JP3613293B2 - Image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an apparatus for forming an image using an electrophotographic process, and more particularly to an image forming apparatus suitable for constituting a color electrophotographic process using electrostatic transfer.
[0002]
[Prior art]
Various apparatuses have been proposed as image forming apparatuses using a color electrophotographic process.
[0003]
In Japanese Patent Laid-Open No. 2-214174, in an apparatus for superimposing colors on an intermediate transfer member and transferring them to a transfer material in a batch, the transfer point from the photosensitive member to the intermediate transfer member is the same as the transfer point from the intermediate transfer member to the transfer material. Thus, it has been proposed to simplify the apparatus by using only one transfer apparatus, which has conventionally been required at two places.
[0004]
Japanese Patent Application Laid-Open No. 1-202771 proposes that the image formation on the photoconductor is improved by adjusting the exposure intensity in an apparatus that superimposes colors on the photoconductor and collectively transfers the image onto a transfer material. .
[0005]
In Japanese Patent Laid-Open No. 6-118807, the amount of toner adhering on the photosensitive member and the intermediate transfer member is read by a sensor so that good transfer can be performed in any temperature and humidity environment, and the transfer voltage is determined for each color based on the output. A method of setting has been proposed.
[0006]
[Problems to be solved by the invention]
However, the prior art has the following problems.
[0007]
In the conventional image forming apparatus, as shown in FIG. 2, when the toner 105 superimposed on the intermediate transfer member or photoconductor as the image carrier 220 is collectively transferred onto the transfer material 110, the image is transferred onto the transfer material 110. The potential of the transfer electrode disposed on the surface opposite to the surface to which the toner 105 is transferred (for example, the potential of the transfer member 107) was the same potential in the transfer nip. When transferring a color image, there are states in which the thickness of the toner layer and the toner charge amount are different as shown in FIG. 2 in the transfer nip, but transfer is performed so that the toner 105 is transferred to the transfer material 110 in all states. It is necessary to set a bias to be applied to the member 107. However, if the potential of the transfer electrode is the same as in the prior art described above, the good transfer region varies depending on the toner layer thickness, that is, the number of toner colors to be transferred. Therefore, as shown in FIG. not exist. Further, the good region changes depending on the resistance value fluctuation of the transfer material 110 and the transfer member 107 and the fluctuation of the toner charge amount with time. For this reason, it is necessary to perform bias control using toner amount detection means, toner charge amount detection means, and the like as disclosed in Japanese Patent Laid-Open No. 6-118807, and there are problems in cost increase by the sensor and sensor detection accuracy.
[0008]
Accordingly, the present invention has been made in view of such conventional problems, and the object of the present invention is to achieve high quality and durability regardless of fluctuations in the resistance value and toner charge amount of the transfer material 110 and the transfer member 107. It is to provide an image forming apparatus excellent in the above.
[0009]
[Means for Solving the Problems]
An image forming apparatus according to the present invention is an image forming apparatus that collectively transfers a color toner image formed on an image carrier onto a transfer material, and is disposed on the opposite side of the image carrier with respect to the transfer material. A potential variable means for changing the potential of the transfer electrode based on toner information formed on the image bearing member is provided. The transfer electrode is a photoconductor, and the potential variable means is statically charged on the uniformly charged photoconductor. An exposure unit for forming an electrostatic latent image, wherein the toner information is data stored in a memory of image data for each color when forming a latent image for visualization.
[0010]
[Action]
According to the present invention, there is provided a potential varying means for varying the potential of the transfer electrode disposed on the surface opposite to the surface on which the toner is transferred, based on the toner information formed on the image carrier, and the potential varying means. Thus, potential differences A, B, and C shown in FIG. 3 are added according to the state of the toner. This will be described with reference to FIG. FIG. 4 is a model diagram of the potentials of the toner layer superimposed on the image carrier and the transfer electrode on the back surface of the transfer material. Since the potential of the transfer electrode 120 is changed to A, B, and C as described above, the electric field applied to the toner layer 105 becomes substantially the same or very close regardless of the thickness of the toner layer 105. For this reason, when the voltage applied to the image carrier 220 is used as a parameter and the transfer good area is shown, as shown in FIG. 5, the good area is widened as compared with FIG. For this reason, even if the resistance values of the transfer material 110 and the transfer member 107 fluctuate or the toner charge amount changes with time, it becomes difficult to cause a transfer failure.
[0011]
According to the present invention, since the potential varying means is an exposure means for forming a latent image on the photoconductor, the potential can be changed even for a high-resolution image.
[0012]
According to the present invention, since the potential varying means is operated when the color toner is sequentially superimposed on the belt-like second photosensitive member as the intermediate transfer member, the potential at only the portion to be transferred can be deepened, and the dot scattering can be increased. And the spread can be reduced and the resolution of the image can be increased.
[0013]
According to the present invention, since the potential variable means is operated even at the time of batch transfer, the good transfer area at the time of batch transfer can be expanded, and the transferability can be improved.
[0014]
According to the present invention, since the toner information is substituted with known image data, data to the potential variable means can be easily created, and a conventional sensor is not required.
[0015]
【Example】
(Example 1)
FIG. 1 is a schematic cross-sectional view of the image forming apparatus of the present invention.
[0016]
First, the operation of the apparatus will be described. The charging unit 102 charges the photoreceptor 101 uniformly to a certain potential (for example, −700 V). In this embodiment, a contact charger that applies a DC voltage to the roller is used, but a scorotron charger may be used. An electrostatic latent image (for example, −100 V) having a resolution of 600 dpi (dot per inch) formed according to the image data is formed by the exposure unit 103 which is a laser scanning optical system. Next, the negatively chargeable yellow toner is reversed and developed by the one-component contact type yellow developing device 104 </ b> Y that can be separated and contacted, and is visualized on the photosensitive member 101. The visualized yellow toner is transferred onto the intermediate transfer member 106 by a bias (for example, +1500 V) applied to the transfer member 107. When the transfer is completed, the untransferred toner on the photoconductor 101 is collected by a cleaner 108 that is cleaned by bringing the blade into contact therewith, and then the photoconductor potential is reset by a static elimination lamp that is a static elimination means 109. By repeating the same operation for the magenta developing unit 104M, the cyan developing unit 104C, and the black developing unit 104Bk, the toner of each color is superimposed on the intermediate transfer member 106 to form a full color image. The full-color image on the intermediate transfer member 106 is collectively transferred to a transfer material 110 conveyed to a transfer position by a sheet feeding unit (not shown). At this time, a voltage (for example, −1500 V) having a polarity opposite to the voltage applied previously is applied to the transfer member 107. The exposure unit 103 forms different electrostatic latent images on the uniformly charged photoconductor 101 by changing the exposure intensity or the exposure time according to the toner layer thickness on the intermediate transfer body 106 (for example, −100 V, -400V, -700V). At this time, a bias that does not develop the toner 105 is applied to the formed electrostatic latent image on the developing device 104 (for example, +100 V), or the developing device 104 is separated from the photosensitive member 101. The untransferred toner 105 on the intermediate transfer member 106 that does not transfer to the transfer material 110 is collected by the intermediate transfer member cleaner 111. However, the intermediate transfer body cleaner 111 is configured so as to be in contact with the transfer material 110 at the time of batch transfer of the color toner image and separated at other times.
[0017]
The transfer material 110 to which the toner 105 has been transferred is fixed by a fixing device (not shown) and discharged outside the apparatus.
[0018]
Next, the potential when the toner 105 is collectively transferred to the transfer material 110 will be described.
[0019]
FIG. 6 is a diagram for explaining the potential at the time of batch transfer in this embodiment. In FIG. 6, the toner and the transfer material are illustrated apart from each other as in the other drawings. However, they are in contact with each other in order to make the movement of the toner visually understandable. In FIG. 6, −1500 V is applied to the transfer member 107, and the same potential surface is formed regardless of the thickness of the toner layer 105. On the other hand, on the transfer electrode surface (in this example, the surface of the photosensitive member 101) disposed on the surface opposite to the surface on which the toner 105 is transferred to the transfer material 110, exposure means is provided according to the thickness of the toner layer on the intermediate transfer member 106. 103, latent images having different potentials are formed. Specifically, it is set to −700 V for a portion without a toner layer or a portion of only one color, −400 V for a portion where two colors, three colors overlap, and −100 V for a portion where four colors overlap.
[0020]
Next, a method for detecting toner information on the intermediate transfer member 106 will be described. The toner layer thickness can be dealt with by providing a surface potential sensor corresponding to the resolution of the image so as to face the intermediate transfer member 106 to detect the surface potential on the toner, or providing a reflective sensor to detect the toner density. However, since the above-mentioned method has a limit in a system with high resolution, information corresponding to the toner layer thickness was created by the following method. First, image data for each color when a latent image is formed for visualization is stored in a memory, and the number of visualized toner colors in each pixel is grasped. In this embodiment, since the toner particle diameter is the same for all color toners, the number of visualized toner colors and the toner layer thickness can be substantially matched. Therefore, the data stored in the memory was used as latent image formation data during batch transfer. If the toner particle size is different for each toner color, or if the toner particle size is the same, but the charge amount is significantly different, the data stored in the memory is stored using a table that converts the visualized color, toner layer thickness, and charge amount. It may be processed and used as latent image formation data at the time of batch transfer.
[0021]
FIG. 7 is a diagram showing the relationship between the voltage applied to the transfer member 107 and the transfer efficiency during batch transfer in this example. As shown in FIG. 6, since the potential of the latent image on the photosensitive member 101 is changed depending on the thickness of the toner 105 layer, the good transfer areas of one color, two colors, three colors, and four colors overlap.
[0022]
The reason why the good transfer areas of the four colors do not completely overlap is that the potentials of the overlapping part of the two colors and the overlapping part of the three colors in FIG. 6 are the same potential. It is. Conventionally, as shown in FIG. 3, there was only a very narrow good range, so it was necessary to control the bias so as to be in the good range according to the environment and toner charge amount, or to compromise the print quality. However, in this embodiment, since a favorable bias range is widened, even if the resistance value of the intermediate transfer member 106, the transfer member 107, or the transfer material 110 changes depending on the environment or the toner charge amount changes with time, The bias to be applied does not require complicated bias control, and a high-quality image can be obtained by constant bias power supply, or simple bias control in which a lower limit voltage is set by a constant current power supply or a constant current power supply.
[0023]
In this example, the electrostatic latent image on the photosensitive member 101 at the time of batch transfer is set to three kinds of potentials (−100, −400, and −700 V), but the resistance values of the intermediate transfer member 106 and the transfer member 107 vary so much. In a system that does not, two types (for example, −100, −700 V) may be used. On the other hand, in a system in which the resistance value fluctuates greatly or the toner charge amount is likely to fluctuate, there are four types (for example, -100, -400, -700, -1000 V). Regardless of whether or not it is almost the same. In this case, when the batch transfer from the intermediate transfer member 106 to the transfer material 110 is performed, the charging unit 102 increases the potential for uniformly charging the photosensitive member 101 (for example, −1000 V), and the potential difference of the electrostatic latent image can be sufficiently obtained. It is preferable to do.
[0024]
The intermediate transfer member 106 used in the present invention is a film in which the surface resistance is made medium resistance (10 ⁵ to 10 ¹¹ Ω) by dispersing or coating a conductive material such as carbon on a substrate such as polycarbonate or polyethylene terephthalate. Use materials. Of course, the length of the intermediate transfer member 106 is longer than the maximum transfer material length supported by the apparatus, and is preferably an integral multiple of the peripheral length of the photosensitive member 101.
[0025]
(Example 2)
FIG. 8 is a schematic cross-sectional view of another embodiment of the image forming apparatus of the present invention. A significant difference from the first embodiment is that a color toner image is superimposed on the photosensitive member 101 and two photosensitive members are used.
[0026]
The operation of the apparatus will be described. Scoroton, which is the non-contact charging unit 112, uniformly charges the photosensitive member 101 to a certain potential (for example, −700 V). An electrostatic latent image (for example, −100 V) having a resolution of 600 dpi (dot per inch) formed according to the image data by the exposure unit 103 is first reversely developed with a negatively charged yellow toner by the yellow developing device 104Y, and then the photosensitive member 101 is exposed. In the visualization. The yellow toner is visualized and then charged by the charging means 102, and the magenta toner is visualized by the magenta developing device 104M on the latent image formed according to the image data by the exposure means 103. Similarly, cyan toner and black toner are also visualized and a full-color image is formed on the photoreceptor 101. The full color image on the photoconductor 101 is collectively transferred by the action of the potential on the second photoconductor 201 shown below onto a transfer material 110 conveyed to a transfer position by a paper supply unit (not shown). The second photoconductor 201 is a positively charged type, and is uniformly charged (for example, +1500 V) by the second charging unit 202 that applies a DC voltage to the roller. The second exposure unit 203 forms different electrostatic latent images on the uniformly charged second photoconductor 201 by changing the exposure intensity or the exposure time according to the toner layer thickness on the photoconductor 101 (for example, + 900V, + 1200V and + 1500V). The toner 105 remaining on the photosensitive member 101 without being transferred to the transfer material 110 is collected by the cleaner 108. The cleaner 108 is separated when the toner 105 is superimposed on the photoconductor 101 and is in contact with the transfer material 110 during batch transfer. The transfer material 110 to which the toner 105 has been transferred is fixed by a fixing device (not shown) and discharged outside the apparatus.
[0027]
Next, the potential when the toner 105 is collectively transferred to the transfer material 110 will be described.
[0028]
FIG. 9 is a diagram for explaining the potential at the time of batch transfer in this embodiment. The potential of the surface of the photoconductor 101 where the toner 105 is present is −100 V, and the same potential surface. On the other hand, the transfer electrode surface (second photoconductor surface 201 in this example) disposed on the surface opposite to the surface on which the toner 105 is transferred to the transfer material 110 is subjected to the second exposure according to the thickness of the toner layer on the photoconductor 101. By means 203, latent images of different potentials are formed. Specifically, it is set to + 900V in a portion where there is no toner layer or only one color, + 1200V in a portion where two colors, three colors overlap, and + 1500V in a portion where four colors overlap.
[0029]
FIG. 10 is a diagram showing the relationship between the surface potential and the transfer efficiency when the second photosensitive member 201 is charged by the second charging unit 202 during batch transfer in this example. Since the electrostatic latent image on the second photoconductor 201 is changed depending on the thickness of the toner 105, the good transfer areas of one color, two colors, three colors, and four colors overlap. According to this embodiment, since a good bias range is widened, the second charging unit 202 does not require complicated bias control even if the resistance value of the transfer material 110 changes depending on the environment or the toner charge amount changes with time. High-quality images can be obtained by constant bias power supply, or simple bias control that sets the lower limit voltage with constant current power supply or constant current power supply.
[0030]
(Example 3)
FIG. 11 is a schematic cross-sectional view of another embodiment of the image forming apparatus of the present invention.
[0031]
The difference from Embodiments 1 and 2 is that the potential on the side to which the toner 105 is transferred not only when transferring to the transfer material 110 at a time but also when overlaying a color image on the belt-like second photosensitive member 211 as an intermediate transfer member. It is a point to change according to toner information.
[0032]
First, the operation of the apparatus will be described. The charging unit 102 charges the photoreceptor 101 uniformly to a certain potential (for example, −700 V). An electrostatic latent image (for example, −100 V) having a resolution of 600 dpi (dot per inch) formed according to the image data by the exposure unit 103 is first reversely developed with a negatively charged yellow toner by the yellow developing device 104Y, and then the photosensitive member 101 is exposed. In the visualization. The visualized yellow toner is transferred onto the belt-like second photosensitive member 211 as an intermediate transfer member by the action of the potential shown below. FIG. 12 is a diagram for explaining the potential when yellow toner is transferred to the belt-like second photosensitive member 211. The belt-like second photoconductor 211 is a positively charged photoconductor and is uniformly charged (for example, +1500 V) by the second non-contact charging means 212 whose bias polarity can be switched. A latent image is formed by the second exposure unit 203 so that the potential on the belt-like second photosensitive member 211 opposite to the position where the yellow toner is developed on the photosensitive member 101 is + 1500V, and the potential at other positions is + 100V. Since the electric field acts only on the position where the toner 105 is to be applied, dots that are sharper than the image on the intermediate transfer member 106 in Example 1 were formed. The transfer residual toner on the photoconductor 101 is collected by the cleaner 108, and then the photoconductor potential is reset by the charge eliminating unit 109. By repeating the same operation for the magenta developing device 104M, the cyan developing device 104C, and the black developing device 104Bk, toner of each color is superimposed on the belt-like second photosensitive member 211 that is an intermediate transfer member to form a full color image. . The full-color image on the belt-like second photosensitive member 211 is collectively transferred to the transfer material 110 conveyed to the transfer position by a sheet feeding unit (not shown) by the action of the following potential. The surface potential on the belt-like second photosensitive member 211 is set to a potential having a polarity opposite to the previous potential by the second non-contact charging unit 212 (for example, −1500 V). Further, the exposure means 103 forms different electrostatic latent images on the uniformly charged photoreceptor 101 by changing the exposure intensity or the exposure time according to the toner layer thickness on the belt-like second photoreceptor 212 (for example, −100V, −400V, −700V). At this time, a bias that does not develop the toner 105 is applied to the formed electrostatic latent image on the developing device 104 (for example, +100 V), or the developing device 104 is separated from the photosensitive member 101. The untransferred toner 105 on the belt-like second photosensitive member 211 that does not transfer to the transfer material 110 is collected by an intermediate transfer member cleaner 111 that contacts the transfer material 110 during batch transfer and leaves otherwise. The transfer material 110 to which the toner 105 has been transferred is fixed by a fixing device (not shown) and discharged outside the apparatus.
[0033]
Next, the potential when the toner 105 is collectively transferred to the transfer material 110 will be described.
[0034]
FIG. 13 is a diagram for explaining the potential at the time of batch transfer in this embodiment. The surface potential on the belt-like second photoreceptor 211 is −1500 V, and the same potential surface is formed regardless of the thickness of the toner layer 105. On the other hand, the transfer electrode surface (in this example, the surface of the photoconductor 101) disposed on the surface opposite to the surface on which the toner 105 is transferred to the transfer material 110 depends on the thickness of the toner layer on the belt-shaped second photoconductor 211. The exposure means 103 forms latent images with different potentials. Specifically, it is set to −700 V for a portion without a toner layer or a portion of only one color, −400 V for a portion where two colors, three colors overlap, and −100 V for a portion where four colors overlap.
[0035]
FIG. 14 is a diagram showing the relationship between the surface potential and the transfer efficiency when the belt-like second photosensitive member 211 is charged by the second non-contact charging means 212 during batch transfer in this example. Since the latent image on the photoconductor 101 is changed depending on the thickness of the toner layer, the good transfer areas of one color, two colors, three colors, and four colors overlap. According to this embodiment, since a favorable bias range is widened, the second non-contact charging unit 212 does not need complicated bias control even if the resistance value of the transfer material 110 changes depending on the environment or the toner charge amount changes with time. First, high-quality images can be obtained by constant bias power supply, or simple bias control that sets the lower limit voltage with constant current power supply or constant current power supply.
[0036]
As described above, the present invention has been described using the three embodiments. The gist of the present invention is to change the potential of the surface opposite to the surface on which the toner is transferred based on the toner information formed on the image carrier. Embodiments are not limited to these examples. In this embodiment, an exposure unit for forming an electrostatic latent image on a uniformly charged photoconductor is used as a potential variable unit. However, in a system where the resolution is not so high, an electrode provided according to the resolution is used for each electrode. May be controlled.
[0037]
【The invention's effect】
The present invention described above has the following effects.
[0038]
According to the present invention, since there is a potential variable means for changing the potential of the transfer electrode arranged on the surface opposite to the surface on which the toner is transferred based on the toner information formed on the image carrier, the bias range in which the transfer is good Therefore, even when the resistance value of the transfer material or the transfer member fluctuates or the toner charge amount changes with time, highly efficient transferability can be secured and a highly reliable image forming apparatus can be provided.
[0039]
According to the present invention, since the potential variable means is an exposure means for forming a latent image on the photosensitive member, the resolution of the potential in the potential variable means can be easily increased and a high quality image forming apparatus can be provided.
[0040]
According to the present invention, when the color image is superimposed on the belt-shaped second photosensitive member that is an intermediate transfer member, the potential varying means is operated, so that it is possible to provide a high-quality image forming apparatus with reduced dot scattering and spread.
[0041]
According to the present invention, since the potential varying means is operated even during batch transfer, it is possible to widen the good transfer area during batch transfer and to provide a highly reliable image forming apparatus.
[0042]
According to the present invention, since toner information is substituted with known image information in advance, a toner layer thickness detecting unit or the like is unnecessary, and a small and low-cost image forming apparatus can be provided.
[Brief description of drawings]
FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is an enlarged view showing a transfer nip.
FIG. 3 is a diagram illustrating a relationship between a transfer voltage and transfer efficiency in an image forming apparatus.
FIG. 4 is a diagram illustrating a potential at the time of transfer in the present invention.
FIG. 5 is a graph showing the relationship between transfer voltage and transfer efficiency according to the present invention.
FIG. 6 is a diagram showing a configuration and potential at the time of batch transfer in the first embodiment of the present invention.
FIG. 7 is a graph showing the relationship between transfer voltage and transfer efficiency in the first embodiment of the present invention.
FIG. 8 is a schematic cross-sectional view of an image forming apparatus according to a second embodiment of the present invention.
FIG. 9 is a diagram showing a configuration and potential at the time of batch transfer according to a second embodiment of the present invention.
FIG. 10 is a graph showing the relationship between the charging potential of a second photoconductor and transfer efficiency in a second embodiment of the present invention.
FIG. 11 is a schematic cross-sectional view of an image forming apparatus according to a third embodiment of the present invention.
FIG. 12 is a diagram showing the configuration and potential during sequential transfer in the third embodiment of the present invention.
FIG. 13 is a diagram showing a configuration and potential at the time of batch transfer according to a third embodiment of the present invention.
FIG. 14 is a graph showing the relationship between the second photoreceptor potential and transfer efficiency in the third embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 Photoconductor 102 Charging means 103 Exposure means 104 Developing device 104Y Yellow developing device 104M Magenta developing device 104C Cyan developing device 104Bk Black developing device 105 Toner 106 Intermediate transfer member 107 Transfer member 108 Cleaner 109 Discharge means 110 Transfer material 111 Intermediate transfer member cleaner 112 Non-contact charging unit 120 Transfer electrode 201 Second photosensitive member 202 Second charging unit 203 Second exposure unit 211 Belt-shaped second photosensitive member 212 Second non-contact charging unit 220 Image carrier

Claims (5)

In an image forming apparatus that collectively transfers a color toner image formed on an image carrier onto a transfer material, the potential of a transfer electrode disposed on the side opposite to the image carrier with respect to the transfer material is applied to the image carrier. Exposure means for forming an electrostatic latent image on the uniformly charged photoreceptor , the transfer electrode being a photoreceptor , the potential changing means being changed based on toner information formed on the body An image forming apparatus , wherein the toner information is data stored in a memory of image data for each color when forming a latent image for visualization. The image forming apparatus according to claim 1 , wherein the image carrier is an intermediate transfer member. The image forming apparatus according to claim 1 , wherein the image carrier is a photoconductor. Charging means for uniformly charging the photosensitive member, exposure means for forming an electrostatic latent image on the photosensitive member based on image information, developing means for developing the electrostatic latent image, and a belt-like second photosensitive member. A second charging means for uniformly charging; a second exposure means for forming an electrostatic latent image on the second photoconductor; and a color toner image developed on the photoconductor on the second photoconductor When sequentially transferring the toner information, the potential of the second photosensitive member is changed by the second exposure unit in accordance with the toner information on the photosensitive member to form a latent image for visualizing the toner information. An image forming apparatus characterized in that image data for each color is stored in a memory. When the transfer material is passed between the second photoconductor and the color toner image superimposed on the second photoconductor is collectively transferred to the transfer material, the potential of the photoconductor is changed to the second photoconductor. 5. The image forming apparatus according to claim 4, wherein the exposure unit changes the toner in accordance with toner information on the photosensitive member.

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