JPH05307323A - Developing device - Google Patents

Abstract

PURPOSE:To eliminate stripe-like irregularity, dust or fogging in an image and to prevent the unevenness of image density from being generated by making the material structure of an electrostatic charge member at a contact part with toner uniform with toner particle size. CONSTITUTION:A replenishment roller 8 which replenishes the toner 6 to a developing roller 5 functioning as a developer carrier and an electrostatic charge roller 9 functioning as the electrostatic charge member which electrostatically charges the toner 6 replenished on the roller 5 to have a prescribed polarity and regulates the layer thickness thereof are provided. Then, the toner 6 is electrostatically charged by electric discharge from the roller 9. In order to uniformly electrostatically charge the roller layer, the roller 9 is made of stainless steel and the material structure of the roller 9 at the contact part with the toner 6 is made uniform with the toner grain size. Besides, the roughness thereof is set to be equal to or under the toner particle size. Therefore, since the surface layer is uniform, the toner layer can be uniformly electrostatically charged and the uniform image without irregularity is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a developer carrying member arranged opposite to a latent image carrying member, and a charging member for contacting the toner replenished to the developer carrying member and charging the toner by discharging. The present invention relates to a developing device such as a copying machine, a facsimile, and a printer.

[0002]

2. Description of the Related Art A developing device of the above type is known and uses a one-component developer as toner. In this type of developing device, it is important to charge the toner and form the toner layer in order to obtain good developing performance, and to eliminate the trailing edge of the image.

As for the charging of the toner, if the toner on the developing roller is about one layer, each toner can be charged to a desired polarity by frictional charging or charge injection. The reason why many toners cannot be charged, and the polarities of the toners are different from each other, resulting in uncharged toners and toners with opposite polarity charges, which deteriorates the image quality of dust and fog. The problem arises. Therefore, in the conventional developing device, about one layer of toner on the developing roller is charged to a predetermined polarity by frictional charging or charge injection.

If there is only one layer of toner on the developing roller, the amount of toner to be used for development tends to be insufficient. Therefore, in the past, in order to obtain a sufficient image density even when the layer of toner on the developing roller is thin. In addition, the linear velocity of the developing roller is set to twice or more the linear velocity of the photoconductor. However, when the linear velocity of the developing roller is faster than the linear velocity of the photoconductor, more toner is developed at the trailing edge of the latent image on the photoconductor, so-called unevenness in the image density near the trailing edge of the image or toner scattering occurs. There was a problem that it was easy. The closer to the trailing edge of this image, the more prominent the greater the speed difference.

Therefore, it is easy to charge the multi-layered toner to the same polarity by using electric discharge, and the toner on the developing roller is charged by a wire.
Japanese Patent Laid-Open No. 73979 proposes a developing device which charges a toner on a developer carrying member by using an electric discharge body discharged through a hole of a porous film.

[0006]

However, in a developing device which is charged by a wire, the discharge surface is small because the wire is thin, and the charging performance is likely to deteriorate due to slight toner scattering. Further, in the apparatus described in Japanese Patent Laid-Open No. 3-73979, it is difficult to uniformly charge the toner layer because the surface is a porous film and does not have a uniform structure and has unevenness. Further, in order to obtain a uniform image without streaky unevenness, it is necessary to make the toner layer on the developing roller developed on the latent image carrier uniform. In this case 10
The unevenness in the range of 100 mm to 100 mm or more is due to the parallelism of the toner layer regulating member and the developing roller, in other words, the uniformity of gaps between them. The stripe-shaped unevenness of about 1 mm or less is due to the uniformity of the surfaces of the toner layer regulating member and the developing roller. The uniformity of the surface depends on the uniformity of the material of the surface and the surface property with less surface roughness. Therefore, JP-A-3-73
In the device described in Japanese Patent No. 979, since the toner layer is regulated by the porous discharge body, a uniform toner layer cannot be formed,
There was a problem that streaky unevenness appeared in the image.

The present invention solves the above-mentioned conventional problems,
The toner on the developer carrier to be developed on the latent image carrier is formed into a uniform multi-layer, and each toner can be surely charged to a desired polarity, and the image is free from streaky unevenness, dust and fog, and further latent image. An object of the present invention is to provide a developing device in which a large amount of toner is developed at the trailing edge and unevenness in image density does not occur.

[0008]

In order to achieve the above-mentioned object, the present invention provides a toner carrying member which is disposed so as to face a latent image carrying member, and a toner replenished to the developer carrying member. In the developing device having a charging member for charging by means of discharge, the material structure of the contact portion of the charging member with the toner can be regarded as uniform with respect to the toner particle size.

Further, according to the present invention, a developing device having a developer carrying member arranged to face the latent image carrying member and a charging member for contacting the toner replenished to the developer carrying member and charging the toner by discharging the toner. In the above, the roughness of the contact portion of the charging member with the toner is equal to or smaller than the toner particle size.

Furthermore, the present invention is characterized in that the resistance between the surface of the developer carrying member and its voltage applying portion is larger than the resistance between the surface of the charging member and its voltage applying portion. ..

Furthermore, the present invention is characterized in that a direct current electric field equal to or higher than a discharge starting voltage is formed between the developer carrying member and the charging member.

Further, according to the present invention, an alternating electric field in which a direct current is superposed is formed between the developer carrying member and the charging member,
It is characterized in that the peak value of the AC electric field is equal to or higher than the discharge starting voltage.

[0013]

According to the above construction, the toner on the developer carrying member is provided with the charging member for discharging the toner whose contact portion roughness is equal to or smaller than the toner particle size, and the developer carrying member is developed on the latent image carrying member. By making the above toner into a uniform multi-layer and surely charging each toner to a desired polarity, the developer carrying member is not so fast as compared with the speed of the latent image carrying member, for example, 2 times or less, preferably etc. Doubled, uniform and sufficient image density can be obtained, there is no streaky unevenness in the image, no dust or fog,
Further, it is possible to prevent a large amount of toner from being developed at the trailing edge of the latent image and causing unevenness in image density.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a side view showing an embodiment of the developing device according to the present invention. In FIG. 1, reference numeral 1 is a photosensitive drum configured as a latent image carrier, and 2 is a developing device. The casing 3 of the developing device 2 is provided with an opening 4, and a developing roller 5 as a developer carrying member, which is arranged to face the photosensitive drum 1 through the opening 4, is provided. Further, in the casing 3 of the developing device 2, an agitator 7 that agitates the contained non-magnetic toner 6 of one component, a replenishing roller 8 that replenishes the developing roller 5 with the toner 6, and a toner replenished on the developing roller 5. Is provided with a charging roller 9 as a charging member that charges the toner to a predetermined polarity and regulates the layer thickness. A minute gap (20 μm to 100 μm) is provided between the developing roller 5 and the charging roller 9, and when the toner passes through this gap, the toner is charged and at the same time, the gap width is approximately equal to this gap width. The thickness of the toner layer is restricted. In this case, since it is difficult to manage a minute gap of 100 μm or less by the distance between the axes of the two rollers, a device such as a spacer roller is provided at the end.

Reference numeral 10 is a scraper for scraping off the toner on the charging roller 9, and the scraper 10 is made of a thin plate of phosphor bronze. The tip of the scraper 10 comes into contact with the charging roller 9 in the counter direction, and the toner 6 attached on the charging roller 9 is scraped off, that is, cleaned. The surface of the cleaned charging roller 9 is always fresh, and there is almost no deterioration with time of discharge.

Further, when the charging roller 9 and the developing roller 5 are rotating together, the fresh surface of the charging roller 9 after being cleaned by the scraper 10 is the developing device 2.
Since the inner surface of the charging roller 9 and the developing roller 5 are opposite to each other, new toner 6 in the developing device 2 adheres to this fresh surface before reaching the discharging portion facing the developing roller 5. It is rotating in the direction. When rotated in this manner, the fresh surface of the charging roller 9 that has been cleaned by the scraper 10 is located outside the developing device 2, so that the fresh surface reaches the discharge portion.

The developing roller 5 includes a cored bar, NBR rubber whose electric resistance is controlled outside the core, urethane in which conductive particles such as carbon are dispersed, rubber such as silicon (10 ⁸ to 10 ^11).
Ωcm), and a resin having a low surface energy such as fluorine (10 ¹⁰ to 10 ¹² Ωc) in which conductive particles such as carbon are dispersed.
m) in a thin layer (10 μm to 100 μm). Further, the replenishing roller 8 is composed of a core metal and a foam (10 ³ to 10 ⁷ Ωcm) of urethane, silicon or the like in which conductive particles such as carbon are dispersed, and the charging roller 9 is made of stainless steel. ing.

In the developing device 2, the bias power source 11 is applied to the developing roller 5, and the charging power source 12 is applied between the developing roller 5 and the charging roller 9. The charging power source 12 causes the charging roller 9 to operate. The developing roller 5 is being discharged. Note that reference numeral 12 is an ammeter, which is not necessary for a practical machine, but is provided experimentally.

Toner charging due to discharge is performed by the developing roller 5
A constant voltage may be applied between the charging roller 9 and the charging roller 9, or an alternating voltage with a superimposed direct current may be applied. FIG. 2 shows the relationship between the voltage and the current when a constant voltage is applied between the developing roller 5 and the charging roller 9. When the voltage exceeds a certain value, the current increases rapidly. This characteristic indicates that the constant value is used as the threshold value and the discharge is performed when the threshold value is exceeded.

The relationship between the voltage applied between the developing roller 5 and the charging roller 9 and the fog toner is shown in FIG. 4, and the relationship between this voltage and the toner charge amount is shown in FIG. When the voltage becomes equal to or higher than the threshold value, the charge amount of the toner rapidly increases, and the fog toner decreases accordingly. Therefore, a DC electric field equal to or higher than the discharge start voltage, that is, equal to or higher than the threshold value may be formed between the developing roller 5 and the charging roller 9.

Next, the relationship between the AC component of the voltage and the current is shown in FIG. 5 when an AC voltage superposed with DC is applied between the developing roller 5 and the charging roller 9 to make the DC component of the voltage constant.
Shown in. When the DC component of the voltage exceeds a certain value, the current rapidly increases. This characteristic indicates that the constant value is used as the threshold value and the discharge is performed when the threshold value is exceeded. Then, while the discharge is being performed, even if the AC component of the voltage is changed, the DC component of the current hardly changes. Although not shown, the direct current component of the voltage and the direct current component of the current are proportional to each other during discharging.

In addition, an alternating current voltage in which a direct current is superposed between the developing roller 5 and the charging roller 9 makes the direct current component of the voltage constant, and the relationship between the alternating current component of this voltage and the fog toner is shown in FIG. FIG. 6 shows the relationship between the AC component and the toner charge amount. When the voltage becomes equal to or higher than the threshold value, the charge amount of the toner rapidly increases, and the fog toner decreases accordingly. Therefore, it suffices to form an alternating current electric field in which a direct current is superposed between the developing roller 5 and the charging roller 9 so that the peak value of the alternating current electric field is equal to or higher than the discharge start voltage, that is, equal to or higher than the threshold value.

Toner charging due to discharge is performed by the developing roller 5
The resistance between the surface of the charging roller 9 and its voltage applying section is set to be larger than the resistance between the surface of the charging roller 9 and its voltage applying section. In this example, the developing roller 5 includes a cored bar, NBR rubber whose electric resistance is controlled or urethane in which conductive particles such as carbon are dispersed, rubber such as silicon (10 ⁸ to 10 ¹¹ Ωcm), and carbon A thin layer (10 μm to 10 μm) of a resin (10 ¹⁰ to 10 ¹² Ωcm) having low surface energy such as fluorine in which uniform conductive particles are dispersed.
Since the charging roller 9 made of stainless steel has a lower resistance, the charging roller 9 is discharged.

Thus, the toner is charged by the discharge from the charging roller 9. At this time, in order to uniformly charge the toner layer, the charging roller 9 is made of stainless steel, and the material of the contact portion of the charging roller 9 with the toner 6 is made. The structure is such that it can be regarded as uniform with respect to the toner particle size, and the roughness is set to be equal to or smaller than the toner particle size. Therefore, it is difficult to uniformly charge the toner layer because the surface of the conventional developing device using a brush or a porous film as the charging member does not have a uniform structure but has unevenness. The layer can be uniformly charged. Further, as described above, the surfaces of the charging roller 9 and the developing roller 5 are made uniform, and the surface roughness is small, so that a uniform image without unevenness can be obtained.

FIG. 8 shows a developing device 2 showing another embodiment of the present invention. In this embodiment, a charging blade 14 is used as a charging member.
Is used. Further, the toner 6 is a one-component magnetic toner, and the developing roller 5 generates a magnetic field, and the magnetic toner 6 is attracted by this magnetic field and is replenished to the developing roller 5.

The charging blade 14 is made of a resin or rubber (10 ³ to 10 ⁷ Ωc) having a low surface energy such as fluorine or silicon in which carbon or the like is mixed in a thin stainless plate 15.
m) is attached. The tip of the charging blade 14 is brought into contact with the developing roller 5 for trading, and the contact pressure is controlled to obtain a toner layer (20 μm to 100 μm) having an appropriate thickness with the developing roller.

A bias power source 11 is applied to the developing roller 5, and a charging power source 12 is applied between the developing roller 5 and the charging blade 14, so that the charging blade 14 discharges the developing roller 5. Be seen. And
When the toner 6 passes between the developing roller 5 and the charging blade 14, the toner 6 is charged and at the same time, the toner layer is regulated. Further, since the surface energy of the charging blade 14 is low, it is difficult for toner to adhere to the charging blade 14.
The surface is always fresh and there is little deterioration with time of discharge.

In order to uniformly charge the toner layer,
It is desirable to use a charging member in which the conductive electrode is brought into direct contact with the toner, or a surface layer in contact with the toner having a single layer structure or a multi-layered structure on the conductive electrode is uniform. Although stainless steel is used in the above-described embodiments, the surface layer material of the charging member may be made of urethane, NBR, or other semiconductive material, or insulating resin or rubber, such as fluorine-based or silicon-based resin or rubber. A conductive filler such as carbon or whiskers dispersed therein may be used. Strictly speaking, the one in which the conductive filler is dispersed does not have a uniform surface structure, but the toner is uniformly charged by dispersing the conductive filler in a structure that is much denser than the size of the toner. For the purpose of making it possible, it can be considered that the surface has a uniform structure.

[0029]

EFFECT OF THE INVENTION By providing the toner on the developer carrying member with a charging member for discharging with little deterioration over time, even if the toner on the developer carrying member developed on the latent image carrying member is a multi-layered toner, individual toners can be formed into desired toner. By positively charging the polarity, a sufficient image density can be obtained without making the developer carrying member much faster than the speed of the latent image carrying member (for example, 2 times or less, preferably 1 ×).
The image had no streaky unevenness, no dust or fog, and more toner was developed at the trailing edge of the latent image to prevent unevenness in image density.

[Brief description of drawings]

FIG. 1 is a side view illustrating an embodiment of a developing device according to the present invention.

FIG. 2 is a graph showing the relationship between voltage and current when a constant voltage is applied to the charging member.

FIG. 3 is a graph showing the relationship between applied voltage and toner charge amount.

FIG. 4 is a graph showing the relationship between applied voltage and fog toner.

FIG. 5 is a graph showing a relationship between an alternating current component of a voltage and a current when an alternating current voltage on which a direct current is superimposed is applied to make a direct current component of the voltage constant.

FIG. 6 is a graph showing a relationship between an AC component of voltage and a charge amount of toner.

FIG. 7 is a graph showing the relationship between the AC component of voltage and fog toner.

FIG. 8 is a side view illustrating another embodiment of the developing device according to the present invention.

[Explanation of symbols]

 1 Photoreceptor Drum 2 Developing Device 3 Casing 5 Developing Roller 9 Charging Roller 14 Charging Blade

Claims (5)

[Claims] 1. A developing device comprising: a developer carrying member disposed opposite to a latent image carrying member; and a charging member for contacting the toner replenished to the developer carrying member to charge the toner by discharging. A developing device characterized in that the material structure of the contact portion of the charging member with the toner can be regarded as uniform with respect to the toner particle size. 2. A developing device comprising: a developer carrying member disposed opposite to the latent image carrying member; and a charging member which contacts the toner replenished to the developer carrying member to charge the toner by discharging. A developing device characterized in that the roughness of the contact portion of the charging member with the toner is not more than the toner particle size. 3. The resistance between the surface of the developer carrying member and its voltage applying section is larger than the resistance between the surface of the charging member and its voltage applying section. 2. The developing device according to 2. 4. The developing device according to claim 1, wherein a DC electric field having a discharge start voltage or higher is formed between the developer carrier and the charging member. 5. An alternating electric field in which a direct current is superposed is formed between the developer carrying member and the charging member, and a peak value of the alternating electric field is equal to or higher than a discharge starting voltage.
4. The developing device according to any one of 1 to 3.