JP2010100044A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which enabling paper reusable and having a security mode. <P>SOLUTION: A mark that suggests confidential information included is marked on paper printed using erasable ink. Consequently, when used paper stacked on a paper tray 16 passes through a mark detecting sensor 123, the mark is read. The paper with the mark detected by the mark detecting sensor 123 is subjected to processing for making the previous image unrecognizable. Ink is erased from usual used paper stacked on a paper feeding tray 16 by an image erasing part 125. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus capable of reusing paper.

  2. Description of the Related Art Conventionally, as an apparatus for reusing paper, an ink jet printer that prints ink containing a leuco dye by an ink jet apparatus and erases it using a thermal bar or a thermal head has been proposed.

  For example, in Japanese Patent Application Laid-Open No. 2001-302954 (Patent Document 1), a color is developed by a chemical bond between a color former and a developer at a room temperature of 40 ° C. or lower, and the chemical bond is broken at a temperature of 100 ° C. or higher. An ink that is colorless by a chemical bond between a colorant and a decolorant is disclosed. Patent Document 1 discloses an ink jet printer using the ink, and further a recording / erasing ink jet printer provided with a heating mechanism for erasing.

  Japanese Patent Application Laid-Open No. 2005-89548 (Patent Document 2) discloses an ink material in which a coloring / decoloring curve has a hysteresis characteristic in order to stabilize coloring and decoloring at room temperature.

  However, when a sheet on which image formation and erasing have been performed using ink as disclosed in Patent Documents 1 and 2 is reused, there is a possibility that the ink may recolor when the sheet is cooled. This is because the dye and the color former once separated by heating are recombined when placed in an environment below a predetermined temperature lower than normal temperature. That is, it is possible to cool the paper after erasing and intentionally reproduce the previous image on the paper. Accordingly, there is a risk that the contents erased for reuse may be leaked to a third party, which is a serious security problem.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an image forming apparatus that suppresses reproduction of erased contents for paper reuse and improves confidentiality.

In order to achieve the above object, an image forming apparatus of the present invention prints an image on paper using erasable ink, and
A paper tray on which paper on which an image is printed using the ink is placed;
A mark detection unit for detecting a mark indicating that the image formed on the used paper conveyed from the paper tray includes confidential information;
When the mark is detected by the mark detection unit, an overcoat unit that performs overcoating that makes an image in an area including at least confidential information out of the image formed on the used paper unrecognizable is provided. It is characterized by.

  According to the present invention, it is possible to prevent the contents erased for paper reuse from being reproduced and improve confidentiality.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to a first embodiment. 3 is a graph showing temperature characteristics of ink used in the image forming apparatus according to the first embodiment. 1 is a schematic diagram showing a system in which an image forming apparatus and a server or the like according to a first embodiment are connected. 3 is a flowchart illustrating image erasing processing of the image forming apparatus according to the first embodiment. 3 is a flowchart illustrating image forming processing of the image forming apparatus according to the first embodiment. Sectional drawing which shows the structure of the image forming apparatus in 2nd Embodiment. Sectional drawing which shows the structure of the image forming apparatus in 3rd Embodiment. Sectional drawing which shows the structure of the image forming apparatus in 4th Embodiment. Schematic showing a sample printed with a mark indicating that it contains confidential information. Schematic which shows the example overwritten so that the image formed in the past could not be read. Schematic which shows the other example overwritten so that the image formed in the past could not be read.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 3.

  FIG. 1 shows an image forming apparatus 1 having an image forming unit using erasable ink and an image erasing unit for erasing the ink. The image forming apparatus 1 includes a paper cassette 10, an image forming unit 12, a paper discharge tray 14, a paper feed tray 16, and a reuse processing unit 18.

  The paper cassette 10 is a cassette that stores paper. The paper cassette 10 stores printing paper P on which an image is printed by the image forming unit 12. The image forming unit 12 forms an image on the paper P. The image forming unit 12 is an ink jet printer. The image forming unit 12 is a color printer. The paper discharge tray 14 holds paper that has been printed by the image forming unit 12.

  The paper feed tray 16 is a paper holding unit that holds paper to be reused by the reuse processing unit 18. The paper feed tray 16 may be loaded with a mixture of paper on which a confidential document is printed and paper on which a general document is printed. In this case, the user only has to stack printed paper on the paper feed tray 16 without considering the presence or absence of confidential information. The paper loaded on the paper feed tray 16 is taken into the apparatus by the take-in roller 17 and is carried to the mark detection sensor 123 by the carry roller 122. In the reuse processing unit 18, the mark detection sensor 123 separates the paper on which the confidential document is printed from the paper on which the general document is printed. When the mark detection sensor 123 detects a mark that suggests that confidential information is included on the target paper, the image forming apparatus 1 cannot recognize an image on the entire surface of the paper or a portion corresponding to the confidential information by the inkjet head 124. Overwrite printing on. In addition, overwriting is not performed on paper on which the mark cannot be detected, but the image printed on the paper P is erased by the image erasing unit 125, and then the paper is guided to the paper cassette 10 via the transport roller 126. To do. An image is formed on the paper P stacked in the paper cassette 10 by the image forming unit 12 in accordance with a print command from the user.

  Next, the configuration of the image forming unit 12 will be described in detail. As shown in FIG. 1, the image forming unit 12 includes a paper feeding roller 102, a conveying roller pair 103, a registration roller pair 104, a driving roller 106, a conveying belt 107, a pressing roller 108, and an inkjet head group 109 (109Bk, 109Y, 109M). And 109C), and a conveyance roller pair 110 and the like.

  The paper feed roller 102 takes out the paper P held in the paper cassette 10 one by one. The paper feed roller 102 transports the paper P taken out from the paper cassette 10 to the transport roller pair 103 and the registration roller pair 104. The registration roller pair 104 conveys the paper P onto the conveyance belt 107 at a predetermined timing. The conveyor belt 107 is given tension by the driving roller 106 and the driven roller 105. The conveyor belt 107 is driven as the driving roller 106 rotates. The pressing roller 108 presses the paper P against the transport belt 107.

  The conveyor belt 107 has holes on the surface at predetermined intervals. Inside the conveyance belt 107, a negative pressure chamber (not shown) connected to a fan (not shown) for adsorbing the paper P to the conveyance belt 107 is installed. The paper P is transported while being attracted to the transport belt 107.

  The inkjet head group 109 includes an inkjet head 109Bk, an inkjet head 109Y, an inkjet head 109M, and an inkjet head 109C. The inkjet heads 109Bk, 109Y, 109M, and 109C are sequentially installed along the conveyance belt 107. For example, in the example shown in FIGS. 1 and 2, the inkjet heads 109 </ b> Bk, 109 </ b> Y, 109 </ b> M, and 109 </ b> C are arranged in this order from the upstream side with respect to the conveyance direction of the paper P by the conveyance belt 107.

  The inkjet head 109Bk is an inkjet head that ejects black (Bk) ink that can be erased. The inkjet head 109 </ b> Y is an inkjet head that discharges yellow (Y) ink that can be erased. The inkjet head 109M is an inkjet head that ejects magenta (M) ink that can be erased. The inkjet head 109 </ b> C is an inkjet head that ejects cyan (C) ink that can be erased.

  The ink used in the image forming unit 12 is not limited to a specific material, and may be any ink that is decolored by being heated to a predetermined temperature. Image forming materials that can be used as ink by the image forming unit 12 are disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-212613, Japanese Patent Application Laid-Open No. 2007-90704, or Japanese Patent No. 3711017.

  For example, basic components of an image forming material such as decolorable ink or toner can be composed of a color developing compound, a developer, a binder resin, and the like. Such an image forming material can be recognized by the user because the color developing compound is colored in advance under the action of the developer. When heat is applied to the colored image forming material, the binder resin is softened, and the developer is easily moved from the inside of the binder resin to the surface, and is easily moved and diffused into the paper. For this reason, the color developing compound is not affected by the developer, and the color developing compound is decolored and cannot recognize the color as an image forming material.

  The color developing compound is a precursor compound of a dye that forms a color image such as letters or figures. Color-forming compounds include electron donating organic substances such as leucooramines, diarylphthalides, polyarylcarbinols, acyloramines, arylolamines, rhodamine B lactams, indoline spiropyrans, and fluorans. It is preferable to use it.

The color developer is a compound that causes the color developing compound to develop a color by interacting with the color developing compound (mainly exchange of electrons or protons). Developers are phenols, phenol metal salts, carboxylic acid metal salts, benzophenones, sulfonic acids, sulfonates, phosphoric acids, phosphate metal salts, acidic phosphate esters, acidic phosphate metal salts, phosphorous acids It is preferable to use metal phosphite salts and the like.
The binder resin is used to disperse the color developing compound and the developer in a colored state. On the other hand, it has a characteristic that it is compatible with the color developing compound during heating and has no affinity with the developer.

  A printer that forms an image using ink as an image forming material that can be erased by heat as described above needs to be designed so that a temperature equal to or higher than the erasing temperature is not applied to the ink in the printing process. If the temperature in the printer may be higher than the erasing temperature, the ink may be erased before it is printed on the paper. In such a case, of course, a normal image is not formed on the paper. Furthermore, considering the energy consumption of the printer itself, the ink erasing temperature is preferably set as low as possible. Therefore, in the printer, it is required to devise so that the temperature applied to the ink does not become as high as possible.

The inkjet heads 109Bk, 109Y, 109M, and 109C each form an image of each color on the paper. The inkjet heads 109Bk, 109Y, 109M, and 109C eject inks corresponding to the black component, yellow component, magenta component, and cyan component, respectively, in the color image. The inkjet head group 109 forms a color image on a sheet by printing each color image on the sheet.

  The conveyance roller pair 110 discharges the sheet on which the image is printed by the inkjet head group 109 to the discharge tray 14.

Image formation is performed according to the following procedure. FIG. 3 is a diagram showing a configuration of the image forming apparatus 1 on the network, and FIG. 5 is a flowchart showing a procedure of image forming processing. The image forming apparatus 1 is connected to a personal computer (hereinafter referred to as a personal computer) 32 and a printer server 33 via a network 31. When the image forming apparatus 1 receives a print command from the personal computer 32, an operation panel provided in the image forming apparatus 30 or the like (512), the image forming apparatus 1 drives the paper feed roller 102 to pick up the paper P stored in the paper cassette 10. Then, the paper P is conveyed to the image forming unit 12 (513). Thereafter, when it is not specified that the image to be printed is in the confidential mode (514: N), the image forming unit 12 uses the erasable ink based on the image data transferred from the printer server as it is. An image is formed on the top (516). The paper P on which the image is formed is discharged to the paper discharge tray 14 (517). The image data may be image data read by a reading unit (not shown) of the image forming apparatus 1.

  If confidential information is included in the image formed at the time of image formation, a confidential mode is designated when giving a print command (414: Y), and a mark is combined with the formed image. (415).

  Marking is performed as follows. When a print command is given to the image forming apparatus 1 through a printer driver installed in advance in the personal computer 32, the driver specifies that confidential information is included in the image to be printed, and performs marking. The marking instruction may be a method of marking according to the selection of the security print mode provided in the image forming apparatus 1. Also, a method may be used in which marking is performed in response to the setting of the confidential mode by pressing a confidential button provided on the operation panel of the image forming apparatus 1. Further, the image forming apparatus 1 is provided with an image reading device, and the header image of the document to be printed is analyzed to read marks or characters such as “top secret”, “secret”, and “secret”. A method of marking according to the recognition result of the mark may be used.

  For example, the mark may be a header image as shown in FIG. When giving a print command, the printer driver or image forming apparatus is provided with an optional function to select and print a mark according to the confidentiality of the document such as “top secret” as shown in FIG. . Also, when an image erasing command is given, the pattern detection unit 123 compares the read image with the pattern stored in the ROM in advance. Is determined to be included.

  In the above process, if it is specified or determined that confidential information is included in the document to be printed, the image forming unit 12 marks all pages with a mark indicating that confidential information is included at the same time as image printing. To do.

  Next, an example of the marking process will be described. When the image forming apparatus 1 is a color image processing apparatus, the marking is made in a form that is difficult for humans to visually recognize by slightly changing the ink amounts of the C, M, and Y color inks printed by the image forming unit 12. Print. For example, a high frequency and low contrast periodic pattern is marked. In embedding the periodic pattern, the ink amount is adjusted so that, for example, modulation is applied in the yellow and blue directions.

  Next, an example of the marking process will be described. When the image forming apparatus 1 is a color image processing apparatus, the marking is made in a form that is difficult for humans to visually recognize by slightly changing the ink amounts of the C, M, and Y color inks printed by the image forming unit 12. Print. For example, a high frequency and low contrast periodic pattern is marked. In embedding the periodic pattern, the ink amount is adjusted so that, for example, modulation is applied in the yellow and blue directions.

この数式１で、αは埋め込む周期成分の振幅、rはその周期成分の周波数（dot/cycle）、θはその周期成分が主走査方向となす角度、ｘは対象画素の主走査方向の位置、ｙは副走査方向の位置を、それぞれ表す。さらに、数式１によって求めたΔｄからＹ、Ｍ、Ｃそれぞれのインク量の調整値を数式２にて求める。

このように色インクのインク量を調整することにより、黄色と青に変調がかかった周期パターンが現れる。また、ｎ個の周期パターンのうち埋め込むパターンと埋め込まないパターンを調整して、機密情報のおおよその位置を表してもよい。 The calculation of the value Δd used for adjusting the ink amount is performed using, for example, Expression 1 when n periodic patterns are embedded in the same portion given when an image is formed.

In Equation 1, α is the amplitude of the periodic component to be embedded, r is the frequency (dot / cycle) of the periodic component, θ is the angle formed by the periodic component with the main scanning direction, x is the position of the target pixel in the main scanning direction, y represents the position in the sub-scanning direction. Further, the adjustment values of the ink amounts of Y, M, and C are obtained from Δd obtained from Equation 1, using Equation 2.

By adjusting the amount of color ink in this way, a periodic pattern in which yellow and blue are modulated appears. Also, the approximate position of the confidential information may be represented by adjusting a pattern to be embedded and a pattern not to be embedded among n periodic patterns.

  The amplitude α is adjusted to be different depending on the frequency and angle of the periodic pattern to be used. For example, the amplitude α is increased as the frequency increases in accordance with human visual characteristics, degradation characteristics of the output device, and the like. In general, it is difficult to recognize other than the periodic components along either the main scanning direction or the sub-scanning direction. Therefore, when the main scanning direction is 0 °, the amplitude α is reduced only in a direction that forms an angle corresponding to a multiple of 90 °. Note that the values of the frequency r, the angle θ, and the corresponding amplitude α are stored in advance in a ROM (not shown) or the like mounted on the image forming apparatus 1.

  The area where the periodic pattern is embedded is a wide area including the area where the image is printed. Further, a preset marking embedding position and region may be stored in the ROM and used. As described above, the periodic pattern for marking needs to be a pattern that is difficult to be recognized by humans and can be embedded at a position where an image is printed. In addition to this periodic pattern embedding, a technique of embedding a recognizable pattern such as a two-dimensional barcode or QR code at a position that does not overlap with the area where the image is printed may be incorporated.

  With the above operation, a mark indicating that confidential information is included is formed on the paper P printed using the confidential mode of the image forming apparatus 1. Thus, when the used paper stacked on the paper feed tray 16 passes through the mark detection sensor 123 via the take-in roller 17 and the transport roller 122, the mark is read. If the mark is not detected by the mark detection sensor 123, the paper P is erased through the erasing unit 125, and the paper P on which the image has been erased is stored in the paper cassette 10.

  Next, image erasing will be described. For example, the image erasing unit 125 heats the paper P so as to have an erasing temperature of ink as an image forming material. The image is erased from the sheet heated at the erasing temperature by the image erasing unit 125. The image erasing unit 125 erases the image by applying heat to the paper. In this case, as the erasing mechanism, a configuration using a thermal head, a thermal bar, or a heat roller can be considered. In the type using a heat roller, it takes time to raise the temperature of the heat roller to a temperature at which erasing processing can be performed. For example, when the heat roller has not been heated in advance, the erasing process cannot be executed immediately on the paper P to be reused placed on the paper feed tray 16. For this reason, depending on the operation status, there is a possibility that sheets to be erased may be accumulated in the paper feed tray 16. Further, in the erasing mechanism using the thermal head or the thermal bar, the waiting time for raising the temperature is short. However, in the configuration in which the thermal head or the thermal bar is brought into contact with the surface of the paper P, the image forming material such as ink or toner tends to adhere to the surface of the thermal head or the thermal bar, so that the erasing performance is greatly deteriorated.

  The used paper erasing process is performed according to the procedure shown in the flowchart of FIG. First, the user stacks used paper on the paper feed tray 16. Then, for example, an erasing command is given by operating an operation panel or the like installed on the image forming apparatus 1 (402). The image forming apparatus 1 drives the take-in roller 17 to take used sheets stacked on the paper feed tray 16 one by one into the apparatus 1 (403). When it is determined that there is a mark indicating that there is confidential information when the sheet passes through the mark detection unit 123 (404: Y), the image on the sheet is overwritten (405) by the inkjet head 124. Then, the image eraser 125 is heated to erase the image formed on the paper (406). If there is no mark (404: N), the image is deleted without overwriting. The image forming apparatus 1 stores the paper from which the image has been erased in the paper cassette 10 (407).

  The paper from which the image has been erased by the image erasing unit 125 is temporarily stored in the paper cassette 10 for a predetermined time. As a result, paper that has been erased by heating and heated is not printed again unless a predetermined time elapses, so even if printing is performed on erasable paper with erasable ink, the image is immediately erased. Can be prevented from occurring. It should be noted that measures are taken such as providing ventilation holes 112 in or around the paper cassette 10 or providing a fan 114 so that wind is applied to the paper loaded in the paper cassette so as not to cause problems during image formation due to residual heat. Good. Alternatively, a thermistor is installed in the vicinity of the uppermost surface of the paper P loaded in the paper cassette 10, and the surface temperature of the paper P is not less than a predetermined temperature, for example, not less than the temperature T2 shown in FIG. In some cases, the paper feed roller 102 is not driven and the paper P is preferably kept in the paper cassette 10.

  By the way, when reusing used paper printed with erasable ink, it is necessary to keep the ink attached in a certain temperature range including a normal temperature environment in a colored state. In addition, after erasing by the image erasing unit 125, the erasing state must be maintained within a certain temperature range including the vicinity of normal temperature. Therefore, this ink is required to have the following temperature and color development characteristics. That is, as shown in FIG. 2, decoloration starts when the temperature T2 (e.g., about 100 ° C.) is higher than room temperature T0 (around 20 ° C.), and completely colorless when the temperature T4 is higher. On the other hand, when the temperature is lower than T1 (for example, 0 ° C.) or less, the color starts to be developed, and all the coloring materials are colored at a lower temperature T3. Further, at room temperature T0, a stable state is maintained without causing color development or colorlessness. When such an ink is used, if the ink is cooled to a temperature equal to or lower than the color development temperature T1, the erased image is reproduced on the paper, which may cause a security problem.

  On the other hand, in the image forming apparatus 1 of the present embodiment, this problem is solved by making an image formed in the past of used paper stacked on the paper feed tray 16 unreadable. That is, when a mark indicating that confidential information is included in an image formed in the past on used paper is detected, the image formed in the past is read by covering the entire image with ink or overwriting a predetermined pattern. Impossible.

  The paper P on which the mark is detected means that an image formed in the past is determined to be a confidential document. In this case, the image forming apparatus 1 performs black printing on the entire surface or an image area corresponding to confidential information with only black ink erasable by the print head 124. Further, when the mark on the paper P is arranged at a position away from the image, the mark may be overwritten on the mark so that the mark is not detected again. Thereafter, the flapper 129 is driven, and the paper P that has been overwritten is guided to the image erasing unit 125 via the paper path 130. Here, the image formed on the paper P is erased together with the overwritten image. As a result, since the image is erased after a solid image is formed, even if the temperature drops and the color reappears, the solid image only emerges, so confidentiality can be maintained.

  As described above, by using the image forming apparatus 1 of the first embodiment, when confidential information is included in an image formed in the past that has been printed on used paper, the image formed in the past on the paper cannot be read. The image to be printed is overwritten and reused. In addition, a pattern that suggests confidential information is marked at the same time as the image is printed, and even if used paper on the paper feed tray 16 contains confidential information, it is a target that is unreadable. Used paper can be identified. Thereby, it is possible to prevent the confidential information from being erroneously reproduced in the image erasing process.

(Second Embodiment)
In the first embodiment described above, the sheet is stored in the shared sheet cassette 10 regardless of whether confidential information is included in an image formed in the past on the sheet. The mark detection sensor 123 recognizes a pattern indicating that confidential information is included in an image formed in the past printed on the paper. However, when the pattern is deteriorated, the mark detection sensor 123 may not be able to read the pattern. In addition, when the used paper includes a sheet on which confidential information is printed and other sheets, it is difficult to switch the heating of the image erasing unit 125 on and off each time. Therefore, in this embodiment, the confidential document cassette 611 is provided separately from the normal sheet cassette 10.

  The paper on which the mark is detected means that the image formed in the past is determined to be a confidential document. In this case, as a result, as shown in FIG. 6, in the image forming apparatus 601, the flapper 624 is driven to store the sheet along the sheet path 632 through the transport roller 627 and stored in the confidential document cassette 611. The erase operation at 125 is not performed. The reuse processing unit 618 includes a flapper 624, a paper path 632, and a conveyance roller 627. In this case, since the paper has not passed through the image erasing unit 125, it is not necessary to cool the paper. Accordingly, the sheet is immediately supplied to the image forming unit 12 and black printing is performed on the entire surface or an image area corresponding to confidential information with only black ink that can be erased by the inkjet head 109Bk. If the image forming unit 12 is provided with a sensor for detecting the remaining amount of ink and the amount of black ink is small, the entire surface may be printed with cyan ink from the inkjet head 109C instead of black ink. By performing this printing, an image (confidential information) formed in the past printed with erasable ink on paper is made unrecognizable, so that the erasable image is overwritten. Thereafter, the flapper 129 is driven, and the paper for which overwriting has been completed is guided to the image erasing unit 125 via the paper path 630. Here, the image formed on the sheet is erased together with the overwritten image. As a result, since the image is erased after the solid image is printed, even if the temperature drops and the color reappears, the solid image only emerges, so that confidentiality can be maintained.

  In the first embodiment described above, the paper is stacked on the common paper feed tray 16 regardless of whether confidential information is included in an image formed in the past printed on the used paper. The mark detection sensor 123 recognizes a pattern indicating that confidential information is included in an image formed in the past printed on the paper. However, when the pattern is deteriorated, the mark detection sensor 123 may not be able to read the pattern. Therefore, in the second embodiment, a confidential document cassette 611 is provided separately from the normal sheet cassette 10.

(Third embodiment)
FIG. 7 is a configuration diagram of an image forming apparatus 701 according to the third embodiment. A point different from the first embodiment is that a confidential document tray 732 is provided in addition to the normal used paper feed tray 16. In this case, the used paper stacked on the confidential document tray 732 passes through the transport roller 734 and the transport roller 727 and goes to the black inkjet head 109Bk without passing through the detection sensor. Then, the black ink jet head 109Bk is used to overwrite all the sheets of paper or the image area corresponding to the confidential information with a black ink on all the sheets. In this way, an image formed in the past is overwritten with a meaningless image on the image formed in the past, thereby making the image formed in the past unrecognizable. The overwritten paper is conveyed to the image erasing unit 125 via the paper path 730 as in the first embodiment. The paper conveyed to the image erasing unit 125 is erased in the same manner as normal used paper and is stored in the paper cassette 10. The reuse processing unit 718 includes transport rollers 734 and 727 for transporting paper taken from the confidential document tray 732.

(Fourth embodiment)
FIG. 8 is a cross-sectional view of an image forming apparatus 801 showing the fourth embodiment. In the configuration shown in FIG. 7, there is a risk that used paper including confidential information in an image formed in the past is erroneously placed on the paper feed tray 16. Therefore, in FIG. 8, a mark detection sensor 123 is provided between the paper feed tray 16 and the image erasing unit 125 as the reuse processing unit 818. Further, a conveyance roller 834 and a security print head 836 are provided between the confidential document tray 832 and the image erasing unit 125.

  In this image forming apparatus 801, when the used paper stacked on the confidential document tray 832 is conveyed to the inside, the print head 836 immediately performs black printing on the entire surface. That is, an image formed in the past is overwritten with a meaningless image on an image formed in the past on the used paper, thereby making the image formed in the past unrecognizable. Thereafter, the image is transferred to the image erasing unit 125 and the image is erased. The paper from which the image has been erased by the image erasing unit 125 is temporarily stored in the paper cassette 10 for a predetermined time. As a result, paper that has been erased by heating and heated is not printed again unless a predetermined time elapses, so even if printing is performed on erasable paper with erasable ink, the image is immediately erased. Can be prevented from occurring. On the other hand, when a used paper including confidential information is stacked on an image formed in the past by mistake on the paper feed tray 16, the mark detection sensor 123 detects that the paper is marked. The detected paper passes through the image erasing unit 125 and the image forming unit 12 and is discharged onto the paper discharge tray 14. In this case, the operator is notified that the sheet is marked. For example, “Please place the paper discharged to the paper discharge tray on the confidential document tray” is displayed on the operation panel.

  In this way, by providing a confidential document tray in addition to the general used paper tray, the used paper loaded on the confidential document tray is fed directly to the image forming unit or print head, The configuration is such that black printing is performed. Therefore, it is possible to make the image formed in the past on the used paper completely unrecognizable. Further, a decoloring agent such as cholic acid may be stored in the print head 836 so that a recognizable image cannot be reproduced by overcoating or randomly coating the entire surface of the image.

  An example of this random coating is shown in FIG. In this way, the pattern to be randomly coated has only to be a density such that an image formed in the past cannot be read, and if it is not regular, it is difficult to recognize the image formed in the past. Further, since the overcoat only needs to be able to hide images formed in the past, an image having a large character string shape as shown in FIG. 11 may be overwritten.

  In the embodiment, ink is used as an example of the erasable color former. However, the present invention is not limited to this, and erasable toner may be used.

The present invention may be modified as appropriate from the above-described embodiment without departing from the gist of the present invention. Moreover, you may combine the embodiment mentioned above suitably.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 10 ... Paper cassette 12 ... Image forming part 16 ... Paper feed tray 125 ... Image erasing part 123 ... Mark detection sensor 109Bk, 109Y, 109M, 109C ... Print head

JP 2001-302954 A JP 2005-89548 A

Claims (9)

An image forming unit that prints an image on paper using erasable ink; and
A paper tray on which paper on which an image is printed using the ink is placed;
A mark detection unit for detecting a mark indicating that the image formed on the used paper conveyed from the paper tray includes confidential information;
When the mark is detected by the mark detection unit, an overwriting unit that overwrites an image in an area including at least confidential information among the images formed on the paper so as to be unrecognizable is provided. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the overwriting is covering the entire surface of the region with a color material.   The image forming apparatus according to claim 1, wherein the overwriting is to form a pattern with a color material on the region.   The image forming apparatus according to claim 1, wherein the image forming unit also serves as the overwriting unit.   The image forming apparatus according to claim 1, wherein the overwriting unit is an image forming unit provided separately from the image forming unit.   The image forming apparatus according to claim 1, wherein the mark is formed using a color material different from a color material used for normal image formation.   The image forming apparatus according to claim 1, wherein the mark is formed by a periodic pattern having at least one of high frequency and low contrast characteristics. A first paper tray for placing used paper having an image printed on the paper using erasable ink;
A second paper tray for placing used paper on which confidential information is printed on the paper using the erasable ink;
An image erasing unit for erasing the image printed on the used paper conveyed from the first paper tray;
Image formation that prints an image on paper using the erasable ink and overwrites a pattern that makes the previous image printed on the used paper conveyed from the second paper tray unrecognizable And
An image forming apparatus comprising: Form an image on paper with erasable ink,
Detects a mark indicating that the image formed on the paper contains confidential information,
An image forming method, wherein when the mark is detected, overwriting is performed to make an image in an area including at least confidential information out of the image unrecognizable.

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