JP2011203413A - Liquid developer, liquid developing device and wet-type image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid developer, a liquid developing device and a wet-type image forming apparatus capable of reducing consumption energy in a wet-type developing method.SOLUTION: The wet-type image forming apparatus 1A comprises: a charging device 11 for charging the surface of a photoreceptor drum 10; an exposure device 12 for forming an electrostatic latent image on the surface of the charged photoreceptor drum 10; a liquid developing device 14 for developing the electrostatic latent image on the surface of the photoreceptor drum 10 by using the liquid developer; and a primary transfer roller 20 and a secondary transfer part 4 for transferring the developed image to a recording medium, wherein the liquid developer having an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid, the colored particles being pigment, contains polyvinyl butyral.

Description

  The present invention belongs to the technical field of a wet developing method which is one of electrophotographic systems that can be employed in a printer, a copying machine, a facsimile machine, or a multifunction machine having these functions.

  In general, electrophotographic methods for developing an electrostatic latent image with charged colored particles are roughly classified into a dry development method and a wet development method depending on the form of the developer. Among them, in the wet development method, a liquid developer in which colored particles are dispersed in an electrically insulating carrier liquid is used. The colored particles charged in the liquid developer move from the surface of the developing roller to the surface of the photosensitive drum according to the principle of electrophoresis, and visualize the electrostatic latent image on the surface of the photosensitive drum. The obtained image is transferred from the photosensitive drum to a recording medium. The liquid developer has almost no possibility that the colored particles are scattered in the atmosphere, so for example, fine colored particles with an average particle diameter of submicron can be used, and high-quality images with high resolution and excellent gradation. Is obtained.

  In the wet development method, a thermal fixing method and a light fixing method are known as methods for fixing an image, that is, colored particles to a recording medium. As described in Patent Document 1, for example, when the colored particles are a toner in which a pigment is dispersed in a binder resin, the toner is fixed on a recording medium by melting the binder resin with heat. It is a method to make it. For example, as described in Patent Document 2, the light fixing method uses a binder resin having a photoreactive functional group as a binder resin when colored particles are a toner in which a pigment is dispersed in a binder resin. In this method, the toner is fixed to the recording medium by polymerizing the binder resin with light.

JP 2008-242039 A (paragraph 0009) JP2003-241440 (paragraph 0006)

  In the conventional heat fixing method and light fixing method in the wet development method, heat energy and light energy are consumed to fix the colored particles on the recording medium. An object of the present invention is to fix colored particles on a recording medium without consuming heat energy or light energy, and to reduce energy consumption in a wet image forming apparatus.

  One aspect of the present invention for solving the above problems is a liquid developer having an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid, the colored particles being a pigment, and polyvinyl butyral. It is a liquid developer characterized by containing.

  In the liquid developer, the carrier liquid is preferably at least one selected from the group consisting of triethylene glycol bis (2-ethylhexanate), castor oil, and epoxidized soybean oil.

  In the liquid developer, the content of polyvinyl butyral is preferably 1 to 10% by mass.

  Another aspect of the present invention for solving the above-described problem is a liquid developing apparatus that develops an electrostatic latent image on the surface of a photosensitive drum using a liquid developer, and an electrically insulating carrier is used as the liquid developer. A liquid developing apparatus comprising a liquid and a colored particle dispersed in a carrier liquid, wherein the colored particle is a pigment and a liquid developer containing polyvinyl butyral is used.

  Still another aspect of the present invention for solving the above problems includes a charging device for charging the surface of the photosensitive drum, an exposure device for forming an electrostatic latent image on the surface of the charged photosensitive drum, and liquid development. A wet image forming apparatus comprising a liquid developing device that develops an electrostatic latent image on the surface of a photosensitive drum using an agent, and a transfer device that transfers the developed image to a recording medium. A wet image forming apparatus comprising an insulating carrier liquid and colored particles dispersed in the carrier liquid, wherein the colored particles are pigments and a liquid developer containing polyvinyl butyral is used.

  According to the liquid developer, the liquid developing device, and the wet image forming apparatus according to the present invention, the pigment as the colored particles can be fixed on the recording medium without consuming heat energy or light energy. Energy consumption can be reduced. Further, it is possible to reduce the fixing device itself using heat and light energy that has been used conventionally, and it is possible to simplify and reduce the cost of the wet image forming apparatus.

1 is a schematic configuration diagram of a wet image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of the periphery of a liquid developing device provided in the wet image forming apparatus shown in FIG. 1.

  In view of the current situation where heat and light energy are consumed to fix an image on a recording medium in the fixing step of the conventional wet development method, the present inventor has eagerly developed a liquid developer that is preferable from the viewpoint of energy saving. As a result of repeated studies, when the pigment itself is used as the colored particles, not the toner in which the pigment is dispersed in the binder resin, and the liquid developer contains polyvinyl butyral, the image is transferred to the recording medium. The present invention has been completed by paying attention to the fact that when the carrier liquid is absorbed into the recording medium, the polyvinyl butyral can remain on the surface of the recording medium to form a film.

  That is, the liquid developer according to this embodiment is a liquid developer having an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid, and the colored particles are pigments and contain polyvinyl butyral. It is a liquid developer. After the image is transferred to the recording medium, when the carrier liquid is absorbed inside the recording medium, the polyvinyl butyral is coated on the surface of the recording medium while covering the pigment remaining on the surface of the recording medium. Since the film stays and forms a film, the pigment is fixed on the recording medium by the polyvinyl butyral film. Accordingly, the pigment, that is, the image can be fixed on the recording medium without consuming heat energy or light energy, and energy consumption in the wet image forming apparatus can be reduced.

<Liquid developing apparatus and wet image forming apparatus>
First, a liquid developing apparatus and a wet image forming apparatus according to the present embodiment will be described with reference to the drawings. It should be noted that the terms representing the directions such as “upper”, “lower”, “left”, “right” and the like used in the following description are merely for the purpose of clarifying the explanation and limit the present invention in any way. It is not a thing. Further, the term “sheet” used in the following description means any recording medium capable of forming an image, such as high-quality plain paper, copy paper, tracing paper, cardboard, and OHP sheet.

  FIG. 1 is a schematic configuration diagram of a wet image forming apparatus according to the present embodiment, and FIG. 2 is a schematic configuration diagram of a periphery of a liquid developing device provided in the wet image forming apparatus shown in FIG. The wet image forming apparatus according to the present embodiment is a color printer. For example, a monochrome printer, a copying machine, a facsimile machine, a multifunction machine having these functions, or the like can form an image on a sheet, that is, a recording medium. Any other wet image forming apparatus that can be used may be used.

  As shown in FIG. 1, a wet image forming apparatus 1A according to the present embodiment accommodates various units and parts for image formation. The image forming apparatus 1A further stores a liquid developer circulating device for each color of yellow (Y), magenta (M), cyan (C), and black (Bk) in the lower part of the portion shown in FIG. However, the illustration is omitted here.

  The wet image forming apparatus 1A transfers a tandem image forming unit 2 that forms an image based on image data, a sheet storage unit 3 that stores a sheet, and an image formed by the image forming unit 2 onto the sheet. The image forming apparatus includes a secondary transfer unit 4, a discharge unit 6 that discharges a sheet on which image fixing is completed, and a sheet conveyance unit 7 that conveys the sheet from the sheet storage unit 3 to the discharge unit 6.

  In general, a wet image forming apparatus usually has a fixing unit 5 (sheet) for fixing a transferred image to a sheet between a secondary transfer unit 4 and a discharge unit 6 as indicated by a virtual line in the figure. Are provided with a heating roller 51 and a pressure roller 52 disposed opposite to each other. However, in the wet image forming apparatus 1A according to the present embodiment, such a fixing unit is not provided, and instead, only rollers 8 and 8 for sheet conveyance are provided. That is, in the wet image forming apparatus 1A according to the present embodiment, by using the liquid developer according to the present embodiment to be described later, the image transferred to the sheet is fixed on the sheet without the need for a fixing unit. Can do. That is, in the present embodiment, it is possible to reduce the fixing unit 5 using heat and light energy that has been conventionally used, and it is possible to simplify the wet image forming apparatus 1A and reduce the cost.

  The image forming unit 2 includes an intermediate transfer belt 21, a cleaning unit 22 for the intermediate transfer belt 21, and an image forming unit corresponding to each of yellow (Y), magenta (M), cyan (C), and black (Bk). FY, FM, FC, FB.

  The intermediate transfer belt 21 is a wide endless belt member having conductivity, and is driven to circulate clockwise in FIG. In the circulation drive of the intermediate transfer belt 21, the surface facing outward is referred to as “front surface”, and the surface facing inward is referred to as “back surface”.

  The image forming units FY, FM, FC, and FB are arranged side by side along the lower running surface of the intermediate transfer belt 21. Note that the order of arrangement of the image forming units FY, FM, FC, and FB is not limited to that shown in the figure, but the arrangement shown in FIG. 1 is preferable from the viewpoint of reducing the influence of the color mixture on the completed image. It is one of.

  The image forming units FY, FM, FC, and FB include a photosensitive drum 10, a charging device 11, an LED exposure device 12, a liquid developing device 14, a primary transfer roller 20, a cleaning device 26, and a charge eliminating device 13. And a carrier liquid removing roller 30. Of the image forming units, the black image forming unit FB located closest to the secondary transfer unit 4 is not provided with the carrier liquid removal roller 30, but the other configurations are the same.

  The surface (circumferential surface) of the cylindrical photosensitive drum 10 can carry an image visualized with colored particles charged (charged to a positive polarity in this embodiment). The illustrated photosensitive drum 10 can rotate counterclockwise.

  The charging device 11 uniformly charges the surface of the photosensitive drum 10. The operation of the charging device 11 constitutes a charging process.

  The LED exposure device 12 has an LED as a light source, and irradiates light onto the uniformly charged surface of the photosensitive drum 10 based on image data input from an external device. As a result, an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 10. The operation of the exposure apparatus 12 constitutes an exposure process.

  The liquid developing device 14 holds a liquid developer having an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid so as to face the electrostatic latent image formed on the surface of the photosensitive drum 10. To do. As a result, the electrostatic latent image on the surface of the photosensitive drum 10 is visualized with the charged colored particles and developed as an image. The operation of the liquid developing device 14 constitutes a developing process. In the liquid developing device 14 and the wet image forming apparatus 1A according to the present embodiment, a colored developer is a pigment and a liquid developer containing polyvinyl butyral is used as the liquid developer, which will be described in detail later.

  As shown in FIG. 2, the liquid developing device 14 includes a developing container 140, a developing roller 141, a supply roller (anilox roller) 142, a support roller 143, a supply roller blade 144, a development cleaning blade 145, a developer collecting device 146, and A developing roller charging device 147 is included.

  The developer container 140 is supplied with a liquid developer and stores the liquid developer. The liquid developer is supplied from the supply nozzle 278 to the inside of the developing container 140 after the concentration of the carrier liquid and the colored particles is adjusted in advance. In that case, the liquid developer is supplied toward the nip portion between the supply roller 142 and the support roller 143, and the excess part falls below the support roller 143 and is stored in the bottom of the developing container 140. The stored liquid developer is recovered through the pipe 82 and then recycled and reused.

  The support roller 143 is disposed substantially at the center of the developing container 140 and abuts against the supply roller 142 from below to form a nip portion. The supply roller 142 is not disposed directly above the support roller 143 but is shifted in a direction away from the supply nozzle 278. A groove for holding the liquid developer is provided on the peripheral surface of the supply roller 142. As indicated by dotted arrows in the figure, the support roller 143 rotates counterclockwise and the supply roller 142 rotates clockwise.

  The liquid developer supplied from the supply nozzle 278 is temporarily retained on the upstream side in the rotation direction of the support roller 143 in the nip portion between the supply roller 142 and the support roller 143, and as the rollers 142 and 143 rotate, It is carried upward while being held in the groove of the supply roller 142. The supply roller blade 144 is pressed against the peripheral surface of the supply roller 142 and regulates the amount of liquid developer held in the groove of the supply roller 142 to be a predetermined amount. Excess liquid developer scraped off by the supply roller blade 144 is stored at the bottom of the developing container 140.

  The developing roller 141 is disposed in the upper opening of the developing container 140 so as to be in contact with the supply roller 142. The developing roller 141 is rotated in the same direction as the supply roller 142. As a result, the surface of the developing roller 141 moves in the opposite direction to the surface of the supplying roller 142 at the nip portion where the developing roller 141 and the supplying roller 142 abut. As a result, the liquid developer held on the peripheral surface of the supply roller 142 is delivered to the peripheral surface of the developing roller 141. Since the amount of liquid developer held in the groove of the supply roller 142 (thickness of the thin layer of liquid developer) is regulated to a predetermined value, the amount of liquid developer carried on the surface of the developing roller 141 (liquid The thickness of the developer thin layer) is also kept at a predetermined value.

  The developing roller charging device 147 applies a bias potential having the same polarity as the charged polarity of the colored particles (in this embodiment, a positive bias potential) to the developing roller 141 from the outer surface side (developing corona charge), thereby developing roller 141. The colored particles in the thin layer of the liquid developer carried on the surface of the developing roller 141 are moved to the surface side of the developing roller 141. As a result, the colored particles in the thin layer of the liquid developer are gathered and compressed on the developing roller 141 side by an electric field action (compaction treatment), and a layer of colored particles having a high concentration is formed on the developing roller 141 side. Thereafter, the thin layer of the liquid developer is supplied to the photosensitive drum 10, and the electrostatic latent image on the photosensitive drum 10 is developed. Thereby, a fine image with improved development efficiency is formed. The developing roller charging device 147 is downstream of the contact portion between the developing roller 141 and the supply roller 142 in the rotation direction of the developing roller 141 and is more than the contact portion between the developing roller 141 and the photosensitive drum 10. It is provided on the upstream side in the rotation direction of the developing roller 141 so as to face the peripheral surface of the developing roller 141. That is, the developing roller charging device 147 generates an electric field by developing corona charge. As a result, the thin layer of the liquid developer on the developing roller 141 is divided into two layers: a colored particle layer on the surface of the developing roller 141 and a carrier liquid layer on the colored particle layer. In the developing area (the area where the developing roller 141 and the photosensitive drum 10 are in contact with each other and the peripheral area thereof), the surface of the photosensitive drum 10 is formed in such a state that the thin layer of the liquid developer on the developing roller 141 is formed into two layers. To touch. At this time, the colored particles collected and compressed on the developing roller 141 side move from the surface of the developing roller 141 to the surface of the photosensitive drum 10 according to the principle of electrophoresis, and the electrostatic latent image on the surface of the photosensitive drum 10 is visualized as an image. Turn into. By the developing corona charge by the developing roller charging device 147, the colored particles in the thin layer of the liquid developer on the developing roller 141 are compressed on the surface of the developing roller 141 before the development (compaction processing), so that the photoconductor In the non-image area on the drum 10, since the colored particles do not contact, fogging can be suppressed. In addition, electric charge is injected into the colored particles in the thin layer of the liquid developer on the developing roller 141 by forming an electric field by developing corona charge, so that the colored particles are transferred onto the electrostatic latent image on the photosensitive drum 10 by the developing electric field. The colored particles adhere electrostatically and firmly to the surface of the photosensitive drum 10.

  The developing roller 141 is in contact with the photosensitive drum 10, and an image based on the image data is generated based on the potential difference between the electrostatic latent image potential on the surface of the photosensitive drum 10 and the developing electric field applied to the developing roller 141. Formed on the surface.

  The developing cleaning blade 145 is disposed so as to contact the downstream side in the rotation direction of the contact portion of the developing roller 141 with the photosensitive drum 10, and the liquid development on the surface of the developing roller 141 that has completed the developing operation on the photosensitive drum 10 is performed. Remove the agent.

  The developer recovery device 146 recovers the liquid developer removed by the development cleaning blade 145 and sends the liquid developer to the pipe 81 of the liquid developer circulation device. The liquid developer flows down along the surface of the development cleaning blade 145. Since the viscosity of the liquid developer is high, the developer recovery device 146 is provided with a feed roller for assisting in feeding the liquid developer.

  The primary transfer roller 20 is disposed on the back surface of the intermediate transfer belt 21 so as to face the photosensitive drum 10. A voltage having a polarity opposite to that of the colored particles in the image (minus in the present embodiment) is applied to the primary transfer roller 20 from a power source (not shown). The primary transfer roller 20 applies a voltage having a polarity opposite to that of the colored particles to the intermediate transfer belt 21 at a position in contact with the intermediate transfer belt 21. Since the intermediate transfer belt 21 has conductivity, the applied voltage attracts colored particles to the surface side of the intermediate transfer belt 21 and its periphery. That is, the developed image on the surface of the photosensitive drum 10 is transferred to the intermediate transfer belt 21. The intermediate transfer belt 21 functions as an image carrier that carries an image and conveys it to a sheet.

  The cleaning device 26 is a device for cleaning the liquid developer remaining without being transferred from the photosensitive drum 10 to the intermediate transfer belt 21. The cleaning device 26 includes a residual developer conveying screw 261 and a cleaning blade 262. The residual developer transport screw 261 disposed in the cleaning device 26 is scraped off by the cleaning blade 262 and transports the residual developer stored in the cleaning device 26 to the outside of the cleaning device 26.

  The plate-like cleaning blade 262 extends in the direction of the rotation axis of the photosensitive drum 10 so as to scrape off the liquid developer remaining on the surface of the photosensitive drum 10. One end of the cleaning blade 262 is in sliding contact with the surface of the photosensitive drum 10 and scrapes off the liquid developer remaining on the photosensitive drum 10 as the photosensitive drum 10 rotates.

  The static eliminator 13 has a light source for static elimination, and removes the liquid developer by the cleaning blade 262 and removes the surface of the photosensitive drum 10 with light from the light source in preparation for the next round of image formation.

  The substantially cylindrical carrier liquid removal roller 30 can rotate in the same direction as the photosensitive drum 10 around a rotational axis parallel to the rotational axis of the photosensitive drum 10. The carrier liquid removing roller 30 is disposed on the side where the secondary transfer unit 4 is disposed with respect to the position where the photosensitive drum 10 and the intermediate transfer belt 21 are in contact with each other, and the carrier liquid is removed from the surface of the intermediate transfer belt 21. Remove.

  The sheet storage unit 3 shown in FIG. 1 stores a sheet on which an image is fixed and formed. The sheet storage unit 3 is disposed below the wet image forming apparatus 1A. The sheet storage unit 3 includes a paper feed cassette (not shown) formed so as to be capable of storing sheets.

  The secondary transfer unit 4 transfers the image formed on the intermediate transfer belt 21 to a sheet. The secondary transfer unit 4 includes a support roller 41 that supports the intermediate transfer belt 21, and a secondary transfer roller 42 that is disposed to face the support roller 41. In the present embodiment, the secondary transfer unit 4 and the primary transfer roller 20 constitute a transfer device. The operation of the secondary transfer unit 4 and the operation of the primary transfer roller 20 constitute a transfer process.

  As described above, the conveyance rollers 8 and 8 are provided above the secondary transfer unit 4 in place of the fixing unit 5.

  An image is transferred to a discharge unit 6 provided on the upper surface of the wet image forming apparatus 1A, and a sheet on which image fixing is completed is discharged. The sheet conveyance unit 7 includes a plurality of conveyance roller pairs, and conveys the sheet from the sheet storage unit 3 through the secondary transfer unit 4 to the discharge unit 6. The operation of the sheet conveying unit 7 to discharge the sheet on which the image is transferred to the discharge unit 6 constitutes a discharge process.

<Wet image forming method>
By forming an image on a sheet using the wet image forming apparatus 1A, the wet image forming method according to the present embodiment is achieved. That is, the wet image forming method according to the present embodiment includes a charging step for charging the surface of the photosensitive drum 10, an exposure step for forming an electrostatic latent image on the charged surface of the photosensitive drum 10, and electrical insulation. And developing the electrostatic latent image on the surface of the photosensitive drum 10 using a liquid developer containing polyvinyl butyral, the colored particles being a pigment. A transfer process for transferring the developed image to the sheet, and a discharge process for discharging the sheet on which the image has been transferred to the discharge unit 6. In the wet image forming method according to the present embodiment, by using the liquid developer described below, the sheet transferred to the sheet using heat or light energy is fixed without passing through a fixing step. The image transferred onto the sheet can be fixed on the sheet.

<Liquid developer>
The liquid developer according to the exemplary embodiment includes, as a basic configuration, an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid. The colored particles are pigments, and the liquid developer contains polyvinyl butyral. In that case, the carrier liquid is preferably at least one selected from the group consisting of triethylene glycol bis (2-ethylhexanate), castor oil, and epoxidized soybean oil. Moreover, it is preferable that content of polyvinyl butyral is 1-10 mass%.

[Carrier liquid]
In general, an electrically insulating carrier liquid serves as a liquid carrier, and is used for the purpose of enhancing the electrical insulating properties of the obtained liquid developer. As the electrically insulating carrier liquid, an organic solvent having an electrically insulating property and having a volume resistance of 10 ¹⁰ Ω · cm or more at 25 ° C. (in other words, an electric conductivity of 100 pS / cm or less) is used. preferable. Examples of such an electrically insulating organic solvent include aliphatic hydrocarbons that are liquid at room temperature, such as liquid n-paraffinic hydrocarbons, iso-paraffinic hydrocarbons, or mixtures thereof, and halogenated aliphatic hydrocarbons. Etc. are preferred. Specific examples include n-hexane, n-heptane, n-octane, nonane, decane, dodecane, cyclohexane, perchloroethylene, and trichloroethane. Moreover, the aliphatic hydrocarbon which has a branched chain is especially preferable. Commercially available aliphatic hydrocarbons having a branched chain may be used. For example, “Isopar G”, “Isopar H”, “Isopar K”, “Isopar L”, “Isopar M” manufactured by ExxonMobil Co., Ltd. “Isopar V” and the like are suitable. In addition, liquid paraffin “MORESCO WHITE P-40”, “MORESCO WHITE P-70”, “MORESCO WHITE P-200” manufactured by Matsumura Oil Research Co., Ltd. can be preferably used. Further, liquid paraffin “Cosmo White P-60”, “Cosmo White P-70”, “Cosmo White P-120” manufactured by Cosmo Oil Co., Ltd. can be preferably used.

  As the carrier liquid that can be used in the present embodiment, in addition to the above physical properties, those capable of dissolving polyvinyl butyral (those having relatively high solubility of polyvinyl butyral) are preferable. Furthermore, from the viewpoint of VOC, those having relatively low volatility are more preferable. Examples of such include alcohols having a boiling point of 200 ° C. or higher, vegetable oils, fatty acid esters, and the like. In particular, triethylene glycol bis (2-ethylhexanate), castor oil (fatty acid composition is unsaturated fatty acid (87% ricinoleic acid, 7% oleic acid, 3% linoleic acid) and saturated fatty acid (3% palmitic acid) Acid, stearic acid, etc.)), and epoxidized soybean oil (the fatty acid composition of soybean oil is about 50% linoleic acid, 20% or more oleic acid, about 10% palmitic acid). These may be used alone or in combination depending on the situation.

  In this embodiment, as long as the polyvinyl butyral is dissolved in the carrier liquid, only the polyvinyl butyral having a relatively high solubility may be used as the carrier liquid, or the polyvinyl butyral having a relatively low solubility is mixed. May be used.

[Colored particles]
In the present embodiment, the colored particles are not the toner in which the pigment is dispersed in the binder resin, but the pigment itself. As such a pigment, for example, a conventionally known organic pigment or inorganic pigment can be used without any particular limitation.

  Examples of black pigments include azine dyes such as carbon black, oil furnace black, channel black, lamp black, acetylene black, and aniline black, metal salt azo dyes, metal oxides, and composite metal oxides. Examples of yellow pigments include cadmium yellow, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake, etc. It is done. Examples of the orange pigment include molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, indanthrene brilliant orange RK, benzidine orange G, indanthrene brilliant orange GK and the like. Examples of red pigments include Bengala, Cadmium Red, Permanent Red 4R, Resol Red, Pyrazolone Red, Watching Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B, and the like. . Examples of purple pigments include Fast Violet B and Methyl Violet Lake. Examples of blue pigments include C.I. I. Pigment Blue 15: 3, cobalt blue, alkali blue, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partial chlorinated product, first sky blue, indanthrene blue BC, and the like. Examples of the green pigment include chrome green, chromium oxide, pigment green B, and malachite green lake.

  The content of the pigment in the liquid developer is preferably 1 to 30% by mass. More preferably, it is 3 mass% or more, More preferably, it is 5 mass% or more. Moreover, More preferably, it is 20 mass% or less, More preferably, it is 10 mass% or less.

The average particle diameter of the pigment in the liquid developer, that is, the volume-based median diameter (D ₅₀ ) is preferably 0.1 to 3.0 μm. More preferably, it is 0.2 μm or more, and further preferably 0.4 μm or more. Further, it is more preferably 2.0 μm or less, and further preferably 1.0 μm or less. If the average particle diameter of the pigment is less than 0.1 μm, the developability is insufficient, the image density is lowered, and the fog may increase. When the average particle diameter of the pigment exceeds 3.0 μm, the fixability may be lowered. Here, the volume-based median diameter (D ₅₀ ) is generally 50% when the cumulative curve is obtained with the total volume of a group of particles whose particle size distribution is required as 100%. The particle diameter of a point.

[Dispersion stabilizer]
The liquid developer according to this embodiment may contain a dispersion stabilizer for promoting and stabilizing the dispersion of particles in the liquid developer. As the dispersion stabilizer that can be used in the present embodiment, for example, “BYK-116” manufactured by Big Chemie is suitable. In addition, “Solsperse 9000”, “Solsperse 11200”, “Solsparse 13940”, “Solspers 16000”, “Solspers 17000”, “Solspers 18000” manufactured by Lubrizol, and “Antaron (registered trademark) V-” manufactured by ISP 216 "," Antaron (registered trademark) V-220 "and the like can be preferably used.

  The content of the dispersion stabilizer in the liquid developer is about 1 to 10% by mass, preferably about 2 to 6% by mass.

[Polyvinyl butyral]
The liquid developer according to this embodiment contains polyvinyl butyral. Polyvinyl butyral (butyral resin: alkyl acetalized polyvinyl alcohol) has a hydroxyl group, a hydrophilic vinyl alcohol unit, a butyral group, a hydrophobic vinyl acetal unit, and an acetyl group, as shown in Formula 1. And is a copolymer of vinyl acetate units having intermediate properties between vinyl alcohol units and vinyl acetal units. In the liquid developer according to the exemplary embodiment, polyvinyl butyral having a degree of butyralization (determining a ratio between a hydrophilic part and a hydrophobic part) having a film forming ability (film forming property) of 60 to 85 mol% is excellent. Is preferable. Polyvinyl butyral has a vinyl acetal unit that is soluble in a nonpolar solvent and a vinyl alcohol unit that improves binding properties to a recording medium such as paper. And high affinity.

  An example of a specific method of blending polyvinyl butyral with the liquid developer will be described. In this embodiment, it is preferable to use a kind of carrier liquid capable of dissolving polyvinyl butyral as the carrier liquid. Examples of such a carrier liquid include alcohols having a boiling point of 200 ° C. or higher, vegetable oils, fatty acid esters and the like as described above. In particular, triethylene glycol bis (2-ethylhexanate), castor oil, and epoxidized soybean oil are preferable. As long as the polyvinyl butyral is dissolved in the carrier liquid, only the polyvinyl butyral having a relatively high solubility may be used as the carrier liquid, or a mixture of the polyvinyl butyral having a relatively low solubility may be used. May be.

  In the liquid developer according to this embodiment, the polyvinyl butyral exists in a state dissolved in the carrier liquid. As a result, the fixing mechanism of the image on the sheet is as follows. That is, the polyvinyl butyral in the liquid developer stored in the developing container 140 of the liquid developing device 14 exists in a state dissolved in the carrier liquid. This state is the same on the developing roller 141, the photosensitive drum 10, and the intermediate transfer belt 21. However, although the ratio of the carrier liquid in the liquid developer gradually decreases, the polyvinyl butyral in the liquid developer remains dissolved in the carrier liquid. When the image is transferred from the intermediate transfer belt 21 to the sheet by the secondary transfer unit 4, the carrier liquid is absorbed into the sheet. Along with this, the polyvinyl butyral concentration in the carrier liquid increases on the surface of the sheet, and exceeds the saturation dissolution amount. The polyvinyl butyral exceeding the saturated dissolution amount stays on the surface of the sheet to form a film while coating the pigment remaining on the surface of the sheet. This polyvinyl butyral film fixes the pigment to the sheet, and the image transferred to the pigment, that is, the sheet, can be fixed to the sheet without consuming heat energy or light energy. Energy saving is achieved. This is a very advantageous action in terms of environmental protection. Further, the wet image forming apparatus 1A according to the present embodiment does not require the fixing unit 5 using heat or light energy that has been conventionally used, and simplification and cost reduction of the wet image forming apparatus 1A are achieved.

  The state in which polyvinyl butyral is dissolved in the carrier liquid includes a gel state. Depending on the type and molecular weight of the polyvinyl butyral, the polyvinyl butyral may be entangled with each other in the carrier liquid, resulting in a gel state having a relatively low fluidity. For example, when the polyvinyl butyral concentration is high, when the affinity between polyvinyl butyral and the solvent is low, or when the temperature is low, the gel is often in a gel state. On the other hand, when the polyvinyl butyral is less entangled in the carrier liquid and the fluidity is relatively high, the solution is in a solution state.

  It does not specifically limit as polyvinyl butyral which can be used by this embodiment. For example, “Mowital (registered trademark)” B20H, B30B, B30H, B60T, B60H, B60HH, B70H manufactured by Hoechst Co., Ltd .; “ESREC (registered trademark)” BL-1 (butyralization degree: 63 ±) manufactured by Sekisui Chemical Co., Ltd. 3 mol%), BL-2 (same: 63 ± 3 mol%), BL-S (same: 70 mol% or more), BL-L, BH-3 (same: 65 ± 3 mol%), BM-1 (same: 65 ± 3 mol%), BM-2 (same: 68 ± 3 mol%), BM-5 (same: 63 ± 3 mol%), BM-S; “Denkabutyral” # 2000-L, # 3000 manufactured by Denki Kagaku Kogyo Co., Ltd. -1, # 3000-2, # 3000-3, # 3000-4, # 3000-K, # 4000-1, # 5000-A, # 6000-C, and the like. These may be used alone or in combination of two or more.

  The content of polyvinyl butyral in the liquid developer is preferably 1 to 10% by mass. More preferably, it is 3 mass% or more, More preferably, it is 5 mass% or more. Moreover, More preferably, it is 8 mass% or less, More preferably, it is 6 mass% or less. When the content of polyvinyl butyral is less than 1% by mass, the amount of the polyvinyl butyral film remaining on the surface of the sheet becomes too small, and there is a possibility that the film-forming property and thus the fixing property is excessively insufficient. When the content of polyvinyl butyral exceeds 10% by mass, the amount of the polyvinyl butyral film remaining on the surface of the sheet is excessively increased, the drying property of the film is excessively decreased, and the adhesiveness (tackiness) of the film is excessively increased. There is a possibility that the scratch resistance of the image is excessively lowered.

[Production method]
The liquid developer according to the exemplary embodiment uses a carrier liquid, a pigment, polyvinyl butyral, and a dispersion stabilizer depending on the situation, for example, using a ball mill, a sand grinder, a dyno mill, a rocking mill, or the like (using zirconia beads or the like). It may be a media dispersion type machine), and can be produced by sufficiently dissolving or mixing / dispersing over several minutes to several tens of hours depending on the situation.

The pigment is finely pulverized by the mixing and dispersion. As described above, the mixing / dispersing time, the rotational speed, and the like are adjusted so that the average particle diameter (D ₅₀ ) of the pigment in the liquid developer is 0.1 to 3.0 μm. If the dispersion time is excessively short or the rotational speed is excessively small, the average particle diameter (D ₅₀ ) of the pigment exceeds 3.0 μm, and as described above, the fixability may be lowered. If the dispersion time is excessively long or the rotational speed is excessively large, the average particle diameter (D ₅₀ ) of the pigment becomes less than 0.1 μm, and as described above, the developability is insufficient and the image density is lowered. There may be more fogging.

In order to calculate the average particle size (D ₅₀ ) of the pigment, it is necessary to measure the particle size distribution of the pigment. The particle size distribution of the pigment can be measured, for example, as follows. A predetermined amount of the manufactured liquid developer is sampled and diluted 100 times (volume) with the same carrier liquid used for the liquid developer, and a laser diffraction particle size distribution measuring apparatus manufactured by MALVERN Using “Mastersizer 2000”, measurement is performed by a flow method.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

(Manufacture of liquid developer A)
After dissolving 1 part by weight of polyvinyl butyral (Sessui Chemical Co., Ltd. “S-LEC (registered trademark) BL-S”) in 94 parts by weight of castor oil (refined castor oil “LAV” manufactured by Ito Oil Co., Ltd.) as a carrier liquid A cyan liquid developer A was prepared by mixing and dispersing 5 parts by mass of cyan pigment (CI Pigment Blue 15: 3) as colored particles. The average particle diameter (D ₅₀ ) of the pigment in the liquid developer A was 0.5 μm.

(Manufacture of liquid developers B to E)
According to the liquid developer A, cyan liquid developers B to E having the compositions shown in Table 1 were produced. However, the liquid developer E did not contain polyvinyl butyral.

(Image formation)
Using the wet image forming apparatus (color printer) 1A (experimental apparatus for wet image forming apparatus manufactured by Kyocera Mita) shown in FIG. Agents A to E were charged, and a solid solid square image corresponding to 0.026 mg / cm ^{2 in} terms of pigment loading on high-quality plain paper (C2 paper manufactured by Oji Paper Co., Ltd .: 90 g / m ² ) as a sheet. (5 cm × 5 cm) was formed. In that case, the thickness of the liquid developer layer on the peripheral surface of the developing roller 141 was set to 5 μm. The developing electric field applied to the developing roller 141 when forming an image based on the image data on the surface of the photosensitive drum 10 was set to 400V. And the sheet | seat discharged | emitted by the discharge part 6 was used for the following fixability test.

(Fixability test)
A solid image was transferred to the sheet by the secondary transfer unit 4, and a scratch resistance test was performed to evaluate the fixability of the image portion of the sheet discharged to the discharge unit 6. That is, 5 seconds after the image was formed by the secondary transfer unit 4, a metal cylindrical weight having a mass of 300 g (diameter: 50 mm, cloth on the bottom surface) was applied on the image portion. The weight was reciprocated 10 times so as to move across the image to the outside of the image. In order to see whether or not the image is rubbed and worn by the mass of the weight, the density of the portion outside the solid image where the weight has moved is measured using a spectral densitometer ("X-rite" manufactured by Gretag Macbeth). Spectroeye ")). Fixing evaluation criteria are “◯” when the density is less than 0.01, “Δ” when the density is 0.01 or more and less than 0.3, and “X” when the density is 0.3 or more. It was. This test also serves as a test for the drying property of the polyvinyl butyral coating.

  The results are shown in Table 1.

(Consideration of results)
As is clear from Table 1, in the liquid developer in which the pigment is dispersed in the carrier liquid, the liquid developers A to D containing polyvinyl butyral are more fixable than the liquid developer E not containing polyvinyl butyral. It was excellent.

  Among the liquid developers A to D, the liquid developers A and B having a polyvinyl butyral content of 1 to 10% by mass were particularly excellent in fixability.

  The liquid developer produced with the same composition as the liquid developer A except that octyl alcohol (“Kalcoal 0880” manufactured by Kao Co., Ltd.) was used instead of castor oil as the carrier liquid. Spots (fogging) occurred in the non-image forming area, and an evaluable image could not be formed. From this, it was found that octyl alcohol is not preferable as a carrier liquid for dissolving polyvinyl butyral.

  As described above in detail with reference to specific examples, in the embodiments and examples, the liquid developer has an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid, and the colored particles are pigments. Since the liquid developer contains polyvinyl butyral, the polyvinyl butyral remains on the surface of the sheet to form a film while coating the pigment remaining on the surface of the sheet. By this, the pigment is fixed on the sheet. Accordingly, the pigment, that is, the image can be fixed on the sheet without consuming heat energy or light energy, and energy consumption in the wet image forming apparatus can be reduced. In addition, the fixing unit itself using heat and light energy that has been conventionally used can be reduced, and the wet image forming apparatus can be simplified and the cost can be reduced.

  When at least one selected from the group consisting of triethylene glycol bis (2-ethylhexanate), castor oil, and epoxidized soybean oil is used as the carrier liquid, polyvinyl butyral can be dissolved well and fixability A liquid developer having excellent resistance can be obtained with certainty.

  When the content of polyvinyl butyral in the liquid developer is 1 to 10% by mass, good drying properties of the film and image scratch resistance are ensured while maintaining excellent fixing properties.

  A liquid developing apparatus using the liquid developer is a preferable liquid developing apparatus from the viewpoint of energy saving.

  The wet image forming apparatus using the liquid developer is a preferable wet image forming apparatus from the viewpoint of energy saving and does not consume heat or light energy for fixing an image on a sheet.

  In the wet image forming method using the liquid developer, the image transferred to the sheet is fixed to the sheet without going through a fixing step of fixing the image transferred to the sheet to the sheet using heat or light energy. This is a preferred wet image forming method from the viewpoint of energy saving.

  INDUSTRIAL APPLICABILITY The present invention can be used in a wide range of industries in the technical field of a wet developing method which is one of electrophotographic systems that can be employed in color printers, printers, copiers, facsimile machines, and multifunction machines having these functions. Have sex.

1A Wet image forming device (color printer)
2 Image forming unit 4 Secondary transfer unit (transfer device)
DESCRIPTION OF SYMBOLS 10 Photosensitive drum 11 Charging apparatus 12 Exposure apparatus 14 Liquid developing apparatus 20 Primary transfer roller (transfer apparatus)
21 Intermediate transfer belt 141 Developing roller 142 Supply roller (Anilox roller)
147 Developing roller charging device

Claims (5)

A liquid developer having an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid,
Colored particles are pigments,
A liquid developer containing polyvinyl butyral.   2. The liquid developer according to claim 1, wherein the carrier liquid is at least one selected from the group consisting of triethylene glycol bis (2-ethylhexanate), castor oil, and epoxidized soybean oil.   The liquid developer according to claim 1 or 2, wherein the content of polyvinyl butyral is 1 to 10% by mass. A liquid developing apparatus for developing an electrostatic latent image on the surface of a photosensitive drum using a liquid developer,
A liquid developer characterized by using an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid as the liquid developer, wherein the colored particles are pigments and a liquid developer containing polyvinyl butyral is used. apparatus. A charging device for charging the surface of the photosensitive drum, an exposure device for forming an electrostatic latent image on the surface of the charged photosensitive drum, and developing the electrostatic latent image on the surface of the photosensitive drum using a liquid developer. A wet image forming apparatus comprising a liquid developing device and a transfer device for transferring a developed image to a recording medium,
As a liquid developer, a wet image having an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid, wherein the colored particles are pigments and a liquid developer containing polyvinyl butyral is used. Forming equipment.