JP5293029B2 - Wet developer - Google Patents

Description

  The present invention relates to a wet developer in which toner is dispersed in an insulating solvent using a dispersant.

2. Description of the Related Art An electrophotographic image forming apparatus that forms an electrostatic latent image on a photoconductor (photosensitive drum), adheres toner to the image, and transfers and fixes the image on paper or the like is widely used. In particular, in an image forming apparatus that requires higher image quality and higher resolution, such as an office printer for large-scale printing and an on-demand printing apparatus, a wet developer that uses a wet developer that has a small toner particle diameter and that does not easily disturb the toner image. Development methods are being used.

In recent years, high-viscosity and high-concentration wet development, consisting of a high-concentration dispersion of toner as a solid component consisting of resin and pigment in an insulating solvent (carrier liquid) such as liquid paraffin and silicone oil Image forming apparatuses using an agent have been proposed.

When developing using this wet developer, a thin layer of developer is formed on a developer carrier such as a developing roller, and the thinned developer is brought into contact with the photoreceptor. It is common to develop.

The latent image on the surface of the photoreceptor is developed with a thin layer of a wet developer, and a toner image is formed on the surface of the photoreceptor. This toner image is transferred to a recording material. Alternatively, the toner image is first temporarily transferred to an intermediate transfer member or the like and then secondarily transferred to a recording material.

The toner image transferred to the recording material is fixed on the recording material, which is usually paper, by being pressurized and heated by a fixing device. However, the toner image is originally developed using a wet developer in which the toner is dispersed in the carrier liquid, and the carrier liquid is contained not only between the toner but also between the toners and between the toner papers. Moreover, it has a fairly high viscosity. This is especially a problem when a non-volatile carrier liquid is used.

It is known that the presence of a high-viscosity carrier liquid hinders fixability during toner image fixing. For example, since the toner image and the recording material are wet with the carrier liquid, the fixability of the toner image may be lowered, and the image may be crushed or disturbed during pressure fixing.

On the other hand, a technique for removing a solvent (carrier liquid) from an unfixed toner image before fixing has been developed.

For example, a heat source is prepared in front of the fixing device, and the solvent on the recording material is removed by volatilization.
Alternatively, the solvent in the toner image is deposited on the surface by heating and removed by a removing means such as squeeze. Further, the adhesion between the toner and the recording material is increased by applying an electric field. Etc. have been proposed.

However, there are problems such as the safety of volatilized solvent and the increased energy to supply heat of vaporization, the risk of damaging the recording material in the squeeze process, and the occurrence of image distortion and roughness. Was difficult.

Factors that inhibit the fixability of high-viscosity solvents are from the viewpoint of storage stability as a wet developer,
This is related to the need for high dispersibility. If the wet developer itself maintains high dispersibility, contact and coalescence of the toner particles do not proceed at the time of fixing, and the toner layer cannot form a condensed state of toner particles and cannot be fixed. become weak.

On the other hand, if the dispersibility is lowered, there is a risk that toner aggregation occurs during storage of the wet developer and storage stability cannot be maintained. That is, the storage stability and the fixing property are incompatible characteristics.

Therefore, it is desirable if the solvent can be removed from the toner layer at the time of fixing. However, in consideration of the above-mentioned difficulties, as a wet developer including a solvent, the storage stability is maintained and the fixing property is not hindered. In order to bring about such dispersibility, studies have been made on binder resins for toners (see, for example, Patent Documents 1 to 4).

In patent document 1, the polyester resin whose acid value is 40-80 mgKOH / g is used as binder resin. However, it uses an ionic dispersant with a low molecular weight,
For this reason, the dispersibility is insufficient and sufficient storage stability is difficult to obtain.

In Patent Documents 2 and 3, a basic dispersant is used, but there is no description about a polyester resin as a binder resin for toner particles. Neither of them originally intended to achieve both fixability and dispersibility, and sufficient fixability and storage stability cannot be obtained.

  Patent Document 4 describes a method using a wet developer having thixotropic properties, but does not describe a polyester resin. Further, it is not intended to achieve both fixing property and dispersibility, and sufficient fixing property and storage stability cannot be obtained.

Various other known documents have proposed techniques using various binder resins and dispersants. However, if either the storage stability or the fixing property is good, there is a problem, and there remains a problem of sufficiently satisfying both.
JP-A-10-268581 JP-A-8-220812 JP 2003-195573 A Japanese Patent Laid-Open No. 2001-100533

As described above, in the wet development, the toner image before fixing transferred to the recording material contains a carrier liquid (solvent) having a considerably high viscosity between the toner and the toner recording material as well as the toner. Therefore, the fixing property at the time of fixing the toner image is inhibited. However, there are many problems in removing the carrier liquid.

Even in the presence of a carrier liquid between toners and between toner recording materials, it is effective to reduce dispersibility as a wet developer in order to promote contact and coalescence of toner particles and improve fixability. It is. However, on the other hand, there is a problem in that the storage stability of the wet developer is impaired due to a decrease in dispersibility.

An object of the present invention is to solve these problems, and to provide a wet developer having characteristics that maintain storage stability as a wet developer and does not impair fixing properties.

In order to solve the above problems, a wet developer of the present invention is a wet developer containing toner particles, a carrier liquid, and a dispersant, wherein the toner particles contain a polyester resin, The acid value is not less than 22 mgKOH / g and not more than 87 mgKOH / g, including phthalic acid and trimellitic acid as acid components, and the ratio of trimellitic acid is 12 by mass ratio to the total acid components. % To 57 %, and the dispersant contains a basic polymer dispersant, and the viscosity η ₁ of the wet developer at a steady shear rate of 1 s ⁻¹ and the viscosity η of the wet developer at 1000 s ⁻¹ . the viscosity ratio of _{1000 (η 1} / _{η 1000)} is Ri 14-8902 der, the polyester resin is a glass transition temperature Tg of 61.1 ° C. or higher, or less 84.5 ° C., the toner The ratio of the dispersant to the particles is 0.25 to 4.4% .

The basic polymer dispersant preferably has an amine, amide, pyrrolidone, or imine in the molecule.

In a wet developer containing toner particles, an insulating solvent, and a dispersant, as a toner,
Mainly polyester resin with phthalic acid and tri- or higher functional aromatic acid as acid component, and using a basic polymer dispersant as the dispersant, the storage stability as a wet developer is maintained. However, it is possible to provide a wet developer having characteristics that do not impair fixing properties.

Wet development using a wet developer is used in image forming apparatuses such as copiers, simple printers, and printers. In general, an electrophotographic image forming process is commonly used for these. First, the electrophotographic wet-type image forming unit will be described with reference to FIG. 1, and further, the fixing property of the toner image developed with the wet developer and transferred to the recording material and the storage stability of the wet developer will be described. The constitution of the wet developer relating to the property, particularly the binder resin of the toner will be described.

(Configuration and functional operation of image forming apparatus)
FIG. 1 shows an example of the overall configuration of the image forming apparatus according to the present embodiment. The overall configuration of the image forming apparatus will be described with reference to FIG. However, only the components related to the image forming process are shown. The components related to the feeding, transporting, and discharging of the recording material are simply shown.

In the image forming apparatus 10 of FIG. 1, a photosensitive drum 1 as an image carrier, a charging device 2,
An exposure device 3, a wet developing device 4, and a cleaning device 6 are provided. The image forming apparatus 10 also
An intermediate transfer roller 5 as an intermediate transfer member and a secondary transfer roller 7 are provided.

In FIG. 1, only one wet developing device 4 is disposed, but a plurality of wet developing devices 4 may be disposed for color image formation. The color development method, the presence / absence of intermediate transfer, and the like may be set arbitrarily, and an arbitrary arrangement configuration corresponding to the method can be taken. In this example of the image forming apparatus, the intermediate transfer roller 5 is used, but an intermediate transfer belt may be used.

The photosensitive drum 1 has a cylindrical shape with a photosensitive layer (not shown) formed on the surface thereof, and rotates in the direction of arrow A in FIG. On the outer periphery of the photosensitive drum 1, a cleaning device 6, a charging device 2, an exposure device 3, a wet developing device 4, and an intermediate transfer roller 5 are sequentially arranged along the rotation direction of the photosensitive drum 1.

  The charging device 2 charges the surface of the photosensitive drum 1 to a predetermined potential.

The exposure device 3 irradiates the surface of the photosensitive drum 1 with light to lower the charge level in the irradiated area, thereby forming an electrostatic latent image.

The wet developing device 4 develops the latent image formed on the photosensitive drum 1. That is, the wet developer is conveyed to the developing area of the photosensitive drum 1, and the toner contained in the wet developer is supplied to the electrostatic latent image on the surface of the photosensitive drum 1 to form a toner image.

In general, the wet developing device 4 bears a thin layer of a wet developer on the surface and abuts against a developing roller 41 and a developing roller 41 that develop a latent image on the photosensitive drum 1 as an image carrier. A transport roller 42 for transferring the wet developer whose liquid amount has been adjusted to the surface thereof, and a supply roller 43 that contacts the transport roller 42 and supplies the wet developer 8 in the developer tank 44 to the surface. .

In the developing process, a developing bias voltage having the same polarity as the toner is applied to the developing roller 41 of the wet developing device 4 from a power source (not shown). Photoconductor drum 1 having the same polarity as that of toner
A difference in electric field is formed in balance with the potential of the upper latent image, and toner in the developer is electrostatically attracted to the photosensitive drum 1 in accordance with the latent image, and the latent image on the photosensitive drum 1 is developed.

The intermediate transfer roller 5 is disposed so as to face the photosensitive drum 1 and rotates in the direction of arrow B while being in contact with the photosensitive drum 1. These intermediate transfer roller 5 and photosensitive drum 1
Primary transfer from the photosensitive drum 1 to the intermediate transfer roller 5 is performed.

In the primary transfer process, a transfer bias voltage having a polarity opposite to that of toner is applied to the intermediate transfer roller 5 from a power source (not shown). As a result, an electric field is formed between the intermediate transfer roller 5 and the photosensitive drum 1 at the primary transfer position, and the toner image on the photosensitive drum 1 is electrostatically adsorbed to the intermediate transfer roller 5, and the intermediate transfer roller 5 is transferred.

When the toner image is transferred to the intermediate transfer roller 5, the cleaning device 6 removes the residual toner on the photoreceptor 1, and the next image formation is performed.

The intermediate transfer roller 5 and the secondary transfer roller 7 are disposed so as to face each other with the recording material 9 interposed therebetween, and rotate in contact with each other via the recording material 9. Secondary transfer from the intermediate transfer roller 5 to the recording material 9 is performed at the nip portion between the intermediate transfer roller 5 and the secondary transfer roller 7.

The recording material 9 is conveyed in the direction of arrow C to the secondary transfer position in synchronization with the secondary transfer timing.

In the secondary transfer process, a transfer bias voltage having a polarity opposite to that of the toner is applied to the secondary transfer roller 7 from a power source (not shown). Thus, the intermediate transfer roller 5 and the secondary transfer roller 7
An electric field is formed between the intermediate transfer roller 5 and the secondary transfer roller 7, and the toner image on the intermediate transfer roller 5 is electrostatically adsorbed onto the recording material 9. 9 is transferred.

The fixing unit includes a pair of fixing rollers 9a and 9b that are arranged to face each other and rotate in contact with each other. The fixing rollers 9a and 9b are provided with heat sources, respectively. When the recording material 9 passes between the fixing rollers 9a and 9b, the recording material 9 is pressurized at a high temperature. As a result, the toner that forms a toner image on the recording material 9 is fused and fixed to the recording material 9.

(Storage stability and fixability of wet developer)
The wet developer contains a carrier liquid having a high viscosity, and the dispersibility of the toner particles in the carrier liquid affects the occurrence of aggregation between the toner particles, and the trade-off between storage stability and fixability is caused. Explain that this is connected to the relationship.

In the image forming apparatus, the toner image developed by the wet developer 8 and transferred to the recording material 9 is fixed to the recording material 9 which is usually paper by being pressurized and heated by a fixing device. (Hereinafter, the recording material is paper).

However, a toner image is originally developed using a wet developer in which toner is dispersed in a carrier liquid, and not only toner particles but also a carrier liquid is contained between toners and between toner papers. . In addition, the carrier liquid has a considerably high viscosity.

The presence of the high-viscosity carrier liquid hinders fixability during toner image fixing. For example, since the toner image and the recording material are wet with the carrier liquid, the fixability of the toner image is lowered, and the image may be crushed or disturbed during pressure fixing.

The factor that hinders the fixability of the high-viscosity carrier liquid is related to the need for high dispersibility from the viewpoint of storage stability as a wet developer. The dispersant adsorbs on the surface of the toner particles, prevents contact and aggregation between the toner particles, and maintains high dispersibility. This
Toner aggregation and sedimentation hardly occur during storage, and good storage stability can be obtained.

However, if the wet developer itself maintains high dispersibility in this way, contact and coalescence of the toner particles do not proceed during fixing, and the toner layer cannot form a condensed state where the toner particles are dense. , The fixability becomes weak. However, if the dispersibility is lowered in order to secure the fixing property, there is a risk that the storage stability cannot be maintained due to the aggregation of toner during storage of the wet developer. That is, from the viewpoint of dispersibility, storage stability and fixability are incompatible characteristics.

(Toner resin, dispersant and fixability, storage stability)
It is the wet developer according to the present embodiment that solves the above-mentioned problem relating to both storage stability and fixability as a wet developer. Although details of the wet developer according to the present embodiment will be described later, an outline of a configuration that achieves both storage stability and fixability will be described.

In the wet developer according to the exemplary embodiment, a polyester resin having a specific acid component is used as a binder resin for the toner, and the combination with a dispersant for a basic polymer makes it possible to achieve both storage stability and fixability. I am trying.

A thermoplastic polyester resin is used as the binder resin for the toner. Polyester resins have sharp melt properties and are suitable for the above-mentioned problems of fixability and storage stability.

The polyester resin is obtained by polycondensation of a polyhydric alcohol and a polybasic acid (polycarboxylic acid). As the acid component, phthalic acid and trifunctional or higher functional aromatic acid are used. The reason is that it has many unreacted carboxyl groups at the terminal.

The reason why the basic polymer dispersant is used as the dispersant is that it is stably adsorbed on the resin having a carboxyl group as described above.

The fact that the polyester resin forming the toner particles has many unreacted carboxyl groups at the ends has the following meanings.
-Unreacted groups on the surface of the toner particles capture the solvent (carrier liquid) or adsorb the above-described dispersant, so that dispersibility is improved and storage stability is improved.
-Unreacted carboxyl groups on the surface of the toner particles have a polarity, and the adhesion to the paper medium at the time of fixing is improved, so that the fixing property can be improved.
The resin on the surface of the toner particles tends to have a three-dimensional structure, and by preventing the carrier liquid from entering the resin, the influence of the carrier liquid during fixing is suppressed and the fixability is improved.
When the polyester resin is three-dimensionally structured, the glass transition temperature Tg is increased, and the storage stability is improved by making the toner particle surface hard.

In this way, the wet developer according to the present embodiment achieves both storage stability and fixability.

(Structure of wet developer)
The configuration of the wet developer according to the embodiment of the present invention will be described.

As already stated, in the wet developer according to the present embodiment, by using a polyester resin having a specific acid component as a binder resin of the toner, and in combination with a basic polymer dispersant, Both storage stability and fixability are achieved.

First, the configuration of a general wet developer will be described, and then the configuration of the wet developer according to the present embodiment will be described.

<General wet developer composition>
A general wet developer will be described. In a wet developer, colored toner particles are dispersed at a high concentration in a carrier liquid which is a solvent. In addition, additives such as a dispersant and a charge control agent may be appropriately selected and added to the wet developer.

As the carrier liquid, an insulating, non-volatile solvent at room temperature is used. As the non-volatile solvent, insulating oil, for example, general liquid paraffin such as Moresco White or Isopar, silicon oil, or the like is used.

The toner particles mainly contain a resin and a pigment or dye for coloring. The resin has a function of uniformly dispersing pigments and dyes in the resin and a function as a binder when being fixed to the recording material.

Examples of the resin include polystyrene resin, styrene-acrylic resin, acrylic resin,
A thermoplastic resin such as a polyester resin, an epoxy resin, a polyamide resin, a polyimide resin, or a polyurethane resin is used. A plurality of these resins may be used in combination.

Commercially available pigments and dyes used for coloring the toner are also used. For example, carbon black, bengara, titanium oxide, silica, phthalocyanine blue, phthalocyanine green, sky blue, benzidine yellow, lake red D, etc. can be used as the pigment. Solvent red 27, acid blue 9, or the like is used as the dye.

  As the dispersant, a general oil-soluble dispersant is used.

The wet developer is prepared based on commonly used techniques. For example, the resin and the pigment are melt kneaded using a pressure kneader, a roll mill or the like at a predetermined blending ratio and uniformly dispersed, and the obtained dispersion is finely pulverized by, for example, a jet mill. Further, the obtained fine powder is classified by, for example, an air classifier to obtain a colored toner having a predetermined particle size.

Subsequently, the obtained toner is mixed with an insulating oil as a carrier liquid at a predetermined blending ratio. This mixture is uniformly dispersed by a dispersing means such as a ball mill to obtain a wet developer.

The volume average particle diameter of the toner is suitably in the range of 0.1 μm or more and 5 μm or less. When the average particle diameter of the toner is less than 0.1 μm, the developability is greatly lowered. On the other hand, the average particle size is 5μ
If it exceeds m, the image quality deteriorates.

The ratio of the toner particle mass to the wet developer mass is suitably about 10 to 50%. If it is less than 10%, toner particles are liable to settle, and there is a problem with the stability over time during long-term storage. Further, in order to obtain a required image density, it is necessary to supply a large amount of developer, the carrier liquid adhering to the paper increases, and it must be dried at the time of fixing, and steam is generated, resulting in environmental problems. If it exceeds 50%, the viscosity of the wet developer becomes too high, making it difficult to manufacture and handle.

The viscosity of the wet developer is preferably from 0.1 mPa · s to 10,000 mPa · s at 25 ° C. When it is 10,000 mPa · s or more, it becomes difficult to stir the carrier liquid and the toner, and the burden on the apparatus surface for obtaining a uniform wet developer is large.

<Configuration of Wet Developer According to this Embodiment>
The wet developer according to the present embodiment further has the following configuration as compared with the configuration of the conventional wet developer. The toner particles are made of a polyester resin as a binder resin. The acid component of the polyester resin is composed of phthalic acid and a tri- or higher functional aromatic acid. These acid components and alcohol are subjected to condensation polymerization to form a polyester resin. Further, a basic polymer dispersant is adsorbed on the surface of the toner particles as a dispersant. In this state, the toner particles are dispersed in an insulating solvent.

The combination of the structure of the polyester resin as the binder resin (having many carboxyl groups at the terminal by an acid component composed of phthalic acid and a trifunctional or higher functional aromatic acid) and the above basic polymer dispersing agent The present invention provides a wet developer having excellent fixing characteristics and storage stability. Details of these configurations will be described below.

(Binder resin for toner)
The binder resin of the toner is composed of a thermoplastic polyester resin. The polyester resin has a sharp melt property and is suitable for achieving both fixing property and storage stability as described above. The polyester resin is obtained by polycondensation of a polyhydric alcohol and a polybasic acid (polycarboxylic acid).

The polybasic acid has phthalic acid and trifunctional or higher functional aromatic acid as essential components.
The phthalic acid is isophthalic acid or terephthalic acid. Both are aromatic polybasic acids, and easily obtain desired thermal characteristics as compared with aliphatic polybasic acids. By containing a tri- or higher functional aromatic acid, the number of carboxyl groups of the resin is increased, and the adhesion to the medium is improved. Moreover, since it becomes easy to bridge | crosslink, it becomes easy to raise glass transition temperature Tg.

The acid value of the polyester resin is preferably 20 mgKOH / g or more and 100 mgKOH / g or less. When the acid value is lower than 20 mgKOH / g, it is difficult to improve the system speed from the viewpoint of fixability. When the acid value is higher than 100 mgKOH / g, it becomes difficult to produce a polyester resin while maintaining a predetermined molecular weight, and various characteristics of the wet developer tend to be unstable.

The glass transition temperature Tg of the polyester resin is preferably 60 ° C. or higher and 85 ° C. or lower. T
When g is lower than 60 ° C., the storage stability is slightly deteriorated. If Tg rises above 85 ° C., the amount of heat required for fixing increases excessively, which is not preferable.

Examples of the trifunctional or higher functional aromatic acid include trimellitic acid, trimesic acid, and pyromellitic acid. Of these, trimellitic acid, which is the most common and easily available, is preferably used. Trimellitic acid is desirably contained in a mass ratio of 5% to 70%, preferably 10% to 50%, based on the total acid component. If it is 5% or less, it is difficult to obtain a desired effect (improving fixability), and if it is 70% or more, crosslinking proceeds and it is difficult to obtain desired thermal characteristics (Tg). The phthalic acid is isophthalic acid or terephthalic acid, and terephthalic acid is more preferable because it has higher crystallinity and easily obtains a rigid resin.

  Furthermore, in order to suppress the formation of sticky precipitates and improve the redispersibility, the ratio of trifunctional or higher aromatic acid is 10% or more and 70% by mass ratio to the total acid components. Hereinafter, it is preferably 20% or more and 60% or less.

As an acid component, you may include components other than said trimellitic acid and phthalic acid. For example,
Malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid,
Itaconic acid and these acid anhydrides are mentioned.

Examples of the polyhydric alcohol include, but are not limited to, propylene glycol such as ethylene glycol, diethylene glycol, triethylene glycol, and 1,2-propylene glycol, butanediol such as 1,4-butanediol, neo Pentyl 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, Alicyclic and aromatic diols such as ring or polycyclic diols, glycerin,
And triols such as trimethylolpropane. These can be used alone or in admixture of two or more.

The desired polyester resin is polymerized by polycondensation of the above polybasic acid and polyhydric alcohol. As the polycondensation method, generally known polycondensation methods can be used. Although it varies depending on the type of raw material monomer, it is generally carried out at a temperature of about 150 ° C to 300 ° C.
Moreover, it can carry out on arbitrary conditions, such as using inert gas as atmospheric gas, using various solvent, or making the pressure in reaction container into a normal pressure or pressure reduction. An esterification catalyst may be used to promote the reaction. As the esterification catalyst, metal organic compounds such as tetrabutyl zirconate, zirconium naphthenate, tetrabutyl titanate, tetraoctyl titanate, 3/1 stannous oxalate / sodium acetate, etc. can be used. What does not color is preferable. Moreover, you may use alkyl phosphate, allyl phosphate, etc. as a catalyst or a hue regulator.

In order to control the molecular weight of the product polyester resin, polymerization temperature, reaction system pressure,
What is necessary is just to adjust reaction time etc. The acid value can be controlled by the molar ratio of the carboxylic acid to be reacted and the alcohol, the molecular weight of the polymer, and the like. In addition to polyester resin, binder resin may be styrene-acrylic copolymer resin, styrene-acrylic modified polyester resin, polyolefin copolymer (especially ethylene copolymer), epoxy resin, rosin modified phenolic resin as required. Further, a resin such as rosin-modified maleic acid resin, paraffin wax or the like may be used by mixing an appropriate amount in a range of 30% by mass or less of the total mass.

(Dispersant)
A basic polymer dispersant is used as the dispersant. In particular, those having an amine, amide, pyrrolidone, or imine in the molecule are preferred from the viewpoint of adsorptivity to the polyester resin.

As the basic polymer dispersant, polyalkylene polyamine, modified polyurethane, polyester polyamine, and the like can be used.

As a specific example of the dispersant, “Disperbyk-109” (BYK Chemie)
Alkylolaminoamide) ”and“ Disperbyk-130 (unsaturated polycarboxylic acid polyaminoamide) ”.

  In addition, “S13940 (polyesteramine type), S17000, S18000, S19000 (fatty acid amine type), S11200” manufactured by Abyssia, etc. may be mentioned.

Furthermore, ISP V-216, V-220, W-660 (polyvinylpyrrolidone having a long-chain alkyl group) and the like can be mentioned.

It is preferable to add 1% to 100% of the above polymer dispersant with respect to the toner particles. 1
If it is less than or equal to%, the dispersibility decreases, and if it is more than 100%, the conductivity of the liquid increases, resulting in a problem in chargeability.

(Carrier liquid)
The carrier liquid is not particularly limited. Resistance value that does not disturb the electrostatic latent image (10 ¹¹ to 10 ¹⁶ Ω
(About cm). Furthermore, a solvent having no odor and toxicity and having a relatively high flash point is preferable. In general, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes and the like can be mentioned. In particular, a normal paraffin solvent and an isoparaffin solvent are preferable in terms of odor, harmlessness, and cost. Specifically, Moresco White [P40 (flash point 140 ° C.), P60 (flash point 170 ° C.), P120 (flash point 200 ° C.), made by Matsumura Oil Research Co., Ltd.], Isopar (made by Exxon Chemical), shell Zor 71 (manufactured by Shell Petrochemical Co., Ltd.), IP solvent 1620 (abbreviated as IP1620), IP solvent 2028 (abbreviated as IP2028, flash point 84 ° C.) (all manufactured by Idemitsu Petrochemical Co., Ltd.) and the like.

(Coloring agent)
The colorant is not particularly limited, and the following pigments can be used.

A typical colorant for black is carbon black. Examples of colorants other than black include yellow pigments, magenta pigments, and cyan pigments. Color image formation is performed by subtractive color mixing based on these pigment colors.

As a cyan pigment, for example, Color Index (CI) Pigment Blu
Examples thereof include copper phthalocyanine blue cyan pigments such as e15: 1 and 15: 3.

Examples of magenta pigments include C.I. I. Pigment Red 48, 57 (Kermin 6B)
Azo lake-based magenta pigments such as 5, 23, 60, 114, 146 and 186, insoluble azo-based magenta pigments, thioindigo-based magenta pigments, C.I. I. Pigment Red122
And quinacridone-based magenta pigments such as 209.

Examples of yellow pigments include C.I. I. Pigment Yellow 12, 13, 14, 1
Examples thereof include disazo yellow pigments represented by 7, 55, 81, 83, and the like.

The amount of the colorant added to the binder resin is preferably about 5 to 30% by mass with respect to the resin.

Furthermore, the wet developer of the present invention has thixotropy and resistance to sedimentation. When the wet developer settles during storage, a sticky precipitate is formed, which may be very difficult to redisperse. This sticky precipitate can be redispersed with strong agitation with a small amount, but there is no problem, but the sticky precipitate generated when storing a large amount of developer is large, extremely hard, like a hard rubber Therefore, there is a problem that it is very difficult to redisperse and handling is difficult. In contrast, in the present invention, the viscosity ratio (η ₁ / η ₁₀₀₀ ) between the viscosity η ₁ of the wet developer at a steady shear rate of 1 s ⁻¹ and the viscosity η ₁₀₀₀ of the wet developer at _{1000 s} ⁻¹ is 10 to 10 By setting it as 10,000, sedimentation resistance can be improved. Here, when the viscosity ratio is less than 10, sedimentation is likely to occur, and when the viscosity ratio is greater than 10,000, it is difficult to feed the developer. More preferably, the viscosity ratio is 20 to 1000.
Thixotropic is an abbreviation for thixotropy, a non-Newtonian substance that has time-dependent flow characteristics, the apparent viscosity decreases with time at a constant shear rate, and the shear deformation force is excluded. It is a property that gradually recovers. The viscosity used in the present invention is an apparent viscosity, which can be measured using a rotational viscometer such as a conical disk viscometer or a rotating cone viscometer.

The viscosity of the wet developer used in the present invention is not particularly limited, but in order to further improve the handleability during use and storage, the viscosity at a steady shear rate of 1 s ⁻¹ is 10 to 100,000 mPa · s, The viscosity at a shear rate of 1000 s ⁻¹ is preferably ¹ to 1,000 mPa · s.

  In addition, by using a polyester resin in which the ratio of trifunctional or higher aromatic acid is 10% or more and 60% or less by mass ratio with respect to the total acid components, the formation of sticky precipitates is suppressed. Redispersibility can be improved.

An example in which the above-described wet developer was prepared and the fixability and storage stability were actually evaluated by an image forming process is shown below.

  Each wet developer used in Examples and Comparative Examples (see Table 2-1) to be described later was prepared as follows.

-10 kinds of polyester resins A to J are synthesized as binder resin for the toner.
-10 kinds of polyester resins A to J are used to obtain 10 kinds of coarsely pulverized toners (the amount of pigment added is shown in parts by mass with the resin as 100 parts),
A developer and a developer used in Examples and Comparative Examples to be described later were prepared by mixing a dispersant and a carrier liquid with any of 10 types of coarsely pulverized toners (10 types of polyester resins). The addition amount is shown in parts by mass with 100 parts of solvent).

(Synthesis of polyester resin)
Table 1 shows the details of Production Examples 1 to 10 in which 10 kinds of polyester resins (polyester resins A to J) were synthesized.

Details of each production example will be described. For the synthesis of the polyester resin, “Mw” represents “mass average molecular weight”, and “Mn” represents “number average molecular weight”. Tg is a glass transition temperature.

<Measurement of molecular weight>
In the following, Mw and Mn were calculated from the results of gel permeation chromatography, respectively. Gel permeation chromatography is a high-performance liquid chromatograph pump TRI ROTAR-V (manufactured by JASCO Corporation), UV spectroscopic detector UVDEC.
-100-V type (manufactured by JASCO Corporation), 50 cm long column Shodex GPC A-
803 (manufactured by Showa Denko KK) was used, and from the chromatographic results, the molecular weight of the test sample was calculated as polystyrene as a standard substance, and was calculated as polystyrene-equivalent Mw and Mn.

  The test sample used was 0.05 g of binder resin dissolved in 20 ml of tetrahydrofuran (THF).

<Measurement of Tg>
The glass transition temperature Tg was measured using a differential scanning calorimeter DSC-6200 (manufactured by Seiko Instruments Inc.) under the conditions of a sample amount of 20 mg and a heating rate of 10 ° C./min.

<Measurement of acid value>
The acid value was measured under the conditions of JIS K5400 method.

<Production Example 1>
In a round bottom flask equipped with a reflux condenser, water / alcohol separator, nitrogen gas inlet tube, thermometer and stirrer, 1600 parts by mass of a propylene oxide adduct of bisphenol A (polyhydric alcohol) and 550 parts by mass of terephthalic acid Part (polybasic acid) and 340 parts by mass of trimellitic acid were added, nitrogen gas was introduced with stirring, and dehydration polycondensation or dealcoholization polycondensation was performed at a temperature of 200 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 polycondensation. A thermoplastic polyester resin (polyester resin A) was thus obtained.

The obtained polyester resin A has Mw = 7500, Mn = 2700, Tg = 62.3 ° C.
The acid value was 64.0 mgKOH / g.

<Production Example 2>
Same as Production Example 1 except that 640 parts terephthalic acid and 160 parts trimellitic acid.

The obtained polyester resin B has Mw = 8800, Mn = 3600, Tg = 66.3 ° C.
The acid value was 26.0 mgKOH / g.

<Production Example 3>
The same procedure as in Production Example 1 except that the propylene oxide adduct of bisphenol A was changed to an ethylene oxide adduct of bisphenol A, and 720 parts of terephthalic acid and 100 parts of trimellitic acid were used.

The obtained polyester resin C has Mw = 6800, Mn = 2500, Tg = 61.1 ° C.
The acid value was 22 mgKOH / g.

<Production Example 4>
The same as Production Example 1 except that the propylene oxide adduct of bisphenol A was changed to the ethylene oxide adduct of bisphenol A.

The obtained polyester resin D has Mw = 7400, Mn = 2600, Tg = 70.3 ° C.
The acid value was 71.0 mgKOH / g.

<Production Example 5>
The same procedure as in Production Example 1 except that the propylene oxide adduct of bisphenol A was changed to an ethylene oxide adduct of bisphenol A and terephthalic acid was added to 450 parts and trimellitic acid was added to 590 parts.

  The obtained polyester resin E had Mw = 14000, Mn = 4700, Tg = 84.5 ° C., and acid value = 87 mgKOH / g.

<Production Example 6>
The same as Production Example 4 except that isophthalic acid was used instead of terephthalic acid.

The obtained polyester resin F has Mw = 12000, Mn = 4200, Tg = 80.3.
C., acid value = 55.0 mgKOH / g.

<Production Example 7>
The same as Production Example 1 except that trimellitic acid was used and 800 parts of isophthalic acid was used.

The obtained polyester resin G has Mw = 8000, Mn = 3200, Tg = 64.3 ° C.
The acid value was 8.0 mgKOH / g.

<Production Example 8>
The same as Production Example 1 except that fumaric acid was used instead of terephthalic acid.

The obtained polyester resin H has Mw = 4600, Mn = 2200, Tg = 54.8 ° C.
The acid value was 33.0 mgKOH / g.

<Production Example 9>
Same as Production Example 1 except that 760 parts of terephthalic acid and 60 parts of trimellitic acid were used.

The obtained polyester resin I has Mw = 9100, Mn = 3800, Tg = 72.2 ° C.
The acid value was 17 mgKOH / g.

<Production Example 10>
This example is the same as Production Example 1 except that 580 parts of isophthalic acid is used instead of terephthalic acid, and 180 parts of hemimellitic acid is used instead of trimellitic acid.

The obtained polyester resin J has Mw = 8900, Mn = 3600, Tg = 68.4 ° C.
The acid value was 33 mgKOH / g.

(Production of wet developer)
With the composition shown in Table 2-1, for each example and each comparative example, a coarsely pulverized toner is obtained from the polyester resins A to J to prepare a wet developer. Further, fixability, storage stability, and sedimentation resistance are obtained. The sample was subjected to a redispersibility test.

<Example 1>
100 parts by weight of polyester resin A and 15 parts by weight of copper phthalocyanine blue are sufficiently mixed with a Henschel mixer, melted and mixed with a twin-screw extruder kneader, cooled, then coarsely pulverized, and an average particle size of 6 μm with a jet pulverizer. Finely ground.

The mixture was melt kneaded using a twin-screw extruder with a heating temperature of 100 ° C. in a biaxial roll, and the resulting mixture was cooled and coarsely pulverized to obtain a coarsely pulverized toner.

  34 parts by mass of the toner particles, 0.25 parts by mass of V-220 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 140 ° C., Moresco White P-40 (manufactured by Matsumura Oil)), zirconia 100 parts by mass of beads were mixed and stirred for 120 hours in a sand mill to obtain a wet developer. The volume average particle diameter was 3.3 μm.

<Example 2>
After 100 parts by mass of polyester resin B and 10 parts by mass of carbon black (MA-100, manufactured by Mitsubishi Kasei Co., Ltd.) were sufficiently mixed with a Henschel mixer, coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 0.25 parts by mass of Solsperse S13940 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 84 ° C., IP-2028 (produced by Idemitsu Kosan Co., Ltd.)), 100 parts by mass of zirconia beads The parts were mixed and stirred in a sand mill for 120 hours to obtain a wet developer. The volume average particle size was 3.0 μm.

<Example 3>
After 100 parts by mass of polyester resin C and 20 parts by mass of quinacridone were sufficiently mixed with a Henschel mixer, coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 0.25 part by mass of V-216 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 140 ° C., Moresco White P-40 (manufactured by Matsumura Oil)), zirconia 100 parts by mass of beads were mixed and stirred for 120 hours in a sand mill to obtain a wet developer. The volume average particle diameter was 2.7 μm.

<Example 4>
100 parts by mass of polyester resin E and 15 parts by mass of copper phthalocyanine blue were sufficiently mixed with a Henschel mixer and then mixed sufficiently, and then a coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 0.25 part by mass of V-220 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 84 ° C., IP2028), and 100 parts by mass of zirconia beads are mixed together in a sand mill. For 120 hours to obtain a wet developer. The volume average particle diameter was 2.8 μm.

<Example 5>
100 parts by mass of polyester resin F and 15 parts by mass of copper phthalocyanine blue were sufficiently mixed with a Henschel mixer, and then sufficiently mixed, and then a coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 0.25 parts by mass of S13940 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 140 ° C., Moresco White P-40 (manufactured by Matsumura Oil)), zirconia beads 100 Mass parts were mixed and stirred in a sand mill for 120 hours to obtain a wet developer. The volume average particle diameter was 2.8 μm.

<Example 6>
100 parts by mass of polyester resin A and 15 parts by mass of copper phthalocyanine blue were sufficiently mixed with a Henschel mixer and then mixed sufficiently, and then a coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 0.5 part by mass of V-220 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 140 ° C., Moresco White P-40 (manufactured by Matsumura Oil)), zirconia 100 parts by mass of beads were mixed and stirred for 120 hours in a sand mill to obtain a wet developer. The volume average particle diameter was 3.3 μm.

<Example 7>
100 parts by mass of polyester resin B and 10 parts by mass of carbon black were sufficiently mixed with a Henschel mixer and then mixed sufficiently, and then a coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 1 part by mass of S11200 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 84 ° C., IP2028) and 100 parts by mass of zirconia beads are mixed and stirred in a sand mill for 120 hours. Thus, a wet developer was obtained. The volume average particle size was 3.0 μm.

<Example 8>
100 parts by mass of polyester resin C and 20 parts by mass of quinacridone were sufficiently mixed with a Henschel mixer and then mixed sufficiently, and then coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 1.5 parts by mass of V-220 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 140 ° C., Moresco White P-40 (manufactured by Matsumura Oil)), zirconia 100 parts by mass of beads were mixed and stirred for 120 hours in a sand mill to obtain a wet developer. The volume average particle diameter was 2.7 μm.

< Reference Example 1 >
100 parts by mass of polyester resin E and 15 parts by mass of copper phthalocyanine blue were sufficiently mixed with a Henschel mixer and then mixed sufficiently, and then a coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 2 parts by mass of V-220 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 84 ° C., IP2028), and 100 parts by mass of zirconia beads are mixed, and 120 parts by sand mill. The mixture was stirred for a time to obtain a wet developer. The volume average particle diameter was 2.8 μm.

< Reference Example 2 >
100 parts by mass of polyester resin I and 15 parts by mass of copper phthalocyanine blue were sufficiently mixed with a Henschel mixer, and then sufficiently mixed, and then a coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 0.2 part by mass of V-220 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 140 ° C., Moresco White P-40 (manufactured by Matsumura Oil)), zirconia 100 parts by mass of beads were mixed and stirred for 120 hours in a sand mill to obtain a wet developer. The volume average particle size was 2.6 μm.

< Reference Example 3 >
100 parts by mass of polyester resin J and 17 parts by mass of copper phthalocyanine blue were sufficiently mixed with a Henschel mixer, and then sufficiently mixed, and then a coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 0.25 part by mass of V-216 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 140 ° C., Moresco White P-40 (manufactured by Matsumura Oil)), zirconia 100 parts by mass of beads were mixed and stirred for 120 hours in a sand mill to obtain a wet developer. The volume average particle size was 3.2 μm.

< Reference Example 4 >
After 100 parts by mass of polyester resin 1 and 15 parts by mass of copper phthalocyanine blue were sufficiently mixed by a Henschel mixer, coarsely pulverized toner was obtained in the same manner as in Example 1.

25 parts by mass of the toner particles, 2 parts by mass of Solsperse S11200 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 200 ° C., Moresco White P-120 (manufactured by Matsumura Oil)), 100 parts by mass of zirconia beads The parts were mixed and stirred in a sand mill for 120 hours to obtain a wet developer. The volume average particle diameter was 1.6 μm.

< Reference Example 5 >
After 100 parts by mass of polyester resin B and 10 parts by mass of carbon black (MA-100, manufactured by Mitsubishi Kasei Co., Ltd.) were sufficiently mixed with a Henschel mixer, coarsely pulverized toner was obtained in the same manner as in Example 1.

25 parts by weight of the toner particles, 2 parts by weight of Solsperse S13940 as a basic polymer dispersant, 100 parts by weight of liquid paraffin (flash point 200 ° C., Moresco White P-120 (manufactured by Matsumura Oil)), 100 parts by weight of zirconia beads The parts were mixed and stirred in a sand mill for 120 hours to obtain a wet developer. The volume average particle diameter was 2.7 μm.

< Reference Example 6 >
After sufficiently mixing 100 parts by weight of polyester resin D and 20 parts by weight of quinacridone with a Henschel mixer, coarsely pulverized toner was obtained in the same manner as in Example 1.

25 parts by mass of this toner particle, Disperbyk-109 as a basic polymer dispersant
2 parts by mass, 100 parts by mass of liquid paraffin (flash point 140 ° C., Moresco White P-40 (manufactured by Matsumura Oil)) and 100 parts by mass of zirconia beads are mixed and stirred for 120 hours in a sand mill. Obtained. The volume average particle diameter was 3.1 μm.

< Reference Example 7 >
After 100 parts by weight of polyester resin F and 17 parts by weight of copper phthalocyanine blue having been subjected to basic treatment were sufficiently mixed with a Henschel mixer, coarsely pulverized toner was obtained in the same manner as in Example 1.

  25 parts by mass of the toner particles, 1.5 parts by mass of V-216 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 170 ° C., Moresco White P-60 (manufactured by Matsumura Oil)), zirconia 100 parts by mass of beads were mixed and stirred for 120 hours in a sand mill to obtain a working wet developer. The volume average particle diameter was 2.4 μm.

< Reference Example 8 >
After 100 parts by mass of polyester resin A and 15 parts by mass of basic copper phthalocyanine blue were sufficiently mixed with a Henschel mixer, coarsely pulverized toner was obtained in the same manner as in Example 1.

  34 parts by mass of the toner particles, 2.5 parts by mass of V-220 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 140 ° C., Moresco White P-40 (manufactured by Matsumura Oil)), zirconia 100 parts by mass of beads were mixed and stirred for 120 hours in a sand mill to obtain a wet developer. The volume average particle diameter was 3.3 μm.

< Reference Example 9 >
After 100 parts by mass of polyester resin B and 10 parts by mass of carbon black were sufficiently mixed with a Henschel mixer, a coarsely pulverized toner was obtained in the same manner as in Example 1.

34 parts by mass of the toner particles, 3 parts by mass of S13940 as a basic polymer dispersant, 100 parts by mass of liquid paraffin (flash point 84 ° C., IP2028), zirconia beads 100
Mass parts were mixed and stirred in a sand mill for 120 hours to obtain a wet developer. The volume average particle size was 3.0 μm.

<Example 9 >
The same as Example 2 except that 11 parts by mass of toner particles were used. The obtained wet developer had a volume average particle size of 3.0 μm.

<Example 10 >
The same as Example 2 except that 54 parts by mass of toner particles were used. The obtained wet developer had a volume average particle size of 3.0 μm.

<Example 11 >
Example 2 is the same as Example 2 except that 100 parts by mass of toner particles are used. The obtained wet developer had a volume average particle size of 3.0 μm.

<Comparative Example 1>
Except for using the polyester resin G, it is the same as Reference Example 4 .

<Comparative example 2>
The same as Reference Example 5 except that the polyester resin H is used.

<Comparative Example 3>
The same as Reference Example 5 except that Solsperse S3000 (acid dispersant, manufactured by Avicia) was used as the dispersant.

<Comparative example 4>
The same as Reference Example 5 except that the polyester resin H was used and 3.75 parts by mass of the dispersant was used.

<Comparative Example 5>
Example 3 is the same as Example 3 except that the polyester resin G is used.

<Comparative Example 6>
The same as Example 4 except that the polyester resin H was used.

(Evaluation of fixability, storage stability, sedimentation resistance, and redispersibility)
For each of the wet developers of Examples 1 to 11, Reference Examples 1 to 9 , and Comparative Examples 1 to 6 produced as described above, the fixability, storage stability, sedimentation resistance, and redispersibility were evaluated. .

<Image forming process conditions>
A toner image for each wet developer was formed and fixed using the image forming apparatus having the configuration shown in FIG. The process conditions for image formation are as follows.

The system speed was 180 mm / s, and negatively charged OPC was used as the photoreceptor. The charging potential of the photosensitive member was −700 v, the developing voltage was −450 v, and the transfer voltage was +600 v.

<Fixability evaluation method>
A fixability test was performed on a fixed sample on which a toner image was formed and fixed by the above process.

In the sample, the development and transfer conditions of the solid image were adjusted so that the toner adhesion amount on the medium was 3 g / m ² for each example and comparative example. The system speed is 180mm / s,
Heat roller fixing (180 ° C. × nip time 40 ms) was performed, and an image sample was taken out.

The fixability of each sample was evaluated by a tape peeling test. The reflection density before and after peeling using a tape (3M mending tape) was measured, and the evaluation was made by the density ratio before and after. The following ○ × evaluation was performed. ◎ and ○ are good, and × is impossible.

A: Image density ratio is 95% or more,
○: Image density ratio is 90% or more and less than 95%,
X: Ratio of image density is less than 90%.

<Storage stability evaluation method>
A storage stability test was performed on the wet developer for each example and comparative example.

The wet developer to be evaluated is put in a glass bottle and stored in a thermostat set at 50 ° C. for 24 hours. The volume average particle size is measured before and after storage (measured by Shimadzu Corporation, SALD-2200).

A judgment table was formed by the value of average particle diameter after storage / average particle diameter before storage. It is the following ○ × evaluation, where ○ is good and × is not possible.

○: Average particle diameter after storage / average particle diameter before storage is 1.2 or less,
X: Average particle diameter after storage / average particle diameter before storage exceeds 1.2.

(Settling resistance evaluation method)
The wet developers obtained in the above Examples and Comparative Examples were allowed to stand for 1 week in an environment of 25 to 30 ° C. Thereafter, the state of the toner in the wet developer was visually confirmed and evaluated according to the following four criteria.
A: No settling of toner particles is observed (the supernatant is generally less than 5%).
○: Sedimentation of toner particles is hardly observed (almost the supernatant is 5 to 10%).
Δ: Slight settling of toner particles is observed (generally the supernatant exceeds 10%).
X: Sedimentation of toner particles is clearly observed (generally the supernatant exceeds 40%).

(Redispersibility evaluation method)
The wet developers obtained in the above Examples and Comparative Examples were allowed to stand for 1 week in an environment of 25 to 30 ° C. Thereafter, the state of the toner of the wet developer was visually confirmed and evaluated according to the following four criteria.
A: Re-dispersed at a tilted degree (no sedimentation occurs in the first place).
○: Re-dispersed when shaken.
Δ: Re-dispersed if stirred vigorously with a spatula or the like.
X: Not redispersed (including solidification and generation of coarse particles).

(Viscosity measurement)
Using a rotational rheometer AERES-RFS manufactured by TA Instruments, measurement was performed at a steady shear rate of 1 s ^-1 and 1000 s ^-1 with a 50 mm cone plate. The measurement temperature is 25 ° C.

  The evaluation results for each example and comparative example are shown in Table 2-2. Further, in order to examine the influence of the toner concentration (Tc), toner particles having the composition shown in Table 3-1 were prepared. The evaluation results are shown in Table 3-2.

<Evaluation results>
In Examples 1 to 11 , good results were obtained in both fixability and storage stability.

Comparative Example 1 is different from Reference Example 4 in that polyester resin G is used. The polyester resin G contains isophthalic acid as an acid component, but does not contain trimellitic acid. That is, it does not contain a trifunctional or higher functional aromatic acid. Accordingly, it can be said that the polyester resin 5 cannot be said to have a sufficiently large number of unreacted carboxyl groups at the ends, and therefore, the adhesiveness to the media is not sufficiently improved, and the fixing property is considered to be deteriorated. In fact, the small number of unreacted groups at the terminal can be estimated from 8.0 mg KOH / g, which is an extremely low acid value as compared with Examples 1 to 11 . Moreover, the comparative example 5 uses the polyester resin G in Example 3. FIG. Since the trifunctional or higher aromatic acid was not included, the fixing property was deteriorated.

Comparative Example 2 is different from Reference Example 5 in that polyester resin H is used. The polyester resin H contains fumaric acid instead of isophthalic acid as an acid component. However, fumaric acid is an aliphatic acid and is thermally weak. Therefore, it is considered that the fumaric acid added to the polyester resin H cannot be a substitute component of phthalic acid, and the storage stability is lowered. Actually, the glass transition temperature Tg is 54.8 ° C., which is lower than those of Examples 1 to 11 . Further, Comparative Example 4 is obtained by increasing the amount of dispersant in Comparative Example 2. However, the viscosity ratio was small and it was easy to settle, and the redispersibility also decreased.

Comparative Example 3 is different from Reference Example 6 in that an acidic dispersant is used. A basic polymer dispersant, particularly a dispersant having amine, imine, amide, pyrrolidone or the like in the molecule, is stably adsorbed on the carboxyl group of the polyester resin. The acidic dispersant does not contain a group that stably adsorbs to such a carboxyl group. As a result, the acidic dispersant cannot be stably adsorbed to the resin, and the toner cannot be uniformly dispersed. Therefore, the toner particle size is 5.1 μm and the toner is aggregated.

  Comparative Example 6 differs from Example 3 in that polyester resin H is used. As the acid component, fumaric acid is contained instead of isophthalic acid. Fixability, storage stability, and redispersibility all decreased.

  Further, as shown in Table 3-2, even when the toner concentration was changed to 10 to 50%, the fixing property, the storage stability, the sedimentation resistance, and the redispersibility were excellent. .

Thus, according to the present embodiment, in a wet developer containing toner particles, an insulating solvent, and a dispersant, phthalic acid and trifunctional or higher functional aromatic acid are used as the acid component as the toner. Wet polyester resin with a characteristic that does not hinder the fixability while maintaining storage stability as a wet developer by using a basic polymer dispersant as a dispersant. Developers can be provided.

In addition, the above-mentioned embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is sectional drawing which shows the schematic structural example of the image formation part in a wet image forming apparatus.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging device 3 Exposure device 4 Wet development device 5 Intermediate transfer member (intermediate transfer roller)
6 Cleaning device (cleaner blade)
7 Secondary transfer roller 8 Wet developer 9 Recording material 9a, 9b Fixing device (fixing roller)
10 Image Forming Device 41 Developing Roller (Developer Carrier)
42 Conveyance roller 43 Supply roller 44 Developer tank

Claims (2)

A wet developer including toner particles, a carrier liquid, and a dispersant, wherein the toner particles include a polyester resin, and the polyester resin has an acid value of 22 mgKOH / g or more and 87 mgKOH / g or less. Wherein the acid component contains phthalic acid and trimellitic acid, and the ratio of the trimellitic acid is 12 % or more and 57 % or less by mass ratio with respect to the total acid component. The viscosity ratio (η ₁ / η ₁₀₀₀ ) between the viscosity η ₁ of the wet developer at a steady shear rate of 1 s ⁻¹ and the viscosity η ₁₀₀₀ of the wet developer at _{1000 s} ⁻¹ is 14 to 8902 der is, the polyester resin is a glass transition temperature Tg of 61.1 ° C. or higher, or less 84.5 ° C., the ratio of the dispersant to the toner particles is 0.25 to 4.4% A wet developer characterized by the above.   2. The wet developer according to claim 1, wherein the basic polymer dispersant has amine, amide, pyrrolidone, or imine in the molecule.

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