JP2010191222A - Liquid developer and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developer excellent in charging characteristics into positive charges and excellent in long-term dispersion stability of toner particles, and to provide an image forming method using the liquid developer. <P>SOLUTION: The liquid developer contains an insulating liquid and toner particles comprising a material containing a modified polyester resin modified with polyalkylene imine. The weight average molecular weight of the polyalkylene imine is preferably 10,000 to 70,000. The polyalkylene imine is preferably polyethylene imine. The insulating liquid preferably contains vegetable oil and fatty acid monoester. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

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.
In general, a polyester resin is widely used as a binder resin used for toner particles constituting such a liquid developer. The polyester resin has high transparency, and when used as a binder resin, it has characteristics that the resulting image has good color developability and high fixing characteristics.

By the way, as a liquid developer, a negatively chargeable liquid developer is generally used, but in recent years, development of a positively chargeable liquid developer has been advanced (for example, see Patent Document 1).
However, since the polyester resin conventionally used for toner particles generally has high negative chargeability, it has been difficult to apply it to positively charged toner particles (liquid developer). In addition, it is conceivable to add a charge control agent or a dispersing agent having a positive charging characteristic to toner particles using a conventional polyester resin as a binder resin, but it is difficult to obtain a sufficient charge amount. Met.

JP 2002-214849 A

  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 method 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,
And toner particles composed of a material containing a modified polyester resin modified with polyalkyleneimine.
In the liquid developer of the present invention, the polyalkylenimine preferably has a weight average molecular weight of 10,000 to 70,000.

In the liquid developer of the present invention, the polyalkyleneimine is preferably polyethyleneimine.
In the liquid developer of the present invention, the insulating liquid preferably contains a vegetable oil and a fatty acid monoester.
In the liquid developer of the present invention, the toner particles may be obtained by adding a water-based liquid to the resin solution preparation step of preparing a resin solution in which the modified polyester resin is dissolved in an organic solvent, and adding W / O to the resin solution. An O / W emulsion preparation step for preparing an O / W emulsion via an emulsion, and a coalescence step for obtaining coalesced particles by coalescing the dispersoids contained in the O / W emulsion. The organic solvent contained in the coalesced particles is preferably removed through an organic solvent removing step for forming the toner particles.

In the liquid developer of the present invention, the modified polyester resin is preferably modified with 1 to 8 parts by weight of a polyalkyleneimine with respect to 100 parts by weight of the polyester resin.
In the liquid developer of the present invention, the acid value of the polyester resin subjected to the modification of the polyalkyleneimine is preferably 5 to 20 mgKOH / g.
The image forming method of the present invention includes a developing step of forming a plurality of single color images corresponding to the plurality of liquid developers using a plurality of liquid developers having different colors,
Transferring a plurality of the monochrome images corresponding to each color to a recording medium, and forming an unfixed toner image formed by superimposing the plurality of monochrome images on the recording medium;
A fixing step of fixing the unfixed toner image on the recording medium,
The liquid developer contains an insulating liquid and toner particles composed of a material containing a modified polyester resin modified with polyalkyleneimine.
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 method using such a liquid developer can be provided.

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

Hereinafter, preferred embodiments of the present invention will be described in detail.
≪Liquid developer≫
First, the liquid developer of the present invention will be described.
The liquid developer of the present invention contains an insulating liquid and toner particles composed of a material containing a modified polyester resin modified with polyalkyleneimine.

Hereinafter, each component will be described in detail.
<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 include a modified polyester resin modified with polyalkyleneimine as a resin material.

  By the way, since the polyester resin conventionally used for the toner particles generally has high negative chargeability, it has been difficult to apply to the positively chargeable toner particles (liquid developer). In addition, it is conceivable to add a charge control agent or a dispersing agent having a positive charging characteristic to toner particles using a conventional polyester resin as a binder resin, but it is difficult to obtain a sufficient charge amount. Met. 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. It is also conceivable to positively charge the entire toner particles using a positively chargeable charge control agent or dispersant. In such a case, the initial dispersibility of the toner particles is good, but over time. As a result, the charge control agent and the dispersant are detached from the toner particles (toner base particles), and it is difficult to maintain stable positive chargeability for a long period of time. In particular, in an image forming apparatus equipped with a mechanism for reusing the liquid developer collected at the developing unit, which will be described later, since stress is applied to the toner particles during collection, the charging is simply positively charged. In a toner using a control agent or a dispersant, the charge control agent or the dispersant is detached or dropped from the toner particles (toner base particles), and the charging characteristics of the toner particles are likely to be rapidly lowered. In addition, when a positively chargeable charge control agent is used to sufficiently positively charge toner particles, the color of the toner particles may be adversely affected by the influence of the charge control agent.

On the other hand, in the present invention, by using a modified polyester resin modified with polyalkyleneimine as a resin material constituting the toner particles, it is excellent in positive charging characteristics and excellent in long-term dispersion stability of toner particles. A liquid developer can be obtained. This is considered to be due to the following reasons.
Since polyalkyleneimine has many amino groups, it is a highly positively charged compound. By modifying the polyester resin with such a polyalkyleneimine, an acidic group such as a carboxyl group, which is a factor of the negative chargeability of the polyester resin, is bonded to the amino group of the polyalkyleneimine and originally possessed by the polyester resin. The negative chargeability is suppressed, and the modified polyester resin (modified polyester resin) is positively charged due to the amino group derived from polyalkyleneimine bonded to the polyester resin.

  By using such a modified polyester resin as a resin material constituting the toner particles, a large number of polyalkyleneimine-derived amino groups are present on the surface of the toner particles, and the liquid developer has excellent positive chargeability. It will have. Further, since a large number of amino groups are present on the toner particle surface, these amino groups repel each other between the toner particles in the liquid developer, and aggregation of the toner particles is prevented. As a result, in the liquid developer, toner particles are stably dispersed over a long period of time, that is, excellent in long-term dispersion stability. Further, the liquid developer of the present invention is excellent in characteristics such as development efficiency because it is excellent in charging characteristics and long-term dispersion stability. 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.

  Such an effect cannot be obtained by simply mixing the polyalkyleneimine in the polyester resin or simply adding the polyalkyleneimine to the liquid developer. That is, if the polyalkyleneimine is simply mixed in the polyester resin, or if the polyalkyleneimine is simply added to the liquid developer, the polyalkyleneimine is detached from the toner particle surface, and the toner particles are positively charged. In addition, the desorbed polyethyleneimine lowers the insulating properties of the insulating liquid, which in turn reduces the charging characteristics.

In the present invention, the modification with polyalkyleneimine is a chemical reaction between at least a part of many amino groups of polyalkyleneimine and at least a part of acidic groups (mainly carboxyl groups) of polyester resin. It means that a covalent bond (amide bond) is formed, or that the acidic group of the polyester resin and the amino group of the polyalkyleneimine form an ionic bond.
The polyester resin used for the modification of polyethyleneimine is not particularly limited, and a known polyester resin can be used.

  In particular, the polyester resin used for the modification of polyethyleneimine is preferably one having an acid value of 5 to 20 mgKOH / g, more preferably 8 to 12 mgKOH / g. As a result, modification with polyalkyleneimine can be performed more suitably, and the charging characteristics and long-term dispersion stability of the toner particles can be further improved.

  Moreover, the glass transition point of the polyester resin subjected to the modification of polyethyleneimine is not particularly limited, but is preferably 15 to 70 ° C, and more preferably 20 to 55 ° C. In this specification, the glass transition point is a measurement condition in a differential scanning calorimeter DSC-220C (manufactured by SII): a sample amount of 10 mg, a heating rate of 10 ° C./min, and a measurement temperature range of 10 to 150 ° C. The temperature at the intersection of the base line extension below the glass transition point and the tangent that indicates the maximum slope from the peak rise to the peak apex.

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

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

The modified polyester resin can be prepared, for example, as follows.
First, a resin solution in which a polyester resin is dissolved in a solvent is prepared.
Next, the temperature of the resin solution is adjusted to 120 to 130 ° C.
On the other hand, a polyalkyleneimine solution in which polyalkyleneimine is dissolved in a solvent is prepared.
The polyalkyleneimine solution is added to the temperature-adjusted resin solution, and the polyester resin and polyalkyleneimine are reacted. Thereby, a modified polyester resin can be obtained.

The modification of the polyester resin is preferably performed by adding 1 to 8 parts by weight of polyalkylenimine to 100 parts by weight of the polyester resin. Thereby, the charge characteristic of the modified polyester resin obtained can be more efficiently made positively charged.
In addition, as resin material, well-known resin other than the modified polyester resin as mentioned above may be contained.

2. Colorant The toner particles may contain a colorant. The colorant is not particularly limited, and for example, known pigments and dyes can be used.
3. Other Components The toner particles may contain components other than those described above. Examples of such components include known waxes and magnetic powders.
In addition to the above materials, for example, zinc stearate, zinc oxide, cerium oxide, silica, titanium oxide, iron oxide, fatty acid, fatty acid metal salt, etc. are used as the constituent material (component) of the toner particles. May be.

[Toner particle shape]
The average particle diameter of the toner particles composed of the above materials is preferably 0.5 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%.

<Insulating liquid>
Next, the insulating liquid will be described.
The insulating liquid may be a liquid having a sufficiently high insulating property. Specifically, the electrical resistance at room temperature (20 ° C.) is preferably 1 × 10 ⁹ to 1 × 10 ¹⁵ Ωcm. It is more preferably x10 ¹¹ to 1 × 10 ¹⁵ Ωcm, and even more preferably 1 × 10 ¹³ to 1 × 10 ¹⁵ Ωcm.
Moreover, it is preferable that the dielectric constant of an insulating liquid is 1.0-4.0.

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 it may be used in combination of two or more. Among the above-mentioned, in particular, vegetable oil and fatty acid monoester have a particularly high affinity (compatibility) with the modified polyester resin, so that the dispersion stability of the toner particles can be further improved. Further, the fatty acid monoester has an effect of plasticizing toner particles (particularly a resin material). Due to this plasticizing effect, the toner particles are plasticized at the time of fixing, and the fixing strength of the toner particles is increased. can do.
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 particularly improved. 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.
The liquid developer of the present invention may contain components other than those described above (for example, external additives).

≪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 of the present embodiment includes a resin solution preparation step of preparing a resin solution in which a modified polyester resin is dissolved in an organic solvent, and an aqueous liquid is added to the prepared resin solution, whereby W / O emulsification is performed. An O / W emulsion preparation step for preparing an O / W emulsion via a solution, and a coalescence step for obtaining a coalesced particle by combining the dispersoids contained in the prepared O / W emulsion. The organic solvent contained in the coalesced particles is removed to form toner particles, and the obtained toner particles are dispersed in the insulating liquid.

Hereafter, each process which comprises the manufacturing method of a liquid developer is demonstrated in detail.
[Resin solution preparation process]
First, a resin solution in which a modified polyester resin is dissolved in an organic solvent is prepared.
The prepared resin solution contains the constituent material of the toner particles as described above and an organic solvent (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 liquid (aqueous dispersion medium) described later (for example, one having a solubility in 100 g of aqueous liquid at 25 ° C. of 30 g or less). Thereby, in the O / W emulsion liquid (water-based emulsion liquid) described later, the dispersoid composed of the base particle material can be finely dispersed in a stable state.

In addition, the composition of the organic solvent can be appropriately selected according to, for example, the resin material and the colorant composition described above, the composition of the aqueous liquid (aqueous dispersion medium), and the like.
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 solution can be obtained, for example, by mixing a resin material, a colorant, an organic solvent and the like with a stirrer or the like. Examples of the stirrer that can be used for preparing the resin solution include DESPA (manufactured by Asada Tekko Co., Ltd.), T.C. K. Robotics / T. K. Examples thereof include a high-speed stirrer such as Homodisper 2.5 type blade (manufactured by PRIMIX Corporation).

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.
The solid content in the resin solution is not particularly limited, but is preferably 40 to 75 wt%, more preferably 50 to 73 wt%, and even more preferably 50 to 70 wt%. When the solid content is within the above range, the dispersoid constituting the dispersion liquid (aqueous dispersion liquid) described later can 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 preparing the resin solution, all the components of the resin solution to be prepared may be mixed at the same time, or a part of the components of the resin solution to be prepared may be mixed in advance to prepare a mixture (master). After that, the mixture (master) may be mixed with other components.

[O / W emulsion preparation process]
Next, an O / W emulsion is prepared via the W / O emulsion by adding an aqueous liquid to the resin solution. When toner particles are formed through such a process, more amino groups derived from polyalkyleneimine can be present on the surface of the toner particles, and the positive chargeability and long-term dispersion stability of the finally obtained liquid developer can be obtained. Can be made more excellent. This is because, among the modified polyester resins, the polyester resin-derived part is lipophilic, while the polyalkyleneimine-derived part (especially amino group) is highly hydrophilic, so when the O / W emulsion was prepared In addition, it is considered that the portion derived from polyalkyleneimine is directed to the aqueous phase side, and as a result, amino groups can be present on the surface of the obtained toner particles.

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).
In addition, an emulsifying dispersant may be added to the aqueous liquid 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 O / W emulsion, for example, a basic substance may be used. Thereby, for example, the functional group (for example, carboxyl group) possessed by the resin material can be neutralized, and the shape and size uniformity of the dispersoid in the prepared O / W emulsion can be improved. Dispersibility can be made particularly excellent. For this reason, the obtained toner particles have a particularly sharp particle size distribution. For example, the basic substance may be added to the resin solution, or may be added to the aqueous liquid. Further, the basic substance may be added in a plurality of times in the preparation of the O / W emulsion.

As a basic substance, sodium hydroxide, potassium hydroxide, ammonia etc. are mentioned, for example, 1 type selected from these, or 2 or more types can be used in combination.
Moreover, the usage-amount of a basic substance 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 solution by any method, but it is preferable to add the aqueous liquid containing water to the resin solution while stirring the resin solution. That is, it is performed by gradually adding (dropping) an aqueous liquid into the resin solution while applying shear to the resin solution with a stirrer or the like, and from the W / O type emulsion (W / O emulsion) to the O / W It is preferable to invert the phase to a type emulsion (O / W emulsion). Thereby, the uniformity of the size and shape of the dispersoid contained in the O / W emulsion can be made particularly high, and the particle size distribution of the toner particles contained in the finally obtained liquid developer can be greatly increased. Sharpness can be achieved, and variation in characteristics among toner particles can be particularly small.

Examples of the stirrer that can be used for the preparation of the O / W emulsion include DESPA (manufactured by Asada Tekko Co., Ltd.), T.W. 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), a cavitron (manufactured by Eurotech), or a high-speed disperser.
Further, at the time of adding the aqueous liquid to the resin solution, 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 O / W emulsion can be obtained efficiently, and the dispersion of the shape and size of the dispersoid in the O / W emulsion should be particularly small. It is possible to make the uniform dispersibility of the dispersoid particularly excellent while preventing the generation of excessively fine dispersoid and coarse particles.

The solid content in the O / W emulsion is not particularly limited, but is preferably 5 to 55 wt%, and more preferably 10 to 50 wt%. Thereby, the productivity of the liquid developer can be made particularly excellent while more reliably preventing unintentional aggregation of dispersoids in the O / W emulsion.
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. The coalescence of dispersoids usually proceeds as a result of collision of dispersoids containing an organic solvent so that they are integrated.
The coalescence of a plurality of dispersoids is performed by adding an electrolyte to the O / W emulsion while stirring the O / W emulsion. 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 made particularly sharp. 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 O / W emulsion to which the electrolyte is added. More preferably, it is part. 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. Thereby, while being able to diffuse an electrolyte to the whole O / W emulsion liquid quickly, the addition amount of an electrolyte can be controlled easily and reliably. As a result, coalesced particles having a desired particle size and a very sharp 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 O / W emulsion particularly quickly, and the amount of electrolyte added can be easily and reliably controlled. In addition, by adding such an aqueous solution, the content of water in the O / W emulsion 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 O / W emulsion to which the aqueous electrolyte solution is added. It is 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 O / W emulsion, and to reliably prevent the generation of coarse particles. Further, the particle size distribution of the coalesced particles becomes sharper. Furthermore, by adding the electrolyte at such a rate, the coalescence rate can be controlled particularly easily, and it becomes particularly easy to control the average particle size of the coalesced particles, and the productivity of the liquid developer can be reduced. It can be made particularly excellent.

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 O / W emulsion. Thereby, coalesced particles with particularly small variations in shape and size among the particles can be obtained.

  For agitation of the O / W emulsion, 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. 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. Moreover, 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 more appropriately set to be appropriate.

[Organic solvent removal step]
Thereafter, the organic solvent contained in the O / W emulsion (particularly in the dispersoid) is removed. As a result, a dispersion liquid in which toner particles are dispersed in an aqueous dispersion medium (aqueous dispersion liquid) is obtained.
The removal of the organic solvent may be performed by any method, but can be performed, for example, under reduced pressure. Thereby, it is possible to efficiently remove the organic solvent 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 O / W emulsion (dispersion). 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 O / W emulsion 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 the steps described later.

[Washing process]
Next, the toner particles obtained as described above are washed.
By performing this step, even when an organic solvent or the like is contained as an impurity, these can be efficiently removed. Moreover, by performing this process, the electrolyte, basic substance, acidic substance, and salt generated by the acid-base reaction used in the above-described process can be efficiently removed. As a result, the amount of volatile organic compounds (TVOC) in the finally obtained toner particles can be made particularly small. In addition, the electrical resistance of the insulating liquid can be made particularly high, and the stability of the characteristics of the toner particles is improved.
In this step, for example, the toner particles are separated by solid-liquid separation (separation from the aqueous liquid), and then the solid content (resin fine particles) is redispersed in water and solid-liquid separation (resin fine particles from the 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. By performing such a process, the water content in the toner particles can be surely made sufficiently low, and the storage stability and characteristic stability of the finally obtained liquid developer are particularly excellent. can do.
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 in insulating liquid]
Next, the toner particles obtained as described above are dispersed in an insulating liquid. Thereby, a liquid developer is obtained.
The toner particles can be dispersed in the insulating liquid by any method, for example, by mixing the insulating liquid and the toner particles with a bead mill, a ball mill, or the like.

Further, at the time of dispersion, components other than the insulating liquid and toner particles may be mixed.
Further, the dispersion of the toner particles in the insulating liquid may be performed by using the whole amount of the insulating liquid constituting the finally obtained liquid developer, or by using a part of the insulating liquid. It may be a thing.
Further, when the toner particles 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, or after the dispersion, Alternatively, 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 manufactured by the method described above, the variation in shape and characteristics between toner particles is small.

≪Image formation method≫
Next, a preferred embodiment of the image forming method of the present invention will be described.
First, a preferred embodiment of an image forming apparatus applied to the image forming method of the present invention will be described.
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 90Y, 90M, 90C, and 90K 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 44 and 45 to which a driving force of a motor (not shown) is transmitted. The intermediate transfer unit 40 is driven to rotate counterclockwise by the belt driving roller 41 while being in contact with the photoreceptors 10Y, 10M, 10C, and 10K by the primary transfer backup rollers 51Y, 51M, 51C, and 51K.

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

  In the intermediate transfer unit 40, the single-color images formed on the plurality of photoconductors 10Y, 10M, 10C, and 10K are secondarily transferred and superposed one after another. Secondary transfer is performed on a recording medium F5 such as paper, film, or cloth. Therefore, when the toner image is transferred to the recording medium F5 in the secondary transfer process, even if the surface of the recording medium F5 is a 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 45 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 49. The non-contact type bias applying member 48 applies a bias voltage having a polarity opposite to that of the toner to the liquid developer toner (solid content) remaining on the intermediate transfer portion 40 after the secondary transfer. As a result, the toner is discharged, and the electrostatic adhesion force of the toner to the intermediate transfer unit 40 is reduced. In this example, a corona charger is used as the non-contact type bias applying member 48.

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

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

The intermediate transfer unit squeeze device 52Y is removed by 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 these pair of secondary transfer rollers, the secondary transfer roller disposed upstream of the moving direction of the intermediate transfer unit 40 is the upstream secondary transfer roller 64. The upstream secondary transfer roller 64 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 in the moving direction of the transfer material is the downstream secondary transfer roller 65. The downstream secondary transfer roller 65 can be brought into pressure contact with the driven roller 44 via the intermediate transfer unit 40.
That is, the upstream side secondary transfer roller 64 and the downstream side secondary transfer roller 65 bring the recording medium F5 into contact with the intermediate transfer unit 40 that is hung on the belt drive roller 41 and the driven roller 44, respectively. The intermediate transfer image formed by superimposing colors on 40 is secondarily transferred to the recording medium F5.

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

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

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

The toner image (transfer image) F5a transferred onto the recording medium F5 by the secondary transfer unit 60 is sent to a fixing unit (fixing device) F40, and is heated and pressurized to be fixed on the recording medium F5.
Specifically, the fixing temperature is preferably 80 to 160 ° C., more preferably 100 to 150 ° C., and further preferably 100 to 140 ° C.

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

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

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

Further, the partition 31cY is provided with a notch, and the liquid developer can overflow from the supply part 31aY to the recovery part 31bY through the notch.
The coating roller 32Y has a function of supplying a liquid developer to the developing roller 20Y.

  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 supply unit 31aY in the groove and transporting the supported liquid developer to the developing roller 20Y. To do.

  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 supply unit 31aY and reused.

  The developer stirring roller 34Y has a function of stirring the liquid developer in a uniformly dispersed state. Thus, even when a plurality of toner particles are aggregated, the toner particles can be suitably dispersed. In particular, since the liquid developer of the present invention is excellent in dispersion stability and redispersibility, even a reused liquid developer can be easily dispersed.

  In the supply unit 31aY, the toner particles in the liquid developer have a positive charge, and the liquid developer is stirred by the developer stirring roller 34Y to be in a uniformly dispersed state, and the coating roller 32Y rotates. Thus, the liquid developer is stored in the liquid developer storage unit 31Y, and the amount of the liquid developer is regulated by the regulating blade 33Y and supplied to the developing roller 20Y. Further, by being stirred by the developer stirring roller 34Y, it is possible to stably overflow the liquid developer beyond the partition 31cY to the collecting unit 31bY side, and to prevent the liquid developer from staying and being compressed. it can.

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

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

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

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

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

In the developing unit 100Y, the coating roller 32Y and the developing roller 20Y are separately driven by different power sources (not shown). 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 24Y. The developing roller cleaning blade 21Y is a device for scraping off and removing the liquid developer remaining on the developing roller 20Y after development is performed at the developing position. The liquid developer removed by the developing roller cleaning blade 21Y is collected in the developer collecting unit 24Y.

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

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

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

  Further, the liquid developer recovered by the recovery unit 31bY is recovered and reused in the liquid developer mixing tank 93Y. The same applies to the liquid developer mixing tanks 93M, 93C, and 93K. Here, as described above, the toner particles are made of a material containing a modified polyester resin, and the polyalkyleneimine is firmly bonded to the polyester resin. For this reason, even when the toner particles are subjected to stress accompanying recovery (for example, stress due to a cleaning blade), the polyalkyleneimine is reliably prevented from detaching / dropping from the toner particles. Such toner particles have high redispersibility in an insulating liquid. Therefore, the collected toner particles can be suitably reused for image formation.

  In the image formation using the above-described apparatus, a plurality of liquid developers having different colors (the liquid developer of the present invention) are used, and a plurality of photoreceptors 10 (10Y, 10M, 10C, 10K) corresponding to the respective colors are used. A developing process for forming a single-color image, and a plurality of single-color images formed on the photoreceptor 10 are transferred to a recording medium F5, and an unfixed toner image F5a formed by superimposing the plurality of single-color images on the recording medium F5 is obtained. The transfer process is performed and the fixing process of fixing the unfixed toner image F5a onto the recording medium F5. By using such a method, an image excellent in color developability can be easily formed.

As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to these.
For example, the liquid developer of the present invention is not limited to that applied to the image forming apparatus as described above.
Further, the liquid developer of the present invention is not limited to those 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] Preparation of modified polyester resin (1) Preparation of modified polyester resin A A 2 L four-necked flask was equipped with a nitrogen gas inlet tube, a thermometer and a stirrer, and a polyester resin (weight average molecular weight: 7500, glass transition point). (Tg): 57 ° C., acid value: 10 mg KOH / g): 100 parts by weight and m-cresol: 227 parts by weight were charged and heated under stirring in a nitrogen atmosphere to 160 ° C. over 2 hours. At this time, it was visually confirmed that the polyester resin was completely dissolved.

Next, the resin solution was cooled to 130 ° C., and polyethyleneimine (weight average molecular weight: 10,000, 30% aqueous solution): 10 parts by weight (3 parts by weight as polyethyleneimine) was dissolved in methyl cellosolve: 10 parts by weight. Polyethyleneimine solution: 13.4 parts by weight were added to the resin solution over 1 hour. Then, it stirred under nitrogen atmosphere for 5 hours.
Next, heating and stirring were stopped, and the mixture was naturally cooled in a nitrogen atmosphere until it reached room temperature. A mixed solvent of methanol: 1430 parts by weight and acetone: 613 parts by weight was added, and stirring was performed for 20 minutes.
The solution was allowed to stand at room temperature for 1 day, and then the solution containing the precipitate was suction filtered to collect the precipitate. The collected precipitate was air-dried and then vacuum-dried at 40 ° C. for 7 hours to remove the organic solvent and obtain a modified polyester resin A.

(2) Preparation of modified polyester resins B to I Modified polyester resin B in the same manner as the modified polyester resin A except that the type and content of polyethyleneimine and the type of polyester resin were changed as shown in Table 1. ~ I was prepared.
Table 1 shows the type and content of polyethyleneimine and the type of polyester resin in the preparation of each modified polyester resin.

[2] Production of Liquid Developer A liquid developer was produced as follows. About the process in which temperature is not described, it performed at room temperature (25 degreeC).
Example 1
(Preparation of colorant masterbatch)
First, 60 parts by weight of modified polyester resin A was prepared as a resin material.
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. And the kneaded material 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 solution preparation process)
The above colorant masterbatch: 97.5 parts by weight, methyl ethyl ketone: 175 parts by weight, modified polyester resin A: 227.6 parts by weight, a high-speed disperser (manufactured by Primix, TK Robotics / TK Homo Dispers 2 .5 type blades) and 1.38 parts by weight of Neogen SC-F (Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier was added to prepare a resin solution. In this solution, the pigment was uniformly finely dispersed.

(O / W emulsion preparation process)
Next, 72.8 parts by weight of 1N ammonia water was added to the resin solution in the container, and the mixture was stirred with a high-speed disperser (Primics Co., Ltd., TK Robotics / TK homodisper type 2.5 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 then the blade tip speed of the stirring blade was 14.7 m / s while stirring. By adding 100 parts by weight of deionized water: 100 parts by weight of deionized water while adding stirring of deionized water by weight and further continuing stirring, the dispersoid containing the resin material is dispersed through the W / O emulsion. / W emulsion was obtained.

(Joint process)
Next, the O / W emulsion was transferred to a stirring vessel having a Max Blend blade, and the temperature of the O / W emulsion 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% sodium sulfate aqueous solution was dropped, and the dispersoids were coalesced to form coalesced particles. After the dropping, stirring was continued until the 50% volume particle diameter Dv (50) [μm] of the coalesced 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.

(Organic solvent removal step)
Next, the O / W emulsion containing the coalesced particles was placed in a reduced pressure environment, and the organic solvent was distilled off until the solid content was 23 wt% to obtain a toner particle slurry (dispersion).
(Washing process)
Next, the slurry (dispersion) was subjected to solid-liquid separation, and further washed again by redispersion in water (reslurry) and solid-liquid separation. The washing treatment was performed until the conductivity of the supernatant of the slurry became 20 μS / cm or less.
Thereafter, a wet cake of toner particles (toner particle cake) 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.

(Dispersion process in insulating liquid)
Toner particles obtained by the above method: 60 parts by weight, rapeseed oil (Nisshin Oilio Co., Ltd., trade name “HIOLEIC Rapeseed Oil”) as an insulating liquid: 144 parts by weight and isopropyl palmitate (Nissho Co., Ltd., trade name “ IPP-R "): 96 parts by weight in a propylene wide-mouthed jar, and φ3 glass beads: 300 parts by weight in a propylene-made wide-mouthed jar, and an inverter in a rocking mill RM-05S (Seiwa Giken Co., Ltd.) Dispersion was performed for 90 minutes at a frequency setting of 52 Hz. Thereafter, the glass beads were removed, and dust and coarse particles were removed from the obtained liquid with a SUS sieve (aperture 150 microns) to obtain a liquid developer.

The Dv (50) of the toner particles in the obtained liquid developer was 2.96 μm. The 50% volume particle diameter Dv (50) [μm] of the obtained toner particles was measured with a microtrack particle size distribution measuring device MT-3300II (manufactured by Nikkiso Co., Ltd.). Moreover, the particle diameter was similarly calculated | required about the particle | grains obtained by each Example and each comparative example demonstrated below.
Further, the viscosity of the obtained liquid developer at 25 ° C. was 50 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.

(Examples 2-9)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the type of the modified polyester resin was changed as shown in Table 1.

(Example 10)
(Preparation of colorant masterbatch)
First, 60 parts by weight of modified polyester resin A was prepared as a resin material.
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. And the kneaded material 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.

(Preparation of toner particles)
The colorant master batch: 15 parts by weight and the modified polyester resin A: 85 parts by weight were kneaded using a biaxial kneading extruder. And the kneaded material extruded from the extrusion port of the biaxial kneading extruder was cooled. The obtained kneaded product was pulverized with a hammer mill, and the pulverized product was used as toner particles.

(Dispersion process in insulating liquid)
Toner particles obtained by the above method: 60 parts by weight, rapeseed oil (Nisshin Oilio Co., Ltd., trade name “HIOLEIC Rapeseed Oil”) as an insulating liquid: 144 parts by weight and isopropyl palmitate (Nissho Co., Ltd., trade name “ IPP-R "): 96 parts by weight in a propylene wide-mouthed jar, and φ3 glass beads: 300 parts by weight in a propylene-made wide-mouthed jar, and an inverter in a rocking mill RM-05S (Seiwa Giken Co., Ltd.) Dispersion was performed for 90 minutes at a frequency setting of 52 Hz. Thereafter, the glass beads were removed, and dust and coarse particles were removed from the obtained liquid with a SUS sieve (aperture 150 microns) to obtain a liquid developer.

The Dv (50) of the toner particles in the obtained liquid developer was 4.92 μm. Further, the viscosity of the obtained liquid developer at 25 ° C. was 60 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.

(Comparative Example 1)
The same as in Example 1 except that a modified polyester resin was not used and an unmodified polyester resin (weight average molecular weight: 7500, glass transition point (Tg): 57 ° C., acid value: 10 mgKOH / g) was used. The liquid developer corresponding to each color was manufactured.
(Comparative Example 2)
A polyamine dispersant (manufactured by Nippon Lubrizol Corporation) was used without using a modified polyester resin and using an unmodified polyester resin (weight average molecular weight: 7500, glass transition point (Tg): 57 ° C., acid value: 10 mgKOH / g). The liquid developer corresponding to each color was produced in the same manner as in Example 1 except that 1 part by weight of the trade name “Solsperse 13940”) was added to 100 parts by weight of the toner particles.

(Comparative Example 3)
Without using a modified polyester resin, an unmodified polyester resin (weight average molecular weight: 7500, glass transition point (Tg): 57 ° C., acid value: 10 mgKOH / g) was used, and polyethyleneimine (weight average molecular weight: 10,000) was used. A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that 3 parts by weight was added to 100 parts by weight of toner particles.

  Table 2 shows the types of resin materials used in the preparation of the liquid developer, the average particle size of the toner particles, the type of insulating liquid, and the like for each of the above Examples and Comparative Examples. In the table, modified polyester resins A to I are simply A to I, polyester resin (weight average molecular weight: 7500, glass transition point (Tg): 57 ° C., acid value: 10 mg KOH / g), PES, and rapeseed oil as HO. In addition, isopropyl palmitate was indicated as IPP, polyamine dispersant as SOL, and polyethyleneimine (weight average molecular weight: 10,000) as PEI.

[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 five-step 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 50% or more and less than 80%, and the development efficiency is inferior.
E: The development efficiency is less than 50%, and the development efficiency is particularly inferior.

[2.2] Charging characteristics of positive charge 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).

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

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

[2.4] Recyclability Using the liquid developers obtained in each of the above examples and comparative examples, 10,000 images of a predetermined pattern were obtained using an image forming apparatus as shown in FIGS. Recording paper (manufactured by Seiko Epson Corporation, high-quality paper LPCPPA4). This image formation was performed in a state where supply of the liquid developer from the liquid developer tank of each color to the corresponding stirring device of each color was stopped. After image formation on 10,000 sheets of recording paper, a liquid developer (recycled) regenerated by diluting the toner particles collected in the stirring device with an insulating liquid so that the solid content is 20 wt% The liquid developer was tested by the following two methods (Method 1 and Method 2) to evaluate the adaptability (recyclability) for recycling.

[2.4.1] Method 1
10 mL of the recycled liquid developer for each Example and each Comparative Example was put in a test tube (12 mm in diameter and 120 mm in length), and the sedimentation depth after standing for 10 days was measured and evaluated according to the following four criteria. did.
A: Settling depth is 1 mm or less.
B: The settled depth is larger than 1 mm and 3 mm or less.
C: The settled depth is larger than 3 mm and 6 mm or less.
D: The settled depth is larger than 6 mm.

[2.4.2] Method 2
Recycled liquid developer 45.5 mL for each example and each comparative example was put in a centrifuge tube, and a centrifuge (manufactured by Kokusan Co., Ltd.) under conditions of a rotation radius of 5 cm, a rotation speed of 500, 1000, 2000, 4000, 5000 rpm for 3 minutes. ), The sedimentation depth 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 <0.006
B: 0.006 ≦ k <0.010
C: 0.010 ≦ k <0.014
D: k ≧ 0.014
These results are shown in Table 3.

  As is apparent from Table 3, the liquid developer of the present invention was excellent in charging characteristics (positive charging characteristics), development efficiency, and long-term dispersion stability of toner particles. The liquid developer of the invention was also excellent in recyclability. On the other hand, satisfactory results were not obtained with the liquid developer of the comparative example.

  1000: Image forming apparatus 10Y, 10M, 10C, 10K ... Photoconductor 11Y ... Charging roller 12Y ... Exposure unit 13M, 13Y ... Photoconductor squeeze roller 14M, 14Y ... Cleaning blade 15M, 15Y ... Developer recovery unit 16Y ... Static elimination unit 17Y ... Photoconductor cleaning blade 18Y ... Developer collection unit 20Y, 20M, 20C, 20K ... Development roller 21Y ... Development roller cleaning blade 24Y ... Developer collection unit 30Y, 30M, 30C, 30K ... Development unit 31Y ... Liquid developer storage unit 31aY ... Supply unit 31bY ... Recovery unit 31cY ... Partition 32Y ... Applying roller 33Y ... Regulator blade 34Y ... Developer stirring roller 35Y ... Communication unit 36Y ... Recovery screw 40 ... Intermediate transfer unit 41 ... Belt drive roller 49 ... Tension Rollers 44, 45 ... driven roller 46 ... intermediate transfer portion cleaning blade 47 ... developer recovery portion 48 ... non-contact type bias applying member 51Y, 51M, 51C, 51K ... primary transfer backup roller 52Y, 52M, 52C, 52K ... intermediate Transfer unit squeeze device 53Y ... Intermediate transfer unit squeeze roller 55Y ... Intermediate transfer unit squeeze cleaning blade 56Y ... Developer recovery unit 60 ... Secondary transfer unit 64 ... Upstream side secondary transfer roller 65 ... Downstream side secondary transfer roller 66, 68 ... secondary transfer roller cleaning blade 67, 69 ... developer recovery unit 90Y, 90M, 90C, 90K ... liquid developer replenishment unit 91Y, 91M, 91C, 91K ... liquid developer tank 92Y, 92M, 92C, 92K ... insulation Liquid tank 93Y, 93M, 93C, 9 3K ... Liquid developer mixing tank 100Y ... Development unit 101Y ... Photoconductor squeeze device F40 ... Fixing unit (fixing device) F5 ... Recording medium F5a ... Toner image

Claims (8)

An insulating liquid;
A liquid developer comprising: toner particles composed of a material containing a modified polyester resin modified with polyalkyleneimine.   The liquid developer according to claim 1, wherein the polyalkyleneimine has a weight average molecular weight of 10,000 to 70,000.   The liquid developer according to claim 1, wherein the polyalkyleneimine is polyethyleneimine.   The liquid developer according to any one of claims 1 to 3, wherein the insulating liquid contains vegetable oil and a fatty acid monoester.   The toner particles are prepared by a resin solution preparation step of preparing a resin solution in which the modified polyester resin is dissolved in an organic solvent, and an aqueous liquid is added to the resin solution, whereby an O-type liquid is added via the W / O emulsion. Included in the coalesced particles, an O / W emulsion preparing step for preparing an / W emulsion, a coalescing step in which dispersoids contained in the O / W emulsion are coalesced to obtain coalesced particles, and the coalesced particles The liquid developer according to claim 1, wherein the liquid developer is obtained through an organic solvent removing step of removing the organic solvent to form toner particles.   6. The liquid developer according to claim 1, wherein the modified polyester resin is modified with 1 to 8 parts by weight of a polyalkyleneimine with respect to 100 parts by weight of the polyester resin.   The liquid developer according to claim 6, wherein an acid value of the polyester resin subjected to modification of the polyalkyleneimine is 5 to 20 mg KOH / g. A developing step of forming a plurality of single color images corresponding to the plurality of liquid developers using a plurality of liquid developers having different colors;
Transferring a plurality of the monochrome images corresponding to each color to a recording medium, and forming an unfixed toner image formed by superimposing the plurality of monochrome images on the recording medium;
A fixing step of fixing the unfixed toner image on the recording medium,
The image forming method, wherein the liquid developer contains an insulating liquid and toner particles composed of a material containing a modified polyester resin modified with polyalkyleneimine.

Images