JPH0643715A - Method and device for forming image - Google Patents

Abstract

PURPOSE:To make the acceleration of charge injection compatible with the stable formation of a toner visible image and to obtain excellent transfer characteristic by using two-component developer, electrostatically charging a photosensitive body through conductive magnetic carrier and forming the visible image by the use of insulating magnetic toner. CONSTITUTION:The two-component developer 6 constituted of the conductive magnetic carrier 8 and the insulating magnetic toner 7 is used, and the charge injection is performed to the surface of the photosensitive body 100 from a developing sleeve 200 through the carrier 8. Meanwhile, the toner 7 is stuck to an exposed and destaticized area, and the visible image 12 is formed. It is desirable that the rate of the insulating toner to the developer 6 is about 1-5%, which is considerably small in comparison with the conventional two- component developer. Thus, electric resistance becomes low as entire developer and the charge injection to the surface of the photosensitive body through the carrier 8 becomes excellent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chargeless image forming method and a chargeless image forming apparatus.

[0002]

2. Description of the Related Art In the electrophotographic recording conventionally used,
In the charging step, which is the first step of the recording process, a corona charger is used, which has features such as low cost and simple structure. However, this method has various problems at present due to the harmfulness of ozone generated by corona discharge, the danger of handling a high voltage, the difficulty of downsizing the device, and the like.

Therefore, in recent years, a simplified electrophotographic recording technique (chargeless process) that enables miniaturization without using charging by corona discharge has been studied. FIG. 4 is a schematic view of a main part for explaining the principle of the image forming apparatus using the chargeless process, which was studied by the present inventor before the present invention. This apparatus performs charging, exposure, development, cleaning, and charge removal all in almost one process (one rotation of the photoconductor). The transparent electrode 2 and the photoconductive layer 3 are formed on the transparent support 1. The conductive magnetic toner 71 is brought into contact with the formed photoconductor 100, and electric charges are injected from the developing sleeve 200 through the toner to charge the photoconductor 100. Then, the back surface of the photoconductor is exposed by the beam 10 to remove the electric charge. The conductive magnetic toner 71 is attached to the exposed portion to obtain a visible toner image.

That is, the developing sleeve 200 comprises a magnetic roller 4 and a non-magnetic conductive sleeve 5, and a developing bias is applied to the sleeve 5 by a voltage source 80, whereby the conductive magnetic toner 71 (toner layer). 7
0) has the same potential as the developing bias. While the toner 71 is captured by the magnetic binding force, the developing sleeve 200 rotates to come into contact with the surface (photoconductive layer 3) of the photoconductor at point A in the figure, and charge injection is started. At the point B, the potential of the photoconductive layer 3 becomes almost the same as the developing bias. The toner 71 moves while being pulled toward the developing sleeve by the magnetic force of the magnetic roller 4. When exposed from the back surface of the photoconductor at point C, the electrons generated in the exposed portion, electrons of the hole pairs move to the photoconductor surface and neutralize with the positive charge in the photoconductive layer 3. The potential drops, and in order to compensate for the lowered potential, the positively charged toner 71 adheres to the photoconductive layer 3 to obtain a visible image of the toner, which is transferred to a transfer medium (not shown) to form an image. To do.

[0005]

According to the study by the present inventor, it has been found that the following problems are likely to occur in the simplified electronic recording process of FIG. That is, in this process, since the conductive magnetic toner is used, when the toner adheres to the portion where the surface potential is lowered by the exposure and a visible image is formed, the developing sleeve 20 passes through the adhered toner.
Charge injection to the surface of the photoconductor starts from 0. If this charge injection continues, the potential difference between the surface of the photoconductor and the toner disappears, the mutual attraction force due to the electric force disappears, and the toner is easily detached from the surface of the photoconductor, and the transfer failure easily occurs. In the process of FIG. 4, in order to prevent such a situation, the exposure point C is set at the downstream portion (t1 in the figure) of the contact range T between the developing sleeve 200 and the photoconductor 100.
At> t2), the toner is separated from the developing sleeve 200 immediately after the toner is attached, the charging time is extremely shortened, and the electric force between the photoconductor and the toner is maintained in a strong state to obtain a visible image. . But as a result,
It is unavoidable to charge the exposed area through the toner, and the control of the detachment time of the toner after exposure from the developing device is
There are many subtle elements, and the variation causes the amount of adhesion to vary. That is, in some cases, a defective image quality may occur as in the portion F in the figure. Further, since the conductive magnetic toner is used, electrical transfer becomes difficult.

The present invention has been made based on such a consideration, and an object thereof is to eliminate the deterioration factor of the transfer characteristics of the prior art and improve the transfer characteristics of the chargeless image forming process.

[0007]

[Means for Solving the Problems]

(1) In the present invention, a two-component developer composed of a conductive magnetic carrier and an insulating magnetic toner is used to perform charge injection (charge) from the developing sleeve to the surface of the photoconductor through the conductive magnetic carrier. On the other hand, the insulating magnetic toner adheres to the exposed and neutralized area to form a visible image. Two
The proportion of the insulating toner in the component developer is preferably about 1 to 4% (weight ratio), which is considerably smaller than the proportion in the conventionally used two-component developer. As a result, the electric resistance of the developer as a whole becomes extremely small, and the charge injection onto the surface of the photoconductor via the carrier becomes good. Carrier particle size is 30-150
The range of μm is desirable, and the magnetic force of the carrier is 50 to 150 emu in order to suppress the adhesion to the photoconductive layer.
It is preferably in the range of / g. Further, the average particle diameter of the toner is preferably 5 to 20 μm. (2) Further, the AC component is superposed on the DC component as the developing bias to promote and stabilize the charge injection by the AC component. The DC component has the same polarity as the charging polarity of the insulating toner. The DC component has a role of moving the toner to the vicinity of the surface of the photoconductor at the time of injecting electric charges and leaving the toner on the photoconductor after the exposure, that is, developing the toner.

[0008]

[Action]

(1) As shown in FIG.
As shown in (a), the two steps of charging the surface of the photoconductor and forming a visible image are continuously performed. The former requires good charge injection characteristics, and the latter requires injection of charges. It must be prevented as much as possible. That is, regarding the movement of charges, the respective processes are inconsistent with each other. Conventionally, both of these contradictory steps are performed using the conductive toner, so that there is a risk that transfer failure will occur. Therefore, in the present invention, FIG.
As shown in (b), a two-component developer was used, and each component was allowed to carry out the role sharing. That is, the charge is performed by the carrier, and the visible image is formed by using the insulating magnetic toner. The insulative toner has no fear of injecting charges to the surface of the photoconductor, thereby eliminating the above contradiction and realizing good transfer characteristics.

(2) The conductive magnetic carrier is used
This is for the purpose of injecting charges and for preventing adhesion and fogging on the surface of the photoconductor due to magnetic restraint. If the average particle size of the carrier is too small, the adhesion and fogging on the surface of the photoconductor will increase, and if it is too large, the charge injection will be uneven and the adhesion of the toner will be hindered. Is desirable. Also,
Considering the wear of the carrier, the magnetic force of the carrier is 5
It is preferably in the range of 0 to 150 emu / g. The conductive magnetic carrier is a metal such as ferrite, iron, chromium, nickel, or a binder type in which they are dispersed in a binder resin, and is 10 ² Ω · cm to 10 ⁸ Ω ·
cm can be used. The charge of the insulating toner has the same polarity as the DC bias of the developing sleeve (charge of the photoconductor), and the potential difference between the charge of the insulating toner and the non-exposed portion of the photoconductor (the region where the charge injected by the carrier remains) is zero. Since fogging (adhesion) to this portion poses a problem, magnetic toner is used and bound by magnetic force to prevent fogging. If the average particle diameter of the toner becomes too small,
The average particle size of the toner is preferably 5 to 15 μm because fogging and adhesion to the photoconductor become easy.

The spherical formation of the carrier particles makes it possible to make the developer layer formed on the developer carrying carrier uniform and to apply a uniform bias voltage to the developer carrying carrier. It also gives an effect. That is, the fact that the carrier particles are spherical means that (1) generally, the carrier particles are easily magnetized and adsorbed in the long axis direction, but due to the spherical shape, the directionality is lost, so that the developer layer is uniformly formed. , (2) to prevent the occurrence of locally low resistance areas and unevenness of layer thickness, (2) the edge portion is eliminated, and the electric field is not concentrated on the edge portion. As a result, a bias voltage is applied to the developer carrier. Even if it is applied, the effect of not unevenly discharging on the surface of the image carrier and disturbing the electrostatic latent image does not occur. The resistivity is 0 for particles.
After tapping in a container having a cross-sectional area of 50 cm ² , a load of 1 kg / cm ² was applied on the packed particles, and a voltage generating an electric field of 1000 V / cm was applied between the load and the bottom electrode. It is a value obtained by reading the current value at that time.

(3) The AC component of the developing bias is used for controlling the degree of charge injection and improving the uniformity. Unlike the conventional uniform charge injection by the conductive toner, in the present invention, the charge injection is performed by the carrier in which the insulating toner is mixed. Therefore, the nonuniformity is prevented and the charge injection is promoted by the AC component. That is, the bias periodically changes from positive to negative with respect to the DC level. This AC component is 100 to 5000 Hz, voltage value V
_{A pp} (peak to peak) of 200 to 2000 V is preferably used. As the DC component, 200 to 800V is used. This promotes charge equilibration and charge injection. The AC component can adjust the image quality by variably providing the voltage V _pp or the frequency. This is effective when the carrier resistance of the developer deteriorates or changes depending on the environment. That is, when the charge injection becomes defective, the injection effect can be improved and stabilized by increasing the voltage value V _pp or decreasing the frequency. The AC component also helps improve the image quality of toner image formation after exposure.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. (Image Forming Method) FIG. 1 is a diagram for explaining the principle of the image forming method of the present invention. The feature of this embodiment is that a two-component developer composed of an insulating magnetic toner 7 and a conductive magnetic carrier 8 is used, and a DC bias from a DC voltage source 14 is superposed with an AC bias from an AC voltage source 13. The thing is that the development bias.

The photoconductor 100 is a negative charge OPC having a two-layer structure in which a transparent electrode 2, a photoconductive layer 3 composed of a charge generation layer and a charge transfer layer are stacked on a transparent support 1, and moves to the right. It is (rotating). The developing sleeve 200 is composed of a magnetic roller 4 and a sleeve 5, and rotates counterclockwise. The exposure for image formation is performed at a point C in the downstream portion (t1> t2 in the drawing) of the contact area T between the developing sleeve 200 and the photoconductor 100.

A conductive magnetic carrier (indicated by a white circle in the figure) 8 is applied to a DC voltage of -300 V at 1 KHz, V.
_It shows the same potential change as the voltage on which the AC component of _pp = 600V is superimposed. The insulating magnetic toner (denoted by a black circle in the figure) 7 has a charge amount of −10 μc / g, which has the same polarity as the DC voltage. In the figure, charges (holes) are injected from the point A through the conductive magnetic carrier 8, and the carrier (two-component developer) is successively supplied to the surface of the photoconductor by the rotation of the developing sleeve 200, and the point B. At,
The potential of the photoconductive layer 3 becomes the same as the developing bias. next,
The exposure beam 10 is radiated from the back surface of the photoconductor to eliminate the charge on that portion, and the insulating magnetic toner 7 is attached to the removed portion to form a visible image.

The toner at the portion where the charge has not been removed is collected by the developing sleeve (developing device) 200. The formed toner image moves while being attached to the surface of the photoconductor by an electric force, and is transferred onto a transfer paper or the like using a transfer roller or the like to which an electric bias is applied (not shown).

The AC component of the developing bias is used to promote charge injection and make it uniform. The injected charges are trapped and exist on the surface of the photoconductor in the non-exposed portion (capture charge 11).
However, since the potential is almost the same as that of the insulating magnetic toner 7, the toner is easily electrically fogged. However, due to the magnetism of the toner, the toner is bound by the magnetic force of the developing sleeve, so that fogging of the toner is actually prevented. The good charge injection (charging) using the AC component through the conductive carrier and the fogging-free visible image formation by the insulating magnetic toner improve the transfer performance.

(Image Forming Apparatus) FIG. 2 is a diagram showing an example of the structure of an image forming apparatus adopting the method of FIG. In the figure,
The same parts as those in FIG. 1 are designated by the same reference numerals. LE is installed inside the photoconductor 100 that rotates clockwise.
A D array 20 is provided and always emits light in the same direction. The output light of the LED array 20 is applied to the photoconductive layer 3 via the optical system 21.

On the other hand, the developing sleeve 200 rotates counterclockwise to continuously supply the two-component developer layer 6 to the surface of the photoreceptor 100. The developing bias is a DC component on which an AC component is superimposed. The AC component of the developing bias has a variable voltage or frequency and can be adjusted. When the injection from the carrier becomes insufficient,
An operation of increasing the voltage V _pp or lowering the frequency is performed.

A visible toner image is formed while the two-component developer layer 6 is in contact with the surface of the photoconductor 100, and the toner image is transferred onto a transfer paper by a transfer roller 40 to which a transfer bias is applied. It Transfer paper is cassette 7
It is supplied from 0 and is sent to the transfer roller 40 via the supply roller 30. In this case, the rotation of the photoconductor 100 and the developing sleeve 200 and the supply of the transfer paper are synchronized with each other by the control using the reference clock. The transfer sheet after transfer is discharged to the outside of the apparatus through the fixing device 50 and the discharge roller 60. The locus of the transfer sheet is indicated by a dotted arrow. After the transfer, the photoconductor 100 is photo-erased from the back surface by the static eliminator 21 using LEDs, and then cleaned by the cleaning blade 22,
Enter the next print cycle. Cleaning blade 2
The toner scraped off in 2 is again collected in the developing device and used.

[0020]

As described above, according to the present invention, the following effects can be obtained. (1) A two-component developer is used, charging of the photoreceptor is performed through a conductive magnetic carrier, and formation of a visible image is performed using an insulating magnetic toner, whereby charge injection is promoted and stable toner is obtained. It is possible to achieve both formation of a visible image and good transfer characteristics. In this case, the charge bias can be promoted by including the AC component in the developing bias, and fogging to the non-image area can be prevented by the magnetism of the toner. (2) Since the image forming apparatus adopting the image forming method of the present invention uses a very realistic and simple means of using a two-component developer, the apparatus configuration does not become complicated.
Therefore, according to the apparatus of the present invention, a corona discharge electrode is not required, and high image quality can be achieved without impairing the characteristics of the chargeless image forming apparatus that are compact and safe.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of an image forming method of the present invention.

FIG. 2 is a diagram showing an example of a structure of an image forming apparatus adopting the method of FIG.

FIGS. 3A and 3B are diagrams showing the characteristics of the conventional image forming method and the characteristics of the image forming method of the present invention, respectively.

FIG. 4 is a diagram showing the principle of a conventional chargeless (simplified electrophotographic method) image forming method.

[Explanation of symbols]

 1 Transparent Support 2 Transparent Electrode 3 Photoconductive Layer 4 Magnetic Roller 5 Sleeve 6 Two-Component Developer 7 Insulating Magnetic Toner 8 Conductive Magnetic Carrier 10 Exposure Beam 11 Captured Charge 12 Toner Visible Image 13 AC Voltage Source 14 DC Voltage source 21 Optical static eliminator 22 Cleaning blade 100 Photoconductor 200 Development sleeve

Claims (4)

[Claims] 1. A two-component developer composed of a conductive magnetic carrier and an insulating magnetic toner is continuously supplied onto a surface of a photosensitive member which moves from above a developing sleeve having a magnetic roller therein, Charge is injected to the surface of the photoconductor through the conductive magnetic carrier, and the charge injection area is image-exposed from the back surface of the photoconductor.Next, the insulating magnetic toner is attached to the exposed part. An image forming method comprising forming a visible toner image and transferring the visible toner image to a transfer medium to form an image. 2. The weight average particle diameter of the conductive magnetic carrier is 3
The image forming method according to claim 2, wherein the conductive magnetic carrier has a resistivity of 10 ² Ω · cm to 10 ⁸ Ω · cm. 3. The image forming method according to claim 1, wherein a developing bias having an AC component is applied to the developing sleeve. 4. A developer comprising a photoconductor having a photoconductive layer on its surface, an exposure unit for performing image exposure from the inside of the photoconductor, and a developing sleeve having a magnetic roller and a conductive sleeve. An image forming apparatus using a two-component developer composed of a conductive magnetic carrier and an insulating magnetic toner.