Method of determining whether or not to perform a decoloring process, and decoloring device

A decoloring device according to an embodiment includes a feeding unit on which sheets are loaded. A first sensor unit is downstream of the feeding unit in a sheet transport direction, detects a front position of the sheet fed from the feeding unit, and detects a presence or absence of an identification mark on a front portion of the sheet outside of an image forming area of the sheet. A control unit determines whether or not an image using the decolorable color material is printed on any one or both sides of the sheet based on whether the first sensor detects an identification mark on the front portion of the sheet, and determines whether to perform the decoloring process based on the determination of whether or not an image using the decolorable color material is printed on the sheet.

FIELD

Embodiments described herein relate generally to a technology for determining whether or not an image printed on a sheet is an image which is suitable for a decoloring process.

BACKGROUND

In order to process a sheet for reuse, an image to be decolored is initially formed on the sheet using a decolorable color material, and then the image is decolored from the sheet by performing a decoloring process with respect to the image. For the decolorable color material, a decolorable toner may be used, for example. The decoloring toner is melted at a fixing temperature, and is fixed onto a sheet so that a color is developed. In addition, when a decoloring temperature higher than the fixing temperature is applied, an image of the decoloring toner which is already fixed is decolored.

In a decoloring unit which performs a decoloring process, only a sheet on which an image printed using the decoloring toner is fed. However, when a sheet on which an image which is printed using non-decolorable toner (hereinafter, referred to as ordinary toner) is fed in the decoloring unit by mistake, there is a problem in that an offset phenomenon occurs in which the ordinary toner is melted by being overheated. The melted ordinary toner then adheres to the face of a heating and pressuring member, such as a roller, included in the decoloring unit.

Accordingly, it is desirable to determine whether or not an image printed on a sheet is suitable for a decoloring process before performing the decoloring process in the decoloring unit.

DETAILED DESCRIPTION

A decoloring device according to an embodiment includes a feeding unit on which sheets are loaded. A first sensor unit is downstream of the feeding unit in a sheet transport direction, detects a front position of the sheet fed from the feeding unit, and detects a presence or absence of an identification mark on a front portion of the sheet outside of an image forming area of the sheet. A control unit determines whether or not an image using the decolorable color material is printed on any one or both sides of the sheet based on whether the first sensor detects an identification mark on the front portion of the sheet, and determines whether to perform the decoloring process based on the determination of whether or not an image using the decolorable color material is printed on the sheet.

Hereinafter, the decoloring device according to the embodiment will be described in detail with reference to drawings.

A decoloring device100includes a feeding tray102in which a sheet S that will be subject to a decoloring process is loaded, a feeding member104, and a reading unit106which reads a first (front) side of the sheet S and a second (rear) side of the sheet S. The decoloring device also includes a decoloring unit108, a first tray110to which a reusable sheet RS (i.e., a decolored sheet) is discharged, and a second tray112to which a rejected sheet JS (i.e., a sheet that is determined to not be subject to a decoloring process for reuse) is discharged.

In addition, the decoloring device100further includes a first transport path114on which a sheet is transported to the first tray110from the feeding tray102, and a second transport path120which is connected to the first transport path114at a first branch point116and a junction118. In addition, a third transport path124branches at a second branch point122from the first transport path114, and discharges a rejected sheet JS (which temporarily stops at a terminal end portion of the first transport path114) to the second tray112. The second transport path120transports a sheet which is transported from the first branch point116toward the junction118.

In addition, a first reversing gate126(i.e., a first branching member) is arranged in the first branch point116. A sheet which is transported on the first transport path114passes by the first reversing gate126in an OFF state (which is denoted by a solid line), and is transported toward the second transport path120when the first reversing gate is switched (reversed) to an ON state (reversed) which is denoted by a dashed line. A second reversing gate128(i.e., a second branching member) is arranged at the second branch point122. A sheet which is transported on the first transport path114passes by the second reversing gate128in the OFF state (which is denoted by the solid line) to the first tray110. In addition, when the second reversing gate126is switched (reversed) to the ON state which is denoted by the dashed line, a sheet is transported toward the third transport path128, and the sheet is fed to the second tray112.

The feeding tray102may be loaded with sheets S of various sizes such as A4, A3, B5, or the like. A sheet which is loaded in the feeding tray102is, for example, a sheet on which an image is formed using a decolorable color material (recording material) which can be decolored by being heated to a predetermined temperature or more.

In addition, the feeding tray102includes a detecting sensor130(i.e., a sensor for detecting start of feeding) which detects a presence or absence of a sheet on the feeding tray102. When the detecting sensor130detects loading of a sheet, a control unit500feeds the loaded sheet to the first transport path114.

The first transport path114transports the sheet from the feeding tray102to the reading unit106. The reading unit106is arranged along the first transport path114downstream of the feeding tray102in a sheet transport direction. The reading unit106includes, for example, a reading unit such as a Charge Coupled Device (CCD) scanner, or a CMOS sensor. According to the embodiment, the reading unit106reads respective images on the first side and the second side of the transported sheet. The reading unit106includes a first reading unit1061and a second reading unit1062which are arranged on opposite sides of the first transport path114for reading images on both sides of a transported sheet.

Image data corresponding to an image read by the reading unit106is stored in a storage unit505which will be described later. For example, when image data corresponding to an image which is decolored is necessary later, it is possible to obtain the image data by storing image data (corresponding to image on a sheet S which is read by the reading unit106) in the storage unit505by converting the image to an electronic form as the image data, before a decoloring process.

The second transport path120may transport a sheet S which is transported from the reading unit106to the reading unit106again by passing through the decoloring unit108.

The decoloring unit108erases a color of an image on a transported sheet. For example, the decoloring unit108heats the sheet up to a predetermined decoloring temperature using a heating roller, or the like, in a state of being in contact with the transported sheet, and erases the color of the image which was formed on the sheet with a decolorable color material. For example, the decoloring unit108of the decoloring device100, according to the embodiment includes two decoloring units1081and1082for the first side and the second side of the sheet, respectively. The decoloring units1081and1082are arranged on opposite sides of the second transport path120.

An operating unit129includes a touch panel display and various operating keys, and is arranged at the upper part of the main body of the decoloring device100, for example. The operating key includes a numeric keypad, a stop key, a start key, or the like.

Discharging rollers117and118discharge a sheet, after a decoloring process, to the first tray110and the second tray112which are arranged above and below the lower part of the main body. The decoloring device100includes a plurality of sheet detecting sensors131which detect a sheet which is transported on the first to third transport paths114,120, and124. The sheet detecting sensors131may be a micro sensor, or a micro actuator, for example. The sheet detecting sensors131are arranged at appropriate positions on the transport path. In addition, transport rollers132are appropriately arranged on the transport path.

The sheet S is printed with a first identification mark201which denotes that the sheet is a reusable sheet on which an image using a decolorable color material is printed, on the first side which is illustrated inFIG. 4A. The first identification mark201is printed in a region out of an image printing region202when an image is printed using the decolorable color material. The first identification mark201is printed on the first side at a predetermined position. The identification mark is printed on the front end side or the rear end side of the sheet, relative to the transport direction (i.e., a first direction), and is performed at one or two portions in a direction which is orthogonal to the sheet transport direction (i.e., a second direction).

In addition, on the sheet S, a second identification mark203which denotes that the sheet is a reusable sheet on which an image using the decolorable color material is printed is printed in a region out of the image printing region202, on the second side which is illustrated inFIG. 4B, similar to the first side. When printing images on both sides of a sheet using the decolorable color material, positions of the first identification mark201(which is printed on the first side of the sheet S which is illustrated inFIG. 4A) and the second identification mark203(which is printed on the second side of the sheet S which is illustrated inFIG. 4B) are printed on opposite ends, relative to the first direction. The first identification mark201is printed on the first side of the sheet S at only any one of the front end and the rear end along the transport direction of the sheet S. Similarly, the second identification mark203is printed on the second side of the sheet S at only any one of the front end and the rear end along the transport direction of the sheet S.

The first identification mark201and the second identification mark203are printed at detection positions so that they can be detected using a first identification mark detector portion11and a second identification mark detector portion12(which will be described later). In addition, the length of the first identification mark201and the second identification mark203in the first direction is differentiated according to a size of a sheet.

Returning toFIG. 1, the sheet S which is loaded in the feeding tray102is fed to the first transport path114one by one by the feeding member104. The first identification mark detector portion11and the second identification mark detector portion12are arranged between the feeding member104and the junction118. The first identification mark detector portion11is arranged at a position of a sheet immediately after being fed from the feeding tray102, and the second identification mark detector portion12is arranged downstream of the first identification mark detector portion in the transport direction.

As illustrated inFIG. 4A, the first identification mark detector portion11includes a first skew sensor11A and a second skew sensor11B, which may be light transmission sensors. The first skew sensor11A and the second skew sensor11B are arranged with a predetermined gap between them, in the second direction, and detect the first identification mark201and the second identification mark203. In the first skew sensor11A and the second skew sensor11B, a projection device and a light receiving device are arranged so as to face each other by interposing a sheet S which is transported on the first transport path114therebetween.

The first skew sensor11A and the second skew sensor11B detect whether the sheet S is transported straight or is obliquely transported depending on whether or not a transported front end of the transported sheet S is simultaneously detected. In addition, when transmission light from the projection device is shielded by the first identification mark201or the second identification mark203, a signal from the light receiving device denotes a light shielding state (ON). In this case, it is possible to determine that an image on the sheet S is printed using a decolorable color material, as described inFIGS. 4A and 4B. However, whether the read identification mark is printed on the first side or the second side is unclear. The fact becomes clear by detecting the second identification mark203using the second identification mark detector portion12. In addition, the projection device may cause a sufficient amount of transmission light to be obtained by setting brightness low at a time of detecting skew in which the front end of the sheet is detected, and setting the brightness high when detecting the identification mark.

As illustrated inFIG. 4A, a size of the fed sheet S may be specified by detecting an identification mark after a time (t1), after detecting the front end of the sheet when the identification mark is printed on the front end of the sheet S in the transport direction, for example. In this case, since the length of the identification mark is different according to a size of the sheet, it is possible to specify the size of the sheet by measuring the time (t1), and to specify the length of the sheet in the first direction.

On the other hand, when the identification mark is printed on the rear end side of the sheet S in the transport direction, since the first identification mark detector portion11detects an image in the image printing region202of the sheet S before the size of the sheet S is specified, it is not possible to distinguish the image from an identification mark which is detected thereafter. However, it is possible to specify the length of the sheet S based on a transport speed of the sheet S by measuring a time until the rear end of the sheet S is detected, after detecting the front end of the sheet S.

Accordingly, as illustrated inFIG. 4A, it is possible to recognize whether or not an identification mark is printed by retrieving whether or not recognition data of the identification mark is present from a distance L3from the front end of the sheet S to a printing position of the identification mark corresponding to a sheet size over the image printing region202to a distance L4. For example, a distance of a detected image is stored after detecting the front end of the sheet S, and when a subsequent image is detected, distance information of the newly detected image (i.e., image distance information) is updated. In addition, when detecting the rear end of the sheet S, it is determined that it is not possible to detect an identification mark when the latest image distance information is in the image printing region202. Accordingly, in such a case, it is determined that the image of the latest image distance information is the identification mark when the latest image distance information is in a region out of the image printing region202.

In this manner, a case in which the identification mark is present on the front end of the sheet in the transport direction, and a case in which the identification mark is present on the rear end are both caused due to a direction of the sheet when loading the sheet S into the feeding tray102.

The second identification mark detector portion12includes a first rear side mark detecting sensor12A and a second rear side mark detecting sensor12B, which may be light reflecting sensors or light transmission sensors, as illustrated inFIG. 4B. According to the embodiment, the second identification mark detector portion12uses light reflecting sensors. The first rear side mark detecting sensor12A and the second rear side mark detecting sensor12B are arranged with a predetermined distance along the second direction on the rear side of the sheet S which is transported on the first transport path114. The first rear side mark detecting sensor12A and the second rear side mark detecting sensor12B receive light from the projection device, and light which is reflected on the rear side of the sheet S using the light receiving device.

When the second identification mark203is printed on the second side, the first rear side mark detecting sensor12A or the second rear side mark detecting sensor12B detects that light from the projection device is not reflected on the light receiving device by being shielded by the second identification mark203. For this reason, when the reflecting light from the projection device is shielded by the second identification mark203, a signal from the light receiving device denotes a non-light reflecting state. In this case, the image on the second side of the sheet S is determined to be an image which is printed using the decolorable color material.

According to the embodiment, the first identification mark detector portion11determines whether the identification mark which is printed on the sheet S is printed on the first side, the second side, or both the sides of the sheet S. The determination is based on a detection position (X) of the identification mark in the first direction based on a signal of detecting the identification mark by the first identification mark detector portion11, and a detection position (X) of the identification mark in the first direction based on a signal of detecting the identification mark by the second identification mark detector portion12.

The control unit500obtains detection information which is detected by the first identification mark detector portion11and the second identification mark detector portion12as a coordinate (distance) in the sheet transport direction by setting the front end position (X0) of the sheet S as a starting point. That is, a position coordinate of the identification mark which is printed on the front end side of the sheet S is set to X1 (distance L1from front end position X0), a detection coordinate position of the identification mark which is printed on the rear end side of the sheet S from the start of the detection is set to X2 (distance L2from coordinate position X1, distance L3from front end position X0), and a detection coordinate position of the identification mark on the rear end side in the first direction is set to X3 (distance L4from coordinate position X2). In addition, L3=L1+L2.

When a mark detection position (X) using the first identification mark detector portion11and a mark detection position (X) using the second identification mark detector portion12are in a range of X0<X<X1 or X2<X<X3, and are in the same range together, it is recognized that a detected identification mark is the second identification mark203on the second side, and it is determined that an image using the decolorable color material is printed on the second side. In addition, when the mark detection position (X) using the first identification mark detector portion and the mark detection position (X) using the second identification mark detector portion12are in a range of X0<X<X1 and X2<X<X3, and are in a different range, it is recognized that detected identification marks are the first identification mark201on the first side and the second identification mark203on the second side, and it is determined that images using the decolorable color material are printed on both sides of the sheet S.

In addition, when the mark detection position (X) using the first identification mark detector portion11is in a range of X0<X<X1, or X2<X<X3, and it is not possible to detect a mark using the second identification mark detector portion12, it is recognized that a detected identification mark is the first identification mark201on the first side, and it is determined that an image using the decolorable color material is printed on the first side of the sheet S.

In addition, when the first identification mark detector portion11and the second identification mark detector portion12may not detect a mark together, it is recognized that identification marks are not printed on both sides of the sheet, and the decoloring process is determined not to be possible.

In addition, when the detection position (X) is in a range of X1<X<X2, it is determined that detected information is not the identification mark.

That is, in a case of the printing on both sides, the first identification mark201and the second identification mark203are not printed overlapping on the front end side or the rear end side in the transport direction, on the first side and the second side of the sheet S. In addition, the identification mark which is detected by the second identification mark detector portion12is the second identification mark203which is printed on the second side of the sheet S. Therefore, when the mark position (X) which is detected by the first identification mark detector portion11and the mark position (X) which is detected by the second identification mark detector portion12are in the same range, it means that the first identification mark detector portion11detects (ON) that transmission light is shielded by the second identification mark203which is printed on the second side of the sheet S. Accordingly, it is possible to determine that an image is printed using the decolorable color material on the second side of the sheet S.

Due to this, when the mark position (X) which is detected by the first identification mark detector portion11and the mark position (X) which is detected by the second identification mark detector portion12are in a different range, it means that the first identification mark detector portion11detects that transmission light is shielded by the first identification mark201which is printed on the first side of the sheet S. Accordingly, in this case, it is recognized that the first identification mark201is printed on the first side of the sheet S, and the second identification mark203is printed on the second side of the sheet S, and it is possible to determine that images using the decolorable color material are printed on both sides.

In addition, when there is detection information of the mark position from the first identification mark detector portion11, but there is no detection information of the mark position from the second identification mark detector portion12, the second identification mark203is not printed on the rear side of the sheet S. Accordingly, the first identification mark201which is printed on the first side of the sheet S is recognized by the first identification mark detector portion11, and it is determined that an image using the decolorable color material is printed on the first side of the sheet S.

In this case, whether the second side of the sheet S is blank, or an image is printed using a non-decolorable material is unclear. Accordingly, when an image is present on the second side which is read in the reading unit106, the control unit determines that the image is formed as a non-decolored image, and determines that the decoloring process is not possible. On the other hand, when an image is not present on the second side, the control unit may determine that the decoloring process is possible by determining that the second side is blank.

On the other hand, when position information of the identification mark is not output from the first identification mark detector portion11and the second identification mark detector portion12, it is determined to be one of the following cases.

(1) Images using the decolorable color material are not printed on both sides of the sheet S, or the images are printed using non-decolorable color material, even when the images are printed.

(2) Images are not formed on both sides of the sheet S, and the sheet is blank.

When it is determined to be the case of (1), it is determined that the decoloring process is not possible. When it is determined to be the case of (2), it is determined that the decoloring process is not necessary. The sheet which is determined not to be possible or necessary for the decoloring process in this manner is transported to a cassette for rejected sheet112without being subject to the decoloring process.

FIG. 3is a block diagram which illustrates a hardware configuration of the decoloring device inFIG. 1. The decoloring device100includes the first identification mark detector portion11, the second identification mark detector portion12, the control unit500, the storage unit505, the first transport path114, the second transport path120, the reading unit106, the decoloring unit108, the operating unit129, the first reversing gate126, and the second reversing gate128. Each component of the decoloring device100is connected through a bus406. The control unit500controls the start of feeding of the sheet S which is loaded into the feeding tray102when obtaining an ON signal from a start button of the operating unit129.

In the operating unit129, it is possible to select a skew checking mode in which skew checking is performed. When the skew checking mode is selected (ON), the first identification mark detector portion11starts the skew checking.

The control unit (controller)500includes a processor501including a Central Processing Unit (CPU) or a Micro Processing Unit (MPU), and a memory502. The control unit500controls the reading unit106, the decoloring unit108, the operating unit129, the first transport path114, the first reversing gate126, and the second reversing gate128. In addition, the control unit500makes a determination on whether or not to perform the decoloring process based on a detection of meandering of the sheet S, a detection of a size of the sheet S, and a detection of a presence or absence of the identification mark using detection information which is detected in the first identification mark detector portion11.

The memory502is, for example, a semiconductor memory, and includes a Read Only Memory (ROM)503which stores various control programs, and a Random Access Memory (RAM)504which provides a temporary work area to the processor501. For example, the ROM503stores a printing position of the identification mark, the distances L1, L2, L3, and L4corresponding to a size of the sheet which are illustrated inFIGS. 4A and 4B, and the table inFIG. 4C. In addition, pieces of detection information which are detected in the first identification mark detector portion11and the second identification mark detector portion12are stored in the storage unit505.

A flow chart for determining whether or not to perform the decoloring process is described based on flowcharts inFIGS. 5A to 5D.

In Act1, feeding of a sheet which is loaded onto the feeding tray102is started, and the process proceeds to Act2.

In Act2, it is determined whether or not a skew checking mode is on, and the process proceeds to Act3when the skew checking mode is on. If not, the process proceeds to Act6.

In Act3, the front end of the sheet is detected by the first skew sensor11A and the second skew sensor11B of the first identification mark detector portion11, and the process proceeds to Act4.

In Act4, when the front end of the sheet is detected at a different timing by the first skew sensor11A and the second skew sensor11B of the first identification mark detector portion11, it is determined that skew has occurred in the sheet, and the process proceeds to Act5. When the front end of the sheet is detected at the same timing, it is determined that skew has not occurred, and the process proceeds to Act6.

In Act5, an error handling such as a stop of sheet feeding is performed, and the process for determining whether or not to perform the decoloring process is ended.

In Act6, when the first identification mark detector portion11detects the front end of the sheet, the process proceeds to Act7.

In Act7, a detection of the identification mark on the front end side is performed by the first identification mark detector portion11. When the identification mark is printed on the front end of the sheet, the identification mark is printed at approximately the same position regardless of a size of the sheet. Accordingly, the detection of the mark between the detection of the front end of the sheet and the detection of the distance (L1) is performed, detected data is stored in the storage unit505, and the process proceeds to Act8.

In Act8, the data which is stored in the storage unit505is retrieved, and the process proceeds to Act9.

In Act9, when the identification mark on the front end is not detected, the process proceeds to Act10, and when the identification mark is detected, the process proceeds to Act11.

In Act10, the fact that there is no identification mark on the front end is stored in the storage unit505, and the process proceeds to Act13.

In Act11, the detection position (X) of the detected identification mark on the front end is stored, and the process proceeds to Act12. In addition, due to the detection position (X) of the identification mark on the front end, a size of the sheet can be determined. In this case, the detection position (X) of the identification mark on the front end is present in the range of X0<X<X1, as illustrated inFIG. 4A.

In Act12, the detection process of the identification mark on the front end is ended, and the process proceeds to Act13.

In Act13, when the rear end of the sheet is detected, the process proceeds to Act14. When the first identification mark detector portion11detects the rear end of the sheet, the size of the sheet can be determined. It is effective when the identification mark on the front end of the sheet is not detected.

In Act14, detection data of detection of the rear end of the sheet is retrieved, and the process proceeds to Act15.

In Act15, when the detection position (X) of the identification mark on the rear end of the mark detection data is in the range of X2<X<X3, as illustrated inFIG. 4A, it is determined to be a normal identification mark on the rear end, and the process proceeds to Act16. In addition, when detection position (X) of the identification mark on the rear end of the mark detection data is not in the range of X2<X<X3, the fact that there is no identification mark on the rear end is stored in the storage unit505, and the process proceeds to Act18.

In the processes from Act6to Act17, whether the detection position (X) of the identification mark is present in the range of X0<X<X1, in the range of X2<X<X3, or the identification mark on the front end side is not present is stored in the storage unit505using the detection information which is detected by the first identification mark detector portion11.

In Act18, when the detection of the front end of the sheet is performed by the second identification mark detector portion12, the process proceeds to Act19.

In Act19, as illustrated inFIG. 4B, the mark detection is performed between the detection of the front end of the sheet and the detection of the distance (L1), by the second identification mark detector portion12, the detected data is stored in the storage unit505, and the process proceeds to Act20.

In Act20, the data which is stored in the storage unit505is retrieved, and the process proceeds to Act21.

In Act21, when the identification mark on the front end is detected, the process proceeds to Act22, and when the identification mark is not detected, the process proceeds to Act23.

In Act22, the detection position (X) of the identification mark on the front end is stored in the storage unit505, and the process proceeds to Act28. In this case, as illustrated inFIG. 4B, the detection position (X) of the identification mark on the front end is in the range of X0<X<X1.

In Act23, the fact that there is no identification mark on the front end is stored in the storage unit505, and the process proceeds to Act24.

In Act24, when the detection of the identification mark on the rear end is started, the process proceeds to Act25. Since the size of the sheet is obtained between Act6to Act15, as illustrated inFIG. 4B, the detection of the identification mark may be performed between the distance L3and the distances L3+L4.

In Act25, when the identification mark on the rear end is detected, the process proceeds to Act26, and when the identification mark is not detected, the process proceeds to Act27.

In Act26, the detection position of the identification mark (X) on the rear end is stored in the storage unit505, and the process proceeds to Act28. In this case, as illustrated inFIG. 4B, the detection position of the identification mark (X) on the rear end is in the range of X2<X<X3.

In Act27, the fact that there is no identification mark on the rear end is stored in the storage unit505, and the process proceeds to Act28.

In Act28, the determination of whether or not to perform the decoloring process is made. The determination of whether or not to perform the decoloring process is made by comprehensively determining the presence or absence of the identification mark on the front end e, and the presence or absence of the identification mark on the rear end on the first side and the second side of the sheet (such data being stored in the storage unit505). Specifically, the determination is made as illustrated inFIG. 4C. That is, when it is determined that the identification mark is printed on the first side, the second side, or on both sides by the information on the detection positions (X) of the identification marks of the first identification mark detector portion11and the second identification mark detector portion12, and the information of no detection, the decoloring process is determined to be possible, and when it is determined that the identification mark is not printed on the first side and the second side, the decoloring process is determined not to be possible, or necessary.

In Act28, the sheet which is determined to be a sheet on which the decoloring process may be performed is subject to the decoloring process in which a color of an image on a transported sheet is erased in the decoloring unit108(Act29). The decoloring unit108heats the sheet up to a predetermined decoloring temperature using a heating roller, or the like, in a state of being in contact with the transported sheet, and decolors the color of the image that was formed on the sheet using the decolorable color material. In Act28, a sheet in which the decoloring process is determined to be not possible, or not to be necessary is discharged to the second tray112without being subject to the decoloring process (Act30).

In the above described embodiment, the case in which the identification mark is printed on the front end or the rear end in the sheet transport direction on the first side and the second side of the sheet S is described. However, the identification mark may be detected on the front end of the sheet, regardless of the direction of the sheet when the sheet is loaded onto the feeding tray102, by printing the identification mark on both the front end and the rear end in the sheet transport direction. At this time, when the identification mark is printed on only one side, the identification mark is printed at a diagonal position of the front end and the rear end of the sheet. In addition, when an image using the decolorable color material is printed on both sides of the sheet, the identification marks are printed according to the first skew sensor11A and the second skew sensor11B on the left and right of the front end side and the rear end side in the sheet transport direction, respectively. In this case, the identification mark may be printed on any one of the first side and the second side. According to the printing method of the identification mark, it is possible to make the determination on whether or not to perform the decoloring process using only the first identification mark detector portion11which is the light transmission type, and the second identification mark detector portion12is not necessary.

In this case, when the printing position of the identification mark is set to the left side when viewed from the sheet transport direction, and the identification mark on the front end side of the sheet S is detected by the first skew sensor11A of the first identification mark detector portion11, a determination that the identification mark is printed on the first side may be made. At this time, when the identification mark on the front end of the sheet is detected by the second skew sensor11B, a determination that the identification mark is printed on the second side may be made. In addition, when the identification mark on the front end of the sheet is detected by first skew sensor11A and the second skew sensor11B at the same time, a determination that images using the decolorable color material are printed on both the first side and the second side may be made.

According to the embodiment, when printing an image on a sheet using the decolorable color material, and using the skew sensor, it is possible to set a sheet on which the identification mark is printed at a predetermined position of the sheet to a target of the decoloring process, and to determine sheets excluding the sheet to be sheets which are not suitable for the decoloring process.

In addition, it is possible to determine whether or not to perform the decoloring process based on a printing position and the number of printing of the identification mark, and detection timing, or the like, of the identification mark.

In addition, according to the embodiment, the second identification mark detector portion12detects the second identification mark which is printed on the second side of the sheet using the reflecting sensor, however, the second identification mark detector portion may detect the first identification mark which is printed on the first side of the sheet.