Abstract:
A method for making phosphor ink is provided which uses ultrasonic vibrations to remove surface defect layers from phosphor particles and to quickly and uniformly disperse the phosphor particles throughout a slurry. Propagation of low frequency vibration through the slurry generates cavitation, causing distortion and then removal of the surface defect layer, and propagation of high frequency vibration through the slurry causes the particles to be dispersed quickly and uniformly throughout the slurry. In this manner, a quantity of light generated in the phosphor and corresponding luminance of a PDP is increased.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to phosphor ink, and in particular to a method for making phosphor ink and a system using the same. 
     2. Description of the Related Art 
     In general, a printing technique using an ink jet system implements an expected image by discharging ink through nozzles, and accordingly unnecessary consumption of materials can be reduced. In addition, the printing technique can implement an image having high resolution by adjusting intervals of the nozzles, and accordingly applying it to display panels for various displays has been examined. In particular, applying it to a phosphor spreading method for a PDP (plasma display panel) has been examined. 
     In the PDP, because an inorganic phosphor having an average particle&#39;s diameter of 1 μm˜10 μm is used as a luminous body, it is very important to use a technique for making phosphor ink in which the inorganic particles are uniformly dispersed. 
     Hereinafter, a method for making phosphor ink in accordance with the conventional art will be described with reference to  FIG. 1 . 
       FIG. 1  shows a method for making phosphor ink in accordance with the conventional art. 
     As depicted in  FIG. 1 , in the conventional method for making phosphor ink, by rubbing mechanically or colliding physically inorganic phosphor  11  (inorganic phosphor particles) mixed in a specific mixed liquor  10  against a ball  12  of a ball mill (not shown) or a dispersing agent  13  or a binder  14 , etc., the inorganic phosphor  11  is dispersed in the mixed liquor  10 , and accordingly phosphor ink can be obtained. Herein, by the ball  12  of the ball mill used in the conventional phosphor ink making method, because a size of each particle of the inorganic phosphor  11  can be reduced, the inorganic phosphor  11  can be passed a nozzle easily, and accordingly spray characteristics of the inorganic phosphor ink can be improved. 
     However, in the conventional method for making phosphor ink, when the inorganic phosphor  11  is dispersed in the mixed liquor  10 , by friction between the particle with the ball of the ball mill or among the particles, a surface defect layer  20  is induced on the surfaces of particles of the inorganic phosphor  11 . The surface defect layer  20  formed on the particle surface of the inorganic phosphor  11  will be described with reference to  FIG. 2 . 
       FIG. 2  illustrates the surface defect layer formed on the particle of the inorganic phosphor in accordance with the conventional art. 
     As depicted in  FIG. 2 , the surface defect layer  20  formed on the inorganic phosphor  11  reduces light generated in the phosphor, and accordingly radiating efficiency of a PDP using the phosphor is remarkably lowered. After a time for dispersing the inorganic phosphor  11  in the mixed liquor  10  has passed, a quantity of light generated in the phosphor is remarkably reduced. Hereinafter, radiating efficiency reduction of the phosphor caused by the surface defect layer  20  formed on the particle surface of the phosphor and a luminance lowering phenomenon caused by that will be described with reference to  FIG. 3 . 
       FIG. 3  is a graph illustrating the luminance lowering phenomenon caused by the surface defect layer formed on the particle surface of the phosphor. 
     As depicted in  FIG. 3 , the more a time for dispersing the inorganic phosphor particles in the mixed liquor  11  has passed, a size of an inorganic phosphor particle  11  gets smaller, because of that, spray characteristics can be improved. However, because the surface defect layer  20  formed on the particle surface of the phosphor  11  is increased, a quantity of light generated in the inorganic phosphor is reduced due to the surface defect layer  20 , and accordingly luminance of the PDP is lowered. In more detail, when phosphor ink is made of inorganic phosphor particles having surface defect layers and a phosphor layer of a PDP is fabricated with that phosphor ink, luminance of the PDP is lowered due to the surface defect layers  20 . 
     As described-above, in the method for making phosphor ink in accordance with the conventional art, a surface defect layer may be formed on the particle surface of the phosphor, a quantity of light generated in the phosphor may be reduced due to the surface defect layer, and accordingly luminance of a PDP may be lowered. 
     As described-above, in the method for fabricating phosphor ink in accordance with the conventional art, because a surface defect layer may be formed on the particle surface of the phosphor, a quantity of light generated in the phosphor may be reduced due to the surface defect layer, and accordingly luminance of a PDP may be lowered. 
     In the meantime, other phosphor inks according to the conventional art were disclosed in detail in U.S. Pat. No. 6,458,294 and U.S. Pat. No. 5,698,614. 
     SUMMARY OF THE INVENTION 
     In order to solve the above-mentioned problems, it is an object of the present invention to provide a method for making phosphor ink and a system using the same capable of increasing a quantity of light generated in the phosphor and increasing luminance of a PDP (plasma display panel) by removing a surface defect layer formed on a particle surface of the phosphor in making of phosphor ink. 
     It is another object of the present invention to provide a method for making phosphor ink and a system using the same capable of dispersing phosphor particles in a slurry quickly and uniformly in making of phosphor ink. 
     In order to achieve the above-mentioned objects, a method for making phosphor ink includes dispersing phosphor particles mixed in a slurry by generating ultrasonic vibrations. 
     In order to achieve the above-mentioned objects, a method for making phosphor ink includes dispersing phosphor particles mixed in a slurry by generating ultrasonic vibrations in a high frequency band; and removing surface defect layers formed on the phosphor particles by generating ultrasonic vibrations in a low frequency band. 
     In order to achieve the above-mentioned objects, a method for making phosphor ink includes obtaining a slurry for phosphor ink by putting a phosphor material and a dispersing agent in a first reaction container in which a solvent is contained and stirring it; obtaining a mixed liquor for phosphor ink by putting a binder into a second reaction container in which the solvent is contained; and putting the mixed liquor and the slurry into a dispersing container in which a piezoelectric element is installed and applying first ultrasonic vibrations and second ultrasonic vibrations to the dispersing container alternately and periodically through the piezoelectric element. 
     In order to achieve the above-mentioned objects, a system for making phosphor ink in accordance with the present invention includes a control unit for generating an electric signal; a piezoelectric element for generating ultrasonic vibrations by an electric signal generated by the control unit; and a dispersing container for containing a slurry in which phosphor particles are mixed; wherein the piezoelectric element is installed at the dispersing container. 
     In order to achieve the above-mentioned objects, the piezoelectric element of the system generates ultrasonic vibrations within several tens Hz˜several hundreds Hz and ultrasonic vibrations within several hundreds Hz˜several thousands KHz alternately and periodically according to an electric signal outputted from the control unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  shows a method for making phosphor ink in accordance with the conventional art; 
         FIG. 2  shows a surface defect layer formed on the surface of an inorganic phosphor particle in accordance with the conventional art; 
         FIG. 3  is a graph showing a luminance lowering phenomenon due to a surface defect layer formed on the surface of a phosphor particle; 
         FIG. 4  shows a system using a method for making phosphor ink in accordance with the present invention; 
         FIG. 5A  shows a process for removing surface defect layers formed on phosphor particles in a slurry by generating ultrasonic vibrations in a low frequency band (several tens Hz˜several hundreds Hz); and 
         FIG. 5B  shows a process for dispersing phosphor particles in a slurry quickly and uniformly by generating ultrasonic vibrations in a high frequency band (several hundreds Hz˜several thousands KHz). 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, a method for making phosphor ink and a system using the same capable of dispersing phosphor particles quickly and uniformly, increasing a quantity of light generated in the phosphor by removing the surface defect layers and increasing luminance of a PDP (plasma display panel) by repeatedly performing a process for dispersing phosphor particles mixed in a slurry with ultrasonic vibrations in a high frequency band and a process for removing surface defect layers formed on the surfaces of the phosphor particles with ultrasonic vibrations in a low frequency band will be described with reference to  FIGS. 4˜5B . 
       FIG. 4  shows a system using a method for making phosphor ink in accordance with the present invention. 
     As depicted in  FIG. 4 , the system using the method for making phosphor ink in accordance with the present invention includes a control unit  40  for generating an electric signal having a high frequency signal or an electric signal having a low frequency signal; a piezoelectric element  50  for generating ultrasonic vibrations in a high frequency band or ultrasonic vibrations in a low frequency band by the electric signal having a high frequency signal or the electric signal having a low frequency signal; and a dispersing container  60  for containing a slurry in which phosphor particles are mixed. Herein, the piezoelectric element is installed at the dispersing container, and surface defect layers  20  formed on the phosphor particles in the slurry in the dispersing container  60  are removed by ultrasonic vibrations in a low frequency band generated by the piezoelectric element  50 . In addition, the phosphor particles mixed in the slurry are dispersed quickly and uniformly by ultrasonic vibrations in a high frequency band generated by the piezoelectric element  50 . 
     Hereinafter, the operation of the system using the method for making phosphor ink in accordance with the present invention will be described. 
     First, the control unit  40  applies a voltage signal having the high frequency signal or a voltage signal having the low frequency signal to the piezoelectric element  50 . 
     The piezoelectric element  50  generates ultrasonic vibrations in a high frequency band by the voltage signal having the high frequency signal and generates ultrasonic vibrations in a low frequency band by the voltage signal having the low frequency signal. The piezoelectric element  50  can be installed at the internal wall or the bottom of the dispersing container  60 . The piezoelectric element  50  generates ultrasonic vibrations in a low frequency band within several tens Hz˜several hundreds Hz and ultrasonic vibrations in a high frequency band within several hundreds Hz˜several thousands KHz. The ultrasonic vibrations disperse the phosphor particles mixed in the slurry quickly and uniformly. Herein, plural piezoelectric elements  50  can be installed at the dispersing container  60 . In addition, a piezoelectric element  50  for generating ultrasonic vibrations in a low frequency band and a piezoelectric element  50  for generating ultrasonic vibrations in a high frequency band can be respectively installed at the dispersing container  60 . 
     For example, cavitation occurs by the ultrasonic vibrations in the low frequency band generated by the piezoelectric element  50 , and the surface defect layers formed on the phosphor particles in the slurry are removed by the cavitation. In addition, vibration acceleration is increased by the ultrasonic vibrations in the high frequency band generated by the piezoelectric element  50 , and the ultrasonic particles mixed in the slurry are dispersed quickly and uniformly by the increased vibration acceleration. It will be described in detail with reference to  FIGS. 5A and 5B . 
       FIG. 5A  shows a process for removing surface defect layers formed on phosphor particles in a slurry by generating ultrasonic vibrations in the low frequency band (several tens Hz˜several hundreds Hz). 
     As depicted in  FIG. 5A , when ultrasonic vibrations in the low frequency band of several tens Hz˜several hundreds Hz are generated through the piezoelectric element  50 , the generated ultrasonic vibrations are propagated to a liquid (for example, a liquid in which the mixed liquor is mixed with the slurry or the slurry) in the dispersing container  60 , a pressure increasing portion and a pressure decreasing portion partially occur, according to that, cavitation  61  occurs in a negative pressure (dilatability) cycle, the surface defect layer is distorted and broken in a positive pressure (compression force) cycle, at that time, an impulsive force is generated, and the surface defect layer  20  formed on the particle of the phosphor inside the slurry is removed by the impulsive force. 
       FIG. 5B  shows a process for dispersing phosphor particles in a slurry quickly and uniformly by generating ultrasonic vibrations in the high frequency band (several hundreds Hz˜several thousands KHz). 
     As depicted in  FIG. 5B , when ultrasonic vibrations in the high frequency band of several hundreds Hz˜several thousands KHz are generated through the piezoelectric element  50 , the generated ultrasonic vibrations in the high frequency band have the amplitude greater than that of ultrasonic vibrations in the low frequency band, a proceeding speed is faster with the passage of time, and accordingly vibration acceleration is increased. By the vibration acceleration, because the phosphor particles mixed in the slurry  11  can be dispersed quickly, a time for dispersing the phosphor particles can be reduced, and the phosphor particles can be dispersed more uniformly in comparison with the conventional art. 
     In addition, by alternately repeating ultrasonic vibrations in the high frequency band and ultrasonic vibrations in the low frequency band periodically, while the phosphor particles are dispersed by the ultrasonic vibrations in the high frequency band, the surface defect layers formed on the phosphor particles are removed once more by the ultrasonic vibrations in the low frequency band. In more detail, it is preferable to repeat the dispersing process and the surface defect layer removing process alternately and periodically. 
     Accordingly, in the present invention, by repeating the process for dispersing phosphor particles mixed in the slurry with ultrasonic vibrations in the high frequency band and the process for removing the surface defect layers formed on the phosphor particles with ultrasonic vibrations in the low frequency band periodically, the phosphor particles can be dispersed quickly and uniformly, and the surface defect layers formed in the dispersing process can be removed. 
     Hereinafter, making phosphor ink used for a phosphor layer of a PDP by the phosphor ink making method in accordance with the present invention will be described. 
     First, a phosphor material selected from a group consisting of phosphor materials for a PDP such Zn 2 SiO 4 :Mn 2+ , (Y,Gd)BO 3 :Eu 3+ , and BaMgAl 10 O 17 :Eu 3+ , at least one kind of organic solvents selected from distilled water, ketones, glycols, and alcohols, and a dispersing agent are put into a first reaction container, it is stirred, and accordingly a slurry is obtained. 
     It is preferable to use a solvent having a boiling point within 90° C.˜200° C. It is more preferable to use a solvent having a boiling point within 90° C.˜180° C. In more detail, when a boiling point of the solvent is lower than 90° C., drying is proceeded quickly around a nozzle for spraying the phosphor ink before the phosphor ink is sprayed, and accordingly inferior ink can be made. On the other hand, when a boiling point of the solvent is higher than 200° C., drying characteristics of a phosphor layer made of the phosphor material can be deteriorated. 
     In the meantime, by separating from the step for obtaining the slurry by stirring the phosphor material and the dispersing agent, a mixed liquor is obtained by putting one material selected from PVA (polyvinyl-acetate), acryls, and celluloses and at least one kind of solvents selected from distilled water, ketones, glycols, and alcohols into a second reaction container and stirring it. 
     Afterward, the mixed liquor and the slurry are put into the dispersing container in which the piezoelectric element  50  is installed at the internal wall or the bottom, ultrasonic vibrations in the low frequency band within several tens Hz˜several hundreds Hz and ultrasonic vibrations in the high frequency band within several hundreds Hz˜several thousands KHz are alternately and periodically generated through the piezoelectric element  50 , and the generated ultrasonic vibrations are propagated to the dispersing container  60 . 
     The ultrasonic vibrations disperse the phosphor particles mixed in the slurry in the mixed liquor quickly and uniformly. Herein, by the ultrasonic vibrations of several tens Hz˜several hundreds Hz, cavitation occurs, and the surface defect layers formed on the phosphor particles in the slurry are removed by the cavitation. In addition, by the ultrasonic vibrations of several hundreds Hz˜several thousands KHz, vibration acceleration is increased, by the increased vibration acceleration, the phosphor particles mixed in the slurry are dispersed in the mixed liquor quickly and uniformly. 
     Accordingly, it is possible to disperse the phosphor particles in the slurry in the mixed liquor quickly and uniformly and obtain the phosphor ink without having surface defect layers. 
     In the meantime, the method for making phosphor in accordance with the present invention can be applied to the process for forming the slurry by stirring the phosphor material and the dispersing agent, and it can be applied again to the process for making the phosphor ink by putting the mixed liquor and the slurry in the dispersing container. 
     As described-above, in the method for making phosphor in accordance with the present invention, by repeatedly performing the dispersing operation for dispersing the phosphor particles mixed in the slurry with ultrasonic vibrations in the high frequency band and the surface defect layer removing operation for removing the surface defect layers formed in the slurry with ultrasonic vibrations in the low frequency band, the phosphor particles can be dispersed quickly and uniformly, and the surface defect layers formed on the phosphor particles in the dispersing operation can be removed. In more detail, by dispersing the phosphor particles in the mixed liquor quickly and uniformly and removing the surface defect layers formed on the phosphor particles in the dispersing process, better phosphor ink can be made. 
     As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.