JPH09160378A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a high quality image by using positively-chargeable toner for a positively-chargeable photoreceptor, and specifying an amount of toner which is held on a developing roller. SOLUTION: The photoreceptive drum 20 is made of a positively-chargeable material, having an electrification characteristic in which it is electrified positively. Therefore, to an electrifier 40 a positive voltage is applied. A bent part formed in the lower end of a layer thickness restriction blade 57 is in pressure- contact with a developing roller 56, and the thickness of a layer of toner 53 supplied from a supply roller and attached to the surface of the developing roller 56 in the form of a layer is restricted to a specific thickness (about 7-12μm), slightly thicker than one layer, by this blade 57. That is, it is so formed as to adjust the amount of toner on the developing roller 56 to 0.5mg/cm<2> or less. Thus, the toner is sufficiently electrified and an electrostatic latent image on the photoreceptor is sufficiently developed. As a result, a high quality image in which a defect such as print fog is reduced can be formed.

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, and more particularly, to positively charged photosensitive materials having a charging characteristic of positive polarity. This belongs to the technical field of an image forming apparatus that performs development using positively charged toner that is positively charged on a drum.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus of this type, reversal development is carried out by using a negatively charged negatively charged toner on a negatively charged photosensitive drum having a negatively charged charging characteristic. It is common to do But,
In such a system of charging the photosensitive drum to a negative polarity, if a scorotron charger having high practicality is used to charge the photosensitive drum, a large amount of ozone is generated. Further, the generated ozone causes deterioration of the negatively chargeable organic photoconductor and the like.

Therefore, in recent years, an image forming apparatus has been developed which adopts a system in which a positively chargeable photosensitive drum is charged by using a scorotron charger to reduce the amount of ozone generated, and further development is performed by using positively charged toner. Has been done.

Since there is a strong general demand for improving image quality in image forming apparatuses, in electrophotographic image forming apparatuses, toner is appropriately provided for development, transfer, cleaning, etc. on the photosensitive drum. The toner is required to have a certain degree of liquidity. Therefore, silica is generally added to the surface of the toner as an external additive for increasing the fluidity.

[0005]

By the way, in the so-called impression development in which toner is carried on the surface of the developing roller, and the developing roller is brought into contact with the photosensitive drum, the so-called impression development is performed. It is necessary to positively charge the toner by friction between the toner and a layer thickness regulating blade that regulates the thickness. However, since silica added externally to improve the fluidity usually has a negative charging property, if the toner layer on the developing roller is thick, the toner is not positively charged and the charging property of silica is increased. May be charged to a negative polarity.

This is because a toner is generally constituted by adding the above-mentioned external additive to the surface of a base resin, but such a toner has a charging property which the resin has when sufficiently rubbed. Is predominant, and the characteristic is that the charging characteristics of the external additive added to the surface become dominant when lightly rubbed.

In other words, in the above example, since the toner layer on the developing roller is thick, less toner is sufficiently rubbed by the layer thickness regulating blade or the like, so that the negative polarity, which is the charging polarity of silica as a whole, is obtained. The proportion of the toner which is charged or positively charged but whose charge amount is insufficient increases.

As a result, a portion on the photosensitive drum where good development is not sufficiently performed due to insufficiently charged toner appears,
Finally, there is a problem in that a defect such as a print fog occurs in the output image and the image quality is deteriorated.

The present invention has been made in view of the above problems, and image formation capable of forming a high-quality image while developing a positively charged photoconductor with a positively charged toner An object is to provide a device.

[0010]

In order to solve the above-mentioned problems, an image forming apparatus according to a first aspect of the present invention has a photosensitive member having a charging characteristic of being positively charged, and a charging member for positively charging the photosensitive member. Means, latent image forming means for forming an electrostatic latent image on the charged photoconductor, and the electrostatic latent image formed by developing the formed electrostatic latent image with a toner layer composed of positively charged toner. A developing roller for forming a toner image thereon, and a layer thickness regulating means for regulating the layer thickness of the toner layer so that the toner layer forms a layer having a toner amount of 0.5 mg / cm ² or less on the developing roller. A transfer means for transferring the formed toner image onto a recording medium.

According to the image forming apparatus of the first aspect,
First, the photoreceptor is positively charged by the charging means. Next, the latent image forming means forms an electrostatic latent image on the charged photoconductor. Next, the developing roller develops the formed electrostatic latent image with a toner layer made of positively charged toner to form a toner image on the photoreceptor.
Here, the layer thickness of the toner layer is regulated by the layer thickness regulating means so that a layer having a toner amount of 0.5 mg / cm ² or less is formed on the developing roller. Therefore, since the layer thickness of the toner on the developing roller is less than two layers based on the toner particles, that is, one layer or a little more than one layer, most of the toner firmly rubs against the developing roller and the layer thickness regulating means. As a result, it is sufficiently charged to the positive polarity. Therefore, the electrostatic latent image on the photosensitive drum is sufficiently developed by the sufficiently charged toner. Finally, the transfer unit transfers the toner image formed on the photoconductor to a recording medium such as recording paper. As a result, the occurrence of defects such as print fog is reduced on the transferred image.

An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the toner is a non-magnetic one-component toner. According to the image forming apparatus of the second aspect, since so-called impression development using the non-magnetic one-component positively-charged toner is performed on the positively-charged photoconductor, the development roller and the layer-thickness regulating means are sufficient. The friction causes the toner to be charged. However, the layer thickness of the toner layer is regulated by the layer thickness regulating means so that a layer having a toner amount of 0.5 mg / cm ² or less is formed on the developing roller. The layer is firmly rubbed by the layer thickness control means and sufficiently charged to the positive polarity.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the toner contains a powdered external additive having a charging characteristic of being negatively charged. And

According to the image forming apparatus of claim 3,
Since the toner contains, for example, a negatively chargeable powdery external additive such as silica which functions as a fluidity imparting agent, if the toner is not firmly rubbed by the developing roller and the layer thickness regulating means, the reverse characteristic (negative The development is performed with the charged toner remaining on the developing roller. However, the layer thickness of the toner layer is regulated by the layer thickness regulating means so that a layer having a toner amount of 0.5 mg / cm ² or less is formed on the developing roller. It is sufficiently rubbed by the layer thickness control means and sufficiently charged.

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 layer thickness regulating means has a predetermined curvature arranged in contact with the developing roller. It is characterized in that it is provided with a layer thickness regulating blade having a bent portion of a radius.

According to the image forming apparatus of claim 4,
The toner layer thickness can be relatively easily regulated by the layer thickness regulating blade so as to form a layer having a toner amount of 0.5 mg / cm ² or less on the developing roller.

An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to any one of the first to fourth aspects, wherein the charging unit includes a scorotron charger.

According to the image forming apparatus of claim 5,
The photoconductor can be positively charged relatively easily with the scorotron charger, and the amount of ozone generated can be reduced compared to the case where the photoconductor is negatively charged with the scorotron charger.
For example, it can be reduced to about 1/10.

[0019]

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 remaining 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 static elimination lamp 41 for removing the residual potential remaining on the photosensitive drum 20 after the transfer, and an electrostatic latent image on the photosensitive drum 20 after the static elimination. The charging device 40 is provided as an example of a charging unit for charging as much as possible.

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

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 generating corona discharge from a charging wire made of tungsten or the like, and the photosensitive drum 2
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.

By changing the bias voltage, the cleaning roller 42 temporarily absorbs the residual toner 53 remaining on the photosensitive drum 20 after the transfer by the transfer roller 60, and the next exposure, development, 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.

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 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 formed 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 approximately 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 the resistance value from the central electrode to which the developing bias voltage is applied to the outer peripheral contact portion is about. 5 x 10 ⁴ to 1 x 1
It is set to 0 ⁷ Ω.

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, 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.

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. Positively charged toner 53 from the roller 56 is transferred 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 a system using various structures as a system 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 configured to be rotated clockwise by a drive mechanism. As shown in FIG. 2, the developing unit 5
The toner storage chamber 54 is provided in the developing unit case 4 at 0, and the toner storage chamber 54 is formed by providing a large upper space S above the supply roller 55. For this reason, even if a large amount of toner 53 in the toner box 51 is supplied to the toner storage chamber 54 via the toner supply port 51a, the toner 53 is not packed and hardened. Therefore, the fluidity is maintained, and the toner supply by the supply roller 55 can be stabilized.

In FIGS. 1 and 2, the developing unit case 4 has a layer thickness regulating blade 5 as an example of a thin plate-like elastic layer thickness regulating means made of stainless steel or phosphor bronze.
7 is attached 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 amount of toner 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 shown in FIG. 3, on the developing roller 56, 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. Therefore, the toner 53 on the developing roller 56
The layer thickness is less than 2 layers based on the toner particles, that is, 1 layer or a little more than 1 layer. As a result, according to the present embodiment, most of the toner 53 is firmly rubbed by the developing roller 56 and the layer thickness regulating blade 57 and is sufficiently charged (in FIG. 3, it is sufficiently charged). A "+" mark is added to the toner 53). Therefore, the electrostatic latent image on the photosensitive drum 20 is sufficiently developed by the sufficiently charged toner 53. Further, since the toner 53 on the developing roller 56 after the layer thickness regulation is one layer or a little more than one layer, the toner 53 that has not been developed is not deposited on the contact portion with the photosensitive drum 20. , Attached to the developing roller 56 and collected.

On the other hand, in FIG. 4, on the developing roller 56, the layer thickness of the toner layer is set to be smaller than that of the layer thickness regulating blade 57 so that a layer having a toner amount exceeding 0.5 mg / cm ² is formed. A state in which the layer thickness regulating blade 157 having a large bent portion 157 a regulates the layer thickness is shown. In FIG. 4, the layer thickness of the toner 53 on the developing roller 56 is two layers or more based on the toner particles. As a result, according to the comparative example shown in FIG. 4, since the toner 53 on the developing roller 56 is not rubbed by the developing roller 56 and the layer thickness regulating blade 157, a large amount of toner 53 that is not sufficiently charged is generated. (In FIG. 4, as in the case of FIG. 3, a “+” mark is added to the sufficiently charged toner 53). Since the electrostatic latent image on the photosensitive drum 20 cannot be sufficiently developed by the toner 53 which is not sufficiently charged as described above, a defect such as a print fog occurs in the image finally output according to this comparative example. Will end up. In particular, when the toner 53 including a negatively chargeable external additive such as silica is used as in the present embodiment, the toner 53 that is not rubbed by the developing roller 56 and the layer thickness regulating blade 57 is Since the toner has a reverse characteristic (negatively charged), such defects such as print fog become remarkable.

As described above, it is understood from FIGS. 3 and 4 that the configuration of the present embodiment is extremely excellent in enhancing the image quality. 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, urethane rubber, or the like. Photosensitive drum 20 of transfer roller 60
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, as shown in FIG. 1, these paper feed rollers 13 that form a transport path PP (indicated by a dashed line in FIG. 1) for transporting the paper P fed from the paper feed cassette 14. The photosensitive drum 20, the fixing unit 70, and the paper discharge tray 77 are arranged in a substantially linear shape.

In FIG. 1, the toner 53 in the present embodiment is a non-magnetic one-component toner made of, for example, 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.

As shown in FIG. 5, particularly in the present embodiment,
The toner 53 is a base toner 201 and silica 2 as an example of an external additive (fluidity imparting agent) added to the base toner 201.
02 is included. The base toner 201 includes, for example, resin, wax, carbon black and CCA.
(For example, a charge control agent such as nigrosine or triphenylmethane), and its charge characteristic is C
It becomes positive due to the action of CA. Silica 202, which is an example of an external additive, is a toner surface modifier, and toner 53
It has the effect of increasing the fluidity of, and generally has a charging characteristic 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 this 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, the raw toner 201. The charging characteristic of CCA included in the toner is dominant, and the toner 53 is charged to the positive polarity which is the charging characteristic of the base toner 201.
On the other hand, when the toner 53 is lightly rubbed, the charging property of the silica 202 as an external additive exposed on the surface of the base toner 201 becomes dominant, and the toner 53
Is negatively charged, which is the charging characteristic of silica 202.

Further, in addition to the function of imparting fluidity, external additives include toner blocking prevention, improvement of cleaning property, and
It is possible to provide functions such as prevention of scratches on the photosensitive drum, improvement of image density, and improvement of image quality. Examples of the external additive other than silica include colloidal silica, titanium oxide, and fine powder of aluminum oxide (alumina).
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. Since the particle size of the base toner 201 is about 6 to 12 μm and the particle size of the silica 202 is about 10 to 30 nm, the silica 202 is actually much larger than the base toner 201 compared to that shown in FIG. Is small.

Next, the operation of the laser beam printer 1 configured as described above will be described with reference to FIGS. 1 and 6 to 9. 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, each particle of the toner 53 is 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. .

In the present embodiment, as described above, the layer thickness regulating blade 57 forms a toner layer with a toner amount of 0.5 mg / cm ² or less 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 53 is the developing roller 5.
6 and the layer thickness regulating blade 57 are rubbed firmly and sufficiently charged. Therefore, the electrostatic latent image on the photosensitive drum 20 is sufficiently developed by the sufficiently charged toner 53.

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. 7, 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 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 the peripheral speed of the photosensitive drum 20. That is, in the nip portion, the toner 53 is slightly left on the developing roller 56 by Van der Waals force so that the developing roller 56 and the photosensitive drum 20 do not come into direct contact with each other.

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. 8, 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 used to drive 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, as shown in FIG. 9, for example. Developing roller 56
To the surface of, the toner 53 of positive polarity is attached with a layer thickness of a little more than one layer with a developing bias voltage of, for example, about +300 V applied as shown in FIG. Charge voltage higher than its own voltage (about +
800 V) and is attracted to an electrostatic latent image voltage (about +100 V) lower than that, and the toner 53 on the developing roller 56 corresponds to the electrostatic latent image formed on the photosensitive drum 20. Only the part is attached and developed, and a visible toner image is formed.

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 linear shape,
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 onto 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 53 once absorbed is exposed from the cleaning roller 42. The photosensitive drum 20 is discharged to the drum 20 and is developed by the developing roller 56.
The residual toner 53 above is collected and the toner 53 is recycled.

As a result, according to the laser beam printer 1 of the present embodiment, the non-magnetic one-component positively charged toner 53 to which the negatively charged silica is added is used for the positively charged photosensitive drum 20. It is possible to form a high quality image on the paper P while developing the image. Further, since the scorotron charger is positively charged, the generation of ozone can be reduced.

According to the above-mentioned 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 (move in opposite directions on the contact surface), these rollers may move in opposite directions (same direction on the contact surface). You may comprise. 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 etc. works effectively. Furthermore, in the present embodiment,
Although the laser beam printer has been described, the present invention effectively functions also in a copying machine, a facsimile machine, and the like as in the case of the present embodiment as long as it is an electrophotographic image forming apparatus using toner.

[0058]

According to the image forming apparatus of the first aspect, even if a positively charged toner is used for a positively charged photoconductor, the toner is sufficiently charged, and the electrostatic latent image on the photoconductor is obtained. The image is fully developed. As a result, it is possible to form a high quality image in which defects such as print fog are reduced.

According to the image forming apparatus of the second aspect,
In impression development using a non-magnetic single-component positively charged toner, it is possible to form a high-quality image in which defects such as print fog are reduced.

According to the image forming apparatus of the third aspect,
Even when a toner containing a negatively chargeable powdery external additive such as silica is used, it is possible to form a high quality image in which defects such as print fog are reduced.

According to the image forming apparatus of the fourth aspect,
By using the layer thickness regulating blade, it is possible to form a high-quality image in which defects such as print fog are reduced relatively easily.

According to the image forming apparatus of the fifth aspect,
By using a scorotron charger, it is possible to form a high-quality image in which defects such as print fog are reduced with relative ease, and further, the amount of ozone generated can be reduced.

As a result of the above, according to the present invention, an electrophotographic image forming apparatus capable of forming a high quality image can be realized.

[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 an enlarged side view of a developing roller and a layer thickness regulating blade portion of the laser beam printer of FIG.

FIG. 4 is an enlarged side view of a developing roller and a layer thickness regulating blade portion in a comparative example.

FIG. 5 is a schematic perspective view of toner used in the laser beam printer of FIG.

FIG. 6 is an enlarged side view of a developing unit of the laser beam printer of FIG.

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

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

9 is an explanatory diagram showing the potential of each portion of the development processing by the reversal development method performed by 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 ejection tray

Claims (5)

[Claims] 1. A photosensitive member having a charging characteristic of positively charging, a charging unit for charging the photosensitive member to positive polarity, and a latent image forming unit for forming an electrostatic latent image on the charged photosensitive member. A developing roller that develops the formed electrostatic latent image with a toner layer composed of positively charged toner to form a toner image on the photoconductor; 5 mg /
a layer thickness regulating unit for regulating the layer thickness of the toner layer so as to form a layer having a toner amount of cm ² or less; and a transfer unit for transferring the formed toner image onto a recording medium. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the toner is a non-magnetic one-component toner. 3. The image forming apparatus according to claim 1, wherein the toner contains a powdered external additive having a charging characteristic of being negatively charged. 4. The layer thickness regulating means comprises a layer thickness regulating blade having a bent portion with a predetermined radius of curvature arranged in contact with the developing roller. The image forming apparatus according to item. 5. The image forming apparatus according to claim 1, wherein the charging unit includes a scorotron charger.