JP2016142847A - Method of manufacturing liquid developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a liquid developer such that toner particles have both a small particle size and high dispersibility of a coloring agent of the toner particles.SOLUTION: A method of manufacturing a liquid developer according to the present invention is a method of manufacturing a liquid developer by dispersing toner particles in an insulation liquid, and comprises: a first agent preparing process of preparing a first agent by incorporating first particles including first resin in a first organic solvent; a second agent preparing process of preparing a second agent by incorporating second resin and a coloring agent in a second organic solvent; and a toner particle preparing process of mixing the first agent and second agent together so as to prepare toner particles having a core/shell structure consisting of a shell layer including the first resin and core particles including the second resin, the first organic solvent having a specific permittivity of 1 to 4 at 20°C and the second agent having a viscosity of 1,000 to 25,000 nPa s at 50°C.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a liquid developer.

  Conventionally, a powdery developer has been widely used as a developer used in an electrophotographic image forming apparatus. However, with a powdery developer, it is necessary to increase the particle size of the powder from the viewpoint of preventing scattering. When the particle size of the toner powder is large, it tends to be difficult to obtain a high-quality image.

  On the other hand, the liquid developer used in the development method by the wet electrophotographic method is obtained by dispersing toner particles including a colorant and a resin in an insulating liquid. For this reason, in the liquid developer, even if the particle size of the toner particles is reduced, the toner particles can be prevented from scattering, so that the toner particles can be reduced in size, thereby improving the image quality. Can do.

  For example, Japanese Unexamined Patent Application Publication No. 2009-96994 (Patent Document 1) discloses a liquid developer including toner particles having a core / shell structure including a shell layer including a first resin and core particles including a second resin. Is disclosed. By adopting such a core / shell structure, toner particles having a small particle size and a sharp particle size distribution can be obtained.

  However, when the particle diameter of the toner particles containing the colorant is reduced, the dispersibility of the colorant in the toner particles may be reduced. When the dispersibility of the colorant is lowered, it becomes difficult to obtain a sufficient image density. In response to such a problem, for example, JP 2013-97294 A (Patent Document 2) discloses a liquid developer containing toner particles containing a basic polymer dispersant containing a structural unit derived from ε-caprolactone. It is disclosed. Patent Document 2 discloses that the dispersibility of the colorant in the toner particles is improved by including such a dispersant in the toner particles.

JP 2009-96994 A JP 2013-97294 A

  However, the degree of improvement in dispersibility with the above technique is still insufficient. In addition, by simply adopting the technique described in Patent Document 2 for toner particles having a core / shell structure, sufficient dispersibility of the colorant may not be ensured. In particular, in toner particles having a core / shell structure, the colorant tends to be unevenly distributed on the surface of the particle (or the surface of the core particle when the core particle includes the colorant). As a result, it becomes difficult to form an image having a sufficient image density with a liquid developer having toner particles in which the colorant is unevenly distributed on the surface.

  The method for producing a liquid developer of the present invention has been made in view of the above situation, and the object is to reduce the particle size of the toner particles and to highly disperse the colorant in the toner particles. Another object of the present invention is to provide a method for producing a liquid developer that is compatible with properties.

  The present inventors do not modify the components constituting the core / shell structure, such as the type of resin constituting the core particle and the type of resin constituting the shell layer, or add other components. We thought that the above problem could be solved by controlling the method. And by repeating earnest examination, in the manufacturing method, the 1st agent at the time of mixing the 1st agent containing resin for shell layers, and the 2nd agent containing resin for core particles, It has been found that the interrelationship with the second agent is greatly involved in the dispersibility of the colorant. Based on this knowledge, the present inventors have conducted further intensive studies, and by making the characteristics of the first organic solvent, which is a component of the first agent, and the second agent specific, toner It was found that the dispersibility of the colorant in the particles can be improved, and the present invention has been completed.

  That is, the present invention is a method for producing a liquid developer in which toner particles are dispersed in an insulating liquid, and a first agent for preparing a first agent in which a first resin is contained in a first organic solvent. A first agent preparation step, a second agent preparation step for preparing a second agent comprising a second resin and a colorant contained in a second organic solvent, a first agent and a second agent, A toner particle preparation step of preparing a toner particle having a core / shell structure composed of a shell layer containing a resin and a core particle containing a second resin, wherein the first organic solvent has a dielectric constant at 20 ° C. The rate is 1 or more and 4 or less, and the second agent has a viscosity at 50 ° C. of 1000 mPa · s or more and 25000 mPa · s or less.

  In the above liquid developer production method, the second resin preferably has an endothermic start temperature in differential scanning calorimetry of 50 ° C. or higher and 60 ° C. or lower.

  In the method for producing a liquid developer, the toner particles preferably have a volume average particle diameter of 0.8 μm or more and 4.0 μm or less.

  In the liquid developer production method, the toner particles preferably have a volume distribution variation coefficient of 10% to 50%.

  In the liquid developer production method, the first organic solvent preferably accounts for 99% by mass or more of the total amount of the insulating liquid.

  The method for producing a liquid developer of the present invention can granulate toner particles having a high dispersibility of a colorant despite having a sufficiently small core / shell structure. Thus, it is possible to produce a liquid developer that achieves both a reduction in toner particle size and a high dispersibility of the colorant in the toner particles. Therefore, according to the method for producing a liquid developer of the present invention, a liquid developer capable of forming a high-quality and high-density image can be produced.

1 is a schematic conceptual diagram of an electrophotographic image forming apparatus.

  Hereinafter, embodiments according to the present invention will be described in more detail, but the present invention is not limited to these.

  The method for producing a liquid developer according to the present embodiment is a method for producing a liquid developer (X) in which toner particles (C) are dispersed in an insulating liquid, and the first resin (a) is the first. A first agent preparation step for preparing the first agent (W) contained in the organic solvent (L), and a second resin (b) and a colorant are contained in the second organic solvent (M). A second agent preparation step for preparing the second agent (O), a shell layer containing the first resin (a), the first agent (W) and the second agent (O), and a second resin; A toner particle preparation step of preparing toner particles (C) having a core / shell structure composed of core particles containing (b).

  In particular, the present embodiment is characterized in that the first organic solvent (L) has a relative dielectric constant at 20 ° C. of 1 or more and 4 or less, and the viscosity of the second agent (O) at 50 ° C. is 1000 mPa · s. It is above 25000 mPa · s. In the present specification, in order to facilitate understanding, each component (a), (b), (A), (C), (L), (M), (O), (W) is included in each component. , (X) or the like may be attached. Hereinafter, each step will be described.

≪First agent preparation process≫
In this step, a first agent (W) is prepared in which the first resin (a) is contained in the first organic solvent (L). One of the characteristics of this step is that the relative permittivity of the first organic solvent (L) at 20 ° C. is 1 or more and 4 or less. The first resin (a) is a main component of the shell layer of the toner particles (C).

<Method for preparing first agent (W)>
As a method for preparing the first agent (W), for example, the first resin (a) is prepared by polymerizing a monomer that is a constituent unit of the first resin (a) with the first organic solvent (L). Thus, the method of preparing the first agent (W) and the first agent (W) are prepared by dispersing the first resin (a) in the first organic solvent (L). ) Can be mentioned.

As the former preferred method, the following method [1] can be mentioned.
[1] A monomer that is a constituent unit of the first resin (a) is polymerized in a solvent containing the first organic solvent (L). Thereby, the 1st agent (W) in which the 1st resin (a) is contained in the 1st organic solvent (L) is manufactured directly. If necessary, a solvent other than the first organic solvent (L) is distilled off from the first agent (W). In addition, when distilling off solvents other than the 1st organic solvent (L), a low boiling point component may be distilled off among 1st organic solvents (L). This is the same in the step of distilling off solvents other than the first organic solvent (L) shown below.

As the latter preferred method, the following methods [2] to [4] can be mentioned.
[2] Solid (powder, etc.) of the first resin (a) obtained in advance by the polymerization reaction is pulverized using a mechanical pulverizer or jet type pulverizer, and then classified. Thereby, the particle | grains which consist of 1st resin (a) are obtained. The obtained particles are dispersed in the first organic solvent (L) in the presence of a suitable dispersant (for example, a known surfactant and oil-soluble polymer).

  [3] A resin solution in which the first resin (a) obtained in advance by a polymerization reaction is dissolved (even if this resin solution is obtained by polymerizing the first resin (a) in a solvent. Spray a good mist. Thereby, the particle | grains which consist of 1st resin (a) are obtained. The obtained particles are dispersed in the first organic solvent (L) in the presence of a suitable dispersant.

  [4] A resin solution in which the first resin (a) obtained in advance by a polymerization reaction is dissolved (this resin solution may be obtained by polymerizing the first resin (a) in a solvent. The first organic solvent (L), which is a poor solvent, is added, or the resin solution obtained by dissolving the first resin (a) in advance is cooled to precipitate the first resin (a). After that, the first organic solvent (L) is added. If necessary, a solvent other than the first organic solvent (L) is distilled off.

  In the above, “polymerization reaction” means a known polymerization reaction such as addition polymerization, ring-opening polymerization, polyaddition, addition condensation and condensation polymerization, and is an emulsion polymerization method, a soap-free emulsion polymerization method, a seed polymerization method, a suspension polymerization method. The monomer can be polymerized by using either the turbid polymerization method or the dispersion polymerization method. In addition, although the case where a monomer was used was demonstrated above, an oligomer may be sufficient as long as it is what is called a "precursor" which can become 1st resin (a) by a polymerization reaction. In the above method, when a dispersion aid is used, for example, an organic solvent and a plasticizer can be used in combination as the dispersion aid.

  According to the above methods [1] to [4], the first resin (a) in which the first resin (a) is contained in the first organic solvent (L) is used as the resin solution for the shell layer. In particular, the first agent (W) containing only the first resin (a) as the resin for the shell layer can be prepared. When the first agent (W) contains a resin other than the first resin (a) as the resin for the shell layer, the monomer (or the first resin (a) in the method [1] above (or Any other monomer (or precursor) may be used together with the precursor, and in the methods [2] to [4], another resin may be used together with the first resin (a). Further, another resin (or resin solution) prepared by any one of the above methods [1] to [4] is added to the resin solution prepared by any one of the above methods [1] to [4]. It may be added.

<First Agent (W)>
The 1st agent (W) prepared by this process contains the 1st resin (a) in the 1st organic solvent (L). More specifically, the first agent (W) is obtained by dispersing the first resin (a) in the first organic solvent (L). The dispersion of the first resin (a) means that the first resin (a) exists as particles (hereinafter referred to as “first particles (A)”) in the first organic solvent (L).

  As long as the 1st agent (W) contains the 1st resin (a), it can contain other arbitrary ingredients. Examples of other optional components include other resins (known resins used for toner particles), colorants and additives described later. These other optional components may be dispersed in or dissolved in the first agent (W). In addition, when other resin other than 1st resin (a) is contained in 1st agent (W), 1st particle | grains (A) which consist of 1st resin (a), and others in 1st agent (W) There are cases where the second particles made of the resin are included, and the first particles (A) made of the first resin (a) and other resins.

<First particle (A)>
As long as the 1st particle (A) contains the 1st resin (a), it can contain other arbitrary ingredients. Examples of other components include other known resins used for toner particles, colorants and additives described later. The volume average particle diameter of the first particles (A) is not particularly limited, but is preferably 0.01 μm or more and 0.50 μm or less from the viewpoint of production efficiency of toner particles having a core / shell structure. The volume average particle diameter of the first particles (A) can be controlled by appropriately adjusting the shearing force, interfacial tension, and the like applied to the first resin (a) in each of the above adjustment methods.

  Here, in this specification, “volume average particle diameter” means a median diameter in a volume-based particle size distribution (volume distribution), and covers all toner particles (C) contained in the liquid developer (X). Means an average particle size of In the present specification, “volume average particle diameter” may be simply referred to as “particle diameter”.

  The volume average particle diameter can be measured using a laser diffraction / scattering particle size distribution measuring device, a flow particle image analyzer, or the like. As the former, for example, “LA-920” manufactured by HORIBA, Ltd. or “Multisizer III” manufactured by Beckman Coulter, Inc., “ELS-800” manufactured by Otsuka Electronics Co., Ltd. using a laser Doppler method as an optical system. Examples of the latter include “FPIA-3000S” manufactured by Sysmex. In addition, the value of the volume average particle diameter in this specification is a measured value by “LA-920”.

<First resin (a)>
The first resin (a) used in this step may be a thermoplastic resin or a thermosetting resin. Specifically, as the first resin (a), vinyl resin, polyester resin, polyurethane resin, epoxy resin, polyamide resin, polyimide resin, silicon resin, phenol resin, melamine resin, urea resin, aniline resin, ionomer resin, And polycarbonate resin etc. are mentioned. Preferably, it is at least one of a vinyl resin, a polyester resin, a polyurethane resin, and an epoxy resin, and more preferably at least one of a polyester resin and a polyurethane resin.

  As the vinyl resin, a homopolymer obtained by homopolymerization of a monomer having a polymerizable double bond (a homopolymer including a bond unit derived from a vinyl monomer) or a polymerizable double bond Examples thereof include a copolymer obtained by copolymerizing two or more monomers (a copolymer containing a bond unit derived from a vinyl monomer).

  Examples of the monomer having a polymerizable double bond include hydrocarbons such as alkenes having 2 to 30 carbon atoms, alkadienes having 4 to 30 carbon atoms, mono- or dicycloalkenes having 6 to 30 carbon atoms, Examples thereof include unsaturated monocarboxylic acids having 3 to 15 carbon atoms, unsaturated dicarboxylic acids having 3 to 30 carbon atoms, and salts thereof.

  Examples of polyester resins include polycondensates of polyols with polycarboxylic acids, acid anhydrides of polycarboxylic acids, or lower alkyl (alkyl group having 1 to 4 carbon atoms) esters of polycarboxylic acids. A known polycondensation catalyst or the like can be used for the polycondensation reaction.

  Examples of the polyol include a diol and a polyol having a valence of 3 to 8 or more. Examples of the polycarboxylic acid include dicarboxylic acids and polycarboxylic acids having a valence of 3 to 6 or more. Examples of acid anhydrides of polycarboxylic acids include acid anhydrides of dicarboxylic acids and acid anhydrides of polycarboxylic acids. Examples of the lower alkyl ester of polycarboxylic acid include a lower alkyl ester of dicarboxylic acid and a lower alkyl ester of polycarboxylic acid. The ratio of polyol to polycarboxylic acid is such that the equivalent ratio of hydroxyl group [OH] to carboxyl group [COOH] ([OH] / [COOH]) is preferably 2/1 to 1/5. What is necessary is just to set so that it may become 1.5 / 1-1/4 more preferably, and still more preferably 1.3 / 1-1/3.

  Examples of polyurethane resins include polyisocyanates and active hydrogen-containing compounds {for example, water; polyols (for example, diols (including diols having functional groups other than hydroxyl groups) or polyols)]; polycarboxylic acids [for example, dicarboxylic acids Or a polycarboxylic acid, etc.]; a polyester polyol obtained by polycondensation of a polyol and a polycarboxylic acid; a ring-opening polymer of a lactone having 6 to 12 carbon atoms; a polyamine; a polythiol; It is preferable that Further, a terminal isocyanate group prepolymer obtained by reacting a polyisocyanate and the active hydrogen-containing compound is reacted with an equal amount of primary and / or secondary monoamine with respect to the isocyanate group of the terminal isocyanate group prepolymer. An amino group-containing polyurethane resin may be obtained. The content of carboxyl groups in the polyurethane resin is preferably 0.1 to 10% by mass.

  Melting | fusing point of 1st resin (a) becomes like this. Preferably it is 0-220 degreeC, More preferably, it is 30-150 degreeC, More preferably, it is 40-80 degreeC. From the viewpoint of the particle size distribution of the toner particles (C), the powder flowability of the liquid developer (X), the heat storage stability and the stress resistance, the melting point of the first resin (a) constituting the shell layer is The temperature is preferably equal to or higher than the temperature set when the liquid developer (X) is produced. If the melting point of the first resin (a) is lower than the temperature set when the liquid developer is produced, it may be difficult to prevent the toner particles from being coalesced, and the toner particles may break up. It may be difficult to prevent. Further, there is a possibility that the variation in the particle diameter of the toner particles becomes large.

  The melting point of the resin was measured in accordance with a method prescribed in ASTM D3418-82 using a differential scanning calorimeter (such as “DSC20” or “SSC / 580” manufactured by Seiko Instruments Inc.). It is.

  The first resin (a) preferably has a number average molecular weight of 15000 or more and 80000 or less (hereinafter sometimes abbreviated as “Mn”), more preferably 20000 or more and 40000 or less. If Mn is less than 15000, the resin tends to be excessively soft, which tends to cause an offset, and if it exceeds 80000, the fixing strength to the recording medium tends to decrease.

  In the present specification, the Mn of the resin is measured under the following conditions by using gel permeation chromatography (GPC) for the soluble content of tetrahydrofuran (hereinafter abbreviated as “THF”). It is.

Measuring device: “HLC-8120” manufactured by Tosoh Corporation
Column: “TSKgelGMHXL” (2) manufactured by Tosoh Corporation and “TSKgelMultiporeHXL-M” (1) manufactured by Tosoh Corporation
Sample solution: 0.25 mass% THF solution Injection amount of THF solution into the column: 100 μl
Flow rate: 1 ml / min Measurement temperature: 40 ° C
Detection device: Refractive index detector Reference material: 12 standard polystyrene (TSK standard POLYSTYRENE) manufactured by Tosoh Corporation (molecular weight: 500, 1050, 2800, 5970, 9100, 18100, 37900, 96400, 190000, 355000, 1090000, 2890000).

<First organic solvent (L)>
As described above, the first organic solvent (L) used in this step has a relative dielectric constant of 1 or more and 4 or less at 20 ° C. Since the first organic solvent (L) finally constitutes the insulating liquid of the liquid developer (X) to be produced, the first organic solvent (L) has a relative dielectric constant at 20 ° C. of 1 or more and 4 or less. The charge maintaining property of the agent (X) can be improved. It is preferable that the insulating liquid constituting the liquid developer (X) is substantially only the first organic solvent (L). However, as long as the effects of the present embodiment can be obtained, other insulating solvents are included. May be. However, the content of other organic solvents is preferably 1% by mass or less.

The relative dielectric constant of the first organic solvent (L) is calculated using the dielectric constant of the first organic solvent (L) obtained by the bridge method (JIS C2101-1999). Specifically, the capacitance C ₀ (pF) before filling the first organic solvent (L) and the equivalent parallel capacitance C _x (pF) in the state filled with the first organic solvent (L) Is substituted into the following formula (1) to calculate the dielectric constant ε of the first organic solvent (L). The relative dielectric constant of the first organic solvent (L) is obtained by the ratio between the calculated ε and the relative dielectric constant of the air 1.000585.
ε = C _x / C ₀ Formula (1).

  In addition to the above characteristics, the first organic solvent (L) is preferably a non-hydrophilic organic solvent, and preferably has low odor and toxicity. In general, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes and the like can be mentioned. In particular, liquid paraffin such as normal paraffin solvent and isoparaffin solvent is preferable in terms of odor, harmlessness and cost. Specifically, “Moresco White” (trade name) manufactured by Matsumura Oil Research Co., Ltd., “Isopar” (trade name) manufactured by ExxonMobil, and “Shellsol” (trade name) manufactured by Shell Chemicals Japan Co., Ltd. ), “IP Solvent 1620”, “IP Solvent 2028”, “IP Solvent 2835” (all trade names) manufactured by Idemitsu Kosan Co., Ltd., and the like.

<Colorant>
In this step, as a colorant that can be optionally used, a conventionally known colorant (dye, pigment, etc.) can be used without any particular limitation. Examples of the colorant include phthalocyanine-based, azo, disazo, polyazo-based azo-based, anthraquinone-based, quinacridone-based, dioxazine-based, perinone-based, thioindigo-based, or isoindoline-based organic colorants. . The volume average particle size of the colorant is preferably 0.3 μm or less. If the volume average particle size of the colorant exceeds 0.3 μm, dispersion may be deteriorated, resulting in a decrease in glossiness and the inability to achieve a desired color.

<Additives>
Additives that can be optionally used in this step include colorant dispersants, waxes, charge control agents, fillers, antistatic agents, mold release agents, UV absorbers, antioxidants, antiblocking agents, and heat resistance. A stabilizer, a flame retardant, etc. can be mentioned. Among these, the use of the colorant dispersant is preferable because it has a function of uniformly dispersing the colorant (pigment) in the toner particles. The colorant dispersant is more preferably one that does not dissolve in the insulating liquid. Specifically, “Ajisper PB-821” (trade name) and “Azisper PB-822” manufactured by Ajinomoto Fine Techno Co., Ltd. (Trade name), “Ajisper PB-881” (trade name), and the like.

  As described above, in this step, the first resin (a) is converted into the first organic solvent (L) by using an appropriate method according to the types of the first resin (a) and the first organic solvent (L). A first agent (W) contained therein can be prepared.

≪Second agent preparation process≫
In this step, a second agent (O) is prepared in which the second resin (b) and the colorant are contained in the second organic solvent (M). One of the characteristics of this step is that the viscosity of the second agent (O) at 50 ° C. is 1000 mPa · s or more and 25000 mPa · s or less. In the second agent (O) prepared in this step, the second resin may be dispersed or dissolved. The second resin (b) is a main constituent component of the core particles constituting the toner particles.

<Method for Preparing Second Agent (O)>
Regarding the preparation method of the second agent (O), a method of adding the second resin (b) and the colorant to one kind of the second organic solvent (M) may be used. Alternatively, two resins (b) may be added, a coloring agent may be added to the other second organic solvent (M), and these may be mixed. When the second organic solvent (M) is a mixed solvent of two or more kinds, it finally contains the second resin (b) and the colorant (that is, before mixing with the first agent (W)). The organic solvent may be the second organic solvent (M) which is a mixed solvent, and the viscosity of the second agent (O) at 50 ° C. may be 1000 mPa · s or more and 25000 mPa · s or less.

  Here, the viscosity at 50 ° C. of the prepared second agent (O) is 1000 mPa · s or more and 25000 mPa · s or less. When the viscosity is less than 1000 mPa · s, the toner particles may be too small, and when it exceeds 25000 mPa · s, the toner particles may be too large. The viscosity at 50 ° C. of the second agent is more preferably 2000 mPa · s to 22000 mPa · s, and further preferably 15000 mPa · s to 22000 mPa · s.

  The viscosity at 50 ° C. of the second agent (O) can be measured using, for example, a B-type viscometer. In the present specification, numerical values measured using a rotational vibration viscometer (trade name: “Viscomate VM-10A”, manufactured by Tokyo Glass Instrument Co., Ltd.) are shown. In this step, after appropriately selecting the second resin (b) and the second organic solvent (M), the addition amount of the second resin (b) to the second organic solvent (M), or the second organic solvent ( By adjusting the use amount of M), the viscosity of the second agent (O) at 50 ° C. can be adjusted within the above range.

<Second agent (O)>
The second agent (O) prepared by this step contains the second resin (b) and a colorant, and other optional components as long as the viscosity at 50 ° C. is 1000 mPa · s or more and 25000 mPa · s or less. Can be included. Examples of other optional components include other known resins and additives used for toner particles. In addition, since the additive which can be used arbitrarily in this process is the same as the additive used by the above-mentioned <1st agent (O)>, the description is not repeated.

  The content (mass%) of the second resin (b) in the second agent (O) is not particularly limited as long as the viscosity value is satisfied, but is preferably 5 mass% or more and 60 mass% or less. When the amount is 5% by mass or more, the production amount of toner particles is excellent, and when the amount is 60% by mass or less, the toner particles are easily formed.

  Further, the content (mass%) of the colorant in the second agent (O) is not particularly limited as long as the viscosity value is satisfied, but is preferably 20 mass% or more and 55 mass% or less. When the amount is 20% by mass or more, the production amount of toner particles is excellent.

<Second resin (b)>
The second resin (b) used in this step may be a thermoplastic resin or a thermosetting resin. Further, it may be a linear polymer or a non-linear polymer. As the second resin (b), vinyl resin, polyester resin, polyurethane resin, epoxy resin, polyamide resin, polyimide resin, silicon resin, phenol resin, melamine resin, urea resin, aniline resin, ionomer resin, polycarbonate resin, etc. Is mentioned. Preferably, it is at least one of a vinyl resin, a polyester resin, a polyurethane resin, and an epoxy resin, and more preferably a polyester resin. The details of the polyester resin are the same as those of the above-described polyester resin, and therefore the description thereof will not be repeated.

  Further, the second resin (b) preferably has an endothermic start temperature in differential scanning calorimetry of 50 ° C. or higher and 60 ° C. or lower, and more preferably 50 ° C. or higher and 55 ° C. or lower. By being 50 degreeC or more, it can prevent that a toner particle (C) fuse | melts at less than 50 degreeC. Therefore, it is possible to prevent melting of the toner particles (C) constituting the image when the two recording media are stored in a high temperature environment with the surfaces on which the images are formed being overlapped with each other. The occurrence of document offset can be prevented. Further, when the temperature is 60 ° C. or lower, the toner can be fixed at a relatively low temperature.

  The endothermic start temperature in the differential scanning calorimetry of the second resin (b) is, for example, as follows using a commercially available differential scanning calorimeter (for example, trade name: “DSC210”, manufactured by Seiko Instruments Inc.). Can be measured. That is, first, the differential scanning calorimetry of the second resin (b) is performed according to the following conditions.

Measuring device: “DSC210” manufactured by Seiko Instruments Inc.
Mass of measurement sample (second resin (b)): 5 mg
Temperature increase rate: 10 ° C./min.

  Next, the obtained result is a curve (DSC curve) in which the vertical axis represents heat flow and the horizontal axis represents temperature. The endothermic reaction appears as a valley peak in the DSC curve, and the temperature at the bottom of the peak (the point at which inflection starts after leaving the base line) becomes the endothermic start temperature in differential scanning calorimetry.

  Moreover, when measuring the said endothermic start temperature of 2nd resin (b) using insulating liquid (X), it can measure as follows using a differential scanning calorimeter. That is, first, the toner particles (C) are separated from the liquid developer (X). Specifically, the supernatant is removed by centrifuging about 1 g of the liquid developer (X). The remaining solid component is washed with an organic solvent (for example, hexane) and then dried at room temperature using a vacuum dryer or the like. These series of operations may be performed twice or more. By these processes, the toner particles (C) are separated from the liquid developer (X).

Next, differential scanning calorimetry of the toner particles (C) is performed according to the following conditions.
Measuring device: “DSC210” manufactured by Seiko Instruments Inc.
Mass of measurement sample (toner particle (C)): 5 mg
Temperature increase rate: 10 ° C./min.

  Next, regarding the obtained result, the endothermic start temperature in the differential scanning calorimetry is calculated by the same method as described above. The calculated endothermic start temperature corresponds to the endothermic start temperature of the toner particles (C). In the toner particles (C) having a core / shell structure, the mass ratio of the shell layer (D) and the core particles (E) [ (D) :( E)] is 35:65 to 1:99, the endothermic start temperature of the toner particles (C) is set to the resin constituting the core particles (E), that is, the second resin (b). It can be regarded as the endothermic start temperature.

  The Mn of the second resin (b) is preferably 2000 or more and 20000 or less, and more preferably 5000 or more and 10,000 or less. If Mn is less than 2000, the resin tends to be excessively soft and offset tends to occur. If it exceeds 20000, the resin is difficult to melt, and the fixing strength tends to decrease. The Mn of the second resin (b) can also be measured according to the above-described method for measuring Mn of the resin.

<Colorant>
A conventionally known colorant can be used for the colorant used in this step without any particular limitation. Examples of the colorant include phthalocyanine-based, azo, disazo, polyazo-based azo-based, anthraquinone-based, quinacridone-based, dioxazine-based, perinone-based, thioindigo-based, or isoindoline-based organic colorants. . The volume average particle size of the colorant is preferably 0.3 μm or less. If the volume average particle size of the colorant exceeds 0.3 μm, dispersion may be deteriorated, resulting in a decrease in glossiness and the inability to achieve a desired color.

<Second organic solvent (M)>
The second organic solvent (M) used in this step is preferably an organic solvent that can dissolve the second resin (b), and is preferably selected as appropriate according to the type of the second resin (b). . Specifically, as the second organic solvent (M), aromatic hydrocarbon solvents such as toluene, xylene, ethylbenzene and tetralin; aliphatic or alicyclic such as n-hexane, n-heptane, mineral spirit and cyclohexane Hydrocarbon solvents; halogen solvents such as methyl chloride, methyl bromide, methyl iodide, methylene dichloride, carbon tetrachloride, trichloroethylene and perchloroethylene; ethyl acetate, butyl acetate, methoxybutyl acetate, methyl cellosolve acetate and ethyl cellosolve Ester or ester ether solvents such as acetate; ether solvents such as diethyl ether, THF, dioxane, ethyl cellosolve, butyl cellosolve and propylene glycol monomethyl ether; acetone, methyl Ketone solvents such as til ketone, methyl isobutyl ketone, di-n-butyl ketone and cyclohexanone; alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, 2-ethylhexyl alcohol and benzyl alcohol Amide solvents such as dimethylformamide and dimethylacetamide; sulfoxide solvents such as dimethyl sulfoxide; heterocyclic compounds solvents such as N-methylpyrrolidone; mixed solvents in which two or more of the above solvents are mixed, etc. Is mentioned.

  In particular, the boiling point of the second organic solvent (M) is preferably 100 ° C. or lower, more preferably 90 ° C. or lower, from the viewpoint of reducing odor and from the viewpoint of ease of distillation.

In addition, the second organic solvent (M) is a first organic solvent (L) from the viewpoint of securing the solubility of the second resin (b) and the dispersibility of the second resin (b) in the toner particle preparation step described later. And a good solvent for the second resin (b) rather than the first organic solvent (L). Specifically, the SP value of the second organic solvent (M) is preferably 8.5 to 20 (cal / cm ³ ) ^1/2 , more preferably 10 to 19 (cal / cm ³ ) ^{1 /. 2} .

  When a mixed solvent is used as the second organic solvent (M), the weighted average value of the SP values calculated from the SP values of the respective solvents on the assumption that additivity is established may be within the above range. If the SP value of the organic solvent (M) is outside the above range, the solubility of the second resin (b) may be insufficient. In this specification, “SP value” is a method by Fedors [Polym. Eng. Sci. 14 (2) 152, (1974)].

  Examples of the second organic solvent (M) satisfying the above boiling point and the preferable range of the SP value include acetone, isopropanol and the like.

  As described above, in this step, after appropriately selecting the second resin (b) and the second organic solvent (M), the addition amount of the second resin (b) to the second organic solvent (M), or By adjusting the amount of the second organic solvent (M) used, the second resin (b) and the colorant are contained in the second organic solvent (M), and the viscosity at 50 ° C. is 1000 mPa · s or more. The 2nd agent (O) of 25000 mPa * s or less can be prepared.

≪Toner particle preparation process≫
In this step, the first agent (W) and the second agent (O) are mixed to form a shell layer containing the first resin (a) and core particles containing the second resin (b). Toner particles (C) having a core / shell structure are prepared. As a result, it is possible to produce toner particles (C) having a highly dispersible colorant despite having a sufficiently small core / shell structure.

  Here, the core / shell structure of the toner particles (C) is a structure in which a shell layer containing the first resin (a) is attached to or coated on the surface of the core particles containing the second resin (b). Show. In other words, the “core / shell structure” includes not only a structure in which the shell layer covers at least a part of the surface of the core particle, but also a structure in which the shell layer is attached to a part of the surface of the core particle. Is also included.

<Method for Preparing Toner Particles (C)>
Regarding the method for preparing the toner particles (C), by dispersing the second agent (O) containing the second resin (b) and the colorant in the first agent (W) containing the first resin (a), A method of mixing the first agent (W) and the second agent (O) and distilling off the second organic solvent (M) in the second agent (O) from the mixed solution can be used. Thereby, the toner particles (C) having the core / shell structure can be granulated.

  In particular, simple and efficient granulation becomes possible by stirring the mixed liquid and applying shear to form droplets. The second organic solvent (M) that is a constituent component of the second agent (O) is a good solvent for the second resin (b), and the first organic solvent (L) that is a constituent component of the first agent (W). ) Is a poor solvent for the second resin (b) compared to the second organic solvent (M).

  The method for dispersing the second agent (O) in the first agent (W) is not particularly limited, but it is preferable to use a dispersing device. Generally as a dispersion apparatus, if it is marketed as an emulsifier or a disperser, it can be used without being specifically limited. For example, a batch type emulsifier, a continuous type emulsifier, a membrane emulsifier, an ultrasonic emulsifier and the like can be mentioned. More specifically, a homogenizer (manufactured by IKA) and a TK auto homomixer (specialized mechanized industry ( Co., Ltd.), Ebara Milder (manufactured by Ebara Corporation), TK Philmix, TK Pipeline Homo Mixer (manufactured by Special Machine Industries Co., Ltd.), and the like.

  The mixing ratio of the second agent (O) and the first agent (W) is not particularly limited. If 50 mass parts or more of 1st agents (W) are contained with respect to 100 mass parts of 2nd resin (b), the dispersibility of 2nd resin (b) will become favorable in a mixed system, and 2nd resin (B) It is preferable that 50-2000 mass parts of 1st agents (W) are contained with respect to 100 mass parts, and it is more preferable that 100-1000 mass parts is contained. 1 agent (W) is 2000 masses. If it is included in less than a part, it becomes economical.

  Further, the method for distilling off the second organic solvent (M) from the mixed solution is not particularly limited. For example, under a reduced pressure of 0.02 to 0.066 MPa, it is 20 ° C. or more and the boiling point of the second organic solvent (M) or less. The method of distilling off the said 2nd organic solvent (M) at the temperature of this is mentioned.

  The content of the second organic solvent (M) in the liquid developer (X) after the second organic solvent (M) has been distilled off is preferably 1% by mass or less, more preferably 0.5% by mass or less. is there. A part of the first organic solvent (L) constituting the insulating liquid together with the second organic solvent (M) (for example, the low boiling point component of the first organic solvent (L)) may also be distilled off. Thereby, the stability of the liquid developer (X) is improved.

<Liquid developer (X)>
The toner particles (C) having a core / shell structure can be granulated by the toner particle preparation step, and thus a liquid developer in which the toner particles (C) are dispersed in an insulating liquid can be produced. . The insulating liquid is composed of the first organic solvent (L).

  The content of the toner particles (C) contained in the liquid developer (X) is preferably 10 to 50% by mass from the viewpoint of the fixability of the toner particles (C) and the heat stability of the liquid developer (X). Yes, more preferably 15 to 45% by mass, still more preferably 20 to 40% by mass. Moreover, the content rate of an insulating liquid can be 50-90 mass%. Such a content rate can be controlled by appropriately adjusting the amounts of the first agent (W) and the second agent (O) used in the toner particle preparation step.

<Toner particles (C)>
As described above, the toner particles (C) prepared in the toner particle preparation step are a core / shell composed of the shell layer containing the first resin (a) and the core particles containing the second resin (b). It has a structure. As long as such a toner particle (C) includes such a core / shell structure, the core particle and / or the shell layer may include other optional components such as the above-described colorant and additive. In particular, the prepared toner particles (C) have a smaller particle size than the toner particles contained in a conventional dry developer, and have a conventional core / shell structure having such a small particle size. Compared to the particles, the colorant is the surface of the particles (if only the core particles contain the colorant, the surface of the core particles, the core particle surface and the toner if both the core particles and the shell layer contain the colorant) The particles are more evenly dispersed in the particles without being unevenly distributed on the particle surface.

  The dispersibility of the colorant in the produced toner particles (C) can be evaluated by, for example, the following method. That is, first, the liquid developer (X) or the toner particles (C) separated from the liquid developer are contained in a curable resin liquid, which is cured to produce a resin sample containing the toner particles (C). To do. Next, this resin sample is cut out to produce a section (ultra thin section), and the section is observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). In this observation field, the dispersibility of the colorant is evaluated by confirming the position of the colorant in the toner particles.

  In the toner particles (C) having a core / shell structure, the mass ratio [(D) :( E)] of the shell layer (D) and the core particles (E) is preferably 1:99 to 70:30. . From the viewpoint of the uniformity of the particle diameter of the toner particles (C) and the heat resistance stability of the liquid developer (X), the ratio [(D) :( E)] is more preferably 2:98 to 50:50. More preferably, it is 3: 97-35: 65. This ratio can be controlled by adjusting the mixing ratio of the first agent (W) and the second agent (O) in this step.

  The toner particles (C) preferably have a volume average particle size of 0.8 μm or more and 4.0 μm or less. Such a volume average particle size is smaller than the particle size of toner particles of a conventional dry developer. If the volume average particle size is less than 0.8 μm, the particles may be too small and the mobility in the electric field may deteriorate, and the developability may deteriorate. If the volume average particle size exceeds 4 μm, the uniformity of the particle shape decreases and the image quality is deteriorated. May decrease. A more preferable range of the volume average particle diameter is 1.1 μm or more and 2.0 μm or less.

  Further, the toner particles (C) preferably have a volume distribution variation coefficient of 10% to 50%. When the coefficient of variation is 50% or less, the toner particles (C) have a relatively uniform particle size, which can significantly contribute to improving the image quality. Further, it is difficult to produce toner particles having a coefficient of variation of less than 10%. A more preferable range of variation coefficient is 10% or more and 40% or less.

The coefficient of variation of the volume distribution can be obtained using a particle size distribution measuring device such as a laser particle size distribution measuring device (for example, trade name: “LA-920”, manufactured by Horiba, Ltd.).
The volume average particle diameter and the coefficient of variation of the volume distribution of the toner particles are appropriately adjusted in this step, such as how to apply shear to the mixed system of the first agent (W) and the second agent (O), and the interfacial tension. Can be controlled by.

  The toner particles (C) preferably have an average circularity of 0.9 or more. Accordingly, even when the liquid developer is repeatedly used in the image forming apparatus, it is possible to suppress the occurrence of granular density unevenness. This is because, when the circularity is low, even if the occurrence of granular density unevenness can be suppressed at the initial stage of use, the shape changes with use and the effect of suppressing the occurrence of granular density unevenness is reduced. Therefore, the circularity is preferably 0.9 or more, and the upper limit is 1.

  The circularity means a numerical value obtained by dividing the perimeter of a circle having an area equal to the particle area projected in two dimensions by the perimeter of the particle, and the average means an arithmetic average value of the numerical values. The circularity of the toner particles (C) can be determined using a flow particle image analyzer (for example, “FPIA-3000S” described above). Since this apparatus can use the insulating liquid as a dispersion medium as it is, it is preferable in that the state of particles in an actual dispersion state can be measured as compared with a system in which measurement is performed in an aqueous system.

  As described above, in this step, the toner particles (C) having a core / shell structure can be prepared by mixing the first agent (W) and the second agent (O). In particular, one of the characteristics of the prepared toner particles (C) is that, as described above, the colorant is not unevenly distributed on the surface of the particles as compared with the conventional toner particles having the same particle diameter. Is more uniformly dispersed. The reason for the high dispersibility of the colorant in the toner particles (C) prepared in this step is not clear, but the relative permittivity of the first organic solvent (L) at 20 ° C. is 1 or more and 4 or less, and Due to the low affinity between the first organic solvent (L) and the colorant, the viscosity at 50 ° C. of the two components (O) is 1000 mPa · s or more and 25000 mPa · s or less. This is presumably because the agent tends to be present in the toner particles and the viscosity is in an appropriate range, so that an appropriate shearing force is generated in the production process and excessive migration of the colorant to the particle surface can be reduced.

  According to the method for producing a liquid developer according to the present embodiment described in detail above, the toner particles having a small particle diameter having a core / shell structure are obtained by passing through the above-described steps. Toner particles in which uneven distribution of the colorant on the surface is suppressed, in other words, toner particles having high dispersibility of the colorant can be prepared. Therefore, according to the method for producing a liquid developer according to the present embodiment, it is possible to produce a liquid developer that achieves both a reduction in the particle size of toner particles and a high dispersibility of the colorant in the toner particles.

  Such a liquid developer is useful as a developer for an electrophotographic image forming apparatus. Specifically, electrophotographic liquid developers, paints, electrostatic recording liquid developers, and inkjet printers used in electrophotographic image forming apparatuses such as copying machines, printers, digital printing machines, and simple printing machines. It can be used as oil-based ink or ink for electronic paper. Thereby, an image with high image quality and high density can be formed.

  The manufactured liquid developer can contain other arbitrary components in addition to the toner particles and the insulating liquid. Examples of other components include a charge control agent, a thickener, a toner particle dispersant, and the like. These other components may be used in any of the steps described above.

<Image formation>
According to the liquid developer manufactured by the method for manufacturing a liquid developer according to the present embodiment, an image can be formed using an image forming apparatus. The configuration of the image forming apparatus is not particularly limited. For example, a single-color image forming apparatus in which a single-color liquid developer is secondarily transferred to a recording medium after primary transfer from the photosensitive member to the intermediate transfer member, or a single-color liquid developer is photosensitive. An image forming apparatus that is directly transferred from a body to a recording medium or a multicolor image forming apparatus that forms a color image by superimposing a plurality of types of liquid developers is preferable.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Production Example 1> [Production of polyester resin]
In a reaction vessel equipped with a stirrer, heating / cooling device, thermometer, cooling tube and nitrogen introduction tube, 286 parts by mass of dodecanedicarboxylic acid, 190 parts by mass of 1,6-hexanediol and titanium dihydroxybis (triethanolamino) as a condensation catalyst. Nate) 1 part by mass was added and reacted at 180 ° C. for 8 hours while distilling off the water produced under a nitrogen stream.

  Next, while gradually raising the temperature to 220 ° C., the reaction was performed for 4 hours while distilling off the generated water under a nitrogen stream, and further, the reaction was performed for 1 hour under a reduced pressure of 0.007 to 0.026 MPa. Thereby, a polyester resin was obtained. When Mn of the polyester resin was measured according to the above-mentioned method, Mn was 4900. Moreover, when the melting point of this polyester resin was measured by the method based on ASTM D3418-82 using the differential scanning calorimeter (brand name: "DSC20", Seiko Instruments Co., Ltd. product), the melting point was 68. ° C. Hereinafter, Mn and melting point of each resin were measured by the same method.

<Production Example 2> [Production of first resin (a1) dispersion (A)]
In a glass beaker, 45 parts by mass of n-octyl methacrylate, 15 parts by mass of 2-decyltetradecyl methacrylate, 15 parts by mass of methacrylic acid, an isocyanate group-containing monomer (trade name: “Karenz MOI”, manufactured by Showa Denko KK And 25 parts by mass of an equimolar reaction product of the polyester resin obtained in Production Example 1 and 0.1 part by mass of azobismethoxydimethylvaleronitrile were added and mixed at 20 ° C. with stirring. Thereby, a monomer solution was obtained.

  A reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, a dropping funnel, a solvent removal device, and a nitrogen introduction tube was prepared. In this reaction vessel, 100 parts by mass of THF was placed, and the monomer solution was placed in the dropping funnel. After replacing the gas phase part of the reaction vessel with nitrogen, the monomer solution was added dropwise to THF at 70 ° C. for 1 hour in a sealed state. Three hours after the completion of the dropwise addition of the monomer solution, a mixture of 0.05 parts by mass of azobismethoxydimethylvaleronitrile and 5 parts by mass of THF was added, reacted at 70 ° C. for 3 hours, and then cooled to room temperature. Thus, a copolymer solution, that is, a resin solution in which the first resin (a1) was dissolved was obtained.

  200 parts by mass of the obtained copolymer solution was dropped into 300 parts by mass of an insulating liquid (trade name: “IP Solvent 2028”, manufactured by Idemitsu Kosan Co., Ltd.) under stirring, and THF was added at 40 ° C. under a reduced pressure of 0.039 MPa. Was distilled off to obtain a dispersion of the first resin (a1). The dispersion liquid (A) of the first resin (a1) corresponds to a solution in which the first resin (a1) is dispersed in “IP solvent 2028” as the first organic solvent (L).

  When Mn of the first resin (a1) contained in the obtained dispersion was measured according to the method described above, Mn was 40000. The relative dielectric constant of “IP Solvent 2028” at 20 ° C. was calculated according to the above-described method. The relative dielectric constant was 2.0.

<Production Example 3> [Production of first resin (a2) dispersion (B)]
A dispersion B of the first resin (a1) was obtained in the same manner as in Production Example 2, except that the insulating liquid (trade name: “IP Solvent 2028”, manufactured by Idemitsu Kosan Co., Ltd.) was changed to chloroform. The dispersion liquid (B) of the first resin (a1) corresponds to a solution in which the first resin (a1) is dispersed in chloroform. When the relative dielectric constant of chloroform at 20 ° C. was calculated according to the above-described method, the relative dielectric constant was 4.8.

<Production Example 4> [Production of second resin (b1) solution]
First, 701 parts by mass of 1,2-propylene glycol (hereinafter referred to as “propylene glycol”), 716 parts by mass of dimethyl terephthalate, and adipic acid in a reaction vessel equipped with a cooling pipe, a stirrer, and a nitrogen introduction pipe 180 parts by mass and 3 parts by mass of tetrabutoxy titanate as a condensation catalyst were added, and the reaction was performed at 180 ° C. for 8 hours while distilling off the produced methanol under a nitrogen stream.

  Next, while gradually raising the temperature to 230 ° C., the reaction was performed for 4 hours while distilling off the generated propylene glycol and water in a nitrogen stream, and further, the reaction was performed for 1 hour under a reduced pressure of 0.007 to 0.026 MPa.

  Subsequently, it cooled to 180 degreeC, 10 mass parts of phthalic anhydrides were added, and it was made to react for 2 hours under normal pressure sealing, Then, the produced | generated resin was taken out. A solution of the second resin (b1), which is a linear polyester resin, is placed in an autoclave reaction vessel equipped with a thermometer, a stirrer, and a nitrogen introduction tube together with 1800 parts by mass of acetone, and the resin is dissolved. Got. The solution of the second resin (b1) corresponds to a solution obtained by dissolving the second resin (b) in acetone as the second organic solvent (M).

  When Mn of the second resin (b1) was measured according to the method described above, Mn was 8000. Moreover, it was 53 degreeC when the endothermic start temperature of this 2nd resin (b1) was measured according to the above-mentioned method. Hereinafter, Mn and endothermic start temperature are measured by the same method.

<Production Example 5> [Production of second resin (b2) solution]
First, 557 parts by mass of propylene glycol, 753 parts by mass of dimethyl terephthalate, and 3 parts by mass of tetrabutoxy titanate as a condensation catalyst were placed in a reaction vessel equipped with a cooling tube, a stirrer, and a nitrogen introduction tube. The reaction was carried out for 8 hours while distilling off the methanol produced under an air stream.

  Next, while gradually raising the temperature to 230 ° C., the reaction was performed for 4 hours while distilling off the generated propylene glycol and water in a nitrogen stream, and further, the reaction was performed for 1 hour under a reduced pressure of 0.007 to 0.026 MPa.

  Subsequently, it cooled to 180 degreeC, 6 mass parts of phthalic anhydride was added, and it was made to react for 2 hours under a normal pressure sealing, Then, after making it react at 220 degreeC and a normal pressure for 2 hours, resin was taken out. The softening point of the removed resin was 180 ° C. The taken-out resin was placed in an autoclave reaction vessel equipped with a thermometer, a stirrer, and a nitrogen introduction tube together with 1800 parts by mass of acetone, and the resin was dissolved to obtain a solution of the second resin (b2) which is a non-linear polyester resin. Obtained. The solution of the second resin (b2) corresponds to a solution obtained by dissolving the second resin (b) in acetone as the second organic solvent (M). The Mn of the second resin (b2) was 8500, and the endothermic start temperature was 63 ° C.

<Production Example 6> [Production of second resin (b3) solution]
First, 570 parts by mass of bisphenol A ethylene oxide 2-mole adduct and 217 parts by mass of terephthalic acid were placed in a reaction vessel equipped with a cooling tube, a stirrer and a nitrogen introduction tube, and reacted at 230 ° C for 8 hours under normal pressure. And reacted for 5 hours under reduced pressure of 0.013 to 0.20 MPa.

  Subsequently, it cooled to 180 degreeC, 4 mass parts of phthalic anhydrides were added, and it was made to react for 2 hours under normal pressure sealing, Then, produced | generated resin was taken out. The taken-out resin was put together with 1800 parts by mass of acetone in an autoclave reaction vessel equipped with a thermometer, a stirrer and a nitrogen introduction tube, and dissolved to obtain a solution of the second resin (b3). The solution of the second resin (b3) corresponds to a solution in which the second resin (b) is dissolved in acetone as the second organic solvent (M). The Mn of this second resin (b3) was 2400, and the endothermic start temperature was 45 ° C.

<Production Example 7> [Production of Colorant Dispersant]
In a beaker, 25 parts by mass of copper phthalocyanine, 4 parts by mass of a colorant dispersant (trade name: “Ajisper PB-822”, manufactured by Ajinomoto Fine Techno Co., Ltd.) and 75 parts by mass of acetone were stirred. After copper phthalocyanine was uniformly dispersed, copper phthalocyanine was finely dispersed using a bead mill. Thereby, a colorant dispersion was obtained. When the volume average particle size of the colorant was measured using a laser diffraction / scattering particle size distribution analyzer (model “LA-920”, manufactured by Horiba, Ltd.), the volume average particle size was 0.2 μm.

<Example 1> [Production of liquid developer (X-1)]
(Second agent (O1) preparation step)
In a beaker, 45 parts by mass of the solution of the second resin (b1) obtained in Production Example 3 and 15 parts by mass of the colorant dispersion obtained in Production Example 6 were added, and further 18.5 parts by mass of acetone were added. The second agent (O1) was obtained by stirring at 8000 rpm using a disperser (product name: “TK Auto Homomixer”, manufactured by Primix Co., Ltd.) at 25 ° C. and uniformly dispersing.

  The second agent (O1) corresponds to the second agent (O) in which the second resin (b1) and the colorant are contained in acetone as the second organic solvent (M). It was 5000 mPa * s when the viscosity at 50 degrees C of this 2nd agent (O1) was measured using the rotational vibration type viscometer (Brand name: "Viscomate VM-10A", Tokyo Glass Instrument Co., Ltd. make).

(First agent (W1) preparation step)
In another beaker, 67 parts by mass of an insulating liquid (trade name: “IP Solvent 2028”, manufactured by Idemitsu Kosan Co., Ltd.) and 6 parts by mass of the dispersion (A) of the first resin (a1) obtained in Production Example 2 were added. It was introduced and dispersed uniformly. Thereby, the 1st agent (W1) in which the 1st resin (a1) is contained in "IP solvent 2028" as the 1st organic solvent (L) was prepared.

(Toner particle preparation process)
Next, 60 parts by mass of the second agent (O1) was added to the first agent (W1) at 25 ° C. using a TK auto homomixer at 10,000 rpm, and stirred for 2 minutes to obtain a mixed solution. . Then, this mixed solution was put into a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a solvent removal device. Acetone was distilled off until the content became 5% by mass or less to obtain a liquid developer (X-1) according to Example 1. This liquid developer (X-1) is composed of toner particles (C) having a core / shell structure composed of a shell layer containing the first resin (a1) and a core layer containing the second resin (b1). This corresponds to a liquid developer contained in “IP solvent 2028” as an insulating liquid.

  In the above operation, the concentration of acetone was quantified by gas chromatography (product name: “GC2010”, manufactured by Shimadzu Corporation) equipped with a flame ion detector.

<Examples 2 to 6 and Comparative Examples 1 to 5> [Production of Liquid Developer]
As shown in Table 1, except for changing the type of the second resin (b) and changing the amount of acetone to be added or distilled off when obtaining the second agents (O2) to (O8), Similarly to Example 1, liquid developers (X-2) to (X-6) according to Examples 2 to 6 and liquid developers (Z-1) to (Z-4) according to Comparative Examples 1 to 4 were used. ) Further, a liquid developer (Z-5) according to Comparative Example 5 was obtained in the same manner as in Example 1 except that the type of the first agent was changed.

  Specifically, 6.4 parts by mass of acetone was added when obtaining the second agent (O2) in Example 2, and 13.4 parts by mass of acetone was obtained when obtaining the second agent (O3) in Example 3. When the second agent (O4) is obtained in Example 4, 6.2 parts by mass of acetone is added. In Example 5, the second agent (O5) is added, and 2.8 parts by mass of acetone is added. In Example 6, 26.7 parts by mass of acetone was added when the second agent (O6) was obtained.

  On the other hand, 29.8 parts by mass of acetone was added when obtaining the second agent (O7) in Comparative Example 1, and 3.1 parts by mass of acetone was added when obtaining the second agent (O8) in Comparative Example 2, In Comparative Example 3, 1.3 parts by mass of acetone was distilled off when obtaining the second agent (O9), and 0.1 part by mass of acetone was distilled off when obtaining the second agent (O10) in Comparative Example 4. Table 1 shows the results of measuring the viscosities at 50 ° C. of the obtained second agents (O2) to (O10) by the method described above.

  The first agent (W2) used in Comparative Example 5 was prepared as follows. That is, 67 parts by mass of chloroform and 6 parts by mass of the dispersion (B) of the first resin (a2) obtained in Production Example 7 were introduced into a beaker and uniformly dispersed. Thereby, the 1st agent (W2) in which 1st resin (a2) was contained in chloroform was prepared. And the liquid developer (Z-5) of the comparative example 5 was obtained using the 1st agent (W2) and the 2nd agent (O2).

  Regarding Table 1, for example, for the liquid developer (X-2), the first agent (W1) similar to that of Example 1 is used as the first agent, and the second resin (b) is contained in acetone as the second agent. This means that the second agent (O2) is used.

<Evaluation>
<Evaluation on dispersibility of colorant>
50 parts by mass of each produced liquid developer (X-1) to (X-6), (Z-1) to (Z-5), a visible light curable resin (trade name: “D-800”, 200 parts by mass of JEOL Ltd. were mixed, and this was irradiated with visible light for 5 minutes using a light irradiator (product name: “LUXSPOT II”, JEOL Ltd.). Thereby, each resin sample cured in a state containing each liquid developer was obtained. Each of the obtained resin materials was cut out under cooling at −80 ° C. using a microtome (product name: “Ultramicrotome EM UC / FC7”, manufactured by JEOL Ltd.) to produce an ultrathin section having a thickness of 80 nm. did. In addition, ten ultrathin sections were prepared for each resin sample. Then, each prepared ultrathin section is observed using TEM (product name: “H-7100”, manufactured by Hitachi High-Technologies Corporation) to determine the degree of dispersion of the colorant in each toner particle (C). did. At this time, at least 10 toner particles (C) were included in the observation field.

The cross section of the toner particles (C) reflected in the observation field was observed, and the following rank evaluation was performed on the dispersion state of the colorant. For each ultrathin section, the cross section of at least 10 toner particles (C) was visually observed.
A: In the cross section of the toner particles, the colorant is uniformly dispersed in the particles. B: In the cross section of the toner particles, the colorant is present on the surface of the particles and in the particles. C: In the cross section of the image toner particles. The result of uneven distribution of the colorant on the surface of the particles is shown in the section “Dispersibility of colorant” in Table 1.

  Referring to Table 1, the dispersibility of the colorant in each toner particle contained in the liquid developer (X-2), (X-4), (X-5) is “A”, and the liquid developer (X -1), (X-3), and (X-6), the dispersibility of the colorant in each toner particle is “B”, and is included in the liquid developers (Z-1) to (Z-4). The dispersibility of the colorant in each toner particle was “C”. For the liquid developer (Z-5), toner particles were not obtained.

  As is clear from Table 1, the dispersibility of the colorant in the toner particles contained in the liquid developers (X-1) to (X-6) in the examples is the liquid developer (Z-1) in the comparative example. It was higher than the dispersibility of the colorant in the toner particles contained in ~ (Z-5). In particular, the dispersibility of the colorant in the toner particles contained in the liquid developers (X-2), (X-4), and (X-5) was high.

<Evaluation on image density>
Images of liquid developers (X-1) to (X-6) and (Z-1) to (Z-4) were formed on a recording material using an image forming apparatus, and the image density was evaluated.

  A schematic conceptual diagram of an image forming apparatus used for evaluation is shown in FIG. The process conditions and process outline of this apparatus are as follows.

  In this evaluation, an image forming apparatus that performs primary transfer from the photosensitive member to the intermediate transfer member and then secondary transfer to the recording material is shown. However, the same effect can be obtained by the method of transferring directly from the photosensitive member to the recording material. can get.

  FIG. 1 shows a single-color image forming apparatus in order to simplify the explanation and make it easy to understand the explanation, but in actual evaluation, it has a plurality of developing tanks and transfer rollers. A multicolor image forming apparatus that forms a color image by superposing a plurality of developers was used.

  First, the developer tank 5 of the image forming apparatus 100 is filled with the liquid developer 6. The liquid developer 6 is pumped up by the anilox roller 22 and sent to the leveling roller 21. Excess liquid developer 6 on the surface of the anilox roller 22 is scraped off by the anilox regulating blade 23 before reaching the leveling roller 21, and the level of the liquid developer 6 is adjusted so that the liquid developer 6 has an equal layer thickness. The Next, the liquid developer 6 is transferred from the leveling roller 21 to the developer carrier 24.

  The photoreceptor 1 is charged by the charging unit 7 and a latent image is formed by the exposure unit 8. Corresponding to the image on which the latent image is formed, the liquid developer 6 is charged on the toner particles by the development charger 26 and then developed on the photoreceptor 1. The liquid developer 6 that has not transferred to the photoreceptor 1 is scraped off and collected by the cleaning blade 25 downstream of the developing unit.

  The liquid developer 6 developed on the photosensitive member 1 is electrostatically primary transferred to the intermediate transfer member 10 in the primary transfer unit 2. The liquid developer 6 (toner particles) carried on the intermediate transfer body 10 is electrostatically secondary transferred onto the recording material 12 in the secondary transfer unit 3. The liquid developer 6 (toner particles) transferred to the recording material 12 is fixed by a fixing device (not shown) and a printed image is completed.

  The liquid developer 6 that has not been transferred and remains on the photosensitive member 1 is scraped off by the cleaning blade 9 of the image carrier cleaning unit, and the photosensitive member 1 repeats charging, exposing, and developing steps to perform a printing operation. Similarly, the liquid developer 6 that cannot be completely transferred and remains on the intermediate transfer member 10 is scraped off by the cleaning blade 11.

  The toner particles are charged to a positive polarity by the development charger 26. The potential of the intermediate transfer member 10 was −400V, and the potential of the transfer roller 4 was −1200V. The conveyance speed was 400 mm / s.

In this evaluation, coated paper (trade name: “OK Top Coat” (128 g / m ² ), manufactured by Oji Paper Co., Ltd.) was used as the recording material.

<Image formation>
Using the image forming apparatus described above, a solid pattern (10 cm × 10 cm) is coated on the same recording material (coat) with the liquid developers (X-1) to (X-6) and (Z-1) to (Z-4). Paper) and subsequently fixed with a heat roller (120 ° C. × nip time 40 msec.). Here, the adhesion amount of the toner particles is 1.0 g / m ^{2 in} Example 3 and Comparative Example 2, and is 1.4 g / m ² in other Examples and Comparative Examples, so that it is included in the solid pattern. The amount of colorant was made equal.

<Measurement of image density>
The image density (ID) of each image formed on the recording material was measured with a reflection densitometer (trade name: “X-Rite model 404”, manufactured by X-Rite), and the following rank evaluation was performed.
A: Image density (ID) 1.5 or more B: Image density (ID) 1.3 or more and less than 1.5 C: Image density (ID) less than 1.3 That is, “A” has the highest image density, and then “B” and “C”. The evaluation results are shown in the “ID evaluation” section of Table 1.

  As is apparent from Table 1, in Comparative Examples 1 to 4 having low dispersibility, the image density was low, although the amount of the colorant in the toner particles was the same as that in the Example.

<Measurement of Volume Average Particle Size and Volume Distribution Coefficient of Variation of Toner Particles>
The volume average particle diameter and the coefficient of variation of the volume distribution of the toner particles contained in each liquid developer were measured using “LA-920” manufactured by Horiba. The results are shown in the sections “Particle Size of Toner Particles” and “Coefficient of Variation of Toner Particles” in Table 1.

  When comparing Examples 1 to 6 from Table 1, there was no great variation in the properties of the toner particles, whereas when Comparative Examples 1 to 4 were compared, there was a large variation in the properties of the toner particles.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Photoconductor, 2 Primary transfer part, 3 Secondary transfer part, 4 Transfer roller, 5 Developing tank, 6 Liquid developer, 7 Charging part, 8 Exposure part, 9 Cleaning blade, 10 Intermediate transfer body, 11 Cleaning blade, 12 recording material, 21 leveling roller, 22 anilox roller, 23 anilox regulating blade, 24 developer carrying member, 25 cleaning blade, 26 developing charger, 100 image forming apparatus.

Claims (5)

A method for producing a liquid developer in which toner particles are dispersed in an insulating liquid,
A first agent preparation step of preparing a first agent comprising a first resin contained in a first organic solvent;
A second agent preparation step of preparing a second agent comprising a second resin and a colorant contained in a second organic solvent;
The first agent and the second agent are mixed to prepare the toner particles having a core / shell structure composed of a shell layer containing the first resin and core particles containing the second resin. A toner particle preparation step,
The first organic solvent has a relative dielectric constant of 1 to 4 at 20 ° C.
The said 2nd agent is a manufacturing method of the liquid developer whose viscosity in 50 degreeC is 1000 mPa * s or more and 25000 mPa * s or less.   2. The method for producing a liquid developer according to claim 1, wherein the second resin has an endothermic start temperature in differential scanning calorimetry of 50 ° C. or more and 60 ° C. or less.   The method for producing a liquid developer according to claim 1, wherein the toner particles have a volume average particle diameter of 0.8 μm or more and 4.0 μm or less.   The method for producing a liquid developer according to claim 1, wherein the toner particles have a volume distribution variation coefficient of 10% to 50%.   5. The method for producing a liquid developer according to claim 1, wherein the first organic solvent occupies 99% by mass or more of the total amount of the insulating liquid.

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