JP2012230238A - Wet image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wet image forming method in which toner is firmly fixed on a recording material and printing quality is good.SOLUTION: The wet image forming method comprises: a step of transferring a liquid developer onto a surface of a recording material; and a first heating step of heating the recording material onto the surface of which the liquid developer is transferred. The liquid developer contains toner particles, an insulating liquid and a dispersant. The dispersant contains a compound having one or more substituents selected from the group consisting of an amide group, a pyrrolidone group, an urethane group and an imine group. If the temperature of the recording material immediately after being subjected to the first heating step is defined as Tand the melting temperature and softening temperature of the toner particles measured by a flow tester are defined as Tm and Ts, respectively, the following relation is satisfied: Ts<T<Tm.

Description

  The present invention relates to a wet image forming method, and more particularly to a wet image forming method used for a copying machine, a printer, a digital printing machine, and the like.

  In the electrophotographic process, it has been conventionally performed to heat the paper in order to fix the toner contained in the liquid developer onto the paper. In this way, the paper is heated to volatilize the insulating liquid contained in the liquid developer, thereby agglomerating the toner particles and fixing the toner particles on the paper. Here, when an insulating liquid having low volatility is used, the insulating liquid cannot be sufficiently volatilized by a single heating, so that the toner particles are fixed on the paper by heating the paper in two stages. Yes.

  For example, in Japanese Patent Laid-Open No. 2008-090113 (Patent Document 1), a liquid developer is fixed by heating paper in two stages using two fixing devices, a first fixing device and a second fixing device. In the first fixing device of Patent Document 1, the paper is heated to a temperature lower than the toner softening temperature, and in the second fixing device, the paper is heated to a temperature higher than the toner softening temperature and lower than the volatilization temperature of the insulating liquid. . Further, a dispersant having a polyesteramine group is used as the dispersant for the liquid developer. Thus, the fixing strength of the liquid developer can be increased by heating the paper in two stages to fix the liquid developer and using the dispersant having a polyesteramine group in the liquid developer.

In Japanese Patent Laid-Open No. 2005-338807 (Patent Document 2), similarly to Patent Document 1, paper is heated using two fixing devices, a first fixing device and a second fixing device. In Patent Document 2, the temperature of the paper after passing through the first fixing unit and T _1, the temperature of the paper after passing through the second fixing device and T _2, the paper before passing through the second fixing device When the temperature is T ₃ , the toner is fixed so as to satisfy the following formulas (I) and (II) in relation to the melting start temperature Tfb of the toner and the softening temperature Ts of the toner.
T ₁ > Tfb (I)
T ₂ > T ₃ > Ts (II)
By heating the paper to a temperature that satisfies the equations (I) and (II), and fixing the toner particles to the paper, the gloss can be printed uniformly without depending on the amount of toner applied. can do.

JP 2008-090113 A JP 2005-338807 A

  As shown in Patent Documents 1 and 2, when the paper is heated in two stages, the insulating liquid in the liquid developer is volatilized by heating the paper in the first stage, resulting in toner particle aggregation and film formation. . Here, it is only necessary that the toner particles are appropriately heated by the heating in the first stage. However, when the toner particles agglomerate and the film formation on the surface proceeds, the insulating liquid contained therein volatilizes. It may be difficult. For this reason, the insulating liquid cannot be sufficiently volatilized even by the second stage heating, and there arises a problem in print quality such as the insulating liquid remaining and show-through.

  Further, when the toner particles shift from the dispersed state to the semi-aggregated state by heating in the first stage, the developer captures the insulating liquid via the dispersant, so that the surface of the liquid developer is in the semi-aggregated state. Becomes unaggregated. In such a liquid developer state, the fixing strength between the toner and paper is lowered, and low temperature offset is likely to occur.

  In summary, the conventional wet image forming method has two major problems. The first problem is that only the surface of the liquid developer is formed into a film by heating in the first stage, and the insulating liquid inside becomes difficult to volatilize. The second problem is that the insulating liquid does not volatilize. The toner does not aggregate and the toner particles are difficult to fix on the paper. Therefore, a wet image forming method that can simultaneously solve these two problems has been desired.

  The present invention has been made under such circumstances, and an object of the present invention is to provide a wet image forming method in which toner is firmly fixed on a recording material and print quality is good.

The inventors of the present invention have completed the present invention by intensive studies on the heating temperature of the recording material and the melting temperature of the toner particles. That is, the wet image forming method of the present invention includes a step of transferring the liquid developer to the surface of the recording material, and a first heating step of heating the recording material to which the liquid developer has been transferred. A toner particle, an insulating liquid, and a dispersant, the dispersant having a compound having one or more substituents selected from the group consisting of an amide group, a pyrrolidone group, a urethane group, and an imine group. In addition, assuming that the temperature of the recording material immediately after the first heating step is T ₁ and the melting temperature and the softening temperature of the toner particles measured by a flow tester are Tm and Ts, respectively, the relationship of Ts <T ₁ <Tm is established. It is characterized by satisfying.

After the first heating step, the recording material further includes a second heating step for heating the recording material, and the temperature T ₂ of the recording material immediately after the second heating step is preferably higher than Tm.

  The liquid developer preferably contains 0.5% by mass or more and 10% by mass or less of a dispersant with respect to the weight of the toner particles. The dispersant preferably contains a pyrrolidone group.

  Since the wet image forming method of the present invention has the above-described configuration, it has an extremely excellent effect that the toner is firmly fixed on the recording material and the printing quality is good.

It is a schematic diagram showing an outline of when measuring the temperature T ₁ of the recording material after a first heating step. It is sectional drawing which shows typically the 1st heating step and 2nd heating step of the wet image forming method of this invention. It is sectional drawing which shows typically the 1st heating step and 2nd heating step of the wet image forming method of this invention. FIG. 6 is a schematic cross-sectional view showing a step of transferring a liquid developer to the surface of a recording material.

  Hereinafter, the wet image forming method of the present invention will be described with reference to the drawings. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

<Wet image forming method>
The wet image forming method of the present invention includes a step of transferring a liquid developer onto the surface of a recording material, and a first heating step of heating the recording material onto which the liquid developer has been transferred. And an insulating liquid and a dispersant, the dispersant including a compound having one or more substituents selected from the group consisting of an amide group, a pyrrolidone group, a urethane group, and an imine group, When the temperature of the recording material immediately after one heating step is T ₁ and the melting temperature and the softening temperature of the toner particles measured by a flow tester are Tm and Ts, respectively, Ts <T ₁ <Tm is satisfied. To do. When the liquid developer containing the dispersant as described above is used and the temperature T ₁ of the recording material immediately after the first heating step satisfies the above relational expression, the print quality is deteriorated or an offset is generated. Can be suppressed. In the following, each step constituting the wet image forming method of the present invention will be described.

<Step of transferring liquid developer>
In the wet image forming method of the present invention, first, a step of transferring a liquid developer to a recording material is performed. The method for transferring the liquid developer is not particularly limited, and a conventionally known method can be used. The amount of the liquid developer transferred to the recording material is preferably 3 g / m ² or more and 5 g / m ² or less in a solid image. By transferring the liquid developer in such an amount, the insulating liquid is easily volatilized and the toner particles are easily fixed on the recording material by the first heating step and the second heating step described later.

  Specifically, the step of transferring the liquid developer is performed using, for example, an apparatus shown in FIG. The step of transferring the liquid developer using the apparatus shown in FIG. 4 and the liquid developer will be described later. Hereinafter, the first heating step and the second heating step included in the wet image forming method of the present invention will be described.

<First heating step>
In the present invention, the first heating step is a step of heating the recording material to which the liquid developer is transferred in the above to a temperature of T _1. In the first heating step, the recording material is heated so as to satisfy Ts <T ₁ <Tm in relation to the melting temperature Tm of the toner particles and the softening temperature Ts of the liquid developer. In this way, by heating the recording material to a temperature T ₁ lower than the melting temperature Tm, the surface of the liquid developer is not completely formed into a film but in a semi-molten state. The semi-molten recording material is further heated in a second heating step, which will be described later, whereby the insulating liquid contained in the liquid developer is volatilized and high-quality printing that is difficult to show through is enabled. If the temperature T _{1 of the} recording material that has undergone the first heating step is equal to or higher than Tm, the surface of the liquid developer becomes a film and the insulating liquid inside cannot be volatilized, and the insulating liquid remains on the printing surface. , Quality deterioration such as show-through occurs.

Further, in the first heating step, the recording material is heated to a temperature T ₁ that exceeds the softening temperature Ts of the liquid developer, so that the toner is melted so as to be easily fixed on the recording material, and the insulating property contained in the liquid developer. The volatilization of the liquid is likely to proceed. As a result, the toner particles can aggregate and be easily fixed on the recording material. On the other hand, when the temperature T _{1 of the} recording material that has undergone the first heating step is Ts or less, the toner is difficult to melt and the insulating liquid is less likely to volatilize.

Here, the softening temperature Ts is a temperature at which the internal void disappears and the phase becomes uniform with a non-uniform stress distribution. The melting temperature Tm (also referred to as T _1/2 ) is a temperature at which the difference between the outflow end point S _max and the minimum value S _min is 1/2 when the piston stroke position is S. The average of the outflow start temperature Tfb and the softening temperature Ts is calculated. The outflow start temperature Tfb is a temperature at which the piston starts to descend again after the piston slightly rises due to thermal expansion of the sample.

The above Tm and Ts are measured by the following flow tester. First, 5 ml of liquid developer is centrifuged at 25 ° C. and a rotation speed of 2000 rpm for 20 minutes. Then, only the supernatant is discarded to leave a precipitate. Hexane is added to the precipitate, stirred, and irradiated with ultrasonic waves for 20 to 30 seconds, followed by washing by centrifugation at 25 ° C. and a rotation speed of 2000 rpm for 20 minutes. Next, the supernatant (hexane) is discarded, and washing in which hexane is added to the precipitate is repeated three times in the same manner as described above. The precipitate thus obtained is taken out on a filter paper and dried in a vacuum dryer at 25 ° C. for 1 hour to prepare about 1 g of a dry toner sample. A paste is prepared by applying pressure to the toner sample with a pressure machine. The paste prepared in this manner is measured using a flow tester (product name: CFT-500D (manufactured by Shimadzu Corporation)) under the following conditions for the melting temperature Tm and the softening temperature Ts of the toner particles.
Measurement start temperature: 50 ° C
Measurement end temperature: 200 ° C
Weight: 0.5kg
Temperature increase rate: 5 ° C / min
Die hole diameter: 0.5mm
Die hole length: 1mm
Residual heating time: 60 seconds The temperature T ₁ of the recording material after the first heating step is the digital temperature of the recording material when 0.025 seconds have elapsed since the completion of the first heating step. A value measured by a temperature sensor (product name: Thermopile FT-H10 (manufactured by Keyence Corporation)) is adopted.

FIG. 1 is a schematic diagram showing an outline when the temperature T ₁ of the recording material after passing through the first heating step is measured. As shown in FIG. 1, the A4 recording material 12 having the liquid developer 11 transferred between the first fixing roller 14 and the first pressure roller 15 is passed at a speed of 400 mm / s, thereby allowing the recording material to pass. Heat. Here, the outer diameter of the first fixing roller 14 and the first pressure roller 15 is 50 mm, and an elastic layer is formed on the outer peripheral surface of the core metal having an outer diameter of 35 mm. Such an elastic layer is obtained by laminating a polytetrafluoroethylene (PTFE) having a thickness of 1 mm on the surface of a silicone rubber layer having a thickness of 15 mm. Each of the first fixing roller 14 and the first pressure roller 15 includes a halogen lamp heater 13 therein.

  The digital radiation temperature sensor 23 has an emissivity of 0.95 and a response time of 0.03 seconds. The digital radiation temperature sensor 23 is installed at a point (D in FIG. 1) that is 35 mm away from the surface of the recording material, and is connected to the digital amplifier 24. The digital radiation temperature sensor 23 calculates the temperature of the recording material by calculating the data received by the digital amplifier 24 with the personal computer 25.

<Second heating step>
In the present invention it, the second heating step, the a step of recording material heated in the first heating step for heating to a temperature of T _2, according T ₂ are a temperature higher than the melting temperature Tm of the toner particles Is preferred. In such a second heating step, by heating the recording material to a temperature higher than the melting temperature Tm, the insulating liquid contained in the liquid developer can be stably volatilized, so that the toner becomes a recording material. It becomes easy to fix. On the other hand, if T ₂ is equal to or lower than the melting temperature Tm, the recording material is not sufficiently heated, so that the insulating liquid is less likely to volatilize and the toner is less likely to agglomerate.

Here, the temperature T ₂ of the recording material after the second heating step is the digital radiation temperature sensor (product) when 0.025 seconds have elapsed since the completion of the second heating step. Name: The value measured by Thermopile FT-H10 (manufactured by Keyence Corporation) is adopted. Since the measurement method is the same as that of the first heating step, description thereof will not be repeated.

<Contact wet image formation>
FIG. 2 is a cross-sectional view schematically showing the first heating step and the second heating step of the wet image forming method of the present invention. In the following description, a case where the recording material is heated by a contact type will be described as an example. However, it goes without saying that the recording material may be heated by a non-contact type as shown in FIG.

In FIG. 1, the recording material 12 to which the liquid developer 11 has been transferred is first heated to T ₁ by passing between the first fixing roller 14 and the first pressure roller 15 as a first heating step. Then, as a second heating step, the sheet is heated to T ₂ by passing between the second fixing roller 16 and the second pressure roller 17. By heating the recording material in this manner by contact, the temperature of the recording material can be increased efficiently, so that the insulating liquid contained in the liquid developer can be efficiently volatilized.

  In addition, you may provide a heating means further before and after the 1st heating step and the 2nd heating step as needed.

  Here, the first fixing roller 14, the first pressure roller 15, the second fixing roller 16, and the second pressure roller 17 appropriately determine the heating temperature depending on the type and thickness of the recording material and the passing speed of the recording material. Is preferred. Further, the first fixing roller 14 is generally set to be 20 to 50 ° C. higher than the first pressure roller 15 in order to prevent an offset at the time of passing through both surfaces. Similarly, the second fixing roller 16 is set 20 to 50 ° C. higher than the second pressure roller 17.

<Non-contact wet image formation>
FIG. 3 is a cross-sectional view schematically showing the first heating step and the second heating step of the wet image forming method of the present invention. Although FIG. 3 shows the case where the second heating step is heated in a non-contact manner, the first heating step may be heated in a non-contact manner.

The wet image forming apparatus shown in FIG. 3 heats the recording material by radiating heat using the heat source 30 in the second heating step. Even if the recording material is heated in this way, it does not depart from the scope of the present invention. When the recording material is heated by such a method, the temperature T ₂ of the recording material immediately after the second heating step is the temperature of the recording material at a point 10 mm away from the position immediately below the heat source 30. . In addition to the non-contact heating method shown in FIG. 3, for example, a belt type may be used, or the recording material may be heated by irradiating the recording material with hot air.

Hereinafter, the liquid developer used in the wet image forming method of the present invention will be described.
<Liquid developer>
The liquid developer used in the wet image forming method of the present invention includes toner particles, an insulating liquid, and a dispersant. Such a liquid developer can contain other arbitrary components as long as these components are contained. Examples of other components include a charge control agent and a viscosity modifier. Such a liquid developer is useful as a developer for an electrophotographic image forming apparatus.

  Here, the mixing ratio of each component is, for example, 10 to 50% by mass of toner particles, 50 to 90% by mass (45 to 89.99% by mass) of insulating liquid, and the dispersant to the mass of toner particles. It can be 0.1-10 mass%. The viscosity of the liquid developer is preferably 0.1 to 10,000 mPa · s at 25 ° C. If it exceeds 10,000 mPa · s, stirring of the insulating liquid and the toner particles becomes difficult, and it becomes difficult to obtain a uniform liquid developer, which is not preferable. Hereinafter, each component contained in the liquid developer will be described.

(Toner particles)
The toner particles contained in the liquid developer of the present invention usually exist in a state where they are not compatible with the insulating liquid and are dispersed in the insulating liquid. At least a resin and a pigment dispersed in the resin are included. Is included. Such toner particles may contain other components as long as they contain a resin and a pigment. Examples of such other components include a wax and a charge control agent.

  The toner particles preferably include 10 to 50 parts by weight with respect to 100 parts by weight of the liquid developer. When the amount is less than 10 parts by weight, there is a problem that toner particles settle in the liquid developer and stability during long-term storage is lowered. In addition, when the amount is less than 10 parts by weight, the toner particle content is small, so that a necessary image density cannot be obtained unless a large amount of liquid developer is supplied. For this reason, the amount of the insulating liquid to be dried at the time of fixing becomes too large, which increases the environmental load, which is not preferable. On the other hand, when the amount exceeds 50 parts by mass, the viscosity of the liquid developer becomes too high, which makes it difficult to produce the liquid developer and to handle it.

  Here, it is preferable that the compounding ratio of resin and pigment contains 8-50 mass% of pigment with respect to resin, for example, More preferably, it is 10-30 mass%. If the amount is less than 8% by mass, the pigment concentration becomes insufficient, and a desired concentration cannot be obtained. If the amount exceeds 50% by mass, the pigment becomes difficult to disperse in the resin or the binder component decreases. The necessary fixing strength cannot be obtained.

  The particle size of the toner particles is not particularly limited, but is preferably 0.1 to 5 μm, more preferably 1 to 4 μm, and still more preferably 1 to 1 for the purpose of obtaining a high-quality image. The thickness is preferably 3 μm. These particle diameters are smaller than the particle diameter of toner particles of a powdery developer (dry developer) that has been conventionally used, and are one of the features of the present invention. By using toner particles having such a particle size, it is possible to print a toner having good developability and high image quality. When the thickness is less than 0.1 μm, the developability is greatly deteriorated, and when it exceeds 5 μm, the image quality is deteriorated. In addition, the particle diameter as used in the field of this invention means an average particle diameter, and can be specified as a volume average particle diameter with various particle size distribution analyzers.

  The resin constituting the toner particles of the present invention can be used without particular limitation as long as it is thermoplastic. Examples of such resins include polyester resins, styrene-acrylic copolymer resins, styrene-acrylic modified polyester resins, polyolefin copolymers (particularly ethylene copolymers), epoxy resins, rosin modified phenolic resins, rosin modified maleic resins. An acid resin etc. can be mentioned.

  The resin used in the present invention preferably has an acid value of 10 mgKOH / g or more and 100 mgKOH / g or less, more preferably 30 mgKOH / g or more and 60 mgKOH / g or less. The higher the oxidation, the better the fixing property with the recording material. When the acid value is less than 10 mgKOH / g, the adhesion between the toner particles and the recording material is small, and the fixability may be deteriorated. On the other hand, if it exceeds 100 mgKOH / g, the toner particles may become too hard and much fixing energy may be required.

  The resin constituting the toner particles preferably has a weight average molecular weight (Mw) of 5,000 to 200,000, more preferably 7,000 to 30,000. If the weight average molecular weight is less than 5,000, uniform dispersion with the pigment may be difficult. On the other hand, if the weight average molecular weight exceeds 200,000, the energy required for fixing on a recording medium increases, which may be undesirable. The weight average molecular weight can be measured by GPC (gel permeation chromatography).

  The resin used in the present invention preferably exhibits thermoplasticity and has a glass transition point (Tg) of 40 ° C. or higher and 85 ° C. or lower. When the glass transition point is less than 40 ° C., storage stability may deteriorate. When the glass transition point exceeds 85 ° C., energy for fixing an image is remarkably increased, which is disadvantageous economically, and heat is applied to each part of the image forming apparatus. If the fixing temperature is low, the glossiness of the image may be lowered. A more preferable glass transition point is 55 ° C. or higher and 75 ° C. or lower.

<Pigment>
The pigment contained in the toner particles of the present invention is dispersed in the above resin and is added to obtain a desired color tone. The particle size of such a pigment is 0.5 μm or less, more preferably 0.15 μm or less. If the particle diameter of the pigment exceeds 0.5 μm, the color value of the image may be shifted and a desired color may not be obtained. Moreover, the lower limit of the particle size of the pigment is not particularly limited.

  The suitable pigment concentration relative to the resin depends on the particle size and color type of the pigment. As the particle size of the pigment is reduced, a desired image quality can be obtained even if the pigment concentration is lowered. Regarding the color type, for example, a cyan pigment preferably has a pigment concentration of 10 to 40% by mass with respect to the resin, and a magenta pigment preferably has a pigment concentration of 15 to 50% by mass, The pigment preferably has a pigment concentration of 8 to 30% by mass relative to the resin.

  The pigment is preferably dispersed in a resin so that its secondary particle size is 50 nm or more and 300 nm or less. When it exceeds 300 nm, there is a tendency that sufficient coloring power, hiding power, and transparency after fixing are difficult to obtain even with a fixed adhesion amount. In order to improve the dispersibility of the pigment, a pigment derivative obtained by treating the surface of the pigment to be basic or acidic may be used. Such pigment is preferably contained in an amount of 10 to 40 parts by mass with respect to 100 parts by mass of the resin. If the pigment content is less than 10 parts by mass, the required image density cannot be obtained. If the pigment content exceeds 40 parts by mass, the resin content in the toner particles decreases, so that sufficient fixing strength can be obtained. become unable. More preferable content is 10-25 mass parts, More preferably, it is 12-20 mass parts.

  As the pigment constituting the toner particles, conventionally known pigments can be used without any particular limitation. As the pigment, an organic pigment can be used. Examples of the organic pigment include phthalocyanine-based, azo, disazo, polyazo-based azo-based, anthraquinone-based, quinacridone-based, dioxazine-based, perinone-based, thioindigo-based, and isoindoline-based pigments. Etc.

  Examples of the pigment include orthoaniline black, toluidine orange, permanent carmine FB, first yellow AAA, disazo orange PMP, lake red C, brilliant carmine 6B, quinacridone red, C.I. I. Pigment blue, C.I. I. Pigment Red, C.I. I. And CI Pigment Yellow, Dioxane Violet, Pictoria Pure Blue, Alkali Blue Toner, Alkali Blue R Toner, First Yellow 10G, Ortho Nitroaniline Orange, Toluidine Red and the like.

<Insulating liquid>
The insulating liquid contained in the liquid developer of the present invention is preferably a non-volatile liquid at normal temperature and electrically insulating, for example, a low dielectric constant having a dielectric constant of 3 or less. This is because the electrostatic latent image is not normally disturbed if it has a resistance value in this range. Further, such an insulating liquid is preferably free from odor and toxicity.

  Examples of such insulating liquids include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes, silicone oils, animal and vegetable oils, mineral oils, and the like. In particular, a normal paraffin solvent and an isoparaffin solvent are preferable from the viewpoint of odor, harmlessness, and cost. More specifically, Moresco White P40 (trade name), P60 (trade name), P120 (trade name), Isopar (trade name, manufactured by Exxon Chemical) manufactured by Matsumura Oil Research Co., Ltd., Shellsol 71 (Trade name, manufactured by Shell Petrochemical Co., Ltd.), IP solvent 1620 (trade name, manufactured by Idemitsu Petrochemical Co., Ltd.), IP solvent 2028 (trade name, manufactured by Idemitsu Petrochemical Co., Ltd.), and the like.

<Dispersant>
The dispersant contained in the liquid developer of the present invention has a function of stably dispersing the toner particles in the insulating liquid. Therefore, the dispersant is usually present (adsorbed) on the surface of the toner particles. Yes. Such a dispersant may be dissolved or dispersed in the liquid developer, and is selected from the group consisting of an amide group, a pyrrolidone group, a urethane group, and an imine group. And a compound having one or more substituents.

  By using a liquid developer containing a dispersant having these functional groups, the toner particles capture the insulating liquid via the dispersant, so that the surface and the inside of the liquid developer 11 are uniformly semi-aggregated. State. Thereby, it is possible to prevent the toner particles only on the surface of the liquid developer 11 from being aggregated to form a film. As a result, the insulating liquid captured by the dispersant can be stably volatilized, and offset can be hardly generated. The dispersant is not particularly limited as long as the toner particles are stably dispersed. For example, a surfactant, a polymer dispersant, or the like may be used.

  As the compound having the above amide group, “product name: Disperbyk-109 (alkylol aminoamide) manufactured by BYK Chemie” can be preferably used. The compound having a urethane group can be obtained by reacting an acid or alcohol group with an isocyanate, and can be formed by reacting the terminal with an isocyanate using, for example, acrylic acid, methacrylic acid, HEMA, or the like. .

  In order for the above dispersant to be uniformly dispersed with the insulating liquid, it is preferable to have a long-chain alkyl group in the molecule of the dispersant. Such a dispersant is preferably added in an amount of 0.5% by mass to 10% by mass, more preferably 0.5% by mass or more and 5% by mass with respect to the mass of the toner particles. If the added amount of the dispersant is less than 0.5% by mass, the dispersibility of the toner particles decreases. This is not preferable, and if it exceeds 10% by mass, the dispersant traps the insulating liquid. Becomes difficult to settle.

  It is preferable to use a basic polymer dispersant as such a dispersant, and it is particularly preferable to use a polymer dispersant having a pyrrolidone group as its basic group. This is probably because the acid value of the above-mentioned vinyl copolymer resin constituting the toner particles is high, so that by using a basic polymer dispersant, good dispersibility of the toner particles due to the interaction between them. This is thought to be due to stabilization over a long period of time. The basic polymer dispersant of the present invention refers to a polymer dispersant having a basic group, and has a weight average molecular weight of about 3000 to 10,000.

  Examples of such basic polymer dispersants include the pyrrolidone group, for example, an aromatic amino group, an aliphatic amino group, a heterocyclic nitrogen-containing group, a heterocyclic oxygen-containing group, and a heterocyclic sulfur-containing group. A polymeric dispersant can be mentioned. Examples of the pyrrolidone group include an N-vinylpyrrolidone group. Examples of the basic polymer dispersant having an N-vinylpyrrolidone group include N-vinyl-2-pyrrolidone, methacrylic acid ester, and acrylic acid. A random copolymer or a graft copolymer with an acid ester or an alkylene compound can be used. Here, when the methacrylic acid ester and the acrylic acid ester are alkyl esters, the alkyl group preferably has about 10 to 20 carbon atoms. Examples of these commercially available products include “Antaron V-216” and “Antaron V-220” (both are trade names, manufactured by GAF / ISP Chemicals). Further, the alkyl group of the alkylene compound preferably has about 10 to 30 carbon atoms. Examples of polyvinylpyrrolidone having a long-chain alkyl group include “W-660” (trade name, manufactured by GAF / ISP Chemicals).

<Method for adjusting liquid developer>
First, the resin constituting the toner particles can be produced by a conventionally known radical polymerization method. That is, although it depends on the type of raw material monomer to be used, it can generally be carried out in a temperature range of 50 to 300 ° C. Moreover, arbitrary conditions, such as using inert gas as atmospheric gas, selecting various solvents arbitrarily, or making the reaction container internal pressure normal pressure or pressure reduction, can be employ | adopted.

  The liquid developer can be prepared based on a conventionally known technique. For example, by using a kneader such as a pressure kneader, a roll mill, or a three roll, the resin and the pigment are melt-kneaded at a predetermined blending ratio, and the pigment is uniformly dispersed in the resin to obtain a pigment-resin dispersion. obtain.

  Subsequently, the pigment-resin dispersion obtained above is cooled, and after cooling, this is coarsely pulverized by, for example, a jet mill. Subsequently, the coarsely pulverized pigment-resin dispersion (also referred to as “coarse pulverized toner”) is further finely pulverized to a desired particle size. Then, for example, a colored toner having a predetermined particle diameter is obtained by classification with an air classifier or the like.

  The pulverization method that can be used as described above is not particularly limited as long as it is a method that can pulverize to a desired particle size with energy saving. In addition to dry pulverization method, wet pulverization method, etc., granulation in oil Or after granulating in a nonpolar solvent, the solvent may be replaced with oil.

  For example, a coarsely pulverized toner is obtained by a cutter mill, and then toner particles are obtained by further pulverizing the coarsely pulverized toner to a desired particle size using a jet mill as a dry pulverization method. Then, the toner particles are mixed with an insulating oil and a dispersant. And a liquid developer can be prepared by disperse | distributing this mixture uniformly by dispersion | distribution means, such as a ball mill.

  On the other hand, when the wet pulverization method is adopted, for example, the coarsely pulverized toner obtained above, an insulating oil, and a dispersant are mixed, and the mixture is pulverized using a sand mill to obtain toner particles having a desired particle size. And a liquid developer can be prepared.

<Image forming apparatus>
In the following, an image forming apparatus for transferring a liquid developer onto the surface of a recording material will be described. FIG. 4 is a schematic cross-sectional view showing the step of transferring the liquid developer onto the surface of the recording material. In the apparatus of FIG. 4, constituent elements related to image formation are shown, and constituent elements related to paper feeding, conveyance, and paper discharge of recording materials not directly related to image formation are shown in a simplified manner.

  An image forming apparatus 10 shown in FIG. 4 includes a photosensitive drum 1 as an image carrier, a charging device 2, an exposure device 3, a wet developing device 4, an intermediate transfer roller 5 as an intermediate transfer member, and a cleaning device 6. A next transfer roller 7 is provided.

  The color development method, the presence / absence of intermediate transfer, and the like can be arbitrarily set, and an arbitrary arrangement configuration corresponding thereto can be taken. For example, instead of the intermediate transfer roller 5 described above, an intermediate transfer belt may be used, or two or more wet developing devices 4 may be arranged to form a color image.

  The photosensitive drum 1 has a cylindrical shape with a photosensitive layer (not shown) formed on the surface thereof, and rotates in the direction of arrow A in FIG. 1, and the recording material 9 is 400 mm / sec. Rotate to move. A cleaning device 6, a charging device 2, an exposure device 3, a wet developing device 4, and an intermediate transfer roller 5 are arranged in this order on the outer periphery of the photosensitive drum 1 along the rotation direction of the photosensitive drum 1. .

  Here, the charging device 2 can charge the surface of the photosensitive drum 1 to a predetermined potential, and the exposure device 3 irradiates the surface of the photosensitive drum 1 with light to lower the charging level in the irradiated region. To form an electrostatic latent image. Then, the latent image formed on the photosensitive drum 1 is developed by the wet developing device 4. That is, the liquid developer is transported to the developing area of the photosensitive drum 1, and the toner contained in the liquid developer is supplied to the electrostatic latent image on the surface of the photosensitive drum 1 to form a toner image.

  Such a wet developing device 4 carries a thin layer of a liquid developer on its surface and develops a latent image on the photosensitive drum 1 as an image carrier, and a contact with the developing roller 41. In contact therewith, a conveying roller 42 for transferring the liquid developer whose liquid amount has been adjusted to the surface thereof, and a supply roller 43 which contacts the conveying roller 42 and supplies the liquid developer 8 in the developer tank 44 to the surface thereof. With.

  In the developing process, a developing bias voltage having the same polarity as the toner is applied to the developing roller 41 of the wet developing device 4 using a power source (not shown). Similarly, a difference in electric field is formed in balance with the potential of the latent image on the photosensitive drum 1 having the same polarity as the toner, and the toner in the developer is electrostatically adsorbed on the photosensitive drum 1 in accordance with the latent image. The latent image on 1 is developed.

  The intermediate transfer roller 5 is disposed so as to face the photosensitive drum 1 and rotates in the direction of arrow B while being in contact with the photosensitive drum 1. Primary transfer from the photosensitive drum 1 to the intermediate transfer roller 5 is performed at the nip portion between the intermediate transfer roller 5 and the photosensitive drum 1. In the primary transfer, a transfer bias voltage having a polarity opposite to that of the toner is applied to the intermediate transfer roller 5 using a power source (not shown).

  As a result, an electric field is formed between the intermediate transfer roller 5 and the photosensitive drum 1 at the primary transfer position, and the toner image on the photosensitive drum 1 is electrostatically attracted to the intermediate transfer roller 5, whereby the intermediate transfer roller 5. Transcribed above. When the toner image is transferred to the intermediate transfer roller 5, the residual toner on the photosensitive drum 1 is removed by the cleaning device 6. The intermediate transfer roller 5 and the secondary transfer roller 7 are disposed so as to face each other with the recording material 9 interposed therebetween, and rotate in contact with each other via the recording material 9. Secondary transfer from the intermediate transfer roller 5 to the recording material 9 is performed at the nip portion between the intermediate transfer roller 5 and the secondary transfer roller 7.

  The recording material 9 is conveyed in the direction of arrow C to the secondary transfer position in synchronization with the secondary transfer timing. In the secondary transfer, an electric field is generated between the intermediate transfer roller 5 and the secondary transfer roller 7 by applying a transfer bias voltage having a polarity opposite to that of the toner to the secondary transfer roller 7 from a power source (not shown). It is formed. By this electric field, the toner image on the intermediate transfer roller 5 is electrostatically attracted to the recording material 9 that has passed between the intermediate transfer roller 5 and the secondary transfer roller 7, and the liquid developer is transferred onto the recording material 9. .

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these. First, Resin I and Resin II were synthesized, and Liquid Developers A to F were blended using the Resin I and Resin II. In Examples 1 to 7 and Comparative Examples 1 to 4, wet development was performed using the liquid developers A to F formulated as described above. Below, Examples 1-7 and Comparative Examples 1-4 are demonstrated in this order.

<Resin synthesis>
(Synthesis of Resin I)
First, 1600 parts by weight of a propylene oxide adduct of bisphenol A (polyhydric alcohol) and terephthalic acid are added to a round bottom flask equipped with a reflux condenser, a water / alcohol separator, a nitrogen gas inlet tube, a thermometer, and a stirring device. 550 parts by weight and trimellitic acid 340 parts by weight. Next, nitrogen gas was introduced while stirring them, and the mixture was heated to a temperature of 200 to 240 ° C. to perform dehydration polycondensation or dealcoholization polycondensation.

  Next, when the acid value of the resin or the viscosity of the reaction solution reaches a predetermined value, the polycondensation is stopped by cooling the temperature of the reaction system to 100 ° C. or less, and the thermoplastic polyester resin (resin I) Obtained. The obtained resin I had Mw = 7500, Mn = 2700, Tg = 65.3 ° C., and acid value = 64.0 mgKOH / g.

(Synthesis of Resin II)
Resin II was synthesized by the same method as the synthesis of Resin I, except that trimellitic acid among the raw material components used in the production of Resin I was changed to terephthalic acid. That is, in resin II, a total of 890 parts by weight of terephthalic acid was mixed to obtain a thermoplastic polyester resin (resin II). The obtained resin II had Mw = 4800, Mn = 2000, Tg = 50.3 ° C., and acid value = 15.0 mgKOH / g.

<Preparation of liquid developer>
(Preparation of liquid developer A)
First, 100 parts by weight of resin I and 15 parts by weight of copper phthalocyanine blue were sufficiently mixed using a Henschel mixer. And it melt-mixed with the twin-screw extrusion kneader, and cooled the mixture. Next, the melted and mixed powder was coarsely pulverized and finely pulverized with a jet pulverizer to an average particle size of 6 μm.

  Next, the obtained finely pulverized mixed powder was melt-kneaded at a heating temperature in a biaxial roll of 150 ° C. using a co-rotating twin-screw extruder. Thereafter, the melt-kneaded powder was cooled and coarsely pulverized to obtain a coarsely pulverized toner. 34 parts by weight of the coarsely pulverized toner, 0.2 parts by weight of Antaron V-216 (manufactured by GAF / ISP Chemicals) as a basic polymer dispersant (0.5% by mass with respect to the toner), liquid paraffin 100 parts by weight (flash point 86 ° C., IP solvent 2028 (Idemitsu Petrochemical Co., Ltd.)) and 100 parts by weight of zirconia beads were mixed and stirred in a sand mill for 120 hours to prepare a liquid developer. The volume average particle size of the toner particles contained in the liquid developer thus obtained was 2.3 μm.

(Preparation of liquid developer B)
With respect to the liquid developer A, the polyester resin I is changed to the polyester resin II, and the blending amount of the basic polymer dispersant is 0.2 to 1.7 parts by weight (5 mass with respect to the toner). The liquid developer B was prepared in the same manner as the liquid developer A, except that the content was changed to%). The volume average particle size of the toner particles contained in the liquid developer thus prepared was 2.7 μm.

(Preparation of liquid developer C)
For the above liquid developer B, the basic polymer dispersant is changed to Disperbyk-109 (made by Big Chemie Japan Co., Ltd.), which is an amide-based dispersant. The liquid developer C was produced in the same manner as the liquid developer B except that the content was changed to 2.9% by mass).

(Preparation of liquid developer D)
Same as liquid developer B, except that the amount of the basic polymer dispersant is changed to 3.4 parts by weight (10% by mass with respect to the toner) with respect to the liquid developer B. A liquid developer D was prepared by the method described above.

(Preparation of liquid developer E)
The same method as the liquid developer B, except that the amount of the basic polymer dispersant is changed to 4 parts by weight (12% by weight based on the toner) with respect to the liquid developer B. Thus, a liquid developer D was prepared.

(Preparation of liquid developer F)
For the liquid developer B, the basic polymer dispersant is changed to polyesteramine (product name: Solspers 13940 (manufactured by Zeneca)), and the blending amount is 3 parts by weight (8. The liquid developer F was produced in the same manner as the liquid developer B except that the content was changed to 8% by mass).

<Measurement of melting temperature Tm and softening temperature Ts>
5 ml of each of the liquid developers A to F produced above was measured, and centrifuged at 25 ° C. and 2000 rpm for 20 minutes. Then, only the supernatant is discarded to leave a precipitate. Hexane was added to the precipitate, stirred, and irradiated with ultrasonic waves for 20 to 30 seconds, and then washed by centrifugation at 25 ° C. and a rotation speed of 2000 rpm for 20 minutes.

  Next, the supernatant (hexane) was discarded, and the washing of adding hexane to the precipitate was repeated three times in the same manner as described above. The precipitate thus obtained was taken out on a filter paper and dried at 25 ° C. for 1 hour with a vacuum dryer to prepare about 1 g of a dried toner sample. A paste was prepared by applying pressure to the toner sample with a pressure machine.

The melt temperature Tm and the softening temperature Ts of the toner particles were measured for the paste thus produced using a flow tester (product name: CFT-500D (manufactured by Shimadzu Corporation)) under the following conditions. The results are shown in the “Ts” and “Tm” columns of Tables 1 and 2.
Measurement start temperature: 50 ° C
Measurement end temperature: 200 ° C
Weight: 0.5kg
Temperature increase rate: 5 ° C / min
Die hole diameter: 0.5mm
Die hole length: 1mm
Residual heat time: 60 seconds

<Examples 1-7 and Comparative Examples 1-4>
In Examples 1 to 7 and Comparative Examples 1 to 4, first, OK top coat 128 g paper (manufactured by Oji Paper Co., Ltd.) or Bon Ivory 360 g paper (manufactured by Oji Paper Co., Ltd.) was used as the recording material. A solid image was placed on the recording material with the liquid developers A to F so that the amount of toner particles was 3 g / m ^{2 in} terms of solid content. And the 1st heating step and the 2nd heating step were performed with the contact-type heating apparatus shown in FIG. In the first heating step, the temperature of the recording material is raised to the temperature shown in the column “T ₁ ” in Table 2 below, and in the second heating step, the temperature is recorded in the temperature shown in the column “T ₂ ” in Table 2 below. The material was warmed. By heating in this way, the insulating liquid contained in the liquid developer was volatilized, and the liquid developer was fixed on the recording material.

<Fixing strength>
In each Example and each Comparative Example, the fixing strength of the liquid developer fixed on the recording material was evaluated as follows. First, a 20 mm wide tape (product name: Scotch Mending Tape 810 (manufactured by 3M)) was applied to an image surface having a length of about 50 mm, and the tape surface was pressed with a finger. Thereafter, the tape was peeled off and replaced with paper (product name: CF-80 paper (manufactured by Konica Minolta)).

Next, the ID of the paper where the toner is not attached was measured with an ID measuring machine (product name: Spectroeye LT (manufactured by X-Rite)), and zero calibration was performed. Then, the ID of the portion where the toner adhered was measured by the same ID measuring machine. The IDs thus obtained were evaluated in four stages based on the following evaluation criteria, and the evaluation results are shown in the “fixing strength” column of Table 2. Note that the smaller the ID is, the more toner is not attached to the tape and the higher the fixing strength to paper.
A: ID is less than 0.02 B: ID is 0.02 or more and less than 0.05 C: ID is 0.05 or more and less than 0.1 D: ID is 0.1 or more <Residual liquid amount>
The weight of the paper immediately after the second heating step was W _1, and the weight of the paper after the fixing process was vacuum dried at room temperature for 1 hour was W ₂ . Also, as a reference, the weight of the paper immediately after performing the fixing process is W ₃ for the paper on which no image is printed, and the weight of the paper after vacuum-drying the paper after the fixing process for 1 hour at room temperature. It was W _4. And the residual liquid amount was measured by the following formula | equation.
Residual liquid amount = (W ₁ −W ₂ ) − (W ₃ −W ₄ )
The residual liquid amount calculated in this way was evaluated in three stages based on the following evaluation criteria, and the evaluation results are shown in the column of “Residual liquid amount” in Table 2. Note that as the amount of remaining liquid increases, show-through tends to occur, which means that printing performance is poor. When the amount of residual liquid was ² g / m ² or more, show-through was likely to occur remarkably.
A: Residual liquid amount is less than 1.5 g / m ² B: Residual liquid amount is 1.5 g / m ² or more and less than 2 g / m ² C: Residual liquid amount is 2 g / m ² or more <Offset>
In each example and each comparative example, after passing through the first heating step and the second heating step, white CF-80 paper was allowed to pass through to visually confirm the presence or absence of paper stains. If the roller stain is attached to the paper, it is evaluated as “B” as an offset has occurred, and if the paper is not contaminated, it is evaluated as “A” as an offset has not occurred. These are shown in the “Offset” column of Table 2, respectively.

As is clear from the results shown in Table 2, the print quality is improved such that show-through occurs when the recording material is heated to satisfy Ts <T ₁ <Tm as in Examples 1 to 7. The toner can be firmly fixed on the recording material without lowering. On the other hand, as in Comparative Examples 2 to 4, when the above Ts <T ₁ <Tm is not satisfied, the fixing strength of the toner to the paper is not sufficient, or the remaining amount of the insulating liquid is large. Thus, the print quality was not excellent.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Photosensitive drum, 2 Charging apparatus, 3 Exposure apparatus, 4 Wet development apparatus, 5 Intermediate transfer roller, 6 Cleaning apparatus, 7 Secondary transfer roller, 8 Liquid developer, 9 Recording material, 10 Image forming apparatus, 11 Liquid development Agent, 12 recording material, 13 heater, 14 first fixing roller, 15 first pressure roller, 16 second fixing roller, 17 second pressure roller, 23 digital radiation temperature sensor, 24 digital amplifier, 25 personal computer, 30 heat source , 41 Development roller, 42 Conveyance roller, 43 Supply roller, 44 Developer tank.

Claims (4)

Transferring the liquid developer to the surface of the recording material;
A first heating step of heating the recording material to which the liquid developer has been transferred,
The liquid developer includes toner particles, an insulating liquid, and a dispersant.
The dispersant includes a compound having one or more substituents selected from the group consisting of an amide group, a pyrrolidone group, a urethane group, and an imine group,
When the temperature of the recording material immediately after the first heating step is T ₁ and the melting temperature and the softening temperature of the toner particles measured by the flow tester are Tm and Ts, respectively, the relationship of Ts <T ₁ <Tm is established. A wet image forming method to satisfy. A second heating step for heating the recording material after the first heating step;
The wet image forming method according to claim 1, wherein the temperature T ₂ of the recording material immediately after the second heating step is higher than the Tm.   3. The wet image forming method according to claim 1, wherein the liquid developer contains 0.5% by mass or more and 10% by mass or less of the dispersant with respect to the mass of the toner particles.   The wet image forming method according to claim 1, wherein the dispersant contains a pyrrolidone group.

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