JPH1020620A - Contact electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a contact electrifying device capable of selecting the material of an electrifying member from a wide range and restraining scaly electrification irregularity to such as extent that it does not matter in practical use. SOLUTION: This contact electrifying device 2 is provided with the electrifying member 21 which is arranged in contact with a photoreceptor drum 1 (body to be electrified) and on which DC voltage VC is applied so as to electrify the drum 1, and the surface resistance ρs of the electrification contributing surfaces fs1 and fs2 of the member 21 is >0Ω/square and <=1×10<5> Ω/square, and the maximum value of a gap distance between the electrification contributing surface and the surface of the drum 1 is set to >=5μm and <=60μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact charging device for an image forming apparatus such as an electrophotographic copying machine and a printer.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or a printer, an electrostatic latent image carrier such as a photosensitive drum is charged by a charging device, and the charged area is exposed to an image to form an electrostatic latent image. Is formed and the latent image is developed into a visible image, which is transferred to a transfer material and fixed. As described above, a charging device is employed to charge the surface of the electrostatic latent image carrier before forming the latent image. In addition, a transfer charger for transferring a visible image formed on an electrostatic latent image carrier to a transfer material, a separation charger for separating a transfer material onto which a visible image has been transferred from an electrostatic latent image carrier, and the like are also available. A charging device is employed.

As the charging device, corona charging devices such as corotrons and scorotrons utilizing corona discharge have been conventionally used. These corona charging devices have an advantage that they can perform stable charging, but require a high voltage. And the large amount of ozone generated, there is a problem in terms of safety and environmental conservation. In order to solve such a problem, various types of contact charging devices and proximity charging devices have recently been proposed.

[0004] The contact charging device brings a charging member to which a voltage is applied into contact with a member to be charged, and mainly includes an area of the charging member which is in contact with the member to be charged and a region which is separated from the member to be charged. The object to be charged is charged by a discharge generated in a gap with the surface. As the charging member, there are various forms such as a charging roller and a charging brush, and a charging blade, a charging film and the like have been proposed.

In the proximity charging device, a charging member to which a voltage is applied is disposed very close to a member to be charged to generate a discharge, thereby charging the surface of the member to be charged. Various types of charging members in the proximity charging device have been proposed. These contact charging devices and proximity charging devices are particularly advantageous in that the amount of ozone generated is significantly smaller than that of corona charging devices. Further, the voltage to be applied can be set lower than that of the corona charging device.

[0006]

However, when looking at the contact charging device, if a charging member made of a low-resistance material such as metal is used, the surface of the member to be charged is non-uniformly charged like a scale. Therefore, when the member to be charged is an electrostatic latent image carrier, for example, one dot / dot as shown in FIG.
When a halftone image of four dots is formed, dot missing or missing dots of halftone dots occur, causing shading of the halftone image. In order to examine the charged state of the surface of the member to be charged by the charging member at this time, when an image for evaluating the charged state described later is created, a scale-like image as shown in FIG. 9 is seen. this is,
This indicates that the surface of the member to be charged is not uniformly charged and scale-like uneven charging has occurred. This problem does not occur when a charging member made of a high-resistance material is employed. Therefore, a charging member made of a low-resistance material such as metal cannot be used, and a charging member made of a high-resistance material such as rubber or resin in which a conductive material is dispersed has to be used.

[0007] In addition, a flaw may be generated on the surface of the charged member due to scratches generated at the contact portion of the charging member with the charged member and foreign matter such as toner clogging there. In order to suppress the charging, it is conceivable to employ a charging member made of a material having high hardness. As one example of such a material, a metal material is conceivable, but cannot be adopted for the above-mentioned reason. Therefore, it is necessary to employ a charging member made of a material in which a conductive material typified by conductive carbon is dispersed in a specific resin having high hardness. The same was true when trying to adopt a charging member that was hard to wear.

For this reason, there is a problem that the range of choice of the material of the charging member is limited. Therefore, the present invention is a contact charging device provided with a charging member that charges a member to be charged by applying a DC voltage to the member to be charged, and a charging member material can be selected from a wide range, In addition, it is an object of the present invention to provide a contact charging device capable of suppressing the occurrence of scale-like uneven charging to a practically acceptable level.

[0009]

A contact charging device according to the present invention for solving the above-mentioned problems has a charging member which is arranged in contact with a member to be charged and charges the member by applying a DC voltage. A contact charging device, wherein a surface resistance ρs of a surface contributing to charging of the charging member is larger than 0Ω / □ and 1 ×
10 ⁵ Ω / □ or less, and the maximum value of the gap distance between the charge-contributing surface and the member to be charged is 5 μm or more and 60 μm or less.

Here, the "subject to be charged" is typically an electrostatic latent image carrier such as a photoreceptor, but it is not necessary to be limited to this. The present invention can be applied to a member to be charged to be prevented or suppressed. The surface resistance ρs of the surface contributing to charging of the charging member is larger than 0Ω / □,
The lower limit may be 1 × 10 ⁵ Ω / □ or less, but the lower limit is a metal material which is generally considered as a charging member material and has a low resistance of approximately 1 × 10 5 even if it has a low resistance. ^-5 Ω / □. From this point of view, the surface resistance ρs of the surface contributing to the charging of the charging member is not limited thereto, but is actually about 1 × 10 ⁻⁵ Ω / □ or more.
It is considered to be selected in the range of × 10 ⁵ Ω / □ or less.

The surface resistance ρs is larger than 0Ω / □ and 1 ×
The material in the range of 10 ⁵ Ω / □ or less is a material that can be selected from a wide range. However, if the charging member made of this material is used without any consideration, the possibility that scale-like charging unevenness occurs may occur. Material of a certain area. If the maximum value of the gap distance between the charging contributing surface and the member to be charged is within the range of 5 μm or more and 60 μm or less as described above, the surface resistance ρs of the surface contributing to charging of the charging member is set to 0Ω / □. For any charging member selected and formed from a wide range of materials that can be made larger than 1 × 10 ⁵ Ω / □, scale-like uneven charging can be sufficiently suppressed.

When the maximum value of the distance exceeds 60 μm, scale-like uneven charging which cannot be ignored in practical use occurs. If the maximum value of the distance is smaller than 5 μm, the charging of the member to be charged becomes insufficient and it becomes difficult to use the member. Various charging members such as a blade charging member, a film charging member, and a charging roller can be considered as the charging member in the contact charging device of the present invention.

[0013] The charging contributing surface of the charging member is a surface of the charging member facing the member on the charging member upstream or downstream of the charging contributing surface or both in the moving direction of the surface of the charging member relative to the charging member. It can be partitioned by covering with an electric insulating layer, or interposing an electric insulating member such as an electric insulating film or a sheet between the surface of the charging member facing the member to be charged and the member to be charged.

According to the charging device of the present invention, the charging member is arranged so as to partially contact the member to be charged, a DC voltage is applied to the charging member, and the charging member and the member to be charged move relatively. As a result, the surface of the member to be charged is charged. The surface resistance ρs of the surface contributing to the charging of the charging member is 0Ω /
□ larger than 1 × 10 ⁵ Ω / □ or less, that is, in spite of the condition in which scale-like charging unevenness is conventionally generated or easily generated, the charging-contributing surface and the charged body The maximum value of the gap distance between 5μm and 60μ
m or less, the occurrence of scale-like uneven charging is suppressed to such an extent that there is no practical problem. Further, the surface resistance ρs of the surface contributing to charging of the charging member can be selected from a wide range of more than 0Ω / □ and 1 × 10 ⁵ Ω / □ or less, so that the selection range of the charging member material is sufficiently wide. In that range,
It is also possible to manufacture a charging member made of a material having excellent abrasion resistance and high hardness (for example, a suitable metal material) which is hard to be scratched or an inexpensive material.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. All of the contact charging devices according to the present invention described below are used by being incorporated in the printer shown in FIG. The printer shown in FIG. 1 includes a photosensitive drum 1 which is an electrostatic latent image carrier (charged body) at the center, and this drum is driven to rotate by a main motor 100 in the direction of arrow a. Around the drum 1, a charging device 2, a developing device 3, a transfer charger 4, a cleaning device 5, and an eraser 6 are sequentially arranged. The charging device 2 is a contact charging device according to the present invention has a charging member 21 as shown in FIG. 2, is when the image forming, the DC voltage V _C is applied thereto from a power source PW. The charging device 2 will be further described later.

An optical system 7 is disposed above the photosensitive drum 1. This optical system is provided in a housing 71 with a semiconductor laser generator, a polygon mirror, a toroidal lens, a half mirror, a spherical mirror, a folding mirror, and a reflection mirror. An exposure slit 72 is formed in the floor of the housing 71 and an image exposure can be performed on the photosensitive drum 1 through the space between the charging device 2 and the developing device 3.

On the right side of the photosensitive drum 1 in the figure, a pair of timing rollers 81, a pair of intermediate rollers 82, and a sheet cassette 83 are provided.
Are sequentially arranged, and a paper feed roller 84 faces the paper feed cassette 83. A pair of fixing rollers 91 and a pair of discharge rollers 92 are sequentially arranged on the left side of the photosensitive drum 1 in the drawing, and a discharge tray 93 faces the pair of discharge rollers 92. The above components are mounted on the printer body 10.

According to this printer, the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential by the charging device 2, and the charged area is image-exposed from the optical system 7 to form an electrostatic latent image. The electrostatic latent image thus formed is developed by the developing device 3 to become a toner image, and moves to a transfer area facing the transfer charger 4. On the other hand, the transfer paper is pulled out from the paper feed cassette 83 by the paper feed roller 84, reaches the timing roller pair 81 via the intermediate roller pair 82, and is fed to the transfer area in synchronization with the toner image on the drum 1. Thus, in the transfer area, the toner image on the drum 1 is transferred onto the transfer paper by the action of the transfer charger 4, and the transfer paper reaches the fixing roller pair 91, where the toner image is fixed and then discharged by the discharge roller pair 92. The sheet is discharged to the paper tray 93.

After the toner image is transferred to the transfer paper, the toner remaining on the photosensitive drum 1 is cleaned by the cleaning device 5. The residual charges are erased by the eraser 6. The system speed of the printer (the peripheral speed of the photosensitive drum 1) is 3.5 cm / sec. The voltage V _C applied to the charging member 21 of the charging device 2 is -1.2 k
V, and the developing device 3 is a one-component contact developing device and performs reversal development.

The photoreceptor drum 1 is a negative charge function-separated type organic photoreceptor having sensitivity to long wavelength light. The charge generation layer is formed of a mixture of τ-type metal-free phthalocyanine and polyvinyl butyral resin to a thickness of about 0.4 μm, and then a charge transport layer is formed of a mixture mainly composed of a hydrazone compound and a polycarbonate resin to a thickness of about 18 μm. Have been. The electrostatic latent image carrier to which the charging device of the present invention can be applied is not limited to the above.

Here, the toner used in the developing device 3 is of a negative charge type, and a mixture mainly composed of a bisphenol A type polyester resin and carbon black is kneaded, crushed and classified by a known method, and the average particle diameter is adjusted. 10μ
m. Accommodated such toner to the developing device 3, and to perform development under a developing bias V _B.

The contact charging device 2 will be further described. As shown in FIG. 2, one end f1 of a film F cut into a predetermined size to become a film charging member 21 is cantilevered by a support member 22. The free end f2 is bent upward, the free end side is disposed in contact with the surface of the photosensitive drum 1, and a DC voltage of -1.2 kV is applied to the charging member 21 from the power supply PW as described above.

The upstream and downstream areas of the portion fo of the film F (charging member 21) in contact with the surface of the photosensitive drum 1 in the direction a of movement of the photosensitive drum surface are defined as the charge contributing surface fs.
1, fs2, and the boundary of the charge contributing surface fs1 is formed by the electrical insulating layer Is1 formed on the film surface on the upstream side of the surface in the photosensitive drum surface moving direction a. The boundary is formed by the electrical insulating layer Is2 formed on the film surface to the free end of the film downstream from the surface in the surface movement direction a.

The maximum distance S1 between the charge contributing surface fs1 and the surface of the photosensitive drum 1 and the maximum distance S2 between the charge contributing surface fs2 and the surface of the photosensitive drum 1 are 5 μm.
Therefore, the maximum distance of the gap between the charge-contributing surface and the surface of the photosensitive drum 1 is set to 5 μm to 60 μm. Further, the length L of the continuous area including the surface fs1, the contact portion fo, and the surface fs2 in the photosensitive drum surface moving direction is limited to this, but is set to 5 mm here.

The film F constituting the charging member 21 is a flexible film of the same type as that disclosed in Japanese Patent Application Laid-Open No. 4-249270. More specifically, in order to improve the contact with the member to be charged, as shown in FIG. 3, when a material having a width b = 1 cm is wound around a core rod R having a circular cross section having an outer diameter D ₁ = 1 cm. The required bending moment Mm is Mm ≦ 20 (g · cm), preferably Mm ≦
It is 10 (g · cm), and also has mechanical strength (strength against tearing, tearing, etc.) as a charging member. Here, the bending moment Mm is EI / ρ (I
= Is a bh ^3/12). E is the Young's modulus (g / cm ² ) of the film F, I is the second moment of area (cm ⁴ ) of the film F, ρ is the radius of curvature (cm) of the film F, and is between the center O of the core rod R and the film F. The distance h from the upright surface NS is the thickness of the film.

As a material of the film F, the surface resistance ρs of the charge contributing surfaces fs1 and fs2 is larger than 0Ω / □,
1 × 10 ⁵ Ω / □ or less, but here selected from materials that fall within the range of 1 × 10 ⁻⁵ Ω / □ or more and 1 × 10 ⁵ Ω / □ or less. As described above, the contact charging device 2 requires the film charging member 21 to have the surface resistance ρs of the charging contributing surface of 1 × 10 ⁻⁵ Ω / □ or more and 1 × 10 ⁵ Ω / □ or less as described above, In this case, the maximum value of the gap distance between the charge-contributing surface and the photosensitive drum 1 is 5 μm despite the conditions under which scale-like charging unevenness occurs or is likely to occur.
Since the length is regulated to not less than m and not more than 60 μm, the occurrence of scale-like uneven charging on the surface of the photosensitive drum 1 is sufficiently suppressed.

Next, if the maximum value of the surface resistance of the charge contributing surface of the charging member 21 of the charging device 2 and the maximum value of the gap distance from the photosensitive drum 1 are as described above, it is shown that the scale-like charging unevenness is sufficiently suppressed. The following Table shows Experimental Examples 1 to 4 in which various materials of the film F constituting the charging member were employed and the maximum value of the gap distance was variously changed for each. The following Table also shows Comparative Experimental Examples 1 and 2 performed for comparison.

All experiments were performed using the printer. The system speed, the voltage applied to the charging member, the toner used in the developing device, and the like are as described above. However, the developing bias voltage V _B is set at −700 V, which is substantially equal to the charging potential at which the photosensitive drum 1 is charged by the charging member 21, and is used to evaluate the uniformity of the charging potential by printing a solid white image. An image for evaluating the state of charge was prepared.

The following four types of films A, B, C and D were used for the film constituting the experimental charging member. A: stainless steel film, thickness 20 μm, surface resistance ρs 1 × 10 ⁻⁵ Ω / □ B: film in which conductive carbon powder is dispersed in polyimide, thickness 30 μm, surface resistance ρs 1 × 10 ³ Ω / □ C: Film in which conductive carbon powder is dispersed in polyimide, thickness 30 μm Surface resistance ρs 1 × 10 ⁵ Ω / □ D: Film in which conductive carbon powder is dispersed in polyimide, thickness 30 μm Surface resistance ρs 1 × 10 ⁷ Ω / □ In addition, when scale-like uneven charging occurs, scale-like noise appears in the image for evaluating the state of charge, and the charging performance was evaluated by observing the scale-like noise on this image. Here, a method of evaluating scale-like noise on an image based on scale-like uneven charging on the surface of the photosensitive drum 1 will be described. (Scaling noise evaluation method) The developing bias potential V _B of the developing device 3 of the printer is
The photosensitive drum 1 is set at −700 V, which is substantially equal to the charging potential charged by the charging member 21, and the so-called bias development is performed with the potential charged by the charging member by printing a solid white image (no exposure). Then, an image for evaluating the state of charge for evaluating the uniformity of the charged potential was prepared and printed on transfer paper. At this time, in the charged state evaluation image, if the charged state is uniform, a uniform image in which the toner is uniformly adhered to the entire transfer paper can be obtained. A non-uniform image in which the portion becomes black is obtained. The image for evaluating the charged state on the transfer paper was visually observed and ranked as follows.
"O" indicates that it is acceptable, and "△" and "x" indicate that it is not practically acceptable.

: No scaly noise (no scaly charge; uniform charge) △: Partially scaly noise (partially scaly uneven charging) ×: Scaling noise entirely (no scaly uneven charging) Maximum gap distance Image evaluation A BCD Experimental example 1 5 μm ○ ○ ○ Not evaluated Experimental example 2 20 μm ○ ○ ○ Not evaluated Experimental example 3 40 μm ○ ○ ○ Not evaluated Experimental example 4 60 μm ○ ○ ○ Not evaluated Comparative Experimental Example 1 80 μm × △ △ Not evaluated Comparative Experimental Example 2 (without insulating layers Is1, Is2) × × △ ○ From the above experimental results, the surface resistance ρs of the charging contributing surface of the film charging member 21 was 1 × 10 ^{− 5} Ω / □ or more 1 × 10 ⁵ Ω / □
Even under the following conditions, it can be seen that if the maximum value of the gap distance between the charge-contributing surface and the photosensitive drum 1 is regulated to 5 μm or more and 60 μm or less, scale-like uneven charging is suppressed. Although not shown here, even for a film charging member in which the surface resistance ρs of the charging contributing surface is smaller than 1 × 10 ⁻⁵ Ω / □, the maximum gap distance between the charging contributing surface and the photosensitive drum 1 is also considered. When the value is regulated to 5 μm or more and 60 μm or less, scale-like uneven charging is suppressed. In the above experiment, the film D was not evaluated for the case where the maximum gap distance was 5 to 80 μm.
The reason why the scale-like uneven charging is not generated is because the surface resistance of the film D is as large as 1 × 10 ⁷ Ω / □, and the scale-like uneven charging is not originally generated or hardly generated regardless of the size of the void. is there.

Although the contact charging device in which the charging member is the film charging member 21 has been described above, the form of the charging member is not limited to a film. In this regard, another example of the contact charging device according to the present invention will be described below. FIG.
The charging device 20A shown in FIG. 4 employs a film charging member 201 in place of the film charging member 21 in the charging device 2, and the charging member 201 moves from the portion foA in contact with the surface of the photosensitive drum 1 to the surface of the photosensitive drum. Direction a
At the surface facing the photoreceptor on the upstream side
And the portions before and after the contact portion foA on the downstream side thereof are defined as charging contribution surfaces fs1A and fs2A. In this case, since the free end surface of the charging member 201 is also included in the charge contributing surface fs2A, the distance X from the upper edge of the free end surface to the surface of the photosensitive drum 1 is also limited to 5 μm or more and 60 μm or less.

A charging device 20B shown in FIG. 6 employs a thick blade charging member 202 instead of the film charging member 21 in the charging device 2, and the charging member 2
Numeral 02 is provided with an electrical insulating layer Is1B on the surface facing the photoconductor upstream from the portion foB in contact with the surface of the photoconductor drum 1 in the direction a of movement of the surface of the photoconductor drum. A layer Is2B is provided, and a charge contributing surface f is provided before or after the contact portion foB of the blade.
sB.

The charging device 20C shown in FIG. 7 has a semi-cylindrical conductive elastic member having a top surface formed in a gentle curved surface as a charging member 203, which is supported by a support member 204, and one of the top surface. A part foC is brought into contact with the surface of the photosensitive drum 1, and electrical insulating layers Is1C and Is2C are provided at the corners of the top surface on the upstream and downstream sides of the contact part foC in the photosensitive drum surface moving direction a, Contact part f
The portions before and after oC are defined as charging contribution surfaces fs1C and fs2C.

A charging device 20D shown in FIG. 8 is a charging device having a rotatable roller charging member 204 which can rotate by partially contacting the photosensitive drum 1 with foD. The electrical insulation layers Is1D and Is2D along the roller surface upstream and downstream of the partial foD
Are arranged, and before and after the contact portion foD, the charge contributing surfaces fs1D, fs1D
This is s2D.

In each of the charging devices shown in FIGS. 5 to 8, the surface resistance ρs of the surface contributing to the charging of the charging member is 0Ω.
/ □ and 1 × 10 ⁵ Ω / □ or less, and the maximum value of the gap distance between the charge-contributing surface and the photosensitive drum 1 is 5 μm.
When the length is not less than m and not more than 60 μm, the scale-like uneven charging can be suppressed similarly to the charging device 2 described above.

[0036]

As described above, according to the present invention, there is provided a contact charging device including a charging member which is disposed in contact with a member to be charged and charges the member by applying a DC voltage. It is possible to provide a contact charging device that can select a charging member material from a wide range and can suppress the occurrence of scale-like charging unevenness to a level that causes no practical problem.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a printer equipped with an example of a charging device according to the present invention.

FIG. 2 is a side view of a charging device in the printer shown in FIG.

FIG. 3 is an explanatory diagram of a film material constituting a film charging member.

FIG. 4 is an explanatory diagram of a halftone image.

FIG. 5 is a side view of another example of the charging device according to the present invention.

FIG. 6 is a side view of still another example of the charging device according to the present invention.

FIG. 7 is a side view of still another example of the charging device according to the present invention.

FIG. 8 is a side view of still another example of the charging device according to the present invention.

FIG. 9 is an example of an image for evaluating a charged state in which only scaly noise is present
It is a figure showing an example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photosensitive drum (charged body) a Surface moving direction of drum 1 2 Charging device 21 Film charging member 22 Film support member PW Charging device power supply F Film f1 One end of film F f2 Free end of film F fo Film F Contact portion with photosensitive drum 1 fs1, fs2 Charging contributing surface of film F Is1, Is2 Electrical insulating layer S1, S2 Gap distance between charging contributing surface and photoreceptor drum 1 surface 20A Charging device 201 Film charging member foA Charging member 201 Contact portion of photosensitive member 1 with IsA electrical insulating layer fs1A, fs2A Charging contributing surface 20B Charging device 202 Blade charging member foB Contact portion of charging member 202 with photoreceptor drum Is1B, Is2B Electric insulating layer fsB Charging contributing surface 20C Charging device 203 Charging member 204 Supporting member foC Contact portion of charging member 203 with photosensitive drum 1 Is1C, Is2C electrically insulating layer Fs1C, contact portion Is1D the photosensitive drum 1 of fs2C charge contributions surface 20D charging device 204 roller charging member foD charging member 204, Is2D electrically insulating layer fs1D, fs2D charge contribution plane

Claims (1)

[Claims] 1. A contact charging device having a charging member which is arranged in contact with a member to be charged and charges the member by applying a DC voltage, the surface resistance of a surface contributing to charging of the charging member. ρs is greater than 0Ω / □, 1 × 10 ⁵ Ω
/ □ or less, and the maximum value of the gap distance between the charge-contributing surface and the member to be charged is 5 μm or more and 60 μm or less.