JP2009186970A - Liquid developer and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developer which has superior positive charge property and has superior dispersion stability of toner particles for a long period of time, and to provide an image forming apparatus using such a liquid developer. <P>SOLUTION: The liquid developer comprises an insulation liquid, toner particles and a dispersant, wherein at least a part of the surface of each of the toner particles contains a rosin resin and the dispersant is a material having an amine value. The amine value of the dispersant is preferably in a range of 1 to 100 mgKOH/g. A content of the dispersant is preferably 0.2 to 10 pts.wt. per 100 pts.wt. of the toner particles. A softening point of the rosin resin is preferably 80 to 190°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

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, a resin material such as a polyester resin, a styrene-acrylic acid ester copolymer, or an epoxy resin has been used for toner particles constituting such a liquid developer. 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, in conventional liquid developers, the affinity between the resin material constituting the toner particles and the insulating liquid is low, and it is difficult to sufficiently disperse the toner particles in the insulating liquid. It was.
In order to improve the dispersibility of such toner particles, an attempt has been made to use a rosin resin having a high affinity with an insulating liquid as a resin material constituting the toner particles (see, for example, Patent Document 1). .)
However, in the liquid developer described in Patent Document 1, the initial dispersibility of the toner particles is good, but the toner particles aggregate over time, and it is difficult to maintain the dispersibility for a long time. It was. Further, conventional liquid developers cannot obtain sufficient charging characteristics, and in particular, it is difficult to obtain positive charging characteristics.

Japanese Patent No. 3332961

  An object of the present invention is to provide a liquid developer having excellent positive charge characteristics and excellent long-term dispersion stability of toner particles, and to provide an image forming apparatus using such a liquid developer. It is in.

Such an object is achieved by the present invention described below.
The liquid developer of the present invention includes an insulating liquid, toner particles, and a dispersant.
The toner particles are those in which a rosin resin is present on at least a part of the surface,
The dispersant has an amine value.
In the liquid developer of the present invention, the amine value of the dispersant is preferably 1 to 100 mgKOH / g.

In the liquid developer of the present invention, the dispersant preferably has at least one structure selected from the group consisting of a secondary amine structure, a tertiary amine structure, and an amide bond structure in the molecule.
In the liquid developer of the present invention, the content of the dispersant is preferably 0.2 to 10 parts by weight with respect to 100 parts by weight of the toner particles.

In the liquid developer of the present invention, it is preferable that the toner particles include a resin material having an ester bond in addition to the rosin resin.
In the liquid developer of the present invention, the rosin resin preferably has a softening point of 80 to 190 ° C.
In the liquid developer of the present invention, the rosin resin preferably has a weight average molecular weight of 500 to 100,000.

In the liquid developer of the present invention, it is preferable that the insulating liquid is mainly composed of vegetable oil.
The image forming apparatus of the present invention includes a plurality of developing units that form a single color image corresponding to the plurality of liquid developers by using a plurality of liquid developers having different colors.
An intermediate transfer unit that sequentially transfers a plurality of the single-color images formed by the plurality of developing units, and forms an intermediate transfer image formed by superimposing the transferred single-color images;
A secondary transfer unit that transfers the intermediate transfer image to the recording medium and forms an unfixed color image on the recording medium;
A fixing unit for fixing the unfixed color image on the recording medium,
The liquid developer includes an insulating liquid, toner particles, and a dispersant.
The toner particles are those in which a rosin resin is present on at least a part of the surface,
The dispersant has an amine value.

  With such a configuration, it is possible to provide a liquid developer having excellent positive charging characteristics and excellent long-term dispersion stability of toner particles. In addition, an image forming apparatus using such a liquid developer can be provided.

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 an insulating liquid, toner particles, and a dispersant having an amine value. In the present invention, the toner particles have a rosin resin on at least a part of the surface.

  By the way, conventionally, in order to improve the dispersibility of the toner particles in the insulating liquid, an attempt has been made to use a rosin resin having a high affinity with the insulating liquid as a resin material constituting the toner particles. . However, in the conventional liquid developer, the initial dispersibility of the toner particles is good, but the toner particles aggregate over time, and it is difficult to maintain the dispersibility over a long period of time. Further, conventional liquid developers cannot obtain sufficient charging characteristics, and in particular, it is difficult to obtain positive charging characteristics.

  In view of the above problems, the present inventors have intensively studied and as a result, completed the present invention. That is, in the present invention, the toner particles having a rosin resin on at least a part of the surface and the dispersant having an amine value are used in combination, so that the positively charged characteristics are excellent and the toner particles are stable over a long period of time. Thus, a liquid developer that can be dispersed can be provided. That is, it is possible to provide a liquid developer having excellent positive charge characteristics and excellent long-term dispersion stability of toner particles. In addition, because of excellent charging characteristics and long-term dispersion stability, the liquid developer is excellent in characteristics such as development efficiency and transfer efficiency.

Hereinafter, each component will be described in detail.
<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)
The toner particles are made of a material containing a resin material as a main component.

In the present invention, the toner particles are those in which a rosin resin is present on at least a part of the surface thereof.
The rosin resin is a component having a high affinity (compatibility) with an insulating liquid as described later. Therefore, toner particles in which such a rosin resin is present on at least a part of the surface have particularly high dispersion stability in an insulating liquid as described later. Further, since the rosin resin has high affinity with a dispersant having an amine value as described later, the dispersant as described later can be firmly attached (adsorbed) to the surface of the toner particles. Further, since such a rosin resin is plasticized by an insulating liquid, a dispersant as described later can be adhered (adsorbed) more firmly to a portion where the rosin resin is exposed. As a result, the dispersibility of the toner particles can be improved over a long period of time, and the charging characteristics of the liquid developer can be improved.

  The rosin resin may be any resin that exists on at least a part of the surface of the toner particles, may be unevenly distributed on the surface of the toner particles, or may exist so as to cover the surface of the toner particles. It may be. In the latter case, a larger amount of the dispersant as described later can be present (adsorbed) near the toner particle surface. As a result, the dispersibility of the toner particles can be increased over a long period of time, and the charging characteristics of the liquid developer can be particularly improved.

Examples of such 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 are combined. Can be used.
The softening point of the rosin resin as described above is preferably 80 to 190 ° C, more preferably 80 to 160 ° C, and further preferably 80 to 130 ° C. As a result, it is possible to achieve a higher level of toner particle fixing characteristics and heat-resistant storage stability while improving the long-term dispersion stability and charging characteristics of the toner particles.

The weight average molecular weight of the rosin resin is preferably 500 to 100,000, more preferably 1000 to 80000, and further preferably 1000 to 50000. As a result, it is possible to achieve a higher level of toner particle fixing characteristics and heat-resistant storage stability while improving the long-term dispersion stability and charging characteristics of the toner particles.
The acid value of the rosin resin is preferably 40 mgKOH / g or less, more preferably 30 mgKOH / g or less, and further preferably 25 mgKOH / g or less. As a result, a larger amount of the dispersant as described later can be present (adsorbed) near the surface of the toner particles.

The content of the rosin resin in the resin material constituting the toner particles is preferably 1 to 50 wt%, and more preferably 5 to 40 wt%. As a result, the rosin resin can be more reliably present on the surface of the toner particles, and the long-term dispersion stability of the toner particles can be more effectively improved.
The toner particles may contain a known resin other than the rosin resin as described above.

  In particular, it is preferable to use a rosin resin as described above in combination with a resin material having an ester bond. The resin material having such a bond tends to be less compatible with the rosin resin, and the rosin resin can be surely present on the surface of the toner particles. As a result, more dispersant can be attached or adsorbed on the surface of the toner particles, the positive charging characteristics of the toner particles can be made higher, and the dispersion stability of the toner particles can be made higher. can do. Further, the high temperature storage stability of the liquid developer can be made higher.

  Examples of the resin material having an ester bond include polyester resins, styrene-acrylic acid ester copolymers, and methacrylic resins. Among these, it is particularly preferable to use a polyester resin. The polyester resin has high transparency, and when used as a binder resin, the color developability of the obtained image can be increased. In addition, the polyester resin can easily control the compatibility / incompatibility balance with the rosin resin, and can easily take a phase separation structure or a gradient structure with the rosin resin in the toner particles. A rosin resin can be present.

  Moreover, as a polyester resin, it is preferable to use together the low molecular weight polyester resin whose weight average molecular weight is 3000-12000, and the high molecular weight polyester resin whose weight average molecular weight Mw is 20000-400000. Thereby, the rosin resin can be surely present on the surface of the toner particles. In addition, the toner particles can be reliably prevented from aggregating during storage, and the toner particles can be fixed to the recording medium at a relatively low temperature during fixing.

  The low molecular weight polyester resin preferably has ethylene glycol (EG) and / or neopentyl glycol (NPG) as a constituent monomer component. In addition, the content of EG in all the constituent monomers used when synthesizing the low molecular weight polyester resin is W (EG) [wt%], and the content of NPG is W (NPG) [wt%]. In this case, the value of the weight ratio W (EG) / W (NPG) between EG and NPG is preferably 0 to 1.1, and more preferably 0.8 to 1.0. Thereby, the storage stability of the toner particles can be made sufficiently excellent. Further, it can be more stably fixed on the recording medium at a low temperature. Further, such a liquid developer can be more suitably applied to image formation at high speed.

  Moreover, it is preferable that it is 30-55 degreeC, and, as for the glass transition point Tg of a low molecular weight polyester resin, it is more preferable that it is 35-50 degreeC. By using a low molecular weight polyester resin that satisfies the above conditions as a constituent material of toner particles, aggregation and fusion of toner particles are more reliably suppressed during storage, and the storage stability of the liquid developer is superior. It becomes. Further, the toner particles can be more suitably fixed on the recording medium at a low temperature.

  The softening point Tf of the low molecular weight polyester resin is preferably 60 to 120 ° C, more preferably 80 to 110 ° C. By using a polyester resin that satisfies the above conditions as a constituent material of the toner particles, during storage, aggregation and fusion of the toner particles are more reliably suppressed, and the storage stability of the liquid developer becomes better. . Further, at the time of fixing, the toner particles can be melted with a smaller amount of heat. Thereby, the toner particles can be fixed more stably at a low temperature. Further, such a liquid developer is more suitably adapted to high-speed image formation.

  In this specification, the glass transition point Tg is a measurement condition in a differential scanning calorimeter DSC-220C (manufactured by SII): a sample amount of 10 mg, a heating rate of 10 ° C./min, and a measuring temperature range of 10 to 150 ° C. When measured, it refers to the temperature at the intersection of an extension of the baseline below the glass transition point and a tangent that indicates the maximum slope from the peak rise to the peak apex.

The softening point refers to a softening start temperature defined by measurement conditions in a Koka flow tester (manufactured by Shimadzu Corporation): temperature rising rate: 5 ° C./min and die hole diameter 1.0 mm.
Further, when the polyester resin is included in the toner particles, the content of the low molecular weight polyester resin in the polyester resin is preferably 50 to 90 wt%, and more preferably 60 to 80 wt%. As a result, the storage stability and low-temperature fixability of the liquid developer are particularly excellent.

  The high molecular weight polyester resin as described above preferably has ethylene glycol (EG) and / or neopentyl glycol (NPG) as a constituent monomer component. In addition, when synthesizing such a polyester resin, the content of EG in all constituent monomers is W (EG) [wt%], and the content of NPG is W (NPG) [wt%]. The value of the weight ratio W (EG) / W (NPG) between EG and NPG is preferably 1.2 to 3.0, more preferably 1.5 to 2.0. As a result, the storage stability of the liquid developer is particularly excellent. Further, at the time of fixing, the toner particles can be more preferably fixed at a low temperature. Further, the fixed toner particles are further improved in adhesion to the recording medium and weather resistance, and the obtained toner image has particularly excellent durability.

  Moreover, it is preferable that it is 45-70 degreeC, and, as for the glass transition point Tg of a high molecular weight polyester resin, it is more preferable that it is 50-65 degreeC. By using a high molecular weight polyester resin that satisfies the above conditions as a constituent material of toner particles, the aggregation and fusion of toner particles are more reliably suppressed during storage, and the storage stability of the liquid developer is superior. It becomes. In particular, even when the liquid developer is stored at a high temperature, the toner particles are more reliably prevented from aggregating with each other, and the liquid developer is particularly excellent in high-temperature storage. Further, the toner particles can be more suitably fixed on the recording medium at a low temperature.

  Moreover, it is preferable that it is 60-220 degreeC, and, as for the softening point Tf of a high molecular weight polyester resin, it is more preferable that it is 80-190 degreeC. By using a polyester resin that satisfies the above conditions as a constituent material of the toner particles, during storage, aggregation and fusion of the toner particles are more reliably suppressed, and the storage stability of the liquid developer becomes better. . Further, at the time of fixing, the toner particles can be fixed more firmly on the recording medium at a low temperature.

  The glass transition point Tg of the low molecular weight polyester resin and the polyester resin containing the high molecular weight polyester resin as described above is preferably 35 to 60 ° C, and more preferably 40 to 50 ° C. By using a polyester resin that satisfies the above conditions as a constituent material of the toner particles, aggregation and fusion of the toner particles are more reliably suppressed during storage, and the storage stability of the liquid developer is further improved. Further, the toner particles can be more suitably fixed on the recording medium at a low temperature.

When the toner particles include a polyester resin, the content of the high molecular weight polyester resin in the polyester resin is preferably 10 to 50 wt%, and more preferably 20 to 40 wt%. As a result, the storage stability and low-temperature fixability of the liquid developer are particularly excellent.
The acid value of the resin material other than the rosin resin contained in the toner particles is preferably 5 to 20 mgKOH / g, and more preferably 5 to 15 mgKOH / g. As a result, the rosin resin can be more reliably present on the toner particle surface, and a dispersant having an amine value as described later can be more effectively adsorbed near the toner particle surface. As a result, it is possible to improve the long-term dispersion stability and positive charging characteristics of the toner particles.

  The softening point of the resin material other than the rosin resin and the polyester resin contained in the toner particles is not particularly limited, but is preferably 50 to 130 ° C, more preferably 50 to 120 ° C, and more preferably 60 to More preferably, it is 115 degreeC. Thereby, the fixing property of the toner particles can be made particularly excellent. In the present specification, the softening point is a measurement condition in a Koka type flow tester (manufactured by Shimadzu Corporation): a temperature increase rate: 5 ° C./min, and a softening start temperature defined by a die hole diameter of 1.0 mm. Point to.

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. Other Components The toner 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 to 3 μm, more preferably 1 to 2.5 μm, and further preferably 1 to 2 μm. 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 content ratio of the toner particles in the liquid developer is preferably 10 to 60 wt%, and more preferably 20 to 50 wt%.

<Dispersant>
Next, the dispersant will be described.
The liquid developer of the present invention contains a dispersant having an amine value.
By the way, rosin-based resins and other resin materials as described above are generally negatively charged. When such a negatively chargeable resin material is used, it is difficult to positively charge the toner particles (liquid developer). In addition, it is conceivable to add a charge control agent to toner particles using such a negatively chargeable resin material for positive charging, but it is difficult to obtain a sufficient charge amount. Although it is conceivable to use a positively chargeable resin material as a constituent material of toner particles, a positively chargeable resin material has low stability of the resin itself and is difficult to apply as a material constituting toner particles. Met.

On the other hand, the following effects can be obtained by using a dispersant having an amine value as in the present invention.
The rosin resin is generally a component having a high acid value. When such a component having a high acid value is present on the surface of the toner particles, the dispersant having an amine value adheres or adsorbs so as to cover the surface of the toner particles. Further, the dispersant having an amine value has high compatibility (affinity) with the above-described rosin resin, and is firmly attached or adsorbed on the surface of the toner particles. As a result, the long-term dispersion stability of the toner particles can be made particularly excellent. Further, in the image forming apparatus described later, when the liquid developer collected in the developing unit or the like is reused, the toner particles in the collected liquid developer can be easily redispersed, and easily Can be reused.

In addition, the dispersant having an amine value has a nitrogen atom derived from an amine structure or an amide structure in the molecule. This nitrogen atom attracts protons (H ⁺ ) liberated from the acidic group of the resin material, so that the toner particles can be positively charged.
Further, the dispersant having an amine value has high compatibility with an insulating liquid as described later, and makes the dispersion stability of the toner particles particularly high by adhering (adsorbing) to the surface of the toner particles. Can do.

As described above, in the present invention, by using the toner particles using the rosin resin together with the dispersant having an amine value, the obtained liquid developer has excellent long-term dispersion stability of the toner particles and is positively charged. The charging characteristics are excellent. In addition, the characteristics such as development efficiency and transfer efficiency are excellent.
The dispersant having an amine value preferably has at least one structure selected from the group consisting of a secondary amine structure, a tertiary amine structure, and an amide bond structure in the molecule. As a result, the dispersant can be more firmly adsorbed on the surface of the toner particles, and the long-term dispersion stability and positive charging characteristics of the toner particles can be further improved.

  The dispersant used in the present invention has an amine value, and the amine value is preferably 1 to 100 mgKOH / g, more preferably 10 to 80 mgKOH / g. Thereby, the toner particles can be positively charged more reliably and the dispersion stability of the toner particles can be further increased. On the other hand, if the amine value of the dispersant is less than the lower limit, sufficient positive charging characteristics may not be obtained. Moreover, when the amine value of the said dispersing agent exceeds the said upper limit, dispersing agents will aggregate, and sufficient dispersion stability may not be obtained.

  Examples of the dispersant having an amine value include EFKA-5044, EFKA-5244, EFKA-6220, EFKA-6225, EFKA-7564, and EFKA-4080 manufactured by Ciba Specialty Chemicals. Tera-U, Disperbyk-101, Disperbyk-106, Disperbyk-108, Disperbyk-109, Disperbyk-116, Disperbyk-140 (“Disperbyk” is a registered trademark of BYK Chemie), New Century FA , Agrisperse 712 and the like, and one or more of them can be used in combination.

  The content of the dispersant having an amine value in the liquid developer is preferably 0.2 to 10 parts by weight, more preferably 1 to 8 parts by weight with respect to 100 parts by weight of the toner particles. More preferably, it is 3 to 6 parts by weight. When the content of the dispersing agent is in the above range, the long-term dispersion stability of the toner particles can be effectively improved, and the positive charging characteristics can be further improved.

<Insulating liquid>
Next, the insulating liquid will be described.
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.
Examples of the insulating liquid that satisfies such conditions include Isopar E, Isopar G, Isopar H, Isopar L (Isopar; trade name of Exxon Chemical), Cielsol 70, Cielsol 71 (Cielsol; Commodity of Ciel Oil) Name), Amsco OMS, Amsco 460 solvent (Amsco; trade name of Spirits), mineral oil (hydrocarbon liquid) such as low viscosity / high viscosity liquid paraffin (Wako Pure Chemical Industries), fatty acid glyceride, fatty acid monoester, 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, mesitylene, etc. 1 out of Or they may be used in combination of two or more. Among the above-mentioned, since the vegetable oil has particularly high affinity (compatibility) with the rosin resin and the dispersant having an amine value, the dispersion stability of the toner particles can be further improved.
Further, the liquid developer (insulating liquid) may contain a known antioxidant, a charge control agent and the like in addition to the components described above.

  The viscosity of the insulating liquid is not particularly limited, but is preferably 5 to 1000 mPa · s, more preferably 50 to 800 mPa · s, and still more preferably 50 to 500 mPa · s. 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 toner particles can be made more highly dispersible, and in an 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, when the viscosity of the insulating liquid is less than the lower limit value, there is a possibility that problems such as dripping of the liquid developer from the application roller or the like may occur in the image forming apparatus described later. On the other hand, if 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 method for producing a liquid developer of the present invention will be described.
The liquid developer manufacturing method according to the present embodiment includes a dispersion preparation step of preparing a dispersion in which a resin material and a colorant as described above are dispersed in an aqueous dispersion medium, and a plurality of dispersoids. Insulating the toner particles and the dispersing agent as described above, a coalescing step for obtaining one particle, a desolvating step for removing the organic solvent contained in the coalesced particle to obtain toner particles containing a resin material and a colorant A dispersion step of dispersing in a liquid.

Hereafter, each process which comprises the manufacturing method of a liquid developer is demonstrated in detail.
[Dispersion Preparation Step (Aqueous Dispersion Preparation Step)]
First, a dispersion (aqueous dispersion) is prepared.
The aqueous dispersion may be prepared by any method. For example, a resin material (rosin resin and other resin materials), a toner particle constituent material (toner material) such as a colorant, and the like are used as an organic solvent. A resin liquid is obtained by dissolving and dispersing in the resin (resin liquid preparation treatment), and an aqueous dispersion medium composed of an aqueous liquid is added to the resin liquid, whereby the dispersoid containing the toner material (liquid dispersoid) is aqueous. A dispersion (aqueous dispersion) in which the dispersoid is dispersed is formed in the liquid (dispersoid formation treatment).

(Resin liquid preparation process)
First, a resin solution in which a resin material (rosin resin and other resin materials) and a hydrolysis inhibitor are dissolved or dispersed in an organic solvent is prepared.
The prepared resin liquid contains the constituent material of the toner particles as described above and the organic solvent as described below.

The organic solvent may be any as long as it dissolves at least a part of the resin material, but it is preferable to use an organic solvent having a boiling point lower than that of the aqueous liquid described later. Thereby, the organic solvent can be easily removed.
The organic solvent is preferably one having low compatibility with an aqueous dispersion medium (aqueous liquid) described later (for example, one having a solubility in 100 g of the aqueous dispersion medium at 25 ° C. of 30 g or less). Thereby, the toner material can be finely dispersed in a stable state in the aqueous emulsion.

Further, the composition of the organic solvent can be appropriately selected according to, for example, the resin material, the composition of the colorant, the composition of the aqueous dispersion medium, and the like as described above.
Such an organic solvent is not particularly limited, and examples thereof include ketone solvents such as MEK and aromatic hydrocarbon solvents such as toluene.
The resin liquid can be obtained, for example, by mixing a resin material, a colorant, an organic solvent, etc. with a stirrer or the like. Examples of the stirrer that can be used for preparing the resin liquid include DESPA (manufactured by Asada Tekko Co., Ltd.), T.C. K. Robotics / T. K. Examples thereof include a high-speed stirrer such as a homodisper 2.5-type blade (manufactured by Primex).
Moreover, it is preferable that the material temperature at the time of stirring is 20-60 degreeC, and it is more preferable that it is 30-50 degreeC.

Although the content rate of solid content in a resin liquid is not specifically limited, It is preferable that it is 40-75 wt%, it is more preferable that it is 50-73 wt%, and it is further more preferable that it is 50-70 wt%. When the solid content is within the above range, the dispersoid constituting the dispersion (emulsion suspension) described later may have a higher sphericity (a shape close to a true sphere). The shape of the toner particles finally obtained can be made more surely suitable.
In the preparation of the resin liquid, all the components of the resin liquid to be prepared may be mixed at the same time, or a part of the components of the resin liquid to be prepared may be mixed in advance to prepare a mixture (master). After that, the mixture (master) may be mixed with other components.

(Dispersoid formation processing)
Next, an aqueous dispersion (dispersion) is prepared.
By adding an aqueous dispersion medium composed of an aqueous liquid to the resin liquid, a dispersoid containing the toner material (liquid dispersoid) is formed in the aqueous liquid, and the dispersion in which the dispersoid is dispersed (aqueous dispersion) Get.

The aqueous dispersion medium is composed of an aqueous liquid.
As the aqueous liquid, a liquid mainly composed of water can be used.
The aqueous liquid may contain, for example, a solvent having excellent compatibility with water (for example, a solvent having a solubility in 100 parts by weight of water at 25 ° C. of 50 parts by weight or more).
Further, an emulsifying dispersant may be added to the aqueous dispersion medium as necessary. By adding an emulsifying dispersant, an aqueous emulsion can be prepared more easily.

The emulsifying dispersant is not particularly limited, and for example, a known emulsifying dispersant can be used.
In preparing the aqueous dispersion, for example, a neutralizing agent may be used. Thereby, for example, the functional group (for example, carboxyl group) of the resin material can be neutralized, and the shape, size uniformity, and dispersibility of the dispersoid in the prepared aqueous dispersion liquid. Can be particularly excellent. For this reason, the obtained toner particles have a particularly narrow particle size distribution.

For example, the neutralizing agent may be added to the resin liquid or may be added to the aqueous liquid.
Further, the neutralizing agent may be added in a plurality of times in the preparation of the aqueous dispersion.
As the neutralizing agent, a basic compound can be used. More specifically, for example, inorganic bases such as sodium hydroxide, potassium hydroxide, and ammonia, and organic bases such as diethylamine, triethylamine, and isopropylamine are used. 1 type selected from these, or 2 or more types can be used in combination. The neutralizing agent may be an aqueous solution containing the above compound.

  Moreover, the usage-amount of a basic compound has the preferable amount (1-3 equivalent) equivalent to 1-3 times the amount required in order to neutralize all the carboxyl groups which a resin material has, and is equivalent to 1-2 times The amount (1 to 2 equivalents) is more preferred. Thereby, it is possible to effectively prevent the formation of irregular dispersoids, and it is possible to make the particle size distribution of the particles obtained in the coalescence step described in detail later sharper.

  The aqueous liquid may be added to the resin liquid by any method, but it is preferable to add the aqueous liquid containing water to the resin liquid while stirring the resin liquid. That is, it is performed by gradually adding (dropping) an aqueous liquid into the resin liquid while applying shear to the resin liquid with a stirrer or the like, and phase-inverting from a W / O type emulsion to an O / W type emulsion. Finally, it is preferable to obtain an aqueous dispersion in which the dispersoid derived from the resin liquid is dispersed in the aqueous liquid.

Examples of the stirrer that can be used for the preparation of the aqueous dispersion include DESPA (manufactured by Asada Tekko Co., Ltd.), T.C. K. Robotics / T. K. Examples thereof include a high-speed stirrer such as a homodisper 2.5-type blade (manufactured by Primics), a slasher (manufactured by Mitsui Mining Co., Ltd.), a Cavitron (manufactured by Eurotech), or a high-speed disperser.
Further, at the time of adding the aqueous liquid to the resin liquid, stirring is preferably performed so that the blade tip speed is 10 to 20 m / sec, and more preferably 12 to 18 m / sec. When the blade tip speed is a value within the above range, an aqueous dispersion can be obtained efficiently, and the dispersion of the shape and size of the dispersoid in the aqueous dispersion can be made particularly small. In particular, the uniform dispersibility of the dispersoid can be made excellent while preventing the generation of fine dispersoids and coarse particles.

The solid content in the aqueous dispersion is not particularly limited, but is preferably 5 to 55 wt%, and more preferably 10 to 50 wt%. Thereby, the productivity of toner particles can be made particularly excellent while preventing unintentional aggregation of the dispersoids in the aqueous dispersion more reliably.
Moreover, it is preferable that the material temperature in this process is 20-60 degreeC, and it is more preferable that it is 20-50 degreeC.

[Joint process]
Next, a plurality of dispersoids are coalesced to obtain coalesced particles (a coalescence step). The coalescence of dispersoids usually proceeds as a result of collision of dispersoids containing an organic solvent so that they are integrated. In the process of coalescence, the compatibility between the rosin resin and the other resin materials tends to decrease, phase separation occurs, and the rosin resin is surely present on the surface of the finally obtained toner particles ( Uneven distribution).

The coalescence of a plurality of dispersoids is performed by adding an electrolyte to the dispersion while stirring the dispersion. Thereby, coalesced particles can be obtained easily and reliably. Moreover, the particle diameter and particle size distribution of the coalesced particles can be controlled easily and reliably by adjusting the amount of electrolyte added.
It does not specifically limit as electrolyte, Well-known organic and inorganic water-soluble salt etc. can be used 1 type or in combination of 2 or more types.

The electrolyte is preferably a monovalent cation salt. Thereby, the particle size distribution of the obtained coalesced particles can be narrowed. In addition, by using a monovalent cation salt, it is possible to reliably prevent generation of coarse particles in this step.
Moreover, among the above-mentioned, it is preferable that electrolyte is a sulfate (for example, sodium sulfate, ammonium sulfate) or carbonate, and it is especially preferable that it is a sulfate. Thereby, the particle diameter of the coalesced particles can be controlled particularly easily.

The amount of the electrolyte added in this step is preferably 0.5 to 3 parts by weight, preferably 1 to 2 parts by weight, based on 100 parts by weight of the solid content in the dispersion to which the electrolyte is added. Is more preferable. As a result, the particle diameter of the coalesced particles can be controlled particularly easily and reliably, and the generation of coarse particles can be reliably prevented.
The electrolyte is preferably added in the form of an aqueous solution. As a result, the electrolyte can be quickly diffused throughout the dispersion, and the amount of electrolyte added can be easily and reliably controlled. As a result, coalesced particles having a desired particle size and a particularly narrow particle size distribution can be obtained.

  Moreover, when adding electrolyte in the state of aqueous solution, it is preferable that the density | concentration of the electrolyte in aqueous solution is 2-10 wt%, and it is more preferable that it is 2.5-6 wt%. As a result, the electrolyte can be diffused through the entire dispersion particularly quickly, and the amount of electrolyte added can be easily and reliably controlled. Further, by adding such an aqueous solution, the content of water in the dispersion when the addition of the electrolyte is completed becomes suitable. For this reason, the growth rate of the coalesced particles after the addition of the electrolyte can be made moderately slow to the extent that productivity does not decrease. As a result, the particle size can be controlled more reliably. In addition, unintentional coalescence of coalesced particles can be reliably prevented.

  When the electrolyte is added as an aqueous solution, the rate of addition of the aqueous electrolyte solution is 0.5 to 10 parts by weight / minute with respect to 100 parts by weight of the solid content in the dispersion to which the aqueous electrolyte solution is added. Is preferable, and it is more preferable that it is 1.5-5 weight part / min. As a result, it is possible to prevent the uneven concentration of the electrolyte from occurring in the dispersion, and reliably prevent the generation of coarse particles. Further, the particle size distribution of the coalesced particles is particularly narrow. Furthermore, by adding the electrolyte at such a rate, the coalescing rate can be controlled particularly easily, the average particle size of the coalesced particles can be controlled particularly easily, and the toner productivity is particularly excellent. Can be.

The addition of the electrolyte may be performed in a plurality of times. As a result, coalescent particles having a desired size can be obtained easily and reliably, and the circularity of the obtained coalescent particles can be surely made sufficiently large.
Moreover, this process is performed in the state which stirred the dispersion liquid. Thereby, coalesced particles with particularly small variations in shape and size among the particles can be obtained.

  For stirring the dispersion, for example, an agitation blade such as an anchor blade, a turbine blade, a fiddler blade, a full zone blade, a max blend blade, or a half moon blade may be used, and among these, a max blend blade or a full zone blade is preferable. As a result, the added electrolyte can be quickly and uniformly dispersed and dissolved to reliably prevent the uneven concentration of the electrolyte from occurring. In addition, it is possible to more reliably prevent the coalesced particles once formed from collapsing while efficiently coalescing the dispersoid. As a result, coalesced particles with small variations in shape and particle size among the particles can be obtained efficiently.

The blade tip speed of the stirring blade is preferably from 0.1 to 10 m / second, more preferably from 0.2 to 8 m / second, and even more preferably from 0.2 to 6 m / second. When the blade tip speed is a value within the above range, the added electrolyte can be uniformly dispersed and dissolved, and the occurrence of uneven concentration of the electrolyte can be reliably prevented. In addition, it is possible to more reliably prevent the coalesced particles once formed from collapsing while more efficiently coalescing the dispersoid.
The average particle diameter of the obtained coalesced particles is preferably 0.5 to 5 μm, and more preferably 1.5 to 3 μm. Thereby, the particle diameter of the toner particles finally obtained can be made moderate.

[Desolvation (desolvation) step]
Thereafter, the organic solvent contained in the dispersion is removed. Thereby, resin fine particles (toner particles) dispersed in the dispersion are obtained. The toner particles thus obtained have rosin resin on at least a part of the surface thereof.
The removal of the organic solvent may be performed by any method, but can be performed, for example, under reduced pressure. Thereby, the organic solvent can be efficiently removed while sufficiently preventing the modification of the constituent material such as the resin material.

Moreover, it is preferable that the process temperature in this process is temperature lower than the glass transition point (Tg) of the resin material which comprises coalesced particle.
Moreover, you may perform this process in the state which added the antifoamer to the dispersion liquid. Thereby, an organic solvent can be removed efficiently.
Antifoaming agents include, for example, mineral oil-based antifoaming agents, polyether-based antifoaming agents, silicone-based antifoaming agents, lower alcohols, higher alcohols, fats and oils, fatty acids, fatty acid esters, phosphoric acid Esters can be used.
Although the usage-amount of an antifoamer is not specifically limited, It is preferable that it is 20-300 ppm by weight ratio with respect to the solid content contained in a dispersion liquid, and it is more preferable that it is 30-100 ppm.

In this step, at least a part of the aqueous liquid may be removed together with the organic solvent.
In this step, it is not always necessary to remove all of the organic solvent (the total amount of the organic solvent contained in the dispersion). Even in such a case, the remaining organic solvent can be sufficiently removed in other steps described later.

[Washing process]
Next, the resin fine particles (toner particles) obtained as described above are cleaned (cleaning step).
By performing this step, even if an organic solvent or the like is contained as an impurity, these can be efficiently removed. As a result, the amount of volatile organic compound (TVOC) in the resin fine particles finally obtained can be made particularly small.
In this step, for example, resin fine particles are separated by solid-liquid separation (separation from an aqueous liquid), and then solid dispersion (resin fine particles) is redispersed in water and solid-liquid separation (resin fine particles from an aqueous liquid is separated). Separation). The redispersion of solids in water and solid-liquid separation may be repeated a plurality of times.

[Drying process]
Thereafter, toner particles can be obtained by performing a drying process (drying step).
The drying step can be performed using, for example, a vacuum dryer (for example, ribocorn (manufactured by Okawara Seisakusho), nauter (manufactured by Hosokawa Micron) etc.), fluidized bed dryer (manufactured by Okawara Seisakusho), etc.

[Dispersion process]
Next, the toner particles obtained as described above and the dispersant as described above are dispersed in an insulating liquid. Thereby, a liquid developer is obtained.
Any method may be used for dispersing the toner particles and the dispersant in the insulating liquid. For example, the insulating liquid, the toner particles, and the dispersant can be mixed by a bead mill, a ball mill, or the like. . By mixing by such a method, the dispersant can be reliably attached or adsorbed on the surface of the toner particles.

Further, at the time of dispersion, components other than the insulating liquid, toner particles, and the dispersant may be mixed.
Further, the dispersion of the toner particles and the dispersant in the insulating liquid may be performed using the entire amount of the insulating liquid constituting the finally obtained liquid developer. It may be performed using

  Further, when the toner particles and the dispersant are dispersed using a part of the insulating liquid, the same liquid as the liquid used for dispersion may be added as the insulating liquid after the dispersion. After dispersion, a liquid different from the liquid used for dispersion may be added as an insulating liquid. In the latter case, characteristics such as the viscosity of the finally obtained liquid developer can be easily adjusted.

  When the liquid developer is produced by the method as described above, the toner particles contained include rosin-based resin on at least a part of the surface, and the variation in shape among the toner particles is small. It becomes. Thereby, the surface area of the particle surface does not vary between the particles, and the dispersing agent as described above can be uniformly adhered or adsorbed on the surface of the toner particle. As a result, while making the long-term dispersion stability of the toner particles excellent, variations in charging characteristics among the toner particles can be effectively suppressed, and the configuration is facilitated in the development and transfer processes.

≪Image forming device≫
Next, a preferred embodiment of the image forming apparatus of the present invention will be described. The image forming apparatus of the present invention forms a color image on a recording medium using the liquid developer of the present invention as described above.
FIG. 1 is a schematic view showing an example 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, an intermediate transfer unit 40, a secondary transfer unit (secondary transfer unit) 60, and a fixing unit. (Fixing device) F40 and four liquid developer supply portions 80Y, 80M, 80C, and 80K are provided.
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. The image forming apparatus 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 of the developing unit 100Y in the rotation direction 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 42 and 43 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 the tension roller 44 so that the slack is removed. The tension roller 44 is disposed downstream of the one driven roller 42 in the rotation (movement) direction of the intermediate transfer unit 40 and upstream of the other driven roller 43 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 sheet material that is not smooth due to fiber or the like, the secondary transfer characteristics follow the surface of the non-smooth sheet material. 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 portion cleaning blade 46 and the developer recovery portion 47 are arranged on the driven roller 43 side.
The intermediate transfer portion cleaning blade 46 scrapes and removes the liquid developer adhering to the intermediate transfer portion 40 after the image is transferred onto the recording medium F5 by the secondary transfer unit (secondary transfer portion) 60. have.

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 44. 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 44. For example, a position between the driven roller 42 and the tension roller 44, such as a position between the driven roller 42 and the intermediate transfer unit. It can be disposed at any position downstream in the movement direction and upstream of the driven roller 43 in the movement direction of the intermediate transfer portion. 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 an intermediate transfer unit squeeze roller 53Y, an intermediate transfer unit squeeze cleaning blade 55Y that presses and slides against the intermediate transfer unit squeeze roller 53Y, and an 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 the 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 61. The upstream secondary transfer roller 61 can be brought into pressure contact with the belt driving roller 41 via the intermediate transfer unit 40.

Of the pair of secondary transfer rollers, the secondary transfer roller disposed downstream of the transfer material in the moving direction is the downstream secondary transfer roller 62. The downstream secondary transfer roller 62 can be brought into pressure contact with the driven roller 42 via the intermediate transfer unit 40.
That is, the upstream side secondary transfer roller 61 and the downstream side secondary transfer roller 62 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 42, 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 42 also function as backup rollers for the upstream side secondary transfer roller 61 and the downstream side secondary transfer roller 62, respectively. In other words, the belt driving 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 42 in the moving direction of the recording medium F5. The driven roller 42 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 61 and the belt drive roller 41 to the downstream secondary transfer roller 62 and the driven roller. 42 is in close contact with the intermediate transfer section 40 in a predetermined movement region of the transfer material up to the press-contact end position (nip end position) with 42. 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.

Further, the secondary transfer unit 60 includes a secondary transfer roller cleaning blade 63 and a developer recovery unit 64 with respect to the upstream side secondary transfer roller 61. Further, the secondary transfer unit 60 includes a secondary transfer roller cleaning blade 65 and a developer recovery unit 66 for the downstream side secondary transfer roller 62. The secondary transfer roller cleaning blades 63 and 65 are in contact with the secondary transfer rollers 61 and 62, respectively, and scrape and remove the liquid developer remaining on the surfaces of the secondary transfer rollers 61 and 62 after the secondary transfer. To do. The developer recovery units 64 and 66 collect and store the liquid developer scraped off from the secondary transfer rollers 61 and 62 by the secondary transfer roller cleaning blades 63 and 65, respectively.
The toner image (transfer image) F5a transferred onto the recording medium F5 by the secondary transfer unit 60 is sent to a fixing unit (fixing device) F40, which will be described later, and fixed.

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 developing roller 20Y, a developing roller cleaning blade 21Y, a corona. And a discharger (compression means) 23Y.

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 coating roller 32Y has a function of supplying a liquid developer to the developing roller 20Y.
The 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 has a diameter of 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 liquid developer storage section 31Y in the groove, and the supported liquid developer is transferred to the developing roller. Transport to 20Y.

  The regulating blade 33Y is in contact with 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 the 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 regulation blade 33Y is about 77 degrees according to JIS-A, and the hardness (about 77 degrees) of the contact portion of the regulation blade 33Y with the surface of the coating roller 32Y is about the elasticity of the developing roller 20Y described later. It is lower than the hardness (about 85 degrees) of the pressure 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 liquid developer storage unit 31Y 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 1 are aggregated, the toner particles 1 can be suitably dispersed. In particular, the liquid developer of the present invention can be more suitably dispersed because of high dispersibility of toner particles. Even a reused liquid developer can be easily dispersed.

In the liquid developer storage unit 31Y, the toner particles 1 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. , The liquid developer is stored in the liquid developer reservoir 31Y, and the amount of liquid developer is regulated by the regulating blade 33Y and supplied to the developing roller 20Y.
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 201Y on the surface thereof 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.

  The corona discharger (compression unit) 23Y is a device having a function of compressing the toner of the liquid developer carried on the developing roller 20Y. In other words, the corona discharger 23Y applies an electric field having the same polarity as that of the toner particles 1 to the liquid developer layer 201Y described above, so that, as shown in FIG. This is an apparatus having a function of unevenly distributing the toner particles 1 near the surface of 20Y. By unevenly distributing the toner particles in this way, the development density (development efficiency) can be improved, and as a result, a clear image with high quality can be obtained. In particular, since the liquid developer of the present invention is excellent in charging characteristics, the charge amount of the toner particles 1 is high. Therefore, even when the electric field applied from the corona discharger 23Y is relatively weak, the toner particles 1 in the liquid developer can be reliably compressed. That is, the voltage applied to the corona discharger 23Y can be lowered, and power saving can be achieved.

In the developing unit 100Y, the coating roller 32Y and the developing roller 20Y are separately driven by different power sources (not shown). The amount of the liquid developer supplied onto the developing roller 20Y can be adjusted by changing the rotation speed (linear speed) ratio between 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 22Y. 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 22Y.

  As shown in FIGS. 1 and 2, the image forming apparatus 1000 includes liquid developer replenishing units 80Y, 80M, 80C, and 80K that replenish liquid developer to the developing units 30Y, 30M, 30C, and 30K. . These liquid developer replenishers 80Y, 80M, 80C, and 80K are respectively provided with liquid developer tanks 81Y, 81M, 81C, and 81K, insulating liquid tanks 82Y, 82M, 82C, and 82K, and stirring devices 83Y, 83M, 83C and 83K.

  Each of the liquid developer tanks 81Y, 81M, 81C, 81K contains a high concentration liquid developer corresponding to each color. Insulating liquid tanks 82Y, 82M, 82C, and 82K contain insulating liquids, respectively. Furthermore, each stirring device 83Y, 83M, 83C, 83K includes a predetermined amount of each high-concentration liquid developer from each liquid developer tank 81Y, 81M, 81C, 81K, and each insulating liquid tank 82Y, 82M, 82C. A predetermined amount of each insulating liquid from 82K is supplied.

  The stirrers 83Y, 83M, 83C, and 83K mix and stir the supplied high-concentration liquid developer and the insulating liquid, respectively, and respectively store the liquid developer reservoirs 31Y, 31M, 31C, and 31K. A liquid developer corresponding to each color used in the above is prepared. Each liquid developer produced by each stirring device 83Y, 83M, 83C, 83K is supplied to each liquid developer reservoir 31Y, 31M, 31C, 31K.

  Further, as shown in FIGS. 1 and 2, the liquid developer replenishing units 80Y, 80M, 80C, and 80K include the liquid developers collected by the developer collecting units 15Y, 15M, 15C, and 15K, respectively. Each liquid developer recovered by the developer recovery units 22Y, 22M, 22C, and 22K is recovered and reused. In particular, the liquid developer of the present invention has a high redispersibility because the dispersant as described above is firmly attached (adsorbed) to the surface of the toner particles, and can be easily reused.

Next, the fixing unit will be described.
The fixing unit F40 fixes the unfixed toner image F5a formed in the above-described developing unit, transfer unit, and the like on the recording medium F5.
As shown in FIG. 4, the fixing unit F40 includes a heat fixing roller F1, a pressure roller F2, a heat-resistant belt F3, a belt stretching member F4, a cleaning member F6, a frame F7, and a spring F9. is doing.

The heat fixing roller (fixing roller) F1 includes a roller base material F1b made of a pipe material, an elastic body F1c covering the outer periphery thereof, and a columnar halogen lamp F1a as a heating source inside the roller base material F1b. It can be rotated counterclockwise as indicated by an arrow in the figure.
Inside the heat fixing roller F1, two columnar halogen lamps F1a and F1a constituting a heating source are incorporated, and the heating elements of these columnar halogen lamps F1a and F1a are arranged at different positions. Yes. Then, by selectively lighting each columnar halogen lamp F1a, F1a, a fixing nip portion where a heat-resistant belt F3, which will be described later, is wound around the heat-fixing roller F1, and a belt stretching member F4, which will be described later, are attached to the heat-fixing roller F1. The temperature controller is easily performed under different conditions from the sliding contact portion, different conditions between the wide recording medium and the narrow recording medium, or the like.

The pressure roller F2 is arranged to face the heat fixing roller F1, and is configured to apply pressure to the recording medium F5 on which the unfixed toner image F5a is formed via a heat-resistant belt F3 described later. Has been.
The pressure roller F2 includes a roller base material F2b made of a pipe material and an elastic body F2c covering the outer periphery thereof, and is rotatable in the clockwise direction indicated by an arrow in the drawing.

  A PFA layer is provided on the surface layer of the elastic body F1c of the heat fixing roller F1. As a result, the elastic bodies F1c and 2c have different thicknesses, but the elastic bodies F1c and 2c are substantially uniformly elastically deformed to form a so-called horizontal nip, and with respect to the peripheral speed of the heat fixing roller F1. Since there is no difference in the conveyance speed of the heat-resistant belt F3 or the recording medium F5, which will be described later, extremely stable image fixing is possible.

The heat-resistant belt F3 is an endless annular belt that is stretched around the outer periphery of the pressure roller F2 and the belt stretching member F4 and is movable, and is sandwiched between the heat fixing roller F1 and the pressure roller F2. is there.
The heat-resistant belt F3 has a thickness of 0.03 mm or more, and its front surface (the surface on which the recording medium F5 comes into contact) is formed of PFA, and the rear surface (the pressure roller F2 and the belt stretching member F4 is in contact). The side surface is formed of a seamless tube having a two-layer structure formed of polyimide. The heat-resistant belt F3 is not limited to this, and can be formed of other materials such as a metal tube such as a stainless steel tube or a nickel electroformed tube, or a heat-resistant resin tube such as silicone.

The belt stretching member F4 is disposed upstream of the fixing nip portion between the heat fixing roller F1 and the pressure roller F2 in the conveyance direction of the recording medium F5, and has an arrow P around the rotation axis F2a of the pressure roller F2. It is arranged so that it can swing in the direction.
The belt stretching member F4 is configured to stretch the heat-resistant belt F3 in the tangential direction of the heat fixing roller F1 in a state where the recording medium F5 does not pass through the fixing nip portion. If the fixing pressure is large at the initial position where the recording medium F5 enters the fixing nip portion, the entry may not be smoothly performed and the recording medium F5 may be fixed in a state where the tip of the recording medium F5 is broken. By adopting a configuration in which F3 is stretched in the tangential direction of the heat fixing roller F1, an inlet port of the recording medium F5 through which the recording medium F5 enters smoothly can be formed, and the stable fixing nip portion of the recording medium F5 can be formed. Can enter.

  The belt stretching member F4 is fitted into the inner periphery of the heat-resistant belt F3 and cooperates with the pressure roller F2 to apply a tension f to the heat-resistant belt F3 (a heat-resistant belt F3 is a belt). Sliding on the tension member F4). This belt stretching member F4 is disposed at a position where the heat-resistant belt F3 is wound around the heat fixing roller F1 side from the pressing portion tangent L between the heat fixing roller F1 and the pressure roller F2 to form a nip. The protruding wall F4a protrudes from one end or both ends of the belt stretching member F4 in the axial direction. The protruding wall F4a is formed by the heat-resistant belt F3 when the heat-resistant belt F3 approaches one of the axial ends. The contact to the end of the heat-resistant belt F3 is regulated by contacting the wall F4a. A spring F9 is contracted between the end of the protruding wall F4a opposite to the heat fixing roller F1 and the frame, and the protruding wall F4a of the belt stretching member F4 is lightly pressed by the heat fixing roller F1, so that the belt tension is increased. The frame member F4 is positioned in sliding contact with the heat fixing roller F1.

The position where the belt stretching member F4 is lightly pressed against the heat fixing roller F1 is the nip initial position, and the position where the pressure roller F2 is pressed against the heat fixing roller F1 is the nip end position.
In the fixing portion F40, the recording medium F5 on which the unfixed toner image F5a is formed enters the fixing nip portion from the nip initial position and passes between the heat-resistant belt F3 and the heat fixing roller F1, and the nip end position. As a result, the unfixed toner image F5a formed on the recording medium F5 is fixed, and then discharged in the tangential direction L of the pressing portion of the pressure roller F2 to the heat fixing roller F1.

The cleaning member F6 is disposed between the pressure roller F2 and the belt stretching member F4.
The cleaning member F6 is in sliding contact with the inner peripheral surface of the heat-resistant belt F3 to clean foreign matter, abrasion powder, and the like on the inner peripheral surface of the heat-resistant belt F3. By cleaning the foreign matter, wear powder, and the like in this way, the heat-resistant belt F3 is refreshed, and the unstable factor of the friction coefficient as described later is removed. Further, the belt stretching member F4 is provided with a recess F4f, and is configured to store foreign matter, abrasion powder, and the like removed from the heat-resistant belt F3.

The fixing unit F40 has a removing blade (removing means) F12 that removes the insulating liquid adhering (remaining) to the surface of the heat fixing roller F1 after fixing the toner image F5a on the recording medium F5. . The removing blade F12 can remove the insulating liquid and simultaneously remove the toner and the like that have moved onto the heat fixing roller F1 during fixing.
In order to stably drive the heat-resistant belt F3 by the pressure roller F2 and the belt stretching member F4 and stably drive the pressure roller F2, the friction coefficient between the pressure roller F2 and the heat-resistant belt F3 is determined by the belt tension. It is good to set larger than the friction coefficient of the frame member F4 and the heat-resistant belt F3. However, the friction coefficient is such that foreign matter enters between the heat-resistant belt F3 and the pressure roller F2 or between the heat-resistant belt F3 and the belt stretching member F4, or the heat-resistant belt F3, the pressure roller F2, and the belt stretching member. It may become unstable due to wear of the contact portion with F4.

Therefore, the belt tension member F4 and the heat-resistant belt F3 have a winding angle smaller than the winding angle of the pressure roller F2 and the heat-resistant belt F3, and the diameter of the belt stretching member F4 is smaller than the diameter of the pressure roller F2. Set as follows. As a result, the length that the heat-resistant belt F3 slides on the belt stretching member F4 is shortened, which can be avoided from instability factors such as changes with time and disturbances, and the heat-resistant belt F3 is driven stably by the pressure roller F2. Will be able to.
Specifically, the heat (fixing temperature) applied by the heat fixing roller F1 is preferably 80 to 160 ° C, more preferably 100 to 150 ° C, and further preferably 100 to 140 ° C.

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 produced by the production method as described above.

Moreover, although embodiment mentioned above demonstrated as what obtains the coalesced particle by obtaining aqueous emulsion and adding electrolyte to this aqueous emulsion, this invention is not limited to this. For example, the coalesced particles are prepared by dispersing a colorant, a monomer, a surfactant, and a polymerization initiator in an aqueous liquid, preparing an aqueous emulsion by emulsion polymerization, and adding an electrolyte to the aqueous emulsion to associate. The emulsion may be prepared using an emulsion polymerization association method, or may be obtained by spray-drying the obtained aqueous emulsion to obtain coalesced particles.
In the above-described embodiment, the configuration having the corona discharger as the image forming apparatus has been described. However, the corona discharger may be omitted.

[1] Production of Liquid Developer A liquid developer was produced as follows.
Example 1
First, toner particles were manufactured. In addition, about the process in which temperature is not described, it performed at room temperature (25 degreeC).

<Dispersion adjustment process>
(Preparation of colorant master solution)
First, as a resin material, a polyester resin (acid value: 10 mgKOH / g, glass transition point (Tg): 55 ° C., softening point: 107 ° C.): 60 parts by weight was prepared.
Next, a mixture (mass ratio 50:50) of the resin material and a cyan pigment as a colorant (manufactured by Dainichi Seika Co., Ltd., Pigment Blue 15: 3) 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 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 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.

(Resin liquid preparation process)
The above colorant master batch: 97.5 parts by weight, methyl ethyl ketone: 175 parts by weight, polyester resin: 172.3 parts by weight, rosin modified phenolic resin (Arakawa Chemical Industries, trade name “Tamanol 135”, acid value: 18 mg KOH) / G or less, softening point: 130 to 140, weight average molecular weight: 15000): 55.3 parts by weight of a high-speed disperser (Primics Co., Ltd., TK Robotics / TK homodisper 2.5 type blade) And 1.38 parts by weight of Neogen SC-F (Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier was added to prepare a resin liquid. In this solution, the pigment was uniformly finely dispersed.

(Dispersoid formation processing)
Next, 72.8 parts by weight of 1N ammonia water was added to the resin liquid in the container, and the mixture was stirred with a high-speed disperser (Primics Co., Ltd., TK Robotics / TK Homo Disperser 2.5 type blade). The blade tip speed of the wing was sufficiently stirred at 7.5 m / s, the temperature of the solution in the flask was adjusted to 25 ° C., and the stirring blade blade speed was then 14.7 m / s while stirring. Part by weight of deionized water was added dropwise to cause phase inversion emulsification. While continuing the stirring, 100 parts by weight of deionized water was further added to the resin liquid. As a result, an aqueous dispersion in which the dispersoid containing the resin material was dispersed was obtained.

<Joint process>
Next, the aqueous dispersion was transferred to a stirring vessel having a Max Blend blade, and the temperature of the aqueous dispersion was adjusted to 25 ° C. while stirring at a blade tip speed of 1.0 m / s.
Next, while maintaining the same temperature and stirring conditions, 200 parts by weight of a 5.0% aqueous sodium sulfate solution was added dropwise to coalesce the dispersoids to form coalesced particles. After the dropping, stirring was continued until the 50% volume particle diameter Dv (50) [μm] of the coalesced toner particles grew to 2.5 μm. When the Dv (50) of the coalesced particles reached 2.5 μm, 200 parts by weight of deionized water was added to complete the coalescence.

<Desolvation process>
The organic solvent was distilled off under reduced pressure until the solid content was 23 wt%, to obtain a slurry of resin fine particles.
<Washing process>
Next, the slurry was subjected to solid-liquid separation, and further subjected to washing treatment by redispersion in water (reslurry) and repeated solid-liquid separation. Thereafter, a wet cake (resin fine particle cake) of colored resin fine particles was obtained by suction filtration. The moisture content of the wet cake was 35 wt%.

<Drying process>
Thereafter, the obtained wet cake was dried using a vacuum dryer to obtain toner particles.
<Dispersing process>
Toner particles obtained by the above method: 37.5 parts by weight, Disperbyk-116 as a dispersant (manufactured by Big Chemie, amine value: 65 mgKOH / g): 1.88 parts by weight, rapeseed oil (Nisshin) as an insulating liquid 150ml by weight, aluminum stearate as a charge control agent (manufactured by Nippon Oil & Fats): 0.5 part by weight in a ceramic pot (internal volume 600ml), zirconia balls (Ball diameter: 1 mm) was placed in a ceramic pot so that the volume filling rate was 85%, and dispersed in a desktop pot mill at a rotational speed of 230 rpm for 24 hours. As a result, a liquid developer was obtained.

  The Dv (50) of the toner particles in the obtained liquid developer was 1.85 μm. The 50% volume particle diameter Dv (50) [μm] of the obtained toner particles was measured with a Mastersizer 2000 particle analyzer (manufactured by Malvern Instruments Ltd.). Moreover, the particle diameter was similarly calculated | required about the particle | grains obtained by each Example and each comparative example demonstrated below.

Further, the viscosity of the obtained liquid developer at 25 ° C. was 55 mPa · s.
Further, instead of cyan pigment, magenta pigment: Pigment Red 238 (manufactured by Sanyo Dye), yellow pigment: Pigment Yellow 180 (manufactured by Clariant), black pigment: carbon black (printex L, manufactured by Degussa) In addition, a magenta liquid developer, a yellow liquid developer, and a black liquid developer were produced in the same manner as described above except that the respective changes were made.

(Example 2)
As rosin resin, rosin-modified maleic resin (Arakawa Chemical Industries, trade name “Marquide No. 1”, acid value: 25 mgKOH / g or less, softening point: 120 to 130, weight average molecular weight: 3100) was used. Produced liquid developers corresponding to the respective colors in the same manner as in Example 1.

(Example 3)
Except for using rosin-modified phenolic resin (trade name “KG2212” manufactured by Arakawa Chemical Industries, Ltd., acid value: 22 mgKOH / g or less, softening point: 172 to 182 and weight average molecular weight: 100,000) as the rosin resin. In the same manner as in Example 1, liquid developers corresponding to the respective colors were produced.

Example 4
As the rosin resin, except that rosin-modified phenol resin (Arakawa Chemical Industries, trade name “Tamanol 145”, acid value: 18 mgKOH / g or less, softening point: 140 to 155, weight average molecular weight: 20000) was used. In the same manner as in Example 1, liquid developers corresponding to the respective colors were produced.

(Example 5)
A liquid developer corresponding to each color is produced in the same manner as in Example 1 except that EFKA-4080 (manufactured by Ciba Specialty Chemicals, amine value: 4 mgKOH / g) is used as a dispersant having an amine value. did.
(Example 6)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that Agrisperse 712 (manufactured by New Century Coatings, amine value: 100 mgKOH / g) was used as the dispersant having an amine value.

(Example 7)
Styrene-acrylic acid ester copolymer obtained by copolymerizing styrene and butyl acrylate in a ratio of 4: 1 instead of polyester resin (acid value: 6 mgKOH / g, glass transition point: 61.6 ° C., softening) A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the point was 116 ° C.).

(Examples 8 and 9)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the blending ratio of the polyester resin and the rosin resin was changed as shown in Table 1.
(Examples 10 and 11)
Liquid developers corresponding to the respective colors were produced in the same manner as in Example 1 except that the content of the dispersant having an amine value was changed as shown in Table 1.

(Comparative Example 1)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the rosin resin was not used.
(Comparative Example 2)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that no dispersant having an amine value was added.

  Table 1 shows the composition of the liquid developer, the physical properties, the physical properties of the dispersant, the content, and the like for each of the above Examples and Comparative Examples. In the table, the polyester resin is PES, the styrene-acrylate copolymer is ST-AC, the rosin-modified phenol is RP, and the rosin-modified male resin is RM. In the table, Disperbyk-116 is indicated as D116, EFKA-4080 is indicated as E4080, and Agrisperse 712 is indicated as A712.

[2] Evaluation Each liquid developer obtained as described above was evaluated as follows.
[2.1] Developing efficiency Using the image forming apparatus as shown in FIGS. 1 and 2, the liquid developer by the liquid developer obtained in each of the embodiments and comparative examples on the developing roller of the image forming apparatus. A layer was formed. Next, the surface potential of the developing roller was set to 300V, the surface potential of the photoconductor was uniformly charged at 500V, the photoconductor was exposed, the charge on the surface of the photoconductor was attenuated, and the surface potential was set to 50V. The toner particles on the developing roller and the toner particles on the photosensitive member after the liquid developer layer passed between the photosensitive member and the developing roller were collected with a tape. Each tape used for sampling was affixed on a recording paper, and the concentration of each toner particle was measured. After the measurement, the value obtained by dividing the concentration of toner particles collected on the photoreceptor by the sum of the concentration of toner particles collected on the photoreceptor and the concentration of toner particles collected on the developing roller is multiplied by 100. Was determined as development efficiency, and evaluated according to the following four-stage criteria.
A: The development efficiency is 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.

[2.2] Transfer efficiency Using the image forming apparatus as shown in FIGS. 1 and 2, a liquid developer using the liquid developer obtained in each of the above examples and comparative examples on the photoreceptor of the image forming apparatus. A layer was formed. Next, the toner particles on the photoconductor and the toner particles on the intermediate transfer portion after the liquid developer layer passed between the photoconductor and the intermediate transfer portion were collected with a tape. Each tape used for sampling was affixed on a recording paper, and the concentration of each toner particle was measured. After the measurement, a value obtained by dividing the concentration of the toner particles collected on the intermediate transfer portion by the sum of the concentration of the toner particles collected on the photoconductor and the concentration of the toner particles collected on the intermediate transfer portion is 100. A value obtained by multiplying by is obtained as transfer efficiency, and evaluated according to the following four criteria.
A: The transfer efficiency is 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.

[2.3] Charging characteristics of positive charging For the liquid developers obtained in each of the examples and comparative examples, the potential difference was measured using a “microscopic laser zeta electrometer” ZC-2000 manufactured by Microtic Nichion. The evaluation was made according to the following five criteria.
Measurement is performed by diluting the liquid developer with a diluting solvent, placing it in a 10 mm transparent cell, applying a voltage of 300 V at 9 mm between the electrodes, and simultaneously observing the moving speed of the particles in the cell with a microscope. Was obtained by calculating the zeta potential from the calculated value.

A: The potential difference is +100 mV or more (very good).
B: Potential difference is +85 mV or more and less than +100 mV (good).
C: The potential difference is +70 mV or more and less than +85 mV (normal).
D: The potential difference is +50 mV or more and less than +70 mV (somewhat bad).
E: Potential difference is less than +50 mV (very bad).

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

[2.5] Dispersion stability test-2
45.5 mL of the liquid developer obtained in each example and each comparative example was put into a centrifuge tube, and a centrifuge (Kokusan Co., Ltd.) was used under the conditions of a rotation radius of 5 cm, a rotation speed of 500, 1000, 2000, 4000, and 5000 rpm for 3 minutes. The depth of sedimentation at each rotational speed was measured.
Centrifugal acceleration rω ² (rω ² = 1118 × rotation radius (cm) × number of revolutions per minute (rpm) ² × 10 ⁻⁸ × g (gravity acceleration)) is taken on the horizontal axis, and the sedimentation depth is taken on the vertical axis. Plotted based on the measurement results. Based on each plot, the slope k was determined by first-order approximation and evaluated according to the following criteria. It can be said that the lower the value of k, the higher the dispersion stability.
A: 0 ≦ k <0.004
B: 0.004 ≦ k <0.008
C: 0.008 ≦ k <0.012
D: k ≧ 0.012

[2.6] Fixing Strength Using an image forming apparatus as shown in FIG. 1 and FIG. 2, an image of a predetermined pattern by the liquid developer obtained in each of the examples and the comparative examples is recorded on a recording paper (Seiko Epson). It was formed on a high-quality paper LPCPPA4) manufactured by the company. Thereafter, heat fixing was performed using a fixing device as shown in FIG.

  Thereafter, 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 95% or more (very good).
B: Image density remaining rate is 90% or more and less than 95% (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).
These results are shown in Table 2.

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

[3] Production of Liquid Developer A liquid developer was produced as follows.
Example 12
First, toner particles were manufactured. In addition, about the process in which temperature is not described, it performed at room temperature (25 degreeC).
<Dispersion adjustment process>
(Preparation of colorant master solution)
First, as a polyester resin, low molecular weight polyester resin L1 (acid value: 8.5 mgKOH / g, weight average molecular weight Mw: 5,200, glass transition point Tg: 46 ° C., softening point Tf: 95 ° C.): 48 parts by weight And a high molecular weight polyester resin H1 (acid value: 16.0 mg KOH / g, weight average molecular weight Mw: 237,000, glass transition point Tg: 63 ° C., softening point Tf: 182 ° C.): 12 parts by weight Prepared.

Next, a mixture (mass ratio 50:50) of the polyester resin mixture and a cyan pigment (manufactured by Dainichi Seika Co., Ltd., Pigment Blue 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 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 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.

(Resin liquid preparation process)
Colorant masterbatch: 97.5 parts by weight methyl ethyl ketone: 175 parts by weight, polyester resin mixture: 172.3 parts by weight, rosin modified phenolic resin (Arakawa Chemical Industries, trade name “Tamanol 135”, acid value) : 18 mg KOH / g or less, softening point: 130 to 140, weight average molecular weight: 15000): 55.3 parts by weight of a high-speed disperser (manufactured by Primics, TK Robotics / TK Homo Disper 2.5 type) The resin solution was prepared by adding 1.38 parts by weight of Neogen SC-F (Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier. In this solution, the pigment was uniformly finely dispersed.

(Dispersoid formation processing)
Next, 72.8 parts by weight of 1N ammonia water was added to the resin liquid in the container, and the mixture was stirred with a high-speed disperser (Primics Co., Ltd., TK Robotics / TK Homo Disperser 2.5 type blade). The blade tip speed of the wing was sufficiently stirred at 7.5 m / s, the temperature of the solution in the flask was adjusted to 25 ° C., and the stirring blade blade speed was then 14.7 m / s while stirring. Part by weight of deionized water was added dropwise to cause phase inversion emulsification. While continuing the stirring, 100 parts by weight of deionized water was further added to the resin liquid. As a result, an aqueous dispersion in which the dispersoid containing the resin material was dispersed was obtained.

<Joint process>
Next, the aqueous dispersion was transferred to a stirring vessel having a Max Blend blade, and the temperature of the aqueous dispersion was adjusted to 25 ° C. while stirring at a blade tip speed of 1.0 m / s.
Next, while maintaining the same temperature and stirring conditions, 200 parts by weight of a 5.0% aqueous sodium sulfate solution was added dropwise to coalesce the dispersoids to form coalesced particles. After the dropping, stirring was continued until the 50% volume particle diameter Dv (50) [μm] of the coalesced toner particles grew to 2.5 μm. When the Dv (50) of the coalesced particles reached 2.5 μm, 200 parts by weight of deionized water was added to complete the coalescence.

<Desolvation process>
The organic solvent was distilled off under reduced pressure until the solid content was 23 wt%, to obtain a slurry of resin fine particles.
<Washing process>
Next, the slurry was subjected to solid-liquid separation, and further subjected to washing treatment by redispersion in water (reslurry) and repeated solid-liquid separation. Thereafter, a wet cake (resin fine particle cake) of colored resin fine particles was obtained by suction filtration. The moisture content of the wet cake was 35 wt%.

<Drying process>
Thereafter, the obtained wet cake was dried using a vacuum dryer to obtain toner particles.
<Dispersing process>
Toner particles obtained by the above method: 37.5 parts by weight, Disperbyk-116 as a dispersant (manufactured by Big Chemie, amine value: 65 mgKOH / g): 1.88 parts by weight, rapeseed oil (Nisshin) as an insulating liquid Product name: “High Oleic Rapeseed Oil” manufactured by Oilio Co., Ltd.): 150 parts by weight, aluminum stearate as a charge control agent (manufactured by Nippon Oil & Fats): 0.5 part by weight is placed in a ceramic pot (internal volume 600 ml), and zirconia balls (Ball diameter: 1 mm) was placed in a ceramic pot so that the volume filling rate was 85%, and dispersed in a desktop pot mill at a rotational speed of 230 rpm for 24 hours. As a result, a liquid developer was obtained.

  The Dv (50) of the toner particles in the obtained liquid developer was 1.86 μm. The 50% volume particle diameter Dv (50) [μm] of the obtained toner particles was measured with a Mastersizer 2000 particle analyzer (manufactured by Malvern Instruments Ltd.). Moreover, the particle diameter was similarly calculated | required about the particle | grains obtained by each Example and each comparative example demonstrated below.

Further, the viscosity of the obtained liquid developer at 25 ° C. was 55 mPa · s.
Further, instead of cyan pigment, magenta pigment: Pigment Red 238 (manufactured by Sanyo Dye), yellow pigment: Pigment Yellow 180 (manufactured by Clariant), black pigment: carbon black (printex L, manufactured by Degussa) In addition, a magenta liquid developer, a yellow liquid developer, and a black liquid developer were produced in the same manner as described above except that the respective changes were made.

(Example 13)
Liquid corresponding to each color in the same manner as in Example 12 except that the low molecular weight polyester resin L2 and the high molecular weight polyester resin H2 shown in Table 3 were used instead of the polyester resin L1. A developer was produced.
(Example 14)
The above implementation except that the low molecular weight polyester resin L3 shown in Table 3 and the high molecular weight polyester resin H3 instead of the polyester resin H1 are used instead of the polyester resin L1, and the blending amounts thereof are shown in Table 4. In the same manner as in Example 12, liquid developers corresponding to the respective colors were produced.

  The ratio of terephthalic acid (TPA) to isophthalic acid (IPA), ethylene glycol (EG) and neopentyl glycol in all the monomer components used when synthesizing each polyester resin used in Examples 12-14 above. Table 3 shows the ratio to (NPG) and the physical properties of each resin. In Examples 12 to 14, Table 3 shows the weight average molecular weight Mw, glass transition point Tg, and softening point Tf of the low molecular weight polyester resin and the high molecular weight polyester resin used.

  Moreover, evaluation of the glass transition point Tg of the polyester resin in Table 3 was carried out using DSC (DSC-220C, manufactured by SII) as a measuring device, taking about 10 mg of the resin material in an aluminum pan, and the heating rate: 10 ° C. / min, measurement temperature range: measured at 30 to 150 ° C. In addition, the measurement used the data measured on the same conditions for the 2nd time, raising / lowering temperature (10 degreeC-150 degreeC-10 degreeC).

Moreover, the softening point Tf of the polyester resin in Table 3 was measured under the conditions of a temperature elevation rate of 5 ° C./min and a die hole diameter of 1.0 mm using a Koka type flow tester (manufactured by Shimadzu Corporation) as a measuring device. did.
In addition, with respect to Examples 12 to 14, Table 4 shows the composition, physical properties, physical properties, content, and the like of the liquid developer. In the table, polyester resins L1, L2, and L3 are respectively indicated as L1, L2, and L3, polyester resins H1, H2, and H3 are respectively indicated as H1, H2, and H3, and rosin-modified phenol is indicated as RP. Moreover, Disperbyk-116 was shown as D116 in the table.

  Further, the same evaluation as in [2] above was performed for each liquid developer obtained in Examples 12 to 14, and Table 5 shows the results.

  As is apparent from Table 5, the liquid developer of the present invention was excellent in charging characteristics (positive charging characteristics) and long-term dispersion stability of toner particles. The liquid developer of the present invention was also excellent in development efficiency, transfer efficiency, and fixing strength.

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. FIG. 6 is a schematic diagram illustrating a state of toner particles in a liquid developer layer on a developing roller. FIG. 2 is a cross-sectional view illustrating an example of a fixing device applied to the image forming apparatus illustrated in FIG. 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Toner particle 1000 ... Image forming apparatus 10Y, 10M, 10C, 10K ... Photoconductor 11Y ... Charging roller 12Y ... Exposure unit 13M, 13Y ... Photoconductor squeeze roller 14M, 14Y ... Cleaning blade 15M, 15Y ... Developer collection part 16Y ... Static elimination unit 17Y ... Photoconductor cleaning blade 18Y ... Developer collection unit 20Y, 20M, 20C, 20K ... Development roller 201Y ... Liquid developer layer 21Y ... Development roller cleaning blade 22Y ... Developer collection unit 23Y ... Corona discharger (compression) Means) 30Y, 30M, 30C, 30K ... developing section 31Y ... liquid developer storage section 32Y ... application roller 33Y ... regulating blade 34Y ... developer stirring roller 40 ... intermediate transfer section 41 ... belt drive rollers 42, 43 ... driven roller 44 ... Roller 46 ... Intermediate transfer section cleaning blade 47 ... Developer recovery section 48 ... Non-contact type bias applying member 51Y, 51M, 51C, 51K ... Primary transfer backup roller 52Y, 52M, 52C, 52K ... Intermediate transfer section squeeze device 53Y ... Intermediate transfer portion squeeze roller 55Y ... Intermediate transfer portion squeeze cleaning blade 56Y ... Developer recovery portion 60 ... Secondary transfer unit 61 ... Upstream side secondary transfer roller 62 ... Downstream side secondary transfer roller 63, 65 ... Secondary transfer roller Cleaning blades 64, 66... Developer collection unit 80Y, 80M, 80C, 80K ... Liquid developer supply unit 81Y, 81M, 81C, 81K ... Liquid developer tank 82Y, 82M, 82C, 82K ... Insulating liquid tank 83Y, 83M , 83C, 83K ... stirring device 00Y ... developing unit 101Y ... photosensitive squeeze device F40 ... fixing section (fixing device) F1 ... heat fixing roller (heating roller) F1a ... column-shaped halogen lamp F1b ... roller base material F1c ... elastic body F12 ... removal blade F2 ... pressure roller F2a ... Rotating shaft F2b ... Roller base material F2c ... Elastic body F3 ... Heat-resistant belt F4 ... Belt tension member F4a ... Projection wall F4f ... Recess F5 ... Recording medium F5a ... Toner image F6 ... Cleaning member F7 ... Frame F9 ... Spring

Claims (9)

Including an insulating liquid, toner particles, and a dispersant;
The toner particles are those in which a rosin resin is present on at least a part of the surface,
The liquid developer is characterized in that the dispersant has an amine value.   The liquid developer according to claim 1, wherein the dispersant has an amine value of 1 to 100 mg KOH / g.   The liquid developer according to claim 1, wherein the dispersant has at least one structure selected from the group consisting of a secondary amine structure, a tertiary amine structure, and an amide bond structure in the molecule.   4. The liquid developer according to claim 1, wherein the content of the dispersant is 0.2 to 10 parts by weight with respect to 100 parts by weight of the toner particles.   The liquid developer according to claim 1, wherein the toner particles include a resin material having an ester bond in addition to the rosin resin.   The liquid developer according to claim 1, wherein the rosin resin has a softening point of 80 to 190 ° C. 6.   The liquid developer according to claim 1, wherein the rosin resin has a weight average molecular weight of 500 to 100,000.   The liquid developer according to claim 1, wherein the insulating liquid is mainly composed of vegetable oil. A plurality of developing units that form a single color image corresponding to the plurality of liquid developers using a plurality of liquid developers having different colors;
An intermediate transfer unit that sequentially transfers a plurality of the single-color images formed by the plurality of developing units, and forms an intermediate transfer image formed by superimposing the transferred single-color images;
A secondary transfer unit that transfers the intermediate transfer image to a recording medium and forms an unfixed color image on the recording medium;
A fixing unit for fixing the unfixed color image on the recording medium,
The liquid developer includes an insulating liquid, toner particles, and a dispersant.
The toner particles are those in which a rosin resin is present on at least a part of the surface,
The image forming apparatus, wherein the dispersant has an amine value.

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