JP2012237767A - Liquid developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid developer that has excellent charge property for positive charging and charge stability, and supports high-speed development.SOLUTION: The liquid developer of the present invention contains toner particles, and insulating liquid. The liquid developer contains fatty acid ester as the insulating liquid, and a material A represented by the following formula (1) with the content of 0.1 mass% or more and 3.0 mass% or less. (In the formula (1), R represents an organic group having 1-15 carbon atoms.)

Description

  The present invention relates to a liquid developer.

As a developer used to develop the electrostatic latent image formed on the latent image carrier, a toner composed of a material containing a colorant such as a pigment and a binder resin is used as an electrically insulating carrier liquid (insulating property). Liquid developers dispersed in (liquid) are known.
Conventionally, resin materials such as a polyester resin, a styrene-acrylic acid ester copolymer, and an epoxy resin have been used for the toner particles constituting such a liquid developer (see, for example, Patent Document 1). Such a resin material has characteristics that it is easy to handle, has good color developability of the obtained image, and can obtain high fixing characteristics.
However, since the resin material used as the constituent material of the toner particles is generally negatively charged, it has been difficult to apply it to positively charged toner particles (liquid developer). In addition, it is conceivable to add a charge control agent to toner particles using such a resin material for positive charging, but it has been difficult to obtain a sufficient charge amount.

JP 2007-219380 A

  An object of the present invention is to provide a liquid developer that is excellent in positive charging characteristics and charging stability and that can cope with high-speed development.

（式（１）中、Ｒは、炭素数が１以上１５以下の有機基を表し、ｎは、１以上３以下の整数である。）
これにより、正帯電の帯電特性・帯電安定性に優れるとともに、高速現像に対応できる液体現像剤を提供することができる。 Such an object is achieved by the present invention described below.
The liquid developer of the present invention is a liquid developer containing toner particles and an insulating liquid,
A fatty acid ester as the insulating liquid,
The substance A represented by the following formula (1) is contained at a content of 0.1% by mass or more and 3.0% by mass or less.

(In formula (1), R represents an organic group having 1 to 15 carbon atoms, and n is an integer of 1 to 3)
Accordingly, it is possible to provide a liquid developer that is excellent in positive charging characteristics and charging stability and that can be used for high-speed development.

In the liquid developer of the present invention, the substance A preferably has a hydrocarbon group having a branched chain.
As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.

In the liquid developer of the present invention, the substance A preferably has a linear alkyl group having 4 to 12 carbon atoms.
As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.

（式（２）中、Ｒ^１は、炭素数が１以上７以下の炭化水素基を表し、Ｒ^２は、炭素数が１以上７以下の炭化水素基を表す。）
これにより、トナー粒子の帯電安定性、絶縁性液体中での分散安定性を特に優れたものとしつつ、トナー粒子の移動度を特に優れたものとすることができ、高速現像により好適に対応することができる。 In the liquid developer of the present invention, the substance A is preferably represented by the following formula (2).

(In Formula (2), R ¹ represents a hydrocarbon group having 1 to 7 carbon atoms, and R ² represents a hydrocarbon group having 1 to 7 carbon atoms.)
As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.

In the liquid developer of the present invention, R ¹ preferably has an unsaturated bond.
As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be further improved, and the mobility of the toner particles can be further improved, and it is more suitable for high-speed development. can do.

In the liquid developer of the present invention, the fatty acid ester is preferably an ester of a monovalent fatty acid and a monovalent alcohol.
As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.

In the liquid developer of the present invention, the fatty acid ester is preferably an ester of a fatty acid and a linear alcohol.
As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.

In the liquid developer of the present invention, the fatty acid ester is preferably an ester of a fatty acid and an alcohol having 4 to 14 carbon atoms.
As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.

In the liquid developer of the present invention, the toner particles are preferably composed of a material containing a polyester resin.
The polyester resin has high transparency, and when used as a binder resin, it can enhance the color developability of the resulting image and can particularly improve the fixing characteristics of the toner particles to the recording medium. it can. Further, in the conventional liquid developer, it is particularly difficult to make the toner particles positively charged when the toner particles are made of a polyester resin. However, in the present invention, the toner particles are made of a polyester resin. Even if it is configured, the charging characteristics and charging stability of positive charging can be sufficiently improved. That is, when the toner particles are made of a material containing a polyester resin, the effects of the present invention are more remarkably exhibited.

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≫
First, the liquid developer of the present invention will be described.
The liquid developer of the present invention contains toner particles and an insulating liquid, which contains a fatty acid ester as the insulating liquid, and further contains a substance A represented by the following formula (1) in the range of 0. It is included at a content of 1% by mass or more and 3.0% by mass or less. With such a configuration, it is possible to provide a liquid developer that is excellent in positive charging characteristics and charging stability and that can cope with high-speed development.

（式（１）中、Ｒは、炭素数が１以上１５以下の有機基を表し、ｎは、１以上３以下の整数である。）

(In formula (1), R represents an organic group having 1 to 15 carbon atoms, and n is an integer of 1 to 3)

<Toner particles>
[Component material of toner particles]
The toner particles include at least a binder resin (resin material) and a colorant.
1. Resin material (binder resin)
Examples of the resin material constituting the toner particles include a polyester resin, a styrene-acrylic acid ester copolymer, a methacrylic resin, an epoxy resin, and a rosin resin. Among these, a polyester resin is preferable. The polyester resin has high transparency, and when used as a binder resin, it can enhance the color developability of the resulting image and can particularly improve the fixing characteristics of the toner particles to the recording medium. it can. Further, when the toner particles are made of a material containing a polyester resin, the color developability of the obtained image can be made particularly excellent. Further, in the conventional liquid developer, it is particularly difficult to make the toner particles positively charged when the toner particles are made of a polyester resin. However, in the present invention, the toner particles are made of a polyester resin. Even if it is configured, the charging characteristics and charging stability of positive charging can be sufficiently improved. That is, when the toner particles are made of a material containing a polyester resin, the effects of the present invention are more remarkably exhibited.

When the polyester resin is included, the acid value of the polyester resin is preferably 5 mgKOH / g or more and 20 mgKOH / g or less, and more preferably 5 mgKOH / g or more and 15 mgKOH / g or less.
The content of the polyester resin in the resin material is preferably 50% by mass or more and 99% by mass or less, and more preferably 60% by mass or more and 95% by mass or less.
Examples of rosin resins include rosin-modified phenolic resins, rosin-modified maleic resins, rosin-modified polyester resins, fumaric acid-modified rosin resins, ester gums, etc., and one or more of these may be combined. Can be used.

  The glass transition temperature (Tg) of the resin material used in the present invention is preferably 15 ° C. or higher and 70 ° C. or lower, and more preferably 20 ° C. or higher and 55 ° C. or lower. In this specification, the glass transition temperature is a measurement condition in a differential scanning calorimeter DSC-220C (manufactured by SII): measured in 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 temperature and the tangent that indicates the maximum slope from the peak rise to the peak apex.

  The softening point (T1 / 2) of the resin material is not particularly limited, but is preferably 50 ° C. or higher and 130 ° C. or lower, more preferably 50 ° C. or higher and 120 ° C. or lower, and 60 ° C. or higher and 115 ° C. or lower. More preferably. 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.

2. Colorant The toner particles may contain a colorant. The colorant is not particularly limited, and for example, known pigments and dyes can be used.
3. Other Components The toner particles 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, etc. are used as the constituent material (component) of the toner particles. May be.

[Toner particle shape]
The average particle diameter of the toner particles composed of the above materials is preferably 0.5 μm or more and 5 μm or less, more preferably 1 μm or more and 3.5 μm or less, and 1 μm or more and 2.5 μm or less. Is more preferable. When the average particle diameter of the toner particles is within the above range, the variation in characteristics among the toner particles is small, and the liquid developer as a whole is made highly reliable while being formed with the liquid developer. The resolution of the toner image can be made sufficiently high. Further, it is possible to improve the dispersion of the toner particles in the insulating liquid and to improve the storage stability of the liquid developer. In the present specification, “average particle diameter” refers to an average particle diameter based on volume.
The toner particle content in the liquid developer is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 50% by mass or less.

<Insulating liquid>
The insulating liquid functions as a dispersion medium for dispersing toner particles in the liquid developer.
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.

  The liquid developer of the present invention contains a fatty acid ester as an insulating liquid. By including the fatty acid ester, charge exchange can be efficiently performed with the substance A described in detail later, and high-speed development can be supported. Further, the dispersion stability of the toner in the liquid developer (insulating liquid) can be made particularly excellent, and the storage stability of the liquid developer can be made particularly excellent. Such an excellent effect cannot be obtained when another insulating liquid is used instead of the fatty acid ester.

  Any fatty acid ester may be used as long as it has an ester structure of a carboxyl group and an alcoholic hydroxyl group constituting the fatty acid in the molecule. For example, fatty acid glyceride, fatty acid monoester, medium chain fatty acid ester And fatty acid esters and vegetable oils containing them. As the fatty acid component constituting the fatty acid ester, one having at least one carboxyl group in the molecule can be used, and monovalent fatty acid, divalent fatty acid, polyvalent (more than trivalent) fatty acid can be used. it can. Moreover, as alcohol which comprises fatty acid ester, what has at least 1 alcoholic hydroxyl group in a molecule | numerator can be used, and monohydric alcohol, bivalent alcohol, and polyhydric (trivalent or more) alcohol are used. be able to.

In the present invention, the fatty acid ester may be a general one, and may be a fat or oil (vegetable oil or animal oil), or a fatty acid ester obtained by a transesterification reaction between these fats and an alcohol, or a transesterification between the fatty acid ester and the alcohol. Processing oils such as fatty acid esters obtained by reaction and fatty acid esters obtained by esterification reaction of fatty acids and alcohols may be used.
Among these, the fatty acid ester is preferably an ester (fatty acid monoester) of a monovalent fatty acid and a monovalent alcohol. As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.

The fatty acid monoester can be obtained, for example, by a transesterification reaction between a vegetable oil and a monohydric alcohol.
Examples of vegetable oils used for transesterification include soybean oil, rapeseed oil, dehydrated castor oil, tung oil, safflower oil, linseed oil, sunflower oil, corn oil, cottonseed oil, sesame oil, corn oil, cannabis oil, evening primrose oil, palm oil (Especially palm kernel oil), coconut oil, coconut oil and the like.

The fatty acid monoester may be produced by, for example, a transesterification reaction between various saturated fatty acids and unsaturated fatty acids and a monohydric alcohol, dihydric alcohol or polyhydric alcohol.
The fatty acid ester is preferably an ester of a fatty acid and a linear alcohol. As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.
The fatty acid ester is preferably an ester of a fatty acid and an alcohol having 4 to 14 carbon atoms. As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.

The liquid developer of the present invention may contain a component other than the fatty acid ester (another insulating liquid component) as a constituent component of the insulating liquid. In this case, the ratio of the other insulating liquid component in the entire insulating liquid is preferably 10% by mass or less, and more preferably 5% by mass or less.
Examples of other insulating liquid components include KF-99, KF-96, KF-995 (above, Shin-Etsu Chemical Co., Ltd.), AK35, AK50, AK100, AK350, AK1000 (above, Wacker Chemie AG), SH200, SH510. , Dimethyl silicone oil such as SH8400 (above, 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 (trimethyl) Siloxy) Low molecular weight siloxane compounds having a polymerization degree of 20 or less such as silane; Isopar E, Isopar G, Isopar H, Isopar L (Isopar; trade name of Exxon Chemical Co., Ltd.), Cielsol 70, Cielsol 7 (Cielsol; trade name of Ciel Oil), Amsco OMS, Amsco 460 solvent (Amsco; trade name of Spirits), low viscosity / high viscosity liquid paraffin (Wako Pure Chemical Industries) and other mineral oils (hydrocarbon liquids) ;; octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, benzene, toluene, xylene, mesitylene, butyl acetate, isopropanol, etc., one or two of these A combination of the above can be used.

  The viscosity of the insulating liquid is not particularly limited, but is preferably 5 mPa · s or more and 1000 mPa · s or less, more preferably 50 mPa · s or more and 800 mPa · s or less, and 100 mPa · s or more and 500 mPa · s or less. More preferably. When the viscosity of the insulating liquid is within the above range, when the liquid developer is squeezed out from the developer container onto the application roller, an appropriate amount of the insulating liquid adheres to the toner particles, and the developability of the toner image. , Transferability can be particularly improved. In addition, aggregation and sedimentation of the toner particles can be more effectively prevented, and the dispersibility of the toner particles in the insulating liquid can be made higher. However, the viscosity in this specification refers to a value measured at 25 ° C.

<Substance A>
The liquid developer of the present invention contains the substance A represented by the above formula (1) in a predetermined amount.
In the liquid developer, the substance A is usually completely dissolved in the insulating liquid. However, when the substance A comes into contact with the toner particles, the substance A acts as an electron acceptor to reinforce the electron acceptability of the fatty acid ester. It is thought to do. This action is considered to cause the toner particles to exhibit positive chargeability and to significantly improve electrophoretic properties.

The liquid developer of the present invention contains the substance A at a content of 0.1% by mass or more and 3.0% by mass or less.
By including a predetermined amount of the substance A together with the fatty acid ester as described above, the liquid developer can be suitably adapted to high-speed development, and the positive charging characteristics and charging stability of the toner particles. Can be made excellent. Further, the dispersion stability of the toner in the liquid developer (insulating liquid) can be made particularly excellent, and the storage stability of the liquid developer can be made particularly excellent. Such an excellent effect cannot be obtained when a predetermined amount of the substance A is not included. That is, when the content of the substance A in the liquid developer is less than the lower limit, the charging characteristics and charging stability of the toner particles are significantly reduced, and the mobility of the toner particles in the liquid developer ( (Moving speed) is remarkably reduced, making it difficult to apply to high-speed development. Further, if the content of the substance A in the liquid developer exceeds the upper limit, the positive charging characteristics and charging stability of the toner particles are remarkably lowered, and the mobility (movement) of the toner particles in the liquid developer is reduced. Speed) is remarkably reduced, making it difficult to apply to high-speed development, and the storage stability of the liquid developer is also significantly reduced.
Note that the liquid developer of the present invention may contain a plurality of types of compounds represented by different structural formulas as the substance A. In this case, the total content of these compounds is defined as the content of the substance A.

As described above, in the present invention, the content of the substance A in the liquid developer is from 0.1% by mass to 3.0% by mass, but from 0.2% by mass to 2.0% by mass. It is preferable that it is 0.3 mass% or more and 1.5 mass% or less. Thereby, the effects as described above are more remarkably exhibited.
The substance A may have a hydrocarbon group having a branched chain. As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.
The substance A may have a linear alkyl group having 4 to 12 carbon atoms. As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.
The substance A may be represented by the following formula (2).

（式（２）中、Ｒ^１は、炭素数が１以上７以下の炭化水素基を表し、Ｒ^２は、炭素数が１以上７以下の炭化水素基を表す。）

(In Formula (2), R ¹ represents a hydrocarbon group having 1 to 7 carbon atoms, and R ² represents a hydrocarbon group having 1 to 7 carbon atoms.)

As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be made particularly excellent, and the mobility of the toner particles can be made particularly excellent, which is more suitable for high-speed development. be able to.
When the substance A is represented by the formula (2), R ¹ in the formula (2) preferably has an unsaturated bond. As a result, the charging stability of the toner particles and the dispersion stability in the insulating liquid can be further improved, and the mobility of the toner particles can be further improved, and it is more suitable for high-speed development. can do.

<Other ingredients>
Further, the liquid developer may contain components other than those described above. Examples of such components include known dispersants, antioxidants, charge control agents, and the like. Such components may be adhered to the toner particles, or may be dispersed or dissolved in the insulating liquid.

≪Liquid developer manufacturing method≫
Next, 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 wet pulverization step of obtaining a dispersion by wet pulverization of a powder composed of a resin material and a material containing a colorant in an insulating liquid using a ball mill or a bead mill. And a bead removing step for removing beads used in a ball mill, a bead mill or the like.
By using such a method, the liquid developer as described above can be produced efficiently.

<Wet grinding process>
In this step, the wet-pulverized powder may be any material that includes a resin material and a colorant-containing material, but the kneaded material obtained by kneading the resin material and the colorant-containing material is pulverized. It is preferable that it is obtained by doing. Thereby, the uniformity of the characteristics among the toner particles can be made particularly excellent. Further, the substance A may be contained in a material that is subjected to wet pulverization, or may be added later in this step.

For the kneading, for example, various kneaders such as a biaxial kneading extruder, a kneader, a batch type triaxial roll, a continuous biaxial roll, a wheel mixer, and a blade type mixer can be used.
This step is performed by a ball mill, a bead mill, or the like. At this time, as the beads (balls), those composed of zirconia, alumina, glass, chrome steel, or the like can be used.
By this step, the powder can be suitably pulverized and finely divided.

<Bead removal process>
Thereafter, the beads (balls) are removed from the dispersion obtained through the wet grinding process. Thereby, a liquid developer is obtained.
The removal of the beads can be performed by filtration, for example. Further, the beads may be settled, and the supernatant may be used as a liquid developer.

≪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.
Further, the liquid developer of the present invention is not limited to those manufactured using the method as described above. For example, the toner particles may be manufactured using a polymerization method or the like.

[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
<Wet grinding process>
First, as a resin material, a polyester resin (acid value: 10 mg KOH / g, glass transition temperature (Tg): 55 ° C., softening point: 107 ° C.) and a cyan pigment as a colorant (Pigment Blue, manufactured by Dainichi Seika Co., Ltd.) 15: 3) and a mixture (mass ratio 85:15) were prepared. These components were mixed using a 20 L type Henschel mixer to obtain a raw material for toner production.
Next, this raw material (mixture) was kneaded using a twin-screw kneading extruder. The kneaded product extruded from the extrusion port of the biaxial kneading extruder was cooled.

The kneaded material cooled as described above was coarsely pulverized to obtain toner particle raw material coarsely pulverized particles having an average particle diameter of 1.0 mm or less. A hammer mill was used for coarse pulverization of the kneaded product.
50 g of coarsely pulverized particles obtained by the above method, 1.0 g of mono-2-ethylhexyl phosphate (JAMP-8, manufactured by Johoku Chemical Co., Ltd.) as substance A, and butyl oleate (viscosity: 18. 5 mPa · s, dielectric constant: 2.78) 150 g is put in a ceramic pot (internal volume 600 ml), and further zirconia beads (ball diameter: 1 mm) are put in the ceramic pot so that the volume filling rate is 40%. Wet grinding was performed for 48 hours at a rotational speed of 230 rpm in a desktop pot mill.

<Bead removal process>
Thereafter, the zirconia beads were removed by suction filtration to obtain a liquid developer. The obtained liquid developer has a viscosity at 25 ° C. of 630 mPa.s. s. Further, the volume average particle diameter (D ₅₀ ) of the toner particles is 2.34 μm. In addition, the viscosity at 25 ° C. of the liquid developer was determined at a share rate of 5.0 sec ⁻¹ using an E-type viscometer.

(Examples 2 to 18)
A liquid developer was produced in the same manner as in Example 1 except that the types and amounts of materials used in the production of the liquid developer were changed so that the compositions shown in Tables 1 and 2 were obtained. .
(Comparative Example 1)
A liquid developer was produced in the same manner as in Example 1 except that the substance A was not used in the wet pulverization step and the amounts of each component used were as shown in Table 2.
(Comparative Examples 2-7)
A liquid developer was produced in the same manner as in Example 1 except that the type and amount of materials used for the production of the liquid developer were changed to have the composition shown in Table 2.

Tables 1 and 2 collectively show the configurations of the liquid developers in the above Examples and Comparative Examples.
In the table, polyester resin (acid value: 10 mg KOH / g, glass transition temperature: 55 ° C., softening point: 107 ° C.) is PES, styrene acrylic resin (styrene-n-butyl methacrylate copolymer, Sanyo Chemical Industries, Ltd.) Manufactured by Hymer SBM-73F), Stac, epoxy resin (manufactured by Japan Epoxy Resin Co., Ltd., Epicoat 1007, melting point: 128 ° C.), EP, mono-2-ethylhexyl phosphate A compound in which n is 1) A1, di2-ethylhexyl phosphate (a compound in which R in formula (1) is a 2-ethylhexyl group, n is 2), A2, mono (2-hydroxyethyl methacrylate) phosphate (formula (1) in the R is _{CH 2 = C (CH 3)} COOC 2 H 4 -, n is compound 1) a 3, di (2-hydroxyethyl methacrylate) phosphate (R in the formula (1) is _{CH 2 = C (CH 3)} COOC 2 H 4 -, n compound is 2) the A4, mono-n- butyl phosphate ( A compound in which R in the formula (1) is an n-butyl group and n is 1) A5, mono n-octyl phosphate (a compound in which R in the formula (1) is an n-octyl group and n is 1) A6, MS for zirconium octylate as a fatty acid metal salt, CS for dodecyltrimethylammonium salt as a cationic surfactant, S1 for butyl oleate, S2 for 2-ethylhexyl linoleate, S3 for tetradecyl caproate, large Soybean oil as S4, polyglyceride as S5, hydrocarbon-based insulating liquid (Cosmo White, Cosmo Oil Co., Ltd.) as S'1, silicone-based insulating liquid Dimethyl silicone (KF-96-20, manufactured by Shin-Etsu Silicone) was designated as S′2.

[2] Evaluation The following evaluation was performed on the liquid developer obtained as described above.
[2-1] Electrophoretic mobility The electrophoretic mobility was evaluated for the liquid developers of Examples and Comparative Examples as follows.
First, a liquid developer was injected between electrodes having an interelectrode distance d = 80 μm, and a voltage was applied between the electrodes so that a potential difference V = 40V. The movement of the toner particles at this time was observed with an optical microscope, and by analyzing the image of the movement state, the movement distance of the particles per unit time (= electrophoretic velocity v) was obtained and evaluated according to the following criteria. It can be said that the higher the electrophoretic mobility, the more suitable for high-speed development.

A: Electrophoretic mobility is 35.0 μm ² / Vs or more.
B: Electrophoretic mobility is 20.0 μm ² / Vs or more and less than 35.0.
C: Electrophoretic mobility is 12.5 μm ² / Vs or more and less than 20.0.
D: The electrophoretic mobility is 10.0 μm ² / Vs or more and less than 12.5.
E: Electrophoretic mobility is 7.5 μm ² / Vs or more and less than 10.0.
F: Electrophoretic mobility is 5.0 μm ² / Vs or more and less than 7.5.
G: Electrophoretic mobility is less than 5.0 μm ² / Vs.

[2-2] Charging stability The liquid developers of each Example and each Comparative Example were collected in a glass container and allowed to stand in a dark room for 30 days in a sealed state.
After 30 days, the electrophoretic mobility was determined by the method described in [2-1] above, and the rate of decrease in electrophoretic mobility was determined from the results, and evaluated according to the following criteria. In addition, the said evaluation was not performed about the thing whose initial electrophoretic mobility (value calculated | required by [2-1]) is less than 5 micrometer < ² > / Vs. It can be said that the smaller the rate of decrease in electrophoretic mobility, the better the charging stability.

A: The rate of decrease in electrophoretic mobility is less than 3%.
B: The rate of decrease in electrophoretic mobility is 3% or more and less than 7%.
C: The rate of decrease in electrophoretic mobility is 7% or more and less than 10%.
D: The rate of decrease in electrophoretic mobility is 10% or more and less than 20%.
E: The rate of decrease in electrophoretic mobility is 20% or more and less than 30%.
F: The rate of decrease in electrophoretic mobility is 30% or more.

[2-3] Dispersion stability test 10 mL of the liquid developer obtained in each example and each comparative example was placed in a test tube (12 mm in diameter, 120 mm in length), and the sedimented depth after standing for 10 days was measured. The evaluation was made according to the following four criteria.
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.

[2-4] Development efficiency Using the image forming apparatus as shown in FIGS. 1 and 2, the liquid developer using the liquid developer obtained in each of the above 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 95% or more, and the development efficiency is particularly excellent.
B: The development efficiency is 90% or more and less than 95%, 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.

[2-5] Transfer efficiency Liquid developer using the liquid developer obtained in each of the examples and comparative examples on the photoreceptor of the image forming apparatus using the image forming apparatus as shown in FIGS. 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 95% or more, and the transfer efficiency is particularly excellent.
B: The transfer efficiency is 90% or more and less than 95%, 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.

[2-6] Fixing Strength Using an image forming apparatus as shown in FIG. 1 and FIG. 2, images of a predetermined pattern with the liquid developer obtained in each of the examples and the comparative examples were 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 160 ° 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).

[2-7] Fog density The reflection density of the non-image area of the recorded material on which the toner image was thermally fixed in [2-6] above was measured with a reflection densitometer (X-Rite), and evaluated according to the following criteria. did.
A: Less than 0.08.
B: 0.08 or more and less than 0.09.
C: 0.09 or more and less than 0.11.
D: 0.11 or more and less than 0.20.
E: 0.20 or more.
These results are shown in Table 3.

As is apparent from Table 3, the liquid developer of the present invention was excellent in electrophoretic mobility and could be suitably adapted to high-speed development. The liquid developer of the present invention was also excellent in positive charging characteristics and charging stability. Furthermore, the liquid developer of the present invention was excellent in dispersion stability of toner particles in the liquid developer, development efficiency, transfer efficiency, and the like. On the other hand, satisfactory results were not obtained with the liquid developer of the comparative example.
In addition, the cyan pigment was changed to a magenta pigment, a yellow pigment, and a black pigment, a liquid developer was produced in the same manner as described above, and the same evaluation was performed. Obtained.

  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 Supply unit 31bY Recovery unit 31cY Partition 32Y Application roller 33Y Restricting blade 34Y Developer stirring roller 35Y Communication unit 36Y Recovery screw 40 Intermediate transfer unit 4 ... belt drive rollers 44, 45 ... driven rollers 46 ... intermediate transfer section cleaning blade 47 ... developer recovery section 48 ... non-contact type bias applying member 49 ... tension rollers 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 ... Secondary transfer roller on upstream side 65 ... Secondary transfer roller on downstream side 66, 68 ... Secondary transfer roller cleaning blade 67, 69 ... Developer recovery unit 90Y, 90M, 90C, 90K ... Liquid developer supply unit 91Y, 91M, 91C, 91K ... Liquid developer tank 92Y, 92M, 92C, 92K ... Insulation Liquid liquid tongue 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 (9)

A liquid developer containing toner particles and an insulating liquid,
A fatty acid ester as the insulating liquid,
A liquid developer comprising a substance A represented by the following formula (1) at a content of 0.1% by mass or more and 3.0% by mass or less.

(In formula (1), R represents an organic group having 1 to 15 carbon atoms, and n is an integer of 1 to 3)   The liquid developer according to claim 1, wherein the substance A has a hydrocarbon group having a branched chain.   The liquid developer according to claim 1, wherein the substance A has a linear alkyl group having 4 to 12 carbon atoms. The liquid developer according to claim 1, wherein the substance A is represented by the following formula (2).

(In Formula (2), R ¹ represents a hydrocarbon group having 1 to 7 carbon atoms, and R ² represents a hydrocarbon group having 1 to 7 carbon atoms.) The liquid developer according to claim 1, wherein R ¹ has an unsaturated bond.   6. The liquid developer according to claim 1, wherein the fatty acid ester is an ester of a monovalent fatty acid and a monovalent alcohol.   The liquid developer according to claim 1, wherein the fatty acid ester is an ester of a fatty acid and a linear alcohol.   The liquid developer according to claim 1, wherein the fatty acid ester is an ester of a fatty acid and an alcohol having 4 to 14 carbon atoms.   The liquid developer according to claim 1, wherein the toner particles are made of a material containing a polyester resin.

Images