JPH07333945A - Electrifying device - Google Patents

Abstract

PURPOSE:To obtain an electrifying device capable of easily and stably attaining uniform electrification in a roll shaft direction without making the cost high nor complicating the manufacture and attachment, etc., by setting a nip width between an electrifying member and an image carrier, and the resistance value of a conductive rubber layer so that a specified condition is satisfied. CONSTITUTION:This device is provided with a roll-state electrifying member 20 which is brought into contact with the image carrier 1 and electrifies the surface of the image carrier 1 and the member 20 is obtained by laminating at least the conductive rubber layer 22 and a resistance surface layer 23 in this order on a roll core material 21. When the nip width between the member 20 and the image carrier 1 is Wmm, the resistance value of the layer 22 is logROMEGA, and the AC current value of a voltage impressed on the member 20 is <=1.5mA, and the member 20 is set to satisfy a condition expressed by W<=6.0-0.91logR. Consequently, the electrification in the roll shaft direction is uniform even through the nip width is not uniform in the roll shaft direction. As a result, such a problem as fogging peculiar to ununiform electrification is not caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device provided with a roll-shaped charging member for charging an image carrier made of a photoconductor, a dielectric or the like in an image forming apparatus such as a copying machine, a facsimile or a printer. is there.

[0002]

2. Description of the Related Art In recent years, in place of a corona discharge device which has been widely used as a charging device for charging the surface of an image carrier such as a photoconductor in an image forming apparatus such as a copying machine or a laser printer, A charging device of a type that performs a charging process by bringing a roll member to which a bias voltage is applied into contact with a photoconductor (hereinafter referred to as a roll charging device)
Is attracting new attention.

This is because the roll charging device has a problem in a corona discharge device, that is, it requires a high power source, ozone generated by discharge causes deterioration of rubber parts and a photosensitive layer, and the discharge wire is contaminated, resulting in poor charging. This is due to the ability to solve problems such as However, on the other hand, in this roll charging device, how to realize uniform charging in the roll axis direction is an important issue. That is, in this type of charging device, it is difficult to uniformly bring the roll member into contact with the image carrier in the roll axis direction. For example, such non-uniform contact causes non-uniform charging in the roll axis direction. In this case, fogging or the like occurs and affects the image quality. Therefore, it is essential to take measures against the uniform charging.

Therefore, conventionally, in order to realize uniform charging in such a roll charging device, for example, a technique in which the nip width and the nip pressure between the photoconductor and the roll charging member are specified (Japanese Patent Laid-Open No. 64-7070). ), Or a technique in which a roll charging member provided with ridges specified according to the relative moving speed at both ends thereof is used (Japanese Patent Application Laid-Open No. Hei.
No. 25870) has been proposed.

[0005]

However, the former one of the above-mentioned techniques causes a difference in the nip width between the central portion of the image forming area of the photoconductor and both end portions thereof,
As a result, there is a problem that the charging is not uniform. On the other hand, the latter is intended to achieve the object by providing a ridge at the end of the roll that hits the outside of the image forming area to achieve a uniform nip in the image forming area. Micron order manufacturing and dimensional control are required, and there is a problem that the cost of the entire device becomes high. In addition, both of them are complicated because they require precision in the work of mounting the roll member, etc., from the viewpoint of making the nip width uniform, and the desired uniform charging can be realized easily and stably. It couldn't be an effective measure to gain.

The present invention has been made in order to solve the above-mentioned problems, and the object thereof is to make uniform in the roll axial direction without increasing costs and complicating manufacturing and mounting. An object of the present invention is to provide a charging device that can easily and stably achieve charging.

[0007]

A charging device of the present invention comprises a roll-shaped charging member that contacts an image carrier in an image forming apparatus to charge its surface, and the roll-shaped charging member is at least a roll core member. In a charging device having a structure in which a conductive rubber layer and a resistance surface layer are laminated in this order, the roll-shaped charging member has a nip width of W (mm) between the charging member and the image carrier, and the resistance of the conductive rubber layer. Value is logR
(Ω), the alternating current value of the voltage applied to the charging member is 1.5
When it is set to be mA or less, it is set so as to satisfy the condition represented by W ≦ 6.0−0.91logR ... "Log" in the above relational expression
Indicates the base 10 base logarithm.

From the above relational expression, in the apparatus of the present invention, the above object can be achieved by appropriately setting the nip width and the resistance value of the conductive rubber layer. The setting can be performed, for example, by adjusting the load applied to the roll-shaped charging member for the nip width, the hardness of the conductive rubber layer, etc., and the rubber value for the resistance value of the conductive rubber layer. It can be performed by adjusting the mixing ratio of the material and the conductive substance. The maximum width and the minimum width of the nip width in the roll axis direction are both 0
The thickness is preferably within the range of 3.0 mm, more preferably within the range of 0.5 to 1.5 mm.

In such technical means, a core material made of a conductive material such as iron, copper, stainless steel or aluminum is used as the roll core material. This roll core material is connected to a charging power source for applying a voltage required for charging. As the applied voltage, for example, a voltage obtained by superimposing an AC voltage on a DC voltage is applied, the current is 0.1 to 3.0 mA, and the frequency is 100.
Although it can be appropriately selected within the range of Hz to 3 kHz, the alternating current is preferably set to 1.5 mA or less, and more preferably set to 1.1 mA or less.

The conductive rubber layer is formed by dispersing conductive particles such as carbon black in a rubber material such as EPDM (ethylene, propylene, diene, methacryl), or a rubber material such as polyurethane rubber such as LiClO ₄ . It is formed of a material in which an ion conductive agent is dispersed. Among them, the one formed of EPDM rubber in which carbon black is dispersed is preferable because there is no problem such as occurrence of bleeding under high temperature and high humidity. This is because when a rubber material is made conductive with an ionic conductive agent, the ionic component or a rubber cross-linking agent such as a polyol easily exudes to the outside of the rubber layer (roll) under high temperature and high humidity, and this exudation occurs. If such a substance adheres to the photoconductor, image quality defects will occur, and in order to prevent this bleeding, it is necessary to stack many layers such as a rubber layer on top of this rubber layer, resulting in a significant cost increase. There is a problem. This can be said similarly in the case of the resistance surface layer described later. The thickness of this rubber layer is 1
It is 10 mm, preferably 2-5 mm. Also,
The hardness of this rubber layer is 30 ° or more, preferably 40 to 70 ° in terms of rubber hardness (JIS standard).

The resistance surface layer is formed of a polyamide resin in which conductive particles such as carbon black or aluminum are dispersed, a synthetic resin such as polyurethane or acrylic, or a polyurethane rubber in which an ion conductive agent such as LiClO ₄ is dispersed. It is what is done. Among them, those formed of a polyamide-based resin in which conductive particles are dispersed are preferable because there is no problem such as bleeding under high temperature and high humidity. This surface layer has a volume resistance value of 10 ⁵ to 10 ⁹ Ω.
-It is set to cm. The thickness of this surface layer is 1
˜50 μm.

The roll-shaped charging member may have a structure in which, in addition to the conductive rubber layer and the resistance surface layer, other functional layers are laminated if necessary. For example, the conductive rubber layer and the resistance surface layer may be formed. A breakdown voltage layer can be provided therebetween. This withstand voltage layer is formed to have a thickness of 10 to 50 μm by using cyanoresin to which BaSO ₄ or the like is added, byron resin or the like.

As the image bearing member, a photosensitive member or a dielectric member is used, and its form may be any type as long as it is a drum-shaped or belt-shaped rotating member. The process speed of the image carrier is appropriately set within the range of 10 to 500 mm / s.

[0014]

According to the present invention, the nip width of the roll-shaped charging member is set so that the nip width with the image carrier and the resistance value of the conductive rubber layer satisfy the relational expression. Even if it is not uniform in the roll axis direction, the charge is made uniform in the roll axis direction. As a result, problems such as fogging peculiar to non-uniform charging do not occur. In addition, when the breakdown voltage layer is provided, pinhole leakage is prevented, and therefore uniform charging can be performed more reliably.

[0015]

The present invention will be described in more detail based on the following examples. FIG. 1 shows an embodiment in which the charging device of the present invention is applied to an electrophotographic image forming apparatus. In the image forming apparatus according to this embodiment, as shown in FIG. 1, a charging device 2, a developing device 3, a transfer unit 4, and a cleaning device 5 are sequentially arranged around a photoconductor 1 which rotates in an arrow direction. At the same time, the image writing device 6 is disposed between the charging device 2 and the developing device 3 and constitutes the main part thereof. A two-dot chain line in the figure indicates a range configured as a process cartridge.

The charging device 2 includes a roll-shaped charging member 20 installed so as to come into contact with the photosensitive member 1. The roll-shaped charging member 20 has a double structure in which a conductive rubber layer 22 and a resistance surface layer 23 are laminated on a conductive core material 21, and a load (not shown) is applied to both ends of the core material 21. A predetermined load is applied by the means, whereby the photosensitive member 1 is pressed against the photosensitive member 1 with a predetermined pressure. Further, the charging device 2 is electrically connected to the conductive core material 21 and a cleaner 24 having a contact blade for removing an adhered matter such as toner adhered to the surface of the charging member 20. A charging power source 25 is provided.

Further, the developing device 3 is provided with a developing roll 30, a regulating member 31, a toner supply roll 32, etc. which are installed so as to contact the photoconductor 1, and the transfer means 4 is a transfer roll 40. And a transfer power source 41 for applying a transfer voltage to the roll 40, and the cleaning device 5 further includes a cleaning blade 50 installed so as to come into contact with the photoconductor 1. is there. Reference numeral 7 in the drawing denotes a recording sheet conveyed so as to pass through between the photoconductor 1 and the transfer roll 40.

In the apparatus of this embodiment having such a structure, image formation is performed as follows. That is, the surface of the photoconductor 1 is uniformly charged to a predetermined potential by the contact rotation of the roll-shaped charging member 20 of the charging device 2, and then the image writing device 6 images the charged charging device 2 surface. A laser beam 60 is irradiated and exposed according to information to form an electrostatic latent image. Thereafter, the electrostatic latent image on the photoconductor 1 is developed with toner at a position close to the developing roller 30 of the developing device 3, and the toner image is transferred onto the transfer paper 7 at a position where the photoconductor 1 and the transfer unit 4 face each other. Transcribed.
On the other hand, the residual toner attached to the surface of the photoconductor 1 is scraped off and removed by the blade 50 of the cleaning device 5. An image for one cycle is formed by the above steps.

Next, based on the apparatus of this embodiment, the following tests were carried out on the charging device.

Roll-shaped charging member 20 in charging device 2
For, the core material 21 made of stainless steel with a diameter of 8 mm
And a conductive rubber layer 22 having a thickness of 3 mm made of carbon black dispersed EPDM rubber and a rubber hardness of 50 °, and a thickness of 30 μ made of carbon black dispersed polyamide resin.
m and a resistance surface layer 23 having a volume resistance value of 10 ⁵ Ω · cm. As the roll-shaped charging member 20, three kinds of members formed by using the conductive rubber layers 22 each having a resistance value R set to 10 ^4.5 Ω, 10 ^5.6 Ω and 10 ^6.4 Ω were used. Further, the roll-shaped charging member 20 has a DC voltage of 500V from the charging power source 25 at 1600V.
A voltage in which an AC voltage of V _pp and 800 Hz was superimposed was applied. On the other hand, as the photoconductor 1, an organic photoconductor having sensitivity in the infrared region was used, and this was rotated at a speed of 130 mm / s.

The charging member 20 is configured so that a load is applied to both ends of the core member 21 by pressure springs so that the charging member 20 is brought into pressure contact with the photosensitive member 1, and the nip portion at that time has a shape as shown in FIG. It is what makes up. The alternate long and short dash line in the figure indicates the axial direction of the roll. The load was adjusted so that both the maximum value W _max and the minimum value W _min of the nip width W were within the range of 0.5 to 1.5 mm. This test was conducted at low temperature and low humidity (10
(° C, 15% RH) environment.

First, the inflection point current (I _AC ) of the charging applied AC voltage with respect to the nip width W was measured for each of the three types of roll-shaped charging members having different resistance values. here,
The inflection point current is the minimum current required to bring the charging potential to a predetermined potential (stable charging region) in the current-charging potential characteristic curve when the charging voltage is applied as shown in FIG. Therefore, the inflection point current actually corresponds to the current value corresponding to this inflection point P because the inflection point is the time point (point P) when the stable charging region of the characteristic curve shown in the figure is reached. .

The measurement results are shown in FIG. From this result, it is understood that the inflection point current, that is, the charging performance is governed by the nip width and the resistance value of the rubber layer in the roll-shaped charging member. On the other hand, according to the research conducted by the present inventors, the voltage applied for charging is economical in that it does not increase the power source cost, and reduces the adhesion of discharge products, toner, etc. to the roll-shaped charging member. From the viewpoint, it has been found that it is desirable that the current value be as small as possible. Generally, it is desirable that the current value be 1.5 mA or less.

In view of this point, in the result shown in FIG. 4, the inflection point current corresponding to the minimum current required for charging is 1.5 mA.
When the nip width that becomes is picked up for each resistance value, the nip width at that time is plotted on the vertical axis and the resistance value is plotted on the horizontal axis, and the results are plotted as a straight line X in FIG. was gotten. This straight line X is W = 6.0-0.
It corresponds to a straight line represented by 91 log R.

Then, the resistance value and the nip width of the conductive rubber layer in the charging device were appropriately changed and a charging test was conducted to determine whether or not fogging occurred. The results are shown in FIG. As a result of this test, as shown in FIG. 5, when the resistance value and the nip width value are in a relationship of entering the area B on the upper right side of the straight line X, fogging may occur frequently. confirmed. On the other hand, in the case of the relationship of entering the area A on the lower left side of the straight line X, it was confirmed that fogging did not occur, and uniform and good charging was performed. Therefore, from the above results, if the resistance value and the nip width of the conductive rubber layer are within the area A shown in FIG. 5, that is, W ≦ 6.0−0.91.
It can be seen that when the relationship represented by logR is satisfied, uniform charging without fogging or the like is possible.

Further, it is more preferable that the voltage applied during charging has a current value of 1.1 mA or less. By reducing the current value of the applied voltage in this manner, it is possible to easily reduce the adhesion of toner and discharge products to the roll-shaped charging member 20, and therefore, for example, as shown in the above-mentioned embodiment, The cleaner 24 installed for the charging member 20 becomes unnecessary. As a result, the charging device can be simplified and downsized, and the cost can be reduced.
It should be noted that if there is an adhered substance on the surface of the roll-shaped charging member 20, it hinders uniform charging, so it is important to reliably remove it with a cleaner or the like as necessary.

In view of this point, in the result shown in FIG. 4, the inflection point current corresponding to the minimum current required for charging is 1.1 mA.
When the nip width to be obtained was picked up for each resistance value in the same manner as in the above example and the values were written together in FIG. 5, the result as a straight line Y shown in the same figure was obtained. The straight line Y corresponds to the straight line represented by W = 3.2-0.4logR.

Then, in the same manner as in the above example, when the resistance value and the nip width of the conductive rubber layer in the charging device were appropriately changed and the charging test was conducted, the resistance value and the nip width value showed the above straight line. It was confirmed that fogging did not occur and uniform and good charging was performed only in the case of being in the area C on the lower left side of Y. Further, at this time, no toner or the like adhered to the surface of the roll-shaped charging member 20, and the stain due to the adhered matter did not occur. Therefore, from this,
If the resistance value and the nip width of the conductive rubber layer are within the region C shown in FIG. 5, that is, if the relationship represented by W ≦ 3.2-0.4logR is satisfied, uniform charging is performed. This has the advantage that it can be performed more reliably, and that it is not necessary to provide the cleaner 24 on the roll-shaped charging member 20.

[0029]

As described above, according to the present invention,
As the roll-shaped charging member, a roll-shaped charging member whose nip width with the image carrier and the resistance value of the conductive rubber layer are set to satisfy the condition of the above relational expression is used, so that the nip width is relative to the roll axial direction. Even if the surface is not uniform, the surface of the image carrier can be uniformly charged in the roll axis direction. As described above, the charging device of the present invention satisfies the specific conditions for the nip width of the roll-shaped charging member and the resistance value of the conductive rubber layer without drastically changing or improving the components of the existing charging device. Since uniform charging can be performed simply by setting the above setting, there is no increase in cost as in the prior art, and the manufacturing and mounting thereof are not complicated. Therefore, uniform charging in the roll axis direction can be achieved easily and stably.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing a nip shape.

FIG. 3 is a graph showing a current-charging potential characteristic.

FIG. 4 is a graph showing the relationship between nip width and inflection point current.

FIG. 5 is a graph showing the relationship between the resistance value of the conductive rubber layer and the nip width.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Charging device, 20 ... Roll-shaped charging member, 21 ... Roll core material, 22 ... Conductive rubber layer, 23 ... Resistive surface layer, W ... Nip width.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsukasa Inou 2274 Hongo, Ebina City, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Hiroyuki Akanuma 2274, Hongo Ebina City, Kanagawa Prefecture, Fuji Xerox Co., Ltd. 72) Inventor Yasutomo Ishii, 2274 Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor, Kumiko Miyazawa, 2274 Hongo, Ebina City, Ebina, Kanagawa Prefecture (72) Inventor Minoru Ueki, Kanagawa Prefecture 2274 Hongo, Ebina City, Fuji Xerox Co., Ltd.

Claims (4)

[Claims] 1. A roll-shaped charging member for contacting with an image carrier in an image forming apparatus to charge the surface thereof, wherein the roll-shaped charging member has at least a conductive rubber layer and a resistance surface layer in this order on a roll core material. In the charging device having a laminated structure, the roll-shaped charging member has a nip width of W (mm) between the charging member and the image carrier and a resistance value of a conductive rubber layer of logR (Ω), When the AC current value of the applied voltage is 1.5 mA or less, the charging device is set so as to satisfy the condition represented by W ≦ 6.0−0.91 logR. 2. The charging device according to claim 1, wherein the conductive rubber layer is formed of EPDM rubber in which carbon black is dispersed. 3. The charging device according to claim 1, wherein the resistance surface layer is formed of a polyamide resin in which conductive particles are dispersed. 4. The charging device according to claim 1, further comprising a pressure resistant layer provided between the conductive rubber layer and the resistance surface layer.