JP2012225954A - Liquid developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid developer excellent in dispersion stability of toner particles.SOLUTION: In the liquid developer, toner particles including toner base particles having porosity of 10% or more and 70% or less, and a surface layer formed on a surface of each of the toner base particles are dispersed in insulation liquid. The toner base particles preferably comprise toner material including polyester resin and colorant. The surface layer preferably comprises material including at least one kind of compound selected from the group consisting of silicone wax and a compound having pyrrolidone skeleton. The surface layer has a through hole communicated with a pore on the surface of the toner base particle, and diameter of the through hole on the outside surface of the surface layer is preferably smaller than diameter of the pore on the surface of the toner base particle.

Description

  The present invention relates to a liquid developer.

For the developer used for developing the electrostatic latent image formed on the latent image carrier, a dry toner using a toner composed of a material containing a colorant such as a pigment and a binder resin in a dry state; and And a liquid developer (liquid toner) in which toner is dispersed in an electrically insulating carrier liquid (insulating liquid).
The method using dry toner handles solid-state toner, so there are advantages in handling, but there are concerns about adverse effects on the human body due to powder, as well as contamination due to scattering of toner, and when toner is dispersed There is a problem with uniformity. Further, the dry toner has a problem that the particles are likely to aggregate and it is difficult to sufficiently reduce the size of the toner particles, and it is difficult to form a toner image with high resolution. In addition, when the size of the toner particles is relatively small, the problem due to the powder as described above becomes more remarkable.

On the other hand, in the method using a liquid developer, the toner particles are effectively prevented from aggregating in the liquid developer, so that fine toner particles can be used, and a dry toner is used as the binder resin. A resin material having a lower softening point (lower softening temperature) than the resin material used can be used. As a result, in the method using a liquid developer, fine line image reproducibility is good, gradation reproducibility is good, color reproducibility is excellent, and it is also excellent as a high-speed image forming method. It has characteristics.
However, the conventional liquid developer has a problem that the toner particles settle during storage and the toner particles aggregate.

JP 2007-219380 A

  An object of the present invention is to provide a liquid developer having excellent dispersion stability of toner particles.

Such an object is achieved by the present invention described below.
In the liquid developer of the present invention, toner particles including toner base particles having a porosity of 10% or more and 70% or less and a surface layer formed on the surface of the toner base particles are dispersed in an insulating liquid. It is characterized by that.
Thereby, a liquid developer having excellent dispersion stability of toner particles can be provided.

In the liquid developer of the present invention, the toner base particles are preferably composed of a toner material containing a polyester resin and a colorant.
Thereby, the dispersion stability can be improved, and the energy at the time of fixing can be made smaller.
In the liquid developer of the present invention, the surface layer is preferably made of a material containing at least one compound selected from the group consisting of a silicone wax and a compound having a pyrrolidone skeleton.
Thereby, the dispersion stability of the toner particles can be made particularly excellent.

In the liquid developer of the present invention, the surface layer has a through hole communicating with a hole on the surface of the toner base particle,
The hole diameter of the through hole on the outer surface of the surface layer is preferably smaller than the hole diameter of the hole on the surface of the toner base particle.
As a result, the specific gravity of the toner particles can be reduced while effectively preventing the insulating liquid from entering the toner base particles. As a result, the dispersion stability of the toner particles can be further improved, and the storage stability can be further improved.

In the liquid developer of the present invention, the volume average particle diameter of the toner particles is 1 μm or more and 10 μm or less,
The average circularity of the toner particles is preferably 0.880 or more and 0.995 or less.
As a result, the storage stability and transfer efficiency of the liquid developer can be made particularly excellent.

In the liquid developer of the present invention, a siloxane compound that contains one functional group selected from the group consisting of an amino group, a hydroxyl group, a carboxyl group, a vinyl group, and an alkyl group as a dispersant and is soluble in the insulating liquid It is preferable to contain.
Thereby, the dispersion stability of the toner particles can be further improved.
The liquid developer of the present invention preferably contains quaternized cationic silicone as a charge control agent.
Thereby, the charging property of the liquid developer can be made particularly excellent.
In the liquid developer of the present invention, the insulating liquid is preferably composed of silicone oil.
Thereby, the productivity of the liquid developer can be made particularly excellent, and the dispersion stability of the toner particles in the liquid developer can be made particularly excellent.

1 is a schematic diagram illustrating an example of an image forming apparatus to which a liquid developer of the present invention is applied. FIG. 2 is an enlarged view of a part of the image forming apparatus shown in FIG. 1.

Hereinafter, preferred embodiments of the present invention will be described in detail.
≪Liquid developer≫
The liquid developer of the present invention is one in which toner particles are dispersed in an insulating liquid.
In the present invention, the toner particles dispersed in the insulating liquid include toner base particles having a porosity of 10% or more and 70% or less, and a surface layer formed on the surface of the toner base particles.

  By having such characteristics, the liquid developer has excellent toner particle dispersion stability and storage stability. This is because the toner particles composed of the toner mother particles and the surface layer as described above have a lower specific gravity than conventional toner particles, so that they do not settle easily in the insulating liquid and are stably dispersed. This is probably because it became easier. Further, since it is difficult to settle, it is considered that the storage stability is improved because aggregation of toner particles due to sedimentation is prevented.

Further, with such a configuration, the amount of resin constituting the toner particles can be made smaller than that of conventional toner particles, and the fixing energy when fixing the toner particles can be reduced. In addition, the cost of the material can be reduced.
The volume average particle size (D ₅₀ ) of the toner particles is preferably 1 μm or more and 10 μm or less. As a result, the storage stability and transfer efficiency of the liquid developer can be made particularly excellent.

In the present specification, the volume average particle diameter (D ₅₀ ) means “50% average particle diameter (D ₅₀ ) in terms of sphere by light scattering method” and is a value obtained as follows. That is, the particles in the dispersion medium are irradiated with light, and the generated diffracted scattered light is measured by detectors arranged in front, side, and rear of the dispersion medium. Using the measured value, assuming that the particles that are originally indefinite are spherical, a cumulative curve is obtained by setting the total volume of the particle population converted to a sphere equal to the volume of the particles as 100%, The point at which the cumulative value becomes 50% is defined as the volume average particle size. Examples of the measuring apparatus include a laser diffraction / scattering particle size analyzer Microtrac MT-3000 (manufactured by Nikkiso Co., Ltd.). The volume average particle diameter _{(D 50)} in Examples described later is a value measured with Microtrac MT-3000 of the.

The circumference of the projected image of the particle to be measured is L ₁ [μm], the circumference of a perfect circle having an area equal to the area of the projected image of the particle to be measured is L ₀ [μm], and the circularity of the particle Is represented by L ₀ / L ₁ , the average circularity of the toner particles is preferably 0.880 or more and 0.995 or less. As a result, the storage stability and transfer efficiency of the liquid developer can be made particularly excellent.

Hereinafter, each component will be described in detail.
<Toner particles>
As described above, the toner particles include toner base particles having a porosity of 10% or more and 70% or less, and a surface layer formed on the surface of the toner base particles. This reduces the specific gravity of the toner particles and improves the dispersibility in the insulating liquid. Further, by having the surface layer, it is possible to prevent the insulating liquid from entering the pores of the toner base particles, and to maintain the dispersion stability of the toner particles.

Hereinafter, the toner base particles and the surface layer will be described in detail.
[Toner mother particles]
The toner base particles have a plurality of holes opened on the surface of the toner base particles. By having such holes, the specific gravity of the toner particles can be lowered, and the toner particles can be excellent in dispersion stability and storage stability.

In the present invention, the porosity of the toner base particles is from 10% to 70%, more preferably from 20% to 50%. Thereby, the dispersion stability of the toner particles can be further improved.
Such toner base particles are composed of a toner material composed of a resin material and a colorant.

(Resin material)
In the present invention, the resin material is not particularly limited, and for example, a known resin can be used.
In particular, it is preferable to use a resin material containing a polyester resin. The polyester resin has high transparency and can be suitably used as a resin material because it can enhance the color developability of an image obtained when used as a binder resin. In addition, the dispersion stability can be improved, and the energy at the time of fixing can be reduced.
Note that the content of the polyester resin in the resin material is preferably 50 wt% or more, and more preferably 80 wt% or more.

The glass transition point of the resin material used in the present invention (Tg _b) is preferably from 15 to 70 ° C., and more preferably 20 to 55 ° C.. Thereby, in the heating process described later, a basic compound as described later can be effectively moved to the surface of the toner particle, and the positive charging characteristics of the obtained liquid developer can be made more stable. Can do. In this specification, the glass transition point is a measurement condition in a differential scanning calorimeter DSC-220C (manufactured by SII): a sample amount of 10 mg, a heating rate of 10 ° C./min, and a measurement temperature range of 10 to 150 ° C. The temperature at the intersection of the base line extension below the glass transition point and the tangent that indicates the maximum slope from the peak rise to the peak apex.

  Further, the softening point (T1 / 2) of the resin material is not particularly limited, but is preferably 50 to 130 ° C, more preferably 50 to 120 ° C, and further preferably 60 to 115 ° C. . In the present specification, the softening temperature is a measurement condition in a Koka type flow tester (manufactured by Shimadzu Corporation): temperature increase rate: 5 ° C./min, softening start temperature defined by a die hole diameter of 1.0 mm. Point to.

(Coloring agent)
The colorant used in the present invention is not particularly limited, and for example, known pigments and dyes can be used.
(Other ingredients)
Further, the toner material may contain components other than those described above. Examples of such components include known waxes and magnetic powders.
In addition to the above materials, for example, zinc stearate, zinc oxide, cerium oxide, silica, titanium oxide, iron oxide, fatty acid, fatty acid metal salt and the like may be used as the toner material.

[Surface layer]
The surface layer is a layer formed so as to cover the toner base particles, and has a function of preventing the insulating liquid from entering the holes of the toner base particles. As a result, it is possible to prevent the dispersion stability from being lowered due to the insulating liquid entering the holes of the toner base particles.
Such a surface layer may be formed so as to completely cover the surface of the toner base particles, or may be formed so that a part of the surface of the toner base particles is exposed.

  In the latter case, the surface layer is preferably as follows. That is, the surface layer has a through hole communicating with the hole on the surface of the toner base particle, and the hole diameter of the through hole on the outer surface of the surface layer is smaller than the hole diameter of the hole on the surface of the toner base particle. preferable. With such a configuration, the specific gravity of the toner particles can be reduced while effectively preventing the insulating liquid from entering the toner base particles. As a result, the dispersion stability of the toner particles can be further improved, and the storage stability can be further improved.

The material for forming such a surface layer is not particularly limited, but a material containing at least one compound selected from the group consisting of silicone wax and a compound having a pyrrolidone skeleton is preferably used. Thereby, the dispersion stability of the toner particles can be made particularly excellent.
Examples of the silicone wax include acrylic modified silicone and alkyl modified silicone.

Examples of the alkyl-modified silicone include AMS-C30 Cosmetic Wax (manufactured by Toray Dow Corning), 2503 Cosmetic Wax (manufactured by Toray Dow Corning), and the like.
Examples of the compound having a pyrrolidone skeleton include polyvinylpyrrolidone (PVP K series, manufactured by ISP Japan), α-olefin / vinylpyrrolidone copolymer (ANTARON series, manufactured by ISP Japan), vinyl acetate / vinylpyrrolidone copolymer (PLASDONE series). , Made by ISP Japan).

The melting point of the material constituting the surface layer is preferably lower than the glass transition temperature of the resin material of the toner base particles. Thereby, the toner particles can be easily produced by a method as described later.
Note that the material constituting the surface layer may be contained in the toner base particles. Thereby, the adhesiveness between the toner base particles and the surface layer can be made higher.

<Insulating liquid>
The insulating liquid functions as a dispersion medium for dispersing the toner particles as described above.
The insulating liquid has a high insulating property in order to transfer charged toner particles during image formation.
The insulating liquid may be a liquid having a sufficiently high insulating property. Specifically, the electric resistance at room temperature (20 ° C.) is preferably 1 × 10 ⁹ Ωcm or more, and preferably 1 × 10 ¹¹ Ωcm. More preferably, it is more preferably 1 × 10 ¹³ Ωcm or more.
The dielectric constant of the insulating liquid is preferably 3.5 or less.

As the insulating liquid, for example, KF-99, KF-96, KF-995 (Shin-Etsu Chemical Co., Ltd.), AK35, AK50, AK100, AK350, AK1000 (Such, Wacker Chemie AG), SH200, SH510, SH8400 ( As described above, dimethyl silicone oil such as Toray Dow Corning), silicone oil having a degree of polymerization greater than 20 such as hydrogen-modified silicone compound; cyclic siloxane compound such as cyclopentanesiloxane and decamethylcyclopentanesiloxane, and methyltris (trimethylsiloxy) silane Such as low molecular weight siloxane compounds having a polymerization degree of 20 or less; Isopar E, Isopar G, Isopar H, Isopar L (Isopar; trade name of Exxon Chemical Co., Ltd.), Cielsol 70, Cielsol 71 (Cie Sol oil (trade name of Ciel Oil), Amsco OMS, Amsco 460 solvent (Amsco; product name of Spirits), mineral oil (hydrocarbon liquid) such as low viscosity / high viscosity liquid paraffin (Wako Pure Chemical Industries); Fatty acid glycerides, fatty acid monoesters, fatty acid esters such as medium chain fatty acid esters or vegetable oils containing them; octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, benzene, toluene, xylene, Examples thereof include mesitylene, butyl acetate, and isopropanol, and one or more of these can be used in combination.
In this step, it is preferable to use silicone oil as the insulating liquid among the above-mentioned ones. Thereby, the productivity of the liquid developer can be made particularly excellent, and the dispersion stability of the toner particles in the liquid developer can be made particularly excellent.

<Dispersant>
The liquid developer of the present invention may contain a dispersant soluble in an insulating liquid in addition to the above components. By including the dispersant, the dispersion stability of the toner particles can be further improved.
Although it does not specifically limit as a dispersing agent, The polysiloxane dispersing agent as shown below can be used. Thereby, the dispersion stability of the toner particles can be further improved.
The polysiloxane dispersant is selected from the group comprising linear polysiloxanes or cyclic polysiloxanes or branched polysiloxanes, or combinations thereof.
The polysiloxane dispersant can be a polysiloxane polymer represented by the following general structure.

（式中、Ｒは、アルキル（−ＣＨ３）基またはヒドロキシル基（−ＯＨ）を表し、Ｘ１およびＸ２は、（１）アミン基（−ＮＨ２）；（２）カルボン酸基（−ＣＯＯＨ）；（３）ビニル基（−ＣＨ＝ＣＨ２）；（４）ヒドロキシル基（−ＯＨ）；（５）アルキル基（−ＣＨ３）、しかし、この場合、Ｘ_１またはＸ_２のいずれかが、上記（１）〜（４）から選択される官能基も含む；（６）適切な化学量論比で、上記（１）〜（４）から選択される官能基を含むアルキル基、すなわち、−ＲＸ、−ＲＸＲ、−ＲＸＲＸ、−ＸＲ、−ＸＲＸ、−ＸＲＸＲ（この場合、Ｘは、上記（１）〜（４）から選択される官能基であり、Ｒは、アルキル基である））

(In the formula, R represents an alkyl (—CH 3) group or a hydroxyl group (—OH), and X 1 and X 2 are (1) an amine group (—NH 2); (2) a carboxylic acid group (—COOH); 3) Vinyl group (—CH═CH2); (4) Hydroxyl group (—OH); (5) Alkyl group (—CH3), but in this case, either X ₁ or X ₂ is the above (1) (6) also includes a functional group selected from (4); (6) an alkyl group containing a functional group selected from (1) to (4) above at an appropriate stoichiometric ratio, that is, -RX, -RXR. , -RXRX, -XR, -XRX, -XRXR (in this case, X is a functional group selected from (1) to (4) above, and R is an alkyl group))

  The viscosity of such a polysiloxane dispersant is 90,000 mPa.s. It is preferable that it is s or less.

<Charge control agent>
The liquid developer of the present invention may contain a charge control agent in addition to the above components.
The charge control agent is not particularly limited as long as it is soluble in the insulating liquid, but quaternary cationic silicone is preferably used. Thereby, the charging property of the liquid developer can be made particularly excellent.
A quaternary cationic silicone means a silicone having a quaternary ammonium group, and the expression “silicone having a quaternary ammonium group” refers to any silicone having one or more quaternary ammonium groups. Means. These quaternary ammonium groups can be attached to the alpha or omega position in the form of lateral groups. They may be bonded directly to the polysiloxane skeleton or may be supported by hydrocarbon base chains.

  In the present invention, as generally accepted, the term “silicone” refers to silicon and oxygen atoms alternating with each other by a bond known as a siloxane bond (—Si—O—Si—). It means any polymer having a structure based on a bond and characterized by the presence of silicon-carbon bonds. These silicones or polysiloxanes are generally obtained by polycondensation of appropriately functionalized silanes. The hydrocarbon base groups most commonly supported by silicon atoms are lower alkyl groups, especially methyl, fluoroalkyl groups and aryl groups, especially phenyl. Such silicones are, for example, from Goldschmidt, under the names AbilQuat 3272, Abil B9905, Abil Quat 3474 and Avil K3270, from LipoFrance, Silquat. ) Q-100, Silk Wat Q-200WS, Silk Wat AX, Silk Wat AC, Silk Wat AD and Silk Wat AM (all manufactured by Siltech), from OSI, Magnasoft Exhaust and Under the name Silsoft C-880 and from UCIB, Pecosil 14-PQ and Pecosyl 36-PQ (Phoenix Chemical) It is sold under the name of (PhoenixChemical) production).

  These silicones are described in particular in EP 530974, German patent 3719086, German patent 3705121, European patent 617607 and European patent 714654. Etc. Among these, Silsense Q-Plus (manufactured by Lubrizol) is particularly preferable. By using Silence Q-Plus (manufactured by Lubrizol) as the substance B, the positive charging characteristics of the toner particles can be made particularly excellent, and the storage stability of the finally obtained liquid developer can be improved. Can be made particularly excellent.

≪Liquid developer manufacturing method≫
Next, an example of a method for producing the liquid developer of the present invention will be described.
The liquid developer manufacturing method of the present embodiment includes a toner base particle forming step for forming toner base particles, and heat-treating the toner base particles in an insulating liquid to form a surface layer on the surface of the toner base particles. And a step of dispersing the toner particles in the insulating liquid.

Hereinafter, each step will be described in detail.
<Toner base particle forming step>
The method for forming the toner base particles having the porosity as described above is not particularly limited, but is preferably formed as follows.
That is, a first step in which a first aqueous solution of finely dispersed pore-stabilized hydrocolloid is mixed in a continuous phase of a toner material dissolved and dispersed in an organic solvent to form a water-in-oil emulsion; A second step of forming a water-in-oil-in-water emulsion by dispersing the water-in-oil emulsion in the second aqueous phase containing the agent polymer, and a third step of removing the liquid component. Thereby, porous toner base particles can be easily formed. In the present embodiment, the toner material includes the material for forming the surface layer described above.

[First step]
In this step, a water-in-oil emulsion is formed by mixing the first aqueous solution of finely dispersed pore-stabilized hydrocolloid into the continuous phase of the toner material dissolved and dispersed in an organic solvent. Form.
Examples of the pore-stabilizing hydrocolloid used in the first step include natural and synthetic water-soluble or water-swellable polymers, for example, cellulose derivatives such as carboxymethyl cellulose (CMC) such as sodium carboxymethyl cellulose, and alkali-treated gelatin (for example, bovine bone). Or cattle skin gelatin), gelatins such as acid-treated gelatin (eg pig skin gelatin), acetylated gelatin, and gelatin derivatives such as phthalate gelatin, substances such as proteins and protein derivatives, poly (vinyl alcohol), poly (vinyl lactam) ), Acrylamide polymers, polyvinyl acetals, polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinyl acetate, polyamides, polyvinyl pyridine, methacrylamide copolymers , Mention may be made of water-soluble microgels, polyelectrolytes, and synthetic polymeric binder such as a mixture thereof.

[Second step]
In this step, a water-in-oil-in-water emulsion is formed by dispersing the water-in-oil emulsion in the second aqueous phase containing the stabilizer polymer.
Examples of the stabilizer polymer include polyvinyl pyrrolidone, polyvinyl alcohol, colloidal silica, and the like.
[Third step]
In this step, porous toner base particles (or precursors of toner base particles) can be obtained by removing the liquid component from the dispersion containing the water-in-oil-in-water emulsion.
Examples of the removing method include spray drying.

<Step of forming a surface layer on the surface of toner base particles>
Next, a surface layer is formed on the surface of the toner base particles obtained as described above.
Specifically, heat treatment is performed while stirring the dispersion in which the obtained toner base particles are dispersed in an insulating liquid. As a result, the constituent material of the surface layer contained in the toner base particles oozes out on the surface of the toner base particles, and a surface layer is formed on the surface of the toner base particles. Thereby, a liquid developer in which toner particles are dispersed in an insulating liquid is obtained.
In this step, it is preferable to perform heat treatment at a temperature higher than the glass transition temperature of the resin material. Thereby, the constituent material of the surface layer contained in the toner base particles can be more easily exuded on the surface of the toner base particles, and the surface layer can be formed more easily.

≪Image forming device≫
Next, a preferred embodiment of an image forming apparatus to which the liquid developer of the present invention is applied will be described.
FIG. 1 is a schematic diagram showing a preferred embodiment of an image forming apparatus to which the liquid developer of the present invention is applied, and FIG. 2 is an enlarged view of a part of the image forming apparatus shown in FIG.

As shown in FIGS. 1 and 2, the image forming apparatus 1000 includes four developing units 30Y, 30M, 30C, and 30K, a transfer unit (intermediate transfer unit 40 and a secondary transfer unit (secondary transfer unit) 60), and , A fixing unit (fixing device) F40 and four liquid developer replenishing units 90Y, 90M, 90C, and 90K.
The developing units 30Y, 30M, and 30C develop a latent image with a yellow liquid developer (Y), a magenta liquid developer (M), and a cyan liquid developer (C), respectively, and correspond to each color. It has a function of forming a single color image. The developing unit 30K has a function of developing a latent image with a black liquid developer (K) to form a black single color image.

Since the developing units 30Y, 30M, 30C, and 30K have the same configuration, the developing unit 30Y will be described below.
As shown in FIG. 2, the developing unit 30Y includes a photoconductor 10Y as an example of an image carrier, a charging roller 11Y, an exposure unit 12Y, a development unit 100Y, and a photoconductor along the rotation direction of the photoconductor 10Y. It includes a body squeeze device 101Y, a primary transfer backup roller 51Y, a charge removal unit 16Y, a photoreceptor cleaning blade 17Y, and a developer recovery unit 18Y.

The photoreceptor 10Y is formed on a cylindrical base material and an outer peripheral surface thereof, has a photosensitive layer made of a material such as amorphous silicon, and is rotatable about a central axis. Rotate clockwise as indicated by the arrow in FIG.
The photoreceptor 10Y is supplied with a liquid developer by a developing unit 100Y described later, and a layer of the liquid developer is formed on the surface.

  The charging roller 11Y is a device for charging the photoconductor 10Y, and the exposure unit 12Y is a device for forming a latent image on the photoconductor 10Y charged by irradiating a laser. The exposure unit 12Y includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and charges a modulated laser based on an image signal input from a host computer (not shown) such as a personal computer or a word processor. Irradiate onto the photoconductor 10Y.

The developing unit 100Y is a device for developing the latent image formed on the photoreceptor 10Y using the liquid developer of the present invention. Details of the developing unit 100Y will be described later.
The photoconductor squeeze device 101Y is disposed on the downstream side in the rotation direction from the developing unit 100Y so as to face the photoconductor 10Y. The photoconductor squeeze roller 13Y and the photoconductor squeeze roller 13Y are pressed and slidably attached to the surface. The cleaning blade 14Y removes the liquid developer and the developer collection unit 15Y that collects the removed liquid developer. The photoreceptor squeeze device 101Y has a function of collecting excess carrier (insulating liquid) and originally unnecessary fog toner from the developer developed on the photoreceptor 10Y, and increasing the ratio of toner particles in the visible image.

The primary transfer backup roller 51Y is a device for transferring a single color image formed on the photoreceptor 10Y to an intermediate transfer unit 40 described later.
The neutralization unit 16Y is a device that removes residual charges on the photoreceptor 10Y after the intermediate transfer image is transferred onto the intermediate transfer unit 40 by the primary transfer backup roller 51Y.
The photoconductor cleaning blade 17Y is a rubber member that is in contact with the surface of the photoconductor 10Y, and remains on the photoconductor 10Y after the image is transferred onto the intermediate transfer portion 40 by the primary transfer backup roller 51Y. It has a function of scraping off and removing the liquid developer.

The developer recovery unit 18Y has a function of recovering the liquid developer removed by the photoconductor cleaning blade 17Y.
The intermediate transfer unit 40 is an endless elastic belt member, and is stretched around a belt driving roller 41 and a pair of driven rollers 44 and 45 to which a driving force of a motor (not shown) is transmitted. The intermediate transfer unit 40 is driven to rotate counterclockwise by the belt driving roller 41 while being in contact with the photoreceptors 10Y, 10M, 10C, and 10K by the primary transfer backup rollers 51Y, 51M, 51C, and 51K.

Further, the intermediate transfer unit 40 is applied with a predetermined tension by a tension roller 49 so that slack is removed. The tension roller 49 is disposed downstream of one driven roller 44 in the rotation (movement) direction of the intermediate transfer unit 40 and upstream of the other driven roller 45 in the rotation (movement) direction of the intermediate transfer unit 40. .
A single color image corresponding to each color formed by the developing units 30Y, 30M, 30C, and 30K is sequentially transferred to the intermediate transfer unit 40 by the primary transfer backup rollers 51Y, 51M, 51C, and 51K, and a single color corresponding to each color is transferred. The images are superimposed. As a result, a full-color developer image (intermediate transfer image) is formed on the intermediate transfer portion 40.

  In the intermediate transfer unit 40, the single-color images formed on the plurality of photoconductors 10Y, 10M, 10C, and 10K are secondarily transferred and superposed one after another. Secondary transfer is performed on a recording medium F5 such as paper, film, or cloth. Therefore, when the toner image is transferred to the recording medium F5 in the secondary transfer process, even if the surface of the recording medium F5 is a non-smooth sheet material due to fiber or the like, the secondary transfer characteristics follow the non-smooth sheet surface. An elastic belt member is employed as means for improving the above.

The intermediate transfer unit 40 is provided with a cleaning device including an intermediate transfer unit cleaning blade 46, a developer recovery unit 47, and a non-contact type bias applying member 48.
The intermediate transfer unit cleaning blade 46 and the developer recovery unit 47 are arranged on the driven roller 45 side.
The intermediate transfer unit cleaning blade 46 scrapes and removes the liquid developer adhering to the intermediate transfer unit 40 after the toner image is transferred onto the recording medium F5 by the secondary transfer unit (secondary transfer unit) 60. It has a function.
The developer recovery unit 47 has a function of recovering the liquid developer removed by the intermediate transfer unit cleaning blade 46.

  The non-contact type bias applying member 48 is disposed away from the intermediate transfer unit 40 at a position facing the tension roller 49. The non-contact type bias applying member 48 applies a bias voltage having a polarity opposite to that of the toner to the liquid developer toner (solid content) remaining on the intermediate transfer portion 40 after the secondary transfer. As a result, the toner is discharged, and the electrostatic adhesion force of the toner to the intermediate transfer unit 40 is reduced. In this example, a corona charger is used as the non-contact type bias applying member 48.

  The non-contact type bias applying member 48 is not necessarily disposed at a position facing the tension roller 49. For example, a position between the driven roller 44 and the tension roller 49, such as a position between the driven roller 44 and the intermediate transfer unit. It can be disposed at any position downstream in the movement direction and upstream of the driven roller 45 in the movement direction of the intermediate transfer unit. The non-contact type bias applying member 48 may be a known non-contact type charger other than the corona charger.

An intermediate transfer unit squeeze device 52Y is disposed downstream of the primary transfer backup roller 51Y in the moving direction of the intermediate transfer unit 40.
The intermediate transfer unit squeeze device 52Y is provided as a means for removing excess insulating liquid from the transferred liquid developer when the liquid developer transferred onto the intermediate transfer unit 40 has not reached the desired dispersion state. ing.

The intermediate transfer unit squeeze device 52Y is removed by the intermediate transfer unit squeeze roller 53Y, the intermediate transfer unit squeeze cleaning blade 55Y that presses and slides against the intermediate transfer unit squeeze roller 53Y, and the intermediate transfer unit squeeze cleaning blade 55Y. The developer collecting section 56Y collects the liquid developer.
The intermediate transfer unit squeeze device 52Y has a function of recovering excess insulating liquid from the developer primarily transferred to the intermediate transfer unit 40, increasing the toner particle ratio in the image, and recovering originally unwanted toner. Have.

  The secondary transfer unit 60 includes a pair of secondary transfer rollers that are spaced apart from each other by a predetermined distance along the transfer material movement direction. Of these pair of secondary transfer rollers, the secondary transfer roller disposed on the upstream side in the moving direction of the intermediate transfer unit 40 is the upstream secondary transfer roller 64. The upstream secondary transfer roller 64 can be pressed against the belt drive roller 41 via the intermediate transfer unit 40.

Of the pair of secondary transfer rollers, the secondary transfer roller disposed on the downstream side in the moving direction of the transfer material is the downstream secondary transfer roller 65. The downstream secondary transfer roller 65 can be brought into pressure contact with the driven roller 44 via the intermediate transfer unit 40.
That is, the upstream side secondary transfer roller 64 and the downstream side secondary transfer roller 65 bring the recording medium F5 into contact with the intermediate transfer unit 40 that is hung on the belt driving roller 41 and the driven roller 44, respectively. The intermediate transfer image formed by superimposing colors on 40 is secondarily transferred to the recording medium F5.

  In this case, the belt driving roller 41 and the driven roller 44 also function as backup rollers for the upstream side secondary transfer roller 64 and the downstream side secondary transfer roller 65, respectively. That is, the belt drive roller 41 is also used as an upstream backup roller disposed in the secondary transfer unit 60 on the upstream side of the driven roller 44 in the moving direction of the recording medium F5. The driven roller 44 is also used as a downstream backup roller disposed in the secondary transfer unit 60 on the downstream side in the moving direction of the recording medium F5 from the belt driving roller 41.

  Therefore, the recording medium F5 conveyed to the secondary transfer unit 60 is moved from the pressure contact start position (nip start position) between the upstream secondary transfer roller 64 and the belt drive roller 41 to the downstream secondary transfer roller 65 and the driven roller. In close contact with the intermediate transfer portion 40 in a predetermined movement region of the transfer material up to the press-contact end position (nip end position) with 44. As a result, the full-color intermediate transfer image on the intermediate transfer unit 40 is secondarily transferred to the recording medium F5 in close contact with the intermediate transfer unit 40 over a predetermined time, so that good secondary transfer is performed.

  The secondary transfer unit 60 includes a secondary transfer roller cleaning blade 66 and a developer recovery unit 67 with respect to the upstream side secondary transfer roller 64. The secondary transfer unit 60 includes a secondary transfer roller cleaning blade 68 and a developer recovery unit 69 with respect to the downstream side secondary transfer roller 65. The secondary transfer roller cleaning blades 66 and 68 are in contact with the secondary transfer rollers 64 and 65, respectively, and scrape and remove the liquid developer remaining on the surfaces of the secondary transfer rollers 64 and 65 after the secondary transfer. To do. Further, the developer collecting units 67 and 69 collect and store the liquid developer scraped off from the secondary transfer rollers 64 and 65 by the secondary transfer roller cleaning blades 66 and 68, respectively.

The toner image (transfer image) transferred onto the recording medium F5 by the secondary transfer unit 60 is sent to a fixing unit (fixing device) F40, and is heated and pressurized to be fixed on the recording medium F5.
Specifically, the fixing temperature (set temperature) is preferably 80 ° C. or higher and 160 ° C. or lower, more preferably 100 ° C. or higher and 150 ° C. or lower, and 100 ° C. or higher and 140 ° C. or lower. Further preferred.

Next, the developing units 100Y, 100M, 100C, and 100K will be described in detail. In the following description, the developing unit 100Y will be typically described.
As shown in FIG. 2, the developing unit 100Y includes a liquid developer storage unit 31Y, a coating roller 32Y, a regulating blade 33Y, a developer stirring roller 34Y, a communication unit 35Y, a recovery screw 36Y, and a developing roller 20Y. And a developing roller cleaning blade 21Y.

The liquid developer storage unit 31Y has a function of storing a liquid developer for developing the latent image formed on the photoreceptor 10Y. The supply unit 31aY supplies the liquid developer to the development unit, and the supply unit A recovery unit 31bY that recovers excess liquid developer generated at 31aY and the like, and a partition 31cY that partitions the supply unit 31aY and the recovery unit 31bY are provided.
The supply unit 31aY has a function of supplying the liquid developer to the application roller 32Y, and has a concave portion in which the developer stirring roller 34Y is installed. Further, the liquid developer is supplied from the liquid developer mixing tank 93Y to the supply unit 31aY through the communication unit 35Y.

The collection unit 31bY collects the liquid developer that is excessively supplied to the supply unit 31aY and excess liquid developer generated in the developer collection units 15Y and 24Y. The collected liquid developer is conveyed to a liquid developer mixing tank 93Y described later and reused. The recovery unit 31bY has a concave portion, and a recovery screw 36Y is installed near the bottom.
A wall-shaped partition 31cY is provided at the boundary between the supply unit 31aY and the recovery unit 31bY. The partition 31cY partitions the supply unit 31aY and the recovery unit 31bY and can prevent the recovered liquid developer from being mixed into the fresh liquid developer. Further, when an excessive liquid developer is supplied to the supply unit 31aY, the excess liquid developer can overflow from the supply unit 31aY to the recovery unit 31bY beyond the partition 31cY. For this reason, the amount of the liquid developer in the supply unit 31aY can be kept constant, and the amount of the liquid developer supplied to the application roller 32Y can be kept constant. For this reason, the image quality of the finally formed image becomes stable.

Further, the partition 31cY is provided with a notch, and the liquid developer can overflow from the supply part 31aY to the recovery part 31bY through the notch.
The coating roller 32Y has a function of supplying a liquid developer to the developing roller 20Y.
This application roller 32Y is a so-called anilox roller in which grooves are uniformly and spirally formed on the surface of a metallic roller such as iron and nickel-plated, and its diameter is about 25 mm. . In the present embodiment, a plurality of grooves are formed obliquely with respect to the rotation direction of the application roller 32Y by so-called cutting or rolling. The application roller 32Y contacts the liquid developer while rotating counterclockwise, thereby supporting the liquid developer in the supply unit 31aY in the groove and transporting the supported liquid developer to the development roller 20Y. To do.

  The regulating blade 33Y contacts the surface of the coating roller 32Y and regulates the amount of liquid developer on the coating roller 32Y. That is, the regulation blade 33Y plays a role of scraping off excess liquid developer on the application roller 32Y and measuring the liquid developer on the application roller 32Y supplied to the development roller 20Y. The restriction blade 33Y is made of urethane rubber as an elastic body, and is supported by a restriction blade support member made of metal such as iron. The regulating blade 33Y is provided on the side where the application roller 32Y rotates and advances from the liquid developer (that is, the right side in FIG. 2). The rubber hardness of the regulating blade 33Y is about 77 degrees according to JIS-A, and the hardness (about 77 degrees) of the contact portion of the regulating blade 33Y with the surface of the application roller 32Y is about the elasticity of the developing roller 20Y described later. It is lower than the hardness (about 85 degrees) of the press contact portion of the body layer to the surface of the application roller 32Y. Further, the excess liquid developer scraped off is collected in the supply unit 31aY and reused.

The developer stirring roller 34Y has a function of stirring the liquid developer in a uniformly dispersed state. Thus, even when a plurality of toner particles are aggregated, the toner particles can be suitably dispersed.
In the supply unit 31aY, the toner particles in the liquid developer have a positive charge, and the liquid developer is stirred by the developer stirring roller 34Y to be in a uniformly dispersed state, and the coating roller 32Y rotates. Thus, the liquid developer is stored in the liquid developer storage unit 31Y, and the amount of the liquid developer is regulated by the regulating blade 33Y and supplied to the developing roller 20Y. In addition, by being stirred by the developer stirring roller 34Y, the liquid developer can be stably overflowed to the collection unit 31bY side beyond the partition 31cY, and the liquid developer can be prevented from staying and being compressed. it can.

  Further, the developer stirring roller 34Y is provided in the vicinity of the communication portion 35Y. For this reason, the liquid developer supplied from the communication unit 35Y can quickly diffuse, and even when the liquid developer is supplied to the supply unit 31aY, the liquid level of the supply unit 31aY is stabilized. can do. By providing such a developer agitation roller 34Y in the vicinity of the communication portion 35Y, the communication portion 35Y has a negative pressure, and the liquid developer can be sucked up naturally.

The communication unit 35Y is provided in the vertical direction below the developer stirring roller 34Y, communicates with the liquid developer storage unit 31Y, and sucks the liquid developer from the liquid developer mixing tank 93Y to the supply unit 31aY.
By providing the communication portion 35Y below the developer stirring roller 34Y, the liquid developer supplied from the communication portion 35Y is stopped by the developer stirring roller 34Y, and the liquid top surface does not rise due to blowing, and the liquid The upper surface is held substantially constant, and the developer can be stably supplied to the coating roller 32Y.

The recovery screw 36Y provided in the vicinity of the bottom of the recovery unit 31bY is made of a cylindrical member, has a spiral rib on the outer periphery, and has a function of maintaining the fluidity of the recovered liquid developer. It has a function of promoting the conveyance of the developer to the liquid developer mixing tank 93Y.
The developing roller 20Y carries the liquid developer and conveys it to the developing position facing the photoconductor 10Y in order to develop the latent image carried on the photoconductor 10Y with the liquid developer.

The developing roller 20Y forms a liquid developer layer on its surface by supplying the liquid developer from the coating roller 32Y described above.
The developing roller 20Y includes a conductive elastic layer on the outer peripheral portion of an inner core made of metal such as iron, and has a diameter of about 20 mm. The elastic body layer has a two-layer structure. As the inner layer, urethane rubber having a rubber hardness of about 30 degrees JIS-A and a thickness of about 5 mm is used, and as the surface layer (outer layer), the rubber hardness is JIS. A urethane rubber having a thickness of about 30 μm at about 85 ° A is provided. The developing roller 20Y is in pressure contact with the coating roller 32Y and the photoreceptor 10Y in a state of being elastically deformed with the surface layer serving as a pressure contact portion.

  Further, the developing roller 20Y can rotate around its central axis, and the central axis is below the rotational central axis of the photoconductor 10Y. Further, the developing roller 20Y rotates in a direction (counterclockwise in FIG. 2) opposite to the rotation direction of the photoreceptor 10Y (clockwise in FIG. 2). When developing the latent image formed on the photoconductor 10Y, an electric field is formed between the developing roller 20Y and the photoconductor 10Y.

In the developing unit 100Y, the coating roller 32Y and the developing roller 20Y are separately driven by different power sources (not shown). And the quantity of the liquid developer supplied on the developing roller 20Y can be adjusted by changing the rotation speed (linear speed) ratio with the application roller 32Y and the developing roller 20Y.
The developing unit 100Y includes a rubber developing roller cleaning blade 21Y that is in contact with the surface of the developing roller 20Y, and a developer recovery unit 24Y. The developing roller cleaning blade 21Y is a device for scraping off and removing the liquid developer remaining on the developing roller 20Y after development is performed at the developing position. The liquid developer removed by the developing roller cleaning blade 21Y is collected in the developer collecting unit 24Y.

  As shown in FIGS. 1 and 2, the image forming apparatus 1000 includes liquid developer replenishing units 90Y, 90M, 90C, and 90K that replenish liquid developer to the developing units 30Y, 30M, 30C, and 30K. . These liquid developer replenishers 90Y, 90M, 90C, and 90K are respectively provided with liquid developer tanks 91Y, 91M, 91C, and 91K, insulating liquid tanks 92Y, 92M, 92C, and 92K, and a liquid developer mixing tank 93Y. , 93M, 93C, 93K.

  Each of the liquid developer tanks 91Y, 91M, 91C, and 91K stores a high concentration liquid developer corresponding to each color. Insulating liquid tanks 92Y, 92M, 92C, and 92K contain insulating liquids, respectively. Further, in each liquid developer mixing tank 93Y, 93M, 93C, 93K, a predetermined amount of each high-concentration liquid developer from each liquid developer tank 91Y, 91M, 91C, 91K, and each insulating liquid tank 92Y, A predetermined amount of each insulating liquid from 92M, 92C, and 92K is supplied.

  The liquid developer mixing tanks 93Y, 93M, 93C, and 93K are respectively mixed and stirred by the stirrers provided with the supplied high-concentration liquid developer and the insulating liquid, respectively, and the supply units 31aY. , 31aM, 31aC, and 31aK, a liquid developer corresponding to each color is prepared. The liquid developers prepared in the liquid developer mixing tanks 93Y, 93M, 93C, and 93K are supplied to the supply units 31aY, 31aM, 31aC, and 31aK, respectively.

Further, the liquid developer recovered by the recovery unit 31bY is recovered and reused in the liquid developer mixing tank 93Y. The same applies to the liquid developer mixing tanks 93M, 93C, and 93K.
In the image formation using the above apparatus, a plurality of single color images corresponding to the respective colors are applied to the photoreceptors 10Y, 10M, 10C, and 10K using a plurality of liquid developers having different colors (the liquid developer of the present invention). And a transfer step of transferring a plurality of single color images formed on the photosensitive member to the recording medium F5 and forming an unfixed toner image formed by superimposing the plurality of single color images on the recording medium F5. And a fixing step of fixing an unfixed toner image on the recording medium F5. By using such a method, an image excellent in color developability can be easily formed.

As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to these.
For example, the liquid developer of the present invention is not limited to that applied to the image forming apparatus as described above.
In the above-described embodiment, the configuration having the corona discharger as the image forming apparatus has been described. However, the corona discharger may be omitted.

[1] Production of Liquid Developer A liquid developer was produced as follows. About the process in which temperature is not described, it performed at room temperature (25 degreeC).
Example 1
[Formation of toner base particles]
CMC (sodium carboxymethylcellulose) molecular weight 90K (6.25 g) was dissolved in 125 g of distilled water.

  This was measured using a Silverson L4R homogenizer equipped with a general purpose grinding head at 6800 r. p. m for 2 minutes, polyester resin (glass transition temperature 55 ° C.): 82.48 g, cyan pigment (manufactured by Dainichi Seika, Pigment Blue 15: 3): 12.58, α-olefin / vinylpyrrolidone copolymer (Antalon V-220F): 12.58 (Equivalent to (pigment) g of ethyl acetate: dispersed in 329.94 g. Resulting using Microfluidics Microfluidizer Model # 110T at 8900 psi pressure The water-in-oil emulsion was further homogenized.

366 g of the resulting water-in-oil emulsion was placed in a second aqueous phase of 900 g containing pH 4 buffer and 4.2 g LUDOX ™, again using a Silverson homogenizer for 2800 r. p. A water-in-oil-in-water double emulsion was formed by dispersing at m followed by homogenization in a Gaulin colloid mill.
The ethyl acetate was then evaporated using a Buchi Rotovapor RE120 at 35 ° C. under low pressure. The resulting suspension was filtered using a glass filter, washed several times with water, and dried in a vacuum oven at 35 ° C. for 16 hours to obtain toner base particles. The volume average particle size of the toner base particles was 10.9 μm, and the porosity was 42%.

<Surface layer forming step>
Next, the obtained toner base particles: 20 g, quaternary cationic silicone (Silsense Q-Plus, manufactured by Lubrizol): 0.1 g, hydroxyl group and alkyl group-containing silicone resin (DC593, manufactured by Toray Dow Corning) A dispersion obtained by mixing 7.6 g and dimethyl silicone oil (KF-96, manufactured by Shin-Etsu Chemical Co., Ltd., 50 cs): 77.4 g as an insulating liquid is heated at 55 ° C. with stirring. did. At that time, a shear of 500 rpm was applied. The heat treatment was performed for 30 minutes. Then, it naturally cooled to room temperature.

The volume average particle size of the toner particles in the obtained liquid developer was 10.8 μm, and the average circularity R ₁ was 0.905.
When the toner particles in the obtained liquid developer were confirmed with a microscope, it was confirmed that the surface was covered with a surface layer. Further, it was confirmed that the surface layer had through holes communicating with the holes of the toner base particles, and the diameter of the through holes on the outer surface of the surface layer was smaller than the diameter of the holes on the surface of the toner base particles.

(Example 2)
A liquid developer was produced in the same manner as in Example 1 except that the Antalon V-220F was changed to an α-olefin / vinylpyrrolidone copolymer (Antalon WP-660).
(Example 3)
A liquid developer was produced in the same manner as in Example 1 except that Antalon V-220F was changed to AMS-C30 Cosmetic Wax (manufactured by Toray Dow Corning).
(Comparative example)
A liquid developer was produced in the same manner as in Example 1 except that the acrylic-modified silicone was not added and the heat treatment step was not performed.

[2] Evaluation The following evaluation was performed on the liquid developer obtained as described above.
[2.1] Developing efficiency Using the image forming apparatus as shown in FIGS. 1 and 2, the liquid developer by the liquid developer obtained in each of the embodiments and comparative examples on the developing roller of the image forming apparatus. A layer was formed. Next, the surface potential of the developing roller was set to 300V, the surface potential of the photoconductor was uniformly charged at 500V, the photoconductor was exposed, the charge on the surface of the photoconductor was attenuated, and the surface potential was set to 50V. The toner particles on the developing roller and the toner particles on the photosensitive member after the liquid developer layer passed between the photosensitive member and the developing roller were collected with a tape. Each tape used for sampling was affixed on a recording paper, and the concentration of each toner particle was measured. After the measurement, the value obtained by dividing the concentration of toner particles collected on the photoreceptor by the sum of the concentration of toner particles collected on the photoreceptor and the concentration of toner particles collected on the developing roller is multiplied by 100. Was determined as development efficiency, and evaluated according to the following four-stage criteria.
A: The development efficiency is 96% or more, and the development efficiency is particularly excellent.
B: The development efficiency is 90% or more and less than 96%, and the development efficiency is excellent.
C: The development efficiency is 80% or more and less than 90%, and there is no practical problem.
D: The development efficiency is less than 80% and the development efficiency is inferior.

[2.2] Transfer efficiency Using the image forming apparatus as shown in FIGS. 1 and 2, a liquid developer using the liquid developer obtained in each of the above examples and comparative examples on the photoreceptor of the image forming apparatus. A layer was formed. Next, the toner particles on the photoconductor and the toner particles on the intermediate transfer portion after the liquid developer layer passed between the photoconductor and the intermediate transfer portion were collected with a tape. Each tape used for sampling was affixed on a recording paper, and the concentration of each toner particle was measured. After the measurement, a value obtained by dividing the concentration of the toner particles collected on the intermediate transfer portion by the sum of the concentration of the toner particles collected on the photoconductor and the concentration of the toner particles collected on the intermediate transfer portion is 100. A value obtained by multiplying by is obtained as transfer efficiency, and evaluated according to the following four criteria.
A: The transfer efficiency is 96% or more, and the transfer efficiency is particularly excellent.
B: The transfer efficiency is 90% or more and less than 96%, and the transfer efficiency is excellent.
C: The transfer efficiency is 80% or more and less than 90%, and there is no practical problem.
D: Transfer efficiency is less than 80% and inferior to transfer efficiency.

[2.3] Fixing Strength Using an image forming apparatus as shown in FIGS. 1 and 2, an image of a predetermined pattern with a liquid developer obtained in each of the examples and the comparative examples is recorded on a recording paper (Seiko Epson). It was formed on a high-quality paper LPCPPA4) manufactured by the company. Thereafter, thermal fixing was performed at a fixing temperature of 60 ° C.
Then, after confirming the non-offset area, the fixed image on the recording paper is erased twice (rubber eraser “LION 261-11” manufactured by Lion Business Machine Co., Ltd.) twice with a pressing load of 1.2 kgf, and the remaining ratio of image density Was measured by “X-Rite model 404” manufactured by X-Rite Inc, and evaluated according to the following five-step criteria.

A: Image density residual ratio is 96% or more (very good).
B: Image density residual ratio is 90% or more and less than 96% (good).
C: Image density remaining rate is 80% or more and less than 90% (normal).
D: Image density residual ratio is 70% or more and less than 80% (slightly bad).
E: Image density residual ratio is less than 70% (very bad).

[2.3] Dispersion stability test [2.3.1] Method 1
10 mL of the liquid developer obtained in each example and each comparative example was placed in a test tube (12 mm in diameter and 120 mm in length), and the settling depth after standing for 10 days was measured. According to the following four-stage criteria evaluated.
A: Settling depth is 0 mm.
B: The settled depth is greater than 0 mm and 2 mm or less.
C: The settled depth is larger than 2 mm and 5 mm or less.
D: The settled depth is larger than 5 mm.

[2.3.2] Method 2
45.5 mL of the liquid developer obtained in each example and each comparative example was put into a centrifuge tube, and a centrifuge (Kokusan Co., Ltd.) was used under the conditions of a rotation radius of 5 cm, a rotation speed of 500, 1000, 2000, 4000, and 5000 rpm for 3 minutes. The depth of sedimentation at each rotational speed was measured.
Centrifugal acceleration rω ² (rω ² = 1118 × rotation radius (cm) × number of revolutions per minute (rpm) ² × 10 ⁻⁸ × g (gravity acceleration)) is taken on the horizontal axis, and the sedimentation depth is taken on the vertical axis. Plotted based on the measurement results. Based on each plot, the slope k was determined by first-order approximation and evaluated according to the following criteria. It can be said that the lower the value of k, the higher the dispersion stability.

A: 0 ≦ k <0.004
B: 0.004 ≦ k <0.008
C: 0.008 ≦ k <0.012
D: k ≧ 0.012
These results are shown in Table 1.

  As is apparent from Table 2, the liquid developer of the present invention was excellent in long-term dispersion stability of toner particles. The liquid developer of the present invention was also excellent in development efficiency, transfer efficiency, and fixing strength. On the other hand, satisfactory results were not obtained with the liquid developer of the comparative example.

  1000: Image forming apparatus 10Y, 10M, 10C, 10K ... Photoconductor 11Y ... Charging roller 12Y, 12M, 12C, 12K ... Exposure unit 13M, 13Y ... Photoconductor squeeze roller 14M, 14Y ... Cleaning blade 15M, 15Y ... Developer recovery Section 16Y ... Static elimination unit 17Y ... Photoconductor cleaning blade 18Y ... Developer collection section 20Y, 20M, 20C, 20K ... Development roller 21Y ... Development roller cleaning blade 24Y ... Developer collection section 30Y, 30M, 30C, 30K ... Development section 31Y ... Liquid developer storage unit 31aY, 31aM, 31aC, 31aK ... Supply unit 31bY ... Collection unit 31cY ... Partition 32Y ... Application roller 33Y ... Restriction blade 34Y ... Developer stirring roller 35Y ... Communication unit 36Y ... Collection Crew 40 ... Intermediate transfer part 41 ... Belt drive roller 44, 45 ... Driven roller 46 ... Intermediate transfer part cleaning blade 47 ... Developer recovery part 48 ... Non-contact type bias applying member 49 ... Tension roller 51Y, 51M, 51C, 51K ... Primary transfer backup roller 52Y ... Intermediate transfer unit squeeze device 53Y ... Intermediate transfer unit squeeze roller 55Y ... Intermediate transfer unit squeeze cleaning blade 56Y ... Developer recovery unit 60 ... Secondary transfer unit 64 ... Upstream secondary transfer roller 65 ... Downstream Side secondary transfer roller 66, 68 ... Secondary transfer roller cleaning blade 67, 69 ... Developer recovery unit 90Y, 90M, 90C, 90K ... Liquid developer replenishment unit 91Y, 91M, 91C, 91K ... Liquid developer tank 92Y, 92M, 2C, 92K ... insulation liquid tanks 93Y, 93M, 93C, 93K ... liquid developer mixing tank 100Y ... developing unit 101Y ... photoreceptor squeeze device F 40 ... fixing portion (fixing device) F5 ... recording medium

Claims (8)

  A liquid developer characterized in that toner particles comprising toner base particles having a porosity of 10% or more and 70% or less and a surface layer formed on the surface of the toner base particles are dispersed in an insulating liquid. .   The liquid developer according to claim 1, wherein the toner base particles are made of a toner material containing a polyester resin and a colorant.   The liquid developer according to claim 1, wherein the surface layer is made of a material containing at least one compound selected from the group consisting of a silicone wax and a compound having a pyrrolidone skeleton. The surface layer has a through hole communicating with a hole on the surface of the toner base particle,
4. The liquid developer according to claim 1, wherein a diameter of the through hole on the outer surface of the surface layer is smaller than a diameter of a hole on the surface of the toner base particle. The volume average particle size of the toner particles is 1 μm or more and 10 μm or less,
The liquid developer according to claim 1, wherein the toner particles have an average circularity of 0.880 or more and 0.995 or less.   The dispersant according to any one of claims 1 to 5, comprising a siloxane compound that contains one functional group selected from the group consisting of an amino group, a hydroxyl group, a carboxyl group, a vinyl group, and an alkyl group and is soluble in the insulating liquid. The liquid developer according to any one of the above.   The liquid developer according to claim 1, comprising a quaternized cationic silicone as the charge control agent.   The liquid developer according to claim 1, wherein the insulating liquid is made of silicone oil.

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