JPH08272213A - Developing device - Google Patents

Abstract

PURPOSE: To enable reversal development and to obtain a sharp visible image by setting the intrinsic resistivity of the outside layer of a toner carrier, so as to maintain the polarity of the charge of a toner grain. CONSTITUTION: The electric resistance value of the outside layer 24 is set high, so that the negative charge of the toner grain facing a surface part except an electrostatic latent image is prevented from leaking to the outside layer 24 of a developing roller 4 and missing, in the case of executing a developing operation and the reverse of the polarity is prevented as well. Thus, only by setting the electric resistance of the outside layer 24, the polarity of the previously triboelectrified toner grain, can be maintained at that in the developing operation. Therefore, the toner grain is not stuck to the surface part except the electrostatic latent image, that is, the toner grain is stuck only to the electrostatic latent image and the sharp visible image can be obtained without any trouble. When the intrinsic resistivity of the outside layer 24 of the developing roller 4 is set >=7×10<6> Ω.cm to keep the polarity of the charge of the previously triboelectrified toner grain carried on the roller 4, during the developing operation, a high-quality visible image can be obtained for a long period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a toner carrier having a conductor and an outer layer located outside the conductor, and a latent image is formed by a triboelectrically charged toner carried on the outer layer of the carrier. The present invention relates to a developing device that visualizes an electrostatic latent image formed on a carrier.

[0002]

2. Description of the Related Art Toner to which an auxiliary agent is externally added, if necessary,
That is, a developing device of the above type using a one-component developer is well known in the prior art, and is used in an image forming device such as an electronic copying machine, a printer or a facsimile.

By the way, this type of developing system can generally be roughly divided into normal development and reversal development. For example, a copying machine for obtaining a positive image from a negative original, or an electrostatic latent image on a latent image carrier by a laser beam. Reversal development is adopted in a laser printer or the like for forming a sheet. However, as a result of recent studies, when reversal development is performed by the developing device of the type described at the beginning, the developed visible image may become unclear and the predetermined visible image may not be obtained in some cases. It became clear.

[0004]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above recognition, and an object of the present invention is to enable the developing device of the type described at the beginning to be used for reversal development without any trouble. To configure.

[0005]

SUMMARY OF THE INVENTION To achieve the above object, the present invention applies a voltage to a conductor of a toner carrier to reverse develop an electrostatic latent image to form toner particles carried on the toner carrier. In order to maintain the charging polarity pre-frictionally charged during development, the resistivity of the outer layer is 7 × 10 ⁶ Ω.
・ Propose a configuration set to cm or higher.

[0006]

Embodiments of the present invention will now be described with reference to the drawings, and the details of the above-mentioned conventional drawbacks will be clarified with reference to the drawings.

FIG. 1 shows an example of an image forming apparatus using a developing device 100 according to an embodiment of the present invention.
It has a toner carrier configured as a developing roller 4, and a toner (one-component developer) 2 is contained in a tank 1 of such a developing device. The toner 2 may be a magnetic toner or a non-magnetic toner, but is assumed to be a non-magnetic toner in the illustrated example.

The toner 2 in the tank 1 is pressed by the agitator 13 toward the supply roller 3 which rotates counterclockwise, and is supplied to the developing roller 4 by the conveying action of the roller 3. The developing roller 4 includes a conductor 14 to which a bias voltage is applied by a power source 20, and an outer layer 24 that is located outside the conductor 14 and is fixed to the conductor 14. The outer layer 24 is, for example, a rigid body or an elastic material. Etc. The illustrated conductor 14 also serves as a core material of the developing roller 4. The developing roller 4 is rotationally driven in the counterclockwise direction in FIG. 1, and the toner supplied to the roller 4 is regulated in layer thickness by a blade-shaped toner layer thickness regulating member 5 pressed against the developing roller 4.

Further, the toner particles of the toner 2 are charged to the same polarity as the polarity of the bias voltage applied to the conductor 14 of the developing roller 4 by friction with the regulation member 5. This polarity may be either positive or negative, but in this example, it is assumed to be negative for convenience of explanation.

The toner, which has passed through the regulating member 5 and whose layer thickness has been regulated, is conveyed while being carried as a thin layer on the outer layer of the developing roller 4, and a latent image carrier (formed in a drum shape in the example of the drawing, It is conveyed to a developing area D, that is, an area where the photoconductor 6 rotating in the direction of arrow A and the developing roller 4 face each other.

The photosensitive member 6 has a grounded drum-shaped conductive substrate 16 and a photosensitive layer 26 on the outside thereof, and its surface is positioned in contact with or in proximity to the developing roller 4. Prior to the development, the photosensitive layer 26 of the photoconductor 6 is uniformly charged with the same polarity as the charging polarity of the toner, that is, the negative polarity, by the charging charger 7. Then, the exposure unit 21 irradiates the original document or the light L from the light emitting device. When the developing device 100 is used in an ordinary electronic copying machine, the light L is transmitted or reflected light from a document, and in the case of a printer using an LED array, a laser printer, or the like, an LED array or a laser device or the like is used. It is the beam from the light emitting device. By irradiating the surface of the photoconductor with light L, an electrostatic latent image is formed on this surface as is well known.

This latent image is strongly exposed to light, and therefore, the charge of the photosensitive layer 26 disappears, or the photoconductor portion where the absolute value of the surface potential is lowered, and the latent image is not exposed to light or its light intensity is weak. Therefore, it is formed by the photoconductor portion in which the negative potential is kept high, and the former portion in which the charge disappears or the absolute value of the surface potential decreases is the electrostatic latent image, and the potential is The latter part, which is kept high, is the background part.

When the electrostatic latent image reaches the developing area D, the latent image is visualized by the triboelectrically charged toner which is also carried there. More specifically, the triboelectrically charged toner particles adhere to the electrostatic latent image having a low surface potential, not to the background portion having a high surface potential on the photoconductor. This is the developing roller 4
Is a phenomenon caused by the action of an electric field generated by applying a voltage having the same polarity as the charging polarity of the toner particles to the conductor 14. In this way, the electrostatic latent image is reversely developed.

As described above, the developing device 10 shown in FIG.
In the case of 0, the electrostatic latent image formed on the photoconductor 6 is made visible by the triboelectrically charged toner carried on the outer layer 24 of the developing roller 4 in a thin layer state, and the electrostatic latent image is inverted at that time. To develop, a voltage having the same polarity as the charging polarity of the toner particles is applied to the conductor 14 of the developing roller 4.

The visible image reversely developed by the developing device 100 is transferred onto the transfer paper 9 by the transfer charger 8. A positive voltage is applied to the charge wire of the transfer charger 8, whereby negatively charged toner is transferred from the photoconductor to the transfer paper side. After the transfer, the photoconductor is cleaned of residual toner by the cleaning device 10, and is subjected to a neutralizing action by a neutralizing device (not shown) including a neutralizing lamp and a neutralizing charger.

Although the electrostatic latent image is reversely developed as described above, conventionally, when the reverse development is attempted by the developing device as shown in FIG. 1, a background portion other than the electrostatic latent image on the photoconductor is formed. There is a possibility that a large amount of toner adheres to the surface, which makes the visible image unclear, or the toner adheres to the entire surface of the photoconductor to prevent predetermined development.

When the present inventor examined this,
It has been clarified that whether or not reversal development is possible depends on the level of electric resistance of the outer layer 24 of the developing roller 4. That is, the electric resistance value of the conventional outer layer of the developing roller is set to be low, whereby the electric charge of the toner particles located opposite to the background portion other than the electrostatic latent image in the developing area D is lost or the polarity thereof is lost. Was reversed, and as a result, the toner particles adhered to the background portion, which made the visible image unclear. The reason why the charge of the toner particles is lost and the polarity thereof is reversed is presumed as follows.

FIG. 2 is an explanatory view schematically showing the photosensitive member 6 and the developing roller 4 in the developing area. As described above with reference to FIG. 1, the power source 2 is applied to the conductor 14 of the developing roller 4.
A negative bias voltage is applied by 0, and the photoconductor 6
Between the developing roller 4 and the developing roller 4, toner particles T having the same polarity as the applied voltage and having a diameter of about 10 .mu. The base 16 of the photoconductor 6 is grounded, and the photosensitive layer 26
, A background portion X having a high surface potential and an electrostatic latent image Y having a lower surface potential are formed on the negative side, as indicated by the symbol "-". The surface potential of the electrostatic latent image may be zero volts.

Of the toner particles reaching the developing area, the toner particles facing the electrostatic latent image Y have a negative charging polarity, and the conductor 14 is applied with a bias voltage of the same polarity. Therefore, the toner electrostatically adheres to the electrostatic latent image Y. On the other hand, the toner particles T facing the background portion X
Is polarized by the action of a high electric field (for example, about 10 to 100 kv / cm) based on the charges of the background portion, and the negative charges are polarized as shown by the symbols "+" and "-" in FIG.
Facing the outer layer 24 of.

At this time, in the conventional developing roller 4,
Since the electric resistance value of the outer layer 24 is set to be low, the negative charge of the toner particles T leaks to the outer layer 24 as shown by a chain line arrow in FIG. 4, and thus the toner particles T facing the background portion X are charged. The polarity reverses from negative to positive. In this way, the toner particles inverted to the positive polarity adhere to the background portion X having a polarity opposite to that of the toner particles, and the completed visible image is inevitable. It is considered that a part of the electric charge of the toner particles facing the electrostatic latent image Y formed on the photoconductor leaks, but the polarity of the toner particles does not usually reverse.

Therefore, in the developing device of this embodiment, the negative charges of the toner particles facing the background portion X other than the electrostatic latent image Y leak to the outer layer 24 of the developing roller 4 during the developing operation, and the charges are lost. The electric resistance value of the outer layer 24 is set to be high so as not to be broken or the polarity thereof is not reversed. As described above, the polarity of the toner particles pre-frictionally charged can be maintained during the developing operation only by setting the electric resistance of the outer layer 24, whereby the toner particles adhere to the background portion X other than the electrostatic latent image Y. Instead, the toner particles adhere only to the electrostatic latent image Y, and a clear visible image can be obtained without any trouble.

Next, an explanation will be given of a process leading to the above-described inference shown in FIG. 2 and an experimental example clarifying the advantages of the developing device shown in the drawing.

FIG. 3 is a graph showing the electric resistance characteristics of the outer layers of three developing rollers 4A, 4B and 4C having a diameter of 20 mm and a length of 210 mm. FIG. 4 is a schematic diagram showing a method for measuring the electric resistance characteristics of these developing rollers. Each of the developing rollers 4A, 4B and 4C has a thickness of 6 mm obtained by coating a stainless steel conductor 14 having a diameter of 8 mm with a silicone rubber in which conductive carbon black as a resistance adjusting agent is dispersed, and grinding the outer peripheral surface thereof. It is a columnar body in which an outer layer 24 composed of the rubber layer is formed. Each developing roller 4 formed in this way
A, 4B, and 4C are brought into contact with a well-polished aluminum cylinder 30 having a diameter of 40 mm, and a load W = on the entire developing roller.
3.5 kg was uniformly added, and the circumferential contact width d was set to 2 mm. In this state, a voltage is applied between the conductor 14 and the aluminum cylinder 30, the current passing through the outer layer 24 of the rubber layer is read, and this is shown as a graph in FIG.

On the other hand, as a latent image carrier, a drum-shaped photoreceptor 6 having a diameter of 40 mm, in which a photosensitive layer 26 (FIGS. 1 and 2) made of an organic photoconductor is laminated on a drum-shaped substrate, is used as shown in FIG. Assembled, rotated at a linear velocity of 48 mm / sec, uniformly charged to −800 V by the charging charger 7, imagewise exposed by the light L, and the exposed portion, that is, the surface of the electrostatic latent image Y (FIG. 2). The potential was set to drop to -50V.

First, the photoconductor 6 is detached from the image forming apparatus shown in FIG. 1, toner of negatively charged non-magnetic toner particles is put in the tank 1 of the developing device 100, and the developing device 100 is
Only the charged toner layer was formed on the developing roller 4A, 4B or 4C by operating only the above. When the charge amount was measured, all of the developing rollers 4A, 4B and 4C were -5 to -30.
It had a charge of μc / g.

Then, the photosensitive member 6 is assembled as shown in FIG. 1 and sequentially combined with the developing rollers 4A, 4B and 4C to apply a negative bias voltage to the conductor 14 of each developing roller, and the reverse development is carried out in the manner described above. I went.

In the developing device in which the developing roller 4A having the outer layer 24 having the lowest electric resistance value is incorporated, the toner adheres to the entire surface of the photoconductor 6 and the conductor 1 of the developing roller 4A.
Even if the bias voltage to 4 was changed, a clear inverted image was not obtained. When a visible image on the photoconductor 6 was transferred to plain paper by the transfer charger 8 with a positive corona charge, a reverse image was transferred, and when a negative corona charge was similarly transferred, a positive image was transferred. As a result, the toner particles facing the background portion X (FIG. 2) during the developing operation are inverted to the positive polarity and adhere to the background portion X, and the photoconductor portion on which the electrostatic latent image Y is formed is negatively charged. It can be seen that the toner particles adhered as they were.

A bias voltage of -400V is applied to the conductor 14 in each developing device using the developing roller 4B in which the electric resistance of the outer layer 24 is higher than that of the developing roller 4A and the developing roller 4C having the highest resistance value. By doing so, a clear inverted visible image was obtained. However, the developing roller 4B
When the continuous printing operation was performed by the developing device with the assembled toner, the toner was adhered to the entire surface of the photosensitive member in the same manner as in the case of the developing roller 4A, after transferring to about 100 sheets of A4 size transfer paper. . On the other hand, with the developing roller 4C, a clear inverted visible image was obtained even after printing was continued for 5000 sheets or more. In the developing roller 4B, the electric resistance value of the rubber layer that constitutes the outer layer 24 of the developing roller 4B decreases with time, and the charge of toner particles leaks, and the toner particles adhere to the background of the photoconductor. it is conceivable that.

As shown by the above experimental results, when the developing rollers 4A and 4B having the outer layer having a low electric resistance are used, the electrostatic charge of the toner particles held on the developing roller is lost from the initial stage or in an extremely short time. It is clear that the polarity is reversed and the visible image is blurred. If the developing roller 4C having the outer layer having high electric resistance is used, a clear inverted visible image can be obtained for a long time.

When various experiments were repeated in addition to the above-mentioned experiment, the electric resistance value of the outer layer 24 was at least 10 ⁶ Ω or more, preferably at least ^{6 6} Ω when a bias voltage of 1000 V was applied in the measuring method shown in FIG. Those showing a resistance value R of 10 ⁷ Ω or more were preferable for obtaining a clear visible image. In the measuring method shown in FIG. 4, the aluminum cylinder 3
The area S of the outer layer 24 in contact with 0 has a developing roller length of 2
Since 10 mm and d = 2 mm, S = 2 × 210 mm ² and the thickness (l) is 6 mm. Therefore the outer layer 2
When the specific resistivity of 4 is ρ, R = ρ × (l / S). Therefore, if R = 10 ⁶ Ω or more, ρ = (420/6) × 10 ⁶ Ω · mm ρ = 7 × 10 ⁶ Ω · cm or more. Similarly, preferably ρ = 7 × 10 ⁷ Ω · cm or more (R = 10 ⁷ Ω or more)
Is.

As can be seen from the above fact, in the developing device 100 shown in FIG. 1, the developing roller can be maintained so that the toner particles carried on the developing roller 4 can maintain the charging polarity pre-frictionally charged during the developing operation. If the specific resistance of the outer layer 24 of No. 4 is set to 7 × 10 ⁶ Ω · cm or more, a high quality visible image can be obtained for a long period of time.

In the above, the embodiment in which the toner carrier is configured as a developing roller and the latent image carrier is configured as a drum-shaped photosensitive member has been described. However, the toner carrier is configured as a sleeve or a belt, The present invention is also applicable when the latent image carrier is composed of a belt-shaped photoconductor, or a dielectric drum or a dielectric belt other than the photoconductor. Further, in a developing device other than the illustrated type, for example, a device that conveys magnetic toner on a toner carrier by using magnetic force, a developing device in which the toner carrier is separated from the latent image carrier, or an image forming apparatus such as a facsimile machine. It is widely applicable to developing devices and the like.

[0033]

According to the present invention, reversal development is made possible by a simple structure in which the specific resistance of the outer layer of the toner carrier is set so as to maintain the charge polarity of the toner particles, and a clear image is obtained. It became possible to obtain a visual image.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of an image forming apparatus having a developing device according to the present invention.

FIG. 2 is a schematic diagram illustrating a situation at the time of reversal development and a cause of a conventional defect.

FIG. 3 is a graph showing electric resistance characteristics of an outer layer of a developing roller used in an experiment.

FIG. 4 is an explanatory diagram showing a method for measuring an electric resistance value of each developing roller.

[Explanation of symbols]

 2 Toner 14 Conductor 24 Outer Layer 100 Developing Device T Toner Particles

Claims (1)

[Claims] 1. A latent image carrier comprising a toner carrier comprising a conductor and an outer layer located on the outer side of the conductor, the triboelectrified toner carried on the outer layer of the carrier. In a developing device that visualizes an electrostatic latent image, a voltage is applied to the conductor of the toner carrier in order to reverse develop the electrostatic latent image, and the toner particles carried on the toner carrier are pre-charged by friction. A developing device, wherein the specific resistance of the outer layer is set to 7 × 10 ⁶ Ω · cm or more so that the charging polarity can be maintained during the developing operation.