JP2007286399A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device which can smoothly supply toner to a developing roller and collecting toner remaining on a developing roller without being consumed while suppressing deterioration of the toner, and an image forming apparatus that can smoothly supply toner for developing an electrostatic latent image for the development while suppressing its deterioration and can, therefore, form an excellent image for a long period. <P>SOLUTION: The developing device D has a developing roller 1 which conveys toner T to a development area Da opposed to a photoreceptor 10, a supply roller 2 which supplies the toner to the roller 1, and a roller 6' for preliminary charging disposed in contact with the roller 2. A peripheral surface of the roller 6' moves in a contact nip part N2 for the roller 2 in the same direction with a peripheral surface of the roller 2 with a speed difference, (for example, no speed difference) smaller than the peripheral speed of the roller 2, from the peripheral surface of the roller 2. The image forming apparatus is equipped with the developing device D. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an electrostatic latent image on an electrostatic latent image carrier, develops the electrostatic latent image to form a toner image, and transfers the toner image to a transfer target. For example, the present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, a facsimile machine, a multifunction machine combining two or more of these, and a developing device mounted on the image forming apparatus.

  In an image forming apparatus such as an electrophotographic method, generally, the surface of an electrostatic latent image carrier that is driven so that the surface moves is charged by a charging device, and an image exposure device or electrostatic device is charged in the charged area. An electrostatic latent image corresponding to an image to be formed by a recording device or the like is formed, the electrostatic latent image is developed by a developing device to form a visible toner image, and the visible toner image is transferred by a transfer device. An image forming process for transferring to the body is performed.

Such image forming apparatuses can be roughly classified into a monochrome image forming apparatus and a color image forming apparatus (typically, a full color image forming apparatus) capable of forming an image using two or more colors of toner.
In a monochrome image forming apparatus, generally, a toner image formed on an electrostatic latent image carrier is directly transferred and fixed onto a recording medium as a transfer target by a transfer device.

Known color image forming apparatuses include so-called four-cycle color image forming apparatuses and tandem color image forming apparatuses.
A four-cycle type color image forming apparatus charges a surface of an electrostatic latent image carrier such as a photoreceptor, forms an electrostatic latent image by subjecting the charged area to image exposure, and develops the electrostatic latent image into a developing device. To develop a toner image. In such toner image formation, toner images of different colors can be sequentially formed on the electrostatic latent image carrier by sequentially using a plurality of developing devices containing toners of different colors. Further, the toner images formed on the electrostatic latent image carrier are sequentially superposed on the intermediate transfer member by using a primary transfer device, and transferred onto the intermediate transfer member, thereby forming the multiple toner on the intermediate transfer member thus formed. The image can be secondarily transferred to a recording medium with a secondary transfer device and fixed to obtain a color image.

  In a tandem type color image forming apparatus, an electrostatic latent image carrier such as a photoreceptor, a charging device for charging the surface thereof, an image exposure device, and a developing device for developing an electrostatic latent image on the electrostatic latent image carrier A plurality of image forming units including a plurality of image forming units are sequentially arranged along the intermediate transfer member according to the color of the toner, and a toner image formed on the image carrier in each image forming unit is obtained by a primary transfer device. The toner image is primary-transferred over the intermediate transfer member, and the multiple toner images on the intermediate transfer member are secondarily transferred and fixed on the recording medium by the secondary transfer device. The intermediate transfer member can be said to be a kind of transfer target.

  There are various types of developing devices, whether monochrome image forming devices or color image forming devices. Among them, a toner is carried on the peripheral surface and an electrostatic latent image carrier is used. There is a developing device that includes a developing roller that conveys the electrostatic latent image to a developing region that develops the toner and a supply roller that supplies toner to the developing roller.

An example of this type of developing device will be described with reference to FIG.
The conventional developing device shown in FIG. 4 is a so-called one-component developing device using a one-component developer containing toner as a main component as a developer. In the illustrated example, the developing roller 1 facing the electrostatic latent image carrier 10 which is a drum-type photosensitive member that is driven to rotate, the toner supply roller 2 disposed in contact with the developing roller 1, and the toner in contact with the developing roller 1 The restricting member 3 is included (but not limited to a blade-type member in this example).

  The developing roller 1 and the supply roller 2 are rotatably supported by the developing device case 5 and can be driven to rotate by a motor (not shown). The toner regulating member 3 is supported by the developing device case. In this example, negatively chargeable toner T is accommodated in the developing device case 5. A portion of the case 5 that faces the upper portion of the developing roller 1 is closed by a seal member 4.

  In the illustrated example, the developing roller 1 faces the photosensitive member 10 with a slight developing gap Dg (for example, 150 μm), and is driven to rotate in the opposite direction to the photosensitive member 10. The supply roller 2 is driven to rotate in the same direction as the developing roller 1. In other words, the supply roller 2 rotates so-called counter at the contact nip portion N1 with the developing roller 1 so that the peripheral surface of the supply roller moves in the direction opposite to the peripheral surface of the developing roller.

  The toner regulating member 3 is in contact with the developing roller 1 at a position downstream from the mutual contact nip N1 between the developing roller 1 and the supply roller 2 in the developing roller circumferential surface moving direction. The toner regulating member 3 is carried on the peripheral surface of the developing roller 1 and regulates the amount of toner conveyed to the developing area Da where the developing roller 1 and the photosensitive member 10 face each other to form a thin toner layer and the toner T Is triboelectrically charged.

  In the illustrated example, the layer including the peripheral surface of the developing roller 1 has elasticity, and the layer including the peripheral surface of the supply roller 2 is formed of a foamed material. It is press-contacted at 1 mm. The toner regulating member 3 is made of stainless steel in this example, and is in contact with the developing roller 1 with a force of about 20 N / m.

  A developing bias power supply PW1 is connected to the developing roller 1. In the illustrated example, the developing bias power source PW1 includes an AC power source Pac and a DC power source Pdc. An electric field that applies an electrostatic force toward the electrostatic latent image on the photosensitive member 10 to the toner on the developing roller 1 is applied to the roller 1 and the photosensitive member. Form between the bodies 10. In this example, a rectangular wave developing bias having a peak-to-peak voltage Vpp = 1320 [V], a DC voltage Vdc = −320 [V], a duty 35% (minus side), and a frequency of 2 kHz is applied to the developing roller 1 from the power source PW1. Is done.

  Between the developing roller 1 and the supply roller 2, a DC potential difference of about 100 [V] is formed by the bias DC power sources PW2 and PW2 ′ to direct the toner T toward the developing roller 1 side. Is transferred from the supply roller 2 to the developing roller 1.

  A direct current potential difference of about 50 [V] is formed between the toner regulating member 3 and the developing roller 1 by the power source PW2 to direct the toner T toward the developing roller 1 side.

  According to the developing device of FIG. 4 described above, the toner T in the developing device case 5 is supplied to the developing roller 1 by the supply roller 2 and transferred from the roller 2 to the roller 1 by the DC potential difference between the rollers 2 and 1. The toner T thus supplied is carried on the peripheral surface of the developing roller 1 and conveyed toward the developing area Da. In the middle of the toner T, the toner amount is regulated by the toner regulating member 3 and has a predetermined thickness. The toner is a thin toner layer, and is triboelectrically charged by passing under the toner regulating member 3 and arrives at the development area Da. In the development area Da, the electrostatic latent image on the photoconductor 10 is developed while reciprocating the development gap Dg by the action of the development bias described above.

  The photosensitive member 10 is a negatively charged photosensitive member, and is charged to about −450 [V] by a charging device (not shown) prior to forming an electrostatic latent image, and the charging region is charged by an image exposure device (not shown). An electrostatic latent image is formed by image exposure. The potential of the image exposure portion is about −50 [V] to −70 [V].

  The toner T remaining on the developing roller 1 without being consumed returns to the developing device case 5 as the roller rotates, and is rubbed by the supply roller 2 to be collected from the developing roller 1 into the case 5.

The operation of the developing device of FIG. 4 is as described above, but actually has the following problems.
The toner T remaining on the developing roller 1 without being consumed returns to the developing device case 5 as described above, and is rubbed by the supply roller 2 to be collected from the developing roller 1 into the case 5. A potential difference for smoothly supplying toner from the supply roller 2 to the development roller 1 is formed between the supply roller 2 and the development roller 1. Therefore, it becomes difficult to collect the residual toner that has returned to the developing device case 5 from the developing roller 1 by the supply roller 2. Further, since the toner that could not be collected is again conveyed to the development area Da as it is, a memory due to so-called residual toner is generated or the toner is likely to deteriorate, leading to a decrease in image quality.

  However, if the potential difference between the supply roller 2 and the developing roller 1 is set small in order to facilitate the collection of residual toner, the toner supply from the supply roller 2 to the developing roller 1 cannot be performed smoothly. It is actually difficult to set the potential difference between the rollers 1 and 2 so that both toner supply and toner recovery can be satisfied.

In order to solve this problem, a developing device as illustrated in FIG. 5 has been proposed.
The developing device shown in FIG. 5 eliminates the potential difference between the developing roller 1 and the supply roller 2 in the developing device of FIG. 4 or sets it small (no potential difference in FIG. 5). It is brought into contact with a toner friction charging member, which is a toner preliminary charging member, at a position upstream of the contact nip portion N1 between the rollers 1 and 2 in the moving direction of the supply roller circumferential surface. In the example of FIG. 6, a part 51 of the developing device case 5 is adopted as the friction charging member.

The other points are the same as those of the developing apparatus shown in FIG. 4, and the same parts and portions as those of the developing apparatus of FIG.
A developing device of the type shown in FIG. 5 is described in, for example, Japanese Patent Application Laid-Open No. 8-314278.

Further, although not a conventional example, according to the research of the present inventor, the potential difference between the developing roller 1 and the supply roller 2 is eliminated or set small in the developing device of FIG. 4 as in the developing device shown in FIG. (There is no potential difference in FIG. 6), and it is also conceivable to rotate the roller 6 for pre-charging the toner in contact with the supply roller 2. The preliminary charging roller 6 is rotationally driven in the same direction as the supply roller 2 in order to frictionally charge the toner on the supply roller 2. In other words, the preliminary charging roller 6 rotates at a so-called counter rotation so that the peripheral surface of the preliminary charging roller moves in the opposite direction to the peripheral surface of the supply roller at the contact nip portion N2 with the supply roller 2.
The other points are the same as those of the developing apparatus shown in FIG. 4, and the same parts and portions as those of the developing apparatus of FIG.

  According to the developing device shown in FIGS. 5 and 6, the toner on the supply roller 2 is preliminarily charged by friction charging with the toner charging member, so that there is no transfer potential difference between the supply roller 2 and the development roller 1. Even if it is set to a small value, residual toner that is smoothly supplied from the supply roller 2 to the developing roller 1 and returns without being consumed is easily collected from the developing roller 1 by the supply roller 2.

JP-A-8-314278

  However, according to the developing device of the type shown in FIG. 5, the toner on the supply roller 2 is substantially fed by the peripheral speed of the supply roller due to a stationary toner friction charging member (part 51 of the developing device case 5 in the example of FIG. 5). According to the developing device of the type shown in FIG. 6, the toner on the supply roller 2 has a peripheral surface speed of the precharging roller 6 in addition to the peripheral surface speed of the supply roller 2. The toner is easily deteriorated because it is rubbed while contacting the roller 6 at a high speed including

  Accordingly, the present invention provides a developing device that develops an electrostatic latent image formed on an electrostatic latent image carrier to form a toner image, and carries the toner on a peripheral surface to form the electrostatic latent image carrier. A developing device having a developing roller for conveying the upper electrostatic latent image to a developing region for developing, a supply roller for supplying toner to the developing roller, and a contact member for pre-charging toner disposed in contact with the supply roller An object of the present invention is to provide a developing device capable of smoothly collecting toner remaining on the developing roller by the supply roller without being consumed in toner supply and development from the supply roller to the developing roller while suppressing deterioration of the toner. Let it be the first problem.

  The present invention also relates to an image forming apparatus for forming an electrostatic latent image on an electrostatic latent image carrier, developing the electrostatic latent image to form a toner image, and transferring the toner image to a transfer target. A second problem is to provide an image forming apparatus capable of smoothly developing a toner used for developing an electrostatic latent image while suppressing its deterioration and capable of forming a good image for a long period of time. And

  In order to solve the first problem, the present invention is a developing device that develops an electrostatic latent image formed on an electrostatic latent image carrier to form a toner image, and carries the toner on the peripheral surface. A developing roller for transporting the electrostatic latent image on the electrostatic latent image carrier to a developing area for developing, a supply roller for supplying toner to the developing roller, and a toner precharge disposed in contact with the supply roller The contact member is a preliminary charging roller, and the peripheral surface of the preliminary charging roller is in the same direction as the peripheral surface of the supply roller at the contact nip with the supply roller. And a developing device that moves relative to the peripheral surface of the supply roller at a speed difference smaller than the peripheral speed of the supply roller.

  According to the developing device of the present invention, the preliminary charging roller is disposed in contact with the supply roller, and the toner supplied to the development roller by the supply roller is preliminarily frictionally charged between the preliminary charging roller and the supply roller. Even if the toner transfer potential difference between the roller and the developing roller is eliminated or set small, the toner can be supplied from the supply roller to the developing roller.

  Further, in the toner supply from the supply roller to the developing roller in this way, even if the toner transfer potential difference between the supply roller and the developing roller is eliminated or set to a small value, there is no practical problem in the toner supply to the developing roller. In this way, the potential difference can be eliminated or set to be small, and by doing so, residual toner that returns from the developing area to the developing device while being carried on the developing roller without being consumed by the development can be obtained. The supply roller can smoothly collect the toner from the developing roller. As a result, if there is a residual toner collection failure, the memory generated by the residual toner and the deterioration of the toner due to the residual toner being used again for development are suppressed. Is done.

The preliminary charging roller has a peripheral surface of the preliminary charging roller in the same direction as the peripheral surface of the supply roller at a contact nip portion with the supply roller, and smaller than the peripheral speed of the supply roller with respect to the peripheral surface of the supply roller. Since the toner is rotated so as to move at a speed difference, as in the developing device of FIG. 5, the toner on the supply roller is substantially equivalent to the peripheral speed of the supply roller by the stationary toner friction charging member (see FIG. 5). As shown in the developing device of FIG. 6, the toner on the supply roller has a large speed obtained by adding the peripheral surface speed of the pre-charging roller rotating counter to the peripheral surface speed of the supply roller as in the developing device of FIG. As compared with the case of rubbing while being in contact with the pre-charging roller, the toner is only rubbed at a lower speed, so that the deterioration of the toner is suppressed accordingly.
Thus, a good toner image can be formed over such a long period.

  In the developing device according to the present invention, the "small speed difference" in "the peripheral surface of the precharging roller moves with a speed difference smaller than the peripheral speed of the supply roller relative to the peripheral surface of the supply roller" includes a speed difference. In the case where there is substantially no, in other words, the case where the peripheral speed of the preliminary charging roller is equal to the peripheral speed of the supply roller is also included. Even in such a case, triboelectric charging is possible before the toner enters and exits the contact nip portion between both rollers.

  As described above, when the setting is made so that “the peripheral surface of the preliminary charging roller moves with a speed difference smaller than the peripheral speed of the supply roller relative to the peripheral surface of the supply roller”, the preliminary charging is performed in order to more reliably precharge the toner. A bias power source for forming a potential difference for charging the toner conveyed by the supply roller to the normal charging polarity of the toner may be provided between the supply roller and the supply roller. The toner can be precharged more reliably by the charge injection from the precharge roller by the bias power source. In particular, when the process speed (image forming speed) in an image forming apparatus equipped with the developing device according to the present invention is high, it is desirable to provide such a bias power source.

  Further, as in the developing device according to the present invention, when the peripheral surface of the preliminary charging roller moves in the same direction as the peripheral surface of the supply roller in the contact nip portion of the preliminary charging roller and the supply roller, Therefore, the toner powder pressure at the contact nip is lower than that when the supply roller is brought into contact with the stationary member as shown in FIG. 5 or when the supply roller is brought into contact with the counter rotating charge roller as shown in FIG. In order to secure the amount of toner held on the supply roller, the toner is accommodated in the developing device to the extent that the supply roller is buried and the contact nip portion between the pre-charging roller and the supply roller. You may do it. In particular, when the process speed (image forming speed) in an image forming apparatus equipped with the developing device according to the present invention is high, it is desirable that sufficient toner is contained in this way.

  The above-mentioned “bias power source for forming a potential difference for charging the toner conveyed by the supply roller between the pre-charging roller and the supply roller to the normal charging polarity of the toner”, and “the toner is the pre-charging” described above. Both of the contact nip portion between the supply roller and the supply roller and “the supply roller is accommodated so as to be buried” may be employed.

  In order to solve the second problem, the present invention forms an electrostatic latent image on an electrostatic latent image carrier, develops the electrostatic latent image to form a toner image, and transfers the toner image. An image forming apparatus that transfers to a body, and includes one or more developing devices for developing a latent electrostatic image to form a toner image, at least one of which is a developing device according to the present invention. An image forming apparatus is provided.

  In the image forming apparatus according to the present invention, since at least one developing device mounted thereon is the developing device according to the present invention, the toner used for developing the electrostatic latent image can be developed smoothly while suppressing deterioration thereof. Therefore, a good image can be formed over a long period of time.

  The image forming apparatus according to the present invention may form a monochrome image, or may be a color image forming apparatus such as the aforementioned 4-cycle color image forming apparatus or tandem color image forming apparatus. In the case of a monochrome image forming apparatus, the toner image formed on the electrostatic latent image carrier is usually directly transferred to a recording medium as a transfer target and fixed. In a color image forming apparatus, generally, a toner image formed on an electrostatic latent image carrier is once transferred to an intermediate transfer body, which is an intermediate transfer body, and finally transferred from the intermediate transfer body. It is transferred and fixed to a recording medium as a body.

  As described above, according to the present invention, the electrostatic latent image formed on the electrostatic latent image carrier is developed to form a toner image. A developing roller for conveying the electrostatic latent image on the electrostatic latent image carrier to a developing region for developing, a supply roller for supplying toner to the developing roller, and a contact member for pre-charging toner disposed in contact with the supply roller A developing device that can smoothly collect toner from the supply roller to the developing roller and collect toner remaining on the developing roller by the supply roller while suppressing toner deterioration. Can be provided.

  The present invention also relates to an image forming apparatus for forming an electrostatic latent image on an electrostatic latent image carrier, developing the electrostatic latent image to form a toner image, and transferring the toner image to a transfer target. Thus, it is possible to provide an image forming apparatus capable of smoothly developing a toner used for developing an electrostatic latent image while suppressing its deterioration and capable of forming a good image for a long period of time.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of an example of a monochrome image forming apparatus according to the present invention.
The image forming apparatus shown in FIG. 1 includes a drum-type rotationally driven photoreceptor 10 as an electrostatic latent image carrier. The photoconductor 10 is a negatively chargeable photoconductor in this example.

  Around the photosensitive member 10, a charging device 20, an image exposure device 30, a developing device D, a transfer device 40, a cleaning device 50, and an eraser 60 are arranged in this order. In this example, the transfer device 40 transfers the toner image on the photosensitive member to the recording medium S using a transfer roller 401.

  A timing roller pair 70 is provided on the upstream side of the transfer roller 401 in the conveyance direction of the recording medium S, and a recording medium supply unit (not shown) is further provided on the upstream side. A fixing device 80 for fixing the toner image to the recording medium S is provided on the downstream side of the transfer roller 401, and a recording medium discharge tray (not shown) is provided on the downstream side thereof.

According to the image forming apparatus of FIG. 1, an image is formed as follows.
The surface of the rotationally driven photoconductor 10 is charged to a predetermined potential (in this example, −450 [V]) by the charging device 20, and image exposure according to the document image is performed from the image exposure device 30 to the charged area. Thereby, an electrostatic latent image corresponding to the document image is formed. In this example, the charged potential of the exposed portion of the photoreceptor 10 is reduced to about −50 [V] to −70 [V].

  This electrostatic latent image is reversely developed using the negatively chargeable toner T by the developing device D to become a visible toner image. On the other hand, the recording medium S is supplied to the timing roller pair 70 from a recording medium supply unit (not shown). The timing roller pair 70 feeds the recording medium S between the photoreceptor 10 and the transfer roller 401 at a timing when the toner image on the photoreceptor 10 arrives at the transfer roller 401.

Thus, the toner image is transferred to the recording medium S by the action of the transfer device 40. This recording medium S is subsequently conveyed to the fixing device 80, where the toner image is fixed, and then discharged to the recording medium discharge tray.
The toner remaining on the photoconductor 10 after the transfer is removed and cleaned by the cleaning device 50, and the residual charge is erased by the eraser 60 to prepare for the next image formation.

Here, the developing device D will be further described.
The developing device D employs a precharging roller 6 ′ in place of the precharging roller 6 in the developing device of FIG. The other points are substantially the same as those of the developing device shown in FIG. The same parts and portions as those of the developing device in FIG. 6 are denoted by the same reference numerals.

  That is, in FIG. 1, 1 is a developing roller, 2 is a supply roller for supplying negatively chargeable toner T to the developing roller 1, 3 is a toner regulating member arranged in contact with the developing roller 1, 4 is a seal member, This is a developing device case. The developing roller 1 faces the photoreceptor 10 with a slight developing gap Dg (150 μm in this example). In developing the electrostatic latent image on the photoconductor 10, the developing roller 1 is driven to rotate in the direction opposite to the photoconductor 10, and the supply roller 2 is rotated in the same direction as the developing roller 1.

  The developing roller 1 applies a developing bias from a developing bias power source PW1 including an AC power source Pac and a DC power source Pdc, and uses the toner carried on the circumferential surface of the developing roller 1 for developing an electrostatic latent image on the photoreceptor 10.

  As described above, the developing bias at this time is a rectangular wave bias having a peak-to-peak voltage Vpp = 1320 [V], a DC voltage Vdc = −320 [V], a duty 35% (minus side), and a frequency of 2 kHz. Under this developing bias, the toner T develops the electrostatic latent image while reciprocating the developing gap Dg.

In addition, a DC potential difference of about 50 [V] is formed between the developing roller 1 and the toner regulating member 3 by the bias power source PW2 to direct the toner T toward the developing roller 1 side.
There is no potential difference between the developing roller 1 and the supply roller 2.

However, unlike the developing device of FIG. 6, the preliminary charging roller 6 ′ has a peripheral surface of the preliminary charging roller in the same direction as the peripheral surface of the supply roller at the contact nip portion N <b> 2 with the supply roller 2. It is rotated so as to move at a speed difference smaller than the peripheral speed of the supply roller with respect to the surface.
Here, the preliminary charging roller 6 ′ is driven and rotated by the supply roller 2 so as to rotate at the same peripheral speed as the supply roller 2.

  According to this developing device D, the preliminary charging roller 6 ′ is disposed in contact with the supply roller 2, and the toner T supplied to the development roller 1 by the supply roller 2 is previously between the preliminary charging roller 6 ′ and the supply roller 2. In this case, the toner is smoothly supplied from the supply roller 2 to the developing roller 1 although there is no toner transfer potential difference between the supply roller 2 and the developing roller 1.

  Further, since the toner transfer potential difference between the supply roller 2 and the developing roller 1 is set as described above, the developing region Da is not consumed for the development and is carried on the developing roller 1 to the developing device D. The returning residual toner can be smoothly recovered from the developing roller 1 by the supply roller 2, and as a result, if there is a residual toner recovery failure, memory is generated due to the residual toner and the residual toner is directly used for development again. Therefore, deterioration of the toner due to this is suppressed.

Further, in the frictional charging of the toner T by the preliminary charging roller 6 ′, the preliminary charging roller 6 ′ rotates at the same peripheral speed as the supply roller 2, so that the deterioration of the toner at the roller 6 ′ portion is suppressed accordingly. The
Thus, a good toner image can be formed over such a long period.

  FIG. 2 shows another example of the developing device according to the present invention. The developing device D ′ shown in FIG. 2 is configured so that a bias can be applied to the preliminary charging roller 6 ′ from the bias DC power source PW3 in the developing device D shown in FIG. A DC potential difference for charging the toner T conveyed by the supply roller 2 to the normal charging polarity (negative in this example) of the toner can be formed between the roller 6 ′ and the supply roller 2. The toner supplied to the developing roller 1 by the supply roller 2 can be precharged more reliably.

The direct current potential difference by the bias power source PW3 is not limited to this, but can be about 100 [V], for example.
When the process speed (image forming speed) of the image forming apparatus is high, it is desirable to provide a potential difference between the preliminary charging roller 6 ′ and the supply roller 2 in this way.
The other points in the developing device D ′ shown in FIG. 2 are substantially the same as those of the developing device D shown in FIG. 1, and the parts and parts of the developing device D shown in FIG. The same reference numerals are attached.

  FIG. 3 shows another example of the developing device according to the present invention. The developing device D ″ shown in FIG. 3 is the same as the developing device D ′ shown in FIG. 2, so that the amount of toner stored in the developing device case 5 is such that the upper surface position Tp of the toner is higher than the supply roller 2. The preliminary charging roller 6 ′, the contact nip portion N 2 of the supply roller 2, and the supply roller 2 are both set to be immersed in the toner.

In the developing devices D and D ′ shown in FIGS. 1 and 2, since the preliminary charging roller peripheral surface moves in the same direction as the supply roller peripheral surface, if the amount of toner in the developing device case 5 is too small, the roller 6 ′ The toner powder pressure at the contact nip portion N2 of the roller 2 may decrease, and the amount of toner held by the supply roller 2 may decrease. However, the toner powder pressure at the contact nip portion N2 can be improved by setting the toner amount so that the upper surface position Tp is higher than the supply roller 2 as in the developing device D ″ in FIG. Thereby, the amount of toner held by the supply roller 2 can be increased.
Also in the developing device D ′ of FIG. 1, the toner amount in the developing device case 5 may be set so that the upper surface thereof is above the supply roller 2.

When the process speed (image forming speed) of the image forming apparatus is high, it is desirable to use such a toner amount.
Other points in the developing device D ″ shown in FIG. 3 are substantially the same as those of the developing device D ′ shown in FIG. 2, and there are substantially the same parts and parts as those in the developing device D ′ shown in FIG. The same reference numerals as those in FIG.

Next, experimental examples performed for confirming the effects of the present invention are shown in the following table together with comparative experimental examples.
In the following table, Experimental Example 1 is an experimental example using the developing device D in FIG. 1, Experimental Example 2 is an experimental example in which the process speed is increased in the developing device D in FIG. 1, and Experimental Example 3 is the developing device D in FIG. Comparative experiment examples 1, 2, and 3 are experimental examples using the developing devices shown in FIGS. 4, 5, and 6, respectively.

  “With” indicates that the peripheral surface of the preliminary charging roller moves in the same direction as the peripheral surface of the supply roller at the contact nip portion N2 between the preliminary charging roller 6 ′ and the supply roller 2. Shows that the preliminary charging roller peripheral surface moves in the direction opposite to the supply roller peripheral surface in the contact nip portion N2.

“Supply bias” is the potential of the supply roller 2 with respect to the developing roller 1.
The “bias (toner charging)” in the “contact member condition” column is the potential of the preliminary charging contact member (in the present invention, the preliminary charging roller 6 ′) with respect to the supply roller 2.

Toner supply capacity from the supply roller 2 to the developing roller 1 is evaluated by the charge amount of the toner on the developing roller 1 transported toner amount and the developing roller 1 by, if 5 g / m ² a to 8 g / m ² for conveying amount Good “◯”, if it is slightly less, “△”, otherwise bad “×”, and if the toner charge amount is −20 μC / g to −40 μC / g, good “○”. Other than that, it was judged as “bad”.

  Regarding the toner recoverability by the supply roller 2 from the developing roller 1, the presence or absence of memory on the obtained image is visually observed, and when it may be determined that the memory is not practically recognized, it is determined as “good”, When the memory was generated in a state that could not be ignored in practice, it was judged as “bad”.

In the evaluation of the presence or absence of toner deterioration, when it is judged that toner scattering is not practically recognized on the obtained image, it is judged as “good”, and when toner scattering occurs in a state that cannot be ignored in practice. Was defined as a defect “Δ” or even a defect “×”.
As shown in the following table, in Experimental Examples 1, 2, and 3 employing the developing device according to the present invention, the amount of toner transport on the developing roller is slightly reduced in Experimental Example 2 due to the increase in the process speed. The overall evaluation as the overall evaluation was also good.
In Experimental Example 3, since the toner amount in the developing device was set to an amount for burying the supply roller, the toner conveyance amount on the developing roller was good.

  Although the monochrome image forming apparatus and the developing device mounted thereon have been described above, the present invention is mounted on a color image forming apparatus such as a 4-cycle color image forming apparatus and a tandem color image forming apparatus, and the color image forming apparatus. The present invention can also be applied to a developing device.

  The present invention provides a developing device that can smoothly develop an electrostatic latent image while suppressing toner deterioration, and can smoothly develop the electrostatic latent image while suppressing toner deterioration to form a good image. It can be used to provide an image forming apparatus.

1 is a diagram illustrating an outline of a configuration of an example of an image forming apparatus according to the present invention. It is a figure which shows the other example of the developing device which concerns on this invention. It is a figure which shows the further another example of the developing device which concerns on this invention. It is a figure which shows the conventional example developing apparatus. It is a figure which shows the other conventional example developing apparatus. It is a figure which shows the example of further possible image development apparatus.

Explanation of symbols

D, D ′, D ″ Developing device 10 Photoconductor 20 Charging device 30 Image exposure device D Developing device 1 Developing roller 2 Supply roller 3 Precharging roller 4 Seal member 5 Developing device case 6, 6 ′ Precharging roller PW1 Bias Power supply Pac AC power supply Pdc DC power supply PW2, PW2 ', PW3 DC bias power supply T Toner Tp Toner upper surface position Da Development area Dg Development gap 40 Transfer device 401 Transfer roller 50 Cleaning device 60 Eraser 70 Timing roller pair 80 Fixing device S Recording medium

Claims (5)

A developing device that develops an electrostatic latent image formed on an electrostatic latent image carrier to form a toner image, and that carries toner on a peripheral surface and electrostatically moves on the electrostatic latent image carrier. A developing device having a developing roller for transporting a latent image to a developing region, a supply roller for supplying toner to the developing roller, and a contact member for pre-charging toner disposed in contact with the supply roller; The contact member is a preliminary charging roller, and in the contact nip portion with the supply roller, the peripheral surface of the preliminary charging roller is in the same direction as the peripheral surface of the supply roller and the supply roller with respect to the peripheral surface of the supply roller The developing device moves at a speed difference smaller than the peripheral speed. The developing device according to claim 1, wherein the preliminary charging roller rotates at the same peripheral speed as the supply roller. 3. The development according to claim 1, further comprising a bias power source for forming a potential difference for charging the toner conveyed by the supply roller to the normal charging polarity of the toner between the preliminary charging roller and the supply roller. apparatus. 4. The developing device according to claim 1, wherein toner is accommodated so as to bury the contact nip portion between the preliminary charging roller and the supply roller and the supply roller. An image forming apparatus that forms an electrostatic latent image on an electrostatic latent image carrier, develops the electrostatic latent image to form a toner image, and transfers the toner image to a transfer target. One or more developing devices for developing an image to form a toner image are provided, and at least one of the developing devices is the developing device according to any one of claims 1 to 4. An image forming apparatus.