JP2012042738A - Development apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of efficiently increasing the toner charge amount of a replenishment developer by the timing when the replenishment developer reaches a developer carrier even if the distance between a developer supply position and the developer carrier is short.SOLUTION: An agitation chamber 24 communicates with a developing chamber 23 at both ends thereof and forms a circulating path of developer. The agitation chamber 24 rotates an agitation screw 26 having screw blades so as to transfer the developer in the reverse direction from the developing chamber 23 while collecting the developer from a developing sleeve. The agitation chamber 24 is configured such that the agitation screw 26 is provided with ribs 53 in a region ranging from a developer supply port 30 to a developing sleeve 28 in the agitation chamber 24 so as to increase friction frequency between a circulating developer and a replenished developer by making a developer transportation capacity of the region ranging from the developer supply port 30 to the developing sleeve 28 lower than that of a region along the developing sleeve 28.

Description

  The present invention relates to a developing device that charges toner by stirring while circulating the developer along a developer carrying member, and more particularly, to a structure for quickly increasing the toner charge amount of the replenished developer.

  2. Description of the Related Art Image forming apparatuses that electrically transfer and thermally fix a toner image formed on an image carrier or intermediate transfer member to a recording material are widely used. In the developing device of the image forming apparatus, a developer circulation path is formed along the developer carrying member, and a so-called two-component developer including toner and carrier is conveyed through the circulation path while being agitated. The carrier is triboelectrically charged to the opposite polarity.

  In the case of a two-component developer, toner is consumed as the image is formed, while the carrier continues to circulate in the developing device. Therefore, the developer replenishing port of the developing device contains toner from the developer replenishing device as a main component. The replenishment developer to be supplied is supplied. Since the toner that has just been replenished is uncharged, it needs to be sufficiently agitated with the circulating developer and given the necessary toner charge amount before being transported through the developing device and reaching the developer carrying member.

  Patent Document 1 discloses a so-called vertical stirring type in which a first chamber (developing chamber) and a second chamber (stirring chamber) that form a developer circulation path along a developer carrier are vertically stacked. A developing device is shown. The vertical stirring type developing device (FIG. 15) is smaller in the width direction of the developing device than the conventional horizontal stirring type developing device (FIG. 14) in which the first chamber and the second chamber are arranged side by side. It is easy to realize.

  On the other hand, the developer replenishing port in the vertical stirring type developing device is desirably arranged at a position where the transport distance can be secured most along the circulation path from the upstream position of the developing chamber. Specifically, as in the case of the lateral stirring type developing device, referring to FIG. 2, a position downstream of the image area end A of the developing sleeve 28 on the downstream side in the developer transport direction in the developing chamber 23 or Its vicinity is preferable.

  However, in the case of a function separation type developing device in which a developing chamber that supplies toner to the developing sleeve and a recovery chamber that collects the developed toner are separated, such as a vertical stirring type developing device, Depending on the position, the following problems occur.

  That is, as shown in FIG. 16, in the vertical stirring type developing device, a part of the circulating developer is bypassed from the first chamber to the second chamber via the developer carrier, so that the first chamber ( Downstream of 23), less developer circulates. For this reason, when the developer is replenished downstream of the first chamber (23), the ratio of “supplemented developer / circulating developer” increases at the replenishment position, and the chance of friction of the replenished developer decreases. As a result, the toner charge amount may be insufficient when the replenishment developer reaches the developer carrying member. If the toner charge amount is insufficient, uneven image density, fogged image, scattered toner, etc. are likely to occur, which is not preferable.

  Therefore, in Patent Document 1, referring to FIG. 3, the developer on the downstream side of the agitating screw 26 is increased by increasing the rotation speed of the developing screw 25 and the agitating screw 26 to improve the developer conveying performance. Yes. However, in this case, the stress on the developer increases. Further, when the rotational speed of the screw conveying member is increased, self-heating is generated and the deterioration of the developer is increased.

  Therefore, in Patent Document 2, a developer replenishing port is disposed upstream of the opening for delivering the developer from the first chamber to the second chamber to retain the replenished developer. As a result, the time until the replenishment developer reaches the developer carrying member is extended, the chance of friction is increased, and the toner charge amount is increased.

Japanese Patent Laid-Open No. 5-333961 JP-A-10-149024

  However, in the case of the configuration of Patent Document 2, the replenished toner immediately after being replenished from the developer replenishing port often exists as a toner aggregate. Accordingly, since mixing of the circulating developer with the carrier is hindered, it is difficult to obtain a sufficient toner charge amount. For example, in the case of a replenishment developer with 100% toner, the charge amount of the toner cannot be increased even if only the replenishment developer is agitated. Even if extended, the toner charge amount does not increase as expected.

  Further, it has been found that the toner charge amount gradually increases in the process of transporting the developer in the second chamber, and therefore, scattered toner and fogged images are generated biased to the upstream side of the second chamber. In particular, as shown in FIG. 15, in the vertical stirring type developing device 4N, not only the developing chamber 23 that supplies the developer to the developing sleeve 28 but also the stirring chamber 24 that collects the developer from the developing sleeve 28 has the entire length of the developing sleeve. It communicates directly with the 28 openings. For this reason, it has been found that dust of uncharged toner generated in the initial process (upstream side of the stirring chamber 24) where the supplied developer is supplied and stirred is easily scattered from the opening of the developing sleeve 28.

  According to the present invention, in the function separation type developing device, even if the position of the developer replenishing port is made as long as possible to the developing position, the toner immediately after replenishment is scattered from the opening facing the developer carrying member. It is an object of the present invention to provide a developing device that can suppress the occurrence of the above.

  The developing device of the present invention includes a developer carrying member for developing an electrostatic image formed on an image carrying member, a first chamber for supplying a developer to the developer carrying member, and a first chamber connected to the first chamber. A developer circulation path is formed, a second chamber for collecting the developer from the developer carrying member, a first transport member provided in the first chamber for transporting the developer, and the second chamber A second conveying member that conveys the developer, and the developer carrying member in the second chamber downstream of the developer carrying region of the developer carrying member in the first chamber in the developer carrying direction. A developer replenishing port for replenishing the developer upstream of the developer carrying area in the developer transport direction; Further, at least a part of the developer carrying capability in a region upstream of the developer carrying direction of the developer carrying member in the second chamber in the second chamber downstream of the developer supply port and in the developer carrying direction of the second chamber. Has been reduced.

  In the developing device of the present invention, the developer transport speed after replenishing the replenished developer to the circulating developer from the developer replenishing port is lowered, and the time until the developer reaches the developer carrying member is extended to increase the stirring property. Reinforcement increases the friction frequency between the circulating developer and the replenishment developer. Developers existing from the downstream side end of the developer carrying region of the developer carrying member in the first chamber to the developer carrying member in the second chamber are concentrated by a difference in speed between the front and rear to “replenish developer / circulate development”. Increase the "agent" ratio locally. Then, the toner charge amount can be rapidly increased by stirring for a long time in a state where the ratio of the replenishment developer / circulating developer is increased.

  Therefore, even if the distance from the developer supply port to the developer carrying member is short, the toner charge amount of the replenishing developer can be efficiently increased before reaching the developer carrying member. By sufficiently increasing the toner charge amount of the replenishment developer before reaching the opening of the developer carrying member, it is possible to prevent the generation of scattered toner and fog image biased upstream.

1 is an explanatory diagram of a configuration of an image forming apparatus. It is explanatory drawing of a cross-sectional structure orthogonal to the longitudinal direction of a developing device. FIG. 3 is a plan sectional view in the longitudinal direction of the developing device. It is explanatory drawing of the relationship between the stirring time in a stirring chamber, and a toner charge amount. FIG. 6 is an explanatory diagram of a relationship between a toner replenishment amount and a toner density after replenishment. 3 is an explanatory diagram of a toner charge amount reinforcing structure in Embodiment 1. FIG. FIG. 6 is an explanatory diagram of a toner charge amount reinforcing structure in Embodiment 2. FIG. 10 is an explanatory diagram of a toner charge amount reinforcing structure in Embodiment 3. 10 is an explanatory diagram of a cross-sectional configuration perpendicular to the longitudinal direction of a developing device in Embodiment 4. FIG. FIG. 10 is an explanatory diagram of an arrangement of a developer supply device in Embodiment 5. FIG. 6 is an explanatory diagram of a change in toner density with time due to an error in developer replenishment amount. FIG. 10 is an explanatory diagram of a toner charge amount reinforcing structure in Embodiment 5. It is an explanatory diagram of a toner charge amount measuring device. It is explanatory drawing of a structure of a horizontal stirring type developing apparatus. It is explanatory drawing of a structure of a vertical stirring type developing device. It is explanatory drawing of the circulation of the developer in a vertical stirring type developing device.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. According to the present invention, in the case of the function separation type developing device, a part or all of the configuration of the embodiment is an alternative configuration as long as the developer transport speed is decreased on the downstream side of the developer supply port. Other alternative embodiments can also be implemented.

  Accordingly, not only the configuration in which the first chamber and the second chamber are arranged vertically (FIG. 15) but also the first chamber and the second chamber are arranged horizontally or obliquely in the case of a function separation type developing device. The configuration (FIG. 14) can also be implemented. Such a developing device can be implemented without distinction in a tandem type / 1 drum type, an intermediate transfer type / a recording material conveyance type / a direct transfer type, and a monochrome / full color image forming apparatus.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. The image forming apparatus can be used for various purposes such as a printer.

  In addition, about the general matter of the developing device shown by patent document 1, 2, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. As shown in FIG. 1, the image forming apparatus 100 is a tandem intermediate transfer type full color printer in which yellow, magenta, cyan, and black image forming portions Pa, Pb, Pc, and Pd are arranged along an intermediate transfer belt 5. is there.

  In the image forming portion Pa, a yellow toner image is formed on the photosensitive drum 1 a and transferred to the intermediate transfer belt 5. In the image forming portion Pb, a magenta toner image is formed on the photosensitive drum 1 b and transferred to the intermediate transfer belt 5. In the image forming portions Pc and Pd, a cyan toner image and a black toner image are formed on the photosensitive drums 1c and 1d, respectively, and transferred to the intermediate transfer belt 5.

  The intermediate transfer belt 5 is suspended by a drive roller 61, a counter roller 62, and a tension roller 63, and is driven by the drive roller 61 to rotate in the direction of arrow R2. The four-color toner images transferred to the intermediate transfer belt 5 are conveyed to the secondary transfer portion T2 and secondarily transferred to the recording material P.

  The recording material P taken out from the recording material cassette 11 by the pickup roller 12 is separated one by one by the separation roller 13 and fed to the registration roller 14. The registration roller 14 sends the recording material P to the secondary transfer portion T2 in time with the toner image on the intermediate transfer belt 5. The recording material P to which the toner image has been transferred is heated and pressurized by the fixing device 16 to fix the toner image on the surface, and then is discharged to the tray 17 outside the machine body.

  The image forming portions Pa, Pb, Pc, and Pd are substantially the same except that the toner colors used in the developing devices 4a, 4b, 4c, and 4d are different. Hereinafter, the image forming unit Pa will be described, and the image forming units Pb, Pc, and Pd will be described by replacing “a” at the end of the reference numerals attached to the components of the image forming unit Pa with “b”, “c”, and “d”. To do.

  In the image forming portion Pa, a corona charger 2a, an exposure device 3a, a developing device 4a, a primary transfer roller 6a, and a drum cleaning device 19a are arranged around the photosensitive drum 1a. A photosensitive drum 1a, which is an example of an image carrier, has a photosensitive layer having a negative polarity on the outer peripheral surface of an aluminum cylinder, and rotates in the direction of arrow R1 at a process speed of 300 mm / sec. The corona charger 2a charges the surface of the photosensitive drum 1a to a uniform dark potential VD having a negative polarity.

  The exposure device 3a has a built-in semiconductor laser, which is controlled in accordance with a document image information signal output from a document reading device having a photoelectric conversion element such as a CCD, and emits a laser beam. The exposure device 3a scans the laser beam with a rotating mirror and writes an electrostatic image of the image on the surface of the charged photosensitive drum 1a. The developing device 4a develops the electrostatic image on the surface of the photosensitive drum 1a using a developer containing toner and a carrier to form a toner image.

  The primary transfer roller 6a presses the inner surface of the intermediate transfer belt 5 to form a primary transfer portion T1 between the photosensitive drum 1a and the intermediate transfer belt 5. By applying a positive DC voltage to the primary transfer roller 6a, a negative toner image carried on the photosensitive drum 1a is primarily transferred to the intermediate transfer belt 5. The drum cleaning device 19a collects the transfer residual toner remaining on the photosensitive drum 1a by escaping from the transfer to the recording material P.

  In this embodiment, the drum-shaped photosensitive drum 1a that is normally used is used. However, an inorganic photosensitive member such as an amorphous silicon photosensitive member can be used, and a belt-shaped photosensitive member can also be used. . The charging method, electrostatic image forming method, transfer method, cleaning method, and fixing method are not limited to the above methods.

<Developing device>
FIG. 2 is an explanatory diagram of a cross-sectional configuration perpendicular to the longitudinal direction of the developing device. FIG. 3 is a plan sectional view in the longitudinal direction of the developing device.

  As shown in FIG. 2, the developing device 4a develops the electrostatic image on the photosensitive drum 1a using a developer (two-component developer) in which toner (non-magnetic) and carrier (magnetic) are mixed. In the developing device 4a, the interior of the developing container 20 is partitioned into a developing chamber 23, which is an example of a first chamber, and a stirring chamber 24, which is an example of a second chamber, by a partition wall 27 extending in a direction perpendicular to the paper surface. The agent is accommodated in the developing chamber 23 and the stirring chamber 24.

  In the developing device 4 a, the developing screw 25 in the developing chamber 23 supplies the developer to the developing sleeve 28. On the other hand, the agitating screw 26 in the agitating chamber 24 collects and conveys the developer from the developing sleeve 28 and mixes and agitates the replenished developer with the circulating developer. For this reason, there always exists only a fresh developer sufficiently stirred in the stirring chamber 24 in the developing chamber 23, and there is an advantage that a uniform concentration developer is always supplied to the developing sleeve 28. Moreover, since the developing screw 25 and the stirring screw 26 are arranged in the vertical direction, the developing device 4a can be easily downsized.

  A developing screw 25, which is an example of a first conveying member, is disposed in the developing chamber 23, which is an example of a circulation path, and an agitating screw 26, which is an example of a second conveying member, is disposed in the stirring chamber 24. . The developing screw 25 is disposed substantially parallel to the bottom of the developing chamber 23 along the axial direction of the developing sleeve 28, and rotates to convey the developer in the developing chamber 23 in one direction along the axial direction. The agitating screw 26 is disposed substantially in parallel with the developing screw 25 at the bottom of the agitating chamber 24, and rotates to convey the developer in the agitating chamber 24 in the opposite direction to the developing screw 25.

  There is an opening at a position corresponding to the developing area D facing the photosensitive drum 1a of the developing container 20, and a developing sleeve 28, which is an example of a developer carrying member, is partially exposed in the direction of the photosensitive drum 1a. Arranged. The diameter of the developing sleeve 28 is 20 mm, the diameter of the photosensitive drum 1a is 80 mm, and the closest distance (SD gap) between the developing sleeve 28 and the photosensitive drum 1a is 400 μm.

  The developing sleeve 28 is made of a nonmagnetic material such as aluminum or stainless steel, and a magnet roller 28m, which is a magnetic field means, is non-rotatably disposed therein. The magnet roller 28m has a developing pole S2 disposed opposite the developing area D of the photosensitive drum 1a, a magnetic pole S1 disposed opposite the ear cutting member 29, and a magnetic pole N1 disposed between the magnetic poles S1 and S2. Yes. Further, magnetic poles N2 and N3 are arranged to face the developing chamber 23 and the stirring chamber 24, respectively. With such an arrangement of magnetic poles, the developer conveyed to the development region D can be developed by bringing it into contact with the photosensitive drum 1a in a magnetic brush state.

  The developing sleeve 28 rotates in the direction of arrow R4 (counterclockwise), and the developer in the developing chamber 23 is pumped and coated on the developing sleeve 28 by the conveying force of the developing screw 25 and the magnetic force of the magnetic pole N2. .

  At the upstream position exposed to the outside of the developing sleeve 28, a spike cutting member 29 is provided as a regulating blade that regulates the spikes of the developer carried on the developing sleeve 28. The ear cutting member 29 cuts the developer carried on the developing sleeve 28 and regulates the layer thickness of the magnetic brush. The ear cutting member 29 is composed of a nonmagnetic member 29a formed of plate-like aluminum or the like opposed to the developing sleeve 28 along the longitudinal direction, and a magnetic member 29b such as an iron material. By adjusting the gap (SB gap) between the ear cutting member 29 and the developing sleeve 28, the amount of developer conveyed to the SD gap in the developing region D is adjusted.

If too much developer is transported to the development area D, the developer stays in the SD gap and an abnormal image such as a cache image is generated. On the other hand, if it is too small, the developability is insufficient and the image density is lowered. To do. For this reason, it is necessary to adjust the gap (SB gap) between the ear cutting member 29 and the developing sleeve 28 to an optimum amount. Here, the developer coating amount per unit area on the developing sleeve 28 is regulated to 30 mg / cm ² by setting the SB gap to 500 μm.

  The developing sleeve 28 conveys the developer whose layer thickness is regulated to the developing region D, supplies the developer to the electrostatic image formed on the photosensitive drum 1a, and reversely develops the electrostatic image into a toner image. At this time, the power source D4 applies an oscillating voltage obtained by superimposing the DC voltage and the AC voltage to the developing sleeve 28 in order to improve the development efficiency (the rate of toner application to the electrostatic image). Here, an oscillating voltage obtained by superimposing a square-wave AC voltage having a peak-to-peak voltage Vpp of 1800 V and a frequency f of 12 kHz on a DC voltage of −500 V was applied. However, the combination of the DC voltage, the AC voltage, and the waveform is not limited to this.

  In the developing area D, the developing sleeve 28 rotates in the forward direction and the moving direction of the surface of the photosensitive drum 1a, and the circumferential speed ratio with respect to the photosensitive drum is 1.75 times. The photosensitive drum peripheral speed ratio can be arbitrarily set between 0 and 3.0 times. However, the larger the ratio of the peripheral speed of the photosensitive drum, the higher the development efficiency. However, if the ratio is too large, problems such as toner scattering and developer deterioration occur. It is preferable.

  The developer which has not been subjected to development after completing the development process in the development region D is taken into the stirring chamber 24 and responds to the repulsive magnetic field formed between the N2 pole and the N3 pole of the magnet roller 28m. Then, it falls from the developing sleeve 28 to the stirring chamber 24.

  As shown in FIG. 3, in the developing device 4a, the developer conveyed by the developing screw 25 and the stirring screw 26 passes between the developing chamber 23 and the stirring chamber 24 through the communication portions 21 and 22 at both ends of the partition wall 27. Circulate. The developer that has been transported through the developing chamber 23 to the end in the longitudinal direction and has not been supplied to the developing sleeve 28 falls at the communicating portion 22 and is transported to the stirring chamber 24.

  The developer container 20 is filled with 350 g of developer. The developing screw 25 and the stirring screw 26 are configured in the same manner, and spiral screw blades having a pitch of 30 mm and an outer diameter of 20 mm are equally provided on a rotating shaft having a shaft diameter of φ8 mm. The developing screw 25 and the agitating screw 26 both adjusted the developer circulation balance by setting the rotational speed to 600 rpm. In the present embodiment, the case where the pitches of the developing screw 25 and the stirring screw 26 are the same will be described as an example. However, the pitch may be varied as long as the circulation balance can be maintained.

<Toner supply control>
When toner is consumed by image formation, the toner density (weight ratio) of the developer in the developing device 4a is lowered and the developing performance is lowered. Therefore, only the consumed toner is supplied to the developing device 4a during image formation. There is a need to. The developer replenishing device 31 is provided in the upper part of the developing device 4a, and supplies a replenishing developer of 100% toner to the developing device 4a by rotating the replenishing screw 32. The toner replenishment amount is controlled by the rotation speed of the replenishment screw 32, and this rotation speed is determined by the control unit 110.

  The controller 110 obtains the toner replenishment amount by using both the video count method and the patch detection control method, and calculates the rotation speed of the replenishment screw 32 according to the toner replenishment amount.

  The video count method is a method in which the number of image dots (image density) for each formed image is integrated to obtain the toner consumption amount per sheet. The amount of toner consumed is predicted by counting the exposure time emitted during electrostatic image formation with an exposure device such as a laser.

  The patch detection control method is a method in which an electrostatic image of a patch image formed under a predetermined exposure condition is actually developed to measure a toner application amount, and a toner replenishment amount is determined so as to induce the toner application amount to a predetermined value. is there. The reference electrostatic image on the photosensitive drum 1a is developed, and the toner loading amount of the toner image is detected using an optical sensor (not shown).

  There are various other methods such as a method of optically or magnetically detecting the toner concentration (TD ratio) of the two-component developer in the developing device and determining the toner replenishment amount so as to keep the toner concentration at a predetermined value. There is a control method. Any one of the methods can be selected as appropriate, and the necessary toner amount to be replenished into the developing device 4a can be calculated singly or in combination.

<Replenishment and mixing of developer>
FIG. 4 is an explanatory diagram of the relationship between the stirring time in the stirring chamber and the toner charge amount. FIG. 5 is an explanatory diagram of the relationship between the toner replenishment amount and the toner density after replenishment. As shown in FIG. 3, in the developing device 4a, a developer having a toner charge amount of 30 μC / g at a temperature of 23 ° C. and a humidity of 50% is used by setting the TD ratio to 8%.

  The TD ratio (toner concentration) is a weight ratio of the carrier to the toner in the two-component developer, and is a parameter correlated with the contact area ratio of the toner to the carrier. When the TD ratio is increased, even when the mixing and stirring time is the same, the chance of friction of the toner with respect to the carrier is reduced, the toner charge amount is reduced, electrostatic restraint is lost, and scattered toner is likely to be generated. On the other hand, when the TD ratio is lowered, even when the mixing and stirring time is the same, the chance of friction of the toner with respect to the carrier increases, the toner charge amount increases, and an abnormal image such as carrier adhesion tends to occur. The TD ratio is usually preferably about 4 to 12%, and more preferably in the range of 6 to 10%.

  In order to determine the optimal location of the developer supply port 30 in the developing device 4a, it is necessary to consider the mixing and stirring time of the supplied developer and the amount of developer in the vicinity of the developer supply port 30.

  As shown in FIG. 4, in an environment where the temperature is 23 ° C. and the humidity is 50%, an uncharged developer is filled in the developing device 4 a and the state of increase in the toner charge amount after startup is measured. As a result, the stirring time required until the toner charge amount reached 30 μC / g and became saturated was 3 seconds or more.

  The uncharged toner replenished from the developer replenishing port 30 reaches the toner charge amount required in the developing process until it reaches the most upstream position Z of the image area end of the developing chamber 23 and is supplied to the developing sleeve 28. There is a need. For this reason, the developer replenishing port 30 is desirably arranged in the vicinity of the image region most downstream A downstream of the developing chamber 23 in the transport direction so as to ensure the maximum mixing and stirring time after toner replenishment. A part of the developing container was made transparent by the developing device 4a, toners of different colors were replenished from the developer replenishing port 30, and the time until the toners of different colors reached the image region X was actually measured. However, it was 5.0 seconds. For this reason, it is considered that the toner replenished from the developer replenishing port 30 reaches the toner charge amount required in the developing process before being supplied to the developing sleeve 28.

  However, the toner replenished from the developer replenishing port 30 is given a toner charge amount by friction with the carrier in the circulating developer. For this reason, if the absolute weight of the developer in the vicinity of the developer supply port 30 (the amount of carrier in the developer) is small, the time until the toner charge amount reaches 30 μC / g and is saturated is 3 seconds shown in FIG. There is a possibility of extending more than this.

  As shown in FIG. 5, the toner replenishment amount was changed, and the toner concentration (TD ratio) after replenishment with respect to the absolute weight of the developer in the vicinity of the developer replenishment port 30 was measured. As a result, when the absolute weight of the developer in the vicinity of the developer supply port 30 is small and the amount of toner to be replenished is large, the TD ratio immediately after replenishment becomes very high, and the replenished toner is sufficiently mixed and stirred. It turned out not to be possible. In FIG. 5, the replenishment amount of 0.5 g is the maximum toner replenishment amount at one time in the developer replenishing device 31 of the developing device 4a. This value corresponds to the amount of toner consumed by a solid image having the maximum image area and the highest density gradation. From this, it has been found that the absolute weight of the developer in the vicinity of the developer supply port 30 is required to be about 20 g.

  However, in the developing device 4a, a part of the developer conveyed in the axial direction of the developing screw 25 through the developing chamber 23 is supplied to the developing sleeve 28 on the way, and passes through the developing region D facing the photosensitive drum 1a and stirred. It is collected in the chamber 24. For this reason, the amount of the developer conveyed downstream in the developing chamber 23 by the developing screw 25 decreases as it goes from the upstream end to the downstream end. For this reason, there is a possibility that the absolute weight of the developer near the developer supply port 30 corresponding to the most downstream position of the developing chamber 23 may cut the necessary 20 g. When an adverse condition such as a decrease in developer fluidity occurs while the developer amount in the developing device 4a is reduced to the lower limit, the developer is actually taken out from the vicinity of the replenishing port and the weight is measured. There was a case where it decreased to near.

  That is, the amount of developer conveyed downstream in the developing chamber 23 decreases as it goes from the upstream end to the downstream end, while the amount of developer conveyed downstream in the stirring chamber 24 is the upstream end. It increases as going from the downstream end to the downstream end. For this reason, the distribution of the developer circulating in the developing device 4a is shifted to the opposite side where the developer supply device 31 in the longitudinal direction is arranged. That is, the toner replenishment position by the developer replenishing device 31 is the position where the amount of developer circulating is the smallest in the developing device 4a, and is the most unfavorable position for frictionally charging uncharged toner.

<Measurement method of toner charge amount>
FIG. 13 is an explanatory diagram of a toner charge amount measuring apparatus. As shown in FIG. 13, the toner charge amount (charge amount, triboelectric charge amount) of the toner of the two-component developer is measured using the measuring apparatus 200 in the following procedure.
(1) A two-component developer whose toner charge amount is to be measured is put in a polyethylene bottle having a capacity of 50 to 100 ml, and is shaken and charged by shaking for about 10 to 40 seconds.
(2) About 0.5 to 1.5 g of the frictionally charged two-component developer is put in a metal measuring container 142 having a 500 mesh screen 143 at the bottom, and a metal lid 144 is formed.
(3) The weight of the entire measurement container 142 at this time is measured and is defined as W1 (kg).
(4) In the suction machine 141 (at least the insulator is in contact with the measurement container 142), suction is performed from the suction port 147, and the air volume control valve 146 is adjusted to set the pressure of the vacuum gauge 145 to 250 (mmAq). In this state, suction is sufficiently performed, preferably for 2 minutes, and only the toner is sucked and removed. In this process, the potential of the electrometer 149 is measured and set to V (V).

When the capacitance of the capacitor 148 is C (F), and the weight of the entire measurement container 142 after suction is weighed and W2 (g), the toner charge amount (μC / g) is calculated as follows.
Toner charge amount (μC / g) = C × V × 10 ⁻³ / (W1-W2)

  With respect to the two-component developer taken out from the developing device 4a, the toner charge amount was measured by performing steps (2) to (4) while omitting the above (1).

<Horizontal stirring type and vertical stirring type>
FIG. 14 is an explanatory diagram of a configuration of a lateral stirring type developing device. FIG. 15 is an explanatory diagram of a configuration of a vertical stirring type developing device. FIG. 16 is an explanatory diagram of developer circulation in a vertical stirring type developing device.

  As shown in FIG. 14, in the conventional lateral stirring type developing device 4 </ b> M, the developing chamber 23 and the stirring chamber 24 of the developing container 20 are separated in a horizontal direction by a partition wall 27. The developing screw 25 in the developing chamber 23 and the agitating screw 26 in the agitating chamber 24 convey the developer in the opposite direction, and deliver the developer through communication portions (openings) provided at both ends of the partition wall 27, thereby developing the developer container. 20 was circulated.

  For this reason, a constant developer circulated between the developing chamber 23 and the stirring chamber 24 even when viewed in a cross section perpendicular to the transport direction. The developer sufficiently circulates even at a position upstream of the developing sleeve 28 in the agitating chamber 24. If the replenishment developer is supplied at this position, the replenishment developer is conveyed while being conveyed downstream by the agitating screw 26. A sufficient toner charge amount was applied. The replenishment developer was sufficiently agitated and mixed with the developer to be circulated until it was conveyed to the agitating screw 26 and delivered to the developing chamber 23.

  As shown in FIG. 15, in the vertical stirring type developing device 4N, the developing chamber 23 and the stirring chamber 24 of the developing container 20 are separated in the vertical direction by the partition wall 27, but the developer conveyed to the developing sleeve 28 is used. Continues to flow from the developing chamber 23 to the stirring chamber 24.

  As shown in FIG. 16A, in the vertical stirring type developing device 4N, the stirring chamber 24 and the developing chamber are pushed up from the bottom by the pressure of the developer accumulated at the downstream end of the stirring chamber 24. The developer is delivered to 23. However, not all of the circulated developer reaches the downstream end of the conveying screw 25 in the developing chamber 23, but is supplied to the developing sleeve 28 in the middle, and passes through the developing portion facing the photosensitive drum for development. After that, there is a developer (a path indicated by an arrow a) collected in the stirring chamber 24.

  As shown in FIG. 16B, the developer is transferred to the developing sleeve 28 over the entire image region X in the axial direction of the developing sleeve 28. For this reason, the amount of developer conveyed by the developing screw 25 in the developing chamber 23 tends to gradually decrease from the upstream end toward the downstream end. On the other hand, the amount of developer conveyed by the stirring screw 26 in the stirring chamber 24 tends to gradually increase from the upstream end to the downstream end. That is, the developer distribution in the developing device 4N is very likely to be offset in the axial direction of the developing sleeve 28 in both the developing chamber 23 and the stirring chamber 24.

  For this reason, if the replenishment developer is replenished upstream of the developing sleeve 28 in the agitating chamber 24 as in the case of the lateral agitation type developing device 4M, the amount of developer that circulates is too small to stir and mix the replenishment developer. It tends to be enough. When the stirring and mixing of the circulating developer and the replenishment developer are insufficient, the toner charge amount is insufficient, and as described above, the problem of scattered toner and fogged images is likely to occur.

  As shown in FIG. 16B, four image region end positions A, B, Y, and Z are defined along the developing sleeve 28. Positions A and Z are determined on the developing chamber side, and positions B and Y are determined on the stirring chamber side.

  The developer replenishing port in the vertical stirring type developing device 4N is located at the position where the transport distance can be secured most from the upstream position Z of the developing chamber 23, specifically, in the developing chamber 23 at the downstream side in the developer transport direction. The vicinity in the downstream of the position A at the edge of the image area is preferable.

  However, in the vicinity of the position A optimum for the position where the developer replenishment port is provided, it is difficult to sufficiently stir and mix because the developer circulation amount is the smallest in the developing device and the developer surface is the lowest. There's a problem.

  In the developing device disclosed in Japanese Patent Application Laid-Open No. 10-149024, if a sufficient amount of toner charge is ensured in the replenishment developer before reaching the developer carrier, the developer is replenished from the developer replenishment position to the developer carrier. Long transport distance is required. As described above, since the developer circulating in the upstream side of the second chamber is small, it is necessary to keep stirring to some extent even after the replenishment developer is mixed and diffused in the circulating developer. Cannot be obtained. If a long transport distance is set from the developer replenishment position to the developer carrier, the length of the developing device in the longitudinal direction becomes long, and the fit into the miniaturized housing structure becomes worse.

<Contamination of developer container with scattered toner>
Further, in the developing device 4a, since the developer is delivered from the developing sleeve 28, it has been found that the stirring chamber 24 faces the developing sleeve 28, thereby causing another problem. It was confirmed that the uncharged toner leaked to the outside through the gap between the developing sleeve 28 and the developing container 20 at the position B of the stirring chamber 24 shown in FIG.

  That is, the developer in the stirring chamber 24 is charged by being mixed and stirred by the stirring screw 26 provided in the stirring chamber 24. At this time, if the uncharged toner replenished from the developer replenishing port 30 has not been sufficiently charged when it reaches the developing region B, the gap (lower jaw gap G) between the developing sleeve 28 and the developing container 20 shown in FIG. ) And the toner is scattered to generate a fogged image on the photosensitive drum 1a. Further, part of the scattered toner adheres to the lower part of the developing container 20 to form a lump, and when the lump grows to a certain size, it falls on the intermediate transfer belt 5 to generate a blurred image.

  Therefore, 100 continuous images were formed on an image of A3 size and image ratio 10% at an air temperature of 23 ° C. and a humidity of 50%, and the state of the scattered toner immediately after was confirmed. As a result, the toner stain at the lower part of the developing container 20 is most severe at the position B in the image region X shown in FIG. 3, and the stain is gradually reduced toward the downstream of the stirring screw 26 in the transport direction. It was almost unclean.

  Next, the image ratio was changed from 10% to 100% (full-color solid image: 0.5 g / toner replenishment), and the same evaluation was performed. As a result, it was confirmed that the level of contamination of the developing container 20 due to scattered toner was significantly deteriorated.

  Next, the toner charge amount at the B position and the Y position of the replenished toner was measured using a method of extracting the replenished toner from the developer replenishing port 30 using different color toners. As a result, the toner charge amount reached the above-mentioned saturation value of 30 μC / g at the Y position, but only reached 20 μC / g at the B position. In addition, the toner charge amount was more significantly reduced in a high temperature and high humidity environment.

  From the above results, the developer container 20 is smeared with the scattered toner because the toner having an insufficient toner charge amount and a little restraining force with the carrier is wound up in the stirring chamber 24 by the rotational force of the stirring screw 26, and from the lower jaw gap G. We could conclude that this was the result of the eruption. FIG. 2 shows the state.

  Then, examination about the lower jaw gap amount G and the scattering toner level was performed. Specifically, the lower jaw gap amount G was changed in three stages, 100 A3 size full-color images were continuously formed, and the fog density on the image output to the recording material in that state was measured. . The fog density was measured using a color difference meter (Tokyo Denshoku Co., Ltd. white photometer DENSIMETER TC-6DS). The results are shown in Table 1.

  As shown in Table 1, when the lower jaw gap amount G was set to about 0.5 mm, the fog level was 1.1% of the maximum density (255/255), which was a problem-free level. However, when the lower jaw gap amount G is narrowed, the developer takes in from the developing sleeve 28 after the development, which causes a problem that the developer overflows from the developing container 20. On the other hand, when the lower jaw gap amount G was set to 0.8 mm, the problem of the developer overflowing from the developing container 20 did not occur, but the fog density was 2.7%, which is 2.5% of the target. Could not fall below. If the fog level is determined to be 1.5% or less, there is no problem. The product target level is 2.5% or less.

  In the following embodiments, a new toner replenished without greatly changing the developer circulation characteristics in a vertical stirring type developing device in which conveying means for stirring and conveying the developer in the developing device is arranged vertically. Can be stirred and mixed with sufficient developer.

<Example 1>
FIG. 6 is an explanatory diagram of a toner charge amount reinforcing structure in the first embodiment. FIG. 6 shows an enlarged view of the downstream side of the developing chamber 23 and the upstream side of the stirring chamber 24 in FIG.

  As shown in FIG. 6, the developing chamber 23, which is an example of the first chamber, conveys the developer along the developing sleeve 28 while rotating the developing screw 25 having screw blades to supply the developer to the developing sleeve 28. To do. The stirring chamber 24 as an example of the second chamber is connected to the developing chamber 23 at both ends to form a developer circulation path. The stirring chamber 24 conveys the developer in the direction opposite to the developing chamber 23 while rotating the stirring screw 26 having screw blades to collect the developer from the developing sleeve.

  The developer supply port 30 is disposed at a predetermined position from the downstream end of the developer carrying region of the developing sleeve 28 in the developing chamber 23 to the developing sleeve 28 in the stirring chamber 24. The rib 53, which is an example of a toner charge amount reinforcing structure, circulates development by lowering the developer conveying performance from the developer supply port 30 to the developing sleeve 28 in the stirring chamber 24 as compared with the region along the developing sleeve 28. Increase the frequency of friction between the developer and the replenished developer.

  The developer replenishing port 30 is disposed “at 10 mm downstream from the position A of the downstream end of the developer carrying region of the developing sleeve 28”, which is an example of a predetermined position in the developer circulation path. The developer carrying region is not the end of the flange of the developing sleeve 28 but the end of the developer coating region on the developing sleeve 28. The reason why the developer replenishing port 30 is set 10 mm downstream from the position A is to prevent the uncharged toner replenished from the developer replenishing port 30 from flowing backward as scattered toner and being coated on the developing sleeve 28. It is.

  Further, a magnetic seal that closes the gap using a magnetic brush of developer is disposed at position A of the developing sleeve 28, so that the position is lower than the position A of the developing chamber 23 and the position A of the stirring chamber 24. On the upstream side, there is no opening that causes toner scattering such as the lower jaw gap.

  In the first embodiment, an example of the stirring protrusion between the developing screw 25 and the screw blade 51 of the stirring screw 26 in order to partially reduce the developer conveying ability from the developer supply port 30 to the position B of the stirring chamber 24. The rib 53 which is is arrange | positioned. As for the arrangement density of the stirring protrusions, the ribs 53 are arranged by being shifted from the position A of the developing chamber 23 to the position B of the stirring chamber 24 by 180 degrees with respect to the screw blade pitch interval of the developing screw 25 and the stirring screw 26. is doing. The arrangement density of the stirring protrusions in the region along the developing sleeve 28 is zero.

  By providing the ribs 53 at the pitch interval of the screw blades 51, the developer positioned at the interval of the screw blades 51 is disturbed by receiving the force in the direction perpendicular to the conveying direction by the effect of the ribs 53. As a result, the developer conveying ability in the axial direction by the developing screw 25 and the agitating screw 26 can be reduced, and the developer circulating between the developer replenishing port 30 and the position B of the agitating chamber 24 can be retained. At the same time, since the developing performance of the developing screw 25 and the stirring screw 26 is enhanced, the developer and the replenishing toner that are circulated are disturbed in the direction perpendicular to the conveying direction and mixed and dispersed with each other, increasing the frequency of friction between the toner and the carrier. As a result, the toner charge amount rises faster.

  In the developer carrying region of the developing sleeve 28, neither the developing screw 25 nor the stirring screw 26 is provided with ribs 53 at the pitch interval of the screw blades 51.

  The circulating developer conveyed by the developing screw 25 through the developer carrying area of the developing sleeve 28 at a relatively high speed is decelerated immediately before the developer supply port 30. For this reason, even if the developer mass speed (g / sec) does not change, the developer to be circulated is congested as much as the conveyance speed (mm / sec) is reduced, and the stirring chamber 24 is fed from the developer supply port 30. The amount of developer up to position B increases. Since the replenishment toner is mixed with the increased developer, the chance of friction of the replenishment toner against the carrier increases.

  In the first exemplary embodiment, the ribs 53 are arranged to secure the amount of developer that can come into contact with the replenishing toner, to improve the performance of imparting the toner charge amount to the replenishment toner, and to improve the toner charge amount imparting performance. . By arranging the ribs 53, the developer amount in the vicinity of the developer supply port 30 is increased by 50% from 10 g before arrangement to 15 g, and the developer amount remaining from position A to position B is increased to 30 g. did.

As a result, the following experimental results were obtained.
(1) When the toner was collected at the position B of the stirring chamber 24 and the toner charge amount was measured, 20 μC / g before the rib 53 was arranged was improved to 25 μC / g.
(2) When the image formation test of 100 sheets of A3 size image ratio 100% (full-surface solid image) was continuously performed, it was confirmed that the fog level was within the allowable 2.5% level.
(3) When the image formation test of 100 sheets of A3 size image ratio 10% was performed and confirmed, the fog level was kept at 1.0% or less which is not a problem at all.
(4) When an image output test of 50,000 sheets was performed using a test image having an A3 size image ratio of 10%, it was confirmed that contamination around the developing device due to toner scattering was not a problem. On the other hand, in the conventional developing device in which the rib 53 is not provided, when the image output test of 50,000 sheets is performed, the contamination due to the scattered toner is conspicuous outside the position B of the stirring chamber 24.

<Example 2>
FIG. 7 is an explanatory diagram of a toner charge amount reinforcing structure in the second embodiment. FIG. 7 is an enlarged view of the downstream side of the developing chamber 23 and the upstream side of the stirring chamber 24 in FIG.

  As shown in FIG. 7, the arrangement of the developing chamber 23, the stirring chamber 24, the developing sleeve 28, the developer supply port 30 and the rib 53 of the stirring screw 26 are configured in the same manner as in the embodiment, and therefore the same as in FIG. 6. The description which attaches a code | symbol and overlaps is abbreviate | omitted.

  In the second embodiment, the screw blade 51 of the developing screw 25 is disposed in a region downstream of the developer supply port 30 in the developer conveying direction in order to partially reduce the developer conveying force downstream of the position A of the developing chamber 23. Is provided with a notch 53E. In the range where the screw blades 51 of the notch 53E are cut off, the developer conveying ability is substantially 0, and therefore it is possible to increase the apparent amount of developer by retaining the developer in the notch 53E. Become.

  In the second embodiment, by setting the notch 53E to one pitch (30 mm) of the screw blade 51, the amount of developer in the vicinity of the developer supply port 30 may be increased from 10 g before cutting to 20 g. did it. Further, by disposing the same rib 53 as in Example 1 on the stirring screw 26, the amount of developer remaining from the position A to the position B increased to 35 g.

  The reason why the notch 53E is provided downstream of the developer supply port 30 is that the developer supply port 30 can be blocked by the swelled developer if the developer is retained immediately below the developer supply port 30. It is because there is sex. For this reason, the notch 53E is more screwed than the developer supply port 30 so that the notch 53E does not appear directly below the developer supply port 30 while the screw blade 51 of the developing screw 25 rotates once. It is preferable to provide at least 1 pitch downstream of the above.

  Further, when the notch 53E is provided over two pitches or more of the screw blades 51, the developer conveying performance of the developing screw 25 is remarkably deteriorated, and the circulation balance of the developer in the developing container 20 is deteriorated. For this reason, it is desirable that the notch 53E is less than 2 pitches of the screw blade 51.

In Example 2, the following experimental results were obtained.
(1) When the image formation test of 100 sheets of A3 size image ratio 100% (full-surface solid image) was continuously performed, it was confirmed that the fog level was 2.0%.
(2) As a result of an image output test of 50,000 sheets using a test image with an A3 size image ratio of 10%, it was confirmed that the contamination around the developing device due to toner scattering was even smaller than that in Example 1.

<Example 3>
FIG. 8 is an explanatory diagram of a toner charge amount reinforcing structure in the third embodiment. FIG. 8 is an enlarged view of the downstream side of the developing chamber 23 and the upstream side of the stirring chamber 24 in FIG. The arrangement of the developing chamber 23, the agitating chamber 24, the developing sleeve 28, the developer replenishing port 30, and the rib 53 of the agitating screw 26 are configured in the same manner as in the embodiment. Description is omitted.

  As shown in FIG. 8, in Example 3, the developer conveying performance from the developer supply port 30 to the developing sleeve 28 in the stirring chamber 24 is from the downstream end of the developer carrying region of the developing sleeve 28 in the developing chamber 23. Partially lower than the developer supply port 30. The permanent magnet 55, which is an example of a magnetic force generating member, is disposed in the stirring chamber 24 located from the developer supply port 30 to the upstream side of the developing sleeve 28. The permanent magnet 55 forms a developer magnetic spike 56 on the inner wall surface of the stirring chamber 24 so as to interfere with the screw blades of the rotating stirring screw 26.

  In the third embodiment, the developing screw 25 disposed in the developing chamber 23 is not provided with the rib (53) and the notch (53E) as in the first embodiment. Instead, a permanent magnet 55 having a magnetic flux density of 1000 G is disposed on the side surface of the developing container 20 so as to be located upstream of the position B of the stirring chamber 24. The magnetic force 56 of the developer is formed on the inner wall surface of the developing container 20 by the magnetic force of the permanent magnet 55.

  The developer conveyed through the agitating chamber 24 by the agitating screw 26 breaks up the aggregation of the replenishing toner in the process of advancing and cutting through the magnetic spike 56 of the developer. Since the rib 53 is arranged up to the position B of the stirring screw 26, the replenished toner whose aggregation has been broken is efficiently mixed and stirred in the developer.

  Generally, the replenished toner immediately after being replenished from the developer replenishing port 30 is often present as a toner aggregate, which prevents mixing of the circulating developer with the carrier. However, the toner aggregates are easily broken by being pressed against the magnetic spikes of the developer, mixed into the circulating developer, and easily brought into contact with the carrier.

  In the configuration of Example 3, the amount of developer remaining from position A to position B did not increase as much as in Examples 1 and 2, but increased by about 5 g compared to the conventional case, but the toner charge amount was not good. The sufficient toner ratio was less than that of Examples 1 and 2. This is presumably because the toner aggregates are reduced, so that the replenished toner is uniformly dispersed in the developer, and the opportunity for the toner to come into contact with the carrier is dramatically increased.

  If the magnetic flux density of the permanent magnet 55 is 500 G or more, there is an effect of loosening the aggregation of the replenishing toner, and the effect of loosening the larger the magnetic flux density. However, as the magnetic flux density increased, the rotational load of the stirring screw 26 increased and noise and vibration were generated. In particular, at 3000 G or more, the conventional drive motor does not rotate, and the drive motor needs to be enlarged, which is not preferable. For this reason, the magnetic flux density of the permanent magnet 55 is preferably 500 to 3000 G.

In Example 3, the following experimental results were obtained.
(1) When the image formation test of 100 sheets of A3 size image ratio 100% (full-surface solid image) was continuously performed, it was confirmed that the fog level was 2.0%.

<Example 4>
FIG. 9 is an explanatory diagram of a cross-sectional configuration perpendicular to the longitudinal direction of the developing device according to the fourth embodiment. In Example 4, a toner charge amount reinforcement structure similar to that in Example 1 was provided in an ACR type developing device.

  In the developing method using the two-component developer, the toner is consumed by the developing operation of the electrostatic image, whereas the carrier remains in the developing device without being consumed and continues to circulate. For this reason, if the toner is used for a long time, toner external additives and toner components adhere to the surface of the carrier and become contaminated. As a result, the charging ability of the carrier decreases, the toner charge amount also decreases, and the scattering fogging occurs. Such as image degradation may occur.

  Therefore, in recent years, an ACR (AUTO CARRYER REPURENISHMENNT) type developing device in which not only toner but also a carrier is replenished together to suppress a decrease in charging performance has been put into practical use. Specifically, the replenishment developer in which the carrier is mixed with the toner is replenished from the developer replenishment device to the development device, and the excess developer in the development device that has become excessive due to the replenishment of the replenishment developer is removed from the wall surface of the development device. Overflow from the developer outlet.

  The carrier concentration in the replenishment developer is called the CD ratio. The CD ratio is the weight ratio of carrier to toner in the replenishment developer. When a replenishment developer with a high CD ratio is used, the carrier replacement ratio increases and the average developer age of the developer circulating in the developing device can be lowered, so that the toner scattering level can be lowered. become. However, since the developer to be discarded increases, the running cost of the developer increases. Therefore, the CD ratio is usually about 5 to 20%, more preferably within the range of 10 to 15%. Here, a 10% agent was used.

  As shown in FIG. 9, the developing device 4 a is configured except that the developer developer having a CD ratio of 10% is supplied from the developer supply device 31 and the excess developer is discharged from the developer discharge port 40. It is the same as that of FIG. For this reason, in FIG. 9, the same code | symbol is attached | subjected to the structure which is common in FIG. 1, and the overlapping description is abbreviate | omitted.

  A developer discharge port 40 is provided on the wall surface of the developing chamber 23 of the developing device 4a, and a part of the circulating developer is discharged in the direction of arrow R40 through the developer discharge port 40. When the developer circulating in the developing device 4a increases due to the replenishment of the replenishment developer, the developer surface in the developing chamber 23 rises according to the increase amount, so that excess developer overflows from the developer discharge port 40. Is discharged. The discharged excess developer is transported to one end in the longitudinal direction by the recovery screw 41 and dropped into a recovery developer storage (not shown).

  Here, the positional relationship between the developer discharge port 40 and the developer supply port 30 is very important. The position of the developer discharge port 40 is formed slightly upstream from the position of the developer supply port 30 in the developer transport direction. This is to prevent a new supply developer supplied through the developer supply port 30 from being immediately discharged from the developer discharge port 40.

  By the way, in the ACR configuration, since the discharge amount is controlled by overflowing when the surface of the circulating developer reaches a predetermined height, the surface of the developer near the developer discharge port 40 is relatively easily maintained at a certain level. be able to.

  However, the bulk density of the developer changes due to a change in the toner charge amount accompanying a change in the installation environment and a change in the degree of aggregation of the developer accompanying the deterioration of the carrier or toner. The bulk density is a density when a powder of a certain volume is filled with powder. Specifically, when the degree of aggregation is increased due to the removal of external additives, or when the developer is left in a low-temperature and low-humidity environment and the toner charge amount is increased, the bulk density is decreased and the surface of the agent is reduced. To rise. When the developer surface circulating increases and the discharge from the developer discharge port 40 increases, the developer amount (total weight) in the developing device 4a decreases while the surface of the developer is kept constant.

  When the developer amount in the developing device 4a is reduced, the toner agitation / mixing performance is reduced, and the toner charge amount is reduced, and as described above, there is a possibility that toner scattering, fogging image, or the like occurs. . In particular, when the installation environment of the image forming apparatus 100 is suddenly changed from a low temperature and low humidity environment to a high temperature and high humidity environment, that is, when the environment is changed to high temperature and high humidity in a state where the developer amount is reduced in the low temperature and low humidity environment, The absolute value of the charge amount tends to decrease. At this time, if the toner charge amount does not rise sufficiently, toner scattering or a fogged image may appear.

  Therefore, as shown in FIG. 6, as in the first embodiment, ribs 53 are arranged in a portion downstream of the developer supply port 30 of the developing screw 25 and a portion upstream of the position B of the stirring screw 26.

In Example 4, the following experimental results were obtained in a high temperature and high humidity environment (30 ° C., 80%).
(1) When the image formation test of 100 sheets of A3 size image ratio 100% (full-surface solid image) was continuously performed, it was confirmed that the fog level is within an allowable range from 3.7% when the rib 53 is not disposed. Of 2.5%.
(2) When 100 consecutive image formation tests were performed using test images with an A3 size image ratio of 10%, the fog level was 1.2%, which was not a problem at all.
(3) As a result of an image output test of 50,000 sheets using a test image with an A3 size image ratio of 10%, it was confirmed that contamination around the developing device due to toner scattering was not a problem. On the other hand, in the developing device in which the rib 53 is not disposed, when the image output test of 50,000 sheets is performed, the contamination due to the scattered toner is conspicuous outside the position B of the stirring chamber 24.

  Therefore, it was possible to suppress the fogged image even with respect to a change in the developer surface due to a sudden change in the environment, which was a problem occurring in the ACR type developing device 4a.

<Example 5>
FIG. 10 is an explanatory diagram of the arrangement of the developer supply device in the fifth embodiment. FIG. 11 is an explanatory diagram of a change in toner density over time due to an error in the developer replenishment amount. FIG. 12 is an explanatory diagram of a toner charge amount reinforcing structure in the fifth embodiment. FIG. 12 is an enlarged view of the downstream side of the developing chamber 23 and the upstream side of the stirring chamber 24 in FIG.

  In the developing device 4a shown in FIG. 3, as described above, the toner supply amount control is performed by adopting the video count supply control system. The video count replenishment control method is a control method in which the toner consumption is predicted from the image data by obtaining the total laser exposure time (video count value), and toner replenishment accuracy is extremely important. Become.

  As shown in FIG. 11, a simulation experiment was conducted to see how the toner density (TD ratio) in the developing device 4a changes depending on the toner replenishment amount error. Assuming a developer amount in the developing device 4a of 350 g, a TD ratio of 8%, a replenishment amount of 0.05 g with a 10% image ratio, the replenishment error was varied between + 10% and + 20%. As a result, when toner replenishment control is performed with a + 20% replenishment error, it has been found that the TD ratio increases by 1.5% simply by forming 100 continuous images.

  In the case of the developing device 4a, it has been found that the cause of the toner replenishment error is that the bulk density of the toner filled in the replenishment screw 32 is greatly affected, and the bulk density of the toner varies considerably depending on the temperature and humidity environment. did.

  Therefore, in the fifth embodiment, as shown in FIG. 10, an auxiliary supply tank 38 is disposed below the developer supply device 31, and the toner in the auxiliary supply tank 38 is subjected to a certain amount of shear compression to thereby obtain a bulk density. The structure which stabilizes is adopted. The auxiliary replenishing tank 38 has a built-in shear screw, which rotates in the opposite direction to the supply screw in the developer replenishing device 31 and scrapes off the replenishing developer so as not to collapse in a pressurized state.

  As a result, the change in the bulk density due to the temperature / humidity environment or the like was suppressed, and the error of the toner replenishment amount could be ± 5% or less. However, as shown in FIG. 10, in order to secure the space for arranging the auxiliary replenishment tank 38, the developer replenishing port 30 of the developer replenishing device 31 is at a position where the stirring screw 26 in the stirring chamber 24 is extended upstream. Was to be placed. For this reason, as compared with Example 1, the opportunity to agitate the replenishment developer and the circulating developer on the downstream side of the developing chamber 23 has been lost.

  In the developing device 4a, the developer dropped into the stirring chamber 24 through the communication portion 22 is conveyed by the stirring screw 26, and is lifted and transferred to the developing chamber 23 by the communication portion 21 on the opposite side. Therefore, the vicinity of the communicating portion 22 on the upstream side of the stirring screw 26 is a place where the developer amount is the smallest in the developing container 20.

  In the developing device configuration of the fifth embodiment in which the developer replenishing port 30 is provided on the upstream side of the communicating portion 22 in the stirring chamber 24, a portion where only the replenishing developer exists from the developer replenishing port 30 to the communicating portion 22. It becomes.

  Since the replenishment developer used in Example 5 is a 10% CD ratio agent, that is, a 90% TD ratio agent, the developer supply port 30 to the communication portion 22 are compared with those in Examples 1 to 4 described above. In the meantime, a state in which almost no carrier was present (10% by weight) occurred.

  Therefore, in Example 5, as shown in FIG. 12, the developer agitation performance between the communication portion 22 and the position B is further improved as compared with Examples 1 and 3. A permanent magnet 55 is disposed on the outer wall of the stirring chamber 24 so that magnetic spikes that interfere with the stirring screw 26 in the vicinity of the communication portion 22 are formed. In addition, a rib 53 is disposed on the stirring screw 26 between the communication portion 22 and the position B. In particular, the ribs 53 are arranged at intervals of 180 degrees in the first embodiment. However, the ribs 53 are arranged at intervals of 90 degrees to make it easier to stir and mix the developer.

As shown in FIG. 12, in Example 5, in addition to the permanent magnet 55 having the effect as in Example 3, it was adopted in Example 1 in a portion upstream of the B position of the stirring chamber 24 in the stirring screw 26. The ribs 53 were arranged at a higher density than in Example 1. As a result, in Example 4, the following experimental results were obtained in a high temperature and high humidity environment (30 ° C., 80%).
(1) When the image formation test of 100 sheets of A3 size image ratio 100% (full-surface solid image) was performed continuously, the fog level was improved to 2.0% or less of the allowable range.

  As described above, in Embodiments 1 to 5, the developer from the end of the developer coat area downstream in the developer transport direction in the developing chamber 23 to the immediately preceding portion of the developer coat area upstream in the developer transport direction in the stirring chamber 24. Correction means capable of changing the conveying force is provided. Further, a correcting means capable of changing the developer conveying force is disposed from the developer replenishing port 30 to a portion immediately downstream of the developer conveying direction in the stirring chamber 24 and immediately upstream of the developer coating area. . As a result, it is possible to provide a developing device that can easily prevent scattered toner and fogged images that are likely to cause problems in the vertical stirring type developing device.

1a, 1b, 1c, 1d Photosensitive drum (image carrier)
2a, 2b, 2c, 2d Corona chargers 3a, 3b, 3c, 3d Exposure devices 4a, 4b, 4c, 4d Developing device 20 Developing container, 23 developing chamber, 24 stirring chamber 25 developing screw, 26 stirring screw 28 developing sleeve ( (Developer carrier), 30 developer supply port 31 developer supply device, 40 developer discharge port 51 screw blade (spiral blade), 53 rib 55 magnetic field generator

Claims (4)

A developer carrier for developing an electrostatic image formed on the image carrier;
A first chamber for supplying a developer to the developer carrier;
A second chamber connected to the first chamber to form a developer circulation path and collecting the developer from the developer carrier;
A first conveying member provided in the first chamber for conveying the developer;
A second transport member provided in the second chamber for transporting the developer;
The developer is replenished downstream of the developer carrying area of the developer carrying body in the first chamber in the developer carrying direction and upstream of the developer carrying area of the developer carrying body in the second chamber. A developer replenishing port,
The developer carrying capability of at least a part of a region in the developer carrying direction upstream of the developer carrying member in the second chamber downstream of the developer supply port in the developer carrying direction is partially A developing device characterized by being lowered. The first and second transport members rotate the screw blades to transport the developer along the developer carrier,
In the portion of the first or second conveying member located from the developer supply port to the developer carrying member, the developer carrying performance by the screw blades is lower than the region along the developer carrying member. The developing device according to claim 1, wherein the developing device is set.   In the portion of the first or second conveying member located from the developer supply port to the developer carrier, the arrangement density of the stirring protrusions provided in the interval between the screw blades is set in the developer carrier. The developing device according to claim 2, wherein the developing device is higher than a region along the line.   A magnetic force generating member in which magnetic spikes of the developer are formed on the inner wall surface so as to interfere with the screw blades of the rotating second conveying member is provided from the developer supply port to the upstream side of the developer carrier. The developing device according to claim 2, wherein the developing device is disposed in the second chamber.

Images