JP3282886B2 - Image forming apparatus using intermediate transfer method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, etc., and more specifically, to a primary transfer process using an intermediate transfer member such as an intermediate transfer belt. And an image forming apparatus using an intermediate transfer method.

[0002]

2. Description of the Related Art Generally, this type of image formation is performed using electrophotographic technology. That is, an electrostatic latent image is formed on the photoreceptor by image exposure, developed with toner, and then the electrostatic force is applied to the toner by a corona charger, a bias roller, or the like, and transferred to a transfer material such as paper. It is obtained by fixing.

[0005] However, such an image forming apparatus has a problem that density unevenness and toner scattering occur in a transferred image, and resolution and dot reproducibility are deteriorated. This is because the paper and photoreceptor do not completely adhere due to the unevenness of the paper surface,
This is considered to be because a non-uniform gap appears, causing an electric field to be disturbed or a Coulomb repulsion between toners, resulting in a non-uniform force acting on the toner. Therefore,
This is a problem particularly in the case of color recording.

[0004] From such a viewpoint, a method in which the toner image is not directly transferred from the photoreceptor to the transfer material, and the superimposed transfer is realized by a corona method using an endless intermediate transfer member such as an intermediate transfer belt is known. This is disclosed in Japanese Unexamined Patent Publication No. Hei 1-166070, Japanese Unexamined Patent Publication No. 1-293380, Japanese Unexamined Patent Publication No. 2-18591, and the like. According to these publications, regarding a color image forming apparatus using an intermediate transfer belt, after repeatedly transferring a toner image from a photoreceptor onto the intermediate transfer belt (primary transfer), the toner image is collectively transferred to a transfer material (2). A series of operations for next transfer) is shown.

[0005]

In an image forming apparatus using such an intermediate transfer system, when the charge amount (Q / M) of the toner primarily transferred on the endless intermediate transfer belt is low, the transfer is performed. At the time of secondary transfer for forming an image on a material, an abnormal image such as traces of paper feed rollers, toner scattering, and honeycomb occurs, so that the optimal secondary transfer bias range is extremely narrowed.
Alternatively, there is a first problem that an optimum region does not exist at all. This phenomenon is particularly noticeable when forming an image of only one color. This means that the primary transfer is also performed two to four times in the case of a superimposed image of 2 to 4 color toners, and the Q / M of the toner on the intermediate transfer belt is only 1 color toner. This is considered to be because the margin for the abnormal image increases.

The second problem is that the Q / M of the toner is
May vary depending on the use environment.

A third problem is that the optimum voltage or current applied during secondary transfer varies depending on the environment even when the type of transfer material is constant (material and thickness). .

[0008]

According to the first aspect of the present invention, a step of primary transferring a toner image on an image carrier to an endless intermediate transfer member is repeated a plurality of times to form a superimposed transferred image,
In an image forming apparatus using an intermediate transfer method in which the superimposed transfer image on the intermediate transfer body is secondarily transferred onto a transfer material in a lump, a detecting means for detecting an absolute humidity in an installation environment of the apparatus main body is provided. are secondary transfer by controlling the output of the power supply for supplying a voltage or current to the primary transfer electric field forming means on the basis of the environmental absolute humidity detected by the detection means only one color mode on the transfer material Charge amount controlling means for setting the charge amount of the toner on the intermediate transfer member to 12 μC / gr or more.

[0009]

[0010]

According to the second aspect of the present invention, the step of primary transferring the toner image on the image carrier to the endless intermediate transfer body is repeated a plurality of times to form a superimposed transfer image, and the superimposed transfer image is formed on the intermediate transfer body. in the image forming apparatus using an intermediate transfer method which is adapted to secondarily transferred onto the transfer material at once transferred image, a detection means for detecting the absolute humidity in the installation environment of the apparatus main body is provided, the only one color mode The output of a power supply for supplying a voltage or a current to a corona discharge unit disposed opposite to the vicinity of the intermediate transfer member based on the absolute humidity detected by the detection unit is controlled to perform the secondary transfer on the transfer material. A charge amount control means for setting the charge amount of the toner on the intermediate transfer member to 12 μC / gr or more was provided.

[0012]

[0013]

After examining the above problems, regarding the first problem (particularly, when forming an image of only one color), if the toner charge amount on the intermediate transfer member is 12 μC / gr or more, no abnormal image is generated. It has been found that an optimum secondary transfer bias range, which is judged to be practically practicable, can be obtained. Therefore, in the first and second aspects of the present invention, the charge amount control means reduces the toner charge amount to 12 μC / g.
Since r is not less than r, occurrence of an abnormal image in the intermediate transfer method is suppressed.

[0014]

Further, the above-mentioned variation of the toner charge amount, which is the second problem, and variation of the optimal secondary transfer bias or current, which is the third problem, depend on the absolute humidity of the environment in which the apparatus main body is installed. It has been found that it has fluctuated. In particular, it is remarkable in a low humidity environment. Therefore, as in the first and second aspects of the present invention, the absolute humidity in the installation environment of the apparatus main body is detected, and only in the one-color mode, the voltage supplied to the primary transfer electric field forming means or the corona discharge means based on this. Alternatively, by determining and controlling the current, the toner charge amount can be maintained at a predetermined value or more, and occurrence of an abnormal image in the intermediate transfer method is prevented .

[0016]

An embodiment of the present invention will be described with reference to the drawings. This embodiment shows an example of a color copying apparatus using a drum-shaped photoreceptor as an image carrier and an intermediate transfer belt as an endless intermediate transfer body. FIG. FIG. 3 shows an enlarged view around the photosensitive member and the intermediate transfer belt.

The color copying apparatus according to the present embodiment can be roughly classified into a color image reading apparatus (hereinafter, referred to as a color scanner) 1 and a color image recording apparatus (hereinafter, referred to as a color printer) 2. Have been.

First, the color scanner 1 forms an image of an original 3 on a color sensor 7 via an illumination lamp 4, a mirror group 5 (5a to 5c) and a lens 6, and outputs color image information of the original. For example, each color separation light of Blue, Green, and Red is read and converted into an electric image signal. Then, based on the B, G, and R color separation image signal intensity levels obtained by the color scanner 1, a color conversion process is performed by an image processing unit.
Black (hereinafter referred to as Bk), Cyan (ibid., C), Mag
Enta (same, M) and Yellow (same, Y) color image data is obtained. This is converted to Bk,
Visualization of C, M, and Y is performed, and these are superimposed to form a four-color full-color image.

Next, an outline of the color printer 2 will be described. The writing optical unit 8 converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the original image, and forms an electrostatic latent image on the photoconductor 9. That is, the laser diode 8a, the polygon mirror 8
b, a polygon motor 8c, an imaging lens 8d, a reflection mirror 8e, and the like.

The photoreceptor 9 rotates counterclockwise as indicated by the arrow. Around it, a cleaning unit (including a pre-cleaning neutralizer 10a, a cleaning roller 10b, and a cleaning blade 10c) 10, a neutralizing lamp 11,
A charging device 12, a potential sensor 13, a Bk developing device 14, a C developing device 15, an M developing device 16, a Y developing device 17, a development density pattern detector 18, an intermediate transfer belt 19 and the like are arranged. Each of the developing devices 14 to 17 is a developing sleeve (14a, 15a, 16a, 17a) that rotates so that the developer faces the photoconductor 9 in order to develop the electrostatic latent image, and pumps and agitates the developer. For this purpose, the image forming apparatus includes a rotating developing paddle and a toner concentration detecting sensor for the developer. Here, the order of the developing operation (color image forming order) is Bk,
The operation will be described below with an example of C, M, and Y (however,
The image forming order is not limited to this.

When the copying operation is started, reading of Bk image data is started at a predetermined timing by the color scanner 1, and light writing and latent image formation by laser light are started based on the image data (hereinafter, Bk image data). Is referred to as a Bk latent image. The same applies to C, M, and Y.) In order to enable development from the leading end of the Bk latent image, the developing sleeve 14a is started to rotate before the leading end of the latent image reaches the developing position of the Bk developing device 14 to transfer the Bk latent image to the Bk latent image.
Develop with toner. Thereafter, the developing operation of the Bk latent image area is continued, but when the rear end of the Bk latent image has passed the Bk developing position, the developing operation is disabled. This is at least the following C
This is completed before the leading end of the C latent image based on the image data arrives.

Next, the Bk toner image formed on the photoreceptor 9 is transferred to the intermediate transfer belt 1 driven at the same speed as the photoreceptor 9.
9 (hereinafter, transfer of the toner image from the photoreceptor 9 to the intermediate transfer belt 19 is referred to as “primary transfer”). 1
The next transfer is performed by applying a predetermined bias voltage to a transfer bias roller (primary transfer electric field forming unit) 20 from a power supply described later in a state where the photoconductor 9 and the intermediate transfer belt 19 are in contact with each other. The Bk, C, M, and Y toner images sequentially formed on the photoreceptor 9 are sequentially aligned on the same surface of the intermediate transfer belt 19 to form a four-color superimposed primary transfer image. Batch transfer (secondary transfer) is performed. The unit configuration and operation of the intermediate transfer belt 19 will be described later.

Here, on the photoreceptor 9 side, after the Bk process, C
Proceeds to the process.
, C image data reading is started, and a C latent image is formed by laser light writing using the image data.

The C developing device 15 starts rotating the developing sleeve 15a with respect to the developing position after the rear end of the preceding Bk latent image has passed and before the leading end of the C latent image has arrived. The latent image is developed with C toner. Thereafter, the development of the C latent image area is continued, but when the trailing end of the latent image passes, the development is disabled as in the case of the Bk developing device. This is also completed before the leading end of the next M latent image arrives.

In the M and Y steps, the operations of reading image data, forming a latent image, and developing are performed in the above-described B mode.
Since the steps are the same as steps k and C, the description is omitted.

Next, the intermediate transfer belt unit will be described. The intermediate transfer belt 19 includes a driving roller 2
1. It is stretched around the transfer bias roller 20 and the driven roller group, and is driven and controlled by a drive motor described later.

The belt cleaning unit 22 includes a brush roller 22a, a rubber blade 22b, and a mechanism 22c for contacting and separating from the belt. The timing of the contact / separation operation of the cleaning unit 22 is set so that the cleaning unit 22 is separated from the surface of the intermediate transfer belt 19 from the start of printing until the end of the primary transfer at the rear end of the Y (final color) image. Then, cleaning is performed by contacting the belt 19 with the contact / separation mechanism 22c.

The paper transfer unit 23 includes a paper transfer bias roller (secondary transfer electric field forming means) 23a, a roller cleaning blade 23b, a mechanism 23c for contacting and separating from the intermediate transfer belt 19, and the like. The bias roller 23 a is normally separated from the surface of the intermediate transfer belt 19, but it is timed when the four-color superimposed images formed on the surface of the intermediate transfer belt 19 are collectively transferred to the transfer paper (transfer material) 24. The roller 2 is pressed by the contact / separation mechanism 23c.
A predetermined bias voltage is applied to 3a by a power supply to be described later, and transfer to the transfer paper 24 is performed.

The transfer paper 24 is fed by a paper feed roller 25 and a registration roller 26 at the timing when the leading end of the four-color superimposed image on the surface of the intermediate transfer belt 19 reaches the paper transfer position.

The transfer paper 24 on which the four-color superimposed toner image is collectively transferred from the surface of the intermediate transfer belt 19 is conveyed to a fixing device 28 by a paper conveyance unit 27, and is heated by a fixing roller 28a controlled to a predetermined temperature. The toner image is fused and fixed by the pressure roller 28b and is carried out to the copy tray 29 to obtain a full-color copy.

The surface of the photoreceptor 9 after the belt transfer is cleaned by the cleaning unit 10, and
The charge is uniformly removed by the charge removing lamp 11.

As described above, the cleaning of the intermediate transfer belt 19 is performed by pressing the cleaning unit 22 against the surface of the belt 19 by the contact / separation mechanism 22c at a predetermined timing after the transfer of the final color Y image belt is completed.

Further, the intermediate transfer belt 19 follows the batch transfer process of the first four-color superimposed image onto transfer paper,
The second Bk toner image is belt-transferred to the area where the front surface is cleaned by the cleaning unit 22. After that, the operation becomes the same as that of the first sheet.

Incidentally, transfer papers of various sizes are stored in the transfer paper cassettes 30 to 33, and are fed and conveyed toward the registration rollers 26 at a timing from the storage cassette of the size paper specified on the operation panel. You. 34 is OH
It is a manual paper feed tray for P paper and thick paper.

Although the above description has been given of the example of the copy mode for obtaining four full colors, in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the required number of times. . In the case of the single-color copy mode, until only a predetermined number of sheets are completed, only the developing device of that color is set in the developing operation state, and the intermediate transfer belt 19 is kept in contact with the surface of the photosensitive member 9 in the forward direction. The copying operation is performed while the blade 22b is kept in contact with the intermediate transfer belt 19 at a high speed.

FIG. 3 shows the configuration of a control system for performing such a basic operation. The control of the entire copying apparatus is performed by a CPU 35, a RAM 36, a ROM 37, a PW
Control unit 3 incorporating M (pulse width modulator) 38 and the like
9 is performed. The controller 39 includes a motor 40 for rotating the photosensitive member 9 and a motor controller 42 for the motor 41 for driving the intermediate transfer belt 19.
Various loads such as 43, a power supply 44 for the transfer bias roller 20, and a power supply 45 for the paper transfer bias roller 23a, the potential sensor 13, and other various sensors are connected.

On the premise of such a basic configuration or operation as an intermediate transfer system, the present embodiment is configured as follows in order to solve the above-mentioned problem.
First, the intermediate transfer belt 19 used in the present embodiment is set to a medium resistance value having a surface resistivity of 1 × 10 ⁷ to 1 × 10 ¹² Ω / cm ² . Correspondingly, the drive roller 21 and the driven roller group for the intermediate transfer belt 19 are grounded. In this embodiment, the environmental absolute humidity in the installation environment of the apparatus main body is regarded as important, and a temperature sensor 46 and a humidity sensor 47 for detecting the temperature in the installation environment are used.
And are installed in the aircraft. The locations where the temperature sensor 46 and the humidity sensor 47 are installed may be set as appropriate. However, in the present embodiment, the location where the thermal effect in the apparatus is relatively small in the apparatus main body and which satisfies the condition close to the external environment as much as possible is assumed. The inside of the sheet supply table 48 in which the paper cassettes 32 and 33 are incorporated is provided. The temperature sensor 46 and the humidity sensor 47 are connected so that the detection information can be taken into the CPU 35, and are used for calculating the environmental absolute humidity as described later.

Although it is optional, a corona discharger (PTC = corona discharge means) 49 facing the intermediate transfer belt 19 at a location before the secondary transfer is provided.
Is connected to the PWM 38 in the control unit 39 via the.

Therefore, in this embodiment, the intermediate transfer belt 1
As a method of increasing the Q / M of the toner present on the toner 9 to a predetermined value or more, the power supply 44 is controlled to control the toner Q / M by the primary transfer bias of the transfer bias roller 20 or the current.
Or a method of controlling the power supply 50 before the secondary transfer to increase the toner Q / M by corona discharge by the PTC 49, or a combination of these methods.

The primary and secondary transfer biases by the bias rollers 20 and 23a are controlled based on the detection outputs of the temperature sensor 46 and the humidity sensor 47. , Relationship between absolute humidity, transfer material type and optimum secondary transfer bias, temperature sensor 4
It is necessary to prepare a conversion table for estimating the absolute environmental humidity from the temperature and humidity output from the humidity sensor 6 and the humidity sensor 47 in advance.

Therefore, each of these relationships found from experimental data and the like based on the actual machine will be described in order.

First, the relationship between the absolute humidity and the amount of increase of the toner Q / M will be described. This means how much charge is required to make the toner Q / M equal to or more than 12 μC / gr under an arbitrary absolute humidity. In practice, a means for increasing the toner Q / M ( It is nothing less than how much voltage or current value is required in the transfer bias roller 20 or the PTC 23a).

When increasing the Q / M by the primary transfer bias or current by the transfer bias roller 20, the relationship between the estimated absolute humidity and the primary transfer bias may be set as shown in Table 1.

[0044]

[Table 1]

When increasing the Q / M by the PTC 49, the relationship between the estimated absolute humidity and the PTC bias or current value may be determined as shown in Table 2. However, in the case of modes 2C to 4C in which two to four colors are copied, the PTC current value is set to zero,
Is set not to perform Q / M up.
In addition, the primary transfer bias for Q / M increase by the PTC 49 is fixed to a value as shown in Table 3 regardless of the absolute humidity.

[0046]

[Table 2]

[0047]

[Table 3]

Next, the absolute humidity and the type of transfer material (paper type)
And the relationship between the transfer bias and the secondary transfer bias will be described. This is determined for each of plain paper, OHP, and thick paper from the mode and the estimated absolute humidity in a relationship as shown in Table 4.

[0049]

[Table 4]

Further, a temperature sensor 46 and a humidity sensor 47
A conversion table for estimating the environmental absolute humidity from the temperature / humidity output from will be described. In this embodiment, R
A conversion table 51 as shown in FIG. 4 is prepared in the OM 37. That is, the present inventors found that based on the results of various experiments, the output from the temperature sensor 46 T _v and humidity sensor 47
When estimating the absolute humidity of the installation environment from the output R _hv from, the absolute humidity D is determined by D = α · R _hv . Here, alpha is any T _v, R _hv and, T _v was determined from the relationship between the environmental absolute humidity at that time, the R _hv 2
The conversion table 51 shown in FIG. 4 is a coefficient composed of an original table, and shows specific numerical values of the coefficient α.

Based on such matters, in the present embodiment, the CPU 35 periodically _{receives the} outputs T _v and R _hv obtained from the temperature sensor 46 and the humidity sensor 47, and
The estimated absolute humidity at each point in time is obtained as the environmental absolute humidity by using the conversion table 51 stored in the memory 37 and the above-described formula for calculating the absolute humidity D. FIG. 4 shows a flowchart for calculating such an absolute humidity. This process is performed periodically, for example, every six seconds. First, the humidity sensor 47 is sampled to obtain an output value R _hv at that time. Also, samples the temperature sensor 46 to obtain an output value T _v at that time. Using these values and the coefficient α in the conversion table 51, the absolute humidity is calculated by a calculation formula of D = α · R _hv . Here, the calculated absolute humidity is stored in the current absolute humidity memory provided in the RAM 36. Similarly, three minutes ago,
The absolute humidity 7 minutes before is stored in the memory for absolute humidity 3 minutes before and 7 minutes before, respectively. Further, the upper limit value and the lower limit value of the output of the humidity sensor 47 are set to _{Rhv Max} , _{Rhh Min} , and the temperature sensor 4 respectively.
The upper limit of the output of 6, each T _{v Max} the lower limit, when the T _{v Min,} these values and the output values R _hv, respectively compares the T _v, within the range of the upper limit value - lower limit value If so, the temperature / humidity sensor abnormality flag is reset, but if not, the temperature / humidity sensor abnormality flag is set.

After calculating the estimated absolute humidity in this way, for example, the PWM 38 in the control unit 35 outputs a signal so that the primary and secondary transfer biases corresponding to the estimated absolute humidity are output from the respective power supplies 44 and 45. Is output. FIG. 6 is a flowchart for determining such a primary transfer bias value. This process is periodically performed at the start of copying and every minute. First, it is checked whether or not the temperature / humidity sensor abnormality flag is set. If the flag is set, it is abnormal. Next transfer output switching is determined. On the other hand, when the flag is not set and the operation is normal, the absolute humidity _DT to be used for the current control is determined from the absolute humidity three minutes before and seven minutes before. Here, assuming that the lower limit value of the switching absolute humidity is D _L and the upper limit value is D _H , a comparison is made between the absolute humidity D _T and D _{T T.}
<D _L , the transfer output switching is set to a low level (V
B1) is determined. If D _T > D _H , the transfer output switching is determined to be high level (VB2). Furthermore, D
_{If L} ≦ _DT ≦ _DH , the transfer output switching is determined to be the normal level (VB0).

After the transfer output switching is determined, the copy mode (1C to 4C) and the type of transfer paper (plain paper / OHP) are selected.
/ Thick paper) and the above-described transfer output switching level, the transfer bias calculation coefficients a and b for the primary transfer and the transfer bias default are determined from the tables 52 to 56 in the ROM 37 as shown in FIGS. The values c and d and the transfer bias ratio E for correction are obtained. Then, the primary transfer bias value is calculated from a · c · E, and the secondary transfer bias value is calculated from b · d · E. Thereafter, the calculated primary transfer bias value is converted into a duty ratio of the PWM signal from the PWM 38 (see FIG. 12) and stored in the PWM output memory. Similarly, the calculated secondary transfer bias value is P
The duty ratio of the PWM signal from the WM 38 is converted into a duty ratio (see FIG. 12) and stored in the PWM output memory. Based on such a result, the power supplies 44 and 45 are controlled to control the primary and secondary transfer biases by the bias rollers 20 and 23a, so that the toner Q / M on the intermediate transfer belt 19 is controlled.
Is maintained at or above a predetermined value.

When the toner Q / M is increased by the PTC 49, the same processing is performed in the same manner, and the PW
The duty ratio of the M signal is determined.

[0055]

According to the first and second aspects of the present invention, in the image forming apparatus using the intermediate transfer system, the charge amount of the toner on the intermediate transfer body which is secondarily transferred onto the transfer material is controlled by the charge amount control means. Is set to 12 μC / gr or more, so that it is possible to obtain an optimum secondary transfer bias region which is considered to be sufficiently practical without any occurrence of an abnormal image. The generation of an image can be suppressed.

[0056]

In particular, attention is paid to the fact that the variation of the toner charge varies depending on the absolute humidity of the environment in which the apparatus main body is installed. Since the absolute humidity in the environment is detected and the voltage or current to be supplied to the primary transfer electric field forming means or corona discharge means is determined and controlled only in the one-color mode, the toner charge amount is equal to or more than a predetermined value. , And the occurrence of an abnormal image in the intermediate transfer system can be prevented.

[0058]

[Brief description of the drawings]

FIG. 1 is a schematic front view showing an area around a photoreceptor and an intermediate transfer belt in an embodiment of the present invention in an extracted and enlarged manner.

FIG. 2 is a schematic front view showing the configuration of the entire color copying apparatus.

FIG. 3 is a block diagram showing a control system configuration.

FIG. 4 is an explanatory diagram showing a conversion table.

FIG. 5 is a flowchart illustrating an absolute humidity calculation process.

FIG. 6 is a flowchart illustrating a transfer bias value determination process.

FIG. 7 is an explanatory diagram showing a transfer bias calculation coefficient table for primary transfer.

FIG. 8 is an explanatory diagram showing a transfer bias calculation coefficient table for secondary transfer.

FIG. 9 is an explanatory diagram showing a transfer bias default value table for primary transfer.

FIG. 10 is an explanatory diagram showing a transfer bias default value table for secondary transfer.

FIG. 11 is an explanatory diagram showing a transfer bias ratio table for correction.

FIG. 12 is an output characteristic diagram showing a relationship between a duty by PWM and an output current or voltage of a power supply.

[Explanation of symbols]

 Reference Signs List 9 image carrier 19 intermediate transfer body 20 primary transfer electric field forming means 23a secondary transfer electric field forming means 24 transfer material 35 charge amount control means 44, 45 power supply 49 corona discharge means 50 power supply

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiaki Motobashi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Katsuya Kawagoe 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Mitsuru Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh (72) Naoko Iwata 1-3-6, Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Co., Ltd. (72) Inventor Kunio Hayakawa 1-3-6 Nakamagome, Ota-ku, Tokyo Co., Ltd. Ricoh Co., Ltd. (56) References JP-A-4-138483 (JP, A) JP-A-4-27987 ( JP, A) JP-A-2-212870 (JP, A) JP-A-63-41170 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/16 G03G 15/01 114 G03G 15/00 303

Claims (2)

(57) [Claims] 1. A process of primary transferring a toner image on an image carrier to an endless intermediate transfer member is repeated a plurality of times to form a superimposed transfer image. in the image forming apparatus using an intermediate transfer method which is adapted to secondarily transferred onto the transfer material, a detecting means for detecting the absolute humidity in the installation environment of the apparatus body is provided, which is detected by the detection means only one color mode The output of a power supply for supplying a voltage or a current to the primary transfer electric field forming means is controlled based on the environmental absolute humidity so that the toner charge amount on the intermediate transfer body that is secondarily transferred onto the transfer material is 12 μC / An image forming apparatus using an intermediate transfer system, comprising a charge amount control unit for controlling the charge amount to gr or more. 2. The method according to claim 1, wherein the step of primary transferring the toner image on the image carrier to an endless intermediate transfer member is repeated a plurality of times to form a superimposed transfer image. in the image forming apparatus using an intermediate transfer method which is adapted to secondarily transferred onto the transfer material, a detecting means for detecting the absolute humidity in the installation environment of the apparatus body is provided, which is detected by the detection means only one color mode The toner on the intermediate transfer body that is secondarily transferred onto the transfer material by controlling the output of a power supply that supplies a voltage or a current to a corona discharge unit disposed opposite to and near the intermediate transfer body based on the environmental absolute humidity An image forming apparatus using an intermediate transfer method, comprising a charge amount control unit for setting a charge amount to 12 μC / gr or more.