Image-forming device and image-forming method

Abstract

To realize an excellent visual effect.SOLUTION: An image-forming device 1 creates a decorative medium MC by successively superposing and printing a silver toner image PSL, a transmission toner image PCL, and a normal toner image PNL to the surface of a medium M. In this case, the image-forming device 1 provides a background area AB by setting a background print duty DB to 100[%] in the silver toner image PSL, and provides a decorative area AC in which a decorative print duty DC is set to 75.00[%] or larger and 93.75[%] or smaller. Accordingly, the image-forming device 1 can give an excellent visual effect in which the decorative area AC appears or is hidden in the surface side of the decorative medium MC when a relationship of relative positions and angles of the user's viewpoint VP, a light source LS, and the decorative medium MC is changed variously.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and an image forming method, and is suitable for application when forming an image having a special visual effect using a metallic color on a medium, for example.

Background Art

[0002] Conventionally, as an image forming apparatus, when performing color printing, toners such as black, magenta, cyan, and yellow (hereinafter collectively referred to as normal colors) (hereinafter these are referred to as normal color toners) are combined to form (i.e., print) a color image of normal colors on a medium such as paper. Also, among image forming apparatuses, there are those that can form a shiny image on paper by using a toner having a shiny property such as silver or gold (hereinafter also referred to as metallic colors) (hereinafter this is referred to as a shiny toner) in addition to these normal colors.

[0003] Also, as an image forming apparatus, there has been proposed one that forms (i.e., prints) an image having a visual effect in which the image appears and disappears by overlapping a normal color image with a normal color toner on a shiny image with a shiny toner (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the image printed by the above-described image forming apparatus, there are regions where the fluorescent toner is disposed and regions where it is not. For this reason, in a medium on which printing processing of superimposing a normal color image on this fluorescent image is performed, steps are formed for each region in the layer of the normal color toner constituting the normal color image. Then, in this medium, a difference in glossiness occurs for each region, and there is a problem that the image may be visually recognized contrary to intention and the visual effect is insufficient.

[0006] The present invention has been made in consideration of the above points, and intends to propose an image forming apparatus and an image forming method capable of realizing a good visual effect.

Means for Solving the Problems

[0007] In order to solve such problems, in the image forming apparatus of the present invention, a first image forming unit capable of forming a fluorescent image by a fluorescent developer on a medium, a second image forming unit capable of forming a transparent image by a transparent developer on the medium, a third image forming unit capable of forming a colored image by a colored developer on the medium, and a control unit that controls the first image forming unit, the second image forming unit, and the third image forming unit according to print data. The control unit causes the first image forming unit to form a fluorescent image having a first region and a second region on the surface of the medium, causes the second image forming unit to form a transparent image by superimposing it on the fluorescent image, and causes the third image forming unit to form a colored image by superimposing it on the transparent image. In the first region and the second region, the formation ratio representing the formation amount of the fluorescent developer per unit area with respect to the medium by the area ratio is set as a first formation ratio and a second formation ratio, respectively, and the difference between the second formation ratio and the first formation ratio is controlled to be 6.25 [%] or more and 25.00 [%] or less.

[0008] Also, in the image forming method of the present invention, a phosphorescent image forming step of forming a phosphorescent image having a first region and a second region on a medium with a phosphorescent developer by a first image forming unit, a transparent image forming step of forming a transparent image with a transparent developer by a second image forming unit and superimposing the transparent image on the phosphorescent image on the medium, and a colored image forming step of forming a colored image with a colored developer by a third image forming unit and superimposing the colored image on the phosphorescent image and the transmissive image on the medium. In the phosphorescent image forming step, when the formation ratio of the phosphorescent developer per unit area with respect to the medium in the first region and the second region, represented by the ratio of the area, is set as a first formation ratio and a second formation ratio, respectively, the difference between the second formation ratio and the first formation ratio is controlled to be 6.25 [%] or more and 25.00 [%] or less.

[0009] Furthermore, in the image forming apparatus of the present invention, a first image forming unit capable of forming a phosphorescent image with a phosphorescent developer on a medium, a second image forming unit capable of forming a transparent image with a transparent developer on the medium, a third image forming unit capable of forming a colored image with a colored developer on the medium, and a control unit for controlling the first image forming unit, the second image forming unit, and the third image forming unit according to print data are provided. The control unit causes the first image forming unit to form a phosphorescent image having a first region and a second region on the surface of the medium, causes the second image forming unit to form a transparent image by superimposing the transparent image on the phosphorescent image, causes the third image forming unit to form a colored image by superimposing the colored image on the transparent image, and sets the formation ratio of the phosphorescent developer per unit area with respect to the medium in the first region and the second region, represented by the ratio of the area, as a first formation ratio and a second formation ratio, respectively, and controls the ratio of the second formation ratio to the first formation ratio to be 75.00 [%] or more and 93.75 [%] or less.

[0010] The present invention forms a luminous image, a transparent image, and a colored image on a medium in an overlapping manner, and relates to the luminous image that becomes the lowermost layer, and controls the difference between the first formation ratio of the first region and the second formation ratio of the second region to be within a predetermined range. For this reason, the present invention enables a visual effect that causes a user viewing the medium to visually recognize the colored image and to transition between a state where the boundary between the first region and the second region is visually recognized and a state where only the colored image is visually recognized without recognizing the boundary, according to the positional relationship with a light source, the angle of the medium, etc.

Effects of the Invention

[0011] According to the present invention, an image forming apparatus and an image forming method capable of realizing a good visual effect can be realized.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0014] [1. Configuration of Image Forming Apparatus] As shown in the schematic side view of FIG. 1, the image forming apparatus 1 according to the present embodiment is an electrophotographic color printer and can form (i.e., print) a color image on a medium M such as paper. Incidentally, the image forming apparatus 1 does not have an image scanner function for reading a document or a communication function using a telephone line, etc., and is a single-function SFP (Single Function Printer) having only a printer function.

[0015] Various components are arranged inside a housing 2 formed in a substantially box shape in the image forming apparatus 1. Incidentally, hereinafter, with the right end portion in FIG. 1 being the front of the image forming apparatus 1, the vertical direction, the left-right direction, and the front-back direction when viewed facing this front will be defined and then described.

[0016] The image forming apparatus 1 is overall controlled by a control unit 3. As will be described later, this control unit 3 executes various processes by reading and executing a predetermined program. Further, the control unit 3 is connected to a host device 100 (FIG. 3) such as a computer device wirelessly or by wire, and when image data representing an image to be printed is given from this host device and printing of the image data is instructed, it executes a printing process for forming a printed image on the surface of the medium M. The display unit 4 is a display device such as a liquid crystal panel, etc., and is arranged on the front side of the upper surface of the housing 2. This display unit 4 displays various information based on the control of the control unit 3.

[0017] Inside the upper part of the housing 2, five image forming units 10K, 10C, 10M, 10SL, and 10CL are arranged in order from the front side to the rear side. The image forming units 10K, 10C, 10M, 10SL, and 10CL respectively correspond to the colors black (K), cyan (C), magenta (M), silver (SL: silver), and transparent (CL: clear). Although they only differ in color, they are all configured in the same way.

[0018] Black (K), cyan (C), and magenta (M) are all colors used in general color printers and are different from both the metallic color and the transparent color described later. Hereinafter, such colors are also referred to as normal colors. In this embodiment, yellow (Y) used in general color printers is not used.

[0019] Silver (SL) is a color that exhibits metallic luster, that is, has a shiny property, and is a special color different from normal colors. Hereinafter, such a color is also referred to as a metallic color. This silver (SL) may be used alone or may be used overlaid on normal colors.

[0020] The transparent color (CL) is a transparent color that has the property of transmitting at least a part of visible light (that is, transparency), and is a special color different from normal colors. Hereinafter, such a color is also referred to as a transparent color. This transparent color (CL) may be used alone or may be used overlaid on normal colors or metallic colors.

[0021] For convenience of explanation, hereinafter, the image forming units 10K, 10C, 10M, 10SL, and 10CL are collectively referred to as the image forming unit 10 or the image forming section. Also hereinafter, the image forming unit 10SL corresponding to the metallic color is also referred to as the first image forming section, the image forming unit 10CL corresponding to the transparent color (CL) is also referred to as the second image forming section, and the image forming units 10K, 10C, and 10M corresponding to normal colors (that is, colors that are neither metallic nor transparent) are also referred to as the third image forming section.

[0022] As shown in FIG. 2, the image forming unit 10 is roughly composed of an image forming main body 11, a toner container 12, a toner supply unit 13, and an LED (Light Emitting Diode) head 14. The toner container 12 stores toner T (also called a developer) inside and is configured to be detachable from the image forming unit 10. When this toner container 12 is attached to the image forming unit 10, it is attached to the image forming main body 11 via the toner supply unit 13. Incidentally, the toner container 12 may be called a toner cartridge.

[0023] As will be described later, for the silver toner T, a toner containing a bright pigment is used. For convenience of explanation, hereinafter, the silver (SL) toner T, which is a bright color, will be referred to as silver toner TSL, silver toner, bright toner, or bright developer. Also, for the transparent toner T, a toner containing a predetermined resin material is used. For convenience of explanation, hereinafter, the transparent (CL) toner T having a transparency that transmits at least a part of visible light will be referred to as transparent toner TCL, transparent color toner, or transparent developer. Regarding the transparent toner TCL, a transparent developer is defined as one that does not contain inorganic pigments such as aluminum pigments or pigments such as organic pigments. In this transparent developer, since there are some that are slightly colored yellow in the resin material used as the binder resin, a fluorescent whitening agent may be added for the purpose of increasing whiteness.

[0024] On the other hand, for the magenta, cyan, and black toners T, toners containing organic pigments such as pigment cyan, pigment magenta, and carbon black are used. For convenience of explanation, hereinafter, the toner T having a normal color, not a bright color or a transparent color, such as magenta, cyan, and black, will also be referred to as normal toner TNL, colored toner, or colored developer.

[0025] The image forming main body 11 (Fig. 2) incorporates an image forming housing 20, a toner storage space 21, a first supply roller 22, a second supply roller 23, a developing roller 24, a developing blade 25, a photosensitive drum 26, a charging roller 27, and a cleaning blade 28. Among these, the first supply roller 22, the second supply roller 23, the developing roller 24, the photosensitive drum 26, and the charging roller 27 are each configured in a columnar shape with their central axes along the left-right direction, and are each rotatably supported by the image forming housing 20.

[0026] The toner storage space 21 stores the toner T supplied from the toner container 12 via the toner supply unit 13. The first supply roller 22 and the second supply roller 23 each have an elastic layer made of conductive urethane rubber foam or the like formed on their circumferential side surfaces. The developing roller 24 has an elastic layer having elasticity or a surface layer having conductivity or the like formed on its circumferential side surface. The developing blade 25 is made of, for example, a stainless steel plate of a predetermined thickness, and a part of it is brought into contact with the circumferential side surface of the developing roller 24 in a state where it is slightly elastically deformed.

[0027] The photosensitive drum 26 as an image carrier has a thin film-like charge generation layer and a charge transport layer sequentially formed on its circumferential side surface and is capable of being charged. The charging roller 27 has a conductive elastic body coated on its circumferential side surface, and this circumferential side surface is brought into contact with the circumferential side surface of the photosensitive drum 26. The cleaning blade 28 is made of, for example, a thin plate-shaped resin, and a part of it is brought into contact with the circumferential side surface of the photosensitive drum 26 in a state where it is slightly elastically deformed.

[0028] The LED head 14 as an exposure unit is located above the photosensitive drum 26 in the image forming main body 11. The LED head 14 has a plurality of light emitting element chips arranged linearly along the left-right direction, and causes each light emitting element to emit light in a light emission pattern based on the image data signal supplied from the control unit 3 (Fig. 1).

[0029] The image forming main body 11 is driven by a driving force supplied from a motor (not shown), and rotates the first supply roller 22, the second supply roller 23, the developing roller 24, and the charging roller 27 in the direction of arrow R1 (clockwise in the figure), and rotates the photosensitive drum 26 in the direction of arrow R2 (counterclockwise in the figure). Further, based on the control of the control unit 3, the image forming main body 11 applies a predetermined bias voltage to the first supply roller 22, the second supply roller 23, the developing roller 24, the developing blade 25, and the charging roller 27, respectively, to charge them.

[0030] Due to charging, the first supply roller 22 and the second supply roller 23 attach the toner T in the toner storage space 21 to the circumferential surface, and rotate to attach this toner T to the circumferential surface of the developing roller 24. The developing roller 24 has excess toner T removed from its circumferential surface by the developing blade 25, and the circumferential surface is brought into contact with the circumferential surface of the photosensitive drum 26 in a state where the toner T adheres in a thin film state.

[0031] On the other hand, the charging roller 27 contacts the photosensitive drum 26 in a charged state to uniformly charge the circumferential surface of the photosensitive drum 26. The LED head 14 performs an exposure process of emitting light at predetermined time intervals in a light emission pattern based on the image data signal supplied from the control unit 3 (FIG. 1), thereby sequentially exposing the photosensitive drum 26. As a result, an electrostatic latent image is sequentially formed on the circumferential surface of the photosensitive drum 26 near its upper end.

[0032] Subsequently, the photosensitive drum 26 rotates in the direction of arrow R2, and the portion where the electrostatic latent image is formed is brought into contact with the developing roller 24. As a result, toner T adheres to the circumferential surface of the photosensitive drum 26 based on the electrostatic latent image, and a toner image P based on the image data is developed. The photosensitive drum 26 further rotates in the direction of arrow R2 to reach the toner image P near the lower end of the photosensitive drum 26.

[0033] For the sake of explanation, hereinafter, the toner image P formed by the silver toner TSL having a brilliance will be also referred to as a silver toner image PSL, a brilliant toner image, or a brilliant image, and the toner image P formed by the transparent toner TCL which is a transparent color will be also referred to as a transparent toner image PCL, a transparent color toner image, or a transparent image. Further, hereinafter, the toner image P formed by the normal toner TNL which is a normal color (i.e., a colored toner) will be also referred to as a normal toner image PNL, a normal color image, or a colored image.

[0034] Below each image forming unit 10 in the housing 2 (FIG. 1), an intermediate transfer unit 30 is disposed. The intermediate transfer unit 30 is provided with a driving roller 31, a driven roller 32, a backup roller 33, an intermediate transfer belt 34, five primary transfer rollers 35, a secondary transfer roller 36, and a reverse bending roller 37. Among these, the driving roller 31, the driven roller 32, the backup roller 33, each primary transfer roller 35, the secondary transfer roller 36, and the reverse bending roller 37 are each formed in a columnar shape with the central axis along the left-right direction and are rotatably supported by the housing 2.

[0035] The driving roller 31 is disposed at the rear lower side of the image forming unit 10SL and rotates in the direction of arrow R1 when a driving force is supplied from a belt motor (not shown). The driven roller 32 is disposed at the front lower side of the image forming unit 10K. The upper ends of the driving roller 31 and the driven roller 32 are each located at the same level as or slightly below the lower end of the photosensitive drum 26 (FIG. 2) in each image forming unit 10. The backup roller 33 is disposed at the front lower side of the driving roller 31 and at the rear lower side of the driven roller 32.

[0036] The intermediate transfer belt 34 is configured as an endless belt by a high-resistance plastic film, and is stretched around the driving roller 31, the driven roller 32, and the backup roller 33. Further, in the intermediate transfer unit 30, below the portion of the intermediate transfer belt 34 stretched between the driving roller 31 and the driven roller 32, that is, at a position directly below each of the five image forming units 10, five primary transfer rollers 35 are respectively arranged at positions facing the respective photosensitive drums 26 with the intermediate transfer belt 34 interposed therebetween. This primary transfer roller 35 is adapted such that a predetermined bias voltage is applied based on the control of the control unit 3.

[0037] The secondary transfer roller 36 is located directly below the backup roller 33 and is biased toward the backup roller 33. That is, the intermediate transfer unit 30 sandwiches the intermediate transfer belt 34 between the secondary transfer roller 36 and the backup roller 33. Also, the secondary transfer roller 36 is adapted such that a predetermined bias voltage is applied. Hereinafter, the secondary transfer roller 36 and the backup roller 33 together are referred to as the secondary transfer unit 39.

[0038] The reverse bending roller 37 is located at a position that is downward and forward of the driving roller 31 and upward and rearward of the backup roller 33, and biases the intermediate transfer belt 34 in the forward and upward direction. Thereby, the intermediate transfer belt 34 is in a state where tension acts between the respective rollers without generating slack. Also, a reverse bending backup roller 38 is provided at a position sandwiching the intermediate transfer belt 34 on the upper front side of the reverse bending roller 37.

[0039] The intermediate transfer unit 30 rotates the drive roller 31 in the direction of arrow R1 by the driving force supplied from a belt motor (not shown), thereby causing the intermediate transfer belt 34 to travel in the direction along arrow E1. Also, each primary transfer roller 35 rotates in the direction of arrow R1 while a predetermined bias voltage is applied thereto. Thereby, each image forming unit 10 transfers the toner image P that has reached the vicinity of the lower end on the circumferential side surface of the photosensitive drum 26 (FIG. 2) to the intermediate transfer belt 34, and can sequentially stack the toner images P of respective colors. At this time, on the surface of the intermediate transfer belt 34, the toner images P of respective colors are sequentially stacked from the upstream silver color (SL). The intermediate transfer unit 30 causes the toner image P transferred from each image forming unit 10 to reach the vicinity of the backup roller 33 by running the intermediate transfer belt 34.

[0040] Incidentally, inside the housing 2 (FIG. 1), a conveyance path W, which is a path for conveying the medium M, is formed. This conveyance path W extends from near the lower end inside the housing 2 toward the front upper direction, makes about a half rotation, and then proceeds rearward below the intermediate transfer unit 30. Subsequently, the conveyance path W goes upward, proceeds upward on the rear sides of the intermediate transfer unit 30 and the image forming unit 10SL, and then goes forward. That is, the conveyance path W is formed so as to depict a capital letter "S" in FIG. 1. Inside the housing 2, various components are arranged along this conveyance path W.

[0041] Near the lower end inside the housing 2 (FIG. 1), a first paper feeding unit 40 is arranged. The first paper feeding unit 40 is provided with a paper cassette 41, a pickup roller 42, a feed roller 43, a retard roller 44, a conveyance guide 45, and conveyance roller pairs 46, 47, and 48, etc. Incidentally, the pickup roller 42, the feed roller 43, the retard roller 44, and the conveyance roller pairs 46, 47, and 48 are all formed in a columnar shape with the central axis along the left-right direction.

[0042] The paper cassette 41 is configured in a hollow rectangular parallelepiped shape and is detachable from the housing 2. This paper cassette 41 stores the media M with the paper surface facing in the vertical direction, that is, in a stacked state. Also, in this embodiment, as the media M, black high-quality paper with an extremely low visible light transmittance is used (details will be described later).

[0043] The pickup roller 42 is in contact with the vicinity of the front end at the uppermost surface of the media M stored in the paper cassette 41. The feed roller 43 is disposed slightly forward and separated from the pickup roller 42. The retard roller 44 is located below the feed roller 43 and forms a gap corresponding to the thickness of one sheet of the media M between it and the feed roller 43.

[0044] When a driving force is supplied from a paper feed motor (not shown), the first paper feed unit 40 appropriately rotates or stops the pickup roller 42, the feed roller 43, and the retard roller 44. Thereby, the pickup roller 42 feeds forward one or more sheets at the uppermost surface among the media M stored in the paper cassette 41. Also, the feed roller 43 and the retard roller 44 further feed forward the uppermost sheet of the media M while blocking the second and subsequent sheets. Thus, the first paper feed unit 40 feeds the media M forward while separating it sheet by sheet.

[0045] The conveyance guide 45 is disposed at the front lower portion in the conveyance path W and advances the media M in the front upper direction and then in the rear upper direction along this conveyance path W. The conveyance roller pairs 46 and 47 are respectively disposed near the center and near the upper end of the conveyance guide 45 and rotate in a predetermined direction when a driving force is supplied from a paper feed motor (not shown). Thereby, the conveyance roller pairs 46 and 47 advance the media M along the conveyance path W.

[0046] Also, a second paper feeding unit 50 is provided in front of the pair of conveying rollers 47 in the housing 2. The second paper feeding unit 50 is provided with a paper tray 51, a pickup roller 52, a feed roller 53, a retard roller 54, and the like. The paper tray 51 is formed in a thin plate shape in the vertical direction, and the medium M2 is placed on the upper side thereof. Incidentally, on the paper tray 51, a medium M2 having a different size and paper quality from the medium M stored in the paper cassette 41, for example, is placed.

[0047] The pickup roller 52, the feed roller 53, and the retard roller 54 are configured in the same manner as the pickup roller 42, the feed roller 43, and the retard roller 44 of the first paper feeding unit 40, respectively. When a driving force is supplied from a paper feeding motor (not shown), the second paper feeding unit 50 appropriately rotates or stops the pickup roller 52, the feed roller 53, and the retard roller 54, thereby feeding out the lowermost one sheet of the medium M2 on the paper tray 51 backward while blocking the second and subsequent sheets. Thus, the second paper feeding unit 50 feeds out the medium M2 one by one while separating it. At this time, the fed-out medium M2 is conveyed along the conveying path W by the pair of conveying rollers 57 in the same manner as the medium M. For the sake of explanation, hereinafter, the medium M2 will be simply referred to as the medium M without distinguishing it from the medium M.

[0048] Incidentally, the rotation of the pair of conveying rollers 47 is appropriately suppressed, and by applying a frictional force to the medium M, a so-called skew in which the side of the medium M is inclined with respect to the traveling direction is corrected, and after the leading and trailing edges are aligned along the left and right, it is sent out backward. The pair of conveying rollers 48 is located at a position a predetermined distance behind the pair of conveying rollers 47, and by rotating in the same manner as the pair of conveying rollers 46 and the like, a driving force is supplied to the medium M conveyed along the conveying path W, and the medium M is further advanced backward along the conveying path W.

[0049] On the rear side of the pair of conveying rollers 48, the secondary transfer unit 39 of the intermediate transfer unit 30 described above, that is, the backup roller 33 and the secondary transfer roller 36 are arranged. In this secondary transfer unit 39, the toner image P in the state transferred to the intermediate transfer belt 34 formed in the image forming unit 10 is close as the intermediate transfer belt 34 travels, and a predetermined bias voltage is applied to the secondary transfer roller 36. Therefore, the secondary transfer unit 39 transfers the toner image P from the intermediate transfer belt 34 to the medium M conveyed along the conveyance path W, and further advances it rearward.

[0050] On the rear side of the secondary transfer unit 39, a fixing unit 60 is arranged. The fixing unit 60 is composed of a heating unit 61 and a pressing unit 62 arranged to face each other with the conveyance path W interposed therebetween. The heating unit 61 has a heater that generates heat, a plurality of rollers, etc. arranged inside a heating belt that is a hollow endless belt. The pressing unit 62 is formed as a columnar pressing roller with its central axis along the left-right direction, and presses the upper surface against the lower surface of the heating unit 61 to form a nip portion.

[0051] Based on the control of the control unit 3, this fixing unit 60 heats the heater of the heating unit 61 to a predetermined temperature, appropriately rotates the roller, and runs the heating belt to rotate in the direction of arrow R1, and also rotates the pressing unit 62 in the direction of arrow R2. Moreover, when the fixing unit 60 receives the medium M onto which the toner image P has been transferred by the secondary transfer unit 39, it sandwiches this (that is, nips it) by the heating unit 61 and the pressing unit 62, applies heat and pressure, fixes the toner image P to the medium M, and sends it out rearward.

[0052] On the rear side of the fixing unit 60, a pair of conveying rollers 64 is arranged, and a switching unit 65 is arranged on its rear side. The switching unit 65 switches the traveling direction of the medium M upward or downward according to the control of the control unit 3. On the upper side of the switching unit 65, a paper discharge unit 70 is provided. The paper discharge unit 70 is composed of a conveyance guide 71 that guides the medium M upward along the conveyance path W, a pair of conveying rollers 72, 73, 74, and 75 that face each other with the conveyance path W interposed therebetween, and a discharge port 76.

[0053] Also, a re-conveying unit 66 is disposed below the switching unit 65, the fixing unit 60, the secondary transfer unit 39, and the like. The re-conveying unit 66 includes a conveyance guide, a pair of conveyance rollers (not shown) that form a re-conveying path Z, and the like. The re-conveying path Z extends downward from below the switching unit 65, then proceeds forward, and finally merges into the conveyance path W on the downstream side of the pair of conveyance rollers 57.

[0054] When discharging the medium M, the control unit 3 switches the traveling direction of the medium M to the upper paper discharge unit 70 side by the switching unit 65. The paper discharge unit 70 conveys the medium M received from the switching unit 65 upward and discharges it from the discharge port 76 to the paper discharge tray 2T. When the control unit 3 turns the medium M over and returns it, the control unit 3 switches the traveling direction of the medium M to the lower re-conveying unit 66 side by the switching unit 65. The re-conveying unit 66 conveys the medium M received from the switching unit 65 along the re-conveying path Z, and finally reaches the downstream side of the pair of conveyance rollers 57 and conveys the medium M again along the conveyance path W. As a result, in the image forming apparatus 1, the medium M can be returned to the conveyance path W with the front and back sides of the paper surface of the medium M reversed, and so-called double-sided printing can be performed.

[0055] In this way, in the image forming apparatus 1, a toner image P using toner T is formed in the image forming unit 10 and transferred to the intermediate transfer belt 34, and the toner image P is transferred from the intermediate transfer belt 34 to the medium M in the secondary transfer unit 39, and further fixed in the fixing unit 60, whereby an image can be printed on the medium M, that is, an image can be formed.

[0056] For example, when the image forming apparatus 1 transfers at least one toner image P among a silver toner image PSL, a transparent toner image PCL, and a normal toner image PNL to the intermediate transfer belt 34 in the image forming unit 10, the toner image P is transferred to the medium M in the secondary transfer unit 39. As a result, the medium M has a state in which any one of the silver toner image PSL, the transparent toner image PCL, and the normal toner image PNL is printed on its surface, or a state in which these are printed in an appropriately overlapped manner.

[0057] Further, after the image forming apparatus 1 sets the medium M in the first paper feeding unit 40, transfers and fixes the toner image P on its surface, and discharges it, the medium M can be set in the first paper feeding unit 40 again, and another toner image P can be transferred and fixed on its surface in an overlapping manner. For example, the image forming apparatus 1 can first transfer and fix the silver toner image PSL on the surface of the medium M, then transfer and fix the transparent toner image PCL on top of this, and further transfer and fix the normal toner image PNL on top of this. In this case, the medium M will be in a state where the silver toner image PSL, the transparent toner image PCL, and the normal toner image PNL are sequentially printed in an overlapping manner on its surface.

[0058] Furthermore, for example, after the image forming apparatus 1 transfers and fixes the silver toner image PSL on the surface of the medium M, it can return the medium M to the downstream side of the pair of conveying rollers 57 without inverting the front and back by the re-conveying unit 66, and transfer and fix the transparent toner image PCL on the same surface of the medium M. At this time, the image forming apparatus 1 can further continue to return the medium M to the downstream side of the pair of conveying rollers 57 without inverting the front and back by the re-conveying unit 66, and transfer and fix the normal toner image PNL on the same surface of the medium M.

[0059] In these cases, the image forming apparatus 1 can also adjust the temperature each time when fixing the toner image P on the medium M by the fixing unit 60. For example, the image forming apparatus 1 can set the fixing temperature of the first fixing process for fixing the silver toner image PSL on the surface of the medium M to a normal temperature (for example, 150 "°C"), and set the fixing temperature of the second fixing process for fixing the transparent toner image PCL on the surface of the medium M to a higher temperature (for example, 190 [°C]) than this.

[0060] Incidentally, in the image forming apparatus 1, by increasing the absolute value of the bias voltage applied to each part under the control of the control unit 3, the adhesion amount of the toner T in the toner image transferred to the medium M can be increased, and by decreasing the absolute value of the bias voltage, the adhesion amount on the medium can also be decreased.

[0061] Next, the circuit configuration of the image forming apparatus 1 will be described with reference to the block diagram of FIG. 3. The control unit 3 of the image forming apparatus 1 is mainly configured around the print control unit 80, and a storage unit 81, an interface unit 82, a display control unit 83, a process control unit 84, a developing voltage control unit 85, a supply voltage control unit 86, an exposure control unit 87, a transfer voltage control unit 88, and a motor control unit 89 are connected to the print control unit 80, respectively.

[0062] The print control unit 80 has a CPU (Central Processing Unit) 91, a ROM (Read Only Memory) 92, a RAM (Random Access Memory) 93, etc. inside. While using the RAM 93 as a work area, various programs read from the ROM 92, the storage unit 81, etc. are executed by the CPU 91 to perform various processes.

[0063] The storage unit 81 is a non-volatile storage medium such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive), and stores various programs and various information. The storage unit 81 is provided with a normal color data conversion table 95, a metallic color data conversion table 96, and a transparent color data conversion table 97. Among these, the normal color data conversion table 95 stores information for forming, as a print pattern for each color, the portion represented by normal colors (black, cyan, and magenta) in the print data acquired from the host device 100. The metallic color data conversion table 96 stores information for forming a print pattern corresponding to the portion represented by the metallic color (silver) in the print data acquired from the host device 100. Further, the transparent color data conversion table 97 stores information for forming a print pattern corresponding to the portion represented by the transparent color in the print data acquired from the host device 100.

[0064] The interface unit 82 functions as an interface for a wired LAN (Local Area Network) compliant with standards such as IEEE (Institute of Electrical and Electronics Engineers) 802.3u / ab / an / ae, or a wireless LAN compliant with standards such as IEEE 802.11a / b / g / n / ac / ax. This interface unit 82 can transmit and receive various information between the host device 100, a predetermined server device (not shown), and the like.

[0065] Based on instructions from the printing control unit 80, the display control unit 83 constructs display screen data representing various display screens on which characters, graphics, etc. are appropriately arranged, and causes the display unit 4 to display the display screen by sending the display screen data to the display unit 4.

[0066] Based on instructions from the printing control unit 80, the process control unit 84 controls the voltage and the like of each part in each color image forming unit 10. Based on instructions from the printing control unit 80, the developing voltage control unit 85 controls the developing voltage applied to the developing roller 24 and the developing blade 25 (Fig. 2). Based on instructions from the printing control unit 80, the supply voltage control unit 86 controls the supply voltage applied to the first supply roller 22 and the second supply roller 23 (Fig. 2).

[0067] Based on instructions from the printing control unit 80, the exposure control unit 87 controls the lighting and extinguishing of each light-emitting element chip provided in the LED head 14. Based on instructions from the printing control unit 80, the transfer voltage control unit 88 controls the transfer voltage applied to the primary transfer roller 35, the secondary transfer roller 36 (Fig. 2), and the like. Based on instructions from the printing control unit 80, the motor control unit 89 controls the rotation of the photosensitive drum 26 (Fig. 2), each roller, and the like.

[0068] The host device 100 is an information processing device such as a personal computer, etc., and executes various application programs such as document creation, spreadsheet calculation, or image editing, etc. based on user operations. Further, a printer driver for printing documents, images, etc. in the image forming apparatus 1 is pre-installed in the host device 100. When the host device 100 receives a print instruction for document data, image data, etc. from the user in the application program, it executes the printer driver to generate print data based on the document data, the image data, etc., and transmits it to the image forming apparatus 1.

[0069] [2. Toner Manufacturing] Next, the toner T (also called a developer) accommodated in the toner container 12 of the image forming unit 10 (Fig. 2) will be described. For the normal colors black (K), cyan (C), and magenta (M), commercially available toners T of each color (black, cyan, and magenta) for the C941dn manufactured by Okidata Corporation were used respectively.

[0070] The shiny silver (SL) toner T (silver toner TSL) and the transparent color (CL) toner T (transparent toner TCL) were manufactured by the following methods respectively.

[0071] First, the manufacture of the silver toner TSL will be described. In the present embodiment, first, an aqueous medium in which an inorganic dispersant is dispersed is generated. Specifically, 600 parts by weight of industrial trisodium phosphate dodecahydrate is mixed with 18400 parts by weight of pure water, dissolved at a liquid temperature of 60 [°C], and then dilute nitric acid for pH (hydrogen ion index) adjustment is added. An aqueous calcium chloride solution in which 300 parts by weight of industrial anhydrous calcium chloride is dissolved in 2600 parts by weight of pure water is added to this aqueous solution, and while maintaining the liquid temperature at 60 [°C], it is rapidly stirred for 34 minutes at a rotational speed of 3566 [rpm] by a line mill (Primix Corporation). Thereby, an aqueous phase which is an aqueous medium in which a suspension stabilizer (inorganic dispersant) is dispersed is adjusted.

[0072] In this embodiment, a material-dispersed oily medium is produced. Specifically, 470 parts by weight of a bright pigment (volume median diameter 5.4 [μm]) containing aluminum powder and 23 parts by weight of a charge control agent (BONTRON E-84: manufactured by Orient Chemical Industries Co., Ltd.) are respectively mixed with 7000 parts by weight of ethyl acetate, which is an organic solvent, to prepare a pigment dispersion liquid.

[0073] In this embodiment, a bright pigment with a volume average particle diameter (also referred to as volume median diameter) of 5.4 [μm] is used, but it is not limited to this. Specifically, the volume average particle diameter of the bright pigment is preferably 5 [μm] or more and 20 [μm] or less, and more preferably within the range of 5.3 to 5.7 [μm].

[0074] Thereafter, in this embodiment, while maintaining the liquid temperature of the pigment dispersion liquid at 60 [°C], 175 parts by weight of an ester wax (WE-4: manufactured by NOF Corporation) and 1670 parts by weight of a polyester resin are added, and the mixture is stirred until no solid matter remains. Thereby, an oil phase, which is a pigment-dispersed oily medium, is prepared.

[0075] Next, in this embodiment, the oil phase is added to the aqueous phase whose liquid temperature has been lowered to 55 [°C], and the mixture is stirred at a rotation speed of 1000 [rpm] for 5 minutes to be suspended, thereby forming particles in the suspension. Subsequently, ethyl acetate is removed by vacuum distillation of the suspension to form a slurry containing toner. Further, nitric acid is added to this slurry to adjust the pH to 1.6 or less, and the mixture is stirred to dissolve tricalcium phosphate, which is a suspension stabilizer, and dehydration is performed to form toner. Subsequently, the dehydrated toner is redispersed in pure water and stirred, and then washed with water. Thereafter, in this embodiment, toner mother particles are produced by performing a dehydration step, a drying step, and a classification step.

[0076] In this embodiment, 1.5 [wt%] of fine silica (RY200: manufactured by Nippon Aerosil Co., Ltd.), 2.29 [wt%] of colloidal silica (X24-9163A: manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.37 [wt%] of melamine particles (EPOSTAR S: manufactured by Nippon Shokubai Co., Ltd.) are added to the toner mother particles thus produced and mixed. Thus, in this embodiment, a silver toner TSL having brilliance can be obtained. When the volume median diameter of the silver toner TSL thus prepared was measured, it was 15.01 [μm]. Note that the volume median diameter of the silver toner TSL is not limited to 15.01 [μm], and may be, for example, 10 to 20 [μm].

[0077] Next, the production of the transparent toner TCL will be described. In this embodiment, first, an aqueous medium in which an inorganic dispersant is dispersed is produced. Specifically, 650 parts by weight of industrial trisodium phosphate dodecahydrate is mixed with 19,540 parts by weight of pure water and dissolved at a liquid temperature of 60 [°C], and then dilute nitric acid for pH (hydrogen ion exponent) adjustment is added. An aqueous calcium chloride solution in which 320 parts by weight of industrial anhydrous calcium chloride is dissolved in 2,560 parts by weight of pure water is added to this aqueous solution, and while maintaining the liquid temperature at 60 [°C], high-speed stirring is performed for 34 minutes at a rotational speed of 3,566 [rpm] using a line mill (manufactured by Primix Corporation). Thereby, an aqueous phase, which is an aqueous medium in which a suspension stabilizer (inorganic dispersant) is dispersed, is prepared.

[0078] Also, in this embodiment, a material-dispersed oily medium is produced. Specifically, 3,120 parts by weight of ethyl acetate, which is an organic solvent, is heated and stirred at a liquid temperature of 50 [°C], and 17 parts by weight of paraffin wax (melting point: 62 [°C]), 1.4 parts by weight of a fluorescent brightening agent, and 640 parts by weight of a polyester resin are sequentially added and stirred until no solid matter remains. Thereby, an oil phase is prepared.

[0079] Next, in the present embodiment, after reducing the liquid temperature of the aqueous phase to 55 [°C], the oil phase is added, and the mixture is stirred at a rotational speed of 1000 [rpm] for 5 minutes to suspend it, forming particles in the suspension. Subsequently, ethyl acetate is removed by vacuum distillation of the suspension to form a slurry containing toner. Further, nitric acid is added to this slurry to adjust the pH to 1.5 or less, and the slurry is stirred to dissolve tricalcium phosphate, which is a suspension stabilizer, and dehydration is performed to form toner. Subsequently, the dehydrated toner is redispersed in pure water and stirred, followed by washing with water. Thereafter, in the present embodiment, toner is produced by performing a dehydration step, a drying step, and a classification step.

[0080] In the present embodiment, with respect to 100 parts by weight of the toner thus produced, 1.0 part by weight of hydrophobic silica RX50 (manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter 40 [nm]) and 0.8 part by weight of hydrophobic silica RX200 (manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter 12 [nm]) are added as an external addition step and mixed. Thus, in the present embodiment, a transparent toner TCL having permeability can be obtained.

[0081] [3. Visual effect by medium] Next, the medium M on which an image is printed by the image forming apparatus 1 will be described. As shown in the schematic diagrams of FIGS. 4(A) and 4(B), the image forming apparatus 1 can print by sequentially superimposing a lower silver toner image PSL, a middle transparent toner image PCL, and an upper normal toner image PNL on the surface of the medium M.

[0082] Also, the image forming apparatus 1 forms a plurality of regions such as a background region AB and a decorative region AC with respect to the silver toner image PSL that forms the lower layer, as shown in the schematic enlarged view of FIG. 4(C), under the control of the control unit 3. In this silver toner image PSL, the amount of silver toner TSL adhered per unit area differs between the background region AB and the decorative region AC.

[0083] For the sake of explanation, hereinafter, the background area AB is also referred to as the first area, and the decorated area AC is also referred to as the second area. Further, hereinafter, a medium M on which three layers of a silver toner image PSL, a transparent toner image PCL, and a normal toner image PNL are sequentially printed in an overlapping manner on the surface of the medium M, and the background area AB and the decorated area AC are formed on the lower silver toner image PSL, is referred to as a decorated medium MC.

[0084] Incidentally, the formation amount per unit area of the toner T (silver toner TSL, transparent toner TCL, or normal toner TNL) on the medium M can be represented by the image density N [%]. This image density N corresponds to the ratio of the area of the printed portion (the portion where the image is formed) to the total area in the printable range of a predetermined area (for example, an area corresponding to one circumference of the photoreceptor drum 26 or an area corresponding to one sheet of the medium M). Also, this image density N is set to 100 [%] when printing an image with an area ratio of 100 [%], similar to so-called solid printing. For example, when printing an image on an area corresponding to 1 [%] of the printable range of the medium M, the image density N becomes 1 [%].

[0085] Incidentally, when the image density N is less than 100 [%], for example, in an image with an image density N of 100 [%], it can be achieved by thinning out the toner in a thin line shape along a direction orthogonal to the predetermined direction at a predetermined thinning interval in the predetermined direction. In this case, the image density N can be adjusted by adjusting the thinning interval and the width (number of dots) of the thin line.

[0086] Alternatively, when the image density N is less than 100 [%], it can also be achieved, for example, by thinning out the toner in a dot pattern in an image with an image density N of 100 [%]. In this case, the image density N can be adjusted by adjusting the number and size of the dots per unit area.

[0087] Here, when the photoreceptor drum 26 rotates by a predetermined number of rotations Cd, the number of dots where toner is actually used in the printing process, that is, the number of exposed dots, is defined as the number of used dots Cm. Also, the number of dots per rotation of the photoreceptor drum 26, that is, regardless of the presence or absence of exposure, is the maximum number of dots that can potentially be printed when the photoreceptor drum 26 makes one rotation, and the number of dots in the case of printing a so-called solid image (also called a solid picture) is defined as the total number of dots C0.

[0088] Then, when the photoreceptor drum 26 rotates Cd times, the maximum number of dots that can potentially be printed is (Cd × C0) dots. Using this, the image density N can be expressed as in the following equation (1).

[0089] N = [Cm / (Cd × C0)] / 100 [%] ……(1)

[0090] Also, the formation amount per unit area of the toner T (normal toner TNL, transparent toner TCL, or silver toner TSL) on the medium M can be represented by the printing duty D in addition to the above-described image density N. This printing duty D is the ratio of the area where toner is used in the printed image based on the print data when the area of printing a solid image in the area where an image can be formed on the medium M is set to 100 [%], and is also the ratio of the area where the toner adheres to the medium M and a toner image is formed. Therefore, hereinafter, the printing duty D will also be referred to as the formation ratio. Note that the solid image here is a toner image on the medium M formed by exposing the entire area within the printable range of the photoreceptor drum 26, and is an image that uses toner T at all dots.

[0091] In other words, the printing duty D is the ratio of the number of dots used in the actual toner image P based on the print data to the total number of dots constituting the area where an image can be formed on the medium M, and is sometimes called the printing rate.

[0092] For example, when the control unit 3 prints an image based on print data on a certain medium M, it sets the dot count of the image data based on the print data as C1, and sets the dot count when the entire surface of the medium M is exposed as C0, and calculates the print duty D by the following formula (2). Note that this formula (2) is just an example, and the control unit 3 can also calculate the print duty D by other calculation formulas.

[0093] D=(C1 / C0)×100[%] ……(2)

[0094] That is, in the silver toner image PSL, the print duty D of the background area AB (hereinafter referred to as the background print duty DB) is different from the print duty D of the decoration area AC (hereinafter referred to as the decoration print duty DC). As an example, in the silver toner image PSL of the decoration medium MC, the background print duty DB can be set to 100[%], and the decoration print duty DC can be set to 75[%]. For the convenience of explanation, hereinafter, the background print duty DB is also referred to as the first formation ratio, and the decoration print duty DC is also referred to as the second formation ratio.

[0095] As shown in FIG. 5(A), when the user views the decoration medium MC from the surface side at a predetermined angle, the upper normal toner image PNL can be visually recognized, and the lower decoration area AC and background area AB cannot be perceived.

[0096] On the other hand, as shown in FIG. 5(B), when the user views the decoration medium MC from the surface side at an angle (posture) different from that in FIG. 5(A), the upper normal toner image PNL is overlapped, and the decoration area AC and the background area AB in the lower silver toner image PSL can be made to look different from each other. That is, in this case, the decoration medium MC can make the user visually recognize an image in which the decoration area AC appears to float above the background area AB.

[0097] In this way, by changing the angle of the decorative medium MC with respect to the user's perspective, the light source, etc., the decorative medium MC can switch between a state in which the decorative area AC is hidden (Fig. 5(A)) and a state in which the decorative area AC is shown (Fig. 5(B)). In other words, the decorative medium MC has a visual effect of making the decorative area AC appear and disappear for the user by changing the position and posture of the decorative medium MC in various ways.

[0098] For example, as a visual effect on the user, the decorative medium MC first allows only the upper normal toner image PNL to be visually recognized, and then, when the posture of the decorative medium MC changes, it can give an impression that the decorative area AC emerges so as to overlap with the normal toner image PNL.

[0099] Next, the principle by which such a visual effect occurs in the decorative medium MC will be described. If the surface of the decorative medium MC is shown to the user in a bright place, the upper normal toner image PNL reflects light, and the user can clearly visually recognize the normal toner image PNL.

[0100] Also, if the medium M shows the user a state in which only the silver toner image PSL is printed, the silver toner image PSL can reflect light well by the luminous pigment (such as aluminum flakes) contained in the silver toner image PSL, and the user can clearly visually recognize the silver toner image PSL. Furthermore, as described above, the silver toner image PSL has different printing duties D in the background area AB and the decorative area AC. Therefore, the medium M makes the degree of light reflection differ between the background area AB and the decorative area AC, and can clearly recognize the boundary between the two and the shape of the decorative area AC, etc.

[0101] Next, as shown in Fig. 6(A), assume a case where both the light source LS and the user's viewpoint VP are located on the surface side of the decorative medium MC. In this case, since the light from the back side of the decorative medium MC is blocked by the medium M which is high-quality black paper, no light passes from the back side to the surface side of the decorative medium MC.

[0102] At this time, the decorative medium MC can reflect the light from the light source LS well by the upper normal toner image PNL, and can deliver light with sufficient intensity from the normal toner image PNL to the user's eyes. Further, the decorative medium MC allows a part of the light from the light source LS to pass through the upper normal toner image PNL and the middle transparent toner image PCL and reach the lower silver toner image PSL. The decorative medium MC reflects this light with a relatively high reflectance by the silver toner image PSL, and a part of it passes through the transparent toner image PCL and the normal toner image PNL and travels toward the user's viewpoint VP.

[0103] Focusing on the intensity of the light reaching the user's viewpoint VP here, the intensity of the light reflected by the normal toner image PNL is sufficiently larger than the intensity of the light reflected by the silver toner image PSL. For this reason, when the user looks at the front side of the decorative medium MC, as shown in Fig. 5(A), the user can clearly recognize the normal toner image PNL, while hardly being able to recognize the silver toner image PSL. In other words, in the state shown in Fig. 6(A), the decorative medium MC can hide the image represented by the decoration area AC of the silver toner image PSL from the user.

[0104] Next, as shown in Fig. 6(B), assume a case where the user's viewpoint VP is located on the front side of the decorative medium MC while the light source LS is located on the back side of the decorative medium MC. Also in this case, since the light from the back side of the decorative medium MC is blocked by the medium M which is a black high-quality paper, no light passes from the back side to the front side of the decorative medium MC.

[0105] At this time, due to the positional relationship with the light source LS, the decorative medium MC cannot sufficiently reflect the light from the light source LS by the upper normal toner image PNL, and relatively weak light from the normal toner image PNL reaches the user's eyes. On the other hand, for a part of the light from the light source LS, the decorative medium MC passes through the upper normal toner image PNL and the middle transparent toner image PCL and reaches the lower silver toner image PSL. The decorative medium MC reflects this light with a relatively high reflectivity by the silver toner image PSL, and a part of it passes through the transparent toner image PCL and the normal toner image PNL and travels toward the user's viewing point VP.

[0106] Focusing on the intensity of the light reaching the user's viewing point VP here, the intensity of the light reflected by the normal toner image PNL is not so large compared to the intensity of the light reflected by the silver toner image PSL. Therefore, when the user looks at the front side of the decorative medium MC, as shown in Fig. 5(B), the user can visually recognize the normal toner image PNL to a certain extent, and at the same time, the silver toner image PSL can also be visually recognized. In other words, in the state shown in Fig. 6(B), the decorative medium MC can show the user an image formed as the decorative area AC of the silver toner image PSL.

[0107] [4. Conditions for Obtaining Visual Effects] Next, in order to find the conditions for obtaining a good visual effect for the decorative medium MC obtained by performing decorative printing on the medium M by the image forming apparatus 1, a plurality of types of evaluation media ME with different printing duties of the silver toner TSL in the silver toner image PSL were created, and evaluation tests were conducted for each of them.

[0108] [4-1. Creation of Evaluation Media] In this evaluation test, as the medium M, "Kishu Premium Paper N Medium Thickness Black" (manufactured by Hokuriku Corporation), which is a black premium paper, was used. This medium M has a size of JIS / ISO A4 size (297×210 [mm]) and a thickness of about 0.09 [mm]. This medium M has an extremely low transmittance of visible light and a sufficiently low reflectivity.

[0109] In this evaluation test, as pre-adjustment processing, various biases and the like were adjusted for silver (SL) and cyan (C) printed by the image forming apparatus 1.

[0110] Regarding silver (SL) among these, using the visual reflectance difference ΔY, adjustment was performed for the silver toner TSL in the image forming apparatus 1. This visual reflectance difference ΔY is calculated by subtracting the visual reflectance Y2 of the medium M before printing from the visual reflectance Y1 on the image after printing. For the measurement of the visual reflectance difference ΔY, a spectrocolorimeter CM-2600d (manufactured by Konica Minolta Japan, Inc.) was used. As the conditions at the time of measurement, the light source was the auxiliary illuminant C for colorimetry (6774 [K]), and SCE (specular component excluded) was adopted for the specularly reflected light.

[0111] In this evaluation test, in the background area AB of the silver toner image PSL printed on the surface of the medium M by the image forming apparatus 1, various bias voltages (such as development voltage) related to the silver (SL) image forming unit 10SL were appropriately adjusted so that the visual reflectance difference ΔY would be a value of 26.

[0112] Regarding cyan (C), only an image with a printing duty of 100 [%] on the surface of the medium M, so-called a solid image (hereinafter referred to as a cyan image), was printed, and the optical density O.D. was measured using a spectrocolorimeter (X-Rite eXact: X-Rite, Inc.). Moreover, in this evaluation test, under the control of the control unit 3, various bias voltages (such as development voltage) related to the cyan (C) image forming unit 10C in the image forming apparatus 1 were adjusted so that this optical density O.D. would be a value of 1.4.

[0113] In this evaluation test, after performing these pre-adjustments, the decoration medium MC was created by the image forming apparatus 1. Specifically, in this evaluation test, first, a silver toner image PSL using silver toner TSL was printed on the surface of the medium M. At this time, in this evaluation test, the printing duty D of the background area AB (i.e., the background printing duty DB) was set to 100 [%], and the printing duty D of the decoration area AC (i.e., the decoration printing duty DC) was set to a value less than 100 [%].

[0114] Next, in this evaluation test, by the image forming apparatus 1, a transparent toner image PCL was printed on the surface of the medium M on which the silver toner image PSL was printed, overlapping the silver toner image PSL. As this transparent toner image PCL, an image with a printing duty of 100 [%] for the transparent toner TCL, that is, a so-called solid image, was used.

[0115] Furthermore, in this evaluation test, by the image forming apparatus 1, an image of a cyan image as a normal toner image PNL, that is, an image with a printing duty of 100 [%] for cyan (C) toner, was printed on the surface of the medium M on which the silver toner image PSL and the transparent toner image PCL were printed.

[0116] Moreover, in this evaluation test, as the silver toner image PSL, evaluation images PE (PE1, PE2,..., PE8) with different decoration printing duties DC (i.e., the printing duty D of the decoration area AC) at intervals of 6.25 [%] from 93.75 [%] to 6.25 [%] were formed and printed on the surface of the medium M. Hereinafter, the evaluation image PE printed on the lower layer on the surface of the medium M in this way, and further overprinted with the middle layer transparent toner image PCL and the upper layer normal toner image PNL, is also referred to as an evaluation medium ME.

[0117] Specifically, the decoration printing duty DC of each evaluation image PE was set to 93.75 [%], 87.50 [%], 81.25 [%], 75.00 [%], 68.75 [%], 62.50 [%], 56.25 [%] and 50.00 [%] as shown in the table TBL1 of FIG. 7(A). Incidentally, in each evaluation image PE, a plurality of "OK" characters (FIGS. 4(C) and 5(B)) were formed by the decoration area AC.

[0118] Also, for each evaluation image PE, a duty difference, which is the difference value between the background printing duty DB and the decorative printing duty DC, was calculated and described in Table TBL1 in FIG. 7(A). This duty difference represents the difference in the adhesion amount per unit area with respect to the silver toner TSL, and as described above, the values differ by 6.25 [%].

[0119] Incidentally, in each evaluation image PE, since the background printing duty DB is 100 [%] in all cases, the value of the decorative printing duty DC represents the ratio of the decorative printing duty DC to the background printing duty DB. For example, in the evaluation image PE1, the value of the decorative printing duty DC is 93.75 [%], and the ratio of the decorative printing duty DC to the background printing duty DB is also 93.75 [%]. Also, for example, in the evaluation image PE3, the value of the decorative printing duty DC is 81.25 [%], and the ratio of the formation amount on the medium in the decorative area AC to the formation amount on the medium in the background area AB becomes 0.82 when rounded to the third decimal place.

[0120] [4-2. Visual Recognition Judgment of Evaluation Medium] Next, in this evaluation test, a visual recognition judgment of the image for each evaluation medium ME was performed. This visual recognition judgment determined whether the background area AB and the decorative area AC could be distinguished, that is, whether the character "OK" could be visually recognized, under each of two types of visual recognition conditions in which the angle of the line of sight with respect to the image was made different under a fixed light source. Hereinafter, this judgment will be referred to as the visual recognition judgment.

[0121] Among these, the two types of visual recognition conditions were the first visual recognition condition shown as a schematic diagram in FIG. 8(A) and the second visual recognition condition shown as a schematic diagram in FIG. 8(B). Among these, in the first visual recognition condition, the light source LS was arranged so that the incident angle with respect to the surface of the evaluation medium ME was 45 degrees, and the viewpoint VP of the user (the person who makes the judgment) was positioned in the direction that forms 90 degrees with respect to the surface, that is, so that the line of sight LVP from the viewpoint VP was perpendicular to the surface.

[0122] In the second visual recognition condition, while arranging the light source LS so that the incident angle with respect to the surface of the evaluation medium is 45 degrees in the same manner as in the first visual recognition condition, the viewpoint VP of the user (the person making the determination) is positioned on the same straight line as the incident direction from the light source LS. That is, it is positioned so that the line of sight LVP from the viewpoint VP is 45 degrees with respect to the surface.

[0123] In any of the visual recognition conditions, a fluorescent lamp was used as the light source LS, and by setting the distance from the light source LS to the evaluation medium ME to 200 [mm], the illuminance on the surface of the evaluation medium ME was set to about 800 [lx]. Also, in this visual recognition determination, the evaluation was carried out in a dark room to exclude the influence of other lighting and the like.

[0124] When such two types of visual recognition determinations were made, a determination result as shown in Table TBL2 in FIG. 7(B) was obtained. That is, in the first visual recognition condition, the background region AB and the decorative region AC could not be distinguished in the evaluation media ME1 to ME4, and the distinction between the two was possible in the evaluation media ME5 to ME8. On the other hand, in the second visual recognition condition, the distinction between the two was possible in all of the evaluation media ME1 to ME8. In Table TBL3, the fact that the background region AB and the decorative region AC could be distinguished is represented by the symbol "○", and the fact that the two could not be distinguished is represented by the symbol "×".

[0125] Here, the relationship between the results of the two types of visual recognition determinations and the visual effect in which the decorative region AC appears and disappears according to the angle of the medium M is organized.

[0126] In the evaluation media ME5 to ME8, in both the first visual recognition condition and the second visual recognition condition, the background region AB and the decorative region AC could be distinguished. In other words, regardless of the angle of the medium M, the decorative region AC remained visible. That is, in the evaluation media ME5 to ME8, a visual effect in which the decorative region AC appears and disappears could not be obtained.

[0127] On the one hand, although the evaluation media ME1 to ME4 could not distinguish the background area AB and the decoration area AC under the first visual recognition condition, they could distinguish the two under the second visual recognition condition. In other words, depending on the angle of the medium M, the decoration area AC changed between a visible state and an invisible (hidden) state. That is, the evaluation media ME1 to ME4 obtained a visual effect in which the decoration area AC appeared and disappeared.

[0128] Therefore, in this evaluation test, as a comprehensive evaluation regarding the visual effect, the symbol "○" was used to indicate that the visual effect was obtained, and the symbol "×" was used to indicate that the visual effect was not obtained, and they were respectively shown in Table TBL2 (Fig. 7(B)).

[0129] Here, based on Tables TBL1 and TBL2 (Fig. 7), the conditions for obtaining the visual effect are sorted out. When the background printing duty DB is 100 [%], the range of the decoration printing duty DC for obtaining the visual effect is 75.00 [%] or more and 93.75 [%] or less, and the duty difference between the two for obtaining the visual effect is 6.25 [%] or more and 25.00 [%] or less. Furthermore, the range of the ratio of the decoration printing duty DC to the background printing duty DB for obtaining the visual effect is 75.00 [%] or more and 93.75 [%] or less, which is also the value of the decoration printing duty DC.

[0130] [4-3. Creation of Comparative Medium and Visual Recognition Judgment] Next, in this evaluation test, a comparative medium MQ for comparing with the evaluation medium ME was created, and for the comparative medium MQ, the visual recognition judgment of the image was performed in the same manner as in the case of the evaluation medium ME.

[0131] When creating the comparative medium MQ, in the image forming apparatus 1, various bias voltages (such as developing voltage) related to the silver (SL) image forming unit 10SL were appropriately adjusted so that the visual reflectance difference ΔY became the value 14. That is, the comparative medium MQ had a visual reflectance difference ΔY that decreased to about half from the value 26 compared with the evaluation medium ME. Along with this, in the comparative medium MQ, the thickness of the silver toner image PSL decreased significantly compared with the evaluation medium ME.

[0132] In this evaluation test, two types of comparison media MQ (MQ1 and MQ2) were created with respect to the presence or absence of the transparent toner image PCL. As shown in the schematic diagram in FIG. 9(A) corresponding to FIG. 4(A), the first type of comparison medium MQ1 has a structure in which a silver toner image PSL and a normal toner image PNL are superimposed on the surface of the medium M. That is, the comparison medium MQ1 has a structure in which the transparent toner image PCL is omitted from the decorative medium MC (FIG. 4(A)) and the evaluation medium ME, and the thickness of the silver toner image PSL is reduced (thinned).

[0133] Furthermore, in this evaluation test, similar to the case of the evaluation medium ME, eight types of evaluation images PE (PE1, PE2,..., PE8) were each made into a silver toner image PSL, thereby creating eight types of comparison media MQ1 (MQ11, MQ12,..., MQ18).

[0134] Moreover, in this evaluation test, similar to the case of the evaluation medium ME, two types of visual recognition determinations were made for each comparison medium MQ1, and the determination results as shown in Table TBL3 in FIG. 10(A) were obtained. That is, with respect to the comparison medium MQ1 in which the transparent toner image PCL was omitted, although the visual effect in which the decorative area AC appears and disappears was not obtained in the comparison media MQ15 to MQ18, the said visual effect was obtained in the comparison media MQ11 to MQ14.

[0135] Thus, when the visual reflectance difference ΔY is set to the value 14 and the range of the decorative printing duty DC for obtaining a visual effect is sorted out in the comparison medium MQ1 in which the transparent toner image PCL is omitted, it is in the range of 75.00 [%] or more and 93.75 [%] or less.

[0136] On the other hand, as shown in the schematic diagram in FIG. 9(B) corresponding to FIG. 9(A), the second type of comparison medium MQ2 has a structure in which a silver toner image PSL, a transparent toner image PCL, and a normal toner image PNL are superimposed on the surface of the medium M. That is, the comparison medium MQ2 has a structure in which the thickness of the silver toner image PSL is reduced (thinned) from the decorative medium MC (FIG. 4(A)) and the evaluation medium ME.

[0137] Furthermore, in this evaluation test, similar to the cases of the evaluation medium ME and the comparison medium MQ1, eight types of evaluation images PE (PE1, PE2, …, PE8) were each made into silver toner images PSL, thereby creating eight types of comparison media MQ2 (MQ21, MQ22, …, MQ28).

[0138] Moreover, in this evaluation test, similar to the cases of the evaluation medium ME and the comparison medium MQ1, two types of visual recognition determinations were made for each comparison medium MQ2, and as a result, a determination result as shown in Table TBL4 of FIG. 10(B) was obtained. That is, regarding the comparison medium MQ2 provided with the transparent toner image PCL, although a visual effect in which the decoration area AC appears and disappears was not obtained in comparison media MQ26 to MQ28, the said visual effect was obtained in comparison media MQ21 to MQ25.

[0139] Thus, when the visual reflectance difference ΔY is set to the value 14, and the range of the decoration printing duty DC for obtaining a visual effect is arranged in the comparison medium MQ2 provided with the transparent toner image PCL, it becomes a range of 68.75 [%] or more and 93.75 [%] or less.

[0140] Here, when comparing the visual recognition determination results of the comparison medium MQ1 and the comparison medium MQ2, it can be seen that by providing the transparent toner image PCL between the silver toner image PSL and the normal toner image PNL, the range of the decoration printing duty DC for obtaining a visual effect can be expanded.

[0141] [5. Decorative medium printing process] Next, the decorative medium printing process when creating a decorative medium MC by printing an image on the medium M with the image forming apparatus 1 so as to obtain a visual effect will be described.

[0142] Based on the results of the above-described evaluation test, the image forming apparatus 1 stores information regarding the silver toner image PSL, the transparent toner image PCL, and the normal toner image PNL in the creation of the decorative medium MC in the specular color data conversion table 96, the transmissive color data conversion table 97, and the normal color data conversion table 95 in advance.

[0143] Specifically, in the specular color data conversion table 96, information is stored such that the background printing duty DB of the background area AB in the silver toner image PSL is 100 [%], and the decoration printing duty DC of the decoration area AC is in the range of 75.00 [%] or more and 93.75 [%] or less. Also, in the transmissive color data conversion table 97, information is stored such that the value of the printing duty D in the transparent toner image PCL is 100 [%]. Further, in the normal color data conversion table 95, information is stored such that the value of the printing duty D in the normal toner image PNL is 100 [%].

[0144] When the control unit 3 (FIG. 3) of the image forming apparatus 1 receives print data from the host device 100 via the interface unit 82, the print control unit 80 reads out and executes the decorative medium printing program from the storage unit 81, starts the decorative medium printing process procedure RT1 shown in FIG. 11, and moves to the first step SP1.

[0145] In step SP1, the control unit 3 displays a predetermined message on the display unit 4 to prompt the user to set the medium M in the first paper feeding unit 40, and then moves to the next step SP2.

[0146] In step SP2, the control unit 3 feeds one sheet of the medium M from the paper cassette 41 by the first paper feeding unit 40 and conveys it along the conveyance path W, and then moves to the next step SP3. As a result, the medium M is conveyed to the secondary transfer unit 39 with its surface facing upward (the side facing the intermediate transfer belt 34).

[0147] In step SP3, the control unit 3 controls the silver image forming unit 10SL based on the received print data, and forms a silver toner image PSL to be printed on the surface of the medium M on the intermediate transfer belt 34 (FIGS. 1 and 2). At this time, the control unit 3 forms a background area AB and a decorative area AC (FIG. 4) on the silver toner image PSL based on the received print data. Further, the control unit 3 refers to the metallic color data conversion table 96 (FIG. 3), and controls the background print duty DB of the background area AB to be 100 [%], and the decorative print duty DC of the decorative area AC to be in the range of 75.00 [%] or more and 93.75 [%] or less.

[0148] Furthermore, the control unit 3 transfers the silver toner image PSL from the intermediate transfer belt 34 to the surface of the medium M by the secondary transfer unit 39, and further fixes the silver toner image PSL to the surface of the medium M by the fixing unit 60, and then moves to the next step SP4. In step SP4, the control unit 3 conveys the medium M along the conveyance path W by the paper discharge unit 70, and discharges it from the discharge port 76 to the paper discharge tray 2T, and then moves to the next step SP5.

[0149] In step SP5, the control unit 3 displays a predetermined message on the display unit 4 to prompt the user to set the medium M on which the silver toner image PSL is printed in the first paper feeding unit 40, and then moves to the next step SP6. In step SP6, the control unit 3 feeds one medium M from the paper cassette 41 by the first paper feeding unit 40 and conveys it along the conveyance path W, and then moves to the next step SP7. As a result, the medium M is conveyed to the secondary transfer unit 39 with the surface on which the silver toner image PSL is printed facing upward.

[0150] In step SP7, the control unit 3 controls the transparent color image forming unit 10CL based on the received print data, and forms a transparent toner image PCL to be printed on the surface of the medium M on which the silver toner image PSL is printed on the intermediate transfer belt 34 (Figs. 1 and 2). At this time, the control unit 3 refers to the transparent color data conversion table 97 (Fig. 3) based on the received print data, and controls the print duty D of the transparent toner image PCL to be 100 [%].

[0151] Subsequently, the control unit 3 causes the secondary transfer unit 39 to transfer the transparent toner image PCL from the intermediate transfer belt 34 so as to overlap it on the upper side of the silver toner image PSL on the surface of the medium M. Further, the control unit 3 causes the fixing unit 60 to fix the transparent toner image PCL in a state of overlapping it on the upper side of the silver toner image PSL on the surface of the medium M, and moves to the next step SP8. In step SP8, the control unit 3 conveys the medium M along the conveyance path W by the paper discharge unit 70, discharges it from the discharge port 76 to the paper discharge tray 2T, and moves to the next step SP9.

[0152] In step SP9, the control unit 3 displays a predetermined message on the display unit 4 to prompt the user to set the medium M on which the silver toner image PSL and the transparent toner image PCL are printed in the first paper supply unit 40, and moves to the next step SP10. In step SP10, the control unit 3 feeds one medium M from the paper cassette 41 by the first paper supply unit 40, conveys it along the conveyance path W, and moves to the next step SP11. As a result, the medium M is conveyed to the secondary transfer unit 39 with the surface on which the silver toner image PSL and the transparent toner image PCL are printed facing upward.

[0153] In step SP11, the control unit 3 controls the cyan image forming unit 10C based on the received print data, and forms a normal toner image PNL to be printed on the surface of the medium M on which the silver toner image PSL and the transparent toner image PCL are printed, on the intermediate transfer belt 34 (FIGS. 1 and 2). At this time, the control unit 3 controls the print duty D of the normal toner image PNL to be 100[%] by referring to the normal color data conversion table 95 (FIG. 3) based on the received print data.

[0154] Subsequently, the control unit 3 causes the secondary transfer unit 39 to transfer the normal toner image PNL from the intermediate transfer belt 34 so as to overlap it on the upper side of the silver toner image PSL and the transparent toner image PCL on the surface of the medium M. Further, the control unit 3 causes the fixing unit 60 to fix the normal toner image PNL in a state of overlapping it on the upper side of the silver toner image PSL and the transparent toner image PCL on the surface of the medium M, and then moves to the next step SP12.

[0155] In step SP12, the control unit 3 conveys the medium M along the conveyance path W by the paper discharge unit 70, discharges it from the discharge port 76 to the paper discharge tray 2T, and then moves to the next step SP13 to end the decorated medium printing process procedure RT1. As a result, the image forming apparatus 1 can create a decorated medium MC in which the silver toner image PSL, the transparent toner image PCL, and the normal toner image PNL having the background region AB and the decoration region AC are sequentially printed and overlapped on the surface of the medium M.

[0156] [6. Effects, etc.] In the above configuration, the image forming apparatus 1 according to the present embodiment creates a decorated medium MC by sequentially superimposing and printing the silver toner image PSL, the transparent toner image PCL, and the normal toner image PNL having the background region AB and the decoration region AC on the surface of the medium M.

[0157] At this time, when the image forming apparatus 1 forms a silver toner image PSL by the silver image forming unit 10SL, the background printing duty DB of the background area AB is set to 100 [%], and the decoration printing duty DC of the decoration area AC is set within the range of 75.00 [%] or more and 93.75 [%] or less. From another perspective, the image forming apparatus 1 sets the duty difference between the background printing duty DB and the decoration printing duty DC to 6.25 [%] or more and 25.00 [%] or less, and also sets the range of the ratio of the decoration printing duty DC to the background printing duty DB to 75.00 [%] or more and 93.75 [%] or less.

[0158] Thereby, when the position and posture of the decoration medium MC are variously changed by the user, etc., and the relative positions and angular relationships of the user's viewpoint VP, the light source LS, and the decoration medium MC are variously changed, the image forming apparatus 1 can provide a good visual effect such that the decoration area AC appears and disappears on the surface side of the decoration medium MC.

[0159] By the way, in the silver toner image PSL, as described above, there is a certain difference in the printing duty D (background printing duty DB and decoration printing duty DC) between the background area AB and the decoration area AC. Therefore, when the silver toner image PSL is printed on the medium M, there is a possibility that a step is formed at the boundary portion between the background area AB and the decoration area AC on its surface.

[0160] Therefore, if a normal toner image PNL is printed on the surface side of the medium M over the silver toner image PSL, that is, in the case of Patent Document 1, the step at the boundary portion between the background area AB and the decoration area AC formed in the silver toner image PSL may also appear as it is on the surface of the normal toner image PNL.

[0161] Then, for example, when the user views the medium M in a situation similar to that shown in FIG. 6(A), there is a risk that the step formed in the normal toner image PNL can be visually recognized, and the shape of the decoration area AC can be perceived. That is, even when it is desired to hide the decoration area AC, there is a risk that the decoration area AC can be visually recognized through the step.

[0162] Therefore, the image forming apparatus 1 prints by superimposing the transparent toner image PCL on the silver toner image PSL on the decorative medium MC, and prints the normal toner image PNL on the upper side thereof (FIG. 4 and the like). That is, although a step is formed between the background area AB and the decoration area AC in the silver toner image PSL, the image forming apparatus 1 can satisfactorily fill this step by superimposing the transparent toner image PCL as an intermediate layer, and can make the upper surface thereof much smoother than the upper surface of the silver toner image PSL and approach a flat state.

[0163] Thereby, the image forming apparatus 1 can form the surface of the normal toner image PNL sufficiently flat on the decorative medium MC, so that it is difficult for the user to notice the step between the background area AB and the decoration area AC formed in the lower layer.

[0164] In other words, the image forming apparatus 1 can appropriately hide the decoration area AC in the printed decorative medium MC, thereby avoiding the situation where the decoration area AC appears in an unnecessarily different form from its original appearance and can give a good visual effect to the user.

[0165] In addition, in the evaluation test regarding the comparison media MQ1 and MQ2, the comparison media MQ2 provided with the transparent toner image PCL has a wider range of decoration printing duty DC in which the background area AB and the decoration area AC cannot be distinguished under the first visual recognition condition than the comparison media MQ1 without the transparent toner image PCL (FIGS. 10(A) and (B)). As can be understood from this, the image forming apparatus 1 can expand the range of the decoration printing duty DC that can obtain a good visual effect by adopting a configuration in which the transparent toner image PCL is sandwiched between the silver toner image PSL and the normal toner image PNL on the decoration medium MC.

[0166] By the way, due to its constituent materials, the transparent toner TCL has a property of being more flexible than toners T of other colors. Therefore, the image forming apparatus 1 can make the transparent toner TCL favorably enter the portion of the decoration area AC formed on the silver toner image PSL and can form the upper surface of the transparent toner image PCL relatively smoothly by adopting a configuration in which the transparent toner image PCL is sandwiched between the silver toner image PSL and the normal toner image PNL. As a result, the image forming apparatus 1 can also form the surface of the normal toner image PNL smoothly and can significantly reduce the possibility that the decoration area AC is visually recognized unnecessarily.

[0167] Furthermore, in the decoration medium printing processing procedure RT1 (FIG. 11), the image forming apparatus 1 transfers and fixes the transparent toner image PCL to the medium M in step SP7 and then transfers and fixes the normal toner image PNL in step SP11. Therefore, the transparent toner image PCL is subjected to the fixing process by the fixing unit 60 twice in steps SP7 and SP11. As a result, the image forming apparatus can make the transparent toner TCL constituting the normal toner image PNL fit well to the step between the background area AB and the decoration area AC in the silver toner image PSL and can form its upper surface flatter compared with the case where the fixing process is performed only once on the printed decoration medium MC.

[0168] Viewed from another perspective, since the transparent toner TCL has a sufficiently high light transmittance, as shown in FIGS. 6(A) and 6(B), light incident from the surface side of the medium M that passes through the normal toner image PNL and travels toward the silver toner image PSL, and light reflected by the silver toner image PSL can pass through at a high rate. That is, the image forming apparatus 1 can enhance the visibility of the decoration area AC in the printed decorated medium MC by making the middle layer a transparent toner image PCL, as compared with the case where the middle layer is a toner image P of another color with a low visible light transmittance. As a result, a better visual effect can be obtained in the decorated medium MC.

[0169] Viewed from yet another perspective, the image forming apparatus 1 can generate image data in which the printing duty D in each of the portion that becomes the background area AB and the portion that becomes the decoration area AC is appropriately set by the silver image forming unit 10SL based on the control of the control unit 3, and perform exposure processing, development processing, etc. based on the image data. That is, the image forming apparatus 1 can easily create a decorated medium MC that provides a good visual effect while using a well-known mechanism that can form and print a toner image using a silver toner that is a metallic color without using special parts or the like for creating the decorated medium MC.

[0170] According to the above configuration, the image forming apparatus 1 according to the present embodiment creates the decorated medium MC by sequentially superimposing and printing the silver toner image PSL, the transparent toner image PCL, and the normal toner image PNL on the surface of the medium M. At this time, the image forming apparatus 1 provides a background area AB with a background printing duty DB of 100[%] in the silver toner image PSL, and provides a decoration area AC with a decoration printing duty DC in the range of 75.00[%] or more and 93.75[%] or less. Thereby, the image forming apparatus 1 can provide a good visual effect such that the decoration area AC appears and disappears on the surface side of the decorated medium MC when the relative positions and angles of the user's viewpoint VP, the light source LS, and the decorated medium MC change in various ways.

[0171] [7. Other Embodiments] In the above-described embodiments, the background printing duty DB of the background area AB in the silver toner image PSL is set to 100%, and the decoration printing duty DC of the decoration area AC is set to 75.00% or more and 93.75% or less, that is, the form in which the decoration printing duty DC is lower than the background printing duty DB has been described. However, the present invention is not limited to this. For example, the decoration printing duty DC of the decoration area AC may be higher than the background printing duty DB of the background area AB.

[0172] Also, in the above-described embodiments, the form in which the background printing duty DB of the background area AB in the silver toner image PSL is set to 100% has been described (Fig. 7(A)). However, the present invention is not limited to this, and the background printing duty DB may be set to various values other than 100%. In this case, the decoration printing duty DC of the decoration area AC may be appropriately adjusted according to the background printing duty DB. In short, the duty difference between the background printing duty DB and the decoration printing duty DC may be in the range of 6.25% or more and 25.00% or less, and the ratio range of the decoration printing duty DC to the background printing duty DB may be in the range of 75.00% or more and 93.75% or less.

[0173] Furthermore, in the above-described embodiments, the form in which the duty difference between the background printing duty DB and the decoration printing duty DC is 6.25% or more and 25.00% or less, and the ratio range of the decoration printing duty DC to the background printing duty DB is 75.00% or more and 93.75% or less has been described. However, the present invention is not limited to this. For example, only one of the following may be satisfied: the duty difference between the background printing duty DB and the decoration printing duty DC is 6.25% or more and 25.00% or less, and the ratio range of the decoration printing duty DC to the background printing duty DB is 75.00% or more and 93.75% or less.

[0174] Furthermore, in the above-described embodiments, the form in which the printing duty D of the silver toner image PSL is divided into two steps, namely the background printing duty DB and the decorative printing duty DC, has been described. However, the present invention is not limited to this, and the printing duty D of the silver toner image PSL may be three steps or more.

[0175] Furthermore, in the above-described embodiments, in the background area AB of the silver toner image PSL printed on the surface of the medium M by the image forming apparatus 1, the form in which various bias voltages (such as developing voltage) related to the silver (SL) image forming unit 10SL are adjusted so that the visual reflectance difference ΔY becomes the value 26 has been described. However, the present invention is not limited to this, and various bias voltages related to the silver (SL) image forming unit 10SL may be adjusted so that the visual reflectance difference ΔY becomes various other values.

[0176] Furthermore, in the above-described embodiments, the form in which various bias voltages (such as developing voltage) related to the cyan (C) image forming unit 10C are adjusted so that the optical density O.D. becomes the value 1.4 in the cyan image printed on the surface of the medium M by the image forming apparatus 1 has been described. However, the present invention is not limited to this, and various bias voltages related to the cyan (C) image forming unit 10C may be adjusted so that the optical density O.D. becomes various other values.

[0177] Furthermore, in the above-described embodiments, the form in which the transparent toner image PCL, which is the middle layer of the decorative medium MC (Fig. 4), is configured by using a transparent color (CL) toner and setting the printing duty D to 100 [%] has been described. However, the present invention is not limited to this, and the printing duty D in the transparent toner image PCL may be set to a value other than 100 [%].

[0178] Furthermore, in the above-described embodiment, the normal toner image PNL, which is the upper layer of the decorative medium MC (Fig. 4), is configured using cyan (C) toner with a printing duty D of 100 [%]. However, the present invention is not limited to this, and the normal toner image PNL may be configured using various colors of toner such as black (K), magenta (M), white, or a combination thereof. Also, the printing duty D in the normal toner image PNL may be a value other than 100 [%]. In short, any toner image P using non-luminous and non-transmissive toner is acceptable.

[0179] Furthermore, in the above-described embodiment, the lower layer of the decorative medium MC (Fig. 4) is configured by a silver (SL) silver toner image PSL. However, the present invention is not limited to this, and it may be configured by a toner image P using various colors of toner T having luster, such as gold or copper. For example, the gold toner T can be manufactured by partially changing the manufacturing process of the silver toner TSL described in the embodiment. Specifically, when adding aluminum powder as a luster pigment, a yellow pigment (e.g., C.I.Pigment Yellow 180, an organic pigment), a magenta pigment (e.g., C.I.Pigment Red 122, an organic pigment), a red-orange fluorescent dye (e.g., FM-34N_Orange (manufactured by Shinroiichi Co., Ltd.)), and a yellow fluorescent dye (e.g., FM-35N_Yellow (manufactured by Shinroiichi Co., Ltd.)) are added respectively to manufacture the gold toner T. Also, as the luster pigment, it is not limited to aluminum (Al), and other various luster pigments such as pearl pigments (natural mica) and inorganic pigments made of titanium oxide may be used.

[0180] Furthermore, in the above-described embodiment, the image forming apparatus 1 is provided with one image forming unit 10SL for forming a silver toner image which is a metallic color, and the background printing duty DB of the background area AB and the decorative printing duty DC of the decorative area AC are made different by using the image forming unit 10SL, and the form for forming the silver toner image PSL has been described. However, the present invention is not limited to this, and for example, two silver image forming units 10SL which are metallic colors may be provided in the image forming apparatus 1. In this case, for example, an image of the background area AB (hereinafter also referred to as the first metallic image) is formed by one image forming unit 10SL (hereinafter also referred to as the first metallic image forming section), and an image of the decorative area AC (hereinafter also referred to as the second metallic image) may be formed by the other image forming unit 10SL (hereinafter also referred to as the second metallic image forming section). Alternatively, for example, an image of the entire range in which the background area AB and the decorative area AC are combined may be formed by one image forming unit 10SL, and only the background area AB may be formed by overlapping with the other image forming unit 10SL.

[0181] In these cases, in the silver toner image PSL formed on the medium M, it is sufficient that the adhesion amount per unit area of the silver toner TSL is appropriately different between the background area AB and the decorative area AC. Specifically, between the two image forming units 10SL, for example, the degree of exposure per unit area at the time of exposure (that is, the exposure amount such as luminance and light amount) may be made different, the respective bias voltages at the time of development and transfer may be made different, and further, these may be appropriately combined. Alternatively, the color, characteristics, etc. of the metallic toner may be made different between the two image forming units 10SL.

[0182] Furthermore, in the above-described embodiment, the temperature during fixing in the fixing unit 60 was set to be constant (for example, 150 [°C]), and the case where the temperature for fixing the silver toner image PSL, the transparent toner image PCL, and the normal toner image PNL was made the same was described. However, the present invention is not limited to this, and various temperatures at which the silver toner image PSL, the transparent toner image PCL, and the normal toner image PNL can be respectively fixed can be adopted. Specifically, for example, the temperature during fixing may be in the range of 145 to 190 [°C]. Also, for example, the temperature for fixing the transparent toner image PCL may be set higher than the temperature for fixing the silver toner image PSL and the normal toner image PNL. Specifically, for example, the fixing temperature of the silver toner image PSL and the normal toner image PNL may be 150 [°C], and the fixing temperature of the transparent toner image PCL may be 190 [°C]. Thereby, the degree to which the transparent toner TCL enters the decorated area AC portion in the silver toner image PSL can be increased.

[0183] Furthermore, in the above-described embodiment, as shown as the decoration medium printing process procedure RT1 (FIG. 11), after printing the silver toner image PSL on the surface of the medium M and discharging the paper, the medium M was set again in the paper cassette 41 and the transparent toner image PCL was printed. However, the present invention is not limited to this, and for example, the silver toner image PSL and the transparent toner image PCL may be superimposed and formed on the intermediate transfer belt 34, and this may be transferred to the medium M by the secondary transfer unit 39 and fixed. In short, it may be appropriately superimposed and formed according to the relationship between the alignment order of each color in the front-rear direction of the image forming unit 10 and the order of superimposing each color on the medium M.

[0184] Furthermore, in the above-described embodiments, each time the silver toner image PSL and the transparent toner image PCL are printed on the surface of the medium M, the medium M is discharged and the user is made to set the medium M again in the paper cassette 41. However, the present invention is not limited to this. For example, after forming and fixing the silver toner image PSL on the surface of the medium M, the medium M is returned to the conveyance path W without being turned over by the re-conveying unit 66, and the transparent toner image PCL may be transferred and fixed on top of the silver toner image PSL. In this case, the medium M may be returned to the conveyance path W again by the re-conveying unit 66, and the normal toner image PNL may be transferred and fixed on top of the silver toner image PSL and the transparent toner image PCL.

[0185] Furthermore, in the first embodiment described above, the case of using black high-quality paper (black paper) as the medium M was described. However, the present invention is not limited to this. For example, high-quality paper of various colored media such as blue or red may be used as the medium M, or paper other than high-quality paper such as cardboard or coated paper may be used as the medium M. In short, any paper-like material that has the property of extremely low transmittance by blocking most of the visible light and on which the toner image P can be transferred and fixed can be used as the medium M.

[0186] Furthermore, in the above-described embodiments, the case of providing five image forming units 10 in the image forming apparatus 1 (FIG. 1) was described. However, the present invention is not limited to this. The image forming apparatus 1 may be provided with four or less or six or more image forming units 10. For example, when six image forming units 10 are provided, black (K), cyan (C), magenta (M), and yellow (Y) may be adopted as the normal colors, silver (SL) may be adopted as the metallic color, and in addition, a transparent color (CL) may be adopted.

[0187] Furthermore, in the above-described embodiment, a form has been described in which the yellow (Y) image forming unit 10 used in a general color printer is omitted, and instead, a transparent color (CL) image forming unit 10 is provided. However, the present invention is not limited to this. For example, any one of the normal colors (i.e., colors that are neither bright colors nor transparent colors), such as omitting the magenta (M) image forming unit 10 and instead providing a transparent color (CL) image forming unit 10, may be omitted and a transparent color image forming unit 10 may be provided instead.

[0188] Furthermore, in the above-described embodiment, a form has been described in which the image forming apparatus (FIG. 1) is a so-called intermediate transfer system, and the toner image formed in each image forming unit 10 is primarily transferred to the intermediate transfer belt 34, and the toner image is secondarily transferred from the intermediate transfer belt 34 to the medium M. However, the present invention is not limited to this. For example, the image forming apparatus may be a so-called direct transfer system, and the toner image formed in each image forming unit 10 may be directly transferred to the medium M.

[0189] Furthermore, in the above-described embodiment, the case where the present invention is applied to the image forming apparatus 1 that forms an image using a developer used in a one-component development system has been described. However, the present invention is not limited to this. The present invention may be applied to an image forming apparatus that forms an image using a developer used in a two-component development system, which is a system in which a carrier and toner are mixed and an appropriate charge amount is imparted to the toner by utilizing the friction between the carrier and the toner. When described in terms of the two-component development system, particles containing a bright pigment, a binder resin, and an external additive, or a powder formed by aggregation of these particles are defined as a bright toner or a bright developer.

[0190] Furthermore, in the above-described first embodiment, the case where the present invention is applied to the image forming apparatus 1 which is a single-function printer has been described. However, the present invention is not limited to this. For example, the present invention may be applied to an image forming apparatus having various other functions, such as an MFP (Multi Function Peripheral) having functions of a copier or a facsimile machine.

[0191] Furthermore, the present invention is not limited to the above-described embodiments and other embodiments. That is, the scope of application of the present invention extends to embodiments in which the above-described embodiments and the other embodiments are combined in part or in whole in any manner, or to embodiments in which parts are extracted.

[0192] Furthermore, in the above-mentioned embodiment, the image forming apparatus 1 is configured as an image forming apparatus by the image forming unit 10SL as the first image forming portion, the image forming unit 10CL as the second image forming portion, the image forming unit 10C as the third image forming portion, and the control unit 3 as the control unit. However, the present invention is not limited to this, and the image forming apparatus may be configured by the first image forming portion, the second image forming portion, the third image forming portion, and the control unit having various other configurations. [Industrial Applicability]

[0193] The present invention can be used in the case where an image is formed on a medium by electrophotography using a developer containing a metal pigment. [Explanation of symbols]

[0194] 1: image forming apparatus, 3: control unit, 10, 10C, 10CL, 10SL: image forming unit, 30: intermediate transfer unit, 34: intermediate transfer belt, 39: secondary transfer unit, 41: paper cassette, 51: paper tray, 60: fixing unit, 66: re-transport unit, 70: paper discharge unit, 80: print control unit, 81: memory unit, 95: normal color data conversion table, 96: glitter color data conversion table, 97: transparent color data conversion table, 100: upper device, AB: background area, AC: decoration area, D: printing duty, DC: decoration printing duty, M: medium, MC: decoration medium, N: image density, P: toner image, PCL: transparent toner image, PNL: normal toner image, PSL: silver toner image, T: toner, TCL: transparent toner, TNL: normal toner, TSL: silver toner, ΔY: visual reflectance difference.

Claims

1. A first image forming unit capable of forming a phosphorescent image on a medium with a phosphorescent developer; A second image forming unit capable of forming a transparent image on the medium with a transparent developer; A third image forming unit capable of forming a colored image on the medium with a colored developer; A control unit that controls the first image forming unit, the second image forming unit, and the third image forming unit according to print data; comprising: The control unit: causes the first image forming unit to form the phosphorescent image having a first region and a second region on the surface of the medium, causes the second image forming unit to form the transparent image by superimposing it on the phosphorescent image, and causes the third image forming unit to form the colored image by superimposing it on the transparent image; In the first region and the second region, the formation ratio of the phosphorescent developer per unit area on the medium represented by the ratio of the area is defined as a first formation ratio and a second formation ratio, respectively; controls such that the difference between the second formation ratio and the first formation ratio is 6.25 [%] or more and 25.00 [%] or less. An image forming apparatus characterized by the above.

2. A fixing unit that fixes the phosphorescent image, the transparent image, and the colored image formed on the medium on the medium based on the control of the control unit; further comprising: The control unit controls such that at least the second image forming unit forms the transparent image on the medium, the fixing unit fixes the transparent image on the medium, then the third image forming unit forms the colored image on the medium, and the fixing unit fixes the colored image on the medium. The image forming apparatus according to claim 1, characterized by the above.

3. A fixing unit that fixes the phosphorescent image, the transparent image, and the colored image formed on the medium on the medium based on the control of the control unit; further comprising The control unit causes the first image forming unit to form the phosphorescent image on the medium, causes the fixing unit to fix the phosphorescent image on the medium, then causes the second image forming unit to form the transparent image on the medium, and causes the fixing unit to fix the transparent image on the medium. The image forming apparatus according to claim 1, wherein the control unit performs the above operations.

4. The medium is a colored medium. The image forming apparatus according to claim 1, wherein the medium is a colored medium.

5. The first image forming unit forms the phosphorescent image by exposing an image carrier with an exposure unit to form an electrostatic latent image and developing the electrostatic latent image with the phosphorescent developer. When the control unit causes the first image forming unit to form the phosphorescent image, the control unit makes the exposure amount per unit area different between the first region and the second region. The image forming apparatus according to claim 1, wherein the exposure amount per unit area is made different between the first region and the second region when the phosphorescent image is formed.

6. The first image forming unit a first phosphorescent image forming unit that forms a first phosphorescent image on the medium at a predetermined formation ratio, and a second phosphorescent image forming unit that forms a second phosphorescent image on the medium at a formation ratio different from that of the first phosphorescent image and has The control unit controls the first phosphorescent image forming unit and the second phosphorescent image forming unit to form the phosphorescent image by combining the first phosphorescent image and the second phosphorescent image. The image forming apparatus according to claim 1, wherein the control unit controls the first phosphorescent image forming unit and the second phosphorescent image forming unit to form the phosphorescent image by combining the first phosphorescent image and the second phosphorescent image.

7. The control unit causes the first phosphorescent image forming unit to form the first region of the phosphorescent image and causes the second phosphorescent image forming unit to form the second region of the phosphorescent image. The image forming apparatus according to claim 6, wherein the control unit causes the first phosphorescent image forming unit to form the first region of the phosphorescent image and causes the second phosphorescent image forming unit to form the second region of the phosphorescent image.

8. The control unit causes the first phosphorescent image forming unit to form the first region and the second region of the phosphorescent image, and causes the second phosphorescent image forming unit to form the first region of the phosphorescent image by superimposing it. The image forming apparatus according to claim 6, characterized in that.

9. The control unit controls so as to make different the bias voltage applied when developing the phosphorescent developer in the first phosphorescent image forming unit and the bias voltage applied when developing the phosphorescent developer in the second phosphorescent image forming unit. The image forming apparatus according to claim 6, characterized in that.

10. The control unit controls so as to make different the exposure amount per unit area when performing exposure processing in the first phosphorescent image forming unit and the exposure amount per unit area when performing exposure processing in the second phosphorescent image forming unit. The image forming apparatus according to claim 6, characterized in that.

11. A phosphorescent image forming step of forming, by a first image forming unit, a phosphorescent image having a first region and a second region on a medium with a phosphorescent developer; A transparent image forming step of forming, by a second image forming unit, a transparent image with a transparent developer by superimposing it on the phosphorescent image on the medium; A colored image forming step of forming, by a third image forming unit, a colored image with a colored developer by superimposing it on the phosphorescent image and the transmissive image on the medium and having In the phosphorescent image forming step, when the formation ratio representing the formation amount of the phosphorescent developer per unit area with respect to the medium in the first region and the second region is the first formation ratio and the second formation ratio, respectively, by the ratio of the area, the difference between the second formation ratio and the first formation ratio is controlled to be 6.25 [%] or more and 25.00 [%] or less. The image forming method characterized by that.

12. A first image forming unit capable of forming a phosphorescent image on a medium with a phosphorescent developer, A second image forming unit capable of forming a transparent image on the medium with a transparent developer, A third image forming unit capable of forming a colored image on the medium with a colored developer, A control unit that controls the first image forming unit, the second image forming unit, and the third image forming unit according to print data, and comprising, wherein the control unit, causes the first image forming unit to form the phosphorescent image having a first region and a second region on the surface of the medium, causes the second image forming unit to form the transparent image by superimposing it on the phosphorescent image, and causes the third image forming unit to form the colored image by overlaying it on the transparent image, in the first region and the second region, the formation ratio representing the formation amount of the phosphorescent developer per unit area with respect to the medium is defined as a first formation ratio and a second formation ratio, respectively, by the ratio of the area, controls such that the ratio of the second formation ratio to the first formation ratio is 75.00 [%] or more and 93.75 [%] or less, characterized by an image forming apparatus.

Images