JP6489697B2 - Method for producing liquid developer - Google Patents

Description

  The present invention relates to a method for producing a liquid developer used for developing a latent image formed in an electrophotographic method, an electrostatic recording method, an electrostatic printing method or the like.

  There are two types of electrophotographic developers: a dry developer using a toner composed of a material containing a colorant and a binder resin in a dry state, and a liquid developer in which the toner is dispersed in an insulating carrier liquid. Among these, the liquid developer is excellent in terms of image quality because the particle size of the toner can be reduced. In recent years, since the demand for higher image quality has increased, liquid developer is required to further reduce the particle size of toner.

  As a method for producing a liquid developer, there is disclosed a method (wet pulverization method) in which toner particles obtained by melt-kneading and pulverizing a pigment and a resin are refined in an insulating liquid in the presence of a dispersant (patent). Reference 1).

  Also disclosed is a method (polymerization method) in which a monomer component is polymerized in an insulating liquid in which a pigment is dispersed to form toner particles (see Patent Document 2).

  Furthermore, a method (precipitation method) is disclosed in which toner particles are precipitated by removing the solvent described above from a mixture of a pigment / resin solution and an insulating liquid (see Patent Document 3).

JP-A-7-234551 JP 2008-310021 A JP 2003-345071 A

  However, in the conventional technique, as the particle size of the toner particles is reduced, the viscosity of the liquid developer increases, so that a large amount of dispersant needs to be added. As a result, there is a problem that the resistance of the liquid developer is lowered and developability is deteriorated.

  The present invention relates to a method for producing a liquid developer having a small particle size and good developability even with a small amount of a dispersant.

The present invention is a method for producing a liquid developer in which toner particles containing a resin and a pigment are dispersed in an insulating liquid,
Step 1: A resin containing a polyester having an acid value of 5 mg KOH / g or more and 35 mg KOH / g or less, a raw material containing a basic compound and an organic solvent are mixed, and 5 mol of the carboxy group of the polyester is contained by the basic compound. A step of phase inversion emulsification of a mixed solution neutralized by at least 40% by mole to 40% by mole to obtain an aqueous dispersion of toner particles having a volume median particle size of 1 μm to 4 μm.
Step 2: Separating toner particles from the aqueous dispersion of toner particles obtained in Step 1, and Step 3: Dispersing the toner particles obtained in Step 2 in an insulating liquid in the presence of a dispersant. The present invention relates to a method for producing a liquid developer including steps.

  The liquid developer obtained by the method of the present invention has an excellent effect that it has a small particle size and good developability even with a small amount of a dispersant.

  The present invention relates to a method for producing a liquid developer in which toner particles are formed by phase inversion emulsification of a mixed solution containing a toner raw material from a solvent system to an aqueous system. The acid value of a polyester used for phase inversion emulsification and its neutralization By adjusting the degree, a liquid developer having a small particle diameter and capable of reducing the viscosity even with a small amount of a dispersant can be obtained. Thereby, since the resistance of the liquid developer does not decrease, an effect is obtained that a liquid developer having good developability can be obtained.

  The reason for such an effect is considered as follows. The polyester resin constituting the toner particles has a polar functional group such as a carboxy group. These polar functional groups are considered to have a function of aggregating toner particles in the insulating liquid. In general, when the particle size of the toner particles is reduced, the specific surface area of the particles is increased, so that the toner particles are likely to aggregate and the viscosity of the liquid developer is increased. As a result, it is considered that a large amount of dispersant is required for lowering the viscosity.

  In contrast, in the method of the present invention, the carboxy group of the polyester having an acid value of 5 mgKOH / g or more and 35 mgKOH / g or less is partially neutralized in the presence of a basic compound, and phase-inversion emulsification is performed in an aqueous system. As a result, toner particles with reduced carboxy groups present on the particle surface can be obtained. As a result, the viscosity can be reduced even with a small particle diameter and even with a small amount of a dispersant, so that the resistance of the liquid developer does not decrease, and a liquid developer having good developability can be obtained.

  The method of the present invention is a method including Steps 1 to 3 to be described later. Step 1 includes a resin containing a polyester having an acid value of 5 mgKOH / g or more and 35 mgKOH / g or less, a pigment, and a raw material containing a basic compound and an organic compound. A solvent is mixed, and the mixture obtained by neutralizing 5 mol% to 40 mol% of the carboxy group of the polyester with the basic compound is phase-inverted and emulsified into an aqueous system, and the volume median particle size is 1 μm to 4 μm. This is a step of obtaining an aqueous dispersion of toner particles.

  The degree of neutralization of the carboxy group of the polyester by the basic compound is 5 mol% or more, preferably 7 mol% or more, more preferably 10 mol% or more, from the viewpoint of reducing the particle size and reducing the viscosity. From the viewpoint of particle size reduction and low viscosity, it is 40 mol% or less, preferably 30 mol% or less, more preferably 20 mol% or less. The neutralization degree can be calculated by the following formula.

  The product of the acid value of the polyester (mgKOH / g) and the degree of neutralization (mol%) of the polyester [the acid value of the polyester (mgKOH / g) × the degree of neutralization of the polyester (mol%)] in Step 1 is small. From the viewpoint of diameter reduction and viscosity reduction, preferably 100 or more, more preferably 150 or more, and from the viewpoint of particle size reduction and viscosity reduction, preferably 900 or less, more preferably 700 or less, and still more preferably 600. Hereinafter, more preferably 500 or less.

  The polyester used in the present invention is obtained by polycondensation of an alcohol component composed of a divalent or higher alcohol and a carboxylic acid component composed of a divalent or higher carboxylic acid compound.

  Examples of the divalent alcohol include diols having 2 to 20 carbon atoms, preferably 2 to 15 carbon atoms, and formula (I):

(In the formula, RO and OR are oxyalkylene groups, R is an ethylene and / or propylene group, x and y are the average number of moles of alkylene oxide added, each being a positive number, The sum value is 1 or more, preferably 1.5 or more, 16 or less, preferably 8 or less, more preferably 4 or less)
An alkylene oxide adduct of bisphenol represented by Specific examples of the divalent alcohol having 2 to 20 carbon atoms include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, bisphenol A, hydrogenated bisphenol A, and the like.

  Examples of the trihydric or higher alcohol include trihydric or higher alcohol having 3 to 20 carbon atoms, preferably 3 to 10 carbon atoms. Specific examples include sorbitol, 1,4-sorbitan, pentaerythritol, glycerol, trimethylolpropane, and the like.

  Examples of the divalent carboxylic acid compound include dicarboxylic acids having 3 to 30 carbon atoms, preferably 3 to 20 carbon atoms, more preferably 3 to 10 carbon atoms, and acid anhydrides, alkyls (carbon number 1 8 or less) Derivatives such as esters are mentioned. Specifically, aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, fumaric acid, maleic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, alkyl groups having 1 to 20 carbon atoms, or carbon Examples thereof include aliphatic dicarboxylic acids such as succinic acid substituted with an alkenyl group having a number of 2 or more and 20 or less.

  Examples of the trivalent or higher carboxylic acid compound include 4 to 30 carbon atoms, preferably 4 to 20 carbon atoms, more preferably a trivalent or higher carboxylic acid having 4 to 10 carbon atoms, and acid anhydrides thereof. Examples thereof include derivatives such as alkyl (having 1 to 8 carbon atoms) esters. Specific examples include 1,2,4-benzenetricarboxylic acid (trimellitic acid) and 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid).

  In addition, a monovalent alcohol may be appropriately contained in the alcohol component, and a monovalent carboxylic acid compound may be appropriately contained in the carboxylic acid component from the viewpoint of adjusting the softening point of the polyester.

  Polyester is produced, for example, by polycondensing an alcohol component and a carboxylic acid component in an inert gas atmosphere at a temperature of 180 ° C. or higher and 250 ° C. or lower in the presence of an esterification catalyst or a polymerization inhibitor as necessary. can do.

  Examples of the esterification catalyst include tin compounds such as dibutyltin oxide and tin (II) 2-ethylhexanoate, and titanium compounds such as titanium diisopropylate bistriethanolamate. The amount of the esterification catalyst used is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, preferably 1 part by mass or less, more preferably with respect to 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component. 0.7 parts by mass or less.

  A cocatalyst may be used to shorten the reaction time. Examples of the cocatalyst include gallic acid. The amount of the cocatalyst used is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass with respect to 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component. It is below mass parts. The mass ratio of the cocatalyst to the catalyst (cocatalyst / catalyst) is preferably 0.01 or more and 0.5 or less.

  From the viewpoint of improving emulsifiability, the acid value of the polyester is 5 mg KOH / g or more, preferably 7 mg KOH / g or more, more preferably 10 mg KOH / g or more, and 35 mg KOH / g or less, preferably 25 mg KOH / g or less. More preferably, it is 15 mgKOH / g or less.

  The softening point of the polyester is preferably 160 ° C. or lower, more preferably 150 ° C. or lower, from the viewpoint of improving the low-temperature fixability of the liquid developer, and the toner particles aggregate when the aqueous medium is removed in Step 3. From the viewpoint of preventing the temperature, it is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. When these viewpoints are put together, 70-160 degreeC is preferable and 80-150 degreeC is more preferable.

  The glass transition temperature of the polyester is preferably 80 ° C. or less, more preferably 75 ° C. or less, from the viewpoint of improving the low-temperature fixability of the liquid developer, and the toner particles aggregate when the aqueous medium is removed in Step 3. From the viewpoint of preventing this, it is preferably 45 ° C. or higher, more preferably 50 ° C. or higher. When these viewpoints are put together, 45-80 degreeC is preferable and 50-75 degreeC is more preferable.

  In the present invention, the polyester may be a polyester modified to such an extent that the characteristics are not substantially impaired. Examples of the modified polyester include grafting and blocking with phenol, urethane, epoxy and the like by the methods described in JP-A-11-133668, JP-A-10-239903, JP-A-8-20636, and the like. Polyester.

  The polyester content in the resin is preferably 90% by mass or more, more preferably 95% by mass or more, substantially more preferably 100% by mass, and more preferably 100% by mass, that is, only the polyester is used as the resin. However, in the range where the effects of the present invention are not impaired, a resin other than polyester may be contained. Examples of resins other than polyester include polystyrene, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene. -Styrenic resin, epoxy resin, rosin-modified maleic acid resin, polyethylene-based resin which is a homopolymer or copolymer containing styrene or a styrene-substituted product such as acrylic acid ester copolymer and styrene-methacrylic acid ester copolymer , Polypropylene resins, polyurethane resins, silicone resins, phenol resins, aliphatic or alicyclic hydrocarbon resins, and the like, and one or more of these can be used in combination.

  As the pigment, all of the pigments used as toner colorants can be used, such as carbon black, phthalocyanine blue, permanent brown FG, brilliant first scarlet, pigment green B, rhodamine-B base, solvent red 49, Solvent Red 146, Solvent Blue 35, Quinacridone, Carmine 6B, Isoindoline, Disazo Yellow and the like can be used. In the present invention, the toner particles may be either black toner or color toner.

  The amount of the pigment used is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more from the viewpoint of improving the image density of the liquid developer with respect to 100 parts by mass of the polyester. From the viewpoint of improving the dispersion stability of the toner particles in the liquid developer, it is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and further preferably 15 parts by mass or less.

  In the present invention, as a toner raw material, a release agent, a charge control agent, a charge control resin, a magnetic powder, a fluidity improver, a conductivity modifier, a reinforcing filler such as a fibrous substance, an antioxidant, Additives such as cleaning improvers may be used as appropriate.

  As the organic solvent for dissolving the resin and the pigment, those having a boiling point lower than that of water are preferable from the viewpoint of dispersing the resin in the aqueous dispersion medium. Moreover, a ketone solvent is preferable from the viewpoint of solubility of the polyester resin. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, dipropyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, and the like, and methyl ethyl ketone is preferable from the viewpoint of the solubility of the polyester and the ease of distilling off the solvent.

  The amount of the organic solvent used is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, still more preferably 150 parts by mass or more, from the viewpoint of the solubility of the polyester in the solvent with respect to 100 parts by mass of the polyester. From the viewpoint of the emulsifiability of the toner particles, it is preferably 400 parts by mass or less, more preferably 300 parts by mass or less, and even more preferably 200 parts by mass or less.

  Basic compounds include aqueous alkaline solutions such as aqueous ammonia and sodium hydroxide, allylamine, isopropylamine, diisopropylamine, ethylamine, diethylamine, triethylamine, 2-ethylhexylamine, tri-n-octylamine, t-butylamine, sec-butylamine. , Propylamine, methylaminopropylamine, dimethylaminopropylamine, n-propanolamine, butanolamine, 5-amino-4-octanol, monoethanolamine, N, N-dimethylethanolamine, isopropanolamine, neopentanolamine, Examples include amines such as diglycolamine, ethylenediamine, and piperazine, and ammonia water is preferred from the viewpoint of drying properties.

  The amount of the basic compound used is preferably an amount (0.05 equivalents or more and 0.4 equivalents or less) corresponding to 5 mol% or more and 40 mol% or less of the amount necessary for neutralizing all carboxy groups of the polyester. Thereby, in the phase inversion emulsification step described later, toner particles having a volume median particle size of 1 to 4 μm can be obtained, and carboxy groups present on the surface of the toner particles can be reduced. When neutralization with a basic compound is not performed, coarse particles are generated in the phase inversion emulsification step described later. In addition, when neutralizing with a basic compound of 0.4 equivalent or more, the particle size of the toner particles generated in the phase inversion emulsification step is 100 nm to 500 nm and penetrates the paper during printing, or the volume Even when toner particles having a median particle size of 1 to 4 μm are obtained, a large number of carboxy groups are present on the surface of the toner particles, so that the toner particles become larger due to aggregation in the liquid developer, resulting in a higher viscosity.

  The phase inversion emulsification performed in Step 1 is a method in which a raw material such as polyester is dissolved in an organic solvent, a basic compound is mixed, the carboxy group of the polyester is neutralized, and then mixed with an aqueous dispersion medium. This is a method of distilling off water to invert to an aqueous system.

Therefore, the step 1 preferably includes the following steps 1-1 to 1-3.
Step 1-1: A step of mixing a raw material containing a resin containing a polyester having an acid value of 5 mgKOH / g or more and 35 mgKOH / g or less, a pigment, and a basic compound and an organic solvent to obtain a mixed solution, the base Step 1-2 in which the degree of neutralization of the carboxy group of the polyester by the functional compound is not less than 5 mol% and not more than 40 mol%: An aqueous dispersion medium is mixed with the mixed liquid obtained in Step 1-1, and toner particles Step 1-3 for Obtaining a Dispersion Liquid: Step for obtaining an aqueous dispersion of toner particles having a particle size of 1 μm or more and 4 μm or less by removing the organic solvent from the dispersion obtained in Step 1-2.

  In step 1-1, the order of mixing the organic solvent with the raw material such as the resin containing the polyester, the pigment, the basic compound, and the organic solvent is not particularly limited, but after dissolving the resin in the organic solvent in advance and preparing the resin solution, It is preferable to mix and disperse raw materials such as pigments, add a basic compound, and neutralize 5 mol% to 40 mol% of the carboxyl group of the polyester.

  In Step 1-2, when mixing the mixture obtained in Step 1-1 and the aqueous dispersion medium, the raw material may be dispersed in the aqueous dispersion medium using a high shearing stirrer. Preferably, the particulate and dispersed raw material becomes toner particles.

  The aqueous dispersion medium used in the present invention has water as a main component, that is, a water content of 50% by mass or more. From the viewpoint of suppressing aggregation of the toner particles, the viewpoint of facilitating the removal of the aqueous medium, and the viewpoint of being environmentally friendly, the water content in the aqueous dispersion medium is preferably 80% by mass or more, more preferably 90% by mass. % Or more, more preferably 100% by mass. The water is preferably deionized water from the viewpoint of improving the dispersibility of the toner particles. Examples of components other than water include organic solvents that dissolve in water, such as methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, and tetrahydrofuran.

  The amount of the aqueous dispersion medium used is preferably 25 parts by mass or more, more preferably 50 parts by mass or more, from the viewpoint of ease of phase inversion emulsification, with respect to 100 parts by mass of the mixed liquid obtained in Step 1-1. More preferably 100 parts by weight or more, from the viewpoint of improving the drying properties of the toner particles in the filtration step of the resin dispersion, preferably 600 parts by weight or less, more preferably 400 parts by weight or less, more preferably 200 parts by weight or less. It is.

  Examples of the high shear force stirrer include a stirrer such as a homomixer.

  In step 1-3, the organic solvent can be removed by, for example, a method of heating a dispersion of toner particles or a method of placing in a reduced-pressure atmosphere. From the viewpoint of suppressing aggregation of toner particles, the toner particles A method of heating the dispersion liquid under reduced pressure is preferred.

From the viewpoint of obtaining high image quality, the volume median particle size (D ₅₀ ) of the toner particles in the aqueous dispersion obtained in Step 1 is 1 μm or more, preferably 1.5 μm or more, more preferably 2 μm or more. From the viewpoint of obtaining an image, it is 4 μm or less, preferably 3 μm or less, more preferably 2.8 μm or less. In the present specification, the volume-median particle size (D ₅₀ ) means a particle size at which the cumulative volume frequency calculated by the volume fraction is 50% when calculated from the smaller particle size.

  Step 2 is a step of separating the toner particles from the aqueous dispersion of toner particles obtained in Step 1.

  The toner particles are taken out from the aqueous dispersion of toner particles through a separation step such as filtration and centrifugation, and if necessary, a step such as washing is added and then dried to obtain toner particles.

  Step 3 is a step of dispersing the toner particles obtained in Step 2 in an insulating liquid in the presence of a dispersant.

  As the dispersant, a dispersant in oil is preferable from the viewpoint of dispersing the toner particles in the insulating liquid. The dispersant in oil is preferably a polymer dispersant having a dispersing group and an adsorbing group, and more preferably has a structure having an adsorbing group in the main chain and a dispersing group in the side chain. Examples of the adsorbing group include an acidic adsorbing group, a neutral adsorbing group, and a basic adsorbing group, and a basic adsorbing group is preferable from the viewpoint of improving the adsorptivity to polyester. Examples of the basic adsorption group include an amino group, an imino group, a pyrrolidone group, a pyridine group, and the like. From the viewpoint of improving the dispersibility of toner particles in the liquid developer, an amino group and an imino group are preferable. As the dispersing group, those having mainly a hydrocarbon chain, a hydroxy hydrocarbon chain and the like are preferable. Specific examples of such dispersants in oil include Solsperse 11200, Solsperse 134000, Solsperse 28000 (all manufactured by Nihon Lubrizol Co., Ltd.), Azisper PB-821, Azisper PB-822 (all of which are Ajinomoto) Fine Techno Co., Ltd.).

  The amount of the dispersant used (the content of the dispersant in the liquid developer) is not limited as long as the toner particles are dispersed up to the primary particle size, and the effect varies depending on the type. On the other hand, from the viewpoint of obtaining a dispersion effect, it is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and from the viewpoint of suppressing the decrease in resistance of the liquid developer and improving developability, preferably 10 parts by mass. It is not more than part by mass, more preferably not more than 8 parts by mass, still more preferably not more than 6 parts by mass.

The insulating liquid means a liquid that does not easily flow electricity. In the present invention, the conductivity of the insulating liquid is preferably 1.0 × 10 ⁻¹¹ S / m or less, more preferably 5.0 × 10 ^−12. S / m or less, preferably 1.0 × 10 ⁻¹³ S / m or more. The insulating liquid preferably has a dielectric constant of 3.5 or less.

  Specific examples of the insulating liquid include, for example, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes, and the like. In particular, aliphatic hydrocarbons such as normal paraffin solvents and isoparaffin solvents are preferred from the viewpoint of odor, harmlessness and cost. Specifically, Isopar G, Isopar H, Isopar L, Isopar K (all of which are manufactured by ExxonMobil), Shellsol 71 (manufactured by Shell Chemicals Japan), IP Solvent 1620, IP Solvent 2080 (and above, All are made by Idemitsu Kosan Co., Ltd.), Moresco White P-55, Moresco White P-70 (all are made by Matsumura Oil Co., Ltd.), Cosmo White P-60, Cosmo White P-70 (above, All include Cosmo Oil Lubricants Co., Ltd.).

  The viscosity at 25 ° C. of the insulating liquid is preferably 100 mPa · s or less, more preferably 50 mPa · s or less, further preferably 20 mPa · s or less, and further preferably 10 mPa · s, from the viewpoint of improving the developability of the liquid developer. s or less, more preferably 5 mPa · s or less, and preferably 1 mPa · s or more, more preferably 1.5 mPa · s or more, from the viewpoint of improving the dispersion stability of the toner particles in the liquid developer. In addition, the viscosity of the insulating liquid is measured by the method described in Examples described later.

  The amount of toner particles used is preferably 13 parts by mass or more, more preferably 20 parts by mass or more, and further preferably 25 parts by mass, from the viewpoint of improving the image density of the liquid developer with respect to 100 parts by mass of the insulating liquid. From the viewpoint of improving the dispersion stability of the toner particles in the liquid developer and improving the storage stability, it is preferably 67 parts by mass or less, more preferably 53 parts by mass or less, and still more preferably 40 parts by mass or more. It is below mass parts.

  As a method of mixing the toner particles, the insulating liquid, and the dispersant, a method of stirring with a stirring and mixing device is preferable.

  The stirring / mixing device is not particularly limited, but a high-speed stirring / mixing device is preferable from the viewpoint of improving the productivity and storage stability of the toner particle dispersion, and specifically, a homomixer (made by IKA), Despa (Asada) Iron Works Co., Ltd.), TK. Homomixer, TK. Homo Disper, TK. Robomix (all of which are manufactured by Primics Co., Ltd.), Claremix (M Technique Co., Ltd.), A KD mill (manufactured by KD International) is preferred.

  The content of the toner particles in the liquid developer is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 40% by mass or less, from the viewpoint of improving the image density of the liquid developer. More preferably, it is 30 mass% or less.

  Further, the content of the pigment in the liquid developer is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 10% by mass or less from the viewpoint of improving the image density of the liquid developer. More preferably, it is 5% by mass or less.

  Further, the content of the insulating liquid in the liquid developer is preferably 60% by mass or more, more preferably 70% by mass or more, and preferably 90% from the viewpoint of improving the dispersion stability of the liquid developer. It is at most 80% by mass, more preferably at most 80% by mass.

  From the viewpoint of improving the image density of the liquid developer, the solid concentration of the liquid developer is preferably 10% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass or more. Further, from the viewpoint of improving the dispersion stability of the toner particles in the liquid developer and improving the storage stability, it is preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass or less. If there is no operation such as dilution or concentration after the preparation of the toner particle dispersion, the solid content concentration of the toner particle dispersion becomes the solid content concentration of the liquid developer.

The volume median particle size (D ₅₀ ) of the toner particles in the liquid developer is preferably 4.0 μm or less from the viewpoint of reducing the particle size of the toner particles in the liquid developer and improving the image quality of the liquid developer. More preferably, it is 3.0 μm or less, and from the viewpoint of reducing the viscosity of the liquid developer, it is preferably 1.0 μm or more, more preferably 2.0 μm or more.

  From the viewpoint of improving the developability of the liquid developer, the viscosity at 25 ° C. of the liquid developer is preferably 30 mPa · s or less, more preferably 20 mPa · s or less, and even more preferably 10 mPa · s or less. From the viewpoint of improving the dispersion stability of the toner particles therein and improving the storage stability, it is preferably 0.8 mPa · s or more, more preferably 1.0 mPa · s or more, and further preferably 1.5 mPa · s or more.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The physical properties of the resin and the like were measured by the following method.

[Softening point of resin]
Using a flow tester “CFT-500D” (manufactured by Shimadzu Corporation), a 1 g sample was heated at a heating rate of 6 ° C./min, and a 1.96 MPa load was applied by a plunger, and the diameter was 1 mm and the length was 1 mm. Extrude from the nozzle. The amount of plunger drop of the flow tester is plotted against the temperature, and the temperature at which half of the sample flows out is taken as the softening point.

[Glass transition temperature of resin]
Using a differential scanning calorimeter “DSC210” (manufactured by Seiko Denshi Kogyo Co., Ltd.), 0.01 to 0.02 g of sample was weighed into an aluminum pan, heated to 200 ° C., and the temperature was reduced to 0 ° C./min. Cool to ° C. Next, the sample is heated at a heating rate of 10 ° C./min, and the endothermic peak is measured. The glass transition temperature is defined as the temperature at the intersection of the base line extension below the maximum peak temperature of endotherm and the tangent line indicating the maximum slope from the peak rising portion to the peak apex.

[Acid value of the resin]
Measured by the method of JIS K0070. However, only the measurement solvent is changed from the mixed solvent of ethanol and ether specified in JIS K0070 to the mixed solvent of acetone and toluene (acetone: toluene = 1: 1 (volume ratio)).

[Volume-median particle size of toner particles in aqueous dispersion]
Using a laser diffraction / scattering particle size measuring device (LA-920, manufactured by Horiba, Ltd.), distilled water is added to the measurement cell, and measurement is performed at a concentration at which the transmittance becomes 70%.

[Conductivity of insulating liquid]
Put 25 g of insulating liquid into a 40 mL glass sample tube “Screw No. 7” (manufactured by Marum Co., Ltd.), and use a non-aqueous conductivity meter “DT-700” (manufactured by Dispersion Technology) Immerse in an insulating liquid, measure 20 times, calculate the average value, and measure the conductivity. The smaller the value, the higher the resistance.

[Viscosity of insulating liquid at 25 ° C]
Put 6-7 mL of the measuring solution into a 10 mL screw tube, and measure the viscosity at 25 ° C. using a rotational vibration viscometer “Viscomate VM-10A-L” (manufactured by Seconic).

[Solid content concentration of liquid developer]
10 parts by mass of the sample is diluted with 90 parts by mass of hexane, and is rotated for 20 minutes at a rotational speed of 25000 r / min using a centrifugal separator “H-201F” (manufactured by Kokusan Co., Ltd.). After standing, the supernatant is removed by decantation, diluted with 90 parts by mass of hexane, and centrifuged again under the same conditions. After removing the supernatant by decantation, the lower layer is dried in a vacuum dryer at 0.5 kPa and 40 ° C. for 8 hours, and the solid content concentration is calculated from the following formula.

[Viscosity of liquid developer at 25 ° C]
Measured at 25 ° C. using a rotational vibration viscometer (Seconic, Viscomate VM-10A-L).

[Volume Median Particle Size (D ₅₀ ) of Toner Particles in Liquid Developer]
Using a laser diffraction / scattering particle size measurement device (Malvern, Mastersizer 2000), add Isopar L (ExxonMobil) to the measurement cell, and at a concentration that results in a scattering intensity of 5-20%. Measured under conditions of a refractive index of 1.58 (imaginary part 0.1) and a dispersion medium refractive index of 1.46.

Resin Production Example 1 [Resin A]
The raw material monomers shown in Table 1, 25.0 g of esterification catalyst (dibutyltin oxide) and 2.5 g of cocatalyst (gallic acid), four 10-liter capacity equipped with nitrogen introduction tube, dehydration tube, stirrer and thermocouple The mixture was placed in a neck flask, heated to 230 ° C. at normal pressure, reacted for 6 hours, and then reacted for 1 hour under a reduced pressure of 8.3 kPa, to obtain Resin A having the physical properties shown in Table 1.

Resin production example 2 [resins B to D]
The raw material monomers shown in Table 1, 25.0 g of esterification catalyst (dibutyltin oxide) and 2.5 g of cocatalyst (gallic acid), four 10-liter capacity equipped with nitrogen introduction tube, dehydration tube, stirrer and thermocouple After putting in a neck flask and raising the temperature to 210 ° C. at normal pressure, the reaction was completed in the time shown in Table 1 to obtain Resins B to D having physical properties shown in Table 1.

Examples 1-6
<Step 1-1>
100 parts by mass of the resin shown in Table 2 was dissolved in 200 parts by mass of methyl ethyl ketone. To the obtained resin solution, 10 parts by mass of “chromofine blue 6337JC” (phthalocyanine blue 15: 3, manufactured by Dainichi Seika Co., Ltd.) (average primary particle size: 0.04 μm, average secondary particle size: 9.6 μm) is added as a pigment. After the dispersion, 10 N ammonia water in the amount shown in Table 2 was added and stirred at 25 ° C. for 30 minutes to neutralize the polyester to the degree of neutralization shown in Table 2. The product of the acid value (mgKOH / g) of the polyester at this time and the neutralization degree (mol%) of the polyester was calculated. The results are shown in Table 2.

<Step 1-2>
Add 150 parts by mass of deionized water to 100 parts by mass of the resulting mixture and use a homomixer (manufactured by IKA, T18 digital ULTRA-TURRAX) to disperse at 25 ° C. for 5 minutes at the stirring rate shown in Table 2. To obtain an aqueous dispersion.

<Step 1-3>
The obtained aqueous dispersion was distilled under reduced pressure at 40 ° C. and 40 kPa using an evaporator (manufactured by Tokyo Rika Kikai Co., Ltd., rotary evaporator N-1000) to remove methyl ethyl ketone to obtain an aqueous dispersion of toner particles. It was. The volume median particle size (D ₅₀ ) of the toner particles in the obtained aqueous dispersion was measured. It shows in Table 2.

<Process 2>
The aqueous dispersion of toner particles was filtered using a filter paper (ADVANTEC, 4A) and dried for 2 days to obtain toner particles.

<Step 3>
25 parts by weight of toner particles and 1.0 part by weight of a dispersant in oil “Solsperse 13440” (manufactured by Nippon Lubrizol Co., Ltd.) and an insulating liquid “Isopar L” (manufactured by ExxonMobil, liquid paraffin, conductivity: 1.4 × 10 ^-12 S / m, viscosity (25 ° C): 1.6 mPa · s) Add to 75 parts by mass and use homomixer (IKA, T18 digital ULTRA-TURRAX) for 10 minutes at 25 ° C, 10,000r / min And a liquid developer having a solid content concentration of 25% by mass was prepared. The volume-median particle diameter (D ₅₀ ) and viscosity of the toner particles in the obtained liquid developer were measured. The results are shown in Table 2. An increase in the volume median particle size of toner particles means that toner particles are aggregated.

Comparative Example 1
In Step 1-1, when ammonia water was not used, the resin particles were solidified in Step 1-2, so that an aqueous dispersion of toner particles could not be obtained. If the product of the acid value and the neutralization degree of the polyester is too low, it is considered that the particles aggregate in water.

Comparative Example 2
In step 1-1, a liquid developer was obtained in the same manner as in Example 2, except that the amount of aqueous ammonia was changed and the neutralization degree of the carboxy group of the polyester was changed to 50 mol%.

Comparative Example 3
In Step 1-1, a liquid developer was obtained in the same manner as in Example 2 except that the amount of aqueous ammonia was changed and the neutralization degree of the carboxy group of the polyester was changed to 60 mol%. However, the aggregation of toner particles in the liquid developer was intense and the viscosity could not be measured.

Comparative Example 4
In Step 1-1 of Example 2, when Resin D having an acid value of 40.1 mg KOH / g was used instead of Resin B, the resin particles were solidified in Step 1-2. Was not obtained. When the acid value of polyester exceeds 30 mgKOH / g, it is considered that particles cannot be stably present in water and aggregate.

As is clear from the above results, it can be seen that the liquid developers of Examples 1 to 6 have small particle diameters of toner particles and little viscosity and little aggregation.
On the other hand, in Comparative Example 2, because the degree of neutralization of the polyester is high, the particle size of the toner particles produced in Step 1 is as small as that in the Example, but in the liquid developer, the toner particles are aggregated due to aggregation. The particle size of the material becomes larger and the viscosity is increased. Further, in Comparative Example 3, since the degree of neutralization of the polyester is higher, the particle size of the toner particles produced in Step 1 is too small, and the aggregation in the liquid developer is such that the viscosity cannot be measured. Intense.

  The liquid developer obtained by the method of the present invention is suitably used for developing a latent image formed in electrophotography, electrostatic recording method, electrostatic printing method and the like.

Claims (4)

A method for producing a liquid developer in which toner particles containing a resin and a pigment are dispersed in an insulating liquid,
Step 1: A resin containing a polyester having an acid value of 5 mg KOH / g or more and 35 mg KOH / g or less, a raw material containing a basic compound and an organic solvent are mixed, and 5 mol of the carboxy group of the polyester is contained by the basic compound. A step of phase inversion emulsification of a mixed solution neutralized by at least 40% by mole to 40% by mole to obtain an aqueous dispersion of toner particles having a volume median particle size of 1 μm to 4 μm.
Step 2: Separating toner particles from the aqueous dispersion of toner particles obtained in Step 1, and Step 3: Dispersing the toner particles obtained in Step 2 in an insulating liquid in the presence of a dispersant. A method for producing a liquid developer, comprising a step.   The production method according to claim 1, wherein the product of the acid value (mgKOH / g) of the polyester and the degree of neutralization (mol%) of the polyester in Step 1 is 100 or more and 900 or less. Step 1
Step 1-1: A step of mixing a raw material containing a resin containing a polyester having an acid value of 5 mgKOH / g or more and 35 mgKOH / g or less, a pigment, and a basic compound and an organic solvent to obtain a mixed solution, the base A step in which the degree of neutralization of the carboxy group of the polyester by the functional compound is 5 mol% or more and 40 mol% or less,
Step 1-2: Mixing the aqueous dispersion medium obtained in Step 1-1 with an aqueous dispersion medium to obtain a dispersion of toner particles, and Step 1-3: From the dispersion obtained in Step 1-2 3. The production method according to claim 1, further comprising a step of obtaining an aqueous dispersion of toner particles having a volume median particle size of 1 μm to 4 μm by removing the organic solvent.   The production method according to any one of claims 1 to 3, wherein the amount of the dispersant in Step 3 is 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the toner particles.