JP4065500B2 - Charging device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a configuration of a charging device, and more particularly to charging or discharging of a transfer material at a transfer portion between a transfer unit and a fixing unit of an electrophotographic image forming apparatus, or a charging device used in an electrophotographic system. The present invention relates to an image forming apparatus.
[0002]
[Prior art]
In recent years, image forming apparatuses using various image forming means such as printing image data read from an output device of a computer such as a printer, an output unit of a facsimile, or an image scanner such as a copying machine have been rapidly spreading in general. Furthermore, many types of image forming means, such as a thermal melting type, a thermal sublimation type, a thermal transfer type, an ink jet type, and an electrophotographic type, have been developed depending on the application. Among these, in recent years, an image forming apparatus (FIG. 8) using four color full-color electrophotographic systems in which four process stations 1 (1a to 1d), which are image forming units of different colors, are arranged side by side. It is marketed as a high-speed color system (so-called inline system).
[0003]
The process station 1 has a photosensitive drum 2 (2a to 2d) as an image carrier, and the surface of the photosensitive drum 2 is uniformly charged by a primary charger 3 (3a to 3d). For example, an electrostatic latent image is formed by exposure based on image information by an exposure device 4 (4a to 4d) such as an LED or a laser. The electrostatic latent image is developed as a toner image by attaching toner of each color by a developing device.
[0004]
Each process station 1 is attachable to and detachable from an image forming apparatus main body (not shown) as a process cartridge. Each process cartridge has a configuration in which the photosensitive drum 2, the primary charger 3, the developing device 5, and the cleaning means 6 are integrated together.
[0005]
As shown in FIG. 8, in the case of the image forming apparatus, the transfer material S is fed from the feeding cassette 15 into the image forming apparatus by the feeding roller 16, conveyed to the registration roller 17, and then positively charged from the suction bias power source 13. Is attracted electrostatically to the transfer conveyance belt 7 of the transfer material carrier by the adsorption roller 12 to which a negative adsorption bias is applied, and is carried and conveyed.
[0006]
In the image forming apparatus, the transfer / conveying belt 7 is wound around four rollers: a driving roller 8, a suction opposing roller 9, and tension rollers 10 and 11. Process stations 1a to 1d for each color of cyan, yellow, magenta, and black are arranged substantially vertically in order from the upstream along the moving direction (arrow direction) of the transfer conveyance belt 7. The transfer material S adsorbed on the transfer conveyance belt 7 sequentially passes through the process stations 1a to 1d of the respective colors, and the toner images of the respective colors on the photosensitive drums 2a to 2d are electrostatically transferred sequentially. Thereafter, these toner images are heated and pressed by the fixing device 18 to be fixed on the transfer material S to form a permanent image. When performing automatic double-sided printing, the transfer material S that has once passed through the fixing device 18 passes through the re-conveying path 20 by the re-conveying roller 21 and is then reversed and sent back to the feeding unit. Printing is performed.
[0007]
[Problems to be solved by the invention]
However, in the case of the above configuration, the transfer material S is charged with a large amount of charge because it passes through four transfer steps when passing through the four process stations 1a to 1d. For this reason, a peeling discharge phenomenon occurs at a separation portion from the transfer conveyance belt 7, and the toner image transferred onto the transfer material S is disturbed along the discharge pattern. In particular, it occurs remarkably when the transfer material S has a high resistance and a low temperature and low humidity environment where it is easy to be charged, or when the second side is printed in a dry state after passing through the fixing process once during double-sided printing. In order to solve the problem due to peeling electrification, the transfer material separation unit may be provided with a charger that performs charging and charge removal to remove charge from the transfer material.
[0008]
As one method of discharging the charged transfer material S, air ions are generated by generating a corona discharge by applying a high voltage between a needle electrode and a ground electrode as shown in FIG. There is a method in which the charged transfer material S is neutralized. Considering the configuration of the charger only from the charge eliminating effect, the charger may have a needle electrode having a charge eliminating needle and a ground electrode. However, the situation is different when safety is taken into consideration. For example, it is necessary to take a configuration in which the user's finger does not directly touch the needle-shaped electrode during jam processing or the like. Also, when assuming a situation where the transfer material enters the charger without being properly separated, the transfer material S must be prevented from touching the needle-like electrode.
[0009]
Accordingly, an object of the present invention is to achieve a stable discharge while guarding a static elimination needle in a charging device.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a typical configuration of the present invention is a charging device including an electrode having a plurality of protrusions, and a discharge assisting member having a potential difference with the electrode to assist discharge of the electrode. not have a member between the discharge auxiliary member and the distal end of the projection, an insulating member between each other of the plurality of projections, that the tip of the projection is recessed than the insulating member Features.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram of an image forming apparatus. As shown in FIG. 1, the image forming apparatus includes a photosensitive drum 2 (2a to 2d) as an image carrier, and a primary charger 3 (3a to 3d) that uniformly charges the photosensitive drum 2. An exposure device 4 (4a to 4d) for forming an electrostatic latent image on the photosensitive drum 2, a developing device 5 (5a to 5d) for developing the electrostatic latent image by supplying a developer, and a photosensitive member The process stations 1 (1a to 1d), which integrally include cleaning means 6 (6a to 6d) for removing excess developer remaining on the body drum 2, are arranged for four colors.
[0012]
Transfer rollers 14 (14a to 14d) as transfer means are arranged at positions facing the process stations 1 (1a to 1d), and the transfer material S is conveyed between the process stations 1 and the transfer rollers 14. The transfer / conveying belt 7 is arranged in a stretched manner on four rollers (a driving roller 8, a suction counter roller 9, tension rollers 10 and 11). A fixing device (fixing means) 18 for fixing the toner image transferred to the transfer material S is disposed further downstream of the process station 1d on the most downstream side of the transport path.
[0013]
During the image forming operation, the images formed at the four color process stations 1 (1a to 1d) are transferred to the transfer material S fed from the feeding cassette 15, and the fixing device 18 fixes the image. Is discharged to the discharge tray 19.
[0014]
First, the characteristics of a needle charger using a needle electrode and a counter metal plate will be described. FIG. 2 is an explanatory diagram showing the characteristics of the needle charger. As shown in FIG. 2, the needle charger 120 generally includes a needle electrode 121 having a plurality of protrusions, a needle electrode 121a, a discharge electrode metal plate 122, a needle electrode 121, and a discharge assistant. And an insulating spacer 123 that is sandwiched between metal plates 122 to insulate. The needle electrode 121 is connected to a high voltage power source 124, and the discharge auxiliary metal plate 122 is grounded.
[0015]
In such a configuration, the spatial distance between the needle electrode 121 and the discharge auxiliary metal plate 122 is D, the pitch between the static elimination needles 121a is P, and the voltage applied between the needle electrode 121 and the discharge auxiliary metal plate 122. FIG. 4 and FIG. 5 show the relationship between P, D, V, etc., where V is V. Specifically, FIG. 4 shows the relationship between the voltage V and the spatial distance D, and FIG. 5 shows the relationship between the voltage V and the current when the spatial distance D is fixed and the pitch P is a parameter.
[0016]
In general, when a high voltage is applied to a conductive member, from the viewpoint of preventing leakage with other conductive members, the spatial distance D ₁ (mm) and the potential difference V ₁ (kV) between the two conductive members are D ₁ ≧ V _1. Is required. Here, in the case of the acicular charger 120 having the configuration as shown in FIG. 2A, if the discharge start voltage at which discharge is started for each spatial distance D is Vs, the condition of D ≧ Vs is satisfied. D is D ≧ 3 from FIG.
[0017]
Next, FIG. 5 shows the relationship between voltage and current when the spatial distance D is fixed to D = 4 (mm) and the pitch P between the static elimination needles 121a is changed as a parameter. As shown in this figure, it can be seen that, for example, at P = 2, the discharge start voltage is high, the current changes rapidly as the voltage is increased, and it is difficult to obtain a stable discharge phenomenon. Here, it can be seen that by increasing P, the discharge start voltage decreases, the relationship between the voltage and current becomes nearly linear, and the discharge phenomenon is stabilized. This is because interference between the potentials of the tips of adjacent static elimination needles 121a is prevented, and an efficient electric field concentration is performed for each static elimination needle.
[0018]
In actual use, it can be used at P ≧ D where the discharge starts to stabilize, and a region satisfying P ≧ 2D is desirable. Moreover, if P is too wide, charging unevenness may occur on the member to be charged. Therefore, when it is necessary to prevent this, it is preferable to set 5D ≧ P. From the above, it can be seen that the relationship of D, P, and V is more preferably P ≧ D ≧ V than D ≧ 3, P ≧ D, and D ≧ V.
[0019]
Furthermore, as a second example, a configuration in which the needle electrode is sandwiched between discharge auxiliary metal plates as shown in FIG. 2B is also effective. By adopting such a structure, the amount of discharge current per discharge needle 121a increases, and the transfer material S can be charged or discharged by having a more stable discharge performance. In this case, when the distance between the needle electrode 121 and the discharge auxiliary metal plate 122 is Da and Db, respectively, and Da ≦ Db, the distance Da between the needle electrode and the discharge auxiliary metal plate closer to the distance is It is necessary to satisfy the following formula. What has been described above are the characteristics of the acicular charger 120 including the acicular electrode 121 and the discharge auxiliary metal plate 122.
[0020]
Next, a case where a protruding insulating member 27 is provided between the static elimination needles 23a of the needle electrode 23, which is a feature of this embodiment, will be described. FIG. 3 shows a needle charger according to the present invention. As shown in FIG. 3A, the acicular charger 22 includes an acicular electrode 23, a counter electrode plate 24 facing the acicular electrode 23 with a predetermined spatial distance D (Da, Db), and an acicular shape. An insulating spacer 25 sandwiched between the electrode 23 and the counter electrode plate 24, and a protruding insulating member 27 disposed between the static elimination needles 23a of the needle electrode 23 are provided. The acicular electrode 23 is connected to a high voltage power source (high voltage applying means) 26, and the counter electrode plate 24 is grounded.
[0021]
FIG. 3B shows a configuration of the protruding insulating member, the counter metal plate, and the insulating member. The static elimination needles 23a are arranged in a straight line at equal intervals, and are arranged so as to be substantially perpendicular to the member to be charged. An insulating member 27 is provided between the static elimination needles 23a. The two counter electrode plates 24 are arranged in parallel to the needle electrode 23 and sandwich the needle electrode 23 therebetween. When the distance between the charged body and the tip of the static elimination needle 23a is a, and the distance between the charged body and the tip of the insulating member 27 is b, the static elimination needle 23a is guarded by the insulating member 27 and is not directly touched. One feature of the present embodiment is that a protruding insulating member is provided so as to satisfy the relationship of a> b.
[0022]
On the other hand, when D = 4 mm, P = 8 mm, and a−b = 1.5 mm, the discharge characteristics when the distance c from the tip of the static elimination needle 23a to the nearest insulating member 27 is changed are shown in FIG. Shown in As can be seen from FIG. 6, when the value of c is 0.6 mm or less, the discharge start voltage is high, the current changes rapidly as the voltage is increased, and a stable discharge phenomenon is difficult to obtain. This is a result of the discharge being inhibited because the insulating member 27 is charged. For this reason, in actual use, it becomes possible to set the value of c to 0.8 mm or more where the discharge starts to stabilize. By adopting the above configuration, it is possible to stabilize the discharge phenomenon of the needle charger 22 while guarding the static elimination needle 23a.
[0023]
(Second Embodiment)
A second embodiment of the present invention will be described. Constituent elements similar to those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted. In the image forming apparatus shown in FIG. 1, in this embodiment, as a typical example, a negatively charged toner is used at a dark portion potential of −700 V and a developing potential of −400 V, and transfer is performed with a positive polarity bias. Perform image formation.
[0024]
The transfer conveyance belt 7 is obtained by adding an ionic conductive agent to PVdF resin and controlling the resistance value to a volume resistance value of 1e9 Ωcm, and has a single-layer structure with a thickness of 100 μm. For the volume resistance value, a value measured by applying 100 V with a high resistance meter R8340 manufactured by ADVANTEST, using a measurement probe based on JIS method K6911, is normalized by the thickness of the belt.
[0025]
The suction roller 12 is formed by molding solid rubber on a core metal having a diameter of 6 mm, and is configured such that a suction bias power source 13 for suction can be applied to the core metal. The suction roller 12 is a solid rubber roller having a diameter of 12 mm in which carbon black is dispersed for resistance adjustment on PDM rubber. A resistance value is a voltage of 500 V between the metal core having a width of 1 cm and wound around the outer periphery of the roller. The resistance is adjusted to 1e5Ω when the voltage is applied.
[0026]
As the transfer roller 14, a single layer roller having a core metal diameter of 6 mm and an outer diameter of 12 mm was used. The roller is made of NBR rubber and epichlorohydrin rubber mixed with an antioxidant such as amine, phenol, phosphorus, or sulfur and extruded and polished. The roller resistance value is 5e6Ω when a metal foil having a width of 1 cm is wound around the roller outer periphery and a voltage of 500 V is applied between the metal core and the core.
[0027]
Here, the needle charger 22 having a protruding insulating member 27 provided between the needle electrodes 23 is disposed on the image surface side of the transfer portion between the transfer conveyance belt 7 and the fixing device 18. At this time, since the transfer material P passes through four process stations and passes through four transfer steps, it receives a large amount of charge and maintains a high potential such as −3000V. Therefore, a peeling discharge phenomenon occurs in the separation portion of the transfer conveyance belt, and a phenomenon occurs in which the toner image transferred onto the transfer material S is disturbed along the discharge pattern. In particular, this phenomenon occurs remarkably in a low-temperature and low-humidity environment in which the transfer material S has high resistance and is easily charged, or in the image formation on the second surface that has passed through the fixing process and dried once during image formation.
[0028]
In order to prevent the image disturbance due to the peeling discharge phenomenon, a needle charger 22 is arranged between the illustrated transfer conveyance belt 7 and the fixing device as shown in FIG. 1, and the transfer material S is separated from the transfer conveyance belt 7. As an example, corona discharge is generated using the needle charger 22 under the conditions of P = 8 mm, D = 4 mm, V = 3.8 kV, a−b = 1.5 mm, and c = 1.0 mm. .
[0029]
When the transfer material S is not present, almost all of the current of, for example, 60 μA due to corona discharge of the needle charger flows into the discharge auxiliary metal plate. From this state, the transfer material having a high potential (eg, −3000 V as described above). When S passes as an opposite body to be charged at a speed of, for example, 100 mm / s, the corona discharge current increases from 60 μA to 70 μA, for example, due to the change in the electric field in the vicinity of the needle electrode 23, and a part thereof is enlarged in FIG. As shown in the drawing, the transfer material S flows as an ionic wind, so that the transfer material S is neutralized, and image defects due to peeling discharge can be prevented. In this case, the amount of current flowing into the transfer material S as an ion wind is at most 3 μA. FIG. 7 shows a schematic diagram of the relationship between the input current to the needle electrode 23 and the current flowing into the counter electrode plate 24.
[0030]
As described above, in the case of the above configuration, the transfer material S can be neutralized by corona discharge by the needle charger 22 at the time of peeling from the transfer conveyance belt 7 to prevent the peeling discharge. On the other hand, since the needle-like electrode 23 is guarded by the insulating member 27 from the viewpoint of safety, the transfer material S is not separated correctly, and the transfer material S enters the needle-like charger 22 even if a situation occurs. S does not contact the acicular electrode 23. It is also possible to prevent the user's finger from directly contacting the tip of the needle electrode 23.
[0031]
(Other embodiments)
In the above-described embodiment, an example of static elimination for the inline type transfer material S has been described. However, the present invention is not limited to this, and for example, charging or static elimination of an image carrier, a transfer conveyance belt, a fixing device, and the like. Are also effective, and these may be combined as appropriate.
[0032]
In the above-described embodiment, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this. For example, the image forming apparatus can be used in a facsimile machine or a copying machine.
[0033]
【The invention's effect】
As described above, in the present invention, stable discharge can be achieved while guarding the static elimination needle at the tip of the needle electrode.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an image forming apparatus.
FIG. 2 is an explanatory diagram showing characteristics of a needle charger.
FIG. 3 is a view showing a needle-shaped charging device according to the present invention.
4 is a diagram illustrating a relationship between a voltage V and a spatial distance D. FIG.
FIG. 5 is a diagram showing the relationship between voltage V and current when the spatial distance D is fixed and the pitch P is used as a parameter.
FIG. 6 is a diagram showing discharge characteristics when the distance c from the tip of the static elimination needle to the nearest insulating member is changed.
FIG. 7 is a schematic diagram showing the relationship between the input current to the needle electrode and the current flowing into the counter electrode plate.
FIG. 8 is an explanatory diagram of a conventional image forming apparatus.
[Explanation of symbols]
D: Spatial distance, P: Pitch, S: Transfer material, V: Voltage,
1 ... process station, 2 ... photosensitive drum,
3 ... Primary charger, 4 ... Exposure device, 5 ... Developer,
6 ... cleaning means, 7 ... transfer conveyance belt,
8 ... Drive roller, 9 ... Adsorption counter roller, 10 ... Tension roller,
11 ... tension roller, 12 ... suction roller, 13 ... suction bias power supply,
14 ... transfer roller, 15 ... feeding cassette, 16 ... feeding roller,
17 ... Registration roller, 18 ... Fixing device, 19 ... Discharge tray,
20 ... re-conveying path, 21 ... re-conveying roller, 22 ... acicular charger,
23 ... acicular electrode, 23a ... static elimination needle, 24 ... counter electrode plate,
25 ... Insulating spacer, 26 ... High-voltage power supply, 27 ... Insulating member,
120 ... acicular charger, 121 ... acicular electrode, 121a ... static elimination needle,
122… discharge auxiliary metal plate, 123… insulating spacer, 124… high voltage power supply

Claims (7)

In a charging device comprising: an electrode having a plurality of protrusions; and a discharge assisting member having a potential difference with the electrode to assist discharge of the electrode.
Characterized in that between the discharge auxiliary member and the tip of the protrusion does not have a member, an insulating member between each other of the plurality of protrusions, the distal end of the projection is recessed than the insulating member The charging device. The value when the distance between the tips of the plurality of protrusions of the electrode is expressed in mm, P, the value of the distance between the tip of the electrode protrusion and the discharge auxiliary member is expressed in mm, D, When the potential difference between the electrode and the discharge assisting member is expressed in units of kV, V,
The charging device according to claim 1, wherein a relationship of P ≧ D ≧ V is satisfied.   The charging device according to claim 1, wherein the discharge assisting member has a plate shape and is disposed in parallel with the electrode.   The charging device according to claim 1, wherein the discharge assisting member is grounded, and a bias is applied to the electrode. When c is a value representing the distance between the tip of the protrusion and the insulating member in the unit of mm,
The charging device according to claim 1, wherein a relationship of c ≧ 0.8 is satisfied. An image forming apparatus comprising the charging device according to claim 1 . Wherein the image forming apparatus, a transfer unit that transfers the toner image on the transfer material, a fixing unit for fixing the toner image to the transfer material, the image forming apparatus the transfer material enters into the fixing means through the transfer means There,
The image forming apparatus according to claim 6, wherein the charging device is disposed between the transfer unit and the fixing unit.

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