JPS60134262A - Developing method - Google Patents

Abstract

PURPOSE:To prevent generation of a negative characteristic and to prevent decrease in density and ground fogging when a frequency decreases by impressing intermittently alternating electric fields between a latent image holding member and a developer holding member so that the final component is formed of the electric field component returning the developer from the former member to the latter member. CONSTITUTION:The developing bias having such a waveform as shown in the figure is impressed to the sleeve of a developing device 4 from a bias power source 15. When the alternating electric fields reversing the developer moving process by intermittent alternating electric fields are intermittently impressed between a developer holding member 10 and a latent image holding member 1, the negative development is remarkably improved under the intermittent alternating electric field which ends in the process of returning the developer from the member 1 to the member 10 side and the fog-free image having an excellent gradation characteristic is obtd. Magnetic particles 9 are stuck to the surface of the member 10 by the magnetic force of a magnetic roller 11 enclosed in the member 10 and are conveyed by the rotation of the member 10 in an arrow direction (b) and are supplied to the member 1. The latent image of the member 1 is thus developed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing method, and more specifically to a developing device that holds developer on the surface of a developer holding member and conveys the developer to a position facing the latent image holding member to perform development. This invention relates to a developing method that is an improved method of applying a developing bias.

Conventionally, a developer holding member having a thin layer of dry developer formed on its surface and a latent image holding member are opposed to each other in a developing section with a development gap that is large depending on the thickness of the thin developer layer. A developing method in which development is carried out by continuously forming an alternating electric field and repeating the transfer and reverse transfer of the developer was disclosed in Japanese Patent Publication No. 58-
It is known from the publication No. 32575. According to this developing method, it is possible to obtain a good image with no background blur, excellent gradation properties, and no thinning of fine lines. The curve of the image density after development against the surface potential (latent image potential) (2) on the latent image holding member by this developing method is generally a curve as shown in FIG. 1(a).

However, if a thin layer of non-magnetic developer is applied onto the developer holding member and development is performed by continuously forming an alternating electric field during development in the developing section, the result will be as shown in (b)K in Figure 1. V
-D curve was found to be obtained. This is different from the general V-D curve (a) mentioned above, and development is abnormally accelerated at the intermediate potential part B, resulting in γ (the slope of image density with respect to latent image potential).
becomes high, and the image density decreases in the high potential area A (hereinafter, this characteristic will be referred to as a negative characteristic).

In this case, the image density of the solid black part becomes lower than the image density of the halftone part, and this is not practical. This negative current i can be improved to some extent by lowering the frequency of the applied alternating electric field, but there is a drawback that lowering the frequency makes it easier for soil burrs to occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing method that eliminates the above-mentioned conventional drawbacks and prevents the occurrence of negative characteristics during the developing process that appears in reproduced images.

To achieve the above object, the present invention provides a developing method in which developer is held on the surface of a developer holding member and developed by conveying the developer to a position facing the latent image holding member. An alternating electric field is applied intermittently between
This is a developing method in which development is performed by forming an electric field component that draws the developer from the latent image holding member back to the developer holding member. Therefore, according to the present invention, negative characteristics can be prevented and a reproduced image that is faithful to the original image and free from blurring can be obtained.

The above-mentioned negative characteristics occur as a result of the developer forming a powder cloud when an alternating electric field is formed in the development gap to cause reciprocating motion of the non-magnetic developer, and as a result of specific development of the powder cloud-formed developer. It is estimated that In other words, the developer repeats reciprocating movement in response to the frequency of the development voltage (earth), but when a high-frequency bias is applied, the developer cannot respond to changes in the voltage (earth) and tends to form a powder cloud state.Especially when the potential In the high part A, the internal pressure of the developing area in the gap between the latent image holding member and the developer holding member is relatively wide (a type of electric field curtain capable of reciprocating the developer is formed, and within this curtain the developer is Since the developer is contained and escapes from the curtain, it is thought that cloud formation is rare.In the area B where the potential is low, the width of the electric field curtain described above is narrow, and the developer is likely to escape from this curtain, causing the cloud to form. It is thought that this occurs frequently.When actually applying an alternating electric field during copying and observing the width of the development area, it was found that the width of the developing area is larger than A in areas A where the potential is higher and areas B where the potential is lower.
The development width is wider in the area, and this is the development area where clouds are generated as described above. B in image quality
In some areas, the edge effect unique to cloud development becomes noticeable. Furthermore, in the potential region C higher than the A part, the A
It is considered that the phenomenon in the area continues and the image density increases depending on the latent image potential.

As a result, in the intermediate potential area indicated by BK in Figure 1, the area to be developed, that is, the development width, is widened and a developed image with high density is obtained, but in the high potential area A, it is affected by the electric field curtain described above. It is thought that the image density will decrease. According to experiments, negative characteristics did not occur when a direct current or a low frequency bias with sufficient frequency response was used as the developing bias.

The following experiment was conducted to confirm that a negative phenomenon occurs under the influence of the electric field curtain caused by the powder cloud-like developer formed between the latent image holding member and the developer holding member described above. went. A dark area potential of -650V and a light area potential of -150V are applied to an imageless holding member using an organic semiconductor as a photoreceptor.
A latent image of V is formed, and a second developing area is formed where the latent image carrying member and the developer carrying member face each other using a positively charged developer.
The intermittent alternating electric field shown in the figure was applied. Since the developer has a positive polarity and the potential of the latent image has a negative polarity, the alternating electric field starts from the process of the electric field component pulling the developer from the latent image bearing member toward the developer carrying member, and then the developer is drawn back to the developer carrying member. The developer is caused to move in a pattern that ends in a step E in which the developer is released and flies. When such an intermittent alternating electric field is applied, the above-mentioned negative phenomenon becomes more pronounced than when a continuous alternating electric field is applied, and capri is more likely to occur.

This is because the intermittent alternating electric field ends in the process of causing the developer to fly away toward the developer carrying member, so the powder cloud-like developer existing between the latent image carrying member and the developer carrying member stops being exposed to the alternating electric field. It is easy to be in a floating state at time t1,
This is thought to be due to the fact that ground force precipitates occur and an electric field curtain is formed, which obstructs the developer from flying to the latent image bearing member in the next developer transfer process.

On the other hand, when the alternating electric field shown in FIG. 3, which is the reverse of the developer movement process caused by the intermittent alternating electric field, is applied intermittently, the process ends when the developer is pulled back from the latent image carrying member to the developer carrying member. Under an intermittent alternating electric field, negative phenomena are significantly improved, and images with excellent gradation without fogging can be obtained.

In such an alternating electric field, the developer leaves the developer carrying member and flies toward the latent image holding member due to the positive alternating current component (development process bias), reaches the latent image holding member, and is used for development. be done. Some of the flying developer cannot reach the latent image surface due to the amount of charge and development time (bias application time), etc., and becomes a floating state. However, due to the bias during the next reversal process, the floating developer is reactivated. During the rest time between the intermittent and alternating electric fields, the developer is drawn back to the developer carrier member, and a state where there is no floating toner in the development gap is created, so in the next development process the developer is not affected by the electric field curtain and is easily removed. It becomes possible to fly.

The negative phenomenon can be improved by simply reducing the frequency of the developing bias, but in this case, a decrease in image density and a tendency to form are caused. Therefore, in the present invention, an alternating electric field is applied intermittently so that development is completed in the process of pulling the developer back from the latent image bearing member, while taking advantage of the high-frequency development bias to prevent fogging and density reduction.
This is intended to reduce the amount of toner floating in space and reduce the number of times the developer travels back and forth, thereby improving negative phenomena.

Furthermore, since the alternating electric field enters a resting state in the process of pulling the developer back toward the developer carrying member, floating developer is generated between the latent image holding member and the developer carrying member, and K<<, the rotation of the latent image holding member is It is also possible to reduce the scattering of the developer into the image forming apparatus due to the airflow caused by the movement.

FIG. 4 is a schematic diagram of a copying apparatus to which the present invention is applied, in which a latent image holding member 1 having a photoconductive layer rotates in the direction of arrow a, and after being uniformly charged by a corona charger 2, it is attached to an original. After receiving a corresponding image exposure 6, the latent image is visualized by a developing device 4. Thereafter, the visible image on the latent image holding member is transferred to the transfer charger 5.
The image is transferred onto a transfer material 6 such as paper, and fixed onto the transfer material by a fixing device (not shown). Further, the latent image holding member after the transfer is cleaned by a cleaning device 7.

Here, the developing device 4, which is the main part of the present invention, will be described in detail. The magnetic particles 9 in the developer container 8 are attracted to the surface of the sleeve by the magnetic force of a magnet roller 11 included in the sleeve 1o, which is a developer holding member, and are transported by the rotation of the sleeve 10 in the direction indicated by the arrow. The conveyed magnetic particles 9 are moved to the developer container 8 by the magnetic force of the regulating blade 12 made of a magnetic material and the magnetic pole N of the magnet roller 11.
It is prevented from leaking out and is pushed back in the direction of arrow C by gravity. Therefore, the sleeve ioJ:< means that only the non-magnetic toner 16 that adheres to the sleeve surface due to the influence force is uniformly applied in a thin layer, and this non-magnetic toner 16 is conveyed on the sleeve in the direction of the arrow to the latent image holding member. It is subjected to development in a developing section opposite to 1. On the other hand, the magnetic particles 9 circulating in the direction of arrow C take in the non-magnetic toner 13 during this circulation, and the above-mentioned circulation is repeated. Regarding the method of applying a thin layer of non-magnetic toner, a patent application filed in 1983 by the applicant of the present invention is disclosed.
No. 75251 provides details, so a detailed explanation will be omitted.

In the figure, reference numeral 14 denotes a sealing member made of a magnetic material, and the magnetic force of the magnetic pole S of the magnet roller 11 and this sealing member prevent magnetic particles from leaking out of the developer container 8. Also, 15
is a bias power supply for applying a developing bias voltage to the sleeve 10.

A developing bias having a waveform as shown in FIG. 6 was applied from the bias power supply 15 to the sleeve 10 of the developing section f4. The bias power supply 14 consists of an oscillator that generates a sinusoidal alternating current, a modulator that generates pulses intermittently, an amplifier that increases the amplitude, and a DC superimposition circuit.
The characteristics of the developing bias are frequency 1.5fG (z, peak-to-peak value 1,6 KVp-p, ?knee V
C - DC component - 350V superimposed as shown in Figure 6 <1
, 3 m5 ec, with a pause time t1, to the sleeve 10 one wavelength at a time. At this time, the dark area surface potential of the latent image holding member is Vo = -650V, and the bright area potential VL = -150V.
K was set. The developer used was an insulating non-magnetic toner that was positively charged by friction with the sleeve or magnetic particles.

When the image was taken under the above conditions, the result was as shown in Figure 1(b).
The negative characteristic shown by K almost disappears, and as shown in Fig. 1(a), V near K
-D curve characteristics were obtained.

In addition, in this embodiment, since the case where a positive polarity toner is used for a negative polarity latent image is given as an example, the alternating current component of the intermittent alternating electric field ends with a negative value and enters the rest period, but the positive polarity latent image In the case of developing using a negative polarity toner, the polarity of the above-mentioned finishing component is reversed and made positive, thereby improving the negative phenomenon.

As a modification of the present invention, two wavelengths may be applied and one wavelength is paused as shown in FIG. 5, and various application methods such as a rectangular wave or a triangular wave as shown in FIG. 6 may be applied. The most appropriate application method can be selected depending on the copying speed and development conditions. Further, favorable results were obtained when the ratio of bias application time to rest time was 1:1/2 to 1:10.

The developing device is not limited to the embodiment shown in FIG. 4, and the present invention can be applied to any developing device that generates negative characteristics when a continuous alternating electric field is applied. Similarly, in this embodiment, an example of non-magnetic toner is shown, but magnetic toner can also be applied to a developing device exhibiting negative characteristics. In addition, in an apparatus that uses magnetic toner and performs development by arranging development magnetic poles, if the magnetic flux density in the longitudinal direction of the magnet roll is uneven, a developed image K1l1 may appear pale. The drawbacks can also be solved by applying this embodiment.

Note that the present invention is also effective in a developing method using a so-called two-component developer containing a magnetic carrier and a toner.

As described above, in the VC1 of the present invention, an alternating electric field is intermittently applied to the development gap where the latent image holding member and the developer holding member face each other, and the final component of the intermittent alternating electric field is used to transfer the developer from the latent image holding member. Since the electric field component is drawn back to the developer holding member, it is possible to improve or prevent the occurrence of negative characteristics, and to reduce image quality such as a decrease in density and the occurrence of ground force precipitates that occur when the frequency is lowered. It was also possible to prevent the decline.

[Brief explanation of the drawing]

Figure 1 is a graph of a normal V-D curve and ■-D curve showing negative characteristics, Figure 2 is a waveform diagram of a conventional developing bias voltage,
FIG. 4 is a schematic diagram of a copying machine showing an embodiment of the present invention;
5 and 6 are waveform diagrams of developing bias voltages showing embodiments of the present invention. In the figure, 1 is a latent image holding member, 4 is a developing device, 8 is a developer container, 9 is a magnetic particle, 10 is a sleeve, 11 is a magnet roller, 12 is a regulating blade, 16 is a non-magnetic toner, and 14 is a sealing member. , 15 represents a bias power supply. Applicant Canon Co., Ltd.

Claims (1)

[Claims] In a developing method in which developer is held on the surface of a developer holding member and developed by being conveyed to a position facing the latent image holding member,
An alternating electric field is intermittently applied between the developer holding member and the latent image holding member, and the final component of the intermittent alternating electric field is formed by an electric field component that draws the developer from the latent image holding member back to the development holding member. A developing method characterized by performing development.