JPH09185256A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the recovering ability of a developing roller recovering toner by a cleanerless system and to form a high-quality image. SOLUTION: This device is provided with a photoreceptor drum 20, a laser scanner unit 30 forming an electrostatic latent image, the developing roller 56 forming a toner image on the drum 20 by developing the electrostatic latent image by using toner 53 and recovering the toner 53 left on the drum 20 and a transfer roller 60 transferring the toner image. Besides, it is constituted so that the toner 53 left on the drum 20 after a transfer action is carried on the turned drum 20 and returned to the roller 56. The surface part of the drum 20, the surface part of the roller 56 and the toner 53 are respectively constituted of such a material that the electrostatic charge quantity of the toner 53 on the drum 20 after a developing action becomes >=30% larger than the electrostatic charge quantity of the toner 53 on the roller 56 before the developing action by being mutually rubbed at a nip part when the developing action is executed by the roller 56.

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 copiers. Belongs to the technical field of image forming apparatuses that collect and collect.

[0002]

2. Description of the Related Art Conventionally, as a developing method in an electrophotographic image forming apparatus of this type, a conductive elastic roller is used as a developing roller for carrying toner, and the developing roller is pressed against a photosensitive drum to develop. The so-called impression development method for performing the above is widely adopted.

In recent years, development of an electrophotographic process which does not generate waste toner has been promoted in this type of developing system from the viewpoint of ecology. As one of such processes, the residual toner remaining on the photosensitive drum after transfer is carried to a developing device while being placed on the photosensitive drum so as not to interfere with charging and latent image formation, and the residual toner is transferred by the developing device. There is a so-called cleanerless process of collecting and reusing at the same time as development or at a timing different from development. By using this cleanerless process, it is not necessary to install a cleaning device such as a conventional cleaning blade, the photosensitive drum is not damaged by pressing the blade directly against the photosensitive drum, and the residual toner is compared. It can be returned to the developing device efficiently.

[0004]

However, according to the above-mentioned conventional cleanerless process, since the residual toner is collected by the developing roller, the collecting ability has a certain limit in order to maintain the developing ability. By forming a cleaning roller that absorbs and discharges the residual toner so that the residual toner does not interfere with other processes such as charging, latent image formation, and development, and a brush that smoothes the residual toner, an image is formed. It is possible to improve the recovery efficiency of the entire apparatus, but even with these means, the recovery capability of the developing roller itself cannot be improved. Therefore, in particular, when the setting of the paper is wrong or when the paper is printed on the paper that is extremely difficult to transfer, a large amount of residual toner is generated, which exceeds the collecting ability of the developing roller, and as a result, the residual toner is not collected. There is a problem in that development failure due to the presence thereof causes deterioration of output image quality.

The present invention has been made in view of the above problems, and an image forming apparatus capable of improving the collecting ability of a developing roller for collecting toner in a cleanerless system and capable of forming a high quality image. The challenge is to provide.

[0006]

In order to solve the above-mentioned problems, an image forming apparatus according to a first aspect of the present invention includes a photoconductor, a drive unit for rotating the photoconductor, and the rotated photoconductor. A latent image forming means for forming an electrostatic latent image and a nip portion are formed between the latent image forming means, which carries the developer and is in contact with the photosensitive member, and the electrostatic latent image formed at the nip portion. The image forming apparatus includes a developer carrying unit that develops an image with the developer to form a visible image, and a transfer unit that transfers the formed visible image onto a recording medium. The residual developer remaining on the photoconductor after the transfer by the transfer unit is configured to be placed on the rotated photoconductor and collected, and the surface portion of the photoconductor and the developer carrying unit The surface portion and the developer are irreversible during development by the developer carrying means. By being rubbed against each other in the developing section, the charge amount of the developer on the photoconductor after the development becomes 30% or more larger than the charge amount of the developer on the developer holding means before the development. It is characterized in that each is made of a material.

According to the image forming apparatus of the first aspect,
The photoconductor is rotated by the driving unit, and first, an electrostatic latent image is formed on the photoconductor by the latent image forming unit. Next, the formed electrostatic latent image is developed by the developer by the developer carrying means to form a visible image on the photoreceptor. Then, the visible image formed on the photoconductor is transferred to the recording medium by the transfer unit. Image formation is performed as described above. On the other hand, the residual developer remaining on the photoconductor after the transfer is placed on the rotated photoconductor and carried toward the developer carrying means. Then, when the residual developer returns to the developer carrying means, the developer carrying means collects the residual developer on the photoconductor. As described above, the residual developer is collected by the cleanerless method, and the developer collected by the developer carrying means is reused for the subsequent development. Here, in particular, during development, when the surface portion of the photoconductor, the surface portion of the developer carrying means and the developer are rubbed against each other at the nip portion, the charge amount of the developer on the photoconductor after development is The charge amount of the developer on the developer carrying means before development is 30% or more, and accordingly, the charge amount of the residual developer consisting of the developer on the photoreceptor after development is also increased.
Therefore, when the residual developer is collected by the developer carrying means,
Since the charge amount of the residual developer becomes larger than the charge amount of the developer on the developer carrying means, when the residual developer is transferred (recovered) to the developer carrying means, the residual developer is charged on the developer carrying means. The electric repulsive force received from the charge of a certain developer becomes small, and the recovery bias is easily applied to the residual developer. That is, for example, when the developer is charged to the saturated charge amount on the developer carrying unit, the charge amount of the developer on the developer carrying unit before the development and the charge amount of the developer on the photosensitive member after the development are different from each other. Since the charge amount of the residual developer returned to the developer carrying means is substantially equal to the charge amount of the developer before development on the developer carrying means, the residual developer is developed with respect to the residual developer. The recovery bias in the agent carrying means becomes less effective. As described above, according to the present invention, the ability of the developer carrying means to collect the residual developer is improved. On the other hand, the developer for development on the developer carrying means is sufficiently charged when it is rubbed at the nip portion, so that the developing ability is not deteriorated and the development is appropriately performed almost at the same time as the recovery.

An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, in which the layer thickness of the developer is regulated on the developer carrying means and the developer is rubbed to remove the first layer. It is further characterized by further comprising a layer thickness regulating blade for charging to a charge amount, and the developer on the photoconductor is charged to a second charge amount that is 30% or more larger than the first charge amount.

According to the image forming apparatus of the second aspect,
The layer thickness regulating blade regulates the layer thickness of the developer on the developer carrying means, and at this time, the developer on the developer carrying means is rubbed by the layer thickness regulating blade and charged to the first charge amount. On the other hand, the developer moved from the developer carrying means onto the photosensitive member is rubbed at the nip portion, so that the first
The second charge amount is 30% or more larger than the charge amount.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the second charge amount is
It is characterized in that it is equal to the saturated charge amount of the developer. According to the image forming apparatus of the third aspect, the developer moved from the developer carrying unit onto the photoconductor is charged until the charge amount of the developer is saturated by rubbing the developer in the nip portion.

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 surface portion of the photoconductor is made of a positively chargeable organic photoconductor. The surface portion of the developer carrying means contains urethane, and the developer is a positively charged toner containing a predetermined amount of a charge control agent for positive charging.

According to the image forming apparatus of claim 4,
When the positively chargeable toner and the positively chargeable photoconductor are relatively easily rubbed against each other at the nip portion, the amount of charge of the toner on the photoconductor after development is the developer before development. It can be set to be 30% or more larger than the charge amount of the toner on the carrying means.

An image forming apparatus according to a fifth aspect is the image forming apparatus according to the first aspect.
The image forming apparatus according to any one of items 1 to 4,
The latent image forming means further includes a charging unit arranged in a non-contact manner to face the photoconductor at a charging position so as to charge the rotated photoconductor. An image is formed, and the residual developer is returned to the developer carrying means via the charging position.

According to the image forming apparatus of claim 5,
The photoconductor is charged by the charging unit, and an electrostatic latent image is formed on the photoconductor charged by the latent image forming unit. After transfer,
Even though the residual developer is carried on the photoconductor, the charging means is positioned so as to be in non-contact with the photoconductor, so that the residual developer does not adhere to the charging means when passing through the charging position. The charging performance of the charging means does not decrease due to the adhesion of the developer.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the charging means includes a scorotron charger for positive charging. According to the image forming apparatus of claim 6, as compared with the case where the photoconductor is positively charged by the scorotron charger for positive charging relatively easily, and the photoconductor is negatively charged by the scorotron charger, charging means is used. The amount of ozone generated due to the ionization of air between the photoconductor and the photoconductor is reduced to, for example, about 1/10.

An image forming apparatus according to a seventh aspect is the image forming apparatus according to any one of the first to sixth aspects, wherein the residual developer is temporarily adsorbed, and the temporary operation is performed at a predetermined timing. It is characterized by further comprising a developer dispersion means for discharging the developer adsorbed on the photosensitive member onto the photoreceptor.

According to the image forming apparatus of claim 7,
The residual developer is temporarily adsorbed by the developer dispersion means. After that, at a predetermined timing at which the photosensitive member portion on which the residual developer is placed does not interfere with other processes such as charging, latent image formation, and development, the developer temporarily adsorbed by the developer dispersion means is developed. It is discharged from the agent dispersion means onto the photoconductor, placed on the photoconductor, and conveyed toward the developer carrying means.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 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 as an example of a recording medium for image formation, and an image forming unit. A photosensitive drum 20 as an example of a photosensitive member on which processes such as exposure, development, transfer, and recovery are sequentially performed; and a fixing unit 70 for fixing the transfer image transferred from the photosensitive drum 20 to the paper P to 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.

The laser beam printer 1 also includes a drive unit (not shown) for rotating the photosensitive drum 20, and the photosensitive drum 20 is rotated by the drive unit in sequence along the periphery of the photosensitive drum 20. A laser scanner unit 30 as an example of a latent image forming unit for forming an electrostatic latent image on the surface of the photosensitive drum 20, and a toner image as an example of a developer for developing the electrostatic latent image formed on the photosensitive drum 20. A developing unit 50 having a developing roller 56 as an example of a developer carrying unit, a transfer roller 60 as an example of a transferring unit that transfers the toner image developed on the photosensitive drum 20 onto the paper P, and a transfer by the transfer roller 60. After that, the residual toner remaining on the photosensitive drum 20 is returned to the developing unit 50 at a predetermined timing using the photosensitive drum 20 by a cleanerless method. Cleaning roller 4 which is an example of a developer dispersion means for temporarily adsorbing the residual toner to
2, a discharging lamp 41 for removing the residual potential remaining on the photosensitive drum 20 after the transfer, and the photosensitive drum 2 after the discharging.
And a charger 40 as an example of a charging unit for charging 0 so that an electrostatic latent image can be formed.

Next, each constituent element of the laser beam printer 1 will be described in detail with reference to FIGS. 1 to 3. 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 a positively chargeable material, for example, an organic photoreceptor having a positively chargeable polycarbonate as a main component. More specifically, as shown in FIG. 2, the photosensitive drum 20 is, for example, a cylindrical cylindrical sleeve 21 made of aluminum.
The main body of which has a predetermined thickness (for example, about 20 μm) in which a photoconductive resin is dispersed in polycarbonate on the outer peripheral portion thereof.
The photoconductive layer 22 is formed into a hollow drum, and is rotatably supported by the main body case 2 with the cylindrical sleeve 21 grounded. That is, the photosensitive drum 2
The toner 53 charged in the positive polarity is developed by the reversal development method with respect to the electrostatic latent image formed in the positive polarity (positive charge). The photosensitive drum 20 is
The drive means is configured to rotate and drive clockwise in a side view.

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, for example, a scorotron type charger for positive charging for generating corona discharge from a charging wire made of tungsten or the like. In the present embodiment, a cleanerless system is adopted, but the charger 40 is arranged so as to face the photosensitive drum 20 in a non-contact manner so that the residual toner on the photosensitive drum 20 does not adhere to the charger 40. ing.

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.

By changing the bias voltage, the cleaning roller 42 once absorbs the residual toner 53 remaining on the photosensitive drum 20 after the transfer by the transfer roller 60, and the next exposure and development performed on the photosensitive drum 20. 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. Although the cleaning roller 42 is provided so that the recovery by the cleanerless method can be performed efficiently, instead of or in addition to the cleaning roller 42, a cleaning brush for smoothing the residual toner on the surface of the photosensitive drum 20. May be provided.

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 accommodates an agitator 52 that is driven to rotate and a positively charging toner 53 that has electrical insulation. In front of the toner box 51, a toner storage chamber 54 for storing the toner 53 supplied by the rotation of the agitator 52 through the toner supply port 51a formed in the toner box 51.
Are formed. In the toner storage chamber 54, a supply roller 55 is horizontally arranged in the longitudinal direction and is rotatably supported. Further, a developing roller 56 is horizontally arranged in the longitudinal direction 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, and is rotatably supported.

The supply roller 55 is made of a conductive elastic foam material such as silicone 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 is a conductive rigid roller made of silicon rubber, urethane rubber, or the like, and in the present embodiment, it is mainly composed of positively chargeable toner and positively chargeable polycarbonate. Since the photosensitive drum 20 made of an organic photosensitive member is used, urethane rubber is used as the material of the developing roller 56. This urethane rubber is particularly used when the toner 53 and the photosensitive drum 20 are rubbed against each other at the nip portion where the developing roller 56 and the photosensitive drum 20 are in contact with each other. The urethane rubber component is blended so as to be 30% or more larger than the charge amount of the toner 53 on the developing roller 56 before development.

The resistance value from the central electrode of the developing roller 56 to which the developing bias voltage is applied to the outer peripheral contact portion is set to about 5 × 10 ⁴ to 1 × 10 ⁷ Ω. The supply roller 55 and the developing roller 56 are configured to be rotationally driven clockwise by a drive mechanism.

The developing roller 56 is configured to perform development on the photosensitive drum 20 by using the positively charged toner 53 and collect the residual toner 53 returned to the photosensitive drum 20 by the cleaning roller 42.

More specifically, for example, for the photosensitive drum 20 in which the residual toner 53 remains about 10% of the toner amount before the transfer after the transfer, first, the residual toner 53 is removed by the laser scanner unit 30. The exposure should be performed so that the laser light reaches the bottom sufficiently. 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.

As shown in FIG. 2, the developing unit case 4 of 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 downward to the developing unit case 4.

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. As described above, since the layer thickness of the toner layer is regulated by the layer thickness regulating blade 57 so as to form a layer having a toner amount of 0.5 mg / cm ² or less on the developing roller 56, the developing roller 5
The layer thickness of the toner 53 on 6 is 2 based on the toner particles.
It is less than one layer, that is, one layer or one layer is strong. As a result,
Most of the toner 53 is firmly rubbed by the developing roller 56 and the layer thickness regulating blade 57 and is positively charged. Since the toner 53 on the developing roller 56 after the layer thickness regulation is one layer or a strong one layer, the toner 53 that has not been developed does not accumulate on the contact portion with the photosensitive drum 20 and is developed. It adheres to the roller 56 and is collected.

As shown in FIG. 3, particularly in this embodiment, when the toner 53 on the developing roller 56 is rubbed by the layer thickness regulating blade 57, the toner 53 on the developing roller 56 is almost rubbed before rubbing. From the charge amount Q0 close to zero to the first charge amount Q1 (Q
The layer thickness regulating blade 57 and the developing roller 56 are configured so as to be charged to 1> Q0). On the other hand, the toner 53 that has moved from the developing roller 56 onto the photosensitive drum 20 is rubbed at the nip portion, so that the second charge equal to the saturated charge amount of the toner 53 that is 30% or more larger than the charge amount Q1.
The materials of the developing roller 56, the photosensitive drum 20, and the toner 53 are selected so as to be charged to the charge amount Q2 (Q2 ≧ 1.3 × Q1). In this way, the photosensitive drum 20
The charge amount Q3 of the residual toner 53 collected by the developing roller 56 is equal to that of the toner 53 on the developing roller 56 before development.
Is larger than the charge amount Q1 (that is, Q3> Q1). The specific configuration and material combination of the developing roller 56, the photosensitive drum 20, the toner 53, and the layer thickness regulating blade 57 satisfying the conditions defined by the charge amounts Q1, Q2, and Q3 are empirically or experimentally determined. It is determined by measuring the charge amounts Q1, Q2, and Q3 of the toner 53 on the developing roller 56 and the photosensitive drum 20, or by simulation using a computer.

Since the photosensitive drum 20, the developing roller 56 and the toner 53 are made of the above materials,
When the residual toner 53 is collected by the developing roller 56, the charge amount Q3 of the residual toner 53 is larger than the charge amount Q1 of the toner 53 on the developing roller 56 (that is, Q3>
Therefore, when the residual toner 53 is moved (collected) to the developing roller 56, the electric repulsive force received from the charge of the toner 53 on the developing roller 56 before development is small. That is, the developing roller 56 facilitates the collection bias of the residual toner 53. That is, for example, when the toner 53 is charged to the saturated charge amount on the developing roller 56, the charge amount Q1 of the toner 53 before the development on the developing roller 56 and the charge amount Q2 after the development on the photoconductor are different from each other. Since they become equal (that is, Q2 = Q1), the charge amount Q3 of the residual toner 53 conveyed on the photosensitive drum 20 and returned to the developing roller 56 is the charge amount of the toner 53 before developing on the developing roller 56. Since it is not larger than Q1 (= Q2), the recovery bias of the developing roller 56 is less effective for the residual toner 53. As described above, in the present embodiment, the residual toner 53 on the developing roller 56 is
It has a structure to improve the recovery ability of. On the other hand, since the developing toner 53 on the developing roller 56 is sufficiently charged when rubbed at the nip portion, the developing ability is not deteriorated, and the developing is appropriately performed almost at the same time as the recovery.

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. The resistance value at the contact portion of the transfer roller 60 with the photosensitive drum 20 is about 1 × 10 ⁶ to 1 ×.
It is set to 10 ¹⁰ Ω. That is, the transfer roller 60 is
Since it is in contact with the surface of the photosensitive drum 20, its resistance value is increased so that the photoconductive layer 22 formed on the photosensitive drum 20 is not destroyed by the voltage applied to the transfer roller 60. The toner image on the photosensitive drum 20 is configured to be reliably transferred to the paper P.

The fixing unit 70 is provided on the downstream side of the photosensitive drum 20 in the conveying direction, and includes a heating roller 71 having a halogen lamp built therein and a pressing roller 72. The toner image transferred onto the lower surface of the paper P is heated. While being pressed, it is pressed 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, as shown in FIG. 1, the paper feed roller 13, the photosensitive drum 20, the fixing unit 70, and the paper discharge tray 77 that convey the paper P fed from the paper feed cassette 14 are They are arranged in a substantially straight line to form a transport path PP shown by a chain line in FIG.

In FIG. 1, the toner 53 in the present embodiment is, for example, a non-magnetic one-component toner made of a pulverized toner or a polymerized toner made of styrene-acrylic having a nearly spherical shape, and its particle size is 6 to 12 μm. It is a degree.

The toner 53 contains a base toner and silica as an example of an external additive (fluidity imparting agent) added to the base toner. The base toner is, for example, resin,
It comprises wax, carbon black and CCA (for example, a charge control agent such as nigrosine or triphenylmethane), and its charging characteristic becomes positive due to the action of CCA. Silica, which is an example of an external additive, is a toner surface modifier, has an effect of increasing the fluidity of the toner 53, and generally has a charging property of being negatively charged. However, amino-modified silica and the like are known as positively-charged silica having a positively charged positive polarity. However, since positively chargeable silica generally does not have a sufficient fluidity improving effect, negatively chargeable silica having a small polarity is often used as an external additive. The difference between positively chargeable silica and negatively chargeable silica is positively chargeable silica when the charge amount of the toner when externally added to the base toner increases in the positive direction, and negative chargeable silica when the charge amount increases in the negative direction. The point is that

In the present embodiment, since the toner 53 has such a structure, when the toner 53 comes into contact with the layer thickness regulating blade 57 or the developing roller 56 and is sufficiently rubbed, it becomes a raw toner. CCA included
The charging characteristic of the toner becomes dominant, and the toner 53 is charged to the positive polarity which is the charging characteristic of the base toner. On the other hand, when the toner 53 is lightly rubbed, the charging property of silica as an external additive exposed on the surface of the base toner becomes dominant, and the toner 53 is charged to the negative polarity which is the charging property of silica. To be done. In addition to the function of imparting fluidity, the external additive can be provided with functions of preventing toner blocking, improving cleaning properties, preventing scratches on the photosensitive drum, improving image density, and improving image quality. The external additives other than silica include fine powders of colloidal silica, titanium oxide, aluminum oxide (alumina), etc., but according to the present embodiment, not only the positively chargeable external additive, It is advantageous because even a negatively chargeable external additive can be used.

Increasing the amount of such a positively chargeable charge control agent used increases the speed at which the toner 53 reaches saturation. Therefore, the layer thickness regulating blade 57 is adjusted by adjusting the amount of the charge control agent contained in the base toner of the toner 53.
It is possible to set the charge amount (Q1) of the toner 53 before development, which has been rubbed against, to a predetermined value smaller than the saturated charge amount.
According to the present embodiment, urethane rubber is used as the material of the developing roller 56. However, when silicon rubber is used as the material of the developing roller 56 instead of this, the silicone rubber has a charging amount. Is saturated with urethane rubber faster than urethane rubber. Therefore, by containing a smaller amount of charge control agent than in the case of urethane rubber, the toner 53 before development rubbed by the layer thickness regulating blade 57 is charged. The amount (Q1) can be set to a predetermined value smaller than the saturated charge amount. If a negatively chargeable toner is used,
As the CCA for negative charging, a metal complex of a monoazo dye, a salicylic acid derivative, a tetraphenylboron derivative or the like may be used.

Next, the operation of the laser beam printer 1 configured as described above will be described with reference to FIGS. 1 and 4 to 7. 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 in a side view by the driving means, and the supply roller 55 and the developing roller 56 are rotationally driven respectively in the clockwise direction. As a result, the respective particles of the toner 53 are rubbed by the supply roller 55 and the developing roller 56, and the developing roller 56 of the layer thickness regulating plate 57, as shown in FIG.
The toner 53 charged to the positive polarity (charge amount Q1) is rubbed by the developing roller 56 and the photosensitive drum 20 in the nip portion up to the saturated charge amount (charge amount Q2) due to the pressing friction against the toner. While being charged, it is attached to the electrostatic latent image formed on the photosensitive drum 20 by the laser light L and is developed by the reversal development method.

In this embodiment, the layer thickness regulating blade 57
As a result, a toner layer having a toner amount of 0.5 mg / cm ² or less is formed on the developing roller 56. Therefore, since the layer thickness of the toner 53 on the developing roller 56 is one layer or a little more than one layer, most of the toner is rubbed firmly against the developing roller 56 and the layer thickness regulating blade 57, and the saturated charge amount of the toner 53 is increased. Will be charged to a smaller predetermined charge amount (Q1).

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.
g / cm ² is required. To this end, as described above, the amount of toner 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 be slightly less than 100%. The peripheral speed of is about twice as high as the peripheral speed of the photosensitive drum 20. That is,
To prevent the developing roller 56 and the photosensitive drum 20 from directly contacting each other at the nip portion, the toner 53 is placed on the developing roller 56.
Toner 5 remains slightly due to van der Waals force
3 acts as a lubricant between the developing roller 56 and the photosensitive drum 20.

The charge amount of the toner 53 is about 25 μC / g in the low temperature and low humidity environment where the temperature is about 10 ° C. and the humidity is about 20%, and from the high temperature and high humidity environment where the temperature is about 32 ° C. and the humidity is 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. 6, 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
It is set to "about 300V".

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 uniformly charged by the charger 40 for positive charging to about +800 V as shown in FIG. Then, in this state, the laser light L emitted from the laser generator 31
Is a lens 33 while being main-scanned by the polygon mirror 32.
And 34 and reflection mirrors 35 and 36 to irradiate the photosensitive drum 20 to form an electrostatic latent image on the photosensitive drum 20. At this time, the voltage of the portion corresponding to the electrostatic latent image on the photosensitive drum 20 is changed by the irradiation of the laser light L.
For example, as shown in FIG. 7, the voltage drops to about + 100V. To the surface of the developing roller 56, as the developing bias voltage of, for example, about +300 V is applied as shown in FIG. 7, the toner 53 of positive polarity is attached with a layer thickness of more than one layer. 53 is not attracted to a charging voltage (about +800 V) higher than its own voltage, but is attracted to an electrostatic latent image voltage (about +100 V) lower than it, so that the toner 53 on the developing roller 56 is exposed to light. Only the electrostatic latent image formed on the drum 20 is attached and developed.

The toner image of the electrostatic latent image developed with the toner 53 is transferred onto the paper P by the transfer roller 60,
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 straight line,
Since the image is formed on the paper P while being conveyed by the substantially linear conveyance path PP, even if a thick paper such as a postcard or an envelope or an OHP film is used as the paper P, the paper P can be neatly and reliably formed. An image can be formed on.

On the other hand, in FIG. 1, the residual toner 53 remaining on the photosensitive drum 20 without being transferred to the sheet P when passing through the transfer roller 60 is changed by changing the bias voltage of the cleaning roller 42 as described above. , And is once absorbed by the cleaning roller 42. Then, 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 residual toner once absorbed is removed from the cleaning roller 42 by the photosensitive drum. 20
To the photosensitive drum 20 by the developing roller 56.
The upper residual toner 53 is collected. In this collecting step, the charge amount of the toner 53 on the developing roller 56 (Q
Since the amount of charge (Q3) of the residual toner 53 is larger than that of 1), when the residual toner 53 is moved (collected) to the developing roller 56, the amount of the undeveloped toner 53 on the developing roller 56 is increased. The electric repulsive force received from electric charges is small. That is, the developing roller 56 effectively applies the collecting bias to the residual toner 53. In parallel with this collecting operation, the undeveloped toner 53 on the developing roller 56 is charged to a charge amount Q2 when it is rubbed at the nip portion and adheres to the exposed portion of the photosensitive roller 20, so that the development is properly performed. Done.

As a result, according to the laser beam printer 1 of the present embodiment, the recovery ability of the developing roller by the cleanerless system is improved and the developing ability is not lowered, so that a high quality image is finally formed. be able to. In particular, the improved collection capability allows the residual toner to be collected sufficiently even when printing on paper that is extremely difficult to transfer, such as thick paper, or when the paper is set incorrectly. It is possible to efficiently prevent the occurrence of defects.

According to the above-described embodiments, only the formation of a monochrome image has been described, but the present invention effectively functions also when forming a color image. Further, although the developing roller 56 and the photosensitive drum 20 are configured to rotate in the same direction (opposite directions on the contact surface), these rollers may move in the opposite directions (move in the same direction on the contact surface). You may comprise. Further, although the photoconductor is composed of the photoconductor drum, the same effect can be expected even if the photoconductor is a belt-shaped photoconductor. 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.

[0055]

According to the image forming apparatus of the present invention, when the residual developer is collected by the developer carrying means, the residual developer is more charged than the charge amount of the developer on the developer carrying means. Since the amount of electrostatic charge is larger, the recovery bias is easily applied to the residual developer, and the residual developer recovery capability of the developer carrying means can be improved. As a result, it is possible to finally form a high-quality image, and especially when printing on a recording medium that is extremely difficult to transfer, such as thick paper, or when the setting of the recording medium is incorrect, a printing failure occurs. It is possible to obtain the effect of effectively preventing the above.

According to the image forming apparatus of the second aspect,
By using the layer thickness regulating blade, the charge amount of the developer on the photoreceptor before development can be charged to a predetermined charge amount smaller than the saturated charge amount, and the developer carrying means can be used with a relatively simple structure. It is possible to improve the ability to recover the residual developer.

According to the image forming apparatus of the third aspect,
Charged until the charge amount of the developer after development is saturated,
A high quality image can be formed without lowering the developing ability.

According to the image forming apparatus of the fourth aspect,
By using the positively chargeable toner and the positively chargeable photoreceptor, the ability of collecting the residual toner in the developer carrying means can be relatively easily improved.

According to the image forming apparatus of the fifth aspect,
When the residual developer passes through the charging position, it does not adhere to the charging means, and the charging performance of the charging means does not deteriorate due to the adhesion of the residual developer, so that it is possible to prevent deterioration in image quality due to defective charging.

According to the image forming apparatus of the sixth aspect,
Compared to the case where the photoconductor can be positively charged by the scorotron charger for positive charging relatively easily, and the photoconductor is negatively charged by the scorotron charger, ozone generated by ionization of air between the charging means and the photoconductor The generation amount can be reduced to, for example, about 1/10.

According to the image forming apparatus of claim 7,
Since the residual developer can be carried to the developer carrying means at a predetermined timing by the developer dispersing means, the residual developer can be collected by the cleanerless method so as not to interfere with charging, latent image formation, development, etc. .

As a result of the above, according to the present invention, an electrophotographic image forming apparatus capable of improving the collecting ability of the developer carrying means for collecting the developer in a cleanerless system and capable of forming a high quality image is provided. realizable.

[Brief description of the 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 side view of a developing unit and a photosensitive drum portion showing a charge amount of toner at each position in the laser beam printer of FIG.

FIG. 4 is an enlarged side view of a developing unit of the laser beam printer of FIG.

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

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

7 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 symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser beam printer 10 ... Feeder unit 13 ... Paper feeding roller 14 ... Paper feeding 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 control blade 60 ... Transfer roller 70 ... Fixing unit 77 ... Paper discharge tray 156 ... Collection-dedicated roller

Claims (7)

[Claims] 1. A photosensitive member, a driving unit for rotating the photosensitive member, a latent image forming unit for forming an electrostatic latent image on the rotated photosensitive member, and a photosensitive member carrying a developer. A developer carrying means for forming a visible image by developing the electrostatic latent image formed at the nip portion with the developer by forming a nip portion between the developer and the photoconductor, And a transfer unit configured to transfer the formed visible image onto a recording medium, wherein the developer carrying unit further rotates the residual developer remaining on the photoconductor after the transfer by the transfer unit. It is configured so as to be placed on the photoconductor and collected, and the surface portion of the photoconductor, the surface portion of the developer carrying means and the developer are mutually in a nip portion during development by the developer carrying means. By rubbing the surface of the photosensitive member after the development, Charge amount of the developer, an image forming apparatus characterized by being respectively composed of larger material 30% or more than the charge amount of the developer carrying means on the developer before the development. 2. A layer thickness regulating blade for regulating the layer thickness of the developer on the developer carrying means and rubbing the developer to charge it to a first charge amount. The developer is 30% more than the first charge amount.
The image forming apparatus according to claim 1, wherein the image forming apparatus is charged to the larger second charge amount. 3. The image forming apparatus according to claim 2, wherein the second charge amount is equal to a saturated charge amount of the developer. 4. The surface portion of the photosensitive member is made of a positively chargeable organic photosensitive member, the surface portion of the developer carrying means contains urethane, and the developer is a predetermined amount of charge control for positive charging. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises a positively charged toner containing an agent. 5. The apparatus further comprises a charging unit arranged in a charging position so as to face the photoconductor in a non-contact manner so as to charge the rotated photoconductor, and the latent image forming unit includes the charged photoconductor. 2. An electrostatic latent image is formed on a body, and the residual developer is returned to the developer carrying means via the charging position.
5. The image forming apparatus according to any one of items 4 to 4. 6. The image forming apparatus according to claim 5, wherein the charging unit includes a scorotron charger for positive charging. 7. A developer dispersion means for temporarily adsorbing the residual developer and discharging the temporarily adsorbed developer onto the photoconductor at a predetermined timing. Item 7. The image forming apparatus according to any one of items 1 to 6.