Patent Publication Number: US-8979233-B2

Title: Image forming apparatus responding to request during use of erasable ink

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 12/766,470, filed on Apr. 23, 2010, which is based upon and claims the benefit of priority from Provisional U.S. Application 61/173,099 filed Apr. 27, 2009, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an image forming apparatus including an image forming unit configured to form an image with erasable ink and an image forming unit configured to form an image with not erasable ink. 
     BACKGROUND 
     In recent years, as an image forming apparatus configured to form an image on a recording medium, there is an apparatus configured to erase an image on a sheet and reuse the sheet. The reuse of the sheet saves paper resources and realizes environmental protection. Further, as the image forming apparatus, there is an apparatus configured to perform, in order to realize low cost and space saving, a process for forming an image with an erasable toner and a process for forming an image with a normal toner. For example, JP-A-06-95494 discloses an apparatus configured to select the normal toner or the erasable toner and perform an image forming process. 
     However, even if the image on the sheet is erased, ingredients of the erasable ink or toner remain on the sheet. Therefore, when the image formation and the image erasing on the sheet are repeated, an area where the ingredients or the erased sheet or toner remain on the sheet expands. In the area where the ingredients of the ink or toner remain, it is likely that the ink less easily penetrates the sheet during the next image formation and image quality is deteriorated. For example, when the image on the sheet is erased by heat, it is likely that, while the image formation and image erasing on the sheet are repeated, characteristics of the sheet are changed by the influence of the heat and image quality is deteriorated. 
     Therefore, there is a demand for development of an image forming apparatus configured to grasp a state of a sheet and control an image forming process according to the state of the sheet. 
     SUMMARY 
     According to an aspect of the invention, a satisfactory image quality is obtained irrespectively of a level of use of a sheet. 
     According to an embodiment, an image forming apparatus including: a first image forming unit configured to form an image with erasable first ink; a second image forming unit configured to share a conveying path with the first image forming unit and forms an image with not erasable second ink; a recording unit configured to record a level of use of a recording medium on the recording medium; a detecting unit configured to detect the level of use; and a control unit configured to control the first image forming unit or the second image forming unit according to a detection result of the detecting unit. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an image forming apparatus according to a first embodiment; 
         FIG. 2  is a schematic explanatory diagram of a sheet having a mark indicating a printing ratio in the first embodiment; 
         FIG. 3  is a schematic explanatory diagram of a sheet having a new mark indicating a printing ratio in addition to the mark shown in  FIG. 2  in the first embodiment; 
         FIG. 4  is a block diagram of a control system in the first embodiment; 
         FIG. 5  is a table of process values corresponding to levels of use of a sheet in the first embodiment; 
         FIG. 6  is a flowchart for explaining print operation in the first embodiment; and 
         FIG. 7  is a schematic explanatory diagram of a sheet having marks indicating a printing ratio in a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments are explained below.  FIG. 1  is a schematic diagram of a hybrid printer  10  as an image forming apparatus according to a first embodiment. A printer unit  11  of the hybrid printer  10  includes a first ink-jet head unit  20  as a first image forming unit and a second ink-jet head unit  30  as a second image forming unit that also functions as a recording unit. The first ink-jet head unit  20  is a color printer of an ink-jet system. The first ink-jet head unit  20  forms an image using erasable ink as first ink that is erased when heated to temperature equal to or higher than erasing temperature. The second ink-jet head unit  30  is a color printer of the ink-jet system. The second ink-jet head unit  30  forms an image using normal ink as not erasable second ink. 
     The hybrid printer  10  includes a cassette  40  configured to store sheets P as recording medium. The hybrid printer  10  includes a first paper discharge tray  51  and a second paper discharge tray  52  to which the sheet P passed through the first ink-jet head unit  20  and the second ink-jet head unit  30  is discharged. The first ink-jet head unit  20  and the second ink-jet head unit  30  share a conveying unit  60  extending from the cassette  40  to the first paper discharge tray  51  or the second paper discharge tray  52  through the first ink-jet head unit  20  and the second ink-jet head unit  30 . The conveying unit  60  includes a pickup roller  61  configured to extract the sheet P from the cassette  40 , a conveying roller pair  62 , a registration roller pair  63 , a conveyor belt  64 , and a paper discharge roller pair  50 . 
     A driving roller  66  and a driven roller  67  rotate the conveyor belt  64  in an arrow q direction. The conveyor belt  64  has holes on the surface thereof at predetermined intervals. The conveyor belt  64  holds a negative pressure chamber  68  on the inner side thereof. The negative pressure chamber  68  attracts the sheet P to the conveyor belt  64  via the holes of the conveyor belt  64 . A pressing roller  70  presses the sheet P, which is conveyed to the conveyor belt  64 , against the conveyor belt  64 . The pressing roller  70  prevents the sheet P from rising on the conveyor belt  64 . A drying unit  71  is opposed to the conveyor belt  64  and dries ink on the sheet P conveyed by the conveyor belt  64 . 
     The first ink-jet head unit  20  includes ink-jet heads  21 Y,  21 M,  21 C, and  21 K for Y (yellow), M (Magenta), C (cyan), and K (Black) arranged in parallel to one another along the conveyor belt  64 . The ink-jet heads  21 Y,  21 M,  21 C, and  21 K respectively eject erasable inks of colors Y (yellow), M (magenta), C (cyan), and K (black) that are erased when heated to temperature equal to or higher than erasing temperature of, for example, 80° C. 
     In the ink-jet head  21 Y for yellow (Y), plural nozzles are arrayed at predetermined intervals over, for example, width of 297 mm that is maximum recording width of the sheet P. The ink-jet heads  21 M,  21 C, and  21 K for magenta (M), cyan (C), and black (K) have structure same as that of the ink-jet head  21 Y for yellow (Y). The ink-jet heads  21 Y,  21 M,  21 C, and  21 K print ink images corresponding to image information to be superimposed one on top of another on the sheet P traveling in the arrow q direction. 
     Erasable ink that is erased when heated to the temperature equal to or higher than the erasing temperature is disclosed in, for example, JP-A-2007-212613 and JP-A-2007-90704. The erasable ink contains, for example, a color-assuming compound such as leuco dye, a developer, and binder resin having an erasing action and the like. When the erasable ink is heated to temperature lower than the erasing temperature, since the color-assuming compound is subjected to the action of the developer and develops a color, the color of the erasable ink can fee recognized. When the erasable ink is heated to temperature equal to or higher than the erasing temperature, the developer in the binder resin moves to the surface thereof according to softening of the binder resin and spreads over the sheet P. The color-assuming compound stops being subjected to the action of the developer and is erased. Therefore, the color of the erasable ink cannot be recognized. The erasing temperature for the erasable ink is adjusted by the material design of the color-assuming compound, the developer, the binder resin, and the like. 
     As the color-assuming compound, it is desirable to use, for example, an electron-donating organic matter such as leuco-auramines, diarylphthalides, polyarylcarbinols, acylauramines, arylauramines, rhodamine B, lactams, indolines, spiropyrans, or fluorans. 
     As the developer, it is desirable to use, for example, phenols, phenolic metal salts, carboxylic metal salts, benzophenones, sulfonic acid, sulfonic salts, phosphoric acids, phosphoric metal salts, acid phosphoric ester, acid phosphoric ester metal salts, phosphorous acids, or phosphorous acid metal salts. 
     The ink-jet heads  21 Y,  21 M,  21 C, and  21 K configure an integral cartridge  22  and are integrally detachably attachable to a main body  10 A of the hybrid printer  10  and replaceable. The ink-jet heads  21 Y,  21 M,  21 C, and  21 K formed as a unit can be set in the main body  10 A as an option according to a demand of a user. 
     The second ink-jet head unit  30  includes ink-jet heads  31 Y,  31 M,  31 C, and  31 K for Y (yellow), M (magenta), C (cyan), and K (black) arranged in parallel to one another along the conveyor belt  64 . The ink-jet heads  31 Y,  31 M,  31 C, and  31 K respectively eject un-erasable normal inks of colors Y (yellow), M (magenta), C (cyan), and K (black). The ink-jet heads  31 Y,  31 M,  31 C, and  31 K have structure same as that of the ink-jet head  21 Y for yellow (Y). 
     The ink-jet heads  31 Y,  31 M,  31 C, and  31 K print ink images corresponding to image information to be superimposed one on top of another on the sheet P traveling in the arrow q direction. For example, the ink-jet head  31 K for K (black) functions as a recording unit. The ink-jet head  31 K for K (black) records a mark indicating a level of use of the sheet P in a part of the sheet P. The ink-jet heads  31 Y,  31 M,  31 C, and  31 K configure an integral cartridge  32  and are integrally detachably attachable to the main body  10 A and replaceable. 
     The mark indicating a level of use of the sheet P indicates a state of deterioration of the sheet P during reuse. The ink-jet head  31 K records, for example, a mark indicating a printing ratio at the time of image forming, by the first ink-jet head unit  20  on the sheet P. The ink-jet head  31 K additionally writes a printing ratio during image formation on the sheet P every time an image forming process is repeated on the sheet P. 
     Example 1 
     (1) When an image with a printing ratio of 10% is formed on an unused sheet p 0  with erasable ink, the ink-jet head  31 K records a mark M 1  as a digital code shown in  FIG. 2  on the sheet p 0 . The mark M 1  represents the printing ratio of 10%. 
     (2) Thereafter, when the image on the sheet p 0  is erased, only the mark M 1  remains on the sheet p 0 . 
     (3) In the following reuse of the sheet p 0 , when an image with a printing ratio of 20% is formed on the sheet p 0 , on which the mark M 1  is recorded, with the erasable ink, the ink-jet head  31 K records a mark M 2  shown in  FIG. 3  on the sheet p 0 . The mark M 2  represents the printing ratio of 20%. 
     (4) Thereafter, when the image on the sheet p 0  is erased, the mark M 1  and the mark M 2  remain on the sheet p 0 . The mark M 1  and the mark M 2  indicate that a cumulative printing ratio in the past of the sheet p 0  is 30%. 
     (5) Similarly, every time reuse of the sheet p 0  is repeated, the ink-jet head  31 K additionally writes a mark Mn corresponding to a printing ratio during the reuse on the sheet p 0 . 
     The cumulative printing ratio is an indicator of a state of use or a state of deterioration of the sheet p 0 . For example, when the cumulative printing ratio is equal to or higher than 150%, this indicates a state in which a desired print image cannot be obtained on the sheet p 0  because of deterioration of the sheet p 0 . 
     The mark Mn indicating a printing ratio can be recorded as a circle or square sign, a digital code such as a barcode or a QR code, or an analog coda such as alphanumeric, kana, or Greek characters. Further, the mark Mn indicating a printing ratio can also be recorded by punching pinholes or the like. 
     The hybrid printer  10  includes, for example, a mark sensor  72  as a detecting unit in the conveying unit  60 . The mark sensor  72  reads a mark recorded on the reuse sheet P using a photosensor. The mark sensor  72  reads both sides of the sheet P to read the mark irrespectively of a conveying direction of the reuse sheet P. A detection result obtained by reading the mark with the mark sensor  72  is fed back to control of a print process of the hybrid printer  10 . 
     The hybrid printer  10  includes an erasing unit  76  as an erasing device in a lower part thereof. The erasing unit  76  heats an ink image formed on the sheet P with the erasable ink to temperature equal to or higher than the erasing temperature and erases the ink image. The erasing unit  76  includes a paper feeding tray  77 , a conveying roller pair  78  configured to convey the sheet P on the paper feeding tray  77 , and a heater  80  configured to heat the sheet P. The conveying roller pair  78  and a transmitting roller  81  store the sheet P passing through the heater  80  in the cassette  40 . The cassette  40  stores the unused or reuse sheet P at random. As the erasing device, a heater of a heat roller type may be used. The erasing device may be externally attached to the hybrid printer  10 . 
       FIG. 4  is a block diagram of a control system  82  as a control unit configured to mainly perform process control for the printer unit  11  based on a reading result of the mark sensor  72 . The control system  82  includes a unit control section  83  and a unit control circuit  87 . The control system  82  connects, via an interface  84 , a host computer  86  configured to control the entire hybrid printer  10  and the unit control section  83 . The control system  82  connects, via an interface  88 , the unit control circuit  87  to the first and second ink-jet head units  20  and  30 , the conveying unit  60 , and the drying unit  71 . 
     The unit control section  83  includes a CPU  83   a , a random access memory (RAM)  83   b , and a read only memory (ROM)  83   c . The CPU  83   a  controls the unit control circuit  87  according to a detection result or the mark sensor  72  to adjust processes of the ink-jet head units  20  and  30 , the conveying unit  60 , and the drying unit  71 . The ROM  83   c  stores, for example, as shown in  FIG. 5 , a table of process values or the ink-jet head units  20  and  30 , the conveying unit  60 , and the drying unit  71  corresponding to a level of use of the reuse sheet P. 
     For example, when a cumulative printing ratio recorded on the sheet P is 0% to lower than 5%, the CPU  83   a  sets the process values to standard process values, i.e., 812 (mm/sec) as printing speed (speed of the sheet P passing through the paper discharge roller pair  50 ), 19.2 (kHz) as a driving frequency of any one of the first and second ink-jet heads  20  and  30  or both, once as the number of times of print pass that is the number of times printing is carried out by any one of the first and second ink-jet heads  20  and  30  or both in order to form one image, and 50° C. as drying temperature of the drying unit  71 . 
     When the cumulative printing ratio recorded on the sheet P is 5% to lower than 20%, the CPU  83   a  sets the process values to 406 (mm/sec) as printing speed (speed of the sheet P passing through the paper discharge roller pair  50 ), 9.6 (kHz) as a driving frequency of any one of the first and second ink-jet heads  20  and  30  or both, once as the number of times of print pass, and 55° C. as drying temperature of the drying unit  71 . 
     When the cumulative printing ratio recorded on the sheet P is 20% to lower than 50%, the CPU  83   a  sets the process values to 203 (mm/sec) as printing speed (speed of the sheet P passing through the paper discharge roller pair  50 ), 4.8 (kHz) as a driving frequency of any one of the first and second ink-jet heads  20  and  30  or both, once as the number of times of print pass, and 60° C. as drying temperature of the drying unit  71 . 
     When the cumulative printing ratio recorded on the sheet P is 50% to lower than 100%, the CPU  83   a  sets the process values to 102 (mm/sec) as printing speed, 4.8 (kHz) as a driving frequency of any one of the first and second ink-let heads  20  and  30  or both, twice as the number of times of print pass, and 60° C. as drying temperature of the drying unit  71 . 
     When the cumulative printing ratio recorded on the sheet P is 100% to lower than 150%, the CPU  83   a  sets the process values to 51 (mm/sec) as printing speed (speed of the sheet P passing through the paper discharge roller pair  50 ), 4.8 (kHz) as a driving frequency of any one of the first and second ink-jet heads  20  and  30  or both, four times as the number of times of print pass, and 60° C. as drying temperature of the drying unit  71 . 
     When the cumulative printing ratio recorded on the sheet P is equal to or higher than 150%, the CPU  83   a  determines that the sheet P is unsuitable for reuse and sets discard processing. 
     The CPU  83   a  determines a cumulative printing ratio of the sheet P from a detection result of the mark sensor  72 . The CPU  83   a  sets, referring to the table shown in  FIG. 5 , the unit control circuit  87  to perform control with process values corresponding to the cumulative printing ratio. 
     Print operation is explained below with reference to a flowchart shown in  FIG. 6 . The cassette  40  stores the unused or reuse sheets P at random. According to print start, the conveying unit  60  extracts the sheet P from the cassette  40  and conveys the sheet P in the direction of the registration roller pair  63 . The mark sensor  72  reads the mark Mn on the sheet P traveling from the conveying roller pair  62  in the direction of the registration roller pair  63  (ACT  100 ). When a cumulative printing ratio is lower than 5% judging from a result of the reading (No in Act  101 ), the CPU  83   a  proceeds to ACT  102 . 
     When the cumulative printing ratio is lower than 5% (No in ACT  101 ), the CPU  83   a  determines that the sheet P is unused or the cumulative printing ratio of the sheet P is lower than 5%. The CPU  83   a  sets the conveying speed of the conveying unit  60  to the standard process value such that the speed of the sheet P passing through the paper discharge roller pair  50  reaches printing speed (ACT  102 ). The CPU  83   a  sets the number of times of print pass to the standard process value (ACT  103 ). The CPU  83   a  sets the driving frequency of the first and second ink-jet head units  20  and  30  to the standard process value (ACT  104 ). The CPU  83   a  sets the drying temperature of the drying unit  71  to the standard process value (ACT  105 ) and proceeds to ACT  126 . 
     When the cumulative printing ratio recorded on the sheet P is equal to or higher than 5% judging from the mark Mn read in ACT  100  (Yes in ACT  101 ), the CPU  83   a  proceeds to ACT  120 . When the cumulative printing ratio recorded on the sheet P is lower than 150% (Yes in ACT  120 ), the CPU  83   a  proceeds to ACT  121 . 
     In ACT  121  to ACT  124 , the CPU  83   a  sets, referring to the table shown in  FIG. 6 , the respective process values according to the cumulative printing ratio. In ACT  121 , the CPU  83   a  sets the conveying speed of the conveying unit  60  such that the speed of the sheet P passing through the paper discharge roller pair  50  reaches the printing speed. In ACT  122 , the CPU  83   a  sets the number of times of print pass. In ACT  123 , the CPU  83   a  sets the driving frequency of the first and second ink jet head units  20  and  30 . In ACT  124 , the CPU  83   a  sets the drying temperature of the drying unit  71  and proceeds to ACT  126 . 
     When the cumulative printing ratio recorded on the sheet P is equal to or higher than 150% in ACT  120 , the CPU  83   a  proceeds to ACT  133  without applying the print operation to the reuse sheet P. In order to subject the reuse sheet P to discard processing, the CPU  83   a  causes the conveying unit  60  to convey and discharge the sheet P to the first paper discharge tray  51  and ends the print operation. 
     In ACT  126 , the CPU  83   a  determines whether the sheet P is printed with the erasable ink. When the sheet P is printed with the normal ink (No in ACT  126 ), the CPU  83   a  proceeds to ACT  127 . In ACT  127 , the CPU  83   a  causes the second ink-jet head unit  30  to form an image by the normal ink on the sheet P at the process values corresponding to the cumulative printing ratio of the sheet P. In ACT  127 , in order to cause the second ink-jet head unit  30  to form an image, the CPU  83   a  causes the pressing roller  70  to press the sheet P against the conveyor belt  64  and causes the negative pressure chamber  68  to attract the sheet P to the conveyor belt  64  to convey the sheet P in the arrow q direction. The ink-jet heads  31 Y,  31 M,  31 C, and  31 K print, according to image information, ink images to be superimposed one on top of another on the sheet P traveling in the arrow q direction and form a color image by the normal ink on the sheet P. 
     When the number of times of print pass set in ACT  122  is plural times and the CPU  83   a  determines in ACT  128  that printing is not performed the number of times of pass set in ACT  122  (No in ACT  128 ), the CPU  83   a  returns to ACT  127  and causes the second ink-jet head unit  30  to repeatedly form images by the normal ink on the sheet P attracted to the conveyor belt  64  and circulated. In ACT  127 , every time an image is formed with the normal ink, the drying unit  71  dries the image formed by the normal ink on the sheet P at the drying temperature set according to the cumulative printing ratio recorded on the sheet P. When the CPU  83   a  determines in ACT  128  that printing is performed the number of times of print pass set in ACT  122  (Yes in ACT  128 ), the CPU  83   a  proceeds to ACT  132 . 
     When the CPU  83   a  determines that the sheet P is printed with the erasable ink (Yes in ACT  126 ), the CPU  83   a  proceeds to ACT  129 . In ACT  129 , the CPU  83   a  causes the first ink-jet head unit  20  to form an image by the erasable ink on the sheet P at the process values corresponding to the cumulative printing ratio of the sheet P. In ACT  129 , in order to cause the first ink-jet head unit  20  to form an image, the CPU  83   a  causes the pressing roller  70  to press the sheet P against the conveyor belt  64  and causes the negative pressure chamber  68  to attract the sheet P to the conveyor belt  64  to convey the sheet P in the arrow q direction. The ink-jet heads  21 Y,  21 M,  21 C, and  21 K print, according to image information, ink images to be superimposed one on top of another on the sheet P traveling in the arrow q direction and form a color image by the erasable ink oh the sheet P. 
     When the number of times of print pass set in act  122  is plural times and the CPU  83   a  determines in ACT  130  that printing is not performed the number of times of pass set in ACT  122  (No in ACT  130 ), the CPU  83   a  returns to ACT  129  and causes the first ink-jet head unit  20  to repeatedly form images by the erasable ink on the sheet P attracted to the conveyor belt  64  and circulated. In ACT  129 , every time an image is formed with the erasable ink, the drying unit  71  dries the image formed with the normal ink on the sheet P at the drying temperature set according to the cumulative printing ratio recorded on the sheet P. When the CPU  83   a  determines in ACT  130  that printing is performed the number of times of print pass set in ACT  122  (Yes in ACT  130 ), the CPU  83   a  proceeds to ACT  131 . 
     In ACT  131 , after causing the first head unit  20  to form an image on the sheet P with the erasable ink and further causing the ink-jet head  31 K for K (black) to record the mark Mn indicating the printing ratio for the image formation in ACT  129  in a part of the sheet P traveling in the arrow q direction, the CPU  83   a  causes the drying unit  71  to dry the image and proceeds to ACT  132 . 
     In ACT  132 , the CPU  32   a  causes the conveying unit  60  to convey and discharge the sheet P having the image formed by using the normal ink or the erasable ink to the second paper discharge tray  52  and ends the print operation. In ACT  129 , the CPU  83   a  causes the first ink-jet head unit  20  to form an image using the erasable ink. The mark Mn indicating the printing ratio is additionally written anew on the sheet P discharged to the second paper discharge tray  52 . 
     The hybrid printer  10  performs printing. On the other hand, the erasing unit  76  erases the image formed on the sheet P in order to reuse the sheet P. The heater  80  of the erasing unit  76  heats the sheet P conveyed by the conveying roller pair  78  to temperature equal to or higher than 80° C. and erases the formed image. The transmitting roller  81  accumulates the sheet P in the cassette  40 . The hybrid printer  10  forms an image on the reuse sheet P accumulated in the cassette  40 . 
     According to the first embodiment, at the time of image forming, a cumulative printing ratio recorded on the sheet P is read from the mark Mn on the sheet P. Process values of the hybrid printer  10  are controlled according to the cumulative printing ratio to perform printing. Therefore, it is possible to obtain a print at more suitable process values and suppress deterioration in image quality irrespectively of a state of deterioration of the reuse sheet P. 
     A second embodiment is explained below. In the second embodiment, the cumulative printing ratio in the first embodiment is recorded more in detail. In the second embodiment, components same as those explained in the first embodiment are denoted by the same reference numerals and signs and detailed explanation of the components is omitted. 
     Example 2 
     (1) As shown in  FIG. 7 , a sheet P 1  is divided into, for example, four areas (A), (B), (C), and (D). 
     (2) Every time reuse of the sheet P 1  is repeated, a printing ratio of each of the areas (A), (B), (C), and (D) is recorded by using QR codes Q 1  to Qn. 
     During printing, the hybrid printer  10  performs the printing at process values corresponding to a cumulative printing ratio of each of the areas of the sheet P 1 . When the cumulative printing ratio of the area (B) is equal to or higher than 150%, even if the cumulative printing ratios of the other areas (A), (C), and (D) are lower than 150%, the hybrid printer  10  determines that the sheet P 1  is unsuitable for reuse and discards the sheet P 1 . 
     According to the second embodiment, when the sheet P 1  is reused, process values of the hybrid printer  10  are controlled for each of the areas of the sheet P 1  according to a cumulative printing ratio of each of the areas of the sheet P 1  to perform printing. Even when the sheet P is locally deteriorated, it is possible to obtain a print at more suitable process values and suppress deterioration in image quality. 
     A third embodiment is explained below. In the third embodiment, components same as those explained in the first embodiment are denoted by the same reference numerals and signs and detailed explanation of the components is omitted. In the third embodiment, instead of a printing ratio of a sheet in the first embodiment, the number of times of use of a sheet (the number of times of erasing) is recorded as a mark indicating a level of use of a reuse sheet. Since the quality of a sheet is deteriorated every time the sheet is heated by the heater  80  to erase an image, the hybrid printer  10  stores a table of process values corresponding to the number of times of use of the sheet (the number of times of erasing) in the ROM  83   c.    
     At the time of image forming, the hybrid printer  10  reads the number of times of use of a sheet (the number of times of erasing) and performs printing at process values corresponding to the number of times of use (the number of times of erasing). For example, when the number of times of use (the number of times of erasing) is equal to or larger than five times, the hybrid printer  10  determines that the sheet P 1  is unsuitable for reuse and discards the sheet P 1 . 
     According to the third embodiment, process values of the hybrid printer  10  are controlled according to the number of times of use of the sheet P (the number of times of erasing). Therefore, it is possible to obtain printing at more suitable process values and suppress deterioration in image quality irrespectively of a state of deterioration of the sheet P. 
     The present invention is not limited to the embodiments and can be variously changed within the scope of the present invention. For example, the first ink may be an ink that is erased when light having predetermined wavelength is irradiated thereon. When the first ink is an ink that is erased by heat, erasing temperature is not limited. Further, process values of the first image forming unit and the second image forming unit controlled by the control unit are not limited and may be arbitrary process values such as printing speed. Wind speed or the like during drying may be adjusted and controlled.