JP2007271982A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus of a tandem type or the like in which even when amorphous silicon drums are used, no letter void generation phenomenon occurs and faulty charge is avoided. <P>SOLUTION: In the image forming apparatus of a tandem type or the like, a toner containing a higher fatty acid metal salt and a titanium oxide is housed in an image forming unit disposed on the most downstream side with respect to a moving direction of a transfer medium, and the relationships of X1>Xn, X1≥Xm≥Xn, Y1>Yn and Y1≥Ym≥Yn are satisfied, wherein X1 and Y1 represent the higher fatty acid metal salt concentration and titanium oxide concentration of the toner, respectively; Xn and Yn represent the higher fatty acid metal salt concentration and titanium oxide concentration of a toner, respectively, housed in an image forming unit disposed on the most upstream side with respect to the moving direction of the transfer medium; and Xm and Ym represent the higher fatty acid metal salt concentration and titanium oxide concentration of a toner, respectively, housed in an image forming unit disposed between the image forming unit on the most downstream side and the image forming unit on the most upstream side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus useful for a copying machine, a laser printer, a facsimile, and a complex machine using electrophotography.

  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 image forming apparatuses that form a color image by superimposing the image on the surface are employed. A typical example of such an image forming apparatus is a tandem type image forming apparatus. In general, a tandem image forming apparatus includes a movable intermediate transfer member that sequentially superimposes and transfers toner images of each color, and an image that is arranged along the moving direction of the intermediate transfer member and carries a toner image for each color. A plurality of image forming units having a carrier, primary transfer means for transferring a toner image on the image carrier to the intermediate transfer member, and secondary transfer for transferring the toner image on the intermediate transfer member to a recording medium; Means.

  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 an image forming apparatus that superimposes toner images formed on a plurality of photoconductors on the same transfer medium, it is so-called. There was often a case of “character dropout phenomenon”. For example, in a tandem type image forming apparatus, the toner first transferred to the intermediate transfer member in the most upstream image forming unit with respect to the moving direction of the intermediate transfer member is the image carrier of the image forming unit on the downstream side of this. When the image bearing member is an amorphous silicon drum having a high frictional resistance, the outermost surface layer of the primary transferred toner adheres to the drum and is peeled off. This causes a “character dropout phenomenon” in which the middle of the toner line drawing is lost.

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

  In general, in order to obtain the effects of metal soap sufficiently to achieve each purpose, a large amount of metal soap must be contained, and a large amount of metal soap is also used in Patent Document 1 and Patent Document 2. ing. However, when a large amount of metal soap is contained, for example, the charging property is lowered in Patent Document 1 and the metal soap is fixed on the blade surface in Patent Document 2. Patent Document 1 solves the above problem by reducing the particle size of metal soap, and Patent Document 2 optimizes the amount of metal soap in the toner according to a plurality of developing units that rotate. This solves the above problem.

  Similar to the above, even if an image forming apparatus having a plurality of photoconductors such as a tandem type using an amorphous silicon drum is used to suppress the character missing phenomenon, the character missing phenomenon does not occur reliably. In order to sufficiently reduce the frictional resistance of the drum, a large amount of metal soap must be added to the toner, which causes a problem of causing charging failure.

  Accordingly, an object of the present invention is an image forming apparatus that superimposes toner images formed on a plurality of photoconductors on the same transfer medium, and even if an amorphous silicon drum is used, a character dropout phenomenon occurs. It is another object of the present invention to provide an image forming apparatus that does not cause charging failure.

  In order to solve the above-mentioned problems, the present inventors have reduced the frictional resistance of the image bearing member by containing a higher fatty acid metal salt, which is a metal soap, in the toner, thereby preventing the character void phenomenon. While keeping the salt content as low as possible so that charging failure does not occur as much as possible, intensive studies were carried out with the aim of reliably preventing the character dropout phenomenon. As a result, it has been found that the ease of occurrence of the phenomenon that the toner is peeled off by contact between the image carrier and the transfer medium varies depending on the position of the image forming unit. In other words, the amount of toner on the transfer medium increases as it goes from upstream to downstream, so that the image forming unit located on the downstream side is more likely to be peeled off due to the contact between the image carrier and the transfer medium. In view of this, the higher fatty acid metal salt concentration of the toner in each image forming unit is changed according to the position so that the higher fatty acid metal salt concentration is higher on the downstream side and lower on the upstream side. The minimum amount required to reduce the frictional resistance of the body was set. In addition, if a higher fatty acid metal salt is contained, the higher fatty acid metal salt adheres to the image carrier, and the problem that the charging ability of the image carrier cannot be maintained may occur. Aiming to keep it in check, we conducted intensive studies. As a result, it was conceived that titanium oxide was contained and the higher fatty acid metal salt adhering to the image carrier was removed by its polishing ability. However, if a large amount of titanium oxide is contained, the image carrier may be scraped off, so that the amount of titanium oxide is minimized as much as possible on the downstream side so as to match the higher fatty acid metal salt concentration of each toner. , I tried to decrease the more upstream. As described above, by setting the content of the higher fatty acid metal salt and titanium oxide in accordance with the position of the image forming unit, it was confirmed that charging failure can be suppressed while preventing the character dropout phenomenon. It came to complete.

That is, the present invention has the following configuration.
(1) In a tandem type image forming apparatus in which a plurality of image forming units are arranged along the movement direction of the transfer medium so that the respective color toner images are sequentially transferred onto the transfer medium, the transfer medium moves in the most direction. The image forming unit disposed downstream contains toner (T1) containing a higher fatty acid metal salt and titanium oxide, and the image forming unit disposed at the most upstream with respect to the moving direction of the transfer medium contains toner ( The toner (Tm) is accommodated in each of the image forming units arranged between the most downstream image forming unit and the most upstream image forming unit, and the higher fatty acid metal salt concentration in each toner and When titanium oxide concentration is expressed by the following abbreviations,
X1: Higher fatty acid metal salt concentration of toner (T1)
Xn: Higher fatty acid metal salt concentration of toner (Tn)
Xm: Concentration of higher fatty acid metal salt in toner (Tm)
Y1: Titanium oxide concentration of toner (T1)
Yn: Titanium oxide concentration of toner (Tn)
Ym: Titanium oxide concentrations X1, Xm, and Xn of the toner (Tm) satisfy the relationship of the following formula (I) and the following formula (II), and Y1, Ym, and Yn satisfy the following formula (III) and the following formula (IV). An image forming apparatus characterized by satisfying.
X1> Xn (I)
X1 ≧ Xm ≧ Xn (II)
Y1> Yn (III)
Y1 ≧ Ym ≧ Yn (IV)
(2) Each toner accommodated in a plurality of image forming units disposed between the most downstream image forming unit and the most upstream image forming unit is a toner accommodated in an image forming unit adjacent to the downstream side. The image forming apparatus according to (1), which has a higher fatty acid metal salt concentration equal to or less than
(3) The image forming apparatus according to (1) or (2), wherein the higher fatty acid metal salt is zinc stearate.
(4) Each toner accommodated in the plurality of image forming units disposed between the most downstream image forming unit and the most upstream image forming unit is the toner accommodated in the image forming unit adjacent to the downstream side. The image forming apparatus according to any one of (1) to (3), wherein the image forming apparatus has a titanium oxide concentration that is equal to or smaller than that.
(5) The image forming apparatus according to any one of (1) to (4), wherein each image forming unit is provided with an amorphous silicon drum.
(6) The transfer medium according to any one of (1) to (5), wherein the transfer medium is an intermediate transfer body, and the toner image transferred to the intermediate transfer body is a tandem image forming apparatus that transfers the recording medium to a recording medium. The image forming apparatus described.

  According to the present invention, there is an effect that it is possible to provide a stable image by suppressing the character dropout phenomenon without causing charging failure.

  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. That is, 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 an 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 achieved.

  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, the image forming unit (that is, the image forming unit 26 in FIG. 1) arranged on the most downstream side with respect to the moving direction of the transfer medium (that is, the primary transfer belt 40 in FIG. 1); The image forming unit is sometimes referred to as “unit (1)”.) It is important that the toner (T1) containing a higher fatty acid metal salt and titanium oxide is contained. By adding a higher fatty acid metal salt to the toner (T1) in at least the most downstream unit (1), the toner transferred onto the transfer medium is adhered to and peeled off from the image carrier. Can be effectively prevented. In addition, the toner (T1) containing a higher fatty acid metal salt can also contain titanium oxide, thereby suppressing charging defects that may be caused by the higher fatty acid metal salt.

  Examples of the higher fatty acid metal salt include zinc stearate, magnesium stearate, calcium stearate, stearic acid amide, and stearic acid bisamide. Among these, zinc stearate is particularly preferable because it can more effectively reduce the frictional resistance of the amorphous silicon drum. Only 1 type may be used for a higher fatty acid metal salt, and 2 or more types may be used together.

In the image forming apparatus of the present invention, the image forming unit disposed in the uppermost stream with respect to the moving direction of the transfer medium (that is, the image forming unit 29 in FIG. 1; hereinafter, the image forming unit is referred to as “unit (n)”). The toner (Tn) is accommodated in the image forming unit, and the image forming unit (ie, FIG. 1) disposed between the most downstream image forming unit (1) and the most upstream image forming unit (n). In the image forming units 27 and 28; hereinafter, the image forming units may be referred to as "unit (m)"), toner (Tm) is accommodated in each toner, and higher fatty acid metal salt in each toner. When the concentration and titanium oxide concentration are expressed by the following abbreviations,
X1: Higher fatty acid metal salt concentration of toner (T1)
Xn: Higher fatty acid metal salt concentration of toner (Tn)
Xm: Concentration of higher fatty acid metal salt in toner (Tm)
Y1: Titanium oxide concentration of toner (T1)
Yn: Titanium oxide concentration of toner (Tn)
Ym: The titanium oxide concentrations X1, Xm, and Xn of the toner (Tm) satisfy the relationship of the following formula (I) and the following formula (II), and Y1, Ym, and Yn satisfy the following formula (III) and the following formula (IV). Must meet.
X1> Xn (I)
X1 ≧ Xm ≧ Xn (II)
Y1> Yn (III)
Y1 ≧ Ym ≧ Yn (IV)
While the toners (T1), (Tn), and (Tm) accommodated in each image forming unit satisfy the above formulas (I) to (IV), respectively, while preventing character dropout phenomenon, Charging failure can be suppressed.

  When there are a plurality of units (m) (that is, when a plurality of image forming units are arranged between the most downstream unit (1) and the most upstream unit (n)), Xm is a plurality of units. It is assumed that the individual higher fatty acid metal salt concentration for each toner contained in the unit (m), and Ym is the individual titanium oxide concentration for each toner contained in the plurality of units (m). It is important that the higher fatty acid metal salt concentration or titanium oxide concentration satisfy the above formulas (II) and (IV) as Xm or Ym, respectively. For example, in the case of a tandem type image forming apparatus having four image forming units as shown in FIG. 1, both the image forming unit 27 and the image forming unit 28 in FIG. 1 become the unit (m). The higher fatty acid metal salt concentration of the toner contained in the toner 27 and the higher fatty acid metal salt concentration of the toner contained in the image forming unit 28 must both satisfy the above formula (II) as Xm. Both the titanium oxide concentration of the toner contained in the toner and the titanium oxide concentration of the toner contained in the image forming unit 28 must satisfy the above formula (IV) as Ym.

In the present invention, each toner (Tm1,...) Accommodated in a plurality of units (m1, m2,...) Disposed between the most downstream unit (1) and the most upstream unit (n). Tm2,...) Preferably have a higher fatty acid metal salt concentration equal to or smaller than that of the toner accommodated in the image forming unit adjacent to the downstream side. That is, among the plurality of units (m1, m2,..., M (n−1)) arranged between the most downstream unit (1) and the most upstream unit (n), The unit (m1), unit (m2),..., Unit (m (n-1)) are arranged in order from the position, and the higher fatty acid gold salt concentrations of the toners contained in the units are arranged in order from the downstream side, Xm1, Xm2. ,..., Xm (n−1), it is preferable that the following formula (V) is satisfied.
Xm1≥Xm2≥ ... ≥Xm (n-1) (V)
As a result, it is possible to more reliably prevent the character dropout phenomenon and the charging failure.
In the present invention, each toner (Tm1,...) Accommodated in a plurality of units (m1, m2,...) Disposed between the most downstream unit (1) and the most upstream unit (n). Tm2,...) Each preferably has a titanium oxide concentration that is equal to or smaller than that of the toner contained in the image forming unit adjacent to the downstream side. That is, among the plurality of units (m1, m2,..., M (n−1)) arranged between the most downstream unit (1) and the most upstream unit (n), The unit (m1), unit (m2),..., Unit (m (n-1)) are arranged in order from the position, and the higher fatty acid gold salt concentration of the toner contained in each unit is designated as Ym1, Ym2 in order from the downstream side. When Ym (n-1) is satisfied, it is preferable to satisfy the following formula (VI).
Ym1≥Ym2≥ ... ≥Ym (n-1) (VI)
As a result, it is possible to more reliably prevent the character dropout phenomenon and the charging failure.

  The concentration of the higher fatty acid metal salt of the toner accommodated in each image forming unit is not particularly limited as long as the relationship of the above formulas (I) and (II) is satisfied, but at least for the toner (T1), On the other hand, it preferably contains 0.01 to 0.5% by weight of a higher fatty acid metal salt. More preferably, the higher fatty acid metal salt is contained in an amount of 0.03 to 0.3% by weight, more preferably 0.03 to 0.2% by weight, based on the toner particles. As for other than the toner (T1), for example, when four image forming units are provided as shown in FIG. 1, the second image forming unit from the most downstream side (that is, the image forming unit 27 in FIG. 1) has toner. It is preferable to use a toner containing 0.05 to 0.10% by weight of a higher fatty acid metal salt with respect to the particles, and the third image forming unit from the most downstream side (that is, the image forming unit 28 in FIG. 1). In this case, it is preferable to use a toner containing 0.02 to 0.05% by weight of a higher fatty acid metal salt with respect to the toner particles, and the most upstream image forming unit (n) (that is, the image forming unit in FIG. 1). In 29), it is preferable to use a toner containing 0.001 to 0.02% by weight of a higher fatty acid metal salt based on the toner particles. In the toner other than the toner (T1), the concentration of the higher fatty acid metal salt may be lower than the above range or may not contain the higher fatty acid metal salt (that is, the formula (I) and the formula (II). ), Xn may be 0, or Xn and Xm may be 0). In any toner, it is desirable that the higher fatty acid metal salt contains 0.5% by weight as an upper limit with respect to the toner particles in order to prevent charging failure more reliably.

  The titanium oxide concentration of the toner accommodated in each image forming unit is not particularly limited as long as the relationship of the above formulas (III) and (IV) is satisfied, but at least with respect to the toner (T1) with respect to the toner particles. It is preferable to contain 2.0 to 3.0% by weight of titanium oxide. As for other than the toner (T1), for example, when four image forming units are provided as shown in FIG. 1, the second image forming unit from the most downstream side (that is, the image forming unit 27 in FIG. 1) has toner. It is preferable to use a toner containing 1.5 to 2.0% by weight of titanium oxide with respect to the particles. In the third image forming unit from the most downstream side (that is, the image forming unit 28 in FIG. 1), the toner is used. It is preferable to use a toner containing 1.0 to 1.5% by weight of titanium oxide with respect to the particles. In the most upstream image forming unit (n) (that is, the image forming unit 29 in FIG. 1), the toner is used. It is preferable to use a toner containing 0.5 to 1.0% by weight of titanium oxide based on the particles. In the toner other than the toner (T1), the titanium oxide concentration may be lower than the above range, and even if it does not contain titanium oxide (that is, in the formula (III) and the formula (IV), Yn Is 0, or Yn and Ym are 0). When the amount of titanium oxide exceeds 3.0% by weight, the image carrier is easily scraped and deteriorated. On the other hand, when the amount is less than 0.5% by weight, the higher fatty acid metal salt adhering to the surface of the image carrier is sufficient. Sometimes it can't be removed.

Note that both the higher fatty acid metal salt concentration and the titanium oxide concentration can be determined by quantification using a calibration curve prepared from a standard sample using fluorescent X-ray analysis.
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 each image forming unit is provided with an amorphous silicon drum having a high frictional resistance as an image carrier, the toner transferred onto the transfer medium is likely to adhere and peel off, and as a result, the character dropout phenomenon is noticeable. Although this occurs, this can be effectively prevented in the present invention.

In the present invention, the toner accommodated in each image forming unit is not particularly limited as long as it satisfies the above-mentioned requirements regarding containing a higher fatty acid metal salt and titanium oxide. For example, binder resin, magnetic powder, or coloring It is possible to obtain toner particles using an agent, a release agent, a charge control agent, and the like, and to obtain the toner particles by externally adding the above-described higher fatty acid metal salt and other components described later. 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, azinda-green BH / C, azine dip black EW and azine black 3RL; nigrosine compounds such as nigrosine, nigrosine salts, nigrosine derivatives ; Acid dyes composed of nigrosine compounds such as nigrosine 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 In addition, quaternary ammonium salts, carboxylates, or resins or oligomers 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 and metal oxides such as aluminum oxide, magnesium oxide, zinc oxide, strontium titanate, barium titanate, magnesium titanate, and calcium titanate. Etc.

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.
In the following description, “parts by weight” is simply indicated as “parts” unless otherwise specified.

Example 1
First, four color developers were prepared as follows.
(Manufacture of black developer (labeled “Bk” in the table))
100 parts of a polyester resin obtained by condensing bisphenol A and fumaric acid, 4 parts of carbon black ("MA-100" manufactured by Mitsubishi Chemical), 3 parts of Fischer-Tropsch wax ("FT-100" manufactured by Nippon Seiki), A mixture of 2 parts 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.), then melt-kneaded with a twin screw extruder to obtain a toner kneaded product. Prepared. The obtained toner kneaded product was finely pulverized with an airflow pulverizer and then classified with an air classifier to obtain toner particles having a volume average particle diameter of 8 μm.

Next, with respect to 100 parts of the obtained toner particles, 1 part of silica particles (“TG-820” manufactured by Cabot Corporation), 2.3 parts of titanium oxide (“TTO-55A” manufactured by Ishihara Sangyo Co., Ltd.), zinc stearate 0.1 parts (manufactured by Nippon Oil & Fats Co., Ltd.) was added and mixed with a Henschel mixer (made by Mitsui Mining Co., Ltd.) at 3000 rpm for 10 minutes to obtain a toner.
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 uniformly stirred and mixed to obtain a two-component developer.

(Manufacture of yellow developer (labeled “Y” in the table))
Toner particles were obtained in the same manner as in the production of the black developer, except that 2 parts of yellow pigment (CI Pigment Yellow 180) was used instead of 4 parts of carbon black.
Next, except that the amount of zinc stearate added was changed to 0.07 parts and the amount of titanium oxide added was changed to 1.7 parts, a toner was obtained in the same manner as in the manufacture of the black developer, and A developer was obtained in the same manner.

(Manufacture of cyan developer (labeled “C” in the table))
Toner particles were obtained in the same manner as in the production of the black developer, except that 3 parts of a cyan pigment (CI Pigment Blue 15-3) was used instead of 4 parts of carbon black.
Next, except that the amount of zinc stearate added was changed to 0.04 parts and the amount of titanium oxide added was changed to 1.2 parts, a toner was obtained in the same manner as in the manufacture of the black developer, and A developer was obtained in the same manner.

(Manufacture of magenta developer (indicated as “M” in the table))
Toner particles were obtained in the same manner as in the production of the black developer except that 3 parts of magenta pigment (CI Pigment Red 238) was used instead of 4 parts of carbon black.
Next, except that the addition amount of zinc stearate was changed to 0.01 part and the addition amount of titanium oxide was changed to 0.7 part, a toner was obtained in the same manner as in the production of the black developer, and A developer was obtained in the same manner.

(Image evaluation)
Using the tandem color image forming apparatus (FS-5016N remodeling machine: built-in amorphous silicon photoconductor) manufactured by Kyocera Mita Co., Ltd. having the structure shown in FIG. With respect to the moving direction of the intermediate transfer member, the setting was made in the order of black, yellow, cyan, and magenta from the downstream side. The machine power was turned on and an image immediately after stabilization was output. Using this as an initial image, the following evaluation was performed. Next, a durability image output test of 100,000 sheets was performed with an image of A4 and a printing ratio of 5%, and the same evaluation was performed for the image after 100,000 sheets. The results are shown in Table 1.

<Text dropout (initial and after 100,000 sheets)>
Each of the obtained images was visually observed using a 10 × magnifier to confirm the presence or absence of character dropouts and the degree thereof, and judged according to the following criteria.
A: There is no occurrence of character missing and there is no unevenness at the end of the character.
◯: There is no missing character, but there is some unevenness at the end of the character.
Δ: When a magnifying glass is used, several missing characters are recognized, but are not recognized visually.
X: Character dropout that can be recognized only by visual observation has occurred.

<Charge amount (initial and after 100,000 sheets) and poor charging>
After outputting the initial image and the image after 100,000 sheets, the developer of each color was taken out and the charge amount (μC) was measured using a suction-type charge amount measuring device (manufactured by Trek).
<Drum adhesion>
After outputting the image after 100,000 sheets, the drum was visually observed, and the adhered matter on the drum was observed.
○: Adhered matter is not visually observed.
(Triangle | delta): A deposit | attachment is observed, but it is a level which does not affect an image.
X: Adhered matter is observed, and the image is affected.

(Example 2)
Except that the amount of zinc stearate added to the toner particles in the production of the black developer was changed to 0.5 part, a black developer was obtained in the same manner as in Example 1 except that this developer was used. In the same manner as in Example 1, image evaluation was performed. The results are shown in Table 1.

(Example 3)
A cyan developer was obtained in the same manner as in Example 1 except that the amount of zinc stearate added to the toner particles in the production of the cyan developer was 0.07 parts, except that this developer was used. In the same manner as in Example 1, image evaluation was performed. The results are shown in Table 1.

Example 4
Example 1 except that no zinc stearate was added to the toner particles (ie the amount of zinc stearate was 0 parts) in the production of the yellow developer, the cyan developer and the magenta developer. A yellow developer, a cyan developer and a magenta developer were obtained in the same manner as in Example 1, and image evaluation was performed in the same manner as in Example 1 except that these developers were used. The results are shown in Table 1.

(Example 5)
A black developer was obtained in the same manner as in Example 1 except that the amount of titanium oxide added to the toner particles in the production of the black developer was 2.9 parts, except that this developer was used. Image evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 6)
A cyan developer was obtained in the same manner as in Example 1 except that the amount of titanium oxide added to the toner particles in the production of the cyan developer was 1.7 parts. Image evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 7)
Except that the amount of titanium oxide added to the toner particles in the production of the magenta developer was 0.5 parts, a magenta developer was obtained in the same manner as in Example 1 except that this developer was used. Image evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 8)
The amount of titanium oxide added to the toner particles in the black developer production is 3 parts, the amount of titanium oxide added to the toner particles in the yellow developer production is 2 parts, and added to the toner particles in the cyan developer production. In the same manner as in Example 1, except that the amount of titanium oxide was 1.5 parts and the amount of titanium oxide added to the toner particles in the production of the magenta developer was 0.5 parts, respectively, A developer, a cyan developer, and a magenta developer were obtained, and image evaluation was performed in the same manner as in Example 1 except that these developers were used. The results are shown in Table 1.

(Comparative Example 1)
Except that the amount of zinc stearate added to the toner particles in the production of the black developer was 0.06 parts, and the amount of zinc stearate added to the toner particles in the production of the yellow developers was 0.07 parts, respectively. A black developer and a yellow developer were obtained in the same manner as in Example 1, and image evaluation was performed in the same manner as in Example 1, except that these developers were used. The results are shown in Table 2.

(Comparative Example 2)
In the same manner as in Example 1 except that the amount of zinc stearate added to the toner particles in the production of the black developer, the yellow developer, the cyan developer and the magenta developer was 0 parts. A black developer, a yellow developer, a cyan developer, and a magenta developer were obtained, and image evaluation was performed in the same manner as in Example 1 except that these developers were used. The results are shown in Table 2.

(Comparative Example 3)
In the production of the black developer, the amount of zinc stearate added to the toner particles is 0.01 parts, in the production of the yellow developer, the amount of zinc stearate added to the toner particles is 0.04 parts, Example 1 and Example 1 except that the amount of zinc stearate added to the toner particles in the production was 0.07 parts and the amount of zinc stearate added to the toner particles in the production of the magenta developer was 0.1 parts. Similarly, a black developer, a yellow developer, a cyan developer, and a magenta developer were obtained, and image evaluation was performed in the same manner as in Example 1 except that these developers were used. The results are shown in Table 2.

(Comparative Example 4)
Except that the amount of titanium oxide added to the toner particles in the production of the black developer was 1.6 parts, a black developer was obtained in the same manner as in Example 1 except that this developer was used. Image evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Example 5)
In the production of the cyan developer, the amount of titanium oxide added to the toner particles in the production of the black developer is 0.7 parts, and in the production of the yellow developer, the amount of titanium oxide added to the toner particles is 1.2 parts. Black in the same manner as in Example 1 except that the amount of titanium oxide added to the toner particles was 1.7 parts and the amount of titanium oxide added to the toner particles in the production of the magenta developer was 2.3 parts. A developer, a yellow developer, a cyan developer, and a magenta developer were obtained, and image evaluation was performed in the same manner as in Example 1 except that these developers were used. The results are shown in Table 2.

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 (6)

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.
The toner (T1) containing the higher fatty acid metal salt and titanium oxide is accommodated in the image forming unit arranged on the most downstream side with respect to the moving direction of the transfer medium, and arranged on the most upstream side with respect to the moving direction of the transfer medium. The image forming unit stores toner (Tn), and the image forming unit disposed between the most downstream image forming unit and the most upstream image forming unit stores toner (Tm).
When the higher fatty acid metal salt concentration and titanium oxide concentration in each toner are expressed by the following abbreviations, X1: higher fatty acid metal salt concentration of toner (T1)
Xn: Higher fatty acid metal salt concentration of toner (Tn)
Xm: Concentration of higher fatty acid metal salt in toner (Tm)
Y1: Titanium oxide concentration of toner (T1)
Yn: Titanium oxide concentration of toner (Tn)
Ym: Titanium oxide concentrations X1, Xm, and Xn of the toner (Tm) satisfy the relationship of the following formula (I) and the following formula (II), and Y1, Ym, and Yn satisfy the following formula (III) and the following formula (IV). An image forming apparatus characterized by satisfying.
X1> Xn (I)
X1 ≧ Xm ≧ Xn (II)
Y1> Yn (III)
Y1 ≧ Ym ≧ Yn (IV)   Each toner contained in a plurality of image forming units arranged between the most downstream image forming unit and the most upstream image forming unit is equivalent to the toner contained in the image forming unit adjacent to the downstream side. The image forming apparatus according to claim 1, wherein the image forming apparatus has a higher fatty acid metal salt concentration.   The image forming apparatus according to claim 1, wherein the higher fatty acid metal salt is zinc stearate.   Each toner contained in a plurality of image forming units arranged between the most downstream image forming unit and the most upstream image forming unit is equivalent to the toner contained in the image forming unit adjacent to the downstream side. The image forming apparatus according to claim 1, wherein the image forming apparatus has a titanium oxide concentration that is smaller than or equal to that.   The image forming apparatus according to claim 1, wherein each image forming unit is provided with an amorphous silicon drum. The image forming apparatus according to claim 1, wherein the transfer medium is an intermediate transfer body, and is a tandem type image forming apparatus in which a toner image transferred to the intermediate transfer body is transferred to a recording medium.

Images