JP2008203372A - Liquid developer and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developer that is environmentally friendly, is capable of fixing toner particles on a recording medium at a low temperature at high speed and capable of firmly fixing the toner particles on the recording medium, and to provide an image forming apparatus using the above liquid developer. <P>SOLUTION: The liquid developer contains toner particles essentially comprising a resin material, the particles dispersed in an insulating liquid, characterized in that: the insulating liquid contains a fatty acid monoester, an aliphatic hydrocarbon liquid and/or silicone oil; and the resin material has a glass transition temperature Tg of 15 to 70°C and a softening temperature Tf of 80 to 140°C. It is preferable that the content X [wt.%] of the fatty acid monoester and the content Z [wt.%] of the aliphatic hydrocarbon liquid and silicone oil in the insulating liquid satisfy the relation of 0.1≤X/Z≤1.0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

A dry toner method in which a toner composed of a material containing a colorant such as a pigment and a binder resin is used in a dry state as a developer used to develop the electrostatic latent image formed on the latent image carrier. And a method using a liquid developer (for example, see Patent Document 1) in which toner is dispersed in an electrically insulating carrier liquid (insulating liquid).
The method using dry toner handles solid-state toner, so there are advantages in handling, but there are concerns about adverse effects on the human body due to powder, as well as contamination due to scattering of toner, and when toner is dispersed There is a problem with uniformity. Further, the dry toner has a problem that the particles are likely to aggregate and it is difficult to sufficiently reduce the size of the toner particles, and it is difficult to form a toner image with high resolution. In addition, when the size of the toner particles is relatively small, the problem due to the powder as described above becomes more remarkable.

On the other hand, in the method using a liquid developer, it is possible to use fine toner particles because aggregation of toner particles in the liquid developer is effectively prevented. As a result, the method using the liquid developer has the characteristics that fine line image reproducibility is good, gradation reproducibility is good, and color reproducibility is excellent. Further, it has a feature that it is superior as a high-speed image forming method as compared with dry toner.
However, since the insulating liquid that has been used in conventional liquid developers is mainly petroleum-based hydrocarbons, it can adversely affect the environment when it goes out of an image forming apparatus or the like. There was concern.

In general, in a liquid developer, an insulating liquid adheres to the surface of toner particles during fixing. In the conventional liquid developer, there is also a problem that the insulating liquid adhering to the surface of the toner particles decreases the fixing strength.
In order to improve the fixing strength of the toner, it may be possible to fix the toner particles by heating at a relatively high temperature for a long time, but this satisfies the recent demand for higher speed and energy saving of image formation. It was difficult.

JP 7-152256 A

  An object of the present invention is to provide a liquid developer that is environmentally friendly, can fix toner particles to a recording medium at a low temperature and at a high speed, and can firmly fix toner particles to a recording medium. Another object is to provide an image forming apparatus using such a liquid developer.

Such an object is achieved by the present invention described below.
In the liquid developer of the present invention, toner particles mainly composed of a resin material are dispersed in an insulating liquid.
The insulating liquid includes a fatty acid monoester, an aliphatic hydrocarbon and / or silicone oil,
The resin material has a glass transition point Tg of 15 to 70 ° C. and a softening temperature Tf of 80 to 140 ° C.

In the liquid developer of the present invention, the content of the fatty acid monoester in the insulating liquid is X [wt%], and the total content of the aliphatic hydrocarbon liquid and the silicone oil is Z [wt%]. In this case, it is preferable that the relationship of 0.1 ≦ X / Z ≦ 1.0 is satisfied.
In the liquid developer of the present invention, the resin material is preferably a polyester resin.
In the liquid developer of the present invention, the fatty acid monoester preferably contains a saturated fatty acid as a fatty acid component.

In the liquid developer of the present invention, the fatty acid monoester preferably contains a monoester of a saturated fatty acid having 8 to 16 carbon atoms and an alcohol having 1 to 4 carbon atoms.
In the liquid developer of the present invention, the viscosity measured according to JIS Z8809 using a vibration viscometer at 25 ° C. is preferably 50 to 1000 mPa · s.

The image forming apparatus of the present invention includes a liquid developer storage unit that stores the liquid developer,
A developing unit for developing using the liquid developer supplied from the liquid developer storage unit;
A transfer unit that transfers the image formed by the developing unit onto a recording medium and forms a transfer image;
A fixing unit for fixing the transfer image formed on the recording medium onto the recording medium,
In the liquid developer, toner particles mainly composed of a resin material are dispersed in an insulating liquid. The insulating liquid includes a fatty acid monoester, an aliphatic hydrocarbon liquid, and / or a silicone oil. The resin material has a glass transition point Tg of 15 to 70 ° C. and a softening temperature Tf of 80 to 140 ° C.

  The above configuration is environmentally friendly and can fix toner particles on a recording medium at low temperature and at high speed, and can firmly fix toner particles on a recording medium and provide a liquid developer. Can do. In addition, it is possible to provide an image forming apparatus that is friendly to the environment, can fix toner particles to a recording medium at a low temperature and at high speed, and can firmly fix the toner particles to the recording medium.

Hereinafter, preferred embodiments of the present invention will be described in detail.
<Liquid developer>
The liquid developer of the present invention is one in which toner particles are dispersed in an insulating liquid.
<Toner particles>
First, toner particles will be described.

[Component material of toner particles]
The toner particles (toner) constituting the liquid developer of the present invention include at least a binder resin (resin material) and a colorant.
1. Resin Material The toner particles constituting the liquid developer are made of a material containing a resin material as a main component.

The present invention is characterized in that a resin material constituting the toner particles is one having a glass transition point of 15 to 70 ° C. and a softening temperature of 80 to 140 ° C.
By the way, in general, when toner particles composed of a resin having a low glass transition point and a low softening temperature are used, the toner particles can be fixed at a relatively low temperature, but it is difficult to obtain a sufficient fixing strength. there were. In addition, toner particles composed of such a resin material are likely to aggregate, making it difficult to form an image with sufficient image quality.

However, when used in combination with an insulating liquid described in detail later, the toner particles can be fixed at a low temperature, the toner particles can be firmly fixed on the recording medium, and a high-quality image can be obtained. Can be formed.
In the present invention, the glass transition point of the resin material constituting the toner particles is 15 to 70 ° C., preferably 20 to 55 ° C., and more preferably 25 to 50 ° C. Thereby, the effect of this invention becomes more remarkable.

In the present invention, the softening temperature of the resin material constituting the toner particles is 80 to 140 ° C., preferably 85 to 130 ° C., and more preferably 90 to 120 ° C. Thereby, the effect of this invention becomes more remarkable.
In the present specification, the softening temperature 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.

  In the present invention, the resin (binder resin) is not particularly limited as long as it has the above-mentioned properties. For example, polystyrene, poly-α-methylstyrene, chloropolystyrene, styrene-chlorostyrene copolymer , Styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer, styrene- Methacrylic acid ester copolymer, styrene-acrylic acid ester-methacrylic acid ester copolymer, styrene-α-chloroacrylic acid methyl copolymer, styrene-acrylonitrile-acrylic acid ester copolymer, styrene-vinyl methyl ether copolymer Styrene resin or styrene resin such as coalescence Homopolymers or copolymers containing vinyl-substituted products, polyester resins, epoxy resins, urethane-modified epoxy resins, silicone-modified epoxy resins, vinyl chloride resins, rosin-modified maleic acid resins, phenyl resins, polyethylene resins, polypropylene, ionomer resins , Polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene resin, polyvinyl butyral resin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, and the like. One or more of these can be used in combination. Among the above, when a polyester resin is used, the dispersibility of the toner particles in the liquid developer can be made particularly excellent. This is thought to be due to the similarity in chemical structure between the polyester resin and the insulating liquid described in detail later.

2. Colorant The toner contains a colorant. Examples of the colorant that can be used include pigments and dyes. Examples of such pigments and dyes include carbon black, spirit black, lamp black (CI No. 77266), magnetite, titanium black, chrome lead, cadmium yellow, mineral fast yellow, navel yellow, and naphthol yellow S. , Hansa Yellow G, Permanent Yellow NCG, Chrome Yellow, Benzidine Yellow, Quinoline Yellow, Tartrazine Lake, Red Mouth Lead, Molybdenum Orange, Permanent Orange GTR, Pyrazolone Orange, Benzidine Orange G, Cadmium Red, Permanent Red 4R, Watching Red Calcium salt, eosin lake, brilliant carmine 3B, manganese purple, fast violet B, methyl violet lake, bitumen, cobalt blue, al Reblue Lake, Victoria Blue Lake, First Sky Blue, Indanthrene Blue BC, Ultramarine, Aniline Blue, Phthalocyanine Blue, Calco Oil Blue, Chrome Green, Chrome Oxide, Pigment Green B, Malachite Green Lake, Phthalocyanine Green, Final Yellow Green G, Rhodamine 6G, quinacridone, rose bengal (C.I. No. 45432), C.I. I. Direct Red 1, C.I. I. Direct Red 4, C.I. I. Acid Red 1, C.I. I. Basic Red 1, C.I. I. Modern Tread 30, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 184, C.I. I. Direct Blue 1, C.I. I. Direct Blue 2, C.I. I. Acid Blue 9, C.I. I. Acid Blue 15, C.I. I. Basic Blue 3, C.I. I. Basic Blue 5, C.I. I. Modern Blue 7, C.I. I. Pigment blue 15: 1, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 5: 1, C.I. I. Direct Green 6, C.I. I. Basic Green 4, C.I. I. Basic Green 6, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 180, C.I. I. Pigment yellow 162, nigrosine dye (CI No. 50415B), metal complex dye, silica, aluminum oxide, magnetite, maghemite, various ferrites, cupric oxide, nickel oxide, zinc oxide, zirconium oxide, titanium oxide, Examples thereof include metal oxides such as magnesium oxide, and magnetic materials containing magnetic metals such as Fe, Co, and Ni, and one or more of these can be used in combination.

3. Other Components The toner may contain components other than those described above. Examples of such components include waxes, charge control agents, magnetic powders, and the like.
Examples of the wax include hydrocarbon waxes such as ozokerite, cercin, paraffin wax, microwax, microcrystalline wax, petrolatum, Fischer-Tropsch wax, carnauba wax, rice wax, methyl laurate, methyl myristate, palmitic acid. Methyl, methyl stearate, butyl stearate, candelilla wax, cotton wax, wood wax, beeswax, lanolin, montan wax, fatty acid ester ester wax, polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax Olefin wax such as 12-hydroxystearic acid amide, stearic acid amide, amide anhydride such as phthalic anhydride, Lauro , Ketone waxes such as stearone, ether waxes, and the like, can be used singly or in combination of two or more of them.

Examples of the charge control agent include benzoic acid metal salt, salicylic acid metal salt, alkyl salicylic acid metal salt, catechol metal salt, metal-containing bisazo dye, nigrosine dye, tetraphenylborate derivative, quaternary ammonium salt, alkyl Examples include pyridinium salts, chlorinated polyesters, and nitrofunic acid.
Examples of the magnetic powder include magnetite, maghemite, various ferrites, cupric oxide, nickel oxide, zinc oxide, zirconium oxide, titanium oxide, magnesium oxide, and other metal oxides, and magnetic materials such as Fe, Co, and Ni. The thing etc. which were comprised with the magnetic material containing a metal are mentioned.
In addition to the above materials, for example, zinc stearate, zinc oxide, cerium oxide, silica, titanium oxide, iron oxide, fatty acid, fatty acid metal salt, etc. are used as the constituent material (component) of the kneaded product. May be.

[Toner particle shape]
The average particle size of the toner particles composed of the above materials is preferably 0.1 to 5 μm, more preferably 0.1 to 4 μm, and further preferably 0.5 to 3 μm. preferable. When the average particle diameter of the toner particles is within the above range, the variation in characteristics among the toner particles is particularly small, and the reliability of the entire liquid developer is particularly high, while the liquid developer ( The resolution of the image formed by the toner can be made sufficiently high.

The standard deviation of the particle size between toner particles constituting the liquid developer is preferably 1.0 μm or less, more preferably 0.1 to 1.0 μm, and more preferably 0.1 to 0. More preferably, it is 8 μm. As a result, the variation in characteristics among the toner particles becomes particularly small, and the reliability of the entire liquid developer is further improved.
Further, the average value (average circularity) of the circularity R represented by the following formula (I) for the toner particles constituting the liquid developer is preferably 0.85 or more, and 0.90 to 0.00. 99 is more preferable, and 0.92 to 0.99 is even more preferable.

R = L ₀ / L ₁ (I)
(Where L ₁ [μm] is the circumference of the projected image of the toner particles to be measured, and L ₀ [μm] is the circumference of a perfect circle having an area equal to the area of the projected image of the toner particles to be measured) Represents length)
Thereby, the transfer efficiency and mechanical strength of the toner particles can be made particularly excellent while the particle diameter of the toner particles is sufficiently small.
The standard deviation of the average circularity between the toner particles constituting the liquid developer is preferably 0.15 or less, more preferably 0.001 to 0.10, and 0.001 to 0. More preferably, .05. As a result, variations in characteristics such as charging characteristics and fixing characteristics among the toner particles are particularly reduced, and the reliability of the entire liquid developer is further improved.

<Insulating liquid>
Next, the insulating liquid will be described.
In the present invention, the insulating liquid contains a fatty acid monoester and an aliphatic hydrocarbon and / or silicone oil.
[Fatty acid monoester]
In the present invention, the fatty acid monoester in the insulating liquid is a monoester between a fatty acid and an alcohol.

In the conventional liquid developer, the insulating liquid leaks out of the image forming apparatus during use (for example, the volatilization of the insulating liquid during fixing) or the used liquid developer is discarded due to disposal of the used liquid developer. There were concerns about the impact on the environment. Further, the conventional liquid developer has a problem that the fixing property of the toner particles to the recording medium is hindered (fixing strength is reduced) due to the presence of the insulating liquid adhering to the surface of the toner particles.
On the other hand, the fatty acid monoester used in the insulating liquid of the present invention is an environmentally friendly component. Therefore, it is possible to reduce the load on the environment of the insulating liquid due to the leakage of the insulating liquid to the outside of the image forming apparatus and the disposal of the used liquid developer. As a result, an environmentally friendly liquid developer can be provided.

  In addition, for resin materials such as polyester and styrene-acrylic copolymer suitably used in the present invention, when fatty acid monoester or fatty acid triglyceride is used as an insulating liquid, the fatty acid component constituting them is It penetrates into the resin particles during the fixing process and develops a plasticizer effect. Due to this plasticizer effect, for example, when paper is used as the recording medium, the toner particles easily enter the gaps between the paper fibers, so that the fixing characteristics between the paper and the toner particles are improved. Among insulating liquids composed of such fatty acid components, in particular, insulating liquids containing fatty acid monoesters are excellent in fixing characteristics. This is because, in general, fatty acid monoesters have a lower molecular weight than liquids having other plasticizer effects such as fatty acid triglycerides, and are easily incorporated into resin particles during the fixing process. It is thought that it becomes easy to express. For this reason, when an image is formed using a liquid developer containing a fatty acid monoester, the toner particles can suitably penetrate into the recording medium in the fixing process, and solidify in the penetrated state, thereby recording. It can be fixed by being entangled with the fibers of the medium. Therefore, even if the resin constituting the toner particles has the softening point and glass transition point as described above, the toner particles can be firmly fixed on the recording medium.

Further, when a polyester resin is used as the resin material constituting the toner particles, the affinity with the insulating liquid containing the fatty acid monoester is particularly good as described above. While the dispersibility is very excellent, the fixing property of the toner particles to the recording medium can be made particularly excellent.
Thus, by including the fatty acid monoester in the insulating liquid, the penetration of the liquid developer into the recording medium becomes suitable, and can be suitably adapted to image formation at low temperature and high speed. Further, the fixing strength of the obtained toner image is excellent.

  Moreover, the fatty acid monoester may contain a saturated fatty acid as a fatty acid component. Thus, when the saturated fatty acid component is contained, the preservability and long-term stability of the insulating liquid can be further improved. Examples of such saturated fatty acids include butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid.

  Among these, the fatty acid monoester preferably contains a fatty acid having 8 to 16 carbon atoms as a saturated fatty acid component. Thereby, it is possible to make the fixing property particularly excellent while making the storage stability and long-term stability of the liquid developer particularly excellent. In particular, when lauric acid, caprylic acid, caproic acid, or myristic acid is used as the saturated fatty acid component, the above-described effects become more prominent.

  The fatty acid monoester may contain an unsaturated fatty acid as a fatty acid component. The unsaturated fatty acid component contained in the fatty acid monoester is a component that can contribute to improving the fixability of toner particles to a recording medium. More specifically, the unsaturated fatty acid component has a function of improving the fixing property of the toner particles by being oxidized (by being oxidized at the time of fixing), causing a polymerization reaction to proceed and curing itself. It is a component that has.

  Therefore, the toner particles can be fixed on the recording medium at a low temperature, and the toner particles can be firmly fixed on the recording medium. In other words, since the toner particles are made of the resin material having a low glass transition point and a low softening temperature as described above, the toner particles can be fixed at a relatively low fixing temperature. The insulating liquid (unsaturated fatty acid component) transferred onto the recording medium together with the toner particles is cured by oxidative polymerization reaction by heating at the time of fixing, and covers the surface of the fixed toner particles. Even toner particles composed of a resin material having a low point and softening temperature can be firmly fixed on the recording medium. Further, since the unsaturated fatty acid component is cured, the fixed toner image can be easily and reliably added with an aqueous ballpoint pen.

  Such a fatty acid monoester preferably contains an unsaturated fatty acid having 16 to 22 carbon atoms as an unsaturated fatty acid component. As a result, the penetration of the liquid developer into the recording medium becomes favorable, and the liquid developer is more preferably cured by the oxidative polymerization reaction, so that the fixing property of the toner particles to the recording medium is more excellent. It becomes. Examples of unsaturated fatty acids that satisfy the above conditions include oleic acid, palmitoleic acid, linoleic acid, α-linolenic acid, γ-linolenic acid, arachidonic acid, docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and these And conjugated unsaturated fatty acids.

The fatty acid monoester is a monoester between a fatty acid and an alcohol, and the alcohol is preferably an alkyl alcohol having 1 to 4 carbon atoms. As a result, the chemical stability of the liquid developer is excellent, and the storage stability and long-term stability of the liquid developer are further improved. Further, the viscosity of the insulating liquid can be made suitable, and the penetration of the liquid developer into the recording medium can be made more suitable. Examples of such alcohol include methanol, ethanol, propanol, butanol, isobutanol and the like.
The insulating liquid of the present invention contains a fatty acid monoester obtained by combining one or two or more selected from fatty acids and those produced by transesterification with alcohol.

In addition, the content of the fatty acid monoester in the insulating liquid is preferably 1.0 to 50 wt%, more preferably 10 to 50 wt%, and further preferably 20 to 50 wt%. If the content of the fatty acid monoester in the insulating liquid is less than the lower limit, toner particles may not be sufficiently plasticized by the fatty acid monoester during fixing. In addition, it may be difficult to make the viscosity of the liquid developer suitable, and the penetration of the liquid developer (insulating liquid) into the recording medium becomes insufficient, and the liquid developer is included in the insulating liquid. It may be difficult to suitably proceed the oxidative polymerization reaction of the unsaturated fatty acid component. As a result, the fixing characteristics of the toner particles on the recording medium may be insufficient. On the other hand, when the upper limit is exceeded, in an image forming apparatus as will be described later, it may be difficult to pump the liquid developer from the developer container with the application roller, and the toner particles are uniformly distributed on the recording medium. In some cases, the resulting image may be uneven. Furthermore, depending on the constituent material of the member, the member in contact with the liquid developer in the image forming apparatus may swell and the life of the image forming apparatus may be significantly reduced.
In the present invention, the insulating liquid contains an aliphatic hydrocarbon and / or silicone oil. As described above, the insulating liquid has excellent fixing characteristics by containing an aliphatic hydrocarbon and / or silicone oil in addition to the fatty acid monoester. Hereinafter, the aliphatic hydrocarbon and the silicone oil will be described.

[Aliphatic hydrocarbon]
Aliphatic hydrocarbons are generally chemically stable liquids with high electrical resistance. For this reason, the liquid developer using the aliphatic hydrocarbon has excellent developability and transferability, and the resulting toner image is clear with few defects. Further, since the liquid developer contains an aliphatic hydrocarbon in addition to the fatty acid monoester as the insulating liquid, high-speed and low-temperature fixing is possible, and the obtained toner image has excellent fixing strength. In addition, the color reproducibility of the toner image is excellent. This is considered as follows. Aliphatic hydrocarbons have a high affinity with fatty acid monoesters and easily penetrate into recording media such as paper. For this reason, at the time of fixing, the insulating liquid containing the aliphatic hydrocarbon type and the fatty acid monoester can quickly penetrate into the recording medium, and the insulating liquid existing between the toner particles may be reduced. it can. In particular, in the liquid developer of the present invention, the resin material constituting the toner particles has a softening point as described above and a glass transition temperature. For this reason, when such a liquid developer is used, even when fixing at high speed and low temperature, the toner particles can be easily contacted, melted and firmly bound at the time of fixing. Conceivable. The aliphatic hydrocarbon liquid is a liquid that absorbs little moisture during storage. For this reason, when an aliphatic hydrocarbon is contained in an insulating liquid, it can prevent suitably that an insulating liquid absorbs moisture at the time of storage, and can prevent suitably that an insulating liquid denatures. That is, aliphatic hydrocarbons with low hygroscopicity and high affinity with fatty acid monoesters surround the periphery of the fatty acid monoester, thereby reliably preventing the fatty acid component from being released by contact with the fatty acid monoester and moisture. can do. Further, as described above, the aliphatic hydrocarbon itself is chemically stable and has little modification during storage. For this reason, the liquid developer has excellent storage stability.

  Although it does not specifically limit as aliphatic hydrocarbon which can be used for an insulating liquid, For example, Isopar E, Isopar G, Isopar H, Isopar L (Exxon Chemical Company), Cosmo white P-60, Cosmo white P-70 , Cosmo White P-120 (Cosmo Oil Lubricants), Dynafresia W-8, Daphne Oil CP, Daphne Oil KP, Transformer Oil H, Transformer Oil G, Transformer Oil A, Transformer Oil B, Transformer Oil S (Idemitsu Kosan Co., Ltd.) ), Cielsol 70, Cielsol 71 (Ciel Oil Co., Ltd.), Amsco OMS, Amsco 460 Solvent (Splits Co., Ltd.), Low Viscosity / High Viscosity Liquid Paraffin (Wako Pure Chemical Industries), Octane, Isooctane, Decane, Isodecane, Decali , Nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, and the like, among these, can be used in combination of two or more.

In addition, the aliphatic hydrocarbon preferably has a branched chain of a hydrocarbon group in the molecule. Thereby, the aliphatic hydrocarbon becomes chemically more stable, and the storage stability of the liquid developer using such an aliphatic hydrocarbon becomes particularly excellent. This is considered to be because the structure of the aliphatic hydrocarbon becomes bulky and thus a structure in which a chemical reaction is difficult to occur.
The aliphatic hydrocarbon is preferably a saturated aliphatic hydrocarbon. Thereby, the electrical resistance of the liquid developer can be made particularly high, and the storage stability of the liquid developer can be made particularly excellent.

[Silicone oil]
Silicone oil is an organic compound having a siloxane bond as a skeleton. Silicone oil generally has a high electrical resistance. For this reason, when silicone oil is used as the insulating liquid, the liquid developer has a particularly high electric resistance, and the toner image has excellent transferability and developability. Further, the liquid developer contains silicone oil in addition to the fatty acid monoester as an insulating liquid, so that high-speed and low-temperature fixing is possible, and the obtained toner image has excellent fixing strength. This is considered as follows. Silicone oil is compatible with the fatty acid monoester, but has low affinity with the resin constituting the toner particles. For this reason, the liquid developer containing silicone oil and fatty acid monoester is particularly suitable for the plasticizer effect at the time of fixing because the fatty acid monoester having high affinity with the resin material selectively permeates near the surface of the toner particles. To express. For this reason, it is considered that the toner image can be firmly fixed on the recording medium even when fixing is performed at a relatively low temperature and at a high speed. Moreover, since the silicone oil has various viscosities depending on the type, the viscosity of the liquid developer can be made particularly suitable by selecting the silicone oil. Silicone oil is generally a substance that is chemically stable and has little influence on the human body. For this reason, the liquid developer can suitably prevent deterioration of the insulating liquid during storage, and has excellent storage stability. Even when the insulating liquid leaks out of the image forming apparatus, a safe liquid developer can be obtained.

  Examples of silicone oils that can be used for the insulating liquid include KF96, KF-4701, KF-965, KS-602A, KS-603, KS-604, KF-41, KF-54, FA-630 ( Shin-Etsu Silicone), TSF410, TFS433, TFS434, TFS451, TSF437, (Momentive Performance Materials Japan GK), SH200 (Toray), etc. The above can be used in combination.

Further, the ratio of the fatty acid monoester to the aliphatic hydrocarbon and / or silicone oil in the insulating liquid is not particularly limited, but it is preferable that the following relationship is satisfied. That is, when the content of fatty acid monoester in the insulating liquid is X [wt%] and the total content of aliphatic hydrocarbon and silicone oil is Z [wt%], 0.1 ≦ X / Z ≦ It is preferable to satisfy the relationship of 1.0, and it is more preferable to satisfy the relationship of 0.25 ≦ X / Z ≦ 1.0. By satisfying such a relationship, the toner particles can be more firmly fixed to the recording medium even when fixing at high speed and low temperature. Further, the viscosity of the liquid developer can be made moderate.
The insulating liquid may contain components other than those described above. Examples include fatty acid glycerides, glycerin, fatty acid glyceride decomposition products such as fatty acids, benzene, toluene, xylene, mesitylene and the like, and one or more of these can be used in combination.

  Further, when the fatty acid monoester contains an unsaturated fatty acid, the liquid developer (insulating liquid) may contain an antioxidant having a function of preventing / suppressing the oxidation of the unsaturated fatty acid component. . Thereby, the unintentional oxidation of the unsaturated fatty acid component in the liquid developer can be prevented. As a result, it is possible to prevent the liquid developer (insulating liquid) from being deteriorated over time, and to have particularly excellent dispersibility of toner particles and fixability to a recording medium over a long period of time. it can. That is, the long-term stability (storage stability) of the liquid developer can be made particularly excellent.

The electrical resistance of the insulating liquid as described above at room temperature (20 ° C.) is preferably 1 × 10 ⁹ Ωcm or more, more preferably 1 × 10 ¹¹ Ωcm or more, and 1 × 10 ¹³ Ωcm or more. More preferably.
The dielectric constant of the insulating liquid is preferably 3.5 or less.
In addition, the viscosity (the viscosity measured according to JIS Z8809 using a vibration viscometer at 25 ° C.) of the liquid developer (liquid developer of the present invention) composed of each component as described above is 50 to 1000 mPa · s, more preferably 100 to 900 mPa · s, and still more preferably 150 to 800 mPa · s. Thereby, since the penetration of the liquid developer into the recording medium becomes more suitable, the fixing property of the toner particles to the recording medium becomes more excellent, and the image obtained on the recording medium is uneven. The liquid developer is particularly suitable as a liquid developer suitable for image formation at high speed.

<< Method for Producing Liquid Developer >>
Next, an example of a method for producing the liquid developer as described above will be described.
The insulating liquid as described above can be produced, for example, by mixing the aliphatic hydrocarbon liquid and / or the silicone oil and the fatty acid monoester as described above. The liquid developer can be manufactured by mixing such an insulating liquid and toner particles, but can also be manufactured using the following method.
The method for producing a liquid developer of the present embodiment mainly includes an association particle forming step for associating resin fine particles composed of a resin material to obtain association particles, and pulverizing the association particles in an insulating liquid to form toner particles. And obtaining a process.

[Preparation of associated particles]
First, an example of a method for preparing associated particles in which resin fine particles mainly composed of a resin material are associated will be described.
The association particles may be prepared by any method, but in this embodiment, a dispersoid (fine particles) mainly composed of a resin material (toner material) in an aqueous dispersion medium composed of an aqueous liquid. ) Is dispersed, and the dispersoids in the aqueous emulsion are associated to obtain associated particles.

(Preparation of aqueous dispersion)
Hereinafter, the preparation of the aqueous dispersion will be described.
The aqueous dispersion may be prepared by any method, but in this embodiment, first, the toner material as described above is dissolved in a solvent to obtain a toner material solution, and the toner material solution, By mixing with an aqueous dispersion medium composed of an aqueous liquid, an aqueous emulsion in which the dispersoid (liquid dispersoid) containing the toner material is dispersed is obtained, and then at least one of the solvents contained in the aqueous emulsion is obtained. An aqueous dispersion is obtained by removing the part.

The aqueous emulsion can be prepared, for example, as follows (aqueous emulsion preparation step).
First, an aqueous dispersion medium is prepared.
The aqueous dispersion medium is composed of an aqueous liquid.
In the present invention, the “aqueous liquid” refers to a liquid that is excellent in water and / or water compatibility (for example, a liquid having a solubility in 100 g of water at 25 ° C. of 30 g or more). As described above, the water-based liquid is composed of water and / or a liquid having excellent compatibility with water, but is preferably composed mainly of water. In particular, the water content is 70 wt%. % Or more is preferable, and 90% by weight or more is more preferable. By using such a material, for example, the dispersibility of the dispersoid in the aqueous dispersion medium can be improved, and the dispersoid in the aqueous emulsion can have a relatively small particle size and a variation in size. It can be less. As a result, the toner particles in the finally obtained liquid developer have a small variation in size and shape between the particles, and have a high degree of circularity.

Examples of the aqueous liquid include water, alcohol solvents, ether solvents, aromatic heterocyclic compound solvents, amide solvents, nitrile solvents, aldehyde solvents, and the like.
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.
On the other hand, the toner material as described above is dissolved in a solvent to prepare a toner material solution.

Any solvent can be used as long as it dissolves at least a part of the toner material, but it is preferable to use a solvent having a boiling point lower than that of the aqueous liquid described above. Thereby, a solvent can be removed easily.
Moreover, it is preferable that a solvent is a thing with low compatibility with the aqueous dispersion medium (aqueous liquid) mentioned above (for example, a thing with the solubility with respect to 100 g of aqueous dispersion media at 25 degreeC is 30 g or less). Thereby, the toner material can be finely dispersed in a stable state in the aqueous emulsion.

The composition of the solvent can be appropriately selected according to, for example, the resin and colorant composition as described above, the composition of the aqueous dispersion medium, and the like.
Such a solvent is not particularly limited, and examples thereof include a ketone solvent such as methyl ethyl ketone, an aromatic hydrocarbon solvent such as toluene, and an ester solvent such as ethyl acetate.

  In preparing the toner material solution, for example, a kneaded material obtained by kneading a toner material such as a resin material or a colorant may be used. By using such a kneaded product, each component in the kneaded product obtained by kneading can be obtained even when the constituent materials of the toner contain components that are hardly dispersed or compatible with each other. It can be in a sufficiently compatible and finely dispersed state. In particular, when a pigment (colorant) having a relatively low dispersibility in the solvent as described above is used, the resin component or the like is effective around the pigment particles by being kneaded in advance before being dispersed in the solvent. Thus, the dispersibility of the pigment in the solvent is improved (particularly fine dispersion in the solvent is possible), and the color developability of the finally obtained toner is also improved. For this reason, in the case where the constituent material of the toner contains a component that is poor in dispersibility in the aqueous dispersion medium of the aqueous emulsion or a component inferior in solubility in the solvent contained in the dispersion medium of the aqueous emulsion. Even so, the dispersibility of the dispersoid in the aqueous emulsion can be made particularly excellent.

Next, the toner material solution is gradually added dropwise to the stirred aqueous dispersion medium to obtain an aqueous emulsion in which the dispersoid containing the toner material is dispersed in the aqueous dispersion medium. It is done. Note that when the toner material solution is dropped, the aqueous dispersion medium and / or the toner material solution may be heated.
Thereafter, the obtained aqueous emulsion is heated or placed in a reduced-pressure atmosphere to remove at least part of the solvent contained in the dispersoid, and the dispersoid (fine particles) composed of the toner material is dispersed. An aqueous dispersion is obtained.

The content of the dispersoid 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 (liquid developer) can be made particularly excellent while more surely preventing unintentional aggregation of dispersoids in the aqueous dispersion.
The average particle size of the dispersoid in the aqueous dispersion is not particularly limited, but is preferably 0.01 to 3 μm, and more preferably 0.1 to 2 μm. Thereby, the size of the toner particles finally obtained can be optimized. In the present specification, “average particle diameter” refers to an average particle diameter based on volume.

(Association particle formation process)
Next, an electrolyte is added to the aqueous dispersion obtained as described above, and the dispersoid is associated to form associated particles (associated particle forming step).
Examples of the electrolyte to be added include acidic substances such as hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, and oxalic acid, sodium sulfate, ammonium sulfate, potassium sulfate, magnesium sulfate, sodium phosphate, sodium dihydrogen phosphate, sodium chloride, and chloride. Organic and inorganic water-soluble salts such as potassium, ammonium chloride, calcium chloride, and sodium acetate can be used, and one or more of these can be used in combination. Among these, monovalent cation sulfates such as sodium sulfate and ammonium sulfate can be suitably used for promoting uniform association.
In addition, before adding electrolyte etc., you may add inorganic dispersion stabilizers, such as a hydroxyapatite, and an ionic and nonionic surfactant as a dispersion stabilizer. By adding an electrolyte in the presence of a dispersion stabilizer (emulsifier), non-uniform association can be prevented.

  Examples of such a dispersion stabilizer include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene Examples include ethylene sorbitan fatty acid esters, various pluronic nonionic surfactants, alkyl sulfate salt type anionic surfactants, quaternary ammonium salt type cationic surfactants, and the like. Among these, anionic and nonionic surfactants are effective in dispersion stability even when added in a small amount, and can be suitably used. The cloud point of the nonionic surfactant is preferably 40 ° C. or higher.

The amount of the electrolyte added is preferably 0.5 to 15 parts by weight, more preferably 1 to 12 parts by weight, with respect to 100 parts by weight of the solid content in the aqueous dispersion. More preferably. When the amount of electrolyte added is less than the lower limit, dispersoid association may not proceed sufficiently. Further, when the amount of electrolyte added exceeds the upper limit, dispersoids are not uniformly associated with each other and coarse particles may be generated, and there is a possibility that the size of finally obtained toner particles may vary. is there.
Then, after associating, the associated particles are obtained by filtration, washing, drying and the like.
The average particle size of the obtained associated particles is preferably 0.1 to 7 μm, and more preferably 0.5 to 3 μm. Thereby, the particle diameter of the toner particles finally obtained can be made moderate.

[Crushing process]
Next, the associated particles obtained as described above are crushed in an insulating liquid containing a fatty acid monoester, a fatty acid aliphatic hydrocarbon liquid and / or silicone oil (a pulverizing step). Thereby, a liquid developer in which toner particles are dispersed in an insulating liquid is obtained.
The toner particles obtained by such a method have irregularities derived from the fine particles (dispersoid) on the surface thereof, so that the fatty acid monoester can be reliably held in the irregularities.

Further, since the particles are crushed in the insulating liquid, it is possible to prevent the generation of toner particles coarsened due to aggregation or the like.
Further, in the present embodiment, toner particles are obtained by crushing the associated particles, so that fine particles (particles extremely smaller than particles of a target size) are obtained as compared with conventional pulverization methods and wet pulverization methods. Generation | occurrence | production can be prevented effectively. As a result, it is possible to effectively prevent a decrease in charging characteristics of the liquid developer due to fine powder.

In addition, since the insulating liquid has a relatively low viscosity, it easily enters between the fine particles (dispersoid) constituting the associated particles, and the associated particles can be suitably crushed.
Moreover, you may crush using a part of insulating liquid. In this case, after crushing, the same liquid as that used for crushing may be added as an insulating liquid, or after crushing, a liquid different from the liquid used for crushing may be added. It 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.

Next, a preferred embodiment of the image forming apparatus to which the liquid developer of the present invention as described above is applied will be described.
FIG. 1 is a diagram showing an example of a contact-type image forming apparatus to which the liquid developer of the present invention is applied.
The image forming apparatus P1 includes a developer container (liquid developer storage unit) P11 that stores liquid developer, a cylindrical photosensitive member (developing unit) P2 that develops an image (toner image), and a developer container P11. A developing device P10 for supplying a liquid developer to the photosensitive member P2, an intermediate transfer roller (transfer portion) P18 for transferring an image developed on the photosensitive member P2 to a recording medium, and a fixing device (fixing portion) F40 described in detail later. And have.

The photoreceptor P2 has a surface coated with a material such as amorphous silicon. As a result, the deterioration of the member due to the insulating liquid in the liquid developer can be minimized, so that the life of the photoreceptor P2 can be further extended, and the development accuracy on the recording medium is high. Can be maintained longer.
The surface of the photoreceptor P2 is uniformly charged by the charger P3, and then subjected to exposure P4 according to information to be recorded by a laser diode or the like, whereby an electrostatic latent image is formed. .

The developing device P10 has a coating roller P12 partly immersed in a developer container P11 and a developing roller P13.
The application roller P12 is, for example, a metal gravure roll such as stainless steel or brass. As a result, the deterioration of the member due to the insulating liquid in the liquid developer can be minimized, so that the life of the application roller P12 can be further extended, and the development accuracy to the recording medium is high. Can be maintained longer.
The application roller P12 rotates to face the developing roller P13.
Further, a liquid developer coating layer P14 is formed on the surface of the coating roller P12, and the thickness thereof is kept constant by the metering blade P15.
Then, the liquid developer is transferred from the coating roller P12 to the developing roller P13.

The developing roller P13 has a low hardness silicone rubber layer on a roller core P16 made of metal such as stainless steel, and the outermost layer is made of conductive PFA (polytetrafluoroethylene-perfluorovinyl ether copolymer) or the like. A configured fluororesin layer is formed. By having a layer made of such a material as the outermost layer, deterioration of the member due to the insulating liquid in the liquid developer can be minimized, so that the life of the developing roller P13 is extended. In addition, the development accuracy on the recording medium can be maintained for a longer time with high accuracy.
Further, the developing roller P13 rotates at the same speed as the photoconductor P2, and transfers the liquid developer to the latent image portion.

The liquid developer remaining on the developing roller P13 after being transferred to the photoreceptor P2 is removed by the developing roller cleaning blade P17 and collected into the developer container P11.
Further, after the transfer of the toner image from the photoreceptor P2 to the intermediate transfer roller P18, the photoreceptor P2 is neutralized by the neutralizing light P21, and the transfer residual toner remaining on the photoreceptor P2 is urethane rubber or the like. It is removed by the constituted cleaning blade P22.

Similarly, untransferred toner remaining on the intermediate transfer roller P18 after being transferred from the intermediate transfer roller P18 (transfer portion) to the recording medium F5 is removed by a cleaning blade P23 made of urethane rubber or the like.
After the toner image formed on the photoreceptor P2 is transferred to the intermediate transfer roller P18, a transfer current is applied to the secondary transfer roller P19, and the recording medium F5 such as paper passing between the two is applied to the recording medium F5. The image is transferred.
Thereafter, the toner image (transfer image) transferred onto the recording medium F5 such as paper is conveyed to a fixing device (fixing unit) F40, which will be described later, and is fixed.

FIG. 2 is a diagram illustrating an example of a non-contact image forming apparatus.
In the non-contact method, the developing roller P13 is provided with a charging blade P24 made of a phosphor bronze plate.
The charging blade P24 has a function of making frictional charging in contact with the liquid developer layer, and since the application roller P12 is a gravure roll, a developer layer corresponding to the unevenness of the surface of the gravure roll is formed on the development roller P13. Therefore, it functions to uniformly level the unevenness, and the arrangement direction may be either the counter direction or the trail direction with respect to the rotation direction of the developing roller, and may be a roller shape instead of a brate shape.

Further, an interval of 200 μm to 800 μm is provided between the developing roller P13 and the photosensitive member P2, and a frequency of 500 to 3000 Vpp superimposed on a DC voltage of 200 to 800 V and a frequency between the developing roller P13 and the photosensitive member P2. An AC voltage of 50 to 3000 Hz is preferably applied. The rest is the same as the image forming apparatus described with reference to FIG.
In FIGS. 1 and 2, the image formation using one color liquid developer has been described. However, when forming an image using a plurality of color toners, each color image is formed using a plurality of color developing devices. Thus, a color image can be formed.

FIG. 3 is a diagram illustrating an example of the fixing device.
The fixing device (fixing unit) F40 fixes the unfixed toner image F5a formed in the developing unit P2, the transfer unit P18, etc. on the recording medium F5.
As shown in FIG. 3, the fixing device F40 includes a heat fixing roller F1, a pressure roller F2, a heat-resistant belt F3, a belt stretching member F4, a cleaning member F6, a frame F7, and an ultraviolet irradiation means F8. And a spring F9.

The heat fixing roller (fixing roller) F1 includes a roller base material F1b made of a pipe material, an elastic body F1c covering the outer periphery thereof, and a columnar halogen lamp F1a as a heating source inside the roller base material F1b. It can be rotated counterclockwise as indicated by an arrow in the figure.
Further, the pressure roller F2 has a roller base material F2b made of a pipe material and an elastic body F2c covering the outer periphery thereof, and is rotatable in the clockwise direction indicated by an arrow in the drawing.

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

  In addition, two columnar halogen lamps F1a and F1a constituting a heating source are built in the heat fixing roller F1, and the heating elements of these columnar halogen lamps F1a and F1a are arranged at different positions. Yes. Then, by selectively lighting each columnar halogen lamp F1a, F1a, a fixing nip portion where a heat-resistant belt F3, which will be described later, is wound around the heat-fixing roller F1, and a belt stretching member F4, which will be described later, are attached to the heat-fixing roller F1. The temperature controller is easily performed under different conditions from the sliding contact portion, different conditions between the wide recording medium and the narrow recording medium, or the like.

  The pressure roller F2 is disposed so as to face the heat fixing roller F1, and is configured to apply pressure to a recording medium F5 on which an unfixed toner image is formed via a heat-resistant belt F3 described later. ing. By applying pressure, the insulating liquid as described above can be more efficiently permeated into the recording medium F5. As a result, the unsaturated fatty acid component contained in the insulating liquid can be more reliably cured inside the recording medium F5 by heat, ultraviolet irradiation, which will be described later, and the toner image F5a is more formed on the recording medium F5 by the anchor effect. It can be firmly fixed.

Further, the pressure roller F2 has a roller base material F2b made of a pipe material and an elastic body F2c covering the outer periphery thereof, and is rotatable in the clockwise direction indicated by an arrow in the drawing.
The aforementioned elastic body F1c of the heat fixing roller F1 and the elastic body F2c of the pressure roller F2 are subjected to substantially uniform elastic deformation to form a so-called horizontal nip. Further, since there is no difference in the conveyance speed of the heat-resistant belt F3 or the recording medium F5 described later with respect to the peripheral speed of the heat fixing roller F1, extremely stable image fixing can be performed.

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

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

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

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

  The ultraviolet irradiation means F8 has a function of irradiating the surface of the recording medium F5 ejected as described above on which the toner image F5a is formed with ultraviolet rays. With such a configuration, the unsaturated fatty acid component contained in the fatty acid monoester can be solidified more strongly by heat and ultraviolet irradiation, and as a result, the toner particles can be more firmly fixed on the recording medium. be able to. Further, since the toner particles can be firmly fixed on the recording medium without being heated to a particularly high temperature by the heat fixing roller F1 due to the irradiation of ultraviolet rays, the effect of using the liquid developer of the present invention can be obtained. Due to this synergistic effect, the toner particles can be fixed to the recording medium at a lower temperature and at a higher speed, and the toner particles can be more firmly fixed to the recording medium. Furthermore, since a large amount of heat is not required for fixing, the toner particles can be sufficiently fixed on the recording medium by irradiation with ultraviolet rays even if the time for passing through the fixing nip is relatively short. That is, since fixing does not take time, the printing speed can be further increased. Further, since a large amount of heat is not required for fixing, energy saving can be achieved. As a result, an environmentally friendly fixing device can be provided.

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

  In order to stably drive the heat-resistant belt F3 by the pressure roller F2 and the belt stretching member F4 and stably drive the pressure roller F2, the friction coefficient between the pressure roller F2 and the heat-resistant belt F3 is determined by the belt tension. It is good to set larger than the friction coefficient of the frame member F4 and the heat-resistant belt F3. However, the friction coefficient is such that foreign matter enters between the heat-resistant belt F3 and the pressure roller F2 or between the heat-resistant belt F3 and the belt stretching member F4, or the heat-resistant belt F3, the pressure roller F2, and the belt stretching member. It may become unstable due to wear of the contact portion with F4.

  Therefore, the belt tension member F4 and the heat-resistant belt F3 have a winding angle smaller than the winding angle of the pressure roller F2 and the heat-resistant belt F3, and the diameter of the belt stretching member F4 is smaller than the diameter of the pressure roller F2. Set as follows. As a result, the length that the heat-resistant belt F3 slides on the belt stretching member F4 is shortened, which can be avoided from instability factors such as changes with time and disturbances, and the heat-resistant belt F3 is driven stably by the pressure roller F2. Will be able to.

  The time required for the toner particles to pass through the fixing nip portion (nip time) is preferably 0.02 to 0.2 seconds, and more preferably 0.03 to 0.1 seconds. Even when the time required for the toner particles to pass through the fixing nip portion is such a short time, the liquid developer of the present invention as described above can be sufficiently fixed, and the printing speed can be reduced. Further speedup can be achieved.

  Specifically, the heat (fixing temperature) applied by the heat fixing roller F1 is preferably 80 to 200 ° C, and more preferably 100 to 180 ° C. When the fixing temperature is within the above range, the fatty acid monoester can suitably plasticize the toner particles. Moreover, the oxidative polymerization reaction (curing reaction) of the unsaturated fatty acid component contained in the fatty acid monoester can be more effectively advanced. Further, when the above-described antioxidant is included, the antioxidant can be easily decomposed, and the fixing strength of the toner particles can be improved more effectively. In addition, this tendency is more prominent when an oxidation polymerization accelerator is contained in the liquid developer.

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 the one manufactured by the method described above, and may be manufactured by any method. For example, in the above-described embodiment, it has been described that an aqueous dispersion liquid is obtained and an association particle is obtained by adding an electrolyte to the aqueous emulsion liquid. However, the present invention is not limited to this. For example, associating particles are prepared by dispersing a colorant, a monomer, a surfactant, and a polymerization initiator in an aqueous liquid, preparing an aqueous dispersion by emulsion polymerization, and adding an electrolyte to the aqueous dispersion to be associated. It may be prepared using an emulsion polymerization association method, or may be obtained by, for example, spray-drying the obtained aqueous dispersion to obtain associated particles. Further, for example, a liquid developer may be obtained by pulverizing a toner material obtained by melting and kneading a pigment, a resin material, or the like in an insulating liquid.

Further, the liquid developer of the present invention is not limited to those applied to the image forming apparatus as described above.
The fatty acid monoester used in the present invention may be chemically synthesized (artificially synthesized).
Further, the image forming apparatus applied to the liquid developer of the present invention is not limited to the above-described configuration, and may have a different configuration. Further, the materials constituting each part of the image forming apparatus are not limited to those described above.

[1] Production of liquid developer (Example 1)
<Preparation of liquid constituting insulating liquid>
A liquid containing fatty acid methyl ester used as the insulating liquid was prepared as follows.

First, crude soybean oil was purified as follows to obtain purified soybean oil.
First, crude soybean oil was roughly purified by a low temperature crystallization method using methanol, diethyl ether, petroleum ether, acetone or the like as a solvent.
Next, 300 parts by volume of roughly refined crude soybean oil (first roughly refined oil) was put into the flask, and then 100 parts by volume of boiled water was poured into the flask, and the flask was stoppered.

Next, the flask was shaken, and the above-described crude soybean oil (first crudely refined oil) and boiled water were mixed.
Next, the flask was allowed to stand until the mixed liquid in the flask was separated into three layers.
After complete separation was confirmed, the flask was transferred to a freezer and left for 24 hours.
Thereafter, the components that were not frozen were transferred to another flask.
The same operation as described above was repeated for the unfrozen component, and the obtained non-frozen component was taken out to obtain a crude oil (second crude oil).

Next, in the flask, the crude oil and fat (second crude oil) obtained as described above: 100 parts by volume and active clay mainly composed of hydrous aluminum silicate: 35 parts by volume were mixed. Stir.
Next, the obtained mixture was stored under pressure (0.18 MPa) for 48 hours to completely precipitate the activated clay.
Thereafter, the precipitate was removed to obtain refined soybean oil (hereinafter simply referred to as soybean oil). In addition, the fatty acid glyceride which has linoleic acid as a main component was contained in soybean oil, and the unsaturated fatty acid glyceride in soybean oil was 98 wt%. Moreover, the linoleic acid component was 53 mol% of the total fatty acid components.

  Next, a transesterification reaction between a part of the soybean oil and methanol was performed, and glycerin generated by this reaction was removed to obtain a liquid mainly composed of fatty acid monoesters. Further, by purifying this liquid, soybean oil fatty acid methyl having a fatty acid monoester content of 99.9 wt% or more was obtained. Fatty acid monoesters thus obtained are mainly unsaturated fatty acid monoesters such as methyl oleate, methyl linoleate and methyl α-linolenate, and saturated fatty acid monoesters such as methyl palmitate and methyl stearate. Of which unsaturated fatty acid monoesters accounted for 84%.

<Preparation of colorant master solution>
First, a polyester resin (softening temperature: 125 ° C., glass transition point: 60.5 ° C., acid value: 7.7) and a cyan pigment as a colorant (Pigment Blue 15: 3, manufactured by Dainichi Seika Co., Ltd.) The mixture (mass ratio 50:50) 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 product cooled as described above was coarsely pulverized to obtain a powder having an average particle size of 1.0 mm or less. A hammer mill was used for coarse pulverization of the kneaded product.
Methyl ethyl ketone was added to the obtained kneaded powder so that the solid content was 30% by mass, and wet dispersion was performed with an Eiger motor mill (manufactured by Eiger, USA: M-1000) to prepare a colorant master solution.

<Preparation of resin solution>
200 parts by weight of methyl ethyl ketone and 73 parts by weight of the polyester resin were added to 33 parts by weight of the colorant master solution, and the mixture was mixed with an Eiger motor mill (manufactured by Eiger, USA: M-1000) to prepare a resin solution. In this solution, the pigment was uniformly finely dispersed.

<Preparation of aqueous emulsion>
500 parts by weight of the above resin liquid and 45.5 parts by weight of methyl ethyl ketone were placed in a cylindrical 2 L separable flask having a Max blend stirring blade, and the solid content of the resin liquid was 55%.
Next, 11.7 ammonia water: 41.7 parts by weight (the molar equivalent ratio with respect to the total amount of carboxyl groups of the polyester resin is 1.1) is added to the resin liquid in the flask, and three-one motor (manufactured by Shinto Kagaku Co., Ltd.) is used. The rotation speed of the stirring blade was set to 210 rpm (peripheral speed of stirring blade: 0.71 m / s), and the mixture was sufficiently stirred, and then 133 parts by weight of deionized water was added while maintaining stirring. While adjusting the temperature of the solution in the flask to 25 ° C. and continuing stirring, 133 parts by weight of deionized water was dropped into the resin liquid to cause phase inversion emulsification, and the dispersoid containing the resin material was dispersed. An aqueous emulsion was obtained.

<Production of associated particles by association>
Next, while continuing stirring in the flask, 285 parts by weight of deionized water was added to the aqueous emulsion so that the total amount of 1N ammonia water and water was 593 parts by weight. Subsequently, 2.6 parts by weight of Emul 0 (manufactured by Kao Corporation), which is an anionic emulsifier, was diluted to 30 parts by weight of deionized water and added to the aqueous emulsion.
Thereafter, while maintaining the temperature of the aqueous emulsion at 25 ° C., the rotation speed of stirring was 150 rpm (peripheral speed of stirring blade: 0.54 m / s), and 3.5% ammonium sulfate aqueous solution: 300 parts by weight was dropped. The particle size of the dispersoid aggregate was 3.5 μm. After dropping, stirring was continued until the particle size of the dispersoid aggregates grew to 5.0 μm, and the association operation was completed.

The resulting aggregate dispersion was dried by distilling off the organic solvent under reduced pressure to obtain associated particles.
In addition, the average particle diameter of each particle in each example and comparative example is a volume-based average particle diameter, and the average particle diameter and particle size distribution of these particles are obtained from a Mastersizer 2000 particle analyzer (manufactured by Malvern Instruments Ltd.). And measured.

<Preparation of liquid developer>
Associated particles obtained by the above method: 40 parts by weight, methyl soybean oil fatty acid: 60 parts by weight, Cosmo White P-60 as an aliphatic hydrocarbon liquid (Idemitsu Kosan Co., Ltd., viscosity: about 15 mPa.s): 100 parts by weight Part, polyamine aliphatic polycondensate (manufactured by Nippon Lubrizol, trade name “Solsperse 11200”): 1 part by weight and aluminum stearate (manufactured by Nippon Oil & Fats): 0.5 part by weight ceramic pot (internal volume 600 ml) Further, zirconia balls (ball diameter: 1 mm) were put in a ceramic pot so that the volume filling rate was 30%. Crushing was performed for 200 hours at a rotational speed of 220 rpm (1 / min) using a desktop pot mill, and the dispersion in the pot was separated from the zirconia balls to obtain a liquid developer.
The average particle size of the toner particles in the obtained liquid developer was 1.5 μm, and the standard deviation of the particle size between the toner particles was 0.49 μm. Moreover, the viscosity of the liquid developer measured according to JIS Z8809 using a vibration viscometer at 25 ° C. was 288 mPa · s. Further, the electric resistance of the liquid developer was 1.06 × 10 ¹³ Ωcm.

(Example 2)
As an insulating liquid, KF96 (made by Shin-Etsu Silicone, viscosity: 100 mPa · s), which is a silicone oil, is used instead of Cosmo White P-60, and a polyester resin (softening temperature: 116 ° C., glass transition point: 61 ° C.) as a resin material. , Acid value: 9.0) was used in the same manner as in Example 1 to prepare a liquid developer.

(Example 3)
As vegetable oil, rapeseed oil was used instead of soybean oil, and in the same manner as in Example 1, rapeseed oil fatty acid methyl having a fatty acid monoester content of 99.9 wt% or more was prepared. The fatty acid monoesters thus obtained were mainly composed of unsaturated fatty acid monoesters such as methyl oleate and methyl linoleate and saturated fatty acid monoesters such as methyl palmitate and methyl stearate. Of these, unsaturated fatty acid fatty acid monoesters accounted for 83%.
Hereinafter, liquid development was performed in the same manner as in Example 1 except that polyester resin (softening temperature: 98 ° C., glass transition point: 43 ° C.) was used as the resin material, and rapeseed oil fatty acid methyl was used instead of soybean oil fatty acid methyl. An agent was produced.
(Examples 4 to 15)
A liquid developer was produced in the same manner as in Example 1 except that the resin material and the insulating liquid were changed to have the configuration shown in Table 2.

(Comparative Example 1)
A polyester resin (softening temperature: 75 ° C., glass transition point: 12 ° C.) was used as the resin material, and a colorant master was prepared using a biaxial kneading extruder under the same conditions as in Example 1. In the obtained colorant master, the pigment and the resin material were not uniformly dispersed. For this reason, the same material was used and kneaded using an open roll type kneader (Niedex, manufactured by Mitsui Mining Co., Ltd.) to obtain a colorant master.
Thereafter, a liquid developer was produced in the same manner as in Example 1 except that the insulating liquid was changed to have the configuration shown in Table 2.
(Comparative Examples 2 to 4)
A liquid developer was produced in the same manner as in Example 1 except that the resin material and the insulating liquid were changed to have the configuration shown in Table 2.

Table 1 shows the configuration of the liquid developer and the evaluation results of the viscosity and the electrical resistance for each of the above Examples and Comparative Examples. In addition, evaluation of the viscosity in Table 1 was performed on the conditions of the measurement temperature of 25 degreeC using the vibration type viscometer (CBC Co., Ltd. product VM-100A) based on JISZ8809. In Table 1, the content of the fatty acid monoester component in the insulating liquid is X [wt%], and the content of the silicone oil and / or hydrocarbon liquid in the insulating liquid is Z [wt%]. The value of X / Z is also shown. In the table, the polyester resin is represented by PEs, and the styrene-acrylate copolymer is represented by st-ac. In addition, the product made from Lion Corporation was used for methyl laurate, methyl caprylate, methyl caprate, and methyl myristate. Cosmo White P-70 is manufactured by Cosmo Oil Lubricants, Dynafresia W-8 is manufactured by Idemitsu Kosan Co., Ltd., Isopar H, and Isopar G are manufactured by Exxon.
In addition, the viscosity and electrical resistance of the insulating liquid in Table 1 are expressed according to the following four-stage criteria.

<Viscosity>
A: 150 mPa · s or more and 800 mPa · s or less.
A: 100 mPa · s or more and 900 mPa · s or less. (Except 150mPa · s to 800mPa · s)
○: 50 mPa · s or more and 1000 mPa · s or less. (Except 100mPa · s to 900mPa · s)
X: Less than 50 mPa · s or more than 1000 mPa · s.

<Electrical resistance>
A: 1 × 10 ¹³ Ωcm or more.
○: 1 × 10 ¹¹ Ωcm or more and less than 1 × 10 ¹³ Ωcm.
Δ: 1 × 10 ⁹ Ωcm or more and less than 1 × 10 ¹¹ Ωcm.
×: Less than 1 × 10 ⁹ Ωcm.

[2] Evaluation Each liquid developer obtained as described above was evaluated for fixing strength, adaptability to image formation at high speed, storage stability, and long-term stability.
[2.1] Fixing Strength Using an image forming apparatus as shown in FIG. 4, an image of a predetermined pattern with a liquid developer obtained in each of the above examples and each of the comparative examples was recorded on a recording paper (manufactured by Seiko Epson Corporation, It was formed on fine paper LPCPPA4). Thereafter, the image formed on the recording paper was thermally fixed by an oven. This heat fixing was performed under the condition of 110 ° C. × 1 minute.
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.) with a pressing load of 1.0 kgf twice, and the remaining ratio of image density Was measured by “X-Rite model 404” manufactured by X-Rite Inc, and evaluated according to the following five-step criteria.

A: Image density residual ratio is 95% or more.
A: Image density residual ratio is 90% or more and less than 95%.
○: Image density remaining rate is 80% or more and less than 90%.
Δ: Image density remaining rate is 70% or more and less than 80%.
X: Image density remaining rate is less than 70%.

[2.2] Evaluation of image formation at high speed With a liquid developing type electrophotographic image forming apparatus as shown in FIG. 4, the heat fixing roll is set at a set temperature of 110 ° C. and a printing speed of 60 sheets / min The degree of image defects such as blurring in the formed image was visually evaluated, and the image density of the formed image was evaluated according to the following four-stage criteria.

<Image defects such as blurring>
A: Image defects such as fading are not recognized at all in the formed image.
○: Image defects such as blurring are hardly observed in the formed image.
Δ: Image defects such as blurring are slightly observed in the formed image.
X: Image defects such as blurring are clearly recognized in the formed image.
<Image density>
A: Image density: 1.6 or more B: Image density: 1.2 or more and less than 1.6 Δ: Image density: 0.8 or more and less than 1.2 ×: Image density: less than 0.8

[2.3] Preservability The liquid developers obtained in the respective Examples and Comparative Examples were allowed to stand for 8 months in an environment at a temperature of 20 to 28 ° C. Thereafter, the state of the toner in the liquid developer was visually confirmed and evaluated according to the following five criteria.
A: No toner particle floating or coagulation sedimentation is observed.
A: Floating toner particles and coagulation sedimentation are hardly observed.
○: Slight floating or coagulation sedimentation of toner particles is observed, but as a liquid developer
There is no problem.
Δ: Floating or coagulating sedimentation of toner particles is clearly observed.
X: Remarkably floating and coagulating sedimentation of toner particles are observed.

[2.4] Long-term stability The liquid developers obtained in the above Examples and Comparative Examples were allowed to stand for 10 months in an environment of 35 ° C. and a relative humidity of 70%. Thereafter, the state of the liquid developer was observed and evaluated according to the following five-step criteria.
A: No thickening / discoloration of the liquid developer is observed.
A: Viscosity / discoloration of the liquid developer is hardly recognized.
○: Slight thickening / discoloration of liquid developer is observed, but no problem as liquid developer
It is the range.
Δ: Thickening / discoloration of the liquid developer is clearly recognized.
X: The thickening / discoloration of the liquid developer is noticeable.
These results are shown in Table 2 together with the toner particle number-based average particle size and particle size standard deviation.

As is clear from Table 2, the liquid developer of the present invention was excellent in low-temperature fixability and excellent in fixing strength. Further, the liquid developer of the present invention was excellent in adaptability to high-speed image formation. Furthermore, as shown in Table 2, the storage stability and long-term stability were also excellent.
Further, in the evaluation of the fixing strength, the fixing temperature was changed to 100 ° C., 95 ° C., 90 ° C., 85 ° C., and 80 ° C., and the fixing strength was evaluated in the same manner as described above, and similar results were obtained. This also shows that the liquid developer of the present invention is suitable for low-temperature fixing.

In the image formation evaluation at high speed, the conveyance speed of the recording medium of the fixing device was increased from 60 sheets / minute to 70 sheets / minute and 80 sheets / minute, and the fixing strength was evaluated in the same manner as described above. Similar results were obtained. This also shows that the liquid developer of the present invention is suitable for high-speed printing.
On the other hand, satisfactory results were not obtained with the liquid developers of the comparative examples.

Further, the liquid developers of Examples 1 and 2 and Comparative Example 1 were sealed and stored in an environment of 55 ° C. for 12 hours. In the liquid developers of Examples 1 and 2, toner particle aggregation was not observed. On the other hand, in the liquid developer of Comparative Example 1, toner particles aggregated, and the aggregate could not be redispersed even when stirred.
In addition, the liquid developer was manufactured and evaluated in the same manner as described above except that Pigment Red 122, Pigment Yellow 180, and Carbon Black (Printex L, manufactured by Degussa) were used as the colorant instead of the cyan pigment. As a result, the same result as above was obtained.

1 is a cross-sectional view illustrating an example of a contact-type image forming apparatus according to the present invention. 1 is a cross-sectional view illustrating an example of a non-contact type image forming apparatus of the present invention. 1 is a cross-sectional view illustrating an example of a fixing device applied to an image forming apparatus of the present invention.

Explanation of symbols

P1 ... Image forming apparatus P2 ... Photoconductor P3 ... Charger P4 ... Exposure P10 ... Developer P11 ... Developer container P12 ... Application roller P13 ... Development roller P14 ... Liquid developer application layer P15 ... Metering blade P16 ... Roller core P17 ... developing roller cleaning blade P18 ... intermediate transfer roller P19 ... secondary transfer roller P21 ... static light P22 ... cleaning blade P23 ... cleaning blade P24 ... charging blade F40 ... fixing device F1 ... heat fixing roller (heating roller) F1a ... column-shaped halogen Lamp F1b ... Roller base material F1c ... Elastic body F2 ... Pressure roller F2a ... Rotating shaft F2b ... Roller base material F2c ... Elastic body F3 ... Heat-resistant belt F4 ... Belt stretch member F4a ... Projection wall F4f ... Recess F5 ... Recording medium F5a ... toner image 6 ... cleaning member F7 ... frame F8 ... ultraviolet radiation means F9 ... Spring

Claims (7)

In the insulating liquid, toner particles mainly composed of a resin material are dispersed,
The insulating liquid includes a fatty acid monoester, an aliphatic hydrocarbon and / or silicone oil,
The liquid developer, wherein the resin material has a glass transition point Tg of 15 to 70 ° C. and a softening temperature Tf of 80 to 140 ° C.   When the content of the fatty acid monoester in the insulating liquid is X [wt%] and the total content of the aliphatic hydrocarbon liquid and the silicone oil is Z [wt%], 0.1 ≦ The liquid developer according to claim 1, wherein a relationship of X / Z ≦ 1.0 is satisfied.   The liquid developer according to claim 1, wherein the resin material is a polyester resin.   The liquid developer according to claim 1, wherein the fatty acid monoester contains a saturated fatty acid as a fatty acid component.   The liquid developer according to any one of claims 1 to 4, wherein the fatty acid monoester contains a monoester of a saturated fatty acid having 8 to 16 carbon atoms and an alcohol having 1 to 4 carbon atoms.   The liquid developer according to any one of claims 1 to 5, wherein a viscosity measured in accordance with JIS Z8809 using a vibration viscometer at 25 ° C is 50 to 1000 mPa · s. A liquid developer reservoir for storing the liquid developer;
A developing unit for developing using the liquid developer supplied from the liquid developer storage unit;
A transfer unit that transfers the image formed by the developing unit onto a recording medium and forms a transfer image;
A fixing unit for fixing the transfer image formed on the recording medium onto the recording medium,
In the liquid developer, toner particles mainly composed of a resin material are dispersed in an insulating liquid. The insulating liquid includes a fatty acid monoester, an aliphatic hydrocarbon liquid, and / or a silicone oil. And the resin material has a glass transition point Tg of 15 to 70 ° C. and a softening temperature Tf of 80 to 140 ° C.

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