JP2010128229A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that suppresses filming of a direct transfer belt and obtains satisfactory transferability. <P>SOLUTION: A color printer 10 includes: a photoreceptor 12 which bears toner images of their respective colors; the direct transfer belt 11 that conveys paper along the photoreceptors 12; and transfer devices 24 disposed opposite the corresponding photoreceptors 12 with the direct transfer belt 11 between them. The contact angle of the plane in which the direct transfer belt 11 comes into contact with paper is ≥90° relative to pure water. The color printer also has a spring that brings the transfer device 24 into pressure contact with the photoreceptor 12. The contact pressure applied to the photoreceptor 12 and the transfer device 24 by the spring is in the range of 8 to 33 kPa. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet by directly transferring a toner image formed on an image carrier onto a transfer material such as a sheet. More specifically, the present invention relates to an image forming apparatus in which a sheet is directly conveyed by a transfer belt and a toner image is transferred onto the sheet by a transfer device during the conveyance.

  Conventionally, in an electrophotographic image forming apparatus, a toner image is formed on an image carrier through processes such as charging, exposure, and development. This toner image is directly transferred to a transfer material such as paper through or without an intermediate transfer member. For example, in a case having a direct transfer belt, the sheet is conveyed by the direct transfer belt, and the toner image is directly transferred from the image carrier to the sheet on the transfer belt. Further, the toner image transferred to the paper is fixed by heating or pressurizing, and an image is formed.

Conventionally, since a direct transfer belt or an intermediate transfer belt has been apt to cause adhesion of toner or dust, a cleaning member is usually provided. For example, the adhering material is scraped off by a blade that contacts the belt surface. Further, for example, in the image forming apparatus described in Patent Document 1, spherical toner is used, and the wear amount of the transfer belt (direct transfer belt or intermediate transfer belt), the contact angle with respect to water, and the like are defined. In this document, it is said that high transfer efficiency and stable cleaning properties can be obtained by appropriately adjusting these.
JP 2002-207342 A

  However, the conventional image forming apparatus described above has a problem that it is necessary to use spherical toner, and it cannot be directly applied to a type of apparatus that has been used. In addition, in the case of a direct transfer belt that also conveys paper, it is inevitable that paper dust resulting from the paper or additives (calcium carbonate, clay, etc.) added to the paper adhere. If the direct transfer belt is pressed between the image carrier and the transfer member in the transfer area with the attached matter attached, filming may occur on the direct transfer belt.

  Further, when filming occurs directly on the transfer belt, fine irregularities tend to be formed on the belt surface. This is because the way filming occurs is not necessarily uniform. For this reason, there is a problem in that a fine gap is formed between the belt and a transfer belt cleaner such as a blade, resulting in poor cleaning. In particular, filming is likely to occur in a low temperature and low humidity environment, which is one of the causes of image quality defects.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, an object of the present invention is to provide an image forming apparatus that can suppress filming of a direct transfer belt and obtain good transferability.

  In order to solve this problem, the image forming apparatus according to the present invention includes an image carrier that carries a toner image for each color, a direct transfer belt that conveys paper along the image carrier, and a direct transfer belt. An image forming apparatus having a transfer member disposed opposite to the image carrier, wherein a contact angle of the surface of the transfer belt directly contacting the sheet with respect to pure water is 90 ° or more, and the transfer member is image-carrying A pressure contact portion that is pressed toward the body, and a pressure contact pressure between the image carrier and the transfer member by the pressure contact portion is within a range of 8 to 33 kPa.

  According to the image forming apparatus of the present invention, the contact angle of the surface of the direct transfer belt that mediates the transfer process and also conveys the sheet with respect to pure water is 90 ° or more, and therefore is very smooth. . Therefore, even if paper dust contacts, it does not continue to adhere and is easily removed. Further, since the pressure contact pressure between the image carrier and the transfer member is in the range of 8 to 33 kPa, good transferability can be obtained and the occurrence of filming is suppressed.

In the present invention, it is more desirable that the contact angle with respect to pure water on the surface of the transfer belt that directly contacts the paper is in the range of 90 to 110 °.
In this way, the transportability of the sheet is surely good.

In the present invention, it is more desirable that the pressure contact between the image carrier and the transfer member by the pressure contact portion is in the range of 8 to 21 kPa.
In this way, the occurrence of filming can be suppressed more reliably.

  According to the image forming apparatus of the present invention, it is possible to suppress filming of the direct transfer belt and to obtain good transferability.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a tandem type color printer using a direct transfer system.

  As shown in FIG. 1, the color printer 10 of the present embodiment has four color image forming units 20 </ b> Y, 20 </ b> M, 20 </ b> C, and 20 </ b> Bk arranged along the direct transfer belt 11. Each of the image forming units 20Y, 20M, 20C, and 20Bk has a photoreceptor 12. Further, a charging device 21, an exposure device 22, a developing device 23, a transfer device 24, and a cleaner device 25 are disposed around each photoconductor 12. Further, a belt cleaner 26 is disposed outside the direct transfer belt 11 outside the range in which the paper P is conveyed.

  In this embodiment, toner images of the respective colors are formed on the respective photoreceptors 12 by the charging device 21, the exposure device 22, and the developing device 23 of the image forming units 20Y, 20M, 20C, and 20Bk. On the other hand, the sheet P is conveyed from the left side in the drawing and is directly inserted along the outer surface of the transfer belt 11 as indicated by the broken arrow in the drawing. Further, the direct transfer belt 11 is rotated as indicated by an arrow A in the drawing at the time of image formation. In other words, the paper P is conveyed by the direct transfer belt 11 while facing the photosensitive members 12 of the respective colors in order. The toner images formed on the photoconductors 12 of the respective colors are sequentially transferred onto the paper P by the transfer device 24 and superimposed. The superimposed toner images are fixed, and an image is formed on the paper P.

  Here, in this embodiment, the direct transfer belt 11 having a contact angle of 90 ° or more with pure water on the surface when new is used is used. The surface of the direct transfer belt 11 is the side on which the paper P is placed and is the outer peripheral surface. Further, as shown in FIG. 2, the contact angle is an angle θ formed between a tangent of a droplet dropped on the solid surface and the solid surface. Since the dropped liquid is rounded by its surface tension, the contact angle becomes larger as the solid is more difficult to wet (repells the liquid).

  Therefore, the surface of the direct transfer belt 11 of this embodiment is smoothed. For example, the belt contact surface in the mold for directly forming the transfer belt 11 may be smoothed by polishing. By using this mold, the direct transfer belt 11 having a smooth surface can be obtained. In addition, it may be smoothed by polishing or the like on the belt that has been prepared. This is because even if the material is the same as that conventionally used, the contact angle θ with respect to pure water can be increased by smoothing the surface. The smoother, that is, the smaller the surface irregularity, the larger the contact angle θ.

  Alternatively, the surface may be coated with a water repellent such as silicone or fluororesin. The contact angle θ can also be increased by improving the water repellency of the belt surface. In this case, the greater the coating amount, the higher the water repellency and the larger the contact angle θ. Alternatively, the contact angle θ can be increased by devising the molecular structure of the direct transfer belt 11 itself. For example, what contains many hydrophobic groups and does not contain many hydrophilic groups may be used.

  Since the paper P is in direct contact with the surface of the direct transfer belt 11 of the present embodiment, paper powder, an additive contained in the paper P, etc. are in contact with a certain degree. However, in this embodiment, the direct transfer belt 11 is very smooth, and the contact angle θ with respect to the pure water 31 is 90 ° or more. In other words, the direct transfer belt 11 has high water repellency on the belt surface, and has high releasability with respect to things other than water. Therefore, even if paper dust or the like directly contacts the transfer belt 11, it is difficult to adhere.

  If the surface of the direct transfer belt 11 is too smooth, the transportability of the paper P is lowered. This is because the frictional force between the direct transfer belt 11 and the paper P becomes too small and slips. Therefore, in this embodiment, the contact angle θ with respect to pure water is more preferably 90 ° or more and 110 ° or less. At this level, the transportability of the paper P is sufficiently good.

  Further, each transfer device 24 of this embodiment has a spring 32 that presses the rotating shaft 24a toward the photosensitive member 12, as shown in FIG. In this embodiment, by appropriately selecting the strength of the spring 32, the transfer device 24 has a contact pressure Q that directly contacts the photoconductor 12 via the transfer belt 11 within the range of 8 to 33 kPa, and more preferably, It is made to be in the range of 8 to 21 kPa. This value is a value of pressure applied to the surface of the photoconductor 12 and is not the pressing force of the transfer device 24 itself.

  When the contact pressure by the transfer device 24 is less than 8 kPa, a sufficient transfer nip cannot be ensured, and transfer failure may occur. On the other hand, if the contact pressure is higher than 33 kPa, the deposit is strongly pressed directly against the transfer belt 11. Therefore, even if a contact angle θ with respect to pure water of 90 ° or more is selected as described above, filming directly on the surface of the transfer belt 11 may occur. In this embodiment, since the contact pressure Q of the transfer device 24 is in the range of 8 to 33 kPa, it is possible to achieve both good transferability and suppression of filming.

  Next, the inventors conducted an experiment in which the contact angle θ and the contact pressure Q were varied to observe the degree of filming and the transferability. An inferior paper was prepared for the experiment, and 1000 sheets of the paper were continuously passed through the color printer 10 in which the contact angle θ and the contact pressure Q were measured in advance to form an image. This inferior paper is a paper that easily generates paper dust. Thereafter, the surface of the direct transfer belt 11 was visually observed to check for the occurrence of filming. In addition, the glossiness was also detected for those judged visually good. The transferability was confirmed by printing a two-layer solid with two colors, magenta and cyan, and visually observing the color. The experiment was conducted in a low-temperature and low-humidity environment (10 ° C., 15% RH) where filming easily occurs.

  The contact angle θ was measured with a contact angle meter CA-XE manufactured by Kyowa Interface Science Co., Ltd. The direct transfer belt 11 having a smooth surface used in the color printer 10 of this embodiment has a contact angle θ of 90 ° or more. The contact angle θ of the direct transfer belt 11 used in this experiment was 92 °. On the other hand, a contact angle θ of less than 90 ° by using no smoothing was used as a comparative example. The contact angle θ of the comparative belt used in this experiment was 87 °.

  Further, the contact pressure Q was measured using a pressure contact force measuring device 41 having the same diameter as that of the photosensitive member 12 as shown in FIG. As shown in FIGS. 4 and 5, the pressure contact force measuring instrument 41 has a strain gauge type load cell 42 therein. When measuring the contact pressure Q, the pressure contact force measuring device 41 is installed in the color printer 10 instead of any one of the photosensitive members 12. Then, the drive portion of the color printer 10 is driven. The pressure contact force detected by the load cell 42 was divided by the pressure contact area (here, 0.1 cm × 24 cm) to obtain a contact pressure Q. The contact pressure Q was changed by exchanging the spring 32 attached to the transfer device 24.

  In each of Examples 1 to 3 of this embodiment, the direct transfer belt 11 having a contact angle θ of 92 ° is used, and the contact pressure Q is set to 8, 21, and 33 kPa, respectively. In Comparative Examples 1 and 2, although the direct transfer belt 11 having a contact angle θ of 92 ° is used, the contact pressure Q is set to 4, 42 kPa, respectively. In Comparative Examples 3 to 7, the direct transfer belt (contact angle θ was 87 °) of the comparative example that was not subjected to surface treatment was used, and the contact pressure Q was set to 4, 8, 21, 33, and 42 kPa, respectively.

The results of this experiment are shown in Table 1. The evaluation criteria were as follows.
Filming: When it is determined that there is no filming even by detecting the glossiness.
When there is no filming that can be recognized visually
△ when there is light filming that does not cause a problem
× when there is filming that can be recognized visually
When there is filming that can be recognized visually in a wide range XX
Transferability: When it can be determined that color development is good by magnifying observation.
○ When it can be judged that the color development is good visually
When color unevenness is observed visually ×

  As shown in Table 1, filming occurred somewhat in each of Comparative Examples 3 to 7 having a contact angle θ of 87 °. In addition, it was found that when the contact pressure Q is reduced to such an extent that filming does not become a problem (4 kPa), transferability deteriorates (Comparative Example 3). When the contact pressure Q was greater than 33 kPa, filming could not be prevented even when the contact angle θ was large (Comparative Example 2).

  On the other hand, in Examples 1 to 3, filming hardly occurred and transferability was good. Accordingly, in the color printer 10 of this embodiment, the contact angle θ is 90 ° or more and the contact pressure Q is in the range of 8 to 33 kPa, so that almost no filming occurs and good transferability is obtained. It was confirmed that

  However, in Example 3 in which the contact pressure Q was 33 kPa, the occurrence of filming was confirmed although it was slight. That is, in order to more reliably prevent filming, the range of the contact pressure Q is more preferably 8 to 21 kPa.

  As described in detail above, according to the color printer 10 of the present embodiment, a sheet is directly conveyed by the transfer belt 11 and a toner image is directly transferred from the photosensitive member 12 of each color to the sheet. A belt 11 having a contact angle θ with respect to pure water of 90 ° or more is used. Further, these contact pressures Q due to the pressing of the photoconductor 12 by the transfer device 24 at the time of transfer are set in the range of 8 to 33 kPa. As a result, the filming of the direct transfer belt can be suppressed and good transferability can be obtained.

  In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.

1 is a schematic configuration diagram illustrating a main part of a color printer according to an embodiment. It is explanatory drawing which shows a contact angle. It is explanatory drawing which shows the press structure of a transfer apparatus. It is explanatory drawing which shows the measuring method of contact pressure. It is explanatory drawing which shows the measuring method of contact pressure.

Explanation of symbols

10 Color Printer 11 Direct Transfer Belt 12 Photoconductor 24 Transfer Device 32 Spring

Claims (3)

An image carrier that carries a toner image for each color; a direct transfer belt that conveys paper along the image carrier; and a transfer member that is disposed to face the image carrier across the direct transfer belt; In an image forming apparatus having
A contact angle with respect to pure water of a surface of the direct transfer belt that contacts the paper is 90 ° or more;
A pressing portion that presses the transfer member toward the image carrier;
An image forming apparatus, wherein a pressure contact pressure between the image carrier and the transfer member by the pressure contact portion is in a range of 8 to 33 kPa. The image forming apparatus according to claim 1,
2. An image forming apparatus according to claim 1, wherein a contact angle with respect to pure water of a surface of the direct transfer belt that contacts the sheet is in a range of 90 to 110 degrees. The image forming apparatus according to claim 1, wherein:
An image forming apparatus, wherein a pressure contact pressure between the image carrier and the transfer member by the pressure contact portion is in a range of 8 to 21 kPa.

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