JP2002091138A - Electrifying device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the quantity of generated ozone and quantity of shaved film of a photoreceptor and to secure an electrifying process with extremely little unevenness in electrification, to realize a process where stable electrifying can be carried out by not having excessive current fed even when there is a pinhole or a scar on the photoreceptor, to extend top and bottom limit of electrified potential and to improve durability of the photoreceptor. SOLUTION: In the device, charge is applied to the photoreceptor by an electrifying member 2a by abutting the electrifying member 2a and a smoothing member 3 to the photoreceptor or installing them in close proximity and excessive charge is removed by the smoothing member 3. The thickness of the film of a photoreceptor layer 12 is made thicker than that of a normally used photoreceptor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, and the like. More specifically, the present invention relates to a charging device for charging an image carrier, and an image bearing member charged by the charging device. And, in an image forming apparatus provided with an exposing means for forming an electrostatic latent image by exposure, to the surface potential uniformity of the charged image carrier.

[0002]

2. Description of the Related Art Heretofore, as an image forming apparatus, there has been known an image forming apparatus which charges an image carrier, selectively erases or reduces the charge by exposure, and forms an electrostatic latent image on the image carrier. ing. As a charging means for charging the image carrier, a method using corona discharge has been mainly used.
However, the charging means using this corona discharge requires a high voltage power supply for applying a high voltage of 5 to 10 kV in order to cause a problem that a large amount of ozone is generated and to perform corona discharge. There is a problem that it is difficult to reduce the cost of the image forming apparatus.

Therefore, corona discharge is not used as charging means that can be adopted in image forming apparatuses in recent years.
Many contact-type charging means for bringing a charging member into contact with an image carrier have been proposed. In the contact type charging means, while many of the problems mentioned in the case of the charging means using corona discharge are solved, non-uniform charging is a serious problem. The uniformity of the charged potential on the image carrier before exposure in the image forming apparatus affects the quality of the electrostatic latent image formed in the subsequent exposure process. For example, unevenness of the charged potential generated on the image carrier before the exposure causes uneven image density and reduced reproducibility of image details, which is a serious problem in image quality.

The mainstream of contact charging is a charging roller. Many charging rollers that have been put into practical use have a multilayer structure, particularly a two-layer structure. Each layer will be referred to as an elastic layer and a surface layer. The elastic layer has a certain degree of elasticity (rubber hardness of 40 to 60 JISA) in order to obtain sufficient adhesion, and a low resistance to medium resistance member is used so that current can easily flow. On the other hand, the surface layer is made to prevent the additive of the elastic layer from adhering to the photoreceptor, and to prevent an excessive current from flowing when a photoreceptor has a pinhole or a scratch, thereby causing a voltage drop. A material that is stable with resistance is used.

[0005] As a voltage application system, two systems in which only a DC voltage (DC) and an AC voltage (AC) are superimposed on the DC voltage (DC) have been put into practical use. Charging uniformity, that is, less charging unevenness is the AC superposition method. However, since the discharge amount is large, the amount of ozone generated is larger than that of the DC method, the film of the photoreceptor is often scraped, and image deletion occurs due to long-term use. Photoreceptor film scraping is caused by photoreceptor damage due to discharge, and image deletion is caused by NOx resulting from discharge becoming ammonium nitrate and adhering to the photoreceptor. These are all phenomena caused by a large amount of discharge. In the case of the DC method, the amount of ozone generated is 1/50 or less of that of the AC superposition method, the amount of film scraping is less than 1/2, and the life before image deletion occurs is twice or more, but uniform charging is obtained. Hateful. By optimizing the material, it is possible to achieve uniform charging to a practically inconspicuous degree, but it is easily affected by unevenness and resistance unevenness of the outermost layer of the roller, and the specification is very strict. For example, the specification value of the surface roughness of a charging roller having a resin layer provided on a hydrin rubber layer is 5 μm in Rz.
It is as follows. In order to obtain a sufficient nip, the rubber layer needs to have a thickness of 2 to 3 mm, and it is very difficult to control the surface roughness Rz to 5 μm or less. In addition, since uniformity of resistance cannot be obtained with carbon dispersion, ionic conductive rubber is used, and there are great restrictions on materials.

As a method for performing uniform charging by the DC method and reducing the above-mentioned restrictions on surface properties and resistance uniformity,
Japanese Patent Application Laid-Open Nos. Hei 6-289687, Hei 7-248668, and Hei 7
-84436. However, these methods do not describe a countermeasure for a pinhole or a scratch on the photoconductor. An invention similar to the present invention is disclosed in
-220837. In this invention, the charger is a contact roller, and the leveling member is a blade. However, there is no invention relating to a pinhole in this invention.

[0007]

SUMMARY OF THE INVENTION In view of the above problems, the present invention is to improve the non-uniformity of charging in a contact type charging means. In particular, a charging process is established in which the amount of ozone generated and the amount of film scraping are the same as those of the DC voltage application method, and the charging unevenness is extremely small. Furthermore, even when the photoconductor has a pinhole or a scratch, an excessive current does not flow, and a process capable of stably charging is realized. At the same time, the upper and lower limits of the charging potential are expanded. Further, with the demand for colorization, the durability of the photoconductor is improved.

[0008]

In order to solve the above problem, according to the first aspect of the present invention, a plurality of members (member 1) are provided.
-Member n) is pressed against or placed close to the photoreceptor, and a voltage is applied or grounded. A charge is applied to the photoreceptor by members 1 to n-1, and an extra charge is applied by member n. A charging device that obtains uniform charge by removing electric charges is characterized in that the thickness of a photosensitive layer (CTL) of a photoconductor is made thicker than a commonly used photoconductor. In the invention according to claim 2, a plurality of members (member 1
-Member n) is pressed against or placed close to the photoreceptor, and a voltage is applied or grounded. A charge is applied to the photoreceptor by members 1 to n-1, and an extra charge is applied by member n. In a charging device that obtains uniform charge by removing charge, use a material with a lower relative dielectric constant than the commonly used photoreceptor for the photosensitive layer (CTL) of the photoreceptor, or use a material with a low relative dielectric constant for a conventional material. And a charging device characterized in that the thickness of the photosensitive layer is not changed. According to the third aspect of the present invention, a plurality of members (members 1 to n) are pressed against or arranged close to the photoreceptor, and a voltage is applied or grounded. In a charging device that applies electric charge on the photoreceptor and removes excess charge by the member n to obtain uniform charging, a material having a higher relative dielectric constant than a commonly used photoreceptor is used for the photosensitive layer (CT) of the photoreceptor.
The charging device is characterized in that the material used for L) or a material having a high relative dielectric constant is mixed into a conventional material, and the thickness of the photosensitive layer is not changed. According to the fourth aspect of the present invention, a plurality of members (members 1 to n) are pressed against or arranged close to the photoconductor, and a voltage is applied or grounded. A charge is applied to the photoreceptor, and the member n
In a charging device that obtains uniform charging by removing excess charge, a surface layer having a higher dielectric constant than the photosensitive layer is provided on the photosensitive layer (CTL) of the photoreceptor, and the film thickness obtained by adding the two layers is usually used. The charging device is characterized in that it is the same as the photoreceptor used. In the invention according to claim 5, a plurality of members (member 1 to member n) are pressed against or arranged close to the photoconductor, and a voltage is applied or grounded.
In a charging device that applies electric charge on the photoreceptor by the members 1 to n-1 and removes excess electric charge by the member n to obtain uniform charging, the charge is applied to the photosensitive layer (CTL) of the photoreceptor from the photosensitive layer. A charging device is characterized in that a surface layer having a low ratio is provided, and the film thickness of the two layers is the same as that of a commonly used photoreceptor. According to a sixth aspect of the present invention, there is provided the charging device according to the fourth or fifth aspect, wherein fine particles having high hardness are mixed in the surface layer of the photoconductor. According to a seventh aspect of the present invention, there is provided the charging device according to the fourth or fifth aspect, wherein high-hardness oxide fine particles are mixed into the surface layer or the photosensitive layer of the photoconductor. According to an eighth aspect of the present invention, there is provided the charging device according to the fourth or fifth aspect, wherein fine particles of a metal oxide having high hardness are mixed into the surface layer or the photosensitive layer of the photoconductor. . According to a ninth aspect of the present invention, there is provided an image forming apparatus including the charging device according to any one of the first to eighth aspects.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of the charging device of the present invention. Aluminum tube (13) and photosensitive layer (12)
A charging member (2a) and a leveling member (3) are arranged on the photoreceptor made from the above. The charging member (2a) is for the purpose of only providing a necessary charge on the photoreceptor, and uniformity does not matter. By making the leveling member (3) uniform,
Very little uneven charging can be realized. In principle, it can be realized with a total of two members, one charging member and one leveling member, but a plurality of members may be used. In this case, a plurality of members (members 1 to n) are arranged on the photoconductor, charges are applied to the photoconductor by members 1 to n-1, and extra charges are removed by member n. Members 1 to n-1
May be disposed in contact with or close to the photoconductor, and the leveling member of the member n is disposed in contact with the photoconductor. The plurality of members are, for example, brushes, rollers, blades, and the like in which conductive fibers are bundled. Considering the ease of cleaning, the roller shape is optimal. The charging member (2a) is applied with an applied voltage of Vp1, and the leveling member (3) is applied with an applied voltage of Vp2. The surface potential of the photoconductor after passing through the charging member (2a) is set to Vs1,
The photoconductor surface potential after passing through the leveling member (3) is set to Vs2. The actual photoreceptor has an under layer, a charge generation layer (CGL layer), and a charge transport layer (CTL layer) on an aluminum tube.
However, here, they are collectively referred to as a photosensitive layer. Hereinafter, the film thickness of the photoconductor refers to the thickness of the CTL layer. This is because the underlayer and the CGL layer are very thin. The illustration is omitted, and the description is omitted. At present, a photoreceptor used in an image forming apparatus such as a copying machine on the market has a CTL layer thickness of 20 to 30 μm and a relative dielectric constant of 2.2 to 3.0. Hereinafter, these values are used as the film thickness and the relative dielectric constant of a commonly used photoreceptor.

Here, means for expanding the charging potential width will be described. As a method for expanding the charging potential width, 2
There are two ways. One is to change the film thickness of the photoconductor, and the other is to change the relative dielectric constant of the photoconductor. FIG. 2 shows a change in the photoconductor surface potential (Vs2) when the photoconductor thickness (d) is changed.
The horizontal axis indicates the absolute value of the maximum value of the applied voltage (Vp2) at which no leakage (excess current) occurs between the leveling member and the photoconductor, and the vertical axis indicates the surface potential of the photoconductor. The relative permittivity of the photoreceptor was set to 3, referring to the relative permittivity of a commonly used photoreceptor. Usually, the thickness of the photoreceptor generally used is about 25 μm, but as shown in FIG.
When the thickness is larger than μm, both the lower limit and the upper limit of the chargeable area are increased, and it can be seen that the entire width is increased. Also, 25μ
When the thickness is smaller than m, both the lower limit and the upper limit of the chargeable area are reduced, and the overall width is reduced. The chargeable area can be raised and lowered by changing the thickness of the photoconductor as described above. However, even if the value of | Vp2 | shown in FIG. 2 is the smallest (photoconductor thickness = 15 μm), the current market It can be seen that the charging potential exceeds the charging potential | 900 V | Therefore, if the photoconductor thickness is 15 μm or more, there is no problem in terms of charging potential. It should be added that changing the thickness of the photoconductor within the above range does not cause any problem in manufacturing. Photoreceptor film forming methods include coating, dipping, and plasma CVD.
Method, a glow discharge decomposition method, a photo CVD method, a sputtering method, a plasma CVD method, and a method of forming a film with a sputtering effect (JP-A-58-49609). You. Photoconductor film
Various kinds of doping elements may be added to the (photosensitive layer) for the purpose of controlling resistance and light transmittance. Further, the film forming method is not limited.

Next, a method for changing the relative permittivity of the photosensitive member will be described. FIG. 3 shows a change in the photoconductor surface potential (Vs2) when the relative dielectric constant is changed from 2 to 4. The horizontal axis is the charging start voltage Vth, and the vertical axis is the photoconductor surface potential Vs2.
Is shown. It can be seen that even if the relative dielectric constant changes, the chargeable width of the photoreceptor does not change. Note that V in FIG. 2 and FIG.
Each value of s2 was calculated by the following formula. &#9; | Vs2 | = | Vth + Vp2 | &#9;&#9; ... (Equation 1) &#9; Vth = 312 + 6.2 * 106 (d / [epsilon] ') + (7737.6 * 106 d / ε ') 1/2 ・ ・ ・ (Equation 2) &#9;&#9; | Vp2 | <312 + 6.2 × 106 × d &#9;&#9; ・ ・ ・ (Equation 3) where d is Photoconductor thickness (m), ε 'is photoconductor relative dielectric constant,
| a | indicates the absolute value of a.

To change the relative dielectric constant of the photosensitive layer of the photosensitive member,
It is necessary to change the material used for the photosensitive layer. For example, as a binder resin (usually using polycarbonate) for lowering the relative dielectric constant of the photosensitive layer, polystyrene, polytetrafluoroethylene, a polypropylene resin and a copolymer thereof,
There are mixtures and the like. Examples of the binder resin for increasing the relative dielectric constant of the photosensitive layer include polyimide, polyvinylidene fluoride resin, a copolymer thereof, and a mixture thereof. Other resins, polymethyl methacrylate, polybutyl methacrylate, polyamide, polyester, polyurethane, polyvinyl formal, silicone resin,
There are also polyvinyl acetal, polyvinyl butyral, ethyl cellulose, melamine resin, and copolymers and mixtures thereof. From these resins, those that are substantially transparent to visible light and have excellent voltage insulation, strength, and adhesion may be used. The materials are not limited to the above. In addition, the dielectric constant of the photosensitive layer may be changed by changing the dielectric constant of the resistance control material of the photosensitive layer. Examples of resistance control materials include fatty acid salts, higher alcohols, sulfates, fatty acid amines, quaternary ammonium salts, alkylpyridium salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, sorbitan acid alkyl esters , Cationic, or nonionic organic electrolytes, such as irons and imidazoline derivatives; metals, such as Au, Ag, Cu, Ni, and Al; ZnO, TiO
2, SnO2, In2O3, SnO2, In2O3 containing Sb2O3
Metal oxides such as SnO2; MgF2, CaF2, BiF2,
Metal fluorides such as AlF2, SnF2, SnF4, TiF4;
Organic titanium compounds such as tetraisopropyl titanate, tetranormal butyl titanate, titanium acetylacetonate, and titanium lactate ethyl ester; and mixtures thereof. Note that the resistance control material is not limited to the above-described materials. Further, the above-described resistance control material can also be used for fine particles mixed in a photosensitive layer or a surface layer of a photosensitive member. The materials are not limited to the above.

A test example in which the present invention is applied to an electrophotographic copying machine (hereinafter, referred to as a copying machine) as an image forming apparatus will be described. (Test Example 1) The thickness of the photoreceptor is 15 μm, 25 μm, and 35 μm
Were prepared and scratched with a needle, and the leakage voltage was measured. -41 when the photoconductor thickness is 15 μm
-471 V for 7 V, 25 μm, -5 for 35 μm
It was 35 V, showing a very good agreement with the values calculated by (Equation 1) to (Equation 3). The slightly higher measured values are due to the under layer or charge generation layer (CG
It is presumed that the thickness of the (L layer) is effective. The leveling member used at this time was a roller having a single-layer structure made of epichlorohydrin rubber, the thickness of the rubber layer was about 3 mm, and the diameter was 1 mm.
4 mm one was used. It was pressed against the photoreceptor with a spring and brought into close contact. The resistivity of epichlorohydrin rubber is 1 × 1
It is 0.5-2.times.10@5 .OMEGA.cm. Next, a photosensitive member having a thickness of 25 μm, a charging roller having a diameter of 12 mm, and the above-mentioned leveling roller are used, and the voltage (Vp2) applied to the leveling roller is reduced by 50 V from the above value so that no leak occurs. By changing the value in a small value range, the charging potential (Vs
2) The change was measured. At this time, the maximum value of the charging potential (Vs2) on the photoreceptor surface is about -1044 V, and the minimum value is about -109.
It became V. Similarly, using a new photoreceptor having a thickness of 35 μm, a charging roller having a diameter of 12 mm, and the above-mentioned leveling roller, the voltage (Vp2) applied to the leveling roller is changed to change the charging potential (Vs2) of the surface of the photoreceptor. The change was measured. The maximum value of the charging potential (Vs2) on the photoreceptor surface is about -1171 V, and the minimum value is about -112 V. The charging potential width is wider and the upper limit of the charging potential is higher than in the case of a normally used photoreceptor of 25 μm. did. Similarly, a new photoreceptor with a thickness of 15 μm and a diameter of 12
The change in the charging potential (Vs2) on the surface of the photoreceptor was measured using a charging metal roller of mm and the above-mentioned leveling roller while changing the voltage (Vp2) applied to the leveling roller. The maximum value of the charging potential (Vs2) on the surface of the photoreceptor was about -887 V, and the minimum value was about -72 V. The lower limit of the charging potential was lower than that of a 25 μm photoreceptor which is usually used.

(Test Example 2) Instead of changing the relative permittivity of the photoreceptor, a 25 μm polystyrene film having a relative permittivity of 2.2 was pasted on an aluminum plate, and the charging start voltage (Vth) was measured. went. At this time, the charging start voltage was about 680 V, which was in good agreement with the calculated value using (Equation 2). Thereafter, the charging potential (Vs2) of the polystyrene film was changed by changing the voltage (Vp2) applied to the leveling roller within a range of ± 470 V using the polystyrene film and the charging roller used in Test Example 1 and the leveling roller. Was measured. Charge potential of polystyrene film (Vs
The maximum value of 2) was about -1153 V, and the minimum value was about -211 V. The upper and lower limits of the charging potential were higher than in the case of a 25 m photoreceptor which is usually used.

(Test Example 3) The charging roller and the leveling roller of Test Example 1 were mounted on a modified actual machine, and fine particles of TiO2 as a metal oxide were formed on a photosensitive layer (charge transport layer) having a thickness of 20 μm. A comparative durability test was carried out using a photoreceptor having a 5 μm surface layer containing the same and a photoreceptor having a 25 μm thick photosensitive layer (charge transport layer). The machine conditions other than the photoconductor were the same. After outputting 20 000 images, the thickness of the photoreceptor was measured, and the thickness of the photoreceptor with the surface layer was 21
μm, the thickness of the photoreceptor without the surface layer was 19 μm. As a result, by providing the surface layer on the photoreceptor, the amount of wear was reduced, and the durability was improved.

[0015]

As described above, by making the thickness of the photosensitive layer of the photoreceptor thicker than that of a commonly used photoreceptor, discharge in a pinhole of the photoreceptor is prevented, and the charging potential is made uniform. And increase the upper limit of the charging potential,
The charging potential width can also be increased. In addition, a material having a lower relative dielectric constant than a commonly used photoconductor is used for the photosensitive layer of the photoconductor, or a material having a lower relative dielectric constant is mixed with a conventional material to lower the dielectric constant, or By providing a surface layer having a lower dielectric constant than the photosensitive layer, it is possible to prevent discharge in the pinhole of the photosensitive member, to make the charging potential uniform, and to raise the upper limit of the charging potential. On the other hand, a material having a higher relative permittivity than a commonly used photoreceptor is used for the photosensitive layer of the photoreceptor, or a material having a higher relative permittivity is mixed with a conventional material to lower the permittivity, or By providing a surface layer having a higher dielectric constant than the photosensitive layer, it is possible to prevent discharge in a pinhole of the photosensitive member, to make the charging potential uniform, and to lower the lower limit of the charging potential. Further, the durability of the photoreceptor can be enhanced by mixing fine particles of high hardness into the surface layer of the photoreceptor. The durability of the photoconductor can be enhanced by mixing high-hardness oxide fine particles or high-hardness metal oxide fine particles into the surface layer or the photosensitive layer of the photoconductor.

[Brief description of the drawings]

FIG. 1 is a schematic view of a charging device of the present invention.

FIG. 2 is a diagram showing a change in a photoconductor surface potential (Vs2) when a film thickness (d) of the photoconductor is changed.

FIG. 3 is a diagram illustrating a change in photoconductor surface potential (Vs2) when the relative dielectric constant is changed.

[Explanation of symbols]

 2a &#9; charging member 3 &#9; leveling member 12 &#9; photoconductor 13 &#9; aluminum tube

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomoko Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H003 BB11 CC05 2H035 CA07 CB01 2H068 AA05 AA08 AA14 AA28 AA35 CA29 FA12 FC01

Claims (9)

[Claims] 1. A structure in which a plurality of members (members 1 to n) are pressed against or arranged close to a photoreceptor and a voltage is applied or grounded. In a charging device that applies electric charges to the photosensitive member and removes excess charges by the member n to obtain uniform charging, the photosensitive layer (CTL) of the photosensitive member is made thicker than a commonly used photosensitive member. Charging device. 2. A configuration in which a plurality of members (members 1 to n) are pressed against or arranged close to the photoconductor, and a voltage is applied or grounded. In a charging device that applies electric charges to the photosensitive member and removes excess charges by the member n to obtain uniform charging, a material having a lower relative dielectric constant than a commonly used photosensitive member is used for the photosensitive layer (CT) of the photosensitive member.
A charging device characterized in that the material used for L) or a material having a low relative dielectric constant is mixed with a conventional material so that the thickness of the photosensitive layer is not changed. 3. A structure in which a plurality of members (members 1 to n) are pressed against or arranged close to the photoconductor and a voltage is applied or grounded, and the members 1 to n-1 are used to apply a voltage to the photoconductor. In a charging device that applies electric charges to the photosensitive member and removes excess charges by the member n to obtain uniform charging, a material having a higher relative dielectric constant than a commonly used photosensitive member is used for the photosensitive layer (CT) of the photosensitive member.
A charging device characterized in that the material used for L) or a material having a high relative dielectric constant is mixed with a conventional material so that the thickness of the photosensitive layer is not changed. 4. A configuration in which a plurality of members (members 1 to n) are pressed against or arranged close to the photoconductor and a voltage is applied or grounded, and the members 1 to n-1 are used to apply a voltage to the photoconductor. In a charging device that applies electric charges to the photosensitive member and obtains uniform charge by removing excess charges by the member n, a surface layer having a higher dielectric constant than the photosensitive layer is provided on the photosensitive layer (CTL) of the photosensitive member,
A charging device, characterized in that the film thickness of the two layers is the same as that of a commonly used photoreceptor. 5. A structure in which a plurality of members (members 1 to n) are pressed against or arranged close to the photoconductor and a voltage is applied or grounded, and the members 1 to n-1 are used to apply a voltage to the photoconductor. In a charging device which applies electric charges to the photosensitive member and removes excess charges by the member n to obtain uniform charging, a surface layer having a lower dielectric constant than the photosensitive layer is provided on the photosensitive layer (CTL) of the photosensitive member,
A charging device, characterized in that the film thickness of the two layers is the same as that of a commonly used photoreceptor. 6. The charging device according to claim 4, wherein high-hardness fine particles are mixed in a surface layer of the photoreceptor. 7. The charging device according to claim 4, wherein fine particles of a high-hardness oxide are mixed into the surface layer or the photosensitive layer of the photoreceptor. 8. The charging device according to claim 4, wherein fine particles of a metal oxide having a high hardness are mixed in the surface layer or the photosensitive layer of the photoreceptor. 9. An image forming apparatus comprising the charging device according to claim 1.