JP5350167B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of acquiring stably excellent cleaning performance and fixing performance, concerning an image forming device using a colored toner and a transparent toner. <P>SOLUTION: In this image forming device having a colored image formation part, a transparent image formation part and an intermediate transfer body, each toner image formed on each image carrier of the colored image formation part and the transparent image formation part is transferred sequentially onto the intermediate transfer body by each transfer means of the colored image formation part and the transparent image formation part, to thereby form an output image to be transferred from the intermediate transfer body to a recording material and outputted. The device has a constitution for performing supply operation such that: inorganic fine powder whose mean particle size is not less than 30 nm and not more than 300 nm, and whose particle shape is in a cubic shape and/or rectangular parallelepiped shape is externally added to the transparent toner; the transparent toner is transferred from the image carrier of the transparent image formation part to the intermediate transfer body during a period other than a formation time of the output image; the transparent toner is transferred from the intermediate transfer body to the image carrier of the colored image formation part; and the transparent toner is supplied to a cleaning device of the colored image formation part. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image using an electrophotographic process.

  In an image forming apparatus using an electrophotographic process, an electrophotographic photosensitive member (hereinafter simply referred to as “photosensitive member”) that is an image carrier is uniformly charged by a charging unit. Next, the surface of the charged photoconductor is irradiated with a laser beam or the like by an exposure unit, and an electrostatic latent image (electrostatic image) is formed on the photoconductor. Next, the electrostatic latent image formed on the photosensitive member is visualized as a toner image by a reversal development method or a regular development method by a developing unit. Next, the toner image is electrostatically transferred onto a recording material (recording medium) by a transfer unit and then fixed on the recording material by a fixing unit. Further, the toner (transfer residual toner) remaining on the surface of the photoreceptor after the toner image is transferred to the recording material is removed and cleaned by a cleaning device. Thereafter, the photoreceptor is subjected to the next image forming process.

  Conventionally, as a cleaning method for removing transfer residual toner from the surface of a photoconductor, a method using a cleaning blade (elastic blade), which is a plate-like member made of an elastic material such as polyurethane, has been widely adopted because of good cleaning properties. Yes.

  The physical properties of the cleaning blade and the manner of contact with the photoconductor greatly depend on the ease of cleaning and the surface properties of the photoconductor due to the degree of adhesion of the transfer residual toner to the photoconductor. Also, the cleaning properties are greatly affected by the physical properties such as the toner shape, particle size, and material. Therefore, it is desired to select an appropriate blade from the above viewpoints and set an appropriate angle and contact load with respect to the photoreceptor.

  On the other hand, a solid lubricant such as zinc stearate is applied to the surface of the photoconductor, and a thin film of the lubricant is formed on the photoconductor to improve the cleaning performance by the cleaning blade, or by the external additive of the toner It is known to prevent “filming”. It is also known that the performance of this lubricant film is effective in suppressing “image flow”. For this reason, an image forming apparatus having a mechanism for applying a lubricant such as zinc stearate to the surface of the photoreceptor by a cleaning brush or the like provided so as to rub the surface of the photoreceptor is proposed (Patent Document 1). .

  In recent years, in order to achieve high durability of the photoreceptor, a photoreceptor with a low wear rate is sometimes used. When a highly durable photoconductor is used, “deterioration of cleaning” due to an increase in the coefficient of friction on the surface of the photoconductor and “image flow” in a high humidity environment may occur. In other words, ozone generated in the charging process for charging the photoconductor reacts with nitrogen in the air to form nitrogen oxides (NOx), and these nitrogen oxides react with moisture in the air to form nitric acid. Adhere to the surface of the body. Since the surface of the photoconductor is difficult to wear, the charged product attached to the surface of the photoconductor becomes difficult to be removed in the cleaning process. The charged product adhering to the surface of the photoconductor lowers the electrical resistance of the surface of the photoconductor, so that the electrostatic latent image on the photoconductor is disturbed during image formation, resulting in an image flow. .

  As a method for improving the image flow, there is known a method in which particles having an abrasive action are added to toner, and a charged product adhering to the surface of the photoreceptor is peeled off. For example, by using an inorganic fine powder of a perovskite crystal whose particle shape is approximately cubic and / or cuboid as an abrasive to be added to the toner, the charged product adhering to the surface of the photoreceptor is efficiently removed. (Patent Document 2). This is because the contact area between the abrasive and the surface of the photoreceptor can be increased by making the particle shape of the abrasive roughly cubic and / or cuboid. Further, it is because the scraping property of the toner can be obtained by the contact of the ridge line of the cube and / or the rectangular parallelepiped of the abrasive with the surface of the photoreceptor.

  In recent years, it has been proposed to use transparent toner or white toner for the purpose of improving the uniformity of gloss of a color image forming apparatus. In correspondence with the thickness of the toner layer formed by the color toner image, it is proposed to transfer the transparent toner to a portion where the toner amount is small, and to make the thickness of the toner layer in the color toner image substantially the same in the image area. (Patent Document 3). As a result, it is possible to obtain an image having no gloss on the surface of the color image portion and uniform gloss.

JP-A-9-90839 JP 2005-338750 A JP 2000-147863 A

  When supplying the lubricant as described above to the surface of the photoreceptor, it is desirable to appropriately apply the lubricant or remove the old lubricant film. If these are not performed properly, poor cleaning / fusion / image flow may occur or the wear of the cleaning blade may progress.

  In order to suppress this problem, a method of adding the above-described abrasive to the toner and supplying it to the cleaning blade can be considered. However, since the abrasive is an inorganic substance, if it is added in a large amount, the fixability is hindered. In particular, in a full-color image forming apparatus equipped with an image forming unit using transparent toner as described above, since the transparent toner is superimposed on the color toner image in order to obtain glossiness, the amount of applied toner increases as a result. Adding an abrasive to the toner tends to cause a decrease in fixability.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can stably obtain good cleaning performance and fixing performance in an image forming apparatus using colored toner and transparent toner.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image carrier on which an electrostatic image is formed, a developing device that forms a toner image by supplying colored toner to the electrostatic image on the image carrier, and the image carrier. A transfer unit that transfers the toner image formed on the transfer member, a cleaning device that removes toner on the image carrier, and a lubricant application unit that applies a lubricant to the surface of the image carrier. A colored image forming unit provided;
An image carrier on which an electrostatic image is formed, a developing device for supplying a transparent toner to the electrostatic image on the image carrier to form a toner image, and a toner image formed on the image carrier. A transparent image forming section comprising a transfer means for transferring to a transfer body;
An intermediate transfer body as the transfer body onto which a toner image is transferred from the image carrier of the colored image forming section and the transparent image forming section;
Have
The toner images formed on the image carriers of the color image forming unit and the transparent image forming unit are sequentially transferred to the intermediate transfer unit by the transfer units of the color image forming unit and the transparent image forming unit, respectively. In an image forming apparatus capable of forming an output image for transfer and output from the intermediate transfer body to a recording material by transferring onto the body,
The transparent toner is externally added with an inorganic fine powder having an average particle size of 30 nm to 300 nm and a particle shape of cubic and / or rectangular parallelepiped,
In a period other than when the output image is formed, the transparent toner is transferred from the image carrier of the transparent image forming unit to the intermediate transfer member, and the transparent toner is transferred from the intermediate transfer member to the colored image forming unit. An image forming apparatus that performs transfer operation of transferring the transparent toner to a cleaning device of the colored image forming unit after being transferred to an image carrier.

  According to the present invention, it is possible to stably obtain good cleaning performance and fixing performance in an image forming apparatus using colored toner and transparent toner.

1 is a schematic cross-sectional configuration diagram of an embodiment of an image forming apparatus according to the present invention. It is a graph which shows the relationship of the charging AC electric current with respect to the peak voltage of charging AC. FIG. 6 is a graph showing the relationship between the discharge current and the surface potential of the photoreceptor with respect to the peak voltage of charging AC. 1 is a schematic cross-sectional configuration diagram of an embodiment of a cleaning device configured according to the present invention. It is a schematic diagram of a toner image. 1 is a schematic cross-sectional configuration diagram of an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a schematic cross-sectional configuration diagram of an embodiment of an image forming unit using a transparent toner that employs a cleanerless system. It is a schematic diagram for demonstrating the state of a cleaning blade missing. It is a schematic diagram for demonstrating the penetration amount and setting angle of a cleaning blade. It is a schematic diagram for demonstrating the contact pressure of a cleaning blade.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. Note that the dimensions, materials, shapes, relative positions, and the like of the components of the image forming apparatus are not intended to limit the scope of the present invention only to those unless otherwise specified.

Example 1
1. First, the overall configuration and operation of the image forming apparatus according to this embodiment will be described with reference to FIG. FIG. 1 shows a schematic cross-sectional configuration of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is a multifunction machine that has both a copying function, a printer function, and a FAX function. The apparatus main body of the image forming apparatus 100 includes a printer unit 10 that performs image forming processing on a recording material, and a document reading device 20. A full-color image is formed by an electrophotographic method in accordance with document image information read by the document reading device 20 or an image information signal from an external device such as a personal computer or a digital camera that is communicably connected to the device body. To do.

  The printer unit 10 has a plurality of image forming units (five in this embodiment) as image forming units. First, there are first, second, third, and fourth colored image forming portions Pa, Pb, Pc, and Pd for forming an image with colored toners of yellow, magenta, cyan, and black. Further, a transparent image forming unit Pt that forms an image with transparent toner.

  That is, the printer unit 10 is provided with five cylindrical photosensitive members (photosensitive drums) 1a, 1b, 1c, 1d, and 1t as image carriers. Each of the five photosensitive members 1a, 1b, 1c, 1d, and 1t is provided with a developing device 4a, 4b, 4c, 4d, and 4t loaded with developers having different spectral characteristics. Yes. Image forming portions Pa, Pb, Pc, Pd, and Pt including a combination of one photoconductor and one developing device face the surface of an intermediate transfer belt 12 that is an intermediate transfer body as a transfer target. And arranged in series along the moving direction of the surface. Then, the toner on each image carrier is transferred (primary transfer) onto the intermediate transfer member, and then transferred (secondary transfer) to a recording material to output an image.

  In this embodiment, the basic configuration and operation of each image forming unit are substantially the same except that the type of toner used is different. Accordingly, in the following, unless there is a particular need to distinguish, the subscripts a, b, c, d, and t given to the reference numerals to indicate that they are elements for any kind of toner are omitted and are summarized. explain.

  In the image forming portion P, the photosensitive member 1 is supported so as to be rotatable in the direction indicated by the arrow R1 (clockwise). The following means are arranged around the photoreceptor 1. First, a charger (charging roller) 2 is disposed as a charging unit (primary charging unit) for charging the photosensitive member 1. Next, an exposure device (laser exposure optical system) 3 is disposed as an exposure unit that exposes the charged photoreceptor 1 in accordance with image information. Next, a developing device 4 is disposed as a developing unit that supplies toner to the photoreceptor 1 to form a toner image. Next, a primary transfer roller 5 as a primary transfer unit is disposed so as to face the photoreceptor 1 with the intermediate transfer belt 12 interposed therebetween. Further, a cleaning device (cleaner) 6 is disposed as a cleaning means for collecting the toner on the photoreceptor 1.

  The intermediate transfer belt 12 is wound around three rollers, a driving roller 13, a driven roller 14, and a secondary transfer counter roller 15, as a plurality of rollers. The intermediate transfer belt 12 moves (rotates) in the direction of the arrow R2 (counterclockwise) in the figure when the driving force is transmitted to the driving roller 13. On the back side of the intermediate transfer belt 12, a primary transfer roller 5 as a primary transfer unit is disposed at a position facing each photoconductor 1 with the intermediate transfer belt 12 interposed therebetween. The intermediate transfer belt 12 contacts the photoreceptor 1 at the position of the primary transfer roller 5 to form a primary transfer portion (primary transfer nip) N1. A secondary transfer roller 11 as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 15 via the intermediate transfer belt 12. The secondary transfer roller 11 contacts the intermediate transfer belt 12 to form a secondary transfer portion (secondary transfer nip) N2. Further, in the moving direction of the intermediate transfer belt 12, the intermediate transfer belt 12 is in contact with the drive roller 13 via the intermediate transfer belt 12 downstream of the secondary transfer portion N2 and upstream of the primary transfer portion N1t of the transparent image forming portion Pt. A transfer body cleaning device 16 is provided.

  For example, at the time of forming a full-color image, the photoreceptors 1a, 1b, 1c, 1d, and 1t are illustrated in the yellow, magenta, cyan, and black colored image forming portions Pa, Pb, Pc, and Pd, and the transparent image forming portion Pt. Rotate in R1 direction. The rotating photoreceptor 1 is uniformly charged by the charging roller 2. Next, for example, according to the image information read by the document reading device 20, a light image is irradiated on each photoconductor 1 for each separated color. Thereby, an electrostatic latent image (electrostatic image) is formed on each photoconductor 1.

  The electrostatic latent image formed on each photoconductor 1 is reversely developed by each developing device 4. That is, in this embodiment, the toner charged to the same polarity (negative polarity in this embodiment) as the charged polarity of the surface of the photoreceptor 1 adheres to the image portion (exposed portion) whose charge has been attenuated by exposure, and the photoreceptor. A toner image is formed on 1. At this time, a developing bias is applied to a developing sleeve as a developer carrying member provided in the developing device 4 by a developing bias power source (not shown) as a developing bias output means.

  The toner image formed on each photoconductor 1 is transferred (primary transfer) by a primary transfer roller 5 onto a belt-like intermediate transfer body as a transfer target, that is, an intermediate transfer belt 12. At this time, each primary transfer roller 5 is supplied with a normal charging polarity of the toner (this embodiment) by a primary transfer bias power source (not shown) serving as a primary transfer bias output means provided for each primary transfer roller 5. In the example, a primary transfer bias having a polarity opposite to that of negative polarity is applied.

  The toner images formed in the color image forming portions Pa to Pd and the transparent image forming portion Pt are sequentially primary transferred onto the intermediate transfer belt 12 so as to be superimposed on the intermediate transfer belt 12. As a result, a full color toner image is formed on the intermediate transfer belt 12.

  Here, in this embodiment, in order to improve the glossiness and smoothness of the image, the multiple toner images are made to have a substantially uniform plane. In other words, in this embodiment, a small amount of transparent toner corresponding to a large amount of colored toner is superimposed on the entire surface of the imageable region, while a small amount of colored toner is superimposed on the portion where the amount of colored toner is small. A large amount of transparent toner is overlaid (see FIG. 5).

  It is also possible to form a toner image by placing a transparent toner on the entire surface of the imageable region and then placing a colored toner and a transparent toner on a substantially uniform plane. Further, a transparent toner image may be further formed on the entire surface on a substantially uniform plane formed by the color toner and the transparent toner.

  Thereafter, the full-color toner image on the intermediate transfer belt 12 is collectively transferred (secondary transfer) to the recording material S at the secondary transfer portion N2. At this time, a secondary transfer bias power source (not shown) serving as a secondary transfer bias output means is applied to the secondary transfer roller 11 with a polarity opposite to the normal charging polarity (negative polarity in this embodiment) of the toner. A secondary transfer bias is applied.

  The recording material S is conveyed from the recording material supply unit 30 to the secondary transfer unit N2. That is, in the recording material supply unit 30, the recording material S stored in the recording material storage unit (cassette) 31 is sent out one by one by a pickup roller 32 as a recording material supply unit. Next, the recording material S is conveyed to the secondary transfer portion N2 by the registration roller 33 at a desired timing.

  The recording material S on which the toner image has been transferred by the secondary transfer unit N2 passes through the transport unit and is transported to a heat roller fixing device (fixing device) 9 as a fixing unit. The toner image is fixed to the recording material S when the transfer material S passes through the fixing nip formed by the heat and pressure roller pair of the fixing device 9. Thereafter, the recording material S is discharged to a discharge tray or a recording material post-processing device (not shown).

  An optical sensor 21 serving as a detecting unit that detects toner on the intermediate transfer belt 12 is disposed at the following position. A roller that forms a transfer surface of the toner image on the intermediate transfer belt 12 and is opposed to the driven roller 14 on the downstream side of the primary transfer portion N1d of the most downstream image forming portion Pd in the moving direction of the intermediate transfer belt 12. It is. The optical sensor 21 detects the positional deviation and density of the images transferred from the photoreceptors 1a, 1b, 1c, 1d, and 1t of the image forming units Pa, Pb, Pc, Pd, and Pt. The detection output of the optical sensor 21 is input to the control circuit 70. Thereby, the control circuit 70 corrects the image density, the toner replenishment amount, the image writing timing, the image writing start position, and the like for each of the image forming units Pa, Pb, Pc, Pd, and Pt as needed. Take control.

  The process speed of the image forming apparatus 100 in this embodiment is 300 mm / sec.

2. Photoconductor Next, the photoconductor 1 will be further described. The photoreceptor 1 is formed by sequentially providing a charge generation layer and a charge transport layer on a support. Further, the photoreceptor 1 having a low wear rate (high mechanical strength) is provided with a protective layer on the outermost surface (Example 4). Further, a binder layer and further an undercoat layer for the purpose of preventing interference fringes may be provided between the support and the charge generation layer.

  As the support, it is possible to use a support that itself has conductivity, such as aluminum, an aluminum alloy, or stainless steel. In addition, the support or plastic having a layer formed by vacuum deposition of aluminum, an aluminum alloy, an indium oxide-tin oxide alloy, or the like can be used. In addition, a support obtained by impregnating plastic or paper with conductive fine particles (for example, carbon black, tin oxide, titanium oxide, and silver particles) together with an appropriate binder resin, a plastic having a conductive binder resin, or the like may be used. it can.

  A binding layer (adhesive layer) having a barrier function and an adhesive function can be provided between the support and the photosensitive layer. The binder layer is used to improve the adhesion of the photosensitive layer, improve the coating property, protect the support, cover defects on the support, improve the charge injection from the support, and protect against electrical breakdown of the photosensitive layer. It is formed. The binder layer can be formed of casein, polyvinyl alcohol, ethyl cellulose, ethylene-acrylic acid copolymer, polyamide, modified polyamide, polyurethane, gelatin, aluminum oxide, or the like. The film thickness of the binder layer is preferably 5 μm or less, and particularly preferably 0.1 to 3 μm.

  Examples of the charge generating substance used include (1) azo pigments such as monoazo, disazo and trisazo, (2) phthalocyanine pigments such as metal phthalocyanine and nonmetal phthalocyanine, (3) indigo pigments such as indigo and thioindigo, ( 4) Perylene pigments such as perylene anhydride and perylene imide, (5) polycyclic quinone pigments such as anthraquinone and pyrenequinone, (6) squarylium dye, (7) pyrylium salt and thiapyrylium salt, (8) tri Phenylmethane dyes, (9) inorganic substances such as selenium, selenium-tellurium and amorphous silicon, (10) quinacridone pigments, (11) azulenium salt pigments, (12) cyanine dyes, (13) xanthene dyes, (14) quinoneimines Dye, (15) styryl dye, (16) sulfur Cadmium and (17) zinc oxide.

  Examples of the binder resin used for the charge generation layer include polycarbonate resin, polyester resin, polyarylate resin, butyral resin, polystyrene resin, polyvinyl acetal resin, diallyl phthalate resin, acrylic resin, methacrylic resin, vinyl acetate resin, phenol resin, Examples thereof include, but are not limited to, silicone resins, polysulfone resins, styrene-butadiene copolymer resins, alkyd resins, epoxy resins, urea resins, and vinyl chloride-vinyl acetate copolymer resins. These can be used singly or in combination as a single or mixed or copolymer polymer.

  The solvent used for the charge generation layer coating is selected from the solubility and dispersion stability of the resin used and the charge generation material, but examples of the organic solvent include alcohols, sulfoxides, ketones, ethers, esters, Aliphatic halogenated hydrocarbons or aromatic compounds can be used.

  The charge generation layer is well dispersed by a method such as a homogenizer, an ultrasonic wave, a ball mill, a sand mill, an attritor, or a roll mill, together with a binder resin and a solvent in an amount of 0.3 to 4 times the mass of the charge generation material, It is formed by coating and drying. The thickness is preferably 5 μm or less, and particularly preferably in the range of 0.01 to 1 μm.

  In addition, various sensitizers, antioxidants, ultraviolet absorbers, plasticizers, and known charge generating substances can be added to the charge generation layer as necessary.

  The charge transport materials used include various triarylamine compounds, various hydrazone compounds, various styryl compounds, various stilbene compounds, various pyrazoline compounds, various oxazole compounds, various thiazole compounds, and various triarylmethane compounds. Compound etc. are mentioned.

  Examples of the binder resin used to form the charge transport layer include acrylic resin, styrene resin, polyester, polycarbonate resin, polyarylate, polysulfone, polyphenylene oxide, epoxy resin, polyurethane resin, alkyd resin, and unsaturated resin. The resin chosen is preferred. Particularly preferred resins include polymethyl methacrylate, polystyrene, styrene-acrylonitrile copolymer, polycarbonate resin and diallyl phthalate resin.

  The charge transport layer is generally formed by dissolving the charge transport material and the binder resin in a solvent and applying them. The mixing ratio (mass ratio) of the charge transport material and the binder resin is about 2: 1 to 1: 2. Solvents include ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate and ethyl acetate, aromatic hydrocarbons such as toluene and xylene, chlorinated hydrocarbons such as chlorobenzene, chloroform and carbon tetrachloride, tetrahydrofuran, Ethers such as dioxane are used. In applying this solution, for example, a coating method such as a dip coating method, a spray coating method, or a spinner coating method can be used. Drying is preferably performed at 10 ° C to 200 ° C, more preferably at a temperature in the range of 20 ° C to 150 ° C, preferably 5 minutes to 5 hours, and more preferably 10 minutes to 2 hours under blast drying or static drying. It can be carried out.

  The charge transport layer is electrically connected to the above-described charge generation layer, and has a function of receiving charge carriers injected from the charge generation layer in the presence of an electric field and transporting these charge carriers. . When a protective layer is provided, the charge transport layer has a function of receiving charge carriers injected from the charge generation layer and transporting these charge carriers to the interface with the protective layer. Since this charge transport layer has a limit to transport charge carriers, the film thickness cannot be increased more than necessary, but it is preferably 5 to 40 μm, and particularly preferably 7 to 30 μm.

  Furthermore, an antioxidant, an ultraviolet absorber, a plasticizer, and a known charge transport material can be added to the charge transport layer as necessary.

  In this example, an aluminum cylinder (JIS A3003 aluminum alloy) was used as a support, and a 5% by mass methanol solution of polyamide resin (trade name: Amilan CM8000, manufactured by Toray) was applied thereon by a dipping method. A subbing layer of 5 μm was formed.

  Next, 3 parts of a crystal of hydroxygallium phthalocyanine and 2 parts of polyvinyl butyral having a diffraction peak 2θ ± 0.2 having a strongest peak at 28.1 ° in X-ray diffraction of CuKα as a charge generation material are added to 100 parts of cyclohexanone. . Then, it is dispersed for 1 hour by a sand mill using 1 mmφ glass beads, and 100 parts of methyl ethyl ketone is added thereto and diluted to prepare a coating material for a charge generation layer. Then, the charge generation layer coating material was dip-coated on the undercoat layer and dried at 90 ° C. for 10 minutes to form a charge generation layer having a thickness of 0.17 μm.

  Next, 7 parts of the charge transport material compound of the following chemical formula (1) and 10 parts of polycarbonate resin (Iupilon Z400, manufactured by Mitsubishi Engineering Plastics Co., Ltd.) were dissolved in 105 parts of monochlorobenzene and 35 parts of dichloromethane. This solution was dip-coated on the charge generation layer and dried with hot air at 110 ° C. for 1 hour to form a charge transport layer having a thickness of 13 μm.

  In this embodiment, no protective layer is provided on the outermost surface of the photoreceptor 1 in any of the color image forming portions Pa to Pd and the transparent image forming portion Pt.

3. Development Next, the developing device 4 will be further described. In the present embodiment, the developing devices 4a, 4b, 4c, 4d, and 4t of the image forming units Pa, Pb, Pc, Pd, and Pt have substantially the same configuration except that the color of the toner to be used is different. It is said. Further, the configuration of the developing device 4 in this embodiment is the same as that of a general developing device using a two-component developer.

  That is, the developing device 4 includes a container (developing device main body) that stores the developer. The container contains a two-component developer in which a nonmagnetic toner (toner) and a magnetic carrier (carrier) are mixed. The container has an opening in a region facing the photosensitive member 1, and a developing sleeve as a developer carrying member is rotatably disposed so as to be partially exposed to the opening. The developing sleeve is made of a non-magnetic material, and a fixed magnet roll serving as a magnetic field generating means is disposed inside the developing sleeve. In the container, a stirring screw is provided as a developer stirring and conveying member. The developer in the container is circulated and conveyed in the container while being stirred by the stirring screw.

  During the developing operation, a carrier having toner adhered to its surface due to frictional charging, that is, a developer is supplied onto the rotating developing sleeve. The amount of the developer on the developing sleeve is regulated by the developer regulating member. The developer conveyed to the developing area (developing part) facing the photoreceptor 1 is raised by a magnetic field generated by a magnet roll to form a magnetic brush. By bringing the magnetic brush close to or in contact with the photoreceptor 1, developer toner is supplied onto the photoreceptor 1 in accordance with the electrostatic latent image. In this embodiment, a contact two-component development system is employed in which development is performed by bringing a magnetic brush into contact with the photoreceptor 1. At this time, a developing bias in which an AC voltage is superimposed on a DC voltage is applied to the developing sleeve by a developing bias power source (not shown). The developer after developing the electrostatic latent image is collected in the container by the rotation of the developing sleeve.

  Here, the two-component developer used in this embodiment will be described.

  In the color image forming units Pa, Pb, Pc, and Pd, the developing devices 4a, 4b, 4c, and 4d contain color toners based on resin and pigment as toners of two-component developers. On the other hand, the developing device 4t of the transparent image forming portion Pt contains a transparent toner based on a resin as a toner of a two-component developer.

  More specifically, the colored toner is colored resin particles including a binder resin and a colorant. The transparent toner is a resin particle having a high light transmittance and containing no colorant.

  Other additives are added to the toner as necessary. In this embodiment, the colored toner includes 1.8 parts by weight of silica (indeterminate shape, average particle diameter of about 20 nm) and 1.8 weights of titanium oxide (indefinite shape, average particle diameter of about 20 nm) with respect to 100 parts by weight of the toner. Parts are added. In addition to 1.8 parts by weight of silica (indefinite shape, average particle size of about 20 nm) and 1.8 parts by weight of titanium oxide (indefinite shape, average particle size of about 20 nm), the transparent toner is primary as an inorganic fine powder. 3.0 parts by weight of strontium titanate having an average particle diameter of 110 nm and a cubic and / or rectangular parallelepiped shape is added.

  The inorganic fine powder has high hardness and polishing performance, but the contact area with the object can be increased by making the particle shape cubic and / or cuboid, and the ridge line of the cube or cuboid is the object. A particularly excellent rubbing property can be obtained by abutting on. The average particle size of the primary particles of the inorganic fine powder is preferably 30 nm or more and 300 nm or less, and if it is less than 30 nm, sufficient polishing performance cannot be obtained. If it exceeds 300 nm, the polishing performance is too strong and the surface of the photoreceptor is scratched. It may become easy to stick. As the inorganic fine powder, strontium titanate is used in this embodiment, but is not limited to this, and barium titanate, calcium titanate, calcium carbonate, and the like can also be used.

  Here, the average particle diameter of the toner external additive was determined by measuring 100 particle diameters from a photograph taken at a magnification of 50,000 with an electron microscope. The particle size was determined as (a + b) / 2, where a is the longest side of the primary particles and b is the shortest side.

  As the color toner and the transparent toner, known toners can be used as appropriate. In this embodiment, the toner is based on a negatively chargeable polyester resin. The volume average particle diameter of the toner is preferably 5 μm or more and 8 μm or less. In this example, it was 7.0 μm.

As the carrier, for example, surface-oxidized or unoxidized iron, nickel, cobalt, manganese, chromium, rare earth and other metals, alloys thereof, oxide ferrite, etc. are preferably usable. The method for producing magnetic particles is not particularly limited. The carrier has a volume average particle size of 20 μm or more and 50 μm or less, preferably 30 μm or more and 40 μm or less. The carrier has a resistivity of 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more. In this example, a carrier having a volume average particle size of 35 μm, a resistivity of 5 × 10 ⁹ Ωcm, and a magnetization of 200 emu / cc was used.

  The toner in each of the developing devices 4a, 4b, 4c, 4d, and 4t is supplied from a toner storage portion (hopper) provided for each color toner (including colored toner and transparent toner). In order to keep the ratio (or toner amount) constant, it is replenished as needed at a desired timing.

4). Charging In this embodiment, the charging means is a roller-shaped charging member (charging roller) 2 that is disposed in proximity to or in contact with the photoreceptor 1. A charging bias voltage of a predetermined condition is applied to the cored bar of the charging roller 2 from a power source (not shown). As a result, the surface of the rotating photoreceptor 1 is contact-charged with a predetermined polarity and potential. In this embodiment, the charging bias voltage for the charging roller 2 is an oscillating voltage obtained by superimposing the DC voltage Vdc and the AC voltage Vac. More specifically, it is an oscillating voltage in which a DC voltage Vdc of −600 V, a frequency of 2.5 kHz, a peak-to-peak voltage Vpp having a value obtained by control described later, and a sinusoidal AC voltage Vac are superimposed.

  By this charging bias voltage, the surface of the rotating photosensitive member 1 is uniformly contact-charged to −600 V (dark potential Vd) which is the same as the DC voltage applied to the charging roller 2.

  When the peak-to-peak voltage Vpp of the AC voltage Vac applied to the charging roller 2 is increased more than necessary, excessive discharge (discharge current) occurs between the charging roller 2 and the photosensitive member 1, and Many charged products adhere to the surface. This charged product induces deterioration of the surface of the photoreceptor 1 and causes image quality deterioration such as image flow and filming. Therefore, it is preferable to suppress the applied voltage to the minimum necessary peak-to-peak voltage (discharge current) that uniformly charges the surface of the photoreceptor 1.

  Therefore, the image forming apparatus 100 of the present embodiment performs the following control. The control circuit 70 sequentially applies six peak-to-peak voltages Vpp <b> 1 to Vpp <b> 6 in FIG. 2 to the charging roller 2 during the image formation preparation rotation operation (pre-rotation operation) of the image forming apparatus 100. The peak-to-peak voltages Vpp4, Vpp5, and Vpp6 are the three peak-to-peak voltages that are discharge regions, and have a relationship of Vpp4 <Vpp5 <Vpp6. The peak-to-peak voltages Vpp1, Vpp2, and Vpp3 are three peak-to-peak voltages that are undischarged regions, and have a relationship of Vpp1 <Vpp2 <Vpp3. Then, an alternating current value (charging AC current amount) flowing through the charging roller 2 via the photosensitive member 1 at that time is measured by an alternating current value measuring circuit (not shown) and input to the control circuit 70. The control circuit 70 linearly approximates the relationship between the peak-to-peak voltage and the alternating current in the discharged region and the undischarged region from the measured current values at the three points using the least square method. Here, the intersection of the approximate straight line of the discharge area and the approximate straight line of the undischarged area is a “discharge start peak voltage” that starts the discharge between the charging roller 2 and the photosensitive member 1, and The difference between the approximate lines is the discharge current.

  FIG. 3 shows the relationship between the peak-to-peak voltage and the discharge current, and the relationship between the surface potential of the photoreceptor 1 when a DC voltage of −600 V is applied to the charging roller 2. From this relationship, when an AC voltage (point A in FIG. 3; 1200 Vpp) equal to or higher than the peak-to-peak voltage for starting discharge is applied to the charging roller 2, the surface potential of the photoreceptor 1 may be charged to about −600 V. Yes (macro potential stable region).

  However, at the peak-to-peak voltage in the vicinity of the discharge-starting peak-to-peak voltage, the surface of the photoconductor 1 cannot be sufficiently uniformly charged, and “fogging” caused by local charging failure, so-called “sandy” "Cover" occurs.

  In order to solve such a problem, it is necessary to generate a discharge (discharge current) above a certain level. In the case of this embodiment, the discharge current of the photosensitive member 1 is set to 40 μA (point B in FIG. 3; 1425 Vpp) or more in an environment of an ambient temperature of 23 ° C. and an atmospheric humidity of 50% RH. It becomes possible to make the surface potential uniform (micro potential stable region).

  That is, the range where the “sand cover” is generated is a macro potential stable region and a region where the micro potential is not stable (between A and B in FIG. 3).

  The target discharge current varies depending on the atmosphere environment in which the image forming apparatus 100 is used. Generally, the target discharge current increases in a low humidity environment, and the target discharge current decreases as the humidity environment increases.

  By carrying out the above control, the peak-to-peak voltage at which the target discharge current is 40 μA (required minimum discharge current) under the environment of the atmospheric temperature of 23 ° C. and the atmospheric humidity of 50% RH is 1425 Vpp (point B in FIG. 3). ) And calculated.

  Similarly, the target discharge current (required minimum discharge current) in an environment of an ambient temperature of 23 ° C. and an ambient humidity of 5% RH is 60 μA, and the target discharge current in an environment of an ambient temperature of 30 ° C. and an ambient humidity of 80% RH. The (required minimum discharge current) was calculated to be 30 μA.

  The charging roller 2 has a three-layer configuration in which a lower layer, an intermediate layer, and a surface layer are sequentially stacked from the bottom around an outer periphery of a core metal (support member). The lower layer is a foamed sponge layer for reducing charging noise, and the surface layer is a protective layer provided to prevent leakage even if there are defects such as pinholes on the photoreceptor 1.

More specifically, the specification of the charging roller 2 in the present embodiment is as follows.
・ Core: Stainless steel rod with a diameter of 6 mm ・ Lower layer: Carbon-dispersed foamed EPDM, specific gravity 0.5 g / cm ³ , volume resistivity 10 ² to 10 ⁹ Ωcm, layer thickness 3.0 mm
Intermediate layer: carbon-dispersed NBR rubber, volume resistance value 10 ² to 10 ⁵ Ωcm, layer thickness 700 μm
Surface layer: tin oxide and carbon dispersed in a resin resin of fluorine compound, volume resistivity 10 ⁷ to 10 ¹⁰ Ωcm, surface roughness (JIS standard 10-point average surface roughness Ra) 1.5 μm, layer thickness 10 μm

  In addition, it is preferable to provide a member for removing toner and external additives attached to the surface of the charging roller 2. In this embodiment, a flexible cleaning film is provided as the member. This cleaning film is arranged in parallel to the longitudinal direction of the charging roller 2 and is fixed at one end to a support member that reciprocates a certain amount in the longitudinal direction. And is arranged to form a contact nip. The support member is driven by a drive motor (not shown) of the image forming apparatus 100 so as to reciprocate a certain amount in the longitudinal direction via a gear train, and the surface layer of the charging roller 2 is a cleaning film. Rubbed. As a result, deposits (fine toner, external additives, etc.) on the surface of the charging roller 2 are removed.

5. Cleaning Device Next, the cleaning device 6 in this embodiment will be described with reference to FIG.

  The cleaning device 6 includes a cleaning blade 61 supported by a sheet metal 65, a toner collection sheet 62, a waste toner collection container 63, a cleaning brush 64, a solid lubricant 66, and the like.

  A cleaning blade 61 as a cleaning member is integrally held at a front end portion of a sheet metal 65 as a support member. The cleaning blade 61 is a rectangular plate-like elastic member, and one end side in the short direction is fixed to the front end portion of the sheet metal 65 so that the longitudinal direction thereof is substantially parallel to the longitudinal direction of the photoreceptor 1. A free end, which is the other end in the short direction, is disposed so as to abut on the photoreceptor 1. In this embodiment, the cleaning blade 61 is in the counter direction with respect to the photoreceptor 1, that is, the free end that contacts the photoreceptor 1 with respect to the fixing portion with the sheet metal 65 is upstream in the moving direction of the surface of the photoreceptor 1. It is arranged to be located on the side. In this embodiment, the cleaning blade 61 is made of polyurethane rubber, and is in contact with the photoreceptor 1 with a predetermined amount of penetration and a set angle.

  The rubber hardness of the cleaning blade 61 is preferably 50 to 85 ° (JIS A), and more preferably 60 to 80 ° (JIS A).

  The contact pressure of the cleaning blade 61 is preferably 10 to 50 g / cm. When the contact pressure of the cleaning blade 61 is less than 10 g / cm, a cleaning failure due to toner slippage is likely to occur, and when it exceeds 50 g / cm, satisfactory durability is obtained due to wear of the cleaning blade 61. It becomes difficult.

  In this embodiment, a cleaning blade 61 made of urethane rubber having a rubber hardness of 70 ° (JIS A) is used, the setting angle is 25 °, and the penetration amount is in the range of 0.5 to 1.3 mm. The contact pressure to the body 1 was set to 25 g / cm.

  Here, as shown in FIG. 9, the “intrusion amount” of the cleaning blade 61 is a virtual amount in which the tip of the cleaning blade 61 has entered the photoreceptor 1 without being deformed (δ in FIG. 9). Further, as shown in FIG. 9, the “set angle” of the cleaning blade 61 is an angle formed by the cleaning blade 61 and a tangent line at the point where the tip of the cleaning blade 61 and the photosensitive member 1 intersect in the virtual state. (Θ in FIG. 9).

  The method for measuring the “contact pressure” of the cleaning blade 61 is as follows. Referring to FIG. 10, first, the cleaning blade 61 cut to a width of 1 cm is set on a blade base 93 that can be moved in the direction of the arrow by a motor 92, and the cleaning blade 61 is set to a desired setting angle. It abuts on the load sensor 94. Next, the blade base 93 is moved in the direction of the load sensor 94 by the amount of penetration desired to be obtained, and the output value of the load sensor 94 at that time is amplified by the amplifier 95 and read by the voltmeter 96. Then, the load per unit voltage obtained in advance is replaced with the linear pressure per unit length, and the value thus obtained is used as the contact pressure.

The cleaning brush 64 is disposed upstream of the cleaning blade 61 in the moving direction of the surface of the photoreceptor 1. The cleaning brush 64 is formed by weaving conductive fibers on a base fabric and winding it around a core metal having a diameter of 6 mm to form a brush shape having a diameter of 16 mm. In this example, as the conductive fiber, an acrylic conductive yarn having a thickness of 6 denier is used, and the fiber is implanted in a base fabric with a W weave so that the fiber density is 50000 / inch ^2, and is formed into a sheet shape. It is wound so as to ensure conduction with the cored bar. The cleaning brush 64 is in contact with the photoconductor 1 so that the amount of penetration into the photoconductor 1 is 1 mm and the contact width (Lnip) is 7 mm. The cleaning brush 64 is rotationally driven in the direction of the arrow R3 in the drawing at a predetermined peripheral speed. That is, the cleaning brush 64 rotates so as to move in the same direction as the photoconductor 1 at the contact portion between the photoconductor 1 and the cleaning brush 64 and rubs the photoconductor 1. The cleaning brush 64 is disposed such that its rotational axis is substantially parallel to the rotational axis of the photoreceptor 1.

  Here, as shown in FIG. 4, the “intrusion amount” of the cleaning brush 64 is a virtual amount that directly enters the photoconductor 1 without deformation of the brush portion of the cleaning brush 64 (I in FIG. 4). Further, the “contact width” of the cleaning brush 64 is a linear distance between intersections between the circumference formed by the tip of the cleaning brush 64 and the photosensitive member 1 in the virtual state (Lnip in FIG. 4).

  As the solid lubricant 66, zinc stearate, aluminum stearate, calcium stearate or the like is preferably used. In this example, a zinc stearate bar (manufactured by Konishi Seisakusho Co., Ltd.) was used. The zinc stearate bar is disposed so that its longitudinal direction is substantially parallel to the longitudinal direction of the photoreceptor 1. The zinc stearate bar is in contact with the cleaning brush 64 and is scraped off as the cleaning brush 64 rotates. When the rotating photoreceptor 1 and the cleaning brush 64 rub against each other, the zinc stearate on the cleaning brush 64 is applied to the surface of the photoreceptor 1. Thus, the cleaning brush 64 functions as a lubricant application unit. In this embodiment, the lubricant application unit is provided in the cleaning device 6 as the cleaning brush 64, but may be provided separately from the cleaning device 6.

  In this embodiment, the purpose of applying zinc stearate to the surface of the photoreceptor 1 is to reduce the amount of abrasion of the photoreceptor 1 and to improve durability by suppressing filming. Further, in order to keep the above effect without any harmful effects, it is necessary to peel off the zinc stearate film adsorbing the discharge product from the surface of the photoreceptor 1 and replace it with fresh zinc stearate as needed.

  When the lubricant film that adsorbs the discharge product remains on the surface of the photoreceptor 1, image flow occurs, or torque between the surface of the photoreceptor 1 and the cleaning blade 61 increases, resulting in poor cleaning. Drowning or damage to the cleaning blade may be induced.

  The zinc stearate film deteriorated by the discharge is usually scraped off by the cleaning blade 61 and replaced with new zinc stearate. However, after long-term use of the photoreceptor 1, the deteriorated zinc stearate is removed from the surface of the photoreceptor 1. It tends to remain on top. In order to remove the deteriorated zinc stearate film, it is effective to supply some kind of abrasive.

  In this regard, the inorganic fine powder having a cubic shape and / or a rectangular parallelepiped shape used as an external additive of the toner in this embodiment is particularly excellent in polishing performance. Therefore, this inorganic fine powder is rubbed by being interposed in the contact portion (cleaning blade nip portion) between the cleaning blade 61 and the photosensitive member 1 to quickly remove the deteriorated zinc stearate film from the photosensitive member 1. be able to.

  In addition, the deteriorated zinc stearate tends to be packed in a blocking layer portion composed of fine particles such as an external additive upstream of the cleaning blade nip portion. Here, the blocking layer is normally required to perform blade cleaning smoothly, and a small amount of fine particles such as an external additive forming the blocking layer passes through the cleaning blade, causing the blade to curl. Is preventing. Further, the presence of the blocking layer prevents the toner from directly entering the blade nip portion, and makes it difficult for the toner to slip through. If the movement of the external additive or the like forming the blocking layer is lost in the state where the blocking layer portion is packed, an appropriate amount of fine powder will not slip through, and the cleaning blade may be chattered or swollen. Therefore, it is necessary to loosen this packing state. In order to loosen it, it is effective to supply the cubic and / or rectangular parallelepiped inorganic fine powder used here to the cleaning blade nip portion.

  That is, in this embodiment, the purpose of supplying the inorganic fine powder to the cleaning blade 61 is, firstly, in the configuration in which the lubricant is applied to the surface of the photoreceptor 1, the image flow due to the remaining of the deteriorated lubricant film is generated. It is not generated. Secondly, a stable cleaning preventing layer is formed to obtain a stable cleaning performance in the long term.

  Here, one of the objects of the present invention is to provide a stable cleaning performance from start to finish even in the image forming apparatus 100 in which the lubricant is supplied to the surface of the photoreceptor 1 and the amount of applied toner increases. And fixing performance.

  Therefore, in this embodiment, a cubic and / or cuboid inorganic fine powder is externally added only to the transparent toner among the colored toner and the transparent toner. The transparent toner is supplied from the transparent image forming unit Pt to the cleaning devices 6a to 6d of the other colored image forming units Pa to Pd.

  That is, if the purpose is to supply the inorganic fine powder to the cleaning device 6, a method of supplying the inorganic fine powder directly to the cleaning device 6 of each image forming unit by externally adding the inorganic fine powder to each color toner is adopted. However, it is considered that the above-mentioned problems related to cleaning are solved.

  However, if inorganic fine powder is externally added to each color toner, the amount of the inorganic fine powder is increased when the color toners are superposed, which is not preferable. In particular, in a high-speed machine such as this embodiment, since the time for passing through the fixing nip is short, the toner must be fixed instantaneously. For this reason, it is desirable to reduce the amount of inorganic fine powder that would be disadvantageous for fixing properties as much as possible. Furthermore, in this embodiment, the image forming apparatus 100 is a full-color image forming apparatus equipped with a transparent image forming unit Pt, and in order to improve the glossiness and smoothness of the image, as shown in FIG. There will be more opportunities to increase overall. In this case, if inorganic fine powders are externally added to all color toners (including colored toners and transparent toners), the fixing property is disadvantageous.

  In addition, an inorganic fine powder is externally added to any one of the colored toners instead of the transparent toner, and the toner is used as a cleaning device for each image forming unit (including the colored image forming unit and the transparent image forming unit). 6 can be considered.

  However, it is difficult to completely stop the toner supplied to the cleaning device 6 with the cleaning blade 61, and the toner passes through the cleaning blade 61 although it is a very small amount. For this reason, toners of other colors may be mixed into the developing device 4. For example, in the contact two-component development as in this embodiment, such other colors of toner are likely to be mixed into the developing device 4. The mixing of other color toners into the developing device 4 causes disturbance in color reproducibility and causes a problem in the full color image forming apparatus. However, when the mixed color toner is a transparent toner, the amount is very large when the amount is small. Does not affect. In order to make it difficult to slip through the cleaning blade 61, a method of making the particle size of the transparent toner slightly larger than the particle size of the colored toner or reducing the circularity may be used.

  On the other hand, in order to avoid color mixing due to retransfer of colored toner into the transparent image forming portion Pt, the transparent image forming portion Pt is the most upstream image in the moving direction of the intermediate transfer belt 12 as in this embodiment. It is preferable to form a forming part. When the transparent image forming unit Pt is brought to the uppermost stream, it is easy to supply transparent toner to the image forming unit downstream thereof. Further, if the transparent image forming unit Pt is disposed at the most upstream, the secondary transfer roller 11 and the intermediate transfer member cleaning device 16 are detached from the intermediate transfer belt 12 in order to supply transparent toner to the image forming unit downstream thereof. You don't have to. Therefore, the transparent toner can be easily supplied to the downstream image forming unit.

6). Next, a specific method for supplying transparent toner to which the inorganic fine powder having a cubic shape and / or a rectangular parallelepiped shape is externally added to the color image forming portions Pa to Pd in the present embodiment is specifically described. explain.

  First, in the transparent image forming unit Pt, a predetermined electrostatic latent image (for example, with a predetermined width in the rotation direction of the photoreceptor 1) for forming a transparent toner image to be supplied to the colored image forming units Pa to Pd. A belt-like electrostatic latent image extending in the rotation axis direction of the photosensitive member 1 is formed. Next, the electrostatic latent image is developed with transparent toner by the developing device 4t. In this way, the negatively charged transparent toner supplied from the developing device 4t onto the photoreceptor 1t is applied with a positive polarity bias to the primary transfer roller 5t in the same manner as in the normal primary transfer step. Let them transcribe. Then, by applying a negative bias to the primary transfer roller 5 of the image forming unit to which the transparent toner is to be supplied, the transparent toner is transferred onto the photosensitive member 1 of the image forming unit, and the photosensitive member 1 is rotated. Accordingly, the transparent toner is supplied to the cleaning device 6 of the image forming unit. For example, when it is desired to supply transparent toner to the cleaning device 6a of the first color image forming unit Pa, a negative bias is applied to the primary transfer roller 5a of the first color image forming unit Pa. As a result, the transparent toner is transferred onto the photoreceptor 1a of the first color image forming portion Pa, and the transparent toner is supplied to the cleaning device 6a of the first color image forming portion Pa. Similarly, when it is desired to supply transparent toner to the cleaning devices 6b, 6c, 6d of the second to fourth colored image forming portions Pb, Pc, Pd, the second to fourth colored image forming portions Pb, Pc, A negative bias is applied to the primary transfer rollers 5b, 5c, and 5d of Pd.

  Incidentally, the bias applied to the primary transfer rollers 5a to 5d in order to transfer the following amount of transparent toner to the photoreceptors 1a to 1d of the colored image forming portions Pa to Pd requires high transferability. Because it is not, it is not necessary to set it to a very large value. For example, the primary transfer bias for primary transfer of transparent toner during image formation is about + 500V to + 1500V. On the other hand, the bias for transferring the transparent toner to the photoreceptors 1a to 1d in the colored image forming portions Pa to Pd is suitably about -200V to -1000V.

The timing for executing the supply operation of sending the transparent toner to the cleaning device 6 of each image forming unit is a period other than the time of image formation for forming an output image to be transferred to a recording material for output (before the image formation) Rotation, paper spacing, post-rotation, adjustment mode, etc.). Here, the pre-rotation is a preparatory operation that is performed by rotating the photosensitive member or the like before the output image forming operation. Further, the interval between the sheets is a period corresponding to the interval between the recording materials during the operation of forming continuous output images for a plurality of recording materials. Further, the post-rotation is an organizing operation performed by rotating the photoconductor after the output image forming operation. The adjustment mode is an adjustment operation such as image density adjustment or registration adjustment. In this embodiment, for every 50 image outputs on the recording material S, a transparent unit having a weight per unit area of 0.5 mg / cm ² over the entire image forming width in the direction substantially perpendicular to the moving direction of the surface of the photoreceptor 1. The toner is supplied for 1 cm in the moving direction of the surface of the photoreceptor 1.

  More specifically, four horizontal bands each having an image forming width of 1 cm are formed by the transparent image forming portion Pt and transferred onto the intermediate transfer belt 12. Then, at the timing when the leading horizontal band on the intermediate transfer belt 12 reaches the transfer portion of the yellow image forming portion Pa which is the closest image forming portion, −500 V is applied to the primary transfer roller 5a, and the photoreceptor 1a is applied. The transparent toner is transferred. At this time, the surface potential of the photoreceptor 1a is set to 0V. The bias is applied to the primary transfer roller 5a until the first horizontal band passes through the primary transfer nip N1a, and is cut off until the second horizontal band reaches. In this embodiment, the transparent toner is transferred to the respective photoconductors in the same manner, in which the second horizontal band is the magenta image forming portion Pb, the third is the cyan image forming portion Pc, the fourth is the black image forming portion Pd. .

  The following image evaluation was performed with the above configuration.

(1) Durability Test L Zone: Atmosphere Temperature 23 ° C, Atmosphere Humidity 5% RH Environment M Zone: Atmosphere Temperature 23 ° C, Atmosphere Humidity 50% RH Environment H Zone: Atmosphere Temperature 30 ° C, Atmosphere Humidity 80% The durability test was conducted in the above three environments under the RH environment. The test condition was a 50,000 sheet passing test in the 5-sheet intermittent mode. Here, the paper passing test is a test in which the operation of forming and outputting the following evaluation chart on the recording material S is repeated. The five-sheet intermittent mode is a mode in which a pause period is provided after five sheets are continuously printed.

  As the evaluation chart, one that is uniform in the longitudinal direction at an image ratio of 5% for each color was used.

  As evaluation items of durability, cleaning blade chipping, charging roller contamination due to slipping, and image flow were evaluated as items related to cleaning properties.

Here, as shown in FIG. 8, the cleaning blade chipping was evaluated based on the level of edge curling (blank) of the cleaning blade 61 and edge dropping of the cleaning blade 61 after the end of the durability test for 50,000 sheets. . Edge curling means that a part of the end surface 61A other than the edge portion 61B on the photosensitive member 1 side in the thickness direction on the end surface 61A on the free end side in the short direction of the cleaning blade 61 is damaged and missing. Further, the edge drop means that a part of the edge portion 61B is damaged and missing. As shown in FIG. 8, the maximum width in the thickness direction of the cleaning blade 61 at the portion missing due to edge curling or edge dropping is W (μm), and the width (depth) in the short direction of the cleaning blade 61. Is the maximum value of D (μm). Then, as the value of D × W, and if it is less than 50 [mu] m ² Evaluation A, rated at 50 to 100 [mu] m ² B, and greater than 100 [mu] m ² and evaluation C. These values are average values when five points are measured in the longitudinal direction of the cleaning blade 61. Evaluations A, B, and C are as follows.
A: Good durability performance was obtained.
B: Durability is somewhat difficult, but there is no practical problem. C: Durability is difficult.

The charging roller contamination was evaluated by forming an image using a charging roller subjected to a durability test under the above conditions. The following two types of evaluation images were used. One is developed directly by the charging roller 2 to the dark portion potential VD formed on the surface of the photoreceptor 1 (hereinafter referred to as analog HT). Specifically, the surface of the photoconductor is charged to about −600 V as the dark portion potential VD, and the developing sleeve is set to about −700 V to develop it to the dark portion potential VD. Under these conditions, the charging unevenness caused by the contamination of the charging roller is directly reflected in the image, so that the contamination can be evaluated under severe conditions. The other used a method of forming an image through normal image exposure (hereinafter referred to as digital HT). Both of the above images were adjusted so as to be halftone images having a reflection density measured by X-rite in the range of 0.3 to 0.6. The halftone image was evaluated in each color single color mode. The evaluation rank was judged as follows.
Rank A: Unevenness due to the charging roller does not appear in the image in analog HT.
Rank B: Streaks appear uneven in the analog HT, but the image does not appear in the digital HT.
Rank C: Unevenness occurs in the digital HT, which is a practical problem.

The image flow was evaluated by the image after the image forming apparatus was left for 2 days after endurance of paper passing. Evaluation images were digital HT and character images. The evaluation rank was judged as follows.
Rank A: The dots can be reproduced in the digital HT.
Rank B: In the digital HT having a reflection density of 0.3 or less, there is a region where the density is slightly lowered and the characters are slightly fine, but there is no practical problem.
Rank C: The character image is blurred, which is a practical problem.

Further, surface roughness and scratches on the surface of the photoreceptor 1 were observed with an optical microscope and evaluated with a digital HT. Evaluation A was given when there was no noticeable surface roughness or scratch in surface observation, and the digital HT image had no image defect due to the scratch. In addition, surface roughness and scratches were confirmed to some extent during surface observation, but evaluation B was given when there were no image defects due to surface roughness or scratches on the surface of the photoreceptor in a digital HT image. In addition, when a digital HT image shows an image defect due to surface roughness or scratches on the surface of the photoreceptor, the evaluation is C. Evaluations A, B, and C are as follows.
A: Good durability performance was obtained.
B: Durability is somewhat difficult, but there is no practical problem. C: Durability is difficult.

  The evaluation results are shown in Table 1.

(2) Fixability test A fixability test of a fixed image was performed as follows. The image obtained on the recording material S was rubbed with Silbon paper 10 times back and forth with a load of about 100 g, and peeling of the image was evaluated by the Macbeth reflection density reduction rate (%). That is, when an image density before rubbing of a fixed image (solid portion) is D1 and an image density after rubbing is D2, fixability F (density reduction rate) is expressed by the following equation:
F = (D1-D2) / D1 × 100 (%)
It is represented by

  In the fixability test, if the reduction rate of the reflection density of the image is 10% or less, the fixability is good. Also, if the reduction rate exceeds 20%, when the user is using the output image, the characters may be peeled off, the halftone image may be blurred, and in some cases, hands, clothes or other paper Since it may become dirty, it is not preferable.

The fixing test was performed in a low temperature and low humidity (5 ° C., 5% RH) environment. Further, the toner adhesion amount (mounting amount) per unit area on the recording material S in this fixing test was set to 1.5 mg / cm ² assuming the maximum loading amount in the full color mode. More specifically, the evaluation was made by superposing yellow, magenta, and cyan toners each at 0.5 mg / cm ² , and superposing black toner 0.5 mg / cm ² and transparent toner 1.0 mg / cm ^2. did.

The evaluation results are shown in Table 1. Evaluations A, B, and C are as follows. The results in Table 1 were the same for the colored image forming portions Pa to Pd of yellow, magenta, cyan, and black.
A: Good fixability was obtained. Concentration reduction rate is 10% or less.
B: Slightly difficult to fix but at a practical level. Range of concentration reduction rate of 10-20%.
C: There is difficulty in fixing. Concentration reduction rate is over 20%.

Comparative Example 1
In this example, 1.8 parts by weight of silica (amorphous, average particle diameter of about 20 nm) and 1.8 parts by weight of titanium oxide (amorphous, average particle diameter of about 20 nm) are used as the transparent toner with respect to 100 parts by weight of the toner. An externally added one was used.

  The other conditions were the same as in Example 1, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

  In this example, a transparent toner to which strontium titanate having a cubic shape and / or a rectangular parallelepiped shape and not externally added is used. For this reason, the zinc stearate film deteriorated by the discharge cannot be removed reliably, the cleaning performance becomes unstable, the charging roller is contaminated in the L zone, and the cleaning blade is missing in the H zone.

Comparative Example 2
In this example, as a colored toner, 1.8 parts by weight of silica and 1.8 parts by weight of titanium oxide with respect to 100 parts by weight of toner, the average particle diameter of primary particles is 110 nm, and the particle shape is cubic and / or rectangular parallelepiped. What added 3.0 weight part of strontium titanates was used. Further, as a transparent toner, in addition to 1.8 parts by weight of silica (indefinite shape, average particle size of about 20 nm) and 1.8 parts by weight of titanium oxide (indefinite shape, average particle size of about 20 nm) with respect to 100 parts by weight of the toner. In addition, an average primary particle diameter of 110 nm and a cubic and / or rectangular parallelepiped strontium titanate of 3.0 parts by weight were used.

  The other conditions were the same as in Example 1, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

  In this example, strontium titanate having a cubic shape and / or a rectangular parallelepiped shape is externally added to all image forming portions. For this reason, the total amount of inorganic fine powder is too large, and good fixability cannot be obtained.

Comparative Example 3
In this example, the transparent toner is 1.8 parts by weight of silica (amorphous, average particle size of about 20 nm) and 1.8 parts by weight of titanium oxide (amorphous, average particle size of about 20 nm) with respect to 100 parts by weight of the toner. In addition, a material obtained by adding 3.0 parts by weight of strontium titanate having an average primary particle size of 20 nm and a cubic and / or rectangular parallelepiped shape was used.

  The other conditions were the same as in Example 1, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

  In this example, the particle shape of strontium titanate having a cubic shape and / or a rectangular parallelepiped shape is 20 nm. Therefore, satisfactory polishing ability was not obtained, the zinc stearate film deteriorated by the discharge could not be removed reliably, and the cleaning blade chipped in the H zone occurred.

Comparative Example 4
In this example, the transparent toner is 1.8 parts by weight of silica (amorphous, average particle size of about 20 nm) and 1.8 parts by weight of titanium oxide (amorphous, average particle size of about 20 nm) with respect to 100 parts by weight of the toner. In addition, a material obtained by adding 3.0 parts by weight of strontium titanate having an average primary particle size of 310 nm and a cubic and / or rectangular parallelepiped shape was used.

  The other conditions were the same as in Example 1, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

  In this example, the particle shape of strontium titanate having a cubic shape and / or a rectangular parallelepiped shape is 310 nm. Therefore, in the L zone and the H zone, the polishing ability was too strong, the surface roughness of the photoreceptor 1 became severe, and scratches were generated in some places.

Comparative Example 5
In this example, the transparent toner is 1.8 parts by weight of silica (amorphous, average particle size of about 20 nm) and 1.8 parts by weight of titanium oxide (amorphous, average particle size of about 20 nm) with respect to 100 parts by weight of the toner. In addition, a material obtained by adding 3.0 parts by weight of strontium titanate having an average primary particle size of 110 nm and an irregular particle shape was used.

  The other conditions were the same as in Example 1, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

  In this example, strontium titanate having an irregular particle shape is used. Therefore, satisfactory polishing ability was not obtained, the zinc stearate film deteriorated by the discharge could not be removed reliably, and the cleaning blade chipped in the H zone occurred.

Example 2
In this embodiment, a colored toner is used in which 1.6 parts by weight of silica and 1.6 parts by weight of titanium oxide are added to 100 parts by weight of the toner. Further, as a transparent toner, in addition to 1.6 parts by weight of silica (indefinite shape, average particle size of about 20 nm) and 1.6 parts by weight of titanium oxide (indefinite shape, average particle size of about 20 nm) with respect to 100 parts by weight of the toner. In addition, a material obtained by adding 3.0 parts by weight of strontium titanate having an average primary particle size of 110 nm and a cubic and / or cuboid particle shape was used.

  The other conditions were the same as in Example 1, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

  In this embodiment, the total amount of external addition is 3.8 parts by weight with respect to 100 parts by weight of the toner, which is smaller than 4.2 parts by weight of Example 1. Thus, by further reducing the total amount of external addition, better fixability was obtained.

  Here, the calculation method of the “total external addition amount (with respect to 100 parts by weight of toner)” is as follows. In the case of this embodiment, since the yellow toner is 1.6 parts by weight of silica and 1.6 parts by weight of titanium oxide, the total amount is 3.2 parts by weight. Similarly, it is 3.2 parts by weight for magenta toner, 3.2 parts by weight for cyan toner, and 3.2 parts by weight for black toner. Further, in the transparent toner, the particle shape is 6.2 parts by weight since 3.0 parts by weight of strontium titanate having a cubic shape and / or a rectangular parallelepiped shape is added. The total of these is 19.0 parts by weight, which is the amount for 500 parts by weight of toner. This is equivalent to 3.8 parts by weight per 100 parts by weight of toner.

  As described above, the total amount of all the toners including the color toner and the transparent toner used in the image forming apparatus 100 is preferably 4.0 parts by weight or less with respect to 100 parts by weight of the toner.

Example 3
In this embodiment, as the colored toner, one obtained by adding 1.5 parts by weight of silica and 1.5 parts by weight of titanium oxide to 100 parts by weight of the toner was used. Further, as a transparent toner, in addition to 1.5 parts by weight of silica (amorphous, average particle size of about 20 nm) and 1.5 parts by weight of titanium oxide (amorphous, average particle size of about 20 nm) with respect to 100 parts by weight of the toner. In addition, a material in which 2.0 parts by weight of strontium titanate having an average primary particle size of 110 nm and a cubic and / or rectangular parallelepiped shape was used.

  The other conditions were the same as in Example 1, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

  In this embodiment, the total amount of external addition is 3.4 parts by weight with respect to 100 parts by weight of the toner, which is smaller than 4.2 parts by weight of Example 1. Thus, by further reducing the total amount of external addition, better fixability was obtained. Further, other durability such as developability was also good.

Example 4
In this embodiment, a protective layer is provided on the surface of the photoreceptor 1 of the color image forming portions Pa to Pd. As the protective layer on the surface of the photoreceptor 1, a surface layer containing a compound obtained by polymerizing a hole transporting compound represented by the following chemical formula (2) by electron beam irradiation was applied and cured.

  A surface obtained by dissolving 45 parts of this hole transporting compound in 55 parts of n-propyl alcohol, adding 5 parts by weight of tetrafluoroethylene fine particles, and dispersing with a high-pressure disperser (Microfluidizer, manufactured by Microfluidics). The protective layer paint was prepared. After applying this coating material on the three-layer photoconductor of Example 1, an electron beam was irradiated under the conditions of an acceleration voltage of 150 KV and a dose of 40 kGy to form a protective layer having a thickness of 3 μm to obtain an electrophotographic photoconductor.

  The wear resistance of the surface of the photoreceptor was evaluated as follows. The Taber abrasion test method was used as a method for evaluating the abrasion resistance of the surface of the photoreceptor. That is, a sample is mounted on a sample stage of a Taber abrasion tester (YSS Taber manufactured by Yasuda Seisakusho). A load of 500 g was applied to each rubber wear wheel (CS-0) with wrapping tape (Fuji Photo Film product name: C2000) on the two surfaces, and the weight loss of the sample after 1000 revolutions was applied to the precision balance. To measure.

  When the Taber abrasion test was conducted on the photoreceptor 1 of this example, it was 0.5 (mg / 1000 rotations). On the other hand, when the Taber abrasion test was done about the photoreceptor 1 used in Example 1, it was 3.0 (mg / 1000 rotation).

  In addition, this surface layer (protective layer) is not limited to that of the present embodiment, and at least polymerized or crosslinked and cured by any one of heat, light, and radiation can be suitably used.

  By using the protective layer on the surface of the photoconductor 1 as in this embodiment, the photoconductor 1 can be prevented from being scraped, and further high durability can be achieved. However, usually, if the wear rate of the photosensitive member 1 is kept low, discharge products, paper dust, and the like accumulate on the surface of the photosensitive member 1, and image quality degradation such as image flow tends to be a problem under high temperature and high humidity.

  On the other hand, in this embodiment, since zinc stearate is applied to the surface of the photoconductor 1 of the colored image forming portions Pa to Pd, the image flow is achieved while using the photoconductor 1 having a low wear rate. Can be suppressed.

  On the other hand, in this embodiment, no protective layer is provided on the surface of the photosensitive member 1 of the transparent image forming portion Pt. However, in this embodiment, the transparent image forming unit Pt is a cleanerless system as shown in FIG. Thereby, further high durability is achieved also in the transparent image forming part Pt.

  Thus, in terms of extending the life of the photoreceptor 1 in the image forming apparatus 100, the surface of the photoreceptor 1 of the colored image forming portions Pa to Pd is polymerized, crosslinked, or cured by at least one of heat, light, and radiation. It is preferable to have a layer. The photosensitive member 1 of the transparent image forming portion Pt preferably has no surface layer, and the transparent image forming portion Pt is preferably a cleanerless system.

  Here, the cleanerless system is such that the cleaning blade is removed, and the transfer residual toner on the photosensitive member is removed from the photosensitive member by “development simultaneous cleaning” by the developing means, and collected and reused in the developing means. This is the device configuration. “Development simultaneous cleaning” means that toner slightly remaining on the photosensitive member after transfer is subjected to fog removal bias (potential difference between the DC voltage applied to the developing means and the surface potential of the photosensitive member) during the development after the next step. This is a method of collecting by a certain fog removal potential difference Vback). According to this method, since the transfer residual toner is collected by the developing means and used after the next step, waste toner can be eliminated. Therefore, the cleanerless system is preferable because the toner consumption can be reduced in the transparent image forming portion where the amount of the transparent toner used for supplying to the other image forming portion is increased.

  In the tandem type image forming apparatus, when a cleanerless system is used in an image forming unit downstream of a certain image forming unit in the moving direction of the transfer object, in the image forming unit using the cleanerless system, It is easy to cause color variation. In other words, when the toner image formed on the transfer medium in the upstream image forming section passes through the image forming section that employs a cleanerless system located downstream thereof, the cleanerless system is employed due to the retransfer phenomenon. Return to the photoreceptor of the image forming unit. This toner image is taken into the developing device by the cleanerless system and tends to cause color fluctuation. Accordingly, also in the present embodiment, as in the first embodiment, the transparent image forming portion Pt is arranged at the most upstream in the moving direction of the intermediate transfer belt 12.

  In this embodiment, the transparent image forming portion Pt, which is a cleanerless system, is configured such that no lubricant is applied to the photoreceptor 1. This is due to the following reason. First, since there is no cleaning blade, the wear of the photoreceptor 1 can be greatly reduced without applying a lubricant. Second, when a lubricant such as zinc stearate is applied, there is no way to remove the lubricant film that has deteriorated due to electric discharge, which may cause image quality degradation such as image flow. It is.

  The other conditions were the same as in Example 2, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

  In this example, there was no problem in both durability and fixing performance, and the consumption of the transparent toner could be suppressed as compared with Example 2.

Example 5
In this embodiment, the transparent image forming portion Pt is a cleanerless system, and a toner discharge / collection mode described below is further provided.

  In this embodiment, as shown in FIG. 7, the transparent image forming portion Pt is provided with first and second auxiliary charging members 7t and 8t as auxiliary charging means.

  The first and second charging auxiliary members 7t and 8t are disposed downstream of the primary transfer portion N1t in the moving direction of the surface of the photoreceptor 1t and upstream of the charging portion of the photoreceptor 1t by the charging roller 2t. Is done. The first and second auxiliary charging members 7t and 8t respectively contact the photosensitive member 1t in the order of the first auxiliary charging member 7t and the second auxiliary charging member 8t from the upstream side in the movement direction of the surface of the photosensitive member 1t. Arranged in contact. The first auxiliary charging member 7t has a function as a residual toner uniformizing unit, and the second auxiliary charging member 8t has a function as a toner charge amount control unit.

  In this embodiment, brush members made of conductive fibers are used as the first and second charging auxiliary members 7t and 8t. A predetermined voltage is applied to the first and second auxiliary charging members 7t and 8t from an auxiliary charging bias power source (not shown) as voltage applying means.

The brush portions of the first and second auxiliary charging members 7t and 8t are formed by adding carbon or metal powder to fibers such as rayon, acrylic and polyester to control the electric resistance value. The brush part preferably has a thickness of 30 denier or less and a density of 1 to 500,000 / inch ² or more so that the surface of the photoreceptor 1t and the transfer residual toner can be uniformly contacted. In this embodiment, the brush portions of the first and second charging auxiliary members 7t and 8t are both 6 denier, 100,000 pieces / inch ² , the length of the bristle leg is 5 mm, and the volume resistivity of the brush is 6 × 10. ³ Ω · cm. Then, the first and second auxiliary charging members 7t and 8t were brought into contact with the photoconductor 1t so that the brush portion had an intrusion amount of 1 mm with respect to the surface of the photoconductor 1t. The width of the contact nip between the brush portion and the photoreceptor 1t in the moving direction of the surface of the photoreceptor 1t was 5 mm. The first and second auxiliary charging members 7t and 8t were reciprocated with an amplitude of 2.5 mm and a frequency of 2.0 Hz in the rotation axis direction of the photoreceptor 1t.

  Here, the “intrusion amount” of the first and second auxiliary charging members 7t and 8t is a virtual amount that has directly entered the photoconductor 1t without deformation of the respective brush portions. The “contact width” of the first and second auxiliary charging members 7t and 8t is the photosensitive region in the contact area with the photosensitive member 1t at the tip of each of the first and second auxiliary charging members 7t and 8t. It is a linear distance between the upstream end portion and the downstream end portion in the moving direction of the surface of 1t.

  Usually, the untransferred toner remaining on the photoreceptor 1t after the primary transfer step includes negative polarity toner (normal polarity toner) and positive polarity toner (reverse polarity toner). In this embodiment, the transfer residual toner in which the normal polarity toner and the reverse polarity toner are mixed is collected by the first auxiliary charging member 7t, so that the transfer residual toner is basically present in the charging portion. Prevent it from being sent. For this purpose, the condition of the voltage applied to the first auxiliary charging member 7t is set so as to enhance the recoverability of the transfer residual toner. In this embodiment, an alternating voltage on which a direct voltage is superimposed is applied to the first auxiliary charging member 7t at the time of image formation. By applying an AC voltage to the first auxiliary charging member 7t, the ability to electrostatically collect the transfer residual toner on the photoreceptor 1t is improved. Further, a DC voltage having a polarity opposite to the normal charging polarity of the toner is applied to the first charging auxiliary member 7t in a manner superimposed on the AC voltage. As a result, the electrostatic latent image on the photoreceptor 1t is neutralized to prevent positive ghosting.

  Further, a negative voltage having the same polarity as the normal charging polarity of the toner is applied to the second auxiliary charging member 8t during image formation. This is to prevent the charging roller 2t from being soiled by the toner slightly slipping from the first charging auxiliary member 7t. In this embodiment, a DC voltage of −700 V or higher, which is equal to or higher than the discharge start voltage, is applied to the second charging auxiliary member 8t. As a result, the toner passing through the first charging auxiliary member 7t and reaching the second charging auxiliary member 8t is charged to a negative polarity (normal polarity) by sufficient discharge. In other words, the polarity of the toner passing through the second auxiliary charging member 8t is uniformly aligned to the negative polarity.

  Thereafter, in the charging process, the surface of the photoreceptor 1t is charged from the transfer residual toner that has passed through the second auxiliary charging member 8t. In this case, since the polarity of the transfer residual toner is uniformly made negative by the second charging auxiliary member 8t, the toner does not adhere to the charging roller 2t. Further, the charged charge of the transfer residual toner is appropriately neutralized by the AC bias applied to the charging roller 2t.

  Subsequently, in the exposure process by the exposure device 3t in the exposure unit, exposure is performed from above the transfer residual toner. However, since the amount of transfer residual toner is small, the transfer residual toner is a transparent toner. The influence of the presence of the transfer residual toner does not appear.

  Then, the untransferred toner is collected from the photoreceptor 1t into the developing device 4c by simultaneous development cleaning at the contact portion (developing portion) between the developing sleeve of the developing device 4t and the photoreceptor 1t.

  As described above, in the transparent image forming portion Pt, the transfer residual toner that is not transferred at the time of image formation and remains on the surface of the photoreceptor 1t is collected by the first auxiliary charging member 7t that is in contact with the photoreceptor 1t. Yes. Therefore, the toner is collected on the first charging auxiliary member 7t. If the toner collected on the first auxiliary charging member 7t is accumulated as it is, the toner collecting ability and toner charging ability of the first auxiliary charging member 7t are hindered.

  Further, the second charging auxiliary member 8t brought into contact with the photosensitive member 1 on the downstream side of the first charging auxiliary member 7t in the moving direction of the surface of the photosensitive member 1t is also transferred by passing through the first charging auxiliary member 7t. Not a little toner is collected. If the toner collected by the second auxiliary charging member 8t is accumulated as it is, the toner charging ability of the second auxiliary charging member 8t is hindered.

  Therefore, in this embodiment, control is performed to discharge toner from the first and second auxiliary charging members 7t and 8t to the non-image area of the photoreceptor 1t.

  First, as a pre-operation in which toner is discharged from the first and second auxiliary charging members 7t and 8t substantially simultaneously, the voltage applied to the charging roller 2t is only an AC voltage, and the potential of the photoconductor 1t is set to approximately 0V. Performs a leveling action. Then, the voltage applied to the first and second auxiliary charging members 7t and 8t is controlled to the toner discharge voltage. This toner discharge voltage is controlled to a voltage (± 300 V in the present embodiment) that is approximately 0 V so that the surface potential of the photoreceptor 1 t does not fluctuate. Further, the potential of the charging roller 2t with respect to the surface of the photoreceptor 1t from which the toner has been discharged is set to approximately 0V. As a result, the toner discharged from the first and second charging auxiliary members 7t and 8t, in which normal polarity toner and reverse polarity toner are mixed, is allowed to pass through the charging unit without adhering to the charging roller 2t. Is possible. That is, contamination of the charging roller 2t by toner discharged from the first and second auxiliary charging members 7t and 8t can be prevented, and occurrence of image defects due to toner contamination of the charging roller 2t can be reduced. .

  Here, the toner discharge voltage applied to the first and second auxiliary charging members 7t and 8t and having a surface potential of the photoreceptor 1t of about 0 V by the toner discharge operation does not fluctuate is charged during image formation. The voltage is preferably not more than the starting voltage.

  The toner discharged from the first and second auxiliary charging members 7t and 8t to the non-image area of the photoreceptor 1t is carried to the developing unit by the rotation of the photoreceptor 1t. The toner conveyed to the developing unit should basically be collected by the developing device 4t. However, when the amount of discharged toner is large, some toner cannot pass through the developing device 4t and passes through the developing portion as it is.

  Therefore, in this embodiment, the toner discharged from the first and second auxiliary charging members 7t and 8t passes from the transparent image forming unit Pt to each of the colored image forming units Pa to Pd in accordance with the timing when the toner passes through the developing unit. The supplied transparent toner is supplied from the developing device 4t onto the photoreceptor 1t. As a result, the toner discharged from the first and second auxiliary charging members 7t and 8t is also simultaneously supplied from the transparent image forming portion Pt to each of the colored image forming portions Pa to Pd and used effectively.

  In the transparent image forming portion Pt of the cleanerless system, the toner is discharged from the first and second auxiliary charging members 7t and 8t to the photoreceptor 1t at the following timing. That is, the toner discharged to the non-image area of the photoconductor 1t when a non-image area other than the area on the photoconductor 1t where the image to be primarily transferred onto the intermediate transfer belt 12 is formed reaches the primary transfer portion N1t. At a timing at which the toner image can be transferred onto the intermediate transfer belt 12.

  The transparent toner to be supplied to the colored image forming portions Pa to Pd transferred to the non-image area of the intermediate transfer belt 12 as described above is downstream of the transparent image forming portion Pt as the intermediate transfer belt 12 moves. It is carried to the colored image forming portions Pa to Pd. Here, the toner transferred from the photoreceptor 1t of the transparent image forming portion Pt to the non-image area of the intermediate transfer belt 12 is the toner discharged from the first and second auxiliary charging members 7t and 8t onto the photoreceptor 1t. And toner supplied from the developing device 4t onto the photoreceptor 1t. And it collect | recovers on the photoreceptors 1a-1d in the primary transfer part N1a-N1d of the color image formation parts Pa-Pd. The transparent toner collected on the photoreceptors 1a to 1d is supplied to the cleaning devices 6a to 6d as the photoreceptors 1a to 1d rotate.

  In this embodiment, the transparent toner to be supplied to the color image forming portions Pa to Pd transferred to the intermediate transfer belt 12 is charged to a negative polarity having a normal charging polarity. In order to supply the transparent toner to the cleaning devices 6a to 6d of the color image forming portions Pa to Pd, regular toner applied to the primary transfer rollers 5a to 5d of the color image forming portions Pa to Pd during normal image formation is used. A bias having a polarity opposite to that of the bias is applied. Note that the amount of transparent toner supplied to the cleaning devices 6a to 6d of the respective color image forming portions Pa to Pd is the same as that of the first embodiment and is not so large. Therefore, it is not necessary to set the reverse polarity bias applied to the primary transfer rollers 5a to 5d of the colored image forming portions Pa to Pd to a very large value.

  As described above, in this embodiment, the transparent image forming unit Pt includes the charging auxiliary means 7t and 8t that collect the toner on the photoreceptor 1t and charge it with the same polarity as the toner for developing the electrostatic image. Yes. In addition, during the period other than the time when the output image is formed, an operation of discharging the collected toner onto the photoconductor 1t from the auxiliary charging means 7t and 8t is performed. The discharged toner is supplied to the cleaning devices 6a to 6d of the color image forming portions Pa to Pd via the intermediate transfer belt 12.

  The other conditions were the same as in Example 4, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

  In this example, good durability and fixing performance were obtained in any environment.

  In this embodiment, the toner collected by the first and second charging auxiliary members 7t and 8t is discharged to the intermediate transfer belt 12. In addition to this, forcible development of unnecessary toner, such as reversal toner charged to a polarity opposite to the normal charging polarity or toner having a low charge amount, included in the developing device 4t of the transparent image forming unit Pt. It is also possible to adopt a configuration for discharging from the device 4t onto the photoreceptor 1t. The discharged transparent toner can be supplied to each of the color image forming portions Pa to Pd. In order to discharge the toner as described above from the developing device 4t, the potential of the developing sleeve may be set on the reverse toner polarity side with respect to the charging potential of the surface of the photoreceptor. For example, when the reversal toner is positive (positive polarity), the reversal toner flies to the surface side of the photoreceptor when the surface potential of the photoreceptor is uniformly −600 V and the developing sleeve potential is −450 V. In order to discharge more positively, an AC component (for example, 2 KVpp) may be superimposed on the developing bias.

  In the present embodiment, the first and second charging auxiliary members 7t and 8t are deck brush-shaped ones. However, the shape is not limited to this, and the same effect can be obtained. For example, a roll brush may be used. Further, the bias value to be controlled is not limited to the numerical value of this embodiment, and good charging performance and discharge performance can be obtained, and transparent toner can be supplied to the colored image forming portions Pa to Pd without any problem. I just need it.

Example 6
In this embodiment, the discharge current of the charging roller 2t of the transparent image forming unit Pt is set to a so-called sandy fog generation region where the macro potential on the surface of the photoreceptor 1t is a stable region and the micro potential is an unstable region.

  When the discharge current setting is increased, the amount of ozone generated increases, and discharge products (such as NOx) adhering to the surface of the photoreceptor 1 and the surface of the charging roller 2 increase. As a result, the surface of the charging roller 2 becomes more sticky, the adhesion of external additives and toner increases, and the surface becomes easily contaminated. The surface of the photoconductor 1 is liable to cause image flow and filming, and at the same time, molecular bonds on the surface of the photoconductor 1 are broken or weakened by discharge energy, and wear of the photoconductor 1 is promoted. The From this point of view, it is better to set the discharge current as low as possible. However, the lower limit value of the discharge current usually has to be set in an area where sandy fog does not occur.

However, in the transparent image forming portion Pt, even if the discharge current of the charging roller 2t is set in the sandy fog generation region, the transparent toner is colorless and transparent, so that the image characteristics are not affected. In this embodiment, the discharge current of the charging roller 2t of the transparent image forming unit Pt was set as follows.
L zone: 50 μA
M zone: 20 μA
H zone: 15 μA

  As described above, the charging means for charging the photosensitive member 1 of the transparent image forming portion Pt is a roller-shaped charging member (charging roller) 2t that is close to or in contact with the photosensitive member 1t, and an AC voltage is superimposed on the DC voltage. By applying the bias, the photosensitive member 1t is charged. In this embodiment, the amount of discharge current generated between the charging roller 2t and the photosensitive member 1t when a bias is applied to the charging roller 2t is set so that the surface to be charged of the photosensitive member 1t has a substantially constant charging potential. Although charging can be performed, control is performed within a range where a region where the charging potential is unstable is generated locally.

  The other conditions were the same as in Example 2, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

  In this example, good durability and fixing performance were obtained in any environment.

  Compared with Example 2, the level of adhesion of the external additive on the surface of the charging roller 2t of the transparent image forming portion Pt was good. Also, the wear of the photoreceptor 1t was reduced. According to this embodiment, the lifetime of the transparent image forming portion Pt can be further extended.

Example 7
In the present embodiment, as in the sixth embodiment, the discharge current of the charging roller 2t of the transparent image forming portion Pt is set in the sandy fog generation region. In this embodiment, the discharge current of the charging roller 2t of the transparent image forming unit Pt was set as follows.
L zone: 50 μA
M zone: 20 μA
H zone: 15 μA

  Other conditions were the same as in Example 5, and the same evaluation as in Example 1 was performed.

  In this example, good durability and fixing performance were obtained in any environment.

  Further, compared to Example 5, the level of external additive adhesion on the surface of the charging roller 2t of the transparent image forming portion Pt was further improved. Even when the transparent image forming portion Pt employs a cleanerless system, according to the present embodiment, the lifetime of the transparent image forming portion Pt can be further extended, and a stable image can be formed in the long term. .

  As described above, according to the present invention, image cleaning / filming can be achieved even when a highly durable photoconductor is used after a stable cleaning is performed with a lubricant applied to the surface of the photoconductor. Occurrence is prevented and stable image characteristics can be maintained at a high level.

1a to 1d, 1t photoconductor (image carrier, electrophotographic photoconductor)
2a to 2d, 2t charger (charging means)
3a to 3d, 3t exposure apparatus (exposure means)
4a to 4d, 4t Developing device (developing means)
5a to 5d, 5t primary transfer roller (primary transfer means, transfer means)
12 Intermediate transfer belt (intermediate transfer member)

Claims (5)

An image carrier on which an electrostatic image is formed, a developing device that supplies colored toner to the electrostatic image on the image carrier to form a toner image, and a toner image formed on the image carrier. A colored image forming unit comprising: transfer means for transferring to a transfer body; a cleaning device for removing toner on the image carrier; and a lubricant application means for applying a lubricant to the surface of the image carrier;
An image carrier on which an electrostatic image is formed, a developing device for supplying a transparent toner to the electrostatic image on the image carrier to form a toner image, and a toner image formed on the image carrier. A transparent image forming section comprising a transfer means for transferring to a transfer body;
An intermediate transfer body as the transfer body onto which a toner image is transferred from the image carrier of the colored image forming section and the transparent image forming section;
Have
The toner images formed on the image carriers of the color image forming unit and the transparent image forming unit are sequentially transferred to the intermediate transfer unit by the transfer units of the color image forming unit and the transparent image forming unit, respectively. In an image forming apparatus capable of forming an output image for transfer and output from the intermediate transfer body to a recording material by transferring onto the body,
The transparent toner is externally added with an inorganic fine powder having an average particle size of 30 nm to 300 nm and a particle shape of cubic and / or rectangular parallelepiped,
In a period other than when the output image is formed, the transparent toner is transferred from the image carrier of the transparent image forming unit to the intermediate transfer member, and the transparent toner is transferred from the intermediate transfer member to the colored image forming unit. An image forming apparatus that performs a supply operation of transferring the transparent toner to a cleaning device of the colored image forming unit after being transferred to an image carrier.   2. The total amount of all external toners including the colored toner and the transparent toner used in the image forming apparatus is 4.0 parts by weight or less with respect to 100 parts by weight of the toner. The image forming apparatus described in 1.   The image carrier of the colored image forming unit has a surface layer that is polymerized or crosslinked and cured by at least one of heat, light, and radiation, and the image carrier of the transparent image forming unit includes The image forming apparatus according to claim 1, wherein the image forming apparatus has no surface layer, and the transparent image forming unit is a cleanerless system.   The transparent image forming unit has charging auxiliary means for collecting toner on the image carrier and charging the electrostatic image with the same polarity as the toner for developing the electrostatic image. An operation of discharging the collected toner onto the image carrier from the charging assisting unit during a period is performed, and the discharged toner is supplied to the cleaning device of the colored image forming unit via the intermediate transfer member. The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus.   The charging means for charging the image carrier of the transparent image forming unit is a roller-shaped charging member that is close to or in contact with the image carrier, and applies a bias in which an AC voltage is superimposed on a DC voltage to the charging member. As a result, the image carrier is charged, and the amount of discharge current generated between the charging member and the image carrier when the bias is applied to the charging member is determined by the charge of the image carrier. The image according to any one of claims 1 to 4, wherein the processing surface can be charged to a substantially constant charging potential, but is controlled within a range where a region where the charging potential is unstable is locally generated. Forming equipment.

Images