JPH01204081A - Electrostatic charging device - Google Patents

Abstract

PURPOSE:To prevent an electrostatic charging member and a body to be charged from being fixed and further to prevent toner from being fixed on the surface of the charging member by composing the charging member of a conductive rubber layer and forming a releasing film at the part in contact with the body to be charged. CONSTITUTION:A photosensitive drum 3 as the body to be charged rotates as shown by an arrow. An electrostatic charging roller 4 as the charging member is in contact with the drum 3 with specific pressure. The roller 4 is constituted by providing the conductive rubber layer 4b to a metallic 4a and further forming a surface layer 4c as the releasing film on its peripheral surface. Consequently, the charging member and body to be charged are prevented from being fixed and none of the curing agent in the conductive rubber of the charging member is never stuck on the body to be charged, so the toner is prevented from being fixed on the surface of the charging member to preclude a defect and an irregularity in electrostatic charging due to the filming of the toner on the body to be charged.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a charging device, and more specifically, to an improvement in a device that performs charging by bringing a charging member to which a voltage is applied from the outside into contact with a member to be charged. It is related to.

[Background Art] Corona dischargers are conventionally known as charging means in electrophotographic devices and the like. However, corona dischargers have problems such as the need to apply high voltage and the amount of ozone generated.

Therefore, recently, consideration has been given to using contact charging means without using a corona discharger. Specifically, a voltage is applied to a conductive roller, which is a charging member, and the roller is brought into contact with a photoreceptor, which is an object to be charged, so that the surface of the photoreceptor is charged to a predetermined potential, and the ozone generator is also reduced.

For example, in Japanese Patent Publication No. 50-13661, by using a roller whose core metal is coated with a dielectric material made of nylon or polyurethane rubber, it is possible to apply a low voltage to charge the photosensitive paper.

However, in the above conventional example, when the core metal is coated with nylon, it does not have the elasticity of rubber or the like, so it cannot maintain sufficient contact with the object to be charged, resulting in charging failure. On the other hand, if the core metal is coated with polyurethane rubber, the softening agent impregnated into the rubber material will seep out, and if a photoreceptor is used as the object to be charged, the charging member will stick to the photoreceptor at the contact area when the photoreceptor stops. However, there is a problem in that the image is blurred or the image is blurred in that area. Furthermore, if the softener in the rubber-based material of the charging member seeps out and adheres to the surface of the photoreceptor, the resistance of the photoreceptor decreases, resulting in image deletion, and in severe cases, it may become unusable. If a large amount of toner adheres to the surface of the charging member, the surface of the charging member becomes insulated, the charging ability of the charging member is lost, and the surface of the photoreceptor becomes non-uniformly charged, which affects the image.

[Object of the Invention] The present invention has been made in view of the above points, and it is possible to maintain sufficient contact between the charging member and the charged object, prevent the charging member from sticking to the charged object, and further prevent the charging. A charging device that prevents the plasticizer contained in the conductive rubber of the member from adhering to the charged object and prevents the toner from sticking to the surface of the charging member, thereby preventing charging defects and uneven charging due to toner filming on the charged object. The purpose is to provide

[Structure of the Present Invention] The above object of the present invention is achieved by a charging device that performs charging by bringing a charging member to which a voltage is applied from the outside into contact with an object to be charged. In addition, a resin is preferably used as the material for the releasable film, and it is more preferable to use a nylon resin as the resin.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an image forming apparatus to which the charging device of the present invention can be applied, and the image forming apparatus of this embodiment is a combination of a sheet material feeding section A and a laser beam printer section B. The device is shown.

The configuration and image forming operation of printer B of this example will be explained.

1 is an exterior casing of the printer, and the front side of the printer in this example is the right end side in the drawing.

IA is the printer front plate, and the front plate can be tilted open as shown by the two-dot chain line and raised and closed as shown by the solid line, centering on the hinge axis lB on the lower side with respect to the printer exterior casing l. be. Process cartridge 2 for inside the printer
For installation/removal operations, inspection/maintenance of the inside of the printer, etc., please use the front panel IA.
This is done by folding down and opening up the inside of the printer.

The process cartridge 2 in this example has a cartridge housing 2a, a photosensitive drum 3, a charging roller 4, and a developing device 5.
．． It contains four image forming process devices, namely a cleaner 6, and can be attached to and removed from a predetermined storage section in the printer exterior casing 1 by folding down and opening the printer front plate IA as shown by the two-dot chain line. When the cartridge 2 is properly installed in the printer, the mechanical drive system and electric circuit system on both the cartridge side and the printer side are connected via a mutual coupling member (not shown), and mechanical and electrical connections are established. to be integrated into.

Reference numeral 7 denotes a laser beam scanner section disposed at the back inside the printer exterior section 1, which includes a semiconductor laser and a scanner motor 7a.
, a polygon mirror 7b, a lens system 70, etc., and the laser beam L from the scanner section 7 enters the housing 2a almost horizontally from the exposure window 2b of the cartridge housing 2a installed in the printer, A cleaner 6 and a developing device 5 are arranged above and below in the housing.
The exposure section 3 on the left side of the photosensitive drum 3 passes through the passage between the
a, and the surface of the photosensitive drum 3 is scanned and exposed in the generatrix direction.

Reference numeral 8 denotes a multi-feet tray which projects outward from the lower side of the printer front plate IA and is inclined toward the front, on which a plurality of sheet materials S can be set at the same time.

10 is a sheet material feeding roller provided at the inner lower part of the printer front plate IA, and 12 is a conveying roller brought into contact with the left side surface of the feeding roller IO.

13 is the feed roller lO inside the printer front plate IA.
A transfer roller is provided above, 15a-15b is a pair of fixing rollers provided on the inside upper part of the printer front plate IA, 14 is a sheet material guide plate provided between the transfer roller 13 and a pair of fixing rollers 15a-15b, and 16 is a pair of fixing rollers. Fixing roller pair 15a-15
Sheet material discharge roller arranged on the sheet material exit side of b, 1
7 is a tray for receiving the discharged sheet material.

When an image formation start signal is input to the control system of the printer, the photosensitive drum 3 is rotated counterclockwise as indicated by the arrow at a predetermined circumferential speed, and the charging roller 4 has a predetermined positive or negative polarity on its circumferential surface. is uniformly charged. The charging roller 4 is a conductive member to which a predetermined voltage is applied, and the photosensitive drum 3 is charged by the roller in a so-called contact (or direct) charging method. The charging roller 4 may be driven to rotate by the photosensitive tram 3, may be driven to rotate in the opposite direction, or may be non-rotatable.

Next, in the exposure section 3a, only the pixel laser light corresponding to the time-series electrical pixel signal of the image information outputted from the laser beam scanner section 7 is incident on the uniformly charged surface of the rotating photosensitive drum 3, and the surface of the drum 3 is illuminated. An electrostatic latent image of image information is formed on the surface of the photosensitive drum 3 by being sequentially main-scanned by the laser beam in the drum generatrix direction.

The latent image formed on the drum 3 surface is the developing sleeve (
The toner is sequentially developed by the developer carried on the roller 5a. 5b is a storage chamber for developer (toner) t.

On the other hand, among the sheet materials (transfer paper) S set on the multi-feet tray 8, the uppermost sheet material is drawn into the printer from the feed roller lO, which is rotationally driven in the direction of the arrow, and continues to be drawn into the printer by the feed roller lO. The photosensitive drum 3 is sandwiched between the nip portion of the conveying roller 12 and fed toward the facing contact portion (transfer portion) between the photosensitive drum 3 and the transfer roller 13 at a constant speed that is the same as the rotational circumferential speed of the photosensitive drum 3 .

The sheet material fed to the transfer section passes between the photosensitive drum 3 and the transfer roller 13 one after another.
The toner image on the surface of the photosensitive drum 3 is sequentially transferred by the voltage applied to the photosensitive drum 3 (a voltage with a polarity opposite to that of the toner) and the pressing force of the transfer roller against the photosensitive drum 3. Transfer roller 1
3, the leading edge of the feeding sheet material is the photosensitive tram 3.
This is performed when the contact portion (transfer portion) with the transfer roller 13 is reached.

The sheet material that has passed through the transfer section is separated from the surface of the photosensitive drum 3, guided by a guide plate 14, and then transferred to a pair of fixing rollers 15a and 1.
5b. Of the fixing roller pair 15a-15b, the roller 15a on the side that contacts the image transfer surface of the sheet material is a heating roller with a built-in halogen heater, and the roller 15b on the side that contacts the back side of the sheet material is made of an elastic material. The pressure roller is placed on the sheet material that has undergone image transfer.
5a-15b, the transferred toner image is fixed on the surface of the sheet material by heat and pressure, and
6, the image is discharged onto the tray 17 as an image formed product (print).

After the toner image has been transferred, the surface of the photosensitive drum 3 is wiped off by the cleaning blade 6a of the cleaner 6 to remove residual toner and other contaminants, and is then turned over and used for image formation.

Also, instead of using the multi-feet tray 8, a sheet material feeding system 'J! When feeding paper from the iA cassette 40,
Among the sheet materials S stacked in the cassette 40, the highest sheet material is picked up by the pickup roller 26 and the registration roller 2 is picked up.
8 and 55 and advances in the direction of the arrow, and as described above, the sheet material is fed between the feeding roller 10 and the conveying roller 12.

Next, a contact charging device of the present invention applicable to the image forming apparatus will be specifically described.

FIG. 2 is a schematic diagram of a contact charging device showing an embodiment of the present invention. Reference numeral 3 denotes a photoconductor drum which is a charged body, and is made up of an aluminum drum base 3a and an organic photoconductor (OPC) layer 3b formed on the outer peripheral surface of the drum base 3a. Rotate. In this embodiment, the photosensitive drum 3 has an outer diameter of 30 m5φ.

A charging roller 4 is a charging member that is brought into contact with the photoreceptor tram 3 under a predetermined pressure.A conductive rubber layer 4b is provided on a metal core 43, and a surface layer 4C that is a releasable film is provided on the peripheral surface of the conductive rubber layer 4b. has been established. If the resistance is too high, the photoreceptor tram 3 will not be charged, and if the resistance is too small, too much voltage will be applied to the photoreceptor tram 3, causing damage to the drum and the formation of pinholes, so the release film should have an appropriate resistance. That is, the resistivity is preferably 109 to 1014 Ωm, and the thickness of the releasable film is preferably 30 Bm or less. In addition, the lower limit of the film thickness is good if the film does not peel or break.<5JL
It is considered that m< leprosy.

In this example, the outer diameter of the charging roller 4 was 125 mφ, the conductive rubber layer 4b was made of EPDM, and the surface layer 4c was made of nylon resin with a thickness loILm. The hardness of the charging roller 4 is 54.5° (ASKER-C
). Reference numeral E denotes a power supply unit that applies a voltage to the charging roller 4, and supplies a predetermined voltage to the core metal 4a of the charging roller 4. In FIG. 2, E indicates a DC voltage, or may be a DC voltage superimposed with an AC voltage.

FIG. 3 shows the results of a durability test using the above charging roller. The chart shows the decrease in charging efficiency after the charging efficiency was set as 100% at the start of durability. The solid line indicates the case where the above-mentioned charging roller was used, and the dotted line indicates the case where a conventional charging roller without a surface layer releasable coating was used as a comparative example. Thus, it can be seen that when the charging roller of the present invention is used, the charging efficiency decreases to a very small extent. This is because the charging roller, which is the charging member of the present invention, uses a nylon-based resin as a release coating on the outside of the conductive rubber layer, so that the part that comes into contact with the photoreceptor, which is the object to be charged, is freed from the conductive rubber. This is because the softener is prevented from seeping out. Therefore, when the softener adheres to the photoreceptor, it is possible to prevent image deletion due to lower resistance of the photoreceptor and a decrease in charging ability due to filming of residual toner on the photoreceptor, thereby suppressing a decrease in charging efficiency.

On the other hand, by using a conductive rubber layer for the charging roller, sufficient contact between the charging roller and the photoreceptor can be maintained, and charging failures will not occur.

FIG. 4 is a schematic diagram of a contact charging member showing another embodiment of the present invention. Components common to those in the device shown in FIG. 2 are designated by the same reference numerals and will not be described again.

The contact charging member 4' of this embodiment is a blade-shaped member brought into contact with the photoreceptor drum 3 in the forward direction with a predetermined pressure.
A conductive rubber 4'b is supported on 'a', and a surface layer 4'c serving as a releasable film is provided at the portion in contact with the photoreceptor tram 3. Nyrose with a thickness of 10 pm was used as the surface layer 4'c. According to this embodiment, there is no problem such as adhesion between the blade and the photoreceptor drum, and the same effects as in the previous embodiment can be obtained.

In the above-described embodiments, a roller-shaped or a plate-shaped charging member is used, but the present invention is not limited to this, and the present invention can be practiced with other shapes as well.

In addition, in this embodiment, the charging member is composed of a conductive rubber layer and a release film, but the charging member is not limited to this. It is preferable to form a resistive layer, for example, a hydrin rubber layer with small environmental fluctuations.

Also, as a mold release coating, PV is used instead of nylon resin.
F (polyvinylidene fluoride) and PVDC (polyvinylidene chloride) may also be used. As the photoreceptor, amorphous silicon, selenium, ZnO, etc. can also be used.

In particular, when amorphous silicon is used for the photoreceptor, compared to when other materials are used, if even a small amount of the softener of the conductive rubber layer adheres to the photoreceptor, image fading will become severe. The effect of applying an insulating coating to the surface is significant. Furthermore, the charging device of the present invention can also be used for transfer.

[Effects of the Invention] As explained above, in the present invention, since the charging member is composed of a conductive rubber layer, it is possible to maintain sufficient contact between the charging member and the object to be charged. Since a mold releasable coating is formed on the outside and at least the part that contacts the charged object, it prevents the charging member from sticking to the charged object, and furthermore, it coats the softening agent in the conductive rubber of the charging member. Since the toner does not adhere to the electrical body, it is possible to prevent the toner from adhering to the surface of the charging member, and to prevent charging defects and uneven charging due to toner filming on the charged object.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a laser beam printer using the present invention, Fig. 2 is an explanatory diagram showing an outline of the charging roller of the present invention, and Fig. 3 is an explanatory diagram showing the number of durable sheets and charging efficiency when the present invention is implemented. FIG. 4 is an explanatory diagram schematically showing a plate according to another embodiment of the present invention. 2...Cartridge 3...Photoconductor drum 4.4'...Charging member E...Power supply surface size or power number (K2 sentence)

Claims (5)

[Claims] (1) In a charging device that performs charging by bringing a charging member to which a voltage is applied from the outside into contact with a charged object, the charging member includes a conductive rubber layer, an area outside the conductive rubber layer, and at least the above-mentioned charging member. A charging device characterized by having a releasable coating on a portion that comes into contact with an object to be charged. (2) The charging device according to claim 1, wherein the releasable film is formed of a resin material. (3) The charging device according to claim 2, wherein the releasable film is formed of a nylon resin. (4) The charging device according to claim 1, wherein the charging member is roller-shaped. (5) The charging device according to claim 1, wherein the charging member has a blade shape.