JPH09218572A - Image forming device and developing roller for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an image of high image quality, enhancing a developing efficiency, by providing a developing roller having a surface part which comes into contact with a photoreceptor drum and which is made of ion conductive material, a bias means and a transfer means. SOLUTION: The developing roller 56 is moved in a direction opposite to the moving direction of the photoreceptor drum 20 at a nip part, so that toner 53 functioning as electrical insulating material above the nip part at black solid printing sticks to the drum 20, then, even in the case the roller 56 directly comes into contact with the drum 20, a discharge hardly occurs at the nip part, because the roller 56 is made of the ion conductive material. Thus, the occurrence of such the situation is reduced that the developing bias voltage impressed on the roller 56 leaks to the drum 20 and the surface potential of the drum 20 becomes instable. Thus, the developing efficiency is enhanced up to >=90%, then, the surface potential of the drum 20 is prevented from becoming instable because of the leakage of the developing bias voltage impressed on the roller 56 to the drum 20 by discharging, even in the case of not leaving the toner 53 at the nip part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the technical field of electrophotographic image forming apparatuses such as laser beam printers, facsimiles, and copying machines. In particular, the developing roller is opposite to the photosensitive drum in the nip portion. The present invention belongs to the technical field of an image forming apparatus that employs an impression developing method in which a developing roller is moved to the image forming apparatus and a developing roller for the image forming apparatus.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus of this type, when a transfer means such as a transfer roller is arranged above a photosensitive drum, the apparatus can be opened from the upper side as compared with the case where the transfer means is arranged below. It has the advantage of being able to access the paper path, making it easier to deal with paper jams, and also having the structure of exposing the paper feed cassette upwards, which has the advantage of making it easier to feed paper. It is possible to have a structure in which the path of (1) is formed in a substantially linear shape, and it is possible to obtain an advantage that printing can be easily performed even on special paper such as thick paper and envelope. Since various advantages are obtained in this way, conventionally, in this type of image forming apparatus, a structure in which the transfer unit is arranged above the photosensitive drum has been desired.

On the other hand, as a developing method in this type of image forming apparatus, an elastic roller made of a conductive material such as silicon is used as a developing roller for carrying toner, and a developing bias voltage is applied to the developing roller. The so-called impression developing method in which development is performed by pressing the photosensitive drum is widely adopted. In order to apply the developing bias voltage in this manner, the developing roller is provided with conductivity by electronic conduction. That is, conductivity is imparted to the developing roller by dispersing conductive particles such as carbon particles.

In this type of developing system, efficient development is possible by increasing the developing efficiency of toner as a developer. On the other hand, the toner is used between the developing roller to which a developing bias is applied and the photosensitive drum. It also plays the role of an electrical insulator between the developing roller and the photosensitive drum, and the presence of the toner in the nip portion where the developing roller and the photosensitive drum are in contact with each other allows the surface potential of the photosensitive drum to be stably maintained for developing.

[0005]

However, in the impression developing system which adopts the structure in which the transfer means is arranged above the photosensitive drum as described above, the rotation direction of the developing roller is changed in relation to the toner conveying direction. The direction is opposite at the nip portion with respect to the photosensitive drum. For this reason, particularly when trying to develop the developing efficiency close to 100%, during black solid printing, most or most of the toner adheres to the photosensitive drum at the upper portion of the nip portion. There is little or almost no toner that also serves as an electrical insulator. As a result, the electric insulation between the developing roller and the photosensitive drum cannot be maintained by the toner existing in the nip portion, and the developing bias voltage applied to the developing roller leaks to the photosensitive drum, and the surface potential of the photosensitive drum is reduced. Becomes unstable, and finally the quality of the output image deteriorates. On the other hand, by lowering the developing efficiency, it is possible to leave the toner on the developing roller at the nip portion even in the case of solid black printing, but if this is done, the developing efficiency will literally decrease.

The present invention has been made in view of the above problems, and an image capable of forming a high-quality image while enhancing the development efficiency by using a developing roller that moves in the opposite direction at the nip portion with respect to the photosensitive member. An object is to provide a forming apparatus and a developing roller for the image forming apparatus.

[0007]

In order to solve the above problems, an image forming apparatus according to a first aspect of the present invention includes a photoconductor, a latent image forming unit that forms an electrostatic latent image on the photoconductor, and the photoconductor. A developing roller for developing the formed electrostatic latent image with toner to form a toner image on the photoconductor while moving in a direction opposite to the moving direction of the photoconductor in a nip portion in contact with the body. , At least the surface portion in contact with the photosensitive member, the developing roller made of an ion conductive material, bias means for applying a developing bias voltage to the developing roller, and the toner image formed on the photosensitive member on a recording medium. And a transfer means for transferring.

According to the image forming apparatus of the first aspect,
First, the latent image forming means forms an electrostatic latent image on the photoconductor. Next, the electrostatic latent image on the photoconductor is developed by the toner on the developing roller while moving in the direction opposite to the moving direction of the photoconductor at the nip portion where the developing roller contacts the photoconductor, A toner image is formed. Here, at least the surface portion of the developing roller, which is in contact with the photosensitive member, is made of an ion conductive material. Therefore, the ionic conductive material imparts conductivity to the developing roller, and a developing bias voltage can be applied by the bias means during development.

Further, firstly, when the electrically insulating toner is used, the developing roller moves in the nip portion in the direction opposite to the moving direction of the photosensitive member. Even if the developing roller and the photosensitive member come into direct contact with each other by the toner acting as an electric insulator being adhered to the photosensitive member at the upper portion, discharge at the nip portion is relatively unlikely to occur. Therefore, it is possible to reduce the occurrence of the situation where the developing bias voltage applied to the developing roller leaks to the photoconductor and the surface potential of the photoconductor becomes unstable.

Secondly, when a conductive toner is used, the developing roller moves in the direction opposite to the moving direction of the photosensitive member in the nip portion, and therefore, at the upper portion of the nip portion during solid black printing. Even if the developing roller directly contacts the photosensitive member due to the toner adhering to the photosensitive member or the toner is present in the nip portion and the developing roller and the photosensitive member contact each other via the toner, the nip portion Is relatively unlikely to occur. Therefore, it is possible to reduce the occurrence of the situation where the developing bias voltage applied to the developing roller leaks to the photoconductor and the surface potential of the photoconductor becomes unstable.

That is, according to the above-mentioned conventional technique, since the developing roller is provided with the conductivity by the electronic conductivity in which the conductive particles are dispersed, when the developing bias voltage is applied, the conductive particles are concerned. Becomes the nucleus of the discharge, so that the discharge is relatively likely to occur. On the other hand, according to the present invention, since the conductivity is imparted by being composed of the ion conductive material, there is no core of the discharge, so that the discharge is relatively unlikely to occur. is there. As a result, by increasing the developing efficiency, that is, by bringing the developing efficiency close to 100%, even if almost no toner remains in the nip portion when solid black printing is performed, the surface potential of the photoconductor is not affected by discharge. Printing defects due to stability are reduced on the transferred image.

An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the ion conductive material is a urethane elastomer as a base material to which a liquid ammonium salt is added. And

According to the image forming apparatus of the present invention,
Since the surface portion is formed by adding a liquid ammonium salt to a urethane elastomer as a base material, abrasion resistance and durability on the surface portion are enhanced.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the developing bias voltage is within a range that does not cause discharge from the surface portion to the photoconductor. It is characterized by being set to a value.

According to the image forming apparatus of the third aspect,
The developing bias voltage is set to a predetermined value within the range that does not cause discharge from the surface of the developing roller to the photosensitive member, so that discharge can be surely prevented, and as a result, developing efficiency is improved. Thus, even if almost no toner remains in the nip portion when performing solid black printing, it is possible to reliably prevent printing defects due to instability of the surface potential of the photoconductor due to discharge.

An image forming apparatus according to a fourth aspect is the image forming apparatus according to any one of the first to third aspects, wherein the transfer means is disposed above the photoconductor and The image forming means is arranged below the photoconductor.

According to the image forming apparatus of the fourth aspect,
Since the transfer unit is arranged above the photoconductor and the latent image forming unit is arranged below the photoconductor, the apparatus can be opened from the upper side as compared with the case where the transfer unit is arranged below. It is possible to have a structure for accessing the path of, and also a structure for exposing the paper feed cassette upward.

An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to the fourth aspect, further comprising a conveying unit that conveys the recording medium along a path extending in a substantially linear shape inside the image forming apparatus. Further, the transfer means transfers the toner image formed on the photoconductor to the recording medium conveyed by the conveying means.

According to the image forming apparatus of the fifth aspect,
Since the path of the recording medium has a substantially linear shape, it is possible to easily construct a structure capable of printing on special paper such as thick paper and envelope. The image forming apparatus according to claim 6 is the image forming apparatus according to any one of claims 1 to 5, wherein the developing roller performs impression development with a developing efficiency of 90% or more. To do.

According to the image forming apparatus of the sixth aspect,
Instability of the surface potential of the photoconductor due to discharge even if the development roller performs impression development with a high development efficiency of 90% or more and almost no toner remains in the nip portion when performing solid black printing. The printing failure due to is reduced on the transferred image.

In order to solve the above-mentioned problems, a developing roller for an image forming apparatus according to a seventh aspect of the present invention forms a latent image on the photoconductor, bias means for applying a developing bias voltage. In an image forming apparatus including a latent image forming unit and a transfer unit that transfers a toner image formed on the photoconductor, the developing bias voltage is applied to the photoconductor at a nip portion in contact with the photoconductor. A developing roller used for developing an electrostatic latent image formed on the photoconductor with toner while moving in a direction opposite to the moving direction to form the toner image, and at least contacting the photoconductor. The surface portion to be formed is made of an ion conductive material.

According to the developing roller for the image forming apparatus of the seventh aspect, as in the case of the image forming apparatus of the first aspect, the toner is added to the nip portion when the solid black printing is performed by increasing the developing efficiency. However, even if almost no image is left, printing defects due to instability of the surface potential of the photoconductor due to discharge are reduced on the transferred image.

A developing roller for an image forming apparatus according to an eighth aspect is the developing roller for an image forming apparatus according to the seventh aspect, wherein the ion conductive material is urethane elastomer as a base material and liquid ammonium salt is used. Is added.

According to the developing roller for an image forming apparatus of the eighth aspect, as in the case of the image forming apparatus of the second aspect, the surface portion has urethane elastomer as a base material and a liquid ammonium salt added thereto. Therefore, the wear resistance and durability of the surface portion are improved.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. 1, a laser beam printer 1 according to an embodiment of the present invention includes a main body case 2, a feeder unit 10 for feeding a sheet P for image formation, and exposure, development, and transfer for image formation. Photosensitive drum 2 as an example of a photoconductor in which the steps such as
0, a fixing unit 70 for fixing the transfer image transferred from the photosensitive drum 20 to the paper P on the paper P, and a paper discharge tray 77 for discharging the paper P on which the image is fixed along the transport path PP. And is configured.

The laser beam printer 1 further includes a laser scanner unit 30 as an example of latent image forming means for forming an electrostatic latent image on the photosensitive drum 20 in order along the periphery of the photosensitive drum 20, and the photosensitive drum 20. As an example of a developing unit 50 having a developing roller 56 for developing the electrostatic latent image formed on the drum 20 with toner, and a transfer unit for transferring the toner image developed on the photosensitive drum 20 to the paper P. The transfer roller 60 and the residual toner left on the photosensitive drum 20 after the transfer by the transfer roller 60 are transferred to the developing unit 50 at a predetermined timing using the photosensitive drum 20.
Cleaning roller 42 for temporarily adsorbing the residual toner in order to restore the residual toner, a discharging lamp 41 for removing the residual potential left on the photosensitive drum 20 after the transfer, and the electrostatic latent image on the photosensitive drum 20 after the discharging. And a charger 40 for forming a charge.

Next, each of the constituent elements of the laser beam printer 1 will be described in detail with reference to FIGS. 1 to 5. In FIG. 1, the feeder unit 10 includes a sheet pressing plate 11 having a width dimension substantially the same as that of the sheet P, which is disposed in the upper feeder section case 3 located at the rear end of the main body case 2. The paper pressing plate 11 is swingably supported at its rear end. A compression spring 12 is provided at the front end of the paper pressing plate 11, and the paper pressing plate 11 is elastically biased upward by the compression spring 12.
The paper pressing plate 11 includes a paper feed roller 13 extending in the left-right direction.
However, it is rotatably supported. The paper feed roller 13 is configured to be rotationally driven at a paper feed timing by a drive system (not shown). In the feeder unit 10, a paper feed cassette 14 capable of accommodating a plurality of sheets P of standard cut paper is detachably mounted in an inclined manner in the feeder case 3, and by rotation of the paper feed roller 13, Among the paper P stored in the paper feed cassette 14, the upper paper P is fed one by one. Further, the feeder unit 10 is provided with a separating member 15 below the paper feeding roller 13 in order to prevent double feeding of the paper P, and the separating member 15 is elastically attached to the paper feeding roller 13 by a compression spring 16. Being energized. A pair of registration rollers 17 and 18 that align the leading ends of the fed paper P are rotatably pivoted downstream of the paper feed roller 13 in the conveying direction (from the rear to the front in FIG. 1). There is.

In FIG. 1 and FIG. 2, the photosensitive drum 20
Is composed of, for example, a positively chargeable material. More specifically, as shown in FIG. 2, the photosensitive drum 20 has, for example, a cylindrical, cylindrical sleeve 21 made of aluminum as a main body, and has a predetermined thickness formed by dispersing a photoconductive resin in polycarbonate on an outer peripheral portion thereof. It is composed of a hollow drum on which a photoconductive layer 22 having a thickness (for example, about 20 μm) is formed, and is rotatably supported by the main body case 2 with the cylindrical sleeve 21 grounded. That is, the toner 53 charged in the positive polarity is developed by the reversal development method with respect to the electrostatic latent image of the positive polarity formed on the photosensitive drum 20. The photosensitive drum 20 is configured to be rotated clockwise in a side view by a drive mechanism.
The photosensitive drum 20 may be made of a negatively chargeable material.

In FIG. 1, the laser scanner unit 3
Reference numeral 0 denotes a laser generator 31 disposed below the photosensitive drum 20, which generates a laser beam L for forming an electrostatic latent image on the photosensitive drum 20, and a polygon mirror (a pentahedron) driven to rotate. Mirror 32, a pair of lenses 33 and 34, and a pair of reflection mirrors 35 and 36. The laser scanner unit 30 is attached to the photosensitive drum 20.
Since the laser beam printer 1 is disposed below the laser beam printer 1, the laser beam printer 1 can be compact in size and can be emitted from the laser scanner unit 30 without interfering with sheet transportation. An electrostatic latent image can be formed on the photosensitive drum 20 with the laser light L.

The charger 40 is composed of a scorotron type charger for generating corona discharge from a charging wire made of, for example, tungsten.
It is supported in a non-contact manner with respect to 0. In the present embodiment, since the photosensitive drum 20 is of a positive charging type, a voltage of positive polarity is applied to the charger 40.

The charge eliminating lamp 41 is constituted by including a light source such as an LED (laser light emitting diode), an EL (Electro Luminescence), a fluorescent lamp or the like, and removes the electric charge remaining on the photosensitive drum 20 after the transfer (eliminating the charge). ), The residual charge affects the next electrostatic latent image,
It finally functions to prevent the image from appearing on the sheet P.

The cleaning roller 42 temporarily absorbs the residual toner 53 remaining on the photosensitive drum 20 after the transfer by the transfer roller 60 by changing the bias voltage, and the next exposure, development, and The residual toner 53 that has been absorbed is discharged to the photosensitive drum 20 at a timing that does not hinder transfer or the like, so that the residual toner 53 is returned from the photosensitive drum 20 to the developing unit 50. The cleaning roller 42 is
For example, it is composed of a conductive foamed elastic body made of silicon rubber or urethane rubber to which a bias voltage can be applied.

1 and 2, the developing unit 50
Includes a double-cylindrical toner box 51 detachably mounted in the developing unit case 4. The toner box 51 includes an agitator 52 that is rotationally driven and a toner 53.
And accommodate. As the toner 53, for example, a positively chargeable toner having an electric insulation property is used. A toner storage chamber 54 for storing the toner 53 supplied by the rotation of the agitator 52 via the toner supply port 51 a formed in the toner box 51 is formed on the front side of the toner box 51. A supply roller 55 is provided in the toner storage chamber 54.
Are arranged horizontally in the longitudinal direction and are rotatably supported. Further, a developing roller 56 is horizontally arranged in the longitudinal direction and is rotatably supported so as to partition the front side of the toner storage chamber 54 and contact the supply roller 55 and the photosensitive drum 20, respectively.

The supply roller 55 is made of a conductive elastic foam material such as silicon rubber or urethane rubber, and the resistance value at the contact portion with the developing roller 56 is about 5 × 10 ⁴ to 1 × 10 5. It is set to ⁹ Ω.

The developing roller 56 forms a nip portion in contact with the photosensitive drum 20, and the surface portion in contact with the photosensitive drum 20 in the nip portion is made of an ion conductive material.

More specifically, the developing roller 56 is made of, for example, a material such as urethane elastomer, and is made of a hard elastic roller provided with conductivity by ionic conduction. Therefore, at the time of development, a developing bias voltage can be applied to the developing roller 56 made of this ion conductive material by the bias means. Such a developing roller 56 is prepared, for example, by mixing a liquid urethane elastomer prepolymer with a cross-linking agent and a liquid ammonium salt for imparting ionic conductivity, and then uniformly mixing them, and then pouring the mixture into a mold to form a solid. It is manufactured by subjecting the surface of the surface to polishing and polishing the surface to obtain the accuracy of the surface dimension. The resistance value from the electrode at the center of the developing roller 56 to which the developing bias voltage is applied to the contact portion on the outer periphery is, for example, about 5 × 10 ⁴ to 1 ×.
It is set to 10 ⁷ Ω.

The developing roller 56 thus constructed is
Since the developing roller 56 moves in the direction opposite to the moving direction of the photosensitive drum 20 in the nip portion, the toner 53 which acts as an electric insulator on the upper portion of the nip portion in the black solid printing is attached to the photosensitive drum 20. Even if the developing roller 56 and the photosensitive drum 20 come into direct contact with each other even if they are attached, the developing roller 56
Since it is made of an ion conductive material, discharge at the nip portion is relatively unlikely to occur. Therefore, it is possible to reduce the occurrence of the situation where the developing bias voltage applied to the developing roller 56 leaks to the photosensitive drum 20 and the surface potential of the photosensitive drum 20 becomes unstable. As a result, by increasing the developing efficiency to 90% or more, that is, by approaching the developing efficiency to 100%, even if almost no toner 53 remains in the nip portion when performing solid black printing, the development is performed by the discharge. The developing bias voltage applied to the roller 56 is the photosensitive drum 2
It is possible to reduce the occurrence of a situation where the surface potential of the photosensitive drum 20 becomes unstable due to the leakage to zero. Even when the conductive toner is used, the discharge is relatively unlikely to occur between the developing roller 56 and the photosensitive drum 20 regardless of the presence of the toner in the nip portion, so that the toner is applied to the developing roller 56. It is possible to reduce the occurrence of the situation where the developing bias voltage leaks to the photosensitive drum 20 and the surface potential of the photosensitive drum becomes unstable.

Here, as a comparative example, conductivity is imparted by dispersing conductive fine particles such as carbon particles on the surface portion of the developing roller (other conditions are the same as in this embodiment). 3 and 4 for the case
This will be described with reference to FIG.

In FIG. 3, the developing roller 156 is provided with conductivity by dispersing carbon particles 156a. Even if the developing roller 156 moves in the nip portion in the direction opposite to the moving direction of the photosensitive drum 20 and the developing efficiency is set to about 100%, a large amount of toner 53 is present in the nip portion during development unlike black solid printing. During the remaining development (close to a white background), a large amount of toner 53a serving as an electric insulator intervenes, so that the developing bias voltage leaks from the developing roller 156 to the photosensitive drum 20. Is less likely to occur, and the surface potential of the photosensitive drum 20 is stably maintained and development is performed. However, under this condition, when performing solid black printing,
Since the toner 53 as an electric insulator adheres to the photosensitive drum 20 before reaching the nip portion, the toner 53 hardly remains in the nip portion. Therefore, the developing roller 156 and the photosensitive drum 20 are in direct contact with each other. As a result, as shown in FIG. 4, the developing bias voltage applied to the developing roller 156 causes the carbon particles 15 contained in the developing roller 156 to have the same voltage.
Since 6a serves as the nucleus of the discharge, discharge easily occurs from the carbon particles 156a as indicated by the arrow 101, and finally, the printing potential is caused by the instability of the surface potential of the photosensitive drum 20 due to the discharge. . In other words, due to the dispersion of the carbon particles 156a, the developing roller 1
The electric resistance is uneven in the vicinity of the surface of 56, and discharge easily occurs from the low-resistance carbon particles 156a. As described above, it can be seen from the comparative example of FIG. 4 that the developing roller 56 of the present embodiment is advantageous in setting a high developing efficiency and forming a high quality image. In FIG. 4, for the sake of explanation, the carbon particles 156a are schematically shown larger than the developing roller 156 and the like, but in reality, the carbon particles 156 are much smaller than the developing roller 156 and the like. is there.

As shown in FIG. 5, the developing roller 56 includes
A developing bias voltage is supplied from a DC voltage power source E as an example of bias means. Particularly in the present embodiment, the developing bias voltage is set to the developing roller 56.
Is set to a predetermined value within a range in which the surface of the photosensitive drum 20 is not discharged. Such a predetermined value is
After concretely specifying the configurations of the developing roller 56, the photosensitive roller 20, etc., they are empirically or experimentally or computer-based.
It can be obtained in advance by simulation or the like. As a result, it is possible to reliably prevent the discharge from the developing roller 56 to the photosensitive drum 20.

The developing roller 56 uses the toner 53 to develop on the photosensitive drum 20, and the residual toner 5 returned onto the photosensitive drum 20 by the cleaning roller 42.
3 is configured to be collected.

More specifically, for example, with respect to the photosensitive drum 20 in which the residual toner 53 after transfer is about 10% of the toner amount before transfer, the residual toner 53 is first removed by the laser scanner unit 30. The exposure should be performed so that the laser light can reach the bottom of the window. Next, in the developing unit 50, the residual toner 53 is attached to the unexposed portion of the photosensitive drum 20 by utilizing the potential difference between the exposed portion and the unexposed portion existing regardless of the presence of the residual toner 53 on the photosensitive drum 20. If so, the residual toner 53 is moved (collected) to the developing roller 56, and at the same time,
If the residual toner 53 has already adhered to the exposed portion of the photosensitive drum 20, it should be adhered (developed) as it is,
If the residual toner 53 does not adhere to the exposed portion of the photosensitive drum 20, the positively charged toner 53 is moved (developed) from the developing roller 56. That is, the developing unit 50 is configured so that the developing cycle and the collecting cycle are performed almost simultaneously.

Further, for example, a collecting-dedicated roller is provided adjacent to the side of the developing roller 56 near the laser scanner unit 30 to collect the residual toner 53 by the collecting-dedicated roller, and the developing roller 56 functions as a developing-dedicated roller. The developing unit 50 may be configured to do so. In this case, the developing unit 50 is configured so that the residual toner 53 collected by the collecting roller is moved toward the supply roller 55 and the developing roller 56 by the rotation of the collecting roller.

Further, for example, by providing a developing cycle and a collecting cycle separately and changing the bias voltage of the developing roller 56 with respect to the photosensitive drum 20 in each cycle, in the developing cycle, the developing bias voltage is applied to develop. The positively charged toner 53 is transferred from the roller 56 to the photosensitive drum 20.
The developing unit 50 may be configured so as to move (develop) to the exposed portion of (3) and apply a collecting bias voltage to move (collect) the residual toner 53 from the photosensitive drum 20 to the developing roller 56 in the collecting cycle.

As described above, in the present embodiment, it is possible to adopt various types of methods for collecting the residual toner in the developing unit 50 using the developing roller 56.

The supply roller 55 and the developing roller 56 are constructed so as to be rotated clockwise by a drive mechanism. The laser beam printer 1 has the developing roller 56 including the conductive hard elastic roller.
To the photosensitive drum 20, and using, for example, a spring, the developing roller 5
Impression development is performed by pressing from both ends with a load of about 500 grams.

As shown in FIG. 2, the developing unit case 4 in the developing unit 50 is provided with a toner storage chamber 54, and the toner storage chamber 54 is formed by providing a large upper space S above the supply roller 55. Has been done. For this reason, the toner 53 of the toner box 51 is not supplied to the toner supply port 51a.
Even when a large amount of toner is supplied to the toner storage chamber 54 via the toner, the toner 53 is not packed and solidified.
The toner 53 is always in powder form, its fluidity is maintained, and the toner supply by the supply roller 55 can be stabilized.

In FIGS. 1 and 2, a thin plate-like elastic layer thickness regulating blade 57 made of stainless steel or phosphor bronze is attached to the developing unit case 4 downward.

The bent portion 57a formed at the lower end of the layer thickness regulating blade 57 is in contact with the developing roller 56 in a pressed state, and is supplied from the supply roller 55 to be supplied to the developing roller 56.
The layer thickness of the toner 53 adhered to the surface of the toner layer in a layered manner is a predetermined thickness of about one layer (about 7 to 12 μm) by the layer thickness regulating blade 57.
m). That is, the toner amount on the developing roller 56 is configured to be 0.5 mg / cm ² or less. The layer thickness regulating blade 57 preferably has a radius of curvature of about 0.3 m, for example, so that the amount of toner on the developing roller 56 is set to about 0.4 mg / cm ^2.
m. The developing bias and the developing roller 56
The minimum required toner amount on the developing roller 56 is determined by the number of rotations of the developing roller 56, and for example, if the toner amount on the developing roller 56 is about 0.3 mg / cm ² , the developing bias and It is possible to perform development with a sufficient toner density by using the rotation speed of the developing roller 56. Instead of the layer thickness regulating blade 57, an elastic body may be pressed against the developing roller 56 by using a spring, or the layer thickness may be regulated by a blade having no bent portion as described above.

The transfer roller 60 is provided so as to be in contact with the upper side of the photosensitive drum 20, is rotatably supported, and is composed of a conductive foamed elastic body made of silicon rubber or urethane rubber. Photosensitive drum 20 of transfer roller
The resistance value at the contact part with is about 1 × 10 ⁶ to 1 × 10
It is set to ¹⁰ Ω. That is, since the transfer roller 60 is in contact with the surface of the photosensitive drum 20, by increasing the resistance value thereof, the photoconductive layer 22 formed on the photosensitive drum 20 is destroyed by the voltage applied to the transfer roller 60. The toner image on the photosensitive drum 20 is surely transferred onto the paper P so as to prevent the occurrence of the above-mentioned problem.

The fixing unit 70 is provided on the downstream side of the photosensitive drum 20 in the conveying direction, and is composed of a heating roller 71 and a pressing roller 72 having a well-known halogen lamp built therein, and the toner image transferred onto the lower surface of the paper P. Is pressed by the heating roller 71 while being heated and fixed on the paper P.

A pair of transport rollers 75 and a paper discharge tray 77 for transporting the paper are respectively provided on the downstream side of the fixing unit 70 in the transport direction. According to the present embodiment, the paper feed roller 13, the photosensitive drum 20, the fixing unit 70, and the paper discharge tray 77 constitute an example of a conveying unit, and have a substantially linear shape as shown by a dashed line in FIG. The paper P fed from the paper feed cassette 14 is configured to be transported along the extending transport path PP.

In FIG. 1, the toner 53 is, for example, a pulverized toner or a polymerized toner made of styrene-acryl or the like having a nearly spherical shape, and its particle size is about 6 to 12 μm. In the present embodiment, in particular, the toner 53 is generated by discharging the developing bias voltage from the developing roller 56 into the photosensitive drum 2.
It is made of a material having an electrical insulating property in order to prevent leakage to zero. In this way, by making the toner 53 serve as an electric insulator, the development efficiency can be reduced to 1
Even when it is brought close to 00%, the toner 53 slightly remaining in the nip portion and the developing roller 20 made of an ion conductive material work together to cause the developing roller 56 to move to the photosensitive drum 2.
The discharge to 0 can be effectively prevented. However, the toner 53 may be made of a conductive material and the discharge of the developing roller 56 to the photosensitive drum 20 may be prevented by the action of the developing roller 20 made of an ion conductive material.

The toner 53 is obtained by adding silica, for example, as an external additive (fluidity imparting agent) for increasing the fluidity of the toner 53. Here, the base toner is configured to include, for example, resin, wax, carbon black, and CCA (charge control agent). Silica, which is an example of an external additive, is a toner surface modifier and has an effect of improving fluidity.

In addition to the function of imparting fluidity, the external additive of the toner 53 should have functions of preventing toner blocking, improving cleaning properties, preventing scratches on the photosensitive drum, improving image density, improving image quality, and the like. Is possible. Also,
Examples of the external additive other than silica include fine powders of colloidal silica, titanium oxide, aluminum oxide (alumina) and the like.

Next, the operation of the laser beam printer 1 configured as described above will be described with reference to FIGS. 1 and 5 to 8. In the present embodiment, it is assumed that the image is formed by the developing process of the reversal developing method.

In FIG. 1, the photosensitive drum 20 is rotationally driven clockwise by a drive mechanism in a side view, and the supply roller 55 and the developing roller 56 are rotationally driven clockwise, respectively. As a result, the respective particles of the toner 53 are rubbed by the supply roller 55 and the developing roller 56 as shown in FIG.
The toner 53 that is positively charged due to the pressure friction on the toner 53 adheres to the electrostatic latent image formed on the photosensitive drum 20 by the laser light L and is developed by the reversal development method. .

Here, for example, as the transmission density (image density) necessary for the image formed on the paper P, for example, "2.
In order to obtain “0”, as shown in FIG. 6, the amount of toner 53 attached to the paper P, that is, the amount of developing toner is about 0.78 m.
g / cm ² is required. To this end, as described above, the toner amount on the developing roller 56 is set to about 0.4 mg / cm ² by the layer thickness regulating plate 57, while the developing efficiency is set to about 100%, and the circumference of the developing roller 56 is set. The speed is set to about twice the peripheral speed of the photosensitive drum 20. As a result, at the time of solid black printing, the surface portion of the developing roller 56 comes into direct contact with the photosensitive drum 20 at the nip portion with almost no toner 53, but the developing roller 56 is made of an ion conductive material. Therefore, the discharge in the nip portion is relatively unlikely to occur, so that the developing bias voltage applied to the developing roller 56 leaks to the photosensitive drum 20 due to the discharge and the surface potential of the photosensitive drum 20 becomes unstable. It can be reduced. Incidentally, the developing efficiency may be made slightly smaller than 100% so that a small amount of the toner 53 remains on the surface portion of the developing roller 56 even after the development due to the van der Waals force. In this case, the toner 53 slightly remaining in the nip portion and the developing roller 20 made of an ion conductive material work together to effectively prevent discharge from the developing roller 56 to the photosensitive drum 20.

The charge amount of the toner 53 is about 25 μC / g in a low temperature and low humidity environment at a temperature of about 10 ° C. and a humidity of about 20%, and from a high temperature and high humidity environment of about 32 ° C. and a humidity of about 80%. It varies up to about 20 μC / g. Therefore, when the developing roller 56 is driven in the same rotation direction as the photosensitive drum 20, as shown in FIG. 7, whichever of the low temperature and low humidity environment indicated by the one-dot chain line and the high temperature and high humidity environment indicated by the two-dot chain line is shown. Even in the environment, a predetermined amount of developing toner (about 0.7
The effective developing bias voltage of the developing roller 56 is set to "about 200 V" so that 8 mg / cm ² ) can be obtained. At the same time, since the electrostatic latent image voltage, which is the voltage of the electrostatic latent image formed on the photosensitive drum 20, is “about 100 V”, the developing bias voltage of the developing power source E applied to the developing roller 56 is set to “about 300 V”. Is set. It is assumed that the value of the developing bias voltage is a predetermined value included in the voltage range in which the surface of the developing roller 56 does not discharge the photosensitive drum 20, as described above.

When the image forming process is started under the voltage setting as described above, first, the charge eliminating lamp 41 is operated by the photosensitive drum 20.
After the upper residual charge is wiped out, the surface of the photosensitive drum 20 is charged by the charger 40 to about +, for example, as shown in FIG.
It is uniformly charged to 800V. Then, in this state, the laser light L emitted from the laser generator 31 is applied to the photosensitive drum 20 through the lenses 33 and 34 and the reflecting mirrors 35 and 36 while being main-scanned by the polygon mirror 32, and the photosensitive drum 20 is irradiated. An electrostatic latent image is formed on 20.
At this time, the voltage of the portion corresponding to the electrostatic latent image on the photosensitive drum 20 is lowered to about +100 V by the irradiation of the laser light L, for example, as shown in FIG. Developing roller 56
On the surface of, the toner 53 of positive polarity is attached with a layer thickness of more than one layer in a state where, for example, about +300 V is applied as the developing bias voltage as shown in FIG. Charge voltage higher than its own voltage (about +
800V) and is attracted to a lower electrostatic latent image voltage (about + 100V), and the toner 53 on the developing roller 56 adheres only to the electrostatic latent image formed on the photosensitive drum 20. And then developed. That is, in the nip portion between the photosensitive drum 20 and the developing roller 56, the developing roller 56 is moved in the opposite direction to the photosensitive drum 20, and the impression development is performed, so that the photosensitive drum 20
A visible toner image is formed on top.

At this time, particularly in the case of solid black printing, the surface portion of the developing roller 56 comes into direct contact with the photosensitive drum 20 at the nip portion with almost no toner 53 interposed therebetween, but the developing roller 56 is ionized. It is made of a conductive material, and the developing bias voltage is applied from the surface of the developing roller 56 to the photosensitive drum 20.
Predetermined value (about 300V) within the range that does not cause discharge
Is set to, the developing roller 5 in the nip portion
No discharge from 6 to the photosensitive drum 20 occurs.

The toner image of the electrostatic latent image developed with the toner 53 is transferred onto the paper P by the transfer roller 60, and thereafter,
The fixing processing is performed by the fixing unit 70 and the sheet is discharged to the sheet discharge tray 77. At this time, the transport path PP for transporting the paper P fed from the paper feed cassette 14 is formed in a substantially linear shape, and the paper P is image-formed while being transported by the substantially linear transport path PP. Even if a thick paper such as a postcard or an envelope or an OHP film is used as the paper P, a clean and reliable image can be formed on the paper P.

On the other hand, in FIG. 1, the residual toner 53 remaining on the photosensitive drum 20 without being transferred onto the paper P when passing through the transfer roller 60 is changed by changing the bias voltage of the cleaning roller 42. Is once absorbed by. Then, the residual toner 53 once absorbed is changed by changing the bias voltage of the cleaning roller 42 at a timing that does not interfere with the next exposure, development, transfer, etc. performed on the photosensitive drum 20.
The toner 53 is discharged from the cleaning roller 42 to the photosensitive drum 20, the residual toner 53 on the photosensitive drum 20 is collected by the developing roller 56, and the toner 53 is recycled.

As a result, according to the laser beam printer 1 of the present embodiment, the developing roller 56 is the photosensitive drum 20.
The electrostatic latent image on the photosensitive drum 20 is impression-developed by the toner 53 on the developing roller 56 with a developing efficiency of about 100% while moving in the direction opposite to the moving direction of the photosensitive drum 20 in the nip portion contacting with. However, it is possible to prevent the developing bias voltage from leaking from the developing roller 56 to the photosensitive drum 20 due to discharge, and thus, the photosensitive drum 2
Degradation of the output image due to instability of the surface potential of 0 can be prevented.

Although only the formation of a monochrome image has been described in the above embodiment, the present invention also effectively functions in the formation of a color image. Further, although the photoconductor is composed of a photoconductor drum, the same effect can be expected even if the photoconductor is a belt-shaped photoconductor and moves in the opposite direction at the nip portion. Further, although the present embodiment is configured to collect and recycle the residual toner 53, when a cleaning device including a cleaning blade or the like is provided, the toner from the cleaning device is further transferred to the developing unit 50 by an auger spring or the like. The developing roller 5 according to the present embodiment is also used when it is returned to be used for recycling.
6 works effectively. Furthermore, in the present embodiment, the laser beam printer has been described. However, in the case of an electrophotographic image forming apparatus using toner, a copying machine, a facsimile device, and the like are also provided as in the case of the present embodiment. The invention works effectively.

[0066]

According to the image forming apparatus of the first aspect of the present invention, the developing bias voltage applied to the developing roller is unlikely to leak to the photoconductor due to discharge, so that the black solid printing is performed by increasing the developing efficiency. Even if almost no toner remains in the nip portion, it is possible to reduce printing defects due to instability of the surface potential of the photoconductor due to discharge.
A high quality image can be formed.

According to the image forming apparatus of the second aspect,
Since the surface portion is formed by adding a liquid ammonium salt to a urethane elastomer as a base material, abrasion resistance and durability on the surface portion are enhanced.

According to the image forming apparatus of the third aspect,
Since the developing bias voltage applied to the developing roller does not leak to the photoconductor due to discharge, even if almost no toner remains in the nip portion when performing solid black printing by increasing the development efficiency, the photoconductor due to discharge does not Printing defects due to instability of the surface potential can be eliminated, and a high quality image can be formed.

According to the image forming apparatus of the fourth aspect,
By opening the device from the upper side and accessing the paper path, it becomes easier to handle paper jams.
Further, by adopting a structure in which the paper feed cassette is exposed upward, it becomes easy to feed paper.

According to the image forming apparatus of the fifth aspect,
Since the paper path is substantially linear, it can be easily printed on special paper such as thick paper and envelopes. According to the image forming apparatus of claim 6, even when almost no toner is left in the nip portion when performing solid image blackening by impression development with a high developing efficiency of 90% or more, exposure by discharge is performed. Printing defects due to instability of the body surface potential can be reduced, and high quality images can be formed.

According to the developing roller for the image forming apparatus of the seventh aspect, as in the case of the image forming apparatus of the first aspect, the toner is added to the nip portion when the solid black printing is performed by increasing the developing efficiency. However, even if almost no image remains, it is possible to reduce printing defects due to instability of the surface potential of the photoconductor due to discharge, and it is possible to form a high quality image.

According to the developing roller for an image forming apparatus of the eighth aspect, as in the case of the image forming apparatus of the second aspect, the surface portion has urethane elastomer as a base material and a liquid ammonium salt added thereto. Therefore, the wear resistance and durability of the surface portion are improved.

As a result, according to the present invention, it is possible to realize an electrophotographic image forming apparatus capable of forming a high quality image while improving the developing efficiency.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view of a laser beam printer according to an embodiment of the present invention.

FIG. 2 is an enlarged side view of a developing unit and a photosensitive drum portion of the laser beam printer of FIG.

FIG. 3 is a schematic enlarged sectional view of a developing roller and a photosensitive drum when toner is present in a nip portion in a comparative example.

FIG. 4 is a schematic enlarged cross-sectional view of a developing roller and a photosensitive drum when toner is not present in a nip portion in a comparative example.

5 is an enlarged side view of a developing unit of the laser beam printer of FIG.

6 is a characteristic diagram showing a relationship between a developing toner amount and a transmission density in the laser beam printer of FIG.

7 is a characteristic diagram showing the relationship between the effective bias voltage and the amount of developing toner in the laser beam printer of FIG.

FIG. 8 is an explanatory diagram showing the potential of each part of the development processing by the reversal development method performed in the laser beam printer of FIG.

[Explanation of Codes] 1 ... Laser beam printer 10 ... Feeder unit 13 ... Paper feed roller 14 ... Paper feed cassette 20 ... Photosensitive drum 30 ... Laser scanner unit 42 ... Cleaning roller 50 ... Developing unit 53 ... Toner 55 ... Supply roller 56 ... Developing roller 57 ... Layer thickness regulating blade 60 ... Transfer roller 70 ... Fixing unit 77 ... Paper ejection tray

Claims (8)

[Claims] 1. A photoconductor, a latent image forming means for forming an electrostatic latent image on the photoconductor, and a nip portion contacting the photoconductor while moving in a direction opposite to a moving direction of the photoconductor. A developing roller for developing the formed electrostatic latent image with toner to form a toner image on the photoconductor, wherein at least the surface portion in contact with the photoconductor is made of an ion conductive material; An image forming apparatus comprising: a bias unit that applies a developing bias voltage to the developing roller; and a transfer unit that transfers the toner image formed on the photoconductor to a recording medium. 2. The image forming apparatus according to claim 1, wherein the ion conductive material is formed by adding a liquid ammonium salt to a urethane elastomer as a base material. 3. The image forming apparatus according to claim 1, wherein the developing bias voltage is set to a predetermined value within a range that does not cause discharge from the surface portion to the photoconductor. . 4. The transfer means is arranged above the photoconductor, and the latent image forming means is arranged below the photoconductor. The image forming apparatus according to item 1. 5. The image forming apparatus further comprises a conveying unit that conveys the recording medium along a path extending in a substantially linear shape, and the transferring unit transfers the toner image formed on the photoconductor. The image forming apparatus according to claim 4, wherein the image is transferred onto the recording medium conveyed by the conveying unit. 6. The image forming apparatus according to claim 1, wherein the developing roller performs an impression development with a developing efficiency of 90% or more. 7. A photoconductor, a latent image forming unit that forms an electrostatic latent image on the photoconductor, a bias unit that applies a developing bias voltage, and a transfer unit that transfers the toner image formed on the photoconductor. And a developing bias voltage is applied to the electrostatic latent image formed on the photoconductor while moving in a direction opposite to the moving direction of the photoconductor at a nip portion in contact with the photoconductor. A developing roller used for developing a latent image with toner to form the toner image, characterized in that at least a surface portion in contact with the photoconductor is made of an ion conductive material. Developing roller. 8. The developing roller for an image forming apparatus according to claim 7, wherein the ion conductive material is formed by adding a liquid ammonium salt to a urethane elastomer as a base material.