JPH1049023A - Cleaning equipment - Google Patents

Abstract

(57) [Problem] To efficiently collect transfer residual toner without deteriorating or soiling an intermediate transfer member. SOLUTION: A charging roller 15 is provided in contact with an intermediate transfer member 8 with a small gap, and a charging bias of a charging bias power supply 16 is applied to the charging roller 15. At this time, the charging bias applied by the charging bias power supply 16 is D
This is a voltage obtained by superimposing an AC voltage on a C voltage. Then, by applying a charging bias power supply 16 to the charging roller 15, the secondary transfer residual toner remaining on the intermediate transfer member 8 is collected on the photosensitive drum 1 in the primary transfer section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cleaning device in an intermediate transfer type image forming apparatus.

[0002]

2. Description of the Related Art In recent years, with the development of the information-oriented society, needs for outputting documents and images in color have been widened, and various types of printers have been released. As a color image forming method, an image forming apparatus such as a sublimation type, a thermal transfer type, and an ink jet method is used, but an electrophotographic method is said to be the most excellent for forming an image at a high speed.

Among the electrophotographic image forming apparatuses, an intermediate transfer method, which can form an image without selecting transfer paper and is excellent in color registration, is becoming mainstream.

In an image forming apparatus of an intermediate transfer system, a yellow image formed on a rotating drum type electrophotographic photosensitive member (hereinafter simply referred to as a "photosensitive drum") as a first image carrier is provided.
Each of the magenta, cyan, and sometimes black single-color images is superimposed on an intermediate transfer drum (solid drum) or a belt-like intermediate transfer member as a second image carrier, and finally, a full-color image is collectively collected as a second image carrier. The transfer is performed on transfer paper as the image carrier of No. 3.

[0005] This intermediate transfer system does not require the transfer paper to be wound around the intermediate transfer drum, so it can be used for envelopes and thick paper, is highly versatile, and has a variable color registration depending on the thickness of the transfer paper. There is no merit that high image quality can be obtained.

However, since the secondary transfer efficiency from the intermediate transfer drum to the transfer paper cannot be 100%, a small amount of transfer residual toner remains on the intermediate transfer drum after image formation. Adversely affects image formation. The toner not transferred to the paper is hereinafter referred to as a secondary transfer residual toner.

In order to prevent this, a cleaning blade is provided on the intermediate transfer drum to collect transfer residual toner, and the transfer residual toner is scattered by a fur brush to form a toner image in the next image formation. Methods have been used to make dirt less noticeable.

[0008]

However, as described above, when the cleaning blade or the fur brush is brought into contact with the intermediate transfer drum to physically recover the transfer residual toner, the surface of the intermediate transfer drum may be damaged. There is a problem that the toner is embedded or the toner is embedded.

The intermediate transfer member as the second image bearing member must be in contact with the photosensitive drum while maintaining a constant nip width, and must perform primary transfer. Therefore, elasticity is required.
When the intermediate transfer body is an intermediate transfer drum, the one coated with a rubber layer is used.In the case of the intermediate transfer belt, the one coated with a rubber belt or a resin belt is generally used. I have. As these coating layers, those obtained by dispersing a lubricant or a filler for resistance adjustment in various organic binders are used, but have a problem that they are weak against physical rubbing.

In particular, since an electrophotographic printer is required to have a long service life and high durability, deterioration and contamination of the intermediate transfer member shortens the life of the image forming apparatus main body. There has been a demand for a method of collecting transfer residual toner without damaging the toner.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and is intended to efficiently collect transfer residual toner without deteriorating or soiling the intermediate transfer member. It is an object of the present invention to provide a cleaning device that has been developed.

[0012]

To achieve the above object, a cleaning apparatus according to the first aspect of the present invention comprises:
A second image carrier on which a toner image formed on the image carrier is primarily transferred at a primary transfer portion between the first image carrier and a third image carrier; A transfer unit for secondary-transferring the toner image to the image carrier; and a toner collecting and charging unit for contacting and charging the transfer residual toner remaining on the second image carrier. Recovering remaining toner from the primary transfer unit to the image carrier, wherein the toner recovery unit includes a cleaning member, and a charging bias power supply for applying a voltage to the cleaning member. The power supply is DC voltage A
A voltage on which the C voltage is superimposed is applied to the cleaning member.

According to the present invention, the toner collecting means uses a charging roller as a cleaning member.

According to a third aspect of the present invention, the charging roller has a multilayer structure, and a volume resistance value of an outermost layer is set to be larger than a volume resistance value of an inner layer inside the outermost layer.

According to the fourth aspect of the invention, the charging bias from the charging bias power supply changes the DC voltage of the polarity opposite to the polarity of the developer charged by the developing means to the second voltage.
The voltage is set to a voltage obtained by superimposing an AC voltage which is a peak-to-peak voltage at least twice as high as a voltage at which a discharge occurs between the image carrier and the cleaning member.

According to a fifth aspect of the present invention, the DC voltage component of the charging bias from the charging bias power supply is set by constant current control, and the AC voltage component is set by constant voltage control.

According to a sixth aspect of the present invention, the AC voltage applied from the charging bias power supply is higher in a high humidity environment than in a low humidity environment.

[0018] According to a seventh aspect, the triboelectric charge of the secondary transfer residual toner before being collected in the first image bearing member is charged by the second image bearing member onto a Q _1, wherein when the triboelectricity of the toner before being primarily transferred is charged by the first image bearing member and Q _2, and Q _1, Q ₂ have opposite polarities, and _{| Q 1 | <| Q 2} | relationship: It is in.

According to the present invention, the first image carrier is a photosensitive drum.

According to the ninth aspect, the second image bearing member is an intermediate transfer member.

[Operation] Based on the above configuration, the cleaning member is brought into contact with the second image carrier, and a charging bias of a charging bias power supply is applied to the cleaning member. The charging bias applied by the charging bias power supply at this time is a voltage obtained by superimposing an AC voltage on a DC voltage. Thereby, the secondary transfer residual toner remaining on the second image carrier is collected by the first image carrier in the primary transfer section.

Further, the volume resistance value of the outermost layer of the cleaning member having a multilayer structure is set to be larger than the volume resistance value of the inner layer.

Further, the AC voltage superimposed on the DC voltage of the charging bias is controlled at a constant voltage, or A
The C voltage is controlled to be low so that toner can be efficiently collected in a high humidity environment, and adverse effects such as excessive application of an AC voltage in a low humidity environment are eliminated.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings. <First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention.
Is an intermediate transfer type electrophotographic full-color printer. In this electrophotographic full-color printer, A3 has a maximum paper passing width size, and a process speed is 100 mm / sec.

In FIG. 1, reference numeral 1 denotes a photosensitive drum, and the photosensitive drum 1 is, for example, an OPC photosensitive drum having a diameter of 86 mm. The photosensitive drum 1 has a configuration in which an undercoat layer, a charge injection preventing layer, a charge generation layer, a charge transport layer, and a protective layer are provided on an aluminum drum substrate. The protective layer is formed by dispersing tin oxide for adjusting a resistance value and Teflon particles for releasing property in a photocurable acrylic binder.

The photosensitive drum 1 includes charging means 2 and 3 for uniformly charging the photosensitive drum 1 to -500 V, image information writing means 4, developing means 6 and 7, and a second A cleaning device 9 having an intermediate transfer member 8 as an image carrier and a cleaning blade 9a is provided.

The charging means has a configuration in which a bias power supply 3 is connected to a charging roller 2 as a charging member. The voltage applied from the bias power supply 3 to the charging roller 2 is a DC voltage of -500 V and a sine wave of 1000 Hz. An AC voltage of 2000 V peak-to-peak voltage Vpp is superimposed. Then, by applying a voltage from the bias power supply 3 to the charging roller 2, the charge is moved by discharging to the insulating photosensitive drum 1 to perform charging.

On the charged surface of the photosensitive drum 1, a laser beam whose intensity is modulated in synchronism with the image signal by the image information writing means 4 is image-exposed to form an electrostatic latent image. The laser beam intensity is set so that the surface potential (bright portion potential) of the photosensitive drum 1 in the portion exposed by the laser beam becomes -200V.

The developing means includes an independent magnetic one-component developing device 6, a rotary non-magnetic one-component developing device 7 provided separately from the developing device 6, and a developing bias power source (not shown). The developing unit 6 develops a black image, and the developing unit 7 develops cyan, magenta, and yellow color images. Then, the electrostatic latent image formed on the photosensitive drum 1 is visualized by the developing devices 6 and 7 to form a toner image. The black toner contained in the developing device 6 is
A pulverized toner having a particle diameter of 6 μm is subjected to a spheroidizing treatment.
0 parts, and a charge control agent, a lubricant, etc. are internally added. The color toner contained in the developing device 7 is
This is a capsule-type spherical non-magnetic toner manufactured by a polymerization method and containing wax.

When printing is performed, the developing units 6 and 7 move to predetermined positions facing the photosensitive drum 1 in accordance with required colors, and develop an electrostatic latent image. A bias in which a rectangular wave of 2000 Hz and a peak-to-peak voltage of 2000 V is superimposed on a direct current of −350 V and a direct current of −350 V is applied to each of the developing units 6 and 7 to form an alternating electric field between the developing sleeve and the photosensitive drum 1, and the toner is discharged. Reversal development is performed by a jumping method of flying.

Next, the intermediate transfer member 8 will be described.

A bias power source 8a for applying a primary transfer bias is connected to the intermediate transfer member 8, and a transfer roller 11 is brought into contact with the intermediate transfer member 8 via a transfer belt 12 which conveys a transfer sheet from a paper supply unit (not shown). ing. Also, the transfer roller 1
1 is a secondary transfer bias power supply 13 to which secondary transfer is applied.
Is connected. A charging roller (contact charging member) 15 as a cleaning member is in contact with the intermediate transfer body 8, and a charging bias power supply 16 is connected to the charging roller 15, and the charging roller 15 and the charging bias power supply 16 This constitutes a toner collecting means 17.

The intermediate transfer member 8 used in the present embodiment is formed on a solid drum having a diameter of 186 mm, and is a transfer paper (A3 size in the present embodiment) as a third image carrier having a maximum paper passing size. ) Has such a circumference that an image corresponding to) can be written.

On the metal drum 8b, a rubber layer 8c of medium resistance is coated as an elastic layer with a thickness of 5 mm, and the rubber layer 8c is coated with a coating of 20 μm in order to secure releasability. The rubber is formed of NBR and ethylene oxide, and the volume resistance is reduced to 10 ⁵ Ωcm by ethylene oxide. The coating is obtained by dispersing 400 parts of PTFE particles in an acrylic binder, and applies a voltage of 100 V between the area of 10 cm ² on the surface of the intermediate transfer member 8 and the metal drum to convert the resistance from the current measured. The value is 10 ⁶ Ω.

In order to primarily transfer the toner on the photosensitive drum 1 onto the intermediate transfer member 8, +100 V is applied to the metal drum from the bias power supply 8a as a primary transfer bias. Actually, the area where the toner image is formed on the photosensitive drum 1 is at VL = -200V, which is the exposure position, so that the primary transfer contrast is 300V which is the difference between these.

When a full-color image is formed, the intermediate transfer member 8 makes four rotations, and in each rotation, a single-color toner image of yellow, magenta, cyan, and black is sequentially transferred from the photosensitive drum 1, and finally each color is transferred. The toner images are stacked to form a full-color toner image.

The primary transfer residual toner on the surface of the photosensitive drum 1 is scraped off by the cleaning blade 9a to prepare for the next image formation.

The toner image on the intermediate transfer member 8 is collectively transferred to transfer paper supplied from a paper supply unit (not shown). −), And the charge transfer occurs in the nip between the photosensitive drum 1 and the intermediate transfer member 8 during the four rotations of the intermediate transfer member 8, so that the toner layer is charged with a corona charger. 10 needs to be recharged negatively. The corona charger 10 is disposed opposite to the intermediate transfer member 8 and is a corotron charger through which a wire current of -200 μA flows by the current source 14, and the toner layer is recharged to increase the absolute value of the tribo. Specifically, the tribo of the magnetic toner, which was about −10 μC / g, is −3.
0 μC / g, and the tribo of the non-magnetic toner is -30 μC.
It rises from C / g to -50 μC / g.

In this embodiment, as a method for measuring the tribo, the toner on the intermediate transfer member is sucked by air, and the weight and the charge amount of the sampled toner are measured by the electronic balance and the Faraday gauge. Calculated from the value measured in
/ G.

Since the intermediate transfer member 8 has a large diameter of 200 mm and cannot separate the transfer paper by curvature, the secondary transfer from the intermediate transfer member 8 to the transfer paper is performed by the transfer belt 12 via the transfer roller 11.

The transfer belt 12 because the adsorption of the transfer sheet, which has a larger capacitance by performing a coating of 30μm of PVDF in conductive urethane belt, and 10 cm ² area and belt base of the belt Between 10
The resistance value measured by applying a voltage of 00 V was 10 ¹⁰ Ω, and the capacitance measured by applying a voltage of 1 V and 1000 Hz in the same measurement region was 1 nF.

The transfer roller 11 is a low-resistance rubber roller, and its impedance substantially depends only on the low resistance of the surface layer of the transfer belt 12.

A +20 μA transfer current is applied to the transfer belt 12 to transfer a toner image onto transfer paper.

The transfer efficiency in a general electrophotographic image forming apparatus is about 85%, and in the printer of the present embodiment, the toner layer before the secondary transfer is recharged.
Although the transfer efficiency can be increased to about 95%, the transfer efficiency is reduced to 10% by the electrostatic transfer method due to the presence of the mirror force between the intermediate transfer body 8 and the toner and the van der Waals force.
It is difficult to achieve 0%, and it is unavoidable that transfer residual toner remains.

The transfer residual toner generally has a positive charge inverted by the transfer current, but may remain negative when the transfer current is low or the resistance value of the transfer paper is low. Is unstable.

In the electrophotographic image forming apparatus of the present embodiment, a process is used in which primary transfer of the next image is performed at the primary transfer nip while simultaneously removing the transfer residual toner of the previous image.

As described above, the photosensitive drum 1 has an electrostatic latent image formed on the surface thereof so that the photosensitive drum 1 has a voltage of -200 to -500V.
, And a bias of +100 V is applied to the intermediate transfer member 8 from the bias power supply 8a. Therefore, the force acting on the primary transfer nip is the force of the minus toner toward the intermediate transfer member 8 and the force of the plus toner returning to the photosensitive drum 1.

The toner to which the next image is to be transferred is-
Since it has a tribo of about 10 μC / g, it can be transferred from the photosensitive drum 1 to the intermediate transfer member 8, but the secondary transfer residual toner has a low toner tribo or an unstable photosensitive drum as described above. In some cases, the ghost image is not collected and appears as a cleaning defect or ghost in the next image, causing image defects.

In view of the above, a method using toner collecting means 17 for forcibly charging the secondary transfer residual toner after the secondary transfer and collecting the toner on the photosensitive drum 1 has been devised, and has achieved a certain effect.

As the toner collecting means 17, a charging roller 15 as a contact charging member is used, and the secondary transfer residual toner is simultaneously charged by flowing a current from a charging bias power supply 16 while being in contact with the intermediate transfer member 8. is there. Less than,
In order to distinguish the charging roller 2 from the charging roller 2 which is in contact with the photosensitive drum 1, the charging roller 15 for removing the secondary transfer residual toner is referred to as an ICL roller 15.

The charging of the toner layer by the ICL roller 15 is performed by discharging. This is because the toner used in the present embodiment is an insulating toner, and almost no charge is injected from the intermediate transfer member 8 having a medium resistance or the ICL roller 15, and only the discharge from the surface of the ICL roller 15 is performed. Is charged only by

However, as in the conventional case, DC is applied to the ICL roller.
When only the voltage is applied to charge the toner layer,
Only the outermost layer of the toner layer is charged. In other words, the surface layer of the toner layer becomes a positive toner having a high tribo, and a relatively low tribo toner which is not charged remains in the inner layer. Attempting to clean the toner layer in such a state causes two problems, that is, cleaning failure and negative ghost as described below. (1) Insufficient Cleaning If the inner layer of the toner that has passed through the ICL roller and has been charged remains at a low tribo, an inferior cleaning occurs in the next image. Since the cleaning is performed by collecting the positively charged secondary transfer residual toner with an electric field between the photosensitive drum and the intermediate transfer member, the toner having a weak plus or minus tribo is not collected. Positive ghosts of poor cleaning appear on solid white portions of the next image, resulting in large image defects.

In order to prevent this, it is necessary to supply a large current to the ICL roller so that the toner in the inner layer also has a positive tribo. However, in this case, the tribo of the surface layer of the toner layer has a higher tribo. (2) Negative Ghost The outermost layer of the toner layer after passing through the ICL roller is strongly charged, and its tribo reaches up to +50 μC / g or more. Such toner adversely affects the next image when it is cleaned at the primary transfer nip. The toner tribo of the next image, which is subjected to the primary transfer simultaneously with the cleaning, is only about −10 μC / g in the case of the black toner. Therefore, such toner is electrostatically attracted to the toner having a strong positive tribo to be cleaned, and returns to the photosensitive drum without being primarily transferred to the intermediate transfer member.

Therefore, for example, even if an attempt is made to form a solid black image, since a portion of the toner corresponding to the previous image has returned to the photosensitive drum, a density difference occurs and the image is observed as a negative ghost.

More specifically, one secondary transfer residual toner of +50 μC / g attracts five toners to be transferred of −10 μC / g to cause a negative ghost. Even if the amount is small, the effect on the image is large.

To prevent such a phenomenon, an IC
It is effective to reduce the current flowing to the L roller to lower the tribo of the strongly positively charged surface layer of the secondary transfer residual toner. However, if such measures are taken, the toner in the inner layer will not be charged, and thus cleaning failure will occur. Becomes intense conversely.

As described above, the poor cleaning and the negative ghost are contrary to each other. When the current flowing through the ICL roller is increased, the negative ghost becomes more intense. Can not be found.

These phenomena become remarkable in a high-humidity environment in which the tribo of the toner to be developed is low or in a magnetic black toner in which the tribo is originally low.

In a high-humidity environment, the resistance of the intermediate transfer member or the ICL roller, which has a medium resistance, decreases due to the absorption of moisture.
Even when a current flows through the CL roller, most of the current directly becomes an injection current, so that it is difficult to generate a discharge and the toner cannot be positively charged, so that a cleaning failure easily occurs.

Similarly, in a high-humidity environment, the toner absorbs moisture and the resistance value decreases. In particular, in the case of the magnetic toner, the tribo of the toner to be developed decreases, and the toner is attracted to the positively charged cleaning toner. As the number of toner returning to the photosensitive drum increases, the negative ghost also worsens.

To solve these two problems, an IC must be used.
It is necessary to equalize the toner tribo after passing through the L roller. Such a problem can be solved by uniformly charging all the toner layers positively because the strong positive toner on the surface layer causes a negative ghost and the weak tribo toner on the inner layer causes poor cleaning. .

In order to realize this, in the present embodiment, I
An AC voltage is superimposed on a DC voltage as a charging bias applied from a charging bias power supply 16 to the CL roller 15.

By applying the AC voltage, not only the discharge from the ICL roller 15 but also the reverse discharge from the intermediate transfer member 8 can be excited, and an electric field can be applied to the inside of the toner layer. Further, when a higher AC voltage is applied, the toner starts to fly between the intermediate transfer member 8 and the ICL roller 15, so that the toner is replaced in the toner layer, and the toner is more uniformly charged. Will be possible.

A specific example will be described below.

The ICL roller 15 used in this embodiment is a single-layer solid roller having a diameter of 20 mm.

The conductive rubber layer provided on the core metal having a diameter of 6 mm has a volume resistivity of 10 ⁷ in which carbon is dispersed in EPDM rubber.
The resistance value of the ICL roller 15 is determined by pressing the ICL roller 15 against the metal drum of the intermediate transfer member 8 to form a contact nip having a width of 3 mm. And a resistance value of 10 ⁶ Ω measured by applying a DC voltage of 100 V to the substrate.

The ICL roller 15 is separated from the intermediate transfer member 8 during non-image formation, and comes into contact with a charging bias only when charging the secondary transfer residual toner. It is not necessary to consider contamination such as bleeding which is a problem in the roller 15.

A bias in which an AC constant current is superimposed on a DC constant current is applied to the ICL roller 15 as an ICL current. The reason why the constant current is controlled is that a constant charge is applied to the toner even when the resistance values of the intermediate transfer member 8 and the ICL roller 15 change.

Specifically, the DC component is a constant current of +60 μA, the AC component is 2000 μA, and the frequency is 1000 Hz.
Sine wave. When this current is applied to the ICL roller 15, the high temperature and high humidity environment of 30 ° C. and 80% RH (hereinafter referred to as H /
H): 4000 V peak-to-peak voltage, 15 ° C., 10% R
Under a low-temperature and low-humidity environment of H (hereinafter referred to as L / L), an AC voltage of 8000 V peak-to-peak voltage is generated. With this voltage, the secondary transfer residual toner receives discharge from both the ICL roller 15 and the intermediate transfer member 8 and is uniformly charged. Furthermore, since jumping occurs between the two, the toner layer is disturbed, and further uniform charging becomes possible.

When the AC voltage is superimposed on the DC voltage,
Since the DC component is also easy to discharge,
DC voltage required to flow +60 μA is 5 for each environment.
00V.

The frequency of the AC voltage superimposed on the DC voltage is determined from the process speed of the image forming apparatus. In this embodiment, the process speed is 100 mm
/ Sec, the period of the AC component on the intermediate transfer member 8 is determined to be sufficiently short, and the frequency is 1000
Hz, the pitch (corresponding to an AC cycle mark when charging the photosensitive drum 1) is 100 μm
Becomes Generally, the period is preferably 1 mm or less.

The AC voltage is applied from the intermediate transfer member 8 to the ICL.
It is necessary to have a peak-to-peak voltage Vpp at which a reverse discharge starts to occur at the roller 15, and it is desirable that the intermediate transfer member 8 and the ICL roller 15 have a peak-to-peak voltage at least twice as high as the discharge start voltage. To cause this, it is necessary to apply a higher voltage.

Since both are functional components in the medium resistance region, it is difficult to define a discharge starting voltage between the intermediate transfer member 8 and the ICL roller 15, but as shown in FIG. A voltage is applied, and a voltage at which the slope of the current-voltage characteristic starts to change is defined as a discharge starting voltage.

Further, regarding the AC waveform,
A sine wave that does not include harmonics is desirable in order to reduce damage to the printer, and a rectangular wave that can maintain the peak-to-peak voltage Vpp long is desirable in order to cause efficient charging and toner flying with a low peak-to-peak voltage Vpp.

The DC voltage on which the AC voltage (current) is superimposed
By changing the voltage (current), the toner tribo after passing through the ICL roller 15 can be controlled. That is, the toner tribo after passing the ICL roller 15 can be set to a high value by increasing the applied DC voltage.

Further, by superimposing the AC component on the DC component, the convergence of the toner tribo can be expected. Even if the toner tribo is not stable before passing through the ICL roller 15, the tribo after passing is set to a stable predetermined value. Will be able to do it.

An example in which an experiment was actually performed in an H / H environment will be described below.

As a comparative example, an experiment was conducted in which only a DC constant current of +60 μA was passed without superimposing an AC component on a DC component. When only the DC component was applied, the voltage required to flow +60 μA was 3000 V.

For evaluation, four continuous prints were performed in the order of a character image, a solid black, a character image, and a solid white, and a negative ghost was evaluated with the second solid black and a cleaning defect was evaluated with the fourth solid white. .

Further, the image forming apparatus is stopped during printing of the solid black image, and the IC during cleaning is performed.
When the secondary transfer residual toner before and after passing through the L roller 15 and the cleaning failure occurred, the tribo of the toner not collected on the photosensitive drum 1 was also measured.

The evaluation was performed in an H / H environment under severe conditions.

First, when evaluation was performed by applying only the DC component of the conventional example, cleaning failure and negative ghost occurred simultaneously. This is because the surface layer of the secondary transfer residual toner is strongly positively charged and the inner layer is still weakly triboelectric. The tribo measurement value at this time is ICL
+3 μC / g before passing through roller 15, +50 μC after passing
/ G, and the tribo of the poorly-cleaned toner not collected on the photosensitive drum 1 was −5 μC / g. The tribo after passing is high because the toner on the surface is extremely positively charged, and the tribo of toner with poor cleaning is negative. It supports the existence of a tribo-distribution within.

On the other hand, when a bias in which the AC component was superimposed on the DC component was applied, neither cleaning failure nor negative ghost occurred. The measured value of the tribo at this time is IC
+ 3μC / g before passing through L roller 15, + 10μ after passing
C / g. The reason why cleaning failure does not occur even though the tribo after passing through the ICL roller 15 is relatively low is that there is no tribo distribution in the toner layer and the toner layer is uniformly charged to +10 μC / g.

Further, the secondary transfer residual toner of the character image is AC
When the image forming apparatus is stopped and the toner image on the intermediate transfer body 8 is observed while passing through the ICL roller 15 to which the image is applied, characters can be read clearly before passing through the ICL roller 15 but after passing through the ICL roller 15, The toner image seemed to be scattered, and it was observed that the toner flies between the intermediate transfer member 8 and the ICL roller 15 and the secondary transfer residual toner is disturbed.

As described above, conventionally, only a DC bias was applied to the ICL roller, so that a tribo distribution was formed in the secondary transfer residual toner layer, and cleaning failure and negative ghost occurred. By superimposing the AC voltage on the DC voltage as in the embodiment, the tribo distribution in the toner layer can be eliminated, and the toner flies between the intermediate transfer body 8 and the ICL roller 15 by the AC electric field. As a result, the toner is disturbed, and the toner tribo is made uniform. <Second Embodiment> This embodiment is characterized in that the AC component applied to the ICL roller 15 is controlled at a constant voltage.

In the first embodiment, the intermediate transfer member 8 and the I
Since the impedance of the CL roller 15 changes due to fluctuations in manufacturing and environmental fluctuations, the electric field applied between each of the AC component and the DC component is controlled to be constant by performing constant current control.

However, the negative ghost actually becomes remarkable only in the H / H environment where the resistance value of the toner is reduced due to moisture absorption and the tribo is reduced.

Conversely, if an unnecessary AC voltage is continuously applied, an oscillating electric field acts between the ICL roller 15 and the intermediate transfer member 8 and further discharge is generated. It causes problems such as fusion.

In order to solve this problem, it is necessary to use AC only in an H / H environment where a negative ghost or a cleaning defect is likely to occur.
It is effective to form an electric field.

Therefore, in the present embodiment, the AC voltage is set to a constant voltage control, and is set to a peak-to-peak voltage so that a sufficient electric field can be formed in an H / H environment.

In other environments, since the resistance of the intermediate transfer member 8 and the ICL roller 15 increases, an AC voltage is consumed in this portion, and a gap electric field causing surface deterioration of the intermediate transfer member 8 and the ICL roller 15 is generated. Can be restricted. In other words, the control aims at automatically correcting the gap electric field depending on the environment.

A specific example will be described.

The full-color image forming apparatus used is the first one.
This is the same as that shown in the embodiment.

The bias applied to the ICL roller 15 is
1000H to the DC component which is controlled to +60 μA
It is assumed that a rectangular wave having a z and a peak-to-peak voltage of 4000 V is superimposed. This is a value set so that a negative ghost and poor cleaning do not occur in the H / H environment.

Table 1 below shows an example in which each environment was evaluated with this setting.

[0096]

[Table 1] Table 1 above shows the AC current flowing by applying an AC voltage of 4000 V peak-to-peak voltage, and +60 μA
3 shows a DC voltage required to flow a DC current.
The gap between the intermediate transfer member 8 and the ICL roller 15 is A
When a C electric field is applied to generate a discharge,
It can be seen that the voltage required to flow the DC current of A is low. Also. In the L / L environment, the effect of AC is completely lost, and the value is the same as the value of DC only.

As described above, especially in the L / L environment, the impedance of the intermediate transfer member 8 and the ICL roller 15 increases, so that the AC voltage is not applied to the gap, and in an environment in which a negative ghost or a cleaning failure does not occur, an unnecessary amount is generated. Discharge can be suppressed.

The occurrence of image defects due to a decrease in toner tribo is caused by the same moisture absorption phenomenon even when the impedance of the intermediate transfer member 8 and the ICL roller 15 is low. Can be automatically detected.

Intermediate transfer member 8 by AC constant voltage control, IC
An example in which a durability test was performed on the effect of preventing the deterioration of the L roller 15 will be described. Since the printer of the present embodiment always returns to the home position when forming an image on the intermediate transfer member 8, the image is always drawn at the same position on the intermediate transfer member 8 when the same image is printed.

In this state, the same character image is
0 sheets were printed, and the stain on the intermediate transfer member 8 was observed. The test environment was performed in an L / L environment where the voltage was highest by AC constant current control.

In the AC constant current control, after printing 10000 sheets, the toner is clearly fused in a character pattern on the intermediate transfer member 8 and the toner is applied to the ICL roller 15 by an AC electric field.
You can see that they are being beaten. On the other hand, AC
Under the constant voltage control, 10,000 sheets were printed, and the intermediate transfer member 8 was hardly stained even after printing, and there was no problem in durability.

In the present embodiment, the control of the electric field applied between the intermediate transfer member 8 and the ICL roller 15 is automatically controlled by utilizing the environmental fluctuation of the impedance of the member. It is also possible to make a judgment and perform it by hardware.

For example, when humidity is high, high A
When the C voltage is applied, and conversely, when the humidity is low, the gap electric field can be controlled to a constant value or a desired value by using a corresponding AC voltage.

As described above, in the present embodiment, the IC
By controlling the AC voltage applied to the L roller 15 to a constant voltage, excessive application of the AC voltage in a low humidity environment can be prevented. Further, by detecting the environment, it is possible to control the AC voltage to an appropriate value, thereby preventing deterioration of the intermediate transfer member 8 and the ICL roller 15 due to unnecessary discharge. <Third Embodiment> In the present embodiment, by efficiently optimizing the configuration of the ICL roller, it is possible to efficiently apply the tribo of the secondary transfer residual toner.

As described above, since the toner used in the present embodiment is an insulating toner, almost no charge is injected from the intermediate transfer member 8 or the ICL roller 15 having a medium resistance. Is charged only by the discharge from the surface of the substrate.

However, when the photosensitive drum 1 is charged by the contact charging member, the discharge current is entirely the charge on the surface of the photosensitive drum 1, while the intermediate transfer member 8 having a medium resistance of about 10 ⁶ Ω is used. When an electric current is caused to flow by contacting the medium resistance ICL roller 15 of about 10 ⁸ Ω, most of the current flows through the contact nip without contributing to the discharge. In other words, most of the ICL current that has flowed becomes a reactive current.

The current paths between the intermediate transfer member 8 and the two-layer type ICL roller 15 are schematically shown in FIGS. 3 (a) and 3 (b).
It can be seen that the surface potential of the CL roller 15 changes.

+100 is applied to the core metal 15a of the ICL roller 15.
0V, the partial pressure of the intermediate transfer member 8 is set to 100 V, and ICL is applied.
The partial pressure of the low-resistance layer of the roller 15 (FIG.
V, assuming that the partial pressure of the high-resistance layer (FIG. 3B) of the ICL roller 15 is 800 V, it is necessary to increase the surface potential of the ICL roller 15 outside the nip where discharge actually occurs. It was found that the resistance value of the outermost layer of No. 15 had to be increased.

In the above example, when the resistance of the base layer of the ICL roller 15 is increased in order to limit the current, most of the generated voltage is a partial pressure of the base layer as shown in FIG. Since the surface voltage of the ICL roller 15 does not increase,
No discharge will occur and the reactive current must be increased.

As can be seen from the above description, in order to efficiently use the ICL current for charging the toner, the surface potential of the ICL roller 15 needs to be close to the potential applied to the ICL roller 15 while reducing the reactive current. To this end, it can be seen that a configuration in which the surface resistance of the ICL roller 15 is increased and the surface potential is increased is effective.

For this purpose, it is necessary to form the ICL roller 15 in a multilayer structure and to increase the surface resistance of the outermost layer. With such a configuration, it is possible to limit the surface current flowing through the ICL roller 15 and reduce the reactive current.

Specifically, the ICL used in this embodiment is
The roller 15 is a two-layer type roller having a high resistance layer on the surface layer, and has a low resistance elastic layer having a thickness of 3 mm and a coating layer having a thickness of 10 μm provided on a core metal 15a having a diameter of 6 mm.

The low resistance layer elastic layer is a sponge layer obtained by dispersing carbon in EPDM rubber, adjusting the volume resistance to 10 ³ Ωcm, and foaming in the mold. Since it is foamed in a mold at the time of molding, a film called a thin skin layer is formed on the roller surface, and subsequent coating is facilitated.

The surface high resistance layer is made of an acrylic resin and has a thickness of 10 μm by dipping coating. It is preferable that the surface resistance is as high as possible for the reason described above. However, when the surface resistance is 10 ¹³ Ωcm or more, local discharge starts, and the toner layer cannot be uniformly charged. Specifically, a spot-shaped discharge mark may be generated around a locally discharged portion, and cleaning failure according to this pattern occurs.

In order to prevent this, it is possible to disperse a conductive filler such as carbon or tin oxide in the coating material to perform the resistance value treatment. However, in the present embodiment, the conductive material has a polar group and has a slight ionic conductivity. This problem has been solved by using a coating resin that exhibits properties.
In this embodiment, the coating material has a volume resistance of 1
Adekabon titer (trade name, manufactured by Asahi Denka Kogyo Co., Ltd.) having a size of 0 ¹² Ωcm was used.

The coating material was coated on a conductive aluminum sheet having a volume of about 100 μm by a bar coating method to a coating resistance of about 30 μm, and the JI was applied to a high and low resistance meter manufactured by ADVANTEST.
It was defined as a value measured by attaching a high / low anti-constant constant chamber according to the S method.

The resistance value of the coated ICL roller was measured by pressing the roller against a metal drum to form a contact nip having a width of 3 mm and applying a DC voltage of 100 V between the nip and the metal core. By value, the resistance was 10 ⁸ Ω. In the single-layer roller of the first embodiment, the entire roller is a resistor. On the other hand, in the ICL roller of the present embodiment, a thin film of 10 μm on the surface bears most of the resistance.

The ICL roller 15 thus manufactured
Here is an example in which an experiment was performed by using.

First, in the example where only the DC bias is applied to the ICL roller 15, the current and voltage required to charge the toner tribo to +50 μC / g after passing through the ICL roller 15 are the same as in the first embodiment. +60 for layer rollers
In contrast to μA and +3000 V, the two-layer roller of the present embodiment only requires a current and voltage of +30 μA and +2000 V.

The reason for this is that in the ICL roller of the first embodiment, since the entire ICL roller is a resistor, the partial voltage applied to the roller itself is large, and the resistance value is low. This is because a large amount of current flows and an extra current is required to cause discharge.

In the roller according to the present embodiment, only the thin layer having a high surface resistance serves as a resistance layer, and the roller itself has a high resistance. Therefore, the voltage applied to the ICL roller 15 directly becomes the roller surface potential. And the reactive current injected into the intermediate transfer member 8 can be largely suppressed.

Next, a search was made for conditions that can prevent negative ghosting and poor cleaning by superimposing an AC voltage on a DC voltage, and found that a single-layer roller had a peak-to-peak voltage of 4000 V in an H / H environment and an AC current of 2500 μA. 3000V,
Although it was necessary to supply a DC current of 60 μA, in the roller of the present embodiment, only a peak-to-peak voltage of 2000 V, an AC current of 2500 μA, a DC current of 2000 V and 20 μA were required in the H / H environment.

In particular, regarding the AC component, since the ICL roller 15 of the present embodiment has a large capacitance, the impedance becomes small, and the partial pressure applied to the ICL roller 15 when a constant AC current flows is small. There is an advantage that it becomes.

Further, the ICL roller 15 of the present embodiment
Since the surface resistance is high, even if a discharge occurs in one part on the roller and a voltage drop occurs, the other part can keep the roller core metal potential without being dragged by this, so the discharge nip is relatively It can be widely used, and more efficient charging can be performed.

As described above, in the present embodiment, the IC
The L roller 15 has a multi-layer structure, and the volume resistance of the surface thereof is increased to minimize the ineffective current due to the injection into the intermediate transfer body 8, and the secondary transfer toner is effectively charged with a lower voltage and a smaller current. Now you can.

[0126]

As described above, according to the present invention, the cleaning member is provided in contact with the second image carrier with a small gap, and the cleaning member is
Since a charging bias in which an AC voltage is superimposed on a DC voltage is applied by a charging bias power source, the secondary transfer residual toner remaining on the second image carrier is removed from the first image carrier in the primary transfer section. Deteriorating the second image carrier,
It is possible to surely collect the toner without making it dirty.

Further, by forming the cleaning member in a multilayer structure and increasing the volume resistance value of the surface layer, the toner can be collected at a lower voltage.

Further, by controlling the AC voltage at a constant voltage or controlling the AC voltage to be low by detecting the environment,
While efficiently collecting toner in a high humidity environment,
The adverse effect in a low humidity environment due to the application of C can be prevented.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating current-voltage characteristics between an intermediate transfer member and an ICL roller.

FIG. 3 shows a configuration of a two-layer type charging roller used in a third embodiment of the present invention.
FIG. 4B is a schematic diagram illustrating an L roller, and FIG. 4B is a schematic diagram illustrating an ICL roller having a high surface resistance.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 First image carrier (photosensitive drum) 4 Image writing means 6 Black developing device 7 Color developing device 8 Second image carrier (intermediate transfer member) 11 Transfer device (transfer roller) 12 Transfer device (transfer belt) 15 Cleaning member (charging roller) 16 Toner collecting means (charging bias power supply) 17 Toner collecting means

Claims (9)

[Claims] 1. A primary transfer section between a first image bearing member and a first image bearing member,
A second image carrier on which a toner image formed on the image carrier is primarily transferred, a transfer unit for secondary-transferring the toner image from the second image carrier to a third image carrier, A toner collection and charging unit that contacts and charges the transfer residual toner remaining on the second image carrier, and transfers the secondary transfer residual toner charged by the toner recovery unit from the primary transfer unit to the image carrier. In the image forming apparatus for collection, the toner collection unit includes a cleaning member and a bias power supply for applying a voltage to the cleaning member, and the charging bias power supply cleans a voltage obtained by superimposing an AC voltage on a DC voltage. A cleaning device, wherein the cleaning device is applied to a member. 2. The cleaning device according to claim 1, wherein the toner collecting unit uses a charging roller as a cleaning member. 3. The charging roller according to claim 1, wherein a volume resistance value of an outermost layer is set to be larger than a volume resistance value of an inner layer inside the outermost layer. 2. The cleaning device according to 2. 4. A charging bias from the charging bias power supply is configured to generate a discharge between the second image bearing member and the cleaning member at a DC voltage having a polarity opposite to a polarity of a developer charged by a developing unit. The voltage according to any one of claims 1 to 3, wherein the voltage is set to a voltage obtained by superimposing an AC voltage that is a peak-to-peak voltage that is at least twice as high as a voltage generated.
A cleaning device as described. 5. The cleaning apparatus according to claim 4, wherein a DC voltage component of the charging bias from the charging bias power supply is set by constant current control, and an AC voltage component is set by constant voltage control. 6. A voltage applied from the charging bias power supply
6. The C voltage according to claim 1, wherein the C voltage is higher in a high humidity environment than in a low humidity environment.
A cleaning device as described. 7. The first image carrier, wherein a tribo of the secondary transfer residual toner before being charged on the second image carrier and collected by the first image carrier is Q _1. when the triboelectric charge of the toner before being primarily transferred is charged to the Q ₂ by the Q _1, Q ₂ have opposite polarities, and _{| Q 1 | <| Q 2} |
7. The method according to claim 1, wherein:
A cleaning device as described. 8. The cleaning device according to claim 1, wherein the first image carrier is a photosensitive drum. 9. The image forming apparatus according to claim 1, wherein the second image bearing member is an intermediate transfer member.
A cleaning device as described.