JP7066981B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

An endless intermediate transfer belt is known as an image carrier that supports a toner image to be transferred to paper. Further, an intermediate transfer belt in which a plurality of layers are laminated is also known.

Examples of the intermediate transfer belt include (Example 1) an elastic belt in which an elastic layer is laminated on a base layer, (Example 2) a belt in which a plurality of resin layers are laminated, and (Example 3) a belt in which a coat layer is laminated on a resin layer or the like. In the elastic belt of Example 1, the elastic layer is elastically deformed in the transfer nip following the surface of the uneven paper, so that the transferability to the uneven paper can be improved. The belt of Example 2 can be combined with necessary functions such as laminating belts having different resistances to improve transferability. The belt of Example 3 can improve the releasability of the toner at the time of transfer to paper.

Further, in addition to the elastic belt of Example 1 above, a method of applying an AC bias is also known in order to improve the transferability to uneven paper. This method of applying an AC bias can be used for both a single-layer belt and a laminated belt.

Further, in a laminated belt, a method of applying a high Duty AC bias in order to prevent overcharging of the toner and ensure transferability is also known.

As a method of preventing overcharging and ensuring transferability, a method of bringing the chargeability of the belt surface closer to positive charge is also known. For example, in the case of a belt in which particles are applied to the surface, it is known that the particles are more effective in preventing overcharging than positive charging in the triboelectric charging series.

This is because the surface particles and the toner rub against each other in a normal laminated belt without an elastic layer, and the toner is entangled in the elastic belt, but there is some movement between the toner and the surface particles in the micro. It is presumed that the presence of rubbing) causes friction and causes the toner to become negatively charged. Since the above effect increases as the surface particles are charged, it is considered that the higher the particle resistance, the more effective.

However, in the method of bringing the chargeability of the belt surface closer to positive charge, the toner is completely wrapped by softening the elasticity of the elastic layer. Therefore, there is a problem that the surface of the belt and the toner hardly rub against each other, and the effect of preventing overcharging is not obtained.

Therefore, an object of the present invention is to provide an image forming apparatus capable of achieving both transferability to uneven paper and prevention of overcharging of toner.

The problem is in an image forming apparatus including an image carrier having an elastic layer and a transfer member for transferring a toner image carried by the image carrier to a recording medium, on the surface of the elastic layer of the image carrier. Fine particles having a volume resistance of 1 × 10 ² [Ω · cm] to 1 × 10 ⁶ [Ω · cm] are provided, and the image carrier having a micro rubber hardness of 50 to 60 is used . The fine particles are solved by an image forming apparatus characterized in that the resin particles are the parent particles and the surface is coated with a conductive layer .

Further, the above-mentioned problem is in an image forming apparatus including an image carrier having an elastic layer and a transfer member for transferring a toner image carried by the image carrier to a recording medium, the surface of the elastic layer of the image carrier. In addition to providing fine particles having a volume resistance of 1 × 10 ² [Ω · cm] to 1 × 10 ⁴ [Ω · cm], the image carrier having a micro rubber hardness of 40 to 50 shall be used. And, the fine particles are also solved by an image forming apparatus characterized in that the resin particles are the parent particles and the surface is coated with a conductive layer .

In the image forming apparatus of the present invention, since the image carrier has an elastic layer (micro rubber hardness is 60 or less), transferability to uneven paper can be improved. Further, by providing fine particles having low resistance on the surface of the elastic layer or by providing a coat layer having a predetermined surface resistivity, overcharging of the toner is suppressed. Therefore, it is possible to achieve both transferability to uneven paper and prevention of toner overcharge.

It is an overall block diagram of the image forming apparatus which concerns on one Embodiment of this invention. It is a block diagram of the image formation part which concerns on one Embodiment of this invention. It is a block diagram which shows the electric structure of the secondary transfer bias power source and power source control part which concerns on one Embodiment of this invention. It is a schematic diagram which shows the secondary transfer nip of a laminated intermediate transfer belt. It is a schematic diagram which shows the secondary transfer nip of the intermediate transfer belt of a single layer. It is an enlarged sectional view partially showing the intermediate transfer belt which concerns on one Embodiment of this invention. It is an enlarged plan view partially showing the intermediate transfer belt which concerns on one Embodiment of this invention. It is a schematic diagram of the fine particles of the core-shell structure which concerns on one Embodiment of this invention. (A) is a schematic view showing the three-dimensional coordinates of the fine particles, (b) is a side view showing the dimensions of the XZ plane of the fine particles, and (c) is a side view showing the dimensions of the YZ plane of the fine particles. It is a graph which compared the secondary transfer rate of the halftone image using the K color toner. It is a schematic diagram which shows one method of applying fine particles to the surface of an elastic layer. It is a graph which shows the relationship between the particle resistance and the secondary transfer rate at the time of micro rubber hardness of 40 or less. It is a graph which shows the relationship between the particle resistance and the secondary transfer rate when the micro rubber hardness is 40 to 50. It is a graph which shows the relationship between the particle resistance and the secondary transfer rate when the micro rubber hardness is 50 to 60. It is a graph which shows the relationship between the toner adhesion amount and the secondary transfer rate in the intermediate transfer belt provided with the coat layer. This is an example of an ideal transfer bias waveform according to the third embodiment. It is an actual output waveform aiming at the transfer bias waveform shown in FIG. (A) to (e) are output waveforms when the Duty is shaken from 90% to 10% under the conditions of the transfer bias waveform shown in FIG.

Hereinafter, embodiments of the present invention including examples will be described in detail with reference to the drawings.

(First Embodiment)
FIG. 1 is an overall configuration diagram of an image forming apparatus according to an embodiment of the present invention. The electrophotographic color printer (hereinafter, referred to as “printer main body”) 500 will be described with reference to FIG. 1. The image forming apparatus according to the present invention is not limited to a printer, and is a copying machine, a single facsimile, or a multifunction device having at least two or more functions among a printer, a copying machine, a facsimile, a scanner, and the like. You may.

The basic configuration of the printer main body 500 will be described. As shown in FIG. 1, the printer main body 500 has four image forming units 1 (Y, M,) for forming a toner image of yellow (Y), magenta (M), cyan (C), and black (K). C, K) is provided. Further, the printer main body 500 includes a transfer unit 30 as a transfer device, an optical writing unit 80 as an exposure means, a fixing device 90, a paper feed cassette 100, and a resist roller pair 101.

The four image forming units 1 (Y, M, C, K) are powders and use toners of different colors Y, M, C, and K as a developer, but have the same configuration other than that. The four image forming units 1 (Y, M, C, K) are detachably provided with respect to the printer main body 500 as the image forming apparatus main body, and can be replaced at the end of the service life.

FIG. 2 is a block diagram of an image forming unit according to an embodiment of the present invention. FIG. 2 is an enlarged schematic configuration diagram of one of the four image forming units 1 (Y, M, C, K). Since the four image forming units 1 (Y, M, C, K) have the same configuration except that the colors of the toners used are different, the subscripts (Y, M) indicating the colors of the toners used are used. , C, K) are omitted.

The image forming unit 1 includes a drum-shaped photoconductor 2, which is an image carrier, a drum cleaning device 3, a static elimination device, a charging device 6, a developing device 8, and the like. The image forming unit 1 constitutes a process cartridge unit in which these plurality of devices are held in a common holder and can be integrally attached to and detached from the printer main body 500. Therefore, it can be replaced in units.

The photoconductor 2 has a drum shape in which an organic photosensitive layer is formed on the surface of a drum substrate, and is rotationally driven in the clockwise direction (arrow direction) in the drawing by a driving means. The charging device 6 generates a discharge between the charging roller 7 and the photoconductor 2 while contacting or bringing the charging roller 7, which is a charging member to which the charging bias is applied, into contact with or close to the photoconductor 2. The surface of the surface is uniformly charged. Instead of the method in which the charging member such as the charging roller 7 is brought into contact with or close to the photoconductor 2, a method using a charging charger may be adopted.

The surface of the photoconductor 2 uniformly charged by the charging roller 7 is light-scanned by an exposure light such as a laser beam emitted from the optical writing unit 80 to carry an electrostatic latent image for each color. This electrostatic latent image is developed by a developing device 8 using each color toner to become a toner image of each color. The toner image of the photoconductor 2 is primarily transferred onto the intermediate transfer belt 31 made of an endless belt member.

The drum cleaning device 3 removes the transfer residual toner adhering to the surface of the photoconductor 2 after undergoing the primary transfer step (primary transfer nip described later). The drum cleaning device 3 includes a cleaning brush roller 4 that is rotationally driven, a cleaning blade 5 that brings the free end into contact with the photoconductor 2 in a cantilevered state, and the like. The drum cleaning device 3 performs cleaning by scraping the transfer residual toner from the surface of the photoconductor 2 with the rotating cleaning brush roller 4 and scraping the transfer residual toner from the surface of the photoconductor 2 with the cleaning blade 5.

The static eliminator removes the residual charge of the photoconductor 2 after being cleaned by the drum cleaning device 3. By this static elimination, the surface of the photoconductor 2 is initialized to prepare for the next image formation.

The developing apparatus 8 has a developing unit 12 including a developing roller 9 serving as a developing agent carrier, and a developing agent conveying unit 13 for stirring and conveying the developing agent. The developer transport unit 13 has a first transport chamber for accommodating the first screw member 10 and a second transport chamber for accommodating the second screw member 11. The first screw member 10 and the second screw member 11 are rotatably supported by a case or the like of the developing device 8. By being rotationally driven, they are conveyed while circulating the developer, and the developer is supplied to the developing roller 9.

As shown in FIG. 1, an optical writing unit 80, which is a latent image writing means, is arranged above the image forming unit 1 (Y, M, C, K). The optical writing unit 80 lightly scans the photoconductor 2 (Y, M, C, K) with a laser beam emitted from a laser diode based on image information sent from an external device such as a personal computer. By this optical scanning, electrostatic latent images for Y, M, C, and K are formed on the photoconductor 2 (Y, M, C, K).

A transfer unit that is a belt unit and a transfer device that moves endlessly in the counterclockwise direction in the figure while an endless intermediate transfer belt 31 is stretched below the image forming unit 1 (Y, M, C, K). 30 is arranged. In addition to the intermediate transfer belt 31 which is an image carrier, the transfer unit 30 includes a drive roller 32 as a plurality of rotating bodies, a secondary transfer back surface roller 33, a cleaning backup roller 34, and four primary transfer rollers 35 ( It has Y, M, C, K). The transfer unit 30 is detachable (replaceable) with respect to the printer main body 500 together with the unit.

Around the outside of the loop of the intermediate transfer belt 31, is an image carrier, a secondary transfer unit 41 provided with a secondary transfer belt 36 as a secondary transfer member, a belt cleaning device 37, and a potential sensor as a detection means. 38 and the like are arranged.

The intermediate transfer belt 31 includes a drive roller 32 arranged inside the loop, a secondary transfer back surface roller 33 which is a transfer member, a cleaning backup roller 34, and four primary transfer rollers 35 (Y, M, C, K). It is wrapped around and supported and stretched. Then, due to the rotational force of the drive roller 32 that is rotationally driven in the counterclockwise direction in the drawing by the drive means, the drive roller 32 is endlessly moved and conveyed in the same direction. That is, the transfer unit 30 winds the belt member with a plurality of rotating bodies, supports it, and conveys it.

The four primary transfer rollers 35 (Y, M, C, K) sandwich the endlessly moved intermediate transfer belt 31 with the photoconductor 2 (Y, M, C, K). Then, a primary transfer nip that serves as a transfer portion for Y, M, C, and K in which the front surface of the intermediate transfer belt 31 and the photoconductor 2 (Y, M, C, K) abut is formed. .. A primary transfer bias is applied to each of the primary transfer rollers 35 (Y, M, C, K) by a transfer bias power supply. As a result, a transfer electric field is formed between the toner image of Y, M, C, K on the photoconductor 2 (Y, M, C, K) and the primary transfer roller 35 (Y, M, C, K). Will be done.

For example, the Y toner image formed on the surface of the yellow photoconductor 2Y enters the yellow primary transfer nip as the yellow photoconductor 2Y rotates. Then, due to the action of the transfer electric field and the nip pressure, the primary transfer is performed from the yellow photoconductor 2Y onto the intermediate transfer belt 31. The intermediate transfer belt 31 on which the Y toner image is primarily transferred in this way then sequentially passes through the primary transfer nips for M, C, and K.

Then, the M, C, K toner images on the photoconductor 2 (M, C, K) are sequentially superposed on the Y toner image and primary transferred. By this superposition primary transfer, a four-color superposition toner image is formed on the intermediate transfer belt 31. As the primary transfer member, a transfer charger, a transfer brush, or the like may be adopted instead of the primary transfer roller 35 (Y, M, C, K).

The secondary transfer unit 41 arranged on the outer side of the loop of the intermediate transfer belt 31 sandwiches the intermediate transfer belt 31 with the secondary transfer back surface roller 33 on the inner side of the loop. Then, a secondary transfer nip N is formed, which is a transfer portion where the front surface of the intermediate transfer belt 31 and the secondary transfer belt 36 come into contact with each other. A secondary transfer bias is applied to the secondary transfer back surface roller 33 by the secondary transfer bias power supply 39, and the secondary transfer belt 36 is grounded. As a result, a secondary transfer electric field that electrostatically moves negatively polar toner between the secondary transfer back surface roller 33 and the secondary transfer belt 36 from the secondary transfer back surface roller 33 side toward the secondary transfer belt 36 side. Is formed.

Below the transfer unit 30, a paper feed cassette 100 is disposed, which serves as an accommodating portion for accommodating a plurality of recording media P such as paper and resin sheets in a stacked state. The paper cassette 100 has a roller 100a in contact with the recording medium P at the top of the bundle, and by rotating the roller 100a at a predetermined timing, the recording medium P is sent out toward the transport path.

A resist roller pair 101 is arranged near the end of the transport path. The resist roller pair 101 stops the rotation of both rollers as soon as the recording medium P sent out from the paper cassette 100 is sandwiched between the rollers. Then, the rotation drive is restarted at a timing when the sandwiched recording medium P can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 31 in the secondary transfer nip N, and the recording medium P is transferred to the secondary transfer nip N. Send out towards.

That is, the transfer unit 30 is a belt unit that conveys the toner image transferred to the intermediate transfer belt 31 to the secondary transfer nip N which is a transfer unit with the recording medium P. Here, the image carrier is an intermediate transfer belt 31 as an endless belt member on which the toner image to be an image is transferred. The intermediate transfer belt 31 is wound and supported by a drive roller 32 as a plurality of rotating bodies, a secondary transfer back surface roller 33, and a cleaning backup roller 34.

The four-color superimposed toner image on the intermediate transfer belt 31 adhered to the recording medium P by the secondary transfer nip N is collectively secondary transferred onto the recording medium P by the action of the secondary transfer electric field and the nip pressure, and is transferred to the recording medium. Combined with the white color of P, it becomes a full-color toner image. The transfer residual toner that has not been transferred to the recording medium P is attached to the intermediate transfer belt 31 after passing through the secondary transfer nip N. This is cleaned from the belt surface by the belt cleaning device 37 which is in contact with the front surface of the intermediate transfer belt 31. The cleaning backup roller 34 arranged inside the loop of the intermediate transfer belt 31 backs up the cleaning of the belt by the belt cleaning device 37 from the inside of the loop.

The potential sensor 38 is arranged outside the loop of the intermediate transfer belt 31. The potential sensor 38 is arranged so as to face the portion of the entire area of the intermediate transfer belt 31 in the circumferential direction where the intermediate transfer belt 31 is hung with respect to the drive roller 32 via a gap. Then, when the toner image primaryly transferred onto the intermediate transfer belt 31 enters a position facing itself, the surface potential of the toner image is measured.

A well-known fixing device 90 is arranged on the right side of the figure of the secondary transfer nip N. The recording medium P on which the full-color toner image is transferred is sent to the fixing device 90. The fed recording medium P is sandwiched between the fixing nips in which the fixing roller 91 having a heat source inside and the pressure roller 92 come into contact with each other. Then, the toner in the full-color toner image is softened and fixed by heating and pressurizing. The fixed recording medium P is discharged from the fixing device 90, passes through a transport path after fixing, and is discharged to the outside of the machine.

The printer body 500 in this embodiment can also form a monochrome image. In that case, the support plate of the transfer unit 30 that supports the primary transfer rollers 35 (Y, M, C) for Y, M, C in the transfer unit 30 is moved to move the primary transfer rollers 35 (Y, M, C). In the direction away from the photoconductor 2 (Y, M, C). As a result, the front surface of the intermediate transfer belt 31 is separated from the photoconductor 2 (Y, M, C), and the intermediate transfer belt 31 is brought into contact with only the black photoconductor 2K. In this state, of the four image forming units 1 (Y, M, C, K), only the black image forming unit 1K is driven to form a K toner image on the black photoconductor 2K.

In the above configuration, a roller-shaped secondary transfer roller may be used as the transfer member that forms the secondary transfer nip with the intermediate transfer belt 31. The position where the secondary transfer bias is applied may be not on the secondary transfer back surface roller 33 inside the intermediate transfer belt 31, but on the transfer member side (for example, the secondary transfer roller). Further, the present invention may be applied not only to a color image forming apparatus but also to a monochrome image forming apparatus.

FIG. 3 is a block diagram showing an electrical configuration of a secondary transfer bias power supply and a power supply control unit according to an embodiment of the present invention. As shown in FIG. 3, the secondary transfer bias power supply 39 has a DC power supply 110 and an AC power supply 140. A power supply control unit 200 is connected to these power supplies. The power supply control unit 200 controls a DC power supply 110 and an AC power supply 140, and is realized by, for example, a control device having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. can.

A DC_PWM signal that controls the magnitude of the DC voltage output is input to the DC power supply 110 from the power supply control unit 200, and a DC voltage corresponding to the magnitude of the DC_PWM signal is output. In the present embodiment, the DC power supply 110 outputs a negative DC voltage (high voltage) having the same polarity as the charging polarity of the toner. The DC power supply 110 is controlled by a constant current.

The AC_PWM signal for controlling the magnitude of the output of the AC voltage and the AC_CLK signal for controlling the output frequency of the AC voltage are input to the AC power supply 140 from the power supply control unit 200. The AC power supply 140 outputs an AC voltage having an amplitude (peak-to-peak voltage) corresponding to the magnitude of the AC_PWM signal and a frequency corresponding to the magnitude of the AC_CLK signal. An AC voltage (AC component) output from the AC power supply 140 and a DC voltage (high voltage) output from the DC power supply 110 are superimposed to generate a superposed voltage.

As shown in FIGS. 1 and 3, the superimposed voltage as the secondary transfer bias is output to the secondary transfer back surface roller 33. In the present embodiment, the AC power supply 140 shall perform constant voltage control, but the present invention is not limited to this, and constant current control may be performed. The same applies to the DC component. A secondary transfer bias having a zero DC component may be used.

The secondary transfer bias power supply 39 can also output a secondary transfer bias consisting of only a DC voltage by setting the output of the AC power supply 140 to zero. Further, the AC voltage generated by the AC voltage transformer in the AC power supply 140 may be either a sine wave or a square wave, and in the present embodiment, it is a short pulse-shaped square wave. This is because the waveform of the AC voltage can be made into a short pulse-shaped square wave, which can further contribute to the improvement of the image quality.

FIG. 4a is a schematic diagram showing the secondary transfer nip of the laminated intermediate transfer belt, and FIG. 4b is a schematic diagram showing the secondary transfer nip of the single layer intermediate transfer belt. As shown in FIG. 4a, in the intermediate transfer belt 31, a flexible elastic layer 31b is laminated on the base layer 31a. When the toner image is secondarily transferred to the recording medium P, a secondary transfer bias is applied to the intermediate transfer belt 31 from the secondary transfer back surface roller 33. The secondary transfer current flows from the secondary transfer back surface roller 33 in the order of the base layer 31a, the elastic layer 31b, the toner image, the recording medium P, the secondary transfer belt 36, and the secondary transfer roller 400.

At this time, the secondary transfer current flows in the circumferential direction of the intermediate transfer belt 31 through the interface between the base layer 31a and the elastic layer 31b, so that the time for the current to flow in the toner image in the nip becomes long. As a result, there is a problem that the toner is backcharged due to overcharging, resulting in transfer failure. Even if the layer structure of the intermediate transfer belt 31 has three or more layers, the same problem occurs.

On the other hand, in the intermediate transfer belt 31'consisting of a single layer, as shown in FIG. 4b, the secondary transfer current is increased by the secondary transfer backside roller 33 due to the secondary transfer bias applied from the secondary transfer backside roller 33. Flows linearly from to the secondary transfer roller 400. Therefore, compared to the laminated intermediate transfer belt 31, the time for the current to flow in the toner image in the nip is shorter, and overcharging is less likely to occur.

FIG. 5 is an enlarged sectional view partially showing an intermediate transfer belt according to an embodiment of the present invention, and FIG. 6 is an enlarged plan view partially showing the intermediate transfer belt.

The intermediate transfer belt 31 is made of an endless belt-shaped base layer (belt substrate made of a hard material) 31a made of a material having a certain degree of flexibility and high rigidity, and an elastic material having excellent flexibility laminated on the surface thereof. The elastic layer 31b is provided. Fine particles 31c are dispersed in the elastic layer 31b, and the fine particles 31c are densely packed in the belt surface direction as shown in FIG. 6 with a part of the fine particles 31c protruding from the surface of the elastic layer 31b. They are lined up. A plurality of protrusions are formed on the belt surface by the plurality of fine particles 31c.

As the material of the base layer 31a, a resin in which an electric resistance adjusting material made of a filler or an additive for adjusting the electric resistance is dispersed can be exemplified. From the viewpoint of flame retardancy, the resin is preferably, for example, a fluororesin such as PVDF (polyvinylidene fluoride) or ETFE (ethylene / ethylene tetrafluoride copolymer), a polyimide resin, a polyamide-imide resin, or the like. .. Further, from the viewpoint of mechanical strength (high elasticity) and heat resistance, polyimide resin or polyamide-imide resin is particularly preferable.

Examples of the electric resistance adjusting material dispersed in the resin include metal oxides, carbon blacks, ionic conductive agents, and conductive polymer materials. Examples of the metal oxide include zinc oxide, tin oxide, titanium oxide, zirconium oxide, aluminum oxide, silicon oxide and the like. In order to improve the dispersibility, a metal oxide that has been surface-treated in advance may be used. Examples of carbon black include Ketjen black, furnace black, acetylene black, thermal black, and gas black. Examples of the ionic conductive agent include tetraalkylammonium salt, trialkylbenzylammonium salt, alkylsulfonate and alkylbenzenesulfonate. Alkyl sulfate, gluserine fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid alcohol ester, alkylbetaine, lithium perchlorate and the like may be used. Two or more kinds of these ion conductive agents may be mixed and used. The electric resistance adjusting material to which the present invention can be applied is not limited to those exemplified so far.

The coating liquid (a liquid resin before curing in which an electric resistance adjusting material is dispersed), which is a precursor of the base layer 31a, contains a dispersion aid, a reinforcing material, a lubricating material, and a heat conductive material, if necessary. , Antioxidants and the like may be added. The amount of the electric resistance adjusting material added to the base layer 31a of the seamless belt preferably equipped as the intermediate transfer belt 31 is preferably 1 × 10 ⁸ to 1 × 10 ¹³ [Ω / □] in terms of surface resistance and volume resistance. The amount is 1 × 10 ⁶ to 1 × 10 ¹² [Ω · cm].

However, from the viewpoint of mechanical strength, it is necessary to select and add an amount within a range in which the molded film is brittle and does not easily crack. That is, using a coating liquid in which the mixing ratio of the resin component (polyimide resin precursor, polyamideimide resin precursor, etc.) and the electric resistance adjusting material is appropriately adjusted, the electrical characteristics (surface resistance and volume resistance) and the mechanical strength are used. It is preferable to manufacture and use a seamless belt having a good balance between the two.

In the case of carbon black, the content of the electric resistance adjusting material is preferably 10 to 25 [wt%] of the total solid content in the coating liquid, and more preferably 15 to 20 [wt%]. The content of the metal oxide is preferably 1 to 50 [wt%] of the total solid content in the coating liquid, and more preferably 10 to 30 [wt%]. If the content is less than the above-mentioned range, a sufficient effect cannot be obtained, and if the content is more than the above-mentioned range, the mechanical strength of the intermediate transfer belt 31 (seamless belt) is significantly lowered, which is preferable in actual use. not.

The thickness of the base layer 31a is not particularly limited and may be appropriately selected depending on the situation, but is preferably 30 μm to 150 μm, more preferably 40 μm to 120 μm, and particularly preferably 50 μm to 80 μm. If the thickness of the base layer 31a is less than 30 μm, the belt is likely to be torn due to cracking, and if it exceeds 150 μm, the belt may be torn due to bending. On the other hand, if the thickness of the base layer 31a is in the above-mentioned particularly preferable range, it is advantageous in terms of durability.

In order to improve the belt running stability, it is preferable to reduce the layer thickness unevenness of the base layer 31a as much as possible. The method for adjusting the thickness of the base layer 31a is not particularly limited, and can be appropriately selected depending on the situation. For example, a method of measuring with a contact type or eddy current type film thickness meter and a method of measuring a cross section of a film with a scanning electron microscope (SEM) can be mentioned.

As described above, the elastic layer 31b of the intermediate transfer belt 31 has a plurality of convex shapes formed by the plurality of dispersed fine particles 31c on the surface. Examples of the elastic material for forming the elastic layer 31b include general-purpose resins, elastomers, and rubbers. In particular, it is preferable to use an elastic material having excellent flexibility (elasticity), and an elastomer material or a rubber material is preferable. Examples of the elastomer material include polyester-based, polyamide-based, polyether-based, polyurethane-based, polyolefin-based, polystyrene-based, polyacrylic-based, polydiene-based, and silicone-modified polycarbonate-based. A thermoplastic elastomer such as a fluorine-based copolymer system may be used.

Further, examples of the thermosetting resin include polyurethane-based, silicone-modified epoxy-based, and silicone-modified acrylic-based resins. Examples of the rubber material include isoprene rubber, styrene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, butyl rubber, silicone rubber, chloroprene rubber, and acrylic rubber. Further, chlorosulfonated polyethylene, fluororubber, urethane rubber, hydrin rubber and the like can be exemplified.

From the materials exemplified so far, it is possible to appropriately select a material that can obtain desired performance. In particular, it is preferable to select a material that is as soft as possible in order to follow the surface irregularities of a recording sheet having an uneven surface, for example, Rezac paper. Further, since the fine particles 31c are dispersed, a thermosetting one is preferable to a thermoplastic one. This is because the thermosetting one has excellent adhesion to the resin particles due to the effect of the functional group contributing to the curing reaction and can be reliably immobilized. Vulcanized rubber is also one of the preferred materials for the same reason.

Among the elastic materials constituting the elastic layer 31b, acrylic rubber is most preferable from the viewpoints of ozone resistance, flexibility, adhesion to particles, flame retardancy, environmental stability and the like. Acrylic rubber may be generally commercially available and is not limited to a specific product. However, among the various cross-linking systems (epoxide group, active chlorine group, carboxyl group) of acrylic rubber, the carboxyl group cross-linking system is superior in terms of rubber physical properties (particularly compression set) and processability, so that it is a carboxyl group. It is preferable to select a cross-linked type. As the cross-linking agent used for the carboxyl group cross-linking acrylic rubber, an amine compound is preferable, and a polyvalent amine compound is most preferable. Specific examples of such an amine compound include an aliphatic polyvalent amine cross-linking agent and an aromatic polyvalent amine cross-linking agent. Further, examples of the aliphatic polyvalent amine cross-linking agent include hexamethylenediamine, hexamethylenediamine carbamate, N, N'-dicinnamylidene-1,6-hexanediamine and the like. Examples of the aromatic polyvalent amine cross-linking agent include 4,4'-methylenedianiline, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 4,4'-(m-). Phenylenediisopropyriden) dianiline and the like. 4,4'-(p-phenylenediisopropyridene) dianiline, 2,2'-bis [4- (4-aminophenoxy) phenyl] propane, 4,4'-diaminobenzanilide and the like may be used. Further, 4,4'-bis (4-aminophenoxy) biphenyl, m-xylylenediamine, p-xylylenediamine, 1,3,5-benzenetriamine, 1,3,5-benzenetriaminomethyl and the like can also be used. good.

The appropriate range of the amount of the cross-linking agent to be blended is preferably 0.05 to 20 parts by weight, more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the acrylic rubber. If the amount of the cross-linking agent is too small, the cross-linking is not sufficiently performed, and it becomes difficult to maintain the shape of the cross-linked product. On the other hand, if the content is too large, the crosslinked product becomes too hard, and the elasticity of the crosslinked rubber is impaired.

The acrylic rubber used for the elastic layer 31b may be blended with a cross-linking accelerator for the purpose of promoting the cross-linking reaction of the above-mentioned cross-linking agent. The type of the cross-linking accelerator is not particularly limited, but it is preferable that the cross-linking accelerator can be used in combination with the above-mentioned polyvalent amine cross-linking agent. Examples of such a cross-linking accelerator include a guanidine compound, an imidazole compound, a quaternary onium salt, a tertiary phosphine compound, and an alkali metal salt of a weak acid. Examples of the guanidine compound include 1,3-diphenylguanidine and 1,3-dioltotrilguanidine. Examples of the imidazole compound include 2-methylimidazole and 2-phenylimidazole. Examples of the quaternary onium salt include tetra n-butylammonium bromide and octadecyltri-n-butylammonium bromide. Examples of the polyvalent tertiary amine compound include triethylenediamine, 1,8-diaza-bicyclo [5.4.0] undecene-7 (DBU) and the like. Examples of the tertiary phosphine compound include triphenylphosphine and tri-p-tolylphosphine. Examples of the alkali metal salt of the weak acid include a phosphate of sodium or potassium, an inorganic weak acid salt such as a carbonate, or an organic weak acid salt such as stearate and lauryl salt.

The appropriate range of the amount of the cross-linking accelerator used is preferably 0.1 to 20 parts by weight, more preferably 0.3 to 10 parts by weight, per 100 parts by weight of the acrylic rubber. If the amount of the cross-linking accelerator is too large, the cross-linking speed may become too high at the time of cross-linking, bloom of the cross-linking accelerator may occur on the surface of the cross-linked product, or the cross-linked product may become too hard. On the other hand, if the amount of the cross-linking accelerator is too small, the tensile strength of the cross-linked product may be significantly reduced, or the change in elongation or the change in tensile strength after heat loading may be too large.

In preparing acrylic rubber, it is possible to adopt an appropriate mixing method such as roll mixing, Banbury mixing, screw mixing, and solution mixing. The blending order is not particularly limited, but after sufficiently mixing the components that are difficult to react or decompose with heat, a component that easily reacts with heat or a component that easily decomposes, for example, a cross-linking agent, is used at a temperature at which reaction or decomposition does not occur. It may be mixed in a short time.

Acrylic rubber can be crosslinked by heating. The preferred heating temperature is 130 to 220 ° C, more preferably 140 ° C to 200 ° C. The preferred cross-linking time is 30 seconds to 5 hours. As the heating method, a method used for cross-linking rubber such as press heating, steam heating, oven heating, and hot air heating may be appropriately selected. Further, after cross-linking once, post-cross-linking may be performed in order to reliably cross-link to the inside of the cross-linked product. The post-crosslinking time varies depending on the heating method, the crosslinking temperature, the shape and the like, but is preferably 1 to 48 hours. The heating method and heating temperature for post-crosslinking can be appropriately selected.

Materials such as electrical resistance regulators for adjusting electrical properties, flame retardants for flame retardancy, and, if necessary, antioxidants, reinforcing agents, fillers, and cross-linking accelerators, may be added to the selected materials. It may be contained. Further, as the electric resistance adjusting agent for adjusting the electric characteristics, various materials already mentioned can be used. However, since carbon black and metal oxides impair flexibility, it is preferable to reduce the amount used, and it is also effective to use an ionic conductive agent or a conductive polymer. Moreover, you may use them together.

Specifically, it is preferable to add 0.01 to 3 parts of various perchlorates and ionic liquids to 100 parts by weight of the rubber. If the amount of the ionic conductive agent added is 0.01 parts or less, the effect of lowering the resistivity cannot be obtained. Further, when the addition amount is 3 parts or more, the possibility that the conductive agent blooms or bleeds to the belt surface increases.

Further, in order to obtain high uneven paper transferability as required by recent electrophotographic apparatus, the flexibility of the elastic layer 31b is required to have a micro rubber hardness value of 35 or less in a 23 ° C. and 50% RH environment. preferable. In the measurement with so-called minute hardness such as Martens hardness and Vickers hardness, only the hardness in the shallow region in the bulk direction of the measurement site, that is, the hardness near the very surface is measured, so the deformation performance of the belt as a whole cannot be evaluated. Therefore, for example, when a flexible material is brought to the outermost surface of the intermediate transfer belt having a structure in which the deformation performance of the belt as a whole is low, the minute hardness value becomes low. Such a belt has low deformation performance, that is, poor followability to uneven paper, and as a result, the transfer performance to uneven paper, which is required in recent years, is insufficient. Therefore, it is preferable to measure the microrubber hardness that can evaluate the deformation performance of the entire belt.

The micro rubber hardness (micro hardness) of the intermediate transfer belt can be measured by, for example, the micro rubber hardness tester MD-1 manufactured by Polymer Meter Co., Ltd. In an environment of 23 ° C. and 50%, the hardness can be measured based on the pushing depth of the pushing needle while deforming the belt piece by pressing the pushing needle against the belt piece at a predetermined pressure.

The layer thickness of the elastic layer 31b is preferably 200 μm to 2 mm, more preferably 400 μm to 1000 μm. If the layer thickness is smaller than 200 μm, the ability of the recording sheet to follow the surface irregularities and the effect of reducing the transfer pressure are lowered, which is not preferable. Further, when the layer thickness is larger than 2 mm, the elastic layer 31b tends to bend due to its own weight, which makes the running performance unstable, and the belt tends to crack when it is hung on the roller on which the belt is stretched. It is not preferable because it may occur. As a method for measuring the layer thickness, a method for measuring the cross section by observing the cross section with a scanning microscope (SEM) can be exemplified.

Subsequently, the fine particles 31c formed on the surface of the elastic layer 31b will be described. The volume resistivity of the fine particles 31c is 1 × 100 [Ω ・ cm] to ¹ × 10 ⁶ [Ω ・ cm], and more preferably 1 × 10 ¹ [Ω ・ cm] to 1 × 10 ³ [Ω ・. cm]. The constituent material and structure of the fine particles 31c are not particularly limited as long as they show the above-mentioned predetermined volume resistivity, and can be appropriately selected depending on the intended purpose. For example, it may have a single-layer structure, or may have a two-layer structure of a core shell formed by coating a base particle with a resin or the like as described below.

For example, fine particles having a core-shell structure are formed by coating the surface of insulating particles or particles having a higher resistance with a conductive resin by coating or polymerization, or by coating the surface of a metal by an electroless plating method. But it may be. The shape of the fine particles is not particularly limited as long as it exhibits the above-mentioned predetermined volume resistivity. It can be appropriately selected depending on the intended purpose, and may be, for example, spherical fine particles, or irregular fine particles instead of spherical ones. Spherical fine particles are preferable, and spherical fine particles having a high degree of sphericity as shown below are particularly preferable.

When the fine particles have the core-shell structure described above, it is preferable that the shape of the parent particles is spherical. This is because when the base particles are spherical, the shape of the fine particles after coating with the resin tends to be spherical easily.

As for the size of the fine particles 31c, the average particle size is preferably 100 μm or less. The particle size of the fine particles 31c may be such that the toner does not enter the gap between the fine particles 31c and the fine particles 31c when the elastic layer 31b is filled with the fine particles 31c. The average particle size of the fine particles 31c is preferably 5 μm or less, more preferably 0.5 μm to 5 μm, and particularly preferably 1 μm to 2 μm.

FIG. 7 is a schematic diagram of fine particles having a core-shell structure according to an embodiment of the present invention. As shown in FIG. 7, the fine particles 31c having a core-shell structure are composed of mother particles (high resistance particles) 13a and a conductive layer 13b that coats the mother particles 13a. As described above, as the fine particles 31c, fine particles obtained by coating the surface of highly resistant particles with a conductive layer are particularly preferable from the viewpoint of transferability.

Examples of the matrix particles (high resistance particles) 13a include acrylic resin particles, melamine resin particles, silicone resin particles, polyamide resin particles, polyester resin particles, polyvinyl chloride resin particles and the like. The conductive layer 13b includes a conductive resin layer coated with a conductive resin such as polypyrrole, polyaniline, polythiol, polythiophene, polyethylenedioxythiophene, poly3,4 ethylenedioxythiophene, and a metal such as copper and silver. Examples thereof include a conductive layer formed by coating with plating. Of these, a conductive resin layer coated with a conductive resin of polythiophene or polypyrrole is more preferable from the viewpoint of toner releasability.

As a method of coating the surface of the base particles 13a with the conductive resin, the surface of the particles may be coated by spray coating, or a known method may be used. Examples of known methods include the methods described in Patent Document 1 and Patent Document 2.

Commercially available products can also be used as the conductive resin, and for example, polythiophene can be obtained from Nagasechemtex Co., Ltd., Heraeus Co., Ltd., Rigaku Co., Ltd., and the like. Polyaniline, polyethylenedioxythiophene, poly-3,4 ethylenedioxythiophene can be obtained from Kaken Sangyo Co., Ltd. and Sankyo Kasei Sangyo Co., Ltd.

The volume resistivity of the fine particles 31c is appropriately adjusted by changing the thickness of the coat layer of a material having low resistance such as a conductive resin. For example, in order to adjust the volume resistivity to be high, the thickness of the coat layer may be reduced, and in order to adjust the volume resistivity to be low, the thickness of the coat layer may be increased. When using a material having too high conductivity such as metal, care should be taken so that the volume resistivity of the fine particles 31c does not become too lower than the lower limit of the above range.

Here, the contents of the study that led to the volume resistivity of the fine particles by the present inventors will be described. In the intermediate transfer material described in Patent Documents 3 to 10, an insulating material having high resistance is used for both particles and a coating agent. The present inventors have found the problem that the transferability of the halftone in the full color mode is deteriorated when the intermediate transfer body in which such high resistance particles are arranged is used.

Further, in Patent Document 10, as the resistivity of the entire intermediate transfer belt, the surface resistivity of the base layer and the elastic layer is 1 × 10 ⁸ to 1 × 10 ¹³ [Ω / □], and the volume resistivity is 1 × 10 ⁷ to. It is described that it should be 1 × 10 ¹² [Ω · cm]. However, the present inventor changed to fine particles showing a volume resistivity in a low resistance region of 1 × ¹⁰⁶ [Ω · cm] or less, which is completely different from the order of resistivity known as the resistivity of the entire intermediate transfer belt. I tried an experiment.

As a result, (1) even if the volume resistivity of the fine particles is changed from high to low, the resistivity of the entire intermediate transfer belt does not change, but (2) the volume resistivity of the fine particles is ¹ × 100 [Ω]. It was found that the problem of halftone transferability in the full color mode can be solved by setting the range from [cm] to 1 × 10 ⁶ [Ω · cm].

It is not clear why the halftone transferability in the full color mode (high transfer current) is improved by setting the volume resistivity of the fine particles in the range of 1 × 100 to ¹ × 10 ⁶ [Ω · cm]. A possible reason is that if the resistance of the fine particles on the surface of the intermediate transfer belt is high, it becomes difficult for the current to flow to the intermediate transfer belt and the toner is discharged, and the charge of the toner itself affected by the current decreases. On the other hand, if the resistance of the fine particles on the surface of the intermediate transfer belt is too low, too much current flows on the surface of the belt, and discharge between the intermediate transfer belt, the image carrier (photoreceptor), and the paper is less likely to occur. As a result, the formation of an electric field for transferring the toner may be hindered.

Therefore, if the volume resistivity of the fine particles on the surface of the intermediate transfer belt is in the range of 1 × 100 to ¹ × 10 ⁶ [Ω · cm], the balance between discharge and electric field formation is maintained, and high transferability can be maintained. I think it might be.

The volume resistivity of the fine particles can be measured by, for example, MCP-PD51 of Mitsubishi Chemical Analytech Co., Ltd. or Loresta GP (High Resta UP if the resistance is high). Specifically, it can be calculated by putting 1 g of fine particles in a pressure container of 15 mmφ in a pressure container of 23 ° C. and 50% RH, applying a load of 4 kN, and then reading the value measured at 20 kV.

Next, the arrangement state of the fine particles will be described. As shown in FIG. 6 above, the surface of the intermediate transfer belt 31 is an independent and orderly arrangement of fine particles 31c having a uniform particle size. That is, almost no overlap of the fine particles 31c is observed. The diameter of the cross section of the elastic layer surface of each fine particle constituting this surface is also preferably uniform, and specifically, the particle size distribution width is preferably ± (average particle size × 0.5) μm or less.

In order to form in this way, it is preferable to use fine particles 31c having as uniform a particle size as possible, but the surface is formed by a method of selectively forming particles having a certain particle size on the surface, and the above particle size distribution width It may be configured as follows. The area occupied by the fine particles 31c on the surface of the elastic layer is preferably 60% or more. When the occupied area ratio is 60% or more, the exposure of the resin portion of the intermediate transfer belt 31 is appropriate, and good transferability can be obtained.

The fine particles 31c take the form of being partially embedded in the elastic layer, and the burial rate thereof is preferably more than 50% and less than 100%, more preferably 51% to 90%. The burial rate is the rate at which the diameter of the fine particles 31c in the depth direction is buried in the elastic layer. However, the burial rate here does not mean that all the fine particles exceed 50% and are less than 100%, and the value of the average burial rate when viewed from a certain field of view must be more than 50% and less than 100%. It means good.

When the burial rate is 50% or less, desorption of particles is likely to occur in long-term use in an image forming apparatus, and the durability is inferior. On the other hand, 100% is not preferable because the effect of spherical particles on transferability is reduced. However, when the burial rate is 50%, almost no particles completely buried in the elastic layer are observed in the cross-sectional observation with an electron microscope (the number% of the fine particles completely buried in the elastic layer is the entire spherical particles). 5% or less of them).

Supplementary information on the sphericity of fine particles. As described above, the shape of the fine particles of the present invention is preferably spherical, and more preferably true spherical with a higher degree of sphericity. The sphericity is determined as follows using, for example, a color laser microscope (device name: VK-8500, manufactured by KEYENCE CORPORATION).

First, the fine particles are uniformly dispersed and adhered on a smooth measurement surface. Then, for 100 fine particles, magnified to an arbitrary magnification (for example, 1,000 times), the major axis r1 (μm), minor axis r2 (μm), and thickness r3 (μm) of the 100 particles are used. ) (See FIGS. 8A to 8C). Then, by calculating the arithmetic mean value of them, the sphericity of the fine particles can be obtained.

In the present invention, the ratio of the major axis to the minor axis (r2 / r1) is 0.9 or more and 1.0 or less, and the ratio of the thickness to the minor axis (r3 / r2) is 0.9 or more and 1.0 or less. What is a range is assumed to be a true sphere.

Next, a supplementary explanation will be given regarding the mechanism for improving the transferability of the low resistance particles. In the present embodiment, the C, M, and Y color toners having a charge amount Q / M of 12 to 15 [μQ / mg] are used, and the K color toner has a charge amount Q / M of 9. The one of [μQ / mg] is used. The amount of charge was measured in a high temperature and high humidity environment (27 ° C., 80% RH).

Since the charge amount of the K color toner is lower than that of the toners of other colors, a good transfer rate cannot be obtained in the K color halftone image even when the same transfer current is applied. This is because the toner is likely to be overcharged due to the low charge amount of the K color toner. Further, in the present embodiment, the C, M, and Y color toners having a relative permittivity of 2.7 to 3.3 are used, and the K color toners have a relative permittivity of 3.7 to 4.3. I am using something. K-color toner with a high relative permittivity tends to overcharge the toner.

When an experiment was conducted to transfer a halftone image to a recording sheet, a color halftone image using C, M, and Y toners (for example, a blue halftone image in which C and Y colors were superimposed) was performed. In the case of, a transfer rate of about 80% or more was obtained regardless of the magnitude of the secondary transfer current. On the other hand, in the halftone image using the K color toner, transfer failure occurred.

FIG. 9 is a graph comparing the secondary transfer rates of halftone images using K color toner. In FIG. 9, the X-axis is the secondary transfer current (μA) and the Y-axis is the secondary transfer rate (%). Further, the P1 belt is a belt having high resistance particles on the surface, and the P2 belt is a belt having particles having lower resistance (particle resistance 6th power or less) than the particles on the surface of the P1 belt on the surface.

As shown in FIG. 9, in the case of a belt having high resistance particles (P1 belt), the secondary transfer rate decreases as the secondary transfer current increases. In particular, when the secondary transfer current exceeds 115 (μA), the transfer rate becomes 30% or less, resulting in transfer failure.

Here, in the case of a belt (P2 belt) having low resistance particles (particle resistance 6th power or less) as in the present invention, a secondary transfer rate of about 60% or more is secured even if the secondary transfer current is increased. rice field. This is because, as in the mechanism described above, when low resistance particles are used, electric charges escape to the elastic layer along the particle surface and continuous discharge occurs, so that discharge to the toner is less likely to start. It is considered that this suppressed overcharging of the K color toner.

By using low resistance particles, the transfer rate of K-color halftone images and color-colored halftone images is high even when a relatively soft belt is used as the image carrier and even if a high secondary transfer current is used. Can be enhanced. A halftone image and a solid image that requires a high secondary transfer current can achieve both transferability, and an image in which a halftone image and a solid image coexist can be transferred satisfactorily.

As described above, in an image forming apparatus using a relatively soft image carrier (micro rubber hardness of 60 degrees or less), a low resistance layer (particle resistance 6th power or less) is provided on the surface of the image carrier. A good image can be obtained. In particular, when a K-color toner having a lower charge amount than other colors and a higher relative permittivity than other color toners is used, transfer defects due to overtransfer are likely to occur. This makes it possible to obtain a good image.

As another embodiment, the C, M, and Y color toners having a charge amount Q / M of 20 to 24 [μQ / mg] are used, and the K color toners have a charge amount Q / M of 21 [μQ / mg]. Was used. Further, as the C, M, and Y color toners, those having a relative permittivity of 2.7 to 3.3 were used, and as the K color toners, those having a relative permittivity of 3.3 to 3.9 were used. The charge amount and the relative permittivity of the K color toner were adjusted by adjusting the amount of carbon black contained in the toner. In the case of this other aspect, since the charge amount and the relative permittivity of the K color toner are the same as those of the C, M, and Y color toners, the secondary transfer rate is lowered when a high secondary transfer current is applied. Was able to be suppressed more.

As in this other aspect, a toner having a charge amount and a relative permittivity close to those of the C, M, and Y color toners may be used. According to this aspect, the transferability can be further improved.

Hereinafter, examples of the present invention and the measurement results of the secondary transfer rate by them will be described. However, the present invention is not limited to these examples.

(Example 1)
The procedure for producing the base layer will be described. A coating liquid for the base layer was prepared, and the base layer of the seamless intermediate transfer belt was prepared using this coating liquid.

<Preparation of coating liquid for base layer>
First, carbon black (SpecialBlack4; Evonik Degusa), which was previously dispersed in N-methyl-2-pyrrolidone in a polyimide varnish (U-varnish A; manufactured by Ube Kosan Co., Ltd.) containing a polyimide resin precursor as a main component, was previously dispersed in N-methyl-2-pyrrolidone by a bead mill. The dispersion liquid of (manufactured by) was prepared so that the carbon black content was 17% by mass of the solid content of the polyamic acid, and the mixture was well stirred and mixed to prepare a coating liquid.

<Manufacturing of polyimide base layer belt>
Next, a metal cylindrical support whose outer surface having an outer diameter of 500 mm and a length of 400 mm was roughened by blasting was used as a mold and attached to a roll coat coating device. Subsequently, the coating liquid for the base layer prepared above is poured into a pan, the paint is pumped up at a rotation speed of the coating roller of 40 mm / sec, the gap between the regulation roller and the coating roller is set to 0.6 mm, and the paint thickness on the coating roller is increased. Controlled.

Next, the rotation speed of the cylindrical support was controlled to 35 mm / sec to bring it closer to the coating roller, the gap with the coating roller was set to 0.4 mm, and the paint on the coating roller was uniformly transferred and applied onto the cylindrical support. Next, the mixture was put into a hot air circulation dryer while maintaining the rotation, gradually heated to 110 ° C. and heated for 30 minutes, further heated and heated at 200 ° C. for 30 minutes, and then the rotation was stopped. Then, this was introduced into a heating furnace (firing furnace) capable of high temperature treatment, the temperature was gradually raised to 320 ° C., and the heat treatment (firing) was performed for 60 minutes. Then, it was sufficiently cooled to obtain a polyimide base layer belt A having a film thickness of 60 μm.

<Preparation of elastic layer>
A rubber composition was prepared by blending and kneading each component and content shown below.
-Acrylic rubber (Nippon Zeon Co., Ltd., NipolAR12): 100 parts by mass-Stearic acid (Nippon Oil Co., Ltd., beaded stearic acid crosslink): 1 part by mass-Red phosphorus (Rin Kagaku Kogyo Co., Ltd., Nova Excel 140F) : 10 parts by mass ・ Aluminum hydroxide (Heidilite H42M, manufactured by Showa Denko Co., Ltd.): 40 parts by mass ・ Crosslinking agent (Dupondau Elastomer Japan, Diak.No.1, Hexamethylenediamine carbamate): 0.6% by mass Part-Crosslinking accelerator (VULCOFAC ACT55 (70% by mass, 1,8-diazabicyclo (5,4,0) undecene-7 and dibasic acid salt, 30% by mass amorphous silica) manufactured by Chemical alcan): 0.6 parts by mass

Next, the obtained rubber composition was dissolved in an organic solvent (MIBK, methyl isobutyl ketone) to prepare a rubber solution having a solid content of 35% by mass. Then, the cylindrical support on which the previously prepared polyimide base layer is formed is rotated, and the rubber solution is continuously discharged from the nozzle onto the polyimide base layer while being moved in the axial direction of the cylindrical support to form a spiral. Applied. The amount of the rubber solution applied was such that the average thickness of the final elastic layer was 400 μm. Then, the cylindrical support coated with the rubber solution was put into a hot air circulation dryer while rotating as it was, and the temperature was raised to 90 ° C. at a heating rate of 4 ° C./min and heated for 30 minutes.

<Manufacturing of conductive fine particles>
After spray-coating the surface of techpolymer SSX102 (Sekisui Kasei Kogyo Co., Ltd., particle size 2 μm), which is a spherical acrylic resin particle, with Denatron PT-434 (Nagase Chemtex Co., Ltd.), which is a polythiophene-based conductive polymer, 120 It was dried at ° C. for 1 hour to prepare conductive fine particles A. The spray coating was adjusted so that the volume resistivity of the fine particles was finally about 1 × 10 ² (Ω · cm).

<Application of fine particles to the surface of the elastic layer>
Next, as shown in FIG. 10, conductive particles A are evenly sprinkled on the surface of the elastic layer 45, and the pressing member 46 made of a polyurethane rubber blade is pressed against the surface of the elastic layer with a pressing pressure of 100 (mN / cm). Fixed to. Subsequently, the mixture was put into a hot air circulation dryer again, heated to 170 ° C. at a heating rate of 4 (° C./min), and heat-treated for 60 minutes to prepare an intermediate transfer belt A.

For the measurement of the volume resistivity of the fine particles, MCP-PD51, Loresta GP, and Highresta UP manufactured by Mitsubishi Chemical Analytech Co., Ltd. were used. Under a 50% RH environment at 23 ° C., 1 g of fine particles was placed in a 15 mmφ pressurized container, a load of 4 kN was applied, and then the value was calculated from the value measured at 20 kV. The resistivity of the intermediate transfer belt A was measured after applying the surface resistivity and volume resistivity at a bias of 500 V for 10 seconds using a high resta UP in a 23 ° C. and 50% RH environment.

In the above-mentioned Example 1, Denatoron PT-434 may be changed to Denatoron P-502RG (Nagase Chemtex Co., Ltd.).

Further, the steps of applying and drying by spray coating when producing the conductive particles A may be repeated twice.

Further, the techpolymer SSX102 may be changed to Epostal S6 (Nippon Catalyst Co., Ltd., average particle size 0.4 μm) which is a melamine resin particle.

Further, the techpolymer SSX102 may be changed to Tospearl 2000B (Momentive Performance Materials Co., Ltd., average particle size 6 μm) which is a silicone resin particle.

As described above, by changing the type of the conductive polymer, changing the step of applying and drying by the spray coating when producing the conductive particles A, and changing the type of the spherical acrylic resin particles, Fine particles having a volume resistivity of 1 × 10 ⁴ , 1 × 10 ⁶ , 1 × 10 ⁸ , 1 × 10 ¹⁰ [Ω · cm] were also prepared.

In Example 1, the techpolymer SSX102 was used as it was without using the conductive particles A. At this time, the volume resistivity of the techpolymer SSX102 was 1 × 10 ¹⁴ Ω · cm or more (this is referred to as Comparative Example 1).

In Comparative Example 1, a fine-grained cut product of STC-3 (Mitsui Kinzoku Co., Ltd., average particle size 2.6 μm), which is a spherical solder powder (tin, silver, copper), was used instead of the techpolymer SSX102. The volume resistivity of STC-3 at this time was 3.2 × 10 ^-6 [Ω · cm] (this is referred to as Comparative Example 2).

In Comparative Example 1, instead of the techpolymer SSX102, Tospearl 120 (Momentive Performance Materials Co., Ltd., average particle size 2 μm), which is a silicone spherical fine particle, was used. At this time, the volume resistivity of Tospearl 120 was 1 × 10 ¹⁴ [Ω · cm] or more (this is referred to as Comparative Example 3).

<Measurement result>
11 to 13 are graphs showing the relationship between particle resistance and transfer rate when the hardness of the micro rubber is changed. In FIGS. 11 to 13, the horizontal axis is the particle resistance (log (Ωcm)), and the vertical axis is the secondary transfer rate (%).

The secondary transfer rate of the black halftone image was measured with the micro rubber hardness of 40 or less (FIG. 11), 40 to 50 (FIG. 12), and 50 to 60 (FIG. 13). As the secondary transfer bias, a bias consisting only of a DC voltage was used. The higher the transfer rate, the more the overcharging is prevented, and the better the image quality. This time, as a guide, we aimed for a transfer rate of 70% or more.

From this result,
Hardness 40 or less (Fig. 11): Particle volume resistivity squared or less Hardness 40 to 50 (Fig. 12): Particle volume resistivity 4 or less Hardness 50 to 60 (Fig. 13): Particle volume resistivity 6 or less It was found that good transfer was obtained. That is, it is desirable that the softer the rubber, the lower the resistance of the particles.

Further, regardless of the hardness of the belt, when the particle volume resistivity exceeds the sixth power, the halftone transfer rate decreases. Further, it was also found that the transfer rate was lowered when the fine particles having a particle volume resistivity of less than the 0th power were used as the fine particles as in Comparative Example 2, regardless of the hardness of the belt. This is because, as described above, too much current flows on the belt surface and discharge between the intermediate transfer belt and the paper is less likely to occur, which hinders the formation of an electric field for transferring toner. Conceivable.

When an intermediate transfer belt having a hardness higher than 60 is used, when the toner image is transferred to uneven paper (embossed paper, etc.) having large irregularities on the surface, the surface of the belt does not sufficiently follow the uneven shape of the surface of the uneven paper. Insufficient transferability. Therefore, the micro rubber hardness is preferably 60. Therefore, as an elastic belt, if the micro rubber hardness is 60 or less and the volume resistivity of the fine particles is in the range of 0 to 6 power, both transferability to uneven paper and prevention of abnormal images due to overcharging can be achieved at the same time. It is possible.

(Second embodiment)
In the second embodiment, a coat layer is provided instead of adhering the low resistance fine particles to the surface of the elastic layer of the intermediate transfer belt. As the coating agent, Denatron P-502RG (trade name) manufactured by Nagase & Co., Ltd. was used. The film thickness of the coat layer was 3 μm. The surface resistivity of the coat layer was ⁴ × 105 [Ω / □].

FIG. 14 is a graph showing the relationship between the toner adhesion amount and the secondary transfer rate in the intermediate transfer belt provided with the coat layer. In FIG. 14, the horizontal axis is the toner adhesion amount (M / A), and the vertical axis is the secondary transfer rate (%). Further, the solid line is a graph by a belt provided with a coat layer, and the broken line is a graph by a belt (comparative example) in which insulating particles are dispersed instead of providing a coat layer.

K-color images having a toner adhesion amount (M / A) of 0.005, 0.016, 0.033, 0.046, 0.058 (mg / cm ² ) were transferred, respectively. As a result, the secondary transfer rate was 90% or more in the images of any adhesion amount, which was improved by 30% or more as compared with the case of using the belt of the comparative example. As a result, it was found that the belt provided with the coat layer can prevent overcharging when transferring the halftone image and can obtain a good image.

As a result of additional experiments by the present inventors, when the surface resistivity was 1 × 10 ² [Ω / □] or less, the transfer current was not formed due to the leakage of the transfer current, and the transfer resistivity decreased. When the surface resistivity was 1 × ¹⁰⁷ [Ω / □] or more, overcharging of the toner occurred and transfer failure occurred. Therefore, it is preferable to use a coat layer having a surface resistivity of more than 1 × 10 ² [Ω / □] and 1 × 10 ⁷ [Ω / □] or less. Further, by providing a coat layer having a surface resistivity of more than 1 × 10 ² [Ω / □] and 1 × 10 ⁷ [Ω / □] or less on the elastic layer of the belt having a hardness of 60 or less. Transferability can be improved.

(Third embodiment)
The third embodiment is different from the first or second embodiment in that a superimposed voltage is used for the secondary transfer bias. Other points are the same as those in the above embodiment.

In order to transfer the toner image to the recording medium P, it is necessary to apply a voltage of a certain magnitude. However, if a constant value voltage (that is, a voltage consisting only of DC components) is continuously applied, the toner may overcharge and a sufficient halftone concentration may not be obtained, as described with reference to FIG. ..

FIG. 15 is an example of an ideal transfer bias waveform according to the third embodiment. In FIG. 15, the horizontal axis is time (s) and the vertical axis is voltage (V). The symbol in the figure, Vr, is the peak value of the positive voltage, and Vt is the peak value of the negative voltage (the peak voltage on the transfer side on the side where the toner image is transferred from the intermediate transfer belt to the recording sheet).

here,
Voff = (Vr + Vt) / 2, Vpp = (Vr-Vt)
Wave = (Vr × Duty / 100) + Vt × (1-Duty) / 100
A: Duration of Vt (duration of transcription side peak waveform)
B: Time of one waveform cycle Duty: (BA) / B × 100 (%)
And.

In the transfer bias waveform shown in FIG. 15, a voltage of a magnitude required for transfer is applied, but the application time is shortened by setting the Duty higher than 50%, and halftone is produced by preventing overcharging of the toner. It is an ideal waveform to be transferred.

FIG. 16 is a waveform actually output aiming at the ideal waveform of FIG.
Vt: -4.8 kV, Vr: 1.2 kV, Voff: -1.8 kV, Wave: 0.08 kV, Vpp: 6.0 kV, Vt peak duration A: 0.10 ms, waveform period B: 0. An AC voltage having a waveform of 66 ms and Duty: 85% was applied.

17 (a) to 17 (e) are output waveforms when the Duty is shaken from 90% to 10% under the conditions of the transfer bias waveform shown in FIG. A K-color (black) halftone image was output from these waveforms, and sensory evaluation was performed.

The experimental conditions are environment: 27 ° C./80%, paper: Mohawk Color Copper Gloss 270 gsm (457 mm × 305 mm), process linear velocity: 630 mm / s, output image: Bk halftone, secondary transfer nip width: 4 mm.

Sufficient halftone concentrations were obtained with Duty of 90% and 70%. On the other hand, in the cases of 50%, 30%, and 10%, the density was acceptable for the image quality to be provided to the user, but the density was lower than that of 90% and 70%.

Further, as a comparison, when the same image was output using only the DC voltage, the same density as in the case where the Duty was 50%, 30%, and 10% was obtained, which was an acceptable density for the image quality to be provided to the user. .. However, the concentration was lower than that of 90% and 70% of Duty. Similar results were obtained not only when the coated paper was transferred but also when the secondary transfer bias described in the third embodiment was used when transferring plain paper or recycled paper.

As described with reference to FIG. 15, when the Duty is 10%, 30%, and 50%, the time for applying the voltage is long, the toner image is overcharged, and the transferability is improved as compared with the case where only the DC voltage is used. I didn't. On the other hand, at 70% and 90% of the high duty, the time for applying the voltage was short, overcharging could be further prevented, and transferability could be improved.

Further, in the output waveform, if the polarities are reversed by Vr and Vt, overcharging can be prevented more reliably. The reason is that even when the paper is charged, an electric field is created in a direction to prevent charging by straddling zero.

As shown in FIGS. 5 and 6, when the particles are dispersed on the surface of the belt, the releasability of the toner is improved. However, when the conventional AC bias (Duty 50% or less or DC constant current) is used, the transferability of the halftone image is at an acceptable level, but the density is slightly low. The cause is that the current leaked from the gaps between the particles and the toner was overcharged. Therefore, when the particles are dispersed on the surface of the belt, the above problem can be solved by using a transfer bias having a high duty. As a result, the releasability can be improved and a sufficient halftone density can be obtained.

Further, when the coat layer is provided on the belt surface (second embodiment), a high duty transfer bias may be used.

As shown in FIG. 15, in a high-Duty waveform in which the Duty exceeds 50%, the center value Voff of the two peak values (Vr and Vt) of the superposed voltage is closer to the transfer direction than the time average value Wave of the superposed voltage. (It is closer to the negative polarity in FIG. 15). By using such a waveform, a sufficient halftone density can be obtained.

The present invention has been described in detail above using the embodiments. This embodiment is an example, and can be variously modified and used within a range that does not deviate from the gist.

1 Image forming unit 2 Photoreceptor 3 Drum cleaning device 4 Cleaning brush roller 5 Cleaning blade 6 Charging device 7 Charging roller 8 Developing device 9 Developing roller 10 1st screw member 11 2nd screw member 12 Developing unit 13 Developer carrier 13a Mother body Particles 13b Conductive layer 30 Transfer unit 31, 31'Intermediate transfer belt 31a Base layer 31b Elastic layer 31c Fine particles 32 Drive roller 33 Secondary transfer backside roller 34 Cleaning backup roller 35 Primary transfer roller 36 Secondary transfer belt 37 Belt cleaning device 38 Potential Sensor 39 Secondary transfer bias power supply 41 Secondary transfer unit 45 Elastic layer 46 Pressing member 80 Optical writing unit 90 Fixing device 91 Fixing roller 92 Pressurizing roller 100 Feed cassette 100a Roller 101 Resist roller vs. 110 DC power supply 140 AC power supply 200 Power supply control unit 400 Secondary transfer roller 500 Printer body N Secondary transfer nip P Recording medium

Japanese Unexamined Patent Publication No. 2007-254558 Japanese Unexamined Patent Publication No. 2002-356654 Japanese Unexamined Patent Publication No. 9-230717 Japanese Unexamined Patent Publication No. 2002-162767 Japanese Unexamined Patent Publication No. 2004-354716 Japanese Unexamined Patent Publication No. 2007-328165 Japanese Unexamined Patent Publication No. 2009-75154 JP-A-2015-148660 Japanese Patent No. 5786181 Japanese Unexamined Patent Publication No. 2012-194223

Claims (3)

An image carrier with an elastic layer and
In an image forming apparatus including a transfer member that transfers a toner image carried by the image carrier to a recording medium.
Fine particles having a volume resistivity of 1 × 10 2 [Ω · cm] to 1 × 10 6 [Ω · cm] are provided on the surface of the elastic layer of the image carrier, and the volume resistivity is 1 × 10 ² [Ω · cm] to 1 × 10 ⁶ [Ω · cm].
As the image carrier, one having a micro rubber hardness of 50 to 60 is used, and the image carrier is used.
The fine particles are an image forming apparatus characterized in that resin particles are used as parent particles and a conductive layer is coated on the surface thereof. An image carrier with an elastic layer and
In an image forming apparatus including a transfer member that transfers a toner image carried by the image carrier to a recording medium.
Fine particles having a volume resistivity of 1 × 10 2 [Ω · cm] to 1 × 10 4 [Ω · cm] are provided on the surface of the elastic layer of the image carrier, and the volume resistivity is 1 × 10 ² [Ω · cm] to 1 × 10 ⁴ [Ω · cm].
As the image carrier, one having a micro rubber hardness of 40 to 50 is used, and the image carrier is used.
The fine particles are an image forming apparatus characterized in that resin particles are used as parent particles and a conductive layer is coated on the surface thereof. A power source for outputting a transfer bias containing an AC component to the transfer member in order to transfer the toner image carried by the image carrier to the recording medium is provided.
In the transfer bias waveform, the duration of the transfer-side peak waveform for transferring the toner image from the image carrier to the recording medium is A, and the period of the waveform is B.
When Duty = (BA) / B × 100 (%)
The image forming apparatus according to claim 1 or 2, wherein the duty is larger than 50%.

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