Abstract:
The present invention provides a screen assembly, a screen printing system and a screen printing method, belonging to the field of screen printing technology, by means of which the problem of prior art that the printed pattern has unsmooth lines caused by deformation of a thin film screen after a plurality of times of printing can be solved. The screen assembly of the present invention comprises a thin film screen and a fixed screen both having a same pattern. When a packaging cover plate is printed, the thin film screen is arranged above the fixed screen, and the fixed screen is arranged on the packaging cover plate, so that the printing material passes through the thin film screen and the fixed screen successively to be printed onto the packaging cover plate. The screen assembly of the present invention is particularly applicable to the printing process of glass material.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention belongs to the field of screen printing technology, and particularly relates to a screen assembly, a screen printing system and a screen printing method. 
       BACKGROUND OF THE INVENTION 
       [0002]    The organic light-emitting diode (OLED) display technology, as a novel flat panel display technology, has drawn increasing attention due to advantages of active emission, high brightness, wide view angle, quick response, low energy consumption, flexibility, etc., and has become a next generation of display technology that may substitute the liquid crystal display technology. 
         [0003]    The existing OLED display panel contains an organic material layer that is quite sensitive to moisture and oxygen, and as a result, the service life of the OLED display panel is greatly reduced. In order to solve this problem, in the prior art, the organic material layer in the OLED display panel is isolated from the outside by using various kinds of material, so that the seal performance reaches the following standards: the amount of moisture penetrated into the OLED display panel is less than 10 −6  g/m 2 /day and the amount of oxygen penetrated is less than 10 −3  cm 3 /m 2 /day. A sealing method usually includes the following steps of: in nitrogen atmosphere, placing a first substrate of the OLED display panel (this substrate is generally known as a packaging cover plate) on a base, and filling frit in a packaging region of the first substrate; aligning the second substrate with the first substrate to form a cell, and then heating the frit by a laser beam to melt the frit so that the molten frit forms a tight packaging connection between the first substrate and the second substrate. 
         [0004]    At present, filling the frit in the packaging region of the packaging cover plate is usually done by means of thin film screen printing, as shown in  FIG. 1 . Specifically, a white glass plate is placed on a base (both the white glass plate and the base are not shown in the figures) first, and then the white glass plate and the thin film screen  12  are mechanically aligned with each other (with a spacing therebetween). Then, the frit  14  on the thin film screen  12  is printed onto the white glass plate by a scrapper  13 , and the position of the frit  14  on the white glass plate is recorded. Next, a packaging cover plate  11  is prepared, and the position of the packaging region of the packaging cover plate  11  is aligned with the position of the frit  14  on the white glass plate recorded previously. That is, the packaging cover plate  11  is aligned with the thin film screen  12 . Finally, the fit  14  on the thin film screen  12  is printed onto the packaging cover plate  11  by the scrapper  13 . 
         [0005]    However, the inventor finds that there are at least following problems in the prior art. Although the position of the packaging region of the packaging cover plate  11  is mechanically aligned with the position of the frit  14  on the white glass plate, deformation of the thin film screen  12  will inevitably occur with the increasing times of use of the thin film screen  12 . In this case, the position of the fit  14  printed onto the packaging cover plate  11  through the thin film screen  12  will not be accurate. Furthermore, as the fit  14  has unsmooth lines due to the deformation of the thin film screen  12 , burrs occur, and the packaging effect is influenced. 
       SUMMARY OF THE INVENTION 
       [0006]    In view of the above problems of the existing thin film screens, the present invention provides a screen assembly, a screen printing system and a screen printing method, by which a pattern having smooth lines may be printed. 
         [0007]    A technical solution adopted for solving the above technical problem is a screen assembly, comprising a thin film screen and a fixed screen both having a same pattern; wherein 
         [0008]    when a packaging cover plate is printed, the thin film screen is arranged above the fixed screen, and the fixed screen is arranged on the packaging cover plate, so that printing material passes through the thin film screen and the fixed screen successively to be printed onto the packaging cover plate. 
         [0009]    Preferably, a non-stick coating is formed on surface of the fixed screen. 
         [0010]    Further preferably, material of the non-stick coating is Teflon. 
         [0011]    Preferably, the fixed screen is made of glass or polyvinyl chloride. 
         [0012]    A technical solution adopted for solving the above technical problem is a screen printing system, comprising the screen assembly described above. 
         [0013]    Preferably, the screen printing system further includes a bearing base and an alignment device; 
         [0014]    the bearing base is configured to bear a packaging cover plate onto which a pattern is to be printed, and the fixed screen is arranged on the packaging cover plate; and 
         [0015]    the alignment device is configured to align the packaging cover plate, the fixed screen and the thin film screen. 
         [0016]    Further preferably, the alignment device comprises a reference glass plate, an image acquisition module and a position adjustment module; 
         [0017]    the reference glass plate is configured to record a pattern on the thin film screen; 
         [0018]    the image acquisition module is configured to acquire a pattern of the thin film screen recorded on the reference glass plate and images of the fixed screen and the packaging cover plate, in order to acquire position information of the pattern recorded on the reference glass plate and the position information of the fixed screen and the packaging cover plate and to transmit the position information to the position adjustment module; and 
         [0019]    the position adjustment module is configured to align the packaging cover plate, the fixed screen and the thin film screen according to the position information transmitted by the image acquisition module. 
         [0020]    Further preferably, the image acquisition module includes a camera. A technical solution adopted for solving the above technical problem is a screen printing method, comprising: 
         [0021]    placing a thin film screen above a reference glass plate, printing a pattern on the thin film screen onto the reference glass plate, and recording position information of the pattern printed on the reference glass plate; and 
         [0022]    placing a fixed screen on a packaging cover plate, and aligning the thin film screen, the fixed screen and the packaging cover plate according to the recorded position information of the pattern printed on the reference glass plate. 
         [0023]    Preferably, aligning the thin film screen, the fixed screen and the packaging cover plate further comprises: 
         [0024]    aligning the fixed screen with the thin film screen according to the recorded position information of the pattern printed on the reference glass plate; and 
         [0025]    aligning the packaging cover plate with the thin film screen and the fixed screen according to the recorded position information of the pattern printed on the reference glass plate. 
         [0026]    Preferably, after aligning the thin film screen, the fixed screen and the packaging cover plate, the method further comprises: printing the printing material onto the packaging cover plate through the thin film screen and the fixed screen. 
         [0027]    Further preferably, the printing material is frit. 
         [0028]    The present invention has the following beneficial effects: 
         [0029]    In the screen assembly of the present invention, as a fixed screen having a same pattern as the thin film screen is additionally provided and the fixed screen is arranged on a packaging cover plate when the packaging cover plate is printed, the printing material can be accurately printed on a region to be printed on the packaging cover plate even if the thin film screen located above the fixed screen deforms during printing, thus avoiding the problem that the printed pattern has unsmooth lines due to the deformation of the thin film screen in the prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a schematic diagram of an existing thin film screen; 
           [0031]      FIG. 2  is a schematic diagram of a screen assembly of a first embodiment of the present invention; 
           [0032]      FIG. 3  is a schematic diagram of a screen printing system of a second embodiment of the present invention; 
           [0033]      FIG. 4  is a schematic flow diagram of a screen printing method of the second embodiment of the present invention; and 
           [0034]      FIG. 5  is a schematic flow diagram of specific process of step S 02  in the method as shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0035]    To make those skilled in the art understand the technical solution of the present invention better, the present invention will be further described as below with reference to the accompanying drawings and specific implementations. 
       First Embodiment 
       [0036]    As shown in  FIG. 2 , this embodiment provides a screen assembly, comprising a thin film screen  12  and a fixed screen  15  both having a same pattern; wherein when a packaging cover plate  11  is printed, the fixed screen  15  is arranged on the packaging cover plate  11 , for printing the printing material  14  onto the packaging cover plate  11  through the thin film screen  12 . 
         [0037]    In the screen assembly of this embodiment, as a fixed screen  15  having a same pattern as the thin film screen  12  is additionally provided and the fixed screen  15  is arranged on a packaging cover plate  11  when the packaging cover plate  11  is printed, the printing material  14  can be accurately printed on a region to be printed on the packaging cover plate  11  even if the thin film screen  12  deforms during printing, thus avoiding the problem that the printed pattern has unsmooth lines due to the deformation of the thin film screen  12  in the prior art. 
         [0038]    Preferably, a non-stick coating is formed on the surface of the fixed screen  15 . The non-stick coating can effectively prevent the printing material  14  from sticking onto the fixed screen  15  during printing of the printing material  14  onto the packaging cover plate  11 . Hence, the printing effect is not influenced when the fixed screen  15  is separated from the packaging cover plate  11  after the end of printing. 
         [0039]    Preferably, material of the non-stick coating is Teflon. Of course, in this embodiment, the material of the non-stick coating is not limited to this one, and other material having a same function as Teflon may be used. 
         [0040]    Preferably, the fixed screen  15  in this embodiment is made of glass or polyvinyl chloride. Similarly, the material of the fixed screen  15  is not limited to the two, and the material of the fixed screen  15  is not specifically limited in this embodiment. 
         [0041]    It should be noted that the screen assembly of this embodiment is particularly applicable to the printing process of materials such as a seal, wherein the seal is usually made of frit. That is, the printing material  14  may be frit. The thin film screen  12  in this embodiment is of the same material as the existing thin film screen  12 , and may be made of a thin film of metal such as copper, aluminum, or the like. This is not exemplified here one by one. 
       Second Embodiment 
       [0042]    As shown in  FIG. 3 , this embodiment provides a screen printing system, including the screen assembly as described in the first embodiment, a bearing base  16  and an alignment device, wherein the bearing base  16  is configured to bear a packaging cover plate  11  onto which a pattern is to be printed, and the fixed screen  15  is arranged on the packaging cover plate  11 ; and the alignment device is configured to align the packaging cover plate  11 , the fixed screen  15  and the thin film screen  12 . 
         [0043]    Specifically, the alignment device comprises a reference glass plate, an image acquisition module  17  and a position adjustment module (both the reference glass plate and the position adjustment module are not shown in the figures). The reference glass plate is configured to record a pattern on the thin film screen  12 . The image acquisition module  17  is configured to acquire a pattern of the thin film screen  12  recorded on the reference glass plate and images of the fixed screen  15  and the packaging cover plate  11  onto which a pattern is to be printed, in order to acquire position information of the pattern (i.e., printing material  14 ) recorded on the reference glass plate and the position information of the fixed screen  15  and the packaging cover plate  11  onto which a pattern is to be printed, and to transmit the position information to the position adjustment module. The position adjustment module is configured to align the packaging cover plate  11 , the fixed screen  15  and the thin film screen  12  according to the position information transmitted by the image acquisition module  17 . Preferably, the image acquisition module  17  includes a camera. It should be noted that, usually, in order to acquire the accurate positions of the packaging cover plate  11 , the fixed screen  15  and the thin film screen  12 , there are two cameras and the cameras are arranged below the bearing base  16 . The reference glass plate may be a white glass plate. 
         [0044]    Correspondingly, this embodiment further provides a screen printing method for the screen printing system described above.  FIG. 4  is a schematic flow diagram of this method which may include the following steps S 01  and S 02 . 
         [0045]    S 01 : a step of recording position information of a pattern printed on a reference glass plate. A thin film screen  12  is placed above a reference glass plate, a pattern on the thin film screen  12  is printed onto the reference glass plate, and position information on the position of the pattern printed on the reference glass plate is recorded. 
         [0046]    Specifically, a reference glass plate is placed on the bearing base  16  first, and then the reference glass plate is mechanically aligned. Then, the printing material  14  on the thin film screen  12  is printed onto the reference glass plate by a scrapper  13 , wherein there is a certain spacing between the thin film screen  12  and the reference glass plate. Finally, the pattern of the printing material  14  on the reference glass plate is acquired by the image acquisition module  17  (camera), in order to acquire the position information of the printing material  14  and to write this position information into the position adjustment module. The position information of the printing material  14  on the reference glass plate is the position information of the pattern on the thin film screen  12 . 
         [0047]    S 02 : a step of aligning the thin film screen, the fixed screen and the packaging cover plate. A fixed screen  15  and a packaging cover plate  11  are provided below the thin film screen  12  so that the fixed screen  15  is located on the packaging cover plate  11 , and the thin film screen  12 , the fixed screen  15  and the packaging cover plate  11  are aligned according to the recorded position information of the pattern printed on the reference glass plate. 
         [0048]    As shown in  FIG. 5 , the step  02  may further comprises: 
         [0049]    S 21 : aligning the fixed screen with the thin film screen according to the recorded position information of the pattern printed on the reference glass plate; and 
         [0050]    S 22 : aligning the packaging cover plate with the thin film screen and the fixed screen according to the recorded position information of the pattern printed on the reference glass plate. 
         [0051]    Specifically, a fixed screen  15  is prepared and the fixed screen  15  is mechanically aligned with the thin film screen  12  subjected to the step S 01 . Then, an image of the fixed screen  15  is acquired by the image acquisition module  17  (camera), in order to acquire the position information of the fixed screen  15  and to write this position information into the position adjustment module. The position adjustment module precisely aligns the fixed screen  15  and the thin film screen  12  according to the recorded position information of the printing material  14  on the reference glass plate in S 01  and the position information of the fixed screen  15 . For example, the position information of the fixed screen  15  may be compared with the position information of the printing material  14 , and the fixed screen  15  and the thin film screen  12  may be accurately aligned according to the result of comparison. In this case, the position of the fixed screen  15  is kept unchanged. 
         [0052]    Next, the packaging cover plate  11  is arranged below the fixed screen  15  in such a manner that the packaging cover plate  11  comes into contact with the fixed screen  15 , and then the packaging cover plate  11  and the fixed screen  15  are mechanically aligned. Then, an image of the packaging cover plate  11  is acquired by the image acquisition module  17  (camera), in order to acquire the position information of the packaging cover plate  11  and to write this position information into the position adjustment module. The position adjustment module precisely aligns the packaging cover plate  11  and the thin film screen  12  according to the recorded position information of the printing material  14  on the reference glass plate in S 01  and the position information of the packaging cover plate  11 . For example, the position information of the packaging cover plate  11  may be compared with the position information of the printing material  14 , and the packaging cover plate  11  and the thin film screen  12  may be accurately aligned according to the result of comparison. 
         [0053]    In this way, alignment of the packaging cover plate  11 , the thin film screen  12  and the fixed screen  15  is accomplished. 
         [0054]    After the above steps S 01  and S 02 , a further step S 03  may be further performed, as shown in  FIG. 4 . 
         [0055]    S 03 : a step of printing the printing material onto the packaging cover plate. The printing material  14  on the thin film screen  12  is printed onto the packaging cover plate  11  through a scrapper  13 . 
         [0056]    This process is particularly applicable to the printing process of a seal. The printing material  14  may be, for example, frit. 
         [0057]    By using the screen printing system and printing method provided by this embodiment, the printed pattern can have smooth lines, thereby avoiding the burrs in the printed pattern. 
         [0058]    It may be understood that the above implementations are merely exemplary implementations used to describe the principle of the present invention, and the present invention is not limited thereto. For a person of ordinary skill in the art, various variations and improvements may be made without departing from the spirit and essence of the present invention, and these variations and improvements should also be regarded as falling into the protection scope of the present invention.