JP3466825B2 - Cleaning equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 an information-oriented society, there is a growing need for outputting documents and images in color, and various types of printers have been put on the market. As a color image forming method, an image forming apparatus such as a sublimation type, a thermal transfer type, or an ink jet method is used, and it is said that an electrophotographic method is the most excellent for high-speed image formation.

Among the electrophotographic image forming apparatuses, an intermediate transfer method which is capable of forming an image regardless of transfer paper and which is excellent in color registration is becoming the mainstream.

In the image forming apparatus of the intermediate transfer system, yellow formed on a rotary drum type electrophotographic photosensitive member (hereinafter simply referred to as "photosensitive drum") as a first image bearing member,
The magenta, cyan, and, in some cases, black single-color images are overlaid on the intermediate transfer drum (solid drum) or the belt-shaped intermediate transfer member as the second image carrier, and finally the full-color image is collectively printed. The transfer is performed on a transfer paper as an image carrier of No. 3.

Since this intermediate transfer system does not need to wind the transfer paper around the intermediate transfer drum, it can be applied to envelopes and thick paper, has high versatility, and the color registration changes depending on the thickness of the transfer paper. Therefore, there is an advantage that high image quality can be obtained.

By the way, 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 the image formation, and it remains as it is. Adversely affect image formation. The toner that has not been transferred to the paper is hereinafter referred to as the secondary transfer residual toner.

In order to prevent this, a cleaning blade is provided on the intermediate transfer drum to collect the transfer residual toner or to scatter the transfer residual toner with a fur brush so that the toner image at the time of the next image formation is formed. 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 collect the untransferred toner, the surface of the intermediate transfer drum is damaged. There is a problem that the toner is loosened or the toner is embedded.

The intermediate transfer member serving as the second image bearing member is required to have elasticity because it has to contact with the photosensitive drum while maintaining a constant nip width for primary transfer.
When the intermediate transfer body is an intermediate transfer drum, a rubber layer with a coating applied is used.When the intermediate transfer belt is an intermediate transfer belt, a rubber belt or a resin belt with a coating applied is generally used. There is. As these coating layers, various organic binders in which a lubricant or a filler for adjusting resistance is dispersed are used, but there is a problem that they are weak against physical rubbing.

In particular, since the electrophotographic printer is required to have a long life and a high durability, deterioration and stain of the intermediate transfer member will shorten the life of the image forming apparatus main body. A method for collecting the transfer residual toner without damaging the toner has been desired.

The present invention has been made to solve the above problems, and it is possible to efficiently collect the transfer residual toner without deteriorating or soiling the intermediate transfer member. An object of the present invention is to provide a cleaning device.

[0012]

In order to achieve the above-mentioned object, a cleaning device according to the invention of claim 1 is
At the primary transfer portion between the first image carrier and the second image carrier to which the toner image formed on the image carrier is primarily transferred, and from the second image carrier to the third image carrier. The secondary transfer device is provided with a transfer unit for secondarily transferring the toner image onto the image carrier and a toner collecting unit for contact-charging the transfer residual toner remaining on the second image carrier. The residual toner after transfer is collected from the primary transfer portion to the image carrier, and the toner collecting means is a charging member for cleaning.
It includes a member, a charging bias power source for applying a voltage to the cleaning charging member, the charging bias power supply, DC
The cleaning voltage is the voltage obtained by superimposing the AC voltage on the voltage .
It is characterized in that it is applied to a charging member .

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

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

According to the fourth aspect of the present invention, the charging bias from the charging bias power source is applied to the DC voltage having the opposite polarity to the polarity of the developer charged by the developing means.
The AC voltage, which is a peak-to-peak voltage that is at least twice as high as the voltage at which discharge occurs between the image carrier and the cleaning charging member , is set.

According to a fifth aspect of the present invention, the DC voltage component of the charging bias from the charging bias power source 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 source is higher in a high humidity environment than in a low humidity environment.

According to a seventh aspect of the present invention, the 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, and When the tribo of the toner charged by the first image carrier and before the primary transfer is Q ₂ , Q ₁ and Q ₂ have opposite polarities and | Q ₁ | <| Q ₂ | It is in.

According to the eighth aspect of the invention, the first image carrier is a photosensitive drum.

According to the invention of claim 9, the second image carrier is an intermediate transfer member.

[Operation] Based on the above construction, the second image carrier is cleaned.
The cleaning belt is brought into contact with the charging member for cleaning.
The charging bias of the charging bias power source is applied to the electric member .
At this time, the charging bias applied by the charging bias power source is D
It is assumed that the AC voltage is superimposed on the C voltage. As a result, the secondary transfer residual toner remaining on the second image carrier is recovered by the first image carrier at the primary transfer portion.

Further, the volume resistance value of the outermost layer of the multi-layered cleaning charging member is set to be larger than the volume resistance value of the inner inner layer.

Further, the AC voltage superimposed on the DC voltage of the charging bias is controlled to a constant voltage, and the A voltage is detected by the environment detection.
By controlling the C voltage to be low, the toner is efficiently collected in a high humidity environment, and the harmful effects such as excessive application of an AC voltage in a low humidity environment are eliminated.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described 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.
The image forming apparatus shown in (1) is an intermediate transfer type electrophotographic full-color printer. In this electrophotographic full-color printer, A3 is the maximum sheet width size, and the process speed is 100 mm / sec.

In the figure, 1 is a photosensitive drum, and this photosensitive drum 1 is, for example, an OPC photosensitive drum having a diameter of 86 mm. The photosensitive drum 1 has a structure in which an undercoat layer, a charge injection prevention layer, a charge generation layer, a charge transport layer and a protective layer are provided on an aluminum drum substrate. The protective layer is a photo-curable acrylic binder in which tin oxide for adjusting the resistance value and Teflon particles for releasability are dispersed.

The photosensitive drum 1 comprises charging means 2 and 3 for uniformly charging the photosensitive drum 1 to -500V, image information writing means 4, developing means 6 and 7, and second one in order along the direction of rotation indicated by arrow R1. A cleaning device 9 having an intermediate transfer member 8 as an image bearing member and a cleaning blade 9a is provided.

The charging means has a structure in which a bias power source 3 is connected to a charging roller 2 as a charging member, and a voltage applied from the bias power source 3 to the charging roller 2 is a DC voltage of -500V and a sine wave of 1000Hz. An AC voltage having a peak-to-peak voltage Vpp of 2000 V is superimposed. Then, by applying a voltage from the bias power source 3 to the charging roller 2, the charge is transferred to the photosensitive drum 1 made of an insulating material by electric discharge to perform charging.

On the charged surface of the photosensitive drum 1, laser light whose intensity is modulated in synchronization with an image signal by the image information writing means 4 is imagewise exposed to form an electrostatic latent image. The laser light intensity is set such that the surface potential (bright portion potential) of the photosensitive drum 1 in the portion exposed by the laser light is −200V.

The developing means comprises 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 device 6 develops a black image, and the developing device 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, and a magnetite 10 is added to a polyester binder
In addition to 0 parts, a charge control agent, a lubricant and the like are internally added. Further, the color toner built in the developing device 7 is
It is a capsule-type spherical non-magnetic toner produced by a polymerization method and containing wax.

When printing is performed, the developing devices 6 and 7 are moved to predetermined positions facing the photosensitive drum 1 according to the required color, and the electrostatic latent image is developed. A bias in which a rectangular wave of 2000 Hz and a peak-to-peak voltage of 2000 V is superimposed on DC of −350 V is applied to each of the developing devices 6 and 7, and an alternating electric field is formed between the developing sleeve and the photosensitive drum 1 to remove toner. 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 paper from a paper supply unit (not shown). ing. In addition, the transfer roller 1
The secondary transfer bias power source 13 to which the secondary transfer is applied
Are connected. Then, the intermediate transfer body 8, Cree
Charging roller as charging member (contact charging member)
15, a charging bias power source 16 is connected to the charging roller 15, and the charging roller 15 and the charging bias power source 16 constitute 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 the third image carrier having the maximum paper passing size. ) Has a perimeter that can be written an image equivalent to.

On the metal drum 8b, a rubber layer 8c having a medium resistance is coated as an elastic layer with a thickness of 5 mm. Further, this rubber layer 8c is coated with a thickness of 20 .mu.m in order to secure releasability. The rubber is formed of NBR and ethylene oxide, and the volume resistance value is reduced to 10 ⁵ Ωcm by ethylene oxide. The coating is 400 parts of PTFE particles dispersed in an acrylic binder, and the resistance converted from the current measured by applying 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. The value is 10 ⁶ Ω.

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

When forming a full-color image, the intermediate transfer member 8 rotates four times, and in each rotation, yellow, magenta, cyan, and black monochromatic toner images are transferred from the photosensitive drum 1, and finally each color image 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 a transfer sheet supplied from a sheet feeding unit (not shown), but a tribo of magnetic toner and non-magnetic toner (toner per unit weight) is used. The charge amount of − is different, and the charge transfer occurs in the nip portion between the photosensitive drum 1 and the intermediate transfer body 8 while the intermediate transfer body 8 rotates four times. It is necessary to recharge negatively by 10. The corona charger 10 is a corotron charger which is arranged opposite to the intermediate transfer member 8 and in which a wire current of -200 μA is supplied by the current source 14, and the absolute value of tribo increases when the toner layer is recharged. Specifically, the magnetic toner tribo, which was about −10 μC / g, was −3.
Increased to 0μC / g, and tribo of non-magnetic toner was -30μ
Increased from C / g to -50 μC / g.

In this embodiment, as a method for measuring tribo, the toner on the intermediate transfer member is sucked by air, and the weight of the sampled toner and the amount of electric charge are compared with an electronic balance and a Faraday gauge. Calculated from the value measured in
It was defined in units of / g.

Since the intermediate transfer member 8 has a large diameter of 200 mm and the transfer paper cannot be curvature-separated, 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.

In order to attract the transfer paper, the transfer belt 12 is a conductive urethane belt coated with 30 μm of PVDF to increase the electrostatic capacity. The transfer belt 12 forms a 10 cm ² area of the belt and the belt base. 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 transfer current of +20 μA is applied to the transfer belt 12 to transfer the toner image onto the transfer paper.

The transfer efficiency in a general electrophotographic image forming apparatus is about 85%, and since the toner layer before the secondary transfer is recharged in the printer of the present embodiment,
The transfer efficiency can be increased to about 95%, but since there is a mirroring force between the intermediate transfer body 8 and the toner and a van der Waals force, the transfer efficiency is 10% by the electrostatic transfer method.
It is difficult to set it to 0%, and it is inevitable that the transfer residual toner remains.

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

In the electrophotographic image forming apparatus of this embodiment, a process of simultaneously collecting the transfer residual toner of the previous image while performing the primary transfer of the next image in the primary transfer nip is used.

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

Further, the toner to be transferred of the next image is −
Since it has a tribo of about 10 μC / g, it can be transferred from the photosensitive drum 1 to the intermediate transfer body 8. However, as described above, the secondary transfer residual toner has a low toner tribo or an unstable photosensitive drum. 1 may not be collected and may appear as a cleaning failure or a ghost in the next image, causing an image failure.

Therefore, a method using a toner collecting means 17 for forcibly charging and collecting the secondary transfer residual toner after the secondary transfer on the photosensitive drum 1 has been devised, and a certain effect is obtained.

As the toner collecting means 17, a charging roller 15 which is a contact charging member is used, and the secondary transfer residual toner is also charged at the same time by bringing the charging roller 15 into contact with the intermediate transfer member 8 and supplying a current from the charging bias power source 16. is there. Less than,
In order to distinguish it from the charging roller 2 that contacts 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 the charge is hardly injected from the intermediate transfer medium 8 having a medium resistance or the ICL roller 15, and the discharge from the surface of the ICL roller 15 is exclusively 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. That is, the surface layer of the toner layer becomes positive toner having high tribo, and the toner of relatively low tribo that is not charged remains in the inner layer. When attempting to clean the toner layer in such a state, the following two problems occur: poor cleaning and negative ghost. (1) Improper cleaning If the inner layer of the toner that has passed through the ICL roller and has been charged remains in a low tribo state, improper cleaning will occur in the next image. Since the cleaning is performed by collecting the secondary transfer residual toner charged positively in the electric field between the photosensitive drum and the intermediate transfer member, the toner having a weak plus or minus tribo is not collected, It appears as a positive ghost of poor cleaning on the solid white part of the next image, and causes a large image defect.

In order to prevent this, it is necessary to apply a large current to the ICL roller so that the tribo of the toner in the inner layer becomes positive. However, in this case, the tribo on the surface layer of the toner layer has a higher tribo. (2) The outermost surface layer of the toner layer after passing through the negative ghost ICL roller is strongly charged, and its tribo reaches +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 adsorbed by 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, even if a solid black image is to be formed, for example, the toner of the portion corresponding to the previous image has returned to the photosensitive drum, so that a density difference occurs and it is observed as a negative ghost.

Specifically, one secondary transfer residual toner of +50 μC / g will cause a negative ghost by attracting five toners of -10 μC / g to be transferred, thus causing a secondary transfer residual toner. Even if the amount is small, the influence on the image becomes large.

In order to prevent such a phenomenon, IC
It is effective to reduce the current flowing to the L roller to lower the tribo on the surface layer of the secondary transfer residual toner which is strongly positively charged. However, if such measures are taken, the toner on the inner layer will not be charged and cleaning failure will occur. On the contrary, it becomes intense.

As described above, the cleaning failure and the negative ghost are opposite to each other. When the current flowing through the ICL roller is increased, the negative ghost becomes severe, and when the current is made small, the cleaning failure becomes severe. Can't find.

These phenomena become noticeable in a high humidity environment where the developed toner has a low tribo, and in a magnetic black toner which originally has a low tribo.

In a high-humidity environment, the intermediate transfer member and the ICL roller, which have medium resistance, absorb moisture to reduce the resistance.
Even if a current is passed through the CL roller, most of it becomes an injection current directly, so that discharge is hard to occur and the toner cannot be positively charged, so that cleaning failure easily occurs.

Similarly, in a high-humidity environment, the toner absorbs moisture and the resistance value decreases, so that the toner tribo of the toner to be developed particularly in the case of the magnetic toner decreases, and the toner is attracted to the cleaning toner charged positively. The negative ghost also deteriorates because the number of toners returning to the photosensitive drum increases.

In order to solve these two problems, IC
It is necessary to make the toner tribo even after passing the L roller. The strong positive toner on the surface layer causes a negative ghost, and the weak tribo toner on the inner layer causes cleaning failure.So, if all the toner layers are uniformly positively charged, such a problem can be solved. .

In order to realize this, in this embodiment, I
An AC voltage is superimposed on the DC voltage as a charging bias applied from the charging bias power source 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 body 8 and the ICL roller 15, so that the toner is replaced in the toner layer and the toner is evenly charged. It will be possible.

A specific example will be shown 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 resistance value of 10 ⁷ obtained by dispersing carbon in EPDM rubber.
It is a medium resistance rubber adjusted to Ωcm, and the resistance value of the ICL roller 15 is such that the ICL roller 15 is pressed against the metal drum of the intermediate transfer member 8 to form a contact nip with a width of 3 mm, and between this and the roller core metal. The resistance value measured by applying a DC voltage of 100 V was 10 ⁶ Ω.

The ICL roller 15 is separated from the intermediate transfer member 8 during non-image formation and abuts so that a charging bias is applied only when the secondary transfer residual toner is charged, so that the photosensitive drum 1 is charged. It is not necessary to consider contamination such as bleeding that causes a problem in the roller 15.

A bias obtained by superimposing an AC constant current on a DC constant current is applied to the ICL roller 15 as an ICL current. The reason for controlling to a constant current is to give a constant charge to the toner even if the resistance values of the intermediate transfer body 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 of. When this current is passed through the ICL roller 15, it is under a high temperature and high humidity environment of 30 ° C. and 80% RH (hereinafter, H /
H): 4000V peak-to-peak voltage, 15 ° C, 10% R
An AC voltage having a peak-to-peak voltage of 8000 V is generated under a low-temperature and low-humidity environment of H (hereinafter, L / L), and a peak-to-peak voltage of 6000 V is generated under a normal environment. Due to this voltage, the secondary transfer residual toner is discharged from both the ICL roller 15 and the intermediate transfer body 8 and is uniformly charged. Furthermore, since flying (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 it is easy for the DC component to discharge,
DC voltage required to flow + 60μA is 5 in each environment
It was 00V.

The frequency of the AC voltage superimposed on the DC voltage is determined by the process speed of the image forming apparatus. In this embodiment, the process speed is 100 mm
/ Sec, the cycle of the AC component on the intermediate transfer member 8 is determined to be sufficiently short.
When Hz is used, the pitch (corresponding to the 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 transferred from the intermediate transfer member 8 to the ICL.
The peak-to-peak voltage Vpp at which the reverse discharge starts to occur in the roller 15 is desirable, and it is preferable that the peak-to-peak voltage Vpp is not less than twice the discharge start voltage of the intermediate transfer body 8 and the ICL roller 15. In order to cause the above, it is necessary to apply a higher voltage.

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

Regarding the AC waveform, the intermediate transfer member 8
A sine wave that does not include harmonics is desirable from the standpoint of reducing damage to the target, and a rectangular wave that can maintain the peak-to-peak voltage Vpp long is desirable in order to cause efficient charging and toner flight at a low peak-to-peak voltage Vpp.

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

By superimposing the AC component on the DC component, the convergence of the toner tribo can be expected, and even if the toner tribo before passing the ICL roller 15 is unstable, the tribo after passing can be set to a stable predetermined value. Will be able to.

The following is an example of an actual experiment conducted in an H / H environment.

As a comparative example, an experiment was conducted in which an AC component was not superimposed on a DC component and only a DC constant current of +60 μA was passed. The voltage required to flow +60 μA when only the DC component was applied was 3000V.

In the evaluation, four sheets are continuously printed in the order of a character image, a solid black, a character image and a solid white, and a negative ghost is evaluated with the second solid black and a cleaning failure is evaluated with the fourth solid white. .

Further, the image forming apparatus is stopped during the printing of the solid black image, and the IC is being cleaned.
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 carried out in the H / H environment, which is a severe condition.

First, when the evaluation was performed by applying only the DC component of the conventional example, a defective cleaning and a negative ghost were simultaneously generated. This is because the surface layer of the secondary transfer residual toner is strongly positively charged and the inner layer remains weak tribo. Tribo measurement value at this time is ICL
+ 3μC / g before passing the roller 15, + 50μC after passing
/ G, the tribo of the cleaning failure toner not collected on the photosensitive drum 1 was -5 μC / g. The reason why the tribo after passing is high is that the toner on the surface is extremely positively charged, and the tribo of the toner with poor cleaning is negative. This proves that there is a tribo distribution within.

On the other hand, when a bias in which the AC component is superimposed on the DC component is applied, neither cleaning failure nor negative ghost occurs. Tribo measurement value at this time is IC
+ 3μC / g before passing L roller 15 and + 10μ after passing
It was C / g. The reason why the cleaning failure does not occur although 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.

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

As described above, since only the DC bias was applied to the ICL roller in the related art, a tribo distribution was formed in the secondary transfer residual toner layer, resulting in defective cleaning and negative ghost. 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 by the AC electric field between the intermediate transfer body 8 and the ICL roller 15. As a result, the toner is disturbed and the toner tribo is made uniform. <Second Embodiment> The present embodiment is characterized in that the AC component applied to the ICL roller 15 is subjected to constant voltage control.

In the first embodiment, the intermediate transfer member 8 or I
Since the impedance of the CL roller 15 changes due to fluctuations in the manufacturing process and environmental fluctuations, the electric field applied between the AC and DC components was controlled to be constant by controlling the constant current.

However, the negative ghost is actually remarkable only in the H / H environment in which the resistance value of the toner is lowered by moisture absorption and the tribo is lowered.

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

In order to solve this problem, AC is used only in the H / H environment where negative ghosts and cleaning defects are likely to occur.
It is effective to form an electric field.

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

In other environments, since the intermediate transfer body 8 and the ICL roller 15 have high resistance, the AC voltage is consumed at this portion, and the gap electric field which causes the surface deterioration of the intermediate transfer body 8 and the ICL roller 15 is generated. Will be able to limit. In other words, the purpose is to control such that the gap electric field is automatically corrected depending on the environment.

A specific example will be shown.

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

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

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

[0096]

[Table 1] Table 1 above shows the AC current that flows when an AC voltage of 4000V peak-to-peak is applied, and +60 μA.
Shows the DC voltage required to flow the DC current.
A in the gap between the intermediate transfer member 8 and the ICL roller 15
+ 60μ when C electric field is applied and electric discharge occurs
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 absent, and the value is the same as the value when only DC is applied.

As described above, since the impedances of the intermediate transfer member 8 and the ICL roller 15 are increased especially in the L / L environment, the AC voltage is prevented from being applied to the gap, and in an environment where negative ghost or cleaning failure does not occur, it is unnecessary. The discharge can be suppressed.

Incidentally, the occurrence of image defects due to the reduction of toner tribo and the low resistance of the impedance of the intermediate transfer member 8 and the ICL roller 15 are caused by the same moisture absorption phenomenon. Will be automatically detected.

Intermediate transfer member 8, IC by AC constant voltage control
An example of performing a durability test on the deterioration preventing effect 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 body 8, when printing the same image, the image is always drawn at the same position on the intermediate transfer body 8.

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

In the AC constant current control, after printing 10,000 sheets, the toner is clearly fused on the intermediate transfer body 8 in a character pattern after printing, and the toner is in the AC electric field and the ICL roller 15
You can see that it has been struck by. On the other hand, AC
With constant voltage control, 10000 sheets were printed, and the intermediate transfer body 8 was hardly soiled even after printing, and there was no problem in durability.

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

For example, when the humidity is high, high A
It is also possible to control the gap electric field to a constant value or to a desired value by applying the C voltage and, conversely, when the humidity is low, to the 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, it becomes possible to prevent excessive application of the AC voltage in a low humidity environment. Further, it becomes possible to control the AC voltage to an appropriate value by detecting the environment and prevent the intermediate transfer body 8 and the ICL roller 15 from being deteriorated due to unnecessary discharge. <Third Embodiment> In the present embodiment, by optimizing the configuration of the ICL roller, it is possible to efficiently apply secondary transfer residual toner tribo.

As described above, since the toner used in this embodiment is an insulating toner, almost no charge is injected from the intermediate transfer medium 8 having a medium resistance or the ICL roller 15, and the ICL roller 15 is exclusively used. It is only charged by the discharge from its surface.

However, when the photosensitive drum 1 is charged by the contact charging member, the discharge current is all the charges on the surface of the photosensitive drum 1, while the intermediate transfer member 8 having a medium resistance of about 10 ⁶ Ω. When an ICL roller 15 having a medium resistance of about 10 ⁸ Ω is brought into contact with and a current is passed, most of it does not contribute to discharge and flows through the contact nip. That is, most of the ICL current that has flowed becomes a reactive current.

The current path between the intermediate transfer member 8 and the two-layer type ICL roller 15 is schematically shown in FIGS. 3A and 3B. When the layer structure of the ICL roller 15 is changed, I
It can be seen that the surface potential of the CL roller 15 changes.

+100 to the core metal 15a of the ICL roller 15
0 V is applied, the partial pressure of the intermediate transfer member 8 is 100 V, ICL
The partial pressure of the low resistance layer (FIG. 3 (a)) of the roller 15 is set to 100.
V, assuming that the partial pressure of the high resistance layer of the ICL roller 15 (FIG. 3B) is 800 V, in order to increase the surface potential of the ICL roller 15 outside the nip that actually causes discharge, the ICL roller 15 is It was found that the resistance value of the outermost layer of 15 must be increased.

In the above example, when the resistance of the base layer of the ICL roller 15 is increased to limit the current, most of the voltage generated as shown in FIG. 3 (a) is a partial voltage of the base layer. Since the surface voltage of the ICL roller 15 does not rise,
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, it is necessary to bring the surface potential of the ICL roller 15 close to the potential applied to the ICL roller 15 while reducing the reactive current. However, for this purpose, it can be seen that it is effective to increase the surface resistance of the ICL roller 15 and increase the surface potential.

For this purpose, it is necessary to make the ICL roller 15 a multi-layered structure and increase the surface resistance of the outermost layer. With such a configuration, it becomes possible to reduce the reactive current by limiting the surface current flowing through the ICL roller 15.

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

Low-resistivity layer The elastic layer is a sponge layer in which carbon is dispersed in EPDM rubber to adjust the volume resistance value to 10 ³ Ωcm and foam in the mold. Since it is foamed in the mold at the time of molding, a film called a thin skin layer is formed on the roller surface, which facilitates subsequent coating.

The high surface resistance layer is made of acrylic resin and has a film thickness of 10 μm by dipping coating. It is preferable that the surface resistance value is as high as possible for the reason described above, but if it is 10 ¹³ Ωcm or more, local discharge starts and the toner layer cannot be uniformly charged. Specifically, spot-shaped discharge marks may occur around the 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 for resistance value treatment. However, in the present embodiment, a polar group is present and some ionic conductivity is maintained. This problem has been solved by using a coating resin that exhibits properties.
In this embodiment, the coating material has a volume resistance value of 1
A product name of ADEKA BON TITER manufactured by Asahi Denka Co., Ltd. having a resistance of 0 ¹² Ωcm was used.

The volume resistance value is obtained by coating a coating material of about 30 μm on a conductive aluminum sheet of 100 μm by the bar coating method and using a JI on a high / low resistance meter manufactured by ADVANTEST.
It was defined as the value measured by attaching a high and low resistance side constant chamber that was subjected 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 contact nip and the core metal. In terms of value, the resistance value was 10 ⁸ Ω. In the single-layer roller of the first embodiment, the entire roller is a resistor, whereas in the ICL roller of this embodiment, the thin film of 10 μm on the surface bears most of the resistance value.

ICL roller 15 produced in this way
An example of an experiment using is shown.

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

This is because in the ICL roller of the first embodiment, the entire ICL roller is a resistor, so that the divided voltage of the applied voltage of the roller itself is large and the resistance value is low, so that the reactive current is reduced. This is because a large amount of current flows, and an extra current was required to cause discharge.

In the roller of this embodiment, only a 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. In addition, the reactive current injected into the intermediate transfer member 8 can be significantly suppressed.

Next, when a condition for preventing the negative ghost and the cleaning failure by superposing the AC voltage on the DC voltage was searched for, the peak voltage of 4000 V and the AC current of 2500 μA in the H / H environment for the single layer roller, 3000V,
The DC current of 60 μA needs to flow, but in the roller of the present embodiment, only the peak-to-peak voltage of 2000 V, the AC current of 2500 μA, the DC current of 2000 V and 20 μA are required in the H / H environment.

With respect to the AC component, in particular, the ICL roller 15 of the present embodiment has a large electrostatic capacitance, so the impedance is small, and the partial pressure applied to the ICL roller 15 when a constant AC current is passed is small. Has the advantage that

Furthermore, the ICL roller 15 of the present embodiment.
Since the surface resistance value is high, even if a discharge occurs at a certain part on the roller and a voltage drop occurs, the core metal potential of the roller can be maintained without being dragged by this at another part, so the discharge nip is relatively It became widely available, and more efficient charging became possible.

As described above, in the present embodiment, the IC
The L roller 15 has a multi-layered structure, and by increasing the volume resistance value of the surface thereof, the reactive current due to the injection into the intermediate transfer body 8 is minimized, and the secondary transfer toner is effectively charged with a lower voltage and a smaller current. I can do it now.

[0126]

As described above, according to the present invention, a cleaning charging member is provided on the second image bearing member in contact with or with a minute gap between the second image carrier and the cleaning member .
Since the charging bias power supply applies the charging bias in which the AC voltage is superimposed on the DC voltage to the charging member , the secondary transfer residual toner remaining on the second image carrier is first transferred at the primary transfer portion. It is possible to surely collect the second image carrier without deteriorating or contaminating the second image carrier.

Further, the cleaning charging member has a multi-layer structure and the volume resistance value of the surface layer is increased, whereby the toner can be collected at a lower voltage.

Further, by controlling the AC voltage at a constant voltage or by controlling the AC voltage to be low by detecting the environment,
While collecting toner efficiently in a high humidity environment,
It is possible to prevent the adverse effect of C application in a low humidity environment.

[Brief description of drawings]

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

FIG. 2 is a diagram showing 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, (a) of which is an IC having a low surface layer resistance.
FIG. 3B is a schematic diagram showing an L roller, and FIG. 3B is a schematic diagram showing an ICL roller having a high surface resistance.

[Explanation of symbols]

Reference Signs List 1 first image carrier (photosensitive drum) 4 image writing unit 6 black developing unit 7 color developing unit 8 second image carrier (intermediate transfer unit) 11 transfer unit (transfer roller) 12 transfer unit (transfer belt) 15 Cleaning charging member (charging roller) 16 Toner collecting means (charging bias power source) 17 Toner collecting means

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-333706 (JP, A) European patent application publication 744672 (EP, A 1) US patent 5079597 (US, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) G03G 15/16-15/16 103 G03G 21/10-21/12

Claims (9)

(57) [Claims] 1. A primary transfer portion between the first image carrier and
A second image carrier on which the toner image formed on the image carrier is primarily transferred; and transfer means for secondarily transferring the toner image from the second image carrier to the third image carrier, toner contact charging residual toner remaining on the second image bearing member
In the image forming apparatus, which includes a collecting unit and collects the secondary transfer residual toner charged by the toner collecting unit from the primary transfer unit to the image carrier, the toner collecting unit includes a cleaning charging member and
Charging bias that applies voltage to the charging member for cleaning
A cleaning device, comprising: a power supply; and the charging bias power supply applies a voltage obtained by superimposing an AC voltage on a DC voltage to the cleaning charging member . 2. The toner collecting means is configured to clean the toner.
The cleaning device according to claim 1, wherein a charging roller is used as the charging member for charging . 3. The charging roller has a multi-layer structure, and the volume resistance value of the outermost surface layer is set to be larger than the volume resistance value of an inner layer inside the outermost surface layer. The cleaning device according to 2. 4. A charging bias from the charging bias power source is applied to a DC voltage having a polarity opposite to the polarity of the developer charged by the developing means, to the second image carrier and the cleaning circuit.
The charging voltage is set to a voltage obtained by superimposing an AC voltage, which is a peak-to-peak voltage that is at least twice as high as a voltage at which discharge occurs between the charging member for charging and the charging member for charging. Any one of three
The cleaning device described. 5. The cleaning device according to claim 4, wherein the DC voltage component of the charging bias from the charging bias power source is set by constant current control, and the AC voltage component is set by constant voltage control. 6. A applied from the charging bias power source
The C voltage is higher under a high-humidity environment than under a low-humidity environment.
The cleaning device described. 7. The 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, and the first image carrier is When the tribo of the toner before being primarily transferred and charged by Q ₂ is Q ₂ , Q ₁ and Q ₂ have opposite polarities, and | Q ₁ | <| Q ₂ |
It has the following relations, Claim 1 thru / or Claim 1 characterized by the above-mentioned.
The cleaning device described. 8. The first image carrier is a photosensitive drum, The cleaning device according to claim 1, wherein the cleaning device is a cleaning device. 9. The first image carrier according to claim 1, wherein the second image carrier is an intermediate transfer member.
The cleaning device described.