Patent Publication Number: US-2012037023-A1

Title: Offset printing method and apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an offset printing apparatus and an offset printing method used for performing fine printing on a print target with high print precision, such as in the case where an electrode pattern is formed on a substrate by printing. 
     Priority is claimed on Japanese Patent Application No. 2009-105385, filed on Apr. 23, 2009, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     As one of the printing techniques, there is known an offset printing technique. This type of technique includes offset printing using an intaglio plate, in which ink is transferred (received) from an inked intaglio plate to a rolling blanket roller and then the ink is retransferred (printed) from the blanket roller to the print target. This method is known to be capable of printing a print pattern of the intaglio plate onto the surface of the print target with good repeatability. 
     In recent years, there have been proposed techniques for forming an electrode pattern (a conductive pattern) such as for liquid crystal displays on a required substrate such as a glass substrate or a substrate made from a resin. As one of them, there is a printing technique of using a conductive paste as printing ink instead of fine machining of a metal vapor-deposited film by etching or the like. As this printing technique, there have been proposed a technique of printing and forming an electrode pattern on a substrate by use of, for example, an intaglio offset printing technique (see Patent Document 1 and Patent Document 2). 
     When the aforementioned electrode pattern such as for liquid crystal displays is formed on a substrate, there are cases where a fine electrode width of, for example, approximately 10 μm is required. In addition, there are cases where a plurality of electrode patterns are formed on a substrate in an overlapping manner. In such cases, electrode patterns are overprinted while the plates are replaced. However, displacement of a printing position results in a spoiled electrode pattern. Therefore, for printing a precise electrode pattern such as one with an electrode width of approximately 10 μm as described above (although the print precision is slightly different according to the print target), it is sometimes required that the displacement of the printing position by the overlap be suppressed to several μm. Therefore, the printing of the electrode pattern on a substrate as described above requires print precision higher than that for the typical intaglio-plate offset printing which prints letters, characters, and images on paper or the like. 
     Conventionally, there have been proposed the following construction and method in order to increase the print precision of the offset printing. For example, as shown in  FIG. 7 , sliders  5  and  6  are secured, in the same size and the same arrangement, respectively to the lower sides of a plate carriage (plate table)  2 , which supports a plate bed (not shown in the figure) for mounting a flat plate  1 , and a print carriage (print target table)  4 , which supports a printing bed (not shown in the figure) for mounting a glass substrate  3  as a print target (material to be printed). On the same rails (guide rails)  7 , the plate carriage  2  and the print carriage  4  are moved (reciprocated) respectively via the sliders  5  and  6 . In addition, a blanket cylinder (blanket roller)  8  is installed so as to cross the rails  7 . 
     With such a construction, the straightness of the rails  7  is decreased directly beneath the blanket cylinder  8 . As a result, even if the plate carriage  2  and the print carriage  4  are inclined in attitude at this position, both carriages  2  and  4  have the same inclination. Namely, attitudinal errors of a plate  1  and a glass substrate  3  are suppressed. This allows the transfer (resin transition) between the plate  1  and the blanket cylinder  8  to be performed at the same position as that of the re-transfer (picture transfer) from the blanket cylinder  8  to the glass substrate  3 , it is possible to increase print precision. 
     When a plate  1  is mounted on the plate bed (not shown in the figure) supported by the plate carriage  2 , markers, back plates, grooves, or other jigs are used as a benchmark. Furthermore, when a glass substrate  3  as a material to be printed is mounted on the printing bed (not shown in the figure) supported by the print carriage  4 , jigs or the like are used as a benchmark (see Patent Document 3). 
     In addition, to increase print precision of the offset printing, another method as described below is available. An offset printer includes: a moving table on the upper surface of which an intaglio plate and a work piece as a print target are held; a blanket roller for transfer (rolling blanket) that is arranged above the moving table; two drive mechanisms one of which independently drives the moving table and the other independently drives the blanket roller; and two numerical value controllers one of which independently controls the drive mechanism for the moving table and the other independently controls the drive mechanism for the blanket roller. Furthermore, while movement of the moving table on which the intaglio plate and the work piece are held and rotation of the blanket roller are performed independently of each other, the operator finely adjusts the peripheral velocity of the blanket roller through manual input. This increases the precision of transfer (reception) from the intaglio plate to the blanket roller and of re-transfer (printing) from the blanket roller to the work piece (see Patent Document 4). 
     In typical offset printing, as schematically shown in  FIG. 8 , when transfer is performed between a blanket roller  9  and a flat-table-like plate  10  held on a plate table (not shown in the figure), and also when transfer or re-transfer is performed between the blanket roller  9  and a flat-table-like print target  11  held on a print target table (not shown in the figure), the blanket roller  9  is adapted to be pressed against the plate  10  or the print target  11  with a predetermined contact pressure (printing pressure). The blanket roller  9  has a surface of its peripheral wall made from a material with required elasticity such as required rubber. Therefore, at the time of the transfer or the re-transfer, the contact portion of the blanket roller  9  with the plate  10  or the print target  11 , on which the predetermined contact pressure is applied, is deformed along the surface of the plate  10  or the print target  11 . 
     To address this, the shape (planar shape) of a roller contact region  12  of the plate  10  or the print target  11  when the roller contact region  12  is contacted by the blanket roller  9  is an elongated rectangular region extending in the direction of the shaft center of the blanket roller  9  with a predetermined width (nip width) A in the direction orthogonal to the shaft center of the blanket roller  9  as shown by single-dot chain lines in  FIG. 9 . 
     DOCUMENTS OF THE PRIOR ART 
     Patent Document 1: Japanese Patent No. 2797567 
     Patent Document 2: Japanese Patent No. 3904433 
     Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2008-129362 
     Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2000-272079 
     PROBLEMS TO BE SOLVED BY THE INVENTION 
     However, for an electrode pattern such as for liquid crystal displays, there are cases where a fine electrode width of approximately 10 μm is required to be formed by printing, and also cases where the displacement of printing position by the overlap when the electrode patterns are overprinted is required to be suppressed to several μm, as described above. Therefore, in the method in which jigs or the like are used as a benchmark when a glass substrate  3  as a material to be printed is mounted onto the printing bed (not shown in the figure) supported by the print carriage  4  as shown in Patent Document 3, it is difficult to always obtain the repeatability of the attachment position of a glass substrate  3 , which will be mounted newly onto the printing bed, with such accuracy as to suppress a positional error to the order of micrometers. 
     Furthermore, in the case of replacing the plate  1 , even if, for example, markers, back plates, grooves, or other jigs are used for registration marks for a plate  1  to be mounted onto the plate bed (not shown in the figure) supported by the plate carriage  2 , it is difficult to obtain the repeatability of the attachment position of a replacement plate to be mounted onto the plate bed with such accuracy as to suppress a positional error to the order of micrometers. In addition, the plate  1  may suffer from a displacement of printing position at the time of inking or transfer to the blanket cylinder  8 . 
     Therefore, in the method shown in Patent Document 3, it is difficult to obtain highly precise repeatability of printing position at the time of offset printing. 
     Furthermore, in the method shown in Patent Document 3, even if there is a decrease in straightness of the rails  7  directly beneath the blanket cylinder  8 , the transfer between the plate  1  and the blanket cylinder  8  is performed at the same position as that of the re-transfer from the blanket cylinder  8  to the glass substrate  3 . However, the print precision may be decreased as a result of the print pattern lines being changed in thickness or the line being blurred. 
     Namely, as shown in  FIG. 9 , when offset printing is performed, the roller contact region  12  at which the plate  10  or the print target  11  is to be brought into contact with the blanket roller  9  has a predetermined width A in the direction orthogonal to the shaft center of the blanket roller  9 . 
     On the other hand, as shown in  FIG. 10A , in the case where, due to a decrease in straightness of the guide rails (not shown in the figure) for guiding a plate table (not shown in the figure) supporting the plate  10  and a print target table (not shown in the figure) supporting the print target  11 , a table moving direction  13  (denoted with an arrow in the figure) of the plate table or the print target table directly beneath the blanket roller  9  is not precisely directed in the direction orthogonal to the shaft center of the blanket roller  9 , for example in the case where the table moving direction  13  is inclined from the direction orthogonal to the shaft center of the blanket roller  9  by an inclination angle of B (in  FIG. 10A , the inclination angle B is emphasized for the sake of convenience.), the following possibilities arise. The plate  10  and the print target  11  come to move along the table moving direction  13  beneath the blanket roller  9 . Therefore, at the time of transfer of the print pattern from the plate  10  to the blanket roller  9  and the re-transfer of the print pattern from the blanket roller  9  to the substrate  11 , a given site (point) of the plate or the print target  11  moving along the table moving direction  13  starts to contact the blanket roller  9  at a contact start position P 0 , moves through the roller contact region  12  with the width A along the table moving direction  13 , and then leaves the blanket roller  9  at a contact end position P 1 , as shown in  FIG. 10B . During this, a lateral displacement of the table moving direction  13  is caused in the direction of the shaft center of the blanket roller  9  by the dimension computed by multiplying A by tan B. Due to this lateral displacement, there is a possibility of the print pattern lines becoming thicker or blurred. In the case of printing a precise print pattern such as an electrode pattern with an electrode width of 10 μm, there is a possibility of insufficient print precision. 
     Furthermore, during the time when the plate  10  or the print target  11  is in contact with the blanket roller  9  while moving along the table moving direction  13  inclined from the direction orthogonal to the shaft center of the blanket roller  9 , a force other than that in the vertical direction (the direction in which the blanket roller  9  is pressed) acts between the plate  10  or the print target  11  and the blanket roller  9 . The action of this force may further decrease the repeatability of the precise print pattern. 
     The method shown in Patent Document 4 makes it possible to improve print precision by adjusting the peripheral velocity of the blanket roller through manual input. However, if the blanket roller is decentered, there is a change in peripheral velocity while the blanket roller rotates 360 degrees even if the rotational speed of the blanket roller is constant. Therefore, it is difficult to synchronize the peripheral velocity of the blanket roller and the moving speed of the intaglio plate held on the moving table or the work piece as a print target held on the moving table, resulting in difficulty in uniform transfer. 
     DISCLOSURE OF INVENTION 
     Therefore, the present invention has an object to provide an offset printing method and an offset printing apparatus as follows. The present invention is capable of aligning a position of a plate held on a plate table with a position of a print target held on a print target table with high accuracy, thus increasing the repeatability of the printing position. Further more, even if the straightness of the guide rails for guiding the travel of the plate table and the print target table is decreased directly beneath the blanket roller, the present invention prevents a possibility of the print pattern lines becoming thicker or blurred, making it possible to obtain high repeatability. Furthermore, even if the blanket roller is decentered, the present invention is capable of easily synchronizing the peripheral velocity of the blanket roller and the moving speed of the plate or the print target in contact with the blanket roller. Thereby, it is possible to increase print precision. In particular, it is possible to print a fine pattern such as an electrode pattern with high precision. In addition, even in the case of overprinting, it is possible to suppress the displacement of the printing position by the overlap to the order of micrometers. 
     To solve the above problems, the present invention adopts the following. An offset printing method of the present invention brings a blanket roller from above into contact with a plate held on a plate table traveling on guide rails on a mount, and then brings the blanket roller from above into contact with a print target held on a print target table traveling on the guide rails, to thereby perform transfer of a print pattern from the plate to the blanket roller and re-transfer of the print pattern from the blanket roller to the print target. Furthermore, the offset printing method of the present invention includes the steps of: causing a plate to be held on an alignment stage provided on an upper portion of the plate table and also causing a print target to be held on an alignment stage provided on an upper portion of the print target table; and correcting a position of the plate by the alignment stage of the plate table and also correcting a position of the print target by the alignment stage of the print target table. Furthermore, in the step of correcting the positions of the plate and the print target, if table moving directions of the plate table and the print target table are not along a direction orthogonal to a shaft center of the blanket roller when the plate table and the print target table pass directly beneath the blanket roller, then the positions of the plate and the print target are corrected so that the plate table and the print target table pass directly beneath the blanket roller and also so that the plate and the print target are moved along the direction orthogonal to the shaft center of the blanket roller by the alignment stages of the plate table and the print target table As a result, after a print pattern is transferred from the plate to the blanket roller, positions of the print pattern are made identical at every re-transfer from the blanket roller to the print target. 
     In the offset printing method of the present invention, an initial alignment may be performed on every plate held on the alignment stage of the plate table and also on every print target held on the alignment stage of the print target table so that the plates and the print targets are respectively put in the same arrangement in a same alignment area provided at a predetermined site on the mount. 
     In the offset printing method of the present invention, if the blanket roller is decentered, a moving speed of the plate table on the alignment stage may be synchronized with a peripheral velocity in accordance with an apparent radius of the blanket roller from a center of rotation thereof to a peripheral position at a lowest end of a peripheral surface thereof when the plate table passes directly beneath the blanket roller. Furthermore, a moving speed of the print target on the alignment stage of the print target table may be synchronized with a peripheral velocity in accordance with an apparent radius of the blanket roller from a center of rotation thereof to a peripheral position at a lowest end of a peripheral surface thereof when the print target table passes directly beneath the blanket roller. 
     An offset printing apparatus of the present invention includes a plate table and a print target table that travel on guide rails provided on a mount, wherein a blanket roller is brought from above into contact sequentially with a plate held on the plate table and a print target held on the print target table, to thereby perform transfer of a print pattern from the plate to the blanket roller and re-transfer of the print pattern from the blanket roller to the print target. The offset printing apparatus further includes: an alignment stage provided on an upper portion of the plate table for supporting the plate from below; an alignment stage provided on an upper portion of the print target table for supporting the print target from below; and a controller for controlling the alignment stages of the tables. 
     In the offset printing apparatus of the present invention, an alignment area including alignment sensors may be provided at a predetermined site on the mount. Furthermore, the controller may include a function of giving a command to the alignment stage of the plate table so that an arrangement of the plate, which is detected by the alignment sensors, held on the alignment stage of the plate table arranged at a predetermined alignment position in the alignment area matches a predetermined arrangement. The controller may include a function of giving a command to the alignment stage of the print target table so that an arrangement of the print target, which is detected by the alignment sensors, held on the alignment stage of the print target table arranged at a predetermined alignment position in the alignment area matches a predetermined arrangement. 
     In the offset printing apparatus of the present invention, the controller may include data on displacement of a table moving direction from a direction orthogonal to a shaft center of the blanket roller resulting from a decrease in straightness of guide rails directly beneath the blanket roller. The controller may include a function of giving a command to the alignment stage of the plate table when the plate table passes directly beneath the blanket roller, to thereby correct a position of the plate so that the plate moves along the direction orthogonal to the shaft center of the blanket roller. The controller may include a function of giving a command to the alignment stage of the print target table when the print target table passes directly beneath the blanket roller, to thereby correct a position of the print target so that the print target moves along the direction orthogonal to the shaft center of the blanket roller. 
     In the offset printing apparatus of the present invention, the controller may include data on rotation angles of a decentered blanket roller and on a change in apparent radius of the blanket roller from a center of rotation thereof to a peripheral position at a lowest end of a peripheral surface thereof. The controller may include a function of providing, when the plate table passes directly beneath the blanket roller, the alignment stage of the plate table with a command to shift in a forward-rearward direction in a table traveling direction, to thereby synchronize a moving speed of the plate held on the alignment stage with a peripheral velocity of the decentered blanket roller at a lowest end of a peripheral surface thereof. The controller may include a function of providing, when the print target table passes directly beneath the blanket roller, the alignment stage of the print target table with a command to shift in the forward-rearward direction in the table moving direction, to thereby synchronize a moving speed of the print target held on the alignment stage with the peripheral velocity of the decentered blanket roller at the lowest end of the peripheral surface thereof. 
     EFFECTS OF THE INVENTION 
     According to the present invention, excellent advantageous effects as follows are obtained. 
     (1) According to the present invention, firstly a blanket roller is brought from above into contact with a plate held on a plate table traveling on guide rails on a mount. Subsequently, the blanket roller is brought from above into contact with a print target held on a print target table traveling on the guide rails. As a result, in the offset printing method of performing transfer from the plate to the blanket roller and re-transfer from the blanket roller to the print target, with the plate being held on the alignment stage provided on an upper portion of the plate table and with the print target being held on the alignment stage provided on an upper portion of the print target table, a positional correction of the plate by the alignment stage of the plate table and a positional correction of the print target by the alignment stage of the print target table are performed. In the positional corrections of the plate and the print target, if a table moving direction when the plate table and the print target table moving along the guide rails pass directly beneath the blanket roller is not along a direction orthogonal to a shaft center of the blanket roller, the table moving direction is corrected. When the plate table passes directly beneath the blanket roller, the position of the plate is corrected by the alignment stage of the plate table, and the plate is moved along the direction orthogonal to the shaft center of the blanket roller. In addition, when the print target table passes directly beneath the blanket roller, the position of the print target is corrected by the alignment stage of the print target table, and the print target is moved along the direction orthogonal to the shaft center of the blanket roller. 
     As a result, even if the straightness of the guide rails for guiding the travel of the plate table and the print target table is decreased directly beneath the blanket roller, it is possible to prevent the possibility of every part of the plate or the print target slipping laterally with respect to the moving direction of the plate table and the print target table from the time when the part starts to contact the blanket roller till the time when the part leaves the blanket roller. Therefore, after a print pattern is transferred from the plate to the blanket roller, it is possible to prevent the lines of the print pattern re-transferred from the blanket roller to the print target from becoming thicker or faded. Thus, it is possible to increase the repeatability of the print pattern. 
     Thus, in the present invention, the positions of the print pattern re-transferred from the blanket roller to the print target after it is transferred from the plate to the blanket roller are the same every time. 
     In particular, it is possible to always make the position of the plate relative to the plate table the same without an influence of an error in the attachment position of the plate table to the alignment stage. Furthermore, it is possible to always make the arrangement of the print target relative to the print target table the same without an influence of an error in the attachment position of the print target to the alignment stage of the print target table. 
     As a result, it is possible to increase the repeatability of the printing position. 
     (2) According to the present invention, for every plate held on the alignment stage of the plate table and for every substrate held on the alignment stage of the print target table, an initial alignment is performed so that the plate and the substrate are in the same arrangement in the same alignment area provided at a predetermined site on the mount. 
     As a result, every time, it is possible to make the relative arrangement the same between the position of the plate when an alignment is performed in the alignment area and the position of the print target when an alignment is performed in the alignment area. Therefore, it is possible to print the print pattern of the plate onto the print target with highly precise positional repeatability. 
     (3) According to the present invention, if the blanket roller is decentered, the moving speed of the plate on the alignment stage of the plate table is synchronized, when the plate table passes directly beneath the blanket roller, with the peripheral velocity in accordance with an apparent radius of the blanket roller from its center of rotation to the peripheral point at the lowest end of its peripheral surface. Furthermore, also when the print target table passes directly beneath the blanket roller, the moving speed of the print target on the alignment stage of the print target table is synchronized with the peripheral velocity in accordance with the apparent radius of the blanket roller from its center of rotation to the peripheral point at the lowest end of its peripheral surface. 
     As a result, even if there is a change in peripheral velocity of the blanket roller while the blanket roller is rotated due to the decentering of the blanket roller, it is possible to move the plate or the substrate at a moving speed in synchronicity with that of the blanket roller. Thereby, it is possible to increase the repeatability of the print pattern. 
     (4) Thus, printing with high repeatability of a printing position and with high repeatability of a print pattern is performed on print targets, to thereby make it possible to print a precise print pattern such as an electrode pattern onto the print targets precisely and with high repeatability. Furthermore, even if a precise print pattern such as an electrode pattern is overprinted onto a print target, it is possible to suppress displacement in the overlap. Accordingly, it is possible to perform precise printing capable of suppressing displacement in the overlap to the order of micrometers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view showing a main part of a first embodiment of an offset printing method and an offset printing apparatus according to the present invention. 
         FIG. 2  is a schematic side view showing a whole construction of the offset printing apparatus of  FIG. 1 . 
         FIG. 3  is an enlarged view of  FIG. 2  taken along the I-I arrow. 
         FIG. 4  is a schematic diagram showing a control configuration of a controller provided in the offset printing apparatus of  FIG. 1 . 
         FIG. 5  is a diagram schematically showing a controlling method of an alignment stage of each table in the offset printing apparatus of  FIG. 1  in the case where a moving direction of each table directly beneath a blanket roller is inclined from a direction orthogonal to a shaft center of the blanket roller. 
         FIG. 6  is a diagram showing a schematic controlling method of the alignment stages of the tables in the case where a blanket roller is decentered in the offset printing apparatus of  FIG. 1 . 
         FIG. 7  is a plan view schematically showing a method for improving print precision of the offset printing as a method conventionally proposed. 
         FIG. 8  is a schematic side view showing a state of the offset printing in which the blanket roller is in contact with a flat-table-like plate held on a plate table or with a print target held on a print target table. 
         FIG. 9  is a schematic plan view showing a roller contact region of a plate or a print target to be in contact with the blanket roller. 
         FIG. 10A  is a plan view schematically showing a moving direction of the plate table or the print target table in the case where the table is inclined from a direction orthogonal to the shaft center of the blanket roller as a result of a decrease in straightness of guide rails directly beneath the blanket roller. 
         FIG. 10B  is an enlarged view of the roller contact region of the plate or the print target held on the plate table or the print target table in the case where the moving direction of the table is inclined from a direction orthogonal to the shaft center of the blanket roller as a result of a decrease in straightness of the guide rails directly beneath the blanket roller. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereunder is a description of an embodiment of the present invention with reference to the drawings. 
       FIG. 1  to  FIG. 6  show an embodiment of an offset printing method and an offset printing apparatus according to the present invention. 
     As shown in  FIG. 1  to  FIG. 3 , guide rails  15  (for example, a set of two rails) extending in one direction (in the x axis direction) are provided on the upper side of a horizontal mount  14 . On the guide rails  15 , a plate table  16  and a substrate table  17  (print target table) are slidably attached each via a set of guide blocks  15   a  so as to be arranged in this order from a first end side of the guide rails  15  in the longitudinal direction (from the left side in  FIG. 1  and  FIG. 2 ). 
     The tables  16 ,  17  each include a drive device  18  such as a linear motor, and are capable of reciprocating (traveling) along the guide rails  15  independently of each other. In addition, with a common linear scale  19  provided along the guide rails  15  at a predetermined site on the mount  14 , it is possible to detect positions of the plate table  16  and the substrate table  17  in the longitudinal direction of the guide rails  15 , that is, absolute positions (coordinates) of the plate table  16  and the substrate table  17  relative to a predetermined point in the X axis direction. 
     On an upper portion of the plate table  16 , there is provided an alignment stage  16   a  allowing for a horizontal movement in the longitudinal direction of the guide rails  15  (in the X axis direction) and in the direction orthogonal to the longitudinal direction of the guide rails  15  (in the Y axis direction), and also allowing for a rotation in the yaw angle (θ) with respect to the longitudinal direction of the guide rails  15 . With this, it is possible to hold a plate  10  on an upper side of the alignment stage  16   a.    
     In addition, similarly to the alignment stage  16   a  of the plate table  16 , on an upper portion of the substrate table  17 , there is provided an alignment stage  17   a  allowing for a horizontal movement in the X axis direction and the Y axis direction, and also a rotation in the yaw angle (θ). With this, it is possible to hold, for example, a substrate  11  (denoted with the same reference numeral as that for the print target  11 , for the sake of convenience) as a print target  11  on an upper surface of the alignment stage  17   a.    
     In a middle portion in the longitudinal direction of the guide rails  15  on the mount  14 , there is provided a transfer mechanism portion  20  including: a blanket roller  9 , which is arranged along the direction orthogonal to the longitudinal direction of the guide rails  15  (along the Y axis direction) so as to cross above the guide rails  15 ; a raising-lowering actuator  21  for raising/lowering the blanket roller  9 ; and a drive motor  22  for rotatingly driving the blanket roller  9 . 
     Furthermore, at a predetermined site on the mount  14 , for example at a site spaced a predetermined distance away from the transfer mechanism portion  20  to a second end side in the longitudinal direction of the guide rails  15 , there is provided an alignment area  23  in which common alignment sensors  24  are used to align the plate  10  held on the alignment stage  16   a  of the plate table  16  and also to align the substrate  11  held on the alignment stage  17   a  of the substrate table  17 . 
     As shown in  FIG. 3 , the offset printing apparatus of the present invention further includes a controller (control device)  25  for giving commands to the alignment stages  16   a,    17   a  respectively on the tables  16 ,  17  based on detection signals, which are input from the linear scale  19 , for the positions of the plate table  16  and the substrate table  17  in the longitudinal direction of the guide rails  15  and also based on signals that are input from the alignment sensors  24 . 
     The offset printing apparatus of the present invention is required to perform offset printing. Therefore, as shown in  FIG. 2 , there is provided a plate table waiting area  26  at a site corresponding to first ends in the longitudinal direction of the guide rails  15  on the mount  14 . The plate table waiting area  26  is for keeping waiting the plate table  16 , which has been moved to the first ends in the longitudinal direction of the guide rails  15 . The offset printing apparatus of the present invention further includes an inking device  27  above the mount  14  between the plate table waiting area  26  and the transfer mechanism portion  20 . The inking device  27  is for inking the plate  10  held on the alignment stage  16   a  of the plate table  16 . The offset printing apparatus of the present invention further includes a substrate installation area  28  at a site on the mount  14  corresponding to second ends in the longitudinal direction of the guide rails  15 . The substrate installation area  28  is for attaching a new substrate  11  to the alignment stage  17   a  of the substrate table  17  and removing a substrate  11  after printing while the substrate table  17  is kept waiting at the second ends in the longitudinal direction of the guide rails  15  after the substrate table  17  is moved to the second end. 
     In more detail, as shown in  FIG. 1  and  FIG. 2 , a support mount  29  and precision cameras  24  (denoted with the same reference numeral as that for the alignment sensors  24 ) as alignment sensors  24  provided on the support mount  29  are provided above the alignment area  23  so as to face downwardly. The support mount  29  allows the plate table  16  and the substrate table  17  traveling along the guide rails  15  to pass therebeneath. The precision cameras  24  are provided so as to correspond to two opposing corners or four corners of the plate  10  held on the alignment stage  16   a  of the plate table  16 , and also of the substrate  11  held on the alignment stage  17   a  of the substrate table  17 . In  FIG. 1 , the precision cameras  24  are provided at four sites corresponding to the four corners of the plate  10  and the substrate  11 . 
     As shown in  FIG. 4 , based on table position detection signals S 1 , for each of the plate table  16  and the substrate table  17 , which have been input from the linear scale  19  provided on the mount  14 , the controller  25  gives a control command C 1  corresponding table position detection signal to the respective drive devices  18  of the plate table  16  and the substrate table  17 . As a result, it is possible to control the positions of the tables  16 ,  17  in the longitudinal direction of the guide rails  15  (in the X axis direction). The controller  25  further includes a table traveling control portion  25   a  capable of controlling a moving direction (traveling direction) and a moving speed (traveling velocity) of the tables  16 ,  17  by controlling the direction of the positional change (an increase/decrease in the X axis direction) and the amount of positional change per unit time when the positions of the tables  16 ,  17  are changed in the X axis direction. 
     The controller  25  further includes an alignment stage control portion  25   b  having a function of giving a correction command for correcting a sensor feedback to the plate table  16  and the substrate table  17  in the following manner. Firstly, in a state with the plate table  16  being arranged at a predetermined alignment position preset in the alignment area  23 , the precision cameras  24  as the alignment sensors provided on the support mount  29  detect pointing markers (not shown in the figure) provided on the opposing corners or the four corners of the plate  10  held on the plate table  16 . When signals S 2  of the image are input from the precision cameras  24  to the alignment stage control portion  25   b,  the alignment stage control portion  25   b  gives a correction command C 2  to the alignment stage  16   a  of the plate table  16 . With the correction command C 2 , a sensor feedback alignment correction is performed so that the positions of the pointing markers detected by the precision cameras  24  match the preset positions. Similarly, in a state with the substrate table  17  being arranged at the predetermined alignment position, the precision cameras  24  detect pointing markers (not shown in the figure) provided on the opposing corners or the four corners of the substrate  11  held on the substrate table  17 . When signals S 2  of the image are input from the precision cameras  24  to the alignment stage control portion  25   b,  the alignment stage control portion  25   b  gives a correction command C 3  to the alignment stage  17   a  of the substrate table  17 . With the correction command C 3 , a sensor feedback alignment correction is performed so that the positions of the pointing markers detected by the precision cameras  24  match the preset positions. Note that the controller  25  is capable of associating the alignment stage control portion  25   b  with the table traveling control portion  25   a  to control the sensor feedback alignment correction. 
     Therefore, to align the plate  10  held on the alignment stage  16   a  of the plate table  16 , the following operations are performed. Firstly, alignment markers (not shown in the figure) are pointed in advance on the opposing corners or the four corners of the plate  10 . Next, in a state with the plate  10  being held on the alignment stage  16   a  of the plate table  16 , a function of the table traveling control portion  25   a  of the controller  25  is used to move the plate table  16  to the alignment area  23  and stop the plate table  16  at the predetermined alignment position. After that, based on a function of the alignment stage control portion  25   b  of the controller  25 , the positions of the alignment markers (not shown in the figure) on the opposing corners or the four corners of the plate  10  detected by the precision cameras  24  in the alignment area  23  are corrected to the preset positions through the horizontal movement in the X axis direction and the Y axis direction and through the rotation in the yaw angle (θ) of the alignment stage  16   a  of the plate table  16 . This makes it possible to render the position of the plate  10  relative to the plate table  16  always the same without an error in the attachment position of the plate  10  with respect to the alignment stage  16   a.  In the case of replacing a plate for overprinting and also in the case of replacing a plate  10  worn (consumed) through use for a printing treatment with a new plate  10 , an alignment of the plate  10  is performed every time it is replaced. Furthermore, a specified plate  10  may be aligned regularly for every predetermined number of printing times, or for every predetermined period of printing time. 
     When an initial alignment is performed on a substrate  11  held on the substrate table  17 , the following operations are performed. Firstly, alignment markers (not shown in the figure) are pointed in advance on the opposing corners or the four corners of the substrate  11  to be used. Next, in a state with a substrate  11  to be used as a new print target being attached to and held on the alignment stage  17   a  of the substrate table  17  in the substrate installation area  28 , a function of the table traveling control portion  25   a  of the controller  25  is used to move the substrate table  17  to the alignment area  23  and stop the substrate table  17  at the predetermined alignment position. After that, based on a function of the alignment stage control portion  25   b  of the controller  25 , the positions of the alignment markers (not shown in the figure) on the opposing corners or the four corners of the substrate  11  detected by the precision cameras  24  in the alignment area  23  are corrected to the preset positions through the horizontal movement in the X axis direction and the Y axis direction and through the rotation in the yaw angle (θ) of the alignment stage  17   a  of the substrate table  17 . This makes it possible to render the position of the substrate  11  relative to the substrate table  17  always the same without an error in the attachment position of the substrate  11  with respect to the alignment stage  17   a.  Therefore, it is possible to make the position of the substrate  11  when an initial alignment is performed thereon in the alignment area  23  relative to the position of the plate  10  when an initial alignment is performed thereon in the alignment area  23  always the same for every substrate  11 . Consequently, after transfer of a print pattern to the blanket roller  9  by the plate  10 , the print pattern can be re-transferred to the target position on the substrate  11  by the blanket roller  9  with high precision and also with high repeatability. 
     In the case where importance is attached to prevention of displacement of print patterns when overprinting is performed on a substrate  11  as a print target without requiring rigid repeatability of the first-layer print pattern for every substrate  11  as a print target, alignment markers may be pointed on the opposing corners or the four corners of the substrate  11  when a first printing is performed on the substrate  11  instead of pointing the alignment markers in advance on the opposing corners or the four corners of the substrate  11 . In this case, an initial alignment need not be performed on the substrate  11  held on the substrate table  17  before the first printing is performed thereon. 
     The controller  25  further includes a database  30  in which is already stored data on the lowering in straightness of a portion of the transfer mechanism portion  20  arranged directly beneath the blanket roller  9  in the longitudinal direction of the guide rails  15 , namely, data on inclination angles of the portion of the guide rails  15  from the direction orthogonal to the shaft center of the blanket roller  9 . Furthermore, when the plate table  16  and the substrate table  17  travels directly beneath the blanket roller  9  of the transfer mechanism portion  20  by use of a function of the table traveling control portion  25   a,  the controller  25  uses the alignment stage control portion  25   b  to give a correction command to the alignment stages  16   a,    17   a  respectively of the tables  16 ,  17  based on the data in the database  30 . 
     To be more specific, such a case is one as shown for example in  FIG. 5 , in which the guide rails  15  (see  FIG. 1  and  FIG. 2 ) are inclined, directly beneath the blanket roller  9 , from the direction orthogonal to the shaft center of the blanket roller  9  by an inclination angle of B. In particular, in the case where table moving direction  13  (denoted with an arrow in the figure) of the plate table  16  or the substrate table  17  is inclined from the direction orthogonal to the shaft center of the blanket roller  9  by an inclination angle of B, the controller  25  associates the table traveling control portion  25   a  with the alignment stage control portion  25   b.  As a result, when transfer from the plate  10  to the blanket roller  9  and re-transfer from the blanket roller  9  to the substrate  11  are performed by causing the plate table  16  and the substrate table  17  to travel directly beneath the blanket roller  9 , a correction command is given to the alignment stages  16   a,    17   a  respectively of the tables  16 ,  17 . Thereby, while the tables  16 ,  17  are advanced a unit distance in the X axis direction, the positions of the alignment stages  16   a,    17   a  are sequentially corrected by tanB to the direction opposite to the direction in which the table moving direction  13  is inclined from the direction orthogonal to the shaft center of the blanket roller  9  (from the X axis direction). In  FIG. 5 , the inclination angle of B and displacement amounts of the alignment stages  16   a,    17   a  of the tables  16 ,  17  are exaggerated for the sake of convenience of illustration. Otherwise, in  FIG. 5 , like constituent elements to those of  FIG. 10A  and  FIG. 10B  are designated with like reference symbols. 
     As for the data on the lowering in straightness of the guide rails  15  directly beneath the blanket roller  9 , for example the plate table  16  or the substrate table  17  may travel at a low speed directly beneath the blanket roller  9  along the guide rails  15  in advance, and a displacement gauge or the like (not shown in the figure) may be used to measure a displacement of the table  16  or  17  in the direction to shaft center of the blanket roller  9 . 
     As described above, even in the case where the table moving direction  13  is inclined from the direction orthogonal to the shaft center of the blanket roller  9 , it is possible to correct the table moving direction  13  to the direction orthogonal to the shaft center of the blanket roller  9  during the time when all the sites (points) on the plate  10  and the substrate  11  held on the alignment stages  16   a,    17   a  respectively on the tables  16 ,  17  pass the roller contact region  12  contacting with the blanket roller  9 ., which has a predetermined width A in the X axis direction. Therefore, after transfer of a print pattern from the plate  10  to the blanket roller  9 , it is possible to prevent a possibility of the lines of the print pattern from becoming thicker or faded at the time of its re-transfer from the blanket roller  9  to the substrate  11 . 
     If the guide rails  15  are curved directly beneath the blanket roller  9 , when the tables  16 ,  17  travel along the curved guide rails  15 , the inclination angle changes between the table moving direction  13  of the plate table  16  as well as the substrate table  17  and the direction orthogonal to the shaft center of the blanket roller  9 . With this change, the angle (attitude) changes between the direction orthogonal to the shaft center of the blanket roller  9  and the plate  10  as well as the substrate  11  held respectively on the tables  16 ,  17 . Therefore, in such a case, with the adjustment of the yaw angle (θ) of the alignment stages  16   a,    17   a  of the tables  16 ,  17 , the attitudes of the plate  10  and the substrate  11  held on the tables  16 ,  17  may be adjusted so as to be along the direction orthogonal to the shaft center of the blanket roller  9 . 
     Incidentally, there are cases where the blanket roller  9  is decentered due to accuracy or the like with which it was manufactured. In this case, due to the decentering, the apparent radius of the blanket roller  9  from its center of rotation to its peripheral positions changes depending on the angle of rotation of the blanket roller  9 . As a result, even if such a blanket roller  9  is rotated with a constant rotational speed, there is a possibility of change in its peripheral velocity. 
     In view of this, the controller  25  includes a sensor for detecting a rotational speed and an angle (attitude) in the circumferential direction of the blanket roller  9  of the transfer mechanism portion  20 . For example, the sensor corresponds to a roller rotation control portion  25   c  that is capable of controlling the rotational speed and the rotational angle in the circumferential direction of the blanket roller  9  by giving a command C 4  to the drive motor  22  based on detection signals S 3  for the rotational speed and the rotational angle. The detection signals S 3  are input from an encoder  31  fixed to the drive motor  22  of the blanket roller  9 . Thus, with the association of the roller rotation control portion  25   c  with the table traveling control portion  25   a  and the alignment stage control portion  25   b,  it is possible to control the alignment stages of the tables. 
     The controller  25  further includes a database  32  in which is accumulated data obtained by previously measuring changes in apparent radius of the decentered blanket roller  9  from its center of rotation to the peripheral position at its lower end of the peripheral surface according to the change in rotational angle. With this, when a function of the table traveling control portion  25   a  is used to travel the plate table  16  and the substrate table  17  directly beneath the blanket roller  9  of the transfer mechanism portion  20 , a correction command is given from the alignment stage control portion  25   b  to the alignment stages  16   a,    17   a  respectively of the tables  16 ,  17  based on the data in the database  32 . 
     To be more specific, the controller  25  associates the table traveling control portion  25   a  with the roller rotation control portion  25   c.  Thereby, when transfer from the plate  10  to the blanket roller  9  or re-transfer from the blanket roller  9  to the substrate  11  is performed while the plate table  16  or the substrate table  17  is caused to travel directly beneath the blanket roller  9  as shown in  FIG. 6  at a speed in synchronicity with the peripheral velocity of the blanket roller  9  found from the rotational speed and the radius of the blanket roller  9 , the controller  25  is capable of correcting the moving speed of the plate  10  or the substrate  11  held on the alignment stages  16   a,    17   a  in the X axis direction by making the moving speed higher or lower than the traveling speed of the tables  16 ,  17 . Firstly, based on the data in the database  32  on the decentering of the blanket roller  9 , it is possible to find the peripheral velocity (an actual peripheral velocity of the contact portion with the plate  10  held on the plate table  16  or the substrate  11  held on the substrate table  17 ) by multiplying an apparent radius of the blanket roller  9  from its center of rotation to the peripheral position at the lower end of its outer peripheral surface by an angular velocity of rotation when the blanket roller  9  is at a specified rotational angle. Depending on the peripheral velocity, the alignment stage  16   a  or  17   a  respectively of the traveling table  16  or  17  is relatively displaced in the X axis direction with respect to the corresponding table  16  or  17  by use of a function of the alignment stage control portion  25   b.  As a result, it is possible to correct the moving speed of the plate  10  or the substrate  11  held on the alignment stage  16   a  in the X axis direction by making moving speed higher or lower than the traveling speed of the tables  16 ,  17 . As a result, if the blanket roller  9  is decentered and an apparent radius of the blanket roller  9  from its center of rotation to the peripheral position at the lower end of its outer peripheral surface is large, then its peripheral velocity is high. Therefore, the alignment stage  16   a  or  17   a  of the traveling tables  16  or  17  is shifted to the forward side in the table traveling direction, to thereby increase the moving speed of the plate  10  or the substrate  11  held on the alignment stage  16   a  or  17   a.  On the other hand, if the apparent radius of the blanket roller  9  from its center of rotation to the peripheral position at the lower end of its outer peripheral surface is small, then the peripheral velocity is low. Therefore, the alignment stage  16   a  or  17   a  of the traveling table  16  or  17  is shifted to the rear side in the table traveling direction, to thereby decrease the moving speed of the plate  10  or the substrate  11  held on the alignment stage  16   a  or  17   a.  Thus, even if the peripheral velocity of the contact portion of the blanket roller  9  with the plate  10  or the substrate  11  is changed while the blanket roller  9  rotates 360 degrees, it is possible to synchronize the moving speed of the plate  10  or the substrate  11  with the peripheral velocity of the contact portion of the blanket roller  9 . Therefore, when a print pattern, which has been transferred from the plate  10  to the blanket roller  9 , is re-transferred from the blanket roller  9  to the substrate  11 , it is possible to make the repeatability of the print pattern highly precise. 
     If the controller  25  includes an inking control portion  25   d  for controlling an operation of the inking device  27  as shown in  FIG. 4  with a double-dotted line and the inking control portion  25   d  can be controlled in synchronicity with the table traveling control portion  25   a,  then the plate  10  held on the plate table  16  may be inked by the inking device  27  when the plate table  16  passes through the inking device  27 . 
     When the offset printing apparatus of the present invention with the above construction is used to perform offset printing, firstly the alignment stage  16   a  of the plate table  16  is used in the alignment area  23  to align a plate  10  held on the plate table  16  every time the plate  10  is replaced after every passage of a predetermined period of printing time even if the same plate  10  is used again. In addition, every time a new substrate  11  is held on the substrate table  17 , the alignment stage  17   a  of the substrate table  17  is used in the alignment area  23  to align the substrate  11 . Thereby, every time, it is possible to repeat the position of the substrate  11  at the time it is aligned relative to the position of the plate  10  at the time it is aligned. 
     After that, the plate  10  is inked by the inking device  27 . The plate table  16  moves the inked plate  10  to the transfer mechanism portion  20 . While the plate table  16  is being traveled, the blanket roller  9  is brought from above into contact with the plate  10  held on the plate table  16  at a synchronized speed. Ink is transferred from the plate  10  to the blanket roller  9 . Next, the substrate table  17  is traveled to move the substrate  11  held on the substrate table  17  to the transfer mechanism portion  20 . Then, while the substrate table  17  is being traveled, the blanket roller  9  is brought from above into contact with the substrate  11  held on the substrate table  17  at a synchronized speed. Re-transfer to the substrate  11  is performed by the blanket roller  9 . This operation is performed while substrates  11  as print targets are replaced, thereby the print pattern on the plate  10  is printed on the substrates  11 . 
     Thus, according to the offset printing apparatus and the offset printing apparatus method of the present invention, an alignment is performed on the alignment stage  16   a  of the plate table  16 , to thereby make it possible to hold the plate  10  at a predetermined position on the plate table  16  without an error of the attachment position of the plate  10  to the plate table  16  when the plate  10  is attached. Similarly, an initial alignment is performed on the alignment stage  17   a  of the substrate table  17 , to thereby make it possible to hold the substrate  11  at a predetermined position on the substrate table  17  without an error of the attachment position of the substrate  11  to the substrate table  17  when the substrate  11  is attached. Therefore, it is possible to print a print pattern of the plate  10  onto a target position on the substrates  11  as print targets with high precision and with high repeatability. 
     Furthermore, even if the straightness of the guide rails  15  for guiding the travel of the plate table  16  or the substrate table  17  is decreased directly beneath the blanket roller  9 , it is possible to prevent the possibility of an occurrence of a lateral displacement of the blanket roller  9  from the time when every part of the plate  10  or the substrate  11  starts to contact the blanket roller  9  till the time when the part leaves the blanket roller  9 . Therefore, it is possible to prevent the lines of a print pattern, which have been transferred from the plate  10  to the blanket roller  9 , from becoming thicker or blurred when the print pattern is re-transferred from the blanket roller  9  to the substrate  11 . This can increase the repeatability of the print pattern. 
     Furthermore, even if due to the decentering of the blanket roller  9 , there is a change in peripheral velocity of the blanket roller  9  when it is rotated, it is possible to move the plate  10  or the substrate  11  at a moving speed in synchronicity with the peripheral velocity of the blanket roller  9 . This makes it possible to further increase the repeatability of the print pattern. 
     It is possible to perform a print onto the substrates  11  with high repeatability of printing position and also with high repeatability of print pattern. Therefore, it is possible to print a precise print pattern such as an electrode pattern onto the substrate  11  accurately and with high repeatability. Furthermore, even if a precise print pattern such as an electrode pattern is overprinted onto the substrate  11 , it is possible to suppress the displacement due to the overlap to the order of micrometers, allowing for highly precise printing. 
     The present invention is not limited only to the above-mentioned embodiment. If the alignment stage  16   a  of the plate table  16  and the alignment stage  17   a  of the substrate table  17  are capable of aligning the corresponding plate  10  and the substrate  11  through the horizontal movement in the X axis and Y axis directions and the rotation in the yaw angle (θ), their size in the up-down direction and their planar shape may be appropriately modified. Alternatively, alignment stages provided with an optional operation mechanism may be used. 
     The alignment area  23  on the mount  14  may be arranged somewhere in the longitudinal direction of the guide rails  15  other than that shown in  FIG. 2  so long as it does not interfere with the transfer mechanism portion  20 , the inking device  27 , the plate table waiting area  26 , and the substrate installation area  28 . 
     As for the alignment sensors  24  in the alignment area  23 , optional alignment sensors other than the precision cameras  24  may be used so long as the position of the plate  10  held on the alignment stage  16   a  of the plate table  16  and the position of the substrate  11  held on the alignment stage  17   a  of the substrate table  17  arranged at a predetermined position in the alignment area  23  can be detected with high accuracy. 
     When the blanket roller  9  is brought into contact with the plate  10  held on the plate table  16  or the substrate  11  held on the substrate table  17  in the transfer mechanism portion  20 , the correction by the alignment stages  16   a,    17   a  of the tables  16 ,  17  for addressing the decrease in straightness of the guide rails as shown in  FIG. 5 , and the correction of the moving speed of the plate  10  or the substrate  11  for addressing the decentering of the blanket roller  9  as shown in  FIG. 6  may be performed in a combined manner. 
     As for the raising-lowering actuator  21 , an optional actuator may be used so long as the blanket roller  9  can be brought from above into contact with the plate  10  held on the plate table  16  or the substrate  11  held on the substrate table  17  traveling along the guide rails  15  in the transfer mechanism portion  20 . 
     As for the inking device  27 , an optional type of inking device  27  may be used so long as the plate  10  held on the plate table  16  can be properly inked. 
     The offset printing method and the offset printing apparatus of the present invention may be applied also to the case where a print target other than the substrate  11  is printed. 
     In the offset printing method and the offset printing apparatus of the invention, a variety of modification can be made without departing from the scope of the invention. 
     DESCRIPTION OF THE REFERENCE SYMBOLS 
       9 : blanket roller 
       10 : plate 
       11 : substrate (print target) 
       13 : table moving direction 
       14 : mount 
       15 : guide rail 
       16 : plate table 
       16   a:  alignment stage 
       17 : substrate table (print target table) 
       17   a:  alignment stage 
       23 : alignment area 
       24 : precision camera (alignment sensor) 
       25 : controller 
       30 ,  32 : database