JP2007147983A - Image forming apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the occurrence of a white streak in a gray image by using a conductive brush stipulated with the fiber density in a specified range, even if the conductive brush is used as a precharge member of a single layer type electrophotographic photoreceptor of positive electrostatic charge, and an image forming method using the same. <P>SOLUTION: The image forming apparatus is sequentially arranged with an electrostatic charging means 12, a developing means 14, a transferring means 15, and a destaticizing means 17 around a single layer type electrophotographic photoreceptor, in which the electrostatic charging means is the electrostatic charging means for electrostatically charging the single layer type electrophotographic photoreceptor to a plus polarity; a preelectrostatic charging means 2 equipped with the conductive brush 4 is arranged between the electrostatic charging means and the destaticizing means to bring the conductive brush into contact with the surface of the single layer type electrophotographic photoreceptor; and the fiber density of the conductive brush is specified to a value of ≤180 (kilo filament/inch<SP>2</SP>). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly to an image forming apparatus excellent in preventing occurrence of white stripes in a gray image even when a positively charged single layer type electrophotographic photosensitive member is used. The present invention relates to the image forming method used.

2. Description of the Related Art Conventionally, an image forming apparatus used for a printer, a copy, and the like forms a latent image by exposing a surface of an electrophotographic photosensitive member to charge the electrophotographic photosensitive member and the surface of the charged photosensitive member. An exposure unit, a developing unit that transfers toner to the latent image and develops, a transfer unit that transfers the toner onto a recording sheet to form an image, and a charge eliminating unit that eliminates residual potential remaining on the surface of the photoreceptor after transfer. And an image forming process in which the means are sequentially arranged.
Further, in such an image forming process, a reversal development method is adopted in which a toner image is transferred onto a recording sheet by applying a polarity opposite to the charged polarity on the surface of the photoreceptor.
When this reversal development method is used, there is a case where a so-called transfer memory occurs in which a potential having a polarity opposite to the charged polarity remains on the surface of the photosensitive member after the transfer.
This transfer memory is erased by the subsequent static elimination means. However, when it is used repeatedly, a small amount of the transfer memory that could not be sufficiently removed by the static elimination means is accumulated in the photoconductor, degrading the image characteristics. There was a problem.
In addition, when the contact charging method is adopted as the charging means, the overall configuration is simpler than that of the non-contact charging method, and no harmful substances such as ozone are generated. Further, there was a problem that it was difficult to apply to a single layer type electrophotographic photoreceptor excellent in productivity because a sufficiently charged saturated region could not be obtained.

Therefore, in order to solve such a problem, as shown in FIG. 10, an image forming apparatus employing a reversal development method, in which a contact primary charging roller 102, a developing unit 104, a transfer unit 106, In the image forming apparatus 100 including the pre-exposure lamp 109, the contact type pre-charging member 108 that is charged to the same polarity as the charging roller 102 is provided on the upstream side of the charging roller 102, so that it is opposite to the contact type primary charging roller. There has been proposed an image forming apparatus capable of erasing a transfer memory by pulling up the surface of a photosensitive member charged to polarity to the same polarity by a pre-charging member. (For example, refer to Patent Document 1.)
Japanese Patent Laid-Open No. 6-83249 (Claims, FIG. 1)

  However, since the charging roller in the image forming apparatus of Patent Document 1 adopts a negative charging type that applies a negative polarity, this image forming apparatus is more positively charged in the photosensitive layer. When it was applied to the charging type, there was a problem that it was difficult to erase the transfer memory. In order to erase the transfer memory, it has been necessary to set the applied voltage between the pre-charging member and the photosensitive member to a larger value. As a result, when a conductive brush is used as the pre-charging member, particularly when a gray image is printed due to abnormal discharge caused by non-uniform contact between conductive brush fibers constituting the conductive brush, the image is printed on the image. There was a problem of white-spotting.

Accordingly, the inventors of the present invention have made extensive studies, and as a result of using a conductive brush whose fiber density is defined within a predetermined range as a pre-charging brush for erasing the transfer memory, abnormal discharge in the pre-charging brush is prevented. The present invention has been completed by finding that it is possible to prevent and suppress the occurrence of white stripes in a gray image.
That is, an object of the present invention is to use a conductive brush having a fiber density defined within a predetermined range even in the case of using a conductive brush as a pre-charging member in a positively charged single-layer electrophotographic photosensitive member. Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of white stripes in a gray image and an image forming method using the same.

According to the present invention, in the image forming apparatus in which the charging unit, the developing unit, the transfer unit, and the charge eliminating unit are sequentially arranged around the single layer type electrophotographic photosensitive member, the charging unit includes the single layer type electrophotographic photosensitive member. It is a charging means for charging a photographic photosensitive member to a positive polarity, and a pre-charging means having a conductive brush is disposed between the charging means and the discharging means, and the conductive brush is a single-layer type electrophotographic photosensitive member. An image forming apparatus, wherein the fiber density of the conductive brush is set to a value of 180 (kilofilament / inch ² ) (≈28 (kilofilament / cm ² )) or less. Can be provided to solve the above-mentioned problems.
That is, according to the image forming apparatus of the present invention, in a positively charged single-layer type electrophotographic photosensitive member, even when a conductive brush is used as a pre-charging member, the conductive density is regulated within a predetermined range. By using the conductive brush, it is possible to prevent the occurrence of abnormal discharge in the vicinity of the contact portion between the conductive brush and the photosensitive member surface. Therefore, it is possible to suppress the occurrence of white stripes in the gray image due to such abnormal discharge.
Further, FIG. 1 shows the appearance of white stripes in an actual gray image. When the conductive brush is thrust (reciprocated) in the axial direction of the photosensitive body, the white streak observed in this manner changes in a wavy shape corresponding to the movement, and is caused by the conductive brush. It can be understood that this occurred.

Further, in constituting the present invention, the material substance in the conductive brush fiber is preferably a polyamide resin or a polyester resin containing conductive particles.
With this configuration, since the conductive brush fiber has appropriate flexibility, the contact with the surface of the photoconductor can be made more uniform, and the wear of the surface of the photoconductor is reduced and long. It can also contribute to life extension.

Moreover, when comprising this invention, it is preferable to make the bristle length in a conductive brush fiber into the value within the range of 2-7 (mm).
By configuring in this way, it becomes easy to make the bending state of the conductive brush fibers uniform when in contact with the surface of the photoreceptor, so that uneven contact between the conductive brush fibers is suppressed. Can do.

In configuring the present invention, it is preferable to set the yarn resistance in the conductive brush fiber to a value of 1 × 10 ¹¹ (Ω · cm) or less.
With this configuration, since the charging voltage applied to the conductive brush can be suppressed within a predetermined range, abnormal discharge near the contact portion between the conductive brush and the photoreceptor surface can be more effectively prevented. However, the transfer memory can be effectively erased.

Further, in constituting the present invention, the conductive brush fibers are sewn into the conductive woven fabric, and the conductive woven fabric sewn with the conductive brush fibers is fixed to the conductive base material. It is preferable.
By comprising in this way, since it becomes easy to hold | maintain the fiber direction in each conductive brush fiber in a uniform state, the non-uniform contact between conductive brush fibers can be suppressed. As a result, it is possible to more effectively prevent abnormal discharge in the vicinity of the contact portion between the conductive brush and the photoreceptor surface.

In configuring the present invention, a stainless steel plate is preferably used as the conductive substrate.
By comprising in this way, the electroconductive brush provided with the outstanding electroconductivity and mechanical strength can be obtained.

In constituting the present invention, the charging means is preferably a contact charging type charging means.
With this configuration, it is possible to provide an image forming apparatus with a simpler configuration, less ozone generation, and excellent environmental resistance.

In constituting the present invention, it is preferable to set the initial charging potential of the single-layer electrophotographic photosensitive member to a value of 400 (V) or more.
With this configuration, the conductive brush can erase the transfer memory while maintaining desired image characteristics, and can exhibit an excellent charge eliminating effect.

In another aspect of the present invention, an image is formed using an image forming apparatus in which a charging unit, a developing unit, a transfer unit, and a charge eliminating unit are sequentially arranged around a single-layer electrophotographic photosensitive member. In the method, the single-layer electrophotographic photosensitive member is charged to a positive polarity by a charging unit, a pre-charging unit including a conductive brush is disposed between the charging unit and the charge eliminating unit, and the conductive brush is a single unit. The image forming method is characterized in that it is brought into contact with the surface of the layer type electrophotographic photosensitive member, and the fiber density of the conductive brush is set to a value of 180 (kilofilament / inch ² ) or less.
That is, according to the image forming method of the present invention, in a positively charged single-layer type electrophotographic photosensitive member, even when a conductive brush is used as a pre-charging member, the conductive density is regulated within a predetermined range. By using the conductive brush, it is possible to prevent the occurrence of abnormal discharge in the vicinity of the contact portion between the conductive brush and the photosensitive member surface. Therefore, it is possible to suppress the generation of white stripes in the gray image due to such abnormal discharge and continuously form high quality images.

[First embodiment]
The first embodiment of the present invention is an image forming apparatus in which a charging unit, a developing unit, a transfer unit, and a charge eliminating unit are sequentially arranged around a single-layer electrophotographic photosensitive member. It is a charging means for charging a single layer type electrophotographic photosensitive member to a positive polarity, and a precharging means having a conductive brush is disposed between the charging means and the charge eliminating means, and the conductive brush is a single layer type. The image forming apparatus is characterized in that it is brought into contact with the surface of the electrophotographic photosensitive member, and the fiber density of the conductive brush is set to a value of 180 (kilofilament / inch ² ) or less.
Hereinafter, a first embodiment relating to an image forming apparatus of the present invention will be specifically described with reference to the drawings as appropriate.

Image forming apparatus 1. Basic Configuration FIG. 2 shows a basic configuration of an image forming apparatus according to the present invention. The image forming apparatus 10 includes a drum-type single-layer electrophotographic photosensitive member (hereinafter also referred to as a photosensitive member) 11, and a rotation direction indicated by an arrow A around the photosensitive member 11. Along with the charging means 12, an exposure means 13 for forming a latent image on the surface of the photoreceptor, a developing means 14 for developing the latent image by attaching toner to the surface of the photoreceptor, and recording the toner A transfer member 15 for transferring onto the paper 20, a cleaning device 17 for removing residual toner on the surface of the photoreceptor, and a conductive brush 4 for erasing a transfer memory generated by the transfer unit are included as conductive members. The pre-charging unit 2 and the neutralizing unit 18 for removing the residual potential on the surface of the photoreceptor are sequentially arranged.
The charging unit 12 is connected to a power source 19 for applying a charging application voltage. The power source 19 can apply only a direct current component (DC), and can also be a superimposed voltage obtained by superimposing an alternating current component (AC) on the direct current component. At this time, the polarity of the power source 19 is connected so that the charging means 12 side is a positive electrode, whereby the image forming apparatus can be of a positive charging type.
A power source 22 is connected to the transfer means 15. The power source 22 is a power source to which a direct current component (DC) can be applied, and its polarity is connected so that the transfer means side is a negative electrode. By connecting in this way, the image forming apparatus can be a reversal developing type image forming apparatus.
When this reversal development method is employed, the surface of the photosensitive member charged to the positive electrode is reversely charged, and a transfer memory having a negative potential is generated on the surface. This transfer memory will be erased by the subsequent neutralization means 18, but if it cannot be erased sufficiently by this neutralization means, the charging uniformity by the charging means 12 will be affected, and charging characteristics will cause image characteristics. It becomes a factor to reduce.

2. Pre-charging means (1) Basic configuration Next, the pre-charging means 2 as means for erasing the transfer memory will be described. Note that a conductive brush is used as the conductive member in the precharging means of the present invention.
As shown in FIG. 2, the pre-charging unit 2 includes a conductive brush 4 that is in direct contact with the surface of the photoconductor 11 and a power source 6 that applies a predetermined voltage to the conductive brush. At this time, the power source 6 is connected so that the conductive brush 4 side becomes a positive electrode, and is configured to be applied with a polarity opposite to that of the transfer unit 15.
Further, the power source 6 can apply only a direct current component (DC) in accordance with the mode of the pre-charging means 2, and furthermore, in order to widen the charging saturation region and obtain stable charging characteristics, An alternating current component (AC) can be used as a superimposed voltage on the direct current component.

(2) Conductive Brush (2) -1 Basic Configuration FIG. 3 shows the basic configuration of the conductive brush in the present invention. The conductive brush 30 is basically composed of a conductive base material 34 connected to the power source 6 shown in FIG. 2 and conductive brush fibers 31 conductively fixed on the conductive base material 34. It is preferable that it is comprised.
(2) -2 Material The material of the conductive brush fiber constituting the conductive brush used in the present invention is not particularly limited as long as it can charge the surface of the photoreceptor. It is preferable to use a polyamide resin or a polyester resin containing conductive particles.
The reason for this is that the conductive brush fiber having such a composition is provided with appropriate flexibility, so that the contact with the surface of the photoconductor can be made more uniform and the wear of the surface of the photoconductor is reduced. This is because it can contribute to a longer life.
In other words, by using the conductive brush fiber having the appropriate flexibility, the conductive brush fiber is appropriately curved, so that it can be contacted even with a cylindrical photosensitive member with a uniform pressing force. This is because it can.
Moreover, the electroconductivity can be easily adjusted by adjusting content of the electroconductive particle in electroconductive brush fiber. In addition, carbon etc. are mentioned as a material substance of the electroconductive particle used.

(2) -3 Fiber density Moreover, the fiber density in a conductive brush shall be 180 (kilofilament / inch < ² >) or less.
This is because, in a positively charged single-layer type electrophotographic photosensitive member, even when a conductive brush is used as a precharging member, the fiber density is set to a value of 180 (kilofilament / inch ² ) or less. This is because the occurrence of abnormal discharge in the vicinity of the contact portion between the conductive brush and the photoreceptor surface can be prevented. As a result, it is possible to suppress the occurrence of white stripes in the gray image due to such abnormal discharge.
That is, by setting the fiber density to a value of 180 (kilofilament / inch ² ) or less, a uniform and appropriate minute space can be more effectively formed between the conductive brush fibers constituting the conductive brush. This is because it can. By forming such a minute space, abnormal discharge resulting from uneven contact between the conductive brush fibers can be more effectively prevented, so that the discharge by the conductive brush is stabilized and more uniform charging is possible. It becomes.

Here, the relationship between the fiber density in the conductive brush and the number of white streaks in the gray image will be described with reference to FIG.
In the characteristic curve shown in FIG. 4, the horizontal axis represents the fiber density of the conductive brush, and the vertical axis represents the number of white streaks per 10 (cm) in the photoreceptor axial direction. As can be understood from this characteristic curve, it can be seen that when the fiber density is a value close to 0 (kilofilament / inch ² ), the number of white streak generation is almost zero. On the other hand, it can be seen that as the fiber density is increased from 0 (kilofilament / inch ² ), the number of white-skinned lines increases. Specifically, when the fiber density is a value of 180 (kilofilament / inch ² ) or less, the number of white muscles generated can be suppressed to almost zero, while the fiber density is 180 (kilofilament / inch2). If the value exceeds inch ² ), it can be seen that the number of white muscles is increasing rapidly.
Therefore, it is more preferably set to a value within the range of such fiber density of 50 to 150 (km filaments / inch ^2), and even more preferably to a value within the range of 70 to 120 (km filaments / inch ^2).

In addition, as shown in FIG. 3, it is preferable that each conductive brush fiber 31 is sewn into a conductive woven fabric 32 made of conductive fibers.
This is because the conductive brush fibers 31 are sewn into the conductive woven fabric 32 to form the conductive brush 30, whereby the density, fiber direction, and the like of the conductive brush fibers 31 become uniform. This is because abnormal discharge resulting from uneven contact between the brush fibers 31 can be more effectively prevented.

(2) -4 Single yarn fineness Moreover, it is preferable to make the single yarn fineness in the conductive brush fiber which comprises a conductive brush into the value more than 6 (denier) (≒ 0.66 (g / km)).
The reason for this is that in a positively charged single-layer electrophotographic photosensitive member, even when a conductive brush is used as the pre-charging member, by setting the single yarn fineness to a value of 6 (denier) or more, This is because the occurrence of abnormal discharge in the vicinity of the contact portion between the conductive brush and the surface of the photoreceptor can be prevented. As a result, it is possible to suppress the occurrence of white stripes in the gray image due to such abnormal discharge.
That is, by setting the single yarn fineness to a value of 6 (denier) or more, a uniform and appropriate minute space can be formed between the conductive brush fibers constituting the conductive brush. By forming such a minute space, abnormal discharge caused by non-uniform contact between the conductive brush fibers can be prevented, so that the discharge by the conductive brush is stabilized and uniform charging becomes possible.

Here, the relationship between the single yarn fineness in the conductive brush fiber which comprises a conductive brush, and the generation | occurrence | production number of white streak in a gray image is demonstrated using FIG.
In the characteristic curve shown in FIG. 5, the horizontal axis represents the single yarn fineness of the conductive brush fiber, and the vertical axis represents the number of white streaks per 10 (cm) in the photoreceptor axial direction. As can be understood from this characteristic curve, the number of white-streaks generated is very large in the range where the single yarn fineness is close to 0 (denier). On the other hand, as the single yarn fineness is changed from 0 (denier) to a larger value, the number of generated white muscles rapidly decreases. Specifically, it can be seen that by setting the single yarn fineness to a value of 6 (denier) or more, the number of white streak generation can be reduced to almost zero.
Therefore, the single yarn fineness is more preferably 8 to 30 (denier) or more, and further preferably 10 to 25 (denier) or more.

(2) -5 Hair length The hair length in the conductive brush fiber is preferably set to a value within the range of 2 to 7 (mm).
The reason for this is that by setting the length of the bristles to a value within the range of 2 to 7 (mm), it is easy to make the bending state of the conductive brush fibers uniform when contacting the surface of the photoreceptor. Therefore, uneven contact between the conductive brush fibers can be suppressed.
That is, when the length of the bristle is less than 2 (mm), when the photoconductor is cylindrical, the surface of the photoconductor becomes a curved surface, so that the conductive brush is uniformly contacted with the surface of the photoconductor. This is because it tends to be difficult. On the other hand, when the length of the bristle exceeds 7 (mm), uneven contact between the conductive brush fibers is likely to occur, and abnormal discharge occurs in the vicinity of the contact portion between the conductive brush and the photoreceptor surface. This is because it tends to be easier.
Therefore, it is more preferable to set the bristle length in the conductive brush fiber to a value within the range of 3 to 6 (mm), and it is even more preferable to set the value within the range of 4 to 5 (mm).

(2) -6 Conductive base material As a conductive base material having a role of fixing the conductive brush fiber to the surface and transmitting the current from the power source to the conductive brush fiber, the conductive base material is sufficient as the conductive base material. Although it will not restrict | limit especially if it has mechanical strength, For example, it is preferable to use metal plates, such as stainless steel, copper, and aluminum, and a stainless steel plate is especially preferable.
The reason for this is that a stainless steel plate is particularly excellent in conductivity and mechanical strength, so that deformation of the conductive brush is prevented and uniform and efficient pre-charging is possible.
Further, the fixing method between the conductive base material and the conductive brush fiber is not particularly limited as long as it is a method capable of firmly fixing each other while maintaining conductivity between each other. As shown in FIG. 3, it is preferable to use a conductive double-sided tape containing a conductive resin composition and a conductive adhesive 33 or the like.
The reason for this is that the conductive base material 34 and the conductive brush fiber 31 are exhibited while exhibiting excellent conductivity by using a conductive double-sided tape containing such a conductive resin composition and a conductive adhesive 33 or the like. This is because it is possible to bond firmly to the extent that there is no practical problem. Moreover, it is because the operation | work which fixes the electroconductive base material 34 and the electroconductive brush fiber 31 mutually becomes very easy, and manufacturing efficiency improves.

(2) -7 Shape Further, as the shape of the conductive brush, for example, it can be a rod shape or a cylindrical shape provided with a rotation mechanism, and further, a curved shape deformed along the curvature of the surface of the photoreceptor. It can also be. These shapes can be appropriately selected according to desired charging characteristics.

(2) -8 Mobility and Detachability Moreover, it is preferable that this conductive brush is movable. This is because, for example, when the electrophotographic photosensitive member is moved in the radial direction, the pressing force between the conductive member and the surface of the photosensitive member can be adjusted, and the charging characteristics can be easily controlled. is there.
At this time, the pressing force of the conductive member against the surface of the photosensitive member is preferably set to a value within the range of 0.1 to 100 (kgf / cm ² ).
When the conductive brush is moved in the radial direction of the electrophotographic photosensitive member, the biting ratio (K) of the conductive brush fiber represented by the following formula (1) to the surface of the photosensitive member is set to 0. A value of 3 or less is preferred.

(In formula (1), a is the distance (mm) between the conductive substrate and the electrophotographic photosensitive member, and b is the length (mm) of the conductive brush fiber.)

The reason for this is that when the biting ratio (K) exceeds 0.3, the conductive brush is excessively pressed against the photoconductor, so that the minute space between the conductive brush fibers constituting the conductive brush is small. This is because non-uniformity is formed, and abnormal discharge tends to occur between the conductive brush fibers.
Accordingly, the biting ratio is more preferably set to a value within the range of 0.05 to 0.25, and further preferably set to a value within the range of 0.1 to 0.2. After this, (ba) (mm) may be referred to as the amount of biting into the hair tip.

It is also preferable that the conductive brush be removable.
The reason for this is to facilitate member replacement. Furthermore, it is possible to easily cope with a case where the specification is changed to a configuration in which the generation of transfer memory is relatively small, such as when the applied voltage at the transfer means is small or when a laminated type photoconductor is used as the photoconductor. It is.

(2) -9 Charging characteristics Further, in the precharging means 2 in FIG. 2, the transfer memory generated by the transfer means can be erased by applying a predetermined voltage to the conductive brush 4 using the power source 6. .
At this time, as an application condition applied to the pre-charging means 2, the current density (I _b ) of the current flowing from the conductive brush 4 to the photoconductor 11 is preferably set to a value of 700 (μA / m ² ) or more. .
Here, FIG. 6 shows the current density (I _b ) of the current injected from the conductive brush and the transfer memory potential (V _t ) when a positively charged single layer type electrophotographic photosensitive member is used as the photosensitive member. The characteristic diagram showing the relationship between and is shown.
In FIG. 6, the horizontal axis represents the current density (I _b ) of the current injected from the conductive brush, and the vertical axis represents the transfer memory potential (V _t ).
That is, in the vertical axis, the upper side means that the transfer memory is erased by the pre-charging means, and the lower side means that the transfer memory is not sufficiently erased by the pre-charging means. is doing.
Further, curves (A) to (D) in FIG. 6 are characteristic curves when using conductive brushes made of conductive brush fibers having different yarn resistances. More specifically, the curves at 1 × 10 ^12.5 (Ω · cm), 1 × 10 ^10.5 (Ω · cm), 1 × 10 ^8.5 (Ω · cm), and 1 × 10 ^6.5 (Ω · cm) in this order. Represents.
In the present invention, the transfer memory potential (V _t ) is defined as the amount of change in the surface potential of the photoreceptor surface at the development position when continuous printing is performed.
More specifically, when a blank paper image is printed by continuously rotating the photoconductor, the surface potential of the photoconductor surface at the development position at the first round is set to (V ₁ ), and the third round the surface potential of the photosensitive member surface at the developing position when the when the _{(V 3), (V 1} ) - is defined as a value expressed by (V _3).

As can be understood from FIG. 6, the remaining transfer memory potential decreases as the current density (I _b ) increases, regardless of the value of the yarn resistance of the conductive brush fibers constituting the conductive brush. In particular, it can be said that the erase is stably performed in a range of 700 (μA / m ² ) or more.
Conversely, when the current density (I _b ) is excessively high, abnormal discharge may occur in the vicinity of the contact portion between the conductive brush and the surface of the photoreceptor, which may cause a problem in charging characteristics.
Therefore, the range of the current density (I _b ) is preferably a value in the range of 700 to 2000 (μA / m ² ), and a value in the range of 1000 to 1500 (μA / m ² ). It is more preferable.
In the present invention, the current density means a value obtained by dividing a current value by an application area per second. That is, when the current having the current value I (A) flows to the photosensitive member rotating at the shaft length L (mm) and the outer peripheral speed D (mm / sec), the current density is I / (L × D ) (ΜA / m ² ).

FIG. 7 is a characteristic diagram showing the relationship between the voltage applied to the conductive brush (V _b ) and the transfer memory potential (V _t ).
In this characteristic diagram, the horizontal axis represents the applied voltage (V _b ) to the conductive brush, and the vertical axis represents the transfer memory potential (V _t ).
That is, FIG. 7 corresponds to the current density (I _b ) in FIG. 6 converted to a voltage using the respective yarn resistance values of the characteristic curves (A) to (D).
As can be understood from FIG. 7, it can be said that the higher the value of the yarn resistance of the conductive brush fiber, the higher the voltage that needs to be applied to erase the transfer memory. In particular, when compared with the same applied voltage, it can be seen that when the yarn resistance of the conductive brush fiber exceeds 1 × 10 ¹¹ (Ω · cm), the erasure of the transfer memory potential becomes extremely insufficient.
Therefore, it is preferable that the yarn resistance of the conductive brush fiber is 1 × 10 ¹¹ (Ω · cm) or less. On the other hand, if the yarn resistance of the conductive brush fiber is excessively low, the triboelectric charge may not be sufficiently performed and the transfer memory may not be completely erased. The range is preferably a value in the range of 1 × 10 ³ to 1 × 10 ¹⁰ (Ω · cm), and a value in the range of 1 × 10 ⁵ to 1 × 10 ⁹ (Ω · cm) More preferably.

Moreover, it is preferable that the applied voltage (V _b ) to the conductive brush is a DC voltage of 1100 (V) or more. This is because, as shown in FIG. 7, the transfer memory potential (V _t ) can be lowered regardless of the specific resistance value of the conductive brush.
On the other hand, when the applied voltage (V _b ) is excessively increased, abnormal discharge may occur between the conductive brush and the photosensitive member, which may adversely affect the charging characteristics.
Therefore, the applied voltage (V _b ) is preferably set to a value within the range of 1100 to 3000 (V), and more preferably set to a value within the range of 1100 to 2000 (V).

When the current density of current injected from the conductive brush is I _b (μA / m ² ) and the current density of current injected from the transfer means is I _t (μA / m ² ), | I _The value represented by _b / I _t | is preferably 2 or more.
Here, in FIG. 8, when a conductive brush fiber having a predetermined yarn resistance is used, the current density (I _b ) of the current injected from the conductive brush, the transfer memory potential (V _t ), Is shown for each current density (I _t ) of current injected from the transfer means 15. The curve in FIG. 8 (E) ~ (G), the current density of the current injected from the transfer means (I _t) is ^{sequentially, -395 (μA / m 2)} , - 316 (μA / m 2 ), −237 (μA / m ² ).
FIG. 9 is a characteristic diagram in which the horizontal axis in FIG. 8 is converted to | I _b / I _t |.
As can be understood from these characteristic diagrams, the larger the absolute value of the current density (I _t ) of the current injected from the transfer means, the higher the transfer memory potential (V _t ), and more specifically, | I _b / I It can be seen that when the value represented by _t | is 2 or more, the transfer memory potential (V _t ) is sufficiently lowered.
That is, in the characteristic curve (E), when the absolute value of the current density (I _b ) of the current injected from the conductive brush is 790 or more, the transfer memory potential is lowered. In addition, the absolute value of I _b is 632 or more in the characteristic curve (F), and the absolute value of I _b is 474 or more in the characteristic curve (G).
Conversely, when the current density (I _b ) is excessively high, abnormal discharge may occur in the vicinity of the contact portion between the conductive brush and the surface of the photoreceptor, which may cause a problem in charging characteristics.
Therefore, the value represented by | I _b / I _t | is preferably set to a value in the range of 2.5 to 8.0, and more preferably set to a value in the range of 3.0 to 6.0. preferable.

3. In the present invention, the charging means for charging the surface of the photoreceptor to a predetermined potential is preferably a contact charging type charging means.
This is because the charging means is smaller than when a non-contact charging type such as corona charging is adopted, and does not generate harmful substances such as ozone generated during corona charging. This is because it is environmentally friendly.
On the other hand, although there are points that do not reach the non-contact charging type in terms of wear on the surface of the photoreceptor and charging uniformity, in the present invention, the fiber density in the conductive brush is set to a value within a predetermined range. Therefore, it can be used without deteriorating the image characteristics.
Further, it is preferable that the initial charging potential of the single-layer type electrophotographic photosensitive member by this charging means is a value of 400 (V) or more.
The reason for this is that although the transfer memory potential generated in the transfer means is increased by raising the initial charging potential to a predetermined value or more, the image unevenness can be suppressed by applying it to the image forming apparatus excellent in the charge eliminating effect in the present invention. This is because a desired image density can be obtained as it is.

Further, in the charging unit, it is preferable to use conductive rubber or conductive sponge as a member of the contact portion with the surface of the photoreceptor.
More specifically, an ionic conductive agent is added to semi-conductive polar rubber (ionic conductive rubber) such as epichlorohydrin rubber and acrylonitrile-butadiene copolymer (NBR), urethane rubber, acrylic rubber, silicone rubber, etc. Thus, ion conductive rubber or the like imparted with semiconductivity can be used. At this time, the volume resistivity is preferably set to a value in the range of 1 × 10 ³ to 1 × 10 ¹⁰ (Ω · cm).

[Second Embodiment]
In another aspect of the present invention, an image is formed using an image forming apparatus in which a charging unit, a developing unit, a transfer unit, and a charge eliminating unit are sequentially arranged around a single-layer electrophotographic photosensitive member. In the method, the single-layer electrophotographic photosensitive member is charged to a positive polarity by a charging unit, a pre-charging unit including a conductive brush is disposed between the charging unit and the charge eliminating unit, and the conductive brush is a single unit. The image forming method is characterized in that it is brought into contact with the surface of the layer type electrophotographic photosensitive member, and the fiber density of the conductive brush is set to a value of 180 (kilofilament / inch ² ) or less.
Hereinafter, the contents already described in the first embodiment will be omitted, and the second embodiment will be described focusing on differences from the first embodiment.

That is, in carrying out the image forming method of the second embodiment, an image forming apparatus 10 as shown in FIG. 2 can be suitably used.
Here, FIG. 2 is a schematic diagram showing the overall configuration of the image forming apparatus. Hereinafter, the operation will be described in order.
First, the photoconductor 11 of the image forming apparatus 10 is rotated at a predetermined process speed (circumferential speed) in the direction indicated by the arrow A, and then the surface is charged to a predetermined potential by the charging unit 12.
Next, the exposure unit 13 exposes the surface of the photoconductor 11 through a reflection mirror or the like while being optically modulated in accordance with image information. By this exposure, an electrostatic latent image is formed on the surface of the photoreceptor 11.
Next, based on the electrostatic latent image, latent image development is performed by the developing unit 14. The developing means 14 contains toner, and the toner adheres corresponding to the electrostatic latent image on the surface of the photoconductor 11 to form a toner image.
Further, the recording paper 20 is conveyed to the lower part of the photoconductor along a predetermined transfer conveyance path. At this time, a toner image can be transferred onto the recording material 20 by applying a predetermined transfer bias between the photoconductor 11 and the transfer means 15.

Next, the recording paper 20 on which the toner image has been transferred is separated from the surface of the photoconductor 11 by a separating unit (not shown) and conveyed to a fixing device by a conveying belt. Next, the toner image is fixed on the surface by being heated and pressed by the fixing device, and then discharged to the outside of the image forming apparatus 10 by a discharge roller.
On the other hand, the photoconductor 11 after the toner image is transferred continues to rotate, and residual toner (adhered matter) that has not been transferred to the recording paper 20 at the time of transfer is removed from the surface of the photoconductor 11 by the cleaning device 17 of the present invention. . In addition, the charge remaining on the surface of the photoconductor 11 is erased by the pre-charging means 2 including the conductive brush 4 as a conductive member, and is completely erased by irradiation of the static elimination light from the static eliminator 18. It will be used for image formation.
Therefore, by using the image forming apparatus of the present invention, it is possible to prevent the occurrence of abnormal discharge in the vicinity of the contact portion between the conductive brush and the photoreceptor surface. Therefore, it is possible to suppress the generation of white stripes in the gray image due to such abnormal discharge and continuously form high quality images.

[Example 1]
1. Preparation of electrophotographic photosensitive member 2.7 parts by weight of X-type metal-free phthalocyanine as a charge generating substance, 50 parts by weight of a stilbene amine compound as a hole transporting agent, 35 parts by weight of an azoquinone compound as an electron transporting agent, and a binder resin As described above, 100 parts by weight of bisphenol Z-type polycarbonate resin and 700 parts by weight of tetrahydrofuran were placed in a stirring vessel, and then mixed and dispersed in a ball mill for 50 hours to prepare a coating solution. Next, the obtained coating solution was applied on a conductive support composed of an alumite tube by a dip coating method, and then dried with hot air under conditions of 130 ° C. for 45 minutes, and a single layer type having a film thickness of 30 μm and a diameter of 30 mm An electrophotographic photoreceptor was obtained.

2. Preparation of conductive brush The conductive brush fiber is a single yarn fineness of 30 (denier) (450T / 15F), length of 3 (mm), and yarn resistance of 1 × 10 ^8.5 (Ω · cm). Nylon fiber was used. Such conductive nylon fibers were sewn into a woven fabric made of similar fibers to prepare a brush portion having a fiber density of 70 (kilofilament / inch ² ).
Next, the brush portion was bonded and fixed to a conductive base material made of a stainless steel plate using a conductive double-sided tape to create a conductive brush.

3. Evaluation (1) Evaluation of generation of white streak Evaluation of white streak generation was performed using an image forming apparatus equipped with the obtained photoreceptor and a conductive brush.
That is, the obtained photoconductor is mounted on a printer KM1500 modified device manufactured by Kyocera Mita Co., Ltd., and the conductive brush is pressed against the surface of the photoconductor so that the nip width is 5 mm and the hair end biting amount is 0.5 mm. Fixed.
Next, the photosensitive member was rotated at a peripheral speed of 110 (mm / sec). Further, a DC voltage of 1200 (V) was applied between the surface of the photoconductor and the charging roller to charge the surface of the photoconductor to about 400 (V).
Next, a direct current is applied between the transfer unit and the surface of the photosensitive member, and the current density (I _t ) of the current injected from the transfer unit is −237 (μA / m ² ) (current value conversion: −6 (ΜA)).
Next, a voltage of 1000 (V) was applied to the conductive brush, and a recording sheet was passed through to print a gray image. The number of white streaks per 10 (cm) in the drum axis direction in the gray image was measured. The obtained results are shown in Table 1.

(2) Transfer Memory Evaluation In addition, the transfer memory potential on the photoconductor when a gray image was printed under the same conditions as those in the above-described evaluation of the occurrence of white streak was measured and evaluated according to the following criteria. The obtained results are shown in Table 1.
○: The absolute value of the transfer memory potential (V) is less than 5.
Δ: The absolute value of the transfer memory potential (V) is a value of 5 or more and less than 8.
X: The absolute value of the transfer memory potential (V) is a value of 8 or more.

[Examples 2 to 4]
In Examples 2 to 4, except that the fiber density 70 (kilofilament / inch ² ) of the conductive brush in Example 1 was set to a value of 180 (kilofilament / inch ² ) or less as shown in Table 1, respectively. An electrophotographic photosensitive member and a conductive brush were prepared and evaluated under the same conditions as in Example 1. The obtained results are shown in Table 1.

[Comparative Examples 1-3]
In Comparative Examples 1 to 3, the fiber density 70 (kilofilament / inch ² ) of the conductive brush fiber in Example 1 was set to a value exceeding 180 (kilofilament / inch ² ) as shown in Table 1, respectively. Were produced and evaluated under the same conditions as in Example 1 for an electrophotographic photosensitive member and a conductive brush. The obtained results are shown in Table 1.

As understood from the results shown in Table 1, in Examples 1 to 4, since the fiber density in the conductive brush is 180 (kilofilament / inch ² ) or less, abnormal discharge is prevented, and the gray image is displayed. The development of white muscle was not observed.
On the other hand, in Comparative Examples 1 to 3, since the fiber density in the conductive brush is a value exceeding 180 (kilofilament / inch ² ), abnormal discharge cannot be sufficiently prevented, and the white color on the gray image is not prevented. Muscle development was observed.

According to the image forming apparatus and the image forming method using the same according to the present invention, even in the case of using a conductive brush as a pre-charging member in a positively charged single layer type electrophotographic photosensitive member, the fiber density is reduced. By using a conductive brush defined within a predetermined range, generation of white streak in a gray image can be suppressed.
Therefore, the image forming apparatus and the image forming method using the image forming apparatus of the present invention are expected to contribute to improving the image quality and speed of the image forming apparatus.

It is a figure which shows the white line in a gray image. 1 is a schematic view of an image forming apparatus according to the present invention. It is the schematic of a conductive brush. It is a characteristic view which shows the relationship between the fiber density (kilofilament / inch < ² >) in an electroconductive brush, and the white line generation | occurrence | production (line / 10cm) in a gray image. It is a characteristic view which shows the relationship between the single yarn fineness (denier) in an electroconductive brush fiber, and the number of white streak generation | occurrence | production (lines / 10cm) in a gray image. FIG. 6 is a characteristic diagram showing a relationship between a current density (I _b ) of a current flowing from the conductive brush to the surface of the photosensitive member and a transfer memory potential (V _t ). It is a characteristic view showing the relationship between the applied voltage (V _b ) applied to the conductive brush and the transfer memory potential (V _t ). FIG. 6 is a characteristic diagram showing the relationship between the current density (I _t ) of the current flowing from the transfer means to the photoreceptor surface and the transfer memory potential (V _t ). FIG. 6 is a characteristic diagram showing a relationship between a current density ratio | I _b / I _t | and a transfer memory potential (V _t ). It is a figure provided in order to demonstrate the structure of the conventional image forming apparatus.

Explanation of symbols

2: pre-charging means, 4: conductive brush, 10: image forming apparatus, 11: electrophotographic photosensitive member, 12: charging means, 13: exposure means, 14: developing means, 15: transfer means, 17: cleaning device, 20: Recording paper, 30: Conductive brush, 31: Conductive brush fiber, 32: Conductive woven fabric, 33: Conductive double-sided tape or conductive adhesive, 34: Conductive base material

Claims (9)

In an image forming apparatus in which a charging unit, a developing unit, a transfer unit, and a charge eliminating unit are sequentially arranged around a single layer type electrophotographic photosensitive member.
The charging means is a charging means for charging the single-layer electrophotographic photosensitive member to a positive polarity;
Between the charging unit and the charge eliminating unit, a pre-charging unit including a conductive brush is disposed,
The conductive brush is in contact with the surface of the single-layer electrophotographic photosensitive member, and the fiber density of the conductive brush is set to a value of 180 (kilofilament / inch ² ) or less. Image forming apparatus.   The image forming apparatus according to claim 1, wherein a material substance in the conductive brush fiber is a polyamide resin or a polyester resin containing conductive particles.   The image forming apparatus according to claim 1, wherein the length of the bristle length in the conductive brush fiber is set to a value within a range of 2 to 7 (mm). The image forming apparatus according to claim 1, wherein the yarn resistance in the conductive brush fiber is set to a value of 1 × 10 ¹¹ (Ω · cm) or less.   2. The conductive brush fiber is sewn into a conductive woven fabric, and the conductive woven fabric sewn with the brush fiber is fixed to a conductive base material. The image forming apparatus as described in any one of -4.   6. The image forming apparatus according to claim 5, wherein a stainless steel plate is used as the conductive substrate.   The image forming apparatus according to claim 1, wherein the charging unit is a contact charging type charging unit.   The image forming apparatus according to claim 1, wherein an initial charging potential of the single-layer type electrophotographic photosensitive member by the charging unit is set to a value of 400 (V) or more. In an image forming method using an image forming apparatus in which a charging unit, a developing unit, a transfer unit, and a charge eliminating unit are sequentially arranged around a single layer type electrophotographic photosensitive member.
The single-layer electrophotographic photosensitive member is charged to a positive polarity by the charging means,
Between the charging unit and the charge eliminating unit, a pre-charging unit including a conductive brush is disposed,
The conductive brush is in contact with the surface of the single-layer electrophotographic photosensitive member, and the fiber density of the conductive brush is set to a value of 180 (kilofilament / inch ² ) or less. Image forming method.