JP2008191604A - Developing device, imaging cartridge, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of preventing developer from staying close to the entrance of a developing area and preventing image noise, and to provide an imaging cartridge and an image forming apparatus. <P>SOLUTION: The developing device 24 includes a magnet roller 41 having a plurality of magnetic poles and fixed in a position, and a cylindrical developing sleeve 42 incorporating the magnetic roller 41 and rotating in one direction. The magnitude of the magnetic attractive force measured outside the developing sleeve 42 continues to increase without decreasing from the intermediate between the position of a main pole N1 which is a magnetic pole closest to a developing position, and the position of a conveying pole S1 which is a magnetic pole upstream of the main pole, in the rotating direction of the developing sleeve 42 up to the position closest to a photoreceptor 21. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developing device using a two-component developer containing a non-magnetic toner and a magnetic carrier, an imaging cartridge including the developing device, and an image forming apparatus. More specifically, the present invention relates to a developing device, an imaging cartridge, and an image forming apparatus having a developing roller including a magnet roller including a plurality of magnetic poles and a non-magnetic cylindrical developing sleeve disposed on the outer periphery thereof.

  As a developing device using a two-component developer containing a non-magnetic toner and a magnetic carrier, there is a device having a developing roller composed of a magnet roller and a developing sleeve. The magnet roller is provided with a plurality of magnetic poles therein at a predetermined position angle, and is fixed at a predetermined position with respect to the image carrier. The developing sleeve is formed of a nonmagnetic material in a cylindrical shape and is disposed on the outer periphery of the magnet roller. The developing sleeve is rotationally driven by a predetermined driving means. The developer is attracted by the magnetic force of the magnet roller, adsorbed onto the developing sleeve, and moved as the developing sleeve rotates.

  Here, among the magnetic poles in the magnet roller, the magnetic pole arranged closest to the image carrier has the highest magnetic flux density in the magnet roller and is generally called a main pole. Further, here, the magnetic pole located on the upstream side in the developer conveyance direction from the main pole and the development location is called a conveyance pole, and the magnetic pole located on the downstream side in the developer conveyance direction from the main pole and the development location is called a sealing pole. When different polarities are used for the main pole and the transport pole, and the main pole and the sealing pole, there is a portion where the magnetic force is 0 gauss and the polarity is switched between these poles. Further, in the vicinity of the main pole, a regulating member that regulates the layer thickness of the developer, a seal member that prevents the leakage of the developer, and the like are arranged, which tends to be a resistance for developer conveyance.

  On the other hand, Patent Document 1 discloses a development in which the central half-value peak magnetic flux density in the normal direction of the transport pole is shifted from the peak angle of the magnetic flux density in the normal direction of the transport pole. An apparatus is disclosed. That is, the angle connecting the position where the magnetic flux density in the normal direction of the transport pole reaches the peak value and the rotation center of the developing roller is the center of the position where the magnetic flux density in the normal direction of the transport pole is half the peak value. The conveyance pole is located on the development region side with respect to the angle connecting the rotation center with the developing roller. As a result, the developer conveying force in the vicinity of the developing region entrance is improved, and the retention of the developer is prevented.

Further, Patent Document 2 discloses a developing device configured as follows with respect to a stripping pole provided on the downstream side of the development location and a stripping pole immediately upstream thereof. That is, the rate of increase of the magnetic attractive force acting perpendicularly to the surface of the developing roller between the peak positions of the magnetic flux densities of the pre-peeling pole and the peeling pole with respect to the rotation direction of the developing roller is 0 or less. ing. Thereby, it is said that even if the magnetization of the carrier is reduced, the retention of the developer can be prevented.
JP 2002-278281 A Japanese Patent Application Laid-Open No. 2004-219577

  However, the conventional developing apparatus described above has the following problems. In the developing device described in Patent Document 1, the normal-direction magnetic flux density of the transport pole is asymmetric. In the production of a magnet having such a shape, there is a problem that it is easy to cause variations and it is difficult to obtain stable performance. Further, in the developing device described in Patent Document 2, it is for preventing the developer from staying on the developer carrying member after development and the carrier from adhering. It cannot be prevented.

  In addition, the inventors measured the magnetic attraction force distribution in the developing roller that has been conventionally used by using a “magnetic attraction force distribution measuring device manufactured by Chubu Electric Co., Ltd.”. The result is shown in FIG. Here, N1 is a main electrode, and S1 is a transport electrode arranged on the upstream side thereof. In this developing roller, it was confirmed that there was a position P at which the magnetic attraction force peaked between them. In the range from P to the development region X, the magnetic attractive force gradually decreased toward the development region X. Therefore, the developer conveyed in the clockwise direction in the drawing along with the rotation of the developing roller is pulled backward toward the P position after passing the P position. Therefore, the developer stays in the vicinity of the entrance of the development area X, causing the developer overflow and image noise.

  The present invention has been made to solve the problems of the conventional developing device described above. That is, an object of the present invention is to provide a developing device, an imaging cartridge, and an image forming apparatus that can prevent the developer from staying near the entrance of the developing area and prevent image noise.

  In order to solve this problem, a developing device according to the present invention includes a magnet roller having a plurality of magnetic poles fixedly provided, and a cylindrical developing sleeve that includes the magnet roller and rotates in one direction. The developing device has a main magnetic pole position closest to the developing position where the magnitude of the magnetic attraction force actually measured on the outside of the developing sleeve and the magnetic pole upstream of the main sleeve in the rotation direction of the developing sleeve. From the center position with respect to the position of the transport pole to the closest position to the developing object, it continues to increase without decreasing.

  According to the developing device of the present invention, the developer is attracted by the magnetic force of the magnet roller and adheres to the surface of the developing sleeve. Further, the developer is transported together by the rotation of the developing sleeve. At this time, when transported from the transport pole to the main pole, the magnetic attraction force that attracts the developer continues to increase from the center position between the transport pole and the main pole to the development position. Accordingly, during this time, the developer does not receive a pulling force in the direction opposite to the conveyance direction. This prevents the developer from staying near the entrance of the development area and prevents image noise.

Further, in the present invention, the position of the main pole is the center position of the half-value position of the peak value of the normal direction component of the magnetic flux density of the main pole, and the position of the transport pole is the position of the normal direction component of the magnetic flux density of the transport pole. The center position of the half value position of the peak value is desirable.
The position of the magnetic pole can be represented at the center position of the half value position of the peak value of the normal direction component of the magnetic flux density.

Further, according to the present invention, the value of the magnetic attraction force actually measured outside the developing sleeve is the value at the closest position to the developing object at the central position between the main pole position and the transport pole position. It is desirable to be in the range of 1.1 to 1.35 times.
The value of the magnetic attraction force actually measured outside the developing sleeve is 1.1 times the value at the center position between the main pole position and the transport pole position at the closest position to the developing object. If it is small, it is not possible to satisfactorily prevent the developer from staying near the entrance of the development area. Alternatively, the value of the magnetic attraction force actually measured outside the developing sleeve at the closest position to the developing object is 1.35 of the value at the center position between the main pole position and the transport pole position. If it is larger than double, there is a risk of unevenness in the image.

  The present invention also includes a magnet roller having a plurality of magnetic poles fixedly provided, and a cylindrical developing sleeve that includes the magnet roller and rotates in one direction, and is used by being attached to an image forming apparatus. An imaging cartridge having an actually measured magnetic attraction force outside the developing sleeve, the position of the main pole that is the magnetic pole closest to the developing position, and the magnetic pole upstream of the rotating direction of the developing sleeve of the main pole It extends to an imaging cartridge that continues to increase without decreasing from the center position with respect to the position of the transport pole to the closest position to the developing object.

  The present invention also includes an image carrier and a developing device that develops a latent image formed on the image carrier, the developing device having a plurality of magnetic poles fixedly provided, and a magnet An image forming apparatus including a cylindrical developing sleeve that encloses a roller and rotates in one direction, and the magnitude of the magnetic attraction force measured outside the developing sleeve is the magnetic pole closest to the developing position Image forming apparatus that continues to increase without decreasing from the center position of the position of the main pole and the position of the transport pole that is the magnetic pole upstream of the developing sleeve of the main pole in the rotation direction, to the closest position to the image carrier It extends to.

  According to the developing device, the imaging cartridge, and the image forming apparatus of the present invention, it is possible to prevent the developer from staying near the entrance of the developing area and to prevent image noise.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a so-called tandem color image forming apparatus having a two-component developing device.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment has four color image forming units 10 </ b> Y, 10 </ b> M, 10 </ b> C, and 10 </ b> K arranged along the primary transfer belt 11. Here, the black image forming unit 10K is larger than the other three colors, but may be of the same size. Although the sizes are different, the functions of the apparatuses for image formation are almost the same. The following description will be made using the largest black image forming unit 10K as a representative.

  In the image forming apparatus 1 of this embodiment, a cleaner unit 12 is disposed on the left side of the primary transfer belt 11 in the drawing, and a secondary transfer roller 13 is disposed on the right side of the drawing. Further, a fixing unit 14 is disposed above the secondary transfer roller 13 in the drawing. On the upper side of the primary transfer belt 11 in the figure, toner cartridges 15Y, 15M, 15C, and 15K for each color are arranged. A waste toner box 16 is disposed on the front side of the image forming units 10Y, 10M, 10C, and 10K for the respective colors, and a paper feeding device 17 is disposed on the lower side of the diagram.

  As shown in FIG. 2, the image forming unit 10 </ b> K has a charging device 22, an exposure device 23, a developing device 24, and a cleaner device 25 arranged around the photoreceptor 21. The photoreceptor 21 is uniformly charged by the charging device 22. Then, an electrostatic latent image based on the image data is formed by the exposure device 23. The electrostatic latent image is developed by the developing device 24. Similarly, in the other three-color image forming units 10Y, 10M, and 10C, toner images are formed on the photoreceptor.

  In the image forming apparatus 1 of the present embodiment, toner images formed by the image forming units 10Y, 10M, 10C, and 10K for the respective colors are transferred to the primary transfer belt 11 and superimposed. The superimposed toner images are transferred to the paper fed from the paper feeding device 17 by the secondary transfer roller 13. Further, the toner image is fixed by the fixing unit 14. The cleaner device 25 collects the toner remaining on the photoconductor 21 after the primary transfer. The cleaner unit 12 collects the toner remaining on the primary transfer belt 11 after the secondary transfer. The collected toner is stored in a waste toner box 16.

  In the developing device 24, the developer is filled in the developing tank 31. As shown in FIG. 2, a developing roller 32, a supply screw 33, and a stirring screw 34 are provided therein. The developing tank 31 is provided with an opening 35 in a portion close to the photosensitive member 21, and a part of the developing roller 32 is exposed from the opening 35 to face the photosensitive member 21. A seal member 36 is provided at the right end of the opening 35 of the developing tank 31 in the drawing. In addition, a partition wall 37 is formed between the supply screw 33 and the stirring screw 34, leaving both axial ends. A regulating member 38 is provided on the left side of the developing roller 32 in the drawing.

  As shown in FIG. 2, the developing roller 32 includes a magnet roller 41 and a developing sleeve 42. The magnet roller 41 has a plurality of magnetic poles fixed at predetermined positions inside the magnet roller 41, and the whole is fixed at a predetermined position with respect to the photoreceptor 21. The developing sleeve 42 is formed of a nonmagnetic material in a cylindrical shape, and is rotatably disposed around the magnet roller 41. In this embodiment, the developing sleeve 42 preferably has an inner diameter of about 20 to 30 mm.

  At the time of image formation, as indicated by an arrow in the figure, both the photosensitive member 21 and the developing sleeve 42 are rotated clockwise in the figure. In this embodiment, since the developer adsorbed on the surface of the developing sleeve 42 is conveyed by the rotation of the developing sleeve 42, the rotation direction of the developing sleeve 42 and the conveying direction of the developer are equal in the range around the developing roller 32. It has become.

  In this embodiment, the developer filled in the developing tank 31 is a two-component developer composed of a nonmagnetic toner and a magnetic carrier. The developer rises around the developing sleeve 42 by the magnetic force of the magnet roller 41 and develops the electrostatic latent image formed on the photoconductor 21 in the vicinity of the closest position to the photoconductor 21. The seal member 36 is in contact with both the developing tank 31 and the photosensitive member 21 to prevent leakage of the developer after development. The regulating member 38 regulates the layer thickness of the developer conveyed by the developing roller 32. When the developer in the developing tank 31 decreases, new developer is appropriately supplied from the toner cartridge 15K (see FIG. 1). The developer is stirred by the stirring screw 34 and circulated to the supply screw 33 at the axial end.

  In the developing roller 32 of this embodiment, each magnetic pole is arranged as shown in FIG. In this figure, the distinction between the magnet roller 41 and the developing sleeve 42 is omitted, and the rotation direction of the developing sleeve 42 is indicated by an arrow. In the present embodiment, the main pole provided at the position closest to the development location is the N1 pole. The N1 pole is a magnetic pole that contributes directly to development, and has a magnetic flux density stronger than other magnetic poles. In the following, the component in the normal direction with respect to the outer peripheral surface of the developing roller 32 out of the magnetic flux density of each magnetic pole is simply referred to as magnetic flux density. Here, the peak value of the magnetic flux density of the N1 pole is preferably about 100 to 150 mT.

  In this embodiment, the N1 pole is provided slightly downstream of the rotation direction of the developing sleeve 42 from the closest position between the photosensitive member 21 and the developing roller 32. Further, the magnet roller 41 is provided with an S3 pole downstream of the N1 pole, followed by S2, N2, and S1 poles in the developer transport direction. The S3 pole located on the downstream side in the developer transport direction of the N1 pole as the main pole is referred to as a sealing pole. The S3 pole prevents the developer from leaking out of the developing tank 31. That is, the developer is transported from the developing tank 31 while being sealed so as not to be scattered.

  Further, the next S2 pole is called a catch pole, and here, developer is received from the supply screw 33 in the lower part of the figure. The S2 pole and the S3 pole have the same polarity, and the gap between the two poles is called a peeling pole. The developer whose toner has been consumed by the developing process is peeled off from the developing roller 32 by the demagnetizing part. Then, the developer that has consumed the toner is replaced with the developer in the developing tank 31.

  The next N2 pole is disposed substantially opposite to the regulating member 38 and is called a regulating pole. The N2 pole is for stably regulating the amount of developer transported on the developing roller 32, and the magnetic flux density distribution has a unique shape different from other magnetic poles with a smooth peak portion. . The next S1 pole is located upstream of the main pole in the developer transport direction, and is called a transport pole. The S1 pole is regulated by the regulating member 38 at the position of the N2 pole, and conveys the developer adjusted to a predetermined layer thickness to the main pole.

  Next, the distribution of the normal direction component with respect to the surface of the developing roller 32 of the magnetic flux density due to each of these magnetic poles is shown in FIG. In this figure, the magnetic flux direction is ignored and the absolute value of the magnetic flux density is shown. In the axial direction of the developing roller 32, almost the same magnetic flux is present everywhere. FIG. 5 shows the magnitude of the magnetic attractive force at each position similar to FIG. These figures are all shown in the same direction as FIG. The magnetic flux density and the magnetic attractive force shown in FIGS. 4 and 5 are values measured by a “magnetic attractive force distribution measuring device manufactured by Chubu Electric Co., Ltd.”.

  4 and 5, the line X indicates the direction of the development area (the closest part to the photoconductor 21). Lines N1 and S1 indicate the direction of the central position of the peak half value of the magnetic flux density of each magnetic pole (N1 pole, S1 pole). That is, it is a line connecting the center of the position (two places) where the half value of the peak value of the magnetic flux density is taken and the rotation center of the developing roller 32. Further, the bisector of the angle formed by the line N1 and the line S1 is a line Y. In this embodiment, as shown in FIG. 5, the magnetic attractive force in the range between the position of the line Y and the position of the line X increases from the value at the position of the line Y to the value at the position of the line X. continuing. That is, although the degree of increase is somewhat undulating, it does not decrease, and there is no peak of magnetic attraction between the position of line Y and the position of line X.

  By doing in this way, the developer conveyed to the position of the line Y by the S1 pole as the conveyance pole does not receive the force pulled back while being conveyed to the position of the line X. Accordingly, the developer stays smoothly without reaching the development area. In order to obtain such a magnetic attraction force distribution, in the developing roller 32 of this embodiment, as the transport pole S1, the peak value of the magnetic flux density is the same as that of the conventional one shown in FIG. A magnetic pole with a small width was used. Further, the peak position of the magnetic flux density of the transport pole S1 is set slightly away from the main pole N1 than the conventional one.

  The magnetic attraction force (Fr) indicated by the broken line in [FIG. 3] of Patent Document 2 described as the background art seems to increase from the transport pole (N1) to the main pole (S1). . However, this part is outside the scope of the object of the invention of this document and is not explained in the text. Moreover, in this document, the magnetic attractive force Fr is not actually measured, but is calculated from the magnetic flux density by a mathematical formula. Therefore, it cannot be said that [FIG. 3] of this document shows a magnet roller in which the magnetic attractive force increases from the transport pole to the main pole. The same applies to [FIG. 4] and [FIG. 5] of this document.

Next, an allowable range of the increase rate of the magnetic attractive force from the position of the line Y to the position of the line X will be described. Here, the rate of increase is represented by the following equation 1 when the magnetic attractive force at the position of the line X is Fr (X) and the magnetic attractive force at the position of the line Y is Fr (Y). (%).
R = ((Fr (X) −Fr (Y)) / Fr (Y)) × 100 (%) (Formula 1)
In this embodiment, this increase rate R (%) is
10 ≦ R ≦ 35
It is desirable to be within the range.

Note that Fr (X) is the maximum value of the magnetic attractive force within this range, and Fr (Y) corresponds to the minimum value. Therefore, this range can also be expressed as the following Expression 2.
Fr (Y) × 1.1 ≦ Fr (X) ≦ Fr (Y) × 1.35 (Formula 2)
It was found that a good development state can be obtained within this range.

For this purpose, the inventors manufactured five types of developing rollers in which the increase rate R was changed in five stages from 0 to 40%, and performed an image formation test using them. That is, from the conventional one, the half width of the main pole N1 and the transport pole S1 and the peak position of the magnetic flux density of the transport pole S1 were changed little by little to obtain a total of five types of developing rollers. As a testing machine, bizhub C550 manufactured by Konica Minolta Co., Ltd. was used, and the developing roller was changed to each of the above five types for testing. Further, the developer conveying amount of the developing device is 200 g / m ² , the distance at the closest position between the developing roller 32 and the photosensitive member 21 is 0.27 mm, and the developer is a two-component developer including toner and carrier. The toner ratio TC 7% was used. In this test, the developer retention level near the entrance of the development area and the occurrence of image unevenness in the formed image were visually observed.

The evaluation criteria for this test were as follows.
Developer retention level: ○
A slight stagnation is observed but there is no effect on development.
× when retention is clearly recognized
Image unevenness: ○ when unevenness is not recognized after enlargement
△ when no unevenness is observed visually
When unevenness is recognized to the extent that it can be seen visually ×
In addition, as a comprehensive evaluation, “Good” is given to those where neither the stay level nor the image unevenness has “X”, and “X” is given to other cases.

  The test results are shown in Table 1. That is, when the increase rate R is 10% to 35%, good results are obtained for both the developer retention level and the image unevenness. On the other hand, when the increase rate R was less than 10%, neither the developer retention level nor the image unevenness was satisfactory. Further, when the increase rate R was 40%, image unevenness occurred.

  As described above in detail, according to the image forming apparatus 1 of the present embodiment, the developing device 24 includes the magnet roller 41 and the developing sleeve 42 and uses the two-component developer. The distribution of suction force satisfies the following conditions. That is, the development which is the closest position to the photoreceptor 21 from the position of the bisector (line Y) of the angle formed by the peak half-value central angle of the magnetic flux density between the main pole (N1 pole) and the transport pole (S1 pole). The magnetic attractive force continues to increase up to the region (line X) position. Furthermore, the increase rate R is in the range of 10 to 35%. In this way, it is possible to prevent the developer from staying near the entrance to the development area and to prevent image noise.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the number of magnetic poles arranged on the magnet roller, the polarity and arrangement thereof are merely examples, and the present invention is not limited to this.
Further, in this embodiment, the line Y position is set with reference to the peak half-value central angle of the magnetic flux density of the N1 pole and the S1 pole. However, the N1 pole and the S1 pole are substantially symmetrical magnetic poles, and the respective peak values The position can also be set as a reference.
The present invention can also be applied to a developing device incorporated in an imaging cartridge. Further, the image forming apparatus is not limited to the one in this embodiment, and can be applied to a monochrome or color copying machine, a printer, a FAX, or a combination of these.

It is sectional drawing which shows the image forming apparatus which concerns on this form. It is sectional drawing which shows an image formation part. It is sectional drawing which shows a developing device. It is explanatory drawing which shows the magnetic flux density of the normal line direction of each pole of a developing roller. It is explanatory drawing which shows the magnetic attraction force of a developing roller. It is explanatory drawing which shows the magnetic attraction force of the conventional developing roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 21 Photoconductor 24 Developing device 41 Magnet roller 42 Developing sleeve N1 Main pole S1 Conveying pole

Claims (5)

In a developing device having a magnet roller having a plurality of magnetic poles fixedly provided, and a cylindrical developing sleeve that includes the magnet roller and rotates in one direction,
The magnitude of the magnetic attraction force actually measured outside the developing sleeve is
From the central position between the position of the main pole, which is the magnetic pole closest to the developing position, and the position of the transport pole, which is the magnetic pole upstream of the developing sleeve in the rotation direction of the main pole,
A developing device characterized in that it continues to increase without decreasing to the closest position with the development object. The developing device according to claim 1,
The position of the main pole is the center position of the half-value position of the peak value of the normal direction component of the magnetic flux density of the main pole;
The developing device, wherein the position of the transport pole is a center position of a half-value position of a peak value of a normal direction component of a magnetic flux density of the transport pole. The developing device according to claim 1 or 2,
The magnitude of the magnetic attraction force measured outside the developing sleeve,
A developing device characterized in that a value at a closest position to a developing object is in a range of 1.1 to 1.35 times a value at a central position between the position of the main pole and the position of the transport pole. . In an imaging cartridge having a plurality of magnetic poles fixedly provided and a cylindrical developing sleeve that encloses the magnet roller and rotates in one direction and is attached to an image forming apparatus ,
The magnitude of the magnetic attraction force actually measured outside the developing sleeve is
From the central position between the position of the main pole, which is the magnetic pole closest to the developing position, and the position of the transport pole, which is the magnetic pole upstream of the developing sleeve in the rotation direction of the main pole,
An imaging cartridge characterized in that it continues to increase without decreasing to the closest position to the development object. An image bearing member; and a developing device that develops a latent image formed on the image bearing member. The developing device includes a magnet roller having a plurality of magnetic poles fixedly provided; and In an image forming apparatus having a cylindrical developing sleeve that encloses and rotates in one direction,
The magnitude of the magnetic attraction force actually measured outside the developing sleeve is
From the central position between the position of the main pole, which is the magnetic pole closest to the developing position, and the position of the transport pole, which is the magnetic pole upstream of the developing sleeve in the rotation direction of the main pole,
An image forming apparatus characterized in that it continues to increase without decreasing to the closest position with the image carrier.

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