JPH1124443A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an excellent image not only on general paper or an OHP sheet but also on more wide-ranging final image carriers by electrostatically transferring a visible image formed on the image carrier on a transfer material by selectively actuating electrostatic attracting force or electrostatic repulsive force according to a transfer condition. SOLUTION: When a color visible image is formed on an intermediate transfer belt 16, a transfer material S is carried toward a second transfer part. Then, the smoothness of the surface of the material S is detected by a smoothness detection means 40. By a control means 25, a developing bias voltage whose the polarity is reverse to an electrostatic charge polarity of the visible image is impressed on a roller 28 from a power source 29 and secondary transfer by electrostatic attracting force is executed by the control of a constant current when the smoothness of the surface of the material S is excellent. Moreover, when the smoothness of the surface of the material S is bad and rugged, a developing bias voltage whose the polarity is identical to the electrostatic charge polarity of the visible image is impressed on a roller 164 from a power source 165 by the control means 25 and secondary transfer by electrostatic repulsive force is executed by the control of the constant current or the control of a constant voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art An image forming apparatus which transfers a "visible image formed by a toner" formed on an image carrier to a transfer material is widely known as an analog or digital copying apparatus or an optical printer. ing. These image forming apparatuses have made great strides, and extremely high quality images have been obtained. As the "final image carrier" that finally carries the image to be formed, a plastic sheet called an "OHP sheet" for an overhead projector can be used in addition to plain paper. On the other hand, with the spread of image forming apparatuses, not only plain paper and OHP sheets,
"Sheet-like media" that depart from the conventional concept of a final image carrier, such as "a woven fabric-based surface coated with an image-bearing layer" or "cardboard with relief-like irregularities formed on the surface" Has a request to form an image.

When a visible image is transferred to such a sheet-like medium, it is affected by the unevenness of the surface of the sheet-like medium.
It was recognized that "a considerably unsightly density unevenness" occurred in the transferred image.

[0004]

SUMMARY OF THE INVENTION The present invention relates to an image forming apparatus for transferring a visible image formed by a toner formed on an image carrier onto a transfer material. It is an object to form a good image on a suitable final image carrier.

[0005]

An image forming apparatus according to the present invention is an "image forming apparatus for electrostatically transferring a visible image by a toner on an image carrier to a transfer material". The transfer is performed by applying an electrostatic repulsive force from the image carrier side ”(claim 1). That is, a voltage having the same polarity as the toner constituting the visible image is generated on the image carrier side, and an electrostatic repulsion is applied to the visible image so as to “remove from the image carrier”. To transfer the visible image to the transfer material.

Conventionally, transfer of a visible image has been performed by "electrostatic attraction". That is, the transfer material is superimposed on the visible image to be transferred, and the voltage and electric charge applied from the back surface of the transfer material apply “electrostatic attraction to attract the visible image to the transfer material side” to transfer the visible image. Is performed. At this time, if the transfer material is the final image carrier, the action of the electrostatic attraction differs depending on the type of transfer material such as plain paper, OHP sheet, or the sheet-like medium. In particular, when the transfer material is the above-described “sheet-shaped medium”, the surface of the transfer material is uneven, and the “transfer electric field between the transfer material surface and the image carrier” is disturbed by the unevenness (transfer). The lines of electric force of the electric field are not aligned in the transfer direction). This is considered to result in non-uniform transfer, and the "density unevenness" described above.

When the transfer is performed by applying an electrostatic repulsive force from the image carrier side as in the present invention, the image carrier is a part of the image forming apparatus, and the surface thereof is smooth. In addition, a uniform transfer electric field (having uniform lines of electric force from the image carrier toward the transfer material) can be applied to the visible image, and uniform transfer can be performed.

The image forming apparatus according to the first aspect of the present invention also has a function of performing "transfer to a visible image by applying electrostatic attraction from the transfer material side, and according to transfer conditions, Alternatively, the visible image on the image carrier is electrostatically transferred to a transfer material by selectively applying an electrostatic repulsion (claim 2). In this case, "the electrostatic repulsion acting on the visible image can be made larger than the electrostatic attraction" (claim 3).

In the image forming apparatus according to the second or third aspect, the "transfer condition for selecting one of the electrostatic repulsion and the electrostatic attraction" can be determined as the quality of the surface smoothness of the transfer material. In this case, if the surface smoothness of the transfer material is good, a visible image is transferred by electrostatic attraction, and if the surface smoothness of the transfer material is poor, transfer by electrostatic repulsion is performed. (Claim 5).

According to a fifth aspect of the present invention, there is provided an image forming apparatus comprising: a smoothness detecting means for detecting whether the surface of the transfer material is smooth; and a transfer or electrostatic force based on an electrostatic attraction based on a detection signal of the smoothness detecting means. It has a control means for selecting and executing transfer by repulsive force "(claim 6), or" manually selecting transfer by electrostatic attraction and transfer by electrostatic repulsive force ". It can also be configured (claim 7).

The image forming apparatus according to any one of claims 1 to 7, further comprising "electrostatic repulsion electrode means" for applying a transfer voltage having the same polarity as that of the visible image on the back side of the image carrier. The electrode means for electrostatic repulsion can be of various types such as a discharge type, a brush contact type, a blade type, etc. Can be used (claim 9).

The image forming apparatus according to any one of the second to ninth aspects has an "electrostatic attraction electrode means" for applying a transfer voltage having a polarity opposite to that of the visible image to the back side of the transfer material. (Claim 10). As the electrode means for electrostatic attraction, various types such as a discharge type, a brush contact type, a blade type and the like can be used. (Claim 1
1).

The "image carrier" in the image forming apparatus according to the present invention can be a "latent image carrier" such as a photoconductive photoconductor, and in this case, the "transfer material" is the final image. It may be plain paper or an OHP sheet as the carrier, the above-mentioned sheet-like medium, or the like, or may be an “intermediate transfer medium” such as an intermediate transfer drum or an intermediate transfer belt. That is, the transfer of the visible image by the electrostatic repulsion can be performed as “transfer from the latent image carrier to the final image carrier” or “transfer from the latent image carrier to the intermediate transfer medium”.
In this case, the form of the latent image carrier may be a drum form or a belt form (end or endless).

The "image carrier" can be an "intermediate transfer medium". In this case, the intermediate transfer medium as the image carrier is subjected to “primary transfer in the first transfer section” of the visible image of the toner formed on the latent image carrier such as the photoconductor, and the final image carrier as the transfer material. This causes the body to "secondarily transfer the visible image at the second transfer portion by electrostatic repulsion or electrostatic attraction" (claim 12). The “intermediate transfer medium as an image carrier” may be configured in a drum shape, but may be configured in a “belt shape” as a preferred embodiment (claim 13).
Since the belt-shaped intermediate transfer medium has a large degree of freedom in the arrangement form in the image forming apparatus, it is possible to reduce the size of the image forming apparatus and increase the degree of freedom in the layout of other equipment by using this. become.

If the image carrier is an intermediate transfer medium, the final image carrier as a transfer material is plain paper or the like, and a visible image on the intermediate transfer medium is transferred in the second transfer section. The transfer material may be conveyed through the second transfer unit by a "transfer material conveying means capable of contacting and separating from the intermediate transfer medium" to perform secondary transfer (claim 14). A visible image may be transferred by secondary transfer while being sandwiched and conveyed by "a roller-like or belt-like electrode device for electrostatic attraction that can be brought into contact with and separated from the intermediate transfer medium" and the intermediate transfer medium. .

The image forming apparatus according to any one of claims 12 to 15, wherein the primary transfer portion and the secondary transfer portion of the intermediate transfer medium are "electrically separated from each other by two or more grounding means". (Claim 16). In this case, even if the primary transfer and the secondary transfer overlap with each other, they do not affect each other.
It can be before the end of the next transfer.
7) Since the time required for image formation can be shortened and the distance from the first transfer unit to the second transfer unit can be reduced, the peripheral length of the intermediate transfer medium can be reduced to the minimum necessary for maintaining a visible image. Length ".

In the case where the intermediate transfer medium is an "intermediate transfer belt", the intermediate transfer belt is composed of a "base layer having a medium resistance region volume resistance" and an intermediate layer having a medium resistance region volume resistance and a thin insulating layer. , And has a volume resistance of the medium resistance region as a whole ”(claim 18). The “medium resistance region” is a volume resistance: 10 ⁷
This is a region of about 10 ¹⁵ Ω · cm. When the intermediate transfer belt has “relatively high volume resistance in the medium resistance region”, “uniform charging unevenness of the primary-transferred visible image is provided downstream of the primary developing unit and upstream of the secondary developing unit. (A pre-transfer charging means for performing the charging). Of course, for the electrical characteristics such as the material / structure and electric resistance of the intermediate transfer medium, various materials, structures / electrical characteristics can be appropriately selected according to the image forming conditions.

In the above-described image forming apparatus, the visible image to be transferred may be a monochromatic visible image or a color visible image. In the case where the image carrier is a latent image carrier, single-color visible images (magenta, cyan, yellow, and yellow) of different colors are sequentially formed on the latent image carrier.
(Black) can be sequentially transferred to a final image bearing member or an intermediate transfer medium as a transfer material by electrostatic repulsion or electrostatic repulsion or electrostatic attraction.

When the image carrier is an intermediate transfer medium as in the image forming apparatus according to any one of the twelfth to nineteenth aspects, the visible image to be transferred is a "visible toner having different colors from each other. It can be a "color visible image in which a plurality of images are superimposed on each other" (claim 20).

[0020]

FIG. 1 is a view for explaining an embodiment of an image forming apparatus according to the present invention. FIG. 1 (a)
In the photoconductive photoconductor 10 as a latent image carrier,
A photoconductive layer is formed on the outer peripheral surface of a drum-shaped conductive substrate, and is rotatable counterclockwise. The conductive substrate is grounded. The charging unit 12 is a charging unit that uniformly charges the photoconductor 10 to a predetermined polarity.

The latent image forming light L is light for exposing the photosensitive member for forming an electrostatic latent image. In this embodiment,
The formed electrostatic latent image is a four-color image for forming a color image.
Color component latent images, that is, a yellow latent image (electrostatic latent image developed with yellow toner), a magenta latent image (electrostatic latent image developed with magenta toner), and a cyan latent image (static latent image developed with cyan toner) An electrostatic latent image) and a black latent image (an electrostatic latent image developed with black toner).

The latent image exposure light L can be, for example, a "color-separated image exposure light beam" for forming an image obtained by color-separating a color image to be formed into a color having a complementary color relationship with the color of the development. (When the image forming apparatus is embodied as an analog color copying machine), or a “writing light flux” for writing each of the color latent images by an “optical writing device” such as an optical scanning device or an LED array. it can. Here, for the sake of specificity of description, it is assumed that the latent image forming light L is a “writing light beam by the optical scanning device”. The image information that modulates the intensity of the writing light beam can be color-separated image information obtained by color-separating a document and read, or an image signal for forming a color image generated by a computer or a word processor.

In this embodiment, the developing device 14 is a well-known "revolver developing device", and includes a yellow developing unit Y for developing a yellow latent image, a magenta developing unit M for developing a magenta latent image, and a cyan developing unit M. It has a cyan developing unit C for developing a latent image and a black developing unit BK for developing a black latent image in a “revolver shape”, and rotates the entire unit to bring a desired developing unit to a developing unit to perform development. I do.

The intermediate transfer belt 16 is an "intermediate transfer medium". As shown in FIG. 1 (b), an intermediate layer 16B is adhered and formed on a base layer 16A, and a surface layer 16 is further formed thereon.
C is formed. The base layer 16A and the intermediate layer 16B have a “medium resistance region” volume resistance, and
Reference numeral 6C denotes an insulating layer, which has "the volume resistance of the intermediate transfer belt as a whole in a medium resistance region". Intermediate transfer belt 16
Are rollers 160, 162, 163, 164, 166
167. The roller 160 is a roller for applying a “transfer bias voltage” and is a “metal roller”.
And a transfer bias voltage is applied from a power supply 161. A constant-voltage power supply or a constant-current power supply can be used as the power supply 161. When a constant-voltage power supply is used, the transfer voltage via the intermediate transfer belt 16 becomes constant.
When a constant current voltage is used, a transfer bias voltage is applied so that a constant current flows through the intermediate transfer belt 16. The roller 167 is a roller for removing electricity from the intermediate transfer belt and is a “metal roller”, and is electrically grounded. The intermediate transfer belt 16 is in area contact with the photoconductor 10 at a portion between the rollers 160 and 167 to form a “nip portion”. "Primary transfer" of the visible image is performed in this nip portion. A grounded neutralization brush 168 is provided on the back side of the intermediate transfer belt 16 in the nip portion, and the conductive tip (made of carbon-containing resin) is attached to the intermediate transfer belt 1.
6 is in contact with the back surface. Primary transfer is "transfer by electrostatic attraction".

The rollers 162, 163, and 166 are "metal or conductive resin rollers" and are grounded. Roller 1
62 is rotated clockwise as a “drive roller”,
The intermediate transfer belt 16 is rotated clockwise. Roller 1
Reference numeral 63 denotes a "tension roller" which is elastically acted on by an elastic force applying means (not shown) to tension the intermediate transfer belt 16 and prevent "slack" from occurring. Roller 1
Reference numeral 66 denotes a “counter roller” that supports the pressing force of the blade 181 in the cleaning unit 18 that cleans the intermediate transfer belt 16. The blade 181 can be brought into contact with and separated from the intermediate transfer belt 16, and at the time of cleaning, the blade edge is pressed against the intermediate transfer belt 16 so as to be in the “counter direction” with respect to the moving direction of the peripheral surface.

The roller 164 is a "counter roller for secondary transfer"
And a roller made of metal or conductive resin.
5, the transfer bias voltage for transfer by electrostatic repulsion is applied. Power supply 165 is a “constant voltage power supply”
Alternatively, a “constant current power supply” can be used.

The static elimination means 20 is a means for neutralizing the surface of the intermediate transfer belt 16. In this embodiment, the static elimination is performed by AC corona discharge on which AC or DC is superimposed.
As another method of static elimination, contact-type static elimination using a static elimination roller or the like is also possible. The brush 23 is a brush for applying a “lubricant” to the surface of the intermediate transfer belt 16. The lubricant 22 is a solid “zinc stearate” and is pressed against the brush 23. The brush 23 rotates to catch the lubricant 23 on the tip of the brush, and applies the lubricant 23 to the surface of the intermediate transfer belt 16.

"Pre-transfer charging means" provided near the portion where the intermediate transfer belt 16 is wound around the roller 162.
Is a scorotron 24 whose discharge current can be controlled by a grid, which is described later for “equalizing uneven charging of a visible image before secondary transfer”.

The transfer belt 30 is a "transfer material transporting means" for transporting the transfer material S, which is the final image carrier, through the secondary transfer section to the fixing section side during the secondary transfer.
01,303. Transfer belt 30
Is, for example, "polyvinylidene fluoride" or the like;
A belt having a material thickness of about 0 ¹³ Ω · cm: about 100 μm. Roller 30 around which transfer belt 30 can be wound
Reference numeral 3 can selectively occupy the position of the solid line and the position of the dashed line, and by occupying the position of the solid line, "contacts the intermediate transfer belt 16 to form the second transfer portion" and the position of the dashed line. Occupation makes it possible to “separate from the intermediate transfer belt 16”. That is, the transfer belt 30 moves toward and away from the intermediate transfer belt 16 depending on whether the position of the roller 303 is a position indicated by a solid line or a position indicated by a broken line.

The static elimination means 32 is a means for neutralizing the transfer material S on which the visible image has been transferred, prior to fixing in order to peel it off from the transfer belt 30, and is neutralization by AC corona discharge with AC or DC superimposed. I do. In addition, the charge removing means 3
Reference numeral 4 denotes a unit that removes electricity from the transfer belt 30 after the transfer material S is peeled off, and removes electricity by AC corona discharge in which AC or DC is superimposed. Cleaning means 360
Is means for cleaning the transfer belt 30,
The blade edge of the blade 361 is pressed against the peripheral surface of the transfer belt 30 so as to be in the counter direction in the moving direction. The roller 301 is an opposing roller that receives the pressing force of the blade 361. The roller 300 is a driving roller for rotating the transfer belt 30 and rotates counterclockwise.

The roller 28 is a "secondary transfer roller" which is formed by covering the peripheral surface of a core roller made of metal or conductive resin with conductive sponge or conductive rubber. , And a “transfer bias voltage for transfer by electrostatic attraction” is applied from the power supply 29. As the power supply 29, a "constant-voltage power supply" or a "constant-current power supply" can be used, but in this embodiment, a "constant-current power supply" is used. The roller 28 is displaced in accordance with the contact and separation of the transfer belt 30 with the intermediate transfer belt 16. The fixing roller pair 38 fixes the secondary-transferred visible image to the transfer material S. The smoothness detecting means 40 provided on the entrance side of the transfer material S to the secondary transfer portion is "means for detecting whether the surface smoothness of the transfer material S is good or bad." The control unit 25 is configured as a “microcomputer, CPU, or the like”, controls each of the above units according to an image forming process, and, as described later, a transfer material S detected by the smoothness detection unit 40.
The second transfer in the second transfer unit is selected to be "transfer by electrostatic attraction or transfer by electrostatic repulsion" in accordance with the smoothness of the transfer. Cleaning means 42
Is a means for cleaning the peripheral surface of the photoreceptor 10 and has a cleaning brush and a cleaning blade.

Hereinafter, a color image forming process by the image forming apparatus shown in FIG. 1A will be described. While rotating the photoreceptor 10 at a constant speed in the counterclockwise direction, the peripheral surface of the photoreceptor is uniformly charged to a predetermined polarity by the charging means 12, and a "yellow latent image" is written by optical writing with the latent image forming light L. When the yellow latent image formed by writing is developed by the yellow developing unit Y of the developing device 14, a “visible image using yellow toner” is formed on the photoconductor 10. This visible image is
In the transfer section, primary transfer is performed on the surface of the intermediate transfer belt 16 by “electrostatic attraction”. After the transfer of the visible image, the peripheral surface of the photoconductor 10 is neutralized by a static eliminator (not shown), cleaned by the cleaning unit 42, the photoconductor 10 is uniformly charged again, and a new “magenta latent image” is written and formed. The magenta latent image is developed by the magenta developing unit M, and the visible image formed by the magenta toner is transferred to the intermediate transfer belt 16.
The primary transfer is performed while being superimposed on the above-mentioned “visible image formed by the yellow toner previously transferred”.

By repeating the same process, the "cyan latent image"
Formation and development by the cyan developing unit C, primary transfer of a visible image to the intermediate transfer belt 16 by cyan toner,
Formation of "black latent image", development by black developing unit BK, intermediate transfer belt 16 of visible image by black toner
When the primary transfer is performed, the four types of visible images formed by the yellow, magenta, cyan, and black toners overlap each other on the intermediate transfer belt 16 to form a “color visible image”. I do. Until a “color visible image” is obtained on the intermediate transfer belt 16, the transfer belt 30 is kept away from the intermediate transfer belt 16, the charge is removed by the charge removing unit 20, the cleaning is performed by the cleaning unit 18, the lubricant is applied by the brush 23, and the transfer is performed. No pre-transfer charging by the pre-charging means 24 is performed. After the primary transfer of the visible image with the black toner, the photosensitive member 10 is neutralized by a neutralizer (not shown), and the residual toner is removed by the cleaning unit 42.

When the color visible image is formed on the intermediate transfer belt 16 in this way, the transfer material S is transported toward the second transfer section. The transferred transfer material S is first detected by the smoothness detecting means 40 for “surface smoothness”, and the transfer belt 30 separated from the intermediate transfer belt 16 is detected.
Transfer belt 30, the intermediate transfer belt 16
, And conveys the transfer material S to the secondary transfer portion (at this time, the transfer material S is electrostatically adsorbed onto the transfer belt 30 by corona discharge means (not shown) as necessary).

As shown in FIG. 1C, the result of detection by the smoothness detecting means 40 is sent to the control means 25. The control unit 25 determines “whether to perform the secondary transfer by using the electrostatic attraction or the electrostatic repulsion” based on whether or not the detected smoothness is good. That is, when the smoothness of the surface of the transfer material S is good, the control means 25 applies a “development bias voltage having a polarity opposite to the charging polarity of the visible image” to the roller 28 by the power supply 29 to control the constant current. Performs secondary transfer by electrostatic attraction. If the smoothness of the surface of the transfer material S is poor and irregularities are present on the surface, the control unit 25 controls the roller 16 by the power supply 165.
4. “Development bias voltage of the same polarity as the charged polarity of the visible image”
And “secondary transfer by electrostatic repulsion” is performed by constant current control or constant voltage control.

When the electrostatic attraction field is formed by the voltage from the back side of the transfer material S when the smoothness of the surface of the transfer material S is poor, the surface of the transfer material S (the side on which the visible image is transferred) is formed. Since the above-mentioned electrostatic attraction field is disturbed by unevenness and the electrostatic attraction acting on each part of the visible image is not uniform, uniform secondary transfer is not realized, and the visible image transferred onto the transfer material S becomes However, when the developing bias voltage is applied to the back side of the intermediate transfer belt 16 as the “image carrier” by the roller 164 to form an electrostatic repulsion field, the surface of the intermediate transfer belt 16 becomes smooth. As a result, a uniform electrostatic repulsion acts on the visible image, and uniform secondary transfer can be realized.

Various means can be implemented as the smoothness detecting means 40. The quality of the smoothness of the surface of the transfer material depends on the degree of unevenness of the surface of the transfer material. For example, when the transfer material is irradiated with light having high directivity, the diffusivity of the reflected light increases as the smoothness becomes poor. Therefore, if the light reflected by the transfer material is detected by the optical sensor at the position of regular reflection, the light receiving amount of the optical sensor increases as the smoothness becomes better, and the light receiving amount decreases as the smoothness becomes worse. , It is possible to detect the smoothness of the transfer material in accordance with the output. Alternatively, the tip of the lightly supported swingable actuator is brought into contact with the transfer material, a lightweight small magnet is attached to the base of the actuator, and a coil is arranged in the vicinity of the magnet, so that the transfer material is If the slight swing of the actuator when passing through the position is detected as a change in the induced current generated in the coil, the less the smoothness of the transfer material, the larger the swing amount of the actuator and the larger the detected current. The smoothness can be detected by the magnitude of the detected current. The control means 25 includes
"Threshold" for the detected smoothness is set,
If the smoothness exceeds the threshold value and is poor, the execution of the secondary transfer by the electrostatic repulsion is determined. Prior to the secondary transfer, the visible image is uniformly charged by the pre-transfer charging unit 24 to even out the charging unevenness.

When the photoreceptor 10 and the intermediate transfer belt 16 contact each other at the nip portion of the primary transfer portion and separate from each other, a peeling discharge is generated via a gap between the two members due to an electric field formed by the separation. The charges due to the peeling discharge “charge mottle” the visible image transferred to the intermediate transfer belt 16. In addition, the lower the image density in the visible image, the higher the charging potential due to the peeling discharge. For this reason, the charging potential of the “halftone image portion” tends to be higher than the so-called “solid portion” in the visible image. If the volume resistance of the intermediate transfer belt 16 is a high value of about 10 ¹³ Ωcm,
“Visible image charging unevenness” generated as described above is difficult to be eliminated through the intermediate transfer belt, and secondary transfer may be performed with the charging unevenness. Then, due to uneven charging in the visible image, the setting range of the optimum conditions for the secondary transfer may be narrowed, or the above-mentioned optimum conditions may not be realized, and good secondary transfer may not be performed. In order to avoid such a problem, the secondary transfer is performed after the non-uniform charging of the visible image is made uniform by the DC corona discharge by the pre-transfer charging unit 24.

As described above, the image forming apparatus according to the embodiment shown in FIG. 1 is an image forming apparatus that electrostatically transfers a visible image formed by the toner on the image carrier 16 to the transfer material S. The transfer is performed by applying an “electrostatic repulsion” to the image from the image carrier 16 side (claim 1), and applying an electrostatic attraction to the visible image from the transfer material S side. And a function of selectively transferring electrostatic attraction or electrostatic repulsion according to transfer conditions to electrostatically transfer the visible image on the image carrier 16 to the transfer material S. (Claim 2) When the transfer condition for selecting one of the electrostatic repulsive force and the electrostatic attraction is the quality of the surface smoothness of the transfer material (Claim 4), and the surface smoothness of the transfer material S is good. Performs transfer of a visible image by electrostatic attraction and, when the surface smoothness of the transfer material S is poor, performs transfer by electrostatic repulsion ( Claim 5) A smoothness detecting means 40 for detecting the quality of the surface smoothness of the transfer material S, and a transfer by electrostatic attraction and a transfer by electrostatic repulsion are selected and executed based on a detection signal of the smoothness detecting means 40. (Claim 6).

Further, on the back side of the image carrier 16, there is provided an electrostatic repulsion electrode means 164 for applying a "transfer bias voltage having the same polarity as the visible image" (claim 8). The means 164 is roller-shaped (claim 9). The electrostatic attraction electrode means 28 (Claim 10), which is provided on the back side of the transfer material S and applies a transfer bias voltage having a polarity opposite to that of the visible image, has a roller shape (Claim 11).

The image carrier 16 is an "intermediate transfer medium".
The visible image of the toner formed on the latent image carrier 10 is
The transfer material S, which is primarily transferred by the transfer unit and is the final image carrier
In the second transfer section, the visible image is secondarily transferred by electrostatic repulsion or electrostatic attraction (Claim 12), and the intermediate transfer medium 16 is belt-shaped (Claim 13). Also,
The transfer material S, which is the final image carrier, is conveyed through the second transfer unit by the transfer belt 30 that can be brought into contact with and separated from the intermediate transfer medium 16 (claim 14).

The primary transfer section and the secondary transfer section of the intermediate transfer medium 16 are connected to two or more grounding means 162, 163, 166, 1
The intermediate transfer belt 16 serving as an intermediate transfer medium is provided on a base layer 16A having a volume resistance of a medium resistance region and an intermediate layer 16B having a volume resistance of a medium resistance region. And a thin insulating layer 16 </ b> C in this order, and have a “medium resistance region volume resistance” as a whole (claim 18). The transferred visible image is a "color visible image in which a plurality of types of toner visible images having different colors are superimposed on each other".

FIG. 2 is a diagram showing another embodiment of the present invention. In order to avoid complication, the same reference numerals as those in FIG. 1A are assigned to components which are considered to have no risk of confusion, and description thereof will be omitted. The first difference from the embodiment of FIG. 1 is that an intermediate transfer medium, which is an “image carrier”, to which a visible image is primarily transferred from a photoconductor 10, which is a latent image carrier, is an intermediate transfer belt 17. The secondary transfer from the intermediate transfer belt 17 to the transfer material S, which is the final image carrier, is performed by the transfer belt 17 and the roller 28 using “conductive rubber”.
The transfer is performed while the transfer material S is pinched and conveyed by A. Roller 28
“A” can be moved toward and away from the transfer belt 17 and “while a color visible image is formed on the intermediate transfer belt 17 by primary transfer”.
Is separated from the intermediate transfer belt 17. The formation of a color visible image on the intermediate transfer belt 17 by primary transfer from the charging of the photoconductor 10 and the elimination and cleaning of the photoconductor 10 are the same as in the embodiment of FIG.

The intermediate transfer belt 17 has rollers 170, 1
72, 173, 175, 176.
Among these rollers, a roller 170 is a roller for applying a voltage for primary transfer and is a “metal roller”, and a transfer bias voltage of constant voltage control or constant current control is applied from a power supply 171. The roller 172 is a “tension roller” and the roller 175 is a “drive roller”. These are formed as metal rollers or conductive resin rollers, and are electrically grounded. The roller 176 is formed as a metal roller by a “static roller” and is grounded. Roller 1
Reference numeral 73 denotes a secondary transfer facing roller also serving as an “electrode for electrostatic repulsion”, which is formed as a metal roller or a conductive resin roller.
From 74, a transfer bias voltage (constant voltage control or constant current control) having the same polarity as the visible image is applied. The charge removing brush 177 is the charge removing brush 168 in the embodiment of FIG.
Is similar to

The second point of difference between the embodiment of FIG. 2 and the embodiment of FIG. 1 is not shown in FIG. 2, but whether the secondary transfer is performed by electrostatic repulsion or electrostatic attraction. Is "switched manually". Of course, also in the embodiment of FIG. 2, similarly to the embodiment of FIG. 1, the smoothness of the surface of the transfer material S is detected by the smoothness detecting means, and the secondary transfer is performed by the control means 25 by the electrostatic repulsive force. Alternatively, it may be possible to select and execute whether to perform the operation by electrostatic attraction. Of course, when the smoothness of the surface of the transfer material S is good, the secondary transfer is performed by electrostatic attraction. When the smoothness is poor, the secondary transfer is performed by electrostatic repulsion.
The next transfer is performed.

Various methods can be used to manually switch "whether to perform the secondary transfer using electrostatic repulsion or electrostatic attraction". Transfer materials having poor smoothness and large irregularities on the surface are often fed by "manual feed" .For example, when "manual feed is performed", the transfer material set for manual feed is set to the use state. The control unit 25 may detect the operation (manual operation) of performing the secondary transfer by an electrostatic repulsion, or store the transfer material having poor smoothness in a dedicated cassette, and When the use of the cassette is manually selected in the operation section, the
The next transfer can also be performed. Alternatively, a button for selecting secondary transfer by electrostatic repulsion may be provided in the operation unit, and the user may manually select secondary transfer by electrostatic repulsion according to the smoothness of the transfer material.

The third difference is that the embodiment of FIG.
"Pre-transfer charging means" performed in the embodiment of FIG.
Is not performed before the secondary transfer.
Also in the embodiment of FIG. 2, the intermediate transfer belt 17
As in the case of the intermediate transfer belt 16 in the embodiment of FIG. 1, the intermediate transfer belt 16 is “an intermediate layer is adhesively formed on a base layer, and a surface layer is further formed thereon”. Area), the surface layer is an insulating layer, and the intermediate transfer belt as a whole has a medium resistance area volume resistance, but the volume resistance of the entire intermediate transfer belt is 10 ⁸ to
Since the resistance is about 10 ¹¹ Ωcm and “the volume resistance is relatively low in the medium resistance area”, the “charging unevenness” of the visible image generated by the peeling discharge in the primary transfer is quickly eliminated through the intermediate transfer belt 17. Therefore, pre-transfer charging is unnecessary.

That is, the image forming apparatus according to the embodiment shown in FIG. 2 is an image forming apparatus for electrostatically transferring a visible image formed by the toner on the image carrier 17 onto the transfer material S. On the other hand, the transfer is performed by applying an electrostatic repulsion from the image carrier side (claim 1).
Has a function of performing transfer by applying electrostatic attraction from the side, and selectively applies electrostatic attraction or electrostatic repulsion according to transfer conditions to transfer a visible image on the image carrier 17 to the transfer material S. The electrostatic transfer is performed (claim 2), and the transfer condition for selecting one of the electrostatic repulsive force and the electrostatic attraction is the quality of the surface smoothness of the transfer material (claim 4). When the surface smoothness of the transfer material S is good, a visible image is transferred by electrostatic attraction. When the surface smoothness of the transfer material S is bad, transfer by electrostatic repulsion is performed (claim 5). Switching of the attraction force is performed manually (claim 7).

Also, on the back side of the image carrier 17, an electrostatic repulsion electrode means 173 for applying a transfer voltage having the same polarity as that of the visible image.
(Claim 8), and the electrostatic repulsion electrode means 173 is in the form of a roller (claim 9). The electrostatic attraction electrode means 28A (Claim 10), which is provided on the back side of the transfer material S and applies a transfer voltage having a polarity opposite to that of the visible image, has a roller shape (Claim 11). The image carrier 17 is an “intermediate transfer medium”, in which the visible image of the toner formed on the latent image carrier 10 is primarily transferred by the first transfer unit, and the second transfer is performed on the transfer material S, which is the final image carrier. The secondary transfer of the visible image is performed by the electrostatic repulsion or the electrostatic attraction at the portion (claim 12), and the intermediate transfer medium 17 is in a belt shape (claim 13). Transfer material S as final image carrier
The visible image is transferred by secondary transfer while being sandwiched and conveyed between the intermediate transfer medium 17 and the roller-like electrostatic attraction electrode means 28A which can be brought into contact with and separated from the intermediate transfer medium 17 (claim 1).
5) The primary transfer section and the secondary transfer section of the intermediate transfer medium 17 are electrically separated from each other by two or more grounding means 172, 175, 176 (Claim 16). Reference numeral 17 denotes a structure in which an intermediate layer having a volume resistance of the medium resistance region and a thin insulating layer are laminated in this order on a base layer having a volume resistance of the medium resistance region, and has a volume resistance of the medium resistance region as a whole ( Claim 18). The transferred visible image is a "color visible image in which a plurality of types of toner visible images having different colors are superimposed on each other".

Of course, the image forming apparatus of the present invention is not limited to the above embodiment. For example, the photoreceptor 10 as a latent image carrier may be in the form of a "belt" or another form instead of the above-mentioned drum-shaped one. It may be of the type. The intermediate transfer media 16 and 17 are not limited to the intermediate transfer belt, and may be a drum-shaped or another type. The structure of the intermediate transfer medium is not limited to the above-described three-layer structure, but may be a single-layer structure or a two-layer structure. Electrical characteristics such as volume resistance and surface resistance, and materials and materials may be changed according to imaging conditions. Can be appropriately selected and set.

The neutralization brushes 168 and 177 of the intermediate transfer medium
Alternatively, a roller or a blade may be used as the charge removing means, and the position of the charge removing brush (or the roller or the blade instead of the roller) is determined in the nip portion between the intermediate transfer belt and the photosensitive member. It suffices if it is downstream of the bias voltage applying unit (the roller 160 in FIG. 1 and the roller 170 in FIG. 2). Also, the transfer bias voltage applying means for the primary transfer in the primary transfer is not limited to the roller shape but may be in the form of a brush or a blade, and the transfer bias voltage application position may be the downstream side of the charge removing means. It may be inside the nip.
Further, instead of the roller 167 in FIG. 1 and the roller 176 in FIG. 2, a charge removing means such as a blade or a brush can be used.

As the secondary transfer electrode means for electrostatic repulsion, a brush-like or blade-like one can be used instead of the roller 164 or the roller 173. "Secondary transfer electrode means for electrostatic attraction" The transfer material is not limited to the roller shape but may be a belt shape, and the “transferring material conveying means” is not limited to the belt shape but may be another shape such as a drum shape. The contact type static elimination means such as the static elimination brush or the static elimination roller applies a voltage having a polarity opposite to the charging polarity of the object to be neutralized in a range that does not affect the primary and secondary transfer, instead of grounding the contact. You may.

[0053]

EXAMPLE The embodiment described with reference to FIG. 1 was specifically implemented as follows. Embodiment 1 A photoreceptor 10, a charging unit 12, a developing unit 14, a cleaning unit 42, and the like are composed of a digital color image forming apparatus capable of copying a document having a maximum size of A-row # 3 (copy function for copying a color document, text Information and / or image information provided as image information).

As the intermediate transfer belt 16, a 75 μm-thick PVDF (polyvinylidene fluoride) having a volume resistance adjusted to 10 ⁸ to 10 ¹¹ Ωcm by mixing titanium oxide as a base layer, and a volume resistance: 10 ¹³ Ωcm, thickness:
75 μm of PVDF was bonded as an intermediate layer, and an insulating layer having a thickness of 1 μm was provided thereon. The overall volume resistance of the intermediate transfer belt is 10 ¹² Ωcm. The size of the intermediate transfer belt 16 is width: 368 mm, length:
440 mm.

The “nip width” of the primary transfer portion between the photosensitive member 10 and the intermediate transfer belt 16 is set to 10 mm.
The distance between the position 8 and the downstream end of the nip width is 7 mm. The roller 160 is a nickel-plated metal roller, the transfer voltage for primary transfer (voltage applied to the roller 160) is 1.0 KV with respect to the first color visible image (yellow visible image),
1.3 to 1.4K for color visible image (magenta visible image)
V, 1.6 to 1. with respect to the third color visible image (cyan visible image).
8 KV, 1.9 for the fourth color visible image (black visible image)
~ 2.2 KV. The width of the transfer belt 30 is 3
70 mm, length: 500 mm, thickness: 100 μm PV
DF film was used. The volume resistance is 10 ¹³ Ωcm. As the transfer material S, a plain paper, an image paper (without calendar smoothness and no smoothness), an OHP sheet, and a thick paper having a surface with reliefs formed in a relief shape were used. When the “transfer material” is the plain paper, the image paper, or the OHP sheet, the threshold value of the smoothness in the control unit 25 is set so that the secondary transfer is performed by the electrostatic attraction. For these transfer materials,
The transfer bias voltage applied to the roller 28 is applied with a constant current control so that the transfer current becomes 10 to 20 μA, the secondary transfer is performed by electrostatic attraction, and the fixing is performed. Thus, a very good color image could be formed. However, in the case where the transfer material is the above-mentioned “thick paper having reliefs formed on the surface in a relief shape”, the result of performing “secondary transfer by electrostatic attraction” under the above conditions is determined according to the relief-like roughness. Unsightly density unevenness occurred. The cardboard has a thickness of about 0.3 mm and a width of about 1.
A groove of about 5 mm was randomly formed in a relief shape, and the density of the transferred color image was low at the groove.

Then, a transfer bias voltage having the same polarity as that of the visible image is applied to the roller 164 on the “thick paper having the relief formed on the surface in a relief shape” to perform “secondary transfer by electrostatic repulsion”. However, as in the case of the above-mentioned plain paper, a good color image could be formed. That is, the visible image was sufficiently transferred also to the "concave section in the thick paper", and there was no insufficient density in the concave section.

Further, since the volume resistance of the intermediate transfer belt 16 is high, regardless of whether the secondary transfer is performed by the electrostatic attraction or the electrostatic repulsion, the pre-transfer charging means 24 before the secondary transfer.
Before the transfer was performed to make uniform the unevenness of charging of the visible image.

In the case where the recorded image is the third size in the column A, when the primary transfer of the rear portion of the black visible image (the visible image of the fourth color) is performed in the primary transfer portion, the color visible Since the leading end of the image reaches the secondary transfer unit, the secondary transfer was performed while the primary transfer was being performed. However, the primary transfer unit and the secondary transfer unit were connected by the ground rollers 163, 166 and the like. There was no "interaction between the primary transfer and the secondary transfer" due to the electrical separation. In the image formation, not only the formation of the color image but also the same result was obtained in the case of a single color image.

The static elimination of the surface of the intermediate transfer belt 16 by the static elimination means 20 is performed by AC corona discharge with DC superimposed. In the case of forming one color image, after the secondary transfer is completed, the intermediate transfer belt is removed. When a color image is repeatedly formed by rotating the rotating roller 16 one turn, the discharging is performed until the next image reaches the discharging position after the secondary transfer, and a single monochrome image is formed. At the time, at least one round of the belt was neutralized after the primary transfer was completed, and when a single-color image was formed as a repeat image, static elimination was performed until the next image reached the neutralization position after the primary transfer was completed.

The embodiment shown in FIG. 2 was specifically implemented as follows. Embodiment 2 The intermediate transfer belt in the embodiment shown in FIG. 1 is replaced with the intermediate transfer belt 17 shown in FIG. 2, and the intermediate transfer belt 17 and the roller 28A (made of conductive rubber) sandwich and transfer the transfer material S. Secondary transfer was performed. The intermediate transfer belt 17 has a volume resistance of 10 ⁸ to 10 by mixing titanium oxide.
A thickness adjusted to ¹¹ Ωcm: 75 μm PVDF (polyvinylidene fluoride) is used as a base layer, and a volume resistance adjusted to the same degree as this base layer is adhered as a 75 μm PVDF as an intermediate layer. Thickness: 1 μm provided with an insulating layer. The overall volume resistance of the intermediate transfer belt is 10 ⁸ to 10 ¹¹ Ωcm, and the size is 368 mm and the length is 4 as in the case of the intermediate transfer belt 16 of the first embodiment.
40 mm. The volume resistance of the intermediate transfer belt 17 is 10
^{Since it is 8} to 10 ¹¹ Ωcm, which is “low value in the intermediate resistance region”, pre-transfer charging by the pre-transfer charger is omitted.

The "nip width" of the primary transfer portion between the photosensitive member 10 and the intermediate transfer belt 17 is 10 mm, and the distance between the neutralizing brush 177 and the downstream end of the nip width is 6 to 7 mm. The roller 170 is a nickel-plated metal roller.
Transfer voltage of next transfer (voltage applied to roller 160)
Is 1.2K from the first color visible image (yellow visible image)
V, 1.3K for the second color visible image (magenta visible image)
V, 1.4 KV for the third color visible image (cyan visible image),
The voltage was set to 1.5 KV with respect to the fourth color visible image (black visible image). As the transfer material S, plain paper, image paper (without smoothness without calendering), OHP sheet, and the above-mentioned thick paper having reliefs formed on the surface in a relief shape were used. When the “transfer material” was the plain paper, the image paper, or the OHP sheet, the secondary transfer was manually set so that the secondary transfer was performed by electrostatic attraction. For these transfer materials, the transfer bias voltage applied to the roller 28 is changed to a transfer current of 10 to 20 μA.
The constant current control is applied so that
As a result of performing the next transfer and fixing, extremely good color images could be formed on any of the transfer materials.
However, when the transfer material is the above-mentioned “thick paper having reliefs formed on the surface in a relief shape”, the result of the secondary transfer by the electrostatic attraction under the above-described conditions shows that the density is unpleasant due to the relief-like roughness. Unevenness occurred.

Accordingly, for the above-mentioned “thick paper having a surface having reliefs formed in a relief shape”, the secondary transfer is manually set for “the transfer voltage having the same polarity as the visible image is applied to the roller 164”. Then, when secondary transfer was performed by electrostatic repulsion,
A good color image could be formed as in the case of the plain paper and the like. The visible image is well transferred to the recesses in the cardboard,
There was no lack of concentration in the concave portions.

When the recorded image is the third size in the column A, the secondary transfer was performed in a state where the primary transfer of the fourth color visible image was performed. Ground roller 172,
175 and the like, there was no "interaction between primary transfer and secondary transfer". The same results were obtained in the image formation as in the above-described color image formation and also in the formation of a single color image. The static elimination on the surface side of the intermediate transfer belt 17 by the static elimination means 20 is performed by A
The charge was removed by C corona discharge in the same manner as in Example 1.

[0064]

As described above, according to the present invention, a novel image forming apparatus can be realized. The image forming apparatus of the present invention applies electrostatic repulsion to the visible image formed by the toner on the image carrier from the image carrier side to electrostatically transfer the image onto the transfer material. In addition, excellent visible image transfer can be realized on a wide range of transfer materials such as thick paper having relief-like irregularities.

According to another aspect of the present invention, the visible image on the image carrier is electrostatically transferred to a transfer material by selectively applying the electrostatic attraction or the electrostatic repulsion according to the transfer conditions. Therefore, appropriate transfer can be performed according to transfer conditions.

Further, in the image forming apparatus according to the present invention, the visible image is transferred via the intermediate transfer medium, and the secondary transfer from the intermediate transfer medium to the final image carrier is performed by electrostatic repulsion. Alternatively, it can be appropriately and well performed by electrostatic repulsion or electrostatic attraction.

In the image forming apparatus according to the present invention,
Since the primary transfer portion and the secondary transfer portion of the intermediate transfer medium are electrically separated from each other by two or more grounding means, the primary transfer and the secondary transfer can be performed while temporally overlapping. It is possible to speed up the image forming process.

In the image forming apparatus according to the nineteenth aspect,
Since the unevenness in the charge of the next transferred visible image is made uniform, the influence of the uneven charge on the secondary transfer can be eliminated. Claim 20
According to the image forming apparatus described above, a high-quality color image can be formed on a wide variety of transfer materials.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a view for explaining another embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

Reference Signs List 16 intermediate transfer belt 164 roller as electrode means for electrostatic repulsion for transfer by electrostatic repulsion 40 smoothness detecting means

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hiroshi Ono 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd.

Claims (20)

[Claims] In an image forming apparatus for electrostatically transferring a visible image formed by a toner on an image carrier to a transfer material, the visible image is transferred by applying an electrostatic repulsive force from the image carrier side. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, further comprising a function of transferring a visible image from the transfer material side by applying an electrostatic attraction from the transfer material side, wherein the electrostatic attraction or the electrostatic attraction is performed in accordance with a transfer condition. An image forming apparatus, wherein a visible image on an image carrier is electrostatically transferred to a transfer material by selectively applying electrostatic repulsion. 3. The image forming apparatus according to claim 2, wherein an electrostatic repulsion applied to the visible image is larger than an electrostatic attraction. 4. The image forming apparatus according to claim 2, wherein the transfer condition for selecting one of the electrostatic repulsion and the electrostatic attraction is good or poor surface smoothness of the transfer material. Image forming device. 5. The image forming apparatus according to claim 4, wherein when the surface of the transfer material has good surface smoothness, a visible image is transferred by electrostatic attraction, and when the surface of the transfer material has poor surface smoothness, a static image is formed. An image forming apparatus that performs transfer by electro-repulsive force. 6. An image forming apparatus according to claim 5, wherein a smoothness detecting means for detecting whether or not the surface smoothness of the transfer material is good or not, and a transfer or static transfer by electrostatic attraction based on a detection signal of said smoothness detecting means. An image forming apparatus comprising a control unit for selectively executing transfer by electro-repulsive force. 7. An image forming apparatus according to claim 5, wherein the user can manually select between transfer by electrostatic attraction and transfer by electrostatic repulsion. 8. An image forming apparatus according to claim 1, further comprising an electrostatic repulsion electrode means for applying a transfer voltage having the same polarity as that of the visible image on a back surface of the image carrier. An image forming apparatus comprising: 9. An image forming apparatus according to claim 8, wherein said electrostatic repulsion electrode means is in the form of a roller. 10. An image forming apparatus according to claim 2, further comprising an electrostatic attraction electrode means for applying a transfer voltage having a polarity opposite to that of the visible image on a back surface of the transfer material. An image forming apparatus comprising: 11. An image forming apparatus according to claim 10, wherein said electrostatic attraction electrode means has a roller shape or a belt shape. 12. The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer medium, and a visible image of the toner formed on the latent image carrier is transferred to the first transfer device. An image forming apparatus, wherein a visible image is secondarily transferred to a transfer material serving as a final image carrier by electrostatic repulsion or electrostatic attraction in a second transfer unit. 13. The image forming apparatus according to claim 12, wherein the intermediate transfer medium has a belt shape. 14. The image forming apparatus according to claim 12, wherein the transfer material as the final image carrier is conveyed through the second transfer unit by a transfer material conveyance unit capable of coming into contact with and separating from the intermediate transfer medium. Characteristic image forming apparatus. 15. The image forming apparatus according to claim 12, wherein the transfer material as the final image carrier is capable of coming into contact with and separating from the intermediate transfer medium, and is provided with a roller-shaped or belt-shaped electrode means for electrostatic attraction. An image forming apparatus wherein a visible image is transferred by secondary transfer while being held and transported by a transfer medium. 16. The image forming apparatus according to claim 12, wherein the primary transfer portion and the secondary transfer portion of the intermediate transfer medium are electrically separated from each other by two or more grounding means. An image forming apparatus comprising: 17. The image forming apparatus according to claim 16, wherein the start time of the secondary transfer is before the end time of the primary transfer. 18. The image forming apparatus according to claim 13, wherein the intermediate transfer medium is an intermediate transfer belt, and the intermediate transfer belt is formed on a base layer having a volume resistance of a medium resistance area. An image forming apparatus comprising: an intermediate layer having a volume resistance of a medium resistance region; and a thin insulating layer laminated in this order, and having a volume resistance of a medium resistance region as a whole. 19. The image forming apparatus according to claim 18, wherein the intermediate transfer belt has a relatively high volume resistance in a medium resistance region, and is located downstream of the primary developing unit and upstream of the secondary developing unit. 1
An image forming apparatus comprising: a pre-transfer charging unit for uniforming charging unevenness of a next transferred visible image. 20. An image forming apparatus according to claim 12, wherein the transferred visible image is a color visible image in which a plurality of toner visible images of different colors are superimposed. An image forming apparatus comprising: