JP2006343474A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging roller of non-contact charging easily obtaining a charging gap of high precision having stable reliability in the non-contact charging of an image carrier. <P>SOLUTION: Ring-like recesses 3d and 3e are formed on the outer peripheral face of both ends of a core metal 3c of the charging roller 3a, respectively. Insulating layers 3j and 3k setting charging gaps by an insulating member are formed on the outer peripheral face of both ends 3h and 3i of the core metal 3c outside of both the recesses 3d and 3e. A conductive layer 3g is formed by painting a conductive paint material on the outer peripheral face of the insulating layers 3j and 3k, on the formation part of both the recesses 3d and 3e of the core metal 3c and on the outer peripheral face of a center part 3f and the core metal 3c inside of both the recesses 3d and 3e. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used in an image forming apparatus such as an electrophotography, an electrostatic copying machine, a printer, and a facsimile, and is a charging roller that places a predetermined charging gap with respect to an image carrier and charges the image carrier in a non-contact manner. Technical field.

2. Description of the Related Art Conventionally, as an image forming apparatus, there is known a charging roller that places a predetermined charging gap with respect to an image carrier and charges the image carrier without contact (see, for example, Patent Document 1). In the charging roller disclosed in Patent Document 1, ring-shaped regulating members are engaged with concave steps formed at both ends with their phases inconsistent with each other. According to the charging roller disclosed in Patent Document 1, a charging gap with a required accuracy can be obtained at a low cost.
JP 2004-109151 A.

  However, in the charging roller disclosed in Patent Document 1, in order to form the concave annular step at both ends, the base shaft of the charging roller is first polished, and then the bottom of the concave step is further polished. There is a need to. In this case, it is extremely difficult to process the polished step so that the depth of the step is constant and the center axis of the base shaft and the center axis of the bottom of the annular step are aligned (concentric). The problem is that it is difficult to manufacture a charging roller so that a stable, reliable and highly accurate charging gap can be obtained even if the mounting positions of the ring-shaped regulating members are adjusted so that their phases are shifted. There is.

  The present invention has been made in view of such circumstances, and an object of the present invention is to make it possible to easily obtain a stable, reliable and highly accurate charging gap in non-contact charging of an image carrier. It is to provide a charging roller with contact charging.

  In order to solve the above-mentioned problems, the charging roller according to the first aspect of the present invention has a conductive layer formed on a conductive shaft, and the conductive layer faces the image carrier with a predetermined charging gap. In the charging roller provided in a non-contact manner for charging the image carrier, annular recesses are formed on the outer peripheral surfaces of both ends of the conductive shaft, and both ends of the conductive shaft outside the recess. An insulating layer for setting the charging gap is formed on the outer peripheral surface of the portion by an insulating member, and the outer peripheral surface of the recess forming portion of the conductive shaft and the center of the conductive shaft inside the recess The conductive layer is formed by coating a conductive coating material on the outer peripheral surface of each part.

The invention of claim 2 is characterized in that the conductive layer made of the conductive coating material is also formed on the outer peripheral surface of the insulating layer.
Furthermore, the invention of claim 3 is characterized in that the depth of the recess is set larger than the film thickness of the conductive layer.
Further, the invention of claim 4 is characterized in that the depth of the recess is set larger than the film thickness of the insulating layer.

Further, the invention of claim 5 is characterized in that the depth of the recess is set larger than the sum of the film thickness of the conductive layer and the film thickness of the insulating layer.
Further, the invention of claim 6 is characterized in that an edge portion forming the recess of the conductive shaft is chamfered.

  According to the charging roller of the present invention configured as described above, since the insulating layer for setting the charging gap is formed on the outer peripheral surface of the conductive shaft, the charging gap can be easily and stably provided with high accuracy. Can be set. In addition, since the recess of the conductive shaft is not directly related to the charging gap, it is not necessary to process the recess with high accuracy, and the charging roller can be manufactured at low cost.

  In addition, the insides of the annular recesses formed at both ends of the conductive shaft are covered with the conductive coating material and the insulating member, respectively. In the state of being in contact with the image carrier, the distance from the image carrier becomes far away and a non-contact charging gap is not formed and the image carrier is not discharged, so that it does not contribute to non-contact charging. Therefore, both depressions can be used as the target for the coating boundary of the conductive coating material and the target for the installation boundary of the insulating member (or the coating boundary if the insulating member is an insulating coating material). The painting and the installation of the insulating member can be performed easily and with high accuracy.

  Furthermore, if these depressions are not formed at both ends of the conductive shaft, insulation is formed when an insulating coating is formed on both ends of the conductive shaft as shown in FIG. 2 (c). The film thickness of the inner edge of the layer tends to increase due to the surface tension during drying after coating the insulating coating material, and the insulating elastic member is fixed to both ends with, for example, an adhesive to form an insulating layer When the insulating layer becomes thicker due to the surface tension during drying of the adhesive or when the insulating layer is formed using a heat shrinkable tube as an insulating elastic member, the insulating layer Since the film thickness of the inner end of the film tends to increase due to shrinkage of the heat-shrinkable tube, it is possible to form a constant film thickness of the insulating layer constituting the gap part, that is, to set a constant charging gap. Can not. In addition, since the film thickness at both ends of the conductive layer tends to increase due to the surface tension during drying after coating the conductive coating material, it is necessary to form a constant film thickness of the conductive layer, that is, to maintain a constant charging gap. Cannot be set. On the other hand, according to the charging roller of the present invention, since the recesses are formed at both ends of the conductive shaft, the insulating member enters the recesses, so that the insulating layer is installed after the insulating member is installed. Even if the film thickness at the end of the film tends to increase, this tendency is absorbed by both depressions. Therefore, the film thickness of the conductive layer constituting the charging part and the insulating layer and conductive layer films constituting the gap part Any thickness can be formed constant. Therefore, it becomes possible to perform even better charging.

  In particular, according to the third to fifth aspects of the present invention, the depth of both depressions is greater than the thickness of the conductive layer, or greater than the thickness of each insulating layer, or the thickness of the conductive layer and each insulating layer. Therefore, it is possible to prevent these conductive coating materials or insulating members from protruding from both recesses, and to form a charging gap with both insulating layers with high accuracy. And it becomes possible to form stably. In that case, according to the invention of claim 5, it is possible to make both depressions deeper than the film thickness assumed when these are overlaid and covered with the conductive coating material and the insulating member. Therefore, it is possible to more effectively prevent the conductive coating material and the insulating member from protruding from both recesses. In this way, by setting the depth of both depressions in consideration of the tendency of the film thickness at the end portions of the conductive layer and the insulating layer to increase, a stable and highly accurate charging gap can be more reliably formed. it can.

  According to the invention of claim 6, since the edges of the conductive shaft forming both recesses are chamfered, the gradient from the outer peripheral surface of the conductive shaft to the both recess surfaces is formed at the edges. There is no sudden change. Therefore, the edge of the conductive shaft that forms both recesses can be reliably covered with the conductive coating material and the insulating member. As a result, it is possible to more reliably prevent charge leakage from the edge of the conductive shaft forming both depressions, and to reduce the thickness of the conductive layer accordingly.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically and partially showing an example of an image forming apparatus provided with an example of an embodiment of a non-contact charging roller according to the present invention.

  As shown in FIG. 1, the image forming apparatus 1 of this example includes a photoconductor 2 that is an image carrier on which an electrostatic latent image and a toner image are formed, and the photoconductor 2 is provided around the photoconductor 2. Are sequentially provided with a charging device 3, an optical writing device 4, a developing device 5, a transfer device 6, and a cleaning device 7 from the upstream side in the rotation direction (clockwise in FIG. 1).

  The charging device 3 has a non-contact charging roller 3a of the present embodiment and a cleaning member 3b made of, for example, a roller. Then, the photoreceptor 2 is uniformly charged by the charging roller 3a, and the cleaning roller 3a is cleaned by the cleaning member 3b to remove foreign matters such as toner and dust adhering to the charging roller 3a.

  As shown in FIG. 2A, the non-contact charging roller 3a includes a cored bar 3c, and the cored bar 3c is configured as a conductive shaft having conductivity, such as a metal shaft. As this conductive shaft, for example, a SUM 22 surface with Ni plating can be used.

  On the outer peripheral surface of both ends of the cored bar 3c, annular recesses 3d and 3e are formed, respectively. Insulating layers 3j and 3k are formed of insulating members on the outer peripheral surfaces of both end portions 3h and 3i of the core 3c outside the depressions 3d and 3e, respectively. In this case, an insulating coating material or an insulating elastic member can be used as the insulating member. Further, the insulating member also enters (invades) into both depressions 3d and 3e so as to partially cover the formation portions of both depressions 3d and 3e of the cored bar 3c and also cover both end surfaces of the cored bar 3c. Become. The outer diameters of these insulating layers 3j and 3k are set to be equal to each other.

  Further, for example, a conductive coating material is sprayed on the outer peripheral surface of the insulating layers 3j and 3k, the portions where the depressions 3d and 3e are formed in the core metal 3c, and the outer peripheral surface of the central portion 3f of the core metal 3c inside the depressions 3d and 3e. The conductive layer 3g is formed by painting. Therefore, the insulating layers 3j and 3k and the conductive layers 3g formed on the outer peripheral surfaces of the insulating layers 3j and 3k are formed between the conductive layers 3g and the photosensitive member 2 by the contact of the conductive layers 3g with the photosensitive member 2. A gap portion for setting a predetermined charging gap G based on the film thickness of the insulating layers 3j and 3k is formed therebetween. Thus, the insulating layers 3j and 3k as gap members are formed on the outer peripheral surface (surface) of the cored bar 3c. The conductive layer 3g formed on the outer peripheral surface of the central portion 3f of the cored bar 3c constitutes a charging unit that performs non-contact charging with respect to the photoreceptor 2 with a predetermined charging gap G.

Then, the depth t ₁ of the 3d recess as shown in FIG. 2 (b), it is set larger than the sum of the thickness t ₂ of the conductive layer 3g with a thickness t ₃ of the insulating layer 3j [t ₁ > (T ₂ + t ₃ )]. Therefore, the depth t ₁ of the recess 3d is set to be larger than both the film thickness t ₂ of the conductive layer 3g and the film thickness t ₃ of the insulating layer 3j (t ₁ > t ₂ , t ₁ > t ₃ ).

  In addition, the edges forming the recess 3d of the cored bar 3C are all chamfered (C cut) c. Further, the edge of the end 3h of the cored bar 3c is also chamfered (C cut) c. These chamfers c are usually referred to as R portions, and the edge portions are cut and rounded with curved surfaces. Of course, the chamfer c can also be formed by cutting the edge with a flat inclined surface.

  2B shows the depression 3d and the insulating layer 3j on the one end 3h side, the depression 3e and the insulating layer 3k on the other end 3i side are also shown on the end 3h side. It is formed in the same manner as the recess 3d and the insulating layer 3j.

  The optical writing device 4 writes an electrostatic latent image on the photosensitive member 2 with, for example, a laser beam. The developing device 5 includes a developing roller 5a, a toner supply roller 5b, and a toner layer thickness regulating member 5c. The toner T, which is a developer, is supplied onto the developing roller 5a by the toner supply roller 5b, and the toner T on the developing roller 5a is regulated in thickness by the toner layer thickness regulating member 5c. The electrostatic latent image on the photoconductor 2 is developed with the conveyed toner T, and a toner image is formed on the photoconductor 2.

  The transfer device 6 has a transfer roller 6a, and a toner image is transferred onto the photosensitive member 2 by the transfer roller 6a onto a transfer medium 8 such as transfer paper or an intermediate transfer medium. When the toner image is transferred to the transfer paper that is the transfer medium 8, the toner image on the transfer paper is fixed by a fixing device (not shown), an image is formed on the transfer paper, and the toner image is transferred to the transfer medium 8. When the toner image is transferred to the intermediate transfer medium, the toner image on the intermediate transfer medium is further transferred to the transfer paper, and then the toner image on the transfer paper is fixed by a fixing device (not shown) to form an image on the transfer paper. Is done.

  The cleaning device 7 includes a cleaning member 7a such as a cleaning blade. The photosensitive member 2 is cleaned by the cleaning member 7a, and the transfer residual toner on the photosensitive member 2 is removed and collected.

  According to the non-contact charging roller 3a of this example configured as described above, the insulating layers 3j and 3k, which are gap members, are formed on the outer peripheral surface of the cored bar 3c. Can be set easily. In addition, since the recesses 3d and 3e of the cored bar 3c are not directly related to the charging gap G, it is not necessary to process the recesses with high accuracy, and the charging roller 3a can be manufactured at low cost.

  In addition, the insides of the annular recesses 3d and 3e formed at both end portions 3h and 3i of the cored bar 3c are covered with the conductive coating material and the insulating member, respectively. In the state where the insulating layers 3j and 3k are in contact with the photosensitive member 2, the coating portion made of the material is not far from the photosensitive member 2 and does not form the non-contact charging gap G and does not discharge to the photosensitive member 2. Does not contribute to charging. Therefore, both recesses 3d and 3e can be used as targets for the coating boundary of the conductive coating material and for the installation boundary of the insulating member (or the coating boundary when the insulating member is an insulating coating material). The coating of the coating material and the installation of the insulating member can be performed easily and with high accuracy.

  Further, when these recesses 3d and 3e are not formed at both end portions 3h and 3i of the cored bar 3c, an insulating coating material is applied to both end portions 3h and 3i as shown in FIG. , 3k, the thickness of the inner end 3m of the insulating layers 3j, 3k (the insulating layer 3k is not labeled) tends to become thicker due to the surface tension during drying after the coating of the insulating coating material, When insulating layers 3j and 3k are formed by fixing insulating elastic members to both ends 3h and 3i with, for example, an adhesive, the film thickness of the inner end 3m of the insulating layers 3j and 3k (the reference number of the insulating layer 3k is not indicated) Tends to become thicker due to the surface tension during drying of the adhesive, or when the insulating layers 3j, 3k are formed using a heat shrinkable tube as the insulating elastic member, the inner end portions 3m ( The thickness of the insulating layer 3k (without the sign) is increased by the shrinkage of the heat shrinkable tube. Therefore, it is impossible to form a constant film thickness of the insulating layers 3j and 3k constituting the gap portion, that is, to set a constant charging gap G. Further, since the film thickness at both ends of the conductive layer 3g tends to increase due to the surface tension at the time of drying after the coating of the conductive coating material, forming a constant film thickness of the conductive layer 3g, that is, constant charging The gap G cannot be set.

  On the other hand, according to the charging roller 3a of this example, since the recesses 3d and 3e are formed at both end portions 3h and 3i of the core metal 3c, the insulating member also enters the recesses 3d and 3e. Therefore, even if the thickness of the end portions of the insulating layers 3j and 3k tends to increase after the insulating member is installed, this tendency is absorbed by both the depressions 3d and 3e, so that the conductive material constituting the charging portion The film thickness of the layer 3g and the film thicknesses of the insulating layers 3j and 3k and the conductive layer 3g constituting the gap can all be formed constant. Therefore, it becomes possible to perform even better charging.

  Further, since the edges of the cored bar 3c forming both the depressions 3d and 3e are chamfered c, the gradient from the outer peripheral surface of the cored bar 3c to the both depressions 3d and 3e is suddenly changed at this edge. There is nothing. Therefore, the edge portion of the cored bar 3c forming both the depressions 3d and 3e can be reliably covered with the conductive coating material and the insulating member. Accordingly, it is possible to more reliably prevent charge leakage from the edge of the cored bar 3c forming both the depressions 3d and 3e, and to reduce the thickness of the conductive layer 3g accordingly.

Furthermore, both recesses 3d, the depth t ₁ of 3e, conductive layer 3g having a thickness t ₂ and the insulating layer 3j, so is set to be larger than the sum of the 3k thickness t ₃ of both recess 3d, 3e can be made deeper than the film thickness assumed when these are overlaid with the conductive coating material and the insulating member. Therefore, it is possible to prevent the conductive coating material and the insulating member from protruding from both the recesses 3d and 3e, and to form the charging gap G by the both insulating layers 3j and 3k with high accuracy and stability. It becomes possible. As described above, the depth of the recesses 3d and 3e is set in consideration of the tendency that the film thickness at the end portions of the conductive layer 3g and the insulating layers 3j and 3k is increased, so that the stable and highly accurate charging gap G Can be more reliably formed.

Next, examples and comparative examples of the non-contact charging roller of the present invention will be described. In order to verify that the charging roller of the present invention can obtain the above-described effects by using the charging rollers 3a of the examples belonging to the present invention and the comparative examples not belonging to the present invention. The experiment conducted in the above will be described.
Table 1 shows the charging rollers and experimental results of Examples and Comparative Examples used in the experiment.

In Table 1, as for No. 1-11, as shown to Fig.2 (a) and (b), hollow 3d, 3e is formed in the both ends of the metal core 3c, and C cut is carried out at the edge of hollow 3d, 3e. No. 12-22 is a charging roller of a comparative example in which dents 3d and 3e are not formed at both ends of the cored bar 3c as shown in FIG. 2 (c).

The shaft diameter of the cored bar (the diameter of the portion where the conductive layer 3g of the cored bar 3c is formed) of each example charging roller is φ8 mm. As the core 3c, a SUM 22 surface with Ni plating was used. The depressions formed in the metal core are set to 100 μm for the charging rollers No. 1 to 6 and 12 to 17, and set to 125 μm for the charging rollers No. 7, 8, 18 and 19. Furthermore, the charging rollers No. 9 to 11 and 20 to 22 were set to 150 μm.
Moreover, the conductive coating material and the insulating member shown in Table 2 were used.

As shown in Table 2, the conductive coating material is a coating liquid in which conductive SnO ₂ is mixed by 19 wt% (wt%), polyurethane (PU) resin is 18 wt%, ionic conductive material is 3 wt%, and water is 60 wt%. It is. Conductive SnO ₂ is available from Gemco Co., Ltd. shown in Table 3. Details of those are available on the Gemco website (http://www.jemco-mmc.co.jp/corporate/index.html). It is posted.

The conductive SnO ₂ used in this example and this comparative example is trade name “T-1” of Gemco Co., Ltd., and “T-1” is a tin-antimony oxide. Of course, other conductive SnO ₂ can be used in the present invention.
In addition, the ion conductive material is for imparting conductivity to the conductive coating material, and the ion conductive material used in this example and this comparative example is “YP-12” (manufactured by Maruhishi Oil Chemical Co., Ltd.). ).
In addition, an insulating layer having a thickness of 20 μm was formed by spray coating using polyimide (PI) resin, which is an insulating coating material, as the insulating member to be applied to the gap portion.

  The charging roller manufacturing method of each example is as follows. First, an insulating coating material is applied to both ends of the core metal by spray coating to form an insulating layer, and then the conductive coating material is applied to the outer peripheral surface of the insulating layer. The conductive layer was formed by spray coating on the depression forming portion of the core metal and the outer peripheral surface of the central portion of the core metal.

  The photoconductor is the same material as LP-9000C manufactured by Seiko Epson Corporation. The photoconductor layer thickness is set to 23 μm, the photoconductor diameter is set to 24 mm, and the peripheral speed of the photoconductor is It was set to 250 mm / sec.

The experimental apparatus of the image forming apparatus was configured to have the same configuration as the LP-9000C described above. The applied voltage V _C (V) of the charging roller 3a is obtained by superimposing the _AC voltage AC component V _AC (V) on the DC voltage DC component V _DC (V),
V _C = V _DC + V _AC = −650 + (1/2) V _PP · sin2πft
(Here, V _PP = 1800 V, f = 1.5 kHz, and V _AC is a sin wave.)
Set to. In the experiment, in a room environment at a temperature of 23 ° C. and a humidity of 50%, a solid printing of 25% halftone on A4 plain paper was performed, and a monochrome durability test of 10k (10000) sheets was performed.

  The images with the desired print density (which can be put to practical use) that are visually determined to be well charged are indicated by ◯, the photoconductor is perforated due to leakage, and the image is charged periodically with the charging roller. Those with spots were judged to be defective and represented by x.

  In each of the charging rollers of Examples Nos. 4 to 11, good charging was obtained with ◯. In the charging rollers of Examples Nos. 1 to 3, since the conductive layer was too thin, the conductive layer was not formed at the edge of the recess, and the core metal at the edge of the recess was exposed. As a result, charge leakage occurred immediately after the start of printing, resulting in a failure. This is not due to the depression in the cored bar of the present invention, but is due to the film thickness of the conductive layer being too thin. Therefore, the film thickness of the conductive layer needs to be set to a predetermined thickness, but this film thickness may be appropriately set as necessary.

Furthermore, in the charging rollers of Nos. 12 to 14 in which no depressions were formed, since the conductive layer was too thin, charge leakage occurred immediately after the start of printing, resulting in a defective result. Further, in each of the charging rollers of Comparative Examples No. 15 to 22, in the printing up to 10k sheets, periodic charging spots of the charging roller occurred in the formed image, resulting in a defective result.
From this experiment, it was proved that the above-described effect of the present invention can be obtained by providing depressions at both ends of the charging roller 3 in the non-contact charging of the photoreceptor 2 by the charging roller 3.

  In the above example, the conductive layer 3g is also formed on the outer peripheral surface of the insulating layers 3j and 3k. However, in the present invention, the conductive layer 3g is not necessarily formed on the outer peripheral surface of the insulating layers 3j and 3k. It can also be formed only in the depressions of the cored bar and the central part of the cored bar.

  In the above-described examples and comparative examples, PI resin is used for the insulating coating material constituting the insulating member for forming the insulating layers 3j and 3k, but other resin such as polyurethane (PU) resin is used. You can also. Moreover, it can replace with an insulating coating material as an insulating member, and can also use a heat-shrinkable tube (for example, PET heat-shrinkable tube etc.) and elastic rubber (for example, a product made from polyurethane (PU) resin etc.).

  The charging roller of the present invention is used in an image forming apparatus such as an electrophotography, an electrostatic copying machine, a printer, and a facsimile, and a charging roller that places a predetermined charging gap on the photosensitive member and charges the photosensitive member in a non-contact manner. And it can utilize suitably for the charging roller in which the conductive layer which is a charging part was formed on the metal shaft.

1 is a diagram schematically and partially showing an example of an image forming apparatus including an example of an embodiment of a non-contact charging roller according to the present invention. 1 shows an example of an embodiment of a charging roller of the present invention and a comparative example thereof, (a) is a sectional view along the axial direction, (b) is a partially enlarged sectional view in (a), and (c) shows a comparative example. It is sectional drawing which follows an axial direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Photoconductor, 3 ... Non-contact charging device, 3a ... Charging roller, 3c ... Core metal (metal shaft), 3d, 3e ... Depression, 3g ... Conductive layer, 3j, 3k ... Insulating layer, c ... Chamfer (C cut)

Claims (6)

In a charging roller in which a conductive layer is formed on a conductive shaft, and the conductive layer is provided to face the image carrier with a predetermined charging gap to charge the image carrier in a non-contact manner.
An annular depression is formed on each of the outer peripheral surfaces of both ends of the conductive shaft,
An insulating layer for setting the charging gap is formed by an insulating member on outer peripheral surfaces of both ends of the conductive shaft outside the recess, and an outer peripheral surface of a portion where the recess is formed on the conductive shaft; The charging roller, wherein the conductive layer is formed by coating a conductive coating material on an outer peripheral surface of a central portion of the conductive shaft inside the recess.   The charging roller according to claim 1, wherein the conductive layer made of the conductive coating material is also formed on an outer peripheral surface of the insulating layer.   3. The charging roller according to claim 1, wherein a depth of the recess is set larger than a film thickness of the conductive layer.   3. The charging roller according to claim 1, wherein a depth of the recess is set larger than a film thickness of the insulating layer.   3. The charging roller according to claim 1, wherein a depth of the depression is set to be larger than a sum of a film thickness of the conductive layer and a film thickness of the insulating layer.   The charging roller according to claim 1, wherein an edge portion of the conductive shaft that forms the depression is chamfered.

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