JPH0214706B2 - - Google Patents

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 with 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 larger than the thickness of the developer thin layer, and the development gap is A developing method is known from Japanese Patent Publication No. 58-32375, in which development is carried out by continuously forming alternating electric fields and repeating transfer and reverse transfer of the developer. According to this developing method, a good image with no background fog, excellent gradation, and no thinning of fine lines can be obtained. A curve of the image density D after development with respect to the surface potential (latent image potential) V on the latent image holding member by this developing method is generally a curve like that shown in FIG. 1A.

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 in the development gap in the development section, then b in Figure 1.
It was found that a V-D curve as shown in FIG. This differs from the general V-D curve a mentioned earlier, in that the development is abnormally accelerated in the intermediate potential area B, and γ (the slope of image density with respect to the latent image potential) increases, and the image density in the high potential area A increases. This is a characteristic in which D decreases (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 phenomenon can be improved to some extent by lowering the frequency of the applied alternating electric field, but lowering the frequency has the disadvantage that background fog is more likely to occur.

The object of the present invention is to overcome the above-mentioned conventional drawbacks and to
It is an object of the present invention to provide a developing method that prevents the occurrence of negative characteristics and background fog that appears in reproduced images during the developing process.

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 the latent image retaining member and the final component of the intermittent alternating electric field, that is, the component immediately before entering the rest period, is formed by an electric field component that pulls the developer from the latent image retaining member to the developer retaining member. This is a developing method in which development is performed using Therefore, according to the present invention, negative characteristics can be prevented and a reproduced image faithful to the original image and free from background fog 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 That is, the developer repeats reciprocating motion in response to the frequency of the developing bias, but when a high frequency bias is applied, the developer cannot respond to changes in the bias and tends to form a powder cloud state. Particularly in the area A where the potential is high, a type of electric field curtain is formed within the development area in the gap between the latent image holding member and the developer holding member, which allows the developer to reciprocate over a relatively wide width. It is thought that the developer is sealed and difficult to escape from outside the curtain, so that cloud formation is less likely. It is thought that in the portion B where the potential is low, the confining force of the electric field curtain described above is weak, and the developer is likely to separate from this curtain, resulting in a large number of cloud formations. When we actually apply an alternating electric field during copying and observe the width of the development area, we find that the development width is wider in area B than in area A where the potential is high and area B where the potential is low.
This is the area where development was performed due to cloud formation as described above. In terms of image quality, the edge effect peculiar to cloud development is noticeable in the B portion.
It is considered that in the potential region C, which is higher than that in the A region, the phenomenon in the A region continues, and the image density increases depending on the latent image potential.

As a result, in the intermediate potential area shown in B in Figure 1, the area to be developed, that is, the development width, is expanded and a developed image with high density is obtained, but in the high potential area A, the influence of the electric field curtain is suppressed. It is thought that the image density decreases as a result. According to experiments,
When a direct current or a low frequency bias with sufficient frequency response was used as the developing bias, no negative characteristics occurred.

In order to prevent negative phenomena from occurring due to 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, the following experiment was conducted. I went. A latent image with a dark potential of -650V and a bright potential of -150V is formed on a latent image holding member using an organic semiconductor as a photoreceptor, and a positively charged developer is used to separate the latent image carrying member and the developer carrying member. An intermittent alternating electric field shown in FIG. 2 was applied to opposing development areas. Since the developer has positive polarity and the potential of the latent image has negative polarity, the alternating electric field starts from process D of the electric field component that pulls the developer from the latent image bearing member toward the developer bearing member, and the developer is drawn back to the developer bearing 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 is improved compared to when a continuous alternating electric field is applied, but further improvements are desired in preventing fog and increasing density.

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. This is believed to be because the toner tends to be in a floating state at time _t1 , causing background fog, and the formation of floating toner 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 intermittent alternating electric fields, the negative phenomena are significantly improved,
Furthermore, an image with excellent gradation and no fogging can be obtained.

In such an alternating electric field, the developer leaves the developer carrying member and flies toward the latent image carrying 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 when the toner is pulled back to the developer carrying member, a state in which there is no floating toner in the development gap is created.
In the next development process, the developer can easily fly without being affected by floating toner.

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 background fog occur. 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. As a result, the amount of toner floating in space is reduced and the number of times the developer moves back and forth, thereby improving the negative phenomenon.

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 less likely to occur between the latent image holding member and the developer carrying member, which prevents rotation of the latent image holding member. It is also possible to reduce the scattering of the developer into the image forming apparatus due to the accompanying airflow.

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 3, the latent image is visualized by a developing device 4. Thereafter, the visible image on the latent image holding member is transferred onto a transfer material 6 such as paper by a transfer charger 5, 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. Magnetic particles 9 in developer container 8
is attracted to the surface of the sleeve by the magnetic force of a magnet roller 11 included in the sleeve 10, which is a developer holding member, and is conveyed by rotation of the sleeve 10 in the direction of arrow b. Transported magnetic particles 9
The developer container 8 is controlled by the regulating blade 12 made of a magnetic material and the magnetic force of 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, on the sleeve 10, only the non-magnetic toner 13 that has adhered to the sleeve surface due to the influence is uniformly applied in a thin layer, and this non-magnetic toner 13 is conveyed on the sleeve in the direction of arrow b to form a latent image. It is subjected to development in a developing section facing the holding member 1. On the other hand, magnetic particles 9 circulating in the direction of arrow C
takes in the non-magnetic toner 13 during this circulation, and the above-mentioned circulation is repeated. Regarding this method of applying a thin layer of non-magnetic toner, see Japanese Patent Application No. 58-73213 (Japanese Unexamined Patent Application Publication No. 1984-198477) filed by the applicant.
Since I am familiar with this, I will omit the detailed explanation.

In the figure, reference numeral 14 denotes a sealing member made of a magnetic material, which prevents leakage of magnetic particles to the outside of the developer container 8 by the magnetic force of the magnetic pole S of the magnet roller 11 and this sealing member. Further, 15 is a bias power supply for applying a developing bias voltage to the sleeve 10.

In the sleeve 10 of such a developing device 4, a third
A developing bias having a waveform as shown in the figure was applied from the bias power supply 15. 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, and has a developing bias frequency of 1.5 KHz, peak to peak value
1.6 KVp-p, with a DC component of -350 V superimposed thereon, was applied to the sleeve 10 one wavelength at a time with a pause time _t1 of 1.3 msec, as shown in FIG. At this time, the dark area surface potential of the latent image holding member is V _D = -650V, and the bright area potential is
V _L was set to −150V. The developer used was an insulating non-magnetic toner that was positively charged by friction with the sleeve or magnetic particles.

When images were produced under the above conditions, the negative characteristics shown in FIG. 1b almost disappeared, and a VD curve characteristic similar to that shown in FIG. 1a was 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 terminating 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.
Also, the ratio of bias application time to pause time is 1:1/
Favorable results were obtained when the ratio was 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. Furthermore, in a device 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, shading may occur in the developed image. This problem can also be solved by applying this embodiment.

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 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 to the latent image holding member. Since the electric field component is drawn back to the developer holding member, the occurrence of negative characteristics can be improved or prevented, and image quality problems such as a decrease in density and background fog that occur when the frequency is lowered can be improved. It was also possible to prevent the decline.

[Brief explanation of drawings]

Figure 1 shows a normal V-D curve and a V-D curve showing negative characteristics.
- D curve graph, Figure 2 is a waveform diagram of a conventional developing bias voltage, Figure 4 is a schematic diagram of a copying machine showing an embodiment of the present invention, Figures 3, 5, and 6 are FIG. 3 is a waveform diagram of a developing bias voltage showing an example of the 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 regulation blade, 13 is a non-magnetic toner, and 14 is a seal Element,
15 represents a bias power supply.

Claims (1)

[Scope of Claims] 1. 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, in which the developer holding member and the latent image holding member are A latent image is developed by a developing process that alternately repeats a first period in which an alternating electric field is formed and a second period in which formation of an alternating electric field is stopped, and the final component of the alternating electric field in the first period is transferred to a developer. A developing method characterized in that an electric field is formed by an electric field component that pulls the latent image back from the latent image holding member to the development holding member. 2 The ratio of the first period to the second period is 1:1/2 to 1:10
A developing method according to claim 1.