JP5509000B2 - Liquid developer, developing device, and image forming apparatus - Google Patents

Description

  The present invention relates to a liquid developer, a developing device using the liquid developer, and an image forming apparatus including the developing device.

  Examples of the electrophotographic image forming apparatus such as a printer, a copying machine, a facsimile machine, and a multifunction machine having these functions include those equipped with developing devices of various developing systems. Specifically, for example, it is roughly classified into a dry development system and a wet development system depending on the form of the developer to be used. Among them, in a wet development type developing device, a liquid developer in which colored particles such as toner particles, a dispersion stabilizer, and the like are dispersed in an electrically insulating carrier liquid is used. In the developing device of the wet development system, the colored particles charged in the liquid developer move from the surface of the developing roller to the surface of the photosensitive drum by the principle of electrophoresis, thereby forming on the surface of the photosensitive drum. The electrostatic latent image is visualized as a colored particle image.

  In addition, in an image forming apparatus using an electrophotographic system, it is conceivable to form a high-quality image with high resolution and excellent gradation when a developer containing colored particles having a relatively small particle size is used. In the case of the dry developer, the colored particles tend to be scattered from the developing device into the atmosphere. In contrast, in the liquid developer, since the colored particles are dispersed in the carrier liquid, it is considered that scattering of the colored particles into the atmosphere can be sufficiently suppressed. As a result, the dry developer is used even if it is a colored particle having a relatively small average particle diameter such that the scattering of the colored particles cannot be sufficiently suppressed, for example, fine colored particles having an average particle diameter of submicron. be able to. Therefore, an image forming apparatus provided with a developing device of a wet development system can use a liquid developer containing such colored particles having a relatively small average particle diameter, so that the image quality is high and the gradation is excellent. A good image can be expected.

  Examples of such a liquid developer include those described in Patent Documents 1 to 3.

  In Patent Document 1, in an electrophotographic liquid developer in which a toner mainly composed of a colorant and a resin is dispersed in an insulating carrier liquid (carrier liquid), the resin is a resin soluble in the carrier liquid. Titanate coupling comprising a combination of resin particles insoluble in the carrier liquid, the colorant comprising at least one of a pigment and a dye coated with a resin insoluble in the carrier liquid, and a charge adjusting agent An electrophotographic liquid developer containing an agent is described.

  According to Patent Document 1, it is disclosed that the charge of the colorant can be held extremely stably even in the presence of the insulating carrier liquid, and an extremely good image can be obtained.

  Patent Document 2 discloses a liquid developer for developing an electrostatic charge image formed on a photoreceptor, which is dispersed in a carrier liquid and a high insulating low dielectric constant carrier liquid. At least one coating material selected from the group consisting of alkylcellulose or a derivative thereof and rosin or a derivative thereof. A liquid developer for developing electrostatic images that is covalently bonded to the binder resin is described.

  According to Patent Document 2, it is disclosed that it is possible to provide a liquid developer that can continuously form a print image having high image density, low fog, and excellent print characteristics.

  Patent Document 3 includes toner particles mainly composed of a resin material and an insulating liquid, and the insulating liquid includes a fatty acid triglyceride and a fatty acid monoester, and the fatty acid triglyceride and the fatty acid monoester. The ester contains an unsaturated fatty acid as a fatty acid component, and the liquid developer in which the alcohol component constituting the fatty acid monoester has an alkyl group having 1 to 8 carbon atoms is described.

  According to Patent Document 3, it is disclosed that the fixability of toner particles to a recording medium can be improved.

JP-A-6-138712 Japanese Patent Laid-Open No. 10-260558 JP 2008-158484 A

  Further, in an image forming apparatus provided with a developing device of a wet development method, examples of a method for fixing a colored particle image on a recording medium include a heat fixing method and a light fixing method. The thermal fixing method is a method in which, when colored particles are toner particles containing a pigment and a binder resin, the toner particles are fixed to a recording medium by melting the binder resin with heat. In the photofixing method, a photocurable resin and a photopolymerization initiator are blended in a liquid developer, a colored particle image is transferred to a recording medium, and then irradiated with light. Is photopolymerized, and the colored particles are fixed to the recording medium with the formed cured film.

  In the case of using a conventional liquid developer, generally, a fixing method using the heat fixing method and the light fixing method as described above has been adopted. Specifically, for example, when the liquid developers described in Patent Documents 1 to 3 are used, the image is fixed on the recording medium by fixing by a heat fixing method, that is, heat fixing.

  In such a case, in order to fix the colored particles to the recording medium, energy such as heat energy and light energy is required. From the viewpoint of energy saving, etc., development of a liquid developer that can be fixed without using the energy has been desired.

  An object of the present invention is to provide a liquid developer capable of sufficiently fixing a colored particle image on a recording medium without consuming energy such as heat energy at the time of fixing. Another object of the present invention is to provide a developing device using the liquid developer and an image forming apparatus including the developing device.

  The present inventor has examined the components of the liquid developer, particularly the components of the colored particles, and when the resin contained in the colored particles is swollen in the liquid developer, It has been found that even when a colored particle image is fixed on a recording medium without using energy such as energy, the fixability tends to increase.

  According to the study of the present inventors, in the image formation using the liquid developer described in Patent Documents 1 to 3, an attempt was made to fix the colored particle image on the recording medium without using energy such as thermal energy. In this case, it was found that the fixability was insufficient. This was thought to be due to the fact that the resin contained in the colored particles was not sufficiently swollen in the liquid developer.

  Therefore, the present inventor can sufficiently fix the colored particle image on the recording medium without using energy such as thermal energy by paying attention to the swelling of the resin contained in the colored particles, as follows. The liquid developer according to the present invention.

  The liquid developer according to one embodiment of the present invention includes an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid, and the colored particles include a resin, a pigment, and a carbon number of 2 to 6. And a diol compound.

  According to such a configuration, it is possible to provide a liquid developer capable of sufficiently fixing the colored particles to the recording medium without consuming energy such as heat energy.

  This is considered to be due to the following.

  First, it is considered that the resin contained in the colored particles is swollen by the carrier liquid when the colored particles contain the diol compound together with the resin.

  The colored particle image formed on the image carrier is considered to be composed of colored particles in which the resin is swollen by the carrier liquid. When the colored particle image is transferred to the recording medium, the carrier liquid is absorbed into the recording medium and solidifies. At that time, it is considered that the colored particles are bonded to each other and exhibit excellent fixability.

  Therefore, it is considered that the fixing property of the colored particle image to the recording medium is sufficiently improved without consuming energy such as heat energy at the time of fixing.

  In the liquid developer, the diol compound is preferably at least one selected from the group consisting of ethylene glycol, propion glycol, and diethylene glycol.

  According to such a configuration, the fixing property of the colored particle image to the recording medium is improved without consuming energy such as heat energy at the time of fixing, and an image having a high image density can be obtained.

  In the liquid developer, the resin is preferably a water-soluble resin.

  According to such a configuration, it is possible to further improve the fixability of the colored particle image to the recording medium without consuming energy such as heat energy at the time of fixing.

Moreover, in the liquid developer, it is preferable that the conductivity of the colored particles is 1 × 10 ⁻⁸ to 1 × 10 ⁻¹ S / cm.

  According to such a configuration, the fixing property of the colored particle image to the recording medium is improved without consuming energy such as heat energy at the time of fixing, and an image having a high image density can be obtained.

  This is considered to be due to the following.

First, it is considered that the conductivity of the colored particles largely depends on the content of the colored particles, particularly the diol compound. That is, in the liquid developer, it is considered that the content of the diol compound is preferably such that the conductivity of the colored particles is 1 × 10 ⁻⁸ to 1 × 10 ⁻¹ S / cm. It is done.

  From this, when the electrical conductivity of the colored particles is within the above range, the content of the diol compound sufficiently exhibits the effect of swelling the resin contained in the colored particles by containing the diol compound. However, it is thought that it becomes content which can suppress generation | occurrence | production of the malfunction by containing the said diol compound too much. Specifically, it is considered that, by increasing the fixability and containing the diol compound too much, it is possible to suppress the developability and the image density from being lowered.

  Therefore, it is considered that the fixability of the colored particle image to the recording medium is improved and an image having a high image density can be obtained.

  In the liquid developer, the carrier liquid is preferably an aliphatic hydrocarbon.

  According to such a configuration, it is possible to further improve the fixability of the colored particle image to the recording medium without consuming energy such as heat energy at the time of fixing.

  A developing device according to another aspect of the present invention is a developing device that develops an electrostatic latent image formed on the surface of an image carrier, and carries the liquid developer on the surface of the image bearing member. A developer carrier for supplying the liquid developer to the carrier, and forming a colored particle image on the image carrier by visualizing the electrostatic latent image with the colored particles in the liquid developer; And a developer supply unit for supplying the liquid developer to the developer carrying member, wherein the liquid developer is used as the liquid developer.

  According to such a configuration, it is possible to form a colored particle image on the image carrier that is sufficiently fixed to the recording medium without consuming energy such as heat energy at the time of fixing. Therefore, this developing device transfers and fixes the colored particle image formed on the image carrier to the recording medium, thereby forming an image having excellent fixability without consuming heat energy or the like during fixing. can do.

  An image forming apparatus according to another aspect of the present invention includes an image carrier on which an electrostatic latent image is formed on a surface, and a developing device that develops the electrostatic latent image, and the developing device includes: It is the developing device.

  According to such a configuration, an image having excellent fixability can be formed without consuming energy such as heat energy at the time of fixing. Accordingly, it is possible to provide an image forming apparatus capable of forming an image with excellent fixability even though the energy consumption of the entire image forming apparatus is small.

  According to the present invention, it is possible to provide a liquid developer that can sufficiently fix a colored particle image to a recording medium without consuming energy such as heat energy during fixing. In addition, a developing device using the liquid developer and an image forming apparatus including the developing device are provided.

1 is a schematic cross-sectional view illustrating an overall configuration of an image forming apparatus to which a liquid developer according to an exemplary embodiment is applied. FIG. 2 is a schematic cross-sectional view showing the periphery of a developing device provided in the image forming apparatus shown in FIG. 1.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

[Liquid developer]
The liquid developer according to the exemplary embodiment includes an electrically insulating carrier liquid and colored particles dispersed in the carrier liquid, and the colored particles include a resin, a pigment, and a diol having 2 to 6 carbon atoms. Containing a compound. By doing so, a liquid developer capable of sufficiently fixing the colored particles to the recording medium without consuming energy such as heat energy can be obtained.

  This is considered to be due to the following.

  First, it is considered that the resin contained in the colored particles is swollen by the carrier liquid when the colored particles contain the diol compound together with the resin. The colored particle image formed on the image carrier is considered to be composed of colored particles in which the resin is swollen by the carrier liquid. When the colored particle image is transferred to the recording medium, the carrier liquid is absorbed into the recording medium and solidifies. At that time, it is considered that the colored particles are bonded to each other and exhibit excellent fixability. Therefore, it is considered that the liquid developer has sufficiently high fixability of the colored particle image to the recording medium without consuming energy such as heat energy at the time of fixing.

(Carrier liquid)
The carrier liquid serves as a liquid carrier and is used for the purpose of enhancing the electrical insulation of the liquid developer obtained. The carrier liquid is not particularly limited as long as it has electrical insulation and can be used as a carrier liquid for a liquid developer. Specifically, for example, an organic solvent having a volume resistivity at 25 ° C. of 10 ¹⁰ Ω · cm or more, that is, an electric conductivity of 100 pS / cm or less, or the like can be given. Although it does not specifically limit as said carrier liquid, For example, liquid aliphatic hydrocarbons, such as a liquid paraffin, are used preferably. Specific examples of the aliphatic hydrocarbon include paraffinic hydrocarbons such as n-paraffinic hydrocarbons and iso-paraffinic hydrocarbons, and halogenated aliphatic hydrocarbons. Specific examples of paraffinic hydrocarbons include n-hexane, n-heptane, n-octane, nonane, decane, dodecane, and cyclohexane. Specific examples of the halogenated aliphatic hydrocarbon include perchloroethylene and trichloroethane. As said carrier liquid, the organic solvent which comprises each illustrated carrier liquid may be used independently, and may be used in combination of 2 or more type. As described above, the carrier liquid preferably contains an aliphatic hydrocarbon that is liquid at room temperature, such as liquid paraffin, and more preferably contains an aliphatic hydrocarbon having a branched chain.

  A commercially available carrier liquid can also be used. Specifically, for example, Isopar G, Isopar H, Isopar K, Isopar L, Isopar M, Isopar V manufactured by ExxonMobil, liquid paraffin “Moresco White P-40” and “Moresco White” manufactured by MORESCO P-70 ”,“ Molesco White P-200 ”, liquid paraffin“ Cosmo White P-60 ”,“ Cosmo White P-70 ”,“ Cosmo White P-120 ”manufactured by Cosmo Oil Co., Ltd. and the like.

[Colored particles]
The colored particles are particles containing a resin, a pigment, and a diol compound having 2 to 6 carbon atoms, without being dissolved in the carrier liquid or being damaged by the carrier liquid. There is no particular limitation as long as it is dispersed in the carrier liquid. Specifically, for example, toner particles in which a pigment is dispersed in a resin containing the diol compound may be used, or particles in which a resin containing the diol compound is coated with a particulate pigment may be used. Good.

Moreover, it is preferable that the electroconductivity of the said colored particle is 1 * 10 < ^-8 > ^-1 * 10 < ^-1 > S / cm. By doing so, the fixing property of the colored particle image to the recording medium is improved without consuming energy such as heat energy at the time of fixing, and an image having a high image density can be obtained.

  This is considered to be due to the following.

First, it is considered that the conductivity of the colored particles largely depends on the content of the colored particles, particularly the diol compound. That is, in the liquid developer, it is considered that the content of the diol compound is preferably such that the conductivity of the colored particles is 1 × 10 ⁻⁸ to 1 × 10 ⁻¹ S / cm. It is done.

  From this, first, when the conductivity of the colored particles is too low, the content of the diol compound is too small, and the effect of swelling the resin contained in the colored particles by containing the diol compound. There is a possibility that it cannot be fully demonstrated. In addition, when the conductivity of the colored particles is too high, the content of the diol compound is too large, and defects due to excessive inclusion of the diol compound, for example, developability is reduced and image density is reduced. There is a possibility that the occurrence of problems such as these cannot be sufficiently suppressed. Therefore, when the electrical conductivity of the colored particles is within the above range, the content of the diol compound sufficiently exhibits the effect of swelling the resin contained in the colored particles by containing the diol compound, It is thought that it becomes content which can suppress generation | occurrence | production of the malfunction by containing the said diol compound too much. Specifically, it is considered that, by increasing the fixability and containing the diol compound too much, it is possible to suppress the developability and the image density from being lowered. From these facts, it is considered that the fixability of the colored particle image to the recording medium is improved and an image having a high image density can be obtained.

Moreover, although it is preferable that the electrical conductivity of the said colored particle is 1 * 10 < ^-8 > ^-1 * 10 < ^-1 > S / cm as above-mentioned, it is more preferable if it is the following ranges. Specifically, for example, it is more preferably 1 × 10 ⁻⁸ to 1 × 10 ⁻² S / cm, and further preferably 1 × 10 ⁻⁶ to 1 × 10 ⁻³ S / cm.

  In addition, the electrical conductivity here is the electrical conductivity of the said colored particle, and is the electrical conductivity of the colored particle as a solid in the state where the said carrier liquid does not exist. Moreover, the electrical conductivity of a colored particle can be measured with the following measuring methods etc., for example.

  First, colored particles are formed into a disk-shaped molded body having a predetermined size using a tablet molding machine. An electrode is stuck so as to sandwich the obtained molded body, and the conductivity between the electrodes is measured using an LCR meter or the like. At that time, the AC bridge method can be used to measure the conductivity between the electrodes. The conductivity of the colored particles is calculated from the measured current, electrode area, and interelectrode distance.

  Further, even when the particle diameter of the colored particles is smaller than the toner particles contained in the dry developer, the scattering of the colored particles into the atmosphere can be sufficiently suppressed. In addition, the smaller the particle size of the colored particles, the higher the image quality and the higher the gradation, the higher the image quality. Therefore, specifically, the particle diameter of the colored particles is, for example, preferably 1 μm or less, more preferably 0.1 to 0.5 μm, in the volume-based median diameter (D50). . If the colored particles are too large, the image quality such as the resolution and gradation of the formed image tends to be lowered, and the advantage of using the liquid developer tends to be impaired. The colored particles are preferably as small as possible, but when they are too small, they tend to aggregate in the liquid developer.

  The volume-based median diameter (D50) is the particle diameter at which the cumulative curve is 50% when the cumulative curve is determined with the total volume of a group of particles whose particle size distribution is determined as 100%. Say. The volume-based median diameter (D50) of the colored particles can be measured using a general particle size distribution measuring device or the like. Examples of the particle size distribution measuring device include a laser diffraction particle size distribution measuring device.

(resin)
The resin can be used without particular limitation, and for example, those conventionally used as a binder resin for toner particles can be used. More specifically, for example, polystyrene resins such as styrene-acrylic resins and styrene-butadiene resins; acrylic resins; olefin resins such as polyethylene resins and polypropylene resins; vinyl chloride resins; polyester resins; Polyamide resins; polyurethane resins; polyvinyl alcohol resins; vinyl ether resins; thermoplastic resins such as N-vinyl resins. Moreover, as said resin, said each resin may be used independently and may be used in combination of 2 or more type.

  As the resin, it is preferable to use the thermoplastic resin as described above from the viewpoint of fixability. However, it is not necessary to use only the thermoplastic resin, and a crosslinking agent or a thermosetting resin is used in combination with the thermoplastic resin. May be. Thus, by introducing a partially crosslinked structure into the binder resin, it is possible to improve the offset resistance while suppressing a decrease in fixing property.

  Specific examples of the thermosetting resin include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins, and cyclic aliphatic type epoxy resins. And cyanate resins such as cyanate resins and cyanate resins. These may be used alone or in combination of two or more.

  Further, the resin is preferably a water-soluble resin, and specific examples of suitable resins include styrene-acrylic resins.

  The acid value, weight average molecular weight, softening point, etc. of the resin differ depending on the type of resin and are not particularly limited. Specifically, the acid value is preferably 50 to 300 mgKOH / g, and more preferably 200 or more. Moreover, it is preferable that a weight average molecular weight is 5000-20000, and it is more preferable that it is 10,000 or more. Moreover, it is preferable that a softening point is 100-200 degreeC, and 150 degreeC or more is more preferable.

(Pigment)
The pigment is not particularly limited as long as it can form an image of a desired color, and a known organic pigment or inorganic pigment can be used. Specifically, the following pigments are mentioned according to the color, for example. Examples of the black pigment include carbon black such as acetylene black, lamp black, and aniline black. Examples of yellow pigments include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, and Benzidine Yellow. GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake, C.I. I. And CI Pigment Yellow 180. Examples of the orange pigment include reddish yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, indanthrene brilliant orange RK, benzidine orange G, indanthrene brilliant orange GK and the like. Red pigments include Bengala, cadmium red, red lead, mercury cadmium sulfide, permanent red 4R, risor red, pyrazolone red, watching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, Brilliant Carmine 3B, C.I. I. Pigment red 238 and the like. Examples of purple pigments include manganese purple, fast violet B, and methyl violet lake. Examples of blue pigments (cyan pigments) include bitumen, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, first sky blue, induslen blue BC, C.I. I. And CI Pigment Blue 15: 3 (copper phthalocyanine blue pigment). Examples of the green pigment include chrome green, chromium oxide, pigment green B, malachite green lake, and final yellow green G. Examples of white pigments include zinc white, titanium oxide, antimony white, zinc sulfide, barite powder, barium carbonate, clay, silica, white carbon, talc, and alumina white.

  The content of the pigment varies depending on the type of pigment, and is not particularly limited as long as a suitable image density can be achieved. Specifically, for example, it is preferably 20 to 180 parts by mass, and more preferably 80 to 120 parts by mass with respect to 100 parts by mass of the resin.

(Diol compound having 2 to 6 carbon atoms)
The diol compound is not particularly limited as long as it is a diol compound having 2 to 6 carbon atoms. Specific examples include compounds having an organic group having 2 to 6 carbon atoms and two hydroxyl groups in the molecule. The organic group is not particularly limited as long as it is a functional group having 2 to 6 carbon atoms. Specifically, an alkyl group etc. are mentioned, for example. Specific examples of the diol compound include, for example, 1,2-ethanediol (ethylene glycol), 1,2-propanediol (propylene glycol), 1,3-propanediol, 1,3-butanediol, and 2 Butanediol such as 1,3-butanediol, pentanediol such as 1,2-pentanediol and 1,5-pentanediol, hexanediol such as 1,2-hexanediol and 1,6-hexanediol, 3-methyl -1,3-butanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2-methyl-2-butene-1,4-diol, 2-ethyl-2- Examples include butene-1,4-diol and diethylene glycol. Among these, ethylene glycol, propylene glycol, and diethylene glycol are preferable from the viewpoint of maintaining excellent fixability and increasing the image density.

As described above, the content of the diol compound is preferably such that the conductivity of the obtained colored particles is 1 × 10 ⁻⁸ to 1 × 10 ⁻¹ S / cm. The content of the diol compound varies depending on the type and composition of the resin, pigment, diol compound, and the like. Specifically, for example, the content is preferably 50 to 200 parts by mass with respect to 100 parts by mass of the resin. More preferably, it is 70-150 mass parts.

(Colored particle additive)
The colored particles only need to contain the resin, the pigment, and the diol compound, but other components may be added as long as the object of the present invention is not impaired.

(Method for producing colored particles)
The method for producing the colored particles is not particularly limited as long as the particles containing the resin, the pigment, and the diol compound can be produced. Specifically, for example, it can be produced as follows.

  First, each component which comprises colored particles, such as the said resin, the said pigment, and the said diol compound, is mixed. In that case, mixing with a solvent such as water is preferred. As the mixer, a known one can be used, and examples thereof include a Henschel type mixing device such as a Henschel mixer, a super mixer, and a mechano mill, an ang mill, a hybridization system, and a cosmo system.

  Next, the obtained mixture is kneaded with a kneader or the like. By doing so, colored particles are obtained. As the kneader, known ones can be used, and examples thereof include a wet disperser such as a media type disperser, an extruder such as a twin screw extruder, a three-roll mill, and a lab blast mill. Moreover, when mixing with solvents, such as water, wet dispersers, such as a media type disperser, are used preferably. In this case, the medium to be used is not particularly limited, and specific examples include zirconia beads having a particle diameter of 0.2 to 1 mm. When mixing and kneading with a solvent such as water, it is necessary to remove the solvent from the dispersion, which is a kneaded product obtained after kneading, by reducing the pressure. By doing so, colored particles are obtained.

  As the wet disperser, a commercially available one can be used. Specific examples include a Glen mill manufactured by Asada Tekko Co., Ltd., an MSC mill manufactured by Nippon Coke Kogyo Co., Ltd., and a dyno mill manufactured by Shinmaru Enterprises Co., Ltd.

  As the above kneading conditions, the particle diameter of the colored particles actually obtained varies depending on the composition and the like, but the particle diameter of the finally obtained colored particles is 1 μm in the volume-based median diameter (D50). The conditions are preferably as follows, and more preferably 0.1 to 0.5 μm. More specifically, there may be mentioned conditions such that the particle diameter of the finally obtained colored particles is about 0.2 μm in volume-based median diameter (D50).

  Moreover, you may grind | pulverize and classify the obtained colored particle as needed. As the pulverizer, known pulverizers can be used. For example, an air pulverizer such as a jet pulverizer (jet mill) that pulverizes using a supersonic jet stream, a mechanical pulverizer such as a turbo mill, or an impact pulverizer. A crusher etc. are mentioned. Further, as the classifier, a known one can be used, and examples thereof include a wind classifier such as a swirling wind classifier (rotary wind classifier) such as an elbow jet classifier, a centrifugal classifier, and the like.

[Additives for liquid developers]
The liquid developer only needs to contain the carrier liquid and the colored particles dispersed in the carrier liquid, but other components may be added as long as the object of the present invention is not impaired. May be. Examples of the additive added to such a liquid developer include a dispersion stabilizer. By adding a dispersion stabilizer to the liquid developer, the dispersibility of the colored particles is improved, and the colored particles are less likely to aggregate.

  The dispersion stabilizer is not particularly limited as long as it is used as a dispersion stabilizer for a liquid developer, and a commercially available one can be used. Specifically, for example, BYK-116 manufactured by Big Chemie, Solsperse 9000, 11200, 13940, 16000, 17000, 18000 manufactured by Lubrizol, Antaron (registered trademark) V-216, V-220 manufactured by ISP, etc. Is mentioned.

[Method for producing liquid developer]
The method for producing the liquid developer is not particularly limited as long as the liquid developer containing the carrier liquid and the colored particles dispersed in the carrier liquid can be produced. Specifically, for example, the liquid developer is produced by mixing the carrier liquid, the colored particles, and, if necessary, additives such as the dispersion stabilizer using a disperser or the like. Can do.

  Further, the disperser is not particularly limited, and specifically, for example, the same disperser as used in the production of colored particles, a ball mill, a sand grinder, and the like can be given. More specifically, for example, a Glen mill manufactured by Asada Tekko Co., Ltd., an MSC mill manufactured by Nippon Coke Industries, Ltd., a dyno mill manufactured by Shinmaru Enterprises Co., Ltd., and the like can be given.

  Further, the mixing time by the disperser is not particularly limited as long as the colored particles are sufficiently dispersed in the carrier liquid. Specifically, the mixing time is, for example, about several hours to about 10 to several hours. preferable.

  Further, the blending ratio of the carrier liquid and the colored particles varies depending on the composition of the carrier liquid and the colored particles. Specifically, for example, the blending amount of the carrier liquid is 100 masses of the colored particles. The amount is preferably 80 to 1000 parts by mass, more preferably 200 to 400 parts by mass with respect to parts. In addition, when the dispersion stabilizer is contained, the blending amount of the dispersion stabilizer is preferably 0.01 to 90 parts by mass, and 1 to 40 parts by mass with respect to 100 parts by mass of the colored particles. It is more preferable.

  The liquid developer according to the exemplary embodiment can be used in, for example, a developing device and an image forming apparatus described later. By doing so, an image having excellent fixability can be formed without consuming energy such as heat energy at the time of fixing.

[Developing device / Image forming device]
The developing device and the image forming apparatus using the liquid developer are not particularly limited as long as they are electrophotographic and can use a liquid developer as the developer. That is, there is no particular limitation as long as it is a so-called liquid developing apparatus and wet image forming apparatus.

  Specifically, the developing device using the liquid developer according to the present embodiment is a developing device that develops an electrostatic latent image formed on the surface of the image carrier, and carries the liquid developer on the surface. However, the developer that supplies the liquid developer to the image carrier and forms a colored particle image on the image carrier, in which the electrostatic latent image is visualized by the colored particles in the liquid developer. Examples of the liquid developer include a carrier and a developer supply unit that supplies the liquid developer to the developer carrier, and the liquid developer includes the liquid developer.

  The image forming apparatus using the liquid developer according to the present embodiment includes an image carrier on which an electrostatic latent image is formed on a surface, and a developing device that develops the electrostatic latent image. However, what is the said developing device is mentioned.

  The liquid developer is capable of forming an image having excellent fixability without consuming energy such as heat energy at the time of fixing. Therefore, as an image forming apparatus using the liquid developer, A fixing device (fixing unit) that performs heat fixing or the like may not be provided, and from the viewpoint of energy saving, a fixing device that does not include a fixing device is preferable.

  Further, a tandem color image forming apparatus using a plurality of color liquid developers as described later is preferable. Specifically, for example, a tandem color image forming apparatus using a plurality of color liquid developers as described later can be given. Here, a tandem color image forming apparatus will be described.

  Hereinafter, a developing device (liquid developing device) and an image forming device (wet image forming device) according to the present embodiment will be described with reference to the drawings. Note that terms used in the following description, such as “up”, “down”, “left”, “right”, and the like, are merely for the purpose of clarifying the explanation and limit the present invention. It is not a thing. The term “sheet” used in the following description means, for example, copy paper, tracing paper, cardboard, an OHP sheet, and other recording media capable of forming an image.

  FIG. 1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus to which a liquid developer according to the present embodiment is applied, and FIG. 2 shows a developing device provided in the image forming apparatus shown in FIG. It is a schematic sectional drawing. Note that the wet image forming apparatus according to the present embodiment is a color printer, but forms an image on a sheet, that is, a recording medium, such as a monochrome printer, a copying machine, a facsimile machine, or a multifunction machine having these functions. Any other wet imaging device that can 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 wet image forming apparatus 1A further stores a liquid developer circulating device for each color of yellow (Y), magenta (M), cyan (C), and black (Bk) at the lower part of the portion shown in FIG. However, the illustration is omitted here.

  The wet image forming apparatus 1 </ b> A includes a tandem image forming unit 2 that forms a colored particle image based on image data, a sheet storage unit 3 that stores a sheet, and a colored particle image formed by the image forming unit 2. A secondary transfer unit 4 that transfers the sheet, a discharge unit 6 that discharges the sheet on which the colored particle image is transferred, and a sheet conveyance unit 7 that conveys the sheet from the sheet storage unit 3 to the discharge unit 6 are provided. ing.

  In general, a wet image forming apparatus usually has a fixing unit 5 for fixing a transferred colored particle image to a sheet between a secondary transfer unit 4 and a discharge unit 6, specifically, for example, a sheet. A fixing unit 5 including a heating roller 51 and a pressure roller 52 arranged to face each other is disposed. However, in the wet image forming apparatus 1A according to the present embodiment, such a fixing unit 5 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, the colored particle image transferred to the sheet can be fixed to the sheet without the need for the fixing unit 5. 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 that is an image carrier, a charging device 11, an LED exposure device 12, a liquid developing device 14, a primary transfer roller 20, and a cleaning device 26. , A static elimination device 13 and a carrier liquid removal roller 30 are provided. 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 other image forming units. Is the same.

  The photosensitive drum 10 has a cylindrical shape, and is an image carrier capable of carrying a colored particle image charged (charged to a positive polarity in the present embodiment) on the surface (circumferential surface) thereof. The illustrated photosensitive drum 10 can rotate counterclockwise.

  The charging device 11 uniformly charges the surface of the photosensitive drum 10.

  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 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. Thereby, colored particles are adhered to the electrostatic latent image, and the electrostatic latent image is developed as a colored particle image.

  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 density adjustment of the colored particles and the carrier liquid is performed 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 at the nip portion between the supply roller 142 and the support roller 143. It is conveyed upward toward the developing roller 141 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 colored particle 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 used as a colored particle image. Visualize. 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. In the non-image area, the colored particles do not come into contact with the surface of the photosensitive drum 10, and thus fog 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 the colored particle image based on the image data is exposed to light by 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. It is formed on the surface of the body drum 10.

  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.

  As described above, the developing roller 141 supplies the liquid developer to the photosensitive drum 10 that is an image carrier, and corresponds to the developer carrier. Further, as described above, the supply roller 142 supplies the liquid developer to the developing roller 141 that is a developer carrier, and corresponds to a developer supply unit.

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. The primary transfer roller 20 is applied with a voltage having a polarity (minus in this embodiment) opposite to that of the colored particles constituting the colored particle image 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. The intermediate transfer belt 21 functions as an image carrier that carries a colored particle 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 for fixing a colored particle image. 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 and fixes the colored particle image formed on the intermediate transfer belt 21 to the 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.

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

  The sheet on which the colored particle image has been transferred and fixed by the secondary transfer unit 4 is discharged to the discharge unit 6 provided on the upper surface of the wet image forming apparatus 1A. 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 image forming apparatus can form an image having excellent fixability on the sheet by the above operation.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited at all by the Example.

(Colored particles A)
As pigment, 10 parts by mass of cyan pigment (PB15-3 manufactured by Dainippon Seika Kogyo Co., Ltd.), as a resin, Joncryl 683 manufactured by BASF (acid value: 160 mgKOH / g, weight average molecular weight Mw: 8000, softening point) 10 parts by mass of 138 ° C, main component: styrene acrylic polymer) neutralized and dissolved with potassium hydroxide (KOH), 10 parts by mass of ethylene glycol and 70 parts by mass of ion-exchanged water were mixed as a diol compound. Next, the obtained mixture was kneaded using a media-type disperser (Glen mill manufactured by Asada Tekko Co., Ltd.). At that time, zirconia beads having a particle diameter of 0.2 to 1 mm were used as media. Further, as the kneading conditions, the particle diameter of the colored particles actually obtained varies depending on the composition and the like, but the particle diameter of the finally obtained colored particles is a volume-based median diameter (D50), The condition was adjusted to about 0.2 μm. Thereafter, water was removed from the dispersion obtained by the kneading by distillation under reduced pressure. By doing so, colored particles A were obtained.

The conductivity of the obtained colored particles A was 4.5 × 10 ⁻⁴ S / cm.

  In addition, the electrical conductivity of the colored particles was measured as follows.

  First, the colored particles were formed into a disk-shaped molded body having a diameter of 17 mm and a thickness of 0.500 to 0.600 mm using a tablet molding machine. The electrode of the powder electrode device (SE43 type manufactured by Ando Electric Co., Ltd.) is pasted so as to sandwich the obtained molded body, and between the electrodes using an LCR meter (AG4311 type manufactured by Ando Electric Co., Ltd.) Conductivity was measured. At that time, the electrical conductivity between the electrodes was measured by an AC bridge method with a sine wave Vpp = 1V and 100 kHz. Then, the conductivity of the colored particles was calculated using the measured current, electrode area, and interelectrode distance.

(Colored particles B)
The diol compound was prepared in the same manner as the colored particles A, except that propylene glycol was used instead of ethylene glycol. The conductivity of the obtained colored particles B was 5.6 × 10 ⁻⁴ S / cm.

(Colored particles C)
The diol compound was prepared in the same manner as the colored particles A except that diethylene glycol was used instead of ethylene glycol. The conductivity of the obtained colored particles C was 1.1 × 10 ⁻⁴ S / cm.

(Colored particles D)
The diol compound was prepared in the same manner as the colored particles A, except that 1,2-hexanediol was used instead of ethylene glycol. The conductivity of the obtained colored particles D was 2.5 × 10 ⁻⁴ S / cm.

(Colored particles E)
Instead of the resin obtained by neutralizing and dissolving BASF Joncrill 683 with potassium hydroxide (KOH), BASF Joncrill 611 (acid value: 53 mg KOH / g, weight average molecular weight Mw: 8100, Softening point: 112 ° C., main component: styrene acrylic polymer) neutralized and dissolved with potassium hydroxide (KOH), and as a diol compound, instead of containing 10 parts by mass of ethylene glycol, 5 mass of ethylene glycol It was prepared in the same manner as the colored particles A except that 5 parts by mass and 5 parts by mass of propylene glycol were contained. The conductivity of the obtained colored particles E was 2.3 × 10 ⁻⁴ S / cm.

(Colored particles F)
As a resin, instead of the one obtained by neutralizing and dissolving Joncrill 683 made by BASF with potassium hydroxide (KOH), Jonkrill 690 made by BASF (acid value: 240 mgKOH / g, weight average molecular weight Mw: 16500, Softening point: 155 ° C., main component: styrene acrylic polymer) neutralized and dissolved with potassium hydroxide (KOH), and instead of containing 10 parts by mass of ethylene glycol as a diol compound, 5 mass of propylene glycol It was prepared in the same manner as the colored particles A except that 5 parts by mass and 5 parts by mass of diethylene glycol were contained. The conductivity of the obtained colored particles F was 3.2 × 10 ⁻⁴ S / cm.

(Colored particles G)
As a diol compound, it is the same as the colored particles A except that 5 parts by mass of ethylene glycol is contained instead of 10 parts by mass of ethylene glycol and 75 parts by mass of ion-exchanged water is contained instead of 70 parts by mass. It was prepared by the method. That is, the content of the diol compound is changed to 5 parts by mass. The conductivity of the obtained colored particles G was 1.0 × 10 ⁻⁸ S / cm.

(Colored particles H)
As a diol compound, instead of containing 10 parts by mass of ethylene glycol, 5 parts by mass of ethylene glycol, 5 parts by mass of propylene glycol, and 5 parts by mass of diethylene glycol are contained, and 65 parts by mass of ion-exchanged water is contained instead of 70 parts by mass. It was prepared in the same manner as the colored particles A except that part thereof was contained. That is, the content of the diol compound is changed to 15 parts by mass. The conductivity of the obtained colored particles H was 9.5 × 10 ⁻³ S / cm.

(Colored particles I)
As a diol compound, instead of containing 10 parts by mass of ethylene glycol, 10 parts by mass of ethylene glycol and 10 parts by mass of diethylene glycol were contained, and 60 parts by mass of ion-exchanged water was contained instead of 70 parts by mass. The same method as for colored particles A was prepared. That is, the content of the diol compound is changed to 20 parts by mass. The conductivity of the obtained colored particles I was 9.8 × 10 ⁻² S / cm.

(Colored particles J)
Colored particles, except that a styrene-acrylic resin (CPR300 manufactured by Mitsui Chemicals, Inc.) was used as the resin, instead of the one obtained by neutralizing and dissolving Joncrill 683 manufactured by BASF with potassium hydroxide (KOH). Prepared in the same manner as A. The conductivity of the obtained colored particles J was 3.3 × 10 ⁻⁴ S / cm.

(Colored particles K)
It was prepared in the same manner as the colored particles A except that 80 parts by mass of ion exchange water was used without using a diol compound. The conductivity of the obtained colored particles K was 9.8 × 10 ⁻⁹ S / cm.

(Colored particles L)
A diol compound (ethylene glycol) was used instead of a resin obtained by neutralizing and dissolving Joncrill 683 manufactured by BASF with potassium hydroxide (KOH) as a resin, CPR300 manufactured by Mitsui Chemicals. ) Was prepared in the same manner as the colored particles A except that sodium lactate was used. The conductivity of the obtained colored particles L was 4.5 × 10 ⁻⁴ S / cm.

(Colored particles M)
As the resin, instead of the one obtained by neutralizing and dissolving Joncrill 683 manufactured by BASF with potassium hydroxide (KOH), a styrene-acrylic resin (CPR300 manufactured by Mitsui Chemicals, Inc.) is used instead of ethylene glycol. This was prepared in the same manner as colored particles A, except that 1,2-octanediol was used. The conductivity of the obtained colored particles M was 5.5 × 10 ⁻⁴ S / cm.

  The above conditions are summarized in Table 1.

[Example 1]
20 parts by weight of colored particles A obtained by the above method, 4 parts by weight of a dispersion stabilizer (Solsperse 13940 manufactured by Lubrizol), 76 parts by weight of liquid paraffin (Cosmo White P-60 manufactured by Cosmo Oil Co., Ltd.) The parts were mixed for 12 hours using a ball mill (UB32 manufactured by Yamato Scientific Co., Ltd.). By doing so, a liquid developer was obtained.

  The particle diameter of the colored particles contained in the obtained liquid developer was 0.19 μm at D50.

  In addition, the particle diameter (D50) of the colored particles was measured as follows.

  First, the obtained liquid developer was diluted 100 times on a volume basis with the same liquid as the carrier liquid contained in the liquid developer. The diluted liquid was measured by a flow method using a laser diffraction particle size distribution measuring device “MASTERSIZER 2000” manufactured by MALVERN.

[Example 2]
It was prepared in the same manner as in Example 1 except that colored particles B were used instead of colored particles A. The particle diameter of the colored particles contained in the obtained liquid developer was 0.21 μm at D50.

[Example 3]
It was prepared in the same manner as in Example 1 except that colored particles C were used instead of colored particles A. The particle diameter of the colored particles contained in the obtained liquid developer was 0.18 μm at D50.

[Example 4]
It was prepared in the same manner as in Example 1 except that colored particles D were used instead of colored particles A. The particle diameter of the colored particles contained in the obtained liquid developer was 0.23 μm at D50.

[Example 5]
A colored particle E was used instead of the colored particle A, and the dispersion stabilizer was prepared in the same manner as in Example 1 except that Solsperse 11200 manufactured by Lubrizol was used instead of Solsperse 13940. The particle diameter of the colored particles contained in the obtained liquid developer was 0.24 μm at D50.

[Example 6]
In the same manner as in Example 1 except that colored particles F were used instead of colored particles A, and Antaron (registered trademark) V-220 manufactured by ISP was used instead of Solsperse 13940 as a dispersion stabilizer. Prepared. The particle diameter of the colored particles contained in the obtained liquid developer was 0.20 μm at D50.

[Example 7]
It was prepared in the same manner as in Example 1 except that the colored particles G were used instead of the colored particles A. The particle diameter of the colored particles contained in the obtained liquid developer was D50 of 0.25 μm.

[Example 8]
It was prepared in the same manner as in Example 1 except that the colored particles H were used instead of the colored particles A. The particle diameter of the colored particles contained in the obtained liquid developer was 0.17 μm at D50.

[Example 9]
It was prepared in the same manner as in Example 1 except that colored particles I were used instead of colored particles A. The particle diameter of the colored particles contained in the obtained liquid developer was 0.22 μm at D50.

[Example 10]
It was prepared in the same manner as in Example 1 except that colored particles J were used instead of colored particles A. The particle diameter of the colored particles contained in the obtained liquid developer was 0.21 μm at D50.

[Comparative Example 1]
It was prepared in the same manner as in Example 1 except that the colored particles K were used in place of the colored particles A. The particle diameter of the colored particles contained in the obtained liquid developer was 0.20 μm at D50.

[Comparative Example 2]
It was prepared in the same manner as in Example 1 except that the colored particles L were used instead of the colored particles A. The particle diameter of the colored particles contained in the obtained liquid developer was 0.22 μm at D50.

[Comparative Example 3]
It was prepared in the same manner as in Example 1 except that the colored particles M were used instead of the colored particles A. The particle diameter of the colored particles contained in the obtained liquid developer was D50 of 0.25 μm.

[Evaluation]
Each liquid developer obtained by the above method was evaluated by the following method.

First, cyan (C) image formation is performed using a wet image forming apparatus (color printer) 1A (an experimental machine of a wet image forming apparatus manufactured by Kyocera Mita Corporation) that does not include a fixing unit as shown in FIG. The unit FC is charged with the above-mentioned liquid developer of cyan (C), and the amount of pigment applied is 0.026 mg / gram on high-quality plain paper (C2 paper manufactured by Oji Paper Co., Ltd., basis weight 90 g / m ² ) as a sheet. A uniformly solid square solid image (5 cm × 5 cm) corresponding to cm ² was formed. At that time, the thickness of the liquid developer layer on the peripheral surface of the developing roller 141 was set to be about 5 μm. The developing electric field applied to the developing roller 141 when the colored particle image based on the image data is formed on the surface of the photosensitive drum 10 is set to 400V.

  As described above, the sheet on which the solid image is formed, that is, the sheet in which the colored particle image is transferred and fixed to the sheet by the secondary transfer unit 4 and is discharged to the discharge unit 6, is described later. And subjected to fixing property evaluation.

(Image density)
The image density of the solid image formed on the sheet was measured using a reflection densitometer (SpectroEyeLT manufactured by Gretag Macbeth). When the measured image density exceeds 1.2, it is evaluated as “◯”, when it exceeds 1.0 and is 1.2 or less, it is evaluated as “Δ”, and when it is 1.0 or less, Evaluated as “x”. In addition, "(circle)" and "(triangle | delta)" were set to pass (within tolerance), and "x" was set to disqualify.

(Fixability)
On the sheet on which the solid image was formed, 500 g of weight wrapped with cotton cloth (exposed) was placed. Thereafter, with the weight of the weight applied to the sheet, the weight was rubbed 5 times with the weight so that the solid image moved across the left and right to the outside of the image. The image density of the solid image before and after this operation was measured using a reflection densitometer (SpectroEyeLT manufactured by Gretag Macbeth). Then, the residual density rate was calculated from the following formula (I) to evaluate the fixability.

Density residual ratio (%) = image density after the operation / image density before the operation × 100 (I)
If the concentration remaining rate is 95% or more, it is evaluated as “◎”, and if the concentration remaining rate is 90% or more and less than 95%, it is evaluated as “◯”, and the concentration remaining rate exceeds 80% and exceeds 90%. If it was less than%, it was evaluated as “Δ”, and if the concentration residual ratio was 80% or less, it was evaluated as “x”. In addition, "(double-circle)", "(circle)", and "(triangle | delta)" were set to pass (within tolerance), and "x" was set to disqualify.

  The results are shown in Table 2 together with the composition of the liquid developer.

As can be seen from Tables 1 and 2, when colored particles containing a resin, a pigment, and a diol compound having 2 to 6 carbon atoms are used as the colored particles dispersed in the carrier liquid (Examples 1 to 10). When using colored particles not containing the diol compound (Comparative Example 1), using colored particles containing sodium lactate instead of the diol compound (Comparative Example 2), and 6 carbon atoms Compared with the case of using colored particles containing a diol compound in excess of (Comparative Example 3), the fixing property was excellent despite the high image density. From this, it was found that the liquid developers according to Examples 1 to 10 can sufficiently fix the colored particle image on the recording medium without consuming energy such as heat energy at the time of fixing. Moreover, since the electrical conductivity of the colored particles contained in the liquid developers according to Examples 1 to 10 is 1 × 10 ⁻⁸ to 1 × 10 ⁻¹ S / cm, the electrical conductivity of the colored particles is within the above range. It can be seen that it is preferable to contain the diol compound as follows.

Further, when colored particles having an electrical conductivity of 1 × 10 ⁻⁸ to 1 × 10 ⁻² S / cm are used (Examples 1 to 8 and Example 10), the electrical conductivity is 1 × 10 ⁻² S. It was found that the fixability was excellent despite the higher image density than when colored particles exceeding / cm were used (Example 9).

Moreover, when using the colored particle whose electrical conductivity is 1 * 10 < ^-6 > ^-1 * 10 < ^-3 > S / cm (Examples 1-6, 10), it is the same Example 7 except the electrical conductivity of a colored particle. To 9, specifically, when using colored particles having an electrical conductivity of less than 1 × 10 ⁻⁶ S / cm (Example 7) or using colored particles having an electrical conductivity of more than 1 × 10 ⁻³ S / cm It was found that the image density and the fixability were superior to those of the cases (Examples 8 and 9).

From these, the conductivity of the colored particles is more preferably 1 × 10 ⁻⁸ to 1 × 10 ⁻² S / cm, and 1 × 10 ⁻⁶ to 1 × 10 ⁻³ S / cm. Was found to be more preferable.

DESCRIPTION OF SYMBOLS 1A Wet image forming apparatus 2 Image forming part 3 Sheet accommodating part 4 Secondary transfer part 6 Ejecting part 7 Sheet conveying part 8 Conveying roller 10 Photosensitive drum 11 Charging device 12 Exposure device 13 Static eliminating device 14 Liquid developing device 20 Primary transfer roller 21 Intermediate transfer belt 22 Cleaning unit 26 Cleaning device 30 Carrier liquid removing roller 41 Support roller 42 Secondary transfer roller 51 Heating roller 52 Pressure roller 81, 82 Pipe 140 Developing container 141 Developing roller 142 Supply roller 143 Support roller 144 Supply roller blade 145 Developing cleaning blade 146 Developer collecting device 147 Developing roller charging device 261 Residual developer conveying screw 262 Cleaning blade 278 Supply nozzle

Claims (7)

An electrically insulating carrier liquid;
Having colored particles dispersed in the carrier liquid,
The liquid developer, wherein the colored particles contain a resin, a pigment, and a diol compound having 2 to 6 carbon atoms.   The liquid developer according to claim 1, wherein the diol compound is at least one selected from the group consisting of ethylene glycol, propion glycol, and diethylene glycol.   The liquid developer according to claim 1, wherein the resin is a water-soluble resin. The liquid developer according to claim 1, wherein the conductivity of the colored particles is 1 × 10 ⁻⁸ to 1 × 10 ⁻¹ S / cm.   The liquid developer according to claim 1, wherein the carrier liquid is an aliphatic hydrocarbon. A developing device for developing an electrostatic latent image formed on the surface of an image carrier,
While holding the liquid developer on the surface, the liquid developer is supplied to the image carrier, and a colored particle image obtained by visualizing the electrostatic latent image with the colored particles in the liquid developer is displayed as the image. A developer carrier formed on the carrier;
A developer supply unit for supplying the liquid developer to the developer carrier,
A developing device using the liquid developer according to claim 1 as the liquid developer. An image carrier on which an electrostatic latent image is formed on the surface;
A developing device for developing the electrostatic latent image,
The image forming apparatus, wherein the developing device is the developing device according to claim 6.

Images