Electrified device and image forming apparatus

Abstract

The present application provides a charging device and an image forming apparatus. The charging device has a first charging section which charges a charged section by contacting the charged section, and a second charging section which charges the charged section by contacting the charged section, and a distribution of a contact area of the second charging section which contacts the charged section is different from the first charging section.

Description

Technical Field

[0001] This invention relates to charged devices and image forming apparatus. Background Technology

[0002] In charging devices employing a contact charging method using charged rollers, uneven wear sometimes occurs at the ends, closer to the center than in the rotational axis direction, due to the unevenness of the so-called contact width (known as the compression width) between the charged roller and the image holder containing the photosensitive layer, which is the charged object. As this uneven wear progresses, the charging voltage at the ends increases, potentially creating a difference in image density between the ends and the center. This can cause the carrier in the developer to leak into the image holder, resulting in image defects.

[0003] Furthermore, as a charging device for purposes other than image forming, Japanese Patent Application Publication No. 2009-132507 discloses a charging device that includes a charging roller that pre-charges an electrically insulating sheet to prevent the occurrence of sheet serpentination or winding deviation, thereby suppressing the occurrence of serpentination or winding deviation through electrostatic force.

[0004] In this electrified device, uneven wear may sometimes occur at the end of the central portion in the direction of rotation axis of the electrified roller due to the uneven contact width formed between the electrified roller and the opposing rotating body.

[0005] Furthermore, in recent years, in order to improve processing speed and thus increase image productivity, a charging device with two charging rollers configured to charge the image in a short time has been proposed (see Japanese Patent Application Publication No. 2005-017383). Summary of the Invention

[0006] The object of the present invention is to provide a charging device that makes the charging voltage in the rotation axis direction more uniform in a structure having two contact charging methods for charging the charged part, compared with the case where the present invention is not applied, and an image forming apparatus using the charging device.

[0007] According to a first aspect of the present invention, a charging device is provided, comprising: a first charged part that contacts a charged part to charge the charged part; and a second charged part that contacts the charged part to charge the charged part, wherein the distribution of the contact area between the second charged part and the charged part is different from that of the first charged part.

[0008] According to a second aspect of the present invention, the first charged part and the second charged part are a first charged roller and a second charged roller that respectively contact and rotate with the charged part, and the diameters of the first charged roller and the second charged roller when not in contact with the charged part are symmetrical in the direction of rotation axis, and the distributions are different from each other.

[0009] According to a third aspect of the present invention, at least one of the first electrified roller and the second electrified roller is a crown-shaped electrified roller with a relatively thick diameter at the center and a relatively thin diameter at the ends in the direction of rotation axis.

[0010] According to a fourth aspect of the present invention, the first charged part and the second charged part are respectively a first charged roller and a second charged roller whose two ends in the direction of rotation are pressed toward the charged part and in contact with the charged part and rotate thereon, and the pressing force of the first charged roller and the second charged roller is different from that of the other.

[0011] According to a fifth aspect of the present invention, the electric roller with relatively weak pressing force in the first electric roller and the second electric roller is a crown-shaped electric roller with a relatively thick diameter at the center and a relatively thin diameter at the ends in the direction of rotation axis.

[0012] According to a sixth aspect of the invention, the electrifying device has a power source that causes the applied voltage applied to the crown-shaped electrified roller to increase over time.

[0013] According to a seventh aspect of the present invention, an image forming apparatus is provided, comprising: the charging device; and an image holding unit, which serves as a charged unit receiving the charging from the charging device, and is charged by the charging device, thereby holding an electrostatic latent image formed by exposure, and further holding a toner image formed by toner development.

[0014] (Effect)

[0015] According to the first or seventh scheme, compared with the case where the first charged part and the second charged part have the same distribution of contact areas, it is possible to achieve uniformity of the charged voltage in the direction of rotation axis.

[0016] According to the second scheme, compared with the case where the diameters of the first and second charged rollers are distributed in the same direction along the rotation axis, it is possible to achieve uniformity of the charged voltage in the direction of rotation axis.

[0017] According to the third scheme, compared with the case where neither the first charged roller nor the second charged roller is a crown-shaped charged roller, it is possible to achieve uniformity of the charged voltage in the direction of rotation axis.

[0018] According to the fourth scheme, compared with the case where the pressing pressure of the first electrified roller and the second electrified roller are the same, it is possible to achieve uniformity of the electrified voltage in the direction of rotation axis.

[0019] According to the fifth scheme, compared with the case where the charged roller with relatively weak pressing force is not a crown-shaped charged roller, it is possible to achieve uniformity of the charged voltage in the direction of rotation axis.

[0020] According to the sixth scheme, compared with the case where a fixed voltage is applied over time, the change in the voltage of the charged layer over time is suppressed. Attached Figure Description

[0021] Figure 1 This is a schematic diagram showing the toner image forming section, which is a major part of the image forming apparatus.

[0022] Figure 2 This is an illustration of potential problems that may occur over time due to electrical charge.

[0023] Figure 3 (A) shows the state in which the charged roller is pressed against the image holder. Figure 3 (B) and (C) are schematic diagrams showing the shape of the extrusion area.

[0024] Figure 4 This is a graph showing the parameters of the main and auxiliary electrified rollers and the results after a period of time. Detailed Implementation

[0025] Hereinafter, embodiments of the present invention will be described. An example will be a charged device used in an image forming apparatus of the electronic photograph method. However, the charged device of the present invention can also be applied to charged devices other than those disclosed in Patent Document 1 and those used in image forming apparatuses.

[0026] Figure 1 This is a schematic diagram showing the toner image forming section, which is a major part of the image forming apparatus.

[0027] The toner image forming section 10 has an image holder 11. While rotating in the direction of arrow R, the image holder 11 forms an electrostatic latent image on its surface through a charging and exposure process, and then forms a toner image through the development of the toner and temporarily holds the toner image.

[0028] Furthermore, the toner image forming section 10 has a charging device 20. This charging device 20 has two charging rollers 12_1 and 12_2. Of these two charging rollers 12_1 and 12_2, the charging roller 12_1 on the upstream side in the rotational direction of the image holder 11 corresponds to an example of the first charging section and the first charging roller as referred to in this invention. And the charging roller 12_2 on the downstream side corresponds to an example of the second charging section and the second charging roller as referred to in this invention.

[0029] Furthermore, the charging device 20 has power supplies 13_1 and 13_2 that apply charging voltages to the two charging rollers 12_1 and 12_2 respectively. The two charging rollers 12_1 and 12_2 receive the applied charging voltages from their respective power supplies 13_1 and 13_2, thereby giving the image holder 10 a uniform potential. In this embodiment, the goal is to suppress uneven charging voltage in the rotational axis direction. Details will be described later. In this toner image forming unit 10, the image holder 11 is charged using two charging rollers 12_1 and 12_2. Therefore, compared to a structure with only one charging roller, the charging capability is higher, which can improve processing speed, including the rotational speed of the image holder 11, thereby improving image productivity.

[0030] Furthermore, the toner image forming unit 10 also includes an exposure unit 14 and a developer 15. The exposure unit 14 irradiates an exposure beam L modulated based on an image signal onto the image holder 11, thereby forming an electrostatic latent image on the surface of the image holder 11. The developer 15 contains a developer comprising toner and a carrier, and uses the toner in the developer to develop the electrostatic latent image on the image holder 11, thus forming a toner image on the image holder 11. This toner image is transferred onto a piece of paper P traveling in the direction of arrow M by the action of the transfer roller 16. Residual toner remaining on the image holder 11 after transfer by the transfer roller 16 is scraped off by a cleaning blade 17.

[0031] The toner image transferred onto paper P is fixed onto the paper by a fixing device (not shown), forming an image on the paper composed of the fixed toner image.

[0032] Figure 2 This is an illustration of potential problems that may occur over time due to electrical charge. Figure 2 (A) is a schematic diagram showing the image holder 11 and the developing roller 12 in their initial state. Figure 2 (B) is a schematic diagram showing the image holder 11 and developing roller 12 in a state after a period of time, for example, after 60,000 images have been formed. Figure 1 As shown, the image forming unit 1 has two charged rollers 12_1 and 12_2, but here, these two are represented by the charged roller 12 without distinction. Furthermore, this... Figure 2The left and right directions are similar to the rotation axis direction of body 11, that is, with Figure 1 The direction perpendicular to the paper surface.

[0033] exist Figure 2 In the initial state shown in (A), the retainer 11 has a uniform voltage Vh of the target value, both at the center and at the ends in the direction of its rotation axis.

[0034] Starting from this initial state, as the paper P travels along, the photosensitive layer (not shown) on the surface of the holder 11 is gradually scraped thinner, but the wear at the ends increases further compared to the central portion. At this time, when the central portion is charged with a target voltage Vh considering the change over time, the thinner portion at the ends has a higher voltage Vh than the target value. Therefore, Figure 1 The carrier in the developer within the developer unit 15 shown tends to move toward the image holder 11, and sometimes the carrier actually adheres to the image holder 11. Consequently, this carrier may sometimes scrape against the toner image in the rotational direction indicated by arrow R, resulting in streaky image defects. This embodiment includes a unit to suppress these image defects.

[0035] Figure 3 (A) is the state in which the charged roller is pressed against the image holder. Figure 3 (B) and (C) are schematic diagrams showing the shape of the extrusion area.

[0036] like Figure 3 As shown in (A), the charged roller 12 is made of a rubber-like elastomer and has a rotating shaft 121 passing through the center of the elastomer and bearings 122 on both sides. Furthermore, the bearings 122 on both sides are pressed against the image holder 11 by spring components (not shown) with a pressing force F. Figure 3 (A) shows a crown-shaped charged roller 12 with a relatively large diameter at its central portion and a relatively small diameter at its ends in the direction of rotation. Therefore, although it is shown that the central portion of the charged roller 12 bites into the image holder 11, in reality, the central portion of the charged roller 12 is squeezed by pressing against the image holder 11, thereby forming a squeezing region N in contact between the image holder 11 and the charged roller 12. This squeezing region N corresponds to the contact region described in this invention.

[0037] exist Figure 3 (B) shows a rectangular extrusion region N (solid line) with an extrusion width W equal to that at the center and ends, and an extrusion region N (dashed line) with an extrusion width W at the center narrower than that at the ends. Figure 3As shown in (A), the bearings 122 on both sides of the charged roller 12 are pressed. Therefore, even when not in contact with the image holder 11, the rotating shaft 121 of the crown-shaped charged roller 12 will slightly flex due to the pressing, thereby forming a rectangular compression region N with a compression width W that is the same at the center and the ends, or a compression region N with a narrow compression width W at the center. The compression width W is related to the charging performance. When the thickness of the photosensitive layer of the image holder 11 is uniform, by making the compression width W the same at the center and the ends, it is possible to make the image holder 11 have a uniform charging voltage Vh at the center and the ends. Alternatively, by making the compression width W at the center narrower than the compression width W at the ends, it is possible to make the charging voltage Vh at the ends higher than that at the center. Figure 3 The extrusion region N shown in (B) is Figure 1 A typical example of the extrusion region N of, for example, the upstream side of the electrified roller 12_1, one of the two electrified rollers 12_1 and 12_2 shown.

[0038] exist Figure 3 (C) shows a compression region N with a relatively wide compression width W in the center and a narrower compression width W at the ends. The compression width W in the center is relatively wide. In this case, the central portion of the retainer 11 has a higher voltage Vh, while the ends have a relatively lower voltage Vh. Figure 3 The extrusion region N shown in (C) is Figure 1 A typical example is the extrusion region N of the downstream electric roller 12_2, one of the two electric rollers 12_1 and 12_2 shown.

[0039] Figure 3 The shape of the extrusion area N shown in (B) and (C) is adjusted by adjusting the following parameters.

[0040] Here, as a premise, the diameter of the charged roller 12 when it is not in contact with the image holder 11 is symmetrical in the direction of rotation, and both sides are pressed against the image holder 11 with the same pressing force F. Therefore, it is also a premise that the width of the extrusion area N in the processing direction, i.e., the extrusion width W, is also symmetrical in the direction of rotation.

[0041] Under this premise, for example,

[0042] • To make the diameter of the electrified roller 12 distributed differently in the direction of rotation, specifically, to adjust the difference between the diameter of the central part and the diameter of the end part.

[0043] • Adjust the pressing force F.

[0044] Therefore, the shape of the extrusion region N can be adjusted.

[0045] In particular, in order to form Figure 3The extrusion area of ​​the (C) shape shall be formed by using a crown-shaped electric roller 12 and in proportion to the shape. Figure 3 The pressing of the electric roller with a weak pressing force F in the extrusion area of ​​the (B) shape is effective.

[0046] In addition, when formed Figure 3 When the central part of the extrusion width W shown by the dashed line in (B) is narrower than the extrusion area N, the electric roller 12 does not necessarily have to be crown-shaped, but even a crown-shaped one can be achieved.

[0047] For through having Figure 3 The electric roller with the shape of (B) extrusion zone and the forming Figure 3 The two charged rollers, shaped like the (C), are used to solve the problem of the extrusion zone. Figure 2 The principles underlying the issues being addressed will be explained.

[0048] Here, based on the fact that the electric roller is the main component that charges the image holder 11, the following will be formed. Figure 3 The charged roller in the extrusion zone of (B) is called the main charged roller. Furthermore, based on the fact that it is a charged roller used to adjust the distribution of charged voltage in the direction of the rotation axis, it will be... Figure 3 The charged roller that forms the extrusion zone in (C) is called the auxiliary charged roller.

[0049] The retainer 11, located at the main charged roller, is charged with a uniform voltage along the rotation axis, or with a slightly stronger charge at its ends. The retainer 11, located at the auxiliary charged roller, is more strongly charged at its central portion along the rotation axis. In the initial state, it operates by adjusting the applied voltage to the auxiliary charged roller to compensate for the charge at the central portion, ensuring that the central portion and the ends have the same charge potential within an acceptable range.

[0050] As time goes by, as shown in the reference Figure 2 As explained in (B), the charging potential at the end increases. Therefore, the applied voltage to the auxiliary charged roller increases. Furthermore, the fact that the charging voltage increases as the thickness of the photosensitive layer of the image holder decreases over time is also utilized. This auxiliary charged roller is formed with... Figure 3 The compression region N of the (C) shape causes the central part to be strongly charged. As a result, the voltage in the central part also increases, and similarly to the initial state, the central part and the ends become the same charging potential within an acceptable range. The applied voltage to the main charged roller can be adjusted so that the overall charging potential Vh becomes the target charging potential.

[0051] The electrification device of this embodiment has two electrified rollers 12_1 and 12_2, and these two electrified rollers 12_1 and 12_2 not only perform the function of powerful electrification, but also share the aforementioned functions. Therefore, compared with a device having only one electrified roller, a high processing speed can be achieved, and the unevenness of the electrified voltage at the center and ends that occurs over time can be eliminated.

[0052] in addition, Figure 1 Either the upstream or downstream charged roller in the two charged rollers 12_1 and 12_2 shown can be either the main charged roller or the auxiliary charged roller.

[0053] Figure 4 This diagram shows the parameters of the main and auxiliary electrified rollers manufactured based on the above concept, as well as the results after a period of time. Here, Example 1 will be used primarily for illustration.

[0054] In Figure 4 In the diagram, the parameters for the main and auxiliary electrified rollers are shown as "extrusion load (N)", "bulge amount (μm)", "Δextrusion width (mm)" and "initial Δpotential (V)".

[0055] "Compressive load (N)" is Figure 3 The total value of the pressing force F shown is for both sides. In Example 1, the pressing load of the main charged roller is 5 N (Newtons), and the pressing load of the auxiliary charged roller is 2 N. The main charged roller presses against the image holder 11 with a stronger force, thereby forming in the main charged roller... Figure 3 The extrusion region N, as shown in (B), is formed in the auxiliary charged roller. Figure 3 The extrusion region N is shown in shape (C).

[0056] "Rainbow (μm)" indicates the degree of diameter difference between the central portion and the end portion. In Example 1, the raft of the main electrified roller is 90 μm. This means that the diameter of the central portion of the main electrified roller is 90 μm larger than the diameter of the end portion. In contrast, the raft of the auxiliary electrified roller in Example 1 is 140 μm. That is, in Example 1, the raft of the auxiliary electrified roller is greater than that of the main electrified roller. This point differs from "compression load (N)" and helps to form the main and auxiliary electrified rollers respectively. Figure 3 (B) Figure 3 The extrusion regions N of various shapes of (C).

[0057] Furthermore, "Δ extrusion width (mm)" involves Figure 3The extrusion width W shown in (B) and (C) indicates how much wider the extrusion width at the end is compared to the extrusion width at the center. In the case of Example 1, the Δ extrusion width of the main electric roller is 0.2 mm. That is, it means that the extrusion width at the end is 0.2 mm wider than the extrusion width at the center. In other words, this means that the extrusion area of ​​the main electric roller is... Figure 3 The extrusion area is shown by the dashed line in (B). In contrast, the Δ extrusion width of the auxiliary electric roller in Example 1 is -0.3 mm. That is, it means that the extrusion width at the end is 0.3 mm narrower than the extrusion width at the center. This means that the extrusion area of ​​the auxiliary electric roller is... Figure 3 The extruded area is the shape shown by the dashed line in (C).

[0058] Furthermore, "initial Δpotential (V)" represents the difference (V) between the charged potential of the central part and the end part in the initial state. Here, the charged potential of the target is set to 500V. Moreover, the allowable range of this difference is set to ±20V.

[0059] In Figure 4 In this example, the individual difference value for the main electrified roller and the individual difference value for the auxiliary electrified roller are shown. The differences between the main and auxiliary electrified rollers are calculated based on the extrusion width W and the applied voltages applied to the main and auxiliary electrified rollers respectively. In Example 1, the "initial Δ potential (V)" of the main electrified roller is 5V. This means that the main electrified roller causes the image holder to have a voltage Vh that is 5V higher at the ends than at the center. On the other hand, in Example 1, the "initial Δ potential (V)" of the auxiliary electrified roller is -10V. This means that the auxiliary electrified roller causes the image holder to have a voltage Vh that is 10V higher at the center than at the ends. Therefore, in calculations, if calculations are performed at both the main and auxiliary electrified rollers, the image holder has a voltage Vh that is 5V higher at the center than at the ends. Here, the voltage difference between the center and the ends is allowed to be ±20V. Therefore, the difference of 5V is well within the acceptable range.

[0060] Here, using a main charged roller and an auxiliary charged roller with the above parameters in the initial state, the same image with an image density of 5% is formed on plain A4 paper. At this time, whenever the wear of the image holder is 1μm, the charged potential of the image holder shifts by 10V. Therefore, the degree of wear can be inferred from the number of images formed, and the applied voltage of the auxiliary charged roller increases accordingly.

[0061] Then, confirm the number of image formations until a strip-shaped image defect extending in the processing direction appears on the image or until a carrier is detected on the image. The goal is to have no abnormalities until 60,000 image formations. The ○ mark in the "Reliability Evaluation Result Abnormal" column indicates that there were no problems until 70,000 sheets. Also, the △ mark indicates that problems occurred when exceeding 60,000 sheets. Additionally, the × mark indicates that problems occurred when less than 60,000 sheets.

[0062] In the "Result" column, data after a certain period of time is shown. Specifically, here are shown the "Uneven Wear Amount (μm) after a Certain Period of Time", the "Δ Potential (V) after a Certain Period of Time" (calculated value for the case of the main charging roller alone), and the "Δ Potential (V) after a Certain Period of Time" (total of the main charging roller and the sub-charging roller). Each value in this "Result" column is the value at 70,000 sheets (in the case of ○) or when problems occurred (in the cases of △ and ×).

[0063] In the case of Example 1, the "Uneven Wear Amount (μm) after a Certain Period of Time" is 2 μm. This means that in the wear of the image holding body, the end part has worn 2 μm more than the central part.

[0064] Also, in the case of Example 1, the "Δ Potential (V) after a Certain Period of Time" (calculated value for the case of the main charging roller alone) is 25 V. This means that in the case of only the main charging roller, the image holding body has a charging voltage where the end part is 25 V higher than the central part.

[0065] Also, in the case of Example 1, the "Δ Potential (V) after a Certain Period of Time" (total of the main charging roller and the sub-charging roller) is 15 V. This means that the image holding body has a charging voltage where the end part is 15 V higher than the central part. That is, compared with the case of only the main charging roller, the difference in the charging voltage between the end part and the central part decreases and falls within the target of ±20 V. The "Reliability Evaluation Result" of this Example 1 is ○.

[0066] When observing the column of the "Δ Potential (V) after a Certain Period of Time" (total of the main charging roller and the sub-charging roller) longitudinally, Examples 1, 2, and 3 all fall within the target of ±20 V. Moreover, for Examples 1 and 2, the "Reliability Evaluation Results" are both ○. Example 3 is exactly 20 V as the target. And the "Reliability Evaluation Result" is △. However, it has been qualified so far. In contrast, in the case of Comparative Example 1, it is 35 V. And the "Reliability Evaluation Result" is ×. Referring to the parameters of the main charging roller and the sub-charging roller in this Comparative Example 1, the same charging roller is used for the main charging roller and the sub-charging roller.

[0067] In addition, here, in each of the examples, it is Figure 1Of the two charged rollers 12_1 and 12_2 shown, the main charged roller is positioned at the upstream position of charged roller 12_1, and the auxiliary charged roller is positioned at the downstream position of charged roller 12_2. However, either the main charged roller or the auxiliary charged roller can be positioned on the upstream or downstream side.

[0068] Thus, the charging device according to this embodiment has two charging rollers that bear a strong charge, and further enable them to share the load or compensate for each other's shortcomings. As a result, compared with a device having only one charging roller, a high processing speed is achieved, and the unevenness of the charging voltage between the central part and the ends caused by the passage of time is suppressed.

[0069] Furthermore, this description takes as an example a charging device assembled in an image forming apparatus of the electrophotographic method, but the charging device of the present invention can be used as the charging device shown in Patent Document 1 above for the purpose of preventing the serpentine or winding deviation of the sheet, or as a charging device for various other purposes.

Claims

1. A live-line device, comprising: The first charged part comes into contact with the charged part, thereby charging the charged part; and The second charged part comes into contact with the charged part, thereby charging the charged part, and the distribution of the contact area between the second charged part and the charged part is different from that of the first charged part. The first charged part and the second charged part are respectively a first charged roller and a second charged roller whose two ends in the direction of rotation are pressed towards the charged part and in contact with and rotate with the charged part. The pressing force of the first charged roller and the second charged roller are different from each other. The electric roller with relatively weaker pressing force among the first and second electric rollers is a crown-shaped electric roller with a relatively thicker diameter at the center and a relatively thinner diameter at the ends in the direction of rotation axis. The electrified device has a power source that causes the applied voltage to the crown-shaped electrified roller to increase over time.

2. The energized device according to claim 1, wherein, The diameters of the first and second charged rollers when they are not in contact with the charged part are symmetrically distributed along the rotation axis, and these distributions are different from each other.

3. The energized device according to claim 2, wherein, The first and second electrified rollers are crown-shaped electrified rollers with a relatively large diameter at the center and a relatively small diameter at the ends in the direction of rotation.

4. An image forming apparatus comprising: The live device according to any one of claims 1 to 3; and The image holding section, which serves as a charged section receiving the charge applied by the charging device, is charged by the charging device and holds the electrostatic latent image formed by exposure, and further holds the toner image formed by toner development. The image forming apparatus forms an image on paper based on a toner image formed in the image holding section.

Images