JP2006030737A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the generation of stains on the rear surface of a sheet which may be generated at the time of frameless printing by forming a transparent toner layer on an underlayer or an upper layer of a colored toner image formed by primary transfer in an image forming apparatus adopting a system for forming a color toner image on an image carrier by primary transfer and collectively transferring a colored toner image formed by secondary transfer to the sheet. <P>SOLUTION: In the image forming apparatus using the secondary transfer system, a transparent toner cartridge is arranged on the upstream side in the intermediate transfer body carrying direction of color toner cartridges. At the time of frameless printing, a transparent toner layer is formed on the underlayer of color toner on an intermediate transfer body to prevent the rear surface of a recording material from being stained due to color toners. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material using an electrophotographic system. Specifically, toner scattering prevention using transparent toner in an image forming apparatus using a system in which a toner image formed on an image carrier is primarily transferred to an intermediate transfer member and then secondarily transferred onto a recording material. It is about the method.

  In a conventional image forming apparatus using an electrophotographic method, a toner image formed on an image carrier is primarily transferred to an intermediate transfer member, and a toner image on the intermediate transfer member is secondarily transferred to a recording material. The image forming apparatus to be used forms an image on a recording material with a configuration as shown in FIG. 2, for example. That is, in this image forming apparatus, the electrophotographic toner image forming unit including the image carrier 2, the charging device 3, the developing device 4, and the exposure device 6 is yellow (Y), magenta (M), cyan (C), black ( K) are arranged side by side for each color of K). The toner image formed by the toner image forming unit is primarily transferred from the image carrier 2 to the intermediate transfer belt 1 by the primary transfer nip with the primary transfer roller 5, and further, the secondary transfer roller 10 and Secondary transfer is performed from the intermediate transfer body 1 onto the recording material 14 by the secondary transfer nip formed by the facing roller 7.

  In the secondary transfer nip, the toner on the intermediate transfer belt 1 is normally secondarily transferred to the recording material 14, but due to toner patches or jams for density control, or fog toner in the non-image area, etc. Since the toner on the intermediate transfer belt 1 directly adheres to the secondary transfer roller, there is a problem that the toner on the secondary transfer roller 10 eventually adheres to the back surface of the recording material 14 (hereinafter, recording material backside contamination). is there.

  In order to solve the above problem, as a cleaning method for the secondary transfer roller 10, a method for electrostatic cleaning and a method for mechanical cleaning have been developed.

  The electrostatic cleaning is a method in which a reverse bias is applied to the applied bias at the time of secondary transfer, and the toner is electrostatically retransferred from the secondary transfer roller 10 to the intermediate transfer body 1. For example, when the colored toner has a negative charge, a positive bias is applied to the intermediate transfer member 1 to the secondary transfer roller 10. This method is often used when the amount of toner to be cleaned is relatively small.

  Mechanical cleaning is a method in which a resin blade, a fur brush, or the like is brought into direct contact with the secondary transfer roller 10 to mechanically scrape off and remove the toner. In order to remove toner more efficiently, a secondary transfer roller has been invented in which the surface layer of a sponge roller is coated with a fluororesin to improve toner releasability (for example, Patent Document 1). The toner adhering to the secondary transfer roller can be removed relatively easily by a resin blade, a fur brush, or the like.

Japanese Patent No. 3139342

  However, in the conventional cleaning method described above, when a large amount of toner adheres to the secondary transfer roller at a time, it is difficult to completely remove the toner and prevent the recording material from being stained. In particular, when performing borderless printing (printing without margins), it is necessary to clean a large amount of toner once for the following reasons.

  Usually, in order to perform borderless printing by the above-described secondary transfer method, on the image carrier 2 and the intermediate transfer member 1 due to a request from a problem that is unavoidable in terms of accuracy such as positional deviation during paper conveyance or toner image formation. Needs to form an image having a size larger than that of the recording material 14. For this reason, all of the toner in the image area (hereinafter referred to as “addition area”) that has not been secondarily transferred to the recording material 14 in the secondary transfer nip adheres to the secondary transfer roller 10, and as a result should be cleaned. Toner becomes too much.

  Also, when toner patches or jams for density control are generated, fog toner can be cleaned by rotating the secondary transfer roller several times, but in borderless printing, the secondary transfer roller rotates once. If the cleaning is not completed within this time, the recording material will become dirty, and the cleaning performance according to the above prior art may be insufficient.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to prevent the recording material from being soiled at the time of secondary transfer with colored toner in an image forming apparatus using a secondary transfer system by applying a transparent toner.

  Conventionally, several techniques related to transparent toner have been introduced, most of which are used for the purpose of controlling the glossiness of a recording material. For example, in Japanese Patent Laid-Open No. 2002-82508, in a method of directly forming a toner image from an image carrier onto a recording material by primary transfer, an image forming unit using transparent toner is placed upstream of an image forming unit using color toner. The glossiness of the recording material can be controlled in multiple stages by using transparent toner.

  However, Japanese Patent Laid-Open No. 2002-82508 differs from the configuration of the present invention using the secondary transfer method, and it is not assumed that transparent toner is applied to non-image areas during borderless printing. It is not possible to completely prevent the backside of the recording material during secondary transfer with colored toner.

  Then, what is shown below is mentioned as a means for solving the said subject in this invention.

  A developing unit that forms a colored toner image on the image carrier based on the image information, the primary transfer of the colored toner image formed on the image carrier onto the intermediate transfer member, and then the color on the intermediate transfer member; In an image forming apparatus for secondary transfer of a toner image by an intermediate transfer member and a secondary transfer roller disposed opposite to the surface of the intermediate transfer member, the image forming apparatus has a secondary transfer member cleaning unit, A developing means and an image carrier using a transparent toner are disposed downstream of the intermediate transfer member conveyance direction.

  2. The image forming apparatus according to claim 1, wherein the control means determines whether or not the developing means and the image carrier are operated by the transparent toner.

  The image forming apparatus having the configuration according to claim 1 is characterized in that when a transparent toner image is formed, an image larger than the image area of the recording material and the image area of the colored toner image is formed.

  2. The image forming apparatus according to claim 1, wherein when the transparent toner image is formed, the amount of the transparent toner is gradually reduced toward the center of the image area.

  According to the present invention, it is usually difficult to remove the toner adhering directly to the roller within one rotation of the roller. However, a transparent toner layer is formed between the colored toner and the secondary transfer roller using the above method. Can be formed. Therefore, even if the toner adheres to the secondary transfer roller during the secondary transfer, it is possible to prevent the colored toner from directly adhering to the secondary transfer roller. Therefore, the color toner can be easily removed by the secondary transfer roller cleaner. In addition, the effect of preventing the recording material from being stained can be obtained.

  In addition, according to the present invention, the amount of transparent toner is gradually reduced from the edge of the image area toward the center, so that the image can be displayed without feeling uncomfortable with the difference in glossiness due to the presence or absence of the transparent toner after fixing. The effect of reducing the transparent toner in the center is obtained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
Hereinafter, an embodiment suitable for the present invention will be described in detail with reference to FIG.

  FIG. 1 is a schematic configuration diagram showing an electrophotographic multicolor image forming apparatus according to an embodiment of the present invention. In this image forming apparatus, toner image forming portions that form images of transparent toner: T and a total of four colors (yellow: Y, magenta: M, cyan: C, black: K) are arranged in a line at regular intervals. Has been.

  In each toner image forming portion, photosensitive drums 2Y, 2M, 2C, 2K, and 2T are installed as image carriers. Around the photosensitive drums 2Y, 2M, 2C, 2K, and 2T, there are charging rollers 3Y, 3M, 3C, 3K, and 3T, developing devices 4Y, 4M, 4C, 4K, and 4T, and primary transfer rollers 5Y, 5M, and 5C. , 5K, 5T are installed. Exposure devices 6Y, 6M, 6C, 6K, and 6T are installed above the charging rollers 3Y, 3M, 3C, 3K, and 3T and the developing devices 4Y, 4M, 4C, 4K, and 4T, respectively.

  The photosensitive drums 2Y, 2M, 2C, 2K, and 2T are negatively charged organic photosensitive drums having an OPC photosensitive layer in the present embodiment, and are respectively driven in the direction of the arrow (counterclockwise) by a driving device (not shown). It is rotationally driven at a predetermined peripheral speed (process speed).

  Charging rollers 3Y, 3M, 3C, 3K, and 3T as contact charging means respectively contact the photosensitive drums 2Y, 2M, 2C, 2K, and 2T with a predetermined pressure contact force, and are applied from a charging bias power source (not shown). The surface of each photosensitive drum 2Y, 2M, 2C, 2K, 2T is uniformly charged to a predetermined negative potential by a charging bias.

  The developing devices 4Y, 4M, 4C, 4K, and 4T are two-component developing systems in the present embodiment, and each photosensitive drum 2Y, 2M, 2C, 2K, and the like is developed by a developing bias applied from a developing bias power source (not shown). The toner is attached to the electrostatic latent image formed on 2T, and is reversely developed as a toner image. The developing devices 4Y, 4M, 4C, 4K, and 4T store Y toner, C toner, M toner, K toner, and T toner, respectively.

  The transfer rollers 5Y, 5M, 5C, 5K, and 5T as contact transfer means contact the surfaces of the photosensitive drums 2Y, 2M, 2C, 2K, and 2T with a predetermined pressing force via the intermediate transfer belt 1 as an intermediate transfer member. Then, the transfer bias having a polarity opposite to that of the toner applied from each transfer bias power source (not shown) is used between the photosensitive drums 2Y, 2M, 2C, 2K, and 2T and the transfer rollers 5Y, 5M, 5C, 5K, and 5T. In each primary transfer section, the respective toner images on the surfaces of the photosensitive drums 2Y, 2M, 2C, 2K, and 2T are sequentially superimposed on the moving intermediate transfer belt 1 and transferred (primary transfer). Here, the transparent toner transfer roller 5T has a mechanism (not shown) for separating a predetermined distance from the photosensitive drum 2T, and the pressure and separation of the transfer roller 5T are controlled by an engine controller (not shown).

  The exposure devices 6Y, 6M, 6C, 6K, and 6T are respectively connected to the photosensitive drums 2Y, 2M, and 2D with laser beams modulated in accordance with time-series electric digital pixel signals of image information input from a host computer (not shown). By exposing the surfaces of the 2C, 2K, and 2T images, the electrostatic drums 2Y, 2M, 2C, 2K, and 2T charged by the charging rollers 3Y, 3M, 3C, 3K, and 3T are electrostatically charged according to image information. A latent image is formed.

  The intermediate transfer belt 1 is stretched by a driving roller 8, a secondary transfer counter roller 7, and a driven roller 9, and is synchronized with the rotation of the photosensitive drums 2Y, 2M, 2C, 2K, and 2T by the rotational driving of the driving roller 8. And moved (rotated) in the direction of the arrow.

  A belt cleaning device 11 is installed near the surface of the intermediate transfer belt 1 between the secondary transfer counter roller 7 and the driving roller 8.

  Next, an image forming operation up to the secondary transfer by the image forming apparatus according to the first embodiment will be described.

  First, the image forming operation up to the secondary transfer when printing an image having margins on the top, bottom, left and right edges on the recording material will be described. In this case, only the color toner (C, M, Y, K) toner image forming unit is operated.

  When an image forming operation start signal is issued, the transparent toner transfer roller 6T is separated from the photosensitive drum 2T and maintains a certain distance. At this time, the toner image forming portions (the photosensitive drum 2T, the charging roller 3T, and the developing device 4T) of the transparent toner are all stopped.

  At this time, the photosensitive drum 2Y of Y toner that is rotationally driven at a predetermined speed is uniformly charged to a predetermined negative potential in the present embodiment by the charging roller 3Y. Then, the exposure device 6Y converts the multi-color-separated image signals input from a host computer (not shown) into optical signals, and the laser light that is the converted optical signals is charged on each photosensitive drum 2Y. Then, an electrostatic latent image is formed by scanning exposure.

  Next, the Y toner is attached to the electrostatic latent image formed on the photosensitive drum 2Y of Y toner by the developing device 4Y to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2Y is applied and reversed. Development is performed to form a toner image.

  The Y toner image is transferred onto the intermediate transfer belt 1 that is moved (rotated) by the primary transfer roller 5Y to which the primary transfer bias is applied from a transfer bias power source (not shown) in the primary transfer portion. Primary transfer is performed.

  The intermediate transfer belt 1 onto which the Y toner image has been transferred is moved to the Y toner image forming portion side by driving of the driving roller 8. In the next M toner image forming unit, the M toner image formed on the photosensitive drum 2Y is similarly transferred from the primary transfer bias power source (not shown) to the primary transfer bias in the primary transfer unit. Is transferred onto the yellow toner image on the intermediate transfer belt 1 by the primary transfer roller 5M to which is applied.

  In the same manner, C and K toner images formed on the photosensitive drums 2C and 2K of the C and K toner image forming portions on the M toner image superimposed and transferred onto the intermediate transfer belt 1 in the same manner. A primary transfer roller 5C, 5K to which a primary transfer bias is applied from each transfer bias power source (not shown) at the next transfer unit is sequentially superposed and transferred to transfer a multicolor toner image onto the intermediate transfer belt 1. To form.

  Then, the conveyed sheet or the like in accordance with the timing at which the front end of the toner image of the multicolor image on the intermediate transfer belt 1 is moved to the secondary transfer portion between the secondary transfer roller 10 and the secondary transfer counter roller 12. The transfer material 14 is conveyed to the secondary transfer portion, and is transferred onto the transfer material 14 by the secondary transfer roller 10 to which a secondary transfer bias having a polarity opposite to that of the toner is applied from a secondary transfer bias power source (not shown). Multi-color toner images are collectively transferred (secondary transfer).

  Next, an image forming operation up to the secondary transfer when performing borderless printing will be described.

  In this case, the toner image forming unit of all toners (Y, M, C, K, T) is operated, and the transparent toner transfer roller 5T is controlled to be in a pressurized state by a predetermined pressure with respect to the photosensitive drum 2T. .

  When the image forming operation start signal is issued, first, the toner image forming unit using the transparent toner creates an electrostatic latent image on the photosensitive drum 2T by the charging roller 3T and the exposure device 6T in the same manner as the image forming using the colored toner. A toner image is created by the developing device 4T, and primary transfer is performed from the photosensitive drum 2T onto the intermediate transfer belt 1 by the transfer roller 5T.

  The toner image forming method for the colored toners (Y, M, C, K) is the same as the image forming method using the transparent toner, and the toner image is superimposed and transferred onto the transparent toner on the intermediate transfer belt 1.

  In the transparent toner layer and the colored toner layer formed on the intermediate transfer body 1, the leading end of the toner image of the multicolor image is moved to the secondary transfer portion between the secondary transfer roller 10 and the secondary transfer counter roller 12. The recording material 14 such as the conveyed paper is conveyed to the secondary transfer unit in accordance with the timing, and a secondary transfer bias having a polarity opposite to that of the toner is applied from a secondary transfer bias power source (not shown). The toner image of the multi-color image is collectively transferred (secondary transfer) onto the transfer material 14 by the transfer roller 10.

  The secondary transfer roller 10 is provided with a secondary transfer roller cleaner 15 as a cleaning member. The resin blade is in contact with the secondary transfer roller at a predetermined angle and pressure, and the toner adhering to the secondary transfer roller is mechanically scraped off.

  The transfer material 14 on which the toner image of the multicolor image is formed is conveyed to the fixing device, and the toner image of the multicolor image is heated and pressed at the fixing nip portion between the fixing roller 12 and the pressure roller 13 of the fixing device. After heat fixing on the surface of the recording material 14, it is discharged to the outside, and a series of image forming operations is completed.

  Note that the transfer residual toner remaining on the photosensitive drums 2a, 2b, 2C, and 2d during the above-described primary transfer is removed and collected by the drum cleaning devices 6a, 6b, 6C, and 6d, respectively. Further, the residual toner remaining on the surface of the intermediate transfer belt 1 after the secondary transfer is removed and collected by the belt cleaning device 11.

  The above is a series of operations of the image forming apparatus in the present embodiment.

  Next, the toner layer forming method in the present embodiment will be described in detail with reference to FIG. 3A and 3B are an upper view (a) and a longitudinal sectional view (b) of the toner image formed on the intermediate transfer member, and a toner image formed in the secondary transfer nip and the longitudinal direction of the recording material for each toner superimposing method. Sectional drawing (c) is shown.

  In the present embodiment, (A) when printing with margins, the transparent toner layer is not formed. In this case, since all the colored toner images on the intermediate transfer belt 1 are secondarily transferred onto the recording material 14, the recording material backside stain is not generated.

  However, when performing borderless printing, the colored toner in the added area directly adheres to the secondary transfer roller in the method B in which no transparent toner is used.

  Therefore, when performing borderless printing in this embodiment (C), a toner layer of transparent toner is uniformly formed on the intermediate transfer belt 1 with a predetermined thickness (about 0.1 mm). Here, in the added region, the amount that the colored toner layer protrudes from the recording material in the transport direction is x (= 0 to 3 mm), and the amount that protrudes in the longitudinal direction is y (= 0 to 3 mm).

  Further, the amount of the transparent toner layer that protrudes from the recording material in the transport direction is X (= 0 to 4 mm), and the amount that protrudes in the longitudinal direction is Y (= 0 to 4 mm). The user can change the setting of the extra area (x, y) and the transparent toner layer area (X, Y) from the host computer via the engine controller. However, X> x and Y> y were set.

<Embodiment 2>
Next, Embodiment 1 suitable for the present invention will be described.

  This embodiment has the configuration shown in FIG. 1 as in the first embodiment, and a series of operations such as an image forming method is the same as that in the first embodiment. However, the present embodiment is different from the first embodiment in the toner layer forming method of the colored toner and the transparent toner, and will be described with reference to FIG.

  First, when printing with margins is performed in this embodiment (A), the transparent toner layer is not formed as in the first embodiment.

  Next, when performing borderless printing in this embodiment, the toner layer forming method D is used. Unlike the first embodiment, the transparent toner layer forms a multi-stage toner layer. For the added region, the amount that the colored toner layer protrudes from the recording material in the transport direction is x (= 0 to 3 mm), and the amount that protrudes in the longitudinal direction is y (= 0 to 3 mm).

  Further, the amount of the transparent toner layer that protrudes from the recording material in the transport direction is X (= 0 to 4 mm), and the amount that protrudes in the longitudinal direction is Y (= 0 to 4 mm). Further, since the transparent toner is unnecessary in the area transferred onto the recording material at the time of the secondary transfer, in this embodiment, the amount of the transparent toner is linear from the end of the recording material area to the center at the time of the secondary transfer. The toner layer made of transparent toner is not formed at the center of the image. An image area formed by transparent toner is defined by X 'and Y'. The transparent toner layer thickness at the X ′ and Y ′ points from the recording material region end is set to 0 mm, and the toner amount is linearly decreased from the recording material end (transparent toner layer thickness = 0.1 mm). The user can change the setting of the extra area (x and y) and the transparent toner layer area (X, Y, X 'and Y') from the host computer via the engine controller.

1 is a schematic configuration diagram illustrating a multicolor image forming apparatus to which Embodiments 1 and 2 of the present invention are applied. FIG. 10 is a schematic configuration diagram illustrating an image forming apparatus using a secondary transfer method in a conventional electrophotography. FIG. 4 is a schematic transfer diagram of colored toner and transparent toner on the ITB and in the secondary transfer nip.

Explanation of symbols

Reference Signs List 1 intermediate transfer belt 2 photosensitive drum 3 charging roller 4 developing device 5 transfer roller 6 exposure device 7 secondary transfer counter roller 8 drive roller 9 driven roller 10 secondary transfer roller 11 belt cleaning device 12 fixing roller 13 pressure roller 14 recording material 15 Secondary transfer roller cleaner

Claims (4)

A developing unit that forms a color toner image on the image carrier based on the image information, and after the primary transfer of the color toner image formed on the image carrier onto the intermediate transfer member, the color on the intermediate transfer member In an image forming apparatus that secondarily transfers a toner image onto a recording material by a secondary transfer roller disposed opposite to the intermediate transfer member and the surface of the intermediate transfer member,
An image forming apparatus comprising: a secondary transfer member cleaning unit, and a developing unit and an image carrier made of transparent toner disposed downstream of a colored toner in a primary transfer position with respect to the intermediate transfer body conveyance direction. .   2. The image forming apparatus according to claim 1, wherein the control means determines whether or not the developing means and the image carrier are operated with the transparent toner.   2. The image forming apparatus according to claim 1, wherein when forming the transparent toner image, an image larger than the image area of the recording material and the image area of the colored toner image is formed.   An image forming apparatus characterized in that when forming a transparent toner image, the amount of transparent toner is gradually reduced toward the center of the image area.

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