JPH0376752B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention supplies a developer containing a carrier and toner in a developer reservoir to a developer transporting carrier surface to form a developer layer, and The present invention relates to a developing method in which toner is caused to fly and adhere to the surface of an image forming body on which a latent image is formed.

[Prior art]

Using a developer called a two-component developer, which contains a carrier and a toner, and optionally also contains a small amount of hydrophobic silica, a developer layer formed on a developer transport carrier is applied to the surface of the image forming body. In the magnetic brush development method, when the toner concentration of the developer in the developer reservoir of the developing device changes, even if other image forming conditions are adjusted, if the toner concentration is low, the image density will decrease, and if the toner concentration is high, the image density will decrease. In this case, fogging tends to occur in non-image areas, so the limit of the appropriate toner density was 3 to 10 wt%.

However, in a developing method using non-contact conditions, in which the toner is ejected from the developer layer under an oscillating electric field and adheres to the surface of the image forming body without bringing the developer layer on the developer transporting carrier into contact with the surface of the image forming body, there is one example. As a result of experiments, it has become clear that the developer density changes as shown in FIG. 1 depending on the toner density of the developer. According to FIG. 1, in a range where the toner concentration in the developer is low, the developed density, that is, the recorded image density, increases as the toner concentration increases, but when the toner concentration becomes too high, the developed density decreases. become. This phenomenon in which the developer density decreases is due to the fact that when the toner concentration becomes too high, the toner in the developer reservoir is not sufficiently charged, and the proportion of fully charged toner decreases. It is thought that this may occur. However, in a developing method using non-contact conditions, the occurrence of fogging can be kept extremely low because the developer layer does not come into contact with the surface of the image forming body, and the allowable range of toner concentration of the developer is wide, about 5 to 60 wt%. This is a major feature. On the other hand, in the magnetic brush development method described above, since the toner tolerance range is narrow, a change in toner density immediately causes a change in image density.

In order to prevent the change in development density as shown in Figure 1, in the conventional development method, for example, (1)
A latent image of a standard density image is formed on the image forming body separately from the recorded image, and the standard developed density of this latent image is constantly measured using a photocoupler, etc., and when this standard developed density falls below a predetermined density, A method that determines that the toner concentration in the developer is insufficient and constantly replenishes toner to the developer reservoir so that the standard developer concentration is always maintained above a predetermined concentration, or (2) a method provided in the developer reservoir. The inductance is constantly measured using a developer inductance measuring means such as a pot core coil sensor, and since the inductance changes depending on the toner concentration, toner is constantly replenished into the developer reservoir so that the inductance is maintained at a predetermined level. By keeping the toner concentration of the developer at a constant level lower than the peak of the curve in Figure 1, and keeping other image forming conditions constant, a clear recorded image without fogging can be obtained. I'm trying to get a stable amount of this.

However, in this method of maintaining the developer density by controlling the toner replenishment so that the toner density of the developer remains constant, the toner replenishment device is not only complicated and expensive, but also requires the above (1). For methods that require precision in measuring the reference developer density in method (2) and developer inductance in method (2), and in which toner density is indirectly determined as in method (1), other methods are required. There is also the problem that a decrease in development density due to this cause may be mistakenly attributed to a decrease in toner concentration, leading to runaway toner replenishment.

Therefore, there has been a strong demand for a developing method that can stably obtain clear recorded images using a two-component developer without using such a problematic toner density control method.

[Purpose of the invention]

The present invention has been made for the purpose of providing a developing method that satisfies the above-mentioned needs, and uses non-contact jumping developing conditions in which toner is caused to fly from a developer layer on a developer transport carrier and adhere to an image forming body. For example, even if the toner concentration in the two-component developer changes,
This method was developed based on the discovery that clear recorded images without fog can be stably obtained by changing other image forming conditions.

[Structure of the invention]

In the present invention, a developer containing a carrier and toner in a developer reservoir is supplied to a developer transporting carrier surface to form a developer layer, and the toner is ejected from the developer layer to form a latent image. In the developing method of attaching the toner to the surface of the forming body, the influence of the change in toner concentration is compensated for by changing other image forming conditions in accordance with the change in the toner concentration of the developer in the developer reservoir. The present invention is a developing method, and this configuration achieves the above object.

In the present invention, other image forming conditions that are changed according to changes in the toner concentration of the developer in the developer reservoir include the electric field condition between the developer transport carrier and the image forming member, the charging potential of the image forming member, and the exposure. These include latent image forming conditions such as the amount of developer, developer layer transport conditions of the developer transport carrier such as the thickness and moving speed of the developer layer, and the gap between the developer transport carrier and the image forming body. At least one or more of them may be changed in response to changes in toner concentration. This change may be made automatically depending on the change in toner concentration, or may be made manually. Image forming conditions that can be easily changed automatically and that can compensate for changes in toner density and obtain a stable developed density are as follows: By changing the bias voltage applied to the developer transport carrier, Most preferably, the electric field between the imager and the imager is varied.

Further, the toner concentration measuring means of the developer in the developer reservoir does not use the measurement result to control toner replenishment as in conventional development methods, but rather to control the development bias, etc. Since the controlled development bias and the like compensate for the effects of changes in the toner concentration of the developer, it is not necessary to measure the toner concentration with the precision required to use the results for toner replenishment control.

Therefore, the toner density of the developer used to control the development bias, etc. can be determined not only by the conventional direct method of measuring the inductance and light reflection intensity of the developer, but also by using the standard density image. Even if it is determined by an indirect method of measuring the standard development density, it can also be determined by a more indirect method such as the number of recording sheets or the amount of residual toner removed by a cleaning device. It is also possible to use the one obtained by analogy with . However, from the viewpoint of the purpose of use, it is more preferable to obtain the density by a direct method or by measuring the standard developed density.

〔Example〕

The present invention will be described below with reference to the examples shown in FIGS. 2 to 8.

FIG. 2 is a schematic configuration diagram showing an example of a recording apparatus that implements the developing method of the present invention, FIGS. 3 and 4 are graphs showing the relationship between electrostatic latent image potential, development bias, and development density. 6 and 6 are graphs showing the relationship between the developer transport speed of the developer transport carrier and the developer density, and FIGS. 7 and 8 are graphs showing the relationship between the developer transport speed of the developer transport carrier and the developed density. FIG. 2 is a cross-sectional view showing an example of a developing device.

The recording apparatus shown in FIG. 2 is an electrophotographic copying machine in which an exposure optical system moves back and forth to scan and expose an image of a document 0, and the exposure optical system consists of an exposure lamp 1, reflection mirrors 2 to 5, and a lens 6. The exposure lamp 1 and reflection mirror 2 move to the right at a speed v, and the reflection mirrors 3 and 4 move to the right at a speed 1/2v to scan and expose the image of the document 0. The exposure optical system also scans and exposes the image of the reference density piece D before scanning and exposing the document 0.

The above scanning exposure by the exposure optical system rotates in the direction of the arrow and is incident on the surface of the photosensitive drum 8, that is, the image forming body, which is uniformly charged by the charging electrode 7. The electrostatic latent image thus formed on the surface of the photoreceptor drum 8 is developed into a toner image by a developing device 9 using a two-component developer, and the developed toner image is transferred to the surface of the photoreceptor drum 8. The image is transferred by the transfer pole 10 onto the recording paper P, which is fed in synchronization with the rotation so as to be in contact with the surface of the recording paper P. The recording paper P onto which the toner image has been transferred is transferred to the photosensitive drum 8 by the separation pole 11.
After the toner image is fixed by a fixing device (not shown), it is discharged outside the machine.

However, the toner image obtained by developing the electrostatic latent image on the reference density piece D passes through the transfer pole 10 and the separation pole 11 first without being transferred to the recording paper P, and the reference developed density is transferred to the light emitting element and the light receiving element. The toner is detected by a developed density detector 12 such as a reflective photosensor consisting of a combination of the above, and is then removed from the surface of the photosensitive drum 8 by a cleaning device 13 in the same way as residual toner after transfer. The developer density detector 12 may be provided between the developing device 9 and the transfer pole 10.

The density information detected by the developed density detector 12 is input to a main control device 14 that also includes an information processing device such as a microcomputer and a drive control device such as a developing bias controlled by the information processing device. Toner concentration information from a toner concentration detector 15 such as a pot core coil sensor provided in the developer reservoir 91 of the developing device 9 is also input to the main control device 14 . Note that only one of the developer concentration detector 12 and the toner concentration detector 15 may be provided.

In the developing device 9, a developing sleeve 92, that is, a developer conveying carrier made of a non-magnetic material such as aluminum or stainless steel, rotates in the direction of the arrow.
N, S magnetized to a magnetic flux density of 500 to 1500 Gauss
The magnet body 93 having magnetic poles rotates in the direction of the arrow,
The developer in the developer reservoir 91 is attracted to the surface of the developing sleeve 92 and moves in the same direction as the rotation of the developing sleeve 92, and the thickness of the developer layer is regulated by the layer thickness regulating blade 94. develops the electrostatic latent image on the photoreceptor drum 8 into a toner image in the development area A without contacting the surface of the photoreceptor drum 8. During this development, a bias voltage is applied to the developing sleeve 92 by the main controller 14, and a developing electric field is generated in the developing area A. Alternatively, only one of the developing sleeve 92 and the magnet 93 may be rotated to move the developer layer in the same direction as described above.

This developing device 9 is provided with a toner hopper 95 for replenishing toner into the developer reservoir 91, but the toner in this toner hopper 95 is not constantly replenished unlike in conventional developing devices, and the toner is not constantly replenished, but due to the development bias, etc. When it becomes impossible to obtain a satisfactory development density by controlling the amount, the bottom plate 96 is opened in the direction shown by the arrow to replenish the amount at once. Note that the developing device 9 may be replaced with a developing device having a higher toner concentration when the toner concentration of the developer in the developer reservoir 91 decreases as described above, and the toner hopper 95 may not be provided.

During development, the developer in the developer reservoir 91 is stirred by the stirring means 97 to uniformly mix the toner and carrier, and to triboelectrically charge the toner. In particular, the toner hopper 95 is placed in the developer reservoir 91.
When the toner is replenished from the toner or when the developing device 9 is replaced, in addition to the stirring during the development described above, the toner is stirred by the stirring means 97 in advance before the development is performed.
Preferably, the stirring is performed automatically for a predetermined period of time when the power switch of the recording device is turned on, when the bottom plate 96 of the toner hopper 95 is opened/closed, or when the developing device is replaced. However, it may be performed by manually operating a stirring switch. This prevents the toner from being mixed unevenly or from being developed using a developer that is insufficiently charged.

The developer layer on the developing sleeve 92 that has passed through the developing area A is removed from the developing sleeve 92 by the cleaning blade 98 and returned to the developer reservoir 91, and is mixed with the developer in the developer reservoir 91 by the stirring means 97. Evenly mixed.

The main controller 14 controls the developing bias applied to the developing sleeve 92 of the developing device 9, the discharge voltage applied to the charging electrode 7, or the magnetic The toner concentration of the developer in the developer reservoir 91 changes until toner is replenished or the developing device 9 is replaced. Even though
This ensures clear development without fogging. This point will be explained with reference to FIGS. 3 to 6.

3 and 4 respectively show a developed density curve when the amplitude of the alternating current component of the developing bias applied to the developing sleeve 92 during development is changed, and a developed density curve when the frequency of the alternating current component is also changed. These development density curves were obtained under the following conditions with the toner density of the developer constant.

The photoreceptor drum 8 has a Se photoreceptor layer on the surface,
It has a diameter of 120 mm, rotates in the direction of the arrow at a surface speed of 120 mm/sec, and is charged to 600 V by the charging electrode 7.
An electrostatic latent image with a surface potential V _S is formed on the charged surface by an exposure device. In the developing device 9, a developing sleeve 92 with a diameter of 30 mm has a surface gap of 0.7 mm between the developing sleeve 92 and the photosensitive drum 8.
rotates counterclockwise at a circumferential speed of 120 mm/sec, and the magnet body 93
Rotates clockwise at 600rpm. The developer consisting of non-magnetic toner and magnetic carrier in the developer reservoir 91 is
The toner is negatively charged, and a developer layer having a thickness of 0.5 mm is formed on the developing sleeve 92 by the layer thickness regulating blade 94. During development, a bias voltage consisting of a DC component V _dc and an AC component superimposed is applied to the development sleeve 92 .

The horizontal axes in Figures 3 and 4 indicate the difference between the surface potential V _S and the DC component of the bias voltage V _dc , and the vertical axes indicate the recorded image density, that is, the developed density. The frequency of the AC component of
Concentration curves when the amplitude, that is, the width from the median to the peak, is changed to 0 kV, 1 kV, and 2 kV, respectively, assuming 1 kHz. , in Figure 4, are the frequency curves when the amplitude of the AC component of the bias voltage is 1 kV.
It shows the concentration curve when changing to 700Hz, 2kHz, and 4kHz.

As is clear from FIG. 3, if the amplitude of the alternating current component of the bias voltage is increased or decreased, the developer density also changes to become higher or lower. Changes in development density can be compensated for. Also, the fourth
As is clear from the figure, even if the frequency of the bias voltage is reduced or increased, the developed density changes to become higher or lower, so that the influence of changes in the toner density of the developer can be similarly compensated for. Furthermore, as shown by the horizontal axes in FIGS. 3 and 4, changing the DC component V _dc of the bias voltage;
Alternatively, the influence of changes in the toner concentration of the developer can be compensated to some extent by changing the surface potential V _S , that is, the charging potential by the charging electrode 7 or the intensity of image exposure by the exposure lamp 1. The developed density curves in FIGS. 3 and 4 are based on the photosensitive drum 8.
The developed density curve was obtained for a photoreceptor layer made of an S _e photoreceptor, but almost the same developed density curve was obtained for an OPC photoreceptor whose photoreceptor layer is an organic photoconductor or other photoreceptors. is obtained.

5 and 6 show the developed density curve when the rotational speed of the magnet body 93 and the developed density curve when the rotational speed of the developing sleeve 92 are changed during development, respectively. The developed density curve was also obtained with the toner density of the developer constant.

In FIGS. 5 and 6, the photoreceptor drum 8 has an OPC photoreceptor layer, has a diameter of 120 mm, and rotates at a surface speed of 120 mm/sec in the direction of the arrow. Similar results can be obtained even with a photoreceptor or the like.

In Figures 5 and 6, V _SD has an absolute value of 150V formed on the photosensitive drum 8 by changing the density of the original.
It shows the absolute value of the difference between the above negative electrostatic latent image potential and the -150V DC component of the bias voltage applied to the developing sleeve 92, assuming that the surface gap between the developing sleeve 92 and the photoreceptor drum 8 is 0.75 mm. The layer thickness of the developer layer on the developing sleeve 92 was regulated to 0.35 mm by a layer thickness regulating blade 94. In the case of FIG. 5, the rotation speed of the developing sleeve 92 in the direction of the arrow is constant at 65 rpm, and the rotation speed of the magnet body 92 in the direction of the arrow, which has 8 N and S magnetic poles magnetized with a magnetic flux density of 900 Gauss at equal intervals. The rotation is changed as shown on the horizontal axis, and in the case of FIG. 6, the rotation speed of the magnet body 93 in the direction of the arrow is constant at 700 rpm, and the rotation of the developing sleeve 92 in the direction of the arrow is changed as shown on the horizontal axis. Changed. In addition, the developer has a weight average particle size of
It consists of an insulating magnetic carrier with a specific resistance of about 1×10 ¹⁴ Ωcm, which contains magnetic powder dispersed in a resin of about 30 μm, and an insulating non-magnetic toner with an average particle size of about 13 μm and positively triboelectrically charged. A component developer was used, and during development, a bias voltage in which a DC voltage of -150V and an AC voltage of 1500V, 2kHz were superimposed was applied to the developing sleeve 92. Note that even when the magnet body 93 is fixed and the rotational speed of the developing sleeve 92 is changed, the dependence of the developed density on the rotational speed of the developing sleeve 92 has the same tendency as shown in FIG. 6.

As can be seen from FIGS. 5 and 6, even if the rotational speeds of the magnet body 93 and the developing sleeve 92 are changed, the influence of changes in the toner concentration of the developer can be compensated for.

The main controller 14 controls the bias voltage, the discharge voltage of the charging electrode 7 or the magnet body 93 based on information from the developer density detector 12 or the toner density detector 15.
Since one or more of the rotational speed of the developing sleeve 92 and the like are changed to compensate for the influence of the change in the toner concentration of the developer (the change in the developer concentration as shown in FIG. 1) as described above, the As mentioned above, until toner is replenished or the developing device is replaced,
Even if the toner density of the developer changes, a constant developed density, that is, a recorded image density, can be obtained for a constant document density.

In the recording apparatus of FIG. 2, even if the main controller 14 changes the image forming conditions as described above, the detection information of the developed density detector 12 still indicates that the reference developed density has decreased below a certain level. In this case, the main control device 14 can easily display a warning message indicating that toner should be replenished or the developing device should be replaced. If you follow the warning and replenish toner and replace the developing device as described above, you will not need a troublesome device that constantly replenishes the amount of toner that has been used up in the developer reservoir, and you will always have a stable supply of toner. Clear recorded images without fog can be obtained. However, the present invention is not limited to the example shown in FIG. 2, and may be such that an operator determines when to replenish toner or replace a developing device by looking at a recorded image.

7 and 8 show an example of a replaceable developing device, and in FIGS. 7 and 8, the same reference numerals as in FIG. 2 indicate the same functional members. The developing device 9 shown in FIGS. 7 and 8 occupies the dotted line position covering the exposed surface of the developing sleeve 92 which provides the developing area A by the urging of a spring or the like when it is not attached to the recording device. When attached to the recording device, the developing sleeve 92 is brought to the solid line position.
a lid member 9a whose surface faces the surface of the image forming body;
is provided to prevent the developer from spilling out from the development area A when the recording apparatus is attached to or removed from the recording apparatus or carried around. Furthermore, a removable partition member 9b is provided between the stirring means 97 and the developing sleeve 92, and the developer is stored on the stirring means 97 side of the partition member 9b.
By removing the partition member 9b immediately before installing the developing device 9 in the recording apparatus, spilling of the developer from the developing device 9 is further prevented. In the developing device 9 shown in FIG. 7, when it is time to replenish toner as described above, the developer replenishment port 9c is opened so that toner can be replenished. This toner replenishment may be performed while the developing device 9 is attached to the recording device, or may be performed while the developing device 9 is removed from the recording device. Furthermore, toner replenishment may be performed by replacing the developing device. The developing device 9 in FIG.
A removable partition member 9d for storing toner is provided on the opposite side of the partition member 9b of the stirring means 97, and when it is time to replenish toner, the partition member 9d can be removed to stir the partition member 9d. The toner stored on the side opposite to the means 97 is supplied to the developer reservoir 91. This toner replenishment may also be performed while the developing device 9 is attached to the recording device, or may be performed while the developing device 9 is removed from the recording device.

The developing device 9 shown in FIGS. 7 and 8 is also used in the developing method of the present invention, with the developing bias and the like being controlled in the same manner as described with respect to FIG.

In the method of the present invention described above, in order to obtain clear recorded images with better reproducibility and no fog, the surface gap between the photosensitive drum 8 and the developing sleeve 92 of the developing device is set in the range of several tens to 2000 μm. Therefore, it is preferable that the thickness of the developer layer regulated by the layer thickness regulating blade 94 be made thinner than that. If the gap in this development area is made too narrow, the thickness of the developer layer must be made extremely thin, which makes it impossible to obtain a uniform layer thickness, and therefore provides a stable supply of toner to the development area A. Not only is this impossible, but also electric discharge is likely to occur between the developing sleeve 92 and the photoreceptor drum 8. On the other hand, development area A
If the gap is made too wide, it becomes difficult to control the flight of toner by the oscillating electric field. Furthermore, a two-component developer consisting of insulating magnetic carrier particles and toner particles with a resistivity of 10 ⁸ Ωcm or more, preferably 10 ¹³ Ωcm or more is used as the developer, since sufficient bias voltage can be applied to the developing sleeve 92. This is desirable because toner flight control can be effectively performed. As such carrier particles, carrier particles having a resin coating formed on the surface of magnetic particles or carrier particles made of resin particles containing magnetic particles dispersed therein are used.

The resistivity of the insulating particles is determined by placing the particles in a container with a cross-sectional area of 0.5 cm ² , adjusting the amount so that the thickness is about 1 mm, and tapping the particles. This value is obtained by applying a load of ² and reading the current value when applying a voltage that generates an electric field of 1000 V/cm between the electrode that also serves as the load and the bottom electrode.

Furthermore, in order to faithfully reproduce delicate images, the average particle size of the toner particles is 20 μm or less.
In particular, it is preferably 1 to 10 μm, and the average particle size of the carrier particles is also preferably in the range of 5 to 50 μm. The average particle size of these particles is a weight average particle size, and is measured with a Coulter Counter (manufactured by Coulter) or Omnicon Alpha (manufactured by Boshilom).
If the average particle size of the toner particles becomes too small, the amount of charge due to friction of a single toner particle becomes small, and the van der Waals force becomes relatively large, making it easier to aggregate and making it difficult to separate and fly. On the other hand, if the average particle size becomes too large, the amount of charge for superimposition decreases, making it difficult to control flight and reducing resolution. Furthermore, if the average particle size of the carrier particles becomes too small, the force of attraction by the magnetic force of the magnet body 93 becomes weak, but the electrical Coulomb force and Van der Waals force become strong, which causes the carrier particles to become too small. The particles tend to migrate to the surface of the photoreceptor drum 8 and the edges of the latent image together with the toner particles, and on the other hand, if the average particle size becomes too large, the allowable range of toner concentration decreases or particles are formed on the developing sleeve 92. The developed developer layer becomes rough, making it difficult to form a thin and uniform developer layer, and the state of adhesion of toner particles in the developer layer becomes uneven.
Breakdown and discharge of the voltage applied to the developing sleeve 92 are more likely to occur, making it difficult to control the flight of toner particles.

〔Effect of the invention〕

The present invention provides a developing method in which a two-component developer consisting of toner and carrier is used to develop the image forming member and the developer layer on the developer transport carrier in a non-contact manner, which is less susceptible to changes in toner density. Based on the discoveries of these researchers and the discovery that the development method described above makes it easy to adjust the development density to compensate for changes in toner density, this was achieved by skillfully combining these two methods, and this book is based on According to the developing method of the invention, there is no need for the troublesome means of constantly replenishing the developer consisting of carrier and toner in the developer reservoir with the amount of toner that has been used up, and sharp images are produced that are stable and have excellent reproducibility. The excellent effect of being able to obtain a recorded image without fogging can be obtained.

Note that the present invention is applicable not only to the case where the recording device is an electrophotographic copying machine, but also to a recording device using an electrostatic recording method or a magnetic recording method.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the toner density and the development density of a two-component developer, and FIG. 2 is a schematic configuration diagram showing an example of a recording apparatus that implements the developing method of the present invention.
3 and 4 are graphs showing the relationship between the electrostatic latent image potential and the developing bias and the developed concentration, and FIGS. 5 and 6 are graphs showing the relationship between the developer conveyance speed of the developer conveying carrier and the developed concentration. The graphs shown in FIGS. 7 and 8 are cross-sectional views showing an example of a developing device used in the method of the present invention, which is different from that shown in FIG. DESCRIPTION OF SYMBOLS 1... Exposure lamp, 2-5... Reflection mirror, 6... Lens, 7... Charging electrode, 8... Photosensitive drum, 9... Developing device, 91... Developer reservoir, 92... Developing sleeve,
93... Magnet body, 94... Layer thickness regulating blade, 95...
Toner hopper, 96... Bottom plate, 97... Stirring means, 9
8...Cleaning blade, 10...Transfer pole, 11
...Separation electrode, 12...Development concentration detector, 13...Cleaning device, 14...Main control device, 15...Toner concentration detector.

Claims (1)

[Scope of Claims] 1. A developer layer is formed by supplying a developer containing a carrier and toner from a developer reservoir to a developer transport carrier surface, and a latent image is formed by flying the toner from the developer layer. In a developing method in which the toner is deposited on the surface of an image forming body, the effect of changes in toner concentration is compensated for by changing other image forming conditions in accordance with changes in the toner concentration of the developer in the developer reservoir. Characteristic development method. 2. The method according to claim 1, wherein when the developer density decreases even when the other image forming conditions are changed, toner is replenished into the developer reservoir to restore the toner density of the developer. Development method. 3. The developing method according to claim 2, wherein when the developer reservoir is replenished with toner, the developer in the developer reservoir is stirred prior to forming a latent image on the image forming body.