JPH0990840A - Cleaning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cleaning device capable of thoroughly removing even toner of a minute grain size and depositions on an image carrier to which the electrostatic induction force of a conductive blush is hardly applied, and eliminating the need for preliminarily making an electrification quantity of the depositions completed by PCC. SOLUTION: In the cleaning device for removing the toner from a surface of an image carrier 1, by rubbing the toner sticking surface of the image carrier 1 with the conductive blush roll 10, while applying bias voltage VB having a polarity opposite to that of the static charge polarity of the toner onto the blush roll 10, at the time of a line along the rotary shaft direction whose width is 1mm on the image carrier 1 allowed to pass a rubbing area of the blush roll 10, when assuming the number of fibers of the blush roll 10 rubbing the line as (n) (number/mm), the bias VB (V) applied onto the blush roll 10 is decided so as to satisfy the following inequality, |-400+1.1n||<=VB<=||-200+1.1n|<=600.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning device for removing residual toner from the surface of an image carrier after transferring a toner image onto a recording sheet in an image forming apparatus such as an electrophotographic copying machine or a laser printer.

[0002]

2. Description of the Related Art Conventionally, as a cleaning device of this type, a brush roll in which fine fibers are implanted is rotated at a high speed, and the brush roll rubs the image carrier on which the residual toner is adhered. It is known that the residual toner is first attached and then removed from the image carrier.

In this cleaning device, since the brush roll removes the residual toner by the mechanical force of rubbing the image carrier, if the rotation speed of the brush roll is too low, cleaning failure will occur. However, if the number of revolutions is too high, there is a disadvantage that residual toner adheres to the surface of the image carrier to form a resin thin film, which is a so-called filming phenomenon, as disclosed in Japanese Patent Publication No. 4-23272. In addition, the setting of the rotation speed of the brush roll had to be significantly restricted.

Therefore, in order to achieve both the prevention of the filming phenomenon and the improvement of the cleaning performance,
Conventionally, there has been proposed a cleaning device in which a bias voltage having a polarity opposite to that of the toner is applied to a brush roll having conductive fibers planted thereon, and the residual toner is transferred from the image carrier to the brush roll by electrostatic attraction.

[0005]

However, in the cleaning device using the conductive brush, although the toner having a relatively large particle diameter can be easily removed, the average particle diameter of 5 has been increasing in frequency in recent years. For toner with a small particle size of about 7 μm, the physical adhesive force with the surface of the image carrier is larger than the electrostatic attraction force that acts on these toner particles from the conductive brush. It is difficult to remove the toner from the surface of the image carrier.

Additives (eg, SiO ₂ and Ti) added to the toner for the purpose of adjusting chargeability and fluidity.
Additives such as metal oxides (O ₂ etc.) and talc contained in the paper have a very small particle size of 1 μm or less, and the image bearing member is formed by the electrostatic attraction of these additives from the conductive brush. It is very difficult to remove it from the surface of the toner, as compared with the above-mentioned small particle size toner.

On the other hand, in order to increase the electrostatic attraction force that acts on the toner from the conductive brush, it suffices to increase the bias voltage of the opposite polarity to the toner applied to the conductive brush. The following disadvantages occur in an image forming apparatus that forms a toner image on a carrier. In other words, in the reversal development method, the charging polarity of the image carrier and the charging polarity of the toner are the same, so if an excessive bias voltage is applied to the conductive brush, the image carrier will be charged in the opposite polarity to that charging polarity. Therefore, it becomes difficult to charge the image carrier to a predetermined potential in the image forming process of the next cycle started after cleaning.

Therefore, it is impossible to completely remove the adhering matter on the image bearing member only by the electrostatic attraction force acting from the conductive brush, and for the adhering matter which cannot be removed by the electrostatic attraction force, this is brushed. There is no choice but to remove it with the mechanical force of rubbing. That is, it can be said that a balance between the cleaning action by the electrostatic attraction force and the cleaning action by the mechanical rubbing force is important in order to complete the cleaning of the image carrier in this type of cleaning device.

Further, when the toner image on the image carrier is transferred to the paper, a voltage having a polarity opposite to the charging polarity of the toner is applied from the back side of the paper, so that the toner adheres to the image carrier after passing through the transfer portion. The residual toner has a large variation in its charge amount, and in extreme cases, the charge polarity may be reversed. Moreover, when the trailing edge of the paper leaves the image carrier after the transfer of the toner image, peeling discharge occurs between the paper and the image carrier, and this discharge also causes variations in the charge amount of the residual toner. Will occur.

Therefore, in order to efficiently clean the image carrier by the electrostatic attraction of the conductive brush, it is necessary to make the charge amount of the residual toner within a predetermined range in advance. According to Japanese Patent Laid-Open No. 19670/1990, a pre-cleaning charger (hereinafter referred to as PCC) provided in front of the conductive brush aligns the absolute value of the charge amount of the residual toner within a predetermined range, and a bias applied to the conductive brush. By controlling the voltage, a current having a magnitude corresponding to the amount of charge of the toner is made to flow between the image carrier and the conductive brush.

However, when the PCC is provided in front of the conductive brush, there is a problem that the cleaning device itself becomes large, and when a corotron is used as the PCC, the surrounding atmosphere is contaminated by the generation of ozone. I'm worried.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image bearing member for toner or adhering matter having a minute particle size to which the electrostatic attraction of the conductive brush is hard to act. It can be removed cleanly from above, and PCC
The purpose of the present invention is to provide a cleaning device that eliminates the need to preliminarily match the charge amounts of the adhered substances.

[0013]

In order to achieve the above object, the cleaning device of the present invention rubs the surface of the image bearing member on which the toner adheres with a conductive brush roll, and at the same time, the brush roll is covered with the above-mentioned material. In a cleaning device that removes toner from the surface of the image carrier by applying a bias voltage having a polarity opposite to the charging polarity of the toner, a line of 1 mm along the rotational axis direction of the brush roller slides on the image carrier. When the number of fibers of the brush roll that rubs this line as it passes through the rubbing region is n (lines / mm), the bias V _B (V) applied to the brush roll is expressed by the following formula: | -400 + 1 .1n | ≦ V _B ≦ | −200 + 1.1n
It is characterized by satisfying | ≦ 600.

According to such a technical means, attention is paid to the number of fibers rubbing a unit length line drawn on the image carrier when passing through the rubbing area of the brush roll, Since the bias voltage applied to the brush roll is determined as a function of the number n of the fibers, the mechanical cleaning force generated by the fibers rubbing the image carrier and the electrostatic voltage generated by the application of the bias potential. Even with small particle size toner and metal oxide particles, which were difficult to remove from the image bearing member by simply applying a bias voltage to the brush roll, a balance with the cleaning force was ensured. It can be removed.

Since the mechanical cleaning force and the electrostatic cleaning force are balanced, even if the residual toner or the like adhering to the image carrier has a non-uniform charge polarity or charge amount, It is possible to reliably remove the attached matter from the image carrier. Therefore, the image carrier can be reliably cleaned without providing the PCC in the preceding stage of the brush roll.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The cleaning device of the present invention will be described in detail below with reference to the accompanying drawings. First, FIG. 1 shows an example of an image forming apparatus in which the cleaning device of the present invention is used. In the figure, reference numeral 1 is a photosensitive drum as an image carrier, reference numeral 2 is a corona discharger for uniformly charging the photosensitive drum 1, and reference numeral 3 exposes the photosensitive drum 1 according to image information. A laser beam scanner, reference numeral 4 is a developing device that develops the electrostatic latent image formed on the photosensitive drum 1 to form a toner image, and reference numeral 5 transfers the toner image from the photosensitive drum 1 to the recording sheet 6. Transfer charger, reference numeral 7 is a peeling corotron for removing the charge from the recording sheet 6 and peeling it from the photosensitive drum, and reference numeral 8 is the recording sheet
A fixing device for fixing the unfixed toner image transferred onto the recording sheet 6 onto the recording sheet 6, and a cleaner (cleaning device) 9 for removing deposits such as residual toner from the photosensitive drum 1 after the transfer of the toner image is completed. .

In such a structure, the photosensitive drum 1 is a negative charging type organic photosensitive member, and is uniformly charged to a negative potential by the corona discharger 2. The laser beam scanner 3 forms a negative latent image on the photosensitive drum 1 by exposing the image portion of the image information, and the developing device 4 develops the negative latent image by reversal development. That is, the developing device 4 develops the negative latent image with the negatively charged toner having the same charge polarity as the photosensitive drum, and the negative latent image is visualized by the toner.

The toner image thus formed is transferred to the recording sheet 6 by the transfer charger 5, and then is heated and pressed while being inserted through the fixing device 8 to be fixed on the recording sheet. The paper is ejected to the external paper ejection tray.

Next, the cleaner 9 to which the present invention is applied.
Will be described. As shown in FIG. 2, the cleaner 9 includes a brush roll 10 formed by implanting innumerable fibers on a rotating shaft, and a toner recovery roll 11 slidingly contacting the brush roll 10. The brush roll 10 rubs the peripheral surface of the photoconductor drum 1 in the direction opposite to the moving direction to remove the residual toner, the toner external additive, and the like from the photoconductor drum 1, while the toner recovery roll 11 brushes the brush. The residual toner and the like attached to the roll 10 are configured to be removed from the roll 10.

A bias voltage V _B having a polarity opposite to that of the residual toner on the photoconductor drum 1 is applied to the brush roll 10 by a power source 12, and the residual toner is applied between the brush roll 10 and the photoconductor drum 1. The electric field formed on the photosensitive drum 1 removes it from the photosensitive drum 1 side by electrostatic attraction to the brush roll 10 side. On the other hand, a bias voltage having a higher absolute value and the same polarity as that of the brush roll 10 is applied to the toner recovery roll 11, and the residual toner adhered to the brush roll 10 re-adheres to the toner recovery roll 11.

As the fiber material of the brush roll 10, a resin such as nylon, polypropylene or acrylic in which a conductive material such as carbon or metal oxide is dispersed, or a conductive material inside or outside each fiber is used. A layered material can be used, and the resistance value is about 5 to 25 denier, and the resistance value of the fiber is 10 ³ to 10 ⁹ Ω · c.
m is preferable.

A scraper 13 is in contact with the toner collecting roll 11, and the toner and the like adhering to the toner collecting roll 11 is removed from the roll 11 by the scraper 13. This scraper 13 is formed of a thin metal plate of stainless steel or phosphor bronze, and its thickness is about 0.05 to 2 mm. Here, the toner recovery roll 11 is a metal roll made of aluminum, stainless steel or the like, and its surface is subjected to an oxidation treatment.

In order to further improve the cleaning performance of the photoconductor drum 1, a blade or roll made of an elastic material such as rubber which is in sliding contact with the photoconductor drum 1 may be used together with the brush roll.

According to the present invention, in the cleaner 9 of the image forming apparatus constructed as above, when a line of 1 mm along the rotation axis direction on the photoconductor drum 1 passes through the rubbing area of the brush roll 10, this line is used. Brush roll 1
0 of the number of fibers (hereinafter, rubbing number hereinafter) when a is n, the bias voltage V _B to the following formula to be applied to the brush roll 10, | -400 + 1.1n | ≦ V B ≦ | -200 + 1.1n
It is set so as to satisfy | ≦ 600.

Here, the calculation of the number n of rubbing lines will be described with reference to FIG. First, the parameters relating to the brush roll and the image carrier are defined as follows. V ₁ : peripheral speed of image carrier (mm / sec) V ₂ : peripheral speed of brush roll (mm / sec) d ₁ : outer diameter of image carrier (mm) d ₂ : outer diameter of brush roll (mm) d _3: shaft outer diameter of the brush roll (mm) L: length of contact between the brush roll in the circumferential direction of the image carrier (mm) X: the amount of interference between the image bearing member of the brush roll (mm) θ _L: image Central angle of the brush roll forming the contact area with the carrier θ _C : Angle at which the brush roll rotates while any point on the image carrier passes through the contact area AB with the brush roll D: Flocking on the brush roller Density of fibers (books / m
m ² )

At this time, the parameter L is geometrically determined by the following equation.

[Equation 1]

The parameter θ _L is determined by the following equation.

[Equation 2]

On the other hand, the parameter θ _C can be expressed by the following equation.

(Equation 3)

From the above formula and, while the arbitrary point on the image carrier passes through the contact area AB with the brush roll, the central angle of the brush roll which rubbed the point is expressed by the following formula. θ = θ _C + θ _L

Therefore, when a line of 1 mm drawn along the direction of the rotation axis on the image carrier passes through the contact area AB, the number n of the fibers of the brush roll which rubs this line n.
Is represented by the following equation.

[Equation 4]

Next, the relationship between the number n of rubbing lines thus calculated and each parameter of the brush roll 10 will be described. FIG. 4 shows the relationship between the peripheral speed V ₂ of the brush roll and the number n of rubbing rubs, and the other parameters were as follows. V ₁ = 300 (mm / sec) d ₁ = 84 (mm) d ₂ = 19 (mm) d ₃ = 6 (mm) X = 1 (mm) D = 93 (pieces / mm ² )

Here, the peripheral speed V ₁ of the photosensitive drum 1 is 30.
Since it is set to 0 (mm / sec), when the peripheral speed V ₂ of the brush roll 10 is −300 (mm / sec),
The rubbing direction of the brush roll 10 and the moving direction of the photosensitive drum 1 and the rubbing speed and the moving speed thereof are the same, and as a result, the above n = 0. Accordingly, as the difference between the circumferential speed V ₂ of the brush roll 10 and the circumferential speed V ₁ of the photosensitive drum 1 increases, the rubbing number n is understood that increases linearly.

FIG. 5 shows the relationship between the density D of the fibers planted on the brush roll 10 and the number n of rubbing rubs. The parameters other than D used the same values as those described above. . However, V ₂ = 300 (mm / sec).
As is clear from the above equation, it is understood from the same drawing that the number n of the rubbing lines linearly increases as the flocking density D increases.

Further, FIG. 6 shows the relationship between the amount of interference X of the brush roll 10 with the photosensitive drum 1 and the number n of rubbing rubs. Parameters other than X have the same values as those described above. did. That is, V ₂ = 300 (mm / sec), D =
It is 93 (pieces / mm ² ). From the figure, it is understood that the number n of rubbing lines also increases with an increase in X. Therefore, the amount of interference X of the brush roll 10 with the photosensitive drum 1
Can also be said to be one of the important parameters that determine the cleaning power of the brush roll 10.

That is, the number of rubbing rubbing n can be used as a standard for indicating the mechanical cleaning force by the rotation of the brush roll 10. The present inventors confirm the difference in cleaning performance due to the difference of rubbing rubbing number n. Well, brush roll 1
Performance tests were performed on several types of cleaning devices in which the number n of rubbing rubs was varied by changing the parameter 0.

In this test, the bias voltage V _B applied to the brush roll 10 is changed by 50 V, and at what bias voltage V _B a cleaning failure occurs or a filming phenomenon occurs on the surface of the photosensitive drum 1. I confirmed. As the fiber of the brush roll used in the test, Bertron B12N (10 denier) manufactured by Kanebo Ltd. was used. As the photoconductor drum 1, a function-separated type organic photoconductor (OPC) in which a charge injection blocking layer, a charge generation layer, and a charge transport layer containing polycarbonate as a main component are sequentially laminated on the outer circumference of an aluminum pipe is used. Two
While the surface potential of the non-image area by -750V,
The surface potential of the image area by exposure was set to -100V. Further, a toner having an average particle diameter of 9 μm was used, and the developing bias voltage was set to −550V.

The test results are shown in Table 1 below.

[Table 1]

The V _B column of Table 1 shows the bias voltage in which the filming phenomenon and the cleaning failure occurred in each test. For example, test No, 1 is V _B
= 50V to 300V, good cleaning performance is exhibited, but at 50V or less, a filming phenomenon occurs, and
A value of V or higher indicates that cleaning failure has occurred. Test No. 9 and 13 show that there is no bias voltage latitude for filming phenomenon and cleaning failure.

FIG. 7 is a graph in which the test results of Table 1 are plotted. The horizontal axis shows the number n of rubbing lines and the vertical axis shows the bias voltage V _B. From this graph, it is possible to recursively derive two linear functions with the number n of rubbing strokes as a variable, and when the bias voltage is set in the region sandwiched between these functions, the filming phenomenon is generated. It was found that neither the cleaning nor the cleaning failure occurred. That is, such a range is | −400 + 1.1n | ≦ V _B ≦ | −200 + 1.1n
|, Which is a region indicated by hatching in the graph of FIG.

Assuming that the bias voltage V _B is │-400 +
When set to a value smaller than 1.1n | (value in the area A in FIG. 8), the mechanical cleaning force of the toner attached to the photosensitive drum 1 is larger than the electrostatic cleaning force of the brush roll 10. It is considered that the filming phenomenon occurs more largely, and as a result, the filming phenomenon occurs. The reason for this is not yet fully verified, but it can be considered as follows. That is, when the fibers of the brush roll 10 rub against the surface of the photoconductor drum 1, it is considered that the adhesion of toner, external additives, talc, etc. to the photoconductor drum 1 is weakened. Since the force for electrostatically holding and conveying and collecting the fibers is insufficient, these adhered substances continue to adhere without being removed from the photosensitive drum 1, and conversely, are rubbed against the photosensitive drum 1 by the brush roll 10. It is considered that filming is gradually formed.

On the other hand, the bias voltage V _{B is set} to │-200 +
When set to a value larger than 1.1n | (value in the area B in FIG. 8), an electrostatic cleaning force is applied to the toner attached to the photosensitive drum 1 rather than a mechanical cleaning force of the brush roll 10. It is considered that the cleaning effect becomes larger, resulting in defective cleaning. That is, when the fibers of the brush roll 10 mechanically rub against the surface of the photoconductor drum 1, the adhesion of toner, external additives, talc, etc. to the photoconductor drum 1 is weakened, but it is applied to the brush roll 10. Bias voltage V _B
When the value is large, an electric charge having a polarity opposite to the original charge polarity is injected into the toner during such rubbing, and the toner is recharged. Since the charging polarity of the photosensitive drum 1 in the reversal developing method is the same as the initial charging polarity of the toner (negative polarity in this embodiment), as described above, the toner has the reverse polarity (in this embodiment) due to the bias voltage V _B. When recharged to positive polarity, the recharged toner reattaches to a higher surface potential on the photosensitive drum 1. In other words, when the bias voltage V _B is high, it is considered that the toner rubbed against the brush roll 10 reattaches to the non-image area, which causes cleaning failure.

[0042] Thus, the scope of the following bias voltage V _B of the brush roll 10 as in the present invention, | -400 + 1.1n | ≦ V B ≦ | -200 + 1.1n
By setting to |, it is possible to secure the balance between the mechanical cleaning force of the brush roll 10 and the electrostatic cleaning force, and as described above, the filming phenomenon when the electrostatic cleaning force is insufficient, It is possible to prevent the occurrence of defective cleaning when the electrostatic cleaning force is excessive.

The present invention also specifies that the setting range of the bias voltage V _B of the brush roll 10 is V _B ≦ | −200 + 1.1n | ≦ 600. This is the bias voltage V _B
When the voltage exceeds 600 V, electric discharge occurs between the brush roll and the photoconductor drum according to the so-called Paschen's rule, and a desired electric field cannot be formed between the brush roll and the photoconductor drum surface. This is because it becomes difficult to attach the toner, the external additive, and the like attached to the drum to the brush roll. In addition, when such discharge T occurs,
This is because charges having a polarity opposite to the charging polarity are injected into the photoconductor drum, and it becomes difficult to uniformly charge the photoconductor drum in the next image forming cycle.

Further, the lower limit of the number of rubbing rubbing n for preventing cleaning failure is when the bias voltage V _B of the brush roll 10 is 0 V, and n = 182 at that time. Therefore, in practicing the present invention, n ≧ 182
Is a condition. However, in this case, the bias voltage V _B is 0V.
Since there is a fear of generating a small even outside the cleaning failure from, it is preferable to set the order of 20% of the upper limit value of the bias voltage V _B as the lower limit value of the bias voltage V _B. As described above, the upper limit value of the bias voltage V _B is 600V.
Therefore, when the lower limit value is set to 120 V, the number of rubbing lines corresponding to this is approximately n = 300. Therefore, considering the ease of control of the bias voltage V _B , the number of rubbing rubbing n
It is preferable that ≧ 300.

Further, according to FIG. 4 showing the relationship between the peripheral speed V ₂ of the brush roll 10 and the number n of rubbing rubbing, the number of rubbing rubbing n ≧ 3
The peripheral speed V ₂ that achieves 00 is 696 when the rubbing direction of the brush roll 10 and the moving direction of the photosensitive drum 1 are the same.
(Mm / sec), and 96 (mm / sec) when the rubbing direction and the moving direction are different. Here, an increase in the number of rotations of the brush roll 10 causes an increase in the cost of the drive motor, and the contact with the toner recovery roll 11 may cause the breakage of the brush fiber. Therefore, in order to keep the number of rotations of the brush roll 10 as low as possible, it is preferable that the rubbing direction of the brush roll 10 and the moving direction of the photosensitive drum 1 are opposite to each other.

[0046]

As described above, according to the cleaning device of the present invention, by balancing the mechanical cleaning force of the brush roll rubbing the image carrier and the electrostatic cleaning force, While suppressing the occurrence of the filming phenomenon, it is possible to reliably remove small-sized toner particles and metal oxide fine particles from the surface of the image carrier, and it is possible to maintain good cleaning performance for a long period of time. Become.

Further, the cleaning performance is improved not only by improving the electrostatic cleaning force of the brush roll but by balancing the mechanical cleaning force and the electrostatic cleaning force. , It is not necessary to provide a PCC in the preceding stage of the brush roll to make the charge polarity and charge amount of the residual toner adhering to the image carrier uniform.
The size and cost of the device can be reduced accordingly.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus to which a cleaning device of the present invention is applied.

FIG. 2 is a schematic configuration diagram showing an example of a cleaning device to which the present invention is applied.

FIG. 3 is a diagram illustrating parameters when a brush roll rubs a photosensitive drum.

FIG. 4 is a graph showing the relationship between the peripheral speed V _{2 of a} brush roll and the number of sliding rubbing n.

FIG. 5 is a graph showing a relationship between a fiber implantation density D of a brush roll fiber and a number of rubbing n.

FIG. 6 is a graph showing the relationship between the amount of interference between the brush roll and the photoconductor drum and the number of rubbing n.

FIG. 7 is a graph showing the relationship between the number of rubbing lines n and the bias voltage V _B of the brush roll, based on the test results shown in Table 1.

FIG. 8 is a graph showing a setting range of a bias voltage V _B of the brush roll according to the present invention.

[Explanation of symbols]

1 ... Photosensitive drum (image bearing member), 9 ... Cleaning device, 10 ... Brush roll

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoji Sasakawa 2274 Hongo, Ebina City, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. An image carrier having the toner adhered thereto is rubbed with a conductive brush roll, and a bias voltage having a polarity opposite to the charging polarity of the toner is applied to the brush roll to form the image carrier. In the cleaning device for removing the toner from the surface of the brush roll, the number of fibers of the brush roll rubbing the line of 1 mm along the rotation axis direction on the image carrier as it passes through the rubbing region of the brush roll. Is n (lines / mm), the bias V applied to the brush roll is
_B (V) is the following formula: | −400 + 1.1n | ≦ V _B ≦ | −200 + 1.1n
A cleaning device satisfying | ≦ 600. 2. The cleaning device according to claim 1, wherein 300 ≦ n. 3. In the rubbing area of the brush roll,
The cleaning device according to claim 1, wherein the moving direction of the image carrier and the sliding direction of the brush roll are opposite to each other.