JP3600304B2 - Image forming device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus using an electrophotographic process.
[0002]
[Prior art]
2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, the surface of a drum-shaped or belt-shaped image carrier is charged by a charger, and then exposed by an exposure device to form an electrostatic latent image. Is visualized by a developer from a developing device, and then transferred onto a transfer material from a sheet feeding device using a transfer device, and is thermally fixed by a fixing roller.
[0003]
As a developing device in such an image forming apparatus, a toner to which a small amount of an external additive is added as necessary is used as a developer, and the developer is frictionally charged by a developer supply roller to form a developing device. And the layer thickness of the developer adhered to the developing roller is regulated by a developer regulating member so that the developing roller and the image carrier are supplied to a developing section facing the developing roller. Component developing devices have been proposed in Japanese Patent Application Laid-Open Nos. 60-229057 and 61-42672.
[0004]
Such a one-component developing device has a developer storage unit for storing the developer in the developing device, and the developer in the developer storage unit is moved by gravity or transport means to a developer supply unit for a developing roller. And so on. Therefore, in the one-component developing device, a mechanism for supplying an appropriate amount of toner into the developing device such as a two-component developing device using a toner and a carrier is not necessary, so that the cost and the size can be reduced. This is advantageous. Then, when the developer is consumed by the development and the developer in the developer storage section is exhausted, a new developer may be supplied to the developer storage section from outside at once. The replenishment of the new developer into the developer storage unit is performed by detecting or predicting the amount of the developer in the developer storage unit by a sensor provided in the developer storage unit, and before starting to hinder image formation. This is done by displaying a request for replenishment with unused developer remaining in the storage section.
[0005]
[Problems to be solved by the invention]
However, in the conventional image forming apparatus, when the amount of the developer in the developer storage unit of the developing device becomes small, there is a problem that the developing density is reduced and the density of the final image is reduced.
That is, the developer remaining in the developer storage unit when the developer is supplied from the outside to the developer storage unit is subjected to agglomeration of the developers while being subjected to an action such as agitation by the developer conveying unit, and the initial state is reduced. Liquidity has been lost. Since such coagulated toner is hard to be supplied to the developing roller, the amount of toner on the developing roller is reduced, and the developing density is reduced.
Further, the developer is charged to a predetermined polarity by friction with a developing roller, a developer supply roller, and a developer regulating member, is thinned on the developing roller, and is conveyed to a developing unit. The developer is consumed by attaching to the image carrier, but the developer charged to the polarity opposite to the predetermined polarity in the developer passes through the developing unit without attaching to the image carrier, and is developed again. It will be returned to the agent storage. Therefore, when the amount of the developer in the developer storage becomes small, the ratios of the cohesive developer and the oppositely charged developer which are not suitable for development in the developer are very high. Therefore, when the amount of the developer in the developer storage becomes small, the developer supplied to the developing roller contains a large amount of the developer that does not contribute to the development, so that the developing density is reduced.
[0006]
Further, in the conventional image forming apparatus, when toner in the developer storage unit of the developing device is reduced and then toner is newly supplied to the developer storage unit from the outside, the developing density increases and the final density increases. As the density of the image suddenly rises, a phenomenon of so-called background contamination in which toner adheres to the non-image portion has occurred.
This is because, when a new developer is mixed into the above-described developer having a high ratio of the cohesive developer and the oppositely charged developer, the newly supplied developer has a high fluidity and a good charge state. The developer is conveyed and satisfactorily attracted to the developing roller, and a uniform thin layer of a new developer is formed on the developing roller. When the aggregating developer and the oppositely charged developer are transported here, these developers have a weak adsorbing force with the developing roller, and adhere to the uniform thin layer of the new developer in the form of particles. I will. Then, since the developer adhered in the form of granules is not sufficiently charged, the electrostatic development inhibiting force in the non-image area on the image carrier does not work, and the non-image area becomes soiled. It will adhere.
[0007]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of always obtaining a good image even before and after replenishing a developing device with a new developer. Is to propose an unconventional configuration of the present invention.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an image carrier, a charging unit for charging the image carrier, and a latent image forming unit for forming an electrostatic latent image on the image carrier charged by the charging unit. Developing the electrostatic latent image using a developer carrier that carries and conveys the one-component developer stored in the developer storage means and charged to a predetermined polarity. Means for detecting the amount of developer stored in the developer storage means in an image forming apparatus having means and developer transport means for stirring and transporting the one-component developer in the developer storage means. When, the developer amount detecting member in response to the output of a voltage control means for controlling a voltage applied to the developer carrying member, or charging means, the developer surface on said developer carrying member potential and the image carrier as the charge potential of the body are substantially equal, the developer Bearing member or has a configuration for controlling a voltage applied to said charging means.
[0012]
[Action]
According to the present invention, even when the amount of the developer in the developer storage unit is reduced, the potential of the developer surface on the developer carrier and the charging potential of the image carrier are substantially equalized. The regular-polarity charged developer and the opposite-polarity charged developer on the body are prevented from adhering to the non-image portion of the image carrier.
[0016]
【Example】
Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.
[0017]
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view showing the developing device of the present embodiment.
In FIG. 1, a photosensitive drum 1 serving as an image carrier rotates so that its surface moves at 200 mm / sec in a direction indicated by an arrow in FIG. The photoconductor drum 1 is an OPC photoconductor, is negatively charged, and forms an electrostatic latent image by a latent image forming unit (not shown). Further, in order to develop the latent image on the photosensitive drum 1 by reversal development, a developing roller 2 which is a developer carrying body carrying toner 7 has a surface at a speed of 220 mm / sec in the direction of the arrow in the figure. Rotate to move.
[0018]
In the one-component developing apparatus shown in FIG. 1, a toner 7 as a developer is stored in a toner hopper 6 as a developer storage unit. The toner 7 is an aggregate of particles having a volume average particle diameter of 10 μm mainly composed of a nonmagnetic styrene acrylic resin and a polyester resin, and 0.7 wt% of hydrophobic silica fine powder is added as an external additive. . A piezoelectric sensor 20 is provided below the toner hopper 6, and detects the presence or absence of the toner 7 on its detection surface.
The toner 7 stored in the toner hopper 6 is transported toward the toner supply roller 4 as a developer supply unit while being stirred by the agitator 5 as a developer transport unit. The toner supply roller 4 is a foamed polyurethane sponge roller kneaded with carbon, the core of which is 6 mm in diameter, and the outer diameter of the roller itself is 16 mm. Is established. Then, the toner 7 conveyed to the toner supply roller 4 is carried on the surface of the toner supply roller 4, and is rotated by the toner supply roller 4 in the direction of the arrow in FIG. Conveyed.
[0019]
Here, the developing roller 2 in this embodiment will be described.
In the prior art, that is, in the conventional developing devices disclosed in Japanese Patent Application Laid-Open Nos. 60-229057 and 61-42672, the toner adhesion amount on the developing roller is 0.2 to 0. It was as low as 0.5 mg / cm2. Usually, the toner adhesion amount is required to be 0.5 to 0.7 mg / cm 2 on the transfer paper, and 0.6 to 1.0 mg / cm 2 is required on the photoreceptor. However, with the conventional toner adhesion amount on the developing roller, a sufficient amount of toner adhesion on the photoreceptor cannot be obtained, so that the speed of the developing roller is two to two times the speed of the photoreceptor. It was quadrupled to cover insufficient toner adhesion on the developing roller.
However, when the rotation speed of the developing roller is increased in this way, when a solid image is developed, a phenomenon occurs in which the density at the rear end of the solid image becomes higher than at the rear end of the toner. Although this phenomenon was a problem in black and white machines, it has been accepted. However, the phenomenon of the rear end of the toner becomes a serious problem in the case of a color image. That is, since the color image is viewed through the toner, the density is high at the rear end, and the color becomes different, especially in the case of a superimposed image.
[0020]
In order to solve such a phenomenon formed by the rear end of the toner, it is necessary to make the speed of the developing roller close to the speed of the photosensitive member. In order to make the developing roller and the photoreceptor substantially the same speed, the toner adhesion amount on the developing roller needs to be about 0.8 to 1.0 mg / cm2. It is necessary to form a plurality of toner layers thereon. Further, in this case, the toner per unit weight of the toner carried on the developing roller is sufficiently charged from the lowermost layer to the uppermost layer to about 5 to 15 μc / g, and there is no uncharged toner. It is necessary not to.
[0021]
In view of this, the developing roller 2 in this embodiment is composed of a dielectric part whose surface is regularly or irregularly distributed over a small area and a conductive part grounded as disclosed in Japanese Patent Application No. 2-15110 by the present applicant. A large number of minute electric fields are formed on the surface of the developing roller 2 by frictional charging with the toner supply roller 4 and the toner 7, and a large amount of toner is generated by the minute electric field. 7.
That is, as shown in FIG. 2, the developing roller 2 is formed on an aluminum core having a roller diameter of 20 mm at a pitch of 0.3 mm, a depth of 0.1 mm, a groove width of 0.2 mm and an angle of 45 degrees. An epoxy-modified silicone resin (Toray SR2115) was coated on the processed product, dried at 50 ° C. for about 90 minutes, and then the roller surface was cut to form an aluminum surface 51 as a conductive part and a dielectric part. Is exposed at a ratio of 3: 7.
By using such a developing roller, two or more toner layers having a stable toner adhesion amount and toner charge amount were formed, and the image quality was improved.
In the present invention, a conventional developing roller may be used according to the required image quality.
[0022]
The toner supply roller 4 is rotationally driven so that the moving speed of the surface thereof becomes 1.5 times the moving speed of the surface of the developing roller 2. The toner 7 conveyed by the roller 4 is negatively charged by friction. At the same time, the dielectric portion 52 of the developing roller 2 is triboelectrically charged by the toner supply roller 4 and is positively charged, which has a polarity opposite to that of the toner 7. At this time, a negative electric charge is induced in the grounded conductive part 51, a minute closed electric field is formed between the dielectric part 52 and the conductive part 51, and the negatively charged toner 7 is electrostatically multilayered. It is carried on.
[0023]
In this manner, the toner 7 carried in multiple layers is formed of urethane rubber to a thickness of 2 mm, and is elastically regulated as a layer thickness regulating means disposed so as to be pressed into the developing roller 2 at an amount of 0.6 mm. The thickness of the layer is made uniform by the blade 3, and furthermore, the layer is further frictionally charged, and the developing roller 2 and the photosensitive drum 1 are conveyed to the opposite developing section with a gap of 150 μm. The latent image on the photosensitive drum 1 is developed by the action of a developing bias applied to the developing roller 2 by a developing bias power supply (not shown). The elastic regulating blade 3 is arranged so that the length from the free end to the free end is 11 mm and the protrusion from the blade contact portion to the free end is 0.5 mm.
[0024]
Thus, the charging potential of the photosensitive drum 1 is -870 V, the potential of the image exposure unit is -100 V, the developing bias potential applied to the developing roller 2 is -750 V, and the potential of the toner supply roller 4 is equal to the potential of the developing roller 2. After setting, the toner hopper 6 was replenished with 60 g of toner, and the toner layer on the developing roller 2 was brought into non-contact with the surface of the photosensitive drum 1 for development. As a result, a good image could be obtained.
At this time, the toner mass per unit area (M / A) of the developing roller 2 was 1.3 mg / cm ² , and the toner charge per unit mass (Q / M) was −12 μC / g.
[0025]
Then, when image formation was continued under the above conditions, the piezoelectric sensor 20 intermittently generated a signal indicating no toner. This is a phenomenon that occurs because the state of the toner present on the detection surface of the piezoelectric sensor 20 changes due to the rotation of the agitator 5, and indicates that the amount of toner in the toner hopper 6 has decreased. Therefore, in this embodiment, the image forming is continued by lowering the charging potential of the photoconductor 1 to -820V. After that, the piezoelectric sensor 20 continuously generates a signal indicating no toner. This indicates that the amount of toner in the toner hopper 6 has become extremely small due to the above-described principle. Therefore, in this embodiment, the image forming was stopped after the image forming was continued for 50 sheets with the developing bias potential applied to the developing roller 2 being -800 V.
[0026]
Then, after the image forming operation was stopped, 60 g of toner was newly supplied to the toner hopper 6, and the charged potential of the photoconductor 1 was set to -870V to form an image.
As a result, good image formation was always achieved.
[0030]
As described above, in the present embodiment, the relationship between the potential of the developing roller 2 and the charging potential of the photosensitive member 1 is changed in accordance with the toner amount in the toner hopper 6.
This is because, for example, in the case of a negatively charged toner, the potential VT on the surface of the toner layer on the developing roller 2 depends on the amount of the carried toner as compared with the potential VB on the surface of the developing roller 2. It becomes higher on the minus side by the minute. Therefore, when the toner amount in the toner hopper 6 is small, the toner amount carried on the developing roller 2 is small, and as shown in FIG. 3A, the rise of the surface potential of the toner layer is small. . On the other hand, immediately after toner replenishment, the amount of toner carried on the developing roller 2 is large, so that the surface potential of the toner layer increases by a large amount as shown in FIG. 3B.
It is desirable that the toner layer surface potential VT and the charging potential VD of the photoconductor 1 (more precisely, the potential after dark decay) are substantially equal. This is because when | VT |> | VD |, the toner tends to adhere to the non-image portion of the photosensitive member 1 of the normally charged toner, and when | VT | <| VD | This is because toner adheres easily to a non-image portion.
As described above, when the amount of toner carried on the developing roller 2 changes, the relationship between the potential VT on the surface of the toner layer on the developing roller 2 and the charging potential of the photoreceptor 1 changes. Normally charged toner or oppositely charged toner adheres to the non-image portion 1, but according to this embodiment, the potential of the toner layer surface on the developing roller 2 and the potential of the non-image portion Are substantially the same, so that the toner does not move to the photoreceptor side even if toner of normal polarity or toner of opposite polarity is present on the toner layer, and before and after toner replenishment. A good image can always be obtained without the occurrence of background contamination on the image.
[0033]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an image forming apparatus capable of always forming an image with a stable density before and after supplying a new developer to the developing apparatus.
[0034]
Further, according to the present invention, there is provided an image forming apparatus capable of always performing image formation without toner adhesion to a non-image portion even before and after replenishing a developing device with a new developer. Can be.
[0035]
[Brief description of the drawings]
FIG. 1 is a main part configuration diagram showing an embodiment of the present invention.
FIG. 2 is a main part configuration diagram showing an embodiment of the present invention.
FIG. 3 is an explanatory diagram illustrating the principle of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 photoconductor 2 developing roller 3 elasticity regulating blade 4 toner supply roller 5 agitator 6 toner hopper 7 toner 8 toner cartridge 9 supply toner

Claims (1)

An image carrier;
Charging means for charging the image carrier,
Latent image forming means for forming an electrostatic latent image on the image carrier charged by the charging means,
Developing means for developing the electrostatic latent image using a developer carrying member which carries and transports the one-component developer charged in a predetermined polarity and stored in the developer storing means; When,
An image forming apparatus comprising: a developer conveying unit configured to stir and convey the one-component developer in the developer storing unit;
A developer amount detecting member for detecting an amount of the developer stored in the developer storing means,
And a voltage control means for controlling a voltage applied to the developer carrying member or the charging means according to an output of the developer amount detecting member, the developer surface on said developer carrying member potential and the image bearing member as the charge potential is substantially equal, the image forming apparatus characterized by controlling the voltage applied to the developer carrying member or the charging unit.

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