JPH05307319A - Developing device - Google Patents

Abstract

PURPOSE:To secure the nip of a developing roller with a photosensitive drum at a required value and to miniaturize the whole of a device by loading a specified electrical conductive rubber roller on the outside circumference of the shaft of the developing roller and forming the diameter thereof to be equal to or under a specified diameter. CONSTITUTION:A developing unit 16 is obtained by arranging the developing roller 20, a toner layer forming blade 21 and a toner supply roller 32 in a developing unit housing 31, and non-magnetic toner 19 being developer is held inside. The roller 20 among them is obtained by loading the electrical conductive rubber roller on the outside circumference if the shaft and forming the diameter thereof to be <=16mm. When the radius of the electrical conductive rubber roller is set to be RD and the thickness of a rubber layer constituting the electrical conductive rubber roller is set to be (h), the condition of 1<=h<=1.2RD-3 {a unit is (mm)} is satisfied. Therefore, the nip of the roller 20 does not become under required width even when the shaft of the roller 20 is bent. Besides, a hindrance does not occur even when the diameter of the roller 20 is formed to be <=16mm. Moreover, since the pressing force of the roller 20 can be set low, load torque can be made small and the device is minuaturized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus adopting an electrophotographic system,
In particular, it relates to a developing device that employs a pressure developing method.

[0002]

2. Description of the Related Art In recent years, miniaturization of personal computers has been remarkable, and A4 size portable personal computers have been developed. Along with this, printers connected to computers have been greatly miniaturized. The same applies to an electrophotographic page printer.

The electrophotographic system is a process of forming an electrostatic latent image on a latent image carrier having a photosensitive layer such as OPC, a developing process of adhering toner to the electrostatic latent image surface, and a latent image carrier. The printing process includes a transfer process of transferring the toner image developed on a recording medium such as paper and a process of fixing the toner image transferred to the recording medium.

Various methods have been developed for each step of the electrophotographic method, and the developing step is no exception.
Among them, the pressure developing method using a one-component developer does not require a magnetic material, so that the entire apparatus can be simplified and downsized, and the most suitable developing method for downsizing a page printer using an electrophotographic method. It can be said that

The conditions desired for the pressure developing method using a one-component developer will be briefly described as follows. That is, in this pressure developing method, since the developing roller holding the toner is pressed against the latent image carrier to perform development, it is necessary to use the developing roller having elasticity and conductivity. In particular,
When the latent image carrier is a rigid body, it is an indispensable condition that the developing roller is composed of an elastic body in order to prevent the latent image carrier from being scratched. In order to obtain the well-known developing electrode effect and bias effect, it is desirable to provide a conductive layer on or near the surface of the developing roller and apply a bias voltage.

Further, when the pressure developing method is executed, it is desirable to adopt a simultaneous developing cleaning system in which the transfer leakage toner of the latent image carrier is again collected on the developing roller. In this simultaneous development cleaning method, the developing bias voltage is appropriately set, and the transfer-leakage toner on the surface of the latent image carrier, which has been recharged in advance, and the toner on the developing roller are agitated and slid, so that the electrostatic latent image is formed. The development for adhering the toner to the developing roller and the cleaning for collecting the transfer leakage toner other than the latent image portion on the developing roller are simultaneously performed. In order to improve the development efficiency and cleaning efficiency of this simultaneous development cleaning method, an appropriate contact width (nip) of 1 (mm) or more is required.
And the peripheral speed of the developing roller is 1.5 to 2.
It is desirable to set the developing roller to about 0 times and press the developing roller against the latent image carrier.

Further, in the pressure developing method, since charge is applied to the toner on the surface of the developing roller by frictional charging between the developing roller and the blade for forming the toner layer, the blade for forming the toner layer is pressed against the developing roller. is necessary. Then, in order to give a sufficient charge to the toner,
For the toner layer forming blade, it is desirable to use a triboelectric series material that matches the polarity of electric charge. In particular, used in laser printers, digital PPCs, etc., negatively charging a photoconductor and developing with toner charged to the same polarity,
In so-called reversal development, silicon rubber, which is easily charged positively in order to impart a negative charge to the toner, is often used as a material for the toner layer forming blade.

Meanwhile, in response to the recent demand for miniaturization of printer devices, the diameter of the photosensitive drum, which is a latent image carrier, has been reduced, and drums having a diameter of 30 mm or less have also appeared. Along with this, the development of a developing roller having a diameter of 16 mm or less is desired. This also applies to a developing device that employs a pressure developing method using a one-component developer.

However, in the case of the pressure developing method, the pressing force in the diametrical direction acts on the developing roller as described above. Therefore, when the developing roller and its shaft are made small in diameter, the roller curvature is reduced and the shaft is bent. The required nip cannot be secured due to the. As a result, the toner is not sufficiently triboelectrically charged, the developing efficiency is lowered, and the cleaning efficiency in the simultaneous developing cleaning is significantly lowered, resulting in a low print image density, fogging, and the same image quality. It causes image deterioration such as unevenness in the plane. Due to such a problem, it is difficult to incorporate a developing roller having a small diameter of 16 mm or less into the one adopting the pressure developing method.

[0010]

As described above, in the conventional developing device employing the pressure developing method, it is difficult to incorporate a small-diameter developing roller having a diameter of 16 mm or less, which can contribute to downsizing of the device. That is, when a developing roller having a small diameter is incorporated, the shaft is bent by the reaction force against the latent image bearing member or the blade pressure contact force, and a necessary nip cannot be obtained, which causes a problem of image quality deterioration.

Therefore, in the present invention, the pressure developing method is adopted, and a developing roller having a diameter of 16 mm or less can be incorporated without deteriorating the developing characteristic and the cleaning characteristic.
It is therefore an object of the present invention to provide a developing device that can be downsized as a whole.

[0012]

In order to achieve the above object, the invention described in claim (1) is characterized by a developing roller. That is, the developing roller is formed to have a diameter of 16 mm or less by mounting a conductive rubber roller on the outer circumference of the shaft, the radius of the conductive rubber roller is Rd, and the thickness of the rubber layer constituting the conductive rubber roller is h. When 1 ≤
The condition of h ≦ 1.2Rd−3 (unit mm) is satisfied.

Further, in order to achieve the above object, the claims
In the invention described in (2), a conductive rubber roller is attached to the outer circumference of the shaft to use a developing roller having a diameter of 14 mm or less, and the bending of the developing roller due to the reaction force against the latent image bearing member is canceled. Thus, the blade and the toner supply roller are pressed against the developing roller.

[0014]

In the invention described in claim (1), even if the shaft of the developing roller is bent, the nip of the developing roller does not fall below the required width. Therefore, the diameter of the developing roller is 1
Even if it is 6 mm or less, no problem occurs.

Further, in the invention described in claim (2),
Since the blade and the toner supply roller are arranged so that the bending of the developing roller is restricted, the reduction of the nip due to the bending is small. Therefore, sufficient developing characteristics and cleaning characteristics can be maintained even with a small-diameter developing roller having a diameter of 14 mm or less.

[0016]

Embodiments will be described below with reference to the drawings.

FIG. 2 is a partially cutaway side view of a personal computer 1 which uses an image forming apparatus incorporating a developing device according to an embodiment of the present invention as a printer device. The personal computer 1 includes a computer main body 2 and a printer device 3 configured to mount the computer main body 2.

The printer device 3 includes a paper stocker 12 containing paper 11, a photosensitive drum 13 as a latent image carrier, a charger 14 as an electrostatic latent image forming means, an optical line head 15, a developing unit 16, a transfer roller. It is provided with a fixing unit 17, a fixing unit 18, and the like, and forms an image on the paper 11 by an electrophotographic printing process.

FIG. 3 is a side view showing a portion for executing the printing process. The photoconductor drum 13 is coated with a photoconductor layer such as an organic photoconductor (OPC) that causes a photoconductive phenomenon when the surface thereof is irradiated with light, and rotates at a constant speed in a direction indicated by a solid line arrow in FIG. Driven. In this example, the photosensitive drum 13 has a diameter of 20 mm.

The surface of the photosensitive drum 13 is a charger 14 which applies a high voltage to a thin wire to cause corona discharge.
Are uniformly charged by. In this example, a charging charger using a scorotron is used, and the surface of the photoconductor is negatively charged with a minus charger. The surface potential of the charged surface is set to about -500V.

The optical line head 15 irradiates the portion corresponding to the printed image on the charging surface with light. Optical line head 15
For this, an LED head in which an LED light emitting element is arranged as one example so as to have 300 dots per inch is used. The emission wavelength is 720 nm. Each light emitting element of the optical line head 15 blinks according to image information, and irradiates the charged surface of the photosensitive drum 13 with light. Carriers are generated in the photosensitive layer in the area irradiated with light, and the charges charged on the surface are removed through the earth line grounded to the conductive area of the photosensitive drum, and the surface potential becomes almost OV, so that the charged surface There is a potential difference between them. This electrostatic image is called an electrostatic latent image.

The developing unit 16 is an element for visualizing the electrostatic latent image with a developer such as toner. In this example, the non-magnetic toner 19 having a particle size of 8 to 14 μm is contained in the developing unit 16.
And a developing roller 20 made of conductive rubber.
A negative bias of about -150 to -200V is applied to the. As the conductive rubber material of the developing roller 20, EPDM, urethane, silicone, chloroprene,
An electrically conductive urethane rubber is used by dispersing an electrically conductive filler in NBR or the like. In this example, electrically conductive urethane rubber is used. The surface of the developing roller 20 is a toner layer forming blade 2 formed of a silicone rubber blade.
Sliding at 1 causes triboelectric charging, thereby forming a charged toner layer having a uniform thickness on the surface of the developing roller 20. The toner negatively charged on the surface of the developing roller 20 comes into contact with the electrostatic latent image on the photosensitive drum 13, and thus adheres only to the portion irradiated with light. This pressure developing method is called a one-component non-magnetic developing method.

The electrostatic latent image visualized by the developing unit 16, that is, the toner image is transferred onto the paper 11 by the transfer roller 17. In this example, the transfer roller 17 is made of a conductive rubber or a conductive sponge and has a thickness of about 1.0 to
By applying a positive bias of about 1.3 kV, the toner image adhering to the surface of the photosensitive drum 13 is transferred to the paper 11
It is transcribed on top. On the surface of the photosensitive drum 13 after the transfer of the toner image, the transfer efficiency of the transfer roller 17 is 100.
%, There is no residual toner, but in reality, some toner remains. Therefore, in this example, the surface of the photosensitive drum 13 is uniformly illuminated by the static elimination lamp 22 using a red LED to remove the charge, and the toner remaining without being transferred by the memory removal brush 23 having a positive bias of 400V to 600V is removed. After being dispersed in the fog on the surface of the photosensitive drum 13, the surface of the photosensitive drum 13 is uniformly charged again by the charger 14. At this time, the transfer residual toner is also electrically conductive with the surface of the photosensitive drum 13.

The LED head 15 blinks according to image information to form an electrostatic latent image. The slight transfer residual toner remaining in the non-exposed portion is attracted to the potential difference from the developing roller 20 and is collected by the developing unit 16. at the same time,
Toner adheres to the exposed portion. As a result, the transfer residual toner remains on the developing roller 2 without providing a cleaning element.
It is recovered to 0, and the image does not deteriorate. This method is called a simultaneous development cleaning process. In this simultaneous development cleaning process, the toner that has been discarded as waste toner is reused, so that the toner utilization efficiency is high, the toner volume held in the developing unit 16 can be reduced, and the cleaning means for the photosensitive drum 13 can be used. Unnecessary.

On the other hand, the toner image transferred onto the paper 11 is
It is melted by the fixing device 18 including a heat roller, and is further pressed onto the surface of the paper 11 to be fixed as a permanent image. Then, the sheet 11 is the sheet unloading roller 2
Then, the sheet is discharged from the printer device by 4.

The sheets 11 stocked in the sheet stocker 12 are taken out at an appropriate timing and fed by the roller 25 to the nip portion between the photosensitive drum 13 and the transfer roller 17. The above is a series of printing processes in this example.

FIG. 1 shows a cross-sectional view of the developing unit 16 incorporated in the printer device 3. As shown in the figure, in the developing unit 16, a developing roller 20, a toner layer forming blade 21, and a toner supplying roller 32 are arranged in a developing unit housing 31 as shown in the drawing, and a non-magnetic toner 19 as a developer is internally contained. Hold on. This developing unit 16
Since the Mg roller, the magnetic carrier, and the toner concentration control are unnecessary, the size and cost can be reduced.

The developing roller 20 holds the toner in a thin layer on the surface thereof and transfers the toner to the electrostatic latent image on the photosensitive drum 13 to visualize the latent image. Developing roller 2
0 is formed of a conductive urethane rubber roller and has appropriate elasticity and conductivity. The width of the rubber layer of the developing roller 20 is set to 220 mm, which is slightly wider than the A4 width (217 mm), and the linear load on the photosensitive drum 13 is 20 to 100 (g / c).
A load of m) is applied to the photosensitive drum 13 so that the contact width (nip) with the photosensitive drum 13 is about 1 to 4 mm. Then, the developing roller 20 is driven so that the roller peripheral speed is 1.5 to 2.0 times the peripheral speed of the photosensitive drum 13. At this time, the rotation direction is set to be the with direction relative to the rotation of the photosensitive drum 13. Further, a developing bias voltage of −150 to −200 V is applied to the developing roller 20 via the shaft.

On the surface of the developing roller 20, the non-magnetic toner 19
The toner layer forming blade 21 made of silicon rubber is provided so as to be uniformly pressed against the developing roller 20 by the compression spring 33. Due to the relationship of the charging series of urethane rubber and silicone rubber, the non-magnetic toner 19 is negatively triboelectrically charged and adheres to the surface of the developing roller 20 in one to three layers.

The toner supply roller 32 supplies the non-magnetic toner 19 to the surface of the developing roller 20, and the developing unit 1
The purpose is to stir the non-magnetic toner 19 accumulated inside 6. The toner supply roller 32 is made of SUS.
A roller having a conductive urethane sponge serving as a toner holding layer is attached to a shaft formed of a material, and is configured to be pressed against the developing roller 20. The rotation direction has a relationship between the developing roller 20 and against. Also,
A bias voltage of −150 V to 200 V is applied to the shaft in order to increase the efficiency of toner supply to the developing roller 20. A toner seal 34 for preventing toner spillage is provided below the developing unit 16 at the developing roller 20.
Is installed so as to come into contact with. This toner seal 3
4 is formed of mylar film.

As shown in FIG. 4, the developing roller 20 is provided with an elastic layer 42 made of conductive urethane rubber on a shaft 41 made of SUS material, and a conductive polyurethane paint is applied to the surface of the elastic layer 42 to make the surface conductive. The layer 43 is formed. The hardness of the elastic layer 42 is 25 to 30 ° in A hardness of JIS standard K6301, and the electric resistance value from the shaft 41 to the conductive layer 43 is 5 × 10 ^3. Ωcm. The radius Rd is 6.
The thickness of the rubber layer is 5 mm and the thickness h of the rubber layer is 3.5 mm.

By the way, in order to downsize the entire printer apparatus, it is desired to reduce the diameter of the developing roller 20. Particularly in small page printers, a photosensitive drum having a diameter of 30 mm or less is often used, and accordingly, the diameter of the developing roller 20 is 1
It is required to be 6 mm or less. However, as described above, the pressing reaction force from the photosensitive drum 13 and the pressure contact force from the toner layer forming blade 21 act on the developing roller 20, and the nip may not be secured due to the bending of the shaft 41.

In the one-component non-magnetic developing method used in this example, the nip between the photosensitive drum 13 and the developing roller 20 is 1 mm.
It has been confirmed by experiments that the above is preferable. Further, pressing the developing roller 20 against the photosensitive drum 13 with an excessive load causes adverse effects such as shortening the life of the surface of the photosensitive drum 13 and increasing the load torque. Therefore, it is desirable that the pressing force is low enough to secure the nip. ..

Therefore, in this example, the nip when the developing roller 20 is pressed against the photosensitive drum 13 and the nip when the shaft 41 is bent by the reaction force at that time are analytically obtained, and based on this result, the above is described. The radius Rd and the rubber layer thickness h are set in the relationship described later.

First, the analysis method will be described. As shown in FIG. 5, the nip 2C when the rubber roller 200 having the rubber layer 201 provided on the outer periphery of the shaft 202 and the rigid roller 210 are pressed under the load W is obtained by the following formula. 2C = 1.515 {(W ・ h ・ D) / (4 ・ L ・ Eg)} ^1/3 (1) However, 2C: Nip width (mm) L: Length of rubber part (mm) W: Load (kg) Eg: Young's modulus of rubber (kg /
mm ² ) D: Converted diameter (mm) R1: Rigid roller radius (mm) h: Rubber thickness (mm) Rd: Rubber roller radius (mm) 1 / D = {(1 / R1) + (1 / Rd)} / 2 The maximum deflection due to a supporting beam that receives an evenly distributed load on the whole is given by the following equation. y = (5 ・ W ・ L ³ ) / (382 E · I) (2) However, y: Maximum deflection (mm) E: Young's modulus (k
g / mm ² ) I: Moment of inertia of area (mm ⁴ ) I = π · Ds ⁴ / 64 Ds: Beam diameter (mm) The change in the nip due to the bending of the shaft is considered as follows. However, the rubber layer is sufficiently soft compared to the shaft,
The effect on the axial deflection of the rubber layer can be ignored.

A line segment mm 'shown in FIG. 6 (a) is a nip when the bending of the shaft is ignored. If the nip width 2C is sufficiently smaller than the roller radius Rd, the nip can be approximated by a straight line. On the other hand, the line segment pp 'is a nip when the roller shaft is bent and the shaft center O is displaced by y, but the roller shaft centers are displayed in an overlapping manner to simplify the explanation.
The nip 2C 'when the roller shaft is bent is obtained by the following equation when the line segment mq is considered as a straight line. 2C ′ = 2C · (v−y) / v (3)

Using the above equations (1), (2) and (3), the roller radius Rd, the rubber layer thickness h and the pressing force W at which the nip width becomes 1 mm or more were determined. The nip width is set to 1 mm or more because this value is the limit at which the simultaneous cleaning process using the one-component non-magnetic toner can function well. The setting conditions are as follows. In consideration of the fact that the length L of the rubber portion can print A4 landscape, the Young's modulus of the rubber portion is the value when the JIS-A hardness is 30 °. Rubber length L = 300 (mm) Rubber Young's modulus Eg = 0.122 (kg / mm ² Further, the shaft diameter of the rubber roller and the thickness of the rubber layer are each set to 1 mm or more in consideration of the feasible range.

In FIGS. 7, 8 and 9, the rigid roller, that is, the photosensitive drum has a diameter of 10 mm, 20 mm and 30 mm.
When the pressing force is changed from 1 to 3 kg, the limit values of the roller radius Rd and the rubber layer thickness h that can obtain a nip of 1 mm or more obtained by calculation are shown. In these figures, the solid line is the case where the bending of the roller shaft is taken into consideration, and the broken line is the case where it is not taken into consideration. The nip of 1 mm or more is within the area surrounded by the line. The radius Rd of the developing roller and the thickness h of the rubber layer may be selected as a combination according to the diameter of the photosensitive drum from the drawing. However, when the diameter of the photosensitive drum is within the range of 10 mm to 30 mm, the nip is applied with a pressing force of 3 kg or less. The range of 1 mm or more is above the straight line H in FIG. This can be expressed numerically as follows. 1 ≤ h ≤ 1.2 Rd-3 (unit: mm) (4)

In the present embodiment, to satisfy the above equation (4),
The developing roller 20 has a diameter 2Rd of 13 mm and a rubber layer thickness h.
Is 3.5 mm, pressing force is 1 kg, and line load is 33 g / cm.
I am trying.

With this setting, even if the developing roller 20 has a small diameter, the nip with the photosensitive drum 13 can be set to 1 mm or more with a relatively small pressing force, and a good printed image can be obtained. Further, since the pressing force can be reduced, the load torque is small, the drive motor can be downsized, and the development unit 16 can be downsized and the printer device can be downsized.

As can be seen from FIG. 7, when the diameter of the photosensitive drum 13 is 10 mm and the radius Rd of the developing roller 20 is 7 mm or less, a nip of 1 mm or more cannot be secured under a pressing force of 1 kg. A strong pressing force is required. On the other hand, if the bending of the shaft can be ignored, as indicated by the broken line in the figure, 1
Even with a pressing force of about kg, the radius of the developing roller can be set to 5 mm, and if the deflection of the shaft can be controlled, a developing roller with a small diameter can be used.

FIG. 10 shows an arrangement example of the photosensitive drum 13, the developing roller 20, the toner layer forming blade 21 and the toner supply roller 32, which introduces such a concept.

Here, the diameter of the photosensitive drum 13 is 20 mm,
The diameter of the developing roller 20 is 10 mm, the thickness of the rubber layer is 3 mm, and the pressing force of the developing roller 20 against the photosensitive drum 13 is 1
kg, and its peripheral speed is set to 1.5 to 2.0 times that of the photosensitive drum 13.

The toner layer forming blade 21 is arranged so as to be pressed against the developing roller 20 by the compression spring 33 at a position of an angle θ ₁ = 130 ° from the contact center point n with the photosensitive drum 13. The pressing force is 1 kg. Developing roller 2
The rubber layer No. 0 and the toner layer forming blade 21 are made of conductive urethane rubber and silicon rubber as in the above-described embodiment.

The toner supply roller 32 is constructed as shown in FIG. That is, SU with diameter Ds = 8 mm
A conductive urethane sponge layer 51 (layer thickness hs = 0.5 mm) is provided on the outer periphery of the S material shaft 50. The toner supply roller 32 is arranged so as to be pressed against the developing roller 20 at a position of an angle θ ₂ = 243.5 ° from the point n. At this time, the axial distance between the developing roller 20 and the toner supply roller 32 is set so that the amount of the bite between them is about 0.5 mm. The developing roller 2 rotates
0 is the against direction.

The grounds for setting the contact angle θ ₂ of the toner supply roller 32 as described above are as follows. FIG. 12 shows the force that the developing roller 20 receives. fd is a pressing reaction force from the photosensitive drum 13, and fd is a pressing force of the toner layer forming blade 21. Since the developing roller 20 bends most in the direction (angle θ ₂ ) of the combined vector fs of the two force vectors, it is effective to dispose the toner supply roller 32 at this position. This position, that is, θ ₂ is calculated to be 243.5 °, and in this example, the toner supply roller 32 is arranged at the above position.

From FIG. 7, with the shape and size of the developing roller 20 incorporated in this example, the pressing force is 2 when the shaft bends.
If it is not more than kg, the nip will not be more than 1mm. However, since the flexure of the shaft of the developing roller 20 can be controlled by adopting the configuration as in this example, a nip of about 1 mm can be realized even with a pressing force of about 1 kg. Therefore, good image quality can be obtained without deteriorating the developing property and the cleaning property.

The present invention is not limited to the above embodiment. That is, although the present invention is applied to the developing device of the page printer using the LED print head in the embodiment, the printer using the laser beam or the printer using other solid heads, the facsimile, the digital PPC, the analog PPC. It can also be applied to developing devices such as. Further, in the embodiment, the toner layer forming blade is pressed by the compression spring in the developing unit, but a pressing structure in which the blade is arranged on a part of the leaf spring may be adopted. Further, in the embodiment, the simultaneous development cleaning system is adopted, and the cleaning unit for cleaning the transfer leakage toner on the surface of the photosensitive drum is omitted, but the simultaneous development cleaning system is not used, and only the developing process is performed with the developing roller. The present invention can also be applied to a developing device having a cleaning unit for cleaning transfer leakage toner.

[0049]

As described above, according to the present invention,
Since the nip with the photosensitive drum can be secured to a necessary value by using the developing roller having a small diameter, it is possible to contribute to downsizing of the entire apparatus. Also, since the pressing force of the developing roller can be set low,
The load torque can be reduced, the drive motor and drive mechanism can be downsized, and this can further contribute to downsizing of the entire apparatus.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a developing device according to an embodiment of the present invention.

FIG. 2 is a side view showing a partially cutaway personal computer using an image forming apparatus incorporating a developing device according to an embodiment of the present invention as a printer device.

FIG. 3 is a schematic side view of a print process execution unit in the printer device.

FIG. 4 is a side view of a developing roller incorporated in a developing unit of the printer device.

FIG. 5 is an explanatory diagram of a contact state between a rubber roller and a rigid roller.

FIG. 6 is a diagram for explaining a change in roller nip.

FIG. 7 is a diagram showing a range in which the nip is 1 mm or more (when the photosensitive drum is 10 mm).

FIG. 8 is a diagram showing a range in which the nip is 1 mm or more (when the photosensitive drum is 20 mm).

FIG. 9 is a diagram showing a range in which the nip is 1 mm or more (when the photosensitive drum is 30 mm).

FIG. 10 is a diagram for explaining the arrangement of each component of the developing unit in the image forming apparatus according to another embodiment of the present invention.

FIG. 11 is a side view of a toner supply roller incorporated in the developing unit.

FIG. 12 is a diagram for explaining a pressing force applied to a developing roller of the developing unit.

[Explanation of symbols]

3 ... Printer device 11 ... Paper 12 ... Paper stocker 13 ... Photosensitive drum 14 ... Charging charger 15 ... Optical line head 16 ... Developing unit 17 ... Transfer roller 18 ... Fixing unit 19 ... Non-magnetic toner 20 ... Developing roller 21 ... Toner layer formation Blade 31 ... Developing unit housing 32 ... Toner supply roller 33 ... Compression spring 41 ... Shaft 42 ... Elastic layer 43 made of conductive urethane rubber ...
Surface conductive layer

Claims (2)

[Claims] 1. A latent image carrier composed of a photosensitive drum is pressed against the surface of the latent image carrier at a speed difference from the surface of the latent image carrier while holding a non-magnetic toner on the surface of the latent image carrier. In a developing device equipped with a developing roller for forming a non-magnetic toner image on a surface on which a latent image is formed and a blade for pressing the non-magnetic toner onto the surface of the developing roller by pressure to adhere the non-magnetic toner to the surface by frictional charging, The developing roller is formed to have a diameter of 16 mm or less by mounting a conductive rubber roller on the outer periphery of the shaft, the radius of the conductive rubber roller is Rd, and the thickness of the rubber layer constituting the conductive rubber roller is h. At this time, the developing device satisfies the condition of 1 ≦ h ≦ 1.2 Rd−3 (unit: mm). 2. A latent image bearing member composed of a photosensitive drum is pressed against the surface of the latent image bearing member with a speed difference from the latent image bearing member while holding a non-magnetic toner on the surface, and electrostatically is applied on the surface of the latent image bearing member. A developing roller that forms an image of non-magnetic toner on the surface on which a latent image is formed, a blade that press-contacts the surface of the developing roller to adhere the non-magnetic toner to the surface by frictional charging, and a position in front of the blade. In a developing device equipped with a toner supply roller that presses against the developing roller and conveys the non-magnetic toner toward the surface of the developing roller, the developing roller is equipped with a conductive rubber roller on the outer periphery of a shaft and has a diameter. The developing roller is formed to have a thickness of 14 mm or less, and the blade and the toner supply roller are arranged so that the developing roller shaft is bent at a position where the bending of the shaft of the developing roller due to the reaction force from the latent image carrier is canceled. Developing apparatus is characterized in that in pressure contact with the La.