JP2010032689A - Liquid developer, and image forming apparatus using liquid developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developer of excellent development efficiency, and an image forming apparatus using the liquid developer. <P>SOLUTION: This liquid developer is dispersed with toner containing a binder resin, a coloring agent and an electromagnetic wave absorbing agent, and a charge control agent, in an insulating organic solvent, and an absolute value of zeta potential is 60-150 mV, in the liquid developer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

As a developing method in the electrophotographic system, a dry developing method using powder toner (dry developer) is generally used. In recent years, a wet development method using a liquid developer in which toner is dispersed in an insulating liquid carrier is known.
In the electrophotographic method, a heat roll method has been mainly used as a method for fixing an image transferred on a recording medium such as paper.
However, in the heat roll method, the recording medium on which the image is transferred is passed between heated rolls so that the toner is thermocompression-bonded to the recording medium. In some cases, the resolution is reduced due to being crushed. For this reason, there is a problem that the type of recording medium to be used is limited. Further, the heat roll method requires a large amount of heat energy to fix the image transferred to the recording medium, and thus tends to increase power consumption. For this reason, the heat roll method is not necessarily suitable in consideration of the recent trend of energy saving.

In order to solve such a problem, for example, Patent Document 1 discloses a liquid toner in which toner particles containing oil or fat having an iodine value of 130 or more are dispersed in an insulating medium. The liquid toner can be solidified by contact with air after the oil and fat having an iodine value of 130 or more contained in the toner is fixed on the recording medium, and power consumption is expected to be suppressed.
In addition, a method for fixing an image transferred onto a recording medium by a chemical reaction using UV or the like has been proposed.

However, in the liquid toner described in Patent Document 1, when a dryer containing a metal is used for the purpose of dissolving fats and oils, a large amount of heat energy may be consumed. In addition, there are problems such as the generation of odor when the fats and oils are dissolved and the time required for fixing.
On the other hand, in the method of fixing an image by a chemical reaction, when an electrostatic latent image on a photoreceptor is developed using a liquid developer, the liquid developer and the liquid carrier contained in the liquid developer have low resistance. May occur or image blur may occur.

  By the way, as a liquid carrier for a liquid developer, there are known carrier oils such as hydrocarbon organic solvents represented by Isoper and Norper, silicone oil, and vegetable oil. The toner is dispersed in the carrier oil to form a liquid developer. Since the liquid developer can prevent the aggregating action between the toners, a toner having a smaller particle diameter than that of the dry developer can be used, and an image with high resolution can be formed.

  However, since such a liquid developer uses a low-volatile solvent (carrier oil) to disperse the toner, it is difficult for the toner to be fixed on the recording medium when the image is fixed on the recording medium. In some cases, the carrier oil does not volatilize even after fixing, and the fretting property is lowered by the remaining carrier oil. In order to solve this, for example, a plurality of removal rollers may be installed to remove the carrier oil before fixing the image, but new problems such as an increase in the size of the apparatus and a complicated mechanism arise.

Therefore, in recent years, a photocurable monomer liquid has been used as an alternative carrier for hydrocarbon-based organic solvents and silicone oil. In the photocurable monomer liquid, a photopolymerization initiator (electromagnetic wave absorber) is dispersed or dissolved in a liquid composed of a monomer or oligomer having a functional unsaturated group between carbons typified by acrylate. Is.
When light such as ultraviolet rays is irradiated to the photocurable monomer liquid, the photopolymerization initiator induces a radical reaction, and the monomer or oligomer having a functional unsaturated group between carbons is crosslinked and cured. Therefore, the liquid developer using the photocurable monomer solution can fix the image on the recording medium together with the solvent, and the installation of a member for removing the solvent can be omitted.

In addition, when a liquid developer using a photocurable monomer liquid is irradiated with light such as ultraviolet rays, a photopolymerization initiator (electromagnetic wave absorber) converts light energy into heat energy and releases heat. It is possible to fix the image on the recording medium by using it, and it is not necessary to adopt the conventional heat roll method, and the energy consumption of the image forming apparatus can be suppressed.
However, since the monomer or oligomer represented by the acrylate described above has polarity, the specific resistance of the solvent is low, and the charge on the surface of the photoreceptor easily moves to the liquid developer during development. As a result, the potential on the surface of the photoconductor is lowered, and image blurring or image blur may occur.

Thus, for example, Patent Documents 2 and 3 disclose a liquid developer containing a photocurable monomer liquid whose resistance is increased by using a high-resistance photoreaction initiator.
In this way, by making the photocurable monomer liquid have a high resistance, it is possible to suppress a decrease in the potential on the surface of the photoreceptor, and it is possible to suppress the occurrence of image bleeding and image blurring.
JP-A-8-272153 JP 2003-57883 A JP 2005-352363 A

  However, the liquid developers described in Patent Documents 2 and 3 do not always satisfy development efficiency sufficiently. For this reason, the image quality of the image formed on the recording medium tends to deteriorate.

  The present invention has been made in view of the above circumstances, and an object thereof is to realize a liquid developer excellent in development efficiency and an image forming apparatus using the liquid developer.

  As a result of intensive studies, the present inventors have determined that the zeta potential of the liquid developer allows the toner to be appropriately electrophoresed and easily fly while spreading appropriately from the developing roller to the photosensitive member. Has been found to improve, and the present invention has been completed.

That is, the liquid developer of the present invention is a liquid developer in which a toner containing a binder resin, a colorant, and an electromagnetic wave absorber, and a charge control agent are dispersed in an insulating organic solvent, and has a zeta potential. The absolute value is 60 to 150 mV.
Here, it is preferable that the electromagnetic wave absorber absorbs a near infrared region having a wavelength of 750 to 1100 nm.
The toner preferably further contains an antioxidant.

  In addition, the image forming apparatus of the present invention includes a light fixing unit that irradiates an image formed on a recording medium using the liquid developer and fixes the image on the recording medium. And

  According to the present invention, it is possible to realize a liquid developer having excellent development efficiency and an image forming apparatus using the liquid developer.

Hereinafter, the present invention will be described in detail.
[Liquid developer]
The liquid developer of the present invention has an absolute value of zeta potential of 60 to 150 mV. If the absolute value of the zeta potential is 60 mV or more, the toner is likely to be electrophoresed. Therefore, when used in the image forming apparatus, the toner can easily fly from the developing roller to the photosensitive member, and the development efficiency is improved.
By the way, when the toner flies on the photoconductor without having an appropriate spread, a portion where the toner is densely adhered and a portion where the toner is loosely formed are generated, and toner density unevenness is likely to occur on the photoconductor. Tend to be. As a result, the toner density is partially reduced, and the development efficiency tends to be lowered. If the absolute value of the zeta potential is 150 mV or less, the toner flies while spreading appropriately, so that the toner easily adheres uniformly on the photoconductor, uneven density of the toner can be reduced, and development efficiency can be maintained well.
The absolute value of the zeta potential is preferably 60 to 130 mV, and more preferably 60 to 100 mV.

In the present invention, the “zeta potential” is a potential obtained from the migration speed of the toner when an electric field is applied to the toner in the liquid developer from the outside according to the principle of electrophoresis. The “zeta potential of the liquid developer” is a value when the liquid developer is diluted 8000 times with an insulating organic solvent described later.
The zeta potential of the liquid developer can be determined as follows.
First, the liquid developer is diluted 8000 times with an insulating organic solvent to prepare a diluted solution, the zeta potential of the diluted solution is measured, and this is set as the zeta potential of the liquid developer. The insulating organic solvent used for dilution may be the same type as the insulating organic solvent constituting the liquid developer, or may be different types, but the same type is preferable.

  As the zeta potential measuring apparatus, an apparatus using the principle of electrophoresis is preferable. For example, “ELS-8000” manufactured by Otsuka Electronics Co., Ltd., “DELSA440SX” manufactured by Beckman Coulter Co., Ltd., and manufactured by Particle Sizing Systems Co., Ltd. "NICOMP Model 380" etc. are mentioned. Further, measurement based on the principle of the ultrasonic method can be substituted, and for example, “DT1200” manufactured by Luft is suitable.

In order to obtain such a liquid developer, it is only necessary to adjust the type and amount of charge control agent among the components constituting the liquid developer.
Hereinafter, each component constituting the liquid developer will be specifically described.
The liquid developer of the present invention is obtained by dispersing a toner and a charge control agent in an insulating organic solvent.

<Insulating organic solvent>
As the insulating organic solvent, a solvent having a resistance value (approximately 10 ¹¹ to 10 ¹⁶ Ω · cm) that does not disturb the electrostatic latent image is used. As the insulating organic solvent, a solvent having no odor and toxicity and having a relatively high flash point is preferable.
Examples of the insulating organic solvent include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes, and the like, and these can be used alone or in combination. . In particular, a normal paraffin solvent and an isoparaffin solvent are preferable in terms of odor, harmlessness, and cost. As specific examples of such solvents, No. 0 Solvent L, No. 0 Solvent M, No. 0 Solvent H (all manufactured by Nippon Petrochemical Co., Ltd.), Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M , Isopar K, Isopar V (all manufactured by Exxon Chemical), Shellsol 71 (manufactured by Shell Petrochemical), IP Solvent 1016, IP Solvent 1620, IP Solvent 2028, IP Solvent 2835 (all manufactured by Idemitsu Petrochemical) , Nisseki Isosol 200, Nisseki Isosol 300, Nisseki Isosol 400 (all manufactured by Nippon Oil Corporation), and the like.

<Toner>
The toner contains a binder resin, a colorant, and an electromagnetic wave absorber as toner raw materials.
(Binder resin)
As the binder resin used in the present invention, a resin having thermoplasticity is preferable. For example, thermoplastic saturated polyester resin, styrene-acrylic copolymer resin, styrene-acrylic modified polyester resin, polyolefin copolymer resin (especially ethylene copolymer), epoxy resin, rosin modified phenolic resin, rosin modified maleic acid resin These can be used alone or in combination.
Moreover, you may mix | blend resin, such as paraffin wax and polyolefin, as a mold release agent as needed. The compounding amount of these release agents is preferably 20% by mass or less in 100% by mass of the binder resin.

  Among these resins having thermoplasticity, thermoplastic saturated polyester resins, ethylene copolymers, styrene-acrylic copolymer resins, epoxy resins and the like are preferably used. In particular, it is preferable to use a thermoplastic saturated polyester resin. This is because a thermoplastic saturated polyester resin can not only change physical properties such as thermal properties over a wide range but also has excellent translucency when obtaining a color image. This is because a beautiful color is obtained, and since the spreadability and viscoelasticity are excellent, the resin film after fixing is tough and has good adhesion to a recording medium such as paper.

The thermoplastic saturated polyester resin is obtained by polycondensation of a polyhydric alcohol and a polyvalent carboxylic acid. As the polycondensation method, generally known polycondensation methods can be used.
The polyhydric alcohol is not particularly limited, but propylene glycol such as ethylene glycol, diethylene glycol, triethylene glycol, and 1,2-propylene glycol, butanediol such as dipropylene glycol and 1,4-butanediol, neopentyl glycol, Alkylene glycols (aliphatic glycols) such as 1,6-hexanediol and their alkylene oxide adducts, bisphenols such as bisphenol A and hydrogenated bisphenol, and phenolic glycols of these alkylene oxide adducts, monocyclic or polycyclic Examples include alicyclics such as ring diols and aromatic diols, triols such as glycerin and trimethylolpropane, and these can be used alone or in admixture of two or more. In particular, neopentyl glycol and a bisphenol A alkylene oxide 2-3 mol adduct are preferred in terms of stability and cost of the product polyester resin. Examples of the alkylene oxide include ethylene oxide and propylene oxide.

  Although it does not specifically limit as polyhydric carboxylic acid, Malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, phthalic acid, and its modified acid (for example, hexahydrophthalic anhydride) , Saturated or unsaturated divalent basic acids such as isophthalic acid and terephthalic acid, trifunctional or more saturated polybasic acids such as trimellitic acid, pyromellitic acid and methylnadic acid, and acid anhydrides thereof, lower Examples include alkyl esters. These can be used alone or in admixture of two or more. In particular, isophthalic acid and terephthalic acid are preferable in terms of the stability and cost of the product polyester resin.

The binder resin preferably has a glass transition temperature (Tg) of 30 to 65 ° C, and more preferably 45 to 55 ° C. When the Tg is less than 30 ° C., the viscosity of the binder resin tends to be too low, and it becomes difficult to mix with toner raw materials other than the binder resin when the toner is produced. On the other hand, when the Tg exceeds 65 ° C., it is necessary to set the temperature high in order to knead with the toner raw materials other than the binder resin, and the electromagnetic wave absorber is sintered and the color tone of the toner is easily changed to black. There is.
In addition, the binder resin preferably has a mass average molecular weight of 3000 to 10000, and more preferably 5000 to 8000. The weight average molecular weight tends to depend on the value of Tg, and the value of the weight average molecular weight tends to increase as the value of Tg increases.

(Coloring agent)
A known pigment or dye can be used as the colorant.
Examples of black pigments include azine dyes such as carbon black, oil furnace black, channel black, lamp black, acetylene black, and aniline black, metal salt azo dyes, metal oxides, and composite metal oxides.
Examples of yellow pigments include cadmium yellow, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake. It is done.
Examples of the orange pigment include molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, indanthrene brilliant orange RK, benzidine orange G, indanthrene brilliant orange GK and the like.
Examples of red pigments include Bengala, Cadmium Red, Permanent Red 4R, Resol Red, Pyrazolone Red, Watching Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B, and the like. .
Examples of purple pigments include fast violet B and methyl violet lake.
Examples of blue pigments include cobalt blue, alkali blue, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, first sky blue, and indanthrene blue BC.
Examples of the green pigment include chrome green, chromium oxide, pigment green B, and malachite green lake.
1-20 mass parts is preferable with respect to 100 mass parts of binder resin, and, as for content of a coloring agent, 3-10 mass parts is more preferable.

(Electromagnetic wave absorber)
The electromagnetic wave absorber preferably absorbs a near infrared region having a wavelength of 750 to 1100 nm, more preferably 800 to 1000 nm. If the absorption wavelength region of the electromagnetic wave absorber is in the near infrared region, the color tone of the colorant described above hardly changes.
As such an electromagnetic wave absorber, a near-infrared absorber is preferable. For example, bisiminium derivatives; pentamethine cyanine derivatives such as pentamethine benzoindolium compounds, pentamethine benzoxazolium compounds, pentamethine benzothiazolium compounds; heptamethine indolium compounds, heptamethine benzoindolium compounds, heptamethine oxazo Heptamethine cyanine derivatives such as lium compounds, heptamethine benzoxazolium compounds, heptamethine thiazolium compounds, heptamethine benzothiazolium compounds; squarylium derivatives; bis (stilbenedithiolato) compounds, bis (benzenedithiolato) nickel Compounds, nickel complexes such as bis (camphage thiolato) nickel compounds; squarylium derivatives; azo dye derivatives; phthalocyanine derivatives; porphyrin derivatives; Such emission metal chelate compounds. Commercially available products may be used, such as NIR-IM1 and NIR-AM1 manufactured by Nagase ChemteX, and MIR series manufactured by Yamamoto Kasei.
0.001-1.0 mass part is preferable with respect to 100 mass parts of binder resins, and, as for content of an electromagnetic wave absorber, 0.05-0.5 mass part is more preferable.

  When irradiated with light such as ultraviolet rays, the electromagnetic wave absorber absorbs light energy, converts the light energy into heat energy, and releases heat. This released heat can be used to fix the image on the recording medium. Therefore, it is not necessary to employ a conventional heat roll method, and energy consumption of the image forming apparatus can be suppressed.

(Other)
The toner used in the present invention preferably contains an antioxidant. The electromagnetic wave absorbers described above, particularly near-infrared absorbers, have an absorption band in the long wavelength region, and therefore are easily deteriorated by the influence of compounds having radicals such as oxygen in the air. Therefore, by adding an antioxidant to the toner, the antioxidant serves as a quencher, and deterioration of the electromagnetic wave absorber due to the radical-containing compound can be suppressed.

Examples of the antioxidant include di-t-butylhydroxytoluene, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl (meth) acrylate, 2 -[1- (2-hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl (meth) acrylate, 2,4-bis (n-octylthio) -6 -(4-hydroxy-3,5-di-t-butylanilino) -1,3,5-triazine, 2,4-dimercapto-6- (4-hydroxy-3,5-di-t-butylanilino) -1 , 3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2,4-bis [(octylthio) methyl] -o - Tetrazole and the like.
The content of the antioxidant is preferably 0.0001 to 0.1 parts by mass, and more preferably 0.0005 to 0.05 parts by mass with respect to 100 parts by mass of the binder resin.

<Charge control agent>
The charge control agent adjusts the zeta potential of the liquid developer.
Examples of the charge control agent include lauryl (meth) acrylate, N-vinyl-2-pyrrolidone, manganese naphthenate, calcium naphthenate, zirconium naphthenate, cobalt naphthenate, iron naphthenate, zinc naphthenate, aluminum naphthenate, and naphthene. Copper, manganese dodecylate, calcium dodecylate, zirconium dodecylate, cobalt dodecylate, iron dodecylate, zinc dodecylate, aluminum dodecylate, copper dodecylate, manganese octylate, calcium octylate, zirconium octylate, cobalt octylate Metal soaps such as iron octylate, zinc octylate, aluminum octylate, copper octylate; di-t-butylmanganic salicylate, di-t-butylcalcium salicylate, di-t-butylzirconium salicylate, Di-t-butylcobaltyl lithylate, di-t-butyliron salicylate, di-t-butylzinc salicylate, di-t-butylaluminum salicylate, di-t-butylchromium salicylate, di-t-butylcopper salicylate, hydroxybis (3,5-t-butylsalicylic acid) manganese, hydroxybis (3,5-t-butylsalicylic acid) calcium, hydroxybis (3,5-t-butylsalicylic acid) zirconium, hydroxybis (3,5-t-butyl) Salicylic acid) iron, hydroxybis (3,5-t-butylsalicylic acid) zinc, hydroxybis (3,5-t-butylsalicylic acid) aluminum, hydroxybis (3,5-t-butylsalicylic acid) chromium, hydroxybis (3 , 5-t-butylsalicylic acid) copper, hydroxybis (salicylic acid) metal salt, Metal salts of salicylic acid such as metal salts of droxybis (monoalkylsalicylic acid), metal salts of hydroxybis (dialkylsalicylic acid), metal salts of hydroxybis (trialkylsalicylic acid), metal salts of hydroxybis (tetraalkylsalicylic acid); sodium dodecylbenzenesulfonate, dodecyl Examples thereof include alkylbenzene sulfonates such as barium benzenesulfonate; phospholipids such as lecithin and sehalin; organic amine salts such as n-decylamine; quaternary ammonium salts; alkylpyridinium salts and the like. These can be used alone or in combination. In particular, a copolymer of lauryl (meth) acrylate and N-vinyl-2-pyrrolidone is preferable.

The amount of charge control agent added depends on the type of toner, and the effect of imparting charge to the toner differs. Therefore, the amount of charge control agent cannot be determined unconditionally. For example, lauryl (meth) acrylate and N-vinyl-2-pyrrolidone are used as charge control agents. When the polymer is used, the amount is preferably 0.1 to 40 parts by weight, more preferably 1 to 20 parts by weight, and particularly preferably 4 to 10 parts by weight with respect to 100 parts by weight of the toner.
The zeta potential of the liquid developer depends on the addition amount of the charge control agent, and the zeta potential tends to increase as the addition amount of the charge control agent increases. If the addition amount of the charge control agent is within the above range, the zeta potential when the liquid developer is diluted 8000 times can be easily adjusted to 60 to 150 mV.

<Other additives>
The liquid developer of the present invention may contain other additives. Other additives include charge control agents.
As the charge control agent, manganese naphthenate, calcium naphthenate, zirconium naphthenate, cobalt naphthenate, iron naphthenate, zinc naphthenate, aluminum naphthenate, copper naphthenate, manganese dodecylate, calcium dodecylate, zirconium dodecylate, Cobalt dodecylate, iron dodecylate, zinc dodecylate, aluminum dodecylate, copper dodecylate, manganese octylate, calcium octylate, zirconium octylate, cobalt octylate, iron octylate, zinc octylate, aluminum octylate, octylate Metal soap such as copper; di-t-butyl manganese salicylate, di-t-butyl calcium salicylate, di-t-butyl zirconium salicylate, di-t-butyl cobalt salicylate, di-t-butyl iron salicylate, sa Di-t-butylzinc tyrrate, di-t-butylaluminum salicylate, di-t-butylchromium salicylate, di-t-butylcopperic salicylate, hydroxybis (3,5-t-butylsalicylate) manganese, hydroxybis (3 , 5-t-butylsalicylic acid) calcium, hydroxybis (3,5-t-butylsalicylic acid) zirconium, hydroxybis (3,5-t-butylsalicylic acid) iron, hydroxybis (3,5-t-butylsalicylic acid) Zinc, hydroxybis (3,5-t-butylsalicylic acid) aluminum, hydroxybis (3,5-t-butylsalicylic acid) chromium, hydroxybis (3,5-t-butylsalicylic acid) copper, hydroxybis (salicylic acid) metal Salt, hydroxybis (monoalkylsalicylic acid) metal salt, hydroxybis ( Salicylic acid metal salts such as alkylsalicylic acid) metal salts, hydroxybis (trialkylsalicylic acid) metal salts, hydroxybis (tetraalkylsalicylic acid) metal salts; alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate and barium dodecylbenzenesulfonate; lecithin And phospholipids such as sehalin; organic amine salts such as n-decylamine; quaternary ammonium salts; alkylpyridinium salts and the like. These may be used alone or in combination of two or more.

[Method for producing liquid developer]
The liquid developer of the present invention can be obtained by dispersing the above-described toner, charge control agent, and, if necessary, other additives in an insulating organic solvent.
As a method for preparing the toner, a known method can be used, and a method in which a colorant and an electromagnetic wave absorber are flushed together with a binder resin is particularly preferable.
Here, an example of a manufacturing method of the liquid developer will be specifically described.

<Preparation of toner>
The toner is obtained through a step of flushing at least a colorant and an electromagnetic wave absorber together with a binder resin, and a step of kneading the toner material.
In the flushing treatment step, the solution A in which the binder resin is dissolved in the solvent, the solution B in which the electromagnetic wave absorber is dissolved in the solvent, and the colorant are mixed, and then the solvent is distilled off. As a result, the colorant and the electromagnetic wave absorber are flushed together with the binder resin. In addition, you may carry out under pressure reduction at the time of mixing or distillation of a solvent.
Examples of the solvent used in the flushing treatment step include ethyl methyl ketone, tetrahydrofuran, methyl t-butyl ether, toluene, xylene and the like.
By performing the flushing treatment in this manner, at least a part of the colorant surface and the electromagnetic wave absorber surface is covered with the binder resin.

In the solution A, the blending amount of the solvent is preferably 30 to 100 parts by mass with respect to 100 parts by mass of the binder resin. Moreover, when using antioxidant, it is preferable to make it contain in the solution A.
On the other hand, in the solution B, the blending amount of the solvent is preferably 50 to 100 parts by mass with respect to 100 parts by mass of the electromagnetic wave absorber.
The mass ratio of the solution A and the solution B (solution A / solution B) is preferably 99/1 to 50/50. Note that the solvent used in the solution A and the solution B may be the same or different. However, in consideration of distillation under reduced pressure, the solvent used in the solution A and the solution B is preferably the same.

In the kneading step, the toner raw material flushed in the flushing step and the other toner raw materials contained as necessary are kneaded to prepare a toner.
When kneading, it is preferable to carry out warm kneading at a temperature of 60 to 100 ° C.
The toner (toner kneaded product) obtained in the kneading step is preferably cooled, then coarsely pulverized using a cutter mill or the like, and further finely pulverized using a jet mill or the like.

Usually, when producing toner, the toner raw material is kneaded at a relatively high temperature of about 100 to 140 ° C. For this reason, when the electromagnetic wave absorber is added during kneading, the toner obtained by sintering the electromagnetic wave absorber is easily changed to black. In addition, since the melting point of the electromagnetic wave absorber is usually higher than the temperature at the time of kneading, the electromagnetic wave absorber was difficult to be uniformly dispersed in the toner. As a result, even if light energy is converted into thermal energy by irradiating light such as ultraviolet rays, heat is hardly released uniformly, image fixability is lowered, and color reproducibility may be lowered.
However, as described above, if the colorant and the electromagnetic wave absorber are flushed together with the binder resin, at least a part of the colorant surface and the electromagnetic wave absorber surface are covered with the binder resin. In particular, the electromagnetic wave absorber is preferable because it can be uniformly dispersed in the toner. In particular, if a binder resin having a glass transition temperature of 30 to 65 ° C. is used as the binder resin, the temperature at the time of kneading can be set to a relatively low temperature, so that the sintering of the electromagnetic wave absorber can be suppressed.

In addition, as long as a flushing process and a kneading | mixing process do not perform a flushing process after a kneading | mixing process, a kneading | mixing process may be performed after a flushing process, and a flushing process and a kneading | mixing process may be performed simultaneously. In particular, from the viewpoint of production efficiency, it is preferable to simultaneously perform the flushing treatment step and the kneading step.
Examples of the method for simultaneously performing the flushing treatment step and the kneading step include the following methods.

First, a solution A in which a binder resin is dissolved in a solvent, a solution B in which an electromagnetic wave absorber is dissolved in a solvent, and a colorant are added to a kneader such as a kneader or a flasher and kneaded while reducing pressure. At this time, the kneading temperature is gradually raised to carry out warm kneading. The kneading temperature is preferably started at 50 to 60 ° C., and is preferably raised to 80 to 100 ° C. finally.
Next, after the solvent is distilled off under reduced pressure to obtain a toner kneaded product, the toner kneaded product is roughly pulverized with a cutter mill or the like, and further finely pulverized with a jet mill or the like to obtain a toner.
In the case where an antioxidant or the like is contained in the toner, the solution A is preferably dissolved in a solvent together with the binder resin.
Also, do not dissolve the binder resin or electromagnetic wave absorber in the solvent, put the binder resin, electromagnetic wave absorber, colorant, and antioxidant as necessary into a kneader such as a kneader or flasher, and reduce the pressure. You may knead | mixing. At this time, the kneading temperature is gradually raised to carry out warm kneading.

  By kneading while flushing in this way, the toner raw material can be more uniformly dispersed as compared with the case of simply kneading the toner raw material. In particular, a toner in which an electromagnetic wave absorber is uniformly dispersed in the toner can be obtained.

A liquid developer is prepared by a known method using the toner thus obtained.
That is, the toner, the charge control agent, and the insulating organic solvent are mixed with a dispersing machine such as a sand grinder to obtain a liquid developer in which the toner and the charge control agent are dispersed in the insulating organic solvent.
In addition, a concentrated liquid developer is prepared by mixing a toner and an insulating organic solvent in advance, and a charge control agent is added to the concentrated liquid developer and diluted with an insulating organic solvent until a desired concentration is obtained. This may be used as a liquid developer.

The blending amount of the insulating organic solvent is preferably 100 to 4000 parts by mass, more preferably 150 to 1000 parts by mass with respect to 100 parts by mass of the toner.
Note that a charge control agent may be added when the toner and the insulating organic solvent are mixed. In this case, the blending amount of the charge control agent is preferably 0.01 to 30 parts by mass and more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the toner.

  The liquid developer thus obtained has an absolute value of zeta potential of 60 to 150 mV when diluted 8000 times with an insulating organic solvent, and is easily electrophoresed moderately. Therefore, when used in the image forming apparatus, the toner flies while appropriately spreading from the developing roller to the photosensitive member, so that the development efficiency can be maintained well.

[Image forming apparatus]
The liquid developer of the present invention can be suitably used in an electrophotographic forming apparatus.
FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention. FIG. 1 shows a color printer adopting a tandem method, but the present invention is not limited to this, and can be suitably used for a copying machine, a facsimile, a laser beam printer, and the like.
The image forming apparatus 1 of this example is formed by an image forming unit 2 that forms an image using the liquid developer of the present invention, a paper feed cassette 3 that stores a recording medium (paper or the like), and an image forming unit 2. Secondary transfer means 4 for transferring the transferred image onto the recording medium, optical fixing means 5 for fixing the transferred image onto the recording medium, discharge means 6 for discharging the recording medium having been fixed, paper feed cassette 3 to a discharge means 6, and a paper transport means 7 for transporting the recording medium.

The image forming unit 2 corresponds to the intermediate transfer belt 20, the cleaning unit 21 that cleans the intermediate transfer belt 20, and yellow (Y), magenta (M), cyan (C), and black (BK) colors, respectively. Image forming units FY, FM, FC, and FB are provided.
The intermediate transfer belt 20 is an endless, ie, loop-like belt-like member, is stretched around the drive roller 22 and the tension roller 23, and runs clockwise in FIG. In the running of the intermediate transfer belt 20, the surface facing outward is referred to as the surface of the intermediate transfer belt 20, and the other surface is referred to as the back surface.
The cleaning unit 21 includes a cleaning roller 211 and a cleaning blade 212.

Four image forming units FY, FM, FC, and FB are arranged near the intermediate transfer belt 21 and arranged between the cleaning unit 21 and the secondary transfer unit 4. The order of arrangement of the image forming units is not limited to this, but the arrangement shown in FIG. 1 is preferable in consideration of the influence on the completed image due to the color mixture of each color.
Each image forming unit includes a photoreceptor 10, a charger 11, an exposure device 12, a developing device 13, a primary transfer roller 14, a cleaning device 15, a charge removal device 16, and a carrier liquid removal roller 17. Prepare.
Each image forming unit is provided with a liquid developer circulating device (not shown) to supply and collect the liquid developer of the present invention corresponding to each color.

The photoreceptor 10 is a cylindrical member, and can carry a toner image including charged toner on the surface thereof.
The charger 11 is a device that can uniformly charge the surface of the photoreceptor 10.
The exposure device 12 has a light source such as an LED, and irradiates light onto the uniformly charged surface of the photoconductor 10 in accordance with image data input from an external machine. As a result, an electrostatic latent image is formed on the surface of the photoreceptor 10.

  The developing device 13 holds the liquid developer so as to face the electrostatic latent image on the photoconductor 10, thereby attaching the toner in the liquid developer to the electrostatic latent image. As a result, the electrostatic latent image is developed as a toner layer. The developing device 13 includes a developing container 130, a developing roller 131, a supply roller 132, a drawing roller 133, a cleaning blade 134, and a developing roller charger 135. The liquid developer 18 of the present invention is accommodated in the developing container 130.

  The primary transfer roller 14 is disposed on the back surface of the intermediate transfer belt 20 so as to face the photoreceptor 10. A voltage having a polarity opposite to that of the toner in the toner image is applied to the primary transfer roller 14 from a power source (not shown). That is, the primary transfer roller 14 applies a voltage having a polarity opposite to that of the toner to the intermediate transfer belt 20 at a position in contact with the intermediate transfer belt 20. Since the intermediate transfer belt 20 has conductivity, the applied voltage attracts toner to the surface side of the intermediate transfer belt 14 and its periphery.

The cleaning device 15 is a device for cleaning the liquid developer remaining without being transferred from the photoconductor 10 to the recording medium, and includes a residual developer conveying screw 151 and a cleaning blade 152.
The static eliminator 16 has a light source for static elimination, and removes the liquid developer by the cleaning blade 152 and removes the surface of the photoconductor 10 with light from the light source in preparation for the next round of image formation.

  The carrier liquid removal roller 17 is a substantially cylindrical member that can rotate in the same direction as the photoconductor 10 around a rotation axis parallel to the rotation axis of the photoconductor 10. The carrier liquid removing roller 17 is disposed on the side where the secondary transfer unit 4 is disposed from the position where the photoreceptor 10 and the intermediate transfer belt 20 are in contact with each other, and removes the carrier liquid from the surface of the intermediate transfer belt 20. It is a member to do.

The paper feed cassette 3 stores a recording medium (such as paper) on which a toner image is fixed.
The secondary transfer unit 4 transfers an image (toner image) formed on the intermediate transfer belt 20 to a recording medium. The secondary transfer unit 4 opposes the drive roller 22 for driving the intermediate transfer belt 20 and the drive roller 22. The secondary transfer roller 41 is arranged.

The light fixing means 5 irradiates the image transferred onto the recording medium with light to fix the image on the recording medium. The light fixing light source 51 and a pair of feed rollers for running the recording medium. 52.
Examples of the light fixing light source 51 include a halogen lamp, a mercury lamp, a flash lamp, and an infrared laser. Among them, a flash lamp is preferable, and an image can be fixed on a recording medium instantly, and energy consumption can be saved.

The discharge unit 6 discharges the recording medium on which the image is fixed by the light fixing unit 5, and is disposed on the upper part of the image forming apparatus 1.
The paper transport unit 7 includes a plurality of transport roller pairs, and transports the recording medium from the paper feed cassette 3 to the secondary transfer unit 4, the fixing unit 5, and the discharge unit 6.

Here, the image forming method will be described with reference to FIG.
First, the surface of the photoreceptor 10 is charged by the charger 11. Next, the exposure device 12 exposes the surface of the photoreceptor to form an electrostatic latent image. Next, the developing device 13 develops the electrostatic latent image as a toner image (image) by attaching the liquid developer of the present invention to the electrostatic latent image on the photoreceptor 10. In this way, the image formed by each image forming unit is transferred from the photoreceptor 10 to the intermediate transfer belt 20, and is superimposed on the intermediate transfer belt 20 to form a color toner image.
Simultaneously with the formation of the color toner image, the recording medium accommodated in the paper feed cassette 3 is conveyed along the sheet conveying means 7 and sent to the secondary transfer means 4 at the same timing as the primary transfer to the intermediate transfer belt 20. The next transfer means 4 transfers the color toner image (image) on the intermediate transfer belt 20 onto the recording medium.

Next, the recording medium on which the image has been transferred is conveyed to the light fixing means 5 and is fixed on the recording medium by irradiating the image with light.
Here, the method of photofixing will be specifically described. The following description is an example in which a flash lamp using a light emission phenomenon in discharge in xenon is used as the light fixing light source 51.

As a method of light fixing, a delay method in which a plurality of flash lamps emit light with a time difference can be used. The delay system is a system in which a plurality of flash lamps are arranged, each lamp is delayed by about 0.01 to 100 msec, light is emitted, and the same portion is illuminated a plurality of times.
By using the delay method, light energy is not supplied to an image with a single emission, but light energy can be divided and supplied, so that fixing conditions can be relaxed and both void resistance and fixability can be achieved.

Emission energy of the light fixing light source 51 is preferably 1.0~7.0J / cm ^2, more preferably 2.0~5.0J / cm ^2.
The emission energy per unit area of the flash light indicating the lamp intensity of xenon is expressed by the following formula (1).
S = {(1/2) × C × V ² } / (u × L) × (n × f) (1)
In equation (1), n is the number of lamps that emit light at one time (f), f is the lighting frequency (Hz), V is the input voltage (V), C is the capacitor capacity (F), u is the process transport speed (cm / S), L represents the effective light emission width of the flash lamp (usually the maximum paper width, cm), and S represents the energy density (J / cm ² ).

When flash light is emitted a plurality of times for an image, the light emission energy of the flash lamp described above indicates the total amount of light emission energy given to the unit area of the flash light for each light emission.
In the present invention, the number of flash lamps is preferably 0 to 20, and more preferably 2 to 10.
Moreover, it is preferable that each time difference between several flash lamps is 0.1-20 msec, and it is more preferable that it is 1-3 msec.
Furthermore, the light-emitting energy from a single light emitting per one flash lamp is preferably 0.1~1J / cm ^2, preferably from it is 0.4~0.8J / cm ^2.

In the image irradiated with light, the electromagnetic wave absorber in the toner absorbs light and converts light energy into heat energy. The heat generated at this time is released, and the toner is melted and fixed on the recording medium.
In particular, if a liquid developer using a toner prepared by a flushing process is used, the electromagnetic wave absorber is uniformly dispersed in the toner. Therefore, the electromagnetic wave absorber is generated when light energy is converted into heat energy. Heat can be released uniformly. In addition, when light is applied to an image formed on a recording medium, heat is uniformly transmitted to the entire image, so that the curing speed of the toner is increased. Accordingly, the toner is sufficiently melted even during a short time during which the recording medium passes through the optical fixing unit, so that the image is easily fixed on the recording medium.

The recording medium on which the image is fixed in this manner is discharged to the outside of the image forming apparatus 1 by the discharge unit 6.
The toner remaining on the intermediate transfer belt 20 after the secondary transfer is removed by the cleaning means 21 of the intermediate transfer belt 20. Further, the liquid developer that is not supplied to the photoreceptor 10 and remains on the developing roller 131 is scraped off and collected by the cleaning blade 134.

As described above, the liquid developer of the present invention has an absolute value of zeta potential of 60 to 150 mV when diluted 8000 times with an insulating organic solvent, so that it easily becomes suitable for electrophoresis. Therefore, when used in the image forming apparatus, the toner flies while appropriately spreading from the developing roller to the photosensitive member, so that the development efficiency can be maintained well.
Further, since the image forming apparatus of the present invention uses the liquid developer of the present invention, the development efficiency is good. Therefore, according to the present invention, a high-quality image can be formed.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to a following example. In the following description, “part” means “part by mass” unless otherwise specified, “Mw” means “mass average molecular weight”, and “Mn” means “number”. It represents “average molecular weight”.
Here, methods for measuring the Mw and Mn of the binder resin, the volume average particle diameter of the toner, and the zeta potential of the liquid developer are described below.

[Measuring method]
<Measurement of Mw>
The Mw of the binder resin was determined by gel permeation chromatography (GPC). For the measurement, a high performance liquid chromatograph pump (manufactured by JASCO Corporation, “TRI ROTAR-V type”), an ultraviolet spectroscopic detector (manufactured by JASCO Corporation, “UVIDEC-100-V type”), a 50 cm length column ( Using Showa Denko Co., Ltd., “Shodex GPC A-803”), 0.05 g of binder resin was dissolved in 20 mL of tetrahydrofuran (THF) and used as a test sample.
The Mw of the binder resin was determined as a polystyrene-reduced mass average molecular weight by calculating the molecular weight of the test sample using polystyrene as a standard substance from the GPC results.
The Mw of the charge control agent was also determined in the same manner as the Mw of the binder resin.

<Measurement of Mn>
The Mn of the binder resin was determined by GPC in the same manner as the Mw measurement.

<Measurement of volume average particle diameter>
The volume average particle diameter of the toner was measured using a laser diffraction particle size distribution measuring apparatus (“SALD-1100” manufactured by Shimadzu Corporation).

<Measurement of zeta potential>
The zeta potential of the liquid developer was determined by diluting the liquid developer 8000 times with IP Solvent 2835 (manufactured by Idemitsu Petrochemical Co., Ltd.) to prepare a diluted solution, and an electrophoresis apparatus (ELS-8000 manufactured by Otsuka Electronics Co., Ltd.). ) Was used to measure the zeta potential of the diluted solution.

[Example 1]
<Preparation of binder resin>
1750 parts of propylene oxide adduct of bisphenol A and 790 parts of isophthalic acid are placed in a round bottom flask equipped with a reflux condenser, water / alcohol separator, nitrogen gas inlet tube, thermometer and stirrer, and nitrogen is stirred. Gas was introduced and dehydration polycondensation was performed at a temperature of 200 ° C to 240 ° C.
When the acid value of the produced polyester resin or the viscosity of the reaction solution reached a predetermined value, the temperature of the reaction system was lowered to 100 ° C. or less to stop the polycondensation to obtain a polyester resin.
The obtained polyester resin was Mw = 10500 and Mn = 4750.

<Preparation of liquid developer>
360 parts of the previously obtained polyester resin as a binder resin, 0.2 part of di-t-butylhydroxytoluene (BHT) as an antioxidant, and a near-infrared absorber (manufactured by Nagase ChemteX Corporation, “ NIR-IM1 ") 1 part and 40 parts of Toner Yellow HG VP2155 (Clariant, PY180) as a colorant are put into a flasher and gradually heated from 40 ° C to 80 ° C under reduced pressure. Kneading was carried out to obtain a colored resin kneaded product having a colorant concentration of 10% by mass.
After sufficiently cooling this colored resin kneaded product, it is coarsely pulverized using a cutter mill, and further finely pulverized using a jet mill (manufactured by Nippon Pneumatic Industry Co., Ltd.) to give colored toner coarse particles having a volume average particle diameter of about 10 μm. (Toner) was obtained.

  30 g of colored toner coarse particles, 2 g of a 0.5% by mass charge control agent (manufactured by SERVO, “Nudex Zr12”) and 70 g of IP solvent 2835 (made by Idemitsu Petrochemical Co., Ltd.) as an insulating organic solvent are mixed. Using 1 mm diameter glass beads (150 mL) as media with a sand grinder (manufactured by IGARASHI KIKAI SEIZO CO., Ltd.) in a 1/8 gallon vessel with a water jacket at a cooling water temperature of 5 ° C. and a disk rotation speed of 2000 rpm Wet grinding was carried out by processing for 10 hours to obtain a concentrated liquid developer having a volume average toner particle diameter of 2.5 μm.

Subsequently, to 100 parts of the concentrated liquid developer, 900 parts of IP solvent 1620 (manufactured by Idemitsu Petrochemical Co., Ltd.) is added for dilution, and lauryl methacrylate / N-vinyl-2 is used as a charge control agent in order to adjust the zeta potential. -3 parts of pyrrolidone copolymer (hereinafter abbreviated as "LMA / VP") (that is, 10.2 parts with respect to 100 parts by weight of colored toner coarse particles) are added, and about 20 using an ultrasonic disperser. A liquid developer was prepared by mixing and dispersing for a minute.
The polymerization ratio of LMA / VP used as the charge control agent was LMA: VP = 95: 5, and Mw was 200000.
The zeta potential of the obtained liquid developer was measured. The results are shown in Table 1. The values shown in Table 1 are the absolute values of the zeta potential measured by the previous method.

<Evaluation of development efficiency>
The obtained liquid developer was set in an image forming apparatus as shown in FIG. Subsequently, a solid image of 2 cm × 10 cm was formed on the photoreceptor. At this time, the image area on the photoconductor is peeled off with an adhesive tape, and the reflection density (tape density on the photoconductor) on the peeled adhesive tape upper surface is measured using a reflection densitometer (“Densitometer PDM5” manufactured by SAKURA). It was measured. Similarly, the residual toner on the developing roller was peeled off with an adhesive tape, the reflection density (tape density on the developing roller) on the peeled adhesive tape upper surface was measured, and the development efficiency was obtained from the following formula (1). As evaluation criteria, those with a development efficiency of 95% or more were judged as “◯ (good)”, and those with a development efficiency of less than 95% were judged as “x (defect)”. The results are shown in Table 1.
Development efficiency (%) = Tape density on photoconductor / (Tape density on photoconductor + Tape density on developing roller) × 100 (1)

[Example 2]
A liquid developer was prepared and evaluated in the same manner as in Example 1 except that the amount of LMA / VP added was changed from 3 parts to 5 parts. The zeta potential and evaluation results are shown in Table 1.

[Example 3]
A liquid developer was prepared and evaluated in the same manner as in Example 1 except that the amount of LMA / VP added was changed from 3 parts to 7 parts. The zeta potential and evaluation results are shown in Table 1.

[Comparative Example 1]
A liquid developer was prepared and evaluated in the same manner as in Example 1 except that the amount of LMA / VP added was changed from 3 parts to 1 part. The zeta potential and evaluation results are shown in Table 1.

[Comparative Example 2]
A liquid developer was prepared and evaluated in the same manner as in Example 1 except that the amount of LMA / VP added was changed from 3 parts to 12 parts. The zeta potential and evaluation results are shown in Table 1.

As is apparent from Table 1, the liquid developer of the example having an absolute value of the zeta potential of 60 to 150 mV was excellent in development efficiency as compared with the comparative example.
On the other hand, the liquid developer of Comparative Example 1 having a zeta potential of 53 mV was inferior in development efficiency compared to the examples. This is because the toner is less likely to electrophores, and as a result, the adhesion of the toner to the electrostatic latent image on the photoconductor is reduced, that is, the toner is difficult to move from the developing roller to the photoconductor. Conceivable.
The liquid developer of Comparative Example 2 having a zeta potential of 154 mV had inferior development efficiency compared to the Examples. This is considered to be due to the fact that the toner becomes difficult to move while spreading appropriately, and thus the toner density unevenness occurs on the photoreceptor and the toner density is partially reduced.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of the present invention.

Explanation of symbols

  1: image forming apparatus, 2: image forming means, 3: paper feed cassette, 4: secondary transfer means, 5: light fixing means, 6: discharge means, 7: paper transport means.

Claims (4)

A toner containing a binder resin, a colorant and an electromagnetic wave absorber in an insulating organic solvent, and a liquid developer in which a charge control agent is dispersed,
A liquid developer having an absolute value of zeta potential of 60 to 150 mV.   The liquid developer according to claim 1, wherein the electromagnetic wave absorber absorbs a near infrared region having a wavelength of 750 to 1100 nm.   The liquid developer according to claim 1, wherein the toner further contains an antioxidant.   An optical fixing means for fixing an image on the recording medium by irradiating light onto an image formed on the recording medium using the liquid developer according to claim 1. An image forming apparatus.

Images