JP5464200B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that discharges fine droplets onto a toner image on an image carrier before a transfer process to form a higher quality image.

  In general, an image forming apparatus first charges a photoconductor and erases the charge in accordance with an original image, so-called exposure to form an electrostatic latent image. Toner is adhered to the electrostatic latent image on the photoreceptor using a developing device. The toner attached to the photosensitive member is transferred to a transfer member such as an intermediate transfer belt or paper to form an image.

  Here, when the charge amount of the toner is higher than an appropriate value, toners having the same polarity repel each other and may deviate from the position where the toner originally adheres, thereby generating dust (transfer dust) or printing. The image may be disturbed (image disorder). Such transfer dust and image disturbance are conspicuous when a high-contrast toner image such as a character image is formed rather than a photographic image. Therefore, various techniques for suppressing transfer dust and the like are mainly applied to the above-described toner image having a high contrast.

  In Patent Document 1, the charge amount of the toner formed on the photosensitive member and the intermediate transfer belt is reduced to an appropriate value using a static eliminator, thereby preventing the toners from repelling each other.

JP 2006-138891 A

  However, since the required charge amount differs depending on the type of image, if the charge amount is adapted to an image using a static eliminator, the charge amount may be lower than an appropriate value in another image, and transfer dust may occur. The present applicant has previously proposed a technique for improving the above points (see Japanese Patent Application No. 2010-266034).

  This proposal suppresses transfer dust by supplying water vapor to the toner image after the developing device attaches the toner to the photosensitive member and before the toner image is transferred to the intermediate transfer belt (transfer unit). It is.

  However, if the generated water vapor is supplied to the entire paper, the paper may be wetted more than necessary, the paper may be swollen, and the product quality may be reduced.

  Therefore, the present invention provides an image forming apparatus that forms a high-quality image without adversely affecting the paper while supplying fine droplets to the formed toner image to increase the cohesion between the toner particles. The purpose is to provide.

  The above object is achieved by the following means.

(1) An image carrier on which an electrostatic latent image is formed, a developing unit that forms a toner image by attaching a developer to the electrostatic latent image, a transfer unit that transfers the toner image to a transfer body, after formation of the toner image to the image bearing member, and have a, a droplet discharge means for discharging droplets to the toner image on the image bearing member prior to transfer to the transfer member, the droplets An image forming apparatus , wherein droplets discharged from the discharge means use pure water or a mixed solvent of pure water and a water-soluble organic solvent .

  (2) The image forming apparatus according to (1), wherein the droplet discharge unit further includes a control unit that controls a discharge range in accordance with image information of the toner image.

  (3) The control unit performs control so that the liquid droplets are ejected to and around the contour of the formed toner image on a pixel basis based on image information of the toner image. ).

( 4 ) The image described in any one of (1) to ( 3 ) above, wherein the droplet ejected by the droplet ejection means is a micro droplet of 0.06 pl to 0.2 pl. Forming equipment.

  According to the present invention, after the toner image is formed and before the transfer, droplets are ejected onto the toner image on the image carrier to prevent dust and image disturbance caused by the electric field at the time of transfer, thereby reducing the contrast. A high and stable image can be obtained, and the product quality can be prevented from deteriorating, such as the paper spreading due to excessive droplet adhesion. Furthermore, since water is used as the droplets, unlike the case where ink is used, there is no possibility of clogging even if the ink is dried, and the reliability is high.

1 is a configuration diagram of an image forming apparatus. FIG. 4 is an enlarged view of the vicinity of an intermediate transfer belt. It is a block diagram of the composition which performs droplet discharge control in this embodiment. It is a figure of the nozzle of a droplet discharge part tip. It is a figure which shows the other Example of a nozzle.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the following description shows the example of embodiment of the invention described in a claim, and does not limit the meaning of a technical range and term. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from actual ratios.

  FIG. 1 is a configuration diagram of an image forming apparatus A according to the embodiment, and FIG. 2 is an enlarged view of the vicinity of an intermediate transfer belt. The image forming apparatus A is called a tandem color image forming apparatus, and performs color image formation by four sets of image forming units.

  The document placed on the document table is scanned and exposed by the scanning exposure optical system of the image reading device SC and read by the line image sensor. The photoelectrically converted image information signal is subjected to A / D conversion, shading correction, image compression processing, and the like in an image information processing unit (see FIG. 3), and then input to the optical writing unit of the image forming unit.

  The four sets of image forming units are an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) color image, and an image forming unit that forms a cyan (C) color image. 10C is an image forming unit 10K that forms a black (K) color image, and is denoted by reference symbols Y, M, C, and K that are formed after a common reference symbol 10, respectively.

  The image forming unit 10Y includes a photosensitive drum (image carrier) 1Y, a charging unit 2Y, an optical writing unit 3Y, a developing device (developing unit) 4Y, a drum cleaner 5Y, and a droplet discharge unit (liquid Droplet discharge means) 8Y.

  Similarly, the image forming unit 10M includes a charging unit 2M, an optical writing unit 3M, a developing device 4M, a drum cleaner 5M, and a droplet discharge unit 8M arranged around the photosensitive drum 1M, and the image forming unit 10C is a photoconductor. The image forming unit 10K includes a charging unit 2C, an optical writing unit 3C, a developing device 4C, a drum cleaner 5C, and a droplet discharge unit 8C arranged around the drum 1C, and a charging unit arranged around the photosensitive drum 1K. 2K, optical writing unit 3K, developing device 4K, drum cleaner 5K, and droplet discharge unit 8K.

  Photosensitive drums 1Y, 1M, 1C, and 1K in the image forming units 10Y, 10M, 10C, and 10K, charging units 2Y, 2M, 2C, and 2K, optical writing units 3Y, 3M, 3C, and 3K, a developing device 4Y, 4M, 4C, and 4K, drum cleaners 5Y, 5M, 5C, and 5K, and droplet discharge units 8Y, 8M, 8C, and 8K have a common configuration. In the following description, symbols Y, M, C, and K are not used unless particularly distinguished.

  The image forming unit 10 writes an image information signal on the photosensitive drum 1 by the optical writing unit 3, and forms an electrostatic latent image on the photosensitive drum 1 based on the image information signal. The electrostatic latent image is developed by the developing device 4 to form a visible toner image on the photosensitive drum 1.

  The photosensitive drums 1Y, 1M, 1C, and 1K in the image forming units 10Y, 10M, 10C, and 10K are respectively yellow (Y), magenta (M), cyan (C), and black (K). Images are formed.

  The intermediate transfer belt (transfer means) 6 is wound around a plurality of rollers and supported so as to be able to run.

  The toner images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred onto the traveling intermediate transfer belt 6 by the primary transfer units 7Y, 7M, 7C, and 7K, and Y (yellow), M ( A color image in which the color layers of magenta), C (cyan), and K (black) are superimposed is formed.

  The paper transport unit 20 transports the paper S. Several types of paper S, such as thick paper and thin paper, are accommodated in the paper feed trays 21, 22, and 23, fed by the first paper feed unit 24, and a loop forming roller pair 51 and a registration roller pair 52 that constitute a paper aligning device. After that, the color image on the intermediate transfer belt 6 is transferred onto the paper S by being conveyed to the secondary transfer portion 7A. The sheet S on which the color image has been transferred is fixed with the toner image on the sheet S by applying heat and pressure in the fixing device 30, and is discharged to the outside through the fixing conveyance roller 25 and the discharge roller 26. .

  Further, the image forming apparatus A includes a paper reversing unit 27, and the fixed paper is guided from the fixing conveyance roller 25 to the paper reversing unit 27 so as to be reversed and discharged, or image formation is performed on both sides of the paper. Is possible.

  The operation display unit 40 installed on the upper part of the main body of the image forming apparatus A can set the type, size, number, etc. of sheets S to be used from among a plurality of sheets when performing image formation. The paper size may be automatically set when the original is read by the image reading device SC.

  FIG. 3 is a block diagram of a configuration for performing droplet discharge control in the present embodiment, and FIG. 4 is a diagram of a nozzle at the tip of the droplet discharge unit 8.

  As shown in FIG. 3, in the configuration for performing the droplet discharge control of the present embodiment, the liquid discharge unit 8 is connected to the control unit 15 and controlled by an instruction from the control unit 15. The control unit 15 includes the image information processing unit 16 and the actuator control unit 17 described above.

  The actuator control unit 17 controls an actuator 14 (described later) of the liquid ejection unit 8 based on the image information acquired from the image information processing unit 16. When the actuator control unit 17 controls the actuator 14, it is possible to control the amount of liquid droplets discharged from the nozzle 11 or the discharge range of the liquid discharge unit 8.

  In the present embodiment, the droplet discharge unit 8 drops droplets on the toner image on the photosensitive drum 1 after the toner image is formed on the photosensitive drum 1 and before transferring to the intermediate transfer belt 6. Discharge w. As shown in FIG. 2, the droplet discharge unit 8 is provided in the downstream area of the developing device 4 in the rotation direction of the photosensitive drum 1.

  The droplet discharge unit 8 is configured by using an ink jet of a printer, and since the configuration itself is well known, detailed description is avoided, but generally the droplet w is discharged to the photosensitive drum 1 as shown in FIG. A nozzle 11 is provided. As shown in FIGS. 3 and 4, the nozzle 11 includes a pressurizing chamber 12 that is a space in which droplets are pressurized, a liquid storage unit 13 that stores liquid to be supplied to the pressurizing chamber 12, and a droplet w. And an actuator 14 that pressurizes the liquid in the liquid storage portion 13 in order to discharge the liquid from the nozzle 11.

  The ejection of the droplet w is performed by applying a voltage to the electrodes constituting the actuator 14 to deform the diaphragm constituting the actuator 14 and thereby changing the pressure in the pressurizing chamber 12. The nozzles 11 are arranged in a line head shape in order to discharge droplets in units of pixels based on the toner image.

  In the present embodiment, with the above configuration, the amount of droplets w and the discharge range are controlled in order to prevent paper blurring and product quality deterioration due to discharge of excessive moisture.

  Droplets are discharged on a pixel basis. For example, an ink jet used in an image forming apparatus can be ejected by about 1 to 2 pl regardless of a piezo system or a thermal system. When a droplet w having such a size is ejected as water or an aqueous solution, a photosensitive drum is used. On the other hand, the toner image on 1 is disturbed. Further, if 100% of smaller droplets w are ejected to all the pixels, moisture is excessively supplied, and transfer failure occurs in the paper and the entire image.

  Therefore, in the present embodiment, a portion with high contrast is detected from the image information acquired by the image information processing unit 16 and the droplet w is ejected in units of pixels. Since the fine droplets are discharged, the toner image is not disturbed and the image can be transferred sharply. Further, since droplets are not ejected on the entire paper based on the image information but are selectively ejected on and around the contour of the toner image, it is possible to prevent the paper from spreading and the product quality from deteriorating. . Further, since the toner containing excessive moisture is transferred, it is possible to prevent the fixing device from spending more energy than necessary and causing a fixing failure. Here, the periphery of the toner image is an area where the toner near the outside of the toner image is not attached, and the entire area of the paper or the unattached area of the paper is not spread over a wide range by the liquid droplets. It is.

  The amount of droplets discharged from the nozzle 11 is considered as follows. First, it is assumed that a droplet w is ejected on the entire surface in one layer on a sheet of A4 size or the like, and the amount of micro droplet w required at that time is obtained. Next, the calculated amount of the required droplet w in the unit of paper is converted into the required amount of water in the unit of pixel.

  For example, toner particles having a diameter of 6 μm are adhered to the entire surface of the photosensitive drum 1 as a single layer, so-called “solid” (when closely packed in a plane), and the toner particles have a diameter of 3 μm and a thickness of 1 μm. Assuming that water adheres, the amount of required droplets is about 0.025 cc per A4 size sheet.

When the resolution is 600 dpi, the number of pixels is 4960 × 7015 = 34794400, so the amount of droplets required per pixel is about 7.18 × 10 ⁻¹⁰ cc. Since the droplet amount in the ink jet system usually uses pl (picoliter) instead of cc, the above value is about 0.000718 pl.

  When the size of the micro droplet w is 0.1 pl, it corresponds to about 140 pixels with respect to 0.000718 pl. However, since it is smaller than the toner having a diameter of 6 μm, the image is distorted even if it is ejected at about 0.1 pl. Will not happen. Hereafter, since it experimented about the appropriate amount of water in Examples 1, 2, it mentions later.

  The liquid used for the droplets w may be any liquid as long as it has a role of preventing repulsion between the toner particles, strengthening the liquid crosslinking force between the toners, and increasing the cohesive force of the toner. . For example, pure water or polyethylene glycol used for surfactants and antifoaming agents is diluted about 10 times to add preservatives, antioxidants, antifungal agents, pH adjusters, etc. to make water-soluble organic solvents. Alternatively, a mixture of pure water may be discharged. If the water-soluble organic solvent is mixed with pure water, the hydrophilicity with the hydrophobically processed toner can be further improved to prevent repulsion between the toners, and transfer dust and the like can be prevented.

  According to the image forming apparatus according to the present embodiment, droplet ejection that ejects minute droplets in units of pixels after the toner image is formed on the photosensitive drum 1 and before the toner image is transferred to the intermediate transfer belt 6. Since the portion 8 is provided, it is possible to increase the cohesive force between the toners to prevent transfer dust and image disturbance and to obtain good image quality. Further, it is possible to save the liquid to be discharged.

  4 is not only the nozzle 11 shown in FIG. 4, but also a nozzle provided with protrusions 18 extending from the top and bottom directions of about 1 μm to 2 μm at the tip of the discharge port as shown in FIG. 11A may be used. If the nozzle 11A is used, the droplets can be made finer than the nozzle 11, and the discharge timing of the droplet discharge unit 8 can be adjusted by the control unit 15 to cope with high-speed discharge. .

Example 1
Next, an experiment on the amount of water necessary for preventing the transfer dust and the like in the droplet discharge unit 8 will be described. In this experiment, a photosensitive drum having a diameter of 100 mm, a linear speed of 400 mm / sec, and a surface potential of −600 V, a developing roller to which φ25, a linear speed of 720 mm / sec, a development potential Vac of 1.0 kVpp, a 9 kHz rectangular wave, and Vdc-400 V were applied, This was carried out using a two-component developer having a ferrite-coated carrier particle size of 30 μm, a toner particle size of 6.5 μm, and a toner concentration of 7.5%. As the nozzle, the nozzle 11 shown in FIG. 4 was used.

  In the first embodiment, the character outline is mixed with pure water and a water-soluble organic solvent on the basis of image information of black and overlapping RGB images that are easily scattered with respect to a character chart having a coverage (printing rate) of 6% for each color of YMCK. The solvent was discharged. The amount of droplet is 0.2 pl. The mixed solvent contained a surfactant, an antiseptic, an antioxidant, an antifoaming agent, an antifungal agent, a pH adjuster, etc., and was adjusted so as to have an affinity for the toner on the photosensitive drum.

(Example 2)
Further, as in Example 1, the amount of liquid droplets discharged using the nozzle 11 was set to 0.1 pl, and the image quality was confirmed. Other conditions were the same as in Example 1.

(Example 3)
In Example 3, an experiment was performed using the nozzle 11A shown in FIG. In the third embodiment, mixed images of pure water and a water-soluble organic solvent in the graphic contour portion of a mixed image of a character chart and a graphic chart having a YCCK image coverage of 20% for a black and overlapping RGB images that are easily scattered. Was discharged. The droplet amount to be discharged is 0.06 pl. Other conditions were the same as in Example 1.

Example 4
The image quality was confirmed by setting the amount of droplets discharged using the nozzle 11 to 0.4 pl. Other conditions were the same as in Example 1.

(Example 5)
The amount of liquid droplets discharged using the nozzle 11A was 0.03 pl, and the image quality was confirmed. Other conditions were the same as in Example 1.

(Comparative Examples 1-3)
As a comparative example with respect to the embodiment, the image quality was confirmed with the amount of liquid droplets ejected being 1 pl and 0.5 pl and when the amount of liquid droplets was not ejected (0 pl). Other conditions were the same as in Example 1. Table 1 shows the experimental results.

  As is clear from this table, in the case of Comparative Examples 1 and 2, since the amount of ejected droplets was too large, an untransferred image was generated and good image quality could not be obtained. In Comparative Example 3, toner scattering occurred around the character portion, and good image quality could not be obtained.

  On the other hand, in Examples 1 to 3, the toner particles were appropriately aggregated by the fine droplets to prevent transfer dust and image disturbance and to improve the image quality.

  In Example 4, an untransferred image was generated, but the image quality was at an acceptable level. In Example 5, although the scattering of toner occurred around the character portion, the image quality was acceptable.

  According to the first to third embodiments, the transfer dust and image disturbance caused by the repulsion of the toners by discharging the droplets from the nozzle of the droplet discharge unit 8 in the range of 0.06 pl to 0.2 pl. It was possible to prevent and improve the image quality. It was found that a range of 0.03 pl to 0.4 pl may be acceptable in terms of an acceptable level.

  In the embodiment, the droplet discharge unit 8 discharges the droplet w when transferring from the photosensitive drum 1 to the intermediate transfer belt 6. However, the present invention is not limited to this, and the intermediate transfer belt 6 transfers to the sheet S. The liquid droplets may be ejected at the time of transfer (secondary transfer) or at the time of transfer from the photosensitive drum to the paper in direct transfer without intermediate transfer. Since the occurrence of transfer dust or the like appears on the paper, it is possible to directly prevent the transfer dust or the like by discharging droplets when transferring to the paper.

1 ... photosensitive drum (image carrier),
4 ... developing device (developing means),
6 ... Intermediate transfer belt (transfer means),
8: Droplet discharge portion (droplet discharge means),
15 ... control unit (control means),
S: Paper (transfer body),
w: Droplet.

Claims (4)

An image carrier on which an electrostatic latent image is formed;
Developing means for forming a toner image by attaching a developer to the electrostatic latent image;
Transfer means for transferring the toner image to a transfer member;
After formation of the toner image to the image bearing member, and have a, a droplet discharge means for discharging droplets to the toner image on the image bearing member prior to transfer to the transfer member,
An image forming apparatus , wherein the droplets ejected from the droplet ejection means use pure water or a mixed solvent of pure water and a water-soluble organic solvent .   The image forming apparatus according to claim 1, wherein the droplet discharge unit further includes a control unit that controls a discharge range according to image information of the toner image.   3. The control unit according to claim 2, wherein the control unit performs control so that the liquid droplets are ejected to and around a contour of the formed toner image on a pixel basis based on image information of the toner image. Image forming apparatus. The droplets the droplet discharge means for discharging the image forming apparatus according to any one of claims 1 to 3, characterized in that the microdroplets 0.06Pl～0.2Pl.