JP5581837B2 - Liquid developer - Google Patents

Description

  The present invention relates to a liquid developer used in an electrophotographic image forming apparatus.

  Conventionally, a powdery developer has been used as a developer used in an electrophotographic image forming apparatus. Since such a powdery developer (so-called toner) has a problem that dust of toner particles generated during handling is sucked into the human body, the lower limit of the particle size needs to be 5 to 6 μm or more. there were. However, since the image formed by the apparatus has a higher image quality as the particle size is smaller, it has been required to make the particle size smaller.

  For this reason, attention has been paid to a liquid developer capable of reducing the particle size of the toner particles because no dust is generated during handling. Such a liquid developer has a configuration in which toner particles are dispersed in an insulating liquid. As such a liquid developer, for example, the liquid developers disclosed in Patent Documents 1 to 4 are known.

JP 2000-010358 A JP 2009-175670 A JP 2009-251087 A JP 2010-026311 A

  The toner particles contained in the liquid developer have a configuration in which a pigment is dispersed in a resin. According to the inventor's research, it has been found that it is advantageous to further pulverize bulk or coarse particles in order to reduce the particle size of such toner particles. However, since a large amount of energy is required for the pulverization, it is desired to obtain toner particles having a small particle diameter with a smaller amount of energy in consideration of the economical efficiency.

  Further, according to the research of the present inventor, it has been found that the pulverizability of toner particles (the property that the particle size can be reduced by pulverization) depends on the molecular weight of the resin contained in the toner particles, and the molecular weight is reduced. As a result, a smaller particle size can be obtained even under the same grinding energy. However, when the molecular weight of the resin is decreased, the glass transition point (Tg) is decreased, and the toner particles are fused by the heat energy generated during pulverization. The study revealed it. For example, polyester resin 5 in paragraph [0046] of Patent Document 1 has a number average molecular weight of 1550, which is quite small, but has a low glass transition point of 32.9 ° C.

  On the other hand, toner particles using such a low Tg resin have increased swellability with respect to an insulating liquid, so that the toner particles are aggregated when stored at a high temperature, particularly when stored at high temperatures. Had.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a liquid developer having both pulverization property and storage property of toner particles.

  As a result of intensive studies to solve the above problems, the present inventor cannot solve the above problems by adopting a resin that does not lower the glass transition point even when the molecular weight is reduced as the resin constituting the toner particles. The present invention has finally been completed by further study based on this finding.

  That is, the liquid developer of the present invention includes toner particles, an insulating liquid, and a dispersant, the toner particles include a resin and a pigment dispersed in the resin, and the resin has a number average molecular weight. (Mn) is a polyester resin having a molecular weight of 500 or more and 1800 or less, and the polyester resin has a trifunctional or higher functional aromatic compound as an acid component at a ratio of 4 mol% to 44 mol% with respect to the total acid component. It is characterized by including.

  Here, the dispersant is preferably a basic polymer dispersant, and preferably has a pyrrolidone group. The resin preferably has a glass transition point (Tg) of 60 ° C. or higher and 80 ° C. or lower, and more preferably has a number average molecular weight of 600 or higher and 1500 or lower.

  The liquid developer of the present invention exhibits an extremely excellent effect that it has succeeded in achieving both pulverization property and storage property of toner particles.

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

Hereinafter, the present invention will be described in more detail.
<Liquid developer>
The liquid developer of the present invention includes toner particles, an insulating liquid, and a dispersant. Such a liquid developer can contain other arbitrary components as long as these components are contained. Examples of other components include a charge control agent and a thickener. Here, the mixing ratio of each component is, for example, 10 to 50% by mass of the toner particles, 50 to 90% by mass of the insulating liquid, and 0.1 to 10% by mass of the dispersant with respect to the mass of the toner particles. be able to.

Such a liquid developer is useful as a developer for an electrophotographic image forming apparatus.
<Toner particles>
The toner particles contained in the liquid developer of the present invention contain a resin and a pigment dispersed in the resin. Such toner particles can contain any other component as long as these components are contained. Examples of other components include a wax and a charge control agent. Here, the blending ratio of the resin and the pigment may be determined so that the concentration expressed when the toner particles are formed with a single thickness is a desired concentration. For example, the resin can be 50 to 95% by mass, more preferably 70 to 90% by mass. When the blending ratio of the resin is less than 50% by mass, the binding force between the toner particles is weakened, and the fixing strength tends to be deteriorated. When the blending ratio of the pigment is less than 5% by mass, it may be difficult to achieve a desired color because the pigment concentration that can be achieved by one toner particle thin layer is low.

  The particle diameter of such toner particles is not particularly limited, but is 0.1 to 3.5 μm, more preferably 0.5 to 2.5 μm for the purpose of obtaining a high-quality image. Is preferred. These particle diameters are smaller than the particle diameter of toner particles of a powdery developer (dry developer) that has been conventionally used, and are one of the features of the present invention.

  In addition, the particle diameter as used in the field of this invention means an average particle diameter, and can be specified as a volume average particle diameter with various particle size distribution analyzers.

<Resin>
The resin constituting the toner particles of the present invention is a polyester resin having a number average molecular weight of 500 or more and 1800 or less, and the polyester resin contains a trifunctional or higher functional aromatic compound as an acid component with respect to the total acid component. It is characterized by containing 4 mol% or more and 44 mol% or less.

  The reason why a polyester resin is employed as the resin composition is that characteristics such as thermal characteristics can be changed over a wide range and are excellent in translucency, spreadability, and viscoelasticity. As described above, the polyester resin is excellent in translucency, so that a beautiful color can be obtained when a color image is obtained, and an image formed on a recording medium such as paper because of excellent spreadability and viscoelasticity. The (resin film) is strong and can be strongly bonded to the recording medium.

  And the polyester resin employ | adopted by this invention requires that a number average molecular weight is 500-1800, More preferably, it is 600-1500. By setting the number average molecular weight to 500 or more and 1800 or less, the particle size of the toner particles can be reduced to a desired size by pulverization while reducing the pulverization energy. If the number average molecular weight is less than 500, the resin becomes too soft and the fixing strength becomes weak. On the other hand, if the number average molecular weight exceeds 1800, the resin becomes too hard and a large amount of energy is required for pulverization. The number average molecular weight can be measured by GPC (gel permeation chromatography).

  Furthermore, the polyester resin employed in the present invention is characterized by containing, as an acid component, a trifunctional or higher functional aromatic compound in a proportion of 4 mol% to 44 mol% with respect to the total acid component. The polyester resin of the present invention has the number average molecular weight as described above, but if only the number average molecular weight is in the above range without any control of the resin composition, the glass transition point becomes too low, Aggregation occurs due to the heat energy generated during pulverization, and as a result, it becomes impossible to obtain a product having a small particle size, and even if a product having a desired particle size is obtained, the swelling property with respect to the insulating liquid becomes remarkable. Therefore, there has been a problem that the toner particles are aggregated when the liquid developer is stored, particularly when stored at a high temperature.

  Since the polyester resin of the present invention has a structure that is appropriately cross-linked by having the above composition, it has succeeded in solving this problem. That is, the excellent effect of achieving both the pulverization property and storage property of the toner particles obtained by the liquid developer of the present invention defines the number average molecular weight of the polyester resin within a specific range, and the chemical composition thereof. By adopting the specific composition as described above, it has been brought about for the first time, and cannot be achieved without any of these requirements.

  The liquid developer of the present invention has succeeded in achieving both the trade-off relationship between the good pulverization property and the stable storage property, and its industrial applicability is extremely high. large.

  Here, the “trifunctional or higher functional aromatic compound” of the present invention refers to a “reaction site” that can react with a polyhydric alcohol component in order to form an ester bond constituting a polyester resin. An aromatic compound having 3 or more. As such a “reaction site”, a “functional group” usually has its function, and “trifunctional or more” usually means that three or more such “functional groups” are contained in the aromatic compound. (The component that reacts with the polyhydric alcohol component is generally referred to as an acid component (polybasic acid)). Specific examples of the functional group include a carboxyl group. In addition, an acid anhydride is also included in such a functional group. For example, when two adjacent carboxyl groups are dehydrated to form an acid anhydride, the bifunctionality (the number of functional groups is two) is assumed. It shall be counted.

  Moreover, the said mol% shows the molar ratio of the trifunctional or more functional aromatic compound which occupies for the whole quantity (namely, total acid component) of the acid component (polybasic acid) which comprises a polyester resin. When the molar ratio is less than 4 mol%, aggregation due to thermal energy generated during pulverization becomes remarkable and desired pulverization properties cannot be obtained. When the molar ratio exceeds 44 mol%, the glass transition point becomes too high, so that the energy for fixing the image is remarkably increased, which is not economically disadvantageous and also decreases the gloss of the image. A more preferable molar ratio is 8 mol% or more and 40 mol% or less.

  Such a molar ratio can be adjusted by controlling the amount of raw material monomer used to synthesize the polyester resin, but is included in the toner particles in the liquid developer or the polyester component in the image. The actual ratio (molar ratio) of the aromatic compound can be measured by performing 1H-NMR analysis and determining its integration ratio using a Fourier transform nuclear magnetic resonance apparatus (FT-NMR).

  Such a polyester resin of the present invention preferably exhibits thermoplasticity and has a glass transition point (Tg) of 60 ° C. or higher and 80 ° C. or lower. When the glass transition point is less than 60 ° C., the pulverization property and storage property of the toner particles may be deteriorated. When the glass transition point exceeds 80 ° C., the energy for fixing the image is remarkably increased, which is disadvantageous economically. When the fixing temperature is low, the glossiness of the image may be lowered.

  Further, the polyester resin of the present invention is an ordinary method as long as it contains a trifunctional or higher functional aromatic compound as an acid component (polybasic acid) in a proportion of 4 mol% to 44 mol% with respect to the total acid component. That is, it can be obtained by polycondensation of a polyhydric alcohol and a polybasic acid (typically a polycarboxylic acid).

  Here, the polyhydric alcohol is not particularly limited. For example, propylene glycol such as ethylene glycol, diethylene glycol, triethylene glycol, and 1,2-propylene glycol, butanediol such as dipropylene glycol and 1,4-butanediol, Alkylene glycols (aliphatic glycols) such as neopentyl glycol and hexanediol such as 1,6-hexanediol and their alkylene oxide adducts, bisphenols such as bisphenol A and hydrogenated bisphenol, and phenols of these alkylene oxide adducts Examples thereof include triglycols, alicyclics such as monocyclic or polycyclic diols, and aromatic diols, glycerol, trimethylolpropane and the like. These can be used alone or in admixture of two or more. In particular, a bisphenol A alkylene oxide 2-3 mol adduct is preferable because it is suitable as a resin for toner particles of a liquid developer in terms of solubility and stability of the product polyester resin and is low in cost. . Examples of the alkylene oxide include ethylene oxide and propylene oxide.

  Examples of the trifunctional or higher functional aromatic compound include trimellitic acid, trimesic acid, pyromellitic acid, methyl nadic acid, and acid anhydrides and lower alkyl esters thereof. These can be used alone or in admixture of two or more. Among these, trimellitic acid which can be obtained at low cost is preferable. By containing such a trifunctional or higher functional aromatic compound at a specific blending ratio as described above, it is possible to prevent the glass transition point from being lowered even if the molecular weight is reduced as described above, and to the insulating liquid. It is possible to prevent swelling.

  Examples of the acid component include polybasic acids (polycarboxylic acids) other than trifunctional or higher aromatic compounds such as malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, and itaconic acid. , Phthalic acid and its modified acids (for example, hexahydrophthalic anhydride), isophthalic acid, saturated or unsaturated (or aromatic) dibasic basic acids such as terephthalic acid, and their acid anhydrides, lower alkyl esters, etc. These can be used alone or in admixture of two or more. Among these, isophthalic acid and terephthalic acid are preferable because they are suitable as a resin for toner particles of a liquid developer in terms of solubility and stability of the product polyester resin and are low in cost.

<Pigment>
The pigment contained in the toner particles of the present invention is dispersed in the above resin. The particle size of such a pigment is preferably 0.2 μm or less. If the particle diameter of the pigment exceeds 0.2 μm, the dispersion of the pigment becomes worse, the glossiness is lowered, and a desired color may not be realized.

  The amount of the pigment added in the toner particles is preferably about 5 to 30 parts by mass with respect to 100 parts by mass of the resin. If the addition amount is less than 5 parts by mass, a sufficient coloring effect may not be obtained, and if it exceeds 30 parts by mass, uniform dispersion of the pigment becomes difficult and may cause a decrease in glossiness due to aggregation of the pigment. is there.

As such a pigment, a conventionally known pigment can be used without any particular limitation, but the following pigments are preferably used from the viewpoint of cost, light resistance, colorability and the like. In terms of color composition, these pigments are usually classified as black pigments, yellow pigments, magenta pigments, and cyan pigments. Basically, colors other than black (color images) are subtractive color mixtures of yellow pigments, magenta pigments, and cyan pigments. Is toned.
Black pigment: Carbon black.
Cyan pigment: C.I. I. (Color Index) Pigment Blue 15: 1, 15: 3, etc. Copper phthalocyanine blue cyan pigment, phthalocyanine green pigment. In addition, although it is preferable that a copper phthalocyanine blue cyan pigment is included as a main component, other pigments can also be included.
Magenta pigment: C.I. I. Pigment Red 48, 57 (Kermin 6B), 5, 23, 60, 114, 146, 186 and the like, azo lake-based magenta pigments and insoluble azo-based magenta pigments, C.I. I. Pigment Red 88, C.I. I. Thioindigo magenta pigments such as CI Pigment Violet 36 and 38; I. Quinacridone magenta pigments such as CI Pigment Red 122 and 209; I. Naphthol-based magenta pigments such as Pigment Red 269. Of these, at least one of quinacridone pigments, carmine pigments, and naphthol pigments is preferably included, and two to three of these three types may be included.
Yellow pigment: C.I. I. Pigment Yellow 12, 13, 14, 17, 55, 81, 83, 180, etc. Disazo yellow pigments.

<Insulating liquid>
The insulating liquid contained in the liquid developer of the present invention is preferably a liquid that is non-volatile at normal temperature and exhibits electrical insulation (for example, a resistance value in the range of 10 ¹¹ to 10 ¹⁶ Ω · cm). . This is because the electrostatic latent image is not normally disturbed if it has a resistance value in this range. Further, as such an insulating liquid, those having no odor and toxicity are preferable.

  Examples of such an insulating liquid include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes, and the like. In particular, a normal paraffin solvent and an isoparaffin solvent are preferable from the viewpoint of odor, harmlessness, and cost. More specifically, Moresco White P40 (trade name, flash point: 140 ° C), P60 (flash point: 170 ° C), P120 (flash point: 200 ° C), Isopar (manufactured by Matsumura Oil Research Co., Ltd.) Trade name, manufactured by Exxon Chemical Co., Ltd.), Shellsol 71 (trade name, manufactured by Shell Petrochemical Co., Ltd.), IP solvent 1620 (trade name, manufactured by Idemitsu Petrochemical Co., Ltd.), IP solvent 2028 (trade name, flash point: 84 ° C., Idemitsu Petrochemical Co., Ltd.).

  Normally, when a low molecular weight resin and an insulating liquid are mixed, the lower the flash point of the insulating liquid, the higher the compatibility with the resin and the easier the resin swells, so that the storage property at high temperatures deteriorates. However, since the polyester resin of the present invention has the composition as described above, such swelling can be prevented, and even when mixed with an insulating liquid having a low flash point, the storage property does not deteriorate.

<Dispersant>
The dispersant contained in the liquid developer of the present invention has a function of stably dispersing the toner particles in the insulating liquid. Therefore, the dispersant is usually present (adsorbed) on the surface of the toner particles. Yes. Such a dispersant is preferably soluble in the insulating liquid.

  Such a dispersant is not particularly limited as long as it can stably disperse toner particles. For example, a surfactant, a polymer dispersant, and the like can be used.

  In particular, in the present invention, since the resin as described above is used as the resin constituting the toner particles, it is preferable to use a basic polymer dispersant as such a dispersant. It is particularly preferable to use a polymer dispersant having a pyrrolidone group. This is probably because the acid value of the above-mentioned polyester resin constituting the toner particles is increased, so that by using a basic polymer dispersant, a good dispersibility of the toner particles can be obtained over a long period of time due to the interaction between the two. It is thought that it may be because of stabilization.

  Examples of such basic polymer dispersants include the pyrrolidone group, for example, an aromatic amino group, an aliphatic amino group, a heterocyclic nitrogen-containing group, a heterocyclic oxygen-containing group, and a heterocyclic sulfur-containing group. A polymeric dispersant can be mentioned. Examples of the pyrrolidone group include an N-vinylpyrrolidone group. Examples of the basic polymer dispersant having an N-vinylpyrrolidone group include N-vinyl-2-pyrrolidone, methacrylic acid ester, and acrylic acid. A random copolymer or a graft copolymer with an acid ester or an alkylene compound can be used. Here, when the methacrylic acid ester and the acrylic acid ester are alkyl esters, the alkyl group preferably has about 10 to 20 carbon atoms. Examples of these commercially available products include “Antaron V-216” and “Antaron V-220” (both are trade names, manufactured by GAF / ISP Chemicals). Further, the alkyl group of the alkylene compound preferably has about 10 to 30 carbon atoms.

<Manufacturing method>
First, the polyester resin constituting the toner particles can be produced by a conventionally known polycondensation method as long as it has the above composition. That is, although it depends on the type of raw material monomer to be used, it can generally be carried out in a temperature range of 150 to 300 ° C. Moreover, arbitrary conditions, such as using inert gas as atmospheric gas, selecting various solvents arbitrarily, or making the reaction container internal pressure normal pressure or pressure reduction, can be employ | adopted.

  In order to accelerate the reaction, an esterification catalyst may be used. Examples of esterification catalysts include metal organic compounds such as tetrabutyl zirconate, zirconium naphthenate, tetrabutyl titanate, tetraoctyl titanate, 3/1 stannous oxalate / sodium acetate, etc. That which does not color the polyester which is is preferable.

  In addition, the molecular weight of the polyester resin that is a reaction product can be adjusted by adjusting the reaction time. This is because the polycondensation reaction to obtain a polyester resin is a sequential reaction in which a low molecular weight substance increases its molecular weight with the passage of time. Since the relationship between the reaction time and the molecular weight varies depending on the type of raw material monomer, various polymerization conditions, lot scale, etc., it is possible to adjust the reaction time to obtain a desired molecular weight in consideration of these various conditions. preferable.

  Next, a liquid developer is prepared using the polyester resin obtained as described above. The liquid developer can be prepared based on a conventionally known technique. For example, by using a kneader such as a pressure kneader, a roll mill, or a three-roller, the polyester resin and the pigment are melt-kneaded at a predetermined blending ratio, and the pigment is uniformly dispersed in the polyester resin. Get the body.

  Subsequently, the pigment-resin dispersion obtained above is cooled, and after cooling, this is coarsely pulverized. Subsequently, the coarsely pulverized pigment-resin dispersion (sometimes referred to as “coarse pulverized toner”) is further pulverized to a desired particle size to obtain toner particles.

  Examples of the pulverization method that can be used above include a dry pulverization method and a wet pulverization method. However, the pulverization method is not particularly limited as long as it can pulverize to a desired particle size with energy saving.

  For example, a coarsely pulverized toner is obtained by a cutter mill, and then toner particles are obtained by further pulverizing the coarsely pulverized toner to a desired particle size using a jet mill as a dry pulverization method. A liquid developer can be prepared by mixing the toner particles with an insulating liquid and a dispersant.

  On the other hand, when the wet pulverization method is employed, for example, the coarsely pulverized toner obtained by the above method, an insulating liquid, and a dispersant are mixed, and the mixture is pulverized using a sand mill to obtain toner particles as desired particles. The diameter of the liquid developer can be prepared.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these. In the examples, “parts” means “parts by mass” unless otherwise specified.

<Synthesis of polyester resin>
700 parts of propylene oxide adduct of bisphenol A (polyhydric alcohol represented by the following formula (I)) as a raw material monomer in a four-necked flask equipped with a stirring rod, partial condenser, nitrogen gas inlet tube, and thermometer 380 parts of terephthalic acid (polybasic acid) and 20 parts of trimellitic acid (polybasic acid which is a trifunctional or higher functional aromatic compound) are introduced, nitrogen gas is introduced with stirring, and heavy is heated at a temperature of about 170 ° C. Condensation was performed. At this time, the number average molecular weight (Mn) during the reaction was monitored, and when the number average molecular weight (Mn) reached about 1500, the temperature was lowered to about 100 ° C., and 0.012 part of hydroquinone was added as a polymerization inhibitor to add A polyester resin was obtained by stopping the condensation. The polyester resin thus obtained was designated as “Polyester Resin A”.

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

  It was 1800 when the number average molecular weight (Mn) of the said "polyester resin A" was measured, and the glass transition point (Tg) was 71 degreeC.

  Furthermore, polyester resins B to J were obtained by the same method as above except that the composition of the raw material monomers (polyhydric alcohol and polybasic acid) was as shown in Table 1. Table 1 shows the number average molecular weight (Mn) and glass transition point (Tg) of these polyester resins.

<Manufacture of toner particles>
100 parts of polyester resin A and 25 parts of “Fastgen Blue GNPT” (trade name, manufactured by DIC) as a copper phthalocyanine blue cyan pigment were charged into a Henschel mixer and mixed thoroughly. Thereafter, this mixture was melt-kneaded using a co-rotating twin-screw extruder having a heating temperature in the roll of 100 ° C., cooled, and then coarsely pulverized using a cutter mill to obtain coarsely pulverized toner A.

Next, the coarsely pulverized toner A was further pulverized using a counter jet mill 200AFG (trade name, manufactured by Hosokawa Micron Corporation) to obtain toner particles A. At this time, the pulverization conditions were air pressure 2.3 m ³ / min. The air pressure was 0.8 kPa, the nozzle diameter was 3 mm, and the rotation speed was 11500 rpm.

  In the above, except that polyester resins B to J were used instead of polyester resin A, coarsely pulverized toners B to J were obtained in the same manner, and toner particles B to J were obtained in the same manner.

<Manufacture of liquid developer>
Hereinafter, the liquid developers of Examples 1 to 3, 7 and 8 , Comparative Examples 1 to 4 , and Reference Examples 4 to 6 were produced.

<Example 1>
As an insulating liquid, 70 parts of “IP Solvent 2028” (trade name, manufactured by Idemitsu Petrochemical Co., Ltd.), 30 parts of toner particles A, N-vinylpyrrolidone / N-vinylpyrrolidone which is a basic polymer dispersant having an N-vinylpyrrolidone group / A liquid developer was obtained by mixing 1 part of an alkylene copolymer “Antaron V-216” (trade name, manufactured by GAF / ISP Chemicals).

<Examples 2 , 3, 7, 8 , Comparative Examples 1-4 , and Reference Examples 4-6 >
Examples 2 , 3, 7, 8 and Comparative Examples 1 to 4 and Reference Examples 4 to 6 were the same except that the toner particles shown in Table 2 were used instead of the toner particles A in Example 1 . A liquid developer was obtained. However, for Reference Examples 5 and 6, the following dispersant was used instead of “Antaron V-216”. That is, in Reference Example 5, “Solspers S13940” (trade name, manufactured by Nippon Lubrizol Co., Ltd.) was used as a basic polymer dispersant having no pyrrolidone group. In Reference Example 6, “Sulhol Ba-30N” (trade name, manufactured by MORESCO), which is barium sulfonate, was used as the ionic dispersant.

<Evaluation>
<Measurement method of molecular weight>
The number average molecular weight (Mn) of the polyester resin was measured by GPC (gel permeation chromatography). The measurement conditions are as follows.
DETECTOR: RI
COLUMN: KF-404HQ (trade name, manufactured by Shodex), KF-402HQ (trade name, manufactured by Shodex)
Solvent: Tetrahydrofuran (THF)
Flow rate: 0.3 ml / min.
Calibration curve: standard polystyrene The results are shown in Table 1.

<Measurement of glass transition point>
The glass transition point (Tg) of the polyester resin was determined by using a differential scanning calorimeter “DSC-6200” (manufactured by Seiko Instruments Inc.), a sample amount of 20 mg, and a heating rate of 10 ° C./min. It measured on condition of this. The results are shown in Table 1.

<Evaluation of grindability>
Using the counter jet mill 200AFG (trade name, manufactured by Hosokawa Micron Co., Ltd.), the coarsely pulverized toners A to J were processed under the conditions of a processing amount of 3.3 kg / h (air pressure amount 2.3 m ³ / min., Air pressure 0.8 kPa). After pulverization and classification at a nozzle diameter of 3 mm and a rotation speed of 11500 rpm, the volume average particle size was measured with a particle size distribution analyzer SALD-2200 (trade name, manufactured by Shimadzu Corporation).

  “A” indicates that the volume average particle size after grinding is 2.5 μm or less, “B” indicates that the particle size is 3.0 μm or less, “C” indicates that the particle size is 3.5 μm or less, " The smaller the particle size, the better the grindability. The results are shown in Table 2 below.

<Evaluation of storage>
10 cc of liquid developer was placed in a 20 cc glass bottle and stored in a thermostat set at 50 ° C. for 24 hours. The particle size before and after storage was measured with a particle size distribution analyzer SALD-2200.

  Average particle diameter after storage / average particle diameter before storage of 1 to less than 1.1 is “A”, 1.1 to less than 1.2 is “B”, 1.2 to less than 1.3 “C” was assigned to those having a thickness of 1.3 and “D” was assigned to those having a value of 1.3 or more. The smaller the ratio is, the better the storage property is. The results are shown in Table 2 below.

<Ratio of trifunctional or higher functional aromatic compound>
The ratio of the aromatic compound was determined from its integration ratio by performing 1H-NMR analysis using a Fourier transform nuclear magnetic resonance apparatus (FT-NMR) (trade name: “Lambda400”, manufactured by JEOL Ltd.). The measurement solvent was chloroform D solvent. The results are shown in Table 2 below (“Ratio (mol%)”).

  “Ratio” in Table 2 indicates the ratio (mol%) of the trifunctional or higher functional aromatic compound to the total acid component measured by the above method, which is consistent with the composition ratio of the raw material monomers. Met.

<Evaluation of fixing strength>
Using the image forming apparatus shown in FIG. 1, solid patterns (10 cm × 10 cm, adhesion amount: 2 mg) of the liquid developers of Examples 1 to 3, 7, 8 and Comparative Examples 1 to 4 and Reference Examples 4 to 6 / M ² ) was formed on a recording medium (quality paper / coated paper) and subsequently fixed with a heat roller (180 ° C. × nip time 80 msec.).

Thereafter, an eraser (trade name: sand eraser “LION 26111”, manufactured by Lion Corporation) was rubbed twice with a pressing load of 1 kgf on the part having no offset, and the residual ratio of the image density was measured by a reflection densitometer “X-Rite model 404”. (Trade name, manufactured by X-Rite), and the following four ranks were evaluated.
A: Image density remaining rate is 90% or more.
B: Image density remaining rate is 80% or more and less than 90%.
C: Image density remaining rate is 70% or more and less than 80%.
D: Image density remaining rate is less than 70%.

  A higher image density remaining rate indicates a higher fixing strength of the image. The results are shown in Table 2 below (“Fixability” section).

The process conditions and process outline of the image forming apparatus are as follows.
<Process conditions>
System speed: 40 cm / s
Photoconductor: negatively charged OPC
Charging potential: -700V
Development voltage (developing roller applied voltage): -450V
Transfer voltage (transfer roller applied voltage): + 600V
Pre-development corona CHG: Adjust appropriately with needle application voltage -3 to 5 kV <Outline of process>
FIG. 1 is a schematic conceptual diagram of an electrophotographic image forming apparatus 1. First, the liquid developer 2 is taken up by the supply roller 3 and scraped by the regulating blade 4 to form a thin layer of liquid developer having a predetermined thickness on the supply roller 3 (in the case of an anilox roller). The roller digging is filled with liquid developer, and the regulated amount is measured by the regulating roller).

  Next, a thin layer of liquid developer moves from the supply roller 3 onto the developing roller 5, and the toner particles move onto the photosensitive member 6 at the nip between the developing roller 5 and the photosensitive member 6, so A toner image is formed. Thereafter, the toner image is transferred onto the recording medium 11 at the nip between the photoreceptor 6 and the backup roller 10, and the image is fixed by the heat roller 12. In addition to the above, the image forming apparatus 1 includes a cleaning blade 7, a cleaning blade 8, and a charging device 9.

  As is clear from Table 2, it was confirmed that the liquid developers of the examples were highly compatible in pulverization and storage while exhibiting a fixed fixability as compared with the liquid developers of the comparative examples. .

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

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

  DESCRIPTION OF SYMBOLS 1 Image forming apparatus, 2 Liquid developer, 3 Supply roller, 4 Regulating blade, 5 Developing roller, 6 Photoconductor, 7 Cleaning blade, 8 Cleaning blade, 9 Charging device, 10 Backup roller, 11 Recording medium, 12 Heat roller

Claims (5)

Including toner particles, an insulating liquid and a dispersant;
The toner particles include a resin and a pigment dispersed in the resin,
The resin is a polyester resin having a number average molecular weight of 500 or more and 1800 or less,
The said polyester resin is a liquid developer which contains a trifunctional or more than trifunctional aromatic compound as an acid component in the ratio of 4 mol% or more and 39 mol% or less with respect to all the acid components.   The liquid developer according to claim 1, wherein the dispersant is a basic polymer dispersant.   The liquid developer according to claim 2, wherein the dispersant has a pyrrolidone group.   The liquid developer according to claim 1, wherein the resin has a glass transition point of 60 ° C. or higher and 80 ° C. or lower.   The liquid developer according to claim 1, wherein the resin has a number average molecular weight of 600 or more and 1500 or less.

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