Patent Publication Number: US-8979248-B2

Title: Ink-jet apparatus

Description:
FIELD OF THE INVENTION 
     The present invention relates to an ink-jet apparatus. 
     BACKGROUND OF THE INVENTION 
     In recent years, methods for manufacturing imaging devices using ink-jet apparatuses have been attracting attention.  FIGS. 8(A) and 8(B)  are plan views of a typical ink-jet apparatus. 
     As shown in  FIGS. 8(A) and 8(B) , the ink-jet apparatus includes a pedestal  41 , a substrate transport stage  42 , a gate-like gantry  43 , and a line scan head  50 . 
     As shown in  FIGS. 8(A) and 8(B) , the substrate transport stage  42  relatively moves. Ink is properly discharged from the line scan head  50  during the movement and is applied to a coating area  44  of a substrate  10  placed on the substrate transport stage  42 , printing the substrate  10 . 
       FIG. 9  is a schematic diagram of the line scan head  50 . As shown in  FIG. 9 , the line scan head  50  includes a plurality of ink-jet heads  51  and a casing  52  that holds the ink-jet heads  51 . The ink-jet heads  51  are arranged in a direction orthogonal to the print-scan direction of a substrate, the ink-jet heads  51  being so wide as to print the substrate in one printing/scanning operation. The line scan head  50  includes ink supply pipes  53  that supply ink for printing from the outside. 
     A feature of an ink-jet apparatus is to inexpensively manufacture devices with a simple manufacturing process. In an ink-jet apparatus provided with the line scan head having the arranged ink-jet heads  51 , however, the positions of the ink-jet heads  51  are hard to stabilize, making it difficult to form fine-pitch patterns on a substrate. 
     In order to overcome this drawback, the line scan head  50  is devised to actively correct the displacements of the ink-jet heads  51  (Japanese Patent Laid-Open No. 2002-228822). 
       FIGS. 10(A) and 10(B)  are schematic diagrams showing the configuration of the conventional line scan head  50  described in Japanese Patent Laid-Open No. 2002-228822.  FIG. 10(A)  is a side view and  FIG. 10(B)  is a perspective view. 
     Ink-jet heads  301 ,  302 , and  303  are fixed to a reference base  321  and stages  322  and  323  via ink-jet head fixing members  311 ,  312 , and  313  shown in  FIG. 10(B) . The stages  322  and  323  are fixed to the reference base  321  via piezoelectric elements  341  and  342  acting as actuators. 
     When the ink-jet heads  301  and  303  are displaced relative to the ink-jet head  302 , the piezoelectric elements  341  and  342  are driven by a desired displacement so as to be corrected to design locations. 
     In the conventional configuration, however, the piezoelectric elements acting as actuators need to be operated to fix the positions of the ink-jet heads. Thus, the ink-jet heads cannot be disposed close to each other with a high density, making it difficult to dispose the ink-jet heads. 
     If the ink-jet heads are disposed in the conventional configuration, the ink-jet heads are sequentially disposed through a predetermined actuator mechanism, increasing spacing between the ink-jet heads. Thus, the line scan head and the ink-jet apparatus including the line scan head increase in size. 
     This may cause a time difference before the application of ink depending on the installation positions of the ink-jet heads, in substrate scanning for printing. The time difference leads to uneven drying, considerably deteriorating printing quality. 
     Moreover, the actuators need to be always driven in order to keep the positions of the ink-jet heads disposed on the line scan head, disadvantageously causing higher power consumption and heat generation. 
     The line scan head containing a heat source, in particular, may reduce the accuracy of component assembly. Furthermore, once power is shut down for maintenance of apparatuses, the kept positions of the ink-jet heads are reset, disadvantageously reducing positional repeatability. 
     An object of the present invention is to provide an ink-jet apparatus including a small line scan head with densely mounted ink-jet heads, which guarantees the positions of the ink-jet heads for a long period to solve the conventional problems. 
     DISCLOSURE OF THE INVENTION 
     In order to attain the object, an ink-jet apparatus according to the present invention is an ink-jet apparatus including a plurality of ink-jet heads, a plate loaded with the ink-jet heads, and a fixing member that fixes the ink-jet heads and the plate, wherein the plate and the ink-jet head have faying surfaces, one faying surface has a plurality of long thin concaves, the other faying surface has a plurality of long thin convexes entered into at least one of the long thin concaves, and the width of a region containing the long thin concaves in a direction orthogonal to the length direction of the long thin concaves is not smaller than the width of a region containing the long thin convexes on the faying surfaces in a direction orthogonal to the length direction of the long thin convexes. 
     As has been discussed, according to the present invention, the ink-jet heads can be densely placed at guaranteed positions, achieving printing with high precision and high definition for a long period of time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1(A)  is a schematic diagram showing the structure of an ink-jet apparatus according to a first embodiment of the present invention; 
         FIG. 1(B)  is a schematic diagram showing one side of a part of a line scan head in the ink-jet apparatus according to the first embodiment; 
         FIG. 1(C)  is a cross-sectional schematic diagram showing the enlarged faying surfaces of a head plate and an ink-jet head in the ink-jet apparatus according to the first embodiment; 
         FIG. 2(A)  is a schematic diagram showing the enlarged faying surface of the head plate in the ink-jet apparatus according to an example of the first embodiment; 
         FIG. 2(B)  is a schematic diagram showing the enlarged faying surface of the head plate in the ink-jet apparatus according to the example of the first embodiment; 
         FIG. 2(C)  is a schematic diagram showing the enlarged faying surface of the ink-jet head in the ink-jet apparatus according to the example of the first embodiment; 
         FIG. 3  shows another example of the relationship between the ink-jet head and the head plate in the ink-jet apparatus according to the first embodiment; 
         FIG. 4(A)  is a partial perspective view showing the shape of uneven portions in the ink-jet apparatus according to the first embodiment; 
         FIGS. 4(B) to 4(G)  are cross-sectional views showing modifications of the shape of uneven portions in the ink-jet apparatus; 
         FIG. 5  is a graph showing the relationship between an angle α formed by a line direction and a print-scan direction and a displacement from an initial position in a direction orthogonal to the print-scan direction; 
         FIG. 6  is a graph showing the relationship between a roughness machining pitch and a displacement in the direction orthogonal to the print-scan direction; 
         FIG. 7  is a graph showing the relationship between the mean roughness of the uneven portion and a displacement in the direction orthogonal to the print-scan direction; 
         FIG. 8(A)  is a schematic diagram showing a state before a printing operation of the ink-jet apparatus; 
         FIG. 8(B)  is a schematic diagram showing a state after the printing operation of the ink-jet apparatus; 
         FIG. 9  is a perspective view showing the structure of a line scan head in a conventional ink-jet apparatus; 
         FIG. 10(A)  is a side view showing the structure of the line scan head in the conventional ink-jet apparatus; and 
         FIG. 10(B)  is a perspective view showing the structure of the line scan head in the conventional ink-jet apparatus. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of the present invention will be described below with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1(A)  is a schematic diagram showing a state of a line scan head  100  viewed from a nozzle surface, that is, an ink discharge surface according to a first embodiment of the present invention. The line scan head  100  in  FIG. 1(A)  includes ink-jet heads  201 ,  202 , and  203 . 
     The ink-jet heads are sequentially disposed in parallel and at regular intervals on a head plate  101  in a direction orthogonal to a print-scan direction (X-axis direction in  FIG. 1(A) ) so as to be inclined with respect to the print-scan direction along which the line scan head  100  and a substrate move relative to each other (Y-axis direction in  FIG. 1(A) ). 
     The head plate  101  has tapped holes for fixing the ink-jet heads  201 ,  202 , and  203  placed on the head plate  101 . 
     For explanation,  FIG. 1(A)  shows a state in which the three ink-jet heads  201 ,  202 , and  203  are mounted. Actually, as shown in  FIG. 9 , the multiple ink-jet heads  51  are sequentially arranged as in the state of  FIG. 1(A) . In this case, in  FIG. 1(A) , the vertical direction along the Y-axis direction is the print-scan direction during printing while the array direction of the ink-jet heads  201 ,  202 , and  203  is the X-axis direction orthogonal to the print-scan direction. 
     In this configuration, the head plate  101  and the ink-jet head  203  are brought into contact and joined with each other in a junction region  120 . 
       FIG. 1(B)  is a schematic diagram showing a cross section of a part taken along the line a-a′ of  FIG. 1(A) . In  FIG. 1(B) , the ink-jet head  203  is temporarily fixed to the head plate  101  by screws  110  serving as fixing members. 
     As shown in  FIG. 1(B) , the ink-jet head  203  is slightly moved to a design location and is positioned thereon such that a nozzle  210  confirmed by a microscope  111  is aligned with desired coordinates. The position of the ink-jet head  203  is then fixed by fastening the screws  110 . At this point, the allocation of error for the ink-jet heads is within ±2 μm, requiring extremely high precision. 
       FIG. 2(A)  is an enlarged schematic diagram of the junction region  120  shown in  FIG. 1(A) . In  FIG. 2(A) , a region indicated by a broken line is a faying surface  130  where the head plate  101  and the ink-jet head  203  are in contact with each other. 
       FIG. 2(A)  is a top view of the ink-jet head  203  mounted on the head plate  101 . For simplification, the fastening screws are omitted. Reference numeral  112  in  FIG. 2(A)  denotes a screw hole. 
       FIG. 2(B)  shows a state in which the ink-jet head  203  is detached from the faying surface  130  of the head plate  101  shown in  FIG. 2(A) .  FIG. 2(C)  shows a faying surface  230  on the ink-jet head  203 . 
     In  FIG. 2(B) , a region indicated by a broken line is a part where the head plate  101  is in contact with the ink-jet head  203  in  FIG. 2(A) , that is, the faying surface  130 . 
     In  FIG. 2(C) , a region indicated by a broken line is a part where the ink-jet head  203  is in contact with the head plate  101  in  FIG. 2(A) , that is, the faying surface  230 . 
     In this configuration, uneven portions  140  and  240  are formed on the faying surface  230  of the ink-jet head  203  in  FIG. 2(C)  and the faying surface  130  of the head plate  101  in  FIG. 2(B) . 
     The uneven portions  140  and  240  are formed like lines (grooves) substantially in parallel with the print-scan direction of a apparatus by a predetermined device beforehand. The uneven portions  140  and  240  are linearly formed so as to extend in the print-scan direction. In this case, the uneven portions  140  and  240  are desirably formed so as to contain the regions of the faying surfaces  130  and  230 . In this example, the uneven portion  140  on the head plate  101  is formed in a region larger than the faying surfaces  130  and  230 . 
     Thus, for simplification of a machining process, the facing surfaces of the head plate  101  and the ink-jet head  203  can be entirely machined without specifying regions. 
     The uneven portions are preferably formed by, for example, grinding with a grindstone and machining with a metallic brush. Chemical polishing such as acid etching may be used for the ink-jet head  203  and the head plate  101  as long as predetermined irregularities are formed. 
       FIG. 3  shows another example of the relationship between the ink-jet head  203  and the head plate  101 . In  FIG. 3 , an ink-jet head  250  is suspended on a head plate  150  and is screwed with screws  160 . Also in this case, an uneven portion can be provided on a portion in contact with a junction region. 
     The screw hole  112  is located at the center of the faying surface  130  to evenly apply a force with the screw  110  in a lateral direction and a longitudinal direction. 
     The uneven portions  140  and  240  will be examined below.  FIG. 4(A)  shows an example of the uneven portions.  FIG. 4(A)  is a perspective view showing a part of the uneven portions  140  and  240  immediately before the uneven portions are joined to each other. The uneven portions are repeated with the same width. 
     The uneven portions  140  and  240  are identical in shape and triangular in cross section. The vertex of the uneven portion may be rounded or flattened (trapezoid). The uneven portions may be engaged with each other. The uneven portion  240  has a peak height H1 that is equal to a peak height H2 of the uneven portion  140 . The uneven portion  240  has a pitch P1 that is equal to a pitch P2 of the uneven portion  140 . The conditions of the uneven portions shaped thus are determined below. 
     The line direction of the uneven portions  140  and  240  may be in parallel with the print-scan direction or may be inclined by an angle α with respect to the print-scan direction ( FIG. 1(A) ). 
     EXAMPLE 
     The Line Direction of the Uneven Portion 
       FIG. 5  is a graph showing the relationship between the angle α formed by a line direction  350  of the uneven portions  140  and  240  and the print-scan direction and a displacement from an initial position in the direction orthogonal to the print-scan direction (X-axis direction, hereinafter will be called a sub scanning direction). The displacement is caused by a temperature change or stress relaxation after the screws of the ink-jet head  203  are fastened. 
     The angle α with respect to the print-scan direction is formed by coordinates in the print-scan direction and the line direction  350  of the uneven portions in  FIG. 1(A) . 
     As shown in  FIGS. 1 and 5 , if the angle α is 30° or less, a displacement caused by stress relaxation of the ink-jet head can satisfy the range of ±2 μm that is a required allocation of error. If the angle α exceeds 30°, however, a displacement caused by the stress relaxation of the ink-jet head rapidly increases (critical phenomenon). This is because an effect recognized in this phenomenon guides a displacement along the print-scan direction until the angle α reaches 30°, and if the angle α exceeds 30°, a movement increases in the sub scanning direction orthogonal to the print-scan direction. 
     It is understood that the angle α is an important factor for suppressing a displacement. Thus, the line direction  350  of the uneven portions  140  and  240  is desirably extended in parallel with the print-scan direction. In other words, the angle α is preferably smaller. If the angle α is at least smaller than 30°, the effect of the present invention can be obtained. 
     In this case, the uneven portion  240  and the uneven portion  140  are respectively formed on the faying surface  230  of the ink-jet head  203  and the faying surface  130  of the head plate  101 . The formation of roughness on at least one of the faying surface  230  and the faying surface  130  increases frictional resistance between the faying surfaces  130  and  230 , suppressing a movement in the sub scanning direction orthogonal to the print-scan direction. 
     If the angle α with respect to the print-scan direction is smaller than 30°, the uneven portion  240  of the faying surface  230  and the uneven portion  140  of the faying surface  130  do not always need to be formed in the same direction. 
     &lt;Pitch P of the Uneven Portion&gt; 
     The pitches of the machined uneven portions  140  and  240  will be described below.  FIG. 6  is a graph showing the relationship between a roughness machining pitch and a displacement in the sub scanning direction orthogonal to the print-scan direction. In this case, the uneven portion has a height H of 0.5 μm. 
     As shown in  FIG. 6 , an increase in machining pitch only slightly changes a displacement in the sub scanning direction orthogonal to the print-scan direction, so that a machining pitch and a displacement in the sub scanning direction orthogonal to the print-scan direction substantially change in a linear form. Thus, the machining pitch does not need to be limited as long as the faying surface  130  is machined into an uneven surface. A pitch of 50 μm or less does not cause any problems. 
     &lt;Height H of the Uneven Portion&gt; 
     The height of the machined uneven portion (a peak height and a bottom depth) will be described below.  FIG. 7  is a graph showing the relationship between the arithmetic mean roughness of the formed uneven portion and a displacement in the sub scanning direction orthogonal to the print-scan direction. At this point, the uneven portion is machined with a 10-μm pitch. 
     As shown in  FIG. 7 , a displacement in the direction orthogonal to the print-scan direction increases with arithmetic mean roughness. The displacement considerably increases particularly in a region where the arithmetic mean roughness exceeds 10 μm (critical phenomenon). This is because surface roughness on the faying surfaces  130  and  230  does not lead to resistance against a moving stress in the sub scanning direction orthogonal to the print-scan direction and rapidly increases a movement over the uneven portion. Hence, the arithmetic mean roughness of the faying surface needs to be set at 10 μm or less. 
     In  FIG. 4(A) , the uneven portions are triangular in cross section. The shape of the uneven portion is not particularly limited. Alternatively, the uneven portions  140  and  240  may not be identical in shape as will be examined below: 
       FIG. 4(B)  is a cross-sectional view of the uneven portions  140  and  240 . In  FIG. 4(B) , the uneven portions are rectangular in cross section. In this case, for the engagement of the uneven portions  140  and  240 , a concave needs to be larger in width than a convex. 
     The uneven portions  140  and  240  in  FIGS. 4(C) to 4(G)  vary in shape unlike in  FIGS. 4(A) and 4(B) . Specifically, in  FIGS. 4(C) to 4(G) , the uneven portions  140  and  240  do not both have convexes and concaves. One of the uneven portions  140  and  240  has concaves while the other uneven portion has convexes. 
       FIG. 4(C)  is a cross-sectional view of the uneven portions  140  and  240 . The uneven portion  240  has convexes that are triangular in cross section while the uneven portion  140  has concaves that are triangular in cross section. The convexes and the concaves are engaged with each other. As in  FIG. 4(A) , the vertexes of the triangles may be rounded or flattened (trapezoid). 
       FIG. 4(D)  is a cross-sectional view of the uneven portions  140  and  240 . The uneven portion  240  has convexes that are rectangular in cross section while the uneven portion  140  has concaves that are rectangular in cross section. The convexes and the concaves are engaged with each other. As in  FIG. 4(B) , for the engagement of the concaves and the convexes, the concave needs to be larger in width than the convex. 
       FIG. 4(E)  shows a modification of  FIG. 4(C) .  FIG. 4(E)  is different from  FIG. 4(C)  in the cross-sectional shape of the uneven portion  140  and the cross-sectional shape of the uneven portion  240 . Specifically, in  FIG. 4(E) , the triangular concave of the uneven portion  140  in cross section has a larger spread angle than that of the triangular convex of the uneven portion  240  in cross section. Thus, the uneven portions  140  and  240  are easily engaged with each other. 
       FIG. 4(F)  is a modification of  FIG. 4(D) .  FIG. 4(F)  is different from  FIG. 4(D)  in the cross-sectional shape of the uneven portion  140  and the cross-sectional shape of the uneven portion  240 . Specifically, in  FIG. 4(F) , the rectangular concave of the uneven portion  140  in cross section is larger in width than the rectangular convex of the uneven portion  240  in cross section. Thus, the uneven portions  140  and  240  are easily engaged with each other. 
     In  FIG. 4(G) , the cross-sectional shape of the uneven portion  140  having concaves is considerably different from that of the uneven portion  240  having convexes. The uneven portion  240  having the triangular convexes in cross section and the uneven portion  140  having the rectangular concaves in cross section are easily engaged with each other. The uneven portion  240  having the convexes needs to be fit into the uneven portion  140  having the concaves. 
     In  FIGS. 4(C) to 4(G) , the shapes of the uneven portion  140  and the uneven portion  240  may be changed with each other. 
     Also in  FIGS. 4(B) to 4(G) , as in  FIG. 4(A) , the pitch P of the convexes may be 50 μm or less and the height H of the convexes may be 10 μm or less. 
     (Summary) 
     In installation of ink-jet heads constituting a line scan head, a stress is concentrated on the ink-jet heads and the installation locations of the ink-jet heads by, for example, an external thermal stress and a stress reduced by unloading after positioning, resulting in a displacement. However, if a line scan head has a rough faying surface as in the present invention, a load generated on a fixing member causes the faying surface to act as a sliding surface having anisotropy. 
     Specifically, according to irregularities formed on a substrate in a print-scan direction, the coordinates of the irregularities move in the print-scan direction. Conversely, a possible displacement can be minimized in a sub scanning direction orthogonal to the print-scan direction. A possible displacement is positively guided in the print-scan direction, minimizing the influence in the sub scanning direction orthogonal to the print-scan direction so as to relax a generated stress. 
     A displacement in the print-scan direction can be easily corrected by adjusting timing for discharging ink droplets from the ink-jet heads during scanning. This can keep the accuracy of printing without causing any problems in production. 
     The ink-jet apparatus of the present invention is applicable to a light-emitting material of an organic electroluminescence device, a hole transport layer, printing of an electron transport layer, printing of a color filter, and so on.