Image forming device

Abstract

To transfer a toner image normally even on metallized paper. [Solution] An image forming apparatus 100 includes image forming units 10y, 10m, 10c, and 10k that form images on an intermediate transfer belt 107, a secondary transfer unit TR2 that transfers the images formed on the intermediate transfer belt 107 to a recording material S, a contact member 201 that is provided upstream of the secondary transfer unit TR2 in the conveyance direction of the recording material S and grounds the recording material S being conveyed to the secondary transfer unit TR2, and a control unit 121. When the recording material S is metallized paper, the control unit 121 does not form an image in an area of ​​the recording material S that passes through the secondary transfer unit TR2 after the recording material S leaves the contact member 201.

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copying machine, or a multifunction machine. [Background technology]

[0002] Image forming devices such as electrophotographic devices and electrostatic recording devices form toner images by developing electrostatic latent images formed on photosensitive drums. The toner images are then transferred to recording materials. Transfer to the recording materials is performed either directly from the photosensitive drum or indirectly from the photosensitive drum via an intermediate transfer belt. Here, we will explain the case where transfer is performed indirectly via an intermediate transfer belt.

[0003] The transfer section that transfers the toner image from the intermediate transfer belt to the recording material includes an inner transfer roller provided inside the intermediate transfer belt and an outer transfer roller provided outside the intermediate transfer belt. During transfer, a predetermined bias voltage is applied to the inner transfer roller. The bias voltage is controlled to be constant during transfer. The constant voltage control adjusts the current flowing through the recording material to be constant during transfer.

[0004] Metal-metallized paper with a metal layer is sometimes used as a recording material. It is desirable to transfer a toner image stably to metal-metallized paper as well. However, metal-metallized paper has higher conductivity and lower impedance than paper recording materials without a metal layer. Therefore, even if the transfer unit is controlled to a constant voltage, the current flowing through the metal-metallized paper may not be stable, making it difficult to transfer a toner image stably. Patent Document 1 discloses an image forming apparatus that flows a stable current through metal-metallized paper during transfer. This image forming apparatus has a contact member located near the transfer unit, and stabilizes the current flowing through the recording material by bringing the recording material into contact with the contact member. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-60072 Summary of the Invention [Problem to be solved by the invention]

[0006] In the configuration of Patent Document 1, a contact member is placed near the transfer unit. If the transfer unit and the contact member are too close, there is a possibility of discharge occurring between the outer transfer roller and the contact member. If discharge occurs during transfer, normal transfer will not be performed, resulting in a defective image. For this reason, the outer transfer roller and the contact member must be placed at least a predetermined distance apart to prevent discharge from occurring regardless of the magnitude of the high voltage output from the transfer unit.

[0007] If the outer transfer roller is too far from the contact member, the trailing edge of the recording material may separate from the contact member during transfer of the toner image. In this case, the recording material is no longer grounded, causing the current to become unstable and preventing normal transfer, resulting in poor transfer at the trailing edge of the recording material.

[0008] SUMMARY OF THE INVENTION In view of the above problems, it is a primary object of the present invention to provide an image forming apparatus that can properly transfer a toner image even onto a recording material with low impedance, such as metallized paper. [Means for solving the problem]

[0009] The image forming apparatus of the present invention comprises an image carrier, an image forming means for forming an image on the image carrier, a transfer means for transferring the image formed on the image carrier to a recording material, a transport means for transporting the recording material to the transfer means, a contact means provided upstream of the transfer means in the transport direction of the recording material and for grounding the recording material transported to the transfer means, and a control means for forming the image on the recording material by the image forming means and transferring the image from the image carrier to the recording material by the transfer means, wherein the control means is characterized in that, when the recording material is a first paper type, the image is not formed in the area of ​​the recording material that passes through the transfer means after the recording material leaves the contact means. Another aspect of the image forming apparatus of the present invention comprises an image carrier, an image forming means for forming an image on the image carrier, a transfer means for transferring the image formed on the image carrier to a recording material, a transport means for transporting the recording material to the transfer means, a contact means arranged upstream of the transfer means in the transport direction of the recording material and for grounding the recording material transported to the transfer means, and a control means for forming the image on the recording material by the image forming means and transferring the image from the image carrier to the recording material by the transfer means, wherein the control means makes the margin area on the trailing end side in the transport direction of the recording material, where an image is not formed, larger when the recording material is a first paper type than when the recording material is a second paper type having a higher impedance than the first paper type. [Effects of the Invention]

[0010] According to the present invention, it is possible to transfer a toner image normally even on a recording material with low impedance such as metallized paper. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Figure 2] FIG. [Figure 3] An explanatory diagram of metallized paper. [Figure 4] 10 is a diagram illustrating an unstable current in a paper passing portion. [Figure 5] FIG. 10 is a diagram illustrating a conventional configuration including a contact member. [Figure 6] 10 is a flowchart showing a process during image formation. [Figure 7] FIG. 7 is an explanatory diagram of an image formed by the processing of FIG. 6. [Figure 8] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0013] 1 is a diagram showing the configuration of an image forming apparatus according to this embodiment. The image forming apparatus 100 according to this embodiment includes four image forming units. The first image forming unit 10y forms yellow images, the second image forming unit 10m forms magenta images, the third image forming unit 10c forms cyan images, and the fourth image forming unit 10k forms black images. The image forming units 10y, 10m, 10c, and 10k have the same configuration except for the color of the toner used as the developer.

[0014] 1, the suffix y at the end of a reference symbol indicates a configuration for forming a yellow image, the suffix m at the end of a reference symbol indicates a configuration for forming a magenta image, the suffix c at the end of a reference symbol indicates a configuration for forming a cyan image, and the suffix k at the end of a reference symbol indicates a configuration for forming a black image. Here, the configuration of the first image forming unit 10y that forms a yellow image will be described, and descriptions of the configurations of the second, third, and fourth image forming units 10m, 10c, and 10k that form images of other colors will be omitted.

[0015] The first image forming unit 10y includes a photosensitive drum 101y, a charging roller 102y, an exposure unit 103y, a developing unit 104y, a primary transfer roller 105y, and a photosensitive cleaner 106y. The photosensitive drum 101y is a first image carrier that rotates in the direction of the arrow and has its surface uniformly charged to a predetermined polarity and potential by the charging roller 102y. The exposure unit 103y scans the charged surface of the photosensitive drum 101y with a laser beam Ey modulated based on image data representing the image to be formed. This forms an electrostatic latent image on the surface of the photosensitive drum 101y. The developing unit 104y develops the electrostatic latent image using yellow toner to form a toner image on the surface of the photosensitive drum 101y. Similarly, a magenta toner image is formed on the photosensitive drum 101m of the second image forming unit 10m, a cyan toner image is formed on the photosensitive drum 101c of the third image forming unit 10c, and a black toner image is formed on the photosensitive drum 101k of the fourth image forming unit 10k.

[0016] An intermediate transfer belt 107, which is a second image carrier, is disposed below the first to fourth image forming units 10y, 10m, 10c, and 10k. The intermediate transfer belt 107 is driven to rotate by an inner secondary transfer roller 109, which functions as a drive roller. An outer secondary transfer roller 108 is disposed opposite the inner secondary transfer roller 109, with the intermediate transfer belt 107 in between. The inner secondary transfer roller 109 and the outer secondary transfer roller 108 form a secondary transfer unit TR2. An intermediate transfer belt cleaner 110 is disposed upstream of the first image forming unit 10y in the rotation direction of the intermediate transfer belt 107.

[0017] The toner images formed on the photosensitive drums 101y, 101m, 101c, and 101k are transferred onto the intermediate transfer belt 107 by primary transfer rollers 105y, 105m, 105c, and 105k in a superimposed manner in synchronization with the rotation of the intermediate transfer belt 107. Toner remaining on the photosensitive drums 101y, 101m, 101c, and 101k after transfer is removed by photosensitive cleaners 106y, 106m, 106c, and 106k. The toner images transferred onto the intermediate transfer belt 107 are transported toward the inner secondary transfer roller 109 by the rotation of the intermediate transfer belt 107.

[0018] The image forming apparatus 100 includes a paper feed cassette 111 that stores recording materials S, such as paper, on which an image is formed. To transport the recording materials S stored in the paper feed cassette 111 to a transport path, the image forming apparatus 100 also includes a guide member 115, a pickup roller 112, a pair of paper feed rollers 113, a pair of registration rollers 114, pairs of transport rollers 117 and 118, and a discharge roller 119. The pickup roller 112 feeds the recording materials S stored in the paper feed cassette 111 to the transport path. The pair of paper feed rollers 113 separates the recording materials S fed by the pickup roller 112 into individual sheets and transports them to the pair of registration rollers 114. The pair of registration rollers 114 corrects skew of the recording materials S. The pair of registration rollers 114 transports the recording materials S to the secondary transfer unit TR2 via the guide member 115 in accordance with the timing at which the toner image transferred to the intermediate transfer belt 107 is transported toward the inner secondary transfer roller 109.

[0019] A contact member 201 is provided upstream of the secondary transfer portion TR2 in the conveying direction of the recording material S. The contact member 201 is a member that contacts the conveyed recording material S to ground the recording material S. Details of the contact member 201 will be described later.

[0020] The four-color toner image carried on the intermediate transfer belt 107 is transferred to a recording material S passing between a secondary transfer inner roller 109 and a secondary transfer outer roller 108. A predetermined high voltage (bias voltage) is applied to either the secondary transfer inner roller 109 or the secondary transfer outer roller 108, thereby transferring the toner image from the intermediate transfer belt 107 to the recording material S. Any toner remaining on the intermediate transfer belt 107 after transfer is scraped off and collected by an intermediate transfer belt cleaner 110.

[0021] The image forming apparatus 100 includes a fixing device 116 that fixes the toner image onto the recording material S. The recording material S onto which the toner image has been transferred is transported to the fixing device 116 by a secondary transfer outer roller 108. The fixing device 116 fixes the toner image onto the recording material S by applying heat and pressure. The recording material S onto which the toner image has been fixed is discharged to the outside of the image forming apparatus 100 via a pair of conveying rollers 117 and 118 and a discharge roller 119. This results in a recording material S (a product) onto which a color image has been formed.

[0022] The image forming apparatus 100 is provided with a control unit 121 for controlling the operation of each of the components described above. The image forming apparatus 100 also has an operation unit 120 as a user interface having an input interface and an output interface. The operation unit 120 has various keys and a touch panel as an input interface. The operation unit 120 has a display and a speaker as an output interface. The control unit 121 accepts instructions from the user via the operation unit 120 or an external device via a network (not shown). When the control unit 121 accepts a print job command (image formation command), it controls the operation of each component as described above to perform a printing operation on the recording material S.

[0023] 2 is an explanatory diagram of the configuration of the secondary transfer unit TR2. The solid arrows in Fig. 2 indicate the rotation direction of the intermediate transfer belt 107 and the rotation directions of the outer secondary transfer roller 108 and the inner secondary transfer roller 109 when the toner image is transferred to the recording material S. The dashed arrow indicates the conveyance direction of the recording material S.

[0024] The contact member 201 provided near the secondary transfer portion TR2 is a conductive member, and is arranged so as to come into contact with one surface (the surface on which the toner image is not transferred) of the recording material S conveyed along the guide member 115. Since the contact member 201 is grounded, the recording material S is also grounded. The contact member 201 is arranged so as to come into contact with at least one point of the recording material S when the recording material S comes into contact with the outer secondary transfer roller 108.

[0025] The outer secondary transfer roller 108 and the inner secondary transfer roller 109 form a nip portion 200. In the nip portion 200, the intermediate transfer belt 107 and the recording material S are sandwiched and conveyed during transfer. In this embodiment, a bias voltage of the same polarity as the toner potential (negative potential in this embodiment) is applied to the inner secondary transfer roller 109, thereby transferring the toner image from the intermediate transfer belt 107 to the recording material S. In order to stabilize the current flowing through the recording material S during transfer, the bias voltage is controlled to a constant voltage.

[0026] In the nip portion 200 formed by the outer secondary transfer roller 108 and the inner secondary transfer roller 109, a current flows through the portion where the recording material S does not pass (non-paper passing portion current), and a paper passing portion current flows through the portion where the recording material S passes. The current value of the current flowing in the secondary transfer portion TR2 is the sum of the non-paper passing portion current and the paper passing portion current. The ratio of the non-paper passing portion current to the paper passing portion current changes depending on the resistance value of the recording material S, which is determined by the size and material of the recording material S.

[0027] Therefore, it is difficult to stabilize the current in the paper-passing portion using constant current control, which keeps the current flowing through the secondary transfer portion TR2 constant. For this reason, constant voltage control is used for the secondary transfer portion TR2. Also, if the impedance of the outer secondary transfer roller 108 becomes low, the current in the non-paper-passing portion increases, making it impossible to flow the necessary current in the paper-passing portion. For this reason, the impedance of the outer secondary transfer roller 108 is set higher than the impedance of the recording material S.

[0028] The inner secondary transfer roller 109 is set to have an impedance lower than that of the recording material S. As described above, a high voltage (bias voltage) generated by the high-voltage power supply 300 is applied to the inner secondary transfer roller 109. The outer secondary transfer roller 108 has an impedance higher than that of the recording material S, and its roller shaft is grounded. In a direction intersecting the conveyance direction of the recording material S (hereinafter referred to as the "width direction"), the widthwise length of the outer secondary transfer roller 108 needs to be longer than that of the recording material S. This is to enable the toner image to be transferred to the entire widthwise area of ​​the recording material S. If the impedance of the outer secondary transfer roller 108 is lower than that of the recording material S, current will flow to non-paper passing portions, making it impossible to transfer toner to the recording material S. Therefore, the impedance of the outer secondary transfer roller 108 is set higher than the impedance of the recording material S.

[0029] A high voltage is applied to the outer secondary transfer roller 108 via the inner secondary transfer roller 109. The maximum voltage applied to the outer secondary transfer roller 108 is approximately -8 kV. To prevent discharge from occurring between the outer secondary transfer roller 108 and the contact member 201 when the high voltage is applied, a distance of at least a predetermined distance must be provided between the outer secondary transfer roller 108 and the contact member 201. In this embodiment, the distance between the outer secondary transfer roller 108 and the contact member 201 is a distance L3 (here, 10 mm).

[0030] When the gap between the outer secondary transfer roller 108 and the contact member 201 becomes distance L3, the gap between the nip portion 200 and the contact member 201 becomes distance L4 (here, 15 mm). In other words, the recording material S contacts the contact member 201 from when its leading edge in the conveying direction is pinched by the nip portion 200 until it is pinched by the nip portion 200 at a position distance L4 from its trailing edge in the conveying direction toward the leading edge. When the recording material S passes through the nip portion 200 at a position distance L4 from its trailing edge in the conveying direction toward the leading edge, the recording material S separates from the contact member 201. Hereinafter, the leading edge in the conveying direction will be simply referred to as the "leading edge" and the trailing edge in the conveying direction will be simply referred to as the "trailing edge."

[0031] The image forming apparatus 100 may also form an image on a recording material S having a metal layer, such as metal-deposited paper. FIG. 3 is an explanatory diagram of metal-deposited paper. FIG. 3 shows a cross-sectional view of metal-deposited paper. Metal-deposited paper generally consists of three layers. In the example of FIG. 3, it consists of three layers: a plain paper layer Pp, a metal layer Pm, and a coating layer Pc. The second metal layer Pm is made of a metal such as aluminum, and is vapor-deposited on the first plain paper layer Pp. Because the metal layer Pm is metal, it has better conductivity and much lower impedance than the plain paper layer Pp.

[0032] It is known that when such metal-deposited paper passes through the nip portion 200, the current at the paper-passing portion is unstable even if the secondary transfer portion TR2 is under constant voltage control. FIG. 4 is an explanatory diagram showing why the current at the paper-passing portion is unstable. FIG. 4 shows a conventional configuration that does not include the contact member 201, and guide members A and B are provided upstream of the secondary transfer portion TR2 in the conveying direction of the recording material S. The metal-deposited paper is conveyed to the secondary transfer portion TR2 via the guide members A and B.

[0033] Guide member A is made of a material with lower impedance than the outer secondary transfer roller 108 and is grounded. Guide member B is made of a material with a predetermined impedance (here, resistance 400). The solid arrows in Figure 4 indicate the paths of currents (non-paper passing section current, paper passing section current) that flow through the secondary transfer unit TR2. The dashed arrows indicate the transport direction of the recording material S (metal-deposited paper).

[0034] 4(a) shows the state where the leading edge of the metal-deposited paper reaches the nip portion 200 of the secondary transfer portion TR2. Because the impedance of the guide member A is smaller than the impedance of the outer secondary transfer roller 108, the current flows from the grounded guide member A through the metal layer Pm of the metal-deposited paper to the inner secondary transfer roller 109.

[0035] At this time, the load impedance seen from the secondary transfer unit TR2 is approximately the sum of the impedances of the guide member A, the metallized paper, the intermediate transfer belt 107, and the inner secondary transfer roller 109. In other words, the load impedance is approximately the sum of the impedances below. Since the secondary transfer unit TR2 is under constant voltage control, a current corresponding to the load impedance flows. Contact impedance at the point where guide member A and metallized paper come into contact Impedance across each layer of metallized paper Contact impedance at the contact point between the intermediate transfer belt 107 and the inner secondary transfer roller 109 Impedance of the inner secondary transfer roller 109

[0036] Figure 4(b) shows the state in which the metal-deposited paper has been transported further from the state in Figure 4(a). The trailing edge of the metal-deposited paper has passed through guide member A, so it is not in contact with guide member A. Therefore, the current flowing through secondary transfer unit TR2 flows from guide member B, which is grounded via resistor 400, to inner secondary transfer roller 109 via metal layer Pm of the metal-deposited paper. At this time, the load impedance seen from secondary transfer unit TR2 is approximately the sum of the following impedances: Resistance of guide member B: 400 Contact impedance at the point where guide member B and metallized paper come into contact Impedance across each layer of metallized paper Contact impedance at the contact point between the intermediate transfer belt 107 and the outer secondary transfer roller 108 Impedance of the inner secondary transfer roller 109

[0037] Because the secondary transfer unit TR2 is under constant voltage control, a current corresponding to the load impedance flows. The load impedance in FIG. 4(b) is smaller than the load impedance in FIG. 4(a) because the resistor 400 of the guide member B intervenes, resulting in a smaller current in the paper passage. Due to this mechanism, the parts that come into contact with the metallized paper change depending on the transport position of the metallized paper, causing fluctuations in the current in the paper passage that flows through the toner. This causes the transferability of the toner image to be impaired, resulting in transfer defects.

[0038] When the distance between the secondary transfer portion TR2 and the guide members A and B is equal to or greater than a predetermined distance, a contact member may be provided between the secondary transfer portion TR2 and the guide member B. FIG. 5 is a diagram showing a conventional configuration including a contact member, in which a contact member 202 is provided between the secondary transfer portion TR2 and the guide member B.

[0039] 5(a) shows a state in which the rear end of the metal-deposited paper has passed the guide member B, and the metal-deposited paper is sandwiched in the nip portion 200 of the secondary transfer portion TR2 and in contact with the contact member 202. The current is the sum of the paper-passing portion current that flows from the contact member 202 through the metal layer Pm of the metal-deposited paper to the inner secondary transfer roller 109, and the non-paper-passing portion current that flows from the outer secondary transfer roller 108 to the inner secondary transfer roller 109.

[0040] 5(b) shows the state in which the trailing edge of the metal-deposited paper has passed the contact member 202 and is sandwiched in the nip portion 200 of the secondary transfer portion TR2. In this case, the load impedance of the secondary transfer portion TR2 increases suddenly, and the current in the paper passage portion stops flowing. This causes poor transfer of the toner image to the trailing edge of the metal-deposited paper.

[0041] 2, in this embodiment, when the recording material S is metallized paper, the load impedance seen from the high-voltage power supply 300 is different before and after the trailing edge of the recording material S passes through the contact member 201. In other words, when the position held in the nip portion 200 is between the leading edge of the recording material S and a position a distance L4 (15 mm) before the trailing edge of the recording material S, the load impedance is smaller than when the holding position is within the distance L4 from the trailing edge. This is because the recording material S (metallized paper) comes into contact with the contact member 201 and is grounded.

[0042] In this way, a large change in impedance occurs at the position of the recording material S. The change in impedance causes poor transfer of the toner image to the recording material S (metal-deposited paper). Note that if the recording material S is not a low-impedance material like metal-deposited paper, no current flows to the contact member 201 via the recording material S, and therefore no change in impedance occurs.

[0043] Fig. 6 is a flowchart showing the processing during image formation. This processing is for transferring a toner image to the trailing edge of the recording material S without causing transfer failure, even if the recording material S is made of a material with lower impedance than plain paper. Here, the case where the recording material S is metallized paper will be described. Fig. 7 is an explanatory diagram of an image formed by the processing of Fig. 6.

[0044] When the image forming apparatus 100 starts operation, the control unit 121 checks whether a print job command has been received from the operation unit 120 of the image forming apparatus 100 or from an external device via a network (S501). If no command has been received (S501: N), the control unit 121 waits until a command is received.

[0045] When a command is received (S501: Y), the control unit 121 checks the paper type of the recording material S stored in the paper feed cassette 111 used in the print job, and determines whether the recording material S is metallized paper (S502). The paper type of the recording material S is checked based on setting values ​​set by the user using the operation unit 120 when the recording material S is stored in the paper feed cassette 111. The setting values ​​include, for example, characteristic information of the recording material S (paper type, size, etc.).

[0046] If the recording material S is other than metallized paper (S502: Y), the control unit 121 sets the margin areas of the recording material S where no printing is to be performed to predetermined default values ​​that are preset in the image forming apparatus 100 (S503). The margins of the recording material S that are preset in the image forming apparatus 100 are, for example, 5 mm for the leading edge margin, trailing edge margin, right edge margin, and left edge margin. The control unit 121 starts a print operation to form an image in accordance with the print job (S504). When the print operation instructed by the print job is completed, the control unit 121 ends a series of processes for image formation in accordance with the print job.

[0047] If the recording material S is metal-deposited paper (S502: N), the control unit 121 displays a setting screen for printing settings on metal-deposited paper on the display of the operation unit 120 (S505), as shown in Fig. 8. This setting screen suggests that the image density of the image in the area from the rear end of the recording material S to the front end by a predetermined distance (here, 15 mm) may be low.

[0048] If "Continue Job" is selected (S506: Y), the control unit 121 makes each of the options "No Change in Settings," "Delete Image," and "Reduce Image" selectable (S507). The option "Delete Image" prevents image formation even if there is image data to be formed in the area from the trailing edge of the recording material S to 15 mm toward the leading edge. In other words, "Delete Image" is a selection that allows for image loss on the trailing edge side. "Reduce Image" is a selection that reduces the image so that it is not formed in the area from the trailing edge of the recording material S to 15 mm toward the leading edge. Specifically, this setting ensures that the entire image to be formed on the recording material S is formed on the recording material S before the recording material S leaves the contact member 201, and no image is formed in the area from the trailing edge to 15 mm toward the leading edge. "No Change in Settings" is a selection that does not perform "Delete Image" or "Reduce Image," and there is a possibility that the image density in the area from the trailing edge of the recording material S to 15 mm toward the leading edge will be lighter. "Job Cancel" is a selection for not printing on metallized paper. The user makes an appropriate selection from these options using the operation unit 120.

[0049] If "No change in settings" is selected (S508: Y), the control unit 121 sets the margins of the recording material S to default values ​​that are preset in the image forming apparatus 100, and starts a print operation to form an image in accordance with the print job (S503, S504). When the print operation instructed by the print job is completed, the control unit 121 ends a series of processes for image formation in accordance with the print job.

[0050] FIG. 7(a) shows an example of an image formed on the recording material S in this case. This image is a print image (halftone image) when an image with the same image density is formed over the entire image formable area 700 of the recording material S. In the image of FIG. 7(a), the image density is lighter in the area from the rear end of the recording material S to a predetermined distance (here, 15 mm) toward the front end. This is because the current (transfer current) flowing through the recording material S is reduced as the recording material S moves away from the contact member 201, resulting in a smaller amount of toner being transferred.

[0051] If "No Setting Change" is not selected (S508: N), the control unit 121 determines whether "Image Deletion" is selected (S509). If "Image Deletion" is selected (S509: Y), the control unit 121 changes the setting so that an image is not formed in the area from the trailing edge of the recording material S to 15 mm from the leading edge (S510). For example, the control unit 121 changes the setting of the margin area so that image data representing an image, which corresponds to an image in the area from the trailing edge of the recording material S to 15 mm from the leading edge, is not used for image formation. In this case, the area on the photosensitive drum 101 corresponding to the area from the trailing edge of the recording material S to 15 mm from the leading edge is not exposed. Alternatively, a development bias is not applied so that this area on the photosensitive drum 101 is not developed. Alternatively, a transfer bias is not applied so that the toner image in this area on the photosensitive drum 101 is not transferred. Therefore, even if there is image data to be formed in the area from the trailing edge of the recording material S to 15 mm from the leading edge, the image in this area will be missing. After changing the settings, the control unit 121 starts a print operation for forming an image in accordance with the print job (S504). When the print operation instructed by the print job is completed, the control unit 121 ends a series of processes for forming an image in accordance with the print job.

[0052] FIG. 7(b) shows an example of an image formed on the recording material S in this case. In this image, no image is formed in the area from the trailing edge of the recording material S to the leading edge by 15 mm. In other words, in FIG. 7(b), no image is formed in the area where the image density in the image in FIG. 7(a) varies. As a result, a print image without variation in image density is obtained. Note that the trailing edge margin does not have to be smaller than the distance L4 described above, and may be 16 mm.

[0053] If the selection is not "Delete image" (S509: N), the control unit 121 determines whether or not "Reduce image" has been selected (S511). If "Reduce image" has been selected (S511: Y), the control unit 121 changes (reduces) the magnification setting of the image so that an image is not formed in an area from the rear end of the recording material S to the leading end by 15 mm (S512). After changing the setting, the control unit 121 starts a print operation for forming an image in accordance with the print job (S504). When the print operation instructed by the print job is completed, the control unit 121 ends a series of processes for image formation in accordance with the print job.

[0054] Changing the image magnification will be described using an example in which an image is formed on an A4 size (210 mm x 297 mm) recording material S. Note that the size is indicated as (width direction length, conveyance direction length). In the case of an A4 size recording material S, with the default margin setting (5 mm in all directions), the size of the image formable area 700 is 200 mm x 287 mm.

[0055] When the recording material S is metallized paper, an area 15 mm from the rear end of the recording material S to the front end cannot be used for image formation, so the image formable area 700 in the conveyance direction of the recording material S is 277 mm. Therefore, the image magnification is changed to 277 / 287, or approximately 96.5%. The image in the width direction is reduced to 96.5%. As a result, an image of 193 mm x 277 mm is formed. Figure 7(c) shows an example of an image formed on the recording material S (metallized paper) in this case.

[0056] If the selection is not "reduce image" (S511: N), the control unit 121 repeats the processes from S505 onwards. If "continue job" is not selected (S506: N), the control unit 121 determines whether "cancel job" is selected (S513). If "cancel job" is selected (S513: Y), the control unit 121 cancels the job and ends the process (S514). If "cancel job" is not selected (S513: N), the control unit 121 repeats the processes from S506 onwards.

[0057] As described above, when the recording material S is metallized paper, an image is not formed in the area on the trailing edge of the recording material S that passes through the nip portion 200 after the trailing edge of the recording material S leaves the contact member 201. This makes it possible to prevent image defects due to poor transfer of the toner image on the trailing edge of the recording material S when forming an image on metallized paper. Note that while metallized paper has been used as an example of such a recording material S, this embodiment is also effective for a first type of recording material S that has an impedance lower than a predetermined value and that would affect the transfer of the toner image if not grounded by the contact member 201. When the recording material S is a second type of paper that has a higher impedance than the first type of paper, an image is formed in the area on the trailing edge of the recording material S that passes through the nip portion 200 after the trailing edge of the recording material S leaves the contact member 201.

[0058] In this embodiment, the settings (image data) are changed so that the image formed in the area from the rear end to the leading end of the recording material S is deleted or the magnification is changed. In addition, the same effect can be obtained by not emitting light from the exposure devices 103y, 103m, 103c, and 103k.

[0059] Furthermore, in this embodiment, a configuration in which a toner image is transferred onto the recording material S by the secondary transfer unit TR2 has been described, but this embodiment is also effective when a toner image is transferred directly from the photosensitive drums 101y, 101m, 101c, and 101k onto the recording material S. For example, some image forming apparatuses that form monochrome images are configured so that a toner image is transferred directly from a photosensitive drum onto the recording material S. Also, some image forming apparatuses that form color images are configured so that toner images of different colors are formed sequentially on a single photosensitive drum and then transferred directly onto the recording material S. The toner image is transferred onto the recording material S at a nip portion that is configured between the photosensitive drum and a primary transfer roller.

[0060] In this case, the contact member 201 is provided upstream of the photosensitive drum in the conveying direction of the recording material S. If the recording material S is of a type that would affect the transfer of the toner image if it were not grounded by the contact member 201, the control unit 121 generates images such as those shown in FIGS. 7(b) and 7(c) by the processes of S505 to S512 in FIG.

[0061] 8 is displayed after a job is accepted in this embodiment, but it is also possible to set print settings for metallized paper in advance before accepting the job. That is, the user sets in advance one of the above-mentioned "no change in settings," "delete image," or "reduce image," and when the control unit 121 accepts a print job for metallized paper, it executes the job based on the preset settings.

[0062] Furthermore, for example, "delete image" or "reduce image" may be set as the default setting for metallized paper, and when a print job for metallized paper is accepted, the margins on the trailing edge of the recording paper may be automatically made larger than the margins for recording paper other than metallized paper.

Claims

1. an image carrier; an image forming means for forming an image on the image carrier; a transfer means for transferring the image formed on the image carrier onto a recording material; a conveying means for conveying the recording material to the transfer means; a contact means provided upstream of the transfer means in the conveyance direction of the recording material, for grounding the recording material being conveyed to the transfer means; a control unit that causes the image forming unit to form the image on the image carrier and the transfer unit to transfer the image from the image carrier to the recording material, thereby forming the image on the recording material; the control means, when the recording material is of a first paper type, does not form the image in an area of ​​the recording material that passes through the transfer means after the recording material leaves the contact means. Image forming device.

2. the control means forms an image in the area when the recording material is a second paper type having a higher impedance than the first paper type.

2. The image forming apparatus according to claim 1.

3. the control means controls the image forming means so that image data corresponding to the image to be formed in the area is not used in image formation when the recording material is the first paper type.

2. The image forming apparatus according to claim 1.

4. the image forming means has an exposure means for exposing the image carrier to light based on image data, the control means does not allow exposure based on image data corresponding to the image to be formed in the area.

4. The image forming apparatus according to claim 3.

5. the control means, when the recording material is the first paper type, changes the magnification at which the image is formed so that the entire image to be formed on the recording material is formed on the recording material before the recording material leaves the contact means and the image is not formed in the area.

2. The image forming apparatus according to claim 1.

6. the transfer means has a first roller and a second roller, and the first roller and the second roller sandwich and transport the image carrier and the recording material, and a predetermined bias voltage is applied to the first roller to transfer the image from the image carrier to the recording material; The second roller and the contact means are spaced apart by a predetermined distance or more so that no discharge occurs between the second roller and the contact means when the bias voltage is applied.

2. The image forming apparatus according to claim 1.

7. It has a display means, The control means, when the recording material is the first paper type, causes the display means to display a first screen including options for selecting not to form an image in the area. The image forming apparatus according to claim 3 .

8. an image carrier; an image forming means for forming an image on the image carrier; a transfer means for transferring the image formed on the image carrier onto a recording material; a conveying means for conveying the recording material to the transfer means; a contact means provided upstream of the transfer means in the conveyance direction of the recording material, for grounding the recording material being conveyed to the transfer means; a control unit that causes the image forming unit to form the image on the image carrier and the transfer unit to transfer the image from the image carrier to the recording material, thereby forming the image on the recording material; the control means makes a margin area on the trailing edge side of the recording material in the conveying direction, where no image is formed, larger when the recording material is a first paper type than when the recording material is a second paper type having a higher impedance than the first paper type. Image forming device.

9. a length of the margin area on the rear end side in the transport direction when the recording material is of a first paper type is not smaller than a distance between the transfer means and the contact means; 9. The image forming apparatus according to claim 8.

10. The first paper type of recording material has an impedance lower than a predetermined value.

9. The image forming apparatus according to claim 1.

11. The first paper type recording material is a metal-deposited paper having a metal layer. The image forming apparatus according to claim 10.

Images