JP2000162897A - Image-forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image-forming device capable of obtaining an supreme image by satisfactorily transferring without causing the dot-shape fall, even if paper is adapted as the recording material. SOLUTION: A contact type adhesion charger 5 mounted in front of a first image forming part Pa of this device is used as a prior charging means. This prior charging means is, according to the environmental temp./humidity, made possible to be switched to a negative charge mode for impressing the electric charges in polarity which is opposite to the polarity of the charge imparted in the rear side of a recording material P prior to transfer, and the insulating mode being grounded through diodes D1 and D2 capable of generating voltage, when the current of transferring time is conducted via a transfer belt 130.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an image on a recording material by using an electrophotographic method and obtaining a hard copy.
The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer.

[0002]

2. Description of the Related Art Conventionally, a plurality of image forming units are provided, and toner images of different colors are formed in each image forming unit, and the toner images are sequentially superimposed and transferred on the same recording material, and are transferred onto the recording material. Various image forming apparatuses for forming a color image have been proposed.

[0003] Among such image forming apparatuses, a multicolor electrophotographic color electrophotographic recording apparatus using an endless recording material carrier is used for high-speed recording. An example of this conventional color electrophotographic recording apparatus will be described with reference to FIG.

As shown in FIG. 1, first, second, third, and fourth image forming units Pa, Pb, Pc, and Pd are provided side by side in the apparatus. Through the processes of latent image formation, development and transfer, toner images of different colors are formed.

The image forming units Pa, Pb, Pc, and Pd are each a dedicated image carrier, in this example, an electrophotographic photosensitive drum 3
a, 3b, 3c, 3d.
A toner image of each color is formed on b, 3c and 3d. Adjacent to each of the photosensitive drums 3a, 3b, 3c, and 3d, a transfer belt 130 of a recording material carrier wound around a drive roller 13 and support rollers 14 and 15 is provided.
The toner images of the respective colors formed on 3b, 3c and 3d are superimposedly transferred onto the recording material P carried and conveyed on the transfer belt 130.

The recording material P on which the toner images of each color are transferred is
After the toner image is fixed by heat and pressure in the fixing device 9, the toner image is discharged out of the device as a color recorded image.

[0007] Exposure lamps 111a, 111b, and 11 are provided on the outer periphery of the photosensitive drums 3a, 3b, 3c, and 3d, respectively.
1c, 111d, drum chargers 2a, 2b, 2c, 2
d, potential sensors 113a, 113b, 113c, 11
3d, developing devices 1a, 1b, 1c, 1d, transfer charger 24
a, 24b, 24c, 24d and cleaners 4a, 4
b, 4c, and 4d are provided, and a light source device (not shown) and a polygon mirror 117 are further installed above the device.

The laser light emitted from the light source device is rotated and scanned by the polygon mirror 117, the light beam of the scanning light is deflected by the reflection mirror, and the bus direction of each of the photosensitive drums 3a, 3b, 3c, and 3d by the fθ lens. The photosensitive drums 3a, 3b, 3c, 3
An electrostatic latent image corresponding to the image signal is formed on d.

The developing devices 1a, 1b, 1c, and 1d are filled with a predetermined amount of cyan, magenta, yellow, and black toners, respectively, by a supply device (not shown). The developing devices 1a, 1b, 1c, and 1d develop the latent images on the photosensitive drums 3a, 3b, 3c, and 3d, respectively, and visualize the latent images as cyan, magenta, yellow, and black toner images.

The recording material P is stored in a recording material cassette 10. The recording material P is supplied onto the transfer belt 130 through a plurality of conveyance rollers and the registration rollers 12 from there.
These are sequentially sent to the transfer sections facing b, 3c and 3d.

The transfer belt 130 is made of polyethylene terephthalate resin (PET), polyvinylidene fluoride resin,
It is made of a sheet of a dielectric resin such as a polyurethane resin, and its both ends are overlapped and joined to form an endless shape, or a seamless (seamless) belt is used.

When the transfer belt 130 is rotated by the drive roller 13 and is confirmed to be at a predetermined position, the recording material P is transferred from the registration roller 12 to the transfer belt 13.
0 and is conveyed to the transfer section of the first image forming section Pa. At the same time, the image writing signal is turned on, and an image is formed on the photosensitive drum 3a of the first image forming unit Pa at a certain timing based on the signal.

When the transfer charger 24a applies an electric field or electric charge at the lower transfer portion of the photosensitive drum 3a, the first color toner image formed on the photosensitive drum 3a is transferred onto the recording material P. You. Due to this transfer, the recording material P is firmly held on the transfer belt 130 by electrostatic attraction, and is conveyed to the second image forming portion Pb and thereafter.

It is to be noted that the recording material P is not electrostatically adsorbed at the same time as the transfer, but the adsorbing charger 5 is provided near the upstream end of the transfer belt 130 so that the recording material P is transferred before the transfer.
In some cases. The adsorption charger 5 includes a non-contact charger such as corona discharge, or a conductive blade,
A contact charger using a charging member such as a roller or a brush is used.

The transfer charger 24 (24a to 24d) includes:
A contact charger using a charging member such as a conductive blade, a roller, or a brush is used. The contact charger has advantages such as ozonelessness, resistance to temperature and humidity environmental changes, and high image quality.

For the sake of transfer stability, each image forming section P
The static elimination needles 7a to 7d may be provided near the downstream side of the transfer section of a to Pd. The static elimination needles 7 (7 a to 7 d) are not in contact with the transfer belt 130, but play a role of discharging a part of the transfer current to escape. Thus, it is possible to prevent discharge due to uneven charging after the photosensitive drum and the recording material are separated.

Image formation and transfer in the second to fourth image forming units Pb to Pd are performed in the same manner as in the first image forming unit Pa.
Next, the recording material P onto which the four color toner images have been transferred is separated from the end of the transfer belt 130 by eliminating the charge by the separation charger 32 at the downstream portion in the transport direction of the transfer belt 130 to attenuate the electrostatic attraction force. . Particularly, in a low humidity environment, the recording material P also dries and the electric resistance increases, so that the transfer belt 13
Since the electrostatic attraction force of the recording material P, which is 0, becomes large, it is effective to remove electricity by the separation charger 32. Normal,
When the toner image is unfixed, the recording material P
, A non-contact charger is used.

The output of the separation charger 32 is an AC voltage having a peak-to-peak voltage of 10 kV and a frequency of about 500 Hz. Further, in order to prevent image defects such as toner scattering, a plus or minus DC component of about 100 μA may be superimposed on the AC voltage.

Recording material P detached from transfer belt 130
Is a separation guide 64 for stabilizing the behavior of the leading end of the recording material P.
Is transported to the fixing device 9 by the transport unit 62.

The fixing device 9 includes a fixing roller 51, a pressure roller 52, heat-resistant cleaning members 54 and 55 for cleaning each of them, heaters 56 and 57 installed in the rollers 51 and 52, and a fixing roller. An application roller 52 for applying a release agent oil such as dimethyl silicone oil to the surface 51; an oil reservoir 53; and a thermistor 58 for detecting the temperature of the surface of the pressure roller 52 and controlling the fixing temperature.
It is composed of

The recording material P to which the four color toner images have been transferred is
By the fixing, the color mixture of the toner image and the fixation to the recording material P are performed to form a full-color copy image, and the image is discharged to the paper discharge tray 63.

The photosensitive drums 3a, 3b, 3 after the transfer is completed
c and 3d are the respective cleaners 4a, 4b, 4c and 4d
Thus, the toner remaining after transfer is cleaned and removed, and the apparatus is ready for the formation of the next latent image.

The toner and other foreign matters remaining on the transfer belt 130 are deposited on the surface of the transfer belt 130 by the cleaning blade 20 and the cleaning web (nonwoven fabric) 19.
To make contact and wipe off. At this time, the charge remaining on the transfer belt 130 is removed by the grounding removal rollers 21 and 22. Note that one of the charge removing rollers 21 is not grounded, and a high voltage of about 2 to 4 kV is applied thereto to charge the transfer belt 130 to the opposite potential as well as to remove the charge of the transfer belt 130 so that the transfer belt potential at the end of the transfer is reduced. There are also things to do.

The transfer belt 130 used in the image forming apparatus having the above-described configuration is a dielectric sheet such as a PET sheet, a polyvinylidene fluoride sheet, or a polyurethane sheet, as described above. 10 ¹³
Those having a density of 10 to 10 ¹⁸ Ωcm are generally used.

The transfer charger 24 (24a to 24d)
If the current that contributes to the transfer (transfer current) is constant at an appropriate current, the image will be stable. Therefore, even when the volume resistance changes due to the type of recording material (thickness, material, etc.), moisture absorption conditions, etc. In general, constant current control is performed so as to obtain a constant current.

[0026]

However, in the above-described image forming apparatus, when paper is used as the recording material P, a point-like transfer omission occurs in the transferred image, and the quality of the image is significantly impaired. Was.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality image by performing good transfer without causing dot-like transfer omission even when paper is used as a recording material. To provide.

[0028]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A visible image is formed on an image carrier, a recording material is carried on the recording material carrier, and is conveyed to the image carrier, and the visible image formed on the image carrier is conveyed by the conveyed recording material. In an image forming apparatus that electrostatically transfers the image by a transfer charging unit,
A pre-charging unit is installed at a position before the recording material reaches the image carrier, and the pre-charging unit has a charge having a polarity opposite to that of the charge applied to the back surface of the recording material during transfer by the transfer charging unit. A reverse charging mode applied to the back surface of the recording material prior to the transfer, and a mode in which a current at the time of transfer by the transfer charging unit is grounded via an element that generates a voltage when the current flows through the recording material carrier. Is switchably provided.

According to another aspect of the present invention, a visible image is formed on an image carrier, a recording material is carried on the recording material carrier, transported to the image carrier, and formed on the image carrier. An image forming apparatus that electrostatically transfers the visible image to the conveyed recording material by a transfer charging unit, at a position before the recording material reaches an image carrier when the recording material is transferred by the transfer charging unit. Charge of the opposite polarity to the charge applied to the back of
An image forming apparatus, comprising: a pre-charging unit provided on a back surface of a recording material prior to transfer; and the pre-charging unit is provided so as to be separated from the recording material carrier.

According to the invention, there is provided detecting means for detecting the temperature and humidity of the atmosphere in the main body of the image forming apparatus, and based on the temperature and humidity information in the main body of the image forming apparatus detected by the detecting means. The charging output of the charging means can be changed. Further, the mode of the pre-charging means can be controlled based on the temperature and humidity information in the main body of the image forming apparatus detected by the detecting means. Further, based on the temperature and humidity information in the main body of the image forming apparatus detected by the detecting means, the separating / contacting operation of the pre-charging means can be controlled.

[0031]

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

Embodiment 1 FIG. 1 is a schematic structural view showing an embodiment of the image forming apparatus of the present invention. The basic configuration of this image forming apparatus is the same as that of the conventional image forming apparatus shown in FIG. 8, except that a non-ground side roller 5a below the contact-type adsorption charger 5 has a high-output controllable high voltage. Power supply E was connected. This will be described later. 1, the same reference numerals as those shown in FIG. 8 denote the same members.

In the present invention, as the dielectric sheet material of the transfer belt 130, PET, polyacetal, polyamide, polyvinyl alcohol, polyether ketone,
Polystyrene, polybutylene phthalate, polymethylpentene, polypropylene, polyethylene, polyphenylene sulfide, polyurethane, silicone resin, polyamide imide, polycarbonate, polyphenylene oxide, polyether sulfone, polysulfone, aromatic polyester, polyether imide, aromatic polyimide, etc. Engineering plastic film-shaped sheets are commonly used.

In this embodiment, the material of the transfer belt 130 is selected from the viewpoints of mechanical characteristics, electrical characteristics, flame retardancy, and the like.
A polyimide resin was used. Its volume resistivity is 10 ¹⁶ Ω
cm, the thickness is 100 μm, and it is a seamless type.
The process speed is 100 mm / sec.

Transfer chargers 24a, 24b, 24c, 24
Reference numeral d denotes a plate-shaped conductive rubber transfer member extending in a direction (thrust direction) orthogonal to the recording material conveyance direction.
a, 3b, 3c, and 3d. The transfer charger 24 (24a to 24d) charges the recording material P conveyed to the transfer portion from the rear surface side with the opposite polarity (positive in this example) to the toner, and the toner image on the photosensitive drum 3 is transferred to the recording material. It is electrostatically transferred to the surface of P. In this embodiment, the transfer charger 24 is controlled at a constant current, and
μA.

The state of the recording material (paper) used in the above-described image forming apparatus significantly changes depending on the temperature and humidity of the environment. According to the study of the present inventor, paper immediately after opening the package and low-humidity environment after opening (for example, 23 ° C., 5% R)
There is a great difference in the electrical characteristics of the paper from the paper which has been left in H) and the water content has been significantly reduced. In particular, when the water content of the paper decreases, the electric charge that can be held on the front and back surfaces of the paper is reduced. It turns out there is a limit.

FIG. 2 is a correlation diagram between the surface charge density externally applied to the recording material surface and the potential of the recording material surface. In FIG. 2, a graph C shows a result when an OHT (made of PET, thickness: 100 μm) is used as a recording material. In the OHT, the surface potential increases linearly with respect to the supplied charge amount. It plays a role as a condenser. Graph D shows the results when the paper immediately after opening was used, and this also has a low slope with respect to the supplied charge amount, but also rises linearly as in the case where the surface potential is C.

On the other hand, the graph A shows the results when the Haga Paper Store NPI fine paper (basis weight 128 g / m ² , thickness 120 μm) was used once through a fixing device to simulate humidity control in a low humidity environment. Graph B shows the results when the double-sided thick paper for Canon CLC (basis weight: 105 g / m ² , thickness: 100 μm) was similarly used once through the fixing device. See, paper Graph A from 450μC / m ² around a paper graph B from 500μC / m ² around, have lost linearity respectively, immediately after opening the paper (graph D) or OH
This tendency is not seen in T (graph C).

This is a paper with reduced moisture (graph A,
B) is that when a charge of a certain value or more is supplied to the surface of the paper, a discharge starts in minute gaps between the fibers in the paper, and the charges on the front and back surfaces of the paper are canceled out. It is considered that no charge can be accumulated on the front and back surfaces of the paper even when the paper is supplied, and the surface potential does not increase.

In the image forming apparatus described above, when an image is formed on paper having a reduced water content, when a certain amount of charge is supplied during the transfer step, the amount of charge held on the paper reaches a limit. Discharge in the paper starts, the paper rapidly loses the holding power for the toner, and an image defect due to dot-like transfer omission as described in the related art section occurs.

According to FIG. 2, a low humidity environment (23 ° C., 5% R
The maximum amount of charge that the paper left in H) can hold is about 50
0 μC / m ² .

In the image forming apparatus, the maximum amount of toner per unit area is 1 mg / cm per color.
^2. Assuming that the charge amount per unit weight of toner is 30 μC / g, every time the transfer step is completed once, 300 μC / m ²
Is applied to the paper. From this, the number of colors of toner that can be transferred to the paper shown by the graphs A and B in FIG. 2 is as follows: 300 × {≦ 500} ≦ 1.67, up to about 1.67 It can be seen that only color components can be transferred.

Generally, in a color image forming apparatus, it is difficult to reproduce black (black) using three colors of cyan, magenta, and yellow, and it is desirable to reduce the amount of toner.
emoval). UCR is, specifically, a common part (black component) of cyan, magenta, and yellow.
With black, and subtract that amount from cyan, magenta, and yellow. UCR not only can improve black reproducibility, but also can greatly reduce the amount of toner.

Although depending on the model, usually, an image is formed with a maximum total amount of toner of about two colors. In this embodiment, U
CR is adopted, and the total amount of the maximum transfer toner is set to two colors. However, in consideration of the fact that the amount is still higher than the above-mentioned 1.67 colors, if transfer is performed on paper having a remarkably low water content in the developing state, the above-mentioned dot-like transfer failure occurs. That is, in order to transfer four colors normally,
The maximum retained charge amount is at least 300 × 2 = 600 μC /
m ² , and transfer to paper having a remarkably low water content causes dot-like transfer failure.

Therefore, according to the study of the present inventor, when transferring to a recording material having a significantly reduced water content, for example, paper conditioned in a low-humidity environment, or paper once passed through a fixing device, it is necessary to use such a recording material. By applying a charge having a polarity opposite to that of the transfer in advance before the transfer and relatively increasing the maximum amount of retained charge of the recording material, it is possible to prevent the above-described point-like transfer failure from occurring and obtain a good image. I understood. Hereinafter, this method will be described in detail.

Based on FIG. 2, a function Qp = Qp which gives the maximum retained charge amount Qp (C / m ² ) per unit area of the recording material as a variable based on the type of the recording material and the environmental atmosphere in which the recording material is placed. (S, k). Here, s is the type of the recording material, and k is the absolute moisture content of the environmental atmosphere (g / air 1k).
g). For example, in the recording material shown by the graph B in FIG. 2, Qp is about 5 × 10 ⁻⁴ C / m ² .

The charge amount Qt per unit weight of the toner
Is a function Qt = Qt that gives the environment atmosphere as a variable
(K), and the UCR upper limit is n colors. In this embodiment, Qt = 3 × 10 ⁻² C / kg and n = 2 colors. Further, the weight per unit area of the toner transferred to the recording material is defined as M (kg / m ² ).

At this time, since the toner charge amount after forming the four color images is M · Qt (k) · n (C / kg), the charge amount per unit area on the front and back surfaces of the recording material is ± M.・ Qt
(K) · n (In the present embodiment, since the negative toner is used, the front surface of the recording material is negative and the back surface is positive).

As described above, at present, Qp (s, k) <M · Qt (k) · n, and the charge amount supplied to the recording material exceeds the maximum holding charge amount of the recording material. In order to prevent the occurrence of dot-like transfer failure, the recording material is charged in reverse to transfer beforehand to relatively increase the maximum retained charge amount of the recording material.

That is, the charge amount of the charge opposite to the transfer is represented by Qr
By satisfying the relationship of Qp (s, k) + Qr ≧ M · Qt (k) · n as (C / m ² ), the occurrence of dot-like transfer omission can be prevented. The amount of reverse charge before transfer at this time is
It suffices to satisfy the relationship of Qr = M.Qt (k) .n-Qp (s, k).

In this embodiment, M = 10 ⁻² kg / m ² , Q
When t (k) = 3 × 10 ^-2 C / kg and n = 2, M · Qt
(K) · n = 600 μC / m ² , and Qp
Assuming that (s, k) = 5 × 10 ⁻⁴ C / m ² , Qr = M · Qt (k) · n−Qp (s, k) = 600−500 = 100 (μC / m ² ). That is, the charge amount before transfer is 100 μC / m ²
By doing so, it is possible to prevent the occurrence of dot transfer defects.

The desired reverse charge amount Qr is determined as follows. FIG. 3 shows the relationship between the water content of the paper and the maximum surface charge density that the paper can hold. The water content of the paper was measured using an infrared moisture meter KJT100 manufactured by Kett Science Laboratory.

As shown in FIG. 3, it can be seen that the maximum surface charge density that the paper can hold has a strong relationship with the water content of the paper, and decreases as the water content decreases.

FIG. 4 shows the relationship between the absolute moisture content of the environment where the paper is left and the moisture content of the paper. From now on, the smaller the absolute moisture content of the environment where the paper is left, the smaller the content of paper. It can be seen that the water content is also small.

Therefore, a temperature and humidity sensor 30 capable of measuring temperature and humidity is provided in the image forming apparatus main body so as to be as close as possible to the recording material storage cassette.
Using the temperature and humidity in the apparatus detected by the temperature / humidity sensor 30, the absolute water content in the apparatus is calculated, and the water content in the paper is obtained from FIG. Further, the maximum holdable surface charge amount Qp (s, k) of the paper is obtained from FIG. 3, and Qr is obtained from the above equation.

However, for a recording material such as the one shown by the graph B in FIG. 2, there is a limit in applying reverse charging before transfer, and the limit value is the same as Qp (s, k), for example, the maximum value. 500 μC / m ² . Therefore, | Qr |
.Ltoreq.Qp (s, k), from which the apparent maximum value of the amount of charge that the paper can hold is apparently Qp (s, k) + Qr = 2.times.Qp (s, k).

In the present embodiment, the reverse charging before the transfer is performed to the maximum, so that 300 × {≦ 2 × Qp (s, k) = 100} ≦ 3.
33, and if the total toner amount regulation by the UCR is up to 3.33 colors, dot transfer omission can be prevented without any problem.

In this embodiment, the reverse charging before the transfer to the recording material P was performed using the adsorption charger 5 shown in FIG. As described above, the high-voltage power supply E whose output can be controlled is connected to the lower non-ground roller 5 a of the adsorption charger 5.

The recording material P is supplied to the transfer belt 130 by the registration roller 12, the recording material P is sandwiched between the rollers 5 a and 5 b of the transfer charger 5, and a charging bias is applied to the roller 5 a from the high voltage power source E. A current is supplied to the grounded roller 5b, which is an opposing roller, by constant current control, and a reverse polarity charge is applied to the back surface of the recording material P to transfer the charge to the photosensitive drum 3a of the first image forming unit Pa. Before the recording material P enters the transfer portion formed by the transfer belt 130, the recording material P
Is charged to a polarity opposite to that of the transfer.

According to the above constant current control, even if the paper type or thickness of the recording material P is changed or the resistance in the vertical direction of the surface of the recording material is changed variously, it is possible to cope with the problem without any problem. There is an advantage that a constant reverse charge can be supplied to the recording material P. In the present embodiment, Qr is, for example, Qr = 10
To achieve 0 μC / m ² , three rollers 5a to 5b
A reverse charging current of μA may be applied. The roller for applying the high voltage may be the roller 5b, in which case the polarity is reversed.

However, in general, this type of apparatus can also use a recording material of a small size smaller than the maximum possible recording width. In some cases, a large amount of current flows in the non-sheet passing portion, and the required reverse charging cannot be performed on the sheet. For example, width 100mm
When the postcard is passed, the resistance between the paper passing portion and the non-paper passing portion becomes as high as 10: 1. Most of the current flowing between the rollers 5a and 5b flows through the non-paper passing portion, and the desired amount of reverse current flows. The charged charges cannot be supplied to the paper, and point-like transfer omissions occur during transfer.

Therefore, in this embodiment, the width of the recording material P to be passed is detected in advance, and the high-voltage power supply E is set in accordance with the width of the recording material.
By changing the output of the charging bias, output control was performed to change the reverse charging current value so that the surface charge density of the recording material was constant. Thus, a desired reverse charging can be performed even with a small-sized recording material.

It is preferable that a plurality of tables are stored in the apparatus for the reverse charging current value according to the paper type, volume resistivity, and thickness of the recording material P. As shown in FIG. 4, the moisture content of the recording material can be obtained from the installation environment of the apparatus. The paper width at that time is detected in a manual paper feeding unit or a cassette paper feeding unit, and the reverse charging current of a necessary table is obtained from these numerical values. The current value may be determined by reading the value.

As a further preferred embodiment of the present embodiment,
The relational expressions as shown in FIG. 4 are stored in the apparatus main body in a number corresponding to the type of the recording material, and when using the image forming apparatus, the user inputs the type of the recording material in advance to the apparatus main body. It is apparent that more preferable results can be obtained by calculating the maximum surface charge density that can be held for each recording material stored in the apparatus main body in advance from the recording material information.

In this embodiment, it is assumed that the recording material P is conveyed along the end of the conveying belt 130 in the conveying direction. However, when the recording material P is constantly regulated at the center in the thrust direction and conveyed. May be.

The paper width of the recording material may be automatically detected by using a mechanical sensor or an optical sensor, or may be detected by an operator inputting the paper width from an operation unit or the like. For detecting the thickness of the recording material, some type of detecting means may be installed in the apparatus, or the operator may input the thickness of the recording material from outside the apparatus.

Although the transfer belt has been described above as the recording material carrier, it may be a transfer drum. Further, it may be a secondary transfer portion of the intermediate transfer member. In this case, the photosensitive drum may be replaced with an intermediate transfer member. The image carrier as a member to be charged is not limited to an electrophotographic photosensitive member such as a photosensitive drum, but may be a dielectric in electrostatic recording.

The developing device 1 (1a to 1d) may use any type of developing method.

In general, the developing method is roughly classified into a one-component developing method and a two-component developing method. In the one-component developing method, a non-magnetic toner is coated on a developing sleeve with a blade or the like.
For the magnetic toner, a one-component non-contact developing method in which the developing sleeve is coated by a magnetic force, is conveyed to a developing unit facing the image carrier by rotation of the developing sleeve, and develops the toner in a non-contact state with the image carrier. There is a one-component contact developing method of developing in contact with an image carrier, and a two-component developing method includes:
Uses a two-component developer in which toner particles and a magnetic carrier are mixed, coats it on the developing sleeve with magnetic force, and transports it to the developing unit by the developing sleeve, where the developer is developed in a non-contact state with the image carrier. Two-component non-contact development method,
There is a two-component contact development method in which development is performed in contact with an image carrier. From the aspects of high image quality and high stability, the two-component contact development method is often used.

The present embodiment may be a monochrome printer or a copying machine as shown in the case of a color printer or a copying machine, and may be a digital type or an analog type.

The present invention is configured as described above, and before the recording material P enters the transfer portion, the rollers 5a of the attraction charger 5
When the recording material is reversely charged by the bias applied to the roller 5a from the high voltage power supply E, the width of the recording material is detected in advance, and the output of the high voltage power supply E is controlled according to the width of the recording material. Therefore, the recording material can be reversely charged before transfer without depending on the paper width regardless of the paper width, and the occurrence of dot-like transfer omission can be prevented even for a small-sized recording material.

Embodiment 2 FIG. 5 is a schematic diagram showing another embodiment of the image forming apparatus of the present invention. In the first embodiment, the amount of the reverse charging current is controlled according to the paper width, so that the reverse charging can be performed on a small-sized recording material without excess or shortage.

In the second embodiment, a countermeasure against another problem that occurs when the reverse charging current flows excessively will be described.

As described above, the present invention is intended to prevent the occurrence of dot-like transfer omissions caused by a decrease in the moisture content of paper in a low-temperature and low-humidity environment.

In a low-temperature and low-humidity environment, when the reverse charging current was made excessive, the excess current disappeared by the discharge, and it was clarified that there was no serious problem when transferring the toner image. However, when an image is formed on paper whose resistance has significantly decreased due to being left in a high-temperature, high-humidity environment, the transfer current of the first color flows to the attraction charger 5 that performs reverse charging through the paper, and the transfer of the toner image is normal. A new problem that does not occur.

Therefore, in this embodiment, as shown in FIG. 5, the diodes D1 and D
2 and the adsorption charger 5 was provided with a reverse charging mode and an insulating mode. In an environment where the transfer of the first color is not normally performed based on the information of the temperature / humidity sensor 30 in the image forming apparatus main body, the connection of the roller 5a of the attraction charger 5 is performed in the insulation mode. Was switched from the high voltage power supply E to the diode D1, and the ground of the roller 5b was switched to the connection to the diode D2, so that the transfer current was controlled so as not to flow into the rollers 5a and 5b.

For example, in the case of the recording material shown in the graph A of FIG. 2 described above, when the recording material is left in an environment of 26 ° C. and 60% or more, no dot-like transfer omission occurs and the transfer of the first color is performed normally. Only issues that did not happen.

Therefore, in an environment of 26 ° C. and 60% or less, the recording material is charged to the opposite polarity prior to the transfer in the reverse charging mode as in Embodiment 1, and in an environment of 26 ° C. and 60% or more. In the insulation mode, the rollers 5a and 5b are connected to the diodes D1 and D2 so that the transfer current is reduced.
b. Thereby, a good image can be obtained in all environments. The current reference table is 26 ° C,
Since there is no problem even if a simple device that generates a situation where an overcurrent flows in an environment of 60% or less is used, the study for determining the current reference table can be simplified, and the memory of the computer can be reduced.

In the above, the rollers 5a, 5a,
Although a diode was used to electrically insulate b, there is no problem if it is connected to a varistor or the like having a sufficiently high withstand voltage.

As described above, according to the present embodiment, reverse charging before transfer can be performed favorably to prevent dot-like transfer omission, and transfer failure due to transfer current flowing to the attraction charger can be prevented at high temperature and high humidity. It was possible to prevent the environment and obtain a good image without transfer failure.

Embodiment 3 FIGS. 6 and 7 show still another embodiment of the present invention. In this embodiment, instead of the lower roller 5a of the adsorption charger 5 of the second embodiment shown in FIG. 5, a conductive rubber blade 6 is provided as shown in FIG. The rubber blade 6 can be separated from the transfer belt 130 by the solenoid 100.

In the second embodiment, the rollers 5a and 5b of the attraction charger 5 are connected to the diodes D1 and D2 from the high-voltage power supply E in the insulation mode in a high-temperature and high-humidity environment. It is only necessary that the adsorption charger 5 can be electrically insulated.

Therefore, in this embodiment, in an environment other than the high-humidity and high-temperature environment, the recording material P is transferred by the upper roller 5a and the conductive rubber blade 6 prior to transfer in the reverse charging mode.
And the rubber blade 6 is separated from the back surface of the transfer belt 130 by the solenoid 100 in an insulating mode in a high-temperature and high-humidity environment.
Was insulated to prevent the transfer current from flowing to the adsorption charger 5.

According to the present embodiment, the reverse charging before the transfer can be performed well to prevent the dot-like transfer omission, and the transfer failure caused by the transfer current flowing to the adsorption charger can be prevented up to the high temperature and high humidity environment. A good image without transfer failure could be obtained.

[0085]

As described above, according to the present invention,
A pre-charging means is installed before the recording material reaches the transfer section, and the pre-charging means is charged with a polarity opposite to the charge applied to the back surface of the recording material at the time of transfer by the transfer charging means according to the environment atmosphere. A reverse charging mode applied to the back surface of the recording material prior to transfer, and an insulation mode grounded via an element that generates a voltage when a current at the time of transfer by the transfer charging means flows through the recording material carrier. Since I used it to be switchable,
Even when paper is used as the recording material, it is possible to transfer satisfactorily without causing spot-like transfer omission, and to obtain a high-quality image free from transfer failure in all environments.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a relationship between a surface charge density given to a recording material and a surface potential of the recording material.

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

FIG. 4 is a graph showing the relationship between the absolute moisture content of an environmental atmosphere and the moisture content of a recording material.

FIG. 5 is a schematic configuration diagram showing another embodiment of the image forming apparatus of the present invention.

FIG. 6 is a schematic configuration diagram showing still another embodiment of the image forming apparatus of the present invention.

FIG. 7 is a perspective view showing a conductive rubber blade of the attraction charger installed in the image forming apparatus of FIG. 6;

FIG. 8 is a schematic view showing a conventional image forming apparatus.

[Explanation of symbols]

 3a-3d Photosensitive drum 5 Adsorption charger 5a, 5b Conductive roller 6 Conductive rubber blade 24a-24d Transfer charger 30 Temperature / humidity sensor 100 Solenoid 130 Transfer belt D1, D2 Diode P Recording material

Claims (5)

[Claims] 1. A visible image is formed on an image carrier, a recording material is carried on the recording material carrier, and is conveyed to the image carrier. The visible image formed on the image carrier is In an image forming apparatus for electrostatically transferring to a conveyed recording material by a transfer charging unit, a pre-charging unit is provided at a position before the recording material reaches an image carrier, and the transfer charging unit is provided on the pre-charging unit. A reverse charge mode in which a charge having a polarity opposite to that of the charge applied to the back surface of the recording material during transfer by the means is applied to the back surface of the recording material prior to transfer; An image forming apparatus, wherein a mode in which a voltage is generated when a current flows through a carrier and a mode in which the voltage is grounded is provided. 2. A visible image is formed on an image carrier, a recording material is carried on the recording material carrier, and is conveyed to the image carrier. The visible image formed on the image carrier is In an image forming apparatus that electrostatically transfers to a conveyed recording material by a transfer charging unit, the recording material is applied to a position just before reaching the image carrier on the back surface of the recording material during transfer by the transfer charging unit. An image, wherein a pre-charging means for applying a charge having a polarity opposite to the electric charge to the back surface of the recording material prior to transfer is provided, and the pre-charging means is provided so as to be separated from the recording material carrier. Forming equipment. A detecting unit for detecting a temperature and a humidity of an atmosphere in the main body of the image forming apparatus; and charging the pre-charging unit based on temperature and humidity information in the main body of the image forming apparatus detected by the detecting unit. 3. The image forming apparatus according to claim 1, wherein the output is changed. 4. A mode of the pre-charging means based on temperature and humidity information in the main body of the image forming apparatus detected by the detecting means for detecting the temperature and humidity of the atmosphere in the main body of the image forming apparatus. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled. 5. A detecting means for detecting the temperature and humidity of the atmosphere in the main body of the image forming apparatus, and based on temperature and humidity information in the main body of the image forming apparatus detected by the detecting means, separation of the pre-charging means. The image forming apparatus according to claim 2, wherein the contact operation is controlled.