JP2016177126A - Liquid developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid developer excellent in re-dispersibility of toner particles.SOLUTION: A liquid developer includes an insulating liquid and toner particles dispersed in the insulating liquid. The toner particles have a core/shell structure, the core/shell structure has a first resin which is provided on at least a part of the surface of core particles and is formed into a shell layer or shell particles, and core particles containing a second resin that is a resin different from the first resin. The insulating liquid has a relative permittivity at 20°C of 1 or more and 4 or less, and the first resin contains 1 mass% or more and 50 mass% or less of a structural unit derived from a monomer having a functional group exhibiting electrostatic repulsion in the insulating liquid.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a liquid developer.

  Various liquid developers have been proposed for use in liquid development type image forming apparatuses. For example, Japanese Unexamined Patent Application Publication No. 2009-96994 (Patent Document 1) discloses a non-aqueous resin in which core-shell type resin particles (toner particles) composed of a shell layer and a core layer are dispersed in a non-aqueous organic solvent. Dispersions are disclosed.

JP 2009-96994 A

  The toner particles dispersed in the liquid developer tend to settle easily. When the toner particles settle, the toner particles easily adhere to each other, and unnecessary aggregation occurs there. That is, when the liquid developer is allowed to stand for a long period (for example, 48 hours or more) in a room temperature (25 ° C.) or a relatively high temperature environment (for example, an environment in the range of 30 ° C. to 50 ° C.), the toner particles settle. In some cases, the state of sedimentation of the toner particles may be maintained (poor redispersibility) even if stirring is performed such as shaking the liquid developer by hand. If the re-dispersibility of the liquid developer is poor, the development, transfer and fixing processes are adversely affected. For this reason, the image quality is deteriorated due to image density unevenness.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a liquid developer having excellent redispersibility of toner particles.

  The liquid developer of the present invention is a liquid developer comprising an insulating liquid and toner particles dispersed in the insulating liquid, wherein the toner particles have a core / shell structure, and the core / shell The structure includes a first resin that is provided on at least a part of the surface of the core particle and serves as a shell layer or a shell particle, and a core particle that includes a second resin that is a resin different from the first resin, and the insulation The conductive liquid has a relative dielectric constant of 1 to 4 at 20 ° C., and the first resin contains 1% by mass or more of a structural unit derived from a monomer having a functional group that exhibits electrostatic repulsion in the insulating liquid. It is characterized by containing 50 mass% or less.

  In the liquid developer of the present invention, the functional group of the monomer preferably contains at least one element selected from N element, O element, and S element.

  In the liquid developer of the present invention, the functional group of the monomer preferably has an amide structure.

  The liquid developer of the present invention is excellent in toner particle redispersibility.

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

  Hereinafter, embodiments of the present invention (hereinafter referred to as “present embodiments”) will be described with reference to the drawings. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

≪Liquid developer≫
The liquid developer according to the present embodiment includes an insulating liquid and toner particles. Such a liquid developer can contain other optional components as long as it contains an insulating liquid and toner particles. For example, as other components, a charge control agent, a thickener, a toner dispersant and the like may be included.

One feature of the liquid developer of this embodiment is that a liquid developer having a relative dielectric constant at 20 ° C. in the range of 1 to 4 is used. This is because when the dielectric constant of the insulating liquid is less than 1, there is a problem that the toner particles are not stable and difficult to manufacture, and when the dielectric constant of the insulating liquid exceeds 4, This is because there is a problem that the charge retention rate tends to deteriorate. From the viewpoint of improving production stability and charge retention, the dielectric constant of the insulating liquid is more preferably in the range of 1.2 to 3.8, and in the range of 1.2 to 3.5. It is particularly preferred. The relative dielectric constant of the insulating liquid is calculated using the dielectric constant of the insulating liquid obtained by the bridge method (JIS C2101-1999). Specifically, the capacitance C ₀ (pF) before filling with the insulating liquid and the equivalent parallel capacitance C _x (pF) in the state filled with the insulating liquid are measured, and the following formula (1) ) To calculate the dielectric constant ε of the insulating liquid.

ε = C _x / C ₀ Formula (1)
The relative dielectric constant of the insulating liquid is obtained by the ratio of the calculated ε and the relative dielectric constant of the air 1.000585.

<Toner particles>
In the present embodiment, the toner particles contained in the liquid developer have a core / shell structure. The core / shell structure is provided on at least a part of the surface of the core particle, and the first resin (a) serving as the shell layer or the shell particle and the second resin (b) which is a resin different from the first resin (a) ) Including core particles. By adopting such a structure for the toner particles, it is easy to control the volume average particle diameter of the toner particles, the coefficient of variation of the particle size distribution of the toner particles, or the shape of the toner particles, so that the diameter of the toner particles can be reduced. It is possible and can contribute to high image quality. In the following description, toner particles having such a core / shell structure may be referred to as “toner particles (C)”, and a liquid developer containing toner particles (C) may be referred to as “liquid developer (X)”. is there.

  Here, the content of the toner particles contained in the liquid developer is preferably 10% by mass or more and 50% by mass or less, more preferably 12% by mass, from the viewpoint of the fixing property of the toner particles and the heat stability of the liquid developer. % To 40% by mass, and more preferably 15% to 35% by mass.

  In the present embodiment, the toner particles preferably have a volume average particle size of 0.5 μm or more and 5.0 μm or less. The volume average particle size of the toner particles is smaller than the particle size of the toner particles of the conventional dry developer, which is one of the features of the present embodiment. If the particle diameter is less than 5 μm, the particle size is too small, the mobility in the electric field is deteriorated, and the developability may be deteriorated. If the particle diameter exceeds 5 μm, the uniformity of the particle shape is deteriorated and the image quality may be deteriorated. A more preferable range of the volume average particle size is 0.5 μm or more and 2.0 μm or less.

  The volume average particle diameter of the toner particles is determined by a laser diffraction / scattering particle size distribution measuring device (for example, “LA-920” manufactured by Horiba, Ltd. or “Multisizer III” manufactured by Beckman Coulter, Inc.), or an optical system. Measurement is possible using "ELS-800" (manufactured by Otsuka Electronics Co., Ltd.) using a laser Doppler method. When the volume average particle diameter is measured with a different measuring apparatus, if a difference occurs in the measured value, the measured value by “ELS-800” is adopted.

<Core / shell structure>
The toner particles in this embodiment have a core / shell structure as described above, and this core / shell structure has only a structure in which the first resin (a) covers at least a part of the surface of the core particles. There is also included a structure in which the first resin (a) is attached to at least a part of the surface of the core particle. The first resin (a) may be formed in a layer shape (film shape) or may be formed in a particle shape on the surface of the core particle. The shell layer (layer containing a shell resin) or shell particles (particles containing a shell resin) may further contain a colorant or an optional component (for example, a pigment dispersant, a wax or a charge control agent).

  In the toner particle (C) having a core / shell structure, the mass ratio [(A) :( B)] of the shell layer or shell particle (A) to the core particle (B) 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 [(A) :( B)] is more preferably 2:98 to 50:50. More preferably, it is 3: 97-35: 65. Hereinafter, the configuration of the shell layer or the shell particles (A) and the core particles (B) will be described.

<Shell layer or shell particle (A) / first resin (a)>
In the present embodiment, the first resin (a) that becomes the shell layer or the shell particle is a polymer dispersant that has an action of adhering to the surface of the core particle and improving its dispersibility. In the liquid developer of this embodiment, the first resin (a) contains 1% by mass to 50% by mass of a structural unit derived from a monomer having a functional group that develops electrostatic repulsion in the insulating liquid. This is a major feature.

  1st resin (a) used as a shell layer or a shell particle contains the structural unit derived from the monomer which has a functional group which expresses electrostatic repulsion in an insulating liquid with the content rate of 1 mass% or more and 50 mass% or less By using the first resin (a), the toner particles are excellent in redispersibility, that is, even when the toner particles settle due to the liquid developer being left for a long period of time, A liquid developer is provided in which the state of toner particles in the liquid developer returns to the state before storage (dispersed state) by performing an agitation operation such as shaking. This is because an electrostatic repulsive force is generated between toner particles because the first resin (a) contains 1% by mass or more of a structural unit derived from a monomer having a functional group that develops electrostatic repulsion in an insulating liquid. This is considered to be caused by the occurrence of toner particles and the suppression of aggregation of toner particles. In addition, as an incidental effect due to the fact that the first resin (a) contains 1% by mass or more of a structural unit derived from a monomer having a functional group that develops electrostatic repulsion in the insulating liquid, the granulation property of the toner particles is also included. It is believed that this is due to electrostatic interactions in non-aqueous dispersions. From the viewpoint that the effects described above can be obtained more remarkably, the content of the structural unit derived from the monomer having a functional group that develops electrostatic repulsion in the insulating liquid in the first resin (a) is 5% by mass. The content is preferably 30% by mass or less and more preferably 6% by mass or more and 26% by mass or less.

  When the content of the structural unit derived from the monomer having a functional group that develops electrostatic repulsion in the insulating liquid in the first resin (a) is less than 1% by mass, the above-described redispersion of the toner particles It becomes worse. This is presumably because the electrostatic repulsive force does not occur between the toner particles, or even if it occurs, it is very weak, so that the aggregation of the toner particles cannot be suppressed and the redispersibility is poor. On the other hand, if the content of the structural unit derived from the monomer having a functional group that develops electrostatic repulsion in the insulating liquid in the first resin (a) exceeds 50% by mass, the redispersibility is good, but fixing Strength will deteriorate. This is presumed that when a large number of positively charged polar groups are contained, the heat melting temperature of the shell layer or the shell particles becomes high, whereby the toner particles are hardly dissolved and the fixing strength is deteriorated.

  1st resin (a) in this embodiment has 1 or more types of monomers which have a functional group which expresses electrostatic repulsion in an insulating liquid, and 1 which has a functional group which does not express electrostatic repulsion in an insulating liquid A polymer obtained by polymerizing at least one kind of monomer is preferable. In order to set the content of the structural unit derived from the monomer having a functional group that exhibits electrostatic repulsion in the insulating liquid in the first resin (a) to 1% by mass or more and 50% by mass or less as described above. , Amount of monomer containing functional group that develops electrostatic repulsion in insulating liquid (total amount when using two or more monomers containing functional group that develops electrostatic repulsion in insulating liquid) May be adjusted as appropriate. That is, among the monomers for polymerizing the first resin (a), the blending amount (blending ratio) of the monomer having a functional group that develops electrostatic repulsion in the insulating liquid is 1% by mass or more and 50% by mass or less. The content is preferably 5% by mass or less and 30% by mass or less, more preferably 7% by mass or more and 25% by mass or less. In addition, the content rate of the structural unit derived from the monomer which has a functional group which expresses electrostatic repulsion in an insulating liquid in 1st resin (a) may measure an infrared absorption spectrum, and may be calculated from the said spectrum. In addition, it may be calculated from a spectrum obtained by nuclear magnetic resonance, or may be measured using a GCMS (Gas Chromatography Mass Spectrometer). By measurement, the content of the structural unit (also referred to as the first structural unit) derived from the monomer having a functional group that develops electrostatic repulsion in the insulating liquid in the first resin (a) can be calculated. .

  The monomer having a functional group that develops electrostatic repulsion in the insulating liquid contains at least one element selected from N element, O element, and S element from the viewpoint of easily developing electrostatic repulsion. It is preferable. Hereinafter, the monomer having a functional group that develops electrostatic repulsion in the insulating liquid, which is preferably used for the first structural unit, will be specifically described.

(1) Monomer having an amide structure (amide monomer)
Examples of the monomer containing N element (N element-containing monomer) include a monomer having an amide structure (amide monomer). For example, (meth) acrylamide, N-methyl (meth) acrylamide, N-butyl (meth) acrylamide, N-aminoethyl (meth) acrylamide, diacetone (meth) acrylamide, N-methylol (meth) acrylamide, N, N ′ -Methylene-bis (meth) acrylamide, cinnamic amide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, hydroxyethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N- [3- (dimethylamino) propyl] (meth) acrylamide, N, N-dibenzyl (meth) acrylamide, (meth) acrylformamide, morpholine (meth) acrylamide, N-methyl-N-vinylacetamide, N-vinylpyrrolidone, etc. Example Can be shown. In this specification, “(meth) acryl” means at least one of methacryl and acryl.

(2) N element-containing monomer having a polymerizable double bond As an N element-containing monomer having a polymerizable double bond other than the amide monomer described above (preferably a monomer having an amide group and a polymerizable double bond) For example, the monomer shown by the following (2-1)-(2-3) is mentioned.

(2-1) Monomer having an amino group and a polymerizable double bond Monomers having an amino group and a polymerizable double bond are, for example, aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl ( (Meth) acrylate, t-butylaminoethyl methacrylate, N-aminoethyl (meth) acrylamide, (meth) allylamine, morpholinoethyl (meth) acrylate, 4-vinylpyridine, 2-vinylpyridine, crotylamine, N, N-dimethylamino Styrene, methyl-α-acetaminoacrylate, vinylimidazole, N-vinylpyrrole, N-vinylthiopyrrolidone, N-arylphenylenediamine, aminocarbazole, aminothiazole, aminoindole, aminopyrrole, aminoyl Imidazole, and the like amino-mercaptothiazole.

  Here, the monomer having an amino group and a polymerizable double bond may be a salt of the monomers listed above. Preferred examples of the monomer salts listed above include alkali metal salts (for example, sodium salt or potassium salt) and alkaline earth metal salts (for example, calcium salt or magnesium salt).

(2-2) Monomer having 3 to 10 carbon atoms having a nitrile group and a polymerizable double bond As a monomer having 3 to 10 carbon atoms having a nitrile group and a polymerizable double bond, for example, (meth) Examples include acrylonitrile, cyanostyrene, and cyanoacrylate.

(2-3) Monomer having 8 to 12 carbon atoms having a nitro group and a polymerizable double bond As a monomer having 8 to 12 carbon atoms having a nitro group and a polymerizable double bond, for example, nitrostyrene Etc.

(3) Monomer containing O element having polymerizable double bond Examples of the monomer containing O element (O element-containing monomer) include monomers having a carboxyl group and a polymerizable double bond, and salts thereof. It is done. The monomer having a carboxyl group and a polymerizable double bond is, for example, an unsaturated monocarboxylic acid having 3 to 15 carbon atoms (for example, (meth) acrylic acid, crotonic acid, isocrotonic acid, cinnamic acid, etc.), having a carbon number. 3 to 30 unsaturated dicarboxylic acids (anhydrides) (for example, (anhydrous) maleic acid, fumaric acid, itaconic acid, (anhydrous) citraconic acid, mesaconic acid, etc., unsaturated dicarboxylic acids having 3 to 10 carbon atoms Monoalkyl (having 1 to 10 carbon atoms) ester (for example, maleic acid monomethyl ester, maleic acid monodecyl ester, fumaric acid monoethyl ester, itaconic acid monobutyl ester, citraconic acid monodecyl ester, etc.) preferable. The salt of the monomer is preferably, for example, an alkali metal salt (for example, sodium salt or potassium salt) or an alkaline earth metal salt (for example, calcium salt or magnesium salt).

(4) Monomer containing S element having polymerizable double bond As a monomer containing S element (S element-containing monomer), for example, sulfone group-containing vinyl monomer, vinyl sulfate monoester product and salts thereof; carbon Alkene sulfonic acids having 2 to 14 carbon atoms such as vinyl sulfonic acid, (meth) allyl sulfonic acid, methyl vinyl sulfonic acid, styrene sulfonic acid; alkyl derivatives having 2 to 24 carbon atoms such as α-methyl styrene sulfonic acid Sulfo (hydroxy) alkyl- (meth) acrylate or (meth) acrylamide, such as sulfopropyl (meth) acrylate, 2-hydroxy-3- (meth) acryloxypropylsulfonic acid, 2- (meth) acryloylamino-2, 2-dimethylethanesulfonic acid, -(Meth) acryloyloxyethanesulfonic acid, 3- (meth) acryloyloxy-2-hydroxypropanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 3- (meth) acrylamido-2-hydroxypropane Sulfonic acid, alkyl (3 to 18 carbon atoms) allylsulfosuccinic acid, poly (n = 2 to 30) oxyalkylene (ethylene, propylene, butylene; may be single, random or block) mono (meth) acrylate sulfate [Poly (n = 5 to 15) oxypropylene monomethacrylate sulfate, etc.], polyoxyethylene polycyclic phenyl ether sulfate, and sulfates represented by the following general formulas (1-1) to (1-3) or Sulfonic acid group-containing monomer; Beauty such as a salt thereof can be mentioned.

  In the above formula, R represents an alkyl group having 1 to 15 carbon atoms, A represents an alkylene group having 2 to 4 carbon atoms, and when n is plural, they may be the same or different. Good. In the above formula, Ar represents a benzene ring, n represents an integer of 1 to 50, and R ′ represents an alkyl group having 1 to 15 carbon atoms which may be substituted with a fluorine atom.

  As the monomer having a functional group that exhibits electrostatic repulsion in the insulating liquid in the present embodiment, among the monomers containing at least one element selected from the N element, O element, and S element described above, redispersibility From the viewpoint of the above, a monomer having an amide structure (amide monomer) is preferable. In particular, when the amide monomer is contained in an amount of 20% or more, preferably 30% or more, it is more effective for redispersibility.

  Moreover, as a monomer which has the functional group which does not express an electrostatic repulsion in an insulating liquid used for 1st resin (a) in this embodiment, it has a monomer and a branched hydrocarbon group which have a linear hydrocarbon group Monomers are preferred. These monomers may be used alone or in combination.

  Examples of the monomer having a linear hydrocarbon group include a linear hydrocarbon having a polymerizable double bond, a mono linear alkyl ester of an unsaturated monocarboxylic acid, and a mono linear alkyl ester of an unsaturated dicarboxylic acid. Can be mentioned.

  Examples of the linear hydrocarbon having a polymerizable double bond include alkenes having 4 to 30 carbon atoms (for example, butene, pentene, heptene, octene, dodecene, octadecene, etc.), alkadienes having 4 to 30 carbon atoms. (Butadiene, isoprene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, etc.) can be exemplified.

  Examples of the unsaturated monocarboxylic acid and unsaturated dicarboxylic acid include (meth) acrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, citraconic acid and the like, a carboxyl group-containing vinyl monomer having 3 to 24 carbon atoms Can be illustrated. Examples of linear alkyl esters obtained from these vinyl monomers include n-octyl (meth) acrylate, n-decyl (meth) acrylate, n-dodecyl (meth) acrylate, and n- (meth) acrylate. Examples include tridecyl, n-stearyl (meth) acrylate, n-behenyl (meth) acrylate, n-hexadecyl (meth) acrylate, n-heptadecyl (meth) acrylate, n-eicosyl (meth) acrylate, and the like. be able to.

  Examples of the monomer having a branched hydrocarbon group include branched alkyl esters of unsaturated monocarboxylic acids and branched alkyl esters of unsaturated dicarboxylic acids. Such a branched alkyl ester can be obtained from the unsaturated monocarboxylic acid and unsaturated dicarboxylic acid described above and an alcohol (or polyol) having a branched hydrocarbon group. Examples of such an alcohol include 2-ethylhexanol, 2-decyltetradecinol, 2-octyldodecanol and the like. Further, ethers of these alcohols and polyols (for example, diethylene glycol) may be used.

  The monomer having a branched hydrocarbon group may be, for example, an ester of a branched unsaturated carboxylic acid and an alcohol. Examples of the branched unsaturated carboxylic acid include dimer acid and alkenyl succinic acid (for example, dodecenyl succinic acid, pentadecenyl succinic acid or octadecenyl succinic acid).

  Specific examples of such a monomer having a branched hydrocarbon group include (meth) acrylic acid 2-decyltetradecyl, (meth) acrylic acid diethylene glycol mono-2-decyltetradecyl ether, and the like.

The mass ratio of each constituent unit of the first resin (a) was determined using a Fourier transform nuclear magnetic resonance analyzer (FT-NMR: Fourier Transform-Nuclear Magnetic Resonance) (trade name “Lambda400”, manufactured by JEOL Ltd.) ¹ H-NMR analysis can be performed and determined by its integration ratio. As a measurement solvent in that case, for example, chloroform-d (deuterated chloroform) solvent is preferable.

  Here, the first resin (a) is composed of 40% by mass or more and 70% by mass or less of a structural unit derived from a monomer having a linear hydrocarbon group and a structural unit derived from a monomer having a branched hydrocarbon group. It is preferable to contain in the range which becomes. When the total amount of the structural unit derived from the monomer having a linear hydrocarbon group and the structural unit derived from the monomer having a branched hydrocarbon group is less than 40% by mass, the lipophilicity of the first resin (a) is decreased. This is because the granulation property may be deteriorated, and if it exceeds 70% by mass, the lipophilicity is excessively increased and the cold offset property may be deteriorated. Here, in consideration of granulation property and cold offset property, the total amount of the structural unit derived from the monomer having a linear hydrocarbon group and the structural unit derived from the monomer having a branched hydrocarbon group is more preferably 40 mass. % To 60% by mass, particularly preferably 50% to 60% by mass.

  The structural unit derived from the monomer having a linear hydrocarbon group is 30% of the total amount of the structural unit derived from the monomer having a linear hydrocarbon group and the structural unit derived from the monomer having a branched hydrocarbon group. It is preferable to occupy a ratio of not less than 90% by mass. When the proportion of the structural unit derived from the monomer having a linear hydrocarbon group is less than 30% by mass, the content of the branched hydrocarbon group exhibiting high lipophilicity is excessively increased. This is because A) may excessively adsorb the insulating liquid (oil) to lower the low-temperature fixability, and if it exceeds 90% by mass, the granulation property may be deteriorated. Here, in consideration of low-temperature fixability and granulation property, the linear hydrocarbon group out of the total amount of the structural unit derived from the monomer having a linear hydrocarbon group and the structural unit derived from the monomer having a branched hydrocarbon group The range occupied by the constitutional unit derived from the monomer having is more preferably 30% by mass to 85% by mass, and particularly preferably 30% by mass to 75% by mass.

The first resin (a) in the present embodiment includes a structural unit derived from at least one (macromonomer) selected from the group consisting of a polystyrene structure and a polymethyl methacrylate structure, in addition to the structural unit derived from the monomer described above. It is preferable to contain the side chain to contain. Here, the “macromonomer” means a monomer having a functional group capable of polymerization reaction and having a large molecular weight. By having a side chain containing a structural unit derived from a macromonomer selected from the group consisting of a polystyrene structure and a polymethylmethacrylate structure having such a high glass transition temperature (Tg), the redispersibility of toner particles is improved. More improved. This is because the inclusion of the side chain keeps the shell solid during granulation and storage, and forms irregularities on the surface of the toner particles, thereby reducing the contact area between the toner particles and regenerating the toner particles. This is probably because the dispersibility was improved. The structural unit derived from such a macromonomer is 10% by mass or more and 50% by mass or less in the first resin (a) (when the structural unit derived from two or more kinds of macromonomer contains the total amount). The content is preferably within the range, and more preferably within the range of 10% by mass to 45% by mass. When the structural unit derived from the macromonomer contained in the first resin (a) is less than 10% by mass, the production stability of the toner particles tends to be poor, and the first resin (a) When the structural unit derived from the contained macromonomer exceeds 50% by mass, the production stability of the toner particles tends to be poor. The content of the constituent unit derived from a macromonomer in the first resin (a), for example, ¹ H-NMR of the shell resin: it can be calculated by measuring the (Nuclear Magnetic Resonance).

  Specific examples of the macromonomer include polystyrene having a (meth) acryloyl group or a styryl group at one end, poly (meth) acrylate methyl, poly (meth) acrylate n-butyl, and poly (meth) acrylic. A macromonomer in which a (meth) acryloyl group is bonded to one end of a molecule of poly (meth) acrylate alkyl (alkyl group having 1 to 4 carbon atoms) such as i-butyl acid.

  The number average molecular weight of the macromonomer is usually 2000 or more and 30000 or less from the viewpoint of heat-resistant storage stability, preferably 2500 or more, more preferably 4000 or more from the viewpoint of heat-resistant storage stability, and from the viewpoint of low-temperature fixability. Preferably it is 20000 or less, More preferably, it is 15000 or less.

  As such a macromonomer available on the market, one-end methacryloylated polystyrene (Mn = 6000, trade name AS-6, manufactured by Toagosei Chemical Co., Ltd.), one-end methyl methacrylate (Mn = 6000, trade name) AA-6, manufactured by Integrative Chemical Co., Ltd.), and one-terminal methacryloylated poly-acrylic acid n-butyl (Mn = 6000, trade name AB-6, manufactured by Toagosei Co., Ltd.).

  Among these, from the viewpoint of heat-resistant storage property, it is preferable to use one-end methacryloylated polystyrene and one-end methyl methacryloylate as macromonomers.

  The weight average molecular weight (hereinafter referred to as “Mw”) of the first resin (a) is preferably 40000 or more and 200000 or less, and more preferably 80000 or more and 120,000 or less. If the Mw of the first resin (a) is 40000 or more, the amount of the oligomer is less than a certain amount, so that it can have a good charge retention, and if the Mw of the first resin (a) is 200000 or less, it is good. This is because it can have a good granulation property and thus a low-temperature fixability.

  In the present specification, the Mw and number average molecular weight (hereinafter referred to as “Mn”) of the first resin (a) are determined by gel permeation chromatography (GPC) with respect to the soluble content of tetrahydrofuran (hereinafter referred to as “THF”). Gel Permeation Chromatography). Specifically, measurement under the following conditions is exemplified.

Measuring apparatus: “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 volume of sample solution to the column: 100 μl,
Flow rate: 1 ml / min,
Measurement temperature: 40 ° C.
Detector: 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).

<Core particle (B) / second resin (b)>
The second resin (b) of the present embodiment constitutes core particles (B) having a core / shell structure. The second resin (b) may be any resin as long as it is a conventionally known resin, but polyester resin, polyurethane resin, styrene acrylic resin, modified polyester resin, and the like are preferable examples from the thermal characteristics of the toner. It is done. Among these, a polyester resin having a high sharp melt property is particularly preferable. Preferred examples of the polyester resin used in the second resin (b) include aliphatic polyesters mainly composed of aliphatic monomers, aromatic polyesters mainly composed of aromatic monomers, and mixed polyester resins of the two. It is done.

  The polyester resin is synthesized by a polycondensation reaction between a carboxylic acid (a structural unit derived from an acid component) and an alcohol (a structural unit derived from an alcohol component). Therefore, the part derived from carboxylic acid becomes a structural unit derived from the acid component, the part derived from alcohol becomes the structural unit derived from the alcohol component, and the polyester resin is configured by repeating these structural units.

  In the polyester resin, examples of the aliphatic monomer that is a structural unit derived from the acid component include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelic acid, sebacic acid, 1, 9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,16 -Hexadecanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, etc. are mentioned. These lower alkyl esters may be used, and these acid anhydrides may be used. In terms of promoting the crystallinity of the polyester resin, it is more preferable to use adipic acid, sebacic acid, 1,10-decanedicarboxylic acid, or 1,12-dodecanedicarboxylic acid. As such an aliphatic monomer, any of the above may be used alone, or two or more of the above may be used in combination.

  In the polyester resin, examples of the aromatic monomer that is a structural unit derived from the acid component include aromatic polyvalent carboxylic acids, lower alkyl esters of aromatic polyvalent carboxylic acids, and acid anhydrides of aromatic polyvalent carboxylic acids. Can be mentioned. Specifically, terephthalic acid, isophthalic acid, orthophthalic acid, 5-tert-butylisophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, trimellitic acid (with 3 functional groups), etc. Can be mentioned. From the viewpoint of availability, terephthalic acid, isophthalic acid, and 5-tert-butylisophthalic acid are preferably used.

  In the polyester resin, examples of the aliphatic monomer serving as a structural unit derived from the alcohol component include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexane. Diol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanedi All, 1,14-tetradecanediol, 1,18-octadecanediol, 1,20-eicosanediol and the like. From the viewpoint of promoting the crystallinity of the polyester resin, it is preferable to use ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,9-nonanediol, or 1,10-decanediol. As such an aliphatic monomer, any of the above may be used alone, or two or more of the above may be used in combination.

  In the polyester resin, examples of the aromatic monomer serving as a structural unit derived from the alcohol component include aromatic polyhydric alcohols. Specific examples include an alkylene oxide adduct of bisphenol A represented by the following formula (I).

In the above formula (I), R ¹ and R ² each independently represents an alkylene group having 2 or 3 carbon atoms. In the above formula (I), m and n each independently represent 0 or a positive integer, and the sum of m and n is 1 or more and 16 or less.

  The number average molecular weight (Mn) of the aliphatic polyester resin is preferably 1000 or more and 25000 or less, and the mass average molecular weight (Mw) of the aliphatic polyester resin is preferably 2000 or more and 200000 or less. The number average molecular weight (Mn) of the aromatic polyester resin is preferably 1000 or more and 25000 or less, and the mass average molecular weight (Mw) of the aromatic polyester resin is preferably 2000 or more and 200000 or less. The number average molecular weight and the mass average molecular weight can be measured by GPC (Gel Permeation Chromatography).

  The resin contained in the core particles may contain less than 10% by mass of a resin other than the polyester resin. Examples of other resins include styrene-acrylic resins, urethane resins, and epoxy resins. When the content of other resins other than the polyester resin is 10% by mass or more, it may be difficult to regularly arrange the molecular chains of the polyester resin.

(Endothermic start temperature of the second resin (b))
The second resin (b) preferably has an endothermic start temperature in differential scanning calorimetry of 50 ° C. or higher and 60 ° C. or lower. This is because, when the endothermic start temperature of the second resin (b) is within the above range, the chargeability of the toner particles tends to increase. The endothermic start temperature in differential scanning calorimetry can be measured using, for example, a conventionally known differential scanning calorimeter (for example, “DSC (Q2000)” manufactured by Seiko Instruments Inc.). As the measurement conditions, the endothermic start temperature can be measured with a measurement sample (5 mg) and a temperature increase rate of 10 ° C./min. The endothermic start temperature of the second resin (b) is more preferably 50 ° C. or higher and 55 ° C. or lower.

<Other components contained in toner particles>
The toner particles (C) in the present embodiment preferably contain a colorant in at least one of the shell layer or the shell particles (A) and the core particles (B), and additives other than the colorant (for example, pigment dispersion) Agent, wax, charge control agent, filler, antistatic agent, mold release agent, ultraviolet absorber, antioxidant, antiblocking agent, heat stabilizer, flame retardant, etc.).

<Colorant>
The colorant is dispersed in at least one of the first resin (a) and the second resin (b) described above. 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.

  As the colorant, conventionally known pigments and the like can be used without any particular limitation. For example, conventionally known black pigments, yellow pigments, magenta pigments, and cyan pigments can be used. Here, in terms of color configuration, basically colors other than black (color image) are toned by subtractive color mixture of yellow pigment, magenta pigment, and cyan pigment.

<Pigment dispersant>
The pigment dispersant has a function of uniformly dispersing the colorant (pigment) in the toner particles, and it is preferable to use a basic dispersant. Further, it is more preferable to select a pigment dispersant that does not dissolve in the insulating liquid (carrier liquid). For these reasons, it is preferable to use “Ajisper PB-821” (trade name), “Ajisper PB-822” (trade name), “Ajisper PB-881” (trade name), etc., manufactured by Ajinomoto Fine Techno Co., Ltd.

<Non-hydrophilic organic solvent (L)>
In the present embodiment, as the non-hydrophilic organic solvent (L), the relative dielectric constant at 20 ° C. is 1 or more and 4 or less. Since the non-hydrophilic organic solvent (L) finally constitutes the insulating liquid of the liquid developer (X) to be produced, the non-hydrophilic organic solvent (L) has a relative dielectric constant of 1 to 4 at 20 ° C. The charge maintaining property of the developer (X) can be improved. The insulating liquid constituting the liquid developer (X) is preferably only the non-hydrophilic organic solvent (L), but may contain other organic solvents as long as the effects of the present embodiment are exhibited. . However, the content of other organic solvents is preferably 1% by mass or less. The relative dielectric constant of the non-hydrophilic organic solvent (L) can be calculated as described above as a method for calculating the relative dielectric constant of the insulating liquid.

  In addition to the above characteristics, the non-hydrophilic organic solvent (L) preferably further 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.

<Method for producing liquid developer>
The liquid developer (X) according to this embodiment can be manufactured as follows. First, the first resin (a) and the second resin (b) are produced by a conventionally known method such as a dispersion polymerization method, an emulsion polymerization method, a soap-free emulsion polymerization method, a seed polymerization method or a suspension polymerization method. Next, a fine particle dispersion in which the first resin (a) is dispersed is prepared. Furthermore, the second resin (b) is dissolved in a good solvent to obtain a resin solution, and the resin solution is mixed with a fine particle dispersion of the first resin (a) in a poor solvent having an SP value different from that of the good solvent. The liquid developer (X) can be produced by volatilizing the good solvent after forming droplets by applying shear. The liquid developer (X) thus produced has a core / layer composed of a shell layer (A) containing the first resin (a) and a core layer (B) containing the second resin (b). Toner particles (C) having a shell structure can be included.

  Here, according to the above method, the volume average particle diameter of the toner particles can be controlled within a desired range by appropriately adjusting the method of applying shear, the difference in interfacial tension, and the like.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to the following.
<Production Example 1> [Production of Fine Particle Dispersion (A1) of First Resin (a1)]
A fine particle dispersion (A1) in which fine particles made of the first resin (a1) were dispersed was produced as follows.

  100 parts by mass of THF was charged into 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. In a glass beaker, 50 parts by mass of 2-decyltetradecyl methacrylate, 1 part by mass of acrylamide, 20 parts by mass of a macromonomer (trade name: “AA-6”, Toagosei Co., Ltd.), 29 parts by mass of methyl methacrylate Then, a mixed solution of 0.1 part by mass of azobismethoxydimethylvaleronitrile was added, stirred and mixed at 20 ° C. to prepare a monomer solution, and charged into a dropping funnel.

  After carrying out nitrogen substitution of the gas phase part of the reaction vessel, the monomer solution was added dropwise at 70 ° C. for 1 hour in a sealed state. Three hours after the completion of the dropwise addition, 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, cooled to room temperature, and the copolymer solution was prepared. Obtained. While stirring 200 parts by mass of this copolymer solution, it was dropped into 300 parts by mass of an insulating liquid (“IP Solvent 2028”, manufactured by Idemitsu Kosan Co., Ltd.), and THF was distilled off at 40 ° C. under a reduced pressure of 0.039 MPa. Thus, a fine particle dispersion (A1) was obtained. When the Mw of the first resin (a1) contained in the fine particle dispersion (A1) was measured according to the above-described method, the Mw was 100,000. Hereinafter, Mw is measured by the same method. In addition, the relative dielectric constant of “IP Solvent 2028” at 20 ° C. was calculated according to the above-described method. As a result, the relative dielectric constant was 2.0.

<Production Example 2> [Production of Fine Particle Dispersion (A2) of First Resin (a2)]
A fine particle dispersion (A2) was obtained in the same manner as in Production Example 1, except that 1 part by mass of acrylamide in Production Example 1 was changed to 30 parts by mass and 29 parts by mass of methyl methacrylate were changed to 0 parts by mass. The Mw of the first resin (a2) contained in this fine particle dispersion (A2) was 100,000.

<Production Example 3> [Production of Fine Particle Dispersion (A3) of First Resin (a3)]
50 parts by mass of acrylamide in Production Example 1, 0 parts by mass of 29 parts by mass of methyl methacrylate, 35 parts by mass of 50 parts by mass of 2-decyltetradecyl methacrylate, macromonomer (trade name: “AA-6” Toagosei Co., Ltd.) A fine particle dispersion (A3) was obtained in the same manner as in Production Example 1 except that 20 parts by mass was changed to 15 parts by mass. The Mw of the first resin (a3) contained in this fine particle dispersion (A3) was 100,000.

<Production Example 4> [Production of fine particle dispersion (A4) of first resin (a4)]
A fine particle dispersion (A4) was obtained in the same manner as in Production Example 1, except that 1 part by mass of acrylamide in Production Example 1 was changed to 30 parts by mass of acrylic acid and 29 parts by mass of methyl methacrylate were changed to 0 parts by mass. The Mw of the first resin (a4) contained in this fine particle dispersion (A4) was 100,000.

<Production Example 5> [Production of fine particle dispersion (A5) of first resin (a5)]
A fine particle dispersion (A5) was obtained in the same manner as in Production Example 4 except that 30 parts by mass of acrylic acid in Production Example 4 was changed to 30 parts by mass of styrene sulfonic acid. The Mw of the first resin (a5) contained in this fine particle dispersion (A5) was 100,000.

<Production Example 6> [Production of fine particle dispersion (A6) of first resin (a6)]
A fine particle dispersion (A6) was obtained in the same manner as in Production Example 4 except that 30 parts by mass of acrylic acid in Production Example 4 was changed to 30 parts by mass of methyl methacrylate. The Mw of the first resin (a6) contained in this fine particle dispersion (A6) was 100,000.

<Production Example 7> [Production of fine particle dispersion (A7) of first resin (a7)]
100 parts by mass of chloroform was charged into 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. In a glass beaker, 50 parts by mass of 2-decyltetradecyl methacrylate, 30 parts by mass of acrylamide, 20 parts by mass of a macromonomer (trade name: “AA-6”, Toagosei Co., Ltd.) and azobismethoxydimethylvaleronitrile A 0.1 part by mass of the mixed solution was charged, stirred and mixed at 20 ° C. to prepare a monomer solution, and charged into a dropping funnel.

  After carrying out nitrogen substitution of the gas phase part of the reaction vessel, the monomer solution was added dropwise at 70 ° C. for 1 hour in a sealed state. Three hours after the completion of the dropping, a mixture of 0.05 part by mass of azobismethoxydimethylvaleronitrile and 5 parts by mass of chloroform was added, reacted at 70 ° C. for 3 hours, cooled to room temperature, and then a copolymer solution. Got. While stirring 200 parts by mass of this copolymer solution, it was dropped into 300 parts by mass of chloroform to obtain a fine particle dispersion (A7). The Mw of the first resin (a7) contained in this fine particle dispersion (A7) was 100,000.

<Production Example 8> [Production of fine particle dispersion (A8) of first resin (a8)]
55 parts by mass of acrylamide in Production Example 1, 0 parts by mass of 29 parts by mass of methyl methacrylate, 30 parts by mass of 50 parts by mass of 2-decyltetradecyl methacrylate, macromonomer (trade name: “AA-6” Toagosei Co., Ltd.) A fine particle dispersion (A8) was obtained in the same manner as in Production Example 1 except that 20 parts by mass was changed to 15 parts by mass. The Mw of the first resin (a8) contained in this fine particle dispersion (A8) was 100,000.

<Production Example 9> [Production of second resin (b1) solution]
A solution of the second resin (b1) was produced as follows.

  In a reaction vessel equipped with a cooling pipe, a stirrer and a nitrogen introduction pipe, 701 parts by mass of 1,2-propylene glycol (hereinafter referred to as “propylene glycol”), 716 parts by mass of dimethyl terephthalate, 180 parts by mass of adipic acid, And 3 parts by mass of tetrabutoxy titanate was added as a condensation catalyst, and the reaction was carried out 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. The taken-out resin was put together with 1800 parts by mass of acetone in an autoclave reaction tank equipped with a thermometer, a stirrer, and a nitrogen introduction tube, and the resin was dissolved to obtain a solution of the second resin (b1). When Mn of this second resin (b1) was measured according to the method described above, Mn was 8000. Moreover, it was 55 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 10> [Production of Colorant Dispersion]
Into a beaker, 25 parts by mass of copper phthalocyanine, 4 parts by mass of a colorant dispersant (trade name “Azisper PB-822”, manufactured by Ajinomoto Fine Techno Co., Ltd.) and 75 parts by mass of acetone are stirred and uniformly dispersed. Thereafter, copper phthalocyanine was finely dispersed by a bead mill to obtain a colorant dispersion. When the volume average particle size of copper phthalocyanine contained in the colorant dispersion 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 (Z-1)]
In a beaker, 45 parts by mass of the second resin (b1) solution and 15 parts by mass of the colorant dispersion obtained in Production Example 8 were added, and a TK auto homomixer (product name, manufactured by Primix Co., Ltd.) at 25 ° C. Was stirred at 8000 rpm and dispersed uniformly to obtain a resin solution.

  In another beaker, 67 parts by mass of the insulating liquid (IP solvent 2028) and 6 parts by mass of the fine particle dispersion (A1) were charged and uniformly dispersed. Next, while stirring at 10,000 rpm using a TK auto homomixer at 25 ° C., 60 parts by mass of the resin solution was added and stirred for 2 minutes to obtain a mixed solution.

  Next, this mixed solution was put into a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a solvent removal device. After the temperature was raised to 35 ° C., the acetone concentration was reduced to 0.039 MPa at a reduced pressure of 0.039 MPa. Acetone was distilled off until the content became 5% by mass or less to obtain a liquid developer (Z-1) according to Example 1. This liquid developer (Z-1) contains toner particles having a core / shell structure composed of a shell layer containing the first resin (a1) and a core layer containing the second resin (b1).

  Here, in the above operation, the concentration of acetone was quantified by gas chromatography equipped with a flame ion detector [product name “GC2010”, manufactured by Shimadzu Corporation].

<Examples 2 to 5 and Comparative Examples 1 and 3> [Production of Liquid Developer]
As shown in Table 1, the liquid developers (Z-2) according to Examples 2 to 5 and Comparative Examples 1 and 3 were the same as Example 1 except that the type of the fine particle dispersion (A) was changed. To (Z-6) and (Z-8) were obtained. Here, the ratio [% by mass] of each structural unit of the first resin (a) shown in Table 1 is a value calculated from the charged amount of each monomer.

<Comparative Example 2> [Production of liquid developer (Z-7)]
In a beaker, 45 parts by mass of the second resin (b1) solution and 15 parts by mass of the colorant dispersion obtained in Production Example 8 were added, and a TK auto homomixer (product name, manufactured by Primix Co., Ltd.) at 25 ° C. Was stirred at 8000 rpm and dispersed uniformly to obtain a resin solution.

  In another beaker, 67 parts by mass of chloroform and 6 parts by mass of the fine particle dispersion (A7) were added and uniformly dispersed. Next, while stirring at 10,000 rpm using a TK auto homomixer at 25 ° C., 60 parts by mass of the resin solution was added and stirred for 2 minutes to obtain a mixed solution. The relative dielectric constant of “chloroform” at 20 ° C. was calculated according to the above-described method. The relative dielectric constant was 4.8.

  Next, this mixed solution was put into a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a solvent removal device. After the temperature was raised to 35 ° C., the acetone concentration was reduced to 0.039 MPa at a reduced pressure of 0.039 MPa. Acetone was distilled off to 5 mass% or less to obtain a liquid developer (Z-7) according to Comparative Example 2. However, toner particles were not obtained.

〔Evaluation test〕
<Evaluation of redispersibility>
20 cc of each liquid developer was placed in a screw tube and stored in a constant temperature bath at 40 ° C. for 1 week. When the liquid developer after storage was observed, the toner particles settled in all cases. The state of the toner particles in the liquid developer was observed after the screw tube containing the wet developer separated into solid and liquid was shaken 20 times by hand and then shaken 30 times and shaken 50 times in total.

  When the state of the toner particles in the liquid developer has returned to the state before storage, that is, when the state where no settled toner particles are confirmed in the liquid developer is achieved by shaking 20 times. The case where the toner particles were settled, and the case where the toner particles settled down even after shaking 50 times were confirmed were evaluated as x.

<Evaluation of granulation>
The median diameter D50 of the toner particles was measured using a flow type particle image analyzer (“FPIA-3000S” (product number) manufactured by Sysmex Corporation). The insulating liquid used for the liquid developer was used as a dispersion medium as it was.

A: The toner particle size is 0.5 μm or more and less than 3 μm, and the variation coefficient of the particle size distribution is 10 or more and 40 or less,
○: The toner particle size is 0.5 μm or more and less than 3 μm, and the variation coefficient of the particle size distribution is 10 or more and 50 or less,
X: The toner particle size does not meet the above conditions and / or the toner particle size distribution does not meet the above conditions.

<Evaluation of fixing strength (fixing property)>
Using the image forming apparatus of FIG. 1, the solid pattern images of the liquid developers of Examples and Comparative Examples obtained above were recorded on coated paper (OK Top Coat Plus, 128 g / m ² , Oji Paper Co., Ltd.). Formed by the company). Thereafter, the image was fixed with a heat roller (set temperature: 150 ° C., nip time: 50 msec, paper temperature immediately after passing through the fixing device at this time: 110 ° C.).

  After the fixed image is left at room temperature for 1 hour, a tape (trade name “Scotch Mending Tape”, manufactured by Sumitomo 3M Co., Ltd.) is applied to the measurement target part of the recording medium on which the image is fixed, and then the tape is peeled off Affixed to standard paper CF paper (manufactured by Konica Minolta). Next, the image density (ID) of the portion where the tape was applied was measured using a reflection densitometer (trade name: “SpectroEye”, manufactured by X-Rite). At that time, a part of the CF paper that was just affixed to the CF paper was measured in advance as a reference concentration, and the difference between the measured values of the reference concentration and the measured concentration was evaluated as ΔID. The smaller the numerical value of the image density of the peeled image, the higher the fixing strength.

A: Image density (ID) less than 0.1,
○: Image density (ID) 0.1 or more and less than 0.15,
X: Image density (ID) 0.15 or more.

<Image formation>
First, the image forming apparatus used for evaluation will be described. FIG. 1 is a schematic conceptual diagram of an electrophotographic image forming apparatus 100. The process conditions and process outline of this apparatus are as follows.

  First, the liquid developer 21 is placed in the developing tank 22 of the image forming apparatus 100. The liquid developer 21 is drawn up by the anilox roller 23 and sent to the leveling roller 25. Excess liquid developer on the surface of the anilox roller 23 is scraped off by the anilox regulating blade 24 before reaching the leveling roller 25, so that the liquid developer becomes a thin layer having a uniform layer thickness at the leveling roller 25. Adjusted. Next, the liquid developer is transferred from the leveling roller 25 to the developer carrier 26.

  The photosensitive member 29 is charged by the charging unit 30 and a latent image is formed by the exposure unit 31. The development charger 28 charges the toner particles contained in the liquid developer. The liquid developer 21 is developed on the photoconductor 29 corresponding to the latent image. The liquid developer 21 that has not transferred to the photoconductor 29 is scraped off and collected by the cleaning blade 27 downstream of the developing unit. Although not shown, this apparatus includes a measuring instrument that can measure the surface potential of a thin layer made of a liquid developer 0.1 seconds and 1 second after the liquid developer is charged.

  The liquid developer developed on the photoreceptor 29 is electrostatically primary transferred to the intermediate transfer member 33 by the primary transfer unit 37. The liquid developer (toner particles) carried on the intermediate transfer member 33 is electrostatically secondary transferred to the recording material 40 by the secondary transfer unit 38. The liquid developer (toner particles) transferred to the recording material 40 is sent to a fixing device having a heating roller and a pressure roller, and the image fixed by the fixing device and printed out is completed.

  The liquid developer that cannot be completely transferred and remains on the photosensitive member 29 is scraped off by the cleaning blade 32 of the image carrier cleaning unit, and the photosensitive member 29 repeats the charging, exposing, and developing steps to perform a printing operation. Similarly, the liquid developer that cannot be transferred and remains on the intermediate transfer member 33 is scraped off by the cleaning blade 34.

In the evaluation of each liquid developer, the toner particles were charged with a positive polarity by the development charger 28. The potential of the intermediate transfer member 33 was −400 V, the potential of the transfer roller 35 was −1200 V, and the conveyance speed was 400 mm / s. Coated paper (trade name: “OK Top Coat (registered trademark)” (128 g / m ² , manufactured by Oji Paper Co., Ltd.)) was used as the recording material.

  Table 2 shows the evaluation results for Examples 1 to 5 and Comparative Examples 1 and 2.

  Although the embodiments and examples of the present invention have been 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.

  21 Liquid developer, 22 Developer tank, 23 Anilox roller, 24 Anilox regulating blade, 25 Leveling roller, 26 Developer carrier, 27 Cleaning blade, 28 Developer charger, 29 Photoconductor, 30 Charging unit, 31 Exposure unit, 32 Cleaning blade, 33 Intermediate transfer member, 34 Cleaning blade, 35 Transfer roller, 37 Primary transfer unit, 38 Secondary transfer unit, 40 Recording material, 100 Image forming apparatus.

Claims (3)

A liquid developer comprising an insulating liquid and toner particles dispersed in the insulating liquid,
The toner particles have a core / shell structure;
The core / shell structure includes a first resin that is provided on at least a part of the surface of the core particle and serves as a shell layer or a shell particle, and a core particle that includes a second resin that is a resin different from the first resin. And
The insulating liquid has a relative dielectric constant of 1 or more and 4 or less at 20 ° C.,
The first resin contains 1% by mass to 50% by mass of a structural unit derived from a monomer having a functional group that develops electrostatic repulsion in an insulating liquid.   The liquid developer according to claim 1, wherein the functional group of the monomer contains at least one element selected from an N element, an O element, and an S element.   The liquid developer according to claim 1, wherein the functional group of the monomer has an amide structure.

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