JPH04141680A - Image forming device - Google Patents

Abstract

PURPOSE:To satisfactorily perform reversal development of toner from a developing device to the electrostatic latent image on the surface of a photosensitive body without applying a bias voltage to a developing electrode by specifying the extent of electrification of toner supplied to the developing device to apply the bias voltage to the developing electrode. CONSTITUTION:Toner preliminarily electrified with a high specific electric charge, concretely, toner adjusted to the range of + or -(15 to 23)muC/g electrification extent is supplied as toner T stored in a development vessel 4B of a developing device 4. When toner whose extent of electrification is adjusted to this range is supplied to the developing device 4, toner T is electrified with high specific electric charge by frictional-electrification to carrier C in the development vessel 4B. The same potential as the bias voltage is given to the sleeve surface of a developing roller 4A by the electric charge held in this electrified toner T though the bias voltage is not applied to the sleeve surface. Thus, a toner image of sufficient density is formed on the electrostatic latent image of a photosensitive drum 1 without the bias voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus for developing a visible image by attaching toner to an electrostatic latent image formed on the surface of a photoreceptor.

[Prior Art] In the electrophotographic process used in copiers, printers, facsimile machines, etc., the surface of a photoconductor charged in a negative manner is exposed to light, and an electrostatic latent film is formed on the surface of the photoconductor by removing the charge on the exposed area. A developing process is used in which an image is formed, and then toner as an image forming substance is applied from a developing device to the electrostatic latent image to form a visible image on the surface of the photoreceptor.

In the case of printers and facsimile machines, a negative latent image is formed by exposing the image area to a laser beam or the like to remove the electrical charges in the image area, and this negative latent image has the same polarity as the unexposed area that becomes the background area. A reversal development method in which charged toner is deposited is generally used.

An overview of this reversal development is shown in FIGS. 2 and 3.

That is, the surface potential V. During the latent image forming process, the charge on the exposed area of the photoreceptor 1, which has been charged in a negative manner (approximately -700 V), is removed, and the surface potential of the exposed area is reduced to VL as shown in FIG.
A latent image of a well type potential lowered to about 100 V is formed. Next, in the development process, as shown in FIG. Due to the electric field formed between them, toner T having the same polarity as the uniform charge is attached to the well-shaped potential.

At this time, the bias voltage ■3 applied to the developer &4a is:
Usually, it is about -(500 to 600)V, and -500V
Below, it is common that the toner T adheres poorly and an image of sufficient density cannot be obtained.

[Problems to be Solved by the Invention] As described above, in the current image forming process using reverse development, it is essential to apply a bias voltage to the development electrode. However, this means that the image forming apparatus must be equipped with a dedicated bias power supply, and from the perspective of reducing the cost of the entire system, an image forming apparatus that does not require a bias power supply is required. .

An object of the present invention is to provide an image forming apparatus that can meet such technical problems.

[Means and Effects for Solving the Problems] The image forming apparatus of the present invention provides an electrostatic latent image formed on the surface of a photoreceptor by removing the electric charge of an exposed area, from which a developing device generates an electrostatic latent image having the same polarity as the electrostatic latent image. A device for forming a toner image by attaching charged toner to the developing device, which measures the amount of charge of the toner supplied to the developing device
23) By adjusting to μC/g, it is possible to form a toner image of sufficient density on the electrostatic latent image on the surface of the photoreceptor without requiring the application of a bias voltage to the developing electrode.

In general, if you use a toner with improved chargeability and developability, even with the current reversal development, for example -
It has been confirmed that a relatively low bias voltage of about 350 V forms a toner image of sufficient density on the surface of the photoreceptor.

This is because when a two-component developer containing toner and carrier is used, the two components are stirred and mixed in the developing device, and the toner has a fairly large specific charge due to frictional charging with the carrier. This is considered to be because the developing electrode (sleeve) of the developing device is already held at a considerably high potential even when no bias voltage is applied.

Based on the results of such tests, the present invention further improves the developability of the toner supplied to the developing device, and in particular adjusts the toner charge amount within the range of ±(15 to 23) μC/g. The present invention has succeeded in providing an image forming apparatus in which a sufficient potential for toner movement can be applied to the developing electrode solely by the charge generated by frictional charging with the toner, in other words, an image forming apparatus that does not require a bias voltage.

Note that if the absolute value of the toner charge amount is less than 15 μC/g,
It has been experimentally confirmed that the development potential becomes insufficient and the density of the formed image becomes unclear, while if it exceeds 23 μC/g, the development potential becomes too high and the image density becomes excessive.

[Example] Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 shows an outline of an electrophotographic system equipped with an image forming apparatus according to the present invention.

In the figure, reference numeral 1 denotes a photoreceptor drum whose surface is coated with a photoconductive substance, and around the photoreceptor drum 1 there is a corona charger 2, an exposure device 3, a developer 4, a transfer device 5, and a cleaner 6.
The system is configured by arranging them in order.

In this system, first, the surface of the photoreceptor drum 1 is uniformly charged (-) using the corona charger 2, and then the drum surface is exposed to light using the exposure device 3. is removed, and an electrostatic latent image corresponding to the exposure pattern is formed on the surface of the photoreceptor drum 1. Next, toner T charged to the same polarity (O) as the electrostatic latent image is applied from the developing roller 4A of the developing device 4 to the electrostatic latent image.
The toner is deposited from A to form a toner image on the drum surface. At this time, the developing roller 4A has a relatively higher potential than the potential of the latent image in the exposed area where the charge has been removed, and due to the action of the electric field between the two, the toner T ( ○) is attached. In this way, the toner image formed on the surface of the photosensitive drum 1 is corona-transferred by the transfer device 5 onto the recording paper P that is fed and superimposed on the bottom surface of the drum 1, and then the surface is cleaned by the cleaner 6. The same process is then repeated.

A developing device 4 that constitutes an image forming apparatus together with the photosensitive drum 1
To be more specific, this developing device 4 includes a developing roller 4A disposed close to and facing the surface of the photoreceptor drum 1 on which an electrostatic latent image has been formed, and a two-component developer (toner T+carrier C) inside. It is equipped with a developing container 4B that stores toner and the like to adhere to the surface of the developing roller 4A, and a doctor blade 4C that uniformizes the toner and the like that is deposited from the container 4B onto the surface of the developing roller 4A. The developing roller 4A includes a magnet roller 4b that is relatively rotatably provided inside a non-magnetic sleeve 4a that serves as a developing electrode for the photosensitive drum 1, and the magnet roller 4b and the doctor blade 4C are connected to each other. They work together to define the amount of toner that is deposited on the surface of the developing sleeve 4a. - On the other hand, in the developer container 4B that accommodates the developer, the toner T stored therein is constantly stirred to form a carrier C.
A stirrer 4C is installed to uniformly mix the ingredients.

In the image forming apparatus according to the present invention, the toner T stored in the developer container 4B of the developer 4 is charged with a large specific charge in advance, specifically, the amount of charge is -(1
5-23) We supply products adjusted to a range of μC/g.

When toner with a charge amount adjusted within this range is supplied to the developer 4, the toner T can be charged with a much larger specific charge than conventional ones due to frictional charging with the carrier C in the developer container 4B. can.

Then, due to the electric charge held in this charged toner T,
The sleeve surface of the developing roller 4A that moves the toner T to the electrostatic latent image on the photoreceptor drum 1 can be given a similar potential (approximately -500 to -600 V) without applying a bias voltage. That is, it is possible to form a toner image of sufficient density on the electrostatic latent image on the photoreceptor drum 1 even without a bias voltage.

In fact, according to results obtained by adjusting the toner charge amount to -19 μC/g and supplying the toner to the developing device 4, it has been confirmed that sufficiently clear images can be obtained even without bias.

In the embodiment, a case was described in which an image is formed by attaching (-) charged toner to the exposed portion of a photoreceptor drum that is charged in a (-) manner. The present invention can be similarly applied to the case where an image is formed by attaching (+) charged toner to the exposed portion of a photoreceptor drum charged in a - direction.

[Effects of the Invention] As described above, in the present invention, by adjusting the amount of toner charge supplied to the developing device to about (15 to 23) μC/g, it is not necessary to apply a bias voltage to the developing electrode. The toner can be successfully reversely developed from the developing device to the electrostatic latent image on the surface of the photoreceptor.

That is, a low-cost image forming apparatus that does not require a bias power source can be realized.

[Brief explanation of the drawing]

FIG. 1 is a system schematic diagram of an electrophotographic system equipped with an image forming apparatus according to the present invention. 2 and 3 show an overview of reversal development, FIG. 2 is a potential model diagram of reversal development, and FIG. 3 is a principle diagram showing a conventional bias reversal development method. 1... Photoreceptor (drum) 2... Corona charger 3... Exposure device 4... Developing device 4A... Developing roller 4B... Developing container 4C... Doctor blade 4a... Developing sleeve 4b... Madai roller 4C... Stirrer T... Toner C... Carrier

Claims (1)

[Claims] An apparatus for forming a toner image by attaching toner charged to the same polarity as the electrostatic latent image from a developing device to an electrostatic latent image formed on the surface of a photoreceptor by removing the electric charge of an exposed area, Adjust the amount of charge of the toner supplied to the developer by ±(15 to 23) μC.
An image forming apparatus characterized in that the image forming apparatus is adjusted to /g.