JP2020085921A - Image formation device - Google Patents

Abstract

To provide an image formation device that forms images of excellent quality suppressing transfer failures without providing a separate developing device other than a developing device having chromatic toner built in, and can suppress waste toner consumption.SOLUTION: A control unit 10 is configured to: when receiving a print instruction command and input image data, generate print image data by color on the basis of the input image data (S402); generate base image data for each print image data by color (S403); form a toner image Q based on the print image data by color, and a base toner layer P based on the base image data generated for each print image data by color on an intermediate transfer belt 421, and secondarily transfer the toner image and base toner layer on a sheet S to thereby form a toner image corresponding to the input image data on the sheet S (S404); and calculate an amount of deteriorated toner (S405) to store the calculated amount thereof in a ROM 12 (S406).SELECTED DRAWING: Figure 4

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art Conventionally, there is known an image forming apparatus of a system (tandem system) in which toner images of a plurality of colors are collectively transferred onto a recording sheet. The image forming apparatus of such a system first visualizes the electrostatic latent image by selectively adhering toner to the surface of the photosensitive drum on which the electrostatic latent image is formed. Next, the toner image visualized on the photosensitive drum is transferred to the intermediate transfer belt, and finally, the toner image on the intermediate transfer belt is transferred to a recording sheet to form an image. In such an image forming apparatus, since the toner located at the lowermost layer of the toner layer formed on the intermediate transfer belt has a strong adhesive force to the intermediate transfer belt, a part of the toner is not transferred to the recording paper and the intermediate transfer belt is not transferred. Will be left behind. The toner left on the intermediate transfer belt is discarded. For this reason, the conventional image forming apparatus has a problem that the toner is unnecessarily consumed.

On the other hand, in Patent Document 1 and Patent Document 2, a transparent toner image is formed on the lowermost layer of the toner layer formed on the intermediate transfer belt, and a colored toner (for example, yellow toner, magenta toner) is formed thereon. , Cyan toner, black toner, etc.) is disclosed. With this technique, the transfer efficiency of the color toner onto the recording paper is improved, and the wasteful consumption of the toner capable of forming an image is suppressed.

JP, 2003-162125, A JP-A-8-106195

However, in the techniques described in Patent Document 1 and Patent Document 2, since the toner image which is the base of the image of the colored toner formed on the intermediate transfer belt is formed by the transparent toner, it is possible to use the developing device other than the developing device incorporating the colored toner. Since it is necessary to separately provide a developing device containing a transparent toner, there are problems that the image forming apparatus becomes huge and the manufacturing cost of the image forming apparatus is high.

The present invention has been conceived in view of such circumstances, and an object thereof is to form an image with good image quality in which transfer defects are suppressed without providing a separate developing device other than a developing device containing a colored toner, Moreover, it is an object of the present invention to provide an image forming apparatus capable of suppressing wasteful toner consumption.

An image forming apparatus according to an aspect of the present invention is an image forming apparatus that forms an image based on input image data, and a toner image for each color is formed by separating the image data into a plurality of colors. A plurality of first image carriers, and a second image carrier on which a toner image based on the image data is formed by transferring toner images of different colors formed on the plurality of first image carriers, Any one of the plurality of developing units for forming toner images of different colors on the plurality of first image carriers and the toner layer as a base of the toner image on the second image carrier is one of the plurality of developing units. Control means for controlling the plurality of developing means so as to be formed on the first image carrier.

Preferably, the control unit controls the plurality of developing units so that the toner layer is formed in at least a region of the toner image on the second image carrier that is formed of black toner.

Preferably, the image forming apparatus further includes a determining unit that determines whether or not the toner contained in each of the plurality of developing units is deteriorated, and the control unit is configured to detect the toner contained in the plurality of developing units. Control is performed so that the toner layer is formed by the deteriorated developing unit.

Preferably, the control unit determines the maximum area of the toner layer based on the image data.

Preferably, the control unit determines the amount of toner used for forming the toner layer based on the transfer efficiency when the toner image is transferred from the second image carrier to the recording medium.

According to the present invention, it is possible to form an image with good image quality in which transfer defects are suppressed and to suppress wasteful toner consumption without providing a developing device separately from a developing device incorporating color toner.

It is a figure which shows the structure of an image forming apparatus schematically. FIG. 3 is a block diagram showing a hardware configuration of the image forming apparatus. FIG. 3 is a diagram showing a base toner layer and a toner image formed in an image forming unit. 6 is a flowchart showing an image forming process. FIG. 6 is a diagram showing a region in which a base toner layer is formed. FIG. 6 is a diagram showing a candidate of an image forming unit used for forming a base toner layer and a process of determining an image forming unit to be used from the candidates. It is a figure for demonstrating an edge effect.

Hereinafter, embodiments will be described in detail with reference to the drawings. It should be noted that the same or corresponding parts in the drawings are designated by the same reference numerals and the description thereof will not be repeated.

FIG. 1 is a diagram schematically showing the configuration of the image forming apparatus 1. FIG. 2 is a block diagram showing the hardware configuration of the image forming apparatus 1. The overall configuration of the image forming apparatus 1 will be described with reference to FIGS. 1 and 2.

1 and 2, the image forming apparatus 1 is an intermediate transfer type color image forming apparatus using an electrophotographic process technique. That is, in the image forming apparatus 1, the Y (yellow) toner image formed on the photosensitive drum 413Y, the M (magenta) toner image formed on the photosensitive drum 413M, and the C formed on the photosensitive drum 413C. The (cyan) toner image and the K (black) toner image formed on the photoconductor drum 413K are transferred to the intermediate transfer belt 421 (hereinafter, also referred to as “primary transfer”), and then transferred onto the intermediate transfer belt 421. An image is formed by superimposing color toner images (hereinafter also referred to as “toner images”) and then transferring them to the paper S (hereinafter also referred to as “secondary transfer”). Further, in the image forming apparatus 1, the photoconductor drums 413Y, 413M, 413C, 413K are arranged in series in the running direction of the intermediate transfer belt 421, and the toner images of respective colors are sequentially transferred to the intermediate transfer belt 421 by one procedure. The tandem system is adopted.

As shown in FIG. 2, the image forming apparatus 1 includes a control unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a conveyance unit 50, a fixing unit 60, a storage unit 70, and a communication unit 80. ing.

The control unit 10 includes a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, and the like. The CPU 11 reads out a program according to the processing content from the ROM 12 and expands it in the RAM 13, and cooperates with the expanded program to operate the operation display unit 20, the image processing unit 30, the image forming unit 40, the conveyance unit 50, and the fixing unit 60. , The storage unit 70 and the communication unit 80 are centrally controlled. At this time, various data stored in the storage unit 70 is referred to. The storage unit 70 is composed of, for example, a nonvolatile semiconductor memory (so-called flash memory), a hard disk drive, or the like.

The control unit 10 exchanges various data with an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 80. Send and receive. The control unit 10 receives, for example, image data transmitted from an external device, and forms an image on a sheet based on the image data (hereinafter, also referred to as “input image data”). The communication unit 80 is composed of a communication control card such as a LAN card.

The control unit 10 functions as a gradation correction unit 14, a gradation correction data generation unit 15, a print image data generation unit 16, and a base image data generation unit 17. The gradation correction unit 14 controls the image processing unit 30 to perform gradation correction on the input image data based on the gradation correction data. The gradation correction data generation unit 15 generates gradation correction data used for gradation correction. The print image data generation unit 16 controls the image processing unit 30 to generate print image data for each color from the input image data. The base image data generation unit 17 generates image data (hereinafter, also referred to as “base image data”) for forming a toner layer which is a base of a toner image on the intermediate transfer belt 421.

The operation display unit 20 is composed of, for example, a liquid crystal display (LCD: Liquid Crystal Display) having a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, image states, or operation states of each function according to a display control signal input from the control unit 10. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs operation signals to the control unit 10.

The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. Specifically, the image processing unit 30 performs the gradation correction based on the gradation correction data under the control of the control unit 10. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction and compression process on the input image data in addition to the gradation correction. The image processing unit 30 also generates print image data and base image data under the control of the control unit 10.

Under the control of the control unit 10, the image forming unit 40 forms a toner image based on the print image data and the base image data generated by the image processing unit 30, and transfers the toner image onto the paper S. The image forming unit 40 includes image forming units 41Y, 41M, 41C, 41K, an intermediate transfer unit 42, and a density detection sensor 43.

The image forming unit 41Y forms a yellow toner image on the photosensitive drum 413Y, the image forming unit 41M forms a magenta toner image on the photosensitive drum 413M, and the image forming unit 41C forms a cyan toner image on the photosensitive drum 413C. The image forming unit 41K forms a black toner image on the photoconductor drum 413K. The image forming units 41Y, 41M, 41C, 41K are provided for each color corresponding to the color of the toner, and have the same configuration except that the color of the contained toner is different. In the following, for convenience of illustration and description, common components are denoted by the same reference numerals, and Y, M, C, and K are added to the reference numerals only when distinguishing each. In FIG. 1, except for the photoconductor drum 413, reference numerals are attached only to the components of the image forming unit 41Y for the Y component, and reference numerals are omitted to the other components of the image forming units 41M, 41C, 41K. .

The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

The photoconductor drum 413 has an undercoat layer (UCL: Under Coat Layer), a charge generation layer (CGL: Charge Generation Layer), and a charge transport layer (ACL) on a peripheral surface of an aluminum conductive cylindrical body (aluminum tube). It is a negative charge type organic photoconductor (OPC: Organic Photo-conductor) in which CTL: Charge Transport Layer) is sequentially laminated.

The charging device 414 uniformly charges the surface of the photoconductive drum 413 having photoconductivity to a negative polarity.

The exposure device 411 is composed of a semiconductor laser. The exposure device 411 irradiates the photoconductor drum 413 with laser light based on the print image data and the base image data for each color. In the portion irradiated with the laser beam, positive charge is generated in the charge generation layer of the photoconductor drum 413, and the generated positive charge is transported to the surface of the charge transport layer. As a result, the surface charge (negative charge) of the photoconductor drum 413 is neutralized, and a potential difference is generated between the portion irradiated with the laser light and the portion not irradiated with the laser light. As a result, an electrostatic latent image based on the print image data for each color and an electrostatic latent image based on the background image data are formed on the surface of the photosensitive drum 413.

The developing device 412 contains a developer of each color component (for example, a two-component developer including a toner having a small particle diameter and a magnetic material), and causes the toner of each color component to adhere to the surface of the photosensitive drum 413. This visualizes the electrostatic latent image to form a toner image.

The drum cleaning device 415 scrapes and removes the transfer residual toner remaining on the surface of the photosensitive drum 413 after the primary transfer. The drum cleaning device 415 has a drum cleaning blade (not shown) that is in sliding contact with the surface of the photosensitive drum 413, and scrapes the transfer residual toner by the drum cleaning blade.

The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a secondary transfer roller 423, a drive roller 424, a driven roller 425, and a belt cleaning device 426.

The intermediate transfer belt 421 is an endless belt and is stretched around a driving roller 424 and a driven roller 425. The intermediate transfer belt 421 runs at a constant speed in the arrow A direction by the rotation of the drive roller 424. When the intermediate transfer belt 421 is pressed against the photoconductor drum 413 by the primary transfer roller 422, the toner images of respective colors are sequentially superposed on the intermediate transfer belt 421 and primarily transferred. After that, when the intermediate transfer belt 421 is pressed against the paper S by the secondary transfer roller 423, only the toner image excluding the base toner layer among the toner images primarily transferred to the intermediate transfer belt 421 is secondary to the paper S. Transcribed. As a result, only the image based on the input image data (print image data) is formed on the sheet S, and the image based on the base image data is not formed.

The belt cleaning device 426 scrapes off the transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer. The belt cleaning device 426 has a belt cleaning blade 426a that is in sliding contact with the surface of the intermediate transfer belt 421, and scrapes the transfer residual toner by the belt cleaning blade 426a.

The density detection sensor 43 is arranged facing the intermediate transfer belt 421 on the upstream side in the traveling direction of the intermediate transfer belt 421 with respect to the secondary transfer position where the toner image is secondarily transferred onto the sheet S. When the secondary transfer roller 423 can be separated from the intermediate transfer belt 421, the density detection sensor 43 can be arranged downstream of the secondary transfer position in the traveling direction of the intermediate transfer belt 421.

The density detection sensor 43 is used when generating gradation correction data, and is a non-image forming area of the intermediate transfer belt 421 (for example, an area between images when images are continuously formed on a large number of sheets). The density of the toner pattern for gradation correction formed in the above is detected. The density detection sensor 43 includes a light emitting element such as a light emitting diode (LED: Light Emitting Diode) and a light receiving element such as a photodiode (PD: Photodiode), and is a reflective optical sensor that detects the reflection density of the toner pattern. is there. The reflection density of the toner pattern is represented by -log(I/I0), where I0 is the amount of light incident on the measurement target and I is the amount of reflection light from the measurement target. When the intermediate transfer belt 421 is made of a translucent material, the density detection sensor 43 is a transmissive type in which a light emitting element and a light receiving element are arranged at positions facing each other with the intermediate transfer belt 421 interposed therebetween. You may apply the optical sensor of.

The transport unit 50 includes a paper feed unit 51, a transport mechanism 52, and a paper discharge unit 53. Sheets (for example, standard sheets, special sheets, etc.) S are categorized on the basis of basis weight, size, etc. and set in advance in the two sheet feeding tray units 51a, 51b constituting the sheet feeding section 51. It is housed by type. The sheets S stored in the sheet feed tray units 51a and 51b are sent out one by one from the top, and are conveyed to the image forming section 40 by a conveyance mechanism 52 including a plurality of conveyance rollers such as a registration roller 52a. At this time, the registration portion provided with the registration roller 52a corrects the inclination of the fed paper S and adjusts the conveyance timing. The toner image is secondarily transferred in the image forming section 40, and the sheet S subjected to the fixing process in the fixing section 60 is ejected to the outside of the image forming apparatus 1 from the sheet ejection section 53 having a sheet ejection roller 53a. .

The fixing unit 60 includes a pressure unit and a heating unit. The pressing portion forms a nip portion for nipping and conveying the sheet S. The heating unit contacts the sheet S on which the toner image is transferred and heats it at the fixing temperature. The fixing unit 60 fixes the toner image secondarily transferred in the image forming unit 40 on the sheet S by heating and pressing.

In this way, the image forming apparatus 1 generates print image data and base image data for each color, forms a toner image and a base toner layer on the intermediate transfer belt 421 based on these image data, A toner image based on the input image data (print image data) is formed on the sheet S by transfer.

FIG. 3 is a diagram showing the base toner layer P and the toner image Q formed in the image forming section 40. FIG. 3A is a diagram showing the base toner layer P and the toner image Q formed on the intermediate transfer belt 421 after the primary transfer. FIG. 3B is a diagram showing the base toner layer P and the toner image Q after the secondary transfer.

With reference to FIG. 3A, in the image forming apparatus 1, the base toner layer P is formed as the lowermost layer of the toner layers formed on the intermediate transfer belt 421 after the primary transfer, and the toner is superposed on the base toner layer P. An image Q is formed. The underlying toner layer P is a layer of toner visualized by the toner being sprayed by the developing device 412 onto the electrostatic latent image formed on the photosensitive drum 413 by the irradiation based on the underlying image data by the exposure device 411. Are transferred to the intermediate transfer belt 421. On the other hand, the toner image Q is visualized by the developing device 412 ejecting toner onto the electrostatic latent image formed on the photoconductor drum 413 by the irradiation based on the print image data for each color by the exposure device 411. The toner image for each color is transferred to the intermediate transfer belt 421.

Referring to FIG. 3B, in image forming apparatus 1, all of toner image Q is transferred to sheet S by secondary transfer. On the other hand, a part of the base toner layer P is transferred to the paper S, but most of it is left on the intermediate transfer belt 421. The base toner layer P left on the intermediate transfer belt 421 is removed by the belt cleaning device 426 and discarded.

As shown in FIGS. 3A and 3B, in the image forming apparatus 1, since the base toner layer P is formed as the lowermost layer of the toner layers formed on the intermediate transfer belt 421, the toner image Q is formed. Does not directly adhere to the intermediate transfer belt 421. As a result, the adhesive force between the toner image Q and the intermediate transfer belt 421 is relaxed, and the transfer efficiency of the toner image Q onto the paper S is increased, so that an image of good quality is formed.

FIG. 4 is a flowchart showing the image forming process. In the image forming process shown in FIG. 4, the CPU 11 executes a predetermined process stored in the ROM 12 when a print instruction command is transmitted to the image forming apparatus 1 from an external device together with input image data (S401). It is realized by executing the program.

Referring to FIG. 4, first, control unit 10 determines whether or not a print instruction command has been transmitted (S401). The control unit 10 repeats the processing of S401 until the print instruction command is transmitted, and when the print instruction command is transmitted (YES in S401), moves to S402.

In S402, the control unit 10 controls the image processing unit 30 to perform processing of converting input image data into colors. As a result, print image data for each color that is separated into Y, M, C, and K from the input image data is generated.

Next, the control unit 10 controls the image processing unit 30 to perform a process of generating base image data for each print image data for each color generated in S402 (S403). When generating the base image data, the control unit 10 determines an area for forming the base toner layer P, an image forming unit 41 for forming the base toner layer P, and an amount of toner for forming the base toner layer P.

Here, the region where the base toner layer P is formed will be described with reference to FIG. FIG. 5 is a diagram showing a region where the base toner layer P is formed. As shown in FIG. 5, the control unit 10 determines the area where the base toner layer P is formed such that the area inside the area where the toner image Q is formed is the maximum area where the base toner layer P is formed. .. In FIG. 5, the base toner layer P is formed in the area where the toner image Q is formed, excluding the area inside one dot (hereinafter, also referred to as “edge portion”) from the area. As shown in FIG. 3B, in the secondary transfer, most of the base toner layer P is left behind on the intermediate transfer belt 421, but a part of it is transferred to the sheet S and is positioned on the uppermost layer on the sheet S. Will be done. The toner located in the uppermost layer is not pressed by another toner from above, and is unstable due to the unevenness of the toner formed in the lower layer, and is easily scattered. If the base toner layer P is formed up to the end of the area where the toner image Q is formed, the base toner layer P may extend beyond the area where the toner image Q is formed, resulting in a very poor appearance. I will end up. However, in the image forming apparatus 1, since the maximum area in which the base toner layer P is formed is an area within one dot from the maximum area in which the toner image Q is formed, the base toner layer P is transferred to the paper S. Even in the case, the area where the toner image Q is formed does not overflow. Note that, in FIG. 5, the base toner layer P is formed in a region of the region where the toner image Q is formed, excluding a region inside one dot from the region, but it does not necessarily have to be one dot. Even if the base toner layer P is transferred to the paper S, the maximum area where the base toner layer P is formed is the area where the toner image Q is formed so that the area where the toner image Q is formed does not overflow. It may be an inner area.

Further, the control unit 10 determines which image forming unit 41 is used to form the base toner layer P in the determined area. Although details will be described with reference to FIG. 6, regarding which image forming unit 41 is used, the toner image Q formed on the photosensitive drum 413 located on the upstream side in the traveling direction of the intermediate transfer belt 421 is the intermediate transfer belt 421. It is determined in consideration of the fact that the toner image Q formed on the photosensitive drum 413 located on the downstream side in the traveling direction is transferred to the intermediate transfer belt 421 before being formed, and is formed as a lower layer on the intermediate transfer belt 421.

Further, the control unit 10 determines the amount of toner forming the base toner layer P in consideration of the secondary transfer efficiency. The secondary transfer efficiency is the transfer efficiency of the toner image Q from the intermediate transfer belt 421 to the sheet S, and varies depending on the glossiness (surface condition) of the intermediate transfer belt 421, temperature, humidity, and durability. To do. In the image forming apparatus 1, the ROM 12 stores a relational expression or a table created based on the relation between these and the ratio of the toner on the intermediate transfer belt 421 transferred to the sheet S in advance. In the process of S403, the control unit 10 calculates the secondary transfer efficiency by referring to the relational expression or table stored in the ROM 12, and determines the amount of toner forming the base toner layer P based on the calculation result. To do. The control unit 10 may calculate the secondary transfer efficiency each time the base image data is generated and determine the amount of toner forming the base toner layer P based on the calculation result. A fixed value may be stored in advance in the ROM 12 as the secondary transfer efficiency of 1, and the amount of toner forming the base toner layer P may be determined based on the fixed value.

As described above, in S403, the control unit 10 analyzes the print image data for each color for each pixel, and determines the area in which the base toner layer P is formed and the image forming unit 41 in which the base toner layer P is formed. Further, in S403, the control unit 10 determines the amount of toner forming the base toner layer P in consideration of the secondary transfer efficiency. In S403, the control unit 10 controls the image processing unit 30 based on the determined content to generate the base image data for each print image data for each color generated in S402.

Next, the control unit 10 controls the image forming unit 40 to cause the exposure device 411 to irradiate the photoconductor drum 413 with laser light based on the base image data and the print image data for each color, and the photoconductor drum 413 is irradiated with the light. The developing device 412 ejects toner onto the electrostatic latent image formed on the toner image to form a toner layer and a toner image, which are transferred to the intermediate transfer belt 421. As a result, as shown in FIG. 3A, a base toner layer P is formed on the lowermost layer of the toner layers formed on the intermediate transfer belt 421, and a toner image Q is formed on it. After that, when the intermediate transfer belt 421 is pressed against the paper S by the secondary transfer roller 423, the entire toner image Q is transferred to the paper S as shown in FIG. As a result, an image based on the input image data (print image data) is formed on the paper S (S404). On the other hand, a part of the base toner layer P is transferred to the paper S, but most of it is left on the intermediate transfer belt 421. The base toner layer P left on the intermediate transfer belt 421 is removed by the belt cleaning device 426 and discarded.

Next, the control unit 10 calculates the amount of deteriorated toner (hereinafter, also referred to as “deteriorated toner”) for each developing device 412 in each image forming unit 41 (S405). Deteriorated toner is toner whose charging characteristics have deteriorated. When image formation with a low printing rate is repeatedly performed, consumption of the toner carried on the developing roller 412a is not promoted. The toner left on the developing roller 412a without being consumed is repeatedly rubbed by the agitating roller 412b, the regulating blade 412c, etc., so that the charging characteristic thereof deteriorates. When the image forming unit 40 forms an image using the toner having the deteriorated charging characteristic, an image with deteriorated image quality is formed. In the conventional image forming apparatus, in order to form a good image with suppressed transfer failure, the developer containing the deteriorated toner is forcibly discharged and discarded. The amount of deteriorated toner is obtained by calculating the print ratio for each color on a page-by-page basis and integrating the difference with a predetermined value.

Next, the control unit 10 stores the amount of deteriorated toner calculated in S405 in the ROM 12 (S406). Next, the control unit 10 ends the series of processes shown in FIG.

In this way, the image forming apparatus 1 calculates the amount of deteriorated toner every time image formation (S404) is completed and stores it in the ROM 12. This is for reference when determining the image forming unit 41 that forms the base toner layer P in the next image formation. Although details will be described with reference to FIG. 6, the control unit 10 preferentially uses the image forming unit 41 having the developing device 412 containing a large amount of deteriorated toner to form the base toner layer P.

The process shown in FIG. 4 is the image forming process when the image forming apparatus 1 functions as a printer. However, when the image forming apparatus 1 functions as a copy machine, the read (scanned) image data is read. Is transmitted, the control unit 10 performs the processing from S402 onward.

FIG. 6 is a diagram showing a candidate of the image forming unit 41 used for forming the base toner layer P and a process of determining the image forming unit 41 to be used from the candidates. FIG. 6A is a table showing candidates of the image forming unit 41 used for forming the base toner layer P, and is stored in the ROM 12. FIG. 6B is a flowchart showing a process of determining the image forming unit 41 used for forming the base toner layer P from the candidates. In the image forming apparatus 1, the control unit 10 refers to the table of FIG. 6A and performs the process of FIG. 6B to determine the image forming unit 41 used to form the base toner layer P. .. The processing of FIG. 6B is realized by the CPU 11 executing a predetermined program stored in the ROM 12.

With reference to FIG. 6A, in image forming apparatus 1, candidates for image forming unit 41 for forming base toner layer P are determined for each color of toner image Q on intermediate transfer belt 421. Specifically, when the toner image Q is formed with black, that is, K toner, the image forming units that form the base toner layer P are the image forming units 41Y, 41M, and 41C. When the toner image Q is formed of cyan, that is, C toner, the image forming units that form the base toner layer P are the image forming units 41Y and 41M. When the toner image Q is formed of magenta, that is, M toner, the candidate of the image forming unit forming the base toner layer P is the image forming unit 41Y. When the toner image Q is formed of yellow, that is, Y toner, the candidate of the image forming unit forming the base toner layer P is the image forming unit 41Y. As described above, in the image forming apparatus 1, except when the toner image Q is yellow, the image forming unit 41 located upstream of the image forming unit 41 that forms the toner image Q in the traveling direction of the intermediate transfer belt 421 is the base. It becomes a candidate for the image forming unit 41 for forming the toner layer P.

With reference to FIG. 6B, the control unit 10 refers to the table shown in FIG. 6A, and finds that the stored toner is one of the candidates of the image forming unit 41 that forms the base toner layer P. It is determined whether or not the image forming unit 41 having the deteriorated developing device 412 exists (S601). Here, whether or not the toner has deteriorated is determined based on the amount of deteriorated toner stored in the ROM 12. The amount of deteriorated toner is calculated after the previous image formation (S404) is completed (S405) and is stored in the ROM 12 (S406). If the image forming unit 41 having the developing device 412 in which the contained toner is deteriorated is present among the candidates of the image forming unit 41 forming the base toner layer P (YES in S601), the control unit In step S602, the image forming unit 41 having the developing device 412 that has the largest amount of deteriorated toner is determined as the image forming unit 41 that forms the base toner layer P (S602). On the other hand, when the image forming unit 41 having the developing device 412 in which the contained toner is deteriorated does not exist among the candidates of the image forming unit 41 forming the base toner layer P (NO in S601), The control unit 10 determines the image forming unit 41 (here, the image forming unit 41Y) located on the most upstream side in the running direction of the intermediate transfer belt 421 as the image forming unit 41 that forms the base toner layer P (S603). The control unit 10 terminates the process illustrated in FIG. 6B after S602 or S603.

By the processing by the control unit 10 shown in FIG. 6B, in the image forming apparatus 1, in principle, the image forming unit 41 located upstream of the image forming unit 41 that forms the toner image Q in the running direction of the intermediate transfer belt 421. Therefore, the image forming unit 41 having the developing device 412 containing a large amount of deteriorated toner is determined as the image forming unit 41 forming the base toner layer P. As a result, the toner image Q is transferred onto the intermediate transfer belt 421 while the base toner layer P is transferred. Further, as shown in FIG. 3B, most of the base toner layer P is discarded without being transferred to the paper S, but since the deteriorated toner is preferentially used for forming the base toner layer P, deterioration is caused. It is possible to prevent wasteful consumption of toner that has not been performed.

FIG. 7 is a diagram for explaining the edge effect. As described above, in the image forming apparatus 1, the base toner layer P is formed in the area inside the area where the toner image Q is formed except the edge portion. That is, in the image forming apparatus 1, the base toner layer P is not formed on the edge portion. Therefore, if no measures are taken, the toner image Q directly adheres to the intermediate transfer belt 421 at the edge portion, and the toner image Q is improperly transferred to the sheet S.

Therefore, the control unit 10 controls the developing device 412 so that the area corresponding to the edge portion in the area of the electrostatic latent image formed on the photosensitive drum 413 is larger than the area other than the edge portion. Of toner. In the following, spraying more toner than the area other than the edge portion to the area corresponding to the edge portion in the area of the electrostatic latent image formed on the photosensitive drum 413 is referred to as the edge effect. Further, for convenience of description, the toner sprayed in a larger amount than the area other than the edge portion is referred to as toner R.

As shown in FIG. 7A, in the area excluding the edge portion of the toner image Q, the base toner layer P is formed as the lowermost layer of the toner layer formed on the intermediate transfer belt 421, so that the toner image Q is formed. Does not directly adhere to the intermediate transfer belt 421. Further, at the edge portion of the toner image Q on the intermediate transfer belt 421, the toner R does not cause the toner image Q to directly adhere to the intermediate transfer belt 421. As shown in FIG. 7B, the toner image Q is completely transferred to the paper S by the secondary transfer, and the transfer failure of the toner image Q to the paper S occurs even in the edge portion where the base toner layer P is not formed. Absent.

As shown in FIG. 7, due to the edge effect, even if the base toner layer P is not formed on the edge portion, the toner adhesion amount on the edge portion on the intermediate transfer belt 421 can be increased, and the toner image on the edge portion can be increased. It is possible to prevent the transfer failure of Q onto the sheet S.

As described above, in principle, the image forming apparatus 1 is the image forming unit 41 that is located on the upstream side in the traveling direction of the intermediate transfer belt 421 with respect to the image forming unit 41 that forms the toner image Q, and contains much deteriorated toner. The base toner layer P is formed using the image forming unit 41 having the developing device 412 housed therein. As a result, the base toner layer P is formed on the lowermost layer of the toner layer formed on the intermediate transfer belt 421, and the toner image Q is formed thereon, so that the toner image Q directly adheres to the intermediate transfer belt 421. There is nothing to do. As a result, the adhesive force between the toner image Q and the intermediate transfer belt 421 is alleviated, and the transfer efficiency of the toner image Q onto the paper S is increased, so that an image of good quality is formed. Further, since the image forming apparatus 1 forms the base toner layer P using any of the developing devices 412 that form the toner image Q, it is not necessary to separately provide a developing device for forming the base toner layer P. Further, most of the base toner layer P is discarded without being transferred to the paper S, but since the image forming apparatus 1 preferentially uses the deteriorated toner for forming the base toner layer P, the toner that has not deteriorated is It is possible to prevent wasteful consumption.

In the above description, the image forming apparatus 1 forms the base toner layer P for each color of the toner image. However, the base toner layer P is formed in at least the area of the toner image Q formed by the black toner, and the base toner layer P is formed. The edge effect may be applied to the region where the layer P is not formed. As an example, the image forming apparatus 1 forms the base toner layer P only on the area of the toner image Q formed by the black toner, and the area of the toner image Q formed by the toner other than black is formed on the background. The edge effect may be applied without forming the toner layer P. As shown in FIG. 3B, a part of the base toner layer P may be transferred onto the paper S, but the area where the base toner layer P is formed is a high density area (formed with black toner). Area), so there is almost no effect on the image. Further, as another example, the image forming apparatus 1 forms the base toner layer P on the area formed by the black toner and the area formed by the cyan toner in the toner image Q, and the base toner layer P is formed in the toner image Q. The edge effect may be applied to the area formed by the yellow toner and the area formed by the magenta toner without forming the base toner layer P.

The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

1 image forming apparatus, 10 control unit, 11 CPU, 12 ROM, 13 RAM, 30 image processing unit, 40 image forming unit, 41 image forming unit, 411 exposure device, 412 developing device, 413 photoconductor drum, 414 charging device, 421 Intermediate transfer belt.

Claims (5)

An image forming apparatus for forming an image based on input image data,
A plurality of first image carriers on which toner images of different colors are formed by separating the image data into a plurality of colors;
A second image carrier on which a toner image based on the image data is formed by transferring toner images of different colors formed on the plurality of first image carriers;
A plurality of developing units for forming toner images of different colors on the plurality of first image carriers,
Control means for controlling the plurality of developing means so that a toner layer as a base of the toner image on the second image bearing body is formed on the first image bearing body by any of the plurality of developing means. An image forming apparatus provided. The control unit controls the plurality of developing units so that the toner layer is formed in at least a region of the toner image on the second image carrier that is formed by black toner. Image forming apparatus. Further comprising determination means for determining whether or not the toner contained in each of the plurality of developing means has deteriorated,
The image forming apparatus according to claim 1, wherein the control unit controls so that the toner layer is formed by a developing unit in which the toner contained in the plurality of developing units is deteriorated. . The image forming apparatus according to claim 1, wherein the control unit determines a maximum area of the toner layer based on the image data. The control unit determines the amount of toner used for forming the toner layer based on a transfer efficiency when the toner image is transferred from the second image carrier to a recording medium. The image forming apparatus according to any one of 4 above.

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