JP2007310011A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tandem type image forming apparatus where, even in the case an amorphous silicon drum is used, a clearing in midsection phenomenon of characters is not generated, and further, a difference in an image and the scattering of toner per color are not generated, thus a stable image can be provided. <P>SOLUTION: In the tandem type image forming apparatus where a plurality of image forming units are arranged along the moving direction of a transferring medium in such a manner that each color toner image is successively transferred, along the moving direction of the transferring medium, provided that the units are defined as U1, U2, U3, U4 in order from the upstream side, the U1 stores toner surface-treated with higher fatty acid zinc, the U2 stores toner surface-treated with higher fatty acid magnesium, and the U3 stores toner surface-treated with higher fatty acid calcium, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a tandem type image forming apparatus useful for a copying machine, a laser printer, a facsimile, and a multifunction machine using the electrophotographic method.

  Conventionally, for forming a color image, for example, images of four different colors (for example, black (K), yellow (Y), cyan (C), and magenta (M)) are formed as a single photoconductor (image carrier). A method of sequentially forming images of the respective colors on the photosensitive member so as to overlap with each other has been taken, but there is a problem that it takes time until a color image is finally formed.

  Therefore, in recent years, a plurality of photoconductors are provided, and each photoconductor is simultaneously scanned and exposed by a plurality of light beams to form images of different colors on the photoconductors. Many so-called tandem-type image forming apparatuses that form a color image by being superimposed on each other are employed. For example, as an example of a tandem type image forming apparatus, a movable intermediate transfer body (transfer medium) that sequentially transfers toner images of each color, and a toner image for each color that is arranged along the moving direction of the intermediate transfer body. A plurality of image forming units having an image carrier, primary transfer means for transferring a toner image on the image carrier to the intermediate transfer member, and a secondary for transferring the toner image on the intermediate transfer member to a recording medium. An apparatus having a transfer unit is widely used.

  By the way, in general, as an image carrier used in an image forming apparatus, an amorphous silicon drum is known to be advantageous in that it can easily achieve a longer machine life and a reduced running cost. ing. Since the amorphous silicon drum has a high surface hardness, even if it is polished by inorganic fine particles on the toner surface, the film hardly scrapes off and can maintain its performance over a long period of time.

  However, on the other hand, the amorphous silicon drum has a property of high frictional resistance, and when used in a tandem type image forming apparatus, a so-called “character dropout phenomenon” sometimes occurs. That is, in the tandem type image forming apparatus, the toner transferred to the transfer medium in the most upstream image forming unit with respect to the moving direction of the transfer medium comes into contact with the image carrier of the image forming unit on the downstream side of this. When the image carrier is an amorphous silicon drum having a high frictional resistance, the outermost surface layer of the transferred toner adheres to and peels off from the drum, and as a result, the middle of the toner line drawing on the transfer medium is removed. This will cause a “character dropout phenomenon”.

In order to avoid such character dropout phenomenon, it is considered that the frictional resistance of the amorphous silicon drum may be reduced. As a means for reducing the frictional resistance of the image carrier, a metal soap is used in the toner to be used. There is known a method of containing. For example, when a metal soap having a specific particle size is contained in the developer together with titanium oxide or silica (see Patent Document 1) or a toner used in an image forming apparatus having a rotary developer, the metal soap is included. A technique for optimizing the amount of metal soap in the toner according to a plurality of rotating developing units (see Patent Document 2) has been proposed.
JP 2001-51443 A Japanese Patent Laid-Open No. 2005-31243

  By the way, in a tandem type image forming apparatus having an intermediate transfer body, which is an example of a tandem type image forming apparatus, the plurality of image forming units are arranged in order from the upstream side along the moving direction of the intermediate transfer body U1, U2, U3. , U4, the toner primarily transferred to the intermediate transfer member in U1 is charged by applying a high voltage alternating electric field in each transfer region in the three image forming units U2, U3, and U4. To do. Similarly, the toner primarily transferred to the intermediate transfer member in U2 is charged up in the transfer regions in the two image forming units U3 and U4, and the toner primarily transferred to the intermediate transfer member in U3 is Charge up in the transfer area of the U4 image forming unit. That is, each toner transferred by each image forming unit has a different degree of charge-up. For this reason, the amount of charge varies depending on the position of the image forming unit in which the toner of each color is accommodated, and the image may be different for each color. Further, although the amount of charge of the toner increases, the toner easily scatters, and the degree of the toner varies depending on the toner of each color.

In the tandem type image forming apparatus, the above-mentioned problem caused by the charge-up in each transfer region tends to appear even more prominently when a higher fatty acid metal salt is used for the purpose of suppressing the “character dropout phenomenon” as described above. there were. This is because the higher fatty acid metal salt reduces the frictional resistance of the amorphous silicon drum to suppress the “character dropout phenomenon” and at the same time has the property of facilitating charging of the toner.
For example, when a toner that does not use a higher fatty acid metal salt is accommodated in the U1 (image forming unit disposed at the uppermost stream with respect to the moving direction of the intermediate transfer member), it is finally transferred onto a recording medium. The toner charge amount is 28 μC / g, and the final toner charge amount is also changed by changing the unit to be stored. When the toner is stored in the U2, it is 26 μC / g, and when it is stored in the U3, 24 μC / g. g, 22 μC / g when housed in U4.
In contrast, a toner using calcium stearate as the higher fatty acid metal salt is 40 μC / g when stored in U1, 36 μC / g when stored in U2, and when stored in U3. 30 μC / g, and 22 μC / g when stored in the U4.
Further, in the toner using magnesium stearate as the higher fatty acid metal salt, 37 μC / g when stored in the U1, 34 μC / g when stored in the U2, and 29 μC / g when stored in the U3. g, 22 μC / g when housed in U4.
Further, in the toner using zinc stearate as the higher fatty acid metal salt, 34 μC / g when stored in the U1, 32 μC / g when stored in the U2, and 28 μC / g when stored in the U3. g, 25 μC / g when housed in the U4.

  Therefore, the problem of the present invention is that even if an amorphous silicon drum is used in an image forming apparatus of a tandem type, the character dropout phenomenon does not occur, and the image is different for each color or toner scattering occurs. It is an object to provide an image forming apparatus that can provide a stable image.

  The present inventors have intensively studied to solve the above problems. As a result, when surface treatment of toner particles is performed using a higher fatty acid metal salt, the effect of reducing the frictional resistance hardly changes even if the type of the metal salt is changed, but the effect on the charging property is greatly affected by the metal type. Focused on the differences. For example, when three types of metal, zinc, magnesium, and calcium, are compared, the chargeability (in other words, ease of charge-up) is in the order of zinc <magnesium <calcium. Using this knowledge, when the tendency of chargeability due to this higher fatty acid metal salt and the charge-up tendency that differs depending on the position of each image forming unit (ie, upstream or downstream) are combined, charging is almost uniform. It has been found that the above-mentioned problems can be solved at once by specifying the optimum metal species for the toner contained in each image forming unit and treating the surface with the specific higher fatty acid metal salt. It was. The present invention has been completed based on these findings.

That is, the image forming apparatus of the present invention is a tandem image forming apparatus in which a plurality of image forming units are arranged along the moving direction of the transfer medium so that each color toner image is sequentially transferred onto the transfer medium.
When U1, U2, U3, and U4 are set in order from the upstream side along the moving direction of the transfer medium, U1 is a toner surface-treated with higher fatty acid zinc, and U2 is a toner surface-treated with higher fatty acid magnesium. However, each of U3 contains toners surface-treated with higher fatty acid calcium.

  According to the present invention, even when an amorphous silicon drum is used in an image forming apparatus of a tandem type, the character dropout phenomenon does not occur, and the image is different for each color or the toner is scattered. In addition, there is an effect that it is possible to provide an image forming apparatus capable of providing a stable image.

  The image forming apparatus of the present invention is a tandem type image forming apparatus in which a plurality of image forming units are arranged along the moving direction of the transfer medium so that each color toner image is sequentially transferred onto the transfer medium. In the tandem type image forming apparatus, 1) the transfer medium is an intermediate transfer member such as a transfer belt, and the toner image temporarily transferred from each image forming unit onto the intermediate transfer member is transferred onto a recording medium such as paper. Next transfer method (hereinafter, this method may be referred to as “indirect transfer method”) and 2) The transfer medium is a recording medium such as paper, and is directly transferred from each image forming unit to a recording medium such as paper. There is a method of transferring a toner image (hereinafter, this method may be referred to as a “direct transfer method”), but the image forming apparatus of the present invention may be any method as long as it is a tandem type. In other words, the transfer medium may be an intermediate transfer member such as a transfer belt or a recording medium such as paper.

Hereinafter, an indirect transfer tandem image forming apparatus will be described in detail with reference to the drawings as an embodiment of the image forming apparatus of the present invention.
An indirect transfer type tandem image forming apparatus generally includes a movable intermediate transfer body (transfer medium) that sequentially transfers each color toner image, and a toner image for each color that is arranged along the moving direction of the intermediate transfer body. A plurality of image forming units having an image carrier to be carried; primary transfer means for transferring a toner image on the image carrier to the intermediate transfer member; and transferring the toner image on the intermediate transfer member to a recording medium. Secondary transfer means. FIG. 1 is a diagram schematically showing the internal configuration of a color printer which is such an indirect transfer tandem image forming apparatus 1.

  The image forming apparatus 1 includes a rectangular box-shaped housing 2 that forms (prints) a color image on paper (recording medium). In the housing 2, a sheet feeding cassette 5 for storing sheets is disposed in the lower part, a stack tray 6 for manually feeding sheets is disposed in the middle part, and transmitted from the outside of the apparatus in the upper part. An image forming unit 7 is provided that forms an image on a sheet based on image data such as incoming characters and pictures. Further, on the upper surface portion of the housing 2, a paper discharge portion (discharge tray) 3 for discharging a paper on which a color image is printed is provided.

  The paper feed cassette 5 is pulled out to the outside of the housing 2 (front side in FIG. 1) to replenish paper, and can selectively store at least two types of paper having different sizes in the paper feed direction. Yes. The stack tray 6 can stack sheets to be manually fed.

  The paper stored in the paper feed cassette 5 is fed out one by one by the paper feed roller 17 and the separating roller 18, and the image forming unit is provided with a plurality of transport rollers 43 arranged at predetermined positions in the first transport path 9. 7 is conveyed. On the other hand, the sheets stacked on the stack tray 6 are fed out one by one by the pickup roller 20 and the separating roller 21, and the image forming unit is provided by a plurality of transport rollers 43 arranged at predetermined positions in the second transport path 10. 7 is conveyed. At this time, the first conveyance path 9 and the second conveyance path 10 are joined and before the image forming unit 7 (specifically, a secondary transfer roller (secondary transfer unit) 23 described later). By the registration roller 22 provided at the front position, the timing of the image forming operation and the paper feeding operation in the image forming unit 7 is measured.

  The image forming unit 7 forms a full-color toner image obtained by superimposing the toner images of the respective colors formed by the image forming units 26 to 29 and the image forming units 26 to 29 for forming the toner images of the respective colors on a sheet (recording medium). And a transfer conveyance unit 30 for transferring to the transfer unit. More specifically, the image forming units 26 to 29 for the respective colors are arranged along the moving direction of a primary transfer belt (intermediate transfer member) 40 described later arranged to run clockwise in the transfer conveyance unit 30. Yes. The order of color arrangement in the image forming units 26 to 29 is not particularly limited, but in FIG. 1, black (B), in order from the downstream side with respect to the moving direction of the primary transfer belt (intermediate transfer member) 40, Image forming units of yellow (Y), cyan (C), and magenta (M) are provided.

  Each of the image forming units 26 to 29 includes a photosensitive drum (image carrier) 32, a charging unit 33 disposed to face the peripheral surface of the photosensitive drum (image carrier) 32, and a charging unit 33. A laser scanning unit 34 for irradiating a laser beam to a specific position on the circumferential surface of the photosensitive drum (image carrier) 32, and a downstream side of a laser beam irradiation position from the laser scanning unit 34. A developing unit 35 disposed to face the peripheral surface of the photosensitive drum 32 and a cleaning unit 36 disposed on the downstream side of the developing unit 35 and opposed to the peripheral surface of the photosensitive drum 32 are provided. ing. The developing units 35 of the image forming units 26 to 29 each include a toner box 51 in which a developer of each color is stored. Note that the photosensitive drum 32 of each of the image forming units 26 to 29 is rotated counterclockwise by a drive motor (not shown).

  The transfer conveyance unit 30 includes a rear roller (drive roller) 38 disposed near the image forming unit 26, a front roller (driven roller) 39 disposed near the image forming unit 29, and a rear roller. Primary transfer belt (intermediate transfer member) 40 disposed across 38 and the front roller 39, and primary transfer to a position downstream of the developing unit 35 in the photosensitive drum 32 of each image forming unit 26-29. A primary transfer roller (primary transfer means) 41 disposed for each photoconductive drum 32 so as to be in pressure contact with the belt 40, and paper (recording) fed from the primary transfer belt 40 and the registration roller 22. And a secondary transfer roller (secondary transfer means) 23 disposed so as to be in pressure contact with the rear roller (drive roller) 38 via the medium).

  In each of the image forming units 26 to 29, first, the surface of the photosensitive drum (image carrier) 32 is charged at a position facing the charging unit 33. Next, an electrostatic latent image is formed on the photosensitive drum (image carrier) 32 by irradiating a laser beam from the laser scanning unit 34 based on image data to be formed on the charged portion. The formed electrostatic latent image is developed when facing the developing unit 35, and a toner image of each color is formed on the photosensitive drum (image carrier) 32. Next, the toner images of the respective colors are sequentially transferred onto the primary transfer belt (intermediate transfer member) 40 at the position of the primary transfer roller 41 of each of the image forming units 26 to 29, and the most downstream image forming unit 26. A full-color toner image is formed on the primary transfer belt (intermediate transfer member) 40 that has passed through. The full-color toner image on the primary transfer belt (intermediate transfer member) 40 is transferred onto the sheet (recording medium) fed from the registration roller 22 at the position of the secondary transfer roller (secondary transfer means) 23. Next transfer is done. In each of the image forming units 26 to 29, the toner remaining on the peripheral surface of the photosensitive drum (image carrier) 32 after being transferred to the primary transfer belt (intermediate transfer member) 40 is removed by the cleaning unit 36. .

  The paper on which the image is formed by the image forming unit 7 is sent to the fixing unit 14 provided in the upper left portion, and a fixing process for fixing the image formed here on the paper is performed. The fixing process is to fix the toner image transferred to the sheet by the image forming unit 7 with heat and pressure. The fixing unit 14 includes a fixing roller 44 heated by a built-in heater, a pressure roller 45 disposed in pressure contact with the fixing roller 44, and a sheet that has passed through a secondary transfer roller (secondary transfer unit) 23. In order to guide the sheet between the fixing roller 44 and the pressure roller 45, the front conveyance path 46 disposed on the upstream side thereof, and the sheet that has passed between the fixing roller 44 and the pressure roller 45 are transferred to the third conveyance path 11 side. And a rear conveyance path 47 disposed on the downstream side thereof.

  The sheet subjected to the fixing process by the fixing unit 14 is transported by a transport roller 48 disposed at a predetermined position in the third transport path 11, and the sheet discharge unit 3 is disposed by a discharge roller 24 disposed on the exit side thereof. To be discharged. Further, if necessary, the sheet subjected to the fixing process is sent to the fourth conveying path 12 side, where it is reversed and image formation is first performed again by the secondary transfer roller (secondary transfer unit) 23. After the image is formed on the opposite surface, it can be discharged from the third transport path 11 to the paper discharge section 3 via the fixing unit 14.

  In the image forming apparatus of the present invention, it is important that each image forming unit accommodates toner specified according to its position (upstream side or downstream side). That is, when the plurality of image forming units 26 to 29 are U1, U2, U3, and U4 in order from the upstream side along the moving direction of the transfer medium (that is, the intermediate transfer body 40 in FIG. 1) (that is, the image). (When forming unit 29 = U1, image forming unit 28 = U2, image forming unit 27 = U3, and image forming unit 26 = U4), U1 contains toner surface-treated with higher fatty acid zinc. Contains a toner surface-treated with higher fatty acid magnesium, and U3 must contain a toner surface-treated with higher fatty acid calcium. In this way, by storing toner that has been surface-treated with a specific higher fatty acid metal salt, the charge-up tendency of the toner is changed stepwise, resulting in differences in images for each color, and toner scattering. Can be prevented. In addition, the surface treatment with the higher fatty acid metal salt also provides an effect that the character dropout phenomenon does not occur even when an amorphous silicon drum is used in the tandem type image forming apparatus.

The U4 (that is, the most downstream image forming unit) can contain toner surface-treated with an arbitrary metal stearate, but the toner contained in the U4 contains higher fatty acid metal. It is preferable that no salt is contained in that the chargeability of the drum is not impaired.
In the present invention, the higher fatty acid metal salt used for the surface treatment of each toner is preferably a fatty acid metal salt having 10 to 20 carbon atoms, such as a stearic acid metal salt, an oleic acid metal salt, and a lauric acid metal salt. Can be mentioned. Among these, a metal stearate salt is particularly preferable because it has a high effect of preventing character dropout when an amorphous silicon drum is used. Therefore, it is a preferable aspect of the present invention that the higher fatty acid zinc is zinc stearate, the higher fatty acid magnesium is magnesium stearate, and the higher fatty acid calcium is calcium stearate.

  In each of the toners contained in U1, U2, and U3, the concentration of each specific higher fatty acid metal salt (that is, higher fatty acid zinc in U1, higher fatty acid magnesium in U2, and higher fatty acid calcium in U3) is Although not particularly limited, in any case, it is usually preferably 0.01 to 0.2% by weight based on the toner particles. More preferably, the content is 0.01 to 0.1% by weight based on the toner particles. In each of the units U1, U2 and U3, if the specific higher fatty acid metal salt concentration of the toner to be stored is too low, the effect of reducing the surface frictional resistance of the amorphous silicon drum may be insufficient. If the concentration of the specific higher fatty acid metal salt in the toner to be used is too high, there is a risk of poor charging of the drum.

  Each toner accommodated in each image forming unit in the present invention is not particularly limited except that the surface treatment with the higher fatty acid metal salt is as described above. For example, binder resin, magnetic powder or colorant, release agent In addition, toner particles can be obtained using a charge control agent and the like, and can be obtained by externally adding the above-described silica and other components described below. In addition, what is necessary is just to set suitably the mixture ratio of each component at the time of obtaining a toner within the range of a conventionally well-known technique. The toner in the present invention may be used, for example, as a one-component developer or a two-component developer with a magnetic carrier (for example, iron powder or ferrite).

  Examples of the binder resin include polystyrene resins, acrylic resins, styrene-acrylic copolymers, polyethylene resins, polypropylene resins, polyvinyl chloride resins, polyester resins, polyamide resins, polyurethane resins, and polyvinyl resins. Thermoplastic resins such as alcohol resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins can be used. In addition to the thermoplastic resin, a part of the thermosetting resin can also be used as the binder resin. Examples of the thermosetting resin include epoxy resins and cyanate resins.

  Examples of magnetic powder include ferrite, magnetite and other irons, cobalt, nickel and other metals exhibiting ferromagnetism, alloys of these metal elements, compounds containing these metal elements, and suitable heat treatments that do not contain ferromagnetic elements. Examples include alloys that exhibit ferromagnetism and chromium dioxide. As these magnetic powders, fine powders having an average particle diameter of 0.1 to 1 μm, preferably 0.1 to 0.5 μm, may be used. Moreover, you may use the magnetic powder surface-treated with surface treatment agents, such as a titanium coupling agent and a silane coupling agent.

  Examples of the colorant include a black colorant such as carbon black; a nitro pigment such as naphthol yellow S; an azo pigment such as Hansa Yellow 5G, Hansa Yellow 3G, Hansa Yellow G, Benzidine Yellow G, and Vulcan Fast Yellow 5G. In addition to inorganic pigments such as yellow iron oxide and ocher, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 180, C.I. I. Solvent Yellow 2, C.I. I. Solvent Yellow 6, C.I. I. Solvent Yellow 14, C.I. I. Solvent Yellow 15, C.I. I. Solvent Yellow 16, C.I. I. Solvent Yellow 19, C.I. I. Yellow colorants such as Solvent Yellow 21; C.I. I. Pigment blue 15, C.I. I. Pigment blue 15-1, C.I. I. Pigment blue 15-3, C.I. Pigment blue 16, C.I. I. Solvent Blue 55, C.I. I. Solvent Blue 70, C.I. I. Direct Blue 86, C.I. I. Cyan colorants such as Direct Blue 25; C.I. I. Pigment red 81, C.I. I. Pigment red 122, C.I. I. Pigment red 57, C.I. Pigment Red 49, C.I. I. Pigment red 238, C.I. I. Solvent Red 49, C.I. I. Solvent Red 19, C.I. I. Solvent Red 52, C.I. I. Basic Red 10, C.I. I. And magenta colorants such as Disperse Red 15.

  Examples of mold release agents include plant waxes such as carnauba wax, sugar wax, and wood wax; animal waxes such as beeswax, insect wax, whale wax, and wool wax; Fischer-Tropsch wax and polyethylene having ester in the side chain Examples thereof include synthetic hydrocarbon waxes such as wax and polypropylene wax.

  As the charge control agent, there are those showing positive chargeability and those showing negative chargeability. Specifically, as the positively chargeable charge control agent, for example, pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2, 4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5- Thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5 -Azine compounds such as oxatriazine, phthalazine, quinazoline, quinoxaline; azine fast red FC, azine fast red 12BK, azine violet Direct dyes composed of azine compounds such as BO, azine brown 3G, azine light brown GR, azine dark green BH / C, azine dip black EW and azine black 3RL; nigrosine compounds such as nigrosine, nigrosine salt, nigrosine derivatives; nigrosine Acid dyes composed of nigrosine compounds such as BK, nigrosine NB, and nigrosine Z; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; quaternary ammonium salts such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride Quaternary ammonium salt, carboxylate, or resin or oligomer having a carboxyl group as a functional group (more specifically, a styrene resin having a quaternary ammonium salt Acrylic resin having quaternary ammonium salt, styrene-acrylic resin having quaternary ammonium salt, polyester resin having quaternary ammonium salt, styrene resin having carboxylate, acrylic resin having carboxylate, Styrene-acrylic resin having carboxylate, polyester resin having carboxylate, polystyrene resin having carboxyl group, acrylic resin having carboxyl group, styrene-acrylic resin having carboxyl group, having carboxyl group Polyester-based resin, etc.). On the other hand, as the negatively chargeable charge control agent, for example, organometallic complexes and chelate compounds are effective. Specific examples include aluminum acetylacetonate, iron (II) acetylacetonate, 3,5-di-tert. -Chromium butylsalicylate etc. are mentioned, An acetylacetone metal complex, a salicylic acid type metal complex or a salt is especially preferable, and a salicylic acid type metal complex or a salicylic acid type metal salt is particularly preferable.

  Examples of other components that can be externally added to the toner particles include silica powder, titanium oxide, aluminum oxide, magnesium oxide, zinc oxide, strontium titanate, barium titanate, magnesium titanate, and calcium titanate. A metal oxide etc. are mentioned.

  The image carrier in the present invention is not particularly limited, and is an organic photoreceptor having an organic photosensitive layer containing at least a charge generating agent and a charge transport agent on a conductive substrate, an amorphous silicon layer, an amorphous layer. Inorganic photoreceptors having a porous silicon layer, a Se-based photosensitive layer, a ZnO photosensitive layer, a CdS-based photosensitive layer, and the like can be used. Among these, an amorphous silicon drum having an amorphous silicon layer is used. It is desirable in that the effect can be exhibited effectively. That is, when an amorphous silicon drum having a high frictional resistance is used as the image carrier, the toner that has been primarily transferred adheres to the intermediate transfer member and is easily peeled off. In the present invention, this can be effectively prevented.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to a following example.
[Example 1]
(Manufacture of black toner and black developer)
100 parts by weight of a polyester resin obtained by condensing bisphenol A and fumaric acid, 4 parts by weight of carbon black (“MA-100” manufactured by Mitsubishi Chemical Corporation), Fischer-Tropsch wax (“FT-100” manufactured by Nippon Seiki) A mixture of 3 parts by weight and 2 parts by weight of a quaternary ammonium salt compound (“P-51” manufactured by Orient Chemical Co., Ltd.) was mixed for 2 minutes with a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.), and then melt-kneaded with a twin-screw extruder. A toner kneaded material was prepared. The obtained toner kneaded product was finely pulverized with an airflow type pulverizer and classified with an air classifier to obtain toner particles having a volume average particle diameter of 8 μm.

Next, 1 part by weight of silica particles (“TG-820” manufactured by Cabot Corporation) and 1 part by weight of titanium oxide (“TTO-55A” manufactured by Ishihara Sangyo Co., Ltd.) are added to 100 parts by weight of the obtained toner particles. The toner was mixed at 3000 rpm for 10 minutes using a Henschel mixer.
The obtained toner and a ferrite carrier (“EF-60B” manufactured by Powdertech Co., Ltd.) having an average particle diameter of 60 μm coated with a silicone resin (“KR251” manufactured by Shin-Etsu Silicone) are blended so that the toner concentration becomes 5% by weight. The mixture was stirred and mixed uniformly to obtain a two-component developer.

(Manufacture of yellow toner and yellow developer)
Toner particles were obtained in the same manner as in the production of the black toner except that 2 parts by weight of yellow pigment (CI Pigment Yellow 180) was used instead of 4 parts by weight of carbon black.
Next, 0.1 parts by weight of calcium stearate ("Calcium stearate" manufactured by NOF Corporation) was added to and mixed with 100 parts by weight of the obtained toner particles together with 1 part by weight of silica particles and 1 part by weight of titanium oxide. Except for this, a toner was obtained in the same manner as in the above black toner production method.
Using the obtained toner, a two-component developer was prepared in the same manner as in the production of the black developer.

(Manufacture of cyan toner and cyan developer)
Toner particles were obtained in the same manner as in the production of the black toner except that 3 parts by weight of a cyan pigment (CI Pigment Blue 15-3) was used instead of 4 parts by weight of carbon black.
Next, 0.1 parts by weight of magnesium stearate (“magnesium stearate GF-200” manufactured by NOF Corporation) is added to 100 parts by weight of the obtained toner particles together with 1 part by weight of silica particles and 1 part by weight of titanium oxide. A toner was obtained in the same manner as in the above black toner production method except that it was added and mixed.
Using the obtained toner, a two-component developer was prepared in the same manner as in the production of the black developer.

(Manufacture of magenta toner and magenta developer)
Toner particles were obtained in the same manner as in the production of the black toner except that 3 parts by weight of magenta pigment (CI Pigment Red 238) was used instead of 4 parts by weight of carbon black.
Next, 0.1 part by weight of zinc stearate (“Zinc stearate” manufactured by NOF Corporation) is added together with 1 part by weight of silica particles and 1 part by weight of titanium oxide to 100 parts by weight of the obtained toner particles. A toner was obtained in the same manner as in the black toner manufacturing method except that the mixing was performed.
Using the obtained toner, a two-component developer was prepared in the same manner as in the production of the black developer.

(Image evaluation)
Using the tandem color image forming apparatus (FS-5016N remodeling machine: built-in amorphous silicon photoconductor) manufactured by Kyocera Mita Co., Ltd., the developer of the four colors obtained above is downstream with respect to the moving direction of the intermediate transfer member. To black, yellow, cyan, and magenta (that is, magenta is set for U1, cyan for U2, yellow for U3, and black for U4). The power was turned on, the image immediately after stabilization was output, and the initial image density was measured using “RD-19I” manufactured by Gretab Macbeth. Immediately thereafter, the developer was taken out of the apparatus and sampled, and the initial charge amount (μC / g) was measured using a suction-type charge amount measuring device (manufactured by Trek).
Next, an endurance image output test for outputting 100,000 sheets of an image having a printing density of 4% was performed, and the image density and the charge amount after 100,000 sheets were measured in the same manner as described above. In addition, the occurrence of defects such as transfer defects and toner dust in image output up to 100,000 sheets was also confirmed.
The image density was determined to be acceptable (appropriate for practical use) at 1.30 or higher. The results are shown in Table 1.

[Comparative Example 1]
Other than using zinc stearate in place of calcium stearate in the production of yellow toner used for yellow developer, and using calcium stearate in place of zinc stearate in production of magenta toner used in magenta developer Was carried out in the same manner as in Example 1. Table 1 shows the results of the image evaluation.

[Comparative Example 2]
Zinc stearate was used in place of calcium stearate in the production of yellow toner used for the yellow developer, and zinc stearate was used in place of magnesium stearate in the production of cyan toner used in the cyan developer. Except for this, the same procedure as in Example 1 was performed. Table 1 shows the results of the image evaluation.

[Comparative Example 3]
Other than using calcium stearate instead of magnesium stearate in the production of cyan toner used in the cyan developer, and using calcium stearate instead of zinc stearate in the production of magenta toner used in the magenta developer. Was carried out in the same manner as in Example 1. Table 1 shows the results of the image evaluation.

1 is a schematic diagram illustrating an example of an image forming apparatus of the present invention.

Explanation of symbols

7 Image forming unit 14 Fixing unit 22 Registration roller 23 Secondary transfer roller (secondary transfer means)
26 to 29 Image forming unit 30 Transfer conveyance unit 32 Photosensitive drum (image carrier)
33 Charging unit 34 Laser scanning unit 35 Developing unit 36 Cleaning unit 40 Primary transfer belt (intermediate transfer member)
41 Primary transfer roller (primary transfer means)
44 Fixing roller 45 Pressure roller

Claims (4)

In a tandem type image forming apparatus in which a plurality of image forming units are arranged along the moving direction of the transfer medium so that each color toner image is sequentially transferred onto the transfer medium.
When U1, U2, U3, and U4 are set in order from the upstream side along the moving direction of the transfer medium, U1 is a toner surface-treated with higher fatty acid zinc, and U2 is a toner surface-treated with higher fatty acid magnesium. However, the U3 contains toners surface-treated with higher fatty acid calcium, respectively.   The image forming apparatus according to claim 1, wherein the higher fatty acid zinc is zinc stearate, the higher fatty acid magnesium is magnesium stearate, and the higher fatty acid calcium is calcium stearate.   The image forming apparatus according to claim 1, wherein the toner contained in the U4 does not contain a higher fatty acid metal salt. The image forming apparatus according to claim 1, further comprising an amorphous silicon drum as the image carrier.

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