JP7363160B2 - Image forming device and image forming method - Google Patents

Description

The present invention relates to an image forming apparatus and an image forming method.

In an electrophotographic image forming apparatus, a charging device is used to charge an image carrier. As a charging device, for example, a charging roller is used that includes a conductive shaft, an elastic layer that covers the conductive shaft, and a surface layer that directly or indirectly covers the elastic layer (Patent Documents 1 to 3). 2). The charging rollers described in Patent Documents 1 and 2 are said to be able to suppress the occurrence of charging unevenness. Note that charging unevenness refers to minute image unevenness (for example, spot-like unevenness or horizontal stripe-like unevenness) that occurs in a halftone image. It is said that charging unevenness occurs when an image bearing member is not uniformly charged by a charging device.

Japanese Patent Application Publication No. 2007-178975 Japanese Patent Application Publication No. 2009-122515

However, even in the image forming apparatus using the charging roller described in Patent Documents 1 and 2, it is difficult to sufficiently suppress the occurrence of charging unevenness.

The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus and an image forming method that can suppress the occurrence of uneven charging.

The image forming apparatus of the present invention includes an image carrier and a charging roller that positively charges a peripheral surface of the image carrier. The image carrier includes a conductive substrate and a single photosensitive layer. The photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent, and a first binder resin. The charging roller includes a conductive shaft, a base layer covering the surface of the conductive shaft, and a surface layer covering the surface of the base layer. The charging ability X [V/(C/m ² )] of the image carrier expressed by the following formula (1) and the surface resistivity Y [logΩ] of the surface layer of the charging roller are expressed by the following formula (2). satisfy.
X=V/(Q/S)...(1)
Y＞5×10 ^-11 X ² +1.062×10 ^-5 ×X-47...(2)

In the formula (1), Q represents the amount of electric charge [C] on the image carrier. S represents the charged area [m ² ] of the image carrier. V is a value calculated from the formula V=V ₀ -V _r . V _r represents a first potential [V] of the peripheral surface of the image carrier before being charged by the charging roller. V ₀ represents a second potential [V] of the peripheral surface of the image carrier after being charged by the charging roller.

The image forming method of the present invention includes a charging step of positively charging the peripheral surface of the image carrier with a charging roller. The image carrier includes a conductive substrate and a single photosensitive layer. The photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent, and a first binder resin. The charging roller includes a conductive shaft, a base layer covering the surface of the conductive shaft, and a surface layer covering the surface of the base layer. The charging ability X [V/(C/m ² )] of the image carrier expressed by the following formula (1) and the surface resistivity Y [logΩ] of the surface layer of the charging roller are expressed by the following formula (2 ) is satisfied.
X=V/(Q/S)...(1)
Y＞5×10 ^-11 X ² +1.062×10 ^-5 ×X-47...(2)

In the formula (1), Q represents the amount of electric charge [C] on the image carrier. S represents the charged area [m ² ] of the image carrier. V is a value calculated from the formula V=V ₀ -V _r . V _r represents a first potential [V] of the peripheral surface of the image carrier before being charged in the charging step. V ₀ represents a second potential [V] of the peripheral surface of the image carrier after being charged in the charging step.

According to the image forming apparatus and image forming method of the present invention, it is possible to suppress the occurrence of charging unevenness.

1 is a sectional view showing an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a photoreceptor and its peripheral portion included in the image forming apparatus shown in FIG. 1. FIG. 2 is a partial cross-sectional view showing an example of a charging roller included in the image forming apparatus shown in FIG. 1. FIG. 2 is a partial cross-sectional view showing an example of a photoreceptor included in the image forming apparatus shown in FIG. 1. FIG. 2 is a partial cross-sectional view showing an example of a photoreceptor included in the image forming apparatus shown in FIG. 1. FIG. 2 is a partial cross-sectional view showing an example of a photoreceptor included in the image forming apparatus shown in FIG. 1. FIG. FIG. 3 is a diagram showing a measuring device that measures a first potential V _r and a second potential V ₀ . 2 is a diagram showing a power supply system for a primary transfer roller included in the image forming apparatus shown in FIG. 1. FIG. It is a figure which shows the drive mechanism which implements a thrust mechanism. It is a graph showing the evaluation results of charging unevenness conducted in Examples.

First, terms used in this specification will be explained. The compound and its derivatives may be collectively referred to by adding "system" after the compound name. Furthermore, when a polymer name is expressed by adding "system" after the compound name, it means that the repeating unit of the polymer is derived from the compound or its derivative.

Hereinafter, halogen atom, alkyl group having 1 to 8 carbon atoms, alkyl group having 1 to 6 carbon atoms, alkyl group having 1 to 5 carbon atoms, alkyl group having 1 to 4 carbon atoms, carbon Unless otherwise specified, an alkyl group having 1 or more and 3 or less atoms and an alkoxy group having 1 or more and 4 or less carbon atoms have the following meanings.

Examples of the halogen atom (halogen group) include a fluorine atom (fluoro group), a chlorine atom (chloro group), a bromine atom (bromo group), and an iodine atom (iodo group).

an alkyl group having 1 to 8 carbon atoms, an alkyl group having 1 to 6 carbon atoms, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 4 carbon atoms, and an alkyl group having 1 to 4 carbon atoms; Each of the three or less alkyl groups is linear or branched and unsubstituted. Examples of the alkyl group having 1 to 8 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, and isopentyl group. group, neopentyl group, 1,1-dimethylpropyl group, 1,2-dimethylpropyl group, linear or branched hexyl group, linear or branched heptyl group, and linear or A branched octyl group is mentioned. Examples of alkyl groups having 1 to 6 carbon atoms, alkyl groups having 1 to 5 carbon atoms, alkyl groups having 1 to 4 carbon atoms, and alkyl groups having 1 to 3 carbon atoms are carbon atoms. Among the groups mentioned as examples of alkyl groups having a number of 1 to 8, groups having 1 to 6 carbon atoms, groups having 1 to 5 carbon atoms, groups having 1 to 4 carbon atoms, and carbon It is a group having 1 or more atoms and 3 or less atoms.

The alkoxy group having 1 to 4 carbon atoms is linear or branched and unsubstituted. Examples of the alkoxy group having 1 to 4 carbon atoms include methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, sec-butoxy group, and tert-butoxy group. The terms used in this specification have been explained above.

[Image forming device]
The image forming apparatus according to the first embodiment of the present invention includes an image carrier and a charging roller that positively charges the circumferential surface of the image carrier. The photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent, and a first binder resin. The charging roller includes a conductive shaft, a base layer covering the surface of the conductive shaft, and a surface layer covering the surface of the base layer. The charging capacity X [V/(C/m ² )] of the image carrier expressed by the following formula (1) and the surface resistivity Y [logΩ] of the surface layer of the charging roller satisfy the following formula (2). .
X=V/(Q/S)...(1)
Y＞5×10 ^-11 X ² +1.062×10 ^-5 ×X-47...(2)

In formula (1), Q represents the amount of electric charge [C] on the image carrier. S represents the charged area [m ² ] of the image carrier. V is a value calculated from the formula V=V ₀ -V _r . V _r represents the first potential [V] of the circumferential surface of the image carrier before being charged by the charging roller. V ₀ represents the second potential [V] of the peripheral surface of the image carrier after being charged by the charging roller.

An image forming apparatus according to this embodiment will be described with reference to the drawings. In addition, in the drawings, the same reference numerals are given to the same or corresponding parts, and the description will not be repeated. In this embodiment, the X-axis, Y-axis, and Z-axis are perpendicular to each other, the X-axis and Y-axis are parallel to the horizontal plane, and the Z-axis is parallel to the vertical line.

First, with reference to FIG. 1, an overview of an image forming apparatus 1 according to the present embodiment will be described. The image forming apparatus 1 according to this embodiment is a full color printer. The image forming apparatus 1 includes a feeding section 10 , a conveying section 20 , an image forming section 30 , a toner supply section 60 , and a discharging section 70 .

The feeding section 10 includes a cassette 11 that accommodates a plurality of sheets P. The feeding section 10 feeds the sheets P from the cassette 11 to the conveying section 20 . The sheet P is made of paper or synthetic resin, for example. The conveying section 20 conveys the sheet P to the image forming section 30.

The image forming section 30 includes an exposure device 31, a magenta unit (hereinafter referred to as M unit) 32M, a cyan unit (hereinafter referred to as C unit) 32C, a yellow unit (hereinafter referred to as Y unit) 32Y, a black unit (hereinafter referred to as BK unit) 32BK, It includes a transfer belt 33, a secondary transfer roller 34, and a fixing device 35. Each of the M unit 32M, C unit 32C, Y unit 32Y, and BK unit 32BK includes a photoreceptor 50, a charging roller 51, a developing roller 52, a primary transfer roller 53, a static elimination lamp 54, and a cleaner 55.

The exposure device 31 irradiates each of the M unit 32M to the BK unit 32BK with light based on image data to form an electrostatic latent image on each of the M unit 32M to the BK unit 32BK. The M unit 32M forms a magenta toner image based on the electrostatic latent image. The C unit 32C forms a cyan toner image based on the electrostatic latent image. The Y unit 32Y forms a yellow toner image based on the electrostatic latent image. The BK unit 32BK forms a black toner image based on the electrostatic latent image.

The photoreceptor 50 is drum-shaped. The photoreceptor 50 rotates around a rotation center 50X (rotation axis, see FIG. 2). Around the photoconductor 50, from the upstream side in the rotation direction R of the photoconductor 50 (see FIG. 2), a charging roller 51, a developing roller 52, a primary transfer roller 53, a static elimination lamp 54, and a cleaner 55 are installed. , arranged in the order listed. The charging roller 51 charges the peripheral surface 50a of the photoreceptor 50 to positive polarity. As described above, the exposure device 31 exposes the charged peripheral surface 50a of the photoreceptor 50 to form an electrostatic latent image on the peripheral surface 50a of the photoreceptor 50. The developing roller 52 attracts and carries the carrier CA carrying the toner T by magnetic force. By applying a developing bias (developing voltage) to the developing roller 52, a potential difference is generated between the potential of the developing roller 52 and the potential of the circumferential surface 50a of the photoreceptor 50, and a difference is formed on the circumferential surface 50a of the photoreceptor 50. Toner T moves and adheres to the electrostatic latent image. In this way, the developing roller 52 supplies the toner T to the electrostatic latent image and develops the electrostatic latent image into a toner image. As a result, a toner image is formed on the peripheral surface 50a of the photoreceptor 50. The toner image includes toner T. The transfer belt 33 contacts the circumferential surface 50a of the photoreceptor 50. The primary transfer roller 53 primarily transfers the toner image formed on the circumferential surface 50a of the photoreceptor 50 onto the transfer belt 33 (more specifically, the outer surface of the transfer belt 33). Toner images of four colors are primarily transferred onto the outer surface of the transfer belt 33 in a superimposed manner. The four-color toner images are a magenta toner image, a cyan toner image, a yellow toner image, and a black toner image. A color toner image is formed on the outer surface of the transfer belt 33 by the primary transfer. The secondary transfer roller 34 secondary transfers the color toner image formed on the outer surface of the transfer belt 33 onto the sheet P. The fixing device 35 heats and presses the sheet P to fix the color toner image on the sheet P. The sheet P on which the color toner image has been fixed is discharged to the discharge section 70. After the primary transfer, the static elimination lamps 54 included in each of the M unit 32M to the BK unit 32BK eliminate static from the peripheral surface 50a of the photoreceptor 50. After the primary transfer (more specifically, after the primary transfer and after static electricity removal), the cleaner 55 collects the toner T remaining on the circumferential surface 50a of the photoreceptor 50.

The toner supply unit 60 includes a cartridge 60M containing magenta toner T, a cartridge 60C containing cyan toner T, a cartridge 60Y containing yellow toner T, and a cartridge 60BK containing black toner T. including. Cartridge 60M, cartridge 60C, cartridge 60Y, and cartridge 60BK supply toner T to developing roller 52 of M unit 32M, C unit 32C, Y unit 32Y, and BK unit 32BK, respectively.

Note that the photoreceptor 50 corresponds to an image carrier. The developing roller 52 corresponds to a developing device. The primary transfer roller 53 corresponds to a transfer device. The transfer belt 33 corresponds to an object to be transferred. The static eliminating lamp 54 corresponds to a static eliminating device. The cleaner 55 corresponds to a cleaning device.

Next, the image forming apparatus 1 according to this embodiment will be further described with reference to FIGS. 2 and 3. FIG. 2 shows the photoreceptor 50 and its surroundings. The image forming apparatus 1 according to the present embodiment includes a photoreceptor 50 corresponding to an image carrier, a charging roller 51, and a cleaner 55. The cleaner 55 includes a cleaning blade 81 that corresponds to a cleaning member. The charging roller 51 charges the peripheral surface 50a of the photoreceptor 50 to positive polarity. The cleaning blade 81 is brought into pressure contact with the circumferential surface 50 a of the photoreceptor 50 and collects the toner T remaining on the circumferential surface 50 a of the photoreceptor 50 .

FIG. 3 shows the charging roller 51. The charging roller 51 includes a conductive shaft 51a, a base layer 51b covering the surface of the conductive shaft 51a, and a surface layer 51c covering the surface of the base layer 51b. The surface layer 51c is the outermost layer of the charging roller 51.

In the image forming apparatus 1, since the charging ability X [V/(C/m ² )] of the image carrier and the surface resistivity Y [logΩ] of the surface layer of the charging roller satisfy equation (2), uneven charging can be avoided. The occurrence can be suppressed. Here, the causes of uneven charging are considered to be as follows. First, the charging roller 51 charges the circumferential surface 50a of the photoreceptor 50 by discharging the photoreceptor 50 from the surface 51d of the charging roller 51. At this time, in the charging roller 51, a radial current is generated from the conductive shaft 51a toward the surface 51d. However, there may be a region on the surface 51d of the charging roller 51 where discharge is more likely to occur than surrounding regions. In a conventional charging roller, if such a region exists on the surface, a lateral current is generated in the surface layer, and discharge may occur intensively in the above-mentioned discharge-prone region. When a concentrated discharge occurs on the surface of a conventional charging roller, a portion of the circumferential surface of the photoreceptor becomes excessively charged. As a result of the above, it is thought that charging unevenness (for example, spotty white spots) occurs in image forming apparatuses equipped with conventional charging rollers.

The present inventor believes that the relationship between the charging ability X of the image carrier and the surface resistivity Y (hereinafter sometimes referred to as surface layer resistance Y) of the surface layer 51c of the charging roller 51 is important in the occurrence of charging unevenness. I discovered something. Specifically, it has been found that an image bearing member with a low charging ability X is less likely to cause uneven charging, and an image bearing member with a high charging ability X is more likely to experience uneven charging. It has also been found that even when an image carrier having a high charging ability X is used, if the surface resistance Y of the surface layer 51c of the charging roller 51 is high, the occurrence of charging unevenness can be suppressed. This is because when the surface layer resistance Y of the charging roller 51 is high, the above-mentioned cross-flow current is suppressed in the surface layer 51c. Further, in order to suppress the occurrence of charging unevenness, specifically, it has been found that the charging ability X of the image carrier and the surface resistance Y of the charging roller 51 should satisfy equation (2). That is, in the image forming apparatus 1, since the surface resistance Y of the charging roller 51 has a value corresponding to the charging ability X of the image carrier, it is possible to suppress the occurrence of charging unevenness.

<Photoreceptor>
The photoreceptor 50 included in the image forming apparatus 1 will be described below with reference to FIGS. 4 to 6. 4 to 6 each show an example of a partial cross-sectional view of the photoreceptor 50. FIG. The photoreceptor 50 is, for example, an OPC (organic photoconductor) drum.

As shown in FIG. 4, the photoreceptor 50 includes, for example, a conductive base 501 and a photosensitive layer 502. The photosensitive layer 502 is a single layer (single layer). The photoreceptor 50 is a single-layer electrophotographic photoreceptor including a single-layer photoreceptor layer 502 . The photosensitive layer 502 contains a charge generating agent, a hole transporting agent, an electron transporting agent, and a first binder resin. The thickness of the photosensitive layer 502 is not particularly limited, but is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 50 μm or less, even more preferably 10 μm or more and 35 μm or less, and 15 μm or more and 30 μm or less. It is more preferable that there be.

As shown in FIG. 5, the photoreceptor 50 may include a conductive base 501, a photosensitive layer 502, and an intermediate layer 503 (undercoat layer). Intermediate layer 503 is provided between conductive substrate 501 and photosensitive layer 502. As shown in FIG. 4, the photosensitive layer 502 may be provided directly on the conductive substrate 501. Alternatively, as shown in FIG. 5, the photosensitive layer 502 may be provided on the conductive substrate 501 with an intermediate layer 503 interposed therebetween. The intermediate layer 503 may be a single layer or may be a plurality of layers.

As shown in FIG. 6, the photoreceptor 50 may include a conductive base 501, a photosensitive layer 502, and a protective layer 504. A protective layer 504 is provided on the photosensitive layer 502. The protective layer 504 may be a single layer or may be a plurality of layers.

(Charging ability)
The charging ability X [V/(C/m ² )] of the photoreceptor 50 is expressed by the above equation (1). Charging ability X [V/(C/m ² )] is a measure of how much the charging potential [V] of the photoreceptor 50 increases with respect to the surface charge density [C/m ² ] of the charges supplied from the charging roller 51. Show what you want to do.

The charging ability X of the photoreceptor 50 is preferably 2.72×10 ⁵ V/(C/m ² ) or more and 1.16×10 ⁶ V/(C/m ² ) or less, and 6.00×10 ⁵ V/ (C/m ² ) or more and 1.00×10 ⁶ V/(C/m ² ) or less is more preferable. In a photoreceptor 50 having a chargeability X of less than 2.72×10 ⁵ V/(C/m ² ), the thickness of the photosensitive layer 502 may be excessively thin. In a photoreceptor 50 having a chargeability X of more than 1.16×10 ⁶ V/(C/m ² ), the thickness of the photosensitive layer 502 may be excessively thick.

Hereinafter, with reference to FIG. 7, a method for measuring V in equation (1) will be described. V is a value calculated from the first potential V _r and the second potential V ₀ .

The first potential V _r and the second potential V ₀ can be measured using a measuring device 100 shown in FIG. 7 . The measuring device 100 can be manufactured by implementing a first modification and a second modification to the image forming apparatus 1. In the first modification, a first potential probe 101 is attached to the image forming apparatus 1. The first potential probe 101 is arranged upstream of the charging roller 51 in the rotation direction R of the photoreceptor 50 . The first potential probe 101 is connected to a first surface electrometer (not shown, “Surface Electrometer MODEL344” manufactured by Trek). In the second modification, the developing roller 52 of the image forming apparatus 1 is replaced with a second potential probe 102. The second potential probe 102 is placed at the position where the rotation center 52X (rotation shaft) of the developing roller 52 was placed. The second potential probe 102 is connected to a second surface electrometer (not shown, "Surface Electrometer MODEL 344" manufactured by Trek).

The measuring device 100 includes at least a charging roller 51 , a second potential probe 102 , a static elimination lamp 54 , and a first potential probe 101 . A photoreceptor 50 to be measured is set in the measuring device 100. Around the photoconductor 50, from the upstream side in the rotation direction R of the photoconductor 50, a charging roller 51, a second potential probe 102, a static elimination lamp 54, and a first potential probe 101 are arranged in the listed order. be done.

A first line L ₁ connecting the rotation center 50X (rotation axis) of the photoconductor 50 and the rotation center 51X (rotation axis) of the charging roller 51, and the second potential probe 102 between the rotation center 50X (rotation axis) of the photoconductor 50 and the rotation center 51X (rotation axis) of the charging roller 51. The second potential probe 102 is arranged so that the angle θ ₁ between the second line L ₂ and the second line L 2 is 120 degrees. The intersection of the first line L ₁ and the circumferential surface 50a of the photoreceptor 50 is the charging position P ₁ . The intersection of the second line _L2 and the peripheral surface 50a of the photoreceptor 50 is the development position _P2 .

A third line L ₃ connecting the rotation center 50X (rotation axis) of the photoreceptor 50 and the first potential probe 101, and the rotation center 50X (rotation axis) of the photoreceptor 50 and the rotation center 51X (rotation axis) of the charging roller 51. The first potential probe 101 is arranged so that the angle θ ₂ between it and the first line L ₁ connecting the two lines is 20 degrees. The intersection of the third line L ₃ and the circumferential surface 50a of the photoreceptor 50 is the position P ₃ immediately before charging.

The position where the peripheral surface 50a of the photoreceptor 50 is irradiated with the static eliminating light from the static eliminating lamp 54 is the static eliminating position _P4 . A fourth line L ₄ connecting the rotation center 50X (rotation axis) of the photoreceptor 50 and the neutralization position P ₄ and a third line L connecting the rotation center 50X (rotation axis) of the photoreceptor 50 and the first potential probe 101 _{3 is} 90 degrees. Note that as the measuring device 100, a modified multifunction device ("TASKalfa356Ci" manufactured by Kyocera Document Solutions Co., Ltd.) can be used.

In the measurement of the first potential V _r and the second potential V ₀ , the charging voltage applied to the charging roller 51 is set to any one of +1000V, +1100V, +1200V, +1300V, +1400V, and +1500V. The amount of static eliminating light emitted from the static eliminating lamp 54 when it reaches the peripheral surface 50a of the photoreceptor 50 (hereinafter referred to as the amount of static eliminating light) is set to 5 μJ/cm ² . The first potential V _r and the second potential V ₀ are measured while rotating the photoreceptor 50 around the rotation center 50X (rotation axis). At the charging position P ₁ of the photoreceptor 50, the charging roller 51 charges the peripheral surface 50a of the photoreceptor 50 to positive polarity. Next, at the static elimination position P ₄ of the photoconductor 50, the static elimination lamp 54 eliminates the static electricity from the peripheral surface 50a of the photoconductor 50. At the point in time when the photoreceptor 50 is rotated 10 times while performing such charging and neutralization (hereinafter sometimes referred to as timing K), the first potential V _r and the second potential V ₀ are measured simultaneously. . Specifically, at timing K, the potential (first potential V _r ) of the circumferential surface 50 a of the photoreceptor 50 is measured using the first potential probe 101 at a position P ₃ of the photoreceptor 50 immediately before charging. Further, at timing K, at the development position P ₂ of the photoreceptor 50, the potential of the charged peripheral surface 50a of the photoreceptor 50 (second potential V ₀ ) is measured using the second potential probe 102. In this way, the first potential V _r and the second potential V ₀ are measured under each condition where the charging voltage applied to the charging roller 51 is +1000V, +1100V, +1200V, +1300V, +1400V, and +1500V.

Note that in the measurement of the first potential V _r and the second potential V ₀ , exposure by the exposure device 31, development by the developing roller 52, primary transfer by the primary transfer roller 53, and cleaning by the cleaning blade 81 are not performed. The linear pressure of the cleaning blade 81 is set to 0 N/m. The method for measuring the first potential V _r and the second potential V ₀ in equation (1) has been described above. Subsequently, a method for measuring the charging capacity X will be explained.

The amount of electrical charge Q in equation (1) is measured by the following method when measuring the first potential V _r and the second potential V ₀ . At the timing K of simultaneously measuring the first potential V _r and the second potential V ₀ , the current value E ₁ flowing through the charging roller 51 is measured using a current voltmeter (“Small Portable Ammeter” manufactured by Yokogawa Meters & Instruments Co., Ltd.). Measure using a voltmeter (Model 2051). The current value E ₁ is measured under each condition where the charging voltage applied to the charging roller 51 is +1000V, +1100V, +1200V, +1300V, +1400V, and +1500V. From the measured current value _E1 , based on the following formula (3), calculate the amount of charged charge Q under each condition where the charging voltage applied to the charging roller 51 is +1000V, +1100V, +1200V, +1300V, +1400V, and +1500V. calculate.
Charged charge amount Q = current value E ₁ [A] x charging time t [seconds] (3)

Note that a high-voltage board (not shown) of the measuring device 100 and the charging roller 51 are connected via a current-voltmeter. While the measuring device 100 is in operation, the current value E ₁ flowing through the charging roller 51 and the charging voltage described in the measurement of the first potential V _r and the second potential V ₀ are constantly measured using a current voltmeter. can be monitored.

The charged area S in Equation (1) is the area of the region of the peripheral surface 50a of the photoreceptor 50 that is charged by the charging roller 51. The charged area S is calculated according to the following formula (4). The charging width in formula (4) is the length of the area of the circumferential surface 50a of the photoreceptor 50 that is charged by the charging roller 51 in the longitudinal direction of the photoreceptor 50 (rotation axis direction D in FIG. 9). be.
Charging area S [m ² ] = Linear speed of photoreceptor 50 [m/sec] x Charging width [m] x Charging time t [sec] (4)

The value of "V" in equation (1) is calculated from the first potential V _r and the second potential V ₀ measured by the above method. The value of "Q/S" in equation (1) is calculated from the charged charge amount Q and the charged area S measured by the above method. Then, a graph is created in which the horizontal axis shows the value of "Q/S" and the vertical axis shows the value of "V". On the graph, six points are plotted showing the measurement results under each condition where the charging voltage applied to the charging roller 51 is +1000V, +1100V, +1200V, +1300V, +1400V, and +1500V. Draw an approximate straight line between these six points. Find the slope of the approximate straight line from the approximate straight line. The obtained slope is defined as "V/(Q/S)" in equation (1).

The Martens hardness of the photosensitive layer 502 is preferably 150 N/mm ² or more, more preferably 180 N/mm ² or more, even more preferably 200 N/mm ² or more, and even more preferably 220 N/mm ² or more. It is even more preferable. When the Martens hardness of the photosensitive layer 502 is 150 N/mm ² or more, the amount of wear of the photosensitive layer 502 is reduced and the wear resistance of the photoreceptor 50 is improved. The upper limit of the Martens hardness of the photosensitive layer 502 is not particularly limited, but may be, for example, 250 N/mm ² or less. The Martens hardness of the photosensitive layer 502 can be measured by the method described in Examples.

The photosensitive layer 502 contains a charge generating agent, a hole transporting agent, an electron transporting agent, and a first binder resin. The photosensitive layer 502 may further contain additives, if necessary. Hereinafter, suitable combinations of the charge generating agent, hole transporting agent, electron transporting agent, first binder resin, additives, and materials will be explained.

(charge generating agent)
The charge generating agent is not particularly limited. Examples of the charge generating agent include phthalocyanine pigments, perylene pigments, bisazo pigments, trisazo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, indigo pigments, azulenium pigments, and cyanine. Pigments, powders of inorganic photoconductive materials (e.g. selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide or amorphous silicon), pyrylium pigments, anthanthrone pigments, triphenylmethane pigments, threnic pigments, toluidine pigments, Examples include pyrazoline pigments and quinacridone pigments. The photosensitive layer 502 may contain only one type of charge generating agent, or may contain two or more types of charge generating agents.

In order to further suppress the occurrence of charging unevenness, the phthalocyanine pigment is preferably metal-free phthalocyanine, titanyl phthalocyanine, or chloroindium phthalocyanine, and titanyl phthalocyanine is more preferable. Titanyl phthalocyanine is represented by the chemical formula (CGM-1).

Titanyl phthalocyanine may have a crystal structure. Examples of titanyl phthalocyanine crystals include α-type, β-type, and Y-type crystals of titanyl phthalocyanine (hereinafter sometimes referred to as α-type, β-type, and Y-type titanyl phthalocyanine). As the titanyl phthalocyanine, Y-type titanyl phthalocyanine is preferable.

Y-type titanyl phthalocyanine has a main peak at, for example, a Bragg angle (2θ±0.2°) of 27.2° in the CuKα characteristic X-ray diffraction spectrum. The main peak in the CuKα characteristic X-ray diffraction spectrum is the peak having the first or second highest intensity in the range where the Bragg angle (2θ±0.2°) is 3° or more and 40° or less.

An example of a method for measuring a CuKα characteristic X-ray diffraction spectrum will be described. A sample (titanyl phthalocyanine) is filled in a sample holder of an X-ray diffraction device (for example, "RINT (registered trademark) 1100" manufactured by Rigaku Co., Ltd.), and an X-ray tube Cu, a tube voltage of 40 kV, a tube current of 30 mA, and a CuKα The X-ray diffraction spectrum is measured under the condition that the characteristic X-ray wavelength is 1.542 Å. The measurement range (2θ) is, for example, 3° or more and 40° or less (start angle of 3°, stop angle of 40°), and the scanning speed is, for example, 10°/min.

Y-type titanyl phthalocyanine is classified, for example, into three types shown in (A) to (C) below, depending on the thermal properties in differential scanning calorimetry (DSC) spectra.
(A) A Y-type titanyl phthalocyanine having a peak in the range of 50° C. or higher and 270° C. or lower in the differential scanning calorimetry spectrum in addition to the peak associated with vaporization of adsorbed water.
(B) A Y-type titanyl phthalocyanine that does not have a peak in the range of 50° C. or higher and 400° C. or lower in the differential scanning calorimetry spectrum, other than the peak associated with vaporization of adsorbed water.
(C) Y-type titanyl phthalocyanine that has no peaks in the range of 50°C or more and 270°C or less and a peak in the range of 270°C or more and 400°C or less in the differential scanning calorimetry spectrum other than the peak associated with vaporization of adsorbed water .

In the differential scanning calorimetry spectrum, Y-type titanyl phthalocyanine has no peaks in the range of 50°C or higher and 270°C or lower, and has a peak in the range of 270°C or higher and 400°C or lower, in the differential scanning calorimetry spectrum. is more preferable. As the Y-type titanyl phthalocyanine having such a peak, one having one peak in the range of 270°C or more and 400°C or less is preferable, and one having one peak at 296°C is more preferable.

An example of a method for measuring a differential scanning calorimetry spectrum will be described. A sample (titanyl phthalocyanine) is placed on a sample pan, and a differential scanning calorimetry spectrum is measured using a differential scanning calorimeter (for example, "TAS-200 model DSC8230D" manufactured by Rigaku Co., Ltd.). The measurement range is, for example, 40°C or higher and 400°C or lower. The temperature increase rate is, for example, 20° C./min.

The content of the charge generating agent in the photosensitive layer 502 is preferably more than 0.0% by mass and not more than 1.0% by mass, and more preferably more than 0.0% by mass and not more than 0.5% by mass. When the content of the charge generating agent in the photosensitive layer 502 is 1.0% by mass or less, the charging ability ratio can be increased. In calculating the content ratio, the mass of the photosensitive layer 502 is the total mass of the materials contained in the photosensitive layer 502. When the photosensitive layer 502 contains a charge generating agent, a hole transporting agent, an electron transporting agent, and a first binder resin, the mass of the photosensitive layer 502 is equal to the mass of the charge generating agent, the mass of the hole transporting agent, and the electron transporting agent. and the mass of the first binder resin. When the photosensitive layer 502 contains a charge generating agent, a hole transporting agent, an electron transporting agent, a first binder resin, and an additive, the mass of the photosensitive layer 502 is equal to the mass of the charge generating agent and the mass of the hole transporting agent. This is the total of the mass of the electron transport agent, the mass of the first binder resin, and the mass of the additive.

(hole transport agent)
The hole transport agent is not particularly limited. Examples of the hole transport agent include nitrogen-containing cyclic compounds and fused polycyclic compounds. Examples of nitrogen-containing cyclic compounds and condensed polycyclic compounds include triphenylamine derivatives; diamine derivatives (more specifically, N,N,N',N'-tetraphenylbenzidine derivatives, N,N,N ',N'-tetraphenylphenylenediamine derivative, N,N,N',N'-tetraphenylnaphthylenediamine derivative, di(aminophenylethenyl)benzene derivative, N,N,N',N'-tetraphenyl phenanthlylene diamine derivatives, etc.); oxadiazole compounds (more specifically, 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole, etc.); styryl compounds (more specifically, Specifically, 9-(4-diethylaminostyryl)anthracene, etc.); carbazole compounds (more specifically, polyvinylcarbazole, etc.); organic polysilane compounds; pyrazoline compounds (more specifically, 1-phenyl- 3-(p-dimethylaminophenyl)pyrazoline, etc.); hydrazone compounds; indole compounds; oxazole compounds; isoxazole compounds; thiazole compounds; thiadiazole compounds; imidazole compounds; pyrazole compounds; and triazole compounds can be mentioned. The photosensitive layer 502 may contain only one type of hole transport agent, or may contain two or more types of hole transport agents.

In order to further suppress the occurrence of charging unevenness, a suitable example of the hole transport agent is a compound represented by the following general formula (10) (hereinafter sometimes referred to as hole transport agent (10)). can be mentioned.

In general formula (10), R ¹³ to R ¹⁵ each independently represent an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms. m and n each independently represent an integer of 1 or more and 3 or less. p and r each independently represent 0 or 1. q represents an integer from 0 to 2. When q represents 2, two R ^14s may be the same or different.

In the general formula (10), R ¹⁴ is preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group, an ethyl group, or an n-butyl group, and particularly preferably an n-butyl group. q preferably represents 1 or 2, and more preferably represents 1. Preferably, p and r represent 0. It is preferable that m and n represent 1 or 2, and it is more preferable that m and n represent 2.

A suitable example of the hole transport agent (10) includes a compound represented by the following chemical formula (HTM-1) (hereinafter sometimes referred to as a hole transport agent (HTM-1)).

The content of the hole transport agent in the photosensitive layer 502 is preferably more than 0.0% by mass and 35.0% by mass or less, and more preferably 10.0% by mass or more and 30.0% by mass or less.

(First binder resin)
Examples of the first binder resin include thermoplastic resins, thermosetting resins, and photocurable resins. Examples of the thermoplastic resin include polycarbonate resin, polyarylate resin, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, acrylic acid polymer, styrene-acrylic acid copolymer, Polyethylene resin, ethylene-vinyl acetate copolymer, chlorinated polyethylene resin, polyvinyl chloride resin, polypropylene resin, ionomer resin, vinyl chloride-vinyl acetate copolymer, alkyd resin, polyamide resin, urethane resin, polysulfone resin, diallyl phthalate resins, ketone resins, polyvinyl butyral resins, polyester resins, and polyether resins. Examples of thermosetting resins include silicone resins, epoxy resins, phenol resins, urea resins, and melamine resins. Examples of the photocurable resin include acrylic acid adducts of epoxy compounds and acrylic acid adducts of urethane compounds. The photosensitive layer 502 may contain only one type of first binder resin, or may contain two or more types of first binder resin.

In order to further suppress the occurrence of charging unevenness, the first binder resin is a polyarylate resin having a repeating unit represented by the following general formula (20) (hereinafter sometimes referred to as repeating unit (20)). (hereinafter sometimes referred to as polyarylate resin (20)).

In general formula (20), R ²⁰ and R ²¹ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R ²² and R ²³ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group. R ²² and R ²³ may be bonded to each other to represent a divalent group represented by general formula (W). Y represents a divalent group represented by the following chemical formula (Y1), (Y2), (Y3), (Y4), (Y5) or (Y6).

In the general formula (W), t represents an integer of 1 or more and 3 or less. * represents a bond.

In chemical formulas (Y1) to (Y6), * represents a bond. Specifically, * in chemical formulas (Y1) to (Y6) represents a bond to the carbon atom to which Y in general formula (20) is bonded.

In general formula (20), R ²⁰ and R ²¹ are preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group. It is preferable that R ²² and R ²³ combine with each other to represent a divalent group represented by the general formula (W). As Y, a divalent group represented by the chemical formula (Y1) or (Y3) is preferable. In general formula (W), t is preferably 2.

Although it is preferable that the polyarylate resin (20) has only the repeating unit (20), it may further have other repeating units. The ratio (mole fraction) of the number of repeating units (20) to the total number of repeating units in the polyarylate resin (20) is preferably 0.80 or more, more preferably 0.90 or more. , 1.00 is more preferable. The polyarylate resin (20) may have only one type of repeating unit (20), or may have two or more types (for example, two types) of repeating units (20).

Note that in the present specification, the ratio (mole fraction) of the number of repeating units (20) to the total number of repeating units in the polyarylate resin (20) is not a value obtained from one resin chain, but a value obtained from a photosensitive layer. It is a number average value obtained from the entire polyarylate resin (20) (a plurality of resin chains) contained in No. 502. This molar fraction can be calculated from the ¹ H-NMR spectrum obtained by measuring the ¹ H-NMR spectrum of the polyarylate resin (20) using, for example, a proton nuclear magnetic resonance spectrometer.

Suitable examples of the repeating unit (20) include a repeating unit represented by the following chemical formula (20-a) and a repeating unit represented by the following chemical formula (20-b) (hereinafter referred to as the repeating unit (20-a), respectively). ) and (20-b)). The polyarylate resin (20) preferably has at least one of repeating units (20-a) and (20-b), and preferably has both repeating units (20-a) and (20-b). More preferred.

When the polyarylate resin (20) has both repeating units (20-a) and (20-b), the arrangement of repeating units (20-a) and (20-b) is not particularly limited. The polyarylate resin (20) having repeating units (20-a) and (20-b) may be any of a random copolymer, a block copolymer, a periodic copolymer, and an alternating copolymer. good.

When the polyarylate resin (20) has both repeating units (20-a) and (20-b), a suitable example of the polyarylate resin (20) is represented by the following general formula (20-1). Examples include polyarylate resins having a main chain of

In the general formula (20-1), u and v each independently represent a number of 30 or more and 70 or less. The sum of u and v is 100.

u and v are each independently preferably a number of 40 or more and 60 or less, more preferably a number of 45 or more and 55 or less, even more preferably a number of 49 or more and 51 or less, and 50. It is particularly preferable. Note that u indicates the percentage of the number of repeating units (20-a) to the total of the number of repeating units (20-a) and the number of repeating units (20-b) that the polyarylate resin (20) has. . v represents the percentage of the number of repeating units (20-b) to the total number of repeating units (20-a) and repeating units (20-b) that the polyarylate resin (20) has. Suitable examples of polyarylate resins having a main chain represented by the general formula (20-1) include polyarylate resins having a main chain represented by the following general formula (20-1a).

The polyarylate resin (20) may have a terminal group represented by the following chemical formula (Z). In the chemical formula (Z), * represents a bond. Specifically, * in chemical formula (Z) represents a bond to the main chain of the polyarylate resin. When the polyarylate resin (20) has a repeating unit (20-a), a repeating unit (20-b), and a terminal group represented by the chemical formula (Z), this terminal group is a repeating unit (20-a). It may be bonded to, or may be bonded to the repeating unit (20-b).

In order to further suppress the occurrence of charging unevenness, the polyarylate resin (20) is a polyarylate resin having a main chain represented by the general formula (20-1) and a terminal group represented by the chemical formula (Z). Preferably, it contains a resin. More preferably, the polyarylate resin (20) includes a polyarylate resin having a main chain represented by the general formula (20-1a) and a terminal group represented by the chemical formula (Z). Hereinafter, a polyarylate resin having a main chain represented by general formula (20-1a) and a terminal group represented by chemical formula (Z) may be referred to as polyarylate resin (R-1).

The viscosity average molecular weight of the first binder resin is preferably 10,000 or more, more preferably 20,000 or more, even more preferably 30,000 or more, and preferably 50,000 or more. More preferably, it is 55,000 or more. When the viscosity average molecular weight of the first binder resin is 10,000 or more, the abrasion resistance of the photoreceptor 50 tends to improve. On the other hand, the viscosity average molecular weight of the first binder resin is preferably 80,000 or less, more preferably 70,000 or less. When the viscosity average molecular weight of the first binder resin is 80,000 or less, the first binder resin tends to be easily dissolved in the solvent for forming the photosensitive layer, and the formation of the photosensitive layer 502 tends to be facilitated.

The content ratio of the first binder resin in the photosensitive layer 502 is preferably 30.0% by mass or more and 70.0% by mass or less, and more preferably 40.0% by mass or more and 60.0% by mass or less.

(electron transport agent)
Examples of electron transport agents include quinone compounds, diimide compounds, hydrazone compounds, malononitrile compounds, thiopyran compounds, trinitrothioxanthone compounds, 3,4,5,7-tetranitro-9-fluorenone compounds, Examples include dinitroanthracene compounds, dinitroacridine compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride, and dibromomaleic anhydride. Examples of quinone compounds include diphenoquinone compounds, azoquinone compounds, anthraquinone compounds, naphthoquinone compounds, nitroanthraquinone compounds, and dinitroanthraquinone compounds. The photosensitive layer 502 may contain only one type of electron transport agent, or may contain two or more types of electron transport agents.

In order to further suppress the occurrence of charging unevenness, suitable examples of the electron transport agent include compounds represented by the following general formula (31), the following general formula (32), and the following general formula (33) (hereinafter, (sometimes referred to as electron transport agents (31), (32), and (33), respectively).

In general formulas (31) to (33), R ¹ to R ⁴ and R ⁹ to R ¹² each independently represent an alkyl group having 1 to 8 carbon atoms. R ⁵ to R ⁸ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a halogen atom.

In general formulas (31) to (33), the alkyl group having 1 to 8 carbon atoms represented by R ¹ to R ⁴ and R ⁹ to R ¹² is preferably an alkyl group having 1 to 5 carbon atoms, More preferred are a methyl group, a tert-butyl group, or a 1,1-dimethylpropyl group. R ⁵ to R ⁸ are preferably hydrogen atoms.

As the electron transport agent (31), a compound represented by the following chemical formula (ETM-1) (hereinafter sometimes referred to as an electron transport agent (ETM-1)) is preferable. As the electron transport agent (32), a compound represented by the following chemical formula (ETM-3) (hereinafter sometimes referred to as an electron transport agent (ETM-3)) is preferable. As the electron transport agent (33), a compound represented by the following chemical formula (ETM-2) (hereinafter sometimes referred to as an electron transport agent (ETM-2)) is preferable.

In order to further suppress the occurrence of charging unevenness, the photosensitive layer 502 preferably contains at least one of an electron transport agent (31) and an electron transport agent (32) as an electron transport agent. It is more preferable to contain both (two types) of the agent (31) and the electron transport agent (32).

In order to further suppress the occurrence of charging unevenness, the photosensitive layer 502 may contain at least one of an electron transport agent (ETM-1) and an electron transport agent (ETM-3) as an electron transport agent. Preferably, it is more preferable to contain both (two types) of an electron transport agent (ETM-1) and an electron transport agent (ETM-3).

The content of the electron transport agent in the photosensitive layer 502 is preferably 5.0% by mass or more and 50.0% by mass or less, more preferably 20.0% by mass or more and 30.0% by mass or less. When the photosensitive layer 502 contains two or more types of electron transport agents, the content ratio of the electron transport agents is the total content ratio of the two or more types of electron transport agents.

(Additive)
The photosensitive layer 502 may further contain a specific compound represented by the following general formula (40) (hereinafter sometimes referred to as an additive (40)), if necessary. However, in order to improve the chargeability ratio, it is preferable not to contain the additive (40). When using the additive (40) as necessary, the content of the additive (40) in the photosensitive layer 502 is set to more than 0.0% by mass and 1.0% by mass or less. The additive (40) can be used, for example, to adjust the chargeability ratio.

In the general formula (40), R ⁴⁰ and R ⁴¹ each independently represent a hydrogen atom or a monovalent group represented by the following general formula (40a).

In general formula (40a), X represents a halogen atom. Examples of the halogen atom represented by X include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The halogen atom represented by X is preferably a chlorine atom. * represents a bond. Specifically, * in general formula (40a) represents a bond to the carbon atom to which R ⁴⁰ or R ⁴¹ in general formula (40) is bonded.

In general formula (40), A represents a divalent group represented by the following chemical formula (A1), (A2), (A3), (A4), (A5) or (A6). In chemical formulas (A1) to (A6), * represents a bond. Specifically, * in chemical formula (A1), (A2), (A3), (A4), (A5), or (A6) represents a bond to the carbon atom to which A in general formula (40) is bonded. represents. The divalent group represented by A is preferably a divalent group represented by chemical formula (A4).

Specific examples of the additive (40) include a compound represented by the following chemical formula (40-1) (hereinafter sometimes referred to as additive (40-1)).

The photosensitive layer 502 may further contain additives other than the additive (40) (hereinafter sometimes referred to as other additives), if necessary. Other additives include, for example, deterioration inhibitors (more specifically, antioxidants, radical scavengers, quenchers, ultraviolet absorbers, etc.), softeners, surface modifiers, fillers, and thickeners. , dispersion stabilizers, waxes, donors, surfactants, and leveling agents. When other additives are contained in the photosensitive layer 502, the photosensitive layer 502 may contain only one type of other additive, or may contain two or more types of other additives.

(Combination of materials)
In order to further suppress the occurrence of charging unevenness, use combination example No. 1 in Table 1 below. Materials of the types and content ratios shown in 1 to 3, combination example No. 2 in Table 2 below. Materials of types and content ratios shown in 4 to 6, or combination example No. 3 in Table 3 below. It is preferable that the photosensitive layer 502 contains materials having the types and content ratios shown in 7 to 9.

In Tables 1 to 3, "wt%", "CGM", "HTM", "ETM", and "resin" respectively refer to "mass%", "charge generating agent", "hole transporting agent", "Electron transport agent" and "first binder resin" are shown. In Tables 1 to 3, “content ratio” indicates the content ratio of the corresponding material in the photosensitive layer 502. In Tables 1 to 3, "ETM-1/ETM-3" indicates that the electron transport agent contains both an electron transport agent (ETM-1) and an electron transport agent (ETM-3). In Tables 1 to 3, "-" indicates that the corresponding material is not contained. In Table 3, "CGM-1" indicates Y-type titanyl phthalocyanine represented by the chemical formula (CGM-1). In the differential scanning calorimetry spectrum of the Y-type titanyl phthalocyanine shown in Table 3, there is no peak in the range of 50°C to 270°C other than the peak associated with vaporization of adsorbed water, and there is no peak in the range of 270°C to 400°C. Y-type titanyl phthalocyanine having a peak (specifically, one peak at 296° C.) is preferable.

(middle class)
The intermediate layer 503 contains, for example, inorganic particles and a resin used for the intermediate layer 503 (intermediate layer resin). By interposing the intermediate layer 503, it is possible to maintain an insulating state sufficient to suppress leakage while smoothing the flow of current generated when the photoreceptor 50 is exposed to light, thereby suppressing an increase in electrical resistance.

Examples of inorganic particles include particles of metals (more specifically, aluminum, iron, copper, etc.), metal oxides (more specifically, titanium oxide, alumina, zirconium oxide, tin oxide, zinc oxide, etc.) and particles of non-metal oxides (more specifically, silica etc.). These inorganic particles may be used alone or in combination of two or more. Note that the inorganic particles may be surface-treated. The intermediate layer resin is not particularly limited as long as it can be used as a resin for forming the intermediate layer 503.

(Method for manufacturing photoreceptor)
In one example of a method for manufacturing the photoreceptor 50, a coating liquid for forming the photosensitive layer 502 (hereinafter sometimes referred to as a photosensitive layer coating liquid) is applied onto the conductive substrate 501. Thereby, a photosensitive layer 502 is formed, and the photoreceptor 50 is manufactured. The photosensitive layer coating liquid is produced by dissolving or dispersing a charge generating agent, a hole transporting agent, an electron transporting agent, a first binder resin, and optional components added as necessary in a solvent.

The solvent contained in the coating liquid for photosensitive layer is not particularly limited as long as it can dissolve or disperse each component contained in the coating liquid. Examples of solvents include alcohols (for example methanol, ethanol, isopropanol or butanol), aliphatic hydrocarbons (for example n-hexane, octane or cyclohexane), aromatic hydrocarbons (for example benzene, toluene or xylene), halogenated hydrocarbons (e.g. dichloromethane, dichloroethane, carbon tetrachloride or chlorobenzene), ethers (e.g. dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether or propylene glycol monomethyl ether), ketones (e.g. acetone, methyl ethyl ketone or cyclohexanone), esters (eg ethyl acetate or methyl acetate), dimethyl formaldehyde, dimethyl formamide, and dimethyl sulfoxide. One type of these solvents may be used alone, or two or more types may be used in combination. In order to improve workability during production of the photoreceptor 50, it is preferable to use a non-halogen solvent (solvent other than halogenated hydrocarbon) as the solvent.

The coating solution for the photosensitive layer is prepared by mixing each component and dispersing it in a solvent. For mixing or dispersion, for example, a bead mill, roll mill, ball mill, attritor, paint shaker or ultrasonic disperser can be used.

The photosensitive layer coating liquid may contain, for example, a surfactant in order to improve the dispersibility of each component.

The method for applying the photosensitive layer coating liquid is not particularly limited as long as it is a method that can uniformly apply the coating liquid onto the conductive substrate 501. Examples of the coating method include a blade coating method, a dip coating method, a spray coating method, a spin coating method, and a bar coating method.

The method for drying the photosensitive layer coating solution is not particularly limited as long as the solvent in the coating solution can be evaporated, but examples include a method of heat treatment (hot air drying) using a high temperature dryer or a vacuum dryer. . The heat treatment temperature is, for example, 40°C or more and 150°C or less. The heat treatment time is, for example, 3 minutes or more and 120 minutes or less.

Note that the method for manufacturing the photoreceptor 50 may further include one or both of a step of forming an intermediate layer 503 and a step of forming a protective layer 504, as necessary. In the step of forming the intermediate layer 503 and the step of forming the protective layer 504, known methods are appropriately selected.

The photoreceptor 50 has been described above. Next, with reference to FIG. 2 again, the toner T, charging roller 51, primary transfer roller 53, static elimination lamp 54, and cleaner 55 included in the image forming apparatus 1 will be described.

<Toner>
The toner T contained in the cartridges 60M to 60BK shown in FIG. 1 and supplied to the circumferential surface 50a of the photoreceptor 50 will be described. Toner T includes toner particles. The toner T is an aggregate (powder) of toner particles. The toner particles include toner base particles and external additives. The toner base particles contain at least one of a binder resin, a release agent, a colorant, a charge control agent, and a magnetic powder. The external additive is attached to the surface of the toner base particles. Note that if it is not necessary, it is not necessary to contain external additives. When no external additive is contained, toner base particles correspond to toner particles. Toner T may be a capsule toner or a non-capsule toner. By forming a shell layer on the surface of toner base particles, toner T, which is a capsule toner, can be manufactured.

The number average circularity of the toner T is preferably 0.960 or more and 0.998 or less. When the number average circularity of the toner T is 0.960 or more, development and transfer can be performed suitably, and a more faithful image can be output. When the number average circularity of the toner T is 0.998 or less, the toner T is difficult to slip between the peripheral surface 50a of the photoreceptor 50 and the cleaning blade 81. The number average circularity of the toner T is preferably 0.960 or more and 0.980 or less, more preferably 0.965 or more and 0.980 or less, and preferably 0.970 or more and 0.980 or less. More preferably, it is 0.975 or more and 0.980 or less. The number average circularity of the toner T can be measured by the method described in Examples.

The volume median diameter (hereinafter sometimes referred to as D ₅₀ ) of the toner T is preferably 4.0 μm or more and 7.0 μm or less. When the D ₅₀ of the toner T is 7.0 μm or less, a fine output image without graininess can be obtained. Furthermore, the smaller the D ₅₀ of the toner T, the smaller the amount of toner T required to obtain a desired image density. Therefore, when the D ₅₀ of the toner T is 7.0 μm or less, the amount of toner T used can be reduced. When the D ₅₀ of the toner T is 4.0 μm or more, the toner T becomes difficult to slip between the peripheral surface 50 a of the photoreceptor 50 and the cleaning blade 81 . The D ₅₀ of the toner T is preferably 4.0 μm or more and 6.0 μm or less, more preferably 4.0 μm or more and 5.0 μm or less. D ₅₀ of toner T can be measured by the method described in Examples. Note that D ₅₀ of the toner T is a 50% integrated diameter of the particle diameter of the toner T measured on a volume basis using a particle size distribution measuring device.

<Charging roller>
The charging roller 51 is arranged so as to be in contact with or close to the peripheral surface 50a of the photoreceptor 50. The image forming apparatus 1 employs a direct discharge method or a proximity discharge method.

The distance between the charging roller 51 and the circumferential surface 50a of the photoreceptor 50 is preferably 50 μm or less, more preferably 30 μm or less.

The charging voltage (charging bias) applied to the charging roller 51 is preferably a DC voltage. When the charging voltage is a DC voltage, the amount of discharge from the charging roller 51 to the photoreceptor 50 is smaller than when the charging voltage is a superimposed voltage, and the amount of wear of the photosensitive layer 502 of the photoreceptor 50 can be reduced.

The surface resistivity Y of the surface layer 51c of the charging roller 51 is preferably 5.0 log Ω or more and 11.3 log Ω or less, and more preferably 6.0 log Ω or more and 10.0 log Ω or less. When the surface resistivity Y of the surface layer 51c of the charging roller 51 is 5.0 logΩ or more, it becomes easier to suppress the occurrence of charging unevenness. When the surface resistivity Y of the surface layer 51c of the charging roller 51 is 11.3 logΩ or less, the photoreceptor 50 can be easily charged. The surface resistivity of the charging roller 51 can be measured by the method described in Examples.

The outer diameter of the charging roller 51 is, for example, 5 mm or more and 20 mm or less. The thickness of the base layer 51b in the charging roller 51 is, for example, 1 mm or more and 5 mm or less. The conductive shaft 51a of the charging roller 51 is made of metal, for example. The thickness of the surface layer is preferably 10 μm or more and 20 μm or less.

The base layer 51b contains, for example, rubber. Examples of the rubber contained in the base layer 51b include polyurethane elastomer, hydrin rubber (specifically, epichlorohydrin rubber), styrene-butadiene rubber (SBR), polynorbornene rubber, ethylene-propylene-diene rubber (EPDM), and acrylonitrile-butadiene. Rubber (NBR), hydrogenated acrylonitrile-butadiene rubber (H-NBR), butadiene rubber (BR), isoprene rubber (IR), natural rubber (NR) and silicone rubber. One type of these rubbers may be used alone, or two or more types may be used in combination. The rubber contained in the base layer 51b is preferably epichlorohydrin rubber. Further, the base layer 51b may further contain a conductive agent to improve conductivity. Examples of conductive agents include carbon black, graphite, potassium titanate particles, iron oxide particles, titanium oxide particles, zinc oxide particles, tin oxide particles, and ionic conductive agents (e.g., quaternary ammonium salts, borates, and surfactants). agent). One type of these conductive agents may be used alone, or two or more types may be used in combination. As the conductive agent, an ionic conductive agent is preferable. Furthermore, the base layer 51b may further contain a foaming agent, a crosslinking agent, a crosslinking accelerator, and oil, if necessary.

The surface layer 51c may contain a second binder resin. Examples of the second binder resin include polyamide resin (eg, N-methoxymethylated nylon), acrylic resin, acrylic fluorine resin, and acrylic silicone resin. One type of these second binder resins may be used alone, or two or more types may be used in combination. As the second binder resin, polyamide resin or acrylic resin is preferable.

The surface layer 51c may further contain a conductive filler if necessary. Examples of the conductive filler include carbon black, graphite, potassium titanate particles, iron oxide particles, titanium oxide particles, zinc oxide particles, and tin oxide particles. As the conductive filler, tin oxide particles are preferred. The average particle size of the conductive filler is preferably 5 nm or more and 200 nm or less. Furthermore, the surface layer 51c may further contain a foaming agent, a crosslinking agent, a crosslinking accelerator, and oil, if necessary.

<Primary transfer roller>
The primary transfer roller 53 that is controlled at a constant voltage will be described below with reference to FIG. FIG. 8 is a diagram showing a power supply system for the four primary transfer rollers 53. As shown in FIG. 8, the image forming section 30 further includes a power supply section 56 connected to the four primary transfer rollers 53. The power supply section 56 can charge each primary transfer roller 53. The power supply section 56 includes one constant voltage source 57 connected to the four primary transfer rollers 53. The constant voltage source 57 applies a transfer voltage (transfer bias) to each primary transfer roller 53 during primary transfer to charge each primary transfer roller 53. A constant voltage source 57 generates a constant transfer voltage (for example, a constant negative transfer voltage). In other words, the primary transfer roller 53 is subjected to constant voltage control. Each toner image supported on the circumferential surface 50a of each photoconductor 50 is rotated due to the potential difference (transfer electric field) between the surface potential of the circumferential surface 50a of each photoconductor 50 and the surface potential of each primary transfer roller 53. The image is primarily transferred onto the outer peripheral surface of the transfer belt 33.

During primary transfer, current (for example, negative current) flows from each primary transfer roller 53 to each photoreceptor 50 via the transfer belt 33. When the primary transfer roller 53 is disposed directly above the photoreceptor 50, the current flowing into the photoreceptor 50 flows from the primary transfer roller 53 in the thickness direction of the transfer belt 33. Since the image forming apparatus 1 including the primary transfer roller 53 whose constant voltage is controlled can reduce the number of constant voltage sources 57 than the number of primary transfer rollers 53, the image forming apparatus 1 can be simplified and downsized. I can do it.

In order to stably primary transfer the toner T from the primary transfer roller 53 to the transfer belt 33, it is preferable that the current flowing through the primary transfer roller 53 (transfer current) when a transfer voltage is applied is −20 μA or more and −10 μA or less. .

<Static elimination lamp>
A static elimination lamp 54 is located downstream of the primary transfer roller 53 in the rotation direction R of the photoreceptor 50 . A cleaner 55 is located downstream of the static elimination lamp 54 in the rotation direction R of the photoreceptor 50. A charging roller 51 is located downstream of the cleaner 55 in the rotation direction R of the photoreceptor 50. By positioning the static elimination lamp 54 between the primary transfer roller 53 and the cleaner 55, the static elimination lamp 54 eliminates static electricity from the peripheral surface 50a of the photoconductor 50, and then the charging roller 51 charges the peripheral surface 50a of the photoconductor 50. It is possible to lengthen the time it takes to remove the static electricity (hereinafter sometimes referred to as static elimination-charging time). This makes it possible to secure time for excitation carriers generated inside the photosensitive layer 502 to disappear. The neutralization-charging time is preferably 20 msec or more, and preferably 50 msec or more.

The amount of static eliminating light from the static eliminating lamp 54 is preferably 0 μJ/cm ² or more and 10 μJ/cm ² or less, more preferably 0 μJ/cm ² or more and 5 μJ/cm ² or less. When the amount of static eliminating light from the static eliminating lamp 54 is 10 μJ/cm ² or less, the amount of charges trapped in the photosensitive layer 502 of the photoreceptor 50 is reduced, and the charging ability of the photoreceptor 50 can be improved. It is preferable that the amount of static eliminating light from the static eliminating lamp 54 is as small as possible. Note that when the amount of static eliminating light from the static eliminating lamp 54 is 0 μJ/cm ² , it means that the photoreceptor 50 is not neutralized by the static eliminating lamp 54, which is a so-called static eliminating system. The amount of static eliminating light from the static eliminating lamp 54 can be measured by the method described in the Examples.

<Cleaner>
The cleaner 55 includes a cleaning blade 81 and a toner seal 82. The cleaning blade 81 is located downstream of the primary transfer roller 53 in the rotation direction R of the photoreceptor 50 . The cleaning blade 81 is pressed against the circumferential surface 50a of the photoconductor 50 and collects the toner T remaining on the circumferential surface 50a of the photoconductor 50. The remaining toner T is toner T that remains on the circumferential surface 50a of the photoreceptor 50 after the primary transfer. Specifically, the tip of the cleaning blade 81 is pressed against the circumferential surface 50a of the photoconductor 50, and the direction from the base end to the tip of the cleaning blade 81 is between the tip of the cleaning blade 81 and the circumference of the photoconductor 50. At the point of contact with the surface 50a, it faces in the opposite direction to the rotational direction R. The cleaning blade 81 is in so-called counter contact with the peripheral surface 50a of the photoreceptor 50. As a result, the cleaning blade 81 is strongly pressed against the circumferential surface 50a of the photoreceptor 50 so that the cleaning blade 81 bites into the rotation of the photoreceptor 50. By applying strong pressure in this way, it is possible to further suppress the occurrence of cleaning failures. The cleaning blade 81 is, for example, a plate-shaped elastic body, and more specifically, a plate-shaped rubber. The cleaning blade 81 makes line contact with the peripheral surface 50a of the photoreceptor 50.

The linear pressure of the cleaning blade 81 against the peripheral surface 50a of the photoreceptor 50 is preferably 10 N/m or more and 40 N/m or less. When the linear pressure of the cleaning blade 81 against the circumferential surface 50a of the photoreceptor 50 is 10 N/m or more, occurrence of cleaning defects can be suppressed. When the linear pressure of the cleaning blade 81 against the circumferential surface 50a of the photoreceptor 50 is 40 N/m or less, the generation of ghost images can be suppressed. In order to further suppress the occurrence of ghost images and cleaning defects, the linear pressure of the cleaning blade 81 against the circumferential surface 50a of the photoreceptor 50 should be 15 N/m or more and 40 N/m or less. It is preferably 20 N/m or more and 40 N/m or less, even more preferably 25 N/m or more and 40 N/m or less, even more preferably 30 N/m or more and 40 N/m or less, and 35 N/m It is particularly preferable that it be 40 N/m or less. The linear pressure of the cleaning blade 81 against the peripheral surface 50a of the photoreceptor 50 is two selected from 10N/m, 15N/m, 20N/m, 25N/m, 30N/m, 35N/m, and 40N/m. May be within a range of values.

The hardness of the cleaning blade 81 is preferably 60 degrees or more and 80 degrees or less, more preferably 70 degrees or more and 78 degrees or less. When the hardness of the cleaning blade 81 is 60 degrees or more, the cleaning blade 81 is not too soft, so that the occurrence of cleaning defects can be suitably suppressed. When the hardness of the cleaning blade 81 is 80 degrees or less, the amount of wear on the photosensitive layer 502 of the photoreceptor 50 can be reduced because the cleaning blade 81 is not too hard. The hardness of the cleaning blade 81 can be measured by the method described in Examples.

The rebound resilience of the cleaning blade 81 is preferably 20% or more and 40% or less, more preferably 25% or more and 35% or less. The resilience modulus of the cleaning blade 81 can be measured by the method described in Examples.

The toner seal 82 contacts the circumferential surface 50a of the photoreceptor 50 between the primary transfer roller 53 and the cleaning blade 81, and prevents the toner T collected by the cleaning blade 81 from scattering.

<Thrust mechanism>
The drive mechanism 90 that implements the thrust mechanism will be described below with reference to FIG. FIG. 9 is a plan view illustrating the photoreceptor 50, the cleaning blade 81, and the drive mechanism 90. The photoreceptor 50 has a cylindrical shape extending along the rotation axis direction D of the photoreceptor 50 . The cleaning blade 81 has a plate shape extending along the rotation axis direction D.

The image forming apparatus 1 further includes a drive mechanism 90. The drive mechanism 90 reciprocates one of the photoreceptor 50 and the cleaning blade 81 along the rotation axis direction D. In this embodiment, the drive mechanism 90 reciprocates the photoreceptor 50 along the rotation axis direction D. The drive mechanism 90 includes, for example, a drive source such as a motor, a gear train, a plurality of cams, and a plurality of elastic members. Cleaning blade 81 is fixed to the housing of image forming apparatus 1 .

As described with reference to FIG. 9, according to the present embodiment, the photoreceptor 50 is reciprocated in the rotation axis direction D relative to the cleaning blade 81. Therefore, the localized deposits on the tip of the cleaning blade 81 can be moved in the rotation axis direction D, causing circumferential scratches (hereinafter referred to as "circumferential scratches") on the circumferential surface 50a of the photoreceptor 50. can be suppressed from occurring. As a result, the occurrence of vertical streaks in the output image due to the toner T entering the circumferential scratches is suppressed, and the image quality of the output image can be maintained at good quality over a long period of time.

Further, according to the present embodiment, since the photoreceptor 50 is moved back and forth, it is easier to obtain the driving force required for the back and forth movement compared to the case where the cleaning blade 81 is moved back and forth. The occurrence of toner leakage from both ends of the toner can be suppressed.

The amount of thrust of the photoreceptor 50 is the amount of movement of the photoreceptor 50 in one round trip. Note that in this embodiment, the amount of thrust on the outward trip and the amount of thrust on the return trip are equal. The thrust amount of the photoreceptor 50 is preferably 0.1 mm or more and 2.0 mm or less, and more preferably 0.5 mm or more and 1.0 mm or less. When the amount of thrust of the photoreceptor 50 is within such a range, occurrence of circumferential scratches on the photoreceptor 50 can be suitably suppressed.

The thrust period of the photoreceptor 50 is the time required for one round trip of the photoreceptor 50. In this specification, the thrust period of the photoreceptor 50 is indicated by the number of rotations of the photoreceptor 50 per one reciprocation of the photoreceptor 50. Since the circumferential speed of the photoreceptor 50 is constant, the longer the thrust period of the photoreceptor 50 (that is, the greater the number of rotations of the photoreceptor 50 per one reciprocation of the photoreceptor 50), the slower the photoreceptor 50 moves back and forth. do. On the other hand, the shorter the thrust period of the photoreceptor 50 (that is, the lower the number of rotations of the photoreceptor 50 per reciprocation of the photoreceptor 50), the faster the photoreceptor 50 moves back and forth.

The thrust period of the photoreceptor 50 is preferably 10 revolutions or more and 200 revolutions or less, and more preferably 50 revolutions or more and 100 revolutions or less. When the thrust cycle of the photoreceptor 50 is 10 rotations or more, the peripheral surface 50a of the photoreceptor 50 is easily cleaned. Further, when the thrust period of the photoreceptor 50 is 10 rotations or more, color misregistration is less likely to occur in the color image forming apparatus 1. On the other hand, when the thrust cycle of the photoreceptor 50 is 200 rotations or less, occurrence of circumferential scratches on the photoreceptor 50 can be suppressed.

An example of the image forming apparatus according to the present embodiment has been described above. However, as long as the image forming apparatus according to the present embodiment includes an image carrier and a charging roller, other members (for example, a static eliminator and a cleaning device) may be omitted. Further, although the case where the charging voltage is a DC voltage has been described, the present invention is also applicable to a case where the charging voltage is an AC voltage or a superimposed voltage. The superimposed voltage is a voltage obtained by superimposing a DC voltage and an AC voltage. Furthermore, although the developing roller 52 using a two-component developer containing carrier CA and toner T has been described, the present invention is also applicable to a developing device using a one-component developer. Further, although the image forming apparatus 1 that uses an intermediate transfer method has been described, the present invention is also applicable to an image forming apparatus that uses a direct transfer method.

[Image forming method]
The image forming method according to the second embodiment of the present invention includes a charging step of positively charging the peripheral surface of the image carrier with a charging roller. The image carrier includes a conductive substrate and a single photosensitive layer. The photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent, and a first binder resin. The charging roller includes a conductive shaft, a base layer covering the surface of the conductive shaft, and a surface layer covering the surface of the base layer. The charging capacity X [V/(C/m ² )] of the image carrier expressed by the following formula (1) and the surface resistivity Y [logΩ] of the surface layer of the charging roller satisfy the following formula (2). .
X=V/(Q/S)...(1)
Y＞5×10 ^-11 X ² +1.062×10 ^-5 ×X-47...(2)

In formula (1), Q represents the amount of electric charge [C] on the image carrier. S represents the charged area [m ² ] of the image carrier. V is a value calculated from the formula V=V ₀ -V _r . Vr represents the first potential [V] of the circumferential surface of the image carrier before being charged in the charging step. V ₀ represents the second potential [V] of the peripheral surface of the image carrier after being charged in the charging step. The image forming method according to the present embodiment can be performed, for example, by the image forming apparatus according to the first embodiment. According to the image forming method according to the present embodiment, it is possible to suppress the occurrence of charging unevenness.

The present invention will be further explained using Examples. Note that the present invention is in no way limited to the scope of the examples.

<Measurement method>
First, a method for measuring the physical property values shown in the following tests of Examples and Comparative Examples will be explained.

( _D50 of toner)
The _D50 of the toner was measured using a particle size distribution measuring device ("Coulter Counter Multisizer 3" manufactured by Beckman Coulter, Inc.).

(Number average circularity of toner)
The number average circularity of the toner was measured using a flow type particle image analyzer ("FPIA (registered trademark) 3000" manufactured by Sysmex Corporation).

(Static charge removal light amount)
An optical power meter ("Optical Power Meter 3664" manufactured by Hioki Electric Co., Ltd.) was embedded in a position facing the static elimination lamp on the circumferential surface of the photoreceptor. While emitting static eliminating light with a wavelength of 660 nm from a static eliminating lamp, the amount of static eliminating light that reached the circumferential surface of the photoreceptor was measured using an optical power meter.

(Cleaning blade linear pressure)
The linear pressure of the cleaning blade was measured using a load cell. Specifically, a jig was prepared in which a load cell was placed in place of the photoreceptor at the position where the cleaning blade abutted against the peripheral surface of the photoreceptor of the evaluation machine. The contact angle of the cleaning blade with respect to the load cell was set to 23 degrees. A cleaning blade was brought into pressure contact with the load cell. Using a load cell, the linear pressure was measured 10 seconds after the start of pressure contact. The measured linear pressure was taken as the linear pressure of the cleaning blade.

(Hardness of cleaning blade)
The hardness of the cleaning blade was measured using a rubber hardness meter ("Asker Rubber Hardness Meter Model JA" manufactured by Kobunshi Keiki Co., Ltd.) according to a method based on JIS K 6301.

(Resilience modulus of cleaning blade)
The rebound modulus of the cleaning blade was measured using a rebound resilience tester ("RT-90" manufactured by Kobunshi Keiki Co., Ltd.) according to a method based on JIS K 6255 (equivalent to ISO 4662). The environment in which the rebound modulus was measured was at a temperature of 25° C. and a relative humidity of 50% RH.

<Evaluation machine>
Next, the evaluation machine used in the tests of the following Examples and Comparative Examples will be explained. The evaluation device was a modified multifunction device (“TASKalfa356Ci” manufactured by Kyocera Document Solutions Co., Ltd.). The configuration and setting conditions of the evaluation machine were as follows.
・Photoconductor: Positively charged single layer OPC drum ・Photoconductor diameter: 30mm
・Film thickness of photosensitive layer of photoreceptor: 30 μm
・Linear speed of photoconductor: 250mm/sec ・Amount of thrust of photoconductor: 0.8mm
・Thrust cycle of photoreceptor: 70 rotations/1 reciprocation ・Charging device: Charging roller ・Charging voltage: Positive DC voltage ・Material of charging roller: Epichlorohydrin rubber with ionic conductive agent dispersed ・Diameter of charging roller: 12 mm
・Thickness of the rubber-containing layer of the charging roller: 3mm
・Resistance value of charging roller: 5.8 logΩ when +500V charging voltage is applied
・Distance between the charging roller and the circumferential surface of the photoreceptor: 0 μm (contact)
・Effective charging length: 226mm
・Transfer method: Intermediate transfer method ・Transfer voltage: Negative polarity DC voltage ・Transfer belt material: Polyimide ・Transfer width: 232 mm
・Static charge removal light amount: 5 μJ/cm ²
- Static neutralization - charging time: 125 milliseconds - Cleaner: Cleaning blade in contact with counter - Cleaning blade contact angle: 23 degrees - Cleaning blade material: polyurethane rubber - Cleaning blade hardness: 73 degrees - Cleaning blade rebound resilience Rate: 30%
・Cleaning blade thickness: 1.8mm
・Cleaning blade pressure contact method: The amount of cleaning blade biting into the photoreceptor is fixed (constant displacement)
- Amount of penetration of the cleaning blade into the photoreceptor: Value within the range of 0.8 mm or more and 1.5 mm or less (value that varies depending on the linear pressure of the cleaning blade)

<Preparation of photoreceptor>
Next, a photoreceptor was produced. The method for producing the photoreceptor was as follows.

(Preparation of photoreceptor (P-1))
A charge generating agent, a hole transporting agent, an electron transporting agent, a first binder resin, and a solvent were placed in a ball mill container (composition A). The contents of the container were mixed for 50 hours using a ball mill to disperse the materials (charge generating agent, hole transporting agent, electron transporting agent, and first binder resin) in the solvent. Thereby, a coating liquid for a photosensitive layer was obtained. The photosensitive layer coating solution was applied onto an aluminum drum-shaped support serving as a conductive substrate using a dip coating method to form a coating film. The coated film was dried with hot air at 100° C. for 40 minutes. As a result, a single photosensitive layer (thickness: 30 μm) was formed on the conductive substrate. As a result, a photoreceptor (P-1) was obtained.

(Preparation of photoreceptors (P-2) to (P-8))
Photoreceptors (P-2) and (P-8) were manufactured using the same method as photoreceptor (P-1), except that the content ratio of each component and the thickness of the single photosensitive layer were changed. It was made with As shown in Table 4 below, photoreceptors (P-2) to (P-6) had the same composition (composition B). Photoreceptors (P-7) to (P-8) had the same composition (composition C). The photoreceptor (P-1), the photoreceptors (P-2) to (P-6), and the photoreceptors (P-7) to (P-8) had different compositions. The thickness of the single-layer photosensitive layer was as shown in Table 4 below. A film thickness measuring device ("FISCHERSCOPE (registered trademark) MMS (registered trademark)" manufactured by Fisher Instruments Co., Ltd.) was used to measure the film thickness of the photosensitive layer of the photoreceptor.

(Measurement of charging ability)
By the method described in the embodiment, a high temperature and high humidity environment (hereinafter sometimes referred to as HH environment) with a temperature of 32.5 °C and a humidity of 80% RH, or a normal temperature and normal humidity environment with a temperature of 23 °C and a humidity of 50% RH (hereinafter sometimes referred to as NN environment), the charging ability of the photoreceptor was measured. The measurement results are shown in Table 4 below.

<Preparation of charging roller>
Next, a charging roller was produced by the following method.

(Preparation of charging roller (A-1))
The surface of a conductive shaft (diameter 9 mm, made of aluminum) was coated with a base layer. The base layer contained an ionic conductive agent and epichlorohydrin rubber. The base layer had a volume resistivity of 2.3×10 ⁴ Ω and a thickness of 3 mm. Thereby, a member including a conductive shaft and a base layer covering the conductive shaft was obtained.

The surface of the base layer of the above member was coated with a surface layer. The surface layer contained a polyamide resin (volume resistivity: 1.3×10 ⁶ Ω) as a second binder resin and tin oxide particles (average particle size: 10 nm) as a conductive filler. The surface layer had a thickness of 10 μm. As a result, a charging roller (A-1) was obtained.

(Preparation of charging roller (A-2))
The charging roller (A-2) was produced in the same manner as the charging roller (A-1) except that the composition of the surface layer was changed. Specifically, the surface layer of the charging roller (A-2) contained an acrylic resin as a second binder resin and tin oxide particles (average particle size: 10 nm) as a conductive filler. The surface layer had a thickness of 10 μm.

(Surface resistivity of surface layer of charging rollers (A-1) to (A-2))
The surface resistivity of charging rollers (A-1) to (A-2) was measured by the following method. Note that the surface resistivity of the charging roller was measured in the above-mentioned HH environment or NN environment. The surface resistivity was measured using a resistivity meter ("Hirestar-UX MCP-HT800" manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

First, a coating liquid having the same composition as the coating liquid used to prepare the surface layer of the charging roller (A-1) or (A-2) is applied onto an aluminum tube (diameter 12 mm). Alternatively, it was applied in the same manner as in the preparation of the surface layer in (A-2). As a result, a sample coating film corresponding to the surface layer of the charging roller (A-1) or (A-2) was formed on the cylindrical aluminum tube. Next, a probe having two metal electrodes (with a spacing of 20 mm) was brought into contact with the sample coating film formed on the aluminum tube. This probe was connected to the resistivity meter described above. A predetermined voltage was applied to this probe, and the surface resistivity of the sample coating film was measured 10 seconds after the start of application. The surface resistivity of this sample coating film was taken as the surface resistivity of the surface layer of the charging roller (A-1) or (A-2). The surface resistivity of the surface layer of the charging roller (A-1) was 6.4 log Ω in the HH environment and 8.4 log Ω in the NN environment. The surface resistivity of the surface layer of the charging roller (A-2) was 7.8 logΩ in the HH environment and 9.6 logΩ in the NN environment.

<Manufacture of image forming apparatuses N1 to N16>
Image forming apparatuses N1 to N16 were manufactured by the following method. First, the photoreceptors (P-1) to (P-8) were mounted on the above-mentioned evaluation machine. Furthermore, the charging roller was removed from the above-mentioned evaluation machine, and a charging roller (A-1) or (A-2) was installed instead. As a result, image forming apparatuses N1 to N16, which are evaluation machines for evaluating charging unevenness, were prepared. Combinations of photoreceptors and charging rollers in image forming apparatuses N1 to N16 are shown in Table 5 below. In the image forming apparatuses N1 to N16, the transfer current was set to -20 μA, the linear pressure of the cleaning blade was set to 40 N/m, and the potential of the circumferential surface of the photoreceptor was set to +500 V.

<Evaluation of charging unevenness>
Halftone images (density 25%) were formed on 5000 sheets of printing paper using image forming apparatuses N1 to N16 in the above-mentioned HH environment or NN environment (printing test). After the printing test, the last halftone image formed was visually observed to confirm the occurrence of charging unevenness (spotted white spots). Based on the following criteria and the following method, it was evaluated whether the image forming apparatuses N1 to N16 could suppress the occurrence of charging unevenness.
A (Good): No charging unevenness was observed. B (Poor): Charging unevenness was observed.

The evaluation results in the HH environment are shown in Table 5 below. The evaluation results in the NN environment are shown in Table 6 below. Tables 5 and 6 below show whether each image forming apparatus satisfies formula (2). Specifically, the case where the above-mentioned formula (2) was satisfied was designated as "Y", and the case where the formula (2) was not satisfied was designated as "N".

A graph summarizing Tables 5 and 6 below is shown in FIG. In FIG. 10, plots with circles indicate that no uneven charging was observed, and plots with x marks indicate that uneven charging was observed. In FIG. 10, the boundary line corresponding to the above equation (2) is shown as a dotted line. Specifically, the dotted line in FIG. 10 indicates that the plot located on the upper left side satisfies the above equation (2), and the plot located on the lower right side does not satisfy the above equation (2). Note that in Tables 5, 6, and FIG. 10 below, the surface layer resistance indicates the surface resistivity of the surface layer of the charging roller.

The image forming apparatuses N1 to N16 were equipped with an image carrier and a charging roller that positively charges the circumferential surface of the image carrier. The image carrier included an electrically conductive substrate and a single photosensitive layer. The photosensitive layer contained a charge generating agent, a hole transporting agent, an electron transporting agent, and a first binder resin. The charging roller included a conductive shaft, a base layer covering the surface of the conductive shaft, and a surface layer covering the surface of the base layer. As is clear from Tables 5, 6, and FIG. 10, the image forming apparatuses N1 to N16 can suppress the occurrence of charging unevenness when the above formula (2) is satisfied, and when the above formula (2) is not satisfied. could not suppress the occurrence of charging unevenness.

The image forming apparatus and image forming method according to the present invention can be used to form an image on a recording medium.

1: Image forming device 50: Photoreceptor (image carrier)
50a: Peripheral surface of photoreceptor (peripheral surface of image carrier)
51: Charging roller (charging device)
55: Cleaner (cleaning device)
81: Cleaning blade (cleaning member)
501: Conductive substrate 502: Photosensitive layer T: Toner

Claims (16)

an image carrier;
a charging roller that positively charges the peripheral surface of the image carrier;
The image carrier includes a conductive substrate and a single photosensitive layer,
The photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent, and a first binder resin,
The charging roller includes a conductive shaft, a base layer covering the surface of the conductive shaft, and a surface layer covering the surface of the base layer,
The chargeability X [V/(C/m ² )] of the image carrier expressed by the following formula (1) is 6.00×10 ⁵ V/(C/m ² ) or more and 8.72×10 ⁵ V/(C/m ² ) or less,
In the image forming apparatus , the surface resistivity Y [logΩ] of the surface layer of the charging roller is 7.8 logΩ or more and 10.0 logΩ or less .
X=V/(Q/S)...(1 )
( In the above formula (1),
Q represents the amount of electrical charge [C] of the image carrier,
S represents the charged area [m ² ] of the image carrier,
V is a value calculated from the formula V = V ₀ - V _r ,
V _r represents a first potential [V] of the peripheral surface of the image carrier before being charged by the charging roller,
V ₀ represents a second potential [V] of the peripheral surface of the image carrier after being charged by the charging roller. ) The image forming apparatus according to claim 1 , wherein the thickness of the surface layer is 10 μm or more and 20 μm or less. The image forming apparatus according to claim 1 , wherein the charging roller applies only a DC voltage to the peripheral surface of the image carrier. The surface layer contains a conductive filler,
The image forming apparatus according to any one of claims 1 to 3 , wherein the conductive filler includes tin oxide particles. The surface layer contains a second binder resin,
The image forming apparatus according to claim 1 , wherein the second binder resin includes a polyamide resin or an acrylic resin. The image forming apparatus according to any one of claims 1 to 5 , wherein the hole transport agent includes a compound represented by the following general formula (10).

(In the general formula (10),
R ¹³ to R ¹⁵ each independently represent an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms,
m and n each independently represent an integer of 1 or more and 3 or less,
p and r each independently represent 0 or 1,
q represents an integer from 0 to 2. ) The image forming apparatus according to claim 6 , wherein the hole transport agent includes a compound represented by the following chemical formula (HTM-1).

The image forming apparatus according to any one of claims 1 to 7 , wherein the first binder resin includes a polyarylate resin having a repeating unit represented by the following general formula (20).

(In the general formula (20),
R ²⁰ and R ²¹ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms,
R ²² and R ²³ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group,
R ²² and R ²³ may be bonded to each other to represent a divalent group represented by the following general formula (W),
Y represents a divalent group represented by the following chemical formula (Y1), (Y2), (Y3), (Y4), (Y5) or (Y6). )

(In the general formula (W),
t represents an integer from 1 to 3,
* represents a bond. )

(In the chemical formulas (Y1) to (Y6) above, * represents a bond.) The image according to claim 8 , wherein the first binder resin includes a polyarylate resin having a main chain represented by the following general formula (20-1) and a terminal group represented by the following chemical formula (Z). Forming device.

(In the general formula (20-1), u and v each independently represent a number from 30 to 70, and the sum of u and v is 100,
In the chemical formula (Z), * represents a bond. ) The image forming apparatus according to claim 9 , wherein the electron transport agent includes both a compound represented by the following general formula (31) and a compound represented by the following general formula (32).

(In the general formulas (31) and (32),
R ¹ to R ⁴ each independently represent an alkyl group having 1 or more and 8 or less carbon atoms,
R ⁵ to R ⁸ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a halogen atom. ) The electron transport agent includes both a compound represented by the following chemical formula (ETM-1) and a compound represented by the following chemical formula (ETM-3), according to any one of claims 1 to 10. image forming device.

The photosensitive layer further contains a specific compound represented by the following general formula (40),
The image forming apparatus according to any one of claims 1 to 11 , wherein the content of the specific compound in the photosensitive layer is more than 0.0% by mass and not more than 1.0% by mass.

(In the general formula (40),
R ⁴⁰ and R ⁴¹ each independently represent a hydrogen atom or a monovalent group represented by the following general formula (40a),
A represents a divalent group represented by the following chemical formula (A1), (A2), (A3), (A4), (A5) or (A6). )

(In the general formula (40a), X represents a halogen atom. * represents a bond.)

(In the chemical formulas (A1) to (A6) above, * represents a bond.) The image forming apparatus according to claim 12 , wherein the specific compound is represented by the following chemical formula (40-1).

The image forming apparatus according to any one of claims 1 to 13 , wherein the content of the charge generating agent in the photosensitive layer is more than 0.0% by mass and not more than 1.0% by mass. The chargeability X [V/(C/m ² )] of the image carrier is 7.70×10 ⁵ V/(C/m ² ) or more and 8.72×10 ⁵ V/(C/m ² ) or less. and
The image forming apparatus according to any one of claims 1 to 14, wherein the surface resistivity Y [logΩ] of the surface layer of the charging roller is 7.8 logΩ or more and 8.4 logΩ or less. An image forming method comprising a charging step of positively charging the peripheral surface of an image carrier with a charging roller,
The image carrier includes a conductive substrate and a single photosensitive layer,
The photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent, and a first binder resin,
The charging roller includes a conductive shaft, a base layer covering the surface of the conductive shaft, and a surface layer covering the surface of the base layer,
The chargeability X [V/(C/m ² )] of the image carrier expressed by the following formula (1) is 6.00×10 ⁵ V/(C/m ² ) or more and 8.72×10 ⁵ V/(C/m ² ) or less,
The image forming method , wherein the surface resistivity Y [logΩ] of the surface layer of the charging roller is 7.8 logΩ or more and 10.0 logΩ or less .
X=V/(Q/S)...(1 )
( In the above formula (1),
Q represents the amount of electrical charge [C] of the image carrier,
S represents the charged area [m ² ] of the image carrier,
V is a value calculated from the formula V = V ₀ - V _r ,
V _r represents a first potential [V] of the peripheral surface of the image carrier before being charged by the charging roller,
V ₀ represents a second potential [V] of the peripheral surface of the image carrier after being charged by the charging roller. )

Images