JP2016114718A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To curb occurrence of a transfer failure of a toner image to an irregularity sheet in comparison with a case where an amount of electric charging of toner is caused not to decrease when forming an image on the irregularity sheet to which a work causing irregularity to be formed on a surface is performed.SOLUTION: An image formation device comprises: a photoreceptor drum that holds a toner image; a developing unit that has a developing housing that houses toner as a developer and a carrier, and develops a static latent image formed on the photoreceptor drum by means of the toner; a secondary transfer belt that transfers the toner image formed on the photoreceptor drum by the developing unit onto a sheet; a secondary transfer roll and backup roll; and a control device that, when using an irregularity sheet to which a work causing irregularity to be formed on a surface is performed as the sheet, causes an amount of electric charging of toner in the developing housing to be reduced before the toner image to be transferred to the irregularity sheet is formed on the photoreceptor drum by the developing unit.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

Conventionally, after the surface of the photosensitive drum is uniformly charged, an electrostatic latent image is formed by exposure, and the electrostatic latent image is developed by a developing device to form a toner image, and the formed toner image is recorded. There is an image forming apparatus that forms an image on a recording material by transferring and fixing on the material.
In such an image forming apparatus, when an image is formed on a recording material such as embossed paper that has been processed to form unevenness on the surface, toner transfer failure may occur in the concave portion of the recording material. .

  Patent Document 1 discloses a transparent toner formed on an intermediate transfer member with a transparent toner in order to suppress a transfer failure of a colored toner image in a recording material such as embossed paper that has been processed to form irregularities on the surface. A technique for forming a colored toner layer formed of colored toner on the layer is disclosed. Further, it is described that when a toner image formed on an intermediate transfer body is transferred to a sheet, transferability to the sheet is improved because the toner image is easily cut between the transparent toner layer and the colored toner layer. ing.

JP 2009-25713 A

  The present invention suppresses the occurrence of transfer failure of the toner image on the concavo-convex paper when an image is formed on the concavo-convex paper that has been processed to form the concavo-convex surface as compared with the case where the toner charge amount is not reduced. The purpose is to do.

The invention according to claim 1 has an image carrier that holds a toner image, and a container that contains toner and a carrier as developers, and develops the electrostatic latent image formed on the image carrier with toner. When using developing means, transfer means for transferring the toner image formed on the image carrier by the developing means onto a recording material, and uneven paper having a surface formed with unevenness as the recording material And a charge amount adjusting means for reducing the charge amount of the toner in the container before the toner image to be transferred onto the uneven paper is formed on the image carrier by the developing means. is there.
According to a second aspect of the present invention, the charge amount adjusting unit discharges toner stored in the storage container of the developing unit to the image holding member and / or supplies new toner to the storage container. The image forming apparatus according to claim 1, wherein the charge amount of the toner in the container is reduced.
According to a third aspect of the present invention, the charge amount adjusting means reduces the charge amount of the toner in the storage container by increasing the toner concentration in the developer stored in the storage container of the developing means. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus.
The invention according to claim 4 is the image forming apparatus according to any one of claims 1 to 3, wherein the uneven paper is embossed paper.
The invention according to claim 5 is characterized in that the charge amount adjusting means does not decrease the charge amount of the toner in the storage container when the basis weight of the uneven paper is smaller than a predetermined value. 5. The image forming apparatus according to any one of items 1 to 4.
According to a sixth aspect of the present invention, the charge amount adjusting unit is configured to transfer the toner image to be transferred onto the uneven paper to a recording material other than the uneven paper after the toner image is formed on the image carrier by the developing unit. 6. The image according to claim 1, wherein the toner charge amount in the storage container is increased before the toner image is formed on the image holding member by the developing unit. Forming device.
According to a seventh aspect of the present invention, there is provided an image holding body for holding a toner image, and developing means for developing an electrostatic latent image formed on the image holding body with toner to form a toner image on the image holding body. A transfer means for transferring the toner image formed on the image carrier by the developing means onto a recording material, and the developing means is not transferred onto the embossed paper when embossed paper is used as the recording material. A non-transferred toner image is formed on the image carrier, and after the toner is discharged onto the image carrier, a toner image to be formed on embossed paper is formed on the image carrier. An image forming apparatus.

According to the first aspect of the present invention, when an image is formed on a concavo-convex paper that has been processed to form undulations on the surface, the toner image on the concavo-convex paper is less than when the toner charge amount is not reduced. Occurrence of transfer failure can be suppressed.
According to the second aspect of the present invention, the charge amount of the toner in the container can be reduced by the same operation as that at the time of image formation.
According to the third aspect of the invention, the charge amount of the toner in the container can be reduced by the same operation as that at the time of image formation.
According to the invention which concerns on Claim 4, when forming an image on embossed paper, generation | occurrence | production of the density unevenness of the image formed on embossed paper and generation | occurrence | production of color loss can be suppressed.
According to the fifth aspect of the present invention, the toner consumption can be reduced compared to the case where the charge amount of the toner is reduced uniformly regardless of the basis weight of the uneven paper.
According to the sixth aspect of the present invention, it is possible to suppress an increase in image density when an image is formed on a recording material other than the uneven paper after an image is formed on the uneven paper.
According to the seventh aspect of the present invention, when an image is formed on embossed paper, it is possible to suppress the occurrence of toner image transfer failure with respect to the embossed paper, compared to the case where toner is not discharged.

1 is a diagram illustrating an overall configuration of a multifunction machine to which the present embodiment is applied. FIG. 2 is a diagram illustrating a configuration of a developing device, and a cross-sectional view of the developing device. FIG. 5 is a diagram illustrating a relationship between a toner charge amount and a toner transferability grade with respect to embossed paper. 6 is a flowchart of processing performed based on control by a control device when an instruction to form an image on an uneven paper is given. FIG. 5 is a diagram illustrating a relationship between a charge amount of toner before and after the first setup process and a transferability grade of toner onto embossed paper. FIG. 5 is a diagram showing a relationship of toner transferability grades when images are formed on embossed papers having different basis weights in the image forming apparatus. 9 is a flowchart of processing performed based on control by a control device when an instruction to form an image on an uneven paper is given in the second embodiment.

(Embodiment 1)
Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing an overall configuration of a multifunction machine 1 to which the present embodiment is applied. Here, the multi function device 1 shown in FIG. 1 is a copier having a copy function, a scan function, and a print function, and further provided with a facsimile function.

  The multifunction device 1 according to the present embodiment receives an image forming apparatus 2 that forms an image on a sheet as an example of a recording material, an image reading apparatus 3 that reads an image formed on a document, and an operation instruction from a user. An operation receiving device 4 that displays various types of information to the user, and a control device 5 as an example of a charge amount adjusting unit that controls the operation of the multifunction device 1 are provided. In this example, the control device 5 is built in the housing of the image forming apparatus 2.

  The operation reception device 4 includes a display panel 4a configured with a touch panel for displaying information to the user and receiving an operation instruction from the user, and a button group 4b for receiving the operation instruction from the user.

The image forming apparatus 2 is configured by a so-called tandem method using an electrophotographic method, and arranged in parallel at predetermined intervals, yellow (Y), magenta (M), cyan (C), black (K ) Four image forming units 11Y, 11M, 11C, and 11K (also collectively referred to as “image forming unit 11”).
The image forming unit 11 uniformly rotates the surface of the photosensitive drum 12 as an example of an image carrier on which an electrostatic latent image is formed while rotating in the direction of arrow A with a predetermined potential. A charging roll 13 for charging, a print head 14 for exposing the photosensitive drum 12 charged by the charging roll 13 based on image data, and a developing means for developing the electrostatic latent image formed on the photosensitive drum 12. A developing unit 15 is provided as an example. Each of the four image forming units 11Y, 11M, 11C, and 11K has the same configuration except for the toner accommodated in the developing device 15, and each of the image forming units 11 has yellow (Y), Magenta (M), cyan (C), and black (K) toner images are formed. In this example, the toner of each color is negatively charged in the developing unit 15.

  In addition, the image forming apparatus 2 performs intermediate transfer on the intermediate transfer belt 20 onto which the color toner images formed on the photosensitive drums 12 of the image forming units 11 are transferred, and the color toner images on the image forming units 11. And a primary transfer roll 21 that sequentially transfers (primary transfer) to the belt 20. Further, the image forming apparatus 2 includes a secondary transfer unit 30 that collectively transfers (secondary transfer) the superimposed toner image transferred onto the intermediate transfer belt 20 to the paper, and the secondary transferred toner image onto the paper. And a fixing device 40 for fixing the toner to the head. Furthermore, the image forming apparatus 2 includes a belt cleaner 23 that is disposed in contact with the surface of the intermediate transfer belt 20 and removes toner (transfer residual toner) attached to the intermediate transfer belt 20.

  The intermediate transfer belt 20 is composed of a film-like endless belt having conductivity, is stretched by a plurality of rolls including a primary transfer roll 21, and circulates in the direction of arrow B.

The secondary transfer unit 30 includes a secondary transfer roll 31 and a backup roll 32 that face each other with the intermediate transfer belt 20 in between. The secondary transfer roll 31 is pressed with a predetermined pressure against the backup roll 32 via the intermediate transfer belt 20. The secondary transfer unit 30 includes a secondary transfer electric field (secondary transfer bias) formed between the secondary transfer roll 31 and the backup roll 32, and between the secondary transfer roll 31 and the backup roll 32. The toner image held on the intermediate transfer belt 20 is transferred onto the sheet by the formed pressure.
Further, in the secondary transfer unit 30 of the present embodiment, when the first setup process described later is performed, the pressing of the secondary transfer roll 31 against the backup roll 32 is released, and the secondary transfer roll 31 is moved to the intermediate transfer belt 20. It can be separated from.
In the present embodiment, the intermediate transfer belt 20, the secondary transfer roll 31, and the backup roll 32 constitute a transfer unit.

  The fixing device 40 includes a fixing roll 41 having a heating source therein, and a pressure roll 42 arranged in pressure contact with the fixing roll 41. The fixing device 40 fixes the toner image on the paper by passing the paper holding the unfixed toner image between the fixing roll 41 and the pressure roll 42 and performing heating and pressurization. .

In addition, the image forming apparatus 2 includes sheet storage trays 51 to 53 that store a plurality of sheets of different sizes or different paper types, and a feed roll 54 that takes out and conveys the sheets from the respective sheet storage trays 51 to 53. I have. As the types of paper stored in the paper storage trays 51 to 53, irregularities are formed on the surface of paper such as plain paper, embossed paper (embossed paper), Japanese paper, and wrinkled paper. And processed paper (hereinafter sometimes referred to as uneven paper). In the image forming apparatus 2 according to the present embodiment, the type of paper stored in each of the paper storage trays 51 to 53 is set in advance using the operation receiving device 4.
Further, the image forming apparatus 2 removes the sheet taken out from the sheet storage tray 51 by the feed roll 54 from the sheet stacking unit 58 provided outside the image forming apparatus 2 via the secondary transfer unit 30 and the fixing device 40. Is provided with a paper transport path R.

Next, the configuration of the developing device 15 of the present embodiment will be described. FIG. 2 is a diagram illustrating the configuration of the developing device 15, and is a cross-sectional view of the developing device 15.
As shown in FIG. 2, the developing device 15 has an opening facing the photosensitive drum 12, and development as an example of a container in which a two-component developer containing toner and carrier as main components is contained. A housing 151 and a developing roll 152 disposed at a location facing the opening of the developing housing 151 and facing the photosensitive drum 12 are provided. The developing roll 152 incorporates a magnet (not shown) and holds the developer on the surface thereof by magnetic force. Then, a magnetic brush formed by the developer held on the developing roll 152 is brought into contact with the photosensitive drum 12, and the electrostatic latent image on the photosensitive drum 12 is developed with toner.

The developing unit 15 includes a pair of conveying screws 153 a and 153 b provided in the developing housing 151 and along the axial direction of the photosensitive drum 12.
Further, the developing device 15 includes a toner supply device 155 that supplies new toner into the developing housing 151.
Furthermore, the developing device 15 includes a density detection sensor 156 that measures the toner density in the developer accommodated in the development housing 151. The density detection sensor 156 measures the magnetic permeability of the developer, for example. Then, the control device 5 estimates the toner concentration in the developer based on the magnetic permeability of the developer measured by the density detection sensor 156.

  In the developing device 15 of the present embodiment, the developer contained in the developing housing 151 is agitated by the conveying screws 153a and 153b, so that the toner and the carrier are rubbed, and the toner is charged negatively. It has become.

Further, in the image forming apparatus 2 of the present embodiment, the control device 5 identifies the toner density in the developing housing 151 based on the detection result by the density detection sensor 156. Then, new toner is supplied into the developing housing 151 by the toner supply device 155 under the control of the control device 5 so that the toner density in the developing housing 151 becomes a predetermined target value.
In this example, when an image is formed on paper (plain paper) other than uneven paper as the paper, the first density value is set as the target value of toner density. Although details will be described later, when an image is formed on uneven paper, a second density value that is higher than the first density value is set as a target value for the toner density.

In the image forming apparatus 2, an image forming operation is performed under the control of the control device 5. That is, when a color image is formed, print job data input from the image reading device 3 or PC (not shown) is subjected to predetermined image processing by the control device 5 and printed for each color. Sent to the head 14. In the black (K) image forming unit 11K, for example, the surface of the photosensitive drum 12 uniformly charged at a predetermined potential by the charging roll 13 is based on K color image data subjected to image processing. Then, the print head 14 exposes and an electrostatic latent image is formed on the photosensitive drum 12. The formed electrostatic latent image is developed by the developing device 15, and a black (K) toner image is formed on the photosensitive drum 12. Similarly, in the image forming units 11Y, 11M, and 11C, yellow (Y), magenta (M), and cyan (C) toner images are formed.
When forming a monochrome image, a black (K) toner image is formed only in the black (K) image forming unit 11K.

  Each color toner image formed by each image forming unit 11 is transferred onto the intermediate transfer belt 20 that circulates in the direction of arrow B from a power supply device (not shown) as a high-voltage primary transfer power source. Electrostatic transfer is sequentially performed by each primary transfer roll 21 to which a voltage is applied, and a superimposed toner image on which the respective color toner images are superimposed is formed on the intermediate transfer belt 20. The superimposed toner image is conveyed toward the secondary transfer unit 30 as the intermediate transfer belt 20 moves.

  In addition, as each color toner image is formed in the image forming unit 11, the paper stored in the paper storage trays 51 to 53 is taken out by the feed roll 54. Then, the sheet is conveyed to the secondary transfer unit 30 by a plurality of conveyance rolls (not shown) in accordance with the timing when each color toner image on the intermediate transfer belt 20 moves to the secondary transfer unit 30. Further, a predetermined secondary transfer bias voltage is applied to the secondary transfer unit 30 from a power supply device (not shown) as a high-voltage secondary transfer power supply. As a result, the toner images of the respective colors are collectively electrostatically transferred (secondary transfer) onto the paper by the action of the transfer electric field formed by the secondary transfer roll 31 and the backup roll 32.

Thereafter, the sheet on which the superimposed toner image is electrostatically transferred is peeled off from the intermediate transfer belt 20 and conveyed to the fixing device 40. The unfixed toner image on the paper conveyed to the fixing device 40 is fixed on the paper by being subjected to a fixing process by heating and pressing by the fixing device 40. Then, the sheet on which the image is formed is discharged to the sheet stacking unit 58 of the image forming apparatus 2.
Note that toner (transfer residual toner) adhering to the intermediate transfer belt 20 after the secondary transfer is removed by a belt cleaner 23 disposed in contact with the intermediate transfer belt 20, and the next image forming operation (image forming cycle). ).

As described above, in the image forming apparatus 2 of the present embodiment, as a sheet, in addition to plain paper, a sheet having large irregularities formed on the surface compared to plain paper and processed to form irregularities on the surface. An image can be formed on (uneven paper). Examples of the uneven paper include embossed paper, Japanese paper, and wrinkled paper.
Here, in the present embodiment, when the paper is set in the paper storage trays 51 to 53 of the image forming apparatus 2, for example, the operation receiving device 4 is used to set the paper type (paper type). That is, when the sheets are stored in the sheet storage trays 51 to 53, a selection screen for selecting the sheet type is displayed on the display panel 4a of the operation reception device 4. Then, when the user operates the selection screen or the button group 4b displayed on the display panel 4a, the type of paper stored in the paper storage trays 51 to 53 is selected. The selected paper type is stored in the control device 5 in association with each of the paper storage trays 51 to 53. In addition, when an instruction to form an image is issued in the image forming apparatus 2, a sheet of a paper type that is an object of image formation is stored in any of the sheet storage trays 51 to 53 based on control by the control apparatus 5. Is selected from the paper to be transferred and conveyed to the secondary transfer unit 30.

  Note that a sensor (not shown) that detects the paper type may be provided in the image forming apparatus 2, and the paper type may be determined and automatically set according to the detection result of the sensor. Examples of such a sensor include an ultrasonic sensor that detects the surface state of a sheet.

By the way, in general, when an image is formed on uneven paper such as embossed paper, there is a possibility that defects such as uneven density and color loss may occur in the image formed on the surface of the uneven paper.
More specifically, as described above, in the image forming apparatus 2, the secondary transfer unit 30 collectively transfers the superimposed toner formed on the intermediate transfer belt 20 onto a sheet. In the concavo-convex paper in which the concave portion and the convex portion are formed on the surface of the paper, the transfer electric field hardly acts on the concave portion as compared with the convex portion. For this reason, in the concavo-convex paper, a sufficient amount of toner is not transferred in the concave portion as compared with the convex portion, and as a result, the image density may be lowered or color loss may occur in the concave portion.

On the other hand, the present inventors have found that the transferability of the toner to the embossed paper is improved by adjusting the charge amount of the toner.
FIG. 3 is a graph showing the relationship between the toner charge amount (μC / g) and the toner transferability grade on the embossed paper. Specifically, the charge amount (μC / toner) per unit mass of the toner when the image forming apparatus 2 performs an operation of forming an image on embossed paper (Resac 66, 203 gsm manufactured by Tokai Paper Co., Ltd.). It shows the relationship between g) and the transferability grade for embossed paper.

In this example, evaluation was made on the transferability grade for embossed paper when using magenta (M), cyan (C) and black (K) toners.
Here, the determination of the transferability grade is performed based on the following criteria when the image after secondary transfer by the secondary transfer unit 30 and fixing by the fixing device 40 is visually confirmed.
1: In the recesses of the embossed paper, there is a gap in the image area of 10% or less, or there is no gap in the recesses of the embossed paper.
2: In the concave portion of the embossed paper, there is a gap when the image area is 30% or less.
3: In the concave portion of the embossed paper, there is a gap when the image area is 50% or less.
4: In the concave portion of the embossed paper, there is a gap when the image area is larger than 50%.
Note that “missing” in the concave portion of the embossed paper means a region where toner is not transferred in the concave portion.

As shown in FIG. 3, in each of magenta (M), cyan (C), and black (K) toners, the toner charge amount (μC / g) is reduced, so that the transferability (transferability) to embossed paper is reduced. Grade) was confirmed to be good.
More specifically, in the example shown in FIG. 3, it was confirmed that when the toner charge amount is less than 30 μC / g, the transferability grade for the embossed paper is improved.

  Therefore, in the image forming apparatus 2 according to the present embodiment, when an instruction to form an image is provided on uneven paper such as embossed paper, the charge amount of the toner is reduced in advance before forming an image on the uneven paper. Processing is in progress. This suppresses a decrease in transferability of toner to uneven paper such as embossed paper, and suppresses uneven density and color loss in an image formed on the uneven paper.

FIG. 4 is a flowchart of processing performed based on control by the control device 5 when an instruction to form an image on the uneven paper is given.
As shown in FIG. 4, the control device 5 first accepts an instruction to execute a new image forming process via the operation accepting device 4 or a PC (not shown) (step 101). Here, when receiving an instruction for image forming processing, the control device 5 also acquires information on the type of paper (paper type) on which an image is formed, the number of images formed, the type of image to be formed, and the like.
Next, based on the information regarding the paper type (paper type) acquired in step 101, the control device 5 determines whether or not the paper type (paper type) to be subjected to image formation corresponds to the uneven paper. Judgment is made (step 102).

When the type of paper (paper type) that is the object of image formation is uneven paper (YES in step 102), the control device 5 reduces the charge amount of toner stored in the developing housing 151 of the developing device 15. Processing (first setup processing) is performed (step 103). Note that when performing the setup process, the image forming operation on the paper (uneven paper) is temporarily stopped, and the conveyance of the uneven paper to the secondary transfer unit 30 is also stopped.
Subsequently, after the first setup process in step 103 is completed, the control device 5 starts an image forming operation on the uneven paper (step 104), and ends a series of processes.

The first setup process in step 103 is performed in the following procedure based on the control by the control device 5.
First, the secondary transfer roll 31 is separated from the intermediate transfer belt 20 (step 103-1).
Subsequently, in the image forming unit 11, a discharge toner image forming operation for discharging the toner from the developing housing 151 is performed (step 103-2). Specifically, a discharged toner image is formed on the photosensitive drum 12 in the image forming unit 11 by a process similar to the normal image forming operation described above. The discharged toner images formed on the photosensitive drum 12 are sequentially transferred onto the intermediate transfer belt 20 by the primary transfer roll 21.

As the discharged toner image, it is preferable to form a high-density image in the entire image area where each image forming unit 11 can form an image from the viewpoint of quickly discharging the toner in the developing housing 151. In this example, as the discharged toner image, the image forming unit 11 forms a solid image in the entire image area.
In this way, by forming a discharge toner image in each image forming unit 11, toner is discharged (discharged) from the developing housing 151 of the developing device 15 in each image forming unit 11 onto the photosensitive drum 12. ).

  The discharged toner image transferred onto the intermediate transfer belt 20 passes through the secondary transfer portion 30 where the secondary transfer roll 31 is separated without being transferred onto the paper. Then, it is removed from the intermediate transfer belt 20 by the belt cleaner 23.

  Further, in the first setup process, new toner is supplied into the developing housing 151 by the toner supply device 155 in each developing unit 15 along with the formation of the discharged toner image (step 103-3).

Here, as described above, in the developing device 15, the toner and the carrier in the developer are stirred and conveyed by the conveying screws 153a and 153b in the developing housing 151, and the toner and the carrier are rubbed to charge the toner. Yes.
Therefore, the toner newly supplied into the developing housing 151 by the toner supplying device 155 has a lower charge amount than the toner already stored in the developing housing 151.
Therefore, in the first setup process of the present embodiment, toner having a high charge amount is discharged from the developing housing 151 by forming discharged toner, and new toner having a low charge amount is discharged from the developing housing 151 by the toner supply device 155. As a result, the charge amount of the toner accommodated in the developing housing 151 is reduced as compared with that before the first setup process is executed.

Further, in the first setup process, the control device 5 performs a process for changing the target value of the toner density in the developing device 15 (step 103-4). Specifically, the toner density target value is set to a second density value higher than the first density value from the first density value set when a sheet other than the uneven paper is selected as the image formation target sheet. Processing to change to is performed.
As a result, new toner is continuously supplied to the developing housing 151 of the developing device 15 by the toner supply device 155, so that the charge amount of the toner accommodated in the developing housing 151 is the same as that before executing the first setup process. Compared to a low state.
Thereafter, the secondary transfer roll 31 is pressed against the backup roll 32 via the intermediate transfer belt 20 (step 103-5), and the first setup process is terminated.

In the first setup process, when the type of image acquired in step 101 is a color image, in each of the image forming units 11Y, 11M, 11C, and 11K, a discharge toner image forming operation and a developing housing are performed. The operation of supplying toner to 151 and the process of changing the target value of toner density are performed.
On the other hand, when the type of image acquired in step 101 is a monochrome image, in the black (K) image forming unit 11K, the discharged toner image forming operation, the toner supplying operation to the developing housing 151, and the toner density The target value is changed. In this case, in the yellow (Y), magenta (M), and cyan (C) image forming units 11Y, 11M, and 11C, the discharge toner image forming operation, the toner supply operation to the developing housing 151, and the target value of the toner density No change processing is performed.

  As described above, in the image forming apparatus 2 according to the present embodiment, when an instruction to form an image on an uneven paper such as an embossed paper is given, the first setup process for reducing the charge amount of the toner is performed in advance. Yes. As a result, when the toner image held on the intermediate transfer belt 20 is transferred to the concavo-convex paper in the secondary transfer unit 30, the concave portion of the concavo-convex paper is compared with the case where the first setup process is not performed. On the other hand, the toner is easily transferred. As a result, compared to the case where the first setup process is not performed, in the image formed on the concavo-convex paper, the occurrence of image density reduction and color loss in the concave portion is suppressed.

FIG. 5 is a diagram illustrating the relationship between the toner charge amount before and after the first setup process and the transferability grade of the toner onto the embossed paper. In FIG. 5, in the image forming apparatus 2, magenta with respect to embossed paper (Resak 66, 203 gsm manufactured by Tokushu Tokai Paper Co., Ltd.) before and after the first setup process. The transferability grade is shown when an operation of forming an image using toners of (M), cyan (C), and black (K) is performed. As the first setup process, in the magenta (M), cyan (C), and black (K) image forming units 11M, 11C, and 11K, 300 A4 size full-scale images are formed as discharged toner images at 60% Cin. And the operation of replenishing new toner in the developing housing 151 were performed. The size of the secondary transfer bias supplied to the secondary transfer unit 30 was 3500V.
The criteria for judging the transferability grade in FIG. 5 are the same as in the example shown in FIG.

  As shown in FIG. 5, it was confirmed that the toner charge amount decreased for each of magenta (M), cyan (C), and black (K) by performing the first setup process. Further, as shown in FIG. 5, by performing the first setup process, the transferability (transferability grade) of the toner to the embossed paper is good for each of magenta (M), cyan (C), and black (K). It was confirmed that

Here, at the end of the image forming operation on the concavo-convex paper, the charge amount of the toner in the developing housing 151 is lower than that before the first setup process. For this reason, after the image forming operation on the concavo-convex paper is completed, when an image is subsequently formed on a paper other than the concavo-convex paper such as plain paper, the toner is easily transferred to the paper in the secondary transfer unit 30. There is a possibility that the image density formed in the above becomes higher than usual.
In order to suppress such a problem, when an instruction to form an image on a sheet (plain paper) other than the concavo-convex sheet is given after the image forming operation is performed on the concavo-convex sheet, the control by the control device 5 is performed. Based on this, a second setup process for increasing the charge amount of the toner may be performed. By performing the second setup process and returning the charge amount of the toner to the state before the first setup process, an image forming operation is performed on the uneven paper, and then an image is formed on a sheet other than the uneven paper. In this case, an increase in image density is suppressed.

The second setup process is performed by the following procedure, for example. First, similarly to the first setup process, the secondary transfer roll 31 is separated from the intermediate transfer belt 20 based on the control by the control device 5.
Subsequently, in the developing devices 15 of the respective image forming units 11, the supply amount of new toner to the developing housing 151 by the toner supply device 155 is reduced or the supply is stopped. Further, each image forming unit 11 forms a discharged toner image in the same manner as in the first setup process.
Furthermore, the control device 5 performs processing for changing the target value of the toner density in the developing device 15 from the second density value to the first density value lower than the second density value.

As a result, the toner density in the developing device 15 is lowered and charging due to the friction between the toner and the carrier is promoted. The toner charge amount in the housing 151 increases.
As a result, when the first setup process is executed and an image is formed on the uneven paper, and then an image is formed on a paper (plain paper) other than the uneven paper, an increase in image density is suppressed.

  In this embodiment, when an instruction to form a color image is given to the uneven paper, the first setup process is executed in all the image forming units 11Y, 11M, 11C, and 11K. The first setup process is performed for the image forming unit 11 of a color (for example, yellow (Y)) in which the density unevenness on the uneven paper is not conspicuous due to the type of color image (photograph, graph, etc.), color image hue, image density, etc. It does not have to be. For example, when an instruction to form a color image is given to the uneven paper, the first setup process is performed only in the magenta (M), cyan (C), and black (K) image forming units 11M, 11C, and 11K. The yellow (Y) image forming unit 11Y may be configured not to perform the first setup process.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.
In the first embodiment described above, when an instruction for image formation is given to an uneven paper such as an embossed paper, the first set-up process is uniformly performed to reduce the charge amount of the toner, so that the transfer property to the uneven paper is reduced. It was set as the structure which suppresses the fall of this. However, although the first set-up process is effective for suppressing a decrease in transferability with respect to the uneven paper, it is preferable to perform it excessively from the viewpoint of resource saving because the toner is consumed by forming the discharged toner image. Absent.

  Even when an image is formed on the uneven paper, the first setup process is not necessarily performed depending on the basis weight (thickness) of the uneven paper, the type of the uneven paper, the type of the image formed on the uneven paper, and the like. It may not be necessary. For example, when the basis weight of the concavo-convex paper is low, the transfer electric field is more likely to act in the concave portion than in the case where the basal weight of the concavo-convex paper is high.

FIG. 6 is a diagram showing the relationship of toner transferability grades when images are formed on embossed paper having different basis weights in the image forming apparatus 2. In FIG. 6, in the image forming apparatus 2, embossed paper having different basis weights (Rezac 66, 151 gsm made by Tokushu Tokai Paper Co., Ltd.) before and after the first setup process are performed. The transferability grade is shown when an image forming operation is performed using black (K) toner with respect to (204 gsm, 250 gsm).
As the first set-up processing, in the black (K) image forming unit 11K, an operation is performed to form 300 A4 size full-scale images as discharged toner images at 60% Cin, and new toner is supplied into the developing housing 151. The operation to be performed. The size of the secondary transfer bias supplied to the secondary transfer unit 30 was 3500V. Further, in the developing device 15, the charge amount of the toner before the first setup process was 33.9 μC / g, and the charge amount of the toner after the first setup process was 29.1 μC / g.

  As shown in FIG. 6, when the basis weight of the embossed paper is 204 gsm and 250 gsm, the transferability grade to the concavo-convex paper is higher by performing the first setup process than before performing the first setup process. It was confirmed to be good. More specifically, when the basis weight of the embossed paper is 204 gsm, the transferability grade is 3 before performing the first setup process, whereas the transferability is obtained by performing the first setup process. It was confirmed that the grade was 1. When the basis weight of the embossed paper is 250 gsm, the transferability grade is 4 before the first setup process, whereas the transferability grade becomes 1 by performing the first setup process. It was confirmed.

  On the other hand, when the basis weight of the embossed paper is 151 gsm, the transferability grade is 1 both before the first setup process and after the first setup process, and the first setup process is not performed. Even in this case, it was confirmed that the transferability to the embossed paper hardly changed.

  Therefore, in the second embodiment, when an instruction to form an image is made on the uneven paper, if the basis weight of the uneven paper is equal to or more than a predetermined basis weight, the first setup process is performed, and the uneven paper When the basis weight is less than a predetermined basis weight, the first setup process is not performed. As a result, when an instruction to form an image on the concavo-convex paper is given, the consumption of toner due to the formation of the discharged toner image is suppressed as compared with the case where the first setup process is uniformly performed.

FIG. 7 is a flowchart of processing performed based on control by the control device 5 when an instruction to form an image on the uneven paper is given in the second embodiment.
As shown in FIG. 7, the control device 5 first receives an instruction to execute a new image forming process via the operation receiving device 4 or a PC (not shown) (step 201). Here, when receiving an instruction for image formation processing, the control device 5 also acquires information on the type of paper (paper type) on which an image is formed, the basis weight of the paper, the number of images to be formed, the type of image to be formed, and the like. To do.
Next, based on the information regarding the paper type (paper type) acquired in step 201, the control device 5 determines whether or not the paper type (paper type) to be subjected to image formation corresponds to the uneven paper. Judgment is made (step 202).

When the type of paper (paper type) to be image-formed is uneven paper (YES in step 202), the control device 5 determines whether the uneven paper is based on the information on the basis weight of the paper acquired in step 201. It is determined whether or not the basis weight Q is equal to or greater than a predetermined basis weight Q1 (step 203).
When the basis weight Q of the concavo-convex paper is equal to or larger than the predetermined basis weight Q1 (YES in Step 203), the control device 5 is the first for reducing the charge amount of the toner accommodated in the developing housing 151 of the developing device 15. Setup processing is performed (step 204). The contents of the first setup process are the same as those described in step 103 of the first embodiment.

Subsequently, after the first setup process in step 204 is completed, the control device 5 starts an image forming operation on the uneven paper (step 205) and ends the series of processes.
On the other hand, when the paper type (paper type) to be image-formed is a paper other than the uneven paper (NO in step 202), the basic weight Q of the uneven paper is less than a predetermined basic weight Q1 (step) If NO in 203, the image forming operation is started without performing the first setup process (step 205), and the series of processes is terminated.

As described above, according to the present embodiment, when an instruction to form an image is given to an uneven paper such as embossed paper, the first setup process is not performed uniformly, but according to the basis weight of the uneven paper. Thus, it is determined whether or not to perform the first setup process.
As a result, for example, on uneven paper with a large basis weight in which uneven density and the like are likely to occur, by performing the first setup process before the image forming operation, the occurrence of uneven density and color loss in the formed image is suppressed. On the other hand, for uneven paper with a small basis weight that is less likely to cause uneven density or color loss, toner consumption is suppressed by not performing the first setup process. Also, by not performing the first setup process, the period from when an instruction to form an image to the concavo-convex paper is made until the image is actually formed is shortened.

In the example shown in FIG. 7, it is determined whether or not the first setup process is performed according to the basis weight of the uneven paper. However, in the present embodiment, the criterion for determining whether or not to perform the first setup process is not limited to this.
For example, when the size of the unevenness on the uneven paper (depth of the recess) exceeds a predetermined size, the first setup process is performed, and when the size of the unevenness is less than the predetermined size, One setup process may not be performed.

In general, when an image having a high image density is formed, a large amount of toner in the developing housing 151 is consumed in the developing device 15 of each image forming unit 11, and a new toner is supplied into the developing housing 151 by the toner supply device 155. A lot of new toner is supplied.
For this reason, when an image forming operation for forming an image having a high image density is performed, the charge amount of the toner in the developing housing 151 tends to be low in each image forming unit 11. In this case, even when an image is formed on a concavo-convex paper, uneven image density and color loss due to poor transfer of toner hardly occur.

Therefore, in this embodiment, an image forming operation for forming an image having a low image density (for example, an image having an image density of 20% or less when the paper is A4 size) is performed before the image formation on the uneven paper. In this case, the first setup process is performed, and an image forming operation for forming an image having a high image density (for example, an image having an image density higher than 20% when the paper is A4 size) is performed before the image formation on the uneven paper. When the above is performed, the first setup process may not be performed.
In this case, the amount of toner consumption is suppressed as compared with the case where the first setup process is uniformly performed when an image is formed on uneven paper.

By the way, as another method for suppressing a decrease in transferability of toner to uneven paper such as embossed paper, the pressure (nip pressure) between the secondary transfer roll 31 and the backup roll 32 in the secondary transfer unit 30. Is higher than the case where the toner image is secondarily transferred to paper other than the uneven paper (plain paper).
However, even when the nip pressure between the secondary transfer roll 31 and the backup roll 32 is increased when the toner image is secondarily transferred to the uneven paper, the uneven paper In some cases, the transferability of the toner to the concave portion of the toner becomes insufficient.

  In addition, when the nip pressure between the secondary transfer roll 31 and the backup roll 32 is excessively increased in order to improve the transferability of the toner to the recesses of the uneven paper, depending on the type of image formed on the uneven paper, Color loss may occur in the toner image transferred to the uneven paper. More specifically, when the nip pressure between the secondary transfer roll 31 and the backup roll 32 is excessively high, the pressure applied to the toner is increased, for example, in the convex part of the uneven paper or the part where the toner overlaps in the image. May be excessive. In this case, in the secondary transfer unit 30, the toner is mechanically crushed and solidified by pressure, and an area where the toner image is not transferred from the intermediate transfer belt 20 to the uneven paper is formed. As a result, color loss may occur in the image formed on the uneven paper.

Furthermore, as another method for suppressing a decrease in transferability of toner to the uneven paper, a method of using a secondary transfer bias applied to the secondary transfer unit 30 as a superimposed bias in which an AC voltage is superimposed on a DC voltage is used. Can be mentioned. In this method, the toner held on the intermediate transfer belt 20 is vibrated to improve the transferability of the toner to the recesses of the uneven paper.
However, even when the secondary transfer bias is a superimposed bias of a DC voltage and an AC voltage, depending on the uneven paper or the type of image, the transferability of toner to the concave portion of the uneven paper may be insufficient. is there.

On the other hand, when the instruction to form an image on the concavo-convex paper is given as in the present embodiment, the basis weight of the concavo-convex paper is reduced by performing the first setup process for reducing the toner charge amount, for example. Even when the toner is difficult to be transferred to the concave portion of the concavo-convex paper, such as when it is large, the transferability of the toner to the concave portion of the concavo-convex paper is suppressed. This suppresses the occurrence of uneven density and color loss in the image formed on the uneven paper.
Furthermore, in the present embodiment, unlike the method of increasing the nip pressure in the secondary transfer unit 30, it is not necessary to apply excessive pressure to the toner in the secondary transfer unit 30. For this reason, the present embodiment is more effectively used when forming a line image or the like on an uneven paper that is liable to cause color loss due to toner solidifying at a portion where a plurality of lines intersect.

Note that the nip pressure in the secondary transfer unit 30 described above is required when the toner transfer property to the concavo-convex paper needs to be further improved, for example, depending on the type and basis weight of the concavo-convex paper or the type of image formed on the concavo-convex paper. The operation of increasing the image quality, or the operation of supplying the superimposed bias as the secondary transfer bias to the secondary transfer unit 30 may be performed together with the first setup process.
In this case, the transferability of the toner to the concave portion of the uneven paper is further suppressed, and the density unevenness and color loss of the image formed on the uneven paper are further suppressed.

DESCRIPTION OF SYMBOLS 1 ... MFP, 2 ... Image forming apparatus, 4 ... Operation reception apparatus, 5 ... Control apparatus, 11 ... Image forming unit, 12 ... Photosensitive drum, 15 ... Developing device, 20 ... Intermediate transfer belt, 30 ... Secondary transfer , 31 ... secondary transfer roll, 32 ... backup roll, 151 ... developing housing, 155 ... toner supply device

Claims (7)

An image carrier for holding a toner image;
A developing unit having a storage container for storing toner and a carrier as a developer, and developing the electrostatic latent image formed on the image carrier with toner;
Transfer means for transferring a toner image formed on the image carrier by the developing means onto a recording material;
When using a concavo-convex paper that has been processed to form irregularities on the surface as a recording material, before the toner image to be transferred to the concavo-convex paper is formed on the image carrier by the developing means, the container An image forming apparatus comprising: a charge amount adjusting unit that reduces a charge amount of toner in the toner.   The charge amount adjusting unit discharges the toner stored in the storage container of the developing unit to the image holding member and / or supplies new toner to the storage container, whereby the toner in the storage container The image forming apparatus according to claim 1, wherein the charge amount of the image forming apparatus is reduced.   3. The charge amount adjusting unit reduces the charge amount of toner in the storage container by increasing the toner concentration in the developer stored in the storage container of the developing unit. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the uneven paper is embossed paper.   5. The charge amount adjustment unit according to claim 1, wherein the charge amount of the toner in the storage container is not reduced when the basis weight of the uneven paper is smaller than a predetermined value. 6. The image forming apparatus described.   The charge amount adjusting means is configured such that after the toner image to be transferred to the uneven paper is formed on the image carrier by the developing means, the toner image to be transferred to a recording material other than the uneven paper is The image forming apparatus according to claim 1, wherein a charge amount of toner in the storage container is increased before being formed on the image holding member. An image carrier for holding a toner image;
Developing means for developing the electrostatic latent image formed on the image carrier with toner to form a toner image on the image carrier;
Transfer means for transferring a toner image formed on the image carrier by the developing means onto a recording material,
In the case where embossed paper is used as the recording material, the developing means forms a non-transferred toner image that is not transferred onto the embossed paper by discharging toner on the image carrier, An image forming apparatus, wherein a toner image for forming is formed on the image carrier.

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