JP2021021786A - Image formation device - Google Patents

Abstract

To provide an art that makes transfer features of a secondary color excellent and can output high-definition images, in a case of forming images using a plurality of different conductivity developers.SOLUTION: The present invention relates to an image formation device, and the image formation device comprises: a first transfer unit that forms a first transfer nip part with a first image carrier, and transfers a first developer image developed in the first image carrier by a first developer in the first transfer nip part to a transferred body; and a second transfer unit that forms a second transfer nip part with a second image carrier, transfers a second developer image developed in the second image carrier by a second developer in the second transfer nip part to the transferred body having the first developer image transferred from the first image carrier. Volume resistivity of the first developer and second developer is equal to or more than 1.0×105 Ω*cm and equal to or less than 1.0×1011 Ω*cm, respectively and the volume resistivity of the first developer is greater than that of the second developer.SELECTED DRAWING: Figure 4

Description

The present invention relates to an electrophotographic image forming apparatus for forming an image on a recording material using an electrophotographic method, and more particularly to a developing apparatus and a process cartridge applied to the electrophotographic image forming apparatus.

In a conventional electrophotographic image forming apparatus, a method of triboelectricly charging an insulating toner as a developing agent to give an electric charge and using it for development is widely and generally used. Here, as a method of charging the toner, the triboelectric property of the toner is controlled in advance by combining the toner with a binder resin or an additive. Then, in the case of a two-component developer, the toner is charged by frictional charging with a carrier in the developing apparatus, and in one-component developing, the toner is mainly charged by friction between the developing blade or the developing roller and the toner. In such a toner charging method, since there is a certain amount of charge distribution in the charge amount of the toner charged by friction, the toner has a low charge amount and is opposite to the charge polarity of the entire toner. Often contains reverse polarity toner having the charge polarity of. At this time, the low-charged toner and the reverse-polarity toner are attracted to the background portion of the electrostatic latent image on the image carrier to which the toner does not originally adhere, and cause so-called fog, which is a uniform stain on the background portion. Further, in this type of triboelectric charging method, the surface property of the toner changes due to the influence of the physical stress applied to the toner surface, and the charging amount tends to change. Further, it is easily affected by changes in the environment and changes over time, and the surface state of the triboelectric charging mechanism such as the toner and the stirring member changes, and as a result, the charged state of the toner tends to become unstable.
Therefore, in order to solve such a problem, a method of using a conductive toner, specifically, a method of injecting an electric charge into the conductive toner to be charged and subject to development is known. This method has various advantages because it does not utilize triboelectric charging. In particular, conductive toner has the greatest effect of being easily affected by changes in the surface properties of the toner, changes in the environment, and deterioration over time because the electric charge can be easily transferred and a uniform electric charge can be given to the toner to prevent fogging. It is a feature. In addition, since a triboelectric charging mechanism is not required, the structure is simple, and it is possible to reduce the size and price, which is also a great attraction.
Although the conductive toner has many merits as described above, a major problem is transferability. Since the conductive toner has a low resistance, it is difficult to maintain the charge amount, the charge amount decreases at the stage of the transfer process, and the transferability deteriorates. Therefore, it is difficult to transfer the toner image (developer image) by the general electrostatic transfer method. In order to solve such a technical problem, various methods are disclosed, for example, in Patent Document 1. That is, by proposing a toner material that makes it easy to inject charges into the toner but does not leak easily, applying an insulating substance to the surface of the transfer material, and heating the conductive toner on the image carrier, transfer using adhesive force. It is a method of trying to transfer to a material.

Japanese Patent No. 4636993

When forming a color image, various colors are reproduced by superimposing color toners of different coloring materials, but there is a problem that the conductive toner cannot superimpose the toner and cannot cope with colorization. The reason for this is that because the toner is conductive, the charge of the upper layer toner is transferred to the lower layer toner when different toners are overlapped. As a result, the charge held by the toner in the upper layer leaks and the amount of charge decreases, and even if a bias is applied between the image carrier (photosensitive drum) and the intermediate transfer body, transfer cannot be performed.

According to the present invention, when an image is formed by using a plurality of different conductive developeres, the transferability of the secondary color (the image of the developer transferred to the transfer material after the second) is improved and the quality is high. The purpose is to provide a technology that can output images.

In order to achieve the above object, the image forming apparatus of the present invention
A first transfer nip portion is formed with the first image carrier, and a first developer image developed on the first image carrier by the first developer is transferred to the first transfer. In the nip part, the first transfer part to be transferred to the transferred body and
A second transfer nip portion is formed with the second image carrier, and the second developer image developed on the second image carrier by the second developer is transferred to the second transfer. In the nip portion, the second transfer portion, which transfers the first developer image to the transferred object to which the image is transferred, and the second transfer portion.
With
Both the volume resistivity of the first developer and the second developer are 1.0 × 10 ⁵ Ω · cm or more and 1.0 × 10 ¹¹ Ω · cm or less, and
The volume resistivity of the first developer is larger than the volume resistivity of the second developer.

According to the present invention, in an image forming apparatus that forms an image by sequentially transferring and superimposing a plurality of developer images formed by using a plurality of different conductive developeres on a transfer target, each developer. Set the volume resistivity of. Further, the volume resistivity of the developer of the developer image transferred first to the transferred object is changed to the volume resistivity of the developer of the developer image transferred later (overlaid on the previous developer image). Make it bigger. This makes it possible to apply electric charge to the conductive developer by using electric charge injection, and to improve the transferability of the secondary color.

Schematic configuration of the image forming apparatus according to the embodiment Schematic cross-sectional view of the process cartridge according to the embodiment Diagram of toner being transferred onto an intermediate transfer member in the primary transfer step Diagram of toner being transferred onto the toner in the primary transfer process The figure in which the protrusion of the toner is in contact with the intermediate transfer body in the primary transfer step. Schematic configuration of the image forming apparatus according to the embodiment Schematic cross-sectional view of the process cartridge according to the embodiment Schematic cross-sectional view of the toner (developer) in this embodiment

Hereinafter, embodiments for carrying out the present invention will be described in detail exemplarily based on examples with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

[Example 1]
In the image forming apparatus according to the first embodiment of the present invention, a plurality of developing devices are arranged, and a toner image (developer agent image) imaged on each image carrier of the developing device is intermediately transferred as a transfer target. It is an image forming apparatus that is transferred onto the body and superposed, and has the following features. That is, the volume resistivity of the toner (developer) used in the developing device is 1.0 × 10 ⁵ Ω · cm or more 1.0 × 10 ¹¹ Ω.
・ It is cm or less. Further, the volume resistivity of the toner of the developing device arranged on the downstream side with respect to the rotation direction (circulating movement direction) of the intermediate transfer body is set higher than the volume resistivity of the toner of the developing device arranged on the upstream side. ing.

<Image forming device>
The configuration of the entire image forming apparatus will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram schematically showing a cross-sectional configuration of a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. Note that FIG. 1 briefly shows each configuration. FIG. 2 is a schematic cross-sectional view of the process cartridge according to this embodiment.
The image forming apparatus 100 according to this embodiment is a cross-sectional view showing the overall configuration of each color image forming apparatus. As shown in the figure, this apparatus is a tandem color image forming apparatus that employs an intermediate transfer body, which is an example of an electrophotographic color image forming apparatus.
Further, the image forming apparatus 100 according to this embodiment has an apparatus configuration that employs a so-called process cartridge method. Here, in the process cartridge, the image carrier and the developing device acting on the image carrier are integrated (made into a cartridge), and the main body of the device (the image carrier, the developing device, etc. in the image forming apparatus 100 is removed). It is configured to be removable with respect to (referring to the device configuration).

The image forming apparatus 100 according to the present embodiment includes four process cartridges 10a, 10b, 10c, and 10d (hereinafter, appropriately referred to as cartridges 10) that are detachably configured with respect to the apparatus main body. Each cartridge 10 includes a photosensitive drum 11 as an image carrier. A charging roller 12 for charging the surface of the photosensitive drum 11 and a cleaning blade 14 for cleaning the surface of the photosensitive drum 11 are provided around the photosensitive drum 11. Further, a developing device 20 for developing an electrostatic latent image formed on the surface of the photosensitive drum 11 with a developing agent is also provided. An opening 13 is also provided in order to secure a path for the laser beam irradiated on the surface of the photosensitive drum 11. Further, the process cartridges 10 (10a, 10b, 10c, 10d) contain toners 22 (22a, 22b, 22c, 22d), respectively.

<Image formation process>
When the image formation starts, the photosensitive drum 11 rotates in the direction of arrow A in FIG. 2, and the charging roller 12 follows the rotation of the photosensitive drum 11 and rotates in the direction of arrow B. Then, the surface of the photosensitive drum 11 is uniformly charged by the charging roller 12. After that, the surface of the photosensitive drum 11 is irradiated with laser light from the exposure device 1 to form an electrostatic latent image. On the other hand, in the developing apparatus 20, after the rotation of the photosensitive drum 11 starts, the developing roller 23 as the developer carrier separated from the photosensitive drum 11 moves in the direction of contact with the photosensitive drum 11. Subsequently, the developing roller 23 starts rotating in the direction of arrow C in FIG. 2, and the toner supply roller 24 as a developing agent supply member starts rotating in the direction of arrow D. Then, the electrostatic latent image formed on the photosensitive drum 11 is developed by the developing device 20. The developed toner image (developer image) is transferred (primary transfer step) to the intermediate transfer body (intermediate transfer belt) 4 in contact with the toner image due to the potential difference with the primary transfer roller 3. In the configuration of this embodiment, in order to transfer the toner image from the photosensitive drum 11 to the intermediate transfer body 4 as the transfer material, the primary transfer forming a transfer nip portion in which the intermediate transfer body 4 faces the photosensitive drum 11. The roller 3 corresponds to the transfer portion of the present invention.

After that, the toner image is transferred (secondary transfer step) to a recording material (recording medium) such as paper due to the potential difference with the secondary transfer roller 5. The recording material to which the toner image is transferred is conveyed to the fixing device 6 to be heated and pressurized. As a result, the toner image is fixed on the recording material. After that, the recording material is discharged to the outside of the image forming apparatus 100. After passing through the intermediate transfer body 4, the toner agent remaining on the photosensitive drum 11 without being transferred is scraped off by the cleaning blade 14. After that, the above process is repeated again.

<Developer>
The developing apparatus 20 will be described in more detail with reference to FIG. The developing devices 20 arranged in each of the four image forming units have the same device configuration except that the colors of the toners 22 contained in the developing devices 20 are different, and the matters described here are described in the four developing devices 20. It will be a common content. The developing device 20 includes a developing container 21 having an opening at a position facing the photosensitive drum 11. The toner 22 is housed in the developing container 21. Further, the developing device 20 includes a developing roller 23 and a toner supply roller 24. The developing roller 23 plays a role of transporting the toner to the electrostatic latent image on the photosensitive drum 11 while supporting the toner. The toner supply roller 24 has a surface layer made of a foaming material that slides on the surface of the developing roller 23. The toner supply roller 24 is responsible for supplying the toner 22 in the developing container 21 to the developing roller 23.

The developing roller 23 is composed of a core metal having a diameter of 6 mm, which is a conductive support, and an elastic body layer provided on the outer periphery of the core metal. The elastic body layer in this embodiment is composed of a 2.75 mm-thick silicon rubber layer provided on the outer periphery of the core metal and a 10 μm-thick urethane resin layer provided on the outer periphery of the silicon rubber layer. The diameter of the entire roller is 11.5 mm.

The toner supply roller 24 is composed of a core metal having a diameter of 5 mm, which is a conductive support, and a surface layer made of a foam material provided on the outer periphery of the core metal. The surface layer in this embodiment is made of urethane foam. The foam cell of this urethane foam is a continuous foam so that toner can enter and exit the urethane, and the diameter of the entire roller including the urethane foam is 13 mm. The axial center of the toner supply roller 24 is located at a position 11.05 mm away from the developing roller 23. Therefore, the toner supply roller 24 is compressed and deformed by a maximum of 1.2 mm along the developing roller 23 at the contact portion with the developing roller 23, and is in the same direction as the rotating direction (arrow C) of the developing roller 23 (arrow D). Rotate to. That is, the abutting portions of both rollers have velocities in opposite directions, and friction occurs. Therefore, the toner supply roller 24 heads toward the developing roller 23 by scraping the toner 22 from the surface of the developing roller 23 at the contact portion with the developing roller 23 and compressing the urethane foam at the time of contact with the developing roller 23. Toner 22 is discharged and supplied.

For charging the toner 22 in this embodiment, a method using charge injection is mainly used. The charge injection of this embodiment is performed by the toner regulation and charge injection member 25. The toner regulating and charge injection member 25 plays a role of regulating the toner adhering to the developing roller and stabilizing the adhering amount, and also plays a role of injecting a charge into the toner. The toner regulation and charge injection member 25 according to one aspect of the present invention needs to be a conductive member so that charge can be injected into the toner, and a metal or resin can be used as the material. Specific examples thereof include metals such as stainless steel, phosphor bronze and aluminum, and resins such as polyethylene terephthalate, acrylic resin and polyester. A conductive material may be added to such a resin in order to impart desired conductivity.

The toner regulation and charge injection member 25 in this embodiment uses a SUS plate having a thickness of 80 μm. Further, in order to provide a predetermined potential difference between the developing roller 23 and the toner regulating / charge injection member 25, the high voltage power supply 26 is transferred to the developing roller 23, and the high voltage power supply 27 is transferred to the toner regulating / charge injection member 25 as voltage application means. A predetermined bias is applied to each.
The toner 22 conveyed from the developing roller 23 passes through the nip portion where the amount of toner adhered is regulated by the toner regulation and charge injection member 25, and an electric field corresponding to the toner charge polarity is applied to the nip portion. When the toner 22 passing through the nip portion comes into contact with the toner regulation / charge injection member 25, charge is transferred between the toner 22 and the toner regulation / charge injection member 25, and the toner 22 is charged. can do.
In Example 1, a voltage of −350 V is applied to the developing roller 23 as a development bias during development, and a voltage of −550 V is applied to the toner regulating / charge injection member 25 to provide a potential difference of −200 V for charge injection. Is going.

<Toner>
The conductive toner 22 used in this embodiment will be described in detail. The toner 22 used in this embodiment imparts conductivity to the toner by forming a shell containing a metal compound on the surface of the toner particles (toner mother particles) 220.
By providing the conductive layer 221 on the surface layer of the toner in this embodiment, the charge can be efficiently injected into the toner by using the toner regulation and charge injection member 25 described above.

The metal compound will be described in detail.
The volume resistivity of the toner 22 of this embodiment is preferably 1.0 × 10 ⁵ Ω · cm or more and 1.0 × 10 ¹¹ Ω · cm or less. When the volume resistivity of the toner 22 is less than 1.0 × 10 ⁵ Ω · cm, sufficient transferability cannot be ensured even in the transfer step of this embodiment, and 1.0 × 10 ¹¹ Ω · cm is used. If it exceeds the value, the toner 22 cannot be charged by charging. The volume resistivity of the toner 22 can be calculated by sandwiching the toner 22 between electrodes and applying a constant load with a torque wrench, and measuring the distance between the electrodes and the resistance value. The detailed measurement method will be described later.

The metal compound in the toner of this example preferably contains at least one metal element M selected from the metal elements contained in Groups 3 to 13. By arranging a metal compound containing at least one metal element selected from the metal elements contained in the 3rd to 13th groups on the surface of the toner particles, the resistance value of the toner surface is lowered and the toner 22 is charged. The sex improves. Specific examples thereof include titanium, zirconium, hafnium, copper, iron, silver, zinc, indium and aluminum.

Further, the metal compound is preferably a reaction product of the compound containing the metal element and a polyhydric acid. The polyvalent acid receives an electron pair and tends to be negatively charged. Therefore, the compound containing the polyhydric acid and the metal element M is also easily negatively charged and has excellent chargeability. Therefore, by having the reaction product of the compound containing the metal element M and the polyhydric acid on the surface of the toner particles, the electric charge is smoothly transferred from the charged member to the toner particles through the compound containing the metal element. As a result, the charge injection property can be effectively performed and the charge distribution of the toner is also improved.

In the toner particles of this example, the electronegativity of the polling of the metal element M is preferably 1.25 or more and 1.85 or less, and more preferably 1.30 or more and 1.70 or less. A metal compound containing a metal element M having an electronegativity in the above range has hydrophobicity, suppresses hygroscopicity, and increases polarization within the metal compound, and thus has an effect on charge injection. Can be further improved.
For the electronegativity of polling, the value described in "The Chemical Society of Japan (2004)" Chemical Handbook Basics "Revised 5th Edition, Maruzen Publishing" was used.

The polyvalent acid may be any acid having a divalent value or higher. The reaction product of the divalent or higher acid and the compound containing the metal element M forms a crosslinked structure between the compound and the polyvalent acid, and the crosslinked structure promotes the movement of electrons to improve the charge injection property. Let me.
Specific examples of the polyhydric acid include the following. Inorganic acids such as phosphoric acid, carbonic acid and sulfuric acid; organic acids such as dicarboxylic acids and tricarboxylic acids.
Specific examples of organic acids include the following. Dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, and terephthalic acid. Tricarboxylic acids such as citric acid, aconitic acid, and trimellitic anhydride.
Among them, it is preferable that the polyhydric acid contains at least one selected from the group consisting of carbonic acid, sulfuric acid, and phosphoric acid because it reacts strongly with the compound containing the metal element M and is difficult to absorb moisture. More preferably, the polyhydric acid contains phosphoric acid.
As the polyhydric acid, the polyhydric acid may be used as it is, or an alkali metal salt of the polyhydric acid and sodium, potassium, lithium or the like; an alkaline earth metal salt of magnesium, calcium, strontium, barium or the like; or , May be used as an ammonium salt of a polyhydric acid.

In the toner particles of this example, the metal compound is preferably a metal phosphate, a metal sulfate, or a metal carbonate. Examples of the compound containing the metal element include a metal alkoxide such as tetraisopropyl titanate and a metal chelate such as titanium lactate. Specific examples of the reaction product of the polyhydric acid and the compound containing the metal element M include the following.
A reaction product of a compound containing phosphoric acid and titanium, a reaction product of a compound containing phosphoric acid and zirconium, a reaction product of a compound containing phosphoric acid and aluminum, a reaction product of a compound containing phosphoric acid and copper, a phosphoric acid Metal phosphate metal phosphate typified by a reaction product of a compound containing iron and a compound product containing sulfuric acid and titanium; a reaction product of a compound containing sulfuric acid and zirconium, a reaction product of a compound containing sulfuric acid and silver. Metal sulfates typified by substances; reactants of compounds containing carbon dioxide and titanium, reactants of compounds containing carbon dioxide and zirconium, reactants of compounds containing carbon dioxide and iron, etc. ..
Of these, metal phosphates and metal carbonates are preferable, and among them, metal phosphates have high strength due to the cross-linking between metals by phosphate ions, and are charged by having an ionic bond in the molecule. It is also excellent in start-up property, which is more preferable. As the metal element, Zr, Ti, and Al are preferable from the viewpoint of obtaining as a compound of a metal phosphate, and specifically, a zirconium phosphate compound, a titanium phosphate compound, and an aluminum phosphate compound are preferable.

<Manufacturing Example of Toner 22a of Example 1>
The method for obtaining toner particles by the suspension polymerization method will be described below.
First, a polymerizable monomer, a colorant, a wax, a charge control agent, and a polymerization initiator capable of producing a binder resin were mixed, and each material was dispersed using a homogenizer as a disperser. Next, the polymerizable monomer composition is put into an aqueous medium containing poorly water-soluble inorganic fine particles, and droplets of the polymerizable monomer composition are prepared using a high-speed disperser (granulation). Process). The polymerizable monomer in the droplet is polymerized to obtain an aqueous dispersion of toner particles (polymerization step). Then, the aqueous dispersion of the toner particles was filtered, separated into solid and liquid, and the solid content was dried to obtain toner particles.

By covering the surface of the toner particles (toner mother particles) 220 created by the above method with conductive fine particles (titanium oxide particles having an average particle diameter of about 10 nm) 221 to impart conductivity to the toner particles, the conductive toner 22 was prepared. .. Specifically, 0.2 parts of titanium oxide particles are mixed with 100 parts of toner particles in a stirring mixer (FM mixer of Nippon Coke Industries Co., Ltd.), and the surface of the toner particles is mixed by stirring and mixing at 12000 rpm × 30 seconds. Titanium oxide particles were attached so as to cover the conductive layer.
FIG. 8A schematically shows a schematic cross-sectional configuration of the toner 22 in this embodiment.
It is possible to control the volume resistivity of the toner according to the amount of titanium oxide present on the toner surface. In this embodiment, the amount of titanium oxide added is changed to change the amount of titanium oxide added to each of the toners of Examples and Comparative Examples. The volume resistivity is controlled.

<Measurement of toner volume resistivity>
The volume resistivity of the toner is measured as follows.
As the device, a 6430 type sub femtoampere remote source meter (manufactured by Keithley Instruments) is used. A SH2-Z4 terminal measurable sample holder (manufactured by Bio-Logic) was connected to the FORCE terminal of the device, 0.20 g of a metal compound was placed on the electrode portion, and a load of 123.7 kgf was applied using a torque wrench. In the state, measure the distance between the electrodes.
The resistance value when a voltage of 20 V is applied to the sample for 1 minute is measured, and the volume resistivity is calculated using the following formula.
Volume resistivity (Ω · cm) = R × S / L
(R: resistance value (Ω), L: distance between electrodes (cm), S: electrode area (cm ² ))

<Primary transfer process>
In this embodiment, the toner image formed on the photosensitive drum is electrostatically transferred to the rotating intermediate transfer body 4 in the primary transfer step. During the primary transfer step, a primary transfer voltage, which is a DC power source having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment), is applied to the primary transfer roller 3 from the primary transfer power source. Will be done. In this embodiment, in the primary transfer step, transfer was performed by providing a potential difference of + 600 V to the intermediate transfer body 4 with respect to the photosensitive drum.

The primary transfer roller 3 is a metal roller member having a roller diameter of 8 mm and a straight shape in the thrust direction, and SUS is used as the material in this embodiment. Further, the primary transfer roller 3 is pressed against the intermediate transfer body 4 so as to penetrate the intermediate transfer body 4 by 0.2 mm.

In this embodiment, a belt-shaped intermediate transfer belt that can be easily miniaturized is used as the intermediate transfer body 4. The intermediate transfer belt is an endless belt in which a conductive material is added to a resin material to impart conductivity. A tension of 100 N in total thickness is applied to the intermediate transfer belt.

The intermediate transfer belt of the present embodiment, the thickness 70μm formed of polyimide resin to adjust the volume resistivity ^{1.0 × 10 9 Ω · cm (} PI) by mixing carbon as a conductive material
The endless belt of was used. The electrical characteristics of this intermediate transfer belt are electronically conductive, and the variation in electrical resistivity with respect to humidity in the atmosphere is small.
In this embodiment, PI is used as the material of the intermediate transfer belt, but the material is not limited to this. For example, if it is a thermoplastic resin, the following other materials may be used. For example, materials such as polyester, polycarbonate, polyarylate, acrylonitrile-butadiene-styrene copolymer (ABS), polyvinylidene fluoride (PVdF), polyethylene naphthalate (PEN), and mixed resins thereof can also be preferably used. ..

The range of the volume resistivity of the intermediate transfer belt, the transfer of the viewpoint from 1.0 × 10 ⁸ Ω · c
A range of m or more and 1.0 × 10 ¹² Ω · cm or less is preferable. That's a low volume resistivity than 1.0 × 10 ⁸ Ω · cm, a transfer failure is a concern that occur due to the escape of the transfer current in the environment of high temperature and high humidity. On the other hand, if the volume resistivity is higher than 1.0 × 10 ¹² Ω · cm, there is a concern that transfer failure due to abnormal discharge may occur in a low temperature and low humidity environment.

For the measurement of the volume resistivity of the intermediate transfer belt, a high resta UP (MCP-HT450) manufactured by Mitsubishi Chemical Corporation was used as a measuring instrument, and a UR was used as a measuring probe. Then, the room temperature at the time of measurement is set to 23 ° C., the room humidity is set to 50%, and charging is performed at an applied voltage of 250 V for 10 seconds.

A case where different toners are transferred onto the toner on the intermediate transfer body 4 in the primary transfer step of this embodiment will be described in detail.
In the process of this embodiment, cartridge 10a, cartridge 10b, cartridge 1
Transferring is performed from the upstream side in the order of 0c and the cartridge 10d, and all the toner images are superimposed on the intermediate transfer body 4.

As described above, since the electric charge easily leaks from the conductive toner, it is difficult to transfer the toner while maintaining the electric charge amount, and the conductive toner tends to have poor transferability. In particular, in the primary transfer step of the secondary color at the time of image formation using a plurality of different toners, when different toners are superposed, the electric charge tends to leak from the upper layer toner to the lower layer toner toward the intermediate transfer body 4. .. As a result, the deterioration of the transferability in the secondary color is remarkable.

FIG. 4 is a diagram showing how the charge of the downstream toner 22q leaks when different downstream toners 22q are transferred from the photosensitive drum 11 to the toner layer (upstream toner) 22p on the intermediate transfer body 4. is there. When the volume resistivity of the downstream toner 22q is lower than the volume resistivity of the upstream toner 22p, the state of FIG. 4A shifts to the state of FIG. 4B, and the downstream toner 22q on the photosensitive drum 11 The charge held by the downstream toner 22q leaks through the upstream toner 22p at the moment when the toner 22p comes into contact with the upstream toner 22p. Therefore, the downstream toner 22q may not be able to be transferred.

In this embodiment, since the volume resistivity of the upstream toner 22p is set to be larger than the volume resistivity of the downstream toner 22q, the transferability of the secondary color can be improved. For example, in the image forming apparatus shown in FIG. 1, consider the case where the toner 22b is transferred onto the toner 22a transferred to the intermediate transfer body 4. In this embodiment, since the volume resistivity of the toner 22a on the intermediate transfer body 4 is set to be larger, the electric charge of the toner 22b does not move to the toner 22a when the toner 22b is transferred. Therefore, since the toner 22b can be transferred while retaining the electric charge, the transferability of the secondary color can be improved.

Although only the relationship between the toner 22a and the toner 22b will be described here, the same effect can be obtained if the relationship between the toner 22b and the toner 22c and the toner 22c and the toner 22d are the same.

<Evaluation method of secondary color transferability>
Using the toner combinations shown in Table 1, the transferability of the secondary color was evaluated by the following method. In the evaluation of this example, the transferability of the secondary color was evaluated using the toner 22a and the toner 22b. The evaluation was performed in an environment with a temperature of 23 ° C. and a humidity of 60%.
Table 1 shows the volume resistivity of the toner 22a, the toner 22b, and the intermediate transfer belt used in each Example and Comparative Example.
A solid image with a loading amount of 0.45 mg / cm ² of each toner was set to be printed on the intermediate transfer belt, a solid image of a secondary color was output, and the transferability level was visually confirmed.

<Example 1-1>
The results of evaluation using the toner prepared under the above-mentioned conditions are shown in Table 1 as Example 1-1. Good transferability was also shown in the secondary color.
<Example 1-2>
In Example 1-2, as shown in Table 1, the evaluation was performed using a toner having a volume resistivity of each toner different from that of Example 1-1. The secondary color was inferior to that of Example 1-1, but was generally at a good level.
<Example 1-3>
In Example 1-3, as shown in Table 1, the evaluation was performed using a toner having a volume resistivity of each toner different from that of Example 1-1. The secondary color was inferior to that of Example 1-1, but was generally at a good level.

<Comparative Example 1-1>
In Comparative Example 1-1, as shown in Table 1, the volume resistivity of each toner was different from that of Example 1-1 for evaluation. Since the volume resistivity of the toner is 1.0 × 10 ⁵ Ω · cm or less, the charge amount of the toner in the transfer process leaks, transferability of the secondary color is significantly deteriorated.
<Comparative Example 1-2>
In Comparative Example 1-2, as shown in Table 1, the volume resistivity of each toner was different from that of Example 1-1 for evaluation. Since the volume resistivity of the upstream toner is lower than the volume resistivity of the downstream toner, the charge amount of the toner leaks in the transfer process, and the transferability of the secondary color is remarkably deteriorated.

(Table 1)

[Example 2]
Example 2 of the present invention will be described. Regarding the matters common to the first embodiment in the second embodiment, the same reference numerals are used and the description thereof will be omitted again. Matters not particularly described here in the second embodiment are the same as those in the first embodiment.

The second embodiment is characterized in that the leakage of electric charge from the toner to the intermediate transfer body is suppressed by setting the volume resistivity of the intermediate transfer body to be larger than the volume resistivity of the toner.
A case where the upstream toner 22a is transferred to the intermediate transfer body 4 in the primary transfer step will be described in detail by taking as an example.

By making the volume resistivity of the intermediate transfer body 4 higher than the volume resistivity of the toner, the transferability of the upstream toner 22a can be improved. The toner of this embodiment has a volume resistivity set lower than that of the conventional insulating toner so that the amount of charge can be given by charging. Therefore, in the transfer step, charges are likely to leak from the toner through the intermediate transfer body 4. As a result, the toner cannot retain the electric charge and the transferability deteriorates. In order to suppress this charge leakage, it is necessary to make the volume resistivity of the intermediate transfer body 4 higher than the resistance value of the toner.

FIG. 3 is a schematic view showing how electric charges leak when the toner 22 is transferred from the photosensitive drum 11 to the intermediate transfer body 4. When the volume resistivity of the intermediate transfer body 4 is lower than the volume resistivity of the toner 22, the state of FIG. 3 (a) shifts to the state of FIG. 3 (b), and the toner 22 comes into contact with the intermediate transfer body 4. At the moment, the charge held by the toner 22 leaks through the intermediate transfer body 4. Therefore, the amount of charge of the toner 22 is greatly reduced, and even if the transfer is performed by applying a bias between the photosensitive drum 11 and the intermediate transfer body 4, the toner 22 cannot be transferred to the intermediate transfer body 4. Therefore, it is an example of a preferred embodiment in which the volume resistivity of the intermediate transfer body 4 is made larger than the volume resistivity of the toner 22.

In this example, an intermediate transfer belt having a volume resistivity of 1.0 × 10 ⁹ Ω · cm was used as the intermediate transfer body 4 in Example 1. That is, the intermediate transfer body 4 having a volume resistivity higher than the volume resistivity of the toner of Example 1 is used. As a result, since the volume resistivity of the toner is lower than the volume resistivity of the intermediate transfer belt, no charge leakage from the toner occurs and the transferability of the secondary color is good.

[Example 3]
Example 3 of the present invention will be described. Regarding the matters common to the first and second embodiments in the third embodiment, the same reference numerals are used and the description thereof will be omitted again. Matters not particularly described here in Example 3 are the same as those in Examples 1 and 2.

The third embodiment is characterized by having an insulating protrusion on the surface of the toner.
FIG. 5 is a diagram showing a state in which the toner and the intermediate transfer body 4 are in contact with each other when the insulating protrusion 15 is present on the toner surface. By providing the insulating protrusion 15 on the surface of the toner as shown in FIG. 5, the transfer of electric charge from the toner can be completely suppressed, and the transfer to the intermediate transfer body is not affected by the volume resistivity of the intermediate transfer body. Transfer defects due to charge leakage can be prevented.
FIG. 8B schematically shows a schematic cross-sectional configuration of the toner 22 in this embodiment. The surface of the toner particles (toner mother particles) 220 is coated with a conductive layer made of conductive fine particles 221 and a protrusion 15 having an insulating property is formed.

<Example 3-1>
In Example 3-1, polystyrene resin particles are used as the insulating protrusions 15 on the toner surface. The toner used in Example 3-1 was prepared according to the following procedure and evaluated.

<Production Example of Toner 22a of Example 3-1>
To 100 parts of the toner of 22a of Example 1, 2.0 parts of polystyrene resin having a volume mean diameter of 100 nm and a volume resistivity of 1.0 × 10 ¹⁶ Ω · cm was added, and an FM mixer (manufactured by Nippon Coke Co., Ltd.) was added. ) For 10 minutes at a peripheral speed of 32 m / s to obtain the toner 22a of Example 3-1.
When this toner was observed by TEM, it was confirmed that protrusions derived from polystyrene particles were formed on the toner surface. The volume resistivity of the toner was 8.0 × 10 ⁸ Ω · cm was measured.

<TEM observation method of toner surface>
Using a transmission electron microscope (TEM), the cross section of the toner is observed by the following method. First, the toner is sufficiently dispersed in a room temperature curable epoxy resin, and then cured in an atmosphere of 40 ° C. for 2 days. A flaky sample having a thickness of 100 nm is cut out from the obtained cured product using a microtome equipped with a diamond blade. This sample is magnified by TEM (trade name: electron microscope Tecnai TF20XT, manufactured by FEI Co., Ltd.) at a magnification of 100,000 times, and the cross section of the toner is observed.
Using this toner as a toner 22a of Example 3-1, change further to 1.0 × 10 ⁷ Ω · cm The intermediate transfer member 4, under the same conditions as in Example 1-1, 1000-sheet continuous image forming The transferability of the secondary color was confirmed. The result was good secondary color transferability even in continuous image formation.

<Example 3-2>
In Example 3-2, an organosilicon polymer is used as the insulating protrusion 15 on the surface of the toner. The organosilicon polymer has high hydrophobicity and can stably suppress charge leakage even in a low humidity environment or a high humidity environment. That is, good transferability can be exhibited regardless of the environment.

The organosilicon polymer will be described in detail. The toner of this example contains an organosilicon polymer on its surface. It is preferable that the silicon polymer is a product of a condensate of at least one organosilicon compound selected from the group consisting of the organosilicon compounds represented by the following formula (I).
Ra (n) -Si-Rb (4-n) (I)

In formula (I), Ra independently represents a halogen atom or an alkoxy group (preferably 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms), and Rb independently (preferably) each. Is an alkyl group having 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, an alkoxy group (preferably 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms), preferably 6 to 14 carbon atoms, more preferably It represents an aryl group (6 to 10), an acyl group (preferably 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms) or a methacryloxyalkyl group (preferably a methacryloxypropyl group).
n represents an integer of 2 or 3.

Examples of the organosilicon compound represented by the above formula (I) include various bifunctional and trifunctional silane compounds.
Specific examples of the bifunctional silane compound include dimethyldimethoxysilane and dimethyldiethoxysilane.

Examples of the trifunctional silane compound include the following compounds.
Trifunctional methylsilane compounds of methyltrimethoxysilane, methyltriethoxysilane, methyldiethoxymethoxysilane, methylethoxydimethoxysilane; ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxy Trifunctional silane compounds such as silane, butyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane; trifunctional phenylsilane compounds such as phenyltrimethoxysilane and phenyltriethoxysilane; vinyltrimethoxysilane, vinyltriethoxy Trifunctional vinylsilane compounds such as silane; trifunctional allylsilane compounds such as allyltrimethoxysilane, allyltriethoxysilane, allyldiethoxymethoxysilane, allylethoxydimethoxysilane; γ-methacryloxypropyltrimethoxysilane, γ-methacryloxy Trifunctional γ-methacryloxypropylsilane compounds such as propyltriethoxysilane, γ-methacryloxypropyldiethoxymethoxysilane, γ-methacryloxypropylethoxydimethoxysilane; etc.

Among them, the silane compound in which n is 3 represented by the following formula (II) has high crosslinkability and can further suppress the migration of the metal compound fine particles to the charged member, so that the effect of the present invention can be more preferably exhibited.
Ra3-Si-Rb1 (II)

In formula (II), Ra independently represents a halogen atom or an alkoxy group, and Rb independently represents an alkyl group, an alkenyl group, an aryl group, an acyl group or a methacryloxyalkyl group.

Specific examples of the silane compound represented by the formula (II) include the above-mentioned trifunctional silane compound.

The content of the organosilicon polymer in the toner is preferably 0.01% by mass or more and 20.0% by mass or less, and more preferably 0.1% by mass or more and 10.0% by mass or less.
When the content of the organosilicon polymer is in the above range, the charge injection property is further improved. The content can be controlled by the amount of the organosilicon compound used as a raw material.

The toner used in Example 3-2 was prepared according to the following procedure and evaluated.
<Production Example of Toner 22a of Example 3-2>
Production Example of Organosilicon Compound Solution ・ 80.0 parts of ion-exchanged water ・ 20.0 parts of methyltriethoxysilane Weighed the above materials in a 200 mL beaker and adjusted the pH to 3.5 with 10% hydrochloric acid. Then, the mixture was stirred for 1.0 hour while heating at 60 ° C. in a water bath to prepare an organosilicon compound solution.

The following samples were weighed in the reaction vessel and mixed using a propeller stirring blade.
-Toner particle dispersion prepared by the suspension polymerization method (solid-liquid ratio 30%) 500.0 parts-The above organosilicon compound solution 40.0 parts The pH of the toner particle dispersion was set to 9 using a 1 mol / L NaOH aqueous solution. The temperature was adjusted to 5.5, and the temperature was maintained at 50 ° C. for 2.0 hours with stirring. After lowering the temperature to 25 ° C., toner particles were obtained through filtration and drying steps.
Further, 0.2 part of titanium oxide particles is mixed with 100 parts of the toner particles in a stirring mixer (FM mixer of Nippon Coke Industries Co., Ltd.), and the surface of the toner particles is covered by stirring and mixing at 12000 rpm × 30 seconds. Titanium oxide particles were attached to form a conductive layer.
When the toner particles were observed by TEM according to the method described above, it was confirmed that protrusions derived from the organosilicon compound were formed on the toner surface. The volume resistivity of the toner was 5.0 × 10 ⁸ Ω · cm was measured.

Using this toner as a toner 22a in Example 3-2, and further changed to 1.0 × 10 ⁷ Ω · cm The intermediate transfer member 4, under the same conditions as in Example 1-1, the high-temperature high-humidity environment (30 Image formation was performed in both a low temperature / low humidity environment (10 ° C./10%) and a secondary color transferability was confirmed. The result was good secondary color transferability in both environments.

[Example 4]
Example 4 of the present invention will be described. Regarding the matters common to the first to third embodiments in the fourth embodiment, the same reference numerals are used and the description thereof will be omitted again. Matters not particularly described here in Example 4 are the same as in Examples 1 to 3.

In the fourth embodiment, a method of directly transferring the transferred body to a recording material such as paper is shown. An image forming apparatus using a transport belt that sequentially conveys a recording material to a portion facing the first image carrier (first transfer section) and to a portion facing the second image carrier (second transfer section). Is.

FIG. 6 is a schematic cross-sectional view showing an example of an image forming apparatus using a transport belt, and FIG. 7 is a schematic cross-sectional view of the process cartridge used in FIG.
The image forming apparatus and the process cartridge according to the fourth embodiment use the transport belt 7 instead of the intermediate transfer belt 4 in the first embodiment, but the types of belts are different and the arrangement of each member is different. Other than that, it is common to the first embodiment.

As shown in FIG. 6, a transport belt 7 that circulates and moves so as to face and contact all the photosensitive drums 11 is arranged. The transport belt 7 is composed of a film-like member having a thickness of about 110 μm and having a volume specific resistance of 1.0 × 10 ¹¹ Ω · cm or more and 1.0 × 10 ¹⁴ Ω · cm or less. The transport belt 7 electrostatically attracts the recording material to the outer peripheral surface on the left side in the drawing and circulates to bring the recording material into contact with all the photosensitive drums 11.

With the above configuration, the recording material is conveyed to the transfer position by the transfer belt 7, and the toner image on the photosensitive drum 11 is transferred. The four photosensitive drums 11 come into contact with the inside of the transport belt 7.
A transfer roller 3 as a transfer means is arranged side by side at a position facing the surface. The transfer roller 3 sandwiches the transport belt 7 between the photosensitive drums 11 and transfers the recording material transported by the transport belt 7 between the transport belt 7 and the photosensitive drums 11, respectively. Four nip portions are formed corresponding to each photosensitive drum 11. Positive charges are applied from these transfer rollers 3 to the recording material via the transport belt 7, and the electric field generated by the charges causes the recording material in contact with the photosensitive drum 11 to have a negative toner image on the photosensitive drum 11. Transferred.

When general paper is used as the recording material used in this embodiment, the volume low efficiency of the paper is 1.0 × 10 ¹⁰ Ω · cm or more and 1.0 × 10 ¹² Ω · cm or less. It becomes larger than the volume resistivity of the developer. Therefore, also in Example 4, good transferability can be exhibited even if the toner images are superimposed.

In the image forming apparatus shown in FIG. 6, using the same developer combination as in Example 1-1 and a paper having a basis weight of 75 g / cm ² as a transfer target, the secondary color transferred onto the paper was visually confirmed. However, it showed good transferability.

Each of the above embodiments can be combined with each other as much as possible.

4 ... Intermediate transfer belt (intermediate transfer body), 7 ... Conveyance belt, 11 ... Photosensitive drum (image carrier), 15 ... Toner protrusion (projection), 20 ... Developing device, 21 ... Developing container, 22 ... Toner (Developer), 220 ... Toner particles (toner mother particles), 221 ... Conductive layer (conductive fine particles), 23 ... Developing rollers (developer carrier), 100 ... Image forming apparatus

Claims (13)

It is an image forming device
A first transfer nip portion is formed with the first image carrier, and a first developer image developed on the first image carrier by the first developer is transferred to the first transfer. In the nip part, the first transfer part to be transferred to the transferred body and
A second transfer nip portion is formed with the second image carrier, and the second developer image developed on the second image carrier by the second developer is transferred to the second transfer. In the nip portion, the second transfer portion, which transfers the first developer image to the transferred object to which the image is transferred, and the second transfer portion.
With
Both the volume resistivity of the first developer and the second developer are 1.0 × 10 ⁵ Ω · cm or more and 1.0 × 10 ¹¹ Ω · cm or less, and
An image forming apparatus characterized in that the volume resistivity of the first developer is larger than the volume resistivity of the second developer. The image forming apparatus according to claim 1, wherein the transferred body is an intermediate transfer belt. The image forming apparatus according to claim 2, wherein the volume resistivity of the intermediate transfer belt is larger than the volume resistivity of the first developer. The image forming apparatus according to claim 3, wherein the volume resistivity of the intermediate transfer belt is 1.0 × 10 ⁸ Ω · cm or more and 1.0 × 10 ¹² Ω · cm or less. The first transfer portion sandwiches the intermediate transfer belt between the first image carrier and the first transfer nip portion between the intermediate transfer belt and the first image carrier. Includes a first transfer roller that forms
The second transfer portion sandwiches the intermediate transfer belt between the second image carrier and the second transfer nip portion between the intermediate transfer belt and the second image carrier. The image forming apparatus according to any one of claims 2 to 4, wherein a second transfer roller is included. The object to be transferred is a recording material, and is characterized in that it is sequentially conveyed by a transport belt to a position facing the first image carrier and a position facing the second image carrier. The image forming apparatus according to 1. The first transfer unit sandwiches the transport belt between the first image carrier and the recording material transported by the transport belt between the transport belt and the first image carrier. Includes a first transfer roller that forms the first transfer nip portion for sandwiching and transporting
The second transfer unit sandwiches the transfer belt between the second image carrier and the recording material conveyed by the transfer belt between the transfer belt and the second image carrier. The image forming apparatus according to claim 6, further comprising a second transfer roller forming the second transfer nip portion for sandwiching and transporting the image. At the position where the second developer image is transferred from the second image carrier to the transferred body, the first developer image is transferred from the first image carrier to the transferred body. The image forming apparatus according to any one of claims 1 to 7, wherein the image forming apparatus is located on the downstream side in the moving direction of the transferred body with respect to the position. The first developer and the second developer include toner particles and conductive fine particles that coat the surface of the toner particles, according to any one of claims 1 to 8. The image forming apparatus described. The image forming according to claim 9, wherein the first developer and the second developer further have insulating protrusions formed on the surface of the toner particles. apparatus. The image forming apparatus according to claim 10, wherein the protrusions are formed by using polystyrene resin particles or an organosilicon polymer. The first developer and the second developer are characterized in that charges are injected before they are used to develop the first developer image and the second developer image, respectively. The image forming apparatus according to any one of claims 1 to 11. With the first developer carrier,
A first regulating member that regulates the amount of the first developing agent image supported on the first developing agent carrier, and a first regulating member.
A first voltage applying means for forming a predetermined potential difference between the first developer carrier and the first regulating member,
With the second developer carrier,
A second regulating member that regulates the amount of the second developer image supported on the second developer carrier, and
A second voltage applying means that forms a predetermined potential difference between the second developer carrier and the second regulating member, and
The image forming apparatus according to any one of claims 1 to 12, further comprising.

Images