JP3264001B2 - Developing device and image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for forming a uniform thin layer of toner on a developing carrier and conveying the toner to a latent image carrier. The present invention also relates to an electrophotographic or electrostatic recording type image forming apparatus in which a latent image is formed on a latent image carrier, for example, on a photoreceptor or a dielectric, and is visualized by a developing device. In recent years, it has been desired to develop a developing device that improves the toner transportability and that requires a small number of replacements of the developing device.

[0002]

2. Description of the Related Art FIG. 8 is a schematic view showing the construction of a conventional developing device, which uses a one-component non-magnetic toner and uses a photosensitive drum 3 as a latent image carrier. Reference numeral 1 denotes a developing device, and a stirrer 24 stirs and conveys the toner 4 stored in the toner tank 7, and supplies a reset roller 6 serving as a supply unit including a rotating shaft 23 in a c direction and a conductive foam layer. Attach to surface.
The reset roller 6 is provided in contact with the developing roller 2 serving as a developing carrier, and has a collecting function of mechanically scraping the toner 4 not used for development from the developing roller 2 and returning the toner 4 to the toner tank 7.

FIG. 9 is a view showing a state in which toner is transferred from a supply unit to a developing carrier in the developing device of FIG. The developing roller 2 is provided so as to face the photosensitive drum 3, and includes a rotating shaft 22 in the direction b and a conductive layer. Then, the rotating shaft 22 supplies the developing bias voltage V
_b is applied. The reset roller 6 comes into contact with the developing roller 2 to rub the toner 4 and negatively charge (charge Q), and supply bias voltage _Vrl and developing bias voltage _Vb (
> V _rl ), the toner 4 is moved to the developing roller 2 by the electrostatic force F = QE ₁ by the electric field E ₁ (V _b −V _rl ) generated between the toner 4 and the developing roller 2. Then, the toner 4 adheres to the surface of the developing roller 2 as the developing roller 2 rotates, and a thin layer of the toner 4 is formed thereon.

The toner layer is elastically pressed against the developing roller 2 by a blade 5 which is a layer thickness regulating means urged in the direction of the developing roller 2 to mechanically scrape off excess toner 4. The toner 4 is uniformly triboelectrically charged (charge Q ') and rectified. Thereafter, the charged toner 4 is conveyed toward a portion where the developing roller 2 and the photosensitive drum 3 are engaged, that is, a developing area. FIG. 10 is a diagram showing a state of toner transfer from the developing carrier to the latent image carrier, and (a) is an initial state. Given the laser printer, is charged to have a potential of V _S by a charger (not shown) to the photosensitive material layer of the photosensitive drum 3 is a latent image carrier. Then, an electrostatic latent image area is formed on the photosensitive material layer by irradiation of the laser optical system, and the electrostatic latent image area (image section)
Is in a state of being raised to a potential _Vl higher than the potential V _S , that is, a state called “charge well”.

[0005] Such an image portion enters the development area.
And the potential V of the image portion_lAnd developing roller 2 as a developing carrier
Potential (development bias voltage V_bElectric field E generated between
_pd= V _b-V_lCharged toner 4 (negatively charged, charged
Q ′) is electrostatic attraction (F ′ = Q′E) from the developing roller 6._pd) Sa
And adheres to the latent image, thereby visualizing the latent image. What
The potential V of the non-image part_SIs the potential V of the developing roller_bLower
The toner 4 is prevented from adhering to the non-image area.
Become.

After the development, the toner 4 not used for the development is conveyed by the rotation of the developing roller 2, scraped by the reset roller 6, and returned to the toner tank 7. By repeating this operation, toner development is performed.

[0007]

However, in such a structure in which the toner is triboelectrically charged and electrostatically conveyed, that is, in a developing device having a layer thickness regulating means urged in the direction of the developing carrier, a long period of time is required. Causes filming of the development carrier. Generally, filming is a phenomenon in which a part of toner adheres to the surface of the development carrier due to frictional heat, mechanical crushing force, or electrostatic force generated when the surface of the development carrier rubs with the toner. Microscopically,
This is a phenomenon in which crushed toner particles enter into minute concave portions of the development carrier, or cover the surface of the development carrier in an island shape or a thin film shape due to adhesion by electrostatic force or heat fusion.

[0008] Therefore, unlike the case where the toner of a predetermined particle size temporarily adheres to the developing carrier due to electrostatic force, the adhesion by filming is an extremely small amount of toner and does not easily come off. As a result, the electrostatic characteristics of the developing carrier are changed, and the toner transportability is reduced. Hereinafter, this problem will be described in detail using a conventional developing device. FIG. 10B is a diagram showing a state of toner transfer from the developing carrier to the latent image carrier when used for a long time.

In the conventional developing device, the toner 4 not used for development is scraped to some extent by the reset roller 6 and the blade 7, but there is a limit in mechanically recovering the charged residual toner, and there is a limit. A small amount of toner that has not been collected is conveyed as it is and becomes stationary toner. FIG.
As shown in FIG. 0 (b), the stagnant toner is charged many times and takes on an excessive charge, and is conveyed to the photosensitive drum 3 and used for development, causing a decrease in print density and being rubbed many times. Developing roller 2 due to electrostatic force or frictional heat with developing roller 2
Adhere to the surface of the.

As a result, the resistance value of the developing roller 2 rises, and the conveyance of the normal toner 4 to the photosensitive drum 3 cannot be carried out smoothly, which may cause the replacement cycle of the developing unit and the life of the image forming apparatus to be shortened. I have. Therefore, it is desirable to eliminate the stagnant toner causing such filming. SUMMARY OF THE INVENTION It is an object of the present invention to provide a developing device capable of preventing filming of a developing carrier and performing stable toner conveyance for a long period of time. Also,
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of preventing filming of a developing carrier and obtaining a stable image for a long period of time.

[0011]

FIG. 1 is a diagram illustrating the principle of the present invention. According to the first aspect of the present invention, the developing carrier 2 that conveys the toner 4 to the latent image carrier 3 and the toner 4 in a toner tank 7 that is provided in contact with the developing carrier 2 and stores toner are used for the developing. A supply unit 6 for recovering the toner on the development carrier while supplying the toner to the carrier 2; and a supply unit 6 urged in the direction of the development carrier 2 to uniformly thin the toner 4 on the development carrier 2 Layer thickness regulating means 5 for layering, and a developing carrier applying power supply 31 for supplying to the developing carrier 2 a potential for transferring toner from the developing carrier 2 to the latent image carrier 3
Supply means for applying a DC component voltage;
2 and a supply means applying AC power supply 34 for applying a voltage of an AC component, and a potential obtained by superimposing a DC component of the supply means applying DC power supply 32 and the supply means applying AC power supply 34 is applied to the developing carrier applying power supply 31. In relation to the potential, the supply means is applied so as to periodically generate a potential for moving the toner from the supply means 6 to the developer carrier 2 and a potential for moving the toner from the developer carrier 2 to the supply means 6. A power supply for generating a voltage of each of the DC power supply 32 and the AC power supply 34 for applying the supply means, and a power supply 33 for applying a layer thickness regulating means for applying a potential for injecting electric charge to the toner to the layer thickness regulating means 5. It is configured with.

According to a second aspect of the present invention, there is provided an image forming apparatus for visualizing a latent image formed on a latent image carrier 3 with toner 4 conveyed by a development carrier 2 of a developing unit and transferring the latent image to a recording medium. A supply unit 6 provided in contact with the development carrier 2 to collect the toner in the development carrier while supplying the toner 4 in a toner tank 7 in which toner is stored to the development carrier 2; A layer thickness regulating unit 5 provided to be urged in the direction of the body 2 to uniformly thin the toner 4 on the developing carrier 2, and transferring the toner from the developing carrier 2 to the latent image carrier 3 A power supply 31 for supplying a potential to the developing carrier 2 to the development carrier 2, a DC power supply 32 for applying a DC component voltage, and an AC power supply 34 for supplying a AC component voltage. And the supply means applied DC The potential obtained by superimposing the DC component of the source 32 and the supply unit applied AC power supply 34 is related to the potential of the developing carrier applied power supply 31, and the potential for moving the toner from the supply unit 6 to the developer carrier 2 and the toner A power supply for generating a voltage of each of the supply unit-applied DC power supply 32 and the supply unit-applied AC power supply so as to periodically generate a potential to be moved from the developer carrier 2 to the supply unit 6; A power supply 33 for applying a potential for performing charge injection to the layer thickness regulating means 5.

[0013]

According to the first and second aspects of the present invention, the supply means includes a DC component voltage for generating a toner supply electric field and an AC component voltage for periodically generating a toner collection electric field.
To supply the toner 4 on the supply means 6 to the developing carrier 2 and supply the toner 4 which remains on the developing carrier 2 and causes the filming. It becomes possible for the means 6 to collect it.

[0014]

FIG. 2 is a schematic view showing the construction of an image forming apparatus according to an embodiment of the present invention. A laser printer is used as an example. FIG.
FIG. 3 is a schematic diagram of a configuration of a developing device in the image forming apparatus of FIG. 2. The recording medium is conveyed from the paper hopper 101 while measuring the paper passage timing by the timing roller 103. In accordance with the timing, the laser optical system 9 performs exposure corresponding to the image information to form an electrostatic latent image on the surface of the photosensitive drum 3, which is a latent image carrier rotating in the a direction, and this electrostatic latent image is formed. The toner is developed by the developing device 1.

The transported recording paper is pressed against the photosensitive drum 3 and reaches the transfer unit 12, where the toner image on the photosensitive drum 3 is electrostatically transferred. Then, the toner image on the recording medium peeled off from the photosensitive drum 3 is fixed by a fixing device 16, here a heat roller fixing. Then, the static eliminator 15
Removes the residual potential on the photosensitive drum 3 and
The upper residual toner 4 is cleaned by the cleaning blade 13 of the cleaner 14, and the photosensitive drum 3 is returned to the initial state. A toner seal 21 prevents the collected toner 4 from flying out of the cleaner 14. .

In the case of single-sided printing, the recording medium on which fixing has been completed is discharged by a discharge roller 104, and the printed paper is stored in a stacker 105. In the case of double-sided printing, although not particularly shown, the single-sided printed recording medium that has exited from the fixing device 16 is supplied to the photosensitive drum 3 upside down from the reversing transport mechanism. In the meantime, a toner image is formed on the front surface of the photosensitive drum 3, and the toner image on the back surface of the sheet is
6 is fixed. Then, the recording medium on which the fixing is completed is discharged to the stacker 105. Reference numeral 30 denotes a main power supply for applying a predetermined voltage to each mechanism.

In FIG. 3, the same components as those of the conventional developing device shown in FIG. 8 are denoted by the same reference numerals, and a one-component polyester non-magnetic toner is used. In addition to the one-component magnetic toner, a two-component toner composed of a carrier and a toner may be used. In particular, the present invention is effective for a developing device having a structure in which only toner is conveyed onto a development carrier with two-component toner and filming occurs (a structure in which toner is rubbed).

The agitator 24 agitates and transports the toner 4 stored in the toner tank 7 partitioned by the partition plate 11, and causes the toner 4 to adhere to the surface of the reset roller 6. The reset roller 6 is formed by covering a rotation shaft 23 in the c direction with a urethane sponge having a resistance of 10 ⁴ Ω. The toner 4 supplied from the toner tank 7 was rubbed and negatively pre-charged, and a supply means applied voltage in which a DC component and an AC component were superimposed was applied by the supply means applied DC power supply 32 and the supply means applied AC power supply 34. Toner supply from the developing roller 2 to the reset roller 6 which is generated between the potential of the reset roller 6 (supply means applied voltage) and the potential of the developing roller 2 (developing bias voltage) applied by the developing carrier applying power supply 31 The toner 4 is transferred to the developing roller 2 by the electrostatic force of the electric field.

The developing roller 2 is provided so as to be in contact with the photosensitive drum 3, and is constituted by a rotating shaft 22 in the b direction and an elastic material such as urethane rubber, silicon rubber, NBR, or a porous urethane sponge having conductivity. Is done. And toner 4
Is attached to the surface of the developing roller 2 with the rotation of the developing roller 2, and a thin layer of the toner 4 is formed thereon. This toner 4
The thin layer is elastically pressed against the surface of the developing roller 2 by a blade 5 serving as a layer thickness regulating means, and the excess toner 4 is mechanically scraped off to have a uniform thickness. Further, the blade 5 uniformly frictionally charges the toner 4 with a voltage (approximately -400 V) applied from a blade (layer thickness regulating means) application power supply 33 in order to increase the amount of charge by charge injection charging. Rectify. The blade 5 uses a leaf spring made of stainless steel with a rounded edge, and the urging force on the developing roller 2 is 35 gf / cm 2.

Thereafter, the charged toner 4 (charge Q ') is transported toward a portion where the developing roller 2 and the photosensitive drum 3 are engaged, that is, a developing area. The state of toner transfer from the developing roller 2 to the photosensitive drum 3 is the same as that shown in FIG. 10A, and is between the potential of the developing roller 2 (developing bias voltage V _b ) and the potential of the photosensitive material layer of the photosensitive drum 3. Generate an electric field.

At this time, the image portion, which is the electrostatic latent image area of the photosensitive drum 3, is charged at the potential of _Vl , and the other non-image portions are charged at the potential of V _S , and the potential difference from the potential _Vb of the developing roller 2 is obtained. field caused by E _pd electrostatic force _{(= V b -V l) F} '= Q'
The charged toner 4 is applied from the developing roller 2 to the image area by _Epd .
Is transferred to develop the latent image into a visible image. After development,
The toner 4 not used for development is conveyed by the rotation of the developing roller 2, mechanically scraped off by the reset roller 6, and a periodically generated toner collection electric field from the reset roller 6 toward the developing roller 2. The toner is collected by the reset roller 6 by electrostatic force and returned to the toner tank 7. Then, the returned toner 4 is again supplied to the developing roller 2 together with the toner 4 transported by the stirrer 24. By repeating this operation, toner development is performed.

The electrical relationship between the reset roller 6, the developing roller 2, and the toner 4 will be described below. FIG. 4 shows FIG.
FIG. 5 is a diagram illustrating a toner transfer state between a supply unit and a developing carrier in the developing device in FIG. The toner 4 is preliminarily negatively charged (charge Q) at an engagement portion between the reset roller 6 as a supply unit and the developing roller 2 as a developing carrier. Then, the DC component and the reset roller voltage obtained by superimposing an AC component of the applied AC power 34 (supply unit applying voltage V _rl + V _a sin ωt) potential of the reset roller 6 is applied with the developing roller 2 of the reset roller applying a DC power source 32 Electric field E (= development bias voltage V _b (> V _rl ))
V _b - V _rl - Toner 4 by electrostatic force F = QE of V _a sin ωt) moves between the developing roller 2.

The principle of the toner transfer will be described in more detail.
As shown in FIG. 4A, the potential of the reset roller 6 (V
_rl + V _a sin _ωt) is when the potential V _b is smaller than the developing roller _{2 (V b> V rl +} V a sin ωt), the toner supply electric field is generated, the toner 4 moves from the reset roller 6 to the developing roller 2. Conversely, as shown in FIG. 4 (b), when a potential higher than V _b of the potential of the reset roller _{6 (V rl + V a sin} ωt) is the developing roller _{2 (V b <V rl +} V a sin ωt),
A toner collection electric field is generated, and the toner 4 moves from the developing roller 2 to the reset roller 6. Thus, the reset roller 6 supplies and collects the toner 4.

FIG. 5 is a diagram showing the relationship between the developing bias voltage and the voltage applied to the supply means. The vertical axis indicates the potential, and the horizontal axis indicates the time. The DC component voltage (V _rl , for example, −400 V) applied to the reset roller 6 varies between the reset roller 6 and the developing roller 2 (developing bias voltage V _b > V _rl , for example, −30).
0V), a potential difference ( _Vb - _Vrl ) is generated to create a toner supply electric field, and the toner 4 is set to transfer from the reset roller 6 to the developing roller 2. The voltage of the AC component applied to the reset roller 6 (V _a sin ωt
The period t = 2 [pi] f For example 800 H _Z) may cause toner recovery field was set to be the potential difference (V _b -V _rl) is greater than the amplitude (e.g., amplitude 150 V).

Thus, the potential of the reset roller 6 (V
_rl + V _a sin _ωt) at is smaller than the potential V _b of the developing roller 2, resulting toner supply electric field, the toner 4 moves from the reset roller 6 to the developing roller 2. Conversely, when a potential higher than V _b of the potential (V _rl + V _a sinωt) the developing roller 2 of the reset roller 6, the toner collecting electric field is generated, the toner 4
Moves from the developing roller 2 to the reset roller 6. However, the supply potential difference of the toner was set to be larger than the toner collection potential difference so as to collect only the stagnant toner.

That is, a voltage in which the DC component and the AC component are superimposed as described above is applied to the reset roller 6, and the AC component is shifted to the DC component side (supply side) so that the developing roller 2
A toner collection electric field is generated periodically (t = 2πf) while supplying the toner 4 to the toner, and the reset roller 6 electrostatically collects the toner 4 remaining on the developing roller 6 without being scraped off mechanically. Can be. Accordingly, since the toner 4 is not rubbed many times on the developing roller 2, filming can be prevented.

In this embodiment, a contact-type supply means (reset roller) in contact with the developing carrier is used. However, a non-contact type supply means can be applied in consideration of how to apply a voltage.
The supply means may be a roller, a brush, a belt, a bucket, or a fixed blade provided with a special transport mechanism. Further, in the present embodiment, the negatively charged toner is used, so that the toner moves in the direction opposite to the direction of the electric field, but the positively charged toner moves in the direction of the electric field. It is necessary to consider the voltage applied between them slightly.

FIG. 6 is a diagram showing the relationship between the number of prints and the toner charge amount, and FIG. 7 is a diagram showing the relationship between the number of prints and the print density. FIGS. 6 and 7 show the results of comparison between the image forming apparatus provided with the developing device shown in FIG. 8 and the image forming apparatus of the present embodiment shown in FIG. 2, respectively. Referring to FIG. 6, it can be seen that in the conventional image forming apparatus, the charge amount of the toner gradually increases as the image forming apparatus is used, and the toner is highly charged. In other words, it indicates that the remaining toner that has not been collected stays and is frictionally charged many times. Conversely, in the image forming apparatus of this embodiment, the toner charge amount is stable even after long-term use (when printing 10,000 sheets). I understand.

Referring to FIG. 7, in the conventional image forming apparatus, the toner is not normally transported due to filming of the highly charged toner or the developing roller, and the print density is reduced.
Therefore, such a decrease in print density necessitates replacement of the developing device. On the other hand, in the image forming apparatus of the present embodiment, the toner is normally conveyed and the print density does not decrease. Therefore, it is clearly understood that a stable print density image can be obtained even when used for a long time.

Therefore, according to the present embodiment, it is possible to collect the stagnant toner causing the filming of the developing carrier from these data, obtain a stable image for a long period of time, and reduce the replacement of the developing device. Can be.

[0031]

As described above, the developing device of the present invention makes it possible to collect the toner remaining on the developing carrier and causing the filming, and to stably carry the toner. Further, the developing device of the present invention can prevent the filming of the developing carrier, extend the replacement cycle, and can be used for a long time.

The image forming apparatus according to the present invention can collect a toner which causes the filming which has stopped on the developing carrier of the developing device, and perform stable toner development to obtain a stable image for a long period of time. Will be possible. Further, since the image forming apparatus of the present invention can use the developing device for a long period of time by preventing filming of the developing carrier, the life of the apparatus can be extended.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of a configuration of a developing device in the image forming apparatus of FIG. 2;

FIG. 4 is a diagram showing a state of toner transfer between a supply unit and a developing carrier in the developing device of FIG. 3; (a) From the supply means to the development carrier (b) From the development carrier to the supply means

FIG. 5 is a diagram illustrating a relationship between a developing bias voltage and a voltage applied to a supply unit.

FIG. 6 is a diagram showing the number of prints and the toner charge amount.

FIG. 7 is a diagram showing the number of prints and print density.

FIG. 8 is a schematic diagram of a configuration of a conventional developing device.

FIG. 9 is a diagram illustrating a state in which toner is transferred from a supply unit to a developing carrier.

FIG. 10 is a diagram illustrating a state in which toner is transferred from a developing carrier to a latent image carrier. (a) Initial state (b) After long-term use

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Developing device 2 Developing roller (development carrier) 3 Photosensitive drum (latent image carrier) 4 Toner 5 Blade (layer thickness regulating means) 6 Reset roller (supply means) 7 Toner tank 31 Developing carrier application power supply 32 Supply means application DC power supply 34 AC power supply

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshimi Takizawa 1015 Kamikodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-3-84569 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/08

Claims (2)

(57) [Claims] A developing carrier (2) for conveying a toner (4) to a latent image carrier (3); and a toner tank (7) provided in contact with the developing carrier (2) and storing toner. Supply means (6) for mechanically scraping and recovering the toner of the development carrier while supplying the toner (4) to the development carrier (2); andthe development carrier (2). A layer thickness regulating means (5) provided to be urged in the direction to uniformly thin the toner (4) on the developing carrier (2); and the latent image carrier from the developing carrier (2). body (3) to supply the voltage for transferring a toner wherein the developer carrying member (2) present
An image carrier power supply (31), a supply means applied DC power supply (32) for applying a DC component voltage, and
Supply means for applying AC and AC component voltage (34)
And a DC component of the supply means applied DC power supply (32).
The superimposed potential of the AC power supply (34)
When the image carrier applying power supply (31) has a potential relationship,
The potential and toner to be transferred from step (6) to the developer carrier (2)
To transfer the toner from the developer carrier (2) to the supply means (6).
DC voltage applied to the supply means so as to periodically generate
Power supply (32) and the AC power supply (34) applied to the supply means.
A power source for generating pressure and a potential for injecting charge into the toner by the layer thickness regulating means.
(5) A developing device comprising: a power supply (33) for applying a layer thickness regulating means to be applied to (5). 2. An image forming apparatus for visualizing a latent image formed on a latent image carrier (3) with toner (4) conveyed by a developing carrier (2) of a developing device and transferring the latent image to a recording medium. The toner of the developing carrier is mechanically supplied while the toner (4) in the toner tank (7), which is provided in contact with the developing carrier (2) and stores toner, is supplied to the developing carrier (2). Supply means (6) for scraping and collecting the toner (4), and the toner (4) on the development carrier (2) is provided in such a manner that the toner (4) on the development carrier (2) is uniformly thinned. A layer thickness regulating means (5) for developing, and a developing carrier application for supplying a potential for transferring toner from the developing carrier (2) to the latent image carrier (3) to the developing carrier (2). A power supply (31) and a DC power supply (32)
Supply means for applying AC and AC component voltage (34)
And a DC component of the supply means applied DC power supply (32).
The superimposed potential of the AC power supply (34)
When the image carrier applying power supply (31) has a potential relationship,
The potential and toner to be transferred from step (6) to the developer carrier (2)
To transfer the toner from the developer carrier (2) to the supply means (6).
DC voltage applied to the supply means so as to periodically generate
Power supply (32) and the AC power supply (34) applied to the supply means.
A power source for generating pressure and a potential for injecting charge into the toner by the layer thickness regulating means.
An image forming apparatus comprising: a power supply (33) for applying a layer thickness regulating means to be applied to (5).