JPH03107977A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a defective picture resulting from offset on an image carrier, or caused by making a picture flow by allowing the toner on material to be moved by applying an electric field to the transfer material again at the time of idle rotation. CONSTITUTION:A transfer material supporting body 93 holds the transfer material P, which has already finished transfer, in a transfer position at the time of the idle rotation of a transfer drum 9; that is, by applying the electric field having the same polarity as that in transfer, from the rear surface of a dielectric body sheet, a toner image transferred on the transfer material P can be firmly held on the material P by the force of the electric field. Thus, the disturbance of transfer picture can be prevented by offsetting the toner on a photosensitive drum surface inversely from the toner on the transfer material P at the idle time or flowing the picture by allowing the toner on the transfer material to be moved.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. The present invention forms a latent image on an image carrier using an electrophotographic method or an electrostatic recording method, converts the latent image into a visible image using a developing means, and converts the visible image into a visible image. It relates to an image forming device that obtains an image by transferring it to a transfer material with a transfer device, and in particular, it has a plurality of developing devices, develops a latent image formed on an image carrier, and transfers the toner image. This can be suitably implemented in a multicolor image forming apparatus in which an image is obtained by sequentially overlapping transfer onto a transfer material using a device.

Various multicolor image forming apparatuses have been proposed and are commercially available, and FIG. 2 shows an example of a typical color electrophotographic copying machine.

In FIG. 2, the color electrophotographic copying machine forms a latent image on an image bearing member 3, which is an electrophotographic photosensitive drum in this example, and transfers the latent image to a plurality of colors, for example, magenta, cyan, etc., which will be described in detail later. , yellow and black, four types of developer IM containing toner with an average particle size of 12 μm based on four types of resin.
, IC1IY, and IBK are used to form a color toner image, and these toner images are transferred to a sheet-like transfer material such as paper attached to a drum-shaped transfer device 9 disposed close to the surface of the photosensitive drum 3. The structure is such that a color image is obtained by superimposing transfer.

As schematically shown in FIG. 3, the transfer device 9 used in such a color electrophotographic copying machine includes a pair of annular members, cylindrical members 9a and 9b in this example, arranged concentrically. Both are integrally connected by a connecting member 9c, and a transfer material support made of a dielectric material over the entire circumference, that is, a transfer drum formed into a cylindrical shape and covered with a dielectric sheet 93 is used. There is.

Further, a gripper 91 is disposed on the outer surface of the connecting member 9c of the transfer drum 9, grips and conveys the transfer material P supplied in synchronization with the toner image on the photosensitive drum 3, and transfers it to the transfer charger. Each time the toner image of each color is transferred to the transfer material at the transfer position where the transfer member 10 is arranged, a color image is formed by transferring the toner image of each color onto the transfer material. Separate from.

The separated transfer material is fed to the fixing means 17 by the conveying means 16.

Furthermore, in recent years, as image forming devices such as color electrophotographic copying machines have become widespread, their uses have expanded to a wide variety.
Demand for image quality is also becoming more intense. When copying images such as ordinary photographs, catalogs, and maps, even the smallest details will not be crushed or cut off.
There is a need for extremely detailed and faithful reproduction.

In recent years, in image forming apparatuses such as color electrophotographic copying machines that use digital image signals, latent images are formed by a collection of dots with a constant potential, and solid areas, halftone areas, and light areas are formed. is expressed by changing the dot density.

However, in such an image forming apparatus, the toner particles do not adhere to the dots faithfully, and when the toner particles protrude from the dots, the toner image corresponds to the dot density ratio of the black and white areas of the digital latent image). There is a problem that gradation cannot be obtained.

Furthermore, when improving resolution by reducing the dot size in order to improve image quality, the reproducibility of the latent image formed from minute dots becomes even more difficult, and the resolution and, in particular, the gradation of highlight areas become more difficult. Images tend to have poor tonality and lack sharpness.

So far, for the purpose of improving image quality,
A developer is provided. Making the toner smaller is also a part of this, and for example, Japanese Patent Application Laid-Open No. 157051/1983 proposes the use of color toner having a volume average particle diameter of 1 to 9 μm.

However, when the volume average particle diameter of the toner is reduced, the adhesion force due to van der Waals force etc. becomes thicker, and the adhesion to the photosensitive drum which is an image carrier increases.

This tendency is exacerbated when an image carrier with high surface free energy, such as one containing an organic polymer with a charge transfer layer on the surface, is used. Image formation, especially the transfer process, must be carried out with this in mind.

In such a color electrophotographic copying machine, the original image is divided into magenta, cyan, yellow, and black images.
The latent image is separated into colors and a latent image is formed on the photosensitive drum for each color, and the latent image is transferred to a transfer material through a development process, so the transfer drum must be rotated at least four times.

However, depending on the size of the transfer material held on the transfer drum, one rotation of the transfer drum may result in
During the next rotation after color transfer, preparations for the image forming process for the next color may not be completed due to reasons such as the development unit not being able to complete its movement or the document reading optical means being unable to return to its starting position. In this case, the transfer drum must rotate one more time and wait for the preparation process for image formation C of the next color to be completed. During the rotation of the transfer drum to wait for the preparation process for image formation (next color) to be completed, the so-called "idle notification", the toner image already transferred to the transfer material is transferred to the photosensitive drum again. will come into contact.

At this time, due to the adhesive force of the toner and the photosensitive drum, the toner may be offset from the toner image on the transfer material to the surface of the photosensitive drum, or the toner may be moved on the transfer material and the image may flow. hand.

A problem occurred in which the transferred image was distorted.

Further, in the transfer drum 9, as shown in FIG.
When the backup member 18 is used to press the dielectric sheet 93 in order to level the dielectric sheet 93 uniformly and to improve the transfer efficiency by increasing the transfer nip and obtaining a clear transferred image, the above-mentioned problem occurs. This occurred significantly.

Therefore, an object of the present invention is to apply an electric field to the transfer material again when the transfer device holds and conveys the transfer material in a transfer device during a series of transfer steps, and when the transfer material is rotated without transfer. To provide an image forming device that can always obtain high-quality images without causing the toner on the transfer material to be offset toward an image bearing member or the toner on the transfer material to be moved and the image to flow. That's true.

for The above object is achieved by an image forming apparatus according to the present invention.

In summary, the present invention provides a transfer method that includes an image carrier on which a toner image is formed and a transfer material support member that supports and conveys a transfer material, and in which the toner image on the image carrier is supported on the transfer material support member. A transfer device that performs transfer onto a material using a transfer electric field, and includes a step of not transferring a toner image from an image carrier to the transfer material while the transfer material is held on a transfer material support during the series of transfer steps. In the image forming apparatus, an electric field is applied to the transfer material by an electric field applying means during a step in which the toner image is not transferred from the image carrier to the transfer material while the transfer material is held on the transfer material support. This is an image forming apparatus with features.

The electric field applying means is a transfer electric field applying means used when transferring the toner image on the image carrier to the transfer material, or an electric field applying means different from the transfer electric field applying means, and the electric field applied by the electric field applying means is is assumed to have the same polarity as the electric field during transfer.

Furthermore, if necessary, the device has temperature/humidity detection means for detecting temperature and/or humidity inside the device, and the electric field applied by the electric field application means is variable according to the signal obtained by the temperature/humidity detection means. be done.

151 Hereinafter, one embodiment of the present invention will be specifically described with reference to the drawings. In this embodiment, a full-color electrophotographic copying machine to which the Carlson process is applied will be described as an example, but it is of course applicable to image forming apparatuses such as multi-color recording devices and color recording devices of computer output sections. Of course, as a process, an electrostatic latent image process such as an NP process can also be used.

The present invention is suitably embodied in the full-color electrophotographic copying machine described above with reference to FIG. 2, and its structure and operation will be briefly described.

In this embodiment, a photosensitive drum 3 as an image carrier is supported rotatably in the direction of arrow X (counterclockwise), and a primary charger 4 is located approximately directly above the photosensitive drum 3. A rotary drum type developing device 1 is disposed on the left side, and a transfer drum 9, which is a transfer device, is disposed substantially directly below the developing device 1, and is driven to rotate in the direction of arrow Y (clockwise). Further, a cleaning device 12 is arranged on the right side.

An exposure section is provided between the primary charger 4 and the developing device 1, and a light signal is irradiated onto the photosensitive drum 3 through a polygon mirror unit 8 and a laser reflection mirror 7 arranged above. .

Further, the full-color electrophotographic copying apparatus has a fixing device 17 and a paper feeding device 23 arranged on the right side thereof, and a transfer paper conveying system is provided between the transfer drum 9 and the fixing device 17 and paper feeding device 23, respectively. 16.20 etc. are arranged.

More specifically, in this example, the photosensitive drum 3 serving as the image carrier is an OPC photosensitive drum containing an organic polymer having a charge transfer layer on its surface. This photosensitive drum 3 had a diameter of 80 mm and was rotated in the direction of arrow X at a speed of 160 mm/sec.

- The charging device 4 charges the surface of the photosensitive drum 3 to -500~
After being charged to -8oo■, the image information signal is color-separated by an image reading device and an image processing device (not shown) in a laser optical system consisting of a polygon mirror unit 8 and a laser reflection mirror 7 arranged above the exposure section. irradiation, forming a latent image.

The developing device has a rotational angle of 9 in the rotation angle direction with respect to the rotating support.
4 developers LM (magenta developer) and IC at 0 degree intervals
(cyan development) IY (yellow development) and IBK (black development) are each removably installed, and latent images of each color formed on the circumferential surface of the photosensitive drum 3 are developed using a corresponding developer. become For this reason, following the control procedure,
The rotating support is rotated in 90 degree increments.

In the state shown in FIG. 1, the developing device IM is connected to the photosensitive drum 3.
Indicates the state that is supported.

In this example, each of the four developing devices contained a developer containing a mixture of toner and carrier, and the toner was prepared by the following method.

After thoroughly premixing the polyester resin obtained by combining propoxylated bisphenol and fumaric acid, the chromium chain acid of di-tert-butylsalicylic acid, and the dye and pigment corresponding to each color using a Henschel mixer, , melt-kneaded at least twice in a three-roll mill,
After cooling, it was coarsely pulverized using a hammer mill to a particle size of about 1 to 2 mm. Next, it was pulverized using an air jet type pulverizer. Further, the obtained finely pulverized material was distributed in portions using a multi-dividing distribution device to produce resin particles having a volume average particle diameter of approximately 8 μm.

To 100 parts of the colorant-containing resin particles obtained in this way, B
0.3 parts of alumina fine powder with a specific surface area of 10ord"7g by the ET method and a specific surface area of 250" by the BET method.
rrr/g, and 0.5 part of silica fine powder having a charge amount of 80 μc/g which had been hydrophobized with hexamethyldisilazane was added externally to obtain each color toner.

Further, as the carrier particles, Cu-Zn-Fe type ferrite particles whose surface was coated with a styrene-methyl methacrylate-styhexyl acrylate copolymer were used.

Therefore, in this embodiment, the latent image on the photosensitive drum 3 is formed by the developing device 1 having the developer containing the toner carrier.
The negatively charged toner is visualized using a reversal development method.

Further, the transfer device 9 is a transfer drum having the same structure as previously explained with reference to FIG.
b are arranged concentrically and are integrally connected by a connecting member 9C, and the thickness is, for example, 100 to 175 μm, and the volume resistance is approximately IQIIΩ·cm over the entire circumference.
A transfer material support, i.e., a dielectric sheet 9, formed of a dielectric material such as polyfluorovinylidene resin (PVdF)
3, its ends are connected to cylindrical members 9a, 9b and connecting member 9.
c using an adhesive or the like to form a cylindrical transfer drum 9.

The transfer drum 9 rotated in synchronization with the photosensitive drum 3, and its rotational speed was 160 mm/sec.

Further, a gripper 91 for gripping the transfer material is provided on the outer surface of the connecting member 9C of the transfer drum 9.

Further, inside the transfer drum 9, a transfer charger 1 is provided on the opposite side of the dielectric sheet 93 from the photosensitive drum 3 corresponding to the transfer position.
0 was set. The transfer charger 10 uses a corona charger,
For example, a voltage of +3 Kv to +9 Kv was applied, and a transfer current was set to +25 μA to +500 μA. Further, a transfer material, a dielectric sheet 93, is placed on the downstream side of the transfer drum 9 in the rotational direction at the transfer position.
An inner static eliminator 13 and an outer static eliminator 11 are provided to eliminate static electricity. These static eliminators used a corona charger configured to be able to apply direct current, alternating current, and direct current as a bias to alternating current.

A separation charger 14 was provided at a position where the transfer material is separated from the transfer drum 9 downstream of these static eliminators in the rotational direction of the transfer drum.

Furthermore, in this embodiment, as shown in FIG.
In order to uniformly level the dielectric sheet 93 on the inside of the transfer drum 9, to improve the transfer efficiency by increasing the transfer nip, and to obtain a clear transferred image, a photosensitive material is applied from the inside of the transfer drum 9 near the transfer charger 10. Dielectric sheet 9 toward drum 3
A backup member 18 is provided in order to push up 3.

This backup member 18 is made of an elastic material such as polyethylene terephthalate film, and applies appropriate pressure to the dielectric sheet 93.

On the other hand, the transfer material P is fed from the transfer material cassette of the paper feeding device 23 to the transfer device 9 via the transfer material conveyance system, the leading end of the transfer material P is gripped by the gripper 91, and the transfer material support 9
3, the toner image of each color is transferred sequentially at the transfer position, and when the transfer of the fourth color is completed, the toner image is removed by the separation claw 15 at the discharge site while being neutralized by the static elimination charger 11, 13 and the separation charger 14. It is removed from the transfer drum 9, sent to a fixing device 17 by a transfer material conveying system 16, where the image is fixed, and then discharged onto a tray.

The transfer process will be explained in more detail using an example of the timing chart shown in FIG.

FIG. 1 shows a case where the size of the transfer paper supported on the transfer drum 9 is long in the direction of rotation, such as A3 size, and it is not possible to prepare for image formation of the next color within the period of one rotation of the transfer drum. That is, this is an example of a timing chart when the transfer drum 9 performs "idle rotation", which is rotation without performing transfer.

First, in order to form the first color magenta (M) image,
The primary charger 4 performs corona discharge for a time corresponding to the paper size to uniformly charge the surface of the photosensitive drum 3, and then irradiates with laser light in accordance with image information to form an M image.

On the other hand, at the development position where the latent image of the M image is formed on the photosensitive drum 3, an M developing device, which has been moved in advance, is waiting and starts a developing drive to visualize the M image. The development drive is performed by adjusting the development position in anticipation of the time t for the development sleeve, which is a developer carrier installed in the development device and carrying the developer in the development device and conveying it toward the photosensitive drum, to rise to a certain rotation speed. Driving is started a time t earlier than the leading edge of the image at .

At this time, the transfer drum is in its second rotation.

At the transfer position, the transfer charger 10 operates in accordance with the movement timing of the transferred transfer material on the transfer drum 9 and the movement of the connecting member 9C of the transfer drum 9 to perform transfer charging. In this state, the transfer drum rotates approximately once and when the "M image transfer" in which the M image is transferred to the transfer material is completed, the rotary developing device rotates and the C developing device is placed in preparation for developing the cyan (C) image. to the developing position. At this time, the transfer drum 9 enters its third rotation.

According to the present invention, during the so-called idle rotation such as the third rotation of the transfer drum 9, no toner image is formed on the photosensitive drum 3, but the transfer charging is performed in the same manner as during normal transfer. -Let's wait. The current applied to the transfer charger during idle rotation has the same polarity as during transfer, and its magnitude is 25 to 400 μA.
, preferably 25 to 100 μA. Further, better results were obtained when a current equal to or smaller than the transfer current applied in the next transfer step (in this example, the cyan (C) image transfer step) was applied. These reasons are as follows.

In other words, at the transfer position when the transfer drum is idling, an electric field of the same polarity as during transfer is applied from the back of the transfer material support, that is, the dielectric sheet, which holds the transfer material that has already been transferred. The toner image transferred onto the material can be held firmly on the transfer material by the force of the electric field. This prevents the toner from being offset from the toner image on the transfer material to the surface of the photosensitive drum during idle rotation, or from disturbing the transferred image due to the toner on the transfer material being moved and causing the image to flow. can.

Also, during this idle rotation, it is sufficient to apply an electric field that is sufficient to hold the transferred toner image on the transfer material, so when considering the transfer of the next color, the charge-up of the dielectric sheet should be minimized (the electric field should be reduced as much as possible). Better transfer can be achieved by applying the current. Therefore, it is preferable that the transfer current applied during idle rotation be a small value, that is, about 25 to 100 .mu.8.

At the same time, in this embodiment, image exposure is stopped so that the toner image on the transfer material is not electrically offset to the photosensitive drum, but charging by the primary charger 4 is continued.

When this idle rotation ends and the transfer drum enters its fourth rotation, the same process as described above is repeated to transfer the C image onto the transfer material.

By performing the above steps in the same manner for yellow (Y) images and black (BK) images, four-color transfer images are obtained.

In the present invention, the volume average particle diameter of toner is reduced to 1 to improve image quality.
Even greater effects were exhibited when the adhesive force to the photosensitive drum was increased by setting the thickness to 0 μm or less. Further, when a photoreceptor containing an organic polymer having a charge transfer layer on the surface was used as the photoreceptor, and the adhesion force was increased, an even greater effect than the above was obtained.

Further, in this embodiment, a transfer charger was used as a charger that applies an electric field during idle rotation, but this is not limited to the transfer charger, and a charger near the transfer area,
For example, the inner static eliminator in this embodiment may be used, or the same effect can be obtained by applying an electric field in advance during idle rotation using another charger installed upstream of the transfer position in the rotational direction of the transfer drum. is obtained.

In this embodiment, the end portions of the dielectric sheet 93 are all fixed to the frame constituting the transfer drum 9 with an adhesive material, but only the front and rear ends of the dielectric sheet 93 are connected to the connecting member. A similar or even better effect of preventing image defects can be obtained with a transfer drum constructed by fixing to 9C and leaving both ends free.

As a result of further research and experiments, the present inventors installed a means for detecting the internal environment such as temperature and humidity in the image forming apparatus shown in the above-mentioned embodiment, and determined that the image forming apparatus rotates idly based on the detected environmental data such as temperature and humidity. It has been found that even better results can be obtained by varying the amount of current applied. A detailed explanation of the configuration and its principle will be given below.

In this example, the image forming apparatus shown in the previous example was used, and a member (not shown) for detecting the internal environment of the machine was provided in the apparatus. After the temperature and humidity data obtained by this component that detects the cabin environment is taken into the arithmetic circuit inside the main body and processed by this arithmetic circuit, the temperature exceeds the absolute moisture content in the general direction, for example, at a temperature of 25 degrees Celsius and a relative humidity of 80%. When it was determined that the absolute amount of moisture was present in the machine, a current of 25 to 100 uA was applied to the transfer material by the transfer charger while the transfer drum was idly rotating as described above, and in all environments, the toner on the transfer material was It was possible to prevent the transferred image from being disturbed due to the toner being offset from the image to the surface of the photosensitive drum or the toner on the transfer material being moved and the image flowing.

This is considered to be due to the reasons described below.

The resistance value of paper commonly used as a transfer material changes depending on its atmospheric environment. In general, the resistance value of paper is large in a low humidity environment, and on the contrary, it is small in a high temperature environment.If the resistance value of paper is large, the electric charge given by the transfer charger during transfer will not attenuate easily due to the large resistance value. , the toner can be held on the transfer material for a long time. Conversely, if the resistance value of the paper is small, the charge applied by the transfer charger during transfer will quickly attenuate, so the toner on the transfer material will be retained for a long time. It turned out that it was not possible to hold it for a long time.

On the other hand, when multiple transfer is performed, prior to transferring the second and subsequent colors, charge-up of the dielectric sheet 93 due to charging during transfer up to the previous color should be minimized (this is important to ensure good performance of the second and subsequent colors). Essential for transcription.

Therefore, as mentioned above, in a high-temperature environment, there is almost no effect of charge-up on the dielectric sheet, so we applied an electric field to the transfer material even during idle rotation to offset the transfer during idle rotation. It has been found that this method can prevent the above problems and enable good image formation. Furthermore, in a low humidity environment, the effect of charge-up is large, resulting in severe image deterioration, and as mentioned above, even during idle rotation, the charge from the previous rotation still remains on the back side of the transfer material. Therefore, during idle rotation, do not apply electric charge again.
Alternatively, it has been found that good image formation without offset can be achieved by making the amount smaller than that in a high temperature environment.

Furthermore, in this embodiment, the environment was divided into two parts such as high temperature and low humidity, and the charging during idle rotation was changed. It goes without saying that even better results can be obtained by continuously switching the charging during idle rotation.

Furthermore, in the above embodiments, the transfer device is described as a transfer drum, but the present invention is not limited to this.
It is obvious that a transfer device using a circulating transfer material carrier, for example in the form of a belt, can also be used.

As explained above, according to the image forming apparatus according to the present invention, during a series of transfer steps, the transfer material is held in a transfer device such as a transfer drum serving as a transfer material support. By applying an electric field again to the transfer material during rotation without transfer, that is, during idle rotation, the toner may be offset from the transfer material toward the image carrier, or the toner on the transfer material may be moved and the image may be distorted. This can prevent image defects caused by running.

You can always get high quality images.

[Brief explanation of drawings]

FIG. 1 is a timing chart illustrating the operation of the image forming apparatus according to the present invention. FIG. 2 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a perspective view of one embodiment of the transfer device. FIG. 4 is an enlarged detail view of the device in the transfer position. Figure 2 1: Developing device 3: Image carrier 9: Transfer device 10: Transfer charger

Claims (1)

[Scope of Claims] 1) An image carrier on which a toner image is formed, and a transfer material support member that supports and conveys a transfer material, the toner image on the image carrier being supported by the transfer material support member. A transfer device that performs transfer onto a transfer material using a transfer electric field, and includes a step of not transferring a toner image from an image carrier to the transfer material while the transfer material is held on a transfer material support during the series of transfer steps. In the image forming apparatus having the above, an electric field is applied to the transfer material by an electric field applying means during a step in which the toner image is not transferred from the image carrier to the transfer material while the transfer material is held on the transfer material support. An image forming apparatus characterized by: 2) The electric field applying means is a transfer electric field applying means used when transferring the toner image on the image carrier to the transfer material, or an electric field applying means different from the transfer electric field applying means. image forming device. 3) The image forming apparatus according to claim 1 or 2, wherein the electric field applied by the electric field applying means has the same polarity as the electric field during transfer. 4) Furthermore, the apparatus further includes a temperature/humidity detection means for detecting the temperature and/or humidity inside the apparatus, and the electric field applied by the electric field application means is variable according to the signal obtained by the temperature/humidity detection means. The image forming apparatus according to any one of claims 1 to 3, characterized in that: 5) The toner image formed on the image carrier has an average particle size of 10
The image forming apparatus according to any one of claims 1 to 4, characterized in that the image forming apparatus has toner particles of .mu.m or less. 6) The image forming apparatus according to claim 1, wherein the image carrier contains an organic polymer having a charge transfer layer on its surface.