JP2006003595A - Developing device and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent toner deterioration and aggregation near a doctor blade and form a uniform toner layer in a developing device.
A doctor blade that regulates the thickness of toner carried on a developing roller carrying and carrying toner is bent until its tip is brought into close contact with the surface of the doctor blade. The bent portion 26a is provided in contact with the developing roller 23 in the direction opposite to the conveying direction (rotating direction) of the developing roller 23. Thereby, since the toner does not stay in the vicinity of the doctor blade 26, the toner is prevented from being deteriorated and aggregated in the vicinity of the doctor blade 26, and a uniform toner layer can be formed.
[Selection] Figure 3

Description

  The present invention relates to a developing device and a process cartridge.

  Developing devices indispensable for realizing an electrophotographic process include a one-component developing type device using a one-component toner not containing a carrier and a two-component developing type device using a two-component toner containing a carrier. . Further, both the one-component toner and the two-component toner include a magnetic toner having magnetism and a non-magnetic toner having no magnetism. Therefore, the development method is determined according to the type of toner to be used. However, in any of the development methods, the toner supplied to the developing container with respect to the electrostatic latent image formed on the photosensitive member. The basic principle of development is to transfer the image by a developing roller driven to rotate.

  Among such developing devices, a one-component developing type device using one-component toner requires a structure for frictionally charging the toner in order to attach the toner in the developing container to the developing roller. Therefore, an apparatus having a structure in which toner is frictionally charged by bringing a doctor blade into contact with the developing roller has been widely used. The doctor blade is formed by bending the tip of a stainless steel sheet metal having a spring property, and the bent part is disposed so as to contact the developing roller.

  In the apparatus having such a structure, when the developing roller is driven to rotate, electrostatic force acts on the outer peripheral surface of the developing roller due to the contact of the doctor blade to charge the toner, and the charged toner is applied to the outer peripheral surface of the developing roller. Adhere electrostatically. Further, the doctor blade has a function of thinning the toner electrostatically attached to the developing roller. At this time, it is important to form a uniform toner layer on the developing roller in order to prevent deterioration of image quality in an image forming apparatus including the developing device.

  Patent Document 1 proposes a technique for preventing toner conveyance unevenness by swinging a developing roller in its axial direction. Patent Document 2 proposes a technique for forming a uniform toner layer by bending the tip of a doctor blade at an acute angle.

  Here, FIG. 4 is a longitudinal side view schematically showing an enlarged conventional doctor blade 101. As shown in FIG. 4, the toner carried on the developing roller 102 is regulated by the doctor blade 101 and a part thereof is scraped off, and only the toner that has passed through the doctor blade 101 passes through the uniform toner layer for development. Will contribute. At this time, if the bending angle of the tip of the doctor blade 101 is larger than 90 °, that is, an obtuse angle, a force that pushes up the doctor blade 101 with the pressure of the toner acts and a uniform toner layer cannot be formed. Therefore, as shown in FIG. 4, a uniform toner layer is formed by bending the tip of the doctor blade 101 at an acute angle.

JP-A-4-342273 JP 2001-92248 A

  However, in Patent Document 1, since the developing roller that swings becomes a heavy load, a large driving force is required to swing the developing roller, which causes various inconveniences such as an increase in the size of the apparatus and an increase in power consumption. Will occur.

  Further, as in Patent Document 2, in a developing device that charges the toner by bringing the doctor blade 101 into contact with the developing roller 102, it is necessary to press the doctor blade against the developing roller 102 with a relatively high pressing force. For this reason, frictional heat is generated at the contact portion between the developing roller 102 and the doctor blade 101, and if the toner stays on the surface of the doctor blade 101, the toner aggregates due to the heat.

  A conventional doctor blade 101 as shown in FIG. 4 has a shape in which toner tends to stay behind the contact portion with the developing roller 102. Further, since the toner in the developing device is in direct contact with the metal surface of the doctor blade 101 on the toner supply side, the toner is easily deteriorated and aggregated by the heat of the doctor blade 101. When such agglomerated toner is conveyed to the contact portion between the doctor blade and the developing roller, the toner layer has uneven thickness, which causes image quality deterioration in an image forming apparatus including the developing device. In addition, the toner adhering to the doctor blade tends to grow greatly, and the larger the toner grows, the more uneven the thickness of the toner layer becomes, and the deterioration of the image quality becomes serious.

  An object of the present invention is to prevent toner deterioration and aggregation near the doctor blade and form a uniform toner layer.

  The invention according to claim 1 is a developing device comprising a toner carrier that carries and conveys toner, and a doctor blade that regulates the thickness of the toner carried on the toner carrier, the doctor blade comprising: It has a bent portion formed by bending the tip until it is brought into close contact with the surface of the doctor blade, and the bent portion is directed to the toner carrying member in a direction opposite to the conveying direction of the toner carrying member. It is provided in contact with each other.

  According to a second aspect of the present invention, in the developing device according to the first aspect, the doctor blade is provided with a heat insulating member having a lower thermal conductivity than the doctor blade on a toner contact surface that comes into contact with the toner carried on the toner carrier. It is characterized by having.

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, the doctor blade is formed by bending its tip at a bending radius of 0.2 mm to 0.5 mm. To do.

  A process cartridge according to a fourth aspect of the invention is a developing device according to the first, second, or third aspect, an image carrier that carries toner supplied from the developing device, and the developing device and the image carrier. And a cartridge case.

  According to the present invention, since toner does not stay in the vicinity of the doctor blade, the toner can be prevented from being deteriorated and aggregated in the vicinity of the doctor blade, and a uniform toner layer can be formed.

  The best mode for carrying out the present invention will be described with reference to FIGS.

  FIG. 1 is a longitudinal side view showing a schematic configuration of the image forming apparatus of the present embodiment, and FIG. 2 is a longitudinal side view showing an enlarged part of the schematic configuration of the image forming apparatus.

  As shown in FIG. 1, the image forming apparatus 1 includes a paper feeding device 2 that stores a transfer paper P as a recording medium, a paper feeding path 4 that connects the paper feeding device 2 and the paper discharge unit 3, and An image processing unit 6 including a fixing device 5 provided in the paper path 4 is provided.

  The image processing unit 6 is mainly composed of a photosensitive member 7 which is an image carrier formed in a drum shape. Around the photoreceptor 7, a charging device 8, a developing device 9 and a transfer device 10 are sequentially arranged. An exposure position EX is between the charging device 8 and the developing device 9, and the image processing unit 6 is provided with an image exposure device 11 that exposes the photoreceptor 7 by irradiating the exposure position EX with a laser beam. It has been.

  In such an image processing unit 6, the charging device 8 charges the photoreceptor 7 uniformly to one polarity, for example, about −750V. As a result, the photoconductor 7 is uniformly charged at the exposure position EX. The image exposure apparatus 11 forms an electrostatic latent image on the photosensitive member 7 by irradiating the exposure position EX with a laser beam. That is, in the photoconductor 7, a potential difference from the charged potential is generated in the exposed portion, and this portion becomes an electrostatic latent image. Specifically, the portion where the surface potential of −750 V is about −50 V is an electrostatic latent image.

  The developing device 9 visualizes the electrostatic latent image formed on the photosensitive member 7 at the exposure position EX by attaching toner having a potential difference from the electrostatic latent image. The transfer device 10 has a structure that sucks the visualized toner image on the photoreceptor 7 by a potential difference and transfers the toner image onto the transfer paper P, and a transport mechanism that transports the transfer paper P in the paper passing path 4. Also works. The fixing device 5 is arranged on the downstream side of the transfer device 10 in the paper passing path 4 and fixes unfixed toner adhering to the transfer paper P after passing through the transfer device 10 by a heating / pressurizing action. In this way, an image is formed on the transfer paper P, and the transfer paper P is discharged to the paper discharge unit 3 via the paper passing path 4.

  A cleaning device 12 is provided between the transfer device 10 and the charging device 8 around the photoconductor 7. The cleaning device 12 removes the toner remaining on the photoconductor 7 that cannot be transferred onto the transfer paper P by the transfer device 10 from the periphery of the photoconductor 7.

  In addition, the photosensitive member 7, the charging device 8, the developing device 9, the cleaning device 12, and the like are provided in the cartridge case 13 to constitute a process cartridge 14. Such a process cartridge 14 is detachably attached to the apparatus main body. The cartridge case 13 is formed with a slit 15 that is elongated along the axial direction of the photoconductor 7 for irradiating the surface of the photoconductor 7 with the laser beam emitted from the image exposure device 11.

  As shown in FIG. 2, the developing device 9 includes a developing roller 23 that is a toner carrier, a toner supply roller 24, an agitator 25, and a doctor blade inside a developing container 22 to which toner is supplied from a toner bottle 21. 26 is formed. The doctor blade 26 is supported by a doctor blade support member 27 provided in the developing container 22. In the present embodiment, for example, a one-component non-magnetic toner is used as the toner supplied from the toner bottle 21 to the inside of the developing container 22.

  The developing roller 23 is rotatably attached to a position where a part of the developing roller 23 is exposed to the outside through an opening 23 a formed in the developing container 22 and faces the photoconductor 7. The developing roller 23 is configured to be rotationally driven by a driving force transmitted from a driving source (not shown) via a power transmission mechanism (not shown). Such a developing roller 23 carries and conveys toner on its surface. As a result, toner is supplied to the photoreceptor 7. At this time, as indicated by an arrow in FIG. 2, the rotation direction of the developing roller 23 is opposite to the rotation direction of the photoconductor 7. The rotation direction of the developing roller 23 is a conveyance direction for conveying the toner.

  The toner supply roller 24 is disposed in contact with the developing roller 23 inside the developing container 22 and has a structure that is rotationally driven in the same direction as the developing roller 23 as indicated by an arrow in FIG. As a result, the developing roller 23 receives frictional force, and the frictionally charged toner is electrostatically attracted to the outer peripheral surface of the developing roller 23.

  The agitator 25 is driven to rotate in the same direction as the developing roller 23 and the toner supply roller 24 and has a structure that strikes the paddle 28. The agitator 25 agitates the toner supplied from the toner bottle 21 to the inside of the developing container 22, and Unravel the lump.

  The doctor blade 26 is formed of a flexible dielectric that makes surface contact with the developing roller 23 with a predetermined contact pressure with an elastic force. Therefore, when the developing roller 23 is driven to rotate, the toner on the developing roller 23 is charged with electrostatic force due to friction with the doctor blade 26. The doctor blade 26 also has a function of thinning toner adhering to the outer peripheral surface of the developing roller 23 by electrostatic force.

  In such a developing device 9, a charging bias is applied to the developing roller 23, the toner supply roller 24, and the doctor blade 26. As a result, the developing roller 23 is charged to about −400V, and the toner supply roller 24 and the doctor blade 26 are charged to about −550V. Further, the toner circulates and moves as an agitator 25, a toner supply roller 24, a developing roller 23, a doctor blade 26, and an agitator 25.

  Here, when the printing operation is continuously performed by the conventional developing device, a white streak-like image defect may sometimes occur along the image traveling direction in printing a solid image. When investigating the cause of white streaks, the part of the doctor blade corresponding to the part where the white streak occurred and the developing roller contact part, that is, between the bent part (ridge line part) of the tip of the doctor blade and the developing roller It was confirmed that aggregates (for example, aggregated toner) were sandwiched and the aggregates hindered the flow of toner passing through the doctor blade. Then, in the location where the aggregate is present, a state in which the toner is not transported onto the developing roller or a state in which the transport amount is extremely small occurs, and the electrostatic latent image on the photosensitive member cannot be developed. Turned out to be. Such agglomerates are not fixed to the doctor blade from the beginning. In some cases, the white streaks of the formed image may disappear due to slipping out of the space between the doctor blade and the developing roller easily due to vibrations such as removal and remounting of the developing device. This can be said to be a state of toner clogging where toner is clogged by being caught between the doctor blade and the developing roller. As a result of investigating the contents of the aggregates, most of them are large aggregates of hydrophobic silica that are externally added to the toner, and minute toner enters and adheres so as to fill the gaps between the silica aggregates. It turned out to be huge.

  In addition, the agglomerates as described above are not contained in the toner from the beginning, and the toner circulates in the developing device in a circulating manner with an agitator, a toner supply roller, a developing roller, a doctor blade, and an agitator. It turned out to be formed while going. This is because part of the silica adhering to the toner surface is desorbed due to the physical load that the toner receives from each of the above members, and they combine with some of the fine powder of the toner to agglomerate into larger particles. is there. In addition, if fine toner or silica aggregates are retained in a part of the developing device, they become large particles due to heat. As a result of measuring the temperature of each part of the developing device, the temperature rise on the surface of the doctor blade is relatively large and directly affects the toner near the surface of the doctor blade. Further, it has been found that the bending angle and the bending radius R of the tip of the doctor blade have a great influence on the regulation of the layer thickness of the toner conveyed to the developing roller. Considering these, the doctor blade 26 is created and attached to the developing device 9 as in the present embodiment.

  The doctor blade 26 of the present embodiment will be described with reference to FIG. 3 is an enlarged schematic view of the doctor blade 26. FIG. 3A is a longitudinal side view when the tip of the doctor blade 26 is bent in a direction away from the developing roller 23, and FIG. 3B is a doctor blade 26. FIG. 6 is a longitudinal side view when the front end of FIG.

  As shown in FIGS. 3A and 3B, the doctor blade 26 is formed with a bag-like tip. The tip of the doctor blade 26 is bent into a bag shape with a predetermined bending radius R until it is substantially in close contact with the surface of the doctor blade 26. At this time, the tip of the doctor blade 26 is bent toward the doctor blade support member 27 and is in close contact with the surface of the doctor blade 26.

  In other words, the doctor blade 26 has a bent portion 26a formed by bending the tip of the doctor blade 26 with a predetermined bending radius R until the tip of the doctor blade 26 is brought into close contact with the surface of the doctor blade 26. The doctor blade 26 is provided with its bent portion 26 a in contact with the developing roller 23 in the direction opposite to the rotation direction of the developing roller 23.

  The same effect can be obtained regardless of the bending direction of the doctor blade 26 in either FIG. 3A or FIG. 3B (the direction away from the developing roller 23 or the direction approaching the developing roller 23).

  Here, when the bending radius R of the bending portion 26a of the doctor blade 26 is small, the toner layer is easily regulated, but too much load is applied to the toner entering between the bending portion 26a of the doctor blade 26 and the developing roller 23. Problems such as toner sticking occur during continuous use. On the other hand, when the bending radius R of the bending portion 26a of the doctor blade 26 is too large, the toner regulating force of the doctor blade 26 is extremely reduced, and a thin and uniform toner layer cannot be formed. Considering these, the bending radius R of the bending portion 26a of the doctor blade 26 is appropriately set. In the present embodiment, the doctor blade 26 is formed, for example, with a bending radius R of the bent portion 26a of 0.2 mm to 0.5 mm. Thereby, a thin and uniform toner layer can be reliably formed.

  Further, the doctor blade 26 as shown in FIGS. 3A and 3B is in contact with the tangent line formed on the peripheral surface of the developing roller 23 at the contact portion between the bent portion 26 a and the developing roller 23. Therefore, a thin and uniform toner layer can be more reliably formed when arranged at an angle of θ = 15 ° to 20 °. Therefore, in the present embodiment, the doctor blade 26 has, for example, an arrangement angle θ at a contact portion between the bent portion 26 a and the developing roller 23 of 15 ° to a tangent line formed on the peripheral surface of the developing roller 23. It is arranged as an angle of 20 °.

  Further, a heat insulating member 29 having a thermal conductivity lower than that of the doctor blade 26 is provided on almost the entire surface of the doctor blade 26 on the toner supply side. That is, the doctor blade 26 includes a heat insulating member 29 having a lower thermal conductivity than the doctor blade 26 on the toner contact surface 26 b that contacts the toner carried on the developing roller 23. As the heat insulating member 29, for example, a resin plate material such as polyester is used. Such a heat insulating member 29 is provided by being adhered to the surface of the doctor blade 26, for example.

  As described above, according to the present embodiment, the doctor blade 26 has its tip bent toward the doctor blade support member 27 with a predetermined bending radius, for example, a radius of 0.2 mm to 0.5 mm. Is formed in a bag shape. This prevents unnecessary toner from entering between the doctor blade 26 and the developing roller 23 to form a toner layer that is thicker than necessary. Further, the toner is smoothly conveyed without staying near the contact portion of the doctor blade 26 with the developing roller 23. That is, since the toner does not stay near the doctor blade 26, the toner is prevented from being deteriorated and aggregated near the doctor blade 26, and a uniform toner layer can be formed.

  Further, even if frictional heat is generated at the contact portion between the bent portion 26a of the doctor blade 26 and the developing roller 23 and the entire surface of the doctor blade 26 rises in temperature, the heat insulating member 29 installed on the doctor blade 26 causes the developing device. 9 does not directly contact the doctor blade 26, the aggregation of the toner is eliminated, and a uniform and thin toner layer is always formed between the doctor blade 26 and the developing roller 23. In other words, since heat conducted from the doctor blade 26 to the toner is blocked by the heat insulating member 29, the toner is prevented from being deteriorated and aggregated by heat near the doctor blade 26, and a uniform toner layer can be formed.

1 is a longitudinal side view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. 1 is an enlarged longitudinal side view showing a part of a schematic configuration of an image forming apparatus according to an embodiment of the present invention. 1 is an enlarged schematic view of a doctor blade according to an embodiment of the present invention, wherein (a) is a longitudinal side view when the tip of the doctor blade is bent in a direction away from the developing roller, and (b) is a doctor. It is a vertical side view when the front end of the blade is bent in a direction approaching the developing roller. It is a vertical side view which expands and shows the conventional doctor blade roughly.

Explanation of symbols

7 Image carrier (photoreceptor)
9 Developing Device 13 Cartridge Case 14 Process Cartridge 23 Toner Carrier (Developing Roller)
26 Doctor blade 26a Bending part 26b Toner contact surface 29 Heat insulation member

Claims (4)

In a developing device including a toner carrier that carries and transports toner, and a doctor blade that regulates the thickness of the toner carried on the toner carrier,
The doctor blade has a bent portion formed by bending the tip of the doctor blade until it is in close contact with the surface of the doctor blade, and the bent portion is directed in a direction opposite to the conveying direction of the toner carrier. Provided in contact with the toner carrier,
A developing device. The doctor blade includes a heat insulating member having a thermal conductivity lower than that of the doctor blade on a toner contact surface that comes into contact with the toner carried on the toner carrier.
The developing device according to claim 1. The bending portion of the doctor blade is formed by bending the tip of the doctor blade with a bending radius of 0.2 mm to 0.5 mm.
3. The developing device according to claim 1, wherein A developing device according to claim 1, 2 or 3,
An image carrier for carrying toner supplied from the developing device;
A cartridge case for holding the developing device and the image carrier;
A process cartridge comprising:

Images