JP2010097125A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device that reduces the degree of deterioration of carrier without increasing the amount of discharged developer. <P>SOLUTION: A supply screw 26 for supplying developer to a developing roller 24 and an agitating screw 25 disposed parallel to the supply screw 26 are provided with spiral vanes 29 and 30, respectively, which convey developer in opposite directions and reverse a conveyance direction at least in one area. Circulation holes 31, 32, and 33 for permitting developer passage are formed in a partition 28 at both ends of each of the spiral vanes 29 and 30 and at a position opposite the position where the conveyance direction reverses. Accordingly, a plurality of circulation paths R1 and R2 where the developer circulates between the adjacent circulate holes 31, 32, and 33 are formed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing device and an image forming apparatus.

  In a developing device of a two-component development type image forming apparatus using a developer including a toner and a carrier, the carrier is replenished with the toner, and the developer is discharged little by little, whereby the carrier is gradually replaced with a new one. A trickle developing device is known.

  In the conventional developing apparatus, the average residence time of the carrier in the apparatus, that is, the degree of deterioration of the carrier is determined by the balance between the amount of the developer in the developing apparatus and the developer supplied and discharged. In order to suppress the deterioration of the image quality due to the deterioration of the carrier, it is sufficient to increase the discharge amount of the developer. However, if the discard amount of the developer increases, it is uneconomical and the maintenance of the collection bottle becomes complicated.

  In Patent Document 1, the developer is not discharged until the developer in the apparatus exceeds a certain amount, and a new carrier is prevented from being discharged. In this method, the carrier utilization efficiency is increased, but the degree of deterioration of the carrier in the apparatus is increased, leading to a decrease in image quality.

Patent Document 2 describes an invention in which a plurality of developer circulation paths are provided in a developing device to homogenize the developer in the device, but it prevents image quality deterioration due to carrier deterioration. I can't.
JP 2007-78757 A JP-A-9-127771

  In view of the above problems, an object of the present invention is to provide a developing device and an image forming apparatus that can reduce the degree of carrier deterioration without increasing the developer discharge amount.

  In order to solve the above-described problems, a developing device according to the present invention rotates a replenishment port for replenishing a developer containing toner and a carrier, adsorbs the carrier on the surface, and supports the toner by the adsorbed carrier. A developing roller that feeds the developer in an axial direction while stirring the developer, and a spiral screw for supplying the developer to the developing roller, and is arranged in parallel with the supply screw, A stirring screw provided with a spiral blade for conveying the developer in the axial direction while stirring the developer, a partition wall separating the supply screw and the stirring screw, and the developer having a certain height or more are allowed to flow out. In the developing device having a discharge port, the spiral blades of the supply screw and the stirring screw convey the developer in opposite directions, and At least in one place, the conveyance direction is reversed, and the partition wall is formed with a circulation hole allowing passage of the developer at a portion facing both ends of the spiral blade and a position where the conveyance direction is reversed. A plurality of circulation paths that circulate between the circulation holes adjacent to each other are formed.

  According to this configuration, while the developer circulates in each of the plurality of circulation paths, the developer is partially mixed with the developer in the adjacent circulation path, so that the circulation path having the replenishing port is changed to the adjacent circulation path. The degree of deterioration of the carrier gradually increases. By discharging the developer in the circulation path with a high degree of deterioration from the discharge port, the carrier of the developer discharged is deteriorated compared to the amount of developer discharged even if the developer replenishment amount is the same as before. The degree of deterioration becomes higher, and the average value of the degree of deterioration of the carrier staying in the developing device becomes lower. The image formed using this developing device is slightly inferior to the image formed using the conventional developing device, although the image quality of the portion where the developer is supplied from the circulation path with the discharge port is somewhat inferior. Since the image quality of the portion to which the developer is supplied from the circulation path is improved, the overall image has a small decrease in image quality due to carrier deterioration.

  Further, in the developing device according to the present invention, the discharge port is provided in the circulation path farthest along the transport direction of the developer by the supply screw and the stirring screw from the position where the supply port is provided. Preferably it is.

  According to this configuration, since the developer is discharged from the circulation path on the most downstream side where the deterioration degree of the carrier becomes the highest, the discharge efficiency of the old carrier is high, and the deterioration degree of the carrier of the entire developing device is effectively reduced. Be made.

  In the developing device according to the present invention, the circulation hole is an opening facing at least one pitch of the spiral blade on both sides from a position where the feeding direction of the spiral blade of the supply screw and the stirring screw is reversed. Also good.

  According to this configuration, since the circulation hole is sufficiently large, it becomes difficult for the developer to mix with the developer in the adjacent circulation path when passing through the circulation hole, and the carrier deterioration degree of the downstream circulation path becomes high, Since the ratio of new carriers discharged from the discharge port is reduced, the degree of deterioration of the carriers is lowered as a whole.

  In the developing device according to the present invention, at least one end of the spiral blade of the supply screw conveys the developer toward the inner side in the axial direction, and the supply port feeds the developer of the supply screw in the axial direction. You may provide in the edge part conveyed toward an inner side.

  According to this configuration, since the most upstream circulation path is formed at one end of the developing device and the most downstream circulation path is formed at the other end, the degree of carrier deterioration monotonously increases from the supply port to the discharge port, The old carrier can be discharged efficiently. Further, since the developer is supplied to the supply screw, the residence time until a new developer is supplied to the developing roller is shortened, and the quality of an image to be formed can be improved.

  In the developing device according to the present invention, the supply screw may collect the developer from the developing roller.

  According to this configuration, since the developer supplied from the circulation path to the developing roller is collected at the same position in the circulation path, the developer does not bypass a part of the circulation path, and the degree of deterioration of the developer. Gradually changes in accordance with the feeding direction of the supply screw and the stirring screw. Thereby, the residence time of the carrier is shortened toward the upstream side, and the carrier having a high degree of deterioration on the downstream side is discharged, whereby the average value of the degree of deterioration of the carrier in the developing device can be kept low.

  The image forming apparatus according to the present invention includes any one of the above developing devices.

  According to the present invention, the spiral blades of the supply screw and the stirring screw that convey the developer in opposite directions are reversed in the middle, and are circulated to both ends of the partition wall between the supply screw and the stirring screw and the reverse position of the spiral blade. By forming holes and forming a plurality of circulation paths around which the developer circulates between adjacent circulation holes, the average residence time of the developer becomes longer in the downstream circulation path, and the carrier having a high degree of deterioration from the discharge port Therefore, the average residence time of the developer in the developing device can be shortened, and the deterioration of the image quality due to the deterioration of the carrier can be reduced.

  Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a configuration of an image forming apparatus 1 according to the first embodiment of the present invention.

  The image forming apparatus 1 includes four developing units 2Y, 2M, 2C, and 2K that form images with toners having negative charges of yellow, magenta, cyan, and black, transfer belts 3, and developing units 2, respectively. A primary transfer roller 4 for transferring the toner image to the transfer belt 3 by electrostatic force, a secondary transfer roller 5 for transferring the toner image transferred to the transfer belt 3 to the recording paper S by electrostatic force, and the recording paper S A fixing device 6 for fixing the toner image by heating the toner, and four toner cartridges 7Y, 7M, 7C and 7K for supplying yellow, magenta, cyan or black toner together with the carrier to each developing unit 2, respectively. Yes.

  Each of the developing units 2Y, 2M, 2C, and 2K includes a rotating drum-shaped photoconductor 8, a charger 9 that charges the photoconductor 8, and a charged photoconductor 8 that is selectively exposed to electrostatic latent image. An exposure device 10 that forms an image, a developing device 11 that supplies toner to an electrostatic latent image to form a toner image, and a lubricant application device 12 that applies a lubricant to the surface of the photoreceptor 9. And a cleaning blade 13 that scrapes off the toner on the surface of the photoconductor 9.

  The transfer belt 3 is stretched around a driving roller 14 that is rotationally driven, a driven roller 15, and a tension roller 16 that applies tension, and is rotated by the driving roller 14 in the direction of the arrow. Further, the image forming apparatus 1 includes a cleaner unit 17 that scrapes off toner remaining on the surface of the transfer belt 3.

  The recording paper S is supplied to the paper supply unit 18, fed one by one by the supply roller 19, transported to the secondary transfer roller 5 by the transport roller 20, passes through the fixing device 6, and is discharged by the paper discharge roller 21. 22 is discharged.

  FIG. 2 shows details of the developing device 11. The developing device 11 has a housing 23 containing a developer P containing toner and a carrier (for example, a toner ratio of 7%), adsorbs the carrier in the housing 23 on the surface, and carries the toner by the adsorbed carrier chain. The developing roller 24 that rotates and carries the toner out of the housing 23 and supplies it to the photosensitive member 8, the stirring screw 25 that transports the developer P in the housing 23 in the axial direction while stirring, and the developer P that is transported by stirring. The supply screw 26 supplied to the developing roller 24 and a plate that regulates the thickness of the developer P (carrier for carrying toner) carried on the developing roller 24 to keep the amount of toner supplied to the photosensitive member 8 constant. Partitioning member 27 and the housing 23 are divided into a space occupied by the stirring screw 25 and a space occupied by the supply screw 26. And a 28.

  FIG. 3 shows a horizontal section of the developing device 11. The stirring screw 25 and the supply screw 26 have spiral blades 29 and 30 for stirring and conveying the developer P in the axial direction, respectively. The spiral blade 29 and the spiral blade 30 are formed in a reverse spiral shape, and the turning direction is reversed at the center. The stirring screw 25 and the supply screw 26 are rotationally driven in the same direction. However, since the spiral blade 29 and the spiral blade 30 are formed in opposite directions, the developer P is reversed in each axial direction. Transport in the direction.

  In the partition wall 28, the space occupied by the stirring screw 25 and the supply screw 26 occupy the both ends of the spiral blades 29 and 30 of the stirring screw 25 and the supply screw 26 and the portions facing the positions where the conveying direction is reversed, respectively. Circulation holes 31, 32, and 33 are formed to communicate with the space. The circulation holes 31 and 32 at both ends are opened slightly larger than one pitch of the spiral blades 29 and 30, respectively. The central circulation hole 33 is slightly larger than one pitch of the spiral blades 29 and 30 on the both sides in the axial direction of the stirring screw 25 and the supply screw 26 from the position where the conveying direction of the spiral blades 29 and 30 is reversed. The opening is larger than the two pitches of the spiral blades 29 and 30.

  In the developing device 11, the developer P circulates through two circulation paths R <b> 1 and R <b> 2 indicated by arrows in the drawing by the rotation of the stirring screw 25 and the supply screw 26. When the developer P passes through the central circulation hole 33, about 10% of the developer P is exchanged between the two circulation paths R1 and R2. In other words, about 90% of the developer continues to circulate in the same circulation path R1, R2.

  Further, the toner cartridges 7Y and 7M are disposed in the housing 23 on the upper side of the supply screw 26 at a position indicated by a two-dot chain line, that is, an end portion of the supply screw 26 and a position where the developer P is conveyed inward in the axial direction. , 7C, 7K, supply ports 34 for supplying toner containing carriers (for example, carrier ratio 15%) are opened. Further, the housing 23 has a large opening at the end far from the supply port 34 through which the shaft of the stirring screw 25 passes, and a discharge port 35 for discharging the developer P having a certain height or more. Forming. A portion of the stirring screw 25 that passes through the discharge port 35 is provided with a spiral blade 36 that conveys the developer P toward the inside of the housing 23, and the height of the developer P is increased, so that the stirring screw is increased. The transport pressure of the developer P by the 25 spiral blades 29 is higher than the transport pressure of the developer P by the spiral blades 36, and the developer P is discharged from the discharge port 35. Since more toner and carrier than the toner supplied to the photoconductor 8 are continuously supplied from the supply port 34, the developer P is discharged little by little from the discharge port 35.

  The developer P that circulates in the upstream circulation path R1 to which new developer P is supplied from the supply port 34 has a short average residence time, but the downstream circulation path R2 enters the developing device 11 from the upstream circulation path 1. The developer P that has stayed and has already deteriorated to some extent is supplied. For this reason, the developer P in the downstream circulation path R2 has a longer average residence time than the upstream circulation path R1, and contains a large number of highly deteriorated carriers. Therefore, the developer P discharged from the discharge port 35 includes more carriers having a higher degree of deterioration than the average of the developer P in the developing device 11.

  Here, when compared with the conventional developing device having only one circulation path in the housing, when the amount of the developer newly supplied into the housing is the same, in this embodiment, the degree of deterioration is lower than in the conventional case. Discharge a lot of expensive carriers. Thereby, in this embodiment, the average residence time of the carrier in the housing 23 becomes shorter than before. In the present embodiment, the deterioration degree of the carrier in the downstream circulation path R2 is slightly higher than the conventional one, but the deterioration degree of the carrier in the upstream circulation path R1 is significantly lower than the conventional one. As a result, the quality of the toner image formed on the photoconductor 8 by the developing device 11 is half as high as the developer P is supplied from the upstream circulation path R1, and the developer P is supplied from the downstream circulation path R2. Although the quality of the remaining half is slightly inferior, the overall image is less deteriorated due to carrier deterioration than in the past.

  In the present embodiment, if the central circulation hole 33 is reduced, the amount of developer P exchanged between the two circulation paths R1 and R2 increases. Then, since the difference in the residence time of the developer P is reduced, it is desirable that the central circulation hole 33 is increased to some extent. In particular, if each of the circulation paths R1 and R2 is opened by one or more pitches of the spiral blades 29 and 30, the developer P is released from the stirring screw 25 and the supply screw 26 in the direction perpendicular to the axis, and the circulation path R1. , R2 can be circulated along the R2.

  In the present embodiment, the replenishment port 34 is provided on the upstream side in the transport direction of the supply screw 26, so that the replenished new developer P is easily supplied to the developing roller 24 in the upstream circulation channel R <b> 1. The adverse effect on the image quality due to the deteriorated carrier staying for a long time can be reduced.

  FIG. 4 shows a developing device 11a according to the second embodiment of the present invention. In the following description, the same components as those described above are denoted by the same reference numerals, and redundant description is omitted.

  In the developing device 11b, the spiral directions of the spiral blades 29 and 30 of the stirring screw 25 and the supply screw 26 are reversed so that the conveying directions are opposite at two locations. Accordingly, circulation holes 37 and 38 are provided in the partition wall 28 at two locations facing the reverse positions of the spiral blades 29 and 30. As a result, in the developing device 11b, three circulation paths R1, R2, and R3 are formed in the housing 23. Accordingly, the discharge port 35 is provided at the end of the supply screw 26 of the most downstream circulation path R3.

  FIG. 5 shows an increase in the average residence time of carriers in each circulation path R1, R2, R3 according to the number of printing (image formation) in the present embodiment. The average residence time is shown as a ratio to the residence time per thousand sheets of carriers in the most downstream circulation path R3. As shown in the drawing, the residence time of the carrier becomes longer as the distance from the replenishing port 34 becomes longer along the conveying direction of the developer P by the stirring screw 25 and the supply screw. In other words, since the upstream circulation path farther from the discharge port 35 has a shorter carrier residence time and a lower degree of deterioration, it is possible to form an image with high image quality.

  FIG. 6 shows changes according to the number of printed sheets in the sensory evaluation of graininess between a solid image developed by the developing device 11a of this embodiment and a solid image developed by a developing device having only one conventional circulation path. . In this sensory evaluation, the highest quality image with no graininess was visually ranked as rank 5, and the lowest level was classified as rank 0 as the graininess increased. As shown in the drawing, in the developing device 11a of the present embodiment, the degree of deterioration of the carriers in the upstream circulation paths R1 and R2 can be reduced. Therefore, when the number of printed sheets is 200,000 or more, the entire image is a conventional developing device. As compared with the above, a good image with less graininess and small deterioration in quality could be formed.

  In the present invention, by forming a plurality of circulation paths, the residence time of the developer becomes shorter in the upstream circulation path, and the toner containing the carrier with the highest degree of deterioration at the most downstream side is discharged. As a result, it is possible to develop high-quality images with little influence of carrier deterioration. If the number of circulation paths is further increased, a larger gradient of the degree of carrier deterioration along the transport direction can be provided, but at the same time, the ratio of carriers contained in the developer is reduced in the downstream circulation path. Even if the carrier ratio is too low, quality deterioration such as image unevenness is caused. Therefore, the number of circulation paths is appropriately about 2 to 4.

  Further, like the developing device 11b of the third embodiment of the present invention shown in FIG. 7, the supply port 34 is not limited to the end portion of the supply screw 26 as in the previous embodiment, but in the upstream circulation path. It can be anywhere. Further, the discharge path 35 need not be provided at the shaft end portions of the stirring screw 25 and the supply screw 26, and may be formed so as to open on the side wall of the housing 23 as in the developing device 11b shown in the drawing.

  The present invention can be widely applied to all trickle-type image forming apparatuses such as a copying machine, a printer, a FAX, and a complex machine of these.

1 is a schematic diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view perpendicular to the axis of the developing device of the image forming apparatus in FIG. 1. FIG. 2 is an axial sectional view of a developing device of the image forming apparatus in FIG. 1. The axial sectional view of the developing device of the second embodiment of the present invention. 5 is a graph showing changes in carrier residence time in the developing device of FIG. 4. The graph which shows the change of the image quality of the developing device of FIG. 4 and the conventional developing device. The axial sectional view of the developing device of the third embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 11, 11a, 11b ... Developing device 23 ... Housing 24 ... Developing roller 25 ... Stirring screw 26 ... Supply screw 28 ... Partition wall 29, 30 ... Spiral blade 31, 32, 33, 37, 38 ... Circulation hole 34 ... Supply port 35 ... Discharge port R1, R2, R3 ... Circulation path P ... Developer

Claims (6)

A replenishing port for replenishing developer containing toner and carrier;
A developing roller that adsorbs the carrier on the surface and rotates the toner carried by the adsorbed carrier;
A supply screw comprising a spiral blade for conveying the developer in the axial direction while stirring the developer and supplying the developer to the developing roller;
An agitation screw provided in parallel with the supply screw and provided with a spiral blade for conveying the developer in the axial direction while agitating;
A partition wall separating the supply screw and the stirring screw;
In a developing device having a discharge port through which the developer of a certain height or more flows out,
The spiral blades of the supply screw and the stirring screw convey the developer in opposite directions, and the conveyance direction is reversed at least at one place,
The partition wall is formed with a circulation hole that allows the developer to pass therethrough at both ends of the spiral blade and a position where the conveyance direction is reversed, and the developer circulates between the circulation holes adjacent to each other. A developing device comprising a plurality of circulation paths.   2. The discharge port is provided in the circulation path farthest along a direction in which the developer is transported by the supply screw and the stirring screw from a position where the supply port is provided. The developing device according to 1.   The said circulation hole is an opening which opposes 1 pitch or more of the said spiral blade on both sides from the position where the conveyance direction of the said spiral blade of the said supply screw and the said stirring screw reverses. The developing device according to 1.   At least one end of the spiral blade of the supply screw conveys the developer inward in the axial direction, and the supply port has an end that conveys the developer in the supply screw inward in the axial direction. The developing device according to claim 1, wherein the developing device is provided.   The developing device according to claim 1, wherein the supply screw collects the developer from the developing roller.   An image forming apparatus comprising the developing device according to claim 1.

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