JP2013097199A - Image forming apparatus, image forming method, and image forming system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means for forming on a recording medium hidden information that cannot be recognized under a standard lighting condition and can be recognized only under a special condition.SOLUTION: An image forming apparatus forms an image by overlapping toner images in a plurality of colors on a recording medium S. At least one of a plurality of colored toner forming the toner images is a fluorescent toner Ft, and a toner forming a toner image in the other color is a transparent toner Tt that is transparent and does not absorb light in the visible light region, and exhibits light absorbing property in the ultraviolet region.

Description

  The present invention relates to an image forming apparatus, an image forming method, and an image forming system.

  In full-color copiers and full-color printers that use electrophotographic processes, toner images of multiple colors (usually four colors of cyan, magenta, yellow, and black) are superimposed on paper or recording sheets as recording media. The toner image is arranged and fixed on the recording sheet by heating and pressurizing the toner image in the fixing means.

  The toner is formed of particles of 1 to 10 μm formed by dispersing a pigment as a colorant mainly composed of a thermoplastic resin such as a polyester resin, a styrene / acrylic copolymer, and a styrene / butadiene copolymer. On the other hand, fine particles having an average particle diameter of about 5 to 100 nm, for example, inorganic fine particles such as silicon oxide, titanium oxide, and aluminum oxide are externally added.

  The pigment dispersed in the toner includes Y (yellow) as disazo yellow, fast yellow, isoindoline yellow, etc., and M (magenta) as brilliant carmine 6B, quinacridone magenta, rhodamine 6G lake, etc. As cyan), phthalocyanine blue and the like are used, and as K (black), carbon black, aniline black and the like are used.

  As an example of the above-described fixing unit, a unit composed of a pair of rollers called a heating roller and a pressure roller has been proposed. A heating source such as a halogen lamp is disposed inside the heating roller. By passing the recording sheet on which the toner image is formed between the pair of fixing rollers, the color toner is thermally melted and fixed on the recording sheet.

  Normally, a toner image for four colors is formed on a recording sheet and then passed through a fixing unit to fix the toner image on the recording sheet. The unfixed toner images for the four colors are fixed as an image on a recording sheet by passing the fixing means once.

  Various techniques have been devised for image forming with higher added value by applying such an image forming apparatus using an electrophotographic process. As one form of such high-value-added images, methods for forming invisible images such as hidden characters have been proposed, such as “embedding information in an invisible state” for the purpose of “information protection” including “forgery prevention”. ing.

  For example, Patent Document 1 discloses a method of printing characters and images using a UV-absorbing colorless toner on a recording sheet containing a fluorescent material. When the printed recording sheet is irradiated with ultraviolet rays, the printed portions of characters and images absorb the ultraviolet rays, so that it is possible to identify the colorless printed portion that sinks in the background that is highlighted by fluorescence. Further, since the ultraviolet absorbing colorless toner is colorless in the visible light region, the printed portion cannot be visually recognized under normal viewing conditions under visible light. By utilizing this fact, it is said that the technology can be used for printing applications such as hidden characters that are not normally visible.

  On the other hand, according to the study by the inventors, when an ultraviolet absorbing colorless toner is formed on a recording sheet as in Patent Document 1, hidden characters and the like are not completely invisible, but a general indoor lighting lamp or the like It was clarified that it was possible to discriminate to the extent that the contents of the hidden characters could be discerned even under the lighting conditions. That is, there are cases where hidden characters can be identified even under special lighting conditions such as black light.

  As a matter of course, the degree of ease (or difficulty) of discrimination required when creating such a hidden character varies greatly depending on the purpose and purpose of the hidden character, and the hidden character It is not always a problem that it can be determined under general lighting conditions. On the other hand, depending on applications and purposes, there are cases where it is desirable that hidden characters cannot be identified under such general lighting conditions.

  An example of a case where it is desirable to be unable to identify hidden characters is a use that expects the effect of attracting customers and strengthening the impression of the printed content to the recipient of the printed matter with hidden characters. It is done.

  This is because customers who have received prints with hidden characters usually do not recognize the content of hidden characters under lighting, so they have the expectation of “what content is written?” In order to perceive the contents of the print, the printed matter is both carried to a special condition that makes it possible to distinguish hidden characters.

  This is a case in which, through such seemingly cumbersome work, the printed content is strongly impressed, and the effect of attracting customers (advertising effect) and the impression of the printed content to the recipient is obtained.

  According to the study by the inventors, it is considered that the content disclosed in the cited document 1 can be used to determine the contents of hidden characters under general illumination conditions. The reason is described below.

[First reason]
In the hidden character disclosed in the cited document 1, the surface state of the toner image constituting the hidden character is different from the surface state of the recording sheet corresponding to the background background portion of the hidden character. That is, since the toner has a composition centered on the resin, the surface structure of the toner image is a surface structure formed of a resin having no gap. On the other hand, the recording sheet has a structure in which paper fibers are entangled and a large amount of air is taken inside.

  For this reason, the surface state of the toner and the surface state of the recording sheet are fundamentally different surface states. As described above, it is difficult to completely match the appearances of both of which the surface states are fundamentally different. Therefore, the viewer feels a difference between the toner image and the recording sheet that is the background of the toner image, and the presence or absence of hidden characters is determined.

  The main point for matching the appearance is thought to correspond to matching the characteristics of the reflected light from both surfaces. The characteristics of the reflected light cannot be perfectly matched.

  For example, the surface of the toner image can be changed by changing the fixing conditions such as the temperature at the time of fixing, so that it matches the appearance of the recording sheet under limited conditions such as “from a specific observation position”. It is thought that it can be made.

  However, even if the surface state of the toner image is adjusted, the appearance of the toner image and the recording sheet do not match from another observation position. In other words, it is impossible to match the appearances from all the observation positions between the two having greatly different surface states. For this reason, due to the difference in surface reflection characteristics, the content of information by hidden characters can be identified relatively easily by slightly changing the observation position under general illumination.

[Second reason]
Even though the toner is colorless and transparent, when the toner image is formed on the recording sheet, the transmittance is not 100%, so it becomes a little dark. According to the study by the inventors, the reflectance of the recording sheet on which the colorless and transparent toner is formed is in a situation where a reflectance reduction of about 1.0 to 3.0% is unavoidable as compared with the recording sheet itself. Even with this difference in reflectance, the contents of hidden characters can still be identified by observation under general illumination.

  Invisible information formed on a recording medium such as paper or recording sheet is not limited to hidden characters, but includes information that can be visually sensed such as a hidden figure. The invention will be described taking a hidden character as an example of hidden information.

  In view of the problem of distinguishability of hidden characters clarified in the background art, the present invention provides hidden information that cannot be identified under general lighting conditions but can be identified only under special conditions. It is an object of the present invention to provide a means that can be formed.

In order to achieve the object, the present invention has the following configuration.
(1): A first means of the present invention is an image forming apparatus for forming an image by superimposing a plurality of color toner images on a recording medium, wherein at least one of the colored toners forming the toner image is A toner of fluorescent color (hereinafter referred to as fluorescent toner) that forms another one-color toner image is a toner that is transparent and non-absorbing in the visible light region and has light absorption characteristics in the ultraviolet region (hereinafter referred to as the toner image). It is called transparent toner.)
(2): The second means of the present invention is the image forming apparatus according to claim 1, wherein the glossiness (60 degrees) of the toner image formed on the recording medium by superimposing the fluorescent toner and the transparent toner. (Glossiness) was 40% or less.
(3): A third means of the present invention is the image forming apparatus according to claim 1 or 2, wherein the toner image on the recording medium in which the fluorescent toner and the transparent toner are overlapped is the fluorescent toner. The lower layer (side closer to the recording medium) and the transparent toner are formed to be the upper layer (side far from the recording medium).
(4): A fourth means of the present invention is the image forming apparatus according to claim 1 or 2, wherein the toner image on the recording medium in which the fluorescent toner and the transparent toner are overlapped is the fluorescent toner. An image forming apparatus comprising: an upper layer (a side far from a recording medium) and a transparent toner on a lower layer (a side closer to the recording medium).
(5): The fifth means of the present invention is the image forming apparatus according to claim 1 or 2, wherein the colored toner for forming a toner image on the recording medium in which the fluorescent toner and the transparent toner are superimposed is formed. At least two colors are the fluorescent toners, and are formed on the lowermost layer (side closer to the recording medium) and uppermost layer (side farther to the recording medium), and the transparent toner is formed on the intermediate layer (uppermost layer and lowermost layer). It was decided to be formed so as to be in the middle.
(6): A sixth means of the present invention is an image forming method for providing a desired image by forming a plurality of color toner images on a recording medium, and at least of colored toners for forming a toner image. A fluorescent toner is used for one color, and a transparent toner is used for a toner that forms a toner image of another color, and a peripheral area of hidden information is formed on the recording medium with the fluorescent toner. The fluorescent area is formed in the peripheral area. The hidden information is created by using the transparent toner so as to overlap the toner layer.
(7): A seventh means of the present invention is an image forming system having the image forming apparatus according to any one of claims 1 to 5, wherein the fluorescent toner and the transparent toner are recorded on a recording medium. An arrangement position input unit that enables designation of the arrangement position is provided.
(8): The eighth means of the present invention is the image forming system having the image forming apparatus according to any one of claims 1 to 5 or the image forming system according to claim 7, wherein the recording medium is a recording medium. It was equipped with a UV irradiation illumination device that made it possible to visualize an image formed by the fluorescent toner and the transparent toner formed on the top.
It was.

  In the present invention, an image forming apparatus, an image forming method, and an image forming system capable of forming hidden information on a recording medium that cannot be identified under general illumination conditions but can be identified only under special conditions. Can provide.

1 is a diagram illustrating a schematic configuration of an image forming apparatus. FIG. 2 is an enlarged view illustrating a configuration of a color print unit of the image forming apparatus. It is the figure which showed the procedure of the image data processing. It is a figure explaining the structure of hidden information. FIG. 5 is an enlarged view illustrating another example of a color print unit of the image forming apparatus. It is a figure explaining how hidden information works FIG. 5 is an enlarged view illustrating another example of a color print unit of the image forming apparatus. It is a figure explaining the structure of hidden information. It is the figure which showed the procedure of the image data processing. It is the figure which showed the arrangement | positioning state of the illuminating device of an ultraviolet irradiation.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified thru | or abbreviate | omitted suitably.

[First embodiment]
Hereinafter, the main configuration and operation of the image forming apparatus that outputs an image including hidden information will be described.

(Overview of overall configuration):
FIG. 1 shows a schematic configuration of an image forming apparatus 10 according to the first embodiment. In FIG. 1, recording sheets S are accommodated in paper feed cassettes 1 and 2 disposed at the lower part of the image forming apparatus 10.

  The recording sheets S stored in the paper feeding cassettes 1 and 2 are so-called papers, and in addition to information papers called OA papers (plain papers) generally used for copying machines, printers, etc., cast coating Any paper such as coated paper such as paper, art paper, and fine coated paper, and non-coated paper such as high quality paper, medium quality paper, and lower grade paper may be used.

  At the time of image recording, the recording sheet S is discharged from one of the sheet feeding cassettes 1 and 2, conveyed toward the upper part of the image forming apparatus 10 along the vertical conveyance path indicated by the broken line, and temporarily stopped by the registration roller 18. Then, it is retransmitted after adjusting the sending timing.

  The re-recorded recording sheet S reaches the conveying belt 3 arranged with the feeding direction set in the vertical direction on the conveying path, and is held and conveyed by the conveying belt 3. A transfer device (secondary transfer device) 17 is disposed in the middle portion of the transport belt 3 in the vertical direction and inside the transport belt 3. One end side of the intermediate transfer belt 8 of the color print unit 4-1 is disposed in contact with the transfer unit 17 via the conveying belt 3 from the lateral direction via a support roller with the intermediate transfer bell.

  The intermediate transfer belt 8 is an endless belt having one end in the horizontal direction supported by the support roller and the other end supported by another support roller. The intermediate transfer belt 8 is transparent (T), yellow (Y), cyan (C), A color superposed toner image with magenta (M) and black (K) toners can be carried and rotated.

  The recording sheet S that has been sent out from the registration roller 18 and has been retransmitted by the conveying belt 3 is transferred to the color on the intermediate transfer belt 8 at the site of the transfer unit (secondary transfer unit) 17 during the conveyance. The toner image is associated with the superimposed toner image, and the color superimposed toner image on the intermediate transfer belt 8 is transferred to the recording sheet 3.

  The recording sheet S carrying the toner image by this transfer is further advanced along the upward arrow by the conveying belt 3 with the toner layer held on the surface, and the toner image is heated and pressurized when passing through the fixing device 5. And fixed on the recording sheet S. The toner image fixed on the recording sheet S further proceeds upward in accordance with the conveyance path, changes the course in the horizontal direction in the middle, and is discharged to the paper discharge unit 7 through the discharge roller 6.

(Color print section):
FIG. 2 is a schematic diagram of the color print unit 4-1 in the image forming apparatus 10. The color print unit 4-1 is configured in accordance with a conventional color image print unit except that the color print unit 4-1 is different from the conventional color print unit in that transparent toner is used.

  In the color print unit 4-1, images corresponding to five types of toner of transparent (T), yellow (Y), cyan (C), magenta (M), and black (K) are superimposed on the intermediate transfer belt 8. Thus, an image can be formed.

  The color print unit 4-1 has five image forming units corresponding to T, Y, C, M, and K colors and toner components in the counterclockwise direction indicated by the arrows from the upstream side to the downstream side. 9T, 9Y, 9C, 9M, and 9K are arranged in this order. The color component toner images formed by the image forming units 9T, 9Y, 9C, 9M, and 9K are disposed in contact with the photosensitive drums of the five image forming units 9T, 9Y, 9C, 9M, and 9K. The toner images are sequentially transferred to the intermediate transfer belt 8 to form a color superimposed toner image, and are carried on the intermediate transfer belt 8.

  The order in which the color toners are superimposed on the intermediate transfer belt 8 is in the order of T, Y, C, M, K from the side closer to the surface of the intermediate transfer belt 8.

  The intermediate transfer belt 8 is rotated in the direction of the arrow at a predetermined timing by a driving unit (not shown), and the color component toner images in the five image forming units 9T, 9Y, 9C, 9M, and 9K are superimposed at a predetermined position. It has come to be. Each color component toner image formed on the intermediate transfer belt 8 is transferred to the recording sheet S on the conveying belt 3 described above with reference to FIG. 1 and becomes a toner image on the recording sheet S. In this example, the order in which the toner images are superimposed on the recording sheet S is the arrangement order of the respective color component toners of “(the side far from the recording sheet) T → Y → C → M → K (the side closer to the recording sheet)”. .

(Image forming unit):
In the color print unit 4-1, the color image forming units 9T, 9Y, 9C, 9M, and 9K corresponding to the five colors have the same mechanical configuration except for the toner used. The image forming unit 9K is arbitrarily selected and will be described in detail.

  As shown in FIG. 2, the image forming unit 9K includes a photosensitive drum 11, a charger 12 that charges the photosensitive drum to a desired potential, and output image data to the photosensitive drum 11 that is charged to the desired potential. A laser optical unit 13 for writing corresponding to (a signal converted into a writing signal in the video signal processing unit based on image data subjected to image processing to be described later), and writing on the photosensitive drum 11 by writing by the laser optical unit 13 A developing device 14 that develops the electrostatic latent image formed on the photosensitive drum 11 with toner corresponding to each color component, and a transfer device that transfers the toner image developed on the photosensitive drum 11 by the developing device 14 onto the intermediate transfer belt 8. Primary transfer device) 15, cleaner 16 for cleaning untransferred toner remaining on the photosensitive drum 11 without being transferred to the intermediate transfer belt 8, and the like It is al configuration.

(toner):
The toner will be described. The toner is a so-called polymerized toner manufactured by a polymerization method. Further, WAX, which is a release agent, is included in the toner so that oilless fixing can be realized at the time of fixing.

  The toner has a volume average particle size of 5.5 μm. The toner particle size was measured using a particle size measuring device “Coulter Counter TAII” manufactured by Coulter Electronics Co., Ltd., with an aperture diameter of 100 μm. The toners for five colors of transparent (T), yellow (Y), cyan (C), magenta (M), and black (K) are manufactured by almost the same manufacturing method. The above-mentioned production method does not limit the specifications of the toner of the present invention, and in addition to the above production method, a toner produced by a dispersion polymerization method or a pulverization method may be used.

  Here, an example of creating hidden characters on a recording sheet will be described as an example of creating hidden information on a recording medium. To create the hidden character, a transparent (T) toner (hereinafter referred to as a transparent toner Tt) that is transparent and non-absorbing in the visible light region and exhibits light absorption characteristics in the ultraviolet region is used. This transparent toner Tt is produced by incorporating a benzotriazole-based UV absorber (manufactured by BASF, UV absorber TINUVIN 900) as a UV absorber. The ultraviolet absorber may be other than this. As an example, a transparent toner satisfying the object of the present invention can be provided by containing an ultraviolet absorber such as a hydroxyphenyl triazine-based ultraviolet absorber or a triazine-based ultraviolet absorber in the transparent toner Tt.

  Further, in this example, in order to create a hidden character, at least one of the five color toners of yellow (Y), cyan (C), magenta (M), and black (K), which are colored toners, is used. Uses a toner exhibiting a characteristic of absorbing fluorescent light and emitting fluorescent light (hereinafter referred to as fluorescent toner). In this example, yellow (Y) toner is exemplified as a fluorescent toner that absorbs ultraviolet rays and emits yellow light, and is represented by Y-color fluorescent toner Ft.

  This Y-color fluorescent toner Ft is produced by including a yellow fluorescent pigment (Shinloihi Co., Ltd., FZ-5050) in the toner. Of course, other yellow fluorescent pigments can be used. The object of the invention can also be achieved by using a commercially available yellow fluorescent pigment.

  In this example, cyan (C) toner, magenta (M) toner, and black (K) toner other than Y-color fluorescent toner Ft are used for an existing electrophotographic image forming apparatus (for example, manufactured by Ricoh Co., Ltd.). The toner used in MP C5001) can be used as it is.

(Image data processing unit):
Processing of the image data is performed by the image processing device 19 shown in FIG. The image processing apparatus 19 is provided in the image forming apparatus 10 shown in FIG. The image processing apparatus 19 may function as a printer when the image forming apparatus 10 is connected to an external device such as a personal computer. In this case, document information held by the external device is input as input image data to the MTF processing unit 20 of the image processing device 19. As the input image data, there are a case of a document by R (abbreviation of Red), G (abbreviation of Green), and B (abbreviation of Blue) constituting an ordinary color image not including hidden information, and these R, G, There is a case of a document in which transparency (T) for hidden information is added to B.

  The image processing apparatus 19 receives input image data from an external device and performs data processing for obtaining output image data in the image forming apparatus 10. The image processing device 19 has a plurality of data processing units in addition to the MTF processing unit 20.

Data processing in the image processing device 19 will be described with reference to FIG. When a normal color image is output without forming hidden characters, the processing flow is the same as that in a conventional image forming apparatus having no transparent (T) image data for hidden information in FIG.
When the image forming apparatus 19 includes a scanner unit, input data from the scanner unit, and when the image forming apparatus 19 functions as a printer, input data from an external device such as a personal computer is This is an RGB multi-valued image (8-bit in many cases) and is enhanced by the MTF filter processing unit 20 in the image processing unit.

  Next to the MTF filter processing unit 20, the color conversion processing unit 21 and the color separation processing unit 22 are used to divide the RGB color space into the CMYK color space. The image data divided into the CMYK color space is subjected to density control for realizing a preset gradation in a gradation correction processing unit (γ conversion unit) 23 for each color. In the course of these processes, the color conversion processing unit 21 exchanges information with the color profile 21a. The gradation processing unit 23 exchanges information with the gradation correction table 23a.

The image data whose density has been controlled in the gradation correction processing unit (γ conversion unit) 23 is then subjected to pseudo halftone processing in the pseudo halftone processing unit 24 so as to match the printer characteristics, and output image data CMYK. (600 dpi, 4 bit data) is obtained. This output image data is sent to the image output system (video signal processing unit 25).
With the above procedure, image data corresponding to each color toner of CMYK when a normal color image not including hidden information is formed is created.

  On the other hand, when a color image having hidden information is output, image data relating to transparency (T) is added to each color image data, RGB, and CMYK added to each processing unit in FIG. This point will be described below.

  The image forming apparatus 10 can record hidden information such as hidden characters and hidden images in addition to a normal color image. The recorded hidden information cannot be recognized under general illumination, but can be perceived with the naked eye by, for example, irradiating ultraviolet rays.

  The hidden information includes a transparent toner Ft (provided that there is no light absorption in the visible light region but an absorption characteristic in the ultraviolet region) and a Y-color fluorescent toner Ft (provided by a yellow fluorescent pigment). Create by matching.

  The mechanism of hidden information is shown in FIG. In FIG. 4, the portion of the hidden character “ABC” as the hidden information is formed on the recording sheet S so that both the transparent toner Tt and the Y-color fluorescent toner Ft are disposed. Further, only the Y-color fluorescent toner Ft is arranged in the area surrounding the hidden character “ABC” and surrounded by the rectangular outline 26. Note that the rectangular outline 26 is an auxiliary line drawn for the purpose of explaining this example, and no image is formed.

  The hidden character “ABC” formed with such toner is not perceived under general illumination because the presence or absence of the transparent toner Tt is not perceived by the transparency of the transparent toner Tt to visible light. On the other hand, when the ultraviolet light is irradiated by the black light, since the ultraviolet ray absorbing action works at the portion where the transparent toner Tt is disposed, light emission by the fluorescent material contained in the Y color fluorescent toner Ft does not occur. On the other hand, in the peripheral part of the hidden character “ABC” within the frame of the rectangular outline 26 where the transparent toner Tt is not arranged, the fluorescence contained in the Y-color fluorescent toner Ft. Light emission from the raw material is generated. In this way, contrast occurs in the light emission of the fluorescent toner corresponding to the presence or absence of the transparent toner Tt, so that the hidden character “ABC” can be perceived.

  In order to form the hidden information in this way, in the designated area on the document, the portion “ABC” of the hidden character itself is transparent so as to form an image with both the transparent toner Tt and the Y color fluorescent toner Ft (T ) Create image data for toner. In addition, image data is created so that an image is formed only with the Y-color fluorescent toner Ft in the peripheral portion of the hidden character.

  In addition, as with a normal color image, it is possible to output an image that has been subjected to pseudo halftone processing even with a toner image produced with the transparent toner Tt and the Y-color fluorescent toner Ft. The pseudo intermediate processing unit 24 also performs pseudo halftone processing on the toner image produced with the transparent toner Tt and the Y-color fluorescent toner Ft to create output image data such as 600 dpi 4 bits.

  In the color image forming apparatus 10 having a configuration having the T, Y, C, M, and K image forming units of FIG. 2, as shown in FIG. Ft, an image is formed with transparent toner Tt + transparent toner Tt in the hidden character portion, and Y, C, M, and K toners are appropriately combined according to the image data in “image region other than the hidden character portion and the peripheral portion of the hidden character”. A normal full color image is formed.

  The above is a method for creating image data of each color corresponding to the transparent toner Tt and the CMYK toner.

(Image writing part):
The image data corresponding to each of the CMYKT colors including the image data corresponding to the normal color image generated by the image processing device 19 and the image data corresponding to the hidden character in this way are shown in FIG. The video signal processing unit 25 converts the signal into a laser modulation signal. Here, only the flow of data for one color (assumed to be Y color) will be described. Since the same processing is performed for the other TCKM4 colors, the data flow for one color will be described here.

  The video signal processing unit 25 receives the output image data from the pseudo halftone processing unit 24, and stores in the line memory data for five light emitting points (laser diodes: LD) as one light source for each color of CMYKT. The data on the line memory corresponding to each pixel is delivered to the PWM control unit 27 at a predetermined timing (pixel clock) in accordance with a signal (so-called synchronization signal) synchronized with the rotation of the polygon mirror as the scanning means. .

  In the PWM control unit 27, this data is converted into a pulse width modulation (PWM) signal and delivered to the five LD drivers 28. In the LD driver 28, the LD element 29 (or the LD array) is optically modulated and driven with a predetermined light amount corresponding to the pulse width modulation signal. In this example, pulse width modulation (PWM) control is performed corresponding to the output image data of each color component, and laser light modulation driving is performed.

  Data that has been light-modulated corresponding to the output image data is irradiated onto the photosensitive drum 11 of the image forming engine section via the laser optical unit 13 shown in FIG. The laser optical unit 13 does not have a characteristic part as compared with the optical writing means in the conventional color print unit, and the conventional color print unit can be used without any problem.

  Hereinafter, an example of a conventional color print unit will be described with reference to the laser optical unit 13 shown in FIG. Although the LD element 29 shown in FIG. 3 is arranged in the laser optical unit 13, it is not shown because it is complicated in the depth direction of the drawing. The emitted light from the LD element 29 forms parallel light in the collimate lens in the laser optical unit 13 and is cut into a light beam corresponding to a desired beam diameter by the aperture. The light beam after passing through the aperture passes through the cylindrical lens and enters the polygon mirror 30.

  The light beam that has become the scanning light by being reflected by the polygon mirror 30 is collected by the scanning lens (f-θ lens), is folded by the folding mirror, and is formed by the image forming units 9T, 9Y, 9C, 9M, and 9K. An electrostatic latent image corresponding to the image data is formed on each of the photosensitive drums 11. These light paths are indicated by broken lines.

  The electrostatic latent image formed on each photoconductive drum 11 is developed with toner while passing through each developing device 14 as the photoconductive drum 11 rotates, and becomes a toner image. The toner images on the respective photosensitive drums 11 are sequentially transferred onto the rotating intermediate transfer belt 8 at the site of the transfer device (primary transfer device) 15 of each image forming unit 9T, 9Y, 9C, 9M, 9K. As a result, a color superimposed toner image is obtained. The color superimposed toner image is collectively transferred to the recording sheet S at the site of the transfer device (secondary transfer device) 17 to reproduce a color image representing the original image on the recording sheet S.

(Fixing part):
A toner image formed with toner for five colors of TYCMK on the recording sheet S at the site of the transfer device (secondary transfer device) 17 shown in FIGS. 1 and 2 is heated and pressed in the fixing device 5. Thus, the image is fixed on the recording sheet S and image formation is completed. The fixing device 5 of this example includes a fixing roller 5a (toner image side) and a pressure roller 5b (non-toner image side).

  The fixing roller 5a has a diameter of 30 mm, an elastic layer of liquid silicone rubber is formed on an aluminum base tube, and a PTFE layer made of a fluororesin is formed on the surface layer as a release layer. The pressure roller 5b is formed to have a diameter of 30 mm, an elastic layer of silicone rubber is formed on an aluminum core, and a fluororesin (PTFE) is formed as a release layer on the surface layer.

  In this example, the temperature of the fixing roller 5a of the fixing device 5 is set to 170 ° C., and the toner image is fixed on the recording sheet S by passing the recording sheet S at a linear speed of 200 mm / sec (primary). Fix).

  A fixing device having a configuration other than the configuration of the fixing device 5 described above may be used. It is also possible to use a conventionally used fixing device. Any material can be used as long as it can fix the toner image according to the present invention on the recording sheet, such as fluorescent toner or transparent toner.

(Example 1: Invention of image forming apparatus for outputting toner image using fluorescent toner and transparent toner: related to claim 1):
In Example 1, as described in the first embodiment, regarding the image forming apparatus 10 that forms an image by superimposing a plurality of color toner images on a recording medium, one of the colored toners forming the toner image is Y The color fluorescent toner Ft, which forms a toner image of another color, is a transparent toner Tt that is transparent in the visible light region, non-light-absorbing, and exhibits light absorption characteristics in the ultraviolet region.

  As described in the section of the background art, the conventional printing method can identify the contents of hidden characters even under general lighting, and as a result, the significance of hidden characters is lost. was there. The reason why the contents of hidden characters are identified even when illuminated in general is because the surface state of the paper and the surface state of the toner image are essentially different, so the surface reflected light state of both is completely the same It was because it was not possible.

  On the other hand, in the invention of Example 1, as described with reference to FIG. 4, the hidden character “ABC” is formed by using two types of toners, that is, the Y-color fluorescent toner Ft and the transparent toner Tt.

  The portion corresponding to the hidden character “ABC” itself is a toner image in which two types of toners, Y-color fluorescent toner Ft in the lower layer and transparent toner Tt in the upper layer, are arranged, and the peripheral portion of the hidden character “ABC” has a rectangular outline. The line 26 has a toner image configuration in which only the Y-color fluorescent toner Tt is disposed.

  By doing in this way, both the portion corresponding to the hidden character itself and the portion other than the hidden character (peripheral portion) are made the surface formed by substantially the same material called toner (material mainly composed of resin). Therefore, unlike the example described in the background art, it was possible to solve the problem that the contents of hidden characters could be identified under general lighting.

  Of course, there is a difference between the hidden character and its peripheral part, such as the presence or absence of transparent toner. However, both are common in that they are made of a resin-based material, and the hidden characters themselves and the peripheral part are made of the same material. I was able to. This eliminates the problem in the background art that the contents of hidden characters can be generally identified under illumination, and enables the formation of images in which the contents of hidden characters are not easily identified under ordinary illumination. become.

  In addition, the image related to the hidden information using the Y-color fluorescent toner Ft and the transparent toner Tt can identify the hidden content under black light illumination (under ultraviolet light illumination). As described above, since the transparent toner having the absorption characteristic in the ultraviolet region is arranged in the hidden character itself, the ultraviolet light from the black light is absorbed by the transparent toner. That is, the ultraviolet light from the black light does not reach the fluorescent toner.

  On the other hand, since there is no transparent toner that absorbs ultraviolet rays around the hidden characters, the ultraviolet rays from the black light reach the fluorescent toner and are emitted as visible light. For this reason, the viewer does not emit visible light (radiation) in the portion of the hidden character itself, but emits visible light (radiation) in the peripheral portion of the hidden character. Can perceive.

  As described above, the configuration of the hidden information using the fluorescent toner and the transparent toner solves the problem of the background technology such that the information of the hidden character can be perceived under the general illumination, and is hidden under the black light illumination. An image of hidden information that can identify the contents of characters was realized.

(Example 2: Invention in which gloss of toner image is limited: related to claim 2):
In the invention of Example 2, the glossiness (60 degree glossiness) of the toner image formed on the recording sheet S as the recording medium by superimposing the Y color fluorescent toner Ft and the transparent toner Tt is 40% or less.

  The invention of Example 1 aims to solve the problem that the content of hidden information can be identified relatively easily even under general illumination. In order to realize the solution, Y-color fluorescent toner Ft The hidden information is formed by using two types of toners, ie, transparent toner Tt.

  According to the study by the inventors, a boundary portion between an image area in which only the Y fluorescent toner Ft is formed on the recording sheet S and an image area in which both the Y fluorescent toner Ft and the transparent toner Tt are formed on the recording sheet. In FIG. 5, it was found that a slight difference in level may occur depending on the presence or absence of the transparent toner Tt.

  A toner image created by an electrophotographic method is characterized in that the thickness of the toner image is 1 to 5 μm (per color), which is larger than that of other image forming methods. Therefore, from the part where the thickness of the toner layer changes, that is, << the part where the toner layer corresponding to the peripheral part of the hidden character in FIG. 4 is one color (one layer) >>, << the part corresponding to the hidden character part [transparent The portion of the toner Tt + Y color fluorescent toner Ft that changes to the location of two colors (two layers)] is visually perceived.

  Since this level difference is perceived even under general lighting, the content of hidden information is still perceived by the user relatively easily (even under general lighting). As a result, the concealment of hidden characters is inferior.

  The invention of Example 2 is based on the invention of Example 1, and solves the problem that the content of hidden information is perceived due to the step difference caused by the presence or absence of transparent toner.

  The above-mentioned level difference is considered to be caused by a large toner image (toner image thickness is 1 to 5 μm) that is peculiar to the electrophotographic method. According to the inventors' investigation, It was found that there is a difference in the level difference perceived depending on the glossiness of the toner image. That is, there is a condition in which a sense of level difference is not perceived even with a thick toner image.

  Focusing on these points, the inventors changed the glossiness of the toner image by changing the fixing conditions to form hidden characters, and conducted a verification experiment to determine whether or not this level difference can be perceived. Table 1 shows the results of the verification experiment.

  The first column of Table 1 shows Conditions 1 to 6. The second row (T + Y patch column) is a patch image (2 cm square) formed by fixing a toner image obtained by superimposing the transparent toner Tt and the Y-color fluorescent toner Ft on the recording sheet S under predetermined fixing conditions. ) With a gloss meter (Konica Minolta Co., Ltd .: GM-268).

  The third column shows the fixing temperature and linear velocity when the patch image is created. The fourth column shows the result of evaluating the presence or absence of a step by visual evaluation by forming a hidden character using the transparent toner Tt and the Y color fluorescent toner Ft.

  The display of the evaluation result is (◯: the feeling of level difference cannot be perceived, Δ: the level difference can be perceived slightly, x: the level difference can be perceived).

  As a hidden character, a hidden character is formed by forming a character with a transparent toner Tt of 30 pt (points) on the solid region of the Y color fluorescent toner Ft, and the presence or absence of a step difference is visually evaluated.

  In Table 1, when the glossiness value in the second column of Table 1 is 40% or less, the hidden character can be formed in a state where the step difference of the hidden character cannot be perceived. That is, by satisfying the condition << the glossiness (60 degree glossiness) of the toner image formed on the recording sheet S by superimposing the Y color fluorescent toner Ft and the transparent toner Tt is 40% or less >>. As a result, a toner image that does not perceive a step difference at the boundary between the portion of the character itself in the hidden character and the peripheral portion of the character can be realized. Therefore, this configuration is used as an example of the invention of Example 2.

  In Example 2, as in Example 1, one of the colored toners is a fluorescent color (Y color fluorescent toner Ft) toner, and the other color toner is transparent (not non-visible) in the visible light range. In the ultraviolet region, the transparent toner Tt exhibits absorption characteristics. The difference between the two inventions is that, in the invention of Example 2, the glossiness (60 degree glossiness) of the toner image formed on the recording medium by superimposing the fluorescent toner and the transparent toner is 40% or less. It is.

  In Example 2, as in Example 1, hidden characters are created using two types of toners, a fluorescent toner and a transparent toner. As a result, a contrast is generated between the portion where the transparent toner is formed and the portion where the transparent toner is not formed when the ultraviolet ray is irradiated, so that a hidden character which can be perceived under the ultraviolet ray irradiation is formed. Then, the surface of both the hidden character itself and the peripheral portion of the hidden character are formed with toner, and the states of the reflected light on the surface of the two regions can be substantially matched.

  From the above, in Example 2, as in Example 1, image formation in which the contents of hidden characters cannot be easily perceived is realized, and the contents of hidden characters can be perceived under general illumination. Eliminates background technology concerns.

  Furthermore, in Example 2, the glossiness (60 degree glossiness) of the toner image formed on the recording medium by superimposing the fluorescent toner and the transparent toner is 40% or less, so that the fluorescent toner and the transparent toner The perception of the level difference generated at the boundary between the hidden character itself created using the two toners and the peripheral portion of the hidden character created using only the fluorescent toner is eliminated.

  A difference in level is particularly likely to occur in an image having a large toner image thickness (the toner image thickness is 1 to 5 μm per toner color) as in an electrophotographic image forming apparatus. Further, as can be seen from Table 1, this step difference is not perceived as the glossiness (60 degree glossiness) of the toner image formed on the recording medium by superimposing the fluorescent toner and the transparent toner is reduced. is there. Further, according to this verification result, it is possible to obtain a level difference by forming an image so that the glossiness (60 degree glossiness) of the toner image formed on the recording medium by superimposing the fluorescent toner and the transparent toner is 40% or less. It has been found that no feeling is perceived.

  It should be noted that the reason why the sense of difference in level is more easily perceived as the glossiness is increased (the surface of the toner image is smooth) is not fully known. However, in a toner image having a high glossiness, regular reflection light on the surface of the toner image does not spread but concentrates in one direction. For this reason, even if the reflection position changes due to a slight inclination at the boundary portion where the toner layer thickness is different, the intensity of the regular reflection light at the visual position changes, so that a sense of step difference is perceived. I think. In other words, the level difference becomes harder to perceive as the glossiness decreases.

  Thus, in addition to the advantages of Example 1, Example 2 solves the problem that hidden characters are perceived due to the step difference that occurs when two types of toner are used to create hidden characters. be able to. As a result, it is possible to realize an image forming apparatus that enables a user to form hidden characters with high confidentiality under normal illumination.

(Example 3: Invention relating to toner stacking order: related to claim 3):
In Example 3, a toner image on a recording sheet, which is a recording medium, in which fluorescent toner and transparent toner are overlapped, has fluorescent toner as a lower layer (side closer to the recording medium) and transparent toner as an upper layer (side far from the recording medium). Formed as follows.

  In the first embodiment, due to the configuration of the color print unit 4-1 shown in FIG. 2, the overlapping state of the Y color fluorescent toner Ft and the transparent toner Tt on the recording sheet S is fluorescent as shown in FIG. The toner Ft is formed as a lower layer (side closer to the recording sheet S) and the transparent toner Tt is formed as an upper layer, and the transparent toner Tt forms a hidden character itself.

A procedure for forming the hidden character “ABC” shown in FIG. 4 will be described.
In FIG. 2, an electrostatic latent image is formed on each photosensitive drum 11 of the image forming units 9T, 9Y, 9C, 9M, and 9K in accordance with the image data, and development is performed with the toner that each developing device 14 has. Assume that an image is carried.

  As shown in FIG. 2, the image forming units 9T, 9Y, 9C, 9M, and 9K are arranged in the order of 9T → 9Y → 9C → 9M → 9K from the upstream in the moving direction of the intermediate transfer belt 8 to the downstream. Accordingly, toner is laminated on the intermediate transfer belt 8 in the order of transparent toner Tt → Y color fluorescent toner Ft → cyan (C) → magenta (M) → black (K) from the side close to the belt surface.

  However, according to the image data, all of these do not always overlap completely, and there are also portions that are missing depending on the location, thereby forming a full-color image.

<Hidden text creation process>
A process of creating a hidden character formed as shown in FIG. 4 will be described with reference to FIG. The photosensitive drum 11 of the image forming unit 9T carries a hidden character “ABC” by the transparent toner Tt. First, the toner image of the hidden character “ABC” by the transparent toner Tt is transferred to the rotating intermediate transfer belt 8. Next, when the hidden character “ABC” by the transparent toner Tt on the intermediate transfer belt 8 moves to the image forming unit 9Y, the Y-color fluorescent toner Ft carried in advance on the photosensitive drum 11 of the image forming unit 9Y. The toner image (solid image filling the rectangular outline 26) is transferred so as to cover the hidden character portion “ABC” with the transparent toner Tt already transferred onto the intermediate transfer belt 8.

  Thus, on the intermediate transfer belt 8, the hidden character “ABC” by the transparent toner Tt is placed on the lower layer, and the Y-color fluorescent toner Ft is placed so as to cover the transparent toner Tt constituting the hidden character “ABC”. It becomes a state. Therefore, the hidden character portion has only two layers, and the peripheral portion of the hidden character has a single layer of only the Y-color fluorescent toner Ft.

  The toner image placed on the intermediate transfer belt 8 with such a configuration is transferred to the recording sheet S at a transfer unit (secondary transfer unit) 17. As a result, each toner image is reversed in the vertical position, and the Y-color fluorescent toner Ft is placed on the upper surface of the recording sheet S in a solid form. Will be in a position. This is the state shown in FIG. The toner image is fixed on the recording sheet S through the fixing device 5.

  In FIG. 4, the hidden character “ABC” itself has a configuration of a superimposed toner image with a total of two layers of Y-color fluorescent toner Ft and transparent toner Tt thereon from the side near the top surface of the recording sheet S. The peripheral area of the hidden character has a toner image configuration with a single layer of only Y-color fluorescent toner Ft.

  On the recording sheet S, other characters and images are formed in parallel to the outside of the hidden character “ABC” formation region, but this is the same as the normal color image formation process, and the image forming unit 9Y. , 9C, 9M, 9K, etc.

  In Example 3, the hidden character portion is composed of a toner image using a fluorescent toner and a transparent toner, and all the advantages of the invention of Example 1 are included when implemented with the contents of the invention of Example 1. Alternatively, when implemented including the contents of the invention of Example 2, in addition to the advantages described in Example 1, the advantages described in Example 2 are also included. In addition, it has the advantages inherent in the invention of Example 3.

  In Example 3, the transparent toner Tt is arranged on the upper layer of the Y-color fluorescent toner Ft in the hidden character portion, and the ultraviolet light is absorbed in the transparent toner Tt when irradiated with the ultraviolet rays. Does not reach the Y-color fluorescent toner Ft formed as a lower layer, and no visible light is emitted from the Y-color fluorescent toner Ft.

  On the other hand, in a portion where the transparent toner Tt is not disposed in the upper layer, the ultraviolet rays reach the Y color fluorescent toner Ft disposed as the lower layer, and as a result, visible light is emitted from the Y color fluorescent toner Ft layer. As described above, according to the invention of Example 3, since the contrast of visible light radiation is obtained when ultraviolet rays are irradiated according to the presence or absence of the transparent toner Tt, it becomes possible to perceive hidden characters.

  In Example 3, in addition to the advantages of the inventions of Examples 1 and 2, there is an inherent advantage that the formation of hidden characters having a large contrast of visible light radiation obtained by irradiation with ultraviolet rays can be realized.

  That is, under general illumination, the hidden character portion is not perceived by the transparency of the transparent toner Tt with respect to visible light, so that the presence or absence of the transparent toner is not perceived. On the other hand, when ultraviolet light is irradiated by black light, the function of absorbing ultraviolet rays works at the place where the transparent toner Tt is disposed, and thus, light emission by the fluorescent material contained in the Y color fluorescent toner Ft is generated, for example. On the other hand, in a place where the transparent toner Tt around the hidden character is not arranged, light emission by the fluorescent material contained in the Y color fluorescent toner Ft is generated. That is, since the contrast is generated in the light emission of the Y color fluorescent toner Ft corresponding to the presence or absence of the transparent toner Tt, the contents of the hidden character can be perceived.

[Second Embodiment] (Example 4: Invention related to toner stacking order: related to claim 4):
In Example 4, the toner image on the recording sheet, which is a recording medium, in which the fluorescent toner and the transparent toner are overlapped, the fluorescent toner is the upper layer (the side far from the recording sheet), and the transparent toner is the lower layer (the side closer to the recording sheet). Formed as follows.

  The configuration of the image forming apparatus in Example 4 is mostly the same as the configuration of the image forming apparatus 10 in the first embodiment. The difference from the first embodiment is that the overlapping order of the toner in the color print unit is different.

  FIG. 5 is a schematic diagram of the color print unit 4-2 in the image forming apparatus according to the second embodiment. The color print unit 4-2 uses the same five types of toners as TYCMK as in the first embodiment, but yellow (Y), cyan (C), magenta (M), black (K), and transparent. (T), the image can be superimposed on the intermediate transfer belt to form an image.

  The color print unit 4-2 includes five image forming units corresponding to T, Y, C, M, and K colors and toner components, in the counterclockwise direction indicated by arrows, from upstream to downstream. 9Y, 9C, 9M, 9K, and 9T are arranged in this order. The color component toner images formed by the image forming units 9Y, 9C, 9M, 9K, and 9T are disposed in contact with the photosensitive drums of the five image forming units 9Y, 9C, 9M, 9K, and 9T. The toner images are sequentially transferred to the intermediate transfer belt 8 to form a color superimposed toner image, and are carried on the intermediate transfer belt 8.

  The order in which the color toners are superimposed on the intermediate transfer belt 8 is in the order of Y, C, M, K, and T from the side closer to the surface of the intermediate transfer belt 8.

  The intermediate transfer belt 8 is rotated in the direction of the arrow at a predetermined timing by a driving unit (not shown), and the color component toner images in the five image forming units 9Y, 9C, 9M, 9K, and 9T are superimposed at a predetermined position. It has come to be. Each color component toner image formed on the intermediate transfer belt 8 is transferred to the recording sheet S on the conveying belt 3 described above with reference to FIG. 1 and becomes a toner image on the recording sheet S. In this example, the order in which the toner images are superimposed on the recording sheet S is the arrangement order of the respective color component toners of “(the far side from the recording sheet) Y → C → M → K → T (the side close to the recording sheet)”. .

  In the invention of Example 4, in the hidden character formed using the transparent toner Tt and the Y color fluorescent toner Ft, the overlapping order of the transparent toner Tt and the Y color fluorescent toner Ft is different from Example 3 in the first embodiment. The structure is reversed. This is shown in FIG.

  In Example 4, as described with reference to FIG. 5, the hidden character “ABC” is formed using two types of toners, that is, the Y-color fluorescent toner Ft and the transparent toner Tt.

  As shown in FIG. 6, a portion corresponding to the hidden character “ABC” itself is a toner image in which two types of toners, that is, a Y-color fluorescent toner Ft on the upper layer and a transparent toner Tt on the lower layer are arranged, and the hidden character “ABC” In the peripheral portion, the rectangular outline 26 has a toner image configuration in which only the Y-color fluorescent toner Tt is arranged.

<Hidden text creation process>
A process of creating a hidden character formed as shown in FIG. 6 will be described with reference to FIG. On the photosensitive drum 11 of the image forming unit 9Y, a toner image (solid image filling the rectangular outline 26) is carried by the Y-color fluorescent toner Ft. First, a toner image (solid image filling the rectangular outline 26) is transferred to the rotating intermediate transfer belt 8 by the Y-color fluorescent toner Ft. Next, when the toner image by the Y-color fluorescent toner Ft on the intermediate transfer belt 8 moves to the image forming unit 9T, the hidden characters by the transparent toner Tt previously carried on the photosensitive drum 11 of the image forming unit 9T. “ABC” is transferred to a position within the solid image that fills the rectangular outline 26 by the Y-color fluorescent toner Ft already transferred onto the intermediate transfer belt 8.

  Thus, on the intermediate transfer belt 8, a solid toner image with the Y-color fluorescent toner Ft is laminated on the lower layer, and a hidden character “ABC” with the transparent toner Tt is laminated on the Y-color fluorescent toner Ft. These toner images are transferred to the recording sheet S at a transfer unit (secondary transfer unit) 17. As a result, the respective toner images are reversed in the vertical position, the hidden character “ABC” by the transparent toner Tt is placed on the upper surface of the recording sheet S, and the solid Y-color fluorescent toner is further covered so as to cover the hidden character “ABC”. Ft is laminated. This is the same as the stacked state shown in FIG. The toner image is fixed on the recording sheet S through the fixing device 5.

  In FIG. 6, the hidden character “ABC” itself has a superposed toner image structure composed of a total of two layers of a transparent toner Tt and a Y-color fluorescent toner Ft on the recording sheet S from the side close to the top surface. The peripheral area of the hidden character has a toner image configuration with a single layer of only Y-color fluorescent toner Ft.

  On the recording sheet S, other characters and images are formed in parallel to the outside of the hidden character “ABC” formation region, but this is the same as the normal color image formation process, and the image forming unit 9Y. , 9C, 9M, 9K, etc.

  In Example 4, as in the invention of Example 3, one of the colored toners is a fluorescent toner, and the other toner is transparent (non-absorbing) in the visible light region. In the ultraviolet region, the toner exhibits absorption characteristics. The difference between the invention of Example 4 and the invention of Example 3 is that in Example 4, the Y-color fluorescent toner Ft is the upper layer (the side far from the recording sheet S), and the transparent toner Tt is the lower layer (the side closer to the recording sheet S). The toner layer is formed so that

  In Example 4, similarly to Example 3, the hidden character “ABC” is created using two types of toners, that is, the Y-color fluorescent toner Ft and the transparent toner Tt. As a result, a contrast is generated between the portion where the transparent toner Tt is formed and the portion where the transparent toner Tt is not formed, and the hidden character “ABC” which can be perceived under the ultraviolet irradiation is formed. can do.

  Both the portion of the hidden character “ABC” itself and the peripheral portion of the hidden character “ABC” form a surface with toner mainly composed of resin. The state of surface reflection in these two regions is almost the same. As a result, the contents of the hidden characters cannot be easily perceived in Example 4 as in Example 3. Image formation that cannot be perceived under general illumination is realized.

  In Example 4, the transparent toner Tt is arranged in the lower layer. When the formed image (hidden character ABC) is irradiated with ultraviolet rays, the ultraviolet rays are absorbed by the Y-color fluorescent toner Ft arranged as the upper layer and visible light is emitted, but the image is irradiated. Not all the ultraviolet rays are absorbed by the fluorescent toner Ft, but there is also a component that reaches the recording sheet S such as paper, is reflected there, and enters the fluorescent toner layer again.

  In Example 4, an image is formed so that a transparent toner Tt layer (ultraviolet absorption layer) is disposed between the Y-color fluorescent toner Ft layer and the recording sheet S. For this reason, the amount of ultraviolet rays when the ultraviolet rays reflected by the recording sheet S enter the fluorescent toner Ft layer again is changed by controlling the arrangement position of the transparent toner Tt layer, and enters the Y fluorescent toner Ft layer. It is the composition which changes the amount of ultraviolet rays to do.

  Here, “controlling the arrangement position of the transparent toner Tt layer” means forming a location “with transparent toner Tt” and a location “without transparent toner Tt”. The amount of visible light emitted from the fluorescent toner is controlled by irradiating and the hidden character is made visible by utilizing the contrast of reflected light.

  That is, in Example 4, the visible light radiation contrast as high as the configuration of Example 3 cannot be obtained, but the perceptible visible light radiation contrast can be obtained, and the hidden character can be perceived.

  In Example 4, since the Y-color fluorescent toner Ft is arranged above the transparent toner Tt, the arrangement of the transparent toner Tt is more difficult to perceive than the structure of Example 3. As shown in FIG. 6, the surface of the toner image is the Y-color fluorescent toner Ft both in the hidden character portion and in the peripheral portion of the hidden character portion. An image surface can be formed.

  For example, it is difficult to make the transparent toner Tt completely transparent, or it is difficult to completely match the thermal characteristics of the transparent toner Tt and the Y color fluorescent toner Ft. In the case of the configuration in which the transparent toner Tt is arranged at the top as in 3, the presence of the transparent toner Tt is easily perceived as a slight difference in color or a slight difference in gloss. In this respect, in the invention of Example 4, it is not necessary to impose strict restrictions on the transparency and thermal characteristics of the transparent toner Tt, and the special feature is that the contents of hidden characters are not perceived under general illumination. Have.

  As described above, in Example 4, in addition to the advantages of Examples 1 and 2, the arrangement of the transparent toner Tt is not easily perceived, and therefore, strict quality conditions regarding transparency and thermal characteristics imposed on the transparent toner Tt are not required. Both are advantageous in that hidden character formation can be realized.

[Third Embodiment] (Example 5: Invention related to toner stacking order: related to claim 5):
In Example 5, at least two of the colored toners that form a toner image on a recording sheet that is a recording medium in which a fluorescent toner and a transparent toner are overlaid are fluorescent toners, and the lowermost layer (close to the recording sheet). Side) and the uppermost layer (the side farther from the recording sheet), and the transparent toner is formed to be an intermediate layer (intermediate between the uppermost layer and the lowermost layer).

  The configuration of the image forming apparatus in Example 5 is mostly the same as the configuration of the first embodiment. The difference from the first embodiment is that, besides the yellow (Y) toner, the magenta (M) toner is also a fluorescent toner, and the order of color overlap between the yellow (Y) toner and the magenta (M) toner is different. A transparent (T) toner is placed between them.

  In Example 5, the magenta (M) toner that is a fluorescent toner is represented as an M color fluorescent toner Ft ′, and the yellow (Y) that is a fluorescent toner is represented as a Y color fluorescent toner Ft as before.

  The M color fluorescent toner Ft ′ is manufactured so as to exhibit a characteristic of absorbing cyan light and emitting cyan light. The M-color fluorescent toner Ft ′ in Example 5 is produced by including a magenta fluorescent pigment (Shinloihi Co., Ltd., FZ-6037) in the toner. Of course, other magenta fluorescent pigments can be used. By using a commercially available magenta fluorescent pigment, a toner capable of achieving the object of the present invention can be produced.

  A color print section in the image forming apparatus of Example 5 is shown in FIG. The color print unit 4-3 of Example 5 uses the same five types of toners as TYCMK as in the first embodiment, but yellow (Y), cyan (C), transparency (T), and magenta (M ) And black (K) in the image forming order so as to be superimposed on the intermediate transfer belt.

  The color print unit 4-3 includes five image forming units corresponding to the colors T and Y, C, M, and K and toner components, in the counterclockwise direction indicated by arrows, from upstream to downstream. 9Y, 9C, 9T, 9M, and 9K are arranged in this order. The color component toner images formed by the image forming units 9Y, 9C, 9T, 9M, and 9K are disposed in contact with the photosensitive drums of the five image forming units 9Y, 9C, 9T, 9M, and 9K. The toner images are sequentially transferred to the intermediate transfer belt 8 to form a color superimposed toner image, and are carried on the intermediate transfer belt 8.

  The order in which the color toners are superimposed on the intermediate transfer belt 8 is in the order of Y, C, T, M, K from the side closer to the surface of the intermediate transfer belt 8. For this reason, in Example 5, the overlapping order of the toner images on the recording sheet S is Y → C → T → M → K (close to the recording sheet) (distant from the recording sheet S).

  In Example 5, as shown in FIG. 8, in the hidden character “ABC” using the transparent toner Tt, the overlapping order of the transparent toner Tt, the Y-color fluorescent toner Ft, and the M-color fluorescent toner Ft ′ is the transparent toner Tt. A toner image is formed so as to be sandwiched between the Y-color fluorescent toner Ft and the M-color fluorescent toner Ft ′.

<Hidden text creation process>
A process of creating a hidden character formed as shown in FIG. 8 will be described with reference to FIG. On the photosensitive drum 11 of the image forming unit 9Y, a toner image (solid image filling the rectangular outline 26) is carried by the Y-color fluorescent toner Ft. First, a toner image (solid image filling the rectangular outline 26) is transferred to the rotating intermediate transfer belt 8 by the Y-color fluorescent toner Ft.

  Next, when the toner image by the Y-color fluorescent toner Ft on the intermediate transfer belt 8 moves to the image forming unit 9T, the hidden characters by the transparent toner Tt previously carried on the photosensitive drum 11 of the image forming unit 9T. “ABC” is transferred to a position within the solid image that fills the rectangular outline 26 by the Y-color fluorescent toner Ft already transferred onto the intermediate transfer belt 8.

  Further, when the toner image of the Y-color fluorescent toner Ft and the toner image of the hidden character “ABC” by the transparent toner Tt move to the image forming unit 9M, they are carried in advance on the photosensitive drum 11 of the image forming unit 9M. A toner image of the M color fluorescent toner Ft ′ (solid image filling the rectangular outline 26) is transferred so as to cover the hidden character portion “ABC” of the transparent toner Tt already transferred onto the intermediate transfer belt 8. The

  In this way, on the intermediate transfer belt 8, a solid toner image with the Y-color fluorescent toner Ft on the lower layer, a hidden character “ABC” with the transparent toner Tt thereon, and an M-color fluorescent toner Ft ′ so as to cover the transparent toner Tt. Are stacked. The phrase and the hidden character part itself are sandwiched between the Y color fluorescent toner Ft and the M color fluorescent toner Ft ′.

  These toner images are transferred to the recording sheet S at a transfer unit (secondary transfer unit) 17. As a result, the respective toner images are reversed in the vertical position, the M color fluorescent toner Ft ′ is placed on the upper surface of the recording sheet S, the hidden character “ABC” by the transparent toner Tt is placed thereon, and this hidden character “ABC”. A solid Y-color fluorescent toner Ft is laminated so as to cover the surface. This is the same as the stacked state shown in FIG. The toner image is fixed on the recording sheet S through the fixing device 5.

  In FIG. 8, the hidden character “ABC” itself is configured from the side closer to the top surface of the recording sheet S, with a total of three layers of M color fluorescent toner Ft ′ transparent toner Tt and Y color fluorescent toner Ft thereon. It is. Further, the peripheral area of the hidden character has a two-layer toner image configuration of the Y color fluorescent toner Ft and the M color fluorescent toner Ft ′.

  On the recording sheet S, other characters and images are formed in parallel to the outside of the hidden character “ABC” formation region, but this is the same as the normal color image formation process, and the image forming unit 9Y. , 9C, 9M, 9K, etc.

  The difference between Example 5 and Example 3 is that, in addition to the configuration in which the fluorescent toner in Example 3 is one color of the Y-color fluorescent toner Ft, the other color of the colored toner is also a fluorescent toner. Specifically, This is the M color fluorescent toner Ft ′. Therefore, it consists of two colors of fluorescent toner and one color of transparent toner. In addition, in the toner image formed on the recording sheet S, the fluorescent toner is formed on the uppermost layer (side closer to the recording sheet S) and the uppermost layer (side far from the recording sheet S), and the transparent toner is formed on the intermediate layer ( It is in a point that it is formed so as to be intermediate between the uppermost layer and the lowermost layer.

  In Example 5, similarly to Example 3, a hidden character is created using fluorescent toner and transparent toner. As a result, different color contrasts are produced between the portion where the transparent toner is formed and the portion where the transparent toner is not formed when the ultraviolet ray is irradiated. Using such color contrast, it becomes possible to form hidden characters that can be perceived under ultraviolet irradiation.

  Similarly to Example 3, as shown in FIG. 8, the surface of both the hidden character “ABC” itself and the peripheral portion of the hidden character “ABC” are formed with toner mainly composed of resin. Will be able to. In other words, the surface reflection states of the two regions can be made almost coincident.

  As a result, in Example 5, as in Example 3, it is possible to realize image formation in which the contents of hidden characters cannot be easily perceived (cannot be perceived under general illumination).

  In the case of the background art, the state of surface reflection between the portion of the hidden character itself and the peripheral portion of the hidden character does not completely match, so that the content of the hidden character can be perceived under general illumination. This has been a problem in applications where the confidentiality of hidden characters is required. In this example, such a problem can be solved.

  In Example 5, as shown in FIG. 8, the transparent toner Tt is arranged between the two types of fluorescent toners, that is, the Y-color fluorescent toner Ft and the M-color fluorescent toner Ft ′. When the image thus formed is irradiated with ultraviolet rays, the ultraviolet rays are absorbed by the Y-color fluorescent toner Ft arranged as the upper layer and radiate visible light, but all are absorbed by the Y-color fluorescent toner Ft of the upper layer. However, it reaches the fluorescent toner of another color, that is, the M fluorescent toner Ft ′ arranged in the lower layer. As a result, the lower M color fluorescent toner Ft ′ also absorbs ultraviolet rays and emits visible light in the same manner as the upper layer.

  Accordingly, in the peripheral portion of the hidden character where the transparent toner Tt is not disposed, the light of the color in which the emitted light from the upper Y fluorescent toner Ft and the emitted light from the lower M fluorescent toner Ft ′ are superimposed ( Green). In the hidden character portion where the transparent toner Ft is disposed as the intermediate layer, the ultraviolet light does not reach the lower M-color fluorescent toner Ft ′ (the ultraviolet light is absorbed by the transparent toner layer Tt), and therefore the upper Y-color fluorescence. Only the Y-color radiation from the toner Ft is perceived. That is, radiant light of different colors such as green and yellow is perceived according to the presence or absence of the transparent toner Tt.

  In the configuration of Example 3, since the change due to the presence or absence of the transparent toner is the presence or absence (strong or weak) of the radiated light, it does not change the color but can simply realize the contrast. On the other hand, in Example 5, it is possible to form an image of a hidden character so that the hidden character can be perceived as a color change (a color realized by mixing the upper layer radiation light and the lower layer radiation light).

  As described above, in Example 5, in addition to the advantages of Example 1 and Example 2, it is possible to perform image formation that can perceive the contents of hidden characters as a color change. As a result, it is possible to meet a variety of image output requests of users.

[Fourth Embodiment] (Example 6: Hidden image forming method: related to claim 6):
Example 6 is an image forming method for providing a desired image by forming toner images of a plurality of colors on a recording sheet as a recording medium, and at least one of the colored toners forming the toner image is used. For the fluorescent toner and the toner that forms another color toner image, a transparent toner is used, and a peripheral area of hidden information (hidden characters) is formed on the recording sheet by the fluorescent toner, and the fluorescent area is formed in the peripheral area. Hidden information (hidden characters) is created on the toner layer with the transparent toner and fixed with a fixing device to obtain a recorded image including the hidden information on the recording sheet.

  The invention of Example 6 relates to the contents of <hidden character creation process> described in Examples 3, 4 and 5. Each includes an embodiment implemented using the image forming apparatus 10, and hidden information having different aspects and features can be recorded depending on the arrangement of the image forming units.

[Fifth Embodiment] (Example 7: Arrangement position input means: related to claim 7):
Example 7 is an image forming system applied to the image forming apparatus according to any one of Examples 1 to 5, in which information such as hidden characters and hidden images formed of fluorescent toner and transparent toner is stored. It is provided with arrangement position input means that enables designation of the arrangement position on the recording medium.

  The portion of the so-called image forming apparatus that forms hidden characters on the recording sheet S is the same as that described in the first embodiment. The difference between the invention of Example 7 and the first embodiment is that the invention of Example 7 has an arrangement position input means for enabling designation of an arrangement position of a hidden character formed by transparent toner and fluorescent toner. .

In the image processing apparatus 19 shown in FIG. 3 according to the first embodiment, the image forming apparatus 10 is connected to a personal computer and functions as a printer.
Since the arrangement position of information such as hidden characters and hidden images formed of fluorescent toner and transparent toner on the recording medium is designated, there is a need for an arrangement position input means that enables designation of the arrangement position on the recording medium. Is scarce.

  On the other hand, when the image data read by the scanner is used as input image data to the image processing device 19 ′, it is necessary to specify the arrangement position of the hidden character formed by the transparent toner and the fluorescent toner. Even if there is no arrangement position input means that can specify the arrangement position on the recording medium, the arrangement position of the hidden character cannot be made.

  Therefore, in Example 7, in the flow of the image processing device 19 ′, the T plate processing unit 31 is connected upstream of the MTF filter processing unit 20, and the input image data (8 bits) R / G / B is hidden on the recording medium. The function to incorporate the data of the character placement position was given.

  Further, a display 32 is connected to the T-plate processing unit 31 so that an image that does not include hidden characters (a so-called normal image) is displayed on the display 32. A mouse 33 and a keyboard are connected to the display 32 as necessary as means for specifying the arrangement position on the recording medium.

  After the user determines the content of the hidden character (sentence made with the hidden character), the user confirms the arrangement position of the normal image such as the scanner data displayed on the display 32, and displays the hidden character on the display 32. While moving the arrangement position, the arrangement position of the hidden character is confirmed. If there is no problem, the arrangement position is determined by the operation of the mouse 33 or the keyboard.

  In the example 7, in this way, since the user can determine the arrangement position of the hidden character at the arrangement position of the normal image while balancing, the hidden character is arranged at the arrangement position where the most effective effect can be expected. Will be able to.

  The T plate processing unit 31, the display 32, the mouse 33, the keyboard, and the like are examples of arrangement position input means.

  Since Example 7 is based on the image forming apparatus of any of Examples 1 to 5, all the advantages of any invention of Examples 1 to 5 are included. In addition to that, it is possible to designate the arrangement positions of the transparent toner and the fluorescent toner. That is, the user can place hidden characters at a desired position. Thereby, since the user can arrange a hidden character at the most effective arrangement position, it becomes possible to realize a hidden character with a large added value.

[Sixth Embodiment] (Example 8: Lighting device: related to claim 8):
Example 8 is the image forming apparatus according to any one of Examples 1 to 5 or the image forming system according to Example 7, which is an illumination with ultraviolet irradiation that makes it possible to visualize an image formed by a fluorescent toner and a transparent toner formed on a recording medium. It is equipped with a device.

  In Example 8, the so-called image forming apparatus for forming hidden characters on the recording sheet is the same as that in the first embodiment. The difference between Example 8 and the first embodiment is that Example 8 has an illumination device that irradiates ultraviolet rays in addition to the part of the image forming apparatus that creates an image including hidden characters.

  In Example 8, the illumination apparatus 32 is configured to irradiate ultraviolet rays toward the image surface of the recording sheet S discharged to the paper discharge unit 7 of the image forming apparatus 10 illustrated in FIG. The user can visually check the state of the hidden characters and (performance) by irradiating the created image including the hidden characters with ultraviolet rays depending on the illumination device 32. Thereby, it becomes possible to quickly confirm the state of the created hidden character. The arrangement position input means of Example 7 can also be used to change the formation position of the hidden character.

  The illumination device 32 can apply a so-called black light that has been generally used. Further, in order to improve the visibility of the image and avoid the line of sight from outsiders, a simple shielding plate 33 is provided as a facility for easily covering the recording sheet S so as to be accommodated and pulled out. The simple shielding plate 33 is made of a resin having a shape memory so as to be lightweight and can be stored in the storage unit 34.

1, 2 Paper feeding cassette 3 Conveying belts 4-1, 4-2, 4-3 Color printing unit 5 Fixing device 5a Fixing roller 5b Pressure roller 6 Discharging roller 7 Discharging unit 8 Intermediate transfer belts 9T, 9Y, 9C, 9M, 9K Image forming unit 10 Image forming apparatus 11 Photosensitive drum 12 Charger 13 Laser optical unit 14 Developer 15 Transfer device (primary transfer device)
16 Cleaner 17 Transfer device (secondary transfer device)
18 Registration roller 19, 19 ′ Image processing device 20 MTF filter processing unit 21 Color conversion processing unit 21a Color profile 22 Color separation processing unit 23 Tone correction processing unit (γ conversion unit)
23a Gradation correction table 24 Pseudo halftone processing unit 25 Video signal processing unit 26 Rectangular outline 27 PWM control unit 28 LD driver 29 LD element 30 Polygon mirror 31 T plate processing unit 32 Verification device S Recording sheet Tt Transparent toner Ft Y color Fluorescent toner Ft 'M color fluorescent toner 1 sheet

JP 2009-210667 A

Claims (8)

An image forming apparatus for forming an image by superimposing a plurality of color toner images on a recording medium,
At least one of the colored toners forming the toner image is a fluorescent toner (hereinafter referred to as a fluorescent toner), and the toner forming another toner image is transparent and non-light in the visible light range. An image forming apparatus characterized by being a toner exhibiting light absorption characteristics in absorption and ultraviolet regions (hereinafter referred to as transparent toner). The image forming apparatus according to claim 1.
An image forming apparatus, wherein a glossiness (60 degree glossiness) of a toner image formed on the recording medium by superimposing the fluorescent toner and the transparent toner is 40% or less. The image forming apparatus according to claim 1, wherein
The toner image on the recording medium in which the fluorescent toner and the transparent toner are overlaid is formed so that the fluorescent toner is a lower layer (side closer to the recording medium) and the transparent toner is an upper layer (side far from the recording medium). An image forming apparatus. The image forming apparatus according to claim 1, wherein
The toner image on the recording medium in which the fluorescent toner and the transparent toner are overlaid is formed so that the fluorescent toner is an upper layer (a side far from the recording medium) and a transparent toner is a lower layer (a side closer to the recording medium). An image forming apparatus. The image forming apparatus according to claim 1, wherein
At least two of the colored toners forming a toner image on the recording medium in which the fluorescent toner and the transparent toner are overlaid are the fluorescent toner, and the lowermost layer (side closer to the recording medium) and the uppermost layer. An image forming apparatus, wherein the image forming apparatus is formed on an upper layer (a side far from a recording medium) so that the transparent toner is an intermediate layer (intermediate between an uppermost layer and a lowermost layer). In an image forming method for providing a desired image by forming toner images of a plurality of colors on a recording medium,
Of the colored toners forming the toner image, at least one color is fluorescent toner, and the toner forming another one color toner image is transparent toner,
An image forming method comprising: forming a peripheral area of hidden information on a recording medium with fluorescent toner; and forming the hidden information with the transparent toner on the fluorescent toner layer in the peripheral area. An image forming system comprising the image forming apparatus according to any one of claims 1 to 5,
An image forming system comprising an arrangement position input unit that enables designation of an arrangement position of the fluorescent toner and the transparent toner on a recording medium. An image forming system having the image forming apparatus according to any one of claims 1 to 5, or an image forming system according to claim 7,
An image forming system comprising an ultraviolet irradiation illumination device that makes it possible to visually view an image formed of fluorescent toner and transparent toner formed on a recording medium.

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