Abstract:
A method of fabricating a color filter includes steps of forming a transparent-matrix on a flexible and transparent substrate for dividing the substrate to a plurality of pixel regions; printing the a plurality of pixel regions with color ink; and curing the ink to form a plurality of color filters on the surface of the substrate. The light transmittance ability of the color filter can be effectively improved by forming a transparent-matrix instead of a black-matrix on the substrate.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a method of fabricating a color filter, especially to a method of fabricating a color filter with a flexible substrate. 
         [0003]    2. Description of Related Art 
         [0004]    Electrophoretic display devices have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption, as compared with liquid crystal displays. Nowadays, electrophoretic display devices are capable of displaying colorful images in two ways: the first way is by controlling each pixel to display a desired color by primary color mixing, such as RGB color mixing or YMC color mixing; and the second way is by covering the electrophoretic display with a color filter. 
         [0005]    A fabrication method for forming a color filter layer by inkjet printing has been developed recently. With this conventional fabrication method, first, a black matrix is formed on a glass substrate to define a plurality of sub-pixel regions. An inkjet printing process is then performed to inject a color ink (red, green, or blue) to fill the sub-pixel regions defined by the black matrix. Next, a thermal baking process may be performed to solidify the color ink. 
         [0006]    When the color filter is stacked on the electrophoretic display, inner gas-holes will be produced because the color filter is formed on the glass substrate and the electrophoretic display is flexible. The above conventional fabrication method, however, it&#39;s not suitable to fabricate the color filter on a flexible substrate because the material of the flexible substrate does not have good thermostability and cannot be baked in the thermal baking process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0008]      FIG. 1  is a flowchart of a process of fabricating a color filter with flexible substrate in accordance with an exemplary embodiment. 
           [0009]      FIG. 2  is a sub-flowchart of the process in  FIG. 1  according to a first embodiment. 
           [0010]      FIGS. 3A-3C  are schematic cross-sectional views illustrating a process of fabricating a color filter with flexible substrate according to the first embodiment of  FIG. 2 . 
           [0011]      FIG. 4  is a schematic view of the photo mask according to the first embodiment of  FIG. 2 . 
           [0012]      FIG. 5  is a sub-flowchart of the process in  FIG. 1  according to a second embodiment. 
           [0013]      FIGS. 6A-6D  are schematic cross-sectional views illustrating a process of fabricating a color filter with flexible substrate according to the second embodiment of  FIG. 5 . 
           [0014]      FIG. 7  is a schematic view of an electronic paper having a color filter with flexible substrate. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The disclosure, including the accompanying, is illustrated by way of example and not by way of limitation. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
         [0016]    Referring to  FIG. 1 , a flowchart is applied in a process of fabricating a color filter. 
         [0017]    In step S 301 , forming a transparent-matrix on a flexible and transparent substrate for dividing the substrate to a plurality of pixel regions, with the transparent-matrix and the pixel regions having different wettability. 
         [0018]    In step S 302 , printing the a plurality of pixel regions with color ink. 
         [0019]    In step S 303 , curing the color ink. 
         [0020]    Referring to  FIG. 2 , a sub-flowchart of the step  301  in  FIG. 1  is applied in the process of fabricating a color filter with flexible substrate according to a first embodiment. 
         [0021]    In step S 3011 , placing the substrate in a plasma gas of carbon tetrafluoride. 
         [0022]    In step S 3012 , shielding some portion of the substrate by a photo mask and exposing other portion in the plasma gas of carbon tetrafluoride. 
         [0023]      FIG. 3A-3C  are schematic cross-sectional views illustrating a process of fabricating a color filter according to the first embodiment. 
         [0024]    Referring to  FIG. 3A , the substrate  11  is exposed in the gas of carbon tetrafluoride by using the photo mask  21 . The substrate  11  is made of flexible plastic with high intensity, such as polyisoprene (PI), polycarbonate (PC), or polyethylene terephthalate (PET). In this embodiment, the substrate  11  is made of PC. 
         [0025]    Referring to  FIG. 4 , the photo mask  21  includes a plurality of photic zones  211 , the plurality of photic zones  211  divide the photo mask  21  into a plurality of photoresistive zones  212 . Light rays can pass through the photic zones  211  and reach the surface of the substrate  11 . The surface of the substrate  11  where not shielded by the photoresistive zones  212  of the photo mask  21  is infiltrated by the plasma gas of carbon tetrafluoride under the photo catalysis of the light rays, to form the transparent matrix  112  with high hydrophobicity and low surface energy. The transparent matrix  112  divides the substrate  11  to a plurality of pixel regions  111 . 
         [0026]    The transparent matrix  112  and the pixel regions  111  have different wettability, in the first embodiment, the transparent matrix  112  is hydrophobic and the pixel regions  111  is hydrophilic. Whether the material is hydrophobic or hydrophilic is determined by a parameter of a material: contact angle. The contact angle less than 90° (low contact angle) usually indicates the material is hydrophilic, and the fluid dropped on the material can spread over a large area of the surface of the material. Contact angles greater than 90° (high contact angle) generally means that the material is hydrophobic, and the fluid will minimize the contact with the surface of the material and form a compact liquid droplet. The contact angles of the transparent matrix  112  and the pixel regions  111  differ more than 10°, In the first embodiment, the contact angles of the transparent matrix  112  and the pixel regions  111  differ more than 50°. 
         [0027]    Referring to  FIG. 3B , an inkjet printing process is performed to inject color ink  41  including red ink  411 , green ink  412  and blue ink  413  to the pixel regions  111  defined by the transparent matrix  112 , a nozzle  31  injects the color ink  41 . The color ink  41  can spread homogeneously on the surface of the pixel regions  111  for the surface of the pixel regions  111  that are hydrophilic. The hydrophobic function of the transparent matrix  112  mainly separates different colors of the ink, for the transparent matrix  112  so the color ink  41  in each of the pixel regions  111  cannot overflow to the adjacent pixel regions. In the first embodiment, the color ink  41  can be a UV-curing ink containing a pigment providing the color, resin adhesive, photopolymerization initiation, dispersing agent and other additives. The pigment in red ink  411  can be naphthol red pigment or azo condensation pigment, the pigment in green ink  412  can be phthalocyanine pigments, and the pigment in blue ink  413  can be metal phthalocyanine. 
         [0028]    Referring to  FIG. 3C , the substrate  11  is exposed in ultraviolet radiation (UV)  51 , the color ink  41  on the surface of the pixel regions  111  is cured by the UV  51 . The substrate  11  is made of PC material, the fusion temperature of PC is about 260° C. to 340° C., and the high temperature resistance of PC material is weak. Therefore the color ink  41  is cured by the UV  51 , the cured energy is less than 1000 mj/cm 2 , In particular, in the first embodiment, the cured energy is less than 500 mj/cm 2 . After cured by the UV, the color ink  41  forms a color filter stacked on the surface of the pixel regions  111 . The thickness of the color filter can be controlled in 0.110 microns by controlling the amount of the color ink  41  injected by the nozzle  31 . 
         [0029]    In another embodiment, the color ink  41  also can be a low temperature curing ink containing pigment providing the color, resin glue, thermal polymerization initiation, dispersing agent and other additives. In this embodiment, the thermocuring temperature of the color ink  41  is less than 100° C. 
         [0030]    Referring to  FIG. 5 , a sub-flowchart of the step  301  in  FIG. 1  is disclosed according to a second embodiment. 
         [0031]    In step S 3013 , coating a photo sensitive layer on the surface of the substrate. 
         [0032]    In step S 3014 , shielding some portion of the substrate by a photo mask and exposing other portion in a UV. 
         [0033]      FIGS. 6A-6D  are schematic cross-sectional views illustrating a process of fabricating a color filter according to the second embodiment. 
         [0034]    Referring to  FIG. 6A , in the second embodiment, a substrate  12  is also made of flexible plastic with high intensity. A photo sensitive layer  60  is coated on the surface of the substrate  12 . In this embodiment, the photo sensitive layer  60  can be a layer of photo sensitive resin containing resin adhesive, photopolymerization initiation, dispersing agent, antioxidant, UV-absorber and other additives. 
         [0035]    Referring to  FIG. 6B , the substrate  12  is exposed under UV by using a photo mask  22 . The surface of the photo sensitive layer  60 , which is not shielded by the photo mask  22  photopolymerizes under the UV, to form a transparent matrix  122  with high hydrophobicity and low surface energy. The transparent matrix  122  divides the substrate  12  to a plurality of pixel regions  121 . The transparent matrix  122  and the pixel regions  121  have different wettability, in this embodiment, the transparent matrix  122  is hydrophobic and the pixel regions  121  is hydrophilic, and the contact angles of the transparent matrix  122  and the pixel regions  121  differ more than 30°. 
         [0036]    Referring to  FIGS. 6C and 6D , the step  302  and step  303  is similar to the first embodiment. A nozzle  32  injects the color ink  42  to the pixel regions  121 , and then the color ink  42  is cured under the UV. In the second embodiment, the cured energy is less than 150 mj/cm 2 , the thickness of the color filter is controlled within 0.1˜10 microns. 
         [0037]    In another embodiment, an etch process or blasting process can be applied to form the transparent-matrix with high hydrophobicity and low surface energy in the step  301 . 
         [0038]    Referring to  FIG. 7 , an electronic paper (E-paper)  70  includes a substrate  71 , a display layer  72  and a color filter  73  with a flexible substrate. The display layer  72  includes a first electrode  721 , an electrophoretic ink layer  723 , and a second electrode  722 , voltage applied to the first electrode  721  and the second electrode  722  causes the electrophoretic ink layer  723  to change the optical state, to display the content on the E-paper. Because of the color filter has a flexible substrate, the color filter can be stacked on the electrophoretic display without generating inner gas-holes. 
         [0039]    It is to be understood, however, that even though numerous characteristics and advantages of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the present disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.