 60 times.

[0021] When plate-like particles cannot be observed using the above-mentioned scanning electron microscope and optical microscope, or when measurements are made (as reference values) instead of values ​​calculated using the scanning electron microscope or optical microscope, values ​​obtained by image particle size distribution measurement can also be used. Specifically, using an image particle size distribution measurement device, images of each plate-like particle in a dispersion of a plurality of plate-like particles are taken under the following measurement conditions, and the major axis diameter (longest length) of each plate-like particle is calculated as the diameter (area basis) to prepare a particle size distribution diagram. The 50% value calculated from the obtained particle size distribution diagram is taken as the particle size of the plate-like particle. However, since image particle size distribution measurement may not be able to measure particles with large particle sizes (the particle size distribution diagram may deviate from the normal distribution), the calculated particle size may be smaller than the actual particle size. <Measurement conditions> Image particle size distribution measurement device: Image particle size distribution measurement FPIA-3000S (manufactured by SYSMEX) Dispersion solvent: Water Number of particles measured: 1,000 particles

[0022] The ratio of the particle diameter to the thickness of plate-like particles, particularly large-diameter plate-like particles, [particle diameter / plate-like particle thickness] is not particularly limited and can be determined as appropriate. In pearl pigments, the ratio [particle diameter / plate-like particle thickness] is usually 25 or more, but in the present invention, in order to significantly exhibit pearlescent luster, it can be 100 or more, or even 1000 or more, and if necessary, can be 4000 or more. The upper limit of the ratio [particle diameter / plate-like particle thickness] is not particularly limited and can be, for example, 10000 or less, and preferably 4200 or less.

[0023] The ratio [particle diameter / thickness of plate-like particle] can be determined by calculating the thickness of the plate-like particle using a scanning electron microscope under the observation conditions below, and dividing the particle diameter calculated as described above by this thickness. Specifically, a plurality of plate-like particles (e.g., three particles) are arbitrarily selected in one field of view observed under the conditions below, and the thickness of each plate-like particle is measured. For each plate-like particle, the particle diameter is divided by the measured thickness to calculate a ratio, and the arithmetic average of these is used as the ratio of the plate-like particle [particle diameter / thickness of plate-like particle]. <Observation conditions> Scanning electron microscope: FESEM, SU6600 (manufactured by Hitachi Corporation) Acceleration voltage: 5 kV Spot size: 1.41 nm Magnification: Can be appropriately determined within the range of 10,000 to 40,000 times.

[0024] The pearl pigment (plate-like particles) of the present invention contains, as a main component, a vanadium phosphate containing at least one of VOP and HVP, i.e., VOP, HVP, or a mixture of VOP and HVP. In the present invention, the term "main component" refers to the component with the highest content among all components (compounds) contained in the pearl pigment. While this content depends on the production method and purification method, it is usually 50% by mass or more, and can be 90% by mass or more, relative to the total mass of the pearl pigment. The pearl pigment of the present invention may contain plate-like particles other than the large-diameter plate-like particles, particles other than plate-like particles, and the like, although this content depends on the production method and production conditions, as well as classification conditions, etc. The content of these particles is not particularly limited, as long as the pearl pigment of the present invention as a whole exhibits pearlescent luster.

[0025] The pearlescent pigment of the present invention is composed of the above-described vanadium phosphate plate-like particles and exhibits pearlescent luster. The presence of plate-like particles can be confirmed, for example, by observation using a scanning electron microscope or an optical microscope. Furthermore, the inclusion of at least one of VOP and HVP in the vanadium phosphate can be identified by powder X-ray diffraction (XRD) or the like in the Examples described below, and the valence of vanadium can be determined by X-ray photoelectron spectroscopy (XPS) or the like. The pearlescent luster exhibited by the pearlescent pigment of the present invention can usually be confirmed visually and can be confirmed by the presence of plate-like particles (layered compounds), as well as their particle size and the ratio [particle size / thickness of plate-like particles]. It can also be confirmed by gloss evaluation (angle dependence of RBG values) described in the Examples described below. Furthermore, unlike conventional pearlescent pigments having a titanium dioxide layer (white pearlescent luster), the pearlescent luster of the present invention can exhibit pearlescent luster in various colors (hues). For example, the hue of the pearl pigment of the present invention can be a hue of 45 to 165° when expressed as an angle of the hue divided into 24 equal parts, and can be a hue from yellow to green. The hue can be measured and identified by a diffuse reflectance method (DRS) in the ultraviolet-visible-near infrared region, which will be described in the examples below. In addition, the hue of the pearl pigment of the present invention can be measured and identified by a diffuse reflectance method (DRS) in the ultraviolet-visible-near infrared region, which will be described in the examples below. ＊ Value, a ＊ value and b ＊ In the pearl pigment of the present invention, the L ＊ The value can be greater than or equal to 50 and less than 100, and a ＊ The value can be negative, for example, greater than or equal to -12 and less than 0, and b ＊ The value can be any positive value, for example, between 25 and 60.

[0026] In the present invention, the hue of the pearl pigment can be changed or adjusted by selecting the type of vanadium phosphate, the valence of vanadium, the method for producing the pearl pigment, and further by controlling defects and the treatment atmosphere. The tendency of the hue change can be exemplified by the tendency shown in the examples described below. The hue of the pearl pigment of the present invention can be changed as described above, and the pigment is suitable as a colored pearl pigment.

[0027] The pearlescent pigment of the present invention and a composition containing the pearlescent pigment of the present invention can be used in a variety of applications, taking advantage of the above-mentioned properties of the pearlescent pigment of the present invention. For example, they can be used as pigments in various products, and preferably as pigments in cosmetics, (automotive) paints, printing inks, gas sensing materials, plastic products (molded products), etc.

[0028] [Composition] The composition of the present invention is a composition containing the pearl pigment of the present invention (hereinafter, sometimes simply referred to as the "pigment composition"). The pearl pigment of the present invention exhibits high stability against organic solvents such as acetone, and can therefore be used for various applications as a composition with an organic solvent, etc. The pigment composition of the present invention contains the pearl pigment of the present invention and various components that are commonly used depending on the application, properties, etc., and preferably contains an organic solvent. The various components are appropriately selected depending on the application of the composition, and include, for example, solvents, resins or elastomers or various polycondensation compounds, polymerization initiators, fillers, colorants, (ordinary) pigments or dyes that do not exhibit pearlescent luster, antioxidants (antiaging agents), glass, plasticizers, etc. The solvent is preferably an organic solvent, and examples thereof include ketone solvents such as acetone, alcohol solvents such as isopropyl alcohol and n-butanol, ester solvents such as ethyl acetate and butyl acetate, and aromatic solvents such as toluene and xylene. Examples of resins, elastomers, and various polycondensation compounds include nitrocellulose, alkyd resins (medium oil content), acrylic resins, styrene monomers, butyl methacrylate monomers, 2-hydroxypropyl methacrylate monomers, and methacrylic acid monomers. Polymerization initiators include those typically used in the polymerization of the above polycondensation compounds, such as peroxides such as benzoyl peroxide. Examples of plasticizers include tributyl acetate and citrate. The content of the pearl pigment of the present invention in the pigment composition is determined appropriately depending on the intended use of the pigment composition, and is not definitive, but can be, for example, 1.0 to 6.0% by mass. The contents of various components in the pigment composition are determined appropriately depending on the intended use of the pigment composition.

[0029] [[Method for producing pearl pigment of the present invention]] The method for producing pearl pigment of the present invention includes the following Production Method 1 for producing VOP (including a mixture with HVP), and the following Production Method 2 for producing HVP (including a mixture with VOP). The method for producing pearl pigment of the present invention also includes a method for converting VOP (including a mixture with HVP) to HVP (referred to as "Production Method 3" in the present invention), and a method for converting HVP (including a mixture with VOP) to VOP (referred to as "Production Method 4" in the present invention). First, Production Method 1 and Production Method 2 will be explained. Production Method 1: A vanadium compound, water, hydrogen peroxide, and phosphoric acid are mixed at a temperature of 100°C or less to produce VOPO. ４ ・2H ２ Method 2: A vanadium compound, water, hydrogen peroxide, and phosphoric acid are hydrothermally treated at a temperature of 100°C or higher to produce H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ Method for producing O

[0030] [Production Method 1] The above-mentioned Production Method 1 (sometimes referred to as "Production Method 1 of the present invention") for producing VOP uses a vanadium compound, water, hydrogen peroxide, and phosphoric acid as raw materials. The vanadium compound is not particularly limited, but examples thereof include vanadium oxide and metavanadate, with vanadium oxide being preferred. Examples of vanadium oxide include V ２ O ３ , V ３ O ５ , V.O. ２ , V ３ O ７ , V ２ O ５ , V ２ O ２ , V ６ O １３ , V ４ O ９ Among them, V ２ O ５(vanadium pentoxide) is preferred. Examples of metavanadates include ammonium metavanadate. The water is not particularly limited, but deionized water, reverse osmosis water, distilled water, purified water, etc. can be used. Hydrogen peroxide is usually used as hydrogen peroxide. The hydrogen peroxide concentration is not particularly limited, but can usually be 30 w / v % (approximately 10 mol / L) to 35 w / v %. Orthophosphoric acid is used as phosphoric acid. Note that the mixing in Production Method 1 is performed in water, but it can also be performed in a mixed solvent with a water-soluble solvent such as alcohol.

[0031] The mixing ratio of the raw material compounds in Production Method 1 is determined appropriately taking into account the assumed reaction formula described below, but is preferably within the following range from the viewpoint of VOP production efficiency, etc. For example, the mixing ratio of water is set to an amount that allows stirring of a mixture of the vanadium compound, water, hydrogen peroxide, and phosphoric acid, and is, for example, preferably 50 to 230 mol, more preferably 100 to 180 mol, and even more preferably 130 to 150 mol, per mol of vanadium element in the vanadium compound. The mixing ratio of hydrogen peroxide is preferably 1 to 20 mol, more preferably 2 to 10 mol, and even more preferably 4 to 5 mol, per mol of vanadium element in the vanadium compound, from the viewpoint of enabling the production of VOP that exhibits pearlescent luster while further increasing the yield of the VOP. The mixing ratio of phosphoric acid is preferably 2.5 to 100 mol, more preferably 2.5 to 15 mol, and even more preferably 2.67 to 12 mol, per mol of vanadium element in the vanadium compound.

[0032] The present invention enables the production of large-sized plate-like particles, which was not possible with conventional production methods, by allowing hydrogen peroxide to coexist (i.e., by conducting an exothermic reaction with the vanadium compound beforehand) during the synthesis of VOP by the reaction of a vanadium compound with phosphoric acid. It is believed that the exothermic reaction between the vanadium compound and hydrogen peroxide allows the vanadium compound to be dissolved in water, then reacted with phosphoric acid to precipitate VOP, which then undergoes Ostwald ripening to increase the particle size. Therefore, in Production Method 1, the order of mixing the raw materials is preferably such that the vanadium compound and hydrogen peroxide are mixed before mixing with phosphoric acid (before reaction), in order to produce large-sized plate-like particles. For example, a preferred method is to add hydrogen peroxide to a mixture of a vanadium compound and water and mix, and then add phosphoric acid to the resulting mixture and mix. In this way, contacting and reacting the vanadium compound with phosphoric acid in the presence of hydrogen peroxide or in water after the reaction with hydrogen peroxide (after reaction with hydrogen peroxide) promotes the growth of VOP plate-like crystals, forming large-sized plate-like crystals and exhibiting pearlescent luster. When hydrogen peroxide is added to the mixture of the vanadium compound and water, an exothermic reaction occurs and progresses, so it is preferable to add phosphoric acid after this exothermic reaction has subsided (after foaming has stopped).

[0033] Production method 1 is a method for producing VOP by a solution process, and the mixing conditions are a temperature of 100°C or less. The lower limit of the mixing temperature is not particularly limited and can be 20°C. The reaction temperature is preferably set at a high temperature, for example, 60°C or higher, and more preferably 90°C or higher, in order to increase the particle size of the plate-like particles. The upper limit of the mixing temperature may be 100°C, and is preferably less than 100°C, and can be, for example, 90°C or lower.

[0034] In Production Method 1, the composition and particle size of the resulting plate-like particles can be controlled by adjusting the mixing temperature and the mixing ratio of phosphoric acid. For example, increasing the mixing temperature tends to increase the particle size regardless of the mixing ratio of phosphoric acid. At a high mixing temperature of around 90°C, plate-like particles consisting of a single VOP phase are obtained regardless of the mixing ratio of phosphoric acid, and their particle size is not affected. On the other hand, at a mixing temperature of 60°C or less, decreasing the mixing ratio of phosphoric acid within the above range results in plate-like particles consisting of a mixed phase of VOP and HVP, and their particle size tends to increase. At a mixing temperature of 60°C or less, increasing the mixing ratio of phosphoric acid results in plate-like particles consisting of a single VOP phase.

[0035] The mixing environment is not particularly limited and may be an oxygen-containing gas atmosphere such as atmospheric air, an inert gas atmosphere, or a vacuum environment. From the viewpoint of workability, atmospheric air is preferred. The mixing environment can be an open or closed system. The environmental pressure during mixing may be reduced, normal, or increased, but normal pressure is preferred from the viewpoint of workability. Note that, in the present invention, normal pressure does not mean exactly 1 atm, but refers to an open system in which mixing is performed. The mixing time is appropriately set depending on the mixing temperature and other factors, and may be, for example, 2 to 48 hours, with 12 to 24 hours being preferred. The mixing method is not particularly limited, and conventional mixing methods, such as mixing with a magnetic bar or a mechanical stirrer, can be used as appropriate depending on the mixing scale and other factors. The stirring speed (rpm / min) is not particularly limited and can be determined appropriately.

[0036] The above-mentioned mixing conditions refer to the conditions under which VOP production from the raw material compounds is completed. The preferred order of mixing the raw material compounds refers to the mixing conditions in the mixed solution preparation step in which a vanadium compound and water are mixed to prepare a mixed solution, the mixing conditions in the pre-mixing step (exothermic reaction) in which hydrogen peroxide is added to the mixed solution and mixed, and the mixing conditions in the post-mixing step in which phosphoric acid is added to the mixture obtained in the pre-mixing step and mixed. In the present invention, the mixing conditions for the mixed solution preparation step and the pre-mixing step are selected from the above conditions. However, the mixing conditions for the mixed solution preparation step and the pre-mixing step in Production Method 2 described below can also be applied. In Production Method 1, the mixing conditions for the mixed solution preparation step, the pre-mixing step, and the post-pre-mixing step may be the same or different. The mixing time for the mixed solution preparation step may be 0.1 to 0.2 hours, for the pre-mixing step 0.05 to 0.4 hours, preferably 0.1 to 0.2 hours, and for the post-mixing step 2 2 to 48 hours, preferably 12 to 24 hours.

[0037] In the production method 1, the vanadium compound is, for example, V ２ O ５ When using a 2V ion, the reaction shown in the following assumed reaction formula is thought to proceed. ２ O ５ +2H ２ O ２ +4H ３ P.O. ４ → 4VOPO ４ ・2H ２ O+O ２

[0038] The plate-like particles obtained by the above-mentioned mixing are usually isolated by washing or purifying the solid content obtained by solid-liquid separation, and drying it. In this way, the pearl pigment of the present invention consisting of plate-like particles of VOP or plate-like particles of VOP and HVP can be produced.

[0039] [Production Method 2] The above-mentioned Production Method 2 for producing HVP (sometimes referred to as "Production Method 2 of the present invention") uses a vanadium compound, water, hydrogen peroxide, and phosphoric acid as raw material compounds. The raw material compounds used in Production Method 2 are the same as those used in Production Method 1. The mixing ratio of the raw material compounds in Production Method 2 is appropriately determined taking into account the assumed reaction formula described below, but is preferably within the following range in terms of HVP production efficiency, etc. For example, the mixing ratio of water is set to an amount that allows a mixture of the vanadium compound, water, hydrogen peroxide, and phosphoric acid to be stirred. For example, the mixing ratio of water is preferably 50 to 230 mol, more preferably 100 to 180 mol, and even more preferably 130 to 150 mol, per mol of vanadium element in the vanadium compound. The mixing ratio of hydrogen peroxide is preferably 1 to 20 mol, more preferably 2 to 10 mol, and even more preferably 4 to 5 mol, per mol of vanadium element in the vanadium compound. From the viewpoint of synthesizing HVP, the mixing ratio of phosphoric acid is preferably 5 to 100 moles, more preferably 5 to 15 moles, and even more preferably 5 to 12 moles, per mole of vanadium element in the vanadium compound.

[0040] In the present invention, HVP can be synthesized by reacting a vanadium compound with phosphoric acid in the presence of hydrogen peroxide (by conducting an exothermic reaction with the vanadium compound beforehand), and large-sized plate-like particles can also be produced, as in Production Method 1. Therefore, in Production Method 2, the order of mixing the raw materials is preferably the same as in Production Method 1, in that the vanadium compound and hydrogen peroxide are mixed before mixing with phosphoric acid (before the hydrothermal reaction), in order to produce large-sized plate-like particles. For example, a preferred method is to add hydrogen peroxide to a mixture of a vanadium compound and water and mix them, and then add phosphoric acid to the resulting mixture and mix them to cause a hydrothermal reaction. In this way, by contacting a vanadium compound with phosphoric acid in the presence of hydrogen peroxide or in water after the reaction with hydrogen peroxide (after the reaction with hydrogen peroxide), and then subjecting it to a hydrothermal reaction, HVP, the synthesis of which has not been reported in many previous reports, can be synthesized in a simple manner. Furthermore, as in Production Method 1, the growth of HVP plate-like crystals can be promoted to form large-sized plate-like crystals, thereby exhibiting pearlescent luster. Here, when hydrogen peroxide is added to a mixture of a vanadium compound and water, an exothermic reaction occurs and progresses, so it is preferable to add phosphoric acid after this exothermic reaction has subsided (after foaming has stopped). In the hydrothermal treatment in Production Method 2, it is preferable to add phosphoric acid to a mixture of a mixture of a vanadium compound and water and hydrogen peroxide, and mix them in the above-mentioned preferred mixing order, and then start the hydrothermal treatment after the exothermic reaction has ended and the mixture with phosphoric acid has become transparent (a solution). The mixing conditions until the mixture becomes transparent can be, for example, the conditions for mixing a vanadium compound and water, which will be described later.

[0041] Production method 2 is a method for producing HVP by a hydrothermal synthesis process, and the hydrothermal synthesis process (hydrothermal treatment) is carried out at a temperature of 100°C or higher. The lower limit of the reaction temperature is not particularly limited and can be a temperature above 100°C, preferably 110°C or higher, and more preferably 120°C or higher. If the reaction temperature is too high, the particle size of the plate-like particles tends to become small, so in order to exhibit pearlescent luster, it is preferable not to set the reaction temperature at an excessively high temperature; for example, it is preferably 210°C or lower, more preferably 180°C or lower, and even more preferably 150°C or lower.

[0042] In Production Method 2, the composition and particle size of the resulting plate-like particles can be controlled by adjusting the reaction temperature and the mixing ratio of phosphoric acid. For example, lowering the reaction temperature tends to increase the particle size regardless of the mixing ratio of phosphoric acid. Changing the mixing ratio of phosphoric acid within the above range does not affect the particle size, but can change the composition. For example, at a high reaction temperature of about 150°C or higher, reducing the mixing ratio of phosphoric acid within the above range results in plate-like particles consisting of a mixed phase of VOP and HVP. On the other hand, at a low reaction temperature of less than about 150°C, reducing the mixing ratio of phosphoric acid within the above range results in plate-like particles consisting of a single phase of HVP.

[0043] The environment in which the hydrothermal treatment is performed is not particularly limited, and may be an oxygen-containing gas atmosphere such as the air environment, an inert gas atmosphere, or a vacuum environment. From the viewpoint of workability, an air environment is preferable. The hydrothermal treatment is typically performed in a sealed system. The environmental pressure during the hydrothermal treatment is typically pressurized and depends on factors such as the reaction temperature, but can be set to, for example, 1 to 18.75 atm, preferably greater than 1 atm and not greater than 1.96 atm. The hydrothermal treatment time is appropriately set depending on factors such as the reaction temperature, and can be, for example, 2 to 48 hours, preferably 12 to 24 hours. The hydrothermal treatment is performed, for example, by heating while stirring using a pressure-resistant reaction vessel such as an autoclave. The stirring speed (rpm / min) is not particularly limited and can be determined appropriately.

[0044] In the above-mentioned preferred mixing order, the mixing conditions for the mixed solution preparation step in which the vanadium compound and water are mixed to prepare a mixed solution are not particularly limited, and for example, the mixing temperature can be 0 to 30° C., preferably 20 to 25° C., and the mixing time can be 3 minutes to 0.5 hours, preferably 5 minutes to 0.25 hours. The environment, environmental pressure, and mixing method for the mixed solution preparation step are not particularly limited, and the conditions in Production Method 1 can be applied.

[0045] In the above-mentioned preferred mixing order, the mixing conditions for the pre-mixing step in which the mixed solution obtained in the mixed solution preparation step is mixed with hydrogen peroxide are not particularly limited and can be set appropriately. For example, the mixing conditions for the mixed solution preparation step can be applied.

[0046] In the production method 2, the vanadium compound is, for example, V ２ O ５ When using a 30V battery, the reaction shown in the following assumed reaction formula is thought to proceed. ２ O ５ +56H ２ O ２ +60H ３ P.O. ４ → 20H ０．６ (V.O.) ３ (P.O. ４ ) ３ (H ２ O) ３ ・4H ２ O+31O ２

[0047] The plate-like particles obtained by the hydrothermal synthesis treatment are usually separated into solid and liquid, and the solid content is then washed or purified and dried to isolate and purify the pearl pigment of the present invention, which is composed of HVP plate-like particles or VOP and HVP plate-like particles.

[0048] [Production Method 3] Production Method 3 is a method for converting VOP (including a mixture with HVP; the same applies hereinafter to Production Method 3) into HVP. The VOP used in Production Method 3 is not particularly limited, but in order to impart pearlescent luster to the HVP obtained by Production Method 3, it is preferably a VOP that exhibits pearlescent luster, for example, a VOP having a particle size of 5 μm or more, more preferably the VOP obtained by Production Method 1 (including a mixture with HVP), and particularly preferably a reaction mixture containing the VOP obtained by Production Method 1 (including a mixture with HVP) (the VOP is used in Production Method 3 as a reaction liquid without isolating the VOP).

[0049] The following describes the particularly preferred Production Method 3, which uses VOP. In Production Method 3, a vanadium compound, water, hydrogen peroxide, and phosphoric acid are mixed at a temperature of 100° C. or lower to produce VOP (in a reaction system), and then an alcohol is further added (to the reaction system) and reduced at a temperature of 100° C. or lower to produce HVP. Production Method 3 is a continuous method (regardless of the time continuity) in which a VOP synthesis step (Production Method 1) and an HVP synthesis step (a step of converting VOP to HVP (reduction step)) are carried out continuously in this order, and is preferably a one-pot continuous reaction.

[0050] In the present invention, the reaction mixture obtained by Production Method 1 is used to reduce VOP with an alcohol in the presence of at least water and in the presence of an alcohol in an amount to be added as described below, thereby reducing VOP to HVP within a range that does not impair the crystal structure, for example, within the range of the valence that the vanadium in the HVP can assume. At this time, the VOP structure (plate-like particles, layer structure) is maintained, and HVP can be obtained without significantly impairing the particle size or the like, while maintaining pearlescent luster. On the other hand, the plate-like particles of vanadium phosphate obtained by Production Method 3 exhibit a hue different from that of VOP, for example, shifted to the blue side, due to variations in the valence of vanadium. Therefore, the plate-like particles of vanadium phosphate obtained by Production Method 3 satisfy the above-described numerical values ​​and other properties of the particle size and ratio [particle size / plate-like particle thickness] of the plate-like particles described above for the pearlescent pigment of the present invention, and also exhibit pearlescent luster. On the other hand, the hue, L ＊ Value, a ＊ value and b＊ The value preferably varies within the above range, and the tendency is as shown in the examples below.

[0051] The VOP synthesis step in Production Method 3 is the same as that in Production Method 1. In Production Method 3, an HVP synthesis step is carried out in which an alcohol is added to a reaction mixture (aqueous suspension of vanadium phosphate) obtained in the same manner as in Production Method 1 and mixed (in the presence of water) at a temperature of 100°C or less.

[0052] The reaction mixture used in Production Method 3 is preferably the same as that obtained in Production Method 1, and the ratio of VOP, water, etc. in the reaction mixture corresponds to the mixing ratio of each component in Production Method 1. The reaction mixture used in Production Method 3 can also be the one obtained in Production Method 1, diluted with water or concentrated as appropriate.

[0053] The alcohol used is not particularly limited, but includes aliphatic alcohols and aromatic alcohols, with aliphatic alcohols being preferred. The number of carbon atoms in the aliphatic alcohol is not particularly limited, and can be, for example, 1 to 12, preferably 2 to 4. The number of carbon atoms in the aromatic alcohol is not particularly limited, and can be, for example, 6 to 20, preferably 6 to 12. The alcohol may have one or more hydroxyl groups, preferably one or two. The position of the hydroxyl group in the alcohol is not particularly limited. The aliphatic alcohol is preferably a saturated aliphatic alcohol. Examples of saturated aliphatic alcohols include saturated aliphatic monoalcohols such as methanol, ethanol, propanol (including various isomers), butanol (including various isomers), pentanol (including various isomers), hexanol (including various isomers), octanol (including various isomers), decanol (including various isomers), and dodecanol (including various isomers). Of these, saturated aliphatic primary monoalcohols are preferred, such as methanol, ethanol, 1-propanol, 1-butanol, isobutanol, isopentanol, neopentanol, 2-methyl-1-butanol, 1-pentanol, 1-hexanol, 1-octanol, 1-decanol, and 1-dodecanol. Of these, ethanol, 1-propanol, and 1-butanol are preferred.

[0054] The amount of alcohol added (mixing ratio) is determined as appropriate, but is preferably within the following range from the viewpoint of synthesizing HVP while maintaining the crystal structure: In Production Method 3, the amount of alcohol added is preferably 1 to 15 moles, more preferably 3 to 10 moles, and even more preferably 4 to 8 moles, relative to 1 mole of vanadium element in the vanadium compound used in Production Method 1, i.e., 1 mole (equivalent amount) of vanadium element that may be present in the reaction mixture used in Production Method 3.

[0055] Production method 3 is a so-called solution process carried out in the presence of at least water and alcohol, and the mixing conditions (reduction reaction conditions) are a temperature of 100°C or less. The lower limit of the reduction reaction temperature is not particularly limited and can be 20°C. The reduction reaction temperature is preferably set to a high temperature in order to increase the particle size of the plate-like particles, and is, for example, preferably 60°C or more, more preferably 75°C or more, and even more preferably 90°C or more. The upper limit of the reduction reaction temperature may be 100°C, and is preferably less than 100°C, and is preferably 90°C or less.

[0056] The environment, environmental pressure, and mixing method for the mixing (reduction reaction) are not particularly limited, and can be the same as those described in Production Method 1. The time for the mixing (reduction reaction) is appropriately set depending on the set reduction reaction temperature and the like, and can be, for example, 2 to 48 hours, and preferably 12 to 24 hours.

[0057] The plate-like particles obtained by the above-mentioned mixing (reduction reaction) are usually isolated by washing or purifying the solid content obtained by solid-liquid separation, and drying it. In this way, the pearl pigment of the present invention consisting of plate-like particles of HVP or plate-like particles of HVP and VOP can be produced.

[0058] [Production Method 4] Production Method 4 is a method for converting HVP (including a mixture with VOP; the same applies hereinafter to Production Method 4) into VOP. The HVP used in Production Method 4 is not particularly limited, but in order to impart pearlescent luster to the VOP obtained by Production Method 4, it is preferably an HVP that exhibits pearlescent luster, for example, an HVP having a particle size of 5 μm or more, more preferably the HVP obtained by Production Method 2 (including a mixture with VOP), and particularly preferably an isolated HVP obtained by Production Method 2 (including a mixture with VOP).

[0059] The following describes Production Method 4, which uses a particularly preferred HVP. Production Method 4 is a method in which HVP is produced by hydrothermal treatment of a vanadium compound, water, hydrogen peroxide, and phosphoric acid at a temperature of 100° C. or higher to produce HVP, and then this HVP is heat-treated at a temperature of 350° C. or higher to produce VOP. Production Method 4 is a method in which an HVP synthesis step (Production Method 2) and a VOP synthesis step (a step of converting HVP to VOP (oxidation step)) are carried out in this order.

[0060] In the present invention, by subjecting the HVP obtained by Production Method 2 to a heat treatment for oxidation reaction, the HVP can be oxidized and converted into VOP within a range that does not damage the crystal structure, for example, within the range of the valence that the vanadium in the VOP can assume. At this time, VOP can be obtained without damaging the structure (plate-like particles, layer structure), particle size, etc. of the HVP, while maintaining pearlescent luster. On the other hand, the plate-like particles of vanadium phosphate obtained by Production Method 4 exhibit a hue different from that of HVP, for example, shifted to the yellow or red side, due to variations in the valence of vanadium. Therefore, the plate-like particles of vanadium phosphate obtained by Production Method 4 satisfy the above-mentioned numerical values ​​and other properties explained for the pearlescent pigment of the present invention with respect to the particle diameter and ratio [particle diameter / plate-like particle thickness] of the plate-like particles, and also exhibit pearlescent luster. On the other hand, the hue, L ＊ Value, a ＊ value and b ＊ The value preferably varies within the above range, and the tendency is as shown in the examples below.

[0061] The synthesis step of HVP in Production Method 4 is the same as that in Production Method 2. In Production Method 4, HVP is isolated from the reaction mixture (aqueous suspension of vanadium phosphate) obtained in the same manner as in Production Method 2, and after purification or drying as necessary, the HVP is subjected to a VOP synthesis step of heat-treating it.

[0062] The heat treatment in Production Method 4 can be carried out either in the presence or absence of oxygen as long as it can oxidize HVP to VOP. In the present invention, "in the absence of oxygen" means that oxygen is not actively present, and includes the presence of oxygen that inevitably remains even after the oxygen removal method described below. Production Method 4 includes Production Method 4A, in which the heat treatment is carried out in an oxygen-containing gas atmosphere; Production Method 4B, in which the heat treatment is carried out in an inert gas atmosphere; and Production Method 4B, in which the heat treatment is carried out in a vacuum (e.g., 0.05 atm or less).

[0063] [Production Method 4A] The oxygen-containing gas atmosphere in the heat treatment of Production Method 4A may be any atmosphere (environment) in which oxygen is actively present, such as an oxygen gas atmosphere or a mixed gas atmosphere of oxygen gas and other gases. From the viewpoint of workability and safety, an atmospheric atmosphere (in air) is preferred. The amount of oxygen present in the oxygen-containing gas atmosphere is not particularly limited as long as it can oxidize HVP to VOP. Although it is not uniquely determined depending on the amount of HVP to be treated, the spatial volume of the heat treatment vessel, etc., it can be, for example, 1% by volume or more, and preferably 10% by volume or more. The oxygen-containing gas atmosphere can also be one in which oxygen-containing gas flows (under airflow), and the flow rate of the oxygen-containing gas is determined appropriately.

[0064] The heat treatment is carried out at a heat treatment temperature of 350°C or higher. The lower limit of the heat treatment temperature is preferably 380°C or higher, more preferably 400°C or higher. The heat treatment temperature is not particularly limited, but it is preferable not to set it at an excessively high temperature. For example, it is preferably 700°C or lower, more preferably 650°C or lower, even more preferably 600°C or lower, and particularly preferably 500°C or lower. The heat treatment conditions other than the heat treatment temperature are not particularly limited and can be determined appropriately. For example, the environmental pressure for the heat treatment may be reduced pressure, atmospheric pressure, or increased pressure, and atmospheric pressure is preferable from the viewpoint of workability. The heat treatment time is also appropriately set depending on the heat treatment temperature to be set, and can be, for example, 1 to 48 hours, and preferably 3 to 24 hours. The heat treatment can be carried out using, for example, a pressure-resistant reaction vessel such as a conventional (open) reaction vessel or an autoclave.

[0065] The plate-like particles obtained by the heat treatment are washed or purified, dried, and isolated as necessary, thereby producing the pearl pigment of the present invention comprising plate-like particles of VOP or plate-like particles of VOP and HVP.

[0066] [Production Method 4B] The inert gas atmosphere used in the heat treatment of Production Method 4B is not particularly limited, and examples thereof include an inert gas-filled atmosphere in a reaction vessel and a flow of inert gas. The flow rate of the inert gas is determined appropriately. The inert gas is not particularly limited, and examples thereof include rare gases such as helium and argon, and nitrogen gas. In Production Method 4B, the inert gas atmosphere used in the heat treatment can be established by replacing the heat treatment atmosphere with an inert gas or flowing an inert gas through the heat treatment atmosphere. In Production Method 4B, VOP is obtained by heat treating HVP in an inert gas atmosphere. Note that the oxidation reaction of HVP is thought to proceed due to oxygen gas inevitably remaining in the inert gas or oxygen dissolved in HVP. The amount of oxygen used in Production Method 4B is not particularly limited as long as it can oxidize HVP to VOP. For example, it can be 1.04 moles or more per mole of HVP to be treated, with the upper limit being less than the oxygen amount used in Production Method 4A. The heat treatment method and conditions in Production Method 4B are the same as those in Production Method 4A.

[0067] The plate-like particles obtained by the heat treatment are washed or purified, dried, and isolated as necessary, thereby producing the pearl pigment of the present invention comprising plate-like particles of VOP or plate-like particles of VOP and HVP.

[0068] The manufacturing methods of the present invention (Manufacturing Methods 1 to 4) do not require a substrate as in conventional pearlescent pigments, and can produce pearlescent pigments composed of plate-like particles of vanadium phosphate by a solution process or hydrothermal synthesis process. As a result, the manufacturing method of the present invention can produce the pearlescent pigment of the present invention at low cost and through a simple manufacturing process. Because the plate-like particles of vanadium phosphate are self-supporting particles that do not require a substrate, Manufacturing Methods 1 and 2, in particular, can produce the pearlescent pigment of the present invention in a single step, thereby further reducing costs and achieving a simpler manufacturing process. Furthermore, by appropriately selecting Manufacturing Methods 1 to 4, the hue of the pearlescent pigment can be changed, making it possible to produce a colored pearlescent pigment at low cost and through a simple manufacturing process. Therefore, the pearlescent pigment of the present invention and the manufacturing method of the pearlescent pigment of the present invention are highly useful, and the pearlescent pigment of the present invention is expected to be applicable to a wide range of applications.

[0069] The present invention will be described in more detail based on examples. The present invention is not to be construed as being limited to the following examples except as defined in the present invention. In the examples and comparative examples, commercially available vanadium pentoxide (V ２ O ５ , purity > 99.0%) powder, hydrogen peroxide solution (H ２ O ２ Water, 30.0-35.5%), phosphoric acid (H ３ P.O. ４ , purity >85.0%) and deionized water were used. In the examples and comparative examples, "room temperature" means 30°C.

[0070] [Example 1: Production of VOP by Production Method 1] V ２ O ５ 1 g of the powder and 28 mL of deionized water (141 moles per mole of vanadium element) were added to a 100 mL beaker and stirred at 90°C and 450 rpm for 5 minutes. ２ O ２ When water (4.45 moles per mole of vanadium element) was added, a dramatic exothermic reaction occurred. After stirring for several minutes (when bubbles no longer appeared), 4 mL of H ３ P.O. ４(0.0585 mol, 5.32 mol per mol of vanadium element) was added and stirred for about 24 hours. The resulting reaction mixture was filtered and the solid content was washed with acetone to produce a yellow-green VOP (hereinafter sometimes referred to as "SP-VOP (90°C)").

[0071] Example 2: Production of HVP by Production Method 3 To the reaction mixture containing VOP (90°C) obtained in Example 1, 4 mL of ethanol (99.5%, 7.85 moles per mole of vanadium element) or 1-butanol (99.7%, 4.89 moles per mole of vanadium element) was added, and the mixture was stirred at 90°C and 450 rpm / min for a further 24 hours to produce HVP. ０．６ (V.O.) ３ (P.O. ４ ) ３ (H ２ O) ３ ・4H ２ Specifically, V ２ O ５ 1 g of powder and 28 mL of deionized water were added to a 100 mL beaker and stirred at 90°C and 450 rpm / min for 5 minutes. ２ O ２ When the solution was added, a dramatic exothermic reaction occurred. After stirring for several minutes (when no more bubbles were generated), 4 mL of H ３ P.O. ４ The mixture was stirred for about 24 hours. To the reaction mixture thus obtained, 4 mL of ethanol (Example 2-1) or 1-butanol (Example 2-2) was added, and the mixture was stirred at 90°C and 450 rpm / min for an additional 24 hours. The reaction mixture thus obtained was filtered, and the solid content was washed with acetone to produce a green HVP (hereinafter, sometimes referred to as "SP-HVP (90°C)").

[0072] [Example 3: Production of HVP by Production Method 2] V ２ O ５ 1 g of powder and 28 mL of deionized water were added to a 100 mL beaker and stirred at room temperature at 450 rpm / min for 5 minutes. ２ O ２ was added to the beaker, and after the exothermic reaction had finished, 4 mL of H ３ P.O. ４After the solution became transparent, the reaction solution was transferred to a 100 mL PTFE-lined stainless steel autoclave and reacted at 120°C for 12 hours. After the reaction, the resulting reaction mixture was cooled to room temperature and filtered, and the solid content was washed with acetone to produce a green HVP (hereinafter sometimes referred to as "HT-HVP (120°C)").

[0073] [Example 4: Production of VOP by Production Method 4A] The HVP (120°C) obtained in Example 3 was heat-treated in air at 500°C for 6 hours to produce VOP. ２ O ５ 1 g of powder and 28 mL of deionized water were added to a 100 mL beaker and stirred at room temperature at 450 rpm / min for 5 minutes. ２ O ２ was added to the beaker, and after the exothermic reaction had finished, 4 mL of H ３ P.O. ４ After the solution became transparent, the reaction solution was transferred to a 100 mL PTFE-lined stainless steel autoclave and reacted at 120°C for 12 hours. After the reaction, the resulting reaction mixture was cooled to room temperature and filtered, and the solid content was washed with acetone to produce green HVP. This HVP was heat-treated in air at 500°C for 6 hours to produce yellow VOP (hereinafter sometimes referred to as "HT(120°C)-O-VOP").

[0074] [Example 5: Production of VOP by Production Method 4B] The HVP (120°C) obtained in Example 3 was heat-treated at 500°C for 6 hours in a nitrogen atmosphere to produce VOP. ２ O ５ 1 g of powder and 28 mL of deionized water were added to a 100 mL beaker and stirred at room temperature at 450 rpm / min for 5 minutes. ２ O ２ was added to the beaker, and after the exothermic reaction had finished, 4 mL of H ３ P.O. ４After the solution became transparent, the reaction solution was transferred to a 100 mL PTFE-lined stainless steel autoclave and reacted at 120°C for 12 hours. After the reaction, the resulting reaction mixture was cooled to room temperature and filtered, and the solid was washed with acetone to produce green HVP. This HVP was heat-treated in nitrogen gas at 500°C for 6 hours to produce grass-green VOP (hereinafter referred to as "HT(120°C)-N"). ２ -VOP".)

[0075] [Evaluation] The VOP and HVP produced in Examples 1 to 5 (HVP produced in Example 2-1 for Example 2) were evaluated as follows. The evaluation results for Examples 1 to 5 are shown in Tables 1 to 3, Figures 1 to 6, etc.

[0076] <Evaluation 1: Identification of VOP or HVP 1> The VOP and HVP produced in each Example were identified by powder X-ray diffraction (XRD) under the following conditions. As a result, it was confirmed that the compounds produced in Examples 1, 4, and 5 were VOP, and the compounds produced in Examples 2-1 and 3 were HVP. The obtained XRD charts are shown in Figures 1 to 5. In the XRD chart of Figure 2, the results for "SP-VOP (90°C)" of Example 1 used in Example 2 are shown below the results for SP-HVP (90°C). Similarly, the XRD charts of Figures 4 and 5 show the results for "HT-HVP (120°C)" of Example 3 used in Examples 4 and 5, as HT(120°C)-O-VOP or HT(120°C)-N ２ The results are also shown below the results of -VOP. (Conditions) XRD device: D2 Phaser (manufactured by Bruker) X-ray wavelength: Cu target used CuKα ray: wavelength approximately 0.15406 nm Measurement time: 845.4 s Scan speed: 0.2° / s Scan range (measurement range): 2θ = 10 to 90° However, since a peak appears only between 10 and 30°, the probe range is set to 10 to 30°.

[0077] <Evaluation 2: Identification of VOP or HVP 2> The vanadium valence of the VOP and HVP produced in each example was measured by X-ray photoelectron spectroscopy (XPS) under the following conditions. The obtained XPS charts are shown in Figures 1 to 5, and the vanadium valence calculated from each chart is shown below. Vanadium valence in VOP of Example 1: +4.9 Vanadium valence in HVP of Example 2: +4.7 Vanadium valence in HVP of Example 3: +4.8 Vanadium valence in VOP of Example 4: +4.9 Vanadium valence in VOP of Example 5: +5.0 (Conditions) XPS device: PHI5000 Versa Probe II (manufactured by ULVAC-PHI, Inc.) XPS provides information on the polar surface Degree of vacuum in measurement chamber: 10x －８ ~10x －９ Torr Measurement conditions (same for all samples): AlKα Scan times: 64 times No sputtering

[0078] <Evaluation 3: Confirmation of Hue 1> The hues of the VOPs and HVPs produced in each Example were confirmed by diffuse reflectance spectroscopy (DRS) under the following conditions. The obtained DRS charts are shown in Figures 1 to 5. The results were consistent with the results of <Evaluation 5: Confirmation of Pearl Luster by Visual Observation 1> described below. In the DRS chart of Figure 2, the results of "SP-VOP (90°C)" of Example 1 used in Example 2 are also shown above the results of SP-HVP (90°C). Similarly, the DRS charts of Figures 4 and 5 show the results of "HT-HVP (120°C)" of Example 3 used in Examples 4 and 5, as HT(120°C)-O-VOP or HT(120°C)-N ２ -The results are also shown below the VOP results. (Conditions) DRS device: V-670 (manufactured by JASCO) Measurement range: ultraviolet - visible - near infrared range (200 to 800 nm) Light source: D2 lamp (200 to 350 nm) and halogen lamp (350 to 800 nm) Photometric mode: %R Response (R): Fast Band width: 2.0 nm Scanning speed: 400 nm / min Data acquisition interval: 1.0 nm Scanning mode: Continuous scan White reference: Spectralon (registered trademark)

[0079] <Evaluation 4: Confirmation of Hue 2> For the VOP and HVP produced in each example, the L in the Lab color space image was ＊ Value, a ＊ value and b ＊ The value was measured to confirm the hue. Measurements were performed using the following device, with vertical measurement performed under standard calibration (BaSO4 white board calibration) and measurement conditions, and the average of six measured values ​​was calculated. The results are shown in Table 1. The results shown in Table 1 are consistent with the results of <Evaluation 5: Visual confirmation of pearlescent luster 1> described below. (Conditions) Device: CR-10 Plus (manufactured by Konica Minolta)

[0080]

[0081] <Evaluation 5: Visual Confirmation of Pearl Luster 1> The VOP and HVP produced in each Example were visually confirmed to determine whether pearl luster was exhibited and its hue. The results are shown below. VOP of Example 1: exhibited yellow-green pearl luster HVP of Example 2-1: exhibited green pearl luster HVP of Example 3: exhibited green pearl luster VOP of Example 4: exhibited yellow pearl luster VOP of Example 5: exhibited grass-green pearl luster

[0082] <Evaluation 6: Confirmation of Pearl Luster by Gloss Evaluation 2> Gloss evaluation (angle dependence of gloss number and angle dependence of RGB values) was performed on the VOP and HVP produced in each example. The angle dependence of gloss number (Table 2) was measured three or more times using the following device under standard calibration (white board calibration (No. G-28206), black board calibration (No. G-28204)) and measurement conditions in automatic measurement mode, with the angle changed to the angle shown in Table 2, and the average value was used. The visual angle dependence of RGB (Table 3) was measured using the camera of an iPhone (registered trademark) 11 manufactured by Apple Inc., where photographs were taken sequentially while changing the angle shown in Table 3. The obtained photographs were then read and numerically analyzed using ColorMeter (Ver. 2.2.0) to obtain each RGB value. The results are shown in Table 2 (angle dependence of gloss number) and Table 3 (visual angle dependence of RGB). In Table 2, the values ​​of a white pearl pigment consisting of a mica substrate and a titanium dioxide layer are also shown as commercially available particles. The results shown in Tables 2 and 3 indicate that the VOPs and HVPs produced in Examples 1 to 5 all agree with the results of <Evaluation 5: Visual confirmation of pearl luster 1>, and demonstrate pearl luster. (Conditions) Apparatus: PG-1M (manufactured by Nippon Denshoku Co., Ltd.)

[0083]

[0084]

[0085] <Evaluation 7: Particle Size Measurement 1> The VOP and HVP produced in each Example were observed using a scanning electron microscope under the method and conditions described above, and their longest lengths (particle sizes) were measured. As representative results, SEM images and their longest lengths (particle sizes) are shown in Figures 1 to 5. Note that Figures 1 to 5 also show the width of each particle in the SEM images. Furthermore, Figure 6 shows an example of an image field when the HVP produced in Example 3 was observed with an optical microscope, along with the particle sizes of the HVP observed within the image field. In Figures 1 to 5, the particle sizes of each plate-like particle are indicated by double-headed arrows, and in Figure 6, the particle sizes of each plate-like particle are indicated by double-headed arrows, with the numerical values ​​near the arrows indicating the measured values ​​(particle sizes).

[0086] <Evaluation 8: Particle Size Measurement 2> The particle sizes of the VOP and HVP produced in each example were measured by image particle size distribution measurement using the method and conditions described above, and for reference, Figures 7 to 11 show particle size distribution diagrams, particle sizes (major axis diameter), and representative SEM images. The SEM images in Figures 7 to 11 also show the width of each particle. In Figures 7 to 11, the particle size and width of each plate-like particle are indicated by double-headed arrows. As described above, image particle size distribution measurement cannot measure particles with large particle sizes, and the particle size distribution diagrams deviate from a normal distribution, and some of the results do not match the maximum particle size in the results of <Evaluation 7: Particle Size Measurement 1> above.

[0087] The compound obtained in Example 2-2 was identified as HVP by XRD. Furthermore, the plate-like particles of HT-HVP (120°C) synthesized in Example 3 had a particle size of 310 μm and a thickness of 75 nm, and thus the ratio [particle size / plate-like particle thickness] measured by the above-mentioned measurement method was 4000 or more. The results of Examples 1 to 5 demonstrate that a pearlescent pigment exhibiting pearl luster, preferably colored, can be produced using a simple solution process or hydrothermal synthesis process, which does not require a substrate and is low-cost. Furthermore, by appropriately selecting Production Methods 1 to 4 in the production method of the present invention, the hue of the pearl luster can be varied (the hue can be controlled) within a range from yellow to green, making the pigment highly useful as a colored pearlescent pigment.

[0088] Example 6: Production of VOP by Production Method 1 In Example 1, the mixing temperature was set to 30°C (Example 6-1), 60°C (Example 6-2), or 90°C (Example 6-3), and the amount of phosphoric acid added was 2 mL (0.0292 mol, 2.66 mol per mol of vanadium element), 3 mL (0.0438 mol, 3.99 mol per mol of vanadium element), 4 mL (0.0585 mol, 5.32 mol per mol of vanadium element), 5 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 6 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 7 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 8 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 9 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 10 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 12 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 14 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 16 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 18 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 19 mL (0.0731 mol, 5.32 mol per mol of vanadium element), 24 mL (0.0731 mol, 5.32 mol per mol of vanadium element VOP was obtained in the same manner as in Example 1, except that the volume of the solution was changed to 6 mL (0.0877 mol, 6.65 mol per mol of elemental vanadium), 6 mL (0.0877 mol, 7.97 mol per mol of elemental vanadium), 7 mL (0.1023 mol, 9.30 mol per mol of elemental vanadium), 8 mL (0.1169 mol, 10.63 mol per mol of elemental vanadium), or 9 mL (0.1315 mol, 11.96 mol per mol of elemental vanadium). In Example 6, the VOP obtained by setting the mixing temperature to 30°C is referred to as "SP-VOP(RT)", the VOP obtained by setting the mixing temperature to 60°C is referred to as "SP-VOP(60°C)", and the VOP obtained by setting the mixing temperature to 90°C is referred to as "SP-VOP(90°C)".

[0089] Each VOP obtained was identified by XRD in the same manner as in <Evaluation 1> above, and the particle size of each VOP was measured in the same manner as in <Evaluation 7: Particle Size Measurement 1> above. The results are shown in Figures 12A to 12C and Figures 13A to 13C. In Figures 13A to 13C, SEM images (a) to (h) correspond to the results of experiments in which the amount of phosphoric acid added was varied from 2 mL to 9 mL. In Figures 13A to 13C, the particle size of each plate-like particle is indicated by a double-headed arrow, and the numerical value near the arrow indicates the measured value (particle size). All VOPs exhibited pearlescent luster. As shown in Figures 12A to 12C and Figures 13A to 13C, temperature dependence and phosphoric acid dependence were confirmed in Production Method 1. Specifically, increasing the mixing temperature tended to increase the particle size, regardless of the phosphoric acid mixing ratio. Furthermore, at a mixing temperature of 90°C, plate-like particles consisting of a single VOP phase were obtained, and their particle size was approximately constant, regardless of the phosphoric acid mixing ratio. On the other hand, at mixing temperatures of 30° C. and 60° C., decreasing the mixing ratio of phosphoric acid resulted in plate-like particles consisting of a mixed phase of VOP and HVP, and the particle size tended to increase. It was also found that increasing the mixing ratio of phosphoric acid at mixing temperatures of 30° C. and 60° C. resulted in plate-like particles consisting of a single VOP phase.

[0090] [Example 7: Production of HVP by Production Method 2] In Example 3, the hydrothermal treatment temperature was set to 120°C (Example 7-1), 150°C (Example 7-2), 180°C (Example 7-3), or 210°C (Example 7-4), and the amount of phosphoric acid added was changed to 4mL (0.0585 mol), 5mL (0.0731 mol), 6mL (0.0877 mol), 7mL (0.1023 mol), 8mL (0.1169 mol), or 9mL (0.1315 mol). Except for this, HVP was obtained in the same manner as in Example 3. In Example 7, the HVP obtained by setting the hydrothermal treatment temperature to 120°C is represented as "HT-HVP (120°C)," the HVP obtained by setting the hydrothermal treatment temperature to 150°C is represented as "HT-HVP (150°C)," the HVP obtained by setting the hydrothermal treatment temperature to 180°C is represented as "HT-HVP (180°C)," and the HVP obtained by setting the hydrothermal treatment temperature to 210°C is represented as "HT-HVP (210°C)."

[0091] Each HVP obtained was identified by XRD as in the above <Evaluation 1>, and the particle size of each HVP was measured as in the above <Evaluation 7: Particle Size Measurement 1>. The results are shown in Figures 14A-14D and Figures 15A-15D. In Figures 15A-15D, the SEM images shown in (a)-(f) correspond to the results of experiments in which the amount of phosphoric acid added was varied from 4 mL to 9 mL. In Figures 15A-15D, the particle size of each plate-like particle is indicated by a double-headed arrow, and the numerical value near the arrow indicates the measured value (particle size). All HVPs exhibited pearlescent luster. As shown in Figures 14A-14D and Figures 15A-15D, temperature dependence and phosphoric acid dependence were confirmed in Production Method 2. Specifically, lowering the hydrothermal treatment temperature tended to increase the particle size regardless of the phosphoric acid mixing ratio. Furthermore, the particle size remained nearly constant even when the phosphoric acid mixing ratio was changed. Changing the phosphoric acid mixing ratio can change the composition of the vanadium phosphate. For example, it was found that when the mixing ratio of phosphoric acid was reduced at 150°C, 180°C, or 210°C, plate-like particles consisting of a mixed phase of VOP and HVP were obtained, while at 120°C, plate-like particles consisting of a single phase of HVP were obtained regardless of the mixing ratio of phosphoric acid.

[0092] Examples 8 and 9: Production of VOP by Production Method 4A The VOP of Example 8 was obtained in the same manner as in Example 4, except that the heat treatment temperature was changed to 400°C or 600°C. The VOP of Example 9 was obtained in the same manner as in Example 4, except that the heat treatment time was changed to 3 hours, 12 hours, or 24 hours. Each of the obtained VOPs was identified by XRD in the same manner as in <Evaluation 1: Identification of VOP or HVP 1> above. The results are shown in Figure 16 along with the results of Example 4. In Figure 16, the results of Example 8 are shown in the top row for a heat treatment temperature of 600°C, in the middle row for a heat treatment temperature of 500°C, and in the bottom row for a heat treatment temperature of 400°C. All of the obtained VOPs exhibited pearl luster. As shown in Figure 16, even when the heat treatment temperature was changed to 400°C or 600°C in Example 8, plate-like crystals consisting of a single phase of HVP were obtained. In Example 9, even when the heat treatment time was changed to 3 hours, 12 hours, or 24 hours, plate-like crystals consisting of a single phase of HVP were obtained.

[0093] Comparative Example 1 Particles were obtained in the same manner as in Example 1, except that no hydrogen peroxide solution was added. Each of the obtained particles was identified by XRD in the same manner as in <Evaluation 1: Identification of VOP or HVP 1> above, and the particle size of the plate-like particles was measured in the same manner as in <Evaluation 7: Measurement of particle size 1> above. The obtained results are shown in Figures 17 and 18 together with the results of Example 1. In Figures 17 and 18, the results of Comparative Example 1 are shown as "0 mL H ２ O ２ The results of Example 1 are shown at the bottom of the figure with "5 mL H ２ O ２ " at the top of the figure. In FIG. 18, the particle size of the plate-like particles is indicated by a double-headed arrow. As shown in FIG. 17, the particles of Comparative Example 1 were VOP, but as shown in FIG. 18, the particle size was about 0.1 times smaller than that of Example 1, and the expression of pearlescent luster was not confirmed visually. In Comparative Example 1, VOP was similarly produced by increasing the amount of water used by 5 mL of hydrogen peroxide solution in Example 1 to 33 mL, but this did not affect the particle size of the obtained particles, and the expression of pearlescent luster was not confirmed visually.

[0094] As described above, the present invention provides a pearl pigment comprising a vanadium phosphate containing at least one of VOP and HVP, which is free-standing, plate-like particles that do not require a substrate, and which exhibits a preferably colored pearlescent luster. Furthermore, the present invention also enables the production of a pearl pigment that exhibits a preferably colored pearlescent luster using a simple solution process or hydrothermal synthesis process, which does not require a substrate and is low-cost. Furthermore, in the above examples, by selecting the conditions for each production method, it was possible to increase the particle size, for example, to 267 μm with VOP and to 310 μm with HVP. These results demonstrate that even larger plate-like particles can be produced by appropriately modifying the type of production method (Production Methods 1 to 4) and production conditions of the present invention, demonstrating the usefulness of the production method for pearlescent pigments. Furthermore, by appropriately selecting Production Methods 1 to 4 in the production method for the present invention, the hue of the pearlescent luster can be varied (hue control), for example, within a range from yellow to green, demonstrating the usefulness of the method for producing colored pearlescent pigments.

[0095] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0096] This application claims priority based on Japanese Patent Application No. 2024-100285, filed on June 21, 2024, the contents of which are incorporated herein by reference as part of the present specification.

Claims

1. VOPO ４ ・2H ２ O and H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ A pearl pigment comprising plate-like particles of at least one vanadium phosphate selected from O.

2. The pearl pigment according to claim 1, wherein the plate-like particles have a layer structure.

3. The pearl pigment according to claim 1, wherein the plate-like particles exhibit pearl luster.

4. The pearl pigment according to claim 1, wherein the particle size of the plate-like particles is 5 μm or more.

5. A composition containing the pearl pigment according to any one of claims 1 to 4.

6. Mix the vanadium compound, water, hydrogen peroxide, and phosphoric acid at a temperature of 100°C or less to obtain the VOPO. ４ ・2H ２ The method for producing a pearl pigment according to any one of claims 1 to 4, wherein O is produced.

7. Mix vanadium compound, water, hydrogen peroxide and phosphoric acid at a temperature below 100°C to obtain VOPO. ４ ・2H ２ After generating O, an alcohol is further added and reduced at a temperature of 100°C or less to generate the H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ The method for producing a pearl pigment according to any one of claims 1 to 4, wherein O is produced.

8. A vanadium compound, water, hydrogen peroxide, and phosphoric acid are hydrothermally treated at a temperature of 100°C or higher to obtain the H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ The method for producing a pearl pigment according to any one of claims 1 to 4, wherein O is produced.

9. Hydrothermally treat a vanadium compound, water, hydrogen peroxide, and phosphoric acid at a temperature of 100°C or higher to obtain H ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ After producing O, ０.６ (V.O.) ３ (PO ４ ) ３ (H ２ O) ３ ・4H ２ O is heat-treated at a temperature of 350° C. or higher to obtain the VOPO ４ ・2H ２ The method for producing a pearl pigment according to any one of claims 1 to 4, wherein O is produced.

10. The method for producing a pearl pigment according to claim 9, wherein the heat treatment is carried out in an oxygen-containing gas atmosphere or an inert gas atmosphere.

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