JPS6073647A - Image forming method - Google Patents

Abstract

PURPOSE:To compensate and control an image density level to a constant level precisely by controlling the duty ratio of an AC bias applied between a latent image holder and toner with which an electrostatic latent image of a copying machine is developed according to the remaining amount of the toner. CONSTITUTION:A sleeve 22 contacts the toner bank in a hopper 21 along its nearly right half circumferential surface all the time and rotates counterclockwise while leveling a layer of toner T with its incorporated magnet 23, and toner is supplied to the latent image in an area A whereas a gap alpha with the latent image holder 1 is held. Fine toner is attracted to the surface of the sleeve 22 preferentially. When coarse toner begins to be attracted as the toner is consumed, the toner T is electrostatically charged sufficiently and gradually. The remaining amount of the toner T is detected from the electrostatic capacity between an electrode 25 in the hopper 21 and the sleeve 22, and the duty ratio of the AC bias applied between the latent image holder and sleeve 22 is controlled according to the remaining amount. Consequently, the charging of the toner T is held invariably constant and an image having no density irregularity is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention forms an electrostatic latent image on a latent image carrier by an appropriate method such as electrophotography, electrostatic recording, or ion flow control method, and a high-resistance component is formed on the surface of the latent image. This invention relates to an improvement in an image forming method in which a latent image is visualized by applying a developer.

An impression development method (
Known methods include U.S. Pat.

Figure 1 shows an example of an apparatus for jumping development. latent image carriers such as photosensitive paper in electrofax method, electrostatic recording paper in direct electrostatic recording method, etc.
An electrostatic latent image is formed on that surface by a latent image forming process device or a process mechanism (not shown), and is moving in the direction of the arrow.

2 is the overall code of the developing device, and 21 is the high-resistance component developer T.
(hereinafter referred to as toner) is accommodated in the hopper; 22 is a rotating cylindrical body (hereinafter referred to as sleeve) as a developing member (developer layer supporting member);
3 is built-in. The sleeve 22 has its substantially right half circumferential surface exposed within the hopper 21 and its substantially left half circumferential surface exposed outside the hopper, supported by a bearing, and is driven to rotate in the direction of the arrow. Reference numeral 24 designates a dofter blade as a toner applying member disposed with the lower edge portion close to one surface of the sleeve 22, and 27 represents a stirring member for toner in the hopper.

The axis of the sleeve 22 is substantially parallel to the generatrix of the latent image holder 1, and the sleeve 22 faces the latent image holder 1 closely with a small gap α therebetween. The respective surface moving speeds (peripheral speeds) of the latent image holding member 1 and the sleeve 22 are approximately the same. Further, an alternating current voltage is applied between the latent image holding member l and the sleeve 22 by an alternating current voltage applying means S.

The substantially right half circumferential surface of the sleeve 22 is in constant contact with the toner pool in the hopper 21, and the toner near the sleeve surface forms a magnetic adhesion layer on the sleeve surface due to the magnetic force of the magnetism generating means 23 in the sleeve, and also generates static electricity. Adhesion is maintained by force.

When the sleeve 22 is rotationally driven, the toner layer adhering to the sleeve surface passes through the position of the doctor blade 23 and is layered into a thin toner layer T1 having approximately uniform thickness at each portion. The toner is charged mainly by frictional contact between the sleeve surface and the toner in the toner reservoir in the vicinity thereof as the sleeve 22 rotates.

As the sleeve rotates, the thin toner layer surface of the sleeve 22 rotates toward the surface of the latent image carrier 1 and passes through the development area A where the latent image carrier 1 and the sleeve 22 are closest. During this passing process, the toner in the thin toner layer on the side of the sleeve 22 is blown away by the AC electric field caused by the AC voltage applied between the latent image holding member 1 and the sleeve 22, and is caused to fly between the latent image holding member 1 side in the development area A and the sleeve 22 side. It moves back and forth between. Finally, the toner on the sleeve 22 side selectively migrates and adheres to the surface of the latent image holder according to the potential pattern of the latent image, resulting in a toner image T2.
are formed sequentially.

The sleeve surface, on which toner has been selectively consumed after passing through the development area A, is rotated again to the toner reservoir of the hopper 21 and is resupplied with toner. The layer T1 surface rotates.

By the way, one of the problems when adopting such a developing method is a phenomenon in which the developability changes over time due to preferential adhesion of small particle size toner to the surface of the sleeve 22 serving as a developing member.

That is, the particle size distribution of the toner T is distributed with a certain spread on the large diameter side and the small diameter side with the standard particle size as the center. Among them, the toner having a smaller particle diameter tends to electrostatically preferentially adhere to the surface of the sleeve 22 than the toner having a larger diameter. Therefore, when toner T is replenished into the hopper 21 and development is executed, for a while after that, the toner with a small particle size preferentially adheres to the surface of the sleeve 22, as shown in FIG. 2(a). In this state, the surface of the sleeve 22 is completely covered with the layer Ta of the small particle size toner. As a result, the toner Tb in the vicinity of the sleeve surface as the sleeve 22 rotates.
The opportunity for direct frictional contact with the surface of the sleeve 22 is reduced, and the amount of charge on the toner tends to be insufficient. Soshiso hopper 21
As the toner consumption progresses, the phenomenon of preferential adhesion of small particle size toner to the sleeve 22 surface tends to gradually weaken, and as shown in FIG. 2(b), the adhesion of small particle size toner to the sleeve 22 surface decreases. However, this increases the chance that the toner near the sleeve 22 surface, including those with small particle diameters and those with large flow diameter, will come into direct contact with the sleeve 22 surface,
Gradually, a sufficient amount of charge is ensured on the toner.

As a result, in response to the change in toner charge amount,
As shown in the graph of FIG. 3, the obtained image density is initially at a relatively low level, and as the copy integration progresses, the image density level gradually increases. That is, a phenomenon in which the developability changes over time occurs. This phenomenon of change in developability over time occurs in hopper 2.
This occurs repeatedly every time toner T is newly replenished within 1 hour.

An object of the present invention is to accurately compensate and control the image density level to a substantially constant level over a long period of time, regardless of the long-term and repetitively variable developability changes as described in Section 112.

That is, the present invention forms an electrostatic latent image on a latent image carrier.

In an image forming method in which the latent image is visualized by applying a high-resistance component developer to the latent image surface, the developing member and the latent image holder are It is characterized by controlling the duty ratio of the alternating current bias applied between the two.

Here, in the present invention, "duty ratio of AC bias (
dujy factorN is defined as shown below.

Duty ratio--' (x lOO) a+b a: Electric field component with a polarity in the direction of transferring the toner toward the latent image carrier in one cycle of an AC bias in which the electric field polarity changes periodically between positive and negative. (Transition electric field) application time or integral amount b: On the other hand, as an example of the application time or integral amount of the electric field component (reverse transition electric field) with a polarity in the direction that separates the toner from the latent image carrier side, the duty ratio is shown in Fig. 8 (a). Approximately 50% square wave AC, the same figure (b) shows approximately 75% duty ratio square wave AC,
Figure (c) shows an example of a sine wave AC in which the duty ratio is controlled to 50% or more by applying a DC bias and adjusting the OV level.

By the way, the principle of development when developing a latent image by applying an alternating current bias between the developing member 22 and the latent image holder 1 is that the latent image holder 1 in the development area A and the development field move back and forth. That is, when a transitional electric field is applied in the alternating electric field, the toner moves in a direction from the developing member 22 side to the latent image holding member l side and comes into contact with the surface of the latent image holding member, and conversely, when a reverse transitional electric field is applied, the toner is retained. The toner moves in the direction from the body 1 side to the developing member 22 side, and unnecessary toner returns to the developing member 22 side. This reciprocating and slow movement of the toner is repeated in response to the alternation of the electric field.
Finally, the toner is selectively transferred and adhered to the surface of the latent image holder according to the latent image potential pattern of the core portion, and a toner image with no fog and good gradation is formed.

This principle is described in the Journal of the Society of Electrophotography, Vol. 20, No. 1 (1)
This is reported in ``Developing mechanism of jumping developing method'' published in 981).

In order for the latent image to be sufficiently developed in this type of development method, the toner itself must have sufficient charge while the latent image surface passes through the development area A. It is necessary that sufficient contact with the toner be made. That is, within the time required for the latent image to pass through the development area, it is necessary to ensure the number of times of contact with the toner necessary for the latent image to be sufficiently developed.

One method is to increase the frequency of the AC bias in order to increase the number of times the toner contacts the latent image surface, but as the frequency increases, a reverse transition electric field is applied before the toner is in sufficient contact with the latent image surface. Developability deteriorates and there is a limit.

On the other hand, in order for the toner to sufficiently reach the latent image surface by the alternating current bias, acceleration a must be applied to the toner, and the force f is given by f=msa, where the weight of the toner is m. Letting the charge of the toner be q, the ability of the toner to reach the latent image surface is determined.

If the application time of the electric field E is long within the development area A, the force f of the toner reaching the latent image surface increases due to the force f that is stronger than the initial force, and conversely, if the application time is short, the force decreases. In other words, f correlates with the duty ratio of the AC bias, and by changing the duty ratio, the developing ability of the apparatus can be controlled.

As a result of actual experiments, it was found that the latent image holding body 1 and the developing member 22
It was confirmed that there is a correlation between the duty ratio of the alternating current bias applied between the two and the image density as shown in the graph example in FIG.

Therefore, the present invention utilizes the dependence of the image density on the duty ratio of the alternating current bias (FIG. 4), and utilizes the phenomenon of change in developability over time based on the preferential adhesion of the small-particle developer to the developing member 22 (Fig. 4). (Fig. 3), that is, the frequency of the AC bias applied between the latent image holding member l and the developing member 22 is controlled over time in response to the change in developability over time by detecting the change over time. The image density level is maintained substantially constant throughout.

The change in developability as shown in the example in FIG. 3 based on the preferential adhesion of small-particle developer to the developing member 22 approximately corresponds to the decrease in toner T in the hopper 21 as it is consumed. By detecting the amount of toner remaining in the toner 21, it is possible to approximately know the developing performance at that point.

There are various possible means for detecting the amount of toner remaining in the hopper 21, including mechanical, electrical, and optical.

FIG. 1 shows an example of an electrical detection means, in which an electrode plate 25 is disposed opposite to the sleeve 22 on the inside of the hopper wall on the opposite side to the side on which the sleeve 22 as a developing member is disposed. Toner T exists between the sleeve 22 and the electrode plate 25,
As the toner T in the hopper 21 is consumed, the amount of toner decreases.

The AC bias applied to the sleeve 22 as a developing member is detected by the electrode plate 25 via the toner present between the sleeve 22 and the electrode plate 2.5. In this case, the sleeve 22 and the electrode plate 25 form a capacitor with toner between them, the capacitance of which depends on the amount of toner present between the sleeve 22 and the electrode plate 25, and the voltage induced in the electrode plate 25 is approximately The graph will look like the example in Figure 5. That is, the absolute value of the induced voltage varies depending on the applied AC voltage, frequency, type of toner, shape of the electrode plate, etc., and changes depending on the amount of toner. Conversely, from the induced voltage value of the electrode plate 25, the change in the induced voltage of the electrode plate 25 (i.e., the change in the remaining amount of toner in the hopper) is detected from the inside of the hopper 21 to the hopper 1. 26a, a comparator circuit 26b, a plurality of switching circuits 26c, etc., is introduced into the rectifier/smoothing circuit 26a of the circuit 26, and is led through the circuit to the comparator circuit 26b, and the switching circuit 26c is operated according to the output voltage to generate an alternating current. The duty ratio of the output end-stream bias of the voltage applying means S is controlled in stages (in three stages in this example circuit) in a direction that compensates for the aging change in developability shown in FIG.

The duty ratio of the AC bias can be changed and controlled by means such as changing the pulse width, converting the waveform, and superimposing the DC bias.

For example, if the AC bias applied to the sleeve is standard AC,
When using rectangular wave alternating current of 800Hz-1200V p P (maximum amplitude), Toner remaining amount Rectangular wave alternating current control duty ratio 1st stage control 200-140g 80%2 2nd stage control 140-100 60% Three-stage control 100-60 50% control.

This makes it possible to maintain the image density level at a constant level from beginning to end over a long period of time, regardless of the phenomenon of changes in developability over time due to preferential adhesion of small-particle developer to the developing member 22, as shown in the graph example in FIG. can.

As described above, the effect of controlling the development characteristics according to the present invention is extremely excellent, and by increasing the number of control steps to more than the three steps of the embodiment, even more precise control becomes possible.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of an example of a developing device, Figure 2 (a) is a schematic diagram showing a state in which the surface of the developing member is covered with a layer of small particle size developer, and Figure 2 (b) is a schematic view of the small particle size developer layer. Figure 3 is a graph showing the change in developability over time; Figure 4 is a graph showing the relationship between AC bias duty ratio and image density; Figure 5 is a graph showing the toner remaining in the hopper. Figure 6 is an example of a control circuit, Figure 7 is a graph of development characteristics obtained by control, and Figure 8 (a).
(b) and (C) are examples of various AC biases with different duty ratios. 1 is a latent image holding member, 2 is a developing device, 21 is a toner hopper,
22 is a rotating sleeve as a developing member, and 25 is an electrode plate. G ←Xg'l? Eikoshi 6 ←Fly Angry Story - Ichinaki Ichinzaki - Ya -3

Claims (1)

[Claims] (1) In an image forming method in which an electrostatic latent image is created on the latent image holding member J, and a high-resistance component developer is applied to the latent image surface to visualize the latent image. An image forming method comprising controlling a duty ratio of an alternating current bias applied between a developing member and a latent image holder according to the remaining amount of developer.