JP2008310184A - Liquid developer, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developer having excellent dispersibility of toner particles, and further having excellent charging properties of positive electrification, and to provide an image forming apparatus using the same. <P>SOLUTION: The liquid developer comprises: an insulating liquid; toner particles mainly composed of a polyester resin; and a dispersant expressed by general formula (I). The content of the dispersant is preferably controlled to 1.0 to 10 pts.wt. to 100 pts.wt. of the toner particles; wherein, n denotes the integer of 5 to 8; R denotes -OH; and R' denotes H- or CH<SB>3</SB>(CH<SB>2</SB>)<SB>16</SB>CO-. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

As a developer used to develop the electrostatic latent image formed on the latent image carrier, a toner composed of a material containing a colorant such as a pigment and a binder resin is used as an electrically insulating carrier liquid (insulating property). Liquid developers dispersed in (liquid) are known.
In general, a polyester resin is widely used as a binder resin used for toner particles constituting such a liquid developer. The polyester resin has high transparency, and when used as a binder resin, it has characteristics that the resulting image has good color developability and high fixing characteristics.

By the way, examples of the liquid developer include a negatively chargeable liquid developer and a positively chargeable liquid developer. When a negatively chargeable liquid developer is used, an image forming apparatus is used for image formation. Ozone is generated inside, causing problems such as environmental problems and adverse effects on peripheral components in the image forming apparatus.
Therefore, in recent years, since it is possible to perform image formation by reducing the amount of discharge products such as ozone, development of a method for forming an image using a positively chargeable liquid developer has been promoted (for example, Patent Document 1).
However, since the polyester resin itself is generally of a negative chargeability, it has been difficult to apply it to positively chargeable toner particles (liquid developer). In addition, it is conceivable to add a charge control agent to toner particles that use a polyester resin as a binder resin for positive charging, but it is difficult to obtain a sufficient charge amount.

JP 2002-214849 A

  An object of the present invention is to provide a liquid developer having excellent dispersibility of toner particles and excellent positive charging characteristics, and to provide an image forming apparatus using the liquid developer.

（ただし、ｎは５〜８の整数、Ｒは−ＯＨ、Ｒ’はＨ−またはＣＨ_３（ＣＨ_２）_１６ＣＯ−である。） 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 polyester resin;
And a dispersant represented by the following general formula (I).

(Where, n is 5-8 integer, R represents -OH, R 'is H- or _CH 3 _{(CH 2)} 16 is a CO-.)

In the liquid developer of the present invention, the content of the dispersant is preferably 1.0 to 10 parts by weight with respect to 100 parts by weight of the toner particles.
In the liquid developer of the present invention, the shape factor SF1 of the toner particles represented by the following formula (II) is 100 to 130,
The shape factor SF2 of the toner particles represented by the following formula (III) is preferably 110 to 150.
SF1 = {(ML) ² / A} × (100π / 4) (II)
SF2 = {(CL) ² / A} × (100 / 4π) (III)
(However, A [μm ² ] is the area of a figure formed by projecting toner particles on a two-dimensional plane, and ML [μm] and CL [μm] are the maximum length and circumference of the figure, respectively. is there.)

In the liquid developer of the present invention, it is preferable that the insulating liquid contains a fatty acid monoester.
In the liquid developer of the present invention, the content of the fatty acid monoester in the insulating liquid is preferably 1.0 to 50 wt%.
In the liquid developer of the present invention, the acid value of the polyester resin is preferably 5-15.
In the liquid developer of the present invention, a step of associating fine particles mainly composed of a polyester resin to obtain associated particles;
It is preferable that the insulating liquid is produced using a method having a step of pulverizing the associated particles in the presence of the dispersant in at least a part of the insulating liquid.

（ただし、ｎは５〜８の整数、Ｒは−ＯＨ、Ｒ’はＨ−またはＣＨ_３（ＣＨ_２）_１６ＣＯ−である。） The image forming apparatus of the present invention includes a plurality of developing units that form the single-color image corresponding to each color using a plurality of liquid developers having different colors.
An intermediate transfer unit that sequentially transfers a plurality of the single-color images formed by the plurality of developing units, and forms an intermediate transfer image formed by superimposing the transferred single-color images;
A secondary transfer unit that transfers the intermediate transfer image to the recording medium and forms an unfixed color image on the recording medium;
A fixing unit for fixing the unfixed color image on the recording medium,
The liquid developer is an insulating liquid;
Toner particles mainly composed of polyester resin;
And a dispersant represented by the following general formula (I).

(Where, n is 5-8 integer, R represents -OH, R 'is H- or _CH 3 _{(CH 2)} 16 is a CO-.)

  By satisfying the above configuration, it is possible to provide a liquid developer having excellent toner particle dispersibility and excellent positive charging characteristics, and an image forming apparatus using such a liquid developer.

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. The liquid developer of the present invention includes a dispersant having a predetermined structure.
<Dispersant>
First, the dispersant will be described.
The liquid developer of the present invention contains a dispersant having a structure represented by the following general formula (I).

（ただし、ｎは５〜８の整数、Ｒは−ＯＨ、Ｒ’はＨ−またはＣＨ_３（ＣＨ_２）_１６ＣＯ−である。）

(Where, n is 5-8 integer, R represents -OH, R 'is H- or _CH 3 _{(CH 2)} 16 is a CO-.)

The dispersant has a positive charge characteristic (positive charge).
By the way, since the polyester resin itself is usually of a negative chargeability, it has been difficult to apply it to positively chargeable toner particles (liquid developer). In addition, it is conceivable to add a charge control agent to toner particles that use a polyester resin as a binder resin for positive charging, but it is difficult to obtain a sufficient charge amount.

On the other hand, in this invention, the following effects are acquired by including the above dispersing agents.
The dispersant represented by the general formula (I) as described above has an ester bond in the molecule. For this reason, the dispersant has a high affinity with the polyester resin constituting the toner particles, and further exhibits positive chargeability, and therefore easily adheres to the surface of the toner particles composed of the polyester resin exhibiting negative chargeability. It has properties. Furthermore, since the dispersant represented by the general formula (I) as described above has a relatively long molecular chain and has a branched chain, there are many opportunities for contact with the surface of the toner particles, and it adheres firmly. Or adsorb.

  Thus, the positively chargeable dispersant adheres to the surface of the toner particles, so that the negative charge caused by the polyester resin can be canceled and the toner particles can be positively charged positively. Further, since the dispersant adheres to the surface of the toner particles, the dispersant is interposed between adjacent toner particles, effectively preventing aggregation of the toner particles and the like, and the dispersibility of the toner particles is particularly good. Become. Further, since the toner particles are mainly composed of a polyester resin, an image obtained using the liquid developer of the present invention has excellent fixing characteristics.

Note that all of the dispersant does not have to be attached or adsorbed in the vicinity of the surface of the toner particles, as long as at least a part thereof is attached or adsorbed.
In the present invention, in the general formula (I), n may be an integer of 5 to 8, but is preferably 7 to 8. Thereby, the dispersant is easily entangled with the toner particles, and the effect of the present invention can be made more remarkable.

  The content of the dispersant in the liquid developer as described above is preferably 1 to 10 parts by weight, more preferably 2.5 to 10 parts by weight with respect to 100 parts by weight of the toner particles. More preferably, it is 0.0-10 weight part. When the content of the dispersing agent is in the above range, it is possible to further improve the charging characteristics of the positive charge while further improving the dispersibility of the toner particles.

<Toner particles>
Next, toner particles will be described.
[Component material of toner particles]
The toner particles include at least a binder resin (resin material) and a colorant.
1. Resin material (binder resin)
The toner particles are made of a material containing a resin material as a main component.

  In the present invention, the resin material is mainly composed of a polyester resin. The polyester resin has high transparency, and when used as a binder resin, it has characteristics that the resulting image has good color developability and high fixing characteristics. However, since the polyester resin is a component exhibiting negative chargeability as described above, toner particles composed of such polyester resin generally exhibit negative chargeability. In the present invention, by attaching the above-described dispersant to the surface of the toner particles, a liquid developer excellent in positive chargeability can be obtained while effectively exhibiting the above-described effects by using the polyester resin. be able to. In addition, it is preferable that content of the polyester resin in resin is 50 wt% or more, and it is more preferable that it is 80 wt% or more.

  The acid value of the polyester resin used in the present invention is preferably 5 to 15 KOHmg / g, and more preferably 5 to 10 KOHmg / g. Thereby, the dispersant as described above can be more effectively held on the surface of the toner base particles. On the other hand, when the acid value of the polyester resin is less than the lower limit, the dispersant is difficult to adhere to the surface of the toner particles, and aggregation of the toner particles may not be sufficiently prevented. On the other hand, when the acid value of the polyester resin exceeds the upper limit, the negative chargeability of the polyester resin becomes strong, and the desired positively charged characteristics may not be sufficiently obtained.

Although the softening temperature of a polyester resin is not specifically limited, It is preferable that it is 50-130 degreeC, It is more preferable that it is 50-120 degreeC, It is further more preferable that it is 60-115 degreeC. 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.
The toner particles may include a resin material other than the polyester resin as described above.

2. Colorant The toner may contain a colorant. The colorant is not particularly limited, and for example, known pigments and dyes can be used.
3. Other Components The toner may contain components other than those described above. Examples of such components include known waxes and magnetic powders.
In addition to the above materials, 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.

Further, the toner particles preferably have a shape factor SF1 of the toner particles represented by the following formula (II) of 100 to 130, more preferably 100 to 120, and more preferably 100 to 120. 110 is more preferable.
SF1 = {(ML) ² / A} × (100π / 4) (II)
However, as shown in FIG. 1A, A [μm ² ] is the area of a figure formed by projecting toner particles to be measured on a two-dimensional plane, and ML [μm] is the maximum length of the figure. It is. In the present invention, the SF1 of the toner particles is obtained as an average value obtained by observing 100 or more toner particles in the liquid developer at random.

  The shape factor SF1 is generally used as an index of the sphericity of the particle. The smaller the SF1, the closer the particle is to the sphere. The minimum value of SF1 is 100. At this time, the particles are true spheres. When the average SF1 of the toner particles is sufficiently small, the above-described dispersant is more likely to adhere to the surface of the toner particles. As a result, the toner particles can be more effectively prevented from aggregating with each other, and the positive charging characteristics of the liquid developer can be further improved. Even when toner particles are aggregated during reuse (recycling), the aggregate can be easily loosened by applying a weak external force by stirring or the like, and dispersed as toner particles in an insulating liquid. be able to. For this reason, the liquid developer is excellent in recyclability. Also, transfer and development are particularly good, and a clear image free from defects can be obtained reliably and easily.

  In addition, if the SF1 of the toner particles is sufficiently small as described above, the toner particles attached to the transfer roller, the developing roller in the developing unit, the photosensitive member, etc. are generally removed in an image forming apparatus as will be described later. In doing so, the toner particles are not suitably removed by the cleaning blade. However, in the present invention, since the SF2 of the toner particles is in the following range, the toner particles adhering to the developing roller, the photoreceptor and the like can be easily removed with a cleaning blade or the like.

The toner particles preferably have an average shape factor SF2 of the toner particles represented by the following formula (III) of 110 to 150, more preferably 110 to 140, and 110 to 130. More preferably.
SF2 = {(CL) ² / A} × (100 / 4π) (III)
However, as shown in FIG. 1B, A [μm ² ] is an area of a figure formed by projecting toner particles on a two-dimensional plane, and CL [μm] is a circumference of the figure. In the present invention, the SF2 of the toner particles is obtained as an average value obtained by observing 100 or more toner particles in the liquid developer at random.

  The shape factor SF2 is generally a value used as an index of the degree of unevenness on the surface of the particle. The smaller the SF2, the smoother the particle surface, and the larger the SF2, the more uneven the particle surface. Become. For this reason, when the average of the shape factor SF2 of the toner particles is within the above range, the toner particles have moderately minute irregularities. Therefore, the dispersant as described above can be reliably held on the surface, and the positive charging characteristics of the liquid developer and the dispersibility of the toner particles can be made particularly excellent. In addition, by having such moderately minute irregularities, it is possible to more effectively prevent the toner particles from contacting each other excessively while holding more dispersant on the particle surface. As a result, during storage, the toner particles can be easily prevented from aggregating while being easily dispersed in the insulating liquid. For this reason, the storage stability of the liquid developer can be improved. Further, the toner particles are easily caught by the blade during cleaning, and the remaining toner particles from the photosensitive member, the intermediate transfer member, and the like can be easily removed. For this reason, the liquid developer has excellent cleaning properties. Further, even when reused after cleaning, aggregation or the like can be suitably prevented. Further, it becomes easy to reuse the liquid developer remaining on the member after the image formation. Further, if the toner particles have minute irregularities, the surface area per volume of the toner particles is large, and the area where the toner particle surface is in contact with the dispersant as described above is large. For this reason, more dispersing agent can be hold | maintained on the surface. In addition, for example, when a fatty acid monoester as described later is included as the insulating liquid, the fatty acid monoester in the insulating liquid acts more effectively as a plasticizer during fixing, as described in detail later, and the toner particles Especially easily plasticized. In addition, since the toner particles have minute irregularities, the contact area between the toner particles on the recording medium is increased, and the toner particles are easily melted during fixing. As a result, the fixing strength of the formed image can be made particularly excellent. Further, particularly high gloss can be obtained, and an image having a target color tone can be obtained particularly easily.

<Insulating liquid>
Next, the insulating liquid will be described.
Next, the insulating liquid will be described. The insulating liquid functions as a medium for dispersing the toner particles, and usually has high electrical insulation and non-volatility.
The insulating liquid is not particularly limited. For example, Isopar E, Isopar G, Isopar H, Isopar L (Isopar; trade name of Exxon Chemical), Cielsol 70, Cielsol 71 (Cielsol; trade name of Ciel Oil) , Amsco OMS, Amsco 460 solvent (Amsco; product name of Spirits), mineral oil such as low viscosity / high viscosity liquid paraffin (Wako Pure Chemical Industries), vegetable oil such as linseed oil, soybean oil, fatty acid monoester, medium chain Fatty acid esters such as fatty acid esters, octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, benzene, toluene, xylene, mesitylene, etc., and one or two of these Use a combination of the above It can be.

Among the above, when the fatty acid monoester fatty acid monoester that is an ester between a fatty acid and a monovalent alcohol is used as the insulating liquid, the following effects are obtained.
Fatty acid monoesters are environmentally friendly components. 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.

  The fatty acid monoester has a property of easily penetrating into the toner particles (polyester resin), and has an effect of plasticizing the toner particles (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 excellent. Further, since the toner particles melt at a relatively low temperature and can be fixed on a recording medium due to the plastic effect, it can be suitably applied to image formation at a low temperature and a high speed. When an image is formed using toner particles of a plurality of colors, the plasticized toner particles come into contact with each other and melt together, so that adjacent toner particles of different colors can be reliably bonded. . As a result, in the region where the toner particles of different colors are combined, the colors of the respective toner particles are mixed and have an intermediate color between them, so that the desired color tone of the image can be obtained more reliably. It becomes possible. Furthermore, since the toner particles are plasticized, the toner particles easily enter the gaps between the fibers of the recording medium, and the resulting toner image is smooth without any unevenness. As a result, the gloss ( (Gloss) can be made excellent. Further, when the toner particles are plasticized in this manner, the above-described dispersant can be easily adhered to the surface of the toner particles and can be held more firmly. As a result, the dispersibility of the toner particles and the positive charging characteristics can be further improved.

  As described above, the fatty acid monoester has an effect of plasticizing the toner particles (polyester resin), but the toner particles thus plasticized usually have a tendency to easily aggregate. However, in the present invention, since the dispersant as described above adheres to the surface of the toner particles, the toner particles are prevented from contacting each other, and the toner particles are effectively prevented from aggregating. Can do.

  The fatty acid monoester is a component that has a high affinity with the polyester resin and the above-described dispersant because of its similar molecular structure, and easily adheres to the surface of the toner particles. In addition, it is a component that easily penetrates into the recording medium. For this reason, the fatty acid monoester adhering to the vicinity of the surface of the toner particles quickly penetrates into the recording medium when the toner particles come into contact with the recording medium during fixing. Along with the permeation of the fatty acid monoester, a part of the toner particles (resin material constituting the toner particles) melted by heat at the time of fixing penetrates into the inside of the recording medium, an anchor effect works, and the fixing strength is 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.

  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. Thereby, 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 fatty acid monoester may be produced by a transesterification reaction between a vegetable oil and a monohydric alcohol as described above. That is, the insulating liquid used in the present invention may include a fatty acid monoester obtained by combining one or more selected from fatty acids and alcohols as described above.
Examples of vegetable oils used for transesterification include soybean oil, rapeseed oil, dehydrated castor oil, tung oil, safflower oil, linseed oil, sunflower oil, corn oil, cottonseed oil, sesame oil, corn oil, cannabis oil, evening primrose oil, palm oil (Especially palm kernel oil), coconut oil, coconut oil and the like.

  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. On the other hand, when the upper limit is exceeded, the electrical resistance of the liquid developer is lowered, and sufficient charging characteristics may not be obtained. In addition, depending on the constituent material of the member, a member that comes into contact with the liquid developer in the image forming apparatus as described later may swell and the life of the image forming apparatus may be significantly reduced.

Moreover, the following effects are acquired when vegetable oil is contained in the insulating liquid.
Vegetable oil is an environmentally friendly component like the fatty acid monoester described above. 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.

The vegetable oil contains unsaturated fatty acid glycerides. An unsaturated fatty acid glyceride is an ester (glyceride) of a fatty acid and glycerin, and contains an unsaturated fatty acid as a fatty acid component.
Unsaturated fatty acid glycerides are components that can contribute to improving the long-term storage stability of the resulting toner image. Details will be described below. An unsaturated fatty acid component is a component that itself can be cured by being oxidized. Therefore, when a toner image is formed and fixed on a recording medium using a liquid developer containing an unsaturated fatty acid glyceride, the unsaturated fatty acid glyceride remaining together with the toner particles on the toner image is oxidized by oxygen in the air or the like. The toner particles can be polymerized, and the toner particles can be firmly bonded to each other or to the recording medium. Further, since the unsaturated fatty acid glyceride can be oxidatively polymerized while covering the surface of the toner image, a protective film of the unsaturated fatty acid glyceride cured on the surface of the toner image can be formed. As described above, the toner image can be reduced in deterioration due to physical external force such as friction, air, light, etc. over a long period of time, and has excellent long-term storage stability.

  Although it does not specifically limit as unsaturated fatty acid which comprises glyceride, Monounsaturated fatty acid, such as crotonic acid, myristoleic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, erucic acid, nervonic acid, linole Of polyunsaturated fatty acids such as acids, α-linolenic acid, γ-linolenic acid, arachidonic acid, eleostearic acid, stearidonic acid, arachidonic acid, succinic acid, docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), etc. Examples thereof include unsaturated fatty acids and derivatives thereof, and one or more selected from these can be used in combination.

  When vegetable oil is contained in the insulating liquid, the content of vegetable oil in the insulating liquid is preferably 20 to 90 wt%, more preferably 30 to 80 wt%, and 40 to 70 wt%. More preferably it is. When the content of vegetable oil in the insulating liquid is within the above range, the unsaturated fatty acid glyceride remaining in the formed toner image becomes appropriate, and the obtained toner image has a protective film as described above on the surface. It is suitably formed and has particularly excellent long-term storage stability.

Moreover, the saturated fatty acid glyceride may contain a saturated fatty acid component. By including the saturated fatty acid component, it is possible to keep the chemical stability of the liquid developer and the electrical insulation of the insulating liquid even higher.
Examples of saturated fatty acids constituting such saturated fatty acid components include butyric acid (C4), caproic acid (C6), caprylic acid (C8), capric acid (C10), lauric acid (C12), and myristylic acid (C14). , Palmitic acid (C16), stearic acid (C18), arachidic acid (C20), behenic acid (C22), lignoceric acid (C24) and the like, and one or more selected from these are used in combination. be able to. Among the saturated fatty acids as described above, the number of carbon atoms in the molecule is preferably 6-22, more preferably 8-20, and even more preferably 10-18. . By including a saturated fatty acid component composed of such a saturated fatty acid, the effects as described above are exhibited more significantly.

  In addition, when the insulating liquid contains naturally-derived components such as fatty acid monoesters and vegetable oils as described above, the liquid developer (insulating liquid) has a function of preventing and suppressing oxidation of the naturally-derived components. The antioxidant which it has may be contained. Thereby, the unintentional oxidation of the naturally derived component in the liquid developer can be prevented. As a result, it is possible to prevent deterioration of the liquid developer (insulating liquid) over time, and the dispersibility of the toner particles, the fixing strength to the recording medium, the charging characteristics, etc. are particularly excellent over a long period of time. can do. That is, the environmental stability of the liquid developer can be made particularly excellent.

Although the viscosity of an insulating liquid is not specifically limited, It is preferable that it is 5-1000 mPa * s, It is more preferable that it is 50-800 mPa * s, It is further more preferable that it is 100-500 mPa * s. When the viscosity of the insulating liquid is within the above range, when the liquid developer is squeezed out from the developer container onto the application roller, an appropriate amount of the insulating liquid adheres to the toner particles, and the developability of the toner image. , Transferability can be made particularly excellent. Further, the toner particles can be made more highly dispersible, and in an image forming apparatus as described later, the liquid developer can be supplied more uniformly to the application roller. It is possible to more effectively prevent the liquid developer from dripping. In addition, aggregation and sedimentation of the toner particles can be prevented, and the dispersibility of the toner particles in the insulating liquid can be made higher. On the other hand, when the viscosity of the insulating liquid is less than the lower limit value, there is a possibility that problems such as dripping of the liquid developer from the application roller or the like may occur in the image forming apparatus described later. On the other hand, if the viscosity of the insulating liquid exceeds the upper limit, the dispersibility of the toner particles cannot be sufficiently increased, and the liquid developer cannot be more uniformly supplied to the application roller in an image forming apparatus as described later. There is a case. However, the viscosity in this specification refers to a value measured at 25 ° C.
The 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.

≪Liquid developer manufacturing method≫
As an example of the method for producing the liquid developer of the present invention, a case where associated disintegrated particles are used as toner particles will be described. The production method to be described mainly involves associating resin fine particles composed of a resin material to obtain associated particles, and in at least a part of the insulating liquid, in the presence of a dispersant as described above. And crushing the associated particles to obtain toner particles.

<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.
Any method may be used to prepare the associated particles, but in the present embodiment, a dispersoid (mainly composed of a polyester resin (toner constituent material) in an aqueous dispersion medium composed of an aqueous liquid). An aqueous emulsion in which (fine particles) are dispersed is obtained, and the dispersoids in the aqueous emulsion are associated to obtain associated particles.

[Aqueous emulsion]
The aqueous emulsion used in this embodiment will be described.
The aqueous emulsion obtained in the aqueous emulsion preparation step described below has a structure in which dispersoids (fine particles) are finely dispersed in an aqueous dispersion medium composed of an aqueous liquid.
(Aqueous dispersion medium (aqueous liquid))
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 aqueous 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.

  Further, the aqueous dispersion medium (aqueous liquid) is preferably one having low compatibility with a high insulating liquid described later (for example, one having a solubility in 100 g of the high insulating liquid at 25 ° C. of 0.01 g or less). . As a result, the shape of the dispersoid can be suitably maintained in the liquid mixture obtained in the liquid mixture preparation step described later, and the shape of the toner particles in the finally obtained liquid developer can be made more uniform. can do.

  Specific examples of the aqueous liquid include, for example, water, alcohol solvents such as methanol, ethanol and propanol, ether solvents such as 1,4-dioxane and tetrahydrofuran (THF), and aromatic heterocycles such as pyridine, pyrazine and pyrrole. Compound solvents, amide solvents such as N, N-dimethylformamide (DMF) and N, N-dimethylacetamide (DMA), nitrile solvents such as acetonitrile, and aldehyde solvents such as acetaldehyde.

(Dispersoid (fine particles))
The dispersoid includes a component constituting the toner particles in the liquid developer, and is composed of a material including at least a polyester resin or a precursor thereof as a main component. Examples of the precursor of the polyester resin include a monomer, a dimer, an oligomer, and a prepolymer of the resin.

  The dispersoid may contain a solvent that dissolves at least a part of the components. Thereby, for example, the fluidity of the dispersoid in the aqueous emulsion can be increased, and the dispersoid in the aqueous emulsion can have a relatively small particle size and small variation in size. it can. 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.

Any solvent may be used as long as it dissolves at least a part of the components constituting the dispersoid, 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 dispersoid can be finely dispersed in a stable state in the aqueous emulsion.

Moreover, the composition of the solvent can be appropriately selected according to, for example, the composition of the resin and the colorant described above, the composition of the aqueous dispersion medium, and the like.
Such a solvent is not particularly limited, and known organic solvents such as ketone solvents such as MEK and aromatic hydrocarbon solvents such as toluene can be used.
Further, the aqueous emulsified liquid may contain an emulsifying dispersant.

  When an emulsifying dispersant is used, the dispersibility of the dispersoid is improved, and the dispersion of the dispersoid in the aqueous emulsion is relatively easily reduced in size and size. Can be substantially spherical. As a result, the final liquid developer can be obtained as a toner composed of toner particles having a substantially spherical shape, a uniform shape, and a uniform size. Here, examples of the emulsifying dispersant include known emulsifiers and dispersants.

The content of the emulsifier and the dispersant in the aqueous emulsion is not particularly limited, but is preferably 3.0 wt% or less, and more preferably 0.01 to 1.0 wt%.
Further, the aqueous emulsion may contain a dispersion aid.
Examples of the dispersion aid include anions, cations, and nonionic surfactants.

The dispersing aid is preferably used in combination with a dispersing agent. When the aqueous emulsion contains a dispersant, the content of the dispersion aid in the aqueous emulsion is not particularly limited, but is preferably 2.0 wt% or less, and is 0.005 to 0.5 wt%. Is more preferable.
In the aqueous emulsion, components other than the dispersoid may be dispersed as an insoluble matter. For example, inorganic fine powders such as silica, titanium oxide, and iron oxide, and organic fine powders such as fatty acids and fatty acid metal salts may be dispersed in the aqueous emulsion.

In the aqueous emulsion used in the present embodiment as described above, since the dispersoid is liquid, the dispersoid tends to have a shape with a high degree of circularity (sphericity) due to its surface tension. Therefore, the finally obtained toner particles in the liquid development have a particularly high degree of circularity, and the variation in shape among the particles is particularly small.
The content of the dispersoid in the aqueous emulsion 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 reliably preventing the dispersoids from binding (aggregating) in the aqueous emulsion.
The average particle size of the dispersoid (liquid dispersoid) in the aqueous emulsion 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.

[Aqueous emulsion preparation process]
The aqueous emulsion as described above can be prepared, for example, as follows (aqueous emulsion preparation step).
First, an aqueous solution in which a dispersant is added to the aqueous liquid as necessary is prepared.
On the other hand, a resin liquid containing a resin as a main component of the toner as described above or a precursor thereof (hereinafter collectively referred to as “resin material”) is prepared. For the preparation of the resin liquid, for example, the above-described solvent may be used in addition to the resin material. The resin liquid may be a molten liquid obtained by heating a resin material. Further, for the preparation of the resin liquid, for example, a kneaded product obtained by kneading a toner material such as a resin material and 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, an aqueous emulsion in which a dispersoid containing a resin material is dispersed in an aqueous dispersion medium is obtained by gradually adding the resin liquid to the stirred aqueous solution while dropping. By preparing an aqueous emulsion by such a method, the circularity of the dispersoid in the aqueous emulsion can be further increased. As a result, the finally obtained toner particles in liquid development have a particularly high degree of circularity, and the variation in shape among the particles is particularly small. In addition, when dripping a resin liquid, you may heat an aqueous solution and / or a resin liquid. In addition, when a solvent is used for the preparation of the resin liquid, for example, after the dropwise addition as described above, the obtained aqueous emulsion is heated or placed in a reduced-pressure atmosphere to be contained in the dispersoid. At least a part of the solvent may be removed.
Further, instead of the above operation, a water-soluble solution may be gradually added dropwise to the stirred resin liquid. By adding an aqueous solution, the resin liquid undergoes phase inversion emulsification, and an aqueous emulsion in which a dispersoid containing a resin material is dispersed in an aqueous dispersion medium, similar to the aqueous emulsion obtained by the above operation, is obtained. It is done.

[Association particle formation process]
Next, an electrolyte is added to the aqueous emulsion 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 emulsion. 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, and coarse particles may be generated, and there is a possibility that the size of toner particles finally obtained may vary. is there.

Then, after associating, filtration and drying are performed to obtain associated particles.
The average particle size of the associated particles obtained is preferably 1 to 10 μm, and more preferably 1 to 7 μm. Thereby, the particle diameter of the toner particles finally obtained can be made moderate. In addition, when the average particle size of the associated particles is in such a range, drying is easy during drying, and aggregation particles are prevented from agglomerating and coarsening during drying. can do.

<Crushing process>
Next, the associated particles obtained as described above are crushed in at least a part of the insulating liquid constituting the liquid developer (crushing step). Accordingly, it is possible to provide a liquid developer in which sufficiently small toner particles are stably dispersed in the insulating liquid, and the width of the particle size distribution of the toner particles is sufficiently narrow. In other words, even when the toner particles are pulverized into relatively small toner particles, they are pulverized in the insulating liquid, so that it is possible to prevent generation of toner particles coarsened due to aggregation or the like.

  In particular, by performing crushing in the presence of the dispersant represented by the general formula (I) as described above, the dispersant can be more reliably attached to the surface of the toner particles. Further, since the toner particle surface has irregularities derived from fine particles (dispersoid), the dispersant can be reliably held on the surface. As a result, the dispersibility of the toner particles can be further improved, and the positive charging characteristics of the liquid developer can be further improved.

In addition, since the toner particles are obtained by crushing the associated particles, the generation of fine powder (particles that are extremely smaller than the target size particles) is more effective than conventional pulverization methods and wet pulverization methods. Can be prevented. As a result, it is possible to effectively prevent deterioration of characteristics such as charging characteristics of the liquid developer finally obtained.
It is also possible to prepare relatively small associated particles and disperse the associated particles as toner particles in an insulating liquid without crushing them to obtain a liquid developer. In this case, the associated particles are dried. At this time, since the particles are small, aggregation or the like is likely to occur, and the size of the toner particles varies.

  When using the thing containing a fatty acid monoester as an insulating liquid, it is preferable to use a fatty acid monoester for crushing. By using the fatty acid monoester, the polyester resin is plasticized at the time of crushing, and the above-described dispersant can be efficiently attached to the surface of the toner particles. Although it is conceivable to use a resin having a low Tg without plasticization, in this case, since there is a high possibility that residual monomers remain, the method of plasticization is preferable also in this respect because it is not good for safety. Moreover, since the fatty acid monoester has a relatively low viscosity, the associated particles can be efficiently crushed.

  Although the time required for crushing depends on the type of equipment used for crushing, for example, when crushing with a ball mill using a ball having a diameter of about 1 to 10 mm, it is preferably about 10 to 300 hours, More preferably, it is about 100 to 200 hours. Thereby, generation of fine powder can be prevented, and a liquid developer having a uniform toner particle diameter can be produced. Further, the liquid developer that can adhere the dispersant represented by the general formula (I) as described above more reliably to the surface of the toner particles and is particularly excellent in the dispersibility of the toner particles and the positively charged characteristics. It can be.

After pulverization, if necessary, the remaining insulating liquid component is added to obtain the liquid developer of the present invention.
In addition, when crushing using a part of the insulating liquid, after crushing, the same liquid as the liquid used for crushing may be added as the insulating liquid, or crushing Later, a liquid having a composition different from the liquid used for crushing 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.
As described above, the case where the associated pulverized particles are used as the toner particles has been described as an embodiment of the liquid developer of the present invention. However, the dispersion liquid containing the resin and the coloring material is discharged, and the discharged liquid is dried. Toner particles may be produced by a method of obtaining 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.
2 is a schematic view showing an example of an image forming apparatus to which the liquid developer of the present invention is applied, FIG. 3 is an enlarged view of a part of the image forming apparatus shown in FIG. 2, and FIG. 4 is a developing roller. FIG. 5 is a schematic view showing the state of toner particles in the upper liquid developer layer, and FIG. 5 is a cross-sectional view showing an example of a fixing device applied to the image forming apparatus shown in FIG.

2 and 3, the image forming apparatus 1000 includes four developing units 30Y, 30M, 30C, and 30K, an intermediate transfer unit 40, a secondary transfer unit (secondary transfer unit) 60, and a fixing unit. (Fixing device) F40 and four liquid developer supply portions 80Y, 80M, 80C, and 80K are provided.
The developing units 30Y, 30M, and 30C develop a latent image with a yellow liquid developer (Y), a magenta liquid developer (M), and a cyan liquid developer (C), respectively, and correspond to each color. It has a function of forming a single color image. The developing unit 30K has a function of developing a latent image with a black liquid developer (K) to form a black monochrome 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. 3, 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.

Photoreceptor 10Y has a cylindrical base material and a photosensitive layer formed on the outer peripheral surface thereof, and is rotatable around a central axis. In the present embodiment, as shown by an arrow in FIG. Rotate clockwise.
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. Irradiation is performed on 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 removed liquid developer, and the developer collection unit 15Y 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 toner particle ratio in the visible image.

The primary transfer backup roller 51Y is a device for transferring a single color image formed on the photoreceptor 10Y to an intermediate transfer unit 40 described later.
The neutralization unit 16Y is a device that removes residual charges on the photoreceptor 10Y after the intermediate transfer image 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, wound around a belt driving roller 41 and a tension roller 42, and stretched between primary transfer backup rollers 51Y, 51M, 51C, and 51K. It is rotationally driven by the drive roller 41 while contacting with 10M, 10C, 10K.

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, and are collectively recorded on paper, film, cloth, and the like. Secondary transfer is performed on the medium F5. 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.

A cleaning device including an intermediate transfer unit cleaning blade 46 and a developer recovery unit 47 is disposed on the tension roller 42 side that stretches the intermediate transfer unit 40 together with the belt drive roller 41.
The intermediate transfer portion cleaning blade 46 has a function of scraping and removing the liquid developer adhering to the intermediate transfer portion 40 after the image is transferred onto the recording medium F5 by the secondary transfer roller 61.

The developer recovery unit 47 has a function of recovering the liquid developer removed by the intermediate transfer unit cleaning blade 46.
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 includes an intermediate transfer unit squeeze roller 53Y, an intermediate transfer unit squeeze backup roller 54Y disposed opposite to the intermediate transfer unit squeeze roller 53Y with the intermediate transfer unit 40 interposed therebetween, and an intermediate transfer unit squeeze roller 53Y. It comprises an intermediate transfer unit squeeze cleaning blade 55Y that cleans the surface by pressing and sliding, and a developer recovery unit 15M.

  The intermediate transfer unit squeeze device 52Y has a function of recovering excess carrier from the developer primarily transferred to the intermediate transfer unit 40, increasing the toner particle ratio in the visible image, and recovering originally unwanted toner. . The developer recovery unit 15M uses a mechanism for recovering the carrier recovered by the cleaning blade 14M of the magenta photosensitive member squeeze roller disposed downstream in the moving direction of the intermediate transfer unit 40. The developer transfer unit squeeze the intermediate transfer unit squeeze roller 53Y. This is also used for the cleaning blade 55Y. In this way, in the developer collection units 15M, 15C, and 15K (developer collection units 15C and 15K are not shown) of the image carrier squeeze device for the second and subsequent colors, the primary transfer backup roller 51 of the previous color ( Y, M, C) is used as a developer recovery unit of the intermediate transfer unit squeeze device 52 (Y, M, C) disposed downstream of the intermediate transfer unit 40 in the moving direction, so that the interval between them is constant. It can be regulated, and the structure can be simplified and the size can be reduced.

The secondary transfer unit 60 includes a cleaning device including a secondary transfer roller 61 facing the belt driving roller 41 with the intermediate transfer unit 40 interposed therebetween, and a cleaning device including a cleaning blade 62 and a developer recovery unit 63 of the secondary transfer roller 61. Be placed.
In the secondary transfer unit 60, the recording medium F5 is conveyed and supplied in accordance with the timing at which the intermediate transfer image formed on the intermediate transfer unit 40 by overlapping colors reaches the transfer position of the secondary transfer unit 60. The intermediate transfer image is secondarily transferred to the recording medium F5.

The toner image (transfer image) F5a transferred onto the recording medium F5 by the secondary transfer unit 60 is sent to a fixing unit F40, which will be described later, and fixed.
The cleaning blade 62 has a function of scraping and removing the liquid developer adhering to the secondary transfer roller 61 after the image is transferred onto the recording medium F5 by the secondary transfer roller 61.
The developer recovery unit 63 has a function of recovering the liquid developer removed by the cleaning blade 62.

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. 3, the developing unit 100Y includes a liquid developer storage unit 31Y, a coating roller 32Y, a regulating blade 33Y, a developer stirring roller 34Y, a developing roller 20Y, a developing roller cleaning blade 21Y, and a developing unit. And an agent compression roller (compression means) 22Y.

The liquid developer storage unit 31Y has a function of storing a liquid developer for developing the latent image formed on the photoreceptor 10Y.
The coating roller 32Y has a function of supplying a liquid developer to the developing roller 20Y.
The application roller 32Y is a so-called anilox roller in which grooves are uniformly and spirally formed on the surface of a metallic roller such as iron and nickel-plated, and has a diameter of about 25 mm. . In the present embodiment, a plurality of grooves are formed obliquely with respect to the rotation direction of the application roller 32Y by so-called cutting or rolling. The application roller 32Y contacts the liquid developer while rotating clockwise, thereby supporting the liquid developer in the liquid developer storage section 31Y in the groove, and the supported liquid developer is transferred to the developing roller 20Y. Transport to.

  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. Further, the regulating blade 33Y is provided on the side where the coating roller 32Y rotates and advances from the liquid developer as viewed from the vertical plane A (that is, the left side in FIG. 3 as viewed from the vertical plane A). The rubber hardness of the regulation blade 33Y is about 77 degrees according to JIS-A, and the hardness (about 77 degrees) of the contact portion of the regulation blade 33Y with the surface of the coating roller 32Y is about the elasticity of the developing roller 20Y described later. It is lower than the hardness (about 85 degrees) of the pressure contact portion of the body layer to the surface of the application roller 32Y. Further, the excess liquid developer scraped off is collected in the liquid developer storage unit 31Y and reused.

The developer stirring roller 34Y has a function of stirring the liquid developer in a uniformly dispersed state. Thus, even when a plurality of toner particles 1 are aggregated, the toner particles 1 can be suitably dispersed. In particular, the toner particles 1 can be suitably dispersed even when the liquid developer once used is reused.
In the liquid developer storage unit 31Y, the toner particles 1 in the liquid developer have a positive charge, and the liquid developer is stirred by the developer stirring roller 34Y to be in a uniformly dispersed state, and the coating roller 32Y. , The liquid developer is stored in the liquid developer reservoir 31Y, and the amount of liquid developer is regulated by the regulating blade 33Y and supplied to the developing roller 20Y.

The developing roller 20Y carries the liquid developer and conveys it to the developing position facing the photoconductor 10Y in order to develop the latent image carried on the photoconductor 10Y with the liquid developer.
The developing roller 20Y forms a liquid developer layer 201Y on the surface thereof by supplying the liquid developer from the coating roller 32Y described above.
The developing roller 20Y includes a conductive elastic layer on the outer peripheral portion of an inner core made of metal such as iron, and has a diameter of about 20 mm. The elastic layer has a two-layer structure. As an inner layer, urethane rubber having a rubber hardness of about 30 degrees and a thickness of about 5 mm is used. As a surface layer (outer layer), the rubber hardness is JIS. -A urethane rubber having a thickness of about 30 μm at about 85 degrees A is provided. The developing roller 20Y is in pressure contact with the application roller 32Y and the photoreceptor 10Y in a state of elastic deformation 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. 3) opposite to the rotation direction of the photoreceptor 10Y (clockwise in FIG. 3). When developing the latent image formed on the photoconductor 10Y, an electric field is formed between the developing roller 20Y and the photoconductor 10Y.

  The developer compression roller 22Y is a device having a function of compressing the liquid developer toner carried on the development roller 20Y. In other words, the developer compression roller 22Y applies an electric field having the same polarity as that of the toner particles 1 to the liquid developer layer 201Y described above, thereby developing the liquid developer layer 201Y in the liquid developer layer 201Y as shown in FIG. This is a device having a function of unevenly distributing the toner particles 1 near the surface of the roller 20Y. By unevenly distributing the toner particles in this way, the development density (development efficiency) can be improved, and as a result, a clear image with high quality can be obtained.

The developer compression roller 22Y is provided with a cleaning blade 23Y.
The cleaning blade 23Y has a function of removing the liquid developer adhering to the developer compression roller 22Y. The liquid developer removed by the cleaning blade 23Y is collected in the liquid developer reservoir 31Y and reused.
Further, the developing unit 100Y includes a rubber developing roller cleaning blade 21Y that is in contact with the surface of the developing roller 20Y. 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 liquid developer storage unit 31Y and reused.

As shown in FIGS. 2 and 3, the image forming apparatus 1000 includes liquid developer replenishing units 80Y, 80M, 80C, and 80K that replenish liquid developer to the developing unit 30Y. Since the configurations of the liquid developer supply units 80Y, 80M, 80C, and 80K are the same, the liquid developer supply unit 80Y will be described below.
The liquid developer supply unit 80Y includes a recovered liquid developer storage unit 81Y, a supply liquid developer storage unit 82Y, transport means 83Y and 84Y, a pump 85Y, and a filter 86Y.

  The recovered liquid developer storage unit 81Y mainly stores the recovered liquid developer recovered by the developer recovery unit 18Y, and supplies the recovered liquid developer to the liquid developer storage unit 31Y of the developing unit 30Y by the transport unit 83Y. . In addition, the liquid developer is stored in the replenishment liquid developer storage portion 82Y, and the liquid developer is supplied to the liquid developer storage portion 31Y by the transport means 84Y. The composition of the liquid developer stored in the replenishment liquid developer storage portion 82Y and the composition of the recovered liquid developer stored in the recovered liquid developer storage portion 81Y are the same as the liquid developer stored in the liquid developer storage portion 31Y. It may be different or different.

Further, the liquid developer collected in the developer collecting unit 18Y is supplied to the liquid developer replenishing unit 80Y through the conveyance path 70Y.
The transport path 70Y is provided with a pump 85Y. The pump 85Y transports the liquid developer recovered by each developer recovery section to the recovered liquid developer storage section 81Y.
Further, a filter 86Y is provided in the conveyance path 70Y, and coarse particles, foreign matter, and the like can be removed from the collected liquid developer. Solid content such as coarse particles and foreign matter removed by the filter 86Y is detected by a filter state detection means (not shown). Then, the filter 86Y is replaced based on the detection result. Thereby, the filtering function of the filter 86Y can be stably maintained.

Next, the fixing unit will be described.
The fixing unit F40 fixes the unfixed toner image F5a formed in the above-described developing unit, transfer unit, and the like on the recording medium F5.
As shown in FIG. 5, the fixing unit F40 includes a heat fixing roller F1, a pressure roller F2, a heat-resistant belt F3, a belt stretching member F4, a cleaning member F6, a frame F7, and a spring F9. is doing.

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

The pressure roller F2 is arranged to face the heat fixing roller F1, and is configured to apply pressure to the recording medium F5 on which the unfixed toner image F5a is formed via a heat-resistant belt F3 described later. Has been.
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.

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

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

The cleaning member F6 is disposed between the pressure roller F2 and the belt stretching member F4.
The cleaning member F6 is in 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.

  The fixing unit F40 has a removing blade (removing means) F12 that removes the insulating liquid adhering (remaining) on the surface of the heat fixing roller F1 after fixing the toner image F5a on the recording medium F5. . The removing blade F12 can remove the insulating liquid and simultaneously remove the toner and the like that have moved onto the heat fixing roller F1 during fixing.

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

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

Specifically, the heat (fixing temperature) applied by the heat fixing roller F1 is preferably 80 to 160 ° C, more preferably 100 to 150 ° C, and further preferably 100 to 140 ° C.
As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to these.

For example, the liquid developer of the present invention is not limited to that applied to the image forming apparatus as described above.
Further, the liquid developer of the present invention is not limited to those produced by the production method as described above.
In the above-described embodiment, the aqueous emulsion is obtained, and the association particles are obtained by adding an electrolyte to the aqueous emulsion. 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 emulsion by emulsion polymerization, and adding an electrolyte to the aqueous emulsion and associating. What was prepared using the emulsion polymerization association method may be used, and the associated particle | grains may be obtained by spray-drying the obtained aqueous emulsion.

[1] Production of liquid developer (Example 1)
<Preparation of liquid containing fatty acid monoester>
A liquid containing a fatty acid monoester constituting 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 the obtained 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%. Moreover, the viscosity of the soybean oil fatty acid methyl measured by using a vibration viscometer at 25 ° C. according to JIS Z8809 was 3.0 mPa · s.

<Preparation of colorant master solution>
First, a mixture (mass ratio 50:50) of a polyester resin (softening temperature: 125 ° C., acid value: 7.7) and a cyan pigment (Dainipei Seika Co., Ltd., Pigment Blue 15: 3) as a colorant. 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 powder of the kneaded material so that the solid content was 30 wt%, and wet-dispersed 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 wt%.
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 polyester resin 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>
Associative particles obtained by the above method: 100 parts by weight, soybean oil fatty acid methyl: 150 parts by weight, dispersant represented by the following structural formula (V): 2.5 parts by weight and aluminum stearate (manufactured by NOF Corporation) : 1.25 parts by weight was placed in a ceramic pot, and zirconia balls (ball diameter: 3 mm) were further placed in the ceramic pot so that the volume filling rate was 30%. Crushing was performed for 200 hours at a rotational speed of 220 rpm in a desktop pot mill to obtain a toner dispersion.

After completion of the crushing, 250 parts by weight of rapeseed oil (manufactured by Nisshin Oilio Co., Ltd., trade name “High Oleic Rapeseed Oil”) was added to disperse the toner particles. Dispersion was performed for 24 hours by putting zirconia balls having a ball diameter of 1 mm. As a result, a liquid developer was obtained.
The same as above except that magenta pigment: pigment red 122, yellow pigment: pigment yellow 180, black pigment: carbon black (Printex L, manufactured by Degussa) was used instead of cyan pigment. Thus, a magenta liquid developer, a yellow liquid developer, and a black liquid developer were produced.

(Examples 2 to 7)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the content of the dispersant represented by the structural formula (V) was as shown in Table 1.
(Examples 8 to 10)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the crushing time in the desktop pot mill was as shown in Table 1.

(Example 11)
Liquid developers corresponding to the respective colors were produced in the same manner as in Example 1 except that in the crushing using a desktop pot mill, zirconia balls having a ball diameter of 1 mm were used and the crushing time was 240 hours.
(Examples 12 to 14)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the polyester resin shown in Table 1 was used.

(Examples 15 to 17)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that the content of soybean oil fatty acid methyl contained in the insulating liquid was adjusted as shown in Table 1.
(Example 18)
Liquid developers corresponding to the respective colors were produced in the same manner as in Example 1 except that soybean oil (Nisshin Oilio Co., Ltd.) was used instead of rapeseed oil.

(Example 19)
Crude rapeseed oil was refined in the same manner as the soybean oil of Example 1 to obtain a refined rapeseed oil (hereinafter simply referred to as rapeseed oil). The rapeseed oil contained fatty acid glycerides mainly composed of oleic acid, and the unsaturated fatty acid glycerides in the rapeseed oil was 98 wt%. The oleic acid component and linoleic acid component were 52 mol% and 24 mol%, respectively, of the total fatty acid components.

Next, a transesterification reaction between a part of the rapeseed oil and methanol was carried out, and glycerin produced by this reaction was removed to obtain a liquid mainly composed of fatty acid monoesters. Further, by purifying this liquid, rapeseed oil fatty acid methyl having a fatty acid monoester content of 99.9 wt% or more was obtained.
Hereinafter, as the insulating liquid, rapeseed oil fatty acid methyl is used instead of soybean oil fatty acid methyl, and liquid paraffin (trade name “Cosmo White P-60” manufactured by Cosmo Oil Co., Ltd.) is used instead of rapeseed oil, In the same manner as in Example 1, liquid developers corresponding to the respective colors were produced.

(Example 20)
A liquid developer corresponding to each color was produced in the same manner as in Example 1, except that Isopar H (trade name of Exxon Chemical Co., Ltd.) was used as the insulating liquid instead of soybean oil fatty acid methyl.
(Example 21)
As an insulating liquid, Isopar H (exxon chemical name) is used instead of soybean oil fatty acid methyl, and liquid paraffin (trade name “Cosmo White P-60” manufactured by Cosmo Oil Co., Ltd.) is used instead of rapeseed oil. A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that it was used.

(Comparative Example 1)
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 2)
As a dispersant, a polyamine aliphatic polycondensate (manufactured by Nippon Lubrizol Co., Ltd., trade name “Solsperse 11200”) was used instead of the compound of the structural formula (V) as in Example 1 above. A liquid developer corresponding to each color was produced.
(Comparative Example 3)
A liquid developer corresponding to each color was produced in the same manner as in Example 1 except that an epoxy resin (softening temperature: 80.5 ° C., acid value: 12) was used instead of the polyester resin as the toner resin.

  Table 1 shows the manufacturing conditions and physical properties of the liquid developer for each of the above Examples and Comparative Examples. In the table, A represents the dispersant represented by the structural formula (V), and B represents the other dispersant. Further, the polyester resin is indicated as PES, and the epoxy resin is indicated as EP. The toner particles SF1 and SF2 were measured as follows. First, regarding the toner particles in the liquid developer, an image of toner particles was randomly sampled 100 times using FE-SEM (S-800, manufactured by Hitachi, Ltd.). Next, the obtained toner particle image was analyzed using an image analyzer (LUSEX3, manufactured by Nireco), and average toner particles SF1 and SF2 were calculated.

[2] Evaluation Each liquid developer obtained as described above was evaluated as follows.
[2.1] Charging characteristic evaluation-1
Using the image forming apparatus as shown in FIG. 2, a liquid developer layer made of the liquid developer obtained in each of the examples and the comparative examples was formed on the developing roller of the image forming apparatus. Next, the potential of the developing roller is 300 V, the potential of the developer compression roller is 500 V, and the toner particles on the developer compression roller after the liquid developer layer passes between the developer compression roller and the development roller. The toner particles on 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 concentration of toner particles collected on the developing roller is divided by the sum of the concentration of toner particles collected on the developing roller and the concentration of toner particles collected on the developer compression roller. The value X multiplied by was determined and evaluated according to the following five-step criteria.

A: X ≧ 95 (Excellent charging characteristics)
B: 90 ≦ X <95 (excellent charging characteristics)
C: 85 ≦ X <90 (Charging characteristics having no practical problem)
D: 80 ≦ X <85 (poor charging characteristics)
E: X <80 (charging property is very bad)

[2.2] Charging characteristic evaluation-2
Using the image forming apparatus as shown in FIG. 2, a liquid developer layer made of the liquid developer obtained in each of the examples and the comparative examples was formed on the developing roller of the image forming apparatus. Next, the developer roller potential is set to 300 V, the surface of the photosensitive member is uniformly charged at 500 V, and the toner particles on the developing roller after the liquid developer layer passes between the photosensitive member and the developing roller; The toner particles on the photoreceptor 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. The value Y was determined and evaluated according to the following five-stage criteria.

A: Y ≧ 95 (particularly excellent in charging characteristics)
B: 90 ≦ Y <95 (excellent charging characteristics)
C: 85 ≦ Y <90 (Charging characteristics having no practical problem)
D: 80 ≦ Y <85 (poor charging characteristics)
E: Y <80 (charging property is very bad)

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

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

[2.4] Dispersion stability test 10 mL of the cyan liquid developer obtained in each example and each comparative example was placed in a centrifuge tube, centrifuged at 1000 G for 10 minutes, and then 200 μL of the supernatant was added. The sample was collected and diluted 100 times with the insulating liquid used in each example and each comparative example to prepare a sample.
The absorption wavelength of each sample was measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, V-570).
Evaluation was performed according to the following four-stage criteria from the absorbance value in the absorption range (685 nm) of the cyan pigment.
A: Absorbance is 1.50 or more (no precipitation is observed).
B: Absorbance is 1.00 or more and less than 1.50 (almost no sedimentation is observed).
C: Absorbance is 0.50 or more and less than 1.00 (precipitation is confirmed).
D: Absorbance is less than 0.50 (sedimentation is remarkable and sedimentation starts even when left standing naturally).

[2.5] Preservability The liquid developers obtained in the above Examples and Comparative Examples were allowed to stand for 6 months in an environment at a temperature of 15 to 25 ° 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.
B: Floating and coagulation sedimentation of toner particles are hardly observed.
C: Slight floating or coagulation sedimentation of toner particles is observed, but as a liquid developer
There is no problem.
D: Floating or coagulation sedimentation of toner particles is clearly observed.
E: Suspension and coagulation sedimentation of toner particles are remarkably observed.

[2.6] Fixing Strength Using an image forming apparatus as shown in FIG. 2, an image of a predetermined pattern with a liquid developer obtained in each of the examples and the comparative examples was recorded on a recording paper (manufactured by Seiko Epson Corporation). It was formed on fine paper LPCPPA4). Thereafter, thermal fixing was performed using a fixing device as shown in FIG. 5 at a set temperature of the heat fixing roller of 100 ° C.

Then, after confirming the non-offset area, the fixed image on the recording paper is erased twice (rubber eraser “LION 261-11” manufactured by Lion Business Machine Co., Ltd.) twice with a pressing load of 1.2 kgf, and the remaining ratio of image density Was measured by “X-Rite model 404” manufactured by X-Rite Inc, and evaluated according to the following five-step criteria.
A: Image density residual ratio is 95% or more (very good).
B: Image density remaining rate is 90% or more and less than 95% (good).
C: Image density remaining rate is 80% or more and less than 90% (normal).
D: Image density residual ratio is 70% or more and less than 80% (slightly bad).
E: Image density residual ratio is less than 70% (very bad).

[2.7] Long-term stability of toner image (stable period)
By using an image forming apparatus as shown in FIG. 2, a single-color image of a predetermined pattern by the liquid developer obtained in each of the examples and the comparative examples is recorded on a recording paper (quality paper LPCPPA4 manufactured by Seiko Epson Corporation). The heat fixing was performed at a set temperature of 150 ° C. for the heat fixing roller. Immediately after fixing, the image density of the toner image was measured by “X-Rite model 404” manufactured by X-Rite Inc. Then, it was left standing under an atmosphere of 15 to 35 ° C. temperature, 50 to 70% humidity, and sunlight. After confirming the non-offset area of the toner image every month, erase the fixed image on the recording paper by rubbing twice with an eraser (LION 261-11, manufactured by Lion Secretariat) with a pressing load of 1.0 kgf. The image density was measured by “X-Rite model 404” manufactured by X-Rite Inc. Compared with the image density after image formation, the period in which the residual ratio of the toner image is 85% or more was defined as the stable period of the toner image, and evaluation was performed according to the following five criteria.

A: The toner image has a stable period of 24 months or more.
B: The toner image has a stable period of 18 months or more and less than 24 months.
C: The stable period of the toner image is 12 months or more and less than 18 months.
D: The stable period of the toner image is 6 months or more and less than 12 months.
E: The toner image has a stable period of less than 6 months.
These results are shown in Table 2.

As is apparent from Table 2, the liquid developer of the present invention was excellent in charging characteristics (positive charging characteristics) and toner particle dispersibility. Further, the liquid developer of the present invention was excellent in storage stability, fixability and long-term stability of the toner image. On the other hand, satisfactory results were not obtained with the liquid developers of the comparative examples.
Further, in the examples using the insulating liquid containing the fatty acid monoester and the vegetable oil, the fixability and the long-term stability of the toner image were particularly excellent.

It is a figure explaining how to obtain shape factors SF1 and SF2. 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. 3 is an enlarged view of a part of the image forming apparatus shown in FIG. 2. FIG. 6 is a schematic diagram illustrating a state of toner particles in a liquid developer layer on a developing roller. FIG. 3 is a cross-sectional view illustrating an example of a fixing device applied to the image forming apparatus illustrated in FIG. 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Toner particle 1000 ... Image forming apparatus 10Y, 10M, 10C, 10K ... Photoconductor 11Y ... Charging roller 12Y ... Exposure unit 13M, 13Y ... Photoconductor squeeze roller 14M, 14Y ... Cleaning blade 15M, 15Y ... Developer collection part 16Y Destaticizing unit 17Y Photoconductor cleaning blade 18Y Developer collecting unit 20Y, 20M, 20C, 20K Developing roller 201Y Liquid developer layer 21Y Developing roller cleaning blade 22Y Developer compressing roller 23Y Cleaning blades 30Y, 30M , 30C, 30K ... developing unit 31Y ... liquid developer storage unit 32Y ... application roller 33Y ... regulator blade 34Y ... developer stirring roller 40 ... intermediate transfer unit 41 ... belt drive roller 42 ... tension roller 46 ... medium Transfer unit cleaning blade 47 ... Developer recovery unit 51Y, 51M, 51C, 51K ... Primary transfer backup roller 52Y, 52M, 52C, 52K ... Intermediate transfer unit squeeze device 53Y ... Intermediate transfer unit squeeze roller 54Y ... Intermediate transfer unit squeeze backup Roller 55Y ... Intermediate transfer unit squeeze cleaning blade 60 ... Secondary transfer unit 61 ... Secondary transfer roller 62 ... Cleaning blade 63 ... Developer recovery unit 70Y ... Conveyance path 80Y, 80M, 80C, 80K ... Liquid developer replenishment unit 81Y ... Collected liquid developer reservoir 82Y ... Supply liquid developer reservoir 83Y, 84Y ... Conveying means 85Y ... Pump 86Y ... Filter 100Y ... Developer unit 101Y ... Photoconductor squeeze device F40 ... Fixing unit (fixing device) F1 ... Heat fixing roller La (Heating roller) F1a ... Column-shaped halogen lamp F1b ... Roller base material F1c ... Elastic body F12 ... Removal blade F2 ... Pressure roller F2a ... Rotating shaft F2b ... Roller base material F2c ... Elastic body F3 ... Heat-resistant belt F4 ... Belt stretch Member F4a ... Projection wall F4f ... Recess F5 ... Recording medium F5a ... Toner image F6 ... Cleaning member F7 ... Frame F9 ... Spring

Claims (8)

An insulating liquid;
Toner particles mainly composed of polyester resin;
A liquid developer comprising a dispersant represented by the following general formula (I):

(Where, n is 5-8 integer, R represents -OH, R 'is H- or _CH 3 _{(CH 2)} 16 is a CO-.)   The liquid developer according to claim 1, wherein the content of the dispersant is 1.0 to 10 parts by weight with respect to 100 parts by weight of the toner particles. The toner particles represented by the following formula (II) have a shape factor SF1 of 100 to 130,
The liquid developer according to claim 1 or 2, wherein a shape factor SF2 of the toner particles represented by the following formula (III) is 110 to 150.
SF1 = {(ML) ² / A} × (100π / 4) (II)
SF2 = {(CL) ² / A} × (100 / 4π) (III)
(However, A [μm ² ] is the area of a figure formed by projecting toner particles on a two-dimensional plane, and ML [μm] and CL [μm] are the maximum length and circumference of the figure, respectively. is there.)   The liquid developer according to claim 1, wherein the insulating liquid contains a fatty acid monoester.   The liquid developer according to claim 4, wherein the content of the fatty acid monoester in the insulating liquid is 1.0 to 50 wt%.   The liquid developer according to any one of claims 1 to 5, wherein the acid value of the polyester resin is 5 to 15. A step of associating fine particles mainly composed of a polyester resin to obtain associated particles;
The liquid developer according to any one of claims 1 to 6, wherein the liquid developer is produced using a method comprising a step of pulverizing the associated particles in the presence of the dispersant in at least a part of the insulating liquid. . Using a plurality of liquid developers having different colors, a plurality of developing units that form the monochromatic image corresponding to each color;
An intermediate transfer unit that sequentially transfers a plurality of the single-color images formed by the plurality of developing units, and forms an intermediate transfer image formed by superimposing the transferred single-color images;
A secondary transfer unit that transfers the intermediate transfer image to the recording medium and forms an unfixed color image on the recording medium;
A fixing unit for fixing the unfixed color image on the recording medium,
The liquid developer is an insulating liquid;
Toner particles mainly composed of polyester resin;
An image forming apparatus comprising a dispersant represented by the following general formula (I):

(Where, n is 5-8 integer, R represents -OH, R 'is H- or _CH 3 _{(CH 2)} 16 is a CO-.)

Images