JP2008175841A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, wherein the stable image quality is obtained and the long service life thereof is achieved by preventing the sticking of transfer residual toner to a charging means, and further, the productivity is improved by reducing the discharge time of the transfer residual toner to a photoreceptor to the most. <P>SOLUTION: The image forming apparatus 100 is equipped with: a brush-shaped roller 40 which becomes in contact with a photoreceptor 1 at a position downstream of a transfer device 6 and upstream of an electrifying device 3, temporarily recovers part of transfer residual toner on the photoreceptor 1 after transfer, and discharges the recovered toner to the photoreceptor 1; an electrode 41 disposed opposite to the brush-shaped roller 40 at a position except a position where the photoreceptor 1 and the brush-shaped roller 40 are in contact with each other; voltage applying means 51, 52 which apply voltage to the brush-shaped roller 40 and the electrode 41 separately; and a light irradiation means 42 which irradiates the contact position between the brush-shaped roller 40 and the electrode 41, with light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for an electrophotographic process, such as a copying machine, a facsimile machine, and a printer. More specifically, the present invention relates to an image forming apparatus referred to as a so-called cleanerless system that does not have a cleaning device for discarding residual toner on an image carrier around the image carrier.

Conventionally, for the purpose of reducing the size of an image forming apparatus, a so-called cleaner-less structure in which transfer residual toner on an image carrier is temporarily collected by a collecting member that contacts the image carrier and then discharged onto the image carrier again. A system has been proposed.
For example, as in Patent Document 1, transfer residual toner having a reversely charged polarity is collected by a collecting member, and the transfer residual toner collected by providing a cleaning mode or the like at the timing of a non-image forming operation such as a job end is used as an image carrier. The method of returning to was taken. However, since the discharged toner passes through the charging unit with the reverse polarity, it may adhere to the charging unit, and the charging member is likely to become dirty, which causes a defective image due to a decrease in the charging potential of the photoreceptor. There was a problem that the replacement cycle of the means was shortened. Further, since it is necessary to return the transfer residual toner stored in the collecting member to the photosensitive member frequently, the user is forced to wait, which is not preferable from the viewpoint of productivity.

  Therefore, for example, as shown in Patent Document 2 and Patent Document 3, a cleanerless method has been proposed in which the charge amount of the transfer residual toner is normalized by injecting charge into the transfer residual toner using a charge control member. However, it is difficult to completely control the toner polarity, and a part of the transfer residual toner adheres to the charging member or is not discharged from the collecting member. This is because the electric charge is forcibly injected by directly applying an electric field to the normal toner, and the normal toner has a high resistance value and cannot easily be charged. Therefore, the current situation is that the applied voltage is increased to exceed the barrier resistance against implantation.

JP 2004-252203 A JP 2006-126469 A JP-A-2005-258323

  Accordingly, the present invention has been made in view of the above-mentioned problems, and its problem is to prevent the transfer residual toner from adhering to the charging means, to obtain a stable image quality and to extend the life of the apparatus. An object of the present invention is to provide an image forming apparatus capable of improving productivity by minimizing the discharge time of the untransferred toner to the photoreceptor.

The features of the present invention, which is a means for solving the above problems, are listed below.
The image forming apparatus of the present invention includes an image carrier that carries an electrostatic latent image, a charging unit that charges the surface of the image carrier, a latent image forming unit that forms a latent image on the image carrier, and an image carrier. In an image forming apparatus comprising at least a developing unit that attaches toner to a latent image and visualizes it as a toner image, and a transfer unit that transfers a toner image of an image carrier onto a recording material, Contacting the image carrier at a position upstream from the charging means, and temporarily recovering at least a part of the residual toner remaining on the image carrier after the transfer, and collecting the collected toner to the image carrier A rotating member that discharges to the body, an electrode that contacts and contacts the rotating member at a position other than a contact position between the image carrier and the rotating member, and a voltage applying unit that separately applies a voltage to the rotating member and the electrode. And contact between the rotating member and the electrode. Characterized in that a light irradiating means for irradiating light to the position.
In the image forming apparatus of the present invention, V0 is a surface potential after transfer of the image carrier, V1 is a voltage applied to the rotating member, and V2 is a voltage applied to the electrode. The polarity of V2 is the same as that of the developing bias applied to the developing means, and its absolute value is | V0 | <| V1 | <| V2 |.
Further, in the image forming apparatus of the present invention, the electrode is made of a transparent material that transmits light, and the light irradiation unit irradiates light from a back surface of the electrode to a contact position of the electrode and the rotating member. To do.
The image forming apparatus of the present invention is further characterized in that the light irradiation by the light irradiation means is controlled to be intermittently performed only when the transfer residual toner from the rotating member to the image carrier is discharged. To do.
The image forming apparatus according to the present invention is further characterized in that the light irradiation is performed in accordance with a timing of a sheet interval.
The image forming apparatus of the present invention is further characterized in that the rotating member is a brush roller.
The image forming apparatus of the present invention is further characterized in that the rotation direction of the rotating member is the opposite direction at the contact position between the image carrier and the rotating member.
The image forming apparatus of the present invention is further characterized in that the toner discharged from the rotating member to the image carrier is collected in the developing device by the developing means.
The image forming apparatus of the present invention is further characterized in that the toner used for image formation is in the range of 100 to 180 in terms of the shape factor SF-1 and in the range of 100 to 180 in terms of the shape factor SF-2. And
In the image forming apparatus of the present invention, the charging unit is a charging roller that contacts and rotates with the image carrier, and a voltage applied to the charging roller is a DC voltage.
Further, in the image forming apparatus of the present invention, the toner used for image formation is a toner containing a photoconductive material in which a charge injection phenomenon is caused by light irradiation and direct application of voltage, and the charge amount of the toner changes. It is characterized by being.

The image forming apparatus of the present invention further includes a bias switching unit that switches a voltage applied by the voltage applying unit.
The image forming apparatus of the present invention further applies the voltage V2 to the electrode so that V2−V1 ≧ 0, where V1 is a voltage applied to the rotating member and V2 is a voltage applied to the electrode. It is characterized by being.
The image forming apparatus of the present invention further includes a discharge mode for discharging the transfer residual toner held by the rotating member to the image carrier during non-image formation.
Further, the image forming apparatus of the present invention further applies to the rotating member when discharging the transfer residual toner from the rotating member to the image carrier when the post-transfer surface potential of the image carrier is V0. The voltage V1 to be applied and the voltage V2 to be applied to the electrodes are switched by the bias switching means so that V1-V0> 0 and V2-V1> 0, respectively, and light irradiation is simultaneously performed by the light irradiation means. To do.
Further, in the image forming apparatus of the present invention, the electrode is made of a transparent material that transmits light, and the light irradiation unit irradiates light from a back surface of the electrode to a contact position of the electrode and the rotating member. And

The image forming apparatus of the present invention is further characterized in that the rotating member is a brush roller.
Further, the image forming apparatus of the present invention is further characterized in that the rotation direction of the rotating member is the opposite direction at the contact position between the image carrier and the rotating member.
In the image forming apparatus of the present invention, the toner discharged from the rotating member to the image carrier in the discharge mode passes through the charging unit and the developing unit, is transferred by the transfer unit, and is transferred to the transfer unit. It is collected by the provided cleaning member.
The image forming apparatus of the present invention is further characterized in that the toner used for image formation is in the range of 100 to 180 in terms of the shape factor SF-1 and in the range of 100 to 180 in terms of the shape factor SF-2. And
In the image forming apparatus of the present invention, the charging unit is a charging roller that contacts and rotates with the image carrier, and a voltage applied to the charging roller is a DC voltage.
Further, in the image forming apparatus of the present invention, the toner used for image formation is a toner containing a photoconductive material in which a charge injection phenomenon is caused by light irradiation and direct application of voltage, and the charge amount of the toner changes. It is characterized by being.

  As described above, in the image forming apparatus of the present invention, the transfer residual toner temporarily held on the rotating member is irradiated with light while a voltage is applied between the electrode and the rotating member. The toner at that location is more easily injected due to a temporary decrease in resistance due to the photoconductivity of the toner. Therefore, the charging polarity can be efficiently changed from the reverse polarity to the normal polarity on the toner rotating member, and only the toner having the normal polarity returns to the photosensitive member. Therefore, there is no risk of reverse polarity toner entering the charging means, so that charging smear does not occur and a stable charging potential is always obtained, so that stable image formation is possible and contributes to a longer life of the apparatus. . Furthermore, since the transfer residual toner is made into a normal polarity and continuously discharged onto the photoconductor during the image forming process, there is no need to provide a cleaning mode, and productivity can be improved.

  Further, the transfer residual toner having the reverse polarity on the rotating member can have the charged polarity uniform to the reverse polarity, and can be efficiently returned to the photoreceptor following the electric field. Further, since the charging polarity is made uniform even when passing through the charging means and there are few weakly charged components, toner adhesion due to contact can be reduced, and charging contamination can be reduced as much as possible. Therefore, since a stable charging potential can be obtained at all times, stable image formation can be achieved, which contributes to extending the life of the apparatus. In addition, the process of collecting the transfer residual toner after being discharged is easy because of the good bias followability.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. Here, an embodiment applied to an electrophotographic image forming apparatus will be described. The image forming apparatus includes yellow (hereinafter referred to as “Y”), cyan (hereinafter referred to as “C”), magenta (hereinafter referred to as “M”), black (hereinafter referred to as “K”). The color image is formed from the four color toners. First, a basic configuration of the image forming apparatus will be described. This image forming apparatus includes four photosensitive members 1Y, 1C, 1M, and 1K as latent image carriers. Here, the drum-shaped photosensitive member 1 is taken as an example, but a belt-shaped photosensitive member can also be adopted. Each of the photoreceptors 1Y, 1C, 1M, and 1K is rotationally driven in the direction of the arrow in the drawing while being in contact with the intermediate transfer belt 10. Each of the photoreceptors 1Y, 1C, 1M, and 1K is rotationally driven in the direction of the arrow in the drawing while being in contact with the intermediate transfer belt 10. Each of the photoreceptors 1Y, 1C, 1M, and 1K is obtained by forming a photosensitive layer on a relatively thin cylindrical conductive substrate and further forming a protective layer on the photosensitive layer. An intermediate layer may be provided between the protective layer.

  FIG. 2 is a schematic view showing a configuration around the photoconductor. Since the configuration around each of the photoconductors 1Y, 1C, 1M, and 1K is the same, only one photoconductor 1 is illustrated, and reference numerals Y, C, M, and K for color coding are omitted. Around the photoreceptor 1, a temporary holding means 40 for temporarily holding toner, a charging device 3 as a charging means, and a developing device 5 as a developing means are arranged in this order along the surface moving direction. The temporary holding means 40 is provided with a partly transparent electrode 41 in contact therewith, and a light irradiation means 42 that can irradiate the transparent part with light is provided. The temporary holding means 40 includes a roller that contacts the surface of the photoreceptor 1. This roller is brought into contact with or rubbed with the photosensitive member 1 to contact the transfer residual toner on the photosensitive member 1. The roller can be an elastic roller or a brush roller, but the brush roller 40 is preferred. The brush-shaped one can increase the surface area and increase the recoverability of the transfer residual toner. For example, the brush-like roller 40 has a configuration in which brush fibers are planted around a metal base material. Here, conductive nylon fiber or the like was used, and the outer diameter of the brush was 10 mm. The density of the brush was set to 50000 (lines / inch ^ 2) to 150,000 (lines / inch ^ 2).

As a result, it is possible to simultaneously collect toner from the photoreceptor 1 and release toner to the photoreceptor 1. Further, a power source is connected to the metal base material, and a voltage can be applied. Assuming that this voltage is V1, by applying a negative polarity voltage, it is possible to collect the positive toner having the reverse polarity among the residual toner on the photosensitive member 1 to the brush roller 40. On the other hand, when a positive polarity voltage is applied, the positive toner on the brush roller 40 can be discharged onto the photoreceptor 1. Here, V1 was set to -500V. The brush roller 40 can be selected from styrene resin, acrylic resin, polyester resin, fluorine resin, polyamide resin, and the like. In particular, a polyamide resin that is resistant to wear and has high strength is preferable. In order to increase the effect of bias application, this brush may contain conductive powder. As the conductive powder, carbon black such as acetylene black and furnace black, graphite, or metal powder such as copper and silver can be used.
The brush-like roller 40 is rotatably installed and rotates in the opposite direction at the contact position between the photoreceptor 1 and the brush-like roller 40. As a result, the efficiency of collecting the toner on the photoconductor 1 can be increased, and a function of appropriately polishing the photoconductor 1 can be added, so that filming of the photoconductor 1 can be prevented.

Next, the electrode 41 member and the light irradiation means 42 will be described. The electrode 41 is made of a resin or rubber conductive member (mixed with a metal oxide such as tin oxide or an ionic conductive agent) that can transmit light, and an end portion is fixed to the unit by a holder (not shown), The brush-like roller 40 is in pressure contact with a force such as a spring or its own elastic force. In addition, a power source is connected to the electrode member, and a voltage V2 is applied. The untransferred toner held on the brush-like roller 40 is conveyed to the electrode 41 by the rotation of the brush-like roller 40 and passes through the pressure contact portion between the brush-like roller 40 and the electrode 41.
On the other hand, the light irradiation means 42 is installed at a position where light can be irradiated from the back side of the electrode 41 with respect to the pressure contact portion between the brush roller 40 and the electrode 41. The light irradiation means 42 is not particularly limited as long as it is a linear light emitting means, and for example, a light emitting device such as an LED, a fluorescent lamp, or electroluminescence can be used. The emission wavelength may be in the wavelength range of 400 nm to 800 nm, and preferably the light wavelength centered around about 700 nm.

  A space is secured between the charging device 3 and the developing device 5 so that light emitted from the exposure device 4 as a latent image forming unit can pass to the photosensitive member 1. The charging device 3 charges the surface of the photoreceptor 1 to a negative polarity. Here, the charging device 3 includes a charging roller 3a as a charging member that performs a charging process by a so-called contact charging method. The charging device 3 is charged by applying a DC voltage Vc and applying a charge to the surface of the photoconductor while the charging roller 3a having a medium resistance elastic layer is pressed against the surface of the photoconductor 1 and rotated. Do. In the present invention, the surface potential of the photoreceptor 1 is set to −500V. In the charging roller used here, two layers of a surface layer and an elastic layer are covered from the surface on the core metal, and the surface layer contains the constituent material of the elastic layer, and polar rubber such as epichlorohydrin And fluorinated non-adhesive resin. For example, the elastic layer is made of synthetic rubber with a thickness of 3 mm and an electric resistance of 10 6 to 10 Ω · cm, and the electric resistance ratio between the elastic layer and the surface layer should be 10 3 Ω · cm or less. Thus, DC current can be made to flow more easily and more uniform charging is possible. Accordingly, the cost of the power source can be reduced and an excessive charge application voltage is not applied, so that the generation of discharge products can be suppressed and the life of the photoreceptor 1 can be extended. The charging device 3 can be provided with a cleaning brush or the like for cleaning the surface of the charging roller 3a.

  An electrostatic latent image corresponding to each color is formed on the surface of the photoreceptor 1 charged in this manner by exposure by the exposure device 4. The exposure device 4 writes an electrostatic latent image corresponding to each color on the photoreceptor 1 based on image information corresponding to each color. The exposure apparatus 4 of the present embodiment is a laser type exposure apparatus, but other types of exposure apparatuses such as an exposure apparatus including an LED array and an image forming unit may be employed.

  In the developing device 5, a developing roller 5a as a developer carrying member is partially exposed from an opening of the casing. Here, a two-component developer composed of a toner and a carrier is used, but a one-component developer not containing a carrier may be used. The developing device 5 receives toner of the corresponding color from the toner bottles 31Y, 31C, 31M, and 31K shown in FIG. The toner bottles 31Y, 31C, 31M, and 31K are configured to be detachable from the main body of the image forming apparatus so that they can be replaced individually. With such a configuration, only the toner bottles 31Y, 31C, 31M, and 31K may be replaced at the time of toner end. Therefore, other components that have not yet reached the end of their life when the toner ends can be used as they are, and the user's expense can be reduced.

  The toner replenished into the developing device 5 from the toner bottles 31Y, 31C, 31M, and 31K is conveyed while being agitated with the carrier by the agitating and conveying screw 5b, and is carried on the developing roller 5a. The developing roller 5a is composed of a magnet roller as magnetic field generating means and a developing sleeve that rotates coaxially therearound. The carrier in the developer is transferred to the developing area facing the photosensitive member 1 in a state where it stands on the developing roller 5a by the magnetic force generated by the magnet roller. Here, the developing roller 5 a moves in the same direction at a linear velocity faster than the surface of the photosensitive member 1 in a region facing the photosensitive member 1 (hereinafter referred to as “developing region”). Then, the carrier spiked on the developing roller 5 a supplies the toner adhering to the carrier surface to the surface of the photoreceptor 1 while rubbing the surface of the photoreceptor 1. At this time, a developing bias VB of −300 V is applied to the developing roller 5a from a power source (not shown), whereby a developing electric field is formed in the developing region. Then, between the electrostatic latent image on the photoreceptor 1 and the developing roller 5a, an electrostatic force directed toward the electrostatic latent image side acts on the toner on the developing roller 5a. As a result, the toner on the developing roller 5 a adheres to the electrostatic latent image on the photoreceptor 1. By this adhesion, the electrostatic latent image on the photoreceptor 1 is developed into a corresponding color toner image. Further, here, the developing roller 5a is connected to a drive device via a clutch, and the rotation of the developing roller 5a can be temporarily stopped by the clutch.

  The intermediate transfer belt 10 in the transfer device 6 is stretched around three support rollers 11, 12, and 13 and is configured to endlessly move in the direction of the arrow in the drawing. On the intermediate transfer belt 10, toner images on the photoreceptors 1Y, 1C, 1M, and 1K are transferred so as to overlap each other by an electrostatic transfer method. Although there is a configuration using a transfer charger in the electrostatic transfer system, a configuration using a transfer roller that generates little transfer dust is adopted here. Specifically, primary transfer rollers 14Y, 14C, 14M, and 14K as transfer devices 6 are disposed on the back surface of the portion of the intermediate transfer belt 10 that contacts the photoreceptors 1Y, 1C, 1M, and 1K, respectively. Here, a primary transfer nip portion is formed by the portions of the intermediate transfer belt 10 pressed by the primary transfer rollers 14Y, 14C, 14M, and 14K and the photoreceptors 1Y, 1C, 1M, and 1K. When transferring the toner images on the photoreceptors 1Y, 1C, 1M, and 1K onto the intermediate transfer belt 10, a positive bias is applied to each primary transfer roller. As a result, a transfer electric field is formed in each primary transfer nip, and the toner images on the photoreceptors 1Y, 1C, 1M, and 1K are electrostatically attached to the intermediate transfer belt 10 and transferred.

A belt cleaning device 15 for removing toner remaining on the surface of the intermediate transfer belt 10 is provided around the intermediate transfer belt 10. The belt cleaning device 15 is configured to collect unnecessary toner adhering to the surface of the intermediate transfer belt 10 with a fur brush and a cleaning blade. The collected unnecessary toner is transported from the belt cleaning device 15 to a waste toner tank (not shown) by a transport means (not shown).
Further, a secondary transfer roller 16 is disposed in contact with the portion of the intermediate transfer belt 10 stretched around the support roller 13. A secondary transfer nip portion is formed between the intermediate transfer belt 10 and the secondary transfer roller 16, and transfer paper as a recording material is fed into this portion at a predetermined timing. This transfer paper is accommodated in a paper feed cassette 20 on the lower side of the exposure apparatus 4 in the drawing, and is conveyed to the secondary transfer nip portion by a paper feed roller 21, a registration roller pair 22, and the like. Then, the toner images superimposed on the intermediate transfer belt 10 are collectively transferred onto the transfer paper at the secondary transfer nip portion. At the time of the secondary transfer, a positive bias is applied to the secondary transfer roller 16, and the toner image on the intermediate transfer belt 10 is transferred onto the transfer paper by a transfer electric field formed thereby.

  A heat fixing device 23 as a fixing unit is disposed downstream of the secondary transfer nip portion in the transfer paper conveyance direction. The heat fixing device 23 includes a heating roller 23a with a built-in heater and a pressure roller 23b for applying pressure. The transfer paper that has passed through the secondary transfer nip is sandwiched between these rollers and receives heat and pressure. As a result, the toner on the transfer paper is melted and the toner image is fixed on the transfer paper. Then, the fixed transfer paper is discharged by a paper discharge roller 24 onto a paper discharge tray on the upper surface of the apparatus.

Next, a process for collecting and releasing the transfer residual toner will be described.
First, the untransferred toner remaining on the surface of the photoreceptor 1 will be described. Among the transfer residual toners, there are a normally charged toner T0 charged to a normal polarity and a reverse charged toner T1 charged to a polarity opposite to the normal polarity. FIG. 3 is a graph showing a toner charge amount distribution. FIG. 3A is a graph showing the toner charge amount distribution immediately before the transfer of the toner carried on the photoreceptor 1. FIG. 3B is a graph showing the toner charge amount distribution of the untransferred toner remaining on the photoreceptor 1 after the transfer. As shown in FIG. 3A, the charge amount of the toner immediately before the transfer is distributed around -30 (μC / g), and most of the charge toner T0 is normally charged to the negative polarity. It is. On the other hand, the charge amount of the transfer residual toner is distributed around about −2 (μC / g). Part of the untransferred toner has its toner charging polarity reversed to positive polarity due to discharge due to a potential difference between the positive polarity bias applied to the primary transfer roller 14 and the photoreceptor potential in the vicinity of the transfer region. As a result, the reverse transfer toner T1 that has been reversed to the positive polarity as indicated by the hatched portion in FIG.

When such a reversely charged toner T1 is conveyed to the charging region of the charging device 3 while adhering to the photoreceptor 1, it is electrostatically attracted to the surface of the charging roller 3a to which a negative charging bias is applied. It will stick. The same applies to the above-described configuration in which the charging roller 3a is disposed close to the surface of the photoreceptor 1. When the toner adheres to the surface of the charging roller 3a, the resistance value and the surface state of the charging roller 3a change, so that the charging start voltage with the surface of the photoreceptor 1 becomes uneven. Thus, even when the same charging bias as that when the reversely charged toner T1 is not attached is applied to the charging roller 3a, the surface of the photosensitive member 1 does not become uniform at a desired potential of −500 (V). As a result, image density unevenness may also occur. Further, when the toner adheres to a very small part of the surface of the charging roller 3a, the current due to the charging bias is concentrated toward the portion where the toner is not adhered. Thus, when the same charging bias as that in the case where toner is not applied is applied to the charging roller 3a, the charging potential on the surface of the photosensitive member 1 becomes higher than a desired potential. As a result, the potential of the portion exposed by the exposure device 4, that is, the electrostatic latent image portion is shifted to the negative polarity side, and the image density is lowered. Further, when the toner adheres to almost the entire surface of the charging roller 3a and the surface of the charging roller 3a is coated with the toner, the charging ability is reduced, and the surface potential of the photosensitive member 1 is higher than the desired potential. Go down. As a result, the potential of the portion that is not exposed by the exposure device 4, that is, the non-electrostatic latent image portion (white background portion) approaches the developing bias applied to the developing roller 5a. As a result, the toner that is not sufficiently charged adheres to the background portion on the photoreceptor 1, and an abnormal image such as background stain occurs.
On the other hand, among the transfer residual toner, there is a regular charged toner T0 that remains negative. Even if the regular charging toner T0 is conveyed to a position facing the charging roller 3a of the charging device 3, if the charging bias is applied, the regular charging toner T0 does not adhere to the surface of the charging roller 3a and reaches the developing region. As a result, most of the regular charged toner T0 attached to the carrier on the developing roller 5a of the developing device 5 is collected.

Next, the collection of the reversely charged toner T1 will be described in detail.
As shown in FIG. 2, the brush-like roller 40 is rotationally driven in the direction of the arrow by a driving device (not shown). As described above, a bias V1 is applied to the brush roller 40 from a power source. A power source is connected to the brush-like roller 40 before the surface portion of the photoreceptor 1 reaches an area where the surface of the photoreceptor 1 is in contact with the brush-like roller 40 (hereinafter referred to as “brush contact area”). As a result, a holding bias is applied to the brush roller 40. When the brush-like roller 40 to which such a holding bias is applied contacts the surface of the photoreceptor 1, among the transfer residual toner adhering to the surface, the reversely charged toner T 1 adheres to the brush-like roller 40 and is held. Will be. The collection of the reversely charged toner T1 is performed by setting each bias in the image forming mode as shown in FIG. FIG. 4 is a schematic diagram showing each bias in the image forming mode. The bias shown in FIG. 4 mainly indicates the direction of polarity, and the magnitude of the bias varies depending on the location.

  More specifically, the surface of the photoreceptor 1 is uniformly charged to −500 (V) by the charging device 3 and then exposed to the exposure device 4 so that the potential of the latent image portion is −50 (V). ) Then, after the developing process for attaching toner to the latent image portion and then the transfer step, the potential of the latent image portion further approaches 0 (V). This potential is set to V0. Most of the transfer residual toner adheres to the surface portion of the photoreceptor 1 which was the latent image portion. Therefore, the positively charged reversely charged toner T1 attached to the surface portion receives an electrostatic force toward the brush roller 40 to which the bias V1 of about −500 (V) is applied in the brush contact region. . On the other hand, the potential -500 (V) of the background portion other than the latent image portion is also shifted to 0 (V) side through the transfer process. Although the transfer residual toner may slightly adhere to the background portion, the electrostatic force directed toward the brush roller 40 in the brush contact area also acts on the positively charged toner T1 having positive polarity attached to the background portion. It will be. Therefore, of the transfer residual toner adhering to the surface of the photosensitive member 1, the reversely charged toner T1 adheres to and is held by the brush roller 40 in the brush contact area. Further, at this time, it is sufficient that a bias equivalent to or slightly larger than V1 is applied to the electrode 41 as the bias V2 so as to satisfy V2-V1 ≧ 0. Here, V2 = −300V. As a result, the transfer residual toner of reverse polarity does not adhere to the electrode 41, and the positive transfer residual toner of the photoreceptor 1 is collected while being held by the brush.

  Next, the reversely charged toner held on the brush roller 40 enters the nip region between the brush roller 40 and the electrode 41. At this time, a bias having the same polarity as V1 and a large absolute value is applied to the electrode 41. -800V is applied to V2. Therefore, a negative polarity bias is applied to the held reversely charged toner. Here, the light irradiating means 42 transmits the electrode 41 directly to the nip region between the brush-like roller 40 and the electrode 41 and directly irradiates the light, so that the photoconductive toner described later receives the light uniformly and the toner resistance. Since the value drops to a value sufficient to inject charge, charge injection is performed on the transfer residual toner with the negative polarity bias described above. As a result, the state (b) can be converted to the state (a) in the charge amount distribution of FIG. The electric field and the amount of light applied at this time are controlled by a controller (not shown), and the intensity can be controlled according to environmental conditions, the amount of residual toner, and the like. Further, a roller member may be used as the brush-like roller 40. In this case, since a thin layer of the transfer residual toner is formed, it becomes possible to perform charge injection by light irradiation and electric field more efficiently.

Next, a description will be given of a process of discharging the toner, which has been normally charged after the charge injection on the brush roller 40, to the photoreceptor 1. As described above, since the bias V1 that is a negative polarity bias is applied to the brush roller 40, when the normally charged toner reaches the brush contact area, it receives an electrostatic force in the direction of the photoreceptor 1. As a result, the normally charged toner is returned to the photoreceptor 1. When light is not irradiated by the light irradiation means 42 described above, charge is not injected into the transfer residual toner and the toner charge remains reversely charged. In this case, the toner is released in the brush contact area. Instead, it is held by the brush roller 40.
Thus, when the post-transfer surface potential on the photoreceptor 1 is V0, the voltage applied to the temporary holding member is V1, and the voltage applied to the electrode 41 is V2, the polarities of V0, V1, and V2 are negative. When the absolute value is | V0 | <| V1 | <| V2 |, the reversely charged toner of the transfer residual toner is collected on the temporary holding member, and in the nip region between the electrode 41 and the temporary holding member. The transfer residual toner is changed from reverse charging to normal charging by forming an electric field and irradiating light, and then the normal charging toner is temporarily returned from the temporary holding member to the photosensitive member 1 and a series of transfer residual toner collection and release processes are switched by bias. Without having to do so.

  Next, the release control of the transfer residual toner from the temporary holding member by light irradiation will be described. As described above, a bias is always applied to the temporary holding member and the electrode 41, and a transfer residual toner having a reverse polarity between the temporary holding member and the electrode 41 is injected into a normal charge only during light irradiation. Therefore, it is desirable that the timing of the light irradiation be performed so that the toner corresponding to the non-image portion is discharged so that the toner discharged to the photosensitive member 1 does not reach the next image forming portion. In other words, if the amount of transfer residual toner released to the photoconductor 1 is large, there is a concern that the surface potential of the photoconductor 1 is lowered in charging at that portion, and that the exposed portion of the exposed image is hidden in the exposed portion. Arise. Although they do not cause problems such as toner contamination in the machine, the intermediate potential of the photoconductor 1 is frequently used in images using halftone such as pictorial images, so that the above-mentioned minute potential difference causes image density unevenness. May appear. Therefore, these problems can be avoided by setting the discharge timing of the transfer residual toner before and after the image forming area which is a non-image portion, particularly at the end of the job. In consideration of the productivity at the time of continuous image output, light is irradiated in accordance with the interval between the sheets of the image (called the interval between the sheets), and the transfer residual toner is discharged to the non-image portion of the photoreceptor 1 little by little. It is possible to provide a cleaner-less system with high productivity without impairing the process. Even when the linear velocity of the photosensitive member is increased, the toner discharge timing is performed by switching light irradiation with quick response, so that no problem occurs. This is not possible because, for example, bias switching is slow because the polarity switching response of the power supply is slow, which is a great merit of using light.

Next, recovery of transfer residual toner after passing through the temporary holding member will be described.
As described above, the normally charged toner of the transfer residual toner passes through the temporary holding member and the charging unit. Also, the reversely charged toner of the transfer residual toner is held by the temporary holding member, is normally charged by light irradiation at the electrode 41 portion, is returned to the photoreceptor 1, and similarly passes through the charging means. Thereafter, the transfer residual toner is collected in the developing unit. As the developing device, it is preferable to use a two-component development consisting of a carrier and a toner as a developer. The positively charged transfer residual toner adheres to the positively charged carrier and is collected in the developing device. Further, the toner on the photoconductor 1 is easily recovered mechanically by rubbing the photoconductor 1 with the magnetic brush in the developing region. On the other hand, a one-component developing device composed only of toner may be used as the developing device. In this case, there is an advantage of downsizing and cost reduction, and the transfer residual toner that is normally charged by the contact pressure and electric field between the photosensitive member 1 and the developing roller is collected in the developing device. In this way, the transfer residual toner is collected by the developing device and reused for development, so that it is not necessary to provide a waste toner tank for storing the toner collected by cleaning from the photoconductor 11, and an image forming apparatus, etc. Miniaturization can be achieved. In particular, in a tandem color image forming apparatus in which four photoconductors 1 are arranged in parallel, the size can be greatly reduced as compared with the case where individual waste toner tanks are provided for each photoconductor 1. Furthermore, the cost can be reduced by toner recycling, and the running cost can be reduced for the user.

  Next, the operation of discharging the reversely charged toner held on the brush roller 40 will be described. The discharge of the reversely charged toner is performed by setting each bias in the discharge mode at a timing other than the image formation as shown in FIG. FIG. 5 is a schematic diagram showing each bias in the discharge mode. The bias shown in FIG. 5 mainly indicates the direction of polarity, and the magnitude of the bias varies depending on the location. First, switching of each bias will be described. The brush-like roller 40V1 'is set so that a bias having a polarity opposite to that of V1 at the time of image formation is applied and V1'-V0> 0. As a result, positive transfer residual toner on the temporary holding member is discharged onto the photoreceptor 1. Here, V1 'was set to + 300V. On the other hand, the bias V2 'applied to the electrode 41 is applied with a positive polarity bias so that V2'-V1'> 0. The reversely charged toner enters the nip region between the brush roller 40 and the electrode 41 to which the electric field is applied. Further, the light irradiating means 42 described above transmits the electrode 41 directly to the nip region between the brush-like roller 40 and the electrode 41 to directly irradiate the light, so that the photoconductive toner described later receives the light uniformly and the toner. Since the resistance value is lowered to a value sufficient to inject electric charge, electric charge is injected into the untransferred toner with the above-described positive polarity bias. As a result, in the charge amount distribution of FIG. 6, the state (b) can be converted to the state (c). The electric field and the amount of light applied at this time are controlled by a controller (not shown), and the intensity can be controlled according to environmental conditions, the amount of residual toner, and the like. Further, a roller member may be used as the brush-like roller 40. In this case, since a thin layer of the transfer residual toner is formed, it becomes possible to perform charge injection by light irradiation and electric field more efficiently. Here, V2 'is set to + 600V. At this time, a process of discharging the toner, which has been positively charged after the charge injection on the brush-like roller 40, to the photoreceptor 1 will be described. As described above, since the bias V1 'that is a positive polarity bias is applied to the brush roller 40, when the reversely charged toner reaches the brush contact area, it receives an electrostatic force in the direction of the photoreceptor. As a result, the reversely charged toner is returned to the photoreceptor 1. Further, the reversely charged toner returned from the brush to the photoreceptor 1 first passes through the charging portion. At this time, since the bias applied to the charging unit is switched to 0 as shown in FIG. 5, the reversely charged toner is not attracted to the charging member by the electric field, and passes as it is. In addition, since there is no weak reverse polarity toner, there is little possibility of adhesion to the charged part by contact. Next, the reverse polarity toner that has passed through the charging portion passes through the developing portion. At this time, since the bias applied to the developing roller is switched to the positive polarity as shown in FIG. 5, the reverse polarity toner passes without returning to the developing device. For this reason, there is no possibility of color mixing or toner scattering due to poorly charged toner. Next, the reverse polarity toner that has passed through the developing unit enters the transfer unit. Here, as shown in FIG. 5, the transfer bias is set to a polarity opposite to that at the time of normal image formation. Reverse polarity toner is transferred to the material. Thereafter, the reverse polarity toner is collected by a cleaning member installed downstream of the intermediate transfer belt.

  The discharge mode, which is a process for discharging the reverse polarity toner in the temporary holding member to the photosensitive member 1, is produced by, for example, the non-image formation before the image forming job or after the image forming job. The transfer residual toner can be discharged without impairing the properties. In particular, since the discharge efficiency of the reverse polarity toner from the temporary holding member is increased by the charge injection by light irradiation, the discharge can be performed in a short time. Further, during continuous paper feeding, a discharge mode may be provided for every predetermined number of sheets. For example, the discharge mode for 10 seconds may be operated for 100 consecutive image outputs. If a certain number of continuous output sheets can be secured, there will be little impact on productivity.

The toner suitably used in the image forming apparatus of the present invention includes a toner material liquid in which at least a polyester prepolymer having a functional group containing a nitrogen atom, a polyester, a colorant, and a release agent are dispersed in an organic solvent. A toner obtained by crosslinking and / or elongation reaction in an aqueous solvent. Hereinafter, the constituent material and the manufacturing method of the toner will be described.
The polyester is obtained by a polycondensation reaction between a polyhydric alcohol compound and a polycarboxylic acid compound.
Examples of the polyhydric alcohol compound (PO) include dihydric alcohol (DIO) and trihydric or higher polyhydric alcohol (TO). (DIO) alone or a mixture of (DIO) and a small amount of (TO) preferable. Examples of the dihydric alcohol (DIO) include alkylene glycol (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, etc.); alkylene ether glycol (diethylene glycol) , Triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, etc.); alicyclic diols (1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.); bisphenols (bisphenol A, bisphenol) F, bisphenol S, etc.); alkylene oxide (ethylene oxide, propylene oxide, butylene oxide, etc.) adduct of the above alicyclic diol; Alkylene oxide bisphenol (ethylene oxide, propylene oxide, butylene oxide, etc.), etc. adducts. Among them, preferred are alkylene glycols having 2 to 12 carbon atoms and alkylene oxide adducts of bisphenols, and particularly preferred are alkylene oxide adducts of bisphenols and alkylene glycols having 2 to 12 carbon atoms. It is a combined use. The trihydric or higher polyhydric alcohol (TO) includes 3 to 8 or higher polyhydric aliphatic alcohols (glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitol, etc.); trihydric or higher phenols (Trisphenol PA, phenol novolak, cresol novolak, etc.); and alkylene oxide adducts of the above trivalent or higher polyphenols.

Examples of the polyvalent carboxylic acid (PC) include divalent carboxylic acid (DIC) and trivalent or higher polyvalent carboxylic acid (TC). (DIC) alone and (DIC) with a small amount of (TC) Mixtures are preferred. Divalent carboxylic acids (DIC) include alkylene dicarboxylic acids (succinic acid, adipic acid, sebacic acid, etc.); alkenylene dicarboxylic acids (maleic acid, fumaric acid, etc.); aromatic dicarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid) And naphthalenedicarboxylic acid). Of these, preferred are alkenylene dicarboxylic acids having 4 to 20 carbon atoms and aromatic dicarboxylic acids having 8 to 20 carbon atoms. Examples of the trivalent or higher polyvalent carboxylic acid (TC) include aromatic polycarboxylic acids having 9 to 20 carbon atoms (such as trimellitic acid and pyromellitic acid). In addition, as polyhydric carboxylic acid (PC), you may make it react with polyhydric alcohol (PO) using the above-mentioned acid anhydride or lower alkyl ester (Methyl ester, ethyl ester, isopropyl ester, etc.).

The ratio of the polyhydric alcohol (PO) to the polycarboxylic acid (PC) is usually 2/1 to 1/1, preferably as the equivalent ratio [OH] / [COOH] of the hydroxyl group [OH] and the carboxyl group [COOH]. Is 1.5 / 1 to 1/1, more preferably 1.3 / 1 to 1.02 / 1.
The polycondensation reaction between a polyhydric alcohol (PO) and a polycarboxylic acid (PC) is carried out in the presence of a known esterification catalyst such as tetrabutoxytitanate or dibutyltin oxide, and heated to 150 to 280 ° C. while reducing the pressure as necessary. The produced water is distilled off to obtain a polyester having a hydroxyl group. The hydroxyl value of the polyester is preferably 5 or more, and the acid value of the polyester is usually 1 to 30, preferably 5 to 20. By giving an acid value, it tends to be negatively charged, and furthermore, when fixing to a recording paper, the affinity between the recording paper and the toner is good and the low-temperature fixability is improved. However, when the acid value exceeds 30, there is a tendency to deteriorate with respect to the stability of charging, particularly environmental fluctuation.
The weight average molecular weight is 10,000 to 400,000, preferably 20,000 to 200,000. A weight average molecular weight of less than 10,000 is not preferable because offset resistance deteriorates. On the other hand, if it exceeds 400,000, the low-temperature fixability is deteriorated.

In addition to the unmodified polyester obtained by the above polycondensation reaction, the polyester preferably contains a urea-modified polyester. The urea-modified polyester is obtained by reacting a terminal carboxyl group or hydroxyl group of the polyester obtained by the above polycondensation reaction with a polyvalent isocyanate compound (PIC) to obtain a polyester prepolymer (A) having an isocyanate group. It is obtained by cross-linking and / or extending the molecular chain by the reaction of the amine with amines. Examples of the polyvalent isocyanate compound (PIC) include aliphatic polyisocyanates (tetramethylene diisocyanate, hexamethylene diisocyanate, 2,6-diisocyanatomethylcaproate, etc.); alicyclic polyisocyanates (isophorone diisocyanate, cyclohexylmethane diisocyanate, etc.) Aromatic diisocyanates (tolylene diisocyanate, diphenylmethane diisocyanate, etc.); araliphatic diisocyanates (α, α, α ′, α′-tetramethylxylylene diisocyanate, etc.); isocyanates; Those blocked with caprolactam or the like; and combinations of two or more of these.
The ratio of the polyvalent isocyanate compound (PIC) is usually 5/1 to 1/1, preferably as an equivalent ratio [NCO] / [OH] of the isocyanate group [NCO] and the hydroxyl group [OH] of the polyester having a hydroxyl group. 4/1 to 1.2 / 1, more preferably 2.5 / 1 to 1.5 / 1. When [NCO] / [OH] exceeds 5, low-temperature fixability deteriorates. When the molar ratio of [NCO] is less than 1, when a urea-modified polyester is used, the urea content in the ester is lowered and hot offset resistance is deteriorated.
The content of the polyvalent isocyanate compound (PIC) component in the polyester prepolymer (A) having an isocyanate group is usually 0.5 to 40 wt%, preferably 1 to 30 wt%, more preferably 2 to 20 wt%. . If it is less than 0.5 wt%, the hot offset resistance deteriorates, and it is disadvantageous in terms of both heat-resistant storage stability and low-temperature fixability. On the other hand, if it exceeds 40 wt%, the low-temperature fixability deteriorates.
The number of isocyanate groups contained per molecule in the polyester prepolymer (A) having an isocyanate group is usually 1 or more, preferably 1.5 to 3 on average, more preferably 1.8 to 2 on average. Five. If it is less than 1 per molecule, the molecular weight of the urea-modified polyester will be low, and the hot offset resistance will deteriorate.

Next, as amines (B) to be reacted with the polyester prepolymer (A), a divalent amine compound (B1), a trivalent or higher polyvalent amine compound (B2), an amino alcohol (B3), an amino mercaptan (B4) ), Amino acid (B5), and amino acid block of B1 to B5 (B6).
Examples of the divalent amine compound (B1) include aromatic diamines (phenylenediamine, diethyltoluenediamine, 4,4′-diaminodiphenylmethane, etc.); alicyclic diamines (4,4′-diamino-3,3′-dimethyldicyclohexyl). Methane, diamine cyclohexane, isophorone diamine, etc.); and aliphatic diamines (ethylene diamine, tetramethylene diamine, hexamethylene diamine, etc.) and the like. Examples of the trivalent or higher polyvalent amine compound (B2) include diethylenetriamine and triethylenetetramine. Examples of amino alcohol (B3) include ethanolamine and hydroxyethylaniline. Examples of amino mercaptan (B4) include aminoethyl mercaptan and aminopropyl mercaptan. Examples of the amino acid (B5) include aminopropionic acid and aminocaproic acid. Examples of the compound (B6) obtained by blocking the amino group of B1 to B5 include ketimine compounds and oxazolidine compounds obtained from the amines of B1 to B5 and ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.). Among these amines (B), preferred are B1 and a mixture of B1 and a small amount of B2.

The ratio of amines (B) is equivalent to the equivalent ratio [NCO] / [NHx] of isocyanate groups [NCO] in the polyester prepolymer (A) having isocyanate groups and amino groups [NHx] in amines (B). Is usually 1/2 to 2/1, preferably 1.5 / 1 to 1 / 1.5, more preferably 1.2 / 1 to 1 / 1.2. When [NCO] / [NHx] is more than 2 or less than 1/2, the molecular weight of the urea-modified polyester is lowered, and the hot offset resistance is deteriorated.
The urea-modified polyester may contain a urethane bond together with a urea bond. The molar ratio of the urea bond content to the urethane bond content is usually 100/0 to 10/90, preferably 80/20 to 20/80, and more preferably 60/40 to 30/70. When the molar ratio of the urea bond is less than 10%, the hot offset resistance is deteriorated.
The urea-modified polyester is produced by a one-shot method or the like. Polyhydric alcohol (PO) and polyvalent carboxylic acid (PC) are heated to 150-280 ° C. in the presence of a known esterification catalyst such as tetrabutoxytitanate, dibutyltin oxide, etc., and water generated while reducing the pressure as necessary. Distill off to obtain a polyester having a hydroxyl group. Subsequently, at 40-140 degreeC, this is made to react with polyvalent isocyanate (PIC), and the polyester prepolymer (A) which has an isocyanate group is obtained. Further, this (A) is reacted with amines (B) at 0 to 140 ° C. to obtain a urea-modified polyester.
When reacting (PIC) and when reacting (A) and (B), a solvent may be used if necessary. Usable solvents include aromatic solvents (toluene, xylene, etc.); ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.); esters (ethyl acetate, etc.); amides (dimethylformamide, dimethylacetamide, etc.) and ethers And those inert to isocyanates (PIC), such as tetrahydrofuran (such as tetrahydrofuran).
In addition, in the crosslinking and / or extension reaction between the polyester prepolymer (A) and the amines (B), a reaction terminator can be used as necessary to adjust the molecular weight of the resulting urea-modified polyester. Examples of the reaction terminator include monoamines (diethylamine, dibutylamine, butylamine, laurylamine, etc.), and those obtained by blocking them (ketimine compounds).

  The weight average molecular weight of the urea-modified polyester is usually 10,000 or more, preferably 20,000 to 10,000,000, and more preferably 30,000 to 1,000,000. If it is less than 10,000, the hot offset resistance deteriorates. The number average molecular weight of the urea-modified polyester or the like is not particularly limited when the above-mentioned unmodified polyester is used, and may be a number average molecular weight that can be easily obtained to obtain the weight average molecular weight. When the urea-modified polyester is used alone, its number average molecular weight is usually 2000-15000, preferably 2000-10000, more preferably 2000-8000. When it exceeds 20000, the low-temperature fixability and the glossiness when used in a full-color apparatus are deteriorated.

By using the unmodified polyester and the urea-modified polyester in combination, the low-temperature fixability and the gloss when used in the full-color image forming apparatus 100 are improved. Therefore, it is preferable to use the urea-modified polyester alone. The unmodified polyester may include a polyester modified with a chemical bond other than a urea bond.
The unmodified polyester and the urea-modified polyester are preferably at least partially compatible with each other in terms of low-temperature fixability and hot offset resistance. Therefore, it is preferable that the unmodified polyester and the urea-modified polyester have a similar composition.
The weight ratio of unmodified polyester to urea-modified polyester is usually 20/80 to 95/5, preferably 70/30 to 95/5, more preferably 75/25 to 95/5, and particularly preferably 80 /. 20-93 / 7. When the weight ratio of the urea-modified polyester is less than 5%, the hot offset resistance is deteriorated, and it is disadvantageous in terms of both heat-resistant storage stability and low-temperature fixability.
The glass transition point (Tg) of the binder resin containing unmodified polyester and urea-modified polyester is usually 45 to 65 ° C, preferably 45 to 60 ° C. If it is less than 45 ° C., the heat resistance of the toner deteriorates, and if it exceeds 65 ° C., the low-temperature fixability becomes insufficient.
In addition, since the urea-modified polyester is likely to be present on the surface of the obtained toner base particles, the heat-resistant storage stability tends to be good even when the glass transition point is low as compared with known polyester-based toners.

As the colorant, all known dyes and pigments can be used. For example, carbon black, nigrosine dye, iron black, naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, ocher , Yellow lead, titanium yellow, polyazo yellow, oil yellow, Hansa yellow (GR, A, RN, R), pigment yellow L, benzidine yellow (G, GR), permanent yellow (NCG), Vulcan fast yellow (5G, R), Tartrazine Lake, Quinoline Yellow Lake, Anthrazan Yellow BGL, Isoindolinone Yellow, Bengala, Red Dan, Lead Zhu, Cadmium Red, Cadmium Mercury Red, Antimon Zhu, Permanent Red 4R, Para Red, Phi Sared,
Parachlor ortho nitroaniline red, Resol Fast Scarlet G, Brilliant Fast Scarlet, Brilliant Carmine BS, Permanent Red (F2R, F4R, FRL, FRLL, F4RH), Fast Scarlet VD, Belkan Fast Rubin B, Brilliant Scarlet G, Resol Rubin GX Permanent Red F5R, Brilliant Carmine 6B, Pigment Scarlet 3B, Bordeaux 5B, Tolujing Maroon, Permanent Bordeaux F2K, Helio Bordeaux BL, Bordeaux 10B, Bon Maroon Light, Bon Maroon Medium, Eosin Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarin Lake, Thioindigo Red B, Thioindigo Maroon, Oil Red, Quinacridone , Pyrazolone red, polyazo red, chrome vermilion, benzidine orange, perinone orange, oil orange, cobalt blue, cerulean blue, alkali blue rake, peacock blue rake, Victoria blue rake, metal-free phthalocyanine blue, phthalocyanine blue, fast sky blue, Indanthrene blue (RS, BC), indigo, ultramarine, bitumen, anthraquinone blue, fast violet B, methyl violet lake, cobalt violet, manganese purple, dioxane violet, anthraquinone violet, chrome green, zinc green, chromium oxide, pyridian, Emerald Green, Pigment Green B, Naphthol Green B, Green Gold, Acid Green Lake, Maracay Green lake, phthalocyanine green, anthraquinone green, titanium oxide, zinc white, lithopone and mixtures thereof can be used. The content of the colorant is usually 1 to 15% by weight, preferably 3 to 10% by weight, based on the toner.

  The colorant can also be used as a master batch combined with a resin. As a binder resin to be kneaded together with the production of the master batch or the master batch, a polymer of styrene such as polystyrene, poly-p-chlorostyrene, polyvinyl toluene or the like, or a copolymer of these and a vinyl compound, Polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, epoxy resin, epoxy polyol resin, polyurethane, polyamide, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, fat Aromatic or alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffins, paraffin waxes and the like can be mentioned, and these can be used alone or in combination.

Known charge control agents can be used, such as nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxy amines, quaternary ammonium salts (fluorine-modified 4 Secondary ammonium salts or compounds, tungsten simple substances or compounds, fluorine activators, salicylic acid metal salts, and metal salts of salicylic acid derivatives. Specifically, Bontron 03 of a nigrosine dye, Bontron P-51 of a quaternary ammonium salt, Bontron S-34 of a metal-containing azo dye, E-82 of an oxynaphthoic acid metal complex, E-84 of a salicylic acid metal complex , Phenolic condensate E-89 (above, Orient Chemical Industries, Ltd.), quaternary ammonium salt molybdenum complex TP-302, TP-415 (above, Hodogaya Chemical Co., Ltd.), quaternary ammonium salt copy Charge PSY VP2038, copy blue PR of triphenylmethane derivative, copy charge of quaternary ammonium salt NEG VP2036, copy charge NX VP434 (manufactured by Hoechst), LRA-901, LR-147 which is a boron complex (Nippon Carlit) Manufactured), copper phthalocyanine, perylene, quinacridone, azo series Fee, a sulfonic acid group, a carboxyl group, and polymer compounds having a functional group such as quaternary ammonium salts. Of these, substances that control the negative polarity of the toner are particularly preferably used.
The amount of charge control agent used is determined by the type of binder resin, the presence or absence of additives used as necessary, and the toner production method including the dispersion method, and is not uniquely limited. Preferably, it is used in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin. The range of 0.2 to 5 parts by weight is preferable. When the amount exceeds 10 parts by weight, the chargeability of the toner is too high, the effect of the charge control agent is reduced, the electrostatic attraction with the developing roller is increased, the developer fluidity is lowered, and the image density is lowered. Invite.

As a release agent, a low melting point wax having a melting point of 50 to 120 ° C. works more effectively as a release agent in the dispersion with the binder resin between the fixing roller and the toner interface. The effect on high temperature offset is exhibited without applying a release agent such as oil. Examples of such a wax component include the following. Examples of waxes and waxes include plant waxes such as carnauba wax, cotton wax, wood wax, and rice wax, animal waxes such as beeswax and lanolin, mineral waxes such as ozokerite and cercin, and paraffin, microcrystalline, And petroleum waxes such as petrolatum. In addition to these natural waxes, synthetic hydrocarbon waxes such as Fischer-Tropsch wax and polyethylene wax, and synthetic waxes such as esters, ketones, and ethers can be used. Furthermore, fatty acid amides such as 12-hydroxystearic acid amide, stearic acid amide, phthalic anhydride imide, chlorinated hydrocarbon, and low molecular weight crystalline polymer resin, poly-n-stearyl methacrylate, poly-n- A crystalline polymer having a long alkyl group in the side chain such as a homopolymer or copolymer of polyacrylate such as lauryl methacrylate (for example, a copolymer of n-stearyl acrylate-ethyl methacrylate, etc.) can also be used. .
The charge control agent and the release agent can be melt-kneaded together with the master batch and the binder resin, and of course, they may be added when dissolved and dispersed in the organic solvent.

Inorganic fine particles are preferably used as an external additive for assisting the fluidity, developability and chargeability of the toner particles. The primary particle diameter of the inorganic fine particles is preferably 5 × ^{10- 3 to 2} [mu] m, it is particularly preferably 5 × ¹⁰ -3 ~0.5μm. Moreover, it is preferable that the specific surface area by BET method is 20-500 m < ² > / g. The use ratio of the inorganic fine particles is preferably 0.01 to 5 wt% of the toner, and particularly preferably 0.01 to 2.0 wt%.
Specific examples of the inorganic fine particles include, for example, silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, tin oxide, quartz sand, clay, mica, wollastonite, diatomaceous earth. Examples include soil, chromium oxide, cerium oxide, bengara, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, and silicon nitride. Among these, as the fluidity imparting agent, it is preferable to use hydrophobic silica fine particles and hydrophobic titanium oxide fine particles in combination. In particular, when stirring and mixing are performed using particles having an average particle diameter of 5 × 10 ⁻² μm or less, the electrostatic force and van der Waals force with the toner are remarkably improved. Even when stirring and mixing inside the developing device is performed to obtain a good image quality that does not cause the release of the fluidity imparting agent from the toner and does not generate firefly, etc., and further reduces the residual toner. It is done.
Titanium oxide fine particles are excellent in environmental stability and image density stability, but have a tendency to deteriorate the charge rise characteristics. Therefore, if the amount of titanium oxide fine particles added is larger than the amount of silica fine particles added, this side effect is affected. It can be considered large. However, when the added amount of the hydrophobic silica fine particles and the hydrophobic titanium oxide fine particles is in the range of 0.3 to 1.5 wt%, the charge rising characteristics are not greatly impaired, and the desired charge rising characteristics can be obtained, that is, repeated copying. Stable image quality can be obtained even if

Next, a toner manufacturing method will be described. Here, although a preferable manufacturing method is shown, it is not limited to this.
1) A toner material solution is prepared by dispersing a colorant, unmodified polyester, a polyester prepolymer having an isocyanate group, and a release agent in an organic solvent.
The organic solvent is preferably volatile with a boiling point of less than 100 ° C. from the viewpoint of easy removal after toner base particle formation. Specifically, toluene, xylene, benzene, carbon tetrachloride, methylene chloride, 1,2-dichloroethane, 1,1,2-trichloroethane, trichloroethylene, chloroform, monochlorobenzene, dichloroethylidene, methyl acetate, ethyl acetate, methyl ethyl ketone, Methyl isobutyl ketone and the like can be used alone or in combination of two or more. In particular, aromatic solvents such as toluene and xylene and halogenated hydrocarbons such as methylene chloride, 1,2-dichloroethane, chloroform, and carbon tetrachloride are preferable. The usage-amount of an organic solvent is 0-300 weight part normally with respect to 100 weight part of polyester prepolymers, Preferably it is 0-100 weight part, More preferably, it is 25-70 weight part.

2) The toner material liquid is emulsified in an aqueous medium in the presence of a surfactant and resin fine particles.
The aqueous medium may be water alone, or an organic solvent such as alcohol (methanol, isopropyl alcohol, ethylene glycol, etc.), dimethylformamide, tetrahydrofuran, cellosolves (methylcellosolve, etc.), lower ketones (acetone, methyl ethyl ketone, etc.). It may be included.
The amount of the aqueous medium used relative to 100 parts by weight of the toner material liquid is usually 50 to 2000 parts by weight, preferably 100 to 1000 parts by weight. If the amount is less than 50 parts by weight, the dispersion state of the toner material liquid is poor, and toner particles having a predetermined particle diameter cannot be obtained. If it exceeds 20000 parts by weight, it is not economical.

Further, in order to improve the dispersion in the aqueous medium, a dispersant such as a surfactant and resin fine particles is appropriately added.
As surfactants, anionic surfactants such as alkylbenzene sulfonates, α-olefin sulfonates, phosphate esters, alkylamine salts, amino alcohol fatty acid derivatives, polyamine fatty acid derivatives, amine salt types such as imidazoline, Quaternary ammonium salt type cationic surfactants such as alkyltrimethylammonium salt, dialkyldimethylammonium salt, alkyldimethylbenzylammonium salt, pyridinium salt, alkylisoquinolinium salt, benzethonium chloride, fatty acid amide derivative, polyhydric alcohol Nonionic surfactants such as derivatives, for example, amphoteric surfactants such as alanine, dodecyldi (aminoethyl) glycine, di (octylaminoethyl) glycine and N-alkyl-N, N-dimethylammonium betaine And the like.

Further, by using a surfactant having a fluoroalkyl group, the effect can be obtained in a very small amount. Preferred anionic surfactants having a fluoroalkyl group include fluoroalkyl carboxylic acids having 2 to 10 carbon atoms and metal salts thereof, disodium perfluorooctanesulfonyl glutamate, 3- [ω-fluoroalkyl (C6-C11 ) Oxy] -1-alkyl (C3-C4) sodium sulfonate, 3- [ω-fluoroalkanoyl (C6-C8) -N-ethylamino] -1-propanesulfonic acid sodium, fluoroalkyl (C11-C20) carvone Acids and metal salts, perfluoroalkylcarboxylic acids (C7 to C13) and metal salts thereof, perfluoroalkyl (C4 to C12) sulfonic acids and metal salts thereof, perfluorooctanesulfonic acid diethanolamide, N-propyl-N- ( 2-Hydroxyethyl) Perful Olooctanesulfonamide, perfluoroalkyl (C6-C10) sulfonamidopropyltrimethylammonium salt, perfluoroalkyl (C6-C10) -N-ethylsulfonylglycine salt, monoperfluoroalkyl (C6-C16) ethyl phosphate, etc. Can be mentioned.
Product names include Surflon S-111, S-112, S-113 (Asahi Glass Co., Ltd.), Florard FC-93, FC-95, FC-98, FC-129 (Sumitomo 3M Co., Ltd.), Unidyne DS-101. DS-102 (manufactured by Daikin Industries, Ltd.), Megafac F-110, F-120, F-113, F-191, F-812, F-833 (manufactured by Dainippon Ink, Inc.), Xtop EF-102, 103, 104, 105, 112, 123A, 123B, 306A, 501, 201, 204 (manufactured by Tochem Products), and Fgentent F-100, F150 (manufactured by Neos).

  Moreover, as the cationic surfactant, aliphatic quaternary ammonium such as aliphatic primary, secondary or secondary amic acid, perfluoroalkyl (C6-C10) sulfonamidopropyltrimethylammonium salt which has a right fluoroalkyl group is used. Salts, benzalkonium salts, benzethonium chloride, pyridinium salts, imidazolinium salts, trade names include Surflon S-121 (Asahi Glass Co., Ltd.), Florard FC-135 (Sumitomo 3M Co., Ltd.), Unidyne DS-202 (Daikin Industries) Smoke), MegaFuck F-150, F-824 (Dainippon Ink Co., Ltd.), Xtop EF-132 (Tochem Products), Footage F-300 (Neos), and the like.

The resin fine particles are added to stabilize the toner base particles formed in the aqueous medium. For this reason, it is preferable to add so that the coverage existing on the surface of the toner base particles is in the range of 10 to 90%. For example, polymethyl methacrylate fine particles 1 μm and 3 μm, polystyrene fine particles 0.5 μm and 2 μm, poly (styrene-acrylonitrile) fine particles 1 μm, trade names are PB-200H (manufactured by Kao), SGP (manufactured by Soken), Techno Examples include polymer SB (manufactured by Sekisui Chemical Co., Ltd.), SGP-3G (manufactured by Sokensha), and micropearl (manufactured by Sekisui Fine Chemical Co., Ltd.).
In addition, inorganic compound dispersants such as tricalcium phosphate, calcium carbonate, titanium oxide, colloidal silica, and hydroxyapatite can also be used.

  As a dispersant that can be used in combination with the above resin fine particles and inorganic compound dispersant, the dispersed droplets may be stabilized by a polymer protective colloid. For example, acrylic acid, methacrylic acid, α-cyanoacrylic acid, α-cyanomethacrylic acid, itaconic acid, crotonic acid, fumaric acid, maleic acid or maleic anhydride and other (meth) acrylic monomers containing hydroxyl groups Such as acrylic acid-β-hydroxyethyl, methacrylic acid-β-hydroxyethyl, acrylic acid-β-hydroxypropyl, methacrylic acid-β-hydroxypropyl, acrylic acid-γ-hydroxypropyl, methacrylic acid-γ-hydroxy Propyl, acrylic acid-3-chloro-2-hydroxypropyl, methacrylic acid-3-chloro-2-hydroxypropyl, diethylene glycol monoacrylate, diethylene glycol monomethacrylate, glycerol monoacrylate, glycerol monomethacrylate Luric acid esters, N-methylol acrylamide, N-methylol methacrylamide, etc., vinyl alcohol or ethers with vinyl alcohol, such as vinyl methyl ether, vinyl ethyl ether, vinyl propyl ether, or compounds containing vinyl alcohol and a carboxyl group Esters such as vinyl acetate, vinyl propionate, vinyl butyrate, acrylamide, methacrylamide, diacetone acrylamide or their methylol compounds, acid chlorides such as acrylic acid chloride, methacrylic acid chloride, vinyl pyridine, vinyl pyrrolidone, vinyl Nitrogen compounds such as imidazole and ethyleneimine, or homopolymers or copolymers such as those having a heterocyclic ring thereof, polyoxyethylene, poly Xoxypropylene, polyoxyethylene alkylamine, polyoxypropylene alkylamine, polyoxyethylene alkylamide, polyoxypropylene alkylamide, polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl phenyl ether, polyoxyethylene stearyl phenyl ester, polyoxy Polyoxyethylenes such as ethylene nonylphenyl ester, celluloses such as methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose can be used.

  The dispersion method is not particularly limited, and known equipment such as a low-speed shear method, a high-speed shear method, a friction method, a high-pressure jet method, and an ultrasonic wave can be applied. Among these, the high-speed shearing method is preferable in order to make the particle size of the dispersion 2 to 20 μm. When a high-speed shearing disperser is used, the rotational speed is not particularly limited, but is usually 1000 to 30000 rpm, preferably 5000 to 20000 rpm. The dispersion time is not particularly limited, but in the case of a batch method, it is usually 0.1 to 5 minutes. The temperature during dispersion is usually 0 to 150 ° C. (under pressure), preferably 40 to 98 ° C.

3) At the same time as the preparation of the emulsion, the amines (B) are added to cause a reaction with the polyester prepolymer (A) having an isocyanate group.
This reaction involves molecular chain crosslinking and / or elongation. The reaction time is selected depending on the reactivity between the isocyanate group structure of the polyester prepolymer (A) and the amines (B), but is usually 10 minutes to 40 hours, preferably 2 to 24 hours. The reaction temperature is generally 0 to 150 ° C, preferably 40 to 98 ° C. Moreover, a well-known catalyst can be used as needed. Specific examples include dibutyltin laurate and dioctyltin laurate.

4) After completion of the reaction, the organic solvent is removed from the emulsified dispersion (reactant), washed and dried to obtain toner base particles.
In order to remove the organic solvent, the temperature of the entire system is gradually raised in a laminar stirring state, and after giving strong stirring in a certain temperature range, the solvent base is removed to produce spindle-shaped toner base particles. . Further, when an acid such as calcium phosphate salt or an alkali-soluble material is used as the dispersion stabilizer, the calcium phosphate salt is dissolved from the toner base particles by a method such as dissolving the calcium phosphate salt with an acid such as hydrochloric acid and washing with water. Remove. It can also be removed by operations such as enzymatic degradation.

5) A charge control agent is injected into the toner base particles obtained above, and then inorganic fine particles such as silica fine particles and titanium oxide fine particles are externally added to obtain a toner.
The injection of the charge control agent and the external addition of the inorganic fine particles are performed by a known method using a mixer or the like.
Thereby, a toner having a small particle size and a sharp particle size distribution can be easily obtained. Furthermore, by giving strong agitation in the process of removing the organic solvent, the shape between the true spherical shape and the rugby ball shape can be controlled, and the surface morphology is also controlled between the smooth shape and the umeboshi shape. be able to.

In the present invention, a toner using a photoconductive resin whose volume resistance is lowered by light can be used. Generally, toner has a high volume resistance, so it can retain the charge generated on the surface by frictional charging. However, if the volume resistance can be controlled by light, the amount of charge leakage at or after charging can be controlled. Therefore, the charge amount of the toner can be controlled.
The photoconductive toner of the present invention is made of a metal-free phthalocyanine, titanyl phthalocyanine, vanadyl phthalocyanine used in an organic photoreceptor, or a material composed of these compounds or inorganic powders such as zinc oxide and amorphous silicon in a resin for toner. The mixture can be easily melted and mixed, and if necessary, a sensitizer is added and dispersed uniformly to make it easy.

The shape factor SF-1 of the toner is preferably in the range of 100 to 180, and the shape factor SF-2 is preferably in the range of 100 to 180. FIG. 7 is a diagram illustrating the shape factor SF-1 and the shape factor SF-2. It is the figure which represented the shape typically. The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-1 = {(MXLNG) 2 / AREA} × (100π / 4) Formula (1)
When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and becomes larger as the value of SF-1 increases.
The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-2 = {(PERI) 2 / AREA} × (100π / 4) Expression (2)
When the value of SF-2 is 100, there is no unevenness on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.
Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.) and introducing it into an image analyzer (LUSEX3: manufactured by Nireco). 100 pieces were analyzed and calculated.
When the shape of the toner is close to a spherical shape, the contact state between the toner and the toner or the toner and the photosensitive member 1 becomes a point contact, so that the adsorbing force between the toners becomes weak and the fluidity becomes high. The attracting force with the body 1 is also weakened, and the transfer rate is increased. Further, the transparent electrode 41 can be thinned easily, so that the light irradiation to the toner and contact with the electrode 41 become uniform, and charge injection can be performed stably. On the other hand, if any of the shape factors SF-1 and SF-2 exceeds 180, the transfer rate decreases, which is not preferable. Further, the transfer rate is lowered, the thinning is not stable, and the charge injection becomes unstable, which is not preferable.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a configuration around a photoconductor. 6 is a graph showing a toner charge amount distribution; It is the schematic which shows each bias at the time of image formation mode. It is the schematic which shows each bias at the time of discharge mode. 6 is a graph showing a toner charge amount distribution; FIG. 4 is a diagram schematically illustrating the shape of a toner for explaining the shape factor SF-1 and the shape factor SF-2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 3 Charging device 3a Charging roller 4 Exposure device 5 Developing device 5a Developing roller 6 Transfer device 10 Intermediate transfer belt 11, 12, 13 Support roller 14 Primary transfer roller 23 Heat fixing device 40 Brush-like roller (temporary holding means)
41 Electrode 42 Light irradiation means 51, 52 Voltage application means

Claims (17)

An image carrier for carrying an electrostatic latent image;
Charging means for charging the surface of the image carrier;
A latent image forming means for forming a latent image on the image carrier;
Developing means for developing a toner image by attaching toner to the latent image of the image carrier;
In an image forming apparatus comprising at least transfer means for transferring a toner image of an image carrier to a recording material,
Contact with the image carrier at a position downstream from the transfer unit and upstream from the charging unit, and temporarily collect at least a part of the residual toner remaining on the image carrier after transfer A rotating member that discharges the toner to the image carrier,
An electrode that faces and contacts the rotating member at a position other than the contact position between the image carrier and the rotating member;
Voltage applying means for separately applying a voltage to the rotating member and the electrode;
An image forming apparatus, comprising: a light irradiating unit that irradiates light to a contact position between the rotating member and the electrode. When the post-transfer surface potential of the image carrier is V0, the voltage applied to the rotating member is V1, and the voltage applied to the electrode is V2, the polarities of V0, V1, and V2 are the developing bias applied to the developing means. And the absolute value thereof is | V0 | <| V1 | <| V2 |
The image forming apparatus according to claim 1, wherein: The electrode is a transparent material that transmits light,
The image forming apparatus according to claim 1, wherein the light irradiation unit irradiates light from a back surface of the electrode to a contact position between the electrode and the rotating member. 4. The image forming apparatus according to claim 1, wherein the light irradiation by the light irradiation unit is controlled to be intermittently performed only when the transfer residual toner from the rotating member to the image carrier is discharged. 5. . The image forming apparatus according to claim 4, wherein the light irradiation is performed in accordance with a timing of a sheet interval. The image forming apparatus according to claim 1, wherein the toner discharged from the rotating member to the image carrier is collected in the developing device by the developing unit. The image forming apparatus according to claim 1, further comprising a bias switching unit that switches a voltage applied by the voltage applying unit. The voltage V2 is applied to the electrode so that V2-V1≥0, where V1 is a voltage applied to the rotating member and V2 is a voltage applied to the electrode. The image forming apparatus described in 1. The image forming apparatus according to claim 1, further comprising a discharge mode for discharging the transfer residual toner held by the rotating member to the image carrier during non-image formation. When the post-transfer surface potential of the image carrier is V0, when discharging residual toner from the rotating member to the image carrier, a voltage V1 applied to the rotating member and a voltage V2 applied to the electrode. Are switched by bias switching means so that V1-V0> 0 and V2-V1> 0 respectively, and light irradiation is simultaneously performed by the light irradiation means. The image forming apparatus described. The said electrode is a transparent material which permeate | transmits light, and the said light irradiation means irradiates light to the contact position of an electrode and a rotation member from the back surface of an electrode. The image forming apparatus described.   The toner discharged from the rotating member to the image carrier in the discharge mode passes through the charging unit and the developing unit, is transferred by the transfer unit, and is collected by the cleaning member provided in the transfer unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The image forming apparatus according to claim 1, wherein the rotating member is a brush-like roller. The image forming apparatus according to claim 13, wherein the rotation direction of the rotation member is an opposite direction at a contact position between the image carrier and the rotation member. The toner used for image formation is in the range of 100 to 180 in terms of the shape factor SF-1, and is in the range of 100 to 180 in terms of the shape factor SF-2. Image forming apparatus. The image forming apparatus according to claim 1, wherein the charging unit is a charging roller that rotates in contact with the image carrier, and a voltage applied to the charging roller is a DC voltage. The toner used for image formation is a toner containing a photoconductive material that causes a charge injection phenomenon by light irradiation and direct application of a voltage and changes its charge amount. The image forming apparatus according to any one of the above.