Patent ID: 12228864

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the drawings. An image forming apparatus10according to the exemplary embodiment is, for example, as shown inFIG.1, a tandem type full-color image forming apparatus, and inFIG.1, an arrow UP is an upward direction of the image forming apparatus10. In addition, components having the same function may be assigned the same reference numeral (reference numeral in which alphabetic characters are omitted). In addition, the drawings used in the following description are all schematic, and the relationship between respective dimensions of elements, the ratio between the elements, and the like shown in the drawings do not always coincide with the reality. In addition, even between a plurality of drawings, the relationship between the respective dimensions of the elements, the ratio between the elements, and the like do not always coincide with each other. In addition, even between the plurality of drawings, elements that are substantially the same are assigned the same reference numeral, description of the elements is provided in the drawings in which the elements first appear, and the description is omitted in the subsequent drawings unless otherwise necessary.

First, an overall configuration of the image forming apparatus10will be described. As shown inFIG.1, the image forming apparatus10has an apparatus body11. Inside the apparatus body11, process cartridges18K,18C,18M, and18Y corresponding to black (K), cyan (C), magenta (M), and yellow (Y) are provided in this order from below. In the following description, the process cartridges18K,18C,18M, and18Y may be collectively referred to as a process cartridge18.

Each process cartridge18includes a photoreceptor12as an example of an image holding body (charged body) capable of holding an image, a charging device15(seeFIG.2) having a charging roll14as an example of a charging member and a cleaning device50, and a developing device24. Each process cartridge18can be attached to and detached from the apparatus body11.

Both end portions of the photoreceptor12in a rotation axis direction thereof are rotatably supported by side plates82(seeFIG.3). An outer peripheral surface of the photoreceptor12is charged by the charging roll14disposed in contact with the outer peripheral surface, and is then exposed to a laser beam LB emitted from an exposure device16disposed downstream of the charging roll14in a rotation direction of the photoreceptor12. Accordingly, an electrostatic latent image corresponding to image information is formed on the outer peripheral surface of the photoreceptor12.

The electrostatic latent images formed on the outer peripheral surfaces of the photoreceptors12are respectively developed by the developing devices24of black (K), cyan (C), magenta (M), and yellow (Y) into toner images of the corresponding colors. That is, by performing charging, exposing, and developing processes on each of the outer peripheral surfaces of the photoreceptors12of black (K), cyan (C), magenta (M), and yellow (Y), the toner images respectively corresponding to black (K), cyan (C), magenta (M), and yellow (Y) are respectively formed on the outer peripheral surfaces of the photoreceptor12of the corresponding colors.

On the other hand, recording paper P is taken out from a paper storage unit28by a take-out roll30, and is transported to a transport belt20by a transport roll32and a transport roll34. The transport belt20is wound in a state where tension is applied to a drive roll36and a driven roll38, and is configured so that a side of the transport belt20facing each photoreceptor12is moved upward from below by a rotational drive of the drive roll36. A transfer roll22corresponding to each photoreceptor12is disposed on an inner peripheral surface side of the transport belt20.

Therefore, the toner images of black (K), cyan (C), magenta (M), and yellow (Y) respectively formed on the outer peripheral surfaces of the photoreceptors12are sequentially transferred from the outer peripheral surfaces of the photoreceptors12to the recording paper P transported by the transport belt20at transfer positions at which the transport belt20supported by the transfer rolls22and the photoreceptors12face each other. The recording paper P on which the toner image is transferred from the outer peripheral surface of each photoreceptor12is transported to a fixing device40and is heated and pressed so that the toner image is fixed on the recording paper P.

Thereafter, in a case of one-sided printing, the recording paper P on which the toner image is fixed is discharged onto a discharge unit44provided in an upper portion of the image forming apparatus10by a discharge roll42. On the other hand, in a case of two-sided printing, a trailing edge portion of the recording paper P having a front surface on which the toner image is fixed by the fixing device40is sandwiched by the discharge roll42, and then the discharge roll42rotates in a reverse direction such that the recording paper P is transported to a transport path46for two-sided printing.

Then, the recording paper P of which front and back sides have been reversed by being transported by the transport roll48disposed on the transport path46is transported to the transport belt20again, and a toner image is transferred from the outer peripheral surface of each photoreceptor12to a back surface of the recording paper P. The toner image of the recording paper P in which the toner image is transferred to the back surface of the recording paper P is fixed by the fixing device40, and the recording paper P having the back surface on which the toner image is fixed is discharged onto the discharge unit44by the discharge roll42.

Residual toner, paper dust, and the like remaining on the outer peripheral surface of the photoreceptor12after a process of transferring the toner image is removed by a cleaning blade26disposed downstream of the transfer position in the rotation direction of each photoreceptor12each time each photoreceptor12makes one revolution. Accordingly, the outer peripheral surface of each photoreceptor12is prepared for the next image forming process.

Next, the cleaning device50having the charging roll14and a cleaning roll52as an example of a cleaning member that cleans the charging roll14will be described.

As shown inFIGS.2and3, for example, the charging roll14is formed in a roll shape in which an elastic layer14B is formed around a shaft14A which is an example of a shaft core, and both end portions of the shaft14A are rotatably supported by support members (not shown). The elastic layer14B of the charging roll14is pressed against the outer peripheral surface of the photoreceptor12by a load F1(seeFIG.2) applied to both end portions of the shaft14A, and forms a nip portion by elastically deforming along the outer peripheral surface of the photoreceptor12.

In addition, as shown inFIG.2, the charging roll14rotates in an arrow Y direction following the rotation of the photoreceptor12as the photoreceptor12is driven to rotate in an arrow X direction by a motor80(seeFIG.3). The cleaning roll52is in contact with the charging roll14on a side opposite to the photoreceptor12, and rotates in an arrow Z direction following the rotation of the charging roll14.

In addition, an elastic layer56of the cleaning roll52, which will be described later, is pressed against an outer peripheral surface of the elastic layer14B of the charging roll14by a load F2(seeFIG.2) applied to both end portions of a shaft54, which will be described later, by a pair of bearing members62and64(seeFIG.3), which will be described later, and forms a nip portion by elastically deforming along the outer peripheral surface of the elastic layer14B. The cleaning roll52is also configured to suppress bending of the charging roll14.

As a material of the shaft14A of the charging roll14, there is a metal such as free-cutting steel or stainless steel having conductivity, and a surface treatment method or the like is appropriately selected depending on an application such as slidability. The elastic layer14B of the charging roll14is, for example, a conductive foam elastic layer, and an elastic material forming the conductive foam elastic layer is formed, for example, by dispersing a conductive agent in a rubber material.

The elastic layer14B of the charging roll14may have a single-layer structure or a laminated structure including a plurality of different layers having a plurality of functions. In addition, a surface layer may be formed on the outer peripheral surface of the elastic layer14B. The surface layer may be any of a resin layer, a rubber layer, and the like, and is not particularly limited.

As shown inFIG.3, the cleaning device50has the cleaning roll52formed in a roll shape. The cleaning roll52includes the shaft54, which is an example of a shaft core, and the elastic layer56spirally wound around an outer peripheral surface of the shaft54.

The shaft54is disposed along a rotation axis direction (hereinafter, simply referred to as “axial direction”) of the charging roll14. An axial length of the shaft54is formed to be longer than an axial length of the elastic layer14B in the charging roll14. That is, one end portion in the axial direction and the other end portion in the axial direction of the shaft54extend axially outward from one end portion in an axial direction and the other end in the axial direction of the elastic layer14B of the charging roll14, respectively.

As a material of the shaft54, there are a metal such as free-cutting steel or stainless steel, and a resin such as polyacetal (POM).

The elastic layer56is a foam elastic layer made of a material having bubbles, and is made of a material that restores an original shape thereof even after being deformed by an applied pressure of, for example, 100 Pa. Examples of the material of the elastic layer56include foam elastic members made of a resin such as polyurethane such as an ester-based polyurethane or an ether-based polyurethane, polyethylene, polyamide, or polypropylene. A diameter of a tip end portion of a cell skeleton protruding to a surface of the elastic layer56is configured to be 50 μm or less.

Here, as shown inFIG.4, the “diameter of the tip end portion of the cell skeleton” means a diameter of a circumscribed circle C circumscribing a cross section of tip end T of a protruding portion on the surface of the foam elastic member. In addition, “the diameter of the tip end portion of the cell skeleton protruding to the surface of the elastic layer56is X μm or less” means that diameters of tip end portions of 80% or more of cell skeletons among the cell skeletons protruding to the surface of the elastic layer56are X μm or less.

The elastic layer56has a configuration in which the band-shaped foam elastic member is spirally disposed with a pitch. An adhesive layer such as double-sided tape is provided on an inner surface of the elastic layer56wound around the outer peripheral surface of the shaft54, and the elastic layer56is attached to the outer peripheral surface of the shaft54by the adhesive layer while being spirally wound from one end portion in the axial direction to the other end portion in the axial direction of the shaft54.

In addition, the cleaning device50includes the pair of bearing members62and64that rotatably support both end portions of the shaft54. The bearing members62and64have a shape in which inner sides thereof in the axial direction of the shaft54are open, and outer sides thereof in the axial direction of the shaft54are respectively closed by side walls62A and64A. The bearing members62and64are respectively fixed to fixing portions84formed on the side plates82on both sides.

In addition, a gear17provided at the end portion of the shaft14A of the charging roll14and a gear57provided at the end portion of the shaft54of the cleaning roll52are connected to each other. A gear diameter of the gear57of the cleaning roll52is 1.43 or more times and 3.33 or less times a gear diameter of the gear17of the charging roll14.

The cleaning roll52is configured to rotate in conjunction with the charging roll14such that a peripheral speed ratio of the cleaning roll52to the charging roll14is 0.3 or more and 0.7 or less.

The cleaning roll52is configured so that in a case where an initial thickness of the elastic layer56of the cleaning roll52is denoted by T0, an initial thickness of the elastic layer56after the cleaning roll52is rotated by 2.8 million revolutions while being in contact with the charging roll14is denoted by T1, and a deformation rate of a thickness of the elastic layer56is denoted by ΔT %=((T0−T1)/T0)×100, ΔT %≤20% is satisfied.

EXAMPLES

Next, examples of the image forming apparatus will be described.FIG.5is a table showing the relationship between configuration contents in Examples 1 to 4 and Comparative Examples 1 to 6 and density unevenness which is an evaluation result of each example.

The following specifications are common to process cartridges mounted on the image forming apparatus of each example. A charging roll has a diameter of 12 mm and a length of 378 mm. A cleaning roll has a diameter of 9 mm and a length of 360 mm. A distance between a rotating shaft of the charging roll and a rotating shaft of the cleaning roll is 10.4 mm. A material of an elastic layer of the cleaning roll is an ester-based polyurethane, and a thickness of the elastic layer is 2.35 mm.

In the table ofFIG.5, as the configuration contents in each example, a “wound shape of a foam elastic member” in the elastic layer of the cleaning roll, a “diameter of a tip end portion of a cell skeleton” in the elastic layer of the cleaning roll, and a “peripheral speed ratio” of the cleaning roll to the charging roll.

In an example described as “spiral” in the item of the “wound shape of the foam elastic member”, a width of a band of the foam elastic member in the elastic layer of the cleaning roll is 22.8 mm, and a spiral pitch is 32.2 mm. In addition, in an example described as “non-spiral” in the item of the “wound shape of the foam elastic member”, the foam elastic member is disposed in a planar shape on an outer peripheral surface of a shaft of the cleaning roll.

In addition, as the evaluation result in each example, a “deformation rate of a thickness of the elastic layer” of the cleaning roll, a “thickness of a contaminant deposition layer”, and “density unevenness” are shown.

Here, the “thickness of the contaminant deposition layer” is a result obtained by measuring, using scanning electron microscope (SEM) observation, a thickness of a deposition layer (contaminant deposition layer) of discharge products and/or external additives deposited on a surface of the charging roll after printing 250,000 sheets of A4 paper in the image forming apparatus. Printing of 250,000 sheets of A4 paper in the image forming apparatus corresponds to making 2.8 million revolutions of the cleaning roll 2.8 while being in contact with the charging roll.

Details of the “density unevenness” are as follows. The process cartridges prepared in each example are mounted on the image forming apparatus, and a halftone image having an image density of 40% is output on 10 sheets of A4 paper in an environment of a temperature of 10° C. and a relative humidity of 15% RH by using the image forming apparatus. Then, image quality of the last output image is evaluated. Evaluation criteria are as follows.

Evaluation Criteria

A: Image defects such as density unevenness are not presentB: Minor density unevenness has occurredC: Density unevenness that is not acceptable in practice has occurred.

In Example 1, the “wound shape of the foam elastic member” is set to be spiral, the “diameter of the tip end portion of the cell skeleton” is set to 30 μm, and the “peripheral speed ratio” is set to 0.3. In this case, the “deformation rate of the thickness of the elastic layer” is 20%, the “thickness of the contaminant deposition layer” is 1.5 μm, and the “density unevenness” is A.

In Example 2, the “wound shape of the foam elastic member” is set to be spiral, the “diameter of the tip end portion of the cell skeleton” is set to 30 μm, and the “peripheral speed ratio” is set to 0.5. In this case, the “deformation rate of the thickness of the elastic layer” is 13%, the “thickness of the contaminant deposition layer” is 1.0 μm, and the “density unevenness” is A.

In Example 3, the “wound shape of the foam elastic member” is set to be spiral, the “diameter of the tip end portion of the cell skeleton” is set to 30 μm, and the “peripheral speed ratio” is set to 0.7. In this case, the “deformation rate of the thickness of the elastic layer” is 10%, the “thickness of the contaminant deposition layer” is 1.8 μm, and the “density unevenness” is A.

In Comparative Example 1, the “wound shape of the foam elastic member” is set to be spiral, the “diameter of the tip end portion of the cell skeleton” is set to 30 μm, and the “peripheral speed ratio” is set to 0.2. In this case, the “deformation rate of the thickness of the elastic layer” is 25%, the “thickness of the contaminant deposition layer” is 2.8 μm, and the “density unevenness” is C.

In Comparative Example 2, the “wound shape of the foam elastic member” is set to be spiral, the “diameter of the tip end portion of the cell skeleton” is set to 30 μm, and the “peripheral speed ratio” is set to 0.8. In this case, the “deformation rate of the thickness of the elastic layer” is 8%, the “thickness of the contaminant deposition layer” is 2.5 μm, and the “density unevenness” is B.

In Comparative Example 3, the “wound shape of the foam elastic member” is set to be spiral, the “diameter of the tip end portion of the cell skeleton” is set to 30 μm, and the “peripheral speed ratio” is set to 1. In this case, the “deformation rate of the thickness of the elastic layer” is 5%, the “thickness of the contaminant deposition layer” is 3.0 μm, and the “density unevenness” is C.

In Comparative Example 4, the “wound shape of the foam elastic member” is set to be non-spiral, the “diameter of the tip end portion of the cell skeleton” is set to 30 μm, and the “peripheral speed ratio” is set to 0.5. In this case, the “deformation rate of the thickness of the elastic layer” is 30%, the “thickness of the contaminant deposition layer” is 2.7 μm, and the “density unevenness” is C.

In Example 4, the “wound shape of the foam elastic member” is set to be spiral, the “diameter of the tip end portion of the cell skeleton” is set to 50 μm, and the “peripheral speed ratio” is set to 0.5. In this case, the “deformation rate of the thickness of the elastic layer” is 10%, the “thickness of the contaminant deposition layer” is 2.0 μm, and the “density unevenness” is A.

In Comparative Example 5, the “wound shape of the foam elastic member” is set to be spiral, the “diameter of the tip end portion of the cell skeleton” is set to 80 μm, and the “peripheral speed ratio” is set to 0.5. In this case, the “deformation rate of the thickness of the elastic layer” is 8%, the “thickness of the contaminant deposition layer” is 3.2 μm, and the “density unevenness” is C.

In Comparative Example 6, the “wound shape of the foam elastic member” is set to be non-spiral, the “diameter of the tip end portion of the cell skeleton” is set to 30 μm, and the “peripheral speed ratio” is set to 0.6. In this case, the “deformation rate of the thickness of the elastic layer” is 25%, the “thickness of the contaminant deposition layer” is 2.5 μm, and the “density unevenness” is B.

From a comparison between Example 2 and Comparative Example 4, it can be seen that the density unevenness can be suppressed by setting the “wound shape of the foam elastic member” to be spiral.

In addition, from a comparison between Examples 1 to 3 and Comparative Examples 1 and 2, it can be seen that the density unevenness can be suppressed by setting the “peripheral speed ratio” to 0.3 or more and 0.7 or less.

In addition, from a comparison between Example 4 and Comparative Example 5, it can be seen that the density unevenness can be suppressed by setting the “diameter of the tip end portion of the cell skeleton” to 50 μm or less.

In addition, from a comparison between Examples 2 to 3 and Comparative Example 6, it can be seen that the density unevenness can be suppressed in a configuration in which the “deformation rate of the thickness of the elastic layer” is 20% or less.

Modification Example

Although the image forming apparatus according to the exemplary embodiment of the present invention and the image forming apparatuses of the examples have been described above, the present invention is not limited to the above description and may be modified as appropriate.

Supplementary Notes

Hereinafter, supplementary notes of aspects of the present disclosure will be described.

(((1)))

A charging device comprising:a charging member that rotates in contact with a charged body and charges the charged body; anda cleaning member that comes into contact with the charging member and rotates in conjunction with the charging member,wherein the cleaning member includes a foam elastic layer in which a band-shaped foam elastic member is spirally disposed with a pitch, and a diameter of a tip end portion of a cell skeleton protruding to a surface of the foam elastic layer is 50 μm or less, anda peripheral speed ratio of the cleaning member to the charging member is 0.3 or more and 0.7 or less.
(((2)))

The charging device according to (((1))),

wherein, in a case where an initial thickness of the foam elastic layer of the cleaning member is denoted by T0, an initial thickness of the foam elastic layer after the cleaning member is rotated by 2.8 million revolutions while being in contact with the charging member is denoted by T1, and a deformation rate of a thickness of the foam elastic layer is denoted by ΔT %=((T0−T1)/T0)×100, ΔT %≤20% is satisfied.

(((3)))

The charging device according to (((2))),wherein the foam elastic layer is formed of an ester-based polyurethane.
(((4)))

The charging device according to any one of (((1))) to (((3))),wherein a gear provided at an end portion of a shaft core of the charging member and a gear provided at an end portion of a shaft core of the cleaning member are connected to each other, andthe cleaning member rotates in conjunction with the charging member such that a peripheral speed ratio of the cleaning member rotates to the charging member is 0.3 or more and 0.7 or less.
(((5)))

The charging device according to (((4))),wherein a gear diameter of the cleaning member is 1.43 or more times and 3.33 or less times a gear diameter of the charging member.
(((6)))

A cartridge comprising the charging device according to any one of (((1))) to (((5))).

(((7)))

An image forming apparatus comprising:the charging device according to any one of (((1))) to (((5))); andan image holding body as the charged body that holds an electrostatic latent image on a surface.

The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.