JP6210766B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer, which transfers a toner image formed on an image carrier using an electrophotographic method or an electrostatic recording method to a transfer material via an intermediate transfer member. It is.

  As an image forming apparatus of an electrophotographic system or an electrostatic recording system, an intermediate transfer system is known. For example, in an electrophotographic image forming apparatus that employs an intermediate transfer method, each image forming device is formed on a plurality of electrophotographic photosensitive members (photosensitive members) as image carriers, or sequentially formed on one photosensitive member. The toner images are sequentially transferred (primary transfer) onto the intermediate transfer member. The toner image transferred onto the intermediate transfer member is then transferred (secondary transfer) collectively onto a transfer material (recording medium, recording material).

  Patent Document 1 discloses an intermediate transfer member in which a silicon oxide layer or an aluminum oxide layer is formed as an oxide layer on the surface.

  In Patent Document 2, a charger is provided in front of the secondary transfer portion in the moving direction of the intermediate transfer member, and the toner on the intermediate transfer member is charged to a larger charge amount with the same polarity by this charger. A configuration for improving secondary transfer efficiency is disclosed.

JP-A-9-212004 JP 2003-57995 A

  In recent years, in image forming apparatuses, there has been an increasing demand for downsizing and cost reduction of the apparatus while maintaining high image quality. For this reason, there is a demand for reduction in running cost and reduction in size of the cleaning device due to reduction in residual toner, and in turn reduction in size and cost of the image forming apparatus.

  In particular, in a color image forming apparatus, since a large amount of toner is transferred when multiple color toners are stacked, the transfer efficiency is reduced in the secondary transfer from the intermediate transfer member to the transfer material, and the toner is transferred onto the intermediate transfer member. The amount of toner remaining as transfer residual toner tends to increase. As long as the charge amount of the toner on the photoconductor is sufficient to obtain sufficient transferability, the charge amount of the toner on the photoconductor may be a condition around the photoconductor such as development. As a result, a sufficient charge amount may not be obtained.

  As a method for improving the secondary transfer property of multicolor toner, as described in Patent Document 2, a charger is provided in front of the secondary transfer unit in the moving direction of the intermediate transfer member, and the toner on the intermediate transfer member is There is a method of increasing the charge amount and increasing the force for electrostatically transferring the toner. However, this method requires a charger, a power source, etc., which increases the size of the apparatus and easily increases costs.

  In view of this, the present inventor increased the charge amount of the toner transferred to the surface of the intermediate transfer member by charging by rubbing between the surface of the intermediate transfer member and the toner (hereinafter also referred to as “rubbing charge”), It has been studied to increase the force for electrostatically transferring the toner. If the toner of a smaller charge amount can be rubbed and charged on the photosensitive member by rubbing the surface of the intermediate transfer member with the toner, the secondary transfer property can be improved without providing a charger or the like in front of the secondary transfer portion. It is because it can improve.

  Here, in Patent Document 1, an oxide layer is formed on the surface layer of the intermediate transfer member, and the secondary transfer property is improved by improving the peelability between the oxide layer and the toner, and the amount of residual toner remaining after the transfer. Is disclosed. However, Patent Document 1 makes no mention of toner rubbing charging due to rubbing between the intermediate transfer member and the toner.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of improving secondary transferability while suppressing an increase in size and cost of the apparatus.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention has an image carrier and an intermediate transfer member, and a toner image primary-transferred from the image carrier to the intermediate transfer member in the primary transfer unit in the secondary transfer unit. In the image forming apparatus for secondary transfer onto a transfer material, the intermediate transfer member has a surface layer formed of Al ₂ O ₃ constituting a surface on which a toner image is transferred, and the toner is slid with the surface layer. Bowed by negatively charged, and, Ri absolute value 25μC / g or more der charge amount due to friction with the surface layer, and, by friction with the surface layer in the primary transfer portion, the primary than said absolute value of the charge amount in the image bearing member before being transferred to the intermediate transfer member, is ing larger towards the absolute value of the charge amount in the intermediate transfer member immediately before the secondary transfer portion by the transfer unit An image forming apparatus characterized by the above.

  According to the present invention, it is possible to improve secondary transferability while suppressing increase in size and cost of the apparatus.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional view of a developing device of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of an intermediate transfer belt in an embodiment of the present invention. FIG. 10 is a schematic diagram for explaining an example of a method for creating an intermediate transfer belt. It is a schematic diagram for demonstrating the measuring method of the rubbing charge amount T. FIG. It is a schematic sectional drawing of a Faraday gauge. FIG. 6 is a schematic cross-sectional view of an image forming apparatus according to another embodiment of the present invention.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
1. FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus according to this embodiment is a tandem type (in-line type) laser beam printer that employs an intermediate transfer method that can form a full-color image by an electrophotographic method.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units (images) that respectively form yellow (Y), magenta (M), cyan (C), and black (K) images. Forming unit) 1Y, 1M, 1C, 1K. These four image forming units 1Y, 1M, 1C, and 1K are arranged in a line at regular intervals.

  In this embodiment, the configurations and operations of the image forming units 1Y, 1M, 1C, and 1K are substantially the same except that the colors of the toners used are different. Therefore, hereinafter, unless there is a particular need for distinction, Y, M, C, and K at the end of a symbol representing an element for any color will be omitted, and the element will be described generally.

  The image forming unit 1 includes a photosensitive drum 2 which is a cylindrical (drum type) electrophotographic photosensitive member as an image carrier. The photosensitive drum 2 is rotationally driven in the direction of arrow R1 in the figure by a drive motor (not shown) as a drive means. The following units are arranged around the photosensitive drum 2 along the rotation direction. First, a charging roller 3 that is a roller-type charging member (charging device) as a charging unit is disposed. Next, an exposure device (laser scanner device) 7 as an exposure unit is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 which is a roller-type primary transfer member as a primary transfer unit is disposed. Next, a drum cleaning device 6 as a photosensitive member cleaning unit is disposed.

  Further, an endless belt-like intermediate transfer belt 8 as an intermediate transfer member is disposed so as to face each photosensitive drum 2 of each image forming unit 1. The intermediate transfer belt 8 is stretched with a predetermined tension between three rollers: a driving roller 11 as a stretching roller, a secondary transfer counter roller 12, and a tension roller 13. The intermediate transfer belt 8 rotates (circulates) in the direction of the arrow R2 in the figure when a driving roller 11 connected to a driving motor (not shown) as driving means is rotated. On the inner peripheral surface side of the intermediate transfer belt 8, the primary transfer rollers 5 described above are arranged at positions facing the photosensitive drums 2. The primary transfer roller 5 is pressed against the photosensitive drum 2 via the intermediate transfer belt 8 to form a primary transfer portion (primary transfer nip) N1 where the intermediate transfer belt 8 and the photosensitive drum 2 are in contact with each other. Further, on the outer peripheral surface side of the intermediate transfer belt 8, a secondary transfer roller 15 that is a roller-type secondary transfer member as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 12. . The secondary transfer roller 15 is pressed against the secondary transfer counter roller 12 via the intermediate transfer belt 8, and a secondary transfer portion (secondary transfer nip) is brought into contact with the intermediate transfer belt 8 and the secondary transfer roller 15. ) N2 is formed. Further, on the outer peripheral surface side of the intermediate transfer belt 8, a belt cleaning as an intermediate transfer member cleaning unit is provided at a position facing the secondary transfer counter roller 12 on the downstream side of the secondary transfer portion N 2 in the moving direction of the intermediate transfer belt 8. A device 75 is installed.

  Next, the image forming operation will be described by taking the case of forming a full color image as an example. When an image forming operation start signal is issued, a transfer material S such as recording paper is sent out one by one from a cassette (not shown) as a transfer material storage unit, and is conveyed to a registration roller (not shown) as a conveying means. Is done. At that time, the registration roller is stopped, and the leading edge of the transfer material S stands by immediately before the secondary transfer portion N2.

  In this embodiment, the photosensitive drum 2 is a negatively charged organic photoreceptor. The photosensitive drum 2 has a photosensitive layer on a conductive drum base such as aluminum. When an image forming signal is issued, the photosensitive drum 2 is rotationally driven at a predetermined peripheral speed (process speed).

  The charging roller 3 is in contact with the photosensitive drum 2 with a predetermined pressure contact force. When an image forming signal is issued, the charging roller 3 is applied with a predetermined charging bias from a charging power source (high voltage power source) (not shown) as a charging bias applying means. As a result, the surface of the photosensitive drum 2 is charged substantially uniformly to a predetermined potential having a predetermined polarity (negative polarity in this embodiment).

  The exposure device 7 outputs a laser beam modulated in response to a time-series electrical digital pixel signal of image information of color components corresponding to each image forming unit 1 input from a host computer (not shown). It has a laser output part. The surface of the photosensitive drum 2 is scanned and exposed by the laser beam that is an optical signal converted from the image signal output from the laser output unit. As a result, an electrostatic latent image (electrostatic image) corresponding to the image information of the color component corresponding to each image forming unit 1 is formed on the surface of the photosensitive drum 2 that is substantially uniformly charged by the charging roller 3. The

  The developing device 4 attaches toner to the electrostatic latent image formed on the photosensitive drum 2 and develops the toner image (visible image). In this embodiment, a hybrid type developing device is used as the developing device 4. The developing device 4 charges the toner by stirring and mixing the two-component developer containing the toner and the carrier, and performs one-component contact development at the developing portion (developing position).

  More specifically, as shown in FIG. 2, the developing device 4 includes a developing container 41 that contains a two-component developer mainly composed of a mixture of toner and carrier. In the developing container 41, conveying members 42 and 42 that convey the two-component developer while stirring and mixing are provided. Further, a developing sleeve 43 as a first developer carrier is rotatably disposed in the developing container 41, and a magnet roller 44 as a magnetic field generating means is disposed in the hollow portion of the developing sleeve 43. Has been. In addition, a regulating member 45 is provided so as to face the outer peripheral surface of the developing sleeve 43 with a predetermined gap. A developing roller 46 as a second developer carrier is rotatably disposed at an opening provided at a position facing the photosensitive drum 2 of the developing container 41.

  The two-component developer in the developing container 41 is conveyed while being agitated and mixed by the conveying members 42 and 42, and is supplied onto the developing sleeve 43 by the magnetic force of the magnet roller 44. The amount of the two-component developer carried on the developing sleeve 43 is regulated by the regulating member 45 as the developing sleeve 43 rotates, and then conveyed to the opposing portion between the developing roller 46 and the developing sleeve 43. In this facing portion, only the toner from the two-component developer is supplied to the developing roller 46 due to the potential difference formed between the developing roller 46 and the developing sleeve 43. The toner carried on the developing roller 46 is conveyed to a contact portion (developing portion) between the developing roller 46 and the photosensitive drum 2 as the developing roller 46 rotates. In the developing unit, due to the potential difference formed between the photosensitive drum 2 and the developing roller 46, toner is transferred from the developing roller 46 to the photosensitive drum 2 in accordance with the electrostatic latent image on the photosensitive drum 2, and photosensitive. A toner image is formed on the drum 2. Connected to the developing sleeve 43 and the developing roller 46 are first and second developing power sources (high voltage power sources) (not shown) as first and second developing bias applying means, respectively. During development, a developing bias having the same polarity as the charging polarity (negative polarity in this embodiment) of the photosensitive drum 2 is applied to the developing roller 46.

  Each of the developing devices 4Y, 4M, 4C, and 4K stores toners of yellow, magenta, cyan, and black as toners. In this embodiment, a toner image is formed by a combination of image portion exposure and reversal development. That is, the charged polarity (negative polarity in this embodiment) of the photosensitive drum 2 is applied to the exposed portion (image portion) on the photosensitive drum 2 where the absolute value of the potential is reduced by being exposed after being charged substantially uniformly. The toner charged with the same polarity as that of the toner adheres to form a toner image.

In this embodiment, the potential of the photosensitive drum 2 after being charged by the charging roller 3 (charging potential, dark portion potential) is −450 V, and the potential after being exposed by the exposure device 7 (image portion potential, bright portion). The charge amount and the exposure amount were adjusted so that the potential was -100V. In this embodiment, the developing bias applied to the developing roller 46 is −300V. In this embodiment, the process speed corresponding to the peripheral speed of the photosensitive drum 2 is 60 mm / sec. In this embodiment, the image formation width, which is the length in the direction orthogonal to the transfer direction of the transfer material S (the rotation direction of the photosensitive drum 2), is 215 mm. Furthermore, in this embodiment, the developing device 4 is set so that the toner amount on the photosensitive drum 2 in the solid image portion is 0.4 mg / cm ² and the charge amount of the toner on the photosensitive drum 2 is −35 μC / g. did. Here, the toner charge amount on the photosensitive drum 2 was measured at the position immediately before the primary transfer portion N1. However, since the change in the charge amount of the toner on the photosensitive drum 2 between the developing portion and the primary transfer portion N1 in the moving direction of the photosensitive drum 2 is normally negligible, the toner at any position during that time The same result can be obtained by measuring the charge amount.

The toner image formed on the photosensitive drum 2 is primarily transferred to the intermediate transfer belt 8 by the action of the primary transfer roller 5 in the primary transfer portion N1. In this embodiment, an elastic roller having a volume resistivity of 10 ⁶ to 10 ⁷ Ω · cm and a rubber hardness of 20 ° (Asker C hardness meter) was used as the primary transfer roller 5. In this embodiment, the primary transfer roller 5 is pressed against the photosensitive drum 2 through the intermediate transfer belt 8 with a total pressure of about 3N. The primary transfer roller 5 rotates following the rotation of the intermediate transfer belt 8. A primary transfer power supply (high voltage power supply) 9 as a primary transfer bias applying unit is connected to the primary transfer roller 5. During the primary transfer process, a primary transfer bias, which is a DC voltage having a polarity opposite to the charging polarity (normal charging polarity) of the toner at the time of development, is applied to the primary transfer roller 5 from the primary transfer power source 9. The In this embodiment, a DC voltage of +400 V is applied as a primary transfer bias from the primary transfer power source 9 to the primary transfer roller 5.

  At the time of forming a full-color image, in each of the image forming units 1Y, 1M, 1C, and 1K, primary toner images of yellow, magenta, cyan, and black are sequentially superimposed on the moving intermediate transfer belt 8. Transcribed. As a result, a full-color toner image is formed on the intermediate transfer belt 8.

The configuration of the intermediate transfer belt 8 in this embodiment will be described in detail later. In this embodiment, the driving roller 11 is provided with a rubber layer having a high friction coefficient on the surface layer for driving the intermediate transfer belt 8, and the rubber layer has a volume resistivity of 10 ⁵ Ω · cm or less. It has conductivity. In this embodiment, the secondary transfer counter roller 12 is provided with a rubber layer as a surface layer, and the rubber layer has conductivity with a volume resistivity of 10 ⁵ Ω · cm or less. In this embodiment, the tension roller 13 is made of a metal roller, applies a tension of a total pressure of about 60 N to the intermediate transfer belt 8, and rotates following the intermediate transfer belt 8. The driving roller 11, the secondary transfer counter roller 12 and the tension roller 13 are electrically grounded (connected to ground (GND)).

The transfer material S is conveyed to the secondary transfer portion N2 by a registration roller (not shown) at the timing when the leading edge of the toner image on which the four colors are superimposed on the intermediate transfer belt 8 reaches the secondary transfer portion N2. Come. The toner image transferred onto the intermediate transfer belt 8 is secondarily transferred collectively to the transfer material S by the action of the secondary transfer roller 15 in the secondary transfer portion N2. In this embodiment, the secondary transfer roller 15 is configured by covering the surface of the core metal with an elastic layer. As the elastic layer, an EPDM foam layer having a volume resistivity of 10 ⁷ to 10 ⁹ Ω · cm and a rubber hardness of 30 ° (Asker C hardness) is used as the elastic layer. It was. In this embodiment, the secondary transfer roller 15 is pressed with a total pressure of about 50 N against the secondary transfer counter roller 12 via the intermediate transfer belt 8. The secondary transfer roller 15 is driven to rotate as the intermediate transfer member 8 rotates. Connected to the secondary transfer roller 15 is a secondary transfer power source (high voltage power source) 19 as a secondary transfer bias applying means. During the secondary transfer process, a secondary transfer bias, which is a DC voltage having a polarity opposite to the normal charging polarity of the toner, is applied from the secondary transfer power source 19 to the secondary transfer roller 15. In this embodiment, a DC voltage of +900 V is applied as a secondary transfer bias from the secondary transfer power source 19 to the secondary transfer roller 15.

  A fixing device 17 as a fixing unit is installed on the downstream side of the secondary transfer portion N2 in the conveyance direction of the transfer material S. The fixing device 17 includes a fixing roller 17a and a pressure roller 17b. The transfer material S onto which the toner image has been transferred is conveyed to the fixing device 17 and heated and pressed at the fixing nip portion between the fixing roller 17a and the pressure roller 17b. As a result, a plurality of color toner images for a full-color image are melted and mixed, and are fixed by being fixed to the surface of the transfer material S. The transfer material S is discharged outside the main body of the image forming apparatus 100 after the toner image is fixed. Thus, a series of image forming operations is completed.

  The toner remaining on the photosensitive drums 2 after the primary transfer process (primary transfer residual toner) is removed from the photosensitive drums 2 by the drum cleaning devices 6 and collected. Further, the toner remaining on the intermediate transfer belt 8 after the secondary transfer process (secondary transfer residual toner) is removed from the intermediate transfer body 8 by the belt cleaning device 75 and collected.

2. Intermediate transfer member Next, the intermediate transfer belt 8 in this embodiment will be described in more detail.

FIG. 3 is a schematic cross-sectional view of the intermediate transfer belt 8 of this embodiment. The intermediate transfer belt 8 of this embodiment includes a base layer 8a and a surface layer 8b provided on the base layer 8a. The base layer 8a is formed of an endless belt in which carbon as a conductive agent is dispersed in a polyimide (PI) resin having a thickness of 65 μm and the electric resistance is adjusted to 10 ⁸ to 10 ¹¹ Ω · cm. The surface layer 8b is formed by evaporating Al ₂ O ₃ with a thickness of 200 nm. In the intermediate transfer belt 8, the base layer 8 a side is disposed on the inner peripheral surface side that contacts the stretching rollers 11, 12, and 13, and the surface layer 8 b is disposed on the outer peripheral surface side that carries the toner image.

  The resin forming the base layer 8a is polyphenylene sulfide (PPS), polyvinylidene fluoride (PVdF), nylon, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate, polyether ether ketone (PEEK), polyethylene naphthalate. Phthalate (PEN) or the like may be used.

  In this embodiment, carbon black, which is a conductive powder (conductive powder), is used as a conductive agent added to the base layer 8a. However, the additive to be mixed for adjusting the electric resistance of the base layer 8a of the intermediate transfer belt 8 is not particularly limited. For example, as the conductive filler for adjusting the electric resistance, there are the carbon black and various conductive metal oxides. Non-filler resistance adjusters include low molecular weight ionic conductive materials such as various metal salts and glycols, antistatic resins containing ether bonds and hydroxyl groups in the molecule, or organic high conductivity that exhibits electronic conductivity. There are molecular compounds.

  The electrical resistance of the base layer 8a of the intermediate transfer belt 8 was measured by using a Hiresta and a probe URS manufactured by Mitsubishi Chemical Corporation and applying an applied voltage of 100 V for 10 seconds with a measurement load of 20N.

  The elastic modulus of the base layer 8a of the intermediate transfer belt 8 of this embodiment is about 5000 MPa. The elastic modulus was measured according to the tensile elastic modulus measurement method of JIS-K7127, and the thickness of the measurement sample was 65 μm.

Next, a method for forming the surface layer 8b of the intermediate transfer belt 8 in this embodiment will be described. As shown in FIG. 4, the base layer 8a of the cylindrical intermediate transfer belt 8 supported by the support 201 is placed in a vapor deposition pot, and the pressure is reduced to 10 ⁻³ to 10 ⁻⁴ Pa. Thereafter, while rotating the entire base layer 8a, Al ₂ O ₃ particles as the material of the surface layer 8b are heated and evaporated by the electron beam EB from the electron beam generator 202, and the surface of the substrate 8a is formed with Al with a thickness of 200 nm. _{A 2} O ₃ layer is formed. The rotation direction of the base layer 8a at this time is as follows. That is, while rotating around the axis passing through the center of the cylindrical radial cross section of the base layer 8a as shown by the arrow A in the figure, the cylindrical radial cross section of the base layer 8a as shown by the arrow B in the figure Is rotated about an axis passing through the center of the tube and passing through the center in the longitudinal direction. Thus, by forming the surface layer 8b while rotating the base body 8a in two directions, the film thickness unevenness can be reduced as much as possible.

The hardness of the Al ₂ O ₃ layer was 7.5 GPa when measured at a load of 50 μN with an Elionix ENT-1100a nanoindenter. Furthermore, when the surface roughness R _Z of the Al ₂ O ₃ layer was measured with a stylus type surface roughness meter, it was 0.4 μm. The water of the the Al ₂ O ₃ layer, n- hexadecane, surface free energy calculated from the contact angle of diiodomethane was 55 mN / m.

In addition, as an intermediate transfer belt 8 for comparison with the present example, a SiO ₂ layer having a thickness of 200 nm was formed as the surface layer 8b on the surface of the same base layer 8a by the same vapor deposition method as in the present example. . When the hardness, surface roughness, and surface free energy of this SiO ₂ layer were measured by the same method as in this example, the hardness was 4 GPa, the surface roughness R _Z was 0.4 μm, and the surface free energy was 59 mN / m. there were.

  In this embodiment, the surface layer 8b of the intermediate transfer belt 8 is formed by a vapor deposition method, but may be formed by a sputtering method, a sol-gel method, or the like.

In this embodiment, the intermediate transfer belt 8 has a two-layer configuration of a base layer 8a and a surface layer 8b. However, the present invention is not limited to this. For example, one or a plurality of intermediate layers are provided between the base layer and the surface layer. May be provided. It is sufficient that at least the surface layer constituting the surface of the intermediate transfer member is formed of an Al ₂ O ₃ layer.

3. Improvement of secondary transfer property by rubbing electrification The present inventors increased the charge amount of the toner transferred to the surface of the intermediate transfer member by rubbing the toner by rubbing between the surface of the intermediate transfer member and the toner, It has been studied to increase the force for electrostatically transferring the toner. As described above, the intermediate transfer member having the oxide layer formed on the surface is advantageous in improving the secondary transfer property since the peelability between the oxide layer on the surface and the toner is good. However, as a result of studies by the present inventors, it has been found that if the surface of the intermediate transfer member is an oxide layer, sufficient equivalent secondary transfer properties cannot be obtained. The inventors have found that the secondary transfer residual toner can be significantly reduced by combining the following configurations. That is, the intermediate transfer member to form the Al ₂ O ₃ layer on the surface layer, and negatively charged by the friction with the the Al ₂ O ₃ layer, and the absolute rubbing charge amount T of the later-described the Al ₂ O ₃ layer This is a combination of toner having a value larger than a predetermined value. This will be described in more detail below.

Here, the secondary transferability was evaluated using the above-described two types of intermediate transfer belts 8, that is, the intermediate transfer belt 8 having an Al ₂ O ₃ layer and the intermediate transfer belt 8 having an SiO ₂ layer.

  For this purpose, first, toner A magenta mainly composed of styrene-acrylic resin and toner A cyan were prepared by suspension polymerization as follows.

3-1. Preparation of toner A magenta When a toner is manufactured by suspension polymerization, a polymerizable monomer, a colorant, a charge control agent, a wax component, a polymerization initiator, and the like, which become a binder resin, are mixed to form a polymerizable monomer. A meter composition is prepared. Then, after dispersing the polymerizable monomer composition in the aqueous medium and granulating the particles of the polymerizable monomer composition, the polymerizable monomer in the particles of the polymerizable monomer composition in the aqueous medium A toner is obtained by polymerizing the body. In the examples, “part” means “part by mass”.

[Polymerizable monomer composition preparation step]
The following composition was mixed and then dispersed for 3 hours by a ball mill.
-Styrene 82.0 parts-2-ethylhexyl acrylate 18.0 parts-Divinylbenzene 0.1 part-C.I. I. Pigment Red 122 5.0 parts / polyester resin 5.0 parts (polycondensation product of propylene oxide modified bisphenol A and isophthalic acid (glass transition point 65 ° C., weight average molecular weight (Mw) 10,000, number average molecular weight (Mn) 6000 ))
-0.7 parts of aluminum salicylate complex (BONTRON E-108, manufactured by Orient Chemical Industries)
・ Polymer compound P (described later) 0.5 part

  The resulting dispersion was heated to 60 ° C. with stirring at 300 rpm. Thereafter, 12.0 parts of ester wax (peak temperature of maximum endothermic peak in DSC measurement: 70 ° C., number average molecular weight (Mn) 704) and 3.0 parts of 2,2′-azobis (2,4-dimethylvaleronitrile) And dissolved to obtain a polymerizable monomer composition.

[Dispersion stabilizer preparation process]
High-speed stirrer K. In a 2 L four-necked flask equipped with a homomixer (manufactured by Primix), 710 parts of ion-exchanged water and 450 parts of a 0.1 mol / L sodium phosphate aqueous solution were added, and the mixture was stirred at 12000 rpm while stirring at 60 ° C. Heated to. To this, 68.0 parts of a 1.0 mol / L calcium chloride aqueous solution was gradually added to prepare an aqueous dispersion medium containing calcium phosphate as a minute hardly water-soluble dispersion stabilizer.

[Granulation and polymerization process]
The polymerizable monomer composition was put into the aqueous dispersion medium and granulated for 15 minutes while maintaining the rotation speed of 12000 rpm. Thereafter, the stirrer was replaced from the high-speed stirrer to the propeller stirring blade, the polymerization was continued for 5 hours at an internal temperature of 60 ° C., the internal temperature was raised to 80 ° C., and the polymerization was further continued for 3 hours. After completion of the polymerization reaction, the residual monomer was distilled off at 80 ° C. under reduced pressure, and then the mixture was cooled to 30 ° C. to obtain a polymer fine particle dispersion.

[Washing and drying process]
The polymer fine particle dispersion was transferred to a washing container, and while stirring, diluted hydrochloric acid was added to adjust the pH to 1.5. The dispersion was stirred for 2 hours and then solid-liquid separated with a filter to obtain polymer fine particles. This was poured into 1.0 L of ion-exchanged water and stirred to obtain a dispersion again, followed by solid-liquid separation with a filter. After performing this operation three times, the polymer particles finally solid-liquid separated were sufficiently dried with a dryer at 30 ° C. to obtain toner particles.

[External addition process]
The resulting toner particles (100.0 parts) were dry-mixed for 5 minutes with a Henschel mixer (manufactured by Nippon Coke Kogyo Co., Ltd.), and the following composition was externally added. 1.0 part of hydrophobic silica fine powder (number average primary particle diameter 7 nm) surface-treated with hexamethyldisilazane, 0.15 part of rutile type titanium oxide fine powder (number average primary particle diameter 45 nm), rutile type titanium oxide 0.5 parts fine powder (number average primary particle size 200 nm).

[Production of polymer compound P]
The polymer compound P is obtained as follows.

A reactor equipped with a cooling tube, a stirrer, a thermometer, and a nitrogen introducing tube was charged with the following composition and subjected to nitrogen bubbling for 30 minutes.
Styrene 100.0 parts 2-acrylamido-2-methylpropanesulfonic acid 11.1 parts tert-butyl peroxyisopropyl carbonate 7.2 parts (Perbutyl I-75, manufactured by NOF Corporation)
・ Propylene glycol monomethyl ether acetate 290.0 parts

  The reaction mixture was heated at 145 ° C. for 8 hours under a nitrogen atmosphere to complete the polymerization reaction. After cooling the reaction solution to room temperature, the solvent was distilled off under reduced pressure. The obtained solid was reprecipitated twice with acetone-methanol and dried under reduced pressure at 50 ° C. and 0.1 kPa or less to obtain a polymer compound P.

3-2. Preparation of Toner A Cyan The colorant used in the preparation step of the polymerizable monomer composition is C.I. I. Pigment Red 122 instead of C.I. I. Pigment Blue 15: 3 and the amount of stitches is 5.5 copies, and is the same as the toner A magenta creation method.

3-3. Evaluation The above-described two types of intermediate transfer belts 8 were incorporated in the image forming apparatus 100 of the present embodiment described with reference to FIG. In each case, the primary transfer bias was +400 V, the secondary transfer bias was +900 V, and a solid image of a secondary color using toner A magenta and toner A cyan was output. Then, the secondary transfer rate (percent display of the value obtained by dividing the amount of toner transferred onto the transfer material from the intermediate transfer member by the amount of toner on the intermediate transfer member) was compared using two types of intermediate transfer belts 8.

As a result, when the intermediate transfer belt 8 having the Al ₂ O ₃ layer was used, the secondary transfer rate was 99.7%, and the secondary transfer residual toner was very small. On the other hand, when the intermediate transfer belt 8 on which the SiO ₂ layer was formed was used, the secondary transfer rate was 98%.

Therefore, the toner of the solid image of the secondary color on the intermediate transfer belt 8 after passing through the primary transfer portion N1K of the fourth image forming portion 1K for black and before the secondary transfer portion N2. Was measured using a suction method using a Faraday gauge. As a result, in the case of using the intermediate transfer belt 8 on which the Al ₂ O ₃ layer is formed, it is −47 μC / g, which is largely charged to the negative polarity side from the charge amount of the toner on the photosensitive drum 2 −35 μC / g. It was. On the other hand, in the case of using the intermediate transfer belt 8 on which the SiO ₂ layer was formed, it was −35 μC / g, and it was found that there was substantially no change from the toner charge amount on the photosensitive drum 2.

  Here, as the position before the secondary transfer portion N2, the toner charge amount at the position immediately before the secondary transfer portion N2 was measured. However, since the change in the charge amount of the toner on the intermediate transfer body between the most downstream primary transfer portion N1 and the secondary transfer portion N2 in the moving direction of the intermediate transfer member is normally negligibly small, The same result can be obtained by measuring the charge amount of the toner at any of the positions. Measurement of the toner charge amount by a suction method using a Faraday gauge will be described later.

It is considered that the difference in charge amount of the toner immediately before the secondary transfer portion N2 causes a difference in secondary transfer properties. The factors that cause the toner to be charged to the negative electrode side when the intermediate transfer belt 8 formed with the Al ₂ O ₃ layer is used are considered as follows. That is, when the toner transferred to the intermediate transfer belt 8 passes through each primary transfer portion N1, it is sandwiched between the photosensitive drum 2 and the Al ₂ O ₃ layer of the intermediate transfer belt 8, and is formed between the Al ₂ O ₃ layers. This is thought to be due to charging by rubbing. In this embodiment, the peripheral speeds of the contact portions between the photosensitive drums 2 and the intermediate transfer belt 8 are set to be substantially the same. However, each photosensitive drum 2 and the intermediate transfer belt are caused by slight speed variations of the drive motors of the photosensitive drum 2 and the intermediate transfer belt 8 and variations of the diameter of the photosensitive drum 2 and the diameter of the drive roller 11 of the intermediate transfer belt 8. A slight speed difference can occur between 8 and 8.

Therefore, when the intermediate transfer belt 8 formed with the Al ₂ O ₃ layer is used, immediately after the primary transfer portion N1M of the second image forming portion 1M for magenta and immediately before the secondary transfer portion N2. The toner charge amount of a solid image of magenta color on the intermediate transfer belt 8 was measured. As a result, −38 μC / g immediately after the primary transfer portion N1M and −51 μC / g immediately before the secondary transfer portion N2, and the toner on the intermediate transfer belt 8 becomes negative as it passes through each primary transfer portion N1. It turned out to be charged to the side. As can be seen from the above results, the toner on the intermediate transfer belt 8 passes through one primary transfer portion N1 (that is, the primary transfer portion N1 where the toner is transferred from the photosensitive drum 2 to the intermediate transfer belt 8). Even just passing, it is charged to the negative polarity side.

From this, it can be seen that in the case of using the intermediate transfer belt 8 on which the Al ₂ O ₃ layer is formed, the toner is charged by rubbing between the Al ₂ O ₃ layer and the toner.

However, since the toner rubbing charge is due to the Al ₂ O ₃ layer and the toner rubbing chargeability, the charge amount is considered to change depending on the characteristics on the toner side. Therefore, two types of toners (toner B and toner C) were prepared and examined as follows.

3-4. Preparation of toner B Basically, in the same manner as the preparation method of toner A magenta and toner A cyan, the amount of part of the material in the preparation process of the polymerizable monomer composition is changed as follows, Toner B magenta and toner B cyan were prepared.
・ 0.4 parts of aluminum salicylate complex (BONTRON E-108, manufactured by Orient Chemical Industries)
・ Polymer compound P 0.31 part

3-5. Preparation of toner C Basically, in the same manner as the preparation method of toner A magenta and toner A cyan, the amount of part of the material in the preparation process of the polymerizable monomer composition is changed as follows, Toner C magenta and toner C cyan were prepared, respectively.
・ 0.3 parts of aluminum salicylate complex (BONTRON E-108, manufactured by Orient Chemical Industries)
・ Polymer compound P 0.26 parts

3-6. Comparative Evaluation Al ₂ O ₃ layer and SiO ₂ layer of toner A (toner A magenta and toner A cyan), toner B (toner B magenta and toner B cyan), and toner C (toner C magenta and toner C cyan), respectively The amount of electrification was investigated using the following method.

  In this embodiment, the magenta and cyan of toner A, toner B, and toner C have substantially the same rubbing chargeability. Therefore, when it is not necessary to distinguish between colors, simply “toner A” is used. ”,“ Toner B ”, and“ Toner C ”.

The cut piece 301 of the intermediate transfer belt 8 is a double-sided tape or the like on an insulating support material formed of an electrical insulator on the back side so that the surface layer (Al ₂ O ₃ layer or SiO ₂ layer) 8b is on the front side. Fix with the fixing means. At this time, in the cut piece 301 of the intermediate transfer belt 8, the size of the surface (support surface) 301a of the surface layer 8b is 2.5 cm × 3 cm. Next, 2.5 mg of uncharged toner t whose rubbing charge amount is to be examined is placed on the surface layer 8b. Also, a rubbing rod (rubbing member) 302 made of an electrical insulator having a circular plane with a weight of 110 g and a diameter of 2 cm at the tip is prepared. In addition, the cut piece 303 of the intermediate transfer belt 8 is placed on the circular flat surface having a diameter of 2 cm at the tip of the rubbing bar so that the surface layer (Al ₂ O ₃ layer or SiO ₂ layer) 8b is the front side. Is fixed with fixing means such as double-sided tape. At this time, the cut piece 303 of the intermediate transfer belt 8 at the tip of the rubbing rod is formed so that the surface (rubbed surface) 303a of the surface layer 8b has a circular shape with a diameter of 2 cm. The cut piece of the intermediate transfer belt 8 fixed to the tip of the rubbing bar 302 is brought into contact with 2.5 mg of toner placed on the cut piece of the intermediate transfer belt 8 on the insulating support material. Then, in a state where the toner is sandwiched between the supporting surface 301a and the rubbing surface 303a only by the own weight of the rubbing rod 302, the rubbing surface 303a is moved in a horizontal direction so as to draw a circle in the supporting surface 301a, and the toner t is set to 10 Rub and charge by rubbing for 2 seconds. At this time, the rubbing bar 302 is rotated 10 to 12 times in 10 seconds so as to draw a circle as described above. However, even if the number of rotations is changed within a range of about 3 times, the measured rubbing charge amount does not change greatly. In the case of measuring the amount of charge of rubbing with the Al ₂ O ₃ layer of the toner, the intermediate transfer belt 8 having an Al ₂ O ₃ layer formed on any of the cut pieces of the intermediate transfer belt 8 on the insulating support material side or the rubbing rod side. The belt 8 is assumed. Similarly, when measuring the rubbing charge amount with the SiO ₂ layer of the toner, the cut piece of the intermediate transfer belt 8 on either the insulating support material side or the rubbing rod side of the intermediate transfer belt 8 on which the SiO ₂ layer is formed. Shall. The charge amount T (μC / g) of the toner thus rubbed and charged is measured by a suction method using a Faraday gauge. This series of operations is performed in an environment maintained at a temperature of 25 ° C. and a humidity of 45%.

  Here, a suction method using a Faraday gauge will be described. The amount of applied toner is calculated by sucking and collecting the toner on the photosensitive drum 2, the intermediate transfer belt 8, or the support surface 301 a when measuring the rubbing charge amount using a metal cylindrical tube and a cylindrical filter. . At this time, a Faraday gauge 400 as shown in FIG. 6 is used. The Faraday gauge 400 is a coaxial double cylinder, and the inner cylinder 422 and the outer cylinder 424 are insulated by insulating members 421 and 425. If a charged body having a charge amount Q is put in the inner cylinder 422, it is as if a metal cylinder having a charge amount Q exists by electrostatic induction. First, the toner at the target portion is sucked by the Faraday gauge 400. The suction port 426 is applied to the toner image or the like at the target location, and the toner at the target location is sucked in the directions indicated by the arrows 431 and 432 by a suction device (not shown). The sucked toner is collected by a cylindrical filter paper (cylindrical filter) 423 disposed in the inner cylinder 422. At this time, the induced charge Q is measured with an electrometer (Kesley) (not shown). Then, the charge amount Q is divided by the toner mass M in the inner cylinder 422 to obtain the toner charge amount Q / M (μC / g) at the target location.

Table 1 shows the measurement results of the rubbing charge amount T between the Al ₂ O ₃ layer and the SiO ₂ layer of three types of toners, toner A, toner B and toner C.

For all three types of toner, the amount of rub charge T with the SiO ₂ layer was small, and there was almost no difference in the amount of rub charge T with the toner. In contrast, the rubbing charge amount T with the Al ₂ O ₃ layers of the three types of toners is larger than the rubbing charge amount T with the respective SiO ₂ layers. Further, the rubbing charge amount T of the three types of toner and the Al ₂ O ₃ layer varies depending on the type of toner.

Next, similarly to the evaluation using toner A, the intermediate transfer belt 8 on which the Al ₂ O ₃ layer and the SiO ₂ layer were formed was incorporated in the image forming apparatus 100, respectively. Then, using this image forming apparatus 100, as in the case of evaluation using toner A, the secondary transfer properties of the secondary colors of toner B and toner C and the intermediate transfer immediately before the secondary transfer portion N2 are performed. The charge amount of the toner on the belt 8 was examined. The results are shown in Table 2.

  The setting of the hybrid developing device 4 when the toner B and the toner C are used is adjusted so that the charge amount and the loading amount of the toner on the photosensitive drum 2 are the same as in the evaluation using the toner A.

  Here, in order to increase the effects of reducing running cost and reducing the size and cost of the apparatus, it is preferable that the secondary transfer rate of the secondary color is 99% or more. For this reason, the secondary transfer rate of the secondary color is evaluated as 99% as a secondary transfer rate, with 99% or more being good (◯) and less than 99% being bad (x).

The secondary transfer rate of toner B to the Al ₂ O ₃ layer was 99.1%.

Based on the measurement result of the rubbing charge amount and the measurement result of the secondary transfer rate in the image forming apparatus 100 and the charge amount of the toner on the intermediate transfer belt 8 immediately before the secondary transfer portion N2, the following combinations are made. Is preferable. A toner that is negatively charged by rubbing between the Al ₂ O ₃ layer and the intermediate transfer belt 8 on which the Al ₂ O ₃ layer is formed, and that the rubbing charge amount T due to the rubbing is 25 μC / g or more. And a combination. With such a combination, the charge amount of the toner immediately before the secondary transfer portion N2 is increased, and the secondary transfer property is remarkably improved. Here, the absolute value of the rubbing charge amount T with the Al ₂ O ₃ layer is usually 60 μC / g or less for reasons of toner production, and a sufficient secondary transfer rate can be obtained even if it is usually 50 μC / g or less. Can be obtained.

As described above, in this embodiment, the intermediate transfer belt 8 has the surface layer 8b formed of Al ₂ O ₃ constituting the surface on which the toner image is transferred. The toner is negatively charged by rubbing with the surface layer 8b, and the absolute value of the charge amount (rubbing charge amount T with the surface layer 8b) due to rubbing with the surface layer 8b is 25 μC / g or more. That is, the toner, the triboelectric series is on the negative side than the Al ₂ O _3, rub charge amount T of the Al ₂ O ₃ is T ≦ -25 / g. As a result, the toner is more secondary than the absolute value of the charge amount on the photosensitive drum 2 before being transferred to the intermediate transfer belt 8 at the primary transfer portion N1 by rubbing against the surface layer 8b at the primary transfer portion N1. The absolute value of the charge amount in the intermediate transfer belt 8 immediately before the transfer portion N2 is larger.

As described above, particularly when two or more colors of toner are superposed, the toner of the color previously transferred to the intermediate transfer belt 8 tends to remain on the intermediate transfer belt 8 during the secondary transfer. As a result, the amount of secondary transfer residual toner increases, which may lead to problems such as an increase in size and cost of the apparatus. Therefore, it is desired to improve the secondary transfer properties of multicolor toners. In contrast, according to this embodiment, the toner transferred to the intermediate transfer belt 8 is rubbed with the Al ₂ O ₃ layer at the primary transfer portion N1 where the photosensitive drum 2 and the intermediate transfer belt 8 are in contact with each other. As a result, the reversely charged toner decreases and the charge amount increases. This effect becomes stronger as the toner near the surface transferred to the intermediate transfer belt 8 first. Therefore, the electrostatic transfer force in the secondary transfer of the toner previously transferred to the intermediate transfer belt 8 during the formation of the multicolor toner image is strengthened, and the toner that is easily transferred to the intermediate transfer belt 8 and tends to remain. The secondary transfer property is improved, and the secondary transfer residual toner is decreased particularly when there are multiple colors.

That is, according to this embodiment, the intermediate transfer belt 8 to form the Al ₂ O ₃ layer on the surface layer, rubbing charge amount T of the Al ₂ O ₃ layer and a large toner above a predetermined value and having a negatively chargeable , The secondary transfer residual toner can be remarkably reduced. With such a combination, the charge amount of the toner transferred from the photosensitive drum 2 onto the intermediate transfer belt 8 is increased, and the reversely charged toner is reduced, so that the secondary transfer residual toner can be particularly greatly reduced. It is. Toner in the vicinity of the surface of the intermediate transfer belt 8 of the toner image on which multiple colors are superimposed (toner having high adhesion to the surface of the intermediate transfer belt 8 and difficult to transfer) is transferred onto the intermediate transfer belt 8 during the secondary transfer process. Especially easy to remain. As described above, according to the present exemplary embodiment, such a toner also more reliably increases the charge amount and decreases the reversely charged toner. As a result, the electrostatic transfer force of the toner at the secondary transfer portion N2 can be increased, the secondary transfer performance can be improved, and the secondary transfer residual toner can be greatly reduced. Such an increase in the charge amount of the toner on the intermediate transfer belt 8 is considered to be due to the rubbing charge between the toner and the Al ₂ O ₃ layer. In this embodiment, all color toners satisfy the above conditions. However, in order to improve the secondary transferability of multicolors in particular, it is important to improve the transferability of toner of a color close to the surface of the intermediate transfer member as described above. Therefore, in an image forming apparatus that superposes a plurality of types (a plurality of colors) of toner, at least one type (1 that can be transferred closer to the surface of the intermediate transfer member (typically, the lowest layer closest to the intermediate transfer member). If the toner of (color) satisfies the above conditions, a corresponding effect can be obtained.

The thickness of the Al ₂ O ₃ layer formed on the surface of the intermediate transfer belt 8 is preferably 100 to 800 nm. If the thickness is less than 100 nm, the Al ₂ O ₃ layer may disappear from a part of the surface of the intermediate transfer belt 8 due to scraping over time, and the base layer 8a may be exposed. Then, the charge amount of the toner changes between the portion where only the base layer 8a is present and the portion where the Al ₂ O ₃ layer remains, which causes a difference in secondary transfer property and contributes to image nonuniformity. There is. On the other hand, when the thickness is greater than 800 nm, problems such as cracks are likely to occur over time due to the influence of bending or the like in the portions wound around the stretching rollers 11, 12, and 13.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, elements having the same functions or configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

Similar to the first embodiment, the image forming apparatus 100 of the present embodiment includes an intermediate transfer belt 8 on which an Al ₂ O ₃ layer is formed. This embodiment is different from the first embodiment in that the peripheral speed of the intermediate transfer belt 8 is 5% faster than the peripheral speed of each photosensitive drum 2. Due to the difference in speed between the photosensitive drums 2 and the intermediate transfer belt 8, the amount of charge for rubbing between the Al ₂ O ₃ layer of toner sandwiched between the photosensitive drum 2 and the intermediate transfer belt 8 increases. As a result, the amount of increase in the amount of charge due to toner rubbing and charging becomes greater than when the photosensitive drum 2 and the intermediate transfer belt 8 are substantially at the same speed as in the first embodiment.

  Here, in the image forming apparatus 100 of the present embodiment, a solid image of one magenta color was formed using the toner A. In this case, the toner charge amount on the intermediate transfer belt 8 immediately after the primary transfer portion N1M and immediately before the secondary transfer portion N2 of the second image forming portion 1M for magenta was measured. As a result, −41 μC / g immediately after the primary transfer portion N1M and −61 μC / g immediately before the secondary transfer portion N2, and the photosensitive drum 2 and the intermediate transfer belt 8 are substantially constant speed as in the first embodiment. The amount of charge increased compared to the case of. Along with this, the secondary transferability was also improved.

  Further, when the secondary transfer rate of a solid image of secondary colors of magenta and cyan using toner A was measured, it was found to be 99.7%, and it was found that sufficient secondary transferability could be obtained.

  In this embodiment, the peripheral speed of the intermediate transfer belt 8 is set to be higher than the peripheral speed of the photosensitive drum 2, but it can be made slower than the peripheral speed of the photosensitive drum 2. In this way, when a peripheral speed difference (peripheral speed ratio) is provided between the photosensitive drum 2 and the intermediate transfer belt 8, about 0.2 to 5% is preferable. That is, the intermediate transfer belt 8 is preferably about 0.2 to 5% faster than the photosensitive drum 2 or about 0.2 to 5% slower than the photosensitive drum 2. When there is a difference in peripheral speed, the degree of rubbing between the toner, the intermediate transfer belt 8 and the photosensitive drum 2 increases, and the amount of abrasion on the surface of the photosensitive drum 2 and the surface of the intermediate transfer belt 8 increases. Therefore, it is desirable that the peripheral speed ratio is not too large.

Example 3
Next, still another embodiment of the present invention will be described. FIG. 7 is a schematic cross-sectional view of the image forming apparatus according to the present embodiment. The image forming apparatus of the present embodiment is a rotary type laser beam printer that employs an intermediate transfer system that can form a full-color image by an electrophotographic system.

  Elements having the same or equivalent mechanism and configuration as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals.

  The image forming apparatus 100 includes a photosensitive drum 2 on which toner images of respective colors are sequentially formed. Around the photosensitive drum 2, a charging roller 3, an exposure device 7, a developing device unit 47, a primary transfer roller 5, and a drum cleaning device 6 are arranged along the rotation direction. The developing device unit 47 includes four developing devices 4a, 4b, 4c, and 4d on a rotatable developing device support (rotary) 48. These four developing devices 4a, 4b, 4c, and 4d store toners of yellow, magenta, cyan, and black, respectively.

  An endless belt-like intermediate transfer belt 8 as an intermediate transfer member is disposed so as to face the photosensitive drum 2. The intermediate transfer belt 8 is stretched between the three stretching rollers of the driving roller 11, the secondary transfer counter roller 12, and the tension roller 13 with a predetermined tension. The intermediate transfer belt 8 rotates (circulates) in the direction of the arrow R2 in the drawing when a driving roller 11 connected to a driving motor (not shown) is driven to rotate. On the inner peripheral surface side of the intermediate transfer belt 8, the above-described primary transfer roller 5 is disposed at a position facing the photosensitive drum 2 to form a primary transfer portion N1. In addition, a secondary transfer roller 15 is disposed on the outer peripheral surface side of the intermediate transfer belt 8 at a position facing the secondary transfer counter roller 12 to form a secondary transfer portion N2. A belt cleaning device 75 is installed on the outer peripheral surface side of the intermediate transfer belt 8 at a position facing the tension roller 13.

  Here, the configurations and operations of the photosensitive drum 2, the charging roller 3, and the exposure device 7 are substantially the same as those in the first embodiment.

  In the present embodiment, the developing devices 4a, 4b, 4c, and 4d adopt a one-component contact developing system. In the present embodiment, the developing devices 4a, 4b, 4c, and 4d use the toner A described in the first embodiment as the toner. In the present embodiment, the developing device 4 of the one-component contact developing system contains a toner which is a non-magnetic one-component developer as a developer in a developing container. This toner is applied to a developing roller as a developer carrying member by a supply roller as a developer supply member. The toner carried on the developing roller is attached to the photosensitive drum 2 in accordance with the electrostatic latent image formed on the photosensitive drum 2 in the developing unit where the photosensitive drum 2 and the developing roller are in contact with each other. As a result, the electrostatic latent image on the photosensitive drum 2 is developed (visualized) as a toner image. The developing container support 48 moves the developing device 4 for a desired color to a position where it can come into contact with the photosensitive drum 2 at a desired timing.

  The configurations and operations of the primary transfer roller 5, the primary transfer power source 9, the drum cleaning device 6, the intermediate transfer belt 8, the drive roller 11, the secondary transfer counter roller 12, and the tension roller 13 are the same as those in the first embodiment. It is substantially the same. The configuration and operation of the secondary transfer roller 15 and the secondary transfer power source 19 are substantially the same as those in the first embodiment. However, in this embodiment, the secondary transfer roller 15 can be brought into contact with and separated from the intermediate transfer belt 8 as required by a contact / separation mechanism (not shown). The configuration and operation of the belt cleaning device 75 are substantially the same as those in the first embodiment. However, in this embodiment, the belt cleaning device 75 can perform contact and separation with the intermediate transfer belt 8 as required by a contact / separation mechanism (not shown). The configuration and operation of the fixing device 17 are substantially the same as those in the first embodiment.

  Next, the image forming operation will be described by taking as an example the case of outputting one full-color image. Detailed description of substantially the same operation as that of the first embodiment will be omitted.

  In this embodiment, first, the yellow electrostatic latent image formed on the photosensitive drum 2 is applied to the developing device 4a for yellow to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2 is applied. As a result, the yellow toner image is developed (visualized). The yellow toner image is primarily transferred onto the rotating intermediate transfer belt 8 by the action of the primary transfer roller 5 to which a primary transfer bias is applied in the primary transfer portion N1. Thereafter, in the same manner, the intermediate transfer belt 8 in which the magenta toner image, the cyan toner image, and the black toner image sequentially formed on the photosensitive drum 2 are rotated so as to be sequentially superimposed at the primary transfer portion N1. Primary transfer is performed on the top. Thereafter, the toner image transferred onto the intermediate transfer belt 8 is secondarily transferred collectively onto the transfer material S in the same manner as in the first embodiment. The toner image is fixed on the transfer material S in the same manner as in the first embodiment, and then the transfer material S is discharged to the outside of the main body of the image forming apparatus 100.

  In the present exemplary embodiment, the secondary transfer roller 15 and the belt cleaning device 75 are used until the toner image of all colors is primarily transferred onto the intermediate transfer belt 8 and is secondarily transferred to the transfer material S. It is separated from the intermediate transfer belt 8 so as not to disturb the image. Then, the secondary transfer roller 15 is moved by the contact / separation mechanism (not shown) according to the timing at which the leading edge of the toner image on which the four colors are superimposed on the intermediate transfer belt 8 reaches the secondary transfer portion N2. 8 is contacted. In synchronization with this timing, the transfer material S is conveyed to the secondary transfer portion N2 by a registration roller (not shown). In addition, the belt cleaning device 75 is in contact with and separated from the contact mechanism (not shown) immediately before the end of the secondary transfer residual toner remaining on the intermediate transfer belt 8 after the secondary transfer process reaches the cleaning position of the intermediate transfer belt 8. ) To contact the intermediate transfer belt 8. The secondary transfer residual toner is removed from the intermediate transfer belt 8 by the belt cleaning device 45 and collected. Further, the primary transfer residual toner remaining on the photosensitive drum 2 after each primary transfer step is removed from the photosensitive drum 2 by the drum cleaning device 6 and collected.

  In this embodiment, the dark portion potential and the light portion potential of the photosensitive drum 2, the developing bias, the process speed, the image forming width, the toner charge amount on the photosensitive drum 2, the toner amount on the photosensitive drum 2 in the solid image portion, and the primary transfer. Each setting of the bias and the secondary transfer bias is the same as in the first embodiment.

In the intermediate transfer belt 8 used in this example, an Al ₂ O ₃ layer having a thickness of 200 nm is formed as a surface layer 8b on the base layer 8a having the same characteristics as in Example 1 by the same vapor deposition method as in Example 1. . The toner A described in the first embodiment is incorporated in the image forming apparatus 100 of the present embodiment, and the secondary transfer rate of the solid image of the secondary color using magenta and cyan is measured to be 99.5%. It was found that secondary transferability can be obtained.

2 Photosensitive drum 4 Developing device 5 Primary transfer roller 8 Intermediate transfer belt 8a Base layer 8b Surface layer

Claims (9)

An image having an image carrier and an intermediate transfer member, wherein a toner image primarily transferred from the image carrier to the intermediate transfer member in a primary transfer portion is secondarily transferred to a transfer material in a secondary transfer portion In the forming device,
The intermediate transfer member has a surface layer formed of Al ₂ O ₃ constituting a surface to which a toner image is transferred,
The toner charged to the negative polarity by the friction with the surface layer, and, Ri absolute value 25μC / g or more der charge amount due to friction with the surface layer, and wherein in the primary transfer portion surface The amount of charge in the intermediate transfer body immediately before the secondary transfer portion is larger than the absolute value of the amount of charge in the image carrier before being transferred to the intermediate transfer body in the primary transfer portion by rubbing with the secondary transfer portion. image forming apparatus toward the absolute value and said large Do Rukoto of. 2. The image forming apparatus according to claim 1 , wherein a peripheral speed difference of 0.2 to 5% is provided between the peripheral speed of the image carrier and the peripheral speed of the intermediate transfer member. The thickness of the surface layer, the image forming apparatus according to claim 1 or 2 characterized in that it is a 100 to 800 nm. In the primary transfer section corresponding to each of the image carriers, a toner image is transferred from each of the image carriers to the intermediate transfer member so as to be sequentially superimposed. the image forming apparatus according to any one of claims 1 to 3, characterized in Rukoto. Each time a toner image is formed on the image carrier, the toner image is transferred from the image carrier to the intermediate transfer member in such a manner that the toner images are sequentially superimposed in the primary transfer unit. Item 4. The image forming apparatus according to any one of Items 1 to 3 . The contact with the intermediate transfer member in the secondary transfer unit, any one of claims 1 to 5, characterized in that it has a secondary transfer means for transferring the secondary toner image to the transfer material from the intermediate transfer member The image forming apparatus described in 1. The intermediate transfer member, the image forming apparatus according to any one of claims 1 to 6, characterized in that an intermediate transfer belt comprising said base layer surface. The image forming apparatus according to claim 7 , wherein the surface layer is formed by evaporating Al ₂ O ₃ on the base layer. A voltage is applied, any one of claims 1-8, characterized in that it comprises a first transfer means for transferring the primary toner image to the intermediate transfer member from the image bearing member at said primary transfer part The image forming apparatus according to one item.

Images