JP2001013779A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device with such optimum developing conditions as to give an image of the best quality even in the case of a high- speed image forming device with >=200 mm/sec process speed. SOLUTION: A photoreceptor 1 with an amorphous silicon photosensitive layer and a nonmagnetic one-component toner formed by polymerization are used. A developing roller 52 which supplies the toner to the photoreceptor 1 is an elastic roller having 104-109 Ω.cm volume resistance and 1-3 uniform thin layers comprising the toner are formed on the surface of the roller. The developing roller with the formed thin layers is brought into contact with the surface of the photoreceptor in 1-10 mm nip width, and developing is carried out under developing bias set at a value lower by 100-500 V absolute value than the potential by electrification on the surface of the photoreceptor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer or a copying machine having a process speed of 200 mm / sec or more, and more particularly, to an electrophotographic system using an amorphous silicon photoreceptor and a non-magnetic one-component polymerization toner. A high-speed image forming apparatus.

[0002]

2. Description of the Related Art With the rapid development of digital technology and the development of a digital environment, the use of image forming apparatuses such as printers and copiers, which are one of the output devices, has been expanded, and the reproduction of high-quality images has been simple. The era of only image quality, which is best if possible, is over and personal, office,
Devices with various added values suitable for printing and engineering, respectively, are expected. Among them,
In apparatuses in the office or printing field, higher printing speed, that is, higher processing speed is required.

Generally, the process speed is 200 mm / sec.
In the high-speed machines described above, printing durability, sensitivity, resolution, and developing capability for photoconductors, which did not cause much problems in low-speed machines and medium-speed machines below, re-emerged as unique issues. Designing a process that satisfies all has been difficult. For example, O with high sensitivity
Photoconductors composed of drums or sheets coated with a PC photosensitive layer are widely used as very effective from the viewpoint of environment and cost. However, if a high-speed process machine using such OPC The known toner-carrier type two-component developing method and the magnetic toner type one-component developing method lacked the inherent characteristics of the OPC photoreceptor and the developing ability to speed up the process. To make up for it,
A configuration in which developing means (for example, a developing roller) are arranged side by side in two or three rows around the photoreceptor has been proposed.
The overall configuration of the apparatus has been increased, and this has been against the market needs for compact products. Also, OP
Because of the C photosensitive layer, problems still remain in the printing durability of the photosensitive member.

On the other hand, for example, Japanese Patent Laid-Open No. 7-2953
No. 88 proposes an apparatus combining an amorphous silicon photoreceptor excellent in printing durability, an elastic developing roller used in contact with the photoreceptor, and a polymerized toner excellent in transferability. According to this apparatus, good characteristics regarding printing durability and transferability can be obtained.
It has the advantage that a cleaner-less device can be realized by also using the developing device for cleaning the residual toner on the photoreceptor.However, the above-mentioned publication does not deal with the problem of increasing the speed of the process. Even if the conditions shown are applied to a high-speed process machine, it is difficult to obtain a high-quality image which is as good as or higher than that of a medium-speed machine or a low-speed machine as described above. For example, taking only the developing roller is elastic,
Only the general disclosure of being conductive cannot solve the above-mentioned problem of responding to high speed.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optimum image forming apparatus having a process speed of 200 mm / sec or more, with an optimum developing condition capable of obtaining the best image. Device is provided.

Further, the present invention provides an image which can be made compact and which can obtain a sufficient image density and image quality even with an image apparatus having a process speed of 200 mm / sec or more by using only a developing device. It is an object to provide a forming apparatus.

[0007]

In order to solve the above-mentioned problems, the present invention provides an electrophotographic photoreceptor, a charger for uniformly charging the surface of the photoreceptor to a specific polarity, and exposing the charged photoreceptor surface to light. Exposure means for forming an electrostatic latent image by performing the reversal development by selectively adhering toner to the latent image formed on the photoreceptor.
mm / sec or more, the photosensitive member has an amorphous silicon photosensitive layer on a substrate, the toner is a non-magnetic one-component toner produced by a polymerization method, and the developing roller has a volume resistance value. 10 ⁴ to 10 ⁹ Ω · c
m, formed on the surface of the roller, a uniform thin layer of the above-mentioned toner of 1 to 3 layers is formed, and the developing roller having the thin layer is brought into contact with the surface of the photoreceptor with a nip width of 1 to 10 mm. And the absolute value of the charge potential on the photoreceptor surface is 10
The development is performed under a development bias set to a value lower by 0 to 500 V.

In such a configuration, a rubber roller having a rubber hardness of 25 to 60 ° in Asker A hardness is used as a developing roller. A suitable toner has an average particle diameter of 7 μm.
m and having a charge amount of 50 μC / g or more.

The speed ratio between the developing roller and the photosensitive member in the developing area is 1.0 to 3.0 times, and furthermore, the speed ratio between the developing roller and the photosensitive member is set in contact with the developing roller and the bias to the developing roller is increased. A supply roller to which a bias having a higher potential than the potential is applied;

Still further, the developing roller also serves to clean toner remaining on the photoreceptor, and sets the polarity of a bias voltage applied to the developing roller and the supply roller to the same polarity as the charging of the surface of the photoreceptor during development. In the cleaning, switching is performed so that the polarity of the surface of the photoreceptor is opposite to that of the charging.

[0011]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic explanatory view of an image forming apparatus to which the present invention is applied. In the figure, reference numeral 1 denotes a photosensitive drum which rotates in the direction indicated by arrow A, that is, counterclockwise, and has a positively charged amorphous silicon photosensitive member on its peripheral surface. Preferably, the photosensitive drum 1
Has a configuration in which an injection blocking layer (undercoat), an amorphous silicon photosensitive layer, and a surface protection layer are sequentially laminated on a drum-shaped substrate.

Around the photosensitive drum 1, an eraser lamp 2 for erasing the residual charge of the photosensitive member along the rotation direction A, and the photosensitive member is uniformly charged to a specific polarity, for example, a positive polarity of 400-400.
A charger 3 that charges to a surface potential of 800 V (in the illustrated example, a plurality of corona chargers are used, but the present invention is not limited to this, and a single corona charger may be used. And a charging means such as a charging brush.), And an exposure LED for forming an electrostatic latent image on the photoconductor by inputting digital light information for an image to be reproduced onto the charged photoconductor surface. An exposure device 4 such as a head, a developing device 5 that supplies toner to a photoreceptor and reversely develops the electrostatic latent image, that is, a toner image that is formed by attaching toner to an exposed portion;
A post lamp 6 for uniformly exposing the surface of the photoreceptor carrying the toner image to uniformly remove the charge of the photoreceptor and toner and to help improve transfer efficiency; and transferring the toner image on the photoreceptor to a transfer material such as paper. A transfer roller 7 for transferring the image to the printer is disposed.

In this arrangement, as shown in FIG. 3, the developing device 5 includes a developing container 51 containing a non-magnetic one-component toner (hereinafter referred to as “polymerized toner”) 50 produced by a polymerization method, and an elastic body. And a layer thickness regulating member 53 such as a blade or a roller which is disposed in contact with the developing roller 52 with an appropriate pressure and regulates the toner layer thickness on the developing roller 52, and is in contact with the developing roller 52. Supply roller 54 for supplying toner to developing roller 52 provided
And a stirring member 55 disposed behind the supply roller 54. The development roller 52, the supply roller 54, and the development blade 53 are connected to an appropriate bias power supply and have predetermined polarities and values, respectively, as described later. Bias voltage is applied.

These will be described in detail. Developing container 5
A predetermined amount of non-magnetic one-component polymerized toner 50 is contained in the photosensitive drum 1, and is developed at a position facing the photosensitive drum 1 so as to expose a part of the peripheral surface through an opening 56 formed therein. A roller 52 is provided. The toner capacity is
For example, as shown in FIG. 3, it is monitored by a sensor 57 provided on the rear wall of the developing container 51, and when the amount becomes less than a predetermined amount, an instruction signal is issued to supply toner.

The developing roller 52 includes an elastic intermediate layer 52b formed around a central axis 52a made of a conductive rigid body such as stainless steel, and an elastic roller having an elastic surface layer 52c formed on the outer periphery of the intermediate layer 52b. Layer 52a, middle layer 5
2b is elastically deformed so that the surface layer 52c is disposed and held so as to be almost uniformly pressed against the surface of the photosensitive drum 1 along the axial direction with a nip width X of 1 to 5 mm, and is transmitted to the central shaft 52a by a drive source (not shown). Due to the applied driving force, the photosensitive drum 1 is rotated in a direction indicated by an arrow B, that is, clockwise with the rotation of the photosensitive drum 1.

As shown in FIG. 2, the center shaft 52a of the developing roller 52 is connected to a bias power source 59 via a switch 58. The bias power supply 59 applies a bias voltage to the central axis 52a for preventing the fogging phenomenon of the toner on the background portion of the image during the later-described development. Such a bias voltage is set to a value that is 100 to 500 V lower in absolute value than the charged potential on the photoconductor surface.

As shown in the figure, the bias power supply section 59 has power supplies A and B of different directions, and switches the bias polarity to the developing roller 52 between positive and negative by a switch 58 having two interlocking contacts a and b. This switching is performed at a predetermined timing depending on when the developing roller 52 contributes to the development and when the developing roller 52 contributes to the cleaning. That is, the developing roller 52 has the same polarity as the charged potential of the photosensitive member surface of the photosensitive drum 1 during the development, and the cleaning potential during the cleaning. Switching is performed so that the polarity is opposite to the charging potential of the photoconductor surface.

Returning to the structure of the developing roller 52, the intermediate layer 52b formed outside the central shaft 52a is
The surface layer 52c formed of an elastic porous foam such as R rubber (acrylonitrile butadiene copolymer rubber) or the like, and the outer surface of the intermediate layer 52b is formed of an elastic material such as urethane rubber.

The volume resistance of the elastic layer composed of the intermediate layer 52b and the surface layer 52c of the developing roller 52 is 10 ⁴ to 10 ⁹ Ω.
Cm is preferable, and the rubber hardness of Asker A is 25 to 60 °. In particular, the surface layer 52c has minute irregularities on the surface to obtain toner conveying force, and separates from the toner. It is preferable that the toner is formed of a material having good moldability and a frictional charge series separated from the toner.

As described above, the developing roller 52 rubs against the photoreceptor of the photosensitive drum 1 with a nip width X of 1 to 5 mm, and rotates in the same direction as the photosensitive drum at the rubbing position, that is, in the developing area. The peripheral speed difference at the contact position is set to be 1.0 to 3.0 times the speed of the photosensitive drum.

A supply roller 54 located at a position rearward of the developing roller 52 extends parallel to the axis of the developing roller 52 and is in contact with the developing roller 52 over its entire length. The developing roller 52 is made of, for example, urethane rubber foam mixed with fine carbon powder, and rotates at a different speed from the developing roller 52 while contacting the developing roller 52 with a predetermined pressure. Is supplied to the developing roller 54, and the toner on the developing roller 52 is charged by frictional charging. The electrification between the developing roller 52 and the supply roller 54 greatly affects the development quality. If the electrification is insufficient, fog and density unevenness occur.

Further, a center shaft 54a of the supply roller 54 is connected to a bias power supply 62 via a switch 61. A bias voltage is applied to a center shaft 54 a of the supply roller 54 by a bias power supply unit 62. The bias power supply unit 62 includes power supplies C and D of different directions, and switches the bias polarity between positive and negative by a switch 61 having two interlocking contacts c and d. This switching is performed in synchronization with the switching of the bias voltage to the developing roller 52 described above, and is switched so that the power supply has the same polarity as the bias voltage to the developing roller 52. The supply roller 54
Is set to a potential 100 to 200 V higher than the bias potential of the developing roller 52, and the toner is transferred from the supply roller to the developing roller due to this potential difference.

A stirring member 55 provided behind the supply roller 54 has a central shaft 55 extending in the same direction as the developing roller 52.
A has a plurality of agitating blades provided at a plurality of positions in the axial direction. The rotation of the agitating blade agitates the toner in the developing container 51 and conveys the toner to the supply roller 54.

On the other hand, the layer thickness of the toner supplied onto the developing roller 52 is regulated by the layer thickness regulating member 53. The layer thickness regulating member 53 is disposed at a contact portion between the developing roller 52 and the photosensitive drum 1, that is, at a downstream position of the developing region, and is formed of a flexible blade-shaped member made of stainless steel or urethane rubber. The toner is held in the developing container by an appropriate fixing means so as to come into contact with the surface layer of the roller 52 with a predetermined pressure. It acts to form a uniform thin layer. The material of the layer thickness regulating member 53 is desirably a material whose frictional charging series is separated from the toner, similarly to the material of the surface layer of the developing roller 52.

Although not shown, the thickness regulating member 5
The roller 3 may have a roller shape in addition to a blade shape. When the layer thickness regulating member 53 is made of a conductive material, it is preferable to apply a bias having substantially the same value and the same polarity as the supply roller 54 described above.

Next, the operation will be described. First, while the photosensitive drum 1 is rotating in the direction of arrow A, the residual potential of the photosensitive member of the photosensitive drum 1 is removed from the eraser lamp 2, and then the wide or plural coronas are removed. The surface of the photoconductor is uniformly charged by the charger 3. Subsequently, digital exposure is performed by the exposure device 4 to form an electrostatic latent image on the photoreceptor.
Is transported to a position in contact with the developing roller 52, that is, a developing area.

On the other hand, in the developing device 5, at the same time as the rotation of the photosensitive drum 1, the developing roller 52, the supply roller 54, and the agitating member 55 rotate in the directions indicated by arrows by a driving source (not shown). A bias voltage is applied to the shaft 52a and the center shaft 54a of the supply roller 54 from bias power supply units 59 and 62, respectively.

The rotation of the stirring member 55 and the supply roller 54 stirs and supplies the toner in the developing container 51 to form a toner layer on the developing roller 52. The toner layer is regulated by the layer thickness regulating member 53 so as to be a uniform thin layer of 1 to 3 layers of toner. The toner whose layer thickness is regulated adheres to the surface layer of the developing roller 52 and It is transported to the developing area by rotation.

The thinned toner is supplied to the electrostatic latent image on the photosensitive drum 1 in the developing area, and is developed by being attracted and adhered to form a visible toner image.

The toner image is conveyed to the transfer area by the rotation of the photosensitive drum 1, where it is transferred to a transfer material such as paper by the action of the transfer roller 7, and then fixed on the transfer material by a fixing unit (not shown). .

On the other hand, the residual toner not transferred to the transfer material is transported to the developing roller 52 again. In the case of continuous printing, the polarity of the bias voltage applied to the developing roller 52 cannot be switched, and the developing roller 52 scrapes off the residual toner on the photosensitive drum 1 at the contact position with the photosensitive drum 1 to the developing device 5. Upon collection, the new toner develops the latent image on the photoreceptor surface.

At the end of printing, it is preferable that the addition is performed so that the photosensitive drum 1 is further rotated one rotation for final cleaning. At this time, the polarity of the bias voltage applied to the developing roller 52, the supply roller 54, and the layer thickness regulating member 53 is switched, thereby promoting the adsorption of the toner from the photosensitive drum 1 to the developing roller 52.

In the present invention, since the photosensitive member and the developing roller are of a contact type, the toner is a polymerized toner and has a high resistance of 10 ⁶ Ω · cm or more or an insulating property because the toner leaks when the resistance is too low. Are used, and in particular, the particle size is 5 to 8 μm.
m and a charge amount of 50 μC / g or more are preferable.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS With the above configuration, the materials of each device and members
The conditions were set as follows. Photosensitive drum
For 1, use an amorphous silicon photosensitive drum
Then, rotate it at 1000mm / sec and use it as a charger 3.
Corona charging, 600 dpi LED head as exposure unit 4
And the developing roller 52 has a volume resistivity of 1.3 × 10 ⁷
Intermediate layer made of NBR rubber with Ω · cm and rubber hardness of 50 °
Has a surface layer made of urethane rubber having a diameter of 100
mm and an elastic roller with a surface roughness of 7.0 μmRz.
A nip width of about 10 mm (contact
Width), and the development blur
Is opposite to the rotation direction B of the developing roller 52.
About 30 ° to the tangent, and
It was arranged so as to bite about 1.0 mm. Of the developing roller 52
The peripheral speed is 1.05 times the peripheral speed of the photosensitive drum 1.
did.

On the other hand, as the supply roller 54, the volume resistivity 2.3 × 10 ⁴ Ω · cm, using a sponge roller with a diameter of 70mm composed of a foam made of carbon reinforced urethane rubber, styrene toner produced by a polymerization method -An acrylic resin to which hydrophobic silica was added as an external additive was used. The peripheral speed of the supply roller 54 is
About 0.5 times as much as the peripheral speed.

The process is set such that the charging potential on the drum after charging by the charger 3 is about 580 V, the potential of the exposed portion (light portion) after the exposure device 4 is about 40 V, and the bias voltage to the developing roller 52 is 300 V. The bias voltage to the roller 54 is 500 V, and the bias voltage to the layer thickness regulating member 53 is 300
V.

A toner image formed under such a configuration and conditions is transferred to a transfer roller 7 composed of a sponge roller having a volume resistance of 10 ⁶ to 10 ⁹ Ω · cm to which a bias of -1500 V to -3000 V is applied. And transferred to a transfer material made of paper, and then fixed by a heat fixing device. As a result, at a resolution of 600 dpi, it was possible to obtain a reproduced image having no fog and a good image density.

In the above configuration, the volume of the developing roller 52 is
Resistance value, rubber hardness, and the distance between the developing roller 52 and the photosensitive drum 1
Nip width of contact area, speed ratio between developing roller and photosensitive drum
And the like, the volume resistance of the developing roller 52 was changed.
10 for resistance⁴-10 ⁹Ωcm range, rubber hardness
Is 25-60 ° in Asker A hardness and feels like developing roller 52
The nip width of the contact area with the optical drum 1 is 1 to 5 mm,
And the speed ratio of the photosensitive drum to the photosensitive drum is in the range of 1.0 to 3.0.
Suitable results can be obtained when
The process speed is 1000 mm / sec.
High quality reproduced image similar to the above 200mm / sec
Could be obtained.

[0039]

As described above, according to the present invention,
In a non-magnetic one-component developing method using an amorphous silicon drum, a clear image free from fog, missing dots, and insufficient density can be obtained.

Further, by switching the polarity of the bias voltage to the developing roller 52 and the like during development and during cleaning, efficient development and cleaning can be performed.

[0041]

[Brief description of the drawings]

FIG. 1 is a diagram showing a preferred example of an image forming apparatus according to the present invention.

FIG. 2 is a view for explaining bias switching to a developing roller and a supply roller in the apparatus of FIG. 1;

FIG. 3 is a diagram illustrating toner transfer in the apparatus of FIG. 1;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 eraser lamp 3 charger 4 exposing device 5 developing device 6 post lamp 7 transfer roller 50 non-magnetic one-component toner 51 developing container 52 developing roller 53 layer thickness regulating member 54 supply roller 55 stirring member

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/06 101 G03G 15/08 507L 507B F term (Reference) 2H005 AB06 DA01 EA01 EA05 FA07 2H068 DA00 2H073 AA05 BA02 BA09 BA13 BA21 BA41 BA43 BA45 CA02 2H077 AA15 AB01 AB14 AC03 AC04 AD02 AD06 AD35 AE03 BA03 CA02 DB08 EA14 FA22 GA17

Claims (6)

[Claims] An electrophotographic photoreceptor; a charger for uniformly charging the surface of the photoreceptor to a specific polarity; an exposure unit for exposing the charged photoreceptor surface to form an electrostatic latent image; And a developing roller for performing reversal development by selectively adhering toner to the latent image formed at the process speed of 200.
mm / sec or more, the photosensitive member has an amorphous silicon photosensitive layer on a substrate, the toner is a non-magnetic one-component toner produced by a polymerization method, and the developing roller has a volume resistance value. 10 ⁴ to 10 ⁹ Ω · c
m, formed on the surface of the roller, a uniform thin layer of the above-mentioned toner of 1 to 3 layers is formed, and the developing roller having the thin layer is brought into contact with the surface of the photoreceptor with a nip width of 1 to 10 mm. And the absolute value of the charge potential on the photoreceptor surface is 10
An image forming apparatus wherein development is performed under a development bias set to a value lower by 0 to 500 V. 2. The developing roller has an Asker A hardness of 25.
2. The image forming apparatus according to claim 1, comprising a rubber roller having a rubber hardness of about 60 [deg.]. 3. The image forming apparatus according to claim 1, wherein the toner is a polymerized toner having a small particle diameter having an average particle diameter of 7 μm or less and a charge amount of 50 μC / g or more. 4. The image forming apparatus according to claim 1, wherein a speed ratio between the developing roller and the photosensitive member in a developing area is 1.0 to 3.0 times. 5. The image forming apparatus according to claim 1, further comprising a supply roller disposed in contact with said developing roller and to which a bias having a higher potential than a bias potential applied to said developing roller is applied. . 6. The developing roller also serves to clean toner remaining on the photoreceptor, and sets the polarity of a bias voltage applied to the developing roller and the supply roller to the same polarity as the charging of the surface of the photoreceptor during development. 6. The image forming apparatus according to claim 1, wherein switching is performed such that the polarity of the photosensitive member surface is opposite to the polarity of the charged photosensitive member.