JP2008203470A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing nonuniform density, falling of toner in a large quantity, and a banding image, by uniformizing a coating of developer on the developer carrier of a contact developing device. <P>SOLUTION: A layer thickness regulating member 15 is a conductive plate-like member 15. The area of contact with at least the developer carrier 12 is composed of an insulation material 15b. DC voltages equal to each other are applied to the layer thickness regulating member 15 and the developer carrier 12. An AC voltage is also applied to the layer thickness regulating member 15. During a certain period of time when the developer carrier 15 rotates without carrying out image formation, the AC voltage applied to the layer thickness regulating member by a voltage application means differs from that applied during image formation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, an electrostatic latent image formed on an image carrier using an electrophotographic method is visualized by a developing means to form a visible image, and then the visible image is transferred and fixed on a recording material to obtain a permanent image. The present invention relates to an image forming apparatus.

  Here, the electrophotographic image forming apparatus includes, for example, a copying machine, a printer (for example, an LED printer, a laser beam printer, etc.), a facsimile apparatus, and a word processor.

  Conventionally, in an electrophotographic image forming apparatus, for example, an image carrier such as an electrophotographic photosensitive member is charged and then exposed according to image information to form an electrostatic latent image. Then, the developer is supplied to the image carrier by the developing means to form a developer image. Next, the developer image is transferred onto a recording material such as a recording paper, an OHP sheet, or a cloth by a transfer unit, and then the developer image is fixed on the recording material by a fixing unit to obtain a recorded image.

  For example, there is an image forming apparatus using a contact charging device as a charging unit and a non-magnetic one-component contact developing device using a non-magnetic toner as a developing unit. Unlike the so-called jumping development method, a contact developing type developing device creates a gap between an image carrier and a developer carrier, and forms an alternating electric field therebetween to develop toner. The developer is carried in contact with the developer carrier. For this reason, it has been put to practical use in recent years because it is excellent in that the developer scattered during the development process is small and can form a developer image faithfully with respect to the electrostatic latent image on the image carrier.

  FIG. 4 shows an example of an image forming apparatus 200 using a contact developing device.

  In this example, the image forming apparatus 200 is a laser beam printer and includes a drum-type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 as an image carrier. A surface of the photosensitive drum 1 is uniformly charged by applying a predetermined charging bias to a charging roller 2 as a contact charging device that rotates following the photosensitive drum 1.

  Next, the surface of the photosensitive drum 1 is exposed with light L corresponding to the image information signal by an exposure device 3 such as a laser beam, and an electrostatic latent image is formed. The electrostatic latent image formed on the photosensitive drum 1 is supplied with toner as the developer T by the developing device 10 and is visualized as a toner image. As the toner T, a spherical toner having excellent transferability is used.

  The developing device 10 includes a developing container 11, and a developing roller 12 that is a roller-type developer carrier, a developing blade 15 that is a blade-shaped regulating member, and toner that is a developer supply member. A supply roller 13 is provided. The toner in the developing container 11 is supplied to the surface of the developing roller 12 as the toner supply roller 13 rotates in the arrow direction. The toner on the developing roller 12 is sent to the contact portion N between the developing blade 15 and the developing roller 12 as the developing roller 12 rotates in the direction of the arrow. Is done. The thinned toner is further sent to the contact portion with the photosensitive drum 1, that is, the developing area A as the developing roller 12 rotates, and is developed according to the electrostatic latent image.

  On the other hand, the recording material P is supplied from the recording material cassette 40 to the transfer portion where the transfer roller 4 is disposed through the conveying means.

  The toner image on the photosensitive drum 1 is transferred onto the recording material P by applying a transfer bias (voltage) to the transfer roller 4 to form an unfixed image. Next, the recording material P is transported to the fixing device 7 where the unfixed image is fixed onto the recording material P, and then transported to the paper discharge tray 25, where the image formation ends.

  Further, the untransferred toner remaining on the photosensitive drum 1 without being transferred at the time of transfer is collected by a cleaning device 6 having a cleaning blade 5 as a cleaning member. As a result, the photosensitive drum 1 is cleaned and repeatedly used for image formation.

  As described above, the toner in the developing device 10 is rubbed with the toner supply roller 13 and the developing blade 15 on the developing roller 12, and is also rubbed with the photosensitive drum 1 during development. . By repeating such rubbing, the toner in the developing container 11 becomes different from the new toner.

  Specifically, an additive such as silica externally added to the toner surface is embedded in or released from the toner particles themselves. Therefore, the toner gradually changes in performance such as fluidity and chargeability required as a developer. This phenomenon, that is, the change in toner physical properties, becomes more prominent when the image forming operation is repeated many times.

  According to the study by the present inventors, the toner whose physical properties have changed in this way (hereinafter referred to as “deteriorated toner”) is reduced in chargeability, fluidity and the like. For this reason, when the toner is mixed with a toner with little deterioration in the developing device, aggregation occurs due to the mutual toner, and uneven density or toner blurring occurs on the image (toner lump falls on the image on the spot). There was a case.

  In particular, in the case of an image forming apparatus using a toner replenishing method, the toner to be replenished is in a state that hardly deteriorates. For this reason, when the toner is replenished and the replenished toner and the deteriorated toner are mixed, the toner is more agglomerated, and the above-described density unevenness and toner dropout are more likely to occur.

  As measures against such unevenness in density and toner drop, a method of reducing the load caused by rubbing on the toner, a method of making the toner itself difficult to change physical properties, and the like can be considered. However, the former is related to basic structures such as tribo application by a blade and contact with a drum, and there is a limit in reducing the load caused by rubbing. In addition, the toner has limitations in view of fluidity as necessary physical properties, tribo application property, securing of fixing property, and the like.

Under such circumstances, a separate countermeasure is desired for these unevenness in density and toner dropout. For example, in the developing device described in Patent Document 1, it has been proposed to form an alternating electric field between the developing roller and the developing blade. In this developing device, the toner is reciprocated between the developing roller and the developing blade to loosen the toner, thereby preventing density unevenness and toner dropping and stabilizing the toner coat of the developing roller.
Japanese Patent No. 3247285

  However, in the contact developing device, there is a problem even if an alternating electric field in the range described in Patent Document 1 is formed between the developing roller and the developing blade. That is, in the state where the physical properties of the toner have changed after the image forming operation has been repeated many times, the above-described toner drop and density unevenness may not be prevented.

  Furthermore, when the developing device is left for a long time, the contact developing device has a problem in that the developing roller is locally recessed by the pressure of the developing blade at the contact position between the developing roller and the developing blade. That is, in some cases, the toner coat amount on the developing roller increases in the recessed portion, and a banding image that becomes darker with the developing roller cycle, that is, a so-called “developing roller set trace image” may occur.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of uniforming a developer coating state on a developer carrying member in a contact developing device and suppressing occurrence of uneven density, toner blurring, and generation of banding images. For the purpose.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises an image carrier,
Charging means for charging the image carrier;
Exposure means for exposing the surface of the image carrier charged by the charging means to form an electrostatic latent image;
A developer container containing a non-magnetic one-component developer, a rotatable developer carrier for conveying the non-magnetic one-component developer to the image carrier, and a layer thickness of the developer on the developer carrier And a layer thickness regulating member for triboelectrically charging the developer, and the static electricity formed on the surface of the image carrier by applying a DC voltage while contacting the image carrier. Developing means for adhering the non-magnetic one-component developer to the image carrier in accordance with an electrostatic latent image;
Voltage application means for applying a voltage obtained by superimposing an AC voltage on a DC voltage to the layer thickness regulating member;
In an image forming apparatus having
The layer thickness regulating member is a conductive plate-like member, and at least a contact portion with the developer carrier is made of an insulating material,
While applying the same DC voltage to the layer thickness regulating member and the developer carrier, also applying an AC voltage to the layer thickness regulating member,
The AC voltage applied to the layer thickness regulating member by the voltage applying means during a part of the rotation of the developer carrier during non-image formation is different from the AC voltage applied during image formation. An image forming apparatus.

  According to the present invention, by forming an alternating electric field different from that at the time of image formation between the developer carrier and the layer thickness regulating member during non-image formation, the developer coat on the developer carrier is stabilized, It is possible to prevent the occurrence of density unevenness and toner blurring and to prevent the occurrence of a banding image, that is, a so-called “development roller set trace image” that occurs after being left for a long time.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the following examples are intended to limit the scope of the present invention only to those unless otherwise specified. is not. Further, the materials, shapes, etc. of the members once described in the following description are the same as those in the first description unless otherwise described.

Example 1
FIG. 1 is a cross-sectional view illustrating a schematic configuration of the image forming apparatus according to the present embodiment. In this embodiment, an image forming apparatus that forms a black monochrome image will be described. However, the present invention is not limited to these embodiments, and is also applicable to a color image forming apparatus that forms a plurality of colors. it can. Further, regarding the reference numbers, members having the same configurations and functions as those of the conventional example described above will be described using the same reference numbers.

  In this embodiment, the image forming apparatus 100 includes a drum-type electrophotographic photosensitive member, that is, a photosensitive drum 1 as an image carrier on which an electrostatic latent image is formed. Furthermore, it has a developing device 10 that develops the electrostatic latent image formed on the photosensitive drum 1 with the developer T. As will be described later, in this embodiment, a negatively chargeable non-magnetic one-component developer (hereinafter referred to as “toner”) is used as the developer T.

  The developing device 10 is supplied with a developer (toner) T from a developer supply means 30, and toner supply from a developer supply means (hereinafter referred to as “toner hopper”) 30 is controlled by a control means (FIG. (Not shown).

  The photosensitive drum 1 is disposed substantially at the center of the image forming apparatus 100 and is supported so as to be rotatable in the arrow R1 direction. When the image forming operation is started, the charging roller 2 as a charging unit uniformly charges the surface of the photosensitive drum 1. Thereafter, a laser irradiation unit 3 as an exposure unit exposes the surface of the photosensitive drum 1 with a laser beam corresponding to image information to form an electrostatic latent image on the photosensitive drum 1.

  In this embodiment, the charged charge of the photosensitive drum 1 is negative. Then, the electrostatic latent image corresponding to the image information is formed in a portion where the negative charged charge is attenuated by the exposure with the laser beam from the laser irradiation means 3.

  Thereafter, the electrostatic latent image is visualized by toner supplied by the developing device 10 as the photosensitive drum 1 rotates, and a toner image is formed on the photosensitive drum 1.

  In this embodiment, the developing method is a reversal developing method. Therefore, toner having the same polarity (negative polarity) as the charged charge adheres to the portion (image portion) on the photosensitive drum 1 where the negative charged charge is attenuated. The toner is supplied from the toner hopper 30 to the developing container 11.

  On the other hand, the recording material P accommodated in the cassette 40 is transferred to the transfer region where the photosensitive drum 1 and the transfer roller 4 as a transfer unit are in contact with each other by the paper feed roller 41, and the toner image on the photosensitive drum 1 reaches the transfer region. It is conveyed synchronously.

  When the toner image on the photosensitive drum 1 and the recording material P reach the transfer region, the toner image is transferred onto the recording material P by the transfer electric field formed in the transfer region by the transfer roller 4. Thereafter, the unfixed toner image carried on the recording material P is fixed on the recording material P as a permanent image by being heated by a fixing means (heat roller) provided in the fixing device 7 and being pressurized by the pressing means. Is done.

  In addition, after the toner image transfer is completed, the transfer residual toner remaining on the surface of the photosensitive drum 1 is removed by a cleaning device 6 including a blade-shaped cleaning member 5 to prepare for a subsequent image forming operation.

  Next, the developing device 10 and the toner hopper 30 will be further described with reference to FIG.

  In this embodiment, the developing device 10 carries and carries toner as the developer T, and contacts the toner with the image carrier, that is, the photosensitive drum 1 to develop an electrostatic latent image (hereinafter referred to as a developer carrier). (Referred to as “developing roller”) 12. That is, the developing device 10 employs a contact developing method in which development is performed in a state where the developing roller 12 is brought into contact with the photosensitive drum 1 and toner is “contacted” with the photosensitive drum 1.

  Further, the developing device 10 includes developer supplying means (hereinafter referred to as “toner supply roller”) 13 for supplying toner to the developing roller 12. Further, a developer layer thickness regulating means (hereinafter referred to as “developing blade”) 15 that regulates the toner supplied by the toner supply roller 13 and forms a thin layer of toner on the developing roller 12 is provided.

  In the toner hopper 30, a stirring member 31 for loosening the toner in the toner hopper 30 and a replenishing roller 32 for replenishing the toner from the toner hopper 30 to the developing device 10 are arranged. The amount of toner is detected by the optical residual detection means 16 (light emitting unit 16a, light receiving unit 16b, light transmitting windows 16c, 16d) of the developing device 10, and the toner amount necessary for the developing device 10 from the replenishing roller 32 according to the detection result. Replenish as appropriate.

  Further, the developer T is a negatively charged non-magnetic one-component developer (toner), and is intended to save energy in the fixing device 7 by forming an internal structure containing a low softening point substance. . As a toner production method, for example, a developer production method by a suspension polymerization method described in JP-B-63-10231, JP-A-59-53856, JP-A-59-61842, or the like is used. I can do it.

  In this embodiment, the toner has a so-called core / shell internal structure in which a low softening point material is coated with an outer shell resin, and a volume average particle diameter of 6 μm formed by polymerization of the shell portion in this structure. The spherical toner is used. According to the suspension polymerization system at room temperature or under pressure, spherical fine particles having a particle size of 3 to 8 μm can be obtained relatively easily with a sharp particle size distribution. For this reason, the distribution of the weight specific charge becomes sharp, and uniform development according to the development contrast is performed.

  In addition to the suspension polymerization method, a toner produced by a dispersion polymerization method in which a monomer is soluble and a polymer obtained by polymerization is insoluble in an aqueous organic solvent that is directly insoluble is used. used. Furthermore, it is possible to use a toner produced using an emulsion polymerization method typified by a soap-free polymerization method in which a toner is produced by direct polymerization in the presence of a water-soluble polar polymerization initiator.

  Next, the shape of the toner used as a developer in this embodiment will be described.

  As described above, spherical toner is used in this embodiment, and specifically, a toner having an average circularity of 0.950 or more is used. As a result, fog characteristics and transferability are greatly enhanced. The reason for this is that the contact area between the toner particles and the photoconductor is small due to the extremely high degree of circularity, and the adhesion of the toner particles to the photoconductor due to mirror image force, van der Waals force, etc. is reduced. It is because it is easy to be done. In addition, as described above, the frictional charge imparting member and the individual toner particles are uniform in frictional charge, so that there is little variation in the amount of charge that causes fogging and a decrease in image quality. The average circularity is more preferably 0.970 or more.

  Hereinafter, a method for measuring the average circularity of the present embodiment will be described.

The average circularity in this example is used as a simple method for quantitatively expressing the shape of the particles. In this example, measurement was performed using a flow type particle image analyzer “FPIA-1000” manufactured by Toago Medical Electronics, and the circularity (Ci) of each particle measured for a particle group having a circle-equivalent diameter of 3 μm or more was expressed by the following equation. Each was determined by (1). Furthermore, as shown by the following formula (2), a value obtained by dividing the total sum of the measured circularity (Ci) of all particles by the total number of particles (m) is defined as an average circularity (Cmean).
Circularity (Ci) = perimeter of a circle having the same projected area as the number of particles / perimeter of a projected image of a particle (1)

  In addition, “FPIA-1000” which is a measuring apparatus used in the present embodiment uses the following calculation method. That is, after calculating the circularity of each particle, in calculating the average circularity, the particles are divided into classes having a circularity of 0.40 to 1.00 divided into 61 according to the obtained circularity, and the central value of the dividing point and A calculation method is used in which the average circularity is calculated using the frequency.

  As a specific measuring method, about 5 mg of developer is dispersed in 10 ml of water in which about 0.1 mg of a surfactant is dissolved to prepare a dispersion. Then, ultrasonic waves (20 kHz, 50 W) are irradiated to the dispersion for 5 minutes, the dispersion concentration is set to 5000 to 20,000 / μl, the measurement is performed with the above apparatus, and the average circle of particles having an equivalent circle diameter of 3 μm or more is measured. Find the degree.

  The average circularity in this embodiment is an index of the degree of unevenness of the developer, and is 1.000 when the developer is a perfect sphere, and the average circularity becomes smaller as the developer surface shape becomes more complicated. It becomes.

  In this measurement, the degree of circularity is measured only for a particle group having an equivalent circle diameter of 3 μm or more for the following reason. In other words, since the particle group having an equivalent circle diameter of less than 3 μm includes a large number of external additive particle groups that exist independently of the toner particles, the circularity of the toner particle group cannot be accurately estimated due to the influence thereof. It is.

  Next, each member arranged in the developing device 10 will be described with reference to FIG.

  The developing device 10 has toner in the developing container 11. The developing container 11 includes a developing chamber 11A in which a developing roller 12, a toner supply roller 13, and a developing blade 15 are disposed, a stirring chamber 11B in which a stirring member 14 is disposed, and a toner from the stirring chamber 11B to the developing chamber 11A. And an opening 11C provided to move. Here, the stirring chamber 11B is disposed above the developing chamber 11A across the opening 11C.

  Further, the developing container 11 is provided with an opening 11 </ b> D in a part of the side facing the photosensitive drum 1. The developing roller 12 is supported by the developing container 11 so as to be partially exposed from the opening 11D and to be rotatable in the arrow R2 direction.

  The developing roller 12 is a semiconductive elastic roller composed of a low-hardness rubber material (silicone, urethane, etc.) in which a conductive agent (carbon, etc.) is dispersed or a foam, and a combination thereof. It is in contact with the photosensitive drum 1 by contact pressure. Further, a blowout prevention sheet 9 is provided in the opening portion 11D in order to prevent toner from scattering from below the developing roller 12.

  Below the stirring region, a toner supply roller 13 that supplies and collects toner is disposed so as to contact the developing roller 12. The toner supply roller 13 is an elastic roller made of an elastic foam and rotates in the direction of the arrow R3.

  The toner in the developing container 11 is sufficiently stirred by the stirring member 14, and then passes through the opening portion 11 </ b> C mainly by movement due to gravity, is conveyed by the toner supply roller 13, and is supplied to the developing roller 12.

A developing blade 15 as a regulating member that regulates the toner layer thickness is provided in pressure contact with the developing roller 12. The developing blade 15 includes a conductive layer (plate-like member) 15a of a leaf spring-like thin metal plate having a thickness of 0.1 mm, an insulating layer of 75 μm on the contact surface side surface of the developing roller 12, and an adhesive layer of 25 μm with a total thickness of 0.1 mm. It is composed of an elastic regulating member provided with an insulating layer (insulator material) 15b. In this embodiment, the insulating layer 15b is formed of a polyamide elastomer having a high charge donating property in order to satisfactorily impart charge to the negative toner. Of course, the resistance between the developing roller 12 and the conductive layer 15b is not less than a predetermined value in terms of preventing leakage, and the volume resistance is preferably 10 ¹⁰ Ω · cm or more.

  An alternating voltage (blade AC bias) in which a direct current is superimposed is applied to the conductive layer 15 a of the developing blade 15 by the power source 21.

  The toner supplied onto the developing roller 12 by the toner supply roller 13 is regulated in layer thickness by the developing blade 15, and a thin layer is formed on the developing roller 12. At this time, the toner is given sufficient charge to be used for development due to friction with the surfaces of the developing roller 12 and the developing blade 15.

  Thereafter, the toner thin layer on the developing roller 12 is conveyed to a developing area (developing nip) A (see FIG. 1) where the photosensitive drum 1 and the developing roller 12 are in contact with the rotation of the developing roller 12. . A DC voltage is applied to the developing roller 12 from the power source 22, and the toner on the developing roller 12 corresponds to the electrostatic latent image on the surface of the photosensitive drum 1 by the action of the developing electric field between the photosensitive drum 1 and the developing roller 12. Thus, a toner image is formed and the electrostatic latent image is visualized.

  The toner that is applied on the developing roller 12 and conveyed to the developing nip A but does not contribute to the development and remains carried on the developing roller 12 is developed by rubbing with the toner supply roller 13. It is peeled off from the roller 12. Thereafter, a part of the removed toner is supplied again onto the developing roller 12 by the toner supplying roller 13 together with the toner newly supplied onto the toner supplying roller 13, and the rest is returned into the developing container 11. .

  In this embodiment, the toner supply roller 13 has two functions as the developer supply and recovery means. However, the present embodiment is not limited to this, and the developer supply means and the developer recovery are not limited thereto. It is also possible to provide the means separately.

  In this embodiment, the process speed of the image forming apparatus 100 is 190 mm / sec, and the peripheral speed of the developing roller 12 is 295 mm / sec.

  Further, the developing device 10 is configured to be detachable from the image forming apparatus 100 and is replaced when a predetermined life is reached.

  Next, a method and an effect of applying an alternating electric field formed between the developing roller 12 and the developing blade 15 in this embodiment will be described in detail.

  During a developing operation, that is, during image formation, −300 V is applied as a DC component from the power source (voltage applying unit) 22 to the developing roller 12 as a developing bias. As a result, negative polarity toner adheres to the latent image potential portion of the exposed portion of the photosensitive drum 1 of −100 V (the potential of the non-exposed portion is set to −600 V), and the latent image is developed.

  As a blade bias to be applied to the conductive layer 15a of the developing blade 15, from the power source (voltage applying means) 22 to the developing blade 15, a DC component is set to −300 V, which is the same as the developing bias, and an AC component has a peak-to-peak voltage of 600 V and a frequency of 1500 Hz. Applied.

  By setting such a developing bias and a blade bias, an alternating electric field can be applied to the toner entering the contact nip N between the developing roller 12 and the developing blade 15 in the vicinity of the entrance. it can. As a result, the toner reciprocates between the developing roller 12 side and the developing blade 15 side, and the toner aggregated in this portion is loosened and is always regulated by the developing blade 15 in a stable state. A thin toner layer is formed on the developing roller 12.

  As a result, it is possible to prevent shading unevenness and toner drop-off that are likely to occur after repeating the image forming operation.

  Further, when the developing device 10 is left for a long time and the developing roller 12 is depressed by the pressing of the developing blade 15, a “developing roller set trace image” that is banding of the developing roller cycle occurs. According to the study by the present inventors, it has been found that an alternating electric field between the developing roller 12 and the developing blade 15 is effective as a measure for preventing such a “developing roller set trace image”.

  That is, when the electric field strength of the alternating electric field between the developing roller 12 and the developing blade 15 is increased to a predetermined value or more, the amount of toner carried in the recessed portion on the developing roller 12 increases with respect to other portions. It was found that can be prevented. This is because the influence of the alternating electric field on the amount of toner entering the contact nip portion between the developing roller 12 and the developing blade 15 becomes stronger, and the toner regulation at the recessed portion becomes larger than when there is no alternating electric field. It is thought to be caused.

  As a result, by setting the electric field strength of the alternating electric field between the developing roller 12 and the developing blade 15 to a predetermined value or more, the developing roller set trace image becomes invisible.

  In this embodiment, the same DC component is applied to the developing roller 12 and the conductive layer 15a. As a result, it is possible to prevent the toner having basically negative polarity and a part of the charge having the reverse polarity from being biased to one of the developing roller 12 and the developing blade 15, and a further effect of loosening the toner can be obtained. Further, since the phenomenon such as so-called development roller fusion or development blade fusion, in which toner is fused to the developing roller 12 or the development blade 15, can be prevented, fogging caused by the development roller fusion or streak image caused by the development blade fusion. Can be prevented.

  As described above, by applying an alternating electric field having a strong electric field strength of a predetermined value or more between the developing roller 12 and the developing blade 15, it is possible to prevent density unevenness and toner blurring and to further suppress the occurrence of a developing roller set trace image. It becomes possible.

  However, according to the study by the present inventors, it has been found that adverse effects occur when the electric field strength of the alternating electric field is increased too much.

  The first adverse effect is a leak phenomenon between the developing blade 15 and the developing roller 12. The second adverse effect is the dropping of toner due to the accumulation of toner on the developing blade 15 on the downstream side of the contact nip between the developing blade 15 and the developing roller 12.

  As described above, toner accumulation on the developing blade 15 (hereinafter referred to as “toner accumulation”) is performed when the alternating electric field strength between the developing roller 12 and the developing blade 15 is too strong. Occurs when done. The present inventors consider that this is because of the following.

  That is, in a state where the alternating electric field is strong, the toner holding force on the upstream side of the contact nip of the developing blade 15 is increased. In this state, when the rotation of the developing roller 12 carrying the toner on its surface is repeated, a large amount of the toner staying upstream of the nip is pushed under the pressure contact of the developing blade 15 and reaches the downstream side. Then, toner adhesion on the developing blade 15 on the downstream side of the contact nip of the developing blade 15 is caused, and this adhered toner is gradually accumulated.

  The toner pool reaches a certain amount, and the toner charge is reduced by being left alone, and the adhesion force to the developing blade 15 is reduced. At this time, the developing blade 15 vibrates when the developing roller 12 starts to rotate. Then, the toner falls on the developing roller 12, is moved by the rotation of the developing roller 12, and adheres on the photosensitive drum 1. As a result, the image drops on the paper during image formation, and is transferred onto the transfer roller 4 and transferred from the transfer roller 4 to the back side of the recording paper P as the recording material P during non-image formation. Dirt is generated.

  In addition, the toner pool may affect the toner coat of the developing roller 12 even when it is attached on the developing blade 15, and may cause a vertical streak image.

  Therefore, the present inventors have prevented the occurrence of this adverse effect, while preventing the occurrence of uneven shading, toner drop, and development roller set trace image, and the electric field strength of the alternating electric field between the developing roller 12 and the developing blade 15. An experiment was performed using the image forming apparatus 100 in order to investigate the optimum range.

  As a developing bias, −300 V was applied as a DC component from the power source 22 to the developing roller 12.

  Further, a voltage control means 50 for controlling the blade bias voltage applied to the developing blade 15 is attached to the power source 22. Then, an experiment is performed in which the image forming operation is continuously repeated 10,000 sheets by changing the peak-to-peak voltage (Vpp) by fixing the frequency from the power source 22 to the developing blade 15 as DC component at −300 V and AC component as 1500 Hz. It was.

  The results are shown in Table 1. The electric field strength between the developing roller 12 and the developing blade 15 corresponding to the peak-to-peak voltage (Vpp) is also shown in Table 1. In the table, with respect to development roller set marks, leaks, and toner blurring, ◯ indicates no occurrence, Δ indicates slight occurrence, and x indicates significant occurrence. Concerning the toner reservoir, ◯ indicates a slight amount of toner adhering, Δ indicates a toner reservoir that causes a slight dropout, and × indicates a toner reservoir that causes a significant dropout.

According to Table 1, toner toner drop can be prevented even at a Vpp lower than that of the developing roller set mark, and was good at a Vpp of 350 V or more and an electric field strength of 1.72 × 10 ⁶ [V / m] or more. Further, the development roller set trace was good at Vpp of 500 V or more and the electric field strength of 2.45 × 10 ⁶ [V / m].

On the other hand, leakage, which is a harmful effect on the higher Vpp side, occurs when Vpp is 1200 V or more and the electric field strength is 5.88 × 10 ⁶ [V / m] or more, and below Δ rank on the downstream side of the developing blade 15 at the nip. The toner reservoir was generated at a Vpp of 500 V or more and an electric field strength of 2.45 × 10 ⁶ [V / m] or more.

  From the results in Table 1, it can be seen that there are no values of Vpp and electric field intensity that satisfy harmful leakage and toner accumulation while preventing toner drop and developing roller setting marks.

  Therefore, the present inventors have found conditions that satisfy all of these conditions by examining the growth mechanism of the toner reservoir. Described below.

First, the inventors conducted an experiment to confirm the occurrence of toner accumulation. The direct current component was made the same as the developing bias as the blade bias. Also, the AC component frequency was fixed at 1500 Hz and Vpp, and a high bias, that is, 1000 V at which toner accumulation occurred in Table 1, and the electric field strength was fixed at 4.90 × 10 ⁶ [V / m]. Then, a change in the amount of accumulated toner in the case of continuous printing was examined. The results are shown in FIG.

  It can be seen that the toner reservoir grows when continuous printing is performed for a long time, and the toner reservoir does not grow if it is 3 minutes or less.

Next, continuous printing is not performed with a high Vpp of 1000 V, but a low Vpp of 450 V and an electric field strength of 2.21 × 10 ⁶ [V / m] and a continuous printing operation was performed to check the degree of toner pool growth. The results are shown in FIG. The squares in FIG. 3 represent the amount of toner remaining after printing for 20 minutes.

  From this result, it has been found that the toner pool growth can be suppressed by intermittently switching to a bias with a low electric field strength instead of applying a bias continuously with a high electric field strength.

  From these results, the present inventors have found a condition that satisfies the harmful leakage and toner accumulation while preventing toner drop and developing roller setting marks.

  That is, the values of Vpp and electric field strength are changed during image formation and non-image formation.

At the time of image formation, the electric field strength is set so as to prevent toner drop, development roller setting traces, and leakage. That is, the electric field intensity E1 at the time of image formation is set to the following range.
2.45 × 10 ⁶ [V / m] ≦ E1 ≦ 4.90 × 10 ⁶ [V / m]

Next, the electric field strength is set so as to suppress toner accumulation without causing dropout during non-image formation. That is, the electric field intensity E2 during non-image formation is set to the following range.
1.72 × 10 ⁶ [V / m] ≦ E2 ≦ 2.21 × 10 ⁶ [V / m]

  Next, the inventors set the electric field strengths E1 and E2 in the above range during image formation and non-image formation between sheets using the image forming apparatus 100, and switch them during a continuous image forming operation to 10000 sheets. The image forming operation was performed.

  As a result, the toner image was not dropped and the developing roller was not set, and toner accumulation could be prevented.

  Consider these phenomena, that is, why the toner reservoir grows at a high electric field strength and can be suppressed by switching to a low electric field strength intermittently.

  It is considered that the holding force staying on the upstream side of the developing blade nip increases as the electric field strength of the alternating electric field between the developing roller and the developing blade increases, and decreases as it decreases. When the electric field strength of the alternating electric field is as strong as about E1, the amount of toner remaining on the upstream side of the developing blade nip gradually increases. When the toner remaining on the upstream side of the developing blade nip exceeds a certain amount, the toner is gradually pushed downstream to the developing blade nip, and a part of the toner adheres to the developing blade 15 on the downstream side of the developing blade nip. It is considered a thing.

  On the other hand, by reducing the electric field strength of the alternating electric field from about E1 to about E2, the force staying on the upstream side of the developing blade nip is weakened, so that the amount of toner remaining on the upstream side of the developing blade nip is reduced, resulting in the downstream of the developing blade nip. It is thought that the toner accumulation on the side may be eliminated.

In summary, as described above, the electric field strength E1 of the alternating electric field between the developing roller and the developing blade during image formation is
2.45 × 10 ⁶ [V / m] ≦ E1 ≦ 4.90 × 10 ⁶ [V / m]
And the electric field strength E2 of the alternating electric field between the developing roller and the developing blade during non-image formation,
1.72 × 10 ⁶ [V / m] ≦ E2 ≦ 2.21 × 10 ⁶ [V / m]
And As a result, it is possible to reduce image defects such as spot images and developing roller set trace images due to toner blurring, and it is possible to suppress the occurrence of stains on the back of printing paper and vertical streak-like images.

  In addition, it is not necessary to switch to a low electric field strength every time during non-image formation, and by reducing the electric field strength once within 3 minutes, the amount of accumulated toner can be reduced, and the backside of printing paper and vertical streak-like images can be reduced. It became possible to suppress the occurrence of.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. It is a schematic structure enlarged view of a developing device. 6 is a graph showing a change in toner accumulation over time. FIG. 10 is a schematic cross-sectional view illustrating an example of a conventional image forming apparatus.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging roller (charging means)
3 Laser irradiation means (exposure means)
4 Transfer roller 6 Cleaning device 7 Fixing device 10 Developing device (developing means)
11 Developing Container 12 Developing Roller (Developer Carrier)
13 Toner supply roller (developer supply means)
14 Stir paddle (stirring member)
15 Development blade (developer layer thickness regulating member)
15a Conductive layer 15b Insulating layer 16 Optical residual detection means 16a Light emitting part 16b Light receiving part 16c, 16d Light transmission window 21 Blade bias power supply (voltage applying means)
22 Development bias power supply (voltage application means)
30 toner hopper (developer supply means)
32 Supply roller 50 Voltage control means 100 Image forming apparatus

Claims (6)

An image carrier;
Charging means for charging the image carrier;
Exposure means for exposing the surface of the image carrier charged by the charging means to form an electrostatic latent image;
A developer container containing a non-magnetic one-component developer, a rotatable developer carrier for conveying the non-magnetic one-component developer to the image carrier, and a layer thickness of the developer on the developer carrier And a layer thickness regulating member for triboelectrically charging the developer, and the static electricity formed on the surface of the image carrier by applying a DC voltage while contacting the image carrier. Developing means for adhering the non-magnetic one-component developer to the image carrier in accordance with an electrostatic latent image;
Voltage application means for applying a voltage obtained by superimposing an AC voltage on a DC voltage to the layer thickness regulating member;
In an image forming apparatus having
The layer thickness regulating member is a conductive plate-like member, and at least a contact portion with the developer carrier is made of an insulating material,
While applying the same DC voltage to the layer thickness regulating member and the developer carrier, also applying an AC voltage to the layer thickness regulating member,
The AC voltage applied to the layer thickness regulating member by the voltage applying means during a part of the rotation of the developer carrier during non-image formation is different from the AC voltage applied during image formation. An image forming apparatus.   In a part of the developer carrier rotating during non-image formation, the electric field strength of the alternating electric field formed between the layer thickness regulating member and the developer carrier is different from that during image formation. The image forming apparatus according to claim 1.   In part of the developer carrying member rotating during non-image formation, the electric field strength of the alternating electric field formed between the layer thickness regulating member and the developer carrying member is made smaller than that during image formation. The image forming apparatus according to claim 2. At the time of image formation, the electric field strength E1 of the alternating electric field formed between the layer thickness regulating member and the developer carrier is
2.45 × 10 ⁶ [V / m] ≦ E1 ≦ 4.90 × 10 ⁶ [V / m]
And
Further, the electric field strength E2 of the alternating electric field formed between the layer thickness regulating member and the developer carrier in a part during rotation of the developer carrier during non-image formation is:
1.72 × 10 ⁶ [V / m] ≦ E2 ≦ 2.21 × 10 ⁶ [V / m]
The image forming apparatus according to claim 3, wherein:   The image forming apparatus according to claim 1, wherein the non-magnetic one-component developer has an average circularity of 0.950 or more.   6. The image forming apparatus according to claim 5, wherein the non-magnetic one-component developer has an average circularity of 0.970 or more.

Images