JP2009217050A - Liquid developer and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developer which superior in the charging characteristics in negative charges, and to provide an image forming apparatus which uses the developer. <P>SOLUTION: The liquid developer comprises an insulating liquid, toner particles, mainly comprising a resin material, and a dispersant having an acid number, and has a hydrogen ion exponent pH of 7 to 11 in the liquid developer at 24°C. The acid number of the dispersant is, preferably, in a range of 10 to 15 mKOH/g. The liquid developer, preferably, contains a pH adjuster. The resin material, preferably, contains polyester resin. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

As a developer used to develop the electrostatic latent image formed on the latent image carrier, a toner composed of a material containing a colorant such as a pigment and a resin material is used as an electrically insulating carrier liquid (insulating liquid). A liquid developer dispersed in (1) is known.
When the liquid developer is used, the toner particles are effectively prevented from aggregating in the liquid developer, so that it is possible to use fine toner particles, and the resin material has a low softening point (low softening point). ) Can be used. As a result, in the method using a liquid developer, fine line image reproducibility is good, gradation reproducibility is good, color reproducibility is excellent, and it is also excellent as a high-speed image forming method. It has characteristics.

In general, such a liquid developer develops an electrostatic latent image on a latent image carrier by negatively charging toner particles.
Conventionally, an attempt has been made to add a negatively chargeable charge control agent for the purpose of improving the charging characteristics of the liquid developer (see, for example, Patent Document 1).
However, in recent years, with higher image quality of formed images, liquid developers have been required to have better charging characteristics. Conventional liquid developers sufficiently satisfy the required charging characteristics. It was not a thing.

JP 11-109680 A

  An object of the present invention is to provide a liquid developer excellent in negative charge characteristics and to provide an image forming apparatus using the liquid developer.

Such an object is achieved by the present invention described below.
The liquid developer of the present invention includes an insulating liquid,
Toner particles mainly composed of a resin material;
A dispersant having an acid value,
The liquid developer at 24 ° C. has a hydrogen ion exponent pH of 7 to 11.
In the liquid developer of the present invention, the acid value of the dispersant is preferably 10 to 15 mgKOH / g.

The liquid developer of the present invention preferably contains a pH adjuster.
In the liquid developer according to the aspect of the invention, it is preferable that the resin material includes a polyester resin.
In the liquid developer of the present invention, the acid value of the polyester resin is preferably 5 to 15 mgKOH / g.
In the liquid developer of the present invention, the resin material preferably contains a rosin-modified resin.

In the liquid developer of the present invention, the acid value of the rosin-modified resin is preferably 10 to 40 mgKOH / g.
In the liquid developer according to the aspect of the invention, it is preferable that the insulating liquid contains a vegetable oil.
In the liquid developer of the present invention, it is preferable that the insulating liquid contains a fatty acid monoester.

The image forming apparatus of the present invention includes a plurality of developing units that form a single color image corresponding to the plurality of liquid developers by using a plurality of liquid developers having different colors.
An intermediate transfer unit that sequentially transfers a plurality of the single-color images formed by the plurality of developing units, and forms an intermediate transfer image formed by superimposing the transferred single-color images;
A secondary transfer unit that transfers the intermediate transfer image to a recording medium and forms an unfixed color image on the recording medium;
A fixing unit for fixing the unfixed color image on the recording medium,
The liquid developer is an insulating liquid;
Toner particles mainly composed of a resin material;
A dispersant having an acid value,
The liquid developer at 24 ° C. has a hydrogen ion exponent pH of 7 to 11.

In the image forming apparatus of the present invention, the developing unit includes a supply unit that supplies the liquid developer for forming the monochrome image, and a recovery unit that recovers excess liquid developer in the supply unit, A partition provided between the recovery unit and the supply unit;
It is preferable that the excess liquid developer in the supply unit is recovered by the recovery unit through the partition.
By satisfying the above configuration, a liquid developer having excellent negative charge characteristics can be provided. In addition, an image forming apparatus using such a liquid developer can be provided.

Hereinafter, preferred embodiments of the present invention will be described in detail.
≪Liquid developer≫
First, the liquid developer of the present invention will be described.
The liquid developer of the present invention is one in which toner particles are dispersed in an insulating liquid and contains a dispersant having an acid value. The liquid developer of the present invention has a hydrogen ion exponent pH (hereinafter simply referred to as pH) of 7 to 11.
By adopting such a configuration, the liquid developer of the present invention has excellent negative charge characteristics. This is considered to be due to the following reasons.

There are usually acidic groups (carboxyl groups and the like) derived from the resin material on the surface of the toner particles. When the pH of the liquid developer is 7 to 11, that is, the liquid property is biased from neutral to alkaline, the acidic groups on the surface of the toner particles are activated and protons (H ⁺ ) are released. As a result, an anionic group is present on the surface of the toner particles, and the toner particles are negatively charged. Usually, the dispersant is present near the surface of the toner particles. In the present invention, since the dispersant has an acid value, it has an acidic group in the same manner as the resin material. And the dispersing agent which has an acid value also activates an acidic group like the above, and discharge | releases a proton. As a result, the toner particles have a large negative charge amount, and the liquid developer has excellent negative charge characteristics. For this reason, the liquid developer has excellent development efficiency and transfer efficiency.

On the other hand, if the pH of the liquid developer is less than the lower limit value, the acidic groups of the resin material and the dispersant are not activated and it becomes difficult to be negatively charged. On the other hand, when the pH of the liquid developer exceeds the upper limit, the stability of the liquid developer itself is lowered.
In addition, when a dispersant having an acid value is not included, a sufficient charge amount cannot be obtained only with an acidic group derived from the resin material on the surface of the toner particles.
The pH of the liquid developer of the present invention is from 7 to 11, more preferably from 8 to 10, and even more preferably from 8.8 to 9.4. As a result, the acidic groups of the resin material and the dispersant can be activated more effectively, and the negative charging characteristics of the liquid developer can be made particularly excellent.
Hereinafter, each component of the liquid developer will be described in detail.

<Dispersant>
The dispersant is usually present near the surface of the toner particles and is a component that contributes to the dispersion stability of the toner particles.
The dispersant used in the present invention has an acid value. Since the dispersing agent having an acid value has an acidic group in the molecule as described above, it releases protons and is negatively charged in the above pH range. As a result, the negative charging characteristics of the liquid developer can be improved.

  Examples of the dispersant having an acid value include Arachid 251, Arachid 310, Arachid 5001, Arachid 6300 (“Arachid” is a trade name of Arakawa Chemical Industries, Ltd.), Disperbyk-101, Disperbyk-102, Disperbyk-106 (“ Disperbyk ”is a trade name of Big Chemie Co., Ltd.), EFKA-5044, EFKA-5244 (“ EFKA ”is a trade name of Ciba Specialty Chemicals Co., Ltd.), etc. They can be used in combination.

  Although the acid value of the dispersing agent used by this invention is not specifically limited, It is preferable that it is 10 mgKOH / g or more, and it is more preferable that it is 10-15 mgKOH / g. Thereby, it is possible to more effectively improve the negative charging characteristics of the liquid developer. On the other hand, if the acid value of the dispersant is too small, it may be difficult to sufficiently improve the negative charging characteristics of the liquid developer. On the other hand, if the acid value of the dispersant is too large, the insulating property of the insulating liquid may be lowered due to the effect of the liberated dispersant, and sufficient negative charging characteristics may not be exhibited.

In the present invention, such a dispersant is preferably attached or adsorbed to the surface of the toner particles as long as it is present near the surface of the toner particles. Thereby, the effect of this invention can be made more remarkable.
The content of such a dispersant in the liquid developer is preferably 0.2 to 10 parts by weight, more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of the toner particles. 1 to 6 parts by weight is more preferable. This makes it possible to more effectively improve the negative charging characteristics of the liquid developer while further improving the dispersion stability of the toner particles.

<Toner particles>
Next, toner particles will be described.
[Component material of toner particles]
The toner particles are mainly composed of a resin material.
1. Resin material (binder resin)
In the present invention, the resin material is not particularly limited, and for example, a known resin can be used.

  In particular, it is preferable to use a resin material containing a polyester resin. Since the polyester resin has a relatively large number of carboxyl groups, which are acidic groups, many acidic groups can be present on the toner particle surface. As a result, in the pH range, a large amount of anionic groups can be present on the surface of the toner particles, and the toner particles can be more effectively negatively charged. The polyester resin has high transparency, and when used as a binder resin, it has characteristics that the resulting image has good color developability and that high fixing characteristics can be obtained.

  The acid value of the polyester resin used in the present invention is preferably 5 to 15 mgKOH / g, and more preferably 5 to 10 mgKOH / g. As a result, an appropriate number of acidic groups can be present on the surface of the toner particles, and the negative charging characteristics of the liquid developer can be further improved. On the other hand, if the acid value of the polyester resin is less than the lower limit, the dispersibility of the toner particles may be lowered depending on the type of the dispersant. On the other hand, if the acid value of the polyester resin exceeds the upper limit, the resin itself may be less stable, the charging stability may be decreased, and the durability of the toner particles may be decreased. is there.

Note that the content of the polyester resin in the resin material is preferably 50 wt% or more, and more preferably 80 wt% or more.
In addition, it is preferable to use a resin material containing a rosin-modified resin.
The rosin-modified resin is a component that is plasticized by an insulating liquid as described later. Therefore, toner particles containing rosin-modified resin as a constituent component can firmly adhere (adsorb) the dispersant to the surface. As a result, the dispersion stability of the toner particles can be made particularly excellent, and the negative charging characteristics of the liquid developer can be made particularly excellent.

In addition, since the rosin-modified resin has a relatively large number of acidic groups, the negative charging characteristics of the liquid developer can be further improved.
Further, when the resin material contains a polyester resin, the rosin-modified resin tends to have low compatibility with the above-described polyester resin. Therefore, by using the polyester resin and the rosin-modified resin in combination, the rosin-modified resin is used as a toner. It can be unevenly distributed on the particle surface. By unevenly distributing in this way, the dispersant can be surely present on the surface of the toner particles, and the negatively charged characteristics can be made particularly excellent.
Examples of such rosin-modified resins include rosin-modified phenol resins, rosin-modified maleic resins, rosin-modified polyester resins, fumaric acid-modified rosin resins, ester gums, and the like, and one or more of these are combined. Can be used.

The softening point of the rosin-modified resin as described above is preferably 80 to 190 ° C, more preferably 80 to 160 ° C, and still more preferably 80 to 130 ° C. As a result, it is possible to make the toner particles have excellent charging characteristics and dispersibility, and at the same time, the fixing characteristics and heat-resistant storage stability of the toner particles can be achieved at higher levels.
The weight average molecular weight of the rosin resin is preferably 500 to 100,000, more preferably 1000 to 80000, and further preferably 1000 to 50000. As a result, it is possible to achieve a higher level of toner particle fixing characteristics and heat-resistant storage stability while improving the long-term dispersion stability and charging characteristics of the toner particles.

The acid value of the rosin resin is preferably 10 to 40 mgKOH / g, more preferably 10 to 30 mgKOH / g, and still more preferably 10 to 25 mgKOH / g. This makes it possible to more effectively improve the negative charging characteristics of the liquid developer while maintaining the durability of the toner particles.
The content of the rosin resin in the resin material constituting the toner particles is preferably 1 to 50 wt%, and more preferably 5 to 40 wt%. As a result, the rosin resin can be more reliably present on the surface of the toner particles, and the dispersant can be adhered (adsorbed) more firmly on the surface of the toner particles.

  The glass transition point Tg of the resin material as described above is preferably 15 to 70 ° C., more preferably 20 to 55 ° C. As a result, the liquid developer containing toner particles to be produced is more reliably prevented from agglomerating and fusing between the toner particles during storage, and the storage stability of the liquid developer is further improved. Further, the toner particles can be more suitably fixed on the recording medium at a low temperature. In this specification, the glass transition point Tg is a measurement condition in a differential scanning calorimeter DSC-220C (manufactured by SII): a sample amount of 10 mg, a heating rate of 10 ° C./min, and a measuring temperature range of 10 to 150 ° C. When measured, it refers to the temperature at the intersection of an extension of the baseline below the glass transition point and a tangent that indicates the maximum slope from the peak rise to the peak apex.

  The softening point (T1 / 2) of the resin material is not particularly limited, but is preferably 50 to 130 ° C, more preferably 50 to 120 ° C, and further preferably 60 to 115 ° C. In the present specification, the softening point is a measurement condition in a Koka type flow tester (manufactured by Shimadzu Corporation): a temperature increase rate: 5 ° C./min, and a softening start temperature defined by a die hole diameter of 1.0 mm. Point to.

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

[Toner particle shape]
The average particle size of the toner particles in the present invention composed of the above materials is preferably 0.7 to 3 μm, more preferably 0.8 to 2.5 μm, and 0.8 to More preferably, it is 2.0 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 10 ¹¹ Ωcm or more, and preferably 10 ¹² Ωcm or more. More preferably, it is more preferably 10 ¹³ Ωcm or more.
The dielectric constant of the insulating liquid is preferably 3.5 or less.

  Examples of the insulating liquid that satisfies such conditions include Isopar E, Isopar G, Isopar H, Isopar L (Isopar; trade name of Exxon Chemical), Cielsol 70, Cielsol 71 (Cielsol; Commodity of Ciel Oil) Name), Amsco OMS, Amsco 460 solvent (Amsco; trade name of Spirits), mineral oil (hydrocarbon liquid) such as low viscosity / high viscosity liquid paraffin (Wako Pure Chemical Industries), fatty acid glyceride, medium chain fatty acid ester Etc. vegetable oils, fatty acid monoesters that are esters between fatty acids and monohydric alcohols, octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, benzene, toluene, xylene , Mesitylene, etc. , It can be used singly or in combination of two or more of them. Among the above-mentioned, in particular, vegetable oil has particularly high affinity (compatibility) with a resin material (particularly a polyester resin), so that the dispersion stability of toner particles can be improved. As a result, variation in charging characteristics among toner particles can be prevented. Vegetable oil is an environmentally friendly component. Therefore, it is possible to reduce the load on the environment of the insulating liquid due to leakage of the insulating liquid to the outside of the image forming apparatus and disposal of the used liquid developer. As a result, an environmentally friendly liquid developer can be provided.

  Moreover, among the above-mentioned, it is preferable to use what contains a fatty acid monoester as an insulating liquid. The fatty acid monoester is a component having an effect of plasticizing the toner particles at the time of fixing (plastic effect). The plasticized toner particles can be easily adhered to a recording medium, and the toner particles can have a higher fixability. Further, by plasticizing in this way, the dispersant as described above can be firmly attached (adsorbed) to the surface, and the negative charging characteristics of the toner particles can be further improved.

  Examples of such fatty acid monoesters include oleic acid, palmitoleic acid, linoleic acid, α-linolenic acid, γ-linolenic acid, arachidonic acid, docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and the like. Unsaturated fatty acid alkyl (methyl, ethyl, propyl, butyl, etc.) monoester, butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, etc. And alkyl (methyl, ethyl, propyl, butyl, etc.) monoesters of saturated fatty acids, and the like, and one or more selected from these can be used in combination.

  When the fatty acid monoester is contained in the insulating liquid, the content of the fatty acid monoester in the insulating liquid is preferably 1 to 50 wt%, and more preferably 5 to 45 wt%. Thus, the toner particles can be suitably plasticized, and the dispersant can be more reliably adhered (adsorbed) to the surface of the toner particles. As a result, the dispersion stability of the toner particles can be further improved, and the negative charging characteristics can be made particularly excellent.

  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, in an image forming apparatus as will be described later, the liquid developer can be supplied more uniformly to the application roller, and the liquid developer dripping from the application roller or the like can be more effectively prevented. it can. In addition, aggregation and sedimentation of the toner particles can be more effectively prevented, and the dispersibility of the toner particles in the insulating liquid can be made higher. On the other hand, when the viscosity of the insulating liquid is less than the lower limit value, there is a possibility that problems such as dripping of the liquid developer from the application roller or the like may occur in the image forming apparatus described later. On the other hand, if the viscosity of the insulating liquid exceeds the upper limit, the dispersibility of the toner particles cannot be sufficiently increased, and the liquid developer cannot be more uniformly supplied to the application roller in an image forming apparatus as described later. There is a case. However, the viscosity in this specification refers to a value measured at 25 ° C.

<Other ingredients>
The liquid developer may contain a pH adjuster in addition to the above components.
pH adjusters include organic bases such as ethanolamine and other amines such as monoethanolamine, diethanolamine, and triethanolamine, sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium carbonate, calcium lactate, and succinate. Examples include inorganic bases such as disodium acid, sodium malate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, and trisodium phosphate, and one or more of these can be used in combination.

Although the content of the pH adjusting agent in the liquid developer varies depending on the pH value to be prepared, it is preferably 2 parts by weight or less, preferably 1 part by weight or less with respect to 100 parts by weight of the insulating liquid. More preferred. When the addition amount of the pH adjusting agent is within the above range, the pH of the liquid developer can be more preferably within the above range while maintaining the storage stability of the liquid developer. As a result, the negative charging characteristics of the liquid developer 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.

≪Liquid developer manufacturing method≫
Next, a preferred embodiment of the liquid developer manufacturing method as described above will be described.
The liquid developer manufacturing method according to the present embodiment includes a dispersion preparation step of preparing a dispersion in which a resin material and a colorant as described above are dispersed in an aqueous dispersion medium, and a plurality of dispersoids. A coalescence step for obtaining one particle, a desolvation step for removing the organic solvent contained in the coalesced particle to obtain toner particles containing a resin material and a colorant, a dispersant and, if necessary, a pH adjuster added A dispersion step of 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 (aqueous dispersion) is prepared.
The aqueous dispersion may be prepared by any method. For example, a resin material, a constituent material of toner particles such as a colorant (toner material) is dissolved and dispersed in an organic solvent, and the resin liquid is obtained. Obtained (resin liquid preparation treatment), by adding an aqueous dispersion medium composed of an aqueous liquid to the resin liquid, a dispersoid containing the toner material (liquid dispersoid) is formed in the aqueous liquid, and the dispersoid is dispersed. The obtained dispersion liquid (aqueous dispersion liquid) is obtained (dispersoid formation treatment).

(Resin liquid preparation process)
First, a resin liquid in which a toner material is dissolved or dispersed in an organic solvent is prepared.
The prepared resin liquid contains the constituent material of the toner particles as described above and the organic solvent as described below.
The organic solvent may be any as long as it dissolves at least a part of the resin material, but it is preferable to use an organic solvent having a boiling point lower than that of the aqueous liquid described later. Thereby, the organic solvent can be easily removed.

The organic solvent is preferably one having low compatibility with an aqueous dispersion medium (aqueous liquid) described later (for example, one having a solubility in 100 g of the aqueous dispersion medium at 25 ° C. of 30 g or less). Thereby, the toner material can be finely dispersed in a stable state in the aqueous emulsion.
Further, the composition of the organic solvent can be appropriately selected according to, for example, the resin material, the composition of the colorant, the composition of the aqueous dispersion medium, and the like as described above.
Such an organic solvent is not particularly limited, and examples thereof include ketone solvents such as MEK and aromatic hydrocarbon solvents such as toluene.

The resin liquid can be obtained, for example, by mixing a resin material, a colorant, an organic solvent, etc. with a stirrer or the like. Examples of the stirrer that can be used for preparing the resin liquid include DESPA (manufactured by Asada Tekko Co., Ltd.), T.C. K. Robotics / T. K. Examples thereof include a high-speed stirrer such as a homodisper 2.5-type blade (manufactured by Primex).
Moreover, it is preferable that the material temperature at the time of stirring is 20-60 degreeC, and it is more preferable that it is 30-50 degreeC.

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

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

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

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

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

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

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

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

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

[Joint process]
Next, a plurality of dispersoids are coalesced to obtain coalesced particles (a coalescence step). The coalescence of dispersoids usually proceeds as a result of collision of dispersoids containing an organic solvent so that they are integrated.
The coalescence of a plurality of dispersoids is performed by adding an electrolyte to the dispersion while stirring the dispersion. Thereby, coalesced particles can be obtained easily and reliably. Moreover, the particle diameter and particle size distribution of the coalesced particles can be controlled easily and reliably by adjusting the amount of electrolyte added.

It does not specifically limit as electrolyte, Well-known organic and inorganic water-soluble salt etc. can be used 1 type or in combination of 2 or more types.
The electrolyte is preferably a monovalent cation salt. Thereby, the particle size distribution of the obtained coalesced particles can be narrowed. In addition, by using a monovalent cation salt, it is possible to reliably prevent generation of coarse particles in this step.

Moreover, among the above-mentioned, it is preferable that electrolyte is a sulfate (for example, sodium sulfate, ammonium sulfate) or carbonate, and it is especially preferable that it is a sulfate. Thereby, the particle diameter of the coalesced particles can be controlled particularly easily.
The amount of the electrolyte added in this step is preferably 0.5 to 3 parts by weight, preferably 1 to 2 parts by weight, based on 100 parts by weight of the solid content in the dispersion to which the electrolyte is added. Is more preferable. As a result, the particle diameter of the coalesced particles can be controlled particularly easily and reliably, and the generation of coarse particles can be reliably prevented.

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

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

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

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

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

[Desolvation (desolvation) step]
Thereafter, the organic solvent contained in the dispersion is removed. Thereby, resin fine particles (toner particles) dispersed in the dispersion are obtained.
The removal of the organic solvent may be performed by any method, but can be performed, for example, under reduced pressure. Thereby, the organic solvent can be efficiently removed while sufficiently preventing the modification of the constituent material such as the resin material.
Moreover, it is preferable that the process temperature in this process is temperature lower than the glass transition point (Tg) of the resin material which comprises coalesced particle.

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

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

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

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

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

Further, at the time of dispersion, components other than the insulating liquid, toner particles, the dispersant and the pH adjuster may be mixed.
Further, the pH adjusting agent may not be added to the insulating liquid in advance, and may be added after the toner particles are dispersed.
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 the 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 as described above, the toner particles contained therein are those in which the constituent materials are uniformly dispersed, and the variation in shape among the toner particles is small. Thereby, variation in charging characteristics among toner particles can be reduced. Further, the surface area of the particle surface is relatively uniform among the particles, and the dispersant can be evenly adhered or adsorbed on the surface of the toner particles. As a result, it is possible to improve the long-term dispersion stability of the toner particles and to further reduce the variation in charging characteristics among the toner particles.

≪Image forming device≫
Next, a preferred embodiment of the image forming apparatus of the present invention will be described. The image forming apparatus of the present invention forms a color image on a recording medium using the liquid developer of the present invention as described above.
FIG. 1 is a schematic view showing an example of an image forming apparatus to which the liquid developer of the present invention is applied, and FIG. 2 is an enlarged view of a part of the image forming apparatus shown in FIG.

As shown in FIGS. 1 and 2, the image forming apparatus 1000 includes four developing units 30Y, 30M, 30C, and 30K, an intermediate transfer unit 40, a secondary transfer unit (secondary transfer unit) 60, and a fixing unit. (Fixing device) F40 and four liquid developer supply portions 90Y, 90M, 90C, and 90K are provided.
The developing units 30Y, 30M, and 30C develop a latent image with a yellow liquid developer (Y), a magenta liquid developer (M), and a cyan liquid developer (C), respectively, and correspond to each color. It has a function of forming a single color image. The developing unit 30K has a function of developing a latent image with a black liquid developer (K) to form a black single color image.

Since the developing units 30Y, 30M, 30C, and 30K have the same configuration, the developing unit 30Y will be described below.
As shown in FIG. 2, the developing unit 30Y includes a photoconductor 10Y as an example of an image carrier, a charging roller 11Y, an exposure unit 12Y, a development unit 100Y, and a photoconductor along the rotation direction of the photoconductor 10Y. The image forming apparatus includes a body squeeze device 101Y, a primary transfer backup roller 51Y, a charge removal unit 16Y, a photoreceptor cleaning blade 17Y, and a developer recovery unit 18Y.

The photoreceptor 10Y is formed on a cylindrical base material and an outer peripheral surface thereof, has a photosensitive layer made of a material such as amorphous silicon, and is rotatable about a central axis. Rotate clockwise as indicated by the arrow in FIG.
The photoreceptor 10Y is supplied with a liquid developer by a developing unit 100Y described later, and a layer of the liquid developer is formed on the surface.
The charging roller 11Y is a device for charging the photoconductor 10Y, and the exposure unit 12Y is a device for forming a latent image on the photoconductor 10Y charged by irradiating a laser. The exposure unit 12Y includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and charges a modulated laser based on an image signal input from a host computer (not shown) such as a personal computer or a word processor. Irradiate onto the photoconductor 10Y.

The developing unit 100Y is a device for developing the latent image formed on the photoreceptor 10Y using the liquid developer of the present invention. Details of the developing unit 100Y will be described later.
The photoconductor squeeze device 101Y is disposed on the downstream side of the developing unit 100Y in the rotation direction so as to face the photoconductor 10Y. The photoconductor squeeze roller 13Y and the photoconductor squeeze roller 13Y are pressed and slidably attached to the surface. The cleaning blade 14Y removes the liquid developer and the developer collection unit 15Y that collects the removed liquid developer. The photoreceptor squeeze device 101Y has a function of collecting excess carrier (insulating liquid) and originally unnecessary fog toner from the developer developed on the photoreceptor 10Y, and increasing the ratio of toner particles in the visible image.

The primary transfer backup roller 51Y is a device for transferring a single color image formed on the photoreceptor 10Y to an intermediate transfer unit 40 described later.
The neutralization unit 16Y is a device that removes residual charges on the photoreceptor 10Y after the intermediate transfer image is transferred onto the intermediate transfer unit 40 by the primary transfer backup roller 51Y.
The photoconductor cleaning blade 17Y is a rubber member that is in contact with the surface of the photoconductor 10Y, and remains on the photoconductor 10Y after the image is transferred onto the intermediate transfer portion 40 by the primary transfer backup roller 51Y. It has a function of scraping off and removing the liquid developer.

The developer recovery unit 18Y has a function of recovering the liquid developer removed by the photoconductor cleaning blade 17Y.
The intermediate transfer unit 40 is an endless elastic belt member, and is stretched around a belt driving roller 41 and a pair of driven rollers 44 and 45 to which a driving force of a motor (not shown) is transmitted. The intermediate transfer unit 40 is driven to rotate counterclockwise by the belt driving roller 41 while being in contact with the photoreceptors 10Y, 10M, 10C, and 10K by the primary transfer backup rollers 51Y, 51M, 51C, and 51K.

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

  In the intermediate transfer unit 40, the single-color images formed on the plurality of photoconductors 10Y, 10M, 10C, and 10K are secondarily transferred and superposed one after another. Secondary transfer is performed on a recording medium F5 such as paper, film, or cloth. Therefore, when the toner image is transferred to the recording medium F5 in the secondary transfer process, even if the surface of the recording medium F5 is a sheet material that is not smooth due to fiber or the like, the secondary transfer characteristics follow the surface of the non-smooth sheet material. An elastic belt member is employed as means for improving the above.

The intermediate transfer unit 40 is provided with a cleaning device including an intermediate transfer unit cleaning blade 46, a developer recovery unit 47, and a non-contact type bias applying member 48.
The intermediate transfer portion cleaning blade 46 and the developer recovery portion 47 are arranged on the driven roller 45 side.
The intermediate transfer portion cleaning blade 46 scrapes and removes the liquid developer adhering to the intermediate transfer portion 40 after the image is transferred onto the recording medium F5 by the secondary transfer unit (secondary transfer portion) 60. have.

The developer recovery unit 47 has a function of recovering the liquid developer removed by the intermediate transfer unit cleaning blade 46.
The non-contact type bias applying member 48 is disposed away from the intermediate transfer unit 40 at a position facing the tension roller 49. The non-contact type bias applying member 48 applies a bias voltage having a polarity opposite to that of the toner to the liquid developer toner (solid content) remaining on the intermediate transfer portion 40 after the secondary transfer. As a result, the toner is discharged, and the electrostatic adhesion force of the toner to the intermediate transfer unit 40 is reduced. In this example, a corona charger is used as the non-contact type bias applying member 48.

The non-contact type bias applying member 48 is not necessarily disposed at a position facing the tension roller 49. For example, a position between the driven roller 44 and the tension roller 49, such as a position between the driven roller 44 and the intermediate transfer unit. It can be disposed at any position downstream in the movement direction and upstream of the driven roller 45 in the movement direction of the intermediate transfer unit. The non-contact type bias applying member 48 may be a known non-contact type charger other than the corona charger.
An intermediate transfer unit squeeze device 52Y is disposed downstream of the primary transfer backup roller 51Y in the moving direction of the intermediate transfer unit 40.

The intermediate transfer unit squeeze device 52Y is provided as a means for removing excess insulating liquid from the transferred liquid developer when the liquid developer transferred onto the intermediate transfer unit 40 has not reached the desired dispersion state. ing.
The intermediate transfer unit squeeze device 52Y is removed by an intermediate transfer unit squeeze roller 53Y, an intermediate transfer unit squeeze cleaning blade 55Y that presses and slides against the intermediate transfer unit squeeze roller 53Y, and an intermediate transfer unit squeeze cleaning blade 55Y. The developer collecting section 56Y collects the liquid developer.

The intermediate transfer unit squeeze device 52Y has a function of recovering excess insulating liquid from the developer primarily transferred to the intermediate transfer unit 40, increasing the toner particle ratio in the image, and recovering originally unwanted toner. Have.
The secondary transfer unit 60 includes a pair of secondary transfer rollers that are spaced apart from each other by a predetermined distance along the transfer material movement direction. Of these pair of secondary transfer rollers, the secondary transfer roller disposed upstream of the moving direction of the intermediate transfer unit 40 is the upstream secondary transfer roller 64. The upstream secondary transfer roller 64 can be brought into pressure contact with the belt driving roller 41 via the intermediate transfer unit 40.

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

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

  Accordingly, the recording medium F5 conveyed to the secondary transfer unit 60 is moved from the pressure contact start position (nip start position) between the upstream side secondary transfer roller 64 and the belt driving roller 41 to the downstream side secondary transfer roller 65 and the driven roller. In close contact with the intermediate transfer portion 40 in a predetermined movement region of the transfer material up to the press-contact end position (nip end position) with 44. As a result, the full-color intermediate transfer image on the intermediate transfer unit 40 is secondarily transferred to the recording medium F5 in close contact with the intermediate transfer unit 40 over a predetermined time, so that good secondary transfer is performed.

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

The toner image (transfer image) F5a transferred onto the recording medium F5 by the secondary transfer unit 60 is sent to a fixing unit (fixing device) F40, and is heated and pressurized to be fixed on the recording medium F5.
Specifically, the fixing temperature is preferably 80 to 160 ° C., more preferably 100 to 150 ° C., and further preferably 100 to 140 ° C.
Next, the developing units 100Y, 100M, 100C, and 100K will be described in detail. In the following description, the developing unit 100Y will be typically described.

As shown in FIG. 2, the developing unit 100Y includes a liquid developer storage unit 31Y, a coating roller 32Y, a regulating blade 33Y, a developer stirring roller 34Y, a communication unit 35Y, a recovery screw 36Y, and a developing roller 20Y. And a developing roller cleaning blade 21Y.
The liquid developer storage unit 31Y has a function of storing a liquid developer for developing the latent image formed on the photoreceptor 10Y. The supply unit 31aY supplies the liquid developer to the development unit, and the supply unit A recovery unit 31bY that recovers excess liquid developer generated at 31aY and the like, and a partition 31cY that partitions the supply unit 31aY and the recovery unit 31bY are provided.

The supply unit 31aY has a function of supplying the liquid developer to the application roller 32Y, and has a concave portion in which the developer stirring roller 34Y is installed. Further, the liquid developer is supplied to the supply unit 31aY from the liquid developer storage unit 31Y through the communication unit 35Y.
The collection unit 31bY collects the liquid developer that is excessively supplied to the supply unit 31aY and excess liquid developer generated in the developer collection units 15Y and 24Y. The collected liquid developer is conveyed to a liquid developer mixing tank 93Y described later and reused. The recovery unit 31bY has a concave portion, and a recovery screw 36Y is installed near the bottom.

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

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

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

  The developer stirring roller 34Y has a function of stirring the liquid developer in a uniformly dispersed state. Thus, even when a plurality of toner particles are aggregated, the toner particles can be suitably dispersed. In particular, since the liquid developer of the present invention contains the dispersant as described above, the dispersibility of the toner particles is high, and the liquid developer can be more suitably dispersed. Even a reused liquid developer can be easily dispersed.

  In the supply unit 31aY, the toner particles in the liquid developer have a negative 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 upper surface does not rise due to the blowing, and the liquid The upper surface is held substantially constant, and the developer can be stably supplied to the application roller 32Y.

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

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

Further, the developing roller 20Y can rotate around its central axis, and the central axis is below the rotational central axis of the photoconductor 10Y. Further, the developing roller 20Y rotates in a direction (counterclockwise in FIG. 2) opposite to the rotation direction of the photoreceptor 10Y (clockwise in FIG. 2). When developing the latent image formed on the photoconductor 10Y, an electric field is formed between the developing roller 20Y and the photoconductor 10Y.
In the developing unit 100Y, the coating roller 32Y and the developing roller 20Y are separately driven by different power sources (not shown). The amount of the liquid developer supplied onto the developing roller 20Y can be adjusted by changing the rotation speed (linear speed) ratio between the application roller 32Y and the developing roller 20Y.

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

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

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

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

Further, the liquid developer recovered by the recovery unit 31bY is recovered and reused in the liquid developer mixing tank 93Y. The same applies to the liquid developer mixing tanks 93M, 93C, and 93K.
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.

[1] Production of Liquid Developer A liquid developer was produced as follows.
Example 1
First, toner particles were manufactured. In addition, about the process in which temperature is not described, it performed at room temperature (25 degreeC).
<Dispersion adjustment process>
(Preparation of colorant master solution)
First, as a resin material, a polyester resin (acid value: 10 mgKOH / g, glass transition point (Tg): 55 ° C., softening point: 107 ° C.): 60 parts by weight was prepared.

Next, a mixture (mass ratio 50:50) of the resin material and a cyan pigment as a colorant (manufactured by Dainichi Seika Co., Ltd., Pigment Blue 15: 3) was prepared. These components were mixed using a 20 L type Henschel mixer to obtain a raw material for toner production.
Next, this raw material (mixture) was kneaded using a twin-screw kneading extruder. The kneaded product extruded from the extrusion port of the biaxial kneading extruder was cooled.
The kneaded material cooled as described above was coarsely pulverized to obtain a colorant master batch having an average particle size of 1.0 mm or less. A hammer mill was used for coarse pulverization of the kneaded product.

(Resin liquid preparation process)
The above colorant master batch: 97.5 parts by weight, methyl ethyl ketone: 175 parts by weight, the polyester resin: 172.3 parts by weight, rosin-modified phenol resin (trade name “KG2212” manufactured by Arakawa Chemical Industries, Ltd., acid value: 22 mgKOH / g or less, softening point: 172 to 182; weight average molecular weight: 100,000): 55.3 parts by weight with a high-speed disperser (manufactured by Primics Co., Ltd., TK Robotics / TK homodisper type 2.5 blade) After mixing, 1.38 parts by weight of Neogen SC-F (Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier was added to prepare a resin solution. In this solution, the pigment was uniformly finely dispersed.

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

<Joint process>
Next, the aqueous dispersion was transferred to a stirring vessel having a Max Blend blade, and the temperature of the aqueous dispersion was adjusted to 25 ° C. while stirring at a blade tip speed of 1.0 m / s.
Next, while maintaining the same temperature and stirring conditions, 200 parts by weight of a 5.0% aqueous sodium sulfate solution was added dropwise to coalesce the dispersoids to form coalesced particles. After the dropping, stirring was continued until the 50% volume particle diameter Dv (50) [μm] of the coalesced toner particles grew to 3.4 μm. When the Dv (50) of the coalesced particles reached 3.4 μm, 200 parts by weight of deionized water was added to complete the coalescence.

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

<Drying process>
Thereafter, the obtained wet cake was dried using a vacuum dryer to obtain toner particles.
<Dispersing process>
First, arachid 310 (Arakawa) as a dispersant in a mixture of rapeseed oil (manufactured by Nisshin Oilio Co., Ltd., trade name “HIOLEIC rapeseed oil”): 90 parts by weight and soybean oil fatty acid methyl (manufactured by Nisshin Oilio Co., Ltd.): 60 parts by weight Chemical Industry Co., Ltd., acid value: 13 mg KOH / g): 1.5 parts by weight were added.

Further, 0.15 part by weight of triethanolamine as a pH adjuster was added and stirred at 50 ° C. for 1 hour.
Next, 37.5 parts by weight of the toner particles obtained by the above method are added, the obtained mixture is put into a ceramic pot (internal volume 600 ml), and zirconia balls (ball diameter: 1 mm) are further added to the volume. It put into the ceramic pot so that it might become a filling rate of 85%, and it disperse | distributed for 24 hours with the rotational speed of 230 rpm with the desktop pot mill. As a result, a liquid developer was obtained.

The Dv (50) of the toner particles in the obtained liquid developer was 3.0 μm. The 50% volume particle diameter Dv (50) [μm] of the obtained toner particles was measured with a Mastersizer 2000 particle analyzer (manufactured by Malvern Instruments Ltd.). Moreover, the particle diameter was similarly calculated | required about the particle | grains obtained by each Example and each comparative example demonstrated below.
Further, when the pH of the obtained liquid developer at 23 ° C. was measured, it was 9.00.

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

(Examples 2 to 6)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the content of the pH adjusting agent was as shown in Table 1 and the pH of the liquid developer was adjusted as shown in Table 1.
(Examples 7 to 9)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the content of the dispersant was as shown in Table 1.

(Example 10)
Liquid developers corresponding to the respective colors were produced in the same manner as in Example 1 except that Arachid 251 (Arakawa Chemical Industries, Ltd., acid value: 10 mgKOH / g) was used as the dispersant.
(Example 11)
A liquid developer corresponding to each color was produced in the same manner as in Example 10 except that the content of the pH adjusting agent was as shown in Table 1 and the pH of the liquid developer was adjusted as shown in Table 1.

Example 12
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that EFKA-5044 (manufactured by Ciba Specialty Chemicals, acid value: 30 mgKOH / g) was used as the dispersant.
(Example 13)
A liquid developer corresponding to each color was produced in the same manner as in Example 12 except that the content of the pH adjusting agent was as shown in Table 1 and the pH of the liquid developer was adjusted as shown in Table 1.

(Example 14)
As the rosin-modified resin, except that rosin-modified phenol resin (Arakawa Chemical Industries, trade name “Tamanol 135”, acid value: 18 mgKOH / g or less, softening point: 130 to 140, weight average molecular weight: 15000) was used. In the same manner as in Example 1, liquid developers corresponding to the respective colors were produced.

(Comparative Example 1)
A liquid developer corresponding to each color was produced in the same manner as in Example 9 except that no pH adjustor was added.
(Comparative Example 2)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the dispersant was not added.

(Comparative Example 3)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that EFKA-8503 (manufactured by Ciba Specialty Chemicals, acid value: none) was used as the dispersant.
Table 1 shows the composition and the like of the liquid developer for each of the above Examples and Comparative Examples. In the table, the polyester resin is indicated as PES, the rosin-modified phenol (trade name “KG2212”) as RP1, and the rosin-modified phenol (trade name “Tamanor 135”) as RP2. The arachid 310 is indicated as A310, the arachid 251 as A251, the EFKA-5044 as E5044, and the EFKA-8503 as E8503. Moreover, soybean oil fatty acid methyl was shown as MONO and rapeseed oil was shown as VO.

[2] Evaluation Each liquid developer obtained as described above was evaluated as follows.
[2.1] Developing efficiency Using the image forming apparatus as shown in FIGS. 1 and 2, the liquid developer by the liquid developer obtained in each of the embodiments and comparative examples on the developing roller of the image forming apparatus. A layer was formed. Next, the surface potential of the developing roller was set to -300V, the surface potential of the photoconductor was uniformly charged at -500V, the photoconductor was exposed, the charge on the surface of the photoconductor was attenuated, and the surface potential was set to 50V. The toner particles on the developing roller and the toner particles on the photosensitive member after the liquid developer layer passed between the photosensitive member and the developing roller were collected with a tape. Each tape used for sampling was affixed on a recording paper, and the concentration of each toner particle was measured. After the measurement, the value obtained by dividing the concentration of toner particles collected on the photoreceptor by the sum of the concentration of toner particles collected on the photoreceptor and the concentration of toner particles collected on the developing roller is multiplied by 100. Was determined as development efficiency, and evaluated according to the following four-stage criteria.
A: The development efficiency is 98% or more, and the development efficiency is particularly excellent.
B: The development efficiency is 93% or more and less than 98%, and the development efficiency is excellent.
C: The development efficiency is 85% or more and less than 93%, and there is no practical problem.
D: The development efficiency is less than 85%, and the development efficiency is inferior.

[2.2] Transfer efficiency Using the image forming apparatus as shown in FIGS. 1 and 2, a liquid developer using the liquid developer obtained in each of the above examples and comparative examples on the photoreceptor of the image forming apparatus. A layer was formed. Next, the toner particles on the photoconductor and the toner particles on the intermediate transfer portion after the liquid developer layer passed between the photoconductor and the intermediate transfer portion were collected with a tape. Each tape used for sampling was affixed on a recording paper, and the concentration of each toner particle was measured. After the measurement, a value obtained by dividing the concentration of the toner particles collected on the intermediate transfer portion by the sum of the concentration of the toner particles collected on the photoconductor and the concentration of the toner particles collected on the intermediate transfer portion is 100. A value obtained by multiplying by is obtained as transfer efficiency, and evaluated according to the following four criteria.
A: The transfer efficiency is 95% or more, and the transfer efficiency is particularly excellent.
B: The transfer efficiency is 90% or more and less than 95%, and the transfer efficiency is excellent.
C: The transfer efficiency is 80% or more and less than 90%, and there is no practical problem.
D: Transfer efficiency is less than 80% and inferior to transfer efficiency.

[2.4] Charging characteristics of negative charging For the liquid developers obtained in the examples and comparative examples, the zeta potential was measured using a “microscopic laser zeta electrometer” ZC-2000 manufactured by Microtech Nichion. Measured and evaluated according to the following five criteria.
In the measurement, the liquid developer is diluted with a diluting solvent, put into a 10 mm square transparent cell, a voltage of −300 V is applied at 9 mm between the electrodes, and at the same time, the moving speed of particles in the cell is observed with a microscope. Thus, the movement speed was calculated, and the zeta potential was obtained from the value. In addition, the dilution solvent used what mixed the insulating liquid in each Example and each comparative example, the dispersing agent, and the pH adjuster in the same composition as each Example and each comparative example.

A: Zeta potential is −150 mV or less (very good).
B: The zeta potential is larger than −150 mV and −125 mV or less (good).
C: Zeta potential is larger than −125 mV and −100 mV or less (normal).
D: The zeta potential is larger than −100 mV and −75 mV or less (somewhat bad).
E: Zeta potential is larger than −75 mV (very bad).

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

  As is apparent from Table 2, the liquid developer of the present invention was excellent in development efficiency, transfer efficiency, and negative charging characteristics. Also, the dispersion stability of the toner particles was excellent. On the other hand, satisfactory results were not obtained with the liquid developers of the comparative examples.

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

Explanation of symbols

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

Claims (11)

An insulating liquid;
Toner particles mainly composed of a resin material;
A dispersant having an acid value,
A liquid developer having a hydrogen ion exponent pH of 7 to 11 at 24 ° C.   The liquid developer according to claim 1, wherein the acid value of the dispersant is 10 to 15 mg KOH / g.   The liquid developer according to claim 1, comprising a pH adjuster.   The liquid developer according to claim 1, wherein the resin material includes a polyester resin.   The liquid developer according to claim 4, wherein an acid value of the polyester resin is 5 to 15 mg KOH / g.   The liquid developer according to claim 1, wherein the resin material includes a rosin-modified resin.   The liquid developer according to claim 6, wherein the acid value of the rosin-modified resin is 10 to 40 mg KOH / g.   The liquid developer according to claim 1, wherein the insulating liquid contains vegetable oil.   The liquid developer according to claim 1, wherein the insulating liquid contains a fatty acid monoester. A plurality of developing units that form a single color image corresponding to the plurality of liquid developers using a plurality of liquid developers having different colors;
An intermediate transfer unit that sequentially transfers a plurality of the single-color images formed by the plurality of developing units, and forms an intermediate transfer image formed by superimposing the transferred single-color images;
A secondary transfer unit that transfers the intermediate transfer image to a recording medium and forms an unfixed color image on the recording medium;
A fixing unit for fixing the unfixed color image on the recording medium,
The liquid developer is an insulating liquid;
Toner particles mainly composed of a resin material;
A dispersant having an acid value,
An image forming apparatus, wherein the liquid developer has a hydrogen ion exponent pH of 7 to 11 at 24 ° C. The developing unit includes a supply unit that supplies the liquid developer for forming the monochromatic image, a recovery unit that recovers excess liquid developer in the supply unit, the recovery unit, and the supply unit. And a partition provided between
The image forming apparatus according to claim 10, wherein excess liquid developer in the supply unit is collected by the collection unit through the partition.

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