JP6569290B2 - Image forming method and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming method and an image forming apparatus.

  As one of techniques for forming a high-value-added image, it is known to form a transparent layer on a color image by an electrophotographic image forming apparatus. Such a high value-added image is formed, for example, by overlapping and fixing a color toner image for a color image and a transparent toner image for a transparent layer formed thereon.

  The technology for forming an image by combining such a color image and special toner includes, for example, a normal color toner (first image forming unit) and a special toner (second image forming unit). There is known an image forming apparatus having means for determining the type of toner (transparency, whiteness, electrical resistance level, etc.) and changing the order of image formation. In the image forming apparatus, for example, when the special color toner is determined to be a low-resistance toner rather than a normal color toner, the image formation order is changed so that the low-resistance toner is finally transferred to the intermediate transfer member. Is done. In addition, the color image is stabilized immediately before using the special toner (see, for example, Patent Document 1).

  As a technique using special toner in the image forming apparatus, for example, it is known to load dummy toner into a process cartridge. As a result, the process cartridges are not distinguished by the colors of Y, M, C, and K, the process cartridges are made common, the inventory management cost is reduced, and the number of parts is reduced, for example, the manufacturing cost is reduced, and the replacement error is made. Reduction and the like. Examples of the dummy toner include various special toners such as a toner coated with conductive fine particles, a toner having a low electric resistance, and a transparent toner. The dummy toner is replaced with color toner conveyed from the toner bottle in the process of image formation (see, for example, Patent Document 2).

JP 2008-020882 A JP 2005-055832 A

  In recent years, high-value-added printing by electrophotography has become common, and the development of the image forming apparatus in the production printing market in which output products are handled as commodities has progressed, and the demand for improved productivity is also increasing.

  However, if the above-described mechanism for forming a high-value-added image is used as it is in an image forming apparatus for general use, in addition to the conventional YMCK 4-color toner, transparent toner, white toner, bright toner, and the like are used for image formation. Therefore, the toner layer on the recording medium becomes thick. For this reason, the recording media (printed materials) after forming the images are easily stuck immediately after being discharged from the image forming apparatus. When the printed matter sticks, image conveyance failure may occur in the post-processing machine, or each page may stick when binding is performed.

  An object of the present invention is to provide an image forming method and an image forming apparatus capable of preventing sticking of recording media on which images formed by stacking a plurality of toner layers are formed.

  The present invention relates to an image forming method for forming an image forming layer in which a second toner is disposed on a first toner image formed by first toner particles for image formation on a recording medium. An image forming method is provided in which toner particles having a volume resistivity lower than that of the first toner particles are used as the toner particles.

  In addition, the present invention provides a first process unit for forming a first toner image on the recording medium with first toner particles for image formation, and a first process unit covering the first toner image on the recording medium. Forming a second toner image with second toner particles, and forming an image forming layer in which the second toner is disposed on the first toner image In the apparatus, there is provided an image forming apparatus, wherein the volume resistivity of the second toner particles is lower than the volume resistivity of the first toner particles.

  According to the present invention, since a lower resistance toner layer is formed on the surface of the formed image, charge accumulation in the recording medium on which the image is formed is suppressed. As a result, in an image forming method or an image forming apparatus capable of forming an image having the image forming layer, sticking between recording media having the image forming layer on which an image having a higher added value is formed is prevented. be able to.

1 is a diagram schematically illustrating a configuration of an example of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows typically the method of measuring the sticking force in an Example.

Hereinafter, embodiments of the present invention will be described from an image forming apparatus.
The image forming apparatus according to the present embodiment includes a first process unit for forming a first toner image with first toner particles for image formation on a recording medium, and the first process unit on the recording medium. And a second process unit for forming a second toner image covering the toner image with the second toner particles. Thus, the image forming apparatus is an apparatus capable of forming an image forming layer. The image forming layer is a layered structure of these toners in which the second toner is arranged in a layer form on the first toner image.

  In the present invention, the toner includes toner particles, and the toner particles include a binder resin, and optionally a toner base particle that may include a colorant, and an outer surface that adheres to the surface. With additives. The toner may be a one-component developer composed only of toner particles or a two-component developer further containing carrier particles.

  The first toner particles are toner particles for forming an image to be formed on a recording medium. The first toner particles may be one kind or more. Color toner particles that can be used in an electrophotographic image forming method can be used as the first toner particles.

  The first toner image is an aggregate of the first toner particles arranged according to an image to be formed. The first toner image may be finally formed on the recording medium below the second toner image described later (on the recording medium side). For example, at the stage where the second toner is disposed, The image may be an image fixed on the recording medium or an image unfixed on the recording medium. Further, the first toner image may be an image to be disposed on the surface of the recording medium, and may be an image formed on the intermediate transfer member, for example.

  The first process unit is an apparatus for forming the first toner image so as to be disposed on the surface of the recording medium or to be disposed. The first process unit is, for example, a process cartridge for forming an image of color toner particles such as yellow (Y), magenta (M), cyan (C), black (Bk), or a plurality of groups thereof. Alternatively, a device group including these and a fixing device for fixing the image of the color toner particles on the recording medium.

  The second toner particles are toner particles for forming a layer covering the first toner image on the recording medium. In the range where the second toner particles satisfy the following requirements for volume resistivity, the toner base particles can be constituted simply by the binder resin particles. The second toner particles may be one kind or more. Examples of the second toner particles include transparent toner particles and white toner particles. The “transparent toner” particles are toner particles that do not contain a colorant (including a white colorant). The transparent toner image may have absorption by a material other than a colorant such as a binder resin and an additive in the toner particles.

The volume resistivity of the second toner particles is lower than the volume resistivity of the first toner particles. The first toner particles have a predetermined volume resistivity for providing electrical characteristics suitable for forming an image by electrophotography. For example, the volume resistivity of the first toner particles is usually 1.0 × 10 ^{14 to} 1.0 × 10 ¹⁹ Ω · cm.

  If the ratio R1 / R2 of the volume resistivity R1 of the first toner particles to the volume resistivity R2 of the second toner particles is too small, the effect of preventing electrostatic sticking between printed materials is insufficient. If it is too large, it may be difficult to apply to the electrophotographic system, the production of the second toner particles may be complicated, or the volume resistivity of the second toner particles may be difficult to control. From these viewpoints, R1 / R2 is preferably 10 or more, more preferably 50 or more, and further preferably 100 or more. Further, from the above viewpoint, R1 / R2 is preferably 10,000 or less, more preferably 5000 or less, and even more preferably 1000 or less.

Alternatively, from the above viewpoint, R2 is preferably 1.0 × 10 ¹³ Ω · cm or more and more preferably 1.0 × 10 ¹⁴ Ω · cm or more in a range smaller than R1. Preferably, it is 1.0 × 10 ¹⁵ Ω · cm or more. From the above viewpoint, R2 is preferably 1.0 × 10 ¹⁸ Ω · cm or less, more preferably 1.0 × 10 ¹⁷ Ω · cm or less, and 1.0 × 10 ^16. More preferably, it is Ω · cm or less. Since the volume resistivity R1 of the first toner particles used in an electrophotographic normal image forming apparatus is generally on the order of 10 ¹⁷ Ω · cm, R2 is 1.0 × 10 ¹⁷ Ω · cm. The following is preferable.

  The volume resistivity of the first toner particles and the volume resistivity of the second toner particles can both be determined by a known method for measuring the volume resistivity of the toner.

  The second toner particles can be configured in the same manner as the toner that can be used in the electrophotographic image forming method except that the second toner particles further contain the resistance adjusting agent. The resistance adjusting agent is a component that increases the conductivity of the toner particles, and may be one kind or more. Examples of the resistance adjusting agent include a surfactant. As the surfactant, a cationic surfactant is preferably used, and more preferably, a quaternary ammonium salt surfactant is used.

Examples of the cationic surfactant include alkylamine acetate represented by the following formula, and more specifically, laurylamine acetate. In the following formulae, R represents an alkyl group having 8 to 22 carbon atoms.
RNH ₂・ CH ₃ COOH

Examples of the surfactant of the quaternary ammonium salt include compounds represented by the following formula, and more specifically, alkyltrimethylamine chloride and dialkyldimethylamine chloride. In the following formulae, R represents an alkyl group having 8 to 22 carbon atoms, and n is 1 or 2.
_{[R n N (CH 3)} 4-n] + [Cl] -

  If the content of the resistance adjusting agent is too small, R1 / R2 may be excessively small, and if too large, R1 / R2 may be excessively large. From the above viewpoint, the content of the resistance adjuster is preferably 5 mass ppm or more, more preferably 50 mass ppm or more with respect to the resin solid content of the toner base particles of the second toner particles. preferable. Further, from the above viewpoint, the content of the resistance adjusting agent is preferably 1000 mass ppm or less, more preferably 500 mass ppm or less with respect to the resin solid content of the toner base particles of the second toner particles. Is more preferable.

  The second toner image is an aggregate of the second toner particles arranged to cover the toner image on the recording medium. As described above, it is sufficient that the second toner image is arranged above the first toner image on the recording medium, and it is more preferable that the second toner image is arranged at the top of the image. The second toner image may be an image that covers only the first toner image, an image that covers the entire surface of the recording medium including the portion of the first toner image, or the above A part or a plurality of parts of the image drawn with the first toner may be covered. The second toner image may be an image formed on the intermediate transfer member on the intermediate transfer member side relative to the first toner image.

  The second toner image may be formed by stacking layers of second toner particles. When there are a plurality of layers of the second toner particles, the volume resistivity of the second toner particles constituting the uppermost layer on the recording medium is the volume resistivity of the second toner particles constituting the other layer. Preferably it is lower than the rate.

  Note that the second toner image layer is positioned above the first toner image layer in the recording medium, so that the second toner image layer is closer to the recording medium than the first toner image layer. It means that it is arranged at a more distant position. The uppermost layer means a layer that is located farthest from the recording medium.

  The second process unit is an apparatus for forming the second toner image at a position on the first toner image on the recording medium or at a position where it should be. The second process unit is, for example, a process cartridge for the second toner particles disposed on the upstream side in the process direction with respect to the process cartridge group, or the first process unit fixed on the recording medium. An apparatus group including a process cartridge for appropriately arranging second toner particles on a toner image and a fixing device for fixing the second toner image on the recording medium.

  The recording medium is an object on which a final image with toner is to be formed. As the recording medium, a recording medium that can be used for forming a toner image in an electrophotographic image forming method can be used. Examples of the recording medium include plain paper, high-quality paper, art paper, coated paper, Japanese paper, postcard paper, and transparent film. In particular, the image forming apparatus is more effective when a recording medium such as coated paper or film that is more likely to be electrostatically stuck on a paper discharge tray is used.

  The volume resistivity of the first toner particles may be a representative value of the volume resistivity. For example, the volume resistivity of the first toner particles may be an average value of the volume resistivity of each first toner particle. Or the volume resistivity of the first toner particles forming the uppermost layer in the toner image. The volume resistivity of the second toner particles may be a representative value of the volume resistivity. For example, the volume resistivity of each second toner particle may be an average value, or the second toner particles It may be the volume resistivity of the second toner particles that form the uppermost layer in the image. In particular, the volume resistivity of the second toner particles is lower than the volume resistivity of the first toner particles having the lowest volume resistivity among the first toner particles, so that the attractive force between the printed materials is reduced. From the viewpoint of

  The image by the first and second toner particles can be formed by, for example, the following image forming method. In the image forming method, when the image forming layer in which the second toner is arranged in layers is formed on the first toner image by the first toner particles for image formation on the recording medium, In the second toner particle, a toner particle having a volume resistivity lower than that of the first toner particle is used. The image forming method can be realized by applying the above characteristics to a method capable of forming the image forming layer.

  In the image forming method, the second toner image only needs to be finally positioned on the first toner image. For example, the image forming method includes a step of transferring the second toner image onto an intermediate transfer member, and a step of transferring the first toner image onto the second toner image on the intermediate transfer member. And a second transfer of the second and first toner images on the intermediate transfer member onto the recording medium. Such an image forming method can be carried out using a tandem type image forming apparatus having image forming units equal to or more than the total number of the first toner and the second toner.

  Of course, the image forming method may be a method of sequentially forming a first toner image and a second toner image on a recording medium. For example, the image forming method includes a step of forming the first toner image on the recording medium, and a step of subsequently forming the second toner image on the first toner image on the recording medium. The method including these may be used. Such an image forming method is a system composed of two connected image forming apparatuses, and the recording medium (printed material) discharged from the first image forming apparatus is added to the second image forming apparatus. It can be realized using a system that supplies paper one by one.

  In the image forming method, it is preferable that a full color image is formed in the step of forming the first toner image, and an image covering the full color image is formed in the step of forming the second toner image. From the viewpoint of forming the full color image, the step of forming the first toner image is preferably a step of forming a color toner image with yellow toner particles, magenta toner particles, cyan toner particles and black toner particles. .

  In the image forming method, various forms of full-color images can be formed according to the second toner image and the optical characteristics of the recording medium. For example, if the second toner particles are transparent toner particles, a full-color image covered with a transparent layer can be formed on a non-transparent recording medium (for example, paper). For example, the second toner particles Is a white toner, and if the recording medium is a transparent sheet, a full-color image coated with a white layer can be formed on the transparent sheet, and has a white background when viewed from the transparent sheet side. A full-color image covered with a transparent sheet can be formed. From the viewpoint of forming a high value-added image such as a high-quality image on a normal recording medium such as paper, it is preferable to use transparent toner particles as the second toner particles.

  The image forming apparatus and the image forming method described above can form an image in which the second toner image is superimposed on the first toner image. Therefore, an image with high added value can be formed. In addition, electrostatic charges are accumulated on a recording medium (printed material) on which an image is formed, and the printed materials are likely to stick to each other due to static electricity. However, the volume resistivity of the second toner particles is lower than the volume resistivity of the first toner particles. Accordingly, accumulation of electric charges on the recording medium on which the image is formed is suppressed, and electrostatic sticking between the printed materials discharged and stacked from the image forming apparatus can be suppressed.

  For example, in the image forming apparatus and the image forming method, the attractive force between the printed materials discharged and stacked from the image forming apparatus can be suppressed to 0.7 N or less in the planar direction of the recording medium. The above attractive force is preferably as small as possible from the viewpoint of preventing sticking between printed materials, more preferably 0.5 N or less, and even more preferably 0.3 N or less.

  Hereinafter, embodiments of the present invention will be described more specifically. FIG. 1 is a diagram schematically illustrating a configuration of an example of the image forming apparatus.

  As shown in FIG. 1, the image forming apparatus forms a toner image forming unit 20S for forming an image of transparent toner particles and an image of colored toner particles of yellow, magenta, cyan, or black. Toner image forming units 20Y, 20M, 20C, and 20Bk, and a toner comprising a plurality of toner layers in which toner images formed by these toner image forming units 20S, 20Y, 20M, 20C, and 20Bk are superposed in this order. An intermediate transfer unit 10 for carrying an image and transferring it to a recording medium P, and a recording medium P carrying a toner image transferred from the intermediate transfer unit 10 are heated and pressurized to apply the toner image to the recording medium. A fixing device 50 for fixing to P. The image forming apparatus is a so-called tandem type image forming apparatus. The recording medium P is a sheet-like recording medium, for example, high-quality paper.

  Note that “S, Y, M, C, Bk” in FIG. 1 indicates the type of toner, and in the following description, a configuration having a common structure regardless of the type of toner in FIG. For the above, a symbol representing the type of toner may be omitted.

  The toner image forming unit 20 includes a photosensitive member 11 that is an electrostatic latent image carrier, a charging device 23 that applies a uniform potential to the surface of the photosensitive member 11, and a uniformly charged photosensitive member 11. And an exposure device 22 for forming an electrostatic latent image having a shape corresponding to a region where a toner layer is to be formed, and a toner image corresponding to the electrostatic latent image is formed by transporting toner particles onto the photoreceptor 11. And a cleaning device 25 for collecting toner particles remaining on the photoconductor 11 after the toner image on the photoconductor 11 is transferred by the intermediate transfer unit 10.

The photoreceptor 11 is, for example, a negatively charged organic photoreceptor having photoconductivity on the surface thereof.
The charging device 23 is, for example, a corona charger. The charging device 23 may be a contact charging device in which a contact charging member such as a charging roller, a charging brush, or a charging blade is brought into contact with the photoconductor 11 to be charged. The exposure device 22 includes, for example, a semiconductor laser as a light source and a light deflecting device (polygon motor) that irradiates the photoconductor 11 with laser light corresponding to an image to be formed.

  The developing device 21 is a two-component developing type developing device. The developing device 21 includes, for example, a developing container that contains a two-component developer, a developing roller (magnetic roller) that is rotatably disposed in an opening of the developing container, and a developing container that allows the two-component developer to communicate with each other. A partition partitioning the interior; a transport roller for transporting the two-component developer on the opening side of the developer container toward the developer roller; and an agitation roller for stirring the two-component developer in the developer container . The developer container contains the toner (two-component developer) according to the above-described embodiment.

The developing device 21 contains a two-component developer having toner particles and carrier particles. The developing device 21S contains a transparent toner developer containing transparent toner particles. The transparent toner particles correspond to the second toner particles described above. The volume resistivity of the transparent toner particles is, for example, 2.0 × 10 ¹⁵ Ω · cm.

  The transparent toner particles have toner base particles containing a binder resin and a resistance adjusting agent, and external additives attached to the surface thereof. The resistance adjuster is, for example, a cationic surfactant, and its content in the toner base particles is, for example, 270 ppm. The toner base particles of the transparent toner particles are configured in the same manner as the toner base particles of a normal color toner except that the resistance adjuster is blended as described above instead of the colorant.

The developing device 21Y contains a yellow developer containing yellow toner particles, the developing device 21M contains a magenta developer containing magenta toner particles, and the developing device 21C contains A cyan developer containing cyan toner particles is accommodated, and a black developer containing black toner particles is accommodated in the developing device 21Bk. The color toner particles of each color described above correspond to the first toner particles described above. The volume resistivity of the color toner particles is, for example, 2.8 × 10 ^{17 to} 3.2 × 10 ¹⁷ Ω · cm.

  Each of the yellow toner particles, magenta toner particles, cyan toner particles, and black toner particles has toner base particles containing a binder resin and a colorant, and an external additive attached to the surface thereof. The toner base particles of these color toner particles are configured in the same manner as the toner base particles of a normal color toner.

  The carrier particles used are ordinary carrier particles used in a two-component developer. The carrier particles are, for example, magnetic particles themselves, but may be resin-coated carrier particles obtained by coating the magnetic particles with a resin, or fine particles of a magnetic material may be dispersed in resin particles. Magnetic material dispersed carrier particles may be used.

  The intermediate transfer unit 10 includes an intermediate transfer body 16 to which the toner image on the photoconductor 11 is to be transferred, and a primary transfer roller 13 for generating an electric field that transfers the toner image on the photoconductor 11 to the intermediate transfer body 16. A secondary transfer roller 13A for generating an electric field for transferring the toner image transferred to the intermediate transfer member 16 to the recording medium P, and the toner image remaining on the intermediate transfer member 16 after the toner image is transferred to the secondary transfer roller 13A. And a cleaning device 12 for collecting the used toner. The intermediate transfer member 16 is an endless belt, is supported by a plurality of support rollers 16a to 16d, and is stretched so as to be rotatable.

  The fixing device 50 includes a heating roller 51 for heating the recording medium P carrying the toner image, and a pressure roller 52 for pressing the recording medium P carrying the toner image toward the outer peripheral surface of the heating roller 51. Have When the heating roller 51 and the pressure roller 52 are pressed against each other, a nip portion N that is a portion where the two are pressed against each other is formed.

  In addition, the image forming apparatus is fed by the paper feed cassette 41 in which the recording medium P is stored, the paper feed roller 42 for taking out the recording medium P from the paper feed cassette 41, and the paper feed roller 42. A plurality of paper feed rollers 44a, 44b, 44c, 44d for transporting the recording medium P toward the secondary transfer roller 13A, and the transport direction and timing of the recording medium P toward the secondary transfer roller 13A are adjusted. A registration roller 46.

  The toner image forming unit 20S corresponds to the above-described second process unit, and the toner image forming units 20Y, 20M, 20C, and 20Bk correspond to the above-described first process unit.

  In the image forming apparatus, first, a transparent toner image is formed by the toner image forming unit 20S. The transparent toner image is uniformly charged on the photoconductor 11S, exposed so as to form an electrostatic latent image corresponding to the intended image, and the electrostatic latent image portion is developed, whereby the photoconductor 11S is developed. It is formed. The transparent toner image is, for example, a solid image when covering the entire surface of the image to be formed on the recording medium P. The transparent toner image is transferred to the intermediate transfer body 16 by applying a voltage from the primary transfer roller 13S.

  Next, in each of the toner image forming units 20Y, 20M, 20C, and 20Bk, yellow, magenta, cyan, and black toner images are formed on the photoreceptor 11 in the same manner as the transparent toner image. The toner images of yellow, magenta, cyan, and black are transferred onto the transparent toner image on the intermediate transfer member 16 in the above order by applying a voltage from the primary transfer roller 13 and are superimposed. In this way, a toner image is formed in which the layers of black, cyan, magenta, yellow, and transparent toner particles are superimposed from the intermediate transfer member 16 side.

  On the other hand, the recording medium P is picked up by the paper feed roller 42 from the paper feed cassette 41 and conveyed to the secondary transfer roller 13A by the paper feed rollers 44a to 44d and the registration roller 46. Then, the toner image on the intermediate transfer body 16 is transferred to the recording medium P by application of a voltage from the secondary transfer roller 13A. In this way, a toner image is carried on the surface of the recording medium P, in which layers of black, cyan, magenta, yellow and transparent toner particles are superimposed from the recording medium P side.

  Next, the recording medium P carrying the toner image receives the heating from the heating roller 51 and the pressing from the pressure roller 52 at the nip portion N, and the toner image is batched by the heating and pressing. To the recording medium P.

The fixing conditions in the fixing device 50 can be set as follows, for example.
・ Heating temperature: 170-230 ° C
・ Nip time: 50-500msec

The heating temperature is the surface temperature of the heating roller 51 at the time of fixing. The nip time Nt is a length Ln (mm) in the conveyance direction of the recording medium P at the nip portion N, as expressed by the following formula, as a conveyance speed Vp (linear speed, mm / sec) of the recording medium P. Divided by 1000 and multiplied by 1000.
Nt (m · sec) = (Ln (mm) / Vp (mm / sec)) × 1000

  By the above fixing by the fixing device 50, a glossy image is formed on the recording medium P by forming a transparent toner layer on the color toner image. The glossy image is discharged out of the image forming apparatus and is superimposed on a paper discharge tray.

  In general, a printed matter of an image on a paper discharge tray has an electrostatic charge accumulated by a series of image forming processes. For this reason, the printed matter attracts each other electrostatically on the paper discharge tray and is likely to stick. However, in the image forming apparatus, printed images of glossy images stacked on the paper discharge tray are difficult to stick to each other. This is because the volume resistivity of the transparent toner particles is lower than that of each color toner particle, so that a layer having a lower electrical resistance (transparent toner layer) is formed on the surface of the printed matter, and is accumulated in the printing section. This is considered to be due to the discharge of the charged electric charge to the outside of the printed matter through the transparent toner layer. Therefore, in the image forming apparatus, it is possible to prevent sticking at the time of discharge between printed materials on which high-value-added images such as glossy images are formed.

  The color toner image is generally formed on substantially the whole of one or both of the front surface and the back surface of the recording medium P. The larger the area on which the color toner image is formed, the more charges are accumulated on the recording medium P, and the printed matter tends to stick. Therefore, when the ratio of the area of the color toner image (that is, the ratio of the area of the transparent toner image in the portion) where the image of the recording medium P is to be formed (for example, the portion excluding the margin) is 50%, The sticking prevention effect appears more remarkably, and if it is 75% or more, it appears more prominently, which is preferable.

  The color toner image described above is formed by a toner layer using one or more toners necessary for color reproduction out of the four color toners. As the number of toner layers forming the color toner image increases, more charges are accumulated on the recording medium P, and sticking of the printed matter is more likely to occur. Therefore, the larger the number of color toner layers, the more remarkable the above effect. Specifically, the above effect is more noticeable in four color toner layers than in one color toner layer. In addition, if the color toner layer is five layers or more, it appears more remarkably. The upper limit of the number of layers can be appropriately determined from the range in which the color toner layer can be fixed to the recording medium P.

  In the image forming apparatus, the color toner image and the transparent toner image are fixed together on the recording medium P. However, as another aspect, an unfixed transparent toner image is fixed on the color toner image fixed on the recording medium P. A toner image may be formed and further fixed. That is, you may fix twice about one recording medium. Such an image forming method includes, for example, a further conveying device such as a plurality of roller pairs for separately conveying a recording medium after fixing a color toner image to a secondary transfer roller without discharging the recording medium from the image forming device. (See, for example, FIG. 1).

  As is apparent from the above description, the image forming apparatus includes a first process unit for forming a first toner image on the recording medium using the first toner particles for image formation, and the recording medium. A second process unit for forming a second toner image covering the first toner image with second toner particles, wherein the second toner is layered on the first toner image. An image forming layer to be disposed can be formed, and the volume resistivity of the second toner particles is lower than the volume resistivity of the first toner particles. Therefore, it is possible to prevent sticking between recording media on which images formed by stacking a plurality of toner layers are formed.

  When the first toner particles include one or more toners selected from the group consisting of yellow toner particles, magenta toner particles, cyan toner particles and black toner particles, a viewpoint of forming a high added value image, and From the viewpoint that the effect of preventing sticking is remarkably brought about, the first toner particles are four kinds of yellow toner particles, magenta toner particles, cyan toner particles and black toner particles. This is more effective from the viewpoint that a high-quality full-color image is more easily formed.

  In addition, the fact that the second toner particles are transparent toner particles is even more effective from the viewpoint of forming an image with a high added value and the effect of significantly preventing the sticking.

  In addition, it is more effective that the second toner particles contain a quaternary ammonium salt surfactant or a cationic surfactant from the viewpoint of enhancing the sticking prevention effect.

  The image forming method forms an image forming layer in which a second toner is arranged in a layer form on a first toner image formed by first toner particles for image formation on a recording medium. In the method, toner particles having a volume resistivity lower than that of the first toner particles are used for the second toner particles. Therefore, it is possible to prevent sticking between recording media on which images formed by stacking a plurality of toner layers are formed.

  The image forming method includes a step of transferring the second toner image onto an intermediate transfer member, a step of transferring the first toner image onto the second toner image on the intermediate transfer member, and the intermediate Including the step of secondary transfer of the second and first toner images on the transfer body onto the recording medium, which is more effective from the viewpoint of realizing the image forming method with a simpler configuration. is there.

  The image forming method includes the steps of forming the first toner image on the recording medium, and subsequently forming the second toner image on the first toner image on the recording medium. It is more effective from the viewpoint of enhancement of added value such as improvement of productivity and quality improvement of the formed image.

  In addition, the step of forming the first toner image is a step of forming a color toner image using yellow toner particles, magenta toner particles, cyan toner particles, and black toner particles. It is much more effective from the viewpoint of being formed. The use of transparent toner particles as the second toner particles is even more effective from the viewpoint of forming a high added-value image and the effect of significantly preventing the sticking.

The toner in the present embodiment includes toner particles having binder resin particles, and the volume resistivity of the toner particles is 1.0 × 10 ¹⁷ Ω · cm or less. Therefore, the toner is used as the second toner capable of preventing the sticking of the printed matter having the image forming layer in which the color toner for forming a full color image that is normally used is the first toner. Can do.

  In addition, it is more effective that the binder resin particles contain a cationic surfactant or a quaternary ammonium salt surfactant from the viewpoint of enhancing the sticking prevention effect.

  The present invention will be described more specifically with reference to the following examples and comparative examples. The present invention is not limited to the following examples.

[Preparation of aqueous dispersion of resin fine particles (X1)]
≪First stage polymerization≫
Into a 5 L reaction vessel equipped with a stirrer, temperature sensor, cooling pipe, and nitrogen introduction device, 8 parts by weight of sodium dodecyl sulfate and 3000 parts by weight of ion-exchanged water were charged, while stirring at a stirring speed of 230 rpm under a nitrogen stream. The temperature was raised to 80 ° C. After raising the temperature, 10 parts by mass of potassium persulfate dissolved in 200 parts by mass of ion-exchanged water was added, and the liquid temperature was again set to 80 ° C.
Styrene 480 parts by weight n-butyl acrylate 250 parts by weight A monomer mixture consisting of 68.0 parts by weight of methacrylic acid was added dropwise over 1 hour, followed by polymerization by heating and stirring at 80 ° C. for 2 hours. A fine particle dispersion (x1) was prepared.

≪Second stage polymerization≫
A 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device was charged with a solution prepared by dissolving 7 parts by mass of polyoxyethylene (2) sodium dodecyl ether sulfate in 3000 parts by mass of ion-exchanged water, and 98 After heating to ° C., 260 parts by mass of resin fine particle dispersion (x1),
Styrene (St) 284 parts by weight n-butyl acrylate (BA) 92 parts by weight Methacrylic acid (MAA) 13 parts by weight n-octyl-3-mercaptopropionate 1.5 parts by weight Release agent: behenate behenate (melting point 73) ° C) A mechanical disperser “CLEARMIX” (M-Technique, “Cleamix”) having a circulation path is added with 190 parts by mass of a monomer and a solution in which a release agent is dissolved at 90 ° C. Manufactured and dispersed for 1 hour to prepare a dispersion containing emulsified particles (oil droplets).

  Next, an initiator solution prepared by dissolving 6 parts by mass of potassium persulfate in 200 parts by mass of ion-exchanged water is added to the dispersion, and polymerization is performed by heating and stirring the system at 84 ° C. for 1 hour. A dispersion (x2) of resin fine particles was prepared.

≪Third stage polymerization≫
Further, after adding 400 parts by mass of ion-exchanged water to the dispersion (x2) of resin fine particles and mixing well, a solution in which 11 parts by mass of potassium persulfate was dissolved in 400 parts by mass of ion-exchanged water was added, and the temperature was changed to 82 ° C. Under the temperature conditions of
Styrene (St) 350 parts by mass n-butyl acrylate (BA) 215 parts by mass Acrylic acid (AA) 30 parts by mass n-octyl-3-mercaptopropionate A monomer mixture consisting of 8 parts by mass over 1 hour It was dripped. After completion of the dropwise addition, polymerization was performed by heating and stirring for 2 hours, followed by cooling to 28 ° C. to prepare an aqueous dispersion (X1) of amorphous resin fine particles made of vinyl resin.

  With respect to the obtained aqueous dispersion (X1) of amorphous resin fine particles, the volume-based median diameter of the amorphous resin fine particles is 220 nm, the glass transition temperature (Tg) is 55 ° C., and the weight average molecular weight (Mw) is 32000. there were.

  The glass transition temperature may be increased by using a differential scanning calorimeter “Diamond DSC” (manufactured by PerkinElmer Co., Ltd.), for example, with an ascending / descending rate of 10 ° C./min and a temperature increase range of 0 ° C. to 150 ° C.・ It is performed according to cooling conditions.

  The weight average molecular weight is determined using a GPC apparatus having “HLC-8220” (manufactured by Tosoh Corp.) and “TSKguardcolumn + TSKgelSuperHZM-M3 series” (manufactured by Tosoh Corp.) as a column and a calibration curve obtained from a standard polystyrene sample. Is required.

[Preparation of dispersion of resin fine particles for shell (S)]
The following monomer and radical polymerization initiator containing both reactive monomers were placed in a dropping funnel in the following amounts to obtain a monomer solution A. The following di-t-butyl peroxide is a polymerization initiator.
Styrene 80 parts by mass n-butyl acrylate 20 parts by mass Acrylic acid 10 parts by mass Di-t-butyl peroxide 16 parts by mass

In addition, the following monomer is charged in the following amount in a four-necked flask equipped with a nitrogen introduction tube, a dehydration tube, a stirrer, and a thermocouple, heated to 170 ° C. and dissolved to obtain monomer solution B. It was.
Bisphenol A propylene oxide 2-mole adduct 285.7 parts by mass Terephthalic acid 66.9 parts by mass Fumaric acid 47.4 parts by mass

  Next, the monomer solution A was added dropwise to the monomer solution B over 90 minutes under stirring and aged for 60 minutes, and then the unreacted monomer was removed under reduced pressure (8 kPa).

Next, 0.4 parts by mass of Ti (OBu) ₄ was added as an esterification catalyst, the temperature was raised to 235 ° C., and the reaction was performed under normal pressure (101.3 kPa) for 5 hours and further under reduced pressure (8 kPa) for 1 hour. Went.

  Subsequently, after cooling the obtained dispersion liquid to 200 degreeC, it reacted until it reached a desired softening point under reduced pressure (20 kPa). Next, the solvent was removed to obtain an amorphous shell resin (s1). The obtained shell resin (s1) had a Tg of 61 ° C. and an Mw of 19000.

  100 parts by mass of the obtained shell resin (s1) was dissolved in 400 parts by mass of ethyl acetate (manufactured by Kanto Chemical Co., Ltd.) and mixed with 638 parts by mass of a 0.26% by mass aqueous sodium lauryl sulfate solution prepared in advance. Then, the mixture was subjected to ultrasonic dispersion for 30 minutes at 300 μA V-LEVEL with an ultrasonic homogenizer “US-150T” (manufactured by Nippon Seiki Seisakusho) while stirring. Then, in a state heated to 40 ° C., the pressure was reduced using a diaphragm vacuum pump “V-700” (manufactured by BUCHI), and ethyl acetate was completely removed while stirring for 3 hours. Thus, a resin fine particle dispersion (S) for shell having a solid content of 13.5% by mass was prepared. The volume-based median diameter of the particles contained in the resin fine particle dispersion (S) for shell was 160 nm.

[Preparation of Cyan Colorant Fine Particle Dispersion (Cy-1)]
90 parts by mass of sodium n-dodecyl sulfate was added to 1600 parts by mass of ion-exchanged water. While stirring this solution, 420 parts by mass of copper phthalocyanine (CI Pigment Blue 15: 3) was gradually added to the solution, and then a stirring device “CLEARMIX” (manufactured by M Technique Co., Ltd.) was used. Then, a cyan colorant fine particle dispersion (Cy-1) was prepared. The volume-based median diameter of the colorant particles in the cyan colorant fine particle dispersion (Cy-1) was 110 nm.

  The volume-based median diameter of the colorant fine particle dispersion (A1) was measured using “MICROTRAC UPA-150” (manufactured by HONEYWELL).

[Preparation of Yellow Colorant Fine Particle Dispersion (Y-1)]
95 parts by mass of sodium n-dodecyl sulfate was added to 1600 parts by mass of ion-exchanged water. While stirring this solution, 250 parts by weight of C.I. I. Pigment Yellow 74 is gradually added to the solution, and then dispersed using a stirrer “CLEAMIX” (manufactured by M Technique Co., Ltd.), whereby the yellow colorant fine particle dispersion (Y-1) is obtained. Prepared. The volume-based median diameter of the colorant particles in the yellow colorant fine particle dispersion (Y-1) was 126 nm.

[Preparation of Magenta Colorant Fine Particle Dispersant (M-1)]
95 parts by mass of sodium n-dodecyl sulfate was added to 1600 parts by mass of ion-exchanged water. While stirring this solution, 250 parts by weight of C.I. I. Pigment Red 122 is gradually added to the solution, and then dispersed using a stirrer “Clearmix” (M Technique Co., Ltd.) to prepare a magenta colorant fine particle dispersant (M-1). did. The volume-based median diameter of the colorant particles in the magenta colorant fine particle dispersant (M-1) was 115 nm.

[Preparation of Black Colorant Fine Particle Dispersant (Bk-1)]
90 parts by mass of sodium n-dodecyl sulfate was added to 1600 parts by mass of ion-exchanged water. While stirring this solution, 320 parts by mass of carbon black “Regal 330R” (Cabot) is gradually added to the solution, and then dispersed using a stirring device “Clearmix” (M Technique Co., Ltd.). By processing, a black colored fine particle dispersion (Bk-1) was prepared. The volume-based median diameter of the colorant fine particles in the black colored fine particle dispersion (Bk-1) was 110 nm.

[Preparation of aqueous dispersion of white pigment (W-1)]
90 parts by mass of sodium n-dodecyl sulfate was added to 1600 parts by mass of ion-exchanged water. While stirring this solution, 700 parts by mass of rutile titanium oxide (manufactured by Ishihara Sangyo Co., Ltd.) is gradually added to the solution, and then dispersed using a stirrer “Clearmix” (manufactured by M Technique Co., Ltd.). By processing, a white colorant particle dispersion (W-1) was prepared. The volume-based median diameter of the colorant particles in the white colorant particle dispersion (W-1) was 180 nm.

[Preparation of cyan toner particles]
Into a reaction vessel equipped with a stirrer, a temperature sensor, and a cooling tube, 358 parts by mass (in terms of solid content) of an aqueous dispersion (X1) of resin fine particles and 2000 parts by mass of ion-exchanged water were added. An aqueous sodium hydroxide solution was added to adjust the pH of the dispersion to 10.

  Next, 30 parts by mass (in terms of solid content) of cyan colorant fine particle dispersion (Cy-1) was added to the dispersion, and then an aqueous solution in which 60 parts by mass of magnesium chloride was dissolved in 60 parts by mass of ion-exchanged water, The mixture was added over 10 minutes at 30 ° C. with stirring. Thereafter, the temperature was increased after standing for 3 minutes, and the dispersion was heated to 80 ° C. over 60 minutes, and maintained at 80 ° C. to continue the particle growth reaction.

  In this state, the particle size of the associated particles was measured with “Coulter Multisizer 3” (manufactured by Coulter Beckman). When the volume-based median diameter of the associated particles reached 6.0 μm, Then, 72 parts by mass (in terms of solid content) of an aqueous dispersion of resin fine particles for shell (S1) was added over 30 minutes, and when the supernatant of the resulting reaction solution became transparent, 190 parts by mass of sodium chloride was ionized. An aqueous solution dissolved in 760 parts by mass of exchange water was added to the reaction solution to stop the particle growth reaction.

  Further, the temperature of the obtained dispersion is increased, and the mixture is heated and stirred in a state of 90 ° C., so that the fusion of the particles proceeds, and a measuring device “FPIA-2100” (manufactured by Sysmex) for measuring the average circularity of the toner base particles. ), The dispersion was cooled to 30 ° C. at a cooling rate of 2.5 ° C./min when the average circularity reached 0.945 under the condition that the number of detected HPFs was 4000.

  Subsequently, the above-mentioned dispersion was subjected to solid-liquid separation, and the dehydrated toner cake was redispersed in ion-exchanged water and subjected to solid-liquid separation, and washed three times. The obtained toner cake was dried at 40 ° C. for 24 hours to obtain cyan toner base particles.

  To 100 parts by mass of the obtained cyan toner base particles, 0.6 part by mass of hydrophobic silica powder (number average primary particle size = 12 nm, degree of hydrophobicity = 68) and hydrophobic titanium oxide powder (number average primary particle size) = 20 nm, degree of hydrophobicity = 63) 1.0 part by mass was added, and mixed with a “Henschel mixer” (manufactured by Nihon Coke Kogyo Co., Ltd.) at a rotating blade peripheral speed of 35 mm / sec at 32 ° C. for 20 minutes. Coarse particles were removed using an open sieve. Cyan toner particles having a volume average particle size MV of 6.3 μm were obtained by subjecting the cyan toner base particles to the above external additive treatment.

  The number average primary particle diameter of the powder may be a catalog value, but can be determined by processing an image taken with a transmission electron microscope. For example, it is calculated from the horizontal direction ferret diameter of, for example, 100 of the binarized external additive particles.

Further, the volume resistivity R of the cyan toner particles was measured by “Digital Ultra High Resistance / Micro Ammeter 5450” (manufactured by ADC Corporation) and found to be 3.0 × 10 ¹⁷ Ω · cm. More specifically, 2 g of toner particles are molded into a disk-shaped pellet having a diameter of 35 mm and a height of 2 mm, and the volume resistivity R is measured by measuring the pellet at a voltage of 500 V using the ammeter. Asked. The pressure at the time of molding the pellet is 150 kN, and the pressurizing time is 10 seconds. The volume resistivity R is based on a measured value 3 minutes after voltage application.

[Preparation of yellow toner particles]
Except for changing 30 parts by mass (in terms of solid content) of cyan colorant fine particle dispersion (Cy-1) to 25 parts by mass (in terms of solid content) of yellow colorant fine particle dispersion (Y-1), the same as for cyan toner particles Yellow toner particles were prepared. The MV of the yellow toner particles was 6.3 μm, and the R was 3.1 × 10 ¹⁷ Ω · cm.

[Production of magenta toner particles]
Except for changing 30 parts by mass (in terms of solid content) of cyan colorant fine particle dispersion (Cy-1) to 33 parts by mass (in terms of solid content) of magenta colorant fine particle dispersion (M-1), the same procedure as for cyan toner particles was performed. Then, magenta toner particles were produced. The MV of the magenta toner particles was 6.3 μm, and R was 3.2 × 10 ¹⁷ Ω · cm.

[Preparation of black toner particles]
Except for changing 30 parts by mass (in terms of solid content) of cyan colorant fine particle dispersion (Cy-1) to 37 parts by mass (in terms of solid content) of black colorant fine particle dispersion (Bk-1), the same as for cyan toner particles Black toner particles were prepared. The MV of the black toner particles was 6.3 μm, and the R was 2.8 × 10 ¹⁷ Ω · cm.

[Preparation of white toner particles]
Cyan colorant fine particle dispersion (Cy-1) 30 parts by mass (solid content conversion) is changed to white colorant fine particle dispersion (W-1) 90 parts by mass (solid content conversion), and then lauryltrimethylammonium chloride. White toner particles were prepared in the same manner as the cyan toner particles, except that 15.6 parts by mass of the aqueous solution was added in terms of solid content. The white toner particles had an MV of 6.3 μm and an R of 2.4 × 10 ¹⁵ Ω · cm.

[Preparation of Transparent Toner Particles 1]
Transparent toner particles 1 were produced in the same manner as the cyan toner particles, except that 12.9 parts by mass of an aqueous solution of laurylamine acetate in terms of solid content was added instead of the cyan colorant fine particle dispersion (Cy-1). The MV of the transparent toner particle 1 was 6.3 μm, and R was 2.0 × 10 ¹⁶ Ω · cm.

[Preparation of Transparent Toner Particles 2]
Transparent toner particles 2 were produced in the same manner as the cyan toner particles, except that 12.9 parts by mass of an aqueous solution of lauryltrimethylammonium chloride in terms of solid content was added instead of the cyan colorant fine particle dispersion (Cy-1). The MV of the transparent toner particles 2 was 6.3 μm, and R was 2.0 × 10 ¹⁵ Ω · cm.

[Preparation of Transparent Toner Particles 3]
Transparent toner particles 3 were produced in the same manner as the cyan toner particles except that the cyan colorant fine particle dispersion (Cy-1) was not used. The MV of the transparent toner particle 3 was 6.3 μm, and R was 4.0 × 10 ¹⁷ Ω · cm.

[Preparation of two-component developer]
Cyan toner particles, yellow toner particles, magenta toner particles, black toner particles, white toner particles, and transparent toner particles 1 to 3 are each made of ferrite carrier particles having a volume average particle diameter of 38 μm and a toner concentration of 6% by mass. The mixture was mixed for 30 minutes using a V-type mixer to prepare cyan developer, yellow developer, magenta developer, black developer, white developer, and transparent developers 1 to 3, respectively.

  The volume average particle size of the carrier particles is determined based on the above-described method using a laser diffraction particle size distribution measuring device “HELOS KA” (manufactured by Nippon Laser Corporation).

[Image formation example 1]
A black developer and a transparent developer 1 are accommodated in a modified machine of “bizhub PRO C7000” (manufactured by Konica Minolta, “bizhub” is a registered trademark of the company), and a black toner layer on the recording medium and a transparent covering the same An image consisting of the toner 1 layer was formed. The remodeling machine is a tandem type image forming apparatus having six process units arranged in parallel to an integral intermediate transfer belt so that 1 to 6 toner layers can be formed on a recording medium. It is configured.

100 double-sided printed materials (printed material 1) were formed by printing solid images of each toner on both sides of the recording medium. The recording medium is OK top coat paper (Oji Paper Co., Ltd., A3 plate, weighing 157 g / m ² ), the toner adhesion amount in each toner layer is 3.5 g / m ² , and the fixing temperature is 180 ° C. is there.

  Eleven sheets of 70 to 80 sheets were taken out from the top of the 100 printed sheets 1 loaded on the discharge tray, and the sticking force between the printed sheets 1 was measured. For the sticking force, the eleven printed products 1 are placed on a flat table, and a tape is applied to the tip of the short side of the printed product 1 located at the top. The force required to slide each printed material 1 in the horizontal direction was measured with a spring alone. And the average value of each measured value of ten printed matter 1 from the top was calculated | required, and this was made into sticking force. When the uppermost printed material 1 was slid, the second and subsequent printed materials 1 were fixed to the table (see FIG. 2). The sticking force of the printed material 1 was 0.1 N.

[Image formation example 2]
A printed material C1 was formed in the same manner as in the image forming example 1 except that the transparent developer 3 was used in place of the transparent developer 1, and the sticking force was determined. As a result, the sticking force of the printed material C1 was 2.0N.

[Image formation example 3]
Five types of developer, transparent developer 1, yellow developer, magenta developer, cyan developer, and black developer, are accommodated in the remodeling machine, and the transparent toner 1 layer, yellow, on the recording medium from above. A printed matter 2 is formed in the same manner as in image formation example 1 except that a toner layer, a magenta toner layer, a cyan toner layer, and a black toner layer are formed in this order. Asked. As a result, the sticking force of the printed material 2 was 0.6N.

[Image formation example 4]
Using the transparent developer 2 instead of the transparent developer 1, a printed material 3 is formed in the same manner as in the image forming example 3 except that the uppermost toner layer on the recording medium is a layer of the transparent lower toner 2. The sticking force was determined. As a result, the sticking force of the printed material 3 was 0.2N.

[Image formation example 5]
A printed material C2 is formed in the same manner as in image formation example 3 except that the transparent toner 3 is used in place of the transparent developer 1 and the uppermost toner layer on the recording medium is the transparent toner 3 layer. The power was sought. As a result, the sticking force of the printed material C2 was 5.1N.

[Image formation example 6]
Six types of developers, a transparent developer 2, a white developer, a yellow developer, a magenta developer, a cyan developer and a black developer, are accommodated in the modified machine, and the transparent toner 2 is placed on the recording medium from above. Printed matter in the same manner as in image formation example 1 except that the toner layer, white toner layer, yellow toner layer, magenta toner layer, cyan toner layer and black toner layer are formed in this order. 4 was formed and the sticking force was determined. As a result, the sticking force of the printed material 4 was 0.4N.

[Image formation example 7]
Five developers of white developer, yellow developer, magenta developer, cyan developer and black developer are accommodated in the modified machine, and the white toner layer and yellow toner layer are placed on the recording medium from above. A printed product 5 is formed in the same manner as in image formation example 1 except that five toner layers, a magenta toner layer, a cyan toner layer, and a black toner layer are formed in this order, and the sticking force is obtained. It was. As a result, the sticking force of the printed matter 5 was 0.3N.

  Table 1 shows the layer structure of the toners in the printed materials 1 to 5 and C1 and C2, the R of each toner, and the sticking force.

  As can be seen from Table 1, by forming a low-resistance toner layer on the outermost surface, the sticking force between the stacked printed materials can be kept low, and sticking of the printed materials can be prevented. Recognize.

  On the other hand, if a toner layer having the same resistance as that of the toner that forms the image is formed on the outermost surface of the printed material, the adhesion between the stacked printed materials becomes stronger, and the printed material is more easily adhered. I understand that

  ADVANTAGE OF THE INVENTION According to this invention, the sticking at the time of image formation of the printed matter in which the high added value image formed by the overlap of a some toner layer was formed can be prevented. Therefore, according to the present invention, it is possible to form a high value-added image even with a general-purpose image forming apparatus, and further spread of an electrophotographic image forming apparatus for such use is expected.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer part 11 Photoconductor 12, 25 Cleaning device 13 Primary transfer roller 13A Secondary transfer roller 16 Intermediate transfer body 16a-16d Support roller 20 Toner image forming part 21 Developing device 22 Exposure device 23 Charging device 41 Paper feed cassette 42 Supply Paper rollers 44a to 44d Paper feed roller 46 Registration roller 50 Fixing device 51 Heating roller 52 Pressure roller N Nip part P Recording medium

Claims (17)

In an image forming method of forming an image forming layer in which a second toner containing second toner particles is disposed on a first toner image formed by first toner particles for image formation on a recording medium.
For the second toner particles, toner particles whose volume resistivity is lower than the volume resistivity of the first toner particles are used.
Said first ratio R1 / R2 to the volume resistivity R2 of the second toner particles having a volume resistivity R1 of the toner particles, the image forming method comprising der Rukoto 10 or more. The image forming method according to claim 1, wherein a ratio R1 / R2 of the volume resistivity R1 of the first toner particles to the volume resistivity R2 of the second toner particles is 100 or more. 3. The image forming method according to claim 1, wherein the second toner particles contain a resistance adjuster of 5 mass ppm or more and 500 mass ppm or less with respect to the resin solid content of the toner base particles. Transferring a second toner image of the second toner onto an intermediate transfer member;
Transferring the first toner image onto the second toner image on the intermediate transfer member;
Secondary transfer of the second and first toner images on the intermediate transfer member onto the recording medium;
The image forming method according to claim 1 comprising a. Forming the first toner image on the recording medium;
Subsequently, forming a second toner image with the second toner on the first toner image on the recording medium;
Including, an image forming method according to any one of claims 1 to 3. The step of forming the first toner image, yellow toner particles, magenta toner particles, a step of forming a color toner image by the cyan toner particles and black toner particles, according to any one of claims 1 to 5 Image forming method. The second use of the transparent toner particles in the toner particles, the image forming method according to any one of claims 1 to 6. The second toner particles contain cationic surfactants, image forming method according to any one of claims 1 to 7. The second toner particles contain a surfactant quaternary ammonium salt, an image forming method according to any one of claims 1-8. A first process unit for forming a first toner image with first toner particles for image formation on a recording medium;
A second process unit for forming a second toner image covering the first toner image on the recording medium with a second toner containing second toner particles;
In the image forming apparatus for forming an image forming layer in which the second toner is disposed on the first toner image,
The volume resistivity of the second toner particles are rather low than the volume resistivity of the first toner particles,
The ratio R1 / R2 of the volume resistivity R1 of the first toner particles to the volume resistivity R2 of the second toner particles is 10 or more . The image forming apparatus according to claim 10, wherein a ratio R1 / R2 of the volume resistivity R1 of the first toner particles to the volume resistivity R2 of the second toner particles is 100 or more. 12. The image forming apparatus according to claim 10, wherein the second toner particles contain a resistance adjuster of 5 ppm by mass to 500 ppm by mass with respect to the resin solid content of the toner base particles. The image according to any one of claims 10 to 12, wherein the first toner particles include one or more toners selected from the group consisting of yellow toner particles, magenta toner particles, cyan toner particles, and black toner particles. Forming equipment. The image forming apparatus according to claim 10, wherein the first toner particles are yellow toner particles, magenta toner particles, cyan toner particles, and black toner particles. The image forming apparatus according to claim 10 , wherein the second toner particles are transparent toner particles. The image forming apparatus according to claim 10 , wherein the second toner particles contain a cationic surfactant. The image forming apparatus according to claim 10 , wherein the second toner particles contain a quaternary ammonium salt surfactant.

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