JP2008170704A - Image forming device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device and method which can obtain excellent uniform and high-density images. <P>SOLUTION: The fixing unit 70 consists of two stages, a first upstream fixing section 71 and a second downstream fixing section 74. Representing the fixing temperature of the first fixing section 71 by Tn1, the solid content flow softening point of the developing agent by Tf, and the dispersant desorption temperature by Td, the relation of Td<Tn1<Tf is satisfied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, a liquid developer is supplied to a developer carrier by a developer supply roller, a latent image on the image carrier is developed by the developer carrier, and an image on the image carrier is transferred to an intermediate transfer member. The present invention relates to an image forming apparatus and an image forming method for forming an image by secondary transfer of an image on an intermediate transfer member to a transfer material.

  Conventionally, as a patent relating to an apparatus for measuring the electrical characteristics of a toner, the measuring means sandwiches a very small amount of toner sample between both electrodes and applies an electric field, whereby the mobility, conductivity, zeta potential of the toner, etc. Some of them were able to quantify their electrical properties. Here, since the above-described conductivity can be said to be the resistance of the toner, in other words, it is known that this conductivity changes as the amount of charged particles in the entire toner increases or decreases (see Patent Document 1). ).

In addition, regarding the fixing device and fixing method in the electrophotographic apparatus using a liquid developer, the fixing device has a two-stage station, the temperature of the second-stage nip fixing device is higher than that of the first stage, and In the first stage, there is known a fixing device capable of obtaining high fixability by evaporating a certain amount of carrier oil (see Patent Document 2).
JP 2001-264294 A Japanese Patent Laid-Open No. 2005-78084

  When the electrical characteristics of the toner are measured using the apparatus described in Patent Document 1, the toner conductivity is generally found to increase as the temperature rises, as will be described in detail later. This is considered to be because the dispersant adhering to the toner solid content is easily detached from the surface of the toner particles due to an increase in thermal kinetic energy accompanying the temperature increase.

  On the other hand, as described in Patent Document 2, it is known that it is necessary to remove carrier oil as much as possible in order to fix the liquid developer efficiently. As a method for removing the carrier oil, evaporation of the carrier oil is used.

  However, the evaporation of the carrier oil goes against the recent flow of VOC regulations (volatile organic matter emission regulations). In addition, when the evaporated carrier oil is not taken out of the apparatus, a recovery mechanism must be newly installed, and there is a problem that the apparatus becomes large.

  SUMMARY An advantage of some aspects of the invention is to provide an image forming apparatus and an image forming method capable of solving the above-described problems and obtaining a uniform and high-density image.

  The present invention is an image forming apparatus that solves the above problems, a developer container for storing a liquid developer comprising a developer solid content containing a pigment component, a dispersant, and a non-volatile liquid carrier, and a liquid A developer carrying member for carrying a developer; a developer supply member for supplying a liquid developer from the developer container to the developer carrying member; and an image carrier for developing a latent image by the developer carrying member. An intermediate transfer member that forms an image by transferring an image on the image carrier, a secondary transfer portion that transfers the image on the intermediate transfer member to a transfer material, and an image transferred by the secondary transfer portion A fixing unit for fixing the toner image onto the transfer material, and the fixing unit has a two-stage configuration of a first fixing device on the upstream side and a second fixing device on the downstream side, the fixing temperature Tn1 of the first fixing device, Developer solids flow softening point Tf and dispersant desorption temperature Td Since the relationship of Td <Tn1 <Tf is established, the dispersant can be separated from the developer solids by the relationship of Td <Tn1, and with the liquid carrier whose viscosity is lowered by heat, Due to the relationship of the high dispersant penetrating into the recording medium and Tn1 <Tf, the first fixing device allows only the liquid carrier and the dispersant to permeate the transfer material and keeps the developer solid content on the transfer material. The developer solid content particle film does not penetrate into the transfer material more than necessary, and a uniform and high-density image can be obtained.

  Further, the relationship between the fixing temperature Tn2 of the second fixing device of the fixing unit, the fixing temperature Tn1 of the first fixing device, the developer solid melting point temperature Tf, and the dispersant desorption temperature Td is expressed as Td <Tn1 <Tf <. Since Tn2 is set, the fixing temperature higher than the developer solid content flow softening point is obtained in the second fixing device because of the relationship of Tf <Tn2. Therefore, a favorable fixing rate can be obtained.

  Further, since the secondary transfer portion is at or below the dispersant desorption temperature Td, an electric field can be efficiently applied, and the resistance of the developer solid content is not reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing main components constituting an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing components for each color of the image forming apparatus. In FIG. 1, for each color composed of yellow (Y), magenta (M), cyan (C), and black (K), the same component is given Y, M, C, and K representing each color. The same number is used. Of these, FIG. 2 shows the configuration of yellow (Y). The image forming apparatus will be described below with reference to FIGS.

  The image forming apparatus 1 includes a cleaning device including a cleaning blade 16Y for the image carrier and a developer recovery unit 17Y, a charging roller 11Y, an exposure unit 12Y, and a developer along the rotation direction (movement direction) of the outer periphery of the image carrier 10Y. A cleaning device including a developing roller 20Y, an image carrier squeeze roller 13Y as an example of a developer carrying member of the unit 30Y, and a cleaning blade 14Y and a developer collecting unit 15Y, which are auxiliary components, is disposed. The development unit 30Y includes a cleaning blade 21Y, a developer supply roller 32Y using an anilox roller as an example of a developer supply member, a regulation blade 33Y for regulating the developer supply amount, and a developer on the outer periphery of the development roller 20Y. A developer that stirs the developer in a uniformly dispersed state in a developer container (reservoir) 31Y in which the compression roller 22Y and the developer on the surface of the compression roller 22Y are written and removed, and the liquid developer is accommodated. A stirring roller 34Y is disposed. Further, a primary transfer roller 51Y of the primary transfer unit 50Y is disposed at a position facing the image carrier 10Y with the intermediate transfer member 40 interposed therebetween, and further along the intermediate transfer member 40, the primary transfer unit of each color further downstream in the moving direction. 50Y (M, C, K) is arranged. A secondary transfer unit 60 is disposed downstream of the primary transfer unit 50Y (M, C, K), and an image is transferred to a transfer material. A fixing unit 70 is disposed on the downstream side of the sheet material conveyance path L from the secondary transfer unit 60.

  The liquid developer 1 accommodated in the developer container 31Y is composed of resin fine particles 2 as a developer solid content containing a pigment component, a dispersant 3, and a carrier oil 4 as a non-volatile liquid carrier. A solid particle having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a plastic resin is added to a liquid solvent such as an organic solvent, silicon oil, mineral oil, or edible oil together with the dispersant, and the toner solid content concentration is increased. It is a liquid developer having a high viscosity (about 30 to 10,000 mPa · s) of about 25%. The liquid developer contained in the developer container 31Y is a developer or carrier dispersed in a high concentration of about 35 to 55% by weight of the toner according to the concentration of the developer that changes as the image carrier is developed. The developer container 31Y is replenished and agitated by the liquid developer agitating roller 34Y to obtain a uniformly dispersed state, and 25% of the toner is dispersed in 75% of the carrier in a weight ratio.

  In the image forming unit and developing unit 30Y, the image carrier 10Y is uniformly charged by the charging roller 11Y, and the input image is input by the exposure unit 12Y having an optical system such as a semiconductor laser, a polygon mirror, and an F-θ lens. Based on the signal, a modulated laser beam is irradiated to form an electrostatic latent image on the charged image carrier 10Y. Then, the amount of developer supplied is regulated by the regulating blade 33Y from the developer container 31Y storing the liquid developer of each color (here yellow), and the developer is supplied from the developer supply roller 32Y to the developing roller 20Y to carry the image. The electrostatic latent image formed on the body 10Y is developed.

  The intermediate transfer member 40 is an endless elastic belt member and is wound around and stretched between a driving roller 41 and a tension roller 42. The image transfer members 10Y, 10M, and 50K are primary transfer units 50Y, 50M, 50C, and 50K. It is rotationally driven by the drive roller 41 while abutting 10C and 10K. The primary transfer portions 50Y, 50M, 50C, and 50K are arranged so that the primary transfer rollers 51Y, 51M, 51C, and 51K are opposed to the image carriers 10Y, 10M, 10C, and 10K with the intermediate transfer member 40 interposed therebetween. Using the contact position with 10M, 10C, and 10K as the transfer position, the developed toner images of the respective colors on the image carriers 10Y, 10M, 10C, and 10K are sequentially superimposed and transferred onto the intermediate transfer body 40 to obtain a full-color toner. An image is formed. The toner images formed on the plurality of image carriers (photosensitive members) 10Y, 10M, 10C, and 10K are sequentially transferred onto the intermediate transfer member 40 in such a manner that the toner images are superimposed and supported on the sheet material. Next transfer. Therefore, when transferring the toner image to the sheet material in the secondary transfer process, even if the sheet material surface is not smooth due to the fiber, etc., the secondary transfer characteristics are improved following this non-smooth sheet material surface. An elastic belt member is employed as the means for making it.

  In the secondary transfer unit 60, a first secondary transfer roller 61 is disposed opposite to the belt drive roller 41 with the intermediate transfer member 40 interposed therebetween, and further includes a cleaning blade 62 for the secondary transfer roller and a cleaning unit 63 including a developer recovery unit 63. The device is arranged. In the secondary transfer unit 60, the sheet material conveyance path L is adjusted in accordance with the timing at which a full-color toner image or a single-color toner image formed by superimposing colors on the intermediate transfer body 40 reaches the transfer position of the secondary transfer unit 60. Then, a sheet material such as paper, film or cloth is conveyed and supplied, and a single color toner image or a full color toner image is secondarily transferred to the sheet material.

  A fixing unit 70 is disposed downstream of the sheet transfer path L of the secondary transfer unit 60. The fixing unit 70 fuses and fixes a single-color toner image or a full-color toner image transferred onto the sheet material to a recording medium (sheet material) such as paper, and ends the final image formation on the sheet material. . Even if the secondary transfer roller 61 is a sheet material whose surface is not smooth due to fibers or the like, as a means for improving the secondary transfer characteristics following the surface of the non-smooth sheet material, the surface is coated with an elastic body. It is composed of rollers. This is an elastic belt employed in the intermediate transfer body 40 that sequentially transfers the toner images formed on the plurality of image carriers 10Y, sequentially superimposes them on the intermediate transfer body 40, and transfers them to the sheet material collectively. The purpose is the same as that of the member.

  On the side of the tension roller 42 that stretches the intermediate transfer member 40 together with the belt driving roller 41, along the outer periphery thereof, a cleaning blade 43 that contacts the intermediate transfer member 40, and development that collects the developer cleaned by the cleaning blade 43 A cleaning device including the agent recovery unit 44 is disposed. The intermediate transfer body 40 after passing through the secondary transfer section 60 is cleaned on the intermediate transfer body 40 by the cleaning blade 43, and again goes to the primary transfer section 50.

  In the developer container 31Y, the toner particles in the liquid developer have a positive charge. The developer is agitated by the agitation roller 34Y to be in a uniformly dispersed state, and the developer supply roller 32Y rotates. The developer is pumped up from the developer container 31Y, the developer amount is regulated by the regulating blade 33Y, and supplied to the developing roller 20Y. Initially, the developer stored in the developer container 31Y is uniformly dispersed in the carrier at approximately a toner weight ratio of about 25%. However, in the development on the image carrier 10Y, the image duty is high. However, in the case of development with a low image duty, the toner consumption ratio decreases. In other words, the toner weight ratio of the developer stored in the developer container 31Y changes with development on the image carrier 10Y, and this change is constantly monitored and dispersed approximately to a toner weight ratio of about 25%. It is necessary to maintain and control the state.

  In order to control the density of the developer in the developer container 31Y, as a means for detecting the density, a transmission type photosensor for detecting the dispersion weight ratio of the toner (not shown) or torque detection for detecting the stirring torque of the developer stirring roller 34Y. Each developing unit 30Y is provided with a reflection type photosensor for detecting the means and the developer liquid level in the developer container 31Y. When the toner dispersion weight ratio decreases at a predetermined developer amount, the developer container 31Y is replenished with a predetermined amount of developer dispersed at a high density of about 35 to 55%. Conversely, when the toner dispersion weight ratio increases, a predetermined amount of carrier is replenished to the developer container 31Y. By these replenishment, the toner weight ratio is controlled to about 25%.

  In order to exhibit a preferable secondary transfer function and fixing function in a stage where an image is formed through various process steps, is secondarily transferred to a final stage sheet material, and proceeds to a fixing step (not shown) using this developer. It is desirable that the liquid developer is in a dispersion state of approximately 40% to 60% in approximate toner weight ratio. For this reason, the image forming apparatus according to the present exemplary embodiment includes a developer collecting unit that removes and collects excess developer and excess carrier at a plurality of positions as appropriate.

  Next, the developer recovery unit will be described. In the image forming apparatus according to the present exemplary embodiment, the developer is scraped off and collected by a cleaning device included in the developer collecting unit. As the developer recovery means, a developing roller cleaning device 21 that cleans the developing roller 20, a developer compression roller cleaning device 23 that cleans the developer compression roller 22, an image carrier squeeze device 13 to 15, and an image carrier cleaning device. Devices 16 and 17, intermediate transfer member cleaning devices 43 to 44, and secondary transfer roller cleaning devices 62 and 63, and the like.

  In the developing unit 30Y, the cleaning blade 23Y and the developing roller 20Y as an example of a developer compressing roller cleaning device that cleans the developer compressing roller 22Y that compresses the liquid developer toner carried on the developing roller 20Y. And a cleaning blade 21Y as an example of a developing roller cleaning device. The cleaning blade 21Y is disposed on the downstream side in the rotation direction of the developing roller 20Y from the developing nip portion where the developing roller 20Y contacts the image carrier 10Y, and scrapes off the developer remaining on the developing roller 20Y. The developer in the developer compression roller 22Y is scraped off and removed by rotating in the direction of the arrow in the figure, and the developer in the reservoir 31Y is joined (joined) to be reused. Note that the merged carrier and toner are not in a mixed color state. Further, the collected developer may be discarded.

  The image carrier squeeze devices 13Y to 15Y are arranged on the downstream side in the rotation direction from the developing roller 20Y so as to face the image carrier 10Y, and are in pressure-sliding contact with the image carrier squeeze roller 13Y. A cleaning blade 14Y for cleaning the surface and a developer collecting unit 15Y, which collects excess carrier and originally unnecessary fog toner from the developer developed on the image carrier 10Y, and increases the toner particle ratio in the visible image. It has a function. In this embodiment, the image carrier squeeze roller 13Y rotates with the image carrier 10Y at substantially the same peripheral speed, and an excess carrier of about 5 to 10% by weight from the developer developed on the image carrier 10Y. Both the rotational driving loads are collected to reduce the disturbance effect on the visible toner image of the image carrier 10Y. Excess carrier and unnecessary fog toner collected by the image carrier squeeze roller 13Y are collected from the image carrier squeeze roller 13Y to the developer collecting unit 15Y by the action of the cleaning blade 14Y. Note that the collected surplus carrier and fog toner are collected from the dedicated isolated image carrier 10Y, so that no color mixing phenomenon occurs in the image forming portions of the respective colors.

  In the primary transfer unit 50Y, the image carrier 10Y and the intermediate transfer member 40 move at the same speed, and the developer image developed on the image carrier 10Y is transferred to the intermediate transfer member 40 by the primary transfer roller 51Y. In addition, the driving load of movement is reduced, and the disturbance effect on the visible toner image of the image carrier 10Y is suppressed. The primary transfer portion 50Y for the first color does not cause a color mixing phenomenon since it is the first primary transfer, but since the second and subsequent colors transfer different toner images onto the already transferred primary toner image portions and superimpose colors, the intermediate transfer body 40 is used. As a result of the so-called reverse transfer development in which the toner moves from the image carrier 10Y (M, C, K) to the image carrier 10Y (M, C, K), the reverse transfer toner and the transfer residual toner are mixed and are carried on the image carrier 10Y (M, C, K) together with the surplus carrier. The developer recovery unit 17Y (M, C, K) is moved from the image carrier 10Y (M, C, K) by the action of a cleaning blade 16Y (M, C, K) as an example of an image carrier cleaning device. To be recovered.

  The sheet material is supplied in accordance with the timing at which the toner image superimposed on the intermediate transfer body 40 reaches the secondary transfer portion, and the toner image is secondarily transferred to the sheet material and proceeds to the fixing process, and the final sheet material When the above image formation is completed, but a sheet material supply trouble such as a jam occurs, not all the toner images are transferred to the secondary transfer roll and collected. In addition, in the normal secondary transfer process, the toner image on the intermediate transfer body 40 is not 100% secondary-transferred and transferred to the sheet material, and a secondary transfer residue of several percent occurs. In particular, when a sheet material supply trouble such as a jam occurs, the toner image is transferred in contact with the secondary transfer roller 61 without the sheet material interposed, and the back surface of the sheet material is stained. These unnecessary toner images are cleaned on the intermediate transfer body 40 by the cleaning blade 43 of the intermediate transfer body 40 and the secondary transfer roller 61 is cleaned by the cleaning blade 62 of the secondary transfer roller 61. As described above, the cleaning blade 62 of the secondary transfer roller is provided as means for removing the developer (toner dispersed in the carrier) transferred to the secondary transfer roller 61, and the developer is collected from the secondary transfer roller 61. The

  Here, the two-stage fixing unit 70 will be described. FIG. 3 is an enlarged view of the fixing unit 70. The fixing unit 70 includes a first fixing device 71 having a first heating roller 72 and a second pressure roller 73 that are opposed to each other across the sheet material conveyance path L, and the sheet material conveyance path L downstream of the first fixing device 71. A second fixing device 74 having a second heating roller 75 and a second pressure roller 76 that are disposed to face each other across the sheet material conveyance path L is disposed.

  Heaters 72a and 75a are installed in the first heating roller 72 and the second heating roller 75 to heat the sheet material. In the present embodiment, the first fixing temperature of the first fixing device 71 by the first heating roller 72 is Tn1, and the second fixing temperature of the second fixing device 74 by the second heating roller 75 is Tn2.

  Next, the temperature change of the developer used in the image forming apparatus having such a configuration will be described. First, a method for measuring developer conductivity will be described. The basic configuration of the developer conductivity measuring device is the same as that shown in Patent Document 1, but, as shown in FIG. 4, the measurement unit 100 includes a first heating so as to contact the first electrode unit 101. The part 102 is arranged, and the second heating part 104 is arranged so as to contact the second electrode part 103. Then, a developer sample is set between the first electrode portion 101 and the second electrode portion 103. For example, a silicon rubber heater or the like is applied to the first heating unit 102 and the second heating unit 104. A sample of the developer 110 includes a developer solid content 111, a carrier oil 112, and a dispersant 113.

  In the measuring method using the developer conductivity measuring device having such a structure, the first electrode unit 101 and the second electrode unit 103 are heated to the target temperature by the first heating unit 102 and the second heating unit 104 in advance, and then A sample of the developer 110 is set, and the resistance value, that is, the conductivity is measured. Since the sample amount of the developer 110 is very small, the sample itself reaches the target temperature very quickly and can be measured quickly.

  FIG. 5 is a schematic graph showing the results of measuring the conductivity with respect to the temperature of the developer. As shown in the graph of FIG. 5, the conductivity of the developer increases from a certain temperature. This is considered to be because the dispersant easily separated from the surface of the toner particles due to an increase in thermal kinetic energy accompanying the temperature increase. In such a graph, the point at which the rate of change in conductivity with respect to the temperature of the liquid developer is maximized is denoted by Td. The glass transition temperature of the resin component of the liquid developer is Tg. At this time, in this embodiment, the maximum change rate point Td, which is the desorption temperature of the dispersant of the liquid developer, satisfies the relationship of the glass transition temperature Tg of the resin component of the liquid developer and Tg <Td. Note that the maximum change rate point Td of the liquid developer may be obtained as an intersection of an approximate line in a region having a small inclination and an approximate line in a region having a large inclination.

  Next, a method for measuring the liquid developer solid content melting point Tf will be described. First, the liquid developer sample is replaced with a low viscosity solvent such as Isopar G. The sample is then centrifuged to perform solids separation. Subsequently, 10 mg of the taken-out solid content is packed into an Al cell and measured using an “automatic differential scanning calorimeter DSC-60A” manufactured by Shimadzu Corporation. The conditions at this time are a measurement temperature: 0 to 200 ° C., and a temperature rising rate: 10 ° C./min. Finally, the DSC curve at the time of the second temperature rise is read, and the temperature having the endothermic peak is defined as the liquid developer solid content melting point Tf.

  In this embodiment, the first fixing temperature Tn1, the second fixing temperature Tn2, the liquid developer solid content melting point Tf, and the developer conductivity maximum change point Td are set so that Td <Tn1 <Tf <Tn2.

  In this way, first, in the first fixing device 71, by setting Td <Tn1, the dispersant can be released from the solid content of the developer, and thereby the affinity with the carrier oil whose viscosity has been lowered by heat. A highly dispersing agent penetrates into the sheet material. In the second fixing device 74, by setting Tf <Tn2 such that the second fixing temperature Tn2 is higher than the liquid developer solid content melting point Tf, a favorable fixing rate can be obtained. Further, by setting Tn1 <Tf, in the first fixing device 71, only the carrier oil and the dispersant are infiltrated, and the developer solid content can be kept on the sheet material. Thereby, since the developer solid content does not penetrate into the sheet material more than necessary, a uniform and high-density image can be obtained.

  Further, at the time of secondary transfer, it is necessary to efficiently apply an electric field, and it is preferable to set the transfer temperature of the secondary transfer portion 60 to Td or lower in order not to lower the developer resistance due to the detachment of the dispersion material. .

  Next, a method for measuring the fixability of the liquid developer and the density on the sheet material will be described.

  First, a method for measuring the fixability of the liquid developer will be described. First, a mending tape (manufactured by Sumitomo 3M) is affixed on the print sample. Next, using a clock meter, the tape is rubbed twice with an eraser wrapped with a cloth. Finally, the tape is peeled off, and (ODU (original) −ODU (after rubbing test) / ODU (original) × 100 [%]) is calculated to determine the fixability of the liquid developer.

  Table 1 compares the results of the fixing property and the density on the sheet material in Examples and Comparative Examples.

表１より、第１定着温度Ｔｎ１、第２定着温度Ｔｎ２、液体現像剤固形分融点Ｔｆ及び現像剤導電率最大変化点ＴｄがＴｄ＜Ｔｎ１＜Ｔｆ＜Ｔｎ２の関係にある実施例１の液体現像剤は、定着率が９８％、シート材上濃度が１．４５であるのに対し、Ｔｎ１＜Ｔｆの関係にない比較例１の液体現像剤は、定着率が９９％とよいものの、シート材上濃度が１．１３にとどまっており、Ｔｄ＜Ｔｎ１の関係にない比較例２の液体現像剤は、定着率が７８％と極端に悪くなることがわかる。

From Table 1, the liquid development of Example 1 in which the first fixing temperature Tn1, the second fixing temperature Tn2, the liquid developer solid content melting point Tf, and the developer conductivity maximum change point Td have a relationship of Td <Tn1 <Tf <Tn2. The developer has a fixing rate of 98% and a density on the sheet material of 1.45, whereas the liquid developer of Comparative Example 1 having no relationship of Tn1 <Tf has a fixing rate of 99%, but the sheet material It can be seen that the liquid developer of Comparative Example 2 having an upper density of only 1.13 and not having a relationship of Td <Tn1 has an extremely poor fixing rate of 78%.

  As described above, the image forming apparatus according to the present exemplary embodiment includes a developer container 31 that stores the liquid developer 110 including the solid developer component 111 containing the pigment component, the dispersant 113, and the non-volatile liquid carrier 112. A developing roller 20 that carries the liquid developer 110, a developer supply roller 32 that supplies the liquid developer 110 from the developer container 31 to the developing roller 20, and an image carrier on which the latent image is developed by the developing roller 20. 10, an intermediate transfer member 40 that forms an image by transferring an image on the image carrier 10, a secondary transfer unit 60 that transfers the image on the intermediate transfer member 40 to a transfer material, and a secondary transfer unit 60 A fixing unit 70 that fixes the image transferred on the transfer material to the transfer material. The fixing unit 70 has a two-stage configuration of a first fixing device 71 on the upstream side and a second fixing device 74 on the downstream side. 71 fixing temperature T 1. Since the temperature between the developer solid content flow softening point Tf and the dispersant desorption temperature Td is set to satisfy the relationship Td <Tn1 <Tf, the dispersant 113 is added to the developer solid content 111 according to the relationship Td <Tn1. In the first fixing device 71, due to the relationship Tn1 <Tf, the dispersant 113 having a high affinity permeates into the transfer material together with the liquid carrier 112 whose viscosity is lowered by heat. Only the liquid carrier 112 and the dispersant 113 are allowed to permeate the transfer material, and the developer solid content 111 can be kept on the transfer material, and the particle film of the developer solid content 111 permeates the transfer material more than necessary. A uniform and high-density image can be obtained.

  Further, the relationship between the fixing temperature Tn2 of the second fixing device of the fixing unit, the fixing temperature Tn1 of the first fixing device, the developer solid melting point temperature Tf, and the dispersant desorption temperature Td is expressed as Td <Tn1 <Tf <. Since Tn2 is set, the second fixing device 74 has a fixing temperature higher than the developer solid content flow softening point Tf because of the relationship of Tf <Tn2. Therefore, a favorable fixing rate can be obtained.

  Further, since the secondary transfer portion 60 is at or below the dispersant desorption temperature Td, an electric field can be efficiently applied, and the resistance of the developer solid content 111 is not reduced.

1 is a diagram illustrating an image forming apparatus according to an exemplary embodiment. FIG. 2 is a diagram illustrating a periphery of a developing unit of the image forming apparatus according to the present exemplary embodiment. 2 is an enlarged view of a fixing unit of the image forming apparatus according to the exemplary embodiment. FIG. It is a figure which shows the measurement part of a developer conductivity measuring apparatus. It is a figure which shows the electrical conductivity with respect to the temperature of a developing agent.

Explanation of symbols

10Y, 10M, 10C, 10K ... image carrier, 11Y, 11M, 11C, 11K ... charging roller, 12Y, 12M, 12C, 12K ... exposure unit, 13Y ... image carrier squeeze roller, 14Y ... image carrier squeeze roller cleaning Blade, 15Y ... developer collecting part, 16Y ... image carrier cleaning blade, 17Y ... developer collecting part, 20Y, 20M, 20C, 20K ... developing roller (developer carrier), 21Y ... developing roller cleaning blade, 22Y ... Developer compression roller (developer compression member), 23Y ... developer compression roller cleaning blade, 30Y, 30M, 30C, 30K ... development unit, 31Y ... developer container, 32Y ... developer supply roller (developer supply member), 33Y: restriction blade, 34Y: stirring roller, 40: intermediate transfer member, 41 Belt drive roller, 42 ... belt driven roller, 43 ... intermediate transfer member cleaning blade, 44 ... developer recovery unit, 50Y, 50M, 50C, 50K ... primary transfer unit, 51Y ... primary transfer backup roller, 60 ... secondary transfer unit , 61 ... Secondary transfer roller, 62 ... Secondary transfer roller cleaning blade, 63 ... Developer recovery unit, 70 ... Fixing unit, 71 ... Heating roller, 72 ... Pressure roller, 100 ... Measuring unit, 101 ... First electrode Part 102: First heating part, 103: Second electrode part, 104: Second heating part, 110: Liquid developer, 111: Developer solid content, 112: Carrier oil (liquid carrier), 113: Dispersant

Claims (4)

  A developer container for storing a liquid developer comprising a developer solid content containing a pigment component, a dispersant, and a non-volatile liquid carrier, a developer carrier for supporting the liquid developer, and the developer container A developer supply member for supplying a liquid developer to the developer carrier, an image carrier on which a latent image is developed by the developer carrier, and an image on the image carrier by transferring an image on the image carrier. An intermediate transfer member to be formed; a secondary transfer unit that transfers an image on the intermediate transfer member to a transfer material; and a fixing unit that fixes the image transferred by the secondary transfer unit to a transfer material. Is a two-stage configuration of a first fixing device on the upstream side and a second fixing device on the downstream side, the fixing temperature Tn1 of the first fixing device, the developer solid content flow softening point Tf, and the dispersant desorption temperature Td. And the relationship Td <Tn1 <Tf. An image forming apparatus comprising.   The relationship between the fixing temperature Tn2 of the second fixing device of the fixing unit, the fixing temperature Tn1 of the first fixing device, the developer solid component melting point temperature Tf, and the dispersant desorption temperature Td is expressed as Td <Tn1 <Tf <Tn2. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 2, wherein the secondary transfer unit has a dispersant desorption temperature Td or lower.   A two-stage configuration of a first fixing device on the upstream side and a second fixing device on the downstream side using a liquid developer comprising a developer solid content containing a pigment component, a dispersant, and a non-volatile liquid carrier. The fixing temperature Tn1 of the first fixing device of the fixing unit is a temperature between the developer solid content flow softening point Tf and the dispersant desorption temperature Td, and the relationship Td <Tn1 <Tf is established. Method.

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