JPH11272092A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an appropriate transfer-voltage even when forming an image on the second side of a recording material as well. SOLUTION: When the recording material S having on its first side a toner image transferred by a transfer part T2 and fixed by a fixing device 60 is re-carried to the transfer part T2 along an inverting-and-returning path 70' and an image is formed on its second side as well, elapsed time from a point in time that it is passed through the fixing device 60 to the start of the transfer of the toner image to the second side is measured, and temperature and humidity are detected. Based on the elapsed time and the temperature and humidity, the transfer voltage for the second side is determined.

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 printer, a facsimile, a copying machine, etc., for forming an image on a recording material such as paper by using an electrophotographic technique. Especially,
The present invention relates to a technique for controlling a transfer voltage in an image forming apparatus capable of forming an image on both sides of a recording material.

[0002]

2. Description of the Related Art In general, an image forming apparatus for forming an image on a recording material such as paper by using an electrophotographic technique includes an image carrier having a surface on which a toner image is formed, and an image carrier. A transfer unit that forms a transfer unit, applies a transfer voltage, and transfers the toner image on the surface of the image carrier to a recording material; and heats the recording material while passing the recording material onto which the toner image has been transferred by the transfer unit. And a fixing unit for fixing the toner image thereon.

In such an apparatus, if the moisture absorption of a recording material such as paper is different due to a change in humidity, the resistance value is also different. Therefore, the optimum value of a transfer voltage for transferring a toner image to the recording material is determined as follows. There is known a device provided with a humidity detecting means so as to determine the value according to the humidity.

[0004] Further, the recording materials are usually held in a stacked state in a paper feeding device or the like, and are fed from the highest one. Easily (moisture absorption easily rises).

Conventionally, focusing on this point, the humidity is detected by the humidity detecting means, and the interval between recordings, that is, the interval time between the fed recording materials (for example, the highest order among the stacked recording materials). A technique has been proposed in which the transfer voltage is determined based on the humidity and the interval time after the recording material is fed until the next recording material is fed. (Japanese Patent Publication No. 7-82271).

[0006]

In recent years, there has been an increasing demand for forming images not only on one side but also on both sides of a recording material.

To form an image on both sides of a recording material, a toner image is transferred to a first surface (for example, the front surface) at a transfer section, and the recording material on which the toner image has been fixed by passing through fixing means is printed on the front and back sides. It can be realized by inverting the image, returning it to the transfer section again, and transferring and fixing the toner image also on the second surface (for example, the back surface).

However, when an attempt is made to form a toner image on both sides of the recording material, the optimum value of the transfer voltage at the time of the first surface transfer and the optimum value of the transfer voltage at the time of the second surface transfer greatly differ. I knew it would go wrong.

At the time of the first surface transfer, the recording material has not yet passed the fixing means, but at the time of the second surface transfer, the recording material has already passed the fixing means once, and the fixing means heats the recording material. Therefore, the moisture absorption of the recording material immediately after passing through the fixing means is not limited to zero as much as possible, and the recording material is extremely sensitive to the influence of humidity. This is because the state becomes easy.

In such a situation, the prior art described in Japanese Patent Publication No. 7-82271 cannot function effectively at all. This is because this conventional technique can function only when an image is formed only on the first surface.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an image forming apparatus capable of obtaining an appropriate transfer voltage even when an image is formed on the second surface of a recording material. Is to provide.

[0012]

According to a first aspect of the present invention, there is provided an image forming apparatus, comprising: an image carrier on which a toner image is formed on a surface; and a transfer unit between the image carrier and the image carrier. Transfer means for forming and applying a transfer voltage to transfer the toner image on the surface of the image carrier to a recording material; and heating while passing the recording material onto which the toner image has been transferred by the transfer means to form a toner on the recording material. A fixing unit for fixing the image; and a reversing return path for reversing the front and back of the recording material that has passed through the fixing unit and returning the recording material to the transfer unit again. An image forming apparatus capable of forming an image on a surface and a second surface, wherein a toner image is transferred to the first surface of the recording material when forming an image on the first surface and the second surface of the recording material. From the time when the sheet passes through the fixing unit, the second
A timer for measuring an elapsed time until transfer of the toner image to the surface, a humidity detector for detecting humidity, an elapsed time after the first surface is fixed measured by the timer, and the humidity detector And control means for determining a transfer voltage for transferring the toner image to the second surface of the recording material based on the humidity detected by the control unit.

[0013] The image forming apparatus according to the second aspect is the first aspect.
In the image forming apparatus described above, the control unit is a control unit that also determines a transfer voltage when transferring a toner image to the first surface of the recording material based on the humidity detected by the humidity detection unit. Features.

According to a third aspect of the present invention, there is provided an image forming apparatus according to the first aspect.
In the above image forming apparatus, the humidity detecting unit is provided for the reverse return path.

According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the third aspect.
In the above-described image forming apparatus, the humidity detecting unit is provided separately from the humidity detecting unit for determining a transfer voltage when the toner image is transferred onto the first surface.

According to a fifth aspect of the present invention, in the image forming apparatus of the first, second, third, or fourth aspect, the image carrier is rotated a plurality of times so that toner images of a plurality of colors are superimposed. An image carrier that may be printed, wherein a plurality of color toner images superimposed on the image carrier are collectively transferred to a recording material in the transfer unit.

According to a sixth aspect of the present invention, there is provided the image forming apparatus according to the first, second, third, fourth or fifth aspect, further comprising a temperature detecting means for detecting a temperature, and the control means. Is a control unit that determines the transfer voltage based on the temperature, the humidity, and the elapsed time detected by the temperature detection unit.

[0018]

According to the image forming apparatus of the present invention, a transfer portion is formed between an image carrier having a toner image formed on a surface thereof and the image carrier, and a transfer voltage is applied to the image carrier. Transfer means for transferring the toner image on the surface to the recording material, fixing means for fixing the toner image on the recording material by heating while passing the recording material onto which the toner image has been transferred by the transfer means, and fixing means for the fixing means. A reversing return path for reversing the front and back of the passed recording material and returning the recording material to the transfer portion again, so that the toner image is transferred to the first surface, passes through the fixing unit, and The recording material on which the toner image has been fixed can be returned to the transfer section again through the reverse return path to transfer the toner image to the second surface and fix it. That is, an image can be formed on both sides of the recording material.

In the image forming apparatus according to the first aspect, when an image is formed on the first surface and the second surface of the recording material, the toner image is transferred to the first surface of the recording material and the fixing unit is moved. A timer for measuring the elapsed time from the passage of the toner image to the transfer of the toner image to the second surface; a humidity detector for detecting humidity; and an elapsed time after the first surface is fixed, which is measured by the timer. And control means for determining a transfer voltage for transferring the toner image onto the second surface of the recording material based on the humidity detected by the humidity detecting means. The transfer voltage at the time of transferring the toner image to the second surface can be determined to an optimum value in accordance with the moisture absorption of the recording material, which may rapidly change due to the elapsed time and the humidity.

Therefore, according to the image forming apparatus of the present invention, an appropriate transfer voltage can be obtained even when an image is formed on the second surface of the recording material. It is possible to form a perfect image.

According to the image forming apparatus of the second aspect, in the image forming apparatus of the first aspect, the control means includes:
Since the control means determines the transfer voltage when transferring the toner image to the first surface of the recording material based on the humidity detected by the humidity detecting means, the transfer when transferring the toner image to the first surface is performed. The voltage can also be determined to an optimum value.

In addition, humidity detecting means for determining a transfer voltage when transferring the toner image to the first surface, and humidity detecting means for determining a transfer voltage when transferring the toner image to the second surface. However, since they are shared, an effect is obtained that only one humidity detecting means is required.

According to the third aspect of the present invention, in the image forming apparatus of the first aspect, since the humidity detecting means is provided for the reverse return path, the humidity detecting means is more abrupt due to the elapsed time and humidity. The transfer voltage for transferring the toner image onto the second surface of the recording material can be more reliably determined to the optimum value in accordance with the moisture absorption of the recording material, which may change to the following value.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the humidity detecting means determines a transfer voltage for determining a transfer voltage when transferring the toner image onto the first surface. Since it is provided separately from the detection means,
As compared with the configuration of the second aspect, it is possible to more reliably determine the transfer voltage when transferring the toner image onto the first surface and the second surface of the recording material.

According to a fifth aspect of the present invention, in the image forming apparatus of the first, second, third, or fourth aspect, the image carrier is rotated a plurality of times to form a toner image of a plurality of colors. Is an image carrier that may be superimposed,
Since the toner images of a plurality of colors superimposed on the image carrier are collectively transferred to the recording material in the transfer unit, only a single-color image is formed on the first and second surfaces of the recording material. Instead, a full-color image can be formed.

By the way, as in the image forming apparatus according to the fifth aspect, by rotating the image carrier a plurality of times,
The image carrier may have a plurality of color toner images superimposed thereon, and the multi-color toner images superimposed on the image carrier may be collectively transferred to a recording material in the transfer unit, and the recording may be performed. When a single color toner image is transferred to the second surface of the material and when a plurality of color toner images superimposed on the image carrier are collectively transferred, the toner image is transferred to the first surface and the fixing means is fixed. , The elapsed time from the point of passing through to the start of transfer of the toner image to the second surface is significantly different depending on the difference in the number of rotations of the image carrier, and therefore, the moisture absorption of the recording material may be significantly different. .

On the other hand, according to the image forming apparatus of the fifth aspect, even in such a case, an appropriate transfer voltage for transferring the toner image to the second surface of the recording material can be obtained. As a result, it is possible to form a beautiful single-color image or full-color image on the second surface.

According to a sixth aspect of the present invention, in the image forming apparatus of the first, second, third, fourth or fifth aspect, the image forming apparatus further comprises a temperature detecting means for detecting a temperature. The controller is a controller that determines the transfer voltage based on the temperature, the humidity, and the elapsed time detected by the temperature detector. Therefore, the transfer voltage (the first surface of the recording material and / or the It is possible to more reliably determine the optimum value for the transfer voltage for transferring the toner image to the two surfaces.

[0029]

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

<First Embodiment> FIG. 1 shows a first embodiment of an image forming apparatus according to the present invention, and a second embodiment described later.
It is a schematic diagram showing an embodiment.

First, an outline of the image forming apparatus will be described.

This image forming apparatus can form a single color image and a full color image using a developing device using four color toners of yellow (Y), cyan (C), magenta (M), and black (K). Device.

In FIG. 1, reference numeral 100 denotes a photoreceptor cartridge, and the photoreceptor 140 is driven to rotate in a direction indicated by an arrow in FIG.

The photosensitive member 140 has a thin cylindrical conductive base material and a photosensitive layer formed on the surface thereof.

Around the photoreceptor 140, along a rotation direction thereof, a charging roller 160 as charging means, a developing device 10 (Y, C, M, K) as developing means, an intermediate transfer device 30, and a cleaning device Means 170 are arranged.

The charging roller 160 contacts the outer peripheral surface of the photoconductor 140 to uniformly charge the outer peripheral surface. On the outer peripheral surface of the uniformly charged photoconductor 140, a selective exposure L1 according to desired image information is performed by the exposure unit 40,
By the exposure L1, an electrostatic latent image is formed on the photoconductor 140.

The electrostatic latent image is developed with toner applied by a developing unit 10.

As a developing device, a developing device 10 for yellow is used.
Developing device 10C for Y and cyan, developing device 10 for magenta
A developing device 10K for M and black is provided. These developing units 10Y, 10C, 10M, and 10K are:
Each is configured to be swingable, so that only the developing roller 11 of one developing unit can selectively contact the photoconductor 140. Therefore, these developing devices 10
Develops an electrostatic latent image on the photoconductor 140 by applying any one of yellow, cyan, magenta, and black toners to the surface of the photoconductor 140.

The developed toner image is transferred to an intermediate transfer device 30.
Is transferred onto an intermediate transfer belt 36 which forms an image carrier.

The cleaning means 170 includes a cleaner blade for scraping off the toner T remaining on and adhering to the outer peripheral surface of the photosensitive member 140 after the transfer, and a receiving portion for receiving the toner scraped off by the cleaner blade. ing.

The intermediate transfer device 30 includes a driving roller 31,
It has four driven rollers 32, 33, 34, 35 and an endless intermediate transfer belt 36 as an image carrier stretched around these rollers.

The drive roller 31 rotates at substantially the same peripheral speed as the photosensitive member 140 because a gear (not shown) fixed to the end of the drive roller 31 meshes with a drive gear (not shown) for the photosensitive member 140. Thus, the intermediate transfer belt 36 is driven to circulate at substantially the same peripheral speed as the photosensitive member 140 in the direction indicated by the arrow in the figure.

The driven roller 35 is disposed at a position where the intermediate transfer belt 36 is pressed against the photosensitive member 140 by its own tension with the driving roller 31.
A primary transfer portion T1 is formed at a pressure contact portion between the intermediate transfer belt 36 and the intermediate transfer belt 36. The driven roller 35 is disposed near the primary transfer portion T1 on the upstream side in the circulation direction of the intermediate transfer belt 36.

The driving roller 31 includes an intermediate transfer belt 36.
A primary transfer voltage is applied to the intermediate transfer belt 36 via the electrode roller (not shown).

The driven roller 32 is a tension roller, and urges the intermediate transfer belt 36 in the direction of its tension by urging means (not shown).

The driven roller 33 is provided at a secondary transfer portion (claim 1).
This is a backup roller for forming the transfer portion (T2). A secondary transfer roller 38 as a transfer unit is opposed to the backup roller 33 via an intermediate transfer belt 36. The secondary transfer roller 38 can be moved toward and away from the intermediate transfer belt 36 by a contact / separation mechanism (not shown). A secondary transfer voltage is applied to the secondary transfer roller 38.

The driven roller 34 is a backup roller for the belt cleaner 39. Belt cleaner 39
Is a cleaner blade 39 which comes into contact with the intermediate transfer belt 36 and scrapes off the toner remaining and adhering to the outer peripheral surface thereof.
a, and a receiving portion 39b for receiving the toner scraped off by the cleaner blade 39a. The belt cleaner 39 can be moved toward and away from the intermediate transfer belt 36 by a contact / separation mechanism (not shown).

The intermediate transfer belt 36 is composed of a multilayer belt having a conductive layer and a resistive layer formed on the conductive layer and pressed against the photosensitive member 140. The conductive layer is formed on an insulating substrate made of a synthetic resin, and a primary transfer voltage is applied to the conductive layer via the above-described electrode roller.

In the process of circulating the intermediate transfer belt 36, the toner image on the photosensitive member 140 is transferred onto the intermediate transfer belt 36 in the primary transfer portion T1, and the toner image transferred onto the intermediate transfer belt 36 is Is transferred to a sheet (recording material) S, such as a sheet, supplied between the secondary transfer roller 38 and the secondary transfer unit T2.

The recording material S is fed from a paper feeding device 50,
The toner is supplied to the secondary transfer portion T2 at a predetermined timing by the gate roller pair G. Reference numeral 51 denotes a paper feed cassette for stacking and holding the recording materials S, and reference numeral 52 denotes a pickup roller.

The recording material S to which the toner image has been transferred in the secondary transfer portion T2 passes through a fixing device 60 serving as fixing means, and the toner image is fixed.

The fixing device 60 has a heating roller 61 having a heat source and a pressing roller 62 pressed against the heating roller 61. The rollers 61 and 62 heat the recording material S passing therethrough while pressing the recording material S therebetween. Then, the toner image is fused and fixed on the recording material S.

The recording material S that has passed through the fixing device 60 is finally discharged through a paper discharge path 70 onto a sheet receiving portion 81 formed on a case 80 of the apparatus main body. The forming apparatus is provided with a reversing return path 70 ′ that can reverse the recording material S that has passed through the fixing device 60 and return the recording material S to the transfer unit T2 (secondary transfer unit T2) again.

The reversing return path 70 ′ is provided with two independent paper discharge paths 71, 72 which can carry in the recording material S which has passed through the fixing device 60 and reversely transport the recording material S once carried in. And a return path 73 for returning the recording material S sent back from the switchback path 74 back to the secondary transfer portion T2. Therefore, the recording material S returned to the secondary transfer portion T2 again by the reverse return path 70 'is turned over and returned to the secondary transfer portion T2.

Such an image forming apparatus can form an image only on the front surface (first surface) of the recording material S, or form an image on both surfaces (first and second surfaces, front and back). You can also.

Reference numeral 90 denotes a control unit, which constitutes control means for controlling the entire apparatus.

The outline of the operation of the entire image forming apparatus as described above is as follows.

(I) When a print command signal (image forming signal) from a host computer or the like (personal computer or the like) (not shown) is input to the control unit 90 of the image forming apparatus, each roller of the photosensitive member 140 and the developing device 10 11 and the intermediate transfer belt 36 are driven to rotate.

(Ii) The outer peripheral surface of the photosensitive member 140 is uniformly charged by the charging roller 160.

(Iii) The exposure unit 40 selectively exposes the outer peripheral surface of the uniformly charged photoreceptor 140 in accordance with the image information of the first color (for example, yellow). An image is formed.

(Iv) Only the developing roller of the developing unit 10Y for the first color (for example, yellow) comes into contact with the photoconductor 140, whereby the electrostatic latent image is developed, and the first color (for example, yellow) is developed. Is formed on the photoconductor 140.

(V) A primary transfer voltage having a polarity opposite to the charging polarity of the toner is applied to the intermediate transfer belt 36, and the toner image formed on the photosensitive member 140 is transferred to the intermediate transfer belt 36 at the primary transfer portion T1. Is transferred to At this time, the secondary transfer roller 38 and the belt cleaner 39 are separated from the intermediate transfer belt 36.

(Vi) After the toner remaining on the photosensitive member 140 is removed by the cleaning means 170,
The photoconductor 140 is neutralized by the neutralization light L2 from the neutralization unit 41.

(Vii) The above operations (ii) to (vi) are repeated as necessary. That is, the second color, the third color, the fourth color,
Is repeated on the intermediate transfer belt 36 to form a toner image corresponding to the content of the print command signal.

(Viii) The recording material S is supplied from the paper feeding device 50 at a predetermined timing, and immediately before or after the leading end of the recording material S reaches the secondary transfer portion T2 (in short, a desired image on the recording material S) (At the timing when the toner image on the intermediate transfer belt 36 is transferred) to the secondary transfer roller 38
Is pressed against the intermediate transfer belt 36 and a secondary transfer voltage is applied, and the toner image on the intermediate transfer belt 36 (basically, a full-color image in which four color toner images are superimposed) is formed on the recording material S. Transcribed. Further, the belt cleaner 39 comes into contact with the intermediate transfer belt 36, and the toner remaining on the intermediate transfer belt 36 after the secondary transfer is removed.

(Ix) The toner image is fixed on the recording material S by passing the recording material S through the fixing device 60, and thereafter, the recording material S is directed to a predetermined position (in a case where it is not double-sided printing, a sheet receiving portion). In the case of duplex printing, the paper is conveyed to the return path 73 via the switchback path 74.

That is, when an image is formed only on the front surface (first surface), the recording material S fed from the paper feeding device 50 is used.
After the image is transferred to the first surface thereof by the secondary transfer unit T2 and fixed by the fixing device 60, the sheet is discharged onto the sheet receiving unit 81 via the sheet discharge path 71 or 72.

To form an image on both sides (first and second sides), the recording material S fed from the sheet feeding device 50 is used.
After the image is transferred to the first surface by the secondary transfer unit T2 and fixed by the fixing device 60, the sheet
2 (switchback path 74), the sheet is fed backward, and is returned to the secondary transfer portion T2 again at a predetermined timing by the gate roller pair G via the return path 73, so that the image is also transferred to the second surface. Thereafter, the image is also fixed on the second surface by the fixing device 60, and is discharged onto the sheet receiving portion 81 via the paper discharge path 71 or 72.

When an image is formed on both sides as described above, the recording material S that has once passed through the fixing unit 60 is returned to the secondary transfer unit T2 again. The optimum value of the transfer voltage (the secondary transfer voltage in this case) at the time of the second transfer is greatly different from the optimum value of the transfer voltage at the time of the second surface transfer.

At the time of the first surface transfer, the recording material S has not yet passed the fixing device 60, but at the time of the second surface transfer, the recording material S has already passed the fixing device 60 once. Since the recording material S is heated to fix the toner image on the recording material S, the moisture absorption of the recording material S immediately after passing through the fixing device 60 is not only infinitely close to zero, but also, This is because S becomes extremely sensitive to the influence of humidity.

Therefore, in this embodiment, when images are formed on the first and second surfaces of the recording material S, the toner image is transferred to the first surface of the recording material S and passes through the fixing device 60. And a temperature / humidity detecting means 92 for detecting humidity and temperature. The control unit 90 measures the time measured by the time measuring means 91. The transfer voltage for transferring the toner image to the second surface of the recording material S is determined based on the elapsed time after the fixing of the first surface and the temperature and humidity detected by the temperature and humidity detecting means 92. Configured. The higher the temperature and humidity, and the longer the elapsed time, the more the recording material S
Moisture absorption increases and its resistance decreases,
The transfer voltage is set to a relatively small value, and the lower the temperature and humidity, and the shorter the elapsed time, the smaller the moisture absorption of the recording material S and the larger the resistance value. .

The transfer voltage for transferring the toner image onto the first surface of the recording material S is determined by the temperature and humidity detecting means 9.
2 based on the detected temperature and humidity. The transfer voltage is set to a relatively small value because the higher the temperature and humidity, the higher the moisture absorption of the recording material S. The lower the temperature and humidity, the smaller the moisture absorption of the recording material S. Therefore, the transfer voltage is set to a relatively large value. And

The time counting means 91 can be constituted by a timer built in the control section 90. The elapsed time is determined by, for example, a detector 93 for detecting the rear end of the recording material S downstream of the fixing device 60. It can be measured by measuring the elapsed time from when the detector 93 detects the rear end of the recording material S.

The temperature / humidity detecting means 92 can be provided at an appropriate position in the apparatus.
It is provided near. Further, the temperature / humidity detecting means 92 can be constituted by a temperature / humidity sensor for detecting temperature and humidity.

According to the above-described image forming apparatus, the following operation and effect can be obtained.

(A) An intermediate transfer belt 36 as an image carrier on which a toner image is formed on the surface, and a transfer portion T2 is formed between the intermediate transfer belt 36 and a transfer voltage is applied.
A secondary transfer roller 38 as a transfer unit for transferring the toner image on the surface of the intermediate transfer belt 36 to the recording material S, and the recording is performed by heating while passing the recording material S onto which the toner image has been transferred by the secondary transfer roller 38. Fixing device 60 as a fixing unit for fixing a toner image on material S, and fixing device 60
The reverse return path 7 is capable of reversing the front and back of the recording material S that has passed through and returning the recording material S to the transfer portion T2 again.
0 ′, the toner image is transferred to the first surface, and the recording material S on which the toner image is fixed after passing through the fixing device 60 is returned to the transfer unit T2 again by the reverse return path 70 ′. Thus, the toner image can be transferred to the second surface and fixed. That is, an image can be formed on both surfaces of the recording material S.

In the image forming apparatus of this embodiment, when images are formed on the first and second surfaces of the recording material S, the toner image is transferred to the first surface of the recording material S and the fixing device 6
0, a time measuring means 91 for measuring an elapsed time from the time when the toner image is transferred to the second surface to the start of transfer of the toner image to the second surface, a humidity detecting means 92 for detecting humidity, and the first surface fixing measured by the time measuring means 91. Elapsed time and humidity detecting means 92
And control means 90 for determining a transfer voltage for transferring the toner image onto the second surface of the recording material S based on the humidity detected by the control means 90.
The transfer voltage at the time of transferring the toner image onto the second surface of the recording material S can be determined to an optimum value according to the moisture absorption of the recording material S which may change abruptly with the elapsed time and the humidity. Becomes

That is, when the recording material S passes through the fixing device 60, the moisture absorption immediately after the fixing device 60 becomes infinitely close to 0, and the recording material S is in a state in which the influence of the humidity is extremely sensitive. Thus, the transfer voltage for transferring the toner image onto the second surface can be determined to an optimum value.

Therefore, according to the image forming apparatus of this embodiment, an appropriate transfer voltage can be obtained even when an image is formed on the second surface of the recording material S, and as a result, a clean image can be formed on the second surface. It is possible to form a perfect image.

(B) The control means 90 includes a humidity detecting means 92
The transfer voltage at the time of transferring the toner image to the first surface of the recording material S is also determined based on the humidity detected by the above. Therefore, the transfer voltage at the time of transferring the toner image to the first surface is also optimal. Value can be determined.

Further, humidity detecting means for determining a transfer voltage when transferring the toner image to the first surface, and humidity detecting means for determining a transfer voltage when transferring the toner image to the second surface are provided. However, since one humidity detecting means 92 is used in common, there is an effect that only one humidity detecting means is required.

(C) Intermediate Transfer Belt 3 as Image Carrier
Reference numeral 6 denotes an image carrier on which a plurality of color toner images may be superimposed by rotating a plurality of times, and the plurality of color toner images superimposed on the image carrier are recorded in the secondary transfer portion T2. Since the configuration is such that the recording material S is collectively transferred to the material S, it is possible to form not only a single-color image but also a full-color image on the first and second surfaces of the recording material S.

By the way, as in this image forming apparatus, the image carrier 36 is an image carrier in which toner images of a plurality of colors may be superimposed by rotating a plurality of times. When the superimposed toner images of a plurality of colors are collectively transferred to the recording material S in the transfer unit T2,
A case where a monochromatic toner image is transferred to the second surface of the recording material S;
In the case where the toner images of a plurality of colors superimposed on the image carrier 36 are collectively transferred, the transfer of the toner image to the second surface from the time when the toner image is transferred to the first surface and passes through the fixing device 60 is performed. The elapsed time until the start is significantly different depending on the difference in the number of rotations of the image carrier 36, and therefore, the moisture absorption of the recording material S may be significantly different.

On the other hand, according to the image forming apparatus of this embodiment, even in such a case, an appropriate transfer voltage for transferring the toner image to the second surface of the recording material S can be obtained. As a result, it is possible to form a beautiful single-color image or full-color image on the second surface.

(D) The humidity detecting means 92 comprises temperature / humidity detecting means for detecting the temperature, and the control means 90 controls the temperature, humidity, and the elapsed time detected by the temperature / humidity detecting means 92. Control means for determining the transfer voltage based on the transfer voltage, the transfer voltage (the transfer voltage for transferring the toner image onto the first surface and / or the second surface of the recording material) is more reliably set to the optimum value. Can be determined.

<Second Embodiment> The second embodiment is different from the first embodiment in that the temperature / humidity detecting means 92 'is connected to the return path 73 of the reverse return path 70'. It is in the point provided, and there is no change in other points. This temperature / humidity detecting means 92 'may be provided separately from the temperature / humidity detecting means 92 in the first embodiment, or may be provided instead of the temperature / humidity detecting means 92 in the first embodiment. When the temperature / humidity detecting means 92 'is provided separately from the temperature / humidity detecting means 92, the temperature / humidity detecting means 92 constitutes a temperature / humidity detecting means for determining a transfer voltage when the toner image is transferred onto the first surface. I do. The temperature / humidity detecting means 92 'is provided at a position where the conveyance of the recording material S is not hindered. That is, providing the humidity detecting means on the reverse return path means providing it near the reverse return path.

According to this embodiment, the following operation and effect can be obtained in addition to the operation and effect of the above-described first embodiment.

That is, since the temperature / humidity detecting means 92 ′ is provided for the reverse return path 70, the reverse return path 70, which is the path of the recording material S that has once passed through the fixing device 60 during double-sided image formation, is used. Temperature, humidity, and fixing device 60
The transfer voltage at the time of transferring the toner image to the second surface of the recording material S is more reliably determined to be the optimum value according to the moisture absorption of the recording material S, which may change drastically depending on the elapsed time after the passage. It is possible to do.

When the temperature / humidity detecting means 92 'is provided separately from the humidity detecting means 92 for determining the transfer voltage when transferring the toner image onto the first surface, the first embodiment or The temperature and humidity detecting means 92 ′ is connected to the first surface and the second surface.
As compared with the case where the toner image is transferred to the surface and used as a means for determining both transfer voltages, the first
Both transfer voltages for transferring the toner image to the surface and the second surface can be more reliably determined to the optimum values.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and can be appropriately modified within the scope of the present invention.

For example, in the above embodiment, the image bearing member is the intermediate transfer belt 36.
And the transfer portion is the secondary transfer portion T2, but the present invention is not limited to this. For example, the image carrier is composed of the photoconductor 10 and the photoconductor 1
The present invention can be applied to a configuration in which a toner image is directly transferred from 0 to the recording material S.

In the above-described embodiment, the detecting means 92 or 92 'is constituted by a temperature and humidity detecting means. However, it may be a humidity detecting means capable of detecting at least humidity.

[0093]

According to the image forming apparatus of any one of claims 1 to 6, an appropriate transfer voltage can be obtained even when an image is formed on the second surface of the recording material. It is also possible to form a beautiful image.

Further, according to the image forming apparatus of the second aspect, the transfer voltage for transferring the toner image to the first surface can be determined to the optimum value. In addition, an effect is obtained that only one humidity detecting means is required.

According to the image forming apparatus of the third aspect, the transfer voltage for transferring the toner image to the second surface of the recording material is
It is possible to more reliably determine the optimum value.

According to the image forming apparatus of the present invention, it is possible to more reliably determine both transfer voltages for transferring the toner image onto the first and second surfaces of the recording material to the optimum values. Become.

According to the image forming apparatus of the present invention, it is possible to form a beautiful monochromatic image or a color image on the second surface.

According to the image forming apparatus of the present invention, the transfer voltage (the transfer voltage for transferring the toner image to the first surface and / or the second surface of the recording material) is more reliably set to the optimum value. It is possible to decide.

[0099]

[Brief description of the drawings]

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

[Explanation of symbols]

T2 Secondary transfer unit (transfer unit) S Recording material 36 Intermediate transfer belt (image carrier) 38 Secondary transfer roller (transfer unit) 60 Fixing device (fixing unit) 70 'Reverse return path 90 Control unit (control unit) 91 Clocking means 92 Temperature / humidity detecting means (humidity detecting means, temperature detecting means)

Claims (6)

[Claims] An image carrier on which a toner image is formed, and a transfer portion formed between the image carrier and a transfer voltage applied to transfer a toner image on the surface of the image carrier to a recording material. Transfer means for fixing, a fixing means for fixing the toner image on the recording material by heating while passing the recording material onto which the toner image has been transferred by the transfer means, and reversing the front and back of the recording material passing through the fixing means. An image forming apparatus, comprising: a reversing return path for returning the recording material to the transfer section again; and forming an image on the first and second surfaces of the recording material. From the time when the toner image is transferred to the first surface of the recording material and the toner image is transferred to the first surface of the recording material and the toner image is transferred to the second surface when the images are formed on the first and second surfaces of the material, Time measuring means for measuring time and humidity detecting means for detecting humidity And a transfer voltage for transferring the toner image to the second surface of the recording material based on the elapsed time after the fixing of the first surface measured by the timer and the humidity detected by the humidity detector. An image forming apparatus, comprising: a control unit for determining. 2. The control unit according to claim 1, wherein the control unit determines a transfer voltage for transferring a toner image onto the first surface of the recording material based on the humidity detected by the humidity detection unit. The image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 1, wherein said humidity detecting means is provided for said reverse return path. 4. An image according to claim 3, wherein said humidity detecting means is provided separately from the humidity detecting means for determining a transfer voltage when a toner image is transferred onto the first surface. Forming equipment. 5. The image carrier, wherein a plurality of color toner images may be superimposed by rotating the image carrier a plurality of times, and the plurality of color toner images superimposed on the image carrier. The image forming apparatus according to claim 1, wherein the image data is collectively transferred to a recording material in the transfer unit. 6. The apparatus further comprises temperature detecting means for detecting a temperature, wherein the control means determines the transfer voltage based on the temperature, the humidity, and the elapsed time detected by the temperature detecting means. 6. The image forming apparatus according to claim 1, wherein the control unit performs the control.