JP2013152347A - Liquid developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid developer that has excellent fixability (including fix level) of toner to various recording media.SOLUTION: A liquid developer according to the present invention has toner particles as dispersoid dispersed in an insulation liquid as dispersant. The dispersant is composed of a non-volatile liquid. And the dispersoid contains a coloring agent and an oxidation polymerization compound, and is liquid at normal temperature under normal pressure. The viscosity η1 at 25°C of the dispersoid is larger than the viscosity η2 at 25°C of the dispersant.

Description

  The present invention relates to a liquid developer.

As a developer used to develop the electrostatic latent image formed on the latent image carrier, a toner composed of a material containing a colorant such as a pigment and a binder resin is used as an electrically insulating carrier liquid (insulating property). Liquid developers dispersed in (liquid) are known.
Conventionally, a solid resin material such as a polyester resin, a styrene-acrylic acid ester copolymer or an epoxy resin has been used for toner particles constituting such a liquid developer (see, for example, Patent Document 1). . Such a resin material has characteristics that it is easy to handle, has good color developability of the obtained image, and can obtain high fixing characteristics.

  However, the conventional liquid developer requires a large amount of heat energy in order to improve the fixing property of the toner to the recording medium. In particular, with a conventional liquid developer, there is a large difference in toner fixability depending on the type of recording medium, and depending on the type of recording medium, fixing strength that can withstand practical use cannot be obtained. In addition, the tendency was particularly remarkable when a non-volatile liquid in consideration of the environment such as VOC countermeasures was used as the dispersion medium.

JP 2007-219380 A

  An object of the present invention is to provide a liquid developer having excellent fixability (fixing strength and the like) of toner to various recording media.

Such an object is achieved by the present invention described below.
The liquid developer of the present invention is a liquid developer in which toner particles as a dispersoid are dispersed in an insulating liquid as a dispersion medium,
The dispersion medium is composed of a non-volatile liquid,
The dispersoid contains a colorant and an oxidative polymerization type compound, and forms a liquid at normal temperature and pressure,
The viscosity η1 of the dispersoid at 25 ° C. is larger than the viscosity η2 of the dispersion medium at 25 ° C.
As a result, it is possible to provide a liquid developer having excellent fixability (fixing strength and the like) of toner to various recording media.

In the liquid developer of the present invention, it is preferable that the oxidatively polymerizable compound constituting the dispersoid includes an unsaturated fatty acid ester having an iodine value of 100 or more.
Thereby, the fixing property of the toner to the recording medium can be made particularly excellent.
In the liquid developer of the present invention, the dispersoid preferably has a viscosity η1 at 25 ° C. of 30 mPa · s to 10,000 mPa · s.
As a result, the toner particles in the liquid developer can maintain a particularly high sphericity, so that the electrophoretic properties of the toner particles are particularly excellent. Further, since the toner particles can be suitably deformed at the time of transfer of the toner particles, the transfer efficiency can be made particularly excellent, and an excessive insulating liquid is prevented from being transferred to the recording medium. The fixing property of the toner to the recording medium can be made particularly excellent.

In the liquid developer of the present invention, the dispersion medium preferably has a viscosity η2 at 25 ° C. of 5 mPa · s or more and 1000 mPa · s or less.
Thereby, the electrophoretic properties of the toner particles in the liquid developer are particularly excellent. As a result, the development efficiency is particularly excellent, and an image with excellent resolution and gradation reproducibility can be formed more suitably.

In the liquid developer of the present invention, the difference (η1−η2) between the viscosity η1 of the dispersoid at 25 ° C. and the viscosity η2 of the dispersion medium at 25 ° C. is preferably 25 mPa · s or more and 9995 mPa · s or less.
Thereby, the electrophoretic property of the toner particles in the liquid developer, the fixing property of the toner particles to the recording medium, and the transfer efficiency can be further improved.

In the liquid developer of the present invention, the average particle size of the dispersoid is preferably 0.1 μm or more and 4.0 μm or less.
Thereby, the electrophoretic property of the toner particles in the liquid developer, the fixing property of the toner particles to the recording medium, and the transfer efficiency can be made particularly excellent.
In the liquid developer of the present invention, the content of the dispersoid in the liquid developer is preferably 1% by mass or more and 40% by mass or less.
Thereby, the electrophoretic property of the toner particles in the liquid developer, the fixing property of the toner particles to the recording medium, and the transfer efficiency can be made particularly excellent.

The liquid developer of the present invention preferably further contains an oxidative polymerization accelerator.
Thereby, the fixing property of the toner particles to the recording medium can be made particularly excellent.
In the liquid developer of the present invention, the oxidative polymerization accelerator is preferably contained in an amount of 0.01 parts by weight to 5 parts by weight with respect to 100 parts by weight of the dispersoid.
Accordingly, the storage stability of the liquid developer can be improved, and the fixability of the toner particles to the recording medium can be particularly improved.

The liquid developer of the present invention preferably further contains a charge adjusting agent.
Thereby, it is possible to make the charging characteristics and developing efficiency of the toner particles particularly excellent.
In the liquid developer of the present invention, the content of the charge adjusting agent in the liquid developer is preferably 0.01% by mass or more and 5% by mass or less.
As a result, it is possible to make the toner particle charging property, development efficiency, and the like particularly excellent while improving the toner particle fixing property and the like.

In the liquid developer of the present invention, the dispersoid constituting the liquid developer is preferably composed of a material in which a part of the oxidative polymerization type compound is oxidatively polymerized.
As a result, the toner particles can be more effectively prevented from adhering to the photoreceptor, the toner particles have particularly excellent durability, and the toner particle transfer efficiency and development efficiency are particularly excellent. can do. Further, since the toner particles can be suitably fixed to the recording medium with lower energy, it is particularly advantageous from the viewpoint of energy saving, high-speed printing, and the like.

1 is a schematic diagram illustrating an example of an image forming apparatus to which a liquid developer of the present invention is applied. FIG. 2 is an enlarged view of a part of the image forming apparatus shown in FIG. 1.

Hereinafter, preferred embodiments of the present invention will be described in detail.
≪Liquid developer≫
First, the liquid developer of the present invention will be described.
The liquid developer of the present invention is one in which toner particles as a dispersoid are dispersed in an insulating liquid as a dispersion medium, and the dispersion medium is composed of a non-volatile liquid, and the dispersion The material contains a colorant and an oxidative polymerization type compound and forms a liquid under normal temperature and normal pressure. The viscosity η1 of the dispersoid at 25 ° C. is larger than the viscosity η2 of the dispersion medium at 25 ° C. It is characterized by being.

  With such a configuration, the liquid toner particles (liquid particles) can be freely deformed as compared with solid ones. Therefore, the toner particles can be suitably deformed at the time of transfer or the like, and the insulating liquid existing between the toner particles is effectively prevented from being transferred to the recording medium more than necessary. As a result, inconvenience due to the presence of the insulating liquid between the toner particles on the recording medium is effectively prevented, and the fixing property of the toner particles to the recording medium can be improved. That is, the fixing strength of the toner particles to the recording medium can be improved, or the toner particles can be fixed to the recording medium in a shorter period of time under milder conditions. In contrast, the effects as described above can be obtained. As a result, the reliability of printed matter produced using the liquid developer of the present invention can be improved, and it is advantageous from the viewpoint of energy saving and high-speed printing. In addition, since there are more choices of recording media, it is possible to enhance variations of printed materials.

On the other hand, the toner particles can maintain a state of high sphericity (circularity) that is more stable in terms of energy in the liquid developer. As a result, the electrophoretic properties of the toner particles are excellent, and the development efficiency and transfer efficiency are remarkably improved. As a result, an image with good resolution and gradation reproducibility can be formed.
Further, the conventional solid toner has been manufactured by using a kneading / pulverizing method or the like. However, in the present invention, since the liquid toner particles are included, the kneading step and the pulverizing step in manufacturing the liquid developer are omitted. Or can be simplified. As a result, the amount of energy required for manufacturing the liquid developer can be suppressed, which is preferable from the viewpoint of energy saving.

  In addition, since the toner particles contain an oxidation polymerization type compound among the polymerization type compounds, the following effects can be obtained. That is, the toner image is less likely to shrink when cured on the recording medium. For this reason, the printing part of a desired pattern can be formed more reliably. In addition, since the toner particles contain a colorant, when the photocurable compound is used, problems such as insufficient polymerization of the polymerization reaction may occur due to light absorption by the colorant. By using an oxidation polymerization type compound, such a problem does not occur. Moreover, when it contains the polymerizable compound by another polymerization system, there exists a problem that it is easy to receive oxygen polymerization inhibition, but such a problem does not arise by using an oxidation polymerization type compound. In addition, the amount of energy required for curing is small and the adhesion of the toner image to the recording medium is excellent as compared with the case where it contains a polymerizable compound by other polymerization methods.

  In the present invention, the insulating liquid is a non-volatile liquid. Thereby, generation | occurrence | production of the environmental load by an insulating liquid volatilizing can be prevented. Moreover, generation | occurrence | production of the odor by the insulating liquid volatilizing is reliably prevented. In addition, as described above, in the present invention, by containing liquid toner particles, it is effectively prevented that an excessive insulating liquid is transferred to the recording medium. Even when the amount of transfer of the toner increases, the insulating liquid is composed of a non-volatile liquid, so that the toner image will be unintentionally uneven due to volatilization of the insulating liquid on the recording medium. Can be effectively prevented from occurring. Further, since the volatilization of the insulating liquid in the apparatus to which the liquid developer is applied is prevented, the member constituting the apparatus is deteriorated due to unintentional contact with the volatilized insulating liquid, Occurrence of failure of the member and device is more reliably prevented.

Further, since the toner particles are configured as described above and the insulating liquid is configured of a non-volatile liquid, they act synergistically so that the non-volatile liquid contains an oxidative polymerization compound. Since it is surrounded without direct contact with oxygen in the air, the storage stability of the liquid developer is particularly excellent.
In the present invention, the nonvolatile liquid means a liquid whose vapor pressure at room temperature (25 ° C.) is 1.0 Pa or less.

<Toner particles (dispersoid)>
The toner particles (dispersoid) include at least a colorant and an oxidation polymerization type compound, and form a liquid at normal temperature and normal pressure (25 ° C., 1 atm).
The viscosity η1 at 25 ° C. of the liquid dispersoid may be larger than the viscosity η2 at 25 ° C. of the insulating liquid as a dispersion medium, but is preferably 30 mPa · s or more and 10000 mPa · s or less, and 50 mPa More preferably, it is s or more and 5000 mPa · s or less. As a result, the toner particles in the liquid developer can maintain a particularly high sphericity, so that the electrophoretic properties of the toner particles are particularly excellent. Further, since the toner particles can be suitably deformed at the time of transfer of the toner particles, the transfer efficiency can be made particularly excellent, and an excessive insulating liquid is prevented from being transferred to the recording medium. The fixing property of the toner to the recording medium can be made particularly excellent.

  The difference (η1−η2) between the viscosity η1 of the dispersoid at 25 ° C. and the viscosity η2 of the dispersion medium at 25 ° C. is preferably 25 mPa · s to 9995 mPa · s, preferably 45 mPa · s to 4995 mPa · s. More preferably. Thereby, the electrophoretic property of the toner particles in the liquid developer, the fixing property of the toner particles to the recording medium, and the transfer efficiency can be further improved.

[Colorant]
The colorant is not particularly limited, and for example, known pigments, dyes, and the like can be used. However, the colorant is preferably insoluble in an insulating liquid described in detail later.
The content of the colorant is not particularly limited, but is preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 15 parts by weight or more and 25 parts by weight or less with respect to 100 parts by weight of the toner particles (dispersoid). More preferred.

[Oxidation polymerization type compound]
The oxidation polymerization type compound is a component that can be polymerized by an oxidation polymerization reaction.
As the oxidative polymerization type compound, one having an unsaturated bond between carbon and carbon, for example, an unsaturated fatty acid or an ester compound thereof can be used. In particular, as the oxidative polymerization type compound, a vegetable oil containing an unsaturated fatty acid as a constituent component and / or a modified product thereof can be preferably used. Such oils include linseed oil, soybean oil, tung oil, castor oil, dehydrated castor oil, tall oil, safflower oil, palm oil (especially palm kernel oil), eno oil, hemp seed oil, mustard oil, nutka oil. Oil, deer oil, kyunui oil, kukui oil, Japanese radish seed oil, daikon oil, niger oil, grape seed oil, gentian oil, mink oil, turtle oil, grape hip oil, sesame oil, corn oil, rape seed oil (rapeseed oil) , Sunflower oil, cottonseed oil, avocado oil, olive oil, jojoba oil (containing unsaturated fatty acid and unsaturated alcohol), peanut oil, kapok oil, camellia oil, tea oil, coconut oil, shiso oil, walnut oil, camellia oil, safflower oil And modified products thereof.
The oxidation polymerization type compound preferably has an iodine value of 100 or more, more preferably 100 or more and 250 or less, and still more preferably 130 or more and 225 or less. Thereby, the fixing property of the toner to the recording medium can be made particularly excellent.

[Other ingredients]
The toner particles may contain components other than those described above. Examples of such components include known waxes, magnetic powders, and resin materials that do not contribute to the oxidative polymerization reaction.
In addition to the above materials, for example, zinc stearate, zinc oxide, cerium oxide, silica, titanium oxide, iron oxide, fatty acid, fatty acid metal salt, etc. are used as the constituent material (component) of the toner particles. May be.

  The average particle diameter of the toner particles is preferably from 0.1 μm to 4.0 μm, more preferably from 1.0 μm to 3.5 μm, and further preferably from 1.0 μm to 2.5 μm. preferable. When the average particle diameter of the toner particles is within the above range, the electrophoretic property of the toner particles in the liquid developer, the fixing property of the toner particles to the recording medium, and the transfer efficiency can be made particularly excellent. In addition, it is possible to reduce the variation in characteristics between the toner particles and to increase the resolution of the toner image formed by the liquid developer while improving the reliability of the entire liquid developer. it can. Further, the toner particles can be dispersed well in the insulating liquid, and the storage stability of the liquid developer can be made particularly high.

In the present specification, “average particle diameter” refers to a volume-based average particle diameter (volume average particle diameter (D ₅₀ )). In the present specification, the volume average particle diameter (D ₅₀ ) means “50% average particle diameter (D ₅₀ ) in terms of sphere by light scattering method” and is a value obtained as follows. That is, the particles in the dispersion medium are irradiated with light, and the generated diffracted scattered light is measured by detectors arranged in front, side, and rear of the dispersion medium. Using the measured value, assuming that the particles that are originally indefinite are spherical, a cumulative curve is obtained by setting the total volume of the particle population converted to a sphere equal to the volume of the particles as 100%, The point at which the cumulative value becomes 50% is defined as the volume average particle size. Examples of the measuring apparatus include a laser diffraction / scattering particle size analyzer Microtrac MT-3000 (manufactured by Nikkiso Co., Ltd.). The volume average particle diameter _{(D 50)} in Examples described later is a value measured with Microtrac MT-3000 of the.

The toner particles (dispersoid) constituting the liquid developer may be composed of a material obtained by oxidation polymerization of a part of the oxidation polymerization type compound. As a result, the toner particles can be more effectively prevented from adhering to the photoreceptor, the toner particles have particularly excellent durability, and the toner particle transfer efficiency and development efficiency are particularly excellent. can do. Further, since the toner particles can be suitably fixed to the recording medium with lower energy, it is particularly advantageous from the viewpoint of energy saving, high-speed printing, and the like. In the present invention, since the toner particles contain an oxidation polymerization type compound, only a part of the compound can be polymerized, and the degree of polymerization can be suitably controlled. On the other hand, when a polymerizable compound other than the oxidation polymerizable compound (for example, a radical polymerizable compound) is used, such control is difficult, and only a part of the polymerizable compound is polymerized. In this case, the polymerization reaction proceeds excessively, and the toner particles (dispersoid) become solid, and the above-described effects cannot be exhibited.
The content of the toner particles (dispersoid) in the liquid developer is preferably 1% by mass or more and 40% by mass or less, and more preferably 5% by mass or more and 35% by mass or less. Thereby, the electrophoretic property of the toner particles in the liquid developer, the fixing property of the toner particles to the recording medium, and the transfer efficiency can be made particularly excellent.

<Insulating liquid (dispersion medium)>
The insulating liquid functions as a dispersion medium for dispersing liquid toner particles in the liquid developer.
The insulating liquid has a high insulating property in order to transfer charged toner particles during image formation.

The insulating liquid may be a liquid having a sufficiently high insulating property. Specifically, the electrical resistance at room temperature (25 ° C.) is preferably 1 × 10 ⁸ Ωcm or more, and preferably 1 × 10 ¹⁰ Ωcm. More preferably, it is more preferably 1 × 10 ¹¹ Ωcm or more, and most preferably 1 × 10 ¹³ Ωcm or more.
The viscosity η2 at 25 ° C. of the insulating liquid as the dispersion medium may be smaller than the viscosity η1 of the dispersoid (toner particles) at 25 ° C., but is preferably 5 mPa · s or more and 1000 mPa · s or less. It is more preferably 10 mPa · s or more and 100 mPa · s or less. Thereby, the electrophoretic properties of the toner particles in the liquid developer are particularly excellent. As a result, the development efficiency is particularly excellent, and an image with excellent resolution and gradation reproducibility can be formed more suitably. Further, aggregation of the toner particles and the like can be prevented more effectively, and the dispersibility of the toner particles in the insulating liquid can be made higher.
The dielectric constant of the insulating liquid is preferably 3.5 or less, more preferably 2.5 or more and 3.5 or less, and further preferably 2.5 or more and 3.0 or less. .

  Examples of the insulating liquid include aliphatic hydrocarbons such as octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, and cyclodecane; KF-99, KF-96, KF-995 (or more , Shin-Etsu Chemical Co., Ltd.), AK35, AK50, AK100, AK350, AK1000 (above, Wacker Chemie AG), SH200, SH510, SH8400 (above, Toray Dow Corning), and silicones such as hydrogen-modified silicone compounds Oils, liquid paraffin, fatty acid esters, aromatic hydrocarbons such as benzene, toluene, xylene, and mesitylene; alcohols such as isopropanol can be used.

  In particular, when the insulating liquid contains one or more selected from the group consisting of aliphatic hydrocarbons, silicone oil, liquid paraffin, and fatty acid esters, oxidative polymerization that constitutes toner particles in the liquid developer. The unintentional oxidation reaction of the mold compound can be prevented more effectively. As a result, the long-term storage stability and durability of the liquid developer can be made particularly excellent, and stable image formation can be achieved over a longer period.

The fatty acid ester has an ester structure of a carboxyl group and an alcoholic hydroxyl group constituting the fatty acid in the molecule. For example, fatty acid esters such as fatty acid glycerides, fatty acid monoesters, medium chain fatty acid esters, and vegetable oils containing them. Etc. As the fatty acid component constituting the fatty acid ester, one having at least one carboxyl group in the molecule can be used, and monovalent fatty acid, divalent fatty acid, polyvalent (more than trivalent) fatty acid can be used. it can. Moreover, as alcohol which comprises fatty acid ester, what has at least 1 alcoholic hydroxyl group in a molecule | numerator can be used, and monohydric alcohol, bivalent alcohol, and polyhydric (trivalent or more) alcohol are used. be able to.
Examples of fatty acid esters include fats and oils (vegetable oils or animal oils), fatty acid esters obtained by transesterification reaction between these fats and alcohols, and fatty acid esters obtained by transesterification reaction between the fatty acid esters and alcohols, fatty acids and alcohols. Processing oils such as fatty acid esters obtained by the esterification reaction can be used.

Among these, the fatty acid ester is preferably an ester (fatty acid monoester) of a monovalent fatty acid and a monovalent alcohol. As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.
The fatty acid monoester can be obtained, for example, by a transesterification reaction between a vegetable oil and a monohydric alcohol.

The fatty acid ester is preferably an ester of a fatty acid and a linear alcohol. As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.
The content of the insulating liquid (dispersion medium) in the liquid developer is preferably 60% by mass or more and 99% by mass or less, and more preferably 65% by mass or more and 95% by mass or less.

<Other ingredients>
Further, the liquid developer may contain components other than those described above. Examples of such components include oxidative polymerization accelerators, known waxes, magnetic particles, zinc stearate, zinc oxide, cerium oxide, silica, titanium oxide, iron oxide, fatty acids, fatty acid metal salts, dispersants, external additives. Agents, known antioxidants, charge control agents and the like. Such a component may be contained in the toner particles, adhered to the surface of the toner particles, dissolved in an insulating liquid, or insulated. It may be dispersed as a dispersoid different from toner particles in a functional liquid.
In particular, when the liquid developer contains an oxidative polymerization accelerator, the fixability of toner particles to a recording medium can be made particularly excellent.

  As the oxidative polymerization accelerator, for example, a metal soap made of a metal such as cobalt, manganese, iron, zinc, and a fatty acid using octylic acid, naphthenic acid, neodecanoic acid, or the like can be used. Moreover, an oxidoreductase and a transition metal complex can be used in combination. Examples of the oxidoreductase include dehydrogenase (dehydrogenase), oxidase (oxidase), oxygenated enzyme (oxygenase), and hydroxyperoxidase. Specifically, lactate dehydrogenase and alcohol dehydrogenase are used as dehydrogenases, glucose oxidase, hexose oxidase, cholesterol oxidase, urate oxidase, ascorbate oxidase, xanthine oxidase and the like are used as oxidases, and catechol 1,2-dioxygenase is used as an oxygenase. Tryptophan 2,3-dioxygenase, lipoxygenase (also known as lipoxydase), ascorbate 2,3-dioxygenase, indole 2,3-dioxygenase, cysteine dioxygenase, beta-carotene 15,15′-dioxygenase, arginine 2- Monooxygenase, lysine 2-monooxygenase, lactate 2-monooxygenase, etc. The oxidase is catalase and peroxidase. Examples of transition metal complexes include metals such as cobalt, manganese, lead, calcium, cerium, zirconium, zinc, iron, copper, octylic acid, naphthenic acid, neodecanoic acid, stearic acid, resin acid, tall oil fatty acid, tung oil Salts with fatty acids, linseed oil fatty acids, soybean oil fatty acids and the like can be used. Moreover, these metal complexes may be used independently and may be used in combination of 2 or more types.

When the liquid developer contains an oxidative polymerization accelerator, the oxidative polymerization accelerator is contained in a ratio of 0.01 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of toner particles (dispersoid). It is more preferable that it is contained at a ratio of 0.1 parts by weight or more and 3 parts by weight or less. Accordingly, the storage stability of the liquid developer can be improved, and the fixability of the toner particles to the recording medium can be particularly improved.
Further, when the liquid developer contains a charge adjusting agent, the charging characteristics of toner particles, development efficiency, and the like can be made particularly excellent.

  Examples of the charge control agent include fatty acid metal salts such as naphthenic acid metal salts and stearic acid metal salts, sulfonic acid metal salts such as dodecylbenzenesulfonic acid metal salts, and metal salts of sulfosuccinic acid esters such as dioctyl sulfosuccinic acid metal salts. , Phosphoric acid esters or metal salts of phosphoric acid esters, metal salts of abietic acid or abietic acid, nonionic surfactants such as polyoxyethylated alkylamines, polyvinyl pyrrolidone resins, organic acid esters of polyhydric alcohols And polyamide resins, quaternary ammonium salt compounds, lecithin, linseed oil and the like can be used.

When the liquid developer contains a charge adjusting agent, the content of the charge adjusting agent in the liquid developer is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 3% by mass. The following is more preferable. As a result, it is possible to make the toner particle charging property, development efficiency, and the like particularly excellent while improving the toner particle fixing property and the like.
Moreover, as a dispersing agent, various surfactants (emulsifier), such as an ionic surfactant, a nonionic surfactant, and an amphoteric surfactant, can be used, for example.

In particular, as the dispersant, polymer dispersants having adsorbing groups such as amine, carboxylic acid, phosphoric acid, ammonium, and salts thereof on polymer skeletons such as acrylic, ester, urethane, ether, etc., lecithin derivatives, fatty acid esters And silicone dispersants can be suitably used. By including such a dispersant, it is possible to effectively prevent toner particles from being settled in the liquid developer, and to increase the particle size by aggregation of the toner particles in the liquid developer. Can be prevented. As a result, the liquid developer can be used for suitable image formation over a longer period of time.
When the liquid developer contains a dispersant, the content of the dispersant in the liquid developer is preferably 0.01% by mass or more and 5% by mass or less, and preferably 0.1% by mass or more and 3% by mass or less. More preferably.

≪Image forming device≫
Next, a preferred embodiment of an image forming apparatus to which the liquid developer of the present invention is applied will be described.
FIG. 1 is a schematic diagram showing a preferred embodiment of an image forming apparatus to which the liquid developer of the present invention is applied, and FIG. 2 is an enlarged view of a part of the image forming apparatus shown in FIG.
As shown in FIGS. 1 and 2, the image forming apparatus 1000 includes four developing units 30Y, 30M, 30C, and 30K, a transfer unit (intermediate transfer unit 40 and a secondary transfer unit (secondary transfer unit) 60), and , A fixing unit (fixing device) F40 and four liquid developer replenishing units 90Y, 90M, 90C, and 90K.

The developing units 30Y, 30M, and 30C develop a latent image with a yellow liquid developer (Y), a magenta liquid developer (M), and a cyan liquid developer (C), respectively, and correspond to each color. It has a function of forming a single color image. The developing unit 30K has a function of developing a latent image with a black liquid developer (K) to form a black single color image.
Since the developing units 30Y, 30M, 30C, and 30K have the same configuration, the developing unit 30Y will be described below.

  As shown in FIG. 2, the developing unit 30Y includes a photoconductor 10Y as an example of an image carrier, a charging roller 11Y, an exposure unit 12Y, a development unit 100Y, and a photoconductor along the rotation direction of the photoconductor 10Y. It includes a body squeeze device 101Y, a primary transfer backup roller 51Y, a charge removal unit 16Y, a photoreceptor cleaning blade 17Y, and a developer recovery unit 18Y.

The photoreceptor 10Y is formed on a cylindrical base material and an outer peripheral surface thereof, has a photosensitive layer made of a material such as amorphous silicon, and is rotatable about a central axis. Rotate clockwise as indicated by the arrow in FIG.
The photoreceptor 10Y is supplied with a liquid developer by a developing unit 100Y described later, and a layer of the liquid developer is formed on the surface.

The charging roller 11Y is a device for charging the photoconductor 10Y, and the exposure unit 12Y is a device for forming a latent image on the photoconductor 10Y charged by irradiating a laser. The exposure unit 12Y includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and charges a modulated laser based on an image signal input from a host computer (not shown) such as a personal computer or a word processor. Irradiate onto the photoconductor 10Y.
The developing unit 100Y is a device for developing the latent image formed on the photoreceptor 10Y using the liquid developer of the present invention. Details of the developing unit 100Y will be described later.

  The photoconductor squeeze device 101Y is disposed on the downstream side in the rotation direction from the developing unit 100Y so as to face the photoconductor 10Y. The photoconductor squeeze roller 13Y and the photoconductor squeeze roller 13Y are pressed and slidably attached to the surface. The cleaning blade 14Y removes the liquid developer and the developer collection unit 15Y that collects the removed liquid developer. The photoreceptor squeeze device 101Y has a function of collecting excess carrier (insulating liquid) and originally unnecessary fog toner from the developer developed on the photoreceptor 10Y, and increasing the ratio of toner particles in the visible image.

The primary transfer backup roller 51Y is a device for transferring a single color image formed on the photoreceptor 10Y to an intermediate transfer unit 40 described later.
The neutralization unit 16Y is a device that removes residual charges on the photoreceptor 10Y after the intermediate transfer image is transferred onto the intermediate transfer unit 40 by the primary transfer backup roller 51Y.
The photoconductor cleaning blade 17Y is a rubber member that is in contact with the surface of the photoconductor 10Y, and remains on the photoconductor 10Y after the image is transferred onto the intermediate transfer portion 40 by the primary transfer backup roller 51Y. It has a function of scraping off and removing the liquid developer.

The developer recovery unit 18Y has a function of recovering the liquid developer removed by the photoconductor cleaning blade 17Y.
The intermediate transfer unit 40 is an endless elastic belt member, and is stretched around a belt driving roller 41 and a pair of driven rollers 44 and 45 to which a driving force of a motor (not shown) is transmitted. The intermediate transfer unit 40 is driven to rotate counterclockwise by the belt driving roller 41 while being in contact with the photoreceptors 10Y, 10M, 10C, and 10K by the primary transfer backup rollers 51Y, 51M, 51C, and 51K.

Further, the intermediate transfer unit 40 is applied with a predetermined tension by a tension roller 49 so that slack is removed. The tension roller 49 is disposed downstream of one driven roller 44 in the rotation (movement) direction of the intermediate transfer unit 40 and upstream of the other driven roller 45 in the rotation (movement) direction of the intermediate transfer unit 40. .
A single color image corresponding to each color formed by the developing units 30Y, 30M, 30C, and 30K is sequentially transferred to the intermediate transfer unit 40 by the primary transfer backup rollers 51Y, 51M, 51C, and 51K, and a single color corresponding to each color is transferred. The images are superimposed. As a result, a full-color developer image (intermediate transfer image) is formed on the intermediate transfer portion 40.

  In the intermediate transfer unit 40, the single-color images formed on the plurality of photoconductors 10Y, 10M, 10C, and 10K are secondarily transferred and superposed one after another. Secondary transfer is performed on a recording medium F5 such as paper, film, or cloth. Therefore, when the toner image is transferred to the recording medium F5 in the secondary transfer process, even if the surface of the recording medium F5 is a non-smooth sheet material due to fiber or the like, the secondary transfer characteristics follow the non-smooth sheet surface. An elastic belt member is employed as means for improving the above.

The intermediate transfer unit 40 is provided with a cleaning device including an intermediate transfer unit cleaning blade 46, a developer recovery unit 47, and a non-contact type bias applying member 48.
The intermediate transfer unit cleaning blade 46 and the developer recovery unit 47 are arranged on the driven roller 45 side.
The intermediate transfer unit cleaning blade 46 scrapes and removes the liquid developer adhering to the intermediate transfer unit 40 after the toner image is transferred onto the recording medium F5 by the secondary transfer unit (secondary transfer unit) 60. It has a function.

The developer recovery unit 47 has a function of recovering the liquid developer removed by the intermediate transfer unit cleaning blade 46.
The non-contact type bias applying member 48 is disposed away from the intermediate transfer unit 40 at a position facing the tension roller 49. The non-contact type bias applying member 48 applies a bias voltage having a polarity opposite to that of the toner to the liquid developer toner (solid content) remaining on the intermediate transfer portion 40 after the secondary transfer. As a result, the toner is discharged, and the electrostatic adhesion force of the toner to the intermediate transfer unit 40 is reduced. In this example, a corona charger is used as the non-contact type bias applying member 48.

  The non-contact type bias applying member 48 is not necessarily disposed at a position facing the tension roller 49. For example, a position between the driven roller 44 and the tension roller 49, such as a position between the driven roller 44 and the intermediate transfer unit. It can be disposed at any position downstream in the movement direction and upstream of the driven roller 45 in the movement direction of the intermediate transfer unit. The non-contact type bias applying member 48 may be a known non-contact type charger other than the corona charger.

An intermediate transfer unit squeeze device 52Y is disposed downstream of the primary transfer backup roller 51Y in the moving direction of the intermediate transfer unit 40.
The intermediate transfer unit squeeze device 52Y is provided as a means for removing excess insulating liquid from the transferred liquid developer when the liquid developer transferred onto the intermediate transfer unit 40 has not reached the desired dispersion state. ing.

The intermediate transfer unit squeeze device 52Y is removed by the intermediate transfer unit squeeze roller 53Y, the intermediate transfer unit squeeze cleaning blade 55Y that presses and slides against the intermediate transfer unit squeeze roller 53Y, and the intermediate transfer unit squeeze cleaning blade 55Y. The developer collecting section 56Y collects the liquid developer.
The intermediate transfer unit squeeze device 52Y has a function of recovering excess insulating liquid from the developer primarily transferred to the intermediate transfer unit 40, increasing the toner particle ratio in the image, and recovering originally unwanted toner. Have.

  The secondary transfer unit 60 includes a pair of secondary transfer rollers that are spaced apart from each other by a predetermined distance along the transfer material movement direction. Of these pair of secondary transfer rollers, the secondary transfer roller disposed on the upstream side in the moving direction of the intermediate transfer unit 40 is the upstream secondary transfer roller 64. The upstream secondary transfer roller 64 can be pressed against the belt drive roller 41 via the intermediate transfer unit 40.

Of the pair of secondary transfer rollers, the secondary transfer roller disposed on the downstream side in the moving direction of the transfer material is the downstream secondary transfer roller 65. The downstream secondary transfer roller 65 can be brought into pressure contact with the driven roller 44 via the intermediate transfer unit 40.
That is, the upstream side secondary transfer roller 64 and the downstream side secondary transfer roller 65 bring the recording medium F5 into contact with the intermediate transfer unit 40 that is hung on the belt driving roller 41 and the driven roller 44, respectively. The intermediate transfer image formed by superimposing colors on 40 is secondarily transferred to the recording medium F5.

  In this case, the belt driving roller 41 and the driven roller 44 also function as backup rollers for the upstream side secondary transfer roller 64 and the downstream side secondary transfer roller 65, respectively. That is, the belt drive roller 41 is also used as an upstream backup roller disposed in the secondary transfer unit 60 on the upstream side of the driven roller 44 in the moving direction of the recording medium F5. The driven roller 44 is also used as a downstream backup roller disposed in the secondary transfer unit 60 on the downstream side in the moving direction of the recording medium F5 from the belt driving roller 41.

  Therefore, the recording medium F5 conveyed to the secondary transfer unit 60 is moved from the pressure contact start position (nip start position) between the upstream secondary transfer roller 64 and the belt drive roller 41 to the downstream secondary transfer roller 65 and the driven roller. In close contact with the intermediate transfer portion 40 in a predetermined movement region of the transfer material up to the press-contact end position (nip end position) with 44. As a result, the full-color intermediate transfer image on the intermediate transfer unit 40 is secondarily transferred to the recording medium F5 in close contact with the intermediate transfer unit 40 over a predetermined time, so that good secondary transfer is performed.

  The secondary transfer unit 60 includes a secondary transfer roller cleaning blade 66 and a developer recovery unit 67 with respect to the upstream side secondary transfer roller 64. The secondary transfer unit 60 includes a secondary transfer roller cleaning blade 68 and a developer recovery unit 69 with respect to the downstream side secondary transfer roller 65. The secondary transfer roller cleaning blades 66 and 68 are in contact with the secondary transfer rollers 64 and 65, respectively, and scrape and remove the liquid developer remaining on the surfaces of the secondary transfer rollers 64 and 65 after the secondary transfer. To do. Further, the developer collecting units 67 and 69 collect and store the liquid developer scraped off from the secondary transfer rollers 64 and 65 by the secondary transfer roller cleaning blades 66 and 68, respectively.

The toner image (transfer image) transferred onto the recording medium F5 by the secondary transfer unit 60 is sent to a fixing unit (fixing device) F40, and is heated and pressurized to be fixed on the recording medium F5.
In addition, since the oxidation polymerization proceeds even when the oxygen in the air is touched even at a temperature near room temperature, the fixing device is not essential, but the fixing temperature (set temperature) is specifically 20 ° C. or higher and 160 ° C. or lower. It is preferable that it is 40 ° C. or higher and 150 ° C. or lower, more preferably 80 ° C. or higher and 140 ° C. or lower.

Next, the developing units 100Y, 100M, 100C, and 100K will be described in detail. In the following description, the developing unit 100Y will be typically described.
As shown in FIG. 2, the developing unit 100Y includes a liquid developer storage unit 31Y, a coating roller 32Y, a regulating blade 33Y, a developer stirring roller 34Y, a communication unit 35Y, a recovery screw 36Y, and a developing roller 20Y. And a developing roller cleaning blade 21Y.

The liquid developer storage unit 31Y has a function of storing a liquid developer for developing the latent image formed on the photoreceptor 10Y. The supply unit 31aY supplies the liquid developer to the development unit, and the supply unit A recovery unit 31bY that recovers excess liquid developer generated at 31aY and the like, and a partition 31cY that partitions the supply unit 31aY and the recovery unit 31bY are provided.
The supply unit 31aY has a function of supplying the liquid developer to the application roller 32Y, and has a concave portion in which the developer stirring roller 34Y is installed. Further, the liquid developer is supplied from the liquid developer mixing tank 93Y to the supply unit 31aY through the communication unit 35Y.

The collection unit 31bY collects the liquid developer that is excessively supplied to the supply unit 31aY and excess liquid developer generated in the developer collection units 15Y and 24Y. The collected liquid developer is conveyed to a liquid developer mixing tank 93Y described later and reused. The recovery unit 31bY has a concave portion, and a recovery screw 36Y is installed near the bottom.
A wall-shaped partition 31cY is provided at the boundary between the supply unit 31aY and the recovery unit 31bY. The partition 31cY partitions the supply unit 31aY and the recovery unit 31bY and can prevent the recovered liquid developer from being mixed into the fresh liquid developer. Further, when an excessive liquid developer is supplied to the supply unit 31aY, the excess liquid developer can overflow from the supply unit 31aY to the recovery unit 31bY beyond the partition 31cY. For this reason, the amount of the liquid developer in the supply unit 31aY can be kept constant, and the amount of the liquid developer supplied to the application roller 32Y can be kept constant. For this reason, the image quality of the finally formed image becomes stable.
Further, the partition 31cY is provided with a notch, and the liquid developer can overflow from the supply part 31aY to the recovery part 31bY through the notch.

The coating roller 32Y has a function of supplying a liquid developer to the developing roller 20Y.
This application roller 32Y is a so-called anilox roller in which grooves are uniformly and spirally formed on the surface of a metallic roller such as iron and nickel-plated, and its diameter is about 25 mm. . In the present embodiment, a plurality of grooves are formed obliquely with respect to the rotation direction of the application roller 32Y by so-called cutting or rolling. The application roller 32Y contacts the liquid developer while rotating counterclockwise, thereby supporting the liquid developer in the supply unit 31aY in the groove and transporting the supported liquid developer to the development roller 20Y. To do.

  The regulating blade 33Y contacts the surface of the coating roller 32Y and regulates the amount of liquid developer on the coating roller 32Y. That is, the regulation blade 33Y plays a role of scraping off excess liquid developer on the application roller 32Y and measuring the liquid developer on the application roller 32Y supplied to the development roller 20Y. The restriction blade 33Y is made of urethane rubber as an elastic body, and is supported by a restriction blade support member made of metal such as iron. The regulating blade 33Y is provided on the side where the application roller 32Y rotates and advances from the liquid developer (that is, the right side in FIG. 2). The rubber hardness of the regulating blade 33Y is about 77 degrees according to JIS-A, and the hardness (about 77 degrees) of the contact portion of the regulating blade 33Y with the surface of the application roller 32Y is about the elasticity of the developing roller 20Y described later. It is lower than the hardness (about 85 degrees) of the press contact portion of the body layer to the surface of the application roller 32Y. Further, the excess liquid developer scraped off is collected in the supply unit 31aY and reused.

The developer stirring roller 34Y has a function of stirring the liquid developer in a uniformly dispersed state. This effectively prevents a plurality of toner particles from aggregating.
In the supply unit 31aY, the toner particles in the liquid developer have a positive charge, and the liquid developer is stirred by the developer stirring roller 34Y to be in a uniformly dispersed state, and the coating roller 32Y rotates. Thus, the liquid developer is stored in the liquid developer storage unit 31Y, and the amount of the liquid developer is regulated by the regulating blade 33Y and supplied to the developing roller 20Y. In addition, by being stirred by the developer stirring roller 34Y, the liquid developer can be stably overflowed to the collection unit 31bY side beyond the partition 31cY, and the liquid developer can be prevented from staying and being compressed. it can.

  Further, the developer stirring roller 34Y is provided in the vicinity of the communication portion 35Y. For this reason, the liquid developer supplied from the communication unit 35Y can quickly diffuse, and even when the liquid developer is supplied to the supply unit 31aY, the liquid level of the supply unit 31aY is stabilized. can do. By providing such a developer agitation roller 34Y in the vicinity of the communication portion 35Y, the communication portion 35Y has a negative pressure, and the liquid developer can be sucked up naturally.

The communication unit 35Y is provided in the vertical direction below the developer stirring roller 34Y, communicates with the liquid developer storage unit 31Y, and sucks the liquid developer from the liquid developer mixing tank 93Y to the supply unit 31aY.
By providing the communication portion 35Y below the developer stirring roller 34Y, the liquid developer supplied from the communication portion 35Y is stopped by the developer stirring roller 34Y, and the liquid top surface does not rise due to blowing, and the liquid The upper surface is held substantially constant, and the developer can be stably supplied to the coating roller 32Y.
The recovery screw 36Y provided in the vicinity of the bottom of the recovery unit 31bY is made of a cylindrical member, has a spiral rib on the outer periphery, and has a function of maintaining the fluidity of the recovered liquid developer. It has a function of promoting the conveyance of the developer to the liquid developer mixing tank 93Y.

The developing roller 20Y carries the liquid developer and conveys it to the developing position facing the photoconductor 10Y in order to develop the latent image carried on the photoconductor 10Y with the liquid developer.
The developing roller 20Y forms a liquid developer layer on its surface by supplying the liquid developer from the coating roller 32Y described above.
The developing roller 20Y includes a conductive elastic layer on the outer peripheral portion of an inner core made of metal such as iron, and has a diameter of about 20 mm. The elastic body layer has a two-layer structure. As the inner layer, urethane rubber having a rubber hardness of about 30 degrees JIS-A and a thickness of about 5 mm is used, and as the surface layer (outer layer), the rubber hardness is JIS. A urethane rubber having a thickness of about 30 μm at about 85 ° A is provided. The developing roller 20Y is in pressure contact with the coating roller 32Y and the photoreceptor 10Y in a state of being elastically deformed with the surface layer serving as a pressure contact portion.

  Further, the developing roller 20Y can rotate around its central axis, and the central axis is below the rotational central axis of the photoconductor 10Y. Further, the developing roller 20Y rotates in a direction (counterclockwise in FIG. 2) opposite to the rotation direction of the photoreceptor 10Y (clockwise in FIG. 2). When developing the latent image formed on the photoconductor 10Y, an electric field is formed between the developing roller 20Y and the photoconductor 10Y.

In the developing unit 100Y, the coating roller 32Y and the developing roller 20Y are separately driven by different power sources (not shown). And the quantity of the liquid developer supplied on the developing roller 20Y can be adjusted by changing the rotation speed (linear speed) ratio with the application roller 32Y and the developing roller 20Y.
The developing unit 100Y includes a rubber developing roller cleaning blade 21Y that is in contact with the surface of the developing roller 20Y, and a developer recovery unit 24Y. The developing roller cleaning blade 21Y is a device for scraping off and removing the liquid developer remaining on the developing roller 20Y after development is performed at the developing position. The liquid developer removed by the developing roller cleaning blade 21Y is collected in the developer collecting unit 24Y.

  As shown in FIGS. 1 and 2, the image forming apparatus 1000 includes liquid developer replenishing units 90Y, 90M, 90C, and 90K that replenish liquid developer to the developing units 30Y, 30M, 30C, and 30K. . These liquid developer replenishers 90Y, 90M, 90C, and 90K are respectively provided with liquid developer tanks 91Y, 91M, 91C, and 91K, insulating liquid tanks 92Y, 92M, 92C, and 92K, and a liquid developer mixing tank 93Y. , 93M, 93C, 93K.

  Each of the liquid developer tanks 91Y, 91M, 91C, and 91K stores a high concentration liquid developer corresponding to each color. Insulating liquid tanks 92Y, 92M, 92C, and 92K contain insulating liquids, respectively. Further, in each liquid developer mixing tank 93Y, 93M, 93C, 93K, a predetermined amount of each high-concentration liquid developer from each liquid developer tank 91Y, 91M, 91C, 91K, and each insulating liquid tank 92Y, A predetermined amount of each insulating liquid from 92M, 92C, and 92K is supplied.

  The liquid developer mixing tanks 93Y, 93M, 93C, and 93K are respectively mixed and stirred by the stirrers provided with the supplied high-concentration liquid developer and the insulating liquid, respectively, and the supply units 31aY. , 31aM, 31aC, and 31aK, a liquid developer corresponding to each color is prepared. The liquid developers prepared in the liquid developer mixing tanks 93Y, 93M, 93C, and 93K are supplied to the supply units 31aY, 31aM, 31aC, and 31aK, respectively.

Further, the liquid developer recovered by the recovery unit 31bY is recovered and reused in the liquid developer mixing tank 93Y. The same applies to the liquid developer mixing tanks 93M, 93C, and 93K.
In the image formation using the above apparatus, a plurality of single color images corresponding to the respective colors are applied to the photoreceptors 10Y, 10M, 10C, and 10K using a plurality of liquid developers having different colors (the liquid developer of the present invention). And a transfer step of transferring a plurality of single color images formed on the photosensitive member to the recording medium F5 and forming an unfixed toner image formed by superimposing the plurality of single color images on the recording medium F5. And a fixing step of fixing an unfixed toner image on the recording medium F5. By using such a method, it is possible to quickly fix the toner image on the recording medium F5, and as a result, it is possible to form an image at a high speed. In the present invention, since the toner particles constituting the liquid developer are in a liquid state, the toner particles can be easily and reliably crushed on the recording medium, and an image with excellent color development can be easily formed. .

As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to these.
For example, the liquid developer of the present invention is not limited to that applied to the image forming apparatus as described above.
In the above-described embodiment, the configuration having the corona discharger as the image forming apparatus has been described. However, the corona discharger may be omitted.

[1] Production of Liquid Developer A liquid developer was produced as follows. About the process in which temperature is not described, it performed at room temperature (25 degreeC).
Example 1
First, a cyan pigment as a colorant (manufactured by Dainichi Seika Co., Ltd., Pigment Blue 15: 3), a paulownia oil as an oxidation polymerization type compound, an oxidation polymerization accelerator (manufactured by DIC, cobalt naphthenate), and a dispersant ( Lubrizol Corp., Solsperse 11200) was placed in a plastic container, 3 mm diameter zirconia beads were added and dispersed with a rocking mill at a frequency of 52 Hz for 24 hours, and then the zirconia beads were removed to produce a colored dispersion.

Next, the colored dispersion, silicone oil as a non-volatile liquid (manufactured by Shin-Etsu Chemical Co., Ltd., KF-96-50cs), charge control agent (zirconium octylate), and dispersant (manufactured by Dow Corning, FA4002ID Silicone Acrylate) ) In a container and dispersed for 10 minutes at 10,000 rpm with an emulsifying disperser, so that the liquid toner particles (dispersoid) containing the colorant and the oxidation polymerization type compound become an insulating liquid (silicone oil) as a dispersion medium. A liquid developer dispersed in was obtained.
(Examples 2 to 4)
A liquid developer was produced in the same manner as in Example 1 except that the material used for the production of the liquid developer was changed to have the composition shown in Table 1.

(Example 5)
First, a colored dispersion was produced in the same manner as in Example 1.
Next, the above colored dispersion, silicone oil as a non-volatile liquid (KF-96-50cs, manufactured by Shin-Etsu Chemical), charge control agent (zirconium octylate), and dispersant (manufactured by Dow Corning, FA4002ID Silicone Acrylate) ) Was placed in a container and dispersed with an emulsifying disperser at 10,000 rpm for 10 minutes. Thereafter, the liquid temperature was raised to 50 ° C., and the mixture was gently stirred at 1500 rpm for 1 hour (heating step) to oxidatively polymerize a part of the oxidation polymerization type compound to obtain a liquid developer.
(Examples 6 to 8)
The liquid was used in the same manner as in Example 5 except that the material used for the production of the liquid developer was changed and the processing temperature in the heating process was changed so that the composition shown in Table 1 was obtained. A developer was produced.

(Comparative Example 1)
[Kneading process, coarse pulverization process]
(Preparation of colorant masterbatch)
First, a styrene-acrylic resin (glass transition point (Tg): 50 ° C.) was prepared as a resin material.

Next, a mixture (mass ratio 50:50) of the resin material and a cyan pigment as a colorant (manufactured by Dainichi Seika Co., Ltd., Pigment Blue 15: 3) was prepared. These components were mixed using a 20 L type Henschel mixer to obtain a raw material for toner production.
Next, this raw material (mixture) was kneaded using a twin-screw kneading extruder. The kneaded product extruded from the extrusion port of the biaxial kneading extruder was cooled.
The kneaded material cooled as described above was coarsely pulverized to obtain a colorant master batch having an average particle size of 1.0 mm or less. A hammer mill was used for coarse pulverization of the kneaded product.
(Preparation of coarsely pulverized product)
The colorant master batch and the styrene-acrylic resin were kneaded using a biaxial kneading extruder. And the kneaded material extruded from the extrusion port of the biaxial kneading extruder was cooled. The obtained kneaded product was pulverized with a hammer mill to obtain a coarsely pulverized product.

[Wet grinding process]
The coarsely pulverized product obtained by the above method and silicone oil as an insulating liquid (manufactured by Shin-Etsu Chemical Co., Ltd., KF-96-50cs) are placed in a ceramic pot (internal volume 600 ml), and further zirconia balls (ball diameter: 10 mm). ) Was placed in a ceramic pot so as to have a volume filling rate of 40%, and wet pulverization was performed in a desktop pot mill at a rotational speed of 230 rpm for 48 hours.

[Heating process]
The dispersion obtained in the wet pulverization step was transferred to a beaker and placed on a hot stirrer and heated at 60 ° C. At that time, a shear of 500 rpm was applied. The heat treatment was performed for 30 minutes. Then, it naturally cooled to room temperature.
Thereafter, a silanol group-containing polysiloxane (DC593, manufactured by Toray Dow Corning Co., Ltd.) is added to the dispersion that has been subjected to the above heat treatment, and mixed and stirred with a disper, so that solid toner particles are converted into an insulating liquid. A dispersed liquid developer was obtained.

(Comparative Example 2)
A liquid developer was produced in the same manner as in Example 1 except that a polyethylene glycol diacrylate monomer as a photopolymerizable compound was used instead of the oxidation polymerization type compound.
(Comparative Example 3)
A liquid developer was produced in the same manner as in Example 5 except that a polyethylene glycol diacrylate monomer as a photopolymerizable compound was used instead of the oxidative polymerization compound. In this comparative example, the polymerization of the photopolymerizable compound could not be controlled, and the toner particles constituting the liquid developer were solid.

(Comparative Example 4)
Except for using a non-volatile liquid silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., KF-96-50cs) as an volatile liquid, an isoparaffin-based solvent (manufactured by ExxonMobil Co., Ltd., Isopar G) is used. A liquid developer was produced in the same manner.
Table 1 summarizes the compositions and the like of the liquid developers of the above Examples and Comparative Examples.

  In the table, pigment blue 15: 3 is “PB”, carbon black is “CB”, Solsperse 11200 is “D1”, BYK-141 is “D2”, tung oil (iodine value: 160) is “О1”, linseed oil (Iodine number: 195) is “O2”, rapeseed oil (iodine number: 110) is “О3”, epoxy-modified linseed oil (iodine number: 120) is “О4”, polyethylene glycol diacrylate is “RP”, liquid paraffin “L1”, Isopar G “L2”, Cobalt naphthenate “M1”, Cobalt naphthenate “M2”, Zirconium octylate “CD”, Silicone acrylate “D3”, Egg yolk lecithin “D4”, Light Radical polymerization initiator “A”, methyl silicone oil (KF-96-50cs, manufactured by Shin-Etsu Chemical Co., Ltd.) “KF”, steel Showed a "StAc": - down Acrylic resin (50 ° C. Glass transition temperature).

[2] Evaluation The following evaluation was performed on the liquid developer obtained as described above.
[2.1] Fixability [2.1.1] Fixing Strength Using an image forming apparatus as shown in FIG. 1 and FIG. 2, predetermined by the liquid developer obtained in each of the above examples and each of the comparative examples. A pattern image was formed on the recording medium. Thereafter, thermal fixing was performed at a fixing temperature of 120 ° C. and a conveyance speed of 250 mm / s.

Then, after confirming the non-offset area, the fixed image on the recording medium is erased twice (rubber eraser “LION 261-11” manufactured by Lion Business Machine Co., Ltd.) with a pressing load of 1.2 kgf, and the image density remains. The rate was measured by “X-Rite model 404” manufactured by X-Rite Inc, and evaluated according to the following criteria.
As recording media, high-quality paper manufactured by Seiko Epson (LPCPPA4), high-quality paper manufactured by Mitsubishi Paper Industries (thickness 120 μm), coated paper manufactured by Mitsubishi Paper Industries (pearl coating thickness 82 μm) ), Zanders Coated Paper (Iconosilk White, thickness: 122 μm), and PET film (thickness: 100 μm).

A: Image density remaining rate is 96% or more.
B: Image density remaining ratio is 90% or more and less than 96%.
C: Image density remaining rate is 80% or more and less than 90%.
D: Image density remaining ratio is 70% or more and less than 80%.
E: Image density remaining rate is less than 70%.

[2.1.2] Low-temperature fixability Using an image forming apparatus as shown in FIGS. 1 and 2, an image of a predetermined pattern by the liquid developer obtained in each of the above examples and each of the comparative examples is recorded as a recording medium. Formed on top. Thereafter, thermal fixing was performed at a fixing set temperature of 60 ° C. and a conveying speed of 250 mm / s.
Thereafter, in the same manner as in [2.1.1] above, the residual ratio of image density was measured and evaluated according to the following criteria.
As recording media, high-quality paper manufactured by Seiko Epson (LPCPPA4), high-quality paper manufactured by Mitsubishi Paper Industries (thickness 120 μm), coated paper manufactured by Mitsubishi Paper Industries (pearl coating thickness 82 μm) ), Zanders Coated Paper (Iconosilk White, thickness: 122 μm), and PET film (thickness: 100 μm).

A: Image density remaining rate is 96% or more.
B: Image density remaining ratio is 90% or more and less than 96%.
C: Image density remaining rate is 80% or more and less than 90%.
D: Image density remaining ratio is 70% or more and less than 80%.
E: Image density remaining rate is less than 70%.

[2.1.3] High-speed printability (energy required for fixing)
Using the image forming apparatus as shown in FIGS. 1 and 2, images of a predetermined pattern were formed on a recording medium using the liquid developers obtained in the respective Examples and Comparative Examples. Thereafter, heat fixing was performed at a fixing temperature of 120 ° C. and a heating time of 500 seconds.
Thereafter, in the same manner as in [2.1.1] above, the residual ratio of image density was measured and evaluated according to the following criteria.
As recording media, high-quality paper manufactured by Seiko Epson (LPCPPA4), high-quality paper manufactured by Mitsubishi Paper Industries (thickness 120 μm), coated paper manufactured by Mitsubishi Paper Industries (pearl coating thickness 82 μm) ), Zanders Coated Paper (Iconosilk White, thickness: 122 μm), and PET film (thickness: 100 μm).

A: Image density remaining rate is 96% or more.
B: Image density remaining ratio is 90% or more and less than 96%.
C: Image density remaining rate is 80% or more and less than 90%.
D: Image density remaining ratio is 70% or more and less than 80%.
E: Image density remaining rate is less than 70%.

[2.2] Development efficiency Using the image forming apparatus as shown in FIGS. 1 and 2, a liquid developer using the liquid developer obtained in each of the examples and comparative examples on the developing roller of the image forming apparatus. A layer was formed. Next, the surface potential of the developing roller was set to 300V, the surface potential of the photoconductor was uniformly charged at 500V, the photoconductor was exposed, the charge on the surface of the photoconductor was attenuated, and the surface potential was set to 50V. The toner particles on the developing roller and the toner particles on the photoconductor after the liquid developer layer passed between the photoconductor and the developing roller were collected with a tape. Each tape used for sampling was affixed on a recording paper, and the concentration of each toner particle was measured. After the measurement, the value obtained by dividing the concentration of toner particles collected on the photoconductor by the sum of the concentration of toner particles collected on the photoconductor and the concentration of toner particles collected on the developing roller is multiplied by 100. The obtained value was determined as the development efficiency and evaluated according to the following four criteria.
A: The development efficiency is 96% or more, and the development efficiency is particularly excellent.
B: The development efficiency is 90% or more and less than 96%, and the development efficiency is excellent.
C: The development efficiency is 80% or more and less than 90%, and there is no practical problem.
D: The development efficiency is less than 80% and the development efficiency is inferior.

[2.3] Transfer Efficiency Using the image forming apparatus as shown in FIGS. 1 and 2, a liquid developer using the liquid developer obtained in each of the examples and comparative examples on the photoreceptor of the image forming apparatus. A layer was formed. Next, the toner particles on the photoconductor and the toner particles on the intermediate transfer portion after the liquid developer layer passed between the photoconductor and the intermediate transfer portion were collected with a tape. Each tape used for sampling was affixed on a recording paper, and the concentration of each toner particle was measured. After the measurement, a value obtained by dividing the concentration of the toner particles collected on the intermediate transfer portion by the sum of the concentration of the toner particles collected on the photoconductor and the concentration of the toner particles collected on the intermediate transfer portion is 100. A value obtained by multiplying by is obtained as transfer efficiency, and evaluated according to the following criteria.
A: The transfer efficiency is 96% or more, and the transfer efficiency is particularly excellent.
B: The transfer efficiency is 90% or more and less than 96%, and the transfer efficiency is excellent.
C: The transfer efficiency is 80% or more and less than 90%, and there is no practical problem.
D: Transfer efficiency is less than 80% and inferior to transfer efficiency.

[2.4] Storage Stability Test The liquid developers obtained in each Example and Comparative Example were allowed to stand for 7 days in an environment of temperature: 40 ° C. and humidity: 85% RH.
Thereafter, the residual ratio of the image density was measured in the same manner as in the above [2.1.1], and the difference in the residual ratio of the image density before and after being left in the environment was determined and evaluated according to the following criteria.

  Note that the evaluation of the storage stability was not performed for the case where the evaluation of [2.1.1] fixing strength was D or E. As recording media, high-quality paper (LPCPPA4) manufactured by Seiko Epson Corporation, high-quality paper manufactured by Mitsubishi Paper Industries Co., Ltd. (thickness of gold diamond 120 μm), coated paper manufactured by Mitsubishi Paper Industries Co., Ltd. (pearl coating thickness 82 μm) ), Zanders Coated Paper (Iconosilk White, thickness: 122 μm), and PET film (thickness: 100 μm). It can be said that the smaller the difference in the residual ratio of image density, the better the storage stability.

A: Difference in residual ratio of image density is less than 3%.
B: Difference in residual ratio of image density is 3% or more and less than 10%.
C: The difference in the residual ratio of the image density is 10% or more and less than 20%.
D: The difference in residual ratio of image density is 20% or more and less than 40%.
E: Difference in residual ratio of image density is 40% or more.

[2.5] Concavities and convexities in the printing section Using an image forming apparatus as shown in FIGS. 1 and 2, an image of a predetermined pattern is recorded with the liquid developer obtained in each of the examples and the comparative examples. It was formed on high-quality paper (LPCPPA4) manufactured by Seiko Epson as a medium. Thereafter, heat fixing was performed at a fixing temperature of 120 ° C. and a conveyance speed of 250 mm / s. In Comparative Examples 2 and 3, after heating, the portion of the recording medium on which the toner image was formed was irradiated with 240 mJ / cm ² of ultraviolet light from a metal halide lamp.
Thereafter, the toner image (fixed image) was visually observed and evaluated according to the following criteria.

A: Unwanted unevenness is not observed at all in the printed part.
B: Involuntary unevenness is hardly observed in the printed part.
C: Involuntary unevenness is slightly observed in the printed part.
D: Unintentional unevenness is clearly observed in the printed part.
E: Unintentional unevenness is noticeably observed in the printed part.

[2.6] Odor Generation Using an image forming apparatus as shown in FIGS. 1 and 2, images of a predetermined pattern using the liquid developers obtained in the respective examples and comparative examples are used as recording media. It was formed on high-quality paper (LPCPPA4) manufactured by Seiko Epson. Thereafter, thermal fixing was performed at a fixing temperature of 120 ° C. and a conveyance speed of 250 mm / s. In Comparative Examples 2 and 3, after heating, the portion of the recording medium on which the toner image was formed was irradiated with 240 mJ / cm ² of ultraviolet light from a metal halide lamp.
The above processing was continuously performed on 1000 recording media, and the state of odor generation at that time was evaluated according to the following criteria.
A: Odor is not generated at all.
B: Odor is hardly generated.
C: Odor is slightly generated.
D: Odor generation is remarkable.

  These results are shown in Table 2. In the table, high-quality paper (LPCPPA4) manufactured by Seiko Epson Corporation is “M1”, high-quality paper manufactured by Mitsubishi Paper Industries (thickness 120 μm) is “M2”, and coated paper manufactured by Mitsubishi Paper Industries Co., Ltd. (Pearl coat thickness 82 μm) is indicated by “M3”, Zanders Coated paper (Iconosilk white, thickness 122 μm) is indicated by “M4”, and PET film (thickness 100 μm) is indicated by “M5”.

  As is apparent from Table 2, the liquid developer of the present invention is excellent in fixability (fixing strength, low-temperature fixability, high-speed printability), and can produce a stable toner image (fixed image) with a small amount of energy. Could be formed. Further, the liquid developer of the present invention was excellent in development efficiency, transfer efficiency, and storage stability. In addition, when the liquid developer of the present invention is used, the occurrence of unintended irregularities in the printing portion is effectively prevented, and the generation of odor during image formation is also effectively prevented. On the other hand, satisfactory results were not obtained with the liquid developer of the comparative example.

  1000: Image forming apparatus 10Y, 10M, 10C, 10K ... Photoconductor 11Y ... Charging roller 12Y ... Exposure unit 13M, 13Y ... Photoconductor squeeze roller 14M, 14Y ... Cleaning blade 15M, 15Y ... Developer recovery unit 16Y ... Static elimination unit 17Y ... Photoconductor cleaning blade 18Y ... Developer collection unit 20Y, 20M, 20C, 20K ... Development roller 21Y ... Development roller cleaning blade 24Y ... Developer collection unit 30Y, 30M, 30C, 30K ... Development unit 31Y ... Liquid developer storage unit 31aY ... Supply unit 31bY ... Recovery unit 31cY ... Partition 32Y ... Applying roller 33Y ... Regulator blade 34Y ... Developer stirring roller 35Y ... Communication unit 36Y ... Recovery screw 40 ... Intermediate transfer unit 41 ... Belt drive roller 4, 45 ... driven roller 46 ... intermediate transfer part cleaning blade 47 ... developer recovery part 48 ... non-contact type bias applying member 49 ... tension roller 51Y, 51M, 51C, 51K ... primary transfer backup roller 52Y ... intermediate transfer part squeeze Device 53Y ... Intermediate transfer unit squeeze roller 55Y ... Intermediate transfer unit squeeze cleaning blade 56Y ... Developer recovery unit 60 ... Secondary transfer unit 64 ... Upstream secondary transfer roller 65 ... Downstream secondary transfer roller 66, 68 ... Secondary Transfer roller cleaning blades 67, 69 ... Developer collection unit 90Y, 90M, 90C, 90K ... Liquid developer supply unit 91Y, 91M, 91C, 91K ... Liquid developer tank 92Y, 92M, 92C, 92K ... Insulating liquid tank 93Y , 93M, 93C 93K ... Liquid developer mixing tank 100Y ... Development unit 101Y ... Photoconductor squeeze device F40 ... Fixing section (fixing device) F5 ... Recording medium

Claims (12)

A liquid developer in which toner particles as a dispersoid are dispersed in an insulating liquid as a dispersion medium,
The dispersion medium is composed of a non-volatile liquid,
The dispersoid contains a colorant and an oxidative polymerization type compound, and forms a liquid at normal temperature and pressure,
A liquid developer, wherein a viscosity η1 of the dispersoid at 25 ° C. is larger than a viscosity η2 of the dispersion medium at 25 ° C.   The liquid developer according to claim 1, wherein the oxidatively polymerizable compound constituting the dispersoid includes an unsaturated fatty acid ester having an iodine value of 100 or more.   The liquid developer according to claim 1, wherein the dispersoid has a viscosity η1 at 25 ° C. of 30 mPa · s or more and 10,000 mPa · s or less.   4. The liquid developer according to claim 1, wherein the dispersion medium has a viscosity η2 at 25 ° C. of 5 mPa · s or more and 1000 mPa · s or less.   5. The difference (η1−η2) between the viscosity η1 of the dispersoid at 25 ° C. and the viscosity η2 of the dispersion medium at 25 ° C. is 25 mPa · s or more and 9995 mPa · s or less. Liquid developer.   The liquid developer according to claim 1, wherein the dispersoid has an average particle size of 0.1 μm or more and 4.0 μm or less.   The liquid developer according to claim 1, wherein a content of the dispersoid in the liquid developer is 1% by mass or more and 40% by mass or less.   The liquid developer according to claim 1, wherein the liquid developer further contains an oxidation polymerization accelerator.   The liquid developer according to claim 8, wherein the liquid developer contains 0.01 to 5 parts by weight of the oxidative polymerization accelerator with respect to 100 parts by weight of the dispersoid.   The liquid developer according to claim 1, wherein the liquid developer further contains a charge adjusting agent.   The liquid developer according to claim 10, wherein the content of the charge adjusting agent in the liquid developer is 0.01% by mass or more and 5% by mass or less.   The liquid developer according to any one of claims 1 to 11, wherein the dispersoid constituting the liquid developer is made of a material in which a part of the oxidative polymerization type compound is oxidatively polymerized.

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