JP2000075573A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high quality image by making the max. of the carried quantity of a toner variable to control the charge quantity of a toner image transferred on a transfer material not to exceed the charge quantity capable of being held by the transfer material to reduce retransferring in forming a toner image on the transfer material and to realize stable transfer. SOLUTION: The max. quantity of the carried toner per unit area of the toner image transferred on the transfer material 6 is made variable so that the charge quantity of the toner image transferred on the transfer material does not exceed the charge quantity capable of being held by the transfer material 6 per unit area. As a means for making the carried quantity of the toner variable, for example a means for making Vcont variable is used. A photosensitive drum 1 is uniformly charged by a primary charger 2 on the drum 1. The potential is irradiated with laser beam to increase the potential of a part irradiated with the laser beam. In such a case when the potential on the photosensitive drum 1, where a monochromatic solid image is formed, is expressed by V1 and the development bias is expressed by Vdc, Vcont is expressed by Vcount=V1-Vdc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an electrostatic latent image on an image carrier by an electrophotographic method or an electrostatic recording method,
The present invention relates to an image forming apparatus that develops this electrostatic latent image into a toner image and transfers the toner image to a transfer material. In particular, the present invention relates to an image forming apparatus that sequentially forms a plurality of color toner images on an image carrier, and Can be suitably embodied in an image forming apparatus that obtains a multicolor image by repeatedly transferring to a transfer material.

[0002]

2. Description of the Related Art FIG. 1 shows an example of an electrophotographic color image forming apparatus. In the color image forming apparatus of the present embodiment, a photosensitive drum 1 serving as an image carrier is rotatably supported to rotate in the direction of an arrow, and a primary charger 2, an exposing device 3, and a surface of the photosensitive drum 1 are provided therearound. A potential sensor 4 for detecting a potential, a developing device 5, a transfer device 8, and a cleaning device 9 are arranged.

The primary charger 2 uniformly charges the photosensitive drum 1, and the exposure device 3 scans the polygon mirror with light corresponding to the image signal of each color component generated from the light source device, and scans the light. Is turned by a reflection mirror and condensed on the generatrix of the photosensitive drum 1 via an fθ lens to form a latent image of each color according to an image signal on the photosensitive drum 1 in order.

In this embodiment, a developing device 5 provided beside the photosensitive drum 1 includes a magenta developing device 5M and a cyan developing device 5M.
C, a yellow developing unit 5Y and a black developing unit 5B. These magenta developing device 5M and cyan developing device 5
C, the yellow developing unit 5Y and the black developing unit 5B
A predetermined amount of each of magenta, cyan, yellow and black developers is filled. Each developing unit 5 (5M, 5M
C, 5Y, and 5B) are moved to and away from a position facing the outer peripheral surface of the photosensitive drum 1 to develop the electrostatic latent image formed on the photosensitive drum 1.

A transfer drum as a transfer device 8 for carrying and transferring a transfer material is installed diagonally below the photosensitive drum 1. The transfer material 6 is fed to the transfer drum 8 from a transfer material cassette 60 installed at a lower portion of the apparatus main body via a registration roller 13 and the like.

[0006] The transfer drum 8 is formed by joining a polyethylene terephthalate, polyvinylidene fluoride, polycarbonate, or polyurethane resin film to the surface of a frame in which two rings are connected by a connecting member to form a drum.

The overall operation of this color image forming apparatus is described as 4
A brief description will be given by taking the case of color image formation as an example.

The photosensitive drum 1 rotates, and its surface is uniformly charged by the primary charger 2. Next, the exposure device 3 irradiates the photosensitive drum 1 with laser light L modulated by the first color of the document, for example, a magenta image signal, and forms a magenta electrostatic latent image on the photosensitive drum 1. This latent image is
The first color magenta toner image is formed on the photosensitive drum 1 by developing with a magenta developing device 5M fixed at a developing position in advance.

On the other hand, the transfer material 6 is extruded from the cassette 60 by a registration roller 13 or the like in a direction along the transfer drum 8. At the same time as the transfer material 6 is extruded, the suction roller 12a of the suction charging unit 12 including the suction roller 12a and the suction charger 12b is pressed against the surface of the transfer drum 8, and is suction-charged from the back side by the suction charger 12b.
The transfer material 6 is electrostatically carried on the transfer drum 8.

The transfer drum 8 rotates in the direction of the arrow in FIG. 1 in synchronization with the photosensitive drum 1, and a magenta toner image formed on the photosensitive drum 1 by the action of a transfer charger 10 arranged at a transfer position T. Is transferred to the transfer material 6 on the transfer drum 8. The transfer drum 8 continues to rotate, and
Prepare for the transfer of the cyan toner image of the color.

After the transfer of the magenta toner image is completed, the transfer residual toner on the photosensitive drum 1 is cleaned by the cleaning member 9, and similarly, charging by the primary charger 2, irradiation of the laser light L, and the like are performed. A cyan toner image of the next second color is formed on the photosensitive drum 1, and the cyan toner image is transferred onto the transfer material 6 by being superimposed on the magenta toner image. The same image forming process is performed for the third color, yellow and black, and the toner images of four colors of magenta, cyan, yellow, and black are superimposed on the transfer material 6 and transferred to obtain a color image.

The transfer material 6 to which the four color toner images have been transferred is
The sheet is separated from the transfer drum 8 by the action of the separation claw, and is sent to the fixing device 7 by a conveyor belt or the like.

The fixing device 7 has a fixing roller 71 and a pressure roller 72. Heating heaters 75 and 76 are accommodated in the fixing roller 71 and the pressure roller 72, respectively. Further, heat-resistant cleaning members 73 and 74 are provided adjacent to the fixing roller 71 and the pressure roller 72, and are used to control the fixing temperature. Is disposed. Further, an application roller 77 for applying a release agent oil such as dimethyl silicone oil to the fixing roller 71 and an oil reservoir 78 for supplying the release agent oil are provided.

The fixing device 7 heats and presses the conveyed transfer material 6 by means of a fixing roller 71 and a pressure roller 72 to mix the toner images of each color and fix the same on the transfer material 6, thereby forming a full-color print image. To form

The toner remaining on the transfer drum 8 is neutralized by static eliminators 14 and 15 to remove electrostatic attraction, and then scraped off by a rotating fur brush 16.
As a means for removing the residual toner, a blade or a nonwoven fabric may be used alone or in combination.

[0016]

However, in particular,
In an image forming apparatus that forms a color image by multiple transfer as described above, in order to repeat the transfer by superimposing the toner image on the transfer material, the already transferred toner image is used in the next transfer step. Then, a phenomenon called so-called retransfer, which is retransferred onto the photosensitive drum, may occur.

For example, when forming a blue image, first, a magenta solid image is formed on a transfer material, and then a cyan solid image is multiplex-transferred thereon.
In the subsequent transfer process, for example, the transfer process of yellow and black, there is no toner to be transferred on the photosensitive drum. If the toner image on the transfer material surface and the photosensitive drum surface approach or come into contact with each other in this state, a part of the toner image on the transfer material (in this case, mainly a cyan toner image) is retransferred onto the photosensitive drum. A phenomenon occurs.

In this case, in the portion where the cyan toner is re-transferred to the photosensitive drum, the density of the cyan toner image decreases, and the magenta color forming the image appears under the cyan toner image layer, and the image quality is reduced. Causes significant deterioration. Further, since this phenomenon changes depending on changes in the charge amount of the toner and the resistance value of the transfer material due to the change in temperature and humidity, it also becomes a factor that makes the stability of the multiple transfer difficult.

Further, in recent years, as the particle size of the toner has been reduced for higher image quality, the amount of charge per toner particle has been reduced, but the total amount of charge has tended to be increased. Accordingly, the amount of transfer current or transfer voltage required to transfer a solid image has been increasing. It has been found that the increase in the transfer current or the transfer voltage has an adverse effect on the retransfer phenomenon.

Accordingly, an object of the present invention is to form a toner image on a transfer material by transferring a toner image formed on an image carrier, and the toner image once transferred onto the transfer material is again transferred onto the image carrier. An object of the present invention is to provide an image forming apparatus capable of reducing the so-called retransfer, realizing stable transfer, and obtaining a high-quality image.

Another object of the present invention is to form a plurality of color toner images on a transfer material by multiplex-transferring toner images formed on an image bearing member. By providing an image forming apparatus capable of mitigating so-called retransfer, realizing stable multiple transfer, and obtaining a high-quality color image, transferring to the image carrier again in the next color transfer step. is there.

[0022]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
In an image forming apparatus for transferring a toner image formed on an image carrier to a transfer material, the amount of charge of toner per unit area of the toner image transferred onto the transfer material is per unit area capable of holding the transfer material. An image forming apparatus, wherein the maximum value of the amount of applied toner per unit area of the toner image transferred onto the transfer material is made variable so as not to exceed the charge amount.

According to another aspect of the present invention, an image forming apparatus for forming a multicolor image by sequentially forming a plurality of color toner images on an image carrier and repeatedly transferring the plurality of color toner images to a transfer material. The toner image transferred onto the transfer material such that the amount of charge of the toner per unit area of the toner image transferred onto the transfer material does not exceed the amount of charge per unit area that the transfer material can hold. An image forming apparatus is characterized in that the maximum value of the amount of applied toner per unit area is variable for at least one color.

According to one embodiment of the present invention, the maximum value of the amount of toner applied per unit area is made variable depending on the type of the transfer material, or the amount of toner applied per unit area is changed depending on environmental conditions. Make the maximum value variable,
Alternatively, there is provided a means for detecting the impedance of the transfer material, and the maximum value of the amount of applied toner per unit area is made variable by the transfer material impedance.

According to another embodiment of the present invention, the amount of electric charge supplied to the back surface of the transfer material is made variable in accordance with the maximum value of the amount of applied toner per unit area.

In the case of forming a multicolor image, the maximum value of the amount of toner to be developed later is larger than the maximum value of the amount of toner to be developed earlier with respect to the color order of the toner to be developed. Will be larger than

According to another embodiment of the present invention, there is provided a toner density detecting means for detecting the toner density on the image carrier in order to detect the amount of the applied toner.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings. In this embodiment, the present invention is embodied in the electrophotographic color image forming apparatus described above with reference to FIG. 1, and therefore, further description of the configuration and operation of the image forming apparatus will be described. Is omitted.

Example 1 The present inventors have conducted many research experiments to solve the above-described retransfer problem, and as a result, the mechanism of retransfer has been elucidated. It was confirmed that there was an upper limit on the amount of charge that the material could hold.

First, the present inventors supplied charges to the transfer material, and measured the surface potential of the transfer material with respect to the supplied charge amount. FIG. 2 shows the resulting relationship between the amount of charge supplied to each transfer material and the surface potential of each transfer material.

FIG. 2 shows that when the OHT is used as the transfer material, the surface potential of the transfer material A or B also increases in proportion to the supplied charge. It turned out to be gone. In the present embodiment, the transfer material A is made of Haga Paper Store NP1 fine paper (weighing 128 g).
/ M ² ; thickness 120 μm), and the transfer material B is a double-sided thick paper for Canon CLC (weighing 105 g / m ² ; thickness 10).
0 μm).

In a normal temperature and normal humidity environment (here, a temperature of 23 ° C. and a humidity of 60%), the surface potential of the transfer material A also increases in proportion to the supplied charge amount, and the transfer material A may be saturated in the range of the measurement region. Absent. However, when the absolute amount of water at a temperature of 23 ° C. and a humidity of 5% is 0.5 g / m ³ , the charge amounts that can be held in the transfer materials A and B are respectively 500 μC / m ² , 4
The transfer material is 50 μC / m ² , which indicates that the transfer material cannot hold the charge even if a charge higher than that is supplied. That is, it can be seen that the amount of charge per unit area that the transfer material can hold is determined by the environment and the type of the transfer material.

FIG. 3 shows the relationship between the water content of the transfer materials A and B and the amount of charge that can be held per unit area.

When the above examination results are applied to the case of the present embodiment, it is possible to analyze the conventional problems.

When an image is formed using the image forming apparatus shown in FIG. 1 of this embodiment, the measured value of the charge amount of the toner developed on the photosensitive drum 1 is 30 μC / g in the low humidity environment. And the amount of applied toner per unit area of the solid image is 10 g / m ² for a single color. Therefore,
The total amount of toner charge per unit area is 300 μC / m ²
Becomes Actually, not only a single-color image but also a full-color image is often formed by multi-transfer of four color toners. In this case, the maximum amount of toner per unit area formed on the transfer material 6 is further increased. Become. In this case, the amount of applied toner on the transfer material 6 is often determined by, for example, fixing conditions.

In the image forming apparatus of the present embodiment, the maximum amount of toner applied per unit area that can be fixed at a fixing temperature of 150 ° C. is 10 g / m ^{2 for} a single color, and the maximum amount of a single color for a full color. In this case, a full-color image is formed with a glue amount up to 2.0 times the glue amount.

Therefore, in the present embodiment, masking is performed on the secondary colors, tertiary colors, and the like in image processing,
Since the maximum amount of toner applied per unit area is set to 20 g / m ² , the maximum charge amount of the toner per unit area is 600 μC / m ² .

From the above, for example, in the case of the transfer material A, in the normal setting of this embodiment, the maximum amount of toner on the transfer material is larger than the maximum charge amount per unit area of 500 μC / m ² that can be held by the transfer material. The charge amount corresponding to the amount is 100
μC / m ² , and the transfer material itself cannot hold the charge as described above. In other words, the toner once transferred from the photosensitive drum onto the transfer material transfers from the transfer material onto the photosensitive drum at the transfer nip when transferring the next color.
This causes so-called retransfer.

Therefore, in the present embodiment, the amount of charge per unit area that can be held by the transfer material, which is determined by the environment and the type of the transfer material, is set in advance, and the amount of toner applied per unit area on the transfer material is set. The maximum value of the toner per unit area on the transfer material is made variable so that the amount of charge corresponding to the maximum value does not exceed the set amount of charge.
The following is a description using a general formula.

That is, the charge amount per unit mass of the toner developed on the photosensitive drum is represented by Qt (k) (C / kg),
The amount of toner applied per unit area is M (kg / m2),
The charge amount per unit area Qp (s,
k), the configuration is such that M is set so as to satisfy Qp (s, k) / Qt (k) ≧ M. However, the letter k in parentheses indicates an environmental factor, and s indicates the type of transfer material, and the environmental factors include temperature, humidity, absolute water content, and the like.

The image forming process in this embodiment will be described below.

First, the environment and the type of transfer material are set. The environment may be automatically detected by a temperature / humidity sensor, or a copy user may enter the environment. Similarly, the automatic detection means may be employed for the type of the transfer material, or the copy user may input the information by himself.
Further, the above means may be used in combination.

When the environment and the type of the transfer material are determined, Qt and Qp obtained in advance from the measurement result are recorded and set in a storage medium, and the set environment and transfer are determined from a table of the set values. Since Qt and Qp for the type of material are determined, the maximum value of the amount of applied toner per unit area is determined by the above equation. If the maximum value M1 of the amount of applied toner per unit area determined here is smaller than the original set value M0, it is reduced to M1. If it is larger than Mo, the maximum limit value of the amount of glue per unit area is 20.
If it is not more than g / m ² , it is made to approach M1 selected from the set value without limit. However, if the maximum value M1 of the amount of applied toner per unit area exceeds 20 g / m ² , M is set to 20 g / m ² . The lower limit value is 60% of the maximum value of the toner amount of the standard setting value, that is, 1%.
If it is set to ² g / m ^2, and the maximum value of the amount of toner per unit area is smaller than the value calculated by the above equation, it is set to 12 g / m ² from the viewpoint of securing the concentration. However, it is not always necessary to set the lower limit, and the lower limit can be set separately.

As a means for varying the amount of applied toner, a means for varying Vcont is used in this embodiment. Next, referring to FIG. 1 and FIG.
ont, Vback, etc. will be briefly described.

According to this embodiment, as described above, the photosensitive drum 1 is uniformly charged on the photosensitive drum 1 by the primary charger 2. This potential is defined as Vd. This potential is irradiated with the laser beam L, and the potential of the irradiated portion rises.

The potential on the photosensitive drum 1 for forming a monochromatic solid image is V1. On the other hand, the developing bias is Vd
c, Vcont = V1-Vdc, and Vb
ack = Vdc−Vd. The toner is V1 and V
Developed on the photosensitive drum 1 so as to fill the potential difference of dc. Therefore, by changing Vcont, the maximum value of the amount of applied toner per unit area can be changed.

Further, the amount of applied toner can be detected by installing a sensor for detecting the density of the developed toner on the photosensitive drum. This density detecting means develops a single-color solid on the photosensitive drum outside the image area, irradiates the photosensitive drum with light from above the image, and detects the reflected light, but other means may be used. Absent. The relationship between the amount of reflected light and the density or the amount of glue is set in advance, and the amount of toner to be glued is immediately calculated from the detection of the amount of reflected light.
nt can be adjusted. The relationship between the maximum value of the amount of applied toner on the photosensitive drum and Vcont is set in advance. However, if the amount of applied toner greatly deviates from the target value as a result of the above measurement, Vcont is automatically set to Vcont. It is adjusted so that the target amount of applied toner is set.

By executing the above-described process, a state in which an image can be formed in a conventional manner can be obtained.

The above contents will be specifically described in light of a part of the present embodiment.
%) And when the transfer material A is selected, Qt = 30 × 10
⁻³ C / kg and Qp = 500 × 10 ⁻⁶ C / m ² , so that M = 16.7 g / m ² (1.67 mg / cm ² ), which is 16.5% of toner from the standard setting. This will reduce the amount of glue. In this case, the amount of toner applied to the solid color solid is 8.3 g / m ² , and the necessary Vcont is 430 V from the conventionally set value to 400 V, and at the same time, Vb
ack is 130V, Vl is -120V, Vd is -6.
What is necessary is just to reduce to 80V and Vdc to -550V.

When a blue image is formed, for example, the color order of image formation in this embodiment is magenta, cyan, yellow, and black. Therefore, in this embodiment, a single-color solid image is multiplexed in the order of magenta and cyan. Transcribed. Therefore, the amount of applied toner of each color may be distributed by half the maximum value M of the amount of applied toner on the transfer material. That is, the amount of magenta toner to be developed first is 8.3 g / m ² ,
Next, the amount of the cyan toner to be developed is set to 8.3 g / m.
It should be ² .

In the above description, the maximum value of the amount of toner applied per unit area of magenta and cyan is distributed at a rate of 1/2, but the toner layer formed on the transfer material is easier to retransfer. In consideration of this, in the case of a blue image, a configuration may be adopted in which the amount of applied toner of cyan is larger than that of magenta.

Further, in the above-described representative example, the case where the amount of applied toner is reduced by 13.5% has been described. However, if the amount of reduction is small, for example, about 2 to 4%, the toner is added to the lowermost layer. A configuration may be adopted in which only the amount of magenta toner that forms an image is reduced.

As described above, by lowering the maximum value of the amount of applied toner per unit area of each color, the toner image once transferred from the photosensitive drum to the transfer material is transferred to the transfer material at the transfer nip at the time of multiple transfer. The retransfer transferred to the photosensitive drum from above can be reduced, and stable multiple transfer can be realized.

Embodiment 2 This embodiment is basically the same as Embodiment 1, except that when the maximum value of the amount of applied toner per unit area is changed, the transfer is further performed accordingly. The current value is also changed.

According to the present embodiment, as shown in FIG. 5, when the amount of applied toner is reduced, the transfer current value required for transferring the toner is also reduced. Unnecessarily supplied charges cause abnormal discharge in and near the transfer nip, causing image defects. Therefore, it is preferable to perform transfer with the minimum necessary supply charge.

In a low-humidity environment (temperature 23 ° C., humidity 5%), when the toner charge amount is 30 μC / g and the maximum amount of toner applied per unit area is 20 g / m ² , transfer current of 24 μA is used. Although necessary, when the amount of applied toner is reduced by 13.5% as in the representative example of the first embodiment, transfer can be sufficiently performed with a transfer current of about 20 μA.

Further, as described in the first embodiment, when the maximum value of the amount of applied toner per unit area is changed for each color, the transfer current value of each color may be changed accordingly. More preferred.

In this embodiment, a table storing the maximum value of the amount of charge that can be held by the transfer material per unit area for each environment, the amount of charge of the toner for each environment, etc.
If OM is used, a necessary transfer current value can be set.

With this configuration, the same effects as those of the first embodiment can be obtained in this embodiment, and an image defect due to abnormal discharge caused by excessive supply of electric charge to the transfer material can be prevented.

Embodiment 3 This embodiment is basically the same as Embodiment 1, except that the state of the transfer material is automatically monitored (detected), and the toner amount per unit area is accordingly adjusted. It is characterized in that the maximum value of the amount is made variable.

That is, in this embodiment, the transfer voltage for the constant current control is monitored during the image formation (this voltage is
And However, i is a color order. Here, a transfer voltage with respect to a transfer current when there is no transfer material in each environment is measured and recorded in a storage medium (this voltage is Voi, which is indicated by dotted lines in FIGS. 6 and 7).

The difference between the transfer voltage monitored during image formation and the transfer voltage recorded on the storage medium (ΔVi = V
i-Voi) is monitored. ΔV for a certain transfer current
Although i is usually constant, ΔVi decreases when a certain color is transferred when the amount of charge supplied to the transfer material exceeds the amount of charge that the transfer material can hold. For example, there is a phenomenon that ΔVi is constant from the first color to the third color, but becomes almost zero in the final color. Accordingly, in the present embodiment, the transfer current is set so that ΔVi is always constant, and the amount of toner that can be transferred with this transfer current is set.

FIG. 6 shows the transfer potential after the countermeasure, and FIG. 7 shows the transfer potential when the charge is supplied in excess of the amount of charge held per unit area of the transfer material.

For example, in a low humidity environment (temperature 23 ° C., humidity 5
%), When the transfer material A was passed, the potential of the first sheet when the transfer was performed at the standard set transfer current value of 24 μA was monitored. From ΔV1 to ΔV3, 540V to 570V
, But only ΔV4 was 180V. In the present embodiment, the following countermeasures are set when a deviation of 20% occurs from the value of ΔV1, but this error region may be another value.

As described above, ΔV4 is 20% less than ΔV1.
Since the above deviation occurred, countermeasures were taken from the following calculation.
Here, since ΔVi = 1890V, the transfer current I1 is set so that ΔVi = ΔVi / 4 to 470V. This is easily obtained from I1 to (Σ △ Vi / 4) / △ V1 × Io (where Io is the initial set current value and △ V1 is also the initial first color difference voltage).
The initial setting of 24 μA is set to 20 μA, and accordingly,
The maximum value of the amount of toner applied per unit area is also determined as M1− (Σ △ Vi / 4) / △ V1 × M0 (where Mo is the maximum value of the amount of applied toner per unit area). Can be

In this way, the amount of applied toner and the transfer current can be automatically varied without inputting the type of transfer material.

However, the above means is merely a means for automatically detecting the impedance of the transfer material, and may be other means. For example, the transfer high-voltage output may be set to a constant voltage control, and the current at that time may be monitored (in this case, the set value previously recorded in the storage medium also becomes the current value), or an infrared moisture meter is used. Alternatively, the amount of water in the transfer material may be detected, and the impedance of the transfer material may be automatically detected from the relationship between the absolute water content and the impedance of the transfer material.

The above embodiments are all shown in FIG.
Although the image forming apparatus that forms an image with one photosensitive drum 1 and one transfer drum 8 has been described, the present invention is also applied to a tandem type image forming apparatus (not shown) using four photosensitive drums, which is often seen in recent years. Needless to say.

The present invention is not limited to the color image forming apparatus described in each of the above embodiments, but can be applied to a single-color image forming apparatus to achieve the same effects.

[0070]

As described above, according to the image forming apparatus of the present invention, in an image forming apparatus for transferring a toner image formed on an image carrier to a transfer material, a unit of the toner image transferred onto the transfer material is used. The maximum value of the amount of toner applied per unit area of the toner image transferred on the transfer material is variably set so that the charge amount of the toner per area does not exceed the charge amount per unit area that the transfer material can hold. Particularly, in an image forming apparatus that sequentially forms a plurality of color toner images on an image carrier and repeatedly transfers the plurality of color toner images onto a transfer material to obtain a multicolor image, the transfer material To ensure that the amount of charge of the toner per unit area of the toner image transferred thereon does not exceed the amount of charge per unit area that the transfer material can hold.
Since the maximum value of the amount of applied toner per unit area of the toner image transferred onto the transfer material is made variable for at least one color, the toner image formed on the image carrier is transferred. When a toner image is formed on a transfer material, the toner image once transferred on the transfer material is transferred to the image carrier again, that is, so-called retransfer is reduced, stable transfer is realized, and a high-quality image is realized. In particular, even in the formation of a color image, the toner image once transferred onto the transfer material is re-transferred to the image carrier again in the next color transfer step, thereby reducing the re-transfer and stably performing multiple transfer. And a high-quality color image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of one embodiment of a typical image forming apparatus of the present invention.

FIG. 2 is a diagram showing the relationship between the amount of charge per unit area supplied to a transfer material and the surface potential of the transfer material at that time.

FIG. 3 is a diagram showing the relationship between the water content of a transfer material and the maximum surface charge density that can be held by the transfer material.

FIG. 4 is an explanatory diagram of a potential of a photosensitive drum.

FIG. 5 is a diagram illustrating a relationship between a transfer current and a density of an output image in the case of a single-color solid image.

FIG. 6 is a diagram illustrating an increase in transfer potential for each color in a normal state.

FIG. 7 is a diagram showing a rise in transfer potential when the surface charge density of a transfer material that can be held is exceeded.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image carrier (photosensitive drum) 2 primary charger 3 exposure device 5 developing device 6 transfer material 8 transfer device (transfer drum) 10 transfer charger

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Haruhiko Omata 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Masahiro Inoue 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon F term in the company (reference) 2H027 DA09 DC02 EA02 EA03 EA05 EB06 EC06 HB09 2H030 BB23 BB36 BB54 2H032 AA02 BA13 CA02 CA11 CA12 CA15

Claims (8)

[Claims] 1. An image forming apparatus for transferring a toner image formed on an image carrier to a transfer material, wherein the amount of toner charge per unit area of the toner image transferred onto the transfer material is capable of holding the transfer material. An image forming apparatus characterized in that the maximum value of the amount of applied toner per unit area of the toner image transferred onto the transfer material is made variable so as not to exceed the amount of charge per unit area. 2. An image forming apparatus for sequentially forming a plurality of color toner images on an image carrier, and repeatedly transferring the plurality of color toner images to a transfer material to obtain a multicolor image, comprising: The amount of toner per unit area of the toner image transferred onto the transfer material is adjusted so that the amount of charge of the toner per unit area of the transferred toner image does not exceed the amount of charge per unit area of the transfer material that can be held. The maximum amount of glue,
An image forming apparatus, wherein at least one color is variable. 3. The image forming apparatus according to claim 1, wherein a maximum value of the amount of applied toner per unit area is variable depending on a type of the transfer material. 4. The image forming apparatus according to claim 1, wherein the maximum value of the amount of applied toner per unit area is made variable depending on environmental conditions. 5. The apparatus according to claim 1, further comprising means for detecting an impedance of the transfer material, wherein a maximum value of the amount of applied toner per unit area is made variable by the transfer material impedance. The image forming apparatus according to any one of Items 1 to 4. 6. The amount of charge supplied to the back surface of the transfer material,
The image forming apparatus according to claim 1, wherein the image forming apparatus is variable according to a maximum value of the amount of applied toner per unit area. 7. The color order of the toner to be developed,
The image forming apparatus according to any one of claims 2 to 6, wherein the maximum value of the amount of toner applied later is larger than the maximum value of the amount of toner applied earlier. . 8. A method for detecting the amount of applied toner,
The image forming apparatus according to claim 1, further comprising a toner density detecting unit configured to detect a toner density on the image carrier.