JP2006243286A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus permitting miniaturization of the entire apparatus by reducing the size of a facing part of an electric potential adjusting means to a photoreceptor. <P>SOLUTION: After a photoreceptor drum 28 is charged by a corotron charging device 42, a charging electric potential is adjusted by a pin scorotron charging device 44. When the charging electric potential is adjusted, electric charges generated from a pointed part of a discharge electrode 45 of the pin scorotron charging device 44 are moved toward the photoreceptor drum 28, and pass through a grid electrode 44C so as to be provided to the photoreceptor drum 28. Because the generation source of the electric charges is limited to the pointed part that is directed to the photoreceptor drum 28, the distribution of the electric charge during the movement is not widely spread, and the electric charges reach the photoreceptor drum 28. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus in which an image is formed on an amorphous silicon photoreceptor.

  In an image forming apparatus, there is a case where a scorotron charger is disposed on the downstream side of a corotron charger in order to charge an amorphous silicon photoconductor having a high dielectric constant to a uniform constant potential (see, for example, Patent Document 1). ). In this scorotron charger, electric charges are radially emitted from the outer peripheral surface of the thin wire.

In order to increase the amount of charge applied to the amorphous silicon photoconductor from such a scorotron charger, the opposing portion to the amorphous silicon photoconductor must be enlarged along the surface of the photoconductor, and the overall size of the apparatus is increased. Is invited.
Japanese Patent Laid-Open No. 5-150615

  In view of the above-described facts, an object of the present invention is to provide an image forming apparatus that reduces the size of the entire apparatus by reducing the portion of the potential adjusting unit facing the photosensitive member.

  The image forming apparatus according to the first aspect of the present invention includes an amorphous silicon photoconductor on which an image is formed, a corotron charger that is disposed opposite to the amorphous silicon photoconductor and charges the amorphous silicon photoconductor, and the amorphous A discharge electrode disposed downstream of the corotron charger with respect to the rotation direction of the silicon photoconductor and having a pointed portion directed to the amorphous silicon photoconductor; and the discharge electrode, the amorphous silicon photoconductor, And a potential adjusting means for adjusting the charging potential of the amorphous silicon photoconductor by generating a charge from the apex and applying it to the amorphous silicon photoconductor.

  According to the image forming apparatus of the present invention described in claim 1, after the amorphous silicon photoconductor is charged by the corotron charger, the charging potential is adjusted by the potential adjusting means. When the charging potential is adjusted, the charge generated from the tip of the discharge electrode moves toward the amorphous silicon photoconductor, passes through the grid electrode, and is applied to the amorphous silicon photoconductor. Here, since the charge generation source is limited to the pointed portion directed to the amorphous silicon photoconductor, the charge reaches the amorphous silicon photoconductor without greatly expanding the distribution of the moving charge.

  An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the corotron charger charges the amorphous silicon photoconductor to a potential higher than a charge setting potential of the amorphous silicon photoconductor, The potential adjusting means sets the charging potential of the amorphous silicon photosensitive member to the charging setting potential.

  Here, the “charge setting potential” refers to a charge potential set in advance immediately before exposure.

  According to the image forming apparatus of the present invention described in claim 2, after the corotron charger charges the amorphous silicon photoconductor to a potential higher than the charge setting potential of the amorphous silicon photoconductor, the potential adjusting means is positively charged. A negative charge is applied to the amorphous silicon photoconductor to set the charging potential of the amorphous silicon photoconductor to the charge setting potential.

  As described above, according to the image forming apparatus of the present invention, there is an excellent effect that it is possible to reduce the size of the entire apparatus by reducing the portion of the potential adjusting unit facing the photoconductor.

  An embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a color laser printer (hereinafter simply referred to as a “printer”) 10 as an image forming apparatus has yellow (Y), magenta (M), cyan (C), and black (K) colors. Print portions 12Y, 12M, 12C, and 12K (hereinafter, referred to as “print portions 12Y to 12K”) that transfer and superimpose toner images onto continuous paper P as a transfer material are conveyed from the upstream side in the transport direction (arrow T direction). Arranged in order.

  A paper transport unit 14 is provided on the upstream side in the transport direction (arrow T direction) of the printing units 12Y to 12K. The paper transport unit 14 includes a main drive roller 16 around which the continuous paper P is wound. Both end portions of the main drive roller 16 in the axial direction are rotatably supported by the paper transport frame 18 via bearings (not shown). An idle roller 19D is in contact with the main drive roller 16, and the continuous paper P is conveyed toward the printing units 12Y to 12K with a nip between the main drive roller 16 and the idle roller 19D. . In addition, idle rollers 19A and 19B and an aligning roller 17 are disposed upstream of the main drive roller 16 in the conveying direction (arrow T direction), and downstream of the main drive roller 16 in the conveying direction (arrow T direction). An idle roller 19C is provided.

  On the downstream side in the transport direction (arrow T direction) of the printing units 12Y to 12K, the fixing unit 20 that fixes the unfixed toner image transferred by the printing units 12Y to 12K to the continuous paper P, and the continuous paper that has passed through the fixing unit 20 A paper discharge unit 26 for discharging P is provided.

  The fixing unit 20 is provided with idle rollers 21A, 21B, and 21C, a flash fixing device 22, and a paper discharge roller 23, which are supported by the fixing frame 24 at both ends in a direction orthogonal to the transport direction. . Here, the flash fixing device 22 fixes the unfixed toner image transferred by the printing units 12Y to 12K to the continuous paper P.

  The paper discharge unit 26 includes a tension applying mechanism 25 composed of a plurality of rollers and the like. Each member of the tension applying mechanism 25 discharges both ends in a direction orthogonal to the transport direction directly or via a support member. Supported by a paper frame 27.

  The printing units 12Y to 12K include a photosensitive drum 28 as an image carrier, and a toner image is formed on the photosensitive drum 28. The photoconductive drum 28 of the present embodiment is an amorphous silicon photoconductive drum having photoconductivity for positive charging, and has excellent durability and long life as compared with an OPC photoconductive drum. Is applied, but the dielectric constant is high. The photoconductor drum 28 includes an aluminum tube as a photoconductor substrate and an amorphous silicon photoconductor film covering the outer peripheral surface thereof.

  As shown in FIG. 2, the photosensitive drum 28 can be rotated about the rotation support shaft 28A, and the peripheral speed is 400 mm / sec in the counterclockwise direction (arrow R direction) in FIG. 2 by a motor (not shown). It is designed to rotate at.

  Around the photosensitive drum 28, the transfer roller 30, the cleaner 40, the erase lamp 41, the corotron charger 42, the pins scorotron charger 44, and the image exposure device are arranged in the order of rotation of the photosensitive drum 28 (arrow R direction). 46 and a developing device 48 are arranged.

  A cleaner 40 is disposed on the downstream side of the transfer roller 30 with respect to the rotation direction (arrow R direction) of the photosensitive drum 28, and the cleaner 40 removes untransferred residual toner on the photosensitive drum 28. It is like that.

  An erase lamp 41 is disposed downstream of the cleaner 40 with respect to the rotation direction of the photosensitive drum 28 (in the direction of arrow R). The erase lamp 41 removes untransferred residual toner by the cleaner 40. The surface of the photosensitive drum 28 is discharged by irradiating the surface of the photosensitive drum 28 with static elimination light.

  A corotron charger 42 as a charging unit is disposed opposite to the photosensitive drum 28 on the downstream side of the erase lamp 41 with respect to the rotation direction (arrow R direction) of the photosensitive drum 28. The corotron charger 42 includes a shield case 42A made of aluminum and opened on the photosensitive drum 28 side. A corotron wire 42B made of a tungsten wire having a diameter of 40 μm is stretched in the shield case 42A. The corotron wire 42B is parallel to the rotation support shaft 28A (see FIG. 2) of the photosensitive drum 28. It extends. The total current to the corotron wire 42B is controlled to be a constant current (in this embodiment, +650 μA), thereby charging the photosensitive drum 28 to a desired potential (in this embodiment, about +600 V). It is supposed to let you.

  On the downstream side of the corotron charger 42 with respect to the rotation direction of the photosensitive drum 28 (in the direction of the arrow R), a pins corotron charger 44 as a potential adjusting unit is disposed to face the photosensitive drum 28. The pins scorotron charger 44 includes an aluminum shield case 44A having an opening on the photosensitive drum 28 side. In the present embodiment, the opening width W of the shield case 44A shown in FIG. 3 (the opening dimension corresponding to the moving direction of the opening portion facing the photosensitive drum 28) is 12 mm.

  A discharge electrode 45 is fixed in the shield case 44A via an insulating support member 44B, and the discharge electrode 45 has a longitudinal direction parallel to the rotation support shaft 28A of the photosensitive drum 28 (see FIG. 2). It is considered as a direction. The discharge electrode 45 is made of SUS and has a thin plate shape, and as shown in FIG. 4, has a sawtooth shape with a plurality of pointed portions 45 </ b> A directed toward the photosensitive drum 28. In the present embodiment, the pitch 45P of the cusp 45A is 2 mm. As shown in FIG. 3, the discharge electrode 45 is connected to a power source 60 and is controlled at a constant current so that the total current to the discharge electrode 45 is a constant current (−700 μA in this embodiment). . As a result, negative charges are generated from the apex 45A and applied to the photosensitive drum 28.

  A grid electrode 44C is attached to the shield case 44A in an electrically insulated state on the opening side, and the grid electrode 44C is disposed between the discharge electrode 45 and the photosensitive drum 28. The grid electrode 44C is made of SUS and has a mesh shape with a predetermined aperture ratio (90% in this embodiment). The grid electrode 44C is separated from the apex 45A of the discharge electrode 45 by a predetermined interval A (4 mm in the present embodiment), and also from the photosensitive drum 28 by a predetermined interval B (see FIG. 4, 1 in the present embodiment). .2 mm) apart. As shown in FIG. 3, the grid electrode 44 </ b> C is connected to a power source 62, and is a constant voltage (in this embodiment, equal to a preset charging potential of the photosensitive drum 28 (a charging potential at a stage immediately before exposure set in advance). , + 500V) is applied.

  As shown in FIG. 2, an image exposure device 46 serving as an exposure unit is disposed on the downstream side of the pin scorotron charger 44 with respect to the rotation direction (arrow R direction) of the photosensitive drum 28. The image exposure device 46 emits a light beam such as LED light to irradiate the photosensitive layer of the photosensitive drum 28 with a light image. In the embodiment, the photosensitive drum 28 charged to +500 V) is exposed to form an electrostatic latent image.

  A developing device 48 as a developing unit is disposed downstream of the image exposure device 46 with respect to the rotation direction of the photosensitive drum 28 (direction of arrow R). The developing device 48 includes a developing device cartridge 50, and the developing device cartridge 50 is filled with a two-component developer composed of toner and a carrier. In the developing device cartridge 50, a stirring screw 52, a conveying magnet roller 54, and a developing magnet roller 56 are disposed. By these, toner is attached to the latent image formed on the photosensitive drum 28 to form a toner image. It is like that.

  A transfer roller 30 as a transfer unit is provided above the photosensitive drum 28, and guide rollers 31 and 32 are arranged on the upstream side and the downstream side in the transport direction (arrow T direction) from the transfer roller 30, respectively. Yes. The transfer roller 30 abuts on the upper surface of the photoconductive drum 28, and sandwiches and conveys the continuous paper P together with the photoconductive drum 28 to transfer the toner image formed on the photoconductive drum 28 onto the continuous paper P. Yes.

  Note that, as in the present embodiment, in regular development using toner having a reverse polarity (minus) with respect to the photoreceptor charge polarity (plus), the voltage applied to the transfer roller 30 is the same as the photoreceptor charge polarity (plus). Become polar. As a result, even if the photosensitive drum 28 receives a charge having the same polarity as the charging polarity (plus) by the transfer roller 30, this can be easily removed by the erase lamp 41, so that the photosensitive memory (transfer ghost) caused by the transfer can be removed. ) Can be suppressed.

  Next, the operation of the above embodiment will be described.

  As shown in FIG. 1, the continuous paper P is transported from the paper transport unit 14 to the printing units 12Y to 12K, and toner of each color of yellow (Y), magenta (M), cyan (C), and black (K). The image is transferred. Since the operation in each of the printing units 12Y to 12K at this time is substantially the same, these will be described together below.

  In the photosensitive drum 28 shown in FIG. 2, after the untransferred residual toner is removed by the cleaner 40 and the charge is eliminated by the erase lamp 41, the corotron charger 42 causes the charging potential of the photosensitive drum 28 (+500 V) to be exceeded. It is charged to a high potential of about + 600V. Next, the pin scorotron charger 44 applies a negative charge to the positively charged photoconductive drum 28 to make the charged potential of the photoconductive drum 28 uniform to the charge setting potential (+500 V). Changes in the surface potential of the photosensitive drum 28 to which charges are applied by the corotron charger 42 and the pins corotron charger 44 are as shown in FIG. In this way, after the photosensitive drum 28 shown in FIG. 2 is once charged to a high potential (about +600 V), the pin scorotron charger 44 applies a negative charge to obtain a charging set potential (+500 V). Generation of ozone can be suppressed and the life of the photosensitive drum 28 and the like can be extended.

  Here, adjustment of the charging potential by the pins scorotron charger 44 will be described with reference to FIGS.

  When a constant current (−700 μA) is supplied to the discharge electrode 45 by the power source 60 shown in FIG. 3, the electric field strength at the point 45 </ b> A directed to the photosensitive drum 28 shown in FIG. It becomes stronger than the electric field strength in a portion other than the point 45A, and only the electric field strength of the point 45A exceeds the dielectric breakdown strength of air. As a result, negative charges (electrons) are generated and emitted only from the tip 45 A directed to the photosensitive drum 28, and the negative charges move toward the photosensitive drum 28. As a result, corona discharge occurs.

  In the photosensitive drum 28 to be charged, the positive charge is widely distributed on the drum surface, so that the distribution of the negative charge during the movement is slightly widened, but the source of the negative charge is directed to the photosensitive drum 28. Since it is limited to the apex 45A, the negative charge distribution during the movement is not greatly expanded, and the negative charge is given to the photosensitive drum 28. For this reason, the directivity is better than in the case where negative charges (electrons) are emitted from the outer peripheral surface (facing in multiple directions) of the conventional thin wire. As a result, the opening width W (opposing portion) of the pins scorotron charger 44 shown in FIG. 3 to the photosensitive drum 28 can be reduced.

  Further, the negative charge generated by the corona discharge passes through the grid electrode 44C and reaches the photosensitive drum 28 until the potential difference between the grid electrode 44C and the photosensitive drum 28 becomes 0V. Thereby, the charging potential of the photosensitive drum 28 can be uniformly adjusted to the charging setting potential (+500 V).

  As shown in FIG. 2, the uniformly charged photosensitive drum 28 is exposed by the image exposure device 46 and developed by the developing device 48, and then the transfer roller 30 sandwiches the continuous paper P together with the photosensitive drum 28. The toner image that is conveyed and formed on the photosensitive drum 28 is transferred onto the continuous paper P.

As described above, according to the printer 10 (see FIG. 1) of the present embodiment, the opening width W (see FIG. 3) that becomes the facing portion of the pins scorotron charger 44 to the photosensitive drum 28 is reduced. Therefore, the diameter of the photosensitive drum 28 can be reduced, and the entire apparatus can be downsized. In particular, in the so-called tandem type image forming apparatus as in the present embodiment, a plurality of photosensitive drums 28 (four in the present embodiment) are arranged, so that the effect of downsizing is great.
(Test Example 1)
In order to confirm the operation of the above-described embodiment, a comparative experiment between an image forming apparatus according to an example shown below (hereinafter simply referred to as an example) and an image forming apparatus according to a comparative example (hereinafter simply referred to as comparative example 1). Went.

An Example is the structure and conditions similar to the said embodiment. (However, the opening width W (the opening dimension corresponding to the moving direction in the portion of the opening facing the photosensitive drum 28 (see FIG. 3)) is changed as a parameter.)
In Comparative Example 1, a scorotron charger in which a scorotron wire made of a tungsten wire having a diameter of 40 μm was placed instead of the discharge electrode 45 in the above embodiment as a potential adjusting means. In Comparative Example 1, the photoconductor drum is charged to +450 V by constant current control so that the total current to the corotron wire of the corotron charger is +600 μA, and the total current to the scorotron wire of the scorotron charger is A positive charge was imparted to the photosensitive drum by constant current control so that +700 μA. Others were the same as in the example. Note that the charge setting potential of the photosensitive drum is +500 V as in the above embodiment.

  In the comparative test, the opening width W in the pin scorotron charger of the example and the scorotron charger of comparative example 1 (opening size corresponding to the moving direction of the opening facing the photosensitive drum 28 (see FIG. 3)). The charging potential on the surface of the photosensitive drum was measured by changing each of the above. The measurement results are shown in FIG. In FIG. 6, the horizontal axis indicates the opening width W (mm), and the vertical axis indicates the surface potential (V) of the photosensitive drum.

As shown in FIG. 6, in order to uniformly charge the photosensitive drum at 500 V, in the case of the comparative example 1, the opening width W is required to be 22 mm or more, whereas in the case of the example, It was confirmed that the opening width W should be 12 mm.
(Test Example 2)
In order to confirm the operation of the above-described embodiment, a comparative experiment between an image forming apparatus according to an example shown below (hereinafter simply referred to as an example) and an image forming apparatus according to a comparative example (hereinafter simply referred to as comparative example 2). Went.

  An Example is the structure and conditions similar to the said embodiment. (The opening width W of the Pins corotron charger is 12 mm.) In Comparative Example 2, the same corotron charger and pins corotron charger as in the example were applied, but the photosensitive drum was charged with the corotron charger. After the photosensitive drum was charged to about 90% of the set potential, a positive charge was applied to the photosensitive drum to the charged set potential of the photosensitive drum with a pins scorotron charger.

  The measurement results are shown in FIG. In FIG. 7, the horizontal axis indicates the discharge time (minutes) by the pin scorotron charger, and the vertical axis indicates the ozone generation amount (ppm). As shown in FIG. 7, except for the case where the discharge time is short (less than about 10 minutes), the amount of ozone generated in the example (in the case of minus discharge) is larger than that in Comparative Example 2 (in the case of plus discharge). It was confirmed that there were few

  In the above embodiment, as shown in FIG. 4, the discharge electrode 45 has a sawtooth shape with a plurality of pointed portions 45 </ b> A directed toward the photosensitive drum 28. A plurality of cusps directed to 28 may be needle-shaped, and the cusps directed to the photosensitive drum 28 extend linearly in a direction perpendicular to the moving direction of the photosensitive drum 28. For example, the discharge electrode may be formed with a cusp of another shape.

1 is a schematic cross-sectional view illustrating a schematic configuration of a color laser printer according to an embodiment of the present invention. 2 is a schematic cross-sectional view illustrating a schematic configuration of a printing unit of the color laser printer according to the embodiment of the present invention. It is a typical sectional view showing a schematic structure of a pins scorotron charger in an embodiment of the present invention. FIG. 4 is an end view corresponding to the end face taken along line 4-4 of FIG. 3. 6 is a graph showing a change in potential of the photosensitive drum in the embodiment of the present invention. 6 is a graph showing measurement results of Test Example 1. 10 is a graph showing measurement results of Test Example 2.

Explanation of symbols

10 Color laser printer (image forming device)
28 Photosensitive drum (Amorphous silicon photoconductor)
42 Corotron charger 44 Pins corotron charger (potential adjustment means)
44C Grid electrode 45 Discharge electrode 45A Point R Rotation direction

Claims (2)

An amorphous silicon photoreceptor on which an image is formed;
A corotron charger disposed opposite to the amorphous silicon photoconductor to charge the amorphous silicon photoconductor,
A discharge electrode disposed downstream of the corotron charger with respect to the rotation direction of the amorphous silicon photoconductor and having a pointed portion directed to the amorphous silicon photoconductor; and the discharge electrode and the amorphous silicon photoconductor A potential adjusting means for providing a grid electrode between the body, generating a charge from the apex and applying it to the amorphous silicon photosensitive member, and adjusting a charging potential of the amorphous silicon photosensitive member;
An image forming apparatus comprising:   The corotron charger charges the amorphous silicon photoconductor to a potential higher than the charge setting potential of the amorphous silicon photoconductor, and the potential adjusting means sets the charge potential of the amorphous silicon photoconductor to the charge setting potential. The image forming apparatus according to claim 1, wherein:

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