JP2006242352A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of stabilizing amount of application of liquid toner on a development roller and preventing occurrence of uneven quality of image and provided with a toner application roller having high durability. <P>SOLUTION: This image forming device using the liquid toner prepared by dispersing toner in carrier liquid made of silicone oil or mineral oil is provided with the development roller for developing an electrostatic latent image formed on a photosensitive body and the toner application roller for forming a thin layer of liquid toner on the development roller. The toner application roller has a channel part on its surface and a surface of the channel part is nitrided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that develops an electrostatic latent image formed on a photoreceptor with a liquid toner obtained by dispersing toner in a carrier liquid made of silicon oil or mineral oil.

  There is known an image forming apparatus that develops an electrostatic latent image formed on a photosensitive member with a liquid toner in which a toner is dispersed in an insulating carrier liquid. In this electrostatic latent image, since the charged toner develops in the insulating carrier liquid by electrostatic force, the developing efficiency is improved as the moving distance is shorter. For this reason, it is necessary to form a thin layer of liquid toner in units of microns on the developing roller, and to develop the thin liquid toner in contact with the photoreceptor.

  In order to form such a thin layer of liquid toner, the liquid toner is held by a toner application roller (anilox roller) having regular grooves formed on the surface thereof, and a toner regulating blade is placed on the surface of the toner application roller. The amount of liquid toner on the surface of the toner application roller is regulated, the toner application roller and the development roller are brought into contact, and the liquid toner of the toner application roller is transferred and applied to the development roller.

When performing development by applying liquid toner to the developing roller in a thin layer, the thickness of the thin layer of liquid toner determines the image density, so it is important to form a thin layer of uniform thickness. It becomes. In Japanese Patent Laid-Open No. 2002-278295 (hereinafter referred to as “known example”), in order to apply a uniform liquid toner to the developing roller, the amount of application due to the adhesion of the liquid toner to the groove of the toner application roller is described. In order to prevent the decrease, a configuration in which an amorphous fluororesin is coated on the groove portion of the toner application roller is disclosed.
JP 2002-278295 A

As in the known example, coating the groove portion of the toner application roller with a fluororesin having high oil repellency for liquid toner improves the releasability (transferability to the developing roller) of the liquid toner from the groove portion. On the other hand, when liquid toner is held in the groove of the toner application roller and pumped up, the oil repellency is too good, so that sufficient liquid toner cannot be held in the groove of the toner application roller. This causes a problem that a liquid toner cannot be applied.
A decrease in the amount of liquid toner applied to the developing roller ultimately causes density unevenness on the recording medium.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the above-described problems and includes a toner application roller that has a stable liquid toner application amount to the developing roller and has high durability, and has no image quality unevenness.

  In order to solve the above problem, the first invention of the present invention is an image forming apparatus using liquid toner in which toner is dispersed in a carrier liquid made of silicon oil or mineral oil. The image forming apparatus is formed on a photoconductor. A developing roller for developing an electrostatic latent image; and a toner applying roller for forming a thin layer of liquid toner on the developing roller. The toner applying roller has a groove on its surface, and the surface of the groove is nitrided It is characterized by being.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, only the crests of the groove portions on the surface of the toner application roller are coated with a fluorine resin.

In the image forming apparatus using the liquid toner in which the toner is dispersed in the carrier liquid made of silicon oil or mineral oil according to the present invention, the image forming apparatus includes a developing roller for developing the electrostatic latent image formed on the photoreceptor. And a toner application roller for forming a thin layer of liquid toner on the developing roller, the toner application roller having a groove on its surface, and the surface of the groove is subjected to nitriding treatment. Both good pumping property of toner and good transferability to the developing roller can be achieved, and stable image quality can be continuously produced.
The fluororesin coating is applied only to the peak of the groove on the surface of the toner application roller, so that the liquid toner held in the groove of the toner application roller is prevented from overflowing into the peak of the groove when the toner application roller and the developing roller are in contact. The highly oil-based fluororesin coating is prevented, and the amount of liquid toner applied to the developing roller is stabilized, so that unevenness in image quality is eliminated, and at the same time, wear of the toner regulating blade can be reduced.

  The image forming apparatus according to the present embodiment will be described by using the black image forming unit K as a representative. The image forming units Y, M, and C for yellow, magenta, cyan, and black have the same configuration as the image forming unit for black, and description thereof is omitted.

  The photoconductor 100 formed of an organic photoconductor or an amorphous silicon photoconductor is a charging roller 110 that rotates in contact with the photoconductor 100 while being applied with a bias having the same polarity as the charging polarity of the liquid toner from a power supply device (not shown). As a result, the surface is uniformly charged.

  The charging roller 110 is preferably an elastic roller in which an elastic member such as conductive urethane rubber and a fluororesin surface layer are arranged on the surface of a metal core. Further, a cleaning pad 111 is slidably contacted with the charging roller 110 to remove dirt from the charging roller.

  Next, an electrostatic latent image for black image is written on the uniformly charged photoreceptor 100 by a laser scanning optical system 200 disposed below each color image forming unit.

  On the other hand, in the developing device 300, a uniform liquid toner layer is formed on the developing roller 301 by a structure described later in FIG. 2, and the developing roller 301 to which a developing bias having the same polarity as the liquid toner is applied from a power supply device (not shown) is photosensitive. The black image electrostatic latent image is visualized with liquid toner by rotating in contact with the black image electrostatic latent image formed on the body 100.

  In the liquid toner used in this embodiment, solid particles having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin are added to a carrier liquid such as silicon oil, mineral oil, and edible oil. However, about 20% by weight was dispersed.

    The developing roller 301 may have a structure in which an elastic member such as conductive urethane rubber and a resin layer or a rubber layer are provided on the outer periphery of a metal core. The developing roller 301 of this embodiment is made of urethane rubber (hardness is JIS-A 30 to 55 °) around an iron core.

  The liquid toner image immediately after being formed on the photoconductor 100 by the developing roller 301 has a high carrier liquid ratio, and if color is superimposed on the intermediate transfer belt 400 by a transfer device described later, there is a possibility of causing an image flow. An excess carrier liquid is copied by a squeezing roller 330 that rotates in contact with the photoreceptor 100 while applying a bias having the same polarity as the charging characteristics of the toner, and a process of increasing the solid particle ratio in the visible image is performed. The carrier liquid copied to the squeezing roller 330 is scraped off by the squeezing roller cleaner 331.

  The squeezing roller 330 is preferably an elastic roller in which an elastic member such as conductive urethane rubber and a fluororesin surface layer are arranged on the surface of a metal core.

  Next, the visible image on the photoconductor 100 is applied to a primary transfer roller 405 that rotates in contact with the intermediate transfer belt 400 by applying a bias having a polarity opposite to the charging characteristic of the liquid toner from a power supply device (not shown). The image is primarily transferred to the transfer belt 400, and is superposed on a visible image of another color formed on the upstream side in the rotational direction of the intermediate transfer belt 400 by a similar image forming procedure to form a full color image.

  After the primary transfer, the electrostatic latent image is erased by the static elimination lamp 120 formed of a rod-shaped light source, and the liquid toner remaining in the primary transfer is scraped off by the photosensitive member cleaning blade 130 that is in contact with the photosensitive member 100. Again, the charging roller 110 is uniformly charged.

  The used liquid toner scraped off by the photoreceptor cleaning blade 130 is transported in the depth direction of FIG. 1 by the transport screw 131 and collected in a waste toner container (not shown).

  Each color visible image formed on the intermediate transfer belt 400 proceeds to a secondary transfer portion constituted by the intermediate transfer belt 400, a driving roller 401, and a secondary transfer roller 430.

  Corresponding to the timing of image formation, a recording medium 501 such as paper stacked in a paper feed cassette 500 is separated by a pickup roller 502 and a separation pad 503, and a pair of conveying rollers 504, skew feeding of the recording medium, and the like. The sheet is fed to the secondary transfer section through a registration roller pair 505 that corrects the feeding timing.

  The secondary transfer roller 430 is urged by an urging means (not shown) to the driving roller 401 via the intermediate transfer belt 400, and an intermediate transfer is performed by applying a bias having a polarity opposite to the charging characteristics of the liquid toner from a power supply device (not shown). The full color image on the belt 400 is secondarily transferred to the recording medium 501.

  The secondary transfer roller 430 is an intermediate transfer belt 400 between the paper dust and the recording medium attached to the surface of the secondary transfer roller 420 by the secondary transfer roller cleaning blade 421 that is in contact with the secondary transfer roller 430 by the secondary transfer roller cleaner 420. The liquid toner adhering to is scraped off. Paper dust and liquid toner scraped off by the secondary transfer roller cleaning blade 421 are conveyed in the depth direction of FIG. 1 by the conveying screw 422 and collected in a waste toner container (not shown).

  After the secondary transfer, the intermediate transfer belt 400 is subjected to secondary transfer residual toner and paper dust remaining on the surface of the intermediate transfer belt 400 by a belt cleaning blade 411 in a belt cleaner 410 that contacts the cleaner backup roller 402 via the intermediate transfer belt 400. Is scraped off. The secondary transfer residual toner and paper dust scraped off by the belt cleaning blade 411 are transported in the depth direction of FIG. 1 by the transport screw 412 and collected in a waste toner container (not shown).

  A recording medium 501 carrying a secondary-transferred full-color image passes through a fixing device 600 including a heat roller 601 having a heating means inside and a pressure roller 602 having an elastic member such as rubber outside. While the thermoplastic resin in the full-color image is melted, it is pressure-fixed to the recording medium 501 to obtain a desired image.

  After the fixing, the recording medium 501 is discharged from the upper surface of the image forming apparatus by a pair of discharge rollers 506. When forming an image on the back side of the same recording medium 501, the recording medium 501 is switched back by a pair of discharge rollers 506 that can be rotated in the forward and reverse directions, and registered by a pair of refeed rollers 507, 508, and 509. The image is again transferred to the back surface of the recording medium 501 by the secondary transfer unit via the roller pair 505, and after the image is fixed by the fixing device 600, the upper surface of the image forming apparatus is discharged by the paper discharge roller pair 506.

FIG. 2 is a partially enlarged view of the black image forming portion K of the image forming apparatus shown in FIG.
The configuration of the developing device of the image forming apparatus of the present invention will be described with reference to FIG.

  FIG. 2 is a partially enlarged view of the black image forming portion K in the image forming apparatus of FIG. The configuration of the developing device of the image forming apparatus will be described in detail with reference to FIG.

  The developing device 300 has a primary reservoir 315 for liquid toner below the container 320. An agitator 303 having a flexible plate-like stirring member 304 is disposed in the primary storage unit 315.

  The plate-like stirring member 304 is made of a flexible metal plate such as stainless steel or phosphor bronze or a flexible resin plate such as polyethylene terephthalate, and its free end is in sliding contact with the inner periphery of the container 320 of the primary reservoir 315. As the agitator 303 rotates, the liquid toner is agitated, and at the same time, the liquid toner is scraped up to the secondary reservoir 302.

  The liquid toner that has been scraped up and overflowed to the secondary reservoir 302 falls to the primary reservoir due to gravity.

  The secondary reservoir 302 is provided with a toner application roller 305 having a surface with fine irregularities such as spiral grooves on its surface, and urethane rubber is applied to the tip of the flexible metal plate so as to contact the rotating toner application roller 305. The toner regulating blade 306 is used to scrape off the liquid toner in the concave and convex grooves on the surface of the toner application roller 305.

  The liquid toner contained in the concave and convex grooves on the surface of the toner application roller 305 is brought into contact with the surface of the developing roller 301 by bringing the developing roller 301 in contact with an elastic member such as conductive urethane rubber on the surface of the metal core. The leveling roller 308 applied with a bias having the same polarity as the charging polarity of the liquid toner higher than that of the developing roller 301 from a power supply device (not shown) is rotated on the surface of the toner application roller 305. The concavo-convex pattern is erased and the liquid toner film thickness is made uniform.

  The leveling roller 308 is preferably a metal roller or a structure in which a conductive resin layer or rubber layer is provided on the surface layer of the metal roller. In this embodiment, the leveling roller 308 counter-rotates with respect to the developing roller 301. However, a speed difference may be provided with respect to the outer peripheral speed of the developing roller 301 to rotate in the driven direction.

  By applying a bias having the same polarity as the charging polarity of the liquid toner higher than that of the developing roller 301 to the leveling roller 308, the solid toner moves to the surface layer of the developing roller 301 and the liquid toner on the developing roller 301 is loosely coupled. Wake up. This loose coupling has an effect of accelerating the rapid movement of solid particles in the liquid toner from the developing roller 301 to the latent image forming portion of the photosensitive member 100 at the developing nip where the developing roller 301 contacts the photosensitive member 100. The image density can be improved.

  The leveling roller blade 309 contacts the leveling roller 308 in the counter direction, and scrapes off the liquid toner adhering to the leveling roller 308. The liquid toner scraped off by the leveling roller blade 309 is returned to the primary storage unit 315 via the recovery port 310 by gravity.

  The developing roller blade 307 is brought into contact with the surface of the developing roller 301 on the downstream side of the developing nip portion, and the remaining development—the liquid toner is scraped off to clean the surface of the developing roller 301. The liquid toner scraped off by the developing roller blade 307 is returned to the primary storage unit 315 via the recovery path 311 by gravity.

  The toner returned to the primary storage unit 315 via the recovery port 310 and the recovery path 311 is agitated by the agitator 303 and scraped up to the secondary storage unit 302 again.

  The toner application roller 305 of the present invention uses stainless steel as a base material, and a groove 321 (see FIGS. 4 and 5) is engraved on the surface at an angle of about 45 ° with respect to the axial direction. The pitch between the crest 322 (see FIGS. 4 and 5) and the trough 323 (see FIG. 4 and 5) of the groove 321 was 120 μm (crest: 90 μm, trough: 30 μm). When the groove 321 is filled with liquid toner and all of the groove is transferred onto the surface of the developing roller, the film thickness formed on the surface of the developing roller 301 is about 12 μm.

  The toner regulating blade 306 of the present invention is made of urethane rubber (hardness is JIS-A62 °), and the toner application roller 305 is in a direction tangential to the toner application roller 305 as shown in FIG. The contact angle was 20 °, the protrusion length was 0.3 mm, and contact was made by fixed position control.

  The developing roller 301 of the present invention is made of urethane rubber (hardness is JIS-A 30 to 55 °) around an iron cored bar.

Example 1
The toner application roller 305 was formed by rolling a stainless steel substrate to form the groove 321. After the rolling process, the surface was washed with chlorofluorocarbon, put in a processing furnace, and held at 300 ° C. for 15 minutes in an N ₂ gas atmosphere containing 5000 ppm of nitrogen fluoride (NF ₃ ). Thereafter, the mixture was heated to 530 ° C., a mixed gas of 50% NH ₃ + 50% N ₂ was introduced into the furnace, subjected to nitriding treatment for about 3 hours, and then air-cooled and taken out from the processing furnace. As shown in FIG. 4, the nitrided cured film 324 formed on the toner application roller 305 had a uniform thickness of 30 μm. The hardness of the base material portion of the stainless steel was 300 Hv (Vickers hardness), whereas the hardness of the cured film 325 subjected to nitriding treatment was 1200 Hv. For evaluation of paintability, the static contact angle when 2 μl of water was dropped was measured and found to be 78 °.

(Example 2)
The toner application roller 305 was formed by rolling a stainless steel substrate to form the groove 321. After the rolling process, the surface is washed with acetone, put in a processing furnace, and at 300 ° C. in an N ₂ gas atmosphere containing 35,000 ppm of nitrogen fluoride (NF ₃ ) and 7000 ppm (0.7%) of O _2. Hold for about 15 minutes. Then, after heating to 500 ° C. and holding for about 30 minutes under 10% N ₂ + 90% H ₂ , 20% NH ₃ + 80% RX (methane, propane, etc. are incompletely combusted in air to form H ₂ O obtained by removal of CO _2, at approximately the composition N ₂ + CO (20%) is a _{+ H 2 (30%))} , was about 3 hours nitride was removed from the air-cooled post-processing furnace. The resulting toner coating roller 305 had a uniform nitride layer thickness of 40-50 μm. Further, the hardness of the stainless steel base material portion was 300 Hv (Vickers hardness), whereas the hardness of the nitrided cured film 325 was 900 Hv. For evaluation of wettability, the static contact angle when 2 μl of water was dropped was measured and found to be 75 °.

(Example 3)
As in the second embodiment, an epoxy resin is embedded in the valley 323 of the groove 321 of the toner application roller 305 that has been subjected to rolling and nitriding. The surface of the crest 322 of the groove 321 of the toner application roller 305 is degreased, and only the crest 322 is activated by chemical polishing surface treatment. Thereafter, a fluororesin was applied by spraying and dried at 150 ° C. for 30 minutes. Finally, acetone is poured into the trough 322 of the groove 321 to dissolve the epoxy resin embedded in the trough 323. With the above procedure, as shown in FIG. 5, the fluororesin coating 325 was applied only to the peak 322 of the groove 321 of the toner application roller 305. The film thickness of the fluororesin coating 325 was about 3 μm. In order to evaluate the wettability of the fluororesin coating 325, the static contact angle when 2 μl of water was dropped was measured to be 108 °.

(Comparative Example 1)
In the same manner as in Example 3, the crest 322 and the entire trough 323 of the groove 321 in which the cured film formed by rolling and nitriding of the toner application roller 305 was formed were applied in Example 3. Fluororesin coated. The film thickness of the fluororesin coating was about 3 μm. For evaluation of paintability, the static contact angle when 2 μl of water was dropped was measured and found to be 108 °.

(Comparative Example 2)
The toner application roller 305 is the same as that of the toner application roller 305 of Example 1 before nitriding. For evaluation of paintability, the static contact angle when 2 μl of water was dropped was measured and found to be 45 °.

  The following image evaluation experiments were performed on the toner application rollers of Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2. Using the same device configuration and the same liquid toner, the film thickness on the developing roller was measured, and in addition, the final image density was measured for each number of printed sheets. The results are shown in Table 1.

(Table 1)
┌───────┬┬───────┬─────┬┬──────┬──────┐
│ │Initial image density │ 10K │ 25K │ 50K │
├───────┼┼───────┼─────┼┼──────┼──────┤
│Example 1 │1.45 │1.42│ 1.46 │1.44 │
│ │Film thickness: 6.8μm │ │Film thickness: 6.6μ
│ │ │ │ │m │
├───────┼┼───────┼─────┼┼──────┼──────┤
│Example 2 │1.46 │1.44│1.45 │1.43 │
│ │ Film thickness: 6.8 │ │ │ Film thickness: 6.5μ
│ │μm │ │ │m │
├───────┼┼───────┼─────┼┼──────┼──────┤
│Example 3 │1.45 │1.45│1.44 │1.45 │
│ │ Film thickness: 6.5 │ │ │ Film thickness: 6.5 |
│ │μm │ │ │μm │
├───────┼┼───────┼─────┼┼──────┼──────┤
│Comparative Example 1 │0.86 │ 0.80│ 0.75 │ 0.83 │
│ │ Film thickness: 4.5 │ │ │ Film thickness: 4.4μ
│ │μm │ │ │m │
├───────┼┼───────┼─────┼┼──────┼──────┤
│Comparative example 2 │1.39 │ 1.08│ 0.95 │ 0.89 │
│ │ Thickness: 6.2 │ │ │ Thickness: 4.7 μ
│ │μm │ │ │m │
└───────┴┴───────┴─────┴┴──────┴──────┘

  From this result, in Example 1 and Example 2, even if the initial image and the image after durability were compared, an equivalent good image was obtained. In Example 3 as well, good images were obtained as in Example 1 and Example 2. In addition, very little image quality unevenness occurred. In Comparative Example 1, the initial image and the image density after the durability were not so stable, and a sufficient density was not obtained from the initial image. Further, there was a density unevenness that was so visible that the groove pattern of the toner application roller was present. In Comparative Example 2, a sufficient density of the initial image was obtained, but a sharp decrease in image density was observed due to durability.

  As a result, in Examples 1 to 3, even when the initial image and the image after durability were compared, good images having the same level in density and image quality were obtained. In the third embodiment, when the toner application roller and the developing roller, which is an elastic body, come into contact with each other, liquid toner that is likely to overflow from the peak portion of the groove portion of the toner application roller is prevented from the oil repellency of the fluorine resin coating in the peak portion. I was able to. As a result, image quality unevenness during transfer from the toner application roller to the developing roller is almost eliminated, and at the same time, wear of the toner regulating blade (elastic body) can be reduced.

It is a figure which shows one Embodiment of this invention. It is a figure which shows one Embodiment of this invention. It is a figure which shows one Embodiment of this invention. It is a figure which shows one Embodiment of this invention. It is a figure which shows one Embodiment of this invention.

Explanation of symbols

100: photoconductor, 110: charging roller, 111: cleaning pad, 120: static elimination lamp, 130: photoconductor cleaning blade, 131: conveying screw, 200: laser scanning optical system, 300: developing device, 301: developing roller, 302 : Secondary storage unit, 303: agitator, 304: plate-like stirring member, 305: toner application roller, 306: toner regulating blade, 307: developing roller blade, 308: leveling roller, 309: leveling roller blade, 310: Recovery port, 311: recovery path, 315: primary storage section, 320: primary storage section container, 321: groove section, 322: peak section, 323: valley section, 324: nitriding cured film, 325: fluororesin coating 400: Intermediate transfer belt 401: Drive roller 402: Cleaner backup roller 4 3, 404: auxiliary roller, 405: primary transfer roller, 410: belt cleaner, 411: belt cleaning blade, 412: transport screw, 420: secondary transfer roller cleaner, 421: secondary transfer roller cleaning blade, 422: transport screw 430: secondary transfer roller, 501: recording medium, 502: pickup roller, 503: separation pad, 504: transport roller, 505: registration roller, 506: paper discharge roller pair, 507, 508, 509: refeed roller 600: fixing device, 601: heat roller, 602: pressure roller

Claims (2)

In an image forming apparatus using liquid toner in which toner is dispersed in a carrier liquid made of silicon oil or mineral oil, the image forming apparatus includes a developing roller for developing an electrostatic latent image formed on a photoreceptor, An image forming apparatus comprising: a developing roller provided with a toner application roller that forms a thin layer of liquid toner; the toner application roller having a groove on a surface thereof; and the surface of the groove is nitrided. The image forming apparatus according to claim 1, wherein only the peak portion of the groove portion on the surface of the toner application roller is coated with a fluorine resin.

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