JP2012025861A - Zinc sulfide phosphor and its manufacturing method - Google Patents

Abstract

The present invention provides a zinc sulfide phosphor having a uniform particle size capable of obtaining high luminance at a low voltage, and a method for producing a zinc sulfide phosphor capable of industrially producing the zinc sulfide phosphor. To do.
The production method of the present invention includes a primary firing step of firing a zinc sulfide-based phosphor precursor to form a primary fired product, and a median diameter (d ₅₀ ) of the primary fired product is 10 μm or more and less than 40 μm. A classifying step for adjusting the particle size so that the primary fired product with the adjusted particle size is irradiated with ultrasonic waves having a total energy (heat amount) of 0.5 to 10 GJ / m ³ per unit volume. An ultrasonic irradiation process for transferring a part of the crystal structure to a cubic structure, and a primary fired product after the ultrasonic irradiation is further fired to obtain a cubic structure of 85% or more and less than 99% and more than 1% and 15% or less. A secondary firing step for obtaining a zinc sulfide-based phosphor mixed with a hexagonal crystal structure is included.
[Selection figure] None

Description

  The present invention relates to a zinc sulfide-based phosphor and a method for producing the same.

  Among inorganic material compositions containing zinc sulfide as a main component, there are zinc sulfide-based phosphors that have the property of self-emission by converting electric energy into light, and are suitable for applications such as light sources and display device elements. Has been put to practical use. However, currently known zinc sulfide-based phosphors are insufficient in light energy conversion efficiency of electric energy, and thus have problems such as heat generation and power consumption, and their applications are limited.

  As a method for producing a zinc sulfide-based phosphor, 0.1 to 1.0 mol% copper sulfate, a coactivator or a flux as an activator is added to a fine powdery zinc sulfide having a particle size of several μm as a base. As an alkali metal or alkaline earth metal halide such as 5 to 20 mol% sodium chloride, the mixture is placed in a crucible, and hydrogen sulfide is added at about 1000 ° C. in an oxygen-containing atmosphere, followed by firing for several hours. Next, a method of obtaining a powdered phosphor by washing and removing impurities such as copper sulfide adhering to the surface with an aqueous potassium cyanide solution and drying it is known.

In order to obtain an EL display element with high EL luminance and a long lifetime, a method of manufacturing a cubic type zinc sulfide phosphor having a large particle size has been proposed (Patent Document 1). In Patent Document 1, a mixture of zinc sulfide, copper sulfate and a flux is calcined in air at 1100 to 1200 ° C. for 3 hours to 10 hours, washed with deionized water, and dried. By pressurizing with water pressure (1000 kg / cm ² ) and annealing in air at 750 to 950 ° C., a cubic zinc sulfide phosphor with a large particle size can be obtained, which realizes high EL luminance and long life. It describes what you can do.

  For the same purpose, an intermediate phosphor of 10 to 40 μm obtained by firing (primary firing) a mixture of zinc sulfide, copper sulfate and a flux at 900 to 1100 ° C. in air for 1 to 5 hours. Then, an impact force is applied by a ball mill treatment to cause distortion inside the particles of the intermediate phosphor, and then firing (secondary firing) in air at 500 to 800 ° C. for 1 to 5 hours. A method of forming a conductive layer by segregating copper in a place where there is a strain is proposed (Patent Document 2). Note that Patent Document 2 teaches that not an isotropic pressure, but an impact force that is concentrated and applied locally is more effective in forming strain.

  However, the methods described in Patent Documents 1 and 2 are insufficient and inhomogeneous in imparting impact to the intermediate phosphor particles, so that the transition from the hexagonal structure to the cubic structure in the secondary firing step is not sufficient. And the EL luminance is not sufficiently improved.

  On the other hand, as a phosphor capable of obtaining a high EL luminance at a low voltage, a method for producing a phosphor having a small particle diameter with a center particle diameter of 20 μm or less and a uniform particle diameter has been proposed (Patent Document 3). Patent Document 3 discloses an intermediate phosphor obtained by mixing 3 to 100% by weight of a grain growth inhibitor in addition to an activator and a flux and performing primary firing in air at 1200 ° C. for 3 hours. Then, ultrasonic vibration is applied to remove the grain growth inhibitor, and further, impact force is applied to the intermediate phosphor by a ball mill or ultrasonic vibration to form strain (crystal defect) in the intermediate phosphor particles, 500 to 900 ° C. And secondary firing for 30 minutes to 3 hours. Reference 3 teaches that a grain growth inhibitor is necessary to obtain a phosphor having a small particle size of 20 μm or less, and aluminum oxide, silicon oxide are used as the grain growth inhibitor. Zirconium oxide, silicon nitride, aluminum nitride, silicon carbide, tungsten carbide, and tantalum carbide are illustrated.

  Further, a mixture of zinc sulfide, at least one activator and a flux is fired at 1050 to 1400 ° C. for 2 to 8 hours to form a hexagonal β-ZnS type (Note: Patent Document 4 describes “hexagonal β -ZnS type ", which is considered to be a misprint of" hexagonal α-ZnS type "in the light of technical common knowledge. The same applies hereinafter in this paragraph). Suspending the first calcined material in a liquid medium and irradiating the suspension with ultrasonic waves to at least partially convert the crystal structure of the first calcined material into a distorted hexagonal β-ZnS form; The partially converted first fired material is fired at 500 to 1000 ° C. for 1 to 5 hours to obtain a cubic α-ZnS type crystal form (Note: Patent Document 4 states that “cubic α-ZnS type” In the light of technical common sense Method of forming a zinc sulfide based phosphor having the same below) in. This paragraph believed Incorrect cubic beta-Zn type "has been proposed (Patent Document 4).

  However, in the method described in Patent Document 3, a grain growth inhibitor is required to control the particle size, and a step of removing the grain growth inhibitor is required before the secondary firing, which makes the manufacturing process complicated. In addition, there is a restriction that the grain growth inhibitor must be a substance that does not react with the base zinc sulfide.

  In the method described in Patent Document 4, the inventors have determined that the transition from the hexagonal structure to the cubic structure at the time of secondary firing depends on the particle size of the phosphor precursor particles, and no transition occurs. It has been confirmed that sufficient performance may not be exhibited as a phosphor. Further, Patent Document 4 describes a mode of ultrasonic irradiation in which a suspension containing the first firing material is circulated through a compartment having an ultrasonic transducer and ultrasonic irradiation is repeated a plurality of times. However, there are problems that the particles of the first fired substance are repeatedly circulated in the circulation pump, thereby causing fusion of the particles in the pump and the piping and undesirable impact.

Japanese Patent Laid-Open No. 61-296085 JP-A-6-306355 JP 11-193378 A JP 2004-2867 A

  The present invention relates to a zinc sulfide phosphor having a uniform particle size capable of obtaining high EL luminance at a low voltage, and a method for producing a zinc sulfide phosphor capable of industrially producing the zinc sulfide phosphor. The purpose is to provide.

  The present inventors paid attention to the fact that the crystal structure change before and after the ultrasonic irradiation significantly affects the physical properties of the zinc sulfide-based phosphor, and as a result of examining the ultrasonic irradiation conditions in detail, the above-mentioned goal can be achieved. The present inventors have found that this can be done and have completed the present invention.

According to the present invention, there is provided a zinc sulfide-based phosphor in which a cubic structure of 85% or more and less than 99% and a hexagonal structure of more than 1% and 15% or less are mixed.
The zinc sulfide phosphor of the present invention has a median diameter (d ₅₀ ) of 10 μm or more and less than 40 μm.

In addition, according to the present invention, a primary firing step of firing a zinc sulfide-based phosphor precursor to form a primary fired product, so that the median diameter (d ₅₀ ) of the primary fired product is 10 μm or more and less than 40 μm. A classification step for adjusting the particle size, and the primary fired product adjusted for the particle size are irradiated with ultrasonic waves with a total amount of energy (heat amount) of 0.5 to 10 GJ / m ³ to form a hexagonal crystal structure. Ultrasonic irradiation process for transferring a part to a cubic structure, and further firing the primary fired product after the ultrasonic irradiation to obtain a cubic structure of 85% or more and less than 99% and a hexagonal structure of more than 1% and 15% or less There is provided a method for producing a zinc sulfide-based phosphor including a secondary firing step for obtaining a zinc sulfide-based phosphor in which is mixed.

In the production method of the present invention, the primary fired product after the ultrasonic irradiation step preferably contains a cubic structure of 10% to 70%.
Moreover, it is preferable that the calcination temperature in a secondary calcination process is 650 degreeC or more and 1000 degrees C or less.

  The ultrasonic irradiation can be performed using a single ultrasonic irradiation device or a plurality of ultrasonic irradiation devices.

  According to the present invention, a zinc sulfide-based phosphor exhibiting blue to blue-green with high practical EL brightness can be obtained by a simple method of controlling ultrasonic irradiation conditions.

  The present invention provides a zinc sulfide-based phosphor in which a cubic structure of 85% or more and less than 99% and a hexagonal structure of more than 1% and 15% or less are mixed. Compared with the ratio of the cubic structure in the conventional zinc sulfide-based phosphor being 80% or less, the ratio of the cubic structure of the zinc sulfide-based phosphor of the present invention is very high. In particular, in order to realize blue light emission, the ratio of the cubic structure is preferably 87% or more, and particularly preferably 90% or more and less than 99%. A zinc sulfide phosphor having a cubic structure ratio of 99% or more has a lower EL luminance. In order to realize higher EL luminance, the ratio of the cubic structure is preferably 98% or less, particularly 97% or less. The ratio of the cubic structure is a value obtained by Rietveld analysis of a diffraction peak obtained by X-ray crystal diffraction.

The zinc sulfide phosphor of the present invention has a median diameter (d ₅₀ ) of 10 μm or more and less than 40 μm, preferably 14 μm or more and 30 μm or less, particularly preferably 18 μm or more and 25 μm or less.
The zinc sulfide based phosphor of the present invention is a primary firing step in which a zinc sulfide based phosphor precursor is fired to form a primary fired product, and the median diameter (d ₅₀ ) of the primary fired product is 10 μm or more and less than 40 μm. In this way, the classification process for adjusting the particle size is performed, and the primary fired product having the adjusted particle size is irradiated with ultrasonic waves having a total energy of 0.5 GJ / m ³ or more and 10 GJ / m ³ or less to form a part of the hexagonal crystal structure. Ultrasonic irradiation process for transition to cubic structure, primary fired product after ultrasonic irradiation is further fired to mix 85% or more and less than 99% cubic structure and more than 1% and 15% or less hexagonal structure The zinc sulfide phosphor can be prepared by a manufacturing method including a secondary firing step.

Hereafter, the manufacturing method of this invention is demonstrated in detail according to process.

1. Primary firing step In the present invention, the primary firing step is a step of firing the zinc sulfide-based phosphor precursor to improve the crystallinity and transferring the cubic structure to the hexagonal structure.

  In the primary firing step, a flux and preferably sulfur are added to the zinc sulfide-based phosphor precursor, and the temperature is raised from room temperature to a constant temperature within the range of 1000 ° C. to 1200 ° C. A primary fired product having a hexagonal crystal structure is formed by rapidly cooling to a temperature of not higher than ° C.

  From normal temperature to a temperature just before the start of crystal growth of zinc sulfide, preferably in the temperature range of 300 ° C. or higher and 850 ° C. or lower, more preferably in the temperature range of 300 ° C. or higher and 600 ° C. or lower, air is continuously introduced into the firing furnace. It is preferable to introduce and raise the temperature in the presence of oxygen. During this temperature increase, the flux is melted and zinc sulfide is granulated. If the temperature is increased in the presence of oxygen to a temperature exceeding 850 ° C., the inside of the zinc sulfide particles is oxidized, and a portion not showing fluorescence is generated, which is not preferable.

  Next, it is preferable to raise the temperature to a certain temperature within a range of 1000 ° C. or more and 1200 ° C. or less under an inert gas atmosphere such as nitrogen. The heating rate is preferably 50 ° C./hr or more and 1000 ° C./hr or less, more preferably 60 ° C./hr or more and 900 ° C./hr or less. If the rate of temperature rise is too fast, the equipment used will be overloaded, reducing the life of the equipment as well as promoting rapid decomposition of the flux and shortening the melt time, resulting in non-uniform dispersion of the flux. Cheap. If the rate of temperature rise is too slow, it is not economical, and in the case of a low-melting flux, the flux is localized and causes coarsening of zinc sulfide, which is not preferable.

  After reaching a certain temperature in the range of 1000 ° C. or more and 1200 ° C. or less, the temperature is preferably maintained for about 1 hour or more and about 5 hours or less, and then rapidly cooled to a temperature of 700 ° C. or less. Here, rapid cooling means cooling with a cooling rate greater than that of natural cooling. The cooling rate is not particularly limited, and it is preferable to cool as quickly as possible. However, considering the heat shock of the container, 600 ° C./hr or more and 30000 ° C./hr or less (that is, 10 ° C./min or more and 500 ° C./min). Or less), and more preferably 720 ° C./hr or more and 18000 ° C./hr or less (that is, 12 ° C./min or more and 300 ° C./min or less).

  A zinc sulfide-based phosphor precursor that has been transformed into a hexagonal crystal structure by raising the temperature to a constant temperature in the range of 1000 ° C. to 1200 ° C. in the primary firing step, maintaining the temperature, and rapidly cooling to a temperature of 700 ° C. or less. The crystal system can be stabilized. When the temperature exceeds about 800 ° C., the crystal system of the zinc sulfide-based phosphor precursor starts to change, and at about 1020 ° C., the crystal structure completely changes from a cubic structure to a hexagonal structure. This transition of the crystal system can be confirmed by the appearance of a (100) plane diffraction pattern by X-ray diffraction.

  The cooled primary fired product is then preferably washed with an acidic aqueous solution. By washing with an acidic aqueous solution, zinc oxide that is partially oxidized by oxygen and the flux used for fusing can be removed, and the aggregated primary fired product can be separated into primary fired product particles. After washing the primary baked product with an acidic aqueous solution, it is washed with ion exchange water until the washing becomes neutral, and the acidic aqueous solution adhering to the primary baked product is removed.

Next, substances used in the primary firing step will be described.
<Zinc sulfide based phosphor precursor>
The “zinc sulfide-based phosphor precursor” used in the production method of the present invention is based on zinc sulfide and does not exhibit fluorescence due to ultraviolet excitation as it is, but is given fluorescence by heat treatment such as baking and zinc sulfide. It means a precursor to be a system phosphor. The method for producing the zinc sulfide-based phosphor precursor is not particularly limited. For example, (1) a method in which a compound containing zinc sulfide and a luminescent center metal is solid-mixed and obtained by solid phase reaction; (2) zinc sulfide is immersed in a solution of a compound containing a luminescent center metal and the zinc sulfide is immersed in zinc sulfide. Either a method of incorporating an emission center metal, or a method of obtaining a composite of zinc sulfide and an emission center metal by coexisting a compound containing an emission center metal when a zinc compound and a sulfurizing agent are reacted is used. be able to.

  Examples of the luminescent center metal species doped into the zinc sulfide-based phosphor precursor include copper, silver, iridium, and rare earth elements. The doping amount of these luminescent center metals is not particularly limited. However, if the concentration is too high, the luminescent center metals interfere with each other and the EL luminance decreases, and on the other hand, the concentration of the luminescent center metal is not preferable. Cannot be obtained sufficiently, and strong EL luminance cannot be obtained. The doping amount of the luminescent center metal is usually preferably not less than 5 ppm by weight and not more than 2000 ppm by weight, more preferably not less than 10 ppm by weight and not more than 1000 ppm by weight with respect to zinc sulfide as a base of the zinc sulfide phosphor. Preferably, it is more preferably 20 ppm by weight or more and 800 ppm by weight or less.

  As the coactivator, a compound containing at least one element of gallium, aluminum or indium and a mixture thereof can be used. Gallium, aluminum and indium act as donors. If the amount of the coactivator added is too large or too small, it is not preferable because it causes a decrease in EL luminance and a decrease in the stability of the zinc sulfide phosphor. The amount added is usually 5 ppm to 5000 ppm by weight, preferably 10 ppm to 1000 ppm, more preferably 20 ppm to 800 ppm, based on zinc sulfide, which is the base of the zinc sulfide phosphor. Weight ppm or less.

  As the coactivator, halogen elements such as chlorine, fluorine, iodine and bromine which act as donors can be used alone or as a mixture. In consideration of color purity and stability, it is preferable to use chlorine. When a halogen element is used as a co-inactivator, the amount of addition is not particularly limited, but it is not economical if it is too much, and may cause concentration quenching. Conversely, if it is too little, high fluorescence efficiency is obtained. It cannot be pulled out. The addition amount is usually 5 ppm to 5000 ppm by weight with respect to zinc sulfide, preferably 10 ppm to 1000 ppm, more preferably 20 ppm to 800 ppm. .

<Flux>
In the production method of the present invention, it is preferable to add a flux to the zinc sulfide-based phosphor precursor in the primary firing step.

  As the flux, a halogen-containing flux, particularly a chlorine-containing flux can be preferably used. Preferable examples of the chlorine-containing flux include alkali metal chlorides such as lithium chloride, sodium chloride, potassium chloride, and cesium chloride, alkaline earth metal chlorides such as calcium chloride, magnesium chloride, barium chloride, and strontium chloride, and ammonium chloride. And zinc chloride. Preferable examples of the bromine-containing flux include alkali metal bromides such as lithium bromide, sodium bromide, potassium bromide and cesium bromide, alkaline earth such as calcium bromide, magnesium bromide, barium bromide and strontium bromide. Examples include metal bromides, ammonium bromides, zinc bromides and the like. Preferable examples of the iodine-containing flux include alkali metal iodides such as lithium iodide, sodium iodide, potassium iodide and cesium iodide, alkalis such as calcium iodide, magnesium iodide, barium iodide and strontium iodide. There may be mentioned earth metal iodide, ammonium iodide, zinc iodide and the like. It is preferable to mix a plurality of metal halides from the viewpoint of persistence and the melting temperature of the flux. More preferably, a mixture of potassium chloride, sodium chloride and magnesium chloride is used.

  The amount of the flux used is not particularly limited, but is usually preferably 0.1% by weight or more and 80% by weight or less with respect to zinc sulfide. Considering the influence of uniform dispersion of the flux, etc., it is more preferably 0.5% by weight or more and 60% by weight or less, particularly preferably 1% by weight or more and 40% by weight or less.

  The method of adding the flux is not particularly limited, and is a solid mixing method in which a solid flux and a zinc sulfide phosphor precursor are mixed. After the flux is dissolved in water, the flux is mixed with the zinc sulfide phosphor precursor. The solid mixing method and the aqueous solution mixing method may be combined in consideration of the drying aqueous solution mixing method and the chemical stability of the flux used.

<Sulfur>
In the production method of the present invention, sulfur may be added together with the flux to the zinc sulfide-based phosphor precursor in the primary firing step. By adding sulfur, the atmosphere in the firing furnace during firing can be maintained in a reducing atmosphere, and the oxidation of zinc sulfide by water and oxygen that may be present can be suppressed. The amount of sulfur added for the purpose of suppressing oxidation of zinc sulfide is preferably 0.01 times or more and 2 times or less, more preferably 0.02 times or more and 1 time or less, based on the weight of zinc sulfide.

<Acid aqueous solution for cleaning>
As the acidic aqueous solution used for washing, an aqueous solution of an organic acid such as formic acid and acetic acid, and an aqueous mineral acid solution such as hydrochloric acid, sulfuric acid and phosphoric acid can be used. In consideration of permeability to the primary fired product and persistence on the surface, it is preferable to use an acetic acid aqueous solution and hydrochloric acid. The concentration of the acid in the acidic aqueous solution is not particularly limited and varies depending on the type of the acid component to be used, but it is usually preferable to use an acidic aqueous solution having a pH of 1 to 5. The amount of the acidic aqueous solution used for washing is 1 to 100 times, preferably 5 to 50 times the amount of the primary fired product.

2. Classification process This classification process is a process necessary to efficiently advance the transition from the hexagonal structure to the cubic structure in the next ultrasonic irradiation process.

If the particle size is too small, the impact force due to ultrasonic waves is difficult to propagate, and the transition from the hexagonal structure to the cubic structure is difficult to proceed. Conversely, if the particle size is too large, the hexagonal structure is cleaved and the particles are destroyed. End up. Therefore, in the production method of the present invention, the particle diameter is then set so that the median diameter (d ₅₀ ) of the primary fired product is 10 μm or more and 40 μm or less, preferably 14 μm or more and 30 μm or less, particularly preferably 20 μm or more and 25 μm or less. Align. Specifically, the primary fired product is passed through a sieve having an opening of 10 μm to remove particles of less than 10 μm, and then passed through a sieve having an opening of 40 μm to remove particles of 40 μm or more. When the particle size is further finely adjusted, particles having a desired particle size range are selected using a sieve having different openings. Or you may sort according to particle size using centrifugal force, such as a cyclone separator.

3. Ultrasonic irradiation step In the production method of the present invention, a primary fired product having a uniform particle size is dispersed in an aqueous liquid, and the dispersion is irradiated with ultrasonic waves to form a hexagonal structure of zinc sulfide particles in the primary fired product. Part is transferred to a cubic structure. Here, the energy per unit volume applied to the primary fired product (heat) is, 0.5GJ / ^{m 3} or more 10GJ / ^m less than ³ in total, preferably 1.0GJ / ^{m 3} or more 8.0GJ / ^{m 3} or less More preferably, it is necessary to control the irradiation with ultrasonic waves so as to be 1.6 GJ / m ³ or more and 8.0 GJ / m ³ or less. When the energy is less than 0.5 GJ / m ^3, it is not preferable because sufficient distortion cannot be introduced into the zinc sulfide particles in the primary fired product, and the transition to the cubic structure in the secondary firing process becomes insufficient. If it exceeds 10 GJ / m ³ , the particles of the primary fired product are destroyed, which is not preferable.

To the total amount of ultrasonic irradiation energy less than 0.5GJ / ^{m 3} or more 10GJ / ^{m 3,} the ultrasonic wave irradiation to 800 kW / ^{m 3} or more 10000kW / ^{m 3} or less in the range of per, preferably 1000 kW / m ³ or more 6000 kW / ^{m 3} at an irradiation output of the range, the irradiation time per within 30 minutes more than 0.1 minutes, preferably as within 20 minutes or 0.5 minutes, less than 50 times more than once, Preferably, continuous irradiation is performed once or more and 20 times or less. If the ultrasonic output per time is too low, the irradiation time will be prolonged and the number of treatments will increase, which is not preferred. If the ultrasonic output per time is too high, the hexagonal structure will be cleaved with the C axis as the axis of symmetry. This is not preferable because the particles are crushed. Moreover, if the irradiation time per time is too short, the number of treatments increases and the productivity is lowered, which is not preferable. If the irradiation time per time is too long, the primary fired product is undesirably settled.

  The frequency of the ultrasonic wave to be irradiated is not particularly limited, but a range in which the effect of cavitation by ultrasonic irradiation is manifested is preferable. Usually, an ultrasonic wave having a frequency of 15 to 50 kHz is used, preferably 15 to 40 kHz, and more preferably. Uses a frequency in the range of 18-37 kHz.

  Ultrasonic irradiation is performed on a dispersion obtained by dispersing the primary fired product in an aqueous liquid. The aqueous liquid is not particularly limited as long as it does not affect the reaction, and examples thereof include water and a mixture of water and a water-soluble organic solvent. The water-soluble organic solvent may be a mixture of two or more compounds, for example, alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, 1,4-butanediol, methyl acetate, ethyl acetate, butyl acetate Esters such as methyl benzoate and dimethyl phthalate, and ethers such as tetrahydrofuran, tetrahydropyran, dipropyl ether, dibutyl ether, diethylene glycol, and tetraethylene glycol can be preferably used. Among them, it is preferable to use alcohols in consideration of low risk of ignition and weak oxidizing power, and methanol and ethanol are particularly preferable.

  The concentration of the primary fired product in the dispersion is 0.1 wt% or more and 50 wt% or less, preferably 0.5 wt% or more and 30 wt% or less, more preferably 0.7 wt% or more and 20 wt% or less, and most preferably Is preferably adjusted in the range of 5 wt% to 20 wt%. If the concentration is too high, impact due to contact between particles frequently occurs to promote the polishing action between particles, and fusion due to contact between particles occurs, and the inner wall of the liquid feed pipe provided in the ultrasonic irradiation device described later Since it adheres and causes clogging, it is not preferable, and when the concentration is too low, the processing cost increases, which is not preferable.

  The temperature of the dispersion at the time of ultrasonic irradiation is desirably in the range of 0.5 ° C. or more and 80 ° C. or less, preferably in the range of 10 ° C. or more and 50 ° C. or less in consideration of the change in the concentration of the dispersion due to volatilization. If the temperature is too low, it is not preferable because the fluidity of the dispersion decreases and the load on the apparatus for circulating the dispersion becomes large, and if the temperature is too high, energy due to ultrasonic irradiation becomes difficult to be added to the particles. Absent.

  Ultrasonic irradiation can be performed using a commercially available general ultrasonic irradiation apparatus. However, in an embodiment in which the dispersion is circulated using a pump, there is a tendency that the impact and fusion between particles due to contact between particles and the particles tend to adhere to the inner wall of the liquid feeding pipe and cause clogging. Ultrasonic irradiation in the present invention is an embodiment in which pressure is applied to the dispersion supply section to extrude the dispersion, and ultrasonic irradiation is performed from a plurality of ultrasonic irradiation sections provided along the flow path of the dispersion, or A dispersion liquid supply unit is provided at the top of a liquid feeding pipe having a plurality of ultrasonic irradiation parts, and ultrasonic waves from the plurality of ultrasonic irradiation parts are continuously generated when the dispersion liquid descends the liquid feeding pipe by gravity. A mode of receiving irradiation is preferred. A commercially available device such as Ginsen GSD600MAT-10 or Hielshrer UIP16000 can be used as a device for performing ultrasonic irradiation in such a manner.

  In the present invention, in the primary fired product after ultrasonic irradiation, a part of the hexagonal crystal structure is transferred to a cubic crystal structure, preferably a cubic crystal structure of 10% to 70%, more preferably 20% to 65%. Of cubic structure.

4). Secondary firing step In the present invention, the primary firing product in which the hexagonal crystal structure and the cubic crystal structure obtained by ultrasonic treatment are mixed is heated in an inert gas atmosphere, and constant within a range of 650 ° C to 1000 ° C. After maintaining the temperature, it is subjected to secondary firing for cooling.

  Prior to the temperature increase, the primary fired product in which a hexagonal structure and a cubic structure are mixed is added to 0.001% by weight to 3% by weight of copper, 0.1% by weight to 15% by weight of zinc, and 0.1% More than 50% by weight of sulfur is contained.

  In order to contain copper, it is preferable to add it as a solid or aqueous copper compound. Preferred examples of the copper compound include copper (I) chloride, copper (II) chloride, copper sulfate, and copper acetate. From the viewpoint of economy and operability, copper sulfate and copper acetate are preferred. The copper compound is added in the range of 0.002 wt% to 10 wt%, preferably 0.004 wt% to 5 wt%, with respect to the primary fired product.

  In order to contain zinc, it is preferable to add it as a zinc compound in a solid or aqueous solution form. Examples of the zinc compound include zinc oxide, zinc sulfide, zinc chloride, zinc bromide, zinc sulfate, zinc nitrate, zinc acetate, and zinc formate. From the viewpoints of economy and operability, zinc sulfate and zinc oxide are preferred. The zinc compound is added in the range of 0.3 wt% to 50 wt%, preferably 0.5 wt% to 30 wt%, with respect to the primary fired product.

  In order to contain sulfur, it is preferable to add sulfur or sulfur compounds such as thioacetamide and thiourea. From the viewpoint of economy and operability, use of sulfur is preferred. Sulfur is added in the range of 0.1 wt% or more and 50 wt% or less, preferably 0.5 wt% or more and 30 wt% or less with respect to the primary fired product.

  A mixture of a primary fired product in which a hexagonal crystal structure and a cubic crystal structure are mixed, and copper, zinc and sulfur is 650 ° C. or higher and 1000 ° C. over 2 to 5 hours in an inert gas atmosphere such as nitrogen gas. The temperature is raised to a constant temperature within the following range, and after reaching that temperature, air is introduced to form an oxygen-containing atmosphere at a constant temperature within the range of 650 ° C. to 1000 ° C. for 30 minutes to 2 hours. Hold and then cool. Although oxygen concentration is not specifically limited, It is preferable to set it as 1 volume% or more and 30 volume% or less.

  The faster the cooling rate, the better. A cooling rate of 8 ° C./min to 500 ° C./min is preferable. In particular, in consideration of the heat shock property of the container, a cooling rate of 12 ° C./min to 300 ° C./min is preferable.

5. Washing and drying Because the cooled secondary fired product has adhered to the unreacted extra zinc compound, the compound containing the extra luminescent center metal element that was not doped, the blackened metal compound, etc. These are removed by washing.

For washing, an acidic aqueous solution, an aqueous cyanide salt solution or the like can be used, but in any case, it is necessary to finally thoroughly wash with ion-exchanged water.
As the acidic aqueous solution, an aqueous solution of a mineral acid such as hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid, or an aqueous solution of an organic acid such as acetic acid, propionic acid or butyric acid can be used. An aqueous solution is particularly preferred. However, since the secondary fired product that is zinc sulfide particles may be decomposed when it comes into contact with a high concentration acidic substance, in the case of an acidic aqueous solution, it is 0.1 wt% or more and 20 wt% or less, preferably 1 wt%. The concentration is preferably 10% by weight or less.

  The aqueous cyanide salt solution is suitable for removing excess copper, silver, gold, manganese, iridium and rare earth elements remaining on the surface of the secondary fired product. As the aqueous cyanide salt solution, an aqueous sodium cyanide solution and an aqueous potassium cyanide solution having a concentration of 0.1 wt% or more and 1 wt% or less can be preferably used. When an aqueous cyanide salt solution is used, it is used in an amount of 10 to 100 times by weight with respect to the secondary fired product.

  After washing, drying is performed by vacuum drying or hot air drying to obtain a zinc sulfide phosphor.

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

[Measurement item]
The measurement conditions of the measurement items in the examples and comparative examples in this specification are as follows.

<Ratio between cubic structure and hexagonal structure>
The ratio of the cubic crystal structure and the hexagonal crystal structure in this specification is based on X-ray diffraction data obtained using RINT-2400 manufactured by Rigaku Corporation as an X-ray diffractometer, and Rietveld analysis method using software TOPAS3 manufactured by BRUKER Corporation. Was used to determine.

<Color analysis>
The produced EL element is sandwiched between the sample holders of a spectrophotometer FP-6500 manufactured by JASCO Corporation, the excitation light shutter is closed, and a black screen is applied so that external light does not enter the sample holder, and a voltage of 200 V and 1 kHz is applied. Then, the element was measured to emit light. At that time, light emission was detected without correcting the luminance. The emission color analysis was converted into chromaticity (x value, y value) using the emission color analysis of Spectra Manager for Windows (registered trademark) 95 / NT Ver. .

<Medium diameter>
It measured using PARTICA LA-950 by Horiba.

[Precursor preparation]
The zinc sulfide-based phosphor precursors used in the examples and comparative examples in this specification were produced by the following production examples.

  An aqueous zinc chloride solution was prepared by dissolving 98 g of zinc chloride, 0.080 g of copper sulfate pentahydrate (equivalent to 290 ppm of copper), 0.016 g of iridium hexachloride 60.0 g, and 2 g of hydrochloric acid in 50 g of ion-exchanged water. On the other hand, thioacetamide aqueous solution was prepared by dissolving 110.0 g of thioacetamide in ion-exchanged water to make 1000 ml.

  To a 2 L four-necked flask equipped with a Dean Stark, reflux tube, thermometer, and stirrer was charged 1000 ml of decane, and the system was purged with nitrogen. The four-necked flask was heated using an oil bath adjusted to an internal temperature of 150 ° C., the decane in the flask was heated to 130 ° C., and then the zinc chloride aqueous solution was added at 0.33 ml / min to the thioacetamide. The aqueous solution was added at 3.3 ml / min while mixing both solutions. The pH of the mixed solution was 2.5. The reaction proceeded while removing the distilled water with Dean Stark. All aqueous solutions were added in about 5 hours, and water in the system was removed for another 30 minutes. After cooling to room temperature, the precipitated sulfide is precipitated, the supernatant is removed, and the target zinc sulfide-based phosphor precursor is recovered and dried at 100 ° C. for 12 hours in a vacuum dryer. . The recovered amount was 57.4 g, and the yield was 82%.

[Example 1]
<Primary firing>
To 27 g of the prepared zinc sulfide phosphor precursor, 1.00 g of potassium chloride, 1.17 g of sodium chloride and 6.87 g of magnesium chloride hexahydrate were added and mixed by a ball mill. To the obtained mixture, 1.45 g of sulfur was further added and put in a crucible. The temperature of the crucible was increased at a rate of 400 ° C./hr while introducing air into the firing furnace. When the furnace temperature reaches 800 ° C., the gas to be introduced is switched from air to nitrogen, the furnace temperature is raised to 1100 ° C., held at 1100 ° C. for 1 hour, and then to room temperature at a rate of 600 ° C./hr. Cooled down.

  The obtained primary fired product was added to 200 g of a 15% acetic acid aqueous solution to disperse the primary fired product. The acetic acid solution was removed by decantation and washed with 500 g of ion-exchanged water until the washing became neutral to obtain a primary fired product.

<Classification>
The obtained primary fired product was passed through a sieve having an opening of 10 μm to remove particles having a particle size of 10 μm or less, and further passed through a sieve having an opening of 40 μm to remove particles having a particle size exceeding 40 μm. After removing the supernatant liquid by decantation, it was put in a vacuum dryer and dried at a drying chamber temperature of 100 ° C. for 12 hours. The yield of the primary fired product was 24 g, and the median diameter (d ₅₀ ) was 22 μm.

<Ultrasonic irradiation>
A continuous ultrasonic irradiation apparatus in which 12 ultrasonic irradiation units each configured by installing one ultrasonic transducer (manufactured by BRANSON, Digital Sonifier, frequency 20 kHz) per irradiation container was used. To 20 g of the classified primary fired product, 180 g of ion exchange water was added and dispersed to obtain a dispersion. The dispersion was supplied at a flow rate such that the residence time per container was 2 minutes. The ultrasonic output of the ultrasonic vibrator was 2500 kW / m ³ and the total energy was 3.6 GJ / m ³ . Fine particles generated by crushing were removed using a wet sieve having an opening of 10 μm. After removing the supernatant by decantation, it was placed in a vacuum dryer and dried at 80 ° C. for 12 hours. The yield of the primary fired product after ultrasonic irradiation was 16 g, and the recovery rate was 80%. The primary fired product after ultrasonic irradiation was subjected to X-ray diffraction analysis, and the ratio between the cubic structure and the hexagonal structure was determined.

<Secondary firing>
0.25 g of copper sulfate pentahydrate and 2.5 g of zinc sulfate heptahydrate were mixed with 10 g of the primary fired product after ultrasonic irradiation and put in a crucible. The crucible was placed in a firing furnace, heated at a rate of 400 ° C./hr in a nitrogen atmosphere, and when the temperature in the firing furnace reached 850 ° C., switching from nitrogen to air was introduced for 1 hour. Thereafter, switching from air to nitrogen was performed again, and the mixture was further maintained for 2 hours, and then cooled to room temperature at 500 ° C./hr.

The obtained secondary fired product was washed with 100 g of 5% hydrochloric acid aqueous solution. The acidic aqueous solution was removed, and washing was repeated using 500 g of ion exchange water until neutrality was achieved. The supernatant was removed by decantation, and then washed with 200 g of a 1% aqueous sodium cyanide solution to remove excess sulfide. Furthermore, after repeatedly washing with ion-exchanged water until neutrality, it was dried at 100 ° C. for 12 hours in a vacuum dryer. The yield of the secondary fired product (zinc sulfide-based phosphor) was 9.2 g, and the median diameter (d ₅₀ ) was 23 μm. The secondary fired product was subjected to X-ray diffraction analysis, and the ratio between the cubic structure and the hexagonal structure was determined.

<Production of EL element>
To 1.5 g of the obtained zinc sulfide-based phosphor, 1.0 g of a fluorine-based binder (7155 manufactured by DuPont) was added, mixed, and degassed to prepare a light emitting layer paste. This light emitting layer paste was applied on a PET film with ITO to a film thickness of 40 μm using a 20 mm square screen plate (200 mesh, 25 μm). On the light emitting layer paste layer, a barium titanate paste (7153 manufactured by DuPont) was applied using a screen plate (150 mesh, 25 μm), dried at 100 ° C. for 10 minutes, and then a barium titanate paste was similarly applied. And dried at 100 ° C. for 10 minutes to form a 20 μm dielectric layer. On the upper surface, a silver paste (461 SS manufactured by Atchison) was applied using a screen plate (150 mesh, 25 μm), dried at 100 ° C. for 10 minutes, and an electrode was formed to form a printing EL device. About the obtained element, EL material evaluation was performed at 200 V and 1 kHz.

[Example 2]
The output of the ultrasonic wave irradiation as 1110kW / ^{m 3,} except that the total energy of the ultrasonic wave irradiation was 1.6GJ / ^{m 3,} was carried out as in Example 1.

[Example 3]
The output of the ultrasonic wave irradiation as 1875kW / ^{m 3,} except that the total energy of the ultrasonic wave irradiation was 2.7GJ / ^{m 3,} was carried out as in Example 1.

[Example 4]
The output of the ultrasonic wave irradiation as 5347kW / ^{m 3,} except that the total energy of the ultrasonic wave irradiation was 7.7GJ / ^{m 3,} was carried out as in Example 1.

[Example 5]
The output of the ultrasonic wave irradiation as 6320kW / ^{m 3,} except that the total energy of the ultrasonic wave irradiation was 9.1GJ / ^{m 3,} was carried out as in Example 1.

[Comparative Example 1]
The output of the ultrasonic wave irradiation as 146kW / ^{m 3,} except that the total energy of the ultrasonic wave irradiation was 0.21GJ / ^{m 3,} was carried out as in Example 1.

[Comparative Example 2]
The output of the ultrasonic wave irradiation as 236kW / ^{m 3,} except that the total energy of the ultrasonic wave irradiation was 0.34GJ / ^{m 3,} was carried out as in Example 1.

[Comparative Example 3]
The same operation as in Example 1 was performed except that the output of ultrasonic irradiation was 28 kW / m ³ and the total energy of ultrasonic irradiation was 0.04 GJ / m ³ .

[Comparative Example 4]
Shanghai Kaiyan Phosphorology Co., which has a cubic structure ratio of 99%. EL brightness and emission color were evaluated in the same manner as in Example 1 using the zinc sulfide phosphor D512-S of Ltd., Ltd.

[Comparative Example 5]
Using 20 g of particles having a particle diameter of less than 10 μm (median diameter d ₅₀ = 9.6 μm) obtained by classifying and removing the primary fired product in Example 1, the output of ultrasonic irradiation was set to 5347 kW / m ³ and ultrasonic irradiation was performed. This was carried out in the same manner as in Example 1 except that the total amount of energy was 7.7 GJ / m ³ .

[Comparative Example 6]
Using 20 g of particles having a particle size of 40 μm or more (median diameter d ₅₀ = 41.4 μm) obtained by classifying and removing the primary fired product in Example 1, the output of ultrasonic irradiation was set to 5347 kW / m ³ and ultrasonic irradiation was performed. This was carried out in the same manner as in Example 1 except that the total amount of energy was 7.7 GJ / m ³ .

From Table 1, when the total amount of ultrasonic irradiation energy is less than 0.5 GJ / m ³ , the ratio of the cubic structure of the secondary fired product is extremely low, the EL luminance of the phosphor is also extremely low, and the ultrasonic irradiation energy. Even if the total amount is 7.7 GJ / m ³ , if the median diameter of the primary fired product is 10 μm or less or exceeds 40 μm, the ratio of the cubic structure of the secondary fired product is low and the EL luminance is also low. I understand. Furthermore, the commercially available zinc sulfide phosphor having a cubic structure ratio of 99% did not have a high EL luminance, contrary to expectations.

On the other hand, according to the method of the present invention, the ratio of the cubic structure of the secondary fired product is as large as 86 to 98%, and the EL luminance of the zinc sulfide phosphor is as high as 176 cd / m ² or more. In particular, it can be seen that when the total amount of ultrasonic irradiation energy exceeds 2 GJ / m ³ , the ratio of the cubic structure of the secondary fired product is 90% or more, and the y value is less than 0.2, whereby a blue phosphor is obtained.

From the above, in order to obtain a blue phosphor with high EL luminance, the ratio of the cubic structure is preferably 85% or more and less than 99%, and more preferably 90% or more and less than 98%. According to the method of the present invention in which the particle size (median diameter) of the primary fired product is classified to 10 μm or more and less than 40 μm and then irradiated with ultrasonic waves of 0.5 J / m ³ or more and 10 GJ / m ³ or less. Thus, a zinc sulfide-based phosphor having a crystal structure in a suitable range can be produced. In addition, in the method of the present invention in which the dispersion containing the classified primary fired product is flowed so as to pass through a plurality of ultrasonic irradiation units and continuously subjected to ultrasonic irradiation, the single ultrasonic irradiation unit and the dispersion storage High productivity can be achieved as compared with batch irradiation in which a dispersion is circulated between parts.

Claims (6)

  A zinc sulfide-based phosphor in which a cubic structure of 85% or more and less than 99% and a hexagonal structure of more than 1% and 15% or less are mixed. 2. The zinc sulfide-based phosphor according to claim 1, having a median diameter (d ₅₀ ) of 10 μm or more and less than 40 μm. A primary firing step of firing a zinc sulfide-based phosphor precursor to form a primary fired product;
A classifying step of adjusting the particle diameter so that the median diameter (d ₅₀ ) of the primary fired product is 10 μm or more and less than 40 μm;
A part of the hexagonal crystal structure is transferred to a cubic crystal structure by irradiating the primary calcined product with adjusted particle size with ultrasonic waves with a total energy (heat value) of 0.5 to 10 GJ / m ^3. An ultrasonic irradiation process,
Secondary firing is performed by further firing the primary fired product after ultrasonic irradiation to obtain a zinc sulfide-based phosphor in which a cubic structure of 85% or more and less than 99% and a hexagonal structure of more than 1% and 15% or less are mixed. The manufacturing method of the zinc sulfide type fluorescent substance including a process.   The manufacturing method according to claim 3, wherein the primary fired product after the ultrasonic irradiation step includes a cubic structure of 10% or more and 70% or less.   The manufacturing method of Claim 3 or 4 whose calcination temperature in a secondary calcination process is 650 degreeC or more and 1000 degrees C or less.   In the ultrasonic irradiation step, an ultrasonic irradiation apparatus comprising a single or a plurality of ultrasonic irradiation units composed of a container and an ultrasonic vibrator provided along the liquid distribution piping of the dispersion containing the primary fired product. The manufacturing method of any one of Claims 3-5 to be used.