JP4639693B2 - Developing device and image forming apparatus using the same - Google Patents

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 is disposed to be opposed and carries the charged conductive toner 2 and between the toner carrying member 3 and the image carrying member 1. 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 that is disposed opposite to the toner carrier 3 and rotates in the same direction at the portion facing the toner carrier 3. Then, a charge injection electric field composed of a DC electric field component larger than the developing electric field is applied in a state where a peripheral speed difference is provided between the charge injection member 6 and the toner carrier 3, and the conductive toner 2 is sandwiched between the two. Charge injection means 5 for injecting charges into the conductive toner 2 while rubbing, and charge injection; The toner supply member 9 is disposed opposite to the toner carrier 3 upstream of the means 5 in the rotation direction of the toner carrier 3, and the toner supply member 9 and the toner carrier 3 are arranged in opposite directions at the opposing portion. and a toner supply means 8 for supplying the conductive toner 2 to the toner carrying member in a state in which the action of the toner supply electric field between the and the toner carrying member 3 and the toner supply member 9 is rotated, the toner supply member 9 and The charge injection member 6 is disposed adjacent to the toner carrier 3 along the rotation direction of the toner carrier 3, and the conductive toner 2 changes to a high resistance in the development electric field application region and the charge injection electric field application region. It is characterized in that the resistance changes to low .

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. 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 the present invention, the charge injection electric field is composed of a DC electric field component larger than the developing electric field.

  The charge injection unit 5 includes a charge injection member 6 that is separately provided on the downstream side of the toner supply unit 8 and injects charges into the toner held on the toner carrier 3. For this reason, since the charge injection member 6 is provided separately from the toner supply member 9 of the toner supply means 8, it is possible to pursue only the functionality for charge injection and to ensure the chargeability of the toner. Preferred above.

In particular, as the 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). rather than preferred, in the present invention, have adopted this method. 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. At this time, 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, thereby enabling uniform charging and effective generation of reverse polarity toner. Can be prevented.

Further, as a typical embodiment of the sliding type charge injection method, in the present invention, a charge injection means 5 has to have 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 reference form related to the present invention, as another specific aspect for giving the peripheral speed difference, a charge injection member 6 is fixedly disposed so as to face the toner carrier 3, and between the toner carrier 3 and the toner carrier 3. A mode in which a difference in peripheral speed is provided is given. The charge injection member 6 of this embodiment is preferably a blade-like member.

Further, in the charge injection means 5 adopting the rubbing type charge injection method, it is possible to inject the charge 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 resistance variable portion 11 that changes to a high resistance in the development electric field application region and changes to a low resistance in the charge injection electric field application region. It shows behavior.

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. to, rather preferably be exerted a large charge injection field from the developing electric field, in the present invention, are allowed to act charge injection electric field consisting of large DC electric field component of the developing 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, 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 obtained. 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, a method of disposing a charge eliminating member capable of eliminating the surface potential of the toner carrying member 3 as the auxiliary charge removing mechanism on the toner carrying member 3 can be cited. In this case, it is possible to provide a charge removal function by devising the toner supply member 9 of the toner supply means 8 without any additional auxiliary charge removal mechanism, as will be described later.

In particular, the present invention is limited to a mode in which the toner supply unit 8 is provided on the upstream side of the charge injection unit 5. The toner supply means 8 has a toner supply member 9 that faces the toner carrier 3. As the toner supply member 9, a roll-like member may be appropriately selected as long as it is a rotation function member that supplies toner to the toner carrier 3, and the toner carrier 3 may be in contact with or not in contact with the toner carrier 3. .
In the present invention, it is necessary to rotate the toner supply member 9 and the toner carrier 3 in the opposite directions at the opposing portions.
As described above, when the toner supply member 9 and the toner carrier 3 are rotated in the opposite directions at the opposing portion, the conductive toner 2 is completely transferred to the opposing portion between the toner supply member 9 and the toner carrier 3. The toner is supplied to the toner carrier 3 side without being pinched. Therefore, the conductive toner 2 is supplied to the toner carrier 3 without being rubbed and charged at the facing portion. As a result, at the time of charge injection into the conductive toner 2 by the charge injection member 6, it is possible to suppress a decrease in charging efficiency to the conductive toner 2 and generation of reverse polarity toner.
In this regard, when the toner supply member 9 and the toner carrier 3 are rotated in the same direction at the opposing portion, the conductive toner 2 is slid and rubbed against the opposing portion between the toner supply member 9 and the toner carrier 3. In this state, the conductive toner 2 may be charged.

In addition, it is necessary to apply a toner supply electric field between the toner supply member 9 and the toner carrier 3. As an element that generates the toner supply electric field, for example, the toner supply member 9 and the toner carrier 3 In between, toner supply electric field forming means 10 such as a power source is used.
At this time, the toner supply electric field is not limited as long as the conductive toner 2 is transferred to the toner carrier 3 side. From the viewpoint of effectively eliminating the charging history of the toner carrier 3, It is preferable that an electric field having the same polarity and small in absolute value with respect to the electric charge injection electric field or an electric field having a reverse polarity applied to the electric charge injection electric field.
Here, when an electric field having the same polarity as the charge injection electric field and having an absolute value smaller than the charge injection electric field is used as the toner supply electric field, charging of the toner carrier 3 charged by the charge injection electric field is performed. Since it acts in the direction of weakening the potential, the charge potential of the toner carrier 3 can be eliminated, and the charge history of the toner carrier 3 can be eliminated accordingly. In particular, when an electric field having a polarity opposite to the electric charge injection electric field is used as the toner supply electric field, the action of weakening the charging potential of the toner carrier 3 is further increased. can do.
Furthermore, the above-described toner supply electric field not only removes the charged potential of the toner carrier 3 but also collects residual toner on the toner carrier 3 to the toner supply member 9 side by the electrostatic force. Residual toner can be peeled and collected at the facing portion between the member 9 and the toner carrier 3, and the development history due to the residual toner can be effectively eliminated accordingly.

  The toner supply electric field may be appropriately selected, but it is preferable to apply an alternating electric field from the viewpoint of enhancing the history cancellation effect on the toner carrier 3. In this way, by applying an alternating electric field as the toner supply electric field, it is possible to promote the effect of attenuating the charging potential of the toner carrier 3 and the effect of collecting the residual toner, and the toner carrier of the toner supply member 8 correspondingly. It is possible to enhance the history elimination effect for 3. In this embodiment, parameters of DC voltage and AC voltage may be appropriately selected, but DC voltage (100 to 400V) and AC voltage (frequency 1 to 10KHz, peak-to-peak voltage 100 to 400V) may be selected. It is preferable to act.

  The toner supply member 9 is preferably formed of a conductive member having a rough surface. The toner supply member 9 is a conductive member as described above in order to ensure the charge-removing property with respect to the toner carrying member 3, and if the surface is provided with a rough surface, the toner transportability can be easily achieved. It is possible to secure. From this point of view, the toner supply member 9 is preferably a conductive roll having a roughened surface, for example, a polished surface.

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 effect region, the resistance variable portion 11 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 11 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 apparatus according to the present invention, the charge injection field effect zone, the conditions of the developing electric field acting area appropriately selected by Rukoto reacted charge injection electric field consisting of large DC electric field from the developing electric field, the charge on the conductive toner When the toner is injected, the conductive toner can be changed to a low resistance, and the charge can be easily injected into the conductive toner. Charge retention can be improved.
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 toner supply member of the toner supply means is disposed on the upstream side of the charge injection member, and the toner supply member and the toner carrier are rotated in the opposite direction at the opposite portion, thereby providing conductivity. The toner can be supplied to the toner carrier without being completely pinched and rubbed at the opposite portion, that is, hardly charged, and guided to the charge injection means.
Then, in the charge injection means of the present invention, the charge injection member is rotated in the same direction at the toner carrier and the facing portion, and a charge injection electric field is applied while rubbing and rubbing the conductive toner therebetween. Charges can be efficiently injected into toner with a low charge injection electric field.
Furthermore, by applying a predetermined toner supply electric field to the toner supply member as a toner supply means, it has a function of eliminating the charged potential of the toner carrier, and it is also possible to collect residual toner on the toner carrier. . As a result, it is possible to effectively prevent a reduction in charging efficiency of the conductive toner and generation of reverse polarity toner during charge injection.
For this reason, low charge toner and reverse polarity toner are rarely generated in the development electric field action region, fog and toner cloud can be effectively prevented, and development performance with respect to 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 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. The charging device 21, an exposure device 22 as a latent image writing device for forming the electrostatic latent image Z on the photosensitive drum 20, and the electrostatic latent image Z formed on the photosensitive drum 20 are visible. A developing device 30 that forms an image, a transfer device 24 that transfers a toner image visualized on the photosensitive drum 20 to a recording paper 28 that is a recording medium, and a cleaning that cleans residual toner on the photosensitive drum 20. The devices 25 are sequentially arranged.

  In the present embodiment, as shown in FIG. 4A, the developing device 30 has a developing housing 31 in which a developer G containing a conductive toner 40 is accommodated. The developing housing 31 includes a photosensitive drum. 20 is opened with a developing opening 32, a developing roll (developing electrode) 33 is disposed facing the developing opening 32, and a predetermined developing bias is applied to the developing roll 33, A developing electric field is applied to a developing region between the photosensitive drum 20 and the developing roll 33, and further, a charge injection roll (injection electrode) 34 and a toner supply roll 35 are opposed to the developing roll 33 in the development housing 31. Is provided.

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 from a developing bias power source 37 is applied to the developing roll 33, and a charge injecting bias from a charge injecting bias power source 38 is applied to the charge injecting roll 34. On the other hand, a toner supply bias from a toner supply bias power source 39 having a polarity opposite to the charge injection bias is applied to the toner supply roll 35. As a result, a developing electric field is generated between the electrostatic latent image Z of the photosensitive drum 20 and the developing roll 33, and a charge injection electric field is generated between the developing roll 33 and the charge injecting roll 34. A toner supply electric field acts between the roll 35.

Here, 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 height is provided around the elastic base layer 332. The resistance layer 333 is covered 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. 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 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 rotation direction of the charge injection roll 34 is rotated in the same direction at the opposite portion to the development roll 33. However, in consideration of the charge injection characteristics, the charge injection roll 34 is the development roll 33. In the same direction and with a peripheral speed difference (for example, 1.5 times or more), and the conductive toner 40 is sandwiched between the charge injection roll 34 and the developing roll 33 and rubbed. An embodiment in which charge is injected is preferable.

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.

Further, in the present embodiment, the developing roll 33 is composed of, for example, an aluminum roll whose surface is anodized, and the charge injection roll 34 has a small and uniform uneven surface on the surface by, for example, a sandblasting method or a chemical etching method. The toner supply roll 35 is formed of a conductive foam roll such as urethane rubber or silicone rubber. The charge injection roll 34 and the toner supply are supplied to the development roll 33. The roll 35 is lightly supported or supported with a minute gap.
Furthermore, the conductive toner 40 as the developer G used in the present embodiment will be described later.

  Note that each device other than the developing device 30 used in the present embodiment may be appropriately selected. For example, as the 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 transfer the photosensitive drum 20 to the transfer drum 24. A transfer electric field is allowed to act between the rolls and the toner image on the photosensitive drum 20 can be electrostatically transferred onto the recording paper 28 that is a recording medium.

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, specific examples of the conductive toner dry manufacturing method include, for example, a predetermined amount (for example, 15 wt%) of IOT fine particles (manufactured by Sumitomo Metal Mining Co., Ltd.) in an insulating core having an average particle diameter of 6.5 μm, 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.

Next, the operation of the image forming apparatus according to the present embodiment will be described.
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 photoconductive drum 20 is conveyed to a transfer site, and the transfer device 24 electrostatically transfers the toner image on the photoconductive drum 20 to a recording paper 28 as a recording medium.
The residual toner on the photosensitive drum 20 is cleaned by the cleaning device 25.

Next, the operation of the developing device 30 according to this embodiment will be described in detail 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 is supplied to the surface of the toner supply roll 35. 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.
Here, between the developing roll 33 and the supply roll 35, the difference between the developing bias of the developing bias power supply 37 connected to the developing roll 33 and the toner supply bias power supply 39 connected to the toner supply roll 35. The conductive toner 40 is supplied and carried from the toner supply roll 35 to the developing roll 33 in the toner supply electric field action region.
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 development bias of the development bias power supply 37 connected to the development roll 33 and the charge injection bias power supply 38 connected to the charge injection roll 34 are provided. A charge injection electric field formed by the difference acts. 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 FIG. 6, reference numeral 40a indicates a conductive toner before charge injection, and 40b indicates a conductive toner after charge injection.

  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.

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. To be implemented.

Further, the undeveloped toner (conductive toner) 40 that has not been transferred to the photosensitive drum 20 and remained 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, 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, and an electrostatic force acts on the toner supply electric field acting region. Since this electrostatic force acts to collect the development residual toner 40 on the development roll 33 toward the toner supply roll 35, the development residual toner 40 on the development roll 33 that has been carried to the position facing the toner supply roll 35. Is recovered by peeling.
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 recorded on the recording paper 28 at a position where the photosensitive drum 20 and the transfer device 24 face each other as shown in FIG. Transcribed.
At this time, in this transfer step, if the transfer electric field formed by the photosensitive drum 20 and the transfer device 24 is set to a lower electric field than the charge injection electric field, it is injected into the conductive toner 40 by the charge injection electric field. As a result, good transfer can be performed without escaping the electric charge in the transfer electric field.

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 FIGS. 7 to 11, when a conductive toner is put 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. 7, when the electric charge injection field is a low electric field, as shown in FIG. 8, toner that has poor charging efficiency and cannot be charged adheres to the charged toner or is non-electrostatic with the developing electrode. It moves to the developing electrode side by 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. 9, the charged toner moves to the developing electrode, and when a multi-layer is formed, the toner exchanges with each other and polarizes, so that the upper 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 occurrence rate of WST, for example, as shown in FIG. 10A, a high injection efficiency is realized with a low electric field, or as shown in FIG. It is conceivable to avoid moving to the developing electrode. Further, as shown in FIG. 11 (a), it should not be polarized between the toner layers even in a high electric field, or as shown in FIGS. 11 (b) and 11 (c). 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. 12 shows an image forming apparatus according to a second embodiment to which the developing device according to the present invention is applied.
In the figure, the image forming apparatus according to the present embodiment is a so-called tandem type, and an image reading unit 61 for reading a document is disposed above the apparatus main body 60, while the apparatus main body 60 includes the image reading unit 61. An image forming engine 62 (specifically 62a to 62d) 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 63 is circulated and conveyed along the arrangement direction of the image forming engines 62, and an image on the intermediate transfer belt 63 is used as a recording medium. A secondary transfer device 65 for transferring the recording paper is disposed, and further, a supply cassette 66 for storing the recording paper 64 is disposed below the device main body 60, and the recording paper 64 from the supply cassette 66 is transferred to the secondary. Roll It is obtained so as to guide to a fixing device 67 through the device 65.

In the present embodiment, the image forming engine 62 includes, for example, a photosensitive drum 71, a charger 72 that charges the photosensitive drum 71, and a charged photosensitive drum 71 around the photosensitive drum 71. A latent image writing device 73 such as a laser device for writing an electrostatic latent image, and a developing device 74 (specifically, 74a to 74d) that visualizes the electrostatic latent image on the photosensitive drum 71 with each color component toner. A primary transfer device 75 that primarily transfers the toner image on the photosensitive drum 71 to the intermediate transfer belt 63 and a drum cleaner 76 that removes residual toner on the photosensitive drum 71 are sequentially arranged.
On the other hand, the intermediate transfer belt 63 is stretched over a plurality of (four in this example) stretching rolls 81 to 84, the stretching roll 81 is a driving roll, and the other stretching rolls 82 to 84 are driven rolls. It is supposed to function.
Furthermore, the developing device 74 according to the present embodiment uses the developing device according to the first embodiment, and a detailed description thereof is omitted.

Next, the operation of the image forming apparatus according to the present embodiment will be described with reference to FIG.
The electrostatic latent image on the photosensitive drum 71 is developed and visualized (toner image) by each developing device 74 (specifically, 74a to 74d).
A voltage having a polarity opposite to that of the toner image on the photosensitive drum 71 is applied to the primary transfer device 75 at a position where the photosensitive drum 71 and the intermediate transfer belt 63 are in contact with each other. The formed toner image is primarily transferred onto the intermediate transfer belt 63.
Further, the toner image primarily transferred onto the intermediate transfer belt 63 is conveyed to the secondary transfer device 65 as the intermediate transfer belt 63 rotates, and the recording paper 64 conveyed from the supply cassette 66 is The toner image on the intermediate transfer belt 63 is recorded by being conveyed to a contact area between the intermediate transfer belt 63 and the secondary transfer device 65 and applying a voltage having a polarity opposite to the charging polarity of the toner to the secondary transfer device 65. It is electrostatically attracted to the paper 64. Thereafter, the recording paper 64 to which the toner image is transferred is fixed by a fixing device 67, and the toner image is fixed to the recording paper 64.

Also in the present embodiment, since the conductive toner has the same characteristics as in the first embodiment, the resistance is changed to a low resistance by applying a charge injection electric field (high electric field) in the charge injection region. Therefore, charge injection into the conductive toner is easily performed. On the other hand, in the development area and the transfer area, the conductive toner maintains a high resistance even when a development electric field and a transfer electric field (both low electric fields) are applied. Therefore, the developed charge can be stably developed without escaping the injected charge.
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 64 and the toner. Therefore, in the electrostatic transfer method, the recording paper 64 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.
The developing device of the first embodiment is used as the developing device 74 in the present embodiment .

Embodiment 3
FIG. 13 shows Embodiment 3 in which the present invention is applied to an image forming apparatus that does not use an electrostatic transfer system.
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.
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.

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.

FIG. 14 shows a developing device model used in each of the following embodiments, and FIG. 15 shows a transfer device model.
<Developer model>
The developing device model shown in FIG. 14 is a model of the developing device 30 (see FIG. 4) according to the first embodiment.
4 and 14, reference numeral 121 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 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 rightward 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. 15 is a model of the transfer device 24 (see FIG. 3) used in the first embodiment.
3 and 15, 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 28 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 injecting plate 131, a charge injection electric field A is generated between the charge injecting 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 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 in a high electric field.
This is supported by the examples described later.

Example 1
FIG. 16 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 according to the first embodiment (see FIG. 14). 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. 17 shows the amount of development toner (converted to the number of layers) with respect to a change in the image carrying bias of the image carrying bias power supply 127 in the developing device model according to the first embodiment (see FIG. 14). 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. 18 shows the measurement results of the relationship between the recording medium plate 133 voltage (transfer bias V6) and the transfer rate (%) in the transfer device model according to Embodiment 1 (see FIG. 15).
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. 20, 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. In this state, a predetermined electric charge injection electric field ED (in this example, V = 100 V is applied) is applied, and the injection current I (A) at this time is measured. Based on this, the volume resistivity of the high resistance layer 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. 21 shows the relationship between the toner supply electric field and the injected charge amount. In FIG. 21, “Against” indicates that the moving direction of the developing electrode and the supply electrode facing each other is the opposite direction, and “With” indicates that the moving direction is the same direction.
According to FIG. 21, 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.

Further, using this developing device model, the rotation direction of the toner supply roll 35 is set to “Against”, the speed ratio between the supply electrode and the development electrode is set to 1.75, only the DC voltage is set as the DC voltage + AC voltage as the toner supply bias. The DC voltage was set to 150 V (constant), the frequency of the AC voltage or the peak-to-peak voltage was changed, and the injected charge amount at that time was measured. The result is shown in FIG.
As is apparent from the results shown in FIG. 21, the AC voltage frequency or peak-to-peak is further reduced under the condition that the amount of injected charge is reduced when the rotation direction of the toner supply roll 35 is “Against”. It is understood that the amount of injected charge is further reduced by increasing the voltage to some extent.

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.
According to FIG. 23, it is understood that the WST occurrence 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. 24 and FIG.
According to FIG. 24, 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.

(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. FIG. 3 is an explanatory diagram illustrating details of a developing device used in the first embodiment. (A) and (b) are explanatory drawings showing the structure of the conductive toner used in the first embodiment. 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. 4 is an explanatory diagram illustrating an overall configuration of an image forming apparatus according to a second embodiment. FIG. 10 is an explanatory diagram illustrating an overall configuration of an image forming apparatus according to a third 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.

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 ... Toner supply means , 9 ... Toner supply member, 10 ... Toner supply electric field forming means, Z ... Electrostatic latent image

Claims (7)

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 to the toner carrier and rotating in the same direction at a portion facing the toner carrier, with a peripheral speed difference between the charge injection member and the toner carrier. A charge injection means for injecting a charge into the conductive toner while applying a charge injection electric field composed of a direct current electric field component larger than the developing electric field and rubbing the conductive toner between the two;
A toner supply member disposed opposite to the toner carrier on the upstream side in the rotation direction of the toner carrier from the charge injecting means, and the toner supply member and the toner carrier are rotated in opposite directions at the opposite portion; And a toner supply means for supplying conductive toner to the toner carrier in a state where a toner supply electric field is applied between the toner carrier and the toner supply member ,
The toner supply member and the charge injection member are arranged adjacent to the toner carrier along the rotation direction of the toner carrier,
The developing apparatus 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 conductive toner is obtained by coating an insulating or semiconductive coating layer around a conductive toner substrate. The developing device according to claim 1,
The toner supply means causes a toner supply electric field having a polarity opposite to the electric charge injection electric field to act between the toner carrier and the toner supply member. The developing device according to claim 1,
2. A developing apparatus according to claim 1, wherein the toner supply means applies a toner supply electric field including an alternating electric field between the toner carrier and the toner supply member. The developing device according to claim 1,
The toner supply means causes a toner supply electric field having the same polarity as the electric charge injection electric field and a small absolute value to the electric charge injection electric field to act between the toner carrier and the toner supply member. The developing device according to claim 1,
The developing device according to claim 1, wherein the toner supply member of the toner supply means is a conductive member having a rough surface. An image carrier that carries an electrostatic latent image, an image forming apparatus comprising the developing device according to 6 or claims 1 disposed opposite to the image carrier.

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