JP3500329B2 - Transfer method of toner image in reversal development system using positively charged toner - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a printer,
The present invention relates to a transfer method using a transfer roller used in an electrophotographic apparatus such as a facsimile, and more particularly, to a transfer method of a toner image applied to a reversal developing system using positively charged toner.

[0002]

2. Description of the Related Art In an electrophotographic apparatus typified by a copying machine, the surface of a photosensitive drum is uniformly charged, and an electrostatic latent image corresponding to an original image is formed on the surface of the photosensitive drum by imagewise exposure. By developing the electrostatic latent image to form a toner image on the surface of the photosensitive drum, transferring the toner image from the surface of the photosensitive drum onto a transfer paper, and fixing the transferred toner image by heat, pressure, etc. , Image formation is performed.

In such an electrophotographic apparatus, a method using a corona charger (transfer charger) or a transfer roller is widely adopted as a transfer means for transferring a toner image formed on the surface of a photosensitive drum onto a transfer material. ing. The method using a corona charger is to charge the back surface of the transfer material to the opposite polarity to the toner image by corona discharge, and transfer the toner image to the transfer paper surface by this charge. In the method using a transfer roller, a voltage is applied to the roller so that the roller is held at a potential having a polarity opposite to that of the toner image, and in this state, transfer paper is placed between the photosensitive drum and the transfer roller. The toner image is transferred onto the surface of the transfer paper by an electric field formed between the transfer roller and the toner image.

However, in the transfer method using the corona charger, the transfer paper is electrostatically adsorbed on the surface of the photosensitive drum, so that the transfer material on which the toner image is transferred is separated from the surface of the photosensitive drum. Since an AC charger must be used together, there is a problem that the transfer mechanism becomes complicated. There is also a problem that ozone is generated by corona charging.
On the other hand, in the transfer method using the transfer roller, it is relatively easy to separate the transfer paper from the surface of the photosensitive drum,
For example, since transfer paper can be separated without using a corona charger such as an AC charger, and there is no problem of ozone generation, a transfer roller tends to be adopted recently.

[0005]

By the way, in the recent electrophotographic apparatus, the reversal developing system has been widely adopted with the spread of digital copying machines, laser printers, facsimiles and the like. The reversal developing system attaches the toner charged to the same polarity as the potential to the light irradiation portion of the electrostatic latent image formed by image exposure, that is, the low potential portion where the main charging potential is attenuated. The electrostatic latent image forms a visible toner image, and the background portion of the image (the portion not irradiated with light) is held at a high potential of the same polarity as the toner. The toner does not adhere to the part.

In particular, when image formation is performed by reversal development using positively charged toner, if a method of transferring a toner image onto transfer paper using a transfer roller is adopted, image formation is repeated. It was confirmed that toner stains on the back surface of the transfer paper gradually began to occur. Therefore, an object of the present invention is to transfer a toner image from the surface of the photosensitive drum to the surface of the transfer paper by using the transfer roller in a reversal development system using positively charged toner without causing toner stain on the back surface of the transfer paper. To provide a transfer method capable of

[0007]

According to the present invention, an electrostatic latent image formed on the surface of a photoconductor drum is developed by a reversal development method using positively charged toner to form a toner image on the surface of the photoconductor drum. In the method of transferring to the surface of a transfer paper, a transfer roller is arranged so as to face the photoconductor drum, and at least a guide surface is near the transfer paper introduction side of the transfer roller, and at least a guide surface has a negative charge series with respect to the transfer paper. An insulating guide plate formed of a conductive insulating layer is provided, and while the transfer roller is held at a negative potential, the transfer paper is introduced between the transfer roller and the photosensitive drum by the guide plate. Provides a method for transferring the toner image formed on the surface of the photoconductor drum to the surface of the transfer paper.

In summary, the transfer method of the present invention is such that a surface of an insulating guide plate disposed in the vicinity of a transfer roller, particularly a guide surface, is provided with an insulating layer having a negative triboelectrification series with respect to a transfer paper. The provision is a remarkable feature. When the toner image is transferred using the transfer roller, the transfer paper is smoothly introduced between the transfer roller and the surface of the photosensitive drum near the transfer paper introduction side of the transfer roller, and Although it is essential to provide a guide plate for increasing the degree of close contact with, the present inventors have found that the guide plate causes the toner stain on the back surface of the transfer paper in the above-described reversal developing system.

That is, since the above guide plate is located near the surface of the photosensitive drum, it is made of an insulating material in order to prevent leakage of electric charges, and in particular, the moldability and the cost are reduced. From the point of view of ABS (acrylonitrile-
It is formed of an insulating resin having excellent mechanical strength such as butadiene-styrene) resin. Such an insulating resin generally has a positive polarity in the triboelectrification series with respect to the transfer paper, so that the contact between the transfer paper and the guide plate (especially the guide surface) occurring in each image forming cycle causes the guide plate to have a positive polarity. Be charged. On the other hand, the positively charged toner used as a developer always contains a certain proportion (usually about several percent) of the oppositely charged toner, and when image formation is repeated, the proportion of the oppositely charged toner in the developing device is Will increase. The oppositely charged toner (negatively charged toner) adheres to the surface of the photoconductor drum in a non-image area such as when the transfer paper is passed between the transfer paper and
The reversely charged toner that adheres stains the guide plate. Therefore,
The toner adhering to the guide plate comes into contact with the back surface of the transfer paper passing through this guide plate, and as a result, toner stains occur on the back surface of the transfer paper.

According to the present invention, however, by providing an insulating layer having a negative triboelectrification series with respect to the transfer paper on at least the guide surface of the guide plate, the reverse surface of the transfer paper is contaminated by the reverse charging toner as described above. Can be effectively prevented. That is, the contact with the transfer paper causes the guide surface to be negatively charged by friction. Therefore, the reversely charged toner (negatively charged toner) does not adhere to the guide surface,
Image defects caused by the reversely charged toner adhering to the surface of the photosensitive drum are effectively prevented. In this case, the positively charged toner easily adheres to the guide surface,
Even if such positively charged toner adheres to the back surface of the transfer paper passing through the guide plate, the back surface of the transfer paper is not stained. That is, when the transfer paper passes between the photosensitive drum and the transfer roller, the positively charged toner adhering to the back surface of the transfer paper is electrically pulled to the transfer roller side and separated from the back surface of the transfer paper. Is. Moreover, the positively charged toner attached to the transfer roller can be collected on the photosensitive drum side by applying a reverse bias voltage to the transfer roller.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on specific examples shown in the accompanying drawings. FIG. 1 is a diagram showing the outline of the overall arrangement of the electrophotographic apparatus, and FIG. 2 is a diagram showing the arrangement of a transfer paper conveyance path in which the transfer method of the present invention can be suitably implemented.

In FIG. 1, in this electrophotographic apparatus, a main charging device 2, an exposure mechanism 3, a developing device 4, a transfer roller are provided around a photosensitive drum 1 which is rotatably provided in a direction of an arrow in the drawing. 5, static eliminator 6, cleaning device 7
Are arranged in this order along the rotation direction of the photoconductor drum 1, and between the photoconductor drum 1 and the transfer roller 5,
The transfer paper 10 is passed through, and a fixing device 11 is provided on the discharge path of the transfer paper 10.

The photosensitive drum 1 is an inorganic photosensitive drum in which a photosensitive layer such as selenium or amorphous silicon is provided on a conductive base roller such as aluminum, or a charge generating agent or a charge transporting agent in a binder resin. An organic photosensitive drum having an organic photosensitive layer in which is dispersed is used, and in particular, one having a positive charging type photosensitive layer is used. A roller-type contact charging device may be used as the main charging device 2, but a corona charging device is generally used, and the surface (photosensitive layer) of the photosensitive drum 1 has a positive polarity. Is charged. At this time, the main charging potential on the surface of the photoconductor is usually +20.
It is about 0 to 1000V. Next, the image exposure mechanism 3 irradiates the surface of the photosensitive drum with dot light such as a laser beam corresponding to the document by reflected light of the document or an electric signal from a computer or the like, and the potential of the light-irradiated portion is attenuated by light and electrostatic. A latent image is formed. In the developing device 4,
A developer carrying sleeve is arranged so as to face the photosensitive drum 1, and the developing sleeve supplies the developer to a developing area between the photosensitive drum 1 and the sleeve.
The electrostatic latent image is developed. As the developer, a two-component developer composed of a magnetic carrier and an insulating toner and a one-component developer composed of a magnetic toner are generally used. The electrostatic latent image is developed by being conveyed in the form of a magnetic brush adjusted to have a constant brush length, and the positively charged toner adheres to a portion having a low potential due to light attenuation.

The transfer roller 5 is made of conductive powder such as metal powder or carbon powder, or rubber or resin to which conductivity is added by the addition of ions, or a foam thereof, and is transferred by the DC power source 20. A voltage is applied to the transfer roller 5, which is generally maintained at a transfer potential of −100 to −3000 V so that the current flowing into the roller at the time of transfer is −2 to −30 μA. The toner image 15 is transferred onto the transfer paper 10 passing between the photosensitive drum 1 and the transfer drum image 16 is formed. Although the transfer roller 5 is arranged so as to follow the rotation of the photosensitive drum 1, its surface may be in contact with the surface of the photosensitive drum 1, but normally the distance between them is 0.1. Through
It is preferably set to be 0.5 mm. If the distance is smaller than 0.1 mm, the toner image 15 is pressed against the surface of the transfer paper 10 passing between the two, and the transfer toner image 16 is liable to have a void, and the distance is 0.5 m.
If it is larger than m, it tends to be difficult to effectively perform the transfer.

The transfer paper 10 having the transfer toner image 16 is
The toner image 16 is conveyed to the fixing device 11, and the transfer toner image 16 is fixed on the surface of the transfer paper 10 by heat, pressure, or the like. On the other hand, after the toner image 15 is transferred onto the transfer paper 10, the surface charge of the photoconductor drum 1 is removed by light irradiation by the charge eliminating device 6. Further, if necessary, the cleaning device 7 having a cleaning blade or the like scrapes off and collects the toner remaining on the surface of the photosensitive drum 1, and the next image forming process is performed. The toner collected by the cleaning device 7 is recycled to the developing device 4 for reuse, if necessary.

In FIG. 2, which shows the arrangement of the transfer paper transport path for preferably carrying out the transfer method of the present invention, the shaft of the transfer roller 5 is rotatably held by a predetermined frame 30 and at the same time, An insulating guide plate 31 is attached to the frame 30. The guide plate 31 is located in the vicinity of the transfer roller 5 so as to maintain the above-mentioned distance between the transfer roller 5 and the photosensitive drum 1, and transfer the transfer paper to the transfer roller 5. The guide surface 31a (contacts the transfer paper 10) so that it can be smoothly introduced into a small gap between the surface of the photoconductor drum 1 and the degree of close contact between the transfer paper 10 and the surface of the photoconductor drum becomes high. surface)
have. Since the guide plate 31 is arranged in the vicinity of the photosensitive drum, it is indispensable that the guide plate 31 be electrically insulating in order to prevent charge leakage and the like.

The transfer paper 10 is transferred from a predetermined cassette (not shown) or the like to a transfer area (between the transfer roller 5 and the photosensitive drum 1) along a transfer path (indicated by A in FIG. 2). , Which is ejected after the transfer is completed,
In general, a paper dust removing device 40 is arranged and the transfer paper 10
Passes through the paper dust removing device 40, and is introduced into the transfer area (gap between the photoconductor drum 1 and the transfer roller 5) via the guide plate 31.

The paper dust removing device 40 is composed of a pair of insulating rollers 41, 41 arranged so as to face each other, one of which is a driving roller and the other of which is a driven roller. The transfer paper 10 is rotated so as to be sent out in the transfer area direction. The insulating roller may have any surface as long as it has an insulating property. For example, the surface of a conductive roller such as a metal roller may be coated with an insulating resin or elastomer. It is also possible to use a conductive roller instead of the insulating roller, but in this case, it is necessary not to ground. Grounding makes it difficult to effectively remove paper dust. Further, a scraping member 42 for removing the paper dust scraped from the transfer paper 10 is pressed against the surfaces of the insulating rollers 41, 41. The scraping member 42 is usually a sponge, felt,
It is preferably formed of a cushioning insulating member such as a brush.

In the present invention, the guide plate 31 described above is used.
At least on the guide surface 31a of the layer 50 formed of an insulator having a negative polarity triboelectricity with respect to the transfer paper 10.
Is provided. That is, the insulator layer 50 is negatively charged by frictional contact with the transfer paper 10 introduced into the transfer area. Therefore, the reversely charged toner contained in the positively charged toner used for the development described above does not adhere to the guide surface 31a of the guide plate 31, and the toner stain on the back surface of the transfer paper 10 due to the reversely charged toner is effectively performed. Can be prevented.

In the present invention, as the insulator forming the above-mentioned insulator layer 50, a fluororesin such as polytetrafluoroethylene (PTFE), polyvinyl fluoride,
Polyvinylidene fluoride, vinyl fluoride / vinylidene fluoride copolymer, tetrafluoroethylene / perfluoroalkoxyethylene copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer, etc. can be used. ,
Especially, PTFE is preferably used. In addition, such an insulator layer 50 preferably has a thickness of at least 10 μm or more in terms of durability. For example, the entire guide plate 31 is made of an insulator forming the insulator layer 50. It may be formed. However, in general, from the viewpoint of cost and moldability, the insulating layer 50 is formed by applying the above-described insulating coating solution onto the surface of an insulating resin such as ABS resin and drying. Is good.

[0021]

Example (Experimental Example 1) A digital printer Antico 80 manufactured by Mita Kogyo Co., Ltd. was modified, and a fluorocarbon resin coating machine was sprayed and dried on the guide surface of a guide plate provided near the transfer roller. An insulator layer was formed, and an image was formed using this modified machine. The specifications and development conditions of the modified machine are as follows.

[0022]     Photoconductor drum: φ30 mm diameter positively charged organic photoconductor drum     Main charging potential: + 700V     Developing device: Two-component magnetic developer (4% by weight positively charged toner)                 Distance between sleeve and drum 0.8mm                 Magnetic brush spike length 0.8mm                 Development method Reverse development                 Development bias + 400V     Transfer roller: φ16mm diameter ion conductive urethane roller                 Distance between roller and drum 0.3mm                 Roller potential -1200 (roller inflow current -12μA)     Guide plate: ABS resin               Insulator layer 30 μm thick PTFE resin

Image formation of 60,000 sheets was continuously performed under the above conditions, but no image defect occurred. After the image formation, it was confirmed that the reversely charged toner did not adhere to the surface of the insulating layer of the guide plate. For comparison, the same experiment was conducted without forming the above-mentioned insulator layer on the guide plate. As a result, image defects frequently occurred when about 1000 images were formed. It was confirmed that the reversely charged toner adhered to the.

[0024]

According to the transfer method of the present invention, when an image is formed by reversal development using positively charged toner, a reversely charged toner (negatively charged toner) is provided on a guide plate provided near the transfer roller. Therefore, it is possible to effectively prevent the toner stain on the back surface of the transfer paper due to the oppositely charged toner.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of the overall arrangement of an electrophotographic apparatus.

FIG. 2 is a diagram showing an arrangement of transfer paper transporting paths for preferably carrying out the transfer method of the present invention.

[Explanation of symbols]

1: photoconductor drum 5: Transfer roller 10: Transfer paper 31: Guide plate 50: Insulator layer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-175276 (JP, A) JP-A-5-134563 (JP, A) JP-A-8-95453 (JP, A) JP-A-10- 133487 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/16 G03G 13/16

Claims (3)

(57) [Claims] 1. A method of developing an electrostatic latent image formed on the surface of a photoconductor drum by a reversal development method using positively charged toner, and transferring the toner image on the surface of the photoconductor drum to the surface of a transfer paper. A transfer roller is disposed so as to face the photoconductor drum, and at least a guide surface is formed of an insulating layer having a negative polarity in a friction surface with respect to the transfer paper in the vicinity of the transfer paper introduction side of the transfer roller. An insulating guide plate is provided, and while the transfer roller is held at a negative potential, a transfer paper is introduced between the transfer roller and the photosensitive drum by the guide plate to form on the surface of the photosensitive drum. A method of transferring a toner image onto the surface of a transfer paper. 2. The method according to claim 1, wherein the insulating layer on the surface of the insulating guide plate is made of fluororesin. 3. The method according to claim 2, wherein the fluororesin is polytetrafluoroethylene.