Image forming apparatus, image forming method, and information recording medium

Abstract

To provide an image forming apparatus that can prevent a special light reaction image from being visually recognized.SOLUTION: An image forming apparatus can form a special light reaction image that is formed of a special light reaction image forming material reacting to special light other than visible light, and a special light non-reaction image that is formed of a special light non-reaction image forming material not reacting to the special light. The image forming apparatus forms an inhibition image 202 formed of the special light non-reaction image forming material and inhibiting the visibility of the special light reaction image 201 so as to overlap an edge of the special light reaction image 201. For at least one image of the special light reaction image 201 and the inhibition image 202, the adhesion density of the image forming material in a portion 203 overlapping the other image is made smaller than the adhesion density of a portion not overlapping the other image.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, an image forming method, and an information recording medium. [Background technology]

[0002] Conventionally, image forming devices are known that can form special light-reactive images that contain special light-reactive image-forming material that reacts to special light other than visible light, and special light non-reactive images that contain less special light-reactive image-forming material than the special light-reactive image.

[0003] Patent Document 1 describes an image forming device that prints a special light reactive image on a recording medium using a black toner having infrared light absorbing properties as a special light reactive image forming material, and prints a concealing layer as an inhibiting image in the background of the special light reactive image using an infrared non-absorbing material as a special light non-reactive image forming material of the same color as the special light reactive image. It describes that by printing a concealing layer of the same color as the special light reactive image in the background of the special light reactive image, the special light reactive image can be concealed so that it cannot be seen. In Patent Document 1, the concealing layer is printed so as not to overlap with the special light reactive image, so that unevenness does not appear on the printing surface of the recording medium. Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, when the concealing layer is printed out of alignment with the special light reactive image, a background area where no image forming material is attached is formed between the special light reactive image and the concealing layer, and the white printed surface of the recording medium is revealed. As a result, the edges of the special light reactive image stand out, and there is a risk that the special light reactive image will be visible. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus capable of forming on a recording medium a special light reactive image containing a special light reactive image forming material that reacts to special light other than visible light, and a special light non-reactive image having less special light reactive image forming material than the special light reactive image, the special light non-reactive image being an inhibiting image that inhibits the visibility of the special light reactive image, and at least one of the special light reactive images being formed so as to overlap the other image. and at least one of the images has a smaller adhesion density of the image forming material in a portion overlapping the other image than an adhesion density in a portion not overlapping the other image; The rise of the overlapping portion relative to the non-overlapping portion is set to 10 μm or less. It is characterized by the above. Effect of the Invention

[0006] According to the present invention, it is possible to prevent a special light reaction image from being visually recognized. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is an explanatory diagram showing the overall configuration of a printer according to an embodiment of the present invention. [Diagram 2] (a) is a diagram showing an IR image and a jamming image when infrared light is irradiated, and (b) is a diagram showing the state under visible light. [Diagram 3] (a) is a cross-sectional view of an IR image and a jamming image when the toner adhesion density of the jamming image in the overlapping area is the same as that of the other areas, and (b) is a cross-sectional view of an IR image and a jamming image when the toner adhesion density of the jamming image in the overlapping area is lower than that of the other areas. [Figure 4] 11 is a graph showing the toner adhesion density at each position of a jamming image. [Diagram 5] FIG. 13 is a diagram showing an example in which the toner adhesion density of both the jamming image and the IR image is reduced in the overlapping portion. [Figure 6] FIG. 13 is a diagram showing an example in which an IR image is superimposed on the edge of a jamming image. [Figure 7] FIG. 13 is a diagram showing a modified example of the image forming apparatus. [Figure 8] FIG. 13 is a diagram showing another modified example of the image forming apparatus. [Figure 9]FIG. 13 is a diagram showing an example of a mixed image around an IR image in which IR toner and normal color toner do not overlap. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment in which the present invention is applied to a color printer (hereinafter referred to as a "printer"), which is an image forming apparatus, will be described with reference to the drawings. In this embodiment, the present invention is applied to an image forming apparatus having four or less stations as an example. The image forming apparatus is not particularly limited as long as it forms an image that is difficult to see on a recording medium using a special toner that forms an image that is difficult to see. Therefore, in addition to a printer, the image forming apparatus may be a single copy machine or facsimile, or a multifunction machine having at least two functions of a printer, copy machine, facsimile, and scanner.

[0009] The printer of this embodiment uses a special toner that forms an image that is difficult to see. Such a special toner is mainly used when additional information is embedded in a visible image. For example, for the purpose of preventing illegal copying, etc., the special toner is used when forming an image that is difficult to see with the naked eye, called an invisible pattern or background pattern (a character image such as "COPY" that cannot be seen by a human even at a glance), on a recording medium together with a visible image using color toner. In addition, for the purpose of increasing the amount of information of a code image such as a barcode or QR code (registered trademark), the special toner is used when a code image using a visible image and a code image using an invisible image are overlapped and formed on a recording medium. Note that the special toner may also be used when only an image that is difficult to see is formed on a recording medium without forming a visible image.

[0010] As described below, a difficult-to-see image is an image formed from a toner that is more transparent under visible light than normal color toner, and in this embodiment, the image is further processed by irradiating it with infrared light or the like to cause it to emit light, develop color, etc., making it easier to see.

[0011] Examples of special toners as special light-reactive image forming materials include transparent infrared light absorbing toners and transparent fluorescent toners that fluoresce when exposed to ultraviolet light, which absorb light outside the visible light range or emit light in the visible light range when exposed to light outside the visible light range. In this embodiment, an example in which infrared light absorbing toner is used as the special toner will be described. In the following description, the toner symbols for each component are "Y" for yellow toner (Y toner), "M" for magenta toner (M toner), "C" for cyan toner (C toner), and "IR" for infrared light absorbing toner (IR toner). As the special toner, a transparent toner (transparent toner) whose color development is suppressed under visible light is preferable. In addition, the special toner has a smaller pigment content than normal color toners as special light non-reactive image forming materials.

[0012] The special light responsive image is an image in which the content of the infrared light absorbing material per unit area is greater than that of the special light non-responsive image. In order to form a special light responsive image, the infrared light absorbing toner (IR toner) that forms the special light responsive image is configured to contain more infrared light absorbing material as a special light responsive image forming material than the color toner that forms the special light non-responsive image.

[0013] In particular, it is desirable that infrared light absorbing toner (IR toner) that forms special light responsive images has an infrared transmittance of 40% or less when printing solid images, and that regular color toner that forms special light non-responsive images has an infrared transmittance of 60% or more. The infrared absorbing material used in the infrared absorbing toner (IR toner) may be either an inorganic material or an organic material.

[0014] Various transparent (invisible) infrared absorbing materials have been studied for the additional data embedding technology, and various materials have been disclosed. For example, inorganic materials include rare earth metals such as ytterbium (JP Patent Publication No. 9-77507, JP Patent Publication No. 9-104857) and infrared absorbing materials containing copper phosphate crystallized glass (JP Patent Publication No. 7-53945, JP Patent Publication No. 2003-186238), and organic materials include aluminum compounds (JP Patent Publication No. 7-271081) and croconium dyes (JP Patent Publication No. 2001-294785). In addition, JP Patent Publication No. 2002-146254 proposes an organic material containing an infrared absorbing material that has a spectral absorption maximum wavelength of 750 nm to 1100 nm and an absorbance at 650 nm that is 5% or less of the absorbance at the spectral absorption maximum wavelength. Furthermore, JP-A-2007-171508, JP-A-2007-3944, JP-A-2010-113368, and JP-A-2008-76663 propose the use of naphthalocyanine pigments, which can be considered an excellent technology in terms of the difference between the absorbance of visible light and the absorbance of infrared light.

[0015] Examples of inorganic infrared light absorbing materials include glass in which transition metal ions, dyes made of inorganic and / or organic compounds, and other materials are added to known glass network forming components that transmit visible wavelengths, such as phosphoric acid, silica, boric acid, etc., and crystallized glass obtained by crystallizing this by heat treatment, etc. These inorganic materials reflect light in the visible range well, making it possible to obtain invisible images.

[0016] Examples of organic infrared light absorbing materials include colored materials such as phthalocyanine compounds, anthraquinone compounds, etc., and colorless materials such as aluminum salt compounds, naphthalocyanine compounds, etc. Among these, colorless materials are preferred because they do not color the image when added, have sufficiently high absorption in the infrared region so that the amount added can be reduced, and as a result, the image quality of the color image is not impaired. Among colorless materials, naphthalocyanine compounds are preferred because they have very low absorbance in the visible light range, are nearly colorless, and have little effect on the charging of the toner.

[0017] First, the overall configuration and operation of the printer according to this embodiment will be described. FIG. 1 is an explanatory diagram showing the overall configuration of a printer according to this embodiment. The printer of this embodiment is mainly composed of an image forming unit 1, a transfer unit 2, a recording medium supply unit 3, a fixing unit 4, a recording medium discharge unit 5, a control unit 30, and an image formation control unit 40.

[0018] The image forming section 1 is provided with four process units 6Y, 6M, 6C, and 6IR as imaging units. Each process unit 6Y, 6M, 6C, and 6IR has the same configuration except that the type of toner used is different. In this embodiment, a process unit using black (K) toner is not provided, so color images and monochrome images are formed using only Y, M, and C color toners. A K process unit may be added, but in that case, there is a disadvantage that the device becomes larger.

[0019] Also, the IR process unit 6IR may be configured to be detachable, and a K process unit may be installed instead of the IR process unit. In this case, when forming an image without using IR toner, by installing the K process unit, a color image or a monochrome image can be formed using the Y, M, and C color toners and the K toner.

[0020] In addition, all process units may be made detachable, and the positions at which the process units are attached may be interchanged. In this case, by interchanging the position of the IR process unit, it is possible to appropriately interchange the positional relationship between the IR toner image and each color toner image on the recording medium (the positional relationship in the toner image stacking direction).

[0021] In this embodiment, each process unit 6Y, 6M, 6C, 6IR is composed of a photoconductor 7 as a latent image carrier that carries a latent image, a charging roller 8 as a charging means for charging the surface of the photoconductor 7, a developing device 9 as a developing means for developing the latent image on the photoconductor 7, and a photoconductor cleaning device 10 as a latent image carrier cleaning means for cleaning the surface of the photoconductor 7. At a position facing each photoconductor 7, an exposure device 11 as a latent image forming means for forming a latent image on the surface of the photoconductor 7 is provided. In this embodiment, an LED unit is used as the exposure device 11, but a laser beam scanning type using a laser diode may also be used.

[0022] The transfer section 2 is provided with an endless intermediate transfer belt 12 serving as an intermediate transfer body onto which the toner image on the photoreceptor 7 is transferred, a plurality of primary transfer rollers 13 serving as primary transfer means for primarily transferring the image on the photoreceptor 7 onto the intermediate transfer belt 12, a secondary transfer roller 14 serving as secondary transfer means for secondarily transferring the toner image transferred onto the intermediate transfer belt 12 onto a recording medium, and a belt cleaning device 17 serving as intermediate transfer body cleaning means for cleaning the surface (outer peripheral surface) of the intermediate transfer belt 12.

[0023] The intermediate transfer belt 12 is stretched around a drive roller 15 and a driven roller 16, and travels (rotates) as the drive roller 15 rotates. Each primary transfer roller 13 is disposed so as to press the intermediate transfer belt 12 against each photoconductor 7. As a result, a primary transfer nip is formed at the contact point between the intermediate transfer belt 12 and each photoconductor 7, where an image on each photoconductor 7 is transferred to the intermediate transfer belt 12. Meanwhile, the secondary transfer roller 14 is disposed so as to contact a portion of the intermediate transfer belt 12 wound around the drive roller 15. At the contact point between the secondary transfer roller 14 and the intermediate transfer belt 12, a secondary transfer nip is formed at the contact point between the intermediate transfer belt 12 and each photoconductor 7, where an image on the intermediate transfer belt 12 is transferred to a recording medium.

[0024] The recording medium supply unit 3 is provided with a paper feed cassette 18 as a recording medium storage unit that stores paper P as a recording medium, a paper feed roller 19 as a recording medium feeding means that feeds paper P from the paper feed cassette 18, and a timing roller 20 as a recording medium conveying means that conveys the paper P fed by the paper feed roller 19 to the secondary transfer nip at a predetermined timing. Note that the recording medium may be an OHP sheet, an OHP film, cloth, etc., in addition to paper. Furthermore, the paper includes, in addition to plain paper, cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), textured paper such as Japanese paper, tracing paper, etc.

[0025] The fixing section 4 is provided with a fixing device 21 as a fixing means for fixing an image onto the paper P. The fixing device 21 is mainly composed of a fixing roller 22 as a fixing member that is heated by a heat source such as a heater, and a pressure roller 23 as a pressure member that comes into contact with the fixing roller 22 with a predetermined pressure to form a fixing nip.

[0026] The recording medium discharge section 5 is provided with a discharge roller 24 as a recording medium discharge means for discharging the paper P sent from the fixing device 21 outside the device, and a discharge tray 25 as a recording medium mounting section for placing the paper P discharged by the discharge roller 24.

[0027] The control unit 30 performs image processing on input image information from a reading device (scanner), a personal computer, etc., and also controls the entire printer. In addition, the image forming control unit 40, under the control of the control unit 30, controls the image forming operations in each part of the printer (the image forming unit 1, the transfer unit 2, the recording medium supply unit 3, the fixing unit 4, the recording medium discharge unit 5, etc.).

[0028] In addition to the above-mentioned components, the printer of this embodiment is equipped with a plurality of toner cartridges 26 as powder storage containers that store toner, which is a powder used in image formation. Each toner cartridge 26 stores toner of the same color as the toner in the corresponding developing device 9, and when the toner in the developing device 9 falls below a predetermined amount, toner is replenished from the toner cartridge 26. Furthermore, the printer is equipped with a waste toner storage container 27 as a powder storage container separate from the toner cartridges 26. This waste toner storage container 27 stores waste toner collected by the belt cleaning device 17 or the photoconductor cleaning device 10.

[0029] 1, the printer of this embodiment includes a cover member 101 for opening and closing an upper portion of the device body (image forming device body) 100. The cover member 101 is rotatable up and down about a rotation shaft 103 provided in the device body 100. In addition, a container holding member 102 for removably holding four toner cartridges 26 is disposed below the cover member 101. The container holding member 102 is rotatable up and down about another rotation shaft 104 provided in the device body 100.

[0030] In this embodiment, the IR process unit 6IR is disposed on the most downstream side in the running direction of the intermediate transfer belt 12, and the color process units 6Y, 6M, 6C are disposed upstream of the IR process unit 6IR, so that an IR toner image (special toner image) made of IR toner is formed on the recording medium closer to the recording medium than a color toner image made of Y, M, and C color toners. In other words, on the intermediate transfer belt 12, a Y toner image, an M toner image, a C toner image, and an IR toner image are stacked in this order from the belt side, and on the recording medium after secondary transfer, the IR toner image, a C toner image, an M toner image, and a Y toner image are stacked in this order from the recording medium side.

[0031] By forming the IR toner image closer to the recording medium than the color toner image, the IR toner image is hidden by the color toner image, reducing its visibility, making it easier to ensure the secrecy of the image formed by the IR toner image. However, it is possible to appropriately set where the IR process unit 6IR is disposed relative to the color process units 6Y, 6M, and 6C. Also, as described above, if the mounting positions of the process units 6Y, 6M, 6C, and 6IR are configured to be interchangeable with each other, the position of the IR process unit can be freely interchanged.

[0032] Next, the basic operation of the printer of this embodiment will be described. When the image forming operation starts, each photoconductor 7 is rotated and the surface of each photoconductor 7 is uniformly charged to a predetermined polarity by the charging roller 8. Next, based on input image information from a reading device (scanner), a personal computer, etc., an exposure device 11 irradiates the charged surface of each photoconductor 7 with laser light to form a latent image (electrostatic latent image).

[0033] The latent images formed on each photoconductor 7 are based on monochrome image information obtained by decomposing a desired full-color image into color information of Y, M, and C. In more detail, a color conversion and decomposition table is used to convert and decompose the color information (RGB, YCM, etc.) of the input image information into color information (YMC) for the printer, and the input image information is converted into color information of Y, M, and C to generate decomposed monochrome image information, and each exposure device 11 for Y, M, and C forms a latent image of each color on the respective photoconductor 7 based on the image information of each color of Y, M, and C.

[0034] In this embodiment, IR image information is generated from additional information included in the input image information or additional information added by the printer. The additional information included in the input image information may be information added by an application on the personal computer or information added by a print driver on the personal computer. The IR exposure device 11 forms an IR latent image on the photoconductor 7 of the IR process unit 6IR based on the IR image information.

[0035] Toner is supplied from the respective developing devices 9 to the latent images of Y, C, M, and IR formed on the photoconductor 7, and the latent images are developed into toner images of Y, C, M, and IR. The toner images on the photoconductors 7 are transferred in sequence onto the intermediate transfer belt 12, which travels around the photoconductor 7, superimposed on one another. In detail, when the toner images on the photoconductors 7 reach the position of the primary transfer nip, the toner images on the photoconductors 7 are transferred in sequence onto the intermediate transfer belt 12 by a transfer electric field formed by applying a predetermined voltage to the primary transfer roller 13. In this way, a full-color toner image (visible image) made of Y, C, and M toners and an IR toner image (invisible image) made of IR toners are formed on the surface of the intermediate transfer belt 12. The toner on each photoconductor 7 that has not been transferred to the intermediate transfer belt 12 is removed by the photoconductor cleaning device 10.

[0036] Furthermore, when the image forming operation is started, the paper feed roller 19 rotates and feeds the paper P from the paper feed cassette 18. The transport of the fed paper P is temporarily stopped by the timing roller 20. Thereafter, the rotational drive of the timing roller 20 is started at a predetermined timing, and the paper P is transported to the secondary transfer nip in time with the toner image on the intermediate transfer belt 12 reaching the secondary transfer nip.

[0037] When the paper P is transported to the secondary transfer nip, a predetermined voltage is applied to the secondary transfer roller 14, and a transfer electric field is formed in the secondary transfer nip. The toner images on the intermediate transfer belt 12 are transferred all at once to the paper P by the transfer electric field formed in the secondary transfer nip. At this time, the toner remaining on the intermediate transfer belt 12 is removed by the belt cleaning device 17.

[0038] Thereafter, the paper P is transported to a fixing device 21, where the toner image is heated and pressed by a fixing roller 22 and a pressure roller 23, thereby being fixed to the paper P. Then, the paper P is discharged outside the device by a paper discharge roller 24, and placed on a paper discharge tray 25.

[0039] The above description is of the image formation operation when forming a full-color image, but it is also possible to form an image using any one of the four process units 6Y, 6M, 6C, and 6IR, or to form an image using any two or three of the process units.

[0040] Since IR images are not completely colorless and transparent under visible light but have a light yellow color, if an IR image exists alone on a recording medium, there is a risk that it may be visible under visible light, and the confidentiality of the IR image may not be adequately guaranteed.

[0041] Therefore, in this embodiment, as shown in FIG. 2, a jamming image 202 can be formed on a recording medium as an obstructing image that obstructs the visibility of the IR image 201 under visible light around the IR image 201. Specifically, a user can select whether or not to form the jamming image 202 by operating an operation display unit of the device or a personal computer on which a printer driver is installed. When the user selects to form the jamming image 202, the control unit 30 controls the image formation control unit 40 to automatically form the jamming image 202 around the IR image 201. In addition, the range of the jamming image 202 may be set manually by operating a personal computer on which a printer driver software is installed. For example, when a user selects manual setting on the printer driver software of the personal computer, the IR image 201 to be formed on the recording medium is displayed ("2018.1.1 code:12345" in FIG. 2), and the formation range of the jamming image 202 is specified by the user's operation.

[0042] The jamming image 202 is created using at least one of color toners Y, C, and M so that the jamming image 202 has the same color as the IR image 201 under visible light. Specifically, the jamming image 202 is formed so that the color difference ΔE between the IR image 201 and the jamming image 202 is 6.5 or less, and the difference in gloss between the IR image 201 and the jamming image 202 is 10% or less. As a result, as shown in FIG. 2B, the IR image 201 blends into the jamming image 202 under visible light, making the IR image 201 difficult to see. When the jamming image 202 is created using a single color toner, it is preferable to use a Y color toner. This is because the IR image 201 becomes difficult to see by forming it in Y color, which is the least noticeable on paper. On the other hand, when infrared light is irradiated, the IR image emits light and develops color, and the IR image becomes easily visible, as shown in Figure 2(a).

[0043] Here, the color difference ΔE can be calculated as follows. That is, a spectrophotometer (X-Rite eXact-scan) is used to measure the colors of the IR image 201 and the jamming image 202 under the conditions of a 2° field of view and a light source of D50, and the color difference ΔE can be calculated from these measured values. The color difference ΔE is calculated according to the definition described in JIS Z 8105 2073.

[0044] The glossiness is a value measured using a glossmeter (PG-1, manufactured by Nippon Denshoku Industries) at an irradiation angle of 60°, and the glossiness was measured according to the specular glossiness measuring method specified in JIS Z8741.

[0045] In addition, due to eccentricity of each photoconductor, the jamming image 202 may be misaligned with respect to the IR image 201. When such misalignment occurs, a background area where no toner adheres is generated between the jamming image 202 and the IR image 201. As a result, due to a color difference between the white recording medium surface of the background area and the IR image 201, the edge of the IR image 201 may be visible under visible light, and the invisibility of the IR image 201 may be impaired. Therefore, in this embodiment, as shown in FIG. 3, the jamming image 202 is formed so that the jamming image 202 overlaps the edge of the IR image 201. As a result, even if the jamming image 202 is slightly misaligned with respect to the IR image 201, it is possible to prevent the background area from being generated between the jamming image 202 and the IR image 201, and it is possible to suppress the edge of the IR image 201 from being visible under visible light, and it is possible to satisfactorily ensure the concealment of the IR image 201 under visible light.

[0046] In this embodiment, the width L of the overlapping portion 203 between the jamming image 202 and the IR image 201 is set to 50 μm to 100 μm. However, the width L of the overlapping portion 203 is not limited to this, and may be 100 μm or more. Also, the jamming image 202 may be formed so as to cover the entire IR image.

[0047] 3(a), an overlapping portion 203 of the edge of the IR image 201 with the jamming image 202 rises by T1 μm compared to other image portions. As a result, the overlapping portion 203 and the surrounding image portions reflect visible light differently, and unevenness between the overlapping portion 203 and its surroundings is visible, and there is a risk that the IR image 201 will be visible due to the unevenness.

[0048] Therefore, in this embodiment, as shown in Fig. 3(b), the toner adhesion density of the overlapping portion 203 of the jamming image 202 and the IR image 201 is made lower than the toner adhesion density of other portions. This makes it possible to make the bulge of the overlapping portion 203 of the jamming image 202 and the IR image 201 T2 μm (T1>T2, for example, T2=10 μm or less), and to reduce the bulge of the overlapping portion 203. This makes it possible to prevent the unevenness between the overlapping portion 203 of the edge of the IR image 201 and the jamming image 202 and its surroundings from being visible under visible light, and ensures the concealment of the IR image 201 well.

[0049] 4 is a graph showing the toner adhesion density at each position of the jamming image 202. The toner adhesion density is the density of toner adhesion per unit area, and is expressed in mg / cm. 2 The toner density can also be expressed as the amount of toner attached, which is the mass of toner attached per unit area. Here, it particularly refers to the density at a level where the background, where no toner is attached, is visible, such as in the case of a single layer or less.

[0050] The toner adhesion density can be determined by calculating the ratio of pixels with toner adhesion to the total number of pixels using an image obtained by binarizing an image magnified 200 times using an optical electron microscope.

[0051] 4, in this embodiment, the toner adhesion density of the jamming image 202 in the overlapping portion 203 is gradually decreased toward the edge of the jamming image 202. In this embodiment, the toner adhesion density of the jamming image 202 starts to decrease from position B in the figure, which is slightly outside the overlapping portion 203. In this way, by starting to decrease the toner adhesion density slightly outside the overlapping portion 203, it is possible to suppress the bulge of the end A of the IR image 201 (the boundary between the overlapping portion 203 and the jamming image 202), and to make the unevenness of the edge of the IR image 201 less noticeable under visible light.

[0052] By controlling the exposure amount of the exposure device to be gradually reduced from position B in the figure, which is slightly outside the overlapping portion 203, the toner adhesion density can be gradually reduced from position B toward the edge of the jamming image 202.

[0053] In addition, the primary transfer conditions may be set to conditions that cause transfer dust, and the transfer dust may be intentionally generated to gradually reduce the toner adhesion density of the jamming image 202 from position B toward the edge of the jamming image 202.

[0054] Furthermore, by using a known dithering method such as an error diffusion method and gradually reducing the printing rate from position B toward the edge of the jamming image 202 through image processing, the toner adhesion density of the jamming image 202 can be gradually reduced from position B toward the edge of the jamming image 202.

[0055] In a method of gradually decreasing the toner adhesion density of the jammed image 202 by gradually decreasing the exposure amount to gradually decrease the toner adhesion amount, the relationship between the toner adhesion amount and the exposure amount may change depending on the environment, etc., and the toner adhesion density of the overlapping portion 203 may not be stably set to a desired adhesion density. In order to stabilize the adhesion density, it is necessary to provide a toner adhesion amount detection sensor, periodically create a test image of toner, and detect the toner adhesion amount of the test image with the toner adhesion amount detection sensor to adjust the image formation conditions. In addition, in a method of decreasing the toner adhesion density of the overlapping portion 203 as a primary transfer condition that generates transfer dust, there is a problem that the transfer dust affects other images formed with the toner color used to create the jammed image. In addition, the degree of dust varies depending on the environment, etc., and the toner adhesion density of the overlapping portion 203 may not be stably set to a desired adhesion density.

[0056] In contrast, by using image processing to gradually reduce the toner adhesion density of the jamming image 202 from position B toward the edge of the jamming image 202, the toner adhesion density can be reduced more stably than when the toner adhesion density is reduced by image-making conditions such as the amount of exposure and primary transfer conditions, which is preferable.

[0057] Also, the toner adhesion density of the overlapping portion 203 with the jamming image 202 near the edge of the IR image 201 may be reduced within a range that does not affect the IR image 201. Also, as shown in Fig. 5, the toner adhesion density of the overlapping portion 203 of both the IR image 201 and the jamming image 202 may be reduced. This can almost completely eliminate the protuberance of the overlapping portion 203, and further improve the concealment of the IR image 201 under visible light.

[0058] 6, the IR image 201 may be overlapped on the edge of the jamming image 202. By disposing the IR process unit 6IR downstream of the process units 6Y, 6M, and 6C in the surface movement direction of the intermediate transfer belt, the IR image 201 can be overlapped on the edge of the jamming image 202 as shown in FIG.

[0059] 5 and 6, if each image is defined by the amount of IR toner, the IR image 201 can be defined as an image with a large amount of IR toner, the jamming image 202 can be defined as an image with a small amount of IR toner, and the overlapping portion can be defined as a mixed image in which IR toner and color toner are mixed and the amount of IR toner is intermediate. Also, the mixed image (overlapping portion) does not have to have IR toner and color toner overlap as shown in FIG. 9.

[0060] Also, the jamming image 202 may be formed so as to cover the entire IR image. In this embodiment, the toner adhesion density of the jamming image 202 in the overlapping portion 203 with the IR image 201 is reduced, so that an increase in the amount of toner adhesion in the overlapping portion can be suppressed. In addition, a method of lowering the printing rate of the overlapping portion by image processing to reduce the toner density also suppresses an increase in the image density in the overlapping portion. Therefore, even if the jamming image 202 is formed so as to cover the entire IR image, problems such as poor fixing or high image density in the IR image portion are unlikely to occur, so the jamming image 202 may be formed so as to cover the entire IR image.

[0061] In the above description, the IR image 201 is formed using a transparent IR toner, but the IR image may be formed using a colored IR toner that is easily visible under visible light. For example, a K toner containing carbon black as an infrared light absorbing material may be used as the colored IR toner. In this case, the IR image is black, and a black jamming image 202 is created using Y toner, M toner, and C toner that do not contain an infrared light absorbing material such as carbon. Also, a coloring material may be added to the transparent IR toner to make it a colored IR toner.

[0062] By forming a jamming image 202 of the same color as the color IR image 201 made of color IR toner around the IR image, the IR image 201 blends into the jamming image, making the IR image 201 difficult to view.

[0063] FIG. 7 is a diagram showing a modified example of the image forming apparatus. The image forming apparatus shown in FIG. 7 is equipped with a process unit 6T that creates an image using clear toner (transparent toner) as a special light non-reactive image forming material that does not absorb infrared light or develop color when irradiated with infrared light, downstream of the process unit 6IR in the surface movement direction of the intermediate transfer belt 12. According to this, clear toner can be used for the jamming image 202, and the glossiness under visible light of the IR image 201 and the jamming image 202 can be made even closer to each other. Therefore, the concealment of the IR image 201 under visible light can be further improved.

[0064] In particular, when the IR toner has a low color tone under visible light and the amount of non-IR toner during color reproduction is originally quite low, there is a risk that the difference in gloss between the IR image 201 and the jamming image 202 cannot be reduced to 10% or less using only the Y, M, and C color toners. When using an IR toner with a low color tone, a process unit 6T is provided and a jamming image is formed using at least one of the Y, M, and C color toners and a clear toner, thereby making it possible to reduce the difference in gloss between the IR image 201 and the jamming image 202 to 10% or less, and to make the IR image 201 and the jamming image 202 the same color.

[0065] FIG. 8 is a diagram showing a further modified example of the image forming apparatus. The image forming apparatus shown in FIG. 8 includes a full-color image forming apparatus 200 and an IR image forming apparatus 300 for forming an IR image. This IR image forming device 300 is set as an option in the full-color image forming device 200, and has an IR process unit 306IR that uses IR toner to create an IR image 201, and a jamming process unit 306J that uses jamming toner as a special light non-reactive image forming material that does not absorb infrared light of the same color as the IR toner under visible light, nor develop color when irradiated with infrared light, and adjusts the color of the jamming toner to be the same as the IR toner under visible light using at least one of Y, M, C, and K color toners and clear toner.

[0066] The paper P on which an image has been formed by the full-color image forming device 200 is transported to the IR image forming device 300, where an IR toner image is formed at a predetermined position on the paper P, and a jamming toner image is formed around the IR image. Then, the IR toner image and the jamming toner image are fixed to the paper P by the fixing device 304, and the paper P is discharged to the paper output tray 301.

[0067] In the image forming apparatus shown in FIG. 1 and FIG. 7, it was necessary to set the fixing conditions so that good images could be obtained for images other than the jamming image and the IR image, but in FIG. 8, the fixing conditions of the fixing device 304 can be set without considering images other than the jamming image and the IR image. Therefore, for example, the fixing conditions of the fixing device 304 can be set to optimal fixing conditions that do not cause a difference in gloss between the jamming image and the IR image. Also, in the configuration shown in FIG. 8, even if the transfer conditions when transferring the jamming toner image to the paper are set to transfer conditions that cause transfer dust, other images are not affected. Also, in FIG. 1 and FIG. 7, when forming an IR image, it was necessary to replace the K-color process unit 6K with the IR process unit 6IR, but in the configuration of FIG. 8, the labor required for replacement is not required.

[0068] The above description is merely an example, and each of the following aspects provides unique effects. (Aspect 1) An image forming device capable of forming on a recording medium a special light reactive image such as an IR image 201 containing a special light reactive image forming material such as an IR toner that reacts to special light other than visible light such as infrared light, and a special light non-reactive image made of Y, M, C toners or the like that has less special light reactive image forming material than the special light reactive image, wherein the special light non-reactive image is an inhibiting image such as a jamming image 202 that inhibits the visibility of the special light reactive image, and at least one of the special light reactive images is formed so as to partially overlap the other image, and the adhesion density of the image forming material in the portion overlapping the other image for at least one of the special light reactive image and the inhibiting image is made smaller than the adhesion density in the portion not overlapping the other image. By forming an inhibition image such as the jamming image 202 so as to overlap a special light response image such as the IR image 201, even if the inhibition image is formed slightly out of alignment with the special light response image, it is possible to prevent a background area from occurring between the special light response image and the inhibition image. This allows the special light response image to be smoothly blended into the inhibition image under visible light, and effectively inhibits the visibility of the special light response image. In addition, for at least one of the inhibition image and the special light reaction image, the adhesion density of the image forming material such as toner in the portion (overlapping portion 203) that is the other image is made lower than the adhesion density in the portion that is not overlapped with the other image. This makes it possible to reduce the protrusion of the portion where the two images overlap compared to when the adhesion density of the portion that is the other image is made the same as the adhesion density of the non-overlapping portion. As a result, it is also possible to prevent the special light reaction image from being visible under visible light due to the unevenness of the image caused by the protrusion of the portion where the two images overlap.

[0069] (Aspect 2) In the first embodiment, the rise of the overlapping portion relative to the non-overlapping portion is set to 10 μm or less. As a result, as described in the embodiment, the unevenness of the overlapping portion 203 between a special light response image such as the IR image 201 and an obstruction image such as the jamming image 202 and its surroundings can be prevented from being visible under visible light, thereby ensuring the confidentiality of the special light response image.

[0070] (Aspect 3) In embodiment 1 or 2, the area of ​​low adhesion density in at least one of the images is larger than the area of ​​the portion overlapping with the other image. As a result, as explained using Figure 4, it is possible to suppress the protrusion of the boundary between the overlapping portion 203 and an inhibiting image such as the jamming image 202, and to make the unevenness of the edges of a special light reaction image such as the IR image 201 less noticeable under visible light.

[0071] (Aspect 4) In any one of the first to third embodiments, the attachment density of at least one of the images in the portion overlapping the other image is decreased toward the edge of the one image. This makes it possible to prevent the unevenness of the overlapping portion 203 between a special light response image such as the IR image 201 and an obstruction image such as the jamming image 202 and its surroundings from being visible under visible light, thereby ensuring the confidentiality of the special light response image.

[0072] (Aspect 5) In any of aspects 1 to 4, for at least one of the special light reaction image such as the IR image 201 and the inhibition image such as the jamming image 202, the printing rate of the portion that overlaps with the other image (overlapping portion 203) is made lower than the printing rate of the portion that does not overlap with the other image. According to this, as described in the embodiment, it is possible to reduce the adhesion density, such as the toner adhesion density, of the overlapping portion 203. In addition, the adhesion density can be reduced by image processing, and the toner adhesion density of the overlapping portion 203 can be stably reduced to a desired adhesion density.

[0073] (Aspect 6) In any of the aspects 1 to 5, the adhesion density in the overlapping portion of both the special light response image such as the IR image 201 and the inhibition image such as the jamming image 202 is reduced. As a result, as explained using Figure 5, the protrusion of the overlapping portion 203 can be further suppressed, and the protrusion of the overlapping portion 203 can be further suppressed from causing special light response images such as IR images to be visible.

[0074] (Aspect 7) In any of aspects 1 to 6, the inhibition image and the special light response image are formed so that only the edge or a region within a predetermined range from the edge of the inhibition image, such as the jamming image 202, and the edge or a region within a predetermined range from the edge of the special light response image, such as the IR image 201, overlap. This makes it possible to reduce toner consumption and to prevent a background region from occurring between the special light response image and the inhibition image.

[0075] (Aspect 8) In aspect 7, the adhesion density of the overlapping portion of a special light response image such as IR image 201 with an inhibiting image such as jamming image 202 is decreased toward the edge of the special light response image, and the adhesion density of the overlapping portion of the inhibiting image with the special light response image is decreased toward the edge of the inhibiting image. This makes it possible to further suppress the protrusion of the overlapping portion 203, as shown in Figures 5 and 6, and further prevents special light response images such as IR images from being seen due to the protrusion of the overlapping portion 203.

[0076] (Aspect 9) An image forming device capable of forming on a recording medium a special light reactive image such as an IR image 201 containing a special light reactive image forming material such as an IR toner that reacts to special light other than visible light such as infrared light, and a special light non-reactive image made of Y, M, C toners or the like that has less special light reactive image forming material than the special light reactive image, in which the inhibiting image and the special light reactive image are formed so that only the edge or a predetermined range from the edge of an inhibiting image such as a jamming image 202 that inhibits the visibility of the special light reactive image overlap with the edge or a predetermined range from the edge of the special light reactive image. This makes it possible to reduce toner consumption and to prevent a background region from occurring between the special light response image and the inhibition image.

[0077] (Aspect 10) In any of the aspects 1 to 9, the color difference ΔE between a special light response image such as the IR image 201 under visible light and an inhibition image such as the jamming image 202 is 6.5 or less. According to this, as described in the embodiment, the color of the inhibition image such as the jamming image 202 under visible light can be made almost the same as the color of the special light reaction image such as the IR image 201. As a result, the jamming image 202 can effectively inhibit the visibility of the special light reaction image under visible light.

[0078] (Aspect 11) In any of the aspects 1 to 10, the difference in glossiness between the special light reaction image such as the IR image 201 and the jamming image 202 is 10% or less. As a result, as described in the embodiment, it is possible to prevent the IR image 201 from being seen under visible light due to the difference in glossiness between an inhibition image such as the jamming image 202 and a special light reaction image such as the IR image 201.

[0079] (Aspect 12) In any one of the first to eleventh aspects, the special light is infrared light. According to this, by irradiating infrared light, a special light non-reactive material such as an IR image 201 can be read.

[0080] (Aspect 13) An image forming method capable of forming on a recording medium a special light reactive image such as an IR image 201 containing a special light reactive image forming material such as an IR toner that reacts to special light other than visible light such as infrared light, and a special light non-reactive image made of Y, M, C toners or the like that contains less special light reactive image forming material than the special light reactive image, wherein the special light non-reactive image is formed so that at least one of an obstructing image such as a jamming image 202 that obstructs the visibility of the special light reactive image and the special light reactive image overlaps with the other image, and the adhesion density of the image forming material in the portion overlapping with the other image for at least one of the images is made smaller than the adhesion density in the portion not overlapping with the other image. According to this, the same effect as in the first aspect can be obtained.

[0081] (Aspect 14) An image forming method capable of forming on a recording medium a special light reactive image such as an IR image 201 containing a special light reactive image forming material such as an IR toner that reacts to special light other than visible light such as infrared light, and a special light non-reactive image made of Y, M, C toners or the like that has less special light reactive image forming material than the special light reactive image, in which the inhibiting image and the special light reactive image are formed so that only the edge or a region within a predetermined range from the edge of an inhibiting image such as a jamming image 202 that inhibits the visibility of the special light reactive image overlap with the edge or a region within a predetermined range from the edge of the special light reactive image. According to this, the same effect as in aspect 9 can be obtained.

[0082] (Aspect 15) An image forming method for forming on a recording medium a special light reactive image such as an IR image containing a special light reactive image forming material such as an IR toner that reacts to special light other than visible light such as infrared light, and a special light non-reactive image such as a jamming image having less special light reactive image forming material than the special light reactive image, wherein a mixed image having less special light reactive image forming material than the special light reactive image and more than the special light non-reactive image is formed around the special light reactive image, and the special light non-reactive image is formed around the mixed area. According to this, the same effect as in the first aspect can be obtained.

[0083] (Aspect 16) An information recording medium such as paper P on which an image is formed has at least one of characters, symbols, codes, and images formed by the image forming method of any one of aspects 13 to 15. This makes it possible to provide an information recording medium in which the visibility of the special light reaction image is effectively inhibited. [Explanation of symbols]

[0084] 1: Image forming section 2: Transfer section 3: Recording medium supply unit 4: Fixing section 5: Recording medium ejection section 6IR: IR process unit 6T: Clear toner process unit 11: Exposure equipment 12: Intermediate transfer belt 13: Primary transfer roller 21: Fixing device 30: Control section 40: Image formation control unit 200: Full color image forming device 201:IR image 202: Jamming image 203: Overlapped area 300: IR image forming device 304: Fixing device 306IR: IR process unit 306J: Jamming Process Unit P:Paper [Prior art documents] [Patent documents]

[0085] [Patent Document 1] Patent No. 5832010

Claims

1. An image forming apparatus capable of forming, on a recording medium, a special light reactive image including a special light reactive image forming material that reacts to special light other than visible light, and a special light non-reactive image having less of the special light reactive image forming material than the special light reactive image, The special light non-reactive image is formed so that at least one of an inhibiting image that inhibits the visibility of the special light non-reactive image and the special light non-reactive image is partially overlapped with the other image, With respect to at least one of the images, the adhesion density of the image forming material in a portion overlapping the other image is made smaller than the adhesion density in a portion not overlapping the other image; The image forming apparatus is characterized in that the rise of the overlapping portion relative to the non-overlapping portion is set to 10 μm or less.

2. An image forming apparatus capable of forming a special light reactive image including a special light reactive image forming material that reacts to special light other than visible light, and a special light non-reactive image having less special light reactive image forming material than the special light reactive image, on a recording medium, The special light non-reactive image is formed so that at least one of an inhibiting image that inhibits the visibility of the special light non-reactive image and the special light non-reactive image is partially overlapped with the other image, With respect to at least one of the images, the adhesion density of the image forming material in a portion overlapping the other image is made smaller than the adhesion density in a portion not overlapping the other image; An image forming apparatus, characterized in that an area of ​​low adhesion density in at least one of the special light reaction image and the inhibition image is larger than an area of ​​a portion overlapping the other image.

3. An image forming apparatus capable of forming a special light reactive image including a special light reactive image forming material that reacts to special light other than visible light, and a special light non-reactive image having less special light reactive image forming material than the special light reactive image, on a recording medium, The special light non-reactive image is formed so that at least one of an inhibiting image that inhibits the visibility of the special light non-reactive image and the special light non-reactive image is partially overlapped with the other image, an image forming apparatus characterized in that a printing rate of one of the images in a portion overlapping the other image is made lower than a printing rate of a portion not overlapping the other image, and an adhesion density of image forming material of one of the images in a portion overlapping the other image is made lower than an adhesion density of image forming material of a portion not overlapping the other image.

4. 4. The image forming apparatus according to claim 1, An image forming apparatus characterized in that the adhesion density of at least one of the special light reaction image and the inhibition image in the portion overlapping the other image decreases toward the edge of the one image.

5. 5. The image forming apparatus according to claim 1, An image forming apparatus characterized in that the adhesion density of both the special light reaction image and the inhibition image is reduced in the overlapping portion.

6. 6. The image forming apparatus according to claim 1, An image forming apparatus characterized by forming the inhibition image and the special light reaction image so that only the edge of the inhibition image or a region within a predetermined range from the edge overlaps with the edge of the special light reaction image or a region within a predetermined range from the edge.

7. 7. The image forming apparatus according to claim 6, An image forming device characterized in that the adhesion density of the overlapping portion of the special light response image with the inhibitory image is decreased toward the edge of the special light response image, and the adhesion density of the overlapping portion of the inhibitory image with the special light response image is decreased toward the edge of the inhibitory image.

8. 8. The image forming apparatus according to claim 1, The image forming apparatus according to claim 1, wherein the special light is infrared light.

9. An image forming method for forming a special light reactive image containing a special light reactive image forming material that reacts to special light other than visible light, and a special light non-reactive image having less special light reactive image forming material than the special light reactive image, on a recording medium, comprising: A mixed image is formed around the special light responsive image, the special light responsive image forming material being smaller than the special light responsive image and being larger than the special light non-responsive image; An image forming method comprising forming the special light non-reactive image around the mixed image.

10. 10. An information recording medium having at least one of a character, a symbol, a code, and an image formed by the image forming apparatus according to claim 1 or the image forming method according to claim 9.

Images