JP4349885B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile.

  In a conventional electrophotographic image forming apparatus using a transfer device such as a transfer belt or a transfer roller, a toner image is formed on a photoconductor, and this is formed between transfer nips formed between the photoconductor and the transfer belt or transfer roller. Image formation is performed by transferring a toner image onto a transfer material such as transfer paper. In the case of this type of apparatus, a technique is known in which toner adhering to a transfer belt or a transfer roller is scraped off by a cleaning blade. Further, in order to prevent the cleaning blade from turning up due to an increase in frictional force between the transfer belt and the cleaning blade, a toner image is formed outside the image area on the photosensitive member, and the toner image is directly transferred onto the transfer device. Accordingly, a technique for reducing the frictional force by supplying toner to the tip of the cleaning blade is also known.

By the way, if the amount of toner supplied to the cleaning blade at once is large, the cleaning blade cannot completely scrape off the toner image directly transferred to the transfer device, and the remaining toner adheres to the back surface of the transfer material. There may be a problem that the transfer material becomes dirty. This phenomenon is more likely to occur when a small particle size toner is used. In order to prevent this, it is necessary to reduce the amount of toner supplied to the cleaning blade. As a method for this, the transfer time is reduced to reduce the amount of toner supply (see Patent Document 1), and toner image formation is performed. It has been proposed to reduce the amount of toner supply by changing the pattern (see Patent Documents 2 and 3). In addition, a method of reducing the developing potential and reducing the amount of toner on the photoconductor from the time of normal toner image formation, specifically, a means of increasing the exposure potential or lowering the developing bias is considered.
JP-A-5-257360 JP 2000-137387 A Japanese Patent Laid-Open No. 11-15292

  However, in the technique disclosed in Patent Document 1 described above, although the total supply amount of the toner is reduced, the blade supply amount per line width is not different from the normal time, and the supplied toner is the blade because the supply amount is large. There is a risk that cleaning failure may occur.

  When the development potential is reduced, it is difficult to vary the exposure potential depending on the required toner supply amount, and carrier adhesion occurs as a side effect of lowering the development bias. When the charging potential is changed in order to prevent carrier adhesion, there is a problem that background contamination occurs depending on the change timing, resulting in an increase in the amount of supplied toner.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can solve the above-described problems without changing the process conditions before transfer between normal toner image creation and blade curling prevention toner image creation.

According to a first aspect of the present invention, a bias applying roller is disposed on the back side of a transfer rotator disposed opposite to an image carrier, and the surface of the transfer rotator can be cleaned with a cleaning blade. Transfer that transfers the toner image on the image carrier to the transfer material by applying a high voltage to the bias application roller while the transfer rotator holding the toner is in contact with the rotating image carrier An image forming apparatus comprising the image forming apparatus, wherein the toner image created between the sheets of the image carrier is transferred onto the transfer rotating body and supplied to the cleaning blade in order to prevent the cleaning blade from being turned over. In the device
When transferring and supplying the toner image for preventing blade curling to the transfer rotator, the amount of toner adhering to the image carrier per area of the exposed area is determined during normal toner image formation on the transfer material . The same applies to the formation of the toner image for preventing the blade curling, and the transfer amount from the image carrier to the transfer material is smaller than that for the transfer to the normal transfer material , and the blade curling prevention toner. The image is formed as a dot independent pattern, and the dot independent pattern is arranged in a regular staggered pattern, and the regular staggered dot independent pattern is formed at least within the image forming range in the main scanning direction. The cleaning blade has a pattern in which there is no place where toner is not supplied .

According to the second aspect of the present invention, the bias applying roller is disposed on the back surface side of the transfer rotator disposed to face the image carrier, the transfer rotator surface can be cleaned with a cleaning blade, and the transfer material is held. An image provided with a transfer device for transferring a toner image on the image carrier to a transfer material by applying a high voltage to the bias applying roller while bringing the transfer rotator into contact with the rotating image carrier. In the image forming apparatus, the toner image created between the sheets of the image carrier is transferred onto the transfer rotating body and supplied to the cleaning blade in order to prevent the cleaning blade from being turned over. The blade curling prevention toner image has a dot independent pattern, and the blade curling prevention toner image is transferred to the transfer rotator and supplied when transferred. Rate, transfer efficiency was smaller than usual, and the addition to creating a dot independent patterns arranged in a regular staggered, the regular staggered dot patterns of independence, at least within the image forming range in the main scanning direction Thus, there is no pattern where no toner is supplied to the cleaning blade .

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the transfer rotator is a roller.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the transfer rotating body is a belt traveling body.

  According to the fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the transfer amount is reduced by not applying a transfer bias when transferring and supplying the blade curling prevention toner image to the belt running body. It is characterized by that.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth aspect, when the blade curling prevention toner image is transferred and supplied to the belt running member, the image carrier is transferred from a normal transfer onto the transfer material. The transfer amount is reduced by reducing the transfer nip with the body.

According to the seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, when the toner image for preventing blade curling is transferred and supplied to the belt running body, transfer to a normal transfer material is performed. The transfer amount is reduced by reducing the transfer nip with the image carrier from time to time .

  The present invention can achieve the object by reducing the amount of toner supplied to the cleaning blade of the transfer device and reducing the transfer rate (transfer toner amount / toner amount on the photoconductor) while maintaining the toner adhesion amount on the photoconductor. .

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

  FIG. 1 is a conceptual diagram showing an image forming apparatus according to the present invention, and FIG. This apparatus forms an image by transferring a toner image onto a transfer material P, and includes a photosensitive drum 1 that is an image carrier that carries a toner image and rotates in the direction of arrow R in the figure. Around the periphery, a charging unit 2 that charges the surface of the photosensitive drum 1 to a negative potential, and a first image that develops the latent image formed on the photosensitive drum 1 with black toner by the laser beam LD emitted from the exposure unit 3. Means 4, a transfer device 5 for transferring the toner image to the transfer material P, a cleaning device 6, and a charge removal lamp 7 as charge removal means. In the figure, reference numeral 8 denotes a registration roller, and the transfer material P fed from the paper feeding device 9 via the paper feeding path is sent out along with the image on the photosensitive drum 1 by the registration roller 8.

  The transfer device 5 includes a transfer belt 11, which is wound around a drive roller 12 and a driven roller 13. A transfer bias roller 14 is in contact with the transfer roller 5, and is driven to rotate by the drive roller 12. Further, the transfer device 5 includes a transfer device contact / separation mechanism (not shown), and the contact pressure and a high voltage applied to the transfer bias roller 14 between the transfer nip N formed when the photosensitive drum 1 and the transfer belt 11 come into contact with each other. The toner image on the photosensitive drum 1 is transferred to the transfer material P. Further, the transfer device 5 includes a cleaning blade 15 for removing toner remaining on the surface of the transfer belt 11 after the toner image is transferred.

  Next, the operation at the time of creating the cleaning blade turning prevention pattern in the above-described image forming apparatus will be described.

As described above, the frictional force between the tip of the cleaning blade 15 and the transfer belt 11 increases with time, and the cleaning blade 15 is easily turned over. Therefore, a blade turn-up prevention pattern (toner image) is created on the transfer belt 11 for each specific number of sheets after transfer of the toner image onto the transfer material P or in a non-image area such as between sheets. Blade curling prevention pattern A shown in FIG. 3 can be arbitrarily created by the image formable range in the exposure device in the main scanning direction. The width in the sub-scanning direction is limited to the time between sheets, but is about 0.01 to 20 mm. The pattern may be a solid black image, a plurality of parallel lines whose length is in the main scanning direction, or a dot independent image.

  A high voltage is applied to the transfer bias roller 14 between the transfer nips N of 4 to 7 mm (transfer bias current value of 10 to 10) as in the case of the transfer condition to the transfer material P in the normal manner. 200 μA) is directly transferred onto the transfer belt by electrostatic force and supplied to the cleaning blade. As described above, the defective cleaning is that the amount of toner supplied to the cleaning blade is large. Originally, the purpose of the transfer belt cleaning device is to clean a small amount of adhering toner such as dirt toner transferred from the photosensitive drum. Therefore, if the toner image on the photosensitive drum 1 is directly transferred onto the transfer belt under the same conditions as those for normal image formation, the supply amount is excessive and a cleaning failure occurs. Further, when the toner forming the toner image is a small particle size toner, cleaning failure is more likely to occur. However, as shown in FIG. 4, even if the total amount of supplied toner is changed by manipulating the width of the blade turning prevention pattern, a blade turning prevention pattern is created under the same conditions as in normal image formation and supplied to the cleaning blade. As a result, the amount of toner transferred per minute area ΔS in the sub-scanning direction does not change, the amount of toner supplied to the cleaning blade at one time is excessive, and a cleaning failure occurs, and the back surface of the transfer material P is stained. End up. Further, as shown in FIG. 5, it is technically difficult to change the exposure potential and suppress the toner adhesion amount on the photosensitive drum 1 per area of the exposed area when creating the pre-transfer toner image. Further, when the toner adhesion amount on the photosensitive drum 1 per exposed area is suppressed by changing the developing bias as shown in FIG. 6, side effects such as carrier adhesion occur. Therefore, in order to solve this problem, in this embodiment, when the toner image for preventing blade curling is transferred and supplied to the transfer belt 11 which is the belt running member, the toner adhesion of the toner image on the photosensitive drum 1 which is the image bearing member. The transfer amount from the photosensitive drum 1 is kept as it is at the time of normal toner image formation, and is smaller than that at the time of transfer to the normal transfer material P, that is, the transfer rate is made smaller than normal.

Examples of the present invention will be described below. First, as Example 1, the transfer current value at the time of transferring the blade turning prevention pattern is set to 0, that is, the transfer bias is turned off. 1 is uniformly charged to a negative potential, for example, −750 V, and then a laser beam LD is irradiated from the exposure unit 3 to form a blade turn-up prevention pattern electrostatic latent image on the photosensitive drum 1. The exposure potential at this time is the same as that at the time of normal toner image creation. This electrostatic latent image is developed by the first developing means 4. When the blade curling prevention pattern toner image is formed, the adhesion amount on the photosensitive drum 1 is 60 to 80 mg / cm ² as in the case of normal toner image creation. Here, the specific number of blade curling prevention patterns is set to five, and each specific number is divided into a left edge, a center, and a right edge. When two types of blade turning prevention patterns having different total supply toner amounts were prepared and supplied to the cleaning blade, the following results were obtained.

図６に示す転写電流値と転写率の関係のように、通常転写率８０〜１００％をねらって転写電流値を設定しているが、転写バイアスをＯＦＦとした際、その転写率は５０％まで低減させることができる。転写バイアスをＯＦＦとしたとき、感光体ドラム１上のトナーが転写ベルト１１上に転移する力は感光体ドラム１と転写ベルト１１の接触圧のみとなり、転写率低減、クリーニングブレード１５へのトナー供給量の低減となり、クリーニング不良を防止することができた。

As shown in the relationship between the transfer current value and the transfer rate shown in FIG. 6, the transfer current value is set for the normal transfer rate of 80 to 100%. When the transfer bias is turned off, the transfer rate is 50%. Can be reduced. When the transfer bias is turned OFF, the force for transferring the toner on the photosensitive drum 1 onto the transfer belt 11 is only the contact pressure between the photosensitive drum 1 and the transfer belt 11, reducing the transfer rate and supplying the toner to the cleaning blade 15. The amount was reduced, and cleaning failure could be prevented.

Here, the following effects can be obtained by creating a blade turnover prevention pattern with a dot independent pattern. That is, during electrostatic latent image development, if no development bias is applied, the electric field is strong at the boundary between the image area and the non-image area, while the electric field is weak at the center area, and the toner does not transfer to the image center area. It becomes a blank image. Similarly, at the time of transfer, when the transfer bias is not applied, when the pattern is formed of a solid black image, the center of the image is not transferred, and there is a possibility that a blank image is formed. Further, there is a risk that the line intermediate portion is missing in the line image. As a result, toner may not be supplied to the blade. Therefore, if the pattern is created with a dot independent pattern, such a phenomenon will not occur. Further, if the pattern shown in FIG. 7 is used, there is no place where the toner is not supplied as shown by t in FIG. 8, and the toner can be supplied more uniformly to the blade. That is, the pattern as shown in FIG. 7 constitutes a regular staggered dot pattern in which dots are arranged in a line in the vertical direction of the figure every other line in the vertical direction of the figure. When the toner is supplied, the length of the pattern image in the sub-scanning direction can be minimized, and the toner can be efficiently supplied to the blade. On the other hand, when a pattern is configured with a large number of scattered dots as shown in FIG. 8, for example, when supplying a necessary amount of toner to the blade, the length of the pattern image in the sub-scanning direction is considered to be long.

  In Example 2, the transfer nip N at the time of transferring the blade curling prevention pattern was reduced from 4 to 7 mm in the normal state. It is possible to reduce the transfer nip by controlling the transfer device 5 with a contact / separation mechanism (not shown). By reducing the transfer nip N from the normal time, the contact area between the photosensitive drum 1 and the transfer belt 11 is shortened, and the time for the toner on the photosensitive drum 1 to transfer to the transfer belt 11 is shortened. As a result, the transfer rate is lower than usual, and the same effect as in Example 1 can be obtained.

  That is, in the image forming apparatus according to the present invention, when the blade turning prevention toner image is transferred to the transfer belt 11 and supplied, the toner adhesion amount of the toner image on the photosensitive drum 1 remains as it is at the time of normal toner image formation. Since the transfer amount from the drum 1 can be made smaller than when transferring to the normal transfer material P, that is, the transfer rate can be made lower than usual and the toner can be supplied to the cleaning blade 15, the pre-transfer process conditions are changed. Therefore, it is possible to prevent a cleaning failure due to the introduction of the cleaning blade turning-up prevention pattern.

  Further, since the transfer amount and transfer rate of the cleaning blade turn-up prevention pattern from the photosensitive drum 1 to the transfer belt 11 can be suppressed by turning off the transfer bias, the cleaning can be performed without changing the pre-transfer process conditions. It is possible to prevent a cleaning failure due to the insertion of the blade turn-up prevention pattern.

  Further, by making the cleaning blade turn-up prevention pattern into a dot independent pattern, the toner can be supplied uniformly to the cleaning blade, and by reducing the transfer nip N, the transfer device can be used from above the photosensitive drum 1 with the cleaning blade turn-up prevention pattern. The amount of transfer of toner to 5 and the transfer rate can be suppressed, and the cleaning failure due to the introduction of the cleaning blade turning-up prevention pattern can be prevented without changing the pre-transfer process conditions. Further, even with a cleaning blade turning prevention pattern formed of a small particle size toner, it is possible to prevent a cleaning failure due to the introduction of the cleaning blade turning prevention pattern.

1 is a conceptual diagram showing an image forming apparatus according to the present invention. 1 is an enlarged cross-sectional view of the main part of the apparatus of FIG. Diagram showing blade turning prevention pattern Diagram showing the relationship between the width of the blade turning prevention pattern and the toner amount The figure which shows the relationship between the exposure potential and the toner adhesion amount on the photosensitive drum per exposed area. Diagram showing the relationship between transfer current value and transfer rate Figure showing an example of a blade turning prevention pattern The figure which shows the other example of a blade turning prevention pattern

Explanation of symbols

1: Photosensitive drum 2: Charging means 3: Exposure means 4: First developing means 5: Transfer device 6: Cleaning device 7: Static elimination lamp 8: Registration roller 9: Paper feeding device 11: Transfer belt 12: Drive roller 13: Driven roller 14: transfer bias roller 15: cleaning blade LD: laser beam P: material to be transferred

Claims (7)

A bias applying roller is disposed on the back side of the transfer rotator disposed opposite the image carrier, the surface of the transfer rotator can be cleaned with a cleaning blade, and the transfer rotator holding the transfer material is rotated. An image forming apparatus comprising a transfer device for transferring a toner image on the image carrier to a transfer material by applying a high voltage to the bias applying roller while being in contact with the image carrier, the cleaning blade In the image forming apparatus for transferring the toner image created between the sheets of the image bearing member onto the transfer rotator and supplying the toner image to the cleaning blade in order to prevent turning up,
When transferring and supplying the toner image for preventing blade curling to the transfer rotator, the amount of toner adhering to the image carrier per area of the exposed area is determined during normal toner image formation on the transfer material . The same applies to the formation of the toner image for preventing the blade curling, and the transfer amount from the image carrier to the transfer material is smaller than that for the transfer to the normal transfer material , and the blade curling prevention toner. The image is formed as a dot independent pattern, and the dot independent pattern is arranged in a regular staggered pattern, and the regular staggered dot independent pattern is formed at least within the image forming range in the main scanning direction. An image forming apparatus having a pattern in which there is no place where toner is not supplied to a cleaning blade .
A bias applying roller is disposed on the back side of the transfer rotator disposed opposite the image carrier, the surface of the transfer rotator can be cleaned with a cleaning blade, and the transfer rotator holding the transfer material is rotated. An image forming apparatus comprising a transfer device for transferring a toner image on the image carrier to a transfer material by applying a high voltage to the bias applying roller while being in contact with the image carrier, the cleaning blade In the image forming apparatus for transferring the toner image created between the sheets of the image bearing member onto the transfer rotator and supplying the toner image to the cleaning blade in order to prevent turning up,
The blade turning prevention toner image has a dot independent pattern, and the transfer rate and transfer efficiency when transferring and supplying the blade turning prevention toner image to the transfer rotator are made smaller than usual. The independent patterns are arranged in a regular zigzag pattern, and the regular zigzag dot independent patterns are not provided in the main scanning direction at least within the image forming range where no toner is supplied to the cleaning blade. An image forming apparatus, characterized in that it is a pattern .
3. The image forming apparatus according to claim 1, wherein the transfer rotator is a roller. 3. The image forming apparatus according to claim 1, wherein the transfer rotating body is a belt traveling body. 5. The image forming apparatus according to claim 4, wherein a transfer amount is reduced by not applying a transfer bias when transferring and supplying the blade curling prevention toner image to the belt running body. 5. The image forming apparatus according to claim 4, wherein when transferring and supplying the blade curling prevention toner image to the belt running body, a transfer nip with the image carrier is reduced compared to a normal transfer onto a transfer material. An image forming apparatus characterized in that a transfer amount is reduced. 7. The image forming apparatus according to claim 1, wherein when the toner image for preventing blade curling is transferred and supplied to the belt running body, the image is transferred to the image carrier from the time of transfer to a normal transfer material. An image forming apparatus characterized in that a transfer amount is reduced by reducing a nip .

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