JP2000231234A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a part of a toner image on a transfer material from being transferred again to an image carrier. SOLUTION: In an electrophotographic method image forming device where a color image is formed by carrying out multiply transferring a multiple color toner image to the transfer material, temperature and humidity information from a temperature and humidity measuring sensor 21, the transfer material type information from a transfer material type detection sensor 22 and information on passed time since the transfer material has been set to a transfer material cassette from a transfer material set time measuring sensor 23 are each input to a control device 20. Control to vary maximum value of toner quality on a toner image per unit area formed on the transfer material is carried out by the control device 20 based on the above-mentioned input information. Thus, one part of the toner image on the transfer material being transferred again to the photoreceptor drum can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer for forming a color image using an electrophotographic system.

[0002]

2. Description of the Related Art As a color image forming apparatus such as a copying machine, a facsimile, a printer, or the like utilizing an electrophotographic system, for example, an image forming unit is provided for each color of yellow, magenta, cyan, and black. A tandem-type color image forming apparatus that forms a full-color image by multiplex-transferring toner images of different colors onto a transfer material is known.

Such an image forming apparatus is installed in a wide range of environments from a high temperature and high humidity environment to a low temperature and low humidity environment, and performs image formation. When the installation environment of the image forming device changes,
Since the amount of triboelectric charge of the toner and the resistivity of the transfer material change, a measuring means for measuring the temperature and humidity in the apparatus is conventionally provided, and the latent image potential, the developing bias, the transfer current, etc. Feedback control is performed.

Further, it is known that paper as a transfer material changes its moisture content depending on the temperature and humidity of the atmosphere, and shows a remarkable change in resistance. For example, when the temperature / humidity changes from 23 ° C./5% to 30 ° C./80%, the moisture content of the paper changes to about 2 to 10%, and the volume resistance ρ becomes about 10 ⁸ to 10 ¹⁴ Ωcm. Change.

In general, paper as a transfer material has a temperature of 23 ° C./40.
% In normal temperature and normal humidity environment. Therefore, depending on the environment in which it is used, dehumidification or moisture absorption results in a gradually stable water content.

For example, FIG. 7 shows a change over time in the water content of a transfer material (paper) opened in an environment where the temperature / humidity is 23 ° C./5%. In FIG. 7, the initial moisture content of the transfer material A is 6.2.
%, And the initial moisture content of the transfer material B is about 5.2%.

It is known that a stable image can be obtained when the transfer charging means makes the current contributing at the time of transfer constant at an appropriate current. Therefore, in the related art, constant current control is performed so that a constant current can be obtained even when the volume resistance value changes depending on the type (thickness, material, and the like) of the transfer material, moisture absorption conditions, and the like.

[0008]

By the way, in the case of the above-described color image forming apparatus for forming a full-color image,
When a phenomenon called so-called retransfer occurs in which the toner image that has already been transferred is re-transferred onto the photosensitive drum in the next transfer step because the toner image is overlaid on the transfer material and the transfer is repeated. There is.

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

In this case, in the portion where the magenta toner is re-transferred, the density of the magenta toner image is reduced, and a yellow color forming an image appears below the magenta toner image layer, resulting in remarkable deterioration of image quality. .

Further, as described above, the phenomenon of retransfer varies depending on the change in the charge amount of the toner and the resistance value of the transfer material due to the change in temperature and humidity, thereby making the stability of multiple transfer difficult. It is also a factor.

Further, in recent years, the use of toner having a small particle size for improving the image quality has led to a tendency that the amount of charge per toner particle is reduced but the total amount of charge is increased.

Accordingly, the amount of transfer current or transfer voltage required to transfer a solid image has been increased, and the increase in the transfer current or transfer voltage adversely affects the retransfer phenomenon. I know it will.

Accordingly, the present invention provides a method for preventing a part of a toner image on a transfer material from being re-transferred onto an image carrier when a color image is formed on a transfer material by superimposing toner images of a plurality of colors. It is an object of the present invention to provide an image forming apparatus capable of preventing the image formation.

[0015]

According to a first aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming a color image by superimposing toner images of a plurality of colors. A temperature / humidity measuring means for measuring a temperature / humidity environment to be installed; a transfer material setting time measuring means for measuring an elapsed time after storing the transfer material in a transfer material cassette for storing the transfer material; Based on each measurement information input from the humidity measurement unit and the transfer material setting time measurement unit, the maximum value of the amount of toner applied per unit area of the toner image formed on the transfer material is set to at least a plurality of colors. And control means for controlling to change one of the toners.

An image carrier for forming and carrying the toner image is provided on the surface thereof. The potential of an exposed portion when the image carrier is exposed to form an electrostatic latent image is V1, and the toner is applied to the image carrier. When the developing bias for developing an image is Vdc, the potential V
If cont = V1-Vdc, the control unit changes the Vcont to change the maximum value of the amount of toner applied per unit area of the toner image formed on the transfer material. And

Further, the control means controls the maximum value of the amount of applied toner per unit area of the toner image formed on the transfer material for at least one of a plurality of color toners. And controlling the transfer charging current when transferring the toner image onto the transfer material to at least one of the plurality of color toners.

According to a second aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming a color image by superimposing a plurality of color toner images, wherein a temperature and a humidity at which the temperature and humidity environment in which the image forming apparatus is installed are measured. A humidity measuring means, a transfer material setting time measuring means for measuring an elapsed time after storing the transfer material in the transfer material cassette storing the transfer material, the temperature / humidity measuring means and the transfer material setting time measuring means Control means for controlling the transfer charging current when transferring the toner image onto the transfer material to at least one of the plurality of color toners based on each measurement information input from the It is characterized by that.

Further, the control means calculates the moisture content after a lapse of time after the transfer material is stored in the transfer material set, based on the measurement information from the transfer material setting time measuring means. Features.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to an embodiment of the present invention. The image forming apparatus of the present embodiment has image forming units for each color of cyan, magenta, yellow, and black, and images of different colors formed by each image forming unit are adsorbed on a transfer belt and conveyed. This is a so-called tandem type full-color copying machine that performs multiple transfer onto a transfer material to form a color image.

In the present image forming apparatus, a photosensitive drum 1a as an image carrier is provided in each of first to fourth image forming units pa, pb, pc, and pd for forming images of yellow, magenta, cyan, and black. , 1b, 1c, 1d.

Around each photosensitive drum 1a, 1b, 1c, 1d, a charger 2a, 2b, 2c, 2d, a developing device 3
a, 3b, 3c, 3d, a transfer belt 4 as a transfer material carrier, and cleaning devices 5a, 5b, 5c, 5d are provided, respectively. Each of the developing devices 3a, 3b, 3
c and 3d have a yellow toner, a magenta toner, a cyan toner, and a black toner, respectively.

An exposure device (laser scanning unit) 8 is provided above each of the photosensitive drums 1a, 1b, 1c, 1d.
An image signal corresponding to an input original (not shown) is converted into an optical signal by a laser output (not shown), and the converted laser light, which is a laser light, is reflected by a polygon mirror 9 rotating at a high speed. Irradiation is performed on the photosensitive drums 1a, 1b, 1c, 1d for each color separation.

The transfer belt 4 is stretched between the driven rollers 6a and 6b and the driving roller 6c, and moves in the direction of the arrow by the rotation of the driving roller 6c. At each transfer portion (transfer nip) where the transfer belt 4 and each of the photosensitive drums 1a, 1b, 1c, 1d are in contact with each other, the transfer portion faces the respective photosensitive drums 1a, 1b, 1c, 1d with the transfer belt 4 therebetween. Charger 4
a, 4b, 4c, and 4d are provided respectively. The transfer chargers 4a, 4b, 4c, 4d include blades, rollers,
A contact charger using a transfer charging member such as a brush is used. The contact charger has advantages such as ozonelessness, resistance to temperature and humidity environmental changes, and high image quality.

On the downstream side of the transfer belt 4 in the transfer material transfer direction of the photosensitive drum 1 d, the fixing device 1 is connected via a transfer belt 17.
0 is set. The fixing device 10 includes the fixing roller 1
1, pressure roller 12, fixing roller 11 and pressure roller 12
Heaters 13, 14 and the like provided in the inside are provided.

The transfer belt 4 is made of a dielectric resin sheet such as a polyethylene terephthalate resin sheet (PET resin), a polyvinylidene fluoride resin sheet, or a polyurethane resin sheet. Or a seamless (seamless) belt. The volume resistance of the transfer belt 4 is 10 ¹³ to 10 ¹⁷ Ωcm.

An adsorption charging member 7 for electrostatically adsorbing the transfer material P onto the transfer belt 4 is provided on the transfer belt 4 on the upstream side of the photosensitive drum 1a in the transfer material transport direction.

The image forming apparatus according to the present embodiment includes:
As shown in FIG. 2, a temperature / humidity measuring sensor 21 for measuring the temperature and humidity in the apparatus, and transfer material cassettes 15a and 15b.
Transfer material type detection sensor 22 for detecting the type of transfer material P stored in the transfer material P, and the elapsed time from when the transfer material P is set in the transfer material cassettes 15a, 15b and the like until an image is formed on the transfer material P Material setting time sensor 2 for measuring
3 is provided.

The control device (CPU) 20 includes a thermo-hygrometer 21,
The developing bias and the transfer current are controlled based on the information input from the transfer material type sensor 22 and the time sensor 23, so that the toner charge amount per unit area of the toner image formed on the transfer material P is reduced. The maximum value of the amount of toner applied per unit area of the toner image formed on the transfer material P is changed so as not to exceed the charge amount per unit area that can be held by the transfer material P ( Details will be described later).
The control device (CPU) 20 controls the developing bias 24, the transfer current 25, and the like.

Next, an image forming operation by the above-described image forming apparatus will be described.

The photosensitive drums 1a, 1b, 1c, 1d rotating clockwise at a predetermined process speed are uniformly charged by chargers 2a, 2b, 2c, 2d, respectively. Then, a document (not shown) is exposed and scanned to obtain a color separation image signal. This image signal is processed by a video processing unit (not shown) and sent to an exposure device (laser scanning unit) 8.

An exposure device (laser scanning unit) 8 converts the input color / color separation image signal into a laser output unit (not shown).
Are converted into optical signals, and the converted laser light, which is an optical signal, is charged into each of the charged photosensitive drums 1a, 1b, 1c,.
1d is scanned and exposed to form an electrostatic latent image.

The electrostatic latent images formed on the photosensitive drums 1a, 1b, 1c, 1d are transferred to the developing devices 3a, 3b, 3c,
By 3d, yellow, magenta, cyan,
The toner image is developed with the black toner and is visualized as a toner image.

The photosensitive drums 1a, 1b, 1c,
The transfer material P is transferred from the transfer material cassettes 15a, 15b and the like to the registration rollers 1 in synchronization with the formation of the toner images of each color on 1d.
The paper is fed onto the transfer belt 4 by 6 or the like.

The transfer material P fed onto the transfer belt 4 is
Each of the transfer chargers 4a, 4b, and 4 of each transfer unit is electrostatically attracted and conveyed onto the transfer belt 4 by the attraction charging member 7.
The respective photosensitive drums 1a, 1b, 1c, 1d
The toner images of the respective colors are sequentially multiplex-transferred to form a full-color image.

The transfer material P on which the full-color image has been formed is
On the downstream side of the transfer belt 4 in the transfer material transport direction, the separation charger 30
And is separated from the transfer belt 4. In particular, in a low humidity environment, the transfer material P also dries and the electric resistance increases,
The electrostatic attraction force with the transfer belt 4 increases, and the effect of the separation charger 30 increases. Normally, the separation charger 30 charges the transfer material P in a state where the toner image is not fixed, so that a non-contact charger is used.

The transfer material P separated from the transfer belt 4 is
The fixing roller 11 of the fixing device 10 passes through the conveyance belt 17.
And between the pressure roller 12. Transfer Material P Conveyed Between Fixing Roller 11 and Pressure Roller 12 of Fixing Device 10
Are heating by the heaters 13 and 14 and the fixing roller 1
After the full-color image is fixed on the surface by the pressure of the roller 1 and the pressure roller 12, the sheet is discharged onto the tray 18.

Further, the photosensitive drums 1a, 1 after the transfer is completed.
The transfer residual toner remaining on b, 1c, and 1d is cleaned and removed by the respective cleaning devices 5a, 5b, 5c, and 5d, and is prepared for the formation of the next latent image. Further, the toner and other foreign matters remaining on the transfer belt 4 are wiped off by bringing the cleaning blade 19a and the cleaning web (nonwoven fabric) 19b into contact with the surface of the transfer belt 4.

According to the study by the present inventors, it has been found that the phenomenon that a part of the toner image on the transfer material is re-transferred onto the photosensitive drum is caused by the following mechanism. .

In this study, it was confirmed that there is an upper limit to the amount of charge that the transfer material can hold depending on the temperature and humidity environment and the type of the transfer material. In this study, the charge is supplied to the transfer material, and the surface potential of the transfer material with respect to the supplied charge amount is measured.

FIG. 3 shows the relationship between the amount of charge supplied to each transfer material and the surface potential of each transfer material obtained in the above study. As is clear from this result, when the transfer material is OHT, the surface potential of the transfer material also increases in proportion to the supplied charge, but the transfer materials A and B shown in FIG. This means that the surface potential does not rise.

Also, under the normal temperature and normal humidity environment (here, at a temperature of 23 ° C. and a humidity of 60%), the surface potential of the transfer material A and the like also increases in proportion to the supplied charge amount, and saturates in the range of the measurement region. Nothing.

However, when the absolute moisture content was 0.5 g / m ^{3 in} an environment of a temperature of 23 ° C. and a humidity of 5%, the amounts of charge that could be held on the transfer materials A and B were determined.
The transfer materials A and B cannot hold the electric charges even if the electric charges are supplied more than 00 μC / m ² and 450 μC / m ² . That is, it can be seen that the amount of charge per unit area that the transfer material can hold depends on the temperature and humidity environment and the type of the transfer material.

When 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 was examined, the results shown in FIG. 4 were obtained.

When the above examination results are applied to the case of the present embodiment, the occurrence of the above-described retransfer can be well explained.

In the present embodiment, the measured value of the charge amount of the toner developed on the photosensitive drum is 30 μC / g in the low humidity environment, and the amount of glue per unit area of the solid toner image is 10 g for a single color. / M ³ . Therefore,
The total amount of toner charge per unit area is 300 μC / m ²
Becomes In practice, full-color images are often formed by multi-transferring not only single-color images but also four-color toners. In this case, the maximum amount of toner per unit area formed on the transfer material is further increased. Becomes larger. In this case, the amount of applied toner on the transfer material is often determined by, for example, fixing conditions.

In this embodiment, the maximum value of the 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 2.0 g of the maximum amount of a single color for a full color. The configuration is such that a full-color image is formed with the amount of application up to twice the amount of application. Therefore, in the present embodiment, the maximum toner amount per unit area is 20 g / m ² by performing masking processing on secondary colors, tertiary colors, and the like in image processing. The maximum charge amount of the toner per unit area is 60
0 μC / m ² .

From the above, for example, in the case of the transfer material A, in the normal setting of the present embodiment, the maximum charge amount per unit area that the transfer material can hold is 500 μC / m ² ,
The charge amount corresponding to the maximum amount of toner on the transfer material is larger by 100 μC / m ² , and the transfer material itself cannot hold the charge as described above.

That is, the toner once transferred from the photosensitive drum onto the transfer material is transferred from the transfer material onto the photosensitive drum at a transfer portion (transfer nip) for transferring the next color.
This will cause so-called retransfer.

Therefore, in this embodiment, the amount of charge per unit area that can be held by the transfer material, which is determined by the temperature and humidity environment and the type of the transfer material, is set in advance, and the amount of charge per unit area on the transfer material is set. The maximum value of the toner per unit area on the transfer material can be variably controlled so that the charge amount corresponding to the maximum value of the amount of applied toner does not exceed the set charge amount.

That is, the description will be made using a general formula as follows.

The charge amount per unit mass of the toner developed on the photosensitive drum is Qt (k) (C / kg), the amount of toner applied per unit area is M (kg / m ² ), and the transfer material is held. Possible charge amount per unit area Qp (s, k, t)
Then, a configuration is adopted in which M is set so as to satisfy Qp (s, k, t) / Qt (k) ≧ M (1). Here, k is an environmental factor, s is the type of the transfer material, t is the time elapsed since the transfer material was stored in the transfer material cassette, and the environmental factors include temperature, humidity, and absolute water content. is there.

As described above, the moisture content of paper, which is one of the transfer materials, changes with temperature and humidity. Accordingly, as the time elapses after opening, the moisture amount changes from the moisture amount at the time of packaging to the moisture amount at the temperature and humidity in the apparatus, and accordingly, the charge amount Qp per unit area that can hold the transfer material. Changes.

Therefore, since this time change is more gradual than the image forming speed, it is effective to detect the leaving time since the paper is opened and set in the transfer material cassette. That is, in a certain temperature and humidity environment, for example, when paper wrapped every 500 sheets is used in a transfer material cassette, 50
It may take several hours to several days to finish using the zeroth paper. In such a case, the amount of electric charge Qp per unit area that can be held by the first sheet of water and the sheet near the 500th sheet that is used after a certain time is greatly different.

Therefore, in the present embodiment, the temperature / humidity inside the image forming apparatus is measured by the temperature / humidity measuring sensor 21 provided in the image forming apparatus shown in FIG. The type of the transfer material P set in the transfer material cassettes 15a, 15b and the like is detected. Regarding the type of the transfer material P, in addition to the detection by the transfer material type detection sensor 22, a configuration in which a user performs an input operation or a configuration in which these are used in combination is also possible.

Further, with the transfer material setting time sensor 23,
The time from when the transfer material P is set in the transfer material cassettes 15a and 15b to when an image is formed on the transfer material P is measured. In this case, the time when the transfer material P is set is also
After detecting that the transfer material P has run out in the transfer material cassettes 15a, 15b, etc., the transfer material cassettes 15a, 15b
Or the like may be detected by opening and closing, and a configuration in which the user performs an input operation or a configuration in which these are used in combination is also possible.

The transfer material cassettes 15a, 15b
Opening / closing of the transfer material P may be opened and closed not by the setting of the transfer material P but by the jam of the transfer material P. Therefore, it is desirable to determine the jam by using the jam detecting means together.

The charge amount Qt per unit mass of the toner developed on the photosensitive drum is determined by the temperature and humidity environment, the type of the transfer material P, and the time from when the transfer material P is set to when the image is formed. And the amount of charge Qp per unit area that can hold the transfer material P are recorded and set in advance in a memory (not shown) in the control device (CPU) 20.

The control device (CPU) 20 sets the temperature / humidity environment, the type of the transfer material P, and the transfer material P from the temperature / humidity measurement sensor 21, the transfer material type detection sensor 22, and the transfer material setting time sensor 23. From the set values (standard set values) previously recorded and set in a memory (not shown), the temperature and humidity environment at the time of input, the type of the transfer material P, and The amount of charge Qt per unit mass of the toner developed on the photosensitive drum and the amount of charge Qp per unit area that the transfer material P can hold with respect to the elapsed time from the setting of the transfer material P are determined. From the determined Qt and Qp, the maximum value of the amount of applied toner per unit area is determined from the above equation (1).

If the maximum value M1 of the amount of applied toner per unit area thus determined is smaller than the original set value M0, it is lowered to the determined maximum value M1.

If the determined maximum value M1 of the amount of toner applied per unit area is larger than the set value M0, the maximum limit value 20 of the amount of applied toner per unit area can be obtained.
g / m ² , the maximum value M selected from the set value
Try to get as close as possible to 1. However, when the maximum value M1 of the amount of applied toner per unit area exceeds 20 g / m ² , the amount is set to 20 g / m ² .

The lower limit of the amount of toner applied per unit area is 60 times the maximum value of the amount of toner applied as a standard value.
%, That is, 12 g / m ² , and when the maximum value of the amount of applied toner per unit area is less than or equal to that from the above equation (1), it is set to 12 g / m ² from the viewpoint of securing the density. did. However, it is not always necessary to set the lower limit of the amount of applied toner per unit area, and the lower limit can be set separately.

In this embodiment, as a means for changing the amount of toner applied per unit area in the above case, a potential Vcont described below is controlled by a control device (CP
U) It is made to vary by the control of 20.

Each of the photosensitive drums 1a, 1b, 1c, 1
d, the amount of toner to be developed on each photosensitive drum 1
A, 1b, 1c, and 1d are detected by a toner density detection sensor (not shown) installed opposite to the sensor.

The toner density detection sensor develops a single-color solid toner image outside the image forming area on each of the photosensitive drums 1a, 1b, 1c, and 1d, irradiates the single-color solid toner image with light, and generates a toner from the reflected light. Detect density. In this case, the relationship between the amount of reflected light and the toner density or the amount of applied toner is stored and set in advance in a memory (not shown) in the control device (CPU) 20. The amount of the glue is determined, and the potential Vcont is adjusted.

In a memory (not shown) in the control device (CPU) 20, the relationship between the maximum value of the amount of applied toner on each of the photosensitive drums 1a, 1b, 1c and 1d and the developing bias Vcont is set in advance. However, from the above measurement results, if the amount of applied toner greatly deviates from the target value,
The potential Vcont is automatically adjusted to set the target amount of application.

Here, the photosensitive drum potentials of the respective photosensitive drums 1a, 1b, 1c, 1d during image formation of the image forming apparatus shown in FIG. 1 will be described.

The photosensitive drum 1a will be described with reference to FIG.
As shown in FIG. 5, the potential when the charging device 2a uniformly charges the photosensitive drum 1 is Vd. By exposing the photosensitive drum 1a charged with the charging potential Vd by irradiating it with laser light, the potential of the exposed portion increases. The photosensitive drum 1 when a single-color solid toner image is formed
The potential of the upper exposed portion is set to V1.

When the developing bias at the time of toner development is Vdc, the potential Vcont is expressed by Vcont = V1-Vdc. The potential difference between Vdc-Vd is Vbac
represented as k.

Then, the toner is developed on the photosensitive drum 1a so as to fill the potential difference (V1-Vdc) between V1 and Vdc. Therefore, the potential Vcont (= V1−Vdc)
, The maximum value of the amount of applied toner per unit area can be changed.

In the following, specific examples will be described. For example, in a low-humidity environment (temperature 23 ° C., humidity 5%), the type of the transfer material is sufficient from the set of the transfer material A and the transfer material P described above. When the time has elapsed, the charge amount Qt per unit mass of the toner developed on each of the photosensitive drums 1a, 1b, 1c, 1d is 30 × 10 ⁻³ C / kg, and the transfer material P can be held. The charge amount Qp per unit area is 500 ×
10 ⁻⁶ C / m ² . Therefore, the amount of toner applied M per unit area is 16.7 g / m ² (1.67 mg / cm 2).
² ) Therefore, the amount of addition is reduced by 13.5% from a preset standard setting value.

In this case, the applied amount of the solid toner image is 8.3 g / m ² , and the potential Vcon required for this is 8.3 g / m ^2.
t is from a preset value of 430 V to 400
It is controlled to lower to V. At this time, the Vback
(= Vdc−Vd) is 130V, V1 is −120V, V
d is -680V and Vdc is -550V.

The time until the amount of applied toner per unit area is reduced is determined by the time when the transfer material is transferred to the transfer material cassette 15a.
It is changed by the time set to 15b or the like. When the type of the transfer material is the transfer material A, when the amount of application is gradually changed every 12 hours and 48 hours have passed,
It was set so that the amount of glue was reduced by 13.5% from the standard setting value. Since this time change differs depending on the type of the transfer material, it is desirable that different settings can be made depending on the transfer material.

Regarding the method of changing the amount of applied toner per unit area, for example, when a blue image is formed, in the present embodiment, a single-color solid toner image is multiplexed in the order of yellow and magenta. Although the image is transferred (the color order of image formation in the image forming apparatus of the present embodiment is yellow, magenta, cyan, and black), the amount of each color is determined by the maximum value M of the amount of toner on the transfer material. May be distributed in half at a time.

That is, the amount of the first developed yellow toner may be 8.3 g / m ² , and the amount of the next developed magenta toner may be 8.3 g / m ² . here,
Although the maximum value of the amount of the glue per unit area of the yellow toner and the magenta toner is distributed in a ratio of 1/2, the toner layer formed on the transfer material P is easier to retransfer. For example, in the case of a red image, a configuration may be adopted in which the amount of application of the magenta toner is larger than that of the yellow toner.

Further, in the above-described embodiment, the case where the amount of reduction by 13.5% is reduced from the standard setting value has been described. However, when this reduction amount is very small, for example, about 2 to 4%, A configuration may be adopted in which only the amount of yellow toner for forming a toner image on the lowermost layer is reduced.

As described above, in this embodiment, based on each information of the temperature and humidity environment, the type of the transfer material, and the elapsed time since the transfer material is set in the transfer material cassette, the per-unit area of each color is determined. By lowering the maximum amount of applied toner, the toner image once transferred from the photosensitive drum to the transfer material is prevented from retransferring from the transfer material to the photosensitive drum at the transfer nip during multiple transfer. As a result, stable and excellent multiple transfer could be realized.

<Embodiment 2> This embodiment also includes the image forming apparatus of Embodiment 1 and the control system shown in FIGS. 1 and 2, and in Embodiment 2, Embodiment 1
When the maximum value of the amount of applied toner per unit area is changed as described above, the transfer current value is changed in accordance with the control of the control device (CPU) 20.

FIG. 6 is a diagram showing the relationship between the amount of transfer current and the image density. FIG. 6A shows a case where the amount of applied toner is normally set, and FIG. 6B shows a case where the amount of applied toner is reduced. (13.5% lower than the normal set value as in the first embodiment). When the amount of applied toner is reduced, the transfer current value required for transferring the toner is also reduced. You can see that it can be done.

At the time of transfer, if an electric charge is supplied more than necessary, an abnormal discharge is caused in and near the transfer portion (transfer nip), thereby causing an image defect. Therefore, it is preferable to perform transfer with the minimum necessary supply charge.

Therefore, in this embodiment, in a low humidity environment (temperature 23 ° C., humidity 5%), the toner charge amount is 30 μC / g,
The maximum value of the amount of toner applied per unit area is 20 kg /
In the case of m ² , as shown in FIG.
Although μA was required, as in the case of the first embodiment, when the amount of application is reduced by 13.5% from the normal set value, it is possible to transfer sufficiently 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, it is more preferable to change the transfer current value of each color accordingly. .

As described above, in the present embodiment as well as in the first embodiment, retransfer in which the toner is transferred from the transfer material to the photosensitive drum at the transfer nip at the time of the multiple transfer is prevented, and stable. To achieve good multiple transfer,
Further, it is possible to prevent image defects due to abnormal discharge caused by excessive supply of electric charge to the transfer material.

<Embodiment 3> This embodiment also includes the image forming apparatus of Embodiment 1 and the control system shown in FIGS. 1 and 2, and in Embodiment 3, Embodiment 1 2, the maximum value of the amount of applied toner per unit area is not changed, and only the transfer current value is changed.

If only the transfer current value is reduced without reducing the amount of applied toner, the transfer efficiency is reduced. That is, the amount of toner that does not cause image defects is applied to the photosensitive drums 1a, 1b, 1c, 1d.
When the toner is transferred from the toner to the transfer material P, the toner not transferred remains on the photosensitive drums 1a, 1b, 1c and 1d. In this case, the load of the photosensitive drum cleaning by the cleaning devices 5a, 5b, 5c, and 5d is increased, and there is a concern that the cleaning may be defective. However, if there is sufficient cleaning capability, the configuration is sufficient because the Vcont need not be changed. There is a merit that can be easily.

The optimum transfer current in this case needs to be different from the transfer current when the amount of applied toner is changed as in the first and second embodiments.

As described above, in the present embodiment as well as in the first embodiment, re-transfer in which the toner is transferred from the transfer material to the photosensitive drum at the transfer nip at the time of the multiple transfer is prevented, and the transfer is stabilized. As a result, good multiple transfer can be realized.

In each of the embodiments described above, the tandem type image forming apparatus for forming a full-color image by using four photosensitive drums and one transfer belt has been described. It is needless to say that the present invention can be applied to an image forming apparatus of a multiple transfer system in which a full-color image is formed by four developing units and one transfer drum arranged around the image forming apparatus.

[0090]

As described above, based on each measurement information input from the temperature / humidity measuring means and the elapsed time measuring means, the toner amount per unit area of the toner image formed on the transfer material is measured. By controlling the maximum value of the amount to be changed for at least one of the toners of a plurality of colors, retransfer in which the toner is transferred from the transfer material to the image carrier at the transfer nip during multiple transfer is performed. Thus, stable multiple good transfer can be realized.

Further, based on each measurement information input from the temperature / humidity measuring means and the transfer material cassette time measuring means,
By controlling the transfer charging current at the time of transferring the toner image onto the transfer material to at least one of the toners of a plurality of colors, the image is carried from the transfer material at the transfer nip during the multiple transfer. It is possible to prevent re-transfer of toner transfer onto the body, and realize stable and excellent multiple transfer.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a control system of the image forming apparatus according to the embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the amount of charge per unit area supplied to the transfer material and the surface potential of the transfer material.

FIG. 4 is a diagram showing the relationship between the water content of the transfer material and the maximum surface charge density that can be held by the transfer material.

FIG. 5 is a diagram for explaining a potential of a photosensitive drum.

FIG. 6 is a diagram illustrating a relationship between a transfer current amount and an image density.

FIG. 7 is a diagram showing a relationship between a leaving time of a transfer material and a moisture content of the transfer material.

[Explanation of symbols]

1a, 1b, 1c, 1d Photosensitive drum (image carrier) 2a, 2b, 2c, 2d Charger 3a, 3b, 3c, 3d Developing device 4 Transfer belt 8 Exposure device 9 Fixing device 15a, 15b Transfer material cassette 20 Control device (Control means) 21 Temperature / humidity measuring sensor (temperature / humidity measuring means) 22 Transfer material type detection sensor 23 Transfer material setting time measuring sensor (transfer material setting time measuring means)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/08 503 G03G 15/08 503A 15/16 15/16 (72) Inventor Yuji Bessho Ota, Tokyo 3-30-2 Shimomaruko-ku, Canon Inc. (72) Inventor Masahiro Inoue 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. F-term (reference) 2H027 DA02 DA04 DA10 DA11 DA14 DA38 DC02 DE07 EA02 EA03 EA05 EB04 EC06 EC19 EF15 ZA07 2H030 AB02 AD01 AD02 AD16 BB02 BB12 BB34 BB54 2H032 AA05 AA15 BA01 BA05 BA13 CA02 CA14 CA15 DA03 2H073 AA10 BA01 BA33 BA45 CA22 2H077 AD35 BA10 DA10 DA18 DB18

Claims (5)

[Claims] 1. An electrophotographic image forming apparatus for forming a color image by superimposing toner images of a plurality of colors, comprising: a temperature / humidity measuring unit for measuring a temperature / humidity environment in which the image forming apparatus is installed; A transfer material setting time measuring means for measuring an elapsed time after storing the transfer material in the transfer material cassette for storing the transfer material; and each measurement input from the temperature / humidity measuring means and the transfer material setting time measuring means. Control means for controlling the maximum value of the amount of applied toner per unit area of the toner image formed on the transfer material based on the information to change at least one of the plurality of color toners; An image forming apparatus comprising: 2. An image bearing member for forming and carrying the toner image on a surface, an exposure portion potential at the time of exposing the image bearing member to form an electrostatic latent image is V1, and a toner is provided on the image bearing member. When the developing bias for developing an image is Vdc, the potential Vco
Assuming that nt = V1−Vdc, the control means controls the V
2. The image forming apparatus according to claim 1, wherein changing the cont changes a maximum value of a toner amount per unit area of a toner image formed on the transfer material. 3. 3. The control unit controls the maximum value of the amount of toner applied per unit area of a toner image formed on the transfer material to at least one of a plurality of color toners. 3. The image forming apparatus according to claim 1, wherein the transfer charging current when transferring the toner image onto the transfer material is controlled so as to be changed for at least one of the plurality of color toners. 4. 4. An electrophotographic image forming apparatus for forming a color image by superimposing toner images of a plurality of colors, a temperature / humidity measuring unit for measuring a temperature / humidity environment in which the image forming apparatus is installed, A transfer material setting time measuring means for measuring an elapsed time after storing the transfer material in the transfer material cassette for storing the transfer material; and each measurement input from the temperature / humidity measuring means and the transfer material setting time measuring means. Control means for controlling a transfer charging current when transferring the toner image onto the transfer material based on the information so as to change at least one of a plurality of color toners. Image forming apparatus. 5. The control unit calculates a moisture content after a lapse of time after the transfer material is stored in the transfer material set, based on measurement information from the transfer material setting time measuring unit. Item 4. The image forming apparatus according to item 1, 2 or 3.