JP6543953B2 - Liquid developer - Google Patents

Description

  The present invention relates to a liquid developer.

  JP-A-2009-96994 (Patent Document 1) and JP-A-2014-66889 (Patent Document 2) disclose a liquid developer in which toner particles of a core / shell structure are dispersed in an insulating liquid. There is. By employing such a core / shell structure, it is possible to obtain toner particles having a small particle diameter and excellent in low temperature fixing ability.

JP, 2009-96994, A JP, 2014-66889, A

  As a method of further improving the low-temperature fixability of toner particles having a core / shell structure (hereinafter, also simply referred to as "toner particles") as described above, there is a method of imparting crystallinity to a resin constituting toner particles. However, by making the resin constituting the toner particles crystalline, the aggregation resistance (the difficulty of aggregation) of the toner particles tends to decrease. That is, at present, it is difficult to simultaneously achieve high low temperature fixability and high aggregation resistance with respect to toner particles having a core / shell structure.

  The present invention has been made in view of the above point, and an object thereof is to provide a liquid developer excellent in both the low temperature fixing property and the aggregation resistance.

  The inventors of the present invention considered that one of the factors is that the toner particles are easily softened by heat as a factor that reduces the aggregation resistance of the toner particles containing a crystalline resin. In particular, in the image forming apparatus, the inside of the apparatus is likely to be high temperature due to the friction between the developing roller and the blade, and it is confirmed that the temperature of the liquid developer may rise to 40 to 50 ° C. depending on use conditions. It was done.

  Based on the above, in order to obtain toner particles excellent in both of the above characteristics, the present inventors improve the low-temperature fixability by using a crystalline resin for the resin constituting the toner particles, and the melting point of the resin We designed a method to improve the cohesion resistance by designing appropriately. Then, the present inventors have intensively studied focusing on these points to complete the present invention.

  That is, the liquid developer of the present invention is a liquid developer in which toner particles are dispersed in an insulating liquid, and in the toner particles, shell particles including a shell resin are on the surface of core particles including a core resin. It has a core / shell structure formed by adhesion or coating, and the melting point of the shell resin is 70 ° C. or more and 100 ° C. or less.

  In the liquid developer, the shell resin is a vinyl resin having a parent oil portion and a parent core portion.

  In the liquid developer, the parent core portion has a crystalline polyester group, the number average molecular weight of the polyester group is 5,000 or more and 15,000 or less, and the carbon number of the monomer constituting the polyester group is 16 or more and 20 or less. is there.

  In the liquid developer, the core resin contains an aliphatic polyester resin and an aromatic polyester resin, and the proportion of the aliphatic polyester resin in the total amount of the aliphatic polyester resin and the aromatic polyester resin is 5 mass. % Or more and 40% by mass or less.

  In the liquid developer, the acid value of the core resin is 20 mg KOH / g or more and 100 mg KOH / g or less.

  According to the above, it is possible to provide a liquid developer excellent in both the low temperature fixing property and the aggregation resistance.

FIG. 1 is a schematic conceptual view showing an example of the configuration of an electrophotographic image forming apparatus. It is a schematic conceptual diagram of the apparatus used in order to evaluate the aggregation resistance of a liquid developer.

  Hereinafter, embodiments according to the present invention will be described in more detail, but the present invention is not limited thereto. In the present specification, “A to B” means the upper and lower limits of the range, and when there is no description of a unit in A and only a unit is described in B, units of A and B Is the same.

[Configuration of liquid developer]
The liquid developer according to the present embodiment is useful as a developer used in an electrophotographic image forming apparatus (for example, a copying machine, a printer, a digital printing machine, a simple printing machine, etc.). Such liquid developers are sometimes referred to as liquid developers for electrophotography, paints, liquid developers for electrostatic recording, oil-based inks for inkjet printers, inks for electronic paper, etc., depending on the application.

  In the liquid developer, toner particles are dispersed in an insulating liquid. The liquid developer can contain any other component as long as it contains an insulating liquid and toner particles. Other components may include charge control agents, thickeners, toner particle dispersants, and the like. The mixture ratio of the toner particles and the insulating liquid in the liquid developer can be, for example, about 10 to 50% by mass of the toner particles and about 50 to 90% by mass of the insulating liquid.

<Toner particles>
The toner particles contain a resin and a colorant (pigment). More specifically, the toner particle of the present embodiment has a core / shell structure in which shell particles containing a shell resin are attached or coated on the surface of core particles containing a core resin, and shell particles and At least one of the core particles contains a colorant.

  Here, in the case of toner particles in which the shell particles coat the surface of the core particles, the shell particles do not have a particle shape, and include, for example, a layered state.

  The toner particles may contain, in addition to the resin and the colorant, for example, additives such as a colorant dispersant, a wax, and a charge control agent. The blending ratio of the resin (total amount of the shell resin and the core resin) and the colorant may be determined such that when the toner particles are used at a predetermined adhesion amount, the developed concentration is a desired concentration.

  In the toner particles, the mass ratio [(A) :( B)] of the shell particles (A) to the core particles (B) is preferably 1:99 to 70:30. The ratio [(A) :( B)] is more preferably 2:98 to 50:50, and still more preferably, from the viewpoints of the uniformity of the particle diameter of the toner particles, the heat stability of the liquid developer, etc. 3: 97-35: 65.

  The median diameter of the toner particles is preferably 0.5 to 5.0 μm. When the median diameter of the toner particles is less than 0.5 μm, the mobility in an electric field may be deteriorated and the developability may be deteriorated because the particle diameter is excessively small, and when it exceeds 5.0 μm, the uniformity of the particles And the image quality may deteriorate.

  Here, the “median diameter” indicates the particle size (so-called D50) at an integrated value of 50% in the volume-based particle size distribution. The range of the median diameter is smaller than the particle size of toner particles in the conventional dry type developer, and shows one of the characteristics of the liquid developer. The median diameter of the toner particles is more preferably 1.0 to 2.0 μm.

  The arithmetic mean value (mean circularity) of the circularity of toner particles is preferably 0.85 to 0.95, and the standard deviation of circularity is preferably 0.01 to 0.1. When the average value and the standard deviation of the degree of circularity occupy the above range, the transferability and the cleaning property are improved.

  Here, "the degree of circularity" indicates a value obtained by dividing the peripheral length of a circle having the same area as the two-dimensionally projected particle area by the particle peripheral length.

  The median diameter, average circularity and standard deviation of circularity of each particle can be measured using a flow type particle image analyzer (for example, trade name “FPIA-3000S”, manufactured by Sysmex Corporation). In "FPIA-3000S", the insulating liquid contained in the liquid developer can be used as a dispersion medium at the time of measurement. Therefore, when this apparatus is used, it is possible to obtain a result reflecting the actual dispersion state more than in the case where toner particles are re-dispersed in an aqueous solvent and measured.

<Shell particle>
The shell particles are so-called polymer dispersants that have the function of adhering to the surface of the core particles and enhancing their dispersibility. The shell particles are mainly composed of shell resin. Also, the shell particles may contain a colorant, an additive and the like.

  The volume average particle diameter (median diameter) of the shell particles may be appropriately adjusted so that the particle diameter of the toner particles falls within a desired range. The median diameter of the shell particles is preferably 0.0005 to 3 μm. The upper limit of the median diameter of the shell particles is more preferably 2 μm, and still more preferably 1 μm. The lower limit of the median diameter of the shell particles is more preferably 0.01 μm, still more preferably 0.02 μm, and most preferably 0.04 μm. For example, when it is desired to obtain toner particles having a median diameter of 1 μm, the median diameter of the shell particles is preferably 0.0005 to 0.3 μm, and more preferably 0.001 to 0.2 μm. For example, when it is desired to obtain toner particles having a median diameter of 10 μm, the median diameter of the shell particles is preferably 0.005 to 3 μm, and more preferably 0.05 to 2 μm.

(Shell resin)
The shell resin of the present embodiment may be a thermoplastic resin or a thermosetting resin. Examples of resins that can be shell resins include vinyl resin, polyester resin, polyurethane resin, epoxy resin, polyamide resin, polyimide resin, silicone resin, phenol resin, melamine resin, urea resin, aniline resin, ionomer resin, polycarbonate resin, etc. can do.

  Among them, it is preferable to use a vinyl resin, a polyester resin, a polyurethane resin and an epoxy resin as the shell resin, in consideration of easy control of the shape of toner particles at the time of production. Shell resin may be comprised from 1 type of resin among these resin, and may be comprised from 2 or more types of resin.

  Particularly preferably, the shell resin is a vinyl resin. The vinyl resin is a resin constituted by polymerizing a monomer having a polymerizable double bond (hereinafter, also referred to as "vinyl monomer"), and as this vinyl monomer, for example, the following (1) to (9) Can be mentioned.

(1) Hydrocarbon having polymerizable double bond (2) Monomer having carboxyl group and polymerizable double bond, and salts thereof (3) Monomer having sulfo group and polymerizable double bond, and salts thereof (4) Monomer having phosphono group and polymerizable double bond and salt thereof (5) Monomer having hydroxyl group and polymerizable double bond (6) Nitrogen-containing monomer having polymerizable double bond (7) Epoxy A C6-C18 monomer having a group and a polymerizable double bond (8) A C2-C16 monomer having a halogen element and a polymerizable double bond (9) A polymerizable double bond Ester having 4 to 30 carbon atoms.

The reason why vinyl resin is particularly preferable as the shell resin is as follows.
The shell resin adheres to the surface of the core particle and maintains its dispersibility in the insulating liquid. Therefore, the shell resin preferably has a parent core portion having high affinity to the core particle and a parent oil portion having high affinity to the insulating liquid. This is because the core / shell structure becomes homogeneous. When the shell resin is a vinyl resin, a vinyl monomer having a parent core portion in a side chain (a monomer having a parent core portion and a polymerizable double bond) and a vinyl monomer having an oil parent portion in a side chain The vinyl copolymer (shell resin) which has a parent oil part and a parent core part in a side chain can be easily manufactured by copolymerizing the monomer which has a part and a polymerizable double bond. Furthermore, by adjusting the ratio and composition of the parent core portion and the parent oil portion, it becomes easy to control various characteristics such as the melting point of the shell resin described later.

  In the shell resin, the proportion of the parent core portion to the total amount of the parent core portion and the parent oil portion is preferably 5 to 70% by mass. When the amount is less than 5% by mass, the contribution of the toner particles to the aggregation resistance decreases, and when the amount is more than 50% by mass, the low-temperature fixability of the toner particles tends to be deteriorated. The ratio is more preferably 10 to 50% by mass, and still more preferably 20 to 50% by mass.

(Melting point of shell resin)
In the present embodiment, the shell resin is characterized by having a melting point of 70 to 100 ° C. The fact that the shell resin has a melting point means that the shell resin has crystallinity. When the toner particles contain a shell resin having crystallinity, the meltability of the toner particles can be enhanced, whereby the low temperature fixability of the toner particles can be enhanced. Furthermore, when the melting point of the shell resin is in the above range, the softening of the toner particles can be sufficiently suppressed even in a high temperature environment which can occur in the image forming apparatus, and the aggregation resistance of the toner particles can be enhanced. .

  Here, in the present specification, the melting point of the resin is measured by a method according to "ASTM D3418-82" using a differential scanning calorimeter (such as "DSC 20" or "SSC / 580" manufactured by Seiko Instruments Inc.). It shall indicate the value.

  In the present specification, "crystalline resin" refers to the softening point of the resin (hereinafter abbreviated as "Tm") and the maximum peak temperature of the heat of fusion of DSC of the resin (hereinafter abbreviated as "Ta"). It means a resin having a ratio (Tm / Ta) of 0.8 or more and 1.55 or less. The result obtained by differential scanning calorimetry (DSC) means that it has a clear endothermic peak rather than showing a stepwise change in endothermic heat. On the other hand, “non-crystalline resin” means a resin in which the ratio of Tm to Ta (Tm / Ta) is greater than 1.55. Tm and Ta can be measured by the following method.

  Tm can be measured using a high-rise flow tester (for example, “CFT-500D” manufactured by Shimadzu Corporation). Specifically, while heating 1 g of the measurement sample at a heating rate of 6 ° C./min, a load of 1.96 MPa is applied to the measurement sample by the plunger, and the measurement sample is extruded from a nozzle of 1 mm in diameter and 1 mm in length. . Then, the relationship between the "plunger descent amount (flow value)" and the "temperature" is drawn on a graph. The temperature when the amount of drop of the plunger is half of the maximum value of the amount of drop is read from the graph, and this value (the temperature when half of the measurement sample is pushed out of the nozzle) is taken as Tm.

  Ta can be measured using a differential scanning calorimeter (for example, “DSC 210” manufactured by Seiko Instruments Inc.). Specifically, first, a sample used to measure Ta is pretreated. The sample is melted at 130 ° C. and then ramped down from 130 ° C. to 70 ° C. at a rate of 1.0 ° C./min and then ramped down from 70 ° C. to 10 ° C. at a rate of 0.5 ° C./min. Next, the sample is heated at a temperature rising rate of 20 ° C./min by DSC method to measure the endothermic change of the sample, and the relationship between the “endothermic amount” and the “temperature” is drawn on a graph. At this time, the temperature of the endothermic peak observed at 20 to 100 ° C. is Ta ′. When there are a plurality of endothermic peaks, the temperature of the peak having the largest endothermic amount is Ta '. Then, the sample is stored at (Ta′-10) ° C. for 6 hours, and then stored at (Ta′-15) ° C. for 6 hours.

  Next, the sample subjected to the above pretreatment is cooled to 0 ° C. at a temperature decrease rate of 10 ° C./min and then heated at a temperature increase rate of 20 ° C./min by DSC method to measure changes in heat absorption and heat generation. Draw a graph on the relationship between the amount of heat absorption and temperature. Then, the temperature at which the heat absorption amount reaches the maximum value is taken as the maximum peak temperature (Ta) of the heat of fusion.

  The following method may be mentioned as a method of measuring the melting point of the shell resin contained in the toner particles in the liquid developer. First, the liquid developer is centrifuged, the supernatant is removed, and the remaining solid component is washed with an organic solvent and then dried. Thereby, toner particles are separated from the liquid developer. Next, the toner particles are dissolved in a solvent, and shell particles (A) and core particles (B) are separated by gel permeation chromatography (GPC: Gel Permeation Chromatography). Thereafter, the shell particles (A) are dried to measure the melting point.

(Mn of shell resin)
The number average molecular weight (Mn) of the shell resin is preferably 100 to 500,000, more preferably 200 to 500,000, and particularly preferably 500 to 500,000.

  Here, the Mn and the weight average molecular weight (hereinafter referred to as “Mw”) of the resin (excluding the polyurethane resin) in the present specification are GPC with respect to the soluble component of tetrahydrofuran (hereinafter abbreviated as “THF”) It is measured under the following conditions (Mn and Mw of the urethane-modified aliphatic polyester resin are also measured by this method).

Measuring device: "HLC-8120" manufactured by Tosoh Corporation
Column: Tosoh's "TSKgel GMHXL" (two) and Tosoh's "TSKgel Multipore HXL-M" (one)
Sample solution: 0.25% by mass THF solution Injection amount of sample solution to column: 100 μl
Flow rate: 1 ml / min Measurement temperature: 40 ° C
Detection device: Refractive index detector Reference substance: Standard polystyrene (TSK standard POLYSTYRENE) 12 points (molecular weight: 500, 1050, 2800, 5970, 9100, 18100, 37900, 96400, 190000, 355000, 1090000, 2890000) .

  Moreover, in this specification, Mn and Mw of a polyurethane resin are measured on condition of the following using GPC.

Measuring device: "HLC-8220GPC" manufactured by Tosoh Corporation
Column: "TSK guardcolumn α" (1) manufactured by Tosoh Corp. and "TSKgel α-M" manufactured by Tosoh Corp. (1)
Sample solution: 0.125% by mass of dimethylformamide solution Injection amount of dimethylformamide solution to the column: 100 μl
Flow rate: 1 ml / min Measurement temperature: 40 ° C
Detection device: Refractive index detector Reference substance: Standard polystyrene (TSK standard POLYSTYRENE) 12 points (molecular weight: 500, 1050, 2800, 5970, 9100, 18100, 37900, 96400, 190000, 355000, 1090000, 2890000) .

(SP value of shell resin)
The SP value of the shell resin is preferably about 7 to 18 (cal / cm ³ ) ^1/2 or so, more preferably about 8 to 14 (cal / cm ³ ) ^1/2 or so. Here, the “SP value” in the present specification is the method by Fedors [Polym. Eng. Sci. 14 (2) 152, (1974)] shall be shown. As described later, the shell resin includes a parent core portion and a parent oil portion having different SP values. However, the SP value of the shell resin is the SP value of the entire shell resin.

(Parent core part included in shell resin)
The shell resin preferably has a parent core portion having high affinity to the core particle, as described above. The parent core portion is a portion of the shell resin where the difference from the SP value of the core resin is 0-2. In particular, when the parent core portion has a crystalline polyester group satisfying the following conditions A and B, the low temperature fixing property and the aggregation resistance of the toner particles having the shell resin are further improved. I know what I can do.
Condition A: The number average molecular weight (Mn) is 5,000 or more and 15,000 or less.
Condition B: The carbon number of the monomer constituting the polyester group is 16 or more and 20 or less.

  Here, in the present specification, "polyester group" means a group having a polyester structure as a main chain. As such a polyester group, the polyester group obtained by polycondensing an acid monomer and an alcohol monomer can be mentioned.

  Examples of the acid monomer include adipic acid, sebacic acid and dodecadioic acid. Examples of the alcohol monomer include ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,9-nonanediol and the like.

  Furthermore, in the present specification, each definition of “crystalline polyester group” and “non-crystalline polyester group” is the same as each definition of “crystalline resin” and “non-crystalline resin”.

The following Chemical Formula (1) can be mentioned as a specific example of a component of a parent core part which has said polyester group. In the following chemical formula (1), R ¹ is a hydrogen atom or a methyl group, R ² is an alkylene group having 1 to 5 carbon atoms, and R ³ is the above-mentioned polyester group. In addition, the polymerizable double bond of following Chemical formula (1) is a part which comprises the principal chain (vinyl copolymer) of shell resin. That is, the chemical formula (1) corresponds to a monomer having a parent core portion and a polymerizable double bond (a vinyl monomer having a parent core portion in a side chain).

R ¹ is preferably a methyl group. In this case, manufacture of the parent core portion is facilitated. Specific examples of R ² include a methylene group, an ethylene group, a propylene group, an n-butylene group and an n-hexylene group. R ² is preferably an ethylene group. Also in this case, manufacture of a parent core part becomes easy.

(Parent oil part contained in shell resin)
As described above, the shell resin preferably has a parent oil portion having high affinity to the insulating liquid. The parent oil portion is a portion of the shell resin in which the difference from the SP value of the insulating liquid is 0-2. The monomer constituting the parent oil moiety is preferably an ester (m1) having a hydrocarbon group in the side chain and having a binding double bond. The side chain hydrocarbon group is preferably a hydrocarbon having a linear hydrocarbon chain having 12 to 27 (preferably 16 to 25) carbon atoms. Examples of m1 include dodecyl (meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate and eicosyl (meth) acrylate, etc. be able to. The side chain hydrocarbon group may be a hydrocarbon (m2) having a branched alkyl hydrocarbon chain having 12 to 27 carbon atoms. As m 2, meta (acrylic acid) 2-decyltetradecyl and the like can be mentioned.

  The Mn of the parent oil portion is preferably 100 to 1000, and more preferably 100 to 500. In particular, the parent oil portion is preferably crystalline. In this case, the control of the melting point of the shell resin is easier.

<Core particle>
Core particles are mainly composed of core resin. The core particles may contain colorants, additives and the like.

  The median diameter of the core particles may be appropriately adjusted so that the particle diameter of the toner particles falls within a desired range. The median diameter of the core particles is preferably 0.8 to 4.0 μm. For example, when it is desired to obtain toner particles having a median diameter of 1.0 μm, the median diameter of the core particles is preferably 0.8 to 1.0 μm, and more preferably 0.9 to 1.0 μm.

(Core resin)
The core resin may be any resin different from the shell resin, for example, vinyl resin, polyester resin, polyurethane resin, epoxy resin, polyamide resin, polyamide resin, polyimide resin, silicon resin, phenol resin, melamine resin, urea resin, aniline resin, ionomer Resin, and polycarbonate resin etc. can be mentioned.

  In particular, in the present embodiment, the core resin preferably contains an aliphatic polyester resin and an aromatic polyester resin, and more preferably, 90% by mass or more of the resin constituting the core resin is an aliphatic polyester resin It consists of an aromatic polyester resin. An aliphatic polyester resin refers to a polyester resin in which 90% by mass or more of the monomers constituting the polymer (resin) is an aliphatic monomer, and an aromatic polyester resin refers to 90% by mass or more of the monomers constituting the polymer A polyester resin consisting of an aromatic monomer.

  The reason why the core resin preferably contains an aliphatic polyester resin and an aromatic polyester resin is as follows.

  Although aliphatic polyester resins have crystallinity, they are superior to low-temperature fixability of toner particles, while they are inferior to the hardness of toner particles because their hardness tends to be low. Therefore, for example, when core particles constituting toner particles contain an aliphatic polyester resin as a main component (for example, 50% by mass or more), toner particles may be easily aggregated.

  On the other hand, since the aromatic polyester resin is non-crystalline, the hardness is higher than that of the aliphatic polyester resin, so it is excellent in the aggregation resistance and tends to be inferior in the low temperature fixing property. For example, although it is possible to enhance the superiority of low temperature fixability by designing the molecular weight of the aromatic polyester resin small and lowering the softening point, in this case, the glass transition point is also caused to decrease. Cohesion may be inferior.

  On the other hand, by mixing the aromatic polyester resin and the aliphatic polyester resin, the inventors significantly lower the softening point of the aromatic polyester resin without designing the molecular weight of the aromatic polyester resin small. I found that. Therefore, by appropriately mixing the two, the inferiority of each other can be effectively compensated, and as a result, it is possible to enhance both the low temperature fixing property and the aggregation resistance of the toner particles.

  In addition, it is preferable that 90% by mass or more of the resin constituting the core resin is made of polyester resin (aliphatic polyester resin and aromatic polyester resin) because the content of resins other than polyester resin exceeds 10% by mass And the regular arrangement of the polyester resin may be inhibited. In addition, core resin can also contain resin other than polyester resin if it is 10 mass% or less among whole quantity. Preferred examples of such a resin are styrene-acrylic resin, urethane resin, epoxy resin and the like.

  More specifically, the proportion of the aliphatic polyester resin in the total amount of the aliphatic polyester resin and the aromatic polyester resin is 5 to 40% by mass or less with respect to the blending ratio of the polyester resin in the shell resin. Is preferred. When the mixing ratio of both resins is in the above range, both the low temperature fixing property and the aggregation resistance of the core particle can be sufficiently improved, and the low temperature fixing property and the aggregation resistance of the toner particle can be enhanced. . The ratio is more preferably 10 to 35% by mass, and particularly preferably 15 to 30% by mass.

  Here, the polyester resin which comprises core resin is synthesize | combined by the polycondensation reaction of polyhydric carboxylic acid (acid component) and polyhydric alcohol (alcohol component). For this reason, in the polyester resin, a constituent unit (acid component constituent unit) as an acid component derived from a polyvalent carboxylic acid and a constituent unit as an alcohol component (alcohol component constituent unit) derived from a polyhydric alcohol alternate with each other. It has a repeated configuration.

  That is, in the aliphatic polyester resin, 90% or more of all the structural units are composed of an acid component structural unit derived from an aliphatic monomer and an alcohol component structural unit derived from an aliphatic monomer. In the aromatic polyester resin, 90% or more of the total structural units are composed of an acid component structural unit derived from an aromatic monomer and an alcohol component structural unit derived from an aromatic monomer.

  Examples of aliphatic monomers to be acid component constitutional units include aliphatic polyvalent carboxylic acids and their lower alkyl esters and acid anhydrides. Specifically, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelinic acid, sebacic acid, 1,9-nonane dicarboxylic acid, 1,10-decanedicarboxylic acid, 1,10 11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, and those Lower alkyl esters or acid anhydrides may be mentioned. Among these, adipic acid, sebacic acid, 1,10-decanedicarboxylic acid, and 1,12-dodecanedicarboxylic acid are preferable from the viewpoint of easily imparting crystallinity to the resin. The aliphatic monomer to be the acid component constitutional unit may be used singly or in combination of two or more.

  Aliphatic polyhydric alcohol etc. are mentioned as an aliphatic monomer which should turn into an alcohol component structural unit. Specifically, 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, 1,14-tetradecanediol, 1,18-octadecanediol 1, 20-Eicosan diol etc. are mentioned. Among these, ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,9-nonanediol and 1,10-decanediol are preferred among them from the viewpoint of easily imparting crystallinity to aliphatic polyester resins. preferable. The aliphatic monomer to be an alcohol component constitutional unit may be used singly or in combination of two or more.

  On the other hand, aromatic polyvalent carboxylic acids and their lower alkyl esters, acid anhydrides and the like can be mentioned as aromatic monomers to be acid component constitutional units. Specifically, terephthalic acid, isophthalic acid, orthophthalic acid, t-butylisophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, trimellitic acid and the like can be exemplified. Among these, terephthalic acid, isophthalic acid, t-butyl isophthalic acid and the like are preferable in view of availability.

  As an aromatic type monomer which should turn into an alcohol component structural unit, the alkylene oxide adduct etc. of bisphenol A represented, for example by following Chemical formula (I) as an aromatic polyhydric alcohol can be illustrated.

In the above chemical formula (2), R ¹ and R ² each independently represent an alkylene group, and m and n each independently represent 0 or a positive integer, but the sum (m + n) of both is 1 to 16 is there.

  The core resin composed of the above polyester resin is a mixture of an aliphatic polyester obtained by copolymerizing only an aliphatic monomer and an aromatic polyester obtained by copolymerizing only an aromatic monomer at the time of toner particle formation. It is preferable to manufacture it. In this case, the low temperature fixing property and the aggregation resistance of the toner particles can be further improved as compared with the case where the both are mixed before the toner particle formation. Moreover, you may use the urethane modified polyester resin which chain-lengthened the said polyester resin by the isocyanate group as core resin.

  The inclusion of the aliphatic polyester resin and the aromatic polyester resin in the core resin can be confirmed by nuclear magnetic resonance (NMR) analysis and mass spectrometry (MS). In addition, the content ratio of the aliphatic polyester resin and the aromatic polyester resin in the core resin is 1H-NMR analysis using a Fourier transform nuclear magnetic resonance analyzer (FT-NMR), for example, "Lambda 400" manufactured by JEOL Ltd. Can be determined by the integral ratio.

(Mn of core resin)
The number average molecular weight (Mn) of the core resin is preferably 1,000 to 25,000, and more preferably 1,500 to 15,000. The weight average molecular weight (Mw) of the core resin is preferably 2,000 to 50,000, and more preferably 3,000 to 30,000.

(Acid value of core resin)
The acid value of the core resin is preferably 20 to 100 mg KOH / g. When the acid value of the core resin is less than 20 mg KOH / g, sufficient low temperature fixability tends not to be maintained, and when the acid value is more than 100 mg KOH / g, sufficient aggregation resistance tends not to be maintained. .

  Here, in the present specification, the acid value of the resin is obtained by dissolving the resin (10 g) in a mixed solvent (100 ml) in which toluene, acetone and methanol are mixed with toluene: acetone: methanol = 50: 25: 25 (mass ratio) It can be determined by titration with 0.1 N potassium hydroxide ethanol solution using phenolphthalein as an indicator.

  The acid value of the core resin is more preferably 10 to 100 mg KOH / g, particularly preferably 20 to 80 mg KOH / g. In addition, when the core resin contains an aliphatic polyester resin and an aromatic polyester resin, the acid value of the core resin means the acid value after mixing both resins.

(SP value of core resin)
The SP value of the core resin is preferably about 9 to 14 (cal / cm ³ ) ^1/2 , more preferably about 9 to 13 (cal / cm ³ ) ^1/2 .

<Insulating liquid>
The insulating liquid contained in the liquid developer may have a resistance (about 10 ¹¹ to 10 ¹⁶ Ω · cm) that does not disturb the electrostatic latent image. Furthermore, solvents having low odor and toxicity are preferred. Generally, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes and the like can be mentioned. In particular, normal paraffin solvents and isoparaffin solvents are preferable in terms of odor, harmlessness and cost. Specifically, Moresco White (trade name, manufactured by Matsumura Petroleum Research Institute), Isopar (trade name, manufactured by ExxonMobil), Shellsol (trade name, manufactured by Shell Petrochemicals), IP Solvent 1620, IP Solvent 2028, IP Solvent 2835 (all are trade names, manufactured by Idemitsu Kosan Co., Ltd.), and the like.

<Colorant>
The colorant is dispersed in at least one of the shell particle and the core particle. The particle size of the colorant is preferably 0.3 μm or less. When the particle size of the coloring agent exceeds 0.3 μm, the dispersibility is deteriorated, and the glossiness may be lowered to fail to achieve a desired color.

  Although a conventionally well-known pigment etc. can be used without a restriction | limiting especially as a coloring agent, It is preferable to use a pigment based on a viewpoint of cost, light resistance, coloring property, etc. Here, in terms of color constitution, pigments are generally classified into black pigments, yellow pigments, magenta pigments, and cyan pigments, and colors other than black (color image) are basically adjusted by subtraction mixing of yellow pigments, magenta pigments, and cyan pigments. It is colored. These pigments may be used alone or in combination of two or more as needed.

<Colorant Dispersant>
The colorant dispersant has an effect of uniformly dispersing the colorant in the toner particles, and it is preferable to use a basic dispersant. The term "basic dispersant" as used herein refers to those defined below.

  That is, the colorant dispersant (0.5 g) and distilled water (20 ml) were placed in a glass screw tube, shaken for 30 minutes using a paint shaker, and then filtered to obtain the pH of the filtrate obtained by Measured using a pH meter (trade name "D-51", manufactured by Horiba, Ltd.), and when the pH is higher than 7 is used as a basic dispersant (when the pH is lower than 7, it is called an acidic dispersant Shall be

  The type of basic dispersant is not particularly limited. For example, an amine group, amino group, amide group, pyrrolidone group, imine group, imino group, urethane group, quaternary ammonium group, ammonium group, pyridino group, pyridinium group, imidazolino group, and imidazolium group are contained in the molecule of the dispersant. The compound (dispersant) which has functional groups, such as, can be mentioned. Here, the dispersant is generally a so-called surfactant having a hydrophilic portion and a hydrophobic portion in the molecule, but various types can be used as long as it has the function of dispersing the colorant (pigment) as described above. The following compounds can be used.

  As a commercial item of a basic dispersing agent, for example, "Ajispar PB-821" (brand name) by Ajinomoto Fine Techno Co., Ltd., "Ajispar PB-822" (brand name), "Ajispar PB-881" (brand name), “Sol spars 28000” (trade name), “Sol spars 32000” (trade name), manufactured by Japan Lubrizol, “Sol s Spaurs 32500” (trade name), “Sol s Spades 35100” (trade name), “Sol s Spaurs 37500” (trade name) Etc. can be mentioned.

  Further, as the colorant dispersant, it is more preferable to select one that does not dissolve in the insulating liquid (carrier liquid). For that reason, “Adispar PB-821” (trade name), “Addasper PB-822” (trade name), and “Addasper PB-881” (trade name) manufactured by Ajinomoto Fine Techno Co., Ltd. are more preferable. The use of such a colorant dispersant tends to control the shape of toner particles, although the detailed mechanism is unknown. The colorant dispersant may be used alone or in combination of two or more.

  The colorant dispersant is preferably added in an amount of 1 to 100% by mass, and more preferably 1 to 40% by mass, based on the colorant (pigment). If the addition amount is less than 1% by mass, the dispersibility of the colorant may be insufficient, and not only the necessary ID (image density) can not be achieved, but also the fixing strength may be lowered. When the addition amount exceeds 100% by mass, the dispersant in excess of the necessary amount is added to the pigment, and the excess dispersant is dissolved in the insulating liquid, whereby the chargeability of the toner particles and fixation are achieved. The strength may be adversely affected.

[Method of producing liquid developer]
The liquid developer of the present embodiment can be manufactured as follows. First, a shell resin and a core resin are prepared. These are produced by conventionally known methods such as dispersion polymerization, emulsion polymerization, soap-free emulsion polymerization, seed polymerization, suspension polymerization and the like.

  Then, using the obtained shell resin, core resin, and insulating liquid, toner particles having a core / shell structure are produced by applying a conventionally known method such as a granulation method or a pulverization method, and the final process is performed. Thus, a liquid developer in which toner particles are dispersed in an insulating liquid is produced.

  The above-mentioned pulverization method is a method of melt-kneading resin and colorant in advance and pulverizing. Such pulverization can be carried out in a dry state or in a wet state (in the insulating liquid). Examples of the granulation method include a suspension polymerization method, an emulsion polymerization method, a fine particle aggregation method, a method of adding a poor solvent to a resin solution to precipitate, and a spray dry method. A granulation method is preferable to a pulverization method in order to obtain toner particles having a small diameter and a sharp particle size distribution. This is because a highly meltable resin or a highly crystalline resin is soft and difficult to be crushed even at room temperature. According to the granulation method, even such a resin can be easily controlled to a desired particle size.

  Hereinafter, as an example of a method of producing a liquid developer using a granulation method, a production method using a method of adding a poor solvent to a resin solution and depositing the same will be described.

  First, a shell resin and a core resin are produced by a conventionally known method. Next, a fine particle dispersion in which shell particles are dispersed is prepared. The method for producing the shell particles is not particularly limited, and may be produced by any conventionally known method. For example, shell particles can be produced by the following methods (1) to (7). Among the following, the methods (4), (6) and (7) are preferable, and the methods (6) and (7) are more preferable, in consideration of the ease of production of shell particles.

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

  Next, the core resin is dissolved in a good solvent to form a core resin solution, and the core resin solution is mixed with the fine particle dispersion of the shell resin in a poor solvent (insulating liquid) having an SP value different from that of the good solvent. After applying shear to form droplets, the good solvent is evaporated. As a result, it is possible to obtain a liquid developer in which toner particles of the core / shell structure are dispersed in the insulating liquid.

  According to this method, the volume average particle diameter and the shape of the toner particles can be controlled within a desired range by appropriately adjusting the manner of giving shear and the interfacial tension difference.

[Image formation]
The liquid developer according to the present embodiment can form an image by being applied to an image forming apparatus. The configuration of the image forming apparatus is not particularly limited. For example, a monochrome image forming apparatus in which a monochrome liquid developer is secondarily transferred to a recording medium after primary transfer from a photoreceptor to an intermediate transfer member, a monochrome liquid developer is photosensitive It is preferable that it is an image forming apparatus which is directly transferred from the body to the recording medium, or a multicolor image forming apparatus which forms a color image by superposing plural kinds of liquid developers.

[Function effect]
The present inventors confirmed, through various studies, that when the resin constituting the toner particles is made crystalline, the low temperature fixability of the toner particles can be improved, but the aggregation resistance tends to decrease. did.

  The inventors of the present invention speculate that one of the causes of the decrease in the aggregation resistance is that the toner particles are easily softened by giving crystallinity to the resin, and the low temperature fixing property and the aggregation resistance In order to achieve compatibility, it was considered that the temperature at which the toner particles (i.e., the resin constituting the toner particles) soften needs to be designed to be higher than at least the temperature to which the toner particles can be exposed in the image forming apparatus. .

  Based on this idea, the present inventors have conducted intensive studies, and in toner particles of core / shell structure, in particular, by setting the melting point of the shell resin to 70 to 100 ° C., both the low temperature fixability and the aggregation resistance are obtained. It has been found that a liquid developer containing excellent toner particles can be obtained. Therefore, according to the liquid developer of the present embodiment, both the low temperature fixability and the aggregation resistance can be excellent as compared with the conventional case.

  By setting the melting point of the shell resin to 70 to 100 ° C., the reason why both the above-described properties of the toner particles are excellent is not clear, but the present inventors speculate as follows from various examination results.

  For example, when the melting point of both the core resin and the shell resin is made higher than in the prior art, the toner particles become too hard to soften and work disadvantageously to the low temperature fixability, so that the above two characteristics are consequently excellent. I can not Further, even if only the melting point of the core resin is increased as compared with the conventional case, the core resin is not located on the outermost surface in the toner particles, and therefore, can not sufficiently contribute to the improvement of the aggregation resistance.

  On the other hand, by raising the melting point of the shell resin as compared with the prior art, the toner particles can be sufficiently softened without being too hard, and since they can sufficiently contribute to the improvement of the aggregation resistance, as a result It is possible to raise both the low temperature fixability and the aggregation resistance of toner particles.

  Preferably, the shell resin has a parent oil part and a parent core part, and the parent core part has a crystalline polyester group (Mn: 5000 to 15000, the number of carbon atoms of the monomer: 16 to 20). In this case, the toner particles can be further excellent in both of the above-mentioned characteristics. Although the reason is not clear, the present inventors speculate that the melting point of the shell resin can be further increased by the presence of the polyester group in the parent core portion of the shell resin based on various studies. .

  In particular, when the Mn of the polyester group is 5000 or more, the adsorptive power of the shell particles to the core particle can be further enhanced, and when the Mn is 15000 or less, the production of the polyester group is further facilitated.

  Moreover, the heat resistant storage property can also be improved by the carbon number of the acid monomer which comprises polyester group, and the carbon number of the alcohol monomer totaling total carbon number being 16-20. Specifically, a polyester group consisting of polycondensation of dodecadioic acid and 1,6 hexanediol, a polyester group consisting of polycondensation of dodecadioic acid and 1,4 butanediol, and a weight of 1,6-hexanediol and sebacic acid Mention may be made of polyester groups which consist of condensation.

  The core resin constituting the core particles contains an aliphatic polyester resin and an aromatic polyester resin, and the proportion of the aliphatic polyester resin in the total of the aliphatic polyester resin and the aromatic polyester resin is 5 to 40 mass. It is preferable that it is% or less. In this case, since the core particle itself can be excellent in both the low temperature fixing property and the aggregation resistance, the low temperature fixing property and the aggregation resistance of the toner particle can be raised as a result. Further, the disadvantage of designing the melting point of the shell resin relatively high can be sufficiently offset by raising the core resin.

  Further, when the acid value of the core resin is 20 to 100 mg KOH / g or less, both the low temperature fixability and the aggregation resistance of the core particle can be further improved, and as a result, the low temperature fixability of the toner particles And aggregation resistance can be raised.

  Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. In addition, the various characteristics of each resin were measured by the above-mentioned method.

<Manufacture of liquid developer>
Production Example 1 Production of Polyester Resin (1) Dodecanedioic acid (338 parts by mass), 1,6-hexanediol was added to a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, a cooling pipe and a nitrogen introducing pipe. (207 parts by mass) and titanium dihydroxybis (triethanolaminate) (1 part by mass) as a condensation catalyst were added, and reacted at 180 ° C. for 8 hours while distilling off generated water under a nitrogen stream. Next, while gradually raising the temperature to 220 ° C., the reaction was carried out for 4 hours while distilling off generated water under a nitrogen stream, and further for 1 hour under a reduced pressure of 0.007 to 0.026 MPa. Thus, a polyester resin (1) was obtained.

  The carbon number of the monomer constituting the polyester resin (1) was 18, and the Mn of the polyester resin (1) was 4,000, and the melting point was 72 ° C.

Production Example 2 Production of Polyester Resin (2) With respect to the amounts of dodecanedioic acid and 1,6-hexanediol input, except that 297 parts by mass of dodecanedioic acid and 169 parts by mass of 1,6-hexanediol are used, A polyester resin (2) was obtained by the same method as in Production Example 1. The carbon number of the monomer constituting the polyester resin (2) was 18, and the Mn of the polyester resin (1) was 6000, and the melting point was 75 ° C.

Production Example 3 Production of Polyester Resin (3) Aside from dodecanedioic acid and 1,6-hexanediol, sebacic acid (303 parts by mass) and 1,4-butanediol (148 parts by mass) were added. In the same manner as in Production Example 1, a polyester resin (3) was obtained. The carbon number of the monomer constituting the polyester resin (3) was 14, and the Mn of the polyester resin (1) was 7,000, and the melting point was 68 ° C.

Production Example 4 Production of Vinyl Polymerizable Monomer (1) The polyester resin obtained in Production Example 1 was 100 parts by mass of THF in a reaction vessel provided with a stirrer, a heating / cooling device, a thermometer, a cooling pipe and a nitrogen introducing pipe. (1) (192 parts by mass) was charged, and nitrogen substitution was carried out in the reaction vessel, and then the polyester resin (1) was dissolved at 65 ° C. Next, 8.5 parts by mass of "Kalens MOI" (manufactured by Showa Denko KK) as an isocyanate group-containing monomer and "Neostan U-600" (manufactured by Nitto Kasei Co., Ltd.) (0.2 parts by mass) are introduced, and 70 ° C. The reaction was carried out for 4 hours to obtain a vinyl polymerizable monomer (1).

Production Example 5 Production of Vinyl Polymerizable Monomer (2) Using the polyester resin (2) (193 parts by mass) obtained in Production Example 2 in place of the polyester resin (1), “Karenz MOI” (Showa Denko KK) A vinyl polymerizable monomer (2) was produced in the same manner as in Production Example 4 except that the amount of the product manufactured by Co., Ltd. was changed to 7.5 parts by mass.

Production Example 6 Production of Vinyl Polymerizable Monomer (3) Using the polyester resin (3) (195 parts by mass) obtained in Production Example 3 in place of the polyester resin (1), “Karenz MOI” (Showa Denko KK) A vinyl polymerizable monomer (3) was produced in the same manner as in Production Example 4 except that the amount of the product manufactured by Co., Ltd. was 5 parts by mass.

Production Example 7 Production of Fine Particle Dispersion of Shell Resin (1) In a glass beaker, n-octyl methacrylate (45 parts by mass), 2-decyltetradecyl methacrylate (15 parts by mass), methacrylic acid (15 parts by mass) A mixed solution of the vinyl polymerizable monomer (1) (25 parts by mass) obtained in Production Example (5) and azobismethoxydimethylvaleronitrile (0.1 parts by mass) and stirring at 20 ° C. Mixed. Thus, a monomer solution (monomer solution) was obtained.

  A reaction vessel equipped with a stirrer, a heating and cooling device, a thermometer, a dropping funnel, a solvent removal apparatus and a nitrogen introduction pipe was prepared. 100 parts by mass of THF was placed in the reaction vessel, and the above monomer solution was placed in the dropping funnel. After the gas phase of the reaction vessel was replaced with nitrogen, the monomer solution was dropped into THF at 70 ° C. for 1 hour under sealing. After 3 hours from the end of dropwise addition of the monomer solution, a mixture of azobismethoxydimethylvaleronitrile (0.05 parts by mass) and THF (5 parts by mass) is added to the monomer solution, and the reaction is performed at 70 ° C. for 3 hours After cooling, it was cooled to room temperature. Thus, a copolymer solution was obtained.

  The obtained copolymer solution (200 parts by mass) is dropped into an insulating liquid (trade name: “IP Solvent 2028”, manufactured by Idemitsu Kosan Co., Ltd.) (300 parts by mass) under stirring, and reduced pressure of 0.039 MPa THF was distilled off at 40 ° C. to obtain a fine particle dispersion of shell resin (1).

  The Mn of the shell resin (1) contained in this fine particle dispersion was 40000. In this Production Example, the polyester structure (parent core portion) contained in the shell resin (1) is derived from the polyester resin (1) produced in Production Example 1.

Production Example 8 Production of Fine Particle Dispersion of Shell Resin (2) A shell resin (2) was prepared in the same manner as in Production Example 7 except that a vinyl polymerizable monomer (2) was used instead of the vinyl polymerizable monomer (1). ) Was obtained. The Mn of the shell resin contained in this fine particle dispersion was 40000. In this production example, the polyester structure (parent core portion) contained in the shell resin (2) is derived from the polyester resin (2) produced in Production Example 2.

Production Example 9 Production of Fine Particle Dispersion of Shell Particles (3) A shell resin (3) was prepared in the same manner as in Production Example 7 except that a vinyl polymerizable monomer (3) was used instead of the vinyl polymerizable monomer (1). ) Was obtained. The Mn of the shell resin contained in this fine particle dispersion was 40000. In this production example, the polyester structure (parent core portion) contained in the shell resin (3) is derived from the polyester resin (3) produced in Production Example 3.

(Production Examples 11 to 13) Production of Aliphatic Polyester Resins A to C With respect to Production Example 11, an aliphatic monomer to be an alcohol constituent structural unit in a reaction vessel provided with a cooling pipe, a stirrer and a nitrogen introducing pipe Water, which is produced under nitrogen stream at 180 ° C. by charging 1,6-hexanediol) and an aliphatic monomer (adipic acid) to be an acid component constitutional unit at a molar ratio of about 1: 1 The reaction was allowed to proceed for 8 hours while distilling off the solvent.

  Next, the temperature is gradually raised to 230 ° C., the reaction is carried out for 4 hours while distilling off generated water under nitrogen flow, and the reaction is further carried out for 1 hour under a reduced pressure of 0.007 to 0.026 MPa. The A predetermined amount of acetone was introduced into an autoclave reaction tank equipped with a thermometer, a stirrer, and a nitrogen inlet tube, to obtain a resin solution A in which aliphatic polyester resin A was dissolved.

  In Production Example 12 and Production Example 13, a resin solution B in which aliphatic polyester resin B is dissolved by the same method as in Production Example 11 except that the molar ratio of 1,6-hexanediol and adipic acid is appropriately changed. And a resin solution C in which the aliphatic polyester resin C was dissolved was obtained.

Production Example 14 Synthesis of Alkylene Oxide Adduct of Bisphenol A First, an alkylene oxide adduct of bisphenol A (bis A-PO adduct) was synthesized as follows. Bisphenol A (228 parts by mass) and potassium hydroxide (2 parts by mass) are added to an autoclave having stirring and temperature control functions, and the temperature is raised to 135 ° C., and then a pressure of 0.1 to 0.4 MPa Propylene oxide (139 parts by mass) was introduced under the conditions and then allowed to react for 3 hours. An adsorbent (product name "Kyoward 600" manufactured by Kyowa Chemical Industry Co., Ltd.) (16 parts by mass) was added to the reaction product thus obtained, and the mixture was stirred and aged for 30 minutes while maintaining at 90 ° C. . Thereafter, filtration was performed to obtain a propylene oxide adduct of bisphenol A. The propylene oxide adduct was a mixture of those in which the sum (m + n) of m and n in the above chemical formula (I) is 2 and 3.

Preparation Examples 15 to 17 Preparation of Aromatic Polyester Resins a to c With respect to Preparation Example 15, an aromatic monomer to be an alcohol constituent structural unit in a reaction vessel provided with a cooling pipe, a stirrer and a nitrogen introducing pipe The bis A-PO adduct) obtained in Production Example 14 and an aromatic monomer (terephthalic acid) to be an acid component constitutional unit are charged at a molar ratio of about 1: 1, and nitrogen is added at 180 ° C. The reaction was carried out for 8 hours while distilling off generated water under an air stream.

  Next, the temperature is gradually raised to 230 ° C., the reaction is carried out for 4 hours while distilling off generated water under nitrogen flow, and the reaction is further carried out for 1 hour under a reduced pressure of 0.007 to 0.026 MPa. The A predetermined amount of acetone was introduced into an autoclave reaction tank equipped with a thermometer, a stirrer, and a nitrogen introduction pipe to obtain a resin solution a in which an aromatic polyester resin a, which is an aromatic polyester resin, was dissolved. .

  In Production Examples 16 and 17, a resin solution b in which an aromatic polyester resin b is dissolved by the same method as in Production Example 15 except that the molar ratio of the bis A-PO adduct to terephthalic acid is appropriately changed The resin solution c in which the aromatic polyester resin c was dissolved was obtained.

  Tables 1 and 2 show the configuration and properties of each of the resins obtained above. Table 1 shows the configurations and properties of shell resins (1) to (3). Table 2 shows the composition and characteristics of aliphatic polyester resins A to C and aromatic polyester resins a to c. The measuring method of each characteristic is as above-mentioned. Aliphatic polyester resins A to C and aromatic polyester resins a to c correspond to resins constituting core particles in toner particles.

Production Example 18 Production of Colorant Dispersion Liquid In a beaker, copper phthalocyanine (trade name "FASTOGEN Blue FDB-14, manufactured by DIC Corporation) (20 parts by mass) and a colorant dispersant (trade name" Aispar PB-821 ") “Ajinomoto Fine Techno Co., Ltd.” (5 parts by mass) and acetone (75 parts by mass) were added and stirred to disperse uniformly. Furthermore, a colorant dispersion was obtained by finely dispersing copper phthalocyanine using a bead mill. In the colorant dispersion, the volume average particle diameter of the colorant (copper phthalocyanine) was 0.2 μm.

Example 1
Resin solution B (5 parts by mass) and resin solution c (95 parts by mass) were mixed to obtain a core resin solution. The core resin solution (100 parts by mass) and the colorant dispersion (50 parts by mass) are charged into a beaker, and stirred at 8000 rpm using a TK autohomomixer (manufactured by Primix) at 25 ° C. to uniformly disperse The

  In a separate beaker, an insulating liquid (trade name "IP Solvent 2028", manufactured by Idemitsu Kosan Co., Ltd.) (30 parts by mass) and the fine particle dispersion (15 parts by mass) of the shell resin (1) obtained above are charged. And dispersed uniformly. Next, while the dispersion was stirred at 10,000 rpm using a TK autohomomixer, a core resin solution (150 parts by mass) in which the above colorant was dispersed was added and stirred for 2 minutes to obtain a mixed solution. Furthermore, this mixed solution is charged into a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a solvent removing device, the temperature is raised to 35 ° C., acetone is maintained under reduced pressure of 0.039 MPa while maintaining the same temperature. The acetone was distilled off until the concentration became 0.5 mass% or less. Thus, a liquid developer according to Example 1 was obtained.

  In this liquid developer, toner particles are obtained by attaching or coating shell particles composed of shell resin (1) on the surface of core particles composed of a mixture of resin B and resin c (toner resin) It had a shell structure.

(Examples 2 to 6 and Comparative Example 1)
As shown in Table 3, various liquid developers were obtained in the same manner as in Example 1 except that combinations of various resins were changed.

<Evaluation of liquid developer>
The liquid developers were evaluated as follows.

(Evaluation of toner particle shape)
The median diameter of toner particles contained in the liquid developer was measured using FPIA-3000S (manufactured by Sysmex Corporation). The results are shown in Table 4. The pretreatment of the measurement sample was performed in the following procedure.

  First, a sample (50 mg) was collected and placed in an IP solvent 2028 (20 g) to which S13940 (manufactured by Nippon Lubrizol Corporation) (30 mg) was added as a dispersant. Further, the suspension was subjected to dispersion treatment for about 5 minutes with an ultrasonic disperser "Ultrasonic Cleaner Model VS-150" (manufactured by Welbo Clear) to obtain a measurement sample. The results of median diameter, mean circularity and their standard deviation are shown in Table 4 for each measurement sample. In addition, the same IP solvent 2028 as the carrier liquid was used as the flow solvent in the measurement.

(Image forming device)
Images were formed from the liquid developers of Examples 1 to 6 and Comparative Example 1, and the fixing strength was evaluated. Here, the configuration and operation of the image forming apparatus used for the evaluation will be described first.

  FIG. 1 is a schematic conceptual view showing an example of the configuration of the image forming apparatus 100. As shown in FIG. Referring to FIG. 1, the liquid developer 6 is placed in the developing tank 5. The liquid developer 6 is drawn up by the anilox roller 22 and sent to the leveling roller 21. Excess liquid developer 6 on the surface of the anilox roller 22 is scraped off by the anilox regulating blade 23 before reaching the leveling roller 21 so that the liquid developer has an even layer thickness on the surface of the leveling roller 21 Adjusted. Thereafter, the liquid developer is transferred from the leveling roller 21 to the developer carrier 24.

  The photosensitive member 1 is charged by the charging unit 14, and a latent image is formed on the photosensitive member 1 in the exposure unit 15. The toner particles contained in the liquid developer are charged by the development charger 26. The charged toner particles are transferred from the developer carrier 24 to the photosensitive member 1 corresponding to the latent image on the photosensitive member 1, and development is performed. At this time, the liquid developer not transferred to the photosensitive member 1 is collected by the cleaning blade 25 disposed downstream of the developing unit.

  The liquid developer developed on the photosensitive member 1 is electrostatically primarily transferred to the intermediate transfer member 16 at the primary transfer portion 13. The liquid developer remaining on the photosensitive member 1 without being transferred to the intermediate transfer member 16 is collected by the cleaning blade 12 of the image carrier cleaning portion.

  The liquid developer 6 carried on the intermediate transfer member 16 is electrostatically secondarily transferred to the medium 40 (for example, paper) in the secondary transfer portion 11. The direction A in FIG. 1 indicates the transport direction of the medium 40. The liquid developer transferred to the medium 40 is fixed by a heat roller fixing device (not shown). Thus, the printed out image is completed. The liquid developer remaining on the intermediate transfer member 16 without being transferred to the medium 40 is collected by the cleaning blade 19 of the intermediate transfer member cleaning portion. The photoreceptor 1 repeats the cycle of charging, exposure and development again, and the printing operation is continued.

In the present evaluation, toner particles were charged to positive polarity by the development charger 26. Further, the potential of the intermediate transfer member 16 was -400 V, and the potential of the transfer roller 30 was -1200 V. The conveyance speed was 400 mm / s, and “OK Top Coat (128 g / m ² )” manufactured by Oji Paper Co., Ltd. was used as the medium 40 (paper).

(Evaluation of low temperature fixability)
An unfixed image (solid pattern of 10 cm × 10 cm) having a toner adhesion amount of 2 g / m ² is formed from each liquid developer using the above-described image forming apparatus, and a heat roller fixing device (heat roller temperature 120 ° C.) , And a NIP time of 30 msec) to prepare a fixed image. At this time, the paper temperature at the NIP was about 80.degree.

  The fixing strength of the solid part in the fixed image was evaluated by a tape peeling test. That is, after sticking a tape ("Scotch Mending Tape" manufactured by 3M Co., Ltd.) to the fixed image, the tape is peeled off, and the image density (ID) of the image peeled off on the tape is a reflection densitometer (brand name " It measured by X-Rite model 404 "and the product made by X-Rite, and evaluated on the following three levels. The results are shown in Table 4.

A: Image density (ID) less than 0.1 B: Image density (ID) 0.1 to less than 0.15 C: Image density (ID) 0.15 or more Here, the image density (numerical value) of the peeled image The smaller the value of V, the higher the fixing strength (low-temperature fixability).

(Evaluation of aggregation resistance)
The cohesion of toner particles contained in each liquid developer was examined using the apparatus shown in FIG. The operation of the device 200 is as follows. In the apparatus 200, the liquid developer 6 is put into the developing tank 50. The liquid developer 6 is drawn up by the first roller 51 and sent to the second roller 52. The first roller 51 and the second roller 52 rotate in the same direction.

  In this evaluation, each liquid developer (200 g) was put in the developing tank of the above-mentioned apparatus, each roller was rotated for 3 hours, and then the median diameter of toner particles in the liquid developer was determined. The rate of change of the median diameter of the toner particles was determined using the following formula: (rate of change) = (median diameter after rotation) / (median diameter before rotation). The results are shown in Table 4.

A: Change rate of less than 1.1 B: Change rate of 1.1 to less than 1.3 C: Change rate of 1.3 to less than 1.5 D: Change rate of 1.5 or more Here, change rate of median diameter of toner particles The smaller the is, the higher the aggregation resistance.

<Results and Discussion>
According to Tables 3 and 4, the liquid developer containing toner particles having a melting point of 70 ° C. or more of the shell resin constituting the shell particles has a low temperature fixing property as compared with the liquid developer of the comparative example not satisfying such conditions. It turned out that it is excellent in both the characteristics of and cohesion resistance.

  In Examples 3 and 6, the number average molecular weight of the polyester resin (2) (polyester group) constituting the parent core portion of the shell resin is 5,000 or more and 150,000 or less, and carbon of the monomer constituting the polyester structure Although the number was 16 or more and 20 or less, these results tended to have high aggregation resistance as compared with other examples and comparative examples. From this, it was found that when the number average molecular weight of the polyester group possessed by the parent core portion of the shell resin and the carbon number of the monomer satisfy the above, both properties are further excellent.

  Further, when Examples 1 to 3 and Examples 4 and 5 are compared, in the core resin, the proportion of the aliphatic polyester resin in the total of the aliphatic polyester resin and the aromatic polyester resin is 5 mass% to 40 mass. In the case of% or less, it was found that the above two characteristics are superior. In Example 6 in which the ratio is 20% by mass, the low-temperature fixability is lower than in Examples 1 to 3, but this is considered to be due to the low acid value of the core resin.

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

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is indicated not by the above description but by the claims, and is intended to include all the modifications within the meaning and scope equivalent to the claims.

  DESCRIPTION OF SYMBOLS 1 photo conductor, 5 developer tank, 6 liquid developer, 11 secondary transfer portion, 12, 19, 25 cleaning blade, 13 primary transfer portion, 14 charging portion, 15 exposure portion, 16 intermediate transfer member, 21 roller, 22 anilox Roller, 23 anilox regulating blade, 24 developer carrier, 26 developer charger, 30 transfer roller, 40 media, 100 image forming apparatus, A direction, 50 developer tank, 51 first roller, 52 second roller, 200 device.

Claims (5)

A liquid developer in which toner particles are dispersed in an insulating liquid,
The toner particles have a core / shell structure in which shell particles containing a shell resin are attached or coated on the surface of core particles containing a core resin,
The liquid developer, wherein the melting point of the shell resin is 70 ° C. or more and 100 ° C. or less. The shell resin has a parent oil part and a parent core part,
The parent core portion has a crystalline polyester group,
The liquid developer according to claim 1, wherein a number average molecular weight of the polyester group is 5,000 or more and 15,000 or less, and a carbon number of a monomer constituting the polyester group is 16 or more and 20 or less.   The liquid developer according to claim 1, wherein the shell resin is a vinyl resin. The core resin comprises an aliphatic polyester resin and an aromatic polyester resin,
The ratio of the aliphatic polyester resin in the total amount of the aliphatic polyester resin and the aromatic polyester resin is 5% by mass or more and 40% by mass or less. The liquid developer as described in Item.   The liquid developer according to any one of claims 1 to 4, wherein an acid value of the core resin is 20 mg KOH / g or more and 100 mg KOH / g or less.

Images