JP2005242198A - Transfer device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain stable image regardless of an environmental change in a transfer device which is capable of performing the primary transfer process in which a toner image with a positive or negative polarity formed on an image carrier is transferred to an intermediate transfer body and then the secondary transfer process in which the toner image held on the intermediate transfer body is further transferred to a recording medium, and which includes as a means for the secondary transfer process: a contact transfer body which is located opposite to the toner image holding face of the intermediate transfer body and conveys the recording medium while holding it between the intermediate transfer body and the contact transfer body itself; an electrode disposed inside the intermediate transfer body, which applies a voltage to the recording medium conveyed while held between the intermediate transfer body and the contact transfer body; and a power source which applies a voltage with the same polarity as the toner image from the electrode under current control. <P>SOLUTION: A sensor (SS1) and a control means (100) are provided as means for altering a secondary transfer current according to the environment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

    The present invention relates to an electrophotographic copying machine having an intermediate transfer member, a laser printer, a transfer device used for a facsimile, and the like, and an image forming apparatus using the transfer device.

  A secondary transfer step of transferring the toner image carried on the intermediate transfer member to a recording medium through a primary transfer step of transferring the toner image having a positive or negative polarity formed on the photosensitive member to the intermediate transfer member. A contact transfer member capable of performing a transfer step, and as a means for performing the secondary transfer step, facing the surface of the intermediate transfer member having the toner image and capable of sandwiching and conveying a recording medium with the intermediate transfer member; An electrode capable of applying a voltage to the recording medium sandwiched and conveyed between the intermediate transfer member and the contact transfer member, and having a voltage of the same polarity as the toner image from the electrode. 2. Description of the Related Art A transfer device having a power source that applies current under current control is known (see, for example, Patent Document 1).

  By the way, in a transfer apparatus and an image forming apparatus that perform constant current control, abnormal images such as white spots are likely to occur during secondary transfer in a low-humidity environment, but the above-mentioned patent document does not mention a solution to such a problem. .

Japanese Patent Laid-Open No. 2003-131479

  The problem to be solved by the present invention is to provide a transfer device and an image forming apparatus capable of preventing the occurrence of abnormal images depending on the environment.

The present invention has the following configuration in order to achieve the above object.
(1). The toner image carried on the intermediate transfer member is further transferred to a recording medium through a primary transfer process in which a toner image having a positive or negative polarity formed on the image carrier is transferred to the intermediate transfer member. As a means for performing the secondary transfer process, a contact transfer body capable of sandwiching and transporting a recording medium between the intermediate transfer body and the surface having the toner image of the intermediate transfer body as a means for performing the secondary transfer process And an electrode that can apply a voltage to a recording medium sandwiched and conveyed between the intermediate transfer member and the contact transfer member, and has the same polarity as the toner image from the electrode. The transfer apparatus having a power source for applying voltage by current control includes means for changing the current value controlled by the current according to the environment.
(2). In the transfer device described in (1), as the means for changing the current value controlled by the current according to the environment, the current value is made different depending on a temperature / humidity sensor and relative humidity or absolute humidity indicated by the temperature / humidity sensor. A control means is provided (claim 2).
(3). In the transfer device described in (2), a CPU is used as the control means.
(4). In the transfer device according to (2) or (3), when the relative humidity or the absolute humidity is lower than normal humidity, the control unit makes the current value smaller than a value at normal humidity. (Claim 4).
(5). In the image forming apparatus according to (2) or (3), when the relative humidity or the absolute humidity is higher than normal humidity, the control unit sets the current value to be larger than a value at normal humidity. (Claim 5).
(6). A primary transfer step for transferring a toner image formed on the image carrier to an intermediate transfer member, and a secondary transfer for further transferring the toner image on the intermediate transfer member obtained in the primary transfer step to a recording medium In the image forming apparatus capable of performing the process, the transfer device according to any one of (1) to (5) is used.

  According to the present invention, a stable transfer image can be obtained by changing the secondary transfer current value depending on the environment (temperature and humidity) in which the transfer device and the image forming apparatus are installed.

[1] Transfer apparatus and image forming apparatus suitable for carrying out the present invention FIG. 1 shows an example of an image forming apparatus to which the transfer apparatus of the present invention is applied, and shows a main part including a primary transfer process and a secondary transfer process. It is. In FIG. 1, around the photosensitive member 8 serving as a drum-shaped image carrier, each device normally provided in the image forming apparatus, that is, each process such as charging, exposure, development, transfer, charge removal, and cleaning is achieved. A device is provided for doing this.

  The intermediate transfer member 10A is supported by the three rollers 10A1, 10A2, and 10A3 so as to be rotated endlessly. The roller 10A1 faces the photoconductor 8 with the intermediate transfer member 10A interposed therebetween, and constitutes a primary transfer device that performs a primary transfer process.

  The electrostatic latent image for each color created on the peripheral surface of the photoconductor 8 is developed for each color by the developing units 9A, 9B, 9C, and 9D constituting the developing device 9, and becomes a toner image. The image is transferred onto an intermediate transfer member 10A configured as a belt as a portion (primary transfer step). In the case of a multi-color image, the above process is repeated for each color, and the toner image is transferred onto the intermediate transfer member 10A so as to carry the color toner image.

  The roller 10A3 is opposed to the contact transfer body 11 formed of a roller with the intermediate transfer body 10A interposed therebetween, and performs a secondary transfer process for performing a secondary transfer process for further transferring the toner image on the intermediate transfer body 10A onto a recording medium. Configure the device.

  The roller 10 </ b> A <b> 3 functions as an electrode for applying a voltage to the recording medium that is nipped and conveyed between the contact transfer body 11. A power source (not shown) for applying a voltage having the same polarity as the toner image on the recording medium is electrically connected to the roller 10A3. The contact transfer body 11 is configured to selectively take either the contact or separation state with the intermediate transfer body 10A as necessary.

  The contact transfer body 11 is in a state of being separated from the intermediate transfer body 10A until all the planned toner images are completely transferred to the intermediate transfer body 10A by the primary transfer device. When the image is overlaid and transferred, the contact transfer body 11 is automatically switched to a position in contact with the intermediate transfer body 10A. When toner images of all colors such as cyan, magenta, and yellow are overlaid and transferred, a recording medium such as paper that is synchronized with the toner image is conveyed from a paper feeding device (not shown), and contact transfer with the intermediate transfer body 10A is performed. The color toner image is transferred to a recording medium by being sandwiched between the body 11 and receiving a predetermined transfer electric field.

[2] Improved transfer apparatus and image forming apparatus The present invention relates to an improvement of a secondary transfer apparatus as a means for performing a secondary transfer process in such an image forming apparatus. FIG. 2 is a schematic configuration diagram of a means for performing a secondary transfer process showing an embodiment of the present invention. The configuration around the primary transfer device and the photosensitive member not shown in FIG. 2 is the same as the configuration shown in FIG.

  The arrangement of the roller 10A3, the contact transfer body 11 and the like described in FIG. 1 and the configuration in the vicinity thereof are shown in detail. Here, a configuration example in which the opposing member 2 is arranged in place of the roller 10A3 is shown. ing. In addition, for the sake of convenience of explanation, a part is exaggerated.

  In FIG. 2, the intermediate transfer member 1 (corresponding to the intermediate transfer member 10A in FIG. 1), which is a transfer belt, moves while being in contact with the opposing member 2 (corresponding to the roller 10A3 in FIG. 1). The facing member 2 is a fixing member made of a conductor 2A such as a metal constituting an electrode. The portion where the conductor 2A is in contact with the intermediate transfer member 1 is formed smoothly so that there is almost no frictional resistance. The contact transfer body 3 (corresponding to the contact transfer body 11 in FIG. 1) has a roller structure including a cored bar 3A and a flexible member 3B surrounding the periphery thereof. The high-voltage power supply 4 applies a predetermined voltage (current) to the conductor 2 </ b> A of the facing member 2.

  The guide plate 5 for guiding the recording medium includes a lower guide plate 5A and an upper guide plate 5B. A recording medium S such as paper passes through the nip portion between the intermediate transfer member 1 and the flexible member 3B while being in contact with the lower guide plate 5A. The recording medium S after the transfer moves while static electricity is removed by the charge removal device 6.

  The current value flowing through the recording medium S to the lower guide plate 5A is detected by the current detection device 7. Although not shown in the drawing, the cored bar 3A, the power source 4, the static eliminator 6, and the current detector 7 are each electrically grounded, and the power source 4 and the current detector 7 are connected to the central processing system 100.

  When a toner image that has been over-transferred on the intermediate transfer body 1 by a primary transfer device (not shown in FIG. 1), which is not shown in FIG. 2, reaches the secondary transfer device, the toner image The recording medium S conveyed in synchronism with the intermediate transfer member 1 is nipped and conveyed between the intermediate transfer member 1 and the contact transfer member 3, and at the same time, from the power source 4, the same polarity as that of the toner having the conductor 2A of the opposing member 2 as an electrode. A polar electric field is applied towards the contact transfer body 3. The toner image is transferred to the recording medium S by this electric field.

  In such an apparatus, by applying a constant current to the intermediate transfer body 1 with a bias having the same polarity as the toner, the influence of the resistance change of the intermediate transfer body and the electrode due to the temperature and humidity of the image forming apparatus and the resistance of the recording medium Since the transfer electric field is kept almost constant without being affected by the change, the change in the secondary transfer rate to the recording medium due to the temperature and humidity where the image forming apparatus is placed is small.

  Further, the secondary transfer rate to the recording medium S slightly changes by receiving a slight change in the toner Q / M due to the temperature and humidity where the image forming apparatus is placed. Referring to FIG. 3, the optimum secondary bias current for obtaining the highest transfer rate is shifted to a slightly larger value in the low humidity environment where the toner Q / M is higher than that in the normal humidity environment. In the high humidity environment where the toner Q / M is low, the optimum secondary bias current for obtaining the maximum transfer rate is shifted to a slightly smaller value than in the normal humidity environment, and the maximum transfer rate is slightly lowered.

  However, the range of the secondary bias current with a high transfer rate is wide. For example, the secondary bias current is selected as the optimum value in the normal humidity environment, and the secondary bias current remains in the low humidity or high humidity environment. Even so, the transfer rate remains within the range of the secondary bias current having a high transfer rate. Even if the image formed on the recording medium S is viewed, the density change is not noticed. In other words, including the Q / M change of the toner, the apparatus shown in FIGS. 1 and 2 can obtain an image in an appropriate category in terms of the transfer rate with respect to the temperature and humidity change with one bias current value. It is done.

  However, in a low humidity environment, peeling discharge occurs when the recording medium S is separated from the intermediate transfer body 1 at the secondary transfer nip exit (nip exit of the opposing member 2 and the contact transfer body 3 via the intermediate transfer body 1). An abnormal image that seems to be caused is likely to occur. At present, the polyimide widely used as the intermediate transfer member 1 can see the background of the recording medium S having a small diameter of 0.5 mm or less, and generally a diameter of 0.3 mm or less, even if the size of white spots (white spots) is large. Such a sharp white-out (white spotted) image is obtained.

  Further, when the intermediate transfer body 1 is PVDF (polyvinylidene fluoride), the diameter of white spots (white spots) is as large as about 1 mm to about 2 mm, but the image becomes confusing with the blurred image when the shading is slightly reduced. In any case, since the peeling discharge trace image starts to appear from the secondary bias current value at which the transfer rate is appropriate, the occurrence of the peeling discharge trace image (white spot image) is avoided and the transfer rate is high and the density is high. The obtained secondary transfer bias current value is limited to a narrow range.

  Furthermore, a blurred image is likely to occur in a high humidity environment. In a high humidity environment, moisture absorption on the surface of the toner and the intermediate transfer member increases, and an adsorption force that seems to be due to the adsorbed hydrogen bonding force occurs between the intermediate transfer member and the toner or toner, and the intermediate transfer member to the recording medium Interfering with transcription.

  The toner becomes an aggregate due to the adsorbing force between the toners, and the toner aggregate is not transferred to the recording medium and remains on the intermediate transfer body, thereby causing transfer unevenness due to a place having a size of about 1 mm, resulting in a blurred image. . Since the toner that is not transferred to the recording medium and is likely to remain on the intermediate transfer member is limited to one or two layers close to the intermediate transfer member, the transfer rate is not greatly reduced, and it seems that only the blur is felt. . Rather, the result is that the transfer electric field becomes so large that the transfer rate starts to decrease and the blur is eliminated.

  Therefore, it is impossible to achieve both the peeled discharge trace image in the low humidity environment and the blurred image in the high humidity environment with one secondary bias current. Therefore, the secondary transfer bias current value can avoid or reduce the peeled discharge trace image in a low humidity environment, but can be reduced to a value at which the image density can be obtained, and the blur can be avoided or reduced in a high humidity environment. By raising the value to the value obtained, an appropriate image can be obtained even in each environment.

  In the present invention, the temperature / humidity sensor SS1 for detecting the environment in which the transfer device or the image forming apparatus is installed, the temperature (humidity sensor SS1) for controlling the voltage (current) by the power source 4 according to the environment, and the temperature. Control means for varying the current value according to the relative humidity or absolute humidity indicated by the humidity sensor is provided (claims 1, 2 and 6). By changing the voltage (current) value of the power supply 4 according to the environment, the secondary transfer current value is adapted to the environment (humidity) in which the transfer device and the image forming apparatus are installed, and a stable transfer image is obtained. Can do.

  The humidity information detected by the temperature / humidity sensor SS1 is input to the central processing system 100 as the control means (claims 3 and 6). Alternatively, a dedicated control circuit can be used instead of the central processing system 100. In this way, a transfer device that has a temperature / humidity sensor, reads the relative humidity or absolute humidity indicated by the temperature / humidity sensor, and automatically controls it so that an optimum current value can be always selected without human intervention. A forming apparatus can be provided.

  The central processing system 100 receives the relative humidity or absolute humidity information indicated by the temperature / humidity sensor, and compares the current value by the power source 4 with the data input in advance. For example, when the relative humidity or the absolute humidity is lower than normal humidity, the central processing system 100 makes the current value smaller than the value at normal humidity (Claims 4 and 6). With this control, it is possible to provide a transfer device and an image forming apparatus that can avoid or reduce a discharge trace image that is likely to occur when humidity is low.

  Alternatively, when the relative humidity or the absolute humidity is higher than normal humidity, the central processing system 100 makes the current value larger than the value at normal humidity (Claims 5 and 6). By such control, it is possible to avoid or reduce a blurred image that tends to occur when the humidity is high.

1 is a diagram illustrating a configuration of an image forming apparatus. It is a figure explaining the structure of the secondary transfer part. It is a figure explaining the relationship between environment, image quality, and electric current.

Explanation of symbols

4 Power supply 100 Central processing system SS1 Temperature / humidity sensor

Claims (6)

The toner image carried on the intermediate transfer member is further transferred to a recording medium through a primary transfer process in which a toner image having a positive or negative polarity formed on the image carrier is transferred to the intermediate transfer member. As a means for performing the secondary transfer process, a contact transfer body capable of sandwiching and transporting a recording medium between the intermediate transfer body and the surface having the toner image of the intermediate transfer body as a means for performing the secondary transfer process And an electrode that can apply a voltage to a recording medium sandwiched and conveyed between the intermediate transfer member and the contact transfer member, and has the same polarity as the toner image from the electrode. In a transfer apparatus equipped with a power supply for applying voltage by current control,
A transfer device comprising means for changing the current value controlled by the current according to the environment. The transfer device according to claim 1,
As a means for changing the current value to be controlled according to the environment, a temperature / humidity sensor and a control means for changing the current value according to relative humidity or absolute humidity indicated by the temperature / humidity sensor are provided. Transfer device. The transfer device according to claim 2,
A transfer apparatus using a CPU as the control means. In the transfer device according to claim 2 or 3,
When the relative humidity or the absolute humidity is lower than normal humidity, the control means makes the current value smaller than a value at normal humidity. The image forming apparatus according to claim 2 or 3,
When the relative humidity or the absolute humidity is higher than normal humidity, the control means makes the current value larger than a value at normal humidity. A primary transfer step for transferring a toner image formed on the image carrier to an intermediate transfer member, and a secondary transfer for further transferring the toner image on the intermediate transfer member obtained in the primary transfer step to a recording medium In an image forming apparatus capable of performing the process,
An image forming apparatus using the transfer device according to claim 1.

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