JP2012123060A - Liquid developer and production method of liquid developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid developer having little variation in characteristics (such as charging characteristics) among toner particles and suitably used for production of printed material having sufficient optical density (OD value).SOLUTION: The liquid developer contains an insulating liquid and toner particles. The toner particles has a single-peak particle diameter distribution, having a volume average particle diameter (D) of 2 μm or more and 4 μm or less, a particle diameter (D) of 0.8 μm or more and 1.8 μm or less at 10% mass cumulative distribution rate from a fine particle side, and a particle diameter (D) of 3 μm or more and 7 μm or less at 90% mass cumulative distribution rate from the fine particle side.

Description

  The present invention relates to a liquid developer and a method for producing the liquid developer.

A dry toner method in which a toner composed of a material containing a colorant such as a pigment and a binder resin is used in a dry state as a developer used to develop the electrostatic latent image formed on the latent image carrier. And a method using a liquid developer in which toner is dispersed in an electrically insulating carrier liquid (insulating liquid) (see, for example, Patent Document 1).
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, since toner particles are relatively less aggregated in the liquid developer, it is possible to use fine toner particles compared to dry toner, and as a binder resin, A resin material having a lower softening point (lower softening temperature) than the resin material used in the dry toner 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 variation in characteristics (for example, charging characteristics) among toner particles constituting the liquid developer is large. Further, when toner particles having a relatively large particle size are contained at a relatively high ratio, there is a problem that it is difficult to obtain a sufficient optical density (OD value).

JP 2002-258541 A

  An object of the present invention is to provide a liquid developer that can be suitably used for producing a printed matter having a small variation in characteristics (for example, charging characteristics) among toner particles and having a sufficient optical density (OD value). Another object of the present invention is to provide a method for producing a liquid developer capable of efficiently producing the liquid developer.

Such an object is achieved by the present invention described below.
The liquid developer of the present invention includes an insulating liquid and toner particles,
The toner particles have a volume average particle diameter (D ₅₀ ) of 2 μm or more and 4 μm or less, and a particle diameter (D ₁₀ ) at a volume cumulative distribution rate of 10% from the fine particle side is 0.8 μm or more and 1.8 μm or less. The particle size (D ₉₀ ) at a volume cumulative distribution rate of 90% from the fine particle side has a unimodal distribution of 3 μm or more and 7 μm or less.
Accordingly, it is possible to provide a liquid developer that can be suitably used for producing printed matter having a small optical density (OD value) with small variations in characteristics (for example, charging characteristics) among toner particles.

In the liquid developer of the present invention, it is preferable that the half width in the particle size distribution of the toner particles is 2 μm or less.
Thereby, variation in characteristics (for example, charging characteristics) among toner particles can be made particularly small.
The method for producing a liquid developer of the present invention is a method for producing a liquid developer containing an insulating liquid and toner particles,
A coarse pulverization step of roughly pulverizing a kneaded product containing a resin material and a colorant to obtain a coarse pulverized product;
A fine pulverization step of finely pulverizing the coarsely pulverized product in the insulating liquid by a wet pulverization method;
A heat treatment step in which the glass transition temperature of the resin material is Tg [° C.] and the softening point of the resin material is Tm [° C.], and heat treatment is performed at a temperature of Tg or higher and Tm or lower,
The toner particles have a volume average particle diameter (D ₅₀ ) of 2 μm or more and 4 μm or less, and a particle diameter (D ₁₀ ) at a volume cumulative distribution rate of 10% from the fine particle side is 0.8 μm or more and 1.8 μm or less. The particle size (D ₉₀ ) at a volume cumulative distribution rate of 90% from the fine particle side has a unimodal distribution of 3 μm or more and 7 μm or less.
As a result, it is possible to efficiently produce a liquid developer that can be suitably used for producing a printed matter having a small variation in characteristics (for example, charging characteristics) among toner particles and having a sufficient optical density (OD value). The manufacturing method of the liquid developer which can be provided can be provided.

In the method for producing a liquid developer of the present invention, it is preferable that the fine pulverization step is performed in the insulating liquid containing a graft copolymer of an acrylic polymer and polysiloxane.
This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. Further, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent.

In the method for producing a liquid developer of the present invention, the acrylic polymer preferably contains an alkyl acrylate as a monomer component.
This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. Further, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent.

In the method for producing a liquid developer according to the present invention, the polysiloxane is preferably dimethylpolysiloxane.
This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. Further, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent.

In the method for producing a liquid developer according to the aspect of the invention, it is preferable that the polysiloxane is obtained by adding an acrylic acid compound to the dimethylpolysiloxane.
This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. Further, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent.

In the method for producing a liquid developer according to the aspect of the invention, it is preferable that the pulverization step is performed in the insulating liquid containing a polyalkyleneimine.
This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. Further, the dispersion stability of the toner particles in the liquid developer and the positive charging characteristics can be made particularly excellent.

In the liquid developer production method of the present invention, it is preferable to use a resin material containing a rosin resin as the resin material.
This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. In particular, when the pulverization step is performed in an insulating liquid containing a polyalkyleneimine, surface modification with the polyalkyleneimine can be more suitably performed, and the positive charging characteristics of the liquid developer can also be achieved. It can be particularly high.

In the method for producing a liquid developer of the present invention, it is preferable to use a liquid containing at least one of silicone oil and siloxane compound as the insulating liquid.
This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. In particular, when the pulverization step is performed in an insulating liquid containing a graft copolymer of an acrylic polymer and polysiloxane, the dispersion stability of the toner particles in the liquid developer is particularly excellent. The storage stability and durability of the liquid developer can be made particularly excellent.

FIG. 2 is a schematic diagram illustrating a preferred embodiment of an image forming apparatus to which the 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 is one in which toner particles are dispersed in an insulating liquid.
<Toner particles>
[Toner particle shape]
In the present invention, the toner particles have a volume average particle diameter (D ₅₀ ) of 2 μm or more and 4 μm or less, and a particle diameter (D ₁₀ ) at a volume cumulative distribution rate of 10% from the fine particle side is 0.8 μm or more and 1.8 μm. The particle size (D ₉₀ ) at a volume cumulative distribution ratio of 90% from the fine particle side is unimodal distribution of 3 μm or more and 7 μm or less. By satisfying such a condition, variation in characteristics (for example, charging characteristics) among toner particles can be made sufficiently small, and optical in a printing part of a printed matter manufactured using a liquid developer. The concentration (OD value) can be made sufficiently high. Such an excellent effect is obtained by satisfying all the above conditions, and when there is one that does not satisfy even one of the above conditions, the above excellent effect is I can't get it. That is, when the volume average particle diameter (D ₅₀ ) is less than the lower limit value, there arises a problem that particles with unstable charge amount increase and the development efficiency decreases. Further, when the volume average particle diameter (D ₅₀₎ exceeds the upper limit, a problem that the OD value was filling rate decreases is lowered. Further, when the particle diameter (D ₁₀ ) at a mass cumulative distribution rate of 10% from the fine particle side is less than the lower limit value, there arises a problem that fog increases and development efficiency decreases. Further, when the particle diameter (D ₁₀ ) at a volume cumulative distribution rate of 10% from the fine particle side exceeds the upper limit value, there arises a problem that the OD value decreases. Further, when the particle diameter (D ₉₀ ) at the volume cumulative distribution rate 90% from the fine particle side is less than the lower limit, there arises a problem that the development efficiency is lowered. Further, when the particle diameter (D ₉₀ ) at a volume cumulative distribution ratio of 90% from the fine particle side exceeds the upper limit, there arises a problem that the OD value decreases. In addition, when there is no unimodal distribution, the charge amount of the particles can be different, and many fine particles with a low charge amount are collected during cleaning, which causes a problem in recycling. In the present invention, the “unimodal distribution” is a particle size distribution having a stationary point that is not the only extreme value and a single maximum value when the particle size distribution is normalized, and the maximum value It means that the strength satisfies the condition of 0.7 or more.

  The volume average particle diameter 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.).

As described above, in the present invention, the volume average particle diameter (D ₅₀ ) of the toner particles is 2 μm or more and 4 μm or less, more preferably 2.0 μm or more and 3.0 μm or less. Thereby, the effects as described above are more remarkably exhibited. Further, the resolution of the toner image formed with the liquid developer 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 invention, the particle diameter (D ₁₀ ) at a volume cumulative distribution rate of 10% from the fine particle side of the toner particles is 0.8 μm or more and 1.8 μm or less, but is 0.9 μm or more and 1.6 μm or less. It is preferable that it is 1.0 μm or more and 1.5 μm or less. Thereby, the effects as described above are more remarkably exhibited.
In the present invention, the particle size (D ₉₀ ) at a volume cumulative distribution rate of 90% from the fine particle side of the toner particles is 3 μm or more and 7 μm or less, but preferably 3.1 μm or more and 6.5 μm or less. More preferably, it is 3.2 μm or more and 5.5 μm or less. Thereby, the effects as described above are more remarkably exhibited.
Further, the full width at half maximum in the particle size distribution of the toner particles is preferably 3 μm or less, more preferably 1 μm or more and 2.5 μm or less. Thereby, variation in characteristics (for example, charging characteristics) among toner particles can be made particularly small.

[Component material of toner particles]
The toner particles include at least a resin material and a colorant.
1. Resin material (binder resin)
The toner particles are made of a material containing a resin material as a main component.
In the present invention, the resin material (binder resin) is not particularly limited, and for example, a known resin can be used. In particular, a resin having a highly polar functional group such as a carbonyl group or a carboxyl group is used. Is preferred. Thereby, for example, when the liquid developer contains a graft copolymer of an acrylic polymer and polysiloxane, which will be described in detail later, the graft copolymer is sufficiently adhered around the toner particles. And the function can be exhibited more effectively.

  Examples of such resins include styrene-acrylic resins, acrylic resins, and polyester resins. In particular, the polyester resin has high transparency, and when used as a binder resin, the color developability of the obtained image can be increased. Further, since the polyester resin is a material having a relatively large number of functional groups (acidic groups) highly reactive with polyalkyleneimine described later, when the liquid developer contains polyalkyleneimine, Thus, the surface modification can be suitably performed, and the positive charging characteristics of the liquid developer can be improved.

  The resin material preferably contains a rosin resin. This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. In addition, since the rosin resin is a material having a large number of functional groups (acidic groups) that are highly reactive with polyalkyleneimine described later, the pulverization step in the liquid developer manufacturing method described later is performed using polyalkylene. When performed in an insulating liquid containing imine, surface modification with polyalkyleneimine can be performed more suitably, and the positive charge characteristics of the liquid developer can be particularly high.

Examples of rosin-based resins include rosin-modified phenolic resins, rosin-modified maleic resins, rosin-modified polyester resins, fumaric acid-modified rosin resins, ester gums, etc., and use one or a combination of two or more of these. Can do.
The weight average molecular weight of the rosin resin is preferably 500 or more and 100,000 or less, more preferably 1000 or more and 80000 or less, and further preferably 1000 or more and 50000 or less. As a result, the fixing characteristics of the toner particles and the heat-resistant storage stability can be achieved at a higher level.

The acid value of the rosin resin is preferably 40 mgKOH / g or less, more preferably 30 mgKOH / g or less, and further preferably 5 mgKOH / g or more and 25 mgKOH / g or less. As a result, the fixing characteristics of the toner particles and the heat-resistant storage stability can be achieved at a higher level.
Further, the content of the rosin resin in the resin material constituting the toner particles is preferably 1% by mass or more and 50% by mass or less, and more preferably 5% by mass or more and 40% by mass or less. As a result, the fixing characteristics of the toner particles and the heat-resistant storage stability can be achieved at a higher level.

  The softening point of the resin material is not particularly limited, but is preferably 50 ° C or higher and 140 ° C or lower, more preferably 50 ° C or higher and 130 ° C or lower, and further preferably 60 ° C or higher and 120 ° C or lower. In the present specification, the softening point is defined by measurement conditions in a Koka type flow tester (manufactured by Shimadzu Corporation): temperature increase rate: 5 ° C./min, die hole diameter 1.0 mm, and pressure 1.96 MPa. Refers to the softening start temperature. Further, the glass transition temperature (Tg) is a glass transition in a differential heat curve obtained by a temperature rise measurement at a temperature rise rate of 5 ° C./min using a differential scanning calorimeter (DSC-60 manufactured by Shimadzu Corporation). It refers to the temperature at the intersection of the baseline before the start temperature and the tangent at the glass transition inflection point.

2. Colorant The toner may contain a colorant. The colorant is not particularly limited, and for example, known pigments and dyes can be used.
3. The surface of the polyalkyleneimine toner particles is preferably modified with polyalkyleneimine. The modification with polyalkyleneimine is a chemical reaction between at least a part of amino groups of polyalkyleneimine and at least a part of acidic groups (mainly carboxyl groups) derived from the resin material on the surface of the toner particles. , A covalent bond (amide bond), or an acidic group of the resin material and an amino group of the polyalkyleneimine form an ionic bond.

  The polyalkyleneimine has a large number of amino groups. Since such polyalkyleneimine is chemically attached (bonded) to the surface of the toner particles, many amino groups are present on the surface of the toner particles. And, when the amino group of the polyalkyleneimine contains a graft copolymer (acryl-polysiloxane graft copolymer) of an acrylic polymer and polysiloxane, which will be described in detail later, the acrylic-polysiloxane The carbonyl group at the acrylic polymer portion of the graft copolymer is attracted and the acryl-polysiloxane graft copolymer is likely to be present near the surface of the toner particles, so that the dispersion stability of the toner particles is particularly excellent. . Moreover, polyalkyleneimine can show high positive charge property, when an amino group attracts a cation. Since the amino group of the polyalkyleneimine and the carbonyl group of the acrylic-polysiloxane graft copolymer are electrically attracted to each other, the amino group and the carbonyl group are further polarized. Especially excellent.

Further, when hydrogen-modified silicone is contained in the insulating liquid, this amino group can efficiently attract protons derived from the hydrogen-modified silicone compound, and the positive charging characteristics of the toner particles can be further improved.
In addition, since such polyalkyleneimine is chemically attached to the surface of the toner particles, it is difficult to detach from the surface of the toner particles, and the positive charging characteristics of the toner particles can be improved over a long period of time. At the same time, the toner particles can be stably dispersed in the insulating liquid over a long period of time.

  Examples of the polyalkyleneimine include polyethyleneimine, polypropyleneimine, polybutyleneimine, polyisopropyleneimine and the like. Of these, polyethyleneimine is preferably used. As a result, the surface of the toner particles can be more suitably modified, and the long-term dispersion stability and positive charging characteristics of the toner particles can be further improved.

  The weight average molecular weight of the polyalkyleneimine is preferably 10,000 or more and 70,000 or less. When the weight average molecular weight of the polyalkyleneimine is in such a range, the toner particle surface can be more effectively modified (chemically modified), and due to steric hindrance due to the relatively long molecular chain of the polyalkyleneimine, Aggregation of the toner particles can be effectively prevented, and the dispersion stability of the toner particles can be effectively improved.

4). 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.
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>
Next, the insulating liquid will be described.
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 mentioned 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 cyclopentasiloxane and decamethylcyclopentasiloxane 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 (Cielzo) Mineral oils (hydrocarbon liquids) such as Le; trade name of Ciel Oil Co., Ltd.), Amsco OMS, Amsco 460 solvent (Amsco; trade name of Spirits), 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.

  Among the above, the insulating liquid preferably contains at least one of silicone oil and a low molecular siloxane compound. As a result, when the liquid developer contains an acrylic-polysiloxane graft copolymer, which will be described in detail later, the affinity between the insulating liquid and the acrylic-polysiloxane graft copolymer becomes high. As a result, the toner particles Becomes easier to disperse more stably in the insulating liquid.

Moreover, as a low molecular siloxane compound, a cyclic siloxane compound is preferable and cyclopentasiloxane and decamethylcyclopentasiloxane are more preferable. By including such a compound as the insulating liquid, the dispersion stability of the toner particles in the liquid developer becomes particularly excellent.
In addition, when the insulating liquid contains a silicone oil containing a hydrogen-modified silicone compound, the following effects can be obtained. The hydrogen-modified silicone compound has a hydrogen group at a part of the side chain or terminal of the polysiloxane. Part of this hydrogen is liberated as hydrogen ions (protons), and these protons are attracted to the functional group (acidic group) derived from the resin material present on the surface of the toner particles. As a result, the toner particles exhibit excellent positive chargeability, and are excellent in development efficiency and transfer efficiency.

  By the way, in general, hydrogen ions released from the hydrogen-modified silicone compound are likely to volatilize from the liquid developer as hydrogen molecules. As a result, the properties of the insulating liquid change due to the low molecular weight or chemical modification of the hydrogen-modified silicone compound. As a result, the dispersion stability of toner particles in the liquid developer and the charging property are reduced. There was a problem to bring. However, in the case where the liquid developer contains an acrylic-polysiloxane graft copolymer described in detail later, the acrylic polymer portion of the acrylic-polysiloxane graft copolymer captures (traps) hydrogen ions, and hydrogen ions Can be prevented from changing to hydrogen molecules. For this reason, even if the liquid developer contains a hydrogen-modified silicone, it contains both an acrylic-polysiloxane graft copolymer, so that there is little change in characteristics, and excellent dispersion stability and charging characteristics of toner particles. Maintained over time.

Here, “having a hydrogen group at a part of the side chain or terminal” means that a hydrogen group is directly bonded to the Si portion of the polysiloxane skeleton of the hydrogen-modified silicone compound.
Examples of the hydrogen-modified silicone compound include poly (methyl hydrogen siloxane), poly (ethyl hydrogen siloxane), poly (phenyl hydrogen siloxane), and the like.

In the hydrogen-modified silicone compound, the polysiloxane skeleton may be branched or linear.
Further, as described above, the hydrogen group is bonded to the side chain or the terminal of the polysiloxane skeleton. However, when bonded to the side chain, the hydrogen group easily releases hydrogen ions. The charging characteristics can be made particularly excellent. On the other hand, when a hydrogen group is bonded to the terminal, hydrogen ions are released relatively slowly, so that the hydrogen-modified silicone compound is hardly deteriorated, and the property change of the liquid developer is small over a long period of time. It becomes.

The hydrogen-modified silicone compound has a kinematic viscosity at 25 ° C. of preferably 20 mm ² / s to 500 mm ² / s, more preferably 20 mm ² / s to 80 mm ² / s, and more preferably 20 mm. more preferably not more than ² / s or more 40 mm ² / s. Thereby, the dispersibility of the toner particles can be further improved while improving the positive charging characteristics.

<Acrylic-polysiloxane graft copolymer>
The liquid developer preferably contains an acrylic-polysiloxane graft copolymer.
In general, with a liquid developer, a charged latent image is formed on a photoreceptor during image formation, and toner particles are attached to the latent image to obtain a toner image. For this reason, the toner particles need to be charged, and the insulating liquid in which the toner particles migrate needs to have insulating properties. In such a case, the toner particles having a high polarity of the constituent material do not have sufficient affinity with the insulating liquid having a low polarity of the constituent material, and the toner particles aggregate in the insulating liquid. There is a problem that the dispersion stability of the toner particles in the agent is not sufficient.

  On the other hand, as a result of earnest research, the present inventors have found that the occurrence of the above problems can be effectively prevented by including an acrylic-polysiloxane graft copolymer. That is, the (meth) acryl portion in the acrylic-polysiloxane graft copolymer has a relatively large polarity due to the carbonyl group in its skeleton. On the other hand, the polysiloxane portion has a relatively small polarity. For this reason, by having such each part, the acrylic-polysiloxane graft copolymer is such that the (meth) acrylic part has high affinity with the toner particles, and the polysiloxane part has affinity with the insulating liquid. It will be expensive. Further, since the acrylic-polysiloxane graft copolymer is present between the toner particles and the insulating liquid, the dispersion stability of the toner particles in the insulating liquid is excellent.

Further, by using such an acrylic-polysiloxane graft copolymer in the pulverization step of the production method described in detail later, the particle size distribution of the toner particles satisfies the predetermined condition as described above. Can be controlled more reliably.
Further, since the liquid developer contains such an acrylic-polysiloxane graft copolymer, the toner particles can be contained even if the toner particles have a relatively high chargeability and the insulating liquid has a relatively high insulation property. Aggregation is prevented. That is, the development and transfer characteristics of the liquid developer (which greatly depends on the charging characteristics of the toner particles) and the dispersion stability of the toner particles can be made excellent at the same time.

In addition, when the insulating liquid contains a hydrogen-modified silicone compound as described later, the acrylic-polysiloxane graft copolymer is suitable for preventing deterioration of the hydrogen-modified silicone compound and changing the characteristics of the liquid developer. Can be prevented.
The monomer component constituting the acrylic polymer is not particularly limited, and examples thereof include acrylic acid, methacrylic acid; acrylic acid or methacrylic acid derivatives such as alkyl acrylate, alkyl methacrylate, etc. Among these, 1 Species or a combination of two or more can be used.

Moreover, as an acrylic polymer comprised by the monomer component mentioned above, it is 1 or more types of monomers chosen from acrylic acid, methacrylic acid, or those alkylesters, Comprising: Carbon number of the alkyl group is 4 Examples thereof include polymers composed of the following monomers (acrylates).
Further, the acrylic-polysiloxane graft copolymer may include a plurality of types of acrylic polymers.

The acrylic polymer that constitutes the acrylic-polysiloxane graft copolymer is preferably acrylates and alkyl acrylates, and more preferably acrylates and ethylhexyl acrylate. Thereby, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent.
In addition, when a liquid developer is produced using a production method described in detail later, the toner particle size distribution can be controlled more reliably so as to satisfy a predetermined condition.
In addition, the acrylic polymer may include a monomer component other than the above.

  The polysiloxane constituting the acrylic-polysiloxane graft copolymer is not particularly limited, and examples thereof include dialkyl polysiloxanes such as dimethylpolysiloxane, diarylpolysiloxanes such as diphenylpolysiloxane, and the like. One kind or a combination of two or more kinds can be used. Among the above, the polysiloxane preferably contains a dialkylsiloxane, more preferably dimethylpolysiloxane. Thereby, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent. In addition, when a liquid developer is produced using a production method described in detail later, the toner particle size distribution can be controlled more reliably so as to satisfy a predetermined condition.

Moreover, the polysiloxane which comprises an acryl-polysiloxane graft copolymer may be substituted by the other functional group etc. in the side chain or the terminal. For example, an acrylic acid compound such as acrylic acid or methacrylic acid may be added to the side chain or terminal of polysiloxane. Thereby, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent. In addition, when a liquid developer is produced using a production method described in detail later, the toner particle size distribution can be controlled more reliably so as to satisfy a predetermined condition.
The polysiloxane may be linear or branched.

The acrylic-polysiloxane graft copolymer is obtained by graft polymerization of an acrylic polymer and polysiloxane. As a result, the acrylic-polysiloxane graft copolymer has many branched chains and is bulky. As a result, a portion having a relatively large polarity (acrylic polymer portion) and a portion having a relatively small polarity (polysiloxane portion) can sufficiently exhibit their functions.
More specifically, examples of the acrylic-polysiloxane graft copolymer as described above include KP-541, KP-575, KP-543, KP-545, KP-549, and the like. One or a combination of two or more can be used.

The acrylic-polysiloxane graft copolymer is preferably contained in an amount of 10 parts by weight to 50 parts by weight, and more preferably 15 parts by weight to 45 parts by weight with respect to 100 parts by weight of the toner particles. preferable. Thereby, the effect of the acrylic-polysiloxane graft copolymer can be sufficiently obtained, and the viscosity of the liquid developer can be made appropriate. On the other hand, if the content of the acrylic-polysiloxane graft copolymer in the liquid developer with respect to the toner particles is less than the lower limit value, the effect of the acrylic-polysiloxane graft copolymer may not be sufficiently obtained. is there. On the other hand, if the content of the acrylic-polysiloxane graft copolymer in the liquid developer with respect to the toner particles exceeds the upper limit, depending on the type of the acrylic-polysiloxane graft copolymer, the viscosity of the liquid developer may be extremely high. In such an image forming apparatus as will be described later, there is a possibility that problems such as dripping of the liquid developer from a coating roller or the like may occur.
In addition to the components described above, the liquid developer may contain, for example, a dispersant other than the acrylic-polysiloxane graft copolymer, an external additive, a known antioxidant, a charge control agent, and the like. .

  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 50 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 made particularly excellent. Further, the dispersibility of the toner particles can be made higher, and in the image forming apparatus as described later, the liquid developer can be supplied more uniformly to the application roller. It is possible to more effectively prevent the liquid developer from dripping. 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. On the other hand, if the viscosity of the insulating liquid is less than the lower limit, problems such as dripping of the liquid developer from the application roller or the like may occur in an image forming apparatus as described later. On the other hand, when the viscosity of the insulating liquid exceeds the upper limit, the dispersibility of the toner particles cannot be sufficiently increased, and the liquid developer cannot be more uniformly supplied to the application roller in an image forming apparatus as described later. There is a case. However, the viscosity in this specification refers to a value measured at 25 ° C.

≪Liquid developer manufacturing method≫
Next, a preferred embodiment of the liquid developer manufacturing method as described above will be described.
The liquid developer production method of the present embodiment includes a coarse pulverization step in which a kneaded product containing a resin material and a colorant is coarsely pulverized to obtain a coarse pulverized product, and the coarsely pulverized product in an insulating liquid is finely divided by a wet pulverization method. A pulverizing step for pulverizing, and a heat treatment step for performing a heat treatment at a temperature not lower than Tg and not higher than Tm when the glass transition temperature of the resin material is Tg [° C.] and the softening point of the resin material is Tm [° C.] Have Thereby, the liquid developer containing the toner particles having the particle size distribution as described above can be produced efficiently and reliably.

Hereafter, each process which comprises the manufacturing method of a liquid developer is demonstrated in detail.
[Coarse grinding process]
First, a kneaded product containing a resin material and a colorant is coarsely pulverized to obtain a coarsely pulverized product.
For pulverization of the kneaded product, for example, a hammer mill, a roll mill, or the like can be used.
As the resin material and the colorant constituting the kneaded material, those described above can be used, and when the kneaded material uses a resin material containing a rosin resin, the following is particularly true. Effects can be obtained. That is, the toner particle size distribution can be more reliably controlled so as to satisfy a predetermined condition. In particular, when the subsequent pulverization step is performed in an insulating liquid containing polyalkyleneimine, surface modification with polyalkyleneimine can be more suitably performed, and the positive charging of the liquid developer can be performed. The characteristics can also be particularly high.
The particle size of the coarsely pulverized product obtained in this step is preferably 5 mm or more and 20 mm or less. Thus, the subsequent fine pulverization step can be efficiently performed, and the liquid developer finally obtained is more surely to contain toner particles having a particle size distribution with more preferable conditions as described above. it can.

[Fine grinding process]
After the coarse pulverization step, the coarsely pulverized product is finely pulverized in an insulating liquid by a wet pulverization method.
This step can be performed by, for example, a planetary ball mill.
This step is preferably performed in an insulating liquid containing the acrylic-polysiloxane graft copolymer as described above. This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. Further, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent.

  As described above, the acrylic polymer constituting the acrylic-polysiloxane graft copolymer preferably contains an alkyl acrylate ester as a monomer component. This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. Further, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent.

  As described above, the polysiloxane constituting the acrylic-polysiloxane graft copolymer is preferably dimethylpolysiloxane. This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. Further, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent.

  In addition, as described above, the polysiloxane constituting the acrylic-polysiloxane graft copolymer is preferably one obtained by adding an acrylic acid compound to dimethylpolysiloxane. This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. Further, the dispersion stability of the toner particles in the liquid developer can be made particularly excellent, and the storage stability and durability of the liquid developer can be made particularly excellent.

The pulverization step is preferably performed in an insulating liquid containing polyalkyleneimine. This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. Further, the dispersion stability of the toner particles in the liquid developer and the positive charging characteristics can be made particularly excellent.
In this step, it is preferable to use a liquid containing at least one of silicone oil and siloxane compound as the insulating liquid. This makes it possible to control the toner particle size distribution more reliably so as to satisfy the predetermined condition. In particular, when the pulverization step is performed in an insulating liquid containing a graft copolymer of an acrylic polymer and polysiloxane, the dispersion stability of the toner particles in the liquid developer is particularly excellent. The storage stability and durability of the liquid developer can be made particularly excellent. Such an effect is particularly remarkable when dimethyl silicone is used.

[Heat treatment process]
Thereafter, the composition subjected to the fine pulverization step is subjected to heat treatment. In particular, in this step, when the glass transition temperature of the resin material is Tg [° C.] and the softening point of the resin material is Tm [° C.], heat treatment is performed at a temperature not lower than Tg and not higher than Tm.
As a result, the particle size distribution of the toner particles constituting the liquid developer can be reliably controlled so as to satisfy the predetermined condition as described above, and the obtained liquid developer can be transferred between the toner particles. Variation in characteristics (for example, charging characteristics) is small, and can be suitably used for the production of printed matter having a sufficient optical density (OD value). Further, by using the above method, the above liquid developer can be produced efficiently.

  As described above, the treatment temperature in this step may be Tg [° C.] or more and Tm [° C.] or less, but is preferably (Tg + 5) [° C.] or more and (Tm−10) [° C.] or less. More preferably, the temperature is (Tg + 10) [° C.] or more and (Tm−35) [° C.] or less. As a result, the particle size distribution of the toner particles can be controlled more reliably so as to satisfy the predetermined condition as described above, and the productivity of the liquid developer can be made particularly excellent. it can. In addition, when the resin material constituting the coarsely pulverized product is composed of a plurality of types of components (resin components), the glass transition temperature and softening point of the mixture as a whole are adopted as Tg and Tm. It shall be.

The heat treatment time in this step is preferably 10 minutes or more and 180 minutes or less, and more preferably 15 minutes or more and 60 minutes or less. As a result, the particle size distribution of the toner particles can be controlled more reliably so as to satisfy the predetermined condition as described above, and the productivity of the liquid developer can be made particularly excellent. it can.
Further, this step is preferably performed while applying shear. Thereby, the effects as described above are more remarkably exhibited. Further, the dispersion stability of the toner particles in the insulating liquid can be made particularly excellent. Further, the uniformity of charging characteristics of each toner particle can be made particularly excellent.
When this step is performed while applying shear, it is preferable to apply a shear of 300 rpm to 1200 rpm, and it is more preferable to apply a shear of 400 rpm to 900 rpm.

≪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 case where a liquid developer is produced using a method having a coarse pulverization step, a fine pulverization step, and a heat treatment step is representatively described. It may not be manufactured using such a method. Moreover, you may manufacture using the method which has processes other than a coarse pulverization process, a fine pulverization process, and a heat treatment process. For example, after the pulverization step (between the pulverization step and the heat treatment step, or after the heat treatment step), there is a step of mixing an insulating liquid having a composition different from that of the insulating liquid used in the pulverization step. May be. That is, the insulating liquid constituting the finally obtained liquid developer may have a different composition. By having such a process, the composition of the finally obtained liquid developer can be made particularly preferable while making the processing efficiency of the pulverization process particularly high.

[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
[Coarse grinding process]
First, a polyester resin (acid value: 10 mgKOH / g, glass transition temperature: 55 ° C., softening point: 120 to 130 ° C.): 60% by mass was prepared as a resin material.

Next, a mixture (mass ratio 50:50) of the resin material and a black pigment (Degussa, Printex L 15: 3) as a colorant was 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 kneader extruded from the extrusion port of the biaxial kneading extruder was cooled.
The kneaded product cooled as described above was roughly pulverized to obtain a colorant master batch having an average particle size of 1.0 mm or less. A hammer mill was used for coarse pulverization of the kneaded product.

  Colorant masterbatch: 15% by mass, polyester resin: 68% by mass, rosin-modified maleic resin (Arakawa Chemical Industries, trade name “Marquide No. 1”, acid value: 25 mgKOH / g or less, glass transition temperature: 55 ° C., softening point: 120 to 130 ° C., weight average molecular weight: 3100): 17% by mass were kneaded using a biaxial kneading extruder. And the kneaded material extruded from the extrusion port of the biaxial kneading extruder was cooled. The obtained kneaded product was pulverized with a hammer mill to obtain a coarsely pulverized product having an average particle size of 10 mm.

[Fine grinding process]
Coarse pulverized product obtained by the above method: 32% by mass, acrylic-polysiloxane graft copolymer solution (KP-545, manufactured by Shin-Etsu Chemical Co., Ltd., copolymer component: alkyl acrylate / dimethylpolysiloxane, solvent: Cyclopentasiloxane, solid content: 30% by mass): 14% by mass, dimethyl silicone oil as an insulating liquid (KF-96-50cs: manufactured by Shin-Etsu Chemical Co., Ltd.): 80% by mass, polyethyleneimine (number average molecular weight; 1800) ): Put 1.2% by mass in a ceramic pot (contents 1600 ml), and then add zirconia balls (ball diameter: 2 mm) into the ceramic pot so that the volume filling rate is 40%, and rotate at a planetary ball mill. Wet grinding was performed at 200 rpm for 24 hours.
The volume average particle diameter (D ₅₀ ) of the fine particles contained in the obtained composition (composition subjected to the fine pulverization step) was 3.2 μm. The particle size of the fine particles contained in the composition was measured with Microtrac MT-3000 (manufactured by Nikkiso Co., Ltd.). Moreover, the particle diameter was similarly calculated | required about the particle | grains obtained by each Example and each comparative example demonstrated below.

[Heat treatment process]
The finely pulverized composition was transferred to a beaker and placed on a hot stirrer and heated at 54 ° C. At that time, a shear of 600 rpm was applied. The heat treatment was performed for 2 hours. Thereafter, it was naturally cooled to room temperature to obtain a liquid developer. The resulting liquid developer has a viscosity at 25 ° C. of 155 mPa.s. s. Further, the volume average particle diameter (D ₅₀ ) of the toner particles is 2.1 μm, the particle diameter (D ₁₀ ) at a mass cumulative distribution rate of 10% from the fine particle side is 1.0 μm, and the mass from the fine particle side. The particle size (D ₉₀ ) at a cumulative distribution rate of 90% was 3.5 μm and had a unimodal distribution. Further, the full width at half maximum in the particle size distribution of the toner particles was 1.9 μm. The viscosity of the liquid developer at 25 ° C. was determined by measurement under the condition of 10 mm / s using an E-type viscometer.
(Examples 2 to 13)
A liquid developer was produced in the same manner as in Example 1 except that the materials used for the production of the liquid developer were as shown in Table 1, and the heat treatment conditions in the heat treatment step were as shown in Table 1.

(Comparative Examples 1-6)
A liquid developer was produced in the same manner as in Example 1 except that the materials used for the production of the liquid developer were as shown in Table 1, and the heat treatment conditions in the heat treatment step were as shown in Table 1.
(Comparative Example 7)
A liquid developer was produced in the same manner as in Comparative Example 1 except that the heat treatment step was omitted.
Table 1 shows the composition and the like of the liquid developer for each of the above Examples and Comparative Examples.
In the table, polyester resin (acid value: 10 mg KOH / g, glass transition temperature: 55 ° C., softening point: 120 to 130 ° C.) is PES1, rosin modified maleic resin (manufactured by Arakawa Chemical Industries, Ltd., trade name “Marquide No. 1 ”, acid value: 25 mgKOH / g or less, glass transition temperature: 54 ° C., softening point: 120 to 130 ° C., weight average molecular weight: 3100) RM1, rosin modified polyester resin (Arakawa Chemical Industries, trade name“ TFS ”) -015 ", acid value: 11.8 mg KOH / g, glass transition temperature: 76 ° C, softening point: 120-130 ° C, weight average molecular weight: 1300) is RPES1, rosin-modified polyester resin (trade name, manufactured by Arakawa Chemical Industries, Ltd.) “Traffus 4102”, acid value: 15 mg KOH / g, glass transition temperature: 55 ° C., softening point: 94 to 105 ° C., weight average molecular weight 1600) RPES2 and rosin modified phenolic resin (Arakawa Chemical Industries, trade name “Tamanol 135”, acid value: 18 mg KOH / g or less, glass transition temperature: 52 ° C., softening point: 130-140 ° C., weight average molecular weight : 15000) with RPH1, acrylic-polysiloxane graft copolymer solution (KP-545, manufactured by Shin-Etsu Chemical Co., Ltd.), copolymer component: (alkyl acrylate / dimethylpolysiloxane) copolymer, solvent: cyclopentasiloxane, solid %: 30% by mass), the acrylic-polysiloxane graft copolymer component is KP-545, an acrylic-polysiloxane graft copolymer solution (KP-575, manufactured by Shin-Etsu Chemical Co., Ltd., copolymer component: acrylates / Ethylhexyl acrylate / dimethylpolysiloxane methacrylate, solvent: de The acrylic-polysiloxane graft copolymer component contained in methylcyclopentasiloxane (solid content: 30% by mass) is KP-575, an acrylic-polysiloxane graft copolymer solution (KP-543, manufactured by Shin-Etsu Chemical Co., Ltd., Polymer component: alkyl acrylate / dimethylpolysiloxane, solvent: butyl acetate, solid content: 50% by mass), the acrylic-polysiloxane graft copolymer component is KP-543, an acrylic-polysiloxane graft copolymer solution. (KP-550, manufactured by Shin-Etsu Chemical Co., Ltd., copolymer component: alkyl acrylate / dimethylpolysiloxane, solvent: isododecane, solid content: 40% by mass), an acrylic-polysiloxane graft copolymer component contained in KP- 550, acrylic-polysiloxane graft copolymer solution (KP-54 1, Shin-Etsu Chemical Co., Ltd., copolymer component: alkyl acrylate / dimethylpolysiloxane, solvent: isopropanol, solid content: 60% by mass), the acrylic-polysiloxane graft copolymer component contained in KP-541, dimethyl Silicone oil (KF-96-50cs, manufactured by Shin-Etsu Chemical Co., Ltd.) was indicated as KF-96-50cs, and polyalkyleneimine (number average molecular weight: 1800) was indicated as PEI.

[2] Evaluation The following evaluation was performed on the liquid developer obtained as described above.
[2.1] Evaluation of Uniformity of Charging Characteristics of Toner Particles The charge bias between the electrodes was measured with a space charge measuring device (PEA). The waveform when a voltage of 300 V was applied to the device was measured, and the charge distribution between the electrodes was observed. The distribution was evaluated according to the following three criteria.
A: Charged particles are concentrated near the electrode B: Charged particles are present within half of the electrode C: Charged particles are diffusing more than half It is shown in 2.

[2.2] Evaluation of Image Density of Printed Material Recording paper (manufactured by Seiko Epson Corporation, high quality) by applying a liquid developer to the image forming apparatus as shown in FIGS. 1 and 2 so that the thickness becomes 5 μm. A printing part was formed on paper LPCPPA4).
The image density of the printed portion thus formed was measured with X-Rite (“X-Rite model 404” manufactured by Inc.).

[2.3] Evaluation of development residue (fogging) Using the image forming apparatus as shown in FIGS. 1 and 2, the liquid development obtained in each of the above examples and comparative examples on the developing roller of the image forming apparatus. A liquid developer layer was formed with the agent.
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: Development efficiency is 90% or more (fogging is very small)
B: Development efficiency is 80% or more and less than 90% (less fogging)
C: Development efficiency is 70% or more and less than 80% (normal)
D: Development efficiency is 60% or less (a lot of fogging)
These results are shown in Table 2.

  As is apparent from Table 2, the liquid developer of the present invention has a small variation in characteristics among toner particles, and can be suitably used for the production of printed matter having a sufficient optical density. Moreover, in the liquid developer of the present invention, it was possible to effectively prevent the development residue (fogging). On the other hand, satisfactory results were not obtained with the liquid developers of the comparative examples.

  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 (10)

Including an insulating liquid and toner particles;
The toner particles have a volume average particle diameter (D ₅₀ ) of 2 μm or more and 4 μm or less, and a particle diameter (D ₁₀ ) at a volume cumulative distribution rate of 10% from the fine particle side is 0.8 μm or more and 1.8 μm or less. A liquid developer having a unimodal distribution in which the particle diameter (D ₉₀ ) at a volume cumulative distribution rate of 90% from the fine particle side is 3 μm or more and 7 μm or less.   The liquid developer according to claim 1, wherein a half width in a particle size distribution of the toner particles is 2 μm or less. A method for producing a liquid developer comprising an insulating liquid and toner particles, comprising:
A coarse pulverization step of roughly pulverizing a kneaded product containing a resin material and a colorant to obtain a coarse pulverized product;
A fine pulverization step of finely pulverizing the coarsely pulverized product in the insulating liquid by a wet pulverization method;
A heat treatment step in which the glass transition temperature of the resin material is Tg [° C.] and the softening point of the resin material is Tm [° C.], and heat treatment is performed at a temperature of Tg or higher and Tm or lower,
The toner particles have a volume average particle diameter (D ₅₀ ) of 2 μm or more and 4 μm or less, and a particle diameter (D ₁₀ ) at a volume cumulative distribution rate of 10% from the fine particle side is 0.8 μm or more and 1.8 μm or less. And a method for producing a liquid developer, wherein the particle diameter (D ₉₀ ) at a volume cumulative distribution rate of 90% from the fine particle side has a unimodal distribution of 3 μm or more and 7 μm or less.   The method for producing a liquid developer according to claim 3, wherein the pulverizing step is performed in the insulating liquid containing a graft copolymer of an acrylic polymer and polysiloxane.   The method for producing a liquid developer according to claim 4, wherein the acrylic polymer contains an acrylic acid alkyl ester as a monomer component.   The method for producing a liquid developer according to claim 4, wherein the polysiloxane is dimethylpolysiloxane.   The method for producing a liquid developer according to claim 4, wherein the polysiloxane is obtained by adding an acrylic acid compound to the dimethylpolysiloxane.   The method for producing a liquid developer according to claim 3, wherein the pulverizing step is performed in the insulating liquid containing polyalkyleneimine.   The method for producing a liquid developer according to claim 3, wherein the resin material includes a rosin resin.   The method for producing a liquid developer according to claim 3, wherein the insulating liquid includes at least one of silicone oil and a siloxane compound.

Images