JPH0152747B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing method, and particularly to a developing method that is fog-free and has excellent gradation.

Conventionally, two-component development method and one-component development method are known as dry development methods for visualizing electrostatic latent images, but compared to the former, the latter develops images due to fluctuations in the mixing ratio of developer components. It is attracting attention as a promising developing method because there is no change in density and the developing device is simple and compact.

As described in Japanese Patent Publication No. 41-9475, etc., the one-component development method maintains a gap where the developer on the developer support cannot come into contact with both the image area and the non-image area of the electrostatic image. A jumping development method is known in which the developer is caused to fly from above the developer support by electric lines of force formed by the developer.

However, the reason why this jumping development method has not been put to practical use until now is that the developer is caused to fly by the electric field formed between the developer support and the electrostatic image carrier, so it is necessary to Furthermore, it is necessary to maintain uniform separation of the developer from the developer support, and there is a threshold value of the electric field at which the developer starts to fly away from the developer support surface. This is thought to be because the problems of poor reproducibility, weak lines of electric force, and thinning due to development of line images have not been solved.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a developing method with less fog in non-image areas and with excellent gradation reproducibility and line image reproducibility.

The developing method of the present invention that achieves the above object is a non-contact development method in which the developing gap between the electrostatic image carrier and the developer support is larger than the thickness of the developer layer supplied onto the developer support. In the method, the developer is substantially spherical and triboelectrically charged toner particles, and the developing agent is used to form an electric field that repeatedly attaches and detaches the toner particles to and from the electrostatic image carrier during the developing process. This is a developing method in which an electrostatic image is developed by applying a periodically changing voltage to a developer support and the friction-charged spherical toner particles detached from the developer support. In a non-contact development method in which the distance between the development agent and the developer support is greater than the thickness of the developer layer supplied onto the developer support, the developer coats the resin core material with a resin shell material that is triboelectrically charged. The spherical microcapsule toner particles have a structure in which a voltage that changes periodically on the developer support is provided to form an electric field that repeatedly attaches and detaches the toner particles to and from the electrostatic image carrier during the development. This is a developing method in which an electrostatic image is developed using the triboelectrically charged toner particles that are released from the developer support.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an apparatus for carrying out a developing method according to the present invention will be described in detail with reference to the drawings.

1 and 2 illustrate the principle of the method of the present invention. In both figures, 1 is a well-known latent image carrier such as a photoconductive layer having a back electrode, and a latent image due to electrostatic charge is formed on the surface by a well-known process such as corona discharge or irradiation with a light image of an original. Ru.

2 is a developer support, and it is possible to use magnetic force (a fixed magnet 4 is shown as a magnetic field generating means in the figure) as a means for holding the one-component developer 3, and it is also possible to use electrostatic force, gravity, etc. It can also be used as a holding force. 5 is a non-magnetic material having a magnetic field generating means 4 on the back side, and here, the developer 3 is a one-component magnetic developer containing magnetic powder, and is substantially spherical. .

6 is an AC power source that applies an alternating voltage to the developer support. By applying this AC voltage, the second
As shown in a and b, the developer 3 makes a reciprocating flying motion in the gap between the developer support 2 and the image carrier 1.
53-92105-108, etc.).

When no alternating current voltage is applied, the image carrier 1 having a surface potential above the electric field threshold at which the developer 3 starts to detach from the surface of the developer support 5 will have approximately the same amount of developer attached. The gradation reproducibility of the developed image deteriorates. A developing mechanism using an alternating electric field is, for example, as described in Japanese Patent Application No. 53-92105.
There is a transfer step (FIG. 2a) in which the developer 3 flies from the developer support 2 to the image carrier 1, and a reverse transfer step (reverse transfer step) in which the developer 3 returns from the image carrier 1 to the developer support 2. It consists of Figure 2 b).

This is because the jumping phenomenon occurs in the developer group, so by repeating the above-mentioned transfer and counter-transfer steps, the gradation reproducibility is improved as shown in FIG. 3. In the figure, the horizontal axis shows the surface potential on the electrostatic image carrier, and the vertical axis shows the amount of developer transferred.
A solid line a represents a transition step, and a broken line b represents a reverse transition step. Therefore, the amount of developer transferred onto the image bearing member after the completion of the transfer/reverse transfer step has good gradation properties in which the slope of γ changes gently and linearly, as shown by the dashed line c.

Experimental results in which such an effect clearly appeared are shown in FIGS. 4A and 4B. This is a measurement of the image reflection density D with respect to the electrostatic image potential V, and a plot of the experimental results is shown. Hereinafter, this curve will be referred to as a V-D curve. The experiment was conducted under the following configuration (see Figure 5). A positive electrostatic latent image is formed on the cylindrical electrostatic imaging surface. A magnetic toner (30% magnetite content), which will be described later, is used as the toner, and is applied to a layer thickness of about 60 μm on the magnetic sleeve, and the friction between the toner and the sleeve surface imparts a negative charge to the toner. . The results obtained when the minimum development gap between the electrostatic image forming surface and the magnetic sleeve is maintained at 100μ are shown in the fourth section.
Figure a shows the results when the same value was maintained at 300μ, and Figure 4b shows the results. The magnetic flux density in the developing section due to the magnet contained in the sleeve is approximately 700 Gauss. The cylindrical electrostatic imaging surface and the sleeve rotate at approximately the same speed, approximately 110 mm/sec. Therefore, the electrostatic image forming surface gradually moves away from the toner support after passing through the minimum gap in the development station. The alternating electric field applied to this sleeve is a sine wave with an amplitude of 400V (800V peak-to-peak) and a DC voltage +
200V is superimposed. Figures 4a and b show that the alternating frequencies of this applied voltage are 100Hz, 400Hz, 800Hz,
The V-D curves in the case of 1 KHz and 2 KHz, and the V-D curve in the case where no external electric field is applied and the back electrode of the electrostatic image forming surface and the sleeve are electrically connected are shown.

These results show that when no external electric field is applied, the slope of the V-D curve, the so-called γ value, is very large, but by applying a low-frequency alternating electric field,
It can be seen that the γ value becomes smaller and the gradation becomes extremely high. As the frequency of the external electric field is increased, the γ value gradually increases, and the effect of tightening the gradation from high to high fades.When the gap is 100μ, the effect becomes extremely weak when the frequency exceeds 1KHz, and when the gap is 300μ, the effect becomes extremely weak.
In the case of , the effect decreases when the frequency becomes around 800Hz, and becomes extremely weak when the frequency exceeds 1KHz. The reason for this is thought to be as follows. When toner repeatedly adheres and detaches between the sleeve surface and the latent image forming surface during the developing process where an alternating electric field is applied,
A finite amount of time is required to reliably perform the reciprocating motion. In particular, toner that transfers when subjected to a weak electric field requires a long time to ensure the transfer. On the other hand, in order to reproduce halftone density, it is necessary that toner subjected to an electric field of a certain threshold value or more is transferred reliably within a half period of the alternating electric field even if the electric field is weak. For this purpose, it is advantageous to have a low frequency of the alternating electric field, and therefore, as shown in the experimental results, particularly good gradation can be obtained with an alternating electric field of a very low frequency. The validity of this argument can be obtained from a comparison of the experimental results shown in Figures 4A and 4B. The results shown in FIG. 4B were conducted under the same conditions as the experiment shown in FIG. 4A, except that the gap between the electrostatic image forming surface and the sleeve surface was increased to 300 μm. When the gap is widened, the electric field strength to which the toner is exposed decreases, and therefore the toner transfer speed decreases. Furthermore, since the flight distance becomes longer, the transfer time becomes longer. In fact, as shown in Figure 4B, γ at about 800Hz
The value becomes considerably large, and when it exceeds 1 KHz, it becomes equivalent to the γ value when almost no alternating voltage is applied. Therefore, in order to produce the same effect as when the gap is narrow in terms of gradation improvement, it is preferable to further lower the frequency or increase the intensity of the alternating voltage.

On the other hand, if the frequency is too low, the reciprocating motion of the toner will not be repeated sufficiently while the latent image forming surface passes through the developing section, and the image will tend to develop unevenly due to the alternating voltage. 40Hz
Until then, generally good images were obtained, but below that, unevenness appeared in the visible images. It has been found that the lower limit of the frequency for preventing unevenness in the microscopic image depends on the development conditions, especially the development speed (also called process speed, Vp (mm/sec)). Since the moving speed of the electromagnetic image forming surface was 110 mm/sec, the lower frequency limit was 40/1
10×Vp0.3×Vp. It has been confirmed that any waveform of the applied alternating voltage, such as a sine wave, a rectangular sawtooth wave, or an asymmetric wave thereof, is effective.

In this way, applying alternate biases has a remarkable effect on improving gradation.

In addition, when the developer adheres to the electrostatic latent image in the transfer step, it is captured by the peripheral electric field (edge effect) and is difficult to reversely transfer to the toner carrier in the reverse transfer step, resulting in a sharp line image. can be maintained.

However, when setting the above-mentioned alternating voltage value, the jumping threshold at the set gap becomes a problem, but this threshold does not have an accurate value depending on the amount of charge of the developer, Van der Waals force, etc. Has a threshold width. Therefore, during the reverse transfer step, the developer attached to the non-image area may not be sufficiently transferred due to Van der Waals force or the like, resulting in so-called fog.

The present invention focuses on this point and solves the problem by using spherical particles as a developer. This is because the spherical developer has good fluidity, can be triboelectrified well on the developer support, has a uniform charge, and has a good bond between the particles and the developer support and between the particles and the image carrier. Because there are few contact points, non-uniform forces such as van der Waals forces are difficult to act on, and the developer is released uniformly from the support body during the transfer step and from the image carrier during the reverse transfer step. This process is easily carried out, and development with good gradation reproducibility with extremely little developer adhesion in non-image areas can be obtained.

Examples of methods for forming the spherical particle developer according to the present invention include the following. One method is called the spray drying method, in which resin materials, pigments, and charge control materials (in the case of magnetic developers, there is magnetic fine powder in addition to the above materials) are melted and kneaded, dissolved in a solvent, and then The liquid is sprayed into hot air from a nozzle in the form of a mist, and the solvent is evaporated from the surface of the liquid. During the evaporation process, the surface tension of the solvent is used to make the developer particles spherical.

Another method is called the flow coater method, in which developer particles are blown into hot air as a powder to melt the resin on the surface of the developer, and the surface tension of the molten resin causes it to become spherical. There is something that makes me

Furthermore, as a simple method, the developer particles can be stirred in hot water to keep the developer particles in a softened state, and then filtered and dried to form a sphere.

The above-mentioned spheroidization process is performed using microcapsule toner, that is, a developer in which a core material with good fixing properties is coated with a shell resin (for example, Japanese Patent Publication No. 49-1588, No. 51-35867).
It can also be applied to

Examples according to the present invention will be described below.

Example 1 A photoreceptor with a three-layer structure consisting of a back electrode, a CdS photoconductive layer, and an insulating layer has a dark potential of about +500 V, which corresponds to the dark part of the image.
An electrostatic latent image with a bright potential of about 0 V corresponding to the bright part of the image was formed.

A photosensitive drum having a diameter of 80 mm and having the above electrostatic charge pattern on its surface was rotated at a circumferential speed of 110 mm/sec, and the developing device shown in FIG. 5 was used.

In the illustrated developing device, 7 is a non-magnetic cylinder (hereinafter referred to as a sleeve) with a diameter of 30 mm that rotates in the direction of the arrow, and has a distance of 300 μm from the opposing photosensitive drum surface.
The photosensitive drum was rotated at the same circumferential speed while maintaining a gap.

Reference numeral 8 denotes a magnetic field generating means fixedly provided within the sleeve 7, and 8a is provided in a developing area facing the photosensitive drum, and a developing magnetic pole is provided on the sleeve surface.
It has a magnetic flux density of 750 gauss, and 8b is a magnetic pole of 800 gauss existing in the 9 part of the toner thickness regulating member.
The thickness of the toner layer is regulated by a regulating member 9 with the toner standing in spikes at this magnetic pole position on the sleeve. The toner thickness regulating member 9 is connected to the surface of the sleeve 7.
The gap is 150 μm, and the toner layer is kept below the gap between the photosensitive drum 1 and the sleeve 7. It is also possible to regulate the thickness of the toner layer by making the toner thickness regulating member 9 a magnetic material and concentrating the magnetic field (see, for example, Japanese Patent Application No. 109240/1982). 8c, 8d
is a developer transport magnetic pole.

As an AC bias that provides an alternating electric field to the sleeve 7, a DC component of +200V is applied peak-to-
A superimposed alternating current of peak 800 V and 200 Hz was applied from power supply 6. Using the above-mentioned developing device, resin polyethylene with high pressure fixing properties and magnetite were mixed as a developer at a weight ratio of 3:1, dispersed in xylene, and spray-dried to 130%
When development was carried out using a one-component magnetic toner that had been spheroidized to an average particle size of 10 μm by being blown out into hot air at 10°C, an image with no fog and excellent gradation reproducibility was obtained.

Example 2 In the photoreceptor and developing device described in Example 1, good results were obtained when an electrostatic image was visualized using a microcapsule toner as described below.

As a core material, 3 parts by weight of polyethylene and 1 part by weight of magnetite were kneaded in a roll mill at 150°, then finely pulverized, and toner with a particle size of 7 μm or less was removed using a classifier.

Styrene butadiene was dissolved in a methyl ethyl ketone solvent, and the resin core material toner was mixed therein. Polyethylene is not soluble in methyl ethyl ketone. This core material mixed liquid is sprayed into hot air at 100°C using a spray drying method to evaporate methyl ethyl ketone, and the polyethylene core material is treated with a spheroidizing coating of styrene butadiene to form microcapsule toner, which is then transferred to the above-mentioned apparatus. It was used for.

This example is a microcapsule toner in which a resin core material is coated with a resin triboelectric charger, so that excellent effects can be achieved under an electric field that causes the toner to reciprocate, as described above.

In other words, since the core material is solid compared to when the core material is liquid, triboelectric charging becomes more stable.
Harder charging characteristics can be obtained, and furthermore, durability in use against loads applied to the spherical toner during reciprocating movement and transport of the developer support is increased, and development characteristics are stabilized during long-term development processes.

In the present invention, a developed image is obtained by repeatedly attaching and detaching toner from an electrostatic image carrier using a periodically changing electric field. Since the developer is triboelectrically charged uniformly and well, it is easy to separate the developer from the support and transfer to the electrostatic image carrier.Also, because the Van der Waals force is small, the developer can separate from the support and transfer to the electrostatic image carrier. Easily transferred to the image carrier. Therefore, the thickness of the developer layer supported by the developer support is the same as that between the developer support and the electrostatic image carrier.
However, according to the present invention, the development efficiency can be further improved. Furthermore, since spherical toner has a smaller Van der Waals force than irregularly shaped toner, once it adheres to the electrostatic image carrier, the toner tends to stay there due to Van der Waals force rather than its electrostatic force. can also be easily separated from the electrostatic image carrier by a periodically changing electric field.
Therefore, according to the present invention, the antifogging effect is further improved. Furthermore, since the spherical toner has good and uniform triboelectric charging, a more faithful developed image can remain as a latent image.

[Brief explanation of drawings]

FIGS. 1 and 2 a and b are explanatory diagrams explaining the principle of the developing method according to the present invention, FIG. 3 is a characteristic diagram showing the relationship between latent image potential and developer transfer amount, and FIGS. b
5 is a characteristic diagram showing the relationship between latent image potential v and image density D, and FIG. 5 is a sectional view showing one embodiment of the developing method according to the present invention. 1...Latent image carrier, 5...Developer support, 6...
...Alternating electric field application power supply.

Claims (1)

[Scope of Claims] 1. A non-contact developing method in which the development distance between the electrostatic image carrier and the developer support is greater than the thickness of the developer layer supplied onto the developer support, The agent is toner particles that are substantially spherical and triboelectrically charged, and is applied periodically to the developer support to form an electric field that repeatedly attaches and detaches the toner particles to and from the electrostatic image carrier during the development. A developing method in which an electrostatic image is developed by the frictionally charged spherical toner particles detached from a developer support by applying a voltage that changes over time. 2. The toner according to claim 1, wherein the toner is a magnetic toner, and the developer layer is formed by a magnetic regulating member facing a magnetic pole provided on the back side of the developer support. Development method. 3. In a non-contact developing method in which the development gap between the electrostatic image carrier and the developer support is made larger than the thickness of the developer layer supplied onto the developer support, the developer is applied to the resin core material. The spherical microcapsule toner particles are coated with a resin shell material that is triboelectrically charged, and the developer support is used to form an electric field that repeatedly attaches and detaches the toner particles to and from the electrostatic image carrier during the development. A developing method in which an electrostatic image is developed by applying a periodically varying voltage to the body and using the triboelectrically charged toner particles detached from the developer support. 4. The toner according to claim 3, wherein the toner is a magnetic toner, and the developer layer is formed by a magnetic regulating member facing a magnetic pole provided on the back side of the developer support. Development method.