Image forming device

Abstract

To provide a developing device having a toner supply roller that supplies only toner to a developing roller, where toner that separated from the developing roller without being used for development is prevented from scattering to the outside of the developing device during an image forming operation.SOLUTION: During an image forming operation, an image forming apparatus applies a bias to each of a toner supply roller, a developing roller, and a conductive member so as to form a first potential difference between the toner supply roller and the developing roller so that a normally-charged toner is directed from the toner supply roller to the developing roller, form a second potential difference between the conductive member and the developing roller so that the normally-charged toner is directed from the conductive member to the developing roller, and form a third potential difference between the conductive member and the toner supply roller so that the normally-charged toner is directed from the conductive member to the toner supply roller. The second potential difference is larger than the first potential difference and larger than the third potential difference.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus equipped with a developing device having a toner supply roller that supplies only toner to a developing roller. [Background technology]

[0002] The developing device described in Patent Document 1 includes a developing container that contains a developer containing toner and a carrier, a developing roller that carries and transports the toner to a developing position, and a toner supply roller that carries and transports the developer supplied from a developer circulation path and supplies only toner to the developing roller. This developing device is provided with a toner blocking member for blocking toner that has been separated from the developing roller without being used for development and that is floating in the space between the toner supply roller, the developing roller, and the wall of the developing container. This blocking member is disposed close to the developing roller in the space between the magnet roller, the developing roller, and the wall of the developing container downstream of the closest position between the toner supply roller and the developing roller in the rotation direction of the toner supply roller. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-21278 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the configuration described in Patent Document 1, during image formation operation, a potential difference is formed between the toner supply roller and the developing roller such that normally charged toner flows from the toner supply roller to the developing roller, and the same potential is applied to the toner blocking member and the toner supply roller.

[0005] In the configuration described in Patent Document 1, among the floating toner that is not used in development and that is separated from the developing roller during the image forming operation, the floating toner that is present in the gap between the toner blocking member and the developing roller can be collected by electric field. However, in the configuration described in Patent Document 1, the same potential is applied to the toner blocking member and the toner supply roller during the image forming operation, so the floating toner that is present in the gap between the toner blocking member and the toner supply roller cannot be collected by electric field. As a result, there is a risk that part of the toner that is not used in development and that is separated from the developing roller during the image forming operation and that is floating in the space between the toner supply roller, the developing roller, and the wall of the developing container will be carried by the air current and scattered outside the developing device.

[0006] The present invention has been made in view of the above problems. An object of the present invention is to provide a developing device having a toner supply roller that supplies only toner to a developing roller, capable of preventing toner that has been separated from the developing roller without being used in development from scattering outside the developing device during image formation operation. [Means for solving the problem]

[0007] In order to achieve the above object, an image forming apparatus according to one aspect of the present invention includes the following configuration: an image carrier, a developing container that contains a developer including a toner and a carrier, a developing roller that carries and transports the toner to a developing position where an electrostatic latent image formed on the image carrier is developed, a toner supply roller that is disposed opposite the developing roller and carries and transports the developer supplied from the developing container and supplies only the toner to the developing roller, and a conductive roller that is disposed opposite each of the toner supply roller and the developing roller downstream of the developing position in the rotation direction of the developing roller and upstream of a closest position on the developing roller where the toner supply roller is closest to the developing roller. Laura a developing device having a developing roller and a toner supply roller, the developing roller and the toner supply roller being arranged to rotate in a direction opposite to the direction of rotation of the toner supply roller at the closest position; Laura A bias applying means for applying a bias to each of the 、 During an image forming operation, the polarity of the DC potential of the toner supply roller, the polarity of the DC potential of the developing roller, and the Laura The polarity of the DC potential of the toner supply roller is the same as the normal charging polarity of the toner, the absolute value of the DC potential of the toner supply roller is greater than the absolute value of the DC potential of the developing roller, and the conductive Laura The absolute value of the DC potential of the conductive layer is greater than the absolute value of the DC potential of the developing roller. Laura The absolute value of the DC potential of the toner supply roller is greater than the absolute value of the DC potential of the conductive Laura the absolute value of the difference between the DC potential of the toner supply roller and the DC potential of the developing roller is greater than the absolute value of the difference between the DC potential of the toner supply roller and the DC potential of the developing roller, Laura and the toner supply roller. The shortest distance between the developing roller and the conductive roller is 0.3 mm or less. It is characterized by: Effect of the Invention

[0008] According to the present invention, in a developing device having a toner supply roller that supplies only toner to a developing roller, it is possible to prevent toner that has detached from the developing roller without being used in development from scattering outside the developing device during image formation operation. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a configuration of an image forming apparatus according to a first embodiment. [Diagram 2] 1 is a cross-sectional view showing a configuration of a developing device according to a first embodiment. [Diagram 3] FIG. 2 is a cross-sectional view (enlarged view) illustrating the configuration of a developing device according to the first embodiment. [Figure 4] 3A to 3C are schematic diagrams showing waveforms of biases applied to a developing roller, a magnet roller, and a toner shielding member in the first embodiment. [Diagram 5]FIG. 4 is a schematic diagram for explaining a duty ratio of a bias waveform. [Figure 6] 10A to 10C are schematic diagrams showing waveforms of biases applied to a developing roller, a magnet roller, and a toner shielding member in a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the present invention according to the claims, and not all of the combinations of features described in the first embodiment are necessarily essential to the solution of the present invention. The present invention can be implemented in various applications, such as printers, various printing machines, copiers, FAX machines, and multifunction machines. Note that in the drawings, the same or corresponding parts are given the same reference symbols and will not be described repeatedly. Also, the X-axis, Y-axis, and Z-axis are mutually orthogonal, the Z-axis is approximately parallel to the vertical direction, and the Y-axis and Z-axis are approximately parallel to the horizontal direction.

[0011] [First embodiment] (Configuration of Image Forming Apparatus) An image forming apparatus 1 according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view showing the image forming apparatus 1 according to the embodiment of the present invention. The image forming apparatus 1 forms an image on a sheet P. In the first embodiment, the image forming apparatus 1 is a printer. The image forming apparatus 1 employs a tandem system and includes a feeding section 10, a conveying section 20, an image forming section 30, and a discharging section 100.

[0012] The feeding section 10 includes a cassette 11 that stores a plurality of sheets P. The sheets P are, for example, sheets made of paper or synthetic resin. The feeding section 10 feeds the sheets P from the cassette 11 to the conveying section 20. The conveying section 20 conveys the sheets P to the image forming section 30. The image forming section 30 forms an image on the sheets P. The conveying section 20 conveys the sheets P with the images formed thereon to the discharge section 100. The discharge section 100 discharges the sheets P outside the image forming apparatus 1.

[0013] The image forming section 30 includes an exposure unit 31, a unit 32a, a unit 32b, a unit 32c, a unit 32d, an intermediate transfer belt 33, a secondary transfer roller , and a fixing unit .

[0014] The exposure unit 31 irradiates each of the units 32a to 32d with light based on image data, and forms an electrostatic latent image on each of the units 32a to 32d.

[0015] The unit 32a forms a yellow toner image based on the electrostatic latent image, the unit 32b forms a magenta toner image based on the electrostatic latent image, the unit 32c forms a cyan toner image based on the electrostatic latent image, and the unit 32d forms a black toner image based on the electrostatic latent image.

[0016] The intermediate transfer belt 33 rotates in a rotation direction R1. Four-color toner images are transferred and superimposed on the outer surface of the intermediate transfer belt 33 from units 32a to 32d, forming an image. A secondary transfer roller 34 transfers the image formed on the outer surface of the intermediate transfer belt 33 onto a sheet P. A fixing unit 35 applies heat and pressure to the sheet P to fix the image onto the sheet P.

[0017] Each of units 32a to 32d includes a photoconductor drum 50 (image carrier), a charging device 51, a developing device 60, a primary transfer roller 53, a static eliminator 54, and a cleaner 55. The multiple photoconductor drums 50 contact the outer surface of the intermediate transfer belt 33 and are arranged along the rotation direction R1 of the intermediate transfer belt 33. The multiple primary transfer rollers 53 are provided corresponding to the multiple photoconductor drums 50 and face the multiple photoconductor drums 50 with the intermediate transfer belt 33 interposed therebetween.

[0018] In each of the units 32a to 32d, the charging device 51, the developing device 60, the primary transfer roller 53, the charge remover 54, and the cleaner 55 are disposed in this order along the circumferential surface of the photosensitive drum 50.

[0019] The photoconductor drum 50 rotates in a rotation direction R2. The charging device 51 charges the peripheral surface of the photoconductor drum 50. The peripheral surface of the photoconductor drum 50 is irradiated with light by the exposure unit 31, and an electrostatic latent image is formed.

[0020] The developing device 60 causes toner to adhere to the electrostatic latent image formed on the circumferential surface of the photoconductor drum 50, developing the electrostatic latent image and forming a toner image on the circumferential surface of the photoconductor drum 50. In other words, the photoconductor drum 50 carries a toner image.

[0021] The primary transfer roller 53 transfers the toner image carried by the photosensitive drum 50 onto the outer surface of the intermediate transfer belt 33 .

[0022] The static eliminator 54 eliminates static electricity from the peripheral surface of the photoconductor drum 50. The cleaner 55 removes the toner image remaining on the peripheral surface of the photoconductor drum 50.

[0023] Although the image forming device 1 is a printer, it may be a copier or a facsimile, or may be a multifunction device. The multifunction device includes at least two of a copier, a printer, a facsimile, and a scanner. Furthermore, the image forming device 1 is color-compatible, but may be monochrome-compatible.

[0024] Next, a developing device 60 according to an embodiment of the present invention will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a cross-sectional view of the developing device 60 according to an embodiment of the present invention. Fig. 3 is an enlarged view of the vicinity of the toner blocking member 65 in the cross section of the developing device 60 shown in Fig. 2.

[0025] As shown in FIG. 2, the developing device 60 includes a housing 70 (developing container), a developer accommodating section 80 (developing container), a magnet roller 63 (toner supply roller), a developing roller 64 (toner carrier), a toner blocking member 65 (conductive member), and a regulating blade 66.

[0026] A developer container 80, a magnet roller 63, a developing roller 64, a toner blocking member 65, and a regulating blade 66 are provided inside the housing 70. The housing 70 has a wall portion 71 and an opening 72.

[0027] A two-component developer (hereinafter simply referred to as developer) containing toner and carrier is contained in the developer container 80. The developer container 80 has a first transport chamber 81, a second transport chamber 82, and a partition wall 83. The developer container 80 is partitioned by the partition wall 83 into the first transport chamber 81 and the second transport chamber 82.

[0028] The first transport chamber 81 has a first transport screw 811. The second transport chamber 82 has a second transport screw 812. The first transport screw 811 rotates in a rotation direction R3, and transports the developer in the first transport chamber 81 while stirring it. In addition, the second transport screw 812 rotates in a rotation direction R4 that is the same as the rotation direction R3, and transports the developer in the second transport chamber 82 while stirring it. As a result, the developer is transported while circulating between the first transport chamber 81 and the second transport chamber 82. That is, a circulation path for the developer is formed between the first transport chamber 81 and the second transport chamber 82.

[0029] The toner is charged by stirring the developer by the first conveying screw 811 and the second conveying screw 812. In the first embodiment, the toner is a positively charged toner. That is, in the first embodiment, the normally charged toner is positively charged.

[0030] The second conveying screw 812 supplies the developer to the magnet roller 63 .

[0031] The magnet roller 63 is disposed inside the housing 70. The magnet roller 63 carries the developer on its surface.

[0032] The magnet roller 63 faces the second conveying chamber 82 and is rotatably supported by the housing 70. The magnet roller 63 includes a magnet 631 and a sleeve 632. The sleeve 632 is rotatable and has a cylindrical shape. The magnet 631 is fixedly disposed inside the sleeve 632 so as not to rotate. That is, the sleeve 632 rotates in a rotation direction R5 while keeping the magnet 631 stationary. The magnet 631 is composed of five magnetic poles, namely, magnetic poles N1, S1, S2, N2, and S3. In the first embodiment, the magnetic poles N1, S1, S2, N2, and S3 have magnetic flux densities (peak values ​​of magnetic flux density Br in the normal direction of the magnet roller 63) of 100 mT, 50 mT, 50 mT, 60 mT, and 60 mT, respectively.

[0033] The regulating blade 66 is attached to the housing 70 along the longitudinal direction of the magnet roller 63. The regulating blade 66 is disposed upstream of the closest position P1 between the magnet roller 63 and the developing roller 64 (the position on the developing roller where the developing roller 64 is closest to the magnet roller 63) in the rotation direction R5 of the magnet roller 63. A small gap is formed between the tip of the regulating blade 66 and the magnet roller 63. The regulating blade 66 is disposed opposite the magnet roller 63 and regulates the thickness of the layer of developer carried by the magnet roller 63 (the amount of developer carried by the magnet roller 63).

[0034] The developing roller 64 is disposed facing the magnet roller 63 inside the housing 70. The developing roller 64 receives toner from the magnet roller 63. The developing roller 64 carries and transports the toner to a position (developing position) where the electrostatic latent image formed on the photosensitive drum 50 is developed. The developing roller 64 is rotatably supported by the housing 70. The developing roller 64 includes a magnet 641 and a sleeve 642. The sleeve 642 is rotatable and has a cylindrical shape. The magnet 641 is disposed inside the sleeve 642 in a fixed non-rotating manner. In other words, the sleeve 642 rotates in a rotation direction R6 while keeping the magnet 641 stationary.

[0035] The magnet 641 is composed of one magnetic pole, magnetic pole S4. The magnet roller 63 and the developing roller 64 face each other at their facing positions (closest position P1) with a predetermined gap between them. In the first embodiment, the predetermined gap is set to 250 μm. The magnetic pole S4 of the magnet 641 has a polarity opposite to that of the opposing magnetic pole (pole N1) of the magnet 631. In the first embodiment, the magnetic flux density of the S4 pole (peak value of magnetic flux density Br in the normal direction of the developing roller 64) is 50 mT.

[0036] The magnet roller 63 supplies only toner to the developing roller 64 by an electric field formed between the magnet roller 63 and the developing roller 64 at the opposing portion (closest position P1) between the magnet roller 63 and the developing roller 64. Note that, at the opposing portion between the magnet roller 63 and the developing roller 64, a small amount of carrier in the developer carried by the magnet roller 63 may adhere to the developing roller 64. Even in this case, the magnet roller 63 is considered to supply only the toner in the developer carried by the magnet roller 63 to the developing roller 64.

[0037] A DC voltage and an AC voltage are applied to the magnet roller 63. A DC voltage and an AC voltage are also applied to the developing roller 64. The DC voltage and the AC voltage are as follows: As a DC and AC power source A developing bias voltage is applied to the magnet roller 63 and the developing roller 64 via a bias control circuit from a developing bias power supply (bias application means). Due to the potential difference between the voltage applied to the magnet roller 63 and the voltage applied to the developing roller 64, the normally charged toner is supplied from the magnet roller 63 to the developing roller 64. In addition, due to the effect of the AC component in the potential difference between the voltage applied to the magnet roller 63 and the voltage applied to the developing roller 64, the toner on the developing roller 64 after development is completed is collected by the magnet roller 63.

[0038] Here, a schematic diagram showing the waveforms of the biases applied to the developing roller, the magnet roller, and the toner shielding member in the first embodiment is shown in Fig. 4. As shown in Fig. 4, a developing bias is applied to the developing roller 64, in which an AC component having a frequency f1 = 4 kHz, a peak-to-peak voltage Vpp1 = 1.4 kV, and a duty ratio Dslv = 40% and a DC component having Vdc1 = 70 V are superimposed.

[0039] In the first embodiment, a developing bias having a frequency f2 of 10 kHz, a peak-to-peak voltage Vpp2 of 1.75 kV, and a duty ratio Dmag of 30% is applied to the magnet roller 63. This developing bias is a superimposed developing bias of an AC component of a so-called blank pulse waveform in which a rest period of 1.5 cycles is provided immediately after the end of the positive (+) component, and a DC component of Vdc2 of 340 V.

[0040] Here, the duty ratio of the bias waveform will be described with reference to the schematic diagram of Fig. 5. Here, the duty ratio Dslv indicates the duty ratio on the time axis on the side (same polarity side as the toner) where toner is caused to fly from the developing roller 64 to the photosensitive drum 50. Moreover, the duty ratio Dmag indicates the duty ratio on the time axis on the side (same polarity side as the toner) where toner is caused to fly from the magnet roller 63 to the developing roller 64.

[0041] For example, in the case where a positively charged toner is used and the upper direction in FIG. 5 is a positive potential and the lower direction is a negative potential, if the time during which the electric field that makes the toner fly is applied is a and the time during which the electric field that pulls the toner back is applied is b, the duty ratio Dp is expressed as Dp={a / (a+b)}×100. In other words, it is expressed as the percentage of the time during which the positive potential is applied relative to the total application time. When a negatively charged toner is used, the duty ratio is Dp={b / (a+b)}×100.

[0042] As described above, since the toner used in the first embodiment is a positively charged toner, by setting the value of Vdc2 to be greater than Vdc1, the toner moves from the magnet roller 63 to the developing roller 64. Also, in the first embodiment, the phase is adjusted so that the timing of application of the positive (+) component of the bias of the developing roller 64 and the timing of application of the negative (-) component of the bias of the magnet roller 63 coincide with each other. By doing so, the magnitude relationship between the potential of the developing roller 64 and the potential of the magnet roller 63 is periodically reversed when the AC component is also taken into account, so that the toner on the developing roller 64 after development is completed is also recovered by the magnet roller 63. Meanwhile, by transferring the toner between the developing roller 64 and the magnet roller 63 by the developing bias in this way, the toner becomes more likely to float.

[0043] As a result, during image formation operation (when the developing device 4 is driven), the rotation of the magnet roller 63 and the developing roller 64 causes toner to scatter from the magnet roller 63, the developing roller 64, and the opposing portion between the magnet roller 63 and the developing roller 64, becoming floating toner. This floating toner floats in the space S between the magnet roller 63, the developing roller 64, and the wall portion 71 of the housing 70.

[0044] 4, in the first embodiment, the AC component of the bias of the magnet roller 63 is almost stopped while the negative (-) component of the bias is being applied to the developing roller 64. This is to prevent the potential difference between the developing roller 64 and the magnet roller 63 from becoming large and causing leakage (discharge).

[0045] Generally, in the space S between the magnet roller 63, the developing roller 64, and the wall portion 71 of the housing 70, the rotation of the magnet roller 63 and the developing roller 64 generates an air flow. Therefore, the pressure inside the housing 70 becomes higher than the pressure outside the housing 70. This generates an air flow that moves air from inside the housing 70 to outside the housing 70. As a result, in the space S, the toner that has not been used for development is separated from the developing roller 64 by the magnetic brush, and the toner separated from the developing roller 64 floats and may be carried by the air flow and scattered outside the developing device 60 from the opening of the housing 70. In particular, when the peripheral speed of the photosensitive drum 50 is equal to or higher than a predetermined peripheral speed (for example, 180 mm / sec or higher), the flow rate of the air flow becomes large, so that the scattering of toner from the magnet roller 63, the developing roller 64, and the opposing portion between the magnet roller 63 and the developing roller 64 becomes noticeable.

[0046] As a countermeasure against this, in the first embodiment, the toner blocking member 65 is disposed downstream of the rotation direction of the magnet roller 63 from the closest position P1 between the magnet roller 63 and the developing roller 64 so as to substantially face both the developing roller 64 and the magnet roller 63. The toner blocking member 65 is disposed downstream of the rotation direction of the developing roller 64 from the position where the developing roller 64 develops the electrostatic latent image formed on the photosensitive drum 50, and upstream of the rotation direction of the developing roller 64 from the closest position P1 between the magnet roller 63 and the developing roller 64. The toner blocking member 65 is disposed at a position closer to the developing roller 64 than the magnet roller 63. That is, the toner blocking member 65 is disposed in the space S between the magnet roller 63, the developing roller 64, and the wall portion 71 so that the shortest distance between the toner blocking member 65 and the developing roller 64 is shorter than the shortest distance between the toner blocking member 65 and the magnet roller 63.

[0047] The toner blocking member 65 is preferably formed in a cylindrical or columnar shape. Compared to a rectangular parallelepiped shape having corners, a cylindrical or columnar shape is less likely to cause warping on the surface, and the toner blocking member 65 can be manufactured with high accuracy. In the first embodiment, the toner blocking member 65 is formed in a columnar shape. The toner blocking member 65 is supported by the housing 70. The toner blocking member 65 is a weakly magnetic or non-magnetic metal member. When the toner blocking member 65 is weakly magnetic, it is preferable that the toner blocking member 65 is an austenitic stainless steel. The toner blocking member 65 is a conductive member made of a conductive material. The diameter of the toner blocking member 65 is, for example, 4 mm or more.

[0048] 3, it is preferable that the distance d1 (shortest distance) between the toner blocking member 65 and the developing roller 64 is equal to or less than a predetermined dimension. In the first embodiment, the distance d1 between the toner blocking member 65 and the developing roller 64 is equal to or less than 0.3 mm. It is also preferable that the distance d2 (shortest distance) between the toner blocking member 65 and the magnet roller 63 is equal to or less than a predetermined dimension.

[0049] In the first embodiment, the distance d2 between the toner blocking member 65 and the magnet roller 63 is 2 mm or less. The magnet roller 63 carries a developer containing a carrier, and the toner shielding effect can be enhanced by setting the distance d2 to approximately the distance of the maximum magnetic ear length at the opposing portion between the toner blocking member 65 and the magnet roller 63. If the distance d2 is 1.0 mm or more wider than the maximum magnetic ear length, the shielding effect is weakened. On the other hand, if the distance d2 is 1.0 mm or more narrower than the maximum magnetic ear length, there is a risk that the developer will stagnate at the opposing portion.

[0050] The maximum magnetic brush length here refers to the maximum distance in the vertical direction from the surface of magnet roller 63 at the portion facing toner blocking member 65 to the tip of the magnetic brush. As for developing roller 64, since it is coated only with toner, it is possible to make it narrower, and conversely, in order to enhance the shielding effect, it is preferable to shorten the distance d2 between toner blocking member 65 and magnet roller 63.

[0051] Simply providing the toner shielding member 65 in the space S between the magnet roller 63, the developing roller 64, and the wall portion 71 is not enough to completely block the flow of toner, so toner leaking from the gap will scatter outside the developing device 60. In addition, the toner will adhere to the toner shielding member 65, and the toner may drip off, affecting the image. In particular, when the toner shielding member 65 is disposed vertically above the magnet roller 63, the dripped toner falls onto the magnet roller 63, so that the toner concentration is high only in that portion, and the image concentration is likely to be high after one rotation.

[0052] Therefore, in the first embodiment, when the magnet roller 63 and the developing roller 64 are driven, a DC potential Vdc3 having the same polarity as the normally charged toner and a larger absolute value than the developing roller 64 and the magnet roller 63 is applied to the toner blocking member 65.

[0053] That is, during the image forming operation, a potential difference (first potential difference) is formed between the magnet roller 63 and the developing roller 64 such that the normally charged toner moves from the magnet roller 63 to the developing roller 64. Also, during the image forming operation, a potential difference (second potential difference) is formed between the toner blocking member 65 and the developing roller 64 such that the normally charged toner moves from the toner blocking member 65 to the developing roller 64. Also, during the image forming operation, a potential difference (third potential difference) is formed between the toner blocking member 65 and the magnet roller 63 such that the normally charged toner moves from the toner blocking member 65 to the magnet roller 63. The second potential difference is larger than the first potential difference and is also larger than the third potential difference. In this way, the bias application means applies a bias to each of the magnet roller 63, the developing roller 64, and the toner blocking member 65 to form the first potential difference, the second potential difference, and the third potential difference.

[0054] By setting in this way, the potential difference formed between the toner blocking member 65 and the developing roller 64 causes the toner to be pressed from the toner blocking member 65 toward the developing roller 64. Also, by setting in this way, the potential difference formed between the toner blocking member 65 and the magnet roller 63 causes the toner to be pressed from the toner blocking member 65 toward the magnet roller 63.

[0055] As a result, the toner floating in the gap between the toner blocking member 65 and the developing roller 64 is collected by the developing roller 64, and the toner floating in the gap between the toner blocking member 65 and the magnet roller 63 is collected by the magnet roller 63. This makes it possible to prevent the toner floating in the space S between the magnet roller 63, the developing roller 64, and the wall portion 71 from scattering outside the developing device 70. It is also possible to prevent the toner from adhering to the surface of the toner blocking member 65 and dripping off.

[0056] In the first embodiment, the applied voltage Vdc3 of the toner shielding member 65 is set to 800 V. The applied voltage Vdc3 of the toner shielding member 65 is set to be larger than the DC component Vdc1 of the bias of the developing roller 64, which is 70 V, and the DC component Vdc2 of the bias of the magnet roller 63, which is 350 V, thereby obtaining the above-mentioned effects.

[0057] Furthermore, in the first embodiment, the applied voltage Vdc3 = 800 V to the toner shielding member 65 is set to be smaller than the maximum value Vpp1(max) = 910 V of the positive (+) component of the bias obtained by superimposing the AC component and DC component of the developing roller 64. In other words, the absolute value of the potential of the DC component of the bias applied to the toner shielding member 65 is set to be smaller than the absolute value of the peak potential of the AC component of the bias applied to the developing roller 64 on the same polarity side as the polarity of the normally charged toner.

[0058] In the first embodiment, the applied voltage Vdc3=800V to the toner shielding member 65 is set to be smaller than the maximum value Vpp2(max)=1565V of the positive (+) component of the bias obtained by superimposing the AC component and DC component of the magnet roller 63. In other words, the absolute value of the potential of the DC component of the bias applied to the toner shielding member 65 is set to be smaller than the absolute value of the peak potential of the AC component of the bias applied to the magnet roller 63 on the same polarity side as the polarity of the normally charged toner.

[0059] There are two reasons for this setting, as described below. The first reason is to suppress leakage caused by the potential difference between the toner blocking member 65 and the developing roller 64 becoming too large due to the AC component of the bias applied to the developing roller 64. The second reason is to suppress leakage caused by the potential difference between the toner blocking member 65 and the magnet roller 63 becoming too large due to the AC component of the bias applied to the magnet roller 63.

[0060] The second reason is that such a setting creates a time when the magnitude relationship between the voltage applied to the toner shielding member 65 and the voltage applied to the developing roller 64 and the magnet roller 63 is reversed, which promotes the removal of toner from the toner shielding member 65. In the first embodiment, the applied voltage Vdc3 of the toner shielding member 65 is set smaller than the maximum values ​​Vpp1(max) and Vpp2(max) of the positive (+) component of the bias of both the developing roller 64 and the magnet roller 63, which is a more preferable setting. On the other hand, in order to obtain the effect of promoting the removal of toner from the toner shielding member 65, the applied voltage Vdc3 of the toner shielding member 65 is set smaller than the maximum value Vpp1(max) of the positive (+) component of the bias of the developing roller 64. Or, it is set smaller than the maximum value Vpp1(max) of the positive (+) component of the bias of the magnet roller 63. Even if only one of these is applied, the corresponding effect can be obtained. In the case of negatively charged toner, the same effect can be obtained by making the absolute value of the applied voltage Vdc3 of the toner shielding member 65 smaller than the maximum values ​​Vpp1(max) and Vpp2(max) of the absolute values ​​of the negative (-) components of the bias of both the developing roller 64 and the magnet roller 63. Hereinafter, in the case of negatively charged toner, the same effect can be obtained when considering the absolute values.

[0061] Here, discharge (leak) will be described. If the applied voltage Vdc3 of the toner shielding member 65 is increased, the potential difference with the DC component Vdc1 of the bias of the developing roller 64 and the DC component Vdc2 of the bias of the magnet roller 63 can be increased, so that the effect of shielding the toner can be improved. However, if the potential difference is too large, leakage may occur. If leakage occurs, the bias may be disturbed, and if the bias is disturbed, image defects may occur.

[0062] As described above, in the first embodiment, the normally charged toner is a positively charged toner. Therefore, in the first embodiment, the DC component Vdc2 of the bias of the magnet roller 63 is set to be larger than the DC component Vdc1 of the bias of the developing roller 64. Also, the applied voltage Vdc3 of the toner shielding member 65 is set to be larger than the DC component Vdc2 of the bias of the magnet roller 63. That is, the relationship of "absolute value of the DC component Vdc1 of the bias of the developing roller 64" < "absolute value of the DC component Vdc2 of the bias of the magnet roller 63" < "absolute value of the applied voltage Vdc3 of the toner shielding member 65" is established. However, the polarities of the DC component Vdc1 of the bias of the developing roller 64, the DC component Vdc2 of the bias of the magnet roller 63, and the applied voltage Vdc3 of the toner shielding member 65 are the same as those of the normally charged toner.

[0063] In this manner, in the first embodiment, since the applied voltage Vdc3 to the toner shielding member 65 is large, the potential difference formed between the developing roller 64 and the toner shielding member 65 in particular tends to become large.

[0064] Therefore, in the first embodiment, an insulating layer is provided on the surface of the toner shielding member 65. In this way, by insulating the surface of the toner shielding member 65, leakage can be suppressed. If the insulating layer is made of an insulating material, the effect of suppressing leakage can be obtained. When using positively charged toner, by selecting a material that is easily charged to the same positive (+) polarity as the toner as the charging polarity of the insulating layer, the same polarity is easily repelled, and the toner is less likely to adhere to the surface of the insulating layer. Therefore, in the first embodiment, a polyimide tube that is easily charged to the positive (+) is used, and an insulating layer is provided on the surface of the toner shielding member 65 by utilizing heat shrinkage. In the case of negatively charged toner, it is preferable to use a PFA (fluorine) tube that is easily charged to the negative (-) polarity.

[0065] Although a new high-voltage power supply unit (separate power supply) may be provided to apply the applied voltage Vdc3 to the toner shielding member 65, if the voltage Vdc3 is generated from the bias applied to the developing roller 64 or the bias applied to the magnet roller 63, there is no need to provide a separate high-voltage power supply unit (separate power supply). For example, if a voltage doubler rectifier circuit is used, it is possible to output a DC bias that is approximately equal to the peak-to-peak of the AC component of the input bias. In the first embodiment, an AC component with a peak-to-peak voltage Vpp1 of 1.4 kV is applied to the developing roller 64, and an AC component with a peak-to-peak voltage Vpp2 of 1.75 kV is applied to the magnet roller 63.

[0066] Therefore, whether the peak-to-peak voltage Vpp1 or Vpp2 is used, the applied voltage Vdc3 = 800 V to the toner shielding member 65 can be generated by using a voltage doubler rectifier circuit. Note that if the peak-to-peak of the AC component of the input bias is small or the effect of voltage drop in resistors or the like is large, and the desired voltage cannot be obtained even by using a voltage doubler rectifier circuit, a peak hold circuit or the like may be used.

[0067] One advantage of generating the applied voltage Vdc3 to the toner shielding member 65 from the bias applied to the developing roller 64 and the magnet roller 63 is that there is no need to provide a new high-voltage power supply unit. Another advantage is that if a high-voltage power supply unit is provided independent of the developing roller 64 and the magnet roller 63, there may be a case where the applied voltage Vdc3 to the toner shielding member 65 is not applied (=0V) due to a malfunction or the like. In this case, the potential relationship with the developing roller 64 and the magnet roller 63 may be reversed, and the toner may move to the toner shielding member 65. In addition, if a high-voltage power supply unit is provided independent of the developing roller 64 and the magnet roller 63 and the applied voltage Vdc3 to the toner shielding member 65 is not applied (=0V) due to a malfunction or the like, the potential difference with the developing roller 64 and the magnet roller 63 may become larger than necessary. In the first embodiment, the maximum value of the voltage applied to the magnet roller 63 is greater than that to the developing roller 64, and the potential difference between the magnet roller 63 and the toner shielding member 65 is 1565 V, so there is a risk of leakage.

[0068] For this reason, in the first embodiment, a voltage doubler rectifier circuit is used to generate the bias to be applied to the toner shielding member 65 from the bias to be applied to the magnet roller 63. Due to the above-mentioned two advantages, (DC power supply) A power supply for generating a bias to be applied to the toner blocking member 65 (DC power supply) It is preferable to use the same power source for both the magnet roller 63 and the bias voltage Vcc, rather than using separate power sources for both the magnet roller 63 and the bias voltage Vcc. (DC power supply) A power supply for generating a bias to be applied to the toner blocking member 65 (DC power supply) It goes without saying that the invention according to the first embodiment can be similarly applied to a modified example in which the power supplies are separate.

[0069] As described above, in the first embodiment, the toner blocking member 65 is disposed in the space S between the magnet roller 63, the developing roller 64, and the wall portion 71, downstream in the rotation direction of the magnet roller 63 from the closest position P1 between the magnet roller 63 and the developing roller 64. Also, the toner blocking member 65 is disposed downstream in the rotation direction of the developing roller 64 from the position where the developing roller 64 develops the electrostatic latent image formed on the photosensitive drum 50, and upstream in the rotation direction of the developing roller 64 from the closest position P1 between the magnet roller 63 and the developing roller 64.

[0070] The toner is pressed from the toner shielding member 65 toward the developing roller 64 by the potential difference formed between the toner shielding member 65 and the developing roller 64. The toner is pressed from the toner shielding member 65 toward the magnetic roller 63 by the potential difference formed between the toner shielding member 65 and the magnetic roller 63. As a result, the toner floating in the gap between the toner shielding member 65 and the developing roller 64 is collected by the developing roller 64, and the toner floating in the gap between the toner shielding member 65 and the magnetic roller 63 is collected by the magnetic roller 63. This makes it possible to prevent the toner floating in the space S between the magnetic roller 63, the developing roller 64, and the wall portion 71 of the housing 70 from being carried by the air current and scattering outside the developing device 70.

[0071] [Second embodiment] In the first embodiment, an example has been described in which only a DC component is applied as the bias to the toner shielding member 65. On the other hand, in the second embodiment, a bias in which a DC component and an AC component are superimposed is applied as the bias to the toner shielding member 65. In the second embodiment, only the points that are different from the first embodiment will be described, and detailed descriptions of the other points that are the same as in the second embodiment will be omitted since the configuration and the operation are the same as those in the second embodiment.

[0072] By applying a DC bias to the toner blocking member 65, it is possible to enhance the blocking effect of the electric field between the toner blocking member 65 and the magnet roller 63, and to enhance the blocking effect of the electric field between the toner blocking member 65 and the developing roller 64. On the other hand, the magnitude relationship of the potential between the biases changes from moment to moment, which may cause new floating toner. In addition, there is a growing concern about leakage due to an excessively large potential difference.

[0073] Therefore, in the second embodiment, a bias having the same AC component as that of the developing roller 64, a frequency f1=4 kHz, a peak-to-peak voltage Vpp1=1.4 kV, and a duty ratio Dslv=40%, and differing only in the DC component (Vdc3=800 V) is applied to the toner shielding member 65. By doing so, the magnitude relationship of the potentials at least between the developing roller 64 and the toner shielding member 65 does not change, and the normally charged toner is always subjected to a force in the direction of the developing roller 64. In addition, since the potential difference between the developing roller 64 and the toner shielding member 65 does not become too large, leakage is also suppressed.

[0074] In the second embodiment, the AC component of the bias applied to the toner shielding member 65 is the same as that of the development roller 64, but it may be the same as that of the magnet roller 63. In this case, the magnitude relationship of the potentials does not change at least between the magnet roller 63 and the toner shielding member 65, and the normally charged toner is always subjected to a force in the direction of the magnet roller 63. In addition, since the potential difference between the magnet roller 63 and the toner shielding member 65 does not become too large, leakage is also suppressed.

[0075] However, among the DC component of the bias applied to the toner shielding member 65, the DC component of the bias applied to the developing roller 64, and the DC component of the bias applied to the magnet roller 63, the absolute value of the DC component of the bias applied to the toner shielding member 65 is set to be the largest. For this reason, there is a high concern about leakage between the developing roller 64 having the smaller value of the minimum value Vpp1(min) of the bias applied to the developing roller 64 and the bias Vpp2(min) of the bias applied to the magnet roller 63. For this reason, it is more preferable to make the AC component of the bias applied to the toner shielding member 65 the same as the AC component of the developing roller 64.

[0076] (Other embodiments) The present invention is not limited to the above-described embodiments, and various modifications (including organic combinations of the respective embodiments) are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0077] In the above embodiment, as shown in Fig. 1, an image forming apparatus using the intermediate transfer belt 33 has been described as an example, but the present invention is not limited to this. It is also possible to apply the present invention to an image forming apparatus configured to transfer images by directly contacting the paper P with the photosensitive drums 50 in sequence. [Explanation of symbols]

[0078] 1. Image forming device 50 Photoconductor drum 60 Developing device 63 Magnetic Roller 64 Developing roller 65 Toner blocking member 70 Housing

Claims

1. An image carrier; a developing device comprising: a developing container containing a developer containing a toner and a carrier; a developing roller which carries and transports the toner to a developing position where an electrostatic latent image formed on the image carrier is developed; a toner supply roller which is disposed opposite the developing roller, carries and transports the developer supplied from the developing container and supplies only the toner to the developing roller; and conductive rollers which are disposed opposite each of the toner supply roller and the developing roller downstream of the developing position in terms of the rotational direction of the developing roller and upstream of a closest position on the developing roller where the toner supply roller is closest to the developing roller, wherein the rotational direction of the developing roller at the closest position is opposite to that of the toner supply roller; a bias applying unit for applying a bias to each of the toner supply roller, the developing roller, and the conductive roller; Equipped with During the image forming operation, the polarity of the DC potential of the toner supply roller, the polarity of the DC potential of the developing roller, and the polarity of the DC potential of the conductive roller are the same as the normal charging polarity of the toner; the absolute value of the DC potential of the toner supply roller is greater than the absolute value of the DC potential of the developing roller; an absolute value of a DC potential of the conductive roller is greater than an absolute value of a DC potential of the developing roller; the absolute value of the DC potential of the conductive roller is greater than the absolute value of the DC potential of the toner supply roller; an absolute value of a difference between a DC potential of the conductive roller and a DC potential of the developing roller is larger than an absolute value of a difference between a DC potential of the toner supply roller and a DC potential of the developing roller, and is also larger than an absolute value of a difference between a DC potential of the conductive roller and a DC potential of the toner supply roller; The shortest distance between the developing roller and the conductive roller is 0.3 mm or less.

1. An image forming apparatus comprising:

2. During the image forming operation, A bias having a DC component and an AC component superimposed thereon is applied to the toner supply roller, A bias having a DC component and an AC component superimposed thereon is applied to the developing roller, A bias in which a DC component and an AC component are superimposed is applied to the conductive roller.

2. The image forming apparatus according to claim 1,

3. The AC component of the bias applied to the conductive roller is the same as the AC component of the bias applied to the toner supply roller.

3. The image forming apparatus according to claim 2,

4. The AC component of the bias applied to the conductive roller is the same as the AC component of the bias applied to the developing roller.

3. The image forming apparatus according to claim 2,

5. During the image forming operation, A bias having a DC component and an AC component superimposed thereon is applied to the toner supply roller, A bias having a DC component and an AC component superimposed thereon is applied to the developing roller, A bias consisting of only a DC component is applied to the conductive roller.

2. The image forming apparatus according to claim 1,

6. The absolute value of the DC potential of the conductive roller is smaller than the absolute value of the peak potential on the same polarity side as the normal charging polarity of the toner, among the AC components of the bias applied to the toner supply roller.

6. The image forming apparatus according to claim 5,

7. The absolute value of the DC potential of the conductive roller is smaller than the absolute value of the peak potential on the same polarity side as the normal charging polarity of the toner, among the AC components of the bias applied to the developing roller.

6. The image forming apparatus according to claim 5,

8. The bias application means has a DC power supply that generates a DC voltage, an AC power supply that generates an AC voltage, and a rectifier circuit that generates a DC voltage from the AC voltage generated by the AC power supply, During the image forming operation, a DC voltage generated by the DC power source and an AC voltage generated by the AC power source are applied to the toner supply roller, A DC voltage generated by the DC power supply and a DC voltage generated by the rectifier circuit are applied to the conductive roller.

2. The image forming apparatus according to claim 1,

9. The bias application means has a DC power supply that generates a DC voltage, an AC power supply that generates an AC voltage, and a rectifier circuit that generates a DC voltage from the AC voltage generated by the AC power supply, During the image forming operation, a DC voltage generated by the DC power supply and an AC voltage generated by the AC power supply are applied to the developing roller, A DC voltage generated by the DC power supply and a DC voltage generated by the rectifier circuit are applied to the conductive roller.

2. The image forming apparatus according to claim 1,

10. The bias application means has a first DC power supply that generates a DC voltage, a second DC power supply that generates a DC voltage, and an AC power supply that generates an AC voltage; During the image forming operation, a DC voltage generated by the first DC power source and an AC voltage generated by the AC power source are applied to the toner supply roller, A DC voltage generated by the first DC power source and a DC voltage generated by the second DC power source are applied to the conductive roller.

2. The image forming apparatus according to claim 1,

11. The bias application means has a first DC power supply that generates a DC voltage, a second DC power supply that generates a DC voltage, and an AC power supply that generates an AC voltage; During the image forming operation, a DC voltage generated by the first DC power source and an AC voltage generated by the AC power source are applied to the developing roller, A DC voltage generated by the first DC power source and a DC voltage generated by the second DC power source are applied to the conductive roller.

2. The image forming apparatus according to claim 1,

12. a first magnet having a plurality of magnetic poles including a first magnetic pole is fixedly disposed in the toner supply roller so as to be non-rotatable; A second magnet having only one magnetic pole, a second magnetic pole that is a different polarity from the first magnetic pole, is fixedly disposed in the developing roller so as to face the first magnetic pole.

12. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

13. The shortest distance between the developing roller and the conductive roller is shorter than the shortest distance between the toner supply roller and the conductive roller.

13. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-layered image forming apparatus.

14. The shortest distance between the toner supply roller and the conductive roller is 2 mm or less.

14. The image forming apparatus according to claim 1,

15. The diameter of the conductive roller is 4 mm or more.

15. The image forming apparatus according to claim 1,

16. The surface of the conductive roller is insulated.

16. The image forming apparatus according to claim 1,

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