Patent Publication Number: US-6704531-B2

Title: Developing system having metering blade with spaced intersecting faces

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Application No. 2002-1694, filed Jan. 11, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a developing system of a liquid electrophotographic image forming device, and more particularly, to a developing system capable of regulating a developer layer on a development roller of a liquid electrophotographic image forming device using a high-concentration liquid developer. 
     2. Description of the Related Art 
     In general, developing systems of liquid electrophotographic image forming devices form an electrostatic latent image corresponding to a desired image by scanning light on a photosensitive body, develop the electrostatic latent image using a developer in which powder-shaped toner is mixed with a liquid solvent, and print the developed electrostatic latent image on a paper. 
     FIG. 1 is an example of a conventional developing system of a liquid electrophotographic image forming device. Referring to FIG. 1, the conventional developing system of a liquid electrophotographic image forming device includes a photosensitive body  10  which is supported by a plurality of rollers  11  and moves as an endless track, a developing unit  20  to develop an electrostatic latent image formed on the photosensitive body  10 , and a transfer unit  30  to transfer the electrostatic latent image onto a paper P. 
     The photosensitive body  10  is charged to a predetermined electric potential by a charger  12 , and the charged electric potential varies depending on light beams scanned by a laser scanning unit (LSU)  13  installed adjacent to the photosensitive body  10  such that the electrostatic latent image is formed. Next, the electrostatic latent image formed on the photosensitive body  10  is developed by the developing unit  20 , and the developed image is transferred onto a transfer roller  14  and is printed onto the paper P passing through the transfer roller  14  and a fusing roller  15 . 
     The structure of the developing unit  20  is shown in FIG.  2 . Referring to FIG. 2, the developing unit  20  develops the electrostatic latent image formed on the photosensitive body  10  using a developer to form an image. The developing unit  20  includes a development roller  23  that is installed to be rotatable in a main body  21 , a manifold  22  to spray the developer between the development roller  23  and the photosensitive body  10 , and a squeeze roller  24 . Reference numerals  25 ,  26 , and  27  denote a cleaning roller to clean the surface of the development roller  23 , a development backup roller, and a squeeze backup roller, respectively. 
     In the structure of FIG. 2, the electrostatic latent image formed on the photosensitive body  10  is developed using a liquid developer that is sprayed between the development roller  23  and the photosensitive body  10  by the manifold  22 , and a liquid carrier left on the photosensitive body  10  is removed with the squeeze roller  24 . 
     A low-concentration liquid developer (less than 2.5-3% solid) is used in the developing system of a liquid electrophotographic image forming device, thereby obtaining a high quality image. However, since the concentration of the developer in an ink cartridge (not shown) to supply the developer to the developing system is 25% solid, a complicated developer supplying unit is required to change the high-concentration developer to the low-concentration developer. Thus, the size of the image forming device increases, and the image forming device has a complicated structure. Also, after development of the image, a system to control the concentration of the liquid developer depending on variations in the toner particles is required when the developer is refilled. 
     Thus, in order to solve these problems, a new developing system using a high-concentration developer greater than 3% solid is required. A developer layer on the development roller should be regulated regardless of the concentration of the developer. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a developing system for a high-concentration liquid electrophotographic image forming device, which is capable of improving the quality of an image by regulating a developer layer on a development roller. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     The foregoing and other objects of the present invention are achieved by providing a developing system of a liquid electrophotographic image forming device. The developing system includes a development container in which a developer is stored; a photosensitive body; a development roller to rotate opposite to the photosensitive body, the development roller being partially soaked in the developer in development container; and a metering blade to maintain a layer of the developer on the development roller at a constant thickness, the metering blade including a first face contacting the development roller, and a second face forming an angle with respect to the first face, wherein a point at which the development roller contacts the first face of the metering blade is spaced from an edge at which the first and second faces intersect. 
     According to an aspect of the present invention, the metering blade is an L-shaped metal plate. 
     According to another aspect of the present invention, the point at which the circumference of the development roller contacts the first face of the metering blade is spaced more than 1 mm apart from the edge, and a force per centimeter applied to the circumference of the development roller by the metering blade is about 100-200 gf/cm. 
     According to still another aspect of the present invention, surface roughness of the metering blade is less than 0.5 μm, and an angle between the first face and the second face of the metering blade is about 90 degrees. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 illustrates a conventional developing system of a liquid electrophotographic image forming device; 
     FIG. 2 illustrates the structure of a developing unit of FIG. 1; 
     FIG. 3 illustrates a developing system of a liquid electrophotographic image forming device according to an embodiment of the present invention; 
     FIG. 4 is a perspective view of a metering blade to regulate a developer layer on a development roller of FIG. 3; and 
     FIG. 5 is a top view of the metering blade of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     FIG. 3 illustrates a developing system of a liquid electrophotographic image forming device according to an embodiment of the present invention. Referring to FIG. 3, the developing system of a liquid electrophotographic image forming device includes a development container  100  to which a developer  102  is supplied from a developer cartridge (not shown). Here, a high-concentration liquid developer of about 3-40% solid is used as the developer  102  supplied to the development container  100 . 
     Within the development container  100  there is a development roller  104  to rotate opposite to a photosensitive body  200 . The development roller  104  is partially soaked in the developer  102 . Within the development container  100 , there further is a metering blade  108  to maintain a developer layer stained on the circumference of the development roller  104  at a predetermined thickness, a depositing roller  106  to apply an electric potential to attach the developer  102  to the circumference of the development roller  104 , and a cleaning roller  110  to clean the surface of the development roller  104 . In FIG. 3, reference numerals  114  and  112  denote a development power supply portion to apply a development voltage to the development roller  104 , and a depositing power supply portion to apply a voltage to the depositing roller  106 , respectively. Reference numerals  127 ,  129 , and  300  respectively denote a charging roller to charge the photosensitive body  200 , a laser scanning unit (LSU) to form an electrostatic image by scanning light onto the photosensitive body  200 , and a transfer medium onto which the electrostatic latent image that is developed on the photosensitive body  200  is transferred, to print the transferred image onto a paper. 
     The development roller  104  may be formed of polyurethane rubber or NBR as a conductive elastomer, having a resistance of about 10 5 -10 8  ohm, a hardness of shore A 25-65 degrees, and a surface roughness of Ra 1-4 μm. 
     The metering blade  108  regulates the thickness and the concentration of the developer layer stained on the development roller  104  by applying a predetermined pressure to the circumference of the development roller  104 . 
     The depositing roller  106  attaches the developer  102  to the development roller  104  by an electric force of a voltage applied from the depositing power supply portion  112 . In this case, the depositing roller  106  may contact the development roller  104  or may be spaced at a predetermined distance apart from the development roller  104 . 
     The cleaning roller  110  rotates to contact the development roller  104  in the same direction as the development roller  104  and cleans the developer  102  stained on the development roller  104  which is not developed. 
     Only one developing system is provided in the image forming device shown in FIG.  3 . However, to form a multi-colored image, a plurality of the developing systems may be provided. 
     In order to perform a development operation, the developer  102  for each color is supplied to the development container  100  from the developer cartridge (not shown) and is charged to a predetermined level. In this case, the charged developer  102  is a high-concentration developer having a concentration greater than 20% solid. Voltages of about 300-550 V and about 500-1500 V are applied to the development roller  104  and to the depositing roller  106 , respectively. If the voltages are applied to the development roller  104  and to the depositing roller  106  in this way, toner particles of the developer  102  are positively charged, and thus the developer  102  attaches to the surface of the development roller  104  due to a voltage difference between the development roller  104  and the depositing roller  106 . In this case, the amount of the developer  102  that attaches to the development roller  104  is larger than the amount required to develop the electrostatic latent image formed on the photosensitive body  200 , and a toner is stained in a region outside of the area of the electrostatic latent image. 
     Accordingly, the metering blade  108  maintains the developer layer stained on the surface of the development roller  104  at a predetermined thickness. In the present invention, as shown in FIGS. 4 and 5, the metering blade  108  is an L-shaped metal plate and includes a first face  108   a  contacting the circumference of the development roller  104 , and a second face  108   b  formed at an angle with respect to the first face  108   a.    
     The developer layer stained on the development roller  104  differs depending on parameters such as a point A at which the metering blade  108  contacts the development roller  104 , pressure applied to the metering blade  108 , surface roughness of the metering blade  108 , and an angle θ between the first face  108   a  and the second face  108   b . Thus, it is very important to optimize these parameters, as discussed below. 
     First, the point A is spaced more than 1 mm apart from an edge at which the first and second faces  108   a  and  108   b  intersect. In particular, the best developer layer was obtained at a point A spaced 1-2 mm apart from the edge. The developer layer on the development roller  104  becomes nonuniform when the point A is spaced less than 1 mm from the edge. 
     Second, according to an aspect of the present invention, a force per centimeter applied to the circumference of the development roller  104  by the metering blade  108  is 100-200 gf/cm. In particular, the best result was obtained when the pressure is 150 gf/cm. In this case, a thickness T of the metering blade  108  is 0.08 mm. When the pressure applied to the circumference of the development roller  104  by the metering blade  108  is too strong, the developer layer on the development roller  104  becomes nonuniform. 
     Third, the best result was obtained when the surface roughness Rz of the metering blade  108  is less than 0.5 μm. Fourth, the best result was obtained when the angle θ between the first face  108   a  and the second face  108   b  of the metering blade  108  is about 90 degrees. The developer layer on the development roller  104  becomes nonuniform at more than 90 degrees. 
     If these optimized parameters are applied to the developing system, the most uniform developer layer on the development roller  104  can be obtained. Thus, even though the developer  102  in a wide range of about 3-20% solid is used in the developing system, the concentration before a development operation can be maintained in a nearly uniform state and can be used in the development operation. 
     Subsequently, after the electrostatic latent image formed on the photosensitive body  200  is developed, the developer  102  left on the development roller  104  is removed using the cleaning roller  110 . 
     As described above, by applying these optimized parameters to the developing system of a liquid electrophotographic image forming device according to the present invention, even though the high-concentration developer in a wide range of concentrations is used, the developer layer on the development roller can be regulated, thereby achieving good image quality. 
     Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.