JP7638776B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus that forms an image on a recording material.

Electrophotographic or electrostatic image forming devices transfer a toner image formed on an image carrier such as a photoreceptor or intermediate transfer body onto a recording material, and then output the resulting product on the recording material after fixing the toner image with a fixing device. In the fixing device, the toner image is fixed by heating and pressurizing the recording material while the recording material is sandwiched and transported between the nip of a pair of rotating bodies consisting of rollers or belts (films).

In order to prevent the easy forgery of the product created by the image forming device, it is known to create a security image as an image (glossy image) in which the background and foreground images have the same density and the glossiness of the background and foreground are different. A security image (security mark) is an image in which the foreground symbol or the like can be easily recognized by the naked eye, but the density difference between the foreground and background is difficult to detect with an image scanner, and it guarantees that the document on which the security image is recorded is the original. A general image scanner reads the intensity of scattered light from the document in a direction perpendicular to the image surface of the document and converts it into image density information, so it is difficult to read a security image created as a glossy image. Patent Document 1 describes a technology in which the background part of the security image is formed in the first image formation, and the fixing temperature is changed to form the foreground part of the security image in the second image formation, thereby creating a difference in glossiness between the background part and the foreground part.

JP 2016-45272 A

However, in the method of the above document, the background and foreground parts of the security image are subjected to different numbers of fixing processes, which results in a difference in glossiness not only in the smoothness of the image surface, but also in the thickness of the toner image between the background and foreground parts. Therefore, depending on the performance of the image scanner, it may be possible to detect the density difference between the background and foreground parts. In addition, if the security image formed by the method of the above document is photographed with a camera from any direction other than the direction perpendicular to the image surface, symbols and the like in the foreground part can be read relatively easily, making it possible for information to be stolen by the camera.

The present invention aims to provide an image forming device capable of forming images that are more difficult to read by an image scanner and to extract information from by a camera.

One aspect of the present invention is an image forming apparatus having a toner image forming means for forming a toner image on a recording material, and a fixing means for applying heat and pressure to the toner image formed by the toner image forming means to fix the toner image to the recording material, the image forming apparatus creating a glossy image including significant information due to gloss, the glossy image including a base image and a surface image formed by superimposing the base image on the base image, the surface image including a first halftone image and a second halftone image disposed in an area excluding an area of the first halftone image from an area of the base image, the image forming apparatus being configured to form the base image on the recording material by the toner image forming means, and then fix the base image by the fixing means, and thereafter form the surface image including the first halftone image and the second halftone image by the toner image forming means on the base image, and then fix the base image and the surface image by the fixing means, at least one of the halftone image and the second halftone image is configured with an anisotropic pattern, and is configured such that a difference in glossiness between an area of the first halftone image and an area of the second halftone image varies depending on an angle at which the glossy image is viewed; a difference between the density of the first halftone image and the density of the second halftone image is equal to or less than a predetermined threshold; when the glossy image is formed on a first recording material and a second recording material having a surface roughness greater than that of the first recording material, the toner amount per unit area of the base image is changed depending on the recording material so that the toner amount per unit area of the base image formed on the second recording material is greater than the toner amount per unit area of the base image formed on the first recording material; and the glossiness of the base image when the glossy image is formed on the second recording material is made higher than the glossiness of the base image when the glossy image is formed on the first recording material .

The present invention provides an image forming device capable of forming images that are more difficult to read by an image scanner and more difficult to extract information from by a camera.

1 is a schematic diagram of an image forming apparatus according to a first embodiment. 1 is a schematic diagram of a fixing device according to a first embodiment. 5A and 5B are schematic diagrams showing a procedure for providing a security image according to the first embodiment. FIG. 2 is a perspective view showing a cross section of a security image according to the first embodiment. 5A and 5B are diagrams for explaining the relationship between the observation direction and glossiness of the security image according to the first embodiment. 6 is a graph showing the measurement results of the glossiness of the security image according to Example 1. 10 is a graph showing the measurement results of the glossiness of a security image according to Example 2. 13 is a graph showing measurement results of the glossiness of a security image according to a comparative example. 11A to 11C are diagrams showing modified examples of halftone patterns used for security images.

Embodiments of the present disclosure are described below with reference to the drawings.

[Example 1]
(1) Image Forming Apparatus First, the configuration of an image forming apparatus 1 according to the embodiment 1 will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view of the image forming apparatus according to the embodiment 1. The image forming apparatus 1 is a laser printer that forms an image on a recording material P by using an electrophotographic method.

The image forming apparatus 1 includes a process cartridge 10 having a photosensitive drum 19 as an image carrier (electrophotographic photosensitive member), a charging roller 16 as a charging means, a developing roller 17 as a developing means, and a cleaning blade 18 as a cleaning means. In this embodiment, the photosensitive drum 19, the charging roller 16, the developing unit including the developing roller 17, and the cleaning unit including the cleaning blade 18 are configured as a process cartridge 10 so as to be detachable from the main body of the image forming apparatus 1. The image forming apparatus 1 also includes a laser scanner 11, a feed tray 21, a feed roller 22, a pair of conveying rollers 23, a top sensor 24, a transfer roller 12, a fixing device 13 as a fixing means (image heating device), a pair of discharge rollers 26, a motor 20, and a control unit 40. The image forming unit 1A including the process cartridge 10, the laser scanner 11 as an exposure means, and the transfer roller 12 as a transfer member functions as a toner image forming means for forming a toner image on the recording material P.

The motor 20 is a driving means for applying a rotational driving force to the image carrier and the members responsible for transporting the recording material P. In this embodiment, the motor 20 provides the rotational driving force for multiple members, such as the feed roller 22, the pair of transport rollers 23, the photosensitive drum 19, the fixing device 13, and the pair of discharge rollers 26.

The photosensitive drum 19 is a photosensitive member molded into a drum shape (cylindrical shape), and is rotated at a predetermined peripheral speed (process speed) in the counterclockwise direction in the figure during image formation. The charging roller 16 uniformly charges the peripheral surface of the photosensitive drum 19 to a predetermined polarity and potential (primary charging). The charged surface of the photosensitive drum 19 that has been primarily charged is scanned and exposed (irradiated) with laser light emitted from the laser scanner 11. The laser scanner 11 as an exposure means outputs laser light that is on/off modulated according to a video signal transmitted from the control unit 40. The video signal refers to a signal (time-series digital pixel signal) that is generated based on data that expands image information to be formed on the image carrier in the main scanning direction and sub-scanning direction of the laser scanner 11, and is transmitted to the exposure device 7 as a signal that specifies the amount of toner for each pixel. In addition, image information representing the image to be formed on the recording material P is input from an external device (information processing terminal) such as an image scanner or a computer connected to the image forming apparatus 1.

By scanning and exposing the laser scanner 11, the charge in the exposed area (bright area) of the peripheral surface of the photosensitive drum 19 is removed, and an electrostatic latent image corresponding to the image information is formed on the peripheral surface of the photosensitive drum 19. The developing roller 17 carries a developer containing toner on its surface and supplies the toner to the photosensitive drum 19, developing the electrostatic latent image formed on the peripheral surface of the photosensitive drum 19 into a toner image. In this embodiment, a reversal development method is used in which toner is attached to the bright area during exposure for development.

The feed tray 21 is detachable from the image forming apparatus 1 and stores the recording materials P stacked thereon. The recording materials P in the feed tray 21 are fed and separated one by one by the feed roller 22 being driven based on a feed start signal from the control unit 40, and are transported to the transport roller pair 23. The transport roller pair 23 further introduces the recording materials P into the transfer nip T, which serves as a transfer section, formed between the photosensitive drum 19 and the transfer roller 12.

The top sensor 24 is installed on the transport path between the transport roller pair 23 and the transfer nip T, and detects the timing of the passage of the leading edge of the recording material P sent from the transport roller pair 23. The control unit 40 adjusts the timing of writing the electrostatic latent image by the laser scanner 11 according to the timing of the leading edge of the recording material P detected by the top sensor 24. In other words, the write timing is controlled so that the leading edge of the toner image on the photosensitive drum 19 reaches the transfer nip T at the same time as the leading edge of the recording material P reaches the transfer nip T.

The recording material P introduced into the transfer nip T is sandwiched and transported between the photosensitive drum 19 and the transfer roller 12 at the transfer nip T. During this time, a transfer voltage controlled to a predetermined voltage value is applied to the transfer roller 12 from a transfer voltage application power source (not shown). A transfer voltage of a polarity opposite to the normal charging polarity of the toner is applied to the transfer roller 12, so that the toner image carried on the peripheral surface of the photosensitive drum 19 is electrostatically transferred to the surface of the recording material P. The recording material P to which the toner image has been transferred is transported from the transfer nip T to the fixing device 13. Note that the peripheral surface of the photosensitive drum 19 that has passed through the transfer nip T has residual toner and paper dust removed by the cleaning blade 18, and is once again primarily charged for use in the formation of the next image.

The fixing device 13 has a fixing film 14 as a fixing member and a pressure roller 15 as a pressure member (details will be described later), and sandwiches and conveys the recording material P in the fixing nip F. During this time, the toner image on the recording material P is heated by the fixing film 14, which is controlled to a predetermined temperature (fixing temperature), thereby fixing the toner image. The recording material P that has passed through the fixing device 13 is discharged and stacked on a discharge tray provided at the top of the image forming apparatus 1 by a pair of discharge rollers 26 that discharge the recording material P. Through the above series of operations, image formation on one sheet of recording material P is completed.

In the case of double-sided printing, the recording material P, which has an image formed on its first side by passing through the transfer nip T and the fixing nip F, is sent to the discharge roller pair 26, and then is pulled back into the image forming apparatus 1 by the reverse rotation of the discharge roller pair 26 at a predetermined timing. The pulled back recording material P is transported again toward the image forming unit 1A by the double-sided transport roller pair 34, 35 provided on the double-sided transport path 33, with the first side and the opposite second side interchanged. Then, the recording material P, which has an image formed on its second side by being transported again from the transport roller pair 23 through the transfer nip T and the fixing nip F, is discharged to the discharge tray by the discharge roller pair 26. In other words, the double-sided transport path 33 functions as a re-transport unit that transports the recording material that has passed through the toner image forming means and the fixing means back toward the toner image forming means. In this embodiment, the discharge roller pair 26 functions as a reversing unit that transports the recording material to the re-transport unit in a reversed state.

By repeating the above operations, images can be formed successively on multiple sheets of recording material P. The image forming apparatus 1 of this embodiment is capable of printing approximately 43 black-and-white images per minute on A4 size [210 mm x 297 mm] plain paper at a transport speed of 230 mm/sec.

The control unit 40 has a CPU 41, a ROM 41a, and a RAM 41b. The CPU 41 executes various programs stored in the ROM 41a, and controls various operations related to image formation while using the RAM 41b as a working area. The ROM 41a is an example of a non-transitory storage medium that stores the control program for the image forming device 1.

(2) Fixing Device Next, the configuration of the fixing device 13 will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing a cross-sectional configuration of the fixing device 13 according to Example 1. The fixing device 13 includes a fixing film 14, a pressure roller 15, a nip forming member 60A having a heater 60 and a heater holder 61 as a heat generating element, and a pressure stay 63.

The fixing film 14 is a flexible cylindrical (endless) film-like member. The heater 60 is a plate-shaped heating element that rapidly heats the fixing film 14 while in contact with the inner circumferential surface of the fixing film 14. The heater 60 has a heating resistor that generates heat when electricity is applied, and generates heat when current is passed through a current circuit mounted on the image forming apparatus 1. The temperature of the heater 60 is detected by a thermistor 62, which serves as a temperature detection means and is in contact with the rear surface of the substrate. The control unit 40 then controls the power supply to the heater 60 based on the detection signal of the thermistor 62 so that the heater 60 reaches a predetermined target temperature.

The heater holder 61 holds the heater 60. In other words, the heater 60 and the heater holder 61 function as a nip forming member 60A that has a heating element for heating the film and is arranged inside the film. The pressure stay 63 is made of a rigid member such as metal, and applies pressure force received from a pressure means such as a spring (not shown) to the pressure roller 15 via the heater holder 61. This pressure force forms a fixing nip F as a nip portion of a predetermined width between the nip forming member 60A and the pressure roller 15, which are pressed against each other with the fixing film 14 sandwiched therebetween.

In the fixing device 13 of this embodiment, the heater 60 is in direct contact with the inner circumferential surface of the fixing film 14, but a plate-like or sheet-like member with high thermal conductivity (e.g., a sheet-like member made of ferroalloy or aluminum) may be placed between the heater 60 and the fixing film 14. In other words, a nip forming member 60A may be used in which the heater 60 heats the fixing film 14 via a sliding member that slides against the inner circumferential surface of the fixing film 14.

(3) Method of Applying Security Image The method of applying a security image (security mark) for the purpose of preventing counterfeiting in this embodiment will be described with reference to Figs. 3(a) and 3(b) and 4. Figs. 3(a) and 3(b) are schematic diagrams showing the procedure for applying a security mark onto a recording material P. Fig. 4 is a perspective view showing a cross section of the security mark applied onto the recording material P.

As shown in Figures 3(a, b) and 4, the security mark of this embodiment is composed of a base image 81 that is in direct contact with the recording material P, and a surface image 82 that is formed on the base image 81. The surface image 82 is composed of a foreground image 82a as a first halftone image, and a background image 82b as a second halftone image.

When the image forming device 1 receives an instruction to form an image including a security mark, it first forms a base image 81 as shown in FIG. 3(a). The base image 81 is an image of uniform density and is sized to encompass (contain) the surface image 82 that will be formed later. In this embodiment, an image with density data of 100% (a so-called solid image) is formed as the base image 81 at a transport speed of 230 mm/sec (the process speed when forming the base image).

When the image formation of the base image 81 is completed, the image forming apparatus 1 uses the double-sided conveying path 33 to make the surface on which the base image 81 is formed (hereinafter referred to as the image surface) available for image formation again as follows. That is, the recording material P on which the base image 81 is fixed by the fixing device 13 is sent to the discharge roller pair 26, and then the discharge roller pair 26 is reversely rotated at a predetermined timing, so that the recording material P is pulled back into the image forming apparatus. The pulled back recording material is conveyed to the conveying roller pair 23 by the double-sided conveying roller pairs 34 and 35 provided on the double-sided conveying path 33, and is conveyed in a state in which the second surface of the recording material P (the back surface of the image surface of the base image 81) faces the photosensitive drum 19. At this time, no image is formed on the second surface of the recording material P. The recording material P conveyed from the conveying roller pair 23 to the discharge roller pair 26 via the transfer nip T and the fixing nip F is drawn back into the image forming apparatus again by the discharge roller pair 26 rotating in reverse at a predetermined timing. The returned recording material is transported to the transport roller pair 23 by the double-sided transport roller pair 34, 35 provided on the double-sided transport path 33, and the first side of the recording material P (the image side of the base image 81) faces the photosensitive drum 19. In other words, the recording material P is in a state where a toner image can be formed again by the image forming unit 1A on the same side on which the base image 81 has already been formed.

Next, the surface image 82 is formed as shown in FIG. 3B. The surface image 82 is formed (transferred) so as to be superimposed on the previously formed base image 81. At this time, the conveying speed of the recording material P (the process speed during the surface image formation) is 77 mm/sec.

As shown in FIG. 3(a), the surface image 82 is composed of a foreground image 82a and a background image 82b. The foreground image 82a is an image (first halftone image) in which specific characters, symbols, figures, patterns, etc., which display information as a security mark, are expressed in halftones consisting of an anisotropic pattern (first pattern). A group of parallel lines with a line width of 250 μm and line spacing of 250 μm are used as the anisotropic halftone.

The foreground image 82a in this embodiment includes two specific characters, "original" and "original." In other words, the security mark as a glossy image in this embodiment, which includes the base image 81 and the surface image 82, is a mark that guarantees that the recording material on which the glossy image is formed is an original.

The background image 82b is formed in the area where the base image 81 is formed, excluding the area where the foreground image 82a is formed. In other words, the image area of the foreground image 82a and the image area of the background image 82b are exclusive, and the two image areas essentially cover the entire image area of the base image 81. In other words, the background image 82b in this embodiment is an image in which the area of the characters "Original" and "Book", which are the foreground image 82a, is whited out from the image area of the base image 81.

The background image 82b is an image (second halftone image) that has a different anisotropy from the halftone of the foreground image 82a and is composed of halftones of the same density as the halftone of the foreground image 82a. The halftone of the background image 82b uses parallel lines with a line width of 250 μm and line spacing of 250 μm that are at an angle of 90 degrees to the parallel lines of the foreground image 82a. In addition, the parallel lines that make up the foreground image 82a and the parallel lines that make up the background image 82b both extend at an angle of 45 degrees to the recording material transport direction.

In other words, in this embodiment, the first halftone image is composed of a pattern of parallel lines extending in a first direction, and the second halftone image is composed of a pattern of parallel lines extending in a second direction intersecting the first direction. In addition, the line width and line spacing of the parallel lines that make up the first halftone image are equal to the line width and line spacing of the parallel lines that make up the second halftone image.

As shown in FIG. 4, the foreground image 82a and the background image 82b have their complementary areas painted with halftones of the same density. Therefore, the surface image 82, which is the sum of the foreground image 82a and the background image 82b, is a halftone image of uniform density overall.

On the other hand, when the front image 82 is formed, an image other than the security mark (so-called main text) 90 is also formed at the same time. The recording material P onto which the front image 82 and main text 90 have been transferred and fixed is discharged through the pair of discharge rollers 26 onto a discharge tray on the image forming device 1, completing image formation.

(4) Effect of security image The effect of the security image (security mark) utilizing the gloss difference of this embodiment will be described. The gloss of an image depends on the intensity of reflected light from the image surface. The reflected light of the security mark of this embodiment is classified into a reflected light component from the base image 81 and a reflected light component from the surface image 82. Of these, the reflected light component from the base image 81 changes significantly depending on the angle of the observer's line of sight, as will be described below. The "reflected light" referred to here refers to the reflected light that is specularly reflected on a plane along the surface of the recording material P on which the security image is applied.

5(a) shows an example of a state in which the line direction of the parallel lines of the surface image 82 and the direction of the observation light source 70 as seen by the observer 71 are nearly perpendicular. Also, FIG. 5(b) shows an example of a state in which the line direction of the parallel lines of the surface image 82 and the direction of the observation light source 70 as seen by the observer 71 are nearly parallel. In the state of FIG. 5(a), part of the incident light from the observation light source 70 is blocked by the parallel lines of the surface image 82 and does not reach the base image 81. Also, part of the reflected light from the base image 81 is blocked by the walls of the parallel lines of the surface image 82 (the edges of each line that constitutes the surface image 82) and does not reach the observer 71. On the other hand, in the state of FIG. 5(b), the light from the observation light source 70 is rarely blocked by the parallel lines of the surface image 82. Therefore, in the state of FIG. 5(b), the intensity of the reflected light that the observer 71 can observe is stronger than in FIG. 5(a), and the gloss is higher.

6 shows the results of measuring the glossiness of the foreground image 82a and background image 82b of the security mark. The recording material used in this measurement was "Futura 100 lb (manufactured by VERSO) with a basis weight of 148 g/ ^m2 ." The glossiness was measured using a glossmeter PG-1 (manufactured by Nippon Denshoku Industries Co., Ltd.) while changing the installation direction of the glossmeter relative to the recording material conveyance direction. The incidence angle of the measurement light of the glossmeter to the recording material surface was set to 75 degrees. The parallel lines of the foreground image 82a and the parallel lines of the background image 82b used in this measurement differ from each other by 90 degrees, and both extend at an angle of 45 degrees relative to the recording material conveyance direction.

The horizontal axis of the graph in FIG. 6 indicates the installation direction of the glossmeter in degrees relative to the recording material transport direction. When the installation direction of the glossmeter is 45 degrees, the foreground image 82a is in the positional relationship shown in FIG. 5(b) relative to the glossmeter and light source, and the glossiness of the foreground image 82a is measured to be relatively high. In addition, the parallel lines used in the foreground image 82a and background image 82b in this embodiment differ in line direction by 90 degrees. Therefore, when the installation direction of the glossmeter is 45 degrees, the background image 82b is in the positional relationship shown in FIG. 5(a) relative to the glossmeter and light source, and the glossiness of the background image 82b is measured to be lower than that of the foreground image 82a.

Similarly, when the installation direction of the gloss meter is 135 degrees, the foreground image 82a is in the positional relationship shown in FIG. 5(a) relative to the gloss meter and light source, and the background image 82b is in the positional relationship shown in FIG. 5(b) relative to the gloss meter and light source. Therefore, in this case, the gloss of the background image 82b is measured to be higher than that of the foreground image 82a.

In this way, the glossiness of the foreground image 82a and background image 82b of the security mark of this embodiment changes depending on the observation angle. When the inventors conducted experiments, they found that if the difference in glossiness between the foreground image 82a and background image 82b is 4 degrees or more, the information on the security mark (the characters "original" and "original") can be easily seen. In other words, for at least one measurement angle, if the difference between the 75-degree specular glossiness of the first halftone image area measured from the measurement angle by a glossmeter and the 75-degree specular glossiness of the second halftone image area measured from the measurement angle by the glossmeter is 4 degrees or more, practical visibility of the security mark can be ensured.

The information on the security mark in this embodiment is most visible at a viewing angle equivalent to 45 degrees or 135 degrees in the installation direction of the gloss meter in Figure 6, and visibility decreases as the viewing angle deviates from that state. In particular, when observed from an angle of 45 degrees to the line direction of the group of parallel lines (corresponding to when the installation direction of the gloss meter in Figure 6 is 0 degrees or 90 degrees) or when observed perpendicular to the image surface, no difference in gloss occurs between the foreground image 82a and the background image 82b. Therefore, it is difficult to read the information on the security mark when observed from these angles.

Here, if the recording material P is held in the hand or the observer's viewpoint can be freely changed, the information on the security mark can be read relatively easily by adjusting the viewing angle to increase visibility. On the other hand, in the case of a fixed camera where the viewing angle cannot be adjusted, the angles at which the information can be read are limited, which makes it possible to suppress information theft.

On the other hand, as mentioned above, the foreground image 82a and the background image 82b have complementary areas painted with halftones of the same density, so the security mark is an image of uniform density overall. Therefore, even if the image is read by an image scanner, it is difficult to read the information in the security mark, which is effective in preventing counterfeiting.

Furthermore, in this embodiment, the base image 81 is fixed once, and then the recording material P is transported again via the double-sided transport path 33 to form the surface image 82. The recording material P is then transported again to the fixing device 13, and the base image 81 is fixed multiple times, resulting in a smoother surface. Therefore, compared to an image that has been fixed only once as in normal printing, the base image 81 is more likely to reflect light from the light source in a regular manner. As a result, the difference in gloss between the foreground image 82a and background image 82b depending on the viewing angle becomes more noticeable, making the information on the security mark easier to see.

[Example 2]
Next, a description will be given of Example 2. In this example, a more preferable security mark can be created by adjusting the toner amount of the base image 81 according to the type of recording material P. The configuration of the image forming apparatus and the basic operation of applying a security image to the recording material P are the same as those in Example 1, and therefore a description thereof will be omitted.

As an example, a case will be described in which "Futura 100 lb (manufactured by VERSO) with a basis weight of 148 g/ ^m2 " and "GF-C081 (Canon Marketing Japan) with a basis weight of 81.4 g/m2" are used as the recording material P. When "Futura 100 lb" is used, the base image 81 is a solid image with density data of 100%, as in the first embodiment. On the other hand, when "GF-C081" is used, the toner amount of the solid image of the base image 81 is set to 1.5 times that of the first embodiment. At this time, the rotation speed of the developing roller 17 is increased to supply more toner to the circumferential surface of the photosensitive drum 19 than during normal image forming operations, thereby increasing the amount of toner.

Figure 7 shows the results of measuring the glossiness of the foreground image 82a and background image 82b of the security mark when "GF-C081" is used as the recording material P. Figure 8 shows the results of measuring the glossiness when "GF-C081" is used as the recording material P and the base image 81 is a solid image with density data of 100% as a comparative example 1. Here, density data of 100% refers to the signal value of the video signal when the laser scanner 11 forms an image with maximum density as a normal image (main text) other than the security mark. An image formed on one side of the recording material P based on a video signal with density data of 100% is a solid image with a toner coverage rate (printing rate) of 100% relative to the area on the recording material P. On the other hand, the 1.5 times base image 81 used in this embodiment is an image with 1.5 times the amount of toner applied per unit area on the recording material P, based on an image with a printing rate of 100% formed with density data of 100%.

In Comparative Example 1, as shown in FIG. 8, the difference in gloss between the foreground image 82a and the background image 82b is at most 2 degrees, which is small. This is because the surface roughness of "GF-C081" is rougher than that of "Futura 100lb", and the surface of the base image 81 formed on the recording material P is relatively rough. Because the surface of the base image 81 is rough, light from the light source is less likely to be reflected specularly, and gloss differences between the foreground image 82a and the background image 82b due to line-of-sight angles are less likely to occur. Therefore, in Comparative Example 1, in which the toner amount of the base image 81 is 100% regardless of the type of recording material, it may be difficult to visually recognize the information on the security mark (the characters "original" and "original").

In Example 2, as shown in FIG. 7, the difference in glossiness between the foreground image 82a and background image 82b is a maximum of 5 degrees, which is larger than in Comparative Example 1. This is because the surface of the base image 81 is smoother than in Comparative Example 1 by increasing the amount of toner in the base image 81 and covering the unevenness on the surface of the recording material P with toner. As in Example 1, the glossiness of the foreground image 82a and background image 82b changes depending on the observation angle, and the security mark information (the characters "Original" and "Book") can be seen as a difference in glossiness.

In this manner, in this embodiment, when the same security mark is applied to a first recording material and a second recording material having a surface roughness greater than that of the first recording material, the amount of toner in the base image 81 applied to the second recording material is made greater than the amount of toner in the base image 81 applied to the first recording material. This makes it possible to apply a security mark that is easily visible according to the material of the recording material. In addition, compared to the case where the amount of toner in the base image 81 is always 1.5 times that of embodiment 1, the amount of toner in the base image 81 is not increased even for recording materials with a relatively smooth surface, which has the advantage of saving on toner consumption and energy consumption during image formation.

Note that ten-point average roughness and arithmetic mean roughness are known as typical measures of the surface roughness of the recording material P, but regardless of which measure is used, the greater the surface roughness (the rougher the surface), the lower the glossiness when a solid image is formed with 100% density data. Therefore, for example, it is possible to increase the amount of toner in the base image 81 for a recording material with a ten-point average roughness equal to or greater than a threshold value compared to when the surface roughness is less than the threshold value, but this is not limited to this, and other surface roughness values may be used as the standard. Also, in the control program executed by the control unit 40 of the image forming apparatus 1, it is not necessary to change the amount of toner in the base image 81 based on the numerical value of the surface roughness. For example, a table in which the amount of toner is predetermined according to the attributes of the recording material (brand, type of paper such as plain paper or coated paper, etc.) may be referenced.

[Other Examples]
The present technology can also be applied to an image forming apparatus (generally known as a color image forming apparatus) having a plurality of process units (a plurality of developing units). In a color image forming apparatus, the amount of toner in the base image 81 can be increased by using a plurality of process units. For example, in a color image forming apparatus having four process units of yellow, magenta, cyan, and black, a base image 81 can be created with a total of 200% toner amount, i.e., 100% cyan and 100% black. By increasing the amount of toner in the base image 81, the surface of the base image 81 can be made smoother, and light from the observation light source can be easily reflected regularly. Therefore, the gloss difference between the foreground image 82a and the background image 82b depending on the line of sight angle becomes more noticeable, and a security mark that is more easily visible can be provided. The toner color is not limited to the above, and the base image 81 or the surface image 82 may be formed with, for example, a transparent toner or a white toner.

In addition, in a color image forming apparatus, a base image 81 and a surface image 82 can be created by overlapping them in a single image forming operation using multiple process units (multiple developing units). That is, the base image 81 is formed in a process unit that creates a toner image located in the lower layer when transferred to a recording material, and the surface image 82 is formed in a process unit that creates a toner image located in the upper layer when transferred to a recording material. Then, the fixing device 13 fixes the recording material to which the base image 81 and the surface image 82 have been transferred, so that the fixing process of the base image 81 and the surface image 82 can be performed simultaneously. In this case, the fixing process by the fixing device 13 can be completed in one go, so that the productivity of image formation can be improved. Note that there are color image forming apparatuses in which multiple process units are arranged along an intermediate transfer body such as an intermediate transfer belt, and in which a direct transfer process unit is arranged along the transport path of the recording material.

In the above embodiment, an example was described in which the background image 82b was made up of parallel lines that had an angle of 90 degrees different from the parallel lines in the foreground image 82a, but the angle between the parallel lines does not have to be 90 degrees. Furthermore, in the embodiment, the surface image 82 was made up of two types of halftone images, the foreground image 82a and the background image 82b, but the surface image 82 may be made up of a combination of three or more types of halftone images, as long as they have different anisotropies and the same density. For example, the surface image 82 can be made up of halftone images made up of three groups of parallel lines that are angled at 60 degrees and 120 degrees from each other.

Furthermore, the foreground image 82a and the background image 82b may have substantially the same density and different anisotropy patterns, and are not limited to the parallel line group pattern shown in the first embodiment. For example, the foreground image 82a may be a halftone image of the pattern in FIG. 9(a), and the foreground image 82b may be a halftone image of the pattern in FIG. 9(b). Also, it is not necessary to have the same pattern but different angles, and for example, a combination of the parallel line group pattern and the pattern in FIG. 9(a) may be acceptable. Also, as long as the density is substantially the same, either one of the foreground image 82a and the background image 82b may be an isotropic pattern as shown in FIG. 9(c). In other words, at least one of the first halftone image and the second halftone image may be configured to have an anisotropic pattern, and the difference between the glossiness of the area of the first halftone image and the glossiness of the area of the second halftone image may vary depending on the angle at which the glossy image is viewed.

Here, the "anisotropy" of the pattern constituting the halftone image refers to the fact that the frequency with which the boundary (edge) between the toner image area and the non-toner image area appears when the pattern is cut along a straight line in a certain direction differs depending on the cutting direction. If the frequency of the pattern edges is high when cut along a certain direction, the proportion of light reflected in a direction different from the regular reflection direction at the edge part and incident light blocked by the pattern when the image is viewed from that direction will be large, and the glossiness will be low. Also, if the frequency of the pattern edges is low when cut along another direction, the proportion of light reflected in a direction different from the regular reflection direction at the edge part and incident light blocked by the pattern when the image is viewed from that direction will be small, and the glossiness will be high. The frequency of the edges when the pattern shown in FIG. 9(a) is cut horizontally is lower than the frequency of the edges when cut vertically, so the glossiness when viewed horizontally is higher than the glossiness when viewed vertically.

In the embodiment, the densities of the foreground image 82a and background image 82b are made the same in the image data to prevent information from being read by an image scanner, but they do not have to be completely identical. In other words, it is sufficient that the difference in density between the first halftone image and the second halftone image is equal to or less than a predetermined threshold value. This will be explained using Table 1.

Table 1 shows the relationship between the color difference ΔE2000 of the CIE L*a*b* values when the foreground image 82a and the background image 82b are changed, and the difficulty of reading the security mark information by an image scanner at that time. Security marks whose information could not be read by the image scanner are marked with an O, and security marks whose information could be read are marked with an X. In addition, security marks whose information could not be read without special settings such as adjusting gamma correction are marked with a △. In other words, if the color difference ΔE2000 of the CIE L*a*b* values of the foreground image 82a and the background image 82b is 3.0 or less (below the threshold), it is difficult to read the information by an image scanner, which is effective in preventing counterfeiting. Note that the threshold value of 3.0 for the color difference ΔE2000 is an example of a predetermined threshold value for suppressing reading by an image scanner, and other scales and numerical values may be used as the threshold value as long as they can effectively suppress reading by an image scanner.

In the embodiment, the recording material P is transported using the double-sided transport path 33 to continuously form the base image 81 and the surface image 82, but the base image 81 and the surface image 82 may be formed separately. For example, the recording material P on which the base image 81 has been fixed by the fixing device 13 may be discharged onto a discharge tray on the image forming apparatus 1, and then fed again from the manual feed tray 27 to form the surface image 82.

In the above-described embodiment, a security mark that guarantees that a document or the like is an original is given as an example of a glossy image that contains significant information due to gloss, but the use of a glossy image is not limited to this. The glossy image may be the main content of a document or the like.

1...Image forming device/1A...Toner image forming means (image forming section)/13...Fixing means (fixing device)/81...Base image/82...Surface image/82a...First halftone image (foreground image)/82b...Second halftone image (background image)

Claims (11)

a toner image forming means for forming a toner image on a recording material;
a fixing unit that applies heat and pressure to the toner image formed by the toner image forming unit to fix the toner image to the recording material, and the image forming apparatus creates a glossy image including significant information due to gloss,
the glossy image includes a base image and a surface image formed by overlaying the base image,
the surface image includes a first halftone image and a second halftone image disposed in an area of the base image excluding an area of the first halftone image;
the image forming apparatus is configured to form the base image on the recording material by the toner image forming means, then fix the base image by the fixing means, and thereafter form the surface image including the first halftone image and the second halftone image on the base image by the toner image forming means, and then fix the base image and the surface image by the fixing means;
At least one of the first halftone image and the second halftone image is configured with a pattern having anisotropy, and is configured such that a difference in glossiness between an area of the first halftone image and an area of the second halftone image varies depending on an angle at which the glossy image is viewed;
a difference between a density of the first halftone image and a density of the second halftone image is equal to or less than a predetermined threshold;
an image forming apparatus for forming a glossy image on a first recording material and a second recording material having a surface roughness greater than that of the first recording material, the image forming apparatus changes the toner amount per unit area of the base image depending on the recording material so that the toner amount per unit area of the base image formed on the second recording material is greater than the toner amount per unit area of the base image formed on the first recording material, and makes the glossiness of the base image when the glossy image is formed on the second recording material higher than the glossiness of the base image when the glossy image is formed on the first recording material . 2. The image forming apparatus according to claim 1,
The second halftone image is formed of a pattern having anisotropy different from that of the first halftone image. 2. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the second halftone image is formed of an isotropic pattern. 2. The image forming apparatus according to claim 1,
the first halftone image is composed of a pattern of parallel lines extending in a first direction;
The image forming apparatus according to claim 1, wherein the second halftone image is configured with a pattern made up of a group of parallel lines extending in a second direction intersecting the first direction. 5. The image forming apparatus according to claim 4,
13. An image forming apparatus, comprising: a first halftone image including a group of parallel lines, the group of parallel lines having a width and a spacing that are equal to ... 6. The image forming apparatus according to claim 1,
13. An image forming apparatus according to claim 12, wherein the base image is an image formed with a uniform density over an area including the surface image. 7. The image forming apparatus according to claim 1,
an image forming apparatus, characterized in that a difference between a density of the first halftone image and a density of the second halftone image is 3.0 or less in terms of a color difference ΔE2000 of CIE L*a*b* values; 8. The image forming apparatus according to claim 1,
An image forming apparatus characterized in that, for at least one measurement angle, the difference between the 75 degree specular gloss of the area of the first halftone image measured from the measurement angle by a gloss meter and the 75 degree specular gloss of the area of the second halftone image measured from the measurement angle by the gloss meter is 4 degrees or more. 9. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the glossy image is a mark for guaranteeing that the recording material to which the glossy image is applied is an original. 10. The image forming apparatus according to claim 1,
a re-transporting section for transporting the recording material that has passed through the fixing section to the toner image forming section again,
The image forming apparatus is characterized in that the recording material, which has been subjected to a fixing process of the base image, is transported again to the toner image forming means by the re-transporting unit in order to form the surface image on the base image. The image forming apparatus according to any one of claims 1 to 10 ,
The fixing means includes a cylindrical film, a nip forming member having a heating element for heating the film and positioned inside the film, and a pressure member that is pressed against the nip forming member while sandwiching the film, and the image on the recording material is heated while being transported while being sandwiched between the film and the pressure member in the nip portion formed between the nip forming member and the pressure member.

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