JP2008145908A - Charging device and image forming apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging device provided with a charging member and a charging roller which charge an image carrier and capable of performing stable and fine charging having no charge irregularity over the temperature range from a low temperature up to a high temperature. <P>SOLUTION: When a temperature in an image forming apparatus is higher than a previously set temperature, a photoreceptor is charged by a W charging mode by a first charging member and a charging roller (second charging member). When the temperature in the image forming apparatus is lower than the set temperature, the photoreceptor is changed in an S charging mode by only the charging roller (second charging member). Thereby even when the temperature in the image forming apparatus is changed and the electric resistance of the charging roller is changed, the S charging mode or the W charging mode is switched according to the temperature and fine charging can be achieved over the temperature range from the low temperature up to the high temperature independently of the temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technical field of an image forming apparatus including a charging device for charging an image carrier and an electrophotographic apparatus.

  In a conventional image forming apparatus including an electrophotographic apparatus such as an electrostatic copying machine, a printer, or a facsimile, the surface of the photosensitive member is uniformly charged by the contact charging device, and then electrostatically applied to the surface of the photosensitive member by the exposure device. A latent image is formed. The electrostatic latent image is developed into a toner image by a developing device, and is transferred to a transfer material such as paper via an intermediate transfer member or directly. Finally, an image is formed by fixing the toner image on the transfer material by a fixing device.

As a conventional image forming apparatus, there is known an image forming apparatus provided with a charging device in which two charging members are brought into contact with the photosensitive member in order to uniformly and satisfactorily charge the surface of the rotating photosensitive member. (For example, see Patent Document 1). In the charging device of this image forming apparatus, the charging unevenness when the surface of the photosensitive member is charged by the first charging member upstream of the photosensitive member rotation direction is removed by the second charging member downstream of the photosensitive member rotation direction, The photoreceptor is uniformly charged.
JP-A-2005-215321.

Incidentally, in the charging device described in Patent Document 1, a charging brush is used for the first charging member and a charging roller is used for the second charging member. In that case, the charging roller is composed of a conductive rubber roller.
However, as will be described later, the conductive rubber roller has a temperature dependency of resistance such that its electric resistance R (Ω) changes with temperature. For this reason, it is difficult for the conductive rubber roller to perform stable and good charging without uneven charging from low to high temperatures.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a single charging member and a charging roller for charging the image carrier, respectively, so that there is no charge unevenness from a low temperature to a high temperature. It is an object of the present invention to provide a charging device and an image forming apparatus including the charging device.

  In order to solve the above-described problem, according to the present invention, the double charging mode is selected by the control device when the temperature in the image forming apparatus is higher than a preset temperature. As a result, the image carrier is primarily charged by the first charging member and then secondary charged by the charging roller. That is, when the temperature in the image forming apparatus is higher than the temperature in the image forming apparatus during normal use, it is possible to perform good charging without uneven charging by selecting the double charging mode in this way. . Therefore, good image formation can be effectively realized in the high temperature environment by the double charging mode.

  On the other hand, when the temperature in the image forming apparatus is equal to or lower than the above set temperature, the single charging mode is selected by the control device. As a result, the image carrier is charged only by the charging roller. That is, when the temperature in the image forming apparatus is equal to or lower than the temperature in the image forming apparatus during normal use (room temperature), the single charging mode is selected in this way, so that excellent charging without uneven charging can be achieved. It can be carried out. Therefore, good image formation can be effectively realized by the single charging mode in an environment of room temperature or lower.

  Thus, according to the present invention, in charging using a charging roller whose electric resistance varies with temperature, either the single charging mode or the double charging mode is selected based on the temperature in the image forming apparatus. Thus, the image carrier can be more effectively charged from a low temperature to a high temperature.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically and partially showing an example of an embodiment of an image forming apparatus according to the present invention.

  As shown in FIG. 1, an image forming apparatus 1 of this example includes a photosensitive member 2 that is an image carrier on which an electrostatic latent image and a toner image are formed. The photosensitive member 2 is, for example, a cylindrical photosensitive member. It consists of a drum and is rotated in the clockwise rotation direction α in FIG. The charging device 3 that sequentially contacts and charges the photoconductor 2 around the photoconductor 2 from the upstream side of the rotation direction α of the photoconductor 2, the optical writing device 4 that writes an electrostatic latent image on the photoconductor 2, and the static of the photoconductor 2 A developing device 5 that performs non-contact jumping development of the electrostatic latent image with toner, a transfer device 6 that transfers the toner image of the photoreceptor 2, and a cleaning device 7 that cleans the photoreceptor 2 are provided.

  The charging device 3 includes a charging roller (CR) 3a (second charging member) that charges the photosensitive member 2, and a charging brush that similarly charges the photosensitive member 2 upstream of the rotation direction α from the charging roller 3a. 3d (first charging member). The charging roller 3a is in contact with the outer peripheral surface of the photoconductor 2 and is rotated in the direction β opposite to the rotation direction α of the photoconductor 2 (counterclockwise in FIG. 1).

  As the charging roller 3a, a known charging roller that has been conventionally used can be used. That is, the charging roller 3a can be manufactured by a manufacturing method described in, for example, JP-A-10-48916. That is, the charging roller 3a is configured by providing, for example, a cylindrical conductive elastomer layer 3c made of, for example, conductive rubber or the like having a surface inclined resistance layer on a metal shaft 3b made of stainless steel. ing. The conductive elastomer layer 3c is set to have a constant outer diameter and a substantially constant electric resistance along the axial direction.

  As an example of the charging roller 3a having the conductive elastomer layer 3c, 100 parts by weight of epichlorohydrium (Epichromer CG-102; manufactured by Daiso Corporation) is used as a conductive material, such as sodium trifluoroacetate, zinc oxide (ZnO), and a vulcanizing agent. 2 parts by weight of 2-mercaptoimidazoline (Accel-22) is kneaded with a roll mixer, press-molded on the surface of a metal shaft having a diameter of 6 mm, polished to a diameter of 12 mm, and a conductive rubber elastic member is formed on the surface of the shaft. A formed roller was obtained. In that case, the respective addition amounts of sodium trifluoroacetate and zinc oxide (ZnO) were arbitrarily adjusted to obtain five charging rollers 3a having different resistance values. Table 1 shows the resistance values of the conductive elastomer layer 3c of the five charging rollers (1) to (5).

As shown in Table 1, the resistance value of the charging roller (1) is 3.0 × 10 ¹⁰ Ω at a relatively low temperature of 10 ° C., 1.6 × 10 ⁷ Ω at a normal temperature of 23 ° C., and a relatively high temperature of 35 It is 2.4 × 10 ⁶ Ω at ° C. The resistance value of the charging roller (2) is 4.0 × 10 ⁸ Ω at 10 ° C., 3.7 × 10 ⁶ Ω at 23 ° C., and 6.8 × 10 ⁵ Ω at 35 ° C. Further, the resistance value of the charging roller (3) is 6.9 × 10 ⁷ Ω at 10 ° C., 1.5 × 10 ⁶ Ω at 23 ° C., and 3.5 × 10 ⁵ Ω at 35 ° C. Further, the resistance value of the charging roller (4) is 1.4 × 10 ⁷ Ω at 10 ° C., 4.5 × 10 ⁵ Ω at 23 ° C., and 1.1 × 10 ⁵ Ω at 35 ° C. Further, the resistance value of the charging roller (5) is 3.0 × 10 ⁵ Ω at 10 ° C., 6.0 × 10 ⁴ Ω at 23 ° C., and 3.0 × 10 ⁴ Ω at 35 ° C.

  A method for measuring the resistance value of each charging roller (CR) will be described. As shown in FIG. 2, a charging roller (CR) 3 a that is an object to be measured is placed on an aluminum tube 9 used for the photoreceptor 2. Further, the metal shaft 3b of the charging roller (CR) 3a and the aluminum tube 9 are electrically connected by a constant voltage power source 10 (R8340A manufactured by Advantest). Then, a load of 250 g is applied to the metal shafts 3b at both ends of the charging roller (CR) 3a so that the charging roller (CR) 3a is pressed against the aluminum tube 9. Further, the aluminum tube 9 is rotated at a rotation speed of 5 rpm. In this state, a voltage of 160 V is applied from the constant voltage power supply 10 and the current value flowing through the constant voltage power supply 10 is read by the ammeter 10a. Finally, based on the read current value and voltage, the resistance value R is calculated from the equation V = IR (V: voltage, I: current, R: resistance).

  The charging brush 3d has a large number of bristles and is supported by a brush support member 3e. The tips of a large number of brush hairs are in contact with the outer peripheral surface of the photoreceptor 2. As the charging brush 3d, a known charging brush that has been conventionally used can be used. Examples of the charging brush 3d are shown in Table 2.

As shown in Table 2, the brush bristles of the brush 1 as an example have a material of 6 nylon, a fineness of 220T / 96F, a density of 240 kf / inch ² , a yarn resistance of 7.1 LogΩ, and a pile length of 5 mm. The overall shape of the brush 1 is 300 mm in length (along the axial direction of the photoreceptor 2), 5 mm in width, and 5 mm in height. As another example, the brush bristles of the brush 2 are made of nylon 6 material, a fineness of 330 T / 48 F, a density of 80 kf / inch ² , a yarn resistance of 9.3 LogΩ, and a pile length of 5 mm. The overall shape of the brush 1 is 300 mm in length (along the axial direction of the photoreceptor 2), 5 mm in width, and 5 mm in height. Both of these brushes 1 and 2 are brushes made by Toei Sangyo Co., Ltd.

  In the image forming apparatus 1 of this example, as described later, the photosensitive member 2 is first charged by the charging brush 3d and then charged by the charging roller 3a according to the use environment (temperature) of the image forming apparatus 1. (W charging) or charged only by the charging roller 3a (S charging).

  The optical writing device 4 writes an electrostatic latent image on the photosensitive member 2 charged by the charging device 3 with, for example, a laser beam. The developing device 5 includes a developing roller 5a, a toner supply roller 5b, and a toner layer thickness regulating member 5c. At both ends of the developing roller 5a, developing rollers 5d (only one developing roller 5a is shown in FIG. 1) are provided. These developing rollers 5d constitute a developing roller / image carrier axis distance regulating member. In other words, the distance between the axial center of the developing roller 5 a and the axial center of the photosensitive member 2 is regulated by the development rollers 5 d coming into contact with the outer peripheral surface of the photosensitive member 2. Thus, a predetermined development gap is set between the outer peripheral surface of the developing roller 5a and the outer peripheral surface of the photoreceptor 2.

  Then, toner (not shown) as a developer is supplied onto the developing roller 5a by the toner supply roller 5b, and the toner on the developing roller 5a is regulated in thickness by the toner layer thickness regulating member 5c, so that the photoconductor. 2, the electrostatic latent image on the photoreceptor 2 is jumped and developed with the conveyed toner, and a toner image is formed on the photoreceptor 2.

  The transfer device 6 has a transfer roller 6a, and a toner image is transferred onto the photosensitive member 2 by the transfer roller 6a onto a transfer medium 8 such as transfer paper or an intermediate transfer medium. When the toner image is transferred to the transfer paper that is the transfer medium 8, the toner image on the transfer paper is fixed by a fixing device (not shown), an image is formed on the transfer paper, and the toner image is transferred to the transfer medium 8. When the toner image is transferred to the intermediate transfer medium, the toner image on the intermediate transfer medium is further transferred to the transfer paper, and then the toner image on the transfer paper is fixed by a fixing device (not shown) to form an image on the transfer paper. Is done.

  The cleaning device 7 has a cleaning blade 7a made of an elastic material such as rubber. The cleaning blade 7a is supported by a blade support member 7b, and the blade support member 7b is an apparatus main body (or, for example, a charging device 3, an optical writing device 4, a developing device 5, and a cleaning device) (not shown). 7 is attached to the cartridge main body integrally incorporated. The cleaning blade 7 a is always in pressure contact with the outer peripheral surface of the photoreceptor 2. The photoconductor 2 is cleaned by the cleaning blade 7a, and the transfer residual toner on the photoconductor 2 is removed and collected by a toner collecting unit (not shown).

  Incidentally, the electric resistance R (Ω) of the conductive elastomer layer 3 c of the charging roller 3 a varies depending on the temperature (° C.) in the image forming apparatus 1. For example, the above-described charging rollers (1) to (5) will be described. As shown in FIG. 3, each of the charging rollers (1) to (5) has a low temperature (10 ° C.) and a resistance R (Ω). high. Further, the resistance R (Ω) is relatively reduced as the temperature rises from this low temperature. Furthermore, the resistance R (Ω) decreases relatively small as the temperature rises toward high temperature (35 ° C.) from around normal temperature (23 ° C.). Thus, the electric resistance R (Ω) of the charging roller 3a is high on the low temperature side and low on the high temperature side. The temperature range in the image forming apparatus 1 is set to a low temperature (10 ° C.) or a high temperature (35 ° C.) because the temperature of the image forming apparatus 1 when the image forming apparatus 1 is normally used is within this temperature range. It is because it is almost the case to enter.

  As described above, when the electric resistance R (Ω) of the charging roller 3a changes depending on the temperature in the image forming apparatus 1, the charging characteristic of the photosensitive member 2 by the charging roller 3a also changes depending on the temperature. For this reason, the charging of the photosensitive member 2 changes depending on the temperature, and the constant charging is not performed. Therefore, in the image forming apparatus 1 of this example, the charging of the photoreceptor 2 by the charging device 3 is made different depending on the temperature in the image forming apparatus 1.

  That is, in the charging device 3 of this example, two charging units selected according to the temperature in the image forming apparatus 1 are sent to a central processing unit (CPU: illustrated in FIG. 6 described later) that is a control unit for controlling the charging device 3. The mode is set. These two charging modes include a double charging mode (W charging mode) and a single charging mode (S charging mode). In the W charging mode, the charging voltage of the charging brush 3d and the charging roller 3a are both set to the discharge start voltage Vth (V) or more, and the photosensitive member 2 is primarily charged by the charging brush 3d and the photosensitive member 2 is charged by the charging roller 3a. This is a secondary charging mode. In the S charging mode, the charging voltage of the charging brush 3d as the first charging member is made smaller than the discharge start voltage Vth (V), and the charging voltage of the charging roller 3a is set to the discharge start voltage Vth (V) or more. In this mode, the photosensitive member 2 is charged only by the charging roller 3a. When the temperature in the image forming apparatus 1 is equal to or lower than a preset temperature, the S charging mode is selected. When the temperature in the image forming apparatus 1 is higher than the set temperature, the W charging mode is selected. The

In that case, in the image forming apparatus 1 of this example, the above-described set temperature is determined as follows.
As shown in FIG. 4, the resistance R (Ω) of the charging roller 3 a that can obtain good charging differs depending on the S charging mode and the W charging mode. This was found by the experiments described later by the present inventors. In the S charging mode, the region of the resistance R (Ω) of the charging roller 3a where good charging can be obtained is 10 ⁶ Ω to 10 ⁸ Ω. If the resistance R (Ω) of the charging roller 3a is smaller than 10 ⁶ Ω, uneven charging due to leakage occurs. If the resistance R (Ω) of the charging roller 3a is larger than 10 ⁸ Ω, uneven charging due to insufficient discharge occurs. On the other hand, in the W charging mode, the region of the resistance R (Ω) of the charging roller 3a from which good charging can be obtained is 10 ⁵ Ω to 10 ⁷ Ω. If the resistance R (Ω) of the charging roller 3a is less than 10 ⁵ Ω, uneven charging due to leakage occurs. If the resistance R (Ω) of the charging roller 3a is greater than 10 ⁷ Ω, uneven charging due to insufficient discharge occurs. In this case, primary charging in the W charging mode is performed by the brush 1 of the above-described charging brush 3d.

Therefore, the region of the resistance R (Ω) of the charging roller 3a in which good charging is obtained in at least one of the S charging mode and the W charging mode is 10 ⁵ Ω to 10 ⁸ Ω. Therefore, the region of the resistance R (Ω) of 10 ⁵ Ω to 10 ⁸ Ω is the region of the resistance R (Ω) of the charging roller 3a where good charging can be obtained by switching between the S charging mode and the W charging mode. . Further, the region of the resistance R (Ω) of the charging roller 3a in which good charging can be obtained in any of the S charging mode and the W charging mode is 10 ⁶ Ω to 10 ⁷ Ω.

  Now, for example, when the above-described charging rollers (1) to (5) are used, the above-described setting of the set temperature will be described. As shown in FIGS. 3 and 4, the resistance R (Ω) of each of the charging rollers (1) to (5) varies depending on the temperature. In that case, in the temperature range from the low temperature (10 ° C.) to the high temperature (35 ° C.) described above, the charging roller that enters the region of good charging resistance R (Ω) obtained by switching between the S charging mode and the W charging mode is: Charge rollers (3) and (4).

Therefore, it is suitable to use the charging rollers (3) and (4) in order to switch between the S charging mode and the W charging mode depending on the temperature in the image forming apparatus and to obtain good charging in the above temperature range. Yes. The set temperature when the S charging mode and the W charging mode are switched using the charging rollers (3) and (4) is set as follows. That is, either good charging resistor R (Omega) is a region 10 ⁶ Ω~10 ⁷ Ω resistor R, 5 × 10 ⁶ Ω and becomes the temperature set temperature midpoint of the S charging mode and W charging mode Is set. That is, the set temperatures when the charging rollers (3) and (4) are used are set to about 19 ° C. and about 14 ° C., respectively.

5A and 5B show an example of the photosensitive layer surface potential of the photosensitive member due to charging. FIG. 5A shows the photosensitive layer surface potential due to W charging, and FIG. 5B shows the photosensitive layer surface potential due to S charging.
As shown in FIG. 5A, in the W charging mode of this example, first, the surface of the photosensitive layer 2b of the substrate 2a of the photoreceptor 2 is (-) charged by the charging brush 3d, and the surface potential of (-) is obtained. It becomes. Next, the surface of the photosensitive layer 2b is (+) charged by the charging roller 3a, and becomes a predetermined surface potential (−) lower than the (−) potential by the charging brush 3d. The present invention is not limited to this. For example, after the surface of the photosensitive layer 2b is set to the surface potential of (−) by the charging brush 3d, the surface of the photosensitive layer 2b is further ( -) It can be charged to a predetermined surface potential of (-) higher than the (-) potential by the charging brush 3d.

  Further, as shown in FIG. 5B, in the S charging mode of this example, the surface of the photosensitive layer 2b is not charged by the charging brush 3d first, and the surface potential becomes (0). Next, the surface of the photosensitive layer 2 b is (−) charged by the charging roller 3 a to have a predetermined surface potential of (−). In addition, this invention is not limited to this, For example, the voltage below the discharge start voltage Vth can also be applied to the charging brush 3d.

FIG. 6 is a block diagram of temperature-dependent charging control for making the charging of the photosensitive member by the charging device different depending on the temperature.
As shown in FIG. 6, the image forming apparatus 1 of this example includes a central processing unit (CPU) 11 for controlling the operation of the image forming apparatus 1 in order to perform temperature-dependent charging control. A temperature sensor 12 for detecting temperature, an image forming operation member 13 such as an operation key on an operation panel for causing the image forming apparatus to perform an image forming operation or an operation touch key on an operation screen, a charging brush 3d, and a charging roller 3a. I have.

  When the image forming operation signal from the image forming operation member 13 is input, the CPU 11 controls the primary charging voltage of the charging brush 3d and the secondary charging voltage of the charging roller 3a based on the temperature detection signal from the temperature sensor 12. . In this case, in the image forming apparatus 1 of this example, the W charging mode is selected when the internal temperature is equal to or lower than the above set temperature. In the W charging mode, a necessary primary charging voltage is applied to the charging brush 3d and a necessary secondary charging voltage is applied to the charging roller 3a. As a result, the photosensitive member 2 is primarily charged by the charging brush 3d and is secondarily charged by the conductive elastomer layer 3c of the charging roller 3a. In that case, the required primary charging voltage and secondary charging voltage are determined by performing batch sensing. When the temperature in the image forming apparatus 1 is higher than a preset temperature, a secondary charging voltage necessary for only the charging roller 3a is applied. As a result, the photoreceptor 2 is charged only by the conductive elastomer layer 3c of the charging roller 3a.

FIG. 7 is a diagram illustrating a flow for performing temperature-dependent charging control of the charging device.
As shown in FIG. 7, the temperature-dependent charging control of the charging voltage of the charging device 3 in this example is first set to enable the image forming operation of the image forming apparatus 1 by turning on the power or returning from the energy saving mode in step S1. The Next, in step S2, it is determined whether an image forming operation has been performed. If it is determined that the image forming operation is not performed, the process of step S2 is repeated.

  If it is determined that an image forming operation has been performed, the temperature in the image forming apparatus 1 is measured in step S3. Next, when the temperature measured in step S4 is higher than the set temperature, the W charging mode is selected in step S5. In step S6, batch sensing is performed to determine a primary charging voltage required for the charging brush 3d in the current image formation, and a secondary charging voltage required for the charging roller 3a. Next, in step S7, the determined primary charging voltage is applied to the charging brush 3d, and the determined secondary charging voltage is applied to the charging roller 3a, whereby the photoconductor 2 by the charging brush 3d and the charging roller 3a is applied. W charging is performed. When the temperature in the image forming apparatus 1 is higher than the normal use temperature (normal temperature: 23 ° C.), the electric resistance R (Ω) of the charging roller 3a becomes relatively small as shown in FIG. Therefore, by charging the photosensitive member 2 in the W charging mode in this way, good charging of the photosensitive member 2 without charging unevenness can be effectively obtained.

  If the temperature detected in step S4 is equal to or lower than the set temperature, the S charging mode is selected in step S8. In step S9, batch sensing is performed to determine a secondary charging voltage required for the charging roller 3a in the current image formation. Next, in step S10, the determined secondary charging voltage is applied to the charging roller 3a, so that the S charging of the photoreceptor 2 is performed only by the charging roller 3a. When the temperature in the image forming apparatus 1 is equal to or lower than the normal use temperature (normal temperature: 23 ° C.), the electrical resistance R (Ω) of the charging roller 3a is relatively large as shown in FIG. Therefore, by charging the photosensitive member 2 in the S charging mode in this way, the surface of the photosensitive member 2 is charged well without uneven charging.

  According to the image forming apparatus 1 of this example, when the temperature in the image forming apparatus 1 is higher than a preset temperature, the W charging mode is selected, and the photosensitive member 2 is primarily charged by the charging brush 3d, and thereafter Secondary charging is performed by the charging roller 3a. That is, when the temperature in the image forming apparatus 1 is higher than the temperature in the image forming apparatus 1 during normal use, the W charging mode is selected in this way, so that satisfactory charging without uneven charging can be performed. it can. Therefore, good image formation can be effectively realized by the W charging mode in a high temperature environment.

  On the other hand, when the temperature in the image forming apparatus 1 is equal to or lower than the above set temperature, the S charging mode is selected, and the photosensitive member 2 is charged only by the charging roller 3a. That is, when the temperature in the image forming apparatus 1 is equal to or lower than the temperature in the image forming apparatus 1 during normal use (room temperature), the S charging mode is selected in this way, so that good charging without uneven charging can be achieved. It can be performed. Therefore, good image formation can be effectively realized by the S charging mode in an environment below room temperature.

  In this way, according to the charging device 3 of the image forming apparatus 1 of this example, either the S charging mode or the W charging mode is used for charging using the charging roller 3a whose electric resistance R (Ω) varies with temperature. Is selected based on the temperature in the image forming apparatus 1, the photosensitive member 2 can be more effectively charged from a low temperature to a high temperature.

Next, an experiment for confirming the effect obtained by the present invention was conducted.
(Experimental device)
As the experimental apparatus, a commercially available laser color printer LP9000C manufactured by Seiko Epson Corporation was used. In that case, the charging unit of the LP9000C photoconductor unit was modified so that a charging brush 3d as a first charging member and a charging roller 3a as a second charging member could be attached. Other photoreceptor drums, cleaning blades, optical writing devices, developing devices (including genuine toner), transfer devices (including intermediate transfer belts), and fixing devices were all LP9000C. The experiment was conducted for Examples 1 to 4 and Comparative Examples 1 to 8 shown in Table 3.

The experimental conditions common to Examples 1 to 4 and Comparative Examples 1 to 8 are a DC voltage with a charging voltage applied to the charging roller 3a of -1200V and a DC voltage with a charging voltage applied to the charging brush 3d of -1500V. Voltage. Further, the process speed is 210 mm / sec, and the peripheral speed ratio between the peripheral speed of the charging roller and the peripheral speed of the photosensitive member is 1. Further, the development application voltage is also a superimposed voltage of the DC voltage and the AC voltage, and the DC voltage V _DC = −200 V, the AC voltage V _PP = 1400 V, the AC voltage frequency f = 3.0 kHz rectangular wave (50% duty) Furthermore, the transfer application voltage is + 200V.

(Print test)
The printing test is the same in all experiments of Examples 1 to 4 and Comparative Examples 1 to 8. That is, two or three halftone images are printed on A4 size plain paper in three temperature environments of 10 ° C., 23 ° C., and 35 ° C. Then, each printed image is visually confirmed, and when there is no density unevenness, it is determined that charging is good, and when density unevenness is recognized, charging unevenness occurs and charging is poor. It was determined.

The individual experimental conditions of Examples 1 to 4 and Comparative Examples 1 to 8 will be described.
(Example 1)
The brush 1 shown in Table 2 was used as the charging brush 3d, and the above-described charging roller (3) was used as the charging roller 3a. The set temperature, which is a threshold value for switching the charging mode, was set to 20 ° C.
(Example 2)
As the charging roller 3a, the above-described charging roller (4) was used, and the set temperature was set to 15 ° C. Others are the same as the first embodiment.
(Example 3)
As the charging brush 3d, the brush 2 shown in Table 2 was used. Others are the same as the first embodiment.
Example 4
The brush 2 was used as the charging brush 3d, the charging roller (4) was used as the charging roller 3a, and the set temperature was further set to 15 ° C. Others are the same as the first embodiment.

(Comparative Example 1)
Only the S charging mode was adopted without switching the charging mode. Others are the same as the first embodiment.
(Comparative Example 2)
Only the W charging mode was adopted without switching the charging mode. Others are the same as the first embodiment.
(Comparative Example 3)
Only the S charging mode was adopted without switching the charging mode. Others are the same as in the second embodiment.
(Comparative Example 4)
Only the W charging mode was adopted without switching the charging mode. Others are the same as in the second embodiment.

(Comparative Example 5)
Only the S charging mode was adopted without switching the charging mode. Others are the same as the third embodiment.
(Comparative Example 6)
Only the W charging mode was adopted without switching the charging mode. Others are the same as the third embodiment.
(Comparative Example 7)
Only the S charging mode was adopted without switching the charging mode. Others are the same as the fourth embodiment.
(Comparative Example 8)
Only the W charging mode was adopted without switching the charging mode. Others are the same as the fourth embodiment.

  The experimental results are shown in Table 3. As apparent from Table 3, in all of Examples 1 to 4 of the present invention, the temperature in the image forming apparatus 1 is any of low temperature (10 ° C.), normal temperature (23 ° C.), and high temperature (35 ° C.). Also, there was no density unevenness and good charging without uneven charging was obtained.

  Further, in Comparative Example 1, no uneven density was observed at a temperature of room temperature (23 ° C.) or lower in the S charging mode, and good charging without uneven charge was obtained. However, density unevenness was observed at a high temperature (35 ° C.), and charging unevenness occurred, resulting in poor charging. Furthermore, in Comparative Example 2, no uneven density was observed at a high temperature (35 ° C.) in the W charging mode, and good charging without uneven charging was obtained. However, density unevenness was observed at a temperature of room temperature (23 ° C.) or less, and charging unevenness occurred, resulting in poor charging.

  Further, in Comparative Example 3, density unevenness was not observed at low temperature (10 ° C.) in the S charging mode, and good charging without uneven charging was obtained. However, density unevenness was observed at a temperature equal to or higher than normal temperature (23 ° C.), and charging unevenness occurred, resulting in poor charging. Further, in Comparative Example 4, in the W charging mode, no density unevenness was observed at a temperature of room temperature (23 ° C.) or higher, and good charging without charge unevenness was obtained. However, density unevenness was observed at a low temperature (10 ° C.), and charging unevenness occurred, resulting in poor charging.

  Further, in Comparative Example 5, in the S charging mode, density unevenness was not observed at a temperature of room temperature (23 ° C.) or less, and good charging without charge unevenness was obtained. However, density unevenness was observed at a high temperature (35 ° C.), and charging unevenness occurred, resulting in poor charging. Further, in Comparative Example 6, density unevenness was not observed at a high temperature (35 ° C.) in the W charging mode, and good charging without uneven charging was obtained. However, density unevenness was observed at a temperature of room temperature (23 ° C.) or less, and charging unevenness occurred, resulting in poor charging.

Furthermore, in Comparative Example 7, in the S charging mode, no density unevenness was observed at a low temperature (10 ° C.), and good charging without charge unevenness was obtained. However, density unevenness was observed at a temperature equal to or higher than normal temperature (23 ° C.), and charging unevenness occurred, resulting in poor charging. Further, in Comparative Example 8, in the W charging mode, no density unevenness was observed at a temperature equal to or higher than normal temperature (23 ° C.), and good charging without charge unevenness was obtained. However, density unevenness was observed at a low temperature (10 ° C.), and charging unevenness occurred, resulting in poor charging.
Thereby, it was confirmed that the intended effect can be obtained by the present invention.

FIGS. 8A and 8B are diagrams showing another example of the embodiment of the charging device according to the present invention.
In the charging device 3 of the above-described example, the charging brush 3d is used as the first charging member, and the charging roller 3a is used as the second charging member. However, in the present invention, as shown in FIG. 8A, the charging roller 3a '(metal shaft 3b', conductive elastomer layer 3c ') can also be used for the first charging member. In this case, the charging roller 3a is used as the second charging member. Further, as shown in FIG. 8B, a charging roller brush 3a ′ (metal shaft 3b ′, charging brush 3d ′) can be used as the first charging member. In this case, the charging roller 3a is used as the second charging member.

1 is a diagram schematically and partially showing an example of an embodiment of an image forming apparatus according to the present invention. It is a figure explaining the measurement of the electrical resistance of a charging roller. It is a figure which shows the temperature dependence of the electrical resistance of a charging roller. It is a figure which shows the electrical resistance area | region of the charging roller from which favorable charging is obtained in each charging mode. FIG. 5 shows an example of the photosensitive layer surface potential of the photosensitive member due to charging, (a) shows the photosensitive layer surface potential by W charging, and (b) shows the photosensitive layer surface potential by S charging. FIG. 6 is a block diagram of temperature-dependent charging control for making the charging of the photoconductor by the charging device different depending on the temperature. It is a figure which shows the flow for performing the temperature dependence charging control of a charging device. (A) And (b) is a figure which shows the other example of embodiment of the charging device concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Photoconductor, 3 ... Charging device, 3a ... Charging roller (second charging member), 3a '... Charging roller or charging roller brush (first charging member), 3c, 3c' ... Conductivity Elastomer layer, 3d, 3d '... Charging brush (first charging member)

Claims (3)

A first charging member which is rotatably provided and contacts the image carrier, and charges the surface of the image carrier;
A charging roller that contacts the image carrier downstream of the first charging member in the rotation direction of the image carrier and charges the surface of the image carrier;
Temperature measuring means for measuring the temperature;
A double charging mode in which the surface of the image carrier is charged by both the first charging member and the charging roller and a single charging mode in which the surface of the image carrier is charged only by the charging roller are set, A control device for controlling a charging voltage applied to each of the first charging member and the charging roller in a charging mode selected from the double charging mode and the single charging mode;
The control device selects the single charging mode when the temperature measured by the temperature measuring means is equal to or lower than a preset temperature, and selects the double charging mode when the temperature is higher than the preset temperature. A charging device. The charging device according to claim 1, wherein the first charging member is a charging brush, a charging roller, or a charging brush roller. An image carrier that is rotatably provided to form an electrostatic latent image, a charging device that charges the image carrier, a writing device that writes an electrostatic latent image on the image carrier, and the image carrier At least a developing device for developing the electrostatic latent image on the image carrier to form a developer image on the image carrier, and a transfer device for transferring the developer image on the image carrier;
The image forming apparatus according to claim 1, wherein the charging device is a charging device according to claim 1.

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