JP2006251717A - Image forming method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which suppresses poor transfer and maintains cleaning property to an image carrier successful. <P>SOLUTION: When a color toner image 4a is transferred to a recording material 2 via an intermediate transfer body 1, an image forming method comprises: a transparent image formation process for forming a transparent toner image 3a on the lowermost layer on the intermediate transfer body 1 using transparent toner with a shape factor of ≤125; a color image formation process for forming the color toner image 4a on the transparent toner image 3a on the intermediate transfer body 1 using color toner with the shape factor exceeding 125; and a lump transfer process for transferring the transparent toner image 3a and the color toner image 4a from the intermediate transfer body 1 to the recording material 2 in block. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and apparatus used in an electrophotographic copying machine or a laser printer using an intermediate transfer member, and more specifically, formed on an image carrier such as a photosensitive drum via an intermediate transfer member. The present invention relates to an image forming method of transferring a toner image to a recording medium such as paper and an improvement of the apparatus.

  Conventionally, as an example of an image forming apparatus employing an intermediate transfer method as an image forming apparatus such as a printer or a copying machine using an electrophotographic method, for example, an image forming unit of each color component of yellow, magenta, cyan and black is used. The electrophotographic devices for charging, exposing, developing, transferring, and cleaning are arranged around each photoconductive drum, and the intermediate transfer belt or other intermediate transfer belt is provided on the photoconductive drum at the transfer bias arrangement site. The toner image is formed on the photosensitive drum, and the toner image is sequentially transferred to the intermediate transfer member by electrostatic action at the primary transfer position between the photosensitive drum and the intermediate transfer member ( (Primary transfer), and then, at the secondary transfer position, the toner image on the intermediate transfer member is collectively transferred (secondary transfer) to the recording material, and a color image is formed on the recording material by electrostatic action. There are things was Unishi.

JP 2002-236392 A (Embodiment of the Invention, FIG. 2 and FIG. 8) JP 2003-162125 A (Embodiment of the Invention, FIG. 1 and FIG. 2)

However, in this type of color toner image forming apparatus, in a transfer nip region where a color toner image is transferred from an intermediate transfer member to a recording material, a local area consisting of a groove of embossed paper as a recording material or adhesion of foreign matter on the intermediate transfer member. There was a technical problem in that when there was a general gap, white transfer failure occurred. This is presumably due to the fact that the transfer distance increases due to the local gap, and the transfer electric field is lowered and the discharge occurs.
As a solution to such a technical problem, a method for improving the transfer efficiency can be considered.
As a prior art of this type, it is known that, for example, spherical toner is used as a color toner, and the toner adhesion force of the spherical toner to the intermediate transfer member is reduced, thereby obtaining good transferability. However, the spherical toner is easily affected by a slight electric field such as electric discharge during primary transfer and secondary transfer due to a reduction in adhesion to the intermediate transfer member, and image quality defects such as toner scattering and dot disturbance are likely to occur.
Further, when forming a color toner image in each image forming unit, residual toner on the photosensitive drum is cleaned by a cleaner. At this time, for example, when the simplest blade cleaning method is employed as the cleaner, there is a problem that spherical toner having a small particle diameter cannot be collected and cleaning is liable to occur. In this case, it is conceivable to improve the cleaning property by increasing the pressing force of the blade, but this is not preferable from the viewpoint of reducing wear on the surface of the photosensitive drum. Therefore, other methods, such as a method that employs an electrostatic adsorption brush cleaning method, can be considered, but good cleaning performance can be obtained without damaging the surface of the photosensitive drum, but the structure is complicated. In addition, there is a problem that the apparatus is increased in size and cost. In particular, in so-called tandem image forming apparatuses, the cleaner for each photosensitive drum is required to be downsized, and therefore it is necessary to employ a blade cleaning method with low reliability and low maintainability. It is.

Further, as a technique for increasing the transfer efficiency, a technique of forming a spherical or non-spherical transparent toner image on the lowermost layer of the intermediate transfer member and forming a spherical color toner image on the transparent toner image (see Patent Documents 1 and 2). ) Has been proposed. Certainly, by interposing a transparent toner image, it is possible to improve the releasability itself of the color toner images in the second and subsequent layers and to improve the secondary transfer efficiency.
However, as long as the spherical color toner is used, the above-mentioned problems (image quality defects such as toner scattering and cleaning defects) cannot be solved.

In the prior art described in Patent Document 2, the difference between the transparent toner and the color toner is only focused on the colorant, and for each toner, it is possible to use a non-spherical toner instead of the spherical toner. This is disclosed.
However, when a non-spherical toner is used for both the transparent toner and the color toner, the high adhesion force of the non-spherical toner increases the adhesion force between the toners. When the color toner and the transparent toner adhere firmly, the releasability of the color toner image is lowered, and there is a possibility that the transferability and the image disturbance accompanying this are deteriorated.

  The present invention has been made to solve the above technical problem, and in the transfer nip region between the intermediate transfer member and the recording material, the groove of the embossed paper as the recording material or on the intermediate transfer member. It is an object of the present invention to provide an image forming apparatus that suppresses the occurrence of white-out transfer failure due to local voids formed by adhesion of foreign matter and the like, and that maintains good cleaning performance for an image carrier.

  That is, according to the present invention, as shown in FIG. 1, when transferring the color toner image 4a to the recording material 2 through the intermediate transfer body 1, the transparent toner having a shape factor of 125 or less is used on the intermediate transfer body 1. A transparent image forming step for forming the transparent toner image 3a in the lowermost layer, and a color image forming for forming the color toner image 4a on the transparent toner image 3a on the intermediate transfer body 1 using a color toner having a shape factor exceeding 125. And a batch transfer step of batch-transferring the transparent toner image 3a and the color toner image 4a from the intermediate transfer member 1 onto the recording material 2.

In such technical means, the application range of the image forming method of the present invention may be appropriately selected as long as the toner image is visualized, and widely includes an electrophotographic method and an electrostatic recording method.
Further, the intermediate transfer member 1 may be either elastic or rigid, and may be appropriately selected such as a belt shape or a drum shape.
Furthermore, the transparent toner supply method in the transparent image forming step may be a method in which a developing roll or the like is directly pressed against the surface of the intermediate transfer body 1 and a supply method by an image forming engine (fifth engine). It may be.
In addition, the transfer rate of the color toner is improved by using the transparent toner. In particular, by forming a transparent toner image having a shape factor of 125 or less on the lowermost layer of the intermediate transfer member 1, the intermediate transfer member 1 and the lowermost layer are formed. The contact area with the transparent toner is reduced, and the adhesion force can be reduced.
Furthermore, the color toner having a shape factor of more than 125 formed on the transparent toner image has a high adhesion factor because of the high shape factor, and the color toners adhere firmly to each other, so that the transfer can be performed without separation. Characteristics can be obtained, and image defects can be suppressed.
Furthermore, the use of a color toner having a shape factor exceeding 125 makes it possible to maintain good blade cleaning properties for the image carrier.

  Further, as an apparatus invention that embodies the above-described method invention, an image forming apparatus that transfers a color toner image 4a to a recording material 2 via an intermediate transfer body 1 is provided opposite to the intermediate transfer body 1 and has a shape. A transparent image forming unit 3 for forming a transparent toner image 3a in the lowermost layer on the intermediate transfer member 1 using a transparent toner having a coefficient of 125 or less, and the intermediate transfer member 1 are provided opposite to each other, and the shape factor exceeds 125. A color image forming unit 4 for forming a color toner image 4a on the transparent toner image 3a using color toner, and the transparent toner image 3a and the color toner image 4a are collectively transferred from the intermediate transfer member 1 to the recording material 2. The one provided with the batch transfer means 6 is mentioned.

  Further, the transparent image forming unit 3 is preferably provided separately from the color image forming unit 4 or partially used as the color image forming unit 4, for example, a tandem engine or a multi-cycle engine, and may be appropriately selected.

Further, in such an image forming apparatus, the transparent image forming unit 3 and the color image forming unit 4 are configured to be operable and selectable by the mode selecting means 7, and the mode selecting means 7 is normally operated only for the color image forming unit 4. The mode and the special mode in which the transparent image forming unit 3 is operated together with the color image forming unit 4 are switched.
In this case, the normal mode in which the transparent toner is not used is used for the recording material 2 having a smooth surface such as plain paper, while the transparent toner is used for the recording material 2 having an uneven surface such as embossed paper. By switching to the special mode, useless use of the transparent toner can be prevented.

Here, the color image forming unit 4 has a primary transfer portion 5 to which the color toner image 4a can be electrostatically transferred on the intermediate transfer body 1, and a transfer bias applied to the primary transfer portion 5 in the special mode is set in the normal mode. It is preferable to set a smaller value.
Specifically, it may be set to be 10 to 20% smaller than the transfer bias in the normal mode, thereby suppressing an increase in the charge amount of the transparent toner and the color toner in the transfer nip region, and by reverse polarity. The reverse transcription that occurs can be reduced. Therefore, it is possible to prevent a situation in which the transparent toner is reversely transferred to the color image forming unit and the spherical transparent toner cannot be collected in the blade method.
Further, it is possible to assist transfer in an electric field that may become unstable in the local gaps of the color toner.

Further, the batch transfer means 6 has a secondary transfer portion on the recording material 2 on which the color toner image on the intermediate transfer body 1 can be electrostatically transferred, and a transfer bias applied to the secondary transfer portion in the special mode is usually set. It is preferable to set larger than that in the mode.
Specifically, it may be set to be 10 to 20% larger than the transfer bias in the normal mode. By setting in this way, the total charge amount of the toner image is increased due to the further increase in the transparent toner image, so that a situation where the charge amount is insufficient with the same transfer bias as in the normal mode can be avoided.

Furthermore, it is preferable that the transparent image forming unit 3 sets the charge amount of the transparent toner in the transparent image forming unit 3 to be larger than the charge amount of the color toner. Thereby, it is possible to suppress an increase in the charge amount of the transparent toner in the transfer nip region, and it is possible to reduce reverse transfer caused by reverse polarity. Therefore, it is possible to prevent a situation in which the transparent toner is reversely transferred to the color image forming unit and the spherical transparent toner cannot be collected by the blade method.
Furthermore, the shape factor of the color toner is preferably 134 or less. Thus, when the shape factor is 134 or less, good transferability can be maintained even for the recording material 2 with particularly low surface smoothness.

Further, the color image forming unit 4 has a cleaning means capable of cleaning the residual toner on the image carrier, forms a band image with color toner in the non-image formation or in the non-image area, and supplies the band image to the cleaning means. Is preferred.
Here, as a method for supplying the transparent toner, when the transparent toner is applied on the entire surface of the intermediate transfer body 1, the transparent toner exists in a single layer in the non-image area other than the image area formed by the color toner image in the imageable area. The part which does is produced. The transparent toner of the single layer portion may be reversely transferred to the color image forming unit 4 side, and if it enters the blade, it may sink under the blade and be not collected. In order to prevent this, a toner band made of irregular color toner is created.

Furthermore, it is preferable that the transparent toner image 3a is formed corresponding to the image forming area by the color toner. With such an embodiment, it is possible to prevent wasteful use of the transparent toner, and it is possible to avoid a situation in which the spherical transparent toner layer enters the blade as a single layer.
Further, it is preferable that the intermediate transfer body 1 has a cleaning means for cleaning the surface on the downstream side of the collective transfer means 6, and a bias application type cleaning member is preferably used as the cleaning means. In this embodiment, the cleaning member may be appropriately selected as long as a bias can be applied, such as a brush or a blade.

According to the image forming method of the present invention, a transparent toner having good transferability is used, and in particular, a transparent toner image having a shape factor of 125 or less is formed on the lowermost layer of the intermediate transfer member, and the shape is formed on the transparent toner image. Since a color toner image having a coefficient exceeding 125 was formed, the adhesion force between the intermediate transfer member and the transparent toner image was reduced as the contact area with the spherical toner decreased. By improving the adhesion, it is possible to prevent separation between the toner layers during transfer. Therefore, according to the present invention, it is possible to have both the releasability by the spherical transparent toner and the adhesion by the irregular color toner, so that the transferability is improved. In contrast, good transferability can be obtained.
Further, since a color toner having a shape factor exceeding 125 is used, a simple blade cleaning method can be adopted as an image carrier cleaner, and it has a simple configuration and has a cleanability with respect to the color toner on the image carrier. Can keep good.
Furthermore, according to the image forming apparatus of the present invention, the above-described image forming method can be easily realized.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 2 is an overall configuration diagram of a color image forming apparatus (for example, a color copying apparatus) to which the present invention is applied.
Note that the present invention is not limited to such an image forming apparatus, but can be applied to a monochrome image forming apparatus.
In FIG. 2, the image forming apparatus includes a document reading device 10 that reads a document 12 on a platen 11, a transparent image forming unit 20 (20a) that forms a transparent toner image by, for example, an electrophotographic method, and four color component images. A color image forming unit 20 (20b to 20e) for forming (toner image), an intermediate transfer belt 30 for sequentially transferring (primary transfer) each color component image formed by each image forming unit 20, and an intermediate transfer belt A batch transfer unit 50 that batch-transfers (secondary transfer) the superimposed image transferred onto the sheet 30 to a sheet (recording material) 90; a fixing device 70 that fixes the batch-transferred image onto the sheet 90; And a paper conveyance system 80 for supplying the paper 90 to the paper.
In this embodiment, the transparent image forming unit 20a, the yellow image forming unit 20b, the magenta image forming unit 20c, the cyan image forming unit 20d, and the black image forming unit 20e are arranged in this order from the upstream side in the conveyance direction of the intermediate transfer body 30. It is arranged by.

  In the present embodiment, the document reading apparatus 10 includes, for example, a light source 13 that is disposed below the platen 11 and irradiates light on the surface of the document 12, and a CCD that converts reflected light from the surface of the document 12 into an electrical signal. The photoelectric conversion element 14, an appropriate number of mirrors 15 that form a path for guiding the reflected light from the surface of the document 12 to the photoelectric conversion element 14, and the reflected light from the surface of the document 12 are coupled on the imaging surface of the photoelectric conversion element 14. And an imaging lens 16 for imaging.

  Each image forming unit 20 (20a to 20e) has a photosensitive drum 21, and a charging device 22 such as a corotron for charging the photosensitive drum 21 is charged around each photosensitive drum 21. A laser scanning device in which an electrostatic latent image (mainly image data read by the photoelectric conversion element 14 or electrostatic latent image based on image data taken from another recording medium) is written on the photosensitive drum 21. An exposure device 23, a developing device 24 for developing the electrostatic latent image written on the photosensitive drum 21 with each color component toner, and a transfer roll for transferring the toner image on the photosensitive drum 21 to the intermediate transfer belt 30 And a drum cleaner 26 from which residual toner on the photosensitive drum 21 is removed.

Further, the intermediate transfer belt 30 is stretched over a plurality of (four in this embodiment) support rolls 31 to 34, and the drive roll is driven by a belt drive motor (not shown). The support roll 32 is used as a driven roll, and the support roll 33 is tilted around a meandering correction roll (steering roll: one axial end as a fulcrum) in a direction substantially perpendicular to the moving direction of the intermediate transfer belt 30. Furthermore, the support roll 34 is used as a backup roll for the batch transfer unit 50.
A belt cleaner 35 using a bias brush 36 for removing residual toner on the intermediate transfer belt 30 after the secondary transfer is provided on the surface side of the intermediate transfer belt 30 facing the support roll 31 so as to be retractable. It has been.

  A sheet 90 as a recording material is accommodated in a supply tray 81, supplied by a pickup roll 82, guided to a secondary transfer portion through a registration roll 83, and fixed to a fixing device 70 through a conveyance belt 84. It is conveyed to and discharged.

Further, each developing device 24 contains toner of each color component, the transparent image forming unit 20a is transparent toner, the yellow image forming unit 20b is yellow toner, the magenta image forming unit 20c is magenta toner, and cyan image forming. Cyan toner is used for the image forming unit 20d, and black toner is used for the black image forming unit 20e.
In particular, in the present embodiment, the transparent toner used in the transparent image forming unit 20a for forming a transparent toner image is a spherical toner having a shape factor of 125 or less, and the color image forming units 20b to 20e for forming color toner images are used. For each color toner used, an irregular toner having a shape factor of 125 to 134 is used.

In addition, a voltage having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roll 25 (specifically, 25a to 25e), whereby the toner image on the photosensitive drum 21 is transferred. The toner images are sequentially electrostatically attracted to the intermediate transfer belt 30 so that a superimposed toner image is formed on the intermediate transfer belt 30.
The batch transfer unit 50 further includes a secondary transfer roll 51 disposed in pressure contact with the toner carrying surface side of the intermediate transfer belt 30 and a counter electrode of the secondary transfer roll 51 disposed on the back surface side of the intermediate transfer belt 30. And a backup roll 34. When a voltage having the same polarity as the charging polarity of the toner is applied to the backup roll 34 (a voltage having a polarity opposite to the charging polarity of the toner may be applied to the transfer roll 51), the backup roll 34 and the transfer roll 51 are used. The unfixed toner image held on the intermediate transfer belt 30 is electrostatically transferred to the sheet 90 at the secondary transfer site by the transfer electric field formed between the two and the second transfer portion.

  In particular, in the present embodiment, the operations of the image forming units 20, the batch transfer unit 50, and the like are made variable depending on the type of paper 90 to be used. That is, as shown in FIG. 3, the control device 41 has a mode switch 40 that can be switched according to the type of paper 90 (embossed paper or plain paper), and based on a switching signal from the mode switch 40. Thus, either the normal mode or the special mode is selected, a control signal is transmitted to each unit or the like, and the setting of each unit or the like is changed according to each mode.

Next, an image forming process of the color image forming apparatus according to the present embodiment will be described.
Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed.
Specifically, for example, when this color image forming apparatus is configured as a digital color copying machine, a document set on a document table (not shown) is read by a color image reading device, and the read signal is image signal processing means. Is converted into a digital image signal and temporarily stored in the memory. Based on the stored digital image signals of four colors (yellow (Y), magenta (M), cyan (C), and black (K)). Thus, toner images of each color are formed.

That is, the image forming unit 20 is driven in accordance with the digital image signal of each color input from the image signal processing means. In each image forming unit 20, an electrostatic latent image corresponding to the digital signal is written on the photosensitive drum 11 uniformly charged by the charging device 22 by the exposure device 23.
Each electrostatic latent image is developed by a developing device 24 containing toner of each color to form a toner image of each color.
Further, the toner image formed on each photoconductive drum 21 is applied with a primary transfer bias by the primary transfer roll 25 at the primary transfer position where each photoconductive drum 21 and the intermediate transfer belt 30 are in contact with each other. The images are sequentially transferred onto the surface of the intermediate transfer belt 30.
The toner remaining on the photosensitive drum 21 after the primary transfer is cleaned by the drum cleaner 26.

The toner image primarily transferred to the intermediate transfer belt 30 in this manner is superimposed on the intermediate transfer belt 30 and conveyed to the secondary transfer position as the intermediate transfer belt 30 rotates.
On the other hand, the sheet 90 is supplied to the secondary transfer position at a predetermined timing.

  Then, at this secondary transfer position, a secondary transfer bias is applied by the power supply roll 52 as the batch transfer unit 50, and the transfer electric field formed between the secondary transfer roll 51 and the backup roll 34 acts as an intermediate. The toner image carried on the transfer belt 30 is collectively transferred (secondary transfer) to the paper 90.

As described above, the sheet 90 on which the toner image is transferred is conveyed to the fixing device 70 by the conveying belt 84 and the toner image is fixed.
Further, the toner remaining on the intermediate transfer belt 30 after the secondary transfer is conveyed to the belt cleaner 35 and electrostatically collected by the bias brush 36 to which a predetermined bias is applied.

In such an image forming process, the control device 41 can be switched between a normal mode and a special mode having different image forming processes when paper is selected in the image forming control process.
That is, as shown in FIG. 4, in the normal mode, the color image forming units 20b to 20e are operated, and the primary transfer bias and the secondary transfer bias are set as normal values. On the other hand, when the mode is switched to the special mode, the transparent image forming unit 20a operates in addition to the color image forming units 20b to 20e, and the primary transfer bias and the secondary transfer bias can be increased as compared with the normal mode. it can.

Here, the operation in the normal mode and the special mode will be described in detail.
<Normal mode>
In this normal mode, when a smooth paper such as plain paper is selected at the time of paper selection, the color image forming units 20b to 20e are operated without operating the transparent image forming unit 20a. That is, the toner images formed on the respective photoconductive drums 21 of the color image forming units 20b to 20e are primary in the normal mode by the primary transfer roll 25 at the primary transfer position where the respective photoconductive drums 21 and the intermediate transfer belt 30 are in contact with each other. A transfer bias 27a is applied and sequentially transferred from the photosensitive drum 21 to the surface of the intermediate transfer belt 30 (see FIG. 5A). At this time, the transfer is performed in the order of YMCK.

The toner image primarily transferred to the intermediate transfer belt 30 in this manner is superimposed on the intermediate transfer belt 30 and conveyed to the secondary transfer position as the intermediate transfer belt 30 rotates.
At this secondary transfer position, the bias applied to the power supply roll 52 is the secondary transfer bias 53a in the normal mode. At this time, the toner image carried on the intermediate transfer belt 30 is collectively transferred onto the paper 90 (plain paper) by the action of the transfer electric field formed between the secondary transfer roll 51 and the backup roll 34 (see FIG. 5 (b)).

<Special mode>
Next, the operation of the special mode when forming an image on uneven paper such as embossed paper will be described in detail.
In this special mode, for example, when embossed paper is selected at the time of paper selection, when the control device 41 sends a control signal based on a switching signal from the mode changeover switch 40, transparent image forming is performed together with the color image forming units 20b to 20e. The unit 20a operates (see FIGS. 3 and 4). That is, the toner image formed on each photosensitive drum 21 in the image forming unit 20 (specifically, 20a to 20e) is primarily transferred at the primary transfer position where each photosensitive drum 21 and the intermediate transfer belt 30 are in contact with each other. The image is sequentially transferred from the photosensitive drum 21 to the surface of the intermediate transfer belt 30 by the roll 25.
Here, the order in which the transfer is performed is transparent toner first, and thereafter the order of YMCK.
At this time, the toner charge amount of the transparent toner charged negatively in the transparent image forming unit 20a is set larger than the toner charge amount of the color toner. Further, the primary transfer bias 27 applied to the primary transfer rolls 25b to 25e is switched from the primary transfer bias 27a in the normal mode to the primary transfer bias 27b in the special mode based on a control signal from the control device 41 (FIG. 5A). )reference).
The special mode primary transfer bias 27b is set to be 10 to 20% smaller than the normal mode primary transfer bias 27a.

Here, it will be described in detail that the special mode primary transfer bias 27b is set to be 10 to 20% smaller than the normal mode primary transfer bias 27a.
FIG. 6A shows the relationship between the charge amount of the transparent toner and the number of toners from when the transparent toner in the transparent image forming unit 20a is transferred onto the intermediate transfer belt 30 until it passes through the image forming units 20b to 20e. Is shown.
Now, it is assumed that the transparent toner of the transparent image forming unit 20a is transferred onto the intermediate transfer belt 30 and has a charge distribution Q1. When the transparent toner having such a charge distribution passes through the color image forming units 20b and 20c, the charge amount of the transparent toner increases due to the transfer current acting on each primary transfer portion. Although it shifts to the left side (negative polarity side), it receives a discharge at each primary transfer portion, so that the distribution is widened from the high charge side to the low charge side.
Similarly, when the transparent toner passes through the color image forming units 20d and 20e, such a shift of the charge distribution and the expansion of the skirt occur.
Here, assuming that the charge distribution Q2 of the transparent toner is weak at the time of the primary transfer (Q2 <Q1), each image forming unit 20 (for example, 20b, 20c) as shown in FIG. 6B. ), The charge distribution of the toner expands due to discharge, and toner that becomes reverse polarity (positive polarity) appears. The transparent toner having the reverse polarity may be reversely transferred to the photosensitive drum 21 side. If the reverse transfer is performed, the toner is not only difficult to collect with a cleaning blade but also causes image distortion. End up.
Such reverse polarity may occur not only when the charge amount of the transparent toner is weak from the beginning, but also when the transfer electric field in the primary transfer region passing therethrough is large.
Therefore, in order to avoid such a situation, the transparent toner charge amount is set larger and the primary toner charge amount is set so as not to reverse polarity even when the charge amount of the transparent toner passes through the four transfer areas of YMCK. It is effective to set the transfer bias to be 10 to 20% smaller than that in the normal mode.
By increasing the charge amount of the transparent toner in this way, the transferability of the transparent toner itself is lowered, but since it is transparent, there is no adverse effect on image quality, and the effect of improving the transfer rate of the color toner is obtained by the presence of the transparent toner. be able to.
Further, the color toner also has the above-described shift of the charge distribution and the expansion of the skirt, which is one of the factors that cause a decrease in transferability in local voids such as embossed paper. Therefore, by setting the primary transfer bias to be 10 to 20% smaller than that in the normal mode, it is possible to reduce the shift of the charge distribution of the color toner itself and the expansion of the skirt, so that the transfer that may become unstable in the local gap is possible. Can assist.

Then, when such primary transfer is performed, each color component toner in a plurality of layers is formed on the intermediate transfer belt 30. At this time, for example, in the case of the most multilayer condition, five layers are formed in the order of transparent toner 61, Y toner 62, M toner 63, C toner 64, and K toner 65 from the intermediate transfer belt 30 side (FIG. 7 (a) to (c)).
The toner image 60 is conveyed to the secondary transfer position as the intermediate transfer belt 30 rotates.
On the other hand, the sheet 90 (embossed sheet) is supplied to the secondary transfer position at a predetermined timing.
At this secondary transfer position, the toner image 60 carried on the intermediate transfer belt 30 is formed by the action of a transfer electric field formed between the secondary transfer roll 51 as the batch transfer unit 50 and the backup roll 34. Batch transfer (secondary transfer) to embossed paper.

At this time, the secondary transfer bias 53 is switched from the secondary transfer bias 53a in the normal mode to the secondary transfer bias 53b in the special mode by a control signal sent from the control device 41 (see FIG. 5B).
The secondary transfer bias 53b in the special mode is set to be 10 to 20% larger than the secondary transfer bias 53a in the normal mode.
In this special mode, as the number of transparent toner images increases and the total toner charge amount correspondingly increases, there is a possibility that an effective transfer electric field may not be applied with the same transfer bias as in the normal mode. The next transfer bias is set large.
Thereby, the transferability is improved, and in particular, transfer defects caused by local gaps such as grooves of embossed paper as a recording material and foreign matter fixing on the intermediate transfer member can be prevented.

Further, in the present embodiment, a band image 211 made of color toner is formed on the photosensitive drum 21 during non-image formation or in a non-image area, and is supplied to the drum cleaner 26 (see FIG. 8A).
Here, as a method for supplying the transparent toner, for example, when the entire surface is applied to the intermediate transfer belt 30, the transparent toner exists in a single layer in the non-image area other than the image area 212 by the color toner image among the imageable areas. The part which does is produced. The transparent toner in the single layer portion may be reversely transferred to the color image forming units 20b to 20e, and if this enters the cleaning blade 26a of the drum cleaner 26, it may sink into the gap of the cleaning blade 26a and be not collected. (See FIG. 8B).
Therefore, in order to remove such stagnation of the spherical toner 213, a band image 211 made of the irregular color toner 214 is created. That is, such a band image 211 can scrape the spherical toner 213 into which the irregular color toner 214 has entered the minute gap.

  Furthermore, in the present embodiment, the transparent toner image is formed corresponding to the image forming area by the color toner. With such an embodiment, it is possible to prevent wasteful use of the transparent toner, reduce the presence of a transparent toner image in a single layer, and reduce the reverse transfer of the transparent toner to the photosensitive drum 21 side. .

Embodiment 2
FIG. 9 shows a schematic configuration of Embodiment 2 of a color image forming apparatus to which the present invention is applied.
In the figure, the color image forming apparatus according to the present embodiment fixes an image forming unit 200 that forms a color image on a sheet 900 and each toner image on the sheet 900 formed by the image forming unit 200. The image forming apparatus includes a fixing device 700 and a conveyance belt 840 that conveys the paper 900 to the fixing device 700.
In the present embodiment, the image structure to be created is obtained by laminating a color toner image and a transparent toner image on a sheet 900 as in the first embodiment.

In the figure, an image forming unit 200 includes a charger (not shown) around a photosensitive drum 210, and an exposure device 230 that exposes and scans a document 120 to form an electrostatic latent image on the photosensitive drum 210. , Transparent toner and developing devices 240a to 240e containing yellow, magenta, cyan, and black color toners (specifically 240a; transparent toner, 240b; yellow toner, 240c; magenta toner, 240d; cyan toner, 240e) A black toner) and a non-illustrated cleaning device for cleaning the residual toner on the photosensitive drum 210, and temporarily holding an image on the photosensitive drum 210. A primary transfer device (for example, a transfer corotron) 250 is provided at a portion of the transfer belt 300 facing the photosensitive drum 210. To set.
In the present embodiment, the transparent image forming unit 200a includes a developing device 240a in which a transparent toner is accommodated in the developing device 240, while each color image forming device is used for each of charging, exposure, transfer, and cleaning devices. It is shared with the units 200b to 200e. Similarly, each color image forming unit 200b to 200e is provided with a developing device (specifically 240b to 240e) for each color in the developing device 240, while the other image forming units 200a to 200e are provided for the other devices. It is shared with 200e.
Further, the intermediate transfer belt 300 is provided with a batch transfer unit 500 (a pair of transfer rolls 510 and a backup roll 340 sandwiching the intermediate transfer belt 300 and the paper 900 in this example) at a portion where the paper 900 passes. .
In addition, the primary transfer device 250 and the batch transfer unit 500 change the applied bias to the control device based on the control signal, as in the first embodiment.

Here, the exposure device 230 irradiates the original 120 with light from the illumination lamp 130, separates the reflected light from the original 120 with the color scanner 131, and performs image processing with the image processing device 132. For example, the electrostatic latent image writing light is irradiated to the exposure point of the photosensitive drum 210 through the laser diode 231 and the optical system 232.
Further, a conveying device 840 made of, for example, a conveying belt is disposed between the fixing device 700 and the image forming portion of the image forming unit 200.

  Further, as in the first embodiment, the control device operates the color toner developing devices 240b to 240e except for the transparent toner developing device 240a when a smooth paper such as plain paper is selected. There is provided a mode changeover switch capable of selecting a mode and a special mode for operating the color toner and transparent toner developing devices 240a to 240e when uneven paper such as embossed paper is selected. Each of the developing devices 240a to 240e is activated when the control device sends a control signal based on the switch switching signal.

Next, the operation in the special mode of the image forming apparatus according to the present embodiment will be described.
As shown in FIG. 9, when color copying is performed using the image forming apparatus according to the present embodiment, first, when embossed paper is selected in paper selection, based on a switching signal from a mode switch. The control device sends a control signal to each unit or the like.
On the other hand, when copying is started, the original 120 to be copied is irradiated with light from the illumination lamp 130, and the reflected light is color-separated by the color scanner 131 and image processing is performed by the image processing device 132 to perform color correction. A plurality of color toner image data and transparent toner image data are converted into laser beams modulated using a laser diode 231 for each color.
This laser beam is irradiated onto the photosensitive drum 210 a plurality of times for each color to form a plurality of electrostatic latent images. For the plurality of electrostatic latent images, transparent toner and yellow, magenta, cyan, and black color toners are used, and these are used as a transparent toner developer 240a, yellow developer 240b, magenta developer 240c, cyan developer 240d, Development is performed in order by the black developing device 240e.

The developed transparent toner image and color toner image are sequentially transferred from the photosensitive drum 210 to the intermediate transfer belt 300 by the primary transfer device 250.
At this time, a transparent toner image is formed on the lowermost layer of the intermediate transfer belt 300. As in Embodiment 1, the primary transfer bias is 10 to 20 compared to the normal mode so that the transparent toner is not reversely transferred to the photosensitive drum 210 when the color toner image is transferred onto the transparent toner image. % Is controlled to be smaller.

Next, the transparent toner image and the color toner image transferred onto the intermediate transfer belt 300 are collectively transferred onto the paper 900 (embossed paper) by the batch transfer unit 500.
At this time, the secondary transfer bias is set to be 10 to 20% larger than that in the normal mode. As described above, by increasing the secondary transfer bias, it is possible not only to obtain good transferability for a toner image in which the total charge amount of the toner has increased due to the addition of the transparent toner, but also particularly for recording. It is possible to prevent a transfer failure caused by a local gap formed by a groove of embossed paper as a material or adhesion of foreign matter on the intermediate transfer member.
In this way, the sheet 900 on which the toner image is transferred is conveyed to the fixing device 700 by the conveying belt 840 and the toner image is fixed.
In the present embodiment, in the normal mode in which image formation is performed on plain paper or the like, the developing devices 240b to 240e that store four color toners are not operated without operating the developing device 240a that stores transparent toner. , The primary transfer bias and the secondary transfer bias are set to normal values, and image formation is performed.

It is explanatory drawing which shows the outline | summary of the color image forming apparatus which concerns on this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing an outline of a first embodiment of a color image forming apparatus to which the present invention is applied. 2 is a block diagram illustrating an image forming control system in the image forming apparatus according to Embodiment 1. FIG. 4 is an explanatory diagram illustrating a flowchart of image formation control processing in the image forming apparatus according to Embodiment 1. FIG. In the image forming apparatus according to the first embodiment, (a) is an explanatory diagram showing details of a primary transfer bias, and (b) is an explanatory diagram showing details of a secondary transfer bias. In the image forming apparatus according to the first embodiment, (a) is an explanatory view showing a charge distribution of the transparent toner from when the transparent toner is transferred onto the intermediate transfer body to when it passes through each image forming unit, and (b) is an explanatory diagram showing the charge distribution of the transparent toner. FIG. 4 is an explanatory diagram showing a charge distribution of a transparent toner that is transferred to an intermediate transfer body and then reverse polarity by passing through each image forming unit. In the image forming apparatus according to the first embodiment, (a) is an explanatory view showing the action of the transparent toner in the primary transfer, (b) is an explanatory view showing the action of the color toner in the primary transfer, and (c) is the secondary transfer. FIG. 6 is an explanatory diagram showing an operation of a toner image in FIG. In the image forming apparatus according to the first embodiment, (a) is an explanatory view showing a band image of color toner, (b) is a cross-section from (B) in FIG. FIG. 6 is an explanatory diagram illustrating an operation of a regular color toner. It is explanatory drawing which shows the outline of Embodiment 2 of the color image forming apparatus to which this invention was applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Intermediate transfer body, 2 ... Recording material, 3 ... Transparent image forming unit, 3a ... Transparent toner image, 4 ... Color image forming unit, 4a ... Color toner image, 5 ... Primary transfer part, 6 ... Collective transfer means, 7 ... Mode selection means

Claims (11)

When transferring a color toner image to a recording material via an intermediate transfer member,
A transparent image forming step of forming a transparent toner image on the lowermost layer on the intermediate transfer member using a transparent toner having a shape factor of 125 or less;
A color image forming step of forming a color toner image on the transparent toner image on the intermediate transfer member using a color toner having a shape factor exceeding 125;
A batch transfer step of batch transferring the transparent toner image and the color toner image onto the recording material from the intermediate transfer member. In an image forming apparatus for transferring a color toner image to a recording material via an intermediate transfer member,
A transparent image forming unit provided opposite to the intermediate transfer member and forming a transparent toner image on the lowermost layer on the intermediate transfer member using a transparent toner having a shape factor of 125 or less;
A color image forming unit provided opposite to the intermediate transfer body and forming a color toner image on the transparent toner image using a color toner having a shape factor exceeding 125;
An image forming apparatus, comprising: a batch transfer unit that batch-transfers the transparent toner image and the color toner image onto the recording material from the intermediate transfer member. The image forming apparatus according to claim 2.
An image forming apparatus, wherein the transparent image forming unit is provided separately or partially as a color image forming unit. The image forming apparatus according to claim 2.
The transparent image forming unit and the color image forming unit are configured to be selectable by the mode selecting means, and the mode selecting means operates the normal image forming mode for operating only the color image forming unit and the transparent image forming unit together with the color image forming unit. An image forming apparatus that switches between a special mode and an image forming apparatus. The image forming apparatus according to claim 4.
The color image forming unit has a primary transfer part that can electrostatically transfer a color toner image on an intermediate transfer member, and the transfer bias applied to the primary transfer part in the special mode is set smaller than in the normal mode. An image forming apparatus. The image forming apparatus according to claim 4.
The batch transfer unit has a secondary transfer part that can electrostatically transfer the color toner image on the intermediate transfer member on the recording material, and the transfer bias applied to the secondary transfer part in the special mode is set larger than in the normal mode. An image forming apparatus. The image forming apparatus according to claim 2.
An image forming apparatus, wherein the transparent image forming unit sets the charge amount of the transparent toner in the transparent image forming unit to be larger than the charge amount of the color toner. The image forming apparatus according to claim 2.
An image forming apparatus, wherein a color toner has a shape factor of 134 or less. The image forming apparatus according to claim 2.
The color image forming unit has a cleaning unit capable of cleaning residual toner on the image carrier, forms a band image with color toner in a non-image formation or in a non-image area, and supplies the band image to the cleaning unit. Image forming apparatus. The image forming apparatus according to claim 2.
An image forming apparatus, wherein a transparent toner image is formed corresponding to an image forming area by color toner. The image forming apparatus according to claim 2.
The intermediate transfer member has a cleaning means for cleaning the surface downstream of the batch transfer means, and a bias application type cleaning member is used as the cleaning means.

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