JP7639446B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device.

In general, in an image forming device using electrophotographic process technology, a photoconductor is placed on the surface of a photoconductor drum, and an electrostatic latent image is formed by irradiating the charged surface of the photoconductor with laser light based on image data. A toner image is formed by supplying toner to the photoconductor drum on which the electrostatic latent image is formed. In general, a cleaning blade is provided to scrape off the residual toner adhering to the surface of the photoconductor drum. However, as the cleaning blade wears out, the cleaning performance deteriorates, so a lubricant is applied to the surface of the photoconductor drum. A roller-shaped application brush is used for this application. The configuration of such an image forming device is described in JP 2017-187638 A (Patent Document 1).

JP 2017-187638 A

Here, we refer to a mechanism that uses an application brush to apply lubricant to a photoconductor drum, which serves as an image carrier, as a "lubricant application device." Two types of lubricant application devices are in practical use: the "counter type," in which the application brush rotates in the opposite direction to the image carrier, and the "with type," in which the application brush rotates in the same direction as the image carrier. In a with type lubricant application device, the application brush and the image carrier are each rotated.

In an image forming apparatus equipped with such a With-type lubricant applicator, repeated printing can cause localized dents in the outer diameter of the application brush of the lubricant applicator. The application brush has a long cylindrical shape, and dents occur at some point along its length. When such localized dents occur, image defects occur in a location corresponding to the location of the dent. In other words, a band-shaped image noise appears on the surface of a recording medium such as paper, extending in the direction in which the recording medium passes.

Therefore, the present invention aims to suppress the occurrence of image noise caused by localized depressions in the application brush.

In order to achieve the above object, the image forming apparatus according to the present invention comprises a cylindrical rotating image carrier, a solid lubricant, and a roller-shaped application brush that includes brush fibers on its outer circumferential surface and is arranged and rotated so as to scrape the lubricant from the solid lubricant with the brush fibers and apply it to the image carrier. The direction of rotation of the application brush is the direction in which the outer circumferential surface of the application brush advances in the same direction as the outer circumferential surface of the image carrier advances at the contact point between the image carrier and the application brush. When a cross section of the application brush cut along a plane perpendicular to the rotation axis thereof is viewed, the tip of the brush fiber faces toward the center of the application brush rather than the tangent to the outer circumferential surface of the image carrier, assuming the posture that the brush fiber takes when the image carrier is not present, at the most upstream position of the contact area between the image carrier and the application brush.

According to the present invention, the brush fibers of the application brush are less likely to curl up, making it less likely that localized dents will occur in the application brush, and as a result, the occurrence of image noise caused by localized dents in the application brush can be reduced.

1 is a schematic diagram of an image forming apparatus according to a first embodiment of the present invention. 1 is an enlarged view of an image carrier and its vicinity provided in an image forming apparatus in accordance with a first embodiment of the present invention. 1 is a perspective view of an application brush provided in an image forming apparatus in accordance with a first embodiment of the present invention. FIG. FIG. 3 is an enlarged view of a portion of the configuration shown in FIG. 2 for explaining the positional relationship around the most upstream position. FIG. 5 is an enlarged view of a portion of the configuration shown in FIG. 4. FIG. 3 is an enlarged view of a portion of the configuration shown in FIG. 2 for explaining the positional relationship around the most downstream position. FIG. 7 is an enlarged view of a portion of the configuration shown in FIG. 6.

The dimensional ratios shown in the drawings do not necessarily represent the actual ratios, and may be exaggerated for the convenience of explanation. In the following explanation, when the concepts of up or down are mentioned, they do not necessarily mean absolute up or down, but may mean relative up or down in the illustrated position.

(Embodiment 1)
(Configuration of Image Forming Apparatus)
An image forming apparatus according to a first embodiment of the present invention will be described with reference to Figures 1 to 5. An overall schematic of an image forming apparatus 101 according to the present embodiment is shown in Figure 1. Image forming apparatus 101 includes an operation display unit 20, an image reading unit 21, an image processing unit 22, a paper transport unit 23, a paper feed unit 24, a fixing unit 27, and a paper discharge unit 28.

The operation display unit 20 may be, for example, a liquid crystal display with a touch panel. The image reading unit 21 includes an automatic document feeder 211 and an original image scanning device 212. The automatic document feeder 211 transports documents placed on a document tray using a transport mechanism and sends them to the original image scanning device 212. The original image scanning device 212 optically scans and reads the documents. The image processing unit 22 performs predetermined image processing on the data generated based on the reading results.

A paper feed unit 24 is disposed at the bottom of the image forming device 101. An image forming unit is disposed between the paper feed unit 24 and the image reading unit 21. The paper feed unit 24 includes tray units 241, 242, and 243. Each of the tray units 241, 242, and 243 stores paper as a recording medium. In each of the tray units 241, 242, and 243, paper is removed one sheet at a time from the top. The removed paper is transported to the image forming unit by the paper transport unit 23.

The image forming section includes an intermediate transfer belt 6 arranged in a loop shape. The intermediate transfer belt 6 travels in the direction of an arrow 91. Four image carriers 1 are arranged in the middle of the travel path of the intermediate transfer belt 6 so as to contact the outer surface of the intermediate transfer belt 6. The image carriers 1 are photosensitive drums. The four image carriers 1 correspond to toner images of each color, for example, Y (yellow), M (magenta), C (cyan), and K (black). At the locations where the image carriers 1 contact the intermediate transfer belt 6, primary transfer rollers 5 are arranged on the opposite side of the image carriers 1. The intermediate transfer belt 6 is sandwiched between the image carriers 1 and the primary transfer roller 5. In the middle of the travel path of the intermediate transfer belt 6, a secondary transfer roller 25 is arranged so as to contact the outer surface of the intermediate transfer belt 6. At this position, the intermediate transfer belt 6 is sandwiched between the secondary transfer roller 25 and the backup roller 26. When the paper conveyed by the paper conveying section 23 passes between the secondary transfer roller 25 and the intermediate transfer belt 6, the paper passes between the secondary transfer roller 25 and the backup roller 26, so that the toner image is transferred from the outer surface of the intermediate transfer belt 6 to the surface of the paper. The paper onto which the image has been transferred is further conveyed and subjected to a fixing process in the fixing section 27, and then discharged from the paper discharge section 28.

2 shows an enlarged view of the image carrier 1 and its vicinity. The intermediate transfer belt 6 runs in the direction of the arrow 91. The image carrier 1 rotates in the direction of the arrow 92. The charging device 2 is arranged to face the outer circumferential surface of the image carrier 1. The exposure device 3 is arranged downstream of the charging device 2 so that the outer circumferential surface of the image carrier 1 can be irradiated with laser light 8. The developing device 4 is arranged downstream of the irradiation position of the laser light 8 so as to contact the outer circumferential surface of the image carrier 1. The location where the image carrier 1 contacts the intermediate transfer belt 6 is downstream of the developing device 4. The cleaning device 7 is arranged downstream of the location where the image carrier 1 contacts the intermediate transfer belt 6 so as to contact the outer circumferential surface of the image carrier 1. The cleaning device 7 includes a cleaning blade 71, a roller-shaped application brush 72, a solid lubricant 73, and a blade 74. Toner remaining on the outer peripheral surface of the image carrier 1 after the primary transfer is removed by a cleaning blade 71. The cleaning blade 71 may be made of, for example, urethane rubber. The application brush 72 applies the lubricant scraped off from the solid lubricant 73 to the outer peripheral surface of the image carrier 1. The lubricant may be made of, for example, zinc stearate. The lubricant applied to the outer peripheral surface of the image carrier 1 by the application brush 72 is pressed by a blade 74.

The application brush 72 is shown in FIG. 3. The application brush 72 includes a shaft 721 and brush fibers 722. The application brush 72 has an outer peripheral surface 723. The brush fibers 722 are curved rather than straight. The brush fibers 722 may be made of acrylic, for example. The image carrier 1, application brush 72, and solid lubricant 73 in FIG. 2 are shown in detail in FIG. 4. The lubricant application device includes the application brush 72 and solid lubricant 73.

(Considerations regarding the cause of dents)
The inventors have considered the phenomenon in which localized dents occur in the roller-shaped application brush of a lubricant application device of a With-type lubricant application device during continued use of the image forming apparatus as follows.

In a With-type lubricant applicator, if the brush fibers of the application brush do not always fall in the same direction, the tips of the brush fibers will become distorted and cause image noise. Therefore, to ensure that the brush fibers of the application brush always fall in the same direction, it is common to set the rotation speed of the application brush to be faster than the rotation speed of the image carrier.

If the application brush is constantly rotating while the image carrier is rotating, the brush fibers of the application brush will fall in a consistent, consistent direction. However, it is known that the operation of the lubricant application device is stopped to reduce the consumption of lubricant at the start and end of an image formation operation, or when an optional device is connected to the image forming apparatus and the image formation operation is interrupted while the optional device is operating. In this state, the image carrier continues to rotate, and the application brush stops rotating.

In this case, where the application brush is in contact with the image carrier, a force is applied to the bristles of the application brush, i.e., the tips of the brush fibers, in the direction of rotation of the image carrier, which can cause the bristles to turn over. When image formation operations are repeated, in some areas of the application brush, the bristles will alternate between being turned over and not being turned over, so the bristles will gradually become tangled and the outer diameter of the application brush will become smaller. This results in a localized dent in the application brush.

When the bristles of the application brush are in contact with the image carrier at their very tip, the frictional force between them and the surface of the image carrier is large, so when the application brush is stopped rotating and the image carrier is rotating, it is thought that the bristles are easily dragged by the surface of the image carrier and curled up. However, when the bristles of the application brush are in contact with the image carrier at a point slightly away from the tip, rather than at their very tip - in other words, when they are in belly contact - the frictional force is smaller, and as a result, the bristles are less likely to curl up. Furthermore, when they are in belly contact, the contact point between the brush fibers and the image carrier is closer to the base of the brush fibers, so their resistance to curling increases. This also makes the bristles less likely to curl up.

The inventors noticed that curling of the bristles often starts at the most upstream position of the contact point between the application brush and the image carrier and spreads downstream. Therefore, the inventors thought that curling of the bristles could be effectively suppressed by making the brush fibers contact the belly at the most upstream position, and as a result, localized dents in the application brush could be prevented.

Furthermore, if there is a point within the contact area between the application brush and the image carrier where the direction of the bristles switches from facing upstream of the normal to the outer periphery of the image carrier to facing downstream of the normal, the bristles may curl up downstream of this changeover point. Therefore, the inventors thought that if the direction of the bristles throughout the entire contact area between the application brush and the image carrier is aligned so that they face upstream of the normal to the outer periphery of the image carrier, the bristles will be less likely to curl up.

(Configuration of Image Forming Apparatus (continued))
Fig. 4 shows in detail the image carrier 1, the application brush 72, and the solid lubricant 73 taken out from the portion shown in Fig. 2. Fig. 5 shows an enlarged view of a portion of Fig. 4.

The image forming apparatus 101 includes a cylindrical rotating image carrier 1, a solid lubricant 73, and a roller-shaped application brush 72. The application brush 72 includes brush fibers 722 on its outer circumferential surface, and is arranged and rotated so that the brush fibers 722 scrape off the lubricant from the solid lubricant 73 and apply it to the image carrier 1. The direction of rotation of the application brush 72 is the same as the direction of movement of the outer circumferential surface of the image carrier 1 at the contact point between the image carrier 1 and the application brush 72. In the example shown here, the direction of movement of the outer circumferential surface of the image carrier 1 is indicated by an arrow 92. The direction of rotation of the application brush 72 is indicated by an arrow 93. The arrows 92 and 93 are in the same direction at the contact point between the image carrier 1 and the application brush 72. In other words, this lubricant application device is a with type.

Figure 4 shows a normal 41 to the outer periphery of the application brush 72 at the most upstream position 51, a tangent 42 to the image carrier 1 at the most upstream position 51, a straight line 43 indicating the tip direction of the brush fiber 722 at the most upstream position 51, and a normal 44 to the outer periphery of the image carrier 1 at the most upstream position 51. In Figure 4, the brush fiber 722 is shown in the shape it would be in if the image carrier 1 were not present. In reality, the brush fiber 722 is deformed by being pressed against the image carrier 1.

When looking at a cross section cut perpendicular to the axis of rotation of the application brush 72, at the most upstream position 51 of the contact area between the image carrier 1 and the application brush 72, assuming the orientation that the brush fibers 722 would assume if the image carrier 1 were not present, the tips of the brush fibers 722 point toward the center of the application brush 72 rather than the tangent 42 to the outer periphery of the image carrier 1. In other words, angle A in Figure 5 is sufficiently large, and as a result, angle B > 0.

(Action and Effects)
In this embodiment, at the most upstream position 51, the tips of the brush fibers 722 face toward the center of the application brush 72 rather than the tangent line 42 to the outer periphery of the image carrier 1, so the brush fibers 722 of the application brush 72 are less likely to turn up. Therefore, localized depressions in the application brush 72 are less likely to occur. As a result, the occurrence of image noise due to localized depressions in the application brush can be suppressed. An experiment verifying this effect will be described later as "Experiment 1."

(Preferred Configuration)
Furthermore, the following can be said about the most downstream position 52 of the contact area between the image carrier 1 and the application brush 72. Figures 4 and 5 show in detail the positional relationship around the most upstream position 51 of the contact area between the image carrier 1 and the application brush 72, but Figure 6 shows in detail the positional relationship around the most downstream position 52 of the contact area between the image carrier 1 and the application brush 72. Furthermore, Figure 7 shows an enlarged view of a part of Figure 6.

When viewed in a cross section cut perpendicular to the axis of rotation of the application brush 72, at the most downstream position 52 of the region where the image carrier 1 and the application brush 72 contact each other, it is preferable that the tip of the brush fiber 722 is parallel to the normal line 62 of the outer periphery of the image carrier 1, or faces upstream of the normal line 62 in terms of the rotation of the application brush 72. In other words, it is preferable that the angle C in FIG. 6 is sufficiently large, and as a result, the angle D>0. By adopting this configuration, the brush fiber 722 of the application brush 72 is less likely to be curled up. Therefore, localized dents in the application brush 72 are less likely to occur. As a result, it is possible to suppress the occurrence of image noise caused by localized dents in the application brush. An experiment verifying this effect will be described later as "Experiment 2".

The speed of the outer peripheral surface of the application brush 72 due to the rotation of the application brush 72 is preferably faster than the speed of the outer peripheral surface of the image carrier 1 due to the rotation of the image carrier 1. By adopting this configuration, curling of the bristles of the application brush 72 can be more reliably prevented.

The following describes the experiments that the inventors conducted to confirm the effects.
(Experiment 1)
Experiment 1 was conducted with the following configuration. The solid lubricant 73 was made of zinc stearate. The application brush 72 had a shaft 721 and brush fibers 722 planted on the outer circumferential surface of the shaft 721. The brush fibers 722 were made of acrylic. The density of the brush fibers 722 was 150 kF per square inch (6.45 square cm). The application brush 72 was connected to a driving source (not shown) so as to rotate in a with-type manner. The rotation speed of the application brush 72 was set to be faster than the rotation speed of the image carrier 1. As an example, in this experiment, the speed of the outer circumferential surface of the image carrier 1 was set to 300 mm/sec, and the speed of the outer circumferential surface of the application brush 72 was set to 400 mm/sec. In this experiment, three types of application brushes 72 with different inclination angles of the bristles were prepared as samples 1 to 3. The "inclination angle of the bristles" refers to the angle between the normal line 41 and the straight line 43, that is, angle A in FIG. 5. Furthermore, attention was paid to whether or not the tip of the brush fiber 722 at the most upstream position 51 faces toward the center of the application brush 72 relative to the tangent line 42 to the outer periphery of the image carrier 1, i.e., whether or not the angle B in Figure 5 is positive. The results of this experiment are shown in Table 1.

In sample 1, the outer diameter of the application brush 72 was reduced. In samples 2 and 3, the outer diameter of the application brush 72 was not reduced. In other words, samples 2 and 3, in which angle B>0, gave good results. From this, it was confirmed that the configuration of the image forming device in this embodiment makes it difficult for localized dents to occur in the application brush 72.

(Experiment 2)
Experiment 2 was conducted with the following configuration. The description of the parts common to Experiment 1 will not be repeated. In this experiment, three types of application brushes 72 with different inclination angles of the bristles were prepared as samples 4 to 6. The "inclination angle of the bristles" refers to the angle between the normal line 41 and the straight line 43, that is, the angle A in FIG. 5 and the angle C in FIG. 7. Furthermore, as in Experiment 1, attention was paid to whether the tip of the brush fiber 722 at the most upstream position 51 faces toward the center of the application brush 72 more than the tangent line 42 to the outer periphery of the image carrier 1, that is, whether the angle B in FIG. 5 is positive or not. Furthermore, attention was paid to the positional relationship of the tip of the brush fiber 722 with respect to the normal line 62 to the outer periphery of the image carrier 1 at the most downstream position 52, that is, whether the angle D in FIG. 7 is 0 or more. The results of this experiment are shown in Table 2.

In sample 4, the outer diameter of the application brush 72 was locally reduced. In samples 5 and 6, the outer diameter of the application brush 72 was not reduced. In other words, samples 5 and 6, in which angle D≧0, showed good results. From this, it was confirmed that in an image forming device configuration in which angle D≧0, localized dents in the application brush 72 are less likely to occur.

In addition, two or more of the above-described embodiments may be appropriately combined and adopted.
The above-described embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, and includes all modifications within the meaning and scope of the claims.

1 Image carrier, 2 Charging device, 3 Exposure device, 4 Development device, 5 Primary transfer roller, 6 Intermediate transfer belt, 7 Cleaning device, 8 Laser light, 20 Operation display unit, 21 Image reading unit, 22 Image processing unit, 23 Paper transport unit, 24 Paper feed unit, 25 Secondary transfer roller, 26 Backup roller, 27 Fixing unit, 28 Paper discharge unit, 41 Normal (of outer circumference of application brush at most upstream position), 42 Tangent (of image carrier at most upstream position), 43 Tip direction (of brush fiber at most upstream position), 44 Normal (of outer circumference of image carrier at most upstream position), 51 Most upstream position, 52 Most downstream position, 61 Normal (of outer circumference of application brush at most downstream position), 62 Normal (of outer circumference of image carrier at most downstream position), 63 Tip direction (of brush fiber at most downstream position), 71 Cleaning blade, 72 Application brush, 73 solid lubricant, 74 blade, 91 arrow (indicating the direction in which the intermediate transfer belt runs), 92 arrow (indicating the direction in which the image carrier rotates), 93 arrow (indicating the direction in which the application brush rotates), 101 image forming device, 211 automatic document feeder, 212 document image scanning device, 241, 242, 243 tray unit, 721 shaft, 722 brush fiber, 723 outer periphery.

Claims (3)

a cylindrical rotating image carrier;
A solid lubricant;
a roller-shaped application brush that includes brush fibers on an outer circumferential surface and is disposed and rotated so as to scrape off the lubricant from the solid lubricant with the brush fibers and apply the lubricant to the image carrier;
a rotation direction of the application brush such that an outer peripheral surface of the application brush moves in the same direction as a moving direction of an outer peripheral surface of the image carrier at a contact point between the application brush and the image carrier;
When the cross section of the application brush is cut on a plane perpendicular to the rotation axis,
An image forming device in which, at the most upstream position of the area where the image carrier and the application brush contact, when assuming the posture that the brush fibers would take if the image carrier were not present, the tips of the brush fibers point toward the center of the application brush rather than the tangent to the outer periphery of the image carrier. When the cross section of the application brush is cut on a plane perpendicular to the rotation axis,
2. An image forming apparatus as described in claim 1, wherein at the most downstream position of the area where the image carrier and the application brush contact each other, the tips of the brush fibers are parallel to a normal to the outer periphery of the image carrier, or point upstream of the normal in terms of the rotation of the application brush. The image forming apparatus according to claim 1 or 2, wherein the speed of the outer peripheral surface of the application brush due to the rotation of the application brush is faster than the speed of the outer peripheral surface of the image carrier due to the rotation of the image carrier.

Images