JP2010049182A - Image-forming device and image-forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image-forming device such as a copier, a facsimile or a printer, the image-forming device using an endless-type rotary member such as an intermediate transfer belt or a transfer conveyance belt, which forms a transfer part which is arranged facing an image carrier such as a photoreceptor and transfers a toner image on the image carrier, to restrain or prevent toner from scattering; and to provide an image-forming method. <P>SOLUTION: The image-forming device uses: a rotary member 11 which forms a transfer part which is arranged facing the image carrier 20Y and transfers a toner image on the image carrier 20Y; a bias-applying member 12Y which is arranged to contact the rotary member 11 and transfers the toner image; a counter electrode member 20Y which is arranged opposite to the bias-applying member 12Y; and a transfer-controlling member 15Y which occupies a transfer upstream position on an A1 direction upstream side in the position where the rotary member 11 and the bias-applying member 12Y face each other. The volume resistivity of a part of the transfer-controlling member 15Y is equal to or more than the volume resistivity of the rotary member 11 and bias-applying member 12Y, the part occupying the transfer upstream position and facing the rotary member 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, and in particular, an intermediate transfer belt that forms a transfer portion that is disposed opposite to an image carrier such as a photoconductor and transfers a toner image on the image carrier. The present invention relates to an image forming apparatus including an endless rotating member such as a transfer conveyance belt, and an image forming method for forming an image using the rotating member.

  2. Description of the Related Art Image forming apparatuses such as copying machines, facsimile machines, and printers that include an image carrier such as a photosensitive member generally include a transfer device for transferring a toner image carried on the image carrier. Yes. Conventionally, various configurations have been proposed as transfer devices (see, for example, [Patent Document 1] to [Patent Document 5]), and various techniques for improving transfer performance, which are important in transfer devices, for example, have been proposed. (For example, see [Patent Document 1] to [Patent Document 3]). As a technique for improving the transfer performance, there is a technique for suppressing and preventing toner scattering (see, for example, [Patent Document 1] and [Patent Document 2]).

  On the other hand, in such an image forming apparatus, the image includes an endless rotating member such as an intermediate transfer belt or a transfer conveyance belt that is disposed opposite to the image carrier and forms a transfer portion that transfers a toner image on the image carrier. Forming devices are widely known. Even in such an image forming apparatus, in order to improve transfer performance, it is required to suppress and prevent toner scattering.

Japanese Patent Laid-Open No. 10-055115 JP-A-11-153916 Japanese Patent Laid-Open No. 2006-220796 Japanese Utility Model Publication No. 5-47947 Japanese Utility Model Publication No. 5-55158

  However, a conventional technique for improving transfer performance in consideration of suppression and prevention of toner scattering has only been proposed for an image forming apparatus of a type that does not include such a rotating member. Therefore, it is necessary to provide a technique for improving transfer performance in consideration of suppression and prevention of toner scattering even in an image forming apparatus having such a rotating member.

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, and in particular, an intermediate transfer belt that forms a transfer portion that is disposed opposite to an image carrier such as a photoconductor and transfers a toner image on the image carrier. An image forming apparatus provided with an endless rotating member such as a transfer conveyance belt, which suppresses and prevents toner scattering, and an image which performs image formation using such a rotating member and which suppresses and prevents toner scattering An object is to provide a forming method.

  In order to achieve the above object, an invention according to claim 1 is directed to an endless rotating member that is disposed opposite to an image bearing member and forms a transfer portion for transferring a toner image on the image bearing member, and abutting against the rotating member. A bias applying member arranged to apply a transfer bias for transferring a toner image; a counter electrode member arranged to face the bias applying member across the rotating member; the rotating member and the bias applying member; A transfer control member that occupies a transfer upstream position on the upstream side of the rotation direction of the rotation member, and the transfer control member is a portion that occupies the transfer upstream position and that faces the rotation member The volume resistivity of the rotating member is equal to or greater than the volume resistivity of at least the portion facing the transfer control member of the rotating member, and the body of at least the portion of the bias applying member facing the transfer control member. In the image forming apparatus or resistivity in which.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, at least one of the bias applying member and the counter electrode member includes a cored bar and an elastic body layer surrounding the cored bar. The electric resistance value at the time of transfer of the elastic body layer between the gold and the rotating member is ½ of the electric resistance value at the time of pressurizing the elastic body layer between the core metal and the rotating member. And / or the electric resistance value of the elastic layer at 20 N pressurization between the cored bar and the rotating member is the weight of the elastic layer between the cored bar and the rotating member. It is characterized by being 1/2 or less of the electric resistance value at the time of pressurization.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, at least a part of the elastic body layer includes a foam.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the second or third aspect, the member having the cored bar and the elastic body layer is driven and rotated by the rotating member.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, a nip expanding member engaged with the rotating member so as to widen a transfer nip formed by the rotating member. It is characterized by having.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the nip expanding member rotates following the rotating member.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the fourth or sixth aspect, the member that rotates following the rotation member is rotatably supported by a ball bearing.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the image forming apparatus further comprises a pressure contact means for pressing the bias applying member and the counter electrode member together. To do.

  According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the pressure contact means uses a pressure contact force between the bias applying member and the counter electrode member during non-transfer, and the bias application member during transfer. It is less than the pressure contact force with the counter electrode member.

  According to a tenth aspect of the present invention, in the image forming apparatus according to the eighth or ninth aspect, the press contact means is a constant pressurization capable of maintaining a constant press contact force between the bias applying member and the counter electrode member. A pressure means and / or a biting dimension constant means capable of maintaining a constant distance between these members so that a pressure contact force between the bias applying member and the counter electrode member is constant. And

  According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first to tenth aspects, the radius of curvature of the bias applying member is smaller than the radius of curvature of the counter electrode member.

  According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, the tip of the transfer control member on the transfer upstream position side is the rotating member and the bias applying member. It is characterized by being engaged with either one of the above.

  According to a thirteenth aspect of the present invention, in the image forming apparatus according to the twelfth aspect of the present invention, the tip of the transfer control member on the transfer upstream position side that engages with either the rotating member or the bias applying member. It is characterized by being made of a fluorine-based resin.

  According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, the transfer control member includes a metal base material and a base portion at a tip portion on the transfer upstream position side. A volume resistivity covering at least a volume resistivity of a portion of the rotating member facing the same transfer control member that covers the material, and a volume resistivity of at least a portion of the bias applying member facing the same transfer control member. It has a layer.

  According to a fifteenth aspect of the present invention, an endless rotating member that is disposed to face the image carrier and forms a transfer portion for transferring the toner image on the image carrier, and an abutting member disposed on the rotating member to transfer the toner image. A bias applying member for applying a transfer bias, a counter electrode member disposed opposite to the bias applying member across the rotating member, and the rotation among the opposing positions of the rotating member and the bias applying member An image forming method using a transfer control member occupying a transfer upstream position upstream of the rotation direction of the member, wherein the transfer control member is a portion occupying the transfer upstream position and a volume of a portion facing the rotation member A body having a resistivity equal to or higher than a volume resistivity of at least a portion of the rotating member facing the transfer control member, and at least a portion of the bias applying member facing the transfer control member In an image forming method is not less than the resistivity.

  The present invention relates to an endless rotating member that is disposed opposite to an image carrier and forms a transfer portion that transfers a toner image on the image carrier, and a transfer bias that is disposed in contact with the rotating member and transfers a toner image. A bias applying member for applying a voltage, a counter electrode member disposed opposite to the bias applying member across the rotating member, and a rotating direction of the rotating member among the opposing positions of the rotating member and the bias applying member A transfer control member that occupies an upstream transfer upstream position, and the transfer control member has a volume resistivity of a portion that occupies the transfer upstream position and that faces the rotation member, at least that of the rotation member. The image forming apparatus has a volume resistivity equal to or higher than a volume resistivity of a portion facing the transfer control member and at least a volume resistivity of a portion of the bias applying member facing the transfer control member. Thus, an image forming apparatus capable of preventing or suppressing toner scattering due to transfer dust by preventing or suppressing discharge between the rotating member and the counter electrode member and capable of forming a high quality image. be able to.

  At least one of the bias applying member and the counter electrode member has a cored bar and an elastic body layer surrounding the cored bar, and electricity at the time of transfer of the elastic body layer between the cored bar and the rotating member. The resistance value is ½ or less of the electric resistance value when the elastic body layer pressurizes between the metal core and the rotating member, and / or between the metal core and the rotating member. If the electric resistance value of the elastic layer when 20 N is pressed is less than or equal to ½ of the electric resistance value when the elastic layer is pressed by its own weight between the core metal and the rotating member. In addition, the discharge between the rotating member and the counter electrode member is prevented or suppressed, and the transfer current flows mainly in the central portion of the contact area between the elastic layer and the rotating member, thereby preventing the toner scattering due to the transfer dust. It can be suppressed and high-quality image formation can be performed. It is possible to provide a that image forming apparatus.

  If at least a part of the elastic layer contains a foam, the discharge between the rotating member and the counter electrode member is prevented or suppressed, and the contact area between the elastic layer and the rotating member is mainly used. The transfer current flows through the central portion to prevent or suppress toner scattering due to transfer dust, and the contact force by the elastic layer is uniformed to prevent or suppress uneven transfer, and the member having the elastic layer It is possible to provide an image forming apparatus capable of reducing the load on the abutting member, extending the life of the member, and performing high-quality image formation over time.

  If the member having the metal core and the elastic body layer is driven and rotated by the rotating member, the elastic body layer and the rotating member are prevented or suppressed from being discharged between the rotating member and the counter electrode member. The transfer current flows mainly in the center of the contact area with the toner, so that toner scattering due to transfer dust can be prevented or suppressed, and the rotation load of the rotation member is suppressed, and the image position due to the rotation unevenness of the rotation member is reduced. It is possible to provide an image forming apparatus that can prevent or suppress misalignment and can perform high-quality image formation.

  If there is a nip expanding member engaged with the rotating member so as to widen the transfer nip formed by the rotating member, the discharge between the rotating member and the counter electrode member is prevented or suppressed and the transfer bias is provided. By reliably positioning the action area in the transfer nip, toner scattering due to transfer dust can be prevented or suppressed, and an image forming apparatus capable of forming a high-quality image can be provided.

  If the nip expanding member is driven to rotate by the rotating member, it prevents or suppresses discharge between the rotating member and the counter electrode member, and reliably places the transfer bias operating region in the transfer nip. As a result, toner scattering due to transfer dust can be prevented or suppressed, and the rotational load of the rotating member can be suppressed to prevent or suppress image position deviation due to uneven rotation of the rotating member, thereby forming a high-quality image. An image forming apparatus capable of performing the above can be provided.

  If the member that rotates following the rotating member is supported rotatably by a ball bearing, it prevents or suppresses the discharge between the rotating member and the counter electrode member, and the transfer bias operating region is reduced. It is possible to prevent or suppress toner scattering due to transfer dust by reliably positioning in the transfer nip or by causing a transfer current to flow mainly in the center of the contact area between the elastic layer and the rotating member. An image forming apparatus capable of forming a high-quality image by reducing the rotational resistance of the member to further suppress the rotational load of the rotating member to prevent or suppress image position shift due to uneven rotation of the rotating member. Can be provided.

  If there is a pressing means for pressing the bias applying member and the counter electrode member together, the discharge between the rotating member and the counter electrode member is prevented or suppressed, and the bias applying member and the rotating member are Therefore, it is possible to provide an image forming apparatus capable of preventing or suppressing toner scattering due to transfer dust and performing high-quality image formation by causing a transfer current to flow mainly in the center of the contact area.

  If the pressure contact means reduces the pressure contact force between the bias application member and the counter electrode member at the time of non-transfer to be smaller than the pressure contact force between the bias application member and the counter electrode member at the time of transfer, By preventing or suppressing discharge between the member and the counter electrode member, toner scattering due to transfer dust can be prevented or suppressed, and the load on the bias applying member and the counter electrode member is reduced. It is possible to provide an image forming apparatus capable of extending the life and performing high-quality image formation over time.

  The pressure contact means can maintain a constant pressure contact force between the bias application member and the counter electrode member, and / or a pressure contact force between the bias application member and the counter electrode member. If there is a biting size constanting means capable of maintaining a constant distance between these members so that a constant occurs, the discharge between the rotating member and the counter electrode member can be prevented or suppressed. A stable transfer current flows mainly in the center of the contact area between the bias applying member and the rotating member by stably applying such a pressure contact force, and toner scattering due to transfer dust can be highly prevented or suppressed. An image forming apparatus capable of forming an image with high image quality can be provided.

  If the radius of curvature of the bias applying member is made smaller than the radius of curvature of the counter electrode member, the discharge between the rotating member and the counter electrode member is prevented or suppressed, and the bias applying member and the rotating member are narrowed. An image forming apparatus that can prevent or suppress toner scattering due to transfer dust and perform high-quality image formation by causing a transfer current to flow in the abutted contact area can be provided.

  If the tip of the transfer control member on the transfer upstream position side is engaged with either the rotating member or the bias applying member, discharge between the rotating member and the counter electrode member is performed. By more stably preventing or suppressing the toner, it is possible to prevent or suppress toner scattering due to transfer dust and to provide an image forming apparatus capable of forming a high-quality image.

  Assuming that the transfer upstream end of the transfer control member that engages with either the rotating member or the bias applying member is formed of a fluororesin, the rotating member and the counter electrode member To prevent or suppress the toner scattering due to transfer dust by more stably preventing or suppressing the discharge between the toner and the toner, and suppressing the rotation load of the member engaged with the transfer control member to rotate. It is possible to provide an image forming apparatus capable of preventing or suppressing a shift in image position due to uneven rotation of a member and capable of forming a high quality image.

  The transfer control member is made of a metal base material and has a volume resistivity equal to or higher than a volume resistivity of at least a portion of the rotation member facing the transfer control member, which covers the base material at a tip portion on the transfer upstream position side. If a coating layer having a volume resistivity equal to or higher than the volume resistivity of at least a portion of the bias application member facing the transfer control member is provided, the size and shape of the transfer control member are maintained with high accuracy and disposed. Thus, the discharge between the rotating member and the counter electrode member can be prevented or suppressed more stably, so that toner scattering due to transfer dust can be prevented or suppressed and an image with high image quality can be formed. A forming apparatus can be provided.

  The present invention relates to an endless rotating member that is disposed opposite to an image carrier and forms a transfer portion that transfers a toner image on the image carrier, and a transfer bias that is disposed in contact with the rotating member and transfers a toner image. A bias applying member for applying a voltage, a counter electrode member disposed opposite to the bias applying member across the rotating member, and a rotating direction of the rotating member among the opposing positions of the rotating member and the bias applying member An image forming method using a transfer control member occupying an upstream transfer upstream position, wherein the transfer control member has a volume resistivity of a portion occupying the transfer upstream position and facing the rotating member, It is at least the volume resistivity of the portion of the rotating member facing the transfer control member, and at least the volume resistivity of the portion of the bias applying member facing the transfer control member. Therefore, by preventing or suppressing discharge between the rotating member and the counter electrode member, toner scattering due to transfer dust can be prevented or suppressed, and high-quality image formation can be performed. An image forming method can be provided.

  FIG. 1 shows an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus 100 is a color laser printer capable of forming a color image. However, the image forming apparatus 100 may be another type of image forming apparatus such as a printer, a facsimile machine, a copier, a copier-printer multifunction machine, or the like. good. The image forming apparatus 100 performs an image forming process based on an image signal corresponding to image information received from the outside. The image forming apparatus 100 is a sheet-like recording medium as a final transfer member, in addition to plain paper generally used for copying or the like, any of a resin film such as an OHP sheet, a thick paper such as a card or a postcard, or an envelope. Image formation can be performed.

  The image forming apparatus 100 includes photosensitive drums 20Y, 20C, 20M, and 20BK as image carriers that can form images as images corresponding to colors separated into yellow, magenta, cyan, and black, respectively. The installed tandem structure, in other words, the tandem system is adopted. Y, M, C, and BK added after the numerals of the respective symbols indicate members for yellow, magenta, cyan, and black.

  The photosensitive drums 20Y, 20C, 20M, and 20BK, which are surface moving members, are intermediate transfer belts as intermediate transfer members that are endless belt-like rotating members disposed almost at the center inside the main body 99 of the image forming apparatus 100. The transfer belt 11 is in contact with the outer peripheral surface side, that is, the image forming surface side.

  The transfer belt 11 is disposed so as to face each of the photosensitive drums 20Y, 20C, 20M, and 20BK, and can move in the direction of the arrow A1 while facing these. The photosensitive drums 20Y, 20C, 20M, and 20BK are arranged in this order from the upstream side in the A1 direction.

  Visible images, that is, toner images formed on the respective photosensitive drums 20Y, 20C, 20M, and 20BK are respectively superimposed and transferred onto the transfer belt 11 that moves in the direction of the arrow A1, and then collectively onto the transfer sheet S that is a recording medium. It is designed to be transcribed. Therefore, the image forming apparatus 100 is an intermediate transfer type image forming apparatus.

  The lower portion of the transfer belt 11 is opposed to the photosensitive drums 20Y, 20C, 20M, and 20BK, and the opposed portions receive the toner images on the photosensitive drums 20Y, 20C, 20M, and 20BK. A primary transfer portion 98 for transferring to the transfer belt 11 is formed.

  In the superimposing transfer to the transfer belt 11, the toner images formed on the photosensitive drums 20Y, 20C, 20M, and 20BK are transferred to the same position on the transfer belt 11 while the transfer belt 11 moves in the A1 direction. As described above, voltage application by primary transfer rollers 12Y, 12C, 12M, and 12BK disposed at positions facing the respective photosensitive drums 20Y, 20C, 20M, and 20BK across the transfer belt 11 causes the A1 direction upstream. The timing is shifted toward the downstream side.

  Each of the photosensitive drums 20Y, 20C, 20M, and 20BK has image forming units 60Y, 60C, and 60M as toner image forming portions as image forming portions for forming yellow, cyan, magenta, and black images, respectively. , 60BK.

  The image forming apparatus 100 includes four image forming units 60Y, 60C, 60M, and 60BK, and is disposed to face the photosensitive drums 20Y, 20C, 20M, and 20BK. The image forming apparatus 100 includes a transfer belt 11. The transfer belt unit 10 is disposed so as to face the transfer belt 11 and is driven so as to be driven by the transfer belt 11 and to be rotated below the image forming units 60Y, 60C, 60M, and 60BK. And an optical scanning device 8 as a writing unit.

  The image forming apparatus 100 also includes a sheet feeding device 61 as a sheet feeding cassette on which the transfer sheets S transported between the photosensitive drums 20Y, 20C, 20M, and 20BK and the transfer belt 11 are stacked, and a sheet feeding apparatus. The recording paper S conveyed from the feeding device 61 is transferred to the respective photosensitive drums 20Y, 20C, 20M, and 20BK at a predetermined timing that matches the toner image formation timing by the image forming units 60Y, 60C, 60M, and 60BK. A registration roller pair 4 that feeds toward the primary transfer portion 98 between the belt 11 and a sensor (not shown) that detects that the leading edge of the transfer paper S has reached the registration roller pair 4 is provided.

  The image forming apparatus 100 also includes a fixing device 6 as a roller fixing type fixing unit for fixing the toner image onto the transfer paper S to which the toner image is transferred, and the fixed transfer paper S outside the main body 99. A discharge roller 7 for discharging, and a toner bottle 9Y as a toner replenishing member which is disposed above the transfer belt unit 10 and is filled with toner of each color of yellow, cyan, magenta, and black and is attached to and detached from the main body 99; 9C, 9M, 9BK, a discharge tray 17 on the upper side of the main body 99, on which the transfer paper S discharged from the main body 99 by the discharge roller 7 is stacked, and waste toner that stores unnecessary materials such as waste toner It has a tank 83 and a separation / neutralizing means 18 for neutralizing the transfer paper S that has passed through the transfer belt 11.

  The image forming apparatus 100 also includes an operation panel (not shown) as input means for performing various settings for the image forming apparatus 100, and a control means including a CPU, memory, and the like (not shown) that control the operation of the entire image forming apparatus 100. And have.

  In addition to the transfer belt 11, the transfer belt unit 10 is disposed at a position facing the driven roller 5 with the transfer belt 11 wound around the primary transfer rollers 12Y, 12C, 12M, and 12BK. The secondary transfer roller 72, the transfer entrance roller 73 as a driving roller, the cleaning counter roller 74, and the spring 75 as a biasing unit that biases the cleaning counter roller 74 in the direction of increasing the tension of the transfer belt 11. And have.

  The transfer belt unit 10 is also provided with a cleaning device 13 as an intermediate transfer belt cleaning device that is disposed to face the cleaning facing roller 74 with the transfer belt 11 interposed therebetween, and 2 with the transfer belt 11 interposed therebetween. A P sensor 14 that is disposed opposite to the secondary transfer roller 72 and optically detects the toner density on the transfer belt 11 by reflection of light, and a transfer control member 15A whose tip abuts against the secondary transfer roller 72. have.

  The transfer belt unit 10 also serves as a drive system (not shown) that rotationally drives the transfer entrance roller 73 and primary transfer bias application means (not shown) that applies a primary transfer bias to the primary transfer rollers 12Y, 12M, 12C, and 12BK. A power source and bias control unit and a power source and bias control unit as a secondary transfer bias application unit (not shown) for applying a secondary transfer bias to the secondary transfer roller 72 are provided.

  The primary transfer rollers 12Y, 12M, 12C, 12BK, the secondary transfer roller 72, and the cleaning counter roller 74 are disposed in contact with the transfer belt 11 that is rotationally driven by the transfer inlet roller 73, and this transfer will be described later. It is a driven roller that rotates around the belt 11.

  The primary transfer rollers 12Y, 12M, 12C, and 12BK respectively apply a bias for applying a primary transfer bias for transferring the toner images carried on the photosensitive drums 20Y, 20C, 20M, and 20BK to the transfer belt 11. Functions as a member. Each of the photoconductor drums 20Y, 20C, 20M, and 20BK includes a grounded metal core that is not shown, and the metal core is sandwiched between the primary transfer rollers 12Y, 12M, 12C, and the transfer belt 11. It functions as a counter electrode member arranged to face 12BK.

  The primary transfer rollers 12Y, 12M, 12C, and 12BK press the transfer belt 11 from the back surface thereof toward the photoconductor drums 20Y, 20M, 20C, and 20BK, and, by the action of the primary transfer bias, the photoconductor drums 20Y, A primary transfer electric field is formed between 20M, 20C, and 20BK. The toner images of the respective colors formed on the photosensitive drums 20Y, 20M, 20C, and 20BK are primarily transferred onto the transfer belt 11 due to the influence of the primary transfer electric field and nip pressure.

  The secondary transfer roller 72 functions as a bias applying member for applying a secondary transfer bias for transferring the toner image carried on the transfer belt 11 onto the transfer sheet S conveyed by the transfer belt 11. The driven roller 5 functions as a counter electrode member disposed to face the secondary transfer roller 72 with the transfer belt 11 interposed therebetween.

  The secondary transfer roller 72 forms a secondary transfer electric field with the driven roller 5 by the action of the secondary transfer bias. The driven roller 5 is pressed from the secondary transfer roller 72 via the transfer belt 11. The toner image carried on the transfer belt 11 is secondarily transferred onto the transfer paper S by the influence of the secondary transfer electric field and nip pressure.

  The transfer belt 11 forms a primary transfer portion 98 that transfers a toner image carried on the photosensitive drums 20Y, 20C, 20M, and 20BK to itself, and also transfers the toner image carried on the transfer belt 11 itself. A secondary transfer portion 90 for transferring to the transfer paper S is formed.

The transfer belt 11 is a single-layer belt made of a single-layer PI (polyimide) belt substrate. This is because it is desirable to use a transfer belt 11 that is difficult to expand and contract for the purpose of suppressing the occurrence of image expansion and contraction. Examples of the material of the transfer belt 11 include known thermoplastic resins, thermoplastic elastomers, and thermosetting resins in addition to PI. For example, PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PC (polycarbonate), polyester resin, polyamide resin, polyurethane resin, polyether resin, polyvinyl resin, and the like. A mixed / synthetic material obtained by dispersing conductive particles or conductive powder in these resins to adjust the electric resistance is used as a material for the transfer belt 11. Examples of the conductive material for conductive particles and conductive powder for adjusting the resistance of the transfer belt 11 include metal powders such as carbon, aluminum and nickel, metal oxides such as titanium oxide, and quaternary ammonium salt-containing polymethyl methacrylate. , Polyvinyl aniline, polyvinyl pyrrole, polydiacetylene, polyethyleneimine, boron-containing polymer compound, conductive polymer compound such as polypyrrole, and the like can be used alone or in combination. The volume resistivity of the transfer belt 11 is preferably 10 ⁷ to 10 ¹³ [Ω · cm] if the voltage level of the primary transfer bias applied during the primary transfer is about 1 [kV], and the primary transfer bias is The surface resistance applied to the back surface is preferably a high resistance of 10 ⁹ [Ω / □] or more, particularly 10 ¹⁰ to 10 ¹¹ [Ω / □], in order to obtain a good transfer image with little transfer dust.

The separation static elimination means 18 is constituted by a static elimination needle, but may be constituted by a static elimination wire, a static elimination brush or the like.
The cleaning counter roller 74 has a function as a tension roller as a pressure member that applies a predetermined tension suitable for transfer to the transfer belt 11 by the action of the spring 75.

The cleaning device 13 is disposed to face the transfer belt 11 at a position on the left side of the cleaning facing roller 74.
Although not shown in detail, the cleaning device 13 includes a cleaning brush and a cleaning blade disposed so as to face and contact the transfer belt 11, and foreign matter such as transfer residual toner on the transfer belt 11. The transfer belt 11 is cleaned by scraping and removing the toner with a cleaning brush and a cleaning blade. Unnecessary items such as waste toner generated by this cleaning are stored in a waste toner tank 83 through a waste toner path (not shown).

  The sheet feeding device 61 accommodates a plurality of transfer sheets S in a stacked state, and is provided at the bottom of the main body 99 and is in contact with the upper surface of the uppermost transfer sheet S. The uppermost transfer sheet S is fed toward the registration roller pair 4 by being driven to rotate counterclockwise. Yes.

  The registration roller pair 4 is precisely machined in outer diameter to match the image forming speed, in other words, the moving speed of the transfer belt 11 and the paper feeding speed. The accuracy is within 0.03 mm in outer diameter.

  The fixing device 6 includes a fixing roller 62 having a heat source therein, and a pressure roller 63 pressed against the fixing roller 62. The fixing sheet 62 carrying the toner image is transferred to the fixing roller 62 and the pressure roller 63. By passing through a fixing portion that is a pressure contact portion, the carried toner image is fixed on the surface of the transfer paper S by the action of heat and pressure.

  Each of the yellow, cyan, magenta, and black toners in the toner bottles 9Y, 9C, 9M, and 9BK is provided in the image forming units 60Y, 60C, 60M, and 60BK by a predetermined supply amount by a toner supply mechanism (not shown). The developing devices 50Y, 50C, 50M, and 50BK are replenished. The toner bottles 9Y, 9C, 9M, and 9BK are consumables that are replaced when the toner in the interior is exhausted, and are removed from the main body 99 and replaced when the toner is exhausted. The regular charging polarity of the toner used in this embodiment is a negative polarity.

  When the black image is formed, the cleaning device 13 and the cleaning counter roller 74 move downward together with the primary transfer rollers 12Y, 12M, 12C and the like so that the transfer belt 11 is separated from the photosensitive drums 20Y, 20M, 20C. It is configured.

  Various types of information input through the operation panel are recognized and identified by the control means. Examples of information that can be input through the operation panel include the number of images formed.

  The configuration of the image forming units 60Y, 60C, 60M, and 60BK will be described as a representative of the configuration of the image forming unit 60Y including the photosensitive drum 20Y. Since the configurations of the other image forming units 60C, 60M, and 60BK are substantially the same, in the following description, for the sake of convenience, reference numerals corresponding to the reference numerals assigned to the configuration of the image forming unit 60Y are used. The other image forming units 60C, 60M, and 60BK will be omitted and detailed description will be omitted as appropriate.

  As shown in FIG. 2, the image forming unit 60Y provided with the photoconductive drum 20Y includes a primary transfer roller 12Y and a charge eliminating device around the photoconductive drum 20Y along a rotation direction B1 that is a clockwise direction in the drawing. A neutralizing device 80Y as a means, a lubricant applying device 70Y for applying a lubricant 71Y as a protective agent for protecting the photosensitive drum 20Y to the photosensitive drum 20Y, a cleaning device 40Y as a cleaning means, and a charging means. It has a charging device 30Y as a charging device and a developing device 50Y as a developing unit as a developing means.

  The image forming unit 60Y also includes a transfer control member 15Y whose tip is in contact with the primary transfer roller 12Y, a winding roller 16Y that widens the winding width of the transfer belt 11 around the photosensitive drum 20Y in the A1 direction, and a primary transfer roller. A pressing unit 19Y that presses 12Y toward the transfer belt 11 and the photosensitive drum 20Y, and a transfer control bias applying unit (not shown) that applies a bias of about several hundred to 2,000 volts to the transfer control member 15Y are provided.

  The charging device 30Y includes a charging roller 31Y that rotates in contact with the surface of the photosensitive drum 20Y, and a cleaning roller 32Y as a charging cleaning member that rotates in contact with the charging roller 31Y. The charging roller 31Y is connected to a voltage applying means (not shown) for applying a bias of an alternating current component to a direct current, and charges the surface of the photosensitive drum 20Y to a negative polarity in a charging region facing the photosensitive drum 20Y. It is like that.

The cleaning roller 32Y is driven to rotate by the charging roller 31Y to clean the charging roller 31Y.
As described above, in this embodiment, the charging system using the contact roller is adopted. However, the charging system may be one using a proximity roller or one using a corotron system. .

  The developing device 50Y employs a reversal developing method, and includes a developing roller 51Y disposed in close proximity to and opposite to the photosensitive drum 20Y. In the developing region between the developing roller 51Y and the photosensitive drum 20Y, yellow is developed. The toner is electrostatically transferred to an electrostatic latent image formed on the surface of the photosensitive drum 20Y, and the electrostatic latent image is visualized as a yellow toner image.

  In addition to the developing roller 51Y, the developing device 50Y includes a developing case 55Y as a casing as a developer container having an opening in a portion facing the photosensitive drum 20Y, and a developer on the developing roller 51Y. A developing blade 52Y that regulates the height of the developing blade 52Y.

  The developing device 50Y is also disposed below the developing case 55Y so as to face each other, and stirs while conveying the developer so as to circulate, and a first conveying screw 53Y as a first conveying member as a conveying means. And a second agitating screw 54Y as a second conveying member which is a conveying means.

  The developing device 50Y also includes a toner concentration detection sensor 92Y as a toner concentration detection unit that detects the toner concentration contained in the developer in the development case 55Y, a bias application unit (not shown) that applies a development bias of a DC component, and the like. The first conveying screw 53Y and the second stirring screw 54Y have driving means (not shown) that rotationally drives the same in the same direction.

  The developing device 50Y performs development using a developer that is a two-component developer that is a dry developer containing a yellow toner that is a non-magnetic toner and a carrier that is a magnetic material mainly composed of iron powder. The developer is accommodated in the developing case 55Y.

  As a yellow toner, a charge control agent (CCA) or a colorant is mixed with a particle base resin such as polyester, polyol, styrene acrylic, and a substance such as silica or titanium oxide is externally added around the particle. And with improved charging characteristics and fluidity. The particle size of the additive is preferably in the range of 0.1 to 1.5 [μm]. Examples of the colorant include carbon black, phthalocyanine blue, quinacridone, and carmine.

  As the yellow toner, a toner obtained by externally adding the above-described additive to a base resin in which wax or the like is dispersed and mixed may be used. In addition, products manufactured by the pulverization method or those manufactured by the polymerization method may be used, but those manufactured by the polymerization method and the like have relatively high sphericity and circularity, so that high image quality can be obtained. It is.

  A yellow toner having a shape factor of 90% or more is used. The shape factor is originally sphericity, and is defined as “surface area of sphere of the same volume as the particle / surface area of actual particle × 100%”, but it is difficult to measure, so it is calculated by circularity. To do. The degree of circularity can be obtained by the formula “circumference of circle having the same projected area as the particle / projection contour length of the actual particle × 100%”. The circularity solution approaches 100% as the circular image onto which the toner particles are projected approaches a perfect circle. The volume average particle diameter of the toner is preferably in the range of 3 to 12 μm, and in this embodiment is 6 μm.

  The yellow toner has a volume average particle diameter of 6 μm and a shape factor of 90% or more. Therefore, the yellow toner can sufficiently cope with a high-resolution image of 1200 dpi or more. Fine color image formation is possible.

As a carrier that is a magnetic substance, magnetic particles containing a magnetic material such as ferrite with a metal or resin as a core and having a surface layer coated with a silicon resin or the like are used. The particle size is preferably in the range of 20-50 μm. The resistance of the magnetic particles is optimally in the range of 10 ⁴ to 10 ⁶ [Ω] in terms of dynamic resistance. The dynamic resistance can be measured as follows. That is, the magnetic particles are supported on a roller (φ20; 600 RPM) containing a magnet. Then, an electrode having an area of 65 mm in width and 1 mm in length is made to face the magnetic particles through a gap of 0.9 mm, and an applied voltage of a withstand voltage upper limit level (from 400 V for high-resistance silicon-coated carrier to several V for iron powder carrier). The dynamic resistance is measured based on the value of the current flowing when.

The developing roller 51Y is disposed in close proximity to the photosensitive drum 20Y so as to face the photosensitive drum 20Y from the opening of the developing case 55Y.
The developing case 55Y includes a developing chamber 58Y in which the first conveying screw 53Y is accommodated, an agitation chamber 59Y in which the second conveying screw 54Y is accommodated, a partition wall 81Y that partitions and partitions the developing chamber 58Y and the agitating chamber 59Y, and a toner supply. It has a supply port 91Y that receives yellow toner from the toner bottle 9Y shown in FIG. 1 through the mechanism.

  Since the first conveying screw 53Y faces the developing roller 51Y so as to supply the developer to the developing roller 51Y, the developing chamber 58Y is positioned closer to the developing roller 51Y in the developing chamber 58Y and the stirring chamber 59Y. is doing.

  Each of the first transport screw 53Y and the second transport screw 54Y is rotationally driven by a driving unit, and transports the developer in a direction perpendicular to the paper surface in FIG. . Therefore, the developer is transported so as to circulate in a certain direction by the rotation of the first transport screw 53Y and the second transport screw 54Y.

  The toner concentration detection sensor 92Y detects the magnetic permeability of the developer in the developing case 55Y and converts the detected value to detect the toner concentration contained in the developer. The toner density sensor 92Y is disposed below the second transport screw 54Y, but is disposed below the first transport screw 53Y, and when the developer is separated from the developing roller 51Y and dropped, as will be described later. The toner density of the developer immediately after the fall may be detected.

  The toner supplied into the main body of the developing device 50Y through the supply port 91Y falls on the second conveying screw 54Y in the stirring chamber 59Y. That is, the supply port 91Y is disposed at a position where the toner is supplied to the second transport screw 54Y.

  The yellow toner replenished from the supply port 91Y is agitated and mixed with the developer by the second conveying screw 54Y and the first agitating screw 53Y, and the agitated and mixed developer is supplied to the developing roller 51Y.

  The stirring and mixing of the newly replenished toner and the developer is mainly performed in the stirring chamber 59Y, so that the stirring chamber 58Y functions as a toner density adjustment space. The newly replenished toner is charged by being charged during stirring and mixing.

  The first conveying screw 53Y and the second stirring screw 54Y function as a developer stirring unit that stirs the developer in the developing case 55Y. This agitation action is obtained by causing the developer to be swung up and down when the developer moves along the screw portions 85Y and 86Y.

  In the developing device 50Y, the developer in the developing chamber 58Y is carried in a spike shape on the developing roller 51Y. The developing roller 51Y functions as an agent carrier that carries the developer contained in the developing case 55Y. The amount of developer carried by the developing sleeve 56Y is regulated by the developing blade 52Y.

  The layered developer, which is regulated and has an appropriate amount on the developing sleeve 56Y, is conveyed to the developing region between the developing roller 51Y and the photosensitive drum 20Y by the rotation in the direction of arrow C1 and the developing bias by the bias applying means.

  In the developing area, the yellow toner in the developer charged by the stirring of the first conveying screw 53Y and the second stirring screw 54Y is electrostatically transferred to the electrostatic latent image formed on the surface of the photosensitive drum 20Y. Then, the electrostatic latent image is visualized as a yellow toner image.

  By developing the electrostatic latent image on the surface of the photosensitive drum 20Y in this manner, the developer whose yellow toner has been consumed and the density of the yellow toner has been lowered is further conveyed by the rotation of the developing roller 51Y and then released. Drop and mix with other developer.

  In this embodiment, the DC component developing bias is applied by the bias applying means. However, the developing bias may be an AC component, or an AC component superimposed on the DC component. The developer may be a one-component developer.

  As shown in FIG. 2, the optical scanning device 8 shown in FIG. 1 irradiates an area between the charging area and the development area on the photosensitive drum 20Y with laser light L that is light-modulated writing light. The surface of the photosensitive drum 20Y after being charged by the charging roller 31Y is exposed, the potential of the exposed portion is lowered to provide an electrostatic potential difference on the surface of the photosensitive drum 20Y, and an electrostatic latent image is formed. . Yellow toner is supplied and adhered to the portion where the potential is lowered by the developing device 50Y, and a visible image is formed as a yellow toner image.

  The cleaning device 40Y cleans the cleaning case 43Y having an opening at a portion facing the photoconductor drum 20Y, and scrapes unnecessary materials such as transfer residual toner on the photoconductor drum 20Y in contact with the photoconductor drum 20Y. A cleaning blade 41Y, which is a cleaning member as a blade, a shaft 44Y that rotatably supports the cleaning blade 41Y with respect to the cleaning case 43Y, and is supported so as to be able to contact and separate from the photosensitive drum 20Y, and a cleaning blade 41Y. The cleaning blade support member 46Y, the cleaning blade support member 47Y that holds the cleaning blade 41Y via the cleaning blade support member 46Y, the cleaning blade support member 46Y, and the cleaning blade support member 47Y To and a pressing spring 48Y is urging member as a pressure member which is biased to pressurized with a predetermined pressure which will be described later a cleaning blade 41Y to the photoconductor drum 20Y.

  The cleaning device 40Y is also rotatably supported by the cleaning case 43Y, and the cleaning blade 41Y scrapes off the transfer residual toner and the like from the photosensitive drum 20Y, and also removes unnecessary items such as waste toner generated by the removal. And a discharge screw 42Y as a waste toner conveyance screw constituting a part of a waste toner path (not shown) for conveying the toner toward the waste toner tank 83.

  The lubricant application device 70Y has a forward direction that is a direction along the rotational direction B1 of the photosensitive drum 20Y at a position facing the photosensitive drum 20Y and the lubricant 71Y that is a solid molded body formed in a bar shape. Rotate in the D1 direction, scrape and carry the lubricant 71Y, and apply a brush roller 76Y as a brush roller-like lubricant application member to apply and supply the carried lubricant to the photosensitive drum 20Y, and a lubricant 71Y. A support body 77Y as a lubricant holding member that holds and supports the cleaning case 43Y and supports the lubricant 71Y in a direction to come in contact with and separate from the brush roller 76Y, and the lubricant 71Y is passed through the support body 77Y. A spring 78Y that is a pressure spring as an elastic member as a biasing member that is a pressure member that biases and presses 47Y, and a drive (not shown) that rotationally drives the brush roller 76Y. And a motor as a source.

  The brush roller 76Y is located downstream of the position where the primary transfer roller 12Y transfers the toner image on the photosensitive drum 20Y onto the transfer belt 11 in the direction B1, which is the rotation direction of the photosensitive drum 20Y, and a cleaning blade. 41Y faces the photoconductor drum 20Y at a position upstream of the position where the transfer residual toner on the photoconductor drum 20Y comes into contact with the photoconductor drum 20Y and is cleaned, and the lubricant 71Y is applied to the photoconductor drum 20Y at this position. Apply.

  The brush roller 76Y has a metallic shaft member extending in the width direction (the depth direction in the drawing) of the photosensitive drum 20Y, and a plurality of raised hairs erected on the outer peripheral surface of the shaft member. For example, it is formed by winding and fixing a base fabric (not shown) in which a plurality of raised hairs are implanted around a shaft member. The length of the brush roller 76Y in the width direction is adjusted so that the raised brush can be brought into contact with at least the entire width direction of the photosensitive drum 20Y. The shaft member is rotatably supported by two bearings (not shown) provided on both side walls of the cleaning case 43Y, and is rotated by a motor.

  The lubricant 71Y applied to the photosensitive drum 20Y by the brush roller 76Y is leveled on the surface of the photosensitive drum 20Y by the cleaning blade 41Y, and is uniformly stretched, and a film-like thin film is formed on the surface of the photosensitive drum 20Y. A protective film which is a protective layer is formed. In this regard, it can be said that the cleaning blade 41Y is provided as a part of the lubricant applying device 70Y.

  Although the brush roller 76Y is not an active function, the brush roller 76Y comes into contact with the photosensitive drum 20Y and comes into contact with unnecessary materials such as transfer residual toner, carrier, and paper dust on the photosensitive drum 20Y, and the unnecessary materials adhere thereto. Therefore, it has a function as a cleaning roller for scraping off and cleaning such unnecessary materials. In this regard, it can be said that the brush roller 76Y or the lubricant application device 70Y including the same is provided as a part of the cleaning device 40Y.

  The film formed on the surface of the photoreceptor drum 20Y by the lubricant 71Y prevents the deterioration such as wear caused by the friction between the photoreceptor drum 20Y and the cleaning blade 41Y, and the lubricant application device 70Y prevents the friction degradation. It functions as a means. Since the friction between the photoconductor drum 20Y and the cleaning blade 41Y is low, the cleaning performance of the cleaning blade 41Y is improved. As described above, cleaning is performed satisfactorily even when toner having a high degree of circularity is used. Further, the film is formed and the cleaning is performed well, so that the photosensitive drum 20Y is protected and filming is prevented or suppressed.

Further, such a film has a function of preventing the surface of the photosensitive drum 20Y from being deteriorated due to the proximity discharge, and the lubricant applying device 70Y functions as a discharge deterioration preventing means. The deterioration here refers to both wear of the photosensitive drum 20Y due to discharge, acceleration of the wear, and activation of the surface of the photosensitive drum 20Y.
As described above, the lubricant applying device 70Y suppresses these deteriorations by applying the lubricant 71Y to the surface of the photosensitive drum 20Y.

  For these intended functions, the lubricant 71Y is, for example, lead oleate, zinc oleate, copper oleate, zinc stearate, cobalt stearate, iron stearate, copper stearate, zinc palmitate, palmitic. Fatty acid metal salts such as acid copper and zinc linolenate, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polytrifluorochloroethylene, dichlorodifluoroethylene, tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene -Fluoro-based resins such as oxafluoropropylene copolymer. That is, the lubricant 71Y is preferably made of a material selected from the group consisting of a fatty acid metal salt and a fluororesin. In particular, a metal stearate having a large effect of reducing the friction of the photosensitive drum 20Y, and further zinc stearate are more preferable. Note that two or more of the above materials may be included.

  The static eliminator 80Y is a PCL as a pre-cleaning static elimination lamp, but may be a PCC as a pre-cleaning static elimination charger.

  As shown in FIG. 3, the winding roller 16Y is a primary transfer nip formed by a range between the most upstream position NYa and the most downstream position NYb where the transfer belt 11 is in contact with the photosensitive drum 20Y in the A1 direction. In order to widen the transfer nip NY, the transfer belt 11 abuts from the back surface side and functions as a nip expansion member. The transfer belt 11 is wound around the photosensitive drum 20Y at the primary transfer nip NY. Since the winding roller 16Y functions to displace the most upstream position NYa upstream in the A1 direction, the most downstream position NYb is displaced downstream in the A1 direction to move the primary transfer nip NY downstream in the A1 direction. Although another nip expansion member may be provided to spread toward the side, the role is played by the winding roller 16C provided in the image forming unit 60C. The expansion member is omitted.

  The winding roller 16Y does not have a dedicated drive means in order to suppress fluctuations in the running speed of the transfer belt 11 due to the contact with the transfer belt 11, and a ball bearing is employed in a bearing portion (not shown). It is rotatably supported by ball bearings. Therefore, the winding roller 16Y rotates along with the transfer belt 11, thereby improving the running stability of the transfer belt 11 to suppress speed deviation and improving transferability by suppressing or preventing abnormal images such as color deviation and banding. Has been made. The winding roller 16Y is in contact with the transfer belt 11 at either the upstream side or the downstream side in the A1 direction of the facing position between the transfer belt 11 and the primary transfer roller 12Y, and widens the primary transfer nip NY in the A1 direction. Anything is fine.

  The primary transfer roller 12Y is in contact with the transfer belt 11 within the range of the primary transfer nip NY, and a cored bar 12Ya having a diameter of about 8 mm as a supporting conductor and an elastic body layer having a thickness of about 4 mm surrounding the cored bar 12Ya. 12Yb.

  The thickness of the elastic layer 12Yb is preferably 1 to 5 mm. This is because, when a thick transfer paper S of about several hundred μm enters the primary transfer nip NY, the drive shock due to the nip pressure fluctuation caused by the step due to the presence or absence of the transfer paper S is mitigated by the deformation of the elastic layer 12Yb. In order to achieve this, it is preferable that the elastic layer 12Yb has a thickness of 1 mm or more. On the other hand, if the elastic layer 12Yb is too thick, the outer diameter of the primary transfer roller 12Y is a space or the like. When restricted due to restrictions, the diameter of the cored bar 12Ya has to be reduced, and the problem of non-uniform nip pressure due to bending deformation and the electric resistance values Rp and R0 described later of the elastic layer 12Yb are within an appropriate range. This is because the thickness of the elastic body layer 12Yb is preferably 5 mm or less because a problem that it is difficult to keep the film stably is caused.

  The elastic body layer 12Yb is made of foamed PUR which is foamed rubber as a foamed material, so that the effective hardness easily becomes 50 degrees (AskerC) or less, and the load on the photosensitive drum 20Y and the transfer belt 11 is reduced. As a result, wear and scratches and toner component fixation are suppressed, the life of the photosensitive drum 20Y and the transfer belt 11 is extended, and a favorable transfer image can be obtained by suppressing the pressure applied to the toner. There is an advantage that a large resistance change is brought about by weak pressurization. In order to obtain this advantage, the hardness is desirably 60 degrees or less, and particularly preferably 40 degrees or less.

  Elastic material rubber and elastomer used for the elastic layer 12Yb include butyl rubber, fluorine rubber, acrylic rubber, EPDM, NBR, acrylonitrile-butadiene-styrene rubber, natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, ethylene -Propylene rubber, ethylene-propylene terpolymer, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, syndiotactic 1,2-polybutadiene, epichlorohydrin rubber, ricone rubber, fluoro rubber, polysulfide rubber, Polynorbornene rubber, hydrogenated nitrile rubber, thermoplastic elastomer (eg polystyrene, polyolefin, polyvinyl chloride, polyurethane, polyamide, polyurea, polyester, fluorine resin) It is possible to use one kind or two kinds or more selected from the group consisting of the system) or the like, but is not limited to these materials.

  As foaming agents for the foamed rubber of the elastic layer 12Yb, organic foaming agents are ADCA (azodicarbonamide), DPT (dinitrosopentamethylenetetraamine), TSH (p-toluenesulfonylhydrazide), OBSH (oxybis). Any of benzenesulfenyl hydrazide) and the like can be used, and the addition amount is suitably 2 to 30 parts by mass with respect to 100 parts by mass of the above-mentioned polymer raw material. Examples of the inorganic foaming agent include sodium bicarbonate and ammonium carbonate. Moreover, it is possible to add a foaming auxiliary agent etc. suitably. Examples of the vulcanizing agent include sulfur, metal oxide, and organic oxide. Examples of the inorganic filler include carbon black, talc, and clay. Other known vulcanization accelerators, process oils, and the like may be appropriately added.

The resistance of the elastic body layer 12Yb is adjusted with a resistance value adjusting conductive agent. There are no particular restrictions on the conductive agent for adjusting the resistance value. For example, carbon black, graphite, metal powder such as aluminum or nickel, tin oxide, titanium oxide, antimony oxide, indium oxide, potassium titanate, antimony oxide-tin oxide composite Conductive metal oxides such as oxide (ATO) and indium oxide-tin oxide composite oxide (ITO) can be used. The conductive metal oxide may be coated with insulating fine particles such as barium sulfate, magnesium silicate, and calcium carbonate, but is not limited to these conductive agents. As a compounding ratio of the conductive agent for adjusting the resistance value, it is preferable to add 5 to 200 parts by mass with respect to 100 parts by mass of the polymer raw material. Thus, the primary transfer roller 12Y has a volume resistivity from 10 ⁷ to 10 ⁸ [Ω · cm] from the cored bar 12Ya to the surface of the elastic layer 12Yb.

  In this embodiment, the primary transfer roller 12Y has only one elastic layer 12Yb as an elastic layer, but may have a plurality of elastic layers including the elastic layer 12Yb, at least of which It suffices if a part contains foam. The foam is not limited to the foamed PUR, and may be another material. In this embodiment, the elastic body layer 12Yb is formed directly on the surface of the core metal 12Ya, but another layer may be formed between the core metal 12Ya and the elastic body layer 12Yb.

  The primary transfer roller 12Y varies in the running speed of the transfer belt 11 due to the change in effective roller radius due to the compression deformation caused by the contact with the transfer belt 11 and the pressing by the pressing means 19Y. As in the case of the winding roller 16Y, a dedicated drive means is not provided, and a ball bearing is employed in a bearing portion (not shown) and is rotatably supported by the ball bearing. Therefore, the primary transfer roller 12Y rotates along with the transfer belt 11, thereby improving the running stability of the transfer belt 11 and suppressing speed deviation, and transferability by suppressing or preventing abnormal images such as color deviation and banding. Improvements have been made. The secondary transfer roller 72 has the same configuration as the primary transfer roller 12Y, including its configuration and support method.

  The primary transfer roller 12 </ b> Y has a positive polarity 0.5 opposite to the toner charging polarity and suitable for primary transfer from the power source based on constant current control by the bias control unit by the primary transfer bias applying unit. A transfer voltage of about ˜1.5 KV is applied as a bias between the core 12Ya and the photosensitive drum 20Y, and the amount of transfer current flowing from the transfer belt 11 to the photosensitive drum 20Y is kept constant. Yes. Thus, the primary transfer roller 12Y transfers the toner image carried on the photosensitive drum 20Y onto the transfer belt 11. The primary transfer roller 12Y ideally transfers all of the toner constituting the toner image carried on the photosensitive drum 20Y onto the transfer belt 11, but a part of the toner is transferred to the photosensitive drum 20Y. Residual toner remains and becomes transfer residual toner.

Note that the secondary transfer roller 72 has a negative polarity maximum of the same polarity as the toner charging polarity suitable for the secondary transfer from the power source based on the constant current control by the bias control unit by the secondary transfer bias applying unit. A transfer voltage of about 3 KV is applied, and the amount of transfer current flowing from the transfer belt 11 to the driven roller 5 is kept constant. As a result, the secondary transfer roller 72 transfers the toner image carried on the transfer belt 11 onto the transfer paper S. It is ideal that the secondary transfer roller 72 transfers all of the toner constituting the toner image carried on the transfer belt 11 onto the transfer sheet S. However, a part of the toner is transferred onto the transfer sheet S. It remains and becomes a transfer residual toner.
The secondary transfer roller 72 is provided with a pressing means (not shown) similar to the pressing means 19Y.

  In the primary transfer nip NY, the transfer belt 11 is in contact with the surface of the photosensitive drum 20Y via toner in an area where the photosensitive drum 20Y carries toner, and the photosensitive drum 20Y does not carry toner. Then, it directly contacts the surface of the photoreceptor drum 20Y.

  The pressing means 19Y functions as a pressure contact means for bringing the primary transfer roller 12Y and the photosensitive drum 20Y into pressure contact with each other. The pressing unit 19Y includes a pressing roller 19Ya that is in contact with the primary transfer roller 12Y, and an urging unit (not shown) for pressing the pressing roller 19Ya against the primary transfer roller 12Y. The urging unit is configured by a spring or the like that urges the pressing roller 19Ya toward the primary transfer roller 12Y. The urging mode of the pressing roller 19Ya by the spring may be urging both ends of the pressing roller 19Ya, or may urge the entire back surface of the pressing roller 19Ya.

  In order to suppress fluctuations in the rotational speed of the primary transfer roller 12Y due to the fact that the pressure roller 19Ya is in contact with the primary transfer roller 12Y, and particularly urged by the urging means, Similarly, a dedicated bearing means is not provided, and a ball bearing is employed in a bearing portion (not shown), and is rotatably supported by the ball bearing. Therefore, the pressure roller 19Ya is rotated along with the primary transfer roller 12Y, thereby improving the rotational qualitative property of the primary transfer roller 12Y to suppress speed deviation and transferability by suppressing or preventing abnormal images such as color deviation and banding. Improvements have been made.

  The urging means reduces the pressure contact force between the primary transfer roller 12Y and the photosensitive drum 20Y at the time of non-transfer, than the pressure contact force between the primary transfer roller 12Y and the photosensitive drum 20Y at the time of transfer. Thus, damage caused by stick slip of the primary transfer roller 12Y, the transfer belt 11, and the photosensitive drum 20Y due to pressurization is reduced.

  FIG. 4A shows the state of the primary transfer roller 12Y during non-transfer, and FIG. 4B shows the state of the primary transfer roller 12Y during transfer. In the figure, the transfer control member 15Y is not shown. As can be seen from the comparison between FIGS. 9A and 9B, the primary transfer roller 12Y at the time of transfer is more crushed by compressive deformation than the primary transfer roller 12Y at the time of non-transfer. Then, in the case shown in FIG. 11A, the primary transfer roller 12Y is in contact with the photosensitive belt 20Y via the transfer belt 11 or the transfer belt 11, and the region x1 shown in FIG. In this case, when comparing the primary transfer roller 12Y with the transfer belt 11 or the region x2 in contact with the photosensitive drum 20Y via the transfer belt 11, x1 <x2. Further, when the thickness t1 of the elastic body layer 12Yb in the region x1 and the thickness t2 of the elastic body layer 12Yb in the region x2 are compared, t1> t2, which is shown in FIG. In this case, the apparent thickness of this portion is thinner than in the case shown in FIG.

  As a configuration for changing the pressure contact force, in addition to a spring that biases the pressing roller 19Ya toward the primary transfer roller 12Y, the biasing unit acts to cancel the biasing force by the spring. A configuration including a pressure release mechanism such as an electromagnetic solenoid and a cam that can be switched in operation at the time of non-transfer. In addition, you may include making this press-contact force zero as an aspect which reduces the press-contact force which an urging means applies. When the pressure contact force is zero, the primary transfer roller 12Y comes into pressure contact with the transfer belt 11 and the photosensitive drum 20Y by its own weight depending on the support mode. The biasing means may be configured such that the pressure contact force becomes zero as a mode of reducing the pressure contact force.

  For the stability of transfer, it is desirable to keep x2 and t2 constant in the state shown in FIG. Therefore, the pressing means 19Y makes the hardness of both ends of the pressing roller 19Ya 70 degrees (AskerC) and hardens the hardness of the central portion, and the diameter of both ends of the pressing roller 19Ya is 0.05 to 0 from the diameter of the central portion. .2mm smaller. The pressing unit 19Y employs a constant pressing unit configured to keep the urging force of the urging unit constant, and the rotation center of the pressing roller 19Ya and the rotation center of the primary transfer roller 12Y. In the case shown in FIG. 6B, the biting dimension stabilizing means is employed in which the distance is maintained at a constant distance of about 0.02 to 0.1 mm shorter than the case shown in FIG. ing. Note that either one of the constant pressurizing means and the biting dimension stabilizing means may be employed, and the pressing roller 19Ya may be a member whose both the hardness and the diameter or one of them is constant in the axial direction.

  The other points of the pressing unit 19Y, for example, the magnitude of the pressure contact force by which the pressing unit 19Y presses the primary transfer roller 12Y and the photosensitive drum 20Y to each other will be described later.

  The transfer control member 15Y occupies the upstream transfer position on the upstream side in the A1 direction among the opposed positions of the transfer belt 11 and the primary transfer roller 12Y. Specifically, the transfer control member 15Y and the transfer belt 15Y and the transfer belt are arranged such that the front end of the transfer control member 15Y intersects a perpendicular line from the most upstream position NYa of the transfer upstream position to the surface of the primary transfer roller 12Y. 11 is provided so as to enter a wedge-shaped space formed by.

The other points of the transfer control member 15Y, for example, the volume resistivity, structure, material, and more detailed arrangement of the transfer control member 15Y will be described later.
The transfer control member 15 </ b> A is also arranged with respect to the secondary transfer roller 72 and the transfer belt 11 in the same manner as described above with respect to the primary transfer roller 12 </ b> Y and the transfer belt 11. It is arranged. In addition, the volume resistivity, structure, material, and more detailed arrangement of the transfer control member 15A are the same as those of the transfer control member 15Y.

  Of the above components constituting the image forming unit 60Y, the components other than the primary transfer roller 12Y, the transfer control member 15Y, the winding roller 16Y, and the pressing unit 19Y are process cartridges 95Y that are process units as units. The process cartridge 95Y is integrated, and is detachable from the image forming apparatus 100 main body toward the front side of the sheet in FIG. 1, and is detachable. Such a process cartridge having a plurality of structures can be handled as a replacement part, so that maintainability is remarkably improved, which is very preferable.

  In the image forming apparatus 100 having such a configuration, when a signal indicating that a color image is to be formed is input, the transfer entrance roller 73 is driven, and the transfer belt 11, the secondary transfer roller 72, the cleaning counter roller 74, and the winding roller 16Y. , 16C, 16M, 16BK and the like are driven to rotate, and the photosensitive drums 20Y, 20M, 20C, 20BK are rotationally driven in the B1 direction.

  As the photosensitive drum 20Y rotates in the B1 direction, the surface is uniformly charged by the charging roller 31Y, and an electrostatic latent image corresponding to the yellow color is formed by exposure scanning of the laser beam L from the optical scanning device 8. The electrostatic latent image is developed with yellow toner by the developing device 50Y, and the toner image, which is a yellow single color image obtained by development, is transferred to the transfer belt 11 that is moved in the A1 direction by the primary transfer roller 12Y. After the primary transfer and neutralization by the static eliminator 80Y, the lubricant 71Y is applied and the unwanted matter including the transfer residual toner remaining after the transfer is satisfactorily performed by the lubricant applicator 70Y and the cleaning device 40Y. It is used for the next charging by the charging roller 31Y.

  At this time, the cleaning device 40Y also removes the lubricant on the photosensitive drum 20Y partially or wholly deteriorated due to charging or the like as a surface residue together with other components such as transfer residual toner. The cleaning device 40 </ b> Y stores the collected unnecessary material in the waste toner tank 83.

  Similarly, toner images of the respective colors are formed on the other photosensitive drums 20C, 20M, and 20BK, and the formed toner images that are single-color images of the respective colors are moved in the A1 direction by the primary transfer rollers 12C, 12M, and 12BK. Primary transfer is sequentially performed at the same position on the moving transfer belt 11. The toner image superimposed on the transfer belt 11 moves to the secondary transfer portion 90 that is the position facing the driven roller 5 as the transfer belt 11 rotates in the A1 direction, and the transfer paper S is transferred to the secondary transfer portion 90. Secondary transfer is performed.

  The transfer sheet S conveyed between the transfer belt 11 and the driven roller 5 is fed out and fed from the sheet feeding device 61 by the feeding roller 3 and is detected by the registration roller pair 4 based on the detection signal from the sensor. The toner image on the transfer belt 11 is sent out at a timing when the leading end of the toner image faces the driven roller 5.

  When the transfer paper S has transferred and carried toner images of all colors, the transfer paper S enters the fixing device 6 and acts by heat and pressure when passing through the fixing portion between the fixing roller 62 and the pressure roller 63. As a result, the carried toner image is fixed, and a color image which is a composite color image is fixed on the transfer paper S. The fixed transfer paper S that has passed through the fixing device 6 is stacked on a paper discharge tray 17 at the top of the main body 99 via a paper discharge roller 7. On the other hand, the transfer belt 11 that has finished the secondary transfer is cleaned by a cleaning brush and a cleaning blade provided in the cleaning device 13 to prepare for the next charging step and developing step.

  In such an image forming process, the yellow, cyan, magenta, and black toners are consumed by the developing devices 50Y, 50C, 50M, and 50BK, respectively. , 9C, 9M, and 9BK are supplied to the developing devices 50Y, 50C, 50M, and 50BK, respectively, by a predetermined replenishment amount of yellow, cyan, magenta, and black toner.

Here, as already mentioned, the transfer belt 11, 1 the back surface of the surface resistance of the primary transfer bias is applied, in order to obtain a less satisfactory transfer images toner scattering, 10 9 ^[Ω / □] or more High resistance, particularly 10 ¹⁰ to 10 ¹¹ [Ω / □]. A good transfer image with little transfer dust is obtained by making the transfer belt 11 high resistance so that the charges generated by the application of the primary transfer bias are transferred to the primary transfer rollers 12Y, 12C, 12M, 12BK and the transfer belt. 11 is prevented or suppressed from propagating to the upstream side in the A1 direction from the contact portion with the electric discharge roller 11, and discharge between the primary transfer rollers 12Y, 12C, 12M, and 12BK and the photosensitive drums 20Y, 20C, 20M, and 20BK is so-called. This is because space discharge is suppressed, and transfer dust images resulting from toner transfer from the photosensitive drums 20Y, 20C, 20M, and 20BK to the transfer belt 11 due to space discharge are suppressed.

  However, even with this configuration, the primary transfer rollers 12Y, 12C, 12M, 12BK and the transfer are transferred like a wedge-shaped space formed by the primary transfer rollers 12Y, 12C, 12M, 12BK and the transfer belt 11. In a portion where the distance from the belt 11 is small, discharge is performed in accordance with Paschen's discharge law (Ricoh Technical Report No. 28 (, 2002/12) P27 to 33 “Mechanism of toner dust phenomenon during transfer depending on paper transport posture”) shown in FIG. Can happen. In the drawing, the gap corresponds to the distance between the primary transfer rollers 12Y, 12C, 12M, and 12BK and the transfer belt 11. From the figure, it can be seen that, for example, when the gap is 260 μm, the discharge start voltage is about 2 KV. Further, as described above, the maximum value of the bias applied by the primary transfer rollers 12Y, 12C, 12M, and 12BK is about 1500 V. Therefore, discharge occurs when the gap is about 200 μm or less. Although not shown in the figure, since the maximum value of the bias applied by the secondary transfer roller 72 is about 3000 V, discharge occurs when the gap is about 4350 μm or less.

  When the discharge occurs, a charge due to the discharge is imparted to the back surface of the transfer belt 11, thereby inducing a charge on the surface of the transfer belt 11, and a discharge between the surface of the transfer belt 11 and the photosensitive drums 20Y, 20C, 20M, 20BK. Therefore, a transfer dust image resulting from this discharge is likely to occur.

  Therefore, by preventing the space discharge between the primary transfer rollers 12Y, 12C, 12M, and 12BK and the transfer belt 11, the induction of electric charges on the surface of the transfer belt 11 is prevented, and the surface of the transfer belt 11 and the photosensitive drum 20Y. , 20C, 20M, and 20BK, transfer control members 15Y, 15C, 15M, and 15BK are provided in order to prevent transfer dust images caused by discharge. Since the transfer control members 15Y, 15C, 15M, and 15BK have the same configuration, the transfer control member 15Y will be described as a representative.

The transfer control member 15Y prevents a space discharge between the primary transfer roller 12Y and the transfer belt 11 to prevent the induction of electric charge on the surface of the transfer belt 11, and the transfer belt 11 surface and the photosensitive drum 20Y. In order to prevent the transfer dust image due to the discharge between the two, the volume resistivity is 10 ⁷ to 10 ¹³ [Ω · cm] or more of the portion of the transfer belt 11 facing the transfer control member 15Y. The volume resistivity 10 ⁷ to 10 ⁸ [Ω · cm] or more of the elastic layer 12Yb, which is the portion facing the transfer control member 15Y of the primary transfer roller 12Y, specifically 10 ¹² to 10 ^14. [Ω · cm]. The volume resistivity is sometimes referred to as resistivity, specific resistance, volume specific resistance, volume specific electrical resistance, or the like.

The reason why the lower limit of the volume resistivity of the transfer control member 15Y is set to 10 ¹² [Ω · cm] is that it is very close to the primary transfer roller 12Y and the transfer belt 11 due to a wave at the tip of the transfer control member 15Y or insufficient mounting accuracy. This is to suppress the discharge and leakage at the spot or contact point to an allowable level of 0.1 μA or less, which is 1% or less of the current required for transfer.

The reason why the upper limit of the volume resistivity of the transfer control member 15Y is set to 10 ¹⁴ [Ω · cm] is that the voltage applied to the transfer control member 15Y is suppressed to a level of 2000 volts to exert the transfer dust prevention function.

  Thus, the transfer control member 15Y prevents discharge in the space by suppressing discharge based on air ionization suppression by preventing ventilation of the space between the primary transfer roller 12Y and the transfer belt 11, and the surface of the transfer belt 11 and the photosensitive member. A transfer dust image caused by discharge between the drum 20Y and the drum 20Y is prevented. Note that the transfer control member 15Y exhibits not only a function of preventing such discharge but also a function of preventing a leakage phenomenon caused by the presence of dust and foreign matter, that is, a tracking phenomenon, thereby contributing to an improvement in transfer performance.

  Since the transfer control member 15Y performs this function better when it is moved deeper into the wedge-shaped space between the primary transfer roller 12Y and the transfer belt 11, the tip of the transfer control member 15Y has a primary transfer roller 12Y. It is arranged in a manner in contact with the surface. The tip of the transfer control member 15Y has a thickness of several hundred μm. The tip of the transfer control member 15Y may be in contact with the surface of the transfer belt 11, but it is better to avoid contacting both the primary transfer roller 12Y and the transfer belt 11. When contacting both the primary transfer roller 12Y and the transfer belt 11, the transfer control member 15Y is sandwiched between the primary transfer roller 12Y and the transfer belt 11, and the rotation between the primary transfer roller 12Y and the transfer belt 11 is performed. This is because the tensile frictional resistance load is increased more than the above, or the wear resistance is easily broken.

  An example of the configuration of the transfer control member 15Y is shown in FIG. In the figure, the upper side shows the primary transfer roller 12Y and the leading end portion on the transfer belt 11 side, the right side shows the primary transfer roller 12Y side, and the left side shows the transfer belt 11 side.

  FIG. 4A shows an example in which the transfer control member 15Y is configured by one plate-like member, and FIG. 4B shows the transfer control member 15Y made of a plate-like base material 15Ya and a base material 15Y. FIG. 2C shows an example in which the coating layer 15Yb covers the primary transfer roller 12Y and the transfer belt 11 at the tip of the plate-like substrate 15Ya. FIG. 4D shows an example in which the coating layer 15Yb is provided on one side facing the primary transfer roller 12Y at the tip of the plate-like substrate 15Ya. Is shown.

In the example shown in FIG. 6A, the whole is made of a material having a volume resistivity of 10 ¹² to 10 ¹⁴ [Ω · cm]. As this material, a resin having a high resistance and a desired dimensional accuracy is desirable, and a molding resin such as polypropylene PP, phenol, nylon, PBT, polyacetal POM, acrylic, ABS, PPE, PC, and silicon wafer is preferable. is there.

  In the example shown in FIGS. 5B to 5D, the coating layer 15Yb is made of a material having a low friction resistance, so that the tip of the transfer control member 15Y is placed on the surface of the primary transfer roller 12Y or the surface of the transfer belt 11. This is an example suitable for contact. The formation mode of the coating layer 15Yb is appropriately selected from the examples shown in FIGS. 5B to 5D in accordance with the position of the member with which the tip of the transfer control member 15Y comes into contact. The covering layer 15Yb is formed as a thin layer having a thickness of about several μm to several 100 μm.

  The coating layer 15Yb is made of a polymer resin film such as PET and PEN, various rubber plates such as NBR, FKM, VMQ, EPDM, CR, and U, and a fluorine-based resin as a flexible elastic sheet member. Integrate. However, from the viewpoint of a low coefficient of friction, fluorine-based resins such as THV, PTFE, FEP, PFE, ETFE, PCTFE, and PVDF are preferable.

The material of the base material 15Ya can be the material described in the example of FIG. However, the size and shape of the transfer control member 15Y are set and maintained with high accuracy, and the above-mentioned functions are more satisfactorily performed by accurately arranging them in the wedge-shaped space between the primary transfer roller 12Y and the transfer belt 11. In addition, the base material 15Ya may be made of metal. However, in this case, the coating layer 15Yb is made of the material having the volume resistivity of 10 ¹² to 10 ¹⁴ [Ω · cm] described in the example of FIG.

  The transfer control member 15Y only needs to satisfy at least the volume resistivity of the tip portion facing the transfer belt 11 so as to satisfy the above-described relationship. Therefore, the material of only the tip portion may exhibit the volume resistivity. . Further, as a material of each part of the transfer control member 15Y, a rubber material having a high electric resistance, for example, isoprene rubber, butadiene rubber, chloroprene rubber, acrylonitrile butadiene rubber, butyl rubber, styrene-butadiene copolymer, styrene-isoprene copolymer is appropriately used. Polymer, styrene-butadiene-acrylonitrile copolymer, ethylene propylene rubber, polyurethane rubber, silicone rubber, fluorine rubber, chlorosulfonated polyethylene rubber, chlorinated polyethylene rubber, acrylic rubber, polysulfide rubber, propylene oxide rubber, ethylene acrylic rubber Polynorbornene rubber and other rubbers may be used.

  The volume resistivity, structure, material, arrangement, etc. of the transfer control member 15Y described above prevent the space discharge between the secondary transfer roller 72 and the transfer belt 11 to reduce the charge on the surface of the transfer belt 11. The same applies to the transfer control member 15A in order to prevent induction and to prevent a transfer dust image due to discharge between the surface of the transfer belt 11 and the transfer paper S.

  By preventing the space discharge between the primary transfer roller 12Y and the transfer belt 11, the induction of charge on the surface of the transfer belt 11 is prevented, and the discharge is caused between the surface of the transfer belt 11 and the photosensitive drum 20Y. In order to prevent the transferred dust image, the pressing force by the pressing means 19Y is also adjusted. This is based on the fact that the effective resistance of the elastic layer 12Yb is proportional to its thickness, for example, the resistance is also halved if the thickness t2 of the elastic layer 12Yb shown in FIG. 4B is halved. It is a thing. Specifically, as the pressure contact force increases and the wall thickness t2 of the elastic body layer 12Yb decreases, the effective resistance of the elastic body layer 12Yb decreases and current flows more easily. Then, the movement of the charge including the charged toner is suppressed, and the transfer dust image caused by the discharge between the surface of the transfer belt 11 and the photosensitive drum 20Y is prevented.

Since the pressure contact force and the wall thickness t2 are substantially proportional, as shown in FIG. 7, the electrical resistance between the pressure contact force and the elastic layer 12Yb is also approximately proportional to each bias voltage.
In addition, even within the region of the primary transfer nip NY shown in FIG. 4, the thickness of the elastic layer 12Yb is the thinnest at the center, so that the current flows best at the center of the primary transfer nip.

  The inventors diligently studied based on experiments. To prevent transfer dust, the total current flowing in the region x2 is reduced to a region about 1/3 of the width of the primary transfer nip NY centered on the central portion. It is preferable that 2/3 of them flow, and for that purpose, the electric resistance value Rp at the time of transfer of the elastic layer 12Yb between the core metal 12Ya and the transfer belt 11 is set to the core metal 12Ya and the transfer belt 11. Between the core metal 12Ya and the transfer belt 11 when the elastic body layer 12Yb is under 20N pressure. It has been found that it is sufficient to satisfy at least one of the conditions that the resistance value is ½ or less of the electric resistance value R0.

  For example, when the bias voltage is 1000 V and the pressure contact force due to the weight of the primary transfer roller 12Y is 3N, the pressure contact force by the pressing means 19Y is set to 18N at the time of transfer with reference to FIG. The electric resistance value Rp is 50% or less of the electric resistance value R0, and this condition is satisfied. In the configuration of this embodiment, it has been found that the pressure contact force during transfer by the pressing means 19Y is preferably 15 to 40N.

  The electrical resistance values Rp and R0 were measured by the apparatus shown in FIG. This apparatus includes a measuring roller 112 having a length of 300 mm corresponding to the primary transfer roller 12Y and a diameter of 30 mm, a counter electrode roller 120 corresponding to the photosensitive drum 20Y, which is in contact with the measuring roller 112 from above, and a voltage. A variable power source 121 and an ammeter 122 are provided. The measuring roller 112 includes a core metal 112a and an elastic body layer 112b corresponding to the core metal 12Ya and the elastic body layer 12Yb, respectively. The counter electrode roller 120 is made of SUS and is conductive. The variable voltage power supply 121 and the ammeter 122 are connected in series between the cored bar 112a and the counter electrode roller 120. When the voltage of the voltage variable power supply 121 is set to 500 V using this device, when a pressure contact force of 16 N is applied as the pressure contact force during transfer, the electrical resistance value Rp≈1.2E + 07Ω and the electrical resistance value R0≈2.6E + 07Ω are obtained. It was found that the above conditions were satisfied, and that the range of application of the electrical resistance value Rp was 1.0E + 06 to 1.0E + 08Ω.

  As described above, when the change in effective resistance due to the elastic deformation of the elastic layer 12Yb is used, if the pressure-sensitive conductive rubber is used for the elastic layer 12Yb, the change becomes more remarkable and the above-described condition is satisfied. It is easy to make adjustments, and is preferable.

The configuration using the change in effective resistance due to the elastic deformation of the elastic layer 12Yb can be similarly applied to the secondary transfer roller 72.
In this embodiment, since the primary transfer nip NY is expanded by the winding roller 16Y, the current surely flows in the region of the primary transfer nip NY, particularly in the central portion thereof. To be prevented. As shown in FIG. 9, the winding roller 16Y may be omitted.

  In order to satisfactorily prevent transfer dust by flowing current intensively in a narrow region, it is desirable that the radius of curvature of the primary transfer roller 12Y is smaller than the radius of curvature of the photosensitive drum 20Y as the counter electrode member. So this relationship is satisfied. The primary transfer roller 12Y is easily bent when the radius of curvature, that is, the diameter is small. However, the bending of the primary transfer roller 12Y is suppressed or prevented by the contact of the pressing roller 19Ya.

  As shown in FIG. 10A, the relationship between the radii of curvature is also satisfied between the secondary transfer roller 72 and the driven roller 5. However, the secondary transfer roller 72 and the driven roller 5 are interchangeable as shown in FIG. 10B. In this case, the polarity of the bias is reversed.

  The counter electrode member such as the image carrier such as the photosensitive drum 20Y and the driven roller 5 may have an endless belt shape. In this case, it is desirable that the relationship of the radius of curvature is satisfied. When the shape of the portion facing the primary transfer roller 12Y or the secondary transfer roller 72 is a plane, the radius of curvature is infinite, and this relationship is satisfied. The bias applying member is not limited to the roller shape as in the present embodiment, but may be an endless belt shape, or may be a brush roller shape. Further, it is sufficient that at least one of the bias applying member and the counter electrode member has a cored bar and an elastic layer surrounding the cored bar. For example, both the secondary transfer roller 72 and the driven roller 5 are provided. You may have such a metal core and an elastic body layer. Note that the core metal when the bias applying member and the counter electrode member are formed into an endless belt shape is configured by a metal roller around which the endless belt shape member is wound, a metal layer provided on the endless belt shape member, or the like.

In FIG. 4B, reference numeral 16 ′ denotes a transfer paper pre-contact roller as a nip expansion member corresponding to the winding roller 16Y. The transfer paper pre-adhesion roller 16 ′ is arranged to bring the transfer paper S into close contact with the transfer belt 11 before the transfer bias acts, and a bias having a polarity opposite to the charging polarity of the transfer belt 11 is applied. Or grounded. The transfer paper pre-adhesion roller 16 ′ has a volume low efficiency of at least 10 ⁷ to 10 ⁸ [Ω · cm] so that the charged charge of the transfer belt 11 is not excessively discharged. Like the transfer paper pre-adhesion roller 16 ', a bias may be applied to the nip expanding member.

  The electrodes used for measuring the electrical resistance values of the transfer belt 11 and the transfer control members 15Y, 15C, 15M, and 15BK described above are as follows: main electrode outer diameter Φ5.9 mm, guard electrode inner diameter Φ11.0 mm, guard electrode outer It is desirable to use a thin material with a diameter of Φ17.8 mm and a thickness of about 50 to 200 μm that is easily bent. Then, a voltage of about 500 V, for example, is applied to the electrode, and the electrical resistance value is obtained from the current value flowing between the electrodes.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  For example, the primary transfer bias application unit and the secondary transfer bias application unit may perform constant voltage control instead of constant current control. The rotating member may be endless, and for example, it may be a drum if possible. The rotating member may not be an intermediate transfer member, but may be a transfer conveyance belt that simply conveys the transfer paper S and transfers the toner image onto the transfer paper S in the course of conveyance. In this regard, the image forming apparatus may not be a so-called tandem image forming apparatus, and may be a monochrome image forming apparatus instead of a color image forming apparatus.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

1 is a schematic front view of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic front view showing a transfer control member, a rotating member, a bias applying member, a counter electrode member, a nip expanding member, a pressure contact unit, and the like provided in the image forming apparatus shown in FIG. 1. FIG. 3 is a schematic front view showing a detailed arrangement of the transfer control member shown in FIG. 2. It is the schematic front view which showed the mode of the deformation | transformation of the bias application member by the press means shown in FIG. It is a discharge start voltage characteristic curve figure of Paschen. FIG. 3 is a schematic front view illustrating various configuration examples of a transfer control member illustrated in FIG. 2. FIG. 3 is a correlation diagram showing that the electric resistance value of the elastic layer provided in the bias applying member shown in FIG. 2 changes due to the pressing force by the pressing means shown in FIG. 2. It is the schematic of the apparatus for measuring the electrical resistance value of the elastic body layer with which the bias application member shown in FIG. 2 was equipped. FIG. 5 is a diagram corresponding to FIG. 4, and is a schematic front view showing a state of deformation of the bias applying member by the pressing means shown in FIG. 2 when no nip expanding member is provided. FIG. 3 is a schematic front view showing a configuration example around another transfer unit formed by the rotating member shown in FIG. 2.

Explanation of symbols

5 Counter electrode member 11 Rotating member 12Y, 12M, 12C, 12BK Bias applying member 12Ya Core 12Yb Elastic layer, elastic layer including foam 15A, 15Y, 15M, 15C, 15BK Transfer control member 15Ya Base material 15Yb Covering layer 16Y, 16M, 16C, 16BK, 16 'Nip expansion member 19Y Pressure contact means, constant pressure pressurization means, biting size constanting means 20Y, 20M, 20C, 20BK Image carrier, counter electrode member 72 Bias application member 90 Transfer section 98 Transfer unit 100 Image forming apparatus

Claims (15)

An endless rotating member that is disposed opposite to the image carrier and forms a transfer portion for transferring a toner image on the image carrier;
A bias applying member for applying a transfer bias for transferring a toner image disposed in contact with the rotating member;
A counter electrode member disposed opposite to the bias applying member across the rotating member;
A transfer control member occupying a transfer upstream position on the upstream side in the rotation direction of the rotation member among the opposed positions of the rotation member and the bias applying member;
The transfer control member is a portion occupying the transfer upstream position, and a volume resistivity of a portion facing the rotating member is at least a volume resistivity of a portion of the rotating member facing the transfer control member, An image forming apparatus having a volume resistivity equal to or greater than at least a portion of the bias applying member facing the transfer control member. The image forming apparatus according to claim 1.
At least one of the bias applying member and the counter electrode member has a cored bar and an elastic body layer surrounding the cored bar,
The electric resistance value at the time of transfer of the elastic body layer between the core metal and the rotating member is 1 of the electric resistance value at the time of self-weight pressurization of the elastic body layer between the core metal and the rotating member. / 2 or less, and / or the elastic layer between the cored bar and the rotating member has an electric resistance value of 20 N under pressure of the elastic layer between the cored bar and the rotating member. An image forming apparatus characterized in that the electric resistance value is ½ or less of its own weight pressurization. The image forming apparatus according to claim 2.
An image forming apparatus, wherein at least a part of the elastic layer includes a foam. The image forming apparatus according to claim 2 or 3,
The image forming apparatus, wherein the member having the metal core and the elastic body layer is driven to rotate by the rotating member. The image forming apparatus according to any one of claims 1 to 4,
An image forming apparatus comprising: a nip expanding member engaged with the rotating member so as to widen a transfer nip formed by the rotating member. The image forming apparatus according to claim 5.
The image forming apparatus, wherein the nip expanding member is driven to rotate by the rotating member. The image forming apparatus according to claim 4 or 6, wherein:
The image forming apparatus, wherein the member that rotates following the rotating member is rotatably supported by a ball bearing. The image forming apparatus according to any one of claims 1 to 7,
An image forming apparatus comprising pressure contact means for pressing the bias applying member and the counter electrode member together. The image forming apparatus according to claim 8.
The pressure contact means reduces a pressure contact force between the bias applying member and the counter electrode member at the time of non-transfer to a pressure contact force between the bias application member and the counter electrode member at the time of transfer. Forming equipment. The image forming apparatus according to claim 8 or 9,
The pressure contact means can maintain a constant pressure contact force between the bias application member and the counter electrode member, and / or a pressure contact force between the bias application member and the counter electrode member. An image forming apparatus characterized by having a biting size constanting means capable of maintaining a constant distance between these members so that a constant distance occurs. The image forming apparatus according to any one of claims 1 to 10,
An image forming apparatus, wherein a radius of curvature of the bias applying member is smaller than a radius of curvature of the counter electrode member. The image forming apparatus according to any one of claims 1 to 11,
An image forming apparatus, wherein a front end portion of the transfer control member on the transfer upstream position side is engaged with either the rotating member or the bias applying member. The image forming apparatus according to claim 12.
An image forming apparatus, wherein a front end portion of the transfer control member that engages with one of the rotating member and the bias applying member is formed of a fluorine-based resin. The image forming apparatus according to any one of claims 1 to 13,
The transfer control member is made of a metal base material and has a volume resistivity equal to or greater than a volume resistivity of at least a portion of the rotating member facing the transfer control member that covers the base material at a tip portion on the transfer upstream position side. An image forming apparatus comprising: a coating layer having a volume resistivity equal to or higher than a volume resistivity of a portion of a bias application member facing at least the transfer control member. An endless rotating member that is disposed opposite to the image carrier and forms a transfer portion for transferring a toner image on the image carrier;
A bias applying member for applying a transfer bias for transferring a toner image disposed in contact with the rotating member;
A counter electrode member disposed opposite to the bias applying member across the rotating member;
An image forming method using a transfer control member that occupies a transfer upstream position on the upstream side in the rotation direction of the rotation member among opposed positions of the rotation member and the bias applying member,
The transfer control member is a portion occupying the transfer upstream position, and a volume resistivity of a portion facing the rotating member is at least a volume resistivity of a portion of the rotating member facing the transfer control member, An image forming method in which at least a volume resistivity of a portion of the bias applying member facing the transfer control member is equal to or higher.

Images