Image forming device

Abstract

To determine the presence or absence of an abnormality in an invisible image used in a wide variety of applications when forming the invisible image.SOLUTION: An image forming apparatus finally transfers, onto a recording material, a toner image for an invisible image that is formed on an image carrier 12 by using a toner for an invisible image based on invisible image information, and forms an invisible image on the recording material, and the image forming apparatus has: detection means 180 that detects the toner for an invisible image attached onto the image carrier over the entirety of a toner carriable area on the image carrier in a width direction orthogonal to a surface movement direction of the image carrier; and determination means 30 that determines an abnormality occurrence position in the width direction based on a result of detection performed by the detection means.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there has been known an image forming apparatus that forms an invisible image on a recording material by finally transferring an invisible image toner image formed on an image carrier using invisible image toner based on invisible image information onto a recording material.

[0003] For example, Patent Document 1 discloses an image forming apparatus that forms a preset invisible image on recording paper (recording material) along with visible images of yellow (Y), magenta (M), cyan (C), and black (K) generated based on print data (image information). The invisible image is a linear image that continues in the sub-scanning direction (paper transport direction) outside the visible image formation area in the main scanning direction where the visible image is formed. This image forming apparatus forms an invisible image toner image on an intermediate transfer belt (image carrier) based on image data (invisible image information) stored in memory. Then, a detection sensor positioned opposite the position where the invisible image toner image is formed detects the invisible image toner image on the intermediate transfer belt and compares it with the invisible image information to determine whether or not there is an abnormality in the invisible image toner image. If an abnormality is determined, it is determined that an image defect, such as pixel misalignment in the main scanning direction or a streak-like image missing (line missing) along the main scanning direction, has occurred in the visible image on the recording paper, and a notification to that effect is provided. Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional image forming apparatuses use invisible images to determine image defects in visible images, but invisible images can be used in a wide range of applications, such as preventing unauthorized copying and increasing the amount of information in code images. Conventional image forming apparatuses have had the problem of being unable to determine whether or not there is an abnormality in invisible images used in such a wide range of applications. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus that finally transfers onto a recording material an invisible image toner image formed on an image carrier using invisible image toner based on invisible image information, thereby forming an invisible image on the recording material, and is characterized by having a detection means that detects invisible image toner adhering to the image carrier over the entire toner-carrying area on the image carrier in a width direction perpendicular to the surface movement direction of the image carrier, and a judgment means that judges the position where an abnormality has occurred in the width direction based on the detection result of the detection means. [Effects of the Invention]

[0006] According to the present invention, when forming an invisible image that is used in a wide range of applications such as preventing illegal copying or increasing the amount of information in a code image, it is possible to determine whether or not there is an abnormality in the image. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is an explanatory diagram showing the overall configuration of a printer according to an embodiment. [Figure 2] FIG. 2 is a block diagram relating to control of the invisible image mode in the printer. [Figure 3] FIG. 2 is a schematic diagram showing the configuration of a toner adhesion amount detection sensor in the printer. [Figure 4] FIG. 4 is a perspective view showing the toner adhesion amount detection sensor together with a part of the intermediate transfer belt from diagonally below. [Figure 5]FIG. 4 is an explanatory diagram showing an IR test toner image formed on the intermediate transfer belt, together with the intermediate transfer belt and a toner adhesion amount detection sensor. [Figure 6] 1A is an explanatory diagram showing an example of an image abnormality in the form of a white stripe extending in the sub-scanning direction (paper transport direction), and FIG. 1B is an explanatory diagram showing an example of an image abnormality in the form of a black stripe extending in the sub-scanning direction. [Figure 7] 10 is a flowchart showing the flow of an image abnormality detection process in the embodiment. [Figure 8] 10 is an explanatory diagram showing an example in which the position in the main scanning direction where an image abnormality such as a black streak occurs overlaps with the position of an invisible image printed in the invisible image mode. [Figure 9] FIG. 10 is an explanatory diagram showing an example of a selection screen that allows the user to select whether to continue or cancel printing. [Figure 10] 1A is an explanatory diagram showing an example of an original image in which an image abnormality of a black streak extending in the sub-scanning direction (paper transport direction) occurs, and FIG. 1B is an explanatory diagram showing an example in which the position of the invisible image has been changed to a position that does not overlap with the position in which the image abnormality of the black streak occurs. [Figure 11] (a) is an explanatory diagram showing an example of an original image in which an image abnormality of a black streak extending in the sub-scanning direction (paper transport direction) occurs. (b) is an explanatory diagram showing an example in which the orientation of the printed image is rotated 180 degrees so that the position of the invisible image does not overlap with the position in which the image abnormality of a black streak occurs. (c) is an explanatory diagram showing an example in which the orientation of the printed image is rotated 90 degrees so that the position of the invisible image does not overlap with the position in which the image abnormality of a black streak occurs. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment in which the present invention is applied to a color printer (hereinafter referred to as "printer"), which is an image forming apparatus, will be described with reference to the drawings. The image forming apparatus may be a single copy machine or facsimile machine other than a printer, or may be a multifunction machine having at least two of the functions of a printer, copy machine, facsimile machine, and scanner.

[0009] The printer of this embodiment has four process units as image forming sections that form images using yellow (Y), magenta (M), cyan (C), and black (K) toners as toners for visible images (hereinafter referred to as "visible toners"). Of these process units, the K process unit can be replaced with an IR process unit that serves as an image forming section that forms images using infrared absorbing toner (IR toner), which is a transparent toner as toner for invisible images (hereinafter referred to as "invisible toner").

[0010] An invisible image formed on a recording material using an invisible toner such as an infrared-absorbing toner includes not only an image that is completely invisible to the human eye, but also an image that is difficult to see compared to a normal visible image. Invisible images are used, for example, when embedding additional information in an image. Specific examples include invisible images that are difficult to recognize visually (text images such as "COPY" that cannot be seen by humans at a glance), called invisible patterns or background patterns, which are formed together with visible images using black or color toner for purposes such as preventing unauthorized copying. Furthermore, invisible images are used, for example, when a visible code image and an invisible code image are superimposed on each other and formed on a recording material to increase the amount of information in a code image such as a QR code (registered trademark).

[0011] An invisible image is, for example, an image formed using a highly transparent invisible toner (transparent toner) that has less color development under visible light than ordinary visible toners (color toners, black toners). Furthermore, invisible toner is a toner that is invisible or difficult to see when an invisible image formed using the invisible toner is formed on a recording material. Specific examples of invisible toner include transparent infrared-absorbing toners and transparent fluorescent toners that fluoresce when exposed to ultraviolet light, and toners that absorb light outside the visible light range or emit light in the visible light range when exposed to light outside the visible light range. This embodiment will be described using an example of using infrared-absorbing toner as the invisible toner, as described above.

[0012] 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), "K" for black toner (K ​​toner), and "IR" for infrared light absorbing toner (IR toner).

[0013] 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 material supply unit 3, a fixing unit 4, a recording material discharge unit 5, a control unit 30, and an image forming control unit 40.

[0014] The image forming unit 1 is provided with four unit holders for holding four process units 6 as replaceable units that are part of the image forming unit. Three of the unit holders correspond to the three process units 6Y, 6M, and 6C, respectively, that correspond to color toners. The remaining unit holder corresponds to the K process unit 6K and the IR process unit 6IR, and selectively mounts and holds either of the process units 6K or 6IR. Note that FIG. 1 illustrates an example in which the IR process unit 6IR is mounted and held in the unit holder, rather than the K process unit 6K. Each of the process units 6Y, 6M, 6C, 6K, and 6IR has the same configuration, except for the type of toner they use.

[0015] Because the printer of this embodiment has four unit holders, it is more compact than a printer equipped with five unit holders corresponding to the above-described five process units 6Y, 6M, 6C, 6K, and 6IR. In other words, a small printer with four unit holders can simultaneously form a full-color image (color black visible image) using Y, M, C, and K toners, and a full-color image (color visible image) and an IR image (invisible image) using Y, M, C, and IR toners.

[0016] Alternatively, all process units may be detachable, and the positions (unit holders) at which the process units are mounted may be interchangeable. 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 material (positional relationship in the toner image stacking direction). In this embodiment, the process units 6 that can be mounted on the unit holders on the most downstream side and the most upstream side in the running direction of the intermediate transfer belt 12 can be interchangeably mounted.

[0017] In this embodiment, each of the process units 6Y, 6M, 6C, 6K, and 6IR includes a photoconductor 7 as a latent image carrier that carries a latent image, a charging roller 8 as charging means for charging the surface of the photoconductor 7, a developing device 9 as developing means for developing the latent image on the photoconductor 7, and a photoconductor cleaning device 10 as latent image carrier cleaning means for cleaning the surface of the photoconductor 7. Opposite each photoconductor 7 is provided an exposure device 11 as latent image forming means that forms a latent image on the surface of the photoconductor 7. 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.

[0018] The transfer section 2 is provided with an endless intermediate transfer belt 12, which is an intermediate transfer body acting as an image carrier onto which the toner image on the photosensitive member 7 is transferred, a plurality of primary transfer rollers 13 acting as primary transfer means for primarily transferring the image on the photosensitive member 7 onto the intermediate transfer belt 12, a secondary transfer roller 14 acting as secondary transfer means for secondarily transferring the toner image transferred onto the intermediate transfer belt 12 onto a recording material, and a belt cleaning device 17 acting as intermediate transfer body cleaning means for cleaning the surface (outer peripheral surface) of the intermediate transfer belt 12.

[0019] The intermediate transfer belt 12 is stretched over a drive roller 15 and a driven roller 16, and rotates in a circular motion (rotation) as the drive roller 15 rotates. Each primary transfer roller 13 is arranged 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 arranged to contact the portion of the intermediate transfer belt 12 that is wrapped around the drive roller 15. A secondary transfer nip is formed at the contact point between this secondary transfer roller 14 and the intermediate transfer belt 12, where an image on the intermediate transfer belt 12 is transferred to a recording material.

[0020] The recording material supply unit 3 is provided with a paper feed cassette 18 as a recording material storage unit that stores paper P as the recording material, a paper feed roller 19 as recording material feeding means that feeds paper P from the paper feed cassette 18, and a timing roller pair 20 as recording material conveying means that conveys paper P fed by the paper feed roller 19 to the secondary transfer nip at a predetermined timing. Note that the recording material may be an OHP sheet, OHP film, cloth, etc., in addition to paper. In addition to plain paper, paper includes cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), textured paper such as Japanese paper, tracing paper, etc.

[0021] The fixing section 4 is provided with a fixing device 21 as a fixing means for fixing an image on 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 contacts the fixing roller 22 with a predetermined pressure to form a fixing nip.

[0022] The recording material discharge section 5 is provided with a pair of discharge rollers 24 as a recording material discharge means for discharging the paper P sent out from the fixing device 21 outside the device, and a paper discharge tray 25 as a recording material loading section for loading the paper P discharged by the pair of discharge rollers 24.

[0023] 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 controls the image forming operations in each part of the printer (image forming unit 1, transfer unit 2, recording material supply unit 3, fixing unit 4, recording material discharge unit 5, etc.) under the control of the control unit 30.

[0024] In addition to the above-described components, the printer of this embodiment is also provided with a container holding member 102 that detachably holds a plurality of toner cartridges 26Y, 26M, 26C, 26K, and 26IR as toner containers that contain powder toner used in image formation. Four toner container holding sections are provided on this container holding member 102, and a corresponding toner cartridge is attached to and held in each toner container holding section. Note that Fig. 1 shows an example in which an IR toner cartridge 26IR is attached to and held in the toner container holding section, rather than the K toner cartridge 26K.

[0025] Each of the toner cartridges 26Y, 26M, 26C, 26K, and 26IR contains the same type (color) of toner as the toner in the developing device 9 of each of the process units 6Y, 6M, 6C, 6K, and 6IR described above. Toner cartridges 26 corresponding to the toner of the process units 6 attached to the four unit holders are attached to the four toner container holders of the container holding member 102. When the toner in the developing device 9 of the attached process unit 6 falls below a predetermined amount, the same type of toner is replenished from the toner cartridge 26 attached to the corresponding toner container holder.

[0026] The printer of this embodiment is also equipped with a waste toner container 27. The waste toner container 27 stores waste toner collected by the belt cleaning device 17 or the photoconductor cleaning device 10.

[0027] 1, the printer of this embodiment is provided with a cover member 101 for opening and closing the top of the device main body (image forming device main body) 100. The cover member 101 is rotatable up and down around a rotation shaft 103 provided in the device main body 100. Also, below the cover member 101, a container holding member 102 is disposed that detachably holds four toner cartridges 26 in a toner container holding portion. The container holding member 102 is rotatable up and down around another rotation shaft 104 provided in the device main body 100.

[0028] 1, when the IR process unit 6IR is attached to the most downstream unit holder, the IR process unit 6IR is disposed at the most downstream side in the running direction of the intermediate transfer belt 12, and the color process units 6Y, 6M, and 6C are disposed upstream of it. In this case, a Y toner image, an M toner image, a C toner image, and an IR toner image are layered on the intermediate transfer belt 12 in this order from the belt side. After secondary transfer, the toner images are layered on the recording material in the order of the IR toner image, the C toner image, the M toner image, and the Y toner image in this order from the recording material side.

[0029] By forming the IR toner image closer to the recording material than the color toner image, the IR toner image is hidden by the color toner image, which makes it easier to increase the invisibility of the invisible image formed by the IR toner image. However, when forming an invisible image, the location of the IR process unit 6IR relative to the color process units 6Y, 6M, and 6C can be changed as needed. Also, as described above, if the mounting positions of the process units 6Y, 6M, 6C, and 6IR are configured to be interchangeable, the position of the IR process unit can be freely interchanged.

[0030] Furthermore, the printer of this embodiment adjusts the image density for each toner by adjusting the adhesion amount (toner adhesion amount per unit area) of each of the Y, M, C, K, and IR toners. Specifically, a toner adhesion amount detection sensor 180 is provided to detect the toner adhesion amount of test toner images (plural toner patches created to achieve different target densities) for each of the Y, M, C, K, and IR toners formed on the intermediate transfer belt 12. Based on the results detected by this toner adhesion amount detection sensor 180, the image creation conditions (image formation conditions) for each of the Y, M, C, K, and IR process units are adjusted so that the desired toner adheres to the desired density.

[0031] The toner adhesion amount detection sensor 180 of this embodiment may be a sensor commonly used for the Y, M, C, K, and IR test toner images, or may be a sensor individually used for each of the Y, M, C, K, and IR test toner images. The toner adhesion amount detection sensor 180 of this embodiment is an optical image density sensor (optical sensor) that irradiates the test toner image with light and receives specularly reflected light and diffusely reflected light from the test toner image. For the Y, M, and C color toners, the toner adhesion amount of the test toner image (image density of the test toner image) is detected based on the amount of both specularly reflected light and diffusely reflected light. However, for the K toner, the toner adhesion amount of the test toner image (image density of the test toner image) is detected based only on the amount of specularly reflected light.

[0032] On the other hand, the IR toner of this embodiment becomes an invisible image (for example, an image that is difficult to see with the naked eye or an image that has substantially no absorption peak in the visible light range) after fixing. However, if the IR toner forms a visible image (an image that can be seen with the naked eye or an image that has substantially an absorption peak in the visible light range) on the intermediate transfer belt 12 before fixing, a toner adhesion amount detection sensor similar to that for C, M, Y, and K can be used. In this embodiment, a common toner adhesion amount detection sensor 180 is used for the K test image and the IR test toner image. However, for the IR toner test toner image (toner image for an invisible image), it is more accurate to detect the toner adhesion amount of the test image by acquiring both specularly reflected light and diffusely reflected light than to detect the toner adhesion amount of the test toner image by acquiring only specularly reflected light.

[0033] 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., the exposure device 11 irradiates the charged surface of each photoconductor 7 with laser light to form a latent image (electrostatic latent image).

[0034] The latent image formed on each photoconductor 7 is a latent image based on monochrome image information (visible image information) obtained by decomposing a desired full-color image into color information of Y, M, and C. Specifically, a color conversion separation table is used to convert and separate 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 and separated into monochrome image information of Y, M, and C. Then, 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.

[0035] If the K process unit 6K is installed, after generating monochrome image information for Y, M, and C, monochrome image information is further generated by extracting K color information, and the monochrome image information for Y, M, and C is corrected. This process generates K image information, similar to UCR (Under Color Removal), and replaces black or gray image information, which is expressed by overlapping Y, M, and C toners, with K image information. The exposure device 11 corresponding to K (shared with the exposure device 11 corresponding to IR) forms a K latent image on the photoconductor 7 of the K process unit 6K based on the K image information.

[0036] Furthermore, in this embodiment, when an invisible image is formed based on additional information included in the input image information or additional information added by the printer, IR image information (invisible image information) is generated from the additional information. 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. When the IR process unit 6IR is installed, the exposure device 11 corresponding to IR (shared with the exposure device 11 corresponding to K) forms an IR latent image on the photoconductor 7 of the IR process unit 6IR based on the IR image information.

[0037] When the K process unit 6K is installed, toner is supplied from the respective developing devices 9 to the Y, C, M, and K latent images formed on the photoconductors 7, and the latent images are developed into Y, C, M, and K toner images. The toner images on the photoconductors 7 are sequentially superimposed and transferred onto the rotating intermediate transfer belt 12. More specifically, when the toner images on the photoconductors 7 reach the position of the primary transfer nip, a predetermined voltage is applied to the primary transfer roller 13 to form a transfer electric field, which sequentially transfers the toner images on the photoconductors 7 onto the intermediate transfer belt 12. In this way, a full-color toner image (visible image) made of Y, C, M, and K toners is formed on the surface of the intermediate transfer belt 12. Any toner on each photoconductor 7 that was not completely transferred to the intermediate transfer belt 12 is removed by the photoconductor cleaning device 10.

[0038] On the other hand, when the IR process unit 6IR is installed, toner is supplied from the respective developing devices 9 to the Y, C, M, and IR latent images formed on the photoconductors 7, and the latent images are developed into Y, C, M, and IR toner images. As described above, the toner images on each photoconductor 7 are transferred in succession onto the circulating intermediate transfer belt 12 in a superimposed state. In this way, a full-color toner image (visible toner image) made of Y, C, and M and an IR toner image (invisible toner image) made of IR toner are formed on the surface of the intermediate transfer belt 12. Note that any toner on each photoconductor 7 that is not completely transferred to the intermediate transfer belt 12 is removed by the photoconductor cleaning device 10, as described above.

[0039] 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 pair 20. Thereafter, the rotation of the timing roller pair 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.

[0040] 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.

[0041] 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 out of the device by a pair of paper discharge rollers 24, and placed on a paper discharge tray 25.

[0042] The above description is of the image forming operation when an image is formed using all four process units 6Y, 6M, 6C, and 6IR (or 6K), but this is not limiting. For example, it is also possible to form an image using any one of the four process units 6Y, 6M, 6C, and 6IR (or 6K), or to form an image using any two or three of the process units.

[0043] FIG. 2 is a block diagram relating to control of the invisible image mode in the printer of this embodiment. In the following explanation, a case where the color information of the input image information is RGB multi-value information will be described. Furthermore, a case where the input image information includes IR image information (additional information) when forming an IR image will be described, and the IR image will be formed based on the IR image information. Note that the additional information included in the input image information does not have to be image information. If it is non-image information, for example, the control unit 30 executes a predetermined IR image generation program to generate IR image information from the additional information. Furthermore, even if the input image information does not include additional information, the control unit 30 may generate IR image information according to user specifications, etc.

[0044] The control unit 30 of this embodiment is mainly composed of a main control unit 31, a memory unit 32 as a storage means, a color conversion / decomposition processing unit 33, a gamma conversion unit 35, a gradation conversion unit 36, and a toner total amount control unit 37.

[0045] The main control unit 31 is composed of a CPU, RAM, ROM, etc., and executes various programs to perform image processing and overall control of the printer. The storage unit 32 stores various data and programs used by each unit of the control unit 30.

[0046] The color conversion and decomposition processing unit 33 uses a color conversion and decomposition table stored in the storage unit 32 to convert and decompose the color information (RGB) of the input image information into color information for the printer, that is, Y, M, and C, to generate image information (visible image information) for each of Y, M, and C. Furthermore, if IR image information is included in the input image information, the color conversion and decomposition processing unit 33 extracts and generates IR image information (invisible image information) from the input image information.

[0047] In order to achieve appropriate gradation on the recording material, the gamma conversion unit 35 performs γ (gamma) conversion on each of the Y, M, and C image information, and, if necessary, on the IR image information, using a gamma conversion table stored in the memory unit 32.

[0048] The tone conversion unit 36 ​​uses the dither pattern data stored in the storage unit 32 to perform tone conversion processing to convert each piece of image information Y, M, C, and IR into a dither pattern according to the halftone density.

[0049] The total toner amount restricting unit 37 is used when the IR process unit 6IR is installed and the invisible image mode is performed. Under the control of the main control unit 31, the total toner amount restricting unit 37 uses a toner adhesion amount conversion table stored in the memory unit 32 to perform toner adhesion amount conversion processing (image processing) on ​​each of the gamma-corrected (gamma-converted) Y, M, and C image information so that the total amount of toner adhesion of Y toner, M toner, C toner, and IR toner per unit area (hereinafter referred to as the "total toner amount") is equal to or less than the upper fixing limit. At this time, the toner adhesion amount conversion processing (image processing) may also be performed on the IR image information.

[0050] The control unit 30 first acquires input image information from a reading device (scanner), a personal computer, etc. Then, the control unit 30 converts and separates the color information (RGB) of the input image information into color information for the printer, Y, M, and C, using a color conversion and separation table stored in the storage unit 32, by the color conversion and separation processing unit 33. At this time, if the K process unit 6K is installed and the normal mode is used, black generation processing is also performed.

[0051] In the invisible image mode using invisible toner, the control unit 30 performs gamma conversion processing on each piece of image information of Y, M, C, and IR, including IR image information (invisible image information) generated based on additional information, using the gamma conversion unit 35. Thereafter, the control unit 30 performs total toner amount control processing.

[0052] In the invisible image mode, since the K process unit 6K is not installed, Y, M, and C toner images are superimposed on black and gray image areas (areas that are replaced with K color information in the normal mode). Therefore, the total amount of toner per unit area for such image areas is greater than in the normal mode, which uses K toner. In this embodiment, the invisibility of the invisible image formed by the IR toner image is improved by superimposing an IR toner image on the Y, M, and C toner image areas with a large total amount of toner. However, if the total amount of toner per unit area becomes too large, there is a risk of poor fixing.

[0053] Therefore, even in the total toner amount control process in the invisible image mode, it is determined whether or not the toner excess portion exceeds the upper limit value, and if it is determined that the toner excess portion is included, the main control unit 31 causes the total toner amount control unit 37 to execute the total toner amount control process.

[0054] In this toner total amount control process, it is preferable to take into consideration the ratio of color toner to IR toner in order to ensure the invisibility of the invisible image produced by the IR toner in the invisible image mode. That is, in the toner total amount control process in the invisible image mode, the ratio of the amount of adhered color toner to the amount of adhered IR toner after the process is adjusted to a predetermined ratio that ensures the invisibility of the invisible image, and the amounts of adhered color toner and IR toner are determined. At this time, the amount of adhered toner in the toner excess portion is prevented from exceeding the upper limit.

[0055] After performing the total toner amount control process in this manner, the control unit 30 performs a gradation conversion process using the gradation conversion unit 36. The image information for Y, M, C, and IR output from the gradation conversion unit 36 ​​is sent to the image formation control unit 40, and the image formation operation (invisible image mode) is performed.

[0056] FIG. 3 is a schematic diagram showing the toner adhesion amount detection sensor 180 in this embodiment. The toner adhesion amount detection sensor 180 of this embodiment is used in common for each of the Y, M, C, K, and IR test toner images formed on the intermediate transfer belt 12. In Fig. 3, the toner adhesion amount detection sensor 180 includes a light source 181, a lens array 182, an image sensor array 183, a detection window 184 made of transparent glass, a shutter member 185, a white reference plate 186, and the like.

[0057] The shutter member 185 is capable of reciprocating along the belt movement direction A of the intermediate transfer belt 12 by being driven by an actuator, and along with this reciprocating movement, opens and closes the detection window 184. In Fig. 3, the shutter member 185 is shown in a state where it has retreated from directly below the detection window 184, exposing the detection window 184.

[0058] An example of the white reference plate 186 is one made of Lumirror E20 (product name), a white film manufactured by Toray Industries, Inc. The white reference plate 186 is fixed to the rear surface of the shutter member 185 with double-sided tape or the like, and moves back and forth together with the shutter member 185 along the belt movement direction A.

[0059] A light emitting element provided at the end of a light guide, an LED array, or the like can be used as light source 181. Light source 181 emits white light, but it is also possible to provide light sources that individually emit R (red), G (green), and B (blue) light and mix these lights to produce white light.

[0060] An example of the lens array 182 is a SELFOC (registered trademark) lens. The imaging element array 183 includes a plurality of image sensors arranged in an array. Each image sensor individually receives R (red) light, G (green) light, and B (blue) light formed by the lens array 182, and outputs a signal corresponding to each light. A CMOS sensor, a CCD sensor, or the like is used as the imaging element array 183.

[0061] An example of the toner adhesion amount detection sensor 180 is a contact image sensor (CIS). As shown in FIG. 4, the toner adhesion amount detection sensor 180 is disposed so as to face the front surface of the intermediate transfer belt 12 with a predetermined gap therebetween, with its longitudinal direction aligned along a direction (main scanning direction or belt width direction) perpendicular to the surface movement direction of the intermediate transfer belt 12. In this embodiment, the longitudinal dimension of the toner adhesion amount detection sensor 180 is larger than the width dimension of the intermediate transfer belt 12. This allows the toner adhesion amount detection sensor 180 to individually detect the toner adhesion amount (image density) of each pixel across the entire longitudinal area of ​​a test toner image (described below) formed on the front surface of the intermediate transfer belt 12. Even if the longitudinal dimension of the toner adhesion amount detection sensor 180 is not larger than the belt width, the following is possible if it is equal to or larger than the dimension of the effective image area (area capable of carrying a toner image) in the belt width direction. That is, it is possible to have the toner adhesion amount detection sensor 180 detect the image density of each pixel over the entire area of ​​the test toner image in the longitudinal direction.

[0062] The control unit 30 performs a shading correction data creation process during the first operation after shipping from the factory. In this shading data creation process, shading correction data is created based on image data obtained by having the toner adhesion amount detection sensor 180 detect the image density of each pixel of the white reference plate 186. Specifically, if the white reference plate 186 or the detection window 184 is completely free of dirt, theoretically, each pixel of the image data obtained by reading the white reference plate 186 should be read as white. However, in reality, slight variations occur in the pixel values ​​of each pixel due to sensitivity errors in the image elements of the image line sensor and variations in the light emission amount of the light source 181. As a result, unevenness in the toner adhesion amount (unevenness in image density) will be erroneously detected. Therefore, to prevent this erroneous detection of unevenness in the toner adhesion amount (unevenness in image density), correction data for recognizing all pixels as white is created as shading correction data.

[0063] In the image forming apparatus according to this embodiment, a streak-like image abnormality (image density abnormality) may occur in an image due to an equipment malfunction. The image density abnormality is significantly lighter or darker than the original image density, and is a streak-like pattern extending in the sub-scanning direction of the image. The sub-scanning direction is the direction along which the surfaces of the photoreceptors 7Y, 7M, 7C, and 7K and the intermediate transfer belt 12 move, which corresponds to the direction of image movement within the image forming apparatus. In contrast, the main scanning direction is the direction along the rotation axes of the photoreceptors 7Y, 7M, 7C, and 7K and the belt width direction of the intermediate transfer belt 12, which is also perpendicular to the sub-scanning direction.

[0064] The control unit 30 periodically performs an image abnormality detection process to determine whether or not there are any streaky image density abnormalities in the test toner image, and if any streaky image density abnormalities are found, to notify the user of the abnormality. FIG. 5 is a diagram showing the IR test toner image TIR formed on the front surface of the intermediate transfer belt 12 during this image abnormality detection process, along with the intermediate transfer belt 12 and the toner adhesion amount detection sensor 180. As shown in FIG. 5, the IR test toner image TIR is formed in a rectangular shape extending in the belt width direction. While the length does not span the entire belt width, it is the same length as the effective image area in the belt width direction.

[0065] 6(a) and 6(b) are explanatory diagrams showing an example in which an IR toner image has an image abnormality in the form of streaks extending in the sub-scanning direction (paper transport direction). 6A, white streaks ws appear in the IR test toner image TIR as streaky image density abnormalities. White streaks ws are streaky image density abnormalities formed with an image density significantly lower than the actual image density. In the IR process unit 6IR, if dirt adheres to the light emitting portion (such as the dustproof glass) of the exposure device 11 or if foreign matter is mixed in the developer in the development device 9, white streaks ws extending in the sub-scanning direction may appear, as shown in the figure.

[0066] 6(b), black streaks ds have occurred as streak-like image density abnormalities. Black streaks ds are streak-like image density abnormalities formed with an image density significantly higher than the actual image density, and appear on the IR test toner image TIR. They can also appear when the IR test toner image TIR is not formed, as shown in the figure. In the IR process unit 6IR, black streaks ds extending in the sub-scanning direction, as shown in the figure, can occur due to factors such as dirt adhering to the charging roller 8.

[0067] When the control unit 30 starts the image abnormality detection process described above, it forms an IR test toner image TIR. Then, it obtains the image density (toner adhesion amount) for each pixel aligned in the main scanning direction in the image data obtained by capturing the IR test toner image TIR with the toner adhesion amount detection sensor 180. Then, it determines the presence or absence of white streaks ws and black streaks ds in the IR test toner image TIR based on the image density of each pixel.

[0068] Because the IR test toner image TIR is created uniformly with a predetermined toner adhesion amount (predetermined image density), the detection results (pixel values ​​of the image data) of the toner adhesion amount detection sensor 180 will show uniform values ​​unless an image abnormality occurs. However, if a white streak ws occurs as shown in the lower diagram of FIG. 6(a), the output value (pixel value) of that area will locally decrease as shown in the graph in the upper diagram of FIG. 6(a). For this reason, a predetermined threshold is determined, and if a value lower than that threshold is shown, it is determined that a white streak has occurred in that area.

[0069] On the other hand, in areas where the IR test toner image TIR has not been created, the detection results (pixel values ​​of the image data) of the toner adhesion amount detection sensor 180 are essentially zero. However, if a black streak ds occurs as shown in the lower diagram of Figure 6(b), the output value (pixel value) of that area will be locally high, as shown in the graph in the upper diagram of Figure 6(b). For this reason, a predetermined threshold is determined, and if a value higher than that threshold is shown, it is determined that a black streak has occurred in that area.

[0070] FIG. 7 is a flowchart showing the flow of the image abnormality detection process in this embodiment. Although the image abnormality detection process of this embodiment is described as being performed when the invisible image mode is executed, the execution timing of the image abnormality detection process is not limited to this. For example, the execution timing of the image abnormality detection process may be set to be set by the user at will, or may be set to be automatically executed when certain conditions are satisfied.

[0071] First, the control unit 30 determines whether to print in invisible image mode (S1). The image abnormality detection process of this embodiment aims to detect abnormalities in the invisible image after printing (the invisible image on the paper). Therefore, if an invisible image is not to be printed, the process proceeds to processing step S20, where normal printing is performed and the process ends. The determination of whether to print in invisible image mode may be made by the user selecting the invisible image mode and printing, or by determining the coverage of the invisible image mode and determining that printing is to be in invisible image mode if the coverage is greater than 0%.

[0072] If printing is performed in the invisible image mode (Yes in S1), the control unit 30 then determines whether the conditions for executing the image abnormality detection process for the invisible image (abnormality detection process execution conditions) are met (S2). Examples of the abnormality detection process execution conditions include that a predetermined number of sheets or more have been printed since the previous image abnormality detection process was performed, that a predetermined amount of time has passed since the previous printing, or that the environment (temperature and humidity) in which the printer is used has changed by a predetermined amount or more.

[0073] If the image abnormality detection process were executed every time printing was performed in invisible image mode, IR toner would be wasted. Image abnormalities often occur due to factors such as deterioration over time. Therefore, by setting an abnormality detection process execution condition, such as printing a specified number of pages or more, and determining the execution timing, the image abnormality detection process can be executed at the appropriate execution timing, thereby reducing toner consumption. Furthermore, environmental changes or a long period of time since the last print can also cause changes in the charge amount of IR toner, making it more likely that abnormal images will develop, such as toner contamination (background smearing). Therefore, by setting an abnormality detection process execution condition, such as a significant change in the environment or a long period of time since the last print, and determining the execution timing, the image abnormality detection process can be executed at the appropriate execution timing, thereby reducing toner consumption.

[0074] If the conditions for executing the abnormality detection process are not met (No in S2), the process proceeds to processing step S20, where normal printing is performed and the process ends. On the other hand, if the conditions for executing the abnormality detection process are met (Yes in S2), the image abnormality detection process is executed (S3). In the image abnormality detection process, an IR test toner image TIR (a long horizontal band pattern spanning the entire area in the main scanning direction) is first created using IR toner as shown in FIG. 5. In this embodiment, the length of the IR test toner image TIR in the sub-scanning direction is set to 100 mm from the perspective of toner consumption.

[0075] For example, if a white streak ws occurs in the IR process unit 6IR, the output value (pixel value) of the toner adhesion amount detection sensor 180 that detected the IR test toner image TIR indicates that the output value (pixel value) of the portion corresponding to the position in the main scanning direction where the white streak ws occurred is lower than a predetermined threshold. This output result of the toner adhesion amount detection sensor 180 indicates that there is an image abnormality in the form of a white streak ws at that portion in the main scanning direction.

[0076] Furthermore, in the image abnormality detection process of this embodiment, the toner adhesion amount detection sensor 180 also detects portions of the sub-scanning direction where the IR test toner image TIR is not created (for example, non-toner image portions adjacent to the IR test toner image TIR in the sub-scanning direction). At this time, if, for example, there is an abnormality in the IR process unit 6IR and a black streak ds has occurred, the output value of the toner adhesion amount detection sensor 180 indicates that the output value (pixel value) of the portion of the main scanning direction where the black streak ds has occurred is higher than a predetermined threshold. The output result of this toner adhesion amount detection sensor 180 indicates that there is an image abnormality in the form of a black streak ds at that portion of the main scanning direction.

[0077] The IR test toner image TIR is not limited to the horizontal band pattern described above, and may be, for example, a pattern (full solid image) covering the entire area corresponding to the entire surface of the paper, as long as it is a pattern formed over the entire area in the main scanning direction where an IR toner image can be carried on the intermediate transfer belt 12. In this way, by creating a pattern that is also long in the sub-scanning direction as the IR test toner image TIR, it becomes possible to detect image abnormalities such as periodic horizontal streaks in the sub-scanning direction that occur when a toner image is being created or when a toner image is not being created.

[0078] The toner adhesion amount detection sensor 180 in this embodiment is a line sensor that can detect IR toner over the entire area in the main scanning direction on the intermediate transfer belt 12 where an IR toner image can be carried. Therefore, it is possible to detect the presence or absence of an image abnormality that occurs anywhere within the area where an IR toner image can be carried. Therefore, even if an invisible image can be formed anywhere in the main scanning direction, it is possible to determine the presence or absence of an abnormality in the invisible image.

[0079] Furthermore, if the toner adhesion amount detection sensor 180 can detect IR toner over the entire supportable area as in this embodiment, it will also be possible to detect periodic vertical streaks (white streaks ws and black streaks ds) in the main scanning direction that occur when a toner image is being created or when a toner image is not being created.

[0080] After executing the image abnormality detection process, the control unit 30 determines whether or not there is an abnormality in the IR toner image based on the detection result of the toner adhesion amount detection sensor 180 (S4). As described above, this determination can be made by determining whether or not there is a pixel value higher or lower than a predetermined threshold. If there is no abnormality in the IR toner image (No in S4), the process proceeds to processing step S20, where normal printing is performed and the process ends.

[0081] On the other hand, if an abnormality has occurred in the IR toner image (Yes in S4), the control unit 30 determines whether the abnormality will affect the invisible image that will be printed in the invisible image mode. Specifically, the control unit 30 determines whether the position where the abnormality occurred in the IR toner image overlaps with the position where the invisible image that will be printed in the invisible image mode will be formed. For example, when it is determined that a black streak ds will occur, the control unit 30 determines whether the position in the main scanning direction where the black streak ds will occur overlaps with the position of the two-dimensional code image, which is the invisible image that will be printed in the invisible image mode, as shown in Figure 8.

[0082] If the control unit 30 determines that an abnormality in the IR toner image will affect the invisible image, it causes the operation display unit 50, which is made up of a touch panel or the like, to display a selection screen that allows the user to select whether to continue or stop printing, as shown in Fig. 9. This selection screen may be displayed on the operation display unit 50 provided in the printer, or alternatively, it may be displayed as part of a printer driver setting screen displayed on the screen of a personal computer or the like operated by the user, and the notification method is not important.

[0083] If the user selects to stop printing on this selection screen (Yes in S5), the control unit 30 will stop the printing operation and end the process. If the degree of the abnormal image is severe, it may not be possible to perform processing to eliminate the impact, as described below. In such cases, the printing will be ended without continuing, and measures will be taken, such as notifying a maintenance company or other organization of the malfunction.

[0084] On the other hand, if the user selects to continue printing on this selection screen (No in S5), the control unit 30 in this embodiment further sets the printing method for the invisible image (S10). As described above, abnormal invisible images cannot be detected visually, so if there is no impact on the quality of the printed matter, they may be acceptable as is. In this case, the user operates the operation display unit 50 or the PC to select the printing method to continue printing as is. This causes the process to proceed to processing step S20, where normal printing is performed and the process ends.

[0085] Furthermore, as described above, abnormalities in the invisible image cannot be detected visually, and therefore changing the relative position of the invisible image with respect to the printed image on the paper often has little effect on the quality of the printed matter. Therefore, even if the position of the invisible image in the original image shown in Figure 10(a) is changed to a position that does not overlap with the position where the abnormality occurs in the IR toner image (the position of the black streak ds) as shown in Figure 10(b), the quality of the printed matter is hardly affected. Therefore, by performing a correction to change the position of the invisible image to a position that does not overlap with the position where the abnormality occurs in the IR toner image, it is possible to form the invisible image on the paper P without being affected by the abnormality.

[0086] In this case, the user operates the operation display unit 50 or the PC to select a printing method in which the position of the invisible image is changed to a position that does not overlap with the position where the abnormality occurred in the IR toner image and then printed. When this selection is made, the control unit 30 executes a process to change the position of the invisible image for the IR image information, then proceeds to processing step S20, where normal printing is performed and the process ends.

[0087] Another example of a printing method is to change the orientation of the print image printed on the paper. Specific examples include a method of rotating the orientation of the original image shown in FIG. 11(a) by 180 degrees as shown in FIG. 11(b), or a method of rotating the orientation of the original image by 90 degrees as shown in FIG. 11(b). These printing methods allow the position of the invisible image to be positioned so that it does not overlap with the position where the IR toner image abnormality occurs, while maintaining the relative position of the invisible image to the print image printed on the paper, i.e., without changing the print image printed on the print.

[0088] Next, the toner used in this embodiment will be described. In the following description, the toner set of this embodiment is a toner set including color toners Y, M, and C and an IR toner which is an invisible toner. The Y, M, and C color toners (visible toners) contain a binder resin and a colorant, and may further contain other components as needed. The K toner (visible toner) also contains a binder resin and a colorant, and may further contain other components as needed. IR toner (invisible toner) contains a binder resin and a near-infrared absorbing material, and may further contain other components as required.

[0089] In this embodiment, when the toner set satisfies any of the following conditions, a toner set is provided that, when the color toner image formed together with the IR toner image (invisible toner image) is visually observed, has good visibility of the image quality of the color toner image and good reading accuracy of the IR toner image. The first condition is that the printer has color toner and IR toner, and the 60-degree gloss of a solid image of the IR toner is 30 or more, and the 60-degree gloss of the solid image of the IR toner is 10 or more higher than the 60-degree gloss of the solid image of the color toner. The second condition is that the toner contains color toner and IR toner, and the loss tangent (tanδi) of the IR toner within the temperature range of 100°C to 140°C is 2.5 or more, and the loss tangent (tanδc) of the color toner within the temperature range of 100°C to 140°C is 2 or less.

[0090] The toner disclosed in JP 2001-265181 A does not specify the type of toner to be used for superimposing the toner images, resulting in the problem of the difference in gloss between the superimposed images making the invisible image visible. To solve this problem, JP 2007-171508 A, JP 2007-003944 A, and JP 2010-113368 A propose using an IR toner with a lower gloss than the color toner used. However, in recent years, electrophotographic image output has seen an increasing demand for relatively low-gloss images, in contrast to the high-gloss images produced by conventional offset printing. Therefore, when using high-gloss color toners, the gloss of high-adhesion areas, such as overlapping areas with the invisible image (IR image), as well as secondary and tertiary colors, is high, resulting in the problem of the position of the IR image being visually noticeable. Furthermore, when color toner is formed on an IR image, the color toner layered on the IR toner layer is likely to get into the IR toner layer when the fixing nip is heated and pressurized, which causes a problem of unstable reading accuracy when mechanically reading the information on the IR image.

[0091] <IRトナー> The IR toner contains a binder resin and a near-infrared absorbing material, and may further contain other components as required.

[0092] <<Binder resin>> The binder resin is not particularly limited, and any conventionally known resin can be used. Examples of binder resins include styrene-based resins such as styrene, α-methylstyrene, chlorostyrene, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, and styrene-acrylonitrile-acrylic acid ester copolymer; polyester resins; vinyl chloride resins; rosin-modified maleic acid resins; phenolic resins; epoxy resins; polyethylene resins; polypropylene resins; ionomer resins; polyurethane resins; silicone resins; ketone resins; xylene resins; petroleum-based resins; and hydrogenated petroleum-based resins. These may be used alone or in combination of two or more. Among these, styrene-based resins and polyester resins containing aromatic compounds as structural units are preferred, with polyester resins being more preferred.

[0093] The polyester resin can be obtained by a generally known polycondensation reaction between an alcohol and an acid. Examples of alcohols include diols such as polyethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-propylene glycol, neopentyl glycol, and 1,4-butenediol; etherified bisphenols such as 1,4-bis(hydroxymethyl)cyclohexane, bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, and polyoxypropylenated bisphenol A; and saturated or unsaturated alcohols having 3 to 22 carbon atoms. Examples of the dihydric alcohol monomer include dihydric alcohol units substituted with hydrocarbon groups, other dihydric alcohol units, sorbitol, 1,2,3,6-hexanetetrol, 1,4-salbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene. These may be used alone or in combination of two or more.

[0094] The acid is not particularly limited and can be appropriately selected depending on the purpose, but carboxylic acids are preferred. Examples of carboxylic acids include monocarboxylic acids such as palmitic acid, stearic acid, and oleic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, and malonic acid, divalent organic acid monomers obtained by substituting these with saturated or unsaturated hydrocarbon groups having 3 to 22 carbon atoms, anhydrides of these acids, dimers of lower alkyl esters and linoleic acid, 1,2,4-benzenetricarboxylic acid, and 1, Examples of suitable carboxylic acid monomers include trivalent or higher polyvalent carboxylic acid monomers such as 2,5-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, embole trimer acid, and anhydrides of these acids. These may be used alone or in combination of two or more.

[0095] The binder resin may also contain a crystalline resin. The crystalline resin is not particularly limited as long as it has crystallinity and can be appropriately selected depending on the purpose, and examples thereof include polyester resins, polyurethane resins, polyurea resins, polyamide resins, polyether resins, vinyl resins, and modified crystalline resins. These may be used alone or in combination of two or more. Among these, polyester resins, polyurethane resins, polyurea resins, polyamide resins, and polyether resins are preferred, and resins having at least one of a urethane skeleton and a urea skeleton are preferred in order to provide moisture resistance and incompatibility with the amorphous resin described below.

[0096] From the viewpoint of fixability, the weight-average molecular weight (Mw) of the crystalline resin is preferably 2,000 to 100,000, more preferably 5,000 to 60,000, and particularly preferably 8,000 to 30,000. When the weight-average molecular weight is 2,000 or more, the problem of deterioration in hot offset resistance can be prevented, and when it is 100,000 or less, the problem of deterioration in low-temperature fixability can be prevented.

[0097] << Near-infrared light absorbing materials >> As the near-infrared light absorbing material, either an inorganic material or an organic material can be used. To date, various transparent (invisible) infrared-absorbing materials have been investigated for additional data embedding technology, and various materials have been disclosed. For example, inorganic materials include rare earth metals such as ytterbium (Japanese Patent Application Laid-Open Nos. 9-77507 and 9-104857) and infrared-absorbing materials containing copper phosphate crystallized glass (Japanese Patent Application Laid-Open Nos. 7-53945 and 2003-186238). Organic materials include aluminum compounds (Japanese Patent Application Laid-Open No. 7-271081) and croconium dyes (Japanese Patent Application Laid-Open No. 2001-294785). Furthermore, Japanese Patent Application Laid-Open No. 2002-146254 proposes an organic material containing an infrared-absorbing material that has a spectral absorption maximum wavelength between 750 nm and 1100 nm and an absorbance at 650 nm that is 5% or less of the absorbance at the spectral absorption maximum wavelength. Furthermore, Japanese Patent Application Laid-Open Nos. 2007-171508, 2007-3944, 2010-113368, and 2008-76663 propose the use of naphthalocyanine pigments, which can be said to be an excellent technology in terms of the difference between the absorbance of visible light and the absorbance of infrared light.

[0098] Examples of inorganic near-infrared light absorbing materials include glass in which transition metal ions or dyes made of inorganic and / or organic compounds are added to known glass network forming components that transmit wavelengths in the visible range, such as phosphoric acid, silica, or boric acid, and glass crystals obtained by crystallizing such glass by heat treatment. These inorganic materials highly reflect light in the visible range, allowing invisible images to be obtained.

[0099] Examples of organic near-infrared light absorbing materials include colored materials such as phthalocyanine compounds and anthraquinone compounds, and colorless materials such as aluminum salt compounds and naphthalocyanine compounds. Among these, colorless materials are preferred because they do not color the image when added, have sufficiently high absorption in the infrared light range 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.

[0100] The naphthalocyanine compound is not particularly limited and can be appropriately selected depending on the purpose, but the compounds exemplified below are preferred.

[0101] [ka]

[0102] In the chemical formula (1), Met represents two hydrogen atoms, a divalent metal atom, or a trivalent or tetravalent substituted metal atom; 1 ~A 8 may be the same or different and each represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthio group, or a substituted or unsubstituted arylthio group, provided that A 1 and A 2 , A 3 and A 4 , A 5 and A 6 , A 7 and A 8 In each combination of Y, both cannot be hydrogen atoms or halogen atoms at the same time. 1 ~Y 16may be the same or different and each represent a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted arylthio group, a substituted or unsubstituted alkylamino group, a substituted or unsubstituted dialkylamino group, a substituted or unsubstituted arylamino group, a substituted or unsubstituted diarylamino group, a substituted or unsubstituted alkylarylamino group, a hydroxy group, a mercapto group, a nitro group, a nitrile group, an oxycarbonyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an aminocarbonyl group, or a mono- or di-substituted aminocarbonyl group.

[0103] The reflectance of the near-infrared light absorbing material at the reading wavelength is preferably 50% or less in order to ensure stable mechanical reading by infrared light irradiation. If the reflectance is 50% or less, the problem of reduced reading accuracy can be prevented. The reflectance can be measured, for example, by measuring the output solid image using a spectrophotometer (for example, V-660 (manufactured by JASCO Corporation), eXact (manufactured by X-Rite), etc.).

[0104] The near-infrared absorbing material is preferably dispersed and contained in the toner particles. If near-infrared light-absorbing materials are externally attached to the toner surface or mixed into toner particle clusters, they may cause material aggregation within the toner particles and developer. Furthermore, even if the required amount is added in bulk, they may be lost due to external attachment to the toner surface or adhesion to the equipment during developer preparation. This can result in a lack of near-infrared light-absorbing material or uneven distribution in the IR image, making it impossible to accurately and stably read information. Furthermore, free near-infrared light-absorbing materials may contaminate the equipment, particularly the photoreceptor, and adversely affect other processes such as development and transfer. Furthermore, organic near-infrared light-absorbing materials, as mentioned above, have better dispersibility in binder resins than inorganic materials, allowing them to disperse uniformly in the IR image formed on the image output medium without impairing invisibility in the visible range. They also exhibit sufficient absorption in the infrared range, allowing for high-density recording of information. Their good dispersibility in the toner enables stable machine reading and decoding of IR images over long periods of time.

[0105] The numerical range of the content of the near-infrared light absorbing material varies depending on the characteristics of the near-infrared light absorbing material. Regardless of the type of near-infrared light absorbing material, if the content is insufficient, near-infrared light absorption will be insufficient. If near-infrared light absorption is insufficient, a large amount of IR toner must be attached to the medium, such as paper. This causes visible unevenness due to IR toner aggregates (clumps) and wastes resources. If the content of the near-infrared light absorbing material is excessive, the near-infrared light absorbing material will have a slight absorption in the visible light wavelength range. This causes the near-infrared light absorbing material itself to be easily visible. In the case of vanadyl naphthalocyanine, which is often used as a transparent (invisible) near-infrared light absorbing material, the content thereof is preferably 0.3% by mass or more and 1.0% by mass or less with respect to the IR toner.

[0106] <<Other ingredients>> The other components are not particularly limited as long as they are normally contained in toner, and can be appropriately selected depending on the purpose. Examples include a release agent, a charge control agent, and an external additive.

[0107] <<<Mold release agent>>> As the release agent, either natural wax or synthetic wax can be used, and these may be used alone or in combination of two or more kinds. Examples of natural waxes include plant waxes such as carnauba wax, cotton wax, wood wax, and rice wax; animal waxes such as beeswax and lanolin; mineral waxes such as ozokerite and cerusine; and petroleum waxes such as paraffin, microcrystalline, and petrolatum.

[0108] Examples of synthetic waxes include synthetic hydrocarbon waxes such as Fischer-Tropsch wax and polyethylene wax; synthetic waxes such as esters, ketones, and ethers; fatty acid amides such as 1,2-hydroxystearic acid amide, stearic acid amide, phthalimide anhydride, and chlorinated hydrocarbons; and crystalline polymers having long-chain alkyl groups in the side chains, such as low-molecular-weight crystalline polymers, such as polyacrylate homopolymers or copolymers (e.g., n-stearyl acrylate-ethyl methacrylate copolymers) of polyacrylates, including poly(n-stearyl methacrylate) and poly(n-lauryl methacrylate).

[0109] Among these, it is preferable to use a monoester wax as the release agent. Monoester wax has low compatibility with general binder resins and therefore tends to bleed to the surface during fixing, exhibiting high release properties and ensuring high gloss and high low-temperature fixability. The monoester wax is preferably a synthetic ester wax. Examples of the synthetic ester wax include a monoester wax synthesized from a long-chain linear saturated fatty acid and a long-chain linear saturated alcohol. The long-chain linear saturated fatty acid is represented by the general formula C n H 2n+1 Preferably, the long-chain saturated alcohol is represented by COOH, and n is about 5 to 28. n H 2n+1 It is preferably represented by OH, and n=5 to 28 or so.

[0110] Specific examples of long-chain saturated fatty acids include capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecanoic acid, tetradecanoic acid, stearic acid, nonadecanoic acid, aramonic acid, behenic acid, lignoceric acid, cerotic acid, heptacosanoic acid, montanic acid, and melissic acid. Specific examples of long-chain saturated alcohols include amyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, capryl alcohol, nonyl alcohol, decyl alcohol, undecyl alcohol, lauryl alcohol, tridecyl alcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, nonadecyl alcohol, eicosyl alcohol, ceryl alcohol, and heptadecannol, which may have a substituent such as a lower alkyl group, an amino group, or a halogen atom.

[0111] The melting point of the release agent is preferably 50°C to 120°C. When the melting point of the release agent is within this range, it can effectively act as a release agent between the interface between the fixing roller and the toner, thereby improving high-temperature offset resistance without applying a release agent such as oil to the fixing roller. Specifically, when the melting point is 50°C or higher, the problem of deterioration in the heat-resistant storage stability of the toner can be prevented, while when it is 120°C or lower, the release property at low temperatures is not exhibited, and problems such as deterioration in cold offset resistance and wrapping of paper around the fixing machine can be prevented. The melting point of the release agent can be measured by measuring the maximum endothermic peak using, for example, a differential scanning calorimeter, TG-DSC System TAS-100 (manufactured by Rigaku Denki Co., Ltd.).

[0112] The content of the release agent is preferably 1% by mass to 20% by mass, more preferably 3% by mass to 10% by mass, relative to the binder resin. If the content is 1% by mass or more, the problem of insufficient offset prevention effect can be prevented, and if it is 20% by mass or less, the problem of reduced transferability and durability can be prevented.

[0113] The content of the monoester wax is preferably 4 to 8 parts by weight, more preferably 5 to 7 parts by weight, per 100 parts by weight of the IR toner. When the content is 4 parts by weight or more, it is possible to prevent problems such as insufficient exudation to the surface during fixing, poor release properties, and reduced gloss, low-temperature fixability, and high-temperature offset resistance. When the content is 8 parts by weight or less, it is possible to prevent problems such as an increased amount of release agent precipitating on the toner surface, reduced storage stability as a toner, and reduced filming tendency on photoreceptors.

[0114] The toner of this embodiment preferably contains a wax dispersant, and the dispersant is preferably a copolymer composition containing at least styrene, butyl acrylate, and acrylonitrile as monomers, or a polyethylene adduct of the copolymer composition. The content of the wax dispersant is preferably 7 parts by mass or less per 100 parts by mass of the IR toner. The inclusion of the wax dispersant provides a wax dispersion effect, which is expected to stably improve storage stability regardless of the manufacturing method. Furthermore, the wax dispersion effect reduces the wax diameter, thereby suppressing filming on the photoreceptor, etc. If the content is 7 parts by mass or less, the amount of incompatible components with the polyester resin increases, resulting in a decrease in gloss. Furthermore, the wax dispersibility becomes too high, which improves filming resistance but prevents poor exudation of the wax to the surface during fixing, resulting in a decrease in low-temperature fixability and hot offset resistance.

[0115] <<<Charge control agent>>> Any known charge control agent can be used, including, for example, nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdic acid chelate pigments, rhodamine dyes, alkoxyamines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts), alkylamides, phosphorus simple substance or compounds, fluorine-based surfactants, salicylic acid metal salts, and metal salts of salicylic acid derivatives. These may be used alone or in combination of two or more.

[0116] The charge control agent may be a synthesized one or a commercially available product, such as Bontron 03, Bontron P-51, Bontron S-34, E-82, E-84, and E-89 (all manufactured by Orient Chemical Industry Co., Ltd.), TP-302, TP-415, Copy Charge PSY VP2038, Copy Blue PR, Copy Charge NEG VP2036, and Copy Charge NX VP434 (all manufactured by Hoechst), LRA-901, and LR-147 (manufactured by Nippon Carlit Co., Ltd.).

[0117] The content of the charge control agent can be appropriately selected depending on the type of binder resin, the presence or absence of additives used as needed, and the toner production method, including the dispersion method, but is preferably 0.1 to 5 parts by mass, and more preferably 0.2 to 2 parts by mass, per 100 parts by mass of binder resin. If the content is 5 parts by mass or less, the toner has too high a chargeability, which reduces the effect of the main charge control agent and increases the electrostatic attraction force with the developing roller, preventing problems such as reduced developer fluidity and reduced image density.

[0118] Furthermore, the thermal properties of the toner can be controlled by using a trivalent or higher metal salt among the charge control agents. By including the metal salt, a crosslinking reaction with the acidic groups of the binder resin proceeds during fixing, forming weak three-dimensional crosslinks, thereby achieving high-temperature offset resistance while maintaining low-temperature fixing properties.

[0119] Examples of metal salts include metal salts of salicylic acid derivatives and metal acetylacetonates. The metal is not particularly limited as long as it is a trivalent or higher polyvalent ionic metal and can be appropriately selected depending on the purpose, and examples include iron, zirconium, aluminum, titanium, nickel, etc. Among these, trivalent or higher valent metal salicylate compounds are preferred.

[0120] The content of the metal salt is not particularly limited and can be appropriately selected depending on the purpose, but for example, it is preferably 0.5 to 2 parts by mass, more preferably 0.5 to 1 part by mass, relative to 100 parts by mass of the IR toner. When the content is 0.5 parts by mass or more, the problem of poor hot offset resistance can be prevented, and when the content is 2 parts by mass or less, the problem of poor gloss can be prevented.

[0121] <<<External additives>>> The external additive is contained to aid in fluidity, developability, and chargeability. There are no particular restrictions on the external additive and it can be appropriately selected depending on the purpose. Examples of the external additive include inorganic fine particles and polymer fine particles. Examples of inorganic fine particles include silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, tin oxide, silica sand, clay, mica, wollastonite, diatomaceous earth, chromium oxide, cerium oxide, penguin, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride, etc. These may be used alone or in combination of two or more. Examples of polymeric fine particles include polystyrene obtained by soap-free emulsion polymerization, suspension polymerization, or dispersion polymerization, methacrylic acid ester or acrylic acid ester copolymers, silicone, benzoguanamine, nylon, or other polycondensation systems, and polymer particles made from thermosetting resins.

[0122] The external additives can be surface-treated with a surface treatment agent to increase their hydrophobicity, thereby preventing deterioration of flowability and charging characteristics even under high humidity conditions. Examples of surface treatment agents include silane coupling agents, silylating agents, silane coupling agents having a fluorinated alkyl group, organic titanate coupling agents, aluminum coupling agents, silicone oils, and modified silicone oils.

[0123] The primary particle diameter of the external additive is preferably 5 nm to 2 μm, more preferably 5 nm to 500 nm. 2 / g~500m 2 / g is preferred. The content of the external additive is preferably 0.01% by mass to 5% by mass, and more preferably 0.01% by mass to 2.0% by mass, based on the IR toner.

[0124] <<<Cleaning improver>>> The cleaning improver is contained to remove the developer remaining on the photoreceptor or primary transfer medium after transfer. Examples of the cleaning improver include fatty acid metal salts such as zinc stearate, calcium stearate, and stearic acid; and polymer fine particles produced by soap-free emulsion polymerization, such as polymethyl methacrylate fine particles and polystyrene fine particles. The polymer fine particles preferably have a relatively narrow particle size distribution and a volume average particle size of 0.01 to 1 μm.

[0125] <Color toner> The color toner contains a binder resin and a colorant, and further contains other components as required. The other components may be the same as those used in the previous examples. The color toner is preferably any one of cyan toner, magenta toner, and yellow toner, and more preferably cyan toner, magenta toner, and yellow toner. In other words, in the toner set, the 60-degree gloss of a solid image of the IR toner is preferably 10 or more higher than the 60-degree gloss of a solid image of any of the cyan toner, magenta toner, and yellow toner, and more preferably 10 or more higher than the 60-degree gloss of all of the cyan toner, magenta toner, and yellow toner.

[0126] <<Binder resin>> It is preferable that the toner image formed by the color toner of this embodiment has a low gloss compared to that of general offset printing. Therefore, the binder resin contained in the color toner is not particularly limited and can be appropriately selected depending on the purpose, but it is preferable that the binder resin contains a gel. The gel fraction is preferably 0.5% by mass or more and 20% by mass or less, and more preferably 1.0% by mass or more and 10% by mass or less, based on the binder resin. Even if it does not contain gel, the binder resin used in the color toner preferably contains a high molecular weight substance with a weight average molecular weight Mwc of 100,000 or more, and more preferably is larger than the weight average molecular weight Mwi of the binder resin used in the IR toner. By making the weight average molecular weight Mwc of the binder resin used in the color toner larger than the weight average molecular weight Mwi of the binder resin used in the IR toner, it is possible to obtain a color image with a gloss of about 10 to 30 at 60° gloss, which is more visible than offset printing.

[0127] <<Coloring agent>> As the colorant, those having small absorption at wavelengths of 800 nm or more are preferred, and examples thereof include naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, yellow ochre, yellow lead, titanium yellow, polyazo yellow, oil yellow, Hansa yellow (GR, A, RN, R), pigment yellow L, benzidine yellow (G, GR), permanent yellow (NCG), Balkan fast yellow (5G, R), tartrazine lake, quinoline yellow lake, anthrazan yellow BGL, isoindolinone yellow, red iron oxide, red lead, Cinnabar, Cadmium Red, Cadmium Mercury Red, Antimony Vermilion, Permanent Red 4R, Para Red, Faise Red, Parachlor Orthonitroaniline Red, Lithol Fast Scarlet G, Brilliant Fast Scarlet, Brilliant Carmine BS, Permanent Red (F2R, F4R, FRL, FRLL, F4RH), Fast Scarlet VD, Belcan Fast Rubin B, Brilliant Scarlet G, Lithol Rubin GX, Permanent Red F5R, Brilliant Carmine 6B, Pogment Scarlet 3B, Rhodamine 5B, Toluidine Maroon, Permanent Bordeaux F2K, Helio Bordeaux BL, Bordeaux 10B, Bon Maroon Light, Bon Maroon Medium, Eosin Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarin Lake, Thioindigo Red B, Thioindigo Maroon, Oil Red, Quinacridone Red, Pyrazolone Red, Polyazo Red, Chrome Vermilion, Benzidine Orange, Perinone Orange, Oil Orange, Cobalt Blue, Cerulean Blue, Alkali Blue Lake, Peacock Blue Lake, Victoria Blue Lake Metal-free phthalocyanine blue, phthalocyanine blue, fast sky blue, indanthrene blue (RS, BC), indigo, dioxane violet, anthraquinone violet, chrome green, zinc green, pyridian, emerald green, pigment green B, naphthol green B, green gold, acid green lake, malachite green lake, phthalocyanine green, anthraquinone green, titanium oxide, zinc white, lithopone, perylene black, perinone black, and mixtures thereof.These may be used individually or in combination of two or more.

[0128] When used as a process color toner, the following colorants are preferred for each of cyan, magenta, and yellow. For cyan, C.I. Pigment Blue 15:3 is preferred. For magenta, C.I. Pigment Red 122, C.I. Pigment Red 269, and C.I. Pigment Red 81:4 are preferred. For yellow, C.I. Pigment Yellow 74, C.I. Pigment Yellow 155, C.I. Pigment Yellow 180, and C.I. Pigment Yellow 185 are preferred. These colorants may be used individually or in combination of two or more.

[0129] The absorbance of the colorant at 800 nm or more is preferably less than 0.05, more preferably less than 0.01. When the absorbance is less than 0.05, it is possible to prevent the problem of inhibiting the reading of information formed by the IR toner when the color toner is overlaid on the IR toner.

[0130] The content of the colorant depends on the coloring power of each colorant, but is preferably 3% to 12% by mass, more preferably 5% to 10% by mass, based on the total color toner of each color. When the content is 3% by mass or more, it is possible to prevent the problem that the coloring power is insufficient and the amount of single-color toner adhesion increases, resulting in waste of resources. When the content is 12% by mass or less, it is possible to prevent the problem that the influence on the chargeability of the toner becomes large and it becomes difficult to maintain a stable toner charge amount.

[0131] <Properties of IR Toner and Color Toner> The 60-degree glossiness of the solid image of the IR toner is 30 or more, preferably 30 or more and 80 or less, more preferably 30 or more and 60 or less. When the 60-degree glossiness of the solid image is less than 30, the visibility of the IR toner image increases, and it cannot form the body as the target hidden image. When it is larger than 80, the molecular weight of the toner resin may become small, and it may become difficult to maintain a sufficient fixing temperature range. The 60 degree gloss of a solid image of color toner is preferably from 10 to 40, and more preferably from 15 to 35. When the gloss is within this numerical range, the color toner image has a relatively low gloss. Furthermore, the 60-degree gloss of a solid image of IR toner is at least 10 higher than the 60-degree gloss of a solid image of color toner, preferably at least 15 higher, and more preferably at least 20 higher. If the difference between the 60-degree gloss of a solid image of IR toner and that of a solid image of color toner is less than 10, when a color toner image is superimposed on an IR toner image on an image output medium before heat fixation during image formation, the upper color toner penetrates into the lower IR toner layer during heat and pressure fixation, degrading the visibility of the color toner image. In other words, because the gloss of a solid image of IR toner is higher than that of a solid image of color toner, the visibility of the upper color toner image is improved, and as a result, the lower IR toner image becomes less visible.

[0132] The absorbance of a solid image of color toner at 800 nm or more is preferably less than 0.05, and more preferably less than 0.01.

[0133] Examples of means for adjusting the glossiness of solid images of IR toner and color toner include adjusting the gel fraction of the binder resin and adjusting the weight average molecular weight of the binder resin. The higher the gel fraction of the binder resin, the lower the gloss tends to be, and the closer the gel fraction is to 0, the higher the gloss tends to be. When a binder resin that does not contain gel is used, the higher the weight average molecular weight of the binder resin, the lower the gloss tends to be, and the lower the weight average molecular weight, the higher the gloss tends to be. Furthermore, when a resin with an acid value is used as the binder resin, it is possible to adjust the gloss by adding a trivalent or higher metal salt. The larger the acid value of the binder resin and the larger the amount of metal salt added, the lower the gloss tends to be, and the smaller the acid value of the binder resin and the smaller the amount of metal salt added, the higher the gloss tends to be.

[0134] The weight average molecular weight (Mwi) of the IR toner is preferably from 6,000 to 12,000, and more preferably from 7,500 to 10,000. The weight average molecular weight can be determined by measuring the molecular weight distribution of the THF soluble portion using a GPC (gel permeation chromatography) measuring device GPC-150C (manufactured by Waters Corporation). The weight average molecular weight is measured, for example, using a column (KF801 to 807: manufactured by Showdex) by the following method. The column is stabilized in a heat chamber at 40°C, and THF is passed through the column at this temperature at a flow rate of 1 ml / min. Next, 0.05 g of sample is thoroughly dissolved in 5 g of THF, and the solution is filtered through a pretreatment filter (e.g., a 0.45 μm pore size Chromatodisc (Kurabo Industries, Ltd.)). Finally, 50 μL to 200 μL of the resin THF sample solution, adjusted to a sample concentration of 0.05% to 0.6% by mass, is injected and measured.

[0135] The gel fraction of the IR toner is preferably 0% by mass to 2% by mass. The gel fraction can be calculated from the dry weight of the components filtered through the pretreatment filter used in measuring the weight-average molecular weight.

[0136] The weight average molecular weight (Mw) / number average molecular weight (Mn) of the IR toner is preferably 5 or less, and more preferably 4 or less. The weight average molecular weight Mw and number average molecular weight Mn are measured by calculating the molecular weight distribution of the IR toner from the relationship between the logarithm of a calibration curve prepared using several monodisperse polystyrene standard samples and the count number. The standard polystyrene sample for creating the calibration curve is, for example, a polystyrene having a molecular weight of 6 x 10 2 , 2.1×10 2 , 4×10 2 , 1.75×10 4 , 5.1×10 4 , 1.1×10 5 , 3.9 × 10 5 , 8.6×10 5 , 2 × 10 6 , 4.48×10 6(Pressure Chemical Co. or Toyo Soda Kogyo Co.) When creating a calibration curve, it is appropriate to use at least 10 standard polystyrene samples. An RI (refractive index) detector is used as the detector.

[0137] The acid value of the IR toner is preferably 12 mgKOH / g or less, and more preferably 6 mgKOH / g to 12 mgKOH / g. The acid value can be kept within this range by using a polyester resin as the binder resin, which makes it easy to achieve both low-temperature fixability and hot offset resistance. In this embodiment, the acid values ​​of the toner and binder resin were measured under the following conditions in accordance with the measurement method described in JIS K0070-1992. To prepare the sample solution, 0.5 g of toner or binder resin (0.3 g of ethyl acetate-soluble components) was added to 120 mL of toluene and dissolved by stirring at room temperature (23°C) for about 10 hours. 30 mL of ethanol was then added to prepare the sample solution. The measurement can be calculated using the device, but specifically, the calculation was as follows: The acid value was calculated by titrating with a pre-standardized N / 10 caustic potassium alcohol solution, and the amount of alcoholic potassium solution consumed was calculated using the following formula. Acid value = KOH (mL) x N x 56.1 / sample mass (where N is the factor N / 10KOH) In the examples and comparative examples shown below, the acid value of the binder resin and the acid value of the toner are almost the same, so the acid value of the binder resin is treated as the acid value of the toner.

[0138] <<Toner particle size>> The weight average particle diameter of the IR toner is preferably 5 μm or more and 7 μm or less, and more preferably 5 μm or more and 6 μm or less. The weight average particle diameter of the color toner is preferably 4 μm or more and 8 μm or less, and more preferably 5 μm or more and 7 μm or less. When the weight average particle size is within the range, it is possible to reproduce minute dots of 600 dpi or more, and obtain high-quality images. This is because it is possible to have toner particles with a particle size sufficiently small for minute latent image dots, and it is possible to obtain the advantage of excellent dot reproducibility. In particular, with IR toner, the toner particles are densely arranged on the image output medium before being transferred and fixed, and by preventing the color toner particles superimposed on top of them from entering the gaps, a highly reproducible image can be obtained after fixing. This highly reproducible image can be read mechanically by irradiating it with infrared light, enabling more stable processing. When the weight average particle diameter (D4) of the color toner is 4 μm or more, phenomena such as a decrease in transfer efficiency and a decrease in blade cleaning ability can be prevented, and when the weight average particle diameter (D4) of the color toner is 8 μm or less, it is possible to prevent problems such as the above-mentioned problem of image information being easily disturbed due to the intrusion of color toner superimposed on the image before fixing, and the difficulty in preventing scattering of letters and lines.

[0139] The ratio (D4 / D1) of the weight average particle diameter (D4) to the number average particle diameter (D1) is preferably 1.00 to 1.40, more preferably 1.05 to 1.30. The closer the ratio (D4 / D1) is to 1.00, the sharper the particle diameter distribution. Such a toner with a small particle size and narrow particle size distribution has a uniform charge distribution, making it possible to obtain high-quality images with little background fogging, and also enabling a high transfer rate in electrostatic transfer systems. In full-color image formation methods, which form multicolor images by superimposing toner images of different colors, a larger amount of toner is deposited on paper than in monochrome image formation methods, which form images using only one color, black toner, and do not require superimposing toner images of different colors. This means that the amount of toner developed, transferred, and fixed is greater, which can lead to problems that degrade image quality, such as the aforementioned reduced transfer efficiency, reduced blade cleaning performance, scattering of letters and lines, and background fogging. Therefore, it is important to control the weight-average particle size (D4) and the ratio (D4 / D1) of the weight-average particle size (D4) to the number-average particle size (D1).

[0140] The particle size distribution of toner particles can be measured using a device for measuring the particle size distribution of toner particles by the Coulter Counter method, such as the Coulter Counter TA-II or Coulter Multisizer II (both manufactured by Coulter). The specific measurement method is as follows. First, 0.1 mL to 5 mL of a surfactant (such as alkylbenzene sulfonate) is added as a dispersant to 100 mL to 150 mL of an aqueous electrolytic solution. The aqueous electrolytic solution is prepared using primary sodium chloride to give an approximately 1% NaCl aqueous solution, such as ISOTON-II (manufactured by Coulter). Next, 2 mg to 20 mg of the measurement sample is added. The electrolyte solution with the suspended sample is dispersed in an ultrasonic disperser for approximately 1 to 3 minutes, and the weight and number of toner particles are measured using a measuring device with a 100 μm aperture, and the weight distribution and number distribution are calculated. The weight average particle size (D4) and number average particle size (D1) of the toner can be determined from the obtained distribution. Thirteen channels are used: 2.00 to less than 2.52 μm; 2.52 to less than 3.17 μm; 3.17 to less than 4.00 μm; 4.00 to less than 5.04 μm; 5.04 to less than 6.35 μm; 6.35 to less than 8.00 μm; 8.00 to less than 10.08 μm; 10.08 to less than 12.70 μm; 12.70 to less than 16.00 μm; 16.00 to less than 20.20 μm; 20.20 to less than 25.40 μm; 25.40 to less than 32.00 μm; and 32.00 to less than 40.30 μm, targeting particles with diameters of 2.00 μm or more and less than 40.30 μm.

[0141] It is known that the loss tangent (tan δ) of electrophotographic toner has a clear correlation with the glossiness of the image. As the tan δ value increases, the toner has better spreadability during fixing, which improves the substrate hiding power and results in a high-gloss image. The loss tangent (tanδi) of the IR toner at 100°C to 140°C is preferably 2.5 or more, more preferably 3.0 or more. Tanδi is preferably 15 or less. Note that the loss tangent (tanδi) of the IR toner at 100°C to 140°C being 2.5 or more means that the loss tangent (tanδi) of the IR toner always has a value of 2.5 or more at 100°C to 140°C. The tangent loss (tan δc) of the color toner is preferably 2 or less. Tan δc is preferably 0.1 or more. When the tangent loss of the color toner is 2 or less, it is possible to prevent the color toner superimposed on the IR image from penetrating into the IR toner image, thereby impairing the stability of the IR toner image. Note that the tangent loss (tan δc) of the color toner at 100°C to 140°C being 2 or less means that the tangent loss (tan δc) of the color toner always takes a value of 2 or less at 100°C to 140°C.

[0142] The loss tangent (tanδ) of an electrophotographic toner is the ratio (G″) / (G′) of the loss modulus (G″) and the storage modulus (G′), and can be measured by viscoelasticity measurement. The loss modulus (G″) and the storage modulus (G′) can be measured, for example, by the following method. 0.8 g of IR toner or color toner is molded using a φ20 mm die at a pressure of 30 MPa, and the loss modulus (G''), storage modulus (G'), and loss tangent (tanδ) can be measured using an ADVANCED RHEOMETRIC EXPANSION SYSTEM (manufactured by TA Corporation) with a φ20 mm parallel cone at a frequency of 1.0 Hz, a heating rate of 2.0°C / min, and a strain of 0.1% (automatic strain control: allowable minimum stress 1.0 g / cm, allowable maximum stress 500 g / cm, maximum added strain 200%, strain adjustment 200%).The gap is set within the range of 0 to 100 gm for force after the sample is set.

[0143] <Toner manufacturing method> The toner set of this embodiment can be manufactured by a conventionally known method such as a melting / kneading / pulverization method, a polymerization method, etc. The color toner and the IR toner may be manufactured by the same manufacturing method, or different manufacturing methods may be used, such as a polymerization method for the color toner and a melting / kneading / pulverization method for the IR toner.

[0144] <<Melt kneading-pulverization method>> In the melt-kneading-pulverization method, the manufacturing process includes (1) a step of melt-kneading at least a binder resin, a colorant or a near-infrared absorbing material, and a release agent, (2) a step of pulverizing / classifying the melt-kneaded toner composition, and (3) a step of externally adding inorganic fine particles. From the viewpoint of cost, it is preferable to side-knead the fine powder produced in the pulverization / classification step (2) as the raw material for step (1).

[0145] The kneader used for kneading may be an internal kneader, a single-screw or twin-screw extruder, an open-roll kneader, etc. Examples of the kneader include a KRC kneader (manufactured by Kurimoto Iron Works), a Buss-Co kneader (manufactured by Buss), a TEM extruder (manufactured by Toshiba Machine Co., Ltd.), a TEX twin-screw kneader (manufactured by The Japan Steel Works, Ltd.), a PCM kneader (manufactured by Ikegai Iron Works, Ltd.), a three-roll mill, a mixing roll mill, a kneader (manufactured by Inoue Manufacturing Co., Ltd.), a Kneadex (manufactured by Mitsui Mining Co., Ltd.), an MS-type pressure kneader, a Niderruder (manufactured by Moriyama Manufacturing Co., Ltd.), and a Banbury mixer (manufactured by Kobe Steel, Ltd.).

[0146] Examples of pulverizers include counter jet mills, micron jets, inomizers (manufactured by Hosokawa Micron Corporation), IDS-type mills, PJM jet pulverizers (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), cross jet mills (manufactured by Kurimoto Iron Works), Urmax (manufactured by Nisso Engineering Co., Ltd.), SK Jet-O-Mill (manufactured by Seishin Enterprise Co., Ltd.), Kryptron (manufactured by Kawasaki Heavy Industries, Ltd.), Turbo Mill (manufactured by Turbo Industrial Co., Ltd.), and Super Rotor (manufactured by Nisshin Engineering Co., Ltd.). Examples of classifiers include Cruseal, Micron Classifier, Spedic Classifier (manufactured by Seishin Enterprise Co., Ltd.), Turbo Classifier (manufactured by Nisshin Engineering Co., Ltd.), Micron Separator, Turboplex (ATP), TSP Separator (manufactured by Hosokawa Micron Corporation), Elbow Jet (manufactured by Nittetsu Mining Co., Ltd.), Dispersion Separator (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and YM Microcut (manufactured by Yaskawa Shoji Co., Ltd.). Examples of sieving devices used to sift out coarse particles include Ultrasonic (manufactured by Koei Sangyo Co., Ltd.), Resonaseave, Gyrosifter (Tokuju Kogyo Co., Ltd.), Vibrasonic System (manufactured by Dalton Co., Ltd.), Soniclean (manufactured by Shinto Kogyo Co., Ltd.), Turboscreener (manufactured by Turbo Industry Co., Ltd.), Microsifter (manufactured by Makino Sangyo Co., Ltd.), and circular vibrating sieves.

[0147] <<Polymerization method>> As the polymerization method, a conventionally known method can be used. For example, the polymerization method may be performed in the following procedure. First, a colorant, a binder resin, and a release agent are dispersed in an organic solvent to prepare a toner material liquid (oil phase). It is preferable to add a polyester prepolymer (A) having an isocyanate group to the toner material liquid and react it during granulation to incorporate a urea-modified polyester resin into the toner.

[0148] Next, the toner material liquid is emulsified in an aqueous medium in the presence of a surfactant and resin particles. The aqueous medium may be water alone or may contain an organic solvent such as alcohol. The amount of the aqueous solvent used per 100 parts by mass of the toner material liquid is usually preferably 50 parts by mass to 2,000 parts by mass, and more preferably 100 parts by mass to 1,000 parts by mass. The resin particles are not particularly limited as long as they are resins capable of forming an aqueous dispersion, and can be appropriately selected depending on the purpose. Examples include vinyl resins, polyurethane resins, epoxy resins, and polyester resins.

[0149] After dispersion, the organic solvent is removed from the emulsified dispersion (reaction product), and the resulting mixture is washed and dried to obtain toner base particles.

[0150] The IR toner and color toner can be used as a one-component developer or a two-component developer. When the toner of this embodiment is used in a two-component developer, it may be mixed with a magnetic carrier, and the content ratio of the carrier to the toner in the developer is preferably 100 parts by weight of the carrier to 1 part by weight to 10 parts by weight of the toner. As the magnetic carrier, conventionally known ones can be used, and examples thereof include iron powder, ferrite powder, magnetite powder, and magnetic resin carriers, each having a particle size of about 20 μm to 200 μm. The magnetic carrier may also be coated. Examples of coating materials for coating the magnetic carrier include amino resins such as urea-formaldehyde resin, melamine resin, benzoguanamine resin, urea resin, polyamide resin, and epoxy resin; polyvinylidene resins such as polyvinyl; polystyrene resins such as acrylic resin, polymethyl methacrylate resin, polyacrylonitrile resin, polyvinyl acetate resin, polyvinyl alcohol resin, polyvinyl butyral resin, polystyrene resin, and styrene-acrylic copolymer resin; and halogenated olefins such as polyvinyl chloride. Examples of the resin include: polyester resins such as polyethylene terephthalate resin and polybutylene terephthalate resin; polycarbonate resins, polyethylene resin, polyvinyl fluoride resin, polyvinylidene fluoride resin, polytrifluoroethylene resin, polyhexafluoropropylene resin, copolymers of vinylidene fluoride and an acrylic monomer, copolymers of vinylidene fluoride and vinyl fluoride, fluoro terpolymers such as terpolymers of tetrafluoroethylene, vinylidene fluoride and a non-fluorinated monomer, and silicone resins. Furthermore, if necessary, conductive powder or the like may be contained in the coating resin. Examples of conductive powder that can be used include metal powder, carbon black, titanium oxide, tin oxide, and zinc oxide. These conductive powders preferably have an average particle size of 1 μm or less. An average particle size of 1 μm or less can prevent the inconvenience of making it difficult to control the electrical resistance.

[0151] In one example of the IR toner in this embodiment, when the IR toner image is a solid image, the 60 degree gloss of the solid image is 30 or more, preferably 30 or more and 80 or less, and more preferably 30 or more and 60 or less. In addition, as another example of the IR toner in this embodiment, when the IR toner image is a solid image, the 60-degree glossiness of the solid image is 10 or more higher, preferably 15 or more higher, and more preferably 20 or more higher than the 60-degree glossiness of the solid image when the color toner image is a solid image. In yet another example of the IR toner in this embodiment, the loss tangent (tanδi) of the IR toner at 100° C. to 140° C. is preferably 2.5 or more, more preferably 3.0 or more. In the image forming method and image forming apparatus, the loss tangent (tanδc) of the color toner is preferably 2 or less.

[0152] The number of color toners used to form a color toner image is not particularly limited and can be appropriately selected depending on the purpose. When using multiple color toners, either a method of simultaneously forming multiple color toners or a method of repeatedly forming single-color toners and overlapping each color can be used, but a method of repeatedly forming single-color toners and overlapping each color is preferred. Note that there is no particular limit to the order in which each color is formed in the color toner image.

[0153] The amount of IR toner adhered to the IR toner image is 0.30 mg / cm 2 More than 0.45mg / cm 2 Preferably less than 0.35 mg / cm 2 More than 0.40mg / cm 2 More preferably, the amount of IR toner adhered is 0.30 mg / cm 2 If the thickness is more than this, the substrate hiding rate of the image becomes sufficient and a stable image can be obtained. In addition, since the near-infrared absorbing material has some absorption in the visible light region and is not completely colorless, increasing the amount of near-infrared absorbing material added to the toner increases visibility. For this reason, the amount of IR toner attached to the image is set to 0.45 mg / cm.2 By setting the following, it is possible to reduce visibility.

[0154] The toner adhesion amount per unit area of ​​the color toner image superimposed on the IR toner image is preferably 30% or more and 80% or less. When the toner adhesion amount per unit area of ​​the color toner image is within this range, it is preferable because it can sufficiently reduce the visibility of the IR toner image underneath the color toner image. The reasons for this are thought to be as follows: The IR toner of this embodiment has some absorption in the visible light region, and a single-color image is not completely transparent. Therefore, in order to make the IR image information invisible (hard to see), it is preferable to mask it with color toner. If the toner adhesion amount per unit area of ​​the color toner image is 30% or more, this is effective in preventing the problem of the IR toner image being easily visible. If the toner adhesion amount per unit area of ​​the color toner image is less than 30%, the visibility of the IR toner image increases, especially when yellow toner is overlaid.

[0155] An image forming method in which the toner adhesion amount per unit area of ​​a color toner image on an IR toner image is 30% to 80% is particularly effective when forming an image by overlapping two-dimensional code images.By overlapping a two-dimensional code image made of IR toner and a two-dimensional code image made of color toner, each containing different information, and using a reader with different light wavelengths (860 nm and 532 nm, respectively), more information can be embedded within the same image area than when only a two-dimensional code image made of color toner is used. On the recording material, it is preferable that the two-dimensional code image (i), which is an IR toner image, is formed closer to the recording material than the two-dimensional code image (c), which is a color toner image. In this case, when the color toner image is a solid image, the absorbance of the solid image from 800 nm to 900 nm is preferably less than 0.05, more preferably less than 0.01. It is also preferable that the information contained in the two-dimensional code image (i) is different from the information contained in the two-dimensional code image (c).

[0156] When a two-dimensional code image made of IR toner and a two-dimensional code image made of color toner are superimposed, it is also possible to use the two-dimensional code image made of color toner as a dummy code. In this case, the two-dimensional code image made of IR toner is invisible and the information can be read only by an infrared two-dimensional code reader, while the two-dimensional code image made of color toner is visible but the information cannot be read by an infrared two-dimensional code reader.

[0157] The above description is merely an example, and each of the following aspects provides unique effects. [First aspect] The first aspect is an image forming device (e.g., a printer) that finally transfers an invisible image toner image formed on an image carrier (e.g., intermediate transfer belt 12) using invisible image toner (e.g., IR toner) based on invisible image information (e.g., IR image information) onto a recording material (e.g., paper P) to form an invisible image (e.g., a two-dimensional code image) on the recording material, and is characterized by having a detection means (e.g., a toner adhesion amount detection sensor 180) that detects invisible image toner adhering to the image carrier over the entire toner-carrying area (e.g., the entire effective image area) on the image carrier in a width direction (e.g., main scanning direction) perpendicular to the surface movement direction of the image carrier, and a judgment means (e.g., control unit 30) that judges the position where an abnormality has occurred in the width direction based on the detection result of the detection means. Invisible images can be widely used, for example, when printing a background pattern to prevent unauthorized copying or when printing a visible code image and an invisible code image overlapping each other to increase the information content of the code image. The position of the invisible image formed in such applications on the recording material in the width direction (main scanning direction) of the image carrier often varies for each image forming operation. However, in conventional image forming apparatuses, the invisible image is formed at a predetermined position in the width direction of the image carrier, and the detection unit is provided to face only that predetermined position. Therefore, the detection unit cannot detect anomalies in the invisible image that occur at positions other than the predetermined position in the width direction of the image carrier, and the presence or absence of such anomalies cannot be determined based on the invisible image formed. According to this aspect, a detection unit capable of detecting invisible image toner is used throughout the toner-carrying area of ​​the image carrier. For example, a detection pattern is formed on the image carrier using invisible image toner. The detection unit can detect the location of an abnormality (e.g., white or black streaks) within the detection pattern, or the location of an abnormality (e.g., black streaks) caused by invisible image toner adhering to a location where it should not normally be adhering, regardless of the location within the toner-carrying area. This allows the determination unit to determine the location of the abnormality in the width direction of the image carrier based on the detection results of the detection unit. Therefore, regardless of the location of the invisible image in the width direction of the image carrier, it is possible to appropriately determine whether or not there is an abnormality in the invisible image. Therefore, it is possible to determine the presence or absence of an abnormality when forming invisible images used in a wide range of applications, such as preventing unauthorized copying or increasing the amount of information in code images.

[0158] [Second mode] A second aspect is characterized in that in the first aspect, the detection means is a line sensor (for example, a toner adhesion amount detection sensor 180) extending in the width direction. This makes it possible to appropriately detect the invisible image toner over the entire area in the width direction (main scanning direction) of the image carrier where the invisible image toner image can be carried.

[0159] [Third aspect] The third aspect is characterized in that in the first or second aspect, the detection means is a reflection density sensor (e.g., a toner adhesion amount detection sensor 180) that detects the reflection density of the invisible image toner on the image carrier. According to this aspect, invisible image toner can be detected with a simple configuration. In particular, some invisible image toners reflect visible light, similar to visible image toners, before being fixed to a recording material, i.e., while being carried on an image carrier. When such invisible image toners are used, a reflection density sensor that detects general visible image toners can be used, and invisible image toner can be detected with a simpler configuration.

[0160] [Fourth aspect] The fourth aspect is characterized in that, in any of the first to third aspects, it has a notification means (e.g., operation display unit 50) that notifies the user before starting image formation of the invisible image when the widthwise abnormality position determined by the determination means overlaps with the widthwise position where the invisible image based on the invisible image information is formed. This allows the user to be notified that the location of the abnormality determined by the determining means will affect the invisible image formed based on the invisible image information before the invisible image is formed, thereby enabling the user to take appropriate measures before the invisible image is formed.

[0161] [Fifth mode] The fifth aspect is characterized in that, in any of the first to fourth aspects, when the widthwise abnormality position determined by the determination means overlaps with the widthwise image formation position of the invisible image based on the invisible image information, processing is performed to change the relative position of the invisible image with respect to the formed image formed on the recording material. This allows the relative position of the invisible image to be changed with respect to the image formed on the recording material so that the image forming position of the invisible image does not overlap with the position of the abnormality determined by the determination means, thereby allowing image formation to continue even if an abnormality occurs.

[0162] [Sixth aspect] The sixth aspect is characterized in that, in any of the first to fourth aspects, when the widthwise abnormality position determined by the determination means overlaps with the widthwise image formation position of the invisible image based on the invisible image information, processing is performed to change the orientation of the formed image formed on the recording material. This allows the orientation of the image formed on the recording material to be changed so that the image formation position of the invisible image does not overlap with the abnormality position determined by the determining means, thereby allowing image formation to continue even if an abnormality occurs in the invisible image toner image. [Explanation of symbols]

[0163] 1: Image forming unit 2: Transfer section 3: Recording material supply section 4: Fixing section 5: Recording material discharge section 6: Process unit 7: Photoreceptor 8: Charging roller 9: Developing device 10: Photoconductor cleaning device 11: Exposure equipment 12: Intermediate transfer belt 13: Primary transfer roller 14: Secondary transfer roller 15: Drive roller 16: Driven roller 17: Belt cleaning device 18: Paper cassette 20: Timing roller pair 21: Fixing device 26: Toner cartridge 27: Waste toner container 30: Control section 31: Main control unit 32: Storage section 33: Decomposition processing section 35: Gamma conversion section 36: Gradation conversion section 37: Toner total amount control unit 40: Image formation control unit 50: Operation display section 180: Toner adhesion amount detection sensor 181 :Light source 182: Lens array 183: Image sensor array 184: Detection window 185: Shutter parts 186:White reference plate ds: black stripes ws: White stripe [Prior art documents] [Patent documents]

[0164] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-286641

Claims

1. An image forming apparatus in which an invisible image toner image formed on an image carrier by an invisible image toner based on invisible image information is finally transferred onto a recording material, thereby forming an invisible image on the recording material, a detecting means for detecting the toner for invisible images adhered to the image carrier over the entire toner-carrying area on the image carrier in a width direction perpendicular to the surface movement direction of the image carrier; a determination means for determining a position where an abnormality has occurred in the width direction based on the detection result of the detection means; An image forming apparatus characterized by having an alert means for alerting a user before starting image formation of an invisible image when the widthwise abnormality position determined by the determination means overlaps with the widthwise position where an invisible image based on the invisible image information is formed.

2. An image forming apparatus for forming an invisible image on a recording material by finally transferring an invisible image toner image formed on an image carrier by an invisible image toner based on invisible image information onto a recording material, a detecting means for detecting the toner for invisible images adhered to the image carrier over the entire toner-carrying area on the image carrier in a width direction perpendicular to the surface movement direction of the image carrier; a determination means for determining a position where an abnormality has occurred in the width direction based on the detection result of the detection means, An image forming apparatus characterized in that, when the widthwise abnormality position determined by the determination means overlaps with the widthwise image formation position of an invisible image based on the invisible image information, a process is performed to change the relative position of the invisible image with respect to the formed image formed on a recording material.

3. An image forming apparatus in which an invisible image toner image formed on an image carrier by an invisible image toner based on invisible image information is finally transferred onto a recording material to form an invisible image on the recording material, a detecting means for detecting the toner for invisible images adhered to the image carrier over the entire toner-carrying area on the image carrier in a width direction perpendicular to the surface movement direction of the image carrier; a determination means for determining a position where an abnormality has occurred in the width direction based on the detection result of the detection means, An image forming apparatus characterized in that when the widthwise abnormality occurrence position determined by the judgment means overlaps with the widthwise image formation position of the invisible image based on the invisible image information, a process is performed to change the orientation of the formed image formed on the recording material.

4. 2. The image forming apparatus according to claim 1, An image forming apparatus characterized in that, when the widthwise abnormality position determined by the determination means overlaps with the widthwise image formation position of an invisible image based on the invisible image information, a process is performed to change the relative position of the invisible image with respect to the formed image formed on a recording material.

5. 2. The image forming apparatus according to claim 1, An image forming apparatus characterized in that when the widthwise abnormality occurrence position determined by the judgment means overlaps with the widthwise image formation position of the invisible image based on the invisible image information, a process is performed to change the orientation of the formed image formed on the recording material.

6. In the image forming apparatus according to any one of claims 1 to 5, The image forming apparatus is characterized in that the detection means is a line sensor extending in the width direction.

7. In the image forming apparatus according to any one of claims 1 to 6, The image forming apparatus is characterized in that the detecting means is a reflection density sensor that detects the reflection density of the toner for invisible images on the image carrier.

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