JP2597540B2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming apparatus.

More specifically, an image carrier for carrying a toner image, a charging device for charging the image carrier, a latent image forming device for forming an electrostatic latent image on the image carrier, and the electrostatic image formed of toner. A developing unit for developing, and a transfer unit in contact with the image carrier, wherein a potential is applied to transfer a toner image from the image carrier to a transfer material sent between the image carrier and the transfer unit. And an image forming apparatus having the same.

(Prior Art) Specific examples of the image forming apparatus as described above include a copying machine, a printer, a microfilm reader printer, and a display device using a transfer type electrophotographic method or an electrostatic recording method. Are also widely used.

Generally, an electrophotographic photosensitive member or an electrostatic recording dielectric as an image carrier is formed into a form of a drum or a belt that is rotationally driven or rotationally driven at a predetermined peripheral speed, and the drum that is rotationally or rotationally driven. And the surface of the belt are uniformly charged positively or negatively by a corona discharger, contact charger, or other charging means, and the charged charge is slit-exposed, laser-beam-scanned,
A light-emitting element array, a charge-removing element array, or the like is selectively discharged or further charged in the opposite polarity to form an electrostatic latent image corresponding to the target image information, and the latent image is visualized by a developing unit using a developer. The visible image is transferred to the transfer material surface by a transfer means, and the transfer material having undergone the image transfer is fixed by an image fixing means and discharged out of the apparatus as an image formed product. The belt surface is configured to be cleaned by a cleaning unit and repeatedly used for image formation.

A transfer charger is generally used as an image transfer means for transferring a visible image (hereinafter, referred to as a developer image) formed by a developer (toner) formed and carried on an image carrier surface on a transfer material surface side. In this method, a transfer material (transfer paper) is fed to the surface of the image carrier holding the developer image, and the polarity of the developer image opposite to the developer polarity of the developer image on the image carrier surface side is supplied to the back surface of the transfer material by corona discharge. By applying a charge, the developer image on the image carrier side is transferred and attracted (transferred) to the transfer material facing side of the image carrier by electrostatic attraction.
This has the advantage that the structure is simple and relatively stable transfer performance can be obtained.

However, on the other hand, there is a drawback that the developer may be wrapped around the transferred character due to the influence of the excessive back surface charge applied to the back surface of the transfer material.

On the other hand, there is a transfer roller device as another type of transfer device that solves such a drawback of the transfer charger. This is the second
The transfer material 10 is fed to the surface of the image carrier 1 carrying the developer image ta as shown in the figure, and the developer of the developer image ta on the image carrier 1 surface side is provided on the back of the transfer material. The image transfer tb is performed by pressing the elastic transfer roller 3 to which a voltage (including ground) having a different polarity from the electric charge e ₁ is applied to apply the transfer material 10 to the surface of the image carrier 1. Compared with the above-described transfer charger, there is less possibility of giving an excessive back surface charge to the back surface of the transfer material, so that the developer is hardly stuck around a transfer character, and an advantage that high image quality can be obtained. There is. Reference numeral 9 denotes a bias power supply. In particular, in an image forming apparatus using the reversal development method is the same polarity charge e ₁ of the developer of the latent image charges e ₂ and the developing agent image ta on the image bearing member surface as shown in FIG. 2 example, transfer The bias voltage applied to the roller 3 can be reduced, and a good transfer image tb free of developer and dust can be obtained.
Is easy to obtain.

(Problems to be Solved by the Invention) However, since the transfer roller 3 is in contact with the surface of the image carrier 1 in the non-sheet passing portion, the surface of the image carrier 1 is soiled. There was a problem that it was immediately stained. Particularly in the case of the reversal development system, when the surface of the image carrier 1 has a specific potential having the same polarity as the charge of the developer in the non-image portion, the developer does not easily adhere to the surface of the image carrier. When the potential is inappropriate, the potential is approximately 0 V, or the potential has a polarity opposite to that of the developer, the developer easily adheres to the surface of the image carrier, and the adhered developer becomes non-conductive. In some cases, the roller 3 is contaminated by adhering to the peripheral portion of the transfer roller that is in contact with the surface of the image carrier in the paper passing portion. Contamination at the end of the roller causes damage such as poor adhesion between the image carrier 1 and the roller 3 and scratches on the surface of the image carrier and the roller surface, which causes a problem with the durability of the apparatus. is there.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent the developer from adhering and contaminating a transfer unit that comes into contact with the image carrier, and to remove damage caused by the developer adhering and contaminating.

(Means for Solving the Problems) The present invention is an image forming apparatus having the following configuration.

[1] An image carrier that carries a toner image, a latent image forming unit that includes a charging unit that charges the image carrier, and forms an electrostatic latent image on the image carrier, and the electrostatic latent image is formed of toner. Developing means for forming a toner image on the image carrier by reversal development;
Transfer means for contacting the image carrier, wherein a potential is applied to transfer the toner image from the image carrier to a transfer material sent between the image carrier and the transfer means In the image forming apparatus having the following configuration, in the direction orthogonal to the moving direction of the image carrier, the transfer unit width where the transfer unit and the image carrier contact each other is set smaller than the effective charging width by the charging unit. An image forming apparatus comprising:

[2] The image forming apparatus according to [1], wherein a developing width of the developing unit in a direction orthogonal to a moving direction of the image carrier is set smaller than the transfer unit width.

[3] The image forming apparatus according to [1] or [2], wherein the transfer unit is a transfer rotating body.

[4] The image forming apparatus has a cleaning unit for cleaning the image carrier, and a cleaning width of the cleaning unit in a direction orthogonal to a moving direction of the image carrier is larger than the effective charging width. The image forming apparatus according to any one of [1] to [3], wherein the image forming apparatus is set.

[5] The method according to any one of [1] to [4], wherein the effective charging width is set to be smaller than the entire width of the image carrier in a direction orthogonal to a moving direction of the image carrier. The image forming apparatus as described in the above.

(Operation) The developer adhering dirt on the non-sheet passing portion of the image carrier surface is outside of both ends of the effective charging width in a direction perpendicular to the direction of relative movement between the image carrier surface and the charging device with respect to the charging section of the image carrier surface by the charging device. Mainly occurs on the surface of the image carrier. This is because the surface of the image bearing member outside the effective charging width has a weaker action of the charging means or is out of the action, so the potential is less appropriate than within the effective charging width, the potential is substantially 0 V, or the developer and This is because the polarity is reversed.

Therefore, since the end of the transfer means extends over and is in opposing contact with the image carrier surface portion outside this effective charging width, developer adhesion contamination at the end of the transfer means is caused.
By setting the width in the longitudinal direction of the transfer unit to be smaller than the effective width in the longitudinal direction of the charging unit, the end of the transfer unit is opposed to the surface of the image bearing member outside the effective charging width where the developer is easily stained as described above. As a result, the transfer member is not substantially contaminated with the developer, and the transfer member is substantially prevented from being contaminated.

Further, by setting the width of the developing section in the longitudinal direction to be smaller than the width of the transfer section, the developer on the image carrier surface portion (the image carrier surface portion outside the effective charging width) corresponding to the end of the transfer roller serving as the transfer unit is used. Adhered dirt itself is reduced, or adhered dirt is not generated, so that the developer adhering contamination of the transfer roller is more effectively prevented.

Example 1 Example 1 (FIGS. 1 to 3) FIG. 1 is a schematic view showing the structure of an image forming apparatus according to an embodiment of the present invention. It is a printer.

1 is a drum type electrophotographic photosensitive member (OP
C photoreceptor), and is driven to rotate around the center support shaft 1a in the clockwise direction indicated by an arrow at a predetermined peripheral speed.

The photoreceptor 1 receives a uniform charge of a predetermined polarity on its outer peripheral surface by a corona charger 2 as a charging means (in this case, a surface charging potential of approximately -700 V) as the photoreceptor 1 rotates. Reference numeral 6 denotes a power supply for applying voltage to the charger 2.

Then, a laser beam scanner (not shown) performs laser beam scanning exposure 4 corresponding to output image information from an electronic computer or a word processor (not shown) on the surface of the photoreceptor. Images are sequentially formed.

The latent image is sequentially developed with toner by the developing device 5. In this embodiment, the latent image is developed by a developing roller or a developing sleeve 5a to which a superimposed voltage of AC + DC is applied as a developing bias by an AC bias power supply 7 and a DC bias power supply (voltage of approximately -500 V) 8.

The developer image ta (FIG. 2) formed on the photoreceptor surface is fed between a photoreceptor 1 and a transfer roller 3 as a transfer unit from a paper feeding mechanism (not shown) in synchronization with the rotation of the photoreceptor 1. The transfer tb is sequentially transferred onto the transferred transfer material 10 surface. In this case, the transfer roller 3 has a resistivity of 10 ⁵ Ω · c over the entire length (full width).
m and a bias power supply 9 to control the potential of the photoconductor 1 and the polarity of the developer image ta to about +
The transfer was performed by applying a transfer bias of 500V.

The transfer material 10 that has received the image transfer tb through the transfer unit is subjected to image fixing by an image fixing unit (not shown), and is output to the outside as an image formed product (print).

After the image transfer, the surface of the photoconductor 1 is cleaned and cleaned by receiving and removing the transfer residual developer by the cleaning device 11.
The entire surface is exposed by 12 and the electric charge is uniformly removed from each part, and the electrical memory is erased. The image is repeatedly provided for image formation.

In the printer as described above, the length of the transfer portion in the longitudinal direction of the photoreceptor, that is, the length of the transfer roller 3 (transfer roller width) is set to be sufficiently larger than the effective width in the longitudinal direction (charge width) of the charging portion. When the printing was performed with the photoconductor 3 facing the photoconductor 1, the developer was stained on the surface of the photoconductor 1 from the point where the charging started to weaken at the end of the charger 2 toward the region having no charging ability. The toner adhered to the opposite portion of the transfer roller 3.

A is the maximum width of an image formed on the surface of the photoconductor 1, B is the width of the transfer section in the longitudinal direction (transfer roller width), and C is the effective width of the charging section in the longitudinal direction (charging width).・ B ・
As shown in FIG. 3, the relative positional relationship of C is A <B <C.
When the setting was made such that, the developer dirt did not adhere to the surface of the photoreceptor 1 on the opposing surface of the transfer roller 3, and the dirt on the transfer roller 3 could be prevented.

It should be noted that, depending on the photoreceptor, there is also a photoreceptor which is not subjected to photo-elimination when reverse charging is applied. For example, in the case of an OPC photoreceptor, the negative charge is removed by exposure, but if the charge is positive, the charge cannot be removed by light. In the case of such a photosensitive member, by using the present invention, by setting the positional relationship A <B <C as shown in FIG. 3, the photosensitive member 1 remains positively charged by the transfer roller 3. And a new effect that the photoreceptor can be protected.

In the above embodiment, although the exposure width of the pre-exposure 12 shown in FIG. 1 is not particularly limited, it is generally preferable that the exposure width is wider than the charging width of the charger 2. Similarly, the cleaning width of the cleaning device 11 needs to be set wider than the charging width shown in FIG.

Embodiment 2 It is a well-known fact that the developing width of the developing unit 5 in FIG. 1 should generally be set wider than the maximum image width A and narrower than the charging width C in FIG. On the other hand, considering the relationship between the transfer roller width B and the developing width, if the relationship (charging width C)> (transfer roller width B) is maintained as described above, the developing width is larger than the transfer roller width B. It can be wide. The reason is that if the surface potential of the photoconductor is maintained at the white background potential in the maximum (transfer roller width B)-(maximum image width A) region, the developer does not adhere to this portion, and the transfer roller 3 This is because no pollution should occur. However, in practice, ground fogging due to the deterioration of the developer, reversal fogging due to the developer charged to the opposite polarity, and the like may occur even in a white background. At this time, the surface of the transfer roller 3 is cleaned with the transfer material 10. I can not expect the effect of doing it at all. In the region of (transfer roller width B)-(maximum image width A), the surface of the transfer roller 3 is gradually contaminated. Therefore, (transfer roller width B)>
(Developing width)> (maximum developing width A) is preferably set to minimize the contamination of the transfer roller 3 in the area of (transfer roller width B)-(maximum image width A).

FIG. 4 shows the above-described specific settings in the reversal development. In FIG. 4, J is a development width, K is a pre-exposure width, and L is a cleaning width by the cleaning device 11. At this time, when the respective lengths were set to A <J <B <C <K <L as shown in FIG. 4, contamination at the edge of the transfer roller 3 could be prevented. Note that the relationship between K and L may be reversed. Here, (Developing width J) <(Transfer roller width B)
If the relationship is maintained, it may be considered that (transfer roller width B)> (charging width C) may be satisfied. However, if the sealing property at the end of the developing device is not perfect,
Since the developer may scatter from the end and adhere to the photoreceptor in some cases, (transfer roller width B) <(charge width C)
It is good to keep.

As is apparent from FIG. 4, the entire width of the photoconductor is set to be larger than the cleaning width, but the effective charging width C is smaller than the entire width of the photoconductor in order to prevent leakage from the end of the photoconductor. Preferably, it is set.

(Effect of the Invention) As described above, by setting the longitudinal width of the transfer section of the transfer unit to be smaller than the charging width of the charging unit,
The transfer means can be prevented from being contaminated by the developer. Further, at this time, by setting the developing width to be narrower than the longitudinal width of the transfer portion of the transfer unit, the effect of preventing the transfer unit from being contaminated could be further improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a laser beam printer as one embodiment of the apparatus, FIG. 2 is an enlarged view of a transfer roller portion, FIG. 3 is a diagram showing a relative positional relationship between a maximum image width, a transfer roller width, and a charging width. FIG. 4 is a diagram showing a relative positional relationship between processing sections in another embodiment. 1 is an electrophotographic photosensitive member of a rotating drum type as an image carrier,
2 is a corona charger as charging means, 3 is a transfer roller as transfer means, 5 is a developing device, and 10 is a transfer material.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Otsuka Yasumasa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hiroto Hasegawa 3-30 Shimomaruko, Ota-ku, Tokyo No. 2 Inside Canon Inc. (72) Inventor Takayasu Yuminomo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-59-195253 (JP, A) JP-A-54 JP-A-1-277268 (JP, A) JP-A-51-9840 (JP, A) JP-A-56-126874 (JP, A) JP-A-56-126875 (JP, A) JP-A-59-192270 (JP, A) JP-A-54-8452 (JP, U) JP-A-63-76868 (JP, U) JP-B-56-39472 (JP, B2)

Claims (5)

(57) [Claims] An image carrier that carries a toner image; a charging device that charges the image carrier; a latent image forming device that forms an electrostatic latent image on the image carrier; Developing means for inverting development with toner to form a toner image on the image carrier, and transfer means for contacting the image carrier, wherein a transfer means is provided between the image carrier and the transfer means from the image carrier. A transfer unit to which a potential is applied to transfer the toner image to the transferred transfer material, wherein an effective charging width of the charging unit in a direction orthogonal to a moving direction of the image carrier is provided. An image forming apparatus, wherein a width of a transfer portion at which the transfer unit and the image carrier come into contact with each other is set smaller than that of the transfer unit. 2. The image forming apparatus according to claim 1, wherein a developing width of said developing means in a direction orthogonal to a moving direction of said image carrier is set smaller than said transfer portion width. 3. An image forming apparatus according to claim 1, wherein said transfer means is a transfer rotating body. 4. The image forming apparatus according to claim 1, further comprising a cleaning unit configured to clean the image carrier, wherein a cleaning width of the cleaning unit in a direction perpendicular to a moving direction of the image carrier is smaller than the effective charging width. The image forming apparatus according to claim 1, wherein the image forming apparatus is also set to be large. 5. The image forming apparatus according to claim 1, wherein the effective charging width is set to be smaller than a total width of the image carrier in a direction orthogonal to a moving direction of the image carrier. The image forming apparatus as described in the above.