JPS5854384B2 - Electrophotographic development method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel electrophotographic development method,
In particular, the present invention relates to a new electrophotographic dry developing method that provides the same resolution as the conventional powder cloud developing method and also provides images without "bleeding".

Conventionally, an electrophotographic development method in which charged powder (hereinafter simply referred to as toner) is supplied to an electrostatic latent image (hereinafter simply referred to as latent image) using an air flow is well known as a powder cloud development method.

This powder cloud development method is characterized in that it can use fine powder, so it can obtain images with high resolution and high contrast.

However, the conventional powder cloud development method uses an air stream to create a toner mist and supplies this mist to the latent image surface with the air stream, thus requiring a large amount of air stream.

Furthermore, it is difficult to create a uniform toner mist using such a method, and the toner density tends to be uneven.

Furthermore, this method has the disadvantage that the toner protrudes from the latent image and adheres in the direction of the airflow, resulting in a so-called "flow" phenomenon.

This is because the force with which the toner adheres to the latent image surface is determined by the resultant force of the latent image charge, the Coulomb force due to the toner charge, and the force that the toner receives from the air flow. This is because, if the Coulomb force has a component and the component is large compared to the Coulomb force, toner directed toward the latent image surface will adhere to the latent image surface downstream of the air flow.

Therefore, when using such means, it can be inferred that an image without "flow" can be obtained by reducing the flow velocity or by making the direction of the air flow perpendicular to the latent image plane. In this case, the amount of toner supplied to the latent image surface may be insufficient, resulting in a toner image with low density.
In the latter case, once the airflow collides with the latent image surface, the airflow changes direction and has a component parallel to the latent image surface, so the toner moves along with the flow, causing the toner to move away from the latent image. In the end, it was difficult to eliminate the "flow" and obtain a good image using this method.

The present inventors applied a voltage whose voltage value changes over time (hereinafter referred to as a transformer voltage) to the toner powder scattered on a substrate whose back surface is conductive at least, so that the toner is dispersed above the substrate. It has been discovered that a latent image can be created by flying up into space in the form of a mist and using no airflow or only a very small amount of airflow.

The present invention aims to provide a method of forming an image with almost no "flow" using such means, and furthermore, even if a sufficient amount of toner is supplied to the latent image surface, almost no "flow" occurs. It is an object of the present invention to provide a method that can form good images with minimal effort.

That is, in the present invention, an electrode whose voltage changes over time is brought close to the surface of a grounded substrate whose back surface is electrically conductive, and a voltage is applied to this electrode to fly up toner for electrophotographic development that has been scattered on the surface of the substrate. The electrophotographic developing method is characterized in that the toner is applied to the electrostatic latent image surface facing the substrate surface for development.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a side sectional view showing a basic embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a grounded conductive substrate, on which, for example, negatively charged powder, ie, toner 2, is sprinkled approximately evenly.

Reference numeral 3 denotes an electric wire consisting of an electrode 4 stretched perpendicularly to the plane of the paper and an insulating coating 5 surrounding the electrode 4.

This electric wire 3 is provided on the substrate 1, either in contact with it or with a very small distance therebetween, and is connected to a displacement voltage (AC voltage in this example) power source 6 via a switch S.

7 is an electrophotographic photosensitive material consisting of a photoconductive layer 8 and a conductive support 9, and the surface of the photoconductive layer 8 has a positive electrostatic potential @10.
is formed.

In the above configuration, when the switch S is closed and a displacement voltage is applied to the electrode 4 of the electric wire 3, the toner near the electric wire flies up in the direction of the arrow 11, is supplied to the surface of the photoconductive layer 80, and is absorbed by the electrostatic latent. It adheres to the image 10 and forms a toner image.

By moving the electric wire 3 in the direction of the arrow 12, toner can be supplied substantially evenly to the entire surface of the photoconductive layer 80, that is, the entire latent image surface.

Since the flying toner has almost no velocity component parallel to the latent image surface, the toner adheres faithfully to the electrostatic latent image, resulting in an image with almost no "flow" and a sufficient amount. Even if the amount of toner is supplied to the latent image surface, the amount of "flow" does not increase, so a good image with high density and no "flow" can be obtained.

Further, in the present invention, since the force applied to the toner can be electrically controlled, the amount of toner supplied can be easily adjusted.

When a displacement voltage is applied between the electrode 4 of the electric wire 3 and the substrate 1, the change in voltage or electric field between the electrode 4 and the substrate 1 causes some kind of electromagnetic effect on the toner. It is estimated to be.

As the toner used in the present invention, any known suitable toner can be used.

Furthermore, this toner is almost independent of its electrical properties, such as electrical conductivity and dielectric constant.

Examples of toners include those in which carbon black is blended with thermoplastic resins such as styrene copolymers and acrylic copolymers, organic pigment powders such as carbon black powder, phthalocyanine pigment powder, and other organic pigments. Finely dispersed powder of the powder and the thermoplastic resin, and further ZnO, Ti01
These include inorganic pigment powders such as CaCO3, 'MgO, and silica, and finely dispersed powders of these inorganic pigment powders and the thermoplastic resin.

It is important that these toners have a weight sufficient to be lifted up by application of a displacement voltage, and even heavy toners can be used if the displacement voltage is sufficiently high.

The weight of the toner is determined by the particle size and specific gravity of the toner, and if the particle size is large, it is desirable that the toner has a small specific gravity.

Specifically, the product of the specific gravity and average particle size of the toner is 0.1 cr/
It is desirable that the thickness be less than L, preferably less than 0.01 cm.

The photosensitive material 7 may be one in which an amorphous Se layer is provided on an aluminum substrate, one in which a photoconductive layer made of ZnO and resin is provided on a paper support, or one in which the surface is subjected to conductive treatment such as metal vapor deposition. A film in which an organic photoconductive layer such as polyvinyl carbazole is provided on a resin film is used.

Furthermore, instead of the electrophotographic light-sensitive material described above, a so-called electrostatic recording material having a highly insulating resin layer provided on the surface of a paper support or the like, on which an electrostatic latent image is formed by an appropriate method, is used. Also good.

For the electrode 4, a single wire or stranded wire made of metal or alloy such as copper, aluminum, brass, iron, stainless steel, etc. with a diameter of 0.1 to 3 is used, for example.

The coating 5 of the electrode 4 is made of a highly insulating resin such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, fluororesin, acrylic resin, polyester resin, etc.
The wall thickness is preferably O61 to 4vtm.

However, the coating 5 is not necessarily required under conditions where no spark discharge occurs between the electrode 4 and the substrate 1.

It is preferable that the voltage applied to the electrode 4 has a voltage value that applies a force sufficient to cause the toner to fly up and does not cause dielectric breakdown of the coating 5.

Further, the voltage applied to the electrode 4 may be any voltage as long as the voltage between the electrode 4 and the substrate 1 changes over time, that is, a displacement voltage.

For example, an alternating current such as a sine wave, a rectangular wave, or a sawtooth wave, an appropriate direct voltage superimposed on the alternating current, a pulsating current, a pulse train, or a combination of some of these can be used.

The frequency of these displacement voltages is preferably below IMHz, preferably below 100 KHz.

The reason for this is that when the frequency becomes too high, the degree of toner flying up becomes low.

Furthermore, from an economical point of view, it is preferable to use a commercial AC power source of 50 Hz or 60 Hz.

The power supply 3 is provided either in contact with the substrate 1 or with a very small gap between them, but if a gap is provided, the gap should be as narrow as possible so that a sufficient voltage or electric field can act on the toner.

The specific value varies depending on the value of the applied voltage, but
It is preferably approximately 10 mm or less.

□If the electrode 4 is covered with a coating 5, the specific value of the voltage applied to the electrode 4 varies depending on the diameter of the electrode 4, the material and thickness of the coating 5, the voltage waveform, etc. The maximum value ranges from 2 to 30 KV, more preferably from 5 to 20 KV.

The reason is that if the voltage is too low, the force acting on the toner is weak (
This is because the toner will not fly up, and on the other hand, if the voltage is too high, it will cause dielectric breakdown of the coating.

Furthermore, if the electrode 4 is not covered with the coating 5, a condition must be established in which spark discharge does not occur between the electrode 4 and the substrate 1, so the toner must be insulating and the specific gravity and average particle size of the toner must be multiplied. The distance between the electrode 4 and the substrate 1 is 2 m or less, 0.001 cm or less.
m or more, and the applied voltage is required to be in the range of 3 to 6 KV.

The applied voltage is determined by applying a voltage to the surrounding area to prevent the AC voltage from neutralizing the charge of the toner when the scattered toner is charged in advance and is to be blown up by an AC voltage. The electrode diameter and voltage must be chosen so as not to ionize the air.

Also, the presence or absence of a covering on the wire, the thickness of the material, the distance between the electrode and the substrate, the potential difference between the electrode and the substrate, etc. must also be taken into consideration.

The conductive substrate 1 may be a single metal plate made of metals such as copper, iron, aluminum, or alloys such as brass. A highly insulating layer made of polypropylene, polyester, polyvinylidene chloride, acrylic resin, fluororesin, etc. may be provided, and toner may be sprinkled thereon.

This method is particularly effective when the toner is conductive.

FIG. 2 is a schematic side view showing another embodiment of the invention.

In this embodiment, a plurality of electric wires 3 each consisting of an electrode 4 and a coating 5 are arranged approximately parallel to each other with appropriate intervals.

By doing this, when the switch S is closed, the toner 2 flies upward almost uniformly over the entire surface as shown by the arrow 11, and almost uniformly hits the surface of the photosensitive layer 80, with almost no velocity component parallel to the surface. It is supplied with N at all times and adheres faithfully to the latent image.

The resulting toner image has almost no "flow".

When the electric wire is moved along the substrate 1 by a distance of about 30 electric wires, the toner scattering will further increase.

It is also effective to vary the phase of the voltage applied to each electrode 4.

FIG. 3 is a schematic side sectional view showing still another embodiment of the present invention.

In Fig. 3, 30 is a conductive endless belt stretched by a pair of grounded metal rollers 31, which is grounded via the pair of rollers 31, and is rotated in the direction of arrow 32 by a drive system not shown in the figure. .

A toner supply device 4 is located above the left end of the endless belt 30.
0 is set.

This toner supply device 40 includes at least a toner reservoir 41. It is composed of a supply roller 42 and a charge imparting device 43,
The toner 2 is stored in the toner reservoir 41, and the charge imparting device 4
3 is connected to one pole of a DC high voltage power supply 44.

As the charge imparting device, for example, a plurality of needle-shaped electrodes arranged substantially parallel to each other with their tips facing the endless belt 30 is used.

It is desirable that the charge signifier 43 is corona discharged.

On the other hand, at the upper right end of the endless belt 30, an electric wire 3 consisting of an electrode 4 and a coating 5 is provided, either in contact with the surface of the endless belt 300 or with a very small distance therebetween.

The electrode 4 is connected to a displacement voltage power source 6.

Further above the right end of the endless belt 30, there is provided a roller 34 rotating in the direction of an arrow 33 and an electrophotographic photosensitive material web 35 that moves on its surface and has an electrostatic latent image on the surface facing the endless belt 30. There is.

The toner 2 contained in the toner reservoir 41 of the toner supply device 40 is pumped up by the supply roller 42 in an approximately fixed amount, falls onto the surface of the endless belt 300, and is dispersed approximately evenly. 43 or combines with ionized ions in the air, and is charged to a polarity opposite to that of the electrostatic latent image on the web 7, for example.

The charged toner scattered on the endless belt 30 moves near the electric wire 3 as the endless belt 300 rotates, and flies upward due to the action of the transformed voltage applied between the electrode 4 and the endless belt 30. web 35
to develop the electrostatic latent image.

At this time, since the toner flies up almost directly above, there is almost no "flow" that sticks out of the electrostatic latent image, and the resulting toner image has a high contrast and is faithful to the latent image.

FIG. 4 is a schematic side sectional view showing still another specific embodiment of the present invention.

The present embodiment is characterized in that toner that has no electric charge or is irregular is thrown up and a substantially uniform electric charge is imparted to the toner before supplying the toner to the latent image surface.

In FIG. 4, reference numeral 52 denotes toner that is almost evenly distributed by known means on a suitable grounded substrate 1, and even if this toner 52 has no electric charge or has uneven electric charge, good.

54 is a screen for imparting an electric charge to the toner 52 passing through the screen, and is connected to a DC high voltage power source 55.

A voltage power source 6 displaces the surface of the substrate 1 on which the toner 52 is scattered.
When the electric wire 3 connected to the screen 54 is moved in the direction of the arrow 53, the toner 52 flies up in the direction of the arrow 11,
The photosensitive material 7 is charged with electric charges and supplied to the surface of the photosensitive material 7, thereby developing a latent image.

In this embodiment as well, an image faithful to the latent image with no "flow" and high contrast can be obtained.

FIG. 5 is a schematic side sectional view showing still another specific embodiment of the present invention.

This embodiment is characterized in that the toner blown up by the application of a displacement voltage is supplied to the latent image surface by supplementary use of a small amount of air flow.

By doing so, a more uniform toner cloud can be formed, and a toner image with high contrast without "flow" can be obtained.

According to this example, the airflow of several to several 101/mvL required by the conventional powder cloud method can be reduced to 1/100 to 1/100 of that.
The amount can be reduced to 1/10.

In Fig. 5, 61 is an air nozzle that moves in the direction of arrow 62 in synchronization with the electric wire 3, and releases a small amount of air upward from this nozzle.
A small amount of air flow is applied to the toner 2 blown up in the direction.

As a result, the toner that has been blown up is moved upward while being distributed more uniformly by the air flow, and is supplied to the latent image surface.

The air released from the air nozzle 61 only transports the toner that has been blown up into a cloud shape, so the amount of air needed to lift up the stationary toner into a cloud shape is 1/100 to 1/1. 10 Only a small amount is required. Therefore, the force that this airflow acts on the toner is very weak, and the force of the component parallel to the latent image surface that the toner receives is also very small, causing the toner to protrude from the latent image and onto the latent image surface. "Flow" that attaches
Almost no toner is generated, and a larger amount of toner can be supplied to the latent image surface.

In addition, in this example, it is also possible to use other gases such as N2, He, Ar, etc. in addition to air. It is effective to use

As detailed above, according to the present invention, a voltage whose value changes over time is applied to charged toner to cause the toner to fly up and to be supplied to the electrostatic latent image surface. By developing the electrostatic latent image, it is possible to obtain a toner image with no "flow" and high contrast.

Further, in the present invention, positive development in which toner is attached to the charged areas of the latent image has been described, but it goes without saying that similarly good results can be obtained with reversal development in which toner is attached to the uncharged areas.

This example was carried out more specifically as follows.

Example 1 Carbon flank 1 was placed on a grounded aluminum substrate.
0%, styrene/butyl methacrylate (85:15)
Toner with an average particle size of about 8μ made of 90% copolymer
The mixture was spread almost evenly through a Menshi sieve, and then exposed to corona discharge to be negatively charged.

This was electrically charged and exposed to a selenium photosensitive plate having a positive electrostatic latent image, and was placed substantially parallel to the plate at a distance of about 8 cm.

After that, an alternating current voltage of 6 V and 50 Hz was applied to a wire with a diameter of about 4 mm in which an electrode of cast-plated copper stranded wire with a diameter of about 1 mm was coated with polyethylene, and the wire was brought into contact with the surface of the aluminum substrate. When scanning, the toner flew up almost directly above and was supplied to the surface of the selenium photosensitive plate while forming a cloud, thereby developing a latent image.

The obtained toner image had almost no "flow" and had a high contrast.

Example ■ When a pulsating current obtained by rectifying the AC voltage in Example ■ with a rectifier was applied instead of the AC voltage, the toner flew up in the same way, there was no "flow," and a toner image with high contrast was obtained. Ta.

Example 2 A polyethylene terephthalate film with a thickness of 30 μm was placed on the surface of a grounded aluminum substrate, and a conductive toner made of carbon black powder with an average particle size of 12 μm was sprinkled thereon using a 60-mesh sieve.

This powder had a resistivity value of approximately 10'Ωcm.

When an alternating current voltage was applied to this in the same manner as in Example 2, the powder flew up and formed a uniform loud, and good development was performed.

Example (2) Toner was scattered in the same manner as in Example (2), and the toner was made to face the latent image surface.

When an electric wire similar to that in Example (2) to which an AC power source of 8 KV and 50 Hz was applied was scanned at a distance of about 1 mm from the substrate, a good toner image was obtained as in Example (2).

Example V Toner was spread in the same manner as in Example I, and was made to face the latent image surface.

When a brass rod having a diameter of 3 mm was applied with a rectangular wave voltage of 15 KHz and was scanned at a distance of about 5 mm from the substrate, a good toner image was obtained as in Example 3.

[Brief explanation of drawings]

1 to 5 are schematic side sectional views showing embodiments of the present invention. 1... Conductive substrate, 2... Toner, 3
...Wire, 4...Electrode, 5...
・Coating, 6... Displacement voltage power supply, 7...
Electrophotographic materials.

Claims (1)

[Claims] 1. By bringing an electrode whose voltage changes over time close to the surface of a grounded substrate whose back surface is conductive at least, and applying a voltage to the electrode to cause the toner for electrophotographic development spread on the surface of the substrate to fly up, An electrophotographic developing method, characterized in that development is performed by attaching the toner to an electrostatic latent image surface facing the surface of the substrate.