JPH01138572A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent image running by forming the thin layer of developer on a surface part area facing the discharging openings of corona dischargers on an image carrier surface and then, suspending or stopping the title device when an image forming action comes to an end. CONSTITUTION:When the image forming action comes to an end, the thin layer of the developer is formed on the surface part area facing the discharging openings of the corona dischargers 2, 7, 10 and 11 on the image carrier 1 surface. After that, the device is kept dormant or stopped. That is, when the device is dormant, the surface part area facing the discharging openings of the corona discharger 2, 7, 10 and 11 on the image carrier 1 surface is coated with the thin layer of the developer. Therefore, when the device is dormant, though attaching corona products in the corona discharger 2, 7, 10 and 11 are volatilized and isolated, they are absorbed by the developer thin layer coating the image carrier 1 surface so as not to directly attach to the image carrier 1 surface. Thus, the image running can be effectively prevented which is caused by the attachment of the corona products.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is applicable to transfer type electrophotographic devices, electrostatic recording devices, etc., in which corona is applied to the surface of an image carrier such as a photoreceptor or dielectric (insulator). Transfer method image formation in which an image is formed by applying an image forming process that includes charge removal processing (charging processing/static charge removal processing) using a discharge device, the image is transferred to a transfer material, and the image carrier is repeatedly used for image formation. Regarding equipment.

[Conventional technology]

As a photoreceptor that is an image bearing member that is repeatedly used for image formation in a transfer type electrophotographic device, Se-CdSΦ Zn is used.
Various types, such as single-layer type or laminated type, have been put into practical use using inorganic photoconductive materials such as O.amorphous silicon or organic photoconductive materials (OPC) such as polyvinylcarbazole phthalocyanine as photosensitive layer materials.

Among them, amorphous silicon (
Amorphous silicon (hereinafter referred to as a-Si) has attracted attention as a particularly excellent material, and photoreceptors with a-3i as a photosensitive layer are used in high-speed electrophotographic devices and laser beam printers (LB).
It is used as a photoreceptor to be incorporated as an image bearing member in P), etc.

In other words, the a-3i photoreceptor has a higher surface hardness of the photosensitive layer ((JIS standard,
Vickers hardness JOOOK g/am2 or more), extremely excellent wear resistance, scratch resistance, impact resistance, etc., excellent heat resistance, moisture resistance, corona ion resistance, potential stability, etc., and good photosensitivity. It has various features such as being highly sensitive to long wavelength light such as lasers (770 nm to 800 nm), showing almost no deterioration in photosensitivity, and being completely non-toxic. However, it is a long-life photoreceptor with almost no physical or chemical deterioration or modification.

On the other hand, the image forming process for an image carrier such as a photoreceptor in electrophotography or a dielectric in electrostatic recording usually includes a step of charging or eliminating static electricity on the surface of the linear image carrier, and the charging/discharging device is uniform. Corona dischargers (corotrons and scorotrons), which have excellent static charge removal properties, are widely used.

A corona discharger has a wire electrode and a shield plate as its main components, and by applying a high voltage to the wire electrode, a corona current generated outward from a discharge opening is applied to the image carrier surface to eliminate static charge on the image carrier surface. This is what we do.

[Problem that the invention seeks to solve]

■However, corona dischargers produce ozone ' due to corona discharge.
See the generation of (03)0 Ozone generated oxidizes nitrogen in the air to produce nitrogen oxides (NOx) and the like. Furthermore, the produced nitrogen oxides react with moisture in the air to form nitric acid (HN).
O3) etc. Corona products such as nitrogen oxides and nitric acid adhere to the inner surface of the shield plate of the corona discharger and the surface of the image carrier due to repeated use of the image forming apparatus. Corona products have strong hygroscopicity, and the surface of the image carrier on which they have adhered has a lower resistance due to moisture absorption of the attached corona products, so that the charge retention ability (surface resistance) of the surface is substantially reduced entirely or partially. As a result, image blurring of the output image and so-called image blurring (charge on the image carrier surface moves (leak) in the surface direction, causing the electrostatic charge latent image pattern to collapse or not be formed), etc. Look at the phenomenon.

■Also, corona products adhering to the inner surface of the shield plate of the corona discharger are particularly susceptible to high humidity such as summer (70%R).
(H or higher), it absorbs moisture and becomes volatile and liberated not only when the image forming apparatus is in operation but also when the apparatus is not in operation such as at night (or while the apparatus is stopped; the same applies hereinafter). The corona product migrates and adheres to the partial area of the surface of the image carrier that faces the discharge opening of the discharge device and has stopped surface movement, thereby lowering the resistance of the partial area of the image carrier surface. Therefore, for the first or several image-formed products (copies) that are output when the device is restarted the next morning after the device is stopped, the image may be blurred on the partial surface corresponding to the discharger opening while the device is out of service. - Image blur (so-called discharger trace flow) is likely to occur.

In particular, when the corona discharger is a discharger containing an AC (alternating current) corona component (AC corona discharger), such as a discharger for the pre-transfer charging process or a discharger for the transfer material separation process, corona products are generated. This phenomenon is clearly observed in many cases.

(2) When the image carrier is an a-9i photoreceptor, problems such as (2) and (2) above due to corona products become more serious. In other words, the a-9i photoreceptor has a lower charge removal efficiency (the amount of corona discharge current required to obtain a predetermined charge removal potential) than other photoreceptors, and therefore the charge removal efficiency of the a-9i photoreceptor due to corona discharge is lower. In the static elimination process, the voltage applied to the discharger is made higher than in the case of other photoreceptors, and the discharge current is significantly increased. The a-9i photoreceptor is often used particularly in high-speed electrophotographic equipment, and the amount of discharge current in such cases can reach, for example, 2000 JLA. Since there is a proportional relationship between the amount of corona discharge current and the amount of ozone generated, the amount of ozone generated is particularly large in systems where the photoreceptor is an a-Si photoreceptor and the charge is removed by corona discharge. The problem caused by the generation of the corona products is particularly great.

The above problem is also common to electrostatic recording devices that use an insulator as an image carrier.

Therefore, conventionally, the following measures have been adopted to prevent image blurring such as the above-mentioned (1) and (2) caused by the adhesion of corona products to the surface of the image carrier.

a. A surface layer of a-9iC, a-SiNx, etc. is provided on the surface of the image carrier. However, even with such processing, the current situation is that image deletion cannot be completely prevented.

b. By heating or heating the surface of the image carrier and keeping it in a dry state by providing a heater on the inner surface of the image carrier, the resistance of the surface of the image carrier is substantially lowered due to moisture absorption of attached corona products. suppress. Although this is a fairly effective means, it has been difficult to sufficiently prevent the so-called discharger trailing phenomenon described in (2) above. That is, the area of the surface of the image carrier corresponding to the opening of the discharger when the apparatus is not in use, such as at night, is subject to migration of volatile free components of corona products adhering inside the discharger even when the apparatus is not in use. This is because the degree of contamination by corona products is higher than in other areas, the adhesion is stronger, and the hygroscopicity is stronger.

An abrasive is externally added to the C1 developer, or a polishing means or a rubbing means is provided in contact with the surface of the image carrier to actively scrape off and remove corona products adhering to the surface of the image carrier. Due to the same reasons as mentioned above, it is also difficult to sufficiently prevent the so-called discharger trace flow phenomenon.As mentioned above, the present invention prevents the discharger trace flow phenomenon, which was difficult to completely prevent in the past. The object of the present invention is to effectively prevent image blur caused by the adhesion of corona products to the surface of an image carrier.

[Means for solving problems]

The present invention is a transfer method in which an image is formed on the surface of an image carrier by applying an image forming process including charge removal treatment using a corona discharger, the image is transferred to a transfer material, and the image carrier is repeatedly subjected to image formation. In the image forming apparatus, when the image forming operation of the apparatus is completed, the apparatus is operated by performing an operation process of forming a thin layer of developer on at least a partial area of the surface of the image carrier facing the discharge opening of the corona discharger. The image forming apparatus is characterized in that the image forming apparatus is maintained in a paused or stopped state.

[For production]

That is, during the period when the image forming apparatus is not in use, at least the area of the surface of the image carrier facing the discharge opening of the corona discharger is covered with a thin layer of developer. Even if the corona products adhering within the corona discharger are volatilized and liberated, they are adsorbed by the thin layer of developer covering the surface of the image carrier and are prevented from directly adhering to the surface of the image carrier.

The thin layer of developer on the surface of the image carrier that has adsorbed corona products is then completely removed from the surface of the image carrier by a cleaning device when the apparatus is restarted.

Therefore, the corona discharger trace phenomenon that tends to occur on image-formed objects when the apparatus is restarted after the apparatus has been shut down can be effectively prevented.

〔Example〕

FIG. 1 shows the schematic structure of an embodiment of the apparatus, and this embodiment is a rotating drum type transfer type electrophotographic apparatus.

Reference numeral 1 denotes a drum-type photoreceptor as an image carrier which is rotated in the direction of arrow a around the central axis 1a at a process speed (peripheral speed of rotation) of 440/sec.
-Si photoreceptor. During the rotation process, the surface of the photoreceptor is sequentially subjected to the following image forming steps by operating process equipment disposed around the photoreceptor to form an image.

(2) --like charging=A corona charge is applied by the main corrosive discharger 2 to which a voltage of +7.4 KV is applied, and the battery is uniformly charged.

■Blank exposure = In order to erase the electrical charge on the unnecessary surface part of the photoreceptor that occurs depending on the size of the transfer material used and to make so-called black sake, blank exposure is performed.
D) Selective exposure is performed in step 3 to erase charges on unnecessary surface portions of the photoreceptor surface.

(2) Light image exposure=Exposure 4 of a light image of a document is performed from a document scanning section (not shown) via an optical system, and electrostatic latent images corresponding to the exposed light image pattern are sequentially formed on the surface of the photoreceptor.

■Development = developer 6 (one-component insulating negative toner developer, /
<Ias V oc 130V, V pc 14
00Vp-p, 1800Hz), the electrostatic latent image is sequentially developed as a toner image.

Reference numeral 5 denotes a photoconductor surface potential sensor disposed between the photoimage exposure section 4 and the developing device 6, and process execution conditions such as the bias value of the developing device 5 are determined according to the photoconductor surface potential detected by the sensor. is automatically controlled to maintain and manage the density of the output image at a constant level.

■Pre-transfer charging/pre-transfer exposure = Pre-transfer corona discharger in which a corona charge of the same polarity as the toner is applied in a superimposed manner with an AC component voltage in order to increase the transfer efficiency of the toner image transferred to the transfer material in the next transfer process. 7 (Voc-1-5KV, VAC
9KVP-P, 500)1z).

Further, if necessary, in addition to the pre-transfer charging, exposure by a pre-transfer exposure device 8 is performed to improve the separability of the transfer material.

<Transfer = A transfer material P is fed one sheet from a transfer material feeding section (not shown), and its leading edge is once received by a pair of registration rollers 9, and the leading edge of the toner image on the first surface of the photoreceptor is used for transfer. When the tip of the transfer material P reaches the position of the corona discharger 10, the transfer material P is moved between the discharger lO and the photoreceptor l by the re-rotation of the registration roller pair 9. A transfer corona discharger which is fed and brought into contact with or close to one surface of the photoconductor in the vicinity of the discharger 10, and a corona charge of the opposite polarity to the toner image and a voltage of +7.8 KV is applied to the back surface thereof. It passes between the discharger 10 and the photoreceptor l while being received by the discharger 10.

As a result, the toner image on the photoreceptor 1 side is sequentially transferred to the surface side of the transfer material P. In the process of passing between the discharger 10 and the photoreceptor 1, the transfer material P passes through the discharger 10. It is charged up by the discharged charge and is strongly attracted electrostatically to the surface of the photoreceptor and comes into close contact with it.

■Transfer material separation charging = The transfer material P that is electrostatically in close contact with one surface of the photoreceptor and has passed the position of the transfer corona discharger 10 has a corona charge on its back surface that is opposite in polarity to the corona charge during transfer.
Separation corona discharger 11 to which AC component voltage was applied in a superimposed manner (
Voc-Q, 5KV, Vpc 1.4KVp-p,
5QOHz) I received a grin. As a result, the transfer material P is neutralized and easily separated from the surface of the photoreceptor, and the separation member 13
Coupled with this, the photoreceptor is sequentially separated from one surface.

The transfer material P separated from the first surface of the photoreceptor is conveyed by a conveyor belt device]
2, the image is introduced into a fixing device (not shown), the image is fixed, and the image is discharged out of the apparatus as a single image-formed product (copy).

(Leaning=The surface of the photoreceptor from which the transfer material P has been separated is cleaned by the cleaning device 14 by removing residual toner, paper powder, dust, and other adhered contaminants.

(2) Static elimination: Electrical memory (charged memory) is erased by uniform exposure from the main static elimination exposure light source 15.

The photoreceptor l whose surface has been physically and electrically cleaned by the cleaning device 14 and the main static eliminating light source 15 is repeatedly used for image formation.

FIG. 5 shows an example of a conventional control timing chart (sequence) for the electrophotographic apparatus as described above.

This chart is from two consecutive copies.

When the main power switch is turned on and the copy start key is turned on, the main motor M of the device is energized and the pre-rotation of the photoreceptor l is started, and the circumferential rotational speed of the photoreceptor reaches a predetermined speed. During this pre-rotation period, the developing device 6 prevents fogging on the developing roller of the developing device so that unnecessary toner (fogging toner) does not adhere to the surface of the photoreceptor. The image forming process cycles of 0, 1st copy and 2nd copy are sequentially executed to which a high bias A (DC+500V) is applied, and then after a predetermined post-rotation drive of the photoreceptor 1 (post-rotation period) After that, the main motor M is de-energized, the photoreceptor l stops rotating, and the apparatus enters a hibernation state. Even during the subsequent rotation period, a bias A to prevent fogging is applied to the developing roller of the developing device.

Main corona discharger (DC) 2, pre-transfer corona discharger (
AC) 7. Corona discharger for transfer (DC) 10 and corona discharger for transfer material separation (AC)ti are sequentially applied with voltage and turned on with a predetermined time difference in the above order during the pre-rotation period of the photoreceptor l. After the image forming process cycle for a predetermined number of copies (first and second copies) is completed, voltage is applied and turned off sequentially with a predetermined time difference in the same order as above during the post-rotation period of the photoreceptor l. This sequence is designed to avoid applying an unreasonable electric field to the photoconductor.
This is suitable for photoconductors that are susceptible to charge memory, such as Se photoconductors and OPC photoconductors other than a-5i photoconductors.

The discharger trace flow phenomenon described above occurs when each corona discharger 2 and 7 is stopped when the photoreceptor 1 is not rotating.
・This is because corona products adhering to the inner surface of the shield plate of each discharger volatilize and become attached to the bond area of the photoreceptor surface facing the discharge opening of 10-11, especially AC corona. Discharge device 7 for pre-transfer and transfer material separation using
- As mentioned above, there are many corona products in it, which tends to cause the discharger trace flow phenomenon.

Therefore, as described above, the present invention maintains the device in a dormant state by forming a thin layer of developer on at least a portion of the surface of the photoreceptor (image carrier) facing the discharge opening of the corona discharger. This is designed to prevent the corona discharger trace flow phenomenon, and a specific example of the procedure for forming the thin developer layer will be described below.

Example 1 In the apparatus shown in the example of FIG. 1, the sequence of each image forming process device during the post-rotation period of the photoreceptor 1 was set as shown in the timing chart of FIG.

That is, a voltage is continuously applied to each of the corona dischargers 2, 7, and 10-11 during the post-rotation period of the photoreceptor 1 to maintain the corona discharge state.

The developing device 6 is also continued during the post-rotation period of the photoreceptor 1 for DC minutes.
AC developing bias (Voe+ 150V, VAC
1400 Vp-p, 1800 Hz) is applied to maintain a developable state.

The exposure lamp (LED) of the blank exposure unit 3 is kept turned off during the post-rotation period of the photoreceptor 1.

The document scanning unit (not shown) returns to the home position and keeps the stationary document illumination lamp in a weakly lit state to illuminate the white plate, and the light corresponding to the intermediate tone reflected from the white plate is exposed through the optical system. The whole surface of the photoreceptor 1 is irradiated 4a (FIG. 1) continuously during the post-rotation period of the body 1.

As a result, the surface of the photoreceptor during post-rotation is uniformly charged by the main corona discharger 2 and the entire surface is irradiated with light corresponding to a halftone 4a, so that the entire surface becomes a halftone potential surface, and this potential surface is developed by the developer 6. A thin layer of developer (toner) is formed on the surface of the photoconductor, and when the post-rotation period ends and the rotation of the photoconductor 1 has stopped, the direction of rotation of the photoconductor 1 can be changed from the position of the developing device 6. The entire lower surface area of the photoreceptor up to the position of the cleaning device 14 on the downstream side is covered with a thin layer of developer, and the apparatus enters a rest state.

That is, the surface of the photoreceptor l covered with a thin layer of developer is connected to each corona discharger 7 for pre-transfer, for transfer, and for transfer material separation.
Therefore, even if the attached corona products in each corona discharger volatilize and release during the idle period of the apparatus, it will not be transferred to the thin developer layer covering one surface of the photoreceptor. It is prevented from being adsorbed and directly attached to the surface of the photoreceptor. In other words, the corona discharger trailing phenomenon caused by the corona discharger 7 and lOφ11 is prevented.

The above-mentioned thin layer of developer formed on the first surface of the photoconductor is then completely removed from the first surface of the photoconductor by the cleaning device 14 during the pre-rotation period when the copy start key is turned on and the rotation of the photoconductor l is started. removed.

The thickness of the developer thin layer formed on one surface of the photoreceptor is
This can be arbitrarily controlled by adjusting the light intensity of the document illumination lamp for exposing the light 4a corresponding to the intermediate tone and the density of the reflective white plate.

The greater the thickness of the developer thin layer formed, the greater the effect of preventing the discharger flow phenomenon, while the thinner the layer, the lower the prevention effect.

Since the thickness of the thin developer layer formed on one surface of the photoreceptor and the reflection density of that layer (solid black reflection density) are approximately in correspondence,
Each photoreceptor has a reflection density of 1.4° and 0.8°. O.J., 0.
The effect of preventing the discharger trailing phenomenon in each case was compared when a thin developer layer of 3 and 0.1 was formed. The results are shown in the table below.

That is, if the thickness of the thin developer layer is made thicker (reflection density - larger), the effect of preventing discharger traces from flowing will be improved. However, toner consumption also increases.

Therefore, considering economic efficiency, generally 0.15 to 066,
It is desirable to control the developer so that a thin layer of developer is formed, preferably with a thickness corresponding to a reflection density of about 0.15 to 0.3.The amount of developer consumed for copies made in offices, etc. is The amount is 0.05 to 0.09 g/piece.

In this example, for the main corona discharger 2, the surface of the photoreceptor on which the thin developer layer is not formed is kept facing the discharge opening of the discharger during the period when the apparatus is not in use. 2 is a corona discharger 7 for use before transfer and for separating transfer material.
11, it is a DC corona discharger that does not contain an AC corona component, and especially in the case of an amorphous silicon photoreceptor, it is generally +DC charged, has less corona products than an AC corona discharger, and has the same effect as conventional image deletion. By using in combination the formation of a surface layer on the photoreceptor in item a, the heating means in item b, and the external addition of an abrasive agent to the developer in item 0, or the attachment of a polishing/rubbing means, etc. as means for preventing the phenomenon. Even if the discharger trailing phenomenon caused by the discharger 2 is observed, it is actually mild and falls within a practically acceptable range.

However, if necessary, during the post-rotation period of the photoconductor 1, at least the contact member of the cleaning device 14 against the photoconductor surface may be automatically released and moved to a position separated from the photoconductor surface. A thin layer of developer can be formed on the circumferential surface, and therefore, the phenomenon of discharger trace flow in all the dischargers 2 and 7Φ10-11 can be effectively prevented.

The sequence shown in Figure 2 turns off charging and exposure at the same time, which is different from the conventional method, but when an a-Si photoreceptor is used as the photoreceptor L, it is difficult for residuals to remain in both the charged memory and the optical memory, which is a problem. is hardly recognized.

In addition, to prevent image blurring caused by corona products generated from each discharger and attached to one surface of the photoreceptor during operation of the apparatus, conventional image blurring prevention means such as those described in items a-C above should be used in combination. This can be prevented by

Example-2 In order to bring the photoreceptor surface to a halftone potential during the post-rotation period of the photoreceptor l, the halftone equivalent light is irradiated on the entire surface of the photoreceptor in Example-1 above.
Instead of using the document illumination lamp (Figure 2) that is controlled to be lit in a weak state as shown in Figure 3, it is also effective to control the blank exposure lamp (LED) to be lit in a weak manner as shown in the sequence in Figure 3. It is.

The main purpose of blank exposure is to erase black according to the size of the transfer material used, and since it is usually a dynamic lighting method, it is possible to control weak lighting relatively easily.

Example-3 During the post-rotation period of photoconductor 1, the surface potential of the photoconductor surface is set to O~50.
Then, the developing bias for the developing device 6 is set to only a negative DC bias as shown in the sequence shown in FIG. 4, and the developer is transferred to the surface of the photoreceptor to form a thin layer of developer.

Example 4 If a thin layer of developer is formed on the surface of the photoreceptor during all copy rotations, good copies can be obtained, but on the other hand, the amount of developer consumed increases, resulting in an uneconomical aspect. In order to avoid this, the timing of the device's operation sequence should be more precise.
In particular, it is also effective to form a thin developer layer only on the partial region of the photoreceptor surface facing the discharge opening of the AC corona dischargers 7 and 11, which is likely to cause the discharger trailing phenomenon.

Example 5 More economically, when the main power switch of the apparatus is turned off, a delay timer switch is used to cause the photoreceptor to rotate later to form a thin layer of developer on the surface of the photoreceptor.
After that, it is effective to turn off the main power supply when the timer expires and keep the device in a dormant state.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to completely prevent the discharger trailing phenomenon caused by an AC corona discharger, which was difficult to completely prevent with conventional means, and the intended purpose is well achieved.

In particular, the present invention provides an apparatus in which the photoreceptor as an image carrier is an a-Si photoreceptor, and the photoreceptor has better chemical stability than other photoreceptors, that is, deterioration due to long-term adhesion of a thin layer of developer. - Since there is no formation of a memory or the like, and the stability of the potential characteristics is good, that is, there is a large degree of freedom in the timing of charging φ exposure, it can be applied without any problems and sufficient effects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an example of an electrophotographic apparatus, and FIGS. 2 to 4 are examples of device control timing charts (sequences) for forming a thin layer of developer on the surface of the photoreceptor during the post-rotation period of the photoreceptor, respectively; FIG. 5 is an example of a conventional device control timing chart (sequence). 1 is a rotating drum type photoreceptor (a-3i photoreceptor), 2.7.
10Φ11 is a corona discharger, 3 is a blank exposure unit)
(LED), 6 is a developing device, and 14 is a cleaning device.

Claims (1)

[Scope of Claims] 1. An image is formed on the surface of the image carrier by applying an image forming process including charge removal treatment using a corona discharger, the image is transferred to a transfer material, and the image carrier is repeatedly used to form an image. In a transfer-type image forming apparatus used for image forming, an operation step is performed to form a thin layer of developer on at least a partial area of the surface of the image carrier facing the discharge opening of the corona discharger when the image forming operation of the apparatus is completed. An image forming apparatus characterized in that the image forming apparatus is configured to keep the apparatus in a paused or stopped state. 2. The image forming apparatus according to claim 1, wherein a thin layer of developer is formed on the surface of the image carrier between the developing device and the cleaning device with respect to the surface movement direction of the image carrier surface. 3. Facing the discharge openings of the corona dischargers for pre-transfer, transfer, and transfer material separation, which are arranged opposite to the image carrier surface between the developing device and the cleaning device in the direction of surface movement of the image carrier surface. The image forming apparatus according to claim 1, wherein a thin layer of developer is formed on a partial area of the surface of the image carrier. 4. The image forming apparatus according to claim 1, wherein the operation step of forming a thin developer layer on the surface of the image carrier is executed after the main power switch of the apparatus is turned off. 5. The image forming apparatus according to claim 1, wherein the image carrier is an amorphous silicon photoreceptor.