JP2010181595A - Liquid developer and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developer excellent in charging characteristics in positive charges and dispersion stability of toner particles in a long period of time, and to provide an image forming apparatus using the liquid developer. <P>SOLUTION: The liquid developer contains: an insulating liquid; and toner particles prepared by surface-modifying the surface of toner base particles comprising a material containing a rosin-based resin, with polyallylamine. The weight average molecular weight of the polyallylamine is preferably from 500 to 100,000. <P>COPYRIGHT: (C)2010,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. For the toner particles constituting such a liquid developer, a resin material such as a polyester resin, a styrene-acrylate copolymer, or an epoxy resin is used. 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). .)

Japanese Patent No. 3332961

  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.

  The present invention is realized as the following forms or application examples so as to solve at least a part of the problems described above.

  Application Example 1 A liquid developer according to this application example includes an insulating liquid and toner particles obtained by modifying the surface of toner base particles having a rosin resin with polyallylamine. .

  Application Example 2 In the liquid developer according to the application example described above, the polyallylamine has a weight average molecular weight of 500 to 100,000.

  Application Example 3 In the liquid developer according to the application example described above, the toner particles include a resin material having an ester bond in addition to the rosin resin.

  Application Example 4 In the liquid developer according to the application example described above, the softening point of the rosin resin is 80 to 190 ° C.

  Application Example 5 The liquid developer according to the application example, wherein the rosin resin has a weight average molecular weight of 500 to 100,000.

  Application Example 6 In the liquid developer according to the application example described above, the insulating liquid contains vegetable oil.

  According to the liquid developer described in the above application example, it is possible to provide a liquid developer having excellent positive charging characteristics and excellent long-term dispersion stability of toner particles.

  Application Example 7 An image forming apparatus according to this application example uses a plurality of liquid developers having different colors to form a plurality of developing units that form a single color image and a plurality of the developing units. A single color image is sequentially transferred, an intermediate transfer unit for forming an intermediate transfer image formed by superimposing the transferred single color images, and the intermediate transfer image is transferred to a recording medium and unfixed color on the recording medium. A surface of toner base particles having a secondary transfer portion for forming an image and a fixing portion for fixing the unfixed color image on the recording medium, wherein the liquid developer includes an insulating liquid and a rosin resin. Contains toner particles surface-modified with polyallylamine.

  According to the image forming apparatus described in the application example, by using this liquid developer, it is possible to provide an image forming apparatus that is excellent in positive charging characteristics and excellent in long-term dispersion stability of toner particles.

FIG. 3 is a schematic diagram illustrating an example of an image forming apparatus to which a liquid developer is applied. FIG. 2 is an enlarged view of a part of the image forming apparatus shown in FIG. 1. FIG. 3 is a conceptual diagram of toner base particles (surface modified particles) that have been surface modified.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

≪Liquid developer≫
First, the liquid developer will be described. The liquid developer of this embodiment contains an insulating liquid and toner particles obtained by modifying the surface of toner base particles made of a material containing a rosin resin with polyallylamine. Hereinafter, each component will be described in detail.

<Toner particles>
As shown in FIG. 3, the toner particles are obtained by modifying the surface of toner base particles made of a material containing a rosin resin with polyallylamine. FIG. 3 is a conceptual diagram of surface modified toner base particles (surface modified particles).

[Toner mother particles]
The toner base particles include at least a binder resin (resin material) and a colorant.
1. Resin material (binder resin)
The toner base particles are made of a material containing a resin material as a main component. In this embodiment, the toner base particles include a rosin resin as a resin material. The rosin resin is advantageous for improving the fixing property of the toner to the recording medium, and is a material that is easily and reliably modified (chemically modified) by polyallylamine. In other words, the rosin resin is a material having a large number of functional groups (acidic groups) that are highly reactive with polyallylamine described later. Therefore, once the rosin resin is modified with polyallylamine, the polyallylamine and the rosin resin are chemically bonded to each other. Less likely to occur. That is, in the liquid developer of this embodiment, polyallylamine is firmly bonded to the rosin resin constituting the toner base particles. Accordingly, the toner particles have excellent fixability of the toner particles, and the toner particles have excellent dispersibility, dispersion stability (long-term dispersion stability), and positive charging characteristics of the toner particles in the insulating liquid. can do.
The rosin-based resin may be present on at least a part of the surface of the toner base particles, may be included in the entire toner base particles, and is unevenly distributed on the surface of the toner base particles. It may also be present so as to cover the surface of the toner base particles.

  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 60 to 190 ° C, more preferably 65 to 170 ° C, and further preferably 70 to 160 ° C. When the softening point is less than 60 ° C., not only the high-temperature storage stability (for example, 55 ° C.) is deteriorated but also melts at the time of particle crushing. When the softening point is higher than 60 and lower than 70 ° C., the high-temperature storage stability (for example, 55 ° C.) may be deteriorated depending on the resin type of the base material and may be melted during particle crushing. Further, when the softening point is higher than 190 ° C., not only the fixing property to paper is deteriorated, but also particles that cannot be melted at the time of fixing are generated, and the paper surface quality such as image density and saturation is lowered. If the softening point is higher than 160 ° C and lower than 190 ° C, depending on the resin type of the base material, the fixability to paper will be deteriorated, and particles that cannot be melted at the time of fixing will be generated, so the paper quality such as image density and saturation will deteriorate. There is a case. Therefore, by setting the softening point of the rosin resin within the above range, the toner particles have excellent long-term dispersion stability and charging characteristics, and at the same time, the toner particle fixing characteristics and heat-resistant storage stability are compatible at a higher level. be able to.

  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. When the weight average molecular weight is less than 500, not only the high-temperature storage stability (for example, 55 ° C.) is deteriorated, but also melts at the time of particle crushing. If the weight average molecular weight is higher than 500 and lower than 1000, depending on the resin type of the base material, the high temperature storage stability (for example, 55 ° C.) may be deteriorated and melt at the time of particle crushing. Further, if the weight average molecular weight is greater than 100,000, not only the fixability to paper is deteriorated, but also particles that cannot be melted at the time of fixing are generated, and the paper surface quality such as image density and saturation is lowered. If the weight average molecular weight is greater than 50000 and less than 100000, depending on the type of resin of the base material, the fixability to paper is deteriorated, and particles that cannot be melted at the time of fixing are generated, so the paper surface quality such as image density and saturation decreases. There is a case. Therefore, by setting the weight average molecular weight of the rosin resin within the above-mentioned range, the toner particles have excellent long-term dispersion stability and charging characteristics, and at the same time, the toner particle fixing characteristics and heat-resistant storage stability are achieved at a higher level. can do.

  The acid value of the rosin resin is preferably 40 mgKOH / g or less, more preferably 30 mgKOH / g or less, and further preferably 5 to 25 mgKOH / g or less. As a result, the surface modification of the toner base particle surface with polyallylamine can be performed more suitably, and the toner particle fixing characteristics and heat-resistant storage stability can be improved while making the long-term dispersion stability and charging characteristics of the toner particles particularly excellent. Can be achieved at a higher level.

  Further, the content of the rosin resin in the resin material constituting the toner base particles is preferably 1 to 50 wt%, and more preferably 5 to 40 wt%. As a result, it is possible to achieve both the fixing characteristics of the toner particles and the heat-resistant storage stability at a higher level while making the long-term dispersion stability and charging characteristics of the toner particles particularly excellent.

  The toner base 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 can easily control the compatibility / incompatibility balance with the rosin resin, and the rosin resin can be surely present on the surface of the toner particles. As a result, the surface of the toner base particles can be modified with a larger amount of polyalkyleneimine, the positive charging characteristics of the toner particles can be improved, and the dispersion stability of the toner particles is higher. Can be. 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 is easy to control the compatibility / incompatibility balance with the rosin resin, and easily takes a phase separation structure or a gradient structure with the rosin resin in the toner particles. Thus, the rosin resin can be effectively present on the surface of the toner particles.

When the toner base particles contain a polyester resin, the acid value thereof is preferably 5 to 20 mgKOH / g, and more preferably 5 to 15 mgKOH / g. Thereby, the rosin resin having a higher acid value than the polyester resin can be more effectively arranged on the surface of the toner particles.
When the toner base particles contain a polyester resin, the softening point is not particularly limited, but is preferably 50 to 130 ° C, more preferably 50 to 120 ° C, and more preferably 60 to 115 ° C. Is more preferable. 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): temperature increase rate: 5 ° C./min, softening start temperature defined by a die hole diameter of 1.0 mm. Point to.

2. Colorant The toner base 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 base particles may contain components other than those described above. Examples of such components include known waxes and magnetic powders.
In addition to the materials described above, the toner base particle constituent material (component) includes, for example, zinc stearate, zinc oxide, cerium oxide, silica, titanium oxide, iron oxide, fatty acid, fatty acid metal salt, and the like. It may be used.

[Polyallylamine]
As described above, the surface of toner base particles composed of a material containing a rosin resin is surface-modified with polyallylamine. The surface modification by polyallylamine means that at least a part of amino groups of polyallylamine and at least a part of acidic groups (mainly carboxyl groups) derived from rosin resin on the surface of toner base particles are acid. A base reaction to form a covalent bond. Polyallylamine is a highly positively charged compound because it has many amino groups.
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.

  The rosin resin as described above is 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. 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.

  In view of the above problems, the present inventors have intensively studied. As a result, the surface of toner base particles composed of a material containing a rosin resin is surface-modified with polyallylamine, thereby positively charging the toner particles. It is possible to provide a liquid developer that has excellent charging characteristics and can stably disperse toner particles in an insulating liquid over a long period of time. That is, as apparent from the skeleton of polyallylamine, basic amine sites are adsorbed on the toner base particles, and the main skeleton of the hydrocarbon faces outward, so that charge injection is suppressed. As a result, it is possible to provide a liquid developer having excellent positive charging characteristics and excellent long-term dispersion stability of toner particles. In addition, since the liquid developer is excellent in charging characteristics and long-term dispersion stability, the liquid developer is also excellent in characteristics such as development efficiency and transfer efficiency.

That is, in this embodiment, the characteristics of the rosin resin are modified by modifying (chemically modifying) the surface of the toner base particles composed of a material containing the rosin resin using polyallylamine having a positive charging property. While sufficiently exhibiting the above, it is possible to reliably prevent the occurrence of the above-described problems, and to sufficiently improve the long-term dispersion stability of toner particles in the liquid developer and the positive charging characteristics. 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.
The excellent effects as described above can be obtained by modifying the surface of the toner base particles with polyallylamine, and cannot be obtained simply by including polyallylamine in the liquid developer. .

As specific examples of polyallylamine, allylamine may be polymerized by a known method in the presence of a polymerization initiator, optionally in the presence of a chain transfer catalyst, or a commercially available product may be used. Examples of commercially available products include Nittobo PAA-01, PAA-03, PAA-05, PAA-08, PAA-15, PAA-25, and PAA-H-10C.
As a result, the surface of the toner base particles can be more suitably modified, and the long-term dispersion stability and positive charging characteristics of the toner particles can be further improved.

  The weight average molecular weight of polyallylamine is preferably 500 to 100,000, more preferably 10,000 to 80,000. When the weight average molecular weight of polyallylamine is less than 500, the positive chargeability is weak and the desired developability cannot be obtained. If the weight average molecular weight is greater than 500 and less than 10,000, the positive chargeability may not be sufficient depending on the resin type of the substrate. If the weight average molecular weight is greater than 100,000, the fixability is deteriorated. If the weight average molecular weight is greater than 80000 and less than 100,000, the fixability may be deteriorated depending on the resin type of the substrate. Therefore, by setting the weight average molecular weight of the polyallylamine within the above range, the surface of the toner base particles can be more effectively modified (chemically modified), and also due to steric hindrance due to the relatively long molecular chain of the polyallylamine. In addition, aggregation of the toner particles can be effectively prevented, and the dispersion stability of the toner particles can be effectively improved.

[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 electric resistance at room temperature (20 ° C.) is preferably 1 × 10 9 Ωcm or more, and preferably 1 × 1011 Ωcm or more. 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 satisfying such conditions include Isopar E, Isopar G, Isopar H, Isopar L (Isopar; trade name of Exxon Chemical), Shellsol 70, Shellsol 71 (Shellsol; Shell Oil) Company name), Amsco OMS, Amsco 460 solvent (Amsco; product name of Spirits), mineral oil (hydrocarbon liquid) such as low viscosity / high viscosity liquid paraffin (Wako Pure Chemical Industries), fatty acid glyceride, fatty acid Fatty acid esters such as monoesters and 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 of these Or it may be used in combination of two or more. Among the above, vegetable oil and fatty acid monoesters, in particular, have a particularly high affinity (compatibility) with the rosin resin, so that 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 dispersibility of the toner particles can be made higher, and in the image forming apparatus as described later, the liquid developer can be supplied more uniformly to the application roller. It is possible to more effectively prevent the liquid developer from dripping. In addition, aggregation and sedimentation of the toner particles can be more effectively prevented, and the dispersibility of the toner particles in the insulating liquid can be made higher. On the other hand, if the viscosity of the insulating liquid is less than the lower limit, problems such as dripping of the liquid developer from the application roller or the like may occur in an image forming apparatus as described later. On the other hand, when the viscosity of the insulating liquid exceeds the upper limit, the dispersibility of the toner particles cannot be sufficiently increased, and the liquid developer cannot be more uniformly supplied to the application roller in an image forming apparatus as described later. There is a case. However, the viscosity in this specification refers to a value measured at 25 ° C. Note that the liquid developer of the present embodiment may include components (for example, external additives) other than the components described above.

≪Liquid developer manufacturing method≫
Next, a preferred method for producing the liquid developer of this embodiment will be described.
The method for producing a liquid developer of the present embodiment comprises a dispersion preparation step of preparing a dispersion in which toner base particles containing a rosin resin are dispersed in an aqueous dispersion medium, and polyallylamine is mixed with the dispersion. It has a chemical modification step for modifying the surface of the toner base particles with polyallylamine to obtain toner particles, and a dispersion step in the insulating liquid for dispersing the toner particles in the insulating 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 liquid (aqueous dispersion liquid) in which toner base particles containing a rosin resin are dispersed in an aqueous dispersion medium is prepared.
The aqueous dispersion may be prepared by any method, but a resin solution preparation step of preparing a resin solution in which a constituent material (base particle material) of toner base particles such as rosin resin is dissolved in an organic solvent And an O / W emulsion preparation step for preparing an O / W emulsion via a W / O emulsion by adding an aqueous liquid to the resin solution; and in the O / W emulsion Through the coalescence step of coalescing the contained dispersoids to obtain coalesced particles and the organic solvent removing step of removing the organic solvent contained in the coalesced particles to form the toner mother particles, It is preferably prepared as a suspension. As a result, the size and shape uniformity of the dispersoid contained in the aqueous dispersion can be made particularly high, and the particle size distribution of the toner particles contained in the finally obtained liquid developer can be very sharp. The variation in characteristics among toner particles can be made particularly small. In the following description, a case where an aqueous dispersion is prepared through a resin solution preparation step, an O / W emulsion preparation step, a coalescence step, and an organic solvent removal step will be representatively described.

(Resin solution preparation process)
First, a resin solution in which rosin resin or the like is dissolved in an organic solvent is prepared. The prepared resin solution contains the constituent material of the toner base 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 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. 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.
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 carried out 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 type. It is preferable to perform phase inversion to an 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), 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 Co., Ltd.), 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 stirring the O / W emulsion, for example, stirring blades such as an anchor blade, a turbine blade, a fiddler blade, a full zone blade, a max blend blade, and a half moon blade can 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. Thereby, a dispersion liquid (aqueous dispersion liquid) in which the toner base particles are dispersed in the aqueous dispersion medium 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 step (first washing step)]
Next, the toner base particles obtained as described above are washed. As a result, a dispersion liquid (aqueous dispersion liquid) containing the washed toner base particles can be obtained.
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.

  This step is performed, for example, by separating the toner base particles by solid-liquid separation (separation from the aqueous liquid), and then redispersing the solid content (toner base particles) in the aqueous liquid (aqueous dispersion medium). be able to. The solid-liquid separation and the redispersion of the solid in water may be repeated a plurality of times. The washing is preferably performed until the conductivity of the supernatant of the dispersion (slurry) obtained by redispersing the solid content (toner base particles) in the aqueous liquid (aqueous dispersion medium) is 20 μS / cm or less.

[Surface modification process]
Next, a dispersion liquid (aqueous dispersion liquid) containing toner mother particles as described above and polyallylamine are mixed, and the toner mother particles as described above are surface-modified with polyallylamine.
Although this process should just be performed by mixing an aqueous dispersion and polyallylamine, it is preferable to carry out in the state which adjusted the hydrogen ion index (pH) of the dispersion (aqueous dispersion) to 2-8. As a result, the reaction between the acidic groups present on the surface of the toner base particles composed of the material containing the rosin resin and the polyallylamine can be further prevented while reliably preventing the unintended alteration of the constituent material of the toner base particles. It is possible to proceed efficiently, and polyallylamine can be more firmly bound to the surface of the toner base particles. As a result, the long-term dispersion stability of toner particles and the stability of charging characteristics can be made particularly excellent. As described above, the hydrogen ion exponent (pH) of the dispersion liquid (aqueous dispersion liquid) in this step is preferably 2 to 8, more preferably 2.5 to 7.5, and more preferably 4 to 7 is more preferable. Thereby, the above effects are more remarkably exhibited.

The pH adjustment of the dispersion liquid described above can be performed by adding, for example, 1N hydrochloric acid or the like.
Moreover, after mixing the dispersion and polyallylamine, the mixture is preferably stirred for about 1 to 3 hours. Thereby, the toner base particle surface can be more uniformly modified (chemically modified).
Moreover, stirring may be performed under normal temperature and may be performed while heating a liquid mixture at about 30-40 degreeC. By performing the heating, the surface of the toner base particles can be modified (chemically modified) more efficiently.

  The amount of polyallylamine used in this step is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 6.0 parts by weight, based on 100 parts by weight of rosin resin. More preferably, it is 0.5 to 3.0 parts by weight. When the amount of polyallylamine is within the above range, in the finally obtained liquid developer, it is possible to reliably prevent inconveniences such as excessive polyallylamine leaching into the insulating liquid and Long-term dispersion stability and positive charging characteristics can be made particularly excellent.

[Washing step (second washing step)]
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. As a result, the amount of volatile organic compounds (TVOC) in the finally obtained toner particles can be made particularly small. In addition, the stability of the characteristics of the toner particles is improved.
As described above, polyallylamine is firmly bonded to toner base particles containing a rosin resin. For this reason, unlike a dispersant or the like used in a conventional liquid developer, it is reliably prevented from detaching / dropping off from the toner base particles even when a cleaning process is performed.

  In this step, for example, the toner particles are separated by solid-liquid separation (separation from the aqueous liquid), and then the re-dispersion and solid-liquid separation of the solid content (toner particles) in the aqueous liquid (aqueous dispersion medium) are performed. Separation of the toner particles from the aqueous liquid). 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. In this embodiment, since the toner particles have a structure in which the surface of the toner base particles composed of a material containing a rosin resin is modified (chemically modified) with polyallylamine, the drying step is performed. Even in this case, aggregation of the toner particles is reliably prevented.

[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 produced by the method described above, the toner particles contained in the liquid developer are obtained by modifying the surface of toner base particles composed of a material containing a rosin resin with polyallylamine. In addition, variations in shape and characteristics among toner particles are small.

≪Image forming device≫
Next, a preferred embodiment of the image forming apparatus according to the present invention will be described. The image forming apparatus according to the present embodiment forms a color image on a recording medium using the liquid developer described in the above embodiments.

FIG. 1 is a schematic view showing an embodiment of an image forming apparatus to which the liquid developer of the present invention is applied, and FIG. 2 is an enlarged view of a part of the image forming apparatus shown in FIG.
As shown in FIGS. 1 and 2, the image forming apparatus 1000 includes four developing units 30Y, 30M, 30C, and 30K, 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. It includes a body squeeze device 101Y, a primary transfer backup roller 51Y, a charge removal unit 16Y, a photoreceptor cleaning blade 17Y, and a developer recovery unit 18Y.

  The photoreceptor 10Y is formed on a cylindrical base material and an outer peripheral surface thereof, and has a photosensitive layer made of a material such as amorphous silicon, and is rotatable around a central axis. It rotates clockwise as shown 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. The exposure unit 12Y is mounted on a charged photoconductor 10Y based on an image signal input from a host computer (not shown) such as a personal computer or a word processor. Irradiate a modulated laser.

  The developing unit 100Y is an apparatus for developing the latent image formed on the photoreceptor 10Y using the liquid developer of the present embodiment. Details of the developing unit 100Y will be described later.

  The photoconductor squeeze device 101Y is disposed on the downstream side in the rotation direction from the developing unit 100Y so as to face the photoconductor 10Y. The photoconductor squeeze roller 13Y and the photoconductor squeeze roller 13Y are pressed and slidably attached to the surface. The cleaning blade 14Y removes the liquid developer and the developer collection unit 15Y that collects the removed liquid developer. The photoreceptor squeeze device 101Y has a function of collecting excess carrier (insulating liquid) and originally unnecessary fog toner from the developer used for developing the photoreceptor 10Y, and increasing the toner particle ratio 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 (monochromatic 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. After the intermediate transfer image (monochromatic image) is transferred onto the intermediate transfer unit 40 by the primary transfer backup roller 51Y, the photoconductor cleaning blade 17Y is exposed to light. The liquid developer remaining on the body 10Y is scraped off and removed.

  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 (intermediate transfer 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 surface of the non-smooth sheet material is copied. As a means for improving the secondary transfer characteristics, an elastic belt member is employed.
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 unit cleaning blade 46 scrapes and removes the liquid developer adhering to the intermediate transfer unit 40 after the intermediate transfer image is transferred onto the recording medium F5 by the secondary transfer unit (secondary transfer unit) 60. It has a function to do.

  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 across the intermediate transfer unit 40. The non-contact 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.

  Note that the non-contact type bias applying member 48 is not necessarily disposed at a position facing the tension roller 49, and the intermediate transfer unit 40 from the driven roller 44 such as a position between the driven roller 44 and the tension roller 49, for example. Can be disposed at an arbitrary position downstream of the driven roller 45 and upstream of the driven roller 45 in the moving direction of the intermediate transfer unit 40. The non-contact type bias applying member 48 may be a known non-contact type charger other than the corona charger.

  Further, as shown in FIG. 2, an intermediate transfer unit squeeze device 52Y is arranged downstream of the primary transfer backup roller 51Y in the moving direction of the intermediate transfer unit 40.

The intermediate transfer unit squeeze device 52Y is provided as a means for removing excess insulating liquid from the transferred liquid developer when the liquid developer transferred onto the intermediate transfer unit 40 has not reached the desired dispersion state. ing.
The intermediate transfer unit squeeze device 52Y is removed by the intermediate transfer unit squeeze roller 53Y, the intermediate transfer unit squeeze cleaning blade 55Y that presses and slides against the intermediate transfer unit squeeze roller 53Y, and the intermediate transfer unit squeeze cleaning blade 55Y. The developer collecting section 56Y collects the liquid developer.
The intermediate transfer unit squeeze device 52Y collects excess insulating liquid from the developer primarily transferred to the intermediate transfer unit 40, increases the toner particle ratio in the intermediate transfer image, and collects originally unnecessary fog toner. It has a function.

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 moving direction of the recording medium F5 (transfer material). Of these pair of secondary transfer rollers, the secondary transfer roller disposed on the upstream side in the moving direction of the intermediate transfer unit 40 is the upstream secondary transfer roller 64. The upstream secondary transfer roller 64 can be pressed against the belt drive roller 41 via the intermediate transfer unit 40.
Of the pair of secondary transfer rollers, the secondary transfer roller disposed downstream in the moving direction of the recording medium F <b> 5 (transfer material) is the downstream secondary transfer roller 65. The downstream secondary transfer roller 65 can be brought into pressure contact with the driven roller 44 via the intermediate transfer unit 40.
That is, the upstream side secondary transfer roller 64 and the downstream side secondary transfer roller 65 bring the recording medium F5 into contact with the intermediate transfer unit 40 that is hung on the belt driving roller 41 and the driven roller 44, respectively. The intermediate transfer image formed by superimposing colors on 40 is secondarily transferred to the recording medium F5.

In this case, the belt driving roller 41 and the driven roller 44 also function as backup rollers for the upstream side secondary transfer roller 64 and the downstream side secondary transfer roller 65, respectively. In other words, the belt drive roller 41 is also used as an upstream backup roller disposed in the secondary transfer unit 60 on the upstream side of the driven roller 44 in the moving direction of the recording medium F5. The driven roller 44 is also used as a downstream backup roller disposed in the secondary transfer unit 60 on the downstream side in the moving direction of the recording medium F5 from the belt driving roller 41.
Therefore, the recording medium F5 conveyed to the secondary transfer unit 60 is moved from the pressure contact start position (nip start position) between the upstream secondary transfer roller 64 and the belt drive roller 41 to the downstream secondary transfer roller 65 and the driven roller. The recording medium F5 (transfer material) is brought into close contact with the intermediate transfer unit 40 in a predetermined movement region 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 for a predetermined time, so that good secondary transfer is performed.

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

The toner image (transfer image) 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 (the developing units 100M, 100C, and 100K are not shown) 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 and a developer recovery unit 24Y.

  The liquid developer storage unit 31Y has a function of storing a liquid developer for developing the latent image formed on the photoreceptor 10Y. The supply unit 31aY supplies the liquid developer to the development unit, and the supply unit A recovery unit 31bY that recovers excess liquid developer generated at 31aY and the like, and a partition 31cY that partitions the supply unit 31aY and the recovery unit 31bY are provided.

  The supply unit 31aY has a function of supplying the liquid developer to the application roller 32Y, and has a concave portion in which the developer stirring roller 34Y is installed. Further, the liquid developer is supplied from the liquid developer mixing tank 93Y to the supply unit 31aY through the communication unit 35Y.

  The collection unit 31bY collects the liquid developer that is excessively supplied to the supply unit 31aY and excess liquid developer generated in the developer collection units 15Y and 24Y. The collected liquid developer is conveyed to a liquid developer mixing tank 93Y described later and reused. The recovery unit 31bY has a concave portion, and a recovery screw 36Y is installed near the bottom.

  A wall-shaped partition 31cY is provided at the boundary between the supply unit 31aY and the recovery unit 31bY. The partition 31cY partitions the supply unit 31aY and the recovery unit 31bY and can prevent the recovered liquid developer from being mixed into the fresh liquid developer. Further, when an excessive liquid developer is supplied to the supply unit 31aY, the excess liquid developer can overflow from the supply unit 31aY to the recovery unit 31bY beyond the partition 31cY. For this reason, the amount of the liquid developer in the supply unit 31aY can be kept constant, and the amount of the liquid developer supplied to the application roller 32Y can be kept constant. For this reason, the image quality of the finally formed image becomes stable.

  Further, the partition 31cY is provided with a notch, and the liquid developer can overflow from the supply part 31aY to the recovery part 31bY through the notch.

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

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

  The developer stirring roller 34Y has a function of stirring the liquid developer in a uniformly dispersed state. Thus, even when a plurality of toner particles are aggregated, the toner particles can be suitably dispersed. In particular, since the liquid developer of the present embodiment has excellent 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. In addition, by stirring with the developer stirring roller 34Y, the liquid developer can be stably overflowed to the collection unit 31bY side beyond the partition 31cY, and the liquid developer can be prevented from staying and being compressed. it can.

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

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

  The recovery screw 36Y provided in the vicinity of the bottom of the recovery unit 31bY is made of a cylindrical member, has a spiral rib on the outer periphery, and has a function of maintaining the fluidity of the recovered liquid developer. It has a function of promoting the conveyance of the developer to the liquid developer mixing tank 93Y.

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

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

  In the developing unit 100Y, the coating roller 32Y and the developing roller 20Y are separately driven by different power sources (not shown). And the quantity of the liquid developer supplied on the developing roller 20Y can be adjusted by changing the rotation speed (linear speed) ratio with the application roller 32Y and the developing roller 20Y.

  The developing unit 100Y includes a rubber developing roller cleaning blade 21Y that is in contact with the surface of the developing roller 20Y, and a developer recovery unit 24Y. The developing roller cleaning blade 21Y is a device for scraping off and removing the liquid developer remaining on the developing roller 20Y after development is performed at the developing position. The liquid developer removed by the developing roller cleaning blade 21Y is collected in the developer collecting unit 24Y.

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

  Each of the liquid developer tanks 91Y, 91M, 91C, and 91K stores a high concentration liquid developer corresponding to each color. Insulating liquid tanks 92Y, 92M, 92C, and 92K contain insulating liquids, respectively. Further, in each liquid developer mixing tank 93Y, 93M, 93C, 93K, a predetermined amount of each high-concentration liquid developer from each liquid developer tank 91Y, 91M, 91C, 91K, and each insulating liquid tank 92Y, A predetermined amount of each insulating liquid from 92M, 92C, and 92K is supplied. The liquid developer mixing tanks 93Y, 93M, 93C, and 93K are 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 (supply portions 31aM, 31aC, and 31aK are not shown), and 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, the toner particles are obtained by modifying the surface of toner base particles containing a rosin resin with polyallylamine as described above, and polyallylamine is firmly bonded to the surface of the toner base particles. . For this reason, even if the toner particles are subjected to stress accompanying recovery (for example, stress due to a cleaning blade), the polyallylamine is reliably prevented from being detached and dropped from the toner base particles. Such toner particles have high redispersibility in an insulating liquid. Therefore, the collected toner particles can be suitably reused for image formation.

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.

Next, examples will be described.
[1] Production of Liquid Developer A liquid developer was produced as follows. About the process in which temperature is not described, it performed at room temperature (25 degreeC).

Example 1
[Dispersion preparation step (aqueous dispersion preparation step)]
(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 solution preparation process)
The above colorant masterbatch: 95.7 parts by weight, methyl ethyl ketone: 231 parts by weight, polyester resin: 169.1 parts by weight, rosin-modified maleic resin (manufactured by Arakawa Chemical Industries, trade name “Marquide No. 1”, acid value : 25 mg KOH / g or less, softening point: 120-130 ° C., weight average molecular weight: 3100: 54.2 parts by weight of a high-speed disperser (manufactured by Primics, TK Robotics / TK Homo Disper 2.5 type 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 which the pigment was uniformly finely dispersed. It was.

(O / W emulsion preparation process)
Next, 73.9 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). While sufficiently stirring the blade tip speed of the blade to 7.5 m / s, adjusting the temperature of the solution in the flask to 25 ° C., and then stirring the blade tip speed of 14.7 m / s, 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 W / O emulsion was transferred to a stirring vessel having a Max blend blade, and the temperature of the W / O 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, 215 parts by weight of a 3.0% aqueous sodium sulfate solution was added dropwise to coalesce the dispersoids to form coalesced particles. After the dropping, stirring was continued until 50% volume particle diameter Dv (50) [μm] of the coalesced particles grew to 2.5 μm. When the Dv (50) of the coalesced particles became 2.3 μm, 200 parts by weight of deionized water was added to complete the coalescence.

(Organic solvent removal step)
Next, the W / O 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 toner mother particle slurry (dispersion).

[Washing step (first washing step)]
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 mother particles (toner mother particle cake) is obtained by suction filtration, and the wet cake is dispersed in water to obtain a dispersion (water-based dispersion) containing the washed toner mother particles. It was.

[Surface modification process]
Next, the hydrogen ion index (pH) was adjusted to 5.5 by adding 1N hydrochloric acid to the dispersion containing the washed toner base particles (aqueous dispersion).
Thereafter, polyallylamine (weight average molecular weight: 15000) was added dropwise to the dispersion (aqueous dispersion) whose hydrogen ion index (pH) was adjusted to 5.5 while stirring. At this time, polyallylamine was added so that it might become 1.5 weight part with respect to rosin-type resin: 100 weight part. Furthermore, after that, the mixture was sufficiently stirred so that the entire dispersion had a sufficiently uniform composition.

[Washing step (second washing step)]
Next, the dispersion liquid in which the toner particles are dispersed 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 of toner particles (toner particle cake) was obtained by suction filtration. The moisture content of the wet cake thus obtained was 35 wt%. When the liquid phase / filtrate separated by solid-liquid separation was examined, polyallylamine was not detected.

[Drying process]
Thereafter, the obtained wet cake was dried using a vacuum dryer to obtain toner particles in which the toner base particles were surface-modified (chemically modified) with polyallylamine.

[Dispersion process in insulating liquid]
Toner particles obtained by the above method: 50 parts by weight, rapeseed oil as an insulating liquid (Nisshin Oilio Co., Ltd., trade name “Hioleic rapeseed oil”): 120 parts by weight and soybean oil fatty acid methyl (Nisshin Oilio Co., Ltd.): 80 parts by weight are put in a ceramic pot (internal volume 600 ml), and zirconia balls (ball diameter: 1 mm) are put in a ceramic pot so that the volume filling rate is 85%, and a tabletop pot mill is rotated at 230 rpm for 24 hours. Dispersion was performed. As a result, a liquid developer was obtained.
The Dv (50) of the toner particles in the obtained liquid developer was 1.95 μm. The 50% volume particle diameter Dv (50) [μm] of the obtained toner particles was measured with Microtrac MT-3000 (manufactured by Nikkiso Co., Ltd.). Moreover, the particle diameter was similarly calculated | required about the particle | grains obtained by each Example and each comparative example demonstrated below.
Further, the viscosity of the obtained liquid developer at 25 ° C. was 48 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) to (Example 24)
Lists the type of rosin resin, the type and amount of polyallylamine, and the hydrogen ion index (pH) of the dispersion (aqueous dispersion) in which the hydrogen ion index (pH) is adjusted when it is used in the surface modification process. A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the changes were made as shown in FIG.

(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 and the amount of the polyester resin used was increased accordingly. When the liquid phase / filtrate separated by solid-liquid separation in the washing step (second washing step) was examined, it was confirmed that polyallylamine was contained.

(Comparative Example 2)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that Arachid 251 (manufactured by Arakawa Chemical Industries, Ltd.) as a dispersant was used instead of polyallylamine.

(Comparative Example 3)
Instead of omitting the surface modification step between the first washing step and the second washing step, polyallylamine is added to the insulating liquid in which the toner mother particles are dispersed after the dispersing step in the insulating liquid. A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the steps were added.

  For each of the above Examples and Comparative Examples, the resin material used for preparing the liquid developer, polyallylamine (for Comparative Example 2, a dispersant instead of polyallylamine), insulating liquid conditions, and viscosity of the liquid developer Table 1 shows the hydrogen ion index (adjusted pH of the dispersion) of the dispersion (aqueous dispersion) in which the hydrogen ion index (pH) was adjusted during the surface modification step. In the table, polyester resin (acid value: 10 mgKOH / g, glass transition point (Tg): 55 ° C., softening point: 107 ° C.) is PES, styrene-acrylate copolymer is ST-AC, and rosin. Modified polyester resin (Arakawa Chemical Industries, trade name “Traffs 4102”, acid value: 15 mg KOH / g, softening point: 98-104 ° C., weight average molecular weight: 1600) RPES and rosin modified phenolic resin (Arakawa Chemical) Made by Kogyo Co., Ltd., trade name “Tamanol 135”, acid value: 18 mgKOH / g or less, softening point: 130-140, weight average molecular weight: 15000) RPH and 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) Allylamine and PAA, the Arakyd 251 shown with the DA. For Comparative Example 2, the conditions for the dispersant are shown in the polyallylamine column.

[2] Evaluation Each liquid developer obtained as described above was evaluated as follows.

[2.1] Development 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 examples 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 300 V, the surface potential of the photoconductor was uniformly charged at 500 V, the photoconductor was exposed, the charge on the surface of the photoconductor was attenuated, and the surface potential was set to 50 V. The toner particles on the developing roller and the toner particles on the photoconductor after the liquid developer layer passed between the photoconductor 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 photoconductor by the sum of the concentration of toner particles collected on the photoconductor and the concentration of toner particles collected on the developing roller is multiplied by 100. Was determined as development efficiency, and evaluated according to the following four-stage criteria.
A: The development efficiency is 96% or more, and the development efficiency is particularly excellent.
B: The development efficiency is 90% or more and less than 96%, and the development efficiency is excellent.
C: 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 toner particles collected on the intermediate transfer portion by the sum of the concentration of toner particles collected on the photoreceptor and the concentration of toner particles collected on the intermediate transfer portion is 100. A value obtained by multiplying by is obtained as transfer efficiency, and evaluated according to the following four criteria.
A: The transfer efficiency is 96% or more, and the transfer efficiency is particularly excellent.
B: The transfer efficiency is 90% or more and less than 96%, and the transfer efficiency is excellent.
C: The transfer efficiency is 80% or more and less than 90%, and there is no practical problem.
D: Transfer efficiency is less than 80% and inferior to transfer efficiency.

[2.3] Fixing Strength Using an image forming apparatus as shown in FIGS. 1 and 2, an image of a predetermined pattern with a liquid developer obtained in each of the examples and the comparative examples is recorded on a recording paper (Seiko Epson). It was formed on a high-quality paper LPCPPA4) manufactured by the company. Thereafter, the fixing temperature was set to 100 ° C., and thermal fixing was performed.
Then, after confirming the non-offset area, the fixed image on the recording paper is erased twice (rubber eraser “LION 261-11” manufactured by Lion Business Machine Co., Ltd.) twice with a pressing load of 1.2 kgf, and the remaining ratio of image density Was measured by “X-Rite model 404” manufactured by X-Rite Inc, and evaluated according to the following five-step criteria.
A: Image density residual ratio is 96% or more (very good).
B: Image density residual ratio is 90% or more and less than 96% (good).
C: Image density remaining rate is 80% or more and less than 90% (normal).
D: Image density residual ratio is 70% or more and less than 80% (slightly bad).
E: Image density residual ratio is less than 70% (very bad).

[2.4] 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).

[2.5] Dispersion stability test [2.5.1] 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.

[2.5.2] 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 rω2 (rω2 = 1118 × rotation radius (cm) × number of rotations 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, Plotting was 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] Recyclability Using the liquid developers obtained in each of the examples and comparative examples, 10,000 images of a predetermined pattern were recorded by the image forming apparatuses as shown in FIGS. It was formed on paper (manufactured by Seiko Epson Corporation, fine 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, the liquid developer (recycled) regenerated by diluting the toner particles collected in the stirrer 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.

[2.6.1] 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.

[2.6.2] 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 rω2 (rω2 = 1118 × rotation radius (cm) × number of revolutions per minute (rpm) 2 × 10 −8 × g (gravity acceleration)) is taken on the horizontal axis, and the subsidence depth is taken on the vertical axis. Plotting was 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 2.

As is apparent from Table 2, the liquid developer of this embodiment was excellent in charging characteristics (positive charging characteristics) and long-term dispersion stability of toner particles. Further, the liquid developer of this embodiment was excellent in recyclability. Further, the liquid developer of this embodiment was 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.
In addition, recording paper (manufactured by Seiko Epson Corporation) is supplied by the image forming apparatus as shown in FIGS. 1 and 2 so that the liquid developer is supplied from the liquid developer mixing tank of each color to the supply unit of each corresponding color. As a result of continuous image formation of 50000 sheets on high-quality paper LPCPPA4), in this embodiment, an image with excellent image quality could be formed even on the 50000th sheet, whereas no deterioration in image quality was observed. In the comparative example, a clear decrease in image quality was observed.

  1000: Image forming apparatus, 10Y, 10M, 10C, 10K ... Photoconductor, 11Y ... Charging roller, 12Y ... Exposure unit, 13Y ... Photoconductor squeeze roller, 14M, 14Y ... Cleaning blade, 15M, 15Y ... Developer recovery unit, 16Y ... Static elimination unit, 17Y ... Photoconductor cleaning blade, 18Y ... Developer recovery unit, 20Y, 20M, 20C, 20K ... Development roller, 21Y ... Development roller cleaning blade, 24Y ... Developer recovery unit, 30Y, 30M, 30C, 30K ... developing section, 31Y ... liquid developer storage section, 31aY ... supply section, 31bY ... collection section, 31cY ... partition, 32Y ... application roller, 33Y ... regulator blade, 34Y ... developer stirring roller, 35Y ... communication section, 36Y ... Recovery screw, 40 ... Intermediate transfer section, 41 ... Belt drive roller 49 ... tension roller, 44, 45 ... driven roller, 46 ... intermediate transfer section cleaning blade, 47 ... developer recovery section, 48 ... non-contact 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, 9 K ... insulating liquid tank, 93Y, 93M, 93C, 93K ... liquid developer mixing tank, 100Y ... developing unit, 101Y ... photoreceptor squeeze device, F 40 ... fixing portion (fixing device), F5 ... recording medium.

Claims (7)

An insulating liquid;
A liquid developer comprising: toner particles whose surface is modified with polyallylamine on the surface of toner base particles having a rosin resin.   The liquid developer according to claim 1, wherein the polyallylamine has a weight average molecular weight of 500 to 100,000.   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.   4. The liquid developer according to claim 1, wherein the rosin resin has a softening point of 80 to 190 ° C. 5.   5. 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 contains vegetable oil. Using a plurality of liquid developers having different colors, a plurality of developing units that form a single color image;
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,
An image forming apparatus, wherein the liquid developer contains toner particles whose surface is modified with polyallylamine on the surface of toner base particles having an insulating liquid and a rosin resin.

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