JP2016170305A - Liquid developer and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent the occurrence of document offset.SOLUTION: A liquid developer comprises an insulating liquid and toner particles dispersed in the insulating liquid. The toner particles include a binder resin, colorant, and polymer dispersant. In a liquid developer having a solid content with a density of 80 mass%, the binder resin has a glass transition point Tg (DSC 2nd Run) of 50°C or more. The binder resin includes an amorphous polyester resin. The glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in a dry state is 65°C or more. The binder resin further includes a crystalline polyester resin having a melting point of 60°C or more in an amount of 20 mass% or less.SELECTED DRAWING: None

Description

  The present invention relates to a liquid developer and an image forming method using the liquid developer.

  The liquid developer includes an insulating liquid and toner particles dispersed in the insulating liquid. Such a liquid developer is required to have various performances such as fixing stability or storage stability. For example, in JP 2009-175670 A (Patent Document 1), the storage stability of an insulating liquid is improved by using a polyester resin (glass transition point: 60 ° C. or higher) as a binder resin contained in toner particles. Is described.

JP 2009-175670 A

  Another performance required for the liquid developer is prevention of occurrence of document offset. Document offset means that images stored on a recording medium are superposed on each other and stored for a long time at a high temperature (for example, about 50 ° C.). As a result, the images adhere to each other, and as a result, the images peel off from each other. It means getting harder.

  As a measure for preventing the occurrence of document offset, conventionally, a measure has been proposed in which the glass transition point of the binder resin contained in the toner particles is set to an image storage temperature (for example, 50 ° C.) or higher. However, it has now been found that document offset may occur even though the glass transition point of the binder resin in the dry state is higher than the image storage temperature.

  The present invention has been made in view of such a point, and an object thereof is to prevent the occurrence of a document offset.

  The present inventors diligently studied why the document offset occurred despite the glass transition point of the binder resin in the dry state being equal to or higher than the image storage temperature, and found the reason. Based on this finding by the present inventors, the present invention has been completed.

  That is, the liquid developer of the present invention includes an insulating liquid and toner particles dispersed in the insulating liquid. The toner particles include a binder resin, a colorant, and a polymer dispersant. In the liquid developer of the present invention, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass is 50 ° C. or higher.

  The binder resin contains an amorphous polyester resin, and the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in a dry state is 65 ° C. or higher. The binder resin further contains 20% by mass or less of a crystalline polyester resin having a melting point of 60 ° C. or higher.

  “The glass transition point Tg (DSC 2nd Run) of the binder resin in a liquid developer having a solid concentration of 80% by mass” means that the binder resin is a liquid developer (solid developer having a solid concentration of 80% by mass). Means the glass transition point of the binder resin in the state of being contained in the agent. The “liquid developer having a solid content concentration of 80% by mass” means a liquid developer comprising 80% by mass of toner particles (solid content of the liquid developer) and 20% by mass of an insulating liquid. .

In the present specification, the solid content concentration of the liquid developer is determined according to the following method. First, the mass of the liquid developer is measured. Next, the liquid developer is dried at 160 ° C. under a reduced pressure of 5 mmHg for 3 hours, and then the mass of the solid content (the mass of the solid content after drying) is measured. The solid content concentration of the liquid developer is determined using the following formula.
(Solid content concentration of liquid developer) (mass%) = (mass of solid content after drying) ÷ (mass of liquid developer) × 100.

  “Amorphous polyester resin in the dry state” includes not only the case where the amorphous polyester resin does not contain any insulating liquid, but also the case where the amorphous polyester resin contains 1% by mass or less of an insulating liquid. It is.

  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.

  "Amorphous polyester resin" means that the content ratio of the structural unit derived from the aromatic monomer in both the structural unit derived from the alcohol component and the structural unit derived from the acid component is 50% by mass or more. Means that. The content ratio of the structural unit derived from the aromatic monomer in both the structural unit derived from the alcohol component and the structural unit derived from the acid component is preferably 60% by mass or more, more preferably 70% by mass. It is above, More preferably, it is 80 mass% or more.

The content ratio of the structural unit derived from the aromatic monomer in both the structural unit derived from the alcohol component and the structural unit derived from the acid component may be obtained using a spectrum obtained by nuclear magnetic resonance. It may be good or may be obtained by GCMS (Gas chromatography mass spectrometry). In the case of obtaining the above content ratio using a spectrum obtained by nuclear magnetic resonance, ¹ H is obtained using a Fourier transform nuclear magnetic resonance apparatus (FT-NMR) (trade name: “Lambda400”, manufactured by JEOL Ltd.). -NMR analysis is performed, and the content ratio can be determined from the integration ratio. A chloroform-d (deuterated chloroform) solvent can be used as a measurement solvent. The content ratio of the structural unit derived from the aliphatic monomer in both the structural unit derived from the alcohol component and the structural unit derived from the acid component, the content ratio of the amorphous polyester resin in the binder resin, and the binding The content ratio of the crystalline polyester resin in the adhesion resin can also be measured by the same method.

  The “structural unit derived from the alcohol component” means a unit in which a hydrogen atom is removed from the hydroxyl group (OH group) of the alcohol, and includes a unit in which a hydrogen atom is removed from at least one hydroxyl group contained in the alcohol. The “constituent unit derived from the acid component” means that the hydroxyl group is removed from the carboxyl group (COOH group) of the carboxylic acid, and the hydroxyl group is removed from at least one carboxyl group contained in the carboxylic acid. Including. “Aromatic monomers” include aromatic carboxylic acids, lower alkyl esters of aromatic carboxylic acids, acid anhydrides of aromatic carboxylic acids, and aromatic alcohols. “Aromatic carboxylic acid” means a carboxylic acid having an aromatic ring in the molecule. “Aromatic alcohol” means an alcohol having an aromatic ring in the molecule.

  “Crystalline polyester resin” means that the content ratio of the structural unit derived from the aliphatic monomer in both the structural unit derived from the alcohol component and the structural unit derived from the acid component is 50% by mass or more. Means. The content ratio of the structural unit derived from the aliphatic monomer in both the structural unit derived from the alcohol component and the structural unit derived from the acid component is preferably 60% by mass or more, more preferably 70% by mass. It is above, More preferably, it is 80 mass% or more.

  “Aliphatic monomers” include aliphatic carboxylic acids, lower alkyl esters of aliphatic carboxylic acids, acid anhydrides of aliphatic carboxylic acids, and aliphatic alcohols. “Aliphatic carboxylic acid” means a carboxylic acid having no aromatic ring in the molecule. “Fatty alcohol” means an alcohol having no aromatic ring in the molecule.

  In this specification, the melting point of the crystalline polyester resin is determined by ASTM D3418-82 using a differential scanning calorimeter (for example, trade name “DSC20” or trade name “SSC / 580” manufactured by Seiko Instruments Inc.). It was measured according to the described method.

  In the present specification, “the binder resin further contains 20% by mass or less of a crystalline polyester resin having a melting point of 60 ° C. or higher” includes the above crystalline polyester resin (melting point of 60 ° C. or higher in the binder resin). The case where the content of a certain crystalline polyester resin) is 0% by mass is included. That is, the present invention includes a case where the binder resin is made of only an amorphous polyester resin.

The acid value of the binder resin is preferably 20 mgKOH / g or more.
In this specification, “the acid value of the binder resin” is described in JIS K 0070: 1992 (acid acid value, saponification value, ester value, iodine value, hydroxyl value, and unsaponified test method for chemical products). This means the acid value of the binder resin measured according to the method, and is based on the amount of carboxyl groups contained in the binder resin. The “carboxyl group contained in the binder resin” corresponds to the amount of the carboxyl group residue that has not reacted with the hydroxyl group in the condensation polymerization reaction when the polyester resin is synthesized.

  The polymer dispersant preferably exhibits basicity. The insulating liquid preferably has a flash point of 70 ° C. or higher.

  In this specification, the flash point of the insulating liquid is measured according to the Cleveland open type of JIS K 2265-4: 2007.

  The image forming method of the present invention is a method of forming an image using the liquid developer of the present invention, and is included in the step of transferring the liquid developer to a recording medium and the liquid developer transferred to the recording medium. Fixing toner particles to a recording medium. In the image fixed on the recording medium, the remaining amount of the insulating liquid is 3% by mass or more and 30% by mass or less of the toner particle content.

  In the present invention, document offset can be prevented from occurring.

The solid content concentration of the liquid developer and the glass transition point of the binder resin in a state where the binder resin is contained in the liquid developer (in FIG. 1, simply indicated as “glass transition point of the binder resin”) It is a graph which shows the relationship. It is a schematic conceptual diagram which shows an example of a transcription | transfer process. It is a side view which shows an example of a fixing process.

  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.

[Configuration of liquid developer]
The liquid developer of this embodiment is an electrophotographic liquid developer, paint, or electrostatic recording liquid used in an electrophotographic image forming apparatus (described later) such as a copying machine, a printer, a digital printing machine, or a simple printing machine. It is useful as a developer, oil-based ink for inkjet printers, or ink for electronic paper. The liquid developer of this embodiment includes an insulating liquid and toner particles dispersed in the insulating liquid, and preferably includes 10 to 50% by mass of toner particles and 50 to 90% by mass of an insulating liquid. The liquid developer of this embodiment may contain an arbitrary component different from the insulating liquid and the toner particles. Examples of such optional components include a toner dispersant, a charge control agent, and a thickener.

  The toner particles of this embodiment include a binder resin, a colorant, and a polymer dispersant. In the following, after showing the possible reason for the occurrence of document offset despite the glass transition point of the binder resin in the dry state being equal to or higher than the image storage temperature, the liquid developer of this embodiment is further added. Show.

  Even if the glass transition point of the binder resin in the dry state is equal to or higher than the storage temperature of the image, for some reason, the glass transition point of the binder resin in a state where the binder resin is included in the image (hereinafter referred to as “in the image”). If the glass transition point of the binder resin ”is lower than the image storage temperature, it is considered that document offset occurs. Recently, the present inventors diligently examined whether or not such a hypothesis is appropriate, and found that the following reasons α to γ can be considered as the above reasons.

(Reason α: Insulating liquid remains in the image)
Usually, using a resin in a dry state, the glass transition point of the resin is measured. However, the glass transition point of the binder resin contained in the toner particles was measured in the presence of an insulating liquid. As a result, the glass transition point of the binder resin decreased as the solid concentration of the liquid developer decreased (FIG. 1). That is, it was found that the glass transition point of the binder resin in the presence of the insulating liquid is lower than the glass transition point of the binder resin in the dry state.

  Incidentally, in order to prevent the insulating liquid volatilized during image formation from adhering to the surface of the transfer roller or the surface of the fixing roller, it is preferable to reduce the volatilization amount of the insulating liquid. It is preferable to use an organic solvent having low volatility (for example, an organic solvent having a flash point of 70 ° C. or higher) as the ionic liquid. However, if an organic solvent with low volatility is used as the insulating liquid, the amount of volatilization of the insulating liquid at the time of image formation is lower than when an organic solvent with high volatility is used as the insulating liquid. The insulating liquid tends to remain in the image.

  In summary, when an organic solvent having low volatility is used as the insulating liquid, the insulating liquid tends to remain in the formed image. It tends to be lower than the glass transition point of the resin. Therefore, the glass transition point of the binder resin in the image tends to be lower than the image storage temperature. Therefore, it is considered that document offset may occur even when the glass transition point of the binder resin in the dry state is higher than the image storage temperature.

  Here, FIG. 1 shows the solid content concentration of the liquid developer and the glass transition point of the binder resin in a state where the binder resin is contained in the liquid developer (hereinafter referred to as “the glass transition of the binder resin in the liquid developer”). FIG. The reason why the result shown in FIG. 1 is obtained is considered as follows. In general, it is said that the SP value is the same between the insulating liquid and the binder resin. Therefore, since the insulating liquid and the binder resin are easily compatible, the insulating liquid is easily dissolved in the binder resin. Thereby, since the binder resin is easily plasticized by the insulating liquid, the glass transition point of the binder resin is lowered. Therefore, the glass transition point of the binder resin in the liquid developer is lower than the glass transition point of the binder resin in the dry state.

(Reason β: toner particles contain a polymeric dispersant)
The polymer dispersant is a dispersant for a colorant made of a polymer, and is added to the toner particles in order to disperse the colorant in the toner particles. In particular, when producing toner particles by a granulation method, it is necessary to prepare a colorant dispersion, so that the polymer dispersant is an essential component of the toner particles.

  Nowadays, when the toner particles contain a polymer dispersant and when the toner particles do not contain the polymer dispersant, the glass transition point of the binder resin in the state where the binder resin is contained in the toner particles (hereinafter, (Denoted as “glass transition point of binder resin in toner particles”). As a result, it was found that the glass transition point of the binder resin in the toner particles is lower when the toner particles contain the polymer dispersant than when the toner particles do not contain the polymer dispersant.

  By the way, when a liquid developer is produced using toner particles containing a polymer dispersant and an image is formed using the liquid developer, the image contains the polymer dispersant. On the other hand, when a liquid developer is produced using toner particles that do not contain a polymer dispersant, and an image is formed using the liquid developer, the image contains no polymer dispersant. In recent years, it has been confirmed that the glass transition point of the binder resin in the toner particles is lowered by the addition of the polymer dispersant to the toner particles. For this reason, when the toner particles contain a polymer dispersant, the glass transition point of the binder resin in the image is lower than when the toner particles do not contain the polymer dispersant. As a result, when the toner particles include a polymer dispersant, the glass transition point of the binder resin in the image is lower than the glass transition point of the binder resin in the dry state, and thus is less than the storage temperature of the image. It becomes easy to become. Therefore, even if the glass transition point of the binder resin in the dry state is higher than the image storage temperature, it is considered that document offset may occur.

  Here, the reason why the glass transition point of the binder resin in the toner particles is lower when the toner particles contain the polymer dispersant than when the toner particles do not contain the polymer dispersant is as follows. It is possible. In general, it is said that the polymer dispersant and the binder resin have the same melting point or softening point. Therefore, since the polymer dispersant and the binder resin are easily compatible with each other, the polymer dispersant is easily dissolved in the binder resin. Thereby, since the binder resin is easily plasticized by the polymer dispersant, the glass transition point of the binder resin is lowered. Therefore, when the toner particles contain a polymer dispersant, the glass transition point of the binder resin in the toner particles is lower than when the toner particles do not contain the polymer dispersant.

(Reason γ: binder resin includes crystalline resin)
When an amorphous resin is used as the binder resin, the hardness of the binder resin can be secured, so that the heat resistant storage stability of the liquid developer can be improved. However, if only an amorphous resin is used as the binder resin, the viscoelasticity of the toner particles is difficult to decrease during fixing (80 to 100 ° C. at the temperature of the recording medium). For this reason, the adhesive strength of the toner particles to the recording medium is reduced, and the fixing strength of the toner particles to the recording medium is reduced. Therefore, it is difficult to realize fixing at a low temperature. Therefore, usually, a mixture of a crystalline resin and an amorphous resin is used as the binder resin.

  Recently, the glass transition point of the binder resin in the toner particles was measured when a crystalline resin and an amorphous resin were used as the binder resin and when only the amorphous resin was used as the binder resin. As a result, the glass transition point of the binder resin in the toner particles is greater when the crystalline resin and the amorphous resin are used as the binder resin than when only the amorphous resin is used as the binder resin. Was found to decrease.

  By the way, when a liquid developer is produced using a mixture of a crystalline resin and an amorphous resin as a binder resin and an image is formed using the liquid developer, the crystalline resin and the amorphous resin are included in the image. And both are included. On the other hand, when a liquid developer is produced using only an amorphous resin as a binder resin and an image is formed using the liquid developer, the image contains an amorphous resin but no crystalline resin. Absent. Recently, it has been confirmed that addition of a crystalline resin to toner particles lowers the glass transition point of the binder resin in the toner particles. Therefore, when a mixture of a crystalline resin and an amorphous resin is used as the binder resin, the glass transition point of the binder resin in the image is higher than when only the amorphous resin is used as the binder resin. Will decline. As a result, when a mixture of a crystalline resin and an amorphous resin is used as the binder resin, the glass transition point of the binder resin in the image is lower than the glass transition point of the binder resin in the dry state. Therefore, the temperature tends to be lower than the image storage temperature. Therefore, even if the glass transition point of the binder resin in the dry state is higher than the image storage temperature, it is considered that document offset may occur.

  Here, the glass transition point of the binder resin in the toner particles is greater when the crystalline resin and the amorphous resin are used as the binder resin than when only the amorphous resin is used as the binder resin. Possible reasons for the decrease are as follows. It is said that the crystalline resin is softer than the amorphous resin. Therefore, the addition of the crystalline resin decreases the hardness of the binder resin, so that the fluidity of the binder resin increases. Therefore, the glass transition point of the binder resin is lowered. Therefore, the glass transition of the binder resin in the toner particles is greater when the mixture of the crystalline resin and the amorphous resin is used as the binder resin than when only the amorphous resin is used as the binder resin. The point goes down.

  From the above, it was confirmed that there are cases where the glass transition point of the binder resin in the image is lower than the storage temperature of the image even though the glass transition point of the binder resin in the dry state is higher than the storage temperature of the image. It was. Therefore, it was found that the glass transition point of the binder resin in the dry state cannot be used as an index for the occurrence of document offset. Therefore, the present inventors diligently examined the index of occurrence or non-occurrence of document offset. As a result, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass was determined as the document offset. It was found that it can be used as an indicator of occurrence. From the above, if the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass is 50 ° C. or higher, one of the above reasons α to γ has occurred. Even in this case, the glass transition point of the binder resin in the image is higher than the storage temperature of the image. Therefore, occurrence of document offset can be prevented.

  Preferably, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass is 55 ° C. or higher. Thereby, even if any of the above-mentioned reasons α to γ occurs, the glass transition point of the binder resin in the image becomes higher than the storage temperature of the image. Therefore, the occurrence of document offset can be further prevented.

  More preferably, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass is 100 ° C. or less. Thereby, since the viscoelasticity of the toner particles can be lowered at the time of fixing (the temperature of the recording medium is 80 to 100 ° C.), the adhesive strength of the toner particles to the recording medium can be maintained high, and thus the recording medium can be maintained. The fixing strength of the toner particles can be kept high. Therefore, fixing at a low temperature can be realized.

  The reason why the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass can be used as an index for the occurrence of document offset is considered as follows. As shown in FIG. 1, as the solid content concentration increases, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer increases. Therefore, if the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass is 50 ° C. or higher, the solid developer has a solid content concentration higher than 80% by mass. The glass transition point Tg (DSC 2nd Run) of the binder resin is higher than 50 ° C. Here, it is considered that an insulating liquid of 20% by mass or less remains in the image. Therefore, if the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass is 50 ° C. or higher, the glass transition point of the binder resin in the image is 50 ° C. or higher. can do. Therefore, it is considered that the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass can be used as an index for the occurrence of document offset.

  In this specification, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass is a temperature measured according to the following method.

  First, according to the method described above, the solid content concentration of the sample (liquid developer) is measured. If the solid content concentration of the sample is not 80 mass%, the solid content concentration of the sample is adjusted to 80 mass% by adjusting the amount of the insulating liquid or the amount of toner particles. Next, a predetermined amount of sample is precisely weighed, and the accurately weighed sample is set in a measurement container. Subsequently, DSC (Differential Scanning Calorimetry) is performed according to the following conditions. Thereby, a DSC curve (vertical axis: heat flow, horizontal axis: time or temperature) is obtained. The exothermic reaction appears as a peak in the DSC curve and the endothermic reaction appears as a valley peak in the DSC curve. The peak temperature of the valley peak appearing in the DSC curve (when there are a plurality of valley peaks, the peak temperature of the valley peak appearing on the lowest temperature side) is the result in a liquid developer having a solid concentration of 80% by mass. It becomes the glass transition point Tg (DSC 2nd Run) of the resin.

(Measurement condition)
Differential scanning calorimeter: Product name “DSC6200” manufactured by Hitachi High-Technologies Corporation
Mass of sample (liquid developer): 5 mg
Reference sample: Aluminum First temperature increase (measurement temperature range, temperature increase rate): 30 to 180 ° C., 10 ° C./minute Measurement temperature retention (hold temperature, retention time): 180 ° C., 10 minutes First temperature decrease (Measurement temperature range, temperature decrease rate): 0 to 180 ° C., 10 ° C./min Second temperature increase (measurement temperature range, temperature increase rate): 0 to 180 ° C., 10 ° C./min (first temperature increase) The measurement temperature is maintained, the first temperature decrease and the second temperature increase are performed in this order).

In order to set the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass to 50 ° C. or higher, the following requirement a and the following requirement b are preferably satisfied. More preferably, at least one of the following requirements cd is further satisfied.
Requirement a: Glass transition point Tg (DSC 2nd Run) of amorphous polyester resin in a dry state is 65 ° C. or more Requirement b: 20 mass of crystalline polyester resin having a melting point of 60 ° C. or more as binder resin Requirement c including% or less: The acid value of the binder resin is 20 mgKOH / g or more Requirement d: The polymer dispersant exhibits basicity.

<Toner particles>
The toner particles of the present embodiment have a binder resin, a colorant, and a polymer dispersant, and preferably 50 to 99% by mass of the binder resin, 0.5 to 40% by mass of the colorant, and 0.5. Up to 40% by weight of a polymeric dispersant. The toner particles of the present exemplary embodiment may include an arbitrary component different from the binder resin, the colorant, and the polymer dispersant, and examples of the optional component include a wax or a charge control agent. .

  Preferably, the median diameter D50 (hereinafter referred to as “toner particle median diameter D50”) when the particle size distribution of the toner particles is measured on a volume basis is 0.5 μm or more and 5.0 μm or less. This median diameter D50 is smaller than the particle diameter of toner particles contained in a conventional dry developer, and is one of the features of this embodiment. When the median diameter D50 of the toner particles is 0.5 μm or more, the particle diameter of the toner particles can be ensured, so that the mobility of the toner particles in the electric field is improved, and thus the developability can be improved. If the median diameter D50 of the toner particles is 5.0 μm or less, the dispersibility of the toner particles can be secured, and the image quality can be improved. More preferably, the median diameter D50 of the toner particles is 1.0 μm or more and 2.0 μm or less.

  Preferably, the average circularity of the toner particles is 0.85 or more and 0.95 or less, and the standard deviation of the circularity of the toner particles is 0.01 or more and 0.1 or less. Thereby, transferability and cleaning properties are improved. The “circularity” means a numerical value obtained by dividing the perimeter of a circle having the same area as the particle area projected in two dimensions by the perimeter of the particle. “Average circularity” means an arithmetic average value of the calculated circularity.

  For example, the median diameter D50 of the toner particles can be measured using a flow type particle image analyzer (product number “FPIA-3000S” manufactured by Sysmex Corporation). In this analyzer, it is possible to use the solvent as a dispersion medium as it is. Therefore, by using this analyzer, it is possible to measure the state of the toner particles in a state closer to the actual dispersed state than measured in the aqueous system.

  The toner particles of this embodiment preferably have a core / shell structure. The core / shell structure includes core particles including a core resin and a shell resin that is provided on at least a part of the surface of the core particles and is a resin different from the core resin. As a result, it is possible to reduce the toner particle size and make the toner particle size uniform. The “shell resin that is a resin different from the core resin” means that at least one of the chemical structure and the molecular weight is different between the core resin and the shell resin.

  When the toner particles have a core / shell structure, both the core resin and the shell resin function as a binder resin. The colorant may be dispersed in at least one of the core resin and the shell resin.

  When the toner particles have a core / shell structure, the mass ratio [(mass of core resin) :( mass of shell resin)] of the core resin and the shell resin is preferably 99: 1 to 30:70. . In terms of uniformity of toner particle diameter and heat stability of the liquid developer, the mass ratio of the shell resin to the core resin is more preferably 98: 2 to 50:50, and still more preferably 97. : 3 to 65:35. When the mass of the shell resin is 1% by mass or more of the total mass of the core resin and the shell resin, the blocking resistance of the toner particles can be maintained high. If the mass of the shell resin is 70% by mass or less of the total of the mass of the core resin and the mass of the shell resin, the particle size uniformity of the toner particles can be maintained high.

(Binder resin)
The binder resin preferably has sharp melt properties. Thereby, fixing at a low temperature can be realized. Examples of the resin having sharp melt property include a polyester resin.

(Amorphous polyester resin)
The binder resin includes an amorphous polyester resin. Thereby, since the hardness of binder resin can be raised, the hardness of a toner particle can be raised. Accordingly, the toner particles can be prevented from being coalesced, so that the heat resistant storage stability of the liquid developer can be improved.

(Requirement a: Glass transition point Tg (DSC 2nd Run) of amorphous polyester resin in a dry state is 65 ° C. or higher)
If the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in the dry state is 65 ° C or higher, the glass transition point of the binder resin is prevented from lowering even if the binder resin is plasticized with an insulating liquid. it can. Therefore, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass can be set to 50 ° C. or higher. Therefore, even if any of the above-mentioned reasons α to γ occurs, the glass transition point of the binder resin in the image is equal to or higher than the storage temperature of the image, so that document offset can be prevented from occurring. More preferably, the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in the dry state is 70 ° C. or higher. More preferably, the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in the dry state is 130 ° C. or lower. Thereby, fixing at a relatively low temperature can be realized.

  In this specification, the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in the dry state is a temperature measured according to the following method.

  First, toner particles are separated from the liquid developer. Specifically, the liquid developer is centrifuged and the supernatant liquid is removed. The obtained solid content (toner particles) 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.

  Next, DSC is performed according to the following conditions using toner particles separated from the liquid developer. Thereby, a DSC curve (vertical axis: heat flow, horizontal axis: time or temperature) is obtained. Amorphous polyester in which the peak temperature of the valley peak (peak derived from endothermic reaction) appearing in the DSC curve (when there are multiple valley peaks, the peak temperature of the valley peak appearing on the lowest temperature side) in the dry state It becomes the glass transition point Tg (DSC 2nd Run) of the resin.

(Measurement condition)
Differential scanning calorimeter: Product name “DSC6200” manufactured by Hitachi High-Technologies Corporation
Mass of sample (toner particles): 5 mg
Reference sample: Aluminum First temperature increase (measurement temperature range, temperature increase rate): 30 to 180 ° C., 10 ° C./minute Measurement temperature retention (hold temperature, retention time): 180 ° C., 10 minutes First temperature decrease (Measurement temperature range, temperature decrease rate): 0 to 180 ° C., 10 ° C./min Second temperature increase (measurement temperature range, temperature increase rate): 0 to 180 ° C., 10 ° C./min (first temperature increase) The measurement temperature is maintained, the first temperature decrease and the second temperature increase are performed in this order).

  The monomer which becomes a structural unit (a structural unit derived from an acid component and a structural unit derived from an alcohol component) contained in the amorphous polyester resin is shown below.

  As a monomer that becomes a structural unit derived from the acid component, it is preferable to use an aromatic monomer. Examples of aromatic monomers that are structural units derived from the acid component include aromatic polycarboxylic acids, lower alkyl esters of aromatic polycarboxylic acids, or acid anhydrides of aromatic polycarboxylic acids. Can do. Specific examples include terephthalic acid, isophthalic acid, orthophthalic acid, 5-tert-butylisophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, or trimellitic acid. . From the viewpoint of availability, terephthalic acid, isophthalic acid, or 5-tert-butylisophthalic acid is preferably used. These acid anhydrides or lower alkyl esters thereof may be used.

  As a monomer which becomes a structural unit derived from an acid component, an aliphatic monomer may be used together with an aromatic monomer. Examples of the aliphatic monomer serving as 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, and 1,9-nonane. Dicarboxylic 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 An acid or 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 one of the above may be used alone, or two or more of the above may be used in combination. These acid anhydrides or lower alkyl esters thereof may be used.

  As a monomer that becomes a structural unit derived from an alcohol component, an aromatic monomer is preferably used. An aromatic polyhydric alcohol etc. can be mentioned as an aromatic monomer used as the structural unit derived from an alcohol component. 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. m and n each independently represent 0 or a positive integer. The sum of m and n is 1 or more and 16 or less.

  As the monomer serving as a structural unit derived from the alcohol component, an aliphatic monomer may be used together with an aromatic monomer. 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, 1,6-hexanediol, 1 , 7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, , 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 one of the above may be used alone, or two or more of the above may be used in combination.

In order to set the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in the dry state to 65 ° C. or higher, it is preferable that at least one of the following requirements a-11 to a-13 is satisfied. .
Requirement a-11: As a monomer serving as a structural unit derived from an alcohol component, an alkylene oxide adduct of bisphenol A represented by the above formula (I), 1,10-decanediol, 1,11-undecanediol, and 1 , 12-dodecanediol is used.
Requirement a-12: At least one of terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid is used as a monomer that is a structural unit derived from the acid component.

In order to set the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in the dry state to 70 ° C. or higher, it is preferable that at least one of the following requirements a-21 to a-23 is satisfied. .
Requirement a-21: An alkylene oxide adduct of bisphenol A represented by the above formula (I) is used as a monomer to be a structural unit derived from an alcohol component.
Requirement a-22: At least one of terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid is used as a monomer that is a structural unit derived from the acid component.

  The number average molecular weight (hereinafter referred to as “Mn”) of the amorphous polyester resin is preferably 1000 or more and 25000 or less, and the mass average molecular weight (hereinafter referred to as “Mw”) of the amorphous polyester resin is 2000 or more. It is preferable that it is 200000 or less.

In this specification, Mn and Mw of the amorphous polyester resin were measured using GPC (Gel Permeation Chromatography, gel permeation chromatography) with respect to the soluble content in tetrahydrofuran (THF) under the following conditions. Is. The crystalline polyester resin Mn and Mw (described later) were also measured under the same method and under the same conditions.
Measuring device: trade name “HLC-8120” manufactured by Tosoh Corporation
Column: Trade name “TSKgelGMHXL” (2) manufactured by Tosoh Corporation and product name “TSKgelMultiporeHXL-M” (1) manufactured by Tosoh Corporation
Sample solution: injection amount of sample solution into a 0.25 mass% THF solution column: 100 μl
Flow rate: 1 ml / min Measurement temperature: 40 ° C
Detector: Refractive index detector Reference material: Standard polystyrene (TSK standard POLYSYRENE) manufactured by Tosoh Corporation 12 points (molecular weight: 500, 1050, 2800, 5970, 9100, 18100, 37900, 96400, 190000, 355000, 1090000, 2890000 ).

(Crystalline polyester resin)
(Requirement b: the binder resin contains 20% by mass or less of a crystalline polyester resin having a melting point of 60 ° C. or higher)
The binder resin further contains 20% by mass or less of a crystalline polyester resin having a melting point of 60 ° C. or higher. As a result, not only document offset can be prevented, but fixing at a low temperature can be realized.

  Specifically, in order to set the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass to 50 ° C. or higher, the amorphous state has a high glass transition point in the dry state. It is conceivable to use a polyester resin as the binder resin (for example, the above requirement a). However, if the glass transition point of the amorphous polyester resin is increased, the viscoelasticity of the binder resin may be difficult to decrease during fixing. For this reason, the adhesion strength of the toner particles to the recording medium may decrease, and thus the fixing strength of the toner particles to the recording medium may decrease. Therefore, it may be difficult to realize fixing at a low temperature.

  However, if a crystalline polyester resin having a melting point of 60 ° C. or higher is contained in the binder resin, it is considered that the crystalline polyester resin is melted at the time of fixing. Can be reduced. As a result, the adhesion strength of the toner particles to the recording medium can be maintained high, so that the fixing strength of the toner particles to the recording medium can be maintained high. Therefore, fixing at a low temperature can be realized.

  Preferably, the crystalline polyester resin contained in the binder resin has a melting point of 65 ° C. or higher. Thereby, when the liquid developer is stored, the crystalline polyester resin can be prevented from melting, so that the toner particles can be prevented from being coalesced. Therefore, the heat resistant storage stability of the liquid developer can be maintained high. More preferably, the melting point of the crystalline polyester resin contained in the binder resin is 130 ° C. or less. Thereby, fixing at a relatively low temperature can be realized.

  Moreover, if the content rate of crystalline polyester resin (melting point is 60 degreeC or more) in binder resin is 20 mass% or less, the content rate of soft resin (crystalline polyester resin) in binder resin can be suppressed low. . Thereby, since the hardness of binder resin can be maintained high, the fluidity | liquidity of binder resin can be maintained low. Therefore, since the above-mentioned reason γ can be prevented, the glass transition point of the binder resin in the image becomes higher than the storage temperature of the image. Therefore, the occurrence of document offset can be further prevented.

  Preferably, the content ratio of the crystalline polyester resin (melting point is 60 ° C. or higher) in the binder resin is 10% by mass or more and 20% by mass or less. When the content ratio is 10% by mass or more, the effect (realization of fixing at low temperature) obtained by adding the crystalline polyester resin to the binder resin can be effectively obtained. That is, the content ratio of the amorphous polyester resin in the binder resin is preferably 80% by mass or more, and more preferably 80% by mass or more and 90% by mass or less.

  As a monomer which becomes a structural unit (a structural unit derived from an acid component and a structural unit derived from an alcohol component) contained in the crystalline polyester resin, an aliphatic monomer (among the monomers serving as a structural unit derived from an acid component) It is preferable to use an aliphatic monomer (described above) among monomers serving as structural units derived from the alcohol component. Along with these monomers, among the aromatic monomers (above) among the monomers that are constituent units derived from the acid component, and among the aromatic monomers (above) among the monomers that are constituent units derived from the alcohol component At least one of the above may be further used.

  The Mn of the crystalline polyester resin is preferably 1000 or more and 25000 or less, and the Mw of the crystalline polyester resin is preferably 2000 or more and 200000 or less. The Mn and Mw of the crystalline polyester resin can be measured according to the method for measuring Mn and Mw of the amorphous polyester resin.

  More preferably, the Mn of the crystalline polyester resin is 2000 or more. Thereby, melting | fusing point of crystalline polyester resin can be 60 degreeC or more. Therefore, it is preferable to appropriately select a monomer as a constituent unit contained in the crystalline polyester resin or to appropriately set the degree of polymerization of the monomer so that the Mn of the crystalline polyester resin is 2000 or more.

  The binder resin may contain less than 10% by mass of a resin (for example, a styrene-acrylic resin, a urethane resin, or an epoxy resin) different from the crystalline polyester resin and the amorphous polyester resin. When the content is 10% by mass or more, it may be difficult to regularly arrange the molecular chains of the polyester resin.

(Crystalline and amorphous)
When the “crystalline polyester resin” is defined in terms of physical properties, it is defined that the heat of fusion of the polyester resin measured by DSC (Differential Scanning Calorimetry) satisfies the following mathematical formulas (1) and (2). On the other hand, when at least one of the following mathematical formulas (1) and (2) is not satisfied, the polyester resin is defined as not having crystallinity.
5 ≦ H1 ≦ 100 (1)
0.2 ≦ H2 / H1 ≦ 1.0 (2)
In the above formulas (1) and (2), H1 represents the heat of fusion (J / g) at the first temperature rise by the DSC method, and H2 is the heat of fusion (J / g) at the second temperature rise by the DSC method. ).

  H1 is an index of the melting rate of the polyester resin. In general, a resin having heat of fusion has a sharp melt property and therefore melts with a small amount of energy. If the H1 of the polyester resin exceeds 100, it is difficult to reduce the fixing energy. For this reason, the fixing property of the toner particles is lowered. On the other hand, if the H1 of the polyester resin is less than 5, the fixing energy becomes too small, and document offset is likely to occur. However, if the H1 of the polyester resin satisfies the above formula (1), the occurrence of document offset can be prevented, and the toner particle fixing property can be prevented from being lowered. Preferably 15 ≦ H1 ≦ 80, more preferably 35 ≦ H1 ≦ 70.

  H2 / H1 in the above formula (2) is an index of the crystallization speed of the polyester resin. In general, when a resin particle (resin particle) is used after being cooled and then cooled, if there is a non-crystallized portion in the crystal component in the resin particle, the resistance value of the resin particle is Inconveniences such as lowering or plasticization of the resin particles occur. When such a malfunction occurs, the performance of the resin particles obtained by cooling may differ from the originally designed performance. From the above, it is necessary to quickly crystallize the crystal component in the resin particles so as not to affect the performance of the resin particles. H2 / H1 is more preferably 0.3 or more, and further preferably 0.4 or more. Further, if the crystallization speed of the polyester resin is high, H2 / H1 approaches 1.0. Therefore, H2 / H1 preferably takes a value close to 1.0.

  Note that H2 / H1 in the above formula (2) does not theoretically exceed 1.0, but it may exceed 1.0 in the actual measurement value by the DSC method. Even when the actual measurement value (H2 / H1) by the DSC method exceeds 1.0, the above formula (2) is satisfied.

  H1 and H2 can be measured in accordance with JIS-K7122 (1987) “Method for measuring transition heat of plastic”. Specifically, first, 5 mg of a polyester resin is collected and placed in an aluminum pan. Using a differential scanning calorimeter (for example, a product number “RDC220” manufactured by SII Nano Technology Co., Ltd. or a product number “DSC20” manufactured by Seiko Instruments Inc.), the heating rate is 10 ° C./min. The temperature (melting point) at the endothermic peak of the polyester resin is measured to determine the endothermic peak area S1. And H1 is computable from the area | region S1 of the calculated | required endothermic peak. After calculating H1, after cooling to 0 ° C at a cooling rate of 90 ° C / min, the temperature (melting point) at the endothermic peak of the polyester resin due to melting was measured at a rate of temperature rise of 10 ° C per minute, and the endothermic peak The area S2 is obtained. And H2 is computable from the area | region S2 of the calculated | required endothermic peak.

  H1 and H2 can also be measured according to the following method using a differential scanning calorimeter (eg, product number “DSC210” manufactured by Seiko Instruments Inc.). First, the standard sample and the polyester resin are heated from 0 ° C. to 180 ° C. at a rate of 10 ° C./min, and the difference between the heat amount of the standard sample and the heat amount of the polyester resin is measured. The difference in the amount of heat measured is the heat of fusion H1 by the DSC method of the polyester resin. Then, after cooling to 0 ° C. at a cooling rate of 90 ° C./min, the standard sample and the polyester resin are heated from 0 ° C. to 180 ° C. at a rate of 10 ° C./min. Measure the difference. The difference in the amount of heat measured is the heat of fusion H2 of the polyester resin by the DSC method.

(Binder resin acid value)
(Requirement c: The acid value of the binder resin is 20 mgKOH / g or more)
The acid value of the binder resin is preferably 20 mgKOH / g or more. Thereby, since the amount of the carboxyl group residue contained in the binder resin increases, the binder resin has polarity. Therefore, the affinity between the binder resin and the insulating liquid is reduced (the difference between the SP value of the binder resin and the SP value of the insulating liquid is increased). In addition, if the acid value of the binder resin is 20 mgKOH / g or more, the amount of carboxyl group residues contained in the binder resin increases, and the binder resin easily forms a crosslinked structure. Therefore, the gap into which the insulating liquid enters in the binder resin can be reduced. From these facts, if the acid value of the binder resin is 20 mgKOH / g or more, the insulating liquid can be prevented from entering the binder resin, so that the above-mentioned reason α can be prevented from occurring. Therefore, since the glass transition point of the binder resin in the image becomes higher than the image storage temperature, the occurrence of document offset can be further prevented.

  Preferably, the acid value of the binder resin is 30 mgKOH / g or more. Thereby, since the amount of the carboxyl group residue contained in the binder resin is further increased, it is possible to further prevent the insulating liquid from entering the binder resin. Therefore, the occurrence of the reason α can be further prevented, so that the glass transition point of the binder resin in the image becomes higher than the storage temperature of the image. Therefore, the occurrence of document offset can be further prevented. In fact, it is difficult to make the acid value of the binder resin larger than 100 mgKOH / g. Even if the acid value of the binder resin can be made larger than 100 mgKOH / g, it is difficult to control its thermophysical properties.

  As described above, the binder resin preferably contains a polyester resin. Therefore, the adjustment of the acid value of the binder resin is performed according to the following method. For example, changing the type of structural unit derived from an alcohol component or the type of structural unit derived from an acid component, a mixed mole of a monomer serving as a structural unit derived from an alcohol component and a monomer serving as a structural unit derived from an acid component Examples include changing the ratio or changing the conditions of the condensation reaction. By adopting any of these methods, the amount (molar amount) of the hydroxyl group contained in the monomer serving as the structural unit derived from the alcohol component is changed to the amount of the carboxyl group contained in the monomer serving as the structural unit derived from the acid component. More than the amount (molar amount). In this way, a polyester resin having hydroxyl groups at both ends (hereinafter referred to as “an intermediate of the polyester resin”) is synthesized. The polyester resin intermediate and the polycarboxylic acid are adjusted by adjusting the size relationship between the amount of hydroxyl group (molar amount) contained in the polyester resin intermediate and the amount of the carboxyl group contained in polycarboxylic acid (molar amount). Can be reacted to optimize the acid value of the polyester resin. Therefore, the acid value of the binder resin can be adjusted. Here, the “polycarboxylic acid” means a carboxylic acid having two or more functional groups (for example, a carboxyl group).

  In addition, if a monomer containing three or more functional groups (for example, carboxyl groups) is used as a monomer serving as a structural unit derived from the acid component, the acid value of the polyester resin increases, so the acid value of the binder resin increases. . Examples of the aliphatic monomer containing three or more functional groups (for example, carboxyl group) include butanetricarboxylic acid, cyclohexanetricarboxylic acid, hexanetetracarboxylic acid, octanetetracarboxylic acid, biphenyltetracarboxylic acid, and butanetetracarboxylic acid. At least one of the acids can be used. Examples of the aromatic monomer containing three or more functional groups (for example, carboxyl group) include at least one of trimellitic acid, trimesic acid, naphthalenetricarboxylic acid, benzophenonetetracarboxylic acid, and pyromellitic acid. Can be used. These acid anhydrides or lower alkyl esters thereof may be used.

(Core resin and shell resin)
When the toner particles have a core / shell structure, the core resin preferably contains a polyester resin (see above (binder resin)). More preferably, the core resin contains an amorphous polyester resin, and the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in a dry state is 65 ° C. or higher (the above (amorphous polyester resin) reference). More preferably, the core resin contains 20% by mass or less of a crystalline polyester resin having a melting point of 60 ° C. or more (see the above (crystalline polyester resin)).

  Further, the acid value of the core resin is preferably 20 mgKOH / g or more, more preferably 30 mgKOH / g or more (see the above (acid value of the binder resin)).

  Shell resin has the effect | action which adheres to the surface of a core particle and improves the dispersibility of a core particle. That is, the shell resin functions as a polymer dispersant. The shell resin may be either a thermoplastic resin or a thermosetting resin. For example, vinyl resin, polyurethane resin, epoxy resin, polyamide resin, polyimide resin, silicon resin, phenol resin, melamine resin, urea resin, aniline A resin, an ionomer resin, or a polycarbonate resin is preferable. The shell resin may be a polyester resin made of a component different from the core resin.

  The shell resin is preferably a vinyl resin, a polyester resin, a polyurethane resin, or an epoxy resin, and more preferably a vinyl resin, from the viewpoint that the shape of the toner particles can be easily controlled during the production of the toner particles. Shell resin may be comprised from one of these resin, and 2 or more types of resin may be mixed and comprised. Hereinafter, the vinyl resin will be described.

(Vinyl resin)
The vinyl resin may be a homopolymer obtained by homopolymerizing a monomer having a polymerizable double bond (a homopolymer containing a bond unit derived from a vinyl monomer), or a polymerizable double bond. It may be a copolymer obtained by copolymerizing two or more kinds of monomers (a copolymer containing a bond unit derived from a vinyl monomer). Examples of the monomer having a polymerizable double bond include the following (1) to (9).

(1) Hydrocarbon having a polymerizable double bond (1-1) Aliphatic hydrocarbon having a polymerizable double bond (1-1-1) Chained aliphatic hydrocarbon having a polymerizable double bond Polymerization Chain aliphatic hydrocarbons having an ionic double bond include, for example, alkenes having 2 to 30 carbon atoms (for example, ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.) Or an alkadiene having 4 to 30 carbon atoms (for example, butadiene, isoprene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, etc.).

(1-1-2) Cyclic aliphatic hydrocarbon having a polymerizable double bond Cyclic aliphatic hydrocarbon having a polymerizable double bond is, for example, a monocycloalkene having 6 to 30 carbon atoms or a dicycloalkene. A cycloalkene (such as cyclohexene, vinylcyclohexene or ethylidenebicycloheptene), or a monocycloalkadiene or dicycloalkadiene having 5 to 30 carbon atoms (such as monocyclopentadiene or dicyclopentadiene) Preferably there is.

(1-2) Aromatic hydrocarbon having a polymerizable double bond The aromatic hydrocarbon having a polymerizable double bond is, for example, styrene or a hydrocarbyl of styrene (for example, an alkyl having 1 to 30 carbon atoms). , Cycloalkyl, aralkyl or alkenyl) substituted (for example, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotylbenzene, Divinylbenzene, divinyltoluene, divinylxylene, trivinylbenzene, etc.) or vinylnaphthalene is preferred.

(2) Monomers having a carboxyl group and a polymerizable double bond and salts thereof Monomers having a carboxyl group and a polymerizable double bond are, for example, unsaturated monocarboxylic acids having 3 to 15 carbon atoms [for example, , (Meth) acrylic acid, crotonic acid, isocrotonic acid or cinnamic acid], unsaturated dicarboxylic acid (anhydride) having 3 to 30 carbon atoms [for example, (anhydrous) maleic acid, fumaric acid, itaconic acid, ( Anhydrous) citraconic acid or mesaconic acid], monoalkyl (carbon number 1 to 10) ester of unsaturated dicarboxylic acid having 3 to 10 carbon atoms (for example, maleic acid monomethyl ester, maleic acid monodecyl ester, fumaric acid) Acid monoethyl ester, itaconic acid monobutyl ester, citraconic acid monodecyl ester, etc.) It is preferable. As used herein, “(meth) acryl” means at least one of acrylic and methacrylic.

  Examples of the salt of the monomer include an alkali metal salt (for example, sodium salt or potassium salt), an alkaline earth metal salt (for example, calcium salt or magnesium salt), an ammonium salt, an amine salt, or a quaternary ammonium salt. A salt or the like is preferable.

  The amine salt is not particularly limited as long as it is an amine compound. For example, a primary amine salt (eg, ethylamine salt, butylamine salt or octylamine salt), secondary amine salt (eg, diethylamine salt or dibutylamine salt) Etc.) or a tertiary amine salt (for example, triethylamine salt or tributylamine salt).

  The quaternary ammonium salt is preferably, for example, a tetraethylammonium salt, a triethyllaurylammonium salt, a tetrabutylammonium salt, or a tributyllaurylammonium salt.

  Examples of the salt of a monomer having a carboxyl group and a polymerizable double bond include sodium acrylate, sodium methacrylate, monosodium maleate, disodium maleate, potassium acrylate, potassium methacrylate, monopotassium maleate, acrylic Lithium acid, cesium acrylate, ammonium acrylate, calcium acrylate, aluminum acrylate, or the like is preferable.

(3) Monomers having a sulfo group and a polymerizable double bond and salts thereof (4) Monomers having a phosphono group and a polymerizable double bond and salts thereof (5) A hydroxyl group and a polymerizable double bond Monomer having (3) to (5) are not listed as specific examples, but can be used as monomers of vinyl resin.

(6) Nitrogen-containing monomer having a polymerizable double bond (6-1) Monomer having an amino group and a polymerizable double bond A monomer having an amino group and a polymerizable double bond is, for example, aminoethyl (meta ) 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-dimethylaminostyrene, methyl-α-acetaminoacrylate, vinylimidazole, N-vinylpyrrole, N-vinylthiopyrrolidone, N-arylphenylenediamine, aminocarbazole, aminothiazole Aminoindole, aminopyrrole, it is preferable that in such aminoimidazole or amino mercaptothiazole.

  The monomer having an amino group and a polymerizable double bond may be a salt of the monomers listed above. Examples of the salts of the monomers listed above include the salts listed as “Salts of the above monomers” in “(2) Monomers having a carboxyl group and a polymerizable double bond and their salts”.

(6-2) Monomer having an amide group and a polymerizable double bond Monomers having an amide group and a polymerizable double bond are, for example, (meth) acrylamide, N-methyl (meth) acrylamide, and N-butylacrylamide. , Diacetone acrylamide, N-methylol (meth) acrylamide, N, N′-methylene-bis (meth) acrylamide, cinnamic acid amide, N, N-dimethylacrylamide, N, N-dibenzylacrylamide, methacrylformamide, N— Methyl-N-vinylacetamide or N-vinylpyrrolidone is preferred.

(6-3) Monomer having 3 to 10 carbon atoms having nitrile group and polymerizable double bond Monomer having 3 to 10 carbon atoms having nitrile group and polymerizable double bond is, for example, (meta ) Acrylonitrile, cyanostyrene or cyanoacrylate is preferred.

(6-4) Monomer having 8 to 12 carbon atoms having nitro group and polymerizable double bond Monomer having 8 to 12 carbon atoms having nitro group and polymerizable double bond is, for example, nitrostyrene And the like.

(7) Monomer having 6 to 18 carbon atoms having an epoxy group and a polymerizable double bond (8) Monomer having 2 to 16 carbon atoms having a halogen element and a polymerizable double bond Above (7) and ( Although a specific example is not enumerated about 8), it can be used as a monomer of a vinyl resin.

(9) Ester having 4 to 16 carbon atoms having a polymerizable double bond Ester having 4 to 16 carbon atoms having a polymerizable double bond includes, for example, vinyl acetate, vinyl propionate, vinyl butyrate, diallyl phthalate , Diallyl adipate, isopropenyl acetate, vinyl methacrylate, methyl-4-vinyl benzoate, cyclohexyl methacrylate, benzyl methacrylate, phenyl (meth) acrylate, vinyl methoxyacetate, vinyl benzoate, ethyl-α-ethoxy acrylate, 1 to 11 carbon atoms Alkyl (meth) acrylates having the following alkyl groups [for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate or 2-ethylhexyl ( Meth) acrylates, etc.], dialkyl fumarate (the two alkyl groups are straight, branched or alicyclic alkyl groups having 2 to 8 carbon atoms), dialkyl maleates (2 Each alkyl group is a straight chain alkyl group having 2 to 8 carbon atoms, a branched alkyl group or an alicyclic alkyl group), poly (meth) allyloxyalkanes (for example, diaryloxyethane, Triaryloxyethane, tetraallyloxyethane, tetraallyloxypropane, tetraallyloxybutane or tetrametaallyloxyethane), a monomer having a polyalkylene glycol chain and a polymerizable double bond [eg, polyethylene glycol (Mn = 300) Mono (meth) acrylate, polypropylene glycol (Mn = 500) monoacrylate , Methyl alcohol ethylene oxide (hereinafter, “ethylene oxide” is referred to as “EO”) 10 mol adduct (meth) acrylate or lauryl alcohol EO 30 mol adduct (meth) acrylate, etc.], or poly (meth) acrylates { For example, poly (meth) acrylates of polyhydric alcohols [for example, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate or polyethylene Glycol di (meth) acrylate and the like]} and the like. As used herein, “(meth) arylo” means at least one of alilo and metallillo.

  Specific examples of the vinyl resin include, for example, a styrene- (meth) acrylic acid ester copolymer, a styrene-butadiene copolymer, a (meth) acrylic acid- (meth) acrylic acid ester copolymer, and a styrene-acrylonitrile copolymer. Polymer, styrene- (maleic anhydride) copolymer, styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid-divinylbenzene copolymer, or styrene-styrenesulfonic acid- (meth) acrylic Examples include acid ester copolymers.

  The vinyl resin may be a homopolymer or copolymer of a monomer having the polymerizable double bond of (1) to (9) above, or the polymerizable double bond of (1) to (9) above. And a monomer having a first molecular chain and a polymerizable double bond may be polymerized. The first molecular chain has an affinity for the insulating liquid, for example, a linear hydrocarbon chain having 12 to 27 carbon atoms, a branched hydrocarbon chain having 12 to 27 carbon atoms. And a fluoroalkyl chain having 4 to 20 carbon atoms, or a polydimethylsiloxane chain. The difference between the SP value of the monomer having the first molecular chain and the polymerizable double bond and the SP value of the insulating liquid is preferably 2 or less. In the present specification, the “SP value” is a method according to Fedors [Polym. Eng. Sci. 14 (2) 152, (1974)].

  The monomer having the first molecular chain and the polymerizable double bond is preferably, for example, the following first to third monomers. The monomer having the first molecular chain and the polymerizable double bond may be any of the first to third monomers, or a combination of two or more of the first to third monomers. There may be.

  The first monomer is a monomer having a linear hydrocarbon chain having 12 to 27 carbon atoms (preferably 16 to 25 carbon atoms) and a polymerizable double bond, such as an unsaturated monocarboxylic acid. Mono-linear alkyl (alkyl having 12 to 27 carbon atoms) ester or unsaturated dicarboxylic acid mono-linear alkyl (alkyl having 12 to 27 carbon atoms) ester. The unsaturated monocarboxylic acid and unsaturated dicarboxylic acid are preferably vinyl monomers containing a carboxyl group and having 3 to 24 carbon atoms. For example, (meth) acrylic acid, maleic acid, fumaric acid, crotonic acid, itacone An acid or citraconic acid is preferred. Specific examples of the first monomer include, for example, dodecyl (meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate or (meth) acrylic. Examples include eicosyl acid.

  The second monomer is a monomer having a branched hydrocarbon chain having 12 to 27 carbon atoms (preferably 16 to 25 carbon atoms) and a polymerizable double bond, for example, an unsaturated monocarboxylic acid Mono-branched alkyl (alkyl having 12 to 27 carbon atoms) ester or mono-branched alkyl (alkyl having 12 to 27 carbon atoms) of unsaturated dicarboxylic acid. The unsaturated monocarboxylic acid and unsaturated dicarboxylic acid are as described for the first monomer. Specific examples of the second monomer include 2-decyltetradecyl (meth) acrylate.

  The third monomer is a monomer having a fluoroalkyl chain having 4 to 20 carbon atoms and a polymerizable double bond. Specific examples of the third monomer include those in which the hydrocarbon chain is replaced with a fluoroalkyl chain in the specific example of the first monomer or the specific example of the second monomer.

  The Mn of the shell resin is preferably 100 or more and 5000000 or less, more preferably 200 or more and 5000000 or less, and further preferably 500 or more and 500000 or less. The Mn of the shell resin can be measured by GPC.

The SP value of the shell resin is preferably about 7 to 18 (cal / cm ³ ) ^1/2 , more preferably about 8 to 14 (cal / cm ³ ) ^1/2 .

  Such a shell resin may be formed in a particle shape on the surface of the core particle, or may be formed in a film shape. The shell particles (particles containing the shell resin) or the shell film (film containing the shell resin) may further contain a colorant or an optional component (for example, a pigment dispersant, a wax or a charge control agent).

  The median diameter D50 when the particle size distribution of the shell particles contained in the shell dispersion is measured on a volume basis so that the median diameter D50 of the toner particles falls within a desired range (hereinafter referred to as “the median diameter D50 of the shell particles”). ) Is suitably adjusted. The median diameter D50 of the shell particles is preferably 0.0005 μm or more and 3 μm or less. The upper limit of the median diameter D50 of the shell particles is more preferably 2 μm, and even more preferably 1 μm. The lower limit of the median diameter D50 of the shell particles is more preferably 0.01 μm, still more preferably 0.02 μm, and still more preferably 0.04 μm. For example, when it is desired to obtain toner particles having a median diameter D50 of 1 μm, the median diameter D50 of the shell particles is preferably 0.0005 μm to 0.3 μm, and more preferably 0.001 μm to 0.2 μm. is there. When it is desired to obtain toner particles having a median diameter D50 of 10 μm, the median diameter D50 of the shell particles is preferably 0.005 μm to 3 μm, and more preferably 0.05 μm to 2 μm.

  The median diameter D50 of the shell particles is determined by a laser diffraction particle size distribution measuring device (for example, product number “LA-920” manufactured by Horiba, Ltd. or product number “Multisizer III” manufactured by Beckman Coulter, Inc.) or an optical system. It can be measured using a particle size distribution measuring apparatus using a laser Doppler method (product number “ELS-800” manufactured by Otsuka Electronics Co., Ltd.). When the median diameter D50 of the shell particles is measured using different measurement measurements, if a difference occurs in the measured values, measurement with a particle size distribution measuring device (product number “ELS-800” manufactured by Otsuka Electronics Co., Ltd.) Adopt value.

(Coloring agent)
The colorant is dispersed in the binder resin, and preferably has a particle size of 0.3 μm or less. If the particle size of the colorant is 0.3 μm or less, the dispersibility of the colorant can be further increased, so that the glossiness of the image can be further increased, and thus the desired color can be easily realized. Become.

  As the colorant, conventionally known pigments and the like can be used without any particular limitation, but the following pigments are preferably used from the viewpoints of cost, light resistance, and colorability. In terms of color composition, these pigments are usually classified into black pigments, yellow pigments, magenta pigments, and cyan pigments. Basically, colors other than black (color image) are toned by a subtractive color mixture of a yellow pigment, a magenta pigment, or a cyan pigment. The pigments shown below may be used alone, or two or more of the pigments shown below may be used in combination as required.

  As the pigment (black pigment) contained in the black colorant, for example, carbon black such as furnace black, channel black, acetylene black, thermal black, or lamp black may be used, or biomass-derived carbon black may be used. Alternatively, magnetic powder such as magnetite or ferrite may be used. Nigrosine (azine compound), which is a purple black dye, may be used alone or in combination. Nigrosine includes C.I. I. Solvent Black 7 or C.I. I. Solvent black 5 or the like can be used.

  Examples of the pigment (magenta pigment) contained in the magenta colorant include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, or C.I. I. And CI Pigment Red 222.

  Examples of the pigment (yellow pigment) contained in the yellow colorant include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 180, or C.I. I. And CI Pigment Yellow 185.

  Examples of the pigment (cyan pigment) contained in the cyan colorant include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. Pigment blue 62, C.I. I. Pigment blue 66 or C.I. I. And CI Pigment Green 7.

(Polymer dispersant)
(Requirement d: the polymer dispersant exhibits basicity)
The polymer dispersant means a dispersant having Mn of 1,000 to 1,000,000, and has a function of uniformly dispersing a colorant (pigment) in toner particles. In the present specification, the Mn of the polymer dispersant is measured by GPC.

  The polymer dispersant is preferably a basic dispersant (basic dispersant). In general, the basic polymer dispersant has a higher melting point or softening point than the binder resin. For this reason, the binder resin is difficult to be compatible with the basic polymer dispersant, and thus is not easily plasticized by the basic polymer dispersant. Thereby, the fall of the glass transition point of binder resin can be prevented. Therefore, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass is 50 ° C. or higher. Therefore, even if any of the above-mentioned reasons α to γ occurs, the glass transition point of the binder resin in the image is equal to or higher than the storage temperature of the image, so that document offset can be prevented from occurring.

  A basic dispersing agent means what is defined below. That is, 0.5 g of the polymer dispersant and 20 ml of distilled water were placed in a glass screw tube, and the glass screw tube was shaken for 30 minutes using a paint shaker and then filtered. The pH of the filtrate thus obtained is measured using a pH meter (trade name: “D-51”, manufactured by HORIBA, Ltd.), and the case where the pH is greater than 7 is defined as a basic dispersant. In addition, when the pH is smaller than 7, it shall call an acidic dispersing agent.

  The kind of such basic dispersant is not particularly limited. Basic dispersants are, for example, amine groups, amino groups, amide groups, pyrrolidone groups, imine groups, imino groups, urethane groups, quaternary ammonium groups, ammonium groups, pyridino groups, pyridium groups, imidazolino groups, or imidazoliums. A compound having a functional group such as a group in the molecule is preferred. In addition, as a dispersing agent, what is called surfactant which has a hydrophilic part and a hydrophobic part in a molecule | numerator normally corresponds. However, as long as it has an action of uniformly dispersing the colorant (pigment) in the toner particles, it is not limited to the surfactant, and various compounds can be used.

  As a commercial item of such a basic dispersant, for example, “Ajisper PB-821” (trade name), “Azisper PB-822” (trade name) or “Azisper PB-881” manufactured by Ajinomoto Fine Techno Co., Ltd. (Trade name) may be used, or “Solspers 28000” (trade name), “Solspurs 32000” (trade name), “Solspurs 32500” (trade name), “Solspurs 35100” manufactured by Nippon Lubrizol Co., Ltd. (Trade name) or “Solspers 37500” (trade name) may be used.

  It is more preferable to select a polymer dispersant that does not dissolve in the insulating liquid. In consideration of this point, use “Ajisper PB-821” (trade name), “Ajisper PB-822” (trade name) or “Ajisper PB-881” (trade name) manufactured by Ajinomoto Fine Techno Co., Ltd. Is more preferable. Although the detailed mechanism is unknown, use of such a polymer dispersant makes it easy to obtain toner particles having a desired shape.

  Such a polymer dispersant is preferably added in an amount of 1 to 100% by mass, more preferably 1 to 40% by mass, based on the colorant (pigment). If the amount of the polymeric dispersant added is 1% by mass or more, the dispersibility of the colorant (pigment) can be secured, so that the necessary ID (image density) can be achieved, and the toner particles are fixed to the recording medium. Strength can be secured. If the addition amount of the polymer dispersant is 100% by mass or less, the addition amount of the polymer dispersant can be prevented from being excessive, so that the excess of the polymer dispersant is prevented from dissolving in the insulating liquid. Therefore, the chargeability of the toner particles or the fixing strength of the toner particles can be maintained in a good state. The polymer dispersant may be used alone, or two or more of the polymer dispersants may be used in combination as necessary.

<Insulating liquid>
The insulating liquid preferably has a resistance value that does not disturb the electrostatic latent image (about 10 ¹¹ to 10 ¹⁶ Ω · cm), and is preferably a solvent having low odor and toxicity.

  Examples of the insulating liquid generally include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes, etc., but organic solvents having a flash point of 70 ° C. or higher. Can be used.

  Specifically, an organic solvent having a flash point of 70 ° C. or higher has low volatility. Therefore, when an organic solvent having a flash point of 70 ° C. or higher is used as the insulating liquid, the insulating liquid tends to remain in the image (occurrence of the above-described reason α). However, in the present embodiment, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass is 50 ° C. or higher. As a result, since the organic solvent having a flash point of 70 ° C. or higher is used as the insulating liquid, even if the insulating liquid remains in the image (occurrence of the above-mentioned reason α), the glass transition point of the binder resin in the image is the image. Above the storage temperature. Therefore, occurrence of document offset can be prevented. Therefore, an organic solvent having a flash point of 70 ° C. or higher can be used as the insulating liquid.

  If an organic solvent having a flash point of 70 ° C. or higher can be used as the insulating liquid, the amount of volatilization of the organic solvent during image formation can be suppressed, so that the volatilized organic solvent is applied to the surface of the transfer roller and the surface of the fixing roller. It can prevent adhesion. As a result, the wear of the surface of the transfer roller and the wear of the surface of the fixing roller can be prevented, so that the life of the transfer roller and the fixing roller can be maintained long.

  In addition, if an organic solvent having a flash point of 70 ° C. or higher can be used as the insulating liquid, the amount of volatilization of the organic solvent at the time of image formation can be suppressed, so that the liquid developer can be manufactured or the image can be formed. Safety can be improved.

  The organic solvent having a flash point of 70 ° C. or higher is preferably, for example, at least one of an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatic hydrocarbon, a halogenated hydrocarbon, and a polysiloxane. . For example, as an organic solvent having a flash point of 70 ° C. or higher, Moresco White (trade name, manufactured by Matsumura Oil Co., Ltd.), Isopar (trade name, manufactured by ExxonMobil) or Shellsol (trade name, Shell Chemicals Japan Co., Ltd.) In addition, IP solvent 1620, IP solvent 2028, or IP solvent 2835 (both trade names, manufactured by Idemitsu Kosan Co., Ltd.) can be used.

[Manufacture of liquid developer]
The method for producing the liquid developer of the present embodiment is not particularly limited, and examples thereof include conventionally known techniques such as a granulation method or a pulverization method. In order to obtain toner particles having a small diameter and a sharp particle size distribution, it is preferable to employ a granulation method rather than a pulverization method. A resin having a high melting property or a resin having a high crystallinity is soft even at room temperature and hardly pulverized. Therefore, in the pulverization method, the particle size of the toner particles may not be controlled to a desired particle size. However, in the granulation method, toner particles having a desired particle size can be obtained.

  The granulation method includes suspension polymerization method, emulsion polymerization method, fine particle aggregation method, method of adding a poor solvent to a resin solution to precipitate toner particles, spray drying method, etc. Is included.

  More preferably, a method of depositing toner particles by adding a poor solvent to the resin solution is employed. For example, when the toner particles have a core / shell structure, a liquid developer can be produced according to the following method. First, the core resin is dissolved in a good solvent to obtain a core resin forming solution (dispersed phase). After the core resin forming solution is mixed with a poor solvent (SP value is different from a good solvent) together with an interfacial tension adjusting agent (for example, a shell resin (continuous phase)), droplets are formed by applying shear. Thereafter, when the good solvent is volatilized, a liquid developer containing toner particles is obtained. In this method, the particle size of the toner particles or the shape of the toner particles can be highly controlled by appropriately adjusting the shearing method, the difference in interfacial tension, or the interfacial tension adjusting agent (for example, shell resin). Therefore, this method is suitable as a method for obtaining toner particles having a desired particle size distribution and a desired shape.

  When the core resin forming solution is mixed with a shell resin in a poor solvent, it is preferable to mix the core resin forming solution with a dispersion liquid (shell dispersion liquid) in which shell particles containing the shell resin are dispersed in the poor solvent. . For example, shell particles are preferably produced by any one of the following methods [1] to [7]. From the viewpoint of easy manufacture of shell particles, it is preferable to manufacture shell particles by the method [4], [6] or [7], and to manufacture shell particles by the method [6] or [7]. Is more preferable.

[1] The shell resin is pulverized dry using a known dry pulverizer such as a jet mill. [2] The shell resin powder is dispersed in an organic solvent, and a known wet disperser such as a bead mill or a roll mill is used. [3] Spray the shell resin solution using a spray dryer and dry it. [4] Add a poor solvent to the shell resin solution or cool it to supersaturate the shell resin and precipitate. [5] Disperse the shell resin solution in water or an organic solvent. [6] Polymerize the precursor of the shell resin in water by emulsion polymerization, soap-free emulsion polymerization, seed polymerization or suspension polymerization. [7] The shell resin precursor is polymerized in an organic solvent by dispersion polymerization or the like.

[Image forming method]
The image forming method of this embodiment includes a transfer process and a fixing process.

<Transfer process>
In the transfer step, the liquid developer of the present embodiment is transferred to a recording medium. FIG. 2 is a schematic conceptual diagram showing an example of a transfer process.

  For example, the liquid developer 21 is transferred to the recording medium 40 according to the following method. The liquid developer 21 is pumped up from the developing tank 22 by the anilox roller 23. The liquid developer 21 on the anilox roller 23 is sent to the leveling roller 25, and excess liquid developer is scraped off by the anilox regulating blade 24. On the leveling roller 25, the liquid developer 21 is adjusted to have a uniform and thin thickness.

  The liquid developer 21 on the leveling roller 25 is sent to the developing roller 26. The liquid developer 21 on the developing roller 26 is charged by the developing charger 28 and developed on the photoconductor 29, and excess liquid developer is scraped off by the developing cleaning blade 27. Specifically, the surface of the photoconductor 29 is uniformly charged by the charging unit 30, and the exposure unit 31 disposed around the photoconductor 29 emits light based on predetermined image information on the surface of the photoconductor 29. Irradiate. As a result, an electrostatic latent image based on predetermined image information is formed on the surface of the photoreceptor 29. By developing the formed electrostatic latent image, a toner image is formed on the photoreceptor 29. The excess liquid developer on the photoconductor 29 is scraped off by the cleaning blade 32.

  The toner image formed on the photosensitive member 29 is primarily transferred to the intermediate transfer member 33 in the primary transfer unit 37, and the liquid developer transferred to the intermediate transfer member 33 is recorded in the recording medium 40 (for example, high-quality paper) in the secondary transfer unit 38. ) Is secondarily transferred. The liquid developer remaining on the intermediate transfer member 33 without being subjected to the secondary transfer is scraped off by the intermediate transfer member cleaning unit 34.

<Fixing process>
In the fixing step, the toner particles contained in the liquid developer transferred to the recording medium are fixed on the recording medium. Preferably, the fixing step includes a step of heating the recording medium and a step of fixing the toner particles to the recording medium while applying pressure to the recording medium. More preferably, in the fixing step, the toner particles are fixed to the recording medium while heating the recording medium and applying pressure to the recording medium. FIG. 3 is a side view showing an example of the fixing process.

  The method of heating the recording medium includes a method of heating the recording medium in a state where the heat source is in contact with the recording medium (contact heating method), and a method of heating the recording medium in a state where the heat source is separated from the recording medium (non-contact). Contact heating method). When combining contact heating and non-contact heating, it is preferable to perform contact heating after non-contact heating (see FIG. 3).

  When non-contact heating and contact heating are combined, the heating step is performed twice. Therefore, even when a sufficient amount of heat cannot be applied to the toner particles (toner particles transferred to the recording medium 40) in the non-contact heating, it is possible to prevent the fixing strength from being lowered. Therefore, an image having excellent gloss can be obtained. Further, if non-contact heating and contact heating are combined, it is possible to prevent the occurrence of cold offset in contact heating. From the above, it is preferable to combine non-contact heating and contact heating. “Cold offset” refers to an adhesive force in which at least a part of a toner image formed on a recording medium works between a fixing roller and a toner particle or a fixing roller and a toner particle when the toner particles are fixed with a heat roller. Means that the recording medium is removed from the recording medium by electrostatic attraction force or the like.

  For example, non-contact heating can be performed using the non-contact heater 51. The non-contact heater 51 preferably has a heating unit 53 and a heat insulating cover 55. The heating unit 53 is preferably a heat source that can be heated to 200 ° C. to 700 ° C., and is preferably a ceramic heater, for example. It is preferable that the heat insulating cover 55 mainly covers a portion of the heating unit 53 that does not face the recording medium 40.

  For example, contact heating can be performed using the first fixing roller 61 and the second fixing roller 63. The first fixing roller 61 is heated by the built-in type heating unit 65, and the second fixing roller 63 is heated by the built-in type heating unit 65. The built-in heating unit 65 is preferably a heat source that can be heated to 200 ° C. or more and 2000 ° C. or less, whereby the temperature of each of the first fixing roller 61 and the second fixing roller 63 is 80 ° C. or more and 130 ° C. or less. can do.

  The toner particles may be fixed to the recording medium 40 only by contact heating without performing non-contact heating. In this case, for example, contact heating may be performed using the first fixing roller 61 and the second fixing roller 63. Note that at least one of the first fixing roller 61 and the second fixing roller 63 may be heated by a heating unit provided outside the roller.

  In the image formation of this embodiment, an image is formed using the liquid developer of this embodiment. This makes it possible to achieve both fixing with low energy and prevention of document offset.

  Specifically, conventionally, when fixing is performed with low energy, it is difficult to reduce the remaining amount of the insulating liquid in the image fixed on the recording medium, and as a result, document offset occurs. On the other hand, if the fixing conditions are optimized so that the remaining amount of the insulating liquid in the image fixed on the recording medium is reduced, the occurrence of document offset can be prevented, but fixing with low energy becomes difficult. For this reason, it has been considered difficult to achieve both low-energy fixing and document offset prevention.

  However, in the present embodiment, the liquid developer of the present embodiment (the liquid developer having a glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid concentration of 80% by mass of 50 ° C. or more. ) To form an image. Therefore, even if the residual amount of the insulating liquid in the image fixed on the recording medium is 3% by mass to 30% by mass of the toner particle content (occurrence of the above-mentioned reason α), the binder resin glass in the image The transition point is above the image storage temperature. Therefore, occurrence of document offset can be prevented.

  In addition, document offset can be prevented even when the remaining amount of the insulating liquid in the image fixed on the recording medium is 3% by mass to 30% by mass of the toner particle content. A part of the insulating liquid may be volatilized from the transferred image. Thereby, at the time of fixing, the amount of heat for volatilizing the insulating liquid can be reduced. Therefore, fixing with low energy is possible. As described above, in this embodiment, it is possible to achieve both fixing with low energy and prevention of occurrence of document offset.

  The condition that the remaining amount of the insulating liquid in the image fixed on the recording medium is 3% by mass or more and 30% by mass or less of the toner particle content is, for example, a trade name “Idemitsu Kosan Co., Ltd.” And the temperature of the recording medium immediately after the fixing step (for example, immediately after passing through the fixing roller) is set to 80 ° C. or higher and 130 ° C. or lower.

In this specification, the ratio of the remaining amount of the insulating liquid to the content of toner particles in the image fixed on the recording medium is measured according to the following method. First, the toner layer is peeled off from the image immediately after being fixed on the recording medium using a cutter or the like. The quality (W1) of the peeled toner layer is measured. Thereafter, the peeled toner layer was heated at 100 ° C. for 30 minutes, and then the mass (W2) of the toner layer was measured, and the ratio (based on the content of toner particles in the image fixed on the recording medium) using the following formula: The ratio of the remaining amount of the insulating liquid) is calculated. The insulating liquid remaining in the image is volatilized from the toner layer by the heating. Therefore, (W1-W2) in the following formula corresponds to the remaining amount of the insulating liquid in the image.
(Ratio of remaining amount of insulating liquid to toner particle content in image fixed on recording medium) = (W1−W2) / W1.

EXAMPLES Hereinafter, although this invention is shown using an Example, this invention is not limited to the Example shown below.
<Production Example 1> [Production of Amorphous Polyester Resin (A)]
In a reaction vessel equipped with a stirrer, a heating / cooling device, and a thermometer, 677 parts by mass of bisphenol A propion oxide 2 mol adduct, 229 parts by mass of terephthalic acid, 28 parts by mass of adipic acid, and titanium dihydroxybis (triethanolamate) (Condensation catalyst) 2 parts by mass were added. While removing generated water, the reaction was carried out at 180 ° C. under a nitrogen stream for 8 hours.

  Next, it was made to react under nitrogen stream for 4 hours, heating up gradually to 220 degreeC and distilling off the water to produce | generate. Then, it was made to react under the reduced pressure of 0.007-0.026 MPa for 1 hour. 45 parts by mass of trimellitic anhydride was further added to the reaction vessel and reacted at 180 ° C. for 1 hour. In this way, an amorphous polyester resin (A) was obtained. In the obtained amorphous polyester resin (A), the acid value was 25 mgKOH / g, and the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin (A) in a dry state was 66 ° C.

<Production Example 2> [Production of Amorphous Polyester Resin (B)]
In a reaction vessel equipped with a stirrer, a heating / cooling device and a thermometer, 674 parts by mass of bisphenol A propion oxide 2-mole adduct, 324 parts by mass of terephthalic acid, and 2 parts by mass of titanium dihydroxybis (triethanolaminate) (condensation catalyst). And put a part. While removing generated water, the reaction was carried out at 180 ° C. under a nitrogen stream for 8 hours.

  Next, it was made to react under nitrogen stream for 4 hours, heating up gradually to 220 degreeC and distilling off the water to produce | generate. Then, it was made to react under the reduced pressure of 0.007-0.026 MPa for 1 hour. 54 parts by mass of trimellitic anhydride was further added to the reaction vessel and reacted at 180 ° C. for 1 hour. In this way, an amorphous polyester resin (B) was obtained. In the obtained amorphous polyester resin (B), the acid value was 30 mgKOH / g, and the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin (B) in a dry state was 74 ° C.

<Production Example 3> [Production of Amorphous Polyester Resin (C)]
In a reaction vessel equipped with a stirrer, a heating / cooling device, and a thermometer, 674 parts by mass of bisphenol A propion oxide 2 mol adduct, 226 parts by mass of terephthalic acid, 97 parts by mass of isophthalic acid, and titanium dihydroxybis (triethanolamate) (Condensation catalyst) 2 parts by mass were added. While removing generated water, the reaction was carried out at 180 ° C. under a nitrogen stream for 8 hours.

  Next, it was made to react under nitrogen stream for 4 hours, heating up gradually to 220 degreeC and distilling off the water to produce | generate. Then, it was made to react under the reduced pressure of 0.007-0.026 MPa for 1 hour. 26 parts by mass of trimellitic anhydride was further added to the reaction vessel and reacted at 180 ° C. for 1 hour. In this way, an amorphous polyester resin (C) was obtained. The obtained amorphous polyester resin (C) had an acid value of 15 mgKOH / g, and the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin (C) in a dry state was 72 ° C.

<Production Example 4> [Production of Amorphous Polyester Resin (D)]
In a reaction vessel equipped with a stirrer, a heating / cooling device, and a thermometer, 679 parts by mass of a 2-mol adduct of bisphenol A propion oxide, 260 parts by mass of terephthalic acid, 57 parts by mass of isophthalic acid, and titanium dihydroxybis (triethanolamate) (Condensation catalyst) 2 parts by mass were added. While removing generated water, the reaction was carried out at 180 ° C. under a nitrogen stream for 8 hours.

  Next, it was made to react under nitrogen stream for 4 hours, heating up gradually to 220 degreeC and distilling off the water to produce | generate. Then, it was made to react under the reduced pressure of 0.007-0.026 MPa for 1 hour. The reaction vessel was further charged with 56 parts by mass of trimellitic anhydride and reacted at 180 ° C. for 1 hour. In this way, an amorphous polyester resin (D) was obtained. In the obtained amorphous polyester resin (D), the acid value was 31 mgKOH / g, and the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin (D) in a dry state was 62 ° C.

<Production Example 5> [Production of crystalline polyester resin (a)]
In a reaction vessel equipped with a stirrer, a heating / cooling device, and a thermometer, 630 parts by mass of dodecanedioic acid, 372 parts by mass of 1,6-hexanediol, and 2 parts by mass of titanium dihydroxybis (triethanolaminate) (condensation catalyst) Put. While removing generated water, the reaction was carried out at 180 ° C. under a nitrogen stream for 8 hours.

  Next, it was made to react under nitrogen stream for 4 hours, heating up gradually to 220 degreeC and distilling off the water to produce | generate. Then, it was made to react under the reduced pressure of 0.007-0.026 MPa for 1 hour. 45 parts by mass of trimellitic anhydride was further added to the reaction vessel and reacted at 180 ° C. for 1 hour. A crystalline polyester resin (a) was thus obtained. The obtained crystalline polyester resin (a) had an acid value of 25 mgKOH / g and a melting point of 64 ° C.

  The melting point of the crystalline polyester resin (a) is based on the method described in ASTM D3418-82 using a differential scanning calorimeter (for example, trade name “DSC20” manufactured by Seiko Instruments Inc.), and the following conditions: Measured in The melting point of the crystalline polyester resin (b) described later was also measured by this method.

Mass of sample (liquid developer): 5 mg
Reference sample: Aluminum First temperature increase (measurement temperature range, temperature increase rate): 30 to 180 ° C., 10 ° C./minute Measurement temperature retention (hold temperature, retention time): 180 ° C., 10 minutes First temperature decrease (Measurement temperature range, temperature decrease rate): 0 to 180 ° C., 10 ° C./min Second temperature increase (measurement temperature range, temperature increase rate): 0 to 180 ° C., 10 ° C./min (first temperature increase) The measurement temperature is maintained, the first temperature decrease and the second temperature increase are performed in this order).

<Production Example 6> [Production of crystalline polyester resin (b)]
In a reaction vessel equipped with a stirrer, a heating / cooling device and a thermometer, 594 parts by mass of sebacic acid, 404 parts by mass of 1,6-hexanediol and 2 parts by mass of titanium dihydroxybis (triethanolaminate) (condensation catalyst) I put it in. While removing generated water, the reaction was carried out at 180 ° C. under a nitrogen stream for 8 hours.

  Next, it was made to react under nitrogen stream for 4 hours, heating up gradually to 220 degreeC and distilling off the water to produce | generate. Then, it was made to react under the reduced pressure of 0.007-0.026 MPa for 1 hour. 35 parts by weight of trimellitic anhydride was further added to the reaction vessel and reacted at 180 ° C. for 1 hour. A crystalline polyester resin (b) was thus obtained. The obtained crystalline polyester resin (b) had an acid value of 20 mgKOH / g and a melting point of 57 ° C.

<Production Example 7> [Production of core resin-forming solution (C-1)]
400 parts by mass of the amorphous polyester resin (A) and 600 parts by mass of acetone were placed in a beaker and stirred to uniformly dissolve the amorphous polyester resin (A) in acetone. As a result, a core resin forming solution (C-1) was obtained. In the obtained core resin-forming solution (C-1), the solid content concentration was 40% by mass, and the acid value of the solid content (corresponding to the acid value of the core resin; the same applies hereinafter) was 25 mgKOH / g.

<Production Example 8> [Production of core resin forming solution (C-2)]
400 parts by mass of the amorphous polyester resin (B) and 600 parts by mass of acetone were placed in a beaker and stirred to uniformly dissolve the amorphous polyester resin (B) in acetone. This obtained the core resin formation solution (C-2). In the obtained core resin forming solution (C-2), the solid content concentration was 40% by mass, and the acid value of the solid content was 30 mgKOH / g.

<Production Example 9> [Production of core resin forming solution (C-3)]
320 parts by mass of the amorphous polyester resin (B), 80 parts by mass of the crystalline polyester resin (a) and 600 parts by mass of acetone were placed in a beaker and stirred, and these polyester resins were uniformly dissolved in acetone. This obtained the core resin formation solution (C-3). In the obtained core resin forming solution (C-3), the solid content concentration was 40% by mass, and the acid value of the solid content was 29 mgKOH / g.

<Production Example 10> [Production of core resin forming solution (C-4)]
360 parts by mass of the amorphous polyester resin (C), 40 parts by mass of the crystalline polyester resin (a), and 600 parts by mass of acetone were placed in a beaker and stirred, and these polyester resins were uniformly dissolved in acetone. This obtained the core resin formation solution (C-4). In the obtained core resin forming solution (C-4), the solid content concentration was 40% by mass, and the acid value of the solid content was 16 mgKOH / g.

<Production Example 11> [Production of core resin forming solution (C-5)]
400 parts by mass of the amorphous polyester resin (D) and 600 parts by mass of acetone were placed in a beaker and stirred to uniformly dissolve the amorphous polyester resin (D) in acetone. This obtained core resin formation solution (C-5). In the obtained core resin forming solution (C-5), the solid content concentration was 40% by mass, and the acid value of the solid content was 31 mgKOH / g.

<Production Example 12> [Production of core resin forming solution (C-6)]
280 parts by mass of the amorphous polyester resin (B), 120 parts by mass of the crystalline polyester resin (a), and 600 parts by mass of acetone were placed in a beaker and stirred, and these polyester resins were uniformly dissolved in acetone. This obtained the core resin formation solution (C-6). In the obtained core resin forming solution (C-6), the solid content concentration was 40% by mass, and the acid value of the solid content was 28.5 mgKOH / g.

<Manufacture example 13> [Manufacture of core resin formation solution (C-7)]
320 parts by mass of the amorphous polyester resin (A), 80 parts by mass of the crystalline polyester resin (b) and 600 parts by mass of acetone were placed in a beaker and stirred, and these polyester resins were uniformly dissolved in acetone. As a result, a core resin forming solution (C-7) was obtained. In the obtained core resin forming solution (C-7), the solid content concentration was 40% by mass, and the acid value of the solid content was 24 mgKOH / g.

<Production Example 14> [Production of Shell Dispersion (S-1)]
In a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, a cooling tube and a nitrogen introduction tube, 338 parts by mass of adipic acid, 162 parts by mass of ethylene glycol and 1 mass of titanium dihydroxybis (triethanolaminate) (condensation catalyst) And put a part. While removing generated water, the reaction was carried out at 180 ° C. under a nitrogen stream for 8 hours.

  Next, it was made to react under nitrogen stream for 4 hours, heating up gradually to 220 degreeC and distilling off the water to produce | generate. Then, it was made to react under the reduced pressure of 0.007-0.026 MPa for 1 hour. In this way, a polyester resin (Mn: 3500) was obtained.

  Subsequently, 100 parts by mass of THF and 192 parts by mass of the obtained polyester resin were placed in a reaction vessel equipped with a stirrer, a heating / cooling apparatus, a thermometer, a cooling pipe, and a nitrogen introduction pipe. After replacing the gas phase part of the reaction vessel with nitrogen, the polyester resin was dissolved at 65 ° C. Thereafter, 8.5 parts by mass of a monomer having an isocyanate group (trade name “Karenz MOI” manufactured by Showa Denko KK) and 0.2 part by mass of a product name “Neostan U-600” (manufactured by Nitto Kasei Co., Ltd.) are further added. And reacted at 70 ° C. for 4 hours. A vinyl monomer was thus obtained.

  Subsequently, 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, 25 parts by mass of the obtained vinyl monomer, and azobismethoxydimethylvaleronitrile 0 .1 part by mass and stirred at 20 ° C. Thereby, a monomer solution was obtained.

  Subsequently, 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. 100 parts by mass of THF was placed in this reaction vessel, and the monomer solution was placed in a dropping funnel. After the gas phase part of the reaction vessel was replaced 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 dropping of the monomer solution, a mixture of 0.05 parts by mass of azobismethoxydimethylvaleronitrile and 5 parts by mass of THF was added to the monomer solution. After reacting at 70 ° C. for 3 hours, the mixture was cooled to room temperature. Thereby, a copolymer solution was obtained.

  200 parts by mass of the obtained copolymer solution was dropped into 300 parts by mass of an insulating liquid under stirring (trade name “IP Solvent 2028” manufactured by Idemitsu Kosan Co., Ltd.), and then at 40 ° C. under a reduced pressure of 0.039 MPa. THF was removed. In this way, a dispersion for shell (S-1) was obtained. The Mn of the solid content of the dispersion for shell (S-1) was 40000.

<Production Example 15> [Production of Colorant Dispersion Liquid (P-1)]
In a beaker, 25 parts by mass of copper phthalocyanine (trade name “Fastogen Blue FDB-14” manufactured by DIC Corporation) (colorant (pigment)) and a pigment dispersant (trade name “Ajisper PB-821 manufactured by Ajinomoto Fine Techno Co., Ltd.) “) 4 parts by mass and 75 parts by mass of acetone were added and stirred to uniformly disperse the copper phthalocyanine. Copper phthalocyanine was finely dispersed using a bead mill to obtain a colorant dispersion (P-1). The median diameter D50 of copper phthalocyanine in the colorant dispersion (P-1) was 0.2 μm.

<Production Example 16> [Production of Colorant Dispersion Liquid (P-2)]
A colorant dispersion (P-2) was obtained according to the method described in Production Example 15 except that trade name “S32000” manufactured by Nippon Lubrizol Co., Ltd. was used as the pigment dispersant.

<Example 1> [Production of liquid developer (1)]
In a beaker, 410 parts by mass of the core resin forming solution (C-1) and 190 parts by mass of the colorant dispersion were put. The obtained solution was stirred at 16000 rpm at 25 ° C. using a TK auto homomixer (manufactured by PRIMIX Corporation). In this way, a resin solution in which the colorant was uniformly dispersed was obtained.

  In another beaker, 670 parts by mass of an insulating liquid (flash point: 86 ° C., trade name “IP Solvent 2028” manufactured by Idemitsu Kosan Co., Ltd.) and 60 parts by mass of the shell dispersion (S-1) were added. While stirring the obtained solution at 20000 rpm using CLEARMIX (M Technique Co., Ltd.) at 25 ° C., 600 parts by mass of the resin solution was added and stirred for 2 minutes.

  The obtained mixed liquid was put into a reaction vessel equipped with a stirring device, a heating / cooling device, a thermometer, and a solvent removal device, and the temperature was raised to 35 ° C. At the same temperature, acetone was removed from the mixed solution under a reduced pressure of 0.039 MPa until the acetone concentration became 0.5% by mass or less. Thereby, a liquid developer (1) was obtained. In the liquid developer (1), the content of the colorant (pigment) in the toner particles was 20% by mass, and the content of the toner particles in the liquid developer was 24% by mass.

  After adjusting the solid content concentration of the liquid developer (1) to 80% by mass, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer (1) was measured. It was 51 ° C.

<Example 2> [Production of liquid developer (2)]
The core resin forming solution (C-2) is used instead of the core resin forming solution (C-1), and the colorant dispersion (P-2) is used instead of the colorant dispersion (P-1). A liquid developer (2) was produced according to the method described in Example 1 except that the above.

  After adjusting the solid content concentration of the liquid developer (2) to 80% by mass, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer (2) was measured. It was 55 ° C.

<Example 3> [Production of liquid developer (3)]
A liquid developer (3) was produced according to the method described in Example 1 except that the core resin forming solution (C-3) was used instead of the core resin forming solution (C-1).

  After adjusting the solid content concentration of the liquid developer (3) to 80% by mass, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer (3) was measured. It was 52 ° C.

<Example 4> [Production of liquid developer (4)]
A liquid developer (4) was produced according to the method described in Example 1 except that the core resin forming solution (C-4) was used instead of the core resin forming solution (C-1).

  After adjusting the solid content concentration of the liquid developer (4) to 80% by mass, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer (4) was measured. It was 55 ° C.

<Comparative Example 1> [Production of Liquid Developer (5)]
A liquid developer (5) was produced according to the method described in Example 1 except that the core resin forming solution (C-5) was used instead of the core resin forming solution (C-1).

  After adjusting the solid content concentration of the liquid developer (5) to 80% by mass, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer (5) was measured. It was 48 ° C.

<Comparative Example 2> [Production of Liquid Developer (6)]
A liquid developer (6) was produced according to the method described in Example 1 except that the core resin forming solution (C-6) was used instead of the core resin forming solution (C-1).

  After adjusting the solid content concentration of the liquid developer (6) to 80% by mass, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer (6) was measured. It was 47 ° C.

<Comparative Example 3> [Production of Liquid Developer (7)]
A liquid developer (7) was produced according to the method described in Example 1 except that the core resin forming solution (C-7) was used instead of the core resin forming solution (C-1).

  After adjusting the solid content concentration of the liquid developer (7) to 80% by mass, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer (7) was measured. It was 44 ° C.

<Evaluation of low-temperature fixability>
First, according to the method described in <Transfer Step> in [Image Forming Method], an image (unfixed) is recorded on a recording medium (trade name “OK Top Coat Plus” (128 g / m ² ) manufactured by Oji Paper Co., Ltd.). State). In this embodiment, the surface of the photosensitive member 29 is positively charged by the charging unit 30, the potential of the intermediate transfer member 33 is −400 V, and the potential of the secondary transfer roller 35 is −1200 V. The conveyance speed of the recording medium 40 was 400 mm / s. The amount of toner particles adhering to the recording medium was 3 g / m ² .

  Next, the non-fixed image was fixed on the recording medium by combining the non-contact heating and the contact heating described in the above <fixing step> of the [image forming method]. In this example, in non-contact heating, the temperature of the heating part was 500 ° C., and the paper passing time was 1 sec. In contact heating, the roller temperature was 100 ° C. and the NIP time was 30 msec.

By the above-described method, the content of toner particles and the remaining amount of the insulating liquid in the image fixed on the recording medium were obtained. The toner particle content was 1 g / m ² , and the remaining amount of the insulating liquid was 0.2 g / m ² . Therefore, the ratio of the remaining amount of the insulating liquid to the toner particle content in the image fixed on the recording medium was 20% by mass.

  Next, a tape (trade name “Scotch Mending Tape” manufactured by Sumitomo 3M Co., Ltd.) was attached to the measurement target portion of the recording medium on which the image was fixed, and then the tape was peeled off. Next, the image density (ID) of the image peeled off on the tape was determined using a reflection densitometer (trade name “X-Rite model 404” manufactured by X-Rite). The results are shown in Table 1.

  In Table 1, “A1” is written when the image density is less than 0.1, and “B1” is written when the image density is 0.1 or more and less than 0.15. It can be said that the lower the image density is, the more difficult the toner image is to be peeled off by the tape. In this embodiment, the set temperature of the roller at the time of fixing is 100 ° C., and the temperature of the recording medium immediately after passing through the heat roller fixing device is 80 ° C. Therefore, if the image density is low, fixing at a low temperature is realized. It can be said that it has excellent low-temperature fixability.

<Evaluation of document offset>
Image samples (2 sheets) were prepared according to the method described in <Evaluation of Low-temperature Fixability> above. After the image surfaces of the image samples were superposed on each other, a metal weight (80 g / m ² ) was placed and stored at 50 ° C. for 1 week. Then, after returning an image sample to normal temperature, the image sample was pulled apart from each other. The results are shown in Table 1.

  In Table 1, “A2” is indicated when the image samples can be separated from each other without making a sound, and “B2” is indicated when the image samples can be separated from each other with some noise. When a part of the image is missing when the samples are separated from each other, “C2” is described. In "A2" and "B2", it can be said that no document offset has occurred because no missing image was confirmed. On the other hand, in “C2,” it can be said that a document offset has occurred because a part of the image is confirmed to be missing.

<Result>
Table 1 shows the results.

In Table 1, “mixing ratio (mass%) ^{* 11} ” is amorphous with respect to the sum of the blending amount (mass) of the amorphous polyester resin and the blending amount (mass) of the crystalline polyester resin (mass of the core resin). It means the ratio of the blending amount (mass) of the conductive polyester resin. Further, “mixing ratio (mass%) ^{* 13} ” indicates the blending amount (mass) of the crystalline polyester resin relative to the sum of the blending amount (mass) of the amorphous polyester resin and the blending amount (mass) of the crystalline polyester resin. Means the percentage of

“Tg ^{* 12} (° C.)” means the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in the dry state. “Tg ^{* 14} (° C.)” means the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass.

<Discussion>
In Examples 1-4, the occurrence of document offset was prevented, whereas in Comparative Examples 1-3, document offset occurred. The following can be considered as the reason.

  In Comparative Example 1, the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in the dry state was 62 ° C. As a result, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass was 48 ° C., and it is considered that document offset occurred.

  In Comparative Example 2, the core resin contained 30% by mass of a crystalline polyester resin having a melting point of 64 ° C. As a result, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass was 47 ° C., and it is considered that document offset occurred.

  In Comparative Example 3, the core resin contained a crystalline polyester resin having a melting point of 57 ° C. As a result, the glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass was 44 ° C., and it is considered that document offset occurred.

  In the second embodiment, the occurrence of document offset can be further prevented as compared with the first, third, and fourth embodiments. The reason is that in Example 2, the core resin is composed only of the amorphous polyester resin and the glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in the dry state is high.

  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 roller, 27 Developer cleaning blade, 28 Developer charger, 29 Photoconductor, 30 Charging unit, 31 Exposure unit, 32 Cleaning Blade, 33 Intermediate transfer member, 34 Intermediate transfer member cleaning unit, 35 Secondary transfer roller, 37 Primary transfer unit, 38 Secondary transfer unit, 40 Recording medium.

Claims (5)

A liquid developer comprising an insulating liquid and toner particles dispersed in the insulating liquid,
The toner particles include a binder resin, a colorant, and a polymer dispersant.
The glass transition point Tg (DSC 2nd Run) of the binder resin in the liquid developer having a solid content concentration of 80% by mass is 50 ° C. or higher,
The binder resin includes an amorphous polyester resin,
The glass transition point Tg (DSC 2nd Run) of the amorphous polyester resin in the dry state is 65 ° C. or higher,
The binder resin is a liquid developer further containing 20% by mass or less of a crystalline polyester resin having a melting point of 60 ° C. or higher.   The liquid developer according to claim 1, wherein the acid value of the binder resin is 20 mgKOH / g or more.   The liquid developer according to claim 1, wherein the polymer dispersant exhibits basicity.   The liquid developer according to claim 1, wherein the insulating liquid has a flash point of 70 ° C. or higher. A method for forming an image using the liquid developer according to claim 1,
Transferring the liquid developer to a recording medium;
Fixing the toner particles contained in the liquid developer transferred to the recording medium to the recording medium,
In the image fixed on the recording medium, the remaining amount of the insulating liquid is 3% by mass or more and 30% by mass or less of the content of the toner particles.

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