JPH07140865A - Electrifying method for photoreceptor - Google Patents

Abstract

PURPOSE:To form an electrostatic latent image with the injection of a charge by bringing an electrically conductive member applied with voltage into contact with the surface layer of a rotary photoreceptor and uniformly electrifying it. CONSTITUTION:The photoreceptor 1 formed with a surface layer having volume resistivity of <=10<11>OMEGA.cm on the outer peripheral part is used, and the conductive member 2 applied with voltage is brought into contact with the surface layer of the rotary photoreceptor 1 to uniformly electrify it, prior to the formation of the electrostatic latent image on the photoreceptor 1. Thus, the photoreceptor 1 having the surface layer of low volume resistivity is used and the conductive member 2 to which the voltage is applied is brought into contact with the surface of the photoreceptor 1, so that even if the voltage applied to the conductive member 2 is low, the photoreceptor 1 can be electrified up to a potential required for forming the electrostatic latent image. At this time, the photoreceptor 1 is electrified mainly by the injection of the charge and the voltage applied to the conductive member 2 is low, so that discharge hardly occurs between the conductive member 2 and the photoreceptor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of charging a photoconductor in an image forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer or a facsimile, which uses a photoconductor, the photoconductor is uniformly charged by various methods before forming an electrostatic latent image.

One of the mainstream charging methods is by corona discharge of a charger. With this,
A large amount of ozone is generated during discharge, and a high voltage power source of about 4 to 10 KV is required.

Therefore, as an alternative charging method, a conductive member such as a conductive roller, a conductive brush, or a conductive elastic blade is brought into contact with the surface of the photoconductor, and a voltage is applied to the conductive member. To charge the photoconductor,
A contact charging method has been proposed (Japanese Patent Laid-Open No. Sho 56-56)
(See JP-A-144453, JP-A-1-93762, etc.).

By the way, as a photoreceptor, in order to retain an electrostatic latent image (latent image charge) in a dark place, the surface generally has a volume resistivity of 10 ¹² Ω · cm or more in the dark. A material having a high resistivity is used.

Even by the conventional contact type charging method,
It is premised on using a high-resistance photoconductor as described above, and in the current technical elucidation state, due to the discharge phenomenon performed between the conductive member and the minute gap between the photoconductor,
The high-resistance photoconductor is supposed to be uniformly charged.

The grounds for this are that ozone is generated between the photoconductor and the conductive member, and that there is a charging start voltage as shown in FIG. Incidentally, FIG. 7 is a diagram showing how the charging potential of the photoconductor changes when the voltage applied to a conductive member such as a conductive roller or brush is gradually increased from zero. Therefore, between zero and E, the photosensitive member is hardly charged, the applied voltage becomes E, and the charging potential rises greatly.

In any case, in this type of charging method, a small amount of ozone is generated, and there is a loss corresponding to the charging start voltage, and charging unevenness is likely to occur. Therefore, in order to prevent such charging unevenness, conventionally, an AC voltage is superimposed and applied to a conductive member.

In order to further suppress the generation of ozone, the value of the voltage applied to the conductive member in contact with the photosensitive member may be lowered and the electric charge may be injected into the photosensitive member to charge the photosensitive member.
However, when using a high-resistance photoconductor as in the past,
As can be understood from FIG. 7, when the voltage applied to the conductive member is low, the charging potential of the photoconductor cannot be increased to the extent that a predetermined electrostatic latent image can be formed on the photoconductor. This can be understood from the following facts.

FIG. 6 is a diagram showing an example of a contact charging system using the conductive member 100.
Is brought into contact with the drum-shaped photosensitive member 101 with a contact width W. The photoreceptor 101 shown here as an example has a drum-shaped conductive substrate and a photosensitive layer on the surface of which a charge generation layer and a charge retention layer are laminated in this order. Here, it is assumed that the specifications of the photoconductor 101 are as follows.

Linear velocity of the photosensitive member v = 100 mm / sec Width at which the conductive member contacts the photosensitive member W = 1 mm Voltage applied to the conductive member V ₁ = 1000 V Capacitance C of the charge holding layer on the surface of the photosensitive member = 100PF / cm ² Thickness of charge retention layer on photoreceptor surface T = 30 μm Volume resistivity of charge retention layer on photoreceptor surface R = 10 ¹² Ω · cm

If a relatively low voltage of 1000 V is applied to the conductive member 100 and the photosensitive member is charged by the charge injection method under the above-mentioned specification conditions, the conductive member 100 and the photosensitive member 101 will be charged. Moreover, it is considered that almost no discharge occurs, and therefore the generation of ozone can be suppressed. However, the volume resistivity R of the charge retention layer on the surface of the photoconductor is
Is as high as 10 ¹² Ω · cm, the charging potential of the photoconductor is 100 V.
The following results, and such a potential is insufficient for forming an electrostatic latent image.

When a high voltage is applied to the conductive member,
Ozone is generated by the discharge, but when this system is stopped and the above-mentioned charge injection system is adopted, it is difficult to set the surface of the photoconductor to a practical potential, for example, about 300 to 1000 V. This also applies to the case of a photoreceptor having a photosensitive layer other than the above-mentioned types.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sufficient photoreceptor to enable electrostatic latent image formation by charge injection rather than by corona discharge such as ozone. An object of the present invention is to provide a method for charging a photoreceptor in an image forming apparatus that can be charged.

[0015]

In order to achieve the above object, the present invention uses a photoreceptor having a surface layer having a volume resistivity of 10 ¹¹ Ω · cm or less and forms an electrostatic latent image on the photoreceptor. Prior to the above, a charging method for uniformly charging the photosensitive member, in which a conductive member to which a voltage was applied was brought into contact with the surface layer of the rotating photosensitive member to uniformly charge the photosensitive member The present invention proposes a charging method for a photoconductor in an image forming apparatus.

The surface layer has a volume resistivity of 10 ¹⁰ Ω.
It is effective if it is less than or equal to cm.

It is also effective to use a conductive member that elastically presses against the photosensitive member.

Further, it is effective to use a conductive member composed of a conductive rotating roller body.

Further, it is effective that the conductive member is driven so as to be brought into contact with or separated from the photoconductor depending on whether the photoconductor is charged or not charged.

Further, it is effective that the conductive member is also used as a cleaning member for cleaning the photosensitive member.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a schematic structure around a photoconductor of an electrophotographic copying machine which is an example of an image forming apparatus embodying the present invention.

In the figure, reference numeral 1 denotes a drum-shaped photoconductor, which is rotationally driven in the clockwise direction at a linear velocity of v.

The photosensitive member 1 driven to rotate in such a direction is
First, the conductive member 2 is uniformly charged. This will be described in detail later. The charged surface of the photoconductor is subjected to optical writing in the exposure unit 3 by, for example, light from a document (not shown), laser light, or the like,
A predetermined electrostatic latent image is formed on the photoconductor 1.

The electrostatic latent image thus formed is visualized as a toner image by the developing device 4, and the toner image is transferred to the transfer paper 7 by the discharging action of the transfer device 5. After that, the transfer paper 7 is separated from the photoconductor 1 by the discharging action of the separating device 6 and sent to a fixing device (not shown), where the toner image on the transfer paper 7 is fixed.

Here, in the photoconductor 1 in this example, as schematically shown in FIG. 2, the charge generation layer 1D laminated on the conductive substrate 1A and the charge retention layer 1B laminated thereon.
And a surface layer 1C laminated thereon, and the charge generation layer 1D and the charge retention layer 1B form a photosensitive layer.

Here, the feature of the charging method for the photosensitive member in this embodiment is that the photosensitive member 1 having the surface layer 1C having a volume resistivity of 10 ¹¹ Ω · cm or less formed on the outer peripheral portion is used. Prior to forming an electrostatic latent image on the body 1, the conductive member 2 to which a voltage is applied is brought into contact with the surface layer 1C of the rotating photoreceptor 1 to uniformly charge the photoreceptor 1.

When the photosensitive member 1 having the surface layer 1C having a low volume resistivity is used and the conductive member 2 to which a voltage is applied is brought into contact with the surface thereof, the voltage applied to the conductive member 2 is low. , The photoconductor 1 can be charged to a potential required for forming an electrostatic latent image. At this time, the photoconductor 1 is mainly charged by the charge injection, and the conductive member 2 is charged.
Since the voltage applied to the electrode is low, almost no discharge occurs between the conductive member 2 and the photoconductor 1, and thus it is possible to effectively suppress the generation of ozone or substantially prevent the generation of ozone. Is.

The formation of the surface layer 1C on the surface of the photosensitive member 1 itself is described in, for example, Japanese Patent Application Laid-Open No. 4 (1998) -264, filed by the applicant.
It is already known as disclosed in Japanese Patent Publication No. 93977, and as shown in this Publication, the surface layer 1C is made of, for example, the following materials.

That is, the surface layer has both abrasion resistance and mechanical strength capable of withstanding the use of about 500,000 copies, and is a resin coated with a resistance agent, a-
There are those formed by p-CVD such as C and a-Si: N.

The binder resin for the surface layer is preferably one that is substantially transparent to visible light and has excellent voltage insulation, strength and adhesiveness. For example, polystyrene, MMA, n-BM
A, polyamide, polyester, polyurethane, polycarbonate, polyvinyl formal, silicone resin,
Polyvinyl acetal, polyvinyl butyral, ethyl cellulose, melamine resin and copolymers and mixtures thereof are used.

As the resistance control agent, fatty acid salts, higher alcohols, sulfuric acid esters, fatty acid amines, quaternary ammonium salts, alkylpyridinium salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, sorbitan Anionic, cationic, or nonionic organic electrolytes such as alkyl esters and imidazoline derivatives; metals such as Au, Ag, Cu, Ni, and Al; ZnO, TiO ₂ , SnO ₂ , In ₂ O ₃ , Sb ₂ O ₃ Contained Sn
O _2, In ₂ O ₃ metal oxides such as containing SnO _2; MgF _2, Ca
Metal fluorides such as F ₂ , BiF ₂ , AlF ₂ , SnF ₂ , SnF ₄ and TiF ₄ ; organotitanium compounds such as tetrainpropyl titanate, tetranormal butyl titanate, titanium acetylacetonate and titanium lactate ethyl ester; And the like.

Various additives may be added to the surface layer for the purpose of improving adhesiveness, smoothness and the like.

The thickness of the surface layer is preferably 10 μm or less, and the resin having a resistance control agent added has a strength of 2 to 6 from the viewpoint of strength.
μm is more preferable, and a film having high film strength such as ac, a-Si; N is more preferably 0.5 to 2 μm.

The volume resistivity of the surface layer 1C as exemplified above is set to 10 ¹¹ Ω · cm or less, but if this resistivity is too low, the electrostatic latent image formed on the photoconductor 1 is reduced. Since the image may be disturbed, it is natural that the actual volume resistivity should be determined in consideration of this.

Next, it will be clarified that the photoconductor 1 can be charged to a predetermined potential by the charge injection as described above, by giving a more specific example.

Here, assuming the specifications of the linear velocity of the photoconductor 1 and the contact width of the conductive member 2 with respect to the photoconductor 1 as follows, the desired photoconductor potential is obtained as follows. . Note that FIG. 3 shows an equivalent circuit thereof. v: linear velocity of the surface of the photoconductor 1 W: contact width of the conductive member (electrode) 2 to the photoconductor ₁ (FIG. 2) V ₁ : voltage applied to the conductive member 2 (FIG. 1) T ₁ : surface layer Thickness of 1C (FIG. 2) T ₂ : Thickness of charge retention layer 1B (FIG. 2) C ₁ : Capacitance of surface layer 1C (dielectric constant ε ₁ ) G ₁ : Conductivity of surface layer 1C (= W / (R · T ₁ )) C ₂ : capacitance of the charge retaining layer 1B R: volume resistivity of the surface layer 1C e ₂ : voltage of the charge retaining layer 1B t: contact time of the conductive member 2 (maximum W / v) ) In the portion of the photoconductor 1 in contact with the conductive member 2, e ₂ is represented by the following formula 1.

[Equation 1]

Here, the photosensitive member 1 separated from the conductive member 2
In the portion, it is considered that only the resistance G ₁ in the equivalent circuit shown in FIG. 3, that is, only the charges that have passed through the surface layer 1C contribute to the potential of the charge holding layer 1B. ,

[Number 2] _{Q = C 2 e 2 -C 1} (V 1 -e 2) = (C 2 + C 1) becomes e ₂ -C ₁ V _1. If the charging potential at this time is e ′ ₂ ,

[Number 3] _{e '2 = Q / C 2} = (1 + C 1 / C 2) e 2 - (C 1
/ C ₂ ) V ₁

[0039] As mentioned previously, although the practical potential of the photosensitive member has a far 300 to 1000V about, the charge potential e _'2 of interest, in order to such potential Can be determined according to the following examples.

[0040]

[Table 1]

If the volume resistivity R of the surface layer 1C of the photoconductor 1 is set to 10 ¹⁰ Ω · cm as in Example 1, the conductive member 2
The photoconductor 1 is electrically connected to the conductive member 2 only by injecting charge via the
The voltage can be charged to 960 V, which is almost the same as the applied voltage (1000 V), and thus a predetermined electrostatic latent image can be reliably formed. In Example 2, surface layer 1
As a result of setting the volume resistivity R of C to 10 ¹¹ Ω · cm, the charging potential of the photoconductor 1 becomes 270 V, which is the lower limit of the practical potential of 30.
Although it is slightly short of 0 V, this can be sufficiently dealt with by increasing the contact width W of the conductive member 2 to the photoconductor 1 to increase the charging potential.

In any case, by using a photoreceptor having a surface layer 1C of 10 ¹¹ Ω · cm or less, preferably 10 ¹⁰ Ω · cm or less, a relatively low voltage, for example, 1000 V (Table By applying a voltage of about 1),
The photoreceptor can be charged to the required potential.

In the conventional charging method using corona discharge, a large amount of ozone is generated and a high voltage power source is required. or,
Even in the contact-type charging method using a high-resistance photoconductor, a small amount of ozone is generated, and it is necessary to apply an AC voltage to the conductive member in order to eliminate uneven charging. On the other hand, in this example, since the value of the voltage applied to the conductive member 2 is low, little or no discharge is generated, which makes it possible to more effectively suppress the generation of ozone.
Moreover, it is not necessary to apply an AC voltage to the conductive member.

By the way, as described above with reference to FIG. 1, the toner image on the photoconductor 1 is transferred onto the transfer paper 7, but the toner is left on the photoconductor 1 after the toner image transfer step. The remaining toner remains and is removed from the photoconductor 1 by the cleaning member of the cleaning device 8. At that time, in the example shown in FIG. 1, the conductive member 2 is also used as a cleaning member for cleaning the photoconductor.

That is, the conductive member 2 shown in FIG.
For example, when it is made of polyurethane rubber in which carbon is dispersed and is brought into contact with the photoconductor 1, the conductive member 2 scrapes off and removes the toner and the like remaining on the photoconductor 1 after the toner image transfer step. You can do it. The conductive member 2 can be used not only for charging the photoconductor but also as a cleaning blade for cleaning the photoconductor. By doing so, the number of parts can be reduced, the cost of the image forming apparatus can be reduced, and the image forming apparatus can be further downsized.

If the conductive member is not used also for cleaning, it may be constituted by a simple metal blade.

Further, as shown in FIG. 4, as the conductive member 12, a conductive elastic member 14 fixed to the tip side of a metallic elastic plate 13 may be used. good. Conductive member 1 configured in this way
The second conductive elastic member 14 is made of a conductive rubber, a conductive sponge, a conductive resin, or the like, and is a portion that comes into contact with the photoconductor 1.

As described above, when the conductive member 12 that is elastically pressed against the photosensitive member 1 is used, the conductive member 12 flexes well following the shape of the surface of the photosensitive member. The homogenization can be further promoted, and the main body only needs to have a simple elastic plate, which is advantageous in terms of cost.

As the conductive member, in addition to the blade-shaped member as described above, a conductive rotating roller body may be used as shown in FIG. The conductive member 22 is composed of a conductive rubber roller, a conductive sponge roller, or the like, and rotates with the photoconductor 1, for example. That is, the conductive member 22 is driven to rotate in the direction of the solid arrow.

On the other hand, the conductive member 22 is driven to rotate in the direction of the broken line arrow, and the conductive member 22 is attached to the surface of the photoconductor 1.
You may make it rub against. Further, even in the entrainment direction, even if the linear velocity of the conductive member 22 is different from the linear velocity of the photoconductor 1, the conductive member 22 rotates so as to slide on the photoconductor 1. In such a rotation method, the conductive member 22
Since the contact point between the photosensitive member 1 and the photosensitive member 1 changes every moment, it is possible to make it difficult to interpose toner or the like between them and to prevent the uniform charging property from being impaired.

As described above, when the rotary roller body is used as the conductive member, the peripheral surface of the rotary roller body continuously contacts the surface of the photoconductor, so that the life of the conductive member is extended. Be useful. When the rotating roller body is made of an elastic body so as to elastically contact the photosensitive body 1, the charging of the photosensitive body 1 can be made uniform. Furthermore, since the contact partner (surface layer 1C) of the conductive member 22 has a low resistance, leakage or the like is less likely to occur while the conductive member 22 composed of the rotating roller body is rotating. When the volume resistivity of the photoconductor is high as in the prior art, it is necessary to provide an insulating layer on the surface of the rotating roller body in order to prevent leakage, but in this example, such treatment is unnecessary.

By the way, in FIG. 1, the voltage V ₁ is applied to the conductive member (also used as the cleaning blade in this example) 2. When the photosensitive member 1 is charged, for example, the switch S shown in FIG. Is closed, and the switch S is opened when it is not charged.

On the other hand, the conductive member 2 may be driven into contact with or separated from the image forming area on the photosensitive member without opening or closing such a switch. The conductive member 2 is fixed to a mounting member 16 pivotally supported by a shaft 15, and is in contact with the photoconductor 1 at a predetermined pressure by the force of a torsion coil spring 17 mounted on the shaft 15. A solenoid 18 is connected to the mounting member 16, and when the solenoid 18 is not charged, the solenoid 18 is excited, and accordingly, the mounting member 16 is rotated clockwise around the shaft 15 so that the conductive member 2 becomes a photosensitive member. Separate from 1. On the other hand, when charged, the solenoid 1
The excitation of No. 8 is released, and the conductive member 2 contacts the photoconductor 1 by the force of the spring 17. As a result, the charged area on the photoconductor 1 can be limited.

As described above, if the conductive member 2 is driven to come into contact with or separate from the photosensitive member 1 depending on whether the photosensitive member is charged or not, the conductive member 2 is driven. ON / OFF control of voltage application to 2 can be simplified,
Also, the voltage power supply can be used in common with other things (for example, a transfer charger). Further, it is possible to prevent abrasion or deformation of the portion of the conductive member that comes into contact with the photosensitive member. The conductive members shown in FIG. 4 and FIG.
The same action and effect can be obtained by adopting a configuration in which they are driven to approach and separate in the same manner.

Here, as shown in FIG. 2, the surface layer 1C is a low-resistance layer that improves uniform charging of the photoconductor,
The charge retention layer 1B is a layer that maintains a latent image potential (latent image charge), but in the present charging method, both functions are skillfully used properly.

As described above, when the surface resistance of the photoconductor is low, it becomes easy to inject charges, and the selection range as a conductive member can be greatly expanded. For example,
A fixed brush, a rotating brush, or the like may be used as the conductive member, and conventionally, streak-like charging unevenness is not likely to occur when such a member is used. Even if the surface layer of the photoconductor has a low resistance, for example, an electrostatic latent image (latent image charge) after optical writing can be held without any problem.

Such a latent image is formed at the interface between the surface layer and the charge retention layer. According to the experiments of the present inventor, the surface layer 1C has a volume resistivity of 10 ⁹ Ω · cm, Thickness 5
It has been confirmed that the latent image is retained for the required time, assuming that it is μm.

The present invention is not limited to the photoconductor provided with the photoconductive layer composed of the charge generation layer 1D and the charge retention layer 1B as shown in FIG. 2, and can be applied to any conventionally known photoconductor charging method. It is applicable.

[0059]

According to the charging method of the first aspect, it is possible to uniformly charge the photoconductor at a low voltage without generating ozone. In addition, uneven charging is less likely to occur, and it is not necessary to apply an AC voltage to the conductive member to prevent it.

According to the charging method of the second aspect, the uniform charging property of the photoconductor can be further improved.

According to the charging method of the third aspect, the uniform charging can be further promoted.

According to the charging method of the fourth aspect, the life of the conductive member and the photoconductor can be extended.

According to the charging method of the fifth aspect, abrasion and deformation of the conductive member can be made difficult to occur, and the power source for applying a voltage to the conductive member can also be used as another power source.

According to the charging method of the sixth aspect, since the conductive member is also used for cleaning the photosensitive member, the number of parts is reduced and the cost of the image forming apparatus is reduced.
It is possible to downsize the image forming apparatus.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration around a photoconductor of an electrophotographic copying machine embodying the present invention.

FIG. 2 is an enlarged schematic view of a part of an outer layer portion of the photoconductor to clarify the structure of the photoconductor.

FIG. 3 is a diagram showing an equivalent circuit.

FIG. 4 is a diagram showing another example of a conductive member.

FIG. 5 is a diagram showing a conductive member of another example.

FIG. 6 is a configuration diagram of a photoconductor charging unit for explaining a conventional method.

FIG. 7 is a diagram showing a correlation characteristic between a voltage applied to a conventional conductive member and a charging potential of a photoconductor.

[Explanation of symbols]

 1 Photoconductor 1C Surface layer 2 Conductive member 12 Conductive member 22 Conductive member

Claims (6)

[Claims] 1. A charging method in which a photoreceptor having a surface layer having a volume resistivity of 10 ¹¹ Ω · cm or less is used, and the photoreceptor is uniformly charged prior to forming an electrostatic latent image on the photoreceptor. A method of charging a photoconductor in an image forming apparatus, wherein the photoconductive member is uniformly charged by bringing a conductive member to which a voltage is applied into contact with a surface layer of a rotating photoconductor. 2. The method for charging a photoreceptor in an image forming apparatus according to claim 1, wherein the surface layer has a volume resistivity of 10 ¹⁰ Ω · cm or less. 3. The method for charging a photoconductor in an image forming apparatus according to claim 1, wherein a conductive member that elastically comes into pressure contact with the photoconductor is used. 4. The method of charging a photoconductor in an image forming apparatus according to claim 1, wherein a conductive member made of a conductive rotating roller body is used. 5. The conductive member is driven into contact with or separated from the photoconductor depending on whether the photoconductor is charged or not charged, according to any one of claims 1 to 4. A method for charging a photoreceptor in the image forming apparatus described in claim 1. 6. The method for charging a photoconductor in an image forming apparatus according to claim 1, wherein the conductive member is also used as a cleaning member for cleaning the photoconductor.