JP2006091269A - Developing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple and general-purpose apparatus improving an electrostatic transfer property and color aptitude which are defects at the time of using a conventional conductive toner, capable of effectively preventing occurrence of fogging and toner cloud and hardly being affected by environmental changes and secular deterioration. <P>SOLUTION: The developing device is provided with: a toner carrier 3 arranged oppositely to an image carrier 1 carrying an electrostatic latent image Z and carrying charged conductive toner 2; a developing field forming means 4 for forming a developing field between the toner carrier 3 and the image carrier 1 and developing the electrostatic latent image Z formed on the image carrier 1 with toner in the developing field area; and a charge injection means 5 having a charge injection member 6 arranged oppositely to the toner carrier 3 and injecting charge into the conductive toner 2 by applying a charge injecting field between the charge injection member 6 and the toner carrier 3. The charge injection means 5 is provided with a charge injection field forming means 7 for forming the charge injection field so as to be controlled in accordance with a change in the use conditions of the device. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device used in an image forming apparatus such as a copying machine or a printer, and more particularly to a developing device that visualizes an electrostatic latent image with a charged conductive toner and an image forming apparatus using the same. About.

In a conventional electrophotographic image forming apparatus, a method in which an insulating toner is triboelectrically charged to give electric charge and used for development is widely used.
Here, as a method for charging the toner, the triboelectric chargeability of the toner is controlled in advance by a combination with the binder resin or additive of the toner, and the toner is stirred or transported in the developing device. In many cases, the toner is charged by friction between a substance that easily causes frictional charging and the toner by rubbing the toners by agitating operation or conveying operation of the toner in the middle of the conveying path.

In such a toner charging method, since a certain amount of charge distribution exists in the charge amount of the toner charged by friction, the toner includes a low charge toner with a small charge amount and a charge polarity of the entire toner. Often contains a reverse polarity toner having a reverse charge polarity.
At this time, the low-charge toner tends to become a so-called toner cloud that floats away from the toner carrier in the developing device and floats in the image forming device, and this toner cloud causes a failure of the image forming device.
Further, the reverse polarity toner is attracted to the background portion to which the toner does not adhere in the electrostatic latent image on the image carrier, and generates a so-called fog that is uniform contamination of the background portion.
Furthermore, this type of triboelectric charging method is easily affected by environmental changes and changes over time, and the surface state of the triboelectric charging mechanism such as the toner and the agitating member changes, resulting in an unsatisfactory charging state of the toner. It tends to be stable.

In order to solve such a problem, a method of using a conductive toner, specifically, a method of injecting a charge into the conductive toner and charging it for development is known.
This method has various advantages because it does not use triboelectric charging.
In particular, since the conductive toner easily moves the charge and can give the toner a uniform charge, the greatest feature is that it can prevent fogging and toner clouding and is less susceptible to environmental changes and deterioration over time. In addition, since a frictional charging mechanism is not required, the structure is simple, and the size and cost can be reduced.

JP-A-10-111604 (page 3-5, FIG. 1) Japanese Examined Patent Publication No. 58-26026 (page 1-5, FIG. 1) Japanese Examined Patent Publication No. 63-10426 (page 1-2, Fig. 2) JP 63-159870 (page 1-4, FIG. 1) JP-A-6-95518 (page 1-6, FIG. 1)

However, the biggest reason why conductive toner does not become versatile is that it is difficult to transfer a toner image onto a moisture-absorbing recording paper in a general-purpose electrostatic transfer system such as a corotron or a bias roll.
Also, when forming a color image, various colors are reproduced by superimposing color toners having different color materials, but the conductive toner cannot superimpose the toner and cannot cope with colorization.
This is due to the fact that the toner charge is transferred between the recording paper and the toner that have absorbed moisture and become low resistance because the toner is conductive, and the electrostatic adsorption force to the toner is lost. .

  As another technical problem, since conductive toner easily injects electric charge, if the latent image potential becomes unstable, a small potential difference between the developing bias and the background portion of the electrostatic latent image (the cleaning potential is set). ) However, charge of reverse polarity is injected into the toner, which is likely to cause fogging.

In order to solve such a technical problem, the following prior arts a to e have been conventionally proposed.
That is,
a As a toner, a proposal that has the property of being easily charged to one of the positive and negative polarities and not easily charged to the other polarity after being charged to the other polarity, in other words, it is easy to inject charges, Proposals related to toner materials that do not leak easily (for example, see Patent Document 1),
b Applying a predetermined amount of an insulating medium to at least one surface of the substrate, and using a recording paper (transfer medium) having a predetermined volume specific resistance value makes the charge retention amount of the paper stable and uniform. Proposal (see, for example, Patent Document 2),
c A proposal for reducing the image portion potential of the electrostatic latent image after development and prior to transfer to a predetermined level of the image portion potential during development to suppress toner scattering (see, for example, Patent Document 3),
d By mixing conductive toner and insulating toner, during transfer, charge injection from the paper to the conductive toner is prevented by the insulating toner (insulator), and the conductive toner and the paper are made non-contact. And a proposal for maintaining the charge retention of the conductive toner (see, for example, Patent Document 4),
e. Heating the conductive toner on the image carrier softens and melts the toner, and uses the adhesive force of the softened and melted toner to maintain good transferability from the image carrier to the recording material. Proposals related to the non-electrostatic transfer technology (see, for example, Patent Document 5) have been attempted.

  However, not all of the prior arts can obtain transfer properties equivalent to insulating toners. For example, in the prior arts a and d, a special material must be used, and in the prior art b. In this case, a special recording paper must be used. Furthermore, in the prior arts c and e, a special image forming process is indispensable. There is a concern that the performance will be greatly impaired, and it has not been put into practical use at this stage.

  The present invention has been made in order to solve the above technical problem, and has improved electrostatic transferability and color suitability, which are disadvantages when using a conventional conductive toner. It is an object of the present invention to provide a simple and versatile developing device that can effectively prevent toner clouding and is not easily affected by environmental changes and deterioration over time, and an image forming apparatus using the developing device.

  That is, according to the present invention, as shown in FIG. 1A, in the developing device that visualizes the electrostatic latent image Z with the conductive toner 2, the image bearing member 1 that carries the electrostatic latent image Z is provided. A developing electric field is formed between the toner carrying member 3 which carries the charged conductive toner 2 which is arranged oppositely and which is charged, and between the toner carrying member 3 and the image carrier 1, and in this developing electric field region the image carrying member. 1 has a developing electric field forming means 4 for developing the electrostatic latent image Z on the toner 1 and a charge injection member 6 disposed opposite to the toner carrier 3, and between the charge injection member 6 and the toner carrier 3. Charge injection means 5 for injecting electric charge into the conductive toner 2 by applying a charge injection electric field is provided. The charge injection means is formed such that the charge injection electric field can be adjusted in accordance with changes in the use conditions of the apparatus. An electric field forming means 7 is provided.

In such technical means, the developing method for handling the conductive toner 2 may be any developing method such as a one-component developing method or a two-component developing method.
The toner carrier 3 may be in any form such as a roll or a belt as long as it carries and transports the conductive toner 2, and the magnetic pole layout may be arbitrarily set.
Further, the developing electric field forming means 4 includes a wide range of devices that form a developing electric field between the image carrier 1 and the toner carrier 3, and the developing electric field here is a direct current electric field or an alternating electric field superimposed. You may select DC electric fields suitably.

In the present invention, the conductive toner 2 may have a conductive toner base as a base and an insulating or semiconductive coating layer provided on the surface thereof, or an insulating toner base as a base. There are various modes such as embedding conductive fine particles on the surface.
In the former mode, the conductive toner substrate may be a toner substrate having conductivity as a result. For example, conductive fine particles may be mixed in the insulating toner substrate, or near the outer surface of the insulating toner substrate. The conductive fine particles may be appropriately selected, for example. Moreover, as a preferable aspect of a coating layer, the coating layer which has an amorphous polymer as a main component is mentioned, for example. Here, the coating layer containing the amorphous polymer as a main component means that at least the ratio of the amorphous polymer phase is 80% or more. Furthermore, the coating layer is not limited to a mode in which the conductive toner substrate is completely coated, but includes a mode in which the conductive toner substrate is completely coated. In this case, the resistance adjustment may be performed by providing a recess in a part of the coating layer or adjusting the layer thickness.
On the other hand, in the latter mode, the insulating toner substrate may be an insulating toner used in an electrophotographic system, and examples thereof include those using styrene acrylic resin or polyester resin. Further, the conductive fine particles preferably have a size of submicron from the viewpoint of embedding in the insulating toner base, and examples thereof include fine particles such as ITO, tin oxide, zinc oxide, and titanium oxide. Further, in the case of the conductive fine particles, in order to apply the conductive toner 2 to the color toner, it is preferable that the conductive toner 2 has transparency, and this allows the conductive toner to have excellent color suitability (particularly color developability). 2 can be obtained.

  Further, as shown in FIG. 1B, the charge injection means 5 injects charges into the conductive toner 2 by applying a charge injection electric field ED between the charge injection member 6 and the toner carrier 3. I just need it. At this time, the charge injection electric field is not necessarily larger than the development electric field, and if the charge injection member 6 is a functional member for injecting electric charge into the toner, for example, a roll, plate, blade or the like is appropriately used. A conductive plate to which a conductive roll or conductive rubber is bonded is typically mentioned, although it may be selected. The material of the charge injection member 6 is aluminum, stainless steel or the like, but is not limited to this, and may be appropriately selected.

Furthermore, as the charge injection means 5, a charge injection electric field forming means 7 such as a normal power source is used as an element for generating a charge injection electric field between the charge injection member 6 and the toner carrier 3.
In the present invention, the charge injection electric field forming means 7 is formed such that the charge injection electric field can be adjusted in accordance with changes in the use conditions of the apparatus.
In this case, the charge injection electric field forming means 7 can cause an appropriate charge injection electric field to act even when the use condition environment such as image density change or environment change is different.
The charge injection field here may be selected as appropriate, such as a direct current electric field or a direct current electric field superimposed with an alternating electric field.

In such a charge injection electric field forming means 7, in order to adjust the charge injection electric field according to the change in the use condition of the apparatus, the sensor 8 capable of detecting the change in the use condition of the apparatus may be used. Typical examples of this type of sensor 8 include a density sensor that detects image density and an environmental sensor that detects the surrounding environment of the apparatus.
In this case, the detection information from the sensor 8 is normally taken into the control means, and this control means sends a predetermined control signal to the charge injection electric field forming means 7 so that the charge injection electric field can be adjusted. You may make it adjust a charge injection electric field formation means directly according to the detection information from the sensor 8, without going through a means.
Further, the density sensor as the sensor 8 may be any sensor that can detect the density (development toner amount) of the toner patch on the image carrier 1 or the recording medium, for example. In this case, since the amount of the developing toner detected by the density sensor mainly depends on the charge injection quantity, the charge injection quantity (specifically, the charge injection electric field) is set according to the detection information from the density sensor. The image density can be adjusted by controlling. Note that the image carrier 1 includes a wide range of ones that carry toner images. For example, in the case of an intermediate transfer type image forming apparatus, the image carrier 1 is not limited to an image forming carrier such as a photosensitive member but also includes an intermediate transfer member. Therefore, the location where the density sensor is disposed may be either an image forming carrier or an intermediate transfer member.
In addition, as a usage model mode of the density sensor, a known optical sensor such as a specular reflection type, a diffuse reflection type, or a transmission type may be appropriately selected.

Furthermore, as a preferable mode when using the density sensor, a mode in which a potential sensor that can detect the latent image potential on the image carrier 1 is provided.
According to this aspect, the developing toner amount detected by the density sensor depends mainly on the latent image potential on the image carrier 1 although it depends mainly on the charge injection amount. Therefore, if the potential sensor is provided so that the latent image potential on the image carrier 1 is always kept within a certain range according to the detection information of the potential sensor, the density sensor always detects under the same conditions. Can be possible.

Moreover, in the aspect using the environmental sensor as the sensor 8, the use condition environment of the apparatus can be detected.
Here, since the toner charge amount changes depending on the use condition environment such as temperature and humidity, it is possible to obtain the charge amount according to the environment change by controlling the charge injection electric field based on the detection information of the environment sensor. Become.
Furthermore, as an aspect of the environmental sensor, in addition to an aspect including both the temperature sensor and the humidity sensor, only the temperature sensor or only the humidity sensor may be selected as appropriate.
Here, the temperature sensor may be appropriately selected such as a thermistor or a silicon IC, and the humidity sensor may be appropriately selected as long as it has a performance equivalent to that of the polymer resistance change type.

The charge injection means 5 may be a mode in which both the charge injection member 6 and a toner supply member capable of supplying toner to the toner carrier 3 may be used, or the toner carried on the toner carrier 3. Alternatively, the charge injection member 6 for injecting electric charges may be provided.
Here, in the former dual-use mode, the charge injection member 6 needs to be a member that realizes a toner supply function in addition to the charge injection function.
On the other hand, the latter mode is a mode in which the charge injection member 6 is provided separately from the toner supply member, and only the functionality for charge injection can be pursued, which is preferable in securing the chargeability of the toner.

  Further, as a charge injection method of the charge injection means 5, there is a method of injecting charges while rubbing the conductive toner 2 between the charge injection member 6 and the toner carrier 3 (sliding type charge injection method). preferable. In this method, the contact probability between the conductive toner 2 and the charge injection member 6 can be increased and the contact resistance of the conductive toner 2 can be reduced. It is possible to inject charges efficiently into the toner.

Further, in the charge injection means 5 adopting the rubbing type charge injection method, it is possible to inject charges with the apparent resistance of the conductive toner 2 lowered, and the charge injection electric field is correspondingly reduced. Even if it is set to a certain level, the charging performance can be kept good.
For this reason, it is possible to inject the electric charge into the conductive toner 2 without necessarily setting the electric charge injection electric field to be larger than the developing electric field.
Therefore, the conductive toner 2 can realize a behavior of changing to a high resistance in the development electric field application region and changing to a low resistance in the charge injection electric field application region. That is, as shown in FIG. 2A, the conductive toner 2 includes a variable resistance portion 9 that changes to high resistance in the development electric field application region and changes to low resistance in the charge injection electric field application region. It shows behavior.
In this type of frictional charge injection method, it is important to sandwich the conductive toner 2 between the charge injection member 6 and the toner carrier 3 in a single layer state. Charging is possible and generation of reverse polarity toner can be effectively prevented.

However, since the conductive toner 2 exhibits a behavior in which the resistance changes depending on the magnitude of the electric field applied to the toner, the conductive toner 2 is made to have a lower resistance in the charge injection field action region than in the development field action region. For this purpose, it is preferable to apply a charge injection electric field larger than the development electric field.
Thus, in the charge injection means 5 that satisfies the relationship of charge injection electric field> development electric field, it is necessary to switch the electric resistance of the conductive toner 2 as follows.
That is, switching from a high resistance to a low resistance (resistance change) may be performed with an electric field larger than the developing electric field formed by the image portion potential of the electrostatic latent image Z and the developing bias potential and smaller than the charge injection electric field. .

In this embodiment, the conductive toner 2 preferably has a volume resistivity of 10 ¹⁰ Ω · cm or less in the charge injection electric field and 10 ¹¹ Ω · cm or more in the development electric field. This is because charges are easily injected when the charge injection electric field is 10 ¹⁰ Ω · cm or less, whereas charges are easily held when the development electric field is 10 ¹¹ Ω · cm or more.

Further, as a preferable aspect of the resistance change of the conductive toner 2, for example, from a high resistance with an electric field that is larger than the cleaning electric field formed by the background portion potential and the developing bias potential of the electrostatic latent image Z and smaller than the charge injection electric field. Examples include switching to low resistance (resistance change).
According to this aspect, since the conductive toner 2 is switched from a high resistance to a low resistance in an intermediate electric field between the cleaning electric field and the charge injection electric field, the conductive toner 2 is kept at a high resistance in the cleaning electric field application region. As a result, a charge of reverse polarity is not induced in the conductive toner 2 at the tip on the toner carrier 3.
For this reason, a so-called fog phenomenon in which a reverse polarity charge is induced in the conductive toner 2 on the toner carrier 3 and adheres to the background portion of the electrostatic latent image is effectively suppressed.
Furthermore, as a preferable aspect of the resistance change of the conductive toner 2, there is an aspect in which switching is performed from high resistance to low resistance with an electric field larger than the transfer electric field formed at the time of transfer and smaller than the charge injection electric field.
According to this aspect, since the conductive toner 2 switches from high resistance to low resistance in the intermediate electric field between the transfer electric field and the charge injection electric field, the conductive toner 2 is kept at high resistance in the transfer electric field application region. Therefore, during transfer, there is no movement of electric charge between the conductive toner 2 and the recording paper. For example, the electric charge of the conductive toner 2 is held even with high water content, and the transfer is good. Transfer performance can be obtained.

Further, as a typical aspect of the rubbing type charge injection method, there is one in which the charge injection means 5 gives a peripheral speed difference between the charge injection member 6 and the toner carrier 3.
More specifically, the charge injection means 5 has a rotatable charge injection member 6, and the charge injection member 6 is rotated with a peripheral speed difference from the toner carrier 3. It is done. In this aspect, the rotation direction of the charge injection member 6 is arbitrary, but considering the chargeability of the toner, the peripheral speed difference between the charge injection member 6 and the toner carrier 3 may be 1.5 times or more. preferable.
Further, as a preferable aspect of the charge injection member 6 also serving as the toner supply member, any member may be used as long as it rotates in the same direction and with a peripheral speed difference at a portion facing the toner carrier 3. At this time, charging is possible in the method in which the rotation direction of the charge injection member 6 is the same direction (With method), but charge injection is performed in the method in which the rotation direction of the charge injection member 6 is reverse (Against method). Since the toner is transferred to the toner carrier 3 before the conductive toner 2 is sandwiched between the member 6 and the toner carrier 3, there is a concern that it is difficult to be charged.

  Further, as another specific mode for providing the peripheral speed difference, the charge injection member 6 is fixedly disposed so as to face the toner carrier 3, and the peripheral speed difference is provided between the toner carrier 3 and the toner carrier 3. The embodiment which was made is mentioned. The charge injection member 6 of this embodiment is preferably a blade-like member.

Further, the toner carrier 3 preferably has a high resistance layer that covers the surface and can suppress charge transfer with the conductive toner 2.
As described above, if the toner carrier 3 is provided with the high resistance layer, it is possible to make it difficult to move the electric charge between the conductive toner 2 and the toner carrier 3, and accordingly, the reverse polarity. There is an advantage that toner is hardly generated.
In this respect, if the surface layer of the toner carrier 3 has a low resistance, the conductive toner 2 and the toner carrier 3 are polarized (charge exchange) during the charge injection operation in the charge injection electric field, and the conductive toner 2 There is a concern that reverse polarity charge is induced and reverse polarity toner is easily generated.

Here, as a preferable aspect of the high resistance layer, any layer may be used as long as it has a discharge time constant such that charge exchange is not performed between the toner carrier 3 and the conductive toner 2 in the electric charge injection electric field region. . In this case, since the transit time of the toner carrier 3 with respect to the electric charge injection electric field region is several tens of milliseconds, if the discharge time constant of the high resistance layer of the toner carrier 3 is obtained for 100 milliseconds or more, the charge between the two is It is estimated that the exchange will be difficult.
And in order to embody such behavior, it is preferable that the high resistivity layer has a volume resistivity of 10 ¹¹ Ω · cm or more in the charge injection field action region.

Supplementing this point, generally, the functions required of the toner carrier 3 include low potential, self-discharge, overcurrent control, and toner charging control. The low potential property means that the charge potential of a general image carrier 1 is limited to a predetermined voltage (for example, 500 V to 600 V), and therefore, the electric capacity of the toner carrier 3 is sufficient to obtain a sufficient development electric field. It is necessary to reduce the typical voltage loss. For this purpose, the higher the resistance layer of the toner carrier 3 is, the better, but it is set to several tens of μm or less in consideration of pinholes and the like. The self-discharge property means setting a resistance so that charges are not accumulated on the toner carrier 3, and in the conventional one-component development method, the toner carrier 3 is rotated several times or less for several hundred milliseconds. The volume resistivity is set to be less than about 10 ¹¹ Ω · cm so that the discharge time constant can be obtained. In addition, overcurrent control requires, for example, a resistance for preventing overcurrent when the charge injection member 6 and the toner carrier 3 are placed in contact with each other and a charge injection electric field is applied between them. From this viewpoint, there is no practical problem if it is 10 ⁹ Ω · cm or more.

Therefore, if it is set to 10 ⁹ Ω · cm to 10 ¹¹ Ω · cm, it is possible to satisfy the self-discharge property and the overcurrent control, but the toner charge controllability (charge injection property) is poor at this resistance value. Therefore, reverse polarity toner is likely to be generated.
Therefore, in order to satisfy other requirements excluding self-discharge, it is preferable to set the volume resistivity of the high resistance layer to 10 ¹¹ Ω · cm or more. By the way, in this embodiment, the toner carrier 3 includes a high resistance layer on the surface, but there is a concern that the self-discharge property may be insufficient. In this state, in order to satisfy the self-discharge property, for example, it is preferable to dispose, as an auxiliary static elimination mechanism, a static elimination member capable of eliminating the surface potential of the toner carrier 3 on the toner carrier 3.

The present invention is also directed to an image forming apparatus incorporating a developing device.
In this case, the image forming apparatus according to the present invention only needs to include the image carrier 1 that carries the electrostatic latent image Z and the developing device that is disposed to face the image carrier 1.

Next, the operation of the developing device according to the present invention will be described.
As shown in FIG. 2B, the conductive toner 2 causes a charge injection electric field to act between the charge injection member 6 of the charge injection means 5 and the toner carrier 3, and the charge injection electric field is charged in this charge injection electric field application region. It is injected and moves to the toner carrier 3 side.
At this time, as shown in FIGS. 1B and 2A, for example, the conductive toner 2 is sandwiched between the charge injection member 6 and the toner carrier 3 and is injected while being rubbed. In the electric charge injection field action region, the resistance variable portion 9 of the conductive toner 2 changes to a low resistance, and the electric charge is easily injected into the conductive toner 2.
Thereafter, as shown in FIG. 2B, the conductive toner 2 carried on the toner carrier 3 is transported to the development region between the image carrier 1 and the toner carrier 3 to develop the developing electric field action. It enters the area and moves to the image carrier 1 to make the electrostatic latent image Z on the image carrier 1 visible.
At this time, for example, the condition in which the resistance of the conductive toner 2 is higher in the development electric field application region than the charge injection electric field application region (for example, the relationship of charge injection electric field> development electric field is satisfied, or the conductive toner 2 is not rubbed. If the developing electric field is applied in the state, the conductive toner 2 has a resistance variable portion 9 of the conductive toner 2 in the developing electric field application region as shown in FIG. Since the resistance is changed to high resistance, the conductive toner 2 keeps the state of holding the charge, and the charge is not transferred between the conductive toners 2.

  According to the developing device of the present invention, by appropriately selecting the conditions of the electric charge injection field application region and the development electric field application region, when injecting electric charge into the conductive toner, the conductive toner is changed to a low resistance, It is possible to easily inject charges into the conductive toner, and to change the conductive toner to a high resistance when developing, thereby improving the charge retention of the conductive toner. Therefore, according to the present invention, the charge injection property for the conductive toner can be stabilized, and accordingly, the charge injection property for the conductive toner and the injected charge retention property can be easily made compatible. Thus, it is possible to effectively avoid the situation where unnecessary charge injection is performed in the developing electric field action region while maintaining good charge injection property to the conductive toner.

In addition, according to the present invention, the resistance of the conductive toner can be easily reduced in the electric charge injection field application region, and otherwise the conductive toner can be kept at a high resistance. For this reason, if the toner is moved in a low electric field without rubbing the conductive toner in the transfer electric field action region, for example, it becomes possible to increase the resistance of the conductive toner. The charge retention of the conductive toner in can be kept good.
Therefore, it is possible to effectively prevent the electric charge held in the conductive toner from moving between the moisture-absorbing recording paper and the toner, and the electrostatic attraction force to the toner can be maintained.
Therefore, it is possible to transfer a toner image onto a highly water-containing paper or the like, and it is also possible to form a color image by overlaying color toners, so that good transfer performance for conductive toner can be easily realized. it can.
As described above, according to the developing device of the present invention, it is possible to effectively prevent fogging and toner cloud by improving electrostatic transferability and color suitability, which are disadvantages when using conventional conductive toner. In addition, it is possible to provide a simple and versatile developing device that is not easily affected by environmental changes and deterioration over time.

In particular, in the present invention, the charge injection electric field forming means can adjust the charge injection electric field according to the change in the use condition of the apparatus. Thus, it is possible to effectively avoid poor charge injection with respect to the conductive toner.
At this time, since the charge injection electric field forming means can easily adjust the charge injection electric field based on detection information from a sensor capable of detecting, for example, a change in the use condition of the device, the device configuration is unnecessarily complicated. There is no.

In addition, since appropriate charge injection can be performed on the conductive toner, low-charge toner and reverse polarity toner are less likely to be generated in the development electric field action region, and fog and toner cloud are reduced accordingly. It can be effectively prevented and the development performance for the conductive toner can be kept good.
Furthermore, according to the image forming apparatus using such a developing device, it is possible to maintain a good developing performance with respect to the conductive toner, and it is possible to easily realize a good transfer performance with respect to the conductive toner. Thus, good image forming performance using conductive toner can be realized easily and reliably.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 3 shows Embodiment 1 of an image forming apparatus including a developing device to which the present invention is applied.
In FIG. 1, the image forming apparatus according to the present embodiment is a so-called tandem type, and an image reading unit 18 for reading a document is disposed above the apparatus main body 17, while the apparatus main body 17 includes the image reading unit 18. An image forming engine 19 (specifically 19a to 19d) of four color components (in this embodiment, Y: yellow, M: magenta, C: cyan, K: black) is arranged in the horizontal direction, and below that The intermediate transfer belt 28 circulated and conveyed along the arrangement direction of the image forming engines 19 is disposed, and an image on the intermediate transfer belt 28 is recorded on the intermediate transfer belt 28 as a recording medium, for example, a recording paper 48. A secondary transfer device (secondary transfer roll in the present embodiment) 49 for transferring the recording paper 48 is disposed, and further, a paper feed cassette 47 for housing the recording paper 48 is disposed below the device main body 17. This paper feed The recording paper 48 from Tsu bets 47 is obtained so as to guide to the fixing unit 60 through the secondary transfer roll 49.

In the figure, the image forming apparatus according to the present embodiment has a photosensitive drum 20 as an image carrier that rotates in a predetermined direction, and the photosensitive drum 20 is charged around the photosensitive drum 20. A charging device 21, an exposure device 22 as a latent image writing device for forming an electrostatic latent image Z on the photosensitive drum 20, and a visible image of the electrostatic latent image formed on the photosensitive drum 20, for example. Developing device 30, a primary transfer device (primary transfer roll 24 in the present embodiment) that primarily transfers the toner image on the photosensitive drum 20 to the intermediate transfer belt 28, and residual toner on the photosensitive drum 20 is removed. The cleaning device 25 that performs this operation and the neutralizing roll 29 that neutralizes the surface potential on the photosensitive drum 20 are sequentially disposed.
On the other hand, the intermediate transfer belt 28 is stretched over a plurality of (four in this example) tension rolls 42 to 46, the tension roll 42 is a drive roll, and the tension roll 43 is a backup of the secondary transfer roll 49. The other tension rolls 44 to 46 function as rolls and function as driven rolls.

  Here, as shown in FIG. 4A, the developing device 30 has a developing housing 31 in which a developer G containing conductive toner 40 is accommodated, and this developing housing 31 faces the photosensitive drum 20. Then, a developing opening 32 is opened, and a developing roll (developing electrode) 33 is provided facing the developing opening 32, and a predetermined developing bias is applied to the developing roll 33, whereby a photosensitive drum is provided. A developing electric field is applied to the developing region between the developing roller 33 and the developing roller 33, and a charge injection roller (injecting electrode) 34 and a toner supply roller 35 are provided in the developing housing 31 so as to face the developing roller 33. Is.

Further, the developing device 30 is provided with an agitator 36 for agitating the developer G containing the conductive toner 40 on the back side of the toner supply roll 35 in the developing housing 31.
A developing bias V _B from a developing bias power source 37 is applied to the developing roll 33, and a charge injection bias V _D from a charge injection bias power source 38 is applied to the charge injecting roll 34.
On the other hand, a toner supply bias V _S from a toner supply bias power source 39 having a polarity opposite to that of the charge injection bias V _D is applied to the toner supply roll 35. As a result, a developing electric field acts between the electrostatic latent image Z of the photosensitive drum 20 and the developing roll 33, and a charge injecting electric field acts between the developing roll 33 and the charge injecting roll 34. A toner supply electric field acts between the toner supply roll 35.

In particular, in the present embodiment, in the developing roll 33, as shown in FIG. 4B, an elastic base layer 332 is provided around the metal shaft 331, and a high resistance is provided around the elastic base layer 332. The layer 333 is coated directly or through an intermediate layer.
As the metal shaft 331, a metal core made of a metal such as aluminum or stainless steel or a cylindrical body made of a blade metal in which the inside is hollowed out is used. In addition, when using the product made from aluminum, you may use what anodized the surface. Examples of the elastic base layer 332 include silicone rubber, ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber (SBR), polyurethane elastomer, and the like, and carbon black, graphite, titanium for imparting conductivity. Potassium acid, iron oxide, ionic conductive agent and the like are added. Furthermore, examples of the high resistance layer 333 include those obtained by adjusting resistance by imparting a conductive material such as carbon black, graphite, or potassium titanate to urethane resin, acrylic resin, polyamide resin, or the like. In addition, as the developing roll 33, there is also an aspect in which a high resistance layer is directly provided on a metal shaft.

As a method for manufacturing the developing roll 33, a metal shaft 331 is set in a hollow portion of a cylindrical mold, and a material for forming the elastic base layer 332 is formed in a gap between the cylindrical mold and the metal shaft 331. Is cast and then heated to crosslink. Furthermore, what coat | covers the high resistance layer 333 by the dipping method, the spray method, the roll coat method etc. on the outer periphery of this intermediate product, and performs drying and heat processing after coating is mentioned.
As described later, the high resistance layer 333 is appropriately selected within a range in which charge exchange is suppressed between the charge injection roll 34 and the developing roll 33 in the charge injection electric field action region. The rate is set to 10 ¹¹ Ω · cm or more.

  Further, in the present embodiment, the charge injection roll 34 is composed of an aluminum roll having a small and even irregular surface formed on the surface by, for example, sandblasting or chemical etching, and the rotation direction of the charge injection roll 34 However, in consideration of the charge injection characteristics, the charge injection roll 34 has the same direction and the circumferential speed difference (for example, the opposite side to the development roll 33). The conductive toner 40 is sandwiched between the charge injection roll 34 and the developing roll 33, and the charge is injected while being rubbed.

Instead of the charge injection roll 34, one end of a charge injection blade (not shown) is fixedly arranged facing the developing roll 33, and the tip of the charge injection blade is arranged in contact with the developing roll 33. Good. As the charge injection blade, a metal support plate with a conductive elastic body made of conductive rubber or resin is used.
In this embodiment, since there is a difference in peripheral speed between the fixed charge injection blade and the developing roll 33, the same effect as in the present embodiment is obtained.

  In the present embodiment, the toner supply roll 35 is composed of a conductive foam roll such as urethane rubber or silicone rubber. The charge injection roll 34 and the toner supply roll 35 are lighter than the developing roll 33. It is supported with contact or micro-gap.

Furthermore, the conductive toner 40 as the developer G used in the present embodiment will be described later.
Here, as the conductive toner 40 in the present embodiment, for example, as shown in FIG. 5A, a conductive toner base (conductive core) 401 made of a conductive material is provided. The periphery of the core 401 is covered with an insulating coating layer (for example, an insulating resin layer) 402, and an appropriate number of recesses 403 are provided in the insulating coating layer 402 so that a part of the conductive core 401 is exposed. Is used.
In the present embodiment, the conductive toner 40 can be produced by a polymerization method or various known encapsulation techniques. At this time, the conductive core 401 has a conductive agent such as conductive carbon black, magnetic powder, transparent conductive powder such as ITO / titanium oxide / tin oxide dispersed in polyester or styrene acrylic resin, polyester or styrene acrylic resin. It is produced by coating the particle surface made of resin with the conductive agent.
The conductive toner 40 having such an aspect tends to decrease in resistance when a high electric field is applied. The magnitude of the electric field that lowers the resistance depends mainly on the occupation ratio of the concave portion 403 of the conductive toner 40 or the thickness of the insulating coating layer 402.
With respect to this mechanism, since the conductive core 401 is covered with the insulating coating layer 402, the conductive core 401 does not directly contact the toner or the electrode member, and the insulating coating layer 402. As a result, it is presumed that, for example, when a high electric field is applied, conduction is caused by a tunnel effect or the like.

As another embodiment of the conductive toner 40, for example, as shown in FIG. 5B, the conductive core 401 is covered with an insulating or semiconductive coating layer 404, and the thickness of the coating layer 404 is determined. A mode in which the resistance of the conductive toner 40 can be adjusted by appropriately adjusting h can be appropriately selected.
At this time, the semiconductive coating layer 404 may itself be made of a semiconductive material. For example, a metal oxide such as titanium oxide or tin oxide or conductive carbon is added to the insulating resin. You may make it use the semiconductive resin made to contain a trace amount.

Here, as a preferable embodiment of the conductive toner 40, the surface of the conductive core 401 is covered with a coating layer 404 containing an amorphous polymer as a main component, in other words, the ratio of the amorphous polymer phase is 80% or more. The thing which was done is mentioned.
In this embodiment, as the conductive core 401, for example, a conductive fine particle is attached to the vicinity of the outer surface of an insulating toner base (insulating core) made of a normal insulating toner, or the conductive core 401 has a conductive property inside the insulating core. It is possible to select an appropriate material such as one containing fine particles.

Next, the conductive toner manufacturing method may be selected as appropriate, such as a wet manufacturing method, a dry manufacturing method, or a combination of both.
First, the insulating core may be produced by any method such as a kneading pulverization method that is a dry production method, an emulsion aggregation method that is a wet production method, or a dissolution suspension method. From the viewpoint of freedom of control and shape control, the emulsion aggregation method is preferred. In the emulsion aggregation method, a resin fine particle dispersion is prepared by emulsion polymerization, and a colorant dispersion in which a colorant is dispersed in a solvent and, if necessary, a release agent dispersion are prepared, and then these are mixed to prepare a toner. In this method, agglomerated particles corresponding to the particle diameter are formed and heated to fuse and coalesce the agglomerated particles to produce a toner. This manufacturing process may be mixed and agglomerated in a lump, or the aggregation process may be performed in a plurality of stages, and after the formation of the first stage of the matrix aggregation, the particles added in the second stage of the agglomeration formation are the first stage. You may make it adhere to the surface of the parent | base aggregate particle.
At the time of toner preparation by such an emulsion aggregation method, conductive fine particles may be attached to the surface of the insulating core, and a coating layer may be formed.
In the above-described manufacturing method, conductive fine particles are adhered to the surface of the insulating core. However, the conductive fine particles may be mixed in the insulating core during toner preparation by the emulsion aggregation method. .

Further, as a dry production method of conductive toner, for example, after drying an insulating core produced by an emulsion aggregation method, conductive fine particles are adhered to the surface, and further, resin fine particles as a coating layer are formed into a film. The thing which was done is mentioned.
In this manufacturing method, for example, after mixing an insulating core and conductive fine particles in a stirring mixer, the mixture is stirred and mixed for a predetermined time, and the conductive fine particles are adhered to the insulating core to form a conductive core (stirring and mixing step ( I)).
After that, after mixing the conductive core and resin fine particles made of polyester, styrene acrylic, etc. into the stirring mixer, the mixture is stirred for a predetermined time to form a coating layer (insulating layer) around the conductive core. (Stirring and mixing step (II)).
Here, a specific example of the dry production method of the conductive toner will be described. For example, a predetermined amount (for example, 15 wt%) of IOT fine particles (manufactured by Sumitomo Metal Mining Co., Ltd.) is added to an insulating core having an average particle diameter of 6.5 μm, and a sample is obtained. The mixture is stirred and mixed for a predetermined time (for example, 12000 rpm, 30 seconds) by a mill (model: SK-M10 type, manufactured by Kyoritsu Riko Co., Ltd.), and ITO fine particles are adhered to the surface of the insulating core. Thereafter, a predetermined amount (eg, 10 wt%) of resin fine particles such as polyester is added to the insulating core (conductive core) to which the ITO fine particles are adhered, and the mixture is stirred and mixed in the sample mill for a predetermined time (eg, 12000 rpm, 30 minutes). ), And the like that form a predetermined insulating layer.
In the examples described later, the conductive toner prepared in the specific example of this dry manufacturing method was used.

  Further, each device other than the developing device 30 used in the present embodiment may be appropriately selected. For example, as the primary transfer device 24, as shown in FIG. 3, for example, a transfer roll (not shown) is arranged opposite to the photosensitive drum 20, and a transfer bias is applied to the transfer roll to A transfer electric field may be applied between the transfer roll and the toner image on the photosensitive drum 20 may be electrostatically transferred to the recording paper 48 as a recording medium.

In particular, in the image forming apparatus according to the present embodiment, the density sensor 26 is disposed in close proximity to the intermediate transfer belt 28 in the intermediate transfer belt 28 immediately after the position where the final color image forming engine 19d is disposed. ing.
The density sensor 26 is provided on the intermediate transfer belt 28 and detects the density of the toner patch of each color component. At this time, each color component toner patch forms a patch-like electrostatic latent image (latent image patch) on the photoconductive drum 20 of each image forming engine 19, and each developing device 30 applies the latent image patch to the toner. For example, the color components are arranged at predetermined pitch intervals for each color component.
Further, in the present embodiment, a potential sensor 23 is disposed around the photosensitive drum 20, and this potential sensor 23 can detect a latent image potential on the photosensitive drum 20.
In this case, the developing toner amount detected by the density sensor 26 mainly depends on the charge injection amount, but also depends on the latent image potential on the image carrier 1. Therefore, if the potential sensor 23 is provided so that the latent image potential on the photosensitive drum 20 is always kept within a certain range, the density sensor 26 can always detect the density of the toner patch under the same conditions. become.

Further, in the present embodiment, as shown in FIG. 3, the image forming apparatus includes a control device 41 that controls the charge injection bias power supply 38 (see FIG. 4), the charging device 20, the exposure device 22, and the like. Is provided.
The control device 41 is constituted by a microcomputer system including, for example, a CPU, a ROM, a RAM, and an I / O port, and an image forming program (for example, refresh mode image forming) necessary for realizing a series of image forming processes. (Including a processing program etc.) in the ROM in advance, input signals from the density sensor 26 and the potential sensor 23 are taken into the CPU, and the CPU executes the image forming processing program to generate a predetermined control signal. The control signals are sent to the charge injection bias power source 38, the charging device 20, the exposure device 22, and the like.

Next, the operation of the image forming apparatus according to the present embodiment will be described with reference to FIG.
When the image forming process is started, first, the surface of the photosensitive drum 20 is charged by the charging device 21, and the electrostatic latent image Z is written on the photosensitive drum 20 charged by the exposure device 22. Makes the electrostatic latent image Z visible.
Thereafter, the toner image on the photosensitive drum 20 is conveyed to a transfer site, and the primary transfer device 24 electrostatically transfers the toner image on the photosensitive drum 20 to the intermediate transfer belt 28 as a recording medium.
The residual toner on the photosensitive drum 20 is cleaned by the cleaning device 25.
Further, the toner image primarily transferred onto the intermediate transfer belt 28 is conveyed to a secondary transfer device (secondary transfer roll in the present embodiment) 49 as the intermediate transfer belt 28 rotates and is supplied. The recording paper 48 conveyed from the paper cassette 47 is conveyed to a contact area between the intermediate transfer belt 28 and the secondary transfer roll 49, and a voltage having a polarity opposite to that of the toner is applied to the secondary transfer roll 49. The toner image on the intermediate transfer belt 28 is electrostatically attracted to the recording paper 48. Thereafter, the recording paper 48 to which the toner image is transferred is fixed by the fixing device 60, and the toner image is fixed to the recording paper 48.

The basic operation of the developing device 30 in such an image forming process will be described as follows.
That is, as shown in FIGS. 4 and 7, in the developing device 30, the conductive toner 40 is stirred by the agitator 36 in the developing housing 31, and the stirred conductive toner 40 is supplied to the surface of the toner supply roll 35. The Next, the toner supplied to the toner supply roll 35 is conveyed to a position where the developing roll 33 and the toner supply roll 35 face each other as the toner supply roll 35 rotates.
At this time, since the toner supply roll 35 and the developing roll 33 are rotated in the opposite directions at the opposed portions, the conductive toner 40 is not charged and rubbed between both rolls, that is, is almost charged. Without being transferred to the developing roll 33.

Then, the conductive toner 40 carried on the developing roll 33 is conveyed to a position facing the charge injection roll 34. At this time, between the developing roll 33 and the charge injection roll 34, the developing bias V _B of the developing bias power supply 37 connected to the developing roll 33 and the charge injection bias power supply 38 connected to the charge injection roll 34. The charge injection electric field formed by the difference from the charge injection bias V _D is acting.
In FIG. 7, reference numeral 40a denotes a conductive toner before charge injection, and 40b denotes a conductive toner after charge injection.
In this charge injection working region, the conductive toner 40 is sandwiched between the developing roll 33 and the charge injection roll 34 in a single layer state, and is sandwiched between the developing roll 33 and the charge injection roll 34 and rubbed. While being charged, it is injected.

  In such a state, the contact probability between the conductive toner 40 and the charge injection roll 34 is increased, and the contact resistance of the conductive toner 40 can be reduced. The upper resistance is reduced, and the conductive toner 40 is charged with a low resistance. For this reason, even if the electric charge injection field is relatively low, the electric charge is efficiently injected into the conductive toner 40.

Here, the control device 41 executes a toner patch density detection cycle, controls the charge injection bias power supply 38 based on the detection information from the density sensor 26, and makes the charge injection electric field adjustable.
In this case, the density sensor 26 detects the density of the toner patch transferred to the intermediate transfer belt 28, the potential sensor 23 detects the latent image patch potential on the photosensitive drum 20, and sends the detected information to the control device 41. Is done.
Here, as shown in FIG. 6, the control device 41 checks whether or not the latent image patch potential on the photosensitive drum 20 is at a constant level based on the detection information from the potential sensor 23, and at a constant level. If there is, the density detection operation by the density sensor 26 is executed. On the other hand, if it is not a certain level, the charging amount of the charging device 21 and / or the exposure amount of the exposure device 22 is controlled, and the latent image patch on the photosensitive drum 20 is controlled. The potential is adjusted to a predetermined level, and the latent image patch potential by the potential sensor 23 is checked again.
In this way, the density sensor 26 can detect the density of the toner patch on the intermediate transfer belt 20 under the condition that the latent image patch potential on the photosensitive drum 20 is always maintained at a predetermined level. Based on the information detected by the density sensor 26, the control device 41 calculates a variable amount of the charge injection amount and sends a predetermined control signal to the charge injection bias power source 38. A charge injection electric field corresponding to a change in usage conditions (change in charge injection amount) of the developing device 30 can be applied to the area 33.

Then, the conductive toner 40 into which the charge has been injected is conveyed on the developing roll 33 as it is, and proceeds to a portion where the developing roll 33 and the photosensitive drum 20 face each other. Here, a developing electric field formed by the difference between the electrostatic latent image Z on the photosensitive drum 20 and the developing bias of the developing bias power source 37 connected to the developing roll 33 is applied to the conductive toner 40. Become.
Further, since the surface charge of the electrostatic latent image portion written on the photosensitive drum 20 by the exposure device 22 (see FIG. 3) is neutralized, the conductive toner 40 is exposed only to this portion by the developing electric field. It moves to the body drum 20 and visualizes the electrostatic latent image Z.
In this embodiment, since the development electric field is lower than the charge injection electric field, the charge injected into the conductive toner 40 by the charge injection electric field does not escape by the development electric field, and good development can be achieved. Done.

Further, the conductive toner 40 not transferred to the photosensitive drum 20 and remaining on the developing roll 33 is carried to a position facing the toner supply roll 35 by the rotation of the developing roll 33.
Here, in particular, in the present embodiment, a toner supply electric field having a polarity opposite to the charge injection electric field acts on a portion where the toner supply roll 35 and the developing roll 33 face each other. There is an electrostatic force at work. Since the electrostatic force acts to collect the conductive toner 40 on the developing roll 33 toward the toner supply roll 35, the toner 40 on the developing roll 33 that has been transported to the position facing the toner supply roll 35 is peeled off. To be recovered.
Further, the toner supply electric field is an electric field having a polarity opposite to that of the charge injection electric field, and acts to weaken the charging potential of the developing roll 33 charged by the charge injection electric field. Accordingly, the charging history of the developing roll 33 is eliminated accordingly.

In this embodiment, the toner image visualized on the photosensitive drum 20 is, as shown in FIG. 3, the intermediate transfer belt 28 at a position where the photosensitive drum 20 and the primary transfer roll 24 face each other. And is further transferred onto the recording paper at a position where the secondary transfer roll 49 and the backup roll 43 face each other.
Further, there is no movement of charge that causes fogging in the cleaning electric field, and no movement of charge occurs between the recording paper 48 and the toner. Therefore, in the electrostatic transfer method, the recording paper 48 that has absorbed moisture is used. The toner image can be transferred to the toner image, and a color image can be formed by overlapping the color toner.
Furthermore, since the conductive toner does not contain a large amount of conductive filler (for example, carbon black), the toner melts at a low temperature, and good image quality by fixing can be realized.

In the present embodiment, the configuration of the tandem type image forming apparatus having a plurality of photosensitive drums has been described as an example. However, the present invention is not limited to this. For example, a plurality of photosensitive drums are provided for one photosensitive drum. This type of development device or rotary type development device is provided to form a color image by forming a toner image of one color every cycle and sequentially transferring it to an intermediate transfer member, and transferring multiple color component toner images in multiple cycles. The same applies to the embodiment. Further, the present invention can be similarly applied to a paper conveyance transfer system in which a paper is held on a recording paper conveyance body, conveyed and transferred.
In the present embodiment, the color machine has been described, but it is needless to say that the present invention can be similarly applied to a monochrome-only machine.
Further, although the developing device of the first embodiment is disposed as the developing device 30 in the present embodiment, it is obvious that the same effect can be obtained even if the developing device of the second embodiment is used.

In the present embodiment, as the charge injection method by the charge injection roll 34, the rubbing type charge injection method is adopted, but this method reduces the generation rate of reverse polarity toner (WST: Wrong Sign Toner). It is preferable in terms of lowering.
Referring to FIG. 8 to FIG. 12, when a conductive toner is inserted between the developing electrode and the injection electrode and a charge injection electric field is applied, for example, as shown in FIG. The generation rate of the reverse polarity toner (WST) changes according to the magnitude of the electric field applied to the toner particle layer.
According to FIG. 8, when the electric charge injection field is a low electric field, as shown in FIG. 9, the toner with poor charging efficiency and which cannot be charged adheres to the charged toner or is non-electrostatic with the developing electrode. It moves to the developing electrode side due to the adhesive force. Therefore, it can be understood that the higher the charge injection field, the lower the WST due to the increase in charging efficiency.
On the other hand, when the charge injection electric field is a high electric field, as shown in FIG. 10, the charged toner moves to the developing electrode, and when a multilayer is formed, the toner exchanges with each other and polarizes, and the upper layer toner becomes WST. Turn into. Therefore, WST due to polarization tends to increase as the charge injection electric field is increased.

Therefore, as a solution for reducing the incidence of WST, for example, as shown in FIG. 11A, a high injection efficiency is realized with a low electric field, or as shown in FIG. It is conceivable to prevent it from moving to the developing electrode. Further, as shown in FIG. 12A, it should not be polarized between the toner layers even in a high electric field, or as shown in FIGS. 12B and 12C. In this way, it is conceivable that the toner is not multilayered, in other words, not to overlap.
The above-described charge injection method is devised based on such a policy, and the conductive toner 40 is provided between the developing roll (corresponding to the developing electrode) 33 and the charge injecting roll (corresponding to the injection electrode) 34. In the method of injecting charges while sandwiching and rubbing, it is possible to increase the contact probability with the charge injection roll 34 and reduce the contact resistance, so that the toner is in a single layer state with a low charge injection electric field. This makes it possible to inject charges efficiently. Further, since a shearing force is applied between the toner layers, the toners can be prevented from overlapping in a polarized state, and the generation of WST can be prevented even in a high electric field.

Embodiment 2
FIG. 13 shows a developing device according to the present embodiment, and FIGS. 14A, 14B, 15A, and 15B are schematic views showing the main part of FIG.
In the figure, the developing device 30 is configured in substantially the same manner as the developing device in the first embodiment, but unlike the first embodiment, the charge injection roll 43 also serves as a toner supply roll.
In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and the detailed description is abbreviate | omitted.

In the present embodiment, the developing device 30 is provided with a charge injection roll 43 at a position facing the developing roll 33. A developing bias V _B from a developing bias power source 37 is applied to the developing roll 33, while a charge injecting bias V _D from a charge injecting bias power source 38 is set to the charge injecting roll 43 (in this example, set larger than the developing bias). Is applied. Further, a layer forming blade 42 for forming a thin layer of conductive toner is disposed in contact with the surface of the charge injection roll 43 in the development housing 31, and on the back side of the charge injection roll 43 in the development housing 31, An agitator 36 for agitating the developer G containing the conductive toner 40 is provided.
Further, in this aspect, the charge injection roll 43 is rotated with a peripheral speed difference between the charge injection roll 43 and the developing roll 33 as in the first embodiment.
In this embodiment, the layer forming blade 42 is formed by bonding silicone rubber or EPDM to a stainless steel leaf spring having a thickness of about 0.03 to 0.3 mm with an adhesive or the like. One end of the layer forming blade 42 is in light contact with the surface of the charge injection roll 43, and the other end is supported by a part of the developing housing 31.
In the present embodiment, the concentration sensor 26 and the potential sensor 23 are disposed in substantially the same manner as in the first embodiment, and the control device 41 injects charges based on the detection information of the concentration sensor 26 and the potential sensor 23. The bias power supply 38 is controlled.

Next, the operation of the developing device 30 according to this embodiment will be described with reference to FIG.
In the developing device 30, the conductive toner 40 is stirred by the agitator 36 in the developing housing 31, and the stirred conductive toner 40 passes between the charge injection roll 43 and the layer forming blade 42 to inject the charge. A uniform toner layer is formed on the surface of the roll 43.
Further, the toner layer is conveyed to a position where the developing roll 33 and the charge injection roll 43 face each other by the rotation of the charge injection roll 43.
In this case, developing between the roll 33 and the charge injection roll 43, the developing and developing bias V _B of the developing bias power supply 37 connected to the roll 33, a charge injection bias power source is connected to the charge injection roll 43 38 The charge injection electric field formed by the difference from the charge injection bias V _D due to the above acts, and the conductive toner 40 is sandwiched between the developing roll 33 and the charge injection roll 43, and the charge is injected while being rubbed.

Further, in a mode in which the conductive toner 40 is sandwiched between the developing roll 33 and the charge injection roll 43 and is charged while being rubbed, the contact probability between the conductive toner 40 and the charge injection roll 43 is increased. In addition, the contact resistance of the conductive toner 40 can be reduced, and the apparent resistance of the conductive toner 40 is reduced accordingly, and the conductive toner 40 is injected with a low resistance. For this reason, even if the electric charge injection field is relatively low, the electric charge is efficiently injected into the conductive toner 40.
In this respect, for example, as shown in FIG. 14B, in a mode in which the charge injection roll 34 is rotated in the reverse direction at the portion facing the developing roll 33, the conductive toner 40 is placed on the charge injection roll 43. After the layer thickness is regulated by the layer forming blade 42, the supplied conductive toner 40 is supplied to the developing roll 33 without passing through the nip portion between the developing roll 33 and the charge injection roll 43. Since it is carried on the developing roll 33, there is a concern that charge injection into the conductive toner 40 is insufficient.

Thereafter, the conductive toner 40 into which the charge has been injected on the developing roll 33 is transported on the developing roll 33 as it is, and proceeds to a portion where the developing roll 33 and the photosensitive drum 20 face each other.
Here, a developing electric field formed by the difference between the electrostatic latent image Z on the photosensitive drum 20 and the developing bias V _B of the developing bias power source 37 connected to the developing roll 33 is applied to the conductive toner 40. It will be.
For this reason, the conductive toner 40 moves to the electrostatic latent image Z on the photosensitive drum 20, and the electrostatic latent image Z is visualized. In this embodiment, since the developing electric field is lower than the charge injection electric field, the charge injected into the conductive toner 40 by the charge injection electric field does not escape by the developing electric field, and good development is achieved. Is done.
In such a developing operation process, the charge injection process to the charge injection roll 43 is performed by controlling the charge injection bias power source 38 based on the detection information from the density sensor 26 and the potential sensor 23 and changing the use condition of the apparatus ( In this example, the electric charge injection electric field is adjusted according to the toner patch density change).

In the present embodiment, instead of the charge injection roll 43, one end of a charge injection blade (not shown) is fixedly arranged facing the developing roll 33, and the tip of the charge injection blade is attached to the developing roll 33. You may make it arrange in contact. As the charge injection blade, a metal support plate with a conductive elastic body made of conductive rubber or resin is used.
In this embodiment, since there is a difference in peripheral speed between the fixed charge injection blade and the developing roll 33, the same effect as in the present embodiment is obtained.

In the present embodiment, the charge injection roll 34 is disposed as shown in FIG. 15A, but is not limited to this, and the rotation direction of the photosensitive drum 20 is reverse. In one embodiment (in this embodiment, the position of the exposure device 22 is limited to the lower side of the photosensitive drum 20), for example, as shown in FIG. 15A, a developing roll 33 and a charge injection roll 34 are arranged. In this embodiment, since the conductive toner 40 can be supplied along the direction of gravity from the charge injection roll 34 to the developing roll 33, the supply of toner to the developing roll 33 can be improved. Is possible.
Furthermore, in this aspect, as shown in FIG. 15B, if a refreshing roll 50 for discharging is disposed on the upstream side of the position of the charge injection roll 34 in the developing roll 33, for example, the developing roll 33 Even if a high resistance layer having a volume resistivity of 10 ¹¹ Ω · cm or more is provided on the surface, for example, in the electric charge injection field effect region, the development roll 33 is always refreshed without unnecessarily accumulating charges. The charge injection operation by the charge injection roll 34 is efficiently performed on the conductive toner 40 on the developing roll 33.
In this embodiment, the refresh roll 50 is disposed in contact with the developing roll 33 at the same potential.

Embodiment 3
FIG. 16 shows an image forming apparatus according to a third embodiment to which the developing device according to the present invention is applied.
In the figure, the image forming apparatus is configured in substantially the same manner as the image forming apparatus in the first embodiment, but is not provided with the potential sensor 23 and the density sensor 26 and is provided with an environment sensor 27. Yes.
In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and the detailed description is abbreviate | omitted.

  The environment sensor 27 is capable of detecting the use condition environment. In this example, the environment sensor 27 is a temperature sensor and a humidity sensor that detect temperature and humidity. The detection information is connected to the control device 41 so as to be transmitted. Then, the control device 41 executes a charge injection amount setting process shown in FIG. 17 based on detection information from the environment sensor, and sends a predetermined control signal to the charge injection bias power source 38.

Next, the operation of the image forming apparatus according to the present embodiment will be described.
In a series of operations of the image forming apparatus, the environment sensor 27 detects the temperature and humidity in the image forming apparatus and sends the detection information to the control device 41.
At this time, as shown in FIG. 17, the control device 41 determines whether the information detected by the environmental sensor 27 applies to the high temperature and high humidity A, the normal temperature and normal humidity B, or the low temperature and low humidity C, and from the determination result. A charge injection bias change amount corresponding to an appropriate charge injection amount is determined.
Then, the control device 41 sends a control signal based on the determined charge injection bias change amount, controls the charge injection bias power source 38 based on the determined information, and performs an appropriate charge injection process according to the use condition environment. .
In the present embodiment, only the environmental sensor 27 is used as the charge injection adjustment sensor. However, if the concentration sensor 26 and the potential sensor 23 according to the first embodiment are additionally provided, more appropriate. It is also possible to apply a charge injection electric field.

Embodiment 4
FIG. 18 shows Embodiment 4 in which the present invention is applied to an image forming apparatus that does not use the electrostatic transfer method.
In the image forming apparatus according to the present embodiment, around the photosensitive drum 90, a charging device 91 that charges the photosensitive drum 90, and each color component (yellow, magenta in this example) on the charged photosensitive drum 90. , Cyan, black) an exposure device 92 for writing an electrostatic latent image, a developing device 93 for visualizing each color component latent image formed on the photosensitive drum 90 with each color component toner, and a photosensitive drum 90. An adhesive intermediate transfer roll 94 for transferring the upper toner image and a cleaning device 95 for cleaning residual toner on the photosensitive drum 90 are provided. In the developing device 93, a developing roll 102, a charge injection roll 103, and a toner supply roll 104 are disposed.
A secondary transfer roll 96 having a heating source is disposed below the adhesive intermediate transfer roll 94.
Reference numeral 98 denotes a recording paper supply device for sending out the recording paper 97, and 99 denotes a conveying belt for conveying the fixed recording paper 97.

In the present embodiment, since the adhesive intermediate transfer roll 94 is made of an elastic member such as silicone rubber, for example, between the photosensitive drum 90 and the adhesive intermediate transfer roll 94 and the secondary transfer roll 96. The adhesive intermediate transfer roll 94 is in elastic contact with a predetermined nip region.
Further, the developing device 93 and the conductive toner in the present embodiment can be the same as those used in the first embodiment or the second embodiment, and other devices are also selected as appropriate. There is no problem.

In particular, in the present embodiment, an environmental sensor 100 is provided in the image forming apparatus. This environmental sensor 100 is a temperature sensor and a humidity sensor that can detect temperature and humidity, and this detection information is connected to the control device 101 so that it can be sent out.
Further, the control device 101 controls the charge injection bias power supply 38 based on the detection information from the environment sensor 100, and controls the charge injection electric field in accordance with a change in use conditions of the device (change in use environment in this example). is there.

Next, the operation of the image forming apparatus according to the present embodiment will be described.
In the present embodiment, the electrostatic latent image carried on the photosensitive drum 90 is overlaid with toner images of different color components for each rotation of the photosensitive drum 90 by the developing device 93. When the superimposed toner images are pressed onto the adhesive intermediate transfer roll 94, the toner images are collectively transferred onto the adhesive intermediate transfer roll 94 by the adhesive force of the adhesive intermediate transfer roll 94.
Thereafter, the toner image transferred onto the adhesive intermediate transfer roll 94 is heated by the secondary transfer roll 96, the releasability of the adhesive intermediate transfer roll 94 is improved, and the toner image is also heated. Viscose. As a result, the toner image is retransferred to the recording paper 97 between the adhesive intermediate transfer roll 94 and the secondary transfer roll 96, and fixing is completed at the same time.

  In such an image forming process, the conductive toner used in the present embodiment has the same characteristics as those in the first embodiment. In this state, the electrostatic latent image on the photosensitive drum 90 can be visualized and the toner images can be superimposed on the photosensitive drum 90.

In such an image forming process, the environment sensor 27 detects the temperature and humidity in the image forming apparatus, and sends this detection information to the control device 41.
At this time, as shown in FIG. 17, the control device 41 determines whether the information detected by the environmental sensor 27 applies to high temperature and high humidity, normal temperature and normal humidity, or low temperature and low humidity. In order to apply the charge injection electric field, the charge injection bias change amount is determined.
Then, the control device 41 can control the charge injection bias and cause an appropriate charge injection electric field to act.

  In the present embodiment, the sensor for adjusting the charge injection uses only the environmental sensor 27, but is not limited to this, and the concentration sensor 26 according to the first embodiment or the like The potential sensor 23 may be used separately or in combination.

A developing device model used in each of the following embodiments is shown in FIG. 19, and a transfer device model is shown in FIG.
<Developer model>
The developing device model shown in FIG. 19 is a model of the developing device 30 (see FIG. 4) according to the first embodiment.
4 and 19, reference numeral 121 denotes a charge injection plate (toner supply plate) corresponding to the charge injection roll 34, which is constituted by an aluminum plate, for example.
A charge injection power source 125 is connected to the charge injection plate 121, and a charge injection bias V1 is applied.
Reference numeral 122 denotes a toner carrying roll corresponding to the developing roll 33 of the developing device 30 and is constituted by an aluminum pipe whose surface is anodized, for example.
A developing bias power supply 126 is connected to the toner carrying roll 122, and a developing bias V2 is applied.
Further, reference numeral 123 denotes an image carrying plate corresponding to the photosensitive drum 20, which is composed of, for example, an aluminum plate having a 55 μm-thick PET film attached to the surface thereof, with a predetermined gap with respect to the toner carrying roll 122. They are arranged opposite to each other and move in a substantially horizontal direction.
An image carrying bias power source 127 is connected to the image carrying plate 123, and a predetermined image carrying bias V3 is applied.

In such a developing device model, about one layer of conductive toner 120 (corresponding to the conductive toner 40 used in Embodiment 1) is sprayed on the charge injection plate 121 and is slid to the right in FIG.
At this time, a charge injection electric field A is formed between the charge injection plate 121 and the toner carrying roll 122 by the charge injection bias V 1 applied to the charge injection plate 121 and the developing bias V 2 applied to the toner carrying roll 122. In addition, electric charges are injected into the conductive toner 120 on the charge injection plate 121 by the electric charge injection electric field A, and the conductive toner 120 moves to the toner carrying roll 122 by electrostatic attraction force.
Next, when the conductive toner 120 moved to the toner carrying roll 122 is conveyed to the development region by the rotation of the toner carrying roll 122, it is applied to the image carrying bias V 3 applied to the image carrying plate 123 and the toner carrying roll 122. The developing electric field B is formed by the developing bias V 2, and the conductive toner 120 moves to the image carrying plate 123 by the developing electric field B.

In such a developing operation process, in order to keep the developing performance of the developing device 30 favorable, the charge injection electric field A is higher than the development electric field B, and is higher than the intermediate electric field between the charge injection electric field A and the development electric field B. It was confirmed that the resistance of the conductive toner 120 is preferably switched from a high resistance to a low resistance in a high electric field.
This is supported by the examples described later.
In addition, in the case of a monochromatic image forming process that does not require the movement of a multilayer toner image, only toner adhesion to the background portion of the photosensitive drum 20 may be prevented.
At this time, due to the influence of the electric field (cleaning electric field) formed by the potential difference between the developing roll 33 and the background portion, a charge having a reverse polarity is induced in the toner at the tip on the developing roll 33, causing adhesion to the background portion. There is a possibility.
Therefore, in this case, as a characteristic of the conductive toner 120, the electric resistance may be switched from a high resistance to a low resistance when the electric field is larger than the cleaning electric field and less than or equal to the electric charge injection electric field A so as to satisfy a predetermined range of electric resistance. .
In general, since the cleaning electric field is smaller than the developing electric field B, the conductive toner (which has a switching characteristic from a high resistance to a low resistance at a high electric field higher than the intermediate electric field between the charge injection electric field A and the developing electric field B is provided. ) 120 can be used as it is.

<Transfer device model>
The transfer device model shown in FIG. 20 is a model of the primary transfer device 24 (see FIG. 3) used in the first embodiment.
3 and 20, reference numeral 131 denotes a charge injection plate (toner supply plate) corresponding to the charge injection roll 34, and is composed of, for example, an aluminum plate.
A charge injection power source 135 is connected to the charge injection plate 131, and a charge injection bias V4 is applied.
Reference numeral 132 denotes an image carrying roll corresponding to the photosensitive drum 20 and is constituted by an aluminum pipe having a 55 μm thick PET film attached to the surface thereof, for example.
An image carrying bias power source 136 is connected to the image carrying roll 132, and an image carrying bias V5 is applied.
Further, reference numeral 133 denotes a recording medium plate corresponding to an electrode member such as a transfer roll of the transfer device 24, and is constituted by an aluminum plate having a recording medium 134 (for example, corresponding to the recording paper 48 in FIG. 3) attached to the surface. Is done.
A transfer bias power source 137 is connected to the recording medium plate 133, and a transfer bias V6 is applied.

In such a transfer device model, about one layer of conductive toner 120 is spread on the toner supply plate 131 and is slid rightward in FIG.
At this time, due to the image carrying bias V5 applied to the image carrying roll 132 and the charge injection bias V4 applied to the charge carrying plate 131, a charge injection electric field A is formed between the charge injection plate 131 and the image carrying roll 132. The electric charge is injected into the conductive toner 120 on the image carrier roll 132 by this electric charge injection electric field A.
Next, when the conductive toner 120 moved to the image carrying roll 132 is conveyed to the transfer region by the rotation of the image carrying roll 132, the transfer bias V 6 applied to the recording medium plate 133 and the image carrying roll 132 are applied. A transfer electric field C is formed by the image bearing bias V 5, and the conductive toner 120 moves to the recording medium plate 133 by the transfer electric field C.

In such a transfer operation process, in order to keep the transfer performance of the primary transfer device 24 good, the charge injection electric field A is higher than the transfer electric field C, and more than the intermediate electric field between the charge injection electric field A and the transfer electric field C. It was confirmed that the resistance of the conductive toner 120 is preferably switched from a high resistance to a low resistance at a high electric field.
This is supported by the examples described later.

Example 1
FIG. 21 shows the volume of the conductive toner 120 when an electric field is applied to the conductive toner 120 corresponding to the conductive toner according to the first embodiment in the developing device model (see FIG. 4) according to the first embodiment. It is the result of having measured resistivity change.
As can be seen from the drawing, the conductive toner 120 rapidly decreases in resistance from a high resistance to a low resistance when a high electric field is applied.

Here, the relationship between the charge injection electric field A and the development electric field B and the electric resistance of the conductive toner 120 will be described.
In general, the electric field E applied to the conductive toner 120 is expressed as follows.
E = (V−VS) / εt (Dp + Dt + Dm + Dg)
Where V: potential of the counter electrode, VS: potential on the toner layer before movement, Dp to Dg: dielectric thickness of each layer forming the nip (Dp: dielectric thickness of the image carrier, Dt: dielectric thickness of the toner layer, Dm: toner carrier dielectric thickness, Dg: void layer dielectric thickness), εt: relative dielectric constant of toner.
Predicting from the above, under the above conditions, the electric field applied to the conductive toner 120 during charge injection is 7 × 10 ⁴ V / cm, and the electric field applied to the conductive toner 120 during development is 8 × 10 ³ V / cm. there were.
At this time, the volume resistivity of the conductive toner 120 is between 10 ¹⁶ Ω · cm and 10 ⁹ Ω · cm between 8 × 10 ³ V / cm and 7 × 10 ⁴ V / cm, as shown in FIG. It has changed to cm.

Since the transit time of the charge injection electric field A region and the development electric field B region is about 0.01 seconds, it is preferable that the time constant is 0.01 seconds or less in order to inject charges easily. The volume resistivity of the toner 120 may be 10 ¹⁰ Ω · cm or less.
Moreover, in order to hold the charged electric charge, it is necessary that no charge transfer or the like occurs within the time during which the developing electric field B is applied. The volume resistivity of the conductive toner 120 may be 10 ¹¹ Ω · cm or more.
The volume resistivity of the conductive toner 120 was calculated by filling the toner in a φ30 mm cell, applying a voltage to the upper and lower surfaces, and measuring the flowing current.

Example 2
FIG. 22 shows the amount of development toner (converted to the number of layers) with respect to the change in the image bearing bias of the image bearing bias power supply 127 in the developing device model according to the first embodiment (see FIG. 4). It is a result of comparative measurement between when the conductive toner 120 corresponding to the toner is used and when the conductive toner 120 that does not have the insulating coating layer 404 (see FIG. 5) according to the comparative example is used.
In this embodiment, the developing bias V2 is fixed to 0 V and the charge injection bias V1 is fixed to -150 V, and a series of image forming processes is repeated three times to perform multiple development on the image carrying plate 123. Here, a PET film having a thickness of 12 μm is wound around the surface of the toner carrying roll 122 and rotates at the same speed as the charge injection plate 121. On the surface of the image carrying plate 123, a film-like photosensitive member having a thickness of 25 μm was attached and moved at a speed half that of the toner carrying roll 122.

In this embodiment, when the voltage of the image carrier plate 123 (image carrier bias V3) is changed to −150 V, the amount of toner (number of layers) developed using the conductive toner 120 increases, while the conductivity according to the comparative example is increased. The amount of development toner using toner (conductive toner not having the insulating coating layer 404) is hardly increased.
As a result, when forming a color image, the conductive toner 120 can reproduce various colors by overlaying color toners of different color materials, but it is understood that the conductive toner according to the comparative example cannot cope with colorization. Is done.

Example 3
FIG. 23 shows the results of measurement of the relationship between the recording medium plate 133 voltage (transfer bias V6) and the transfer rate (%) in the transfer device model (see FIG. 20) according to the first embodiment.
In this example, as the recording medium 134 attached to the surface of the recording medium plate 133, insulating paper or semiconductive paper (5 × 10 ⁸ Ω · cm, high water content paper state) was used.
Then, the image carrying roll 132 voltage (image carrying bias V5) is fixed to 0 V, the charge injection plate 131 voltage (charge injection bias V4) is fixed to -400 V, and the insulating coating layer 404 (FIG. 5) is applied to the semiconductive paper. In the comparative example using the conductive toner not coated with the insulation in the reference), it was also measured. At this time, a 55 μm thick PET film is wound around the surface of the image carrying roll 132 and rotates at the same speed as the charge injection plate 131.
According to the measurement results of this example, the conductive toner 120 according to this example can achieve a transfer rate of 80% or more on insulating paper and semi-conductive paper (highly water-containing paper), while the conductive toner 120 according to the comparative example has the conductivity of The toner can only obtain a transfer rate of about 30% on semiconductive paper (highly water-containing paper), resulting in transfer failure.
As described above, the conductive toner 120 according to this embodiment (switching in which resistance is changed from high resistance to low resistance at an intermediate electric field greater than the transfer electric field C formed at the time of transfer and smaller than the electric charge injection electric field A is switched. If a variable resistance portion is used, high water content transfer and multiple transfer are possible.

Example 4
In this example, a model similar to that in Example 2 is used, and the volume resistivity of the high resistance layer of the toner carrying roll (corresponding to the developing roll) 122 is used as a parameter, and the electric field applied to the particle layer and WST generation with respect to the conductive toner. It is a measurement of the relationship with the rate.
As an experimental condition of this embodiment, the charge injection plate 121 has a speed of 210 mm / sec. The surface of the plate is aluminum, the amount of biting into the toner carrying roll 122 is set to 1100 μm, and the speed of the toner carrying roll 122 is 120 mm / sec. The high resistance layer has a thickness of 20 μm and a hardness of Asuka C50 ° and is appropriately configured with a volume resistivity. Further, the toner is the same as in the first embodiment.
The results are shown in FIG.
According to the figure, it can be understood that the high resistance layer of the toner carrying roll 122 is 10 ¹¹ Ω · cm or more, and the WST occurrence rate is greatly reduced.
Incidentally, as a device for measuring the volume resistivity of the high resistance layer of the toner carrying roll 122, as shown in FIG. 25, a predetermined pressing force P (for example, 2 kg / unit length) is applied to the toner carrying roll 122 on the charge injection plate 121. ), And in this state, a predetermined charge injection electric field ED (100 V is applied in this example) is applied between them, the injection current at this time is measured, and the high resistance layer of the high resistance layer is measured based on the measurement result. The volume resistivity is calculated.

Example 5
Using the developing device model shown in FIG. 4, the toner supply electric field (electric field applied to the particle layer of the conductive toner) is changed using the rotation direction and speed ratio of the toner supply roll (supply electrode) 35 as parameters, and charged at that time. The amount of charge injected into the toner was measured.
Here, as an experimental condition, the toner supply roll (supply electrode) 35 has a surface made of elemental aluminum and is disposed so as to bite into the development roll (development electrode) 33 by 1100 μm.
The developing roll 33 has a diameter of 40 mm, and the electrode surface is made of 25 μm thick polyester and conductive sponge, and the speed is 120 mm / sec. Move at. Further, the conductive toner shown in the specific example of Embodiment 1 was used. Moreover, the measurement of the amount of injected charges was carried out using an Isopart analyzer made by Hosokawa Micron.

FIG. 26 shows the relationship between the toner supply electric field and the injected charge amount. In FIG. 26, “Against” indicates that the moving direction of the developing electrode and the supply electrode at the opposite portion is the reverse direction, and “With” indicates that the moving direction is the same direction.
According to FIG. 26, it is confirmed that the model in which the supply electrode moving direction is Against has a small amount of injected charges.
This is presumed that since the conductive toner 40 does not pass through the nip region between the developing electrode and the supply electrode, it is not charged by that amount, and the amount of injected charge is small accordingly.

Furthermore, using this developing device model, the rotation direction of the toner supply roll 35 is set to “Against”, the speed ratio of the supply electrode to the development electrode is 1.75, the DC of the DC + AC voltage is 150 V, and the AC injection voltage is changed. The amount of charge injected at that time was measured. The result is shown in FIG.
As is apparent from the results shown in FIG. 26, the AC injection voltage and frequency are further increased to some extent under the condition that the injection charge amount is reduced with the rotation direction of the toner supply roll 35 being “Against”. It can be understood that the amount of injected charges is further reduced by the above.

Example 6
In this example, a developing device model similar to that in Example 5 is used, the rotation direction of the charge injection roll (injection electrode) 34 is “With”, the injection electrode / development electrode speed ratio is a parameter, and the charge injection electric field (conductivity) Then, the WST generation rate, the amount of toner movement, and the amount of injected charge were measured. The results are shown in FIGS. The experimental conditions are the same as in Example 5.
It can be seen from FIG. 28 that the WST generation rate is lowered by providing the injection electrode / development electrode speed difference. In particular, in this embodiment, an example of the speed ratio is illustrated as a parameter. However, if a speed difference of 1.5 times or more is provided, for example, about 1/10 or less compared to the case of constant speed. The WST occurrence rate can be reduced. In addition, when the same experiment was conducted about the model of Embodiment 2, the same tendency was seen.
This is presumed that this example model contributes to the improvement of charge injection efficiency and the prevention of multilayering.
This is supported by FIG. 29 and FIG.
According to FIG. 29, it is understood that the amount of toner movement (number of layers) is 1 or less by providing the injection electrode / development electrode speed difference, and according to FIG. It can be understood that the amount of injected charge is increased by the provision.

Example 7
In this example, the same developing device model as in Example 1 was used, and the toner charge amount was changed to 6 μC / g, 11 μC / g, and 18 μC / g, and the image carrying plate voltage and the developing toner amount were measured. . The result is shown in FIG. In FIG. 31, the image carrying plate voltage on the horizontal axis indicates the charging voltage by the potential sensor, and the developing toner amount on the vertical axis indicates the toner amount with respect to the toner patch.
It can be seen from FIG. 31 that if the charging potential by the potential sensor is constant, a correlation is recognized between the toner charge amount and the developing toner amount (corresponding to the toner patch density). For this reason, it is understood that the toner charge amount can be adjusted according to the developing toner amount (toner patch density) if the potential sensor keeps the latent image patch potential constant.

Example 8
In this example, the same developing device model as in Example 1 was used, and the environmental conditions were temperature and humidity (22 ° C., 55%), (28 ° C., 85%), and (10 ° C., 15%), respectively. The relationship between the electric field applied to the particle layer and the amount of injected charge was investigated. The results are shown in FIG.
According to FIG. 32, it is confirmed that the amount of injected charge is higher in the high-temperature and high-humidity environment than in the low-temperature and low-humidity environment, and it is understood that the charge injection property of the conductive toner changes as the environmental conditions change.
Here, since the change in injected charge amount due to the environmental condition change is relatively small, it is not always necessary to control the injected charge amount according to the environmental condition change, but the injection charge amount is controlled according to the environmental condition change. Thus, it is possible to provide a system with high image quality stability, such as controlling the halftone of an image with high accuracy.

(A) is explanatory drawing which shows the outline | summary of the image development apparatus and image forming apparatus concerning this invention, (b) is explanatory drawing which shows the principal part of an electric charge injection means. (A) is explanatory drawing which shows the resistance change state of the electroconductive toner which concerns on this invention, (b) is explanatory drawing which shows the operation state of the developing device which concerns on this invention. 1 is an explanatory diagram showing Embodiment 1 of an image forming apparatus to which the present invention is applied. (A) (b) It is explanatory drawing which shows the detail of the image development apparatus used in Embodiment 1. FIG. (A) and (b) are explanatory drawings showing the structure of the conductive toner used in the first embodiment. It is a figure which shows the control action of the control apparatus based on the detection information from the electric potential sensor which concerns on Embodiment 1, and a density | concentration sensor. FIG. 6 is an explanatory diagram illustrating an operating state of the developing device according to the first embodiment. It is explanatory drawing which shows the relationship between the electric field applied to the particle layer with respect to the conventional electroconductive toner, and the generation rate of reverse polarity toner (Wrong Sign Toner). It is explanatory drawing which shows typically the behavior at the time of charge injection (at the time of a low electric field effect | action) of the conventional conductive toner. It is explanatory drawing which shows typically the behavior at the time of charge injection (at the time of a high electric field effect | action) of the conventional conductive toner. (A) (b) is explanatory drawing which shows the solution policy with respect to the technical subject at the time of the electric charge injection of a conductive toner (at the time of a low electric field effect | action). (A)-(c) is explanatory drawing which shows the solution policy with respect to the technical subject at the time of the charge injection of a conductive toner (at the time of a high electric field effect | action). FIG. 10 is an explanatory diagram illustrating a developing device according to a second embodiment. (A) is a figure which shows the operating state of the developing device which concerns on Embodiment 2, (b) is a figure which shows the operating state of the developing device which concerns on the comparative form model. (A) is explanatory drawing which shows the deformation | transformation form of the image development apparatus concerning Embodiment 2, (b) is a figure which shows the deformation | transformation form further. FIG. 10 is an explanatory diagram illustrating an overall configuration of an image forming apparatus according to a third embodiment. It is a figure which shows the control action of the control apparatus based on the detection information of the environmental sensor which concerns on Embodiment 3. FIG. FIG. 10 is an explanatory diagram illustrating an overall configuration of an image forming apparatus according to a fourth embodiment. FIG. 3 is an explanatory diagram in which the developing device according to Embodiment 1 is modeled as an example. FIG. 3 is an explanatory diagram in which the transfer device according to Embodiment 1 is modeled as an example. FIG. 6 is an explanatory diagram showing a change in volume resistivity of conductive toner with respect to an applied electric field in Example 1. FIG. 10 is an explanatory diagram showing a developing toner amount with respect to an image carrying plate voltage change in Example 2. FIG. 10 is an explanatory diagram showing a transfer rate with respect to a change in recording medium plate voltage in Example 3. In Example 4, it is explanatory drawing which shows the relationship between the electric field applied to the particle layer with respect to electroconductive toner, and the generation rate of reverse polarity toner (Wrong Sign Toner) by using the high resistance layer of the toner carrying roll as a parameter. It is explanatory drawing which shows the principle which measures the volume resistivity of the high resistance layer of a toner carrying roll. In Example 5, it is explanatory drawing which shows the relationship between a particle layer application electric field and the amount of injection electric charges by making a supply electrode moving direction and a supply electrode / development electrode speed ratio into parameters. In Example 5, it is explanatory drawing which shows the relationship between AC voltage and the amount of injection electric charges. In Example 6, it is explanatory drawing which shows the relationship between an injection electrode / development electrode speed ratio as a parameter and a particle layer application electric field and the generation rate of a reverse polarity toner. In Example 6, it is explanatory drawing which shows the relationship between an injection electrode / development electrode speed ratio as a parameter and a particle layer application electric field and a toner moving amount (number of layers). In Example 6, it is explanatory drawing which shows the relationship between an injection electrode / development electrode speed ratio as a parameter and a particle layer application electric field and the amount of injection charges. In Example 7, it is a figure which shows the relationship between an image carrier plate voltage and a developing toner amount by using the toner charge amount as a parameter. In Example 7, it is a figure which shows the relationship between the particle layer applied voltage and injection charge amount in each environmental condition.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Conductive toner, 3 ... Toner carrier, 4 ... Development electric field formation means, 5 ... Charge injection means, 6 ... Charge injection member, 7 ... Charge injection electric field formation means, 8 ... Sensor, 9 ... resistance variable part, Z ... electrostatic latent image

Claims (10)

In a developing device that visualizes an electrostatic latent image with conductive toner,
A toner carrier that is disposed opposite to an image carrier carrying an electrostatic latent image and carries a charged conductive toner; and
A developing electric field is formed between the toner carrier and the image carrier, and a developing electric field forming means for developing the electrostatic latent image on the image carrier in the developing electric field region;
A charge injection member disposed opposite the toner carrier, and a charge injection means for injecting a charge into the conductive toner by applying a charge injection electric field between the charge injection member and the toner carrier;
The developing device, wherein the charge injection means comprises charge injection electric field forming means for adjusting the charge injection electric field in accordance with a change in use conditions of the apparatus. The developing device according to claim 1,
A developing device having a sensor capable of detecting a change in use conditions of the device, wherein the charge injection electric field forming means forms the charge injection electric field in an adjustable manner based on detection information from the sensor. The developing device according to claim 1,
The developing device, wherein the sensor includes a density sensor capable of detecting the density of the toner image on the image carrier. The developing device according to claim 1,
The developing device, wherein the sensor includes a potential sensor capable of detecting a latent image potential on the image carrier. The developing device according to claim 1,
The developing device characterized in that the sensor includes an environmental sensor capable of detecting a use condition environment of the apparatus. The developing device according to claim 1,
2. A developing device according to claim 1, wherein the conductive toner changes to a high resistance in a developing electric field application region and changes to a low resistance in a charge injection electric field application region. The developing device according to claim 1,
The developing apparatus according to claim 1, wherein the charge injection means causes a charge injection electric field larger than the development electric field to act between the charge injection member and the toner carrier. The developing device according to claim 1,
The developing device according to claim 1, wherein the charge injecting means injects the charge while rubbing the conductive toner between the charge injecting member and the toner carrier. The developing device according to claim 1,
The developing device, wherein the toner carrying member is provided with a high resistance layer that covers a surface and can suppress charge transfer between the toner carrying member and the conductive toner.   An image forming apparatus comprising: an image carrier that carries an electrostatic latent image; and the developing device according to claim 1 disposed opposite to the image carrier.

Images