JP2019028233A - Liquid developer, liquid developer cartridge, image forming apparatus, and image forming method - Google Patents

Abstract

To provide a positively-charged liquid developer excellent in stability of image density.SOLUTION: A positively-charged liquid developer contains toner particles containing a polyester resin and a colorant, where the concentration of titanium element is 10 to 500 ppm; and carrier liquid containing nonpolar solvent and an aluminum-containing organic compound, where the concentration of the aluminum-containing organic compound is 10 to 500 ppm.SELECTED DRAWING: None

Description

  The present invention relates to a liquid developer, a liquid developer cartridge, an image forming apparatus, and an image forming method.

  As a developer used for electrophotographic image formation, a liquid developer in which toner particles are dispersed in a carrier liquid is known.

  Patent Document 1 discloses a liquid developer in which toner particles containing a polyester resin having a weight average molecular weight of 2000 to 20000 and a release agent having a melting point of 50 ° C. to 100 ° C. are dispersed in an insulating liquid. .

  Patent Document 2 discloses a liquid developer containing a toner containing a binder resin including an amorphous polyester resin, a crystalline polyester resin and a polyurethane-type thermoplastic elastomer, and an insulating carrier liquid. .

  Patent Document 3 contains an amorphous polyester resin obtained by copolymerizing a monomer group containing at least a bisphenol A propylene oxide adduct and a sulfonic acid group-containing monomer in the presence of a titanium catalyst, An electrostatic charge image developing toner having a titanium content in a resin mass ratio of 1 ppm to 1000 ppm is disclosed.

  Patent Document 4 discloses a method for producing a polyester resin for a toner in which a polyvalent carboxylic acid component containing a tri- or higher functional carboxylic acid and a polyhydric alcohol component are polycondensed in the presence of an ester wax. A production method is disclosed in which the titanium catalyst is used in an amount of 50 ppm to 200 ppm based on the total amount of the components, the polyhydric alcohol component, and the ester wax.

JP 2004-205843 A Japanese Patent No. 5929257 JP 2007-004033 A JP, 2015-010199, A

  An object of the present invention is to provide a positively chargeable liquid developer having excellent image density stability.

  Specific means for solving the above-described problems include the following modes.

The invention according to claim 1
Toner particles containing a polyester resin and a colorant and having a titanium element concentration of 10 to 500 ppm;
A carrier liquid containing a nonpolar solvent and an aluminum-containing organic compound, wherein the concentration of the aluminum-containing organic compound is 10 to 500 ppm;
A positively chargeable liquid developer.

The invention according to claim 2
The liquid developer according to claim 1, wherein the aluminum-containing organic compound contains at least one selected from aluminum chelates and aluminum alkoxides.

The invention according to claim 3
The said polyester resin is a polyester resin which contains 5-25 mol% of monomer units which consist of a C2-C5 saturated hydrocarbon chain between ester bonds with respect to all the monomer units. The liquid developer according to claim 2.

The invention according to claim 4
The liquid according to any one of claims 1 to 3, wherein the polyester resin is a polyester resin containing 50 to 95 mol% of a monomer unit having an aromatic ring with respect to all monomer units. Developer.

The invention according to claim 5
The liquid developer according to claim 4, wherein the aromatic ring is a benzene ring.

The invention according to claim 6
The liquid developer according to any one of claims 1 to 5, wherein the nonpolar solvent has a dry point of 150 to 300C.

The invention according to claim 7 provides:
A liquid developer cartridge that contains the liquid developer according to claim 1 and is detachable from an image forming apparatus.

The invention according to claim 8 provides:
An image carrier,
Charging means for charging the surface of the image carrier;
An electrostatic charge image forming means for forming an electrostatic charge image on the surface of the charged image carrier;
A developing unit that contains the liquid developer according to any one of claims 1 to 6 and that develops an electrostatic image formed on the surface of the image carrier as a toner image by the liquid developer. ,
Transfer means for transferring a toner image formed on the surface of the image carrier to the surface of a recording medium;
Fixing means for fixing the toner image transferred to the surface of the recording medium;
An image forming apparatus comprising:

The invention according to claim 9 is:
The developing means includes: a developing roll on which the liquid developer layer is formed; and a device for charging toner particles by applying corona irradiation to the liquid developer layer on the developing roll. The image forming apparatus described in 1.

The invention according to claim 10 is:
The image forming apparatus according to claim 8, wherein the image carrier has an inorganic layer on an outermost surface.

The invention according to claim 11 is:
A charging step for charging the surface of the image carrier;
An electrostatic charge image forming step of forming an electrostatic charge image on the surface of the charged image carrier;
A developing step of developing an electrostatic image formed on the surface of the image carrier as a toner image with the liquid developer according to any one of claims 1 to 6,
A transfer step of transferring a toner image formed on the surface of the image carrier to the surface of a recording medium;
A fixing step of fixing the toner image transferred to the surface of the recording medium;
An image forming method comprising:

The invention according to claim 12
The developing step includes: forming a layer of the liquid developer on a developing roll; and charging the toner particles by performing corona irradiation on the liquid developer layer on the developing roll. Item 12. The image forming method according to Item 11.

The invention according to claim 13 is:
The image forming method according to claim 11, wherein the image carrier has an inorganic layer on an outermost surface.

According to the first or second aspect of the invention, the image density is more stable than when the concentration of the titanium element in the toner particles is less than 10 ppm or when the concentration of the aluminum-containing organic compound in the carrier liquid is less than 10 ppm. A liquid developer is provided.
According to the invention of claim 3, the polyester resin contains less than 5 mol% of monomer units consisting of saturated hydrocarbon chains having 2 to 5 carbon atoms between the ester bonds. A liquid developer that is superior in stability of image density as compared with the case of using a resin is provided.
According to the invention according to claim 4 or 5, compared with the case where the polyester resin is a polyester resin containing less than 50 mol% of monomer units having an aromatic ring with respect to all monomer units, toner particles There is provided a liquid developer having an excellent affinity for the carrier liquid.
According to the invention of claim 6, the occurrence of image defects is suppressed as compared with the case where the dry point of the nonpolar solvent is less than 150 ° C., compared with the case where the dry point of the nonpolar solvent is higher than 300 ° C. A liquid developer having excellent image strength is provided.

According to the seventh aspect of the invention, the liquid development is superior in image density stability as compared with the case where the concentration of the titanium element in the toner particles is less than 10 ppm or the case where the concentration of the aluminum-containing organic compound in the carrier liquid is less than 10 ppm. An agent cartridge is provided.
According to the invention according to claim 8, 9 or 10, the image density is more stable than when the concentration of the titanium element in the toner particles is less than 10 ppm or when the concentration of the aluminum-containing organic compound in the carrier liquid is less than 10 ppm. An image forming apparatus excellent in the above is provided.
According to the invention of claim 11, 12 or 13, the image density stability is higher than when the concentration of the titanium element in the toner particles is less than 10 ppm or when the concentration of the aluminum-containing organic compound in the carrier liquid is less than 10 ppm. An image forming method excellent in the above is provided.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an exemplary embodiment.

  Embodiments of the invention will be described below. These descriptions and examples illustrate embodiments and do not limit the scope of the invention.

  In the present disclosure, when referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, the plurality of the substances present in the composition unless otherwise specified. It means the total amount of substance.

  In the present disclosure, the term “process” is not only included in an independent process, but is included in the term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes.

  In the present disclosure, numerical ranges indicated using “to” indicate ranges including numerical values described before and after “to” as the minimum value and the maximum value, respectively.

  In the present disclosure, “(meth) acryl” means that either “acryl” or “methacryl” may be used.

  In the present disclosure, “ppm” is an abbreviation for “parts per million” and means parts per million.

<Liquid developer>
The liquid developer according to this embodiment includes toner particles and a carrier liquid. The toner particles contain a polyester resin and a colorant and have a titanium element concentration of 10 ppm to 500 ppm. The carrier liquid contains a nonpolar solvent and an aluminum-containing organic compound, and the concentration of the aluminum-containing organic compound is 10 ppm to 500 ppm.

In the present embodiment, the concentration of titanium element contained in the toner particles is a concentration measured by the following method.
Toner particles are dissolved in tetrahydrofuran (THF) to prepare a solution, and the filtrate of the solution is dried to obtain a solid (THF-soluble component of toner particles). Fluorescent X-ray analysis is performed using a solid obtained by shaping the solid in a disk shape as a measurement sample, and the titanium element concentration is determined. A more detailed measurement method is as described in [Example] described later.

  The concentration of the titanium element contained in the toner particles in this embodiment is measured as the titanium element concentration in the THF-soluble component of the toner particles as described above. Since most of the THF-soluble component of toner particles is a binder resin, the titanium element concentration in the THF-soluble component correlates with the titanium element concentration in the binder resin.

  The liquid developer according to the exemplary embodiment includes toner element (specifically, toner particle binder resin) containing titanium element, and the carrier liquid contains an aluminum-containing organic compound to positively charge the toner particles. Let Titanium atoms are more likely to emit electrons than carbon and other atoms that make up the binder resin, while aluminum atoms in aluminum-containing organic compounds receive electrons released from titanium atoms and dissipate into the carrier liquid. It is presumed to have the effect of This effect is likely to occur at the interface where the polyester resin of the toner particles and the carrier oil are in contact with each other. As a result, electrons are dissipated from the toner particle surface, and the toner particle surface becomes positively charged. Therefore, it is presumed that the liquid developer according to the present embodiment can stably maintain a state in which the toner particles are positively charged.

  In this embodiment, the titanium element concentration in the THF-soluble component of the toner particles (here, the titanium element concentration in the binder resin is reflected) is 10 ppm to 500 ppm. If the titanium element concentration is less than 10 ppm, the toner particles are not positively charged and the image density is not stable. In this respect, the titanium element concentration is 10 ppm or more, more preferably 20 ppm or more, and further preferably 40 ppm or more. On the other hand, if the titanium element concentration exceeds 500 ppm, the polyester resin becomes brittle and the fixed image strength is lowered. In addition, the resin may be colored and the color of the resulting image may be dull. In this respect, the titanium element concentration is 500 ppm or less, more preferably 400 ppm or less, and still more preferably 300 ppm or less.

  In the present embodiment, the concentration of the aluminum-containing organic compound contained in the carrier liquid is 10 ppm to 500 ppm. If the concentration of the aluminum-containing organic compound is less than 10 ppm, the toner particles are not positively charged and the image density is not stable. From this viewpoint, the concentration of the aluminum-containing organic compound contained in the carrier liquid is 10 ppm or more, more preferably 20 ppm or more, and still more preferably 40 ppm or more. On the other hand, if the concentration of the aluminum-containing organic compound exceeds 500 ppm, the electrical resistivity of the carrier oil decreases, and when discharge is generated by an electric field applied to the nip portion during development, it is locally between the developing roll and the image carrier. Therefore, there is a possibility that an overcurrent flows, and the surface of the image carrier is deteriorated to easily fix the toner. When the toner adheres to the surface of the image holding member, a dot-like image quality defect or a streak-like image stain occurs when the output image becomes noticeable. From this viewpoint, the concentration of the aluminum-containing organic compound contained in the carrier liquid is 500 ppm or less, more preferably 400 ppm or less, and even more preferably 300 ppm or less.

  In the liquid developer according to the present embodiment, toner particles contain titanium element and the carrier liquid contains an aluminum-containing organic compound to positively charge the toner particles. Therefore, the amount of metal soap used as a charge control agent is reduced. Since the metal soap can be used or not, the following phenomenon caused by the metal soap is suppressed. In this case, it is presumed that the liquid developer of this embodiment is excellent in stability of image density and excellent in image strength.

Conventionally, metal soap is sometimes added to toner particles or carrier liquid as a charge control agent for the purpose of controlling the charge of toner particles constituting the liquid developer to positive charge.
When metal soap is added to the toner particles, the affinity between the binder resin and the metal soap is relatively low, so the fixed image may be easily broken at the interface between the binder resin and the charge control agent, and the image may be easily peeled off. . In particular, when an image with a large amount of toner is formed on a flexible resin film, the fixed image is easily broken at the interface between the binder resin and the charge control agent, and the image is easily peeled off.
On the other hand, when a metal soap is added to the carrier liquid, the metal soap may remain between the fixed image and the recording medium, weakening the fixation of the fixed image and reducing the image strength. Further, when metal soap is added to the carrier liquid, the image density may be unstable. In particular, when image formation in which the image area ratio changes sequentially (for example, alternately forming line images and solid images) The destabilization of image density is remarkable. The following can be considered as the mechanism of instability of the image density.
At the time of image formation, liquid developer (that is, toner particles and carrier liquid) is supplied to the developing roll, and the liquid developer is transferred from the developing roll to the image carrier, and the electrostatic image is developed and used for development. The missing toner particles are collected from the developing roll and returned to the developer container. Further, a new liquid developer is supplied to the developer container according to the amount of consumption of the liquid developer. When metal soap is added to the carrier liquid, some metal soap adheres to the toner particles, and some metal soap is considered to be dispersed or dissolved in the carrier liquid. If the image formation is repeated, the amount of metal soap consumed as part of the liquid developer, the amount of metal soap collected together with the residual toner particles, and the metal supplied as part of the new liquid developer The total amount with the soap amount is likely to fluctuate, and as a result, the charge amount of the toner particles contained in the liquid developer contained in the developer containing container fluctuates, so it is estimated that the image density is not stable.

  The liquid developer of the present embodiment can reduce the amount of metal soap used as a charge control agent, or can eliminate the use of metal soap, so that the above phenomenon is suppressed, and the stability of image density is excellent. It is estimated that the image strength is excellent.

  Hereinafter, the components of the liquid developer according to this embodiment will be described in detail.

[Toner particles]
The toner particles contain at least a polyester resin and a colorant, and may further contain a release agent and other additives. An external additive (for example, inorganic particles) may adhere to the surface of the toner particles.

  Examples of the titanium element contained in the toner particles include titanium chelates such as titanium tetraacetylacetonate, titanium diisopropoxybis (acetylacetonate), titanium diisopropoxybis (ethylacetoacetate); titanium (IV) ethoxide, titanium (IV) titanium element derived from isopropoxide, titanium (IV) sec-butoxide, titanium alkoxide such as titanium (IV) tert-butoxide, titanium (III) sec-butoxide, titanium (III) tert-butoxide; is there.

  The concentration of the elemental titanium contained in the toner particles is determined by, for example, synthesizing the polyester compound constituting the toner particles using the above-described titanium compound by mixing the monomer with the titanium compound. Polymerizing; dissolving the polyester resin constituting the toner particles with heat or a solvent, adding and mixing a titanium compound therein; adding a titanium compound to the toner material when preparing the toner particles by a kneading and pulverizing method Melt-mixing; when producing toner particles by an aggregation and coalescence method, a titanium compound is added to the polyester resin dispersion, and the polyester resin particles are allowed to contain a titanium compound; A titanium compound may be used individually by 1 type, and may use 2 or more types together.

-Polyester resin-
The toner particles contain at least a polyester resin as a binder resin. As a polyester resin, the condensation polymer of polyhydric carboxylic acid and polyhydric alcohol is mentioned, for example. It is preferable to use a mixture of a plurality of polyester resins selected from an amorphous polyester resin and a crystalline polyester resin.

  The polyester resin constituting the toner particles is preferably a polyester resin synthesized using a titanium compound as a catalyst. In this case, it is presumed that a titanium atom is bonded to the polyester chain, and it is presumed that electron emission from the titanium atom directly generates a positive charge in the polyester chain.

  Examples of the titanium compound used as a catalyst when synthesizing the polyester resin include the aforementioned titanium chelates and titanium alkoxides. The titanium compound used when synthesizing the polyester resin may be used alone or in combination of two or more.

  As the polyester resin, a polyester resin containing 5 mol% to 25 mol% of monomer units composed of a saturated hydrocarbon chain having 2 to 5 carbon atoms between ester bonds is preferable. Hereinafter, a polyester resin containing 5 mol% to 25 mol% of a monomer unit composed of a saturated hydrocarbon chain having 2 to 5 carbon atoms between ester bonds is also referred to as a “specific polyester resin”. A monomer unit consisting of a saturated hydrocarbon chain having 2 to 5 carbon atoms between the ester bonds is also referred to as a “specific monomer unit”.

  In the present disclosure, the “monomer unit” of the polyester resin means a structural unit formed by condensation polymerization of a monomer. In the present disclosure, regarding the monomer unit of the polyester resin, the number of carbon atoms in the saturated hydrocarbon chain between ester bonds is a number that does not include carbon atoms in the ester bond (—COO—).

  In the polyester resin, the greater the content of the specific monomer unit, the smaller the degree of steric hindrance between the molecular chains and the closer the distance between the molecular chains. As a result, it is presumed that the electron transfer is likely to occur between the molecular chains, and thus the polyester resin is easily charged and the stability of the image density is improved. In this respect, the content of the specific monomer unit in the polyester resin is preferably 5 mol% or more, more preferably 10 mol% or more, and further preferably 15 mol% or more.

In addition, the greater the content of the specific monomer unit, the higher the affinity of the polyester resin with the colorant, and the easier it is to incorporate the colorant into the polyester resin during the toner particle production process. Presumed to suppress exposure.
If the colorant toner particle surface is exposed to a large amount, the area of the interface where the polyester resin on the toner particle surface and the carrier liquid come into contact with each other is relatively reduced, which limits the ability of electrons to dissipate from the toner particle surface. Therefore, it is presumed that the positive chargeability of the toner is lowered.
The higher the specific monomer unit content, the less the surface exposure of the colorant in the toner particles, the larger the area of the interface between the polyester resin on the toner particle surface and the carrier liquid, and the more stable the toner particles. Positive chargeability can be maintained. As a result, it is estimated that the stability of the image density is excellent. In this respect, the content of the specific monomer unit in the polyester resin is preferably 5 mol% or more, more preferably 10 mol% or more, and further preferably 15 mol% or more.

  On the other hand, the specific monomer unit is considered to have lower affinity with the carrier liquid than other monomer units, and if it is too much, it may cause separation of the toner particles and the carrier liquid. The content of the specific monomer unit contained in the polyester resin is preferably 25 mol% or less. If the separation between the toner particles and the carrier liquid is significant, the toner particles adhere firmly to the image carrier and cause toner stains on the image carrier. By constituting the toner particles with a polyester resin having a specific monomer unit content of 25 mol% or less, excessive separation between the toner particles and the carrier liquid is suppressed, and toner staining of the image carrier is suppressed. Can do. In this respect, the content of the specific monomer unit in the polyester resin is preferably 25 mol% or less, more preferably 20 mol% or less, and still more preferably 18 mol% or less.

  The specific monomer unit is a monomer unit consisting of only a saturated hydrocarbon chain having 2 to 5 carbon atoms between ester bonds, and the saturated hydrocarbon chain having 2 to 5 carbon atoms is a straight chain, branched chain or Any of cyclic | annular form may be sufficient and a linear or branched chain is preferable. The specific monomer unit may be a monomer unit derived from a polyhydric carboxylic acid, may be a monomer unit derived from a polyhydric alcohol, and is derived from a polyhydric carboxylic acid and a polyhydric alcohol. Is preferably 5 to 25 mol%. The specific monomer unit is preferably a monomer unit derived from a dicarboxylic acid or a monomer unit derived from a diol.

  The polycarboxylic acid constituting the specific monomer unit is preferably a dicarboxylic acid composed of a linear or branched saturated hydrocarbon chain having 2 to 5 carbon atoms between two carboxy groups. The number of carbon atoms in the saturated hydrocarbon chain of the polyvalent carboxylic acid is the number not including the carbon atoms in the carboxy group. Examples of the polyvalent carboxylic acid constituting the specific monomer unit include methylmalonic acid (saturated hydrocarbon chain having 2 carbon atoms, branched chain), succinic acid (2 carbon atoms, straight chain), methyl succinic acid (3 carbon atoms, Branched chain), glutaric acid (3 carbon atoms, straight chain), 3-methylglutaric acid (4 carbon atoms, branched chain), adipic acid (4 carbon atoms, straight chain), 3-methyladipic acid (5 carbon atoms, Branched chain), 2-ethylglutaric acid (5 carbon atoms, branched chain), pimelic acid (5 carbon atoms, straight chain) and the like. These polyvalent carboxylic acids may be used alone or in combination of two or more.

  Examples of other polyvalent carboxylic acids constituting the specific polyester resin include suberic acid, sebacic acid, dodecanedioic acid, oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, glutaconic acid, and alicyclic dicarboxylic acid. (For example, cyclohexanedicarboxylic acid), aromatic dicarboxylic acid (for example, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, etc.), trimellitic acid, pyromellitic acid, their anhydrides, or lower (for example, C1-C5) alkyl ester is mentioned, Aromatic dicarboxylic acid is preferable. These polyvalent carboxylic acids may be used alone or in combination of two or more.

  As a polyhydric alcohol which comprises a specific monomer unit, the diol which consists of a C2-C5 linear or branched saturated hydrocarbon chain between two hydroxy groups is preferable. Examples of the polyhydric alcohol constituting the specific monomer unit include ethylene glycol (saturated hydrocarbon chain having 2 carbon atoms, straight chain), 1,3-propanediol (3 carbon atoms, straight chain), propylene glycol (alias 1 , 2-propanediol, carbon number 3, branched chain), 1,4-butanediol (carbon number 4, straight chain), 1,2-butanediol (carbon number 4, branched chain), 1,5-pentanediol (5 carbon atoms, straight chain), 1,2-pentanediol (5 carbon atoms, branched chain), neopentyl glycol (5 carbon atoms, branched chain) and the like. These polyhydric alcohols may be used individually by 1 type, and may use 2 or more types together.

  Examples of other polyhydric alcohols constituting the specific polyester resin include 1,6-hexanediol, 1,2-hexanediol, and alicyclic diols (for example, cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, etc.). , Diethylene glycol, triethylene glycol, aromatic diol (for example, bisphenol A, bisphenol A ethylene oxide adduct, bisphenol A propylene oxide adduct, etc.) and glycerin, and aromatic diol is preferred. These polyhydric alcohols may be used individually by 1 type, and may use 2 or more types together.

  The specific polyester resin preferably has a monomer unit having an aromatic ring from the viewpoint of the affinity between the toner particles and the carrier liquid. The content of the monomer unit having an aromatic ring in the specific polyester resin is preferably 50 mol% to 95 mol%, more preferably 60 mol% to 90 mol%, and more preferably 70 mol% with respect to all monomer units. More preferred is ˜85 mol%.

  The aromatic ring in the monomer unit having an aromatic ring is preferably a benzene ring, a naphthalene ring or an anthracene ring, more preferably a benzene ring or a naphthalene ring, and still more preferably a benzene ring. The number of aromatic rings in the monomer unit having an aromatic ring is not limited, but is preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 or 2. The monomer unit having an aromatic ring may be a monomer unit derived from a polyvalent carboxylic acid, may be a monomer unit derived from a polyhydric alcohol, It is preferable that the sum of the value derived from the monohydric alcohol is within the above range. The monomer unit having an aromatic ring is preferably a monomer unit derived from dicarboxylic acid or a monomer unit derived from diol.

  Examples of the polyvalent carboxylic acid constituting the monomer unit having an aromatic ring include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and 2,3-naphthalene. Aromatic dicarboxylic acids such as dicarboxylic acids can be mentioned.

  Examples of the polyhydric alcohol constituting the monomer unit having an aromatic ring include bisphenols such as bisphenol A, bisphenol AP, bisphenol B, bisphenol BP, bisphenol C, bisphenol E, and bisphenol F; ethylene oxide adducts of these bisphenols Aromatic diols such as propylene oxide adducts of these bisphenols;

  The weight average molecular weight (Mw) of the specific polyester resin is preferably 5,000 to 100,000, more preferably 7,000 to 50,000, still more preferably 8,000 to 30,000, and still more preferably 8,000 to 20,000. The number average molecular weight (Mn) of the specific polyester resin is preferably 2000 to 100,000. 1.5-100 are preferable and, as for molecular weight distribution Mw / Mn of specific polyester resin, 2-60 are more preferable.

  The toner particles may contain a binder resin other than the polyester resin. However, the proportion of the polyester resin in the total binder resin contained in the toner particles is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and further preferably 95% by mass or more. It is particularly preferable that the binder resin contained in the toner particles is substantially only a polyester resin. The polyester resin is preferably a specific polyester resin, and the ratio of the specific polyester resin in the entire binder resin contained in the toner particles is preferably 50% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more. 95 mass% or more is more preferable, and it is particularly preferable that the binder resin contained in the toner particles is substantially only the specific polyester resin.

  Examples of other binder resins other than the polyester resin include styrenes (for example, styrene, parachlorostyrene, α-methylstyrene, etc.), (meth) acrylates (for example, methyl acrylate, ethyl acrylate, acrylic acid). n-propyl, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated Nitriles (eg, acrylonitrile, methacrylonitrile, etc.), vinyl ethers (eg, vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), olefins Vinyl resins comprising homopolymers of monomers such as ethylene (eg, ethylene, propylene, butadiene, etc.), or copolymers obtained by combining two or more of these monomers; epoxy resins, polyurethane resins, polyamide resins, Non-vinyl resins such as cellulose resins, polyether resins and modified rosins, mixtures of these with vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the presence of these resins. These binder resins may be used individually by 1 type, and may use 2 or more types together.

  In the toner particles according to the exemplary embodiment, the total content of the binder resin is preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and more preferably 60% by mass to 60% by mass with respect to the entire toner particles. 85 mass% is still more preferable.

-Colorant-
Examples of the colorant include carbon black, chrome yellow, hansa yellow, benzidine yellow, sren yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, vulcan orange, watch young red, permanent red, brilliant carmine 3B, and brilliant. Carmine 6B, Dupont Oil Red, Pyrazolone Red, Resol Red, Rhodamine B Lake, Lake Red C, Pigment Red, Rose Bengal, Aniline Blue, Ultramarine Blue, Calco Oil Blue, Methylene Blue Chloride, Phthalocyanine Blue, Pigment Blue, Phthalocyanine Green, Pigments such as malachite green oxalate; acridine, xanthene, azo, benzox , Azine, anthraquinone, thioindico, dioxazine, thiazine, azomethine, indico, phthalocyanine, aniline black, polymethine, triphenylmethane, diphenylmethane, thiazole, etc. It is done. A coloring agent may be used individually by 1 type, and may use 2 or more types together.

  Among the colorants, azo pigments have a relatively low affinity with the carrier liquid. Therefore, toner particles containing an azo pigment are likely to aggregate in the carrier liquid when the azo pigment is exposed on the surface, resulting in poor image granularity. On the other hand, the specific polyester resin has a good affinity for the colorant by containing the specific monomer unit in an amount of 5 mol% or more based on the total monomer units. It is presumed that the colorant can be easily taken into the resin and the colorant is prevented from being exposed on the surface of the toner particles. Therefore, it is presumed that by including a specific polyester resin in the toner particles, the toner particles are applied with an azo pigment as a colorant and thus aggregation of the toner particles is suppressed and the image granularity is excellent.

  Examples of the azo pigment include C.I. I. Pigment Red 238, 269, 57: 1, 184; C.I. I. Pigment yellow 74, 155, 180; and the like.

  As the colorant, a surface-treated colorant may be used as necessary, or it may be used in combination with a dispersant. A plurality of colorants may be used in combination.

  The content of the colorant is preferably 1% by mass to 30% by mass, more preferably 1% by mass to 20% by mass, and still more preferably 3% by mass to 15% by mass with respect to the entire toner particles.

-Release agent-
Examples of the release agent include low molecular weight polyolefins such as polyethylene, polypropylene, and polybutene; silicones; fatty acid amides such as oleic acid amide, erucic acid amide, ricinoleic acid amide, and stearic acid amide; carnauba wax, rice wax, Plant waxes such as candelilla wax, tree wax, jojoba oil; animal waxes such as beeswax; mineral waxes such as montan wax, ozokerite, ceresin, paraffin wax, microcrystalline wax, and Fischer-Tropsch wax; etc. Is mentioned. A mold release agent may be used individually by 1 type, and may use 2 or more types together.

  The melting temperature of the release agent is preferably 50 ° C to 110 ° C, and more preferably 60 ° C to 100 ° C. The melting temperature of the release agent is determined by the “melting peak temperature” described in JIS K7121: 1987 “Method of measuring the melting temperature of plastics” from the DSC curve obtained by differential scanning calorimetry (DSC). Ask.

  The content of the release agent is, for example, preferably 0.5% by mass to 50% by mass, more preferably 1% by mass to 30% by mass, and further more preferably 1% by mass to 20% by mass with respect to the entire toner particles. Preferably, 5% by mass to 15% by mass is more preferable.

-Other additives-
Examples of other additives include known additives such as a magnetic material, a charge control agent, and inorganic powder. These additives are contained in the toner particles as internal additives.

  In this embodiment, the toner particles may contain a metal soap as a charge control agent. However, from the viewpoint of image strength, the content of the metal soap is preferably as small as possible. The amount of the metal soap contained in the toner particles is preferably 5% by mass or less, more preferably 1% by mass or less, still more preferably 0.1% by mass or less, and substantially not contained. preferable.

  Examples of the metal soap include metal salts of fatty acids such as octanoic acid, octylic acid, and naphthenic acid. Examples of the metal forming the metal salt include manganese, calcium, zirconium, cobalt, iron, zinc, copper and the like.

[Carrier liquid]
The carrier liquid contains at least a nonpolar solvent and an aluminum-containing organic compound, and may further contain a dispersant and the like.

-Non-polar solvent-
The nonpolar solvent is an insulating liquid for dispersing toner particles.

As the nonpolar solvent, a chemical substance having no polar group in the molecular structure is preferably selected, and a chemical substance having a solubility parameter of 8 or less is particularly suitable. The solubility parameter is a value calculated from the following equation.
Solubility parameter δ = √ ((ΔH−RT) / V)
ΔH: Evaporation enthalpy (J / mol), R: Gas constant (J / (K · mol)), T: Temperature (K), V: Molar volume (cm ³ / mol)

The nonpolar solvent preferably has a dry point of 100 ° C to 300 ° C. If the dry point of the nonpolar solvent is 100 ° C. or higher, the nonpolar solvent is less likely to volatilize during image formation, and toner particles are prevented from sticking on the image carrier or intermediate transfer member, resulting in image defects. Is suppressed. In this respect, the dry point of the nonpolar solvent is more preferably 130 ° C or higher, further preferably 140 ° C or higher, and further preferably 150 ° C or higher.
On the other hand, when the dry point of the nonpolar solvent is 300 ° C. or less, the nonpolar solvent hardly remains between the fixed image and the recording medium, and the fixed image is more firmly fixed to the recording medium. In particular, when an image with a large amount of toner is formed on a flexible resin film, the fixed image is easily peeled off. From the viewpoint of improving the image strength of the fixed image on the resin film, the dry point of the nonpolar solvent is reduced. It is preferable that it is 300 degrees C or less. In this respect, the dry point of the nonpolar solvent is more preferably 290 ° C. or less, further preferably 280 ° C. or less, and further preferably 250 ° C. or less. Further, from the viewpoint of suppressing toner contamination on the image carrier, the dry point of the nonpolar solvent is more preferably 290 ° C. or less, further preferably 280 ° C. or less, and further preferably 250 ° C. or less.

  The dry point of the nonpolar solvent is measured according to the atmospheric distillation test method of JIS K 2254: 1998. The dry point of the nonpolar solvent contained in the liquid developer is measured by the following method.

  Put the liquid developer in a sealed container and set the whole sealed container in a centrifuge (Ultra Centrifuge CP56GII (Hitachi Koki Co., Ltd.), Ultra Centrifuge Angle Rotor P50A2 (Hitachi Koki Co., Ltd.)), 5000 rpm Centrifuge for 10 minutes. After centrifugation, the supernatant is collected from the sealed container, and the supernatant is filtered through a polytetrafluoroethylene membrane filter having a pore size of 0.1 μm to collect the filtrate. The filtrate is distilled with an evaporator to remove the aluminum-containing organic compounds. Using this as a measurement sample, the dry point is measured according to the atmospheric distillation test method of JIS K 2254: 1998.

  Nonpolar solvents include mineral oils (aliphatic hydrocarbons and aromatic hydrocarbons); silicone oils such as dimethyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil; perfluoropolyether, perfluoroalkyl ether, etc. Fluorine oil; ethers such as diethyl ether; These nonpolar solvents may be used alone or in combination of two or more.

  As the nonpolar solvent, mineral oil is preferable from the viewpoint of dispersion stability of the toner particles. Mineral oil includes not only hydrocarbons derived from underground resources such as petroleum, natural gas and coal, but also hydrocarbons obtained by refining and modifying hydrocarbons derived from underground resources and oils synthesized from them as raw materials. Examples of the mineral oil include aliphatic hydrocarbons such as normal hexane, normal pentane, normal paraffin, isoparaffin, naphthene and olefin; and aromatic hydrocarbons such as benzene, toluene, xylene and mesitylene. These may be used individually by 1 type and may use 2 or more types together. As the mineral oil, aliphatic hydrocarbons are preferable, paraffins are more preferable, and isoparaffins are still more preferable.

  The proportion of mineral oil in the entire nonpolar solvent is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, still more preferably 95% by mass or more, and the nonpolar solvent is substantially Particularly preferred is mineral oil only.

  Examples of commercially available mineral oil products include “Isopar L” (isoparaffin), “Isopar M” (isoparaffin), “Exol D80” (naphthene), “Exsol D110” (naphthene), “Solvesso 100” (ex. "Aromatic hydrocarbons", "Solvesso 150" (aromatic hydrocarbons); "Moresco White P-40" (paraffin), "Moresco White P-70" (paraffin), "Moresco White P-" manufactured by MORESCO 80 (paraffin), “Moresco White P-100” (paraffin), “Moresco White P-200” (paraffin); “Naphthezol 200” (naphthene), “Naphthezol 220” from JX Nippon Oil & Energy Naphthene); and the like.

-Aluminum-containing organic compounds-
Examples of the aluminum-containing organic compound include aluminum alkyl acetoacetate diisopropylate (the alkyl group is, for example, an alkyl group having 1 to 20 carbon atoms), aluminum monoacetylacetonate bis (ethylacetoacetate), aluminum tris (acetylacetate). And aluminum chelates such as aluminum tris (ethyl acetoacetate); aluminum alkoxides such as aluminum ethoxide, aluminum isopropoxide, aluminum sec-butoxide, and aluminum tert-butoxide. An aluminum containing organic compound may be used individually by 1 type, and may use 2 or more types together.

  The concentration of the aluminum-containing organic compound contained in the carrier liquid is 10 ppm to 500 ppm. The measuring method is as described in [Example] described later.

-Dispersant-
There is no restriction | limiting in particular as a dispersing agent, A well-known dispersing agent (a low molecular dispersing agent, a high molecular dispersing agent) is applied. As the dispersant, a polymer dispersant is preferable from the viewpoint of dispersion stability of the toner particles. A dispersing agent may be used individually by 1 type, and may use 2 or more types together.

  As the polymer dispersant, from the viewpoint of dispersion stability of the toner particles, a polymer amine compound having an affinity for the acidic group of the polyester resin present on the surface of the toner particles is preferable. The high molecular amine compound also functions as a positively chargeable charge control agent.

  Examples of the polymer amine compound include, in the molecule, at least one selected from a polyalkyleneimine chain (polyethyleneimine chain, polypropyleneimine chain, etc.), a polyallylamine chain, a polyvinylamine chain, a polydiallylamine chain, and a polyvinylpyrrolidone chain. The compound which has is mentioned.

  The polymer amine compound is preferably a compound having at least one of a polyethyleneimine chain and a polyallylamine chain in the molecule. Examples of the compound having a polyethyleneimine chain in the molecule include a reaction product of polyethyleneimine and 12-hydroxystearic acid self-condensate (for example, Solsperse 13940, Lubrizol). Examples of the compound having a polyallylamine chain in the molecule include a reaction product of polyallylamine and polycaprolactone (for example, Ajisper PB821, Ajinomoto Fine Techno Co.).

  The weight average molecular weight of the polymer dispersant is preferably from 100 to 1,000,000, more preferably from 1,000 to 100,000, from the viewpoint of dispersion stability of the toner particles.

  The content of the polymer dispersant is preferably 0.01 parts by mass to 100 parts by mass, and preferably 0.1 parts by mass to 10 parts by mass with respect to 100 parts by mass of the toner particles, from the viewpoints of dispersion stability and chargeability of the toner particles. Part is more preferred.

-Charge control agent-
The carrier liquid may contain a charge control agent. There is no restriction | limiting in particular as a charge control agent, A well-known charge control agent is applied. Examples of the charge control agent include unmodified nigrosine dyes, fatty acid-modified nigrosine dyes, nigrosine dyes such as carboxyl group-containing fatty acid-modified nigrosine dyes, and commercially available products such as "Bontron N-01" “Bontron N-07” (manufactured by Orient Chemical Co., Ltd.), “CHUO CCA-3” (manufactured by Chuo Gosei Co., Ltd.) and the like; a triphenylmethane dye having a tertiary amine as a side chain; a quaternary ammonium salt compound, As commercial products, “Bontron P-51” (manufactured by Orient Chemical Co., Ltd.), “TP-415” (manufactured by Hodogaya Chemical Industry Co., Ltd.); ); Amine compounds; amide compounds; imide compounds; gold oxycarboxylic acid Genus complex; metal complex of azo compound; metal complex dye; salicylic acid derivative; olefin monomer, N-phenylmaleimide monomer and maleic acid monoamide monomer or maleic acid monoester monomer Maleimide compounds such as polymers (copolymers described in JP2013-167848); o-toluenesulfonamide, p-toluenesulfonamide, N-ethyl-p-toluenesulfonamide, N-butyl-p-toluenesulfone Toluenesulfonamide compounds such as amides; metal soaps; A charge control agent may be used individually by 1 type, and may use 2 or more types together. As the charge control agent, a positively chargeable charge control agent is preferable.

  In this embodiment, the carrier liquid may contain a metal soap, but from the viewpoint of image density stability and image strength, the smaller the metal soap content, the better. The amount of the metal soap contained in the carrier liquid is preferably 5% by mass or less, more preferably 1% by mass or less, still more preferably 0.1% by mass or less, and substantially no inclusion in the carrier liquid. preferable.

  Examples of the metal soap include metal salts of fatty acids such as octanoic acid, octylic acid, and naphthenic acid. Examples of the metal forming the metal salt include manganese, calcium, zirconium, cobalt, iron, zinc, copper and the like.

-Other additives-
Carrier liquids include surfactants, wetting agents, thickeners, anti-settling agents, foaming agents, antifoaming agents, anti-aging agents, softeners, fillers, flavoring agents, anti-sticking agents, and mold release agents. An agent or the like may be included.

[Method for producing liquid developer]
The liquid developer according to the exemplary embodiment is manufactured through, for example, a granulation process for producing toner coarse particles and a wet pulverization process for pulverizing toner coarse particles in a carrier liquid.

  The granulation step may be any of a dry production method (for example, a kneading pulverization method) and a wet production method (for example, an aggregation coalescence method, a suspension polymerization method, a dissolution suspension method). There is no restriction | limiting in particular in these manufacturing methods, You may employ | adopt a well-known manufacturing method. The coarse toner particles obtained by the wet manufacturing method are preferably subjected to a washing step, a solid-liquid separation step, and a drying step to obtain dry toner coarse particles. The dry toner coarse particles and the inorganic fine particles may be mixed, and an external additive may be adhered to the surface of the toner coarse particles.

  In the present embodiment, the polyester resin used in the granulation step is preferably a polyester resin synthesized using a titanium compound as a catalyst. When the granulation step is performed by a kneading and pulverizing method, a titanium compound may be added to the toner material and melt mixed. When performing a granulation process by the aggregation coalescence method, a titanium compound may be added to a polyester resin dispersion liquid and a polyester compound may be made to contain a titanium compound.

  In the wet pulverization step, after the toner coarse particles are dispersed in the carrier liquid, the toner coarse particles are wet pulverized in the carrier liquid using a media-type wet pulverizer such as a bead mill, a ball mill, a sand mill, or an attritor. For example, the aluminum-containing organic compound is added in advance to the carrier liquid, and the toner coarse particles are dispersed in the carrier liquid containing the aluminum-containing organic compound, and wet pulverization is performed. Alternatively, after the toner coarse particles are wet-ground in the carrier liquid, the aluminum-containing organic compound is added to the carrier liquid. The dispersant is the same as the aluminum-containing organic compound.

  In addition, the liquid developer according to the exemplary embodiment is manufactured, for example, by preparing toner particles in a solvent by a wet manufacturing method and replacing the solvent with a carrier liquid as necessary. In this production method, the wet production method may be any of an aggregation coalescence method, a suspension polymerization method, a dissolution suspension method, and the like, and a known production method may be adopted. As the solvent used in the wet manufacturing method, the same type of solvent as the carrier liquid, a solvent that can replace the carrier liquid (for example, a solvent having a boiling point lower than that of the carrier liquid), or a mixed solvent thereof is preferable. In this production method, for example, after toner particles are produced in a carrier liquid by a wet production method, an aluminum-containing organic compound is added to the carrier liquid; or a solvent using a carrier liquid containing an aluminum-containing organic compound in the wet production method Replace with

  The content ratio of the carrier liquid and the toner particles in the liquid developer according to this embodiment is, for example, 5 to 35 parts by mass of toner particles with respect to 100 parts by mass of the carrier liquid.

<Liquid developer cartridge>
The liquid developer cartridge according to the present embodiment accommodates the liquid developer according to the present embodiment, and is attached to and detached from the image forming apparatus. The liquid developer accommodated in the liquid developer cartridge according to this embodiment is supplied to the developing unit of the image forming apparatus through, for example, a supply pipe provided in the image forming apparatus. The form of the liquid developer cartridge according to the present embodiment is not limited, and examples thereof include a tank form and a bottle form. The capacity of the liquid developer cartridge according to this embodiment may be selected according to the size of the image forming apparatus.

<Image Forming Apparatus and Image Forming Method>
The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic image forming unit that forms an electrostatic image on the surface of the charged image carrier, and liquid development. A developer that contains the developer and develops the electrostatic image formed on the surface of the image carrier as a toner image with a liquid developer, and transfers the toner image formed on the surface of the image carrier to the surface of the recording medium. A transfer unit that fixes the toner image transferred to the surface of the recording medium. The image forming apparatus according to the present embodiment uses the liquid developer according to the present embodiment as the liquid developer.

  In the image forming apparatus according to the present embodiment, an image holding is performed by a charging process for charging the surface of the image carrier, an electrostatic charge image forming process for forming an electrostatic image on the surface of the charged image carrier, and a liquid developer. A development process for developing the electrostatic image formed on the surface of the body as a toner image, a transfer process for transferring the toner image formed on the surface of the image carrier to the surface of the recording medium, and a transfer process to the surface of the recording medium. Then, an image forming method (an image forming method according to the present embodiment) including a fixing step of fixing the toner image is performed.

  The image forming apparatus according to the present embodiment is, for example, a direct transfer type apparatus that directly transfers a toner image formed on the surface of the image carrier to a recording medium; an intermediate transfer of the toner image formed on the surface of the image carrier An intermediate transfer type device that primarily transfers the toner image transferred onto the surface of the body and then transfers the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium; after transferring the toner image, the surface of the image carrier before charging An image forming apparatus such as an apparatus provided with cleaning means for cleaning; an apparatus provided with charge eliminating means for irradiating the surface of the image holding member with charge removing light after the toner image is transferred and before charging. In the case where the image forming apparatus according to this embodiment is an intermediate transfer type apparatus, for example, the transfer unit intermediately transfers an intermediate transfer body on which a toner image is transferred onto the surface and a toner image formed on the surface of the image holding body. Primary transfer means for primary transfer to the surface of the body, and secondary transfer means for secondary transfer of the toner image transferred to the surface of the intermediate transfer body to the surface of the recording medium.

  In the image forming apparatus (image forming method) according to the present embodiment, the fixing device (fixing step) is preferably configured to perform two-stage fixing. Specifically, the fixing device (fixing step) includes a non-contact type heating device (non-contact type heating step) for heating the toner image in a non-contact manner, and after heating by a non-contact type heating device (non-contact type). It is preferable to have a heating and pressing apparatus (heating and pressing step) that applies pressure while heating after the heating step).

  The recording medium is not particularly limited, and a known recording medium is applied. For example, a thermoplastic resin film, paper, an OHP sheet, etc. are mentioned. Applications of the thermoplastic resin film include labels, packaging materials, posters, and the like.

  Examples of thermoplastic resin films include polyolefin films such as polyethylene and polypropylene; polyester films such as polyethylene terephthalate and polybutylene terephthalate; polyamide films such as nylon; polycarbonate, polystyrene, modified polystyrene, polyvinyl chloride, polyvinyl alcohol, and polylactic acid. Film; and the like. These films may be any of an unstretched film and a stretched film stretched in a uniaxial direction or a biaxial direction. The thermoplastic resin film may be either a single layer or a multilayer. The thermoplastic resin film may be a film having a surface coat layer for assisting toner fixing, a film subjected to corona treatment, ozone treatment, plasma treatment, flame treatment, glow discharge treatment or the like. The thickness of the thermoplastic resin film for use in the flexible packaging material is, for example, 5 μm to 250 μm, preferably 10 μm to 100 μm.

Hereinafter, an image forming apparatus according to the present embodiment will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present embodiment.
An image forming apparatus 100 illustrated in FIG. 1 includes a photoconductor 110 (an example of an image carrier), a charging device 112 (an example of a charging unit), an exposure device 114 (an example of an electrostatic charge image forming unit), and a developing device 120. (An example of a developing unit), a transfer device 130 (an example of a transfer unit), a fixing device 140 (an example of a fixing unit), and a cleaner 116.

  The photoconductor 110 has a cylindrical shape, and a charging device 112, an exposure device 114, a developing device 120, a transfer device 130, and a cleaner 116 are sequentially provided around the photoconductor 110.

  As the photoreceptor 110, a photoreceptor whose outermost layer is an inorganic layer is preferable. Since the inorganic layer is less likely to swell by the carrier liquid compared to the organic layer, the toner particles are less likely to remain on the photoreceptor whose outermost surface layer is an inorganic layer compared to the photoreceptor whose outermost surface layer is an organic layer. Therefore, the photoreceptor whose outermost surface layer is an inorganic layer suppresses the occurrence of image defects. Examples of the photoreceptor whose outermost layer is an inorganic layer include a selenium photoreceptor, an amorphous silicon photoreceptor, and a photoreceptor having an inorganic layer formed on the outermost surface of an organic photoreceptor, and an amorphous silicon photoreceptor is preferred.

The charging device 112 charges the surface of the photoconductor 110.
The exposure device 114 exposes the surface of the charged photoreceptor 110 based on an image signal, for example, with a laser beam to form an electrostatic charge image.

The developing device 120 includes a developer container 122, a developer supply roll (anilox roll) 124, a regulating member 126, a developing roll 128, a corona irradiation device 129, and a cleaner 127.
The developer storage container 122 stores the liquid developer G. The developer container 122 may be provided with a stirring member (not shown) that stirs the liquid developer G.
The developer supply roll 124 is provided so that a part of the developer supply roll 124 is immersed in the liquid developer G stored in the developer storage container 122 and close to (or in contact with) the development roll 128, and the developer storage container 122. The liquid developer G contained therein is supplied to the surface of the developing roll 128. The regulating member 126 controls the supply amount of the liquid developer G by the developer supply roll 124.
The developing roll 128 holds the liquid developer G supplied from the developer supply roll 124, and develops the electrostatic image formed on the surface of the photoconductor 110 as the toner image T with the liquid developer G.
The corona irradiation device 129 is a device that charges the toner particles by applying corona irradiation to the layer of the liquid developer G on the developing roll 128 and can be installed as necessary.
The cleaner 127 removes and collects residual toner remaining on the surface of the developing roll 128 after development.

The transfer device 130 transfers a drum-shaped intermediate transfer body 132 onto which the toner image T formed on the surface of the photoconductor 110 is transferred, and the toner image T transferred onto the surface of the intermediate transfer body 132 to the recording medium P. And an intermediate transfer type apparatus including a transfer roll 134.
For example, the transfer device 130 may be configured to include a belt-shaped intermediate transfer member 132, or may not include the intermediate transfer member 132, and may be directly transferred from the photosensitive member 110 to the recording medium P by the transfer roller 134. Alternatively, a direct transfer system configuration may be used.

The fixing device 140 is provided on the downstream side of the transfer device 130 in the traveling direction of the recording medium P, and includes a non-contact heating device 142 and a heating and pressing device 144.
The non-contact type heating device 142 is, for example, a plate-like heating device provided with a heat source inside a metal housing. The non-contact type heating device 142 may include a blower device together with a heat source inside the housing. The non-contact heating device 142 may be provided on the side of the recording medium where the toner image is formed, may be provided on the back side of the recording medium (the side where the toner image is not formed), or may be provided on both sides. Also good.
The heating and pressing device 144 is, for example, a pair of heating rolls 144A and a pressing roll 144B. The heating roll 144A and the pressure roll 144B are arranged to face each other so as to form a nip across the recording medium. A heat source is provided inside the heating roll 144A. In addition, the heating and pressing apparatus 144 may be an apparatus that combines a heating and pressing roll and a pressing belt, an apparatus that combines a pressing roll and a heating and pressing belt, and the like.

The cleaner 116 is provided for the purpose of removing and collecting the transfer residual toner remaining on the surface of the photoreceptor 110 after the toner image is transferred.
The image forming apparatus 100 may further include a neutralization device (not shown) that neutralizes the surface of the photoconductor 110 after the transfer and before the next charging.

Hereinafter, an image forming method by the image forming apparatus 100 will be described.
The charging device 112, the exposure device 114, the developing device 120, the transfer device 130, the fixing device 140, and the cleaner 116 are operated in synchronization with the rotation speed of the photoconductor 110.
First, the charging device 112 charges the surface of the photoconductor 110 rotating in the direction of arrow B to a predetermined potential.
Next, the exposure device 114 exposes the surface of the charged photoconductor 110 based on the image signal to form an electrostatic charge image.

In the developing device 120, the developer supply roll 124 supplies the liquid developer G to the surface of the developing roll 128, and the developing roll 128 that rotates in the direction of arrow A conveys the liquid developer G to the photoconductor 110.
The liquid developer G is supplied to the electrostatic image on the photoconductor 110 at a position where the developing roller 128 and the photoconductor 110 are close to (or in contact with), and the electrostatic image is developed (visualized) to form a toner image. T is formed.

Next, the toner image T on the surface of the photoconductor 110 is transferred to the surface of the intermediate transfer body 132 that rotates in the direction of arrow C.
Next, the toner image T transferred to the surface of the intermediate transfer body 132 is transferred to the recording medium P at a position where the toner image T is in contact with the transfer roll 134. The main transfer is performed by sandwiching the recording medium P between the transfer roll 134 and the intermediate transfer body 132 and bringing the toner image T on the surface of the intermediate transfer body 132 into close contact with the recording medium P.

  The recording medium P to which the toner image T has been transferred is conveyed to the fixing device 140 and passes through the non-contact type heating device 142 and the heating and pressing device 144 in order, whereby a fixed image is formed on the surface of the recording medium P. .

  When paper is used as the recording medium P, the heating temperature of the non-contact heating device 142 is preferably 100 ° C. to 160 ° C., more preferably 110 ° C. to 150 ° C. When a thermoplastic resin film is used as the recording medium P, the heating temperature of the non-contact heating device 142 is preferably 70 ° C. to 110 ° C., and more preferably 80 ° C. to 100 ° C. The heating time is determined by the process speed of the non-contact heating device 142.

  The toner image heated by the non-contact type heating device 142 is further fixed to the recording medium P by being heated and pressed by the heating and pressing device 144 (the heating roll 144A and the pressing roll 144B). The

When paper is used as the recording medium P, the heating temperature of the heating and pressing device 144 is preferably 100 ° C. to 160 ° C., more preferably 110 ° C. to 150 ° C. When a thermoplastic resin film is used as the recording medium P, the heating temperature of the heating and pressing device 144 is preferably 70 ° C to 110 ° C, and more preferably 80 ° C to 100 ° C. The pressure applied by the heat and pressure device 44 is preferably ^{1.5kg / cm 2 ~5kg / cm 2} , 2kg / cm 2 ~3.5kg / cm 2 is more preferable.

  After the toner image T is transferred to the intermediate transfer body 132, the transfer residual toner is removed and collected by the cleaner 116, and the process proceeds to the charging process again.

  The image forming apparatus 100 includes a photoconductor 110, a charging device 112, an exposure device 114, a developing device 120, a transfer device 130, and a cleaner 116 as one unit, and a tandem full-color image in which four units are mounted side by side. It may be a forming device.

  The image forming apparatus 100 may supply a toner particle or an externally added toner from a toner cartridge (not shown) to the developer container 122, or supply a liquid developer from a liquid developer cartridge (not shown). It is good. The toner cartridge or the liquid developer cartridge may be configured to be attached to and detached from the image forming apparatus so that it can be replaced when the remaining amount of the liquid developer runs out.

  Hereinafter, embodiments of the present invention will be described in detail by way of examples, but the embodiments of the present invention are not limited to these examples.

<Measurement method>
The measuring method of each physical property in the liquid developer is as follows.

[Titanium element concentration of tetrahydrofuran-soluble component in toner particles]
Put the liquid developer in a sealed container and set the whole sealed container in a centrifuge (Ultra Centrifuge CP56GII (Hitachi Koki Co., Ltd.), Ultra Centrifuge Angle Rotor P50A2 (Hitachi Koki Co., Ltd.)), 5000 rpm Centrifuge for 10 minutes. After centrifugation, the supernatant is removed from the sealed container to obtain a sediment. The precipitate is dried at 30 ° C. for 24 hours while reducing the pressure in a vacuum dryer to obtain a dried product (toner particles). The dried product is dissolved in tetrahydrofuran (THF) to prepare a solution. The solution is filtered through a polytetrafluoroethylene membrane filter having a pore size of 0.1 μm, and the filtrate is recovered. The filtrate is spread on a glass dish and dried at 30 ° C. for 24 hours while reducing the pressure with a vacuum dryer to obtain a solid (THF-soluble component of toner particles). 0.3 g of solid material is molded into a disk shape with a compression molding machine. If it is difficult to mold, the solid material is crushed with a mortar in advance and then molded. Using the solid material formed into a disk shape as a measurement sample, fluorescent X-ray analysis is performed under the following conditions, and the titanium element concentration is determined from the detected titanium signal. The titanium element concentration may be determined using a He-MIP-AES apparatus described later using a powder obtained by pulverizing a solid as a measurement sample.

Measuring device: X-ray fluorescence analyzer, XRF-1500 manufactured by Shimadzu Corporation
Measurement conditions: tube voltage 40KV, tube current 90mA, measurement time 30 minutes

[Content of specific monomer unit in polyester resin]
About 20 mg of the above-mentioned solid matter (THF-soluble component of toner particles) is weighed in a sample bottle, 1 mL of deuterated chloroform is added and dissolved, and NMR spectrum measurement is performed under the following conditions using the solution as a measurement sample.

Measuring apparatus: Fourier transform NMR apparatus, JNM-AL400 manufactured by JEOL Ltd.
Sample container: NMR sample tube with a diameter of 5 mm Solvent: Deuterated chloroform Sample temperature: 20 ° C
Observation nucleus: ¹ H
Integration count: 128 times Reference material: tetramethylsilane

  By detecting a peak in the range of 9 ppm to 7 ppm in the NMR spectrum, it can be confirmed that the toner contains a polyester resin. The structure is specified from the peak position and peak integral value in the NMR spectrum, and the content of the specific monomer unit is determined.

[Concentration of aluminum-containing organic compound in carrier liquid]
Put the liquid developer in a sealed container and set the whole sealed container in a centrifuge (Ultra Centrifuge CP56GII (Hitachi Koki Co., Ltd.), Ultra Centrifuge Angle Rotor P50A2 (Hitachi Koki Co., Ltd.)), 5000 rpm Centrifuge for 10 minutes. After centrifugation, the supernatant is collected from the sealed container, and the supernatant is filtered through a polytetrafluoroethylene membrane filter having a pore size of 0.1 μm to collect the filtrate. The filtrate is spread on a glass dish and dried at 30 ° C. for 24 hours while reducing the pressure in a vacuum dryer to obtain a solid. Using the powder obtained by pulverizing the solid as a measurement sample, component analysis is performed under the following conditions to confirm the presence or absence of an aluminum element and the presence or absence of a carbon element detected in synchronization with the aluminum element. When the carbon element is detected in synchronization with the aluminum element, it is determined as an aluminum-containing organic compound, and when the carbon element is not detected in synchronization with the aluminum element, it is determined as aluminum metal or alumina. Then, the aluminum-containing organic compound is quantified.

Measuring apparatus: He-MIP-AES apparatus, HORIBA, Ltd. particle analyzer DP-1000
Measurement conditions: The suction conditions are set so that the amount of powder suction from the sample suction aspirator unit is 1500 counts to 3000 counts per scan.

<Manufacture of liquid developer>
[Example 1]
45 mol parts terephthalic acid, 2 mol parts succinic acid, 3 mol parts adipic acid, 10 mol parts bisphenol A ethylene oxide 2 mol adduct, 30 mol parts bisphenol A propylene oxide 2 mol adduct, ethylene glycol 5 A monomer mixture composed of a mole part and 5 mole parts of propylene glycol was charged into a flask equipped with a stirrer, a nitrogen inlet tube, a temperature sensor, and a rectifying tower. While stirring in a nitrogen atmosphere, the temperature in the reaction system was increased to 70 ° C. over 3 hours. Next, 0.7 parts by mass of dibutyltin oxide and 0.3 parts by mass of titanium tetraacetylacetonate were added to 100 parts by mass of the monomer mixture while stirring was continued. While distilling off the water generated by reducing the pressure in the reaction system, the temperature in the reaction system was increased to 175 ° C. over 2 hours, and stirring was continued at 175 ° C. for another 8 hours to obtain a polyester resin. .

  80 parts by mass of the obtained polyester resin; I. 20 parts by weight of Pigment Red 238 (azo pigment) was mixed with a Henschel mixer. Next, the mixture was kneaded using a Banbury mixer, and the cooled product was coarsely pulverized to 2 mm square or less to obtain coarsely crushed particles.

  25 parts by mass of coarsely pulverized particles and 75 parts by mass of isoparaffin (trade name: Isopar L, ExxonMobil, dry point: 200 ° C.) are mixed, pulverized for 150 hours using a ball mill and zirconia beads having a diameter of 5 mm, and toner A particle dispersion was prepared.

  5 parts by mass of a reaction product of polyethyleneimine having a molecular weight of 20,000 to 30,000 and 12-hydroxystearic acid self-condensate and 1 part by mass of aluminum alkyl acetoacetate diisopropylate are added to 100 parts by mass of the toner particle dispersion. Then, the dispersion treatment was performed for 24 hours using a roll mill. The dispersion after the dispersion treatment was placed in a sealed container, submerged in an ultrasonic cleaning tank containing ice water, and 45 kHz ultrasonic waves were applied for 30 seconds three times. Next, the dispersion in the sealed container was filtered through a 20 μm mesh to obtain a liquid developer.

[Examples 2 to 10]
A liquid developer was produced in the same manner as in Example 1 except that the titanium compound used for the synthesis of the polyester resin and the aluminum-containing organic compound used for the production of the liquid developer were changed as shown in Table 1. .

[Example 11]
A liquid developer was obtained in the same manner as in Example 1 except that Trade Name: Exol D130 (Esso Petroleum Corporation, dry point: 309 ° C.) was used instead of Isopar L.

[Example 12]
A liquid developer was obtained in the same manner as in Example 1 except that Trade Name: Exol D80 / 100 (Esso Petroleum Corporation, dry point: 101 ° C.) was used instead of Isopar L.

[Example 13]
In the synthesis of the polyester resin, a liquid developer was prepared in the same manner as in Example 1 except that dibutyltin oxide was not used and the amount of the titanium compound was changed as shown in Table 1.

[Example 14]
Except that the titanium compound used for the synthesis of the polyester resin was changed to the two combined use as shown in Table 1, and the aluminum-containing organic compound used for the preparation of the liquid developer was changed as shown in Table 1, Example In the same manner as in Example 1, a liquid developer was prepared.

[Example 15]
45 mol parts terephthalic acid, 2 mol parts succinic acid, 3 mol parts adipic acid, 10 mol parts bisphenol A ethylene oxide 2 mol adduct, 30 mol parts bisphenol A propylene oxide 2 mol adduct, ethylene glycol 5 A monomer mixture composed of a mole part and 5 mole parts of propylene glycol was charged into a flask equipped with a stirrer, a nitrogen inlet tube, a temperature sensor, and a rectifying tower. While stirring in a nitrogen atmosphere, the temperature in the reaction system was increased to 70 ° C. over 3 hours. Next, 1.0 part by mass of dibutyltin oxide was added to 100 parts by mass of the monomer mixture while continuing stirring. While distilling off the water generated by reducing the pressure in the reaction system, the temperature in the reaction system was increased to 175 ° C. over 2 hours, and stirring was continued at 175 ° C. for another 8 hours to obtain a polyester resin. .

  80 parts by mass of the obtained polyester resin; I. 20 parts by mass of Pigment Red 238 (azo pigment) and 0.6 parts by mass of titanium tetraacetylacetonate were mixed with a Henschel mixer. Next, the mixture was kneaded using a Banbury mixer, and the cooled product was coarsely pulverized to 2 mm square or less to obtain coarsely crushed particles. A liquid developer was produced in the same manner as in Example 1 using the coarsely crushed particles.

[Example 16]
(Production of oil phase liquid)
100 parts of coarsely pulverized particles prepared in Example 1 and 500 parts of ethyl acetate were mixed with stirring to obtain an oil phase liquid.

(Preparation of styrene acrylic resin particle dispersion)
Styrene: 450 parts by mass n-butyl acrylate: 10 parts by mass Acrylic acid: 5 parts by mass Dodecanethiol: 15 parts by mass Carbon tetrabromide: 5 parts by mass In an aqueous solution in which 7 parts by mass of an ionic surfactant (Sanyo Chemical Industries, Nonipol 400) and 8 parts by weight of an anionic surfactant (Daiichi Kogyo Seiyaku, Neogen SC) are dissolved in 550 parts by mass of ion-exchanged water, Dispersed and emulsified in. Next, an aqueous solution in which 5 parts by mass of ammonium persulfate was dissolved in 50 parts by mass of ion-exchanged water was added over 10 minutes while stirring the flask. Subsequently, after carrying out nitrogen substitution, the contents in the flask were heated with an oil bath until the contents reached 80 ° C. while stirring, and emulsion polymerization was continued for 3 hours to obtain a styrene acrylic resin particle dispersion.

(Preparation of aqueous phase liquid)
-Styrene acrylic resin particle dispersion: 60 parts by mass-2% aqueous solution of Serogen BS-H (Daiichi Kogyo Seiyaku): 200 parts by mass-Ion-exchanged water: 200 parts by mass The above materials are stirred and mixed to obtain an aqueous phase liquid. It was.

(Production of toner particles (16))
300 parts by mass of the oil phase liquid was placed in a container and stirred for 2 minutes with a homogenizer (Ultra Turrax, IKA), and then 1000 parts by mass of the aqueous phase liquid was added to the container and stirred for 20 minutes with a homogenizer. Next, this mixture was stirred with a propeller-type stirrer at room temperature (25 ° C.) / Normal pressure (1 atm) for 48 hours to remove the organic solvent and form a granular material. Next, the granular material was washed with water, dried and classified to obtain toner particles (16).

  25 parts by mass of toner particles (16) and 75 parts by mass of isoparaffin (trade name: Isopar L, ExxonMobil, dry point: 200 ° C.) are mixed, and 2 with a homogenizer (Ultra Tarrax, IKA) while cooling. The mixture was stirred for a minute to obtain a toner particle dispersion (16).

(Preparation of liquid developer (16))
Toner particle dispersion (16) 100 parts by mass, 5 parts by mass of a reaction product of polyethyleneimine with a molecular weight of 20,000 to 30,000 and 12-hydroxystearic acid self-condensate, and 1 part of aluminum alkyl acetoacetate diisopropylate Then, the mixture was stirred and dispersed for 2 minutes with a homogenizer (Ultra Turrax, IKA) while cooling. The dispersion after the dispersion treatment was placed in a sealed container, submerged in an ultrasonic cleaning tank containing ice water, and 45 kHz ultrasonic waves were applied for 30 seconds three times. Next, the dispersion in the sealed container was filtered through a 20 μm mesh to obtain a liquid developer (16).

[Comparative Example 1]
In the same manner as in Example 1, except that no titanium compound is used in the synthesis of the polyester resin, and 0.1 parts by mass of zirconium octylate, which is a metal soap, is used instead of the aluminum-containing organic compound in the production of the liquid developer. Thus, a liquid developer was prepared.

[Comparative Examples 2 to 5]
A liquid developer was produced in the same manner as in Example 1 except that the titanium compound used for the synthesis of the polyester resin and the aluminum-containing organic compound used for the production of the liquid developer were changed as shown in Table 1. .

[Examples 101 to 134]
A liquid developer was prepared in the same manner as in Example 1 except that the composition of the polyester resin (type of monomer and copolymerization ratio) was changed as shown in Table 2.

<Performance evaluation of liquid developer>
For the liquid developers of the examples and comparative examples, performance evaluation was performed as follows. Tables 1 and 2 show the results.

[Image density stability]
An image forming apparatus having the configuration shown in FIG. 1 and having an amorphous silicon photoconductor as a photoconductor is prepared. The liquid developer was loaded into the image forming apparatus, and image formation was performed on a PET film (PET50 (A) PAT1 8LK manufactured by Lintec Corporation) as follows. The “solid image density” described below is a density measured using a spectral densitometer (X-Rite 939 manufactured by X-Rite Co., Ltd., aperture diameter 4 mm).

  A full line image having an image area ratio of 5% in the image forming area was output 90 m. Subsequently, a vertical band image having an image area ratio of 90% in the image forming region (having a non-image forming portion having a width of 10% in the central portion in the width direction and a width of 90% is a solid image. "Is a direction perpendicular to the image output direction.) Subsequently, 2 m of blank paper without an image was output. This was regarded as one set, and 10 sets were output continuously. The amount of applied toner was set so that the solid image density at the front end of the first set of vertical band images was 1.4.

  Five solid image densities at the front end of each set of vertical band images were measured, and the average value was used as the solid image density of each set. Based on the solid image density of the first set, the fluctuation range of the solid image density with respect to the first set was calculated from the second set to the tenth set and classified as follows.

G1 (◎): The density variation is 0.2 or less from the second set to the tenth set, and the image density is extremely stable even when a large amount of image is output.
G2 (◯): The density fluctuation is 0.3 or less from the second set to the tenth set, and the image density is stable even when a large amount of image output is performed.
G3 (△): Density fluctuation is 0.3 or less in the first half, but density fluctuation may be more than 0.3 and 0.4 or less in the second half, and long-term image density stability is slightly inferior, but actual use It is a level with no problem.
G4 (×): Density fluctuation is 0.4 or less in the first half, but density fluctuation may exceed 0.4 in the second half, and long-term image density stability is lacking.
G5 (XX): The density fluctuation exceeds 0.4 from the second set, and the image stability is inferior from the beginning.

[Image intensity]
The rear end portion of the tenth set of solid images was cut out by 10 cm × 10 cm and fixed on a glass flat plate. Using a pencil-type scratch hardness meter (Model 318S, manufactured by Eriksen Co., Ltd., head: standard pin No. 1), the head portion was pressed against the image and slid, and the scraped state of the image was observed. The springs were adjusted to start with weak pressure, and the spring pressure was gradually increased to reduce the image and the front pressure at which the substrate could be seen through was set as the image intensity, and classified as follows.

G1 (◎): The image intensity is 15 N or more, and the image intensity is extremely excellent.
G2 (◯): The image intensity is 10N or more and less than 15N, and the image intensity is excellent.
G3 (Δ): The image intensity is 7N or more and less than 10N, and the image intensity is slightly inferior, but at a level where there is no problem in actual use.
G4 (x): The image intensity is 4N or more and less than 7N, and the image intensity is inferior.
G5 (XX): The image intensity is less than 4N, and the image intensity is extremely inferior.

[Toner stains on image carrier]
After the 10 sets were output, 10 m of a full-surface image (image having no non-image forming portion in the image forming area) with an image area ratio of 100% was output and the image was observed. Also, take out the image carrier from the image forming apparatus, wipe the surface of the image carrier lightly with a cotton cloth soaked in ethyl alcohol, remove the toner adhering to the surface, and then observe the dirt adhering to the surface of the image carrier. did. The observation results of the image carrier surface and the entire solid image were classified as follows.

G1 (◎): The toner is not fixed on the surface of the image carrier, and the entire solid image has no density unevenness and is of high quality.
G2 (◯): When light is applied to the surface of the image carrier, a slight difference in glossiness is seen at the boundary between the portion corresponding to the solid image portion of the vertical belt image and the portion corresponding to the non-image forming portion. This suggests that a very small amount of toner is fixed, but the entire solid image has no density unevenness and is of high quality.
G3 (Δ): The surface of the image carrier is colored and the toner is fixed, but the entire solid image is high in quality without density unevenness.
G4 (×): The surface of the image carrier is colored and the toner is fixed, and the entire solid image has a portion between the portion corresponding to the solid image portion of the vertical band image and the portion corresponding to the non-image forming portion. There is a slight density difference.
G5 (XX): Color is present on the surface of the image carrier and toner fixation occurs, and the entire solid image has a space between the portion corresponding to the solid image portion of the vertical band image and the portion corresponding to the non-image forming portion. There is a clear difference in density.

100 Image Forming Device 110 Photoconductor (Example of Image Holding Body)
112 Charging device (an example of charging means)
114 Exposure apparatus (an example of electrostatic charge image forming means)
116 cleaner 120 developing device (an example of developing means)
122 developer container 124 developer supply roll 126 regulating member 127 cleaner 128 developing roll 129 corona irradiation device 130 transfer device (an example of transfer means)
132 Intermediate transfer member 134 Transfer roll 140 Fixing device (an example of fixing means)
142 Non-Contact Heating Device 144 Heating and Pressing Device 144A Heating Roll 144B Pressing Roll G Liquid Developer T Toner Image P Recording Medium

Claims (13)

Toner particles containing a polyester resin and a colorant and having a titanium element concentration of 10 to 500 ppm;
A carrier liquid containing a nonpolar solvent and an aluminum-containing organic compound, wherein the concentration of the aluminum-containing organic compound is 10 to 500 ppm;
A positively chargeable liquid developer.   The liquid developer according to claim 1, wherein the aluminum-containing organic compound contains at least one selected from aluminum chelates and aluminum alkoxides.   The said polyester resin is a polyester resin which contains 5-25 mol% of monomer units which consist of a C2-C5 saturated hydrocarbon chain between ester bonds with respect to all the monomer units. The liquid developer according to claim 2.   The liquid according to any one of claims 1 to 3, wherein the polyester resin is a polyester resin containing 50 to 95 mol% of a monomer unit having an aromatic ring with respect to all monomer units. Developer.   The liquid developer according to claim 4, wherein the aromatic ring is a benzene ring.   The liquid developer according to any one of claims 1 to 5, wherein the nonpolar solvent has a dry point of 150 to 300C.   A liquid developer cartridge that contains the liquid developer according to claim 1 and is detachable from an image forming apparatus. An image carrier,
Charging means for charging the surface of the image carrier;
An electrostatic charge image forming means for forming an electrostatic charge image on the surface of the charged image carrier;
A developing unit that contains the liquid developer according to any one of claims 1 to 6 and that develops an electrostatic image formed on the surface of the image carrier as a toner image by the liquid developer. ,
Transfer means for transferring a toner image formed on the surface of the image carrier to the surface of a recording medium;
Fixing means for fixing the toner image transferred to the surface of the recording medium;
An image forming apparatus comprising:   The developing means includes: a developing roll on which the liquid developer layer is formed; and a device for charging toner particles by applying corona irradiation to the liquid developer layer on the developing roll. The image forming apparatus described in 1.   The image forming apparatus according to claim 8, wherein the image carrier has an inorganic layer on an outermost surface. A charging step for charging the surface of the image carrier;
An electrostatic charge image forming step of forming an electrostatic charge image on the surface of the charged image carrier;
A developing step of developing an electrostatic image formed on the surface of the image carrier as a toner image with the liquid developer according to any one of claims 1 to 6,
A transfer step of transferring a toner image formed on the surface of the image carrier to the surface of a recording medium;
A fixing step of fixing the toner image transferred to the surface of the recording medium;
An image forming method comprising:   The developing step includes: forming a layer of the liquid developer on a developing roll; and charging the toner particles by performing corona irradiation on the liquid developer layer on the developing roll. Item 12. The image forming method according to Item 11.   The image forming method according to claim 11, wherein the image carrier has an inorganic layer on an outermost surface.