JP2015041042A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform charging processing so that the surface potential of a latent image carrier becomes the maximum charge potential to suppress the occurrence of unevenness in charging potential, and suppress a variation in image quality, such as glossiness of images due to a reduction in absolute value of the charging potential of the latent image carrier according to a change in characteristics of the latent image carrier without requiring the control of imaging conditions.SOLUTION: The capacitance C of a latent image carrier, the absolute value Vof the maximum charging potential that can be taken by the latent image carrier, and the absolute value Q of the amount of charge supplied to the latent image carrier per unit area through charging processing satisfy the following relational expression (1): C×V<Q≤1.5×C×V; the flow start temperature Tof toner, 1/2 flow temperature T, and flow end temperature Tsatisfy the following relational expressions (2): T-T≤24.0, and (3): T-T≥7.0.

Description

  The present invention forms a latent image after uniformly charging the surface of a latent image carrier such as a photosensitive member, and develops the latent image with toner to finally transfer the toner image to a recording material. The present invention relates to an image forming apparatus such as a printer, a printer, a facsimile, or a plotter.

  In general, an electrophotographic image forming apparatus forms an electrostatic latent image on the surface of a latent image carrier such as a photoconductor formed of a photoconductive substance, and charged toner is applied to the latent image. A toner image is formed by adhering. Thereafter, the toner image is finally transferred onto a recording material such as paper, and then the toner image is fixed to the recording material using heat and pressure or solvent gas. As the latent image forming means, normally, a latent image pattern corresponding to image information is formed by irradiating the surface of the latent image carrier with light to lower the absolute value of the surface potential of the latent image carrier.

  In such an electrophotographic system, in order to stably obtain a high-quality image, the surface potential unevenness of the latent image carrier after the charging process by the charging means (hereinafter referred to as “charging potential unevenness”) is suppressed. is important. The main cause of the charging potential unevenness is the residual potential due to the past latent image pattern. When the charging potential unevenness occurs due to the influence of the residual potential, a ghost image in which the past image is superimposed on the formed image is formed. Arise.

Conventionally, various measures have been proposed to suppress the charging potential unevenness due to such residual potential.
For example, Patent Document 1 discloses a detection unit that detects a ghost image in a halftone image by detecting a surface potential difference or a toner adhesion amount difference, and an image forming condition (charging current or transfer current) based on the detection result. An image forming apparatus having a correcting unit that corrects (1) is disclosed.
Patent Document 2 discloses an image forming apparatus having an auxiliary charging brush that erases a residual potential of a previous image by applying a bias in contact with the surface of a photoreceptor. In this image forming apparatus, the residual potential on the surface of the photoconductor is detected on the upstream side of the auxiliary charging brush in the movement direction of the photoconductor, and the bias application condition to the auxiliary charging brush is controlled according to the detection result. Turn off the residual potential on the body surface.
Japanese Patent Application Laid-Open No. H10-228867 eliminates an afterimage that is a side effect of pre-transfer exposure in an image forming apparatus that performs transfer pre-exposure on the surface of a photoconductor to improve transfer performance and attenuates the charged potential of the background portion. Therefore, an image forming apparatus provided with a pre-charging bias unit is disclosed. In this image forming apparatus, the pre-charging bias potential is the same as the charging polarity of the charging unit and greater than the charging start voltage immediately after the cleaning process by the cleaning unit and immediately before the charging process by the charging unit. Applied to the photoreceptor surface. Thereby, the residual potential due to the pre-transfer exposure is erased.

  However, the image forming apparatus disclosed in Patent Document 1 requires dedicated means such as a detection means for detecting the occurrence of a ghost image and an image forming condition correction means in order to eliminate the residual potential. Also in the image forming apparatus disclosed in Patent Document 2, in order to erase the residual potential, the auxiliary charging brush, the residual potential detecting means, and the control means for controlling the bias application condition to the auxiliary charging brush according to the detection result. Dedicated means such as are required. The image forming apparatus disclosed in Patent Document 3 also requires a dedicated unit such as a pre-charging bias unit in order to erase the residual potential. As described above, since the conventional image forming apparatus is provided with a dedicated means to eliminate the residual potential and suppress the uneven charging potential, there is a problem in that the number of parts is increased and the cost is increased.

  Therefore, the present inventors have intensively studied a method that can suppress charging potential unevenness without providing a dedicated means. As a result, the charging process is performed so that the latent image carrier surface potential after charging in the image forming operation becomes the maximum potential (maximum charging potential) that the surface of the latent image carrier can maintain. It has been found that uneven charging potential can be stably suppressed without adding means. Hereinafter, this point will be described in detail.

FIG. 5 shows the absolute value of the surface potential of the latent image carrier after charging (hereinafter referred to as “charging potential”) V and the absolute value of the amount of charge supplied per unit area supplied to the latent image carrier by the charging process. (Hereinafter referred to as “supplied charge amount”) A graph schematically showing a relationship with Q.
Note that the supplied charge amount Q includes the amount of current I [A] flowing through the latent image carrier during the charging process, the length W [m] of the charged region in the rotation axis direction of the latent image carrier, and the latent image carrier. It is calculated from the following equation (4) using the surface moving speed V [m / s].
Q = A / (W × V) (4)

As shown in FIG. 5, the charge potential V of the latent image carrier increases in proportion to the supply charge amount Q in the range where the supply charge amount Q is low, but when the supply charge amount Q becomes excessive, the supply charge amount Q The latent image carrier cannot hold a part of the image, and excess charge leaks. As a result, the charge potential V of the latent image bearing member becomes saturated, exhibits a constant potential V _0. This potential V ₀ is the maximum potential that the surface of the latent image carrier can maintain, that is, the maximum charging potential. Here, the minimum supply charge amount (necessary supply charge amount) necessary for setting the surface potential of the latent image carrier to the maximum charging potential V ₀ is Q ₀ . As shown in FIG. 5, the required supply charge amount Q ₀ is the supply charge amount when the charging potential V and the supply charge amount Q reach the maximum charging potential V ₀ while maintaining the proportional relationship.

  In a conventional image forming apparatus, the supply charge amount Q is generally controlled in a range in which a proportional relationship is established between the charging potential V and the supply charge amount Q (approximately the range indicated by B in FIG. 5). In the proportional range B, the charging potential V can be accurately changed by controlling the supplied charge amount Q, and the image quality can be improved by adjusting the charging potential V during image quality adjustment control (process control). It is to become. In particular, when multi-level control of the exposure portion potential is performed by controlling the exposure intensity to express the halftone of the image, the adjustment of the charging potential V greatly affects the image quality improvement. It is very advantageous to be able to adjust the charging potential V by controlling in the proportional range B.

  In this way, when the supplied charge amount Q is controlled within the proportional range B, the surface of the latent image carrier is made uniform with the target supplied charge amount Q if the surface of the latent image carrier before charging is in a state where there is no potential unevenness. As a result of charging, the charged potential unevenness does not occur on the surface of the latent image carrier after charging. However, if there is a residual potential due to the past latent image pattern on the surface of the latent image carrier before charging, the potential corresponding to the supplied charge amount Q is added to the residual potential at the location where the residual potential exists. On the other hand, at a portion where no residual potential exists, the potential corresponds to the supplied charge amount Q, and uneven charging potential occurs.

Therefore, the present inventors devised setting the supplied charge amount Q in a saturation range (approximately the range indicated by the symbol A in FIG. 5) in which the charging potential V hardly changes even when the supplied charge amount Q is increased. did. By setting the supplied charge amount Q in the saturation range A, at a portion where a residual potential exists, even if a potential component corresponding to the supplied charge amount Q is added to the residual potential component, only the maximum charged potential V ₀ is obtained. Don't be. On the other hand, at a portion where no residual potential exists, the potential according to the supplied charge amount Q, that is, the maximum charging potential V ₀ is obtained. Therefore, even if there is a residual potential due to a past latent image pattern on the surface of the latent image carrier before charging, charging potential unevenness does not occur on the surface of the latent image carrier after charging.

However, as a result of further studies by the present inventors, it has been found that when the supplied charge amount Q is set to the saturation range A, the following new problem occurs.
That is, when the supplied charge amount Q is set in the saturation range A, the charging potential of the latent image carrier is a value depending on the characteristics of the latent image carrier (such as the film thickness of the photosensitive layer in the case of an electrophotographic photoreceptor). Become. Therefore, when the characteristics of the latent image carrier (such as the thickness of the photosensitive layer) change over time, the absolute value of the charging potential of the latent image carrier decreases, and the exposed portion potential changes to cause toner adhesion per unit area. The amount increases. As a result, there arises a problem that the image quality such as the glossiness of the image changes.

  When the supply charge amount Q is set in the saturation range A, it is impossible to adjust the charging potential of the latent image carrier so that such image quality change does not occur. Therefore, in order to cope with this problem, the image forming conditions other than the charged potential of the latent image carrier are adjusted to change the amount of toner attached per unit area that adheres to the latent image on the latent image carrier. It is necessary to suppress fluctuations in concentration.

  As a coping method, for example, there is a method in which the developing bias is controlled so that the toner adhesion amount per unit area is reduced in accordance with the decrease in the charging potential of the latent image carrier. However, since a relatively simple image forming apparatus does not include a control mechanism for executing such control, it is necessary to add a new control mechanism to adopt this countermeasure, which increases costs. The problem of being connected arises.

  In addition, image quality adjustment control (process) that controls the development bias so that the toner adhesion amount per unit area changes by looking at the result of detecting the image density of the toner pattern during non-image forming operation. Some image forming apparatuses execute control. In such an image forming apparatus, it is possible to suppress changes in image quality such as gloss due to a decrease in the charged potential of the latent image carrier described above without adding a new control mechanism. However, the image quality adjustment control cannot be executed frequently because it causes downtime during which the image forming operation cannot be performed or a large amount of toner is consumed. Therefore, until the next image quality adjustment control is executed, the developing bias is not controlled so that the toner adhesion amount per unit area changes. Therefore, there arises a problem that a change in image quality such as gloss due to a decrease in the charging potential of the latent image carrier that occurs during that period cannot be suppressed.

  The present invention has been made in view of the above problems, and the object of the present invention is to suppress the occurrence of uneven charging potential by performing a charging process so that the surface potential of the latent image carrier becomes the maximum charging potential. However, without controlling the image forming conditions, it suppresses changes in image quality such as image gloss due to a decrease in the absolute value of the charging potential of the latent image carrier in accordance with changes in the characteristics of the latent image carrier. An image forming apparatus is provided.

In order to achieve the above object, the present invention comprises a latent image carrier that carries a latent image and moves on the surface, and a charging means that performs a charging process for uniformly charging the surface of the latent image carrier, A latent image forming unit that forms a latent image according to image information by lowering the absolute value of the surface potential of the latent image carrier charged by the charging unit; and a latent image formed on the surface of the latent image carrier. A developing unit that performs a developing process for attaching toner to the image, a transfer unit that finally transfers the toner image formed on the surface of the latent image carrier by the developing process of the developing unit onto a recording material, and the transfer unit. In an image forming apparatus having fixing means for performing a fixing process for fixing a toner image transferred onto a recording material to the recording material by the action of heat and pressure, the electrostatic capacity of the latent image carrier is C, The surface of the latent image carrier after the charging process of the charging means The absolute value of the maximum potential that can take the potential and V _0, the absolute value of the supply amount of charge per unit area to be supplied to the latent image bearing member by a charging process of the charging means when is Q, the following relationship The outflow of toner used in the developing process by the developing unit, measured by an elevated flow tester under the measurement conditions that satisfy the formula (1), the load is 10 [kg], and the heating rate is 3.0 [° C./min]. When the start temperature is T _fb , the _1/2 outflow temperature is T _1/2 , and the outflow end temperature is T _end , the following relational expressions (2) and (3) are satisfied.
C × V ₀ <Q ≦ 1.5 × C × V ₀ (1)
T _1/2 −T _fb ≦ 24.0 (2)
T _end -T _1/2 ≧ 7.0 (3)

  According to the present invention, charging is performed so that the surface potential of the latent image carrier becomes the maximum charging potential to suppress the occurrence of uneven charging potential, but the latent image carrier is not required to control the image forming conditions. An excellent effect is obtained in that a change in image quality due to a decrease in the absolute value of the charging potential of the latent image carrier corresponding to a change in the characteristics of the image carrier can be suppressed.

1 is a schematic diagram illustrating an example of an image forming apparatus according to an embodiment. FIG. 2 is a schematic diagram showing one of four process cartridges that are detachably provided in the image forming apparatus. It is a fragmentary sectional view showing typically an example of photoconductor 1 in an embodiment. It is the table | surface which put together the conditions and evaluation result in Examples 1-9 used for the evaluation test, and Comparative Examples 1-4. 3 is a graph schematically showing a relationship between a charging potential V of a latent image carrier after charging and an absolute value (supplied charge amount) Q of a supplied charge amount per unit area supplied to the latent image carrier by a charging process. is there.

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings.
In this specification, “recording material” means, for example, a material made of paper, thread, fiber, leather, metal, plastic, glass, wood, ceramics, etc., on which an image is formed. .
“Image formation” refers to the application of images such as characters, figures, patterns, etc. to the recording material, and the latent image is visualized with colored or non-colored toner, and if necessary, via an intermediate transfer member. Is transferred to a recording material and fixed.
“Toner” means a single resin powder, a composite powder, a single or multiple color materials, a composite of resin and color materials, and a powder obtained by adding a wax component or an inorganic material to these. It is used as a general term for all powders that can perform image formation, such as functional powder whose form is controlled, and includes, for example, gloss suppressing powder, gloss imparting powder, baking powder, and foaming powder.
The “process cartridge” is an integrated part or all of the components necessary for image formation. At least an electrophotographic photosensitive member (hereinafter simply referred to as “photosensitive member”) as a latent image carrier. Body "). Also, a charging process for applying a predetermined potential to the photosensitive member, a writing process for forming an electrostatic latent image, a developing process for converting the electrostatic latent image on the photosensitive member into a toner image, and a toner image on the photosensitive member. All or a part of the constituent members necessary for performing a transfer process for finally transferring the toner to the recording material and a cleaning process for removing the residual toner image on the photosensitive member may be included. Moreover, it comprises in the form which can arrange | position each member so that a required process can be implemented among these processes.

FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus 100 according to the present embodiment.
FIG. 2 is a schematic diagram showing one of the four process cartridges 300 detachably provided in the image forming apparatus 100.
The image forming unit of the image forming apparatus 100 includes drum-shaped photoreceptors 1Y, 1C, 1M, and 1K. The photoreceptors 1Y, 1C, 1M, and 1K are provided side by side along the surface movement direction of the intermediate transfer belt 5 as an intermediate transfer member. The photoreceptors 1Y, 1C, 1M, and 1K can carry latent images of toners of various colors (in this embodiment, yellow, cyan, magenta, and black) and have a photoconductive layer. This latent image is written by the writing device 3. Around each of the photoconductors 1Y, 1C, 1M, and 1K, a charging device 2, a developing device 4, a cleaning device 6, and the like are arranged.

  The intermediate transfer belt 5 is stretched around support rollers 50 and 51. On the inner peripheral surface side of the intermediate transfer belt 5, primary transfer rollers 52Y, 52C, 52M, and 52K as primary transfer units are disposed corresponding to the photoreceptors 1Y, 1C, 1M, and 1K. A secondary transfer roller 53 as a secondary transfer unit for secondary transfer of the toner image on the intermediate transfer belt 5 onto the recording material is disposed at a position facing one of the support rollers 51.

  The charging device 2 is not particularly limited and may be appropriately selected depending on the intended purpose. For example, the charging device 2 may include a conductive or semiconductive roll, brush, film, rubber blade, etc. Examples thereof include non-contact charging devices using corona discharge such as devices, corotrons, and scorotrons. Among them, a charging device having a charging roller that performs contact charging by bringing a conductive or semiconductive roll to which a DC voltage is applied into contact with the photoreceptor is preferable. When a charging device having a contact charging roller is used, a soft contact charging roller is used, or a charging means configuration without a pressure member is used so that a large pressing force is not applied at the contact portion. It is more preferable to take. As shown in FIG. 2, the charging device 2 of the present embodiment is of a contact charging type having a charging roller 20.

In the present embodiment, the charging device 2 performs the charging process so that the absolute value (supply charge amount) Q of the supplied charge amount per unit area supplied to the photoconductor 1 by the charging process satisfies the following relational expression (1). I do. Here, C × V ₀ is obtained by multiplying the electrostatic capacitance C of the photosensitive member 1 by the maximum charging potential V _{0 of} the photosensitive member 1, and the surface potential of the photosensitive member 1 is set to the maximum charging potential V ₀ . Therefore, it means the minimum supply charge amount (necessary supply charge amount) Q ₀ necessary for this purpose. Therefore, the charging device 2 of this embodiment, the charging process is performed so that more than the supply amount Q necessary supply amount Q _0. Accordingly, the surface potential of the photosensitive member 1 after being charged by the charging device 2, so that a maximum charge potential V _0.
C × V ₀ <Q ≦ 1.5 × C × V ₀ (1)

By performing such a charging process, as described above, even if there is a residual potential due to a past latent image pattern, the occurrence of charging potential unevenness can be suppressed. However, if the supplied charge amount Q is too large, electrostatic damage to the photoconductor 1 becomes large, and a decrease in the durability life of the photoconductor 1 becomes serious. Therefore, in this embodiment, so that not required supply charge amount Q ₀ of 1.5 times the supply amount of electric charge Q.

  The latent image forming means is not particularly limited as long as it can form a latent image according to image information by lowering the absolute value of the surface potential of the photoreceptor 1 charged by the charging device 2. It can be appropriately selected depending on the case. The writing device 3 of the present embodiment forms a latent image by exposing the surface of the photoconductor imagewise as indicated by a symbol L in FIG. In addition, for example, various writing devices such as a copying optical system, a rod lens array system, a laser optical system, a liquid crystal shutter optical system, and an LED optical system can be used. Further, an optical back side system that performs image-like writing exposure from the back side of the photoreceptor may be adopted. Further, when forming a halftone image, it is preferable to use area gradation performed by changing the exposure area according to the image.

The developing device 4 is an example of a unit that develops the electrostatic latent image formed on the photoreceptor 1 using a developer to form a visible image. The developing device 40 includes a developing sleeve 40, a developer stirring and conveying mechanism 41, 42 and the like. A toner replenishing section (not shown) is provided above the developer stirring and conveying mechanism 42.
The developing sleeve 40 carries the developer and conveys it to a position facing the photoconductor. A developing gap is formed between the photoreceptor 1 and the developing sleeve 40. The development gap is set to a substantially uniform gap in consideration of the amount of developer drawn up, the strength of the magnetic field for holding the developer on the development sleeve, the magnetization of the carrier in the developer, the rotation speed of the development sleeve, etc. Although it is not necessarily specified because it is formed by adjusting, it is generally preferable that the average value is about 0.2 to 0.4 mm.

  Although the developing device 4 of the present embodiment is a two-component developing type developing device, a one-component developing type developing device using only toner as a developer may be used. The developing device is not particularly limited as long as it has these configurations, and can be appropriately selected from known ones. For example, the developer is accommodated and the developer is contained in the electrostatic latent image. It is preferable to have at least a developing device that can be applied in a contact or non-contact manner.

As the developer, a two-component developer composed of toner and carrier, or a one-component developer composed only of toner can be used. However, in this embodiment, the toner outflow start temperature T _fb , 1/2 measured by the elevated flow tester under the measurement conditions where the load is 10 [kg] and the temperature rising rate is 3.0 [° C./min]. A toner whose outflow temperature T _1/2 and outflow end temperature T _end satisfy the following relational expressions (2) and (3) is used.
T _1/2 −T _fb ≦ 24.0 (2)
T _end -T _1/2 ≧ 7.0 (3)

The reason why the toner having such characteristics is used is as follows. That is, since the charging process of the present embodiment is performed so that the surface potential of the photosensitive member 1 after charging becomes the maximum charging potential V ₀ , the photosensitive member 1 is caused by the characteristic change of the photosensitive member 1 as described above. A decrease in the absolute value of the charging potential occurs. When the absolute value of the charging potential of the photosensitive member 1 is reduced, the toner adhesion amount per unit area attached to the latent image is increased, and the image quality such as the glossiness of the image is changed. Such a change in image quality can be suppressed by adjusting the image forming conditions. However, in that case, various members necessary for adjusting the image forming conditions are required, leading to high costs. There is a problem that the image quality change cannot be suppressed until the adjustment of the image forming conditions is completed. Therefore, in this embodiment, the toner characteristics are adjusted so that even if the toner adhesion amount per unit area that adheres to the latent image increases, the change in image quality such as the glossiness of the image is less likely to be affected. . In other words, this embodiment optimizes the toner characteristics with respect to image quality changes such as image gloss that may occur when the charging process is performed such that the surface potential of the photoreceptor 1 after charging becomes the maximum charging potential V _0. This is what we are trying to suppress.

T _1/2 -T _{fb in} the relational expression (2) is a state where a certain amount of toner flows and fills and fills the gaps in the recording material immediately after the toner becomes flowable. The temperature difference is shown. If this value is small, the toner melts earlier and can flow on the recording material when subjected to the heat and pressure fixing process at the fixing temperature set to be equal to or higher than the toner outflow start temperature T _fb. Means that. Therefore, even if the amount of toner attached per unit area that adheres to the latent image increases and the amount of heat received by each toner during the heat and pressure fixing process changes slightly, The toner can be sufficiently melted, and the difference in the degree of melting of the toner is hardly generated. As a result, even if the toner adhesion amount per unit area increases, the image quality such as the glossiness of the image hardly changes. As will be described in detail later, as shown in the relational expression (2), if T _1/2 -T _fb is 24.0 ° C. or less, the increase range of the toner adhesion amount per unit area that can occur in the present embodiment. In particular, there is no significant difference in the degree of melting of the toner, and the influence on the image quality change such as the gloss of the image can be suppressed to a practically sufficient level.

  On the other hand, when the relational expression (2) is satisfied, the toner is melted at an early stage during the hot-pressure fixing process. In this case, the toner further receives the amount of heat during the hot-pressure fixing process, and the temperature of the toner further increases. As it rises and melts, the toner easily flows and diffuses into the recording material. If much of the toner flows and diffuses into the recording material, the amount of toner remaining on the surface of the recording material is reduced, and image quality deterioration such as a blur due to the surface properties of the recording material is likely to occur.

Therefore, in the present embodiment, even when the relational expression (2) is satisfied, the relational expression (3) is satisfied, thereby making it difficult for image quality degradation such as blurring to occur. That is, T _end -T _{1/2 in} the relational expression (3) is such that after the toner melts and flows and fills in the gaps in the recording material, it flows into a deeper portion in the recording material thickness direction. The temperature difference until it becomes easy to diffuse is shown. The smaller this value, the easier the molten toner flows and diffuses into the gaps in the recording material. Therefore, if this value is too small, the melted toner does not stay on the surface of the recording material when it is subjected to the heat and pressure fixing process by the fixing device 7, and moves to the inside of the recording material. Inconveniences such as vomits are likely to appear. Although details will be described later, as shown in the equation _(3), if the T end The _{-T 1/2} is 7.0 ° C. or higher, even if you satisfy the relational expression (2), irregularity, etc. Image quality deterioration can be suppressed to a practically sufficient level.

The toner of the exemplary embodiment is not particularly limited with respect to conditions other than those described above, and can be appropriately selected according to the purpose.
For example, a toner having an average circularity of 0.93 to 1.00, which is an average value of the circularity SR shown in the following formula (5), is preferable, and 0.95 to 0.99 is more preferable. This average circularity is an index of the degree of unevenness of the toner particles, and indicates 1.00 when the toner is perfectly spherical, and the average circularity becomes smaller as the surface shape becomes more complex.
SR = (circumference of circle having area equal to projected area of toner particles) / (peripheral length of toner particles) (5)

  The mass average particle diameter (D4) of the toner is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably in the range of 3 [μm] to 10 [μm], and 4 [μm]. ] Is more preferably in the range of 8 [μm] or less. In this range, since the toner particles have a sufficiently small particle size with respect to the minute latent image dots, the dot reproducibility is excellent. If the mass average particle diameter (D4) is less than 3 [μm], phenomena such as a decrease in transfer efficiency and a decrease in blade cleaning properties may occur, and if it exceeds 10 [μm], characters and lines are scattered. It can be difficult to suppress.

  The cleaning device 6 is not particularly limited as long as it is a means for cleaning the surface of the photosensitive member 1 and can be appropriately selected according to the purpose. Among them, the surface of the photosensitive member is cleaned as in the present embodiment. It is preferable to have a cleaning blade 60 for the purpose. In general, as a cleaning method of the photoconductor, in addition to the method using the cleaning blade 60, there is an electrostatic cleaning method using a brush to which a voltage is applied so as to be opposite in polarity to the toner remaining on the photoconductor. It is done.

  In the present embodiment, the photosensitive member 1, the developing device 4, and the like are integrally supported and configured as a process cartridge that is detachable from the main body of the image forming apparatus 100. The process cartridge 300 of this embodiment is provided for each color (yellow, cyan, magenta, black), and as shown in FIG. 2, the photosensitive member 1, the charging device 2, the developing device 4, and the cleaning device. 6 is integrally supported and accommodated inside.

FIG. 3 is a partial cross-sectional view schematically showing an example of the photoreceptor 1 in the present embodiment.
The photoreceptor 1 of the present embodiment includes a support 10, an undercoat layer 11, and a photosensitive layer 12. The photosensitive layer 12 includes a charge generation layer 120 and a charge transfer layer 121.

As the support 10 used for the photoreceptor 1, a material having a volume resistivity of 1.0 × 10 ¹⁰ [Ω · cm] or less is preferably used, and can be appropriately selected according to the purpose. For example, a metal such as aluminum, nickel, chromium, nichrome, copper, gold, silver, platinum, or a metal oxide such as tin oxide or indium oxide coated on plastic, tempered glass, or the like by vapor deposition or sputtering, or aluminum Examples of the pipe include aluminum alloy, nickel, stainless steel, etc., which are formed into a drum shape by a method such as extrusion and drawing, and then subjected to surface treatment such as cutting, finishing, and polishing. From the standpoints of alignment accuracy during image formation and dimensional stability, the support 10 is preferably a hard tube or a thin tube having sufficient tensile strength.

  There is no restriction | limiting in particular as a diameter of the support body 10, Although it can select suitably according to the objective, The inside of the range of 20 [mm] or more and 150 [mm] or less is preferable, and 24 [mm] or more and 100 [mm] The following range is more preferable, and the range of 28 [mm] or more and 70 or less is particularly preferable. If the diameter is less than 20 [mm], it may be physically difficult to dispose a member that performs charging, exposure, development, transfer, and cleaning processes around the photoreceptor 1. ], The image forming apparatus 100 may become large.

  The undercoat layer 11 is not particularly limited, and may be a single layer or a plurality of layers. For example, the undercoat layer 11 may be composed mainly of a resin, an electron accepting material, and N-type semiconductor particles. Examples thereof include those composed mainly of a resin, and metal oxide films obtained by chemically or electrochemically oxidizing the surface of a conductive support. Among these, those containing an electron accepting material, N-type semiconductive particles, and a resin as main components are preferable.

  As the electron-accepting material, any material can be used as long as desired characteristics can be obtained, but materials having high affinity with N-type semiconductor particles are preferably used. A compound having an anthraquinone structure having a hydroxyl group as a basic skeleton is preferable, and a hydroxyanthraquinone compound, an aminohydroxyanthraquinone compound, and the like can be preferably used. Specifically, 1,2-dihydroxy-9,10-anthraquinone, 1,4-dihydroxy-9,10-anthraquinone, 1,5-dihydroxy-9,10-anthraquinone, 1,2,4-trihydroxy- 9,10-anthraquinone, 1-hydroxyanthraquinone, 2-amino-3-hydroxyanthraquinone, 1-amino-4-hydroxyanthraquinone and the like can be mentioned. Further, fullerene derivatives can also be used as the electron-accepting material, and any of phenyl C61 butyric acid methyl ester, phenyl C61 butyric acid butyl ester, phenyl C61 butyric acid isobutyl ester and the like can be preferably used.

The N-type semiconductor particles are not particularly limited, and are, for example, metal oxides such as zinc oxide, tin dioxide, indium oxide, and ITO (for example, In ₂ O ₃ : SnO ₂ = 90: 10 [wt%]). Or the particle | grains which processed the base-material particle | grain surface of the inorganic oxide with these materials are mentioned.

  The resin is not particularly limited, and examples thereof include thermoplastic resins such as polyamide, polyvinyl alcohol, casein, and methyl cellulose; thermosetting resins such as acrylic, phenol, melamine, alkyd, unsaturated polyester, and epoxy. It is done. These may be used individually by 1 type and may use 2 or more types together.

  Since it is preferable to change the thickness of the undercoat layer 11 depending on the type and combination of the materials to be used, the range is not generally determined, but is preferably about 0.5 [μm] to 20 [μm]. In order to more surely prevent charge injection from the support and to quickly attenuate charges generated in the charge generation layer and surplus charges during charging, about 2 [μm] to 15 [μm] is more preferable. preferable.

There is no restriction | limiting in particular as the photosensitive layer 12, According to the objective, it can select suitably.
For example, a single layer type in which a charge generation material and a charge transport material are mixed, a forward layer type having a charge transport layer containing a charge transport material on a charge generation layer containing a charge generation material, or a charge transport layer And a reverse layer type having a charge generation layer. Moreover, an appropriate amount of a plasticizer, an antioxidant, a leveling agent or the like can be added to each layer as necessary.

  There is no restriction | limiting in particular as thickness of the photosensitive layer 12, According to the objective, it can select suitably, The inside of the range of 10 [micrometers] or more and 50 [micrometers] or less is preferable. The total thickness of the undercoat layer 11 and the photosensitive layer 12 is preferably in the range of 20 [μm] to 60 [μm]. When these relationships are satisfied, a uniform visible image can be formed over a long period of time, so that a stable image forming apparatus with little temporal variation can be provided. When the total thickness is less than 20 [μm], it may be difficult to ensure electrical uniformity as a photoreceptor, and when the total thickness exceeds 60 [μm], the electrostatic latent image resolution This is not preferable because it may cause a decrease in the temperature.

In general photoconductors, materials and layer configurations are selected so that more charged charges can be retained. The photosensitive member 1 used in the image forming apparatus 100 in the present embodiment also needs to hold a charged charge. However, the charging process of the present embodiment is such that the surface potential of the photosensitive member 1 after charging becomes the maximum charged potential V _0. For this reason, in the existing photoconductor, the charge potential (maximum charge potential V ₀ ) that can be maintained may be too high. The maximum charging potential V ₀ is influenced not only by the electrostatic capacitance C of the photoreceptor 1 but also by the dark resistance and the magnitude of the withstand voltage. Therefore, in order to obtain a photosensitive member 1 with the maximum charge potential V ₀ aim, it is desired to stably as escape of excess charge from the photoreceptor surface configuration.

  Examples of the charge generation material in the photosensitive layer 12 include a compound having a tetrabenzoporphyrin skeleton. Examples of compounds having a tetrabenzoporphyrin skeleton include unsubstituted tetrabenzoporphyrin, and copper, silver, gold, platinum, nickel, calcium, strontium, barium, titanium, manganese, iron, cobalt, nickel, aluminum, and gallium as central metals. And the like, and compounds having introduced an alkyl group, phenyl group, halogen group, hydroxy group, amino group, nitro group, carboxyl group or the like as a characteristic group, and the like can be appropriately selected and used as necessary. .

  Also, for example, monoazo pigments, bisazo pigments, trisazo pigments, azo pigments such as tetrakisazo pigments, triarylmethane dyes, thiazine dyes, oxazine dyes, xanthene dyes, cyanine dyes, styryl dyes, Organic pigments or dyes such as pyrylium dyes, quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, bisbenzimidazole pigments, indanthrone pigments, squarylium pigments, phthalocyanine pigments; cadmium sulfide Inorganic materials such as zinc oxide and titanium oxide can also be used as charge generating materials. These charge generation materials may be used in combination.

  Examples of the charge transport material in the photosensitive layer 12 include anthracene derivatives, pyrene derivatives, carbazole derivatives, tetrazole derivatives, metallocene derivatives, phenothiazine derivatives, pyrazoline compounds, hydrazone compounds, styryl compounds, styrylhydrazone compounds, enamine compounds, butadiene compounds, and distyryl. Examples thereof include compounds, oxazole compounds, oxadiazole compounds, thiazole compounds, imidazole compounds, triphenylamine derivatives, phenylenediamine derivatives, aminostilbene derivatives, and triphenylmethane derivatives. These may be used individually by 1 type and may use 2 or more types together.

The binder resin in the photosensitive layer 12 is moderately electrically insulating, and known thermoplastic resins, thermosetting resins, photocurable resins, photoconductive resins, and the like can be used.
Examples of the binder resin include polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, ethylene-vinyl acetate copolymer, polyvinyl butyral, polyvinyl Thermoplastic resins such as acetal, polyester, phenoxy resin, (meth) acrylic resin, polystyrene, polycarbonate, polyarylate, polysulfone, polyethersulfone, ABS resin, phenol resin, epoxy resin, urethane resin, melamine resin, isocyanate resin , Alkyd resins, silicone resins, thermosetting resins such as thermosetting acrylic resins, polyvinyl carbazole, polyvinyl anthracene, polyvinyl pyrene, and the like. These may be used individually by 1 type and may use 2 or more types together.

Examples of the antioxidant in the photosensitive layer include phenolic compounds, paraphenylenediamines, hydroquinones, organic sulfur compounds, and organic phosphorus compounds.
Examples of the phenol compound include 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, stearyl-β- (3, 5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2'-methylene-bis- (4-methyl-6-t-butylphenol), 2,2'-methylene-bis- (4-ethyl- 6-t-butylphenol), 4,4′-thiobis- (3-methyl-6-tert-butylphenol), 4,4′-butylidenebis- (3-methyl-6-tert-butylphenol), 1,1,3 -Tris- (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxy Ben ) Benzene, tetrakis- [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane, bis [3,3′-bis (4′-hydroxy-3 ′) -T-butylphenyl) butyric acid] cricol ester, tocopherols and the like.
Examples of the paraphenylenediamines include N-phenyl-N′-isopropyl-p-phenylenediamine, N, N′-di-sec-butyl-p-phenylenediamine, N-phenyl-N-sec-butyl- Examples include p-phenylenediamine, N, N′-di-isopropyl-p-phenylenediamine, N, N′-dimethyl-N, N′-di-t-butyl-p-phenylenediamine, and the like.
Examples of the hydroquinones include 2,5-di-t-octyl hydroquinone, 2,6-didodecyl hydroquinone, 2-dodecyl hydroquinone, 2-dodecyl-5-chlorohydroquinone, 2-t-octyl-5-methyl. Examples include hydroquinone and 2- (2-octadecenyl) -5-methylhydroquinone.
Examples of the organic sulfur compounds include dilauryl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, ditetradecyl-3,3′-thiodipropionate, and the like. .
Examples of the organic phosphorus compounds include triphenylphosphine, tri (nonylphenyl) phosphine, tri (dinonylphenyl) phosphine, tricresylphosphine, tri (2,4-dibutylphenoxy) phosphine, and the like.

  These compounds are known as antioxidants such as rubbers, plastics and fats and oils, and commercially available products can be easily obtained. As addition amount of the said antioxidant, 0.01 mass%-10 mass% are preferable with respect to the total mass of the layer to add.

  As the plasticizer in the photosensitive layer 12, those used as plasticizers for general resins such as dibutyl phthalate and dioctyl phthalate can be used as they are, and the amount used is 0 parts by mass with respect to 100 parts by mass of the binder resin. About 30 parts by mass is appropriate.

  Further, a leveling agent may be added in the photosensitive layer 12. As the leveling agent, for example, silicone oils such as dimethyl silicone oil and methylphenyl silicone oil; polymers having a perfluoroalkyl group in the chain, or oligomers are used. The amount of the leveling agent used is preferably 0 to 1 part by mass with respect to 100 parts by mass of the binder resin.

The image forming process of this embodiment will be described as a so-called negative-positive process.
The photoreceptor 1 having the photoconductive layer is uniformly charged to a negative polarity by the charging process of the charging device 2. When charging the photosensitive member 1 by the charging device 2 is performed, the charging roller 20 from the voltage applying unit, a photosensitive member 1 maximum charge potential V supply electric quantity so as to charge up to ₀ Q is the relationship (1) A charging voltage of an appropriate magnitude that satisfies the above is applied. At this time, electric charge is supplied from the charging roller 20 to the photoconductor 1, but excess charge exceeding the charge that can be held by the photoconductor 1 passes through the photoconductor 1 and becomes a leak current, and finally is grounded. Flows to the electrode. Thus the surface potential of the photosensitive member 1 becomes constant at the maximum charge potential V _0.

  The charged photoreceptor 1 is formed with a latent image by the laser beam L irradiated by the writing device 3 such as a laser optical system (the absolute value of the exposed portion potential is lower than the absolute value of the non-exposed portion potential). Done. Laser light L is emitted from a semiconductor laser and scans the surface of the photoconductor 1 in the direction of the rotation axis of the photoconductor 1 by a polygonal polygon mirror that rotates at high speed.

  The electrostatic latent image formed in this way is developed with the developer supplied onto the developing sleeve 40 of the developing device 4 to form a toner image. At the time of developing the electrostatic latent image, a voltage of an appropriate magnitude or a developing bias in which an alternating voltage is superimposed thereon is applied to the developing sleeve 40 from the voltage applying device to the developing sleeve 40. Is done. Due to the action of the developing electric field formed by the developing bias, the negatively charged toner on the developing sleeve 40 moves to the latent image portion (exposure portion) to form a toner image.

  The toner images formed on the photoreceptors 1Y, 1C, 1M, and 1K of the respective colors in this manner are sequentially transferred onto the intermediate transfer belt 5 by the primary transfer rollers 52Y, 52C, 52M, and 52K. At this time, a positive potential having a polarity opposite to the toner charging polarity is applied to each primary transfer roller 52 as a primary transfer bias.

  The superimposed toner image primarily transferred onto the intermediate transfer belt 5 is collectively transferred by a secondary transfer roller 53 onto a recording material such as paper fed from the paper feeding device 200. The recording material fed from the selected paper feed cassette of the paper feed device 200 is temporarily stopped by the pair of registration rollers to correct the oblique shift, and then is transferred to the secondary transfer portion of the secondary transfer roller 53 at a predetermined timing. Be transported. The recording material onto which the superimposed images have been transferred is sent to the fixing device 7 where the toner image is fixed by heat and pressure. After the fixing, the recording material is discharged and stacked on the discharge tray 8 by a pair of discharge rollers.

The toner remaining on the photoreceptor 1 after the primary transfer is removed and collected by the cleaning device 6, and the toner remaining on the intermediate transfer belt 5 after the secondary transfer is removed and collected by the intermediate transfer belt cleaning device. .
In the present embodiment, the image forming apparatus is configured to perform secondary transfer using the intermediate transfer belt 5, but is not limited thereto, and for example, a plurality of photosensitive members while conveying a recording material with a conveyance belt. One toner image may be sequentially transferred onto a recording material.

Next, an evaluation test performed for confirming the effect of the present invention will be described.
FIG. 4 is a table summarizing the conditions and evaluation results in Examples 1 to 9 and Comparative Examples 1 to 4 used in this evaluation test.
In this evaluation test, the charging potential V of the photosensitive member 1 is a direct current voltage applied to a charging device disposed in a testing machine (made by Ricoh, an image forming unit of imgio MP C4500 modified to a contact roller charging method). The surface potential of the photosensitive member charged by being applied and charged by this is measured using a surface potential meter (MODEL 344 manufactured by Trek).
The exposed portion potential VL of the photosensitive member 1 is the surface potential after the entire surface of the photosensitive member charged in this way is exposed by a writing device provided in a tester. Measured using MODEL 344).
The supplied charge amount Q is a passing area calculated from a current value measured between the photosensitive member 1 and the ground point based on the length of the charging region in the rotation axis direction of the photosensitive member 1 and the linear velocity of the photosensitive member 1. It is calculated by dividing by.
The electrostatic capacity of the photoconductor was measured by the method used in the process of calculating the electrostatic capacity of the photoconductor described in Patent Document 4.

The initial image quality in this evaluation test is roughly the quality of the image formed on the first to tenth sheets. The image quality after 50000 sheets refers to the quality of an image formed on the 50000th sheet.
As for the image quality, the recording material is formed by repeatedly forming a portion having a pixel density of 100% and a portion having 0% every 20 [mm] perpendicular to the recording material conveyance direction (recording material width direction). Immediately after the belt-like image having a length of 150 mm in the conveying direction, an image pattern in which a 2 × 2 full-tone image having a pixel density of 25% is formed is used. This is a visual evaluation of the presence or absence of uneven glossiness and the presence or absence of other defects. The image quality after 50000 sheets is the quality of an image whose stability after use over time was confirmed by re-evaluating the quality of the image after passing 50000 sheets of a text chart with a pixel density of 5 [%].

The evaluation of the ghost image in this evaluation test is as follows.
○: Excellent (level at which ghost images cannot be detected over the entire surface)
△: Level where there is no problem in practical use (level at which ghost images can be detected slightly when viewed alongside ○)
×: Unusable (level that can clearly detect ghost images by itself)
Evaluation of gloss unevenness in this evaluation test is as follows.
○: Extremely excellent (level where gloss unevenness in the image area cannot be detected over the entire surface)
△: Level where there is no problem in practical use (level at which slight gloss unevenness in the image area can be detected when viewed alongside ○)
×: Cannot be used (level that can clearly detect gloss unevenness in the image area by itself)

  Hereinafter, the preconditions of Examples 1 to 9 and Comparative Examples 1 to 4 used in this evaluation test will be described.

[Example 1]
<Creation of electrophotographic photoreceptor A>
An aluminum cylinder having an outer diameter of 40 [mm] and a wall thickness of 0.8 [mm] was used as the conductive cylindrical support. On this aluminum cylinder, an undercoat layer coating solution, a charge generation layer coating solution, and a charge transport layer coating solution having the following composition are successively applied by dip coating and drying. An electrophotographic photosensitive member A was obtained by forming a pulling layer, a 0.2 [μm] charge generation layer, and a charge transport layer of about 30 [μm].

An undercoat layer coating solution having the following composition was dip-coated on the aluminum cylinder, and then heated and dried at 120 [° C.] for 25 minutes to form an undercoat layer of 15 [μm].
Alkyd resin 6 parts (Beccosol 1307-60-EL, manufactured by Dainippon Ink & Chemicals, Inc.)
Melamine resin 4 parts (Super Becamine G-821-60, manufactured by Dainippon Ink & Chemicals, Inc.)
N-type semiconductor Aluminum-doped zinc oxide 25 parts (Pazet CK, manufactured by Hakusui Tech Co., Ltd.)
Charge accepting material 1,2-dihydroxy-9,10-anthraquinone 0.6 part Titanium oxide 15 parts (CR-EL, manufactured by Ishihara Sangyo Co., Ltd.)
200 parts of methyl ethyl ketone

  After dip-coating the coating solution for charge generation layer having the following composition on the undercoat layer, followed by heating and drying at 120 [° C.] for 20 minutes, the heating rate is 5 [° C.] per minute at 180 [° C.]. The temperature was raised to 50 ° C. and held for another 15 minutes, whereby the tetrabenzoporphyrin precursor was thermally converted to tetrabenzoporphyrin to form a 0.2 [μm] charge generation layer.

ポリビニルブチラール ０．１部
（エスレックＢＭ−Ｓ、積水化学工業社製）
テトラヒドロフラン ５０部 2 parts of tetrabenzoporphyrin precursor of the following chemical formula (1)

Polyvinyl butyral 0.1 part (ESREC BM-S, manufactured by Sekisui Chemical Co., Ltd.)
50 parts of tetrahydrofuran

下記化学式（３）で表されるフラーレン誘導体 ０．５部

ビスフェノールＺポリカーボネート ９部
（パンライトＴＳ−２０５０：帝人化成社製）
シリコーンオイル ０．００２部
（ＫＦ−５０、信越化学工業社製）
テトラヒドロフラン １００部 A coating solution for charge transport layer having the following composition is dip coated on the charge generation layer, and then heated and dried at 135 [° C.] for 20 minutes to form a charge transport layer of 30 [μm] to form an electrophotographic photoreceptor A. Got.
9 parts of a charge transport material represented by the following structural formula (D-1)

0.5 part of fullerene derivative represented by the following chemical formula (3)

9 parts of bisphenol Z polycarbonate (Panlite TS-2050: manufactured by Teijin Chemicals Ltd.)
0.002 part of silicone oil (KF-50, manufactured by Shin-Etsu Chemical Co., Ltd.)
Tetrahydrofuran 100 parts

The coating layer thickness of the obtained electrophotographic photoreceptor A was 45.2 [μm] on average.
The electrostatic capacity of this electrophotographic photosensitive member A was 118 [pF / cm ² ] as measured by the method of Patent Document 4. The electrophotographic photoreceptor A was provided with flanges at both ends.

<Creation of toner 1>
First, a mixture having the following composition was kneaded for 30 minutes with a two-roll kneader and then pulverized and classified using a mechanical pulverizer / airflow classifier to obtain a toner base.
79.5 parts of partially crosslinked polyester resin (ethylene oxide addition alcohol of bisphenol A, propylene oxide addition alcohol of bisphenol A, terephthalic acid, trimellitic acid condensation polymer, Mw = 15000, glass transition point = 61 [° C.])
Carbon black 15 parts Zirconium salt of di-tert-butylsalicylic acid 0.6 parts Carnauba wax; manufactured by Noda Wax Co. 5 parts Further, 1 part of hydrophobic silica fine particles and 1 part of hydrophobic titanium oxide fine particles per 100 parts of toner base Toner 1 was obtained by mixing for 2 minutes with a Henschel mixer.

The particle size distribution of the toner 1 was measured with a Coulter counter TA2, and the weight average diameter D4 was 6.5 [μm]. Further, when the toner 1 was measured with a flow tester (CFT-500 manufactured by Shimadzu Corporation, load 10 [kg], temperature increase rate 3.0 [° C./min]), the outflow start temperature T _fb was 94.8 [° C. The outflow temperature T _1/2 was 118.1 [° C.], and the outflow end temperature T _end was 125.4 [° C.].

<Creation of carrier 1>
First, the following formulation was dispersed with a homomixer for 30 minutes to prepare a coating solution for forming a coat layer.
Acrylic resin solution (solid content = 50% by weight) 60 parts Guanamin solution (solid content = 70% by weight) 15 parts Straight silicone resin (solid content = 20%) 150 parts Dibutyltin diacetate 1.5 parts Alumina particles (number average particles) Diameter = 0.3 [μm]) 100 parts Carbon black 4 parts Aminosilane 2.0 parts Toluene 1500 parts Then, this is applied to the surface of 5000 parts of manganese ferrite core material having an average particle diameter of 35 [μm] by a fluidized bed type spray coater. After coating, carrier 1 was obtained by heating for 1 hour at an ambient temperature of 150 [° C.].

  When the particle size distribution of the carrier 1 was measured with a Microtrac particle size distribution analyzer (Model X100 manufactured by Microtrac), the weight average particle diameter (D4) was 36.1 [μm], and the number average diameter (D1) was 34. 0.7 [μm].

<Creation of two-component developer>
920 parts of the carrier and 80 parts of the toner were mixed with a turbula mixer for 1 minute to obtain a two-component developer.

<Checking image quality>
The electrophotographic photosensitive member A is set in a black process cartridge in the testing machine, a two-component developer using toner 1 is used as a toner, and the charging voltage applied to the electrophotographic photosensitive member A from the charging device, that is, the charging roller The direct current voltage was adjusted so that the surface potential was −400 [V], the development bias voltage was adjusted as appropriate, and image evaluation was performed according to the above procedure. At this time, the surface potential after the transfer of the electrophotographic photosensitive member A was not neutralized.

[Example 2]
<Creation of electrophotographic photoreceptor B>
In the same manner as in the electrophotographic photoreceptor A, except that the coating conditions were changed from the electrophotographic photoreceptor A, the thickness of the undercoat layer was 12 [μm], and the thickness of the charge transport layer was 40 [μm]. Photoreceptor B was prepared.

<Checking image quality>
The electrophotographic photosensitive member B is set in a black process cartridge in the test machine, a two-component developer using toner 1 as a toner is used, and a DC voltage is applied so that the surface potential of the charging roller becomes −500 [V]. The image was evaluated according to the procedure described above after adjusting the development bias voltage as appropriate. At this time, the surface potential after the transfer of the electrophotographic photosensitive member B was not neutralized.

[Example 3]
<Creation of electrophotographic photoreceptor C>
In the same manner as in the electrophotographic photoreceptor A, except that the coating conditions were changed from the electrophotographic photoreceptor A, the thickness of the undercoat layer was 20 [μm], and the thickness of the charge transport layer was 20 [μm]. Photoconductor C was prepared.

<Checking image quality>
The electrophotographic photosensitive member C is set in a black process cartridge in the test machine, a two-component developer using toner 1 is used as a toner, and a DC voltage is applied so that the surface potential of the charging roller becomes −250 [V]. The image was evaluated according to the procedure described above after adjusting the development bias voltage as appropriate. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

[Example 4]
<Creation of electrophotographic photoreceptor D>
In the same manner as in the electrophotographic photoreceptor A, except that the coating conditions are changed from the electrophotographic photoreceptor A, the thickness of the undercoat layer is 8 [μm], and the thickness of the charge transport layer is 45 [μm]. Photosensitive member D was prepared.

<Checking image quality>
The electrophotographic photosensitive member D is set in a black process cartridge in the test machine, a two-component developer using toner 1 is used as a toner, and a DC voltage is applied so that the surface potential of the charging roller becomes −500 [V]. The image was evaluated according to the procedure described above after adjusting the development bias voltage as appropriate. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

[Example 5]
<Creation of electrophotographic photoreceptor E>
In the same manner as in the electrophotographic photosensitive member A, except that the coating conditions are changed from the electrophotographic photosensitive member A, the thickness of the undercoat layer is 22 [μm], and the thickness of the charge transporting layer is 15 [μm]. Photoconductor E was prepared.

<Checking image quality>
The electrophotographic photosensitive member E is set in a black process cartridge in the test machine, a two-component developer using toner 1 is used as a toner, and a DC voltage is applied so that the surface potential of the charging roller becomes −250 [V]. The image was evaluated according to the procedure described above after adjusting the development bias voltage as appropriate. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

[Example 6]
In Example 6, in order to confirm a suitable upper limit of the supplied charge amount Q with respect to the electrostatic capacity and the surface potential of the photosensitive member, the electrophotographic photosensitive member A is set in the black process cartridge in the test machine, and the toner is used as the toner. Using the two-component developer using No. 1, the DC voltage was adjusted so that the surface potential of the charging roller was −450 [V], the developing bias voltage was adjusted appropriately, and image evaluation was performed according to the above procedure. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

[Comparative Example 1]
In Comparative Example 1, the electrophotographic photosensitive member A is set in the black process cartridge in the test machine in order to confirm the influence when the supplied charge amount Q on the electrostatic capacity and surface potential of the photosensitive member exceeds a suitable upper limit. Then, using a two-component developer using toner 1 as the toner, adjusting the DC voltage so that the surface potential of the charging roller becomes −500 [V], adjusting the developing bias voltage as appropriate, and performing the image according to the above procedure. Evaluation was performed. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

[Example 7]
In Example 7, in order to confirm the preferable lower limit of the supplied charge amount Q with respect to the electrostatic capacity and the surface potential of the photoconductor, the electrophotographic photoconductor A is set in the black process cartridge in the test machine, and the toner is used as the toner. Using the two-component developer using No. 1, the DC voltage was adjusted so that the surface potential of the charging roller was −310 [V], the developing bias voltage was adjusted appropriately, and image evaluation was performed according to the above procedure. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

[Comparative Example 2]
In Comparative Example 2, the electrophotographic photosensitive member A was set in the black process cartridge in the test machine in order to confirm the influence when the supplied charge amount Q with respect to the electrostatic capacity and the surface potential of the photosensitive member was below a suitable lower limit. Then, using a two-component developer using toner 1 as the toner, adjusting the DC voltage so that the surface potential of the charging roller becomes −200 [V], adjusting the developing bias voltage appropriately, and adjusting the image according to the above procedure. Evaluation was performed. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

[Example 8]
<Creation of toner 2>
The partially cross-linked polyester resin of the toner base formulation was the same as that of the toner 1 except that a resin having a molecular weight Mw = 16500 and a resin having a molecular weight Mw = 12000 were premixed at a weight ratio of 90/10. Thus, Toner 2 was obtained.
When the toner 2 was measured with a flow tester (CFT-500 manufactured by Shimadzu Corporation, load 10 [kg], temperature increase rate 3.0 [° C./min]), the outflow start temperature T _fb was 95.5 [° C.]. Yes, 1/2 outlet temperature _{T 1/2} is 119.5 [° C.], the flow ending temperature _{T end} was 127.1 [° C.].

<Checking image quality>
The electrophotographic photosensitive member A is set in a black process cartridge in the test machine, a two-component developer using toner 2 is used as a toner, and a DC voltage is applied so that the surface potential of the charging roller becomes −400 [V]. The image was evaluated according to the procedure described above after adjusting the development bias voltage as appropriate. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

[Example 9]
<Creation of toner 3>
The partially cross-linked polyester resin of the toner base formulation was the same as that of the toner 1 except that a resin having a molecular weight Mw = 15500 and a resin having a molecular weight Mw = 11000 were premixed at a weight ratio of 85/15. Thus, Toner 3 was obtained.
When the toner 3 was measured with a flow tester (CFT-500 manufactured by Shimadzu Corporation, load 10 [kg], temperature rising rate 3.0 [° C./min]), the outflow start temperature T _fb was 94.2 [° C.]. Yes, 1/2 outlet temperature _{T 1/2} is 115.8 [° C.], the flow ending temperature _{T end} was 122.8 [° C.].

<Checking image quality>
The electrophotographic photosensitive member A is set in a black process cartridge in the test machine, a two-component developer using toner 3 is used as a toner, and a DC voltage is applied so that the surface potential of the charging roller becomes −400 [V]. The image was evaluated according to the procedure described above after adjusting the development bias voltage as appropriate. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

[Comparative Example 3]
<Creation of toner 4>
The partially cross-linked polyester resin of the toner base formulation was the same as that of the toner 1 except that a resin having a molecular weight Mw = 17000 and a resin having a molecular weight Mw = 12000 were premixed at a weight ratio of 90/10. Thus, toner 4 was obtained.
When the toner 4 was measured with a flow tester (CFT-500 manufactured by Shimadzu Corporation, load 10 [kg], temperature rising rate 3.0 [° C./min]), the outflow start temperature T _fb was 95.9 [° C.]. Yes, 1/2 outlet temperature _{T 1/2} is 120.8 [° C.], the flow ending temperature _{T end} was 128.9 [° C.].

<Checking image quality>
The electrophotographic photosensitive member A is set in a black process cartridge in the test machine, a two-component developer using toner 4 is used as a toner, and a DC voltage is applied so that the surface potential of the charging roller becomes −400 [V]. The image was evaluated according to the procedure described above after adjusting the development bias voltage as appropriate. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

[Comparative Example 4]
<Creation of toner 5>
The partially cross-linked polyester resin of the toner base formulation was the same as that of the toner 1 except that a resin having a molecular weight Mw = 14500 and a resin having a molecular weight Mw = 16000 were premixed at a weight ratio of 80/20. Thus, Toner 5 was obtained.
When the toner 5 was measured with a flow tester (CFT-500 manufactured by Shimadzu Corporation, load 10 [kg], temperature increase rate 3.0 [° C./min]), the outflow start temperature T _fb was 95.5 [° C.]. Yes, 1/2 outlet temperature _{T 1/2} is 119.5 [° C.], the flow ending temperature _{T end} was 127.1 [° C.].

<Checking image quality>
The electrophotographic photosensitive member A is set in a black process cartridge in the test machine, a two-component developer using toner 5 is used as a toner, and a DC voltage is applied so that the surface potential of the charging roller is −400 [V]. The image was evaluated according to the procedure described above after adjusting the development bias voltage as appropriate. At this time, the surface potential after the transfer of the electrophotographic photosensitive member C was not neutralized.

Next, the results of this evaluation test will be described.
In Comparative Examples 1 to 4 that do not satisfy at least one of the relational expressions (1) to (3), a ghost image due to an afterimage potential of the photoreceptor or occurrence of uneven gloss after use over time is recognized, and image quality deteriorates. Became prominent. On the other hand, in Examples 1 to 9 satisfying the relational expressions (1) to (3), such deterioration of the image quality was not recognized.
From the results of this evaluation test, it was confirmed that by satisfying at least the relational expressions (1) to (3), it is possible to suppress the occurrence of gloss unevenness after use over time while suppressing the ghost image.

  Further, when Examples 1 to 3 are compared with Examples 4 and 5, the absolute value V of the charging potential of the photoconductor is an Example 4 that deviates from the Examples 1 to 3 which is a more preferable range. In No. 5, there was a case in which a slight deterioration tendency was observed in the image after initial or continuous paper feeding. Therefore, it has been shown that it is preferable that the charged potential after charging be in the range of 200 [V] to 400 [V].

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A latent image carrier such as a photosensitive member 1 that carries a latent image and moves on the surface; a charging unit such as a charging device 2 that performs a charging process for uniformly charging the surface of the latent image carrier; A latent image forming means such as a writing device 3 that forms a latent image according to image information by lowering the absolute value of the surface potential of the latent image carrier charged by the means, and formed on the surface of the latent image carrier. A developing unit such as a developing device 4 that performs a developing process for attaching toner to the latent image formed, and a toner image formed on the surface of the latent image carrier by the developing process of the developing unit are finally transferred onto a recording material. A transfer unit such as an intermediate transfer belt 5; and a fixing unit such as a fixing device 7 that performs a fixing process for fixing the toner image transferred onto the recording material by the transfer unit to the recording material by the action of heat and pressure. In the image forming apparatus, the electrostatic latent image carrier The amount is C, the absolute value of the maximum potential after charging treatment can take a surface potential of the latent image bearing member of the charging unit and V _0, the unit to be supplied to the latent image bearing member by a charging process of the charging means When the absolute value of the supplied charge amount per area is Q, the following relational expression (1) is satisfied, the load is 10 [kg], and the heating rate is 3.0 [° C./min]. When the outflow start temperature of the toner used in the developing process by the developing means is T _fb , the _1/2 outflow temperature is T _1/2 , and the outflow end temperature is T _{end as} measured by an elevated flow tester, The relational expressions (2) and (3) are satisfied.
C × V ₀ <Q ≦ 1.5 × C × V ₀ (1)
T _1/2 −T _fb ≦ 24.0 (2)
T _end -T _1/2 ≧ 7.0 (3)

In the relational expression (1), C × V ₀ is a product of the electrostatic capacity C of the latent image carrier and the maximum charged potential V _{0 of} the latent image carrier, and the surface potential of the latent image carrier. Means the minimum supply charge amount (necessary supply charge amount) Q ₀ required to set the maximum charging potential V ₀ . Therefore, in this embodiment, the charging process line as the absolute value of the supply amount of charge (amount of supplied charge) Q becomes greater than the required supply amount of charge Q ₀ per unit area to be supplied to the latent image bearing member by a charging process In other words, the surface potential of the latent image carrier after charging takes a maximum charging potential. Therefore, according to this aspect, even if there is a residual potential due to a past latent image pattern, the occurrence of charging potential unevenness can be suppressed. However, if the supplied charge amount Q is too large, electrostatic damage to the latent image carrier increases, and the durability life of the latent image carrier becomes serious. Therefore, as described above, the supplied charge amount Q is preferably to avoid the need supply the charge amount Q ₀ of 1.5 times or more.
Here, since the charging process is performed so that the surface potential of the latent image carrier after charging becomes the maximum charging potential, as described above, the latent image carrier is charged due to the characteristic change of the latent image carrier. A decrease in the absolute value of the potential occurs. When a decrease in the absolute value of the charging potential of the latent image carrier occurs, the latent image forming means lowers the absolute value of the surface potential of the latent image carrier after charging to form a latent image. As a result, the toner adhesion amount per unit area that adheres to the toner increases, resulting in a change in image quality such as gloss of the image.
Therefore, in this embodiment, by using the toner having the characteristics satisfying the relational expressions (2) and (3), the absolute potential of the charging potential of the latent image carrier due to the change in the characteristics of the latent image carrier. Even if the value decreases and the toner adhesion amount per unit area adhering to the latent image increases, the influence on the image quality change is reduced.
Specifically, the toner transferred onto the recording material is melted by heat and subjected to pressure during the fixing process, so that a part of the toner is filled into a gap (a minute space) existing in the recording material and becomes a recording material. It is fixed. At this time, as the toner adhesion amount per unit area increases, the amount of heat received by each individual toner decreases, so that the individual toner becomes difficult to melt. The difference in the melting degree of the toner mainly appears in the image quality as a difference in gloss of the image. Therefore, when the toner adhesion amount per unit area increases due to a change in the characteristics of the latent image carrier, the greater the difference in the degree of toner melting during the fixing process, the more the change in the image quality such as the glossiness of the image becomes noticeable. Become. According to this aspect, by using the toner having the characteristics satisfying the relational expression (2), the toner is easily melted early in the fixing process. Even if the toner adhesion amount increases, the difference in the melting degree of the toner decreases. Therefore, by using the toner having such characteristics, even when the toner adhesion amount per unit area is increased due to the characteristic change of the latent image carrier, the change in image quality such as gloss of the image is reduced.
On the other hand, satisfying the relational expression (2) makes it easier for the toner to flow and diffuse into the recording material when the toner further receives a heat amount during the fixing process and the toner further rises in temperature and melts. . If much of the toner flows and diffuses into the recording material, the amount of toner remaining on the surface of the recording material is reduced, and image quality deterioration such as a blur due to the surface properties of the recording material is likely to occur. Therefore, in this aspect, by further satisfying the relational expression (3), it is difficult to cause such image quality degradation such as blurring. That is, by satisfying the relational expression (3), as described above, the toner melted during the fixing process tends to stay on the surface of the recording material and can be prevented from moving into the recording material. Image quality deterioration can be suppressed to a practically sufficient level.

(Aspect B)
In the aspect A, the latent image carrier has an absolute value V _{0 of a} maximum potential that the surface potential of the latent image carrier can take after the charging process of the charging unit is in a range of 200 [V] to 400 [V]. It is the inside.
According to this, since no excessive stress is applied to the latent image carrier, the change in the charged potential with time is small, and the consumption of the latent image carrier is also small, so that the maintenance cost is low. Become.

(Aspect C)
In the aspect A or B, the charging unit applies a DC voltage to the roller-shaped charging member such as the charging roller 20 provided so as to be in contact with or close to the surface of the latent image carrier, and the roller-shaped charging member. And a voltage applying means.
According to this, the power supply cost which applies a charging voltage to a roller-shaped charging member can be reduced.

(Aspect D)
In any one of the aspects A to C, the latent image forming unit forms a latent image according to image information by binary control of whether or not to reduce the absolute value of the surface potential of the latent image carrier. It is a thing to do.
According to this, since the latent image portion potential does not take an intermediate value, in this aspect in which the latent image carrier potential is constant at the maximum charged potential V ₀ , a plurality of latent image portion potential values are obtained. Compared with the case of multi-level control that controls in stages, an image with stable quality can be obtained.

(Aspect E)
In any one of the aspects A to D, the potential of the surface portion of the latent image carrier is changed after the toner image is transferred from the latent image carrier and before the charging process of the charging unit. The electric potential changing means is not provided.
According to this, cost and power consumption can be further suppressed, and stress applied to the latent image carrier can be reduced.

(Aspect F)
In any one of the aspects A to E, at least the latent image carrier and the charging unit are integrally supported, and the process cartridge is detachable from the image forming apparatus main body.
According to this, since the reproduction | regeneration and reuse of a member become easy, an environmental load can be reduced.

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging apparatus 3 Writing apparatus 4 Developing apparatus 5 Intermediate transfer belt 6 Cleaning apparatus 7 Fixing apparatus 10 Support body 11 Undercoat layer 12 Photosensitive layer 20 Charging roller 40 Developing sleeves 41 and 42 Developer stirring and conveying mechanism 52 Primary transfer roller 53 Secondary transfer roller 60 Cleaning blade 100 Image forming device 120 Charge generation layer 121 Charge transfer layer 200 Paper feed device 300 Process cartridge

JP 2008-122440 A JP 2005-189319 A JP 2010-134153 A JP 2008-216704 A

Claims (6)

A latent image carrier that carries the latent image and moves on the surface;
A charging means for performing a charging process for uniformly charging the surface of the latent image carrier;
Latent image forming means for forming a latent image according to image information by reducing the absolute value of the surface potential of the latent image carrier charged by the charging means;
Developing means for performing development processing for attaching toner to the latent image formed on the surface of the latent image carrier;
Transfer means for finally transferring the toner image formed on the surface of the latent image carrier by the development processing of the developing means onto a recording material;
An image forming apparatus having a fixing unit that performs a fixing process for fixing the toner image transferred onto the recording material by the transfer unit to the recording material by the action of heat and pressure.
The electrostatic capacity of the latent image carrier is C, the absolute value of the maximum potential that can be taken by the surface potential of the latent image carrier after the charging process of the charging unit is V _0, and the latent image carrier is charged by the charging process. When the absolute value of the supplied charge amount per unit area supplied to the image carrier is Q, the following relational expression (1) is satisfied:
T _fb is the outflow start temperature of the toner used in the developing process, measured by an elevated flow tester under the measurement conditions of a load of 10 [kg] and a heating rate of 3.0 [° C./min], An image forming apparatus characterized by satisfying the following relational expressions (2) and (3) when a 1/2 outflow temperature is T1 _{/ 2} and an outflow end temperature is _Tend .
C × V ₀ <Q ≦ 1.5 × C × V ₀ (1)
T _1/2 −T _fb ≦ 24.0 (2)
T _end -T _1/2 ≧ 7.0 (3) The image forming apparatus according to claim 1.
In the latent image carrier, the absolute value V _{0 of the} maximum potential that the surface potential of the latent image carrier can take after the charging process of the charging unit is in the range of 200 [V] to 400 [V]. An image forming apparatus, comprising: The image forming apparatus according to claim 1 or 2,
The charging unit includes a roller-shaped charging member provided so as to be in contact with or close to the surface of the latent image carrier, and a voltage applying unit that applies a DC voltage to the roller-shaped charging member. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The latent image forming means forms a latent image according to image information by binary control of whether or not to reduce the absolute value of the surface potential of the latent image carrier. . The image forming apparatus according to any one of claims 1 to 4, wherein:
No potential changing means for changing the potential of the surface portion of the latent image carrier after the toner image is transferred from the latent image carrier and before the charging process of the charging means is provided. Image forming apparatus. The image forming apparatus according to any one of claims 1 to 5,
An image forming apparatus comprising: a process cartridge that integrally supports at least the latent image carrier and the charging unit and is detachable from the main body of the image forming apparatus.

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