JPH03136068A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of the flow of a picture caused by soil by applying a bias voltage to a contact electrifying member after an image carrier surface part facing to a cleaning means passes through the position where the contact electrifying member abuts on the image carrier at the time of starting an image carrier. CONSTITUTION:Applying of a bias voltage to an electrifying roller 2a is started after the elapse of DELTAt minutes after the initiation of its rotation caused by the start of the drum 1. DELTAt is set so as to establish the following relation: DELTAt>=l/Vp, where l(nm) is a distance between the cleaning-blade-abutting part E and the electrifying-roller-abutting part D, both of which are in the area of a drum surface part B, and Vp(nm/sec) is the peripheral velocity on the photosensitive drum 1. Therefore, even if rubber, etc., sticks to the drum surface part B when the device stops operation or is in a stand-by condition, or even if developer is taken from the part E abutting on the cleaning blade 11 at the time of starting the drum 1, a bias voltage is applied to the electrifying roller 2a after they pass through the electrifying-roller-abutting part D in the DELTAt time which is the beginning of the prerotation of the drum. Thus, soil of the electrifying roller is prevented, and picture flaw does not occur.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an image forming apparatus.

More specifically, a contact charging member that contacts the surface of the image carrier to which a bias voltage is applied and is driven one rotation or rotationally and charges the surface of the image carrier in a predetermined manner, and an image carrier after one image formation. The present invention relates to an image forming apparatus in which an image forming process means includes a cleaning means that cleans the body surface and enables repeated use of the image bearing member.

(Prior Art) In the image forming apparatus as described above, one image forming process means is a conventionally known electrophotographic process means, electrostatic recording process means, etc.

The image carrier that is rotated or rotationally driven is, for example, an electrophotographic photoreceptor, an electrostatic recording dielectric material, etc., such as a two-rotation drum type or a fist rotation belt type.

The contact charging member is a conductive member in the form of a roller, belt, web, blade, fist pad, block, or rod, and a bias voltage is applied to it to form an image as a charged object. The image carrier surface is charged to a predetermined potential by being brought into contact with the carrier surface, and the voltage of the charging system can be lowered compared to the corona discharger that has been commonly used as a charging processing device. It has the advantages of producing only a very small amount of ozone and having a simple configuration, and many development proposals have been made by study groups for its practical application as a charging treatment device in place of corona dischargers, and it is being put into practical use. Yes (Japanese Patent Application Laid-Open No. 57-178287/5Ei-1043
51・58-40568・58-139158-58-
150975 etc.).

The present applicant applied a DC voltage to the charging member and an oscillating voltage that is more than twice the charging start voltage of the charged object (the voltage value changes periodically with the gap between the ribs) for the purpose of uniform charging processing without charging unevenness. Various proposals have been made, such as applying a superimposed voltage (voltage) and forming a charging member into a multi-layer structure to eliminate abnormal discharge and dielectric breakdown from the charging member to the charged object. 81-298419-82-230334
No. etc.).

A cleaning device that cleans the surface of the image carrier after image formation and makes it possible to reuse the LT carrier is a cleaning device that wipes the surface of the image carrier by bringing a blade made of rubber or the like into contact with the image carrier as a cleaning member. There are blade cleaning devices that clean by sweeping, and devices that clean by pressing a cleaning member in the form of a rotating roller body 9, a running web body, a pad body, etc. against the image carrier surface.

The image forming device 2 of the present invention is a transfer type copying machine, a laser beam printer, a recording device, etc., in which an image of target image information formed and carried on an image carrier surface is transferred to a copying material, and image transfer is performed. In addition to cleaning the image carrier surface with a cleaning device and repeatedly performing image formation, it is also possible to place an image of desired image information formed on the image carrier surface as an image display device, display device, etc. on a monitor unit. The image forming apparatus also includes an image forming apparatus in which the image bearing member is repeatedly used for displaying and reading images, and then cleaning and erasing the formed and carried image with a cleaning device, so that the image bearing member is repeatedly used for forming display images.

FIG. 5 shows a schematic configuration of an example of an image forming apparatus to which the present invention is applied. It's a printer.

l is a rotating drum-type electrophotographic photoreceptor (
The photosensitive drum (hereinafter referred to as a photosensitive drum) is rotated in the clockwise direction of arrow A at a predetermined circumferential speed (process speed).

Reference numeral 2 denotes a charger that charges the surface of the photosensitive drum to a predetermined potential, and one example is a contact charging ml! using a roller-type I-shaped member (hereinafter referred to as a charging roller) 2a. It is.

The charging roller 2a is brought into contact with the surface of the photosensitive drum 1 with a predetermined pressure by a pressure mechanism (not shown), and in this example, the charging roller 2a rotates as the photosensitive drum 1 rotates. In this example, a direct current bias in which alternating current is superimposed is applied to the charging roller 2a by an alternating current power source 7 and a direct current power source 8, so that the surface of the rotating photosensitive drum 1 is charged to a predetermined potential.

Next, image exposure of the target image information is performed on the surface of the charged photoreceptor 1 by the exposure means 3 (slit exposure means pot, laser beam scanning exposure means, etc.) in the exposure section C, so that the portion of the photoreceptor drum surface that is exposed to light is exposed. The charge is erased, and an electrostatic PPl image corresponding to the image exposure pattern is formed on the photosensitive drum.

The formed latent image is then developed with toner by the developing device 4 which applies a bias to the developing sleeve 9, and the toner developed image is transferred to the transfer section between the photosensitive drum 1 and the transfer charger 5.
The image is transferred to the transfer material P conveyed to the transfer section from a paper feed section (not shown) at an appropriate timing.

The transfer material P that has passed through the transfer section and received the image transfer is separated from the surface of the photosensitive drum and introduced into an image fixing device (not shown).

After the image has been transferred, the surface of the photosensitive drum is cleaned by a cleaning device 6 to remove residual toner and other substances adhering to the surface of the photosensitive drum, and is used repeatedly for image formation.

The cleaning device 6 of this example is a blade cleaning device, in which a cleaning blade 11 made of rubber or the like is brought into contact with the rotation of the photosensitive drum 1 in a counter direction, and the edge portion of the blade is used to wipe the surface of the photosensitive drum 1. As a result, transfer residual toner and the like on the surface of the photosensitive drum are scraped off and removed.

(Problems to be Solved by the Invention) FIG. 6 is a timing chart of the operation sequence of a conventional image forming apparatus of this type.

That is, the photosensitive drum 1 is activated and starts rotating based on a print start signal, and when a predetermined pre-rotation process is completed, the printing process begins and the image is printed! Exposure is started, and application of bias to the sleeve 9 of the developing device 4 and voltage application to the transfer charger 5 are sequentially started at predetermined timings.

The bias voltage (bias voltage for charging the surface of the photosensitive drum 1 to a predetermined potential) to the band roller 2a is applied at the same time as the photosensitive drum 1 is started, thereby equalizing the potential on the photosensitive drum 1. Before doing so, it was in the rotation process.

However, it has been found that when the photosensitive drum 1 is started and a bias voltage is applied to the charging roller 2a at the same time as described above to start up and execute the pre-rotation process, the following problems may occur.

That is, when the image forming apparatus is stopped or on standby, the cleaning blade 11 as a cleaning member on the downstream side in the drum rotation direction contacts the photosensitive drum l from the contact portion of the charging roller 2a with respect to the photosensitive drum 1 as an image carrier. Even if there is residual developer (toner), paper powder, dust, or other adhered contaminants on the drum surface up to the contact area E, the drum L will remove the adhered contaminants from the drum surface member based on the print start signal. Although the cleaning blade 11 of the cleaning device 6 is removed during the drum pre-rotation process from when it starts to rotate until it enters the printing process, it is removed from the contact part E of the cleaning blade 11 against the photosensitive drum l. If there is adhering contaminant lO on the drum surface portion B up to the contact portion of the charging roller 2a with respect to the photosensitive drum 1 on the downstream side in the drum rotation direction as shown in FIG. 7, the adhesion will be removed by the previous rotation of the drum. When the dirt substance 10 passes through the contact area between the photosensitive drum 1 and the charging roller 2a, it easily transfers and adheres to the side of the charging roller 2a to which a bias voltage is applied.

Further, when the drum is started, the developer remaining in the abutting part E of the cleaning blade 11 against the drum 1, scraps of the photosensitive drum l, etc. pass through the abutting part E of the blade IT, ride on the surface of the drum 1, and are taken out. However, similarly to the above, when the developer, etc. taken out is passed through the contact area between the photosensitive drum l and the charging roller 2a, it easily hits the side of the charging roller 2a to which the bias voltage is applied. Easy to metastasize and adhere.

As a result, the charging roller 2a becomes contaminated locally or in the form of streaks in the circumferential direction with the transferred contaminant described above, and the surface of the drum is not uniformly charged, resulting in defects such as black dots, white dots, or black lines on the formed image. resulting in the occurrence of

The present invention aims to eliminate such problems.

(Means for Solving the Problems) The present invention provides a contact that contacts the surface of an image carrier to which a bias voltage is applied and is rotated or rotationally driven, and charges the surface of the image carrier in a predetermined manner. With a charging member.

The image forming apparatus includes a cleaning means in the image forming process means that cleans the surface of the image carrier after image formation to enable repeated use of the image carrier, and when the image carrier is activated, the image carrier is rotated or When the rotation starts and the image carrier is activated, the surface portion of the image carrier facing the cleaning means passes through the contact position of the contact charging member with the image carrier, and then the image carrier is moved against the contact charging member. The image forming apparatus is characterized in that a bias voltage for carrying out a predetermined charging process is applied.

The present invention also provides a device (a) as described above, in which rotation or rotation of the image carrier is started when the image carrier is started, and when the image carrier is started (t), the surface portion of the image carrier facing the cleaning means comes into contact with the image carrier. Until the charging member passes through the contact position with the image carrier, a bias voltage having the same polarity as the charge polarity of the contaminant that is about to adhere from the image carrier surface side to the contact charging member surface side is applied to the contact charging member. The image forming apparatus is characterized in that a bias voltage is applied to charge the image bearing member in a predetermined manner after one pass through the image bearing member.

In other words, by delaying the timing of applying the bias voltage to the contact charging member from the starting point of the image carrier according to the relationship described above, it is possible to move the area from the area where the cleaning means acts on the image carrier to the lower IIt side in the direction of movement of the image carrier surface. Even if dirt exists between the contact portion of the contact charging member and the image carrier, and even if the dirt is taken out from the action part of the cleaning means when the image carrier is started, the dirt will be removed. Since no bias voltage is applied to the contact charging member at the time when the dirt substance passes through the contact portion between the contact charging member and the image carrier, or a bias voltage having the same polarity as the charged polarity of the dirt substance is applied. This allows the image carrier to ride on the surface of the contact charging member and pass through the contact area with the contact charging member without substantially transferring or adhering to the surface of the contact charging member. In step), the particles reach the cleaning means and are removed from the surface of the image carrier.

Therefore, the stains on the surface of the contact charging member due to the causes mentioned above are eliminated, and the occurrence of image defects due to #A stains is prevented.

(Example) Example 1 (Figures 1 and 2) The image forming apparatus shown in the example shown in FIG. 5 was constructed with the following specifications.

Photosensitive drum l: OPc photosensitive member charging. -9°a: about 1 O' to 1 O'Ω. A conductive urethane rubber roller (as the charging roller 2a, at least the surface is conductive, and its resistance is approximately 10 to 10 Ω is appropriate), and a pressure of approximately 700 g is applied to each of the shafts at both ends of the roller is applied to the photosensitive drum. Let me press it against 1.

It is driven to rotate as the drum l rotates.

Bias voltage applied to charging roller 2a: 1800V
p-p (7) An AC bias with a DC bias of about -1200V.

Image exposure L: Laser beam scanning exposure.

Developing device 4: Reversing developing device The operation sequence of this device was set as shown in the timing chart of FIG. 1 according to the present invention.

That is, based on the print start signal, the photosensitive drum l is first
is activated and the drum 1 enters the pre-rotation process. After ΔL seconds from the start of rotation by activation of the drum l, the charging roller 2
Application of a bias voltage to a is started.

FIG. 2 shows the photosensitive drum 1 on the downstream side in the drum rotation direction from the contact portion E of the cleaning blade 11 with respect to the photosensitive drum l.
A portion B of the drum surface up to the contact portion of the charging roller 2a is shown. The charging roller 2a forms a nip portion N by pressing force against the photosensitive drum l.

The distance (drum arc length) between the cleaning blade abutting part E, which is the drum surface area B, and the charging roller abutting part (the downstream end of the lug N in the drum rotational direction). ；L（■謹）
, if the circumferential speed of the photosensitive drum l is Vp (layer 17 seconds), Δt is set to the relationship Δt≧K/Vp, and due to this, when the device is stopped or in a standby state, the drum surface portion B
Even if rubber or the like adheres to the charging roller contact area D or developer is taken out from the contact area E of the cleaning blade 11 when the drum L is started, the difference between Δ at the beginning of the drum's pre-rotation process and the charging roller contact area D After passing through (N), the charging roller 2a
This is the timing when the bias voltage is applied.

As explained in the above (effect) section, the charging roller is prevented from becoming dirty.

When we experimentally deposited developer, stainless steel chips, etc. on the drum surface area B and started a printing operation according to the sequence shown in FIG. 1, no particular adverse effect was caused on the printed image.

On the other hand, when printing according to the conventional sequence shown in Figure 6, white spots may appear on solid black images when developer is applied, and solid black spots may occur when stainless steel chips are used. A black spot appeared on my self-portrait. This is because in this example, reversal development is used to develop the laser-exposed areas, so the white spots are caused by developer adhering to the surface of the photosensitive drum l, and the black spots are caused by chips. This is because pinholes were formed in the photosensitive drum 1 due to discharge. Of course, as the number of prints increases, developer and photosensitive drum scraps may be taken out from the cleaning blade 11 when the photosensitive drum is started, but even in this case, by taking the timing as shown in Figure 1, the image quality can be improved. Defects can be prevented.

Implementation g42 (Figure 3/4) The dirt substance 10a is on the charging roller 2a than on the photosensitive drum 1 side.
If the material has a strong affinity for the surface, the charging roller 2a will not work even if the period Δt during which no bias voltage is applied to the charging roller is set to a predetermined value at the beginning of the pre-rotation process of the drum.
You may see the dirt attached to the surface.

In order to cope with this problem, the present embodiment is provided with a cleaning member 13 for removing the contaminant lO attached to the surface of the charging roller 2a, as shown in FIG. The operating sequence of the device is the same as the first ryi.

By using the cleaning member 13 in combination, it is possible to remove the dirt lO attached to the surface of the charging roller 2a and allow a clean charging roller to act on the photosensitive drum 1, thereby preventing damage to the photosensitive drum 1 when the charging roller 2a is in a biased state. can be prevented from giving.

The cleaning member 13 in this embodiment is a polyethylene terephthalate sheet (cleaning blade) that is brought into contact with the charging roller 2a, but the material of the charging roller 2a is made of a material with good slip properties. if,
It is also possible to make contact with the edges. It is also effective to use a block 14 of sponge material such as Moltoprene as the cleaning member, as shown in FIGS. 4(a) and 4(b). In this case, FIG. 4(a) shows that the dirty substance 10 is collected downstream of the rotation of the charging roller 2a, and FIG.
) is to scrape off the dirt substance 10 onto the photosensitive drum 1 upstream of the rotation of the charging roller, but either method may be used.

Furthermore, the arrangement shown in FIG. 4(b) is also effective in the case of the leaning blade 13 as shown in FIG.
3 may be brought into contact with the charging roller 2a in either the counter direction or the forward direction.

In addition, in FIG. 4(b), the dirt substance 10 scraped off from the surface of the charging roller 2a onto the photosensitive drum 1 by the cleaning member 13 continues to ride on the surface of the photosensitive drum 1 which rotates forward, and reaches the cleaning device 6. It is removed from one side of the photosensitive drum.

Embodiment 3 As shown in FIG. 1, in the apparatus of the above-mentioned embodiment and the second embodiment, the application of bias voltage to the charging roller is completely turned off during a predetermined time Δt at the beginning of the pre-rotation process of the photosensitive drum, and the charging roller 2a is turned off. During the predetermined time Δt, in order to more actively prevent the dirt from adhering to the surface of the charging roller 2a, It is preferable to apply a bias voltage having the same polarity as the dirt substance 10 such as developer to the charging roller 2a.

The device 21 (Fig. R5) of Examples 1 and 2 described above uses a reversal development method, and in this case, the toner as the developer has the same polarity as the photosensitive drum 1, that is, negative polarity. . Therefore, it is sufficient to apply a negative DC bias to the charging roller 2a during the period Δt.

When we experimentally determined the upper limit of the bias value that would not damage the photosensitive drum 1, we found that no particular problem occurs up to about -1.5 KV, but defects occur in the image at bias values of about -2 to -3 KV. It turned out that. Also, -500
A bias value of about V or less did not have a sufficient effect.

This depends on the resistance value of the charging roller 2ac7), but in this example device, the charging bias voltage is an AC bias of 1800 Vpp and a D of 1200 V.
Since the C bias is applied, a sufficient effect can be obtained by turning off only the AC bias in order to prevent the charging roller 2a from becoming contaminated.

Actually, during the first Δt, the AC bias power supply 7 in FIG.
When the DC bias m: source 8 was turned on, the toner adhering to the surface of the photosensitive drum 1 as the dirt substance 10 did not adhere to the charging roller 2a, and the AC bias was turned off. The toner did not strongly adhere to the photosensitive drum 1 and was collected as is by the cleaning device 6, and the charging roller 2a did not damage the photosensitive drum 1 via the toner.

Above, examples of laser beam printers or copying machines using a transfer type electrophotographic process have been shown.

The present invention is applicable to electrostatic recording devices, image display devices, and other image forming devices that utilize various conventionally known image forming processes. It can be effectively applied to things that have been changed. The image carrier is not limited to a rotating drum type, but may be a rotating belt type.

The contact charging member is not limited to the roller type, but may also be of the rotating belt type, blade type, pad type, rod type, block type, etc. (Effects of the Invention) As described above, the present invention Accordingly, it is possible to prevent the occurrence of image defects caused by contamination on the surface of the image carrier transferring and adhering to the surface of the contact charging member brought into contact with the image carrier and causing contamination on the member. , the intended purpose is well achieved with simple means.

[Brief explanation of the drawing]

FIG. 1 is a timing chart of the operation sequence of the device of the first embodiment. Figure wljz is a partial view of a photosensitive drum, a charging roller and a cleaning blade that are brought into contact with the photosensitive drum. FIG. 3 is a partial view of an example in which a cleaning blade is added to the charging roller. FIGS. 4(a) and 4(b) are partial views of other examples of the cleaning member. FIG. 5 is a schematic configuration diagram of an example of an image forming apparatus to which the present invention can be applied. FIG. 6 is a timing chart of the operation sequence of the conventional device. FIG. 7 is a diagram illustrating the occurrence of dirt on the charging roller. 1 is a rotating photosensitive drum as an image carrier, 2a is a charging roller as a contact charging member, 4 is a developing device, 6 is a photosensitive drum surface cleaning device, 11 is a cleaning blade thereof, 10 is a dirty substance, and 13 and 14 are charging devices. Roller surface cleaning member.

Claims (2)

[Claims] (1) A contact charging member to which a bias voltage is applied and is in contact with the surface of the image carrier that is rotated or rotationally driven to charge the surface of the image carrier in a predetermined manner, and the surface of the image carrier after image formation. The image forming apparatus includes a cleaning means in the image forming process means for cleaning the image carrier to enable repeated use of the image carrier, and when the image carrier is activated, rotation or rotation of the image carrier is started and the image is removed. After the surface portion of the image carrier facing the cleaning means passes through the contact position of the contact charging member with the image carrier when the carrier is activated, the image carrier is charged to a predetermined value by the contact charging member. An image forming apparatus characterized in that a bias voltage is applied. (2) Rotation or rotation of the image carrier is started when the image carrier is started, and when the image carrier is started, the surface portion of the image carrier facing the cleaning means comes into contact with the image carrier of the contact charging member. Until it passes through the contact position, a bias voltage with the same polarity as the charged polarity of the contaminant that is about to adhere from the image carrier surface side to the contact charging member surface side is applied to the contact charging member, and after passing the image carrier, the image carrier is fixed in a predetermined position. 2. The image forming apparatus according to claim 1, wherein a bias voltage for performing charging processing is applied to the image forming apparatus.