Developing device

Abstract

To provide a structure that can suppress rise of the temperature of a developer in a development container 41 and also can prevent the space between a development blade 42 and a first development sleeve 44b from becoming uneven.SOLUTION: A heat sink 51 forms a part of a cooling duct 53 in which an air current flows to cool a developer in a development container 41, and has a higher heat conductivity than the development container 41. The heat sink 51 is located in the upstream side of a development blade 42 with regard to the direction of rotation of a first development sleeve 44b, and has a contact unit 56 which contacts with a developer storage 49 generated in the upstream of the development blade 42 when the first development sleeve 44b rotates and carries the developer by supporting the developer.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier with a developer. [Background technology]

[0002] In an electrophotographic image forming apparatus, a toner image is formed by developing an electrostatic latent image formed on an image carrier such as a photosensitive drum using a developing device. The developing device has a developer container that contains developer containing toner, a developer carrier that carries and transports the developer within the developer container, and a regulating member that regulates the layer thickness of the developer carried on the developer carrier. A transport member that agitates and transports the developer is also provided within the developer container.

[0003] In such a developing device, the developer contained therein is stirred and transported, which tends to increase the temperature of the developer. When the temperature of the developer increases, the toner's charging ability deteriorates, which can lead to image defects such as reduced image density. In particular, when the temperature of the toner rises above its melting point, the toner melts and adheres to the developer carrier and the regulating member. This can lead to uneven coating of the developer on the developer carrier, resulting in image defects such as uneven density and streaks.

[0004] For this reason, a configuration has been proposed in which a highly heat-conductive member is provided in the developing device, and the highly heat-conductive member comes into contact with the developer inside the developing container and a regulating member to cool the developer (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-266249 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, the regulating member is positioned so that the gap between it and the developer carrier is uniform in the longitudinal direction of the developer carrier. In a configuration in which a highly thermally conductive member is in contact with the regulating member, as in the configuration described in Patent Document 1 above, if the highly thermally conductive member and the regulating member are made of different materials, the position of the regulating member may fluctuate due to the difference in thermal expansion of the materials. In this case, the gap between the regulating member and the developer carrier may become non-uniform in the longitudinal direction, which may result in poor image quality.

[0007] An object of the present invention is to provide a configuration that can suppress the temperature rise of the developer in the developer container while suppressing the gap between the regulating member and the developer carrier from becoming uneven. [Means for solving the problem]

[0008] The developing device of the present invention includes a developer container that contains a developer, a developer carrier that rotates to carry and transport the developer in the developer container in order to develop an electrostatic latent image formed on an image carrier, a regulating member that faces the surface of the developer carrier with a predetermined gap therebetween and regulates the layer thickness of the developer carried on the developer carrier, and a development-side duct portion that constitutes a part of a cooling duct through which air flows to cool the developer in the developer container and has a higher thermal conductivity than the developer container, and the development-side duct portion is located upstream of the regulating member in the rotation direction of the developer carrier. and a position where the regulating member is not contacted. and has a contact portion that contacts a developer reservoir that is generated upstream of the regulating member when the developer carrier rotates to carry and transport the developer. The material of the contact portion is different from the material of the regulating member. It is characterized by: [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress the temperature rise of the developer in the developer container, while suppressing the gap between the regulating member and the developer carrier from becoming uneven. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Figure 2]FIG. 2 is a cross-sectional view showing the schematic configuration of a developing device according to the embodiment. [Figure 3] FIG. 3 is a schematic diagram showing an air blowing path to a developing device according to an embodiment. [Figure 4] FIG. 2 is a perspective view of a developing device and a cooling duct according to the embodiment. [Figure 5] FIG. 2 is a schematic cross-sectional view of a developing device according to an embodiment, illustrating the state of developer in a developing container. DETAILED DESCRIPTION OF THE INVENTION

[0011] The embodiment will be described with reference to Figures 1 to 5. First, the schematic configuration of the image forming apparatus of the present embodiment will be described.

[0012] [Image forming device] FIG. 1 is a schematic cross-sectional view showing an example of an image forming apparatus according to the present embodiment. The image forming apparatus 100 shown in FIG. 1 is an electrophotographic full-color laser printer. The image forming apparatus 100 forms four different color toner images through charging, exposure, development, and transfer processes using first, second, third, and fourth image forming units PY, PM, PC, and PK arranged side by side inside the image forming apparatus main body. Each image forming unit PY, PM, PC, and PK forms a yellow, magenta, cyan, and black toner image, respectively. The image forming units PY, PM, PC, and PK have the same configuration except for the developing color. In the following description, the Y, M, C, and K symbols indicating the configuration of each image forming unit will be omitted.

[0013] Image formation in the image forming apparatus 100 is performed as follows: The surface of the photosensitive drum 1, which serves as an image carrier, is uniformly charged by the charging device 2. An electrostatic latent image is formed on the photosensitive drum 1 by exposing this charged surface to light by the exposure device 3. Toner is applied from the developing device 4 to the electrostatic latent image thus obtained, and the image is developed into a toner image.

[0014] This toner image is transferred onto intermediate transfer belt 62 by primary transfer roller 61. After multiple color toner images are transferred onto intermediate transfer belt 62 in a superimposed state, the four color toner images are transferred onto a recording medium that has been conveyed from a feed cassette (not shown) through conveying rollers to a secondary transfer section where secondary transfer roller 63 and outer secondary transfer roller 64 come into contact. The recording medium is, for example, a sheet material such as paper or a plastic sheet.

[0015] The recording medium onto which the toner image has been transferred is heated and pressed by the fixing device 7 to fix the image, and then discharged outside the image forming apparatus 100. Any residual toner remaining on the photosensitive drum 1 after transfer is removed by the cleaning device 8.

[0016] [Developing device] Next, the developing device 4 of this embodiment will be described with reference to FIG. 2. The developing device 4 develops the electrostatic latent image formed on the photosensitive drum 1 with a developer containing toner and a carrier. The developer of this embodiment is a so-called two-component developer containing non-magnetic toner and a magnetic carrier. The developing device 4 includes a developer container 41 as a housing that contains the developer therein, and supports rotation of a first screw 46a, a second screw 46b, and a third screw 46c disposed in the developer container. The first screw 46a, the second screw 46b, and the third screw 46c as transport members agitate and transport the developer inside the developer container 41.

[0017] A first developing sleeve 44b as a developer carrier and a first developing sleeve 44b as a first developer carrier, and a second developing sleeve 45b as a second developer carrier are rotatably supported on the surface of the developing container 41 facing the photosensitive drum 1. The second developing sleeve 45b is located below the first developing sleeve 44b and is arranged in parallel with the first developing sleeve 44b with a predetermined gap therebetween.

[0018] The first developing sleeve 44b and the second developing sleeve 45b are each formed in a cylindrical shape, and magnetic rolls 44a and 45a serving as magnetic field generating means are disposed therein in a non-rotating manner. The first developing sleeve 44b and the second developing sleeve 45b are each driven to rotate in the direction of the arrows shown in FIG. 2, and the developer is carried and transported by the magnetic attraction force of the magnetic rolls 44a and 45a. A developing blade 42 serving as a regulating member is fixed to a position upstream of the surface of the first developing sleeve 44b facing the photosensitive drum, with a predetermined gap between them. The developing blade 42 regulates the thickness of the developer layer carried on the first developing sleeve 44b.

[0019] The developing container 41 is partitioned by a horizontally extending partition wall 48 into an upper developing chamber (developer transport path) 47a serving as a first chamber, and an agitating chamber (developer transport path) 47b located below the developing chamber 47a serving as a second chamber. The developing chamber 47a is a functional chamber that supplies developer to the first developing sleeve 44b. The agitating chamber 47b is a functional chamber that receives and agitates recovered developer recovered from the second developing sleeve 45b, excess developer that was not supplied to the first developing sleeve 44b in the developing chamber 47a, and replenishment developer replenished from outside the developing device 4.

[0020] The developing chamber 47a and the stirring chamber 47b are provided with a first screw 46a, a second screw 46b, and a third screw 46c, respectively. The first screw 46a, the second screw 46b, and the third screw 46c are all screw members with helical blades provided on rotation axes that are arranged substantially parallel to the rotational axis directions (longitudinal directions) of the first developing sleeve 44b and the second developing sleeve 45b.

[0021] A first communication portion and a second communication portion, which are transfer portions (developer transport paths) that transport developer between the developing chamber 47a and the stirring chamber 47b, are provided on both longitudinal end sides of the partition wall 48. The first screw 46a and the second screw 46b transport developer in opposite directions. The developer moves from the stirring chamber 47b to the developing chamber 47a through the first communication portion, and the developer moves from the developing chamber 47a to the stirring chamber 47b through the second communication portion, thereby forming a developer circulation path.

[0022] The developer transported by the second screw 46b and the first screw 46a is transported along the surface of the first developing sleeve 44b and is limited to a predetermined thickness by the developing blade 42. Then, at a development position facing the photosensitive drum 1, the developer develops the electrostatic latent image formed on the surface of the photosensitive drum 1. The developer remaining on the first developing sleeve 44b is transported by the first developing sleeve 44b, then transferred to the second developing sleeve 45b, and transported along the surface of the second developing sleeve 45b, and then collected into the developing container 41 through between the second developing sleeve 45b and the collection roller 46d. The developer collected in the developing container 41 is stirred and transported by the third screw 46c and the second screw 46b, and then transported to the first screw 46a.

[0023] In this embodiment, the developer contained in the developing container 41 is a two-component developer made by mixing negatively charged non-magnetic toner and magnetic carrier. The non-magnetic toner is made by incorporating colorants, wax components, etc. into resins such as polyester or styrene, and then pulverizing or polymerizing it to form a powder. The average particle size used is 5 μm. The magnetic carrier is made by coating the surface of a core made of resin particles kneaded with ferrite particles or magnetic powder.

[0024] The process of developing toner onto the photosensitive drum 1 in the development area will be described. After the photosensitive drum 1 is uniformly charged to a charging potential Vd [V] by the charging device 2, the image area is exposed to an exposure potential Vl [V] by the exposure device 3. A DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the first developing sleeve 44b and the second developing sleeve 45b. When the DC component voltage of the first developing sleeve 44b and the second developing sleeve 45b is Vdc, the absolute value of the difference between the exposure potential and Vcont is called |Vdc-Vl|, which creates an electric field that transports toner to the image area. The absolute value of the difference between the DC voltage Vdc and the charging potential Vd is called |Vdc-Vd|, which creates an electric field that pulls toner back from the photosensitive drum 1 to the first developing sleeve 44b and the second developing sleeve 45b. This is provided to prevent toner from adhering to non-image areas, known as fogging.

[0025] In this embodiment, the developer carrier is described as having two sleeves, a first developing sleeve and a second developing sleeve, but this is not limited to this and the developer carrier may be one or three or more.

[0026] [Cooling structure of the developing device] Next, the cooling configuration of developing device 4 will be described with reference to Figures 2 to 5. As shown in Figures 3 and 4, image forming apparatus 100 is provided with air intake fan 57 that supplies air from outside image forming apparatus 100 into image forming apparatus 100. In this embodiment, a sirocco fan is used as air intake fan 57, and it is installed on the back surface of image forming apparatus 100. Outside air is introduced by air intake fan 57, and the introduced air passes through air intake duct 58 provided inside a door on the front surface of image forming apparatus 100, and is sent as cooling air to cooling duct 53 above developing device 4.

[0027] 2, the cooling duct 53 has a duct wall 52, a heat sink 51, and a plurality of ribs 54. The duct wall 52, which serves as a main body-side duct portion, is provided on the image forming apparatus main body side. The duct wall 52 may be made of the same material as the heat sink 51, or may be made of a different material. The duct wall 52 is preferably made of a material having a higher thermal conductivity than the developing container 41. In this embodiment, the duct wall 52 is made of a metal such as an aluminum alloy, but may also be made of a resin having a high thermal conductivity, similar to the heat sink 51 described below.

[0028] On the other hand, the heat sink 51 as a development-side duct portion is provided on the developer container side, and forms an airflow space 53a through which airflow flows between it and the duct wall 52. A plurality of ribs 54 as a plurality of heat dissipation portions are provided so as to protrude from the heat sink 51 toward the airflow space. The plurality of ribs 54 are arranged along the direction in which the airflow flows within the cooling duct 53. In this embodiment, the cooling duct 53 through which airflow can pass is formed between the duct wall 52 and the heat sink 51. Furthermore, a plurality of ribs 54 are arranged in the airflow space 53a within the cooling duct along the airflow direction W.

[0029] The cooling duct 53 will be described in more detail. A heat sink 51 made of a material with a higher thermal conductivity than the developing container 41 is disposed in the upper part of the developing device 4. In this embodiment, the heat sink 51 also functions as a top cover that covers the upper part of the developing container 41, and is disposed above the developing chamber 47a in the longitudinal direction. For example, the developing container 41 is made of PC+ABS (polycarbonate-acrylonitrile-butadiene-styrene mixture) resin, and the heat sink 51 is made of an aluminum alloy. Note that the heat sink 51 may be made of other metals, such as copper, as long as it has a higher thermal conductivity than the developing container 41, or may be made of a resin material with a high thermal conductivity function.

[0030] The heat sink 51 has a contact wall portion 55 having a contact surface 55a that can come into contact with the developer in the developing container 41. The plurality of ribs 54 are provided so as to protrude from a heat dissipation surface 55b, which is the surface of the contact wall portion 55 opposite to the contact surface 55a. In this embodiment, the plurality of ribs 54 are arranged with a thickness of 1 mm, intervals of 3 mm, and a height of 8 mm, and are configured to increase the surface area while preventing the impedance of the cooling air from becoming large.

[0031] [Developing blade] Next, the configuration of the developing blade 42 of the developing device 4 will be described with reference to FIG. 5. FIG. 5 shows the vicinity of the developing blade 42 of the developing device 4. The hatched portion in FIG. 5 indicates the developer. As described above, in the developing device 4, the developing blade 42 serves as a developer regulating member that regulates the amount of developer carried on the surface of the first developing sleeve 44b (also called the developer coat amount), and faces the surface of the first developing sleeve 44b in a non-contact manner. The developing blade 42 is supported by a support member 43.

[0032] Such a developing blade 42 regulates the amount of developer carried on the surface of the first developing sleeve 44b. The developing blade 42 and the support member 43 are made of the same material, or materials with similar thermal expansion coefficients so as not to affect fluctuations in the SB gap (the gap between the developing blade 42 and the first developing sleeve 44b) under the usage environment. In addition, fluctuations in the position of the developing blade 42 due to temperature changes such as temperature increases due to self-heating of the developer or temperature decreases due to cooling of the heat sink 51 are prevented, thereby preventing image defects from occurring.

[0033] [Cooling of developer upstream of the developing blade] As described above, if the temperature of the developer in the developing container 41 rises, the chargeability of the toner deteriorates, and there is a risk of image defects such as a drop in image density. In particular, if the temperature of the toner rises above its melting point, the toner melts and adheres to the developing sleeve or developing blade. This can cause the amount of developer coated on the developing sleeve to become uneven, which can lead to image defects such as uneven density and streaks.

[0034] One possible solution is to bring a highly heat-conductive member into contact with the developing blade and use it to cool the developer, but if the developing blade and the highly heat-conductive member are made of different materials, the difference in thermal expansion may cause the position of the developing blade to fluctuate, which may result in unevenness in the SB gap in the longitudinal direction and lead to image defects.

[0035] For this reason, in this embodiment, the developing blade 42 is supported by a support member 43 made of the same material or a member with a similar thermal expansion coefficient. Meanwhile, a portion of the heat sink 51 is inserted into a developer reservoir upstream of the developing blade 42 to cool the developer. That is, the heat sink 51 is located upstream of the developing blade 42 in the rotation direction of the first developing sleeve 44b, and has a contact portion 56 that comes into contact with the developer reservoir 49 that is generated upstream of the developing blade 42 when the first developing sleeve 44b rotates to carry and transport the developer. In other words, the contact portion 56 comes into contact with the developer reservoir (accumulation area) 49 whose circulation is restricted by the developing blade 42.

[0036] In this way, the contact portion 56, which is a part of the heat sink 51, is formed to protrude from the contact wall portion 55 toward the first developing sleeve 44b. By bringing the contact portion 56 into contact with the developer reservoir 49, the slow-moving developer present in the developer reservoir 49 can be cooled, and the temperature of the developer can be sufficiently reduced before the developer passes through the gap between the developing blade 42 and the first developing sleeve 44b. This makes it possible to efficiently prevent the developer from becoming too hot due to frictional heat generated when passing through the gap.

[0037] The heat sources of the developer are the self-heating caused by the circulation of the developer itself and frictional heat caused by friction between the developer particles as the developer passes through the gap between the developing blade 42 and the first developing sleeve 44b. With the above configuration, the circulating developer comes into contact with the contact surface 55a of the heat sink 51 and is cooled, while the developer reservoir 49 is cooled by the contact portion 56, which is part of the heat sink 51. This allows the temperature of the developer to be sufficiently reduced before it passes through the gap between the developing blade 42 and the first developing sleeve 44b, preventing the developer temperature from becoming too high. This allows for a more compact device and suppresses image defects caused by a rise in developer temperature.

[0038] The position of the contact portion 56 is set as follows in relation to the magnetic pole of the magnet roll 44a disposed inside the first developing sleeve 44b: First, the magnet roll 44a is a non-rotating magnetic field generating means having multiple magnetic poles, including a regulating magnetic pole disposed in a position facing the developing blade 42 with the first developing sleeve 44b interposed therebetween, and a pumping pole disposed upstream of the regulating magnetic pole in the rotation direction of the first developing sleeve 44b, for pumping the developer in the developer container onto the surface of the first developing sleeve 44b.

[0039] The contact portion 56 is located in an area facing the first developing sleeve 44b across a gap that is larger than the gap (predetermined gap) between the developing blade 42 and the first developing sleeve 44b, in the range from the draw-up pole to the regulating magnetic pole in the rotation direction of the first developing sleeve 44b. By arranging the contact portion 56 in this manner, the contact portion 56 can be located in the developer reservoir 49. Furthermore, because the contact portion 56 is located farther from the first developing sleeve 44b than the developing blade 42, the contact portion 56 does not impede the transport of the developer or regulate the thickness of the developer layer on the first developing sleeve 44b.

[0040] In this embodiment, the heat sink 51 including the contact portion 56 is made of an aluminum alloy, but other metals such as copper, or resin may be used as long as they have high thermal conductivity. On the other hand, the developing blade 42 and the support member 43 are preferably made of stainless steel because they require strength, rigidity, and processing precision. Even if the developing blade 42 and the support member 43 are made of different materials, they are preferably made of materials with a thermal expansion coefficient that ensures that the amount of thermal deformation due to temperature changes in the expected usage environment is no more than several tens of micrometers.

[0041] The support member 43 and the contact portion 56 are made of different materials, and the support member 43 has higher rigidity than the contact portion 56. This is because the contact portion 56 is used for cooling and can be made of a material with low rigidity, but the support member 43 must have rigidity in order to support the developing blade 42.

[0042] The contact portion 56 is shaped like a plate with a longitudinal length that is approximately the same as that of the developing blade 42. However, the shape of the contact portion 56 is not limited to this. Since it is desirable for the contact portion 56 to have a shape that provides a large contact area with the developer, for example, the surface may be uneven. If unevenness is formed, it is desirable that the shape does not obstruct the flow of the developer. Furthermore, from the perspective of enhancing the cooling effect, the contact portion 56 may be shaped like a cylinder that allows cooling air to pass through the inside.

[0043] 5, in this embodiment, the rotation direction of the first screw 46a is set to a direction that scrapes up the toner toward the heat sink 51. This allows for more efficient cooling of the developer. That is, the developer amount distribution in the lateral direction perpendicular to the longitudinal direction of the first screw 46a is greater on the heat sink 51 side, and the surface area of ​​the developer in contact with the heat sink 51 increases, further improving cooling efficiency. [Explanation of symbols]

[0044] 1 (1Y, 1M, 1C, 1K)...Photosensitive drum (image carrier) 4(4Y, 4M, 4C, 4K)...Development device 41 Developer container 42 Developing blade (regulating member) 43 Support member 44a: Magnet roll (magnetic field generating means) 44b: First developing sleeve (developer carrier, first developer carrier) 45b: Second developing sleeve (second developer carrier) 49 Developer reservoir 51 Heat sink (development side duct part) 53 Cooling duct 53a Airflow space 54 Rib (heat dissipation part) 55...Contact wall part 55a...Contact surface 56...Contact part

Claims

1. a developer container that contains a developer; a developer carrier that rotates to carry and transport the developer in the developer container in order to develop the electrostatic latent image formed on the image carrier; a regulating member that faces the surface of the developer carrier with a predetermined gap therebetween and regulates the layer thickness of the developer carried on the developer carrier; a development-side duct portion that constitutes a part of a cooling duct through which air flows to cool the developer in the developer container, the development-side duct portion having a higher thermal conductivity than the developer container; the development-side duct portion is located upstream of the regulating member in the rotation direction of the developer carrier and at a position not in contact with the regulating member, and has a contact portion that comes into contact with a developer reservoir that is generated upstream of the regulating member when the developer carrier rotates to carry and transport the developer, The material of the contact portion is different from the material of the regulating member. A developing device characterized by:

2. a non-rotating magnetic field generating means having a plurality of magnetic poles, including a regulating magnetic pole disposed inside the developer carrier and positioned opposite the regulating member with the developer carrier interposed therebetween, and a pumping pole disposed upstream of the regulating magnetic pole in the direction of rotation of the developer carrier and configured to pump the developer in the developing container onto the surface of the developer carrier, The contact portion is located in a region facing the developer carrier across a gap larger than the predetermined gap, in a range from the scooping pole to the regulating magnetic pole in the rotation direction of the developer carrier.

2. The developing device according to claim 1.

3. a support member for supporting the restricting member, The support member has a higher rigidity than the contact portion.

3. The developing device according to claim 1, wherein the developing device is a developing unit.

4. The developing-side duct portion has a plurality of heat dissipation portions provided so as to protrude into an airflow space in the cooling duct where air flows.

4. The developing device according to claim 1, wherein the developing device is a developing unit.

5. the developing-side duct portion has a contact wall portion having a contact surface capable of coming into contact with the developer in the developing container, The contact portion is formed to protrude from the contact wall portion toward the developer carrier.

5. The developing device according to claim 1, wherein the developing device is a developing unit.

6. When the developer carrier is a first developer carrier, the developing device has a second developer carrier that is arranged in parallel with the first developer carrier with a predetermined gap therebetween and carries and transports developer in order to develop an electrostatic latent image formed on the image carrier.

6. The developing device according to claim 1, wherein the developing device is a developing unit.

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