JP2005331836A - Charging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging device capable of stably keeping a gap between a charging member and an image carrier constant when the charging member is disposed close to the image carrier in order to charge the image carrier without coming into contact with it. <P>SOLUTION: A charging roller 3a includes a cylindrical metal core 3b, and a conductive elastic member 3c disposed around the circumferential face of the metal core 3b so as to face the image carrier 2. A pair of annular gap members 8 and 9, each of which is formed from a heat-shrinkable tube, are disposed around the circumferential face of the elastic member 3c at the left and right ends. The gap members 8 and 9 set a gap G between the elastic member 3c of the charging roller 3a and the image carrier 2. In the case, since the gap members 8 and 9 are formed from the heat-shrinkable tube, the need for joints for the gap members 8 and 9 is eliminated. This makes it possible to stably keep the gap G constant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is used in, for example, an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, and the like, and is provided in the vicinity of an image carrier such as a photoconductor to charge the image carrier in a non-contact manner. The present invention relates to a technical field of a charging device including a charging member.

Conventionally, in this type of image forming apparatus, prior to forming an electrostatic latent image on the surface of an image carrier such as a photoconductor, the image carrier is uniformly charged.
As one of the charging devices for charging the image carrier in this way, a film member having a diameter larger than that of the central portion of the elastic member at both ends of the conductive elastic member of the charging roller as a charging member. The elastic member of the charging roller between the gap members is arranged close to the outer peripheral surface of the image carrier with a predetermined gap so that the image carrier is charged without contact. There has been proposed a non-contact charging device (see, for example, Patent Document 1).

  FIG. 5 is a diagram schematically illustrating an image forming apparatus including the charging device disclosed in Patent Document 1. In FIG. 5, 1 is an image forming apparatus, 2 is an image carrier, 3 is a charging device for charging the image carrier 2 with a charging roller 3a, 4 is an exposure device, 5 is a developing device, 6 is a transfer medium such as paper, Reference numeral 7 denotes a transfer device.

  As shown in FIG. 6, the charging roller 3a of the charging device 3 includes a cylindrical cored bar 3b and a conductive elastic member 3c provided on the outer peripheral surface excluding both ends of the cored bar 3b. Yes. Gap members 8 and 9 each made of a belt-like film material are provided around both ends of the elastic member 3c so as to be wound in the circumferential direction. The film material of the gap members 8 and 9 has an adhesive layer formed on one side thereof, and both end edges thereof are cut obliquely. This film material is fixed to the elastic member 3c with an adhesive layer in a state of being wound around both ends of the elastic member 3c. In the state where the film material is fixed to the elastic member 3c, both end edges of the film material do not overlap each other in the circumferential direction, a gap S is formed between them, and the charging roller 3a extends in the axial direction over the entire circumference. There is no part where there is no film material.

Both end portions of the charging roller 3a are pressed toward the image carrier by a pressing means such as a spring, and the gap members 8 and 9 are pressed against the outer peripheral surface of the image carrier 2, thereby the elasticity of the charging roller 3a. A gap G of the thickness of the film material is set between the member 3c and the image carrier 2. In this case, the gap G, that is, the proximity distance between the image carrier 2 and the charging roller 3a is set to 5 μm to 300 μm.
Then, the image carrier 2 is charged by applying a superimposed voltage of the DC voltage V _DC and the AC voltage V _AC to the charging roller 3a.

JP 2001-296723 A ([Summary] etc.)

  By the way, in the above-described conventional charging roller 3a, the gap members 8 and 9 have a seam due to the gap S. In order to keep the gap G between the image carrier 2 and the charging roller 3a constant, it is required to suppress the influence of the joint of the gap members 8 and 9 as much as possible. Therefore, the charging roller 3a disclosed in Patent Document 1 is devised so that there are no portions where the gap members 8 and 9 do not exist in the axial direction of the charging roller 3a over the entire circumference.

  However, even with such a device, as long as there is a seam, the size of the gap G due to the seam cannot be made constant, and it is difficult to reliably eliminate the influence of the seam. Specifically, a pressing force is applied to both ends of the charging roller 3a so that the gap member 8 on one side is brought into pressure contact with the image carrier 2 at the joint portion, and the gap member 9 on the other side is in the seamless portion. There may be a case where the image carrier 2 is pressed. For this reason, the contact stability of the gap members 8 and 9 with the image carrier 2 is impaired, and the size of the gap G varies. The fluctuation of the gap G is periodically generated by the rotation of the charging roller 3a, causing fine vibrations, and nonuniform charging occurs.

  Moreover, since both ends of the film material are cut obliquely, it is considered that the film material peels off when printing is repeated for a long time. This is because the film material is adhered to the image carrier by an adhesive made of an adhesive layer formed on one side, but the charging roller 3a is pressed against the image carrier 2 and driven rotation over a long period of use. This is because peeling is started from the tip of the oblique seam of the film member. For this reason, a part of gap member 3c will peel off from the elastic member 3b. Then, the gap between the charging roller 3a and the image carrier 2 due to such peeling of the gap member 3c, or mixing of foreign matter such as residual toner or paper dust into the gap between the peeled portion and the elastic member 3b. G fluctuates and is not held constant. Therefore, non-uniform charging occurs due to such instability of the gap G.

Further, when the gap member 3c is peeled off from the elastic member 3c, the peeled portion of the elastic member 3c may be in direct contact with the image carrier 2. However, when uniform charging is performed in non-contact charging, a voltage obtained by superimposing the _AC voltage VAC on the DC voltage _VDC is applied to the charging roller 3a. In this case, the AC voltage V _AC is applied with a voltage (≧ 2 V _TH ) that is at least twice as large as the discharge start voltage V _TH set to a certain frequency. When the elastic member 3c is in direct contact with the image carrier 2 as described above in a state where such a large voltage is applied to the charging roller 3a, a pinhole is generated in the image carrier 2 and a dielectric breakdown may occur. In other words, good image formation cannot be performed.

  The present invention has been made in view of such circumstances, and its object is to provide a charging member and an image carrier when the charging member is disposed in proximity to the image carrier and charges the image carrier in a non-contact manner. It is an object of the present invention to provide a charging device capable of stably maintaining a constant gap with a body.

  In order to solve the above-described problems, in the charging device according to the first aspect of the present invention, the charging member is disposed close to the image carrier by the gap members provided at both ends thereof, and the image is formed by the charging member. In the charging device for charging the carrier in a non-contact manner, the gap member is constituted by an endless heat shrinkable tube.

The invention according to claim 2 is characterized in that the charging member comprises a charging roller.
Further, in the invention of claim 3, the charging member is composed of a cored bar and a rubber material formed from one end of the cored bar to the other end on the surface of the cored bar facing the image carrier. The gap member is disposed at least on the rubber material.

Further, in the invention of claim 4, the charging member is composed of a cored bar and a rubber material formed on a surface of the cored bar facing the image carrier and excluding both ends of the cored bar. The gap member is disposed across at least the rubber material or the core metal and the rubber material.
Furthermore, the invention of claim 5 is characterized in that the heat shrinkable tube has a predetermined number of holes or cuts penetrating from the inner peripheral surface to the outer peripheral surface.

  According to the charging device of the present invention configured as described above, since the gap member for setting the gap between the charging member and the image carrier is formed of the heat shrinkable tube, it is possible to eliminate the seam in the gap member. Thereby, the contact instability of the gap member to the image carrier due to the joint can be eliminated. Therefore, it is possible to eliminate the influence of the seam on the gap between the charging member and the image carrier, and to make the gap constant in the axial direction of the charging member (the axial direction of the image carrier).

  In addition, since there is no seam in the gap member, the conventional gap member is not peeled off from the seam, and the heat shrinkable tube is shrunk by heat to fix the gap member to the conductive elastic member. Since the adhesive force of the adhesive in the pressure-sensitive adhesive layer does not become weak as in the prior art, the gap member does not peel off the elastic member. As a result, the above-described gap can be further stabilized, and the image carrier can be uniformly charged more reliably.

  Furthermore, since the gap member does not peel off from the elastic member, the charging roller can be prevented from coming into direct contact with the image carrier, and dielectric breakdown due to pinholes in the image carrier can be prevented, and good image formation can be performed. Can do.

  Furthermore, since the conventional adhesive layer is eliminated by using a heat shrinkable tube for the gap member, the gap between the charging member and the image carrier can be reduced by the amount of the adhesive layer. Therefore, the discharge start voltage in non-contact charging can be reduced. As a result, charging can be performed at a low voltage, ozone generation accompanying a decrease in discharge current, and cost reduction of the power source can be achieved. In addition, since charging is performed at a low voltage, destruction of the image carrier can be prevented more reliably.

  Furthermore, when the heat shrinkable tube is provided on the elastic member, the heat shrinkable tube is provided by pressing the elastic member from the outer peripheral side with a uniform pressure due to the shrinkage force of the heat shrinkable tube. And the thickness of the elastic member in the circumferential direction can be made uniform. Therefore, the aforementioned gap can be made more uniform in the circumferential direction.

  Further, when the charging member is constituted by a charging roller, even if the charging roller and the image carrier are rotated, the fine vibration as described above can be suppressed and the gap can be stabilized, and the image carrier can be charged more uniformly. Can be.

  Furthermore, by providing a heat-shrinkable tube on the elastic member and pressing the gap member of the heat-shrinkable tube against the image carrier, the charging roller can be reliably driven and rotated when the image carrier is rotated. Accordingly, when a cleaning member such as a brush or a blade is provided in contact with the charging roller, the charging roller can be reliably rotated, and the cleaning of the charging roller by the cleaning member can be reliably performed.

  Furthermore, since the heat-shrinkable tube is provided between the cored bar and the elastic member, the heat-shrinkable tube is pressed against the relatively hard and flat cored bar and the relatively soft elastic member by the contracting force. Since they can be fixed to each other in a state, they can be fixed securely without moving the gap member. As a result, the gap can be held more stably and constant, and stable uniform charging can be realized. Therefore, good image formation can be performed stably.

  Furthermore, since a predetermined number of holes or cuts are provided in the heat-shrinkable tube, when the heat-shrinkable tube shrinks during manufacturing, relief is formed by these holes or cuts, so that the heat-shrinkable tube may be wrinkled. The heat shrinkable tube can be reliably prevented from being doubled. Further, for example, foreign matters such as residual toner and paper dust enter these holes or cuts, so that gap variation due to these foreign matters can be suppressed. Therefore, the gap can be kept more stable and constant, and stable uniform charging can be realized. Thereby, good image formation can be performed stably.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 shows a first example of an embodiment of a charging device according to the present invention. FIG. 1A schematically shows a basic configuration of an image forming apparatus including the charging device of the first example. Is a front view of the charging roller of the charging device, and FIG. 5C is a left side view of the charging roller. The same components as those of the image forming apparatus shown in FIGS. 5 and 6 are given the same reference numerals.

  As shown in FIG. 1, an image forming apparatus 1 includes an image carrier 2 on which an electrostatic latent image and a developer image are formed, and a charging device 3 that charges the image carrier 2 with a charging roller 3a that is a charging member. An exposure device 4 that exposes the image carrier 2 to write an electrostatic latent image on the image carrier 2, and a developer that carries and transports the electrostatic latent image on the image carrier 2 by the developing roller 5a. A developing device 5 for developing and at least a transfer device 7 for transferring the developer image on the image carrier 2 developed by the developing device 5 to a transfer medium 6 such as paper by a transfer roller 7a are provided.

  The charging roller 3a includes a cylindrical cored bar 3b and a conductive elastic member 3c provided on the outer peripheral surface of the cored bar 3b so as to face the image carrier 2. A pair of annular gap members 8 and 9 are respectively provided on the outer peripheral surfaces of the left and right ends of the elastic member 3c.

The metal core 3b is formed to have an outer diameter of 9 mm by, for example, SUM-Ni plating (steel surface is nickel-plated). The elastic member 3c is formed of a rubber layer made of, for example, epichlorohydrin rubber. The outer diameter of this rubber layer is 11.14 mm and the manufacturing tolerances are set to +0 mm and -0.2 mm. The elastic member 3c has a conductivity with a volume resistivity of 1 × 10 ³ Ω · cm to 1 × 10 ¹⁰ Ω · cm, and has a rubber hardness of 25 to 90 degrees according to the old JIS-A. .

  The pair of gap members 8 and 9 are both the same, and are formed from seamless heat-shrinkable tubes. As the heat-shrinkable tube, for example, a fluororesin PFA / FEP heat-shrinkable tube (Gunze Co., Ltd.) and a super teletube (registered trademark: manufactured by Teijin Chemicals Ltd.) can be used. A heat shrinkable tube having an inner diameter slightly larger than the outer diameter of the image carrier 2 and a width of 50 μm to 100 μm is used.

  The charging roller 3a configured as described above is manufactured as follows. First, the elastic member 3c is formed by a known method on the outer peripheral surface of the portion excluding both ends of the cored bar 3b. Next, the heat shrinkable tube is fitted to both ends of the elastic member 3c and set at a predetermined position. In this state, heat is applied to the heat-shrinkable tube, the heat-shrinkable tube is shrunk, and the elastic member 3c is fixed, thereby providing gap members 8 and 9 at both ends of the elastic member 3c. In that case, a method for shrinking the heat-shrinkable tube by heat and fixing it to the elastic member 3c is as follows as an example. A heat-shrinkable tube is fitted to both ends of the elastic member 3c, arranged at a predetermined position, and placed in a heating furnace. The temperature of the heating furnace is set to 120 ° C., left for 3 minutes, then taken out from the heating furnace, and naturally cooled at the room environment temperature (normal temperature), thereby fixing the heat shrinkable tube to the elastic member 3c. It is also possible to use a heat gun instead of the heating furnace and locally heat the heat shrinkable tubes arranged and formed at both ends of the elastic member 3c with a heat gun. Thus, the charging roller 3a is manufactured.

  As shown in FIGS. 1A and 1B, the charging roller 3a is arranged such that the outer peripheral surfaces of the gap members 8 and 9 at both ends are in contact with the image carrier 2, and the pair of gap members 8 and A predetermined gap G (proximity distance between the elastic member 3 c and the image carrier 2) is set between the outer peripheral surface of the elastic member 3 c and the outer peripheral surface of the image carrier 2. At this time, although not shown, the pair of gap members 8 and 9 are moved to the image carrier 2 by pressurizing both ends of the cored bar 3b to the image carrier 2 side through a sliding bearing by a pressure means such as a pressure spring. Is pressed with a predetermined force. The gap G is set to 5 μm to 300 μm, but it is preferable that the gap G is smaller, that is, the charging roller 3a is closer to the image carrier 2 because the amount of generated ozone can be reduced. In the present invention, the outer diameter of the image carrier 2 of the image forming apparatus 1 is 20 mm to 50 mm.

  Next, an example of a method for measuring the gap G will be described. First, gap gauges having thicknesses of 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm,..., 90 μm, 95 μm, 100 μm (in 5 μm increments from 5 μm to 100 μm) were prepared. Then, after incorporating the charging roller 3 a into the image forming apparatus, one of these gap gauges is sandwiched between the charging roller 3 a and the image carrier 2. If the gap gauge sandwiched between the gaps does not rattle and can be moved without load in the axial direction of the image carrier 2, the thickness of the gap gauge is taken as the size of the gap G. Needless to say, other known measurement methods can be adopted as the measurement method of the gap G.

The charging roller 3a is rotated at the same linear speed as the image carrier 2 by a motor (not shown). The surface of the image carrier 2 is charged by applying a voltage between the charging roller 3a and the image carrier 2 from a power source (not shown). As for the voltage to the charging roller 3a, the DC voltage V _DC (V) is applied to the cored bar 3b by constant voltage control, and the AC voltage V _AC (V) of (1/2) · V _PP · sin (2πft) is applied. ) Is applied under constant current control. In this case, the amplitude V _{PP that} is twice the _AC voltage V _AC is applied by setting a large voltage (≧ 2 V _TH ) that is at least twice the discharge start voltage V _TH to a certain frequency. Specifically, V _DC (V) is set to, for example, −600 V to −700 V, V _PP in V _AC is set to, for example, 1500 to 2800 (V), and f in V _AC is 500 (Hz) to 8000 (Hz).

  According to the charging device 3 of the first example configured as described above, the gap members 8 and 9 for setting the gap G between the charging roller 3a and the image carrier 2 are formed of heat shrinkable tubes. You can eliminate the seam at 8,9. Thereby, instability of contact of the gap members 8 and 9 with the image carrier 2 due to the joint can be eliminated. Therefore, the influence of the seam on the gap G between the charging roller 3a and the image carrier 2 can be eliminated, and the gap G can be made constant in the axial direction of the charging roller 3a. Further, even if the charging roller 3a and the image carrier 2 are rotated, the conventional slight vibration is suppressed and the gap G can be stabilized, and the charging of the image carrier 2 can be made more uniform.

  Moreover, since there is no seam in the gap members 8 and 9, the gap members 8 and 9 are not peeled off from the seam as in the prior art, and the heat shrinkable tube is contracted by heat to make the gap members 8 and 9 conductive. Since the adhesive force of the adhesive in the adhesive layer is not weakened as in the prior art, the gap members 8 and 9 are not peeled off. As a result, the gap G can be further stabilized, and the image carrier 2 can be uniformly charged more reliably.

  Further, since the gap members 8 and 9 are not peeled off from the elastic member 3c, the charging roller 3a can be prevented from coming into direct contact with the image carrier 2, and dielectric breakdown due to pinholes in the image carrier 2 can be prevented. Good image formation can be performed.

  Furthermore, since the heat-shrinkable tube is used for the gap members 8 and 9, the conventional adhesive layer is eliminated, so that the gap G between the charging roller 3a and the image carrier 2 can be reduced by the amount of the adhesive layer. Therefore, the discharge start voltage in non-contact charging can be reduced. As a result, charging can be performed at a low voltage, ozone generation accompanying a decrease in discharge current, and cost reduction of the power source can be achieved. In addition, since charging is performed at a low voltage, the destruction of the image carrier 2 can be further reliably prevented.

  Further, when a heat shrinkable tube is provided on the elastic member 3c, the heat shrinkable tube is provided by pressing the elastic member 3c from the outer peripheral side with a uniform pressure due to the shrinkage force of the heat shrinkable tube. The film thickness in the circumferential direction and the thickness in the circumferential direction of the elastic member 3c can be made uniform. Therefore, the gap G can be made more uniform in the circumferential direction.

  Furthermore, a heat shrinkable tube is provided on the elastic member 3c, and the gap members 8 and 9 of the heat shrinkable tube are pressed against the image carrier 2, so that the charging roller 3a is reliably driven and rotated when the image carrier 2 is rotated. Can be made. Accordingly, when a cleaning member such as a brush or a blade is brought into contact with the charging roller 3a, the charging roller 3a can be reliably rotated, and the charging roller can be reliably cleaned by the cleaning member. .

FIGS. 2A to 2C are views showing second to fourth examples of the charging roller 3a in the embodiment of the present invention, respectively.
In the charging roller 3a of the first example described above, the annular gap members 8 and 9 are provided on the outer peripheral surface of the elastic member 3c. As shown in FIGS. 2 (a) to 2 (c), the second to Each of the four charging rollers 3a is provided between a relatively hard and flat cored bar 3b and a relatively soft elastic member 3c having elasticity.
In that case, the core metal 3b together with are formed in stepped consisting small diameter portion 3b ₁ and the large-diameter portion 3b ₂ Prefecture, gap members 8, 9 of the large diameter portion 3b ₂ and the elastic member 3c of the core 3b It straddles between.

In the second example shown in FIG. 2A, the outer diameter of the large-diameter portion 3b ₂ of the cored bar 3b and the outer diameter of the elastic member 3c are set to be substantially the same. In this second example, the outer peripheral surfaces of the gap members 8 and 9 are substantially flush with each other in the width direction, and the outer peripheral surfaces of the gap members 8 and 9 are fully wide on the outer peripheral surface of the image carrier 2 (the width in the axial direction of the charging roller 3a). ). Therefore, in this second example, the gap G between the charging roller 3a and the image carrier 2 is set with the full width of the outer peripheral surface of the gap members 8 and 9.

In this second example, since the heat shrinkable tube is provided between the cored bar 3b and the elastic member 3c, the heat contracted tube is relatively hard and flat cored bar 3b with a relatively soft elasticity. Since the certain elastic members 3c can be fixed to each other in a pressed state, the gap members 8 and 9 can be securely fixed without moving. As a result, the gap G can be kept more stable and constant, and stable uniform charging can be realized. Therefore, good image formation can be performed stably.
Other configurations and other operational effects of the second example are substantially the same as those of the first example.

In the third example shown in FIG. 2 (b), the outer diameter of the large-diameter portion 3b ₂ of the core 3b is set to be slightly smaller than the outer diameter of the elastic member 3c. In this third example, the outer peripheral surface of the gap member 8 has a slight step in the width direction, and the outer peripheral surface of the large-diameter portion of the gap member 8 located on the elastic member 3 c is the outer peripheral surface of the image carrier 2. Come into contact. Accordingly, in the third example, the gap G between the charging roller 3a and the image carrier 2 is set on the outer peripheral surface of the large diameter portion of the gap member 8 on the elastic member 3c side. The other gap member 9 is similarly provided.
The effect of the third example is substantially the same as that of the second example. In addition, other configurations and other operational effects of the third example are substantially the same as those of the first example.

Further, in the fourth example shown in FIG. 2C, the outer diameter of the large diameter portion 3b ₂ of the cored bar 3b is set slightly larger than the outer diameter of the elastic member 3c. In the fourth example, the outer peripheral surface of the gap member 8 has a slight step in the width direction, and the outer peripheral surface of the large-diameter portion 3b ₂ of the gap member 8 located on the core metal 3b is the outer periphery of the image carrier 2. It comes into contact with the surface. Therefore, in this fourth example, the outer peripheral surface of the large-diameter portion 3b ₂ of the gap members 8 on the metal core 3b side, the gap G between the charging roller 3a and the image carrier 2 is set. The other gap member 9 is similarly provided.
In the fourth example, since the gap G is set based on the gap member 8 on the relatively hard and flat cored bar 3b side, fluctuation of the gap G can be suppressed and a stable gap G is realized. be able to.
Other configurations and other functions and effects of the fourth example are substantially the same as those of the first example.

FIG. 3 is a diagram showing a fifth example of the charging roller 3a in the embodiment of the present invention.
In the above-described charging roller 3a of the first example, the annular gap members 8 and 9 are continuously provided in the circumferential direction over the entire width without partially missing, but as shown in FIG. In the charging roller 3a, the annular gap members 8, 9 have a predetermined number of parallelogram holes 3d provided at equal intervals in the circumferential direction and penetrating between the inner and outer peripheral surfaces of the gap members 8, 9. Partially missing. Each of the holes 3d is provided so as to be inclined leftward with respect to the axial direction of the charging roller 3a. The inclination of each hole 3d may be inclined downwardly to the right. The holes 3d can also be formed in a rectangular or square shape. In this case, each hole 3d extends along the axial direction of the charging roller 3a.

In this fifth example, a predetermined number of holes 3d are provided in the heat-shrinkable tube. Therefore, when the heat-shrinkable tube shrinks during manufacturing, relief is formed by these holes 3d, so that wrinkles are generated in the heat-shrinkable tube. And the heat shrinkable tube can be reliably prevented from being doubled. In addition, for example, foreign matters such as residual toner and paper dust enter the holes 3d, so that fluctuations in the gap G due to these foreign matters can be suppressed. Therefore, the gap G can be kept stable and constant, and stable uniform charging can be realized. Thereby, good image formation can be performed stably.
Other configurations and other functions and effects of the fifth example are substantially the same as those of the first example.

FIG. 4 is a diagram showing a sixth example of the charging roller 3a in the embodiment of the present invention.
In the charging roller 3a of the fifth example described above, the heat shrinkable tubes of the annular gap members 8 and 9 have a predetermined number of holes 3d. As shown in FIG. 4, the charging roller 3a of the sixth example is used. Has a predetermined number of rectangular cutouts 3e and 3f which are provided in the heat shrinkable tube at equal intervals in the circumferential direction and along the axial direction of the charging roller 3a and are the cuts of the present invention, instead of the hole 3d. Yes. In that case, the notches 3e and 3f are alternately provided with notches 3e cut out from the right peripheral edge of the gap members 8 and 9 and notches 3f cut out from the left peripheral edge of the gap members 8 and 9 in the circumferential direction. It has been. The notches 3e and 3f can be formed in a square shape, or can be inclined with respect to the axial direction of the charging roller 3a as in the hole 3d of the fifth example shown in FIG.
In the sixth example, the same effect as the hole 3d of the fifth example can be obtained by the notches 3e and 3f provided in the heat shrinkable tube.
Other configurations and other operational effects of the sixth example are substantially the same as those of the first example.

  Next, the printed image quality evaluation test and the ozone emission amount measurement evaluation test were performed using Examples 1 to 10 and Comparative Example 1 of the charging device 3 of the present invention, and these tests will be described. Table 1 shows the gap G between the charging roller 3a and the image carrier 2 and the voltage applied to the charging roller 3a as printing conditions in Examples 1 to 10 and Comparative Example 1.

(Example 1)
First, a rubber layer elastic member 3c made of epichlorohydrin rubber was formed by a known method on the outer peripheral surface of a core metal 3b having an outer diameter of φ9 mm formed by SUM-Ni plating. The outer diameter of this rubber layer was 11.10 mm. The elastic member 3c has a volume resistivity of 10 ⁸ Ω · cm and a rubber hardness of 80 degrees according to the old JIS-A. Next, as shown in FIG. 1 (b), heat-shrinkable tubes made of Gunze Co., Ltd. made of fluororesin PFA / FEP having a thickness of 50 μm and an inner diameter of 11.20 mm are fixed to both ends of the elastic member 3c by the method described above. By providing the gap members 8 and 9, the charging roller 3a of Example 1 was manufactured. The film width of these gap members 8 and 9 was 8 mm.

  Then, instead of the charging roller of this printer, the manufactured charging roller 3a of Example 1 was incorporated into a printer LP-9000C manufactured by Seiko Epson Corporation, and the above-described both evaluation tests were performed. At this time, as shown in Table 1, the gap G between the charging roller 3a and the image carrier 2 of the printer was 50 μm. The outer diameter of the image carrier 2 of the printer LP-9000C is φ40 mm.

In the image quality evaluation test, as described above, the printer incorporating the charging roller 3a of Example 1 was used, and the print density was changed to 0%, 20%, 40%, 60%, 80%, and 100% while changing to A3. Monochrome solid printing was performed on the entire paper. At this time, as shown in Table 1, the voltage applied to the charging roller 3a is a voltage obtained by superimposing V _DC and V _AC. V _DC was −630 V, V _AC was an AC voltage given by the above formula, V _PP was 2000 V, and f was 3.0 Hz.

  Then, 50,000 (50k) sheets were printed for each printing density. Then, for each printed sheet number 10k, the non-uniformity of the printed toner density was visually observed. In this way, an image having a uniform toner density was printed on the entire surface of the A3 sheet for each density, and the unevenness of the toner density was visually observed to evaluate the charging spots caused by the charging roller 3a.

  Further, in the measurement and evaluation test of the ozone discharge amount, 100 k monochrome solid printing was performed on the entire A3 paper at a printing density of 60%. At this time, the amount of ozone discharged into the printer was measured. The measurement of the ozone discharge amount was performed using an ozone concentration measuring device (A = 21ZX: manufactured by Sato Corporation).

(Example 2)
A heat-shrinkable tube made of a fluororesin PFA / FEP made of Gunze Co., Ltd. having a thickness of 30 μm and an inner diameter of 11.20 mm is formed at both ends of the elastic member 3c formed on the outer peripheral surface of the same metal core 3b as in Example 1. The charging roller 3a of Example 2 was manufactured by providing the gap members 8 and 9 in the same manner as described above. The film width of these gap members 8 and 9 was 8 mm.

In the same manner as the charging roller 3a of the first embodiment, the charging roller 3a of the second embodiment is incorporated into a printer LP-9000C manufactured by Seiko Epson Corporation, and both the above-described evaluation tests are performed by the same method as the first embodiment. went. At this time, as shown in Table 1, the gap G between the charging roller 3a and the image carrier 2 of the printer was 30 μm. The voltage applied to the charging roller 3a was −630 V _DC , V _PP was 1700 V, and f was 3.0 Hz.

(Example 3)
A heat-shrinkable tube made of a fluororesin PFA / FEP with a thickness of 20 μm and an inner diameter of 11.20 mm made by Gunze Co., Ltd. is applied to both ends of the elastic member 3c formed on the outer peripheral surface of the same core 3b as in the first embodiment. The charging roller 3a of Example 3 was manufactured by providing the gap members 8 and 9 in the same manner as described above. The film width of these gap members 8 and 9 was 8 mm.

In the same manner as the charging roller 3a of the first embodiment, the charging roller 3a of the third embodiment is incorporated into a printer LP-9000C manufactured by Seiko Epson Corporation, and both evaluation tests described above are performed in the same manner as the first embodiment. went. At this time, as shown in Table 1, the gap G between the charging roller 3a and the image carrier 2 of the printer was 20 μm. The voltage applied to the charging roller 3a was −630 V _DC , V _PP was 1550 V, and f was 3.0 Hz.

Example 4
A core metal 3b of the same material as in Example 1 at a stepped shape shown in FIG. 2 (a), substantially the same outer diameter as the outer diameter of the large-diameter portion 3b ₂ of the same material a and the core metal 3b of Example 1 The elastic member 3c was used. At this time, the outer diameter of the small-diameter portion 3b ₁ of the cored bar 3b was an outer diameter of 9 mm, and the outer diameter of the elastic member 3c was the same as that in Example 1. Next, after setting a heat shrinkable tube made of fluororesin PFA / FEP with a thickness of 30 μm and an inner diameter of 11.20 mm made by Gunze Co., Ltd., straddling the large diameter portion 3b ₂ of the core metal 3b and the elastic member 3c The charging roller 3a of Example 4 was manufactured by fixing the same as in Example 1 and providing the gap members 8 and 9. The elastic member 3c of Example 4 had the same outer diameter, the same volume specific resistance value, and the same rubber hardness as the elastic member 3c of Example 1. The film width of these gap members 8 and 9 was 8 mm.

In the same manner as the charging roller 3a of the first embodiment, the charging roller 3a of the fourth embodiment is incorporated into a printer LP-9000C manufactured by Seiko Epson Corporation, and both the above-described evaluation tests are performed by the same method as the first embodiment. went. At this time, as shown in Table 1, the gap G between the charging roller 3a and the image carrier 2 of the printer was 30 μm. The voltage applied to the charging roller 3a was −630 V _DC , V _PP was 1700 V, and f was 3.0 Hz.

(Example 5)
A heat-shrinkable tube made of fluororesin PFA · FEP having a thickness of 30 μm and an inner diameter of 9.2 mm and having a hole 3d shown in FIG. 3 was used. At this time, the hole 3d has an inclination angle of 45 ° with respect to the axial direction of the tube, a width along the axial direction of the charging roller 3a of 4 mm, and a width perpendicular to the inclination of 2 mm. At equal intervals. The heat-shrinkable tube made of fluororesin PFA / FEP was fixed to both ends of the elastic member 3c in the same manner as in Example 1 to provide the gap members 8 and 9, thereby manufacturing the charging roller 3a of Example 5. . The film width of these gap members 8 and 9 was 8 mm.

In the same manner as the charging roller 3a of the first embodiment, the charging roller 3a of the fifth embodiment is incorporated into a printer LP-9000C manufactured by Seiko Epson Corporation, and both the above-described evaluation tests are performed by the same method as the first embodiment. went. At this time, as shown in Table 1, the gap G between the charging roller 3a and the image carrier 2 of the printer was 30 μm. The voltage applied to the charging roller 3a was −630 V _DC , V _PP was 1550 V, and f was 3.0 Hz.

(Example 6)
As a material for the gap members 8 and 9, a tube super teletube (registered trademark) manufactured by Teijin Chemicals Ltd. was used in place of the heat-shrinkable tube made of PFA / FEP manufactured by Gunze Co., Ltd. in Example 1. Otherwise, the charging roller 3a of Example 6 was manufactured in the same manner as the charging roller 3a of Example 1. Then, both the above-described evaluation tests were performed using the charging roller 3a of Example 8 in the same printer as Example 1, under exactly the same printing conditions as in Example 1.

(Example 7)
As a material for the gap members 8 and 9, a tube super teletube (registered trademark) manufactured by Teijin Chemicals Ltd. was used in place of the heat-shrinkable tube made of PFA / FEP manufactured by Gunze Co., Ltd. in Example 2. Otherwise, the charging roller 3a of Example 7 was manufactured in the same manner as the charging roller 3a of Example 2. Then, both the above-described evaluation tests were performed using the charging roller 3a of Example 7 in the same printer as in Example 2 under exactly the same printing conditions as in Example 2.

(Example 8)
As a material for the gap members 8 and 9, a tube super teletube (registered trademark) manufactured by Teijin Chemicals Ltd. was used in place of the heat-shrinkable tube made of PFA / FEP manufactured by Gunze Co., Ltd. in Example 3. Otherwise, the charging roller 3a of Example 8 was manufactured in the same manner as the charging roller 3a of Example 3. Then, both the above-described evaluation tests were performed using the charging roller 3a of Example 8 in the same printer as in Example 3 under exactly the same printing conditions as in Example 3.

Example 9
As a material for the gap members 8 and 9, a tube super tele tube (registered trademark) manufactured by Teijin Chemicals Ltd. was used in place of the heat-shrinkable tube manufactured by Gunze Co., Ltd. in Example 4 and made of PFA / FEP. Otherwise, the charging roller 3a of Example 9 was manufactured in the same manner as the charging roller 3a of Example 4. Then, both the above-described evaluation tests were performed using the charging roller 3a of Example 9 in the same printer as in Example 4 under the same printing conditions as in Example 4.

(Example 10)
As a material for the gap members 8 and 9, a tube super teletube (registered trademark) manufactured by Teijin Chemicals Ltd. was used in place of the heat-shrinkable tube made of PFA / FEP manufactured by Gunze Co., Ltd. in Example 5. Otherwise, the charging roller 3a of Example 10 was manufactured in the same manner as the charging roller 3a of Example 5. Then, using a charging roller 3a of Example 10 in the same printer as in Example 5, except that instead of a printing condition V _AC of V _PP to (V) to 1550V in Example 5, the printing conditions of Example 5 In the same manner, the two evaluation tests described above were performed.

(Comparative Example 1)
A band-shaped film material having a width of 8 μm, which is an adhesive sheet having an adhesive layer formed on one side of a sheet made of polypropylene, was cut at 45 ° obliquely at both ends. And the gap members 8 and 9 are provided by winding this film material to the both ends of the elastic member 3c formed in the outer peripheral surface of the same metal core 3b as Example 1 as shown in FIG. A charging roller 3a of Comparative Example 1 was manufactured.

  In that case, the adhesive surface side is affixed so that the gap S is formed without the edges of the film material overlapping each other in the circumferential direction, and there is no portion where the film material does not exist in the axial direction of the charging roller 3a at all positions. Fixed by wearing. At this time, the thickness of the film material composed of the thickness of the polypropylene sheet and the thickness of the adhesive layer was 50 μm, and the width of the gap S was 0.7 mm. Both the above-described evaluation tests were performed using the charging roller 3a of Comparative Example 1 in the same printer as in Example 1 under the same printing conditions as in Example 1.

  Table 2 shows the evaluation test results of the image quality, and Table 3 shows the measurement evaluation test results of the ozone emission amount. In Table 2, ○ indicates that all printed images were evaluated as being good images with no toner density unevenness and no charged spots, and × indicates toner density unevenness in the printed images. This is the case when it is evaluated that the generated defective image. In Table 3, ◯ indicates a case where the ozone emission amount is evaluated as being satisfactory without any particular problem, and ◎ is a case where the ozone emission amount is small and is evaluated as being particularly favorable.

  As can be seen from Table 2, the charging devices using the charging rollers 3a of Examples 1 to 10 were all evaluated as “Good”, and good images without charging spots were obtained. On the other hand, in the charging roller 3a of Comparative Example 1, in the printing of 30k sheets, 40k sheets, and 50k sheets, a defective image in which charging spots occurred in a part of the printed image occurred. This charging unevenness is caused by peeling of the gap members 8 and 9 from the seam of the film material, so that the gap G becomes non-uniform so that uniform charging cannot be performed, or part of the charging roller 3a due to peeling of the film material. This is considered to be due to the fact that the dielectric breakdown of the photoconductor is promoted and charging failure occurs due to the contact between the photoconductor and a part of the photoconductor as the image carrier 2.

  Further, as is apparent from Table 3, it was found that the ozone discharge amount decreases as the gap G, that is, the proximity distance between the charging roller 3a and the image carrier 2 decreases. Therefore, by using the heat-shrinkable tube of the present invention that does not have an adhesive layer, the amount of ozone discharged can be effectively reduced.

  In each of the above-described examples, the charging roller is used as the charging member. However, the present invention is not limited to this, and the charging member can be formed of a plate-like member. In that case, after the heat-shrinkable tube is fitted into the plate-like member, it may be contracted by heat.

  The charging device of the present invention is used in an image forming apparatus for forming an electrostatic image in electrophotography, electrostatic recording, electrostatic printing, and the like, and is disposed in the vicinity of an image carrier such as a photosensitive member. It can be suitably used for a charging device including a charging roller for charging.

1 shows a first example of an embodiment of a charging device according to the present invention, in which (a) schematically shows a basic configuration of an image forming apparatus including the charging device of the first example, and (b) shows the charging device. FIG. 4C is a front view of the charging roller, and FIG. (A) thru | or (c) is a figure which shows the 2nd thru | or 4th example of the charging roller in embodiment of this invention, respectively. It is a figure which shows the 5th example of the charging roller in embodiment of this invention. It is a figure which shows the 6th example of the charging roller in embodiment of this invention. It is a figure which shows typically the basic composition of the image forming apparatus provided with the conventional charging device. It is a figure which shows the charging roller of the prior art example shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Image carrier, 3 ... Charging apparatus, 3a ... Charging roller, 3b ... Core metal, 3c ... Conductive elastic member, 3d ... Hole, 3e, 3f ... Notch, 4 ... Exposure apparatus 5 ... developing device, 6 ... transfer medium, 7 ... transfer device, 8, 9 ... gap member

Claims (5)

In the charging device in which the charging member is disposed in proximity to the image carrier by gap members provided at both ends thereof, and the image carrier is charged in a non-contact manner by the charging member.
The charging device is characterized in that the gap member is constituted by an endless heat shrinkable tube. The charging device according to claim 1, wherein the charging member includes a charging roller. The charging member includes a cored bar and a rubber material formed from one end of the cored bar to the other end on a surface of the cored bar facing the image carrier, and the gap member includes at least the rubber material. The charging device according to claim 1, wherein the charging device is disposed on the charging device. The charging member includes a cored bar and a rubber material formed on a surface of the cored bar facing the image carrier and excluding both ends of the cored bar, and the gap member includes at least the rubber The charging device according to claim 1, wherein the charging device is disposed across a metal or the core metal and the rubber material. 5. The charging device according to claim 1, wherein the heat-shrinkable tube has a predetermined number of holes or cuts penetrating from the inner peripheral surface to the outer peripheral surface.

Images