JP2012098349A - Production method of liquid developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a liquid developer having a low viscosity and containing toner particles having a small particle diameter in a high concentration, by suppressing aggregation of the toner particles when a solvent for the toner particles dispersed in an aqueous dispersion medium is replaced by an insulating liquid.SOLUTION: The production method of a liquid developer containing toner particles dispersed in an insulating liquid includes: a step 1 of preparing an aqueous toner particle dispersion liquid comprising toner particles containing a resin and a pigment dispersed in an aqueous dispersion medium; a step 2 of mixing the aqueous toner particle dispersion liquid obtained in the step 1 with an aqueous dispersant; a step 3 of mixing the mixture obtained in the step 2 with an insulating liquid and an in-oil dispersant; and a step 4 of removing the aqueous dispersion medium from the mixture liquid obtained in the step 3. The aqueous dispersant comprises a polycarboxylic acid amine salt; the in-oil dispersant comprises a condensate of a polyimine and a carboxylic acid; the content of the toner particles in the liquid developer is from 10 to 40 wt.%; and the volume median particle diameter of the toner particles is from 0.03 to 2.5 μm.

Description

  The present invention relates to a method for producing a liquid developer used in an image forming apparatus such as an electrophotographic copying machine or a printer.

  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.

  The liquid developer is excellent in terms of image quality because the particle size of the toner can be reduced. However, in recent years, the demand for higher image quality has increased, so even in the liquid developer, the toner There is a demand for smaller particle sizes.

  As a method for producing a liquid developer having toner particles having a small particle size, an aqueous emulsion in which a dispersoid composed of a toner material is dispersed in an aqueous dispersion medium composed of an aqueous liquid, a highly insulating liquid, An insulating liquid having an average particle size of toner particles of 1.6 to 4.2 μm and a toner particle content of about 3% by weight is obtained by mixing methyl 1,2-hydroxystearate and removing the aqueous dispersion medium. Is disclosed (see Patent Document 1).

  In addition, the associated particles (toner particles) obtained by associating the dispersoid in the aqueous emulsion, washing with water, and drying are dissolved in an insulating liquid to which a polyamine aliphatic polycondensate dispersant is added. It is disclosed that an insulating liquid having an average particle diameter of toner particles of 1.2 to 1.8 μm and a toner particle content of 16.6% by weight can be obtained by a method of crushing (see Patent Document 2).

  Further, the surface of the toner base particles is chemically modified with a polycarboxylate in an aqueous medium, then further chemically modified with a polyalkyleneimine, and the toner particles obtained by drying are dispersed in an insulating liquid. It is disclosed that an insulating liquid having an average particle diameter of toner particles of 1.95 μm and a toner particle content of 20% by weight can be obtained (see Patent Document 3).

JP 2006-195010 A JP 2008-102292 A JP 2010-060931 A

  However, in order to obtain a liquid developer containing high-concentration toner particles having a small particle diameter, in the method disclosed in Patent Document 1, aggregation occurs when the solvent is replaced from an aqueous dispersion medium to an insulating liquid. There is a problem that the image quality deteriorates because the particle size becomes large. In addition, in the methods disclosed in Patent Documents 2 and 3, in order to dry the particles having a small particle size in the aqueous medium, it is necessary to wet pulverize again in the insulating liquid, which increases the viscosity of the developer. There is a problem that developability deteriorates and a problem that a large amount of energy is required for production and a long time is required for production.

  An object of the present invention is to suppress aggregation of toner particles when replacing the solvent of toner particles dispersed in an aqueous dispersion medium with an insulating liquid, to contain toner particles having a small particle size at a high concentration, The object is to provide a method for producing a low liquid developer.

The present invention
Step 1: A step of obtaining an aqueous toner particle dispersion in which toner particles containing a resin and a pigment are dispersed in an aqueous dispersion medium.
Step 2: A step of mixing the aqueous toner particle dispersion obtained in Step 1 and an aqueous dispersant,
Step 3: a toner including a step of mixing the mixed liquid obtained in Step 2, an insulating liquid, and a dispersant in oil, and Step 4: a step of removing the aqueous dispersion medium from the mixed liquid obtained in Step 3. A method for producing a liquid developer in which particles are dispersed in an insulating liquid, wherein the aqueous dispersant is a polycarboxylic acid amine salt, and the dispersant in oil is a condensate of polyimine and carboxylic acid, The present invention relates to a method for producing a liquid developer in which the content of toner particles in the liquid developer is 10 to 40% by weight and the volume median particle size of the toner particles is 0.03 to 2.5 μm.

  The method for producing a liquid developer according to the present invention suppresses aggregation of toner particles when a solvent for toner particles dispersed in an aqueous dispersion medium is replaced with an insulating liquid to obtain a liquid developer, and has a small particle size. It has an effect that a liquid developer containing toner particles at a high concentration and having a low viscosity can be obtained. Furthermore, since the toner particles prepared in the aqueous dispersion medium are dried and replaced directly with the insulating liquid without being wet pulverized in the insulating liquid, the toner having a small particle size is efficient in terms of energy and production time. Particles can be obtained.

The present invention
Step 1: obtaining an aqueous toner particle dispersion in which toner particles are dispersed in an aqueous dispersion medium;
Step 2: A step of mixing the aqueous toner particle dispersion obtained in Step 1 and an aqueous dispersant,
Step 3: a step of mixing the mixed liquid obtained in Step 2 with an insulating liquid and a dispersant in oil, and Step 4: a step of removing the aqueous dispersion medium from the mixed liquid obtained in Step 3, A method for producing a liquid developer in which toner particles are dispersed in an insulating liquid using a polycarboxylic acid amine salt as a dispersant and a polyimine-carboxylic acid condensate as a dispersant in oil. The liquid developer having a toner particle content of 10 to 40% by weight and a toner particle volume median particle size of 0.03 to 2.5 μm can be obtained.

The reason for such an effect is not clear, but is considered as follows.
In general, when an aqueous dispersant and a dispersant in oil are used in combination, particles are aggregated due to the interaction between the aqueous dispersant and the dispersant in oil. However, since the liquid developer obtained by the method of the present invention is obtained by using an aqueous dispersant having a specific structure and a dispersant in oil together, the aqueous dispersant and the dispersant in oil inhibit their functions. Therefore, while the solvent composition changes from an aqueous dispersion medium to an insulating liquid, aggregation of toner particles can be suppressed in any solvent composition, and a liquid developer in which toner particles having a small particle diameter are dispersed can be obtained. can get.
<Step 1>

  Step 1 is a step of obtaining an aqueous toner particle dispersion in which toner particles are dispersed in an aqueous dispersion medium.

  An aqueous toner particle dispersion in which toner particles are dispersed in an aqueous dispersion medium (hereinafter referred to as an aqueous toner particle dispersion) is obtained by dispersing toner particles containing at least a resin and a pigment in an aqueous dispersion medium. The toner particles may contain a release agent, a charge control agent and the like in addition to the pigment and the resin.

  The aqueous dispersion medium used in the present invention is one having water as a main component, that is, a water content of 50% by weight or more. From the viewpoint of suppressing aggregation of 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 weight or more, more preferably 90% by weight or more. Preferably, 100% by weight is more preferable. 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 resin is not particularly limited as long as it is a resin used as a binder resin for toner particles. For example, polystyrene, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene -A homopolymer or copolymer containing styrene or a styrene-substituted product such as vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer. Styrene resin, polyester, epoxy resin, urethane-modified epoxy resin, silicone-modified epoxy resin, vinyl chloride resin, rosin-modified maleic acid resin, phenyl resin, polyethylene resin, polypropylene, ionomer resin, polyurethane, silicone resin, ketone resin, terpene Resin, phenol resin Aliphatic or alicyclic hydrocarbon resins, and the like, can be used singly or in combination of two or more of these.

  Among the resins, polyester is preferable from the viewpoint of improving the fixability of the liquid developer. The polyester may be a polyester that has been modified to an extent that does not substantially impair the properties of the polyester. 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.

  In the present invention, the polyester is obtained by polycondensing 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 indicate the number of added moles of alkylene oxide, each being a positive number, and the sum of x and y. 1 to 16 is preferable, 1 to 8 is more preferable, and 1.5 to 4 is more preferable)
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 trihydric or higher alcohols include trihydric or higher polyhydric alcohols 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.

  From the viewpoint of obtaining toner particles having a small particle diameter, the alcohol component is preferably an alkylene oxide adduct of bisphenol represented by the formula (I).

  As the divalent carboxylic acid compound, a dicarboxylic acid having 3 to 30 carbon atoms, preferably 3 to 20 carbon atoms, more preferably 3 to 10 carbon atoms, and an acid anhydride or alkyl thereof (1 to 8 carbon atoms). Examples thereof include derivatives such as esters. Specifically, aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, fumaric acid, maleic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, an alkyl group or alkenyl group having 1 to 20 carbon atoms And an aliphatic dicarboxylic acid such as succinic acid substituted with.

  Examples of the trivalent or higher carboxylic acid compound include 4 to 30 carbon atoms, preferably 4 to 20 carbon atoms, and more preferably 4 to 10 carbon atoms trivalent or higher polyvalent carboxylic acids, and acid anhydrides and alkyls thereof. (C1-C8) Derivatives, such as ester etc. are mentioned. Specific examples include 1,2,4-benzenetricarboxylic acid (trimellitic acid) and 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid).

  From the viewpoint of obtaining toner particles having a small particle size, fumaric acid, terephthalic acid and trimellitic anhydride are preferred as the carboxylic component.

  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 subjecting an alcohol component and a carboxylic acid component to condensation polymerization at a temperature of about 180 to 250 ° C. in an inert gas atmosphere, if necessary, in the presence of an esterification catalyst or a polymerization inhibitor. 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 to 1 part by weight, more preferably 0.1 to 0.7 part by weight based on 100 parts by weight of the total amount of the alcohol component and the carboxylic acid component.

  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 to 0.5 parts by weight and more preferably 0.01 to 0.3 parts by weight with respect to 100 parts by weight of the total amount of the alcohol component and the carboxylic acid component. The weight ratio of promoter to catalyst (promoter / catalyst) is preferably 0.01 to 0.5.

  The softening point of the polyester is preferably 160 ° C. or lower and more preferably 150 ° C. or lower from the viewpoint of improving the low-temperature fixability of the liquid developer. Further, from the viewpoint of preventing toner particles from aggregating when the aqueous medium is removed in Step 4, it is preferably 70 ° C. or higher, and 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 point of the polyester is preferably 80 ° C. or less and more preferably 75 ° C. or less from the viewpoint of improving the low temperature fixability of the liquid developer. Further, from the viewpoint of preventing toner particles from aggregating when the aqueous medium is removed in Step 4, 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.

  The acid value of the polyester is preferably 120 mgKOH / g or less, more preferably 60 mgKOH / g or less, from the viewpoint of improving the dispersibility of the polyester in the aqueous dispersion medium. Further, from the viewpoint of improving the fixability of the liquid developer and improving the dispersibility of the polyester in the aqueous dispersion medium, it is preferably 1 mgKOH / g or more, more preferably 10 mgKOH / g or more. Taking these viewpoints together, the acid value of the polyester is preferably 1 to 120 mgKOH / g, more preferably 10 to 60 mgKOH / g.

  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. The toner of the present invention may be either black toner or color toner.

  From the viewpoint of improving the fixability of the liquid developer, the pigment content is preferably 100 parts by weight or less and more preferably 70 parts by weight or less with respect to 100 parts by weight of the resin. Further, from the viewpoint of improving the image density of the liquid developer, 5 parts by weight or more is preferable, and 15 parts by weight or more is more preferable. Taking these viewpoints together, 5 to 100 parts by weight is preferable, and 15 to 70 parts by weight is more preferable.

  Examples of the method for obtaining the aqueous toner particle dispersion in Step 1 include a method in which a melt kneaded material obtained by melt-kneading a toner raw material containing a resin and a pigment is wet-ground in an aqueous medium and dispersed, and an aqueous resin dispersion Examples thereof include a method of mixing an aqueous pigment dispersion and combining the resin particles and the pigment particles, and a method of stirring the aqueous resin dispersion and the pigment at high speed. From the viewpoint of reducing the particle size of the toner particles in the aqueous toner particle dispersion and narrowing the particle size distribution, a method of stirring the aqueous resin dispersion and the pigment at high speed is preferable.

  Examples of a method for obtaining an aqueous resin dispersion include a method of polymerizing a polymerizable monomer in an aqueous dispersion medium, a method of phase inversion emulsification of a resin dissolved in an organic solvent, and the like. From the viewpoint of reducing the particle size of the resin in the aqueous resin dispersion and narrowing the particle size distribution, a method in which the resin dissolved in the organic solvent is phase-inverted and emulsified in the aqueous dispersion medium is preferable. In particular, when a polyester resin is used, a method in which a resin dissolved in an organic solvent is phase-inverted and emulsified in an aqueous dispersion medium is preferable.

  A method in which a resin dissolved in an organic solvent is phase-inverted and emulsified in an aqueous dispersion medium is obtained by dissolving a resin, for example, polyester in an organic solvent, adding a neutralizing agent to ionize the carboxyl group of the polyester, and then aqueous A method in which the organic solvent is removed and the phase is changed to an aqueous system after adding the dispersion medium is preferable.

  Note that toner raw materials other than pigments, for example, release agents, charge control agents, and the like may be mixed in advance with the resin.

  The organic solvent for dissolving the resin is preferably one having a boiling point lower than that of water from the viewpoint of dispersing the resin in the aqueous dispersion medium. Moreover, a ketone solvent is preferable from the viewpoint of solubility of polyester. Examples of the ketone solvent used include acetone, methyl ethyl ketone, diethyl ketone, dipropyl ketone, methyl isobutyl ketone, and methyl isopropyl ketone. From the viewpoint of the solubility of the polyester and the ease of removing the solvent, methyl ethyl ketone is used. preferable.

  The aqueous dispersion medium is preferably deionized water from the viewpoint of improving the dispersibility of the aqueous resin dispersion.

  The removal of the organic solvent can be performed after adding the aqueous medium to the resin dissolved in the organic solvent, before mixing with the pigment, or after mixing with the pigment.

The volume median particle size (D _50W ) of the resin in the aqueous resin dispersion is preferably 1 μm or less, more preferably 0.5 μm or less, and more preferably 0.2 μm or less from the viewpoint of reducing the particle size of the toner particles in the liquid developer. Is more preferable. The volume median particle size of the resin is measured by the method described in the examples described later.

  The solid content concentration in the aqueous resin dispersion is preferably 10% by weight or more, more preferably 15% by weight or more, from the viewpoint of improving the productivity of the obtained liquid developer. Further, from the viewpoint of improving the dispersibility of the resin in the aqueous dispersion medium, it is preferably 45% by weight or less, more preferably 40% by weight or less. When these viewpoints are put together, 10 to 45% by weight is preferable, and 15 to 40% by weight or less is more preferable.

  Further, an aqueous resin dispersion obtained by phase inversion emulsification of a resin dissolved in an organic solvent in an aqueous dispersion medium, and even if the organic solvent is not removed, the solid in the aqueous resin dispersion The partial concentration is preferably in the above range.

  The aqueous resin dispersion and the pigment are preferably mixed while being stirred at a high speed by a stirring and mixing device. At that time, an aqueous dispersion of another toner material such as a release agent may be mixed together.

  The stirring and mixing apparatus is not particularly limited, but from the viewpoint of improving the productivity of Step 1, Ultra Disper (manufactured by Asada Tekko Co., Ltd.), Ebara Milder (manufactured by Ebara Seisakusho Co., Ltd.), TK Homomixer, TK High-speed stirring and mixing devices such as homodispers, TK Robomix (manufactured by Primix), clear mix (manufactured by M Technique), and KD mill (manufactured by Kinetic Dispersion) are preferred.

  It is preferable that the aqueous resin dispersion and the pigment are mixed by a high-speed stirring and mixing device and then further dispersed by a high-pressure wet atomizer.

  Examples of the high-pressure wet atomizer include those having a chamber in which the flow path of the processing liquid is fixed, and those having a homogeneous valve capable of adjusting the width of the flow path of the processing liquid. Examples of the high-pressure wet atomizer having a chamber in which the flow path of the processing liquid is fixed include a microfluidizer (manufactured by Microfluidics), a nanomizer (manufactured by Nanomizer), an optimizer (manufactured by Sugino Machine), and the like. . Examples of the high-pressure wet atomizer having a homogeneous valve include a high-pressure homogenizer (manufactured by Runny), a high-pressure homogenizer (manufactured by Sanmaru Machinery Co., Ltd.), a high-pressure homogenizer (manufactured by Izumi Food Machinery). By processing at a high pressure, it is considered that the adsorption state of the resin to the pigment changes and the toner particles are stably dispersed, resulting in a decrease in the viscosity of the liquid developer. From the viewpoint of reducing the particle size of the toner particles in the liquid developer and lowering the viscosity of the liquid developer, a high-pressure wet atomizer having a chamber in which the flow path of the processing liquid is fixed is preferable.

  When the organic solvent is contained in the aqueous resin dispersion, the aqueous solvent dispersion is obtained by removing the organic solvent after mixing with the pigment. The removal of the organic solvent can be performed by, for example, a method of heating a mixed solution of an aqueous resin dispersion and a pigment or a method of placing in a reduced pressure atmosphere. However, from the viewpoint of suppressing aggregation of resin particles, heating is performed under reduced pressure. Is preferred.

The volume median particle size (D _50W ) of the toner particles in the aqueous toner particle dispersion obtained in Step 1 is preferably 2 μm or less, and preferably 0.5 μm or less from the viewpoint of reducing the particle size of the toner particles in the liquid developer. Is more preferable, and 0.2 μm or less is more preferable. The average particle diameter of the toner particles in the aqueous toner particle dispersion is measured by the method described in the examples below.

  The viscosity of the aqueous toner particle dispersion obtained in Step 1 is preferably 300 mPa · s or less, and more preferably 150 mPa · s or less, from the viewpoint of reducing the viscosity of the liquid developer. Further, from the same viewpoint, 5 mPa · s or more is preferable, and 10 mPa · s or more is more preferable. The viscosity of the aqueous toner particle dispersion obtained in step 1 is measured by the method described in the examples below.

The solid content concentration of the toner particles in the aqueous toner particle dispersion obtained in Step 1 is preferably 15% by weight or more, more preferably 20% by weight or more, from the viewpoint of improving the productivity of the obtained liquid developer. Further, from the viewpoint of improving the dispersibility of the toner particles in the aqueous toner particle dispersion, it is preferably 50% by weight or less, and more preferably 45% by weight or less. Taking these viewpoints together, the solid content concentration of the toner particles in the aqueous toner particle dispersion is preferably 15 to 50% by weight, more preferably 20 to 45% by weight or less.
<Process 2>

  Step 2 is a step of mixing the aqueous toner particle dispersion obtained in Step 1 and the aqueous dispersant.

  The aqueous dispersant used in Step 2 is a polycarboxylic acid amine salt from the viewpoint of obtaining a liquid developer having a low concentration of toner particles having a small particle diameter and a low viscosity.

  Examples of the polycarboxylic acid constituting the polycarboxylic acid amine salt include polyacrylic acid, polymethacrylic acid, polymaleic acid, polyphthalic acid, and acrylic acid / maleic acid copolymer. From the viewpoint of lowering the viscosity of the liquid developer and improving the dispersibility of the toner particles in the liquid developer, polyacrylic acid is preferable.

  Examples of the amine constituting the polycarboxylic acid amine salt include primary alkyl amine, secondary alkyl amine, and tertiary alkyl amine. From the viewpoint of reducing the viscosity of the liquid developer and improving the dispersibility of the toner particles in the liquid developer, a tertiary alkylamine is preferable.

  The polycarboxylic acid and the amine do not have to be in equal amounts, and the polycarboxylic acid may be excessive or the amine may be excessive.

  The acid value of the polycarboxylic acid amine salt is preferably 5 mgKOH / g or more, and more preferably 10 mgKOH / g or more, from the viewpoint of improving the dispersibility of the liquid developer. Further, from the viewpoint of improving developability in the liquid developer, it is preferably 60 mgKOH / g or less, more preferably 40 mgKOH / g or less, and further preferably 20 mgKOH / g or less. Taking these viewpoints together, the acid value of the polycarboxylic acid amine salt is preferably 5 to 60 mgKOH / g, more preferably 10 to 40 mgKOH / g, and even more preferably 10 to 20 mgKOH / g. The acid value of the polycarboxylic acid amine salt is determined by [acid value of polycarboxylic acid amine salt aqueous solution] / [concentration of polycarboxylic acid amine salt aqueous solution] × 100.

  The amine value of the polycarboxylic acid amine salt is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, from the viewpoint of improving the dispersibility of the toner particles in the liquid developer. Further, from the viewpoint of improving the developability of the liquid developer, 60 mgKOH / g or less is preferable, 40 mgKOH / g or less is more preferable, and 30 mgKOH / g or less is more preferable. Taking these viewpoints together, the amine value of the polycarboxylic acid amine salt is preferably 5 to 60 mgKOH / g, more preferably 10 to 40 mgKOH / g, and even more preferably 10 to 30 mgKOH / g. The amine value of the polycarboxylic acid amine salt is determined by [Amine value of polycarboxylic acid amine salt aqueous solution] / [Concentration of polycarboxylic acid amine salt aqueous solution] × 100.

  Specific examples of the polyacrylic acid amine salt include DISPERBYK-191, DISPERBYK-2010, DISPERBYK-2015 (all of which are manufactured by Big Chemie).

  The mixing amount of the aqueous dispersant is preferably 4 parts by weight or more and more preferably 6 parts by weight or more with respect to 100 parts by weight of the toner particles from the viewpoint of suppressing aggregation of the toner particles. Further, from the viewpoint of improving the developability of the liquid developer, it is preferably 16 parts by weight or less, and more preferably 14 parts by weight or less. Taking these viewpoints together, 4 to 16 parts by weight is preferable, and 6 to 14 parts by weight is more preferable.

The mixing method of the aqueous dispersant is preferably a method in which the aqueous dispersant is added to the aqueous toner particle dispersion and stirred by a stirring and mixing device.
<Step 3>

  Step 3 is a step of mixing the mixed liquid obtained in Step 2, the insulating liquid, and the dispersant in oil.

  In this step, a toner raw material other than the pigment, such as a charge control agent, may be dissolved or dispersed in an insulating liquid and mixed with the mixed liquid obtained in step 2 and the dispersant in oil.

The insulating liquid may be a liquid having a dielectric constant of 3.5 or less and a volume resistivity of 10 ⁷ Ωcm or more.

  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 are made by Exxon Chemical), Shellsol 71 (manufactured by Shell Petrochemical), IP Solvent 1620, IP Solvent 2080 (all Idemitsu Petrochemical Co., Ltd.), Moresco White P-55, Moresco White P-70 (all are Matsumura Oil Co., Ltd.), Cosmo White P-60, Cosmo White P-70 (all are Cosmo Oil Lubricants) Etc.).

  The viscosity of the insulating liquid at 25 ° C. is preferably 100 mPa · s or less, more preferably 50 mPa · s or less, and even more preferably 20 mPa · s or less, from the viewpoint of improving the developability of the liquid developer. Further, from the viewpoint of improving the dispersion stability of the toner particles in the liquid developer, it is preferably 1 mPa · s or more, more preferably 3 mPa · s or more, and further preferably 5 mPa · s or more. In summary, the viscosity of the liquid developer at 25 ° C. is preferably 1 to 100 mPa · s, more preferably 3 to 50 mPa · s, and further preferably 5 to 20 mPa · s. In addition, the viscosity of the insulating liquid is measured by the method described in Examples described later.

  The dispersant in oil used in Step 3 is a condensate of polyimine and carboxylic acid from the viewpoint of obtaining a liquid developer having a small concentration of toner particles at a high concentration and a low viscosity.

  Examples of the polyimine include polyethyleneimine, polypropyleneimine, polybutyleneimine, and the like. From the viewpoint of reducing the viscosity of the liquid developer and improving the dispersibility of the toner particles in the liquid developer, polyethyleneimine is preferable.

  As the carboxylic acid, a long-chain carboxylic acid is preferable from the viewpoint of reducing the viscosity of the liquid developer and improving the dispersibility of the toner particles in the liquid developer. Long-chain carboxylic acids include saturated fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, mevalonic acid, ricinoleic acid, 12-hydroxystearic acid, etc. Hydroxycarboxylic acid (and its condensate). Among these, hydroxycarboxylic acid is preferable from the viewpoint of lowering the viscosity of the liquid developer and improving dispersibility of the toner particles in the liquid developer, and among these, 12-hydroxystearic acid is more preferable.

  The acid value of the polyimine-carboxylic acid condensate is preferably 1 mgKOH / g or more, more preferably 5 mgKOH / g or more, from the viewpoint of improving the dispersibility of the toner particles in the liquid developer. Further, from the viewpoint of improving the developability of the liquid developer, 40 mgKOH / g or less is preferable, and 20 mgKOH / g or less is more preferable. Taking these viewpoints together, the acid value of the polyimine-carboxylic acid condensate is preferably 1 to 40 mgKOH / g, more preferably 5 to 20 mgKOH / g. The acid value of the polyimine-carboxylic acid condensate is obtained by [the acid value of the polyimine-carboxylic acid condensate solution] / [concentration of the polyimine-carboxylic acid condensate solution] × 100.

  The amine value of the polyimine and carboxylic acid condensate is preferably 50 mgKOH / g or more, more preferably 70 mgKOH / g or more, and even more preferably 90 mgKOH / g or more, from the viewpoint of improving the dispersibility of the toner particles in the liquid developer. . Further, from the viewpoint of improving the developability of the liquid developer, 160 mgKOH / g or less is preferable, 150 mgKOH / g or less is more preferable, and 140 mgKOH / g or less is more preferable. Taking these viewpoints together, the amine value of the polyimine-carboxylic acid condensate is preferably 50 to 160 mgKOH / g, more preferably 70 to 150 mgKOH / g, and still more preferably 90 to 140 mgKOH / g. The amine value of the polyimine-carboxylic acid condensate is determined by [Amine number of polyimine-carboxylic acid condensate solution] / [Concentration of polyimine-carboxylic acid condensate solution] × 100.

  Specific examples of the condensate of polyimine and carboxylic acid include Solsperse 11200, Solsperse 13040 (all of which are manufactured by Nihon Lubrizol).

  From the viewpoint of reducing the viscosity of the liquid developer, the mixing amount of the dispersant in oil is preferably 4 parts by weight or more, and more preferably 7 parts by weight or more with respect to 100 parts by weight of the toner particles. Further, from the viewpoint of improving the developability of the liquid developer, it is preferably 23 parts by weight or less, and more preferably 20 parts by weight or less. Taking these viewpoints together, 4 to 23 parts by weight is preferable, and 7 to 20 parts by weight is more preferable.

  As a method of mixing the mixed liquid obtained in step 2, the insulating liquid, and the dispersant in oil, a method in which the dispersant in oil is previously dissolved in the insulating liquid and added to the mixed liquid obtained in step 2. For example, a method of simultaneously adding an insulating liquid and a dispersant in oil to the mixed liquid obtained in step 2 is used. From the viewpoint of suppressing aggregation of toner particles, the dispersant in oil is previously added to the insulating liquid. The method of dissolving and adding to the mixed solution obtained in step 2 is preferable. While stirring the mixed solution obtained in step 2 with a stirring and mixing device, the insulating liquid in which the dispersant in oil is dissolved is gradually dropped. Is preferred.

The weight ratio of the dispersant in oil to the aqueous dispersant in the mixture obtained in step 3 (dispersant in oil / aqueous dispersant) reduces the particle size of the liquid developer and reduces the viscosity of the liquid developer. Therefore, 90/10 to 20/80 is preferable, 80/20 to 40/60 is more preferable, and 70/30 to 55/45 is still more preferable.
<Step 4>

  Step 4 is a step of removing the aqueous dispersion medium from the mixed liquid obtained in Step 3. Thereby, a liquid developer in which toner particles are dispersed in an insulating liquid is obtained. In the present invention, since the toner particles prepared in the aqueous dispersion medium are dried and then directly replaced with the insulating liquid without wet pulverization in the insulating liquid, the small particle size is efficient in terms of energy and production time. Toner particles can be obtained. In addition, it is possible to obtain a liquid developer containing toner particles having a small particle size at a high concentration and having a low viscosity.

  The removal of the aqueous dispersion medium can be performed by, for example, a method of heating a mixed liquid of an aqueous toner particle dispersion and an insulating liquid or a method of placing in a reduced pressure atmosphere, from the viewpoint of suppressing aggregation of toner particles. A method of heating the mixture under reduced pressure is preferred.

  When heating the mixed solution, the heating temperature is preferably 40 ° C. or higher, and more preferably 50 ° C. or higher, from the viewpoint of ease of solvent removal. Further, from the viewpoint of suppressing aggregation of toner particles, 80 ° C. or lower is preferable, and 65 ° C. or lower is more preferable. When these viewpoints are put together, 40-80 degreeC is preferable and 50-65 degreeC or less is more preferable.

  When the mixed solution is placed in a reduced pressure atmosphere, the pressure is preferably 45 kPa or less, more preferably 35 kPa or less, from the viewpoint of ease of solvent removal. Further, from the viewpoint of suppressing aggregation of toner particles, 0.5 kPa or more is preferable, and 1 kPa or more is more preferable. Taking these viewpoints together, 0.5 to 45 kPa is preferable, and 1 to 35 kPa is more preferable.

From the viewpoint of improving the image quality of the liquid developer, the volume median particle size (D _50O ) of the toner particles in the liquid developer obtained through the above steps is 2.5 μm or less, preferably 1.5 μm or less, 0.8 μm or less is more preferable, and 0.6 μm or less is more preferable. Further, from the viewpoint of improving the productivity of the liquid developer and improving the dispersion stability of the toner particles in the liquid developer, it is 0.03 μm or more, preferably 0.05 μm or more, and more preferably 0.1 μm or more. To _{sum up} these viewpoints, the volume median particle size (D _50O ) of the toner particles in the liquid developer is 0.03 to 2.5 μm, preferably 0.05 to 1.5 μm, more preferably 0.1 to 0.8 μm, and more preferably 0.1 to More preferably, it is 0.6 μm or less. The volume median particle size of the toner particles is measured by the method described in the examples described later.

  In the method of the present invention, aggregation of toner particles can be suppressed, so that a liquid developer containing a small concentration of toner particles at a high concentration and having a low viscosity can be obtained.

A volume median particle size of the toner particles in the liquid developer (D _50O), the ratio of the volume median particle size of the toner particles of the aqueous toner particle dispersion obtained in step _{1 (D 50W) (D 50O} / D _50W ) is preferably 13 or less, more preferably 10 or less, and even more preferably 6 or less, from the viewpoint of improving the image quality of the liquid developer. Further, from the viewpoint of improving the dispersion stability of the toner particles in the liquid developer, 1 or more is preferable, 1.5 or more is more preferable, and 2 or more is more preferable. Collectively considering the viewpoints, the volume-median particle size of the toner particles in the liquid developer (D _50O), the volume median particle size of the toner particles of the aqueous toner particle dispersion obtained in step 1 (D _{50 W)} the ratio of (D _50O / D _50W) is preferably from 1 to 13, more preferably from 1.5 to 10, 2 to 6 is more preferred.

  The content of the toner particles in the liquid developer is 10% by weight or more, preferably 20% by weight or more, and more preferably 22% by weight or more from the viewpoint of reducing the consumption of the liquid developer. Further, from the viewpoint of reducing the viscosity of the liquid developer, it is 40% by weight or less, preferably 35% by weight or less, and more preferably 30% by weight or less. Taking these viewpoints together, the content of the toner particles in the liquid developer is 10 to 40% by weight, preferably 20 to 35% by weight, and more preferably 22 to 30% by weight. The toner particle content of the liquid developer is measured by the method described in Examples below.

  The viscosity at 25 ° C. of the liquid developer is preferably 200 mPa · s or less, more preferably 100 mPa · s or less, further preferably 70 mPa · s or less, and more preferably 45 mPa · s or less, from the viewpoint of improving the developability of the liquid developer. Even more preferred. Further, from the viewpoint of improving the dispersion stability of the toner particles in the liquid developer, it is preferably 5 mPa · s or more, more preferably 10 mPa · s or more, and further preferably 20 mPa · s or more. Taking these viewpoints together, the viscosity at 25 ° C. of the liquid developer is preferably 5 to 200 mPa · s, more preferably 10 to 100 mPa · s, further preferably 20 to 70 mPa · s, and further preferably 20 to 45 mPa · s. preferable. The viscosity of the liquid developer is measured by the method described in the examples below.

[Softening point of resin]
Using a flow tester (manufactured by Shimadzu Corporation, CFT-500D), a 1 g sample was heated at a heating rate of 6 ° C / min, and a load of 1.96 MPa was applied by a plunger and pushed from a nozzle with a diameter of 1 mm and a length of 1 mm. put out. 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 point of resin]
Using a differential scanning calorimeter (Seiko Denshi Kogyo Co., Ltd., DSC210), the temperature was increased to 200 ° C, and the sample was cooled to 0 ° C at a temperature decrease rate of 10 ° C / min. The temperature at the intersection of the extended line of the baseline 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 resin, aqueous dispersant, dispersant in oil]
Measured by the method of JIS K0070. However, only the measurement solvent was 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)).

[Amine value of water-based dispersant and dispersant in oil]
Measure based on JIS K2501 method. Titrate with 0.2 mol / L ethanolic hydrochloric acid standard solution or 0.1 mol / L perchloric acid acetic acid standard solution using potentiometric titrator, and calculate from titration.

[Volume-Medium Particle Size (D _50W ) of Resin in Aqueous Resin Dispersion and Toner Particles in Aqueous Toner Particle Dispersion Obtained in Step 1]
Using a laser diffraction / scattering particle size measurement device (Horiba, LA-920), add distilled water to the measurement cell and adjust the volume-median particle size (D _50W ).

[Viscosity of aqueous toner particle dispersion, insulating liquid and liquid developer obtained in step 1]
The viscosity is measured at 25 ° C. using a rotational vibration viscometer (CBC, Viscomate VM-10A-L).

[Concentration of toner particles in liquid developer]
10 parts by weight of the liquid developer is diluted with 90 parts by weight of hexane, and is rotated for 20 minutes at a rotation speed of 3000 r / min using a centrifugal separator (K-san, H-201F). The supernatant is removed by decantation, diluted with 90 parts by weight of hexane, and centrifuged again under the same conditions. The supernatant is removed by decantation, and then dried in a vacuum dryer at 0.5 kPa and 40 ° C. for 3 hours. The weight after drying ÷ the weight of the liquid developer is taken as the concentration of toner particles.

[Volume _Median Particle Size ( _D50O ) of Toner Particles in Liquid Developer]
Using a laser diffraction / scattering particle size measuring device (Malvern, Mastersizer 2000), add Isopar G (Exxon Chemical) to the measurement cell, at a concentration that gives a scattering intensity of 5-15%. The volume-median particle size ( _D50O ) is measured under the conditions of a refractive index of 1.58 (imaginary part 0.1) and a dispersion medium refractive index of 1.42.

Resin production example 1
Equipped with raw material monomer other than trimellitic anhydride shown in Table 1, 50.0 g of esterification catalyst (dibutyltin oxide), 3.0 g of cocatalyst (gallic acid), equipped with nitrogen introduction tube, dehydration tube, stirrer and thermocouple The reaction mixture was placed in the 10-liter four-necked flask, heated to 230 ° C. until the reaction rate reached 90%, and further reacted at 8.3 kPa for 1 hour. Thereafter, trimellitic anhydride was added and reacted at normal pressure for 1 hour, followed by reaction at 8.3 kPa. The reaction was terminated when the softening point reached 144 ° C. and has the physical properties shown in Table 1. Polyester 1 was obtained. The reaction rate means a value of the amount of generated reaction water (mol) / theoretical generated water amount (mol) × 100.

Resin production example 2
A raw material monomer other than fumaric acid shown in Table 1, 50.0 g of an esterification catalyst (dibutyltin oxide) and 3.0 g of a cocatalyst (gallic acid), 10 equipped with a nitrogen introduction tube, a dehydration tube, a stirrer and a thermocouple It was put into a liter volume four-necked flask, heated to 230 ° C. until the reaction rate reached 90%, and further reacted at 8.3 kPa for 1 hour. After cooling to 180 ° C., fumaric acid was added and reacted at 180 ° C. The reaction was terminated when the softening point reached 85 ° C. to obtain polyester 2 having the physical properties shown in Table 1.

  Tables 2 and 3 show the structures and physical properties of the aqueous dispersants and the dispersants in oil used in Examples and Comparative Examples.

Examples 1-3, Comparative Examples 1-12
[Step 1]
A predetermined amount of polyester and methyl ethyl ketone shown in Table 4 were placed in a three-necked flask equipped with a stirrer, and the polyester was dissolved in methyl ethyl ketone at 25 ° C. Next, a predetermined amount of 25 wt% aqueous ammonia was added and stirred, and then a predetermined amount of deionized water was added dropwise with stirring to obtain aqueous resin dispersions 1 and 2 having the physical properties shown in Table 4, respectively.

  Next, a predetermined amount of the aqueous resin dispersion shown in Table 5 and the pigment “chromofine blue 6337JC” (phthalocyanine blue 15: 3, manufactured by Dainichi Seika Co., Ltd.) are placed in a 3 liter polyethylene container, and “TK Robotics” (Plymix Co., Ltd.) was used and stirred for 2 hours under ice cooling at a rotation speed of 8000 r / min to obtain pigment and resin mixtures 1 and 2 having the physical properties shown in Table 5.

Next, the obtained mixture was subjected to 15-pass treatment at 150 MPa with a high-pressure wet atomizer “Microfluidizer M-140K” (manufactured by Microfluidics). Next, the treated product is put into a 2 liter eggplant flask and subjected to vacuum distillation at 40 ° C. and 40 kPa using “Rotary evaporator N-1000” (manufactured by Tokyo Rika Kikai Co., Ltd.) to remove methyl ethyl ketone. The aqueous toner particle dispersion 1 was obtained from the mixture 2, and the aqueous toner particle dispersion 2 was obtained from the mixture 2. Table 6 shows the viscosity of the obtained aqueous toner particle dispersion and the volume median particle size (D _50W ) of the toner particles.

[Step 2 and Step 3]
Next, a predetermined amount of the aqueous toner particle dispersion and the aqueous dispersant shown in Table 7 and Table 8 are put into a 500 ml polyethylene container, and “TK Robomix” (manufactured by Primix) is used at 20 ° C. The mixture was stirred for 10 minutes at a rotational speed of 1400 r / min. Furthermore, under stirring at 20 ° C. and a rotation speed of 5000 r / min, a predetermined amount of the dispersant in oil and the insulating liquid “Cosmo White P-70” shown in Tables 7 and 8 (Cosmo Oil Lubricants, 25 ° C.) After the dropwise addition of the mixed solution in which the viscosity was 15 mPa · s), the mixture was stirred for 6 hours at 8000 r / min under ice cooling to obtain a mixed solution.

[Step 4]
Next, the obtained mixed solution is put into a 1 liter eggplant flask and distilled under reduced pressure at 55 ° C. and 10 kPa using “Rotary evaporator N-1000” (manufactured by Tokyo Rika Kikai Co., Ltd.) to remove water. A liquid developer having physical properties shown in Tables 7 and 8 was obtained.

Example 4 and Comparative Examples 13 and 14
[Step 1]
100 parts by weight of the resin dispersion 1 prepared in Example 1 and 12 parts by weight of the pigment “chromofine blue 6337JC” (phthalocyanine blue 15: 3, manufactured by Dainichi Seika Co., Ltd.) are placed in a 3 liter polyethylene container, and the homogenizer “ In ULT25 Digital Inline Ultra Turrax (manufactured by IKA), S25KV-25FIL was used as a generator, and the mixture was stirred for 3 hours at 15,000 r / min under ice cooling to obtain a mixture of pigment and resin.

Next, the obtained mixture was put into a 1 liter eggplant flask, and using a “rotary evaporator N-1000” (manufactured by Tokyo Rika Kikai Co., Ltd.), vacuum distillation was performed at 40 ° C. and 40 kPa to remove methyl ethyl ketone, An aqueous toner particle dispersion 3 was obtained. Table 9 shows the viscosity of the aqueous toner particle dispersion 3 obtained and the volume median particle size (D _50W ) of the toner particles.

[Steps 2 to 4]
Next, using this aqueous toner particle dispersion, Steps 2 to 4 similar to those in Example 1 were performed to obtain a liquid developer having physical properties shown in Table 10.

As is clear from Tables 7, 8, and 10, the liquid developers of Examples 1 to 4 were compared with Comparative Examples 1 to 14 in _terms of the volume median particle size (D _50O ) of the toner particles in the liquid developer. and it can be seen that the ratio of the volume median particle size of the toner particles of the aqueous toner particle dispersion _{(D 50W) (D 50O /} D 50W) is small.
Further, by adjusting the mixing ratio of the aqueous dispersant and the dispersant in oil, a liquid developer having a lower viscosity can be obtained as in Examples 1, 3, and 4.

  The liquid developer obtained by the method of the present invention is used in image forming apparatuses such as electrophotographic copying machines and printers.

Claims (3)

Step 1: A step of obtaining an aqueous toner particle dispersion in which toner particles containing a resin and a pigment are dispersed in an aqueous dispersion medium.
Step 2: A step of mixing the aqueous toner particle dispersion obtained in Step 1 and an aqueous dispersant,
Step 3: a toner including a step of mixing the mixed liquid obtained in Step 2, an insulating liquid, and a dispersant in oil, and Step 4: a step of removing the aqueous dispersion medium from the mixed liquid obtained in Step 3. A method for producing a liquid developer in which particles are dispersed in an insulating liquid, wherein the aqueous dispersant is a polycarboxylic acid amine salt, and the dispersant in oil is a condensate of polyimine and carboxylic acid, A method for producing a liquid developer, wherein the content of toner particles in the liquid developer is 10 to 40% by weight, and the volume median particle size of the toner particles is 0.03 to 2.5 μm.   The method for producing a liquid developer according to claim 1, wherein the weight ratio of the dispersant in oil and the aqueous dispersant (dispersant in oil / aqueous dispersant) in the mixture obtained in Step 3 is 90/10 to 20/80. .   The method for producing a liquid developer according to claim 1 or 2, wherein the viscosity of the liquid developer at 25 ° C is 5 to 200 mPa · s.