JP2008209488A - Charging device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging device capable of preventing wear of a charging member when foreign matter such as toner stuck to the charging member is removed, and to provide a process cartridge provided with the charging device and an image forming apparatus provided with the charging device. <P>SOLUTION: The charging device includes: a charging roll 2 disposed in contact with a rotating image holder and used to charge the surface of the image holder while following the rotation of the image holder; and a cleaning roll 1 disposed in contact with the charging roll 2, wherein the dynamic friction coefficient of an elastic layer 1b relative to the charging roll 2 is distributed so as to increase from one end of the elastic layer 1b to the other end in the lengthwise direction and then decrease. The process cartridge has the charging device, and the image forming apparatus has the charging device. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a charging device, a process cartridge, and an image forming apparatus.

  In recent years, image forming apparatuses such as printers and copiers have been widely used, and technologies relating to various elements constituting the image forming apparatus have also been widely used. Among image forming apparatuses that employ an electrophotographic method, a photosensitive member such as a photosensitive member (image holding member) drum is charged by using a charging device, and an ambient potential is applied on the charged photosensitive member. In many cases, a pattern to be printed is formed by forming an electrostatic latent image having a potential different from that of the electrostatic latent image. The electrostatic latent image formed in this way is developed with toner, and finally recorded. It is transferred onto a transfer medium such as paper.

  The charging device is a device that plays an important role of charging the photoconductor. It is a contact charging type charging device that directly contacts the photoconductor to charge the photoconductor, and the vicinity of the photoconductor without contacting the photoconductor. The charging device is roughly classified into two types, that is, a non-contact charging device that charges the photosensitive member by corona discharge or the like. In recent years, there has been an increase in charging devices that employ a contact charging method that generates less chemical substances such as ozone and nitrogen oxides than non-contact charging devices.

  The charging device of the contact charging system includes a charging member that directly contacts a photosensitive member such as a charging roll to charge the photosensitive member. When the photosensitive member is charged, foreign matter such as toner on the photosensitive member or an external additive of the toner may adhere to the charging member. For this reason, the contact charging type charging device includes a mechanism for cleaning the surface of the charging member.

As a cleaning method, a method in which a rubber blade or pad is brought into contact with the surface of the charging member with a predetermined pressure to scrape off the deposits. 2. Description of the Related Art A charging device that employs a method of cleaning a charging member surface while suppressing an influence on the charging member by intermittently pressing a rubber blade or pad against the charging member surface is known. In addition, there has been proposed a method in which the surface of the charging member is constantly cleaned by a cleaning roll that is rotated in contact with the rotating charging roll (see, for example, Patent Document 1 or 2).
JP-A-2-272594 JP-A-8-62948

  The present invention provides a charging device capable of preventing wear of the charging member when removing foreign matters such as toner adhering to the charging member, a process cartridge including the charging device, and an image forming apparatus including the charging device. The purpose is to do.

  As a result of intensive studies to solve the above problems, the present inventor has found that the following problems can be solved by the present invention.

  That is, the invention according to claim 1 is a cylindrical charging member that contacts the rotating image carrier and charges the surface of the image carrier while rotating around the image carrier, a core, and an outer periphery of the core A porous cylindrical elastic layer having an open cell structure formed on the outer surface, and a foreign matter removing means that comes into contact with the charging member, and the dynamic friction coefficient of the elastic layer with respect to the charging member is The charging device is distributed so as to decrease after increasing in the longitudinal direction from one end of the layer to the other end.

  The invention according to claim 2 is characterized in that a dynamic friction coefficient A at a central portion in the longitudinal direction from one end to the other end of the elastic layer with respect to the charging member according to claim 1 and a dynamic friction coefficient B at an end portion in the longitudinal direction are: The charging device satisfies the relationship of the following formula 1.

                      B <A <B + 0.2 Formula 1

  According to a third aspect of the present invention, there is provided a charging device in which the difference between the hardness of the central portion in the longitudinal direction and the hardness of the end portion in the longitudinal direction of the elastic layer according to the first or second aspect is 1N or more and 200N or less. It is.

  The invention according to claim 4 is characterized in that the difference between the number of cells in the central portion in the longitudinal direction and the number of cells in the end portion in the longitudinal direction of the elastic layer according to any one of claims 1 to 3 is 1. It is a charging device that is / 25 mm or more and 50/25 mm or less.

  The invention according to claim 5 is the charging device in which the elastic layer according to any one of claims 1 to 4 is urethane foam.

  According to a sixth aspect of the present invention, the amount of biting into the charging member of the foreign matter removing means according to any one of the first to fifth aspects is not less than 1/10 and not more than 1/2 of the thickness of the elastic layer. It is a charging device.

  In the invention according to claim 7, the pressure required to reduce the amount of biting into the charging member of the foreign matter removing means according to any one of claims 1 to 6 by half of the thickness of the elastic layer, The charging device is a contact pressure of the charging member with respect to the image carrier.

  An invention according to an eighth aspect is a process cartridge including the image holding member and the charging device according to any one of the first to seventh aspects.

  According to a ninth aspect of the present invention, there is provided an image carrier, a charging device according to any one of claims 1 to 7 that charges the image carrier, and a latent image formed on the surface of the charged image carrier. Latent image forming means, developing means for developing a latent image formed on the surface of the image carrier with toner to form a toner image, and toner image formed on the surface of the image carrier to be transferred The image forming apparatus includes a transfer unit that transfers the toner to the surface and a cleaning unit that removes residual toner on the surface of the image carrier after the transfer.

  According to the first aspect of the present invention, it is possible to prevent wear of the charging member when removing foreign matters such as toner adhering to the charging member as compared with the case where this configuration is not provided.

  According to the second aspect of the present invention, it is possible to prevent wear of the charging member when removing foreign matters such as toner adhering to the charging member as compared with the case where the present configuration is not provided.

  According to the invention of claim 3, the dynamic friction coefficient of the elastic layer with respect to the charging member can be distributed so as to decrease after increasing in the longitudinal direction from one end of the elastic layer to the other end. The relationship of Formula 1 can be easily satisfied as compared with the case where it does not have.

  According to the invention of claim 4, the dynamic friction coefficient of the elastic layer with respect to the charging member can be distributed so as to decrease after increasing in the longitudinal direction from one end to the other end of the elastic layer, and this configuration The relationship of Formula 1 can be easily satisfied as compared with the case where it does not have.

  According to the invention which concerns on Claim 5, generation | occurrence | production of the damage | wound by rubbing with the foreign material removal means on the surface of a charging member can be suppressed compared with the case where it does not have this structure.

  According to the sixth aspect of the present invention, it is possible to further prevent wear of the charging member when removing foreign matters such as toner adhering to the charging member as compared with the case where this configuration is not provided.

  According to the seventh aspect of the present invention, stable charging performance can be exhibited as compared with the case where this configuration is not provided.

  According to the eighth aspect of the present invention, it is possible to prevent wear of the charging member when removing foreign matters such as toner adhering to the charging member as compared with the case where this configuration is not provided.

  According to the ninth aspect of the present invention, it is possible to prevent wear of the charging member when removing foreign matters such as toner adhering to the charging member as compared with the case where this configuration is not provided, and for a long period of time. Stable image formation is possible.

  Hereinafter, the charging device, the process cartridge, and the image forming apparatus of the present invention will be described in detail.

<Charging device>
The charging device according to the present invention is formed on the outer periphery of the core member, a cylindrical charging member that contacts the rotating image carrier and charges the surface of the image carrier while rotating with the image carrier. A porous cylindrical elastic layer having an open cell structure, and a foreign matter removing means that contacts the charging member, and the dynamic friction coefficient of the elastic layer with respect to the charging member is It is distributed so as to decrease after increasing in the longitudinal direction from one end to the other end.

  In addition, the dynamic friction coefficient A at the center in the longitudinal direction from one end to the other end of the elastic layer with respect to the charging member of the present invention and the dynamic friction coefficient B at the end in the longitudinal direction satisfy the relationship of the following formula 1. Is preferred.

                      B <A <B + 0.2 Formula 1

In the present invention, the central portion of the elastic layer is a portion having a width of 10 mm including the central portion in the longitudinal direction of the cylindrical elastic roll.
In the present invention, the end portion of the elastic layer is a portion having a width of 10 mm including the outermost portion at both ends in the longitudinal direction of the cylindrical elastic roll.

In the present invention, “dynamic friction coefficient” means a value measured by the following method.
The dynamic friction coefficient is determined by cutting out the elastic layer with a width of 10 mm, a length of 10 mm and a thickness of 3 mm in a pin-on-disk type friction player (Rheasca FPR-2100), and setting the charging member (charging roll) Use as it is as a base member, set the previously cut elastic layer so that it comes into contact with the charging roll, and load the cut elastic layer so that the three conditions of load 10g, 20g and 30g are applied to the charging roll. The dynamic friction coefficient was measured for each load by a linear reciprocating sliding measurement method at a length of 50 mm and a measurement speed of 25 mm / second, and the average value was taken as the dynamic friction coefficient.

  In the contact charging type charging device, a cylindrical charging member is in contact with the image holding member, and the surface of the image holding member is charged while the charging member rotates with the rotating image holding member. At this time, when the charging member that rotates around the image holding member slips, foreign matters such as toner and toner external additives may be rubbed and fixed on the surface of the charging member, making it difficult to separate from the surface of the charging member. In particular, in order to make the contact pressure of the charging member uniform with the image carrier in the axial direction, there are many cases where a crown shape is formed by making a difference in the outer diameter between the central portion and the end portion of the charging member. As a result, a difference in outer periphery occurs and minute slips frequently occur with the image carrier at the central portion, so that the above-mentioned contamination is likely to occur.

  If the coefficient of dynamic friction between the foreign matter removing means and the charging member is increased in order to make it easier to remove dirt at the central portion of the charging member (that is, if the contact pressure of the foreign matter removing means to the charging member is increased), the contamination becomes more dirty than the central portion. The end portion of the charging member having a small amount may be worn out, and uniform charging performance may not be exhibited over time. On the other hand, if the coefficient of dynamic friction between the foreign matter removing means and the charging member is reduced in order to reduce wear at the end of the charging member (that is, the contact pressure of the foreign matter removing means to the charging member is reduced), the charging member has a large central portion. Dirt may not be completely removed.

  In the charging device of the present invention, the dynamic friction coefficient of the elastic layer related to the foreign matter removing means is distributed so as to decrease after increasing in the longitudinal direction from one end to the other end of the elastic layer. As a result, it is possible to remove the contamination of the charging member and reduce wear of the end portion of the charging member. As a result, it is possible to prevent the charging member from being worn when the foreign matter adhering to the charging member is removed.

  Further, in the charging device of the present invention, the dynamic friction coefficient A at the longitudinal center from the one end to the other end of the elastic layer with respect to the charging member and the dynamic friction coefficient B at the longitudinal end satisfy the relationship of the above formula 1. In this case, it is possible to remove the dirt at the center of the charging member and reduce the wear of the end of the charging member. As a result, it is possible to prevent the charging member from being worn when the foreign matter adhering to the charging member is removed.

  In the charging device of the present invention, it is preferable that the difference between the hardness of the central portion in the longitudinal direction of the elastic layer and the hardness of the end portion in the longitudinal direction is 1 N or more and 200 N or less, and 20 N or more. 100N or less is more preferable, and 50N or more and 100N or less is particularly preferable.

In the present invention, “hardness” refers to a value measured by the following method.
The material constituting the elastic layer is sliced in length 400mm x width 400mm x thickness 50mm, the center of the sliced sheet is loaded with a φ200mm compression jig, and the force required to compress the thickness by 25% (N) Is defined as “hardness” in the present invention. In order to measure the force (N) required for compression, a load measuring device (MODEL-1311) manufactured by AIKOH was used.

  In the charging device of the present invention, the difference between the number of cells in the longitudinal center of the elastic layer according to the foreign matter removing means and the number of cells at the end in the longitudinal direction is set to 1/25 mm or more and 50/25 mm or less. It is preferably 10/25 mm or more and 50/25 mm or less, more preferably 10/25 mm or more and 20/25 mm or less.

  In the present invention, the “number of cells” is a value indicated as an average number of cells existing on a straight line of a material 25 mm constituting the elastic layer.

  In the charging device of the present invention, the amount of biting of the foreign matter removing means into the charging member is preferably 1/10 or more and 1/2 or less of the thickness of the elastic layer according to the foreign matter removing means, and is 1/8 or more 1 / 3 or less is more preferable, and 1/7 or more and 1/5 or less is particularly preferable.

  If the amount of biting is 1/10 or more, it is possible to prevent the foreign matter removing means from spinning around when it is accompanied by the charging member, and it is possible to reliably remove foreign matter on the surface of the charging member. If the amount of biting is ½ or less, the charging member can be prevented from being worn.

The following method can be used to make the amount of biting of the foreign matter removing means into the charging member 1/10 or more and 1/2 or less of the thickness of the elastic layer related to the foreign matter removing means.
The elastic layer of the foreign matter removing means is formed on a support such as a metal shaft, and a bearing such as a bearing that holds the metal shaft and a bearing that holds the shaft of the charging member are integrated. Accordingly, the distance between the elastic layer and the shaft of the charging member can be controlled with a constant displacement, and the amount of biting of the foreign matter removing means into the charging member can be adjusted to a predetermined amount.

  In the charging device of the present invention, it is preferable that the pressure required to reduce the amount of the foreign matter removing means to the charging member to be ½ of the thickness of the elastic layer is equal to or lower than the contact pressure of the charging member with respect to the image carrier. .

In general, even in a charging device having the same amount of foreign matter removing means with respect to the charging member, if the material of the elastic layer of the foreign matter removing means is different, the load (contact pressure) when the charging member is in contact with the foreign matter removing means is different. . If the contact pressure when the charging member is in contact with the foreign matter removing means exceeds the contact pressure when the charging member is in contact with the image carrier, the contact pressure with the foreign matter removing means is reduced for the charging member. The contact pressure with the image carrier may be surpassed, and the charging member may not be rotated with the image carrier. As a result, there may be a problem that the charging member does not exhibit sufficient charging performance.
For this reason, it is necessary to adjust the contact pressure between the charging member and the foreign matter removing means so as to be lower than the contact pressure between the charging member and the image carrier. The contact pressure between the charging member and the foreign matter removing means may change due to changes over time or changes in the external environment, and the contact pressure between the charging member and the foreign matter removing means may change between the charging member and the image carrier. It is desirable to ensure that the contact pressure during

  By setting the pressure required to reduce the amount of the foreign material removing means to the charging member to be ½ of the thickness of the elastic layer, the charging member removes the foreign material from the charging member. Even when the amount is half the thickness of the elastic layer, which is the maximum biting amount that can avoid wear of the charging member, the contact pressure between the charging member and the foreign matter removing means at that time Is lower than the contact pressure between the charging member and the image carrier. Therefore, wear of the charging member is suppressed, and it is ensured that the charging member exhibits sufficient charging performance.

The following method can be used to reduce the pressure required to reduce the amount of the foreign material removing means to the charging member to ½ of the thickness of the elastic layer below the contact pressure of the charging member to the image carrier.
In the integrated bearing, the foreign matter removing means is adjusted so as to come into contact with the charging member with a constant load. By using a member such as a spring and bringing the charging member into contact with the image carrier with a load that exceeds the load of the foreign matter removing unit with respect to the charging member, the pressure can be reduced to the predetermined contact pressure or less. Thereby, stable charging performance can be exhibited.

Hereinafter, an embodiment of a charging device of the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a front view according to an embodiment of the charging device of the present invention, and FIG. 2 is a schematic view of a cleaning roll which is a foreign matter removing unit according to the present embodiment. In FIG. 1, the cleaning roll 1 which is a foreign material removal means which has the electroconductive shaft 1a which is a core material, and the cylindrical elastic layer 1b formed in the outer periphery of the electroconductive shaft 1a, and the electroconductive shaft which is a core material The charging roll 2 which is a charging member having 2a and a cylindrical charging layer 2b formed on the outer periphery of the conductive shaft 2a is in contact with a predetermined amount of biting. Both ends of the conductive shaft 1a and the conductive shaft 2a are rotatably held by a conductive bearing 3. A high voltage power supply 4 is connected to one of the conductive bearings 3.

  Here, the amount of biting is determined when the distance between the axis of the conductive shaft 1a and the axis of the conductive shaft 2a is L, the radius of the cleaning roll 1 is R1, and the radius of the charging roll 2 is R2. , (R1 + R2) -L.

As shown in FIG. 2, the elastic layer 1b of the cleaning roll 1 is divided into three equal parts in the longitudinal direction from one end to the other end of the elastic layer 1b, and the elastic layer 1b-2 located at the center is an end portion. A material having a larger dynamic friction coefficient with respect to the charging roll 2 than that of the elastic layer 1b-1 and the elastic layer 1b-3 is used, and is configured to satisfy the above formula 1.
By setting it as the said structure, the dynamic friction coefficient with respect to the charging roll 2 of the elastic layer 1b can be distributed so that it may decrease after increasing toward the longitudinal direction from the one end to the other end of the elastic layer 1b.

  In this embodiment, the elastic layer 1b is composed of an elastic layer 1b-1, an elastic layer 1b-2, and an elastic layer 1b-3 that are divided into three equal parts in the longitudinal direction from one end to the other end. However, the present invention is not limited to this embodiment, and the ratio of the elastic layer 1b-1, the elastic layer 1b-2, and the elastic layer 1b-3 in the longitudinal direction may be adjusted. A material whose coefficient of dynamic friction changes continuously toward the elastic layer 1b can also be used.

  As the material of the conductive shaft 1a, free-cutting steel, stainless steel or the like is used. The material and the surface treatment method are appropriately selected according to the use such as slidability, and the non-conductive material is processed by a general process such as a plating process and subjected to a conductive process. In addition, since the cleaning roll 1 is in contact with the charging roll 2 through the elastic layer 1b at an appropriate pressure (nip pressure), the cleaning roll 1 is sufficiently rigid with respect to a material having a strength that does not bend in the contact state or the shaft length. The shaft diameter is selected.

The elastic layer 1b is made of a porous material having an open cell structure. Examples of such a material include resins such as polyurethane, polyethylene, polyamide, and polypropylene.
In the present invention, the “continuous bubble structure” means that bubbles exist in the elastic layer, and bubbles are connected to each other by opening small holes in the walls forming the bubbles.

  A material constituting the elastic layer 1b in order to efficiently remove foreign matters such as toner and external additives attached to the surface of the charging roll 2 and to prevent the surface of the charging roll 2 from being scratched by rubbing of the cleaning roll 1. It is particularly preferable to use foamed urethane with low slip and low resilience.

  The number of cells of the elastic layer 1b is preferably 20/25 mm or more and 80/25 mm or less, more preferably 30/25 mm or more and 80/25 mm or less, and 30/25 mm or more and 50/25 mm or less. Particularly preferred.

  The hardness of the elastic layer 1b is preferably 100N or more and 500N or less, more preferably 100N or more and 400N or less, and particularly preferably 150N or more and 400N or less.

  In the charging roll 2, a charging layer 2b composed of a conductive foam elastic layer, a resistance layer, and a surface layer is formed on the outer periphery of the conductive shaft 2a in this order. The charging layer 2b is not limited to the above configuration as long as it has a predetermined charging performance.

  The conductive shaft 2 a is selected in the same manner as the conductive shaft 1 a of the cleaning roll 1.

  The conductive foamed elastic layer constituting the charging layer 2b is, for example, an elastic material such as rubber having elasticity, a conductive material such as carbon black for adjusting the resistance of the conductive foamed elastic layer, and a foaming agent as necessary. It is formed by coating the surface of the conductive shaft 2a with a mixture to which materials usually added to rubber such as a curing agent, a plasticizer, and a vulcanization accelerator are added. The foaming treatment of this mixture may be performed before or after the surface of the conductive shaft 2a is coated. Further, the resistance layer may be formed directly on the surface of the conductive shaft 2a without providing the conductive foamed elastic layer.

As the elastic material of the conductive foamed elastic layer constituting the charging layer 2b, urethane rubber, nitrile rubber, isoprene rubber, butadiene rubber, epichlorohydrin-ethylene oxide copolymer rubber, ethylene-propylene-diene rubber, acrylonitrile-butadiene rubber, styrene-butadiene Elastic materials such as rubber and silicone rubber are used, and these elastic materials can be used alone or in combination of two or more.
The resistance of an elastic material such as rubber is adjusted by a conductive material such as carbon black. Materials that can be usually added to rubber, such as softeners, plasticizers, curing agents, vulcanizing agents, vulcanization accelerators, anti-aging agents, fillers such as silica and calcium carbonate, etc. may be added to the elastic material as necessary. Good.

  The resistance layer constituting the charging layer 2b is a conductive polymer material such as polyacetylene, polypyrrole, polythiophene, polyurethane rubber, silicone rubber, epichlorohydrin rubber, ethylene propylene rubber, acrylic rubber, fluorine rubber, styrene-butadiene rubber, butadiene rubber, etc. As a conductive agent for the purpose of adjusting the resistance value of the elastomer material, carbon black and conductive metal oxide particles mixed in the matrix material, or ions and / or ions such as ionic conductive agent are used as charge carriers. A material in which an electrically conductive material is dispersed can be used.

  Specifically, carbon black as a conductive agent includes “Special Black 350”, “Special Black 100”, “Special Black 250”, “Special Black 5”, “Special Black 4” manufactured by Degussa, "Special Black 4A", "Special Black 550", "Special Black 6", "Color Black FW200", "Color Black FW2", "Color Black FW2V", "MONARCH1000" manufactured by Cabot, Cabot “MONARCH1300” manufactured by the company, “MONARCH1400” manufactured by Cabot, “MOGUL-L”, “REGAL400R”, and the like.

  The carbon black has a pH of 4.0 or less, and, compared with general carbon black, due to the effect of oxygen-containing functional groups present on the surface, the dispersibility in the resin composition is good and the conductive effect is high. By blending the carbon black having a pH of 4.0 or less, the charging uniformity can be improved, and the variation of the resistance value can be reduced.

  Conductive metal oxide particles, which are conductive agents used in the resistance layer, are conductive particles such as tin oxide, antimony-doped tin oxide, zinc oxide, anatase-type titanium oxide, and ITO, and charge electrons. Any conductive agent may be used as long as it is a carrier, and it is not particularly limited. These may be used alone or in combination of two or more. Any particle size may be used as long as the present invention is not inhibited. From the viewpoint of resistance adjustment and rubber strength, tin oxide, antimony-doped tin oxide, and anatase-type titanium oxide are preferred. Furthermore, tin oxide and tin oxide doped with antimony are preferred.

  The amount of the conductive metal oxide particles when only conductive metal oxide particles are blended in the elastic material without using carbon black having a pH of 4.0 or less is 3 masses per 100 parts by mass of the elastic material. The blending amount is preferably 10 parts by weight or more and 100 parts by weight or less, more preferably 10 parts by weight or more and 80 parts by weight or less, and particularly preferably 15 parts by weight or more and 70 parts by weight or less.

  When both carbon black having a pH of 4.0 or less and conductive metal oxide particles are used, the blending amount of the carbon black having a pH of 4.0 or less and the conductive metal oxide particles is 1 ≦ CB + (dc × MO / dm) ≦ 30 is preferable to satisfy the formula.

In the above formula, CB represents the blending amount (parts by mass) of carbon black blended with 100 parts by mass of the elastomer material, and MO represents conductive metal oxide particles blended with 100 parts by mass of the elastomer material. Represents the blending amount (part by mass). In addition, dc represents the density of carbon black (g / cm ³ ), and dm represents the density of conductive metal oxide particles (g / cm ³ ). In general, dc is 1.8 g / cm ³ or more. It is in the range of 9 g / cm ³ or less, and dm is in the range of 3 g / cm ³ or more and 7 g / cm ³ or less.

As the material for the surface layer, any of resin, rubber and the like may be used, and it is not particularly limited. The surface layer is formed for the purpose of preventing contamination with toner or the like.
Examples of the resin that can be used for the surface layer include urethane resin, polyester, phenol resin, acrylic resin, polyurethane, epoxy resin, cellulose, and copolymerized nylon. Among these, copolymer nylon includes one or more of 610 nylon, 11 nylon, and 12 nylon as polymerized units, and other polymer units included in the copolymer include: , 6 nylon, 66 nylon and the like. Here, it is preferable that the proportion of polymer units composed of 610 nylon, 11 nylon, and 12 nylon contained in the copolymer is 10% or more in total by mass ratio.

The surface layer can contain a conductive material. The conductive material preferably has a particle size of 3 μm or less and a volume resistivity of 10 ⁹ Ωcm or less. For example, fine particles made of metal oxides such as tin oxide, titanium oxide, zinc oxide, CeO ₂ , ZrO ₂ , In ₂ O ₃ or alloys thereof, or these metals on the surface of fine particles such as BaSO ₄ or TiO _2. An oxide-coated one or carbon black can be used.
By performing resistance control with such a conductive material, the resistance value of the surface layer does not change depending on environmental conditions, and stable characteristics can be obtained.

Furthermore, a fluorine-based or silicone-based resin or fine particles may be added to the surface layer, and in this case, the surface becomes hydrophobic and acts to prevent foreign matter from adhering to the roll surface. In addition, insulating particles such as alumina and silica are added to give unevenness to the surface of the roll, reducing the burden when rubbing against the image carrier, and wear resistance between the roll and the image carrier. It is also possible to improve the performance.
It is also possible to add a coupling agent in order to improve the adhesion with the lower layer.
Furthermore, by chemically treating the resistance layer with UV irradiation, heat treatment, a coupling agent or the like, the physical properties of the resistance layer surface can be changed to form a surface layer.

  The conductive bearing 3 holds the cleaning roll 1 and the charging roll 2 so that the amount of biting of the cleaning roll 1 with respect to the charging roll 2 becomes a predetermined amount. The conductive bearing 3 may be of any material and form as long as it is made of a conductive material. For example, a conductive bearing or a conductive sliding bearing can be used.

  The high-voltage power supply 4 is a device that charges the charging roll 2 and the cleaning roll 1 with the same polarity by applying a voltage to the conductive bearing 3, and a known high-voltage power supply device can be used.

<Process cartridge>
The process cartridge of the present invention includes an image carrier and the charging device of the present invention. The process cartridge of the present invention includes a latent image forming means for forming a latent image on the surface of the charged image carrier, if necessary, and developing the latent image formed on the surface of the image carrier with toner to form a toner image. At least one selected from the group consisting of developing means for forming, transfer means for transferring the toner image formed on the surface of the image carrier to the transfer target, and cleaning means for removing residual toner on the surface of the image carrier after transfer May be provided.
Each of these means will be described later.

<Image forming apparatus>
The image forming apparatus of the present invention includes an image carrier, the charging device of the present invention that charges the image carrier, a latent image forming unit that forms a latent image on the surface of the charged image carrier, and the image carrier. A developing means for developing a latent image formed on the surface of the body with toner to form a toner image, a transfer means for transferring the toner image formed on the surface of the image holding body to the transfer body, and a post-transfer Cleaning means for removing residual toner on the surface of the image carrier. The image forming apparatus of the present invention will be described with reference to the drawings.

  FIG. 3 is a configuration diagram showing an embodiment of the image forming apparatus of the present invention. The image forming apparatus 20 shown in FIG. 3 includes the image carrier 5, the charging roll 2, the cleaning roll 1, the conductive bearing 3, and the high-voltage power supply 4, and the charging device according to the above-described embodiment that charges the image carrier 5. The exposure device 6 is a latent image forming unit that exposes the image carrier 5 charged by the charging device to form a latent image, and the latent image formed by the exposure device 6 is developed with toner to form a toner image. A developing device 7 that is a developing device, a transfer device 9 that is a transfer device that transfers a toner image formed by the developing device 7 to the transfer target A, and a cleaning device that removes residual toner on the surface of the image carrier 5 after the transfer. And a fixing device 10 that fixes the toner image transferred to the transfer target A by heat and / or pressure.

  Since the image forming apparatus of this embodiment includes the charging device of the present invention, stable image formation is possible over a long period of time.

  When a voltage is applied to the conductive bearing 3 from the high-voltage power supply 4, the charging roll 2 and the cleaning roll 1 are charged with the same polarity. Thereby, the foreign matter on the surface of the image carrier 5 can be transferred to the image carrier 5 without being accumulated on the surfaces of the cleaning roll 1 and the charging roll 2, and the foreign matter is collected by the cleaning device 8. Therefore, dirt is not accumulated on the charging roll 2 and the cleaning roll 1 over a long period of time, so that the uniform charging performance is excellent and stable charging performance can be maintained.

  As the configuration other than the charging device of the image forming apparatus using the charging device of the present invention, conventionally known configurations can be applied as the respective configurations of the electrophotographic image forming apparatus.

  As the exposure device 6, for example, a laser optical system, an LED array, or the like is used.

The developing device 7, for example, brings a toner image onto the latent image on the surface of the image holding member 5 by bringing a developer holding member having a developer layer formed on the surface thereof into contact with or close to the image holding member 5. Form.
The development method can be performed using a known method, but examples of the development method using a two-component developer include a cascade method and a magnetic brush method.

  The toner image formed on the surface of the image carrier 5 is transferred to a transfer target body to form a transfer image. In the image forming apparatus according to this embodiment, a toner image is directly transferred to a transfer medium such as paper. However, after the toner image is transferred to a drum-like or belt-like intermediate transfer body, the toner image is transferred to a transfer medium such as paper. You may make it do.

  A corotron can be used as the transfer device 9 that transfers the toner image from the image holding member 5 to paper or the like. The corotron is effective as a means for uniformly charging the paper, but a high voltage of several kV must be applied and a high voltage power supply is required in order to give a predetermined charge to the paper as a transfer target. Further, since ozone is generated by corona discharge, the rubber parts and the image carrier may be deteriorated. Therefore, a conductive transfer roll made of an elastic material is brought into contact with the image carrier 5 to form a toner image on the paper. A contact transfer method for transferring is preferable, but the transfer device is not particularly limited.

  The cleaning device 8 directly contacts the surface of the image carrier 5 with a cleaning blade as a cleaning unit to remove toner, paper dust, dust, and the like attached to the surface. As the cleaning means, a cleaning brush, a cleaning roll, or the like can be used in addition to the cleaning blade.

  The toner image transferred to the transfer target A is fixed by the fixing device 10. As the fixing device 10, a heat fixing device using a heat roll is preferably used. The heat fixing device includes a fixing roller having a heater lamp for heating inside a cylindrical metal core, a so-called release layer formed on the outer peripheral surface by a heat resistant resin film layer or a heat resistant rubber film layer, and the fixing roller. The pressure roller or the pressure belt is disposed so as to come into contact with the roller at a predetermined contact pressure and has a heat-resistant elastic body layer formed on the outer peripheral surface of the cylindrical metal core or the surface of the belt-like base material. The fixing process of an unfixed toner image is performed by inserting a transfer body on which an unfixed toner image is formed between a fixing roller and a pressure roller or a pressure belt, and using a binder resin, an additive, etc. in the toner. Fix by heat melting.

  As the image carrier 5 used in the image forming apparatus of the present invention, a known photoreceptor can be used without any particular limitation. However, from the viewpoint of sensitivity and stability, a so-called functional separation in which the charge generation layer and the charge transport layer are separated. An organic photoreceptor having a structure called a mold can be preferably used. Further, it is preferable to use a photoconductor made of a siloxane resin or a phenol resin having a charge transport property in the photoconductor surface layer and a crosslinked structure.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited by the following Example.

[Example 1]
(Creating a cleaning roll)
Hot melt (manufactured by Nisshin Chemical Co., Ltd .: BR4301) was applied as an adhesive on a SUS303 Φ6 mm cylindrical shaft. As an elastic layer, ether type urethane foam (INOAC: trade name ERG-H) having a hardness of 170 N and a cell number of 45/25 mm, and ether type urethane foam (INOAC) having a hardness of 100 N and a cell number of 30/25 mm The product name: ERG-S Foaming LOT: A) was cut into one-third of the shaft length, and then hollowed with a through drill. Place urethane (end part) of hardness 100N on both sides of urethane (center part) of hardness 170N, and form the urethane on the outer periphery of the shaft as shown in Fig. 2 and bond it in 90 ° C oven Went. The outer periphery of the molded urethane foam was processed into a wall thickness of 3 mm (outside diameter Φ12 mm) using a cylindrical grinder to obtain cleaning rolls having different hardness and cell number at the center and at the end.
Using the obtained cleaning roll, the dynamic friction coefficient was measured based on the above-described method. The obtained results are shown in Table 1.

  The cleaning roll obtained above was integrated with a conductive roller together with a charging roll having a diameter of 14 mm and an outer diameter difference (crown) of 100 μm between the center and the end to obtain a charging unit. The amount of biting of the cleaning roll into the charging roll at this time was 0.5 mm. Further, the pressure required to make the amount of biting of the cleaning roll into the charging roll 1.5 mm (that is, 1/2 of the thickness of the elastic layer) was 120 g.

The structure of the charging roll is as follows.
A mixture having the following composition is kneaded with an open roll, and this mixture is used to form a roll with a diameter of 15 mm using a press molding machine with an adhesive on the surface of a conductive support made of SUS303 and having a diameter of 8 mm. Thus, a conductive elastic roll having a diameter of 14 mm was obtained.

Mixture composition, rubber material (epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber (Gechron 3106: manufactured by Nippon Zeon)) 100 parts by mass, conductive agent (carbon black Asahi Thermal: manufactured by Asahi Carbon Co.), 15 parts by mass, conductive agent (ket CHENBLACK EC: Lion Corporation) 5 parts by mass, ionic conductive agent (lithium perchlorate) 1 part by mass, vulcanizing agent (sulfur 200 mesh: manufactured by Tsurumi Chemical Co., Ltd.) 1 part by mass, vulcanization accelerator (NOXELLER DM) : Ouchi Shinsei Chemical Co., Ltd.) 2 parts by mass, vulcanization accelerator (Noxeller TT: Ouchi Shinsei Chemical Industry Co., Ltd.) 0.5 parts by mass, vulcanization acceleration aid (Zinc oxide, zinc oxide, 1 type: exact (Made by Chemical Industry Co., Ltd.) 3 parts by mass / stearic acid: 1.5 parts by mass

-Formation of surface layer-
Dispersion A obtained by dispersing a mixture having the following composition with a bead mill is diluted with methyl ethyl ketone, dip-coated on the surface of the conductive elastic roll, and then heated and dried at 180 ° C. for 30 minutes to form a surface layer having a thickness of 7 μm. Thus, a charging roll 1 was obtained.

Surface layer composition / polymer material (saturated copolymerized polyester solution, Byron 30SS: manufactured by Toyobo Co., Ltd.) 100 parts by mass / curing agent (amino resin solution Super Becamine G-821-60: manufactured by Dainippon Ink & Chemicals, Inc.) 26 .3 parts by mass / conductive agent a1 (carbon black MONARCH1000: manufactured by Cabot) 10 parts by mass

The modified cartridge for the DocuCenter Color f450 equipped with the charging unit obtained above is mounted on the DocuCenter Color f450 modified machine (manufactured by Fuji Xerox Co., Ltd.) with the contact pressure (Nip load) with the image carrier at 800 g. Printed 10,000 sheets of 50% half-tone images on P paper (A3 size) made by Fuji Xerox Office Supply in a humid (28 ℃, 85%) environment, and then low temperature and low humidity (10 ℃, 15%) ) A printing test under the following conditions was conducted after standing for 12 hours in an environment, and evaluation was performed based on the following criteria. The results are shown in Table 1.
Printing condition (image pattern): A 50% halftone image was formed on a P paper (A3 size) manufactured by Fuji Xerox Office Supply and evaluated.

Evaluation criteria A: The charging roll is free of stains, and there is no occurrence of streaks or density unevenness due to the charging roll in the printed image in the printing process direction.
B: Dirt is generated on the charging roll, but there are no streaks due to the charging roll and density unevenness in the printed image in the printing process direction.
C: Streaks or density unevenness due to the charging roll occurs in the printing process direction, affecting the image.

In addition, using a sample having the same configuration as described above, 10,000 sheets of a 50% halftone image were printed on P paper (A3 size) made by Fuji Xerox Office Supply in a low-temperature, low-humidity (10 ° C, 15%) environment. A printing test under the following conditions was performed after standing for 12 hours in the same environment, and evaluation was performed based on the following criteria. The results are shown in Table 1.
Printing condition (image pattern): A 50% halftone image was formed on a P paper (A3 size) manufactured by Fuji Xerox Office Supply and evaluated.

Evaluation criteria A: The charging roll is free of stains, and no streaking or density unevenness occurs in the printed image in the direction of the printing process.
B: Dirt is generated on the charging roll, but there are no streaks due to the charging roll and density unevenness in the printed image in the printing process direction.
C: Streaks or density unevenness due to the charging roll occurs in the printing process direction, affecting the image.

[Example 2]
LOT: B urethane (INOAC: ERG-S) with 120N hardness and 40 / 25mm cell number is placed in the center of the cleaning roll, and the hardness is 100N on both sides (ends). Samples were prepared in the same manner as in Example 1 except that LOT: A urethane having a number of 30/25 mm was disposed, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[Example 3]
Urethane with a hardness of 150 N and a cell number of 50/25 mm (manufactured by INOAC: trade name ER-80) is placed at the center of the cleaning roll, and the hardness is 100 N and the number of cells on both sides (ends). A sample was prepared in the same manner as in Example 1 except that 30/25 mm (made by urethane foam INOAC: trade name ERG-S) was installed, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[Example 4]
A urethane foam (made by INOAC: trade name EGR-2) having a hardness of 210 N and a cell number of 80/25 mm is disposed in the center of the cleaning roll, and the number of cells is 100 N on both sides (ends). A sample was prepared in the same manner as in Example 1 except that 30/25 mm urethane foam INOAC (trade name ERG-S) was installed, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[Comparative Example 1]
A sample was prepared in the same manner as in Example 1 except that an ester foamed urethane (manufactured by INOAC: trade name ERG-H) having a hardness of 170 N and a cell number of 45/25 mm was used alone for the elastic layer of the cleaning roll. The same evaluation as in Example 1 was performed. The results are shown in Table 1.

[Comparative Example 2]
A sample was prepared in the same manner as in Example 1 except that an ester foamed urethane (manufactured by INOAC: trade name ERG-S) having a hardness of 100 N and a cell number of 30/25 mm was used alone for the elastic layer of the cleaning roll. The same evaluation as in Example 1 was performed. The results are shown in Table 1.

It is a front view which shows one Embodiment of the charging device of this invention. It is a schematic diagram of a cleaning roll. 1 is a configuration diagram illustrating an embodiment of an image forming apparatus of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cleaning roll 1a Conductive shaft 1b Elastic layer 2 Charging roll 2a Conductive shaft 2b Charging layer 3 Conductive bearing 4 High voltage power source 5 Image holding body 6 Exposure device 7 Developing device 8 Cleaning device 9 Transfer device 10 Fixing device 20 Image forming device

Claims (9)

A cylindrical charging member that contacts the rotating image carrier and charges the surface of the image carrier while rotating with the image carrier;
A foreign material removing means having a core material and a porous cylindrical elastic layer having an open cell structure formed on the outer periphery of the core material, and contacting the charging member,
A charging device in which a dynamic friction coefficient of the elastic layer with respect to the charging member is distributed so as to decrease after increasing in a longitudinal direction from one end to the other end of the elastic layer. 2. The dynamic friction coefficient A in the center portion in the longitudinal direction from one end to the other end of the elastic layer with respect to the charging member and the dynamic friction coefficient B in the end portion in the longitudinal direction satisfy the relationship of the following formula 1. Charging device.
B <A <B + 0.2 Formula 1   3. The charging device according to claim 1, wherein a difference between a hardness of a central portion in the longitudinal direction of the elastic layer and a hardness of an end portion in the longitudinal direction is 1 N or more and 200 N or less.   The difference between the number of cells in the central portion in the longitudinal direction of the elastic layer and the number of cells in the end portion in the longitudinal direction is 1/25 mm or more and 50/25 mm or less. The charging device described.   The charging device according to claim 1, wherein the elastic layer is urethane foam.   6. The charging device according to claim 1, wherein an amount of biting of the foreign matter removing unit into the charging member is 1/10 or more and 1/2 or less of a thickness of the elastic layer.   7. The pressure required to make the amount of biting of the foreign matter removing means into the charging member ½ of the thickness of the elastic layer is equal to or less than the contact pressure of the charging member with respect to the image carrier. The charging device according to any one of the above.   A process cartridge comprising an image carrier and the charging device according to any one of claims 1 to 7.   An image carrier, the charging device according to any one of claims 1 to 7, which charges the image carrier, a latent image forming unit that forms a latent image on the surface of the charged image carrier, and A developing unit that develops a latent image formed on the surface of the image carrier with toner to form a toner image, a transfer unit that transfers the toner image formed on the surface of the image carrier to a transfer target, and a transfer An image forming apparatus comprising: a cleaning unit that removes residual toner on the surface of the subsequent image carrier.

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