JP3475697B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for transferring a toner image formed on an image carrier to an intermediate transfer member and then transferring the toner image on the intermediate transfer member to a recording medium. Specifically, it relates to an image forming apparatus utilizing electrophotographic recording, electrostatic recording, ionography, magnetic latent image and the like.

[0002]

2. Description of the Related Art In a conventionally known image forming apparatus, a recorded image is obtained by transferring a toner image formed on an image carrier to a recording sheet or the like and fixing it. The toner remaining on the image carrier after the transfer is generally collected and discarded. For example, in an electrophotographic image forming apparatus, an electrostatic latent image is formed by irradiating an image light on the surface of a charged image carrier, which is a charging step of uniformly charging an image carrier having a photosensitive layer on the surface. An exposing step, a developing step of forming a toner image by attaching toner to the electrostatic latent image, a transferring step of transferring the toner image to a recording medium, a fixing step of fixing the toner image on the recording medium, and An image is formed by a cleaning process that removes the toner remaining on the image carrier in the transfer process. Further, in a color image forming apparatus, for example, a plurality of color toner images are sequentially formed on an image carrier, and the color images are superimposed on the image carrier as it is, or on the intermediate transfer member or the recording medium. To form. Then, in the cleaning step after the toner image on the image carrier is transferred, an elastic rubber blade or brush is pressed against the surface of the image carrier,
The residual toner is collected, and the collected toner is accumulated in a collection container and is regularly discarded.

In such an apparatus, the photoconductor is worn due to the friction of the image bearing member by the rubber blade or the like, so that the photoconductor is required to be replaced, or the image quality is deteriorated due to the damage of the photoconductor or the adhesion of dirt to the blade. cause. In addition, the amount of collected toner accumulated in the collection container must always be detected or measured, and the toner must be discarded or the collection container must be replaced before the collection container becomes full. In addition, the collected toner is being reused from the viewpoints of environmental protection and resource usage reduction, but there are many problems such as separation problems, energy problems for transportation and recycling, and problems of collection methods and collection places. Including the problem of.

As means for improving such a problem, for example, image forming apparatuses described in JP-A-56-159666 and JP-A-5-249796 are known. The image forming apparatus described in Japanese Patent Application Laid-Open No. 56-159666 forms a yellow, magenta, and cyan toner image on an image carrier in sequence, and sequentially transfers the toner images to the transfer medium for each color formation. A color image is formed on the upper surface of the image carrier, and the toner remaining on the image carrier after being transferred to the transfer medium is collected by a developing device having the same color as the toner. Such an image forming apparatus has an advantage that toner can be effectively used because waste toner is not generated, but since a color image is formed from three colors of yellow, magenta, and cyan,
It is difficult to obtain a high-quality image including black, and it takes time to form a color image because toner is collected in the developing device, resulting in a slow print speed.

On the other hand, the image forming apparatus described in Japanese Patent Laid-Open No. 5-249796 introduces a black developing device and collects the residual toner on the image carrier into the developing device regardless of the color of the toner. It is a thing. Since this image forming apparatus collects the residual toner in the developing device that contains the black toner, it has an advantage that the drawbacks found in the technique described in Japanese Patent Laid-Open No. 56-159666 can be considerably eliminated.

However, each of the image forming apparatuses described above collects residual toner after the exposure step. Basically, in such a system, the toner transfer rate is a normal electrostatic transfer transfer rate (70). If it does not exceed 90%), so-called negative ghost will occur due to the light shielding effect of the residual toner. This is because the residual toner before collection blocks the light beam during the exposure of the next cycle, and therefore, for example, in the case of reversal development, the electric potential of the image portion of the next cycle does not drop, and the image density of the next cycle is similar to the image density of the previous cycle. This is because it will decrease. This phenomenon is remarkable in the case of a black toner having a low light transmittance, and therefore, in the case of the black toner, an extremely high transfer rate, which is 9
A transfer rate of 9.2% or more is required.

To solve such a problem, for example, as disclosed in Japanese Patent Application Laid-Open No. 56-126872, a method of increasing the area of a bias applying portion of a transfer roll to increase a region where a transfer electric field is formed. And JP-A-58-8877
No. 0, JP-A-58-140769, an alternating electric field is formed at the transfer position to impart a force that causes the toner on the image carrier to sway, and the toner is released from the image carrier. Methods to promote separation have been proposed. Although the toner transfer rate can be improved by such a method, the toner particles directly attached to the image carrier cannot be completely transferred, and it is still insufficient in the sense of increasing the transfer efficiency. .

Another method is disclosed in Japanese Patent Laid-Open No. 2-511.
As disclosed in Japanese Unexamined Patent Publication No. 68, a method has been proposed in which a spherical toner is used to reduce the area of adhesion to the image carrier and increase the transfer rate of the toner. But,
In order to facilitate registration when forming a color image, when toner images of a plurality of colors are superposed on the intermediate transfer member, toner is not collected by the developing device, and the toner is not collected on the intermediate transfer member. If there is no means for collecting the residual toner, the so-called positive ghost in which the residual toner of the previous cycle appears as a ghost as it is on the transfer medium occurs remarkably. In such a case, it is not enough to increase the transfer rate by using spherical toner. Specifically, according to the experiments performed by the inventors of the present application, when the toner image on the intermediate transfer member is transferred onto the recording medium as described above, the minimum transfer rate required to suppress the occurrence of positive ghosts is 99. 8%.

On the other hand, the spherical toner in the developing device has SiO ₂
When a transfer aid such as is externally added, the external additive is transferred from the developing device together with the toner to the image carrier and adheres to the surface of the image carrier, so that the adhesive force between the toner and the image carrier is weakened. It is considered that the transfer rate is improved. However, only by externally adding the transfer aid to the toner, the external additive cannot be uniformly attached to the surface of the image carrier, and when the amount of attachment is small, the transfer rate is about 80 to 90%, which is insufficient. is there. Further, since the external additive is not directly supplied to the surface of the intermediate transfer body, even if spherical toner is used, a sufficient transfer rate cannot be obtained when transferring from the intermediate transfer body to the recording medium.

Further, even when the residual toner is present to some extent or more, the residual toner on the image bearing member is disturbed by using a rotating brush or the like as disclosed in Japanese Patent Laid-Open No. 3-4283, and a negative ghost image is generated. Methods for removing patterns have also been proposed. However, such a method cannot avoid color mixing of the toner in the developing device, and cannot prevent the rotating brush in contact with the image carrier from being soiled, which is important for reliability. This will cause problems.

[0011]

As described above,
Minimize the amount of discarded toner, or discard toner
In order to eliminate the need for processing, it is necessary to collect the toner in the developing device and reuse it for development, or to improve the transfer efficiency of the toner image. Further, in order to eliminate all the toner that must be discarded, it is necessary to improve the transfer efficiency to the extent that image defects such as ghost and fog do not occur without cleaning the residual toner after transfer.

The present invention has been made in view of the above problems, and an object of the present invention is to eliminate the wear of a cleaning blade of an image carrier by a cleaning blade and the generation of waste toner by using a cleanerless structure, and to eliminate the residual toner. An object of the present invention is to provide an image forming apparatus capable of avoiding the generation of negative ghosts and positive ghosts due to toner and obtaining high quality images.

[0013]

In order to solve the above-mentioned problems, the invention according to claim 1 is an image carrier in which an electrostatic latent image is formed on a circumferential surface which circulates due to a difference in charging potential. A charging device for charging the image carrier substantially uniformly; an image exposure device for irradiating the image carrier charged substantially uniformly by the charging device with image light to form an electrostatic latent image; A developing device for transferring toner to the electrostatic latent image on the body to visualize the toner; an intermediate transfer body for supporting the toner image on the image carrier, the peripheral surface being supported so as to be orbitable; and the toner. A potential having a polarity opposite to that of the charging polarity of the image carrier is applied, and an electric field is formed at a position where the image carrier and the intermediate transfer member come into contact with each other to transfer the toner image on the image carrier to the intermediate transfer member. Transfer device, and a second transfer device for transferring the toner image on the intermediate transfer member to a recording medium. In an image forming apparatus having a device, fine particles having a particle size smaller than that of the toner are substantially uniformly attached to the peripheral surface of the image carrier and the peripheral surface of the intermediate transfer member, It is assumed that the particle size and the resistivity are set so that the toner is charged with the same polarity as the toner by the device, is transferred to the intermediate transfer member by the first transfer device, and is charged with the opposite polarity to the toner. .

In the above-mentioned image forming apparatus, the fine particles are adhered to the image carrier substantially uniformly, and when the image carrier is charged substantially uniformly by the charging device in the image forming process, the image carrier is The upper particles are also charged to the same polarity as the toner by the charging device. Then, after the electrostatic latent image is formed on the surface of the image carrier by the image light emitted from the image exposure device, the electrostatic latent image on the image carrier is visualized when the electrostatic latent image is circulated to a position facing the developing device. The resulting toner is transferred onto the fine particles, and a toner image is formed through the fine particles. At this time, it is desirable that the potentials of the image portion and the non-image portion on the image carrier and the developing bias are appropriately set so that the fine particles on the image carrier are not transferred into the developing device.

After that, the image carrier moves to a position facing the first transfer device, and the fine particles charged to the same polarity as the toner are transferred to the intermediate transfer member together with the toner by the action of the transfer electric field. At this time, the particle size and the resistivity of the fine particles are appropriately set, and when the fine particles are transferred onto the intermediate transfer body by discharging in the minute gap between the image carrier and the intermediate transfer body or by injecting charges into the fine particles. Most of the fine particles are charged in the opposite polarity to the toner. Therefore, the fine particles on the intermediate transfer member do not transfer to the recording medium together with the toner when they move to the position facing the second transfer device, and the first transfer device remains on the intermediate transfer member. The fine particles are transferred to the image bearing member by the action of the transfer electric field that returns the toner to the position opposite to the above and transfers the toner onto the intermediate transfer member. The fine particles transferred onto the image carrier are charged again to the same polarity as the toner by the charging device, and move to the position facing the first transfer device. In this way, the fine particles circulate between the image bearing member and the intermediate transfer member through the above-mentioned path, whereby the fine particles are always maintained on the peripheral surface of the image bearing member and the peripheral surface of the intermediate transfer member. .

Therefore, the toner image formed on the image carrier or the toner image transferred on the intermediate transfer member is always carried through the fine particles, and the toner and the image carrier or the intermediate transfer member are carried. The non-electrostatic adhesion force such as the Van der Waals force acting between the two is reduced. Therefore, due to the action of the transfer electric field, the toner particles are easily detached from the image carrier or the intermediate transfer member, and the transfer can be performed with an efficiency close to 100%.

The fine particles attached to the peripheral surface of the image carrier and the peripheral surface of the intermediate transfer member have a particle size of 100 nm or less and a resistivity of 10 ¹⁰ Ω, as in the invention described in claim 2.
-It is desirable that the height is cm or more. By using fine particles having a small particle size and high resistivity in this manner, the electric force is dominant over the non-electrical force such as the Van der Waals force as the adhesive force acting between the fine particles. Next to
The fine particles can be easily desorbed by the action of the transfer electric field. Therefore, the fine particles can be reliably circulated between the image carrier and the intermediate transfer member, and a substantially uniform amount of fine particles can be maintained on the peripheral surface of the image carrier and the peripheral surface of the intermediate transfer member. The resistivity of the fine particles is 10 ¹⁰ Ω · cm.
If it is below, an electric current easily flows in the particles, and in particular in a high humidity environment, the charges on the image bearing member flow laterally through the particles, causing image deterioration such as image deletion. Further, the particle size of the fine particles is at least 100 nm, considering that the particles can be easily transferred by the action of the transfer electric field and that the light shielding effect is reduced as much as possible at the time of exposure to the image carrier.
The following is preferable. In addition, the measuring method of the resistivity is as follows. After the fine particles are placed in a cylindrical container having a diameter of 50 mm and a height of 1 mm and tapped, 3340 g is put on the packed particles.
Is obtained by reading the current value when a voltage of 1000 V / cm is applied and a voltage is applied.

According to the third aspect of the invention, the toner contained in the developing device is fine particles having substantially the same particle size and resistivity as the fine particles adhered on the image carrier and the intermediate transfer member. It is preferable that the fine particles include as an external additive, and the fine particles are transferred onto the image carrier together with the toner during development. That is, at the position facing the second transfer device, the fine particles charged to the opposite polarity to the toner are not transferred to the recording medium in the transfer electric field and are maintained on the intermediate transfer body. The fine particles may be transferred to the recording medium together with the toner. In this case, the amount of fine particles as a whole decreases with the number of prints, but by including fine particles as an external additive in the developing device as described above, the fine particles and the toner carry images during development. The particles are transferred to the body and the surface of the image carrier is replenished with fine particles. Therefore, it is possible to maintain a substantially uniform amount of fine particles on the peripheral surface of the image carrier and the peripheral surface of the intermediate transfer member for a long period of time, and it is possible to stably obtain a high transfer rate.

The fine particles on the peripheral surface of the image bearing member or the intermediate transfer member may be uniformly attached in advance before the image forming apparatus is put into service. For example, instead of toner in the developing device. The particles may be supplied onto the image carrier substantially uniformly in the initial stage of service of the image forming apparatus by means of a particle supplying means containing particles. Further, the toner used in the image forming apparatus can be used in any particle shape such as a spherical shape or an irregular shape, but it is particularly preferable to use a spherical toner. That is, the spherical toner can reduce the contact area with the image carrier or the fine particles, and in combination with the effect of the fine particles, the transfer efficiency of the toner image can be significantly improved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an image forming apparatus which is an embodiment of the invention described in claim 1, claim 2 or claim 3. This image forming apparatus is
The image carrier 1 on which an electrostatic latent image is formed by irradiating the image light after uniform charging, and the periphery of the image carrier,
A charging roll 2 that uniformly charges the surface of the image carrier, an image writing device 3 that irradiates the uniformly charged image carrier 1 with image light to form an electrostatic latent image, and black and yellow, respectively. , A rotary type developing device 4 equipped with four developing devices containing magenta and cyan developers, and contacted with the image carrier 1 and stretched by a plurality of supporting rolls 11, 12 and 13 so as to be orbitable. Endless belt-shaped intermediate transfer member 5
And a first transfer roll 6 for transferring the toner image formed on the image carrier 1 to the intermediate transfer member 5. Further, in the apparatus, a second transfer roll 8 that transfers the toner image on the intermediate transfer body 5 to the recording paper 7 that is sequentially conveyed to a position facing the intermediate transfer body 5, and the second transfer roll 8 that is transferred onto the recording paper 7. Fixing device 9 for fixing the toner image, and eraser lamp 1 for removing the charge on the surface of the image carrier 1 after the toner image is transferred.
It has 0 and.

The image carrier 1 is a drum-shaped organic photosensitive member having an outer diameter of 20 mm and an axial length of 320 mm, and is rotationally driven in the direction of arrow A at 100 mm / s by a driving means (not shown). .

The charging roll 2 has an elastic layer such as EPDM in which carbon is dispersed around a shaft made of SUS, and further has an overcoat layer such as acrylic resin in which carbon is dispersed on the surface thereof. is there.
The charging roll 2 has an outer diameter of 10 mm and an axial length of 320 mm. A power source (not shown) is connected to the charging roll 2, and a desired potential is applied almost uniformly to the surface of the image carrier 1 by superimposing an AC component on a predetermined bias potential.

The image writing device 3 emits a laser beam according to an image signal and scans the laser beam in the main scanning direction of the image carrier by a polygon mirror, whereby an image is formed on the surface of the image carrier 1. An electrostatic latent image is formed according to the signal.

The above four developing devices 4a, 4b, 4c, 4
d is supported by a rotator 14 which is rotationally driven in the direction of arrow B, and is arranged so as to sequentially approach and face the image carrier 1, and transfers toner to a latent image corresponding to each color. To form a visible image (toner image). Each developing device contains a two-component developer in which toner of each color of black, yellow, magenta, and cyan and a magnetic carrier are adjusted to have a constant mixing ratio. As the toner, a spherical toner having a particle diameter of 3 to 7 μm is used, and is negatively charged by friction with the carrier. Further, fine particles having a particle size smaller than that of the toner are mixed in advance as an external additive in the developer, and are transferred to the image carrier together with the toner from the developing device and applied to the surface of the image carrier. As the external additive, SiO ₂ particles are used, and the same fine particles as the particles previously attached to the image carrier 1 are used as described later.

Further, each developing device 4 is provided with a non-magnetic hollow cylindrical developing sleeve 15, in which a 7-pole magnet roll fixed coaxially is arranged. Has been done. The developer is mixed and charged by a paddle 16 arranged adjacent to the developing sleeve 15 and is supplied to the peripheral surface of the developing sleeve 15, and the developer is leveled by a layer thickness regulating member (not shown). A developer layer having a predetermined thickness is formed on the developing sleeve 15. The developing sleeve 1
The outer diameter of 5 is 10 mm, the axial length thereof is 320 mm, and the distance between the developing sleeve 15 and the image carrier 1 is 0.5 m.
It is set to m. Further, the magnet roll in the developing sleeve 15 is arranged so that the portion facing the image carrier 1 is located between the poles, the toner layer thickness is thinner than 0.5 mm at the facing portion, and the toner acts on the developing electric field. It flies and is transferred onto the image carrier.

The intermediate transfer member 5 comprises a first transfer roll 6
Is pressed against the image carrier 1 from the back side by 100 mm in the direction of arrow C by a driving means (not shown).
It is driven by / s. On the outer surface of the intermediate transfer member 5, a second transfer roll 8 is press-contacted so as to be retractable at a position different from the position where it is in contact with the image carrier 1, and a support roll 13 is press-contacted on the opposite side. There is. The recording paper 7 is sequentially conveyed between the second transfer roll 8 and the intermediate transfer body 5 by a conveying unit (not shown).
The intermediate transfer member 5 is a PET substrate surface coated with PC (polycarbonate) and has a volume resistivity of 10 ^10.
It is Ω · cm.

The first transfer roll 6 has a shaft made of SUS coated with an elastic layer of urethane or the like in which carbon is dispersed to make it electrically conductive. The outer diameter of the first transfer roll 6 is 10 mm. The axial length is 320 mm. The first transfer roll 6 is connected to a power source (not shown) so as to be applied with a desired potential so that the toner image formed on the image carrier is transferred to the intermediate transfer body 5. It has become.

The second transfer roll 8 is composed of a conductive or semi-conductive roll-shaped member and records a multi-layered toner image formed on the intermediate transfer member 5 by applying a voltage from a power source (not shown). It can be collectively transferred onto the sheet 7.

Further, fine particles having a particle size smaller than that of the toner are previously attached to the surfaces of the image carrier 1 and the intermediate transfer member 5. The fine particles used in this example are SiO ₂ having an average primary particle diameter of 20 nm. As the SiO ₂ particles, those having a surface subjected to a hydrophobic treatment are used, and the volume resistivity is about 10 ¹⁴ Ω · cm. The fine particles are supplied to the surface of the image carrier 1 and the surface of the intermediate transfer member 5 through a mesh of 10 μm, and are dispersed and attached. The amount of the fine particles deposited is 0.0001 g / m ²
It is desirable to be in the range of 0.1 g / m ² . 0.0
This is because if it is 001 g / m ² or less, the effect of improving the transferability is small, while on the other hand, if the adhered amount is large, it interferes with the charging, exposing and developing processes.

Next, the process of forming a color image in the operation of the image forming apparatus having the above-mentioned structure will be described. The drum-shaped image carrier 1 is rotationally driven, and is approximately uniformly charged to about -650 V by the charging roll 2.
After that, it moves to a position facing the image writing device 3, and a laser beam for forming a latent image of the first color (black) according to the image signal is irradiated from above the fine particles on the surface of the image carrier. At this time, there is almost no light-shielding effect due to the fine particles used, the charge of the photoconductor layer of the image carrier is reduced by exposure, and a latent image is formed due to the difference in electrostatic potential.

At the same time, the black developing device 4a causes the image carrier 1 to move.
The latent image formed on the image bearing member is set to face the black developing device 4a. Then, the AC component is superposed between the image carrier 1 and -500.
By applying the bias voltage of V, the black toner is transferred onto the fine particles on the image carrier 1 so as to be superposed, and the latent image is visualized. The toner image 20a thus formed is
Transferred onto the intermediate transfer body 5 by the electric field created by the positive charges given to the intermediate transfer body 5 by the first transfer roll 6,
A black transferred image 20b is obtained. At this time, the toner adheres to the image carrier via the fine particles, and the non-electrical adhesive force such as the Van der Waals force between the toner and the image carrier becomes small. The toner is easily released from the image carrier by the electric field generated by the transfer roll 6.

The above is the cycle of the first color, and since the cleaning device is not provided in this image forming apparatus, the erase lamp 10 removes the charge while the fine particles are maintained on the surface of the image carrier 1. Enter the second color cycle. The basic formation process of the second color (yellow) is the same as that of the first color, but with respect to development, the rotary developing device 4 rotates 1/4 rotation and the yellow developing device 4b becomes the image carrier 1. Set to face each other. Then, the electrostatic latent image on the image carrier 1 is the developing device 4b for yellow.
A visible image is formed by the toner that is visualized by and is attached through the fine particles. Then, this toner image is transferred onto the intermediate transfer member 5 by the electric field created by the positive charges applied to the intermediate transfer member 5 by the first transfer roll 6, and a yellow transfer image is obtained. At this time, the intermediate transfer member 5 is moved by one turn to match the registration, and is controlled so that the transfer image of the first color and the transfer image of the second color overlap. The second transfer roll 8 is retracted to a position where it does not come into contact with the intermediate transfer body 5 while the intermediate transfer body 5 is moving around.

Thereafter, the transfer images of the third color (magenta) and the fourth color (cyan) are superposed on the intermediate transfer member 5 in the same procedure to obtain a full-color image. After that, the full-color image on the intermediate transfer body 5 is conveyed to a position facing the second transfer roll 8, and the recording paper 7 is sent by the electric field created by the positive charge applied to the recording paper 7 sent to the facing position.
It is collectively transferred onto the recording paper 7 and a full-color transfer image 20c is formed on the recording paper 7. At this time, since the adhesion of the full-color image on the intermediate transfer body 5 is reduced by the fine particles, the full-color image is easily detached from the intermediate transfer body 5 by the action of the transfer electric field. Finally, the recording paper 7 on which the full-color transfer image is formed passes through a position facing the fixing device 9, and the transfer image is melted on the recording paper by the heat applied there to obtain a fixed image, thus forming a full-color image. Ends.

In such an image forming process, the SiO ₂ particles applied to the image carrier 1 and the intermediate transfer member 5 circulate between the image carrier 1 and the intermediate transfer member 5 in the following route. . First, the fine particles on the image carrier 1 are negatively charged when passing through a position facing the charging roll 2. The amount of the above-mentioned fine particles, even if they are agglomerated to some extent, is not such an amount that the light is shielded in the next exposure step, so that the exposure is performed as usual. Next, at the position facing the developing device 4,
Developing sleeve 1 for the negatively charged fine particles in the non-image area
Although a bias is exerted by a force acting on the 5 side, the electric field is not so large as to cause the fine particles on the image carrier 1 to fly, as will be described later.

After that, at the position facing the first transfer roll 6, the negatively charged fine particles are transferred to the intermediate transfer member 5 together with the toner by the action of the transfer electric field. Immediately after this, it was revealed from the experiments by the present inventors that most of the fine particles were positively charged. The reason for this is considered to be discharge or charge injection in a minute gap between the image carrier 1 and the first transfer roll 6. Therefore, the fine particles transferred onto the intermediate transfer body 5 are hardly transferred to the recording paper 7 at the position facing the second transfer roll 8 and are returned to the position facing the first transfer roll 6 as they are. , Are transferred to the image carrier 1 by the action of the transfer electric field. At the same time, the negatively charged fine particles on the image carrier 1 are
It is transferred onto the intermediate transfer body 5 together with the toner by the action of the transfer electric field. In this way, the fine particles circulate between the image carrier 1 and the intermediate transfer member 5, so that the fine particles are always maintained on the surfaces of the image carrier 1 and the intermediate transfer member 5.

Actually, since a small amount of fine particles are transferred to the recording paper 7 at the position facing the second transfer roll 8, the amount of the fine particles as a whole decreases with the number of prints, but that amount is reduced. Fine particles of the same kind that are originally externally added to the toner are replenished by being transferred together with the toner onto the image carrier 1 during development.

Here, the conditions under which the SiO ₂ particles used in this example fly by the transfer electric field will be described in detail. According to the experiments conducted by the present inventors, SiO ₂ particles have a volume resistivity of 1 or less.
Since it is as high as 0 ¹⁴ Ω · cm, it is known that the electric force becomes dominant rather than the Van der Waals force, and the flight starts at an electric field of about 400 V / mm. For example, as shown in FIG. 2, the fine particles existing in the non-image area on the image carrier 1 are subjected to the action of the developing electric field at the position facing the developing sleeve 15. In the case of this example, this voltage is 650V. -500
V = 150V, and the image carrier 1 and the developing sleeve 1
Since the gap with 5 is 0.5 mm, the electric field strength is 300 V / mm. Therefore, most of the fine particles in this portion do not transfer to the developing sleeve 15 side.

On the other hand, the fine particles existing on the developing sleeve 15 together with the toner or separated from the toner exist in the image carrier 1 at the portion where the potential of the image portion exceeds -300V.
Will fly up. Because, as shown in FIG. 2, when the potential of the image portion is −300 V, the developing bias −5
The difference from 00V is 200V, and the electric field strength is 40
This is because it becomes 0 V / mm. As a result, the fine particles are always replenished on the image carrier 1. Further, the electric field is 400 at the transfer portion facing the first transfer roll 6.
It is much stronger than V / mm, so that the transition of fine particles almost certainly occurs.

Such behavior of the fine particles is realized when the volume resistivity of the fine particles is 10 ¹⁰ Ω · cm or more, and below that, the fine particles do not exhibit the above-mentioned charging characteristics. A mechanism for circulating fine particles between the image carrier 1 and the intermediate transfer member 5 is not established. In such a case, conversely, it is conceivable to retain fine particles on the image carrier 1 and the intermediate transfer member 5 to maintain a high transfer rate, but the volume resistivity is 10 ¹⁰ Ω · cm. When the following fine particles are used, there is a problem that image deletion occurs particularly in a high humidity environment. This is because the current easily flows through the fine particles and the charges on the image carrier laterally flow.

Due to the movement of the fine particles as described above, the fine particles always exist on the peripheral surfaces of the image carrier 1 and the intermediate transfer member 5. Further, in this example, since the spherical toner as shown in FIG. 3B is used, the surface of the image carrier 1 or the intermediate transfer member 5 is originally different from that of the irregular toner as shown in FIG. 3C. Although the contact area of the toner with respect to the toner is small, the adhesive force between the toner and the image bearing member is further reduced by the fine particles as shown in FIG. To be Therefore, even in the primary transfer by the first transfer roll 6,
Also in the secondary transfer by the second transfer roll 8, it is 99.8.
The transfer rate of 10% or more (approximately 100.0%) is maintained.

As a result, in the primary transfer, the residual toner is much lower than the level at which the negative ghost is generated, and even if the residual toner is hardly collected by the developing device, it is still lower than the level at which the positive ghost is generated. It can be suppressed. Furthermore, in the secondary transfer, the residual toner is not collected at all, but the residual toner amount is
It can be kept below the level at which positive ghosts occur. Therefore, both the image carrier 1 and the intermediate transfer member 5
It does not require a cleaning mechanism such as a cleaning blade. Therefore, the image carrier 1 and the intermediate transfer member 5 are not worn away, and the life is dramatically extended.

When a print test was carried out using the above-mentioned image forming apparatus, the obtained full-color image was good without defects such as ghost. Also,
Since the cleaner is not used, waste toner is not generated, and abrasion of the image carrier is prevented, so that a color image forming apparatus having a long life can be realized.

In the above example, hydrophobized SiO ₂ was used as the fine particles, but the present invention is not limited to this and any powder having a volume resistivity of 10 ¹⁰ Ω · cm or more can be used. Can be used. As examples of such fine particles, specifically, titanium oxide, alumina, barium titanate, calcium titanate, strontium titanate,
Inorganic fine powder such as zinc oxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride, chromium oxide and red iron oxide, polyacrylate, polymethacrylate, polymethylmethacrylate, polyethylene, polypropylene, polyfluoride Organic fine powders such as vinylidene chloride and polytetrafluoroethylene can be used. In consideration of environmental stability, it is desirable that these fine particles have low hygroscopicity, and in the case of inorganic fine powder having hygroscopicity such as titanium oxide, alumina and silica, those subjected to a hydrophobic treatment are used.
Hydrophobicizing treatment of these inorganic fine powders includes, for example, dialkyldihalogenated silane, trialkylhalogenated silane,
It can be carried out by reacting a silane coupling agent such as an alkyltrihalogenated silane or a hydrophobizing agent such as dimethyl silicone oil with the fine powder at a high temperature.

Further, since the fine particles used here form a latent image in a state where the fine particles are attached to the image carrier, it is not desirable that these fine particles have a light shielding effect. The allowable light-shielding effect of the fine particles depends on the required image quality, the amount of the fine particles attached, and the adhesion state, but it is preferable that the fine particles themselves have a low light-shielding effect as much as possible, and transparent or light-color fine particles are desirable. Considering that the light-shielding effect is particularly small in terms of image quality when used, it is desirable to use an acrylic fine powder such as polyacrylate, polymethacrylate, or polymethylmethacrylate having excellent transparency as the organic fine powder. Further, in the case of the inorganic fine powder, the above-mentioned silica is desirable because it has a low light shielding effect.

Further, in the present example, the method of preliminarily dispersing and applying the fine particles to the image bearing member and the intermediate transfer member is adopted, but the method of applying the fine particles is not limited to this.
For example, a method of applying fine particles to the surface of the image bearing member by a fine particle supply means containing the fine particles and the carrier instead of the toner in the same configuration as the developing device may be adopted. In addition, a roll-shaped, brush-shaped, felt-shaped, web-shaped, or brush-shaped member for rubbing the image carrier and the intermediate transfer member may be separately provided. As the roll, an elastic roll, a metal, or a roll formed of a material having high rigidity such as hard plastic can be used. However, the elastic roll is easier to use because the pressure at the rubbing nip and the nip width can be easily adjusted. Specifically as a brush-like thing, a magnetic brush using magnetism,
There is a fur brush. By applying an electric field in addition to such a mechanical attachment means, the attachment state of the fine particles can be further stabilized.

Further, although the spherical toner is used in this example, the toner is not limited to this, and the same applies when an irregular toner as shown in FIG. 3C produced by kneading and pulverization is used. Further, the effect of improving the transfer efficiency can be obtained. Further, although a belt-shaped member is used as the intermediate transfer member in the present example, the present invention is not limited to this, and an intermediate drum may be used, for example.

[0047]

As described above, in the image forming apparatus according to the present invention, the fine particles circulate between the peripheral surface of the image carrier and the peripheral surface of the intermediate transfer member, and the fine particles are laid on each peripheral surface. Since the particles are maintained substantially uniform, fine particles are present between the image carrier and the toner image carried on the image carrier and between the intermediate transfer member and the toner image, and the transfer efficiency of the toner image is significantly improved.
For this reason, the residual toner on the peripheral surface of the image carrier and the peripheral surface of the intermediate transfer member becomes extremely small, and negative ghosts and positive ghosts due to the residual toner are generated without cleaning the image carrier and the intermediate transfer member. Can be prevented. Therefore, it is not necessary to provide a cleaning mechanism on the image carrier and the intermediate transfer member, and the size and cost of the apparatus can be reduced. Further, generation of waste toner is prevented and abrasion of the image carrier and the intermediate transfer member is avoided, so that an image forming apparatus having a long life can be realized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a potential relationship between an electrostatic latent image on an image carrier and a developing bias in the image forming apparatus, and is a diagram illustrating an electric field to which fine particles are transferred.

FIG. 3 is a diagram showing a state in which toner adheres through fine particles on an image carrier or an intermediate transfer member in the image forming apparatus.

[Explanation of symbols]

1 Image carrier 2 charging roll 3 Image writing device 4 Developing device 5 Intermediate transfer body 6 First transfer roll 7 Recording paper 8 Second transfer roll 9 Fixing device 10 Eraser lamp 11, 12, 13 Support roll 14 rotating body 15 Development sleeve 16 paddles

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-166923 (JP, A) JP-A-6-175510 (JP, A) JP-A-2-109061 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G03G 15/16 G03G 15/01 114

Claims (3)

(57) [Claims] 1. An image carrier on which an electrostatic latent image is formed on a revolving peripheral surface due to a difference in charging potential, a charging device for charging the image carrier substantially uniformly, and a charging device for substantially uniform charging by the charging device. An image exposure device that irradiates an image carrier, which is charged on the surface, with image light to form an electrostatic latent image; a developing device that transfers toner to the electrostatic latent image on the image carrier to visualize it; And an intermediate transfer body to which a toner image on the image carrier is transferred, and a potential having a polarity opposite to the charging polarity of the toner are applied to the image carrier and the intermediate transfer body. A first transfer device for transferring an toner image on the image carrier to the intermediate transfer member by forming an electric field at a position where the toner image on the image carrier is contacted; and a second transfer device for transferring the toner image on the intermediate transfer member to a recording medium.
In the image forming apparatus including the transfer device, fine particles having a particle size smaller than that of the toner are substantially uniformly attached to the peripheral surface of the image carrier and the peripheral surface of the intermediate transfer body. The particle size and the resistivity are set so that the charging device charges the toner to the same polarity as the toner, the first transfer device transfers the toner to the intermediate transfer member, and the toner charges to the opposite polarity to the toner. An image forming apparatus characterized by. 2. The image forming apparatus according to claim 1, wherein the fine particles attached to the peripheral surface of the image carrier and the peripheral surface of the intermediate transfer member have a particle size of 100 nm or less and a resistivity of 10 nm. An image forming apparatus having a resistance of ¹⁰ Ω · cm or more. 3. The image forming apparatus according to claim 1, wherein the toner contained in the developing device has substantially the same particle size and resistivity as the fine particles adhered on the image carrier and the intermediate transfer member. An image forming apparatus comprising fine particles as an external additive, wherein the fine particles are transferred onto the image carrier together with the toner during development.