JP7739078B2 - Developing device - Google Patents

Description

The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier using a developer.

In electrophotographic image forming devices, a toner image is formed by using a developing device to develop an electrostatic latent image formed on an image carrier such as a photosensitive drum. 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. It also has a transport member that agitates and transports the developer within the developer container.

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

For this reason, a configuration has been proposed in which a highly thermally conductive member is installed inside the developing device, and this highly thermally conductive member cools the developer inside the developing container by coming into contact with the regulating member (Patent Document 1).

Japanese Patent Application Laid-Open No. 2005-266249

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, there is a risk that the position of the regulating member will fluctuate due to differences in the thermal expansion of the materials. In this case, there is a risk that the gap between the regulating member and the developer carrier will be uneven in the longitudinal direction, resulting in poor image quality.

The present invention aims to provide a configuration that can suppress temperature increases in the developer inside the developer container while preventing the gap between the regulating member and the developer carrier from becoming uneven.

The developing device of the present invention comprises a developing container that contains developer, a developer carrier that rotates to carry and transport the developer in the developing 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 via a predetermined gap and regulates the layer thickness of the developer carried on the developer carrier, and a developing side duct portion that forms part of a cooling duct through which air flows to cool the developer in the developing container and has a higher thermal conductivity than the developing container, wherein the developing side duct portion is located upstream of the regulating member in terms of the rotation direction of the developer carrier but at a position that does not contact the regulating member, and has a contact portion that comes into contact with a developer puddle that occurs upstream of the regulating member when the developer carrier rotates to carry and transport the developer, and the material of the contact portion is different from the material of the regulating member .

This invention makes it possible to suppress temperature increases in the developer inside the developer container while also preventing the gap between the regulating member and the developer carrier from becoming uneven.

1 is a schematic diagram of an image forming apparatus according to an embodiment. FIG. 2 is a cross-sectional view showing the schematic configuration of a developing device according to the embodiment. FIG. 3 is a schematic diagram showing an air blowing path to a developing device according to an embodiment. FIG. 2 is a perspective view of a developing device and a cooling duct according to the embodiment. 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.

This embodiment will be described using Figures 1 to 5. First, the general configuration of the image forming apparatus of this embodiment will be described.

[Image forming apparatus]
FIG. 1 is a schematic cross-sectional view illustrating 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, which are 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 color of development. In the following description, the Y, M, C, and K symbols indicating the configuration of each image forming unit will be omitted.

Image formation in the image forming apparatus 100 is carried out 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 using the exposure device 3. Toner is then applied from the developing device 4 to the electrostatic latent image thus obtained, thereby developing it into a toner image.

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 layers, the four color toner images are transferred onto a recording medium transported from a feed cassette (not shown) via a transport roller 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.

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 ejected from the image forming apparatus 100. Any residual toner remaining on the photosensitive drum 1 after transfer is removed by the cleaning device 8.

[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 46 a, a second screw 46 b, and a third screw 46 c disposed within the developer container. The first screw 46 a, the second screw 46 b, and the third screw 46 c as transport members agitate and transport the developer inside the developer container 41.

A first developing sleeve 44b, which serves as a developer carrier and a first developing sleeve, and a second developing sleeve 45b, which serves as a second developing sleeve, 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 parallel to the first developing sleeve 44b with a predetermined gap between them.

The first developing sleeve 44b and the second developing sleeve 45b are each cylindrical, and have magnetic rolls 44a and 45a, respectively, disposed therein as non-rotating magnetic field generating means. The first developing sleeve 44b and the second developing sleeve 45b are each driven to rotate in the direction of the arrows shown in Figure 2, and the magnetic attraction force of the magnetic rolls 44a and 45a carries and transports developer. Furthermore, a developing blade 42, which serves as a regulating member, is fixed to a position upstream of the surface of the first developing sleeve 44b that faces the photosensitive drum, with a predetermined gap between it and the surface of the first developing sleeve 44b. The developing blade 42 regulates the thickness of the developer layer carried on the first developing sleeve 44b.

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 not supplied to the first developing sleeve 44b in the developing chamber 47a, and replenished developer replenished from outside the developing device 4.

A first screw 46a, a second screw 46b, and a third screw 46c are provided in the developing chamber 47a and the stirring chamber 47b, respectively. The first screw 46a, the second screw 46b, and the third screw 46c are all screw members with helical blades on rotational axes that are positioned approximately parallel to the rotational axis direction (longitudinal direction) of the first developing sleeve 44b and the second developing sleeve 45b.

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

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

In this embodiment, the developer contained in the developer container 41 is a two-component developer consisting of a mixture of negatively charged non-magnetic toner and magnetic carrier. The non-magnetic toner is made by incorporating colorants, wax components, etc. into a resin such as polyester or styrene, and then pulverizing or polymerizing it into a powder. The average particle size used was 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.

This section explains the process of developing toner onto the photosensitive drum 1 in the development area. After the photosensitive drum 1 is uniformly charged to a charging potential Vd [V] by the charging device 2, the image area is exposed by the exposure device 3 to an exposure potential Vl [V]. A DC voltage, or a voltage consisting of a DC voltage superimposed on an AC voltage, is applied to the first developing sleeve 44b and the second developing sleeve 45b. When the DC component of the 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, |Vdc - Vl|, is called Vcont, and this 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, |Vdc - Vd|, is called Vback, and 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 designed to prevent toner from adhering to non-image areas, a phenomenon known as fogging.

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.

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

As shown in FIG. 2, the cooling duct 53 has a duct wall 52, a heat sink 51, and multiple ribs 54. The duct wall 52, which serves as the main body duct section, 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 a different material. Furthermore, the duct wall 52 is preferably made of a material with a higher thermal conductivity than the developing container 41. In this embodiment, the duct wall 52 is made of metal, such as an aluminum alloy, but it may also be made of a resin with a high thermal conductivity, similar to the heat sink 51 described below.

Meanwhile, the heat sink 51 serving as the development-side duct portion is provided on the developer container side, and forms an airflow space 53a through which air flows between it and the duct wall 52. A plurality of ribs 54 serving as heat dissipation portions are provided to protrude from the heat sink 51 into the airflow space. The ribs 54 are arranged along the direction of airflow 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.

The cooling duct 53 will now 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 above the developing device 4. In this embodiment, the heat sink 51 also functions as a top lid covering the top 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 they have a higher thermal conductivity than the developing container 41, or a resin material with added high thermal conductivity properties.

The heat sink 51 has a contact wall portion 55 with a contact surface 55a that can come into contact with the developer in the developing container 41. Multiple ribs 54 are provided to protrude from the heat dissipation surface 55b, which is the surface of the contact wall portion 55 opposite the contact surface 55a. In this embodiment, the multiple ribs 54 are arranged with a thickness of 1 mm, spaced 3 mm apart, and a height of 8 mm, which increases the surface area while preventing the impedance of the cooling air from increasing.

[Developing blade]
Next, the configuration of the developing blade 42 of the developing device 4 will be described using Figure 5. Figure 5 shows the vicinity of the developing blade 42 of the developing device 4. The hatched area in Figure 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.

This type of developing blade 42 regulates the amount of developer carried on the surface of the first developing sleeve 44b. The developing blade 42 and supporting 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 operating environment. This also prevents the position of the developing blade 42 from fluctuating and resulting in poor image quality due to temperature changes such as temperature increases caused by the self-heating of the developer or temperature decreases caused by cooling the heat sink 51.

[Cooling of developer upstream of development blade]
As described above, if the temperature of the developer in the developer container 41 rises, the charging property of the toner deteriorates, and there is a risk of image defects such as a decrease 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.

One option is to bring a highly thermally conductive member into contact with the developing blade and use the developing blade to cool the developer. However, if the developing blade and the highly thermally conductive member are made of different materials, there is a risk that the position of the developing blade will fluctuate due to differences in thermal expansion. This could result in unevenness in the SB gap in the longitudinal direction, potentially resulting in poor image quality.

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 the 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 forms 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 (stagnation area) 49, the circulation of which is restricted by the developing blade 42.

In this way, the contact portion 56, which is 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 it passes through the gap between the developing blade 42 and the first developing sleeve 44b. This effectively prevents the developer from becoming too hot due to frictional heat generated when passing through the gap.

The heat sources of the developer are the self-heating caused by the developer itself circulating and frictional heat caused by friction between the developer as it 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 from becoming too hot. This not only allows for a more compact device, but also reduces image defects caused by rising developer temperatures.

The position of the contact portion 56 is as follows, relative to the magnetic pole of the magnet roll 44a disposed within 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 across the first developing sleeve 44b, and a pumping pole disposed upstream of the regulating magnetic pole in the direction of rotation of the first developing sleeve 44b, which pumps the developer in the developing container onto the surface of the first developing sleeve 44b.

The contact portion 56 is located in an area facing the first developing sleeve 44b across a gap larger than the gap (predetermined gap) between the developing blade 42 and the first developing sleeve 44b, in the range from the drawing pole to the regulating magnetic pole in the direction of rotation of the first developing sleeve 44b. By arranging it in this manner, the contact portion 56 can be positioned in the developer reservoir 49. Furthermore, because the contact portion 56 is farther away 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.

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 support member 43 are preferably made of stainless steel, as they require strength, rigidity, and processing precision. Even if the developing blade 42 and 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 microns.

The support member 43 and contact portion 56 are made of different materials, with the support member 43 being more rigid than the contact portion 56. This is because the contact portion 56 is used for cooling purposes and can be made of a material with low rigidity, whereas the support member 43 requires rigidity to support the development blade 42.

The contact portion 56 is shaped like a plate with a longitudinal length roughly the same as that of the developing blade 42. However, the shape of the contact portion 56 is not limited to this. It is desirable for the contact portion 56 to have a shape that provides a large contact area with the developer, so for example, the surface may be uneven. If unevenness is formed, it is desirable that the shape does not impede the flow of the developer. Furthermore, from the perspective of enhancing the cooling effect, the contact portion 56 may be cylindrical in shape, allowing cooling air to pass through the inside.

In this embodiment, as shown in Figure 5, the rotation direction of the first screw 46a is set to a direction that scrapes up toner toward the heat sink 51. This allows for more efficient cooling of the developer. That is, the developer amount distribution in the short direction, which is perpendicular to the long 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.

1 (1Y, 1M, 1C, 1K)...photosensitive drum (image carrier)
4 (4Y, 4M, 4C, 4K)...Developing device 41...Developing 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 portion)
53: Cooling duct 53a: Airflow space 54: Rib (heat dissipation portion)
55...Contact wall part 55a...Contact surface 56...Contact part

Claims (6)

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: 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 developing device according to claim 1, wherein the contact portion is located in an area 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 rotational direction of the developer carrier. a support member for supporting the regulating member,
3. The developing device according to claim 1, wherein the support member has a higher rigidity than the contact portion. 4. The developing device according to claim 1, wherein the developing-side duct portion has a plurality of heat-dissipating portions provided so as to protrude into an airflow space in the cooling duct where an airflow flows. 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,
5. The developing device according to claim 1, wherein the contact portion is formed so as to protrude from the contact wall portion toward the developer carrier. 6. The developing device according to claim 1, wherein when the developer carrier is a first developer carrier, the developing device further comprises a second developer carrier arranged in parallel with the first developer carrier via a predetermined gap, which carries and transports the developer, in order to develop the electrostatic latent image formed on the image carrier.