Patent Grant
10175590
This application is a national stage of International Application No. PCT/JP2015/084240, filed Dec. 7, 2015, which claims the benefit of priority to Japanese Application No. 2015-017235, filed Jan. 30, 2015, and Japanese Application No. 2015-216765, filed Nov. 4, 2015, in the Japanese Patent Office, the disclosures of which are incorporated herein in their entireties by reference.
The present invention relates to an electrophotographic photosensitive body on the surface of which a toner image is formed, and also relates to an image forming apparatus provided with such an electrophotographic photosensitive body.
As image forming apparatuses such as printers, copiers, facsimile machines, multifunction peripherals provided with their functions, etc., there are known those that are provided with a photosensitive drum as one example of an electrophotographic photosensitive body, a charging device which electrostatically charges the surface of the photosensitive drum, and a cleaning blade which is arranged in contact with the surface of the photosensitive drum and which removes the toner and additive that remain on the surface of the photosensitive drum.
The photosensitive drum is composed of, for example, a drum pipe made of metal which serves as a support body and a photosensitive layer which is formed on the surface of the drum pipe. As photosensitive drums, there are proposed, for example, those that use amorphous silicon for the photosensitive layer and that has the surface of the drum pipe coarsened (e.g., Patent Documents 1 and 2).
In the photosensitive drum described in Patent Document 1, a plurality of spherical vestigial dents are formed on the surface of the drum pipe such that, over a reference length of 2.5 mm on the surface of the photosensitive drum, the ten-point average roughness Rz is in the range of 0.72 [μm] or more but 1.25 [μm] or less. In this way, adhesion of toner at the time of remaining toner cleaning is suppressed, and the scar resistance of the surface of the photosensitive drum is improved.
On the other hand, in the photosensitive drum of Patent Document 2, linear grooves in a triangular shape are formed on the surface of the photosensitive drum in the circumferential direction so that the surface condition of the photosensitive drum is such that the center-line arithmetic average roughness Ra is in the range of 0.08 [μm] to 0.12 [μm] and the ten-point average roughness Rz is in the range of 0.45 [μm] to 0.75 [μm]. In this way, the rotation torque of the photosensitive drum is reduced.
With the configuration described in Patent Document 1, the surface irregularities on the surface of the drum pipe are so large that toner additive or the like scrapes through the gaps between the cleaning blade and the surface of the photosensitive drum. In particular, in a case where the charging device is arranged close, the cleaning by the charging device may fall behind, rather causing contamination of the charging device.
On the other hand, with the configuration described in Patent Document 2, on the surface of the photosensitive drum, there are surface irregularities in the axial direction but not in the circumferential direction, and thus fine convexities on the side faces of the hills and valleys eventually wear and flatten. The edge of the cleaning blade, in minute regions in which it makes contact with a flat surface, is dragged in the rotation direction (circumferential direction) of the photosensitive drum, and stick-slip, though slight, occurs. At this time, additive scrapes through the grooves running in the circumferential direction, and thus the charging device is contaminated.
With consideration given to the problems mentioned above, an object of the present invention is to provide an electrophotographic photosensitive body that can suppress image defects for a long period, and to provide an image forming apparatus provided with such an electrophotographic photosensitive body.
To achieve the above object, according to a first configuration of the present invention, an electrophotographic photosensitive body includes a support body and a photosensitive layer formed on the surface of the support body. In this electrophotographic photosensitive body, at the initial stage of use, the surface of the photosensitive layer has an arithmetic average roughness Ra in the range of 20 nm or more but 100 nm or less, a ten-point average roughness Rz in the range of 0.2 μm or more but 1.0 μm or less, and an average peak-valley interval Sm of 20 μm or less.
In the present description, “arithmetic average roughness Ra”, “ten-point average roughness Rz”, and “average interval Sm” are based on the surface roughness defined in the 1994 edition of JIS B0601.
According to the first configuration of the present invention, an electrophotographic photosensitive body has a satisfactory surface condition that prevents toner additive or the like from scraping through the gap with a cleaning blade and that prevents the rotation torque from rising due to contact with the cleaning blade, and thus occurrence of image defects can be suppressed for a long period.
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
1. Configuration of Image Forming Apparatus 11
(Overall Configuration)
As shown in
(Configuration of Image Formation Processing Unit 15)
The image formation processing unit 15 adopts a tandem system which performs image formation processing by using toner (developer) of four colors, namely, for example, yellow (Y), magenta (M), cyan (C), and black (K). In the following description, wherever a particular color needs to be specified, a reference numeral will be suffixed with a color designation (Y, M, C, or K) in parentheses; for common description, a reference numeral alone will be used.
The image formation processing unit 15 includes, to correspond to the different colors (Y, M, C, and K), a plurality of toner containers 19 which store replenishment toner, a plurality of photosensitive drums 20 for forming toner images of the different colors based on print data (image data) transmitted from an externally connected device such as a personal computer, a plurality of developing devices 21 which feed toner to the photosensitive drums 20, an intermediary transfer belt 22 in an endless shape to which the toner images formed on the photosensitive drums 20 are primarily transferred, a belt cleaning device 24 which is arranged upstream of the most upstream-side photosensitive drum 20 in the rotating movement direction of the intermediary transfer belt 22 and which removes remaining toner and the like adhered on the surface of the intermediary transfer belt 22, an exposure unit 25 which emits beam light to the photosensitive drums 20, charging devices 26 which electrostatically charge the surfaces of the photosensitive drums 20 evenly, cleaning devices 28 which remove remaining toner and the like adhered to the surfaces of the photosensitive drums 20, and destaticizing devices 29 which eliminate remaining electric charge on the surfaces of the photosensitive drums 20. The photosensitive drums 20 correspond to one example of an “electrophotographic photosensitive body” in the present invention.
(Configuration of Photosensitive Drum 20)
The photosensitive drum 20 has a photosensitive layer formed on the surface of a support body (base body). Here, as shown in
As shown in
The toner images transferred to the intermediary transfer belt 22 in primary transfer sections each composed of the photosensitive drum 20 and the primary transfer roller 27 cooperating together are, in the secondary transfer unit 17, transferred to the recording sheet that has been transported through the recording sheet transport passage 16 from the sheet feed cassette 13 or from the manual feed tray.
(Configuration of Developing Device 21)
The developing devices 21 of basically the same configuration are arranged side by side under the intermediary transfer belt 22, along its rotating movement direction. The developing devices 21 develop electrostatic latent images formed on the surfaces of the photosensitive drums 20 into toner images by adhering toner containing toner additive (abrasive particles) comprising particles of metal such as titanium oxide. As the developing devices 21, conventionally known ones can be used.
(Configuration of Intermediary Transfer Belt 22)
The intermediary transfer belt 22 is an endless belt extended in the horizontal direction between a driving roller and a following roller inside the printer main body 12, and is driven to circulate during image forming operation as the driving roller is rotated by a belt driving motor (unillustrated).
(Configuration of Toner Concentration Sensor 23)
A toner concentration sensor 23 measures the reflected density of the toner image on the intermediary transfer belt 22, and outputs the detected value to a control unit (unillustrated). The toner concentration sensor 23 may be provided at a plurality of places along each of the rotating movement direction of the intermediary transfer belt 22 and the width direction perpendicular to the rotating movement direction. Here, arranging the toner concentration sensor 23 such that it detects toner density only on one side in the width direction of the intermediary transfer belt 22 makes it impossible to cope with, for example, a phenomenon in which density differs between opposite end parts in the width direction of the intermediary transfer belt 22 (a phenomenon of laterally uneven density), if such a phenomenon occurs. Thus, it is preferable that the toner concentration sensor 23 be arranged near opposite ends in the width direction.
(Configuration of Charging Device 26)
As shown in
The charging roller 42 is formed of, for example, electrically conductive rubber, and is arranged in contact with the photosensitive drum 20. As shown in
Moreover, as shown in
(Configuration of Cleaning Device 28)
The cleaning device 28 includes a cleaning housing 50 which has a depth in the recording sheet width direction (the direction perpendicular to the recording sheet transport direction), a collecting spiral 51 which is arranged in a lower part of the cleaning housing 50 inside it and which rotates in the clockwise direction in
The cleaning blade 52 is formed of urethane rubber or the like. The cleaning blade 52 is arranged such that its tip end makes contact with the surface of the photosensitive drum 20 from below the rotary shaft of the photosensitive drum 20. Here, the tip end of the cleaning blade 52 makes contact in the counter direction with respect to the rotation direction of the photosensitive drum 20 (see the arrow in
The rubbing roller 53 collects waste toner from the surface of the photosensitive drum 20, and also rubs the surface of the photosensitive drum 20 with the waste toner that has adhered to the surface of the rubbing roller 53. Accordingly, to maintain a high waste toner retention capability, the rubbing roller 53 is formed of foamed rubber (e.g., carbon-containing electrically conductive foamed EPDM) in a cylindrical shape extending in the recording sheet width direction, and is arranged upstream of the tip end of the cleaning blade 52 in the rotation direction of the photosensitive drum 20. The rotation direction of the rubbing roller 53 is opposite to the rotation direction of the photosensitive drum 20.
The toner feed guide plate 45 partitions between the side where the rubbing roller 53 is located and the side where the collecting spiral 51 is located, and guides the waste toner collected by the rubbing roller 53 to the collecting spiral 51.
(Configuration of Destaticizing Device 29)
The destaticizing device 29 is arranged downstream of the primary transfer roller 27 along the rotation direction of the photosensitive drum 20. In the destaticizing device 29, as shown in
2. Image Forming Procedure
Next, an image forming procedure in an image forming apparatus 100 will be described. When image data is input from an externally connected device such as a personal computer, first, the surfaces of the photosensitive drums 20 are electrostatically charged evenly by the charging devices 26, and then beam light is shone to the surfaces of the photosensitive drums 20 by the exposure unit 25 so that electrostatic latent images based on the image data are formed on the photosensitive drums 20. The developing devices 21 are charged with predetermined amounts of two-component developer (hereinafter also referred to simply as developer) of different colors, namely yellow, magenta, cyan, and black respectively. The developing devices 21 are replenished with toner from the toner containers 19 when the proportion of toner in the two-component developer charged in the developing devices 21 falls below a prescribed value as toner images are formed as will be described later. The toner in the developer is fed onto the photosensitive drums 20 by the developing devices 21, and electrostatically adheres to them, and thereby toner images based on the electrostatic latent images formed by exposure to light from the exposure unit 25 are formed.
On the other hand, in coordination with the timing with which the toner images are formed in the image formation processing unit 15, a recording sheet is fed out of the sheet feed cassette 13 (or the manual feed tray), passes through the recording sheet transport passage 16, and is transported to a registration roller pair 30a.
Then, an electric field is applied at a predetermined transfer voltage between the primary transfer rollers 27 and the photosensitive drums 20 by the primary transfer rollers 27, and thereby the yellow, magenta, cyan, and black toner images on the photosensitive drums 20 are primarily transferred to the intermediary transfer belt 22. These images of four colors are formed with a positional relationship previously determined for the formation of a predetermined full-color image. Then, in preparation for the subsequent formation of new electrostatic latent images, the toner and the like that remains on the surfaces of the photosensitive drums 20 after primary transfer is removed by the cleaning devices 28. Also, the electric charge remaining on the surfaces of the photosensitive drums 20 is eliminated by the destaticizing devices 29.
When the intermediary transfer belt 22 starts to rotate in the clockwise direction, the recording sheet is transferred from the registration roller pair 30a to the secondary transfer unit 17, which is provided to adjoin the intermediary transfer belt 22, with predetermined timing, and the full-color image on the intermediary transfer belt 22 is secondarily transferred to the recording sheet. The recording sheet having the toner image transferred to it is transported to the fixing unit 18. The remaining toner and the like adhered to the surface of the intermediary transfer belt 22 are removed by the belt cleaning device 24.
The recording sheet transported to the fixing unit 18 is heated and pressed so that the toner image is fixed to the surface of the recording sheet, and thereby the predetermined full-color image is formed. The recording sheet having the full-color image formed on it is guided to the terminal end part of the recording sheet transport passage 16, and is discharged onto a discharge tray 12a, which serves also as the top face of the printer main body 12, by a discharge roller pair 30b.
3. Properties of Photosensitive Layer of Photosensitive Drum 20
<1st Embodiment>
A description will now be given of the properties of a photosensitive layer 20b that constitutes a characteristic part of a photosensitive drum 20 according to a first embodiment. The photosensitive drum 20 of this embodiment has such a surface roughness that, at the initial stage of use, the surface of the photosensitive layer 20b has an arithmetic average roughness Ra in the range of 20 [nm] or more but 80 [nm] or less, a ten-point average roughness Rz in the range of 0.2 [μm] or more but 0.9 [μm] or less, and an average peak-valley interval Sm of 20 [μm] or less. The photosensitive drum 20 has to have this surface condition at least at the initial stage of its use (in a state at the start of its use, in other words, in a state after factory shipment). The arithmetic average roughness Ra, the ten-point average roughness Rz, and the average interval Sm are measured by a surface roughness measurement method defined in the 1994 edition of JIS B0601, by using a stylus-type two-dimensional roughness tester.
(1) Arithmetic Average Roughness Ra
The arithmetic average roughness Ra of the surface of the photosensitive layer 20b at the initial stage of use has to be in the range of 20 [nm] or more but 100 [nm] or less. When the arithmetic average roughness Ra is less than 20 [nm], the cleaning blade 52 wears during use for a long time, increasing the amount of additive that scrapes through, which leads to an image defect. When the arithmetic average roughness Ra is more than 100 [nm], the gap between the cleaning blade 52 and the surface of the photosensitive layer 20b is large. Thus, at a comparatively early stage of durability printing, additive starts to scrape through, and as a result the charging device 26 starts to be contaminated, leading to an image defect due to uneven electrostatic charging of the surface of the photosensitive drum 20.
When the arithmetic average roughness Ra of the surface of the photosensitive layer 20b is less than 20 [nm], the friction between the cleaning blade 52 and the photosensitive drum 20 is high, and the cleaning blade 52 wears heavily, resulting in extremely short durability thereafter. That is, it is impossible to obtain a satisfactory image for a long period.
As described above, when the arithmetic average roughness Ra of the surface of the photosensitive layer 20b at the initial stage of use of the photosensitive drum 20 is more than 80 [nm], the charging roller 42 starts to be contaminated at a comparatively early stage of printing 30000 sheets, making use for a long period difficult. That is, when the surface of the photosensitive drum 20 has large surface irregularities, scraping-through of toner additive occurs at the initial stage. It is preferable that the arithmetic average roughness Ra of the surface of the photosensitive layer 20b at the initial stage of use of the photosensitive drum 20 be in the range of 20 [nm] or more but 80 [nm] or less, more preferably in the range of 40 [nm] or more but 60 [nm] or less.
The reason is that, as will be described later in connection with practical examples, when the arithmetic average roughness Ra is in the above-mentioned range, the gap between the cleaning blade 52 and the photosensitive drum 20 can be reduced, and in addition the contact area between the cleaning blade 52 and the photosensitive drum 20 can be suppressed. Accordingly, a low torque can be maintained for a long period, and the wear of the edge of the cleaning blade 52 can be suppressed.
Incidentally, while the durability of the photosensitive drum 20 and how the cleaning blade 52 is durable depends on the additive used, the materials of the photosensitive layer 20b and the cleaning blade 52, etc., when the arithmetic average roughness Ra is in the above-mentioned range, it is possible to cope with various additives and the photosensitive layer 20b and the cleaning blade 52 of various materials.
(2) Ten-Point Average Roughness Rz
When the arithmetic average roughness Ra of the surface of the photosensitive layer 20b in the initial stage of use of the photosensitive drum 20 is in the range of 20 [nm] or more but 100 [nm] or less, it is preferable that the ten-point average roughness Rz of the surface of the photosensitive layer 20b at the initial stage of use of the photosensitive drum 20 be in the range of 0.2 [μm] or more but 1.0 [nm] or less.
This is a definition for preventing the following tendency: even when the arithmetic average roughness Ra is in the above-mentioned range, if there are large surface irregularities, whereas the cleaning blade 52 deforms to a certain degree, it cannot follow the surface of the photosensitive drum 20, and the gap formed between the photosensitive drum 20 and the cleaning blade 52 tends to grow large. Incidentally, when the gap between the photosensitive drum 20 and the cleaning blade 52 grows large, scraping-through of additive or the like occurs.
In other words, when there are large convex parts on the surface of the photosensitive drum 20, and the tips of those convex parts make contact with the cleaning blade 52, the concave parts located between the large convex parts do not make contact with the cleaning blade 52, and it is then senseless to define the arithmetic average roughness Ra in a certain range. That is, it is preferable that the surface of the photosensitive drum 20 have no extraordinary surface irregularities but fine surface irregularities, and the conditions for that are defined in terms of ten-point average roughness Rz and arithmetic average roughness Ra. Here, the absence of extraordinary surface irregularities is defined by the ten-point average roughness Rz.
When the arithmetic average roughness Ra of the surface of the photosensitive layer 20b at the initial stage of use of the photosensitive drum 20 is in the range of 40 [nm] or more but 60 [nm] or less, it is preferable that the ten-point average roughness Rz of the surface of the photosensitive layer 20b at the initial stage of use of the photosensitive drum 20 be in the range of 0.4 [μm] or more but 0.9 [μm] or less. The purpose is to narrow down the range of the ten-point average roughness Rz in accordance with the narrowed range of the arithmetic average roughness Ra.
(3) Average Peak-Valley Interval Sm
When, at the initial stage of use of the photosensitive drum 20, the surface of the photosensitive layer 20b has an arithmetic average roughness Ra in the range of 20 [nm] or more but 100 [nm] or less and a ten-point average roughness Rz in the range of 0.2 [μm] or more but 1.0 [μm] or less, it is preferable that the average peak-valley interval Sm be 20 [μm] or less.
The reason is as follows. Even when the arithmetic average roughness Ra and the ten-point average roughness Rz are in the above-mentioned ranges, if there are large convex, parts that are apart from each other, the cleaning blade 52 makes contact with (is supported on) those large convex parts. Here, to determine whether or not the large convex parts are apart from each other, the average peak-valley interval Sm is utilized.
A cleaning blade is elastically deformable, and deforms so as to make contact with the photosensitive drum 20 between large convexities (convex parts). In particular, where the intervals between the convex parts are large, the contact area between the cleaning blade 52 and the photosensitive drum 20 increases. As the contact area increases, due to the friction with the cleaning blade 52, the driving torque of the photosensitive drum 20 increases, the wear of the cleaning blade 52 becomes severe, and eventually the cleaning blade 52 causes stick-slip, resulting in scraping-through of additive and chipping of the edge of the cleaning blade 52. Needless to say, chipping of the edge of the cleaning blade 52 makes it impossible to obtain a satisfactory image.
Moreover, when the average interval Sm is large, convex parts (hills) are large (with broader skirts), and as the peak parts of the convex parts wear during use for a long time, the peak parts come to have flat parts, resulting in an increased contact area with the cleaning blade 52. When, at the initial stage of use of the photosensitive drum, the surface of the photosensitive drum has an arithmetic average roughness Ra of 40 [nm] or more but 60 [nm] or less and a ten-point average roughness Rz of 0.4 [μm] or more but 0.7 [μm] or less, it is preferable that the average interval Sm be 14 [μm] or less. The purpose is to reduce the range of the average interval Sm in accordance with the narrowed ranges of the arithmetic average roughness Ra and the ten-point average roughness Rz.
(4) DUH Hardness
It is preferable that the DUH hardness of the photosensitive layer 20b at the initial stage of use of the photosensitive drum 20 be in the range of 500 [kgf/mm2] or more but 1200 [kgf/mm2] or less. When the DUB hardness is less than 500 [kgf/mm2], the photosensitive layer 20b of the photosensitive drum 20 tends to wear due to contact with the cleaning blade 52 and the charger cleaning roller 43, and this makes use for a long period impossible. From this viewpoint, it is preferable that the DUH hardness be high. Accordingly, the upper limit of the DUH hardness is defined by the hardness of the photosensitive layer 20b with the highest hardness that is currently available. DUH hardness refers to indentation hardness (Martens hardness) as measured on a dynamic ultra-micro hardness tester (in the DUH series, manufactured by Shimadzu Corporation).
(5) Appearance of Surface Irregularities
It is preferable that, as shown in
In
On the other hand, in the surface condition after durability printing of 300000 sheets, as shown in
Where surface irregularities are present irregularly in the axial direction and in the circumferential direction as shown in
Even in the surface condition after printing 300000 sheets, as shown in
(6) Region
It is preferable that the arithmetic average roughness Ra, the ten-point average roughness Rz, and the average interval Sm be in the ranges described above over the entire area of the image formation region on the surface of the photosensitive drum 20.
(7) Toner Additive
As an additive, electrically conductive abrasive fine particles, such as of titanium oxide, silica, or the like, are added to the toner. When the arithmetic average roughness Ra on the surface of the photosensitive layer 20b is large, the additive scrapes through the gaps between surface irregularities that the cleaning blade 52 cannot follow. Accordingly, it is preferable that the toner additive used for the photosensitive drum 20 of this embodiment have an average primary particle diameter of 10 nm or more.
<2nd Embodiment>
A description will now be given of the properties of a photosensitive layer 20b that constitutes a characteristic part of a photosensitive drum 20 according to a second embodiment. The photosensitive drum 20 of this embodiment has such a surface roughness that, at the initial stage of use, the surface of the photosensitive layer 20b has an arithmetic average roughness Ra in the range of 20 [nm] or more but 100 [nm] or less, a ten-point average roughness Rz in the range of 0.2 [μm] or more but 1.0 [μm] or less, and a skewness Rsk of 0.3 or more. The measurement methods for the arithmetic average roughness Ra, the ten-point average roughness Rz, and the average interval Sm are similar to those in the first and second embodiments.
Here, skewness Rsk is one of those parameters which indicate the intensity of surface roughness, represents the degree of symmetry between hill parts and valley parts about the average line (the degree of skewness of surface irregularities), and is expressed, as given by formula (1) below, as the root mean cube of Z(x) over a reference length that is made non-dimensional by the cube of the root-mean-square square-root height Rq.
When Rsk is larger than zero, as shown in
Moreover, it is preferable that, as in the first embodiment, the DUH hardness of the photosensitive layer 20b be set at 500 to 1200 kgf/mm2, and that the pitch of surface irregularities (the average interval Sm) be as small as possible (Sm<20 μm). Furthermore, it is preferable that the toner additive used for the photosensitive drum 20 of this embodiment have an average primary particle diameter of 10 nm or more.
<Third Embodiment>
A description will now be given of the properties of a photosensitive layer 20b that constitutes a characteristic part of a photosensitive drum 20 according to a third embodiment. The photosensitive drum 20 of this embodiment has such a surface roughness that, at the initial stage of use, the surface of the photosensitive layer 20b has an arithmetic average roughness Ra in the range of 20 [nm] or more but 100 [nm] or less, a ten-point average roughness Rz in the range of 0.2 [μm] or more but 1.0 [μm] or less, and a ratio (Ra [nm]/Sm [μm]) of 3 or more as the ratio of the arithmetic average roughness Ra [nm] to the average peak-valley interval Sm [μm]. The measurement methods for the arithmetic average roughness Ra, the ten-point average roughness Rz, and the average peak-valley interval Sm are similar to those in the first embodiment.
By irregularly forming surface irregularities such that the surface roughness fulfills the ranges mentioned above on the surface of the photosensitive layer 20b in the axial direction and the circumferential direction of the photosensitive drum 20, it is possible to reduce the friction between the photosensitive drum 20 and the cleaning blade 52, and to reduce the driving torque of the photosensitive drum 20 and the wear of the edge of the cleaning blade 52. In particular, fulfilling Ra [nm]/Sm [μm]≥3 produces surface irregularities that have a height (depth) three times or more as large as the average interval Sm, and this helps reduce the contact area between photosensitive drum 20 and the cleaning blade 52 and helps effectively reduce friction.
While the surface irregularities formed on the surface of the photosensitive layer 20b gradually wear during printing for a long period, by setting the DUH hardness of the photosensitive layer 20b at 500 to 1200 kgf/mm2 as in the first and second embodiments, it is possible to maintain the surface irregularities satisfactorily throughout the period of use of the photosensitive drum 20. Thus, the contact area between the photosensitive drum 20 and the cleaning blade 52 does not increase up to the final stage of use of the photosensitive drum 20, it is thus possible to reduce the load that acts on the cleaning blade 52 for a long period, and it is possible to suppress wear and chipping of the edge of the cleaning blade 52 and thereby maintain cleanability on a long-term basis.
The surface irregularities wear starting with convex portions, and thus, with a view to making flat parts as small as possible, it is preferable to set the pitch of surface irregularities (average interval Sm) as small as possible (Sm<20 μm). Moreover, to suppress scraping-through of additive through the gaps between the surface irregularities on the photosensitive layer 20b and the cleaning blade 52, it is preferable that the toner additive used for the photosensitive drum 20 of this embodiment have an average primary particle diameter of 10 nm or more.
<Modified Examples>
Although the photosensitive drum 20 and the image forming apparatus 11 according to the present invention have been described above by way of embodiments, the present invention is not limited by those embodiments, but may be implemented as in the modified examples described below. The present invention encompasses any example that is not described in those embodiments and any design change within a range not departing from the spirit of the present invention.
(Modified Example 1)
In the above embodiments, as an example of the image forming apparatus 11, a tandem-type color printer has been described, but application is also possible to, for example, a rotary-type color printer or a monochrome printer. Application is also possible to image forming apparatuses such as copiers, facsimile machines, multifunctional peripherals provided with their functions, etc. The image forming apparatus 11 may have the configuration of the color printer described in connection with the embodiments, or may have any other configuration. However, it is necessary to provide an electrophotographic photosensitive body as described above with the photosensitive drum 20 taken as an example. As a means for cleaning the electrophotographic photosensitive body, it is preferable to provide a cleaning blade 52.
(Modified Example 2)
The photosensitive drum 20 in the embodiments described above use a cylindrical drum pipe 20a as a support body, but may instead use a support body of any other shape. Other shapes include shapes like a plate and like an endless belt. Although the photosensitive drum 20 in the embodiments uses amorphous silicon as the photosensitive layer 20b, it may instead have a charge injection inhibition layer for inhibiting injection of electric charge from the support body.
(Modified Example 3)
The cleaning device in the embodiments described above has a structure in which the cleaning housing 50, the collecting spiral 51, the cleaning blade 52, the rubbing roller 53, etc. are provided integrally, and it is preferable that it include the cleaning blade 52. Hereinafter, the effects of the present invention will be described in more detail by way of practical examples.
(1) Fabricating Photosensitive Drum 20 (Present Invention 1)
A photosensitive drum 20 (Present Invention 1) was fabricated by forming a photosensitive layer 20b of amorphous silicon on the surface of a drum pipe 20a of aluminum. The drum pipe 20a had a diameter of 30 [mm], and had its surface elastically deformed by wet-blast treatment or the like to form fine surface irregularities on the surface. The wet-blast treatment was performed such that the arithmetic average roughness Ra of the surface is in the range of 4 [nm] to 60 [nm].
When the surface roughness of the amorphous silicon photosensitive drum 20 after the deposition of the photosensitive layer 20b was measured, the arithmetic average roughness Ra was 45 [nm], the ten-point average roughness Rz was 0.5 [μm], and the average peak-valley interval Sm was 12 [μm].
Moreover, the DUH hardness of the surface of the photosensitive drum 20 was measured by use of a DUH hardness tester (DYNAMIC ULTRA MICRO HARDNESS TESTER DUH-201•202, manufactured by Shimadzu Corporation). The measurement conditions were: inspection depth, 150 nm; load speed, 0.284393 mN/sec; load range, 19.6 mN; holding time 10 sec. The result was that the DUH hardness of the surface was 900 [kgf/mm2].
The surface roughness was measured over a measurement length of 2.5 mm by use of a stylus-type two-dimensional roughness tester (Surfcom 1500DX, manufactured by Tokyo Seimitsu Co., Ltd.). The measurement terminal was of a stylus type with 60-degrees conical diamond, and had a tip radius of 2 [μm]. The measurement length was 2.5 [mm], and the cutoff value was 0.08 [mm]. The filter type was Gaussian, and the inclination correction was least-square linear correction. The cutoff ratio was 300, and the measurement magnification was ×100 k.
(2) Fabricating Photosensitive Drum 20 (Comparative Example 1)
A photosensitive drum 20 (Comparative Example 1) was fabricated by forming a photosensitive layer 20b of amorphous silicon on the surface of a drum pipe 20a of aluminum. The surface of the drum pipe 20a was mirror-finished, and when the surface roughness of the photosensitive drum 20 after the deposition of the amorphous-silicon photosensitive layer 20b was measured, the arithmetic average roughness Ra was 3 [nm], the ten-point average roughness Rz was 0.1 [μm], and the average peak-valley interval Sm was 8 [μm]. When the DUH hardness of the surface of the photosensitive drum 20 was measured as in Present Invention 1, it was 900 [kgf/mm2].
(3) Comparative Testing
Durability tests were performed by use of the image forming apparatus 11 provided with the photosensitive drums 20 of Present Invention 1 and Comparative Example fabricated as described at (1) and (2) above. The test conditions were: the linear velocity of the photosensitive drum 20 was 267 mm/sec, and, as a test image, a text document with a printing ratio of 5% was printed on 20000 sheets a day, on a total of 600000 sheets. As the cleaning blade 52, a rubber blade made of urethane rubber with a base-to-tip length (free length) of 11.0 mm and a thickness of 2.0 mm was used, and the angle relative to the outer circumferential face of the photosensitive drum 20 was set at 24°, and the amount of overlay was set at 1.2 mm.
(3-1) Torque During Printing
To explain the effects of the photosensitive drum 20 of Present Invention 1, also on the image forming apparatus 11 provided with the photosensitive drum 20 of Comparative Example 1, after 300000 sheets were printed, torque measurement was performed during printing, and is shown as “D” is
Specifically, the arithmetic average roughness Ra (14 nm) after printing 600000 sheets when continuous printing was performed by use of the image forming apparatus 11 provided with the photosensitive drum 20 of Present Invention 1 was larger than the arithmetic average roughness Ra (3 nm) after printing 300000 by use of the photosensitive drum of Comparative Example 1. On the other hand, the rotation torque (about 23 mNm) after printing 600000 by use of the photosensitive drum 20 of Present Invention 1 was smaller than the rotation torque (about 30 mNm) after printing 300000 sheets by use of the photosensitive drum of Comparative Example 1. These results reveal that the photosensitive drum 20 of Present Invention 1, although its surface gradually wears and flattens as the number of prints increases, flattens at lower speed than the photosensitive drum 20 of Comparative Example 1, and excels the photosensitive drum 20 of Comparative Example 1 in durability.
(3-2) Blade Wear
6 types of photosensitive drums 20 (Present Inventions 2 to 8 and Comparative Examples 2 and 3) with varying arithmetic averages Ra, ten-point averages Rz, average intervals Sm, and ratios Ra/Sm on the surface of the photosensitive layer 20b were fabricated, and the relationship among the surface roughness of the photosensitive layer 20b at the initial stage of use, the amount of blade wear, and the driving torque of the photosensitive drum 20 was evaluated. The testing method involved mounting the photosensitive drums 20 of Present Inventions 2 to 8 and Comparative Examples 2 and 3 in the image forming apparatus 11, and evaluating the amount of wear of the cleaning blade 52 after durability printing of 300000 sheets and 600000 sheets, occurrence of image defects after durability printing of 600000 sheets, and the driving torque of the photosensitive drum 20. The fabrication method of the photosensitive drums 20 was similar to that for Present Invention 1.
The criteria for evaluating the amount of blade wear were as follows: an instance where the amount of wear in an edge part of the blade was less than 30 μm was evaluated as Good, an instance where it was 30 μm or more but less than 40 μm was evaluated as Fair, and an instance where it was 40 μm or more was evaluated as Poor. The criteria for evaluating image defects were as follows: an instance where reducing the charging bias to below the standard charging bias did not cause an image defect was evaluated as Good, an instance where the standard charging bias did not cause an image defect but a lower-than-the-standard charging bias caused an image defect was evaluated as Fair, and an instance where even the standard charging bias caused an image defect was evaluated as evaluated as Poor. The criteria for evaluating the driving torque were as follows: an instance where the driving torque was below 20 mNm was evaluated as Good, an instance where it was 20 mNm or more but less than 30 mNm was evaluated as Fair, and an instance where it was 30 mNm or more was evaluated as Poor. The results of evaluation of the amount of blade wear, image effects, and the driving torque with each photosensitive drum 20 are, along with surface roughness measurement values, shown in Table 1. The variation of the driving torque of the photosensitive drums 20 is shown in
As will be clear from Table 1 and
Present Inventions 2 to 8, where the arithmetic average roughness Ra was 20 to 100 nm and the ten-point average roughness Rz was 0.20 to 1.0 μm, the blade ware amount after durability printing of 300000 sheets was less than 30 μm. Moreover, after durability printing of 600000 sheets, applying the standard charging bias did not cause image defects, and the driving torque of the photosensitive drum 20 was less than 30 mNm.
In particular, with Present Inventions 3, 4, and 6, where Ra/Sm is equal to or more than 3 and Rsk equals to or more than 0.3, even after durability printing of 600000 sheets, the blade wear amount was less than 30 μm, and even a lower-than-the-standard charging bias did not cause image defects, and in addition the driving torque of the photosensitive drum 20 was less than 20 mNm.
By contrast, with the photosensitive drum 20 of Comparative Example 2, where the arithmetic average roughness Ra was more than 100 nm and the ten-point average roughness Rz was more than 1.0 μm, after durability printing of 600000 sheets, the blade wear amount was less than 30 μm, and the driving torque of the photosensitive drum 20 was less than 20 mNm, but even applying the standard charging bias caused image defects. This is considered to be because, when the surface irregularities of the photosensitive layer 20b at the initial stage of use of the photosensitive drum 20 are too large, scraping-through of additive through concave and convex parts of the photosensitive layer 20b occurs, and the charging roller 42 is contaminated with the additive, resulting in uneven electrostatic charging.
With the photosensitive drum 20 of Comparative Example 3, where Ra/Sm=3 and Rsk=0.33 but the arithmetic average roughness Ra was less than 20 nm and the ten-point average roughness Rz was less than 0.2 μm, after durability printing of 300000 sheets, the blade wear amount was as large as 40 μm or more. Also, the driving torque of the photosensitive drum 20 was as large as 30 mNm or more. This is considered to be because, when the surface irregularities on the photosensitive layer 20b at the initial stage of use of the photosensitive layer 20b are too small, the surface irregularities on the photosensitive layer 20b quickly flatten during durability printing, and the contact area between the photosensitive drum 20 and the cleaning blade 52 increases.
The present invention finds application in electrophotographic photosensitive bodies on the surface of which a toner image is formed. By use of the present invention, it is possible to provide an electrophotographic photosensitive body, and an image forming apparatus provided with one, that can suppress image defects for a long period.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-017235 | Jan 2015 | JP | national |
| 2015-216765 | Nov 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/084240 | 12/7/2015 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2016/121231 | 8/4/2016 | WO | A |
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|---|---|---|---|
| 9507287 | Takagami | Nov 2016 | B2 |
| 20020001482 | Iinuma | Jan 2002 | A1 |
| 20110129770 | Aoki et al. | Jun 2011 | A1 |
| 20160238961 | Takagami | Aug 2016 | A1 |
| Number | Date | Country |
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| H 11-143099 | May 1999 | JP |
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| 2008-216306 | Sep 2008 | JP |
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| Entry |
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| Japanese Office Action dated Sep. 5, 2017, issued by the Japanese Patent Office in corresponding application JP 2016-571795. |
| Number | Date | Country | |
|---|---|---|---|
| 20180217512 A1 | Aug 2018 | US |
